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Title: Zoonomia, Vol. I
       Or, the Laws of Organic Life

Author: Erasmus Darwin

Release Date: April 25, 2005 [EBook #15707]

Language: English

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ZOONOMIA;

OR,

THE LAWS

OF

ORGANIC LIFE.

VOL. I.

_By ERASMUS DARWIN, M.D. F.R.S._

AUTHOR OF THE BOTANIC GARDEN.

       *       *       *       *       *

  Principio coelum, ac terras, camposque liquentes,
  Lucentemque globum lunae, titaniaque astra,
  Spiritus intus alit, totamque infusa per artus
  Mens agitat molem, et magno se corpore miscet.--VIRG. AEn. vi.

  Earth, on whose lap a thousand nations tread,
  And Ocean, brooding his prolific bed,
  Night's changeful orb, blue pole, and silvery zones,
  Where other worlds encircle other suns,
  One Mind inhabits, one diffusive Soul
  Wields the large limbs, and mingles with the whole.

       *       *       *       *       *

_THE SECOND EDITION, CORRECTED._

       *       *       *       *       *

LONDON:
PRINTED FOR. J. JOHNSON, IN ST. PAUL'S CHURCH-YARD.
1796.

Entered at Stationers' Hall.

       *       *       *       *       *

DEDICATION.

To the candid and ingenious Members of the College of Physicians, of the
Royal Philosophical Society, of the Two Universities, and to all those, who
study the Operations of the Mind as a Science, or who practice Medicine as
a Profession, the subsequent Work is, with great respect, inscribed by the
Author,

DERBY, May 1, 1794.

CONTENTS.

            _Preface._
  SECT. I.  _Of Motion._
       II.  _Explanations and Definitions._
      III.  _The Motions of the Retina demonstrated by Experiments._
       IV.  _Laws of Animal Causation._
        V.  _Of the four Faculties or Motions of the Sensorium._
       VI.  _Of the four Classes of Fibrous Motions._
      VII.  _Of Irritative Motions._
     VIII.  _Of Sensitive Motions._
       IX.  _Of Voluntary Motions._
        X.  _Of Associate Motions._
       XI.  _Additional Observations on the Sensorial Powers._
      XII.  _Of Stimulus, Sensorial Exertion, and Fibrous Contraction._
     XIII.  _Of Vegetable Animation._
      XIV.  _Of the Production of Ideas._
       XV.  _Of the Classes of Ideas._
      XVI.  _Of Instinct._
     XVII.  _The Catenation of Animal Motions._
    XVIII.  _Of Sleep._
      XIX.  _Of Reverie._
       XX.  _Of Vertigo._
      XXI.  _Of Drunkenness._
     XXII.  _Of Propensity to Motion. Repetition. Imitation._
    XXIII.  _Of the Circulatory System._
     XXIV.  _Of the Secretion of Saliva, and of Tears. And of the
            Lacrymal Sack._
      XXV.  _Of the Stomach and Intestines._
     XXVI.  _Of the Capillary Glands, and of the Membranes._
    XXVII.  _Of Hemorrhages._
   XXVIII.  _The Paralysis of the Lacteals._
     XXIX.  _The Retrograde Motions of the Absorbent Vessels._
      XXX.  _The Paralysis of the Liver._
     XXXI.  _Of Temperaments._
    XXXII.  _Diseases of Irritation._
   XXXIII.  ---- _of Sensation._
    XXXIV.  ---- _of Volition._
     XXXV.  ---- _of Relation._
    XXXVI.  _The Periods of Diseases._
   XXXVII.  _Of Digestion, Secretion, Nutrition._
  XXXVIII.  _Of the Oxygenation of the Blood in the Lungs and Placenta._
    XXXIX.  _Of Generation._
       XL.  _Of Ocular Spectra._

       *       *       *       *       *

TO

ERASMUS DARWIN,

ON HIS WORK INTITLED

ZOONOMIA,

_By DEWHURST BILSBORROW._

       *       *       *       *       *

  HAIL TO THE BARD! who sung, from Chaos hurl'd
  How suns and planets form'd the whirling world;
  How sphere on sphere Earth's hidden strata bend,
  And caves of rock her central fires defend;
  Where gems new-born their twinkling eyes unfold,               5
  And young ores shoot in arborescent gold.
    How the fair Flower, by Zephyr woo'd, unfurls
  Its panting leaves, and waves its azure curls;
  Or spreads in gay undress its lucid form
  To meet the sun, and shuts it to the storm;                   10
  While in green veins impassion'd eddies move,
  And Beauty kindles into life and love.
    How the first embryon-fibre, sphere, or cube,
  Lives in new forms,--a line,--a ring,--a tube;
  Closed in the womb with limbs unfinish'd laves,               15
  Sips with rude mouth the salutary waves;
  Seeks round its cell the sanguine streams, that pass,
  And drinks with crimson gills the vital gas;
  Weaves with soft threads the blue meandering vein,
  The heart's red concave, and the silver brain;                20
  Leads the long nerve, expands the impatient sense,
  And clothes in silken skin the nascent Ens.
    Erewhile, emerging from its liquid bed,
  It lifts in gelid air its nodding head;
  The lights first dawn with trembling eyelid hails,            25
  With lungs untaught arrests the balmy gales;
  Tries its new tongue in tones unknown, and hears
  The strange vibrations with unpractised ears;
  Seeks with spread hands the bosom's velvet orbs.
  With closing lips the milky fount absorbs;                    30
  And, as compress'd the dulcet streams distil,
  Drinks warmth and fragrance from the living rill;--
  Eyes with mute rapture every waving line,
  Prints with adoring kiss the Paphian shrine,
  And learns erelong, the perfect form confess'd,               35
  Ideal Beauty from its mother's breast.
    Now in strong lines, with bolder tints design'd,
  You sketch ideas, and portray the mind;
  Teach how fine atoms of impinging light
  To ceaseless change the visual sense excite;                  40
  While the bright lens collects the rays, that swerve,
  And bends their focus on the moving nerve.
  How thoughts to thoughts are link'd with viewless chains,
  Tribes leading tribes, and trains pursuing trains;
  With shadowy trident how Volition guides,                     45
  Surge after surge, his intellectual tides;
  Or, Queen of Sleep, Imagination roves
  With frantic Sorrows, or delirious Loves.
    Go on, O FRIEND! explore with eagle-eye;
  Where wrapp'd in night retiring Causes lie:                   50
  Trace their slight bands, their secret haunts betray,
  And give new wonders to the beam of day;
  Till, link by link with step aspiring trod,
  You climb from NATURE to the throne of GOD.
  --So saw the Patriarch with admiring eyes                     55
  From earth to heaven a golden ladder rise;
  Involv'd in clouds the mystic scale ascends,
  And brutes and angels crowd the distant ends.

TRIN. COL. CAMBRIDGE, _Jan._ 1, 1794.

       *       *       *       *       *

REFERENCES TO THE WORK.

          _Botanic Garden._ Part I.

  Line 1.  Canto I.  l. 105.
  ---- 3.  ---- IV.  l. 402.
  ---- 4.  ---- I.  l. 140.
  ---- 5.  ---- III.  l. 401.
  ---- 8.  ---- IV.  l. 452.
  ---- 9.  ---- I.  l. 14.


          _Zoonomia._

  ---- 12.  Sect. XIII.
  ---- 13.  ---- XXXIX. 4. 1.
  ---- 18.  ---- XVI. 2. and XXXVIII.
  ---- 26.  ---- XVI. 4.
  ---- 30.  ---- XVI. 4.
  ---- 36.  ---- XVI. 6.
  ---- 38.  ---- III. and VII.
  ---- 43.  ---- X.
  ---- 44.  ---- XVIII. 17.
  ---- 45.  ---- XVII. 3. 7.
  ---- 47.  ---- XVIII. 8.
  ---- 50.  ---- XXXIX. 4. 8.
  ---- 51.  ---- XXXIX the Motto.
  ---- 54.  ---- XXXIX. 8.

       *       *       *       *       *

PREFACE.

       *       *       *       *       *

The purport of the following pages is an endeavour to reduce the facts
belonging to ANIMAL LIFE into classes, orders, genera, and species; and, by
comparing them with each other, to unravel the theory of diseases. It
happened, perhaps unfortunately for the inquirers into the knowledge of
diseases, that other sciences had received improvement previous to their
own; whence, instead of comparing the properties belonging to animated
nature with each other, they, idly ingenious, busied themselves in
attempting to explain the laws of life by those of mechanism and chemistry;
they considered the body as an hydraulic machine, and the fluids as passing
through a series of chemical changes, forgetting that animation was its
essential characteristic.

The great CREATOR of all things has infinitely diversified the works of his
hands, but has at the same time stamped a certain similitude on the
features of nature, that demonstrates to us, that _the whole is one family
of one parent_. On this similitude is founded all rational analogy; which,
so long as it is concerned in comparing the essential properties of bodies,
leads us to many and important discoveries; but when with licentious
activity it links together objects, otherwise discordant, by some fanciful
similitude; it may indeed collect ornaments for wit and poetry, but
philosophy and truth recoil from its combinations.

The want of a theory, deduced from such strict analogy, to conduct the
practice of medicine is lamented by its professors; for, as a great number
of unconnected facts are difficult to be acquired, and to be reasoned from,
the art of medicine is in many instances less efficacious under the
direction of its wisest practitioners; and by that busy crowd, who either
boldly wade in darkness, or are led into endless error by the glare of
false theory, it is daily practised to the destruction of thousands; add to
this the unceasing injury which accrues to the public by the perpetual
advertisements of pretended nostrums; the minds of the indolent become
superstitiously fearful of diseases, which they do not labour under; and
thus become the daily prey of some crafty empyric.

A theory founded upon nature, that should bind together the scattered facts
of medical knowledge, and converge into one point of view the laws of
organic life, would thus on many accounts contribute to the interest of
society. It would capacitate men of moderate abilities to practise the art
of healing with real advantage to the public; it would enable every one of
literary acquirements to distinguish the genuine disciples of medicine from
those of boastful effrontery, or of wily address; and would teach mankind
in some important situations the _knowledge of themselves_.

There are some modern practitioners, who declaim against medical theory in
general, not considering that to think is to theorize; and that no one can
direct a method of cure to a person labouring under disease without
thinking, that is, without theorizing; and happy therefore is the patient,
whose physician possesses the best theory.

The words idea, perception, sensation, recollection, suggestion, and
association, are each of them used in this treatise in a more limited sense
than in the writers of metaphysic. The author was in doubt, whether he
should rather have substituted new words instead of them; but was at length
of opinion, that new definitions of words already in use would be less
burthensome to the memory of the reader.

A great part of this work has lain by the writer above twenty years, as
some of his friends can testify: he had hoped by frequent revision to have
made it more worthy the acceptance of the public; this however his other
perpetual occupations have in part prevented, and may continue to prevent,
as long as he may be capable of revising it; he therefore begs of the
candid reader to accept of it in its present state, and to excuse any
inaccuracies of expression, or of conclusion, into which the intricacy of
his subject, the general imperfection of language, or the frailty he has in
common with other men, may have betrayed him; and from which he has not the
vanity to believe this treatise to be exempt.

       *       *       *       *       *

ZOONOMIA.

       *       *       *       *       *

SECT. I.

OF MOTION.

The whole of nature may be supposed to consist of two essences or
substances; one of which may be termed spirit, and the other matter. The
former of these possesses the power to commence or produce motion, and the
latter to receive and communicate it. So that motion, considered as a
cause, immediately precedes every effect; and, considered as an effect, it
immediately succeeds every cause.

The MOTIONS OF MATTER may be divided into two kinds, primary and secondary.
The secondary motions are those, which are given to or received from other
matter in motion. Their laws have been successfully investigated by
philosophers in their treatises on mechanic powers. These motions are
distinguished by this circumstance, that the velocity multiplied into the
quantity of matter of the body acted upon is equal to the velocity
multiplied into the quantity of matter of the acting body.

The primary motions of matter may be divided into three classes, those
belonging to gravitation, to chemistry, and to life; and each class has its
peculiar laws. Though these three classes include the motions of solid,
liquid, and aerial bodies; there is nevertheless a fourth division of
motions; I mean those of the supposed ethereal fluids of magnetism,
electricity, heat, and light; whose properties are not so well investigated
as to be classed with sufficient accuracy.

_1st._ The gravitating motions include the annual and diurnal rotation of
the earth and planets, the flux and reflux of the ocean, the descent of
heavy bodies, and other phaenomena of gravitation. The unparalleled sagacity
of the great NEWTON has deduced the laws of this class of motions from the
simple principle of the general attraction of matter. These motions are
distinguished by their tendency to or from the centers of the sun or
planets.

_2d._ The chemical class of motions includes all the various appearances of
chemistry. Many of the facts, which belong to these branches of science,
are nicely ascertained, and elegantly classed; but their laws have not yet
been developed from such simple principles as those above-mentioned; though
it is probable, that they depend on the specific attractions belonging to
the particles of bodies, or to the difference of the quantity of attraction
belonging to the sides and angles of those particles. The chemical motions
are distinguished by their being generally attended with an evident
decomposition or new combination of the active materials.

_3d._ The third class includes all the motions of the animal and vegetable
world; as well those of the vessels, which circulate their juices, and of
the muscles, which perform their locomotion, as those of the organs of
sense, which constitute their ideas.

This last class of motion is the subject of the following pages; which,
though conscious of their many imperfections, I hope may give some pleasure
to the patient reader, and contribute something to the knowledge and to the
cure of diseases.

       *       *       *       *       *

SECT. II.

EXPLANATIONS AND DEFINITIONS.

    I. _Outline of the animal economy._--II. 1. _Of the sensorium._ 2. _Of
    the brain and nervous medulla._ 3. _A nerve._ 4. _A muscular fibre._ 5.
    _The immediate organs of sense._ 6. _The external organs of sense._ 7.
    _An idea or sensual motion._ 8. _Perception._ 9. _Sensation._ 10.
    _Recollection and suggestion._ 11. _Habit, causation, association,
    catenation._ 12. _Reflex ideas._ 13. _Stimulus defined._

       *       *       *       *       *

    As some explanations and definitions will be necessary in the
    prosecution of the work, the reader is troubled with them in this
    place, and is intreated to keep them in his mind as he proceeds, and to
    take them for granted, till an apt opportunity occurs to evince their
    truth; to which I shall premise a very short outline of the animal
    economy.

       *       *       *       *       *

I.--1. The nervous system has its origin from the brain, and is distributed
to every part of the body. Those nerves, which serve the senses,
principally arise from that part of the brain, which is lodged in the head;
and those, which serve the purposes of muscular motion, principally arise
from that part of the brain, which is lodged in the neck and back, and
which is erroneously called the spinal marrow. The ultimate fibrils of
these nerves terminate in the immediate organs of sense and muscular
fibres, and if a ligature be put on any part of their passage from the head
or spine, all motion and perception cease in the parts beneath the
ligature.

2. The longitudinal muscular fibres compose the locomotive muscles, whose
contractions move the bones of the limbs and trunk, to which their
extremities are attached. The annular or spiral muscular fibres compose the
vascular muscles, which constitute the intestinal canal, the arteries,
veins, glands, and absorbent vessels.

3. The immediate organs of sense, as the retina of the eye, probably
consist of moving fibrils, with a power of contraction similar to that of
the larger muscles above described.

4. The cellular membrane consists of cells, which resemble those of a
sponge, communicating with each other, and connecting together all the
other parts of the body.

5. The arterial system consists of the aortal and the pulmonary artery,
which are attended through their whole course with their correspondent
veins. The pulmonary artery receives the blood from the right chamber of
the heart, and carries it to the minute extensive ramifications of the
lungs, where it is exposed to the action of the air on a surface equal to
that of the whole external skin, through the thin moist coats of those
vessels, which are spread on the air-cells, which constitute the minute
terminal ramifications of the wind-pipe. Here the blood changes its colour
from a dark red to a bright scarlet. It is then collected by the branches
of the pulmonary vein, and conveyed to the left chamber of the heart.

6. The aorta is another large artery, which receives the blood from the
left chamber of the heart, after it has been thus aerated in the lungs, and
conveys it by ascending and descending branches to every other part of the
system; the extremities of this artery terminate either in glands, as the
salivary glands, lacrymal glands, &c. or in capillary vessels, which are
probably less involuted glands; in these some fluid, as saliva, tears,
perspiration, are separated from the blood; and the remainder of the blood
is absorbed or drank up by branches of veins correspondent to the branches
of the artery; which are furnished with valves to prevent its return; and
is thus carried back, after having again changed its colour to a dark red,
to the right chamber of the heart. The circulation of the blood in the
liver differs from this general system; for the veins which drink up the
refluent blood from those arteries, which are spread on the bowels and
mesentery, unite into a trunk in the liver, and form a kind of artery,
which is branched into the whole substance of the liver, and is called the
vena portarum; and from which the bile is separated by the numerous hepatic
glands, which constitute that viscus.

7. The glands may be divided into three systems, the convoluted glands,
such as those above described, which separate bile, tears, saliva, &c.
Secondly, the glands without convolution, as the capillary vessels, which
unite the terminations of the arteries and veins; and separate both the
mucus, which lubricates the cellular membrane, and the perspirable matter,
which preserves the skin moist and flexible. And thirdly, the whole
absorbent system, consisting of the lacteals, which open their mouths into
the stomach and intestines, and of the lymphatics, which open their mouths
on the external surface of the body, and on the internal linings of all the
cells of the cellular membrane, and other cavities of the body.

These lacteal and lymphatic vessels are furnished with numerous valves to
prevent the return of the fluids, which they absorb, and terminate in
glands, called lymphatic glands, and may hence be considered as long necks
or mouths belonging to these glands. To these they convey the chyle and
mucus, with a part of the perspirable matter, and atmospheric moisture; all
which, after having passed through these glands, and having suffered some
change in them, are carried forward into the blood, and supply perpetual
nourishment to the system, or replace its hourly waste.

8. The stomach and intestinal canal have a constant vermicular motion,
which carries forwards their contents, after the lacteals have drank up the
chyle from them; and which is excited into action by the stimulus of the
aliment we swallow, but which becomes occasionally inverted or retrograde,
as in vomiting, and in the iliac passion.

II. 1. The word _sensorium_ in the following pages is designed to express
not only the medullary part of the brain, spinal marrow, nerves, organs of
sense, and of the muscles; but also at the same time that living principle,
or spirit of animation, which resides throughout the body, without being
cognizable to our senses, except by its effects. The changes which
occasionally take place in the sensorium, as during the exertions of
volition, or the sensations of pleasure or pain, are termed _sensorial
motions_.

2. The similarity of the texture of the brain to that of the pancreas, and
some other glands of the body, has induced the inquirers into this subject
to believe, that a fluid, perhaps much more subtile than the electric aura,
is separated from the blood by that organ for the purposes of motion and
sensation. When we recollect, that the electric fluid itself is actually
accumulated and given out voluntarily by the torpedo and the gymnotus
electricus, that an electric shock will frequently stimulate into motion a
paralytic limb, and lastly that it needs no perceptible tubes to convey it,
this opinion seems not without probability; and the singular figure of the
brain and nervous system seems well adapted to distribute it over every
part of the body.

For the medullary substance of the brain not only occupies the cavities of
the head and spine, but passes along the innumerable ramifications of the
nerves to the various muscles and organs of sense. In these it lays aside
its coverings, and is intermixed with the slender fibres, which constitute
those muscles and organs of sense. Thus all these distant ramifications of
the sensorium are united at one of their extremities, that is, in the head
and spine; and thus these central parts of the sensorium constitute a
communication between all the organs of sense and muscles.

3. A _nerve_ is a continuation of the medullary substance of the brain from
the head or spine towards the other parts of the body, wrapped in its
proper membrane.

4. The _muscular fibres_ are moving organs intermixed with that medullary
substance, which is continued along the nerves, as mentioned above. They
are indued with the power of contraction, and are again elongated either by
antagonist muscles, by circulating fluids, or by elastic ligaments. So the
muscles on one side of the forearm bend the fingers by means of their
tendons, and those on the other side of the fore-arm extend them again. The
arteries are distended by the circulating blood; and in the necks of
quadrupeds there is a strong elastic ligament, which assists the muscles,
which elevate the head, to keep it in its horizontal position, and to raise
it after it has been depressed.

5. The _immediate organs of sense_ consist in like manner of moving fibres
enveloped in the medullary substance above mentioned; and are erroneously
supposed to be simply an expansion of the nervous medulla, as the retina of
the eye, and the rete mucosum of the skin, which are the immediate organs
of vision, and of touch. Hence when we speak of the contractions of the
fibrous parts of the body, we shall mean both the contractions of the
muscles, and those of the immediate organs of sense. These _fibrous
motions_ are thus distinguished from the _sensorial motions_ above
mentioned.

6. The _external organs_ of sense are the coverings of the immediate organs
of sense, and are mechanically adapted for the reception or transmission of
peculiar bodies, or of their qualities, as the cornea and humours of the
eye, the tympanum of the ear, the cuticle of the finders and tongue.

7. The word _idea_ has various meanings in the writers of metaphysic: it is
here used simply for those notions of external things, which our organs of
sense bring us acquainted with originally; and is defined a contraction, or
motion, or configuration, of the fibres, which constitute the immediate
organ of sense; which will be explained at large in another part of the
work. Synonymous with the word idea, we shall sometimes use the words
_sensual motion_ in contradistinction to _muscular motion_.

8. The word _perception_ includes both the action of the organ of sense in
consequence of the impact of external objects, and our attention to that
action; that is, it expresses both the motion of the organ of sense, or
idea, and the pain or pleasure that succeeds or accompanies it.

9. The pleasure or pain which necessarily accompanies all those perceptions
or ideas which we attend to, either gradually subsides, or is succeeded by
other fibrous motions. In the latter case it is termed _sensation_, as
explained in Sect. V. 2, and VI. 2.--The reader is intreated to keep this
in his mind, that through all this treatise the word sensation is used to
express pleasure or pain only in its active state, by whatever means it is
introduced into the system, without any reference to the stimulation of
external objects.

10. The vulgar use of the word _memory_ is too unlimited for our purpose:
those ideas which we voluntarily recall are here termed ideas of
_recollection_, as when we will to repeat the alphabet backwards. And those
ideas which are suggested to us by preceding ideas are here termed ideas of
_suggestion_, as whilst we repeat the alphabet in the usual order; when by
habits previously acquired B is suggested by A, and C by B, without any
effort of deliberation.

11. The word _association_ properly signifies a society or convention of
things in some respects similar to each other. We never say in common
language, that the effect is associated with the cause, though they
necessarily accompany or succeed each other. Thus the contractions of our
muscles and organs of sense may be said to be associated together, but
cannot with propriety be said to be associated with irritations, or with
volition, or with sensation; because they are caused by them, as mentioned
in Sect. IV. When fibrous contractions succeed other fibrous contractions,
the connection is termed _association_; when fibrous contractions succeed
sensorial motions, the connection is termed _causation_; when fibrous and
sensorial motions reciprocally introduce each other in progressive trains
or tribes, it is termed _catenation_ of animal motions. All these
connections are said to be produced by _habit_; that is, by frequent
repetition.

12. It may be proper to observe, that by the unavoidable idiom of our
language the ideas of perception, of recollection, or of imagination, in
the plural number signify the ideas belonging to perception, to
recollection, or to imagination; whilst the idea of perception, of
recollection, or of imagination, in the singular number is used for what is
termed "a reflex idea of any of those operations of the sensorium."

13. By the word _stimulus_ is not only meant the application of external
bodies to our organs of sense and muscular fibres, which excites into
action the sensorial power termed irritation; but also pleasure or pain,
when they excite into action the sensorial power termed sensation; and
desire or aversion, when they excite into action the power of volition; and
lastly, the fibrous contractions which precede association; as is further
explained in Sect. XII. 2. 1.

       *       *       *       *       *

SECT. III.

THE MOTIONS OF THE RETINA DEMONSTRATED BY EXPERIMENTS.

    I. _Of animal motions and of ideas._ II. _The fibrous structure of the
    retina._ III. _The activity of the retina in vision._ 1. _Rays of light
    have no momentum._ 2. _Objects long viewed become fainter._ 3. _Spectra
    of black objects become luminous._ 4. _Varying spectra from gyration._
    5. _From long inspection of various colours._ IV. _Motions of the
    organs of sense constitute ideas._ 1. _Light from pressing the
    eye-ball, and sound from the pulsation of the carotid artery._ 2.
    _Ideas in sleep mistaken for perceptions._ 3. _Ideas of imagination
    produce pain and sickness like sensations._ 4. _When the organ of sense
    is destroyed, the ideas belonging to that sense perish._ V. _Analogy
    between muscular motions and sensual motions, or ideas._ 1. _They are
    both originally excited by irritations._ 2. _And associated together in
    the same manner._ 3. _Both act in nearly the same times._ 4. _Are alike
    strengthened or fatigued by exercise._ 5. _Are alike painful from
    inflammation._ 6. _Are alike benumbed by compression._ 7. _Are alike
    liable to paralysis._ 8. _To convulsion._ 9. _To the influence of old
    age._--VI. _Objections answered._ 1. _Why we cannot invent new ideas._
    2. _If ideas resemble external objects._ 3. _Of the imagined sensation
    in an amputated limb._ 4. _Abstract ideas._--VII. _What are ideas, if
    they are not animal motions?_

Before the great variety of animal motions can be duly arranged into
natural classes and orders, it is necessary to smooth the way to this yet
unconquered field of science, by removing some obstacles which thwart our
passage. I. To demonstrate that the retina and other immediate organs of
sense possess a power of motion, and that these motions constitute our
ideas, according to the fifth and seventh of the preceding assertions,
claims our first attention.

Animal motions are distinguished from the communicated motions, mentioned
in the first section, as they have no mechanical proportion to their cause;
for the goad of a spur on the skin of a horse shall induce him to move a
load of hay. They differ from the gravitating motions there mentioned as
they are exerted with equal facility in all directions, and they differ
from the chemical class of motions, because no apparent decompositions or
new combinations are produced in the moving materials.

Hence, when we say animal motion is excited by irritation, we do not mean
that the motion bears any proportion to the mechanical impulse of the
stimulus; nor that it is affected by the general gravitation of the two
bodies; nor by their chemical properties, but solely that certain animal
fibres are excited into action by something external to the moving organ.

In this sense the stimulus of the blood produces the contractions of the
heart; and the substances we take into our stomach and bowels stimulate
them to perform their necessary functions. The rays of light excite the
retina into animal motion by their stimulus; at the same time that those
rays of light themselves are physically converged to a focus by the
inactive humours of the eye. The vibrations of the air stimulate the
auditory nerve into animal action; while it is probable that the tympanum
of the ear at the same time undergoes a mechanical vibration.

To render this circumstance more easy to be comprehended, _motion may be
defined to be a variation of figure_; for the whole universe may be
considered as one thing possessing a certain figure; the motions of any of
its parts are a variation of this figure of the whole: this definition of
motion will be further explained in Section XIV. 2. 2. on the production of
ideas.

Now the motions of an organ of sense are a succession of configurations of
that organ; these configurations succeed each other quicker or slower; and
whatever configuration of this organ of sense, that is, whatever portion of
the motion of it is, or has usually been, attended to, constitutes an idea.
Hence the configuration is not to be considered as an effect of the motion
of the organ, but rather as a part or temporary termination of it; and
that, whether a pause succeeds it, or a new configuration immediately takes
place. Thus when a succession of moving objects are presented to our view,
the ideas of trumpets, horns, lords and ladies, trains and canopies, are
configurations, that is, parts or links of the successive motions of the
organ of vision.

[Illustration: Plate I.]

These motions or configurations of the organs of sense differ from the
sensorial motions to be described hereafter, as they appear to be simply
contractions of the fibrous extremities of those organs, and in that
respect exactly resemble the motions or contractions of the larger muscles,
as appears from the following experiment. Place a circular piece of red
silk about an inch in diameter on a sheet of white paper in a strong light,
as in Plate I.--look for a minute on this area, or till the eye becomes
somewhat fatigued, and then, gently closing your eyes, and shading them
with your hand, a circular green area of the same apparent diameter becomes
visible in the closed eye. This green area is the colour reverse to the red
area, which had been previously inspected, as explained in the experiments
on ocular spectra at the end of the work, and in Botanical Garden, P. 1.
additional note, No. 1. Hence it appears, that a part of the retina, which
had been fatigued by contraction in one direction, relieves itself by
exerting the antagonist fibres, and producing a contraction in an opposite
direction, as is common in the exertions of our muscles. Thus when we are
tired with long action of our arms in one direction, as in holding a bridle
on a journey, we occasionally throw them into an opposite position to
relieve the fatigued muscles.

Mr. Locke has defined an idea to be "whatever is present to the mind;" but
this would include the exertions of volition, and the sensations of
pleasure and pain, as well as those operations of our system, which
acquaint us with external objects; and is therefore too unlimited for our
purpose. Mr. Lock seems to have fallen into a further error, by conceiving,
that the mind could form a general or abstract idea by its own operation,
which was the copy of no particular perception; as of a triangle in
general, that was neither acute, obtuse, nor right angled. The ingenious
Dr. Berkley and Mr. Hume have demonstrated, that such general ideas have no
existence in nature, not even in the mind of their celebrated inventor. We
shall therefore take for granted at present, that our recollection or
imagination of external objects consists of a partial repetition of the
perceptions, which were excited by those external objects, at the time we
became acquainted with them; and that our reflex ideas of the operations of
our minds are partial repetitions of those operations.

II. The following article evinces that the organ of vision consists of a
fibrous part as well as of the nervous medulla, like other white muscles;
and hence, as it resembles the muscular parts of the body in its structure,
we may conclude, that it must resemble them in possessing a power of being
excited into animal motion.--The subsequent experiments on the optic nerve,
and on the colours remaining in the eye, are copied from a paper on ocular
spectra published in the seventy-sixth volume of the Philos. Trans. by Dr.
R. Darwin of Shrewsbury; which, as I shall have frequent occasion to refer
to, is reprinted in this work, Sect. XL. The retina of an ox's eye was
suspended in a glass of warm water, and forcibly torn in a few places; the
edges of these parts appeared jagged and hairy, and did not contract and
become smooth like simple mucus, when it is distended till it breaks; which
evinced that it consisted of fibres. This fibrous construction became still
more distinct to the light by adding some caustic alcali to the water; as
the adhering mucus was first eroded, and the hair-like fibres remained
floating in the vessel. Nor does the degree of transparency of the retina
invalidate this evidence of its fibrous structure, since Leeuwenhoek has
shewn, that the crystalline humour itself consists of fibres. Arc. Nat. V.
I. 70.

Hence it appears, that as the muscles consist of larger fibres intermixed
with a smaller quantity of nervous medulla, the organ of vision consists of
a greater quantity of nervous medulla intermixed with smaller fibres. It is
probable that the locomotive muscles of microscopic animals may have
greater tenuity than these of the retina; and there is reason to conclude
from analogy, that the other immediate organs of sense, as the portio
mollis of the auditory nerve, and the rete mucosum of the skin, possess a
similarity of structure with the retina, and a similar power of being
excited into animal motion.

III. The subsequent articles shew, that neither mechanical impressions, nor
chemical combinations of light, but that the animal activity of the retina
constitutes vision.

1. Much has been conjectured by philosophers about the momentum of the rays
of light; to subject this to experiment a very light horizontal balance was
constructed by Mr. Michel, with about an inch square of thin leaf-copper
suspended at each end of it, as described in Dr. Priestley's History of
Light and Colours. The focus of a very large convex mirror was thrown by
Dr. Powel, in his lectures on experimental philosophy, in my presence, on
one wing of this delicate balance, and it receded from the light; thrown on
the other wing, it approached towards the light, and this repeatedly; so
that no sensible impulse could be observed, but what might well be ascribed
to the ascent of heated air.

Whence it is reasonable to conclude, that the light of the day must be much
too weak in its dilute state to make any mechanical impression on so
tenacious a substance as the retina of the eye.--Add to this, that as the
retina is nearly transparent, it could therefore make less resistance to
the mechanical impulse of light; which, according, to the observations
related by Mr. Melvil in the Edinburgh Literary Essays, only communicates
heat, and should therefore only communicate momentum, where it is
obstructed, reflected, or refracted.--From whence also may be collected the
final cause of this degree of transparency of the retina, viz. left by the
focus of stronger lights, heat and pain should have been produced in the
retina, instead of that stimulus which excites it into animal motion.

2. On looking long on an area of scarlet silk of about an inch in diameter
laid on white paper, as in Plate I. the scarlet colour becomes fainter,
till at length it entirely vanishes, though the eye is kept uniformly and
steadily upon it. Now if the change or motion of the retina was a
mechanical impression, or a chemical tinge of coloured light, the
perception would every minute become stronger and stronger,--whereas in
this experiment it becomes every instant weaker and weaker. The same
circumstance obtains in the continued application of sound, or of sapid
bodies, or of odorous ones, or of tangible ones, to their adapted organs of
sense.

