Transcriber’s Notes

Obvious typographical errors have been silently corrected. Variations
in hyphenation and accents have been standardised but all other
spelling and punctuation remains unchanged.

In the section on The Instinct of Life, fifth paragraph “and Flourens
has reduced the ratio to that of 5:1, which would still give us 120
years.” the 120 has been corrected to 100.

In Book V, Chapter III, Chemical Changes, “and at the same time would
transform an amido-group into an amido-group.” is as printed.

Italics are represented thus _italic_, superscripts thus y^ and
subscripts thus y⌄.




                            LIFE AND DEATH.




                            LIFE AND DEATH

                                  BY

                              A. DASTRE,
               PROFESSOR OF PHYSIOLOGY AT THE SORBONNE.

                             TRANSLATED BY
                   W. J. GREENSTREET, M.A., F.R.A.S.

                THE WALTER SCOTT PUBLISHING CO., LTD.,
                   PATERNOSTER SQUARE, LONDON, E.C.
                       CHARLES SCRIBNER’S SONS,
                    153-157 FIFTH AVENUE, NEW YORK.
                                 1911




                               PREFACE.


The educated and inquiring public of the present day addresses to the
experts who have specialized in every imaginable subject the question
that was asked in olden times of Euclid by King Ptolemy Philadelphus,
Protector of Letters. Recoiling in dismay from the difficulties
presented by the study of mathematics and annoyed at his slow progress,
he inquired of the celebrated geometer if there was not some royal
road, could he not learn geometry more easily than by studying the
Elements. The learned Greek replied, “There is no royal road.” These
royal roads making every branch of science accessible to the cultivated
mind did not exist in the days of Ptolemy and Euclid. But they do exist
to-day. These roads form what we call Scientific Philosophy.

Scientific philosophy opens a path through the hitherto inextricable
medley of natural phenomena. It throws light on facts, it lays bare
principles, it replaces contingent details by essential facts. And
thus it makes science accessible and communicable. Intellectually it
performs a very lofty function.

There is virtually a philosophy of every science. There is therefore
a philosophy of the science which deals with the phenomena of life
and death—_i.e._, of physiology. I have endeavoured to give a summary
of this philosophy in this volume. I have had in view two classes of
readers. In the first place there are readers of general culture who
are desirous of knowing something of the trend of ideas in biology.
They already form quite a large section of the great public.

These scholars and inquirers, with Bacon, believe that the only science
is general science. What they want to know is not what instruments we
use, our processes, our technique, and the thousand and one details of
the experiments on which we spend our lives in the laboratory. What
they are interested in are the general truths we have acquired, the
problems we are trying to solve, the principles of our methods, the
progress of our science in the past, its state in the present, its
probable course in the future.

But I venture to think that this book is also addressed to another
class of readers, to those whose professional study is physiology.
To them it is dedicated. They have been initiated into the mysteries
of the science. They are learning it by practice. That is the right
method. Practice makes perfect. Claude Bernard used to say that in
order to be an expert in experimental science you must first be “a
laboratory rat.” And among us there are many such “laboratory rats.”
They are guided in the daily task of investigation by a dim instinct
of the path and of the direction of contemporary physiology. Perhaps
it may be of assistance to them to find their more or less unconscious
ideas here expressed in an explicit form.

  A. DASTRE.




                               CONTENTS.


  BOOK I.

  THE FRONTIERS OF SCIENCE. GENERAL THEORIES OF
  LIFE AND DEATH. THEIR SUCCESSIVE TRANSFORMATIONS.

  CHAP.                                                             PAGE

  I. EARLY THEORIES                                                    1

  II. ANIMISM                                                          5

  III. VITALISM                                                       15

  IV. THE MONISTIC THEORY                                             34

  V. THE EMANCIPATION OF SCIENTIFIC RESEARCH FROM
  THE YOKE OF PHILOSOPHICAL DOCTRINE                                  42


  BOOK II.

  THE DOCTRINE OF ENERGY AND THE LIVING WORLD.
  GENERAL IDEAS OF LIFE. ALIMENTARY LIFE.

  I. ENERGY IN GENERAL                                                57

  II. ENERGY IN BIOLOGY                                               97

  III. ALIMENTARY ENERGETICS                                         116


  BOOK III.

  THE CHARACTERS COMMON TO LIVING BEINGS.

  I. DOCTRINE OF VITAL UNITY                                         146

  II. MORPHOLOGICAL UNITY OF LIVING BEINGS                           157

  III. CHEMICAL UNITY OF LIVING BEINGS                               173

  IV. TWOFOLD CONDITIONS OF VITAL PHENOMENA.
  IRRITABILITY                                                       188

  V. THE SPECIFIC FORM: ITS ACQUISITION, ITS REPARATION              199

  VI. NUTRITION. FUNCTIONAL ASSIMILATION. FUNCTIONAL
  DISTRIBUTION. ASSIMILATING SYNTHESIS                               209


  BOOK IV.

  THE LIFE OF MATTER.

  I. UNIVERSAL LIFE (OPINIONS OF THE PHILOSOPHERS
  AND POETS). CONTINUITY BETWEEN BRUTE BODIES
  AND LIVING BODIES. ORIGIN OF THE PRINCIPLE OF
  CONTINUITY                                                         239

  II. ORIGIN OF LIVING MATTER IN BRUTE MATTER                        249

  III. ORGANIZATION AND CHEMICAL COMPOSITION OF LIVING
  MATTER AND BRUTE MATTER                                            255

  IV. EVOLUTION AND MUTABILITY OF LIVING MATTER AND
  BRUTE MATTER                                                       259

  V. THE COMPOSITION OF THE SPECIFIC FORM. LIVING
  BODIES AND CRYSTALS. CICATRIZATION                                 281

  VI. NUTRITION IN THE LIVING BEING AND IN THE
  CRYSTAL                                                            290

  VII. GENERATION IN BRUTE BODIES AND LIVING BODIES.
  SPONTANEOUS GENERATION                                             294


  BOOK V.

  SENESCENCE AND DEATH.

  I. THE DIFFERENT POINTS OF VIEW FROM WHICH DEATH
  MAY BE REGARDED                                                    307

  II. CONSTITUTION OF THE ORGANISMS. PARTIAL DEATH.
  COLLECTIVE DEATHS                                                  312

  III. PHYSICAL AND CHEMICAL CHARACTERISTICS OF
  CELLULAR DEATHS. NECROBIOSIS                                       321

  IV. APPARENT PERRENNITY OF COMPLEX INDIVIDUALS                     330

  V. IMMORTALITY OF THE PROTOZOA AND OF SLIGHTLY
  DIFFERENTIATED CELLS                                               334

  VI. LETHALITY OF THE METAZOA AND OF DIFFERENTIATED
  CELLS                                                              340

  VII. MAN. THE INSTINCT OF LIFE AND THE INSTINCT OF
  DEATH                                                              345

  INDEX                                                              361




                            LIFE AND DEATH.

                                BOOK I.

 THE FRONTIERS OF SCIENCE—GENERAL THEORIES OF LIFE AND DEATH—THEIR
 SUCCESSIVE TRANSFORMATIONS.

 Chapter I. Early Theories.—II. Animism.—III. Vitalism.—IV. Monism.—V.
 Emancipation of Scientific Research from the Yoke of Philosophy.


                              CHAPTER I.

                            EARLY THEORIES.

    Animism—Vitalism—The Physico-Chemical Theory—Their Survival and
                           Transformations.


The fundamental theories of science are but the expression of its
most general results. What, then, is the most general result of the
development of physiology or biology—that is to say, of that department
of science which has life as its object? What glimpse do we get of the
fruit of all our efforts? The answer is evidently the response to that
essential question—What is Life?

There are beings which we call living beings; there are bodies which
have never been alive—inanimate bodies; and there are bodies which are
no longer alive—dead bodies. The fact that we use these terms implies
the idea of a common attribute, of a _quid proprium_, life, which
exists in the first, has never existed in the second, and has ceased
to exist in the last. Is this idea correct? Suppose for a moment that
this is so, that this implicit supposition has a foundation, and that
there really is something which corresponds to the word “_life_.” Must
we then wait for the last days of physiology, and in a measure for its
last word before we know what is hidden behind this word, “life”?

Yes, no doubt positive science should be precluded from dealing with
questions of this kind, which are far too general. It should be limited
to the study of second causes. But, as a matter of fact, scientific men
in no age have entirely conformed to this provisional or definitive
antagonism. As the human mind cannot rest satisfied with indefinite
attempts, or with ignorance pure and simple, it has always asked, and
even now asks, from the spirit of system the solution which science
refuses. It appeals to philosophical speculation. Now, philosophy, in
order to explain life and death, offers us hypotheses. It offers us
the hypotheses of thirty, of a hundred, or two thousand years ago.
It offers us animism; vitalism in its two forms, unitary vitalism
or the doctrine of vital force, and dismembered vitalism or the
doctrine of vital properties; and finally, materialism, a mechanical
theory, unicism or monism,—to give it all its names—_i.e._, the
physico-chemical doctrine of life. There are, therefore, at the present
day, in biology, representatives of these three systems which have
never agreed on the explanation of vital phenomena—namely, animists,
vitalists, and monists. But it is pretty clear that there must have
been some change between yesterday and to-day. Not in vain has general
science and biology itself made the progress which we know has been
made since the Renaissance, and especially during the course of the
nineteenth century. The old theories have been compelled to take new
shape, such parts as have become obsolete have been cut away, another
language is spoken—in a word, the theories have become rejuvenated. The
neo-animists of our day, Chauffard in 1878, von Bunge in 1889, and more
recently Rindfleisch, do not hold exactly the same views as Aristotle,
St. Thomas Aquinas, or Stahl. Contemporary neo-vitalists, physiologists
like Heidenhain, chemists like Armand Gautier, or botanists like Reinke
do not between 1880 and 1900 hold the same views as Paracelsus in
the fifteenth century and Van Helmont in the seventeenth, as Barthez
and Bordeu at the end of the eighteenth, or as Cuvier and Bichat at
the beginning of the nineteenth century. Finally, the mechanicians
themselves, whether they be disciples of Darwin and Haeckel, as
most biologists of our own time, or disciples of Lavoisier, as most
physiologists of the present day, have passed far beyond the ideas of
Descartes. They would reject the coarse materialism of the celebrated
philosopher. They would no longer consider the living organism as a
machine, composed of nothing but wheels, springs, levers, presses,
sieves, pipes, and valves; or again of matrasses, retorts, or alembics,
as the iatro-mechanicians and would-be chemists of other days believed.

All that is changed, at any rate in form. If we look back only thirty
or forty years we see that the old doctrines have undergone more or
less profound modifications. The changes of form, which have been
made necessary by the acquisitions of contemporary science, enable us
to appreciate its progress. They enable us to give an account of the
progress of biology, and for this reason they deserve to be examined
with some attention. It is into this examination that I ask my readers
to accompany me.




                              CHAPTER II.

                               ANIMISM.

 The Common Characteristic of Animism and Vitalism: the Human
 Statue—Primitive Animism—Stahl’s Animism—First Objection with
 Reference to the Relation between Soul and Body—Second Objection: the
 Unconscious Character of Vital Operations—Twofold Modality of the
 Soul—Continuity of the Soul and Life.


Children are taught that there are three kingdoms in Nature—the mineral
kingdom and the two living kingdoms, animal and vegetable. This is the
whole of the sensible world. Then above all that is placed the world of
the soul. School-boys therefore have no doubts on the doctrines that we
discuss here. They have the solution. To them there are three distinct
spheres, three separate worlds—matter, life, and thought.

It is this preconceived idea that we are about to examine. Current
opinion solves _a priori_ the question of the fundamental homogeneity
or lack of resemblance of these three orders of phenomena—the phenomena
of inanimate nature, of living nature, and of the thinking soul.
_Animism_, _vitalism_, and _monism_ are, in reality, different ways of
looking at them. They are the different answers to this question:—Are
vital, psychic, and physico-chemical manifestations essentially
distinct? Vitalists distinguish between life and thought, animists
identify them. In the opposite camp mechanicians, materialists, or
monists make the same mistake as the animists, but to that mistake they
add another: they assimilate the forces at play in animals and plants
to the general forces of the universe; they confuse all three—soul,
life, inanimate nature.

These problems belong on many sides to metaphysical speculation. They
have been discussed by philosophers; they have been solved from time
immemorial in different ways, for reasons and by arguments which it is
not our purpose to examine here, and which, moreover, have not changed.
But on some sides they belong to science, and must be tested in the
light of its progress. Cuvier and Bichat, for example, considered that
the forces in action in living beings were not only different from
physico-mechanical forces, but were utterly opposed to them. We now
know that this antagonism does not exist.

The preceding doctrines, therefore, depend up to a certain point on
experiment and observation. They are subject to the test of experiment
and observation in proportion as the latter can give us information
on the degree of difference or analogy presented by psychic, vital,
and physico-chemical facts. Now, scientific investigations have thrown
light on these points. There is no doubt that the analogies and the
resemblances of these three orders of manifestations have appeared more
and more numerous and striking as our knowledge has advanced. Hence it
is that animism can count to-day but very few advocates in biological
science. Vitalism in its different forms counts more supporters, but
the great majority have adopted the physico-chemical theory.

Both animism and vitalism separate from matter a directing principle
which guides it. At bottom they are mythological theories somewhat
similar to the paganism of old. The fable of Prometheus or the story
of Pygmalion contains all that is essential. An immaterial principle,
divine, stolen by the Titan from Jupiter, or obtained from Venus by
the Cypriot sculptor, descends from Olympus and animates the form,
till then inert, which has been carved in the marble or modelled in
the clay. In a word, there is a human statue. It receives a breath of
heavenly fire, a vital force, a divine spark, a soul, and behold! it is
alive. But this breath can also leave it. An accident happens, a clot
in a vein, a grain of lead in the brain—the life escapes, and all that
is left is a corpse. A single instant has proved sufficient to destroy
its fascination. This is how all men picture to their minds the scene
of death. The breath escapes; something flies away, or flows away with
the blood. The happy genius of the Greeks conceived a graceful image
of this, for they represented the life or the soul in the form of a
butterfly (Psyche) leaving the body, an ethereal butterfly, as it were,
opening its sapphire wings.

But what is this subtle and transient guest of the human statue, this
passing stranger which makes of the living body an inhabited house?
According to the animists it is the soul itself, in the sense in which
the word is understood by philosophers; the immortal and reasoning
soul. To the vitalists it is an inferior, subordinate soul; a soul, as
it were, of secondary majesty, the vital force, or in a word, life.

_Primitive Animism._—Animism is the oldest and most primitive of the
conceptions presented to the human mind. But in so far as it is a
co-ordinated doctrine, it is the most recent. In fact it only received
its definitive expression in the eighteenth century, from Stahl, the
philosopher-physician and chemist.

According to Tylor, one of the first speculations of primitive man, of
the savage, is as to the difference between the living body and the
corpse. The former is an inhabited house, the latter is empty. To such
rudimentary intellects the mysterious inhabitant is a kind of _double_
or duplicate of the human form. It is only revealed by the shadow
which follows the body when illuminated by the sun, by the image of
its reflection in the water, by the echo which repeats the voice. It
is only seen in a dream, and the figures which people and animate our
dreams are nothing but these doubled, impalpable beings. Some savages
believe that at the moment of death the double, or the soul, takes up
its residence in another body. Sometimes each individual possesses, not
one of these souls, but several. According to Maspero, the Egyptians
counted at least five, of which the principle, the _ka_ or _double_,
would be the aeriform or vaporous image of the living form. Space is
peopled by souls on their travels, which leave one set of bodies to
occupy another set. After having been the cause of life in the bodies
which they animated, they react from without on other beings, and are
the cause of all sorts of unexpected events. They are benevolent or
malevolent spirits.

Analogy inevitably leads simple minds to extend the same ideas to
animals and plants; in a word, to attribute souls to everything alive,
souls more or less nomadic, wandering, or interchangeable, as is
taught in the doctrine of metempsychosis. Mons. L. Errera points out
that this primitive, co-ordinated, hierarchized doctrine—meet subject
for the poet’s art—is the basis of all ancient mythologies.

_The Animism of Stahl._—Modern animism was much more narrow in scope.
It was a medical theory—_i.e._ almost exclusive to man. Stahl had
adopted it in a kind of reaction against the exaggerations of the
mechanical school of his time. According to him, the life of the body
is due to the intelligent and reasoning soul. It governs the corporeal
substance and directs it towards an assigned end. The organs are its
instruments. It acts on them directly, without intermediaries. It
makes the heart beat, the muscles contract, the glands secrete, and
all the organs perform their functions. Nay more, it is itself the
architectonic soul, which has constructed and which maintains the body
which it rules. It is the _mens agitat molem_ of Virgil.

It is remarkable that these ideas, so excessively and exaggeratedly
spiritualistic, should have been brought forward by a chemist and a
physician, while ideas completely opposed to these were admitted by
philosophers like Descartes and Leibniz, who were decided believers
in the spirituality of the soul. Stahl had been Professor of Medicine
at the University of Halle, physician to the Duke of Saxe-Weimar,
and later to the King of Prussia. He left an important medical and
chemical work, both theoretical and practical. He is the author of the
celebrated theory of phlogiston, which held its ground in chemistry up
to the time of Lavoisier. He died about 1734.

Animism survived him for some time, maintained by the zeal of a few
faithful disciples. But after the witty mockery of Bordeu,[1] in 1742,
it began to decay. We must, however, point out that an attempt to
revive this theory was made in 1878 by a well-known doctor of the last
generation, E. Chauffard. While preserving the essential features of
the theory, this learned physician proposed to bring it into harmony
with modern science, and to free it from all the reproaches which had
been levelled at it.

 [1] In a thesis presented in 1742 at Montpellier, Bordeu, then only
 twenty years of age, made game of the tasks imposed by animists on
 the Soul, “which has to moisten the lips when required;” or, “whose
 anger produces the symptoms of certain diseases;” or again, “which
 is prevented by the consequences of original sin from guiding and
 directing the body.”

_The Animism of E. Chauffard._—These reproaches were numerous. The
most serious is of a philosophic nature. It rises from the difficulty
of conceiving a direct and immediate action of the soul, considered as
a spiritual principle, upon the matter of the body. There is such an
abyss—hewn by the philosophic mind itself—between soul and body, that
it is impossible to imagine any relation between them. We can only get
a glimpse of how the soul might become an instrument of action.

This was the problem which sorely tried the genius of Leibniz.
Descartes, in earlier days, attacked it vigorously, like an Alexander
cutting the Gordian knot. He separated the soul from the body, and
made of the latter a pure machine in the government of which the soul
had no part. He attributed all the known manifestations of vital
activity to inanimate forces. Leibniz, also, was compelled to reject
all action, all contact, all direct relation, every real bond between
soul and body, and to imagine between them a purely metaphysical
relation—pre-established harmony:—“Soul and body agree in virtue of
this harmony, the harmony pre-established since the creation, and
in no way by a mutual, actual, physical influence. Everything that
takes place in the soul takes place as if there were no body, and so
everything takes place in the body as if there were no soul.” At this
point we almost reach a scientific materialism. It is easy for the
materialist to break this frail tie of pre-established harmony which so
loosely unites body and soul, and to exhibit the organism as under the
sole control of universal mechanics and physics.

Thus the weak point of Stahl’s animism was the supposition of a
direct action exercised on the organism by a distinct, heterogeneous,
spiritual principle.

Chauffard has endeavoured to avoid this pitfall. In conformity with
modern ideas, he has brought together what the ancient philosophers
and Stahl himself separated—the activity of matter and the activity of
the soul. “Thought, action, function, are embraced in an indissoluble
union.” This is the classical but not very lucid theory which has been
so often reproduced—_Homo factus est anima vivens_—which Bossuet has
expressed in the celebrated formula: “Soul and body form a natural
whole.”

A second objection raised against animism is that the soul acts
consciously, with reflection, and with volition, and that its essential
attributes are not found in most physiological phenomena, which, on the
contrary are automatic, involuntary, and unconscious. The contradictory
nature of these characteristics has obliged vitalists to conceive of
a vital principle distinct from thought. Chauffard, agreeing here
with Boullieu, Tissot, and Stahl himself, does not accept this
distinction; he refuses to shatter the unity of the vivifying and
thinking principle. He prefers to attribute to the soul two modes of
action: the one which is exercised on the acts of thought, and hence
it proceeds consciously, with reflection, and with volition; the other
exercising control over the physiological phenomena which it governs,
“by unconscious impressions, and by instinctive determinations, obeying
primordial laws.” This soul is hardly in keeping with his definition of
a conscious, reflecting, and voluntary principle; it is a new soul, a
somatic soul, singularly akin to that _rachidian soul_ which, according
to Pflüger, a well-known German physiologist, resides in each segment
of the spinal marrow, and is responsible for reflex movements.

_Twofold Modality of the Soul._—This twofold modality of the soul, this
duality admitted by Stahl and his disciples, was repugnant to many
thinkers, and it is this repugnance that gave rise to the vitalistic
school. It appeared to them to be a heresy tainted by materialism—and
so it was. In this lay the strength and the weakness of animism. It
admits of a unique animating principle for all the manifestations of
the living being, for the higher facts in the realm of thought, and for
the lower facts connected with the body. It throws down the barriers
which separate them. It fills up the gap between the different forms of
human activity, and assimilates them the one to the other.

Now this is precisely what materialism does. It, too, reduces to
a single order the psychical and physiological phenomena, between
which it no longer recognizes anything but a difference of degree,
thought being only a maximum of the vital movement, or life a minimum
of thought. In truth, the aims of the two schools are diametrically
opposed; the one claims to raise corporeal activity to the dignity
of thinking activity, and to spiritualize the vital fact; the other
lowers the former to the level of the latter and materializes the
psychic fact. But, though the intentions are different, the result is
identical. Spiritualistic monism inclines towards materialistic monism.
One step more, and the soul, confused with life, will be confused with
physical forces.

On the other hand, twofold modality has this advantage, that it
escapes the objection drawn from the existence of so many living
beings to which a thinking soul cannot be attributed; an anencephalous
fœtus, the young of the higher animals, the lower animals and plants,
living without thought, or with a minimum of real, conscious thought.
The advocate of animism replies that this physiological activity
is still a soul, but one which is barely aware of its existence—a
gleam of consciousness. In this theory, the knowledge of self, the
consciousness, is of all degrees. On the other hand, in the eyes of the
vitalist, it is an absolute fact which allows of no attenuation, of no
middle course between the being and the non-being.

It is this conception of the continuity of the soul and life, it is
the affirmation of a possible lowering of the complete consciousness
down to a mere gleam of knowledge, and finally down to unconscious
vital activity, which saved animism from complete shipwreck. That is
why this ancient doctrine finds, even in the present day, a few rare
supporters. An able German scientist, G. von Bunge, well known for
his researches in physiological chemistry, professes animistic views
in a work which appeared in 1889. He attributes to organized beings a
guiding principle, a kind of vital soul. A distinguished naturalist,
Rindfleisch, of Lübeck, has likewise taken his place among the
advocates of what we may call neo-animism.




                             CHAPTER III.

                               VITALISM.

 Its Extreme Forms—Early Vitalism, and Modern Neo-vitalism—Advantage
 of distinguishing between Soul and Life—§ 1. _The Vitalism of
 Barthez_—Its Extension—The Seat of the Vital Principle—The Vital
 Knot—The Vital Tripod—Decentralisation of the Vital Principle—§ 2.
 _The Doctrine of Vital Properties_—Galen, Van Helmont, Xavier Bichat,
 and Cuvier—Vital and Physical Properties antagonistic—§ 3. _Scientific
 Neo-vitalism_—Heidenhain—§ 4. _Philosophical Neo-vitalism_—Reinke.


_Extreme Forms: Early Vitalism and Modern Neo-vitalism._—Contemporary
neo-vitalism has weakened primitive vitalism in some important points.
The latter made of the vital fact something quite specific, irreducible
either to the phenomena of general physics or to those of thought.
It absolutely isolated life, separating it above from the soul, and
below from inanimate matter. This sequestration is nowadays much less
rigorous. On the psychical side the barrier remains, but it is lowered
on the material side. The neo-vitalists of to-day recognize that the
laws of physics and chemistry are observed within, as well as without,
the living body; the same natural forces intervene in both, only they
are “otherwise directed.”

The vital principle of early times was a kind of anthromorphic, pagan
divinity. To Aristotle, this force, the _anima_, _the Psyche_, worked,
so to speak, with human hands. According to the well-known expression,
its situation in the human body corresponds to that of a pilot on a
vessel, or to that of a sculptor or his assistant before the marble or
clay. And, in fact, we have no other clear image of a cause external
to the object. We have no other representation of a force external to
matter than that which is offered by the craftsman making an object, or
in general by the human being with his activity, free, or supposed to
be free, and directed towards an end to be realized.

Personifications of this kind, the mythological entities, the imaginary
beings, the ontological fictions, which ever filled the stage in the
mind of our predecessors, have definitely disappeared; no longer
have they a place in the scientific explanations of our time. The
neo-vitalists replace them by _the idea of direction_, which is another
form of the same idea of finality. The series of second causes in the
living being seems to be regulated in conformity with a plan, and
directed with a view to carrying it out. The tendency which exists
in every being to carry out this plan,—that is to say, the tendency
towards its end,—gives the impulse that is necessary to carry it out.
Neo-vitalists claim that vital force directs the phenomena which it
does not produce, and which are in reality carried out by the general
forces of physics and chemistry.

Thus, the directing impulse, _considered as really active_, is the last
concession of modern vitalism. If we go further, and if we refuse to
the directing idea executive power and efficient activity, the vital
principle is weakened, and we abandon the doctrine. We can no longer
invoke it. We cease to be vitalists if the part played by the vital
principle is thus far restricted. At first it was both the author of
the plan and the universal architect of the organic edifice; it is
now only the architect directing his workmen, and they are physical
and chemical agents. It is now reduced to the plan of the work, and
even this plan has no objective existence; it is now only an _idea_. It
has only a shadow of reality. To this it has been reduced by certain
biologists. For this we may thank Claude Bernard; and he has thereby
placed himself outside and beyond the weakest form of vitalism. He
did not consider the _idea of direction_ as a real principle. The
connection of phenomena, their harmony, their conformity to a plan
grasped by the intellect, their fitness for a purpose known to the
intellect, are to him but a mental necessity, a metaphysical concept.
The plan which is carried out has only a subjective existence; the
directing force has no efficient virtue, no executive power; it does
not emerge from the intellectual domain in which it took its rise, and
does not “react on the phenomena which enabled the mind to create it.”

It is between these two extreme incarnations of the vital principle, on
the one hand an executive agent, on the other a simple directing plan,
that the motley procession of vitalist doctrines passes on its way.
At the point of departure we have a vital force, personified, acting,
as we have stated, as if with human hands fashioning obedient matter;
this is the pure and primitive form of the theory. At the other extreme
we have a vital force which is now only a directing idea, without
objective existence, and without an executive rôle; a mere concept
by which the mind gathers together and conceives of a succession of
physico-chemical phenomena. On this side we are brought into touch with
monism.

_The Reasons given by the Vitalists for distinguishing Soul from
Life._—It is, in particular, on the opposite side, in the psychical
world, that the early vitalists professed to entrench themselves.
We have just seen that their doctrines were not so subtle as those
of to-day; the vital principle to them was a real agent, and not an
ideal plan in the process of being carried out. But they distinguished
this spiritual principle from another co-existent with it in superior
living beings—at any rate, in man: the thinking soul. They boldly
distinguished between them, because the activity of the one is
manifested by knowledge and volition, while on the contrary, the
manifestations of the other for the most part escape both consciousness
and volition.

In fact, we know nothing of what goes on in the normal state of our
organs. Their perfect performance of their functions is translated to
us solely by an obscure feeling of comfort. We do not feel the beating
of the heart, the periodic dilations of the arteries, the movements of
the lungs or intestine, the glands at their work of secretion, or the
thousand reflex manifestations of our nervous system. The soul, which
is conscious of itself, is nevertheless ignorant of all this vital
movement, and is therefore external to it.

This is the view of all the philosophers of antiquity. Pythagoras
distinguished the real soul, the thinking soul, the _Nous_, the
intelligent and immortal principle, characterized by the attributes of
consciousness and volition, from the vital principle, the _Psyche_,
which gives breath and animation to the body, and which is a soul of
secondary majesty, active, transient, and mortal. Aristotle did the
same. On the one side he placed the soul properly so called, the _Nous_
or intellect—that is to say, the understanding with its rational
intelligence; on the other side was the directing principle of life,
the irrational and vegetative Psyche.

This distinction agrees with the fact of the diffusion of life. Life
does not belong to the superior animals alone, and to the man in whom
we can recognize a reasoning soul. It is extended to the vast multitude
of humbler beings to which such lofty faculties cannot be attributed,
the invertebrates, microscopic animals, and plants. The advantage is
compensated for by the inconvenience of breaking down all continuity
between the soul and life; a continuity which is the principle of the
two other doctrines, animism and monism, and which is, we may say, the
very aim and the unquestionable tendency of science.

As for classical philosophy, it satisfies the necessity of establishing
the unity of the living being,—_i.e._, of bringing into harmony soul
and body,—but in a manner which we need not here discuss. It attributes
to the soul several modalities, several distinct powers: powers of
the vegetative life, powers of the sensitive life, and powers of the
intellectual life. And this other solution of the problem would be, in
the opinion of M. Gardair, in complete agreement with the doctrines of
St. Thomas Aquinas.


             § 1. THE VITALISM OF BARTHEZ: ITS EXTENSION.


Vitalism reached its most perfect expression in the second half
of the eighteenth century in the hands of the representatives of
the Montpellier school—Bordeu, Grimaud, and Barthez. The last, in
particular, contributed to the prevalence of the doctrine in medical
circles. A man of profound erudition, a collaborates with d’Alembert
in the _Encyclopædia_, he exercised quite a preponderant influence
on the medicine of his day. Stationed at Paris during part of his
career, physician to the King and the Duke of Orleans, we may say
that he supported his theories by every imaginable influence which
might contribute to their success. In consequence of this, the medical
schools taught that vital phenomena are the immediate effects of a
force which has no analogues outside the living body. This conception
reigned unchallenged up to the days of Bichat.

After Bichat, the vitalism of Barthez, more or less modified by the
ideas of the celebrated anatomist, continued to hold its own in all the
schools of Europe until about the middle of the nineteenth century.
Johannes Müller, the founder of physiology in Germany, admitted, about
1833, the existence of a unique vital force “aware of all the secrets
of the forces of physics and chemistry, but continually in conflict
with them, as the supreme cause and regulator of all phenomena.” When
death came, this principle disappeared and left no trace behind. One
of the founders of biological chemistry, Justus Liebig, who died in
1873, shared these ideas. The celebrated botanist, Candolle, who lived
up to 1893, taught at the beginning of his career that the vital
force was one of the four forces ruling in nature, the other three
being—attraction, affinity, and intellectual force. Flourens, in
France, made the vital principle one of the five properties of forces
residing in the nervous system. Another contemporary, Dressel, in 1883,
endeavoured to bring back into fashion this rather primitive, monistic,
and efficient vitalism.

_The Seat of the Vital Principle._—Meanwhile, another question was
asked with reference to this vital principle. It was a question of
ascertaining its seat: or, in other words, of finding its place in
the organism. Is it spread throughout the organism, or is it situated
in some particular spot from which it acts upon every part of the
body? Van Helmont, a celebrated scientist at the end of the sixteenth
century, who was both physician and alchemist, gave the first and
rather quaint solution of this difficulty. The vital principle,
according to him, was situated in the stomach, or rather in the opening
of the pylorus. It was the _concierge_, so to speak, of the stomach.
The Hebrew idea was more reasonable. The life was connected with the
blood, and was circulated with it by means of all the veins of the
organism. It escaped from a wound at the same time as the liquid blood.
It is clear that in this belief we see why the Jews were forbidden to
eat meat which had not been bled.

_The Vital Knot._—In 1748 a doctor named Lorry found that a very small
wound in a certain region of the spinal marrow brought on sudden
death. The position of this remarkable point was ascertained in 1812
by Legallois, and more accurately still by Flourens in 1827. It is
situated in the rachidian bulb, at the level of the junction of the
neck and the head; or more precisely, on the floor of the fourth
ventricle, near the origin of the eighth pair of cranial nerves. This
is what was called the _vital knot_. Upon the integrity of this spot,
which is no bigger than the head of a pin, depends the life of the
animal. Those who believed in a localisation of the vital principle
thought that they had found the seat desired; but for that to be so the
destruction of this spot must be irremediable, and must necessarily
cause death. But if the _vital knot_ be destroyed, and respiration be
artificially induced by means of a bellows, the animal resists: it
continues to live. It is only the nervous stimulating mechanism of the
respiratory movements which has been attacked in one of its essential
parts.

Life, therefore, resides no more in this point than it does in the
blood or in the stomach. Later experiment has shown that it resides
everywhere, that each organ enjoys an independent life. Each part of
the body is, to use Bordeu’s strong expression, “_an animal in an
animal_”; or to adopt the phrase due to Bichat, “_a particular machine
within the general machine_.”

_The Vital Tripod._—What then is life, or, in other words, what is the
biological activity of the individual, of the animal, of man? It is
clearly the sum total, or rather, the harmony of these partial lives
of the different organs. But in this harmony it seems that there are
certain instruments which dominate and sustain the others. There are
some whose integrity is more necessary to the preservation of existence
and health, and of which any lesion makes death more inevitable. They
are the lungs, the heart, and the brain. Death always ensues, said
the early doctors, if any one of these three organs be injured. Life
depends, therefore, on them, as if upon a three-legged support. Hence
the idea of the _vital tripod_. It is no longer a single seat for
the vital principle, but a kind of throne on three-supports. Life is
decentralized.

This was only the first step, very soon followed by many others, in the
direction of vital decentralization. Experiment showed, in fact, that
every organ separated from the body will continue to live if provided
with the proper conditions. And here, it is not only a question of
inferior beings; of plants that are propagated by slips; of the _hydra_
which Trembley cut into pieces, each of which generated a complete
hydra; of the _naïs_ which C. Bonnet cut up into sections, each of
which reconstituted a complete annelid. There is no exception to the
rule.

_Decentralization of the Vital Principle._—The result is the same in
the higher vertebrates, only the experiment is much more difficult. At
the Physiological Congress of Turin in 1901, Locke showed the heart
of a hare, extracted from the body of the animal, and beating for
hours as energetically and as regularly as if it were in its place.
He suspended it in the air of a room at the normal temperature, the
sole condition being that it was irrigated with a liquid composed of
certain constituents. The animal had been dead some time. More recently
Kuliabko has shown in the same way the heart of a man still beating,
although the man had been dead some eighteen hours. The same experiment
is repeated in any physiological laboratory, in a much easier manner,
with the heart of a tortoise. This organ, extracted from the body,
fitted up with rubber tubes to represent its arteries and veins, and
filled with the defibrinated blood of a horse or an ox taken from the
slaughter-house, works for hours and days pumping the liquid blood into
its rubber aorta, just as if it were pumping it into the living aorta.

But it is unnecessary to multiply examples. Every organ can be made
to live for a longer or shorter period even though removed from its
natural position; muscles, nerves, glands, and even the brain itself.
Each organ, each tissue therefore enjoys an independent existence;
it lives and works for itself. No doubt it shares in the activity of
the whole, but it may be separated therefrom without being thereby
placed in the category of dead substances. For each aliquot part of the
organism there is a partial life and a partial death.

This decentralization of the vital activity is finally extended in
complex beings from the organs to the tissues, and from the tissues
to the anatomical elements—the cells. The idea of decentralization
has given birth to the second form of vitalism, a softened down and
weakened form—namely, pluri-vitalism, or the theory of vital properties.


                 § 2. THE THEORY OF VITAL PROPERTIES.


The advocates of the theory of vital properties have cut up into
fragments the monistic and indivisible guiding principle of Bordeu and
Barthez. They have given it new currency—pluri-vitalism. This theory
maintains the existence of spiritual powers of a lower order, which
control phenomena more intimately than the vital principle did. These
powers, less lofty in their dignity than the rational soul of the
animists, or the soul of secondary majesty of the unitarian vitalists,
are eventually incorporated in the living matter of which they will
then be no longer more than the properties. Brought into closer
connection therefore with the sensible world, they will be more in
harmony with the spirit of research and with scientific progress.

The defect of the earlier conceptions, their common illusion, rose from
their seeking the cause outside the object, from their demanding an
explanation of vital phenomena from a principle external to living,
immaterial, and unsubstantial matter. Here this defect is less marked.
The pluri-vitalists will in turn appeal to the vital properties as
modes of activity, inherent in the living substance in which and by
which they are manifested, and derived from the arrangement of the
molecules of this substance—that is to say, from its organization. This
is almost the conception of the present day.

But this progress will only be realized at the end of the evolution
of the pluri-vitalist theory. At the outset this theory seems an
exaggeration of its predecessor, and a still more exaggerated form of
the mythological paganism with which it was reproached. The archeus,
the blas, the properties, the spirits—all have at first the effect
of the genii or of the gods imagined by the ancients to preside over
natural phenomena, of Neptune stirring up the waters of the sea, and
of Eolus unchaining the winds. These divinities of the ancient world,
the nymphs, the dryads, and the sylvan gods, seem to be transported to
the Middle Ages, to that age of argument, that philosophical period of
the history of humanity, and there metamorphosed into occult causes,
immaterial powers, and personified forces.

_Galen._—The first of the pluri-vitalists was Galen, the physician of
Marcus Aurelius, the celebrated author of an Encyclopædia of which the
greater part has been lost, and of which the one book preserved held
its own as the anatomical oracle and breviary throughout the Middle
Ages. According to Galen the human machine is guided by three kinds
of spirits: _animal spirits_, presiding over the activity of the
nervous system; _vital spirits_ governing most of the other functions;
and finally, _natural spirits_ regulating the liver and susceptible
of incorporation in the blood. In the sixteenth century, in the time
of Paracelsus, Galen’s spirits became _Olympic spirits_. They still
presided over the functional activity of the organs, the liver, heart,
and brain, but they also existed in all the bodies of nature.

_Van Helmont._—Finally, the theory was laid down by Van Helmont,
physician, chemist, experimentalist, and philosopher, endowed with
a rare and penetrating intellect. Here we find many profound truths
combined with fantastic dreams. Refusing to admit the direct action of
an immaterial agent, such as the soul, on inert matter, on the body, he
filled up the abyss which separated them by creating a whole hierarchy
of immaterial principles which played the part of mediators and
executive agents. At the head of this hierarchy was placed the thinking
and immortal soul; below was the sensitive and mortal soul, having for
its minister the _principal archeus_, the _aura vitalis_, a kind of
incorporeal agent, which is remarkably like the vital principle, and
which had its seat at the orifice of the stomach. Below again were the
subordinate agents, the _blas_, or _vulcans_ placed in each organ, and
intelligently directing its mechanism like skillful workmen.

These chimerical ideas are not, however, so far astray as the theory
of vital properties. When we see a muscle contract, we say that this
phenomenon is due to a vital property—_i.e._, a property without any
analogue in the physical world, namely _contractility_, in the same
way the nerve possesses two vital properties, _excitability_ and
_conductibility_, which Vulpian proposed to blend into one, calling it
_neurility_. These are mere names, serving as a kind of shorthand; but
to those who believe that there is something real in it, this something
is not very far from the _blas_ of Van Helmont. _Vulcans_, hidden in
the muscle or the nerve, are here detected by attraction, there by
the production and the propagation of the nervous influx; that is to
say, by phenomena of which we as yet know no analogues in the physical
world, but of which we cannot say that they do not exist.

_X. Bichat and G. Cuvier: Vital and Physical Properties
Antagonistic._—The archeus and the blas of Van Helmont were but a
first rough outline of vital properties. Xavier Bichat, the founder of
general anatomy, wearied of all these incorporeal entities, of these
unsubstantial principles with which biology was encumbered, undertook
to get rid of them by the methods of the physicist and the chemist. The
physics and the chemistry of his day referred phenomenal manifestations
to the properties of matter, gravity, capillarity, magnetism, etc.
Bichat did the same. He referred vital manifestations to the properties
of living tissues, if not, indeed, of living matter. Of these
properties as yet but very few were known: the irritability described
by Glisson, which is the excitability of current physiology; and the
irritability of Haller, which is nothing but muscular contractility.
Others had to be discovered.

There is no need to recall the mistake made by Bichat and followed
by most scientific men of his time, such as Cuvier in France, and J.
Müller in Germany, for the story has been told by Claude Bernard. His
mistake was in considering the vital properties not only as distinct
from physical properties but even as opposed to them. The one
preserve the body, the others tend to destroy it. They are always in
conflict. Life is the victory of the one; death is the triumph of the
other. Hence the celebrated definition given by Bichat: “Life is the
sum total of functions which resist death,” or the definition of the
Encyclopædia: “Life is the contrary of death.”

Cuvier has illustrated this conception by a graphic picture. He
represents a young woman in all the health and strength of youth
suddenly stricken by death. The sculptural forms collapse and show the
angularities of the bones; the eyes so lately sparkling become dull;
the flesh tint gives place to a livid pallor; the graceful suppleness
of the body is now rigidity, “and it will not be long before more
horrible changes ensue; the flesh becomes blue, green, black, one part
flows away in putrid poison, and another part evaporates in infectious
emanations. Finally, nothing is left but saline or earthy mineral
principles, all the rest has vanished.” Now, according to Cuvier, what
has happened?

These alterations are the effect of external agents, air, humidity, and
heat. They have acted on the corpse just as they used to act on the
living being; but before death their assault had no effect, because it
was repelled by the vital properties. Now that life has disappeared
the assault is successful. We know now that external agents are not
the cause of these disorders. They are caused by the microbes of
putrefaction. It is against _them_ that the organs were struggling, and
not against physical forces.

The mistake made by Bichat and Cuvier was inexcusable, even in their
day. They were wrong not to attach the importance they deserved to
Lavoisier’s researches. He had asserted, apropos of animal heat and
respiration, the identity of the action of physical agents in the
living body and in the external world. On the other hand, Bichat, by a
flash of genius, decentralized life, dispersing the vital properties
in the tissues, or, as we should now say, in the living matter. It was
from the comparison between the constitution and the properties of
living matter and those of inanimate matter that light was to come.


                     § 3. SCIENTIFIC NEO-VITALISM.


We can now understand the nature of modern neo-vitalism. It borrows
from its predecessor its fundamental principle—namely, the specificity
of the _vital fact_. But this specificity is no longer _essential_, it
is only _formal_. The difference between it and the physical fact grows
less and almost vanishes. It consists of a diversity of mechanisms or
executive agents. For example, digestion transforms the alimentary
starch in the intestines into sugar; the chemist does the same in his
laboratory, only he employs acids, while the organism employs special
agents, ferments, in this case a diastase. It is a particular form of
chemistry, but still it is a chemistry. That is how Claude Bernard
looked at it. The vital fact was not fundamentally distinguished from
the physico-chemical fact, but only in form.

This expurgated and accommodated vitalism (Claude Bernard pushed his
concessions so far as to call his doctrine “physico-chemical vitalism”)
was revived a few years ago by Chr. Bohr and Heidenhain.

Other biologists, instead of attributing the difference between the
phenomena of the two orders to the manner of their occurrence, seem to
admit the complete identity of the mechanisms. It is no longer then in
itself, individually, that the vital act is particularized, but in the
manner in which it is linked to others. The vital order is a series of
physico-chemical acts realizing an ideal plan.

Neo-vitalism has therefore assumed two forms, one the more scientific
and the other the more philosophical.

_Chr. Bohr and Heidenhain._—Its scientific form was given to it by
Chr. Bohr, an able physiologist at Copenhagen, and by Heidenhain,
a professor at Breslau, who was one of the lights of contemporary
German physiology. The course of their researches led these two
experimentalists, working independently, to submit to fresh
investigation the ideas of Lavoisier and those of Bichat, on the
relation of physico-chemical forces to the vital forces.

It was by no means a question of a general inquiry, deliberately
instituted with the object of discovering the part played respectively
by physical and physiological factors in the performance of the various
functions. Such an investigation would have taken several generations
to complete. No; the question had only come up incidentally. Chr. Bohr
had studied with the utmost care the gaseous exchanges which take place
between the air and the blood in the lungs. The gaseous mixture and
the liquid blood are face to face; they are separated by thin membrane
formed of living cells. Will this membrane behave as an inert membrane
deprived of vitality, and therefore obeying the physical laws of the
diffusion of gases? Well! no. It does not so behave. The most careful
measurements of pressures and of solubilities leave no doubt in this
respect. The living elements of the pulmonary membrane must therefore
intervene in order to disturb the physical phenomenon. Things happen
as if the exchanged gases were subjected not to a simple diffusion,
a physical fact obeying certain rules, but to a real secretion, a
physiological or vital phenomenon, obeying laws which are also fixed,
but different from the former.

On the other hand, Heidenhain was led about the same time to analogous
conclusions with respect to the liquid exchanges which take place
within the tissues, between the liquids (lymphs) which bathe the
blood-vessels externally and the blood which those vessels contain.
The phenomenon is very important because it is the prologue of the
actions of nutrition and assimilation. Here again, the two factors of
exchange are brought into relation through a thin wall, the wall of
the blood-vessel. The physical laws of diffusion, of osmosis, and of
dialysis, enable us to foretell what would take place if the vitality
of the elements of the wall did not intervene. Heidenhain thought he
observed that things took place otherwise. The passage of the liquids
is disturbed by the fact that the cellular elements are alive. It
assumes the characteristics of a physiological act, and no longer
those of a physical act. Let us add that the interpretation of these
experiments is difficult, and it has given rise to controversies which
still persist.

These two examples, around which others might be grouped, have led
certain physiologists to diminish the importance of the physical
factors in the functional activity of the living being to the advantage
of the physiological factors. It would therefore seem that the vital
force, to use a rather questionable form of language, withdraws in
a certain measure the organized being from the realm of physical
forces—and this conclusion is one form of contemporary neo-vitalism.


                   § 4. PHILOSOPHICAL NEO-VITALISM.


Contemporary neo-vitalism has assumed another form, more philosophical
than scientific, by which it is brought closer to vitalism, properly
so called. We should like to mention the experiment of Reinke,[2] in
Germany. Reinke is a botanist of distinction, who distinguishes the
speculative from the positive domain of science, and cultivates both
with success.

 [2] Reinke, _Die Welt als That_; Berlin, 1899.

His ideas are analogous to those of A. Gautier, of Chevreul, and of
Claude Bernard himself. He thinks, with these masters, that the mystery
of life is not to be found in the nature of the forces that it brings
into play, but in the direction that it gives them. All these thinkers
are struck by the order and the direction impressed upon the phenomena
which take place in the living being, by their interconnection, by
their apparent adaptation to an end, by the kind of impression that
they give of a plan which is being carried out. All these reflections
lead Reinke to attach great weight to the idea of a “directing force.”

The physico-chemical energies are no doubt the only ones which are
manifested in the organized being, but they are directed as a blind man
is by his guide. It seems as if a _double_ accompanies them like a
shadow. This intelligent guide of blind, material force is what Reinke
calls a _dominant_. Nothing could be more like the blas and the archeus
of Van Helmont. Material energies would thus be paired off with their
blas, their dominants, in the living organisms. In them there would
therefore be two categories of force: “material forces,” or rather,
material energies obeying the laws of universal energetics; and in the
second place, intelligent “spiritual forces,” the dominants. When the
sculptor is working his marble, in every blow which elicits a spark
there is something more than the strong force of the hammer. There is
thought, the volition of the artist, which is realizing a plan. In a
machine there is more than machinery. Behind the wheels is the object
which the author had in view when he adjusted them for a determined
end. The energies spent in action are regulated by the adjustment—that
is to say, by the dominants due to the intellect of the constructor.

Thus it is in the living machine. The dominants in this case are the
guardians of the plan, the agents of the aim in view. Some regulate
the functional activity of the living body, and some regulate its
development and its construction. Such is the second form, the
philosophical form, extreme and teleological, of contemporary
neo-vitalism.




                              CHAPTER IV.

                         THE MONISTIC THEORY.

 Physico-chemical Theory of Life.—Iatro-mechanism.—Descartes,
 Borelli.—Iatro-chemistry.—Sylvius le Boë.—The Physico-chemical Theory
 of Life.—Matter and Energy.—Heterogeneity is merely the result of the
 arrangement or combination of homogeneous bodies.—Reservation relative
 to the world of thought.—The Kinetic Theory.


The unicist or monistic doctrine gives us a third way of conceiving
the functional activity of the living being, by levelling and
blending its three forms of activity—spiritual, vital, and material.
It was expressed in the seventeenth and eighteenth centuries in
“iatro-mechanism” and “iatro-chemistry,” conceptions to which have more
recently succeeded the physico-chemical doctrine of life, and finally
“current materialism.”

Materialism is not only a biological interpretation; it is a universal
interpretation applicable to the whole of nature, because it is
based on a determinate conception of matter. Here we find ourselves
confronted by the eternal enigma discussed by philosophers relative
to this fundamental problem of force and matter. We know what
answers were given to the problem by the Ionic philosophers—Thales,
Democritus, Heraclitus, and Anaxagoras, who discarded the agency of
every spiritual power external to matter. The explanation of the
world, the explanation of life, were reduced to the play of physical
or mechanical forces. Epicurus, a little later, maintained that the
knowledge of matter and its different forms accounts for all phenomena,
and therefore for those of life.

Descartes, sharply separating the metaphysical world—that is to say,
the soul defined by its attribute, thought—from the physical or
material world characterized by extension, practically came to the same
conclusions as the materialists of antiquity. To him, as to them, the
living body was a mere machine.

_Iatro-mechanism. Descartes. Borelli._—This, then, is the theory of the
iatro-mechanicians, of which we may consider Descartes the founder,
instead of the Greek philosophers. These ideas held their own for two
centuries, and were productive of such fruitful results in the hands of
Borelli, Pitcairn, Hales, Bernoulli, and Boerhaave, as to justify the
jest of Bacon that “the philosophy of Epicurus had done less harm to
science than that of Plato.” The iatro-mechanic school tenaciously held
its own until Bichat came upon the scene.

_Iatro-chemistry. Sylvius le Boë._—It was from a reaction against their
exaggerations that Stahl created animism, and the Montpellier school
created vitalism. We gather some idea of the extravagant character
of their explanations by reading Boerhaave. To this celebrated
doctor the muscles were springs, the heart was a pump, the kidneys
a sieve, and the secretions of the glandular juices were produced
by pressure; the heat of the body was the result of the friction of
the globules of blood against the walls of the blood-vessels; it was
greater in the lungs because the vessels of the lungs were supposed
to be narrower than those of other organs. The inadequacy of these
explanations suggested the idea of completing them by the aid of
the chemistry which was then springing into being. This chemistry,
rudimentary as it was, longed for a share in the government of living
bodies and in the explanation of their phenomena. Distillations,
fermentations, and effervescences are now seen to play their rôle, a
rôle which was premature and carried to excess. Iatro-chemistry from
the general point of view is only an aspect of iatro-mechanics; but it
is also an auxiliary. Sylvius le Boë and Willis were its most eminent
representatives. This theory remained in the background until chemistry
made its great advance—that is to say, in the days of Lavoisier. After
that, its importance has gradually increased, particularly in the
present day. Nowadays, the general tendency is to regard the organic
functional activity, or even morphogeny—_i.e._, whatever there is
that is most peculiar to and characteristic of living beings—as a
consequence of the chemical composition of their substance. This is a
point of capital importance, and to it we must recur.

_The Physico-chemical Theory of Life._—Contemporary biological schools
have made many efforts to secure themselves from any slips on the
philosophical side. They have avoided in most cases the psychological
problem; they have deliberately refrained from penetrating into the
world of the soul. Hence, _the physico-chemical theory_ of life has
been built up free from spiritualistic difficulties and objections.
But this prudence did not exclude the tendency. And there is no doubt,
as Armand Gautier said, that “real science can affirm nothing, but
it also can deny nothing outside observable facts;” and again, that
“only a science progressing backwards can venture to assert that matter
alone exists, and that its laws alone govern the world.” It is none the
less true that by establishing the continuity between inert matter and
living matter, we thereby render probable the continuity between the
world of life and the world of thought.

_Matter and Energy._—Besides, and without any wish to enter into
this burning controversy, it is only too evident that there is no
agreement as to the terms that are used, and in particular as to
“matter” and “laws of matter.” It is not necessary to repeat that the
geometrical mould in which Descartes cast his philosophy has long
since been broken. The celebrated philosopher, in defining matter by
one attribute—extension, does not enable us to grasp its activity, an
activity revealed by all natural facts; and in defining the soul by
thought alone, prevents us from seeking in it the principle of this
material activity. This purely passive matter, consisting of extension
alone, this _bare matter_ was to Leibniz a pure concept. A philosopher
of our own time, M. Magy, has called it a sensorial illusion. The
bodies of nature exhibit to us _matter clad_ with energy, formed by
the indissoluble union of extension with an inseparable dynamical
principle. The Stoics declared that matter is mobile and not immobile,
active and not inert. Leibniz also had this in his mind when he
associated it indissolubly with an active principle, an “entelechy.”
Others have said that matter is “an assemblage of forces,” or with P.
Boscovitch, “a system of indivisible points without extension, centres
of force, in fact.” Space would be the geometrical locus of these
points.

In this conception the materialistic school finds the explanation of
all phenomenality. Physical properties, vital phenomena, psychical
facts, all have their foundation in this immanent activity. Material
activity is a minimum of soul or thought which, by continuous gradation
and progressive complexity, without solution of continuity, without
an abrupt transition from the homogeneous to the heterogeneous, rises
through the series of living beings to the dignity of the human soul.
The observation of the transitions, an imperfect tracing of the
geometrical method of limits, thus enables us to pass from material to
vital, and from thence to psychical activity.

_Apparent Heterogeneity is the Result of the Arrangement or the
Combination of Homogeneous Bodies._—In this system, material energy,
life, soul would only be more and more complex combinations of the
consubstantial activity with material atoms. Life appears distinct from
physical force, and thought from life, because the analysis has not yet
advanced far enough. Thus, glass would appear to the ancient Chaldeans
distinct from the sand and salt of which they made it. In the same way,
again, water, to modern eyes, is distinct from its constituents, oxygen
and hydrogen. The whole difficulty is that of explaining what this
“arrangement” of the elements can introduce that is new in the aspect
of the compound. We must know what novelty and apparent homogeneity
the variety of the combinations, which are only special arrangements
of the elementary parts, may produce in the phenomena. But we do
not know, and it is this ignorance which leads us to consider them
as heterogeneous, irreducible, and distinct in principle. The vital
phenomenon, the complexus of physico-chemical facts, thus appears to us
essentially different from those facts, and that is why we picture to
ourselves “dominants” and “directing forces” more or less analogous to
the sidereal guiding principle of Kepler, which, before the discovery
of universal attraction, regulated the harmony of the movements of the
planets.

_A Reservation relative to the Psychical Order._—The scientific mind
has shown in every age a real predilection towards the mechanical or
materialistic theory. Contemporary scientists as a whole have accepted
it in so far as it blends the vital and the physical orders. Objections
and contradictions are only offered in the realm of psychology. A.
Gautier, for example, has contested with infinite originality and
vigour the claims of the materialists who would reduce the phenomenon
of thought to a material phenomenon. The most general characteristic
of material phenomenality is—as we shall later see—that it may be
considered as a mutation of energy—_i.e._, it obeys the laws of
energetics. Now thought, says A. Gautier, is not a form of material
energy. Thought, comparison, volition, are not acts of material
phenomenality; they are states. They are realities; they have no
mass; they have no physical existence. They respond to adjustments,
arrangements, and concerted groupings of material manifestations of
chemical molecules. They escape the laws of energetics.

_Kinetic Theory._—We shall lay aside for a moment this serious problem
relative to the limits of the world of conscious thought and of the
world of life. It is on the other side, on the frontiers of living and
inanimate nature, that the mechanical view triumphs. It has furnished a
universal conception agreeing with phenomena of every kind—viz., the
kinetic theory, which ascribes everything in nature to the movements of
particles, molecules, or atoms.

The living and the physical orders are here reduced to one unique
order, because all the phenomena of the sensible universe are
themselves reduced to one and the same mechanics, and are represented
by means of the atom and of motion. This conception of the world,
which was that of the philosophers of the Ionic school in the remotest
antiquity, which was modified later by Descartes and Leibniz, has
passed into modern science under the name of the kinetic theory. The
mechanics of atoms ponderable or imponderable, would contain the
explanation of all phenomenality. If it were a question of physical
properties or vital manifestations, the objective world in final
analysis would offer us nothing but motion. Every phenomenon would be
expressed by an atomistic integral, and that is the inner reason of
the majestic unity which reigns in modern physics. The forces which
are brought into play by Life are no longer to be distinguished in
this ultimate analysis from other natural forces. All are blended in
molecular mechanics.

The philosophical value of this theory is undeniable. It has exercised
on physical science an influence which is justified by the discoveries
which it has suggested. But to biology, on the other hand, it has lent
no aid. It is precisely because it descends too deeply into things, and
analyzes them to the uttermost, that it ceases to throw any light upon
them. The distance between the hypothetical atom and the apparent and
concrete fact is too great for the one to be able to throw light on the
other. The vital phenomenon vanishes with its individual aspect; its
features can no longer be distinguished.

Besides, a whole school of contemporary physicists (Ostwald of Leipzig,
Mach of Vienna) is beginning to cast some doubt on the utility of the
kinetic hypothesis in the future of physics itself, and is inclined to
propose to substitute for it the theory of energetics. We shall see,
in every case, that this other conception, as universal as the kinetic
theory, _the theory of Energy_, causes a vivid light to penetrate into
the depths of the most difficult problems in physiology.

Such are, with their successive transformations, the three principal
theories, the three great currents between which biology has been
tossed to and fro. They are sufficiently indicative of the state of
positive science in each age, but one is astonished that they are not
more so; and this is due to the fact that these conceptions are too
general. They soar too high above reality. More characteristic in this
respect will be particular theories of the principal manifestations of
living matter, of its perpetuity by generation, of the development by
which it acquires its individual form, on heredity. It is here that it
is of importance to grasp the progressive march of science—that is to
say, the design and the plan of the building which is being erected,
“blindly, so to speak,” by the efforts of an army of workers, an army
becoming more numerous day by day.




                              CHAPTER V.

THE EMANCIPATION OF SCIENTIFIC RESEARCH FROM THE YOKE OF PHILOSOPHICAL
                               THEORIES.

 The excessive use of Hypothetical Agents in Physiological
 Explanations—§ 1. _Vital Phenomena in Fully-constituted
 Organisms_—Provisory Exclusion of the Morphogenic idea—The Realm
 of the Morphogenic Idea as the Sanctuary of Vital Force—§ 2. _The
 Physiological Domain properly so called_—Harmony and Connection
 of Phenomena—Directive Forces—Claude Bernard’s Work—Exclusion
 of Vital Force, of Final Cause, of the “Caprice” of Living
 Nature—Determinism—The Comparative Method—Generality of Vital
 Phenomena—Views of Pasteur.


The theories whose history we have just sketched in broad outline long
dominated science and exercised their influence on its progress.

This domination has ceased to exist. Physiology has emancipated itself
from their sway, and this, perhaps, is the most important revolution
in the whole history of biology. Animism, vitalism, materialism,
have ceased to exercise their tyranny on scientific research. These
conceptions have passed from the laboratory to the study; from being
physiological, they have become philosophical.

This result is the work of the physiologists of sixty years ago. It
is also the consequence of the general march of science and of the
progress of the scientific spirit, which shows a more and more marked
tendency to separate completely the domain of facts from the domain of
hypotheses.