[Illustration: Plate II.]

Thus when a circular coin, as a shilling, is pressed on the palm of the
hand, the sense of touch is mechanically compressed; but it is the stimulus
of this pressure that excites the organ of touch into animal action, which
constitutes the perception of hardness and of figure; for in some minutes
the perception ceases, though the mechanical pressure of the object
remains.

3. Make with ink on white paper a very black spot about half an inch in
diameter, with a tail about an inch in length, so as to resemble a tadpole,
as in Plate II.; look steadfastly for a minute on the center of this spot,
and, on moving the eye a little, the figure of the tadpole will be seen on
the white part of the paper; which figure of the tadpole will appear more
luminous than the other part of the white paper; which can only be
explained by supposing that a part of the retina, on which the tadpole was
delineated, to have become more sensible to light than the other parts of
it, which were exposed to the white paper; and not from any idea of
mechanical impression or chemical combination of light with the retina.

4. When any one turns round rapidly, till he becomes dizzy, and falls upon
the ground, the spectra of the ambient objects continue to present
themselves in rotation, and he seems to behold the objects still in motion.
Now if these spectra were impressions on a passive organ, they either must
continue as they were received last, or not continue at all.

5. Place a piece of red silk about an inch in diameter on a sheet of white
paper in a strong light, as in Plate I; look steadily upon it from the
distance of about half a yard for a minute; then closing your eye-lids,
cover them with your hands and handkerchief, and a green spectrum will be
seen in your eyes resembling in form the piece of red silk. After some
seconds of time the spectrum will disappear, and in a few more seconds will
reappear; and thus alternately three or four times, if the experiment be
well made, till at length it vanishes entirely.

[Illustration: Plate III.]

6. Place a circular piece of white paper, about four inches in diameter, in
the sunshine, cover the center of this with a circular piece of black silk,
about three inches in diameter; and the center of the black silk with a
circle of pink silk, about two inches in diameter; and the center of the
pink silk with a circle of yellow silk, about one inch in diameter; and the
center of this with a circle of blue silk, about half an inch in diameter;
make a small spot with ink in the center of the blue silk, as in Plate
III.; look steadily for a minute on this central spot, and then closing
your eyes, and applying your hand at about an inch distance before them, so
as to prevent too much or too little light from passing through the
eye-lids, and you will see the most beautiful circles of colours that
imagination can conceive; which are most resembled by the colours
occasioned by pouring a drop or two of oil on a still lake in a bright day.
But these circular irises of colours are not only different from the
colours of the silks above mentioned, but are at the same time perpetually
changing as long as they exist.

From all these experiments it appears, that these spectra in the eye are
not owing to the mechanical impulse of light impressed on the retina; nor
to its chemical combination with that organ; nor to the absorption and
emission of light, as is supposed, perhaps erroneously, to take place in
calcined shells and other phosphorescent bodies, after having been exposed
to the light: for in all these cases the spectra in the eye should either
remain of the same colour, or gradually decay, when the object is
withdrawn; and neither their evanescence during the presence of their
object, as in the second experiment, nor their change from dark to
luminous, as in the third experiment, nor their rotation, as in the fourth
experiment, nor the alternate presence and evanescence of them, as in the
fifth experiment, nor the perpetual change of colours of them, as in the
last experiment, could exist.

IV. The subsequent articles shew, that these animal motions or
configurations of our organs of sense constitute our ideas.

1. If any one in the dark presses the ball of his eye, by applying his
finger to the external corner of it, a luminous appearance is observed; and
by a smart stroke on the eye great slashes of fire are perceived. (Newton's
Optics.) So that when the arteries, that are near the auditory nerve, make
stronger pulsations than usual, as in some fevers, an undulating sound is
excited in the ears. Hence it is not the presence of the light and sound,
but the motions of the organ, that are immediately necessary to constitute
the perception or idea of light and sound.

2. During the time of sleep, or in delirium, the ideas of imagination are
mistaken for the perceptions of external objects; whence it appears, that
these ideas of imagination, are no other than a reiteration of those
motions of the organs of sense, which were originally excited by the
stimulus of external objects: and in our waking hours the simple ideas,
that we call up by recollection or by imagination, as the colour of red, or
the smell of a rose, are exact resemblances of the same simple ideas from
perception; and in consequence must be a repetition of those very motions.

3. The disagreeable sensation called the tooth-edge is originally excited
by the painful jarring of the teeth in biting the edge of the glass, or
porcelain cup, in which our food was given us in our infancy, as is further
explained in the Section XVI. 10, on Instinct.--This disagreeable sensation
is afterwards excitable not only by a repetition of the sound, that was
then produced, but by imagination alone, as I have myself frequently
experienced; in this case the idea of biting a china cup, when I imagine it
very distinctly, or when I see another person bite a cup or glass, excites
an actual pain in the nerves of my teeth. So that this idea and pain seem
to be nothing more than the reiterated motions of those nerves, that were
formerly so disagreeably affected.

Other ideas that are excited by imagination or recollection in many
instances produce similar effects on the constitution, as our perceptions
had formerly produced, and are therefore undoubtedly a repetition of the
same motions. A story which the celebrated Baron Van Swieton relates of
himself is to this purpose. He was present when the putrid carcase of a
dead dog exploded with prodigious stench; and some years afterwards,
accidentally riding along the same road, he was thrown into the same
sickness and vomiting by the idea of the stench, as he had before
experienced from the perception of it.

4. Where the organ of sense is totally destroyed, the ideas which were
received by that organ seem to perish along with it, as well as the power
of perception. Of this a satisfactory instance has fallen under my
observation. A gentleman about sixty years of age had been totally deaf for
near thirty years: he appeared to be a man of good understanding, and
amused himself with reading, and by conversing either by the use of the
pen, or by signs made with his fingers, to represent letters. I observed
that he had so far forgot the pronunciation of the language, that when he
attempted to speak, none of his words had distinct articulation, though his
relations could sometimes understand his meaning. But, which is much to the
point, he assured me, that in his dreams he always imagined that people
conversed with him by signs or writing, and never that he heard any one
speak to him. From hence it appears, that with the perceptions of sounds he
has also lost the ideas of them; though the organs of speech still retain
somewhat of their usual habits of articulation.

This observation may throw some light on the medical treatment of deaf
people; as it may be learnt from their dreams whether the auditory nerve be
paralytic, or their deafness be owing to some defect of the external organ.

It rarely happens that the immediate organ of vision is perfectly
destroyed. The most frequent causes of blindness are occasioned by defects
of the external organ, as in cataracts and obfuscations of the cornea. But
I have had the opportunity of conversing with two men, who had been some
years blind; one of them had a complete gutta serena, and the other had
lost the whole substance of his eyes. They both told me that they did not
remember to have ever dreamt of visible objects, since the total loss of
their sight.

V. Another method of discovering that our ideas are animal motions of the
organs of sense, is from considering the great analogy they bear to the
motions of the larger muscles of the body. In the following articles it
will appear that they are originally excited into action by the irritation
of external objects like our muscles; are associated together like our
muscular motions; act in similar time with them; are fatigued by continued
exertion like them; and that the organs of sense are subject to
inflammation, numbness, palsy, convulsion, and the defects of old age, in
the same manner as the muscular fibres.

1. All our perceptions or ideas of external objects are universally allowed
to have been originally excited by the stimulus of those external objects;
and it will be shewn in a succeeding section, that it is probable that all
our muscular motions, as well those that are become voluntary as those of
the heart and glandular system, were originally in like manner excited by
the stimulus of something external to the organ of motion.

2. Our ideas are also associated together after their production precisely
in the same manner as our muscular motions; which will likewise be fully
explained in the succeeding section.

3. The time taken up in performing an idea is likewise much the same as
that taken up in performing a muscular motion. A musician can press the
keys of an harpsichord with his fingers in the order of a tune he has been
accustomed to play, in as little time as he can run over those notes in his
mind. So we many times in an hour cover our eye-balls with our eye-lids
without perceiving that we are in the dark; hence the perception or idea of
light is not changed for that of darkness in so small a time as the
twinkling of an eye; so that in this case the muscular motion of the
eye-lid is performed quicker than the perception of light can be changed
for that of darkness.--So if a fire-stick be whirled round in the dark, a
luminous circle appears to the observer; if it be whirled somewhat slower,
this circle becomes interrupted in one part; and then the time taken up in
such a revolution of the stick is the same that the observer uses in
changing his ideas: thus the [Greek: dolikoskoton enkos] of Homer, the long
shadow of the flying javelin, is elegantly designed to give us an idea of
its velocity, and not of its length.

4. The fatigue that follows a continued attention of the mind to one object
is relieved by changing the subject of our thoughts; as the continued
movement of one limb is relieved by moving another in its stead. Whereas a
due exercise of the faculties of the mind strengthens and improves those
faculties, whether of imagination or recollection; as the exercise of our
limbs in dancing or fencing increases the strength and agility of the
muscles thus employed.

5. If the muscles of any limb are inflamed, they do not move without pain;
so when the retina is inflamed, its motions also are painful. Hence light
is as intolerable in this kind of ophthalmia, as pressure is to the finger
in the paronychia. In this disease the patients frequently dream of having
their eyes painfully dazzled; hence the idea of strong light is painful as
well as the reality. The first of these facts evinces that our perceptions
are motions of the organs of sense; and the latter, that our imaginations
are also motions of the same organs.

6. The organs of sense, like the moving muscles, are liable to become
benumbed, or less sensible, from compression. Thus, if any person on a
light day looks on a white wall, he may perceive the ramifications of the
optic artery, at every pulsation of it, represented by darker branches on
the white wall; which is evidently owing to its compressing the retina
during the diastole of the artery. Savage Nosolog.

7. The organs of sense and the moving muscles are alike liable to be
affected with palsy, as in the gutta serena, and in some cases of deafness;
and one side of the face has sometimes lost its power of sensation, but
retained its power of motion; other parts of the body have lost their
motions but retained their sensation, as in the common hemiplagia; and in
other instances both these powers have perished together.

8. In some convulsive diseases a delirium or insanity supervenes, and the
convulsions cease; and conversely the convulsions shall supervene, and the
delirium cease. Of this I have been a witness many times in a day in the
paroxysms of violent epilepsies; which evinces that one kind of delirium is
a convulsion of the organs of sense, and that our ideas are the motions of
these organs: the subsequent cases will illustrate this observation.

Miss G----, a fair young lady, with light eyes and hair, was seized with
most violent convulsions of her limbs, with outrageous hiccough, and most
vehement efforts to vomit: after near an hour was elapsed this tragedy
ceased, and a calm talkative delirium supervened for about another hour;
and these relieved each other at intervals during the greatest part of
three or four days. After having carefully considered this disease, I
thought the convulsions of her ideas less dangerous than those of her
muscles; and having in vain attempted to make any opiate continue in her
stomach, an ounce of laudanum was rubbed along the spine of her back, and a
dram of it was used as an enema; by this medicine a kind of drunken
delirium was continued many hours; and when it ceased the convulsions did
not return; and the lady continued well many years, except some lighter
relapses, which were relieved in the same manner.

Miss H----, an accomplished young lady, with light eyes and hair, was
seized with convulsions of her limbs, with hiccough, and efforts to vomit,
more violent than words can express; these continued near an hour, and were
succeeded with a cataleptic spasm of one arm, with the hand applied to her
head; and after about twenty minutes these spasms ceased, and a talkative
reverie supervened for near an other hour, from which no violence, which it
was proper to use, could awaken her. These periods of convulsions, first of
the muscles, and then of the ideas, returned twice a day for several weeks;
and were at length removed by great doses of opium, after a great variety
of other medicines and applications had been in vain experienced. This lady
was subject to frequent relapses, once or twice a year for many years, and
was as frequently relieved by the same method.

Miss W----, an elegant young lady, with black eyes and hair, had sometimes
a violent pain of her side, at other times a most painful strangury, which
were every day succeeded by delirium; which gave a temporary relief to the
painful spasms. After the vain exhibition of variety of medicines and
applications by different physicians, for more than a twelvemonth, she was
directed to take some doses of opium, which were gradually increased, by
which a drunken delirium was kept up for a day or two, and the pains
prevented from returning. A flesh diet, with a little wine or beer, instead
of the low regimen she had previously used, in a few weeks completely
established her health; which, except a few relapses, has continued for
many years.

9. Lastly, as we advance in life all the parts of the body become more
rigid, and are rendered less susceptible of new habits of motion, though
they retain those that were before established. This is sensibly observed
by those who apply themselves late in life to music, fencing, or any of the
mechanic arts. In the same manner many elderly people retain the ideas they
had learned early in life, but find great difficulty in acquiring new
trains of memory; insomuch that in extreme old age we frequently see a
forgetfulness of the business of yesterday, and at the same time a
circumstantial remembrance of the amusements of their youth; till at length
the ideas of recollection and activity of the body gradually cease
together,--such is the condition of humanity!--and nothing remains but the
vital motions and sensations.

VI. 1. In opposition to this doctrine of the production of our ideas, it
may be asked, if some of our ideas, like other animal motions, are
voluntary, why can we not invent new ones, that have not been received by
perception? The answer will be better understood after having perused the
succeeding section, where it will be explained, that the muscular motions
likewise are originally excited by the stimulus of bodies external to the
moving organ; and that the will has only the power of repeating the motions
thus excited.

2. Another objector may ask, Can the motion of an organ of sense resemble
an odour or a colour? To which I can only answer, that it has not been
demonstrated that any of our ideas resemble the objects that excite them;
it has generally been believed that they do not; but this shall be
discussed at large in Sect. XIV.

3. There is another objection that at first view would seem less easy to
surmount. After the amputation, of a foot or a finger, it has frequently
happened, that an injury being offered to the stump of the amputated limb,
whether from cold air, too great pressure, or other accidents, the patient
has complained, of a sensation of pain in the foot or finger, that was cut
off. Does not this evince that all our ideas are excited in the brain, and
not in the organs of sense? This objection is answered, by observing that
our ideas of the shape, place, and solidity of our limbs, are acquired by
our organs of touch and of sight, which are situated in our fingers and
eyes, and not by any sensations in the limb itself.

In this case the pain or sensation, which formerly has arisen in the foot
or toes, and been propagated along the nerves to the central part of the
sensorium, was at the same time accompanied with a visible idea of the
shape and place, and with a tangible idea of the solidity of the affected
limb: now when these nerves are afterwards affected by any injury done to
the remaining stump with a similar degree or kind of pain, the ideas of the
shape, place, or solidity of the lost limb, return by association; as these
ideas belong to the organs of sight and touch, on which they were first
excited.

4. If you wonder what organs of sense can be excited into motion, when you
call up the ideas of wisdom or benevolence, which Mr. Locke has termed
abstracted ideas; I ask you by what organs of sense you first became
acquainted with these ideas? And the answer will be reciprocal; for it is
certain that all our ideas were originally acquired by our organs of sense;
for whatever excites our perception must be external to the organ that
perceives it, and we have no other inlets to knowledge but by our
perceptions: as will be further explained in Section XIV. and XV. on the
Productions and Classes of Ideas.

VII. If our recollection or imagination be not a repetition of animal
movements, I ask, in my turn, What is it? You tell me it consists of images
or pictures of things. Where is this extensive canvas hung up? or where are
the numerous receptacles in which those are deposited? or to what else in
the animal system have they any similitude?

That pleasing picture of objects, represented in miniature on the retina of
the eye, seems to have given rise to this illusive oratory! It was forgot
that this representation belongs rather to the laws of light, than to those
of life; and may with equal elegance be seen in the camera obscura as in
the eye; and that the picture vanishes for ever, when the object is
withdrawn.

       *       *       *       *       *

SECT. IV.

LAWS OF ANIMAL CAUSATION.

I. The fibres, which constitute the muscles and organs of sense, possess a
power of contraction. The circumstances attending the exertion of this
power of CONTRACTION constitute the laws of animal motion, as the
circumstances attending the exertion of the power of ATTRACTION constitute
the laws of motion of inanimate matter.

II. The spirit of animation is the immediate cause of the contraction of
animal fibres, it resides in the brain and nerves, and is liable to general
or partial diminution or accumulation.

III. The stimulus of bodies external to the moving organ is the remote
cause of the original contractions of animal fibres.

IV. A certain quantity of stimulus produces irritation, which is an
exertion of the spirit of animation exciting the fibres into contraction.

V. A certain quantity of contraction of animal fibres, if it be perceived
at all, produces pleasure; a greater or less quantity of contraction, if it
be perceived at all, produces pain; these constitute sensation.

VI. A certain quantity of sensation produces desire or aversion; these
constitute volition.

VII. All animal motions which have occurred at the same time, or in
immediate succession, become so connected, that when one of them is
reproduced, the other has a tendency to accompany or succeed it. When
fibrous contractions succeed or accompany other fibrous contractions, the
connection is termed association; when fibrous contractions succeed
sensorial motions, the connexion is termed causation; when fibrous and
sensorial motions reciprocally introduce each other, it is termed
catenation of animal motions. All these connections are said to be produced
by habit, that is, by frequent repetition. These laws of animal causation
will be evinced by numerous facts, which occur in our daily exertions; and
will afterwards be employed to explain the more recondite phaenomena of the
production, growth, diseases, and decay of the animal system.

       *       *       *       *       *

SECT. V.

OF THE FOUR FACULTIES OR MOTIONS OF THE SENSORIUM.

    1. _Four sensorial powers._ 2. _Irritation, sensation, volition,
    association defined._ 3. _Sensorial motions distinguished from fibrous
    motions._

1. The spirit of animation has four different modes of action, or in other
words the animal sensorium possesses four different faculties, which are
occasionally exerted, and cause all the contractions of the fibrous parts
of the body. These are the faculty of causing fibrous contractions in
consequence of the irritations excited by external bodies, in consequence
of the sensations of pleasure or pain, in consequence of volition, and in
consequence of the associations of fibrous contractions with other fibrous
contractions, which precede or accompany them.

These four faculties of the sensorium during their inactive state are
termed irritability, sensibility, voluntarity, and associability; in their
active state they are termed as above, irritation, sensation, volition,
association.

2. IRRITATION is an exertion or change of some extreme part of the
sensorium residing in the muscles or organs of sense, in consequence of the
appulses of external bodies.

SENSATION is an exertion or change of the central parts of the sensorium,
or of the whole of it, _beginning_ at some of those extreme parts of it,
which reside in the muscles or organs of sense.

VOLITION is an exertion or change of the central parts of the sensorium, or
of the whole of it, _terminating_ in some of those extreme parts of it,
which reside in the muscles or organs of sense.

ASSOCIATION is an exertion or change of some extreme part of the sensorium
residing in the muscles or organs of sense, in consequence of some
antecedent or attendant fibrous contractions.

3. These four faculties of the animal sensorium may at the time of their
exertions be termed motions without impropriety of language; for we cannot
pass from a state of insensibility or inaction to a state of sensibility or
of exertion without some change of the sensorium, and every change includes
motion. We shall therefore sometimes term the above described faculties
_sensorial motions_ to distinguish them from _fibrous motions_; which
latter expression includes the motions of the muscles and organs of sense.

The active motions of the fibres, whether those of the muscles or organs of
sense, are probably simple contractions; the fibres being again elongated
by antagonist muscles, by circulating fluids, or sometimes by elastic
ligaments, as in the necks of quadrupeds. The sensorial motions, which
constitute the sensations of pleasure or pain, and which constitute
volition, and which cause the fibrous contractions in consequence of
irritation or of association, are not here supposed to be fluctuations or
refluctuations of the spirit of animation; nor are they supposed to be
vibrations or revibrations, nor condensations or equilibrations of it; but
to be changes or motions of it peculiar to life.

       *       *       *       *       *

SECT. VI.

OF THE FOUR CLASSES OF FIBROUS MOTIONS.

    I. _Origin of fibrous contractions._ II. _Distribution of them into
    four classes, irritative motions, sensitive motions, voluntary motions,
    and associate motions, defined._

I. All the fibrous contractions of animal bodies originate from the
sensorium, and resolve themselves into four classes, correspondent with the
four powers or motions of the sensorium above described, and from which
they have their causation.

1. These fibrous contractions were originally caused by the irritations
excited by objects, which are external to the moving organ. As the
pulsations of the heart are owing to the irritations excited by the
stimulus of the blood; and the ideas of perception are owing to the
irritations excited by external bodies.

2. But as painful or pleasurable sensations frequently accompanied those
irritations, by habit these fibrous contractions became causeable by the
sensations, and the irritations ceased to be necessary to their production.
As the secretion of tears in grief is caused by the sensation of pain; and
the ideas of imagination, as in dreams or delirium, are excited by the
pleasure or pain, with which they were formerly accompanied.

3. But as the efforts of the will frequently accompanied these painful or
pleasureable sensations, by habit the fibrous contractions became causable
by volition; and both the irritations and sensations ceased to be necessary
to their production. As the deliberate locomotions of the body, and the
ideas of recollection, as when we will to repeat the alphabet backwards.

4. But as many of these fibrous contractions frequently accompanied other
fibrous contractions, by habit they became causable by their associations
with them; and the irritations, sensations, and volition, ceased to be
necessary to their production. As the actions of the muscles of the lower
limbs in fencing are associated with those of the arms; and the ideas of
suggestion are associated with other ideas, which precede or accompany
them; as in repeating carelessly the alphabet in its usual order after
having began it.

II. We shall give the following names to these four classes of fibrous
motions, and subjoin their definitions.

1. Irritative motions. That exertion or change of the sensorium, which is
caused by the appulses of external bodies, either simply subsides, or is
succeeded by sensation, or it produces fibrous motions; it is termed
irritation, and irritative motions are those contractions of the muscular
fibres, or of the organs of sense, that are immediately consequent to this
exertion or change of the sensorium.

2. Sensitive motions. That exertion or change of the sensorium, which
constitutes pleasure or pain, either simply subsides, or is succeeded by
volition, or it produces fibrous motions; it is termed sensation, and the
sensitive motions are those contractions of the muscular fibres, or of the
organs of sense, that are immediately consequent to this exertion or change
of the sensorium.

3. Voluntary motions. That exertion or change of the sensorium, which
constitutes desire or aversion, either simply subsides, or is succeeded by
fibrous motions; it is then termed volition, and voluntary motions are
those contractions of the muscular fibres, or of the organs of sense, that
are immediately consequent to this exertion or change of the sensorium.

4. Associate motions. That exertion or change of the sensorium, which
accompanies fibrous motions, either simply subsides, or is succeeded by
sensation or volition, or it produces other fibrous motions; it is then
termed association, and the associate motions are those contractions of the
muscular fibres, or of the organs of sense, that are immediately consequent
to this exertion or change of the sensorium.

       *       *       *       *       *

SECT. VII.

OF IRRITATIVE MOTIONS.

    I. 1. _Some muscular motions are excited by perpetual irritations._ 2.
    _Others more frequently by sensations._ 3. _Others by volition. Case of
    involuntary stretchings in paralytic limbs._ 4. _Some sensual motions
    are excited by perpetual irritations._ 5. _Others more frequently by
    sensation or volition._

    II. 1. _Muscular motions excited by perpetual irritations occasionally
    become obedient sensation and to volition._ 2. _And the sensual
    motions._

    III. 1. _Other muscular motions are associated with the irritative
    ones._ 2. _And other ideas with irritative ones. Of letters, language,
    hieroglyphics. Irritative ideas exist without our attention to them._

I. 1. Many of our muscular motions are excited by perpetual irritations, as
those of the heart and arterial system by the circumfluent blood. Many
other of them are excited by intermitted irritations, as those of the
stomach and bowels by the aliment we swallow; of the bile-ducts by the
bile; of the kidneys, pancreas, and many other glands, by the peculiar
fluids they separate from the blood; and those of the lacteal and other
absorbent vessels by the chyle, lymph, and moisture of the atmosphere.
These motions are accelerated or retarded, as their correspondent
irritations are increased or diminished, without our attention or
consciousness, in the same manner as the various secretions of fruit, gum,
resin, wax, and, honey, are produced in the vegetable world, and as the
juices of the earth and the moisture of the atmosphere are absorbed by
their roots and foliage.

2. Other muscular motions, that are most frequently connected with our
sensations, as those of the sphincters of the bladder and anus, and the
musculi erectores penis, were originally excited into motion by irritation,
for young children make water, and have other evacuations without attention
to these circumstances; "et primis etiam ab incunabulis tenduntur saepius
puerorum penes, amore nondum expergefacto." So the nipples of young women
are liable to become turgid by irritation, long before they are in a
situation to be excited by the pleasure of giving milk to the lips of a
child.

3. The contractions of the larger muscles of our bodies, that are most
frequently connected with volition, were originally excited into action by
internal irritations: as appears from the stretching or yawning of all
animals after long sleep. In the beginning of some fevers this irritation
of the muscles produces perpetual stretching and yawning; in other periods
of fever an universal restlessness arises from the same cause, the patient
changing the attitude of his body every minute. The repeated struggles of
the foetus in the uterus must be owing to this internal irritation: for the
foetus can have no other inducement to move its limbs but the taedium or
irksomeness of a continued posture.

The following case evinces, that the motions of stretching the limbs after
a continued attitude are not always owing to the power of the will. Mr.
Dean, a mason, of Austry in Leicestershire, had the spine of the third
vertebra of the back enlarged; in some weeks his lower extremities became
feeble, and at length quite paralytic: neither the pain of blisters, the
heat of fomentations, nor the utmost efforts of the will could produce the
least motion in these limbs; yet twice or thrice a day for many months his
feet, legs, and thighs, were affected for many minutes with forceable
stretchings, attended with the sensation of fatigue; and he at length
recovered the use of his limbs, though the spine continued protuberant. The
same circumstance is frequently seen in a less degree in the common
hemiplagia; and when this happens, I have believed repeated and strong
shocks of electricity to have been of great advantage.

4. In like manner the various organs of sense are originally excited into
motion by various external stimuli adapted to this purpose, which motions
are termed perceptions or ideas; and many of these motions during our
waking hours are excited by perpetual irritation, as those of the organs of
hearing and of touch. The former by the constant low indistinct noises that
murmur around us, and the latter by the weight of our bodies on the parts
which support them; and by the unceasing variations of the heat, moisture,
and pressure of the atmosphere; and these sensual motions, precisely as the
muscular ones above mentioned, obey their correspondent irritations without
our attention or consciousness.

5. Other classes of our ideas are more frequently excited by our sensations
of pleasure or pain, and others by volition: but that these have all been
originally excited by stimuli from external objects, and only vary in their
combinations or reparations, has been fully evinced by Mr. Locke: and are
by him termed the ideas of perception in contradistinction to those, which
he calls the ideas of reflection.

II. 1. These muscular motions, that are excited by perpetual irritation,
are nevertheless occasionally excitable by the sensations of pleasure or
pain, or by volition; as appears by the palpitation of the heart from fear,
the increased secretion of saliva at the sight of agreeable food, and the
glow on the skin of those who are ashamed. There is an instance told in the
Philosophical Transactions of a man, who could for a time stop the motion
of his heart when he pleased; and Mr. D. has often told me, be could so far
increase the peristaltic motion of his bowels by voluntary efforts, as to
produce an evacuation by stool at any time in half an hour.

2. In like manner the sensual motions, or ideas, that are excited by
perpetual irritation, are nevertheless occasionally excited by sensation or
volition; as in the night, when we listen under the influence of fear, or
from voluntary attention, the motions excited in the organ of hearing by
the whispering of the air in our room, the pulsation of our own arteries,
or the faint beating of a distant watch, become objects of perception.

III. 1. Innumerable trains or tribes of other motions are associated with
these muscular motions which are excited by irritation; as by the stimulus
of the blood in the right chamber of the heart, the lungs are induced to
expand themselves; and the pectoral and intercostal muscles, and the
diaphragm, act at the same time by their associations with them. And when
the pharinx is irritated by agreeable food, the muscles of deglutition are
brought into action by association. Thus when a greater light falls on the
eye, the iris is brought into action without our attention; and the ciliary
process, when the focus is formed before or behind the retina, by their
associations with the increased irritative motions of the organ of vision.
Many common actions of life are produced in a similar manner. If a fly
settle on my forehead, whilst I am intent on my present occupation, I
dislodge it with my finger, without exciting my attention or breaking the
train of my ideas.

2. In like manner the irritative ideas suggest to us many other trains or
tribes of ideas that are associated with them. On this kind of connection,
language, letters, hieroglyphics, and every kind of symbol, depend. The
symbols themselves produce irritative ideas, or sensual motions, which we
do not attend to; and other ideas, that are succeeded by sensation, are
excited by their association with them. And as these irritative ideas make
up a part of the chain of our waking thoughts, introducing other ideas that
engage our attention, though themselves are unattended to, we find it very
difficult to investigate by what steps many of our hourly trains of ideas
gain their admittance.

It may appear paradoxical, that ideas can exist, and not be attended to;
but all our perceptions are ideas excited by irritation, and succeeded by
sensation. Now when these ideas excited by irritation give us neither
pleasure nor pain, we cease to attend to them. Thus whilst I am walking
through that grove before my window, I do not run against the trees or the
benches, though my thoughts are strenuously exerted on some other object.
This leads us to a distinct knowledge of irritative ideas, for the idea of
the tree or bench, which I avoid, exists on my retina, and induces by
association the action of certain locomotive muscles; though neither itself
nor the actions of those muscles engage my attention.

Thus whilst we are conversing on this subject, the tone, note, and
articulation of every individual word forms its correspondent irritative
idea on the organ of hearing; but we only attend to the associated ideas,
that are attached by habit to these irritative ones, and are succeeded by
sensation; thus when we read the words "PRINTING-PRESS" we do not attend to
the shape, size, or existence of the letters which compose these words,
though each of them excites a correspondent irritative motion of our organ
of vision, but they introduce by association our idea of the most useful of
modern inventions; the capacious reservoir of human knowledge, whose
branching streams diffuse sciences, arts, and morality, through all nations
and all ages.

       *       *       *       *       *

SECT. VIII.

OF SENSITIVE MOTIONS.

    I. 1. _Sensitive muscular motions were originally excited into action
    by irritation._ 2. _And sensitive sensual motions, ideas of
    imagination, dreams._ II. 1. _Sensitive muscular motions are
    occasionally obedient to volition._ 2. _And sensitive sensual motions._
    III. 1. _Other muscular motions are associated with the sensitive
    ones._ 2. _And other sensual motions._

I. 1. Many of the motions of our muscles, that are excited into action by
irritation, are at the same time accompanied with painful or pleasurable
sensations; and at length become by habit causable by the sensations. Thus
the motions of the sphincters of the bladder and anus were originally
excited into action by irritation; for young children give no attention to
these evacuations; but as soon as they become sensible of the inconvenience
of obeying these irritations, they suffer the water or excrement to
accumulate, till it disagreeably affects them; and the action of those
sphincters is then in consequence of this disagreeable sensation. So the
secretion of saliva, which in young children is copiously produced by
irritation, and drops from their mouths, is frequently attended with the
agreeable sensation produced by the mastication of tasteful food;, till at
length the sight of such food to a hungry person excites into action these
salival glands; as is seen in the slavering of hungry dogs.

The motions of those muscles, which are affected by lascivious ideas, and
those which are exerted in smiling, weeping, starting from fear, and
winking at the approach of danger to the eye, and at times the actions of
every large muscle of the body become causable by our sensations. And all
these motions are performed with strength and velocity in proportion to the
energy of the sensation that excites them, and the quantity of sensorial
power.

2. Many of the motions of our organs of sense, or ideas, that were
originally excited into action by irritation, become in like manner more
frequently causable by our sensations of pleasure or pain. These motions
are then termed the ideas of imagination, and make up all the scenery and
transactions of our dreams. Thus when any painful or pleasurable sensations
possess us, as of love, anger, fear; whether in our sleep or waking hours,
the ideas, that have been formerly excited by the objects of these
sensations, now vividly recur before us by their connection with these
sensations themselves. So the fair smiling virgin, that excited your love
by her presence, whenever that sensation recurs, rises before you in
imagination; and that with all the pleasing circumstances, that had before
engaged your attention. And in sleep, when you dream under the influence of
fear, all the robbers, fires, and precipices, that you formerly have seen
or heard of, arise before you with terrible vivacity. All these sensual
motions, like the muscular ones above mentioned, are performed with
strength and velocity in proportion to the energy of the sensation of
pleasure or pain, which excites them, and the quantity of sensorial power.

II. 1. Many of these muscular motions above described, that are most
frequently excited by our sensations, are nevertheless occasionally
causable by volition; for we can smile or frown spontaneously, can make
water before the quantity or acrimony of the urine produces a disagreeable
sensation, and can voluntarily masticate a nauseous drug, or swallow a
bitter draught, though our sensation would strongly dissuade us.

2. In like manner the sensual motions, or ideas, that are most frequently
excited by our sensations, are nevertheless occasionally causeable by
volition, as we can spontaneously call up our last night's dream before us,
tracing it industriously step by step through all its variety of scenery
and transaction; or can voluntarily examine or repeat the ideas, that have
been excited by out disgust or admiration.

III. 1. Innumerable trains or tribes of motions are associated with these
sensitive muscular motions above mentioned; as when a drop of water falling
into the wind-pipe disagreeably affects the air-vessels of the lungs, they
are excited into violent action; and with these sensitive motions are
associated the actions of the pectoral and intercostal muscles, and the
diaphragm; till by their united and repeated succussions the drop is
returned through the larinx. The same occurs when any thing disagreeably
affects the nostrils, or the stomach, or the uterus; variety of muscles are
excited by association into forcible action, not to be suppressed by the
utmost efforts of the will; as in sneezing, vomiting, and parturition.

2. In like manner with these sensitive sensual motions, or ideas of
imagination, are associated many other trains or tribes of ideas, which by
some writers of metaphysics have been classed under the terms of
resemblance, causation, and contiguity; and will be more fully treated of
hereafter.

       *       *       *       *       *

SECT. IX.

OF VOLUNTARY MOTIONS.

    I. 1. _Voluntary muscular motions are originally excited by
    irritations._ 2. _And voluntary ideas. Of reason._ II. 1. _Voluntary
    muscular motions are occasionally causable by sensations._ 2. _And
    voluntary ideas._ III. 1. _Voluntary muscular motions are occasionally
    obedient to irritations._ 2. _And voluntary ideas._ IV. 1. _Voluntary
    muscular motions are associated with other muscular motions._ 2. _And
    voluntary ideas._

When pleasure or pain affect the animal system, many of its motions both
muscular and sensual are brought into action; as was shewn in the preceding
section, and were called sensitive motions. The general tendency of these
motions is to arrest and to possess the pleasure, or to dislodge or avoid
the pain: but if this cannot immediately be accomplished, desire or
aversion are produced, and the motions in consequence of this new faculty
of the sensorium are called voluntary.

I. 1. Those muscles of the body that are attached to bones, have in general
their principal connections with volition, as I move my pen or raise my
body. These motions were originally excited by irritation, as was explained
in the section on that subject, afterwards the sensations of pleasure or
pain, that accompanied the motions thus excited, induced a repetition of
them; and at length many of them were voluntarily practised in succession
or in combination for the common purposes of life, as in learning to walk,
or to speak; and are performed with strength and velocity in proportion to
the energy of the volition, that excites them, and the quantity of
sensorial power.

2. Another great class of voluntary motions consists of the ideas of
recollection. We will to repeat a certain train of ideas, as of the
alphabet backwards; and if any ideas, that do not belong to this intended
train, intrude themselves by other connections, we will to reject them, and
voluntarily persist in the determined train. So at my approach to a house
which I have but once visited, and that at the distance of many months, I
will to recollect the names of the numerous family I expect to see there,
and I do recollect them.

On this voluntary recollection of ideas our faculty of reason depends, as
it enables us to acquire an idea of the dissimilitude of any two ideas.
Thus if you voluntarily produce the idea of a right-angled triangle, and
then of a square; and after having excited these ideas repeatedly, you
excite the idea of their difference, which is that of another right-angled
triangle inverted over the former; you are said to reason upon this
subject, or to compare your ideas.

These ideas of recollection, like the muscular motions above mentioned,
were originally excited by the irritation of external bodies, and were
termed ideas of perception: afterwards the pleasure or pain, that
accompanied these motions, induced a repetition of them in the absence of
the external body, by which they were first excited; and then they were
termed ideas of imagination. At length they become voluntarily practised in
succession or in combination for the common purposes of life; as when we
make ourselves masters of the history of mankind, or of the sciences they
have investigated; and are then called ideas of recollection; and are
performed with strength and velocity in proportion to the energy of the
volition that excites them, and the quantity of sensorial power.

II. 1. The muscular motions above described, that are most frequently
obedient to the will are nevertheless occasionally causable by painful or
pleasurable sensation, as in the starting from fear, and the contraction of
the calf of the leg in the cramp.

2. In like manner the sensual motions, or ideas, that are most frequently
connected with volition, are nevertheless occasionally causable by painful
or pleasurable sensation. As the histories of men, or the description of
places, which we have voluntarily taken pains to remember, sometimes occur
to us in our dreams.

III. 1. The muscular motions that are generally subservient to volition,
are also occasionally causable by irritation, as in stretching the limbs
after sleep, and yawning. In this manner a contraction of the arm is
produced by passing the electric fluid from the Leyden phial along its
muscles; and that even though the limb is paralytic. The sudden motion of
the arm produces a disagreeable sensation in the joint, but the muscles
seem to be brought into action simply by irritation.

2. The ideas, that are generally subservient to the will, are in like
manner occasionally excited by irritation; as when we view again an object,
we have before well studied, and often recollected.

IV. 1. Innumerable trains or tribes of motions are associated with these
voluntary muscular motions above mentioned; as when I will to extend my arm
to a distant object, some other muscles are brought into action, and
preserve the balance of my body. And when I wish to perform any steady
exertion, as in threading a needle, or chopping with an ax, the pectoral
muscles are at the same time brought into action to preserve the trunk of
the body motionless, and we cease to respire for a time.

2. In like manner the voluntary sensual motions, or ideas of recollection,
are associated with many other trains or tribes of ideas. As when I
voluntarily recollect a gothic window, that I saw some time ago, the whole
front of the cathedral occurs to me at the same time.

       *       *       *       *       *

SECT. X.

OF ASSOCIATE MOTIONS.

    I. 1. _Many muscular motions excited by irritations in trains or tribes
    become associated._ 2. _And many ideas._ II. 1. _Many sensitive
    muscular motions become associated._ 2. _And many sensitive ideas._
    III. 1. _Many voluntary muscular motions become associated._ 2. _And
    then become obedient to sensation or irritation._ 3. _And many
    voluntary ideas become associated._

All the fibrous motions, whether muscular or sensual, which are frequently
brought into action together, either in combined tribes, or in successive
trains, become so connected by habit, that when one of them is reproduced
the others have a tendency to succeed or accompany it.

I. 1. Many of our muscular motions were originally excited in successive
trains, as the contractions of the auricles and of the ventricles of the
heart; and others in combined tribes, as the various divisions of the
muscles which compose the calf of the leg, which were originally irritated
into synchronous action by the taedium or irksomeness of a continued
posture. By frequent repetitions these motions acquire associations, which
continue during our lives, and even after the destruction of the greatest
part of the sensorium; for the heart of a viper or frog will continue to
pulsate long after it is taken from the body; and when it has entirely
ceased to move, if any part of it is goaded with a pin, the whole heart
will again renew its pulsations. This kind of connection we shall term
irritative association, to distinguish it from sensitive and voluntary
associations.

2. In like manner many of our ideas are originally excited in tribes; as
all the objects of sight, after we become so well acquainted with the laws
of vision, as to distinguish figure and distance as well as colour; or in
trains, as while we pass along the objects that surround us. The tribes
thus received by irritation become associated by habit, and have been
termed complex ideas by the writers of metaphysics, as this book, or that
orange. The trains have received no particular name, but these are alike
associations of ideas, and frequently continue during our lives. So the
taste of a pine-apple, though we eat it blindfold, recalls the colour and
shape of it; and we can scarcely think on solidity without figure.

II. 1. By the various efforts of our sensations to acquire or avoid their
objects, many muscles are daily brought into successive or synchronous
actions; these become associated by habit, and are then excited together
with great facility, and in many instances gain indissoluble connections.
So the play of puppies and kittens is a representation of their mode of
fighting or of taking their prey; and the motions of the muscles necessary
for those purposes become associated by habit, and gain a great adroitness
of action by these early repetitions: so the motions of the abdominal
muscles, which were originally brought into concurrent action, with the
protrusive motion of the rectum or bladder by sensation, become so
conjoined with them by habit, that they not only easily obey these
sensations occasioned by the stimulus of the excrement and urine, but are
brought into violent and unrestrainable action in the strangury and
tenesmus. This kind of connection we shall term sensitive association.

2. So many of our ideas, that have been excited together or in succession
by our sensations, gain synchronous or successive associations, that are
sometimes indissoluble but with life. Hence the idea of an inhuman or
dishonourable action perpetually calls up before us the idea of the wretch
that was guilty of it. And hence those unconquerable antipathies are
formed, which some people have to the sight of peculiar kinds of food, of
which in their infancy they have eaten to excess or by constraint.

III. 1. In learning any mechanic art, as music, dancing, or the use of the
sword, we teach many of our muscles to act together or in succession by
repeated voluntary efforts; which by habit become formed into tribes or
trains of association, and serve all our purposes with great facility, and
in some instances acquire an indissoluble union. These motions are
gradually formed into a habit of acting together by a multitude of
repetitions, whilst they are yet separately causable by the will, as is
evident from the long time that is taken up by children in learning to walk
and to speak; and is experienced by every one, when he first attempts to
skate upon the ice or to swim: these we shall term voluntary associations.

2. All these muscular movements, when they are thus associated into tribes
or trains, become afterwards not only obedient to volition, but to the
sensations and irritations; and the same movement composes a part of many
different tribes or trains of motion. Thus a single muscle, when it acts in
consort with its neighbours on one side, assists to move the limb in one
direction; and in another, when, it acts with those in its neighbourhood on
the other side; and in other directions, when it acts separately or jointly
with those that lie immediately under or above it; and all these with equal
facility after their associations have been well established.

The facility, with which each muscle changes from one associated tribe to
another, and that either backwards or forwards, is well observable in the
muscles of the arm in moving the windlass of an air-pump; and the slowness
of those muscular movements, that have not been associated by habit, may be
experienced by any one, who shall attempt to saw the air quick
perpendicularly with one hand, and horizontally with the other at the same
time.

3. In learning every kind of science we voluntarily associate many tribes
and trains of ideas, which afterwards are ready for all the purposes either
of volition, sensation, or irritation; and in some instances acquire
indissoluble habits of acting together, so as to affect our reasoning, and
influence our actions. Hence the necessity of a good education.

These associate ideas are gradually formed into habits of acting together
by frequent repetition, while they are yet separately obedient to the will;
as is evident from the difficulty we experience in gaining so exact an idea
of the front of St. Paul's church, as to be able to delineate it with
accuracy, or in recollecting a poem of a few pages.

And these ideas, thus associated into tribes, not only make up the parts of
the trains of volition, sensation, and irritation; but the same idea
composes a part of many different tribes and trains of ideas. So the simple
idea of whiteness composes a part of the complex idea of snow, milk, ivory;
and the complex idea of the letter A composes a part of the several
associated trains of ideas that make up the variety of words, in which this
letter enters.

The numerous trains of these associated ideas are divided by Mr. Hume into
three classes, which he has termed contiguity, causation, and resemblance.
Nor should we wonder to find them thus connected together, since it is the
business of our lives to dispose them into those three classes; and we
become valuable to ourselves and our friends, as we succeed in it. Those
who have combined an extensive class of ideas by the contiguity of time or
place, are men learned in the history of mankind, and of the sciences they
have cultivated. Those who have connected a great class of ideas of
resemblances, possess the source of the ornaments of poetry and oratory,
and of all rational analogy. While those who have connected great classes
of ideas of causation, are furnished with the powers of producing effects.
These are the men of active wisdom, who lead armies to victory, and
kingdoms to prosperity; or discover and improve the sciences, which
meliorate and adorn the condition of humanity.

       *       *       *       *       *

SECT. XI.

ADDITIONAL OBSERVATIONS ON THE SENSORIAL POWERS.

    I. _Stimulation is of various kinds adapted to the organs of sense, to
    the muscles, to hollow membranes, and glands. Some objects irritate our
    senses by repeated impulses._ II. 1. _Sensation and volition frequently
    affect the whole sensorium._ 2. _Emotions, passions, appetites._ 3.
    _Origin of desire and aversion. Criterion of voluntary actions,
    difference of brutes and men._ 4. _Sensibility and voluntarity._ III.
    _Associations formed before nativity, irritative motions mistaken for
    officiated ones._

_Irritation._

I. The various organs of sense require various kinds of stimulation to
excite them into action; the particles of light penetrate the cornea and
humours of the eye, and then irritate the naked retina; rapid particles,
dissolved or diffused in water or saliva, and odorous ones, mixed or
combined with the air, irritate the extremities of the nerves of taste and
smell; which either penetrate, or are expanded on the membranes of the
tongue and nostrils; the auditory nerves are stimulated by the vibrations
of the atmosphere communicated by means of the tympanum and of the fluid,
whether of air or of water, behind it; and the nerves of touch by the
hardness of surrounding bodies, though the cuticle is interposed between
these bodies and the medulla of the nerve.

As the nerves of the senses have each their appropriated objects, which
stimulate them into activity; so the muscular fibres, which are the
terminations of other sets of nerves, have their peculiar objects, which
excite them into action; the longitudinal muscles are stimulated into
contraction by extension, whence the stretching or pandiculation after a
long continued posture, during which they have been kept in a state of
extension; and the hollow muscles are excited into action by distention, as
those of the rectum and bladder are induced to protrude their contents from
their sense of the distention rather than of the acrimony of those
contents.

There are other objects adapted to stimulate the nerves, which terminate in
variety of membranes, and those especially which form the terminations of
canals; thus the preparations of mercury particularly affect the salivary
glands, ipecacuanha the stomach, aloe the sphincter of the anus,
cantharides that of the bladder, and lastly every gland of the body appears
to be indued with a kind of taste, by which it selects or forms each its
peculiar fluid from the blood; and by which it is irritated into activity.

Many of these external properties of bodies, which stimulate our organs of
sense, do not seem to effect this by a single impulse, but by repeated
impulses; as the nerve of the ear is probably not excitable by a single
vibration of air, nor the optic nerve by a single particle of light; which
circumstance produces some analogy between those two senses, at the same
time the solidity of bodies is perceived by a single application of a solid
body to the nerves of touch, and that even through the cuticle; and we are
probably possessed of a peculiar sense to distinguish the nice degrees of
heat and cold.

The senses of touch and of hearing acquaint us with the mechanical impact
and vibration of bodies, those of smell and taste seem to acquaint us with
some of their chemical properties, while the sense of vision and of heat
acquaint us with the existence of their peculiar fluids.

_Sensation and Volition._

II. Many motions are produced by pleasure or pain, and that even in
contradiction to the power of volition, as in laughing, or in the
strangury; but as no name has been given to pleasure or pain, at the time
it is exerted so as to cause fibrous motions, we have used the term
sensation for this purpose; and mean it to bear the same analogy to
pleasure and pain, that the word volition does to desire and aversion.

1. It was mentioned in the fifth Section, that, what we have termed
sensation is a motion of the central parts, or of the whole sensorium,
_beginning_ at some of the extremities of it. This appears first, because
our pains and pleasures are always caused by our ideas or muscular motions,
which are the motions of the extremities of the sensorium. And, secondly,
because the sensation of pleasure or pain frequently continues some time
after the ideas or muscular motions which excited it have ceased: for we
often feel a glow of pleasure from an agreeable reverie, for many minutes
after the ideas, that were the subject of it, have escaped our memory; and
frequently experience a dejection of spirits without being able to assign
the cause of it but by much recollection.

When the sensorial faculty of desire or aversion is exerted so as to cause
fibrous motions, it is termed volition; which is said in Sect. V. to be a
motion of the central parts, or of the whole sensorium, _terminating_ in
some of the extremities of it. This appears, first, because our desires and
aversions always terminate in recollecting and comparing our ideas, or in
exerting our muscles; which are the motions of the extremities of the
sensorium. And, secondly, because desire or aversion begins, and frequently
continues for a time in the central parts of the sensorium, before it is
peculiarly exerted at the extremities of it; for we sometimes feel desire
or aversion without immediately knowing their objects, and in consequence
without immediately exerting any of our muscular or sensual motions to
attain them: as in the beginning of the passion of love, and perhaps of
hunger, or in the ennui of indolent people.

Though sensation and volition begin or terminate at the extremities or
central parts of the sensorium, yet the whole of it is frequently
influenced by the exertion of these faculties, as appears from their
effects on the external habit: for the whole skin is reddened by shame, and
an universal trembling is produced by fear: and every muscle of the body is
agitated in angry people by the desire of revenge.

There is another very curious circumstance, which shews that sensation and
volition are movements of the sensorium in contrary directions; that is,
that volition begins at the central parts of it, and proceeds to the
extremities; and that sensation begins at the extremities, and proceeds to
the central parts: I mean that these two sensorial faculties cannot be
strongly exerted at the same time; for when we exert our volition strongly,
we do not attend to pleasure or pain; and conversely, when we are strongly
affected with the sensation of pleasure or pain, we use no volition. As
will be further explained in Section XVIII. on sleep, and Section XXXIV. on
volition.

2. All our emotions and passions seem to arise out of the exertions of
these two faculties of the animal sensorium. Pride, hope, joy, are the
names of particular pleasures: shame, despair, sorrow, are the names of
peculiar pains: and love, ambition, avarice, of particular desires: hatred,
disgust, fear, anxiety, of particular aversions. Whilst the passion of
anger includes the pain from a recent injury, and the aversion to the
adversary that occasioned it. And compassion is the pain we experience at
the sight of misery, and the desire of relieving it.

There is another tribe of desires, which are commonly termed appetites, and
are the immediate consequences of the absence of some irritative motions.
Those, which arise from defect of internal irritations, have proper names
conferred upon them, as hunger, thirst, lust, and the desire of air, when
our respiration is impaired by noxious vapours; and of warmth, when we are
exposed to too great a degree of cold. But those, whose stimuli are
external to the body, are named from the objects, which are by nature
constituted to excite them; these desires originate from our past
experience of the pleasurable sensations they occasion, as the smell of an
hyacinth, or the taste of a pine-apple.

Whence it appears, that our pleasures and pains are at least as various and
as numerous as our irritations; and that our desires and aversions must be
as numerous as our pleasures and pains. And that as sensation is here used
as a general term for our numerous pleasures and pains, when they produce
the contractions of our fibres; so volition is the general name for our
desires and aversions, when they produce fibrous contractions. Thus when a
motion of the central parts, or of the whole sensorium, terminates in the
exertion of our muscles, it is generally called voluntary action; when it
terminates in the exertion of our ideas, it is termed recollection,
reasoning, determining.

3. As the sensations of pleasure and pain are originally introduced by the
irritations of external objects: so our desires and aversions are
originally introduced by those sensations; for when the objects of our
pleasures or pains are at a distance, and we cannot instantaneously possess
the one, or avoid the other, then desire or aversion is produced, and a
voluntary exertion of our ideas or muscles succeeds.

The pain of hunger excites you to look out for food, the tree, that shades
you, presents its odoriferous fruit before your eyes, you approach, pluck,
and eat.

The various movements of walking to the tree, gathering the fruit, and
masticating it, are associated motions introduced by their connection with
sensation; but if from the uncommon height of the tree, the fruit be
inaccessible, and you are prevented from quickly possessing the intended
pleasure, desire is produced. The consequence of this desire is, first, a
deliberation about the means to gain the object of pleasure in process of
time, as it cannot be procured immediately; and, secondly, the muscular
action necessary for this purpose.

You voluntarily call up all your ideas of causation, that are related to
the effect you desire, and voluntarily examine and compare them, and at
length determine whether to ascend the tree, or to gather stones from the
neighbouring brook, is easier to practise, or more promising of success;
and, finally, you gather the stones, and repeatedly fling them to dislodge
the fruit.

Hence then we gain a criterion to distinguish voluntary acts or thoughts
from those caused by sensation. As the former are always employed about the
_means_ to acquire pleasurable objects, or the _means_ to avoid painful
ones; while the latter are employed in the possession of those, which are
already in our power.

Hence the activity of this power of volition produces the great difference
between the human and the brute creation. The ideas and the actions of
brutes are almost perpetually employed about their present pleasures, or
their present pains; and, except in the few instances which are mentioned
in Section XVI, on instinct, they seldom busy themselves about the means of
procuring future bliss, or of avoiding future misery; so that the acquiring
of languages, the making of tools, and labouring for money, which are all
only the means to procure pleasures; and the praying to the Deity, as
another means to procure happiness, are characteristic of human nature.

4. As there are many diseases produced by the quantity of the sensation of
pain or pleasure being too great or too little; so are there diseases
produced by the susceptibility of the constitution to motions causable by
these sensations being too dull or too vivid. This susceptibility of the
system to sensitive motions is termed sensibility, to distinguish it from
sensation, which is the actual existence or exertion of pain or pleasure.

Other classes of diseases are owing to the excessive promptitude, or
sluggishness of the constitution to voluntary exertions, as well as to the
quantity of desire or of aversion. This susceptibility of the system to
voluntary motions is termed voluntarity, to distinguish it from volition,
which is the exertion of desire or aversion; these diseases will be treated
of at length in the progress of the work.

_Association._

III. 1. It is not easy to assign a cause, why those animal movements, that
have once occurred in succession, or in combination, should afterwards have
a tendency to succeed or accompany each other. It is a property of
animation, and distinguishes this order of being from the other productions
of nature.

When a child first wrote the word man, it was distinguished in his mind
into three letters, and those letters into many parts of letters; but by
repeated use the word man becomes to his hand in writing it, as to his
organs of speech in pronouncing it, but one movement without any
deliberation, or sensation, or irritation, interposed between the parts of
it. And as many separate motions of our muscles thus become united, and
form, as it were, one motion; so each separate motion before such union may
be conceived to consist of many parts or spaces moved through; and perhaps
even the individual fibres of our muscles have thus gradually been brought
to act in concert, which habits began to be acquired as early as the very
formation of the moving organs, long before the nativity of the animal; as
explained in the Section XVI. 2. on instinct.

2. There are many motions of the body, belonging to the irritative class,
which might by a hasty observer be mistaken for associated ones; as the
peristaltic motion of the stomach and intestines, and the contractions of
the heart and arteries, might be supposed to be associated with the
irritative motions of their nerves of sense, rather than to be excited by
the irritation of their muscular fibres by the distention, acrimony, or
momentum of the blood. So the distention or elongation of muscles by
objects external to them irritates them into contraction, though the
cuticle or other parts may intervene between the stimulating body and the
contracting muscle. Thus a horse voids his excrement when its weight or
bulk irritates the rectum or sphincter ani. These muscles act from the
irritation of distention, when he excludes his excrement, but the muscles
of the abdomen and diaphragm are brought into motion by association with
those of the sphincter and rectum.

       *       *       *       *       *

SECT. XII.

OF STIMULUS, SENSORIAL EXERTION, AND FIBROUS CONTRACTION.

    I. Of fibrous contraction. 1. _Two particles of a fibre cannot approach
    without the intervention of something, as in magnetism, electricity,
    elasticity. Spirit of life is not electric ether. Galvani's
    experiments._ 2. _Contraction of a fibre._ 3. _Relaxation succeeds._ 4.
    _Successive contractions, with intervals. Quick pulse from debility,
    from paucity of blood. Weak contractions performed in less time, and
    with shorter intervals._ 5. _Last situation of the fibres continues
    after contraction._ 6. _Contraction greater than usual induces pleasure
    or pain._ 7. _Mobility of the fibres uniform. Quantity of sensorial
    power fluctuates. Constitutes excitability._ II. Of sensorial exertion.
    1. _Animal motion includes stimulus, sensorial power, and contractile
    fibres. The sensorial faculties act separately or conjointly. Stimulus
    of four kinds. Strength and weakness defined. Sensorial power
    perpetually exhausted and renewed. Weakness from defect of stimulus.
    From defect of sensorial power, the direct and indirect debility of Dr.
    Brown. Why we become warm in Buxton bath after a time, and see well
    after a time in a darkish room. Fibres may act violently, or with their
    whole force, and yet feebly. Great exertion in inflammation explained.
    Great muscular force of some insane people._ 2. _Occasional
    accumulation of sensorial power in muscles subject to constant
    stimulus. In animals sleeping in winter. In eggs, seeds, schirrous
    tumours, tendons, bones._ 3. _Great exertion introduces pleasure or
    pain. Inflammation. Libration of the system between torpor and
    activity. Fever-fits._ 4. _Desire and aversion introduced. Excess of
    volition cures fevers._ III. Of repeated stimulus. 1. _A stimulus
    repeated too frequently looses effect. As opium, wine, grief. Hence old
    age. Opium and aloes in small doses._ 2. _A stimulus not repeated too
    frequently does not lose effect. Perpetual movement of the vital
    organs._ 3. _A stimulus repeated at uniform times produces greater
    effect. Irritation combined with association._ 4. _A stimulus repeated
    frequently and uniformly may be withdrawn, and the action of the organ
    will continue. Hence the bark cures agues, and strengthens weak
    constitutions._ 5. _Defect of stimulus repeated at certain intervals
    causes fever-fits._ 6. _Stimulus long applied ceases to act a second
    time._ 7. _If a stimulus excites sensation in an organ not usually
    excited into sensation, inflammation is produced._ IV. Of stimulus
    greater than natural. 1. _A stimulus greater than natural diminishes
    the quantity of sensorial power in general._ 2. _In particular organs._
    3. _Induces the organ into spasmodic actions._ 4. _Induces the
    antagonist fibres into action._ 5. _Induces the organ into convulsive
    or fixed spasms._ 6. _Produces paralysis of the organ._ V. Of stimulus
    less than natural. 1. _Stimulus less than natural occasions
    accumulation of sensorial power in general._ 2. _In particular organs,
    flushing of the face in a frosty morning. In fibres subject to
    perpetual stimulus only. Quantity of sensorial power inversely as the
    stimulus._ 3. _Induces pain. As of cold, hunger, head-ach._ 4. _Induces
    more feeble and frequent contraction. As in low fevers. Which are
    frequently owing to deficiency of sensorial power rather than to
    deficiency of stimulus._ 5. _Inverts successive trains of motion.
    Inverts ideas._ 6. _Induces paralysis and death._ VI. Cure of increased
    exertion. 1. _Natural cure of exhaustion of sensorial power._ 2.
    _Decrease the irritations. Venesection. Cold. Abstinence._ 3. _Prevent
    the previous cold fit. Opium. Bark. Warmth. Anger. Surprise._ 4.
    _Excite some other part of the system. Opium and warm bath relieve
    pains both from defect and from excess of stimulus._ 5. _First increase
    the stimulus above, and then decrease it beneath the natural quantity._
    VII. Cure of decreased exertion. 1. _Natural cure by accumulation of
    sensorial power. Ague-fits. Syncope._ 2. _Increase the stimulation, by
    wine, opium, given so as not to intoxicate. Cheerful ideas._ 3. _Change
    the kinds of stimulus._ 4. _Stimulate the associated organs. Blisters
    of use in heart-burn, and cold extremities._ 5. _Decrease the
    stimulation for a time, cold bath._ 6. _Decrease the stimulation below
    natural, and then increase it above natural. Bark after emetics. Opium
    after venesection. Practice of Sydenham in chlorosis._ 7. _Prevent
    unnecessary expenditure of sensorial power. Decumbent posture, silence,
    darkness. Pulse quickened by rising out of bed._ 8. _To the greatest
    degree of quiescence apply the least stimulus. Otherwise paralysis or
    inflammation of the organ ensues. Gin, wine, blisters, destroy by too
    great stimulation in fevers with debility. Intoxication in the
    slightest degree succeeded by debility. Golden rule for determining the
    best degree of stimulus in low fevers. Another golden rule for
    determining the quantity of spirit which those, who are debilitated by
    drinking it, may safely omit._

I. _Of fibrous contraction._

1. If two particles of iron lie near each other without motion, and
afterwards approach each other; it is reasonable to conclude that something
besides the iron particles is the cause of their approximation; this
invisible something is termed magnetism. In the same manner, if the
particles, which compose an animal muscle, do not touch each other in the
relaxed state of the muscle, and are brought into contact during the
contraction of the muscle, it is reasonable to conclude, that some other
agent is the cause of this new approximation. For nothing can act, where it
does not exist; for to act includes to exist; and therefore the particles
of the muscular fibre (which in its state of relaxation are supposed not to
touch) cannot affect each other without the influence of some intermediate
agent; this agent is here termed the spirit of animation, or sensorial
power, but may with equal propriety be termed the power, which causes
contraction; or may be called by any other name, which the reader may
choose to affix to it.

The contraction of a muscular fibre may be compared to the following
electric experiment, which is here mentioned not as a philosophical
analogy, but as an illustration or simile to facilitate the conception of a
difficult subject. Let twenty very small Leyden phials properly coated be
hung in a row by fine silk threads at a small distance from each other; let
the internal charge of one phial be positive, and of the other negative
alternately, if a communication be made from the internal surface of the
first to the external surface of the last in the row, they will all of them
instantly approach each other, and thus shorten a line that might connect
them like a muscular fibre. See Botanic Garden, p. 1. Canto I. 1. 202, note
on Gymnotus.

The attractions of electricity or of magnetism do not apply philosophically
to the illustration of the contraction of animal fibres, since the force of
those attractions increases in some proportion inversely as the distance,
but in muscular motion there appears no difference in velocity or strength
during the beginning or end of the contraction, but what may be clearly
ascribed to the varying mechanic advantage in the approximation of one bone
to another. Nor can muscular motion be assimilated with greater
plausibility to the attraction of cohesion or elasticity; for in bending a
steel spring, as a small sword, a less force is required to bend it the
first inch than the second; and the second than the third; the particles of
steel on the convex side of the bent spring endeavouring to restore
themselves more powerfully the further they are drawn from each other. See
Botanic Garden, P. I. addit. Note XVIII.

I am aware that this may be explained another way, by supposing the
elasticity of the spring to depend more on the compression of the particles
on the concave side than on the extension of them on the convex side; and
by supposing the elasticity of the elastic gum to depend more on the
resistance to the lateral compression of its particles than to the
longitudinal extension of them. Nevertheless in muscular contraction, as
above observed, there appears no difference in the velocity or force of it
at its commencement or at its termination; from whence we must conclude
that animal contraction is governed by laws of its own, and not by those of
mechanics, chemistry, magnetism, or electricity.

On these accounts I do not think the experiments conclusive, which were
lately published by Galvani, Volta, and others, to shew a similitude
between the spirit of animation, which contracts the muscular fibres, and
the electric fluid. Since the electric fluid may act only as a more potent
stimulus exciting the muscular fibres into action, and not by supplying
them with a new quantity of the spirit of life. Thus in a recent hemiplegia
I have frequently observed, when the patient yawned and stretched himself,
that the paralytic limbs moved also, though they were totally disobedient
to the will. And when he was electrified by passing shocks from the
affected hand to the affected foot, a motion of the paralytic limbs was
also produced. Now as in the act of yawning the muscles of the paralytic
limbs were excited into action by the stimulus of the irksomeness of a
continued posture, and not by any additional quantity of the spirit of
life; so we may conclude, that the passage of the electric fluid, which
produced a similar effect, acted only as a stimulus, and not by supplying
any addition of sensorial power.

If nevertheless this theory should ever become established, a stimulus must
be called an eductor of vital ether; which stimulus may consist of
sensation or volition, as in the electric eel, as well as in the appulses
of external bodies; and by drawing off the charges of vital fluid may
occasion the contraction or motions of the muscular fibres, and organs of
sense.

2. The immediate effect of the action of the spirit of animation or
sensorial power on the fibrous parts of the body, whether it acts in the
mode of irritation, sensation, volition, or association, is a contraction
of the animal fibre, according to the second law of animal causation. Sect.
IV. Thus the stimulus of the blood induces the contraction of the heart;
the agreeable taste of a strawberry produces the contraction of the muscles
of deglutition; the effort of the will contracts the muscles, which move
the limbs in walking; and by association other muscles of the trunk are
brought into contraction to preserve the balance of the body. The fibrous
extremities of the organs of sense have been shewn, by the ocular spectra
in Sect. III. to suffer similar contraction by each of the above modes of
excitation; and by their configurations to constitute our ideas.

3. After animal fibres have for some time been excited into contraction, a
relaxation succeeds, even though the exciting cause continues to act. In
respect to the irritative motions this is exemplified in the peristaltic
contractions of the bowels; which cease and are renewed alternately, though
the stimulus of the aliment continues to be uniformly applied; in the
sensitive motions, as in strangury, tenesmus, and parturition, the
alternate contractions and relaxations of the muscles exist, though the
stimulus is perpetual. In our voluntary exertions it is experienced, as no
one can hang long by the hands, however vehemently he wills so to do; and
in the associate motions the constant change of our attitudes evinces the
necessity of relaxation to those muscles, which have been long in action.