_Excessive Use of Hypothetical Agents in Physiological
Explanations._—It may be said that in the early part of the nineteenth
century, in spite of the efforts of a few real experimenters from
Harvey to Spallanzani, Hales, Laplace, Lavoisier, and Magendie, the
science of the phenomena of life had not followed the progress of
the other natural sciences. It remained in the fog of scholasticism.
Hypotheses were mingled with facts, and imaginary agents carried out
real acts, in inexpressible confusion. The soul (_animism_), the vital
force (_vitalism_), and the final cause (_finalism_, _teleology_)
served to explain everything.

In truth, it was also at this time that physical agents, electric and
magnetic fluids, or, again, chemical affinity, played an analogous
part in the science of inanimate nature. But there was at least this
difference in favour of physicists and chemists, that when they had
attributed some new property or aptitude to their hypothetical agents
they respected what they attributed. The physiological physicians
respected no law, they were subject to no restraint. Their vital force
was capricious; its spontaneity made anticipation impossible; it acted
arbitrarily in the healthy body; it acted more arbitrarily still in the
diseased body. All the subtlety of medical genius was called into play
to divine the fantastic behaviour of the spirit of disease. If we speak
here of physiologists and doctors alone and do not quote biologists, it
is because the latter had not yet made their appearance as authorities;
their science had remained purely descriptive, and they had not yet
begun to explain phenomena.

Such was the state of things during the first years of the nineteenth
century. It lasted, thanks to the founders of contemporary
physiology—Claude Bernard in France, and Brücke, Dubois-Reymond,
Helmholtz, and Ludwig in Germany—until a separation took place between
biological research and philosophical theories. This delimitation
operated in physiology properly so called—_i.e._ in a branch of the
biological domain in which as yet joint tenancy had been the rule. An
important revolution fixed the respective divisions of experimental
science and philosophical interpretation. It was understood that the
one ends where the other begins, that the one follows the other,
that one may not cross the other’s path. There is between them only
one doubtful region about which there is dispute, and this uncertain
frontier is constantly being shifted and science daily gains what
philosophy loses.


            § 1. VITAL PHENOMENA IN CONSTITUTED ORGANISMS.


A displacement of this kind had taken place at the time of which we
speak. It was agreed, that as far as concerns the phenomena which take
place in _a constructed and constituted living organism_, it would
no longer be permissible to allow to intervene in their explanation
forces or energies other than those which are brought into play in
inanimate nature. Just as when explaining the working of a clock, the
physicist will not invoke the volition or the art of the maker, or
the design that he had in view, but only the connection of causes and
effects which he has utilized; so, for the living machine, whether
the most complex, such as the human body, or the most elementary,
such as the cell, we may not invoke a final cause, a vital force,
external to that organism and acting on it from without, but only the
connections and the fluctuations of effects which are the sole actual
and efficient causes. In other words Ludwig, and Claude Bernard in
particular, expelled from the domain of active phenomenality the three
chimeras—Vital Force, Final Cause, and the “Caprice” of Living Nature.

But the living being is not only a _completely constructed and
completely constituted_ organism. It is not a finished clock. It is a
clock which is making itself, a mechanism which is constructing and
perpetuating itself. Nothing of the kind is known to us in inanimate
nature. Physiology has found—in what is called morphogeny—its temporary
limit. It is beyond this limit, it is in the study of phenomena by
which the organism is constructed and perpetuated, it is in the region
of the functions of generation and development, that philosophical
doctrines expand and flourish. This is the present frontier of these
two powers, philosophy and science. We shall presently delimit them
more precisely. W. Kühne, a well-known scientist whose death is
deplored, not in Germany alone, amused himself by studying the division
of biological doctrines among the members of learned societies and in
the world of academies. He summed up this kind of statistical inquiry
by saying in 1898 at the Cambridge Congress, that physiologists were
nearly all advocates of the physico-chemical doctrine of life, and that
the majority of naturalists were advocates of vital force, and of the
theory of final causes.

_Domain of the Morphogenic Idea as the Last Sanctuary of Vital
Force._—We see the reason for this. Physiology, in fact, has taken
up its position in the explanation of the functional activity of
the constituted organism—_i.e._, on a ground where intervene, as we
shall show further on, no energies and no matter other than universal
energies and matter. Naturalists, on the other hand, have more
especially considered—and from the descriptive point of view alone,
at least up to the times of Lamarck and Darwin—the functions, the
generation, the development and the evolution of species. Now these
functions are most refractory and inaccessible to physico-chemical
explanations. So, when the time came to give an account of what they
had done, the zoologists had substituted for executive agents nothing
but vital force under its different names. To Aristotle it is the vital
force itself which, as soon as it is introduced into the body of the
child, moulds its flesh and fashions it in the human form. Contemporary
naturalists, the Americans C. O. Whitman and C. Philpotts, for example,
take the same line of argument. Others, such as Blumenbach and Needham,
in the eighteenth century, invoked the same division under another
name, that of the _nisus formativus_. Finally, others play with words;
they talk of heredity, of adaptation, of atavism, as if these were
real, active, and efficient beings; while they are only appellations,
names applied to collections of facts.

This region was therefore eminently favourable to the rapid increase of
hypotheses, and so they abounded. There were the theories of Buffon,
of Lamarck, of Darwin, of Herbert Spencer, of E. Haeckel, of His, of
Weismann, of De Vries, and of W. Roux. Each biologist of any mark
had his own, and the list is endless. But here already this domain of
theoretical speculation is checked on various sides by experiment.
J. Loeb, a pure physiologist, has recently given his researches a
direction in which zoology believes may be found the explanation of
the mysterious part played by the male element in fecundation. On
the other hand, the first experiment of the artificial division of
the living cell (_merotomy_), with its light upon the part played by
the nucleus in the preservation and regeneration of the living form,
is also the work of a physiological experimenter. It dates back to
1852, and is due to Augustus Waller. This experiment was made on the
sensitive nervous cell of the spinal ganglions and on the motor cell
of the anterior cornua of the spinal cord. The effects were correctly
interpreted twelve or fifteen years later. All that zoologists have
done is to repeat, perhaps unconsciously, this celebrated experiment
and to confirm the result.

Thus we see that the attack upon the vitalist sanctuary has commenced.
But it would be a grave mistake to suppose that final cause and vital
force are on the point of being dislodged from their entrenchments.
Philosophical speculation has an ample field before it. Its frontiers
may recede. For a long time yet there will be room for a more or less
modernized vitalism.


           § 2. THE PHYSIOLOGICAL DOMAIN PROPERLY SO CALLED.


Vitalism is even found installed in the region of physiology, although
for the moment this science limits its ambition to the consideration
of the completely constructed organized being, perfected in its form.
The explanation of the working of this constituted machine cannot be
complete until we take into account the harmony and the adjustment of
its parts.

_Harmony and Connection of Parts: Directive Forces._—These constituent
parts are the cells. We know that the progress of anatomy has resulted
in the cellular doctrine—_i.e._, in the two-fold affirmation that the
most complicated organism is composed of microscopic elements, the
cells, all similar, true stones of the living building, and that it
derives its origin from a single cell, egg, or spore, the sexual cell,
or cell of germination. The phenomena of life, looked at from the point
of view of the formed individual, are therefore harmonized in space;
just as, regarded from the point of view of the individual in formation
and in the species, they are connected in time. This harmony and this
connection are in the eyes of the majority of men of science the most
characteristic properties of the living being. This is the domain of
_vital specificity_, of the _directive forces_ of Claude Bernard and A.
Gautier, and of the _dominants_ of Reinke. It is not certain, however,
that this order of facts is more specific than the other. Generation
and development have been considered by many physiologists, and quite
recently by Le Dantec, as simple aspects or modalities of nutrition or
assimilation, the common and fundamental property of every living cell.

_The Work of Claude Bernard. Exclusion of Vital Force, of Vital Cause,
of the “Caprice” of Living Nature._—It is not, however, a slight
advance or inconsiderable advantage to have eliminated vitalistic
hypotheses from almost the whole domain of present-day physiology, and
to have them, as it were, thrown back into its hinterland. This is the
work of the scientific men of the first half of the nineteenth century,
and particularly of Claude Bernard, who has thereby won the name of
the founder or lawgiver of physiology. They found in the old medical
school an obstinate adversary glorying in its sterile traditions. In
vain was it proved that vital force cannot be an efficient cause; that
it was a creation of the brain, an insubstantial phantom introduced
into the anatomical marionette and moving it by strings at the will of
any one—its adepts having only to confer upon it a new kind of activity
to account for the new act. All that had been shown with the utmost
clearness by Bonnet of Geneva, and by many others. It had also been
said that the teleological explanation is equally futile, since it
assigns to the present, which exists, an inaccessible, and evidently
ultimately inadequate cause, which does not yet exist. These objections
were in vain.

_Determinism._—And so it was not by theoretical arguments that the
celebrated physiologist dealt with his adversaries, but by a kind of
lesson on things. In fact he was continually showing by examples that
vitalism and the theory of final causes were idle errors which led
astray experimental investigation; that they had prevented the progress
of research and the discovery of the truth in every case and on every
point in which they had been invoked. He laid down the principle of
_biological determinism_, which is nothing but the negation of the
“caprice” of living nature. This postulate, so evident that there was
no need to enunciate it in the physical sciences, had to be shouted
from the housetops for the benefit of supporters of vital spontaneity.
It is the statement that, under determined circumstances materially
identical, the same vital phenomena will be identically reproduced.

_Comparative Method._—Claude Bernard completed this critical work by
laying down the laws of experiment on living beings. He commended as
the rational method of research the _comparative method_. This should
be, and is in fact, the daily instrument of all those who work in
physiology. It compels the investigator in every research bearing
on organized beings to institute a series of tests, such that the
conditions which are unknown and impossible to know may be regarded
as identical from one test to another; and when we are certain that a
single condition is variable, it compels him to discover the character
of the condition we are dealing with, and to learn to appreciate, and
to measure its influence. It is safe to say that the errors which are
daily committed in biological work have their cause in some infraction
of this golden rule. In physical science the obligation to follow
the comparative method is much less felt. In most cases the _witness
test_[3] is useless. In physiology the witness test is indispensable.

 [3] In an article on the experimental method recently published in the
 _Dictionnaire de Physiologie_, M. Ch. Richet writes as follows:—“We
 must therefore never cease to carry out comparative experiments.
 I do not hesitate to say that this comparison is the basis of the
 experimental method.” It is in fact what was taught by Claude
 Bernard in maxim and by example. It is no exaggeration to assert
 that nine-tenths of the errors which take place in research work
 are imputable to some breach of this method. When an investigator
 makes a mistake, save in the case of material error, it is almost
 certainly due to the fact that he has neglected to carry out one
 of the comparative tests required in the problem before him. The
 following is an instance which happened since the above pages were
 written:—Several years ago a chemist announced the existence in the
 blood serum of a ferment, lipase, capable of saponifying fats—that is
 to say, of extracting from them the fatty acid. From this he deduced
 many consequences relative to the mechanism of fermentations. But on
 the other hand, it has been since shown (April 1902) that this lipase
 of the serum does not exist. How did the error arise? The author in
 question had mixed normally obtained serum with oil, and he had noted
 the acidification of the mixture; he assured himself of the fact by
 adding carbonate of soda. He saw the alkalinity of the mixture, serum
 + oil + carbonate of soda, diminish, and he drew the conclusion that
 the acid came from the saponified oil. He did not make the comparative
 test, serum + carbonate of soda. If he had done so, he would have
 ascertained that it also succeeded, and that therefore as the acid did
 not come from the saponification of the oil, since there was none, its
 production could not prove the existence of a lipase.

_Generality of Vital Phenomena._—If we add that Claude Bernard opposed
the narrow opinion, so dear to early medicine, which limited the
consideration of vitality to man, and the contrary notion of the
essential generality of the phenomena of life from man to the animal,
and from the animal to the plant, we shall have given very briefly an
idea of the kind of revolution which was accomplished about the year
1864, the date of the appearance of the celebrated _l’Introduction à la
médecine expérimentale_.

The ideas we have just recalled seem to be as evident as they are
simple. These principles appear so well founded that in a measure they
form an integral part of contemporary mentality. What scientist would
nowadays deliberately venture to explain some biological fact by the
intervention of the evidently inadequate vital force or final cause?
And who, to account for the apparent inconsistency of the result,
would bring forward the “caprice” of living nature? And who again would
openly dispute the utility of the comparative method?

What the physiologists of to-day, according to Claude Bernard, would no
longer do, their predecessors would do, and not the least important of
them. Longet, for example, at a full meeting of the Académie, apropos
of recurrent sensibility, and Colin (of Alfort), communicating his
statistical results on the temperature of two hearts, accepted more or
less explicitly the indetermination of vital facts. And why confine
our remarks to our predecessors? The scientists of to-day are much
the same. So here again we see the reappearance of the phantom of the
final cause in so-called scientific explanations. One fact is accounted
for by the necessity of the self-defence of the organism; another by
the necessity to a warm-blooded animal of keeping its temperature
constant. Le Dantec has recently reproached zoologists for giving as
an explanation of fecundation the advantage that an animal enjoys in
having a double line of ancestors. We might as well say, as L. Errera
has pointed out, that the inundations of the Nile occur in order to
bring fertility to Egypt.

We must not therefore depreciate the marvellous work which has
emancipated modern physiology from the tutelage of early theories.
The witnesses of this revolution appreciated its importance. One of
them remarked as follows, on the appearance of _l’Introduction à la
médecine expérimentale_, which contained, however, only a portion of
the theory:—“Nothing more luminous, more complete, or more profound,
has ever been written upon the true principles of an art so difficult
as that of experiment. This book is scarcely known because it is on a
level to which few people nowadays attain. The influence it will have
on medical science, on its progress, and on its very language, will
be enormous. I cannot now prove my assertion, but the reading of this
book will leave so strong an impression that I cannot help thinking
that a new spirit will at once inspire these splendid researches.”
This was said by Pasteur in 1866. That is what he thought of the work
of his senior and his rival, at the moment when he himself was about
to inspire those “splendid researches” with the movement of reform,
the importance and the consequences of which have no equivalent in
the history of science. By their discoveries and their teaching, by
their examples and their principles, Claude Bernard and Pasteur have
succeeded in emancipating a portion of the domain of vital facts from
the direct intervention of hypothetical agents and first causes. They
were compelled, however, to leave to philosophical speculation, to
directing forces, to animism, to vitalism, an immense provisory field,
the field which corresponds to the functions of generation and of
development, to the life of the species and to its variations. Here we
find them again in various disguises.




                               BOOK II.

             THE DOCTRINE OF ENERGY AND THE LIVING WORLD.

 Summary: General Ideas of Life.—Elementary Life.—Chapter I. Energy
 in General.—Chapter II. Energy in Biology.—Chapter III. Alimentary
 Energetics.


                GENERAL IDEAS OF LIFE. ELEMENTARY LIFE.


_Life is the Sum-total of the Phenomena Common to all Living Beings.
Elementary Life._—Living beings differ more in form and configuration
than in their manner of being. They are distinguished more by their
anatomy than by their physiology. There are, in fact, phenomena common
to all, from the highest to the lowest. This is because there is that
similar or identical foundation, that _quid commune_ which has enabled
us to apply to them the common name of “living beings.” Claude Bernard
gave to this sum-total of manifestations common to all (nutrition,
reproduction) the name of _elementary life_. To him _general
physiology_ was _the study of elementary life_; the two expressions
were equivalent, and they were equivalent to a longer formula which
the illustrious biologist has given as a title to one of his most
celebrated works—_The Study of the Phenomena Common to all Living
Beings, Animals, and Plants_. From this point of view each being is
distinguished from another being as a given _individual_ and as a
particular _species_; but all are in some way alike and thus resemble
one another: common life, elementary life, the essential phenomena of
life; it is _life itself_.[4]

 [4] Le Dantec has objected to this conception of phenomena common to
 different living beings. He insists that all phenomena which take
 place in a given living being are proper to him, and differ, however
 slightly, from those of another individual. The objection is more
 specious than real.

The manifestations of life may therefore be regarded from the point
of view of what is most general among them. As we go down the scale
of anatomical organization, as we pass from apparatus (circulatory,
digestive, respiratory, nervous) to the _organs_ which compose them,
from the organs to the _tissues_, and finally from the tissues to the
_anatomical elements_ or _cells_ of which they are formed, we approach
that common, physiological dynamism which is _elementary life_, but we
do not actually reach it. The cell, the anatomical element, is still a
complicated structure. The elementary fact is further from us and lower
down. It is in the living matter, in the molecule of this matter, and
there we must seek it.

Galen gave in days gone by as the object of researches on life, the
knowledge of the use of the different organs of the animal machine;
“de usu partium.” Later, Bichat assigned to them as their end the
determination of the _properties of tissues_. Modern anatomists and
zoologists try to reach the constituent element of these tissue—the
cell. Their dream is to construct a _cellular physiology_, a
_physiological cytology_; but we must go further than that.

_General Physiology, Cellular Physiology, the Energetics of Living
Beings._—General physiology, as was taught by Pflüger and his school,
claims to go deeper down than the apparatus, or the organ, or even
the cell. As in the case of physics, general physiology endeavours to
reach, and really does in many cases reach, as far as the molecule.
It is not cellular, it is _molecular_. Already, in fact, the efforts
of modern science have succeeded in penetrating into the most general
phenomena of the living being—those attributable to living matter,
or, to speak more clearly, those which result from the play of the
universal laws of matter at work in this particular medium which is the
organized being.

Robert Mayer and Helmholtz have the honour of having set physiology in
the right road. They founded _the energetics of living beings_—_i.e._,
they regarded the phenomena of life from the point of view of energy,
which is the factor of all the phenomena of the universe.




                              CHAPTER I.

                          ENERGY IN GENERAL.

 Origin of the Idea of Energy.—The Phenomena of Nature bring into play
 only two Elements, Matter and Energy.—§ 1. Matter.—§ 2. Energy.—§ 3.
 Mechanical Energy.—§ 4. Thermal Energy.—§ 5. Chemical Energy.—§ 6.
 The Transformations of Energy.—§ 7. The Principles of Energetics.—The
 Principle of the Conservation of Energy.—§ 8. Carnot’s Principle.—The
 Degradation of Energy.


_Origin of the Idea of Energy._—A new term, namely _energy_, has been
for some years introduced into natural science, and has ever since
assumed a more and more important place. It is owing to the English
physicists, and especially to the English electrical engineers, that
this expression has made its way into technology, an expression which
is part and parcel of both languages, and which has the same meaning
in both. The idea it expresses is, in fact, of infinite value in
industrial applications, and that is why its use has gradually spread
and become generalized. But it is not merely a practical idea. It is
above all a theoretical idea of capital importance to pure theory. It
has become the point of departure of a science, _energetics_, which,
although born but yesterday, already claims to embrace, co-ordinate,
and blend within itself all the other sciences of physical and living
nature, which the imperfection of our knowledge alone had hitherto kept
distinct and apart.

On the threshold of this new science we find inscribed _the principle
of the conservation of energy_, which has been presented to us by
some as Nature’s supreme law, and which we may say dominates natural
philosophy. Its discovery marked a new era and accomplished a profound
revolution in our conception of the universe. It is due to a doctor,
Robert Mayer, who practised in a little town in Wurtemberg, and who
formulated the new principle in 1842, and afterwards developed its
consequences in a series of publications between 1845 and 1851. They
remained almost unknown until Helmholtz, in his celebrated memoir on
the conservation of force, brought them to light and gave them the
importance they deserved. From that time forward the name of the doctor
of Heilbronn, until then obscure, has taken its place among the most
honoured names in the history of science.[5]

 [5] Mayer’s claim to fame has been disputed. A Scotch physicist, P.
 G. Tait, has investigated the history of the law of the conservation
 of energy, which is the history of the idea of energy. The conception
 has taken time to penetrate the human mind, but its experimental proof
 is of recent date. P. G. Tait finds an almost complete expression
 of the law of the conservation of energy in Newton’s third law of
 motion—namely, “the law of the equality of action and reaction,” or
 rather, in the second explanation which Newton gave of that law. In
 fact, it was from this law that Helmholtz deduced it in 1847. He
 showed that the law of the equality of action and reaction, considered
 as a law of nature, involved the impossibility of perpetual motion,
 and the impossibility of perpetual motion is, in another form, the
 conservation of energy.

 At a meeting of the Academy of Science, at Berlin, 28th March 1878,
 Du Bois-Reymond violently attacked Tait’s contention. The honour
 of having been the first to conceive of the idea of energy and
 conservation was awarded to Leibniz. Newton had no right to it, for
 he appealed to divine intervention to set the planetary system on its
 path when disturbed by accumulated perturbations. On the other hand,
 Colding claims to have drawn his knowledge of the law of conservation
 from d’Alembert’s principle. Whatever may be the theoretical
 foundations of this law, we are here dealing with its experimental
 proof. According to Tait, the proof can no more be attributed to R.
 Mayer than to Seguin. The real modern authors of the principle of the
 conservation of energy, who gave an experimental proof of it, are
 Colding, of Copenhagen, and Joule, of Manchester.

As for _energetics_, of which thermodynamics is only a section, it is
agreed that even if it cannot forthwith absorb mechanics, astronomy,
physics, chemistry, and physiology, and build up that general science
which will be in the future the one and only science of nature, it
furnishes a preparation for that ideal state, and is a first step in
the ascent to definite progress.

Here I propose to expound these new ideas, in so far as they contain
anything universally accessible; and in the second place, I propose to
show their application to physiology—that is to say, to point out their
rôle and their influence in the phenomena of life.

_Postulate: the Phenomena of Nature bring into play only two Elements,
Matter and Energy._—If we try to account for the phenomena of the
universe, we must admit with most physicists that they bring into play
two elements, and two elements only; namely, _matter_ and _energy_. All
manifestations are exhibited in one or other of these two forms. This,
we may say, is the postulate of experimental science.

Just as gold, lead, oxygen, the metalloids, and the metals are
different kinds of matter, so it has been recognized that sound, light,
heat, and generally, the imponderable agents of the days of early
physics, are different varieties of energy. The first of these ideas
is older and more familiar to us, but it has not for that reason a more
certain existence. Energy is objective reality for the same reason that
matter is. The latter certainly appears more tangible and more easily
grasped by the senses. But, upon reflection, we are assured that the
best proof of their existence, in both cases, is given by the law of
their conservation—that is to say, their persistence in subsisting.

The objective existence of matter and that of energy will therefore
be taken here as a postulate of physical science. Metaphysicians may
discuss them. We have but little room for such a discussion.


                             § I. MATTER.


It is certainly difficult to give a definition of matter which will
satisfy both physicists and metaphysicians.

_Mechanical Explanation of the Universe. Matter is Mass._—Physicists
have a tendency to consider all natural phenomena from the point of
view of mechanics. They believe that there is a mechanical explanation
of the universe. They are always on the look out for it, implicitly or
explicitly. They endeavour to reduce each category of physical facts
to the type of the facts of mechanics. They have made up their minds
to see nowhere anything but the play of motion and force. Astronomy
is celestial mechanics. Acoustics is the mechanics of the vibratory
movements of the air or of sonorous bodies. Physical optics has become
the mechanics of the undulations of the ether, after having been the
mechanics of emission—a wonderful mechanics which represents exactly
all the phenomena of light, and furnishes us with a perfect objective
image of it. Heat, in its turn, has been reduced to a mode of motion,
and thermodynamics claims to embrace all its manifestations. As early
as 1812, Sir Humphry Davy wrote as follows:—“The immediate cause of
heat is motion, and the laws of transmission are precisely the same
as those of the transmission of motion.” From that time forth, this
conception developed into what is really a science. The constitution
of gases has been conceived by means of two elements—particles, and
the motions of these particles, determined in the strictest detail.
And finally, in spite of the difficulties of the representation of
electrical and magnetic phenomena after Ampère and before Maxwell and
Hertz, physicists have been able to announce in the second half of the
nineteenth century the unity of the physical forces realized in and
by mechanics. From that time forth, all phenomena have been conceived
as motion or modes of motion, only differing essentially one from the
other in so far as motions may differ—that is to say, in the masses of
the moving particles, their velocities, and their trajectories. The
external world has appeared essentially homogeneous; it has fallen a
prize to mechanics. Above all, there is heterogeneity in ourselves. It
is in the brain, which responds to the nervous influx engendered by the
longitudinal vibration of the air, by the specific sensation of sound,
which responds to the transverse vibration of the ether by a luminous
sensation, and in general to each form of motion by an irreducible
specific sensation.

Forty years have passed since the mechanical explanation of the
universe reached its definite and perfect form. It dominates physics
under the name of the _theory of kinetic energy_. The minds of men
in our own time are so strongly impregnated with this idea that most
scientists of ordinary culture get no glimpse of the world of phenomena
but by means of this conception. And yet it is only an hypothesis.
But it is so simple, so intuitive, and appears to be so thoroughly
verified by experiment, that we have ceased to recognize its arbitrary
and unnecessarily contingent character. Many physicists from this
standpoint consider the kinetic theory as an imperishable monument.

However, as in the case of H. Poincaré, the most eminent physicists and
mathematicians are not the dupes of this system; and without failing to
recognize the immense services which it has rendered to science, they
are perfectly well aware that it is only a system, and that there may
be other systems. Certain among them, such as Ostwald, Mach, and Duhem,
believe that the monument is showing signs of decay, and at present the
theory is opposed by another theory—namely, the theory of _energy_.

The theory of _energy_ is usually considered and presented as a
consequence of the kinetic theory; but it is perfectly independent of
it, and it is, in fact, without relying on the kinetic theory, without
assuming the unity of physical forces, which are combined in molecular
mechanics, that we shall expound the general system.

This is not the point at issue for the moment. It is not a question
of deciding the reality or the merit of this or that mechanical
explanation; it is a question of something more general, because upon
it depends the _idea of matter_. It is a question of knowing if there
are any explanations other than mechanical. The illustrious English
physicist, Lord Kelvin, does not seem willing to admit this. “I am
never satisfied,” he said, in his _Molecular Mechanics_, “until I have
made a mechanical model of the object. If I can make this model, I
understand; if I cannot, I do not understand.”

This tendency of so vigorous a mind to be content only with mechanical
explanations, has been that of the majority of scientific men up to the
present day, and from it has arisen the scientific idea of matter.

What is matter, in fact, to the student of mechanics? It is mass. All
mechanics is constructed of masses and forces. Laplace said: “The mass
of a body is the sum of its material points.” To Poisson, mass is the
quantity of matter of which a body is composed. Matter is therefore
confused with mass. Now, mass is the characteristic of the motion of
a body under the action of a given force; it defines obedience or
resistance to the causes of motion; it is the _mechanical parameter_;
it is the co-efficient proper to every mobile body; it is the first
_invariant_ of which a conception has been established by science.

In fact, the word matter appears to be used in other senses by
physicists, but this is only apparently so. They have but broadened the
idea of the mechanicians. They have characterized matter by the whole
series of phenomenal manifestations which are _proportional to mass_,
such as weight, volume, chemical properties—so that we may say that the
notion of matter does not intervene scientifically with a different
signification from that of mass.

_Two kinds of Matter. Ponderable and Imponderable._—In physics we
distinguish between two kinds of matter—ponderable, obeying the law of
universal attraction or weight, and imponderable matter or ether, which
we assume to exist and to escape the action of that force. Ether has no
weight, or extremely little weight. It is material in so far as it has
mass. It is its mass which confers existence on it from the mechanical
point of view—a logical existence, inferred from the necessity of
explaining the propagation of heat, light, or electricity.

It may be observed that the use of mass really comes to bringing
another element, force, to intervene, and we shall see that force is
connected with energy; thus it comes to defining matter indirectly by
energy. The two fundamental elements are not therefore irreducible; on
the contrary, they should be one and the same thing.

_Energy is the only Objective Reality._—This fusion into one will
become more evident still when we examine the different kinds of
energy, each of which exactly corresponds to one of the aspects of
active matter. Shall we define matter by _extension_, by the portion
of space it occupies, as certain philosophers do? The physicist will
answer that space is only known to us by the expenditure of energy
necessary to penetrate it (the activity of our different senses). And
then what is weight? It is _energy of position_ (universal attraction).
And so with the other attributes. So that if matter were separated
from the energetic phenomena by means of which it is revealed to
us—weight or energy of position, impenetrability or energy of volume,
chemical properties or chemical energies, mass or capacity for kinetic
energy—the very idea of matter would vanish. And that comes to saying
that fundamentally there is only one objective reality, _energy_.

_Philosophical Point of View._—But from the philosophical point of view
are there objective realities? That is a wider question which throws
doubt upon matter itself, and which it is not our place to investigate
here. A metaphysician may always discuss and deny the existence of
the objective world. It may be maintained that man knows nothing
beyond his sensations, and that he only objectivates them and projects
them outside himself by a kind of hereditary illusion. We must avoid
taking sides in all these difficulties. Physics for the moment ignores
them—_i.e._, postpones their consideration.

In a first approximation we agree to consider ponderable matter only.
Chemistry acquaints us with its different forms. They are the different
simple bodies, metalloids, metals, and the compound bodies, mineral
or organic. Hence we may say that chemistry is _the history of the
transformations of matter_. From the time of Lavoisier this science has
followed the transformations of matter, balance in hand, and ascertains
that they are accomplished without change of weight.

_Law of the Conservation of Matter._—Imagine a system of bodies
enclosed in a closed vessel, and the vessel placed in the scale of a
balance. All the chemical reactions capable of completely modifying the
state of this system have no effect upon the scale of the balance. The
total weight is the same before, during, and after. It is precisely
this equality of weight which is expressed in all the equations with
which treatises on chemistry are filled.

From a higher point of view we recognize here, in this _law of
Lavoisier_ or of the _conservation of weight_, the verification of one
of the great laws of nature which we extend to every kind of matter,
ponderable or not. It is the _law of the conservation of matter_, or
again, of the indestructibility of matter—“Nothing is lost, nothing
is created, all is transformation.” This is exactly what Tait held,
this impossibility of creating or destroying matter which at the same
time is a proof of its objective existence. This indestructibility
of ponderable matter is at the same time the fundamental basis of
chemistry. Chemical analysis could not exist if the chemist were not
sure that the contents of his vessel at the end of his operations ought
to be quantitatively, that is to say by weight, the same as at the
beginning, and during the whole course of the experiment.[6]

 [6] It must be added that the absolute rigour of this law has been
 called in question in recent researches. It would only have an
 approximate value.


                             § 2. ENERGY.


_The Idea of Energy Derived from the Kinetic Theory._—The notion of
energy is not less clear than the notion of matter, it is only more
novel to our minds. We are led to it by the mechanical conception which
now dominates the whole of physics, _the kinetic conception_, according
to which in the sensible universe there are no phenomena but those of
motion. Heat, sound, light, with all their manifestations so complex
and so varied, may, according to this theory, be explained by motion.
But then, if outside the brain and the mind which has consciousness and
which perceives, Nature really offers us only motion, it follows that
all phenomena are essentially homogenous among one another, and that
their apparent heterogeneity is only the result of the intervention of
our sensorium. They differ only in so far as movements are capable of
differing—that is to say, in velocity, mass, and trajectory. There is
something fundamental which is common to them and this _quid commune_
is _energy_. Thus the idea of energy may be derived from the kinetic
conception, and this is the usual method of exposition.

This method has the great inconvenience of causing an idea which lays
claim to reality to depend upon an hypothesis. And besides that, it
gives a view of it which may be false. It makes of the different forms
of energy something more than varieties which are equivalent to one
another. It makes of them _one and the same thing_. It blends into one
the modalities of energy and mechanical energy. For the experimental
idea of equivalence, the kinetic theory substitutes the arbitrary idea
of the equality, the blending, and the fundamental homogeneity of
phenomena. This no doubt is how the founders of energetics, Helmholtz,
Clausius, and Lord Kelvin understood things. But a more attentive study
and a more scrupulous determination not to go beyond the teaching
of experiment should compel us to reform this manner of looking at
it. And it is Ostwald’s merit that, after Hamilton, he insisted on
this truth—that the various kinds of physical magnitudes furnished
by the observation of phenomena are different and characteristic. In
particular, we may distinguish among them those which belong to the
order of _scalar_ magnitudes and others which are of the order of
_vector_ magnitudes.

_The Idea of Energy derived from the Connection of Phenomena._—The idea
of energy is not absolutely connected with the kinetic theory, and it
should not be exposed therefore to the vicissitudes experienced by that
theory. It is of a higher order of truth. We can derive it from a less
unsafe idea, namely that of the _connection of natural phenomena_. To
conceive it we must get accustomed to this primordial truth, that there
are no _phenomena isolated_ in time and space. This statement contains
the whole point of view of energetics.

The physics of early days had only an incomplete view of things, for it
considered phenomena independently the one of the other.

Phenomena for purposes of analysis were classed in separate and
distinct compartments: weight, heat, electricity, magnetism, light.
Each phenomenon was studied without reference to that it succeeded or
that which should follow. Nothing could be more artificial than such a
method as this. In fact, there is a sequence in everything, everything
is connected up, _everything precedes and succeeds in nature_—in
nature there are only series. The isolated fact without antecedent or
consequent is a myth. Each phenomenal manifestation is in solidarity
with another. It is a metamorphosis of one state of things into
another. It is transformation. It implies a state of things anterior to
that which we are observing, a phenomenal form which has preceded the
form of the present moment.

Now there exists a link between the anterior state and the succeeding
state—that is to say, between the new form which is appearing and the
preceding form which is disappearing. The science of energy shows
that something has passed from the first condition to the second,
but covering itself as it were with a new garment; in a word, that
something active and permanent subsists in the passage from one
condition to another, and that what has changed is only the aspect, the
appearance.

This constant something which is perceived beneath the inconstancy and
the variety of forms, and which circulates in a certain manner from the
antecedent phenomenon to its successor, is energy.

But still this is only a very vague view, and it may seem arbitrary.
It may be made more exact by examples borrowed from the different
categories of natural phenomena. There are energetic modalities in
relation with the different phenomenal modalities. The different orders
of phenomena which may be presented—mechanical, chemical, thermal,
electrical—give rise to corresponding forms of energy.

When to a mechanical phenomenon succeeds a mechanical, thermal,
or electrical phenomenon, we say, embracing transformation in its
totality, that there has been a transformation of mechanical energy
into another form of energy, mechanical, thermal, or electrical, etc.

This idea becomes more precise if we examine successively each of these
cases and the laws which regulate them.


                        § 3. MECHANICAL ENERGY.


Mechanical energy is the simplest and the oldest known.

_Mechanical Elements: Time, Space, Force, Work, Power._—Mechanical
phenomena may be considered under two fundamental conditions—_time_ and
_space_, which are, in a measure, logical elements, to which may be
joined a third element, itself experimental, having its foundations in
our sensations—namely, _force_, _work_, or _power_.

The ideas of force, work, and power, are drawn from the experience man
has of his muscular activity. Nevertheless the greatest mathematical
minds from from Descartes to Leibniz have been obliged to define and
explain them clearly.

_Force_.—The prototype of force is weight, universal attraction.
Experiment shows us that every body falls as long as no obstacle
opposes its fall. This is so universal a property of matter that it
serves to define it. The _force_, weight, is therefore the name given
to the cause of the fall of the bodies.

Force in general is the _cause of motion_. Hence force exists only in
so far as there is motion. There would be no force without action. This
is Newton’s point of view. It did not prevail, and was not the point
of view of his successors. The name of force has been given not only
to the cause which produces or modifies motion, but to the cause which
resists and prevents it. And then not only have _forces in action_ been
considered (dynamics), but _forces at rest_ (statics). Now, to Newton
there was no statics. Forces do not continue to exist when they produce
no motion; they are not in equilibrium, they are destroyed.

The idea of force therefore is a metaphysical idea which contains the
idea of _cause_. But it becomes experimental immediately it is looked
upon as resisting motion, according to the point of view of Newton’s
opponents. Its foundations lie in the muscular activity of man.

Man can support a burden without bending or moving. This burden is
a weight—that is to say, a mass acted on by the force of weight.
Man resists this force so as to prevent its effect. If it were not
annihilated by man’s _effort_, this effect would be the motion or
the fall of the heavy body. The _effort_ and the force are thus in
equilibrium, and the effort is equal and opposite to the force. It
gives to the man who exercises it the conscious idea of _force_. Thus
we know of force through effort. Every clear idea that we can have of
_force_ springs from the observation of our muscular effort.

The notion of force is thus an anthropomorphic notion. When an effect
is produced in nature outside human intervention, we say that it is
by something analogous to what in man is effort, and we give to this
something a name which is also analogous, namely _force_. To give a
name to _effort_ and to compare efforts in magnitude, we need not know
all about them, nor need we know in what they essentially consist, of
what series of physical, chemical, and physiological actions they are
the consequence. And so it is with force. It is a resistance to motion
or the cause of motion. This cause of motion may be an anterior motion
(kinetic force). It may be an anterior physical energy (physical and
chemical forces).

Forces are measured in the C.G.S. system by comparing them with the
unit called the Dyne.[7] In practice they are compared with a much
larger unit—the gramme, which is the weight, the force acting on a unit
of mass of one centimetre of distilled water at a temperature of 4° C.

 [7] The dyne is the force which applied to the unit of mass produces a
 unit of acceleration.

_Work._—The muscular activity of man may be brought into play in yet
another manner. When we employ workmen, as Carnot said in his _Essai
sur l’équilibre et le mouvement_, it is not a question of “knowing the
burdens that they can carry without moving from their position,” but
rather the burdens that they can carry from one point to another. For
instance, a workman may have to lift the water from the bottom of a
well to a given height, and the case is the same for the animals we
employ. “This is what we understand by force when we say that the force
of a horse is equal to the force of seven men. We do not mean that if
seven men were pulling in one direction and the horse in another that
there would be equilibrium, but that in a piece of work the horse alone
would lift, for example, as much water from the bottom of a well to a
given height as the seven men together would do in the same time.”[8]

 [8] These words spoil the statement, for time has nothing to do with
 it.

Here, then, we have to do with the second form of muscular activity,
which is called in mechanics, “work”—at least, if in the preceding
quotation we attach no particular importance to the words “in the same
time,” and retain the employment of muscular activity only “under
constant conditions.” Mechanical work is compared with the elevation of
a certain weight to a certain height. It is measured by the product of
the force (understood in the sense in which it was used just now—that
is to say, as causing or resisting motion) and the displacement due to
this motion. The unit is the Kilogrammetre—that is to say, the work
necessary to lift a weight of one kilogramme to the height of one
metre.

It will be remarked that the idea of time does not intervene in our
estimation of work. The notion of work is independent of the ideas
of velocity and time. “The greater or less time that we take to do a
piece of work is of no more assistance in measuring its magnitude than
the number of years that a man may have taken to grow rich or to ruin
himself can help to estimate the present amount of his fortune.”

Going back to Carnot’s comparison, an employer who employed his workmen
only on piece-work,—that is to say, who would only care about the
amount of work done, and would be indifferent to the time that they
took over it,—would be at the same point of view as the advocates of
the mechanical theory. M. Bouasse, whom we follow here, has remarked
that this idea of mechanical work may be traced back to Descartes. His
predecessors, and Galileo in particular, had quite a different idea of
the way in which mechanical activity should be measured; and so, among
the mathematicians of the eighteenth century, Leibniz and, later, John
Bernoulli were almost alone in looking at it from this point of view.

_Energy._—Work thus understood is _mechanical energy_. It represents
the lasting and objective effect of the mechanical activity independent
of all the circumstances under which it was carried out. The same
work may be done under very different conditions of time, velocity,
force, and displacement. It is therefore the permanent element in the
variety of mechanical aspects. Work, for example, in the collision of
bodies when the motion of a body appears to be destroyed on impact
with another, reappears as indestructible _vis viva_. This, then, is
exactly what we call _energy_; and if we agree to give it this name,
we may say that the conservation of energy is invariable throughout all
mechanical transformations.

_Distinction between Work and Force, and between Energy and Work._—The
history of mechanics shows us what trouble has been taken and what
efforts have been made to distinguish work (now mechanical energy) from
force.

It is worth while insisting on this distinction. It could be easily
shown that force has no objective existence. It has no duration,
no permanence. It does not survive its effect, motion. There is no
conservation of force. It passes instantly from infinity to zero.
It is a _vectorial magnitude_—that is to say, it involves the idea
of direction. Work, on the other hand, is the real element; it is
a _scalar magnitude_ involving the idea of opposite directions,
indicated by the signs + and-. Work and force are heterogeneous
magnitudes. Energy, and this is the only characteristic by which it is
distinguished from work, is an _absolute magnitude_ to which we may not
even give opposite signs.

An example may perhaps throw these characteristics into relief—namely,
the hydraulic press. We have on the platform exactly the work which has
been done on the other side. The machine has only made it change its
form. On the contrary, the force has been infinitely multiplied. We
may, in fact, consider an infinite number of surfaces equal to that of
a small piston, placed and orientated at will within the liquid; each,
according to Pascal’s principle, will support a pressure equal to that
which is exercised. As soon as we cease to support it, this infinity
falls at once to zero. Now what real thing could pass instantly from
infinity to zero?

That skilful and very able physiologist, M. Chauveau, has endeavoured
to use the same term _energy of contraction_ for the two phenomena of
effort (force) and work. It seems, however, from the point of view
of the expenditure imposed on the organism, that these two modes of
activity, _static contraction_ (effort), and _dynamical contraction_
(work), may be, in fact, perfectly comparable. But although this manner
of conceiving the phenomena may certainly be exact, and may be of great
value, the idea of force must none the less remain distinct from that
of work. The persistence of the author in violating established custom
in this connection has prevented him from enabling mechanicians and
even some physiologists to understand and accept very useful truths.

_Power._—The idea of mechanical _power_ differs from those of force
and work. The idea of time must intervene. It is not sufficient, in
fact, in order to characterize a mechanical operation, to point to
the task accomplished. It may be necessary or useful to know how much
time it required. This is true, especially when we are concerned with
the circumstances as well as the results of the performance of the
work; and this is the case when we wish to compare machines. We say
that the machine which does the work in the shortest space of time is
the most powerful. The unit of power is the Kilogrammetre-second—that
is to say, the power of a machine which does a kilogrammetre in a
second. In manufactures we generally employ a unit 75 times greater
than this—a _horse-power_. This is the power of a machine which does
75 kilogrammetres a second. In the electrical industry we measure by
_kilowatts_, which are equivalent to 1.36 horse power, or by a _watt_,
a unit a thousand times smaller.

Let us add that the power of a machine is not an absolute and permanent
characteristic of the machine. It depends on the circumstances under
which the work is carried out, and that is why, in particular, we
cannot appreciate the power of the human machine in comparison with
industrial machines. Experience has shown that the mechanical power
of living beings depends upon the nature of the work they are doing.
In this connection we may mention some very interesting experiments
communicated to the Institute, in the year VI., by the celebrated
physicist, Coulomb. A man of the average weight of 70 kilogrammes was
made to climb the stairs of a house 20 metres high. He ascended at the
rate of 14 metres a minute, and he performed this daily task for four
effective hours. This work was equivalent to 235,000 kilogrammetres.
But if, instead of climbing without a burden, the same man had had to
carry a load, the result would have been quite different. Coulomb’s
workman took up six loads of wood a day to a height of 12 metres in 66
journeys, corresponding to a maximum work of 109,000 instead of 235,000
kilogrammetres. The mechanical power of the human machine thus varied
in the two cases in the ratio of 235 to 109.

_The Two Aspects of Mechanical Energy: Kinetic and Potential._—Energy,
or mechanical work, may present itself in two forms—kinetic energy,
corresponding to the mechanical phenomenon which has really taken
place, and _potential energy_, or the energy of reserve.

A body which has been raised to a certain height will, if it be let
fall, perform work which can be exactly measured in kilogrammetres by
the product of its weight into the height it falls. Such work may be
utilized in many ways. In this way, for instance, public clocks are
worked. Now, as long as the clock-weight is raised and not let go, and
as long as it is motionless, the physics of early days would say that
there is nothing to discuss; the phenomenon is the fall; it is going to
take place, but at the present moment there has been no fall.

In energetics we do not reason in this way. We say that the body
possesses a _capacity for work_ which will be manifested when the
opportunity arises, a storage of energy, a virtual or _potential
energy_, or again, an _energy of position_, which will be transformed
into actual energy or real work as soon as the body falls.

Let us ask whence this energy arises. It proceeds from the previous
operation which has raised the weight from the surface of the soil
to the position it occupies. For example, if it is a question of the
weights of a public clock, which, by its fall, will develop in 15
days the work that is necessary to turn the wheels, to strike the
bell, and to turn the hands, this work ought to bring to our minds the
exactly equal and opposite work done by the clockmaker, who has to
carry the clock-weight and to lift it up from the ground to its point
of departure. The work of the fall is the faithful counterpart of the
work of elevation. The phenomenon has therefore in reality two phases.
We find in the second exactly what was put into the first, the same
quantity of energy—_i.e._, the same work. Between these phases comes
the intermediary phase of which we say that it is a period of virtual
_or potential energy_. This is a way of remembering in some measure the
preceding phenomenon—_i.e._, the work of lifting up, and of indicating
the phenomena which will follow—_i.e._, the work of the fall. And thus
we connect by our thoughts the present situation with the antecedent
and with the consequent position, and it is from this consideration of
continuity alone that the conception of energy springs—that is to say,
of something which is conserved and is found to be permanent in the
succession of phenomena. This energy of which we lose no trace does
not appear to us new when it is manifested. Our imagination eventually
materializes the idea of it. We follow it as a real thing, having
an objective existence, which is asleep during the latent potential
period, and is revealed or manifested later.

Among other examples, that of the coiled spring which is unwound is
particularly suitable for showing this fundamental character of the
idea of mechanical energy, an idea which is the clearest of all.
Machines are only transformers and not creators of mechanical energy.
They only change one form into another.

In the same way, too, a stream of water or the torrent of a mountainous
region may be utilized for setting in motion the wheels and the
turbines of the factories situated in the valley. Its descent produces
the mechanical work which would be a creation _ex nihilo_ if we do not
connect the phenomenon with its antecedents. We look on it as a simple
restitution, if we think of the origin of this water which has been
transported and lifted in some way to its level by the play of natural
forces—evaporation under the action of the sun, the formation of
clouds, transport by winds, etc. And we here again see that a complex
energy has been transformed, in its first phenomenal condition, into
_potential energy_, and that this potential energy is always expended
in the second phase without loss or gain.

_The Different Kinds of Mechanical Energy; of Motion, of
Position._—There are as many forms of energy as there are distinct
categories of phenomena or of varieties in these categories. Physicists
distinguish between two kinds of mechanical energy—energy of motion
and energy of position. The energy of position presents several
variants—energy of distance, which corresponds to force: of this we
have just spoken; energy of surface, which corresponds to particular
phenomena of surface tension; and energy of volume which corresponds
to the phenomena of pressure. Energy of motion, _kinetic energy_, is
measured in two ways: as work (the product of force and displacement,
W = _fs_) or as _vis viva_ (half the product of the mass into the square
of the velocity U = _mv^2_∕2.)[9]

 [9] We therefore notice that the measures of force and work bring in
 mass, space, and time. The typical force, weight, is given by w = mg.
 On the other hand, we have by the laws of falling bodies _v_ = _gt_;
 _s_ = 1∕2_gt^2_; whence _g_ = 2_s_∕_t^2_; _w_ = _m_(2_s_∕_t^2_); or,
 if F be the force, M the mass, L the space described, and T the time,
 we have F = MLT^{-2}, which expresses what are called the dimensions
 of the force—that is to say, the magnitudes with their degree, which
 enter into its expression. We may thus easily obtain the dimensions of
 work:—

 _Work_ = _f_ × _s_ = _mv^2_∕2 = ML^2T^{-2}.


                         § 4. THERMAL ENERGY.


In the elements of physics it is nowadays taught that mechanical
work may be transformed into heat, and reciprocally that heat may be
transformed into mechanical work. Friction, impact, pressure, and
expansion destroy or annihilate the mechanical energy communicated to
a body or to the organs of a machine. With the disappearance of motion
we note the appearance of heat. Examples abound. The tyre of a wheel
is heated by the friction of the road. Portions of steel are warmed
by the impact with stone, as in the old flint and steel. Two pieces
of ice were melted by Davy, who rubbed them one against the other,
the external temperature being below zero. The boiling of a mass of
water caused by a drill was noticed by Rumford in 1790, during the
manufacture of bronze cannon. Metal, beaten on an anvil, is heated. A
leaden ball flattened against a resisting obstacle shows increase of
temperature carried to the point of fusion. Finally, and symbolically,
we have the origin of fire in the fable of Prometheus, by rubbing
together the pieces of wood which the Hindoos called _pramantha_.
Correlation is constant between the thermal and mechanical phenomena,
a correlation that becomes evident as soon as observers have ceased to
restrict themselves to the determination in isolation of the one fact
or the other. There is never any real destruction of heat and motion
in the true sense of the word; what disappears in one form appears
again in another; just as if something indestructible were appearing in
a series of successive disguises. This impression is translated into
words when we speak of the metamorphosis of mechanical into thermal
energy.

_The Mechanical Equivalent of Heat._—The interpretation assumes a
remarkable character of precision, which at once strikes the mind
when physics applies to these transformations the almost absolute
accuracy of its measurements. We then find that the rate of exchange
is invariable. Transformations of heat into motion, and of motion into
heat, take place according to a rigorous numerical law, which brings
into exact correspondence the quantity of each. Mechanical effect
is estimated, as we have seen, by work, that is in kilogrammetres.
Heat is measured in calories, the calorie being the quantity of heat
necessary to raise from 0°C to 1°C a kilogramme of water (Calorie) or
one gramme of water (calorie). It is found that whatever may be the
bodies and the phenomena which serve as intermediaries for carrying
out this transformation, we must always expend 425 kilogrammetres to
create a Calorie, or expend 0·00234 Calories to create a kilogrammetre.
The number 425 is the mechanical equivalent of the Calorie, or, as
is incorrectly stated, of the heat. It is this constant fact which
constitutes _the principle of the equivalence of heat and of mechanical
work_.


                         § 5. CHEMICAL ENERGY.


We cannot yet actually measure chemical activity directly, but we know
that chemical action may give rise to all other phenomenal modalities.
It is their most ordinary source, and it is to it that industries
appeal to obtain heat, electricity, and mechanical action. In the
steam engine, for instance, the work that is received arises from the
combustion of carbon by the oxygen of the air. This gives rise to the
heat which vaporizes the water, produces the tension of the steam,
and ultimately produces the displacement of the piston. The theory of
the steam engine might be reduced to these two propositions: chemical
activity gives rise to heat, and heat gives rise to motion; or to use
the language to which the reader by now will be accustomed, chemical
energy is transformed into thermal energy, and that into mechanical
energy. It is a series of phases and of instantaneous changes, and the
exchange is always affected according to a fixed rate.

_The Measurement of Chemical Energy._—Our knowledge of chemical energy
is less advanced than that of the energies of heat and sensible motion.
We have not yet reached the stage of numerical verifications. We can
only therefore affirm the equivalence of chemical and thermal energies
without the aid of numerical constants, because we do not yet, in
the present state of science, know how to measure chemical energy
directly. Other known energies are always the product of two factors:
the mechanical energy of position, or work, is measured by the product
of the force _f_, and the displacement _s_; work = _fs_; the mechanical
energy of motion, U = 1∕2_mv^2_, is measured by the product of the mass
into half the square of the velocity. Thermal energy is measured by
the product of the temperature and the specific heat; electric energy
by the product of the quantity of electricity (in coulombs) and of the
electromotive force (in volts). As for chemical energy, we guess that
it may be valued directly according to Berthollet’s system, adopted by
the Norwegian chemists, Guldberg and Waage, by means of the product of
the masses and of a force, or co-efficient of affinity, which depends
on the nature of the substances which are brought together, on the
temperature, and on the other physical circumstances of the reaction.
On the other hand, the researches of M. Berthelot enable us in many
cases to obtain an indirect valuation in terms of the equivalent heat.

_Its Two Forms._—It is interesting to note that chemical energy may
also be regarded from the two states of _potential_ and _kinetic
energy_. The coal-oxygen system, to burn in the furnace of the steam
engine, must be primed by preliminary work (local ignition), just as
the weight that is raised and left motionless at a certain height
requires a small effort to be detached from its support. When this
condition is fulfilled, energy is at once manifest. We must admit that
it existed in the latent state, in the state of _chemical potential
energy_. Under the impulse received, the carbon combines with the
oxygen and forms carbonic acid, C + 2O becomes CO⌄{2}; potential energy
is changed into actual chemical energy, and immediately afterwards into
thermal energy. We should have only a very incomplete and fragmentary
view of the reality of things if we were to consider this phenomenon
of combustion in isolation. We must consider it in connection with
what has actually created the energy which it is about to dissipate.
This antecedent fact is the action of the sun upon the green leaf. The
carbon which burns in the furnace of the machine comes from the mine in
which it was stored in the form of coal—that is to say, of a product
which was vegetable in its primitive form, and which was formed at the
expense of the carbonic acid of the air. The plant had separated, at
the expense of the solar energy, the carbon from the oxygen to which it
was united in the carbonic acid of the atmosphere. It had created the
system C + 2O. So that the solar energy produces the chemical potential
energy which was so long before it was utilized. Combustion expends
this energy in making carbonic acid over again.

_Materialization of Energy._—The fertility of the idea of energy is
therefore, as we see from all these examples, due to the relations
it establishes between the natural phenomena of which it exhibits
the necessary relation, destroyed by the excessive analysis of early
science. It shows us that in the world of phenomena there is nothing
but transformations of energy. And we regard these transformations
themselves as the circulation of a kind of indestructible agent which
passes from one form of determination to another, as if it were
simply putting on a fresh disguise. If our intellect requires images
or symbols to embrace the facts and to grasp their relation, it may
introduce them here. It will materialize energy, it will make of it a
kind of imaginary being, and confer upon it an objective reality. And
for the mind, as long as it does not become the dupe of the phantom
which it itself has created, this is an eminently comprehensive
artifice which enables us to grasp readily the relations between
phenomena and their bond of affiliation.

The world appears to us then, as we said at the outset, constructed
with singular symmetry. It offers to us nothing but transformations of
matter and transformations of energy; these two kinds of metamorphoses
being governed by two laws equally inevitable, the conservation
of matter and the conservation of energy. The first of these laws
expresses the fact that matter is indestructible, and passes from
one phenomenal determination to another at a rate of equivalence
measured by weight; the second, that energy is indestructible, and
that it passes from one phenomenal determination to another at a rate
of equivalence fixed for each category by the discoveries of the
physicists.


                    § 6. TRANSFORMATIONS OF ENERGY.


The idea of energy has become the point of departure of a science,
_Energetics_, to the establishment of which a large number of
contemporary physicists, among whom are Ostwald, Le Châtelier, etc.,
have devoted their efforts. It is the study of phenomena, regarded
from the point of view of _energy_. I have said that it claims to
co-ordinate and to embrace all other sciences.

The first object of energetics should be the consideration of the
different forms of energy at present known, their definition and their
measurement. This is what we have just done in broad outline.

In the second place, each form of energy must be regarded with
reference to the rest, so as to determine if the transformation of this
into that is directly realizable, and by what means, and, finally,
according to what rate of equivalence. This new chapter is a laborious
task which would compel us to traverse the whole field of physics.

Of this long examination we need only concern ourselves here with three
or four results which will be more particularly important in the case
of applications to living beings. They refer to mechanical energy, to
the relations of thermal energy and chemical energy, to the complete
rôle of thermal energy, and finally to the extreme adaptability of
electrical energy.

1. _Transformation of Mechanical Energy._—Mechanical energy may change
into every other form of energy, and all others can change into it,
with but one exception, that of chemical energy. Mechanical effort does
not produce chemical combination. What we know of the part played by
pressure in the reactions of dissociation seems at first to contradict
this assertion. But this is only in appearance. Pressure intervenes in
these operations only as _preliminary work_ or _priming_, the purpose
of which is to bring the bodies into contact in the exact state in
which they must be for the chemical affinities to be able to enter into
play.

2. _Transformation of Thermal Energy; Priming._—Thermal (or luminous)
energy does not change directly into chemical energy. In fact, heat and
light favour and even determine a large number of chemical reactions;
but if we go down to the foundation of things we are not long before
we feel assured that heat and light only serve in some measure for
_priming_ for the phenomenon, for preparing the chemical action, for
bringing the body into the physical state (liquid, steam) or to the
degree of temperature (400° C. for instance, for the combination of
oxygen and hydrogen) which are the preliminary indispensable conditions
for the entry upon the scene of chemical affinities.

On the contrary, chemical energy may really be transformed into
thermal energy. We have an instance of this in the reactions which
take place without the aid of external energy; and again, in those
very numerous cases which, such as the combustion of hydrogen and
carbon, or the decomposition of explosives, the reactions continue
when once primed. I may make a further observation apropos of thermal
and photic energy. These are not two really and essentially distinct
forms, as was thought in the early days of physics. When we consider
things objectively, there is absolutely no light without heat; light
and heat are one and the same agent. According as it is at this or
that degree of its scale of magnitude, it makes a stronger impression
on the skin (sensation of heat) or on the retina (sensation of light)
of man and animals. The difference may be put down to the diversity of
the work and not to that of the agent. The kinetic theory shows us that
the agent is qualitatively identical. The words heat and light only
express the chance of the meeting of the radiant agent with a skin and
a retina. At the lowest degree of activity this agent exerts no action
on the terminations of the thermal cutaneous nerves, nor on the optic
nerve-terminations. As this degree is raised the former of these nerves
are affected (cold, heat) and are so to the exclusion of the nerves of
vision. Then they are both affected (sensation of heat and light), and
finally, beyond that, sight alone is affected. The transformation of
one energy into the other is therefore here reduced to the possibility
of increasing or decreasing the intensity of the action of this common
agent in the exact proportions suitable for passing from one of the
conditions to the other; and this is easy when it is a question of
going up the scale in the case of light, and, on the contrary, it is
not realizable directly, that is to say without external assistance,
when it is a question of going down the scale again, in the case of
heat.

3. _Heat a Degraded Form of Energy._—We have seen that thermal energy
is not directly transformed into chemical energy. There is yet another
restriction in the case of this thermal energy if we study the laws
which govern the circulation and the transformations of thermal energy;
and the most important comes from the impossibility of transporting it
from a body at a lower temperature to a body at a higher temperature.
On the whole, and because of these restrictions, thermal energy is an
imperfect variety of universal energy, or, as the English physicists
call it, a degraded form.

4. _Simple Transformations of Electrical Energy. Its Intermediary
Rôle._—On the other hand, electrical energy represents a perfected and
infinitely advantageous form of this same universal energy, and this
explains the vast development of its industrial applications within
less than a century. It is not that it is better known than the others
in its nature and in the secret of its action. On the contrary, there
is more dispute than ever as to its nature. To some, electricity,
which is transported and propagated with the speed of light, is a real
flux of the ether as was taught by Father Secchi, who compared it to a
current of water in a pipe. It would do its work, just as the water of
the mill does its work by flowing over a wheel or through a turbine.
Electricity, like water in this case, would not be an energy in itself,
but a means of transporting energy.

To others, such as Clausius, Hertz, and Maxwell, it is not so; the
electric current is not a transport of energy. It is a state of the
ether of a peculiar, specific kind, periodically produced (electric
oscillation), and propagated with a speed of the order of that of light.

However that may be, what constitutes the essential peculiarity
of electrical energy, and what causes its value, is that it is an
incomparable agent of transformation. Every known form of energy
may be converted into it, and inversely, electrical energy may be
changed with the utmost facility into all other energies. This extreme
adaptability assigns to it the part of an intermediary between the
other less tractable agents. Mechanical energy, for instance, lends
itself with difficulty to the production of light, that is to say, to
a metamorphosis into photic energy (a variety of thermal energy). A
fall of water cannot be directly utilized for lighting purposes. The
mechanical work of this fall, which cannot be exploited in its present
form, serves to set in motion in industrial lighting the installations,
the electric machines, and the dynamos which feed the incandescent
lamps. Mechanical work is changed into electrical energy, and it, in
its turn, into thermal or photic energy. Electricity has here played
the part of a useful intermediary.

The last part of energetics must be consecrated to the study of the
general principles of this science. These principles are two in number,
the principle of the _conservation of energy_, or Mayer’s principle,
and the principle of the transformation of energy, or Carnot’s
principle. The doctrine of energy thus reduces to two fundamental laws
the multitude of laws, often known as “general,” to which natural
science is subject.


           § 7. THE PRINCIPLE OF THE CONSERVATION OF ENERGY.


In all that precedes, the principle of conservation has intervened at
every step. In fact, the very idea of energy is connected with the
existence of this principle. We first discover the idea in the work of
the philosophical mathematicians who established the foundations of
mechanics:—Newton, Leibniz, d’Alembert, and Helmholtz; or of inductive
physicists such as Lord Kelvin. Its experimental proof, sketched by
Marc Seguin and R. Mayer, is due to Colding and Joule.

_It is Independent of the Kinetic Theory._—Mayer’s law states that
energy is indestructible; that all phenomenality is nothing but a
transformation of energy from one form to another, and that this
transformation takes place either at equal values, or rather, at a
certain rate of equivalence. This is what takes place when thermal
energy is transformed into mechanical energy (equivalent 425). This
rate of equivalence is fixed by the researches of physicists for each
category of energy.

It will be noticed that this law and this theory of energy, which
is always presented by authors of elementary books as a consequence
of the kinetic theory, is quite independent of it. In the preceding
lines we have not even mentioned its name. We have not assumed that
all phenomena are movements or transformations of movements, whether
sensible or vibratory; we have not affirmed that what was passing from
one phenomenal determination to another was the _vis viva_ of the
motion, as is the case in the impact of elastic bodies. No doubt the
kinetic theory affords us a very striking image of these truths which
are independent of it; but it may be false: and the theory of energy
which assumes the minimum of possible hypotheses would yet be true.

_It contains a great many other Principles._—The principle of the
conservation of energy contains a large number of the most general
principles of science. It may be shown without much difficulty that,
for example, it contains the principle of the inertia of matter, laid
down by Galileo and Descartes; that of the equality of action and
reaction, due to Newton; and even that of the conservation of matter,
or rather of mass, due to Lavoisier. And finally, it contains the
experimental law of equivalence connected with the name of the English
physicist Joule, from which may be derived the Law of Hess and the
principle of the initial and final states which we owe to Berthelot.

_It involves the Law of Equivalence._—Here we may be content with
noticing that the law of the conservation of energy involves the
existence of relations of equivalence between the different varieties.
A certain quantity of a given energy, measured, as we have seen, by
the product of two factors, is equivalent to a certain fixed quantity
of quite a different form of energy into which it may be converted.
The laws which govern energetic transformations therefore contain,
from both the qualitative and the quantitative points of view, all the
connections of the phenomena of the universe. To study these laws in
their detail is the task that physics must take upon itself.

The conversion one into the other of the different forms of energy by
means of equivalents is only a possibility. It is subject, in fact, to
all sorts of restrictions, of which the most important are due to the
second principle.


               § 8. CARNOT’S PRINCIPLE. ITS GENERALITY.


The second fundamental principle is that of the transformations of
equilibrium, or of the conditions of reversibility, or again, Carnot’s
principle. This principle, which first assumed a concrete form in
thermodynamics, has been very widely extended. It has reached a degree
of generality such that contemporary theoretical physicists such as
Lord Kelvin, Le Châtelier, etc., consider it the universal law of
physical, mechanical, and chemical equilibrium.

Carnot’s principle contains, as was shown by G. Robin, d’Alembert’s
principle of virtual velocities, and according to physicists of
to-day, as we have just remarked, it contains the laws peculiar to
physico-chemical equilibrium. The application of this principle
gives us the differential equations from which are derived numerical
relations between the different energies, or the different modalities
of universal energy.

_Its Character._—It is very remarkable that we cannot give a general
enunciation of this principle which by its revealing power has changed
the face of physics. This is because it is less a law, properly so
called, than a method or manner of interpreting the relations of the
different forms of energy, and particularly the relations of heat and
mechanical energy.

_Conversion of Work into Heat and Vice-versâ._—The conversion of
work into heat is accomplished without difficulty. For example, the
hammering of a piece of iron on an anvil may bring it to a red heat.
A shell which passes through an armour plate is heated, and melts and
volatilizes the metal all round the hole it has made. By utilizing
mechanical action under the form of friction all energy can be
converted into heat.

The inverse transformation of heat into work, on the contrary, cannot
be complete. The best motor that we can think of, and _à fortiori_ the
best we can realize, can only transform a third or a fourth of the heat
with which it is supplied.

This is an extremely important fact. It is of incalculable importance
to natural philosophy, and may be ranked among the greatest discoveries.

_Higher and Degraded Forms of Energy._—Of these we may give an account
by distinguishing among the forms of universal energy _higher forms_,
and _lower_ or _degraded forms_. Here we have the principle of the
_degradation of energy_ on its trial, and it may be regarded as a
particular aspect of the second principle of energetics, or Carnot’s
principle. Mechanical energy is a higher form. Thermal energy is
a lower form, a degraded form, and one which has degrees in its
degradation. Higher energy, in general, may be completely converted
into lower energy; for example, work into heat: the slope is easy to
descend, but it is difficult to retrace our steps; lower energy can be
only partially transformed into higher energy, and the fraction thus
utilizable depends upon certain conditions on which Carnot’s principle
has thrown considerable light.

Thus, although in theory the thermal energy of a body may have its
equivalent in mechanical energy, the complete transformation is only
realizable from the latter to the former, and not from the former to
the latter. This is due to a condition of thermal energy which is
called _temperature_. The same quantity of thermal energy, of heat,
may be stored in the same thermal body at different temperatures. If
this quantity of thermal energy is in a very hot body we can utilize
a large portion of it; if it is in a relatively cold body we can only
convert a small portion of it into mechanical work. Thus the value of
energy,—_i.e._, its capacity of being converted into a higher and more
useful form,—depends on temperature.

_The Capacity of Conversion depends on Temperature._—The conversion
of heat into work assumes two bodies of different temperatures, the
one warm and the other cold; a boiler and a condenser. Every thermal
machine conveys a certain amount of heat from the boiler to the
condenser, and what is not thus carried is changed into work. This
residue is only a small fraction, a quarter, or at most a third of the
heat employed, and that, too, in the theoretically perfect machine, in
the ideal machine.

This output, this utilizable fraction depends on the fall of
temperature from the higher to the lower level, just as the work of a
turbine depends on the height of the waterfall which passes through it.
But it also depends on the conditions of this fall, on the accessory
losses from radiation and conduction. However, Carnot has shown that
the output is the same, and a maximum for the same fall of temperature,
whatever be the working agent (steam, hot air, etc.), and whatever be
the machine—provided that this agent, this substance which works is not
exposed to accessory losses, that it is never in contact with a body
having temperature different to its own—or again, that it is connected
only with bodies impermeable to heat.

This is Carnot’s principle in one of its concrete forms.

A machine which realizes this condition, that the agent (steam,
alcohol, ether) is in relation, at all phases of its function, with
bodies which can neither take heat from it nor give heat to it, is a
_reversible machine_. Such a machine is perfect. The fraction of heat
that it transforms into motion is constant; it is a maximum; it is
independent of the motor, of its organs, of the agent: it accurately
expresses the transformability of the heat agent into a mechanical
agent under the given conditions.

_The Degradation and Restoration of Energy._—The fraction not utilized,
that which is carried to the condenser at a lower temperature, is
_degraded_. It can only be used by a new agent, in a new machine in
which the boiler has exactly the same temperature as the condenser in
the first machine, and the new condenser has a lower temperature, and
so on. The proportion of utilizable energy thus goes on diminishing.
Its utilization requires conditions more and more difficult to
realize. The thermal energy loses its potential and its value, and is
further and further degraded as its temperature approaches that of the
surrounding medium.

The degraded energy, theoretically, has kept its equivalent value but,
practically, it is incapable of conversion. However, it is shown in
physics that it can be raised and re-established at its initial level.
But for that purpose another energy must be utilized and degraded for
its benefit.

_The End of the Universe._—What we have just seen with respect to
heat and motion is to some degree true of all other forms of energy,
as Lord Kelvin has shown. The principle of the degradation of energy
is very general. Every manifestation of nature is an energetic
transformation. In each of these transformations there is a degradation
of energy—_i.e._, a certain fraction is lowered and becomes less easily
transformable. So that the energy of the universe is more and more
degraded; the higher forms are lowered to the thermal form, the latter
increasing at temperatures which become more and more uniform. The
end of the universe, from this point of view, would then be unity of
(thermal) energy in uniformity of temperature.

_Importance of the Idea of Energy in Physiology._—I have said that the
application of Carnot’s principle furnished numerical relations between
the different energetic transformations.

The science of living beings has not yet reached that point of
development at which it is possible for us to obtain its numerical
relations. However, the consideration of energy and the principle of
conservation has altered the outlook of physiology on many questions
which are of the highest importance.

The determination of the sources from which plants and animals draw
their vital energies; the mediate transformation of chemical energy
into animal heat in nutrition, or into motion in muscular contraction;
the chemical evolution of foods; the study of soluble ferments—all
these questions are of considerable importance when we wish to
understand the mechanisms of life. They are therefore departments of
physiological energetics in which great advances have already been
made.




                              CHAPTER II.

                          ENERGY IN BIOLOGY.

 § 1. Energy in Living Beings.—§ 2. The First Law of Biological
 Energetics:—All Vital Phenomena are Energetic Transformations.—§
 3. Second Law:—The Origin of Vital Energy is in Chemical Energy.
 Functional Activity and Destruction.—§ 4. Third Law:—The Final Form of
 Energetic Transformation in the Animal is Thermal Energy. Heat is an
 Excretum.


The theory of energy was thought of and utilized in physiology before
it was introduced into physics, in which it has exercised such an
extraordinary influence. Robert Mayer was a physicist and a doctor.
Helmholtz was equally at home in physiology and in physics. From
the outset both had seen in this new idea a powerful instrument of
physiological research. The volume in which Robert Mayer expounded,
in 1845, his remarkable views on organic movement in relation to
nutrition, and Helmholtz’ commentary leave us in no doubt in this
respect. The essay on the mechanical equivalent of heat, of a more
particularly physical character, is six years later than the earlier
work.

_The Relations between Energetics and Biology._—The theory of energy is
therefore only returning to its cradle; and to that cradle it returns
with all the sanction of physical proof, as the most general theory
ever proposed in natural philosophy, and the theory least encumbered
with hypotheses. It reduces all particular laws to two fundamental
principles—that of the conservation of energy, which contains the
principles of Galileo and Descartes, of Newton, of Lavoisier, Joule’s
law, Hess’s law, and Berthelot’s principle of the initial and final
states; and also Carnot’s principle, from which are deduced the laws
of physico-chemical and chemical equilibrium. These two principles
therefore sum up the whole of natural science. They express the
necessary relation of all the phenomena of the universe, their
uninterrupted gentic connection, and their continuity.

_A priori_ there would be little likelihood that a doctrine, so
universal and so thoroughly verified in the physical world, could be
restricted, and thus be useless to the living world. Such a supposition
would be contrary to the scientific method, which always tends to the
generalization and the explanation of elementary laws. The human mind
has always proceeded thus: it has applied to the unknown order of
living phenomena the most general laws of contemporary physics.

This application has been found legitimate, and has been justified by
experiment whenever it has been a question of the laws or of the really
fundamental or elementary conditions of phenomena. It has, on the other
hand, however, been unfortunate when it has stopped short of secondary
characteristics. When we now concede the subjection of living beings
to these general laws of energetics, we are following a traditional
method. There is no doubt that this application is legitimate, and that
experiment will justify it _a posteriori_.

I will therefore grant, as a provisional _postulate_, the consequences
of which will have to be ultimately justified, that the living and
inanimate world alike show us nothing but _transformations of matter_
and _transformations of energy_. The word phenomenon will have no
other signification, whatever be the circumstances under which the
phenomenon occurs. The varied manifestations which translate the
activity of living beings thus correspond to transformations of energy,
to conversions of one form into another, in conformity with the rules
of equivalence laid down by the physicists. This conception may be
formulated in the following manner:—_The phenomena of life have the
same claim to be energetic metamorphoses as the other phenomena of
nature_.

This postulate is the foundation of biological energetics. It may be
useful to give some explanation relative to the signification, the
origin, and the scope of this statement.

Biological energetics is nothing but general physiology reduced to the
principles that are common to all the physical sciences. Robert Mayer
and Helmholtz gave the best description of this science, and laid
down its limits by defining it as “the study of the phenomena of life
regarded from the point of view of energy.”


 § 1. ENERGY AT PLAY IN LIVING BEINGS. COMMON OR PHYSICAL ENERGIES.
 VITAL ENERGIES.


Our first object will be to define and to enumerate the energies
at play in living beings; to determine their more or less easy
transformations from one to another, to bring to light the general
laws which govern those transformations, and finally to apply them to
the detailed study of phenomena. This programme may be divided into
four parts.

In the physical world the specific forms of energy are not numerous.
When we have mentioned mechanical, chemical, radiant (thermal and
photic) energies, electrical energy, with which is blended magnetic
energy, we have exhausted the catalogue of natural agents.

But is this list for ever closed? Are vital energies comprised in this
list? These are the first questions which we must ask ourselves.

The iatro-mechanical school, on _a priori_ grounds give an affirmative
answer. No doubt there are in the living organism many manifestations
which are pure physical manifestations of known energies, mechanical,
chemical, thermal, etc. But are all the manifestations of the living
being of this order? Are they all, henceforth, reducible to the
categories and varieties of energy which are investigated in physics?
This is the claim of the mechanical school. But the claim is rash. Our
fundamental postulate affirms, in principle, that universal energy is
manifested in living beings; but, as a matter of fact, there is no
reason for the assertion that it does not assume particular forms,
according to the circumstances peculiar to the conditions under which
they are produced.

These _special forms of energy_ manifested in the conditions suitable
to living beings would swell the list drawn up by the physicists. And
it would not be the first instance of an extension of this kind. The
history of science records many remarkable cases. Scarcely a century
has passed since we first heard of electrical energy. This discovery
in the world of energy, which took place, so to speak, before our very
eyes, of an agent which plays so large a part in nature, clearly leaves
the door open to other surprises.

We shall therefore concede that there may be other forms of energy
at work in living beings than those we already know in the physical
world. This reservation would enable us to discover at once the
essential characteristics by which vital phenomena are henceforth
reduced to universal physics, and the purely formal differences still
distinguishing them.

If there are really special energies in living beings, our monistic
postulate leads us to assert that these energies are homogeneous with
the others, and that they do not differ from them more than they differ
among themselves. It is probable that some day they will be discovered
external to living bodies, if the material conditions (which it is
always possible to imagine) are realized externally to them. And if we
must admit that the peculiarity of the medium is such that these forms
must remain indefinitely peculiar to living beings, we may assert with
every confidence that these special energies do not obey special laws.
They are subject to the two fundamental principles of Robert Mayer
and Carnot. They are exchanged according to fixed laws with the other
physical forms of energies at present known.

To sum up, then, we must establish three categories in the forms of
energy which express the phenomena of vitality.

In the first place, most of these energies are those which have
already been studied and recognized in general physics. They are
the same energies: chemical, thermal, mechanical, with their
characteristics of mutability, their lists of equivalents, and their
actual and potential stales.

In the second place, it may happen, and it probably will happen, as it
happened in the last century in the case of electricity, that some new
form of energy will be discovered belonging to the universal order as
to the living order. This will be a conquest of general physics as well
as of biology.

And finally we may rigorously and provisionally admit a last category
of _vital energies properly so called_.

It is difficult to give much precision to the idea of _vital energies
properly so called_.

It will be easier to measure them by means of equivalents than to
indicate their nature. Besides, this is the ordinary rule in the case
of physical agents. We can measure them, although we know not what they
are.

_Characteristics of Vital Energies._—We see why we cannot exhibit
with precision, _a priori_, the nature of vital energies. In the
first place, they are expressed by what takes place in the tissues
in activity, and this cannot at present be identified with the known
types of physical, chemical, and mechanical phenomena. This is a first,
intrinsic reason for not being able to distinguish them readily, since
what takes place is not distinguished by the phenomenal appearances to
which we are accustomed.

There is a second, intrinsic reason. These vital phenomena are
intermediary, as we shall see, between manifestations of known
energies. They lie between a chemical phenomenon which always precedes
them, and a thermal phenomenon which always follows them. They are
lost sight of, as it were, between manifestations which strike our
attention. Generally speaking, intermediary energies often escape us
even in physics. Only the extreme manifestations are clearly seen.
In the presence of the organism we are, as it were, in electric
lighting works which are run by a fall of water, and at first we only
see the mechanical energy of the falling water, of the turbine and
dynamo at work, and the photic energy of the lamps which give the
light. Electrical energy, an intermediary, which has only a transient
existence, does not impose itself on our attention.

And so _vital energies_ for this twofold reason, intrinsic and
extrinsic, are not readily apparent. To reveal them, the careful
analysis of the physiologists is required. They are acts, in most
cases silent and invisible, which we should scarcely recognize but
by their effects, after they have terminated in familiar, phenomenal
forms. This is, for example, what goes on in the muscle in process of
shortening, in the nerve carrying the nervous influx, in the secreting
gland. And this is what constitutes the different forms of energy
which we call _vital properties_. M. Chauveau and M. Laulanié use
the phrase _physiological work_ to distinguish them. _Vital energy_
would be preferable. It better expresses the analogy of this special
form with the other forms of universal energy; it helps us better to
understand that we must henceforth consider it as exchangeable by means
of equivalents with the energies of the physical world just as they are
exchangeable one with another.


               § 2. FIRST LAW OF BIOLOGICAL ENERGETICS.


It is easy to understand, after these remarks, the significance and
the scope of this assertion which contains the first principle of
biological energetics—namely, that the phenomena of life have the same
claim to be called energetic metamorphoses as the other phenomena of
nature.

_Irreversibility of Vital Energies._—However, there is one
characteristic of vital energies which deserves the closest attention.
Their transformations have a direction which is in some measure
inevitable. They descend a slope which they never re-ascend. They
appear to be irreversible. Ostwald has rightly insisted on this
fundamental characteristic, which no doubt is not that of all the
phenomena of the living being without exception, but which is certainly
that of the most essential phenomena. There are reversible phenomena
in organisms; there are energetic transformations which may take
place from one form of energy to another, or _vice versâ_. But the
most characteristic phenomena of vitality do not act in this way. We
shall presently see that most functional physiological acts begin
with chemical and end with thermal action. The series of energetic
transformations takes place in an inevitable direction, from chemical
to thermal energy. The order of succession of ordinary energies is
thus determined in the machine of the organism, and therefore by
the conditions of the machine. The order of transformation of vital
energies is still more rigorously regulated, and the phenomena of life
evolve from childhood to ripened years, and thence to old age, without
a possible return.

The laws of biological energetics are three in number. First of all,
there is the fundamental principle which we have just developed, and
which is, so to speak, laid down _a priori_; and there are two other
principles, those established by experiment and summing-up, as it were,
the multitude of known physiological effects. Of these two experimental
laws, one refers to the _origin_ and the other to the _termination of
the energies developed in living beings_.


               § 3. SECOND LAW OF BIOLOGICAL ENERGETICS.


_The Origin of Vital Energy._—Vital energies have their origin in one
of the _external or common energies_—not in any one we choose, as might
be supposed, but in one only: chemical energy. The third principle will
show us that they terminate in another energy or a few others, also
completely fixed.

It follows that the phenomena of life must appear to us to be a
circulation of energy which, starting from one fixed point in the
physical world, returns to that world by a few points, also fixed,
after a transient passage through the animal organism.

Or more precisely, it is a transposition from the realm of matter
into the world of energy, of the idea of the _vital vortex_ of
Cuvier and the biologists. They defined life by its most constant
property—nutrition. Nutrition was exactly this current of matter which
the organism obtains from without by alimentation, and which it throws
out again by excretion; and the even momentary interruption of which,
if complete, would be the signal of death. The cycle of energy is the
exact counterpart of this cycle of matter.

The second truth taught us by general physiology, a truth which
physiology learned from experiment, is enunciated as follows:—_The
maintenance of life consumes none of its energy. It borrows from the
external world all the energy which it expends, and borrows it in the
form of potential chemical energy._ This is a translation into the
language of energetics of the results acquired in animal physiology
during the last fifty years. No comment is needed to exhibit the
importance of such a truth. It reveals the origin of animal activity.
It reveals the source from which proceeds that energy which at some
moment of its transformations in the animal organism will be a _vital
energy_.

The _primum movens_ of vital activity is, therefore, according to this
law, the chemical energy stored up in the immediate principles of the
organism.

Let us try to follow, for a moment, this energy through the organism
and to specify the circumstances of its transformations.

_Organic Functional Activity, and the Destruction of
Reserve-stuff._—Let us suppose then, for this purpose, that our
attention is directed to a given limited part of this organism, to
a certain tissue. Let us seize it, so to speak, by observation at a
given moment, and let us make an examination of the functional activity
starting from this conventional moment. This functional activity,
like all other vital phenomena, will be the result, as we have just
explained, of a transformation of the potential chemical energy
contained in the materials held in reserve in the tissue. This is our
first perceptible fact. This energy, when disengaged, will furnish to
the vital action the means by which it may be prolonged.

There is, then, a _functional destruction_. There is, at the beginning
of the functional process, and by a necessary effect of that very
process, a liberation of chemical energy; and that can only take place
by a decomposition of the immediate principles of the tissue, or, as we
may say, by a destruction of organic material. Claude Bernard insisted
on this consideration, that the vital function is accompanied by a
destruction of organic material. “When a movement is produced, when a
muscle is contracted, when volition and sensibility are manifested,
when thought is exercised, when a gland secretes, then the substance
of the muscles, of the nerves, of the brain, of the glandular tissue,
is disorganized, is destroyed, and is consumed.” Energetics enables us
to grasp the deeply-seated reason of this coincidence between chemical
destruction and the functional activity, the existence of which Claude
Bernard intuitively suspected. A portion of organic material is
decomposed, is chemically simplified, becomes less complex, and loses
in this kind of descent the chemical energy which it contained in its
potential state. It is this energy which becomes the very texture of
the vital phenomenon.

It is clear that the reserve of energy thus expended must be replaced,
because the organism remains in equilibrium. Alimentation provides for
this.

How does it provide for it? This is a question which deserves detailed
examination. We cannot incidentally treat it in full; we can only
indicate its main features.

_How the supply of Reserve Stuff is kept up._—We know that food does
not directly replace the reserve of energy consumed by the functional
activity. It is not its potential chemical energy which replaces,
purely and simply, the energy brought into play, consumed, or, better
still, transformed in the active organ, or tissue. Food as it is
introduced, inert food, does not, in fact, take up its place _as it
is_, without undergoing changes in that organ and that tissue, in order
to restore the _status quo ante_.

Before building up the tissue it will have undergone various
modifications in the digestive apparatus. It will have also undergone
changes in the circulatory apparatus, in the liver, and in the
very organ we are considering. It is after all these changes that
assimilation takes place. It will find its place and will have then
passed into the state of _reserve_.

The food digested, modified, and finally incorporated as an integral
part in the tissue in which it will be expended, is therefore in a new
state, differing more or less from its state when it was ingested. It
is a part of the living tissue in the state of constitutive reserve.
Its potential chemical energy is not the same as that of the food
introduced. It may differ from it very remarkably in consequence of
sudden alterations.

We do not know for certain at the expense of what category of foods
this or that given organ builds up its reserve stuff. There is a
belief, for instance, according to M. Chauveau, that the muscle does
its work at the expense of the reserve of glycogen which it contains.
The potential chemical energy of this substance would be a source of
muscular mechanical energy. But we do not know exactly at the expense
of what foods, albumenoids, fats, or carbohydrates the muscle builds
up the reserve of _glycogen_ expended during its contraction. It is
probable that it builds it up at the expense of each of the three
categories after the various more or less simple alterations undergone
by the materials in the digestive tube, the blood, the liver, or other
organs.

This building up of reserve stuff, the complement and counterpart of
_functional destruction_, is not chemical synthesis. It is, on the
contrary, generally, and on the whole, a simplification of the food
that has been introduced. This is true, at least as far as the muscle
is concerned. However, to this operation, Claude Bernard has given the
name of _organizing synthesis_, but the phrase is not a happy one. But
in no case was the eminent physiologist deceived as to the character of
the operation. “The organizing synthesis,” says he, “remains internal,
silent, hidden in its phenomenal expression, gathering together
noiselessly the materials which will be expended.”

These considerations enable us to understand the existence of the
two great categories into which the eminent physiologist divides
the phenomena of animal life: the phenomena of the _destruction of
reserve-stuff_ corresponding to _functional facts_—that is to say
expenditures of energy; and the _plastic phenomena_ of the _building-up
of reserves_ of organic regeneration, corresponding to _functional
repose_—_i.e._, to the supply of food to the tissues.

_Distinction between Active Protoplasm and Reserve-stuff._—If it is not
exactly in these terms that Claude Bernard formulated this fruitful
idea, it is at any rate in this way that it is to be interpreted.
This can be done by giving it a little more precision. We apply
more rigorously than that great physiologist the distinction drawn
by himself between _really active and living protoplasm_ and the
_reserve-stuff_ which it prepares. To the latter is restricted the
destruction by the functional activity and the building up by repose.

The classification of Claude Bernard is strictly true for
reserve-stuff. It is easy to criticize the wavering and, as it were,
dimly groping expressions in which the celebrated physiologist has
shrouded his ideas. The old adage will excuse him: _Obscuritate rerum
verba obscurantur_. In the depths of his ignorance he had a flash
of genius; perhaps he did not find the definitive and, as it were,
clearly-cut formula defining what was in his mind. But, in this
respect, he has left his successors an easy task.

_The Law of Functional Assimilation._—The progress of physiological
knowledge compels us therefore to distinguish in the constitution of
anatomical elements two parts—the materials of _reserve-stuff_ and the
_really active_ and _living protoplasm_. We have just seen how the
reserve-stuff behaves, alternately destroyed by functional activity,
and built up afterwards by the ingestion of food, followed by the
operations of digestion, elaboration, and assimilation. It remains to
ask how this really living and protoplasmic matter behaves. Does it
follow the same law? Is it destroyed during the functional activity,
and is it afterwards replaced? As to this we can express no opinion.
M. le Dantec fills a gap in our knowledge, in this respect, by an
hypothesis. He assumes that this essentially active matter grows during
functional activity, and is destroyed during repose. This is what
he calls the _law of functional assimilation_. The protoplasm would
therefore behave in an exactly contrary manner to the reserve-stuff.
It will be its counterpart. But this is only an hypothesis which, in
the present state of our knowledge, cannot be verified by experiment
We are at liberty to assert either that the protoplasm increases by
functional activity or that it is destroyed. Neither the arguments nor
the objections pro or con have any decisive value. The facts alleged on
either side are capable of too many interpretations.[10]

 [10] The reason is to be found in the large number of indeterminates
 in the problem we have to solve. It will be sufficient to enumerate
 them: the two substances which exist in the anatomical element,
 protoplasm and reserve-stuff, to which are attributed contrary roles;
 the two conditions attributable to the protoplasm, of manifested or
 latent activity; the faculty possessed by both of being prolonged for
 an indeterminate period, and of encroaching each on its protagonist
 when its existence is at stake. Here are more elements than are
 necessary to explain the positive or negative results of all the
 experiments in the world.

The only favourable argument (not demonstrative) is furnished by
energetics. It is this. The _re-building of the protoplasm_ is not
like the _organisation of reserve-stuff_, a slightly complicated or
even simplified phenomenon, as happens in the case of the reserve of
muscular glycogen. The glycogen, in fact, is built up at the expense
of foods chemically more complex. It is, on the contrary, a clearly
synthetic phenomenon, certainly of chemical complexity, since it ends
in building up the active protoplasm which is, in some measure, of
the highest scale of complexity. Its formation at the expense of the
simplest alimentary materials requires, therefore, an appreciable
quantity of energy.

The assimilation which organizes the active protoplasm therefore
requires energy for its realization. Now, at the moment of functional
activity, and by a necessary consequence thereof, the chemical
destruction or simplification of the substance of reserve takes place.
Here is something that meets the case, and we may note the coincidence.
It does not mean that the disposable energy is really used to increase
the protoplasm, nor that the protoplasm itself is thereby increased.
It merely signifies that the wherewithal exists to provide for that
increase if it takes place.

It is therefore _possible_ that the active protoplasm follows the law
of functional assimilation; but it is _certain_ that the reserve-stuff
follows the law laid down by Claude Bernard.

All these considerations definitely result in the confirmation of this
second law of general physiology, according to which all vital energies
are borrowed from the potential chemical energy of the reserve-stuff of
alimentary origin.


             § 4. THE THIRD LAW OF BIOLOGICAL ENERGETICS.


The third law of biological energetics is also drawn from experiment.
It relates no longer to the point of departure of the cycle of animal
energy, but to its final position. _The energetic transformations of
the animal end in thermal energy._

This is the most novel part of the theory, and, if we may say so, that
least understood by physiologists themselves. The energy resulting
from the chemical potential of food, having passed through the
organism (or simply through the organ which we are considering in
action), and having given rise to phenomenal appearances more or less
diversified, more or less dim or clear, obscure or obvious, which are
the characteristic or still irreducible manifestations of vitality,
finally returns to the physical world. This return takes place (with
certain exceptions which will be presently indicated) under the
ultimate form of thermal energy. This we are taught by experiment. The
phenomena of functional activity are exothermal.

Real vital phenomena thus lie between the chemical energy which gives
rise to them, and the thermal phenomena to which they in their turn
give rise. The place of the vital fact in the cycle of universal energy
is therefore completely determined. This conclusion is of the utmost
importance to biology. It may be expressed in a concise formula which
sums up in a few words all that natural philosophy can teach as to
energetics applied to living beings. “Vital energy is a transformation
of chemical energy into thermal energy.”

_Exceptions._—There are some exceptions to the rigour of this
statement, but they are not many in number. We must first of all remark
that it applies to _animal life_ alone.

In the case of vegetables, looked at as a whole, the law must be
modified. Their vital energy has another origin, and another final
form. Instead of being the destroyers of chemical potential energy,
they are its creators. They build up by means of the inert and simple
materials afforded them by the atmosphere and the soil, the immediate
principles by which their cells are filled. Their vital functional
activity forms by synthesis of the reserves, carbo-hydrates (sugars and
starches), fats, albuminoid nitrogenous materials—that is to say, the
same three principal categories of foods as those used by animals.

And to return to the latter, it should be observed that thermal energy
is not the only final form of vital energy, as this dogmatic statement
would have it supposed. It is only the principle of the final forms.
The cycle of energy occasionally terminates in mechanical energy
(phenomena of motion) and in a less degree in other energies; such
as, for example, the electrical energy produced by the functional
activity of the nerves and muscles in all animals, or in the functional
activity of special organs in rays, torpedo-fish, and the malapterurus
electricus, or finally, in the photic energy of phosphorescent animals.
But these are secondary facts.

_Heat is an Excretum._-The third principle of biological energetics
may be therefore thus enunciated:—_Vital energy in its final form
becomes thermal energy._ This principle teaches us that if chemical
energy is the primitive generating form of vital energies, thermal
energy is the form of waste, of emunctory, the degraded form as the
physicists would say. Heat is in the dynamical order an excretion of
animal life, as urea, carbonic acid and water, are excreta in the
substantial order. By a false interpretation of the principle of the
mechanical equivalence of heat, or through ignorance of Carnot’s
principle, certain physiologists have fallen into error when they
still speak of the transformation of heat into motion or into into
electricity in the animal organism. Heat is transformed into nothing
in the animal organism. It is dissipated. Its utility arises not from
its energetic value, but from the part it plays as a primer in the
chemical reactions, as has been explained with reference to the general
characteristics of chemical energy.

_The Effect of Energetics on our Knowledge of the Relations of
the Universe._—The consequences of these principles of energetic
physiology, which give us so much and which are so clear, are of the
greatest importance from the practical as well as from the theoretical
point of view.

In the first place, they show us the position and the rank of the
phenomena of life in the universe as a whole. They throw fresh light on
the noble harmony of the animal and vegetable kingdoms which Priestley,
Ingenhousz, Senebier, and the chemical school of the beginning of the
nineteenth century discovered, and which was expounded by Dumas with
incomparable lucidity and brilliance. Energetics is expressed in a
line. “The animal world expends the energy accumulated by the vegetable
world.” It extends these views beyond the living kingdoms. It shows how
the vegetable world itself draws its activity from the energy radiated
by the sun, and how animals restore it again, in dissipated heat,
to the cosmic medium. It extends the harmony of the two kingdoms to
the whole of nature. The new science makes of the whole universe one
connected system.

From a more limited point of view, and so that we may not restrict
ourselves to a consideration of the domain of animal physiology,
the laws of energetics sum up and explain a multitude of facts and
of experimental laws—for example, the law of the intermittence of
physiological activity, the facts of fatigue, the rôle and the general
principles of alimentation, and the conditions of muscular contraction.




                             CHAPTER III.

                        ALIMENTARY ENERGETICS.

 Various Problems of Alimentation. § 1. _Food the source of Energy
 and Matter._ The two forms of Energy afforded by Food—Vital Energy,
 Thermal Energy. Food the source of Heat. The rôle of Heat.—§ 2.
 _Measure of the output of Energy_—by the Calometric Method—by the
 Chemical Method.—§ 3. The regular type of Food, Biothermogenic, and
 the irregular type, Thermogenic.—§ 4. Food considered as the source
 of Heat. The Law of Surfaces. The limits of Isodynamics.—§ 5. Plastic
 rôle of Food. Preponderance of Nitrogenous Foods.


Among the problems on which energetics has thrown a vivid light we have
mentioned alimentation, muscular contraction, and, more general still,
the intermittence of vital functional activity. We shall begin with the
study of alimentation.

_The Different Problems of Alimentation._—What is a food? In what does
alimentation consist? The dictionary of the _Académie_ will give us
our first answer. It tells us that the word food is applied to “every
kind of matter, whatever may be its nature, which habitually serves
or may serve for nutrition.” This is very well put, but here again
we must know what nutrition is, and that is not a simple matter; in
fact, it practically means whatever is usually placed on the table in
a civilized and polished society. But it is just the profound reasons
for this traditional practice that we are trying to discover.

The problem of alimentation may be looked at in a thousand ways. It
is culinary, no doubt, and gastronomic; but it is also economical and
social, agricultural, fiscal, hygienic, medical, and even moral. But
first and foremost, it is physiological. It comprises and assumes the
knowledge of the general composition of foods, of their transformations
in the digestive apparatus, and their comparative utility in the
maintenance and the sound functional activity of the organism. To
this first group of subjects for our discussion are attached others
relating to the effects of inanition, of insufficient alimentation, and
of over-feeding. And in order to throw light on all these aspects of
the problem of alimentation, we have to lay bare the most intimate and
delicate reactions by which the organism is maintained and recruited,
and, in the words of a celebrated physiologist, “to penetrate into
the kitchen of vital phenomena.” And here neither Apicius, nor
Brillat-Savarin, nor Berchoux, nor the moralists, nor the economists
are of any use to us as guides. We must appeal to the scientists, who,
following the example of Lavoisier, Berzelius, Regnault, and Liebig,
have applied to the study of living beings the resources of general
science, and have thus founded _chemical biology_.

This branch of science developed considerably in the second half of
the nineteenth century. It has now its methods, its technique, its
chairs at the universities, its laboratories, and its literature.
It has particularly applied itself to the study of the “material
changes” or the _metabolism_ of living beings, and with that object in
view it has done two things. In the first place, it has determined
the composition of the constituent materials of the organism; then
analyzing qualitatively and quantitatively all that penetrates into
that organism in a given time—that is to say, all the alimentary or
respiratory ingesta, and all that issues from the organism, _i.e._,
all the excreta, all the _egesta_,—it has drawn up _nutritive balance
sheets_, corresponding to the various conditions of life, whether
naturally or artificially created. And thus we can determine the
alimentary régimes which give too much, and which give too little, and
which finally restore equilibrium.

We do not propose to give a detailed account of this scientific
movement. This may be done in monographs. All we wish to indicate
here is the most general result of these laborious researches—that is
to say, the laws and the doctrines which are derived from them, and
the theories to which they have given birth. It is by this alone that
they are brought into relation with general science, and may therefore
interest the reader. The facts of detail are never lacking to the
historian; it is more profitable to show the movement of ideas. The
theories of alimentation bring into conflict very different conceptions
of the vital functional activity. And here we find a confused medley of
opinions on which it is not without interest to endeavour to throw some
light.


               § 1. FOOD, A SOURCE OF ENERGY AND MATTER.


_Definitions of Food._—Before the introduction into physiology of the
notion of energy, no one had succeeded in giving an exact idea and a
precise definition of food and alimentation. Every physiologist and
medical man who attempted it had failed, and this for various reasons.

The general cause of this failure was that most definitions, popular or
technical, interposed the condition that the food must be introduced
into the digestive apparatus. “It is,” said they, “a substance which
when introduced into the digestive tube undergoes, etc., etc.”
But plants draw food from the soil, and they possess no digestive
apparatus; many animals have no intestinal tube; and in the case of
certain rotifera, the females possess a digestive apparatus, while the
males have none. Nevertheless all animals feed.

On the other hand, there are other substances than those which use the
digestive tract for the purpose of entering the organism, and which are
eminently useful or necessary to the maintenance of life. In particular
we may mention oxygen.

The distinctive feature of food is its _utility_—when conveniently
introduced or employed—to the living being. Claude Bernard’s definition
is this:—A substance taken in the external medium “necessary for the
maintenance of the phenomena of the healthy organism and for the
reparation of the losses it constantly suffers.” “A substance which
supplies an element necessary for the constitution of the organism, or
which _diminishes its disintegration_” (stored-up food); this is the
definition of C. Voit, the German physiologist. M. Duclaux says, in
his turn, but in far too general terms, that it is a substance which
contributes to assure the sound functional activity of any of the
organs of the living being. None of these ways of describing food gives
a complete idea.

_Food, the Source of Energy and Matter._—The intervention of the
notion of energy enables us more completely to understand the true
nature of food. We must, in fact, have recourse to the energetic
conception if we desire to take into account all that the organism
requires from food. It not only requires _matter_, but also, and most
important of all, energy.

Investigators so far concentrated their thoughts exclusively on the
necessity of a supply of matter—that is to say, they only looked upon
one side of the problem. The living body presents, at each of its
points, an uninterrupted series of disintegrations and reconstitutions,
the materials being supplied from without by alimentation, and rejected
by excretion. Cuvier gave to this unceasing circulation of ambient
matter throughout the vital world the name of _vital vortex_, and he
rightly saw in it the characteristic of nutrition, and the distinctive
feature of life.

This idea of the _cycle of matter_ has been completed in our own
time by that of the _cycle of energy_. All the phenomena of the
universe, and therefore those of life, are conceived of as energetic
transformations. We now look at them in their relationship instead of
considering them individually as of old. Each has an antecedent and a
consequent unity with which it is connected in magnitude by the law of
equivalents taught us by contemporary physics. And thus we may conceive
of their succession as the cycle of a kind of indestructible agent,
which changes only apparently, or assumes another form as it passes
from one to the other, but its magnitude remains unaltered. This is
energy. Thus, in the living being there is not only a circulation of
matter, but also a circulation of energy.

The most general result of research in physiological chemistry
from the time of Lavoisier down to our own day has been to teach us
that _the antecedent of the vital phenomenon is always a chemical
phenomenon_. The vital energies are derived from the potential chemical
energy accumulated in the immediate constituent principles of the
organism. In the same way _the consequent phenomenon of the vital
phenomenon is in general a thermal phenomenon_. The final form of vital
energy is thermal energy. These three assertions as to the nature, the
origin, and the final form of vital phenomena constitute the three
fundamental principles, the three laws, of biological energetics.

_Food, a Source of Heat. It is not quâ source of heat that food is
the source of vital energy._—The place of vital energy in the cycle
of universal energy is completely determined. It lies between the
chemical energy which is its generating form and the thermal energy
which is its form of disappearance, of breakdown, the “degraded form,”
as the physicists say. Hence we have a result which can be immediately
applied in the theory of food—namely, that heat is in the dynamical
order an excretum of the animal life rejected by the living being,
just as in the substantial order, urea, carbonic acid and water, are
the materials used up and again rejected by it. We therefore must
not think of the transformation in the animal organism of heat into
vital energy, as certain physiologists always do. Nor must we think,
with Béclard, of its transformation into muscular movement; or, as
others have maintained, into animal electricity. This is not only
an error of doctrine but an error of fact. It proceeds from a false
interpretation of the principle of the mechanical equivalent of heat
and a misunderstanding of Carnot’s principle. Thermal energy does not
repeat the course of the energetic flux in the animal organism. The
heat is not transformed into anything. It is simply dissipated.

_The Part played by Animal Heat as a Condition of Physiological
Manifestations._—Does this mean that heat is useless to life in the
very beings in which it is most abundantly produced—_i.e._, in man
and in the warm-blooded vertebrates? So far from this being so, it is
necessary to life. But its utility has a peculiar character which must
neither be misunderstood nor exaggerated. It is not transformed into
chemical or vital reactions, but merely creates for them a favourable
condition.

According to the first principle of energetics, for the vital fact
to be derived from the thermal fact, the heat must be preliminarily
transformed into chemical energy, since chemical energy is necessarily
an antecedent and generating form of vital energy. Now this regressive
transformation is impossible according to the current theories of
general physics. The part played by heat in the act of chemical
combination is that of a primer to the reaction. It consists in
placing the reacting bodies, by changing their state or by modifying
their temperature, in the condition in which they ought to be for the
chemical forces to come into play. For example, in the combination of
hydrogen and oxygen by setting light to an explosive mixture, heat
only acts as a primer to the phenomenon, because the two gases which
are passive at ordinary temperatures, require to be raised to 400°
C. before chemical affinity comes into play. And so it is with the
reactions which go on in the organism. They have a maximum temperature,
and the part played by animal heat is to furnish them with it.

It follows that heat intervenes in animal life in two capacities—first
and foremost as _excretum_, or end of the vital phenomenon, of
_physiological work_; and on the other hand, as a _condition_ or
_primer_ of the chemical reactions of the organism; and generally,
as a favourable condition for the appearance of the physiological
manifestations of living matter. Thus, it is not dissipated in sheer
waste.

I was led to adopt these views some years ago from certain experiments
on the rôle played in food by alcohol. I did not then know that they
had already been expressed by one of the masters of contemporary
physiology, M. A. Chauveau, and that they were related in his mind to
a series of conceptions and of researches of great interest, in the
development of which I have since then taken a share.

_Two Forms of Energy supplied to Animals by Food._—To say that food is
simultaneously a supply of energy and a supply of matter, is really to
express in a single sentence the fundamental conception of biology, in
virtue of which life brings into play no substratum or characteristic
dynamism. According to this, the living being appears to us as the seat
of an incessant circulation of matter and energy, starting from the
external world and returning to it. All food is nothing but this matter
and this energy. All its characteristics, our views as to its rôle, its
evolution, all the rules of alimentation are simple consequences of
this principle, interpreted by the light of energetics.

And first of all, let us ask what forms of energy are afforded by food?
It is easy to see that there are two—food is essentially a source of
chemical energy; and secondarily and accessorily, it is a source of
heat. Chemical energy is the only energy, according to the second
law of energetics, which may be transformed into vital energy. It is
true at any rate for animals; for in plants it is otherwise. There the
vital cycle has neither the same point of departure nor the same final
position. The circulation of energy does not take place in the same
manner.

On the other hand, and this we are taught by the third law, energy
brought into play in vital phenomena is finally liberated and restored
to the physical world in the form of heat. We have just said that this
release of heat is employed in raising the temperature of the living
being. It is animal heat.

Thus there are two forms of energy supplied by food, chemical and
thermal.

It must be added that these are not the only forms, but the principal,
and by far the most important. It is not absolutely true that heat is
the only outcome of the vital cycle. It is only so in the subject in
repose, contented to live idly without doing external mechanical work,
without lifting a tool or a weight, even that of its own body. And
again, speaking in this way, we neglect all the movements and all the
mechanical work which is done without exercise of the volition, by the
beating of the heart and of the arteries, the movements of respiration,
and the contractions of the digestive tube.

Mechanical work is, in fact, another possible termination of the cycle
of energy. But there is no longer anything necessary or inevitable
in this, since motion and the use of force are in a certain measure
subordinated to the capricious volition of the animal.[11]

 [11] There is another reason why the rôle of mechanical energy,
 compared with that of thermal energy, is reduced, in the partition of
 afferent, alimentary energy—at least, in animals which have not to do
 excessive work. The unit of heat, the Calorie, is equivalent to 425
 units of work—_i.e._, to 425 kilogrammetres. In the animal at rest,
 the number of kilogrammetres representing the different quantities
 of work done is small, the number of corresponding Calories is 425
 times smaller. It becomes almost negligeable in comparison with the
 considerable number of Calories dissipated in the form of heat.

At other times, again, it is an electrical phenomenon which terminates
the vital cycle, and it is, in fact, in this way that things happen
in the functional activity of the nerves and muscles in all animals,
and in the functional activity of the electrical organ in fish, such
as the ray and the torpedo. Finally, the termination may be a photic
phenomenon, and this is what happens in phosphorescent animals.

It is idle to diminish the power of these principles by proceeding
to enumerate the whole of the exceptions to their validity. We know
perfectly well that there are no absolute principles in nature. Let
us say, then, that the energy which temporarily animates the living
being is furnished to it by the external world under the exclusive
form of potential chemical energy; but that, if there is only one door
of entry, there are two exits. It may return to the external world
in the principal form of thermal energy and in the accessory form of
mechanical energy.


         § 2. MEASUREMENT OF THE SUPPLY OF ALIMENTARY ENERGY.


_Calorimetric Method._—From what has preceded it is clear that if the
energetic _flux_ which circulates through the animal emerges, _in
toto_, in the state of heat, the measurement of this heat becomes the
measurement of the vital energy itself, for the origin of which we
must go back to the food. If the flux is divided into two currents,
mechanical and thermal, they must both be measured and the sum of their
values taken. If the animal does not produce mechanical work, and all
ends in heat, we have only to capture, by means of a calorimeter,
this energetic flux as it emerges, and thus measure in magnitude and
numerically the energy in motion in the living being. Physiologists use
for this purpose various types of apparatus. Lavoisier and Laplace used
an ice calorimeter—that is to say, a block of ice in which they shut up
a small animal, such as a guinea-pig; they then measured its thermal
production by the quantity of ice it caused to melt. In one of their
experiments, for instance, they found that a guinea-pig had melted 341
grammes of ice in the space of ten hours, and had therefore set free 27
Calories.

But since those days more perfect instruments have been invented.
M. d’Arsonval employed an air calorimeter, which is nothing but a
differential thermometer very ingeniously arranged, and giving an
automatic record. Messrs. Rosenthal, Richet, Hirn and Kaufmann,
and Lefèvre have used more or less simplified or complicated air
calorimeters. Others, following the example of Dulong and Despretz,
have used calorimeters of air and mercury, or with Liebermester,
Winternitz, and J. Lefèvre (of Havre), have had recourse to baths.
Here, then, there is a considerable movement of research which has led
to the discovery of very interesting facts.

_Measurement of the Supply of Alimentary Energy by the Chemical
Method._—We may again reach our result in another way. Instead of
surprising the current of energy as it emerges and in the form of
heat, we may try and capture it at its entry in the form of potential
chemical energy.

The evaluation of potential chemical energy may be effected with the
same unit of measurement as the preceding—that is to say, the Calorie.
If we consider man and mammals, for example, we know that there is
only apparently an infinite variety in their foods. We may say that
they feed on only three substances. It is a very remarkable fact that
all the complexity and multiplicity of foods, fruits, grains, leaves,
animal tissues, and vegetable products of which use is made, reduce to
so great a simplicity and uniformity, that all these substances are of
three types only: albuminoids, such as albumen or white of egg—foods of
animal origin or varieties of albumen; carbo-hydrates, which are more
or less disguised varieties of sugar; and finally, fats.

Here, then, from the chemical point of view, leaving out certain
mineral substances, are the principal categories of alimentary
substances. Here, with the oxygen that is brought in by respiration, is
everything that penetrates the organism.

And now, what comes out of the organism? Three things only, water,
carbonic acid, and urea. But the former are the products of the
combustion of the latter. If we consider an adult organism in perfect
equilibrium, which varies throughout the experiment neither in
weight nor in composition, we may say that the receipts balance the
expenditure. Albumen, sugar, fat, plus the oxygen brought in, balance
quantitatively the water, carbonic acid, and urea expelled. Things
happen, in fact, as if the foods of the three categories were burned up
more or less completely by the oxygen.

It is this combustion that we have known since the days of Lavoisier
to be the source of animal heat. We can easily determine the quantity
of heat left by albumen passing into the state of urea, and by the
starch, the sugars, and the fats reduced to the state of water and
carbonic acid. This quantity of heat does not depend on the variety
of the unknown intermediary products which have been formed in the
organism. Berthelot has shown that this quantity of heat which measures
the chemical energy liberated by these substances is identical with
the quantity obtained by burning the sugar and the fats in a chemical
apparatus, in a calorimetric bomb, until we get carbonic acid and
water, and by burning albumen till we get urea. This result is a
consequence of Berthelot’s _principle of initial and final states_.
The liberated heat only depends on the initial and final states, and
not on the intermediary states. The heat left in the economy by the
food being the same as that left in the calorimetric bomb, it is easy
for the chemist to determine it. It has thus been discovered that
one gramme of albumen produces 4.8 Calories, one gramme of sugar 4.2
Calories, and one gramme of fat 9.4 Calories. We thus gather what a
given ration—a mixture in certain proportions of these different kinds
of foods—supplies to the organism and what energy it gives it, measured
in Calories.

The calculation may be carried out to a high degree of accuracy if,
instead of confining ourselves to the broad features of the problem, we
enter into rigorous detail. It is only, in fact, approximately that we
have reduced all foods to albumen, sugar, and fat, and all excreta to
water, carbonic acid, and urea.

The reality is a little more complicated. There are varieties of
albumen, carbo-hydrates, and fatty bodies, the heats of combustion of
which in the organism oscillate in the neighbourhood of the numbers
4.8, 4.2, and 9.4. Each of these bodies has been individually examined,
and numerical tables have been drawn up by Berthelot, Rubner, Stohmann,
Van Noorden, etc. The tables exhibit the thermal value or energetic
value of very different kinds of foods.

In our climate, the adult average man, doing no laborious work, daily
consumes a maintenance ration composed, as a rule, of 100 grammes of
albuminoids, 49 grammes of fats, and 403 grammes of carbo-hydrates.
This ration has an energetic value of 2,600 Calories.

It is therefore, thanks to the victories won in the field of
thermo-chemistry, and to the principles laid down since 1864 by M.
Berthelot, that this second method of attack on nutritive dynamism has
been rendered possible. Physiologists, by the aid of these methods,
have drawn up _balance-sheets of energy_ for living beings just as they
had previously established _balance-sheets of matter_.

Now, it is precisely researches of this kind that we have indicated
here as a consequence of biological energetics, which in reality have
helped to build up that principle. These researches have shown us
that, in conformity with the _principles of thermodynamics_, there
was not, in fact, in the organism, any transformation of heat into
mechanical work, as the physiologists for a short time supposed, on
the authority of Berthelot. With the help of our theory this mistake
is no longer possible. The doctrine of energetics shows us in fact
the current of energy dividing itself, as it issues from the living
being, into two divergent branches, the one thermal and the other
mechanical, external the one to the other although both issuing from
the same common trunk, and having between them no relation but this,
that the sum of their discharges represents the total of the energy
in motion. Let us now translate these very simple notions into the
more or less barbarous jargon in use in physiology. We shall be
convinced as we go on of the truth of the saying of Buffon, that
“the language of science is more difficult to learn than the science
itself.” We shall say, then, that chemical energy, that the unit of
weight of the food which may be placed in the organism, constitutes
the alimentary _potential_, the _energetic value_ of this substance,
its _dynamogenic power_. It is measured in units of heat, in Calories,
which the substance may leave in the organism. The evaluation is made
according to the principles of thermo-chemistry, by means of the
numerical tables of Berthelot, Rubner, and Stohmann. The same number
also expresses the _thermogenic power_, virtual or theoretical, of the
alimentary substance. This energy being destined to be transformed
into _vital energies_ (Chauveau’s _physiological work_, _physiological
energy_), the dynamogenic or thermogenic value of the food is at the
same time its biogenetic value. Two weights of different foods which
supply the organism with the same number of Calories,—_i.e._ for which
these numerical values are the same,—will be called _isodynamic_ or
_isodynamogenic_, _isobiogenetic_, _isoenergetic_ weights. They will
be equivalent from the point of view of their alimentary value. And
finally, if, as is usually the case, the cycle of energy ends in the
production of heat, the food which has been utilized for this purpose
has a real _thermogenic value_, identical with its theoretical
thermogenic value. In this case it might be determined experimentally
by direct calorimetry, measuring the heat produced by the animal
supposed absolutely unchanged and identical before and after the
consumption of the food.


 § 3. DIFFERENT TYPES OF FOODS. THE REGULAR, BIOTHERMOGENIC TYPE AND
 THE IRREGULAR, THERMOGENIC TYPE.


Food is a source of thermal energy for the organism because it is
decomposed within it, and undergoes within it a chemical degradation.
Physiological chemistry tells us that whatever be the manner in which
it is broken up, it always results in the same body and always sets
free the same quantity of heat. But if the point of departure and the
point of arrival are the same, it is possible that the path pursued is
not constantly identical. For example, one gramme of fat will always
give the same quantity of heat, 9.4 Calories, and will always come
to its final state of carbonic acid and water; but from the fat to
the mixture of carbonic acid gas and water there are many different
intermediaries. In a word we get the conception of varied cycles of
alimentary evolutions.

From the point of view of the heat produced it has just been said that
these cycles are equivalent. But are they equivalent from the vital
point of view? This is an essential question.

Let us imagine the most ordinary alternative. Food passes from the
natural to the final state after being incorporated with the elements
of the tissues, and after having taken part in the vital operations.
The chemical potential only passes into thermal energy after having
passed through a certain intermediary phase of vital energy. This
is the normal case, _the regular type of alimentary evolution_. It
may be said in this case that the food has fulfilled the whole of
its function, it has served for the vital functional activity before
producing heat. It has been _biothermogenic_.

_The irregular or pure thermogenic type._—And now let us conceive of
the most simple _irregular or aberrant type_. Food passes from the
initial to the final state without incorporation in the living cells of
the organism, and without taking part in the vital functional activity.
It remains confined in the blood and the circulating liquids, but it
undergoes in the end, however, the same molecular disintegration as
before, and sets free the same quantity of heat Its chemical energy
changes at once into thermal energy. Food is a _pure thermogen_. It
has fulfilled only one part of its work. It has been of slight vital
utility.

Does this ever occur in reality? Are there foods which would be only
_pure thermogens_—that is to say, which would not in reality be
incorporated with the living anatomical elements, which would form no
part of them either in a state of provisory constituents of the living
protoplasm, or in the state of reserve-stuff; which would remain in the
internal medium, in the blood and the lymph, and would there undergo
their chemical evolution? Or again, if the whole of the food does not
escape assimilation, would it be possible for part to escape it? Would
it be possible for one part of the same alimentary substance to be
incorporated, and for the rest to be kept in the blood or the lymph,
in the circulating liquids _ad limina corporis_, so to speak? In other
words, can the same food be according to circumstances a _biothermogen_
or a _pure thermogen_? Some physiologists—Fick of Wurzburg, for
instance—have claimed that this is really the case for most
nitrogenous elements, carbohydrates, and fats; all would be capable
of evolving according to the two types. On the other hand, Zuntz and
von Mering have absolutely denied the existence of the aberrant or
pure thermogenic type. No substances would be directly decomposed in
the organic liquids apart from the functional intervention of the
histological elements. Finally, other authors teach that there is a
small number of alimentary substances which thus undergoes direct
combustion, and among them is alcohol.

_Liebig’s Superfluous Consumption._—Liebig’s _theory of superfluous
consumption_ and Voit’s _theory of the circulating albumen_ assert
that the proteid foods undergo partial direct combustion in the
blood vessels. The organism only incorporates what is necessary for
physiological requirements. As for the surplus of the food that is
offered it, it accepts it, and, so to speak, squanders it; it burns it
directly; and we have a “sumptuary” consumption, consumption _de luxe_.

In this connection arose a celebrated discussion which still divides
physiologists. If we disengage the essential body of the discussion
from all that envelops it, we see that it is fundamentally a question
of deciding whether a food always follows the same evolution whatever
the circumstances may be, and particularly when it is introduced in
great excess. Liebig thought that the superabundant part, escaping
the ordinary process, was destroyed by direct combustion. He affirmed,
for instance, that nitrogenous substances in excess were directly
burned in the blood instead of passing through their usual cycle of
vital operations. We might express the same idea by saying that they
then undergo an accelerated evolution. Instead of passing through the
blood in the anatomical element, to return in the dismembered form from
the anatomical element to the blood, their breaking up takes place in
the blood itself. They save a displacement, and therefore in reality
remain external to the construction of the living edifice. Their
energy, crossing the intermediary vital stage, passes with a leap from
the chemical to the thermal form. Liebig’s doctrine reduced to this
fundamental idea deserved to survive, but mistakes in minor details
involved its ruin.

_Voit’s Circulating Albumen._—A few years later C. Voit, a celebrated
physiological chemist of Munich, revived it in a more extravagant form.
He held that almost the whole of the albuminoid element is burned
directly in the blood. He interpreted certain experiments on the
utilization of nitrogenous foods by imagining that these substances
when introduced into the blood were divided as a result of digestion
into two parts: the one very small, which was incorporated with the
living elements, and passed into the stage of _organized albumen_, the
other, corresponding to the greater part of the alimentary albumen,
remained mingled with the blood and lymph, and was subjected in this
medium to direct combustion. This was _circulating albumen_. In this
theory the tissues are almost stable; the organic liquids alone are
subjected to oxydizing transformations, to nutritive metabolism. The
accelerated evolution, which Liebig considered as an exceptional case,
was to C. Voit the rule.

_Current Ideas as to the Rôle of Foods._—The ideas of to-day are not
those of Voit; but they do not, however, differ from them essentially.
We no longer admit that the greater part of the ingested and digested
albumen remains confined in the circulating medium external to the
anatomical elements. It is held, with Pflüger and the school of Bonn,
that it penetrates the anatomical element and is incorporated in it;
but in agreement with Voit it is believed that a very small part is
assimilated to the really living matter, to the protoplasm properly
so called; the greater part is deposited in the cellular element as
reserve-stuff. The material, properly so called, of the living machine
does not undergo destruction and reparation as extensively as our
predecessors supposed. There is no need for great reparation. On the
contrary, the physiological activity consumes to a great extent the
reserve-stuff. And the greater part of the food, after having undergone
suitable elaboration, serves to replace the reserve-stuff destroyed in
each anatomical element by the vital functional activity.

_Experimental Facts._—Among the facts which brought physiologists
of the school of Voit to believe that most foods do not get beyond
the internal medium, there is one which may well be mentioned here.
It has been observed that the consumption of oxygen in respiration
increases notably (about a fifth of its value) immediately after a
meal. What does this mean? The interval is too short for the digested
alimentary substances to have been elaborated and incorporated in the
living cells. It is supposed that an appreciable time is required
for this complete assimilation. The products of alimentary digestion
are therefore in all probability still in the blood, and in the
interstitial liquids in communication with it. The increase of oxygen
consumed would show that a considerable portion of these nutritive
substances absorbed and passed into the blood would be oxydized and
then and there destroyed. But this interpretation, however probable
it may be, does not really fit in with the facts in such a way that
we may consider it as proved. Certain experiments by Zuntz and Mering
are opposed to the idea that combustion in the blood is easy. These
physiologists injected certain oxydizable substances into the vessels
without being able to detect any instantaneous oxidation. It is only
fair to add that against these fruitless attempts other more fortunate
experiments may be quoted.