This relaxation of a muscle after its contraction, even though the stimulus
continues to be applied, appears to arise from the expenditure or
diminution of the spirit of animation previously resident in the muscle,
according to the second law of animal causation in Sect. IV. In those
constitutions, which are termed weak, the spirit of animation becomes
sooner exhausted, and tremulous motions are produced, as in the hands of
infirm people, when they lift a cup to their mouths. This quicker
exhaustion of the spirit of animation is probably owing to a less quantity
of it residing in the acting fibres, which therefore more frequently
require a supply from the nerves, which belong to them.

4. If the sensorial power continues to act, whether it acts in the mode of
irritation, sensation, volition, or association, a new contraction of the
animal fibre succeeds after a certain interval; which interval is of
shorter continuance in weak people than in strong ones. This is exemplified
in the shaking of the hands of weak people, when they attempt to write. In
a manuscript epistle of one of my correspondents, which is written in a
small hand, I observed from four to six zigzags in the perpendicular stroke
of every letter, which shews that both the contractions of the fingers, and
intervals between them, must have been performed in very short periods of
time.

The times of contraction of the muscles of enfeebled people being less, and
the intervals between those contractions being less also, accounts for the
quick pulse in fevers with debility, and in dying animals. The shortness of
the intervals between one contraction and another in weak constitutions, is
probably owing to the general deficiency of the quantity of the spirit of
animation, and that therefore there is a less quantity of it to be received
at each interval of the activity of the fibres. Hence in repeated motions,
as of the fingers in performing on the harpsichord, it would at first sight
appear, that swiftness and strength were incompatible; nevertheless the
single contraction of a muscle is performed with greater velocity as well
as with greater force by vigorous constitutions, as in throwing a javelin.

There is however another circumstance, which may often contribute to cause
the quickness of the pulse in nervous fevers, as in animals bleeding to
death in the slaughter-house; which is the deficient quantity of blood;
whence the heart is but half distended, and in consequence sooner
contracts. See Sect. XXXII. 2. 1.

For we must not confound frequency of repetition with quickness of motion,
or the number of pulsations with the velocity, with which the fibres, which
constitute the coats of the arteries, contract themselves. For where the
frequency of the pulsations is but seventy-five in a minute, as in health;
the contracting fibres, which constitute the sides of the arteries, may
move through a greater space in a given time, than where the frequency of
pulsation is one hundred and fifty in a minute, as in some fevers with
great debility. For if in those fevers the arteries do not expand
themselves in their diastole to more than half the usual diameter of their
diastole in health, the fibres which constitute their coats, will move
through a less space in a minute than in health, though they make two
pulsations for one.

Suppose the diameter of the artery during its systole to be one line, and
that the diameter of the same artery during its diastole is in health is
four lines, and in a fever with, great debility only two lines. It follows,
that the arterial fibres contract in health from a circle of twelve lines
in circumference to a circle of three lines in circumference, that is they
move through a space of nine lines in length. While the arterial fibres in
the fever with debility would twice contract from a circle of six lines to
a circle of three lines; that is while they move through a space equal to
six lines. Hence though the frequency of pulsation in fever be greater as
two to one, yet the velocity of contraction in health is greater as nine to
six, or as three to two.

On the contrary in inflammatory diseases with strength, as in the pleurisy,
the velocity of the contracting sides of the arteries is much greater than
in health, for if we suppose the number of pulsations in a pleurisy to be
half as much more than in health, that is as one hundred and twenty to
eighty, (which is about what generally happens in inflammatory diseases)
and if the diameter of the artery in diastole be one third greater than in
health, which I believe is near the truth, the result will be, that the
velocity of the contractile sides of the arteries will be in a pleurisy as
two and a half to one, compared to the velocity of their contraction in a
state of health, for if the circumference of the systole of the artery be
three lines, and the diastole in health be twelve lines in circumference,
and in a pleurisy eighteen lines; and secondly, if the artery pulsates
thrice in the diseased state for twice in the healthy one, it follows, that
the velocity of contraction in the diseased state to that in the healthy
state will be forty-five to eighteen, or as two and a half to one.

From hence it would appear, that if we had a criterion to determine the
velocity of the arterial contractions, it would at the same time give us
their strength, and thus be of more service in distinguishing diseases,
than the knowledge of their frequency. As such a criterion cannot be had,
the frequency of pulsation, the age of the patient being allowed for, will
in some measure assist us to distinguish arterial strength from arterial
debility, since in inflammatory diseases with strength the frequency seldom
exceeds one hundred and eighteen or one hundred and twenty pulsations in a
minute; unless under peculiar circumstance, as the great additional stimuli
of wine or of external heat.

5. After a muscle or organ of sense has been excited into contraction, and
the sensorial power ceases to act, the last situation or configuration of
it continues; unless it be disturbed by the action of some antagonist
fibres, or other extraneous power. Thus in weak or languid people, wherever
they throw their limbs on their bed or sofa, there they lie, till another
exertion changes their attitude; hence one kind of ocular spectra seems to
be produced after looking at bright objects; thus when a fire-stick is
whirled round in the night, there appears in the eye a complete circle of
fire; the action or configuration of one part of the retina not ceasing
before the return of the whirling fire.

Thus if any one looks at the setting sun for a short time, and then covers
his closed eyes with his hand, he will for many seconds of time perceive
the image of the sun on his retina. A similar image of all other bodies
would remain some time in the eye, but is effaced by the eternal change of
the motions of the extremity of this nerve in our attention to other
objects. See Sect. XVIII. 5. on Sleep. Hence the dark spots, and other
ocular spectra, are more frequently attended to, and remain longer in the
eyes of weak people, as after violent exercise, intoxication, or want of
sleep.

6. A contraction of the fibres somewhat greater than usual introduces
pleasurable sensation into the system, according to the fourth law of
animal causation. Hence the pleasure in the beginning of drunkenness is
owing to the increased action of the system from the stimulus of vinous
spirit or of opium. If the contractions be still greater in energy or
duration, painful sensations are introduced, as in consequence of great
heat, or caustic applications, or fatigue.

If any part of the system, which is used to perpetual activity, as the
stomach, or heart, or the fine vessels of the skin, acts for a time with
less energy, another kind of painful sensation ensues, which is called
hunger, or faintness, or cold. This occurs in a less degree in the
locomotive muscles, and is called wearysomeness. In the two former kinds of
sensation there is an expenditure of sensorial power, in these latter there
is an accumulation of it.

7. We have used the words exertion of sensorial power as a general term to
express either irritation, sensation, volition, or association; that is, to
express the activity or motion of the spirit of animation, at the time it
produces the contractions of the fibrous parts of the system. It may be
supposed that there may exist a greater or less mobility of the fibrous
parts of our system, or a propensity to be stimulated into contraction by
the greater or less quantity or energy of the spirit of animation; and that
hence if the exertion of the sensorial power be in its natural state, and
the mobility of the fibres be increased, the same quantity of fibrous
contraction will be caused, as if the mobility of the fibres continues in
its natural state, and the sensorial exertion be increased.

Thus it may be conceived, that in diseases accompanied with strength, as in
inflammatory fevers with arterial strength, that the cause of greater
fibrous contraction, may exist in the increased mobility of the fibres,
whose contractions are thence both more forceable and more frequent. And
that in diseases attended with debility, as in nervous fevers, where the
fibrous contractions are weaker, and more frequent, it may be conceived
that the cause consists in a decrease of mobility of the fibres; and that
those weak constitutions, which are attended with cold extremities and
large pupils of the eyes, may possess less mobility of the contractile
fibres, as well as less quantity of exertion of the spirit of animation.

In answer to this mode of reasoning it may be sufficient to observe, that
the contractile fibres consist of inert matter, and when the sensorial
power is withdrawn, as in death, they possess no power of motion at all,
but remain in their last state, whether of contraction or relaxation, and
must thence derive the whole of this property from the spirit of animation.
At the same time it is not improbable, that the moving fibres of strong
people may possess a capability of receiving or containing a greater
quantity of the spirit of animation than those of weak people.

In every contraction of a fibre there is an expenditure of the sensorial
power, or spirit of animation; and where the exertion of this sensorial
power has been for some time increased, and the muscles or organs of sense
have in consequence acted with greater energy, its propensity to activity
is proportionally lessened; which is to be ascribed to the exhaustion or
diminution of its quantity. On the contrary, where there has been less
fibrous contraction than usual for a certain time, the sensorial power or
spirit of animation becomes accumulated in the inactive part of the system.
Hence vigour succeeds rest, and hence the propensity to action of all our
organs of sense and muscles is in a state of perpetual fluctuation. The
irritability for instance of the retina, that is, its quantity of sensorial
power, varies every moment according to the brightness or obscurity of the
object last beheld compared with the present one. The same occurs to our
sense of heat, and to every part of our system, which is capable of being
excited into action.

When this variation of the exertion of the sensorial power becomes much and
permanently above or beneath the natural quantity, it becomes a disease. If
the irritative motions be too great or too little, it shews that the
stimulus of external things affect this sensorial power too violently or
too inertly. If the sensitive motions be too great or too little, the cause
arises from the deficient or exuberant quantity of sensation produced in
consequence of the motions of the muscular fibres or organs of sense; if
the voluntary actions are diseased the cause is to be looked for in the
quantity of volition produced in consequence of the desire or aversion
occasioned by the painful or pleasurable sensations above mentioned. And
the diseases of associations probably depend on the greater or less
quantity of the other three sensorial powers by which they were formed.

From whence it appears that the propensity to action, whether it be called
irritability, sensibility, voluntarity, or associability, is only another
mode of expression for the quantity of sensorial power residing in the
organ to be excited. And that on the contrary the words inirritability and
insensibility, together with inaptitude to voluntary and associate motions,
are synonymous with deficiency of the quantity of sensorial power, or of
the spirit of animation, residing in the organs to be excited.

II. _Of sensorial Exertion._

1. There are three circumstances to be attended to in the production of
animal motions, 1st. The stimulus. 2d. The sensorial power. 3d. The
contractile fibre. 1st. A stimulus, external to the organ, originally
induces into action the sensorial faculty termed irritation; this produces
the contraction of the fibres, which, if it be perceived at all, introduces
pleasure or pain; which in their active state are termed sensation; which
is another sensorial faculty, and occasionally produces contraction of the
fibres; this pleasure or pain is therefore to be considered as another
stimulus, which may either act alone or in conjunction with the former
faculty of the sensorium termed irritation.

This new stimulus of pleasure or pain either induces into action the
sensorial faculty termed sensation, which then produces the contraction of
the fibres; or it introduces desire or aversion, which excite into action
another sensorial faculty, termed volition, and may therefore be considered
as another stimulus, which either alone or in conjunction with one or both
of the two former faculties of the sensorium produces the contraction of
animal fibres. There is another sensorial power, that of association, which
perpetually, in conjunction with one or more of the above, and frequently
singly, produces the contraction of animal fibres, and which is itself
excited into action by the previous motions of contracting fibres.

Now as the sensorial power, termed irritation, residing in any particular
fibres, is excited into exertion by the stimulus of external bodies acting
on those fibres; the sensorial power, termed sensation, residing in any
particular fibres is excited into exertion by the stimulus of pleasure or
pain acting on those fibres; the sensorial power, termed volition, residing
in any particular fibres is excited into exertion by the stimulus of desire
or aversion; and the sensorial power, termed association, residing in any
particular fibres, is excited into action by the stimulus of other fibrous
motions, which had frequently preceded them. The word stimulus may
therefore be used without impropriety of language, for any of these four
causes, which excite the four sensorial powers into exertion. For though
the immediate cause of volition has generally been termed _a motive_; and
that of irritation only has generally obtained the name of _stimulus_; yet
as the immediate cause, which excites the sensorial powers of sensation, or
of association into exertion, have obtained no general name, we shall use
the word stimulus for them all.

Hence the quantity of motion produced in any particular part of the animal
system will be as the quantity of stimulus and the quantity of sensorial
power, or spirit of animation, residing in the contracting fibres. Where
both these quantities are great, _strength_ is produced, when that word is
applied to the motions of animal bodies. Where either of them is deficient,
_weakness_ is produced, as applied to the motions of animal bodies.

Now as the sensorial power, or spirit of animation, is perpetually
exhausted by the expenditure of it in fibrous contractions, and is
perpetually renewed by the secretion or production of it in the brain and
spinal marrow, the quantity of animal strength must be in a perpetual state
of fluctuation on this account; and if to this be added the unceasing
variation of all the four kinds of stimulus above described, which produce
the exertions of the sensorial powers, the ceaseless vicissitude of animal
strength becomes easily comprehended.

If the quantity of sensorial power remains the same, and the quantity of
stimulus be lessened, a weakness of the fibrous contractions ensues, which
may be denominated _debility from defect of stimulus_. If the quantity of
stimulus remains the same, and the quantity of sensorial power be lessened,
another kind of weakness ensues, which may be termed _debility from defect
of sensorial power_; the former of these is called by Dr. Brown, in his
Elements of Medicine, direct debility, and the latter indirect debility.
The coincidence of some parts of this work with correspondent deductions in
the Brunonian Elementa Medicina, a work (with some exceptions) of great
genius, must be considered as confirmations of the truth of the theory, as
they were probably arrived at by different trains of reasoning.

Thus in those who have been exposed to cold and hunger there is a
deficiency of stimulus. While in nervous fever there is a deficiency of
sensorial power. And in habitual drunkards, in a morning before their usual
potation, there is a deficiency both of stimulus and of sensorial power.
While, on the other hand, in the beginning of intoxication there is an
excess of stimulus; in the hot-ach, after the hands have been immersed in
snow, there is a redundancy of sensorial power; and in inflammatory
diseases with arterial strength, there is an excess of both.

Hence if the sensorial power be lessened, while the quantity of stimulus
remains the same as in nervous fever, the frequency of repetition of the
arterial contractions may continue, but their force in respect to removing
obstacles, as in promoting the circulation of the blood, or the velocity of
each contraction, will be diminished, that is, the animal strength will be
lessened. And secondly, if the quantity of sensorial power be lessened, and
the stimulus be increased to a certain degree, as in giving opium in
nervous fevers, the arterial contractions may be performed more frequently
than natural, yet with less strength.

And thirdly, if the sensorial power continues the same in respect to
quantity, and the stimulus be somewhat diminished, as in going into a
darkish room, or into a coldish bath, suppose of about eighty degrees of
heat, as Buxton-bath, a temporary weakness of the affected fibres is
induced, till an accumulation of sensorial power gradually succeeds, and
counterbalances the deficiency of stimulus, and then the bath ceases to
feel cold, and the room ceases to appear dark; because the fibres of the
subcutaneous vessels, or of the organs of sense, act with their usual
energy.

A set of muscular fibres may thus be stimulated into violent exertion, that
is, they may act frequently, and with their whole sensorial power, but may
nevertheless not act strongly; because the quantity of their sensorial
power was originally small, or was previously exhausted. Hence a stimulus
may be great, and the irritation in consequence act with its full force, as
in the hot paroxysms of nervous fever; but if the sensorial power, termed
irritation, be small in quantity, the force of the fibrous contractions,
and the times of their continuance in their contracted state, will be
proportionally small.

In the same manner in the hot paroxysm of putrid fevers, which are shewn in
Sect. XXXIII. to be inflammatory fevers with arterial debility, the
sensorial power termed sensation is exerted with great activity, yet the
fibrous contractions, which produce the circulation of the blood, are
performed without strength, because the quantity of sensorial power then
residing in that part of the system is small.

Thus in irritative fever with arterial strength, that is, with excess of
spirit of animation, the quantity of exertion during the hot part of the
paroxysm is to be estimated from the quantity of stimulus, and the quantity
of sensorial power. While in sensitive (or inflammatory) fever with
arterial strength, that is, with excess of spirit of animation, the violent
and forcible actions of the vascular system during the hot part of the
paroxysm are induced by the exertions of two sensorial powers, which are
excited by two kinds of stimulus. These are the sensorial power of
irritation excited by the stimulus of bodies external to the moving fibres,
and the sensorial power of sensation excited by the pain in consequence of
the increased contractions of those moving fibres.

And in insane people in some cases the force of their muscular actions will
be in proportion to the quantity of sensorial power, which they possess,
and the quantity of the stimulus of desire or aversion, which excites their
volition into action. At the same time in other cases the stimulus of pain
or pleasure, and the stimulus of external bodies, may excite into action
the sensorial powers of sensation and irritation, and thus add greater
force to their muscular actions.

2. The application of the stimulus, whether that stimulus be some quality
of external bodies, or pleasure or pain, or desire or aversion, or a link
of association, excites the correspondent sensorial power into action, and
this causes the contraction of the fibre. On the contraction of the fibre a
part of the spirit of animation becomes expended, and the fibre ceases to
contract, though the stimulus continues to be applied; till in a certain
time the fibre having received a supply of sensorial power is ready to
contract again, if the stimulus continues to be applied. If the stimulus on
the contrary be withdrawn, the same quantity of quiescent sensorial power
becomes resident in the fibre as before its contraction; as appears from
the readiness for action of the large locomotive muscles of the body in a
short time after common exertion.

But in those muscular fibres, which are subject to constant stimulus, as
the arteries, glands, and capillary vessels, another phenomenon occurs, if
their accustomed stimulus be withdrawn; which is, that the sensorial power
becomes accumulated in the contractile fibres, owing to the want of its
being perpetually expended, or carried away, by their usual unremitted
contractions. And on this account those muscular fibres become afterwards
excitable into their natural actions by a much weaker stimulus; or into
unnatural violence of action by their accustomed stimulus, as is seen in
the hot fits of intermittent fevers, which are in consequence of the
previous cold ones. Thus the minute vessels of the skin are constantly
stimulated by the fluid matter of heat; if the quantity of this stimulus of
heat be a while diminished, as in covering the hands with snow, the vessels
cease to act, as appears from the paleness of the skin; if this cold
application of snow be continued but a short time, the sensorial power,
which had habitually been supplied to the fibres, becomes now accumulated
in them, owing to the want of its being expended by their accustomed
contractions. And thence a less stimulus of heat will now excite them into
violent contractions.

If the quiescence of fibres, which had previously been subject to perpetual
stimulus, continues a longer time; or their accustomed stimulus be more
completely withdrawn; the accumulation of sensorial power becomes still
greater, as in those exposed to cold and hunger; pain is produced, and the
organ gradually dies from the chemical changes, which take place in it; or
it is at a great distance of time restored to action by stimulus applied
with great caution in small quantity, as happens to some larger animals and
to many insects, which during the winter months lie benumbed with cold, and
are said to sleep, and to persons apparently drowned, or apparently frozen
to death. Snails have been said to revive by throwing them into water after
having been many years shut up in the cabinets of the curious; and eggs and
seeds in general are restored to life after many months of torpor by the
stimulus of warmth and moisture.

The inflammation of schirrous tumours, which have long existed in a state
of inaction, is a process of this kind; as well as the sensibility acquired
by inflamed tendons and bones, which had at their formation a similar
sensibility, which had so long lain dormant in their uninflamed state.

3. If after long quiescence from defect of stimulus the fibres, which had
previously been habituated to perpetual stimulus, are again exposed to but
their usual quantity of it; as in those who have suffered the extremes of
cold or hunger; a violent exertion of the affected organ commences, owing,
as above explained, to the great accumulation of sensorial power. This
violent exertion not only diminishes the accumulated spirit of animation,
but at the same time induces pleasure or pain into the system, which,
whether it be succeeded by inflammation or not, becomes an additional
stimulus, and acting along with the former one, produces still greater
exertions; and thus reduces the sensorial power in the contracting fibres
beneath its natural quantity.

When the spirit of animation is thus exhausted by useless exertions, the
organ becomes torpid or unexcitable into action, and a second fit of
quiescence succeeds that of abundant activity. During this second fit of
quiescence the sensorial power becomes again accumulated, and another fit
of exertion follows in train. These vicissitudes of exertion and inertion
of the arterial system constitute the paroxysms of remittent fevers; or
intermittent ones, when there is an interval of the natural action of the
arteries between the exacerbations.

In these paroxysms of fevers, which consist of the libration of the
arterial system between the extremes of exertion and quiescence, either the
fits become less and less violent from the contractile fibres becoming
coming less excitable to the stimulus by habit, that is, by becoming
accustomed to it, as explained below XII. 3. 1. or the whole sensorial
power becomes exhausted, and the arteries cease to beat, and the patient
dies in the cold part of the paroxysm. Or secondly, so much pain is
introduced into the system by the violent contractions of the fibres, that
inflammation arises, which prevents future cold fits by expending a part of
the sensorial power in the extension of old vessels or the production of
new ones; and thus preventing the too great accumulation or exertion of it
in other parts of the system; or which by the great increase of stimulus
excites into great action the whole glandular system as well as the
arterial, and thence a greater quantity of sensorial power is produced in
the brain, and thus its exhaustion in any peculiar part of the system
ceases to be affected.

4. Or thirdly, in consequence of the painful or pleasurable sensation above
mentioned, desire and aversion are introduced, and inordinate volition
succeeds; which by its own exertions expends so much of the spirit of
animation, that the two other sensorial faculties, or irritation and
sensation, act so much more feebly; that the paroxysms of fever, or that
libration between the extremes of exertion and inactivity of the arterial
system, gradually subsides. On this account a temporary insanity is a
favourable sign in fevers, as I have had some opportunities of observing.

III. _Of repeated Stimulus._

1. When a stimulus is repeated more frequently than the expenditure of
sensorial power can be renewed in the acting organ, the effect of the
stimulus becomes gradually diminished. Thus if two grains of opium be
swallowed by a person unused to so strong a stimulus, all the vascular
systems in the body act with greater energy, all the secretions and the
absorption from those secreted fluids are increased in quantity; and
pleasure or pain are introduced into the system, which adds an additional
stimulus to that already too great. After some hours the sensorial power
becomes diminished in quantity, expended by the great activity of the
system; and thence, when the stimulus of the opium is withdrawn, the fibres
will not obey their usual degree of natural stimulus, and a consequent
torpor or quiescence succeeds, as is experienced by drunkards, who on the
day after a great excess of spirituous potation feel indigestion, head-ach,
and general debility.

In this fit of torpor or quiescence of a part or of the whole of the
system, an accumulation of the sensorial power in the affected fibres is
formed, and occasions a second paroxysm of exertion by the application only
of the natural stimulus, and thus a libration of the sensorial exertion
between one excess and the other continues for two or three days, where the
stimulus was violent in degree; and for weeks in some fevers, from the
stimulus of contagious matter.

But if a second dose of opium be exhibited before the fibres have regained
their natural quantity of sensorial power, its effect will be much less
than the former, because the spirit of animation or sensorial power is in
part exhausted by the previous excess of exertion. Hence all medicines
repeated too frequently gradually lose their effect, as opium and wine.
Many things of disagreeable taste at first cease to be disagreeable by
frequent repetition, as tobacco; grief and pain gradually diminish, and at
length cease altogether, and hence life itself becomes tolerable.

Besides the temporary diminution of the spirit of animation or sensorial
power, which is naturally stationary or resident in every living fibre, by
a single exhibition of a powerful stimulus, the contractile fibres
themselves, by the perpetual application of a new quantity of stimulus,
before they have regained their natural quantity of sensorial power, appear
to suffer in their capability of receiving so much as the natural quantity
of sensorial power; and hence a permanent deficiency of spirit of animation
takes place, however long the stimulus may have been withdrawn. On this
cause depends the permanent debility of those, who have been addicted to
intoxication, the general weakness of old age, and the natural debility or
inirritability of those, who have pale skins and large pupils of their
eyes.

There is a curious phenomenon belongs to this place, which has always
appeared difficult of solution; and that is, that opium or aloes may be
exhibited in small doses at first, and gradually increased to very large
ones without producing stupor or diarrhoea. In this case, though the opium
and aloes are given in such small doses as not to produce intoxication or
catharsis, yet they are exhibited in quantities sufficient in some degree
to exhaust the sensorial power, and hence a stronger and a stronger dose is
required; otherwise the medicine would soon cease to act at all.

On the contrary, if the opium or aloes be exhibited in a large dose at
first, so as to produce intoxication or diarrhoea; after a few repetitions
the quantity of either of them may be diminished, and they will still
produce this effect. For the more powerful stimulus dissevers the
progressive catenations of animal motions, described in Sect. XVII. and
introduces a new link between them; whence every repetition strengthens
this new association or catenation, and the stimulus may be gradually
decreased, or be nearly withdrawn, and yet the effect shall continue;
because the sensorial power of association or catenation being united with
the stimulus, increases in energy with every repetition of the catenated
circle; and it is by these means that all the irritative associations of
motions are originally produced.

2. When a stimulus is repeated at such distant intervals of time, that the
natural quantity of sensorial power becomes completely restored in the
acting fibres, it will act with the same energy as when first applied.
Hence those who have lately accustomed themselves to large doses of opium
by beginning with small ones, and gradually increasing them, and repeating
them frequently, as mentioned in the preceding paragraph; if they intermit
the use of it for a few days only, must begin again with as small doses as
they took at first, otherwise they will experience the inconveniences of
intoxication.

On this circumstance depend the constant unfailing effects of the various
kinds of stimulus, which excite into action all the vascular systems in the
body; the arterial, venous, absorbent, and glandular vessels, are brought
into perpetual unwearied action by the fluids, which are adapted to
stimulate them; but these have the sensorial power of association added to
that of irritation, and even in some degree that of sensation, and even of
volition, as will be spoken of in their places; and life itself is thus
carried on by the production of sensorial power being equal to its waste or
expenditure in the perpetual movement of the vascular organization.

3. When a stimulus is repeated at uniform intervals of time with such
distances between them, that the expenditure of sensorial power in the
acting fibres becomes completely renewed, the effect is produced with
greater facility or energy. For the sensorial power of association is
combined with the sensorial power of irritation, or, in common language,
the acquired habit assists the power of the stimulus.

This circumstance not only obtains in the annual and diurnal catenations of
animal motions explained in Sect. XXXVI. but in every less circle of
actions or ideas, as in the burthen of a song, or the iterations of a
dance; and constitutes the pleasure we receive from repetition and
imitation; as treated of in Sect. XXII. 2.

4. When a stimulus has been many times repeated at uniform intervals, so as
to produce the complete action of the organ, it may then be gradually
diminished, or totally withdrawn, and the action of the organ will
continue. For the sensorial power of association becomes united with that
of irritation, and by frequent repetition becomes at length of sufficient
energy to carry on the new link in the circle of actions, without the
irritation which at first introduced it.

Hence, when the bark is given at stated intervals for the cure of
intermittent fevers, if sixty grains of it be given every three hours for
the twenty-four hours preceding the expected paroxysm, so as to stimulate
the defective part of the system into action, and by that means to prevent
the torpor or quiescence of the fibres, which constitutes the cold fit;
much less than half the quantity, given before the time at which another
paroxysm of quiescence would have taken place, will be sufficient to
prevent it; because now the sensorial power, termed association, acts in a
twofold manner. First, in respect to the period of the catenation in which
the cold fit was produced, which is now dissevered by the stronger stimulus
of the first doses of the bark; and, secondly, because each dose of bark
being repeated at periodical times, has its effect increased by the
sensorial faculty of association being combined with that of irritation.

Now, when sixty grains of Peruvian bark are taken twice a day, suppose at
ten o'clock and at six, for a fortnight, the irritation excited by this
additional stimulus becomes a part of the diurnal circle of actions, and
will at length carry on the increased action of the system without the
assistance of the stimulus of the bark. On this theory the bitter
medicines, chalybeates, and opiates in appropriated doses, exhibited for a
fortnight, give permanent strength to pale feeble children, and other weak
constitutions.

5. When a defect of stimulus, as of heat, recurs at certain diurnal
intervals, which induces some torpor or quiescence of a part of the system,
the diurnal catenation of actions becomes disordered, and a new association
with this link of torpid action is formed; on the next period the quantity
of quiescence will be increased, suppose the same defect of stimulus to
recur, because now the new association conspires with the defective
irritation in introducing the torpid action of this part of the diurnal
catenation. In this manner many fever-fits commence, where the patient is
for some days indisposed at certain hours, before the cold paroxysm of
fever is completely formed. See Sect. XVII. 3. 3. on Catenation of Animal
Motions.

6. If a stimulus, which at first excited the affected organ into so great
exertion as to produce sensation, be continued for a certain time, it will
cease to produce sensation both then and when repeated, though the
irritative motions in consequence of it may continue or be re-excited.

Many catenations of irritative motions were at first succeeded by
sensation, as the apparent motions of objects when we walk past them, and
probably the vital motions themselves in the early state of our existence.
But as those sensations were followed by no movements of the system in
consequence of them, they gradually ceased to be produced, not being joined
to any succeeding link of catenation. Hence contagious matter, which has
for some weeks stimulated the system into great and permanent sensation,
ceases afterwards to produce general sensation, or inflammation, though it
may still induce topical irritations. See Sect. XXXIII. 2. 8. XIX. 9.

Our absorbent system then seems to receive those contagious matters, which
it has before experienced, in the same manner as it imbibes common moisture
or other fluids; that is, without being thrown into so violent action as to
produce sensation; the consequence of which is an increase of daily energy
or activity, till inflammation and its consequences succeed.

7. If a stimulus excites an organ into such violent contractions as to
produce sensation, the motions of which organ had not usually produced
sensation, this new sensorial power, added to the irritation occasioned by
the stimulus, increases the activity of the organ. And if this activity be
catenated with the diurnal circle of actions, an increasing inflammation is
produced; as in the evening paroxysms of small-pox, and other fevers with
inflammation. And hence schirrous tumours, tendons and membranes, and
probably the arteries themselves become inflamed, when they are strongly
stimulated.

IV. _Of Stimulus greater than natural._

1. A quantity of stimulus greater than natural, producing an increased
exertion of sensorial power, whether that exertion be in the mode of
irritation, sensation, volition, or association, diminishes the general
quantity of it. This fact is observable in the progress of intoxication, as
the increased quantity or energy of the irritative motions, owing to the
stimulus of vinous spirit, introduces much pleasurable sensation into the
system, and much exertion of muscular or sensual motions in consequence of
this increased sensation; the voluntary motions, and even the associate
ones, become much impaired or diminished; and delirium and staggering
succeed. See Sect. XXI. on Drunkenness. And hence the great prostration of
the strength of the locomotive muscles in some fevers, is owing to the
exhaustion of sensorial power by the increased action of the arterial
system.

In like manner a stimulus greater than natural, applied to a part of the
system, increases the exertion of sensorial power in that part, and
diminishes it in some other part. As in the commencement of scarlet fever,
it is usual to see great redness and heat on the faces and breasts of
children, while at the same time their feet are colder than natural;
partial heats are observable in other fevers with debility, and are
generally attended with torpor or quiescence of some other part of the
system. But these partial exertions of sensorial power are sometimes
attended with increased partial exertions in other parts of the system,
which sympathize with them, as the flushing of the face after a full meal.
Both these therefore are to be ascribed to sympathetic associations,
explained in Sect. XXXV. and not to general exhaustion or accumulation of
sensorial power.

2. A quantity of stimulus greater than natural, producing an increased
exertion of sensorial power in any particular organ, diminishes the
quantity of it in that organ. This appears from the contractions of animal
fibres being not so easily excited by a less stimulus after the organ has
been subjected to a greater. Thus after looking at any luminous object of a
small size, as at the setting sun, for a short time, so as not much to
fatigue the eye, this part of the retina becomes less sensible to smaller
quantities of light; hence when the eyes are turned on other less luminous
parts of the sky, a dark spot is seen resembling the shape of the sun, or
other luminous object which we last behold. See Sect. XL. No. 2.

Thus we are some time before we can distinguish objects in an obscure room
after coming from bright day-light, though the iris presently contracts
itself. We are not able to hear weak sounds after loud ones. And the
stomachs of those who have been much habituated to the stronger stimulus of
fermented or spirituous liquors, are not excited into due action by weaker
ones.

3. A quantity of stimulus something greater than the last mentioned, or
longer continued, induces the organ into spasmodic action, which ceases and
recurs alternately. Thus on looking for a time on the setting sun, so as
not greatly to fatigue the sight, a yellow spectrum is seen when the eyes
are closed and covered, which continues for a time, and then disappears and
recurs repeatedly before it entirely vanishes. See Sect. XL. No. 5. Thus
the action of vomiting ceases and is renewed by intervals, although the
emetic drug is thrown up with the first effort. A tenesmus continues by
intervals some time after the exclusion of acrid excrement; and the
pulsations of the heart of a viper are said to continue some time after it
is cleared from its blood.

In these cases the violent contractions of the fibres produce pain
according to law 4; and this pain constitutes an additional kind or
quantity of excitement, which again induces the fibres into contraction,
and which painful excitement is again renewed, and again induces
contractions of the fibres with gradually diminishing effect.

4. A quantity of stimulus greater than that last mentioned, or longer
continued, induces the antagonist muscles into spasmodic action. This is
beautifully illustrated by the ocular spectra described in Sect. XL. No. 6.
to which the reader is referred. From those experiments there is reason to
conclude that the fatigued part of the retina throws itself into a contrary
mode of action like oscitation or pandiculation, as soon as the stimulus,
which has fatigued it, is withdrawn; but that it still remains liable to be
excited into action by any other colours except the colour with which it
has been fatigued. Thus the yawning and stretching the limbs after a
continued action or attitude seems occasioned by the antagonist muscles
being stimulated by their extension during the contractions of those in
action, or in the situation in which that action last left them.

5. A quantity of stimulus greater than the last, or longer continued,
induces variety of convulsions or fixed spasms either of the affected organ
or of the moving fibres in the other parts of the body. In respect to the
spectra in the eye, this is well illustrated in No. 7 and 8, of Sect. XL.
Epileptic convulsions, as the emprosthotonos and opisthotonos, with the
cramp of the calf of the leg, locked jaw, and other cataleptic fits, appear
to originate from pain, as some of these patients scream aloud before the
convulsion takes place; which seems at first to be an effort to relieve
painful sensation, and afterwards an effort to prevent it.

In these cases the violent contractions of the fibres produce so much pain,
as to constitute a perpetual excitement; and that in so great a degree as
to allow but small intervals of relaxation of the contracting fibres as in
convulsions, or no intervals at all as in fixed spasms.

6. A quantity of stimulus greater than the last, or longer continued,
produces a paralysis of the organ. In many cases this paralysis is only a
temporary effect, as on looking long on a small area of bright red silk
placed on a sheet of white paper on the floor in a strong light, the red
silk gradually becomes paler, and at length disappears; which evinces that
a part of the retina, by being violently excited, becomes for a time
unaffected by the stimulus of that colour. Thus cathartic medicines,
opiates, poisons, contagious matter, cease to influence our system after it
has been habituated to the use of them, except by the exhibition of
increased quantities of them; our fibres not only become unaffected by
stimuli, by which they have previously been violently irritated, as by the
matter of the small-pox or measles; but they also become unaffected by
sensation, where the violent exertions, which disabled them, were in
consequence of too great quantity of sensation. And lastly the fibres,
which become disobedient to volition, are probably disabled by their too
violent exertions in consequence of too great a quantity of volition.

After every exertion of our fibres a temporary paralysis succeeds, whence
the intervals of all muscular contractions, as mentioned in No. 3 and 4 of
this Section; the immediate cause of these more permanent kinds of
paralysis is probably owing in the same manner to the too great exhaustion
of the spirit of animation in the affected part; so that a stronger
stimulus is required, or one of a different kind from that, which
occasioned those too violent contractions, to again excite the affected
organ into activity; and if a stronger stimulus could be applied, it must
again induce paralysis.

For these powerful stimuli excite pain at the same time, that they produce
irritation; and this pain not only excites fibrous motions by its stimulus,
but it also produces volition; and thus all these stimuli acting at the
same time, and sometimes with the addition of their associations, produce
so great exertion as to expend the whole of the sensorial power in the
affected fibres.

V. _Of Stimulus less than natural._

1. A quantity of stimulus less than natural, producing a decreased exertion
of sensorial power, occasions an accumulation of the general quantity of
it. This circumstance is observable in the hemiplagia, in which the
patients are perpetually moving the muscles, which are unaffected. On this
account we awake with greater vigour after sleep, because during so many
hours, the great usual expenditure of sensorial power in the performance of
voluntary actions, and in the exertions of our organs of sense, in
consequence of the irritations occasioned by external objects had been
suspended, and a consequent accumulation had taken place.

In like manner the exertion of the sensorial power less than natural in one
part of the system, is liable to produce an increase of the exertion of it
in some other part. Thus by the action of vomiting, in which the natural
exertion of the motions of the stomach are destroyed or diminished, an
increased absorption of the pulmonary and cellular lymphatics is produced,
as is known by the increased absorption of the fluid deposited in them in
dropsical cases. But these partial quiescences of sensorial power are also
sometimes attended with other partial quiescences, which sympathize with
them, as cold and pale extremities from hunger. These therefore are to be
ascribed to the associations of sympathy explained in Sect. XXXV. and not
to the general accumulation of sensorial power.

2. A quantity of stimulus less than natural, applied to fibres previously
accustomed to perpetual stimulus, is succeeded by accumulation of sensorial
power in the affected organ. The truth of this proposition is evinced,
because a stimulus less than natural, if it be somewhat greater than that
above mentioned, will excite the organ so circumstanced into violent
activity. Thus on a frosty day with wind, the face of a person exposed to
the wind is at first pale and shrunk; but on turning the face from the
wind, it becomes soon of a glow with warmth and flushing. The glow of the
skin in emerging from the cold-bath is owing to the same cause.

It does not appear, that an accumulation of sensorial power above the
natural quantity is acquired by those muscles, which are not subject to
perpetual stimulus, as the locomotive muscles: these, after the greatest
fatigue, only acquire by rest their usual aptitude to motion; whereas the
vascular system, as the heart and arteries, after a short quiescence, are
thrown into violent action by their natural quantity of stimulus.

Nevertheless by this accumulation of sensorial power during the application
of decreased stimulus, and by the exhaustion of it during the action of
increased stimulus, it is wisely provided, that the actions of the vascular
muscles and organs of sense are not much deranged by small variations of
stimulus; as the quantity of sensorial power becomes in some measure
inversely as the quantity of stimulus.

3. A quantity of stimulus less than that mentioned above, and continued for
some time, induces pain in the affected organ, as the pain of cold in the
hands, when they are immersed in snow, is owing to a deficiency of the
stimulation of heat. Hunger is a pain from the deficiency of the
stimulation of food. Pain in the back at the commencement of ague-fits, and
the head-achs which attend feeble people, are pains from defect of
stimulus, and are hence relieved by opium, essential oils, spirit of wine.

As the pains, which originate from defect of stimulus, only occur in those
parts of the system, which have been previously subjected to perpetual
stimulus; and as an accumulation of sensorial power is produced in the
quiescent organ along with the pain, as in cold or hunger, there is reason
to believe, that the pain is owing to the accumulation of sensorial power.
For, in the locomotive muscles, in the retina of the eye, and other organs
of senses, no pain occurs from the absence of stimulus, nor any great
accumulation of sensorial power beyond their natural quantity, since these
organs have not been used to a perpetual supply of it. There is indeed a
greater accumulation occurs in the organ of vision after its quiescence,
because it is subject to more constant stimulus.

4. A certain quantity of stimulus less than natural induces the moving
organ into feebler and more frequent contractions, as mentioned in No. I.
4. of this Section. For each contraction moving through a less space, or
with less force, that is, with less expenditure of the spirit of animation,
is sooner relaxed, and the spirit of animation derived at each interval
into the acting fibres being less, these intervals likewise become shorter.
Hence the tremours of the hands of people accustomed to vinous spirit, till
they take their usual stimulus; hence the quick pulse in fevers attended
with debility, which is greater than in fevers attended with strength; in
the latter the pulse seldom beats above 120 times in a minute, in the
former it frequently exceeds 140.

It must be observed, that in this and the two following articles the
decreased action of the system is probably more frequently occasioned by
deficiency in the quantity of sensorial power, than in the quantity of
stimulus. Thus those feeble constitutions which have large pupils of their
eyes, and all who labour under nervous fevers, seem to owe their want of
natural quantity of activity in the system to the deficiency of sensorial
power; since, as far as can be seen, they frequently possess the natural
quantity of stimulus.

5. A certain quantity of stimulus, less than that above mentioned, inverts
the order of successive fibrous contractions; as in vomiting the vermicular
motions of the stomach and duodenum are inverted, and their contents
ejected, which is probably owing to the exhaustion of the spirit of
animation in the acting muscles by a previous excessive stimulus, as by the
root of ipecacuanha, and the consequent defect of sensorial power. The same
retrograde motions affect the whole intestinal canal in ileus; and the
oesophagus in globus hystericus. See this further explained in Sect. XXIX.
No. 11. on Retrograde Motions.

I must observe, also, that something similar happens in the production of
our ideas, or sensual motions, when they are too weakly excited; when any
one is thinking intensely about one thing, and carelessly conversing about
another, he is liable to use the word of a contrary meaning to that which
he designed, as cold weather for hot weather, summer for winter.

6. A certain quantity of stimulus, less than that above mentioned, is
succeeded by paralysis, first of the voluntary and sensitive motions, and
afterwards of those of irritation, and of association, which constitutes
death.

VI. _Cure of increased Exertion._

1. The cure, which nature has provided for the increased exertion of any
part of the system, consists in the consequent expenditure of the sensorial
power. But as a greater torpor follows this exhaustion of sensorial power,
as explained in the next paragraph, and a greater exertion succeeds this
torpor, the constitution frequently sinks under these increasing librations
between exertion and quiescence; till at length complete quiescence, that
is, death, closes the scene.

For, during the great exertion of the system in the hot fit of fever, an
increase of stimulus is produced from the greater momentum of the blood,
the greater distention of the heart and arteries, and the increased
production of heat, by the violent actions of the system occasioned by this
augmentation of stimulus, the sensorial power becomes diminished in a few
hours much beneath its natural quantity, the vessels at length cease to
obey even these great degrees of stimulus, as shewn in Sect. XL. 9. 1. and
a torpor of the whole or of a part of the system ensues.

Now as this second cold fit commences with a greater deficiency of
sensorial power, it is also attended with a greater deficiency of stimulus
than in the preceding cold fit, that is, with less momentum of blood, less
distention of the heart. On this account the second cold fit becomes more
violent and of longer duration than the first; and as a greater
accumulation of sensorial power must be produced before the system of
vessels will again obey the diminished stimulus, it follows, that the
second hot fit of fever will be more violent than the former one. And that
unless some other causes counteract either the violent exertions in the hot
fit, or the great torpor in the cold fit, life will at length be
extinguished by the expenditure of the whole of the sensorial power. And
from hence it appears, that the true means of curing fevers must be such as
decrease the action of the system in the hot fit, and increase it in the
cold fit; that is, such as prevent the too great diminution of sensorial
power in the hot fit, and the too great accumulation of it in the cold one.

2. Where the exertion of the sensorial powers is much increased, as in the
hot fits of fever or inflammation, the following are the usual means of
relieving it. Decrease the irritations by blood-letting, and other
evacuations; by cold water taken into the stomach, or injected as an enema,
or used externally; by cold air breathed into the lungs, and diffused over
the skin; with food of less stimulus than the patient has been accustomed
to.

3. As a cold fit, or paroxysm of inactivity of some parts of the system,
generally precedes the hot fit, or paroxysm of exertion, by which the
sensorial power becomes accumulated, this cold paroxysm should be prevented
by stimulant medicines and diet, as wine, opium, bark, warmth,
cheerfulness, anger, surprise.

4. Excite into greater action some other part of the system, by which means
the spirit of animation may be in part expended, and thence the inordinate
actions of the diseased part may be lessened. Hence when a part of the skin
acts violently, as of the face in the eruption of the small-pox, if the
feet be cold they should be covered. Hence the use of a blister applied
near a topical inflammation. Hence opium and warm bath relieve pains both
from excess and defect of stimulus.

5. First increase the general stimulation above its natural quantity, which
may in some degree exhaust the spirit of animation, and then decrease the
stimulation beneath its natural quantity. Hence after sudorific medicines
and warm air, the application of refrigerants may have greater effect, if
they could be administered without danger of producing too great torpor of
some part of the system; as frequently happens to people in health from
coming out of a warm room into the cold air, by which a topical
inflammation in consequence of torpor of the mucous membrane of the nostril
is produced, and is termed a cold in the head.

VII. _Cure of decreased Exertion._

1. Where the exertion of the sensorial powers is much decreased, as in the
cold fits of fever, a gradual accumulation of the spirit of animation takes
place; as occurs in all cases where inactivity or torpor of a part of the
system exists; this accumulation of sensorial power increases, till stimuli
less than natural are sufficient to throw it into action, then the cold fit
ceases; and from the action of the natural stimuli a hot one succeeds with
increased activity of the whole system.

So in fainting fits, or syncope, there is a temporary deficiency of
sensorial exertion, and a consequent quiescence of a great part of the
system. This quiescence continues, till the sensorial power becomes again
accumulated in the torpid organs; and then the usual diurnal stimuli excite
the revivescent parts again into action; but as this kind of quiescence
continues but a short time compared to the cold paroxysm of an ague, and
less affects the circulatory system, a less superabundancy of exertion
succeeds in the organs previously torpid, and a less excess of arterial
activity. See Sect. XXXIV. 1. 6.

2. In the diseases occasioned by a defect of sensorial exertion, as in cold
fits of ague, hysteric complaint, and nervous fever, the following means
are those commonly used. 1. Increase the stimulation above its natural
quantity for some weeks, till a new habit of more energetic contraction of
the fibres is established. This is to be done by wine, opium, bark, steel,
given at exact periods, and in appropriate quantities; for if these
medicines be given in such quantity, as to induce the least degree of
intoxication, a debility succeeds from the useless exhaustion of spirit of
animation in consequence of too great exertion of the muscles or organs of
sense. To these irritative stimuli should be added the sensitive ones of
cheerful ideas, hope, affection.

3. Change the kinds of stimulus. The habits acquired by the constitution
depend on such nice circumstances, that when one kind of stimulus ceases to
excite the sensorial power into the quantity of exertion necessary to
health, it is often sufficient to change the stimulus for another
apparently similar in quantity and quality. Thus when wine ceases to
stimulate the constitution, opium in appropriate doses supplies the defect;
and the contrary. This is also observed in the effects of cathartic
medicines, when one loses its power, another, apparently less efficacious,
will succeed. Hence a change of diet, drink, and stimulating medicines, is
often advantageous in diseases of debility.

4. Stimulate the organs, whose motions are associated with the torpid parts
of the system. The actions of the minute vessels of the various parts of
the external skin are not only associated with each other, but are strongly
associated with those of some of the internal membranes, and particularly
of the stomach. Hence when the exertion of the stomach is less than
natural, and indigestion and heartburn succeed, nothing so certainly
removes these symptoms as the stimulus of a blister on the back. The
coldness of the extremities, as of the nose, ears, or fingers, are hence
the best indication for the successful application of blisters.

5. Decrease the stimulus for a time. By lessening the quantity of heat for
a minute or two by going into the cold bath, a great accumulation of
sensorial power is produced; for not only the minute vessels of the whole
external skin for a time become inactive, as appears by their paleness; but
the minute vessels of the lungs lose much of their activity also by concert
with those of the skin, as appears from the difficulty of breathing at
first going into cold water. On emerging from the bath the sensorial power
is thrown into great exertion by the stimulus of the common degree of the
warmth of the atmosphere, and a great production of animal heat is the
consequence. The longer a person continues in the cold bath the greater
must be the present inertion of a great part of the system, and in
consequence a greater accumulation of sensorial power. Whence M. Pome
recommends some melancholy patients to be kept from two to six hours in
spring-water, and in baths still colder.

6. Decrease the stimulus for a time below the natural, and then increase it
above natural. The effect of this process, improperly used, is seen in
giving much food, or applying much warmth, to those who have been
previously exposed to great hunger, or to great cold. The accumulated
sensorial power is thrown into so violent exertion, that inflammations and
mortifications supervene, and death closes the catastrophe. In many
diseases this method is the most successful; hence the bark in agues
produces more certain effect after the previous exhibition of emetics. In
diseases attended with violent pain, opium has double the effect, if
venesection and a cathartic have been previously used. On this seems to
have been founded the successful practice of Sydenham, who used venesection
and a cathartic in chlorosis before the exhibition of the bark, steel, and
opiates.

7. Prevent any unnecessary expenditure of sensorial power. Hence in fevers
with debility, a decumbent posture is preferred, with silence, little
light, and such a quantity of heat as may prevent any chill sensation, or
any coldness of the extremities. The pulse of patients in fevers with
debility increases in frequency above ten pulsations in a minute on their
rising out of bed. For the expenditure of sensorial power to preserve an
erect posture of the body adds to the general deficiency of it, and thus
affects the circulation.

8. The longer in time and the greater in degree the quiescence or inertion
of an organ has been, so that it still retains life or excitability, the
less stimulus should at first be applied to it. The quantity of stimulation
is a matter of great nicety to determine, where the torpor or quiescence of
the fibres has been experienced in a great degree, or for a considerable
time, as in cold fits of the ague, in continued fevers with great debility,
or in people famished at sea, or perishing with cold. In the two last
cases, very minute quantities of food should be first supplied, and very
few additional degrees of heat. In the two former cases, but little
stimulus of wine or medicine, above what they had been lately accustomed
to, should be exhibited, and this at frequent and stated intervals, so that
the effect of one quantity may be observed before the exhibition of
another.

If these circumstances are not attended to, as the sensorial power becomes
accumulated in the quiescent fibres, an inordinate exertion takes place by
the increase of stimulus acting on the accumulated quantity of sensorial
power, and either the paralysis, or death of the contractile fibres ensues,
from the total expenditure of the sensorial power in the affected organ,
owing to this increase of exertion, like the debility after intoxication.
Or, secondly, the violent exertions above mentioned produce painful
sensation, which becomes a new stimulus, and by thus producing
inflammation, and increasing the activity of the fibres already too great,
sooner exhausts the whole of the sensorial power in the acting organ, and
mortification, that is, the death of the part, supervenes.

Hence there have been many instances of people, whose limbs have been long
benumbed by exposure to cold, who have lost them by mortification on their
being too hastily brought to the fire; and of others, who were nearly
famished at sea, who have died soon after having taken not more than an
usual meal of food. I have heard of two well-attested instances of patients
in the cold fit of ague, who have died from the exhibition of gin and
vinegar, by the inflammation which ensued. And in many fevers attended with
debility, the unlimited use of wine, and the wanton application of
blisters, I believe, has destroyed numbers by the debility consequent to
too great stimulation, that is, by the exhaustion of the sensorial power by
its inordinate exertion.

Wherever the least degree of intoxication exists, a proportional debility
is the consequence; but there is a golden rule by which the necessary and
useful quantity of stimulus in fevers with debility may be ascertained.
When wine or beer are exhibited either alone or diluted with water, if the
pulse becomes slower the stimulus is of a proper quantity; and should be
repeated every two or three hours, or when the pulse again becomes quicker.

In the chronical debility brought on by drinking spirituous or fermented
liquors, there is another golden rule by which I have successfully directed
the quantity of spirit which they may safely lessen, for there is no other
means by which they can recover their health. It should be premised, that
where the power of digestion in these patients is totally destroyed, there
is not much reason to expect a return to healthful vigour.

I have directed several of these patients to omit one fourth part of the
quantity of vinous spirit they have been lately accustomed to, and if in a
fortnight their appetite increases, they are advised to omit another fourth
part; but if they perceive that their digestion becomes impaired from the
want of this quantity of spirituous potation, they are advised to continue
as they are, and rather bear the ills they have, than risk the encounter of
greater. At the same time flesh-meat with or without spice is recommended,
with Peruvian bark and steel in small quantities between their meals, and
half a grain of opium or a grain, with five or eight grains of rhubarb at
night.

       *       *       *       *       *

SECT. XIII.

OF VEGETABLE ANIMATION.

    I. 1. _Vegetables are irritable; mimosa, dionaea muscipula. Vegetable
    secretions._ 2. _Vegetable buds are inferior animals, are liable to
    greater or less irritability._ II. _Stamens and pistils of plants shew
    marks of sensibility._ III. _Vegetables possess some degree of
    volition._ IV. _Motions of plants are associated like those of
    animals._ V. 1. _Vegetable structure like that of animals, their
    anthers and stigmas are living creatures. Male-flowers of Vallisneria._
    2. _Whether vegetables, possess ideas? They have organs of sense as of
    touch and smell, and ideas of external things?_

I. 1. The fibres of the vegetable world, as well as those of the animal,
are excitable into a variety of motion by irritations of external objects.
This appears particularly in the mimosa or sensitive plant, whose leaves
contract on the slightest injury; the dionaea muscipula, which was lately
brought over from the marshes of America, presents us with another curious
instance of vegetable irritability; its leaves are armed with spines on
their upper edge, and are spread on the ground around the stem; when an
insect creeps on any of them in its passage to the flower or seed, the leaf
shuts up like a steel rat-trap, and destroys its enemy. See Botanic Garden,
Part II. note on Silene.

The various secretions of vegetables, as of odour, fruit, gum, resin, wax,
honey, seem brought about in the same manner as in the glands of animals;
the tasteless moisture of the earth is converted by the hop-plant into a
bitter juice; as by the caterpillar in the nut-shell the sweet kernel is
converted into a bitter powder. While the power of absorption in the roots
and barks of vegetables is excited into action by the fluids applied to
their mouths like the lacteals and lymphatics of animals.

2. The individuals of the vegetable world may be considered as inferior or
less perfect animals; a tree is a congeries of many living buds, and in
this respect resembles the branches of coralline, which are a congeries of
a multitude of animals. Each of these buds of a tree has its proper leaves
or petals for lungs, produces its viviparous or its oviparous offspring in
buds or seeds; has its own roots, which extending down the stem of the tree
are interwoven with the roots of the other buds, and form the bark, which
is the only living part of the stem, is annually renewed, and is
superinduced upon the former bark, which then dies, and with its stagnated
juices gradually hardening into wood forms the concentric circles, which we
see in blocks of timber.

The following circumstances evince the individuality of the buds of trees.
First, there are many trees, whose whole internal wood is perished, and yet
the branches are vegete and healthy. Secondly, the fibres of the barks of
trees are chiefly longitudinal, resembling roots, as is beautifully seen in
those prepared barks, that were lately brought from Otaheita. Thirdly, in
horizontal wounds of the bark of trees, the fibres of the upper lip are
always elongated downwards like roots, but those of the lower lip do not
approach to meet them. Fourthly, if you wrap wet moss round any joint of a
vine, or cover it with moist earth, roots will shoot out from it. Fifthly,
by the inoculation or engrafting of trees many fruits are produced from one
stem. Sixthly, a new tree is produced from a branch plucked from an old
one, and set in the ground. Whence it appears that the buds of deciduous
trees are so many annual plants, that the bark is a contexture of the roots
of each individual bud; and that the internal wood is of no other use but
to support them in the air, and that thus they resemble the animal world in
their individuality.

The irritability of plants, like that of animals, appears liable to be
increased or decreased by habit; for those trees or shrubs, which are
brought from a colder climate to a warmer, put out their leaves and
blossoms a fortnight sooner than the indigenous ones.

Professor Kalm, in his Travels in New York, observes that the apple-trees
brought from England blossom a fortnight sooner than the native ones. In
our country the shrubs, that are brought a degree or two from the north,
are observed to flourish better than those, which come from the south. The
Siberian barley and cabbage are said to grow larger in this climate than
the similar more southern vegetables. And our hoards of roots, as of
potatoes and onions, germinate with less heat in spring, after they have
been accustomed to the winter's cold, than in autumn after the summer's
heat.

II. The stamens and pistils of flowers shew evident marks of sensibility,
not only from many of the stamens and some pistils approaching towards each
other at the season of impregnation, but from many of them closing their
petals and calyxes during the cold parts of the day. For this cannot be
ascribed to irritation, because cold means a defect of the stimulus of
heat; but as the want of accustomed stimuli produces pain, as in coldness,
hunger, and thirst of animals, these motions of vegetables in closing up
their flowers must be ascribed to the disgreeable sensation, and not to the
irritation of cold. Others close up their leaves during darkness, which,
like the former, cannot be owing to irritation, as the irritating material
is withdrawn.

The approach of the anthers in many flowers to the stigmas, and of the
pistils of some flowers to the anthers, must be ascribed to the passion of
love, and hence belongs to sensation, not to irritation.

III. That the vegetable world possesses some degree of voluntary powers,
appears from their necessity to sleep, which we have shewn in Sect. XVIII.
to consist in the temporary abolition of voluntary power. This voluntary
power seems to be exerted in the circular movement of the tendrils of
vines, and other climbing vegetables; or in the efforts to turn the upper
surface of their leaves, or their flowers to the light.

IV. The associations of fibrous motions are observable in the vegetable
world, as well as in the animal. The divisions of the leaves of the
sensitive plant have been accustomed to contract at the same time from the
absence of light; hence if by any other circumstance, as a slight stroke or
injury, one division is irritated into contraction, the neighbouring ones
contract also, from their motions being associated with those of the
irritated part. So the various stamina of the class of syngenesia have been
accustomed to contract together in the evening, and thence if you stimulate
one of them with a pin, according to the experiment of M. Colvolo, they all
contract from their acquired associations.

To evince that the collapsing of the sensitive plant is not owing to any
mechanical vibrations propagated along the whole branch, when a single leaf
is struck with the finger, a leaf of it was slit with sharp scissors, and
some seconds of time passed before the plant seemed sensible of the injury;
and then the whole branch collapsed as far as the principal stem: this
experiment was repeated several times with the least possible impulse to
the plant.

V. 1. For the numerous circumstances in which vegetable buds are analogous
to animals, the reader is referred to the additional notes at the end of
the Botanic Garden, Part I. It is there shewn, that the roots of vegetables
resemble the lacteal system of animals; the sap-vessels in the early
spring, before their leaves expand, are analogous to the placental vessels
of the foetus; that the leaves of land-plants resemble lungs, and those of
aquatic plants the gills of fish; that there are other systems of vessels
resembling the vena portarum of quadrupeds, or the aorta of fish; that the
digestive power of vegetables is similar to that of animals converting the
fluids, which they absorb, into sugar; that their seeds resemble the eggs
of animals, and their buds and bulbs their viviparous offspring. And,
lastly, that the anthers and stigmas are real animals, attached indeed to
their parent tree like polypi or coral insects, but capable of spontaneous
motion; that they are affected with the passion of love, and furnished with
powers of reproducing their species, and are fed with honey like the moths
and butterflies, which plunder their nectaries. See Botanic Garden, Part I.
add. note XXXIX.

The male flowers of vallisneria approach still nearer to apparent
animality, as they detach themselves from the parent plant, and float on
the surface of the water to the female ones. Botanic Garden, Part II. Art.
Vallisneria. Other flowers of the classes of monecia and diecia, and
polygamia, discharge the fecundating farina, which floating in the air is
carried to the stigma of the female flowers, and that at considerable
distances. Can this be effected by any specific attraction? or, like the
diffusion of the odorous particles of flowers, is it left to the currents
of winds, and the accidental miscarriages of it counteracted by the
quantity of its production?

2. This leads us to a curious enquiry, whether vegetables have ideas of
external things? As all our ideas are originally received by our senses,
the question may be changed to, whether vegetables possess any organs of
sense? Certain it is, that they possess a sense of heat and cold, another
of moisture and dryness, and another of light and darkness; for they close
their petals occasionally from the presence of cold, moisture, or darkness.
And it has been already shewn, that these actions cannot be performed
simply from irritation, because cold and darkness are negative quantities,
and on that account sensation or volition are implied, and in consequence a
sensorium or union of their nerves. So when we go into the light, we
contract the iris; not from any stimulus of the light on the fine muscles
of the iris, but from its motions being associated with the sensation of
too much light on the retina: which could not take place without a
sensorium or center of union of the nerves of the iris with those of
vision. See Botanic Garden, Part I. Canto 3. l. 440. note.

Besides these organs of sense, which distinguish cold, moisture, and
darkness, the leaves of mimosa, and of dionaea, and of drosera, and the
stamens of many flowers, as of the berbery, and the numerous class of
syngenesia, are sensible to mechanic impact, that is, they possess a sense
of touch, as well as a common sensorium; by the medium of which their
muscles are excited into action. Lastly, in many flowers the anthers, when
mature, approach the stigma, in others the female organ approaches to the
male. In a plant of collinsonia, a branch of which is now before me, the
two yellow stamens are about three eights of an inch high, and diverge from
each other, at an angle of about fifteen degrees, the purple style is half
an inch high, and in some flowers is now applied to the stamen on the right
hand, and in others to that of the left; and will, I suppose, change place
to-morrow in those, where the anthers have not yet effused their powder.

I ask, by what means are the anthers in many flowers, and stigmas in other
flowers, directed to find their paramours? How do either of them know, that
the other exists in their vicinity? Is this curious kind of storge produced
by mechanic attraction, or by the sensation of love? The latter opinion is
supported by the strongest analogy, because a reproduction of the species
is the consequence; and then another organ of sense must be wanted to
direct these vegetable amourettes to find each other, one probably
analogous to our sense of smell, which in the animal world directs the
new-born infant to its source of nourishment, and they may thus possess a
faculty of perceiving as well as of producing odours.

Thus, besides a kind of taste at the extremities of their roots, similar to
that of the extremities of our lacteal vessels, for the purpose of
selecting their proper food: and besides different kinds of irritability
residing in the various glands, which separate honey, wax, resin, and other
juices from their blood; vegetable life seems to possess an organ of sense
to distinguish the variations of heat, another to distinguish the varying
degrees of moisture, another of light, another of touch, and probably
another analogous to our sense of smell. To these must be added the
indubitable evidence of their passion of love, and I think we may truly
conclude, that they are furnished with a common sensorium belonging to each
bud and that they must occasionally repeat those perceptions either in
their dreams or waking hours, and consequently possess ideas of so many of
the properties of the external world, and of their own existence.

       *       *       *       *       *

SECT. XIV.

OF THE PRODUCTION OF IDEAS.

    I. _Of material and immaterial beings. Doctrine of St. Paul._ II. 1.
    _Of the sense of touch. Of solidity._ 2. _Of figure. Motion. Time.
    Place. Space. Number._ 3. _Of the penetrability of matter._ 4. _Spirit
    of animation possesses solidity, figure, visibility, &c. Of Spirits and
    angels._ 5. _The existence of external things._ III. _Of vision._ IV.
    _Of hearing._ V. _Of smell and taste._ VI. _Of the organ of sense by
    which we perceive heat and cold, not by the sense of touch._ VII. _Of
    the sense of extension, the whole of the locomotive muscles may be
    considered as one organ of sense._ VIII. _Of the senses of hunger,
    thirst, want of fresh air, suckling children, and lust._ IX. _Of many
    other organs of sense belonging to the glands. Of painful sensations
    from the excess of light, pressure, heat, itching, caustics, and
    electricity._

I. Philosophers have been much perplexed to understand, in what manner we
become acquainted with the external world; insomuch that Dr. Berkly even
doubted its existence, from having observed (as he thought) that none of
our ideas resemble their correspondent objects. Mr. Hume asserts, that our
belief depends on the greater distinctness or energy of our ideas from
perception; and Mr. Reid has lately contended, that our belief of external
objects is an innate principle necessarily joined with our perceptions.

So true is the observation of the famous Malbranch, "that our senses are
not given us to discover the essences of things, but to acquaint us with
the means of preserving our existence," (L. I. ch. v.) a melancholy
reflection to philosophers!

Some philosophers have divided all created beings into material and
immaterial: the former including all that part of being, which obeys the
mechanic laws of action and reaction, but which can begin no motion of
itself; the other is the cause of all motion, and is either termed the
power of gravity, or of specific attraction, or the spirit of animation.
This immaterial agent is supposed to exist in or with matter, but to be
quite distinct from it, and to be equally capable of existence, after the
matter, which now possesses it, is decomposed.

Nor is this theory ill supported by analogy, since heat, electricity, and
magnetism, can be given to or taken from a piece of iron; and must
therefore exist, whether separated from the metal, or combined with it.
From a parity of reasoning, the spirit of animation, would appear to be
capable of existing as well separately from the body as with it.

I beg to be understood, that I do not wish to dispute about words, and am
ready to allow, that the powers of gravity, specific attraction,
electricity, magnetism, and even the spirit of animation, may consist of
matter of a finer kind; and to believe, with St. Paul and Malbranch, that
the ultimate cause only of all motion is immaterial, that is God. St. Paul
says, "in him we live and move, and have our being;" and, in the 15th
chapter to the Corinthians, distinguishes between the psyche or living
spirit, and the pneuma or reviving spirit. By the words spirit of animation
or sensorial power, I mean only that animal life, which mankind possesses
in common with brutes, and in some degree even with vegetables, and leave
the consideration of the immortal part of us, which is the object of
religion, to those who treat of revelation.

II. 1. _Of the Sense of Touch._

The first idea we become acquainted with, are those of the sense of touch;
for the foetus must experience some varieties of agitation, and exert some
muscular action, in the womb; and may with great probability be supposed
thus to gain some ideas of its own figure, of that of the uterus, and of
the tenacity of the fluid, that surrounds it, (as appears from the facts
mentioned in the succeeding Section upon Instinct.)