_Category of Purely Thermogenic Foods, with Accelerated Evolution.
Alcohol. Acids of Fruits._—The accelerated evolution of foods—an
evolution which takes place in the blood, that is to say outside the
really living elements—remains, therefore, very uncertain as far as
ordinary food is concerned. It has been thought that it was a little
less uncertain as far as the special category of alcohol, acids of
fruits, and glycerine is concerned.

Some authors consider these bodies as pure thermogens. When alcohol
is ingested in moderate doses, they say that about a tenth of the
quantity absorbed becomes fixed in the living tissues; the rest is
“circulating alcohol.” It is oxidized directly in the blood and in
the lymph, without intervening in the vital functions other than by
the heat it produces. From the point of view of the energetic theory
these are not real foods, because their potential energy is not
transformed into any kind of vital energy, but passes at once to the
thermal form. On the other hand, other physiologists look upon alcohol
as really a food. According to them everything is called a food which
is transformed in the organism with the production of heat; and they
measure the nutritive value of a substance by the number of Calories
it can give up to the organism. So that alcohol would be a better food
than carbohydrated and nitrogenous substances. A definite quantity of
alcohol, a gramme for instance, is equivalent from the thermal point of
view to 1.66 grammes of sugar, 1.44 of albumen, or 0.73 of fat. These
quantities would be _isodynamic_.

Experiment has not entirely decided for or against this theory.
However, the first tests have not been very favourable to it.
The researches of C. von Noorden and his pupils, Stammreich and
Miura, have clearly and directly established that alcohol cannot
be substituted in a maintenance ration for an exactly isodynamic
quantity of carbohydrates. If the substitution is effected, a ration
only just capable of maintaining the organism in equilibrium becomes
insufficient. The animal decreases in weight. It loses more nitrogenous
matter than it can recover from its diet, and this situation cannot be
sustained for long. On the other hand, the celebrated researches of
the American physiologist, Atwater, would plead, on the contrary, in
favour of almost isodynamic substitution. Finally, Duclaux has shown
that alcohol is a real food, biothermogenic for certain vegetable
organisms. But urea is also a food for _micrococcus ureæ_. It does not
follow that it is a food for mammals. We have not reached the solution
yet—_adhuc sub judice_.

_Conclusion: The Energetic Character of Food._—To sum up we have
confined ourselves, in what has been said, to the consideration of a
single character of food, and really the most essential, its energetic
character. Food must furnish energy to the organism, and for that
purpose it is decomposed and broken up within it, and issues from it
simplified. It is thus, for instance, that the fats, which from the
chemical point of view are complicated molecular edifices, escape in
the form of carbonic acid and water. And so it is with carbo-hydrates,
starchy and sugary substances. This is because these compounds descend
to a lower degree of complexity during their passage through the
organism, and by this drop, as it were, they get rid of the chemical
energy which they contained in the potential state. Thermo-chemistry
enables us to deduce from the comparison of the initial and final
states the value of the energy absorbed by the living being. This
energetic, dynamogenic or thermogenic value, thus gives a measure
of the alimentary capacity of the substance. A gramme of fat, for
instance, gives to the organism a quantity of energy equivalent to 9.4
Calories; the thermogenic value of the albumenoids is 4.8 Calories.
The thermogenic or thermal value of carbohydrates is less than 4.7
calories. This being so, we understand why the animal is nourished by
foods which are products very high in the scale of chemical complexity.


         § 4. FOOD CONSIDERED EXCLUSIVELYY AS SOURCE OF HEAT.


We have seen that food is, in the first place, a source of _chemical
energy_; and, in the second place, a source of _vital energy_—finally,
and consequently, a source of thermal energy. It is this last point
of view which has exclusively struck the attention of certain
physiologists, and hence has arisen a peculiar manner of conceiving the
rôle of food. It consists in looking on food as a source of thermal
energy.

This conception is easily applied to warm-blooded animals, but to them
exclusively—and this is where it first fails. The animal is warmer than
the environment in general. It is constantly giving out heat to it. To
repair this loss of heat it takes in food in exact proportion to the
loss it sustains. When it is a question of cold-blooded vertebrates,
which live in water and in most cases have an internal temperature
which is not distinguishable from that of the environment, we see less
clearly the thermal rôle of food. It seems then that the production of
heat is an episodic phenomenon, not existing for itself.

However that may be, food is in the second place a source of thermal
energy for the organism. Can it be said, inversely, that every
substance which we introduce into the economy, and which is there
broken up and gives off heat, is a food? This is a moot point. We dealt
just now with purely thermogenic foods. However, most physiologists
are inclined to give a positive answer. In their eyes the idea of food
cannot be considered apart from the fact of the production of heat.
They take the effect for the cause. To these physiologists everything
ingested is called food, if it gives off heat within the body.

To be heated by food is, indeed, an imperious necessity for the higher
animals. If this need be not satisfied the functional activities
become enervated; the animal falls into a state of torpor; and if it
is capable of attenuated, of more or less latent, life it sleeps in
a state of hibernation; but if it is not capable of this, it dies.
The warm-blooded animal with a fixed temperature is so organized that
this constancy of temperature is necessary to the exercise and to the
conservation of life. To maintain this indispensable temperature there
must be a continual supply of thermal energy. According to this, the
necessity of alimentation is confused with the necessity of a supply
of heat to cover the deficit which is due to the inevitable cooling
of the organism. This is the point of view taken up by theorists, and
we cannot say that they have no right to do so. We can only protest
against the exaggeration of this principle, and the subordination
of the other rôles of food to this single role as a thermogen. It
is the magnitude of the thermal losses which, according to these
physiologists, determines the need for food, and regulates the total
value of the maintenance ration. From the quantitative view it is
approximately true. From the qualitative point of view it is false.

Such is the theory opposed to the theory of chemical and vital energy.
It has on its side a large number of experts, among whom are Rubner,
Stohmann, and von Noorden. It has been defended in an article in
the _Dictionnaire de Physiologie_ by Ch. Richet and Lapicque. They
hold that thermogenesis absolutely dominates the play of nutritive
exchanges; and it is the need for the production of heat that
regulates the total demand for Calories which every organism requires
from its ration. It is not because it produces too much heat that
the organism gets rid of it peripherally: it is rather because it
inevitably disperses it that it is adapted to produce it.

_Rubner’s Experiments._—This conception of the rôle of alimentation
is based on two arguments. The first is furnished by Rubner’s last
experiment (1893). A dog in a calorimeter is kept alive for a rather
long period (two to twelve days); the quantity of heat produced in this
lapse of time is measured, and it is compared with the heat afforded by
the food. In all cases the agreement is remarkable. But is it possible
that there should be no such agreement? Clearly no, because there is a
well-known regulating mechanism which always exactly proportions the
losses and the gains of heat to the necessity of maintaining the fixed
internal temperature. This first argument is, therefore, not conclusive.

The second argument is drawn from what has been called the _law of
surfaces_, clearly perceived by Regnault and Reiset in their celebrated
memoir in 1849, formulated by Rubner in 1884, and beautifully
demonstrated by Ch. Richet. In comparing the maintenance rations
for subjects of very different weights, placed under very different
conditions, it is found that the food always introduces the same
number of Calories for the same extent of skin—_i.e._, for the same
cooling surface. The numerical data collected by E. Voit show that,
under identical conditions, warm-blooded animals daily expend the same
quantity of heat per unit of surface—namely, 1.036 Calories per square
yard. The average ration introduces exactly the amount of food which
gives off sensibly this number of Calories. Now, this is an interesting
fact, but, like the preceding, it has no demonstrative force.

_Objections. The Limits of Isodynamism._—On the contrary, there are
serious objections. The thermal value of the nutritive principles only
represents one feature of their physiological rôle. In fact, animals
and man are capable of extracting the same profit and the same results
from rations in which one of the foods is replaced by an _isodynamic_
proportion of the other two—that is to say, a proportion developing the
same quantity of heat. But this substitution has very narrow limits.
Isodynamism—that is to say, the faculty that food has of supplying _pro
ratâ_ its thermal values—is limited all round by exceptions. In the
first place, there are a few nitrogenous foods that no other nutritive
principle can supply; and besides, beyond this minimum, when the
supply takes place, it is not perfect. Lying between the albuminoids
and the carbohydrates relatively to the fats, it is not between these
two categories relatively to nitrogenous substances if the thermal
power of food were the only thing that had to be considered in it, the
isodynamic supply would not fail in a whole category of principles such
as alcohol, glycerin, and the fatty acids. Finally, if the thermal
power of a food is the sole measure of its physiological utility,
we are compelled to ask why a dose of food may not be replaced by a
dose of heat. External warming might take the place of the internal
warming given by food. We might be ambitious enough to substitute for
rations of sugar and fat an isodynamic quantity of heat-giving coal,
and so nourish the man by suitably warming his room. In reality, food
has many other offices to fulfill than that of warming the body and
of giving it energy—that is to say, of providing for the functional
activity of the living machine. It must also serve to provide for
wear and tear. The organism needs a suitable quantity of certain
fixed principles, organic and mineral. These substances are evidently
intended to replace those which have been involved in the cycle of
matter, and to reconstitute the organic material. To these materials we
may give the name of _histogenetic_ foods (repairing the tissues), or
of _plastic_ foods.


                    § 5. THE PLASTIC RÔLE OF FOOD.


_Opinions of the Early Physiologists._—It is from this point of view
that the ancients regarded the rôle of alimentation. Hippocrates,
Aristotle, and Galen believed in the existence of a unique nutritive
substance, existing in all the infinitely different bodies that man
and the animals utilize for their nourishment. It was Lavoisier
who first had the idea of a dynamogenic or thermal rôle of foods.
Finally, the general view of these two species of attributes and their
marked distinction is due to J. Liebig, who called them _plastic_ and
_dynamogenic_ foods. In addition he thought that the same substance
should accumulate the same attributes, and that this was the case with
the albuminoid foods, which were at once _plastic_ and _dynamogenic_.

_Preponderance of Nitrogenous Foods._—Magendie, in 1836, was the
pioneer who introduced in this interminable list of foods the first
simple division. He divided them into proteid substances, still called
albuminoids, nitrogenous, quaternary, and _ternary substances_. Proteid
substances are capable of maintaining life. Hence the preponderant
importance given by the eminent physiologist to this order of foods.
These results have since been verified. Pflüger, of Bonn, gave a
very convincing proof of this a few years ago. He fed a dog, made it
work, and finally fattened it, by giving it nothing at all to eat but
meat from which had been extracted, as thoroughly as possible, every
other substance.[12] The same experiment showed that the organism can
manufacture fats and carbo-hydrates at the expense of the nitrogenous
food, when it does not find them ready formed in the ration. The
albumen will suffice for all the needs of energy and and matter. To
sum up, there is no necessary fat, no carbohydrate is necessary;
albuminoids alone are indispensable. Theoretically, the animal and man
alike could maintain life by the exclusive use of proteid food; but,
practically, this is not possible for man, because of the enormous
amount of meat which would have to be used (3 kilogrammes a day).

 [12] It is not certain, however, that all the precautions taken
 have the desired result. You cannot entirely deprive meat of its
 carbohydrates.

Ordinary alimentation comprises a mixture of three orders of
substances, and to this mixture albumen brings the plastic element
materially necessary for the reparation of the organism; it also is
the source of energy. The two other varieties only bring energy. In
this mixed regimen the quantity of albumen must never descend below a
certain minimum. The efforts of physiologists of late years have tended
to fix with precision this minimum ration of albuminoids—or as we may
briefly put it, of _albumen_—below which the organism would perish.
Voit had found 118 grammes of albumen necessary for the average adult
man weighing 70 kilos. This figure is certainly too high. The Japanese
doctors, Mori, Tsuboï, and Murato, have shown that a considerable
portion of the population of Japan is content with a diet much poorer
in nitrogen, and suffers no inconvenience. The Abyssinians, according
to Lapicque, ingest, on the average, only 67 grammes of albumen per
day. A Scandinavian physiologist, Siven, experimenting on himself,
found that he could reduce the ration of albumen necessary to the
maintenance and equilibrium of the organism to the lowest figures
which have been yet reached—namely, from 35 to 46 grammes a day. These
experiments, however, must be confirmed and interpreted. Besides, it
is important to point out that the most advantageous ration of albumen
requires to be a good deal above the strictly sufficient quantity.

It only remains to refer to several other recent researches. The most
important of many are those published by M. Chauveau, on the reciprocal
transformation of the immediate principles in the organism according
to the conditions of its functioning and the circumstances of its
activity. To deal with these researches with as much detail as they
deserve, we must study the physiology of muscular contraction and of
movement—that is to say, of muscular energetics.




                               BOOK III.

                THE CHARACTERS COMMON TO LIVING BEINGS.

 Chapter I. Summary: The doctrine of vital unity.—Chapter II. The
 morphological unity of living beings.—Chapter III. The chemical unity
 of living beings.—Chapter IV. The mutability of living beings.—Chapter
 V. The specific form, its acquisition, and reparation.—Chapter VI.
 Nutrition.


                              CHAPTER I.

                     THE DOCTRINE OF VITAL UNITY.

 Phenomena common to all living beings—Theory of vital duality—Unity in
 the formation of immediate principles—Unity in the digestive acts—The
 common vital fund.


When we ask the various philosophical schools what life is, some show
us a chemical retort, and others show us a soul. Whether vitalists
or of the mechanical school, these are the adversaries who since
philosophy began have vainly contested the possession of the secret
of life. We need not concern ourselves with this eternal quarrel. We
need not ask Pythagoras, Plato, Aristotle, Hippocrates, Paracelsus,
Van Helmont, and Stahl what idea they formed of the vital principle;
nor need we probe to the depths the ideas of living nature held by
Epicurus, Democritus, Boerhaave, Willis, and Lamettrie; nor need we
apply to the iatromechanicians nor to the chemists. We may do better
than that. We may ask nature itself.

_Phenomena Common to Living Beings._—Nature shows us an infinite number
of beings, animal or vegetable, described in ordinary language as
_living beings_. This language implicitly assumes something common to
them all, a universal manner of being which belongs to them without
distinction, without regard to differences of species, types, or
kingdoms. On the other hand, anatomical analysis teaches us that
animated beings and plants may be divided into parts ever decreasing
in complexity, of which the last and the simplest is the _anatomical
element_, the _cell_, the microscopic organic unit which, too, is
alive. Common opinion suspects that all these beings, whether entire
as in the case of animal and vegetable individuals, or fragmentary as
in the case of cellular elements, have the same manner of being, and
present the same body of common characteristics which rightly gives
them this unmistakable title of living beings. Life then essentially
would be this manner of being, common to animals, vegetables, and their
elements. To seize in isolation these common, necessary, and permanent
features, and then to synthetize them into a whole, will be the really
scientific method of defining life, and of explaining its nature.

And here then immediately arises a fundamental question which gives
one pause, a question of fact which must be solved before we can
go further. Is there really a common manner of being in all these
things? Are _animal life, vegetable life_, and the life of the
elements or _elementary life_, all the same? Is there a sum total of
characteristics which may define life in general?

The physiologists, following in the steps of Claude Bernard, respond in
the affirmative. They accept as valid and convincing the proof given of
this vital community by the illustrious experimentalist. However there
are some rare exceptions to this universal assent. In this concert
of approval there is at least one discordant voice, that of M. F. Le
Dantec.[13]

 [13] M. Le Dantec, of whose philosophical and rigorously systematic
 mind I have the highest opinion, has laid down a new conception of
 life, the essential basis of which is this very distinction between
 elementary life and ordinary life; between the life of the elements
 or of the beings formed from a single cell, protophytes and protozoa,
 and the life of ordinary animals and plants, which are multicellular
 complexes, and for that reason called _metazoa_ and _metaphytes_.

 Further, in the _elementary life_ peculiar to monocellular beings
 (protozoa and cellular elements), M. Le Dantec distinguishes three
 manners of being:—The first condition, which is elementary life
 manifested in all its perfection, cellular health; the second
 condition is deteriorated elementary life, _cellular disease_; and the
 third condition, which is _latent life_. I should say at once that in
 so far as the fundamental distinction of the phenomena of _elementary
 life_ and those of the general life of animals and ordinary plants,
 metazoa or metaphytes is concerned, we find it neither justified nor
 useful. And further, _manifested elementary life_, as M. Le Dantec
 understands it, would only belong to a small number of _elementary
 beings_—for the protozoa, starting with the infusoria, are not among
 the number—and to a still smaller number of _anatomical elements_,
 since among the vertebrates we recognize as almost the only elements
 satisfying it, the ovule, and perhaps the leucocyte. Physiologists,
 therefore, do not agree with M. Le Dantec as to the utility of adding
 one condition more to those we all admit—namely, manifested animal
 life and latent life.

_The Doctrine of the Vital Duality of Animals and Plants._—There are,
therefore, biologists who, in the domain of theory and in virtue of
more or less well-founded conceptions or interpretations, separate
_elementary life_ from other vital forms, and thus break the bond of
vital unity proclaimed by Claude Bernard. This monistic doctrine at the
outset met with other opponents, and that, too, in the domain of facts.
But it triumphed over them and became established. We have to deal with
scientists like J. B. Dumas and Boussingault, who drew a dividing line
between _animal life_ and _vegetable life_.

But let us in a few words recall to the reader this victorious struggle
of the monistic doctrine against the dualism of the two kingdoms. If
we consider an animal in action, said the champions of vital dualism,
we agree that it feels, moves, breathes, digests, and finally, that
it destroys by a real operation of chemical analysis the materials
afforded to it by its ambient world. It is in these phenomena that are
manifested its activity, its life. Now, added the dualists, plants do
not feel, do not move, do not breathe, and do not digest. They build
up from immediate principles, by an operation of chemical synthesis,
the materials they borrow from the soil which bears them, or from the
atmosphere which surrounds them. There is, therefore, nothing in common
between the representatives of the two kingdoms if we confine ourselves
to the examination of the actual phenomena which take place in them.
To find a resemblance between the animal and the vegetable, said the
dualists, we must set aside what they _do_, for they do different,
or even contrary things. We must consider whence they come and what
they _become_. Both originate in organisms similar to themselves.
They grow, evolve, and generate as they themselves were generated.
In other words, while their acts separate plants from animals, their
mode of origin and evolution alone bring them together. Such analogies
are of no slight importance; but they were neutralized by their
dissimilarities, which were exaggerated by the dualistic school.

It is clear that the word _life_ would lose all actual significance to
those who would reduce it to the faculty of evolution, and who would
separate all its real manifestations in animated beings and in plants.
If there are two lives, the one animal and the other vegetable, there
are no more; or, what comes to the same thing, there is an infinite
number of lives which have nothing in common but the name, or at most,
the possession of some secondary characteristics. There are as many of
them as there are different beings, for each has its own particular
evolution. Here the specific is the negation of the general and it
destroys it instead of being subordinate to it. The principle of life
becomes for each being something as individual as its own evolution.
And this, if we think it out, is how the philosophers look at life,
and it is the real reason of their disagreement with the physiological
school.

_Proof of the Monistic Theory._—On the other hand, under the
disguise of living forms, the physiologist recognizes the existence
of an identical basis. His trained ear marks amid the overcharged
instrumentation of the vital work the recognizable undertones of
a constant theme. It was the work of Claude Bernard to bring this
common basis to light. He shows that plants live as animals do, that
they breathe, digest, have sensory reactions, move essentially like
animals, destroy and build up in the same manner the immediate chemical
principles. For that purpose it was necessary to pass in review,
examining them from their foundation and distinguishing the essential
from the secondary, the different vital manifestations—digestion,
respiration, sensibility, motility, and nutrition. This is what Claude
Bernard did in his work _Sur les Phénomènes de la vie communs aux
animaux et aux plantes_. We need only to sketch in broad outline the
characteristic features of his lengthy demonstration.

_Unity in the Formation of Immediate Chemical Principles._—The first
and most important of the differences pointed out between the life of
animals and that of plants was relative to the formation of immediate
principles. On this ground, indeed, vital dualism raised its fortress.
The animal kingdom was considered in its totality as the parasite of
the vegetable kingdom. To J. B. Dumas, animals, whatever they may be,
make neither fat nor any elementary organic matter; they borrow all
their foods, whether they be sugars or starches, fats or nitrogenous
substances, from the vegetable kingdom. About the year 1843 the
researches of the chemists, and of Payen in particular, succeeded in
proving the presence, almost constant, of fatty matters in vegetables;
and, further, these matters existed there in proportions more than
sufficient to explain how the beast which fed upon them was fattened.
The chemists attributed to nature as much practical sense as they
themselves possessed; and since the hay and the grass of the ration
brought fat ready made to the horse, the cow, and the sheep, they
declared that the animal organism had nothing whatever to do but to
put this food into the tissues, or to arrange for it to pass into the
milk. But nature is not so wise and economical as was supposed at
the Académie des Sciences. After a memorable debate, in which Dumas,
Boussingault, Payen, Liebig, Persoz, Chossat, Milne-Edwards, and
Flourens took part, and, later on, Berthelot and Claude Bernard, it was
agreed that the animal does not grow fat from the fatty food which is
supplied it, and that it makes its own fat just as the vegetable does,
but in another manner. In the same way sugar, the normal constituent
substance necessary for the nutrition of animals and plants, instead of
being a vegetable product passing by alimentation from the herbivorous
animals and thence to the carnivorous, is manufactured by the animal
itself. Generally speaking, immediate principles have an equal claim
to existence in the two kingdoms. Both form and destroy the substances
indispensable to life.

Here, then, one of the barriers between animal life and vegetable life
is overthrown and destroyed.

_Unity of Digestive Acts in Animals and Plants._—Similarly, another
barrier falls if we show that digestion, long considered the exclusive
function of animals, and, in particular, of the higher animals, is in
reality universal.

Cuvier pointed out the absence of a digestive apparatus as a very
general and distinctive characteristic of plants. But the absence
of a digestive apparatus does not necessarily imply the absence of
digestion. The essential act of digestion is independent of the
infinite variety of the organs, just as a reaction is independent of
the form of the vessel in which it takes place. It is, in fact, a
chemical transformation of an alimentary substance. This transformation
may be realized outside the organism, _in vitro_, just as it can in
the living being without masticating organs, without an intestinal
apparatus, without glands, in a vessel placed in a stove, simply by
means of a few soluble ferments—pepsine, trypsine, amylolytic diastases.

All alimentary substances, whether taken from without or borrowed
from the reserves accumulated in the internal stores of the organism,
must undergo preparation. This preparation is digestion. Digestion is
the prologue of nutrition. It is over when the reparative substance,
whether food or reserve-stuff, is brought into a state enabling it to
pass into the blood, and to be utilized by the organism.

_The Identity of Categories of Foods in the Two Kingdoms._—Now the
alimentary substances are the same in the two kingdoms, and so
is their digestive preparation. Alimentary materials are of four
kinds: albuminoid, starchy, fatty, and sugary substances. The animal
takes them from without (food properly so-called), or from within
(reserve-stuff). Man obtains starch, for instance, from different
farinaceous dishes. It may, however, equally well be borrowed from
the reserve of flour that we carry within us in our liver, which is a
veritable granary, full of floury substance, glycogen. And so it is
with vegetables. The potato has its store of flour in its tuber just as
the animal has in its liver. The grain which is about to germinate has
it in reserve-stuff in its cotyledons, or in its albumen. The bud which
is about to develop into a tree or a flower carries it at its base.

The same conclusions are true for another class of substances, the
sugars. They may be a food taken from without, or a reserve deposited
in the tissues. The animal takes from without, in fruits for instance,
the ordinary sugar which pleases its taste. Beetroot, when flowering
and fructifying, draws this substance from its roots in which stores
have been amassed. The sugar cane when running to seed takes the sugar
from the stores which it possesses in its cane. Brewer’s yeast, the
_saccharomyces cerevisiæ_, the agent of alcoholic fermentation, finds
this same substance in the sugary juices favourable to its development.

In the same way, identically fatty substances, either in the
form of food or of reserve-stuff, serve for nutrition to animals
and vegetables; and that is again true of the substances of the
fourth class, albuminoids, identical in the two kingdoms, foods or
reserve-stuff, equally utilizable in both after digestion.

_Identity of the Digestive Agents and Mechanisms in Plants and
Animals._—Now, the results of contemporary research have been to
establish a surprising resemblance in the modifications experienced
by these foods, or reserve stuffs, in animals and plants; and even
resemblances in the agents which realize them, and in the mechanisms by
which they are performed. There is a real unity. The flour accumulated
in the tuber of the potato is liquefied and digested on the appearance
of the buds or of the flower, just as the starch of the liver or the
alimentary flour is digested by the animal. The fatty matter which
is stored up in the oleaginous grain is digested at the moment of
germination, just as the fat during a meal is digested in the animal’s
intestine. As the beetroot begins to run to seed, the root gives up
part of its store of sugar, and this reserve stuff is distributed
throughout the stalk after having been digested, exactly as would have
been the case in the digestive canal of man.

Vegetables, then, really digest. The four classes of substances
mentioned above are really digested in order to pass from their
actual form, a form unsuitable for interstitial exchanges, to another
form suitable for nutrition. As there are four kinds of foods, so
there are four kinds of digestions, four kinds of ferment-producing
agents—amylolytic,[14] proteolytic,[15] saccharine, and lipasic[16]
diastases, identical in the animal and the plant. Identity of ferments
implies identity of digestions. Going down to the very basis of things,
the digestive act is nothing but the action of this ferment. This
is the crux of the whole question. All else is only difference in
scene, varying in the means of execution and in the accessories. The
difference arises from the stage on which it takes place, but the piece
which is being played is the same, and the actors are the same, and so
is the action of the play.

 [14] Amylolytic ferments change starch and glycogen (_amyloses_) into
 sugar.—TR.

 [15] Proteolytic ferments change proteids into peptones and
 proteoses.—TR.

 [16] The enzyme known as lipase splits the fat or oil in germinating
 seeds into a fatty acid and glycerine.—TR.

This identity between animal and vegetable life is found in the
phenomena of respiration and of motility. The limits of this book do
not allow of our entering into the details of facts. Besides, the facts
are well known, and may be found in any treatise on general physiology.
This science, therefore, enables us to perceive the imposing unity of
life in its essential manifestations.

The community of the phenomena of vitality in animals and plants being
thus placed beyond a doubt, we must now discover the reason why. This
reason is to be found in their anatomical and in their chemical unity.
The fundamental phenomena are common because the composition is common,
and because the universal anatomical basis, the cell, possesses in all
cases a sum total of identical properties.

If we appeal to physiology for the characteristics common to living
beings, it will generally give us the following:—A structure or
organization; a certain chemical composition which is that of _living
matter_; a specific form; an evolution which in the earliest stage
occasions the being to grow and develop until it is divided, and
which in the highest stage includes one or more evolutive cycles
with growth, the adult stage, senility, and death; a property of
increase or nutrition, with its consequence—namely, a relation of
material exchanges with the ambient medium;—and finally, a property of
reproduction. It is important to pass them rapidly in review.




                              CHAPTER II.

                 MORPHOLOGICAL UNITY OF LIVING BEINGS.

 § 1. The cellular theory. First period: division of the organism—§
 2. Second period: division of the cell—Cytoplasm—The nucleus—§ 3.
 Physical constitution of living matter—The micellar theory—§ 4.
 Individuality of complex beings—The law of the constitution of
 organisms.


The first characteristic of the living beings is _organization_.
By that we mean that they have a structure; that they are complex
bodies formed of smaller aliquot parts and grouped according to a
certain disposition. The most simple elementary being is not yet
homogeneous. It is heterogeneous. It is organized. The least complex
protoplasms, those of bacteria, for example, still possess a physical
structure; Kunstler distinguishes in them two non-miscible substances,
presenting an alveolar organization. Thus animals and plants present an
organization, and it is sensibly constant from one end to the other of
the scale of beings. There is a _morphological unity_.


 § 1. THE CELLULAR THEORY. FIRST PERIOD: DIVISION OF THE ORGANISM INTO
                                CELLS.


_Cellular Theory. First Period._—Morphological unity results from the
existence of a universal anatomical basis, the _cell_. The cellular
theory sums up the teaching of general anatomy or histology.

At the beginning of the nineteenth century anatomy was following a
routine dating from ancient times. It divided animal and vegetable
machines into units in descending order, first into different forms
of apparatus (circulatory, respiratory, digestive, etc.); then the
apparatus into organs examined one by one, figuring and describing each
of them from every point of view with scrupulous accuracy and untiring
patience. If we think of the duration of these researches—the _Iliad_,
as Malgaigne says, already containing the elements of a very fine
regional anatomy—and especially of the powerful impulse they received
in the seventeenth and eighteenth centuries, we shall understand the
illusion of those who, in the days of X. Bichat, could fancy that the
task of anatomy was almost ended.

As a matter of fact this task was barely begun, for nothing was known
of the intimate structure of the organs. X. Bichat accomplished a
revolution when he decomposed the living body into tissues. His
successors, advancing a step in the analysis, dissociated the
tissues into elements. These elements, which one would have thought
were infinitely varied, were reduced in their turn to one common
_prototype_, the cell.

The living body, disaggregated by the histologist, resolves under the
microscope into a dust, every grain of which is a cell. A cell is an
anatomical element the constitution of which is the same from one
part to the other of the same being, and from one being to another;
and its dimensions, which are sensibly constant throughout the whole
of the living world, have an average diameter of several thousandths
of a millimetre—_i.e._, of several _microns_. This element, the cell,
is a real organ. It is smaller, no doubt, than those described by the
ancient anatomists, but it is not less complex. Its complexity is only
revealed later. It is an organic unit. Its form varies from one element
to another. Its substance is a semi-fluid mass, a mixture of different
albuminoids. In the mean value of its dimensions, so carefully
measured—_exceptis excipiendis_—we have a condition the significance of
which has not yet been discovered, but which may be of great value in
the explanation of its peculiar activities.

Such is the result to which have converged the researches of the
biologists who have examined plants or the lower animals, as well as
of the anatomists who have been more especially occupied with the
vertebrates and with man. All their researches have brought them to the
same conclusion—the cellular theory. Either living beings are composed
of a single cell—as is the case with the microscopic animals called
_protozoa_, and the microscopic vegetables called _protophytes_—or,
they are cellular complexes, _metazoa_ or _metaphytes_—that is to say,
associations of these microscopic organic units which are called cells.

_The Law of the Composition of Organisms._—The law of the composition
of organisms was discovered in 1838 by Schleiden and Schwann. From that
time up to 1875 it may be said that micrographers have spent their
time in examining every organ and every tissue, muscular, glandular,
conjunctive, nervous, etc., and in showing that in spite of their
varieties of aspect and form, of the complexity of structures due to
cohesion and fusion, they all resolve into the common element, the
cell. Contemporary anatomists, Koelliker, Max Schultze, and Ranvier,
have thus established the generality of the cellular constitution,
while zoologists and botanists confirm the same law for all animals and
vegetables, and exhibit them all as either unicellular or multicellular.

_The Cellular Origin of Complex Beings._—At the same time embryogenic
researches showed that all beings spring from a corpuscle of the same
type. Going back in the history of their development to the most remote
period, we find a cell of very constant constitution—namely, the
_ovule_. This truth may be expressed by changing a word in Harvey’s
celebrated aphorism—_omne vivum ex ovo_; we now say omne _vivum e
cellula_. The myriads of differentiated anatomical elements whose
association forms complex beings are the posterity of a cell, of the
_primordial ovule_, unless they are the posterity of another equivalent
cell. The second task of histology in the latter half of the nineteenth
century consisted in following up the filiation of each anatomical
element from the cell-egg to its state of complete development.

The whole cellular theory is contained in the two following statements,
which establish the morphological unity of living beings:—_Everything
is a cell, everything comes from an initial cell_; the cell being
defined as a mass of substance, protoplasm or protoplasms, of an
average diameter of a few microns.


           § 2. THE SECOND PERIOD: THE DIVISION OF THE CELL.


_Second Period: Constitution of the Cell._—This was, however, only the
first phase in the analytical study of the living being. A second
period began in 1873 with the researches of Strassburger, Bütschli,
Flemming, Kuppfer, Fromann, Heitzmann, Balbiani, Guignard, Kunstler,
etc. These observers in their turn submitted this anatomical, this
infinitely small cellular microcosm, to the same penetrating dissection
their predecessors had applied to the whole organism. They brought
us down one degree lower into the abyss of the infinitely small. And
as Pascal, losing himself in these wonders of the imperceptible, saw
in the body of the mite which is only a point, “parts incomparably
smaller, legs with joints, veins in the legs, blood in the veins,
humours in the blood, drops in the humours, vapours in these drops,” so
contemporary biologists have shown in the epitome of organism called a
cell, an edifice which itself is marvellously complex.

_The Cytoplasm._—The observers named above revealed to us the extreme
complexity of this organic unit. Their researches have shown us the
structure of the two parts of which it is composed—the cellular
protoplasm and the nucleus. They have determined the part played by
each in genetic multiplication. They have shown that the protoplasm
which forms the body of the cell is not homogeneous, as was at first
supposed. The idea which was mooted later, that this protoplasm was
formed, to use Sachs’ words, of a kind of “protoplasmic mud,”—_i.e._,
of a dust consisting of grains and granules connected by a liquid,—is
no longer accurate. There is a much simpler view of the case. According
to Leydig and his pupils, we must compare the protoplasm to a sponge in
the meshes of which is lodged a fluid, transparent, hyaline substance,
a kind of cellular juice, hyaloplasm. From the chemical point of
view this cellular juice is a mixture of very different materials,
albumens, globulins, carbohydrates, and fats, elaborated by the cell
itself. It is a product of vital activity; it is not yet the seat of
this activity. The living matter has taken refuge in the spongy tissue
itself, in the _spongioplasm_.

According to other histologists, the comparison of protoplasm to a
spongy mass does not give the most exact idea, and, in particular, it
does not furnish the most general idea. It would be far better to say
that the protoplasm possesses the structure of foam or lather. As was
seen by Kunstler in 1880, a comparison with some familiar objects gives
the best idea. Nothing could be more like protoplasm physically than
the culinary preparation known as _sauce mayonnaise_, made with the aid
of oil and a liquid with which oil does not mix. Emulsions of this kind
were made artificially by Bütschli. He noted that these preparations
mimicked all the aspects of cellular protoplasm. Thus, in the living
cell there is a mixture of two liquids, non-miscible and of unequal
fluidity. This mixture gives rise to the formation of little cells. The
more consistent substance forms their supporting framework (Leydig’s
spongioplasm), while the other, which is more fluid, fills its interior
(hyaloplasm).

However that may be, whether the primitive organization of the cellular
protoplasm be that of a sponge, as is asserted by Leydig, or that of
a _sauce mayonnaise_, as is claimed by Bütschli and Kunstler, the
complexity does not rest there. Further recourse must be made to
analysis. Just as the tissue of a sponge, when torn, shows the fibres
which constitute it, so the spongioplasm, the parietal substance,
is exhibited as formed of a tangle of fibrils, or better still, of
filaments or ribbons (in Greek, _mitome_), which are called _chromatic
filaments_, because they are deeply stained when the cell is plunged
into aniline dye. In each of these filaments, the substance of which
is called chromatin, the devices of microscopic examination enable
us to discover a series of granulations like beads on a string, the
_microsomes_ or bioblasts, connected one with the other by a sort of
cement, Schwartz’s _linin_, which is a kind of nuclein.

And let us add, to complete this summary of the constitution of
cellular protoplasm, that it presents, at any rate at a certain moment,
a remarkable organ, the _centrosome_, which plays an important part
in cellular division. Its pre-existence is not certain. Some writers
make it issue from the nucleus. At the moment of cellular division it
appears like a compressed mass of granulations, which may be deeply
stained. Around it is seen a clear unstainable zone, called the
attraction-sphere; and finally, beyond this is a crown of striæ, which
diverge like the rays of a halo—_i.e._, the _aster_. In conclusion,
there are yet in the cellular body three kinds of non-essential bodies:
the vacuoles, the leucites, and various inclusions. The _vacuoles_ are
cavities, some inert, some contractile; the _leucites_ are organs for
the manufacture of particular substances; the _inclusions_ are the
manufactured products, or wastes.

_The Nucleus_.—Every cell capable of living, growing, and multiplying,
possesses a _nucleus_ of constitution very analogous to the cellular
mass which surrounds it. The anatomical elements in which no nucleus
is found, such as the red globules of blood in adult mammals, are
bodies which are certain, sooner or later, to disappear. There is
therefore no real cell without a nucleus, any more than there is a
nucleus without a cell. The exceptions to this law are only apparent.
Histologists have examined them one by one, and have shown their purely
specious character. We may therefore lay aside, subject to possible
appeal from this decision, organisms such as Haeckel’s _monera_ and
the problem of finding out if bacteria really have a nucleus. The very
great, if not the absolute generality of the nuclear body, must be
admitted.

It hence follows that there is a nuclear protoplasm and a nuclear
juice, just as we have seen that there is a protoplasm and a cellular
juice. What was just said of the one may now be repeated of the other,
and perhaps with even more emphasis. The nuclear protoplasm is a
filamentary mass sometimes formed of a single mitome or cord, folded
over on itself and capable of being unrolled. The mitome in its turn
is a string of microsomes united by the cement of the linin. These are
the same constituent elements as before, and the language of science
distinguishes them one from the other by a prefix to their name of
the words _cyto_ or _karyo_, which in Greek signify cell and nucleus,
according as they belong to one or the other of these organs. These
are mere matters of nomenclature, but we know that in the descriptive
sciences such matters are not of minor importance.

We have just indicated that in a state of repose,—that is to say, under
ordinary conditions,—the structure of a nucleus reproduces clearly the
structure of the cellular protoplasm which surrounds it. The nuclear
essence is best separated from the spongioplasm. It takes more clearly
the form of a filamentary thread, and the filaments themselves
(mitome) show very thick chromatic granulations, or microsomes,
connected by the linin.

At the moment of reproduction of the cell these granulations blend
into a stainable sheath which surrounds the filaments, and the latter
dispose themselves so as to form a single thread. This chromatic
filament, which has now become a single thread, is shortened as
it thickens (_spireme_); it is then cut into segments, twelve or
twenty-four in the case of animals and a larger number in the case of
plants. These are _chromosomes_, or _nuclear segments_, or _chromatic_
loops. Their part is a very important one. They are constant in number
and permanent during the whole of the life of the cell. Let us add that
the nucleus still contains accessory elements (nucleoli).

_The Rôle of the Nucleus_.—Experiment has shown that the nucleus
presides over the nutrition, the growth, and the conservation of
the cell. If, following the example of Balbiani, Gruber, Nussbaum,
and W. Roux of Leipzig, we cut into two a cell without injuring the
nucleus, the fragment which is denuded of the nucleus continues to
perform its functions for some time in the ordinary manner, and in
some measure in virtue of its former impulse. It then declines and
dies. On the contrary, the fragment provided with the nucleus repairs
its wound, is reconstituted and continues to live. Thus the nucleus
takes a very remarkable part in the reproduction of the cell, but it
is still a matter of uncertainty whether its rôle is here subordinated
to that of the cellular body, or if it is pre-eminent. However that
may be, it follows from this experiment that the nucleus presents all
the characteristics of a vigorous vitality, and that it is in its
protoplasm that the chemists should be able to find the compounds, the
special albuminoids, which, _par excellence_, form living matter.


 § 3. THE PHYSICAL CONSTITUTION OF LIVING MATTER. THE MICELLAR THEORY.


_Physical Constitution of Living Matter_.—Microscopic examination
does not take us much farther. The microscope, with the strongest
magnification of which it is capable at present, shows us nothing
beyond these links of aligned microsomes forming the species of
protoplasmic thread or mitome, whose cellular body is a confused
tangle or a very tangled ball. It is not probable that direct sight
can penetrate much farther than this. No doubt the microscope, which
has been so vastly improved, is capable of still further improvement.
But these improvements are not indefinite. We have already reached a
linear magnification of 2000, and theory tells us that a magnification
of 4000 is the limit which cannot be passed. The penetrating power of
the instrument is therefore near its culminating point. It has already
given almost all that we have a right to expect from it.

We must, however, penetrate beyond this microscopic structure at which
the sense of sight has been arrested. How is this to be done? When
observation is arrested, hypothesis takes its place. Here there are two
kinds of hypotheses, the one purely anatomical, the other physical.
Anatomically, beyond the visible microsomes there have been imagined
invisible hyper-microscopic corpuscles, the plastidules of Haeckel,
the idioblasts of Hertwig, the pangenes of de Vries, the plasomes of
Wiesner, the gemmules of Darwin, and the biophores of Weismann.

Biologists who have not got all that they hoped from microscopic
structure are therefore thrown back on hyper-microscopic structure.

It is very remarkable that all this profound knowledge of structure has
been so sterile from the point of view of the knowledge of cellular
functional activity. All that is known of the life of the cell has
been revealed by experiment. Nothing has resulted from microscopic
observation but ideas as to configuration. When it is a question of
giving or imagining an explanation of vital facts, of heredity, etc.,
biologists unable to supply anything beyond the details of structure
revealed by anatomy have had recourse to hypothetical elements,
gemmules, pangenes, biophores, and different kinds of determinants.

Anatomy never has explained and never will explain anything. “Happy
physicists!” wrote Loeb, “in never having known the method of research
by sections and stainings! What would have happened if by chance a
steam engine had fallen into the hands of a histological physicist?
How many thousands of sections differently stained and unstained, how
many drawings, how many figures, would have been produced before they
knew for certain that the machine is an engine, and that it is used for
transforming heat into motion!”

The study of physical properties, continued on rational hypotheses, has
also thrown some light on the possible constitution of living matter.
The gap between microscopical structure and molecular or chemical
structure has thus been filled.

The consideration of the properties of _turgescence_ and of _swelling_,
which very generally belong to organized tissues, and therefore to the
organic substance of protoplasm, has enabled us to obtain some idea of
its ultra-microscopic constitution. If we wet a piece of sugar or a
morsel of salt, before they are dissolved they absorb and imbibe the
water without sensibly increasing their volume. It is quite otherwise
with a tissue (_i.e._, with a protoplasm) when weakened in water as a
preliminary. The tissue, plunged into the liquid, absorbs it, swells,
and often grows considerably. And this water does not lodge in the
gaps, in pre-existing lacunar spaces, for organic matter presents no
gaps of this kind. It does not resemble a porous mass with capillary
canals, such as sandstone, tempered mortar, clay, or refined sugar.
The molecules of water interpose between and separate the organic
molecules, thus increasing by a sort of intussusception the intervals
separating the one from the other—molecular intervals escaping the
senses, as do the molecules themselves because they are of the same
order of magnitude.

_Micellar Theory._—While pondering over this phenomenon, an eminent
physiologist, Nägeli, was led in 1877 to propose his _micellar theory_.
Micellæ are groups of molecules in the sense in which physicists
and chemists use the word. They are molecular structures with a
configuration. They rapidly absorb water and are capable of fixing a
more or less thick and adherent layer of it to their surface. In a
word, they are aggregates of organic matter and water.

There is therefore every reason for believing that the _microsomes_ of
spongy protoplasm, the physical support or basis of cellular life,
are _groups of micellæ_ formed of albuminoid substances and water.
These clustered forms, these micellæ, are not absolutely peculiar to
organized matter. Pfeffer, the learned botanist, has pointed them
out under another name, _tagmata_, in the membranes of chemical
precipitates.

Beyond this limit analysis finds nothing but the chemical molecule
and the atom. So that if we wish to reconstruct the hierarchy of the
materials of constitution of the protoplasm in order of ascending
complexity, we shall find at the foundation the atom or atoms of simple
bodies. They are principally carbon, hydrogen, oxygen, nitrogen, the
elements of all organic compounds, to which may be added sulphur
and phosphorus. At the head we have the albuminoid molecule, or the
albuminoid molecules, aggregates of the preceding atoms. In the third
stage the micellæ or tagmata, aggregates of albuminoids and water, are
still too small to be observed by the senses. They unite in their turn
to form the microsomes, the first elements visible to the microscope.
The microsomes, cemented by linin, form the filaments or links which
are called mitomes. The living protoplasm is therefore nothing but a
chain, or tangled skein, or a spongy skeleton formed by its filaments.

Such is the typical constitution of living matter according to
microscopic observation, supplemented by a perfectly reasonable
hypothesis, which is, so to speak, only a translation of one of its
most evident physical properties. This relatively simple scheme has
become a complex scheme in the hands of later biologists. On the
micellar hypothesis, which seems almost inevitable in its character,
new hypotheses have been grafted, merely for the sake of convenience.
Hence, we are led farther and farther from the real truth, and this is
why, in order to explain the phenomena of heredity, we find ourselves
compelled to intercalate hypothetical elements between micellæ and the
microsome in the higher hierarchy quoted above—gemmules, pangenes,
plasomes, which are only mental pictures or simple images to represent
them.


§ 4. THE INDIVIDUALITY OF COMPLEX BEINGS. LAW OF THE CONSTITUTION OF
ORGANISMS.


_Individuality of Complex Beings._—From the cellular doctrine follows a
remarkably suggestive conception of living beings. The metazoa and the
metaphytes—that is to say, the multicellular living beings which may be
seen with the eyes and do not require the microscope to reveal them—are
an assemblage of anatomical elements and the posterity of a cell.
The animal or the plant, instead of being an individual unity, is a
“multitude,” a term which is used by Goëthe himself when pondering, in
1807, over the doctrine taught by Bichat; or, according to the equally
correct expression of Hegel, it is a “nation”; it springs from a common
cellular ancestor, just as the Jewish people sprang from the loins of
Abraham.

We now picture to ourselves the complex living being, animal or plant,
with its configuration which distinguishes it from every other being,
just as a populous city is distinguished by a thousand characteristics
from its neighbour. The elements of this city are independent and
autonomous for the same reason as the anatomical elements of the
organism. Both have in themselves the means of life, which they neither
borrow nor take from their neighbours nor from the whole. All these
inhabitants live in the same way, are nourished and breathe in the
same manner, all possessing the same general faculties, those of man;
but each has besides, his profession, his trade, his aptitudes, his
talents, by which he contributes to social life, and by which in his
turn he depends on it. Professional men, the mason, the baker, the
butcher, the manufacturer, the artist, carry out different tasks and
furnish different products, the more varied, the more numerous and the
more differentiated, in proportion as the social state has reached a
higher degree of perfection. The living being, animal or plant, is a
city of this kind.

_Law of the Constitution of Organisms._—Such is the complex animal.
It is organized like the city. But the higher law of this city is
that the conditions of the elementary or individual life of all the
anatomical citizens are respected, the conditions being the same for
all. Food, air, and light must be brought everywhere to each sedentary
element; the waste must be carried off in discharges which will free
the whole from the inconvenience or the danger of such debris; and that
is why we have the different forms of apparatus in the circulatory,
respiratory, and excretory economy. The organization of the whole
is therefore dominated by the necessities of cellular life. This is
expressed in _the law of the constitution of organisms_ formulated by
Claude Bernard. The organic edifice is made up of apparatus and organs,
which furnish to each anatomical element the necessary conditions and
materials for the maintenance of life and the exercise of its activity.
We now understand what is the life, and at the same time what is the
death, of a complex being. The life of the complex animal, of the
metazoon, is of two degrees; at the foundation, the activity proper
to each cell, _elementary life_, cellular life; above, the forms of
activity resulting from the association of the cells, _the life of the
whole_, the sum or rather the complex of elementary partial lives.
There is a solidarity between them produced by the nervous system,
by the community of the general circulatory, respiratory apparatus,
etc., and by the free communication and mixture of the liquids which
constitute the media of culture for each cell. We shall have an
opportunity of recurring to current ideas as to the morphological
constitution of organisms.




                             CHAPTER III.

                 THE CHEMICAL UNITY OF LIVING BEINGS.

 The varieties and essential unity of the protoplasm—Its affinity for
 oxygen—The chemical composition of protoplasm—Its characteristic
 substances.—§ 1. The different categories of albuminoid
 substances—Nucleo-proteids—Albumins and histones—Nucleins.—§
 2. Constitution of nucleins.—§ 3. Constitution of histones and
 albumins—Schultzenberger’s analysis of albumin—Kossol’s analysis—The
 hexonic nucleus.


The chemical unity of living beings corresponds to their morphological
unity.

_The Varieties and Essential Unity of the Protoplasm._—One essential
feature of the living being is that it is composed of matter peculiar
to it, which is called _living matter_, or _protoplasm_. But this is
a somewhat incorrect way of expressing the facts. There is no unique
living matter, no single protoplasm; their number is infinite, there
are as many as there are distinct individuals. However like one man may
be to another, we are compelled to admit that they differ according to
the substance of which they are constituted. That of the first offers
a certain characteristic personal to the first, and found in all his
anatomical elements; similarly for the second. With Le Dantec we shall
say that the chemical substance of Primus is not only of the substance
of man, but in all parts of his body and in all his constituent cells
it is the exclusive substance of Primus; and, in the same way, the
living matter of another individual Secundus will carry everywhere his
personal impress, which differs from that of Primus.

But it is none the less true that this absolute specificity is based
with certainty only on differences which from the chemical point
of view are exceedingly slight. All these protoplasms have a very
analogous composition. And, if we regard as negligible the smallest
individual, specific, generic, or ordinal variations we may then speak
in a general manner of _protoplasm_ or _living matter_.

Experiment shows us, in fact, that the real living substance—apart
from the products it manufactures and can retain or reject—is in every
cell tolerably similar to itself. The fundamental chemical resemblance
of all protoplasms is certain, and thus we may speak of their typical
composition. We may sum up the work of physiological chemistry for the
last three quarters of a century by affirming that it has established
the chemical unity of all living beings—that is to say, a very notable
analogy in the composition of their protoplasm.

This living matter is essentially a mixture of the proteid or
albuminoid substances, to which may be added other categories of
immediate principles, such as carbohydrates and fatty matters. But
the latter are of secondary importance. The essential element is the
proteid substance. The most skilful chemists have tried for more than
half a century to discover its composition. Only during the last few
years—thanks to the researches of Kossel, the German chemist, following
on those of Schultzenberger and Miescher—we are beginning to know the
outer walls or the framework of the albuminoid molecule; in other
words, its chemical nucleus.

_Physical Characters of Protoplasm._—About 1860 Ch. Robin thought
that he had defined living matter sufficiently—or, at least, as
perfectly as could be expected at that time—by attributing to it
three physical characteristics. They were:—Absence of homogeneity,
molecular symmetry, and the association of three orders of immediate
principles—albuminoids, carbohydrates and fats. These characteristics
assist, but do not suffice, to define the organization.

No doubt the characteristics must be completed by the addition of a
certain number of more subtle physical features.

One of them refers to the structure of protoplasm as revealed by the
microscope. Throughout the whole of the living kingdom, from the
bacteria studied by Kunstler and Busquet to the most complicated
protozoa, protoplasmic matter presents the same constitution, and in
consequence, this structure of the protoplasm must be considered as
one of its distinctive characters. It is not homogeneous; it is not
the last term of the visible organization: it is itself organized.
Experiment shows that it does not resist breaking up or crushing.
Mutilations cause it to lose its properties. As for the kind of
structure that it presents, it may be expressed by saying that it is
that of a foamy emulsion.

We saw above that our knowledge as to the physical condition of
protoplasm has been completed by the theories of Bütschli’s micellæ or
Pfeffer’s tagmata.

_Properties of the Protoplasm. Its Affinity for Oxygen._—From the
chemical point of view, living matter presents a very remarkable
property—namely, a great affinity for oxygen. It absorbs it
so greedily that the gas cannot remain in a free state in its
neighbourhood. Living protoplasm, therefore, exercises a reducing
power. But it does not absorb oxygen in this way for its own advantage;
oxygen is not absorbed, as was supposed thirty years ago, to supply
fuel wherewith to burn the protoplasm. The products are not those of
its oxidation, of its own disintegration. They are the products of
combustion of the reserve-stuff which is incorporated in it. These
substances have been supplied to it from without, like the oxygen
itself, with the blood. This was proved by G. Pflüger in 1872 to
1876. The protoplasm is only the focus, the scene, or the factor of
combustion. It is not its victim, it does not itself furnish the fuel.
It works like the chemist, who obtains a reaction with the substances
that are given to him.

As for the reducing power of protoplasm, A. Gautier in 1881 and Ehrlich
in 1890 have given fresh proofs. A. Gautier in particular has insisted
that the phenomena of combustion take place, so to speak, outside the
cell, and at the expense of the products which surround it; while on
the contrary the really active and living parts of the nucleus and of
the cellular body, work protected by the oxygen, as in the case of
anaerobic microbes.

This result is of great importance. Burdon Sanderson, the late
learned professor of physiology at the University of Oxford, has not
hesitated to compare it to the discovery of respiratory combustion
by Lavoisier. There is no doubt some exaggeration in the comparison;
but there is, on the other hand, no less exaggeration in supposing
that it is not of great importance. We may no longer in these days
speak without reservation of the vital vortex of Cuvier, and of the
incessant twofold movement of assimilation and dissimilation which is
ever destroying living matter and building it up again. In reality, the
living protoplasm varies very little; it only undergoes oscillations of
very slight extent; it is the materials, the reserve stuff on which it
operates, which are subject to continual transformations.

_Chemical Composition of Protoplasm._—One of the the three
characters attributed by Ch. Robin to living matter was its chemical
composition, of which little was known in his time. He insisted on
the constant presence in the living elements of three orders of
immediate principles—proteid substances, carbohydrates, and fatty
bodies. In reality the proteid substances, or albuminoids, alone are
characteristic. The two other groups, carbohydrates and fatty bodies,
are rather the signs and the products of the vital activity, than
constituents of the matter on which it is exercised.

It is therefore on the knowledge of the proteid substances that all the
sagacity of biological chemists has been exercised. Their efforts for
thirty years, and particularly in the last few years, have not been
barren; they enable us to give a first rough sketch of the constitution
of these substances.


       § 1. THE CHARACTERISTIC SUBSTANCES OF THE PROTOPLASM. THE
                           NUCLEO-PROTEIDS.


_The Different Categories of Albuminoid Substances._—Albuminoid or
proteid substances are extremely complex compounds, much more so than
any of those which are being constantly studied by the chemist.
They also are to be found in great variety. It has been difficult to
separate them one from the other, to characterize them rigorously,
or, in other words, to classify them. However, it has been done now,
and we distinguish three classes which are differentiated at once
from the physiological and from the chemical points of view. The
first comprises the complete or typical albuminoids. They are the
_proteids_ or _nucleo-albuminoids_. They are to be found in the most
active and most living parts of the protoplasm, and therefore in the
spongioplasm of the cell and around the nucleus. The second group
is formed of _albumins_ and _globulins_, compounds already simpler,
fragments derived from the destruction of the preceding, into which
they enter as constituent elements. In the isolated state they do not
belong to the really living protoplasm; they exist in the cellular
juice, in the interstitial and circulating liquids in the blood
and in the lymph. The third category comprises real but incomplete
albuminoids. They are to be found in the portions of the economy which
have a specialized or attenuated life, and are destined to serve as
a support to the more active elements—_i.e._, they contribute to the
building up of the bony, cartilaginous, conjunctive, elastic tissues.
They are called _albumoids_. It is naturally the first group, that of
the proteids—_i.e._, of the complete and characteristic compounds of
the living substance—upon which the attention of the physiologists
must be fixed. It is only quite recently that the clear definition of
these substances has been given, and proteid compounds detected in the
confused mass.

_The Nucleo-proteids._—This progress in the characterization and
specification of the proteids required in the first place a knowledge
of two particular compounds, the _nucleins_ and the _histones_. This
did not become possible until after the researches of Miescher and
Kossel on the nucleins, which went on from 1874 to 1892, and those of
Lilienfeld and d’Yvor Bang on the histones, from 1893 to 1899. The
complete albuminoids are constituted by the combination of two kinds of
substances—albumins or histones on the one hand, and nucleins on the
other. By combining solutions of albumins or histones with solutions
of nuclein, the synthesis of the proteid is effected. The study of
the properties and characteristics of these nucleo-albumins and
nucleo-histones is going on at the present moment. It is being carried
out with much method and with wonderful patience by the German school.

All the proteids contain phosphorus in addition to the five chemical
elements, carbon, oxygen, hydrogen, nitrogen, and sulphur, which are
common to the other albuminoids. Another interesting feature in their
history is that the action of the gastric juice divides them into
their two constituents:—the nuclein, which is deposited and resists
the destructive action of the digestive liquid, and the albumin or
histone, which on the contrary experiences this action with the usual
consequences. Thus the gastric juice furnishes a process which is very
simple and very convenient in the analysis of the proteids.

_Localization of the Nucleo-Proteids._—What we said before as to
the important physiological rôle of the cellular nucleus may arouse
the expectation that in it will be found the living matter which
is chemically the most differentiated, the albuminoids of highest
rank—_i.e._, the nucleo-proteids and their constituents. Not that they
would not be found in the protoplasm of the rest of the cell, but there
is certainly a risk that they would be less concentrated there and more
blended with accessory products; they are there connected with much
more secondary vital functions. This conclusion inspired the early
researches of Professor Miescher, of Basle, in 1874, and, twenty years
later, those of Professor Kossel, one of the most eminent physiological
chemists in Germany.

In fact, these compounds have been found in all tissues which are rich
in cellular elements with well-developed nuclei. The white globules
of the blood furnished to Lilienfeld the first nucleo-histone ever
isolated. The red globules themselves, when they possess a nucleus,
which is the case in birds and reptiles as well as in the embryo of
mammals, contain a nucleo-proteid which was easily isolated by Plosz
and Kossel. Hammarsten, the Swedish chemist, who has acquired a
great reputation from his researches in other domains of biological
chemistry, prepared the nucleo-proteids of the pancreas in 1893. They
have been obtained from the liver, from the thyroid gland (Ostwald),
from brewers’ yeast (Kossel), from mushrooms, and from barley (Petit).
They have been detected in starchy bodies and in bacteria (Galeotti).


                    § 2. CONSTITUTION OF NUCLEINS.


_Constitution of Nucleins._—Our path is already marked out if we wish
to penetrate farther into the constitution of these proteids, which are
the immediate principles highest in complexity among those which form
the living protoplasm. We must analyze the two components, the albumins
and the histones on the one hand, and the nucleins on the other. As for
the nucleins, this has already been done, or very nearly so.

Kossel, in fact, decomposed the nuclein by a series of very carefully
arranged operations, and has reduced it step by step to its
crystallizable organic radicals. At each stage that we descend in the
scale of simplification a body appears which is more acid and more rich
in phosphorus. At the third stage we come to phosphoric acid itself.
The first operation divides the nuclein into two substances: the new
albumin and nucleinic acid. After separating these elements they can
be reunited: a solution of albumin with a solution of nucleinic acid
reconstitutes the nuclein. A second operation separates the nucleinic
acid in its turn into three parts. One is a body of the nature of
the sugars—_i.e._, a carbohydrate. The appearance of a sugar in this
portion of the molecule of nucleinic acid is an interesting fact and
fertile in results. The second part is constituted by a mixture of
nitrogenous bodies, well known in organic chemistry under the name of
_xanthic bases_ (xanthin, hypoxanthin, guanin, and adenin). The third
part is a very acid body and full of phosphorus—thymic acid. If in a
third and last operation the thymic acid is analyzed, it is finally
separated into phosphoric acid and into thymene, a crystallizable base,
and thus we are brought back to the physical world, for all these
bodies incontestably belong to it.


            § 3. THE CONSTITUTION OF HISTONES AND ALBUMINS.


_Constitution of Histones._—But we are only half-way through our task.
We are acquainted in its origin with one of the genealogical branches
of the proteid, the nucleinic branch. We must also learn something
of the other branch, the albumin or histone branch. But on this side
the problem assumes a character of difficulty and complexity which is
admirably adapted to discourage the most untiring patience.

The analysis of albumin for a long time baulked the chemist “Here,”
said Danilewsky, “we come to a closed door which resists all our
efforts.” We know how vastly interesting what is taking place on the
other side must be, but we cannot get there. We get a mere glimpse
through the cracks or chinks which we have been able to make.

This analysis of albuminous matter at first requires great precautions.
The chemist finds himself in the presence of architecture of a very
subtle kind. The molecule of albumin is a complex edifice which has
used up several thousand atoms. To perceive the plan and structure, it
must be dismantled and separated into parts which are neither too large
nor too small. Such careful demolition is difficult. Processes too
rough or too violent will reduce the whole to the tiniest of fragments.
It is a statue which may be reduced to dust, instead of being separated
into recognizable fragments, easily fitted in place along their
fractured faces.

_Analysis of Albumin by Schützenberger._—Schützenberger, a chemist
of great merit, attempted (about 1875) this thankless task. Others
before him had experimented in various ways. Two Austrian scientists,
Hlasitwetz and Habermann, in 1873, and a little later Drechsel in 1892,
had used concentrated hydrochloric acid to break down albumin. They
also employed bromine for the same purpose. More recently Fuerth had
used nitric acid with a similar object. Schützenberger tried another
way. The battering ram which he used against the edifice of albumin
was a concentrated alkali, baryta. He warmed the white of an egg with
barium hydrate in a closed vessel at a temperature of 200°. The albumin
of egg then divides into a certain number of simpler groups. The
difficulty is to isolate and to recognize each part in this mass of the
materials of demolition. That can be done by the aid of the processes
of direct analysis. By mentally combining these different fragments,
the original building is reconstructed. This method of demolition is
certainly too rough and violent. Schützenberger’s operation gives us
very fine fragments—small molecules of free hydrogen, of ammonia, of
carbonic, acetic, and oxalic, acids which reveal extreme pulverization.
These products represent about a quarter of the total mass. The other
three-quarters are formed of larger fragments, the examination of which
is most instructive. They belong to four groups. The first comprises
five or six bodies, amido-acids or _leucins_. It proves the existence
in the molecule of albumin of compounds of the series of fats—_i.e._,
arranged in an open chain. The second group is formed by tyrosin and
kindred products—_i.e._, by the bodies of the aromatic series, which
force us to acknowledge the presence in the molecule of albumin of a
benzene nucleus. The third group forms around the nucleus known to
chemists under the name of pyrrol. The fourth comprises bodies such as
the glucoproteins, connected with the sugars, or carbohydrates.

Does the fact that the molecule of albumin is destroyed in producing
these compounds raise the question as to whether it implies the idea
that in reality they pre-exist in it? Chemists are rather inclined to
admit this. However, the conclusion does not appear to be permissible.
Duclaux considers it doubtful. It is not certain that all these
fragmentary bodies pre-exist in reality, and it is no more certain that
a simple bringing of them together represents the primitive edifice.
Materials of demolition from a house that has been pulled down give no
idea of its natural architectural character. There is only one way of
justifying the hypothesis, and that is to reconstitute the original
molecule of albumin by bringing the fragments together. We have not got
to that stage yet. The era of syntheses of such complexity is more or
less near, but it has certainly not yet begun.

Moreover, it is not correct to say that the simple juxtaposition of the
surfaces of fracture will reproduce the initial body. The fragments, so
far as analysis has obtained them, are not absolutely what they might
have been in the original structure. There they adhered the one to the
other, not only by the mere contact of their surfaces of fracture, as
is supposed, but in a slightly more complex manner. The fragments of
the molecule are joined by bonds. We can picture them to ourselves
by supposing these bonds to be like hooks. The hooks, which could
only be broken by violence, are called by the chemists _satisfied
atomicities_. These atomicities, set free by the breaking up, cannot
remain in this condition; they must be satisfied anew. The hook tries
to attach itself. In Schützenberger’s experiment the addition of water
provides for this necessity. A molecule of water (H⌄{2}O) splits
into two, the hydrogen (H) on the one side and the hydroxyl (OH) on
the other. These two elements cling to the liberated bonds of the
fragments of the molecule of albumin, and thus the bodies were found
complete. Schützenberger’s experiment was too violent, too radical,
and it gave too large a number of fragments, with their free hooks and
atomicities unsatisfied, for rather a large proportion of the water
added disappeared during the experiment. In one case this quantity was
as much as 17 grammes per 100 grammes of albumin. The molecules of this
water were employed in the reparation of the incomplete fragmentary
molecules of the albumin.

It follows that Schützenberger’s experiment gave too large a number of
very small pieces corresponding to far too great a pulverization. The
very small fragments are the molecules of acids such as acetic acid,
oxalic acid, carbonic acid, molecules of ammonia, and even of hydrogen,
which we know we are setting free.

But, apart from these products which represent a quarter of the
molecule of albumin submitted to analysis, the other three quarters
represent larger fragments which may be considered as the real
constituents of the building. Thus we find four kinds of groups which
may be accepted as natural. The first of these groups is that of the
leucins or amido-acids. It proves the existence in the molecule of
albumin of compounds of the fatty series. There is also an aromatic
group—a pyridine group—and a group belonging to the category of sugars.
Imagine a certain grouping of these four series. This would be the
nucleus of the molecule of albumin. If we graft on to this nucleus, on
to this framework as it were, so many annexes, or lateral chains, the
building will be loaded with embellishments; it will have been made
unstable and _ipso facto_ appropriate for the part that it plays in the
incessant transformations of the organism.

_Kossel’s Analysis. Hexonic Nucleus._—Kossel has approached the
problem in another fashion. He did not attempt to attack the albumin
of the egg. This body is, in fact, a heterogeneous mixture as complex
as the needs of the embryo of which it forms the food. Kossel tried
a physiologically simpler albuminoid. He got it from an anatomical
element having no nutritive rôle, of a very elementary organization
and physiological functional activity, and yet one of energetic
vitality—the male generating cell. Instead of the hen’s egg he
therefore analyzed the milt of fish, and, in the first place, of
salmon. As was to be expected from what has been said of the proteids,
this living matter gives a combination of the nuclein, already known,
with an albumin. The latter is abundant, forming a quarter of the
total mass. Its reaction is strongly alkaline, which is the general
characteristic of the variety of albumin known by the name of histones.
Miescher, the learned chemist of Basle, who had noticed this basic
albumin when working on the Rhine salmon, gave it the name of protamin.
This is the substance submitted by Kossel to analysis in preference
to the albumin of egg, so dear to the chemists who had preceded him.
The disintegration of this molecule, instead of giving the series of
bodies obtained by Schützenberger, gave but one, a real chemical base,
_arginin_. At the first trial the albumin examined was reduced to a
simple crystallizable element. The conclusion was obvious. The protamin
of salmon is the simplest of albumins. To form this elementary proteid
substance a hexonic base with water is all that is required.

Continuing on these lines other male generating cells were examined
and a series of protamines constructed on the same type was found,
and these albuminous bodies proved to be formed of a base or mixture
of analogous hexonic bases: arginin, histidin, and lysin—all bodies
closely akin in their properties and entirely belonging to the physical
world.

Once aware of the existence of this fundamental nucleus, chemists
found it in the more complex albumins where it had been missed. It was
found in the albumin of egg hidden under the mass of other groups.
It was recognized in all animal or vegetable albumins. The nuclei
of Schützenberger may be missing. Hexonic bases are the constant
and universal element of all varieties of albumins. They prevail in
the chemical nucleus of the albuminous molecule, and perhaps as is
suggested by Kossel, they may form it exclusively. All the other
elements are superadded and accessory. The essential type of this
molecular edifice, sought for so long, is known at last.

_Conclusion._—To sum up, the chemical unity of living beings is
expressed by saying that living matter, protoplasm, is a mixture or a
complex of proteid substances with an hexonic nucleus.




                              CHAPTER IV.

      THE TWOFOLD CONDITIONING OF VITAL PHENOMENA. IRRITABILITY.

 Appearance of internal activity of the living being—Vital phenomena
 regarded as a reaction of the ambient world.—§ 1. Extrinsic
 conditions—The optimum law.—§ 2. Intrinsic conditions—The structure
 of organs and apparatus—How experiment attacks the phenomena of life.
 Generalization of the law of inertia—Irritability.


_Instability. Mutability. The Appearance of Internal Activity of the
Living Being._—One of the most remarkable characteristics of the living
being is its instability. It is in a state of continual change. The
simplest of the elementary beings, the plastid, grows and goes on
growing and becoming more complex, until it reaches a stage at which it
divides, and thus rejuvenated it commences the upward march which leads
it once again to the same segmentation. Its evolution is thus betrayed
by its growth, by the variations of form which correspond to it, and by
its division.

If it be a question of beings higher in organization than the cellular
element the evolutionary character of this mutability becomes more
obvious. The being is formed, it grows; then in most cases, after
having passed through the stages of youth and adult age, it grows old,
declines and dies, and is disorganized after having gone through
what we may call an ideal trajectory. This march in a fixed direction
with its points of departure, its degrees, and its termination, is a
repetition of the path that the ancestors of the living being have
already followed.

Here, then, is a characteristic fact of vitality, or rather there
are two facts. The one consists in this morphological and organic
evolution, the negation of immutability, the negation of the indefinite
maintenance of a permanent state or form which is regarded, on the
contrary, as the condition of inert, fixed stable bodies, eternally at
rest. The other consists in the repetition, realized by this evolution,
of the similar evolution of its ancestors; this is a fact of heredity.
Finally, evolution is always in a cycle—that is to say, that it comes
to an end which brings the course of things to their point of departure.

This kind of internal activity of the living being is so striking, that
not only does it serve us to differentiate the living being from the
inert body, but it gives rise to the illusion of a kind of internal
demon, vital force, manifested by the more or less apparent acts of the
life of relation, of the motricity, of the displacement, or by the less
obvious acts of vegetative life.

_Vital Phenomena regarded as a Reaction of the Ambient World. Their
Twofold Conditioning._—In reality, as the doctrine of energetics
teaches us, the phenomena of vitality are not the effect of a purely
internal activity. They are a reaction of the environment. “The idea
of life,” says Auguste Comte, “constantly assumes the necessary
correlation of two indispensable elements:—an appropriate organism and
a suitable environment. It is from the reciprocal action of these two
elements that all vital phenomena inevitably result.” The environment
furnishes the living being with three things:—its matter, its energy,
and the exciting forces of its vitality. All vital manifestation
results from the conflict of two factors: the extrinsic factor which
provokes its appearance; the intrinsic factor, the very organization
of the living body, which determines its form. Bichat and Cuvier saw
in the phenomena of life the exclusive intervention of a principle of
action entirely internal, checked rather than aided by the universal
forces of nature. The exact opposite is true. The protozoan finds the
stimuli of its vitality in the aquatic medium which is its habitat.
The really living particles of the metazoan—that is to say, its
cells, its anatomical elements—meet these stimuli in the lymph, in
the interstitial liquids which bathe them and which form their real
external environment.

Auguste Comte thoroughly understood this truth, and has clearly
expressed it in the passage we have just quoted. Claude Bernard has
fully developed it and given it its classical form.

In order to manifest the phenomena of vitality, the elementary being,
the protoplasmic being, requires from the external world certain
favourable conditions; these it finds there, and they may be called the
stimuli, or extrinsic conditions of vitality. This being possesses no
initiative or spontaneity in itself, it has only a faculty of entering
into action when an external stimulus provokes it. This subjection of
the living matter is called _irritability_. The term expresses that
life is not solely an internal attribute, but an internal principle of
action.


                      § 1. EXTRINSIC CONDITIONS.


_Extrinsic Conditions._—By showing that every vital manifestation
results from the conflict of two factors: the extrinsic or
physico-chemical conditions which determine its appearance, and the
intrinsic or organic conditions which regulate its form, Claude
Bernard dealt a mortal blow at the old vitalist theories. For he has
not only asserted the close dependence of the two kinds of factors,
but he has shown them in action in most physiological phenomena. The
study of the extrinsic or physico-chemical conditions necessary to
vital manifestations teaches us our first truth—namely, that they
are not infinitely varied as might be supposed. They present, on the
contrary, a remarkable uniformity in their essential qualities. The
fundamental conditions are the same for the animal or vegetable cells
of every species. They are four in number:—_moisture_, the air, or
rather _oxygen_, _heat_, and a certain _chemical constitution_ of the
medium, and the last condition, the enunciation of which seems vague,
becomes more precise if we look at it a little closer. The chemical
constitution of media favourable to life, the media of culture, obeys
three general laws. It is the knowledge of these laws which formerly
enabled Pasteur, Raulin, Cohn, and Balbiani to provide the media
appropriate to the existence of certain relatively simple organisms,
and thus to create an infinitely valuable method for the study of
nutrition, etc.,—namely, the _method of artificial cultures_, numerous
developments of which have been shown us by microbiology and physiology.

_The Optimum Law._—It has been said, and it is more than a play on
words, that the conditions of the vital medium were the conditions
of the _juste milieu_. Water is wanted, there must not be too much or
too little. Oxygen is necessary, and also in certain proportions. Heat
is required, and for that, too, there is an optimum degree. Certain
chemical compounds are needed and, in this respect too, there must also
be _optima_ proportions.

Water is a constituent element of the organisms. They contain fixed
proportions for the same tissue, proportions varying from one tissue to
another (between 2∕3 and 9∕10). The cell of a living tissue requires
around it an aqueous atmosphere, formed by the different juices of the
organism, the interstitial liquids, the blood, and the lymph. We are
deceived by appearances when we distinguish between aerial, aquatic,
and land-dwelling animals, and when we speak of the air, the water,
and the land as their natural environment. If we go to the bottom
of things, and fix our attention on the real living unities, on the
cells of which the organism is composed, we shall find around them
the juices, rich in water, which are their real environment. If these
juices are diluted or concentrated the least in the world, life stops.
The cell, the whole animal, falls into a state of latent life, or
dies. “All living beings are aquatic,” said Claude Bernard. “Beings
that live in the air are in reality wandering aquariums,” said another
physiologist. “No moisture, no life,” wrote Preyer. The environment
must contain water, but it must contain it in certain proportions. In
the higher animals there is a mechanism which works automatically to
keep at a constant level the quantity of water in the blood. Researches
on the lavage of the blood (A. Dastre and Loye) have clearly shown
this.

Oxygen is also necessary to life. It is the _pabulum vitæ_. But the
discovery of the beings called by Pasteur _anaerobia_ appears to
contradict this statement. Pfeffer, the illustrious botanist, was
certain, in 1897, that the dogma of the necessity of oxygen no longer
held good. This is no longer tenable. In 1898 Beijerinck carried out
most careful researches on anaerobia said to have been cultivated in a
vacuum, such as the _bacteria of tetanus_ and the _septic vibrion_; or
on those to which oxygen seems to be a poison, such as the _butyric_
and the _butylic ferments_, the anaerobia of putrefaction, the reducing
spirilla of the sulphates. All use free oxygen. They consume very
little it is true; they are micro-aerobia. The other organisms, on
the contrary, need more. They are macro-aerobia or simply _aerobia_.
Besides, if the so-called anaerobia take little or no free oxygen, it
matters little. They take the oxygen in combination. It may be said
with L. Errera that they have an affinity for oxygen, for they extract
it from its combinations, and that “they are so well adapted to this
mode of existence that life in the open air being too easy no longer
suits them.” There are for the different animal species different
optima of oxygen.

Living beings require a certain amount of heat. Life, which could not
have existed on the globe when it was incandescent, will not be able to
exist when it is frozen. For each organism and each function there is a
maximum and a minimum of temperature compatible with activity. There is
also an optimum. For instance, the optimum is 29° C for the germination
of corn.

The condition of the optimum exists in the same way for the chemical
composition of the vital medium—and for the other ambient physical
conditions, such as atmospheric pressure.

It is therefore a law of _universal_ scope, a regulating law, as it
were, of life. Life is a function of extrinsic variables, water, air,
heat, the chemical composition of the medium, and pressure. “Every
vital phenomenon begins to be produced, starting from a certain
stage of the variable (minimum), becomes more and more vigorous as
it increases up to a determinate value (optimum), weakens if the
variable continues to increase, and disappears when it has reached
a certain limiting value (maximum).” This law, proved by Sachs, the
German botanist, in 1860, apropos of the action of temperature on the
germination of plants, by Paul Bert in 1875, apropos of the action of
oxygen and of atmospheric pressure on animals, and already formulated
at that time by Claude Bernard, was illustrated by Leo Errera in 1895.
It is a law of moderation. It expresses La Fontaine’s “_rien de trop_”
Terence’s “_ne quid nimis_,” the μηδὲν ἄγαν of Theognis, and the
biblical phrase “_omnia in mensura et numero et pondere_.” L. Errera
sees the profound cause of this optimum law in the properties of the
living protoplasm, which are mean properties. It is semi-liquid. It is
composed of albuminoid substances, which can stand no extremes either
from the physical or from the chemical points of view.


 § 2. INTRINSIC CONDITIONS. THE LAW OF THE CONSTITUTION OF ORGANS AND
                              APPARATUS.


_Law of the Constitution of Organs and Apparatus._—If we consider
more highly organized beings, the influence of the intrinsic
conditions appears quite as clearly. As we have seen, this is so that
the requisite fundamental materials may be spent by each element in
suitable proportions,—water, chemical compounds, air, and heat,—that
organs may be added to organs, and that apparatus may be set to work in
complex structures. Why a digestive apparatus? To prepare and introduce
into the internal medium liquid materials which are necessary to
life. Why a respiratory apparatus? To impart the vital gas necessary
to the cells, and to expel the gaseous excrement, the carbonic acid
which they reject. Why a circulatory apparatus? To transport and renew
this medium throughout. The apparatus, the functional wheels, the
vessels, the digestive and respiratory mechanisms do not exist for
themselves, like the random sketches of an artistic nature. They exist
for the innumerable anatomical elements which people the economy.
They are arranged to assist and more rigorously to regulate cellular
life with respect to the extrinsic conditions which it demands. They
are, in the living body, as in civilized society, the manufactories
and the workshops which provide for the different members of society
dress, warmth, and food. In a word, the _law of the construction of
organisms_ or of the _bringing to perfection of an organism_ is the
same as the law of cellular life. It is otherwise suggestive as the
law of _division of physiological labour_ formerly enunciated by Henry
Milne-Edwards; and in every case it has a more concrete significance.
Finally, it brings the organic functional activity into relation with
the conditions of the ambient medium.

_How Experiment acts on the Phenomena of Life._— The two orders of
conditions, the one provided by the being itself, the other by external
agents, are equally indispensable—and therefore of equal importance or
dignity. But they are not equally accessible to the experimentalist.
It is not easy to exercise on the organization direct and measurable
actions. On the contrary, the physical conditions are in the hands
and at the discretion of the experimenter. By them he may reach the
vital manifestations as they appear, stimulate or check them, defer
or precipitate them. Thus, for instance, the physiologist suspends
or re-establishes at his will full vital activity in a multitude of
reviviscent or hibernating beings, such as grains, the infusoria
capable of _encystment_, the vibrio, the tardigrade, the cold-blooded
animals, and perennial plants.

The ambient world therefore furnishes to the animal and to the
vegetable, whole or fragmentary, those materials of its organization
which are at the same time the stimuli of its vitality. That is to say,
the vital mechanism would be a dormant and inert mechanism if nothing
in the surrounding medium could provoke it to action or give it a
check. It would be a kind of steam engine without coal and fire.

Living matter, in other words, does not possess real spontaneity. As I
have shown elsewhere, the law of inertia which it is supposed it obeys
with inert bodies is not special to them. It is applied to the living
bodies whose apparent spontaneity is only an illusion contradicted by
physiology as a whole. All the vital manifestations are responses to a
stimulus of acts provoked, and not of spontaneous acts.

_Generalization of the Law of Inertia in Living Bodies.
Irritability._—In fact, vulgar prejudice opposes this view. The
opinion of the average man distrusts it. It applies the law of inertia
only to inert matter. This is because the vital response does not
always immediately succeed the external stimulus, and is not always
proportional to it. But it is sufficient to have seen the flywheel of a
steam engine to understand that the restitution of a mechanical force
cannot be instantaneous. It is sufficient to have had a finger on the
trigger of a firearm to know that there is no necessary proportion
between the intensity of the stimulus and the magnitude of the force
produced. Things happen in the living just as in the inert machine.

The faculty of entering into action when provoked by an external
stimulus has received, as we have said, the name of _irritability_.
The word is not used of inert matter. However, the condition of the
latter is the same. But there is no need to affirm its irritability,
because no one denies it. We know perfectly well that brute matter
is inert, that all the manifestations of activity of which it is the
theatre are provoked. Inertia is for it the equivalent of irritability
in living matter. But while it is not necessary to introduce this idea
into the physical sciences, where it has reigned since the days of
Galileo, it was, on the contrary, necessary to affirm it in biology,
precisely because it was in biology that the opposing doctrine of vital
spontaneity ruled supreme.

Such was the view held by Claude Bernard. He never varied on this
point. _Irritability_, said he, is the property possessed “by every
anatomical element (that is to say, the protoplasm which enters into
its constitution) of being stimulated into activity and of reacting
in a certain manner under the influence of the external stimuli.” He
could not claim that this was a distinguishing characteristic between
living bodies and brute bodies, and that all the less because he always
tried to efface on this point the distinctions which were current in
his time, and which were established by Bichat and Cuvier. And so also
Le Dantec does not seem to have thoroughly grasped the ideas of the
celebrated physiologist on this point when he asserts, as if he were
thereby contradicting the opinion of Claude Bernard and his school,
that irritability is not something peculiar to living bodies.[17]

 [17] These ideas are clearly brought to light in a series of articles
 in the _Revue Philosophique_, published in 1879 under the title of “La
 problème physiologique de la vie,” and endorsed by A. Dastre in his
 commentary on the _Phénomènes communs aux animaux et aux plantes_.




                              CHAPTER V.

          THE SPECIFIC FORM. ITS ACQUISITION. ITS REPARATION.

 § 1. Specific form not special to living beings—Connected with the
 whole of the material conditions of the body and the medium—Is it a
 property of chemical substance?—§ 2. Acquisition and re-establishment
 of the specific form—Normal regeneration—Accidental regeneration in
 the protozoa and the plastids—In the metazoa.


                        § 1. THE SPECIFIC FORM.


_The Specific Form is not Peculiar to Living Beings._—The position of
a _specific form_—the acquisition of this typical form progressively
realized—the re-establishment when some accident has altered it—these
are the features which we consider distinctive of living beings, from
the protophytes and the lowest protozoa to the highest animals. Nothing
gives a better idea of the unity and the individuality of the living
being than the existence of this typical form. We do not mean, however,
that this characteristic belongs to the living being alone, and is by
itself capable of defining it. We repeat that this is not a case with
any characteristic. In particular the _typical form_ belongs to crystal
as well as to living beings.

_The Specific Form depends on the sum of Material Conditions of the
Body and the Medium._—The consideration of mineral bodies shows us
form dependent on the physico-chemical conditions of the body and the
medium. The form depends mainly on physical conditions in the cases
of a drop of water falling from a tap, of the liquid meniscus in a
narrow tube, of a small navel-shaped mass of mercury on a marble slab,
of a drop of oil “emulsioned” in a solution, and of the metal which
is hardened by hammering or annealed. In the case of crystals the
form depends more on chemical conditions. It is crystallization which
has introduced into physics the idea that has now become a kind of
postulate—namely, that the specific form is connected with the chemical
composition. However, it is sufficient to instance the dimorphism
of a simple body, such as sulphur, sometimes prismatic, sometimes
octahedric, to realize that substance is only one of the factors of
form, and that the physical conditions of the body and of the medium
are other factors quite as influential.

_Is the Specific Form a Property of the Chemical Substance?_—How much
truer this restriction would be if we consider, instead of a given
chemical compound, an astonishingly complex mixture, such as protoplasm
or living matter, or the more complex organism still—the cell, the
plastid.

Are there not great differences between the substance of the cellular
protoplasm, or cytoplasmic substance, and that of the nucleus? Should
we not distinguish in the former the hyaloplasmic substance; the
microsomic in the microsomes; the linin between its granulations; the
centrosomic in the centrosome; the archoplasmic in the attraction
sphere; not to mention the different leucins, the vacuolar juice, and
the various inclusions? And in the nucleus must we not consider the
nuclear juice, the substance of the chromosomes, and that of the
nucleoles? And is not each of these probably a very complex mixture?

However, it is to this mixture that we attribute the possession
of a form, in virtue of and by extension of the principles of
crystallization, which definitely teach us that these mixtures cannot
have form; that form is the attribute of pure bodies, and is only
obtained by the separation of the blended parts—_i.e._, by a return
to homogeneity. There are therefore very good reasons for hesitating
before we transfer the absolute principle of the dependence between
chemical form and composition, as some philosophical biologists have
done, from the physical sciences—where it is already subject to serious
restrictions—to the biological sciences.

Le Dantec, however, has made this principle the basis of his biological
system. He therefore finds in the crystal the model of the living
being. He thus gives a physical basis to life.

Is it a question in this system of explaining this incomprehensible,
this unfathomable mystery, which shows the egg cell attracting to
itself materials from without and progressively building up that
amazing structure which is the body of the animal, the body of a
man, of any given man, of Primus, for example? It is said that the
substance of Primus is specific. His living substance is his own,
special to him; and that, too, from the beginning of the egg to the end
of its metamorphosis. It only remains to apply to this substance the
postulate, borrowed from crystallography, of the absolute dependence
of the nature of substance on the form it assumes. The form of the
body of the animal, of the man, of Primus, is the crystalline form of
their living substance. It is the only form of equilibrium that this
substance can assume under the given conditions, just as the cube is
the crystallized form of sea salt, the only state of equilibrium of
chloride of sodium in slowly evaporated sea water. Thus the problem
of the living form is reduced to the problem of the living substance,
which seems easier; and at the same time the biological mystery is
reduced to a physical mystery. It is clear that this way of looking
at things simplifies prodigiously—and, we must add, simplifies far
too much—the obscure problem of the relation of form to substance,
simultaneously in the two orders of science. This may be summed up in a
single sentence: There is an established relation between the specific
form and the chemical composition: the chemical composition _directs_
and implies the specific form.

We need not now examine the basis of this opinion. If it is nothing but
a verbal simplification, a unification of the language applied to the
two orders of phenomena, it implies an assimilation of the mechanisms
which realize them. To the organogenic forces which direct the
building up of the living organisms it brings into correspondence the
crystallogenic forces which group, adjust, equilibrate, and harmonize
the materials of the crystal.

When it is a question of the application of a principle such as
this, in order to test its legitimacy we must always return to the
experimental foundations. Let us imagine, for example, a simple body,
such as sulphur, heated and brought to a state of fusion—that is to
say, homogeneous, isotropic, in an undisturbed medium the only change
in which will be a very gradual cooling down. These are the typical
crystallogenic conditions. The body would take a given crystalline
form. It is from experiments such as this that we derive the idea of _a
specific form connected with a chemical constitution_.

But in drawing this conclusion our logic is at fault. The real
interpretation suitable to this case, as in all others, is that the
specific form is suitable to the substance, and also to the physical,
chemical, and mechanical conditions in which it is placed. And the
proof is that this same substance, sulphur, which takes the prismatic
form immediately after fusion, will not retain that form, but will pass
on to the quite different octahedral form.

It is so with the specific form of the living being—that is to say,
with the assemblage of its constituent materials co-ordinated in a
given system—in a word, with its organization. This is suitable to its
substance, and to all the material, physical, chemical, and mechanical
conditions in which it is placed. This form is the condition of
material equilibrium corresponding to a very complex situation, to a
sum of given conditions. The chemical condition is only one of these.
And further, it is hardly proper to speak of a “chemical substance”
when we refer to an astonishingly complex mixture which is in addition
variable from one point to the other of the living body. When we thus
reduce phenomena to their original signification, false analogies
disappear. To say with Le Dantec that the form of the greyhound is
the condition of equilibrium of the “greyhound chemical substance” is
saying much; and too much, if it means that the body of the greyhound
has a substance which behaves in the same way as homogeneous, isotropic
masses like melted sulphur and dissolved salt. It were better to say
much less, if it means, as it will in the minds of the physiologists,
that the body of the greyhound is the condition of equilibrium of a
heterogeneous, anisotropic, material system, subjected to an infinite
number of physical and chemical conditions.

The idea of connecting form, and by that we mean organization, with
chemical composition did not arise in the minds of chemists or
physiologists. Both have expressed themselves very clearly on this
point.

“We must distinguish,” said Berthelot, “between the formation of the
chemical substances, the assemblage of which constitutes organized
beings, and the formation of the organs themselves. This last problem
does not come into the domain of chemistry. No chemist will ever
claim to have formed in his laboratory a leaf, a fruit, a muscle, or
an organ.... But chemistry has a right to claim that it forms direct
principles—that is to say, the chemical materials which constitute the
organs.” And Claude Bernard in the same way writes:—“In a word, the
chemist in his laboratory, and the living organism in its apparatus,
work in the same way, but each with its own tools. The chemist can make
the products of the living being, but he will never make the tools,
because they are the result of organic morphology.”


    § 2. THE ACQUISITION AND RE-ESTABLISHMENT OF THE SPECIFIC FORM.


_Acquisition of the Typical Form._—The acquisition of the typical
form in the living being is the result of ontogenic work which cannot
be examined here. In the elementary being, the plastid, this work is
blended with the work of nutrition. It is _directed nutrition_. It
consists of a simple increase from the moment the element is born by
the division of an anterior element, and of a necessarily restricted
differentiation. It is a rudimentary embryogeny. In the complex being,
metazoan or metaphyte, the organism is constituted, starting from the
egg, by the growth, by the bipartition of the elements, and their
differentiation, accomplished in a certain direction and in conformity
with a given plan. This, again, is directed nutrition, but here the
embryogeny is complex. The directing plan of operations is no doubt
the consequence of the material conditions realized each moment in the
organism.

_Normal Regeneration._—Not only do living beings themselves
construct their typical architecture, but they re-establish it
and continually reconstitute it, according as accidents, or even
ordinary circumstances, tend to destroy it; in a word, they become
rejuvenescent. This regeneration consists in the reformation of the
parts that are altered or carried away in the normal play of life, or
by the accidents which disturb its course.

Thus there is a _normal physiological regeneration_, which is, so to
speak, the prolongation of the ontogenesis—_i.e._, of the work of
formation of the individual. We have examples in the reconstitution
of the skin of mammals—in the throwing off of the epidermic products
constantly used up in their superficial and distal parts and
regenerated in their deeply-seated parts; in the loss and the renewal
of teeth at the first dentition and in certain fish in the fact of
successive dentitions; in the periodical renewal of the integument
in the larvæ of insects, and in the crustaceæ; and finally in the
destruction and the neo-formation of the globules of the blood of
vertebrates, of the glandular cells, and of the epithelial cells of the
intestine.

_Accidental Regeneration in Protozoa and Plastids._—There is also an
_accidental regeneration_ which more or less perfectly renews the parts
that are lost. This regeneration has its degrees, from the simple
cicatrization of a wound to the complete reproduction of the part cut
off. It is very unequally developed in zoological groups even when they
are connected. In the elementary monocellular beings—_i.e._, in the
anatomical elements and in the protozoa,—the experiments in merotomy,
_i.e._, in _partial section_, enable us to appreciate the extent of
this faculty of regeneration. These experiments, inaugurated by the
researches of Augustus Waller in 1851, were repeated by Gruber in 1885,
continued by Nussbaum in 1886, Balbiani in 1889, Verworn in 1891, and
have been reproduced by a large number of observers. They have shown
that the two fragments cicatrize, and are repaired, building up an
organism externally similar to the primitive organism, but smaller.
The two new organic units do not, however, behave in the same way.
That which retains the nucleus possesses the faculty of regeneration,
and of living as the primitive being lived. The protoplasmic fragment,
which does not contain the nucleus, cannot rebuild this absent organ;
and though it has functional activity in most respects, just as the
nucleated fragment, yet it is distinguished from it in others of great
importance. The anucleated fragment of an infusorian behaves as the
nucleated, and as the whole animal so far as the movements of the body,
the cilia, prehension of food, evacuation of fæces, and the rhythmical
contraction of the pulsatile vesicules are concerned. But Balbiani’s
researches in 1892 have shown us that secretion, complete regeneration,
and the faculty of reproduction by fission can take place only in the
nucleated fragment—_i.e._, in the nucleus.

_Accidental Reproduction in the Metazoa._—Among multicellular beings
the faculty of reproduction is met with in the highest degree in
plants, where we find it in the process of propagation by slips. In
animals it is the most marked in Cœlenterata. Trembley’s experiments
are a striking instance. We know that when the hydra is cut into
tiny pieces it reproduces exactly as many complete beings. Among the
worms, Planaria afford a similar example. Every fragment, provided its
volume is not less than a tenth of that of the whole, can reproduce
a complete, entire being. The snail can produce a large part of its
head, including the tentacles and the mouth. Among the Tritons and
the Salamanders the faculty of regeneration reproduces the limbs, the
tail, and the eye. In the Frog family, on the contrary, the work of
regeneration does not go beyond cicatrization, and it is the same with
Birds and Insects.

It is really startling to see in a vertebrate like the Triton the stump
of an arm with its fragment of humerus reproducing the forearm and
the hand in all their complexity, with their skeleton, blood vessels,
nerves, and teguments. We say that the limb has _budded_, as if there
were a germ of it which develops like the seed of a plant, or as if
each transverse portion of the limb, each slice, so to speak, could
re-form the slice that follows.

The mechanism of generation and that of regeneration alike raise
problems of the highest importance. Does the part become regenerated
just as it was formed at first? Does the regeneration repeat the
ontogeny? Is it true that a lost organ is never regenerated (the
kidney for instance)? Does the symmetrical organ enjoy a compensating
and hypertrophic development, as Ribbert has asserted? And further,
if the organ be removed and transplanted to another position, can it
be grafted there, as Y. Delage maintains? These are very important
questions; but if we dwell upon them, we shall be diverted from our
immediate object. Our task is to look at these facts from the point
of view of their significant and characteristic meaning in vitality.
Flourens invoked on their behalf the intervention of vital forces,
_plastic_ and _morphoplastic_. But, as we shall see later, these
phenomena of cicatrization, of reparation, of regeneration, these more
or less complete efforts for the re-establishment of the specific form,
although they are found in all living beings in different degrees,
are not exclusively confined to them. We find them again in some
representatives of the mineral world—in crystals, for instance.




                              CHAPTER VI.

                              NUTRITION.

 FUNCTIONAL ASSIMILATION. FUNCTIONAL DESTRUCTION. ORGANIC DESTRUCTION.
 ASSIMILATING SYNTHESIS.

 The extreme importance of nutrition—§ 1. Effect of vital
 activity—Destruction or growth—Distinction between the living
 substance and the reserve-stuff mingled with it—Organic
 destruction—Destruction of reserve-stuff—Destruction of living
 matter—Growth of living matter—§ 2. The two categories of vital
 phenomena—Foundations of the idea of functional destruction—The two
 kinds of phenomena of vitality—Criticism of Claude Bernard—Current
 views—Criticism of Le Dantec’s new theory of life.—§ 3. Correlation of
 the two kinds of vital facts—Law of connection—Contradictions in the
 new theory.—§ 4. The characteristics of nutrition—Its definition—Its
 permanence—Erroneous idea of the vital vortex—Formative assimilation
 of reserve-stuff—Formative assimilation of protoplasm—Death, real and
 apparent.


_The Immense Importance of Nutrition._—We now come to the important
feature of vitality. All other characteristics of living matter, its
unstable equilibrium, its chemical and anatomical organization, the
acquisition and the maintenance of a typical form, are only secondary
properties, so to speak, subordinate with reference to _nutrition_.
Generation itself is only a mode. _Nutrition_ is the essential
attribute of life. It is life itself.

Before we define it a few preliminary explanations are necessary.

The most striking thing in living matter is its _growth_. An animal, a
vegetable, is something which is first more or less minute, and which
grows. Its characteristic is to expand—from the spore, the seed, the
slip, the egg—it grows.

Whether we are dealing with a cellular element, a plastid, or a complex
being, their condition is the same in this respect. No doubt when the
animal or plant has reached a certain stage of development its growth
is stopped, and for a more or less lengthy period it remains in the
adult stage, in what seems to be equilibrium. But even then there is no
check in the manufacture of living matter; there is only a compensation
between its production and its destruction.

It is important to reduce to order the ideas on this important subject,
which at present are confused, inconsistent, and contradictory. In
biology grievous confusion reigns.


       § 1. EFFECT OF THE VITAL ACTIVITY. DESTRUCTION OR GROWTH?


_Distinction between the Living Substance and the Reserve-stuff mingled
with it._—The physiology of nutrition has given rise to a vast body
of research during the last half-century. Physiological schools,
masters and pupils, such as the school at Munich under Voit and
Pettenkofer, Pflüger’s at Bonn, Rubner’s, and those of Zuntz and von
Noorden at Berlin, and a large number of zootechnical and agricultural
laboratories through the whole world have for years past been engaged
in analyzing ingesta and egesta, in drawing up schedules of nutrition,
in order to determine the course of decomposition and reconstitution of
the living material.

If I were asked what, in my opinion, is the most general result of
all this labour, I would reply that it has affirmed and corroborated
the important distinction which must be drawn between _living
substance, properly so called_, and _reserve-stuff_. The latter,
the _reserve-stuff_ of albuminoids, carbohydrates, and fats, are so
intimately intermingled with the living substance that they are in most
cases very difficult to distinguish from it.

_Organic Destruction._—A second point, which is placed equally
beyond doubt, is that the vital functional activity is accompanied
by a destruction of the immediate principles of the organism, in the
direction of their simplification. This functional destruction cannot
be doubted in the case of differentiated organs in which the functional
activity is evident, intermittent, and in some measure distinct from
the other vital phenomena which take place in them. For example, in the
case of contracting muscles the respiratory carbonic acid and urinary
carbon are the irrefutable proofs of this destruction: weak in repose,
abundant during activity, and in proportion to it. There can be no
doubt on this point. The truth laid down by Claude Bernard under the
name of the _law of functional destruction_ has been doubly consecrated
by experiment and theory. According to the energetic theory, in fact,
mechanical and thermal energies manifested in the vital functional
activity can only have their source in the chemical energy set free by
the destruction of the immediate principles of the organism, reduced
to a lower degree of complexity.

_Destruction of Reserve-stuff._—But now the disagreement begins. What
are these decomposed, destroyed principles? Do they belong to the
cellular reserve-stuff or to the living matter properly so called?
There is no doubt that most of them belong to the reserve-stuff.
For example, this is especially true of glycogen, which is consumed
in muscular contraction just as coal is consumed in the furnace of
the locomotive; and glycogen is a reserve-stuff of muscle. These
reserve-stuffs destroyed in the functional activity can be built up
again only during repose.

But it is not yet certain whether the living matter itself, the
active protoplasm, the muscular protoplasm, takes part in this
destruction, whether it provides it with elements. Experiments have
proved contradictory. Experimenters have isolated the nitrogenous
wastes (urea) after muscular labour, and they have compared them with
the wastes of the period of repose. These nitrogenous wastes bear
witness to the destruction of albuminoid substances, and the latter are
the constituent principles of living matter. If—under conditions of
sufficient alimentation—the muscular functional activity involves more
nitrogenous waste, _i.e._, a greater destruction of albuminoids, it
might be supposed that the living material properly so called has been
used up and destroyed for its own purposes. (And here again there might
be a reserve-stuff of albuminoids, distinct from the living protoplasm
itself, and more or less incorporated with it.)

But experiment so far has not given decisive results. The latest
experimental researches, such as those of Igo Kaup, of Vienna, which
date from 1902, tell us as uncertain a tale as their predecessors.
The increase in the destruction of albumen has not been constant; the
conditions of the observations do not justify our making an assertion
either _pro_ or _con_.

_Destruction of Living Matter._—As no certain answer is supplied by
experiment, theory intervenes and gives two conflicting answers. The
majority of physiologists are inclined to believe in _the destruction
of the living substance as the result of its own functional activity_.
The functional activity would therefore destroy not only the
reserve-stuff, but also the protoplasmic material. This is the current
view. Only this opinion is strongly challenged by the positive teaching
of science. It is certain that this material, in the muscle, is but
little attacked, if it is attacked at all. We have seen above that the
physiologists, with Pflüger and Chauveau, are agreed on this point.
The vital functional activity in particular is destructive to the
reserve-stuffs. It does not destroy them much; it destroys the organic
material still less. Both would be repaired in functional repose.

_Growth of Living Matter._—The second assertion is diametrically
opposed to this. Not only, says Le Dantec, is the muscle not destroyed
in the functional activity, but it grows. Contrary to universal
opinion, the protoplasmic material increases by activity, and it is
destroyed in repose. There would thus be a general law—_the law of
functional assimilation_. “A cell of brewers’ yeast when introduced
into a sugared must makes this must ferment, and at the same time, so
far from destroying it, it increases it. Now, the fermentation of the
must is exactly the same as the functional activity of the yeast.” It
is, says the same author, a mistake to believe that the phenomena of
functional activity, of _vital activity_, only takes place at the price
of organic destruction. Here, then, are these two competing views.
They are not so very far apart as a matter of fact, since the question
at issue is one of deciding between a slight destruction and a slight
growth, but theoretically they are strongly opposed. Moreover, they are
arbitrary, and _experiment_ has not decided between them.


              § 2. THE TWO CATEGORIES OF VITAL PHENOMENA.


_Foundation of the Idea of Functional Destruction. Claude Bernard._—The
doctrine of functional destruction has been laid down with remarkable
power by Claude Bernard. But the terms in which he has expressed it
in a measure betray the thoughts of the great physiologist, or, at
any rate, overstep the immediate fact he had in view. “The phenomena
of destruction are very obvious. When movement is produced, when the
muscle contracts, when volition and sensibility are manifested, when
thought is exercised, when the gland secretes, then the substance
of the muscles, of the nerves, of the brain, of the glandular
tissue, becomes disorganized, destroyed, and consumed. So that every
manifestation of a phenomenon in the living being is necessarily
connected with an organic destruction.” To Claude Bernard organic
destruction is a truth. To Le Dantec it is an error. Which is right?
Clearly Claude Bernard. He bases his conviction on the analyses of
the materials excreted in the process of physiological work. The
excreta bear witness to a certain organic demolition. Generalizing
this teaching of experiment the illustrious biologist divined the
fundamental law of energetics before the idea of energetics had made
much way in France. Every act which expends energy, which produces heat
or motion, any manifestation whatever that may be looked upon as an
energetic transformation, necessarily expends energy, and that energy
is borrowed from the substance of the organism. These substances are
simplified, broken up, and destroyed. Now the functional activity of
the muscle produces heat and movement in warm-blooded as well as in
cold-blooded animals. The functional activity of the glands produces
heat, as has been shown by the celebrated experiments of C. Ludwig on
the salivary secretion, and as is also shown by the study of thermal
topography in the vertebrates. The functional activity of the nerves
and the brain produces a slight quantity of electricity and heat, as
most observers have agreed. The functional activity of the electrical
and of the photic apparatus also expends energy. Finally, the eye
which receives the photic impression destroys the purple matter of the
retina, and that purple matter, as we well know, is recuperated in
the dark during the repose of the organ. Everything that is expressed
objectively, everything that is a phenomenon in the living being—with
the exception of growth and formation, which are generally slow
phenomena, and of which we can only get an idea by the comparison
of successive states—all these energetic manifestations suppose a
destruction of organic matter, a chemical simplification, the source
of the energy manifested. And that is why material destruction does
not merely coincide with functional activity, but is its measure and
expression.

_The Two Kinds of Phenomena of Vitality._—Another point on which
Claude Bernard is right and his opponent is wrong is not less
fundamental. What are we to understand by functional phenomena?
This is the very point at issue. Now, in the mind of physiologists,
this expression has a perfectly definite meaning. It is not so with
Le Dantec. Physiologists who have studied animals rather high in
organization—in which the differentiation of phenomena enables us to
grasp the fundamental distinction—have readily recognized that the
phenomena of living beings are divided into two categories. There are
some which are intermittent, alternative, which take place, or grow
stronger at certain moments, but which cannot be continuous—they are
the _functional acts_; there are others in which this characteristic of
explosives, energetic expenditure and intermittence, do not appear—they
are, in general, the _nutritive acts_. The muscle which contracts shows
functional activity. It has an activity and a repose. During this
apparent repose we must not say that it is dead; it has a life, but
that life is obscure as far as the salient fact of functional movement
is concerned. The salivary gland which throws up waves of saliva when
the food is introduced and masticated in the mouth, or when the chord
of the tympanum is at work, is in a state of functional activity; this
is the salient phenomenon. But before, though nothing, absolutely
nothing, was flowing through the glandular canal, yet the gland was
not reduced to the condition of a dead organ: it was living a more
obscure, a less evident life. The microscopical researches of Kühne,
Lea, and Langley, now universally verified, show us that during this
time of apparent repose the cells were loading up their granulations
and getting ready the materials of secretion, as just now the muscle
at rest was accumulating glycogen and the reserve-stuff which are to
be expended and destroyed in contraction. Similarly, with regard to
the functional activity of the other glands, of the brain, etc. Claude
Bernard was, therefore, perfectly right, when he took as his model
the chemists who distinguished between exothermic and endothermic
reactions, and who classed the phenomena of life into two great
divisions: those of functional activity, and those of functional repose.

1st. _The phenomena of functional activity_ “are those which ‘leap to
the eyes,’ and by which we are inclined to characterize life. They are
conditioned by the effects of wear and tear, of chemical simplication,
and of the organic destruction which liberates energy.” And it must
be so, because these functional manifestations expend energy. These
phenomena, which are the most obvious, are also the least specific
phenomena of vitality. They form part of the general phenomenality.

2nd. The _phenomena_ which accompany _functional repose_ correspond to
the building up of the reserve-stuff destroyed in the preceding period,
to the organizing synthesis. The latter remains “internal, silent,
concealed in its phenomenal expression, noiselessly gathering together
the materials which will be expended. We do not see these phenomena
of organization directly. The histologist and the embryogenist alone,
following the development of the element or of the living being, sees
the changes and the phases which reveal this silent effort. Here is a
store of substance; there, the formation of an envelope or a nucleus;
there, a division or multiplication, a renewal.” This type of phenomena
is the only type which has no direct analogues: it is peculiar, special
to the living being: what is really vital is this evolutive synthesis.
Life is creation.

_Criticism of Claude Bernard._—All this is perfectly true. Thirty years
of the most intensive scientific development have run by since these
lines were written, and have not essentially changed the ideas therein
expressed. His work in its broad lines remains intact. Does that imply,
however, that everything is perfect in detail and expression, and that
there is no reason for making it more precise or for giving it fresh
form? No doubt this is not so. Although Claude Bernard contributed to
establish the essential distinction between the real living protoplasm
and the materials of reserve-stuff which it contains, he has not drawn
a sufficiently clear distinction between what belongs to each of the
categories. He has not specified, in relation to organic destruction,
what bearing it has on the organic materials of reserve-stuff.
Sometimes he uses the term “organic destruction,” which is correct, and
sometimes “vital destruction,” which is of doubtful import. Further, he
employs an obscure and paradoxical formula to characterize the obvious
but nevertheless not specific phenomena of organic destruction, and he
says: “life is death.”

_Current Views._—Nowadays, if I may express a personal opinion on
this important distinction between functional activity and functional
repose, I should say that after having distinguished between the
two categories of phenomena we must try to correlate them. We must
try to discover, for instance, what there is in common between the
muscle in repose and the muscle in contraction, and to perceive in the
_muscular tonus_ a kind of bridge thrown between these two conditions.
The functional activity would be uninterrupted, but it would have
its degrees of activity. The muscular tonus would be the permanent
condition of an activity which is capable only of being considerably
raised or lowered. Similarly for the glandular functional activity;
the periods of charge must be connected with the periods of discharge.
In a word, following the constant path of the human mind in scientific
knowledge, after having drawn the distinctions that are necessary to
our understanding of things, we must obliterate them. After having
dug our ditches we must fill them up again. After having analyzed we
must synthesize. The distinction between the phenomena of _functional
activity_ and the phenomena of _functional repose_ or _purely
vegetative_ and nutritive _activity_, though only valid in the case of
a provisional and approximate truth, none the less throws light on the
obscure regions of biology.

The succession of energy and repose, of sleep and awakening, is a
universal law, or at least a very general law, connected with the laws
of energetics. The heart, the lungs, the muscles, the glands, the brain
obey in the most obvious manner this obligation of rhythmical activity.
The reason is clear. It is because the functional activity involves
what is generally a sudden expenditure of energy, and this has to be
replaced by what is generally a slow process of reparation. Functional
activity is an explosive destruction of a chemical reserve which is
built up again more or less slowly.

_Criticism of Le Dantec’s “New Theory of Life.”_—Let us now examine the
antithesis of Claude Bernard’s views. There are evidently rudimentary
organisms in which the differentiation of the two categories of
phenomena is but little marked; in which, apart from the movement,
it is impossible to recognize intermittent, functional activities
clearly distinct from morphogenic activity. It is not in this domain
of the indistinct that we must seek the touchstone of physiological
distinctions. Clearly, we must not choose these elementary plastids
to test the doctrine of functional assimilation and functional
destruction. But is not this exactly what Le Dantec did when he began
his researches on brewers’ yeast? When we try to examine things,
we must choose the conditions under which they are differentiated,
and not those in which they are confused. And this is why, in the
significant words of Auguste Comte, “the more complex living beings
are, the better known they are to us.” The philosopher goes still
farther in this direction, and adds “directly it is a question of the
characteristics of animality we must start from the man, and see how
those characteristics are little by little degraded, rather than start
from the sponge and endeavour to discover how these characteristics are
developed. The animal life of the man assists us to understand the life
of the sponge, but the converse is not true.”

When, moreover, we consider a vegetable organism such as yeast, which
derives its energy, not from itself, not from the potential chemical
energy of its reserve-stuff, but directly from the medium—that is to
say, from the potential chemical energy of the compounds which form
its medium of culture,—we then find ourselves in the worst possible
situation for the recognition of organic destruction. Further, it is
doubly wrong to assert that in so ill-chosen a type the functional
phenomena do not result from an organic destruction—for at first there
are no very distinct functional phenomena here—and, in the second
place, there certainly is organic destruction. The phenomena of the
morphogenic vitality detected in the yeast are the exact concomitants,
or the results, of the destruction of an organic compound, which in
this case is sugar. The yeast destroys an immediate principle, and
this is the point of departure of its vital manifestations; only, it
has not, as a preliminary, clearly incorporated and assimilated this
principle. When, therefore, the functional phenomena are effaced and
disappear, we none the less find phenomena of destruction of organic
compounds which are in a measure, a preface to the phenomena of growth.
This is what happens in the case of brewers’ yeast: and here, again,
the two categories of facts exist. Once more, we find, in the first
place, the phenomena of destruction (destruction of sugar, reduced
by simplification to alcohol and carbonic acid)—phenomena which this
time no longer respond to obvious functional manifestations; and, in
the second place, the phenomena of chemical and organogenic synthesis,
corresponding to the growth of the yeast and the multiplication of its
protoplasm. The former are no longer detected, as we have just said, by
striking manifestations. However, it is not true that everything which
is visible and which may be isolated outside the activity of the yeast
is part of those phenomena. The boiling of the juice or the mash,
the heat given off by the copper, all this phenomenal apparatus is
but the consequence of the production of the carbonic acid and of its
liberations—_i.e._, the consequence of the act of destruction of the
sugar. Here is organic destruction with its energetic manifestations!

This example of the life of brewers’ yeast, of the saccharomyces,
specially chosen by Le Dantec as being absolutely clear and giving the
best illustration of his argument, contradicts him at every point. The
general thesis of this vigorous thinker is that we cannot distinguish
between the two parts of the vital act, organic destruction, and
assimilating synthesis; that these two acts are not successive; that
they give rise to phenomenal manifestations equally evident, apparent,
or striking. Now, in the case of yeast, the phenomenon of destruction
is clearly distinct from that of the assimilating synthesis which
multiplies the substance of the saccharomyces. In fact, the action is
realized by means of an alcoholic diastase manufactured by the cell;
and Büchner succeeded in isolating this alcoholic ferment which splits
up the sugar into alcohol and carbonic acid, and also _in vitro_ and
_in vivo_, makes the vat boil and heats the liquid. All the yeast is at
work at once, says M. Dantec. No, and this is the proof.

And, further, Pasteur himself, who had shown the relation of the
decomposition of the sugar to the fact of the growth of the yeast and
of the production of accessory substances such as succinic acid and
glycerine, always referred to _correlation_ between these phenomena.
The destruction of the sugar is the _correlative_ of the life of the
yeast. This was his favourite formula. It never entered his head
that there could be a confusion instead of a correlation, and that
there might be only one and the same act, the phases of which would
be indistinguishable. This unfortunate idea, which was fated to be so
rapidly contradicted, is due to Le Dantec. Far from it being the case,
Pasteur had distinguished the _ferment function_ from the life of the
yeast. According to him, the yeast may exist sometimes as a ferment and
sometimes otherwise.


            § 3. CORRELATION OF TWO ORDERS OF VITAL FACTS.


It is this correlation between acts _distinct in themselves_ but
_usually connected_ that was announced by Claude Bernard. And,
_mirabile dictu_—and this is the natural outcome of the perfect sanity
of mind of this great physiologist—it happens that not only Pasteur’s
researches, but the development of a new science, Energetics, and
Büchner’s discovery lend support to his views, and that, too, in a
field where one would have thought they had no application. Le Dantec
is wrong when he declares that these ideas only apply to vertebrates.
“It is clear,” he says on several occasions, “that the author has
in view the metazoa and even the vertebrates.” Well! no. All that
is general, universally applicable, and universally true. So that
there are two orders of distinct phenomena energetically opposed and
certainly connected. We need only repeat Claude Bernard’s own words
quoted by Le Dantec in order to confute them.

_Law of Connection of Two Orders of Vital Facts._—“These phenomena [of
organic destruction and of assimilating synthesis] are simultaneously
produced in every living being, in a connection which cannot be broken.
The disorganization or dissimilation uses up living matter [by this
we must understand the reserve-stuff, as will be seen later on in the
quotation] in the organs _in function_: the assimilating synthesis
regenerates the tissues; it gathers together the reserve-stuff which
the vital activity must expend. These two operations of destruction
and renovation, inverse the one to the other, are absolutely connected
and inseparable, in this sense at any rate, that destruction is
the necessary condition of renovation. The phenomena of functional
destruction are themselves the precursors and the instigators of
material regeneration, of the formative process which is silently going
on in the intimacy of the tissues. The losses are repaired as they take
place; and equilibrium being re-established as soon as it tends to be
broken, the body is maintained in its composition.”

It is perfectly right and wise to say with Claude Bernard that the two
orders of facts are successive, and that one is normally the inciting
condition of the other. The possibility of the development of the yeast
when fermentation fails, and the weakness of this development on the
other hand under these conditions, are an excellent proof of this. The
one proves the essential independence of the two orders of facts, the
other the inciting and provoking virtue of the first relatively to the
second. The experimental truth is thus expressed with a minimum of
uncertainty. We know the facts which led Le Dantec to formulate his
law of functional assimilation—namely, that the functional activity is
useful or indispensable to the growth of the organ; that the organs
which are functionally active grow, and those which do not act
become atrophied. We are only expressing the facts when we say that
the organic destructions that go on in the living being (whether at
the expense of its reserve-stuff or at the expense of its medium, or
whether it be even slightly at the expense of the plastic substance
itself) are the antecedent, the inciting agent or the normal condition
of the chemical and organogenic syntheses which create the new
protoplasm.

On the other hand, we are wrong if we hold with Le Dantec that
instead of two chemical operations there is only one, that which
creates the new protoplasm. The obvious destruction is neglected; it
is deliberately passed over. He does not see that it is necessary to
liberate the energy employed in the construction, by complication, of
this highly complex substance which is the new protoplasm. He really
seems to have made up his mind not to analyze the phenomenon. If we
decline to admit that to the first act of functional destruction
succeeds a second, assimilation or organogenic synthesis, we are
looking at elementary beings, in which the succession cannot be
grasped, as we look on brewers’ yeast. We not only mean that the
morphogenic assimilation results from the functional activity; we
mean that it results from it directly, immediately, that it is the
functional activity itself. Experiment tells us nothing of all this.
It shows us the real facts, the facts of the destruction of an organic
immediate principle, the sugar, and the fact that an assimilating
synthesis is the correlative of this destruction. Besides, if it is
impossible in examples of this kind to exhibit the succession, it is
perfectly easy in beings of a higher order. It is, then, clearly seen
that the preliminary destruction of a reserve-stuff (and perhaps of
a small quantity of the living substance) precedes and conditions the
formation of a greater quantity of this living matter—in other words,
the growth of the protoplasm of the organ.

_Contradictions in the New Theory._—Moreover, these mistakes involve
those who make them in a series of inextricable contradictions. Here,
for example, is life; it is found, they say, in three forms:—Life
manifested, or condition 1º; latent life, or condition 3º. So far
this is the classical theory; but they add a condition 2º, which
is what might be called _pathological or incomplete life_. This
is defined by the following characteristic:—That its functional
phenomena are identical with those in the first form, but that they
are not accompanied by assimilation and by protoplasmic growth, But
since, they say, growth is the chemical consequence of the functional
activity, since it is so to speak its metabolic aspect, since it is
confused with it, and inseparable from it, by the argument—then it is
contradictory and logically absurd to speak of condition 2º. It would
be acknowledging in the case of the anucleated merozoite, for example,
a functional activity unaccompanied by assimilation, yet identical
with the functional activity which is accompanied by assimilation in
the nucleated merozoite. The general movement, that of the cilia, the
taking of food, the evacuation of the fæces, the contraction of the
pulsatile vacuoles, are the same. And this fact is the best proof that
this vital functional activity (with the organic destruction which is
its energetic source) must be distinguished from the assimilation which
usually follows it, and which in exceptional cases may not follow it.

We shall carry this discussion no farther. We have examined at some
length Le Dantec’s views, and we have contrasted them with the doctrine
which has been current in general physiology since the time of
Claude Bernard, and this comparison does not turn out quite to their
advantage. It was inevitable that the experimental and realistic spirit
which inspired the doctrine of the celebrated physiologist made his
work really too systematic. His formula, “life is death,” and the form
he gave his ideas, are not always irreproachably correct. They lend
themselves at times to criticism. Sometimes they require commentary.
These are errors of detail which Le Dantec has summarized somewhat
roughly. There is no necessity to do this in his own case. We pay our
tribute to the clearness of his language, although we believe the
foundations of his system are false and ill-founded. Their rigour is
purely verbal. Their external qualities, their careful arrangement
are well adapted to the seduction of the systematic mind prepared
by mathematical teaching. This new theory of life is presented with
pedagogic talent of the highest order. We think we have shown that the
foundations are entirely fallacious, in particular the following:—Vital
condition No. 2º; the confusion between functional activity and
assimilating synthesis; the so-called absolute connection between
morphogeny and chemical composition; the fundamental distinction
between elementary life and individual life.


                  § 4. CHARACTERISTICS OF NUTRITION.


_Definition of Nutrition._—As we have just seen, the organism is the
scene of chemical reactions of two kinds, the one destructive and
simplifying, the other synthetic, constructive, or assimilating. This
totality of reactions constitutes nutrition. Hence the two phases
that it is convenient to consider in this function—_assimilation_ and
_disassimilation_. This twofold chemical movement or _metabolism_
corresponding to the two categories of vital phenomena, of destruction
(catabolism) and of synthesis (anabolism) is therefore the chemical
sign of vitality in all its forms. But it is clear that disassimilation
or organic destruction, which is destined to furnish energy to the
organism for its different operations, reappears in the plan of the
general phenomena of nature. It is not specifically vital in its
principle. Assimilation, on the other hand, is in this respect much
more characteristic.