Many of the organs of sense are confined to a small part of the body, as
the nostrils, ear, or eye, whilst the sense of touch is diffused over the
whole skin, but exists with a more exquisite degree of delicacy at the
extremities of the fingers and thumbs, and in the lips. The sense of touch
is thus very commodiously disposed for the purpose of encompassing smaller
bodies, and for adapting itself to the inequalities of larger ones. The
figure of small bodies seems to be learnt by children by their lips as much
as by their fingers; on which account they put every new object to their
mouths, when they are satiated with food, as well as when they are hungry.
And puppies seem to learn their ideas of figure principally by the lips in
their mode of play.

We acquire our tangible ideas of objects either by the simple pressure of
this organ of touch against a solid body, or by moving our organ of touch
along the surface of it. In the former case we learn the length and breadth
of the object by the quantity of our organ of touch, that is impressed by
it: in the latter case we learn the length and breadth of objects by the
continuance of their pressure on our moving organ of touch.

It is hence, that we are very slow in acquiring our tangible ideas, and
very slow in recollecting them; for if I now think of the tangible idea of
a cube, that is, if I think of its figure, and of the solidity of every
part of that figure, I must conceive myself as passing my fingers over it,
and seem in some measure to feel the idea, as I formerly did the
impression, at the ends of them, and am thus very slow in distinctly
recollecting it.

When a body compresses any part of our sense of touch, what happens? First,
this part of our sensorium undergoes a mechanical compression, which is
termed a stimulus; secondly, an idea, or contraction of a part of the organ
of sense is excited; thirdly, a motion of the central parts, or of the
whole sensorium, which is termed sensation, is produced; and these three
constitute the perception of solidity.

2. _Of Figure, Motion, Time, Place, Space, Number._

No one will deny, that the medulla of the brain and nerves has a certain
figure; which, as it is diffused through nearly the whole of the body, must
have nearly the figure of that body. Now it follows, that the spirit of
animation, or living principle, as it occupies this medulla, and no other
part, (which is evinced by a great variety of cruel experiments on living
animals,) it follows, that this spirit of animation has also the same
figure as the medulla above described. I appeal to common sense! the spirit
of animation acts, Where does it act? It acts wherever there is the medulla
above mentioned; and that whether the limb is yet joined to a living
animal, or whether it be recently detached from it; as the heart of a viper
or frog will renew its contractions, when pricked with a pin, for many
minutes of time after its exsection from the body.--Does it act any where
else?--No; then it certainly exists in this part of space, and no where
else; that is, it hath figure; namely, the figure of the nervous system,
which is nearly the figure of the body. When the idea of solidity is
excited, as above explained, a part of the extensive organ of touch is
compressed by some external body, and this part of the sensorium so
compressed exactly resembles _in figure_ the figure of the body that
compressed it. Hence, when we acquire the idea of solidity, we acquire at
the same time the idea of FIGURE; and this idea of figure, or motion of _a
part_ of the organ of touch, exactly resembles _in its figure_ the figure
of the body that occasions it; and thus exactly acquaints us with this
property of the external world.

Now, as the whole universe with all its parts possesses a certain form or
figure, if any part of it moves, that form or figure of the whole is
varied: hence, as MOTION is no other than a perpetual variation of figure,
our idea of motion is also a real resemblance of the motion that produced
it.

It may be said in objection to this definition of motion, that an ivory
globe may revolve on its axis, and that here will be a motion without
change of figure. But the figure of the particle _x_ on one side of this
globe is not the _same_ figure as the figure of _y_ on the other side, any
more than the particles themselves are the same, though they are _similar_
figures; and hence they cannot change place with each other without
disturbing or changing the figure of the whole.

Our idea of TIME is from the same source, but is more abstracted, as it
includes only the comparative velocities of these variations of figure;
hence if it be asked, How long was this book in printing? it may be
answered, Whilst the sun was passing through Aries.

Our idea of PLACE includes only the figure of a group of bodies, not the
figures of the bodies themselves. If it be asked where is Nottinghamshire,
the answer is, it is surrounded by Derbyshire, Lincolnshire and
Leicestershire; hence place is our idea of the figure of one body
surrounded by the figures of other bodies.

The idea of SPACE is a more abstracted idea of place excluding the group of
bodies.

The idea of NUMBER includes only the particular arrangements, or
distributions of a group of bodies, and is therefore only a more abstracted
idea of the parts of the figure of the group of bodies; thus when I say
England is divided into forty counties, I only speak of certain divisions
of its figure.

Hence arises the certainty of the mathematical sciences, as they explain
these properties of bodies, which are exactly resembled by our ideas of
them, whilst we are obliged to collect almost all our other knowledge from
experiment; that is, by observing the effects exerted by one body upon
another.

3. _Of the Penetrability of Matter._

The impossibility of two bodies existing together in the same space cannot
be deduced from our idea of solidity, or of figure. As soon as we perceive
the motions of objects that surround us, and learn that we possess a power
to move our own bodies, we experience, that those objects, which excite in
us the idea of solidity and of figure, oppose this voluntary movement of
our own organs; as whilst I endeavour to compress between my hands an ivory
ball into a spheroid. And we are hence taught by experience, that our own
body and those, which we touch, cannot exist in the same part of space.

But this by no means demonstrates, that no two bodies can exist together in
the same part of space. Galilaeo in the preface to his works seems to be of
opinion, that matter is not impenetrable; Mr. Michel, and Mr. Boscowich in
his Theoria. Philos. Natur. have espoused this hypothesis: which has been
lately published by Dr. Priestley, to whom the world is much indebted for
so many important discoveries in science. (Hist. of Light and Colours, p.
391.) The uninterrupted passage of light through transparent bodies, of the
electric aether through metallic and aqueous bodies, and of the magnetic
effluvia through all bodies, would seem to give some probability to this
opinion. Hence it appears, that beings may exist without possessing the
property of solidity, as well as they can exist without possessing the
properties, which excite our smell or taste, and can thence occupy space
without detruding other bodies from it; but we cannot become acquainted
with such beings by our sense of touch, any more than we can with odours or
flavours without our senses of smell and taste.

But that any being can exist without existing in space, is to my ideas
utterly incomprehensible. My appeal is to common sense. _To be_ implies a
when and a where; the one is comparing it with the motions of other beings,
and the other with their situations.

If there was but one object, as the whole creation may be considered as one
object, then I cannot ask where it exists? for there are no other objects
to compare its situation with. Hence if any one denies, that a being exists
in space, he denies, that there are any other beings but that one; for to
answer the question, "Where does it exist?" is only to mention the
situation of the objects that surround it.

In the same manner if it be asked--"When does a being exist?" The answer
only specifies the successive motions either of itself, or of other bodies;
hence to say, a body exists not in time, is to say, that there is, or was,
no motion in the world.

4. _Of the Spirit of Animation._

But though there may exist beings in the universe, that have not the
property of solidity; that is, which can possess any part of space, at the
same time that it is occupied by other bodies; yet there may be other
beings, that can assume this property of solidity, or disrobe themselves of
it occasionally, as we are taught of spirits, and of angels; and it would
seem, that THE SPIRIT OF ANIMATION must be endued with this property,
otherwise how could it occasionally give motion to the limbs of
animals?--or be itself stimulated into motion by the obtrusions of
surrounding bodies, as of light, or odour?

If the spirit of animation was always necessarily penetrable, it could not
influence or be influenced by the solidity of common matter; they would
exist together, but could not detrude each other from the part of space,
where they exist; that is, they could not communicate motion to each other.
_No two things can influence or affect each other, which have not some
property common to both of them_; for to influence or affect another body
is to give or communicate some property to it, that it had not before; but
how can one body give that to another, which it does not possess
itself?--The words imply, that they must agree in having the power or
faculty of possessing some common property. Thus if one body removes
another from the part of space, that it possesses, it must have the power
of occupying that space itself: and if one body communicates heat or motion
to another, it follows, that they have alike the property of possessing
heat or motion.

Hence the spirit of animation at the time it communicates or receives
motion from solid bodies, must itself possess some property of solidity.
And in consequence at the time it receives other kinds of motion from
light, it must possess that property, which light possesses, to communicate
that kind of motion; and for which no language has a name, unless it may be
termed Visibility. And at the time it is stimulated into other kinds of
animal motion by the particles of sapid and odorous bodies affecting the
senses of taste and smell, it must resemble these particles of flavour, and
of odour, in possessing some similar or correspondent property; and for
which language has no name, unless we may use the words Saporosity and
Odorosity for those common properties, which are possessed by our organs of
taste and smell, and by the particles of sapid and odorous bodies; as the
words Tangibility and Audibility may express the common property possessed
by our organs of touch, and of hearing, and by the solid bodies, or their
vibrations, which affect those organs.

5. Finally, though the figures of bodies are in truth resembled by the
figure of the part of the organ of touch, which is stimulated into motion;
and that organ resembles the solid body, which stimulates it, in its
property of solidity; and though the sense of hearing resembles the
vibrations of external bodies in its capability of being stimulated into
motion by those vibrations; and though our other organs of sense resemble
the bodies, that stimulate them, in their capability of being stimulated by
them; and we hence become acquainted with these properties of the external
world; yet as we can repeat all these motions of our organs of sense by the
efforts of volition, or in consequence of the sensation of pleasure or
pain, or by their association with other fibrous motions, as happens in our
reveries or in sleep, there would still appear to be some difficulty in
demonstrating the existence of any thing external to us.

In our dreams we cannot determine this circumstance, because our power of
volition is suspended, and the stimuli of external objects are excluded;
but in our waking hours we can compare our ideas belonging to one sense
with those belonging to another, and can thus distinguish the ideas
occasioned by irritation from those excited by sensation, volition, or
association. Thus if the idea of the sweetness of sugar should be excited
in our dreams, the whiteness and hardness of it occur at the same time by
association; and we believe a material lump of sugar present before us. But
if, in our waking hours, the idea of the sweetness of sugar occurs to us,
the stimuli of surrounding objects, as the edge of the table, on which we
press, or green colour of the grass, on which we tread, prevent the other
ideas of the hardness and whiteness of the sugar from being exerted by
association. Or if they should occur, we voluntarily compare them with the
irritative ideas of the table or grass above mentioned, and detect their
fallacy. We can thus distinguish the ideas caused by the stimuli of
external objects from those, which are introduced by association,
sensation, or volition; and during our waking hours can thus acquire a
knowledge of the external world. Which nevertheless we cannot do in our
dreams, because we have neither perceptions of external bodies, nor the
power of volition to enable us to compare them with the ideas of
imagination.

III. _Of Vision._

Our eyes observe a difference of colour, or of shade, in the prominences
and depressions of objects, and that those shades uniformly vary, when the
sense of touch observes any variation. Hence when the retina becomes
stimulated by colours or shades of light in a certain form, as in a
circular spot; we know by experience, that this is a sign, that a tangible
body is before us; and that its figure is resembled by the miniature figure
of the part of the organ of vision, that is thus stimulated.

Here whilst the stimulated part of the retina resembles exactly the visible
figure of the whole in miniature, the various kinds of stimuli from
different colours mark the visible figures of the minuter parts; and by
habit we instantly recall the tangible figures.

Thus when a tree is the object of sight, a part of the retina resembling a
flat branching figure is stimulated by various shades of colours; but it is
by suggestion, that the gibbosity of the tree, and the moss, that fringes
its trunk, appear before us. These are ideas of suggestion, which we feel
or attend to, associated with the motions of the retina, or irritative
ideas, which we do not attend to.

So that though our visible ideas resemble in miniature the outline of the
figure of coloured bodies, in other respects they serve only as a language,
which by acquired associations introduce the tangible ideas of bodies.
Hence it is, that this sense is so readily deceived by the art of the
painter to our amusement and instruction. The reader will find much very
curious knowledge on this subject in Bishop Berkley's Essay on Vision, a
work of great ingenuity.

The immediate object however of the sense of vision is light; this fluid,
though its velocity is so great, appears to have no perceptible mechanical
impulse, as was mentioned in the third Section, but seems to stimulate the
retina into animal motion by its transmission through this part of the
sensorium: for though the eyes of cats or other animals appear luminous in
obscure places; yet it is probable, that none of the light, which falls on
the retina, is reflected from it, but adheres to or enters into combination
with the choroide coat behind it.

The combination of the particles of light with opake bodies, and therefore
with the choroide coat of the eye, is evinced from the heat, which is given
out, as in other chemical combinations. For the sunbeams communicate no
heat in their passage through transparent bodies, with which they do not
combine, as the air continues cool even in the focus of the largest
burning-glasses, which in a moment vitrifies a particle of opaque matter.

IV. _Of the Organ of Hearing._

It is generally believed, that the tympanum of the ear vibrates
mechanically, when exposed to audible sounds, like the strings of one
musical instrument, when the same notes are struck upon another. Nor is
this opinion improbable, as the muscles and cartilages of the larynx are
employed in producing variety of tones by mechanical vibration: so the
muscles and bones of the ear seem adapted to increase or diminish the
tension of the tympanum for the purposes of similar mechanical vibrations.

But it appears from dissection, that the tympanum is not the immediate
organ of hearing, but that like the humours and cornea of the eye, it is
only of use to prepare the object for the immediate organ. For the portio
mollis of the auditory nerve is not spread upon the tympanum, but upon the
vestibulum, and cochlea, and semicircular canals of the ear; while between
the tympanum and the expansion of the auditory nerve the cavity is said by
Dr. Cotunnus and Dr. Meckel to be filled with water; as they had frequently
observed by freezing the heads of dead animals before they dissected them;
and water being a more dense fluid than air is much better adapted to the
propagation of vibrations. We may add, that even the external opening of
the ear is not absolutely necessary for the perception of sound: for some
people, who from these defects would have been completely deaf, have
distinguished acute or grave sounds by the tremours of a stick held between
their teeth propagated along the bones of the head, (Haller. Phys. T. V. p.
295).

Hence it appears, that the immediate organ of hearing is not affected by
the particles of the air themselves, but is stimulated into animal motion
by the vibrations of them. And it is probable from the loose bones, which
are found in the heads of some fishes, that the vibrations of water are
sensible to the inhabitants of that element by a similar organ.

The motions of the atmosphere, which we become acquainted with by the sense
of touch, are combined with its solidity, weight, or vis intertiae; whereas
those, that are perceived by this organ, depend alone on its elasticity.
But though the vibration of the air is the immediate object of the sense of
hearing, yet the ideas, we receive by this sense, like those received from
light, are only as a language, which by acquired associations acquaints us
with those motions of tangible bodies, which depend on their elasticity;
and which we had before learned by our sense of touch.

V. _Of Smell and of Taste._

The objects of smell are dissolved in the fluid atmosphere, and those of
taste in the saliva, or other aqueous fluid, for the better diffusing them
on their respective organs, which seem to be stimulated into animal motion
perhaps by the chemical affinities of these particles, which constitute the
sapidity and odorosity of bodies with the nerves of sense, which perceive
them.

Mr. Volta has lately observed a curious circumstance relative to our sense
of taste. If a bit of clean lead and a bit of clean silver be separately
applied to the tongue and palate no taste is perceived; but by applying
them in contact in respect to the parts out of the mouth, and nearly so in
respect to the parts, which are immediately applied to the tongue and
palate, a saline or acidulous taste is perceived, as of a fluid like a
stream of electricity passing from one of them to the other. This new
application of the sense of taste deserves further investigation, as it may
acquaint us with new properties of matter.

From the experiments above mentioned of Galvani, Volta, Fowler, and others,
it appears, that a plate of zinc and a plate of silver have greater effect
than lead and silver. If one edge of a plate of silver about the size of
half a crown-piece be placed upon the tongue, and one edge of a plate of
zinc about the same size beneath the tongue, and if their opposite edges
are then brought into contact before the point of the tongue, a taste is
perceived at the moment of their coming into contact; secondly, if one of
the above plates be put between the upper lip and the gum of the
fore-teeth, and the other be placed under the tongue, and their exterior
edges be then brought into contact in a darkish room, a flash of light is
perceived in the eyes.

These effects I imagine only shew the sensibility of our nerves of sense to
very small quantities of the electric fluid, as it passes through them; for
I suppose these sensations are occasioned by slight electric shocks
produced in the following manner. By the experiments published by Mr.
Bennet, with his ingenious doubler of electricity, which is the greatest
discovery made in that science since the coated jar, and the eduction of
lightning from the skies, it appears that zinc was always found minus, and
silver was always found plus, when both of them were in their separate
state. Hence, when they are placed in the manner above described, as soon
as their exterior edges come nearly into contact, so near as to have an
extremely thin plate of air between them, that plate of air becomes charged
in the same manner as a plate of coated glass; and is at the same instant
discharged through the nerves of taste or of sight, and gives the
sensations, as above described, of light or of saporocity; and only shews
the great sensibility of these organs of sense to the stimulus of the
electric fluid in suddenly passing through them.

VI. _Of the Sense of Heat._

There are many experiments in chemical writers, that evince the existence
of heat as a fluid element, which covers and pervades all bodies, and is
attracted by the solutions of some of them, and is detruded from the
combination of others. Thus from the combinations of metals with acids, and
from those combinations of animal fluids, which are termed secretions, this
fluid matter of heat is given out amongst the neighbouring bodies; and in
the solutions of salts in water, or of water in air, it is absorbed from
the bodies, that surround them; whilst in its facility in passing through
metallic bodies, and its difficulty in pervading resins and glass, it
resembles the properties of the electric aura; and is like that excited by
friction, and seems like that to gravitate amongst other bodies in its
uncombined state, and to find its equilibrium.

There is no circumstance of more consequence in the animal economy than a
due proportion of this fluid of heat; for the digestion of our nutriment in
the stomach and bowels, and the proper qualities of all our secreted
fluids, as they are produced or prepared partly by animal and partly by
chemical processes, depend much on the quantity of heat; the excess of
which, or its deficiency, alike gives us pain, and induces us to avoid the
circumstances that occasion them. And in this the perception of heat
essentially differs from the perceptions of the sense of touch, as we
receive pain from too great pressure of solid bodies, but none from the
absence of it. It is hence probable, that nature has provided us with a set
of nerves for the perception of this fluid, which anatomists have not yet
attended to.

There may be some difficulty in the proof of this assertion; if we look at
a hot fire, we experience no pain of the optic nerve, though the heat along
with the light must be concentrated upon it. Nor does warm water or warm
oil poured into the ear give pain to the organ of hearing; and hence as
these organs of sense do not perceive small excesses or deficiences of
heat; and as heat has no greater analogy to the solidity or to the figures
of bodies, than it has to their colours or vibrations; there seems no
sufficient reason for our ascribing the perception of heat and cold to the
sense of touch; to which it has generally been attributed, either because
it is diffused beneath the whole skin like the sense of touch, or owing to
the inaccuracy of our observations, or the defect of our languages.

There is another circumstance would induce us to believe, that the
perceptions of heat and cold do not belong to the organ of touch; since the
teeth, which are the least adapted for the perceptions of solidity or
figure, are the most sensible to heat or cold; whence we are forewarned
from swallowing those materials, whose degree of coldness or of heat would
injure our stomachs.

The following is an extract from a letter of Dr. R.W. Darwin, of
Shrewsbury, when he was a student at Edinburgh. "I made an experiment
yesterday in our hospital, which much favours your opinion, that the
sensation of heat and of touch depend on different sets of nerves. A man
who had lately recovered from a fever, and was still weak, was seized with
violent cramps in his legs and feet; which were removed by opiates, except
that one of his feet remained insensible. Mr. Ewart pricked him with a pin
in five or six places, and the patient declared he did not feel it in the
least, nor was he sensible of a very smart pinch. I then held a red-hot
poker at some distance, and brought it gradually nearer till it came within
three inches, when he asserted that he felt it quite distinctly. I suppose
some violent irritation on the nerves of touch had caused the cramps, and
had left them paralytic; while the nerves of heat, having suffered no
increased stimulus, retained their irritability."

Add to this, that the lungs, though easily stimulated into inflammation,
are not sensible to heat. See Class. III. 1. 1. 10.

VII. _Of the Sense of Extension._

The organ of touch is properly the sense of pressure, but the muscular
fibres themselves constitute the organ of sense, that feels extension. The
sense of pressure is always attended with the ideas of the figure and
solidity of the object, neither of which accompany our perception of
extension. The whole set of muscles, whether they are hollow ones, as the
heart, arteries, and intestines, or longitudinal ones attached to bones,
contract themselves, whenever they are stimulated by forcible elongation;
and it is observable, that the white muscles, which constitute the arterial
system, seem to be excited into contraction from no other kinds of
stimulus, according to the experiments of Haller. And hence the violent
pain in some inflammations, as in the paronychia, obtains immediate relief
by cutting the membrane, that was stretched by the tumour of the subjacent
parts.

Hence the whole muscular system may be considered as one organ of sense,
and the various attitudes of the body, as ideas belonging to this organ, of
many of which we are hourly conscious, while many others, like the
irritative ideas of the other senses, are performed without our attention.

When the muscles of the heart cease to act, the refluent blood again
distends or elongates them; and thus irritated they contract as before. The
same happens to the arterial system, and I suppose to the capillaries,
intestines, and various glands of the body.

When the quantity of urine, or of excrement, distends the bladder, or
rectum, those parts contract, and exclude their contents, and many other
muscles by association act along with them; but if these evacuations are
not soon complied with, pain is produced by a little further extension of
the muscular fibres: a similar pain is caused in the muscles, when a limb
is much extended for the reduction of dislocated bones; and in the
punishment of the rack: and in the painful cramps of the calf of the leg,
or of other muscles, for a greater degree of contraction of a muscle, than
the movement of the two bones, to which its ends are affixed, will admit
of, must give similar pain to that, which is produced by extending it
beyond its due length. And the pain from punctures or incisions arises from
the distention of the fibres, as the knife passes through them; for it
nearly ceases as soon as the division is completed.

All these motions of the muscles, that are thus naturally excited by the
stimulus of distending bodies, are also liable to be called into strong
action by their catenation, with the irritations or sensations produced by
the momentum of the progressive particles of blood in the arteries, as in
inflammatory fevers, or by acrid substances on other sensible organs, as in
the strangury, or tenesmus, or cholera.

We shall conclude this account of the sense of extension by observing, that
the want of its object is attended with a disagreeable sensation, as well
as the excess of it. In those hollow muscles, which have been accustomed to
it, this disagreeable sensation is called faintness, emptiness, and
sinking; and, when it arises to a certain degree, is attended with syncope,
or a total quiescence of all motions, but the internal irritative ones, as
happens from sudden loss of blood, or in the operation of tapping in the
dropsy.

VIII. _Of the Appetites of Hunger, Thirst, Heat, Extension, the want of
fresh Air, animal Love, and the Suckling of Children._

Hunger is most probably perceived by those numerous ramifications of nerves
that are seen about the upper opening of the stomach; and thirst by the
nerves about the fauces, and the top of the gula. The ideas of these senses
are few in the generality of mankind, but are more numerous in those, who
by disease, or indulgence, desire particular kinds of foods or liquids.

A sense of heat has already been spoken of, which may with propriety be
called an appetite, as we painfully desire it, when it is deficient in
quantity.

The sense of extension may be ranked amongst these appetites, since the
deficiency of its object gives disagreeable sensation; when this happens in
the arterial system, it is called faintness, and seems to bear some analogy
to hunger and to cold; which like it are attended with emptiness of a part
of the vascular system.

The sense of want of fresh air has not been attended to, but is as distinct
as the others, and the first perhaps that we experience after our nativity;
from the want of the object of this sense many diseases are produced, as
the jail-fever, plague, and other epidemic maladies. Animal love is another
appetite, which occurs later in life, and the females of lactiferous
animals have another natural inlet of pleasure or pain from the suckling
their offspring. The want of which either owing to the death of their
progeny, or to the fashion of their country, has been fatal to many of the
sex. The males have also pectoral glands, which are frequently turgid with
a thin milk at their nativity, and are furnished with nipples, which erect
on titillation like those of the female; but which seem now to be of no
further use, owing perhaps to some change which these animals have
undergone in the gradual progression of the formation of the earth, and of
all that it inhabit.

These seven last mentioned senses may properly be termed appetites, as they
differ from those of touch, sight, hearing, taste, and smell, in this
respect; that they are affected with pain as well by the defect of their
objects as by the excess of them, which is not so in the latter. Thus cold
and hunger give us pain, as well as an excess of heat or satiety; but it is
not so with darkness and silence.

IX. Before we conclude this Section on the organs of sense, we must
observe, that, as far as we know, there are many more senses, than have
been here mentioned, as every gland seems to be influenced to separate from
the blood, or to absorb from the cavities of the body, or from the
atmosphere, its appropriated fluid, by the stimulus of that fluid on the
living gland; and not by mechanical capillary absorption, nor by chemical
affinity. Hence it appears, that each of these glands must have a peculiar
organ to perceive these irritations, but as these irritations are not
succeeded by sensation, they have not acquired the names of senses.

However when these glands are excited into motions stronger than usual,
either by the acrimony of their fluids, or by their own irritability being
much increased, then the sensation of pain is produced in them as in all
the other senses of the body; and these pains are all of different kinds,
and hence the glands at this time really become each a different organ of
sense, though these different kinds of pain have acquired no names.

Thus a great excess of light does not give the idea of light but of pain;
as in forcibly opening the eye when it is much inflamed. The great excess
of pressure or distention, as when the point of a pin is pressed upon our
skin, produces pain, (and when this pain of the sense of distention is
slighter, it is termed itching, or tickling), without any idea of solidity
or of figure: an excess of heat produces smarting, of cold another kind of
pain; it is probable by this sense of heat the pain produced by caustic
bodies is perceived, and of electricity, as all these are fluids, that
permeate, distend, or decompose the parts that feel them.

       *       *       *       *       *

SECT. XV.

OF THE CLASSES OF IDEAS.

    I. 1. _Ideas received in tribes._ 2. _We combine them further, or
    abstract from these tribes._ 3. _Complex ideas._ 4. _Compounded ideas._
    5. _Simple ideas, modes, substances, relations, general ideas._ 6.
    _Ideas of reflexion._ 7. _Memory and imagination imperfectly defined.
    Ideal presence. Memorandum-rings._ II. 1. _Irritative ideas.
    Perception._ 2. _Sensitive ideas, imagination._ 3. _Voluntary ideas,
    recollection._ 4. _Associated ideas, suggestion._ III. 1. _Definitions
    of perception, memory._ 2. _Reasoning, judgment, doubting,
    distinguishing, comparing._ 3. _Invention._ 4. _Consciousness._ 5.
    _Identity._ 6. _Lapse of time._ 7. _Free-will._

I. 1. As the constituent elements of the material world are only
perceptible to our organs of sense in a state of combination; it follows,
that the ideas or sensual motions excited by them, are never received
singly, but ever with a greater or less degree of combination. So the
colours of bodies or their hardnesses occur with their figures: every smell
and taste has its degree of pungency as well as its peculiar flavour: and
each note in music is combined with the tone of some instrument. It appears
from hence, that we can be sensible of a number of ideas at the same time,
such as the whiteness, hardness, and coldness, of a snow-ball, and can
experience at the same time many irritative ideas of surrounding bodies,
which we do not attend to, as mentioned in Section VII. 3. 2. But those
ideas which belong to the same sense, seem to be more easily combined into
synchronous tribes, than those which were not received by the same sense,
as we can more easily think of the whiteness and figure of a lump of sugar
at the same time, than the whiteness and sweetness of it.

2. As these ideas, or sensual motions, are thus excited with greater or
less degrees of combination; so we have a power, when we repeat them either
by our volition or sensation, to increase or diminish this degree of
combination, that is, to form compounded ideas from those, which were more
simple; and abstract ones from those, which were more complex, when they
were first excited; that is, we can repeat a part or the whole of those
sensual motions, which did constitute our ideas of perception; and the
repetition of which now constitutes our ideas of recollection, or of
imagination.

3. Those ideas, which we repeat without change of the quantity of that
combination, with which we first received them, are called complex ideas,
as when you recollect Westminster Abbey, or the planet Saturn: but it must
be observed, that these complex ideas, thus re-excited by volition,
sensation, or association, are seldom perfect copies of their correspondent
perceptions, except in our dreams, where other external objects do not
detract our attention.

4. Those ideas, which are more complex than the natural objects that first
excited them, have been called compounded ideas, as when we think of a
sphinx, or griffin.

5. And those that are less complex than the correspondent natural objects,
have been termed abstracted ideas: thus sweetness, and whiteness, and
solidity, are received at the same time from a lump of sugar, yet I can
recollect any of these qualities without thinking of the others, that were
excited along with them.

When ideas are so far abstracted as in the above example, they have been
termed simple by the writers of metaphysics, and seem indeed to be more
complete repetitions of the ideas or sensual motions, originally excited by
external objects.

Other classes of these ideas, where the abstraction has not been so great,
have been termed, by Mr. Locke, modes, substances, and relations, but they
seem only to differ in their degree of abstraction from the complex ideas
that were at first excited; for as these complex or natural ideas are
themselves imperfect copies of their correspondent perceptions, so these
abstract or general ideas are only still more imperfect copies of the same
perceptions. Thus when I have seen an object but once, as a rhinoceros, my
abstract idea of this animal is the same as my complex one. I may think
more or less distinctly of a rhinoceros, but it is the very rhinoceros that
I saw, or some part or property of him, which recurs to my mind.

But when any class of complex objects becomes the subject of conversation,
of which I have seen many individuals, as a castle or an army, some
property or circumstance belonging to it is peculiarly alluded to; and then
I feel in my own mind, that my abstract idea of this complex object is only
an idea of that part, property, or attitude of it, that employs the present
conversation, and varies with every sentence that is spoken concerning it.
So if any one should say, "one may sit upon a horse safer than on a camel,"
my abstract idea of the two animals includes only an outline of the level
back of the one, and the gibbosity on the back of the other. What noise is
that in the street?--Some horses trotting over the pavement. Here my idea
of the horses includes principally the shape and motion of their legs. So
also the abstract ideas of goodness and courage are still more imperfect
representations of the objects they were received from; for here we
abstract the material parts, and recollect only the qualities.

Thus we abstract so much from some of our complex ideas, that at length it
becomes difficult to determine of what perception they partake; and in many
instances our idea seems to be no other than of the sound or letters of the
word, that stands for the collective tribe, of which we are said to have an
abstracted idea, as noun, verb, chimaera, apparition.

6. Ideas have been divided into those of perception and those of
reflection, but as whatever is perceived must be external to the organ that
perceives it, all our ideas must originally be ideas of perception.

7. Others have divided our ideas into those of memory, and those of
imagination; they have said that a recollection of ideas in the order they
were received constitutes memory, and without that order imagination; but
all the ideas of imagination, excepting the few that are termed simple
ideas, are parts of trains or tribes in the order they were received; as if
I think of a sphinx, or a griffin, the fair face, bosom, wings, claws,
tail, are all complex ideas in the order they were received: and it behoves
the writers, who adhere to this definition, to determine, how small the
trains must be, that shall be called imagination; and how great those, that
shall be called memory.

Others have thought that the ideas of memory have a greater vivacity than
those of imagination: but the ideas of a person in sleep, or in a waking
reverie, where the trains connected with sensation are uninterrupted, are
more vivid and distinct than those of memory, so that they cannot be
distinguished by this criterion.

The very ingenious author of the Elements of Criticism has described what
he conceives to be a species of memory, and calls it ideal presence; but
the instances he produces are the reveries of sensation, and are therefore
in truth connections of the imagination, though they are recalled in the
order they were received.

The ideas connected by association are in common discourse attributed to
memory, as we talk of memorandum-rings, and tie a knot on our handkerchiefs
to bring something into our minds at a distance of time. And a school-boy,
who can repeat a thousand unmeaning lines in Lilly's Grammar, is said to
have a good memory. But these have been already shewn to belong to the
class of association; and are termed ideas of suggestion.

II. Lastly, the method already explained of classing ideas into those
excited by irritation, sensation, volition, or association, we hope will be
found more convenient both for explaining the operations of the mind, and
for comparing them with those of the body; and for the illustration and the
cure of the diseases of both, and which we shall here recapitulate.

1. Irritative ideas are those, which are preceded by irritation, which is
excited by objects external to the organs of sense: as the idea of that
tree, which either I attend to, or which I shun in walking near it without
attention. In the former case it is termed perception, in the latter it is
termed simply an irritative idea.

2. Sensitive ideas are those, which are preceded by the sensation of
pleasure or pain; as the ideas, which constitute our dreams or reveries,
this is called imagination.

3. Voluntary ideas are those, which are preceded by voluntary exertion, as
when I repeat the alphabet backwards: this is called recollection.

4. Associate ideas are those, which are preceded by other ideas or muscular
motions, as when we think over or repeat the alphabet by rote in its usual
order; or sing a tune we are accustomed to; this is called suggestion.

III. 1. Perceptions signify those ideas, which are preceded by irritation
and succeeded by the sensation of pleasure or pain, for whatever excites
our attention interests us; that is, it is accompanied with, pleasure or
pain; however slight may be the degree or quantity of either of them.