To some physiologists nutrition is only assimilation. Of the two
aspects of metabolism they consider only one, the most typical,
_Ad-similare_, to assimilate, to restore the substance borrowed
from the ambient medium, the alimentary substances, _similar_ to
living matter, to make living matter of them, to increase active
protoplasm—this is indeed the most striking phenomenon of vitality.
To grow, to increase, to expand, to invade, is the law of living
matter. Assimilation, nutrition in its essentials, is, according to
the definition of Ch. Robin, “the production by the living being of a
substance identical with its own.” It is the act by which the living
matter, the protoplasm of a given being, is created.

_Permanence in Nutrition._—Nutrition presents one quite remarkable
character—permanence. It is a vital manifestation, a property if
we look at it in the cell, in the living substance, a function if
we consider it in the animal or in the plant as a whole, which is
never arrested. Its suspension involves _ipso facto_ the suspension
of life itself. It is, in the words of Claude Bernard, that property
of nutrition “which, as long as it exists in an element, compels us
to believe that this element is alive, and which, when it is absent,
compels us to believe that it is dead. It dominates all others by its
generality and its importance. In a word, it is the absolute test of
vitality.”

_Biological Energetics shows the Importance of Nutrition._—We have
indicated in advance the reason of its importance, showing that its two
phases, disassimilation and assimilation, are the energetic condition
of the two kinds of vital phenomena which we can distinguish.

Nutrition is a manufacture of protoplasm at the expense of the
materials of the cellular ambient medium, which are assimilated—_i.e._,
made chemically and physically similar to living matter and to the
reserves it stores up. This operation, which is peculiarly chemical,
is therefore indicated by the borrowing of materials from the external
world, a borrowing which is always going on, because the operation is
permanent, and, let me add, because of the continual rejection of the
waste products of this manufacture. Our formula is:—Nutrition is a
chemistry which persists.

_The Idea of the Vital Vortex is Erroneous._—Here the effect has hidden
the cause from the eyes of the biologists. They have been struck by
the incessant entry and exit, by the never-ceasing passage, by the
_cycle_ of matter through the living being without guessing its why
and wherefore; and they have taken as a picture of the living being a
vortex in which the essential form is maintained while the matter,
which is accessory, flows on without a check. This is Cuvier’s _vital
vortex_. But for what purpose is this circulating matter used? They
thought that it was employed entirely for the reconstitution of the
living substance, continually and inevitably destroyed by the vital
Minotaur.

_Destruction of Reserve-stuff_.—Here again there is a mistake. Really
living substance is but little destroyed, and consequently requires
very little renewal by the functional activity of the animal machine.
Its metabolism—destruction and renewal—is in every case infinitely less
than is supposed in the classical image of the vital vortex. It is
the merit of physiologists, and particularly of Pflüger and Chauveau,
to have worked for nearly forty years to establish this truth. They
have proved it, at least as far as the muscular tissue is concerned.
Protoplasm, properly so-called, is only destroyed as the organs of a
steam engine are destroyed—its tubes, its boiler, its furnace. And
it matters little. We know that such an engine uses much coal, and
we know very little of its machinery and its metallic frame. And so
it is with the cell, the living machine. A very small portion of the
food introduced will be assimilated in the living substance. By far
the greater part of it is destined to be worked up by the protoplasm
and placed in reserve under the form of glycogen, albumen, and fat,
etc.—_i.e._, compounds which are not the really living substance, the
hereditary protoplasm, but the products of its industry, just as they
are or may be the products of the industry of the chemist working in
his laboratory. They will be expended for the purpose of furnishing
the necessary energy to the vital functional activity, muscular
contraction, secretion, heat, etc., just as coal is expended to set
the steam engine going. The proof as far as the muscle is concerned
does not stand alone. There are other examples. In particular,
micrographic physiologists who have studied nervous phenomena say
that the anatomical elements of the brain last indefinitely, and that
they continue as they are, without renewal from birth to death. The
permanence of the consciousness, be it said in passing, is connected by
them with the permanence of the cerebral element (Marinesco).

Thus destruction is very restricted. There is only a very slight
disassimilation of the living matter, properly so-called, in the course
of the vital functional activity. We may even go farther than this
experimental fact. This is what Le Dantec has done when he claims that
there is even an assimilation, an increase of the protoplasm. Strictly
speaking, this is possible, but there is no certain proof of it; and
in any case we cannot agree with him when he affirms that the increase
is the _direct result_ of the functional activity and blends with
it in one single, unique operation. We must, on the contrary, agree
with Claude Bernard that it is only a _consequence_ of it, that it
is produced in consequence of the existence of a bond of correlation
between organic destruction and assimilating synthesis.

Why is there this bond? That is easily understood if we reflect that
the assimilating synthesis, an operation of endothermic, chemical
complexity, naturally requires an exothermic counterpart, the organic
destruction which will set free this necessary energy.

_Formative Assimilation of Reserve-stuff. Formative Assimilation of
Protoplasm._—It follows that there are in nutritive assimilation
itself two distinct acts. The one consisting of the manufacture
of reserve-stuff is the more obvious but the less specific; the
other, really essential, is assimilation properly so-called, the
reconstitution of the protoplasm. The former is indispensable to the
production of the most prominent acts of vitality—movement, secretion,
production of heat. If it is suspended, functional activity is
arrested. We get _apparent death_, or _latent life_. But if the real
assimilation is arrested, we have _real death_.

According to this there would be a fundamental distinction between real
and apparent death. The former would be characterized by an _arrest
of the protoplasmic assimilation_ which is externally indicated by
no sign. On the other hand, apparent death would be characterized
by _the arrest of the formation and destruction of reserve-stuff_.
It would be externally manifested by two signs:—The suppression of
material exchanges with the medium (respiration, alimentation) and the
suppression of the functional acts (production of movement, of heat, of
electricity, of glandular excretion).

Such would be the most expedient test for apparent or real death. The
question occurs in the case of grains of corn in Egyptian tombs, and
also of hibernating animals and reviviscent beings, and, in general, in
the case of what has been called the state of _latent life_. But from
the practical point of view it is extremely difficult to apply this
test and to decide if the phenomena which are arrested in the grain
at maturity, in Leeuwenhoek’s tardigrada,[18] and in the dried-up
Anguillulidæ[19] of Baker and Spallanzani, in the encysted colpoda[20]
that a drop of warm water will revive, in the animals exposed by E.
Yung and Pictet to a cold of more than a 100° C. below zero, are due
to the general arrest of the two forms of assimilation, or to the
arrest of the manufacture and utilization of reserve-stuff alone, or
finally, to the arrest of protoplasmic assimilation alone. The latter,
which is already very restricted in beings in a normal condition whose
growth is terminated, may fall to the lowest degree in the being which,
having no functional activity, is assimilating nothing. So that, to
cut the question short, the experimenter who measures the value of
the exchanges between the being and the medium has seldom to do more
than decide between little and nothing. Hence his perplexity. But if
experiment hesitates, theory affirms: it admits _a priori_ that the
movement of protoplasmic assimilation, an essential sign of vitality,
is neither checked nor renewed, but proceeds continuously.

 [18] Bear-animalcules, Sloth-animalcules. An order of Arachnida.—TR.

 [19] Minute thread worms, known as paste-eels and vinegar-eels.—TR.

 [20] Genus of Infusoria. Colpodea cucullus is found in infusions of
 hay.—TR.


_Is Nutrition, the Assimilating Synthesis, interrupted?_—Nevertheless,
there are many reasons for suspending all judgment as to this
interpretation. It is questioned by most biologists. According to A.
Gautier, the preserved grain of corn and the dried up rotifera are not
really alive; they are like clocks in working order, ready to tell the
time, but awaiting in absolute repose the first vibration which will
set them going. As for the grain, it is the air, heat, and moisture
which supply the first impulse. In other words, the organization
proper to the manifestation of life remains, but there is no life. The
so-called arrested life is not a life.

It must be said, however, that the majority of physiologists refuse
to accept this interpretation. They believe in an attenuation of the
nutritive synthesis and not in its complete destruction. They think
that this total suppression would be contrary to current ideas relative
to the perpetuity of the protoplasm and the limited duration of the
living element. The natural medium is variable, and even the mineral
cannot remain eternally fixed. Still less is perennity a property of
the living being. If ordinary life is for each individual of limited
duration, the arrested life must also be of limited duration. We cannot
believe that after an indefinitely prolonged sleep the grain of corn,
or the paste-eel, or the colpoda, emerging from their torpor can resume
their existence, like the Sleeping Beauty, at the point at which it
was interrupted, and thus pass with a bound, as it were, through the
centuries.

In fact the maintenance of the vitality of grains of corn from the
Egyptian tombs and their aptitude to germinate after thousands of
years are only fables or the result of imposture. Maspero, in a letter
addressed to M. E. Griffon on the 15th July 1901, has clearly summed up
the situation by saying that the grains of corn bought from the fellahs
almost always germinate, but that this is never the case with those
that the experimenter himself takes from the tombs.

To sum up, we must use the same language of nutrition and of life,
of their uninterrupted progress, of their continuity, of their
permanence, of their activity, and of their slackening. Living
matter is always growing, much or little, slowly or quickly, in its
reserve-stuff or in its protoplasm, for expenditure or accumulation.
This inevitability of growth defines it, characterizes it, and sums up
its activity. Development and the evolution of growth are consequences
or aspects of nutrition.




BOOK IV.

THE LIFE OF MATTER.

 Summary: Chap. I. Universal life—Opinions of philosophers and
 poets—Continuity between brute and living bodies—Origin of this
 principle.—Chap. II. Origin of brute matter in living matter.—Chap.
 III. Organization and chemical composition of brute and living
 bodies.—Chap. IV. Evolution and transformation of brute and living
 bodies.—Chap. V. Possession of a specific form—Living bodies and
 crystals—Cicatrization.—Chap. VI. Nutrition in the living body
 and in the crystal.—Chap. VII. Generation in brute and in living
 bodies—Spontaneous generation.


_Apparent Differences between Living and Brute Bodies. The Two
Kingdoms._—It seems at first impossible that there should be any
essential similarity between an inanimate object and a living being.
What resemblance can be discovered between a stone, a lion, and an
oak? A comparison of the inert and immovable pebble with the leaping
animal, and with the plant extending its foliage gives an impression
of vivid contrast. Between the organic and the inorganic worlds there
seems to be an abyss. The first impressions we receive confirm this
view; superficial investigation furnishes arguments for it. There is
thus aroused in the mind of the child, and later in that of the man, a
sharply marked distinction between the natural objects of the mineral
kingdom on the one hand, and those of the two kingdoms of living beings
on the other.

But a more intimate knowledge daily tends to throw doubt upon the
rigour or the absolute character of such a distinction. It shows that
brute matter can no longer be placed on one side and living beings on
the other. Scientists deliberately speak of “the life of matter,” which
seems to the average man a contradiction in terms. They discover in
certain classes of mineral bodies almost all the attributes of life.
They find in others fainter, but still recognizable indications of an
undeniable relationship.

We propose to pass in review these analogies and resemblances, as has
already been done in a fairly complete manner by Leo Errera, C. E.
Guillaume, L. Bourdeau, Ed. Griffon, and others. We will consider the
fine researches of Rauber, of Ostwald, and of Tammann upon crystals
and crystalline germs—researches which are merely a continuation of
those of Pasteur and of Gernez. These show that crystalline bodies
are endowed with the principal attributes of living beings—_i.e._,
a rigorously defined form; an aptitude for acquiring it, and for
re-establishing it by repairing any mutilations that may be inflicted
upon it; nutritive growth at the expense of the mother liquor which
constitutes its culture medium; and, finally—a still more incredible
property—all the characteristics of reproduction by generation. Other
curious facts observed by skilful physicists—W. Roberts-Austen, W.
Spring, Stead, Osmond, Guillemin, Charpy, C. E. Guillaume—show that
the immutability even of bodies supposed to be the most rigid of all,
such as glass, the metals, steel, and brass, is apparent rather than
real. Beneath the surface of the metal that seems to us inert there
is a swarming population of molecules, displacing each other, moving
about, and arranging themselves so as to form definite figures, and
assuming forms adapted to the conditions of the environment. Sometimes
it is years before they arrive at the state of ultimate and final
equilibrium—which is that of eternal rest.

However, in order to understand these facts and their interpretations,
it is necessary to pass in review the fundamental characteristics of
living beings. It will be shown that these very characteristics are
found in inanimate matter.




                              CHAPTER I.

          UNIVERSAL LIFE. OPINIONS OF PHILOSOPHERS AND POETS.

 § 1. Primitive beliefs; the ideas of poets.—§ 2. Opinions of
 philosophers—Transition from brute to living bodies—The principle of
 continuity: continuity by transition: continuity by summation—Ideas of
 philosophers as to sensibility and consciousness in brute bodies—The
 general principle of homogeneity—The principle of continuity as a
 consequence of the principle of homogeneity.


              § 1. PRIMITIVE BELIEFS. IDEAS OF THE POETS.


The teaching of science as to the analogies between brute bodies and
living bodies accords with the conceptions of the philosophers and
the fancies of the poets. The ancients held that all bodies in nature
were the constituent parts of a universal organism, the macrocosm,
which they compared to the human microcosm. They attributed to it a
principle of action, the _psyche_, analogous to the vital principle,
and this psyche directed phenomena; and also an intelligent principle,
the _nous_, analogous to the soul, and the _nous_ served for the
comprehension of phenomena. This universal life and this universal soul
played an important part in their metaphysical systems.

It was the same with the poets. Their tendency has always been to
attribute life to Nature, so as to bring her into harmony with our
thoughts and feelings. They seek to discover the life or soul hidden in
the background of things.

    “Hark to the voices. Nothing is silent.

    Winds, waves, and flames, trees, reeds, and rocks
    All live; all are instinct with soul.”

After making proper allowance for emotional exaggeration, ought we
to consider these ideas as the prophetic divination of a truth which
science is only just beginning to dimly perceive? By no means. As
Renan has said, this universal animism, instead of being a product
of refined reflection, is merely a legacy from the most primitive of
mental processes, a residue of conceptions belonging to the childhood
of humanity. It recalls the time when men conceived of external things
only in terms of themselves; when they pictured each object of nature
as a living being. Thus, they personified the sky, the earth, the sea,
the mountains, the rivers, the fountains, and the fields. They likened
to animate voices the murmur of the forest:—

    “ ... The oak chides and the birch
    Is whispering....
    And the beech murmurs....
    The willow’s shiver, soft and faint, sounds like a word.
    The pine-tree utters mysterious moans.”

For primitive man, as for the poet of all times, everything is alive,
and every sound is due to a being with feelings similar to our own.
The sighing of the breeze, the moan of the wave upon the shore, the
babbling of the brook, the roaring of the sea, and the pealing of the
thunder are nothing less than sad, joyous, or angry living voices.

These impressions were embodied in ancient mythology, the graceful
beauty of which does not conceal its inadequacy. Then they passed
into philosophy and approached the realm of science. Thales believed
that all bodies in nature were animate and living. Origen considered
the stars as actual beings. Even Kepler himself attributed to the
celestial bodies an internal principle of action, which, it may be
said in passing, is contrary to the law of the inertia of matter,
which has been wrongly ascribed to him instead of to Galileo. The
terrestrial globe was, according to him, a huge animal, sensitive to
astral influences, frightened at the approach of the other planets, and
manifesting its terror by tempests, hurricanes, and earthquakes. The
wonderful flux and reflux of the ocean was its breathing. The earth had
its blood, its perspiration, its excretions; it also had its foods,
among which was the sea water which it absorbs by numerous channels.
It is only fair to add that at the end of his life Kepler retracted
these vague dreams, ascribing them to the influence of J. C. Scaliger.
He explained that by the soul of the celestial bodies he meant nothing
more than their motive force.


                   § 2. OPINION OF THE PHILOSOPHERS.


_Transition from Brute to Living Bodies._—The lowering of the barrier
between brute bodies and living bodies began with those philosophers
who introduced into the world the great principles of continuity and
evolution.

_The Principle of Continuity._—First and foremost we must mention
Leibniz. According to the teaching of that illustrious philosopher,
as interpreted by M. Fouillée, “there is no inorganic kingdom, only
a great organic kingdom, of which mineral, vegetable, and animal
forms are the various developments.... Continuity exists everywhere
throughout the world; everywhere is life and organization. Nothing is
dead; life is universal.” It follows that there is no interruption
or break in the succession of natural phenomena; that everything is
gradually developed; and finally, that the origin of the organic being
must be sought in the inorganic. Life, properly so called, has not,
in fact, always existed on the surface of the globe. It appeared at a
certain geological epoch, in a purely inorganic medium, by reason of
favourable conditions. The doctrine of continuity compels us, however,
to admit that it pre-existed on the globe under some rudimentary form.

The modern philosophers who are imbued with these principles, MM.
Fouillée, L. Bourdeau, and A. Sabatier, express themselves in similar
language. “Dead matter and living matter are not two absolutely
different entities, but represent two forms of the same matter,
differing only in degree, sometimes but slightly.” When it is only
a matter of degree, it cannot be held that these views are opposed.
Inequalities must not be interpreted as contrary attributes, as when
the untrained mind considers heat and cold as objective states,
qualitatively opposed to each other.

_Continuity by Transition._—The argument which leads us to remove the
barrier between the two kingdoms, and to consider minerals as endowed
with a sort of rudimentary life, is the same as that which compels
us to admit that there is no fundamental difference between natural
phenomena. There are transitions between what lives and what does not,
between the animate being and the brute body. And in the same way there
are transitions between what thinks and what does not think, between
what is thought and what is not thought, between the conscious and
the unconscious. This idea of insensible transition, of a continuous
path between apparent antitheses, at first arouses an insuperable
opposition in minds not prepared for it by a long comparison of facts.
It is slowly realized, and finally is accepted by those who, in the
world of things, follow the infinity of gradations presented by natural
phenomena. The principle of continuity comes at last to constitute,
as one may say, a mental habit. Thus the man of science may be led,
like the philosopher, to entertain the idea of a rudimentary form of
life animating matter. He may, like the philosopher, be guided by
this idea; he may attribute _a priori_ to brute matter all the really
essential qualities of living beings. But this must be on the condition
that, assuming these properties to be common, he must afterwards
demonstrate them by means of observation and experiment. He must show
that molecules and atoms, far from being inert and dead masses, are in
reality active elements, endowed with a kind of inferior life, which
is manifested by all the transformations observed in brute matter,
by attractions and repulsions, by movements in response to external
stimuli, by variations of state and of equilibrium; and finally, by the
systematic methods according to which these elements group themselves,
conforming to those definite types of structure by means of which they
produce different species of chemical compounds.

_Continuity by Summation._—The idea of summation leads by another path
to the same result. It is another form of the principle of continuity.
A sum total of effects, obscure and indistinct in themselves, produces
a phenomenon appreciable, perceptible, and distinct, apparently,
but not really, heterogeneous in its components. The manifestations
of atomic or molecular activity thus become manifestations of vital
activity.

This is another consequence of the teaching of Leibniz. For, according
to his philosophical theory, individual consciousness, like individual
life, is the collective expression of a multitude of elementary lives
or consciousnesses. These elements are inappreciable because of their
low degree, and the real phenomenon is found in the sum, or rather
the _integral_, of all these insensible effects. The elementary
consciousnesses are harmonized, unified, integrated into a result that
becomes manifest, just as “the sounds of the waves, not one of which
would be heard if by itself, yet, when united together and perceived at
the same instant, become the resounding voice of the ocean.”

_Ideas of the Philosophers as to Sensibility and Consciousness in
Brute Bodies._—The philosophers have gone still further in the way
of analogies, and have recognized in the play of the forces of brute
matter, particularly in the play of chemical forces, a mere rudiment
of the appetitions and tendencies that regulate, as they believe, the
functional activity of living beings—a trace, as it were, of their
sensibility. To them reactions of matter indicate the existence of a
kind of _hedonic consciousness_—_i.e._, a consciousness reduced simply
to a distinction between comfort and discomfort, a desire for good and
repulsion from evil, which they suppose to be the universal principle
of all activity. This was the view held by Empedocles in antiquity;
it was that of Diderot, of Cabanis, and, in general, of the modern
materialistic school, eager to find, even in the lowest representatives
of the inorganic world, the first traces of the vitality and
intellectual life which blossom out at the top of the scale in the
living world.

Similar ideas are clearly seen in the early history of all natural
sciences. It was this same principle of appetition, or of love and of
repulsion or hate that, under the names of affinity, selection, and
incompatibility, was thought to direct the transformations of bodies
when chemistry first began; when Boerhaave, for example, compared
chemical combinations to voluntary and conscious alliances, in which
the respective elements, drawn together by sympathy, contracted
appropriate marriages.

_General Principle of the Homogeneity of the Complex and its
Components._—The assimilation of brute bodies to living bodies, and
of the inorganic kingdom to the organic, was, in the mind of these
philosophers, the natural consequence of positing _a priori_ the
principles of continuity and evolution. There is, however, a principle
underlying these principles. This principle is not expressed explicitly
by the philosophers; it is not formulated in precise terms, but is more
or less unconsciously implied; it is everywhere applied. It, however,
may be clearly seen behind the apparatus of philosophical argument It
is the assertion that no arrangement or combination of elements can
put forth any new activity essentially different from the activities
of the elements of which it is composed. Man is living clay, say
Diderot and Cabanis; and, on the other hand, he is a thinking being.
_As it is impossible to produce that which thinks from that which
does not think_, the clay must possess a rudiment of thought. But is
there not another alternative? May not the new phenomenon, thought,
be the effect of the arrangement of this clay? If we exclude this
alternative, we must then consider arrangement and organization as
incapable of producing in arranged and organized matter a new property
different from that which it presented before such arrangement. Living
protoplasm, says another, is merely an assemblage of brute elements;
“these brute elements must therefore possess a rudiment of life.” This
is the same implied supposition which we have just considered; if life
is not the basis of each element, it cannot result from their simple
assemblage.

Man and animals are combinations of atoms, says M. le Dantec. It is
more natural to admit that human consciousness is the result of the
elementary consciousness of the constituent atoms than to consider
it as resulting from construction by means of elements with no
consciousness. “Life,” says Haeckel, “is universal; we could not
conceive of its existence in certain aggregates of matter if it did not
belong to their constituent elements.” Here the postulate is almost
expressed.

The argument is always the same; even the same words are used:
the fundamental hypothesis is the same; only it remains more or
less unexpressed, more or less unperceived. It may be stated as
follows:—Arrangement, assemblage, construction, and aggregation are
powerless to bring to light in the complex anything new and essentially
heterogeneous to what already exists in the elements. Reciprocally,
grouping reveals in a complex a property and character which is the
gradual development of an analogous property and character in the
elements. It is in this sense that there exists a collective soul in
crowds, the psychology of which has been discussed by M. G. Le Bon. In
the same way, many sociologists, adopting the views advanced by P. de
Lilienfeld in 1865, attribute to nations a formal individuality, after
the type of that possessed by each of their constituent members. M.
Izolet considers society as an organism, which he calls a “hyperzoan.”
Herbert Spencer has developed the comparison of the collective organism
with the individual organism, insisting on their resemblances and
differences. Th. Ribot has dwelt, in particular, on the resemblances.

The postulate that we have clearly stated here is accepted by many as
an axiom. But it is not an axiom. When we say that there is nothing
in the complex that cannot be found in the parts, we think we are
expressing a self-evident truth; but we are, in fact, merely stating
an hypothesis. It is assumed that arrangement, aggregation, and
complicated and skilful grouping of elements can produce nothing really
new in the order of phenomena. And this is an assertion that requires
verification in each particular case.

_The Principle of Continuity, a Consequence of the Preceding._—Let us
apply this principle to the beings in nature. All beings in nature are,
according to current ideas, arrangements, aggregates, or groupings of
the same universal matter, that is to say, of the same simple chemical
bodies. It results from the preceding postulate that their activities
can only differ in degree and form, and not fundamentally. There is
no essential difference of nature between the activities of various
categories of beings, no heterogeneity, no discontinuity. We may pass
from one to another without coming to an hiatus or impassable gulf.
The law of continuity thus appears as a simple consequence of the
fundamental postulate. And so it is with the law of evolution, for
evolution is merely continuity of action.

Such are the origins of the philosophical doctrine which universalizes
life and extends it to all bodies in nature.

It may be remarked that this doctrine is not confined to any particular
school or sect. Leibniz was by no means a materialist, and he endowed
his mundane elements, his _monads_, not only with a sort of life, but
even with a sort of soul. Father Boscovitch, Jesuit as he was, and
professor in the college of Rome, did not deny to his _indivisible
points_ a kind of inferior vitality. St. Thomas, too, the angelical
doctor, attributed, according to M. Gardair, to inanimate substances a
certain kind of activity, inborn inclinations, and a real appetition
towards certain acts.




CHAPTER II.

ORIGIN OF BRUTE MATTER IN LIVING MATTER.

 Spontaneous generation: an episode in the history of the
 globe—Verification of the identity between brute and living
 matter—Slow identification—Rapid identification—Contrary
 opinion—Hypothesis of cosmozoa; cosmic panspermia—Hypothesis of
 pyrozoa.


There should be two ways of testing the doctrine of the essential
identity of brute and living matter—one slow and more laborious, the
other more rapid and decisive.

_Identification of the Two Matters, Brute and Living._—The laborious
method, which we will be obliged to follow, consists in the attentive
examination of the various activities by which life is manifested, and
in finding more or less crude equivalents for them in all brute beings,
or in certain of them.

_Rapid Verification. Spontaneous Generation._—The rapid and decisive
method, which, unhappily, is beyond our resources, would consist in
showing unquestionable, clearly marked life, the superior life, arising
from the kind of inferior life that is attributed to matter in general.
It would be necessary completely to construct in all its parts, by a
suitable combination of inorganic materials, a single living being,
even the humblest plant or the most rudimentary animal. This would
indeed be an irrefutable proof that the germs of all vital activity are
contained in the molecular activity of brute bodies, and that there is
nothing essential to the latter that is not found in the former.

Unhappily this demonstration cannot be given. Science furnishes no
example of it, and we are forced to have recourse to the slow method.

The question here involved is that of spontaneous generation. It is
well known that the ancients believed in spontaneous generation,
even for animals high in the scale of organization. According to Van
Helmont, mice could be born by some incomprehensible fermentation in
dirty linen mixed with wheat. Diodorus speaks of animal forms which
were seen to emerge, partly developed, from the mud of the Nile.
Aristotle believed in the spontaneous birth of certain fishes. This
belief, though rejected as to the higher forms, was for a long time
held with regard to the lower forms of animals, and to insects—such as
the bees which the shepherd of Virgil saw coming out from the flanks
of the dead bullock—flies engendered in putrefying meat, fruit worms
and intestinal worms; finally, with regard to infusoria and the most
rudimentary vegetables. The hypothesis of the spontaneous generation of
the living being at the expense of the materials of the ambient medium
has been successively driven from one classificatory group to another.
The history of the sciences of observation is also a history of the
confutation of this theory. Pasteur gave it the finishing stroke, when
he showed that the simplest microorganisms obeyed the general law which
declares that the living being is formed only by _filiation_—that is
to say, by the intervention of a pre-existing living organism.

_Spontaneous Generation an Episode in the History of the Globe._—Though
we have been unable to effect spontaneous generation up to the present,
it has been referred by Haeckel to a more or less distant past, to
the time when the cooling of the globe, the solidification of its
crust, and the condensation of aqueous vapour upon its surface created
conditions compatible with the existence of living beings similar
to those with which we are acquainted. Lord Kelvin has fixed these
geological events as occurring from twenty to forty million years ago.
Then circumstances became propitious for the appearance of the first
organisms, whence were successively derived those which now people the
earth and the waters.

Circumstances favourable to the appearance of the first beings
apparently occurred only in a far distant past; but most physiologists
admit that if we knew exactly these circumstances, and could reproduce
them, we might also expect to produce their effect—namely, the creation
of a living being, formed in all its parts, developed from the
inorganic kingdom. To all those who held this view the impotence of
experiment at the present time is purely temporary. It is comparable to
that of primitive men before the time of Prometheus; they, not knowing
how to produce fire, could only get it by transmitting it from one to
another. It is due to the inadequacy of our knowledge and the weakness
of our means; it does not contradict the possibility of the fact.

_Contrary Opinion. Life did not Originate on our Globe._—But all
biologists do not share this opinion. Some, and not the least eminent,
hold it to be an established fact that it is impossible for life to
arise from a concurrence of inorganic materials and forces. This was
the opinion of Ferdinand Cohn, the great botanist; of H. Richter, the
Saxon physician, and of W. Preyer, a physiologist well known from his
remarkable researches in biological chemistry. According to these
scientists, life on the surface of the globe cannot have appeared as a
result of the reactions of brute matter and the forces that continue to
control it.

According to F. Cohn and PI. Richter, life had no beginning on our
planet. It was transported to the earth from another world, from the
cosmic medium, under the form of cosmic germs, or _cosmozoa_, more
or less comparable to the living cells with which we are acquainted.
They may have made the journey either enclosed in meteorites, or
floating in space in the form of cosmic dust. The theory in question
has been presented in two forms:—_The Hypothesis of Meteoric Cosmozoa_,
by a French writer, the Count de Salles-Guyon; and that of _cosmic
panspermia_ brought forward in 1865 and 1872 by F. Cohn and H. Richter.

_Hypothesis of the Cosmozoa._—The hypothesis of the cosmozoa, living
particles, protoplasmic germs emanating from other worlds and reaching
the earth by means of aerolites, is not so destitute of probability
as one might at first suppose. Lord Kelvin and Helmholtz gave it the
support of their high authority. Spectrum analysis shows in cometary
nebulæ the four or five lines characteristic of hydro-carbons. Cosmic
matter, therefore, contains compounds of carbon, substances that are
especially typical of organic chemistry. Besides, carbon and a sort
of humus have been found in several meteorites. To the objection
that these aerolites are heated while passing through our atmosphere,
Helmholtz replies that this elevation of temperature may be quite
superficial and may allow micro-organisms to subsist in their interior.
But other objections retain their force:—First, that of M. Verworn, who
considers the hypothesis of cosmic germs as inconsistent with the laws
of evolution; and that of L. Errera, who denies that the conditions
necessary for life exist in interplanetary bodies.

_Hypothesis of Cosmic Panspermia._—Du Bois-Reymond has given the name
of _cosmic panspermia_ to a theory very similar to the preceding,
formulated by F. Cohn in 1872. The first living germs arrived on our
globe mingled with the cosmic dust that floats in space and falls
slowly to the surface of the earth. L. Errera observes that if they
escape by this gentle fall the dangerous heating of meteorites, they
still remain exposed to the action of the photic rays, which is
generally destructive to germs.

_Hypothesis of Pyrozoa._—W. Preyer declined to accept this cosmic
transmigration of the simplest living beings, nor would he allow
the intervention of other worlds into the history of our own. Life,
according to him, must have existed from all time, even when the globe
was an incandescent mass. But it was not the same life as at present.
Vitality must have undergone many profound changes in the course of
ages. The _pyrozoa_, the first living beings, vulcanians, were very
different from the beings of the present day that are destroyed by
a slight elevation of temperature. No doubt this theory of pyrozoa,
proposed by W. Preyer in 1872, seems quite chimerical, and akin
to Kepler’s dreamy visions. But in a certain way it accords with
contemporary ideas concerning the life of _matter_. It is related
to them by the evolution which it implies in the materials of the
terrestrial globe.

According to Preyer, primitive life existed in fire. Being igneous
masses in fusion, the pyrozoa lived after their own manner; their
vitality, slowly modified, assumed the form which it presents to-day.
Yet, in this profound transformation their number has not varied, and
the total quantity of life in the universe has remained unchanged.

Here we recognize the ideas of Buffon. These cosmozoa, these pyrozoa,
have a singular resemblance to the _organic molecules_ of “live matter”
of the illustrious naturalist—distributed everywhere, indestructible,
and forming living structures by their concentration.

But we must leave these scientific or philosophical theories, and come
to arguments based upon facts.

It is in a spirit quite different from that of the poets, the
metaphysicians, and the more or less philosophical scientists that
the science of our days looks at the more or less obscure vitality of
inanimate bodies. It claims that we may recognize in them, in a more or
less rudimentary state, the action of the factors which intervene in
the case of living beings, the manifestation of the same fundamental
properties.




CHAPTER III.

ORGANIZATION AND CHEMICAL COMPOSITION OF LIVING AND BRUTE MATTER.

 Laws of the organization and of the chemical composition of living
 beings—Relative value of these laws; vital phenomena in crushed
 protoplasm—Vital phenomena in brute bodies.


_Enumeration of the Principal Characters of Living Beings._—The
programme which we have just sketched compels us to look in the brute
being for the properties of living beings. What, then, are, in fact,
the characteristics of an authentic, complete, living being? What are
its fundamental properties? We have enumerated them above as follows:—A
certain chemical composition, which is that of living matter; a
structure or organization; a specific form; an evolution which has a
duration, that of life, and an end, death; a property of growth or
nutrition; a property of reproduction. Which of these characters counts
for most in the definition of life? Are they all equally necessary? If
some of them were wanting, would that justify the transference of a
being, who might possess the rest, from the animate world to that of
minerals? This is precisely the question that is under consideration.

_Organization and Chemical Composition of Living Beings._—All that we
know concerning the constitution of living matter and its organization
is summed up in the laws of the _chemical unity_ and the _morphological
unity of living beings_ (v. Book III.). These laws seem to be a
legitimate generalization from all the facts observed. The first
states that the phenomena of life are manifested only in and through
living matter, protoplasm—_i.e._, in and through a substance which
has a certain chemical and physical composition. Chemically it is a
proteid complexus with a hexonic nucleus. Physically it shows a frothy
structure analogous to that resulting from the mixture of two granular,
immiscible liquids, of different viscosities. The second law states
that the phenomena of life can only be maintained in a protoplasm which
has the organization of the complete cell, with its cellular body and
nucleus.

_Relative Value of these Laws. Exceptions._—What is the signification
of these laws of the chemical composition and organization of living
beings? Evidently that life in all its plenitude can only exist and be
perpetuated under their protection. If these laws were absolute, if
it were true that no life were possible but in and through albuminous
protoplasm, but in and through the cell, the problem of “the life of
matter” would be decided in the negative.

May it not happen, however, that fragmentary and incomplete vital
manifestations, progressive traces of a true life, may occur under
different conditions; for example, in matter which is not protoplasm,
and in a body which has a structure differing from that of a cell—that
is to say, in a being which would be neither animal nor plant? We must
seek the answer to this question by an appeal to experiment.

Without leaving the animal and vegetable kingdoms—_i.e._, real living
beings—we already see less rigour in the laws governing chemical
constitution and cellular organization.

Experiments in merotomy—_i.e._, in amputation—carried out on the
nervous element by Waller, on infusoria by Brandt, Gruber, Balbiani,
Nussbaum, and Verworn, show us the necessity of the presence of the
cellular body and the nucleus—_i.e._, of the integrity of the cell. But
they also teach us that when that integrity no longer exists death does
not immediately follow. A part of the vital functions continues to be
performed in denucleated protoplasm, in a cell which is mutilated and
incomplete.

_Vital Phenomena in Crushed Protoplasm._—It is true also that grinding
and crushing suppress the greater part of the functions of the cell.
But tests with pulps of various organs and with those of certain
yeasts also show that protoplasm, even though ground and disorganized,
cannot be considered as inert, and that it still exhibits many of its
characteristic phenomena; for example, the production of diastases,
the specific agents of vital chemistry. Finally, while we do not
know enough about the actions of which the secondary elements of
protoplasm—its granulations, its filaments—are capable, which this or
that method of destruction may bring to light, at least we know that
actions of this kind exist.

To sum up, we are far from being able to deny that rudimentary,
isolated vital acts may be produced by the various bodies that result
from the dismemberment of protoplasm. The integrity of the cellular
organization, even the integrity of protoplasm itself, are therefore
not indispensable for these partial manifestations of vitality.

Besides, biologists admit that there exist within the protoplasm
aliquot parts, elements of an inferior order, which possess special
activities. These secondary elements must have the principle of their
activity within themselves. Such are the _biophors_ to which Weismann
attributes the vital functions of the cell, nutrition, growth, and
multiplication. If there are biophors within the cell, we may imagine
them outside the cell, and since they carry within themselves the
principle of their activity they may exercise it in an independent
manner. Unhappily the biophors, and other constituent elements of
that kind, are purely hypothetical. They are like Darwin’s gemmules,
Altmann’s bioblasts, and the pangens of De Vries. They have no relation
to facts of observation and to real existence.

_Vital Phenomena in Brute Bodies._—There is no doubt that certain
phenomena of vitality may occur outside of the cellular atmosphere.
And carrying this further, we may admit that they may be produced in
certain slightly organized bodies (crushed cells), and then in certain
unorganized bodies in certain brute beings. In every case it is certain
that effects are produced at any rate similar to those which are
characteristic of living matter. It is for observation and experiment
to decide as to the degree of similarity, and their verdict is that the
similarity is complete. The crystals and the crystalline germs studied
by Ostwald and Tammann are the seat of phenomena which are quite
comparable to those of vitality.




                              CHAPTER IV.

      EVOLUTION AND MUTABILITY OF LIVING MATTER AND BRUTE MATTER.

 Supposed immobility of brute bodies—Mobility and mutability of the
 sidereal world.—§ 1. The movement of particles and molecules in brute
 bodies—The internal movements of brute bodies—Kinetic conception of
 molecular motion—Reality of the motion of particles—Comparison of the
 activity of particles with vital activity.—§ 2. Brownian movement—Its
 existence—Its character—Its independence of the nature of the bodies
 and of the nature of the environment—Its indefinite duration—Its
 independence of external conditions—The Brownian movement must be the
 first stage of molecular motion.—§ 3. Motion of particles—Migration of
 material particles—Migration under the action of weight; of diffusion;
 of electrolysis; of mechanical pressure.—§ 4. Internal activity of
 alloys—Their structure—Changes produced by deforming agencies—Slow
 return to equilibrium—Residual effect—Effect of annealing; effect of
 stretching—Nickel steel—Colour photography—Conclusion—Relations of the
 environment to the living or brute matter.


One of the most remarkable characteristics of a living being is its
evolution. It undergoes a continuous change. It starts from something
very small; it assumes a configuration and grows; in most cases
it declines and disappears, having followed a course which may be
predicted—a sort of ideal trajectory.

_Supposed Immobility of Brute Bodies._—It may be asked whether this
evolution, this directed mobility, is so exclusively a feature of the
living being as it appears, and if many brute bodies do not present
something analogous to it. We may answer in no uncertain tones.

Bichat was wrong when he contrasted in this respect brute bodies with
living bodies. Vital properties, he said, are temporary; it is their
nature to be exhausted; in time they are used up in the same body.
Physical properties, on the contrary, are eternal. Brute bodies have
neither a beginning nor an inevitable end, neither age, nor evolution;
they remain as immutable as death, of which they are the image.

_Mobility and Mutability of the Sidereal World._—This is not true,
in the first place, of the sidereal bodies. The ancients held the
sidereal world to be immutable and incorruptible. The doctrine of
the incorruptibility of the heavens prevailed up to the seventeenth
century. The observers who at that epoch directed towards the heavens
the first telescope, which Galileo had just invented, were struck with
astonishment at discovering a change in that celestial firmament which
they had hitherto believed incorruptible, and at perceiving a new star
that appeared in the constellation Ophiuchus. Such changes no longer
surprise us. The cosmogonic system of Laplace has become familiar to
all cultivated minds, and every one is accustomed to the idea of the
continual mobility and evolution of the celestial world. “The stars
have not always existed,” writes M. Faye; “they have had a period of
formation; they will likewise have a period of decline, followed by
final extinction.”

Thus all the bodies of inanimate nature are not eternal and immutable;
the celestial bodies are eminently susceptible of evolution, slow
indeed with that we observe on the surface of our globe; but this
disproportion, corresponding to the immensity of time and of cosmic
spaces as compared with terrestrial measurements, should not mislead us
as to the fundamental analogy of the phenomena.


     § 1. THE MOVEMENT OF PARTICLES AND MOLECULES IN BRUTE BODIES.


It is not only in celestial spaces that we must search for that
mobility of brute matter which imitates the mobility of living matter.
In order to find it we have only to look about us, or to inquire from
physicists and chemists.

As far as geologists are concerned, M. le Dantec tells us somewhere of
one who divided minerals into _living rocks_—rocks capable of change
of structure, of evolution under the influence of atmospheric causes;
and _dead rocks_—rocks which, like clay, have found at the end of all
their changes a final state of repose. Jerome Cardan, a celebrated
scientist of the sixteenth century, at once mathematician, naturalist,
and physician, declared not only that stones live, but that they suffer
from disease, grow old, and die. The jewellers of the present day use
similar language of certain precious stones; the torquoise, for example.

The alchemists carried these ideas to an extreme. It is not necessary
here to recall the past, to evoke the hermetic beliefs and the dreams
of the alchemists, who held that the different kinds of matter lived,
developed, and were transmuted into each other.

I refer to precise and recent data, established by the most expert
investigators, and related by one of them, Charles Edward Guillaume,
some years ago, before the _Société helvétique des Sciences
naturelles_. These data show that determinate forms of matter may
live and die, in the sense that they may be slowly and continuously
modified, always in the same direction, until they have attained an
ultimate and definitive state of eternal repose.

_The Internal Movements of Bodies._—Swift’s reply to an idle fellow who
spoke slightingly of work is well known. “In England,” said the author
of _Gulliver’s Travels_, “men work, women work, horses work, oxen work,
water works, fire works, and beer works; it is only the pig who does
nothing at all; he must, therefore, be the only gentleman in England.”
We know very well that English gentlemen also work. Indeed, everybody
and everything works. And the great wit was nearer right than he
supposed in comparing men and things in this respect. Everything is at
work; everything in nature strives and toils, at every stage, in every
degree. Immobility and repose in the case of natural things are usually
deceptive; the seeming quietude of matter is caused by our inability
to appreciate its internal movements. Because of their minuteness we
do not perceive the swarming particles that compose it, and which,
under the impassible surface of the bodies, oscillate, displace each
other, move to and fro, and group themselves into forms and positions
adapted to the conditions of the environment. In comparison with these
microscopic elements we are like Swift’s giant among the Lilliputians;
and this is far from being a sufficiently forcible comparison.

_Kinetic Conception of Molecular Motion._—The idea of this peculiar
form of motion is by no means new to us. We were familiarized with
it in scientific theories during our school days. The atomic theory
teaches us that matter behaves, from a chemical point of view, as if it
were divided into molecules and atoms. The kinetic theory explains the
constitution of gases and the effects of heat by supposing that these
particles are endowed with movements of rotation and displacement.
The wave theory explains photic phenomena by supposing peculiar
vibratory movements in a special medium—the ether. But these are merely
hypotheses which are not at all necessary; they are the images of
things, not the things themselves.

_Reality of the Motion of Particles._—Here there is no question of
hypotheses. This internal agitation, this interior labour, this
incessant activity of matter are positive facts, an objective reality.
It is true that when the chemical or mechanical equilibrium of bodies
is disturbed it is only restored more or less slowly. Sometimes days
and years are required before it is regained. Scarcely do they attain
this relative repose when they are again disturbed, for the environment
itself is not fixed; it experiences variations which react in their
turn upon the body under consideration; and it is only at the end of
these variations, at the end of their respective periods, that they
will attain together, in a universal uniformity, an eternal repose.

We shall see that metallic alloys undergo continual physical and
chemical changes. They are always seeking a more or less elusive
equilibrium. Physicists in modern times have given their attention to
this internal activity of material bodies, to the pursuit of stability.
Wiedemann, Warburg, Tomlinson, MM. Duguet, Brillouin, Duhem, and
Bouasse have revived the old experimental researches of Coulomb and
Wertheim on the elasticity of bodies, the effects of pressures and
thrusts, the hammering, tempering, and annealing of metals.

The internal activity manifested under these circumstances presents
quite remarkable characteristics which cannot but be compared to the
analogous phenomena presented by living bodies. Thus have arisen even
in physics, a figurative terminology, and metaphorical expressions
borrowed from biology.

_Comparison of the Activity of Particles with Vital Activity._—Since
Lord Kelvin first spoke of the _fatigue_ of metals, or the _fatigue_
of elasticity, Bose has shown in these same bodies the fatigue of
electrical contact. The term _accommodation_ has been employed in the
study of torsion, and according to Tomlinson for the very phenomena
which are the inverse of those of fatigue. The phenomena presented by
glass when acted on by an external force which slowly bends it, have
been called facts of adaptation. The manner in which a bar of steel
resists wire-drawing has been compared to _defensive_ processes against
threatened rupture. And M. C. E. Guillaume speaks somewhere of “the
heroic resistance of the bar of nickel-steel.” The term “defence” has
also been applied to the behaviour of chloride or iodide of silver when
exposed to light.

There has been no hesitation in using the term “memory” concurrently
with that of hysteresis to designate the behaviour of bodies acted
on by magnetism or by certain mechanical forces. It is true that
M. H. Bouasse protests in the name of the physico-mathematicians
against the employment of these figurative expressions. But has he not
himself written “a twisted wire is a wound-up watch,” and elsewhere,
“the properties of bodies depend at every moment upon all anterior
modifications”? Does not this imply that they retain in some manner the
impression of their past evolution? Powerful deformative agencies leave
a trace of their action; they modify the body’s condition of molecular
aggregation, and some physicists go so far as to say that they even
modify its chemical constitution. With the exception of M. Duhem, the
disciples of the mechanical school who have studied elasticity admit
that the effect of an external force upon a body depends upon the
forces which have been previously acting on it, and not merely upon
those which are acting on it at the present moment. Its present state
cannot be anticipated, it is the recapitulation of preceding states.
The effect of a torsional force upon a new wire will be different from
that of the same force upon a wire previously subjected to torsions
and detorsions. It was with reference to actions of this kind that
Boltzmann, in 1876, declared that “a wire that has been twisted or
drawn out remembers for a certain time the deformations which it has
undergone.” This memory is obliterated and disappears after a certain
definite period. Here then, in a problem of static equilibrium, we find
introduced an unexpected factor—time.

To sum up, it is the physicists themselves who have indicated the
correspondence between the condition of existence in many brute bodies
and that in many living bodies. It cannot be expected that these
analogies will in any way serve as explanations. We should rather
seek to derive the vital from the physical phenomenon. This is the
sole ambition of the physiologist. To derive the physical from the
vital phenomenon would be unreasonable. We do not attempt to do this
here. It is nevertheless true that analogies are of service, were it
only to shake the support which, from the time of Aristotle, has been
accorded to the division of the bodies of nature into _psuchia_ and
_apsuchia_—_i.e._, into living and brute bodies.


                      § 2. THE BROWNIAN MOVEMENT.


_The Existence of the Brownian Movement._—The simplest way of judging
of the working activity of matter is to observe it when the liberty of
the particles is not interfered with by the action of the neighbouring
particles. We approximate to this condition when we watch, through the
microscope, grains of dust suspended in a liquid, or globules of oil
suspended in water. Now what we see is well known to all microscopists.
If the granulations are sufficiently small, they seem to be never at
rest. They are animated by a kind of incessant tremor; we see the
phenomena called the “Brownian movement.” This movement has struck
all observers since the invention of the magnifying glass or simple
microscope. But the English botanist, Brown, in 1827, made it the
object of special research and gave it his name. The exact explanation
of it remained for a long time obscure. It was given in 1894 by M.
Gouy, the learned physicist of the Faculty of Lyons.

The observer who for the first time looks through the microscope at
a drop of water from the river, from the sea, or from any ordinary
source—that is to say, water not specially purified—is struck with
surprise and admiration at the motion revealed to him. Infusoria,
microscopic articulata, and various micro-organisms people the
microscopic field, and animate it by their movements; but at the same
time all sorts of particles are also agitated, particles which cannot
be considered as living beings, and which are, in fact, nothing but
organic detritus, mineral dust, and debris of every description. Very
often the singular movements of these granulations, which simulate up
to a certain point those of living beings, have perplexed the observer
or led him to erroneous conclusions, and the bodies have been taken for
animalcules or for bacteria.

_Characters of this Movement._—But it is as a rule quite easy to avoid
this confusion. The Brownian movement is a kind of oscillation, a
stationary, dancing to-and-fro movement. It is a Saint Vitus’s dance
on one and the same spot, and is thus distinguished from the movements
of displacement customary with animate beings. Each particle has its
own special dance. Each one acts on its own account, independently of
its neighbour. There is, however, in the execution of these individual
oscillations a kind of common and regular character which arises from
the fact that their amplitudes differ little from each other. The
largest particles are the slowest; when above four thousandths of a
millimetre in diameter, they almost cease to be mobile. The smallest
are the most active. When so small as to be barely visible in the
microscope, the movement is extremely rapid, and can only occasionally
be perceived. It is probable that it would be still more accelerated in
smaller objects; but the latter will always escape our observation.

_Its Independence of the Nature of the Bodies and of the
Environment._—M. Gouy remarked that the movement depends neither on the
nature nor on the form of the particles. Even the nature of the liquid
has but little effect. Its degree of viscosity alone comes into play.
The movements are, indeed, more lively in alcohol or ether, which are
very mobile liquids; they are slow in sulphuric acid and in glycerine.
In water, a grain one two-thousandth of a millimetre in diameter
traverses, in a second, ten or twelve times its own length.

The fact that the Brownian movement is seen in liquors which have been
boiled, in acids and in concentrated alkalies, in toxic solutions of
all degrees of temperature, shows conclusively that the phenomenon
has no vital significance; that it is in no way connected with vital
activity so called.

_Its Indefinite Duration._—The most remarkable character of this
phenomenon is its permanence, its indefinite duration. The movement
never ceases, the particles never attain repose and equilibrium.
Granitic rocks contain quartz crystals which, at the moment of their
formation, include within a closed cavity a drop of water containing
a bubble of gas. These bubbles, contemporary with the Plutonian age
of the globe, have never since their formation ceased to manifest the
Brownian movement.

_Its Independence of External Conditions._—What is the cause of this
eternal oscillation? Is it a tremor of the earth? No! M. Gouy saw the
Brownian movement far away from cities, where the mercurial mirror of
a seismoscope showed no subterranean vibration. It does not increase
when the vibrations occur and become quite appreciable. Neither is
it changed by variation in light, magnetism, or electric influences;
in a word, by any external occurrences. The result of observation
is to place before us the paradox of a phenomenon which is kept up
and indefinitely perpetuated in the interior of a body without known
external cause.

_The Brownian Movement must be the First Stage of Molecular
Motion._—When we take in our hands a sheet of quartz containing a
gaseous inclusion, we seem to be holding a perfectly inert object. When
we have placed it upon the stage of the microscope, and have seen the
agitation of the bubble, we are convinced that this seeming inertia is
merely an illusion.

Repose exists only because of our limited vision. We see the objects as
we see from afar a crowd of people. We perceive them only as a whole,
without being able to discern the individuals or their movements.
A visible object is, in the same way, a mass of particles. It is a
molecular crowd. It gives us the impression of an indivisible mass, of
a block in repose.

But as soon as the lens brings us near to this crowd, as soon as the
microscope enlarges for us the minute elements of the brute body,
then they appear to us, and we perceive the continual agitation of
those elements which are less than four thousandths of a millimetre
in diameter. The smaller the particles under consideration, the more
lively are their movements. From this we infer that if we could
perceive molecules, whose probable dimensions are about one thousand
times less, their probable velocity would be, as required by the
kinetic theory, some hundreds of metres per second. In the case of
objects we can only just see, the Brownian velocity is only a few
thousandths of a millimetre per second. No doubt, concludes M. Gouy,
the particles that show this velocity are really enormous when compared
with true molecules. From this point of view the Brownian movement
is but the first degree, and a magnified picture of the molecular
vibrations assumed in the kinetic theory.


                 § 3. THE INTERNAL ACTIVITY OF BODIES.


_Migration of Material Particles._—In the Brownian movement we
take into account only very small, isolated masses, small free
fragments—_i.e._, material particles which are not hampered by their
relations to neighbouring particles. Any one but a physicist might
believe that in true solids endowed with cohesion and tenacity, in
which the molecules were bound one to the other, in which form and
volume are fixed, there could be no longer movements or changes. This
is a mistake. Physics teaches us the contrary, and, in late years
especially, has furnished us characteristic examples. There are real
migrations of material particles throughout solid bodies—migrations
of considerable extent. They are accomplished through the agency
of diverse forces acting externally—pressures, thrusts, torsions;
sometimes under the action of light, sometimes under the action of
electricity, sometimes under the influence of forces of diffusion.
The microscopic observation of alloys by H. and A. Lechatelier, J.
Hopkinson, Osmond, Charpy, J. R. Benoit; researches into their physical
and chemical properties by Calvert, Matthiessen, Riche, Roberts Austen,
Lodge, Laurie, and C. E. Guillaume; experiments on the electrolysis
of glass, and the curious results of Bose upon electrical contact of
metals, show in a striking manner the chemical and kinetic evolutions
which occur in the interior of bodies.

_Migration under the Action of Weight._—An experiment by Obermeyer,
dating from 1877, furnishes a good example of the motions of solid
bodies through a hardened viscid mass, taking place under the influence
of weight. The black wax that shoemakers and boatbuilders use, is a
kind of resin extracted from the pine and other resinous trees, melted
in water, and separated from the more fluid part which rises from it.
Its colour is due to the lampblack produced by the combustion of straw
and fragments of bark. At an ordinary temperature it is a mass so hard
that it cannot always be easily scratched by the finger-nail; but if it
is left to itself in a receptacle, it finally yields, spreads out as
if it were a liquid, and conforms to the shape of the vessel. Suppose
we place within a cavity hollowed out of a piece of wood a portion of
this substance, and keep it there by means of a few pebbles, having
previously placed at the bottom of the cavity a few fragments of some
light substance, such as cork. The piece of wax is thus between a light
body below and a heavy body above. If we wait a few days, this order
is reversed—the wax has filled the cavity by conforming to it; the
cork has passed through the wax and appears on the surface, while the
stones are at the bottom. We have here the celebrated experiment of the
flask with the three elements, in which are seen the liquids mercury,
oil, and water superposed in the order of their density, but in this
case demonstrated with solid bodies.

_Influence of Diffusion._—Diffusion, which disseminates liquids
throughout each other, may also cause solids to pass through other
solids. Of this W. Roberts Austen gave a convincing proof. This
ingenious physicist placed a little cylinder of lead upon a disc of
gold, and kept the whole at the temperature of boiling water. At this
temperature both metals are perfectly solid, for the melting point of
gold is 1,200° C., and of lead is 330°. Still, after this contact has
been prolonged for a month and a half, analysis shows that the gold has
become diffused through the top of the cylinder of lead.

_Influence of Electrolysis._—Electrolysis offers another no less
remarkable means of transportation. By its means we may force metals,
such as sodium or lithium, through glass walls. The experiment may be
performed as indicated by M. Charles Guillaume. A glass bulb containing
mercury is placed in a bath of sodium amalgam, and a current is then
made to pass from within outward. After some time it can be shown that
the metal has penetrated the wall of the bulb, and has become dissolved
within it.

_Influence of Mechanical Pressure._—Mechanical pressure is also capable
of causing one metal to pass into another. We need not recall the
well-known experiment of Cailletet, who, by employing considerable
pressure, caused mercury to sweat through a block of iron. In a more
simple manner W. Spring showed that a disc of copper could be welded
to a disc of tin by pressing them strongly one against the other. Up to
a certain distance from the surfaces of contact a real alloy is formed;
a layer of bronze of a certain thickness unites the two metals, and
this could not take place did not the particles of both metals mutually
interpenetrate.


                   § 4. INTERNAL ACTIVITY OF ALLOYS.


_Structure of Alloys._—Metallic alloys have a remarkable structure,
which is essentially mobile, and which we have only now begun to
understand by the aid of the microscope. Microscopical examination
justifies to a certain degree Coulomb’s conjecture. That illustrious
physicist explained the physical properties of metals by imagining them
to be formed of two kinds of elements—integral particles, to which
the metal owes its elastic properties, and a _cement_ which binds the
particles, and to which it owes its coherence. M. Brillouin has also
taken up this hypothesis of duality of structure. The metal is supposed
to be formed of very small, isolated, crystalline grains, embedded in
an almost continuous network of viscous matter. A more or less compact
mass surrounding more or less distinct crystals is the conception which
may be formed of an alloy.

_Changes of Structure produced by Deforming Agencies._—It has been
shown that profound changes of crystalline structure can be produced
by various mechanical means, such as hammering, and the stretching
of metallic bars carried to the point of rupture. Some of these
changes are very slow, and it is only after months and years that
they are completed, and the metal attains the definite equilibrium
corresponding to the conditions to which it is exposed. Though there
may be discussions concerning the extent of the transformations to
which it is subjected, though some believe they affect the chemical
condition of the alloy, while others limit its power to physical
effects, it is nevertheless true—and this brings us back to our
subject—that the mass of these metals is at work, and that it only
slowly attains the phase of complete repose.

_The Slow Re-establishment of Equilibrium. Residual Effect._—These
operations by which the physical characters of metals are changed, and
by which they are adapted to a variety of industrial needs—compression,
hammering, rolling, stretching, and torsion—have an immediate, very
apparent effect; but they have also a consecutive effect, slowly
produced, much less marked and less evident. This is the “residual
effect,” or “Nachwirkung” of the Germans. It is not without importance,
even in practical applications.

Heat also creates a kind of _forced equilibrium_. This becomes but
slowly modified, so that a body may remain for a long time in a state
which is, however, not the most stable for the conditions under which
it is considered. The number of these bodies _not in equilibrium_ is as
great as that of the substances which have been exposed to fusion. All
the Plutonic rocks are in this condition. Glass presents a condition of
the same kind. Thermometers placed in melting ice do not always mark
the zero Centigrade. This displacement of the zero point falsifies all
records if care is not taken to correct it. The correction usually
requires prolonged observation. The theory of the displacement of the
thermometric zero is not entirely established; but we may suppose,
with the author of the _Traité de Thermométrie_, that in glass, as
in alloys, are to be found compounds which vary according to the
temperature. At each temperature glass tends to assume a determinate
composition and a corresponding state of equilibrium; but the previous
temperature to which it has been subjected clearly has an influence
on the rapidity with which it attains its state of repose. The effect
of variation is more marked when we observe glass of more complicated
composition. We can understand that those which contain comparable
quantities of the two alkalies, soda and potash, may be more subject to
these modifications than those having a more simple composition based
on a single alkali.

_Effects of Annealing._—A piece of brass wire that has been drawn and
then heated is the scene of certain very remarkable internal changes,
and these have been only recently recognized. The violent treatment
of the metallic thread in forcing it through the hole in the die has
crushed the crystalline particles; the interior state of the wire is
that of broken crystals embedded in a granular mass. Heating changes
all that. The crystals separate, repair themselves, and are built
up again; they are then hard, geometrical bodies, in an amorphous,
relatively soft and plastic mass; their number keeps on increasing;
equilibrium is not established until the entire mass is crystallized.
We may imagine how many displacements, enormous when compared with
their dimensions, the molecules have to undergo when passing through
the resisting mass, and arranging themselves in definite places in the
crystalline structures.

In the same way, too, in the manufacture of steel, the particles of
coal at first applied to the surface pass through the iron.

This _faculty of molecular displacement_ enables the metal in some
cases to modify its state at one point or another. The use made of this
faculty under certain circumstances is very curious, greatly resembling
the adaptation of an animal to its environment, or the methods of
defence against agents that might destroy it.

_Effect of Stretching. Hartmann’s Experiment._—When a cylindrical
rod of metal, held firmly at either end—a test-piece, as it is
called in metallurgy—is pulled sufficiently hard, it often elongates
considerably, part of the elongation disappearing as soon as the strain
ceases, and the other part remaining. The total elongation is thus the
sum of an “elastic elongation,” which is temporary, and a “permanent
elongation.” If we continue the stretching, there appears at some point
of the rod a local extension with contraction of sectional area. It is
here that the rod will break.

But in place of continuing the stretching, Mr. Hartmann suspends it.
He stops, as if to give the “metal-being” time to rally. During this
delay it would seem that the molecules hasten to the menaced point
to reinforce and harden the weak part. In fact the metal, which was
soft at other points, at this spot looks like tempered metal. It is no
longer extensible.

When the experimenter begins the stretching again after this rest, and
after the narrowed bar has been rolled and become cylindrical again,
the local extension and sectional contraction is forced to occur at
another point. If another rest is given at this point the metal will
also become hardened.

If we repeat the experiment a sufficient number of times, we shall find
a total transformation of the rod, which becomes hardened throughout
its entire extent. It will break rather than elongate if the stretching
is sufficiently severe.

_Nickel Steels—their “Heroic” Resistance._—Nickel steels present this
phenomena in an exaggerated degree. The alternation of operations which
we have just described, bringing the various parts of an ordinary
steel rod into a tempered state, is not necessary with nickel steel.
The effect is produced in the course of a single trial. As soon as
there is any tendency to contraction the alloy hardens at that precise
place; the contraction is hardly noticeable; the movement is stopped at
this point to attack another weak point, stops there again and attacks
a third, and so on; and, finally, the paradoxical fact appears that
a rod of metal which was in a soft state and could be considerably
elongated has now become throughout its whole extent as hard, brittle,
and inextensible as tempered steel. It is in connection with this point
that M. C. E. Guillaume spoke of “heroic resistance to rupture.” It
would seem, in fact, as if the ferro-nickel bar had reinforced each
weak point as it was threatened. It is only at the end of these efforts
that the inevitable catastrophe occurs.

_Effect of Temperature._—When the temperature changes, it is seen that
these ferro-nickel bars elongate or retract, modifying at the same time
their chemical constitution. But these effects, like those which occur
in the glass bulb of a thermometer, do not occur at once. They are
produced rapidly for one part, and more slowly for a small remaining
portion. Bars of ferro-nickel which have been kept at the same
temperature change gradually in length in the course of a year. Can
we find a better proof of internal activity occurring in a substance
differing so greatly from living matter?

_Nature of the Activity of Particles._—These are examples of the
internal activity that occurs in brute bodies. Besides, these facts
that we are quoting merely to refute Bichat’s assertion relative to
the immutability of brute bodies, and to show us their activity, also
afford us another proof. They show that this activity, like that of
animals, wards off foreign intervention, and that this parrying of
the attack, again like that of animals, is adapted for the defence
and preservation of the brute mass. So that if we consider of special
importance the adaptative, teleological characteristic of vital
phenomena, a characteristic which is so easily made too much of in
biological interpretations, we may also find it again in the inanimate
world. To this end we may add to the preceding examples one more which
is no less remarkable. This is the famous case of Becquerel’s process
for colour-photography.

_Colour-Photography._—A greyish plate, treated with chloride or iodide
of silver and exposed to a red light, rapidly becomes red. It is then
exposed to green light, and after passing through dull and obscure
tints it becomes green. To explain this remarkable phenomenon, we
cannot improve on the following statement:—The silver salt protects
itself against the light that threatens its existence; that light
causes it to pass through all kinds of stages of coloration before
reducing it; the salt stops at the stage which protects it best. It
stops at red, if it is red light that assails it, because in becoming
red by reflection it best repels that light—_i.e._, it absorbs it the
least.

It may then be advantageous, for the comprehension of natural
phenomena, to regard the transformation of inanimate matter as
manifestations of a kind of internal life.

_Conclusion. Relations of the Surrounding Medium to the Living Being
and the Brute Body._—Brute bodies, then, are not immutable any more
than are living bodies. Both depend on the medium that surrounds them,
and they depend upon it in the same way. Life brings together, brings
into conflict, an appropriate organism and a suitable environment.
Auguste Comte and Claude Bernard have taught us that vital phenomena
result from the reciprocal action of these two factors which are
in close correlation. It is also from the reciprocal action of the
environment and the brute body that inevitably result the phenomena
which that body presents. The living body is sometimes more sensitive
to variations of the ambient medium than is the brute body, but at
other times the reverse is the case. For example, there is no living
organism as impressionable to any kind of stimulus whatever as the
bolometer is to the slightest variations of temperature.

There can only be, then, one chemically immutable body—namely, the atom
of a simple body, since, by its very definition, it remains unaltered
and intangible in combinations. This notion of an unalterable atom
has, however, itself been attacked by the doctrine of the ionization
of particles due to Sir J. J. Thomson; and besides, with very few
exceptions—those of cadmium, mercury, and the gases of the argon
series—the atoms of simple bodies cannot exist in a free state.

Thus, as in the vital struggle, the ambient medium by means of
alimentation furnishes to the living being, whether whole or
fragmentary, the materials of its organization and the energies which
it brings into play. It also furnishes to brute bodies their materials
and their energies.

It is also said that the ambient medium furnishes to the living being
a third class of things, the _stimuli_ of its activities—_i.e._, its
“provocation to action.” The protozoon finds in the aquatic environment
which is its habitat the stimuli which provoke it to move and to absorb
its food. The cells of the metazoon encounter in the same way in the
lymph, the blood, and the interstitial liquids which bathe them, the
shock, the stimulus which brings their energies into play. They do not
derive from themselves, by a mysterious spontaneity without parallel in
the rest of nature, the capricious principle which sets them in motion.

Vital spontaneity, so readily accepted by persons ignorant of biology,
is disproved by the whole history of the science. Every vital
manifestation is a response to a stimulus, a provoked phenomenon. It
is unnecessary to say this is also the case with brute bodies, since
that is precisely the foundation of the great principle of the inertia
of matter. It is plain that it is also as applicable to living as to
inanimate matter.




                              CHAPTER V.

              SPECIFIC FORM. LIVING BODIES AND CRYSTALS.

 § 1. Specific form and chemical constitution—The wide distribution
 of crystalline forms—Organization of crystals—Law of relation
 between specific form and chemical constitution—Value of form as a
 characteristic of brute and living beings—Parentage, living beings and
 mineral parentage—Iso-morphism and the faculty of cross-breeding—Other
 analogies. § 2. Acquisition and re-establishment of the specific
 form—Mutilation and regeneration of crystals—Mechanism of reparation.


§ 1. _Specific Form and Chemical Constitution._—In the enumeration
which we have made of the essential features of vitality there are
three that are, so to speak, of the highest value. They are, in
the order of their importance:—The possession of a specific form;
the faculty of growth or nutrition; and finally, the faculty of
reproduction by generation. By restricting our comparison between
brute bodies and living bodies to these truly fundamental characters
we sensibly restrict the field, but we shall see that it does not
disappear.

_Wide Distribution of Crystalline Forms._—The consideration of specific
forms shows us that in the mineral world we need only consider
crystallized bodies, as they are almost the only ones that possess
definite form. In restricting ourselves to this category we do not
limit our field as much as might be supposed. Crystalline forms are
very widely distributed. They are, in a measure, universal. Matter
has a decided tendency to assume these forms whenever the physical
forces which it obeys act with order and regularity, and when their
action is undisturbed by accidental occurrences. In the same way, too,
living forms are only possible in regulated environments, under normal
conditions, protected from cataclysms and convulsions of nature.

The possession of a specific form is the most significant feature of
an organized being. Its tendency, from the time it begins to develop
from the germ, is toward the acquirement of that form. The progressive
manner in which it seeks to realize its architectural plan in spite of
the obstacles and difficulties that arise—healing its wounds, repairing
its mutilations—all this, in the eyes of the philosophical biologist,
forms what is perhaps the most striking characteristic of a living
being, that which best shows its unity and its individuality. This
property of organogenesis seems pre-eminently the vital property. It is
not so, however, for crystalline bodies possess it in an almost equal
degree.

The parallel between the crystal and a living being has been often
drawn. I will not reproduce it here in detail. My sole desire, after
sketching its principal features, is to call attention to the new
information that has been brought out by recent investigations.

_Organization of Crystals. Views of Haüy, Delafosse, Bravais, and of
Wallerant._—In botany, zoology, and crystallography we understand by
form an assemblage of material constituents co-ordinated in a definite
system—_i.e._, the organization itself. The body of man, for example,
is an edifice in which sixty trillion cells ought each to find its own
predetermined place.

In crystallography also we understand by form the organization which
crystals present. The grouping of the elements of crystals is, perhaps,
more simple. They are none the less organized, in the same sense that
living bodies are.

Their organization, while more uniform than that of living bodies,
still shows a considerable amount of variation. It should not be
assumed that the area of a crystal is completely filled, with
contiguous parts applied one to the other by plane faces, as might
be supposed from the phenomenon of cleavage which dissociates the
parts of the crystalline body into solids of this kind. In reality,
the constituent parts are separated from each other by spaces. They
are arranged in a quincunx, as Haüy put it, or along the lines of a
network, to use the terms of Delafosse and Bravais. The intervals left
between them are incomparably larger than their diameters. So that in
the organization of a crystal it is necessary to take into account two
quite different things:—An element, the crystalline particle, which
is a certain aggregate of chemical molecules having a determinate
geometrical form; and a more or less regular, parallelopipedic network,
along the edges of which are arranged in a constant and definite manner
the aforesaid particles. The external form of the crystal indicates the
existence of the network. Its optical properties depend upon the action
of the particles, as Wallerant has shown: Thus we must distinguish in
a crystal between two kinds of geometrical figures—that of the network
and that of the particle—and their characters of symmetry may be either
concordant or discordant.

The crystalline particle, the element of the crystal, is therefore
a certain molecular complex that repeats itself identically and is
identically placed at the nodes of the parallelopipedic network. It has
been given different names well calculated to produce confusion-the
crystallographic molecule of Mallard, the complex particle of other
authors. Some have separated this element into subordinate elements
(the fundamental particles of Wallerant and of Lapparent).

These very general outlines will suffice to show how complex and
adjustable is the organization of the crystalline individual, which in
spite of its geometric regularity and its rigidity, may be compared
with the still more flexible organization of the living element. The
mineral individual is more stable, more labile—_i.e._, less prone
to undergo change than is the living individual. We may say with
M. Lapparent that “crystallized matter presents the most perfect
and stable orderly arrangement of which the particles of bodies are
susceptible.”

_Law of Relation of Specific Form to Chemical
Constitution._—Crystallization is a method of acquiring specific form.
The geometrical architecture of the mineral individual is but little
less wonderful or characteristic than that of the living individual.
Its form is the result of the mutual reactions of its substances and
of the medium in which it is produced; it is the condition of material
equilibrium corresponding to a given situation. This idea of a specific
form belonging to a given substance under given conditions must be
borne in mind. We may consider it as a kind of principle of nature,
an elementary law, which may serve as a point of departure for the
explanation of phenomena. A particular substance under identical
conditions of environment, must always assume a certain form.

This close linking of substance and form, admitted as a postulate in
physical sciences, has been carried into biology by some philosophical
naturalists, by M. Le Dantec, for instance.

Let us imitate them for a moment. Let us cease to seek in the living
being for the prototype of the crystal; let us, on the contrary, seek
in the crystal the prototype of the living being. If we succeed in
this, we shall then have found the physical basis of life.

Let us say, then, with the biologists we have mentioned, that the
substance of each living being is peculiar to it; that it is specific,
and that its form—that is to say its organization—follows from it.
The morpholpgy of any being whatever, of an animal—of a setter, for
example—or even of a determinate being—of Peter, of Paul—is the
“crystalline form of their living matter.” It is the only form of
equilibrium that can be assumed under the given conditions by the
substance of the setter, of Peter, or of Paul, just as the cube is the
crystalline form of sea-salt. In this manner these biologists have
supposed that they could carry back the problem of living form to the
problem of living substance, and at the same time reduce the biological
mystery to the physical mystery. I have shown above (Chap. V. pp.
199-204) how far this idea is legitimate, and how far and with what
restrictions it may be welcomed and adopted.

_Value of Form as a Characteristic of Living and Brute Beings._—However
this may be, we may say, without fear of exaggeration, that the
crystalline form characterizes the mineral with no less precision than
the anatomical form characterizes the animal and the plant. In both
cases, form—regarded as a method of distribution of the parts—indicates
the individual and allows us to diagnose it with more or less facility.

_Parentage of Living Beings and Mineral Parentage._—Still another
analogy has been noted. In animals and plants similarity in form
indicates similarity in descent, community of origin, and proximity in
any scheme of classification. In the same way identity of crystalline
form indicates mineral relationship. Substances chemically analogous
show identical, geometrically superposable forms, and are thus arranged
in family or generic groups recognizable at a glance.

_Isomorphism and the Faculty of Cross-breeding._—And further, the
possibility in the case of isomorphous bodies, of their replacing each
other in the same crystal during the process of formation and of thus
mingling, so to speak, their congenital elements, may be compared
with the possibility of inter-breeding with living beings of the same
species. Isomorphism is thus a kind of faculty of crossing. And as the
impossibility of crossing is the touchstone of taxonomic relationship,
testing it, and separating stocks that ought to be separated, so the
operation of crystallization is also a means of separating from an
accidental mixture of mineral species the pure forms which are blended
therein. Crystallization is the touchstone of the specific purity of
minerals; it is the great process in chemical purification.

_Other Analogies._—The analogies between crystalline and living forms
have been pushed still further even to the verge of exaggeration.

The internal and external symmetry of animals and plants has been
compared to that of crystals. Transitions or intergradations have been
sought between the rigid and faceted architecture of the latter and the
flexible structure and curved surface of the former; the utricular form
of flowers of sulphur on the one hand, and the geometrical structure
of the shells of radiolarians on the other, have shown an exchange of
typical forms between the two systems. An effort has even been made
to draw a parallel between six of the principal types of the animal
kingdom and the six crystalline systems. If carried as far as this, our
thesis becomes puerile. Real analogies will suffice. Among these the
curious facts of crystalline renewal come first.


         § 2. CICATRIZATION IN LIVING BEINGS AND IN CRYSTALS.


We know that living beings not only possess a typical architecture
which they have themselves constructed, but that they defend it against
destructive agencies, and that if need arise they repair it. The
living organism cicatrizes its wounds, repairs losses of substance,
regenerates more or less perfectly the parts that have been removed;
in other terms, when it has been mutilated it tends to reconstruct
itself according to the laws of its own morphology. This phenomenon of
reconstitution or reintegration, these more or less successful efforts
to re-establish its form and its integrity, at first appear to be a
characteristic feature of living beings. This is not the case.

_Mutilation and Re-integration of Crystals._—Crystals—let us say
crystalline individuals—show a similar aptitude for repairing their
mutilations. Pasteur, in an early work, discussed these curious facts.
Other experimenters, Gernez a little later and Rauber more recently,
took up the same subject, but could do no more than extend and confirm
his observations. Crystals are formed from a primitive nucleus, as the
animal is formed from an egg; their integral particles are disposed
according to efficient geometrical laws, so as to produce the typical
form by a constructive process that may be compared to the embryogenic
process which builds up the body of an animal. Now this operation
may be disturbed by accidents in the surrounding medium or by the
deliberate intervention of the experimenter. The crystal is then
mutilated. Pasteur saw that these mutilations repaired themselves.
“When,” said he, “a crystal from which a piece has been broken off
is replaced in the mother liquor, we see that while it increases in
every direction by a deposit of crystalline particles, activity occurs
at the place where it was broken off or deformed; and in a few hours
this suffices not only to build up the regular amount required for the
increase of all parts of the crystal, but to re-establish regularity
of form in the mutilated part.” In other words, the work of formation
of the crystal is carried on much more actively at the point of lesion
than it would have been had there been no lesion. The same thing would
have occurred with a living being.

_Mechanism of Reparation._—Gernez some years later made known the
mechanism of this reparation, or, at least, its immediate cause. He
showed that on the injured surface the crystal becomes less soluble
than on the other facets. This is not, however, an exceptional
phenomenon. It is, on the contrary, quite frequently observed that the
different faces of a crystal show marked differences in solubility.
This is what happens in every case for the mutilated face in comparison
with the others; the matter is less soluble there. The consequence
of this is clear; the growth must preponderate on that face, since
there the mother liquor will become super-saturated before being
super-saturated for the others. We may explain this result in another
way. Each face of the crystal in contact with the mother liquor is
exposed to two antagonistic actions: The matter deposited upon a
surface may be taken away and redissolved if, for any reason whatever,
such matter becomes more soluble than that of the liquid stratum in
contact with it; in the second place, the matter of this liquid stratum
may, under contrary conditions, be deposited, and thus increase the
body of the crystal. There is, then, for each point of the crystalline
facet, a positive operation of deposit which results in a gain, and a
negative operation of redissolution which results in a loss. One or
the other effect predominates according as the relative solubility is
greater or less for the matter of the facet under consideration. On the
mutilated surface it is diminished, deposition then prevails.

But this is only the immediate cause of the phenomenon; and if we wish
to know why the solubility has diminished on the mutilated surface
Ostwald explains it to us by showing that crystallization tends to form
a polyhedron in which the surface energy is a relative minimum.




CHAPTER VI.

NUTRITION IN THE LIVING BEING AND IN THE CRYSTAL.

 Assimilation and growth in the crystal.—Methods of growth
 in the crystal and in the living being; intussusception;
 apposition.—Secondary and unimportant character of the process of
 intussusception.


I have already stated (Chap. VI. p. 209) that nutrition may be
considered as the most characteristic and essential property of living
beings. Such beings are in a state of continual exchange with the
surrounding medium. They assimilate and dissimilate. By assimilation
the substance of their being increases at the expense of the
surrounding alimentary material, which is rendered similar to that of
the being itself.

_Assimilation and Growth in the Crystal._—There exists in the crystal
a property analogous to nutrition, a kind of nutrility, which is
the rudiment of this fundamental property of living beings. The
development of a crystal starts from a primitive nucleus, the germ
of the crystalline individual that we will presently compare to
the ovum or embryo of a plant or an animal. Placed in a suitable
culture-medium—_i.e._, in a solution of the substance—this germ
develops. It assimilates the matter in solution, incorporates the
particles of it, and increases, preserving at the same time its form,
reproducing its specific type or a variety of it. Its growth proceeds
without interruption. The crystalline individual may attain quite a
large size if we know how to nourish it properly—we might say, to
fatten it. Very frequently, at a given time, a new particle of the
crystal serves in its turn as a primitive nucleus, and becomes the
point of departure for a new crystal engrafted upon the first.

Taken from its mother liquor, placed where it cannot be nourished,
the crystal, arrested in its growth, falls into a condition of rest
not without analogy to that of a seed or of a reviviscent animal. Its
evolution is resumed with the return of favourable conditions—the bath
of soluble matter.

The crystal is in a relation of continual exchange with the surrounding
medium which feeds it. These exchanges are regulated by the state of
this medium, or, more exactly, by the state of the liquid stratum
which is in immediate contact with the crystals. It loses or it gains
in substance if, for example, this layer becomes heated or cooled
more rapidly than the crystal. In a general way, it assimilates or
dissimilates according as its immediate environment is saturated or
diluted. Here, then, we have a kind of mobile equilibrium, comparable,
in some measure, to that of the living being.

_Methods of Growth of the Crystal and of the Living Being.
Intussusception. Apposition._—In truth, there seems to be a complete
opposition between the crystal and the living being as regards
their manner of nutrition and growth. In the one case the method
is intussusception; in the other it is apposition. The crystalline
individual is all surface. Its mass is impenetrable to the nutritive
materials. Since only the surface is accessible, the incorporation of
similar particles is possible only by external juxtaposition, and the
edifice increases only because a new layer of stones has been added to
those which were there before. On the contrary, the body of an animal
is a mass essentially penetrable. The cellular elements that compose
it have more or less rounded and flexible forms. Their contact is by
no means perfect. They have neither the stiffness nor the precision
of adjustment that the crystalline particles have. Liquids and gases
can insinuate themselves from without and circulate within the meshes
of this loose construction. Assimilation can therefore take place
throughout its whole depth, and the edifice increases because each
stone is itself increasing.

_The Secondary and Commonplace Character of the Process of
Intussusception._—The apparent opposition of these two processes is
doubtless diminished if we compare the simple mineral individual
with the elementary living unit, the crystalline particle with the
protoplasmic mass of a cell. Without carrying analysis so far as
this, it is yet easy to see that apposition and intussusception are
mechanical means that living beings employ at one and the same time and
combine according to their necessities. The hard parts of the internal
and external skeleton increase both by interposition and superposition,
at once. It is by the last method that bones increase in diameter,
and the shells of molluscs, the scales of reptiles and fishes, and
the testae of many radiate animals are formed. In these organs, as in
crystals, life and nutrition occur at the surface.

Apposition and intussusception are then secondary, mechanical
arrangements having relation to the physical characters of the
body—solidity in the crystal, semi-fluidity in the cellular protoplasm.
If we compare the inorganic liquid matter with the semi-fluid organized
matter, we recognize that the addition of substance takes place in
the same manner in each—_i.e._, by interposition. If we add a soluble
salt to a fluid, the molecules of the salt separate themselves and
interpose themselves between those of the fluid. There is, therefore,
nothing especially mysterious or particularly vital about the process
of intussusception. Applied to fluid protoplasm, it is merely the
diffusion that ordinarily occurs in mixed liquids.




CHAPTER VII.

GENERATION IN BRUTE BODIES AND LIVING BODIES. SPONTANEOUS GENERATION.

 Protoplasm a substance which continues—Case of the
 crystal—Characteristics of generation in the living being—Property of
 growth—Supposed to be confined to the living being—Fertilization of
 micro-organisms—Fertilization of crystals—Sterilization of crystalline
 and living media—Spontaneous generation of crystals—Metastable and
 labile zones—Glycerine crystals—Possible extinction of a crystalline
 species—Conclusion.


We have not yet exhausted the analogies between a crystal and the
living being. The possession of a specific form, the tendency to
re-establish it by redisintegration and the existence of a kind of
nutrition are not sufficient to constitute complete similarity. It
still lacks a fundamental character, that of generation. Chauffard
some time ago, in an attack which he made upon the physiological ideas
of his day, aptly exhibited this weak point. “Let us disregard,”
he said, “those interesting facts relative to the acquisition of a
typical form—facts that are common to the mineral world as well as
to living beings. It is none the less true that the crystalline type
is in no way derived from other pre-existing types, and that nothing
in crystallization recalls the actions of ascendants and the laws of
heredity.”

This gap has since been filled. The work of Gernez, of Violette, of
Lecoq de Boisbaudran, the experiments of Ostwald and of Tammann, the
observations of Crookes and of Armstrong—all this series of researches,
so lucidly summarized by M. Leo Errera in his essays in botanical
philosophy, had for their result the establishment of an unsuspected
relation between the processes of crystallization and those of
generation in animals and plants.

_Protoplasm is a Substance which Continues. The Case of the
Crystal._—Under present conditions a living being of any kind springs
from another living being similar to itself.

Its protoplasm is always a continuation of the protoplasm of an
ancestor. It is an atavic substance of which we do not see the
beginning; we only see it continue. The anatomical element comes from a
preceding anatomical element, and the higher animal itself comes from
a pre-existing cell of the material organism, the ovum. The ladder of
filiation reaches back indefinitely into the past.

We shall see that there is something analogous to this in certain
crystals. They are born of a preceding individual; they may be
considered as the posterity of the antecedent crystal. If we speak of
the matter of a crystal as the matter of a living being is spoken of,
in cases of this kind we would say that the crystalline substance is an
atavic substance of which we see only the continuation, as in the case
of protoplasm.

_Characters of Generation in the Living Being._—Growth of the living
substance, and consequently of the being itself, is the fundamental
law of vitality. Generation is the necessary consequence of growth (p.
210).

Living elements or cells cannot subsist indefinitely without increasing
and multiplying. The time must come when the cell divides, either
directly or indirectly; and then, instead of one cell, there are
two. This is the method of generation for the anatomical element.
In a complex individual it is a more or less restricted part of the
organism, usually a simple sexual cell, that takes on the formation
of the new being, and assures the perpetuity of the protoplasm, and
therefore of the species.

_Property of Growth. Its Supposed Restriction to Living Beings._—At
first it would appear that nothing like this occurs in inanimate
nature. The physical machine, if we furnish it matter and energy, could
go on working indefinitely, without being compelled to increase and
reproduce. Here, then, there is an entirely new condition peculiar to
the organized being, a property well adapted, it would seem—and this
time without any possible doubt—for separating living matter from brute
matter. It is not so.

It would not be impossible to imagine a system of chemical bodies
organized like the animal or vegetable economy, so that a destruction
would be compensated for by a growth. The only thing impossible is to
suppose, with M. le Dantec, a destruction that would at the same time
be an analysis. And an additional perplexity occurs when he supposes
that in the successive acts exchanges of material may occur.

There is no necessity for making this impossible chemistry a
characteristic of the living being. The chemistry of the living being
is general chemistry. Lavoisier and Berthelot enforced this view. We
should not lose sight of the teachings of the masters.

Let us return to generation, properly so called, and find in it the
characteristics of brute bodies and of crystals.

_The Sowing of Micro-organisms._—When a microbiologist wishes to
propagate a species of micro-organisms, he places in a culture medium
a few individuals (one is all that is actually necessary), and soon
observes their rapid multiplication. Usually, if only the ordinary
microbes in atmospheric dust are wanted, the operator need not trouble
to charge the culture; if the culture tube remains open and the medium
is suitably chosen, some germ of a common species will fall in and the
liquid will become colonized. This has the appearance of spontaneous
generation.

_The Sowing of Crystals._—Concentrated solutions of various substances,
supersaturated solutions of sodium magnesium sulphate, and sodium
chlorate are also wonderful culture media for certain mineral organic
units—certain crystalline germs. Ch. Dufour, experimenting with water
cooled below 0° C., its point of solidification; Ostwald, with salol
kept below 39°.5, its point of fusion; Tammann, with betol, which
melts at 96°; and, before them, Gernez, with melted phosphorus and
sulphur—all these physicists have shown that liquids in superfusion are
also media specially appropriate for the culture and propagation of
certain kinds of crystalline individuals.

Some of these facts have become classic. Lowitz showed in 1785 that a
solution of sodium sulphate could be concentrated by evaporation so
as to contain more salt than was conformable with the temperature,
without, however, depositing the excess. But if a solid fragment, a
crystal of salt, is thrown into the liquor, the whole of the excess
immediately passes into the state of a crystallized mass. The first
crystal has engendered a second similar to itself; the latter has
engendered a third, and so on from one to the other. If we compare
this phenomenon with that of the rapid multiplication of a species of
microbes in a suitable culture medium, no difference will be perceived.
Or perhaps we may note one unimportant difference—the rapidity of
the propagation of the crystalline germs as opposed to the relative
slowness of the generation of the micro-organisms.

Again, the propagation of crystallization in a supersaturated
or superfused liquid may be delayed by appropriate devices. The
crystalline individual gives birth, then, to another individual that
conforms to its own type, or even to varieties of that type when such
exist. Into the right branch of a U tube filled with sulphur in a state
of superfusion Gernez dropped octahedric crystals of sulphur, and into
the left branch prismatic crystals. On either side were produced new
crystals conforming to the type that had been sown.

_Sterilization of Crystalline Media and Living Media._—Ostwald varied
these experiments by using salol. He melted the substance by heating
it above 39∙5°C.; then, protecting it from crystals of any kind, he
let the solution stand in a closed tube. The salol remained liquid
indefinitely—until it was touched with a platinum wire that had been
in contact with solid salol—_i.e._, until a crystalline germ was
introduced. But if the platinum wire has been previously sterilized by
passing it, as the bacteriologists do, through a flame, it can then be
introduced into the liquor with impunity.

_The Dimensions of Crystalline Germs Comparable to those of
Microbes._—We may dilute the solid salol with inert powder—lactin,
for example—dilute the first mixture with a second, the second with a
third, and so on; then, throwing into the solution of surfused salol
a tenth of a milligram from one of these various mixtures, we find
that the production of crystals will not take place if the fragment
thrown in weighs less than a millionth of a milligram, or measures
less than ten thousandths of a millimetre in length. It would seem,
then, that these are the dimensions of the crystalline particle or
crystallographic molecule of salol. In the same way Ostwald satisfied
himself that the crystalline germ of hyposulphite of soda weighs
about a thousand-millionth of a milligram, and measures a thousandth
of a millimetre; that of chlorate of soda weighs a ten-millionth of
a milligram. These dimensions are entirely comparable with those of
microbes.

All these phenomena have been studied with a detail into which it
is impossible to enter here, and which clearly shows more and more
intimate analogies between the formation of crystals and the generation
of micro-organisms.

_Extension and Propagation of Crystallization. Optimum Temperature
of Incubation._—Crystallization which has commenced around a germ is
propagated more or less rapidly, and ends by invading the whole of the
liquor.

The rapidity of this movement of extension depends upon the conditions
of the medium, especially upon its temperature. This is shown very
well by Tammann’s experiments with betol. This body, the salicylic
ester of naphthol, fuses at 96° C. If it is melted in tubes sealed
at a temperature of 100° C., it may be cooled to lower and lower
temperatures—to + 70°, to + 25°, to + 10°, to-5° without solidifying.
Let us suppose that by some combination of circumstances a few centres
of crystallization—that is to say, of crystalline germs—have appeared
in the solution. Solidification will extend slowly at the ordinary
temperature, at 20° to 25° and thereabouts. On the other hand, it will
be propagated with great rapidity if the liquor is kept at about 70°.
This point—70°—is the thermal optimum for the propagation of germs.
It is the most favourable temperature for what may be called their
incubation. As soon as the germs find themselves in a liquor at 70°
they increase, multiply, and show that they are in the best conditions
for growth.

_Spontaneous Generation of Crystals. Optimum Temperature for the
Appearance of Germs._—If we consider various supersaturated solutions
or liquids in superfusion, we shall soon discover that they can be
arranged in two categories. Some remain indefinitely liquid under
given conditions unless a crystalline germ is introduced into them.
Others solidify spontaneously without artificial intervention, and such
crystallization may even be propagated very rapidly under determinate
conditions. This implies that these are conditions favouring the
spontaneous appearance of germs.

This distinction between substances of crystalline generation by
filiation and substances of spontaneous crystalline generation is not
specific. The same substance may present the two methods of generation
according to the conditions in which it is placed. Betol furnishes a
good example of this. Liquefy it at 100° in a sealed tube and keep
it by means of a stove above 30°, and it will remain liquid almost
indefinitely. On the other hand, lower its temperature and leave it
for one or two minutes at 10°, and germs will appear in the liquor;
prolong the exposure to this degree of heat and the number of these
spontaneously appearing germs, appearing in isolation, will rapidly
increase. On the other hand, you will observe that propagation by
filiation—that is to say, by extension from one to another—is almost
absent. The temperature of 10° is not favourable to that method of
generation; and we have just seen, in fact, that it is at a temperature
of about 70° that extension of crystallization from one to another
is best accomplished. The temperature of 70° was the optimum for
propagation by filiation. Inversely, the temperature of 10° is the
optimum for spontaneous generation. Above and below this optimum the
action is slower. We may count the centres of crystallization, which
slowly extend further and further, as in a microbic culture one counts
the colonies corresponding to the germs primitively formed. To sum
up, if there is an optimum for the formation of crystals, there is a
different optimum for their rapid extension.

_The Metastable and Labile Zones._—This phenomena is general. There
is for each substance a set of conditions (temperature, degree of
concentration, volume of the solution) in which the crystalline
individuals can be produced only by germs or by filiation. This is what
occurs for betol above the temperature of 30°. The body is then in what
Ostwald has called a _metastable_ zone. There is, however, for the same
body another set of circumstances more or less complete, in which its
gems appear simultaneously. This is what happens for betol at about the
temperature of 10°. These circumstances are those of the _labile zone_
or zone of spontaneous generation.

_Crystals of Glycerine._—We may go a step further. Let us suppose, with
L. Errera, that we have a liquid in a state of metastable equilibrium,
whose labile equilibrium is as yet unknown. This is what actually
occurs for a very widely known body, glycerine. We do not know under
what conditions glycerine crystallizes spontaneously. If we cool it,
it becomes viscous; we cannot obtain its crystals in that way. It was
not found in crystals until 1867. In that year, in a cask sent from
Vienna to London during winter, crystallised glycerine was found,
and Crookes showed these crystals to the Chemical Society of London.
What circumstances had determined their formation? We knew not then,
and we know not now. It may be observed that this case of spontaneous
generation of the crystals of glycerine has not remained the solitary
instance. M. Henninger has noted the accidental formation of glycerine
crystals in a manufactory in St. Denis.

It may be remarked that this crystalline species appeared, as living
species may have done, at a given moment in an environment in which a
favourable chance combined the necessary conditions for its production.
It is also quite comparable to the creation of a living species;
for having once appeared we have been able to perpetuate it. The
crystalline individuals of 1867 have had a posterity. They have been
sown in glycerine in a state of superfusion, and there they reproduced
themselves. These generations have been sufficiently numerous to
spread the species throughout a great part of Europe. M. Hoogewerf
showed a great flask full to the Dutch biologists who met at Utrecht
in 1891. M. L. Errera presented others in June 1899, to the Society of
Medical and Natural Sciences at Brussels. To-day the great manufactory
of Sarg & Co., of Vienna, is engaged in their production on a large
scale for industrial purposes.

Thus we are able to study this crystalline species of glycerine and to
determine with precision the conditions of its continued existence. It
has been shown that it does not resist a temperature of 18°, so that
if precautions were not taken to preserve it, a single summer would
suffice to annihilate all the crystalline individuals existing on the
surface of the globe, and thus the species would be extinguished.

_Possible Extinction of a Crystalline Species._—As these crystals
melt at 18°, this temperature represents the point of fusion of solid
glycerine or the point of solidification of liquid glycerine. But the
liquor does not solidify at all if its temperature falls below 18° C.,
as we well know, for it is at that temperature we use it. Nor does it
solidify at zero, nor even at 18° below zero; at 20°, for instance, it
merely thickens and becomes pasty. We only know glycerine, then, in a
state of superfusion, a fact which chemists have not learned without
amazement. Under these conditions, so analogous to the appearance of
a living species, to its unlimited propagation and to its extinction,
the mineral world offers a quite faithful counterpart to the animal
world. The living body illustrates here the history of the brute body
and facilitates its exposition. Inversely, the brute body in its
turn throws remarkable light on the subject of the living body, and
on one of the most serious problems relative to its origin, that of
spontaneous generation.

_Conclusion._—These facts lead to one conclusion. Until the concourse
of propitious circumstances favourable to their spontaneous generation
was brought about, crystals were obtained only by filiation. Until the
discovery of electro-magnetism, magnets were made only by filiation,
by means of the simple or double application of a pre-existing magnet.
Before the discovery which fable attributes to Prometheus, every new
fire was produced only by means of a spark from a pre-existing fire.
We are at the same historical stage as regards the living world,
and that is why, up to the present, there has never been formed a
single particle of living matter except by filiation, except by the
intervention of a pre-existing living organism.




BOOK V.

SENESCENCE AND DEATH.

 Chap. I. The different points of view from which death may
 be regarded.—Chap. II. Constitution of the organisms—Partial
 death—Collective death.—Chap. III. Physical and chemical
 characteristics of cellular death—Necrobiosis.— Chap. IV. Apparent
 perennity of complex individuals.—Chap. V. Immortality of the protozoa
 and of slightly differentiated cells.


We grow old and we die. We see the beings which surround us grow old
and disappear. At first we see no exceptions to this inexorable law,
and we consider it as a universal and inevitable law of nature. But
is this generalization well founded? Is it true that no being can
escape the cruel fate of old age and death, to which we and all the
representatives of the higher animality are exposed? Or, on the other
hand, are any beings immortal? Biology answers that, in fact, some
beings are immortal. There are beings to whose life no law assigns a
limit, and they are the simplest, the least differentiated and the
least perfect. Death thus appears to be a singular privilege attached
to organic superiority, the ransom paid for a masterly complexity.
Above these elementary, monocellular, undifferentiated beings,
which are protected from mortality, we find others, higher in their
organization, which are exposed to it, but with whom death seems but
an accident, avoidable in principle if not in fact. The anatomical
elements of this higher animal are a case in point. Flourens once tried
to persuade us that the threshold of old age might be made to recede
considerably, and there are biologists in the present day who give us
some glimpse of a kind of vague immortality. We may, therefore, ask our
readers to follow us in our examination of these re-opened if not novel
questions, and we shall explain the views of contemporary physiology as
to the nature of death, its causes, its mechanisms, and its signs.




CHAPTER I.

VARIOUS WAYS OF REGARDING DEATH.

 Different meanings of the word death—Physiological distinction between
 elementary and general death—Non-scientific opinions—The ordinary
 point of view—Medical point of view.—The signs of death are prognostic
 signs.


_Different Meanings of the Word Death._—An English philosopher has
asserted that the word we translate by “cause” has no less than
sixty-four different meanings in Plato and forty-eight in Aristotle.
The word “death” has not so many meanings in modern languages, but
still it has many. Sometimes it indicates an action which is taking
place, the action of dying, and sometimes a state, the state which
succeeds the action of dying. The phenomena it connotes are in the eyes
of many biologists quite different, according as we watch them in an
animal of complex organization, or on the other hand, in monocellular
beings, protozoa and protophytes.

_Physiological Distinction between Elementary Death and General
Death._—We distinguish the death of the anatomical elements,
_elementary death_, from the death of the individual regarded as
a whole, _general death_. Hence we recognize an _apparent death_,
which is an incomplete and temporary suspension of the phenomena of
vitality, and a _real death_, which is a final and total arrest of
these phenomena. When we consider it in its essential nature (assumed,
but not known) we look on it as the _contrary of life_, as did the
Encyclopædia, Cuvier, and Bichat; or we regard it with others either as
the consequence of life, or simply as the end of life.

_Non-scientific Opinions._—What is death to those outside the realm of
science? First of all we find the consoling solution given by those
who believe death to be the commencement of another life. We next find
ourselves involved in a confused medley, an infinite diversity of
philosophical doubt and superstition. “A leap into the unknown,” says
one. “Dreamless and unconscious night,” says another. And again, “A
sleep which knows no waking.” Or, with Horace, “the eternal exile,” or
with Seneca, annihilation. _Post mortem nihil; ipsaque mors nihil._

The idea which is constantly supervening in the midst of this conflict
of opinion is that of the _breaking up_ of the elements, the union
of which forms the living being. It has, as we shall see, a real
foundation which may perhaps receive the support of science. We shall
not find that the best way of defining death is to say that it consists
of the “dissolution of the society formed by the anatomical elements,
or again, in the dissolution of the consciousness that the individual
possesses of himself—_i.e._, of the existence of this society.” It is
the rupture of the social bond. The old idea of dispersion is a variant
of the same notion. But the ancients evidently could not understand,
as we do, the nature of these elements which are associated to form
the living being, and which are liberated or dispersed by death.
We, as biologists, can see microscopical organic unity with a real
objective existence. The ancients were thinking of spiritual elements,
of principles, of entities. To the Romans, who may be said to have held
that there are three souls, death was produced by their separation
from the body. The first, the breath, the _spiritus_, mounting towards
celestial regions (_astra petit_); the second, the _shade_, regaining
on the surface of the earth and wandering around the tombs; the third,
the _manes_, descending to the lower regions. The belief of the Hindoos
was slightly different. The body returned to the earth, the breath to
the winds, the fire of the glance to the sun, and the ethereal soul to
the world of the pure. Such were the ideas of mortal dispersion formed
by ancient humanity.

Modern science takes a more objective point of view. It asks by
what facts, by what observable events death is indicated. Generally
speaking, we may say that these facts interrupt an interior state of
things which was life and to which they put an end. Thus death is
defined by life. It is the cessation of the events and of the phenomena
which characterize life. We must, therefore, know what life is to
understand the meaning of death. How wise was Confucius when he said to
his disciple, Li-Kou:—“If we do not know life, how can we know death?”
According to biology there are two kinds of death because there are two
kinds of life; elementary life and death correspond just as general
life and death do, and this is where scientific opinion diverges from
commonly received opinion.

What cares the man who reasons as most human beings do, about this life
of the anatomical elements of his body, the existence and the silent
activity of which are in no way revealed to him. What does their death
matter to him? To him there is but one poignant question, that of being
separated or not being separated from the society of his fellows. Death
is no longer to feel, no longer to think; it is the assurance that one
will never feel, one will never think again. Sleep, dreamless sleep,
is already in our eyes a kind of transient death; but, when we fall
asleep we are sure of waking again. There is no awaking from the sleep
of death. But that is not all. Man knows that death, this dreamless
sleep that knows no waking, will be followed by the dissolution of his
body. And what a dissolution will there be for the body, the object
of his continual care! Remember the description of Cuvier—the flesh
that passes from green to blue and from blue to black, the part which
flows away in putrid venom, the other part which evaporates in foul
emanations, and finally, the few ashes that remain, the tiny pinch of
minerals, saline or earthy, which are all that is left of that once
animated masterpiece.

_The Popular View._—To the man afraid of death it seems, in the
presence of so great a catastrophe, that the patient analysis of the
physiologist scrupulously noting the succession of phenomena and
explaining their sequence is uninteresting. He will only attach the
slightest importance to knowing that vestiges of vitality remain in
this or that part of his body, if they do not re-establish in every
part the _status quo ante_. He cares not to hear that a certain time
after the formal declaration of his death his nails and his hair will
continue to grow, that his muscles will still have the useless faculty
of contraction, that every organ, every tissue, every element, will
oppose a more or less prolonged resistance to the invasion of death.

_Medical View._—It is, however, these very facts and details, this
why and wherefore, which interest the physiologist. The state of
mind of the doctor in this respect, again, is different. When, for
instance, the doctor declares that such and such a person is dead,
he is really making not so much a statement of fact as a prediction.
How many elements are still living and will be capable of new birth
in this corpse that he has before his eyes? That is not what he asks
himself, nor is it what we should ask of him. He knows, besides, that
all these partial survivals will be extinguished and will never find
the conditions necessary to reviviscence, and that the organization
will never be restored to its primal activity; and this is what he
affirms. The fear of premature burial which haunts so many imaginations
is the fear of an error in the prediction. It is to avoid this that
practical medicine has devoted so much of its attention to the
discovery of a _certain_—and early—sign of death. By this we understand
the discovery of a _certain prognostic sign of general death_. We want
a prognostic sign enabling us to assert that the life of the brain is
now extinguished and will never be reanimated. And yet there are in
that organism many elements which are still alive. Many others even
may be born anew if we could give them suitable conditions which they
no longer meet with in the animal machine now thrown out of gear.
What finer example could we give than the experiment of Kuliabko, the
Russian physiologist, who kept a man’s heart working and beating for
eighteen hours after the official verification of his death.




CHAPTER II.

THE PROCESS OF DEATH.

 Constitution of organisms.—Partial lives.—Collective life.—The
 rôle of apparatus.—Death by lesion of the major apparatus.—The
 vital tripod.—Solidarity of the anatomical elements.—Humoral
 solidarity.—Nervous solidarity.—Independence and subordination of the
 anatomical elements.


_Partial Lives._ _Collective Life._—With the exception of the
physiologist, no one, neither he who is ignorant nor he who is
intellectual, nor even the doctor, troubles his head about the life
or the death of the element, although this is the basis, the real
foundation, of the activity manifested by the social body and by its
different organs. The life of the individual, of the animal, depends
on these elementary partial lives just as the existence of the State
depends upon that of its citizens. To the physiologist, the organism
is a federation of cellular elements unified by close association.
Goethe compared them to a “multitude”; Kant to a “nation”; and others
have likened them to a populous city the anatomical elements of which
are the citizens, and which possesses an individuality of its own. So
that the activity of the federated organism may be discussed in each
of its parts, and then it is _elementary life_, or in its totality,
and then it is _general life_. Paracelsus and Bordeu had a glimpse
of this truth when they considered a life appropriate to each part
(_vita propria_) and a collective life, the life of the whole (_vita
communis_). In the same way we must distinguish the _elementary death_,
which is the cessation of the vital phenomena in the isolated cell,
from the _general death_, which is the disappearance of the phenomena
which characterised the collectivity, the totality, the federation, the
nation, the city, the whole in so far as it is a unit.

These comparisons enable us to understand how general life depends on
the partial lives of each anatomical citizen. If all die, the nation,
the federation, the total being clearly ceases to exist. This city
has an enormous population—there are thirty trillion cellules in the
body of man; it is peopled with absolutely sedentary citizens, each
of which has its fixed place, which it never leaves, and in which
it lives and dies. It must possess a system of more or less perfect
arrangements to secure the material life of each inhabitant. All have
analogous requirements: they feed very much the same; they breathe in
the same way; each in fact has its profession, industry, talents, and
aptitudes by which it contributes to social life, and on which, in its
turn, it depends. But the process of alimentation is the same for all.
They must have water, nitrogenous materials and analogous ternaries;
the same mineral substances, and the same vital gas, oxygen. It is no
less necessary that the wastes and the egesta, very much alike in every
respect, should be carried off and borne away in discharges arranged so
as to free the whole system from the inconvenience, the unhealthiness,
and the danger of these residues.

_Secondary Organization in Organs._—That is why, as we said above, the
secondary organizations of the economy exist:—the digestive apparatus
which prepares the food and enables it to pass into the blood, into the
lymph, and finally into the liquid medium which bathes each cell and
constitutes its real medium; the respiratory apparatus which imports
the oxygen and exports the gaseous excrement, carbonic acid; the heart
and the circulatory system which distributes through the system the
internal medium, suitably purified and recuperated. The organization
is dominated by the necessities of cellular life. This is the law of
the city, to which Claude Bernard has given the name of the _law of the
constitution of organisms_.

_Death by Lesion of the Major Organs. Vital Tripod._—Thus we understand
what life is, and at the same time what is the death of a complex
living being. The city perishes if its more or less complicated
mechanisms which look after its revictualling and its discharge are
seriously affected at any point. The different groups may survive for
a more or less lengthy period, but progressively deprived of the means
of food or of discharge, they are finally involved in the general
ruin. If the heart stops, there is a universal famine; if the lungs
are seriously injured, we are asphyxiated; if the principal organ of
discharge, the kidney, ceases to perform its allotted task, there is a
general poisoning by the used-up and toxic materials retained in the
blood.

We understand how the integrity of the major organs,—the heart, the
lungs, the kidney,—is indispensable to the maintenance of existence. We
understand that their lesion, by a series of successive repercussions,
involves universal death. We always die, said the doctors of old,
because of the failure of one of these three organs, the heart, the
lungs, or the brain. Life, they said in their inaccurate language,
depends upon these as upon three supports. Hence the idea of the _vital
tripod_. But it is not only this trio of organs which maintain the
organism; the kidney and the liver are no less important. In different
degrees each part exercises its action on the rest. Life is based in
reality on the immense multitude of living cells associated for the
formation of the body; on the thirty trillion anatomical elements,
each part is more or less necessary to all the rest, according as the
bond of solidarity is drawn more or less closely in the organism under
consideration.

_Death and the Brain._—There are indeed more noble elements charged
with higher functions than the rest. These are the nervous elements.
Those of the brain preside over the higher functions of animality,
sensibility, voluntary movement, and the exercise of the intellect. The
rest of the nervous system forms an instrument of centralization which
establishes the relations of the parts one with the other and secures
their solidarity. When the brain is stricken and its functions cease,
man has lost the consciousness of his existence. Life seems to have
disappeared. We say of a man in this plight that he no longer lives,
thus confusing general life with the cerebral life which is its highest
manifestation. But the man or the animal without a brain lives what may
be called a vegetative life. The human anencephalic foetus lives for
some time, just as the foetus which is properly formed. Observation
always shows that this existence of the other parts of the body cannot
be sustained indefinitely in the absence of that of the brain. By a
series of impulses due to the solidarity of the grouping of the parts,
the injury received by the brain affects by repercussion the other
organs, and leads in the long run to the arrest of elementary life in
all the anatomical elements. The death of the whole is then complete.

Doctors have therefore a two-fold reason for saying that the brain
may cause death. The death of the brain suppresses the highest
manifestation of life, and, in the second place, by a more or less
remote counter stroke, it suppresses life in all the rest of the system.

_Death is a Process._—Besides, the fact is general. The death of one
part always involves the death of the rest—_i.e._, universal death. A
living organism cannot be at the same time alive and a cemetery. The
corpses cannot exist side by side with the living elements. The dead
contaminates the living, or in some other way involves it in its ruin.
Death is propagated; it is a progressive phenomenon which begins at one
point and gradually is extended to the whole. It has a beginning and a
duration. In other words, the death of a complex organism is a process.
And further, the end of a simple organism, of a protozoan, of a cell,
is itself a process infinitely more shortened.

The very perfection of the organism is therefore the cause of its
fragility. It is the degree of solidarity of the parts one with another
which involves the one set in the catastrophe of the rest, just as in
a delicate piece of mechanism the derangement of a wheel brings nearer
and nearer the total breakdown. The important parts, the lungs, the
heart, the brain, suffer no serious alteration without the reflex being
felt throughout. But there are also wheels less evident, the integrity
of which is scarcely less necessary.

_The Solidarity of the Anatomical Elements._—The cause of the mortal
process—_i.e._, of the extension and the propagation of an initial
destruction—is therefore to be found in the solidarity of the parts
of the organism. The closer it is the greater do the chances of
destruction become, for the accident which has happened to one will by
repercussions affect the others.

Now the solidarity of the parts of the organism may be carried out in
two ways; there is a _humoral solidarity_ and a _nervous solidarity_.

_Humoral Solidarity._—Humoral solidarity is realized by the mixture
of humours. All the liquids of the organism which have lodged in the
interstices of the elements and which soak the tissues, are in contact
and in relation of exchange one with another, and through the permeable
wall of the small vessels they are in relation with the blood and the
lymph.

All the liquid atmospheres which surround the cells and form their
ambient medium have intercommunication. A change having taken place in
one cellular group, and therefore in the corresponding liquid, modifies
the medium of the further or nearer groups, and therefore these groups
themselves.

_Nervous Solidarity._—But the real instrument of the solidarity of the
part is the nervous system. Thanks to it in the living machine the
component activities of the cellular multitude restrain and control
one another. Nervous solidarity makes of the complex being not a mob
of cells, but a connected system, an individual in which the parts are
subordinated to the whole and the whole to the parts; in which the
social organism has its rights just as the individual has his rights.
The whole secret of the vital functional activity of the complex
being is contained in these two factors:—the independence and the
subordination of the elementary lives. General life is the harmony of
the elementary lives, their symphony.

_Independence and Subordination of the Anatomical Elements._—The
independence of the anatomical elements results from the fact that
they are the real depositaries of the vital properties, the really
active components. On the other hand the subordination of the parts
to the whole is the very condition of the preservation of form in
animals and plants. The architecture which is characteristic of
them, the morphological plan which they realize in their evolutive
development which they are ever preserving and repairing, form a
striking proof of this. This dependence in no way contradicts the
autonomy of the elements. For when with Claude Bernard and Virchow
we study the circumstances we see that the element accommodates
itself to the organic plan without violence to its nature. It behaves
in its natural place as it would behave elsewhere, if elsewhere it
were to meet around it the same liquid medium which at once is a
stimulant and a food. This at least is the conclusion we may draw from
experiments on transplanting, or on animal and vegetable grafting.
Neither the neighbouring elements, nor the whole system act on it at
a distance by a kind of mysterious induction, according to the ideas
of the vitalists, in order to regulate the activity of the element.
They contribute solely to the composition of the liquid atmosphere
which bathes it. They intervene in order to provide it with a
certain environment whose very characteristic physical and chemical
constitution regulates its activity. This constitution may be some day
imitated by the devices of experiment. When that result is achieved
the anatomical element will live in isolation exactly as it lives in
the organic association, and the mysterious bond which causes its
solidarity with the rest of the economy will become intelligible. In
fact, we may defer more or less the maturity of this prophecy, but
there is no doubt that we are daily nearing its fulfilment.

The general life of the complex being is therefore the more or less
perfect synergy, the _ordered process_ of elementary lives. General
death is the destruction of these partial lives. The nervous system,
the instrument of this harmony of the parts, represents the social
bond. It keeps most of the partial elements under its sway, and is
thus the intermediary of their relations. The closer this dependence,
the higher the development of the nervous apparatus, and the better,
also, is assured the universal solidarity and therefore the unity of
the organism. Cellular federation assumes the characteristic of a
unique individuality in proportion to the development of this nervous
centralization. With an ideal perfect nervous system the correlation
of the parts would also attain perfection. As Cuvier said: “None could
experience change without a change in the rest.”

But no animal possesses this extreme solidarity of the parts of the
living economy. It is a philosopher’s dream. It is the dream of Kant,
to whom the perfect organism would be “a teleological system,” a system
of reciprocal ends and means, a sum total of parts each existing for
and by the rest, for and by the whole. An organism so completely
connected would be unlikely to live. In fact, living organisms show
a little more freedom in the interplay of their parts. Their nervous
apparatus fortunately does not attain this imaginary perfection; their
unity is not so rigorous. The idea of individuality, of individual
existence, is therefore not absolute but relative. There are all
degrees of it according to the development of the nervous system. What
the man in the street and the doctor himself understand by death is the
situation created by the stopping of the general wheels, the brain, the
heart, and the lungs. If the breath leaves no trace on the glass held
to the mouth, if the beating of the heart is no longer perceptible by
the hand which touches or the ear which listens, if the movement and
the reaction of sensitiveness have ceased to be manifest, these signs
make us conclude that it is death. But this conclusion, as we have said
before, is a prognostic rather than a judgment of fact. It expresses
the belief that the subject will certainly die, and not that it is from
this moment dead. To the physiologist the subject is only on the way to
die. The process has started. The only real death is when the universal
death of all the elements has been consummated.




CHAPTER III.

PHYSICAL AND CHEMICAL CHARACTERS OF CELLULAR DEATH. NECROBIOSIS.
GROWING OLD.

 Characteristic of elementary life—Changes produced by death in the
 composition and the death of the cell—Schlemm; Loew; Bokorny; Pflüger;
 A. Gautier; Duclaux—The processive character of death—Accidental
 death—Necrobiosis—Atrophy—Degeneration—So-called natural
 death—Senescence—Metchnikoff’s theory of senescence—Objections.


Elementary death is nothing but the suppression in the anatomical
elements of all the phenomena of vitality.

_Characteristics of Elementary Life._—The characteristic features of
elementary life have been sufficiently fixed by science. First of
all, there is _morphological unity_. All the living elements have
an identical morphological composition. That is to say that life is
only accomplished and sustained in all its fulness in organic units
possessing the anatomical constitution of the cell, with its cytoplasm
and its nucleus, constituted on the classical type. In the second
place, there is _chemical unity_. The constituent matter, the matter of
which the cell is built up, diverges but little from a chemical type—a
proteid complex, with a hexonic nucleus, and from a physical model
which is an emulsion of granulous, immiscible liquids, of different
viscosities. The third character consists in the possession of a
_specific form_ acquired, preserved, and repaired by the element.
The fourth character, and perhaps the most essential of all, is _the
property of growth_ or _nutrition_ with its consequence, namely, a
relation of exchanges with the external medium, exchanges in which
oxygen plays considerable part. Finally, there is a last property,
that of _reproduction_, which in a certain measure is a necessary
consequence of the preceding,—_i.e._, of growth.

These five vital characters of the elements are most in evidence
in cells living in isolation, in microscopical beings formed of a
single cell, protophytes and protozoa. But we find them also in
the associations formed by the cells among one another—_i.e._, in
ordinary plants and animals, multicellular complexes, called for this
reason metaphytes and metazoa. Free or associated, the anatomical
elements behave in the same way—feed, grow, breathe, digest in the
same manner. As a matter of fact, the grouping of the cells, the
relations, proximity and contiguity, which they assume, introduce
some variants into the expression of the common phenomena; but these
slight differences cannot disguise the essential community of the vital
processes.

The majority of physiologists, following Claude Bernard, admit as
valent and convincing the proof that the illustrious experimenter
furnished of this unity of the vital processes. There are, however, a
few voices crying in the wilderness. M. Le Dantec is one. In his new
theory of life he amplifies and exalts the differences which exist
between the elementary life of the proteids and the associated life of
the metazoa. In them he can see nothing but contrasts and deviations.

If this is elementary life, let us ask what is _elementary
death_—_i.e._, the death of the cell. And in this connection let us
ask the questions which we have to examine in the case of animals high
in organization, and of man himself. What are the characteristics
of elementary death? When the cell dies, is its death preceded by a
growing old or senescence? What are the preliminary signs and the
acknowledged symptoms?

_Changes Produced by Death._—The state of death is only truly realized
when the fundamental properties of living matter enumerated above have
entirely disappeared. We must follow step by step this disappearance in
all the anatomical elements of the metazoan.

Now the properties of the cell are connected with the physical and
chemical organization of living matter. For them to disappear entirely,
this organization must be destroyed as far as all that is essential in
it is concerned. We cannot admit with the vitalists that there is any
material difference between the dead and the living, and that only an
immaterial principle which has escaped into the air distinguishes the
corpse from the animated being. In fact, the external configuration may
be almost preserved, and the corpse may bear the aspect and the forms
of the preceding state. But this appearance is deceptive. Something in
reality has changed. The structure, the chemical composition of the
living substance, have undergone essential changes. What are these
changes?

_Physical Changes._—Certain physiologists have endeavoured to determine
them. Klemm, a botanist, pointed out in 1895 the physical changes
which characterize the death of vegetable cells—loss of turgescence,
fragmentation of the protoplasm, the formation of granules, and the
appearance of vacuoles.

_Chemical Changes._—O. Loew and Bokorny laid great stress in 1886 and
1896 on the chemical changes. The living protoplasm according to them
is an unstable proteid compound. A slight change would detach from the
albuminoid molecule a nucleus with the function of aldehyde, and at the
same time would transform an amido-group into an amido-group. This
would suffice for the transition of the protoplasm from the living to
the dead state. This theory is based on the fact that the compounds
which exercise a toxic action on the living cell, without acting
chemically on the dead albumin, are easily fixed by the aldehydes; and
on the fact that many of them, which attack simultaneously the living
albuminoids and the dead albumin, easily combine with the amido-group.

E. Pflüger, a celebrated German scientist, has considered living matter
as an albumin spontaneously decomposable, the essential nucleus of
which is formed by cyanogen. Its active instability would be due to the
penetration into the molecule of the oxygen which fixes on the carbon
and separates it from the nitrogen. Armand Gautier has not confirmed
this view. Duclaux (1898) has stated that the difference between the
living and the dead albumin would be of a stereochemical order.

_Progressive Character of Death. Accidental Death._—We have seen that
in general the disappearance of the characteristics of vitality is not
instantaneous, at least in the natural course of things, in complex
organisms. It is the end of a more or less rapid process. But death
is not instantaneous in the isolated anatomical element any more than
it is in the protozoan or protophyte. We must have recourse to very
violent devices of destruction to kill the cell at a blow, to leave
absolutely nothing of its organization existing. The protoplasm of
yeast when violently crushed by Büchner still possessed the power of
secreting soluble ferments. A powerful action, a very high temperature,
is necessary to obtain the result. _A fortiori_, the difficulty
increases in the case of complex organisms, all of whose living
elements cannot be attacked at the same moment by the destructive
cause. A mechanical action, capable of destroying at one blow all the
living parts of a complex being, of an animal, of a plant, must be of
almost inconceivable power. The blow of a Nasmyth hammer would not be
strong enough.

The chemical alteration produced by a very toxic substance distributed
throughout the blood, and thus brought into contact with each element,
would produce a disorganization which, however rapid it were, could not
be called instantaneous. And the same holds good of physical agents.

But these are not the processes of nature under normal circumstances.
They are accidents or devices. We shall leave on one side their
consideration and we shall only deal here with the natural processes of
the organism.

Imagine it placed in a medium appropriate to its needs and following
out without intervening complications the evolution assigned to it by
its constitution. Experiment tells us that this natural evolution in
every case known to us ends in death. Death supervenes sooner or later.
For beings higher in organization, which we can bring into closer
and closer resemblance to man, we find that they die of disease,
by accident, or of old age. And as disease is an accident, we may
naturally ask if what we call old age is not also a disease.