The word memory includes two classes of ideas, either those which, are
preceded by voluntary exertion, or those which are suggested by their
associations with other ideas.

2. Reasoning is that operation of the sensorium, by which we excite two or
many tribes of ideas; and then re-excite the ideas, in which they differ,
or correspond. If we determine this difference, it is called judgment; if
we in vain endeavour to determine it, it is called doubting.

If we re-excited the ideas, in which they differ, it is called
distinguishing. If we re-excite those in which they correspond, it is
called comparing.

3. Invention is an operation of the sensorium, by which we voluntarily
continue to excite one train of ideas, suppose the design of raising water
by a machine; and at the same time attend to all other ideas, which are
connected with this by every kind of catenation; and combine or separate
them voluntarily for the purpose of obtaining some end.

For we can create nothing new, we can only combine or separate the ideas,
which we have already received by our perceptions: thus if I wish to
represent a monster, I call to my mind the ideas of every thing
disagreeable and horrible, and combine the nastiness and gluttony of a hog,
the stupidity and obstinacy of an ass, with the fur and awkwardness of a
bear, and call the new combination Caliban. Yet such a monster may exist in
nature, as all his attributes are parts of nature. So when I wish to
represent every thing, that is excellent, and amiable; when I combine
benevolence with cheerfulness, wisdom, knowledge, taste, wit, beauty of
person, and elegance of manners, and associate them in one lady as a
pattern to the world, it is called invention; yet such a person may
exist,--such a person does exist!--It is ---- ----, who is as much a
monster as Caliban.

4. In respect to consciousness, we are only conscious of our existence,
when we think about it; as we only perceive the lapse of time, when we
attend to it; when we are busied about other objects, neither the lapse of
time nor the consciousness of our own existence can occupy our attention.
Hence, when we think of our own existence, we only excite abstracted or
reflex ideas (as they are termed), of our principal pleasures or pains, of
our desires or aversions, or of the figure, solidity, colour, or other
properties of our bodies, and call that act of the sensorium a
consciousness of our existence. Some philosopher, I believe it is Des
Cartes, has said, "I think, therefore I exist." But this is not right
reasoning, because thinking is a mode of existence; and it is thence only
saying, "I exist, therefore I exist." For there are three modes of
existence, or in the language of grammarians three kinds of verbs. First,
simply I am, or exist. Secondly, I am acting, or exist in a state of
activity, as I move. Thirdly, I am suffering, or exist in a state of being
acted upon, as I am moved. The when, and the where, as applicable to this
existence, depends on the successive motions of our own or of other bodies;
and on their respective situations, as spoken of Sect. XIV. 2. 5.

5. Our identity is known by our acquired habits or catenated trains of
ideas and muscular motions; and perhaps, when we compare infancy with old
age, in those alone can our identity be supposed to exist. For what else is
there of similitude between the first speck of living entity and the mature
man?--every deduction of reasoning, every sentiment or passion, with every
fibre of the corporeal part of our system, has been subject almost to
annual mutation; while some catenations alone of our ideas and muscular
actions have continued in part unchanged.

By the facility, with which we can in our waking hours voluntarily produce
certain successive trains of ideas, we know by experience, that we have
before reproduced them; that is, we are conscious of a time of our
existence previous to the present time; that is, of our identity now and
heretofore. It is these habits of action, these catenations of ideas and
muscular motions, which begin with life, and only terminate with it; and
which we can in some measure deliver to our posterity; as explained in
Sect. XXXIX.

6. When the progressive motions of external bodies make a part of our
present catenation of ideas, we attend to the lapse of time; which appears
the longer, the more frequently we thus attend to it; as when we expect
something at a certain hour, which much interests us, whether it be an
agreeable or disagreeable event; or when we count the passing seconds on a
stop-watch.

When an idea of our own person, or a reflex idea of our pleasures and
pains, desires and aversions, makes a part of this catenation, it is termed
consciousness; and if this idea of consciousness makes a part of a
catenation, which we excite by recollection, and know by the facility with
which we excite it, that we have before experienced it, it is called
identity, as explained above.

7. In respect to freewill, it is certain, that we cannot will to think of a
new train of ideas, without previously thinking of the first link of it; as
I cannot will to think of a black swan, without previously thinking of a
black swan. But if I now think of a tail, I can voluntarily recollect all
animals, which have tails; my will is so far free, that I can pursue the
ideas linked to this idea of tail, as far as my knowledge of the subject
extends; but to will without motive is to will without desire or aversion;
which is as absurd as to feel without pleasure or pain; they are both
solecisms in the terms. So far are we governed by the catenations of
motions, which affect both the body and the mind of man, and which begin
with our irritability, and end with it.

       *       *       *       *       *

SECT. XVI.

OF INSTINCT.

  Haud equidem credo, quia sit divinitus illis
  Ingenium, aut rerum fato prudentia major.--Virg. Georg. L. I. 415.

    I. _Instinctive actions defined. Of connate passions._ II. _Of the
    sensations and motions of the foetus in the womb._ III. _Some animals
    are more perfectly formed than others before nativity. Of learning to
    walk._ IV. _Of the swallowing, breathing, sucking, pecking, and lapping
    of young animals._ V. _Of the sense of smell, and its uses to animals.
    Why cats do not eat their kittens._ VI. _Of the accuracy of sight in
    mankind, and their sense of beauty. Of the sense of touch in elephants,
    monkies, beavers, men._ VII. _Of natural language._ VIII. _The origin
    of natural language;_ 1. _the language of fear;_ 2. _of grief;_ 3. _of
    tender pleasure;_ 4. _of serene pleasure;_ 5. _of anger;_ 6. _of
    attention._ IX. _Artificial language of turkies, hens, ducklings,
    wagtails, cuckoos, rabbits, dogs, and nightingales._ X. _Of music; of
    tooth-edge; of a good ear; of architecture._ XI. _Of acquired
    knowledge; of foxes, rooks, fieldfares, lapwings, dogs, cats, horses,
    crows, and pelicans._ XII. _Of birds of passage, dormice, snakes, bats,
    swallows, quails, ringdoves, stare, chaffinch, hoopoe, chatterer,
    hawfinch, crossbill, rails and cranes._ XIII. _Of birds nests; of the
    cuckoo; of swallows nests; of the taylor bird._ XIV. _Of the old
    soldier; of haddocks, cods, and dog fish; of the remora; of crabs,
    herrings, and salmon._ XV. _Of spiders, caterpillars, ants, and the
    ichneumon._ XVI. 1. _Of locusts, gnats;_ 2. _bees;_ 3. _dormice, flies,
    worms, ants, and wasps._ XVII. _Of the faculty that distinguishes man
    from the brutes._

I. All those internal motions of animal bodies, which contribute to digest
their aliment, produce their secretions, repair their injuries, or increase
their growth, are performed without our attention or consciousness. They
exist as well in our sleep, as in our waking hours, as well in the foetus
during the time of gestation, as in the infant after nativity, and proceed
with equal regularity in the vegetable as in the animal system. These
motions have been shewn in a former part of this work to depend on the
irritations of peculiar fluids, and as they have never been classed amongst
the instinctive actions of animals, are precluded from our present
disquisition.

But all those actions of men or animals, that are attended with
consciousness, and seem neither to have been directed by their appetites,
taught by their experience, nor deduced from observation or tradition, have
been referred to the power of instinct. And this power has been explained
to be a _divine something_, a kind of inspiration; whilst the poor animal,
that possesses it, has been thought little better than _a machine_!

The _irksomeness_, that attends a continued attitude of the body, or the
_pains_, that we receive from heat, cold, hunger, or other injurious
circumstances, excite us to _general locomotion_: and our senses are so
formed and constituted by the hand of nature, that certain objects present
us with pleasure, others with pain, and we are induced to approach and
embrace these, to avoid and abhor those, as such sensations direct us.

Thus the palates of some animals are gratefully affected by the mastication
of fruits, others of grains, and others of flesh; and they are thence
instigated to attain, and to consume those materials; and are furnished
with powers of muscular motion, and of digestion proper for such purposes.

These _sensations_ and _desires_ constitute a part of our system, as our
_muscles_ and _bones_ constitute another part: and hence they may alike be
termed _natural_ or _connate_; but neither of them can properly be termed
_instinctive_: as the word instinct in its usual acceptation refers only to
the _actions_ of animals, as above explained: the origin of these _actions_
is the subject of our present enquiry.

The reader is intreated carefully to attend to this definition of
_instinctive actions_, lest by using the word instinct without adjoining
any accurate idea to it, he may not only include the natural desires of
love and hunger, and the natural sensations of pain or pleasure, but the
figure and contexture of the body, and the faculty of reason itself under
this general term.

II. We experience some sensations, and perform some actions before our
nativity; the sensations of cold and warmth, agitation and rest, fulness
and inanition, are instances of the former; and the repeated struggles of
the limbs of the foetus, which begin about the middle of gestation, and
those motions by which it frequently wraps the umbilical chord around its
neck or body, and even sometimes ties it on a knot; are instances of the
latter. Smellie's Midwifery, (Vol. I. p. 182.)

By a due attention to these circumstances many of the actions of young
animals, which at first sight seemed only referable to an inexplicable
instinct, will appear to have been acquired like all other animal actions,
that are attended with consciousness, _by the repeated efforts of our
muscles under the conduct of our sensations or desires_.

The chick in the shell begins to move its feet and legs on the sixth day of
incubation (Mattreican, p. 138); or on the seventh day, (Langley);
afterwards they are seen to move themselves gently in the liquid that
surrounds them, and to open and shut their mouths, (Harvei, de Generat. p.
62, and 197. Form de Poulet. ii. p. 129). Puppies before the membranes are
broken, that involve them, are seen to move themselves, to put out their
tongues, and to open and shut their mouths, (Harvey, Gipson, Riolan,
Haller). And calves lick themselves and swallow many of their hairs before
their nativity: which however puppies do not, (Swammerden, p. 319. Flemyng
Phil. Trans. Ann. 1755. 42). And towards the end of gestation, the foetus
of all animals are proved to drink part of the liquid in which they swim,
(Haller. Physiol. T. 8. 204). The white of egg is found in the mouth and
gizzard of the chick, and is nearly or quite consumed before it is hatched,
(Harvie de Generat. 58). And the liquor amnii is found in the mouth and
stomach of the human foetus, and of calves; and how else should that
excrement be produced in the intestines of all animals, which is voided in
great quantity soon after their birth; (Gipson, Med. Essays, Edinb. V. i.
13. Halleri Physiolog. T. 3. p. 318. and T. 8). In the stomach of a calf
the quantity of this liquid amounted to about three pints, and the hairs
amongst it were of the same colour with those on its skin, (Blasii Anat.
Animal, p.m. 122). These facts are attested by many other writers of
credit, besides those above mentioned.

III. It has been deemed a surprising instance of instinct, that calves and
chickens should be able to walk by a few efforts almost immediately after
their nativity: whilst the human infant in those countries where he is not
incumbered with clothes, as in India, is five or six months, and in our
climate almost a twelvemonth, before he can safely stand upon his feet.

The struggles of all animals in the womb must resemble their mode of
swimming, as by this kind of motion they can best change their attitude in
water. But the swimming of the calf and chicken resembles their manner of
walking, which they have thus in part acquired before their nativity, and
hence accomplish it afterwards with very few efforts, whilst the swimming
of the human creature resembles that of the frog, and totally differs from
his mode of walking.

There is another circumstance to be attended to in this affair, that not
only the growth of those peculiar parts of animals, which are first wanted
to secure their subsistence, are in general furthest advanced before their
nativity: but some animals come into the world more completely formed
throughout their whole system than others: and are thence much forwarder in
all their habits of motion. Thus the colt, and the lamb, are much more
perfect animals than the blind puppy, and the naked rabbit; and the chick
of the pheasant, and the partridge, has more perfect plumage, and more
perfect eyes, as well as greater aptitude to locomotion, than the callow
nestlings of the dove, and of the wren. The parents of the former only find
it necessary to shew them their food, and to teach them to take it up;
whilst those of the latter are obliged for many days to obtrude it into
their gaping mouths.

IV. From the facts mentioned in No. 2. of this Section, it is evinced that
the foetus learns to swallow before its nativity; for it is seen to open
its mouth, and its stomach is found filled with the liquid that surrounds
it. It opens its mouth, either instigated by hunger, or by the irksomeness
of a continued attitude of the muscles of its face; the liquor amnii, in
which it swims, is agreeable to its palate, as it consists of a nourishing
material, (Haller Phys. T. 8. p. 204). It is tempted to experience its
taste further in the mouth, and by a few efforts learns to swallow, in the
same manner as we learn all other animal actions, which are attended with
consciousness, _by the repeated efforts of our muscles under the conduct of
our sensations or volitions_.

The inspiration of air into the lungs is so totally different from that of
swallowing a fluid in which we are immersed, that it cannot be acquired
before our nativity. But at this time, when the circulation of the blood is
no longer continued through the placenta, that suffocating sensation, which
we feel about the precordia, when we are in want of fresh air, disagreeably
affects the infant: and all the muscles of the body are excited into action
to relieve this oppression; those of the breast, ribs, and diaphragm are
found to answer this purpose, and thus respiration is discovered, and is
continued throughout our lives, as often as the oppression begins to recur.
Many infants, both of the human creature, and of quadrupeds, struggle for a
minute after they are born before they begin to breathe, (Haller Phys. T.
8. p. 400. ib pt. 2. p. 1). Mr. Buffon thinks the action of the dry air
upon the nerves of smell of new-born animals, by producing an endeavour to
sneeze, may contribute to induce this first inspiration, and that the
rarefaction of the air by the warmth of the lungs contributes to induce
expiration, (Hist. Nat. Tom. 4. p. 174). Which latter it may effect by
producing a disagreeable sensation by its delay, and a consequent effort to
relieve it. Many children sneeze before they respire, but not all, as far
as I have observed, or can learn from others.

At length, by the direction of its sense of smell, or by the officious care
of its mother, the young animal approaches the odoriferous rill of its
future nourishment, already experienced to swallow. But in the act of
swallowing, it is necessary nearly to close the mouth, whether the creature
be immersed in the fluid it is about to drink, or not: hence, when the
child first attempts to suck, it does not slightly compress the nipple
between its lips, and suck as an adult person would do, by absorbing the
milk; but it takes the whole nipple into its mouth for this purpose,
compresses it between its gums, and thus repeatedly chewing (as it were)
the nipple, presses out the milk, exactly in the same manner as it is drawn
from the teats of cows by the hands of the milkmaid. The celebrated Harvey
observes, that the foetus in the womb must have sucked in a part of its
nourishment, because it knows how to suck the minute it is born, as any one
may experience by putting a finger between its lips, and because in a few
days it forgets this art of sucking, and cannot without some difficulty
again acquire it, (Exercit. de Gener. Anim. 48). The same observation is
made by Hippocrates.

A little further experience teaches the young animal to suck by absorption,
as well as by compression; that is, to open the chest as in the beginning
of respiration, and thus to rarefy the air in the mouth, that the pressure
of the denser external atmosphere may contribute to force out the milk.

The chick yet in the shell has learnt to drink by swallowing a part of the
white of the egg for its food; but not having experienced how to take up
and swallow solid seeds, or grains, is either taught by the felicitous
industry of its mother; or by many repeated attempts is enabled at length
to distinguish and to swallow this kind of nutriment.

And puppies, though they know how to suck like other animals from their
previous experience in swallowing, and in respiration; yet are they long in
acquiring the art of lapping with their tongues, which from the flaccidity
of their cheeks, and length of their mouths, is afterwards a more
convenient way for them to take in water.

V. The senses of smell and taste in many other animals greatly excel those
of mankind, for in civilized society, as our victuals are generally
prepared by others, and are adulterated with salt, spice, oil, and
empyreuma, we do not hesitate about eating whatever is set before us, and
neglect to cultivate these senses: whereas other animals try every morsel
by the smell, before they take it into their mouths, and by the taste
before they swallow it: and are led not only each to his proper nourishment
by this organ of sense, but it also at a maturer age directs them in the
gratification of their appetite of love. Which may be further understood by
considering the sympathies of these parts described in Class IV. 2. 1. 7.
While the human animal is directed to the object of his love by his sense
of beauty, as mentioned in No. VI. of this Section. Thus Virgil. Georg.
III. 250.

  Nonne vides, ut tota tremor pertentat equorum
  Corpora, si tantum notas odor attulit auras?
  Nonne canis nidum veneris nasutus odore
  Quaerit, et erranti trahitur sublambere lingua?
  Respuit at gustum cupidus, labiisque retractis
  Elevat os, trepidansque novis impellitur aestris
  Inserit et vivum felici vomere semen.--
  Quam tenui filo caecos adnectit amores
  Docta Venus, vitaeque monet renovare favillam!--ANON.

The following curious experiment is related by Galen. "On dissecting a goat
great with young I found a brisk embryon, and having detached it from the
matrix, and snatching it away before it saw its dam, I brought it into a
certain room, where there were many vessels, some filled with wine, others
with oil, some with honey, others with milk, or some other liquor; and in
others were grains and fruits; we first observed the young animal get upon
its feet, and walk; then it shook itself, and afterwards scratched its side
with one of its feet: then we saw it smelling to every one of these things,
that were set in the room; and when it had smelt to them all, it drank up
the milk." L. 6. de locis. cap. 6.

Parturient quadrupeds, as cats, and bitches, and sows, are led by their
sense of smell to eat the placenta as other common food; why then do they
not devour their whole progeny, as is represented in an antient emblem of
TIME? This is said sometimes to happen in the unnatural state in which we
confine sows; and indeed nature would seem to have endangered her offspring
in this nice circumstance! But at this time the stimulus of the milk in the
tumid teats of the mother excites her to look out for, and to desire some
unknown circumstance to relieve her. At the same time the smell of the milk
attracts the exertions of the young animals towards its source, and thus
the delighted mother discovers a new appetite, as mentioned in Sect. XIV.
8. and her little progeny are led to receive and to communicate pleasure by
this most beautiful contrivance.

VI. But though the human species in some of their sensations are much
inferior to other animals, yet the accuracy of the sense of touch, which
they possess in so eminent a degree, gives them a great superiority of
understanding; as is well observed by the ingenious Mr. Buffon. The
extremities of other animals terminate in horns, and hoofs, and claws, very
unfit for the sensation of touch; whilst the human hand is finely adapted
to encompass its object with this organ of sense.

The elephant is indeed endued with a fine sense of feeling at the extremity
of his proboscis, and hence has acquired much more accurate ideas of touch
and of sight than most other creatures. The two following instances of the
sagacity of these animals may entertain the reader, as they were told me by
some gentlemen of distinct observation, and undoubted veracity, who had
been much conversant with our eastern settlements. First, the elephants
that are used to carry the baggage of our armies, are put each under the
care of one of the natives of Indostan, and whilst himself and his wife go
into the woods to collect leaves and branches of trees for his food, they
fix him to the ground by a length of chain, and frequently leave a child
yet unable to walk, under his protection: and the intelligent animal not
only defends it, but as it creeps about, when it arrives near the extremity
of his chain, he wraps his trunk gently round its body, and brings it again
into the centre of his circle. Secondly, the traitor elephants are taught
to walk on a narrow path between two pit-falls, which are covered with
turf, and then to go into the woods, and to seduce the wild elephants to
come that way, who fall into these wells, whilst he passes safe between
them: and it is universally observed, that those wild elephants that escape
the snare, pursue the traitor with the utmost vehemence, and if they can
overtake him, which sometimes happens, they always beat him to death.

The monkey has a hand well enough adapted for the sense of touch, which
contributes to his great facility of imitation; but in taking objects with
his hands, as a stick or an apple, he puts his thumb on the same side of
them with his fingers, instead of counteracting the pressure of his fingers
with it: from this neglect he is much slower in acquiring the figures of
objects, as he is less able to determine the distances or diameters of
their parts, or to distinguish their vis inertiae from their hardness.
Helvetius adds, that the shortness of his life, his being fugitive before
mankind, and his not inhabiting all climates, combine to prevent his
improvement. (De l'Esprit. T. 1. p.) There is however at this time an old
monkey shewn in Exeter Change, London, who having lost his teeth, when nuts
are given him, takes a stone into his hand, and cracks them with it one by
one; thus using tools to effect his purpose like mankind.

The beaver is another animal that makes much use of his hands, and if we
may credit the reports of travellers, is possessed of amazing ingenuity.
This however, M. Buffon affirms, is only where they exist in large numbers,
and in countries thinly peopled with men; while in France in their solitary
state they shew no uncommon ingenuity.

Indeed all the quadrupeds, that have collar-bones, (claviculae) use their
fore-limbs in some measure as we use our hands, as the cat, squirrel,
tyger, bear and lion; and as they exercise the sense of touch more
universally than other animals, so are they more sagacious in watching and
surprising their prey. All those birds, that use their claws for hands, as
the hawk, parrot, and cuckoo, appear to be more docile and intelligent;
though the gregarious tribes of birds have more acquired knowledge.

Now as the images, that are painted on the retina of the eye, are no other
than signs, which recall to our imaginations the objects we had before
examined by the organ of touch, as is fully demonstrated by Dr. Berkley in
his treatise on vision; it follows that the human creature has greatly more
accurate and distinct sense of vision than that of any other animal. Whence
as he advances to maturity he gradually acquires a sense of female beauty,
which at this time directs him to the object of his new passion.

Sentimental love, as distinguished from the animal passion of that name,
with which it is frequently accompanied, consists in the desire or
sensation of beholding, embracing, and saluting a beautiful object.

The characteristic of beauty therefore is that it is the object of love;
and though many other objects are in common language called beautiful, yet
they are only called so metaphorically, and ought to be termed agreeable. A
Grecian temple may give us the pleasurable idea of sublimity, a Gothic
temple may give us the pleasurable idea of variety, and a modern house the
pleasurable idea of utility; music and poetry may inspire our love by
association of ideas; but none of these, except metaphorically, can be
termed beautiful; as we have no wish to embrace or salute them.

Our perception of beauty consists in our recognition by the sense of vision
of those objects, first, which have before inspired our love by the
pleasure, which they have afforded to many of our senses: as to our sense
of warmth, of touch, of smell, of taste, hunger and thirst; and, secondly,
which bear any analogy of form to such objects.

When the babe, soon after it is born into this cold world, is applied to
its mother's bosom; its sense of perceiving warmth is first agreeably
affected; next its sense of smell is delighted with the odour of her milk;
then its taste is gratified by the flavour of it: afterwards the appetites
of hunger and of thirst afford pleasure by the possession of their objects,
and by the subsequent digestion of the aliment; and, lastly, the sense of
touch is delighted by the softness and smoothness of the milky fountain,
the source of such variety of happiness.

All these various kinds of pleasure at length become associated with the
form of the mother's breast; which the infant embraces with its hands,
presses with its lips, and watches with its eyes; and thus acquires more
accurate ideas of the form of its mother's bosom, than of the odour and
flavour or warmth, which it perceives by its other senses. And hence at our
maturer years, when any object of vision is presented to us, which by its
waving or spiral lines bears any similitude to the form of the female
bosom, whether it be found in a landscape with soft gradations of rising
and descending surface, or in the forms of some antique vases, or in other
works of the pencil or the chissel, we feel a general glow of delight,
which seems to influence all our senses; and, if the object be not too
large, we experience an attraction to embrace it with our arms, and to
salute it with our lips, as we did in our early infancy the bosom of our
mother. And thus we find, according to the ingenious idea of Hogarth, that
the waving lines of beauty were originally taken from the temple of Venus.

This animal attraction is love; which is a sensation, when the object is
present; and a desire, when it is absent. Which constitutes the purest
source of human felicity, the cordial drop in the otherwise vapid cup of
life, and which overpays mankind for the care and labour, which are
attached to the pre-eminence of his situation above other animals.

It should have been observed, that colour as well as form sometimes enters
into our idea of a beautiful object, as a good complexion for instance,
because a fine or fair colour is in general a sign of health, and conveys
to us an idea of the warmth of the object; and a pale countenance on the
contrary gives an idea of its being cold to the touch.

It was before remarked, that young animals use their lips to distinguish
the forms of things, as well as their fingers, and hence we learn the
origin of our inclination to salute beautiful objects with our lips. For a
definition of Grace, see Class III. 1. 2. 4.

VII. There are two ways by which we become acquainted with the passions of
others: first, by having observed the effects of them, as of fear or anger,
on our own bodies, we know at sight when others are under the influence of
these affections. So when two cocks are preparing to fight, each feels the
feathers rise round his own neck, and knows from the same sign the
disposition of his adversary: and children long before they can speak, or
understand the language of their parents, may be frightened by an angry
countenance, or soothed by smiles and blandishments.

Secondly, when we put ourselves into the attitude that any passion
naturally occasions, we soon in some degree acquire that passion; hence
when those that scold indulge themselves in loud oaths, and violent actions
of the arms, they increase their anger by the mode of expressing
themselves: and on the contrary the counterfeited smile of pleasure in
disagreeable company soon brings along with it a portion of the reality, as
is well illustrated by Mr. Burke. (Essay on the Sublime and Beautiful.)

This latter method of entering into the passions of others is rendered of
very extensive use by the pleasure we take in imitation, which is every day
presented before our eyes, in the actions of children, and indeed in all
the customs and fashions of the world. From this our aptitude to imitation,
arises what is generally understood by the word sympathy so well explained
by Dr. Smith of Glasgow. Thus the appearance of a cheerful countenance
gives us pleasure, and of a melancholy one makes us sorrowful. Yawning and
sometimes vomiting are thus propagated by sympathy, and some people of
delicate fibres, at the presence of a spectacle of misery, have felt pain
in the same parts of their own bodies, that were diseased or mangled in the
other. Amongst the writers of antiquity Aristotle thought this aptitude to
imitation an essential property of the human species, and calls man an
imitative animal. [Greek: To zoon mimomenon].

These then are the natural signs by which we understand each other, and on
this slender basis is built all human language. For without some natural
signs, no artificial ones could have been invented or understood, as is
very ingeniously observed by Dr. Reid. (Inquiry into the Human Mind.)

VIII. The origin of this universal language is a subject of the highest
curiosity, the knowledge of which has always been thought utterly
inaccessible. A part of which we shall however here attempt.

Light, sound, and odours, are unknown to the foetus in the womb, which,
except the few sensations and motions already mentioned, sleeps away its
time insensible of the busy world. But the moment he arrives into day, he
begins to experience many vivid pains and pleasures; these are at the same
time attended with certain muscular motions, and from this their early, and
individual association, they acquire habits of occurring together, that are
afterwards indissoluble.

1. _Of Fear._

As soon as the young animal is born, the first important sensations, that
occur to him, are occasioned by the oppression about his precordia for want
of respiration, and by his sudden transition from ninety-eight degrees of
heat into so cold a climate.--He trembles, that is, he exerts alternately
all the muscles of his body, to enfranchise himself from the oppression
about his bosom, and begins to breathe with frequent and short
respirations; at the same time the cold contracts his red skin, gradually
turning it pale; the contents of the bladder and of the bowels are
evacuated: and from the experience of these first disagreeable sensations
the passion of fear is excited, which is no other than the expectation of
disagreeable sensations. This early association of motions and sensations
persists throughout life; the passion of fear produces a cold and pale
skin, with tremblings, quick respiration, and an evacuation of the bladder
and bowels, and thus constitutes the natural or universal language of this
passion.

On observing a Canary bird this morning, January 28, 1772, at the house of
Mr. Harvey, near Tutbury, in Derbyshire, I was told it always fainted away,
when its cage was cleaned, and desired to see the experiment. The cage
being taken from the ceiling, and its bottom drawn out, the bird began to
tremble, and turned quite white about the root of his bill: he then opened
his mouth as if for breath, and respired quick, stood straighter up on his
perch, hung his wings, spread his tail, closed his eyes, and appeared quite
stiff and cataleptic for near half an hour, and at length with much
trembling and deep respirations came gradually to himself.

2. _Of Grief._

That the internal membrane of the nostrils may be kept always moist, for
the better perception of odours, there are two canals, that conduct the
tears after they have done their office in moistening and cleaning the ball
of the eye into a sack, which is called the lacrymal sack; and from which
there is a duct, that opens into the nostrils: the aperture of this duct is
formed of exquisite sensibility, and when it is stimulated by odorous
particles, or by the dryness or coldness of the air, the sack contracts
itself, and pours more of its contained moisture on the organ of smell. By
this contrivance the organ is rendered more fit for perceiving such odours,
and is preserved from being injured by those that are more strong or
corrosive. Many other receptacles of peculiar fluids disgorge their
contents, when the ends of their ducts are stimulated; as the gall bladder,
when the contents of the duodenum stimulate the extremity of the common
bile duct: and the salivary glands, when the termination of their ducts in
the mouth are excited by the stimulus of the food we masticate. Atque
vesiculae seminales suum exprimunt fluidum glande penis fricata.

The coldness and dryness of the atmosphere, compared with the warmth and
moisture, which the new-born infant had just before experienced,
disagreeably affects the aperture of this lacrymal sack: the tears, that
are contained in this sack, are poured into the nostrils, and a further
supply is secreted by the lacrymal glands, and diffused upon the eye-balls;
as is very visible in the eyes and nostrils of children soon after their
nativity. The same happens to us at our maturer age, for in severe frosty
weather, snivelling and tears are produced by the coldness and dryness of
the air.

But the lacrymal glands, which separate the tears from the blood, are
situated on the upper external part of the globes of each eye; and, when a
greater quantity of tears are wanted, we contract the forehead, and bring
down the eye-brows, and use many other distortions of the face, to compress
these glands.

Now as the suffocating sensation, that produces respiration, is removed
almost as soon as perceived, and does not recur again: this disagreeable
irritation of the lacrymal ducts, as it must frequently recur, till the
tender organ becomes used to variety of odours, is one of the first pains
that is repeatedly attended to: and hence throughout our infancy, and in
many people throughout their lives, all disagreeable sensations are
attended with snivelling at the nose, a profusion of tears, and some
peculiar distortions of countenance: according to the laws of early
association before mentioned, which constitutes the natural or universal
language of grief.

You may assure yourself of the truth of this observation, if you will
attend to what passes, when you read a distressful tale alone; before the
tears overflow your eyes, you will invariably feel a titillation at that
extremity of the lacrymal duct, which terminates in the nostril, then the
compression of the eyes succeeds, and the profusion of tears.

Linnaeus asserts, that the female bear sheds tears in grief; the same has
been said of the hind, and some other animals.

3. _Of Tender Pleasure._

The first most lively impression of pleasure, that the infant enjoys after
its nativity, is excited by the odour of its mother's milk. The organ of
smell is irritated by this perfume, and the lacrymal sack empties itself
into the nostrils, as before explained, and an increase of tears is poured
into the eyes. Any one may observe this, when very young infants are about
to suck; for at those early periods of life, the sensation affects the
organ of smell, much more powerfully, than after the repeated habits of
smelling has inured it to odours of common strength: and in our adult
years, the stronger smells, though they are at the same time agreeable to
us, as of volatile spirits, continue to produce an increased secretion of
tears.

This pleasing sensation of smell is followed by the early affection of the
infant to the mother that suckles it, and hence the tender feelings of
gratitude and love, as well as of hopeless grief, are ever after joined
with the titillation of the extremity of the lacrymal ducts, and a
profusion of tears.

Nor is it singular, that the lacrymal sack should be influenced by pleasing
ideas, as the sight of agreeable food produces the same effect on the
salivary glands. Ac dum vidimus insomniis lascivae puellae simulacrum
tenditur penis.

Lambs shake or wriggle their tails, at the time when they first suck, to
get free of the hard excrement, which had been long lodged in their bowels.
Hence this becomes afterwards a mark of pleasure in them, and in dogs, and
other tailed animals. But cats gently extend and contract their paws when
they are pleased, and purr by drawing in their breath, both which resemble
their manner of sucking, and thus become their language of pleasure, for
these animals having collar-bones use their paws like hands when they suck,
which dogs and sheep do not.

4. _Of Serene Pleasure._

In the action of sucking, the lips of the infant are closed around the
nipple of its mother, till he has filled his stomach, and the pleasure
occasioned by the stimulus of this grateful food succeeds. Then the
sphincter of the mouth, fatigued by the continued action of sucking, is
relaxed; and the antagonist muscles of the face gently acting, produce the
smile of pleasure: as cannot but be seen by all who are conversant with
children.

Hence this smile during our lives is associated with gentle pleasure; it is
visible in kittens, and puppies, when they are played with, and tickled;
but more particularly marks the human features. For in children this
expression of pleasure is much encouraged, by their imitation of their
parents, or friends; who generally address them with a smiling countenance:
and hence some nations are more remarkable for the gaiety, and others for
the gravity of their looks.