However that may be, the mortal process, being never instantaneous, has
a duration, a beginning, a development, an end—in a word, a history.
It constitutes an intermediary phase between perfect life and certain
death.

_Necrobiosis._ _Atrophy._ _Degeneration._—The process according to
the circumstances may be shortened or prolonged. When death is the
result of violence events are precipitated. The physical and chemical
transformations of the living matter constitute a kind of acute
alteration called by Schultze and Virchow _necrobiosis_. According
to the pathologists, there are two kinds of _necrobiosis_:—that by
_destruction_, by _simple atrophy_, which causes the anatomical
elements to disappear gradually without undergoing appreciable
modifications; and _necrobiosis by degeneration_, which transforms the
protoplasm into fatty matter into calcareous matter, into granulations
(fatty degeneration, calcification, granulous degeneration). There is
no disagreement as to the causes of this necrobiosis. They are always
accidental; they originate in external circumstances:—the insufficiency
of the alimentary materials, of water, of oxygen; the presence in the
medium of real poisons destroying the organized matter; the violent
intervention of physical agents, heat, electricity; the reflex on the
composition of the cellular atmosphere of a violent attack on some
essential organ, the heart, the lungs, the kidneys.

_Senescence._ _Old Age._—In a second category we must place the
mortal processes, slow in their movement, in which we cannot see the
intervention of clearly accidental and abnormal disturbing agents.
Death appears to be the termination of a breaking-up proceeding by
insensible degrees in consequence of the progressive accumulation
of very small inappreciable perturbations. This slow breaking up
is adequately expressed by the term—growing old, or senescence.
The alterations by which it is betrayed in the cell are especially
_atrophic_, but they are also accompanied, however, by different
forms of degeneration. An extremely important question arises on this
subject, and that is whether the phenomena of senility have their cause
in the cell itself, if they are inevitably found in its organization,
and therefore if old age and death are natural and necessary phenomena.
Or, on the other hand, should we consider them as due to a progressive
alteration of the medium, the character of which would be accidental
although frequent or habitual? This, in a word, is the problem which
has so often engaged the attention of philosophical biologists. Are old
age and death natural and inevitable phenomena?

The recent experiments of Loeb and Calkins, and all similar
observations, tend to attribute to the phenomenon of growing old the
character of a remediable accident. But the remedy has not been found,
and the animal finally succumbs to these slow transformations of its
anatomical elements. We then say that it _dies of old age_.

_Metchnikoff’s Theory of Senescence. Objections._—Metchnikoff has
proposed a theory of the mechanism of this general senescence. The
elements of the conjunctive tissue, phagocytes, macrophages, which
exist everywhere around the specialized and higher anatomical elements
would destroy and devour them as soon as their vitality diminishes,
and would take their place. In the brain, for example, it would be the
phagocytes which, attacking the nervous cellules, would disorganize the
higher elements, incapable of defending themselves. This substitution
of the conjunctive tissue, which only possesses vegetative properties
of a low order, for the nervous tissues, which possesses very high
vegetative properties, results in an evident breaking-up. The gross
element of violent and energetic vitality stifles the refined and
higher element.

This expulsion is a very real fact. It constitutes what is called
senile sclerosis. But the active _rôle_ attributed to it by Metchnikoff
in the process of degeneration is not so certain. An expert observer
in the microscopic study of the nervous system, M. Marinesco, does not
accept this interpretation as far as the senescence of the elements of
the brain is concerned. Diminution of the cell, the decrease in the
number of its stainable granulations, chromatolysis, the formation of
inert, pigmented substances—all these phenomena which characterize the
breaking-up of the cerebral cells would be accomplished, according to
this observer, without the intervention of the conjunctive elements,
the phagocytes.

The characteristic of extensive and progressive process presented
by death necessitates in a complex organism, which is a prey to it,
the existence side by side of living and dead cells. Similarly, in
the organism which is growing old, there are young elements and
elements of every age side by side with senile elements. As long as
the disorganization of the last has not gone too far, they may be
rejuvenated. All we have to do is to restore to them an appropriate
ambient medium. The whole question is one of knowing and being able
to realize, for this or that part which we wish to reanimate and to
rejuvenate, the very special or very delicate conditions that this
medium must fulfil. As we have said, success is attained in this
respect as far as the heart is concerned, and this is why we are able
to reanimate and to revive the heart of a dead man. It is hoped that
ideas along these lines will extend with the progress of physiology.

After this sketch of the conditions and of the varieties of cellular
death we must return to the essential problem which is engaging the
curiosity of biologists and philosophers. Is death unavoidable,
inevitable? Is it the necessary consequence of life itself, the
inevitable issue, the inevitable end?

There are two ways of endeavouring to solve this question of the
inevitability of death. The first is to examine popular observation,
practised, so to speak, unintelligently and without special
precautions. The second is to analyze everything we know relative to
the conditions of elementary life.




CHAPTER IV.

THE APPARENT PERENNITY OF COMPLEX INDIVIDUALS.

 Millenary trees—Plants with a definite rhizome—Vegetables
 reproduced by cuttings—Animal colonies—Destruction due to extrinsic
 causes—Difficulty of interpretation.


Popular opinion teaches us that living beings have only a transient
existence, and as a poet has said: “Life is but a flash between two
dark nights.” But, on the other hand, simple observation shows us, or
appears to show us, beings whose duration of existence is far longer,
and practically illimitable.

_Millenary Trees._—We know of trees of venerable antiquity. Among these
patriarchs of the vegetable world there is a chestnut tree on Mount
Etna which is ten centuries old, and an ivy in Scotland which is said
to be thirty centuries old. Trees of 5000 years old are not absolutely
unknown. We may mention among those of that age the famous dragon
tree[21] at Orotava, in the island of Teneriffe. Two other examples are
known in California—the pseudo-cedar, or _Tascodium_, at Sacramento,
and a _Sequoïa gigantea_. We know that the olive tree may live 700
years. There are cedars 800 years old and oaks of the age of 1,500
years.

 [21] Lately destroyed in a storm. [Tr.]

_Plants with a Rhizome._—Vegetable species of almost unlimited
duration of life are known to botanists. Such, for instance, are plants
with a definite rhizome, such as colchicum. Autumnal colchicum has a
subterranean root, the bulb of which pushes out every year fresh axes
for a new bloom; and as each of these new axes stretches out an almost
constant length, a botanist once set himself the singular problem of
discovering how long it would take such a foot, if suitably directed,
to travel round the world.

_Vegetables Reproduced by Cuttings._—Vegetables reproduced by slips
furnish another example of living beings of indefinite duration. The
weeping willows which adorn the banks of sheets of water in the parks
and gardens throughout the whole of Europe have sprung, directly or
indirectly, from slips of the first _Salix Babylonica_ introduced to
the West. May it not be said that they are the permanent fragments of
that one and the same willow?

_Animal Colonies._—These examples, as well as those furnished to
zoologists by the consideration of the polypi which have produced by
their slow growth the reefs, or _atolls_, of the Polynesian seas,
do not, however, prove the perennity of living beings. The argument
is valueless, for it is founded upon a confusion. It turns on the
difficulty that biologists experience in defining the individual. The
oak and the polypus are not simple individuals, but associations of
individuals, or, to use Hegel’s expression, the nations of which we see
the successive generations. We give to this succession of generations
a unique existence, and our reasoning comes to this, that we confer on
each present citizen of this social body the antiquity which belongs to
the whole.

_Destruction of the Social Individual due to Extrinsic Causes._—As
for the destruction, the death of this social individual, of this
hundred-year-old tree, it seems indeed that there is no ground for
considering it a natural necessity. We find the sufficient reason of
its usual end in the repercussion on the individual of external and
contingent circumstances. The cause of the death of a tree, of an oak
many centuries old, is to be found in the ambient conditions, and not
in some internal condition. Cold and heat, damp and dryness, the weight
of the snow, the mechanical action of the rain, of hail, of winds
unchained, of lightning; the ravages of insects and parasites—these are
what really work its ruin. And further, the new branches, appearing
every year and increasing the load the trunk has to bear, increase the
pressure of the parts, and make more difficult the motion of the sap.
But for these obstacles, external, so to speak, to the vegetable being
itself, it would continue indefinitely to bloom, to fructify, and as
each spring returned to show fresh buds.

_Difficulty of Interpretation._—In this as in all other examples we
must know the nature of the beings that we see lasting on and braving
the centuries. Is it the individual? Is it the species? Is it a living
being, properly so called, having its unity and its individuality,
or is it a series of generations succeeding one another in time and
extending in space? In a word, the question is one of knowing if we
have to do with a real tree or with a genealogical tree. We are just
as uncertain when we deal with animals. What is the being that lasts
on—a series of generations or an individual? This doubt forbids us to
draw any conclusion from the observation of complex beings. We must
therefore return from them to the _elementary being_; and we must
examine it from the point of view of perennity or of vital decay. Let
us then ask the questions that we have already examined with reference
to animals high in organization and to man himself. Is the death of the
cell an inevitable characteristic? Are there any cells, protophytes,
protozoa, which are immortal?




CHAPTER V.

THE IMMORTALITY OF THE PROTOZOA.

 Impossibility of life without evolution—Law of increase and
 division—Immortality of the protozoa—Death, a phenomenon of adaptation
 which has appeared in the course of the ages—The infusoria—The
 death of the infusoria—Two kinds of reproduction—The caryogamic
 rejuvenescence of Maupas—Calkins on rejuvenescence—Causes of
 senescence—Impossibility of life without evolution.


We take into account, _a priori_, the conditions that must be fulfilled
by the monocellular being in order to escape the inevitability of
evolution, of the succession of ages, of old age, and of death. It must
be able indefinitely to maintain itself in a normal régime, without
changing, without increasing, maintaining its constant morphological
and chemical composition, in an environment vast enough for it to
be unaltered by the borrowings or the spendings resulting from its
nutrition—_i.e._, it must remain constant in the presence of the
constant being. We might conceive of a nutrition perfect enough, of
exchanges exact enough, and regular enough, for the state of things to
be indefinitely maintained. This would be absolute permanence realized
in the vital mobility.

_The Law of Growth and Division._—This model of a perfect and
invariable machine does not exist in nature. Life is incompatible with
the absolute permanence of the dimensions and the forms of the living
organism.

In a word, it is a rigorous law of living nature that the cell can
neither live indefinitely without growth, nor grow indefinitely without
division.

Why is this so? Why is there this impossibility of a regular régime in
which the cell would be maintained in magnitude without diminution or
increase? Why has nutrition as a necessary consequence the growth of
the element? This is what we do not positively know.

Things are so. It is an irreducible fact, peculiar to the protoplasm, a
characteristic of the living matter of the cell. It is the fundamental
basis of the property of generation. That is all we can say about it.
Real living beings have therefore inevitably an evolution. They are not
unchangeable. In its simple form this evolution consists in the fact
that the cell grows, divides, and diminishes by this division, begins
the upward march which ends in a new division. And so on.

_Immortality of the Protozoa._—It may happen, and it does happen
in fact, that this series of acts is repeated indefinitely at any
rate unless an accidental cause should interrupt it. The animal thus
describes an indefinite curve, constituted by a series of indentations,
the highest point of which corresponds to the maximum of size, and the
lowest point to the diminution which succeeds the division. This state
of things has no inevitable end if the medium does not change. The
being is immortal.

In fact, the compound beings of a single cell, protophytes and
protozoa, the algae and the unicellular mushrooms, at the minimum stage
of differentiation, escape the necessity of death. They have not, as
Weismann remarks, the real immortality of the gods of mythology, who
were invulnerable. On the contrary, they are infinitely vulnerable,
fragile, and perishable; myriads die every moment. But their death is
not inevitable. They succumb to accidents, never to old age.

Imagine one of these beings placed in a culture medium favourable to
the full exercise of its activities, and, moreover, wide enough in
its extent to be unaffected by the infinitely small quantities of
material which the animal may take from it or expel into it. Suppose,
for example, it is an infusorian in an ocean. In this invariable medium
the being lives, increases, and grows continually. When it has reached
the limits of a size fixed by its specific law, it divides into two
parts, which are indistinguishable the one from the other. It leaves
one of its halves to colonize in its neighbourhood, and it begins its
evolution as before. There is no reason why the fact should not be
repeated indefinitely, since nothing is changed, either in the medium
or in the animal.

To sum up. The phenomena which take place in the cell of the protozoan
do not behave as a cause of check. The medium allows the organism
to revictual and to discharge itself in such a way and with such
perfection that the animal is always living in a regular régime, and,
with the exception of its growth and later on of its division, there is
nothing changed in it.

_Death a Phenomenon of Adaptation—It appeared in the Course of the
Ages._—This immortality belongs in principle to all the protista which
are reproduced by simple and equal division. If it be remarked that
these rudimentary organisms endowed with perennity are the first living
forms which have shown themselves on the surface of the globe, and
that they have no doubt preceded many others—the multicellular, for
instance, which are liable, on the contrary, to decay—the conclusion
is obvious:—Life has long existed without death. Death has been a
phenomenon of adaptation which has appeared in the course of the ages
in consequence of the evolution of species.

_The Death of Infusoria._—We may ask ourselves at what moment in the
history of the globe, at what period of the evolution of its fauna,
this novelty, death, made its appearance. The celebrated experiments of
Maupas on the senescence of the infusoria seem to authorize us to give
a precise answer to this question. By means of these experiments we are
led to believe that death must have appeared at the same time as sexual
reproduction. Death became possible when this process of generation was
established, not in all its plenitude, but in its humblest beginnings,
under the rudimentary forms of unequal division and of conjugation.
This happened when the infusoria began to people the waters.

_The Two Modes of Multiplication._—Infusoria are, in fact, capable of
multiplication by simple division. It is true to say that in addition
to this resource, the only one which interests us here, because it
is the only one which confers immortality, they possess another.
They present and exercise under certain circumstances a second mode
of reproduction, caryogamic conjugation. It is a rather complicated
process in its detail, but it is definitively summed up as the
temporary pairing of two individuals, which are otherwise very much
alike, and which cannot be distinguished as male and female. They
become closely united on one of their faces; they reciprocally exchange
a semi-nucleus which passes into the conjoint individual; and then
they separate. But infusoria can be prevented from this conjunction by
regularly isolating them immediately after their birth. Then they grow,
and are constrained after a lapse of time to divide according to the
first method.

Maupas has shown that the infusoria could not accommodate themselves
to this régime indefinitely; they could not go on dividing for ever.
After a certain number of divisions they show signs of degeneration
and of evident decay. The size diminishes, the nuclear organs become
atrophied, all the activities fail, and the infusorian perishes.
It succumbs to this kind of senile atrophy unless it is given an
opportunity of conjugation with another infusorian in the same plight.
In this act it then derives new strength, it grows larger, attains its
proper size, and builds up its organs once more. Conjugation gives it
life, youth, and immortality.

_Alimentary Rejuvenescence._—Recent observations due to Mr. G. N.
Calkins, an American biologist, and confirmed by other investigators,
have shown that this method of rejuvenescence is not the only one,
and is not even the most efficacious. Conjugation has no mysterious,
specific virtue. The infusoria need not be married in order to be
rejuvenated. It is sufficient to improve their food. In the case of
the “tailed” paramecium we may substitute beef broth and phosphates
for conjugation. Calkins observed 665 consecutive generations without
blemish, without exhaustion, and without any sign of old age. Plenty of
food and simple drugs have successfully resisted senility and the train
of atrophic degenerations which it involves.

_Causes of Senescence._—As for the causes of senescence which have
been remedied with such success, they are not exactly known. Calkins
thinks that senescence results from the progressive losses to the
organism of some substance essential to life. Conjugation or intensive
alimentation would act by building up again this necessary compound.
G. Loisel believes on the contrary that it is a matter of the
progressive accumulation of toxic products due to a kind of alimentary
auto-intoxication.




CHAPTER VI.

LETHALITY OF THE METAZOA AND OF DIFFERENTIATED CELLS.

 Evolution and death of metazoa.—Possible rejuvenescence of the
 differentiated cells by the conditions of the medium.—Conditions of
 the medium for immortal cells.—The immortal elements of metazoa.—The
 element in accidental and remediable death.—Somatic cells and sexual
 cells.


_Evolution and Death of Metazoa._—We have seen that the infusoria
are no longer animals in which material exchanges take place with
sufficient perfection, and in which cellular division, the consequence
of growth, is produced with sufficient precision and equality for
life to be carried on indefinitely in a perfect equilibrium in the
appropriate medium without alteration or check. _A fortiori_ we no
longer find the perfect regularity of nutritive exchange in the classes
above them. In a word, starting from this inferior group, there are
no animated beings in the state of existence which Le Dantec calls
“condition Iº of manifested life?” Living matter, instead of being
continually kept identical in conditions of identical media, is
modified in the course of existence. It becomes dependent on time. It
describes a declining trajectory; it experiences evolution, decay,
and death. Thus the fundamental condition of invariable youth and of
immortality fails in all metazoa. The vital wastes accumulate in all
through the insufficiency or the imperfection of nutritive absorption
or of excretion. Life decays; the organism progressively alters, and
thus is constituted that state of decrepitude by atrophy or chemical
modification which we call senescence, and which ends in death. To sum
up, old age and death may be attributed to cellular differentiation.

_Possible Alimentary Rejuvenescence of the Differentiated
Cells—Conditions of Medium._—We must add, however—as the teaching
of experiments in general and in particular as the teaching of the
experiments of Loeb and of Calkins—that a slight change of the
environment, made at the right time, is capable of re-establishing
equilibrium and of completely rejuvenating the infusorian. Senescence
has not in this case a definitive any more than an intrinsic character;
a modification in the composition of the alimentary medium will
successfully resist it. If we are allowed to generalize this result, it
may be said that senescence, the declining trajectory, the evolution
step by step down to death, are not for the cells considered in
isolation an inevitable and essentially inherent in the organism, and
a rigorous consequence of life itself. They preserve an accidental
character. In senescence and death there is no really natural, internal
cause, inexorable, and irremediable, as was claimed in the past by J.
Müller, and more recently by Cohnheim in Germany and Sedgwick Minot in
America.

_Conditions of the Medium for Immortal Cells._—As for the cells which
are less differentiated, the protophytes and the protozoa situated
one degree lower in the scale than the infusoria, we must admit the
possibility of that perfect and continuous equilibrium which would
save them from senile decrepitude. And it is quite understood that
this privilege remains subordinated to the perfect constancy of the
appropriate medium. If the latter changes, the equilibrium is broken,
the small insensible perturbations of nutrition accumulate, vital
activity decays, and in sole consequence of the imperfection of the
extrinsic conditions or of the medium, the living being finds itself
once more dragged down to decay and to death.

_Immortal Elements of the Metazoa._—All the preceding facts and
considerations refer to isolated cells, to monocellular beings.
But, and this is what makes these truths so interesting, they may
be extended to all cells grouped in collectivity—i.e., to all the
animals and living beings that we know. In the complicated edifice
of the organism, the anatomical elements, at any rate the least
differentiated, would have a continual brevet of immortality. Generally
speaking, this would be the case for the egg, for the sexual elements,
and perhaps, too, for the white globules of the blood, the leucocytes.
And, further, around each of these elements must be realized the
invariably perfect medium which is the necessary condition. This does
not take place.

_Elements in Accidental and Remediable Death._—As for the other
elements, they are like the infusoria, but without the resource of
conjugation. The ambient medium becomes exhausted and intoxicated
around each cell, in consequence of the accidents which happen to the
other cells. Each therefore undergoes progressive decay, and finally
they perish—the decay and destruction being perhaps in principle
accidental, but, in fact, they are the rule.

The different anatomical elements of the organism are more or less
sensitive to those perturbations which cause senescence, necrobiosis,
and death. There are some more fragile and more exposed. Some are more
resisting, and finally, there are some which are really immortal. We
have just said that the sexual cell, the ovum, is one. It follows that
the metazoan, man for instance, cannot entirely die. Let us consider
one of these beings. Its ancestors, so to speak, have not entirely
disappeared; each has left the fertile egg, the surviving element from
which has issued the being of which we speak; and when it in its turn
has developed, part of that ovum has been placed in reserve for a new
generation. The death of the elements is not therefore universal. The
metazoan is divided from the beginning into two parts. On the one
hand are the cells destined to form the body, _somatic_ cells. They
will die. On the other hand are the _reproductive_, or _germinal_, or
_sexual_ cells, capable of living indefinitely.

_Somatic and Sexual Cells._—In this sense we may say with Weismann
that there are two things in the animal and in man—the one mortal,
the _soma_ the body, the other immortal, the _germen_. These germinal
cells, as in the case of the protozoa we mentioned above, possess a
conditional immortality. They are imperishable, but on the contrary,
are fragile and vulnerable. Millions of ova are destroyed and are
disappearing every moment. They may die by accident, but never of old
age.

We now understand that if the protistae are immortal, it is because
these living beings, reduced to a single cell, accumulate in it the
compound characters of the somatic cell and germinal cell, and enjoy
the privilege which is attached to the latter.




CHAPTER VII.

MAN. THE INSTINCT OF LIFE AND THE INSTINCT OF DEATH.

 The miseries of humanity: 1. Disease; 2. Old age.—Old age considered
 as a chronic disease.—Its occasional cause.—3. The disharmonies of
 human nature; 4. The instinct of life and the instinct of death.


Man’s unhappy plight is the constant theme of philosophies and
religions. Without referring to its moral basis, it has a physical
basis due to four causes—the physical imperfection or disharmony of
nature, disease, old age, and death—or rather of three, for what we
call old age is perhaps a simple disease. These are the great sorrows
of man, the sources of all his woes. Disease attacks him, old age
awaits him, and death must tear him from all the ties which he has
formed. All his pleasures are poisoned by the certain knowledge that
they last but for a moment, that they are as precarious as his health,
his youth, and his life itself.


                             § 1. DISEASE.


Disease, frequent, constant, and inevitable as it is, is, however,
nothing but a fact outside the natural order. Its character is clearly
accidental, and it interrupts the normal cycle of evolution. Medical
observation teaches us, on the other hand, that the health of the body
reacts on that of the mind; and therefore man as a whole, moral and
physical, is affected by disease. Bacon described a diseased body as a
jailer to the soul, and the healthy body as a host. Pascal recognized
in diseases a principle of error. “They spoil our judgment and our
senses.”

I am not expressing a chimerical hope when I predict that science will
conquer disease. Medicine has at last issued from the contemplative
attitude of so many centuries; it has engaged in the struggle, and
signs of victory are already appearing. Disease is no longer the
mysterious power which it was impossible to escape. Pasteur gave to it
a body. The microbe can be caught. In the words of Schopenhauer, an
alteration of the atmosphere so slight that it is impossible to detect
it by chemical analysis may bring on cholera, yellow fever, the black
plague, diseases which carry off thousands of men; and a slightly
greater alteration might endanger all life. The at once mysterious
and terrifying spectacle of the cholera at Berlin in 1831 had such
an effect on the philosopher that he fled in terror to Frankfort. It
has been said that this was the origin of his pessimism, and that
but for this he would have continued to teach idealistic philosophy
in some Prussian university. L. Hartmann, another celebrated leader
of contemporary pessimism, has also said that disease will always be
beyond the resources of medicine. Facts have given the lie to these
sombre prognostics. The microbic origin of most infectious diseases has
been recognized. The discovery of attenuated poisons and serums has
diminished their gravity. An exact knowledge of methods of contagion
has enabled us to erect against them impregnable barriers. Cholera,
yellow fever, the plague knock in vain at our doors. Diphtheria,
dreaded by every mother, has partially lost its deadly character.
Puerperal fever and blindness of the new-born child are tending to
disappear. Legend tells us that Buddha in his youth, frightened at
the sight of a sick man, expressed in his father’s presence the wish
to be always in perfect health and sheltered from disease. The King
answered: “My son! you are asking the impossible.” But it is towards
the realization of this impossibility that we are on our way. Science
is repelling the attacks of disease.


                             § 2. OLD AGE.


Old age is another sorrow of humanity. The stage of existence in
which the strength grows less and never grows greater, and in which
a thousand infirmities appear, is not, however, a stage universal in
animals. Most of them die without our perceiving in them any apparent
signs of senile weakness. On the other hand, some vegetables exhibit
these signs. Some trees are old; but it is in birds and mammals that
this decay, with the train of evils which accompanies it, becomes a
very marked phase of existence. In man to debility is added a bodily
shrinkage, grey hairs, withered skin, and the wearing out and loss of
teeth. The exhausted and atrophied organism offers a favourable field
to all intercurrent diseases and to every cause of destruction. It is
this discrepitude which makes old age so hateful. All desire to be old,
said Cicero; and when they are old, they say that old age has come
quicker than they expected. La Bruyère expresses it in an apothegm,
“We want to grow old, and we fear old age.” One would like longevity
without old age.

But can life be prolonged without senility diminishing its value?
Metchnikoff thinks it can. He more or less clearly catches a glimpse
of a normal evolution of existence which would make it longer and
nevertheless exempt from senile decay.

It is remarkable that we have so few scientific data on the old age of
man, and we have still fewer on that of animals. The biologist knows
no more than the layman. The old age of the dog is betrayed by its
gait. Its coat loses its lustre, just as in disease. The hair whitens
around the forehead and the muzzle. The teeth grow blunt and drop out.
The character loses its gaiety and becomes gloomy; the animal becomes
indifferent. He ceases to bark, and often becomes blind and deaf.

It is admitted that senile degeneration is due to an alteration
affecting most of the tissues. The cells, the special anatomical
elements of the liver, the kidney, and the brain are reduced by atrophy
and degeneration. At the same time, the conjunctive woof which serves
them as a support develops, on the contrary, at the expense in a
measure of the higher elements. For this reason the tissues harden.
We know that the flesh of old animals is tough. We know in pathology
that this is happening to the tissues. It is due to growth, to injury
to the active and important elements, to the elements of support of
the organs. They form a tissue sometimes called packed tissue, to
show its secondary rôle with reference to the elements which are
deposited in it. This kind of degeneration of the organs is known as
sclerosis. It constitutes the characteristic lesion of a certain number
of chronic diseases; and these diseases are serious, for the stifling
of the characteristic elements by the less important elements of the
conjunctive or packed tissue results in the more or less complete
reduction or suppression of the function.

The blood vessels also undergo this transformation, and what we
may call universal trouble and danger ensue. This sclerosis of the
arteries, this arterio-sclerosis, not only deprives the walls of the
blood vessels of the suppleness and elasticity which are necessary for
the proper irrigation of the organs, but it makes them more fragile.
Thus it becomes a cause of hemorrhage, which is a very serious matter
as far as the brain and lungs are concerned.

It is remarkable that the alteration of the tissues during old age
should be exactly similar to this. This is inferred from the few
researches that have been made on the subject—from those of Demange in
1886, of Merkel in 1891, and finally from the researches of Metchnikoff
himself. It is a generalized sclerosis. As its consequence we have
the lowering of the proper activity of the organs and the danger of
cerebral hemorrhage created by arterio-sclerosis. The transformations
of the tissues in old men are therefore summed up in the atrophy of the
important and specific elements of the tissues, and their replacement
by the hypertrophied conjunctive tissue. This sclerosis is comparable
to that of chronic diseases; it is a pathological condition. Thus old
age, as we understand it, is a chronic disease and not a normal phase
of the vital cycle.

On the other hand, if we ask ourselves what is the origin of the
scleroses which engender chronic diseases, we find that they are due
to the action of various poisons, among which syphilitic poison and
the immoderate use of alcohol take the first place. These are also the
usual causes of senile degeneration. But there must be some other,
some very general cause to explain the universality of the process of
senescence. Metchnikoff thinks that he has found this cause in the
microbes which swarm in man’s digestive tube, particularly in the
large intestine. Their number is enormous. Strassburger has given
an approximate calculation, but words fail to express it. We have
to imagine a figure followed by fifteen zeros. This microbic flora
is composed of “bacilli” and of “cocci,” and comprises a third of
the rejected matter. It produces slow poisons, which, being at once
reabsorbed, pass into the blood and provoke the constant irritation
from which results arterio-sclerosis and the universal sclerosis of old
age. Instead of enjoying a healthy and normal old age, in which the
faculties of ripening years are preserved, we drag out a diminished
life, a kind of chronic disease, which is ordinary old age. This is
due, according to Metchnikoff, to the parasitism and the symbiosis
of microbic flora, lodged in a part of the economy in which it finds
all the conditions favourable to its prolific expansion. Such is the
specious theory, held to the verge of intrepidity, by which this
investigator explains the misery of our old age, and which inspires him
with the idea of a remedy. For his observations conclude with a régime,
a series of prescriptions by which the author fancies that life may be
lengthened and the evils of old age swept from our path. The dangerous
flora must be transformed into a cultivated and selected flora.
Although the organ in question may be of doubtful utility, and although
its existence, the legacy of atavic heredity, must be considered as
a disharmony of human nature, Metchnikoff does not go so far as to
propose that it should be cut away, and that we should call in surgery
to assist in making mankind perfect! But the rational means he proposes
will be endorsed by the most judicious students of hygiene; and their
effect, if it is not as wonderful as one hopes for, cannot fail to
ameliorate the conditions of old age and make it more vigorous.


                  § 3. DISHARMONIES IN HUMAN NATURE.


Another misery in the condition of man is due to the dissidencies
of his nature—that is to say, to his physical imperfections and the
discordancies which exist between the physiological functions and the
instincts which should regulate them.

This discordance reigns throughout the physical organism. The body of
man is not the perfect masterpiece it was once supposed to be. It is
encumbered with annoying inutilities, with rudimentary organs that have
neither rôle nor function, unfinished sketches which nature has left
in the different parts of his body. Such are the lachrymal caruncle, a
vestige of the third eyebrow in mammals; the extrinsic muscles of the
ear; the pineal gland of the brain, which is only the rudiment of an
ancestral organ; the third eye, or the Cyclopean eye of the saurians.
The list is interminable. Wiedersheim has counted in man 107 of these
abortive hereditary organs, the useless vestiges of organs useful
to our remote animal ancestors, atrophied in the course of ages in
consequence of modifications that have taken place in the external
medium.

These rudimentary organs are not only useless; they are often
positively harmful.

But the most serious discordance is that which exists between the
physiological functions and the instincts which regulate them. In a
well-regulated organism slowly developed by adaptation the instincts
and the organs alike should be in relation with the functions. All
really natural acts are solicited by an instinct, the satisfaction
of which is at once a need and a pleasure. The maternal instinct is
awakened at the proper moment in animals, and it disappears as soon as
the offspring requires no more assistance. A craving for milk is shown
in all newborn children, and often disappears at an early age.

Nature has endowed man as well as the other animals with peculiar
instincts, destined to preside over the different functions and to
ensure their accomplishment. And, at the same time, it has enabled him
in a measure to deceive those instincts and to satisfy them by other
means than the execution of the physiological acts with a view to which
they exist. Love and the instinct of reproduction exist in man before
the age of puberty. Canova felt the spur of love at the age of five.
Dante was in love with Beatrice at nine; and Byron, then scarcely
seven, was already in love with Maria Duff. On the other hand, puberty
has no necessary relation to the general maturity of the organism.

The family instinct is subject to the same aberrations. Man limits
the number of his children. The Turks of to-day follow the ancient
Greeks in the practice of abortion. Plato approved of the custom, and
Aristotle sanctioned its general prevalence. In the province of Canton
the Chinese of the agricultural classes kill two-thirds of their girl
children, and the same is done at Tahiti. All these customs co-exist
with the perfect love and tender care of the living children.

Because of these different discordancies the physical life of man is
insufficiently regulated by nature. Neither the physiological instinct,
nor the family instinct, nor the social instinct is, in general,
sufficiently imperative and precise. Hence, since the internal impulse
has not sufficient power, the necessity arises for a rule of conduct
exercising its influence from without. Philosophies, religions, and
legislation have provided for this. They have regulated man’s hygiene
and the carrying out of his different physiological functions. Their
control has, moreover, had its hygienic side. The scientific hygiene of
to-day has inherited their rôle.

The idea of the fundamental perversity of human nature is born of our
cognizance of its discordancies, unduly amplified and exaggerated. Soul
and body have been considered as distinctly discordant and hostile
elements. The body, the shroud of the soul, the temporary host, the
prison, the present source of miseries, has been subjected to every
kind of mortification. Asceticism has treated the body and all the
innate instincts as our mortal foes.

This suspicion, this depreciation of human nature was the great
error of the mystics. This view was as fatal as the inverse view
of pagan antiquity. The model of the perfect life according to
Greek philosophy is a life in conformity with nature. To aim at the
harmonious development of man was the precept of the ancient Academy,
formulated by Plato. The Stoics and the Epicureans had adopted the
same principle. Physical nature is considered as good. It gives us
the type, the rule, and the measure. The moral rule itself is exactly
appropriate to the physical nature. We may say that pagan morality was
hygiene, the hygiene of the soul and the body alike; the _mens sana in
corpore sano_ gave individual and social direction. The Rationalists,
the philosophers of the eighteenth century, such as Baron d’Holbach
and later W. Von Humboldt, Darwin, and Herbert Spencer, have adopted
analogous views. If these views have been contested, it is because of
the imperfections or aberrations of the natural instincts of man. Also,
if we wish to base individual family or social morality on the natural
instincts of man, it must be specified that these instincts are to be
regularized. We must necessarily appeal from the imperfect instincts of
the present to the perfected instincts of the future. Their perfection,
moreover, will only be a more exact approximation to the real nature of
man, and he, having avoided by the aid of science the accidents which
cause disease and senile decrepitude, will enjoy a healthy youth and an
ideal old age.

The reason of the discrepancies between instinct and function in man is
given by the natural history of his development. We know that man has
within him original sin—his long atavism. He has sprung, according to
the transformists, from a simian stock. He is a cousin, the successful
relation, of a type of antinomorphic monkeys, the chimpanzees. He
has “arrived,” they have remained undeveloped. Probably he had a
common ancestor with them, some dryopithecan of an extinct species.
From that type sprang a new type already on the way to progress, the
_Pithecanthropus erectus_. Finally, the anthropoid ancestor became
one fine day the father of a scion, clearly superior to himself, a
miraculously gifted being, man. Here, then, is no sign of the slow
evolution and gradual progress, which is the doctrine held at present
by Transformists. The Dutch botanist De Vries has shown us, in fact,
that nature does leap: _natura facit saltus_. There would thus be
crises, as it were, in the life of species. At certain critical epochs
considerable differences of a specific value appear in their offspring.
It is at one of these critical periods in the simian life that man
has appeared as the phenomenal child of an anthropoid. He was born
with a brain and an intellect superior to those of his humble parents;
and on the other hand, he has inherited from them an organization
which is only inadequately adapted to the new conditions of existence
created by the development of his sensitiveness and his brain power.
This intellect is not proportioned to his organization, which has not
developed at the same rate; it protests against the discordances which
adaptation has not yet had time to efface. But it will efface them in
the future.


         § 4. THE INSTINCT OF LIFE AND THE INSTINCT OF DEATH.


The greatest discrepancy of this kind is the knowledge of inevitable
death without the instinct which makes it longed for.

There are immortal animals. Man is not of the number. He belongs,
like all highly organized beings, to the class of beings which have
an end. They die from accident or from disease. They perish in the
struggle with other animals, or with microbes, or with external
conditions. There are certainly very few, if there are any, which die a
really natural death. And so it is with man. We see old men gradually
declining who appear to doze gently off into the last sleep, and become
extinguished without disease, like a lamp whose oil is exhausted. But
this is in most cases only apparently so. Besides the fact that the old
age to which they seemed to succumb is really a disease, a generalized
sclerosis, autopsy always reveals some lesion more or less directly
responsible for the fatal issue.

Man, like all the higher animals, is therefore subject to the law
of lethality. But while animals have no idea of death and are not
tormented by the sentiment of their inevitable end, man knows and
understands this destiny. He has with the animals the instinct of
self-preservation, the instinct of life, and at the same time the
knowledge and the fear of death. This contradiction, this discordance,
is one of the sources of his woes.

Whether it be an accident or the regular term of the normal cycle,
death always comes too soon. It surprises the man at a time when he
has not yet completed his physiological evolution; hence the aversion
and the terror it inspires. “We cannot fix our eyes on the sun or on
death,” said La Rochefoucauld. The old man does not regard death with
less aversion than the young man. “He who is most like the dead dies
with most regret.” Man knows that he is not getting his full measure.

Further, all the really natural acts are solicited by an instinct, the
satisfaction of which is a need and a joy. The need of death should
therefore appear at the end of life, just as the need of sleep appears
at the end of the day. It would appear, no doubt, if the normal cycle
of existence were fulfilled, and if the harmonious evolution were not
always interrupted by accident. Death would then be welcomed and longed
for. It would lose its horror. The instinct of death would replace at
the wished for moment the instinct of life. Man would pass from the
banquet of life with no other desire. He would die without regret,
“being old and full of days,” according to the expression used in the
Bible in the case of Abraham, Isaac, and Jacob. No doubt there are some
analogies to this in the insects which only assume the perfect form
for the purpose of procreation and immediately perish in their full
perfection. In these animals the approach of death is blended with the
intoxication of hymen. Thus we see some of them, the ephemerae, lose at
that moment the instinct of life and the instinct of self-preservation.
They allow themselves to be approached, taken, and seized, and make no
effort at flight.

But what is this full measure of life which is imparted to us?
Metchnikoff holds that the ages attributed to several persons in the
Bible are very probable. Abraham lived 175 years, Ishmael 137, Joseph
110, Moses 120. Buffon believed in the existence of a ratio between the
longevity of animals and the duration of their growth. He fixed it at
7:1. The animal whose development lasts two years would thus have 14
years of life. This law would give us 140 years, but the figure is too
high, and Flourens has reduced the ratio to that of 5:1, which would
still give us 100 years. Plato died in the act of conversation at 81;
Isocrates wrote his _Panathenaïcus_ at 94; Gorgias died in the full
possession of his intellect at 107.

To reach the end of the promised longevity we must neither count on the
elixir of life nor on the potable gold of the alchemists, nor on the
stone of immortality which did not prevent its inventor, Paracelsus,
from dying at the age of 58, nor on transfusion, nor on Graham’s
celestial bed, nor on King David’s gerocomy, nor on any nostrum or
remedy. _Contra vim mortis non est medicamen in hortis_, said the
Salernian school. What Feuchtersleben said is most true, “The art of
prolonging life consists in not cutting it short,” and it is a hygiene,
but a brilliant hygiene, such as that of which Metchnikoff traces us
the future lines, which will realize the desires of nature.

And now shall we find that physiology has solved the enigma proposed by
the Sphinx, and that it has answered these poignant questions:—Whence
do we come? whither do we go? what is the end of life? The end of life
is, to the physiologist as well as to Herbert Spencer, the tendency
towards an existence as full and as long as possible, towards a life
in conformity with real nature freed from the discordancies which
still remain; it is the accomplishment of the harmonious cycle of our
normal evolution. This ideal human nature, without discordancies, no
longer vitiated as it is at present but improved, will be the work of
time and science. Realized at last it will serve as a solid basis for
individual, family, and social morality. Healthy youth fit for action;
prolonged, adult age, the symbol of strength; normal old age, wise in
council, these would have their natural places in harmonious society.
“Great actions,” said one of old, “are not achieved by exertions
of strength, or speed, or agility, but rather by the prudence, the
authority, and the judgment which are found in a higher degree in old
age.” The old age of which Cicero here speaks is the ideal old age,
regular and normal, and not the premature, deformed, incapable and
egoistic old age which results from a pathological condition. At the
end of this full life, the old man being full of days, will crave for
the eternal sleep and will resign himself to it with joy....

Death, then, “the last enemy that shall be destroyed,” to use the
expression of St. Paul, will yield to the power of science. Instead of
being “the king of terrors,” it will become after a long and healthy
life, after a life exempt from morbid accidents, a natural and longed
for event, a satisfied need. Then will be realized the wish of the
fabulist:—

 “_I should like to leave life at this age, just as one leaves a
 banquet, thanking the host, and departing._”

Has this physiological solution of the problem of death the virtue
attributed to it by Metchnikoff? Is it as optimistic as he thinks
it is? The instinct of death supervening at the end of a normal and
well-filled cycle will no doubt facilitate to the aged their departure
on the great voyage. The wrench will no longer exist for the dead.
Will it not exist for those who are left behind? And since the instinct
of death can only exist about the time at which death is expected,
will the young man and the man of ripened years look with less horror
than to-day at the law which cannot be escaped, when they are in full
possession of the instinct of life, but warned of the inevitability of
death?




                           INDEX OF AUTHORS.


  Altmann, 258

  Anaxagoras, 34

  Aquinas, St. Thomas, 3, 19, 248

  Aristotle, 3, 15, 18, 143, 146, 307

  Armstrong, 295

  Atwater, 137


  Bacon, vi., 35, 346

  Baker, 233

  Balbiani, 161, 165, 191, 206-7, 257

  Bang, d’Yvor, 179

  Barthez, 3, 19, 24

  Beclard, 121

  Becquerel, 278

  Beijerinck, 193

  Benoit, 271

  Bernard, Claude, vi., 17, 27, 29, 32, 48, 50-4, 107, 109, 112, 119,
    148, 150-1, 171, 190-2, 194, 197, 204, 210, 214-218, 220 _et seq._,
    310, 318

  Bernoulli, John, 35, 73

  Bert, Paul, 194

  Berthelot, 91, 98, 128-130, 152, 204, 296

  Berthollet, 82

  Berzelius, 117

  Bichat, 3, 6, 20, 22, 27-30, 35, 55, 158, 170, 198, 308

  Blumenbach, 46

  Boë, Sylvius Le, 35-6

  Boerhaave, 35, 147, 245

  Bohr, 29-30

  Bokorny, 324

  Boltzmann, 265

  Bonnet, 23, 49

  Bordeu, 3, 10, 19, 22, 24, 312

  Borelli, 35

  Boscovitch, 37, 248

  Bose, 264

  Bossuet, 11

  Bouasse, 73, 264-5

  Boullier, 12

  Bourdeau, 237, 242

  Boussingault, 149

  Brandt, 257

  Bravais, 282

  Brillouin, 264, 273

  Brown, 266 _et seq._

  Brücke, 44

  Büchner, 325

  Buffon, 46, 254, 357

  Bunge, von, 3, 14

  Burdon, Sanderson, 176

  Busquet, 175

  Bütschli, 161-2, 175


  Cabanis, 245, 246

  Cailletet, 272

  Calkins, 327, 338

  Calvert, 271

  Candolle, 20

  Cardan, 261

  Carnot, 72-3, 89, 92 _et seq._, 101, 114, 121

  Charpy, 237, 271

  Chauffard, 3, 10, 11, 294

  Chauveau, 75, 103, 108, 123, 130, 145, 213

  Chevreul, 32

  Chossat, 152

  Cicero, 347, 359

  Clausius, 67, 88

  Cohn, 191, 252

  Cohnheim, 341

  Colding, 58 _note_, 90

  Colin, 52

  Comte, 189-190, 310

  Confucius, 309

  Coulomb, 76, 264, 273

  Crookes, 295, 302

  Cuvier, 3, 6, 27-8, 105, 120, 152, 190, 198, 308, 310, 319


  D’Alembert, 20, 59 _note_, 90, 92

  Dantec, Le, 48, 52, 55 _note_, 110, 148, 173, 198, 201, 203, 213, 216,
    220, 223 _et seq._, 231, 246, 261, 285, 296, 340

  D’Arsonval, 126

  Darwin, 3, 46, 167, 258, 354

  Dastre, A., 192, 198 _note_

  Davy, Sir Humphry, 61, 80

  Delafosse, 282

  Delage, 208

  Demange, 349

  Democritus, 34, 146

  Descartes, 3, 9, 35, 37, 40, 73, 91, 98

  Despretz, 126

  Diderot, 245, 246

  Drechsel, 183

  Dressel, 20

  Dubois-Reymond, 44, 58 _note_, 253

  Duclaux, 119, 137, 184, 324

  Dufour, 297

  Duguet, 264

  Duhem, 62, 264, 265

  Dulong, 126

  Dumas, 115, 149, 151-2


  Epicurus, 35, 146

  Ehrlich, 176

  Errera, 52, 193-4, 237, 153, 295, 302 _et seq._

  Euclid, v.


  Faye, 260

  Feuchterslehen, 358

  Flemming, 161

  Flourens, 20-1, 152, 208, 306, 358

  Fouillée, 242

  Fromann, 161

  Fuerth, 183


  Galen, 25, 55, 143

  Galeotti, 180

  Galileo, 73, 91, 98, 197, 241, 260

  Gardair, 19, 248

  Gautier, A., 3, 32, 36, 39, 176, 233, 324

  Gernez, 237, 288, 295 _et seq._

  Glisson, 27

  Goethe, 170, 312

  Gouy, 266, 268

  Grimaud, 19

  Gruber, 165, 206, 257

  Guignard, 161

  Guillaume, 237, 262, 264, 271, 277

  Guillemin, 237

  Guldberg, 83


  Harbermann, 183

  Haeckel, 3, 46, 164, 167, 246, 251

  Hales, 43

  Haller, 27

  Hamilton, Sir W. Rowan, 67

  Hammarsten, 180

  Hartmann, 276, 346

  Harvey, 43, 160

  Haüy, 282

  Hegel, 170, 331

  Heidenhain, 3, 29, 30-1

  Heitzmann, 161

  Helmholtz, 44, 56, 58, 67, 90, 97, 99, 252

  Helmont, van, 3, 21, 26, 33, 146, 250

  Henninger, 302

  Heraclitus, 34

  Hertwig, 167

  Hertz, 88

  Hess, 91, 98

  Hippocrates, 146

  Hirn, 126

  His, 46

  Hlasitwetz, 183

  Holbach, d’, 354

  Hoogewerf, 303

  Hopkinson, 271

  Humboldt, W. von, 354


  Ingenhousz, 115

  Izolet, 247


  Joule, 53 _note_, 90-1, 93, 133 _et seq._, 143, 152


  Kant, 312, 319

  Kaup, 213

  Kaufmann, 126

  Kelvin, Lord, 63, 67, 90, 92, 251-2, 264;
    and the idea of energy, 66

  Kepler, 29, 241

  Klemm, 323

  Koelliker, 160

  Kossel, 174, 179, 130-1, 136 _et seq._

  Kuhne, 45

  Kuhm, 216

  Kuliabko, 23, 311

  Kunstler, 157, 161-2, 175

  Kuppfer, 161


  Lammettrie, 147

  Lamarck, 46

  Lapparent, 284

  Lapicque, 140, 145

  Langley, 216

  Laplace, 43, 63, 126, 260

  Laulanié, 103

  Laurie, 271

  La Rochefoucauld, 356

  Lavoisier, 3, 28, 30, 36, 43, 65, 117, 121, 126, 128, 143, 176, 296

  Lea, 216

  Le Châtelier, 85, 92

  Lechatelier, H. and A., 271

  Lecocq de Boisbaudran, 295

  Leeuwenhoek, 232

  Lefèvre, 126

  Legallois, 21

  Leydig, 161-2

  Liebermeister, 136

  Liebig, 26, 53 _note_, 117

  Lilienfeld, 179, 247

  Locke, 23

  Lodge, 271

  Loeb, 43, 167, 327, 341

  Loew, 324

  Loisel, 339, 341

  Lorry, 21

  Longet, 52

  Lowitz, 297

  Loye, 192

  Ludwig, 44, 215


  Mach, 41, 62

  Magendie, 43, 143

  Magy, 37

  Malgaigne, 153

  Mallard, 284

  Marinesco, 231, 328

  Markel, 349

  Maspero, 3, 234

  Matthiesson, 271

  Maupas, 337

  Maxwell, 88

  Mayer, R., 56, 58, 89, 90, 97, 99, 101

  Mering, von, 133, 136

  Metchnikoff, 327 _et seq._

  Miescher, 174, 179

  Milne-Edwards, 152, 195

  Minot, 341

  Miura, 137

  Mori, 145

  Müller, 20, 27, 341

  Murato, 45


  Naegeli, 168

  Needham, 46

  Newton, 58 _note_, 70, 90-1, 93

  Noorden, van, 129, 137, 140, 210

  Nussbaum, 165, 206, 215, 217


  Obermeyer, 271

  Osmond, 237, 271

  Ostwald, 41, 62, 67, 85, 104, 237, 258, 289, 295 _et seq._


  Paracelsus, 26, 146, 312

  Pascal, 74, 161

  Pasteur, 53, 191, 222 _et seq._, 237, 250, 288, 346

  Payen, 151

  Persoz, 152

  Petit, 180

  Pettenkofer, 210

  Pfeffer, 175, 193

  Pflüger, 12, 56, 135, 144, 176, 210, 213

  Philpotts, 46

  Pictet, 233

  Pitcairn, 35

  Plato, 35, 307

  Plosz, 180

  Poincaré, 62

  Poisson, 63

  Preyer, 192, 252 _et seq._

  Priestley, 115

  Ptolemy, v.

  Pythagoras, 18


  Rauber, 237, 288

  Raulin, 191

  Regnault, 117

  Reinke, 3, 32

  Renan, 240

  Ribbert, 208

  Ribot, 247

  Riche, 271

  Richet, 50, 126, 140

  Richter, 252

  Rindfleisch, 4

  Roberts-Austen, 237, 271-2

  Robin, 62, 177

  Rosenthal, 126

  Rouvier, 160

  Roux, 46, 165

  Rubner, 129, 130, 140 _et seq._, 210

  Rumford, 80


  Sabatier, 242

  Sachs, 161, 194

  Salles-Guyon, 252

  Sanderson, Burdon, 176

  Scaliger, 241

  Schleiden, 159

  Schopenhauer, 346

  Schwartz, 162

  Schultze, 160, 326

  Schultzenberger, 174, 162 _et seq._

  Secchi, 88

  Seguin, 58 _note_, 90

  Senebier, 115

  Siven, 145

  Spallanzani, 43, 233

  Spencer, Herbert, 46, 247, 354, 358

  Spring, 272

  Stahl, 3, 9, 12, 35, 146

  Stammreich, 137

  Stead, 237

  Stohmann, 129, 130, 140

  Strassburger, 161, 350

  Swann, 159

  Swift, 262


  Tait, 53 _note_, 66

  Tammann, 237, 253, 295 _et seq._

  Thales, 34

  Thomson, Sir J. J., 279

  Tissot, 12

  Tomlinson, 264

  Trembley, 22, 206

  Tsuboï, 145

  Tylor, 8


  Verworn, 206, 252, 257

  Violette, 295

  Virchow, 318, 326

  Voit, 119, 133 _et seq._, 210

  Vries, de, 46, 258, 355

  Vulpian, 24


  Waage, 83

  Waller, 47, 206

  Wallerant, 282-3

  Warburg, 264

  Watt, 76

  Weismann, 46, 167, 336, 343

  Wertheim, 264

  Whitman, 46

  Widersheim, 351

  Wiedermann, 264

  Wiesner, 167

  Willis, 36, 147

  Winternitz, 126


  Yung, 233


  Zuntz, 133, 136, 210




                          INDEX OF SUBJECTS.


  Activity, functional and vital, 106 _et seq._, 217 _et seq._

  Aerobia, 193

  Age, old, Book v.

  Albumin, 178

  Albuminoids, 178

  Alcohol, 136

  Alimentation, 116 _et seq._

  Alloys, structure of, 273

  Anærobia, 193

  Animism, 6, 7, Chap. ii., _passim_

  Annealing, 275

  Apposition, 291

  Archeus, the, 25, 26, 33

  Arginin, 187

  Assimilation, law of functional, 110, 213

  Atomicities, satisfied, 185

  Atrophy, 326

  Attraction, energy of position, 64


  Balance, sheet, nutritive, 118

  Beliefs, primitive, 239

  Bioblasts, 253

  Biophors, 167

  Blas, the, 25, 33

  Blood, lavage of, 192

  Brain, and death, 315

  Butylic ferments, 193

  Butyric ferments, 193


  Calorie, 125 _note_

  Calorimeter, ice, 126;
    bomb, 128

  Caprice, of Nature, 45

  Cause, final, 45

  Cells, 48, 147;
    somatic and sexual, 343

  Cellular theory, 158 _et seq._

  Centrosome, 163

  Chromosome, 165

  Cicatrization, 287

  Complex, homogeneity of the, 245

  Conductibility, 26

  Consciousness, in brute bodies, 244 _et seq._

  Continuity, principle of, 242, 247

  Contractility, 26

  Contraction, energy of static and dynamic, 75

  Conservation, of energy, 58;
    of force, 58

  Crystals, 200 _et seq._, 237 _et seq._, 281 _et seq._

  Cytoplasm, 161 _et seq._


  Death, apparent, 232;
    senescence of, 305 _et seq._;
    cellular, 321 _et seq._

  Decentralization, 24

  Degeneration, 326

  Destruction, functional, 106;
    organic, 211;
    of living matter, 213

  Determinism, 49

  Digestion, of plants and animals, 152 _et seq._

  Direction, idea of, 16

  Dominants, 33, 39, 45

  Dyne, the, 71


  Effort, of force, 71

  Electrolysis, 272

  Energetics, 39, 56;
    laws of biological, 105 _et seq._, 229;
    alimentary, 116 _et seq._

  Energy, 37, Book ii., _passim_;
    origin of idea of, 57;
    theory of, 62;
    the only objective reality, 64-5;
    and kinetic conception, 67;
    mechanical, 69, 73;
    of contraction, 75;
    kinetic, 76, 83;
    potential, 76, 83;
    virtual, 77;
    of motion and position, 79;
    thermal, and its measurements, 80-2;
    chemical, and its measurements, 81-2;
    chemical and potential, 83;
    materialization of, 84;
    transformations of, 85 _et seq._;
    luminous, 86 _et seq._;
    conservation of, 90 _et seq._;
    capacity of conversion of, 93;
    in biology, 97;
    in living beings, 99 _et seq._;
    physical, 99 _et seq._;
    vital, 99 _et seq._

  Ether, 89

  Equivalence, law of, 91

  Excitability, 26-7


  Fatigue, of metals, 264

  Ferments, butylic and butyric, 193

  Filiation, 250

  Finalism, 43

  Food, a source of energy, 118 _et seq._;
    thermogenic and biothermogenic types of, 131 _et seq._;
    dynamogenic type of, 143;
    nitrogenous, 143;
    of animals and plants, 153 _et seq._

  Force, directive, 16 _et seq._, 32, 39, 48;
    vital, 45;
    an anthromorphic notion, 71;
    and work, 74;
    measurement of, 71;
    plastic, 143;
    plastic and morphoplastic forces, 208

  Form, specific, 199 _et seq._, 281

  Fruits, acids of, 136


  Gemmules, 167, 258

  Generation, spontaneous, 249 _et seq._, 294 _et seq._

  Globulin, 178

  Glycerine, crystals of, 302

  Glycogen, 108, 153 _et seq._

  Gramme, 71


  Heat, a mode of motion, 61;
    rôle of animal heat, 122;
    mechanical equivalent of, 81;
    an excretum, 114;
    a degraded form of energy, 88;
    converted into work, 92

  Heterogeneity, 38, 61

  Histones, 179, 182 _et seq._

  Horse-power, 75

  Hyaloplasm, 161


  Iatro-chemistry and mechanics, 34-5

  Idioblasts, 167

  Infusoria, death of, 337

  Instability, 188 _et seq._

  Instinct, of life and death, 345 _et seq._

  Intussusception, 291

  Invariant, mass the first, 63

  Irreversibility, of vital energies, 104

  Irritability, 27, 196 _et seq._

  Isodynamism, 142

  Isomorphism, 286


  Ka, the, 8

  Kilogrammetre, 72, 75;
    per second, 75

  Kilowatt, 76

  Kinetic theory, 39, 62

  Knot, the vital, 21


  Leucines, 183

  Leucites, 163

  Life, defined, 28;
    latent, 233;
    physico-chemical theory of, 36;
    elementary, 321

  Linin, 163


  Mass, and matter, 63

  Materialism, 34

  Matter, 37, 60, 62;
    and mass, 63;
    two kinds of, 63;
    life of, 236 _et seq._;
    brute and living, 249 _et seq._;
    organization and constitution of, 255 _et seq._;
    defined as extension, 64;
    conservation of, 65

  “Memory,” of metals, etc., 265

  Merotomy, 47

  Metabolism, 117

  Metazoa, evolution and death of, 340 _et seq._

  Meteoric cosmozoa, 252

  Micellar theory, 166 _et seq._

  Microcosms, 163

  Micro-organisms, culture of, 297

  Mitomes, 169

  Mobility of stars, 260

  Modality, twofold, of soul, 12

  Molecules, organic, 254

  Monism, 34, Chap. iv. _passim_, 63

  Montpellier, the school of, 35

  Motion, cause of, 71;
    kinetic conception of molecular, 263

  Morphogenesis, idea of, 46

  Movements, internal of bodies, 262;
    Brownian, 266 _et seq._

  Mutability, 80, 188 _et seq._;
    of living matter, 259 _et seq._;
    of brute bodies, 259 _et seq._


  Necrobiosis, 326

  Neo-vitalism, 15, 29, 32

  Neurility, 27

  Nickel, steels, 277

  Nisus _formativus_, 46

  Nous, the, 18, 239

  Nucleins, 179, 180 _et seq._

  Nucleo-albuminoids, 178;
    -proteids, 177 _et seq._

  Nucleus, 163 _et seq._;
    hexonic, 186

  Nutrition, directed, 205, 209 _et seq._, 227 _et seq._, 290 _et seq._


  Organogenesis, 282

  Organs, organization of, 314;
    death of, 315;
    perfect, 319


  Pangenes, 167

  Panspermia, 252

  Parameter, mass the mechanical, 63

  Phenomena, vital, 44, 51, 189;
    modes of motion, 61

  Photography, colour, 277

  Physiology, general, 56;
    cellular, 56

  Plants, and immortality, 330

  Plasomes, 167

  Plurivitalism, 25

  Power, 70, 75

  Principle, vital, 15 _et seq._

  Properties, vital, 25, 103

  Proteids, 178

  Protoplasm, 109 _et seq._, 175 _et seq._, 231 _et seq._;
    life in crushed, 257 _et seq._

  Protozoa, immortality of, 352 _et seq._

  Psyche, 239

  Pyrozoa, 253


  Regeneration, normal, 205;
    accidental, 206

  Reparation, mechanism of, 288

  Repose, functional, 109, 217 _et seq._

  Reserve stuff, 106 _et seq._, 212, 230 _et seq._

  Rachidian, soul, 12


  Senescence, 305 _et seq._

  Sensibility, in brute bodies, 244

  Solidarity, of anatomical elements, humoral and nervous, 317

  Soul, the, 7 _et seq._

  Space, 69

  Specificity, vital, 48

  Spireme, 165

  Spongioplasm, 162

  States, initial and final, 128

  Swelling, 167

  Synthesis, organizing, 109


  Tagmata, 169, 175

  Teleology, 43

  Tetanus, bacteria of, 193

  Thermogenesis, 140

  Time, 69

  Tonus, muscular, 119

  Trees, and immortality, 330 _et seq._

  Tripod, vital, 2, 314

  Turgescence, 168


  Universe, the, mechanical explanation of, 60;
    the end of the, 95

  Unity, chemical, of living beings, 173 _et seq._, 321;
    morphological, 321


  Vacuoles, 113

  Vibrion, septic, 193

  Vis viva, 73

  Vital properties, theory of, 29 _et seq._

  Vitalism, 6, 7, Chap. iii. _passim_;
    physico-chemical, 29

  Vitality, phenomena of, 216

  Vortex, vital, 105, 120, 229 _et seq._

  Vulcans, 26-7


  Weight, energy of position, 64;
    conservation of, 65;
    movement under action of, 271 _et seq._

  Work, 70, 72;
    and force, 74, 77;
    converted into heat, 92;
    physiological, 103


  Xanthic bases, 180


  Zones, metastable and labile, 301


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