5. _Of Anger._

The actions that constitute the mode of fighting, are the immediate
language of anger in all animals; and a preparation for these actions is
the natural language of threatening. Hence the human creature clenches his
fist, and sternly surveys his adversary, as if meditating where to make the
attack; the ram, and the bull, draws himself some steps backwards, and
levels his horns; and the horse, as he most frequently fights by striking
with his hinder feet, turns his heels to his foe, and bends back his ears,
to listen out the place of his adversary, that the threatened blow may not
be ineffectual.

6. _Of Attention._

The eye takes in at once but half our horizon, and that only in the day,
and our smell informs us of no very distant objects, hence we confide
principally in the organ of hearing to apprize us of danger: when we hear
any the smallest sound, that we cannot immediately account for, our fears
are alarmed, we suspend our steps, hold every muscle still, open our mouths
a little, erect our ears, and listen to gain further information: and this
by habit becomes the general language of attention to objects of sight, as
well as of hearing; and even to the successive trains of our ideas.

The natural language of violent pain, which is expressed by writhing the
body, grinning, and screaming; and that of tumultuous pleasure, expressed
in loud laughter; belong to Section XXXIV. on Diseases from Volition.

IX. It must have already appeared to the reader, that all other animals, as
well as man, are possessed of this natural language of the passions,
expressed in signs or tones; and we shall endeavour to evince, that those
animals, which have preserved themselves from being enslaved by mankind,
and are associated in flocks, are also possessed of some artificial
language, and of some traditional knowledge.

The mother-turkey, when she eyes a kite hovering high in air, has either
seen her own parents thrown into fear at his presence, or has by
observation been acquainted with his dangerous designs upon her young. She
becomes agitated with fear, and uses the natural language of that passion,
her young ones catch the fear by imitation, and in an instant conceal
themselves in the grass.

At the same time that she shews her fears by her gesture and deportment,
she uses a certain exclamation, Koe-ut, Koe-ut, and the young ones
afterwards know, when they hear this note, though they do not see their
dam, that the presence of their adversary is denounced, and hide themselves
as before.

The wild tribes of birds have very frequent opportunities of knowing their
enemies, by observing the destruction they make among their progeny, of
which every year but a small part escapes to maturity: but to our domestic
birds these opportunities so rarely occur, that their knowledge of their
distant enemies must frequently be delivered by tradition in the manner
above explained, through many generations.

This note of danger, as well as the other notes of the mother-turkey, when
she calls her flock to their food, or to sleep under her wings, appears to
be an artificial language, both as expressed by the mother, and as
understood by the progeny. For a hen teaches this language with equal ease
to the ducklings, she has hatched from suppositious eggs, and educates as
her own offspring: and the wagtails, or hedge-sparrows, learn it from the
young cuckoo their softer nursling, and supply him with food long after he
can fly about, whenever they hear his cuckooing, which Linnaeus tells us, is
his call of hunger, (Syst. Nat.) And all our domestic animals are readily
taught to come to us for food, when we use one tone of voice, and to fly
from our anger, when we use another.

Rabbits, as they cannot easily articulate sounds, and are formed into
societies, that live under ground, have a very different method of giving
alarm. When danger is threatened, they thump on the ground with one of
their hinder feet, and produce a sound, that can be heard a great way by
animals near the surface of the earth, which would seem to be an artificial
sign both from its singularity and its aptness to the situation of the
animal.

The rabbits on the island of Sor, near Senegal, have white flesh, and are
well tasted, but do not burrow in the earth, so that we may suspect their
digging themselves houses in this cold climate is an acquired art, as well
as their note of alarm, (Adanson's Voyage to Senegal).

The barking of dogs is another curious note of alarm, and would seem to be
an acquired language, rather than a natural sign: for "in the island of
Juan Fernandes, the dogs did not attempt to bark, till some European dogs
were put among them, and then they gradually begun to imitate them, but in
a strange manner at first, as if they were learning a thing that was not
natural to them," (Voyage to South America by Don G. Juan, and Don Ant. de
Ulloa. B. 2. c. 4).

Linnaeus also observes, that the dogs of South America do not bark at
strangers, (Syst. Nat.) And the European dogs, that have been carried to
Guinea, are said in three or four generations to cease to bark, and only
howl, like the dogs that are natives of that coast, (World Displayed, Vol.
XVII. p. 26.)

A circumstance not dissimilar to this, and equally curious, is mentioned by
Kircherus, de Musurgia, in his Chapter de Lusciniis, "That the young
nightingales, that are hatched under other birds, never sing till they are
instructed by the company of other nightingales." And Jonston affirms, that
the nightingales that visit Scotland, have not the same harmony as those of
Italy, (Pennant's Zoology, octavo, p. 255); which would lead us to suspect
that the singing of birds, like human music, is an artificial language
rather than a natural expression of passion.

X. Our music like our language, is perhaps entirely constituted of
artificial tones, which by habit suggest certain agreeable passions. For
the same combination of notes and tones do not excite devotion, love, or
poetic melancholy in a native of Indostan and of Europe. And "the
Highlander has the same warlike ideas annexed to the sound of a bagpipe (an
instrument which an Englishman derides), as the Englishman has to that of a
trumpet or fife," (Dr. Brown's Union of Poetry and Music, p. 58.) So "the
music of the Turks is very different from the Italian, and the people of
Fez and Morocco have again a different kind, which to us appears very rough
and horrid, but is highly pleasing to them," (L'Arte Armoniaca a Giorgio
Antoniotto). Hence we see why the Italian opera does not delight an
untutored Englishman; and why those, who are unaccustomed to music, are
more pleased with a tune, the second or third time they hear it, than the
first. For then the same melodious train of sounds excites the melancholy,
they had learned from the song; or the same vivid combination of them
recalls all the mirthful ideas of the dance and company.

Even the sounds, that were once disagreeable to us, may by habit be
associated with other ideas, so as to become agreeable. Father Lasitau, in
his account of the Iroquois, says "the music and dance of those Americans,
have something in them extremely barbarous, which at first disgusts. We
grow reconciled to them by degrees, and in the end partake of them with
pleasure, the savages themselves are fond of them to distraction," (Moeurs
des Savages, Tom. ii.)

There are indeed a few sounds, that we very generally associate with
agreeable ideas, as the whistling of birds, or purring of animals, that are
delighted; and some others, that we as generally associate with
disagreeable ideas, as the cries of animals in pain, the hiss of some of
them in anger, and the midnight howl of beasts of prey. Yet we receive no
terrible or sublime ideas from the lowing of a cow, or the braying of an
ass. Which evinces, that these emotions are owing to previous associations.
So if the rumbling of a carriage in the street be for a moment mistaken for
thunder, we receive a sublime sensation, which ceases as soon as we know it
is the noise of a coach and six.

There are other disagreeable sounds, that are said to set the teeth on
edge; which, as they have always been thought a necessary effect of certain
discordant notes, become a proper subject of our enquiry. Every one in his
childhood has repeatedly bit a part of the glass or earthen vessel, in
which his food has been given him, and has thence had a very disagreeable
sensation in the teeth, which sensation was designed by nature to prevent
us from exerting them on objects harder than themselves. The jarring sound
produced between the cup and the teeth is always attendant on this
disagreeable sensation: and ever after when such a sound is accidentally
produced by the conflict of two hard bodies, we feel by association of
ideas the concomitant disagreeable sensation in our teeth.

Others have in their infancy frequently held the corner of a silk
handkerchief in their mouth, or the end of the velvet cape of their coat,
whilst their companions in play have plucked it from them, and have given
another disagreeable sensation to their teeth, which has afterwards
recurred on touching those materials. And the sight of a knife drawn along
a china plate, though no sound is excited by it, and even the imagination
of such a knife and plate so scraped together, I know by repeated
experience will produce the same disagreeable sensation of the teeth.

These circumstances indisputably prove, that this sensation of the
tooth-edge is owing to associated ideas; as it is equally excitable by
sight, touch, hearing, or imagination.

In respect to the artificial proportions of sound excited by musical
instruments, those, who have early in life associated them with agreeable
ideas, and have nicely attended to distinguish them from each other, are
said to have a good ear, in that country where such proportions are in
fashion: and not from any superior perfection in the organ of hearing, or
any intuitive sympathy between certain sounds and passions.

I have observed a child to be exquisitely delighted with music, and who
could with great facility learn to sing any tune that he heard distinctly,
and yet whole organ of hearing was so imperfect, that it was necessary to
speak louder to him in common conversation than to others.

Our music, like our architecture, seems to have no foundation in nature,
they are both arts purely of human creation, as they imitate nothing. And
the professors of them have only classed those circumstances, that are most
agreeable to the accidental taste of their age, or country; and have called
it Proportion. But this proportion must always fluctuate, as it rests on
the caprices, that are introduced into our minds by our various modes of
education. And these fluctuations of taste must become more frequent in the
present age, where mankind have enfranchised themselves from the blind
obedience to the rules of antiquity in perhaps every science, but that of
architecture. See Sect. XII. 7. 3.

XI. There are many articles of knowledge, which the animals in cultivated
countries seem to learn very early in their lives, either from each other,
or from experience, or observation: one of the most general of these is to
avoid mankind. There is so great a resemblance in the natural language of
the passions of all animals, that we generally know, when they are in a
pacific, or in a malevolent humour, they have the same knowledge of us; and
hence we can scold them from us by some tones and gestures, and could
possibly attract them to us by others, if they were not already apprized of
our general malevolence towards them. Mr. Gmelin, Professor at Petersburg,
assures us, that in his journey into Siberia, undertaken by order of the
Empress of Russia, he saw foxes, that expressed no fear of himself or
companions, but permitted him to come quite near them, having never seen
the human creature before. And Mr. Bongainville relates, that at his
arrival at the Malouine, or Falkland's Islands, which were not inhabited by
men, all the animals came about himself and his people; the fowls settling
upon their heads and shoulders, and the quadrupeds running about their
feet. From the difficulty of acquiring the confidence of old animals, and
the ease of taming young ones, it appears that the fear, they all conceive
at the sight of mankind, is an acquired article of knowledge.

This knowledge is more nicely understood by rooks, who are formed into
societies, and build, as it were, cities over our heads; they evidently
distinguish, that the danger is greater when a man is armed with a gun.
Every one has seen this, who in the spring of the year has walked under a
rookery with a gun in his hand: the inhabitants of the trees rise on their
wings, and scream to the unfledged young to shrink into their nests from
the sight of the enemy. The vulgar observing this circumstance so uniformly
to occur, assert that rooks can smell gun-powder.

The fieldfares, (turdus pilarus) which breed in Norway, and come hither in
the cold season for our winter berries; as they are associated in flocks,
and are in a foreign country, have evident marks of keeping a kind of
watch, to remark and announce the appearance of danger. On approaching a
tree, that is covered with them, they continue fearless till one at the
extremity of the bush rising on his wings gives a loud and peculiar note of
alarm, when they all immediately fly, except one other, who continues till
you approach still nearer, to certify as it were the reality of the danger,
and then he also flies off repeating the note of alarm.

And in the woods about Senegal there is a bird called uett-uett by the
negroes, and squallers by the French, which, as soon as they see a man, set
up a loud scream, and keep flying round him, as if their intent was to warn
other birds, which upon hearing the cry immediately take wing. These birds
are the bane of sportsmen, and frequently put me into a passion, and
obliged me to shoot them, (Adanson's Voyage to Senegal, 78). For the same
intent the lesser birds of our climate seem to fly after a hawk, cuckoo, or
owl, and scream to prevent their companions from being surprised by the
general enemies of themselves, or of their eggs and progeny.

But the lapwing, (charadrius pluvialis Lin.) when her unfledged offspring
run about the marshes, where they were hatched, not only gives the note of
alarm at the approach of men or dogs, that her young may conceal
themselves; but flying and screaming near the adversary, she appears more
felicitous and impatient, as he recedes from her family, and thus
endeavours to mislead him, and frequently succeeds in her design. These
last instances are so apposite to the situation, rather than to the natures
of the creatures, that use them; and are so similar to the actions of men
in the same circumstances, that we cannot but believe, that they proceed
from a similar principle.

Miss M.E. Jacson acquainted me, that she witnessed this autumn an agreeable
instance of sagacity in a little bird, which seemed to use the means to
obtain an end; the bird repeatedly hopped upon a poppy-stem, and shook the
head with its bill, till many seeds were scattered, then it settled on the
ground, and eat the seeds, and again repeated the same management. Sept. 1,
1794.

On the northern coast of Ireland a friend of mine saw above a hundred crows
at once preying upon muscles; each crow took a muscle up into the air
twenty or forty yards high, and let it fall on the stones, and thus by
breaking the shell, got possession of the animal.--A certain philosopher (I
think it was Anaxagoras) walking along the sea-shore to gather shells, one
of these unlucky birds mistaking his bald head for a stone, dropped a
shell-fish upon it, and killed at once a philosopher and an oyster.

Our domestic animals, that have some liberty, are also possessed of some
peculiar traditional knowledge: dogs and cats have been forced into each
other's society, though naturally animals of a very different kind, and
have hence learned from each other to eat dog's grass (agrostis canina)
when they are sick, to promote vomiting. I have seen a cat mistake the
blade of barley for this grass, which evinces it is an acquired knowledge.
They have also learnt of each other to cover their excrement and
urine;--about a spoonful of water was spilt upon my hearth from the
tea-kettle, and I observed a kitten cover it with ashes. Hence this must
also be an acquired art, as the creature mistook the application of it.

To preserve their fur clean, and especially their whiskers, cats wash their
faces, and generally quite behind their ears, every time they eat. As they
cannot lick those places with their tongues, they first wet the inside of
the leg with saliva, and then repeatedly wash their faces with it, which
must originally be an effect of reasoning, because a means is used to
produce an effect; and seems afterwards to be taught or acquired by
imitation, like the greatest part of human arts.

These animals seem to possess something like an additional sense by means
of their whiskers; which have perhaps some analogy to the antennae of moths
and butterflies. The whiskers of cats consist not only of the long hairs on
their upper lips, but they have also four or five long hairs standing up
from each eyebrow, and also two or three on each cheek; all which, when the
animal erects them, make with their points so many parts of the periphery
of a circle, of an extent at least equal to the circumference of any part
of their own bodies. With this instrument, I conceive, by a little
experience, they can at once determine, whether any aperture amongst hedges
or shrubs, in which animals of this genus live in their wild state, is
large enough to admit their bodies; which to them is a matter of the
greatest consequence, whether pursuing or pursued. They have likewise a
power of erecting and bringing forward the whiskers on their lips; which
probably is for the purpose of feeling, whether a dark hole be further
permeable.

The antennae, or horns, of butterflies and moths, who have awkward wings,
the minute feathers of which are very liable to injury, serve, I suppose, a
similar purpose of measuring, as they fly or creep amongst the leaves of
plants and trees, whither their wings can pass without touching them.

Mr. Leonard, a very intelligent friend of mine, saw a cat catch a trout by
darting upon it in a deep clear water at the mill at Weaford, near
Lichfield. The cat belonged to Mr. Stanley, who had often seen her catch
fish in the same manner in summer, when the mill-pool was drawn so low,
that the fish could be seen. I have heard of other cats taking fish in
shallow water, as they stood on the bank. This seems a natural art of
taking their prey in cats, which their acquired delicacy by domestication
has in general prevented them from using, though their desire of eating
fish continues in its original strength.

Mr. White, in his ingenious History of Selbourn, was witness to a cat's
suckling a young hare, which followed her about the garden, and came
jumping to her call of affection. At Elford, near Lichfield, the Rev. Mr.
Sawley had taken the young ones out of a hare, which was shot; they were
alive, and the cat, who had just lost her own kittens, carried them away,
as it was supposed, to eat them; but it presently appeared, that it was
affection not hunger which incited her, as she suckled them, and brought
them up as their mother.

Other instances of the mistaken application of what has been termed
instinct may be observed in flies in the night, who mistaking a candle for
day-light, approach and perish in the flame. So the putrid smell of the
stapelia, or carrion-flower, allures the large flesh-fly to deposit its
young worms on its beautiful petals, which perish there for want of
nourishment. This therefore cannot be a necessary instinct, because the
creature mistakes the application of it.

Though in this country horses shew little vestiges of policy, yet in the
deserts of Tartary, and Siberia, when hunted by the Tartars they are seen
to form a kind of community, set watches to prevent their being surprised,
and have commanders, who direct, and hasten their flight, Origin of
Language, Vol. I. p. 212. In this country, where four or five horses travel
in a line, the first always points his ears forward, and the last points
his backward, while the intermediate ones seem quite careless in this
respect; which seems a part of policy to prevent surprise. As all animals
depend most on the ear to apprize them of the approach of danger, the eye
taking in only half the horizon at once, and horses possess a great nicety
of this sense; as appears from their mode of fighting mentioned No. 8. 5.
of this Section, as well as by common observation.

There are some parts of a horse, which he cannot conveniently rub, when
they itch, as about the shoulder, which he can neither bite with his teeth,
nor scratch with his hind foot; when this part itches, he goes to another
horse, and gently bites him in the part which he wishes to be bitten, which
is immediately done by his intelligent friend. I once observed a young foal
thus bite its large mother, who did not choose to drop the grass she had in
her mouth, and rubbed her nose against the foal's neck instead of biting
it; which evinces that she knew the design of her progeny, and was not
governed by a necessary instinct to bite where she was bitten.

Many of our shrubs, which would otherwise afford an agreeable food to
horses, are armed with thorns or prickles, which secure them from those
animals; as the holly, hawthorn, gooseberry, gorse. In the extensive
moorlands of Staffordshire, the horses have learnt to stamp upon a
gorse-bush with one of their fore-feet for a minute together, and when the
points are broken, they eat it without injury. The horses in the new forest
in Hampshire are affirmed to do the same by Mr. Gilpin. Forest Scenery, II.
251, and 112. Which is an art other horses in the fertile parts of the
country do not possess, and prick their mouths till they bleed, if they are
induced by hunger or caprice to attempt eating gorse.

Swine have a sense of touch as well as of smell at the end of their nose,
which they use as a hand, both to root up the soil, and to turn over and
examine objects of food, somewhat like the proboscis of an elephant. As
they require shelter from the cold in this climate, they have learnt to
collect straw in their mouths to make their nest, when the wind blows cold;
and to call their companions by repeated cries to assist in the work, and
add to their warmth by their numerous bedfellows. Hence these animals,
which are esteemed so unclean, have also learned never to befoul their
dens, where they have liberty, with their own excrement; an art, which cows
and horses, which have open hovels to run into, have never acquired. I have
observed great sagacity in swine; but the short lives we allow them, and
their general confinement, prevents their improvement, which might probably
be otherwise greater than that of dogs.

Instances of the sagacity and knowledge of animals are very numerous to
every observer, and their docility in learning various arts from mankind,
evinces that they may learn similar arts from their own species, and thus
be possessed of much acquired and traditional knowledge.

A dog whose natural prey is sheep, is taught by mankind, not only to leave
them unmolested, but to guard them; and to hunt, to set, or to destroy
other kinds of animals, as birds, or vermin; and in some countries to catch
fish, in others to find truffles, and to practise a great variety of
tricks; is it more surprising that the crows should teach each other, that
the hawk can catch less birds, by the superior swiftness of his wing, and
if two of them follow him, till he succeeds in his design, that they can by
force share a part of the capture? This I have formerly observed with
attention and astonishment.

There is one kind of pelican mentioned by Mr. Osbeck, one of Linnaeus's
travelling pupils (the pelicanus aquilus), whose food is fish; and which it
takes from other birds, because it is not formed to catch them itself;
hence it is called by the English a Man-of-war-bird, Voyage to China, p.
88. There are many other interesting anecdotes of the pelican and
cormorant, collected from authors of the best authority, in a well-managed
Natural History for Children, published by Mr. Galton. Johnson. London.

And the following narration from the very accurate Mons. Adanson, in his
Voyage to Senegal, may gain credit with the reader: as his employment in
this country was solely to make observations in natural history. On the
river Niger, in his road to the island Griel, he saw a great number of
pelicans, or wide throats. "They moved with great state like swans upon the
water, and are the largest bird next to the ostrich; the bill of the one I
killed was upwards of a foot and half long, and the bag fastened underneath
it held two and twenty pints of water. They swim in flocks, and form a
large circle, which they contract afterwards, driving the fish before them
with their legs: when they see the fish in sufficient number confined in
this space, they plunge their bill wide open into the water, and shut it
again with great quickness. They thus get fish into their throat-bag, which
they eat afterwards on shore at their leisure." P. 247.

XII. The knowledge and language of those birds, that frequently change
their climate with the seasons, is still more extensive: as they perform
these migrations in large societies, and are less subject to the power of
man, than the resident tribes of birds. They are said to follow a leader
during the day, who is occasionally changed, and to keep a continual cry
during the night to keep themselves together. It is probable that these
emigrations were at first undertaken as accident directed, by the more
adventurous of their species, and learned from one another like the
discoveries of mankind in navigation. The following circumstances strongly
support this opinion.

1. Nature has provided these animals, in the climates where they are
produced, with another resource: when the season becomes too cold for their
constitutions, or the food they were supported with ceases to be supplied,
I mean that of sleeping. Dormice, snakes, and bats, have not the means of
changing their country; the two former from the want of wings, and the
latter from his being not able to bear the light of the day. Hence these
animals are obliged to make use of this resource, and sleep during the
winter. And those swallows that have been hatched too late in the year to
acquire their full strength of pinion, or that have been maimed by accident
or disease, have been frequently found in the hollows of rocks on the sea
coasts, and even under water in this torpid state, from which they have
been revived by the warmth of a fire. This torpid state of swallows is
testified by innumerable evidences both of antient and modern names.
Aristotle speaking of the swallows says, "They pass into warmer climates in
winter, if such places are at no great distance; if they are, they bury
themselves in the climates where they dwell," (8. Hist. c. 16. See also
Derham's Phys. Theol. v. ii. p. 177.)

Hence their emigrations cannot depend on a _necessary_ instinct, as the
emigrations themselves are not _necessary_.

2. When the weather becomes cold, the swallows in the neighbourhood
assemble in large flocks; that is, the unexperienced attend those that have
before experienced the journey they are about to undertake: they are then
seen some time to hover on the coast, till there is calm whether, or a
wind, that suits the direction of their flight. Other birds of passage have
been drowned by thousands in the sea, or have settled on ships quite
exhausted with fatigue. And others, either by mistaking their course, or by
distress of weather, have arrived in countries where they were never seen
before: and thus are evidently subject to the same hazards that the human
species undergo, in the execution of their artificial purposes.

3. The same birds are emigrant from some countries and not so from others:
the swallows were seen at Goree in January by an ingenious philosopher of
my acquaintance, and he was told that they continued there all the year; as
the warmth of the climate was at all seasons sufficient for their own
constitutions, and for the production of the flies that supply them with
nourishment. Herodotus says, that in Libya, about the springs of the Nile,
the swallows continue all the year. (L. 2.)

Quails (tetrao corturnix, Lin.) are birds of passage from the coast of
Barbary to Italy, and have frequently settled in large shoals on ships
fatigued with their flight. (Ray, Wisdom of God, p. 129. Derham. Physic.
Theol. v. ii. p. 178,) Dr. Ruffel, in his History of Aleppo, observes that
the swallows visit that country about the end of February, and having
hatched their young disappear about the end of July; and returning again
about the beginning of October, continue about a fortnight, and then again
disappear. (P. 70.)

When my late friend Dr. Chambres, of Derby, was on the island of Caprea in
the bay of Naples, he was informed that great flights of quails annually
settle on that island about the beginning of May, in their passage from
Africa to Europe. And that they always come when the south-east wind blows,
are fatigued when they rest on this island, and are taken in such amazing
quantities and sold to the Continent, that the inhabitants pay the bishop
his stipend out of the profits arising from the sale of them.

The flights of these birds across the Mediterranean are recorded near three
thousand years ago. "There went forth a wind from the Lord and brought
quails from the sea, and let them fall upon the camp, a day's journey round
about it, and they were two cubits above the earth," (Numbers, chap. ii.
ver. 31.)

In our country, Mr. Pennant informs us, that some quails migrate, and
others only remove from the internal parts of the island to the coasts,
(Zoology, octavo, 210.) Some of the ringdoves and stares breed here, others
migrate, (ibid. 510, ii.) And the slender billed small birds do not all
quit these kingdoms in the winter, though the difficulty of procuring the
worms and insects, that they feed on, supplies the same reason for
migration to them all, (ibid. 511.)

Linnaeus has observed, that in Sweden the female chaffinches quit that
country in September, migrating into Holland, and leave their mates behind
till their return in spring. Hence he has called them Fringilla caelebs,
(Amaen. Acad. ii. 42. iv. 595.) Now in our climate both sexes of them are
perennial birds. And Mr. Pennant observes that the hoopoe, chatterer,
hawfinch, and crossbill, migrate into England so rarely, and at such
uncertain times, as not to deserve to be ranked among our birds of passage,
(ibid. 511.)

The water fowl, as geese and ducks, are better adapted for long migrations,
than the other tribes of birds, as, when the weather is calm, they can not
only rest themselves, or sleep upon the ocean, but possibly procure some
kind of food from it.

Hence in Siberia, as soon as the lakes are frozen, the water fowl, which
are very numerous, all disappear, and are supposed to fly to warmer
climates, except the rail, which, from its inability for long flights,
probably sleeps, like our bat, in their winter. The following account from
the Journey of Professor Gmelin, may entertain the reader. "In the
neighbourhood of Krasnoiark, amongst many other emigrant water fowls, we
observed a great number of rails, which when pursued never took flight, but
endeavoured to escape by running. We enquired how these birds, that could
not fly, could retire into other countries in the winter, and were told,
both by the Tartars and Assanians, that they well knew those birds could
not alone pass into other countries: but when the cranes (les grues) retire
in autumn, each one takes a rail (un rale) upon his back, and carries him
to a warmer climate."

_Recapitulation._

1. All birds of passage can exist in the climates, where they are produced.

2. They are subject in their migrations to the same accidents and
difficulties, that mankind are subject to in navigation.

3. The same species of birds migrate from some countries, and are resident
in others.

From all these circumstances it appears that the migrations of birds are
not produced by a necessary instinct, but are accidental improvements, like
the arts among mankind, taught by their cotemporaries, or delivered by
tradition from one generation of them to another.

XIII. In that season of the year which supplies the nourishment proper for
the expected brood, the birds enter into a contract of marriage, and with
joint labour construct a bed for the reception of their offspring. Their
choice of the proper season, their contracts of marriage, and the
regularity with which they construct their nests, have in all ages excited
the admiration of naturalists; and have always been attributed to the power
of instinct, which, like the occult qualities of the antient philosophers,
prevented all further enquiry. We shall consider them in their order.

_Their Choice of the Season._

Our domestic birds, that are plentifully supplied throughout the year with
their adapted food, and are covered with houses from the inclemency of the
weather, lay their eggs at any season: which evinces that the spring of the
year is not pointed out to them by a necessary instinct.

Whilst the wild tribes of birds choose this time of the year from their
acquired knowledge, that the mild temperature of the air is more convenient
for hatching their eggs, and is soon likely to supply that kind of
nourishment, that is wanted for their young.

If the genial warmth of the spring produced the passion of love, as it
expands the foliage of trees, all other animals should feel its influence
as well as birds: but, the viviparous creatures, as they suckle their
young, that is, as they previously digest the natural food, that it may
better suit the tender stomachs of their offspring, experience the
influence of this passion at all seasons of the year, as cats and bitches.
The graminivorous animals indeed generally produce their young about the
time when grass is supplied in the greatest plenty, but this is without any
degree of exactness, as appears from our cows, sheep, and hares, and may be
a part of the traditional knowledge, which they learn from the example of
their parents.

_Their Contracts of Marriage._

Their mutual passion, and the acquired knowledge, that their joint labour
is necessary to procure sustenance for their numerous family, induces the
wild birds to enter into a contract of marriage, which does not however
take place among the ducks, geese, and fowls, that are provided with their
daily food from our barns.

An ingenious philosopher has lately denied, that animals can enter into
contracts, and thinks this an essential difference between them and the
human creature:--but does not daily observation convince us, that they form
contracts of friendship with each other, and with mankind? When puppies and
kittens play together, is there not a tacit contract, that they will not
hurt each other? And does not your favorite dog expect you should give him
his daily food, for his services and attention to you? And thus barters his
love for your protection? In the same manner that all contracts are made
amongst men, that do not understand each others arbitrary language.

_Construction of their Nests._

1. They seem to be instructed how to build their nests from their
observation of that, in which they were educated, and from their knowledge
of those things, that are most agreeable to their touch in respect: to
warmth, cleanliness, and stability. They choose their situations from their
ideas of safety from their enemies, and of shelter from the weather. Nor is
the colour of their nests a circumstance unthought of; the finches, that
build in green hedges, cover their habitations with green moss; the swallow
or martin, that builds against rocks and houses, covers her's with clay,
whilst the lark chooses vegetable straw nearly of the colour of the ground
she inhabits: by this contrivance, they are all less liable to be
discovered by their adversaries.

2. Nor are the nests of the same species of birds constructed always of the
same materials, nor in the same form; which is another circumstance that
ascertains, that they are led by observation.

In the trees before Mr. Levet's house in Lichfield, there are annually
nests built by sparrows, a bird which usually builds under the tiles of
houses, or the thatch of barns. Not finding such convenient situations for
their nests, they build a covered nest bigger than a man's head, with an
opening like a mouth at the side, resembling that of a magpie, except that
it is built with straw and hay, and lined with feathers, and so nicely
managed as to be a defence against both wind and rain.

The following extract from a Letter of the Rev. Mr. J. Darwin, of Carleton
Scroop in Lincolnshire, authenticates a curious fact of this kind. "When I
mentioned to you the circumstance of crows or rooks building in the spire
of Welbourn church, you expressed a desire of being well informed of the
certainty of the fact. Welbourn is situated in the road from Grantham to
Lincoln on the Cliff row; I yesterday took a ride thither, and enquired of
the rector, Mr. Ridgehill, whether the report was true, that rooks built in
the spire of his church. He assured me it was true, and that they had done
so time immemorial, as his parishioners affirmed. There was a common
tradition, he said, that formerly a rookery in some high trees adjoined the
church yard, which being cut down (probably in the spring, the building
season), the rooks removed to the church, and built their nests on the
outside of the spire on the tops of windows, which by their projection a
little from the spire made them convenient room, but that they built also
on the inside. I saw two nests made with sticks on the outside, and in the
spires, and Mr. Ridgehill said there were always a great many.

"I spent the day with Mr. Wright, a clergyman, at Fulbeck, near Welbourn,
and in the afternoon Dr. Ellis of Headenham, about two miles from Welbourn,
drank tea at Mr. Wright's, who said he remembered, when Mr. Welby lived at
Welbourn, that he received a letter from an acquaintance in the west of
England, desiring an answer, whether the report of rooks building in
Welbourn church was true, as a wager was depending on that subject; to
which he returned an answer ascertaining the fact, and decided the wager."
Aug. 30, 1794.

So the jackdaw (corvus monedula) generally builds in church-steeples, or
under the roofs of high houses; but at Selbourn, in Southamptonshire, where
towers and steeples are not sufficiently numerous, these birds build in
forsaken rabbit burrows. See a curious account of these subterranean nests
in White's History of Selbourn, p. 59. Can the skilful change of
architecture in these birds and the sparrows above mentioned be governed by
instinct? Then they must have two instincts, one for common, and the other
for extraordinary occasions.

I have seen green worsted in a nest, which no where exists in nature: and
the down of thistles in those nests, that were by some accident constructed
later in the summer, which material could not be procured for the earlier
nests: in many different climates they cannot procure the same materials,
that they use in ours. And it is well known, that the canary birds, that
are propagated in this country, and the finches, that are kept tame, will
build their nests of any flexile materials, that are given them. Plutarch,
in his Book on Rivers, speaking of the Nile, says, "that the swallows
collect a material, when the waters recede, with which they form nests,
that are impervious to water." And in India there is a swallow that
collects a glutinous substance for this purpose, whose nest is esculent,
and esteemed a principal rarity amongst epicures, (Lin. Syst. Nat.) Both
these must be constructed of very different materials from those used by
the swallows of our country.

In India the birds exert more artifice in building their nests on account
of the monkeys and snakes: some form their pensile nests in the shape of a
purse, deep and open at top; others with a hole in the side; and others,
still more cautious, with an entrance at the very bottom, forming their
lodge near the summit. But the taylor-bird will not ever trust its nest to
the extremity of a tender twig, but makes one more advance to safety by
fixing it to the leaf itself. It picks up a dead leaf, and sews it to the
side of a living one, its slender bill being its needle, and its thread
some fine fibres; the lining consists of feathers, gossamer, and down; its
eggs are white, the colour of the bird light yellow, its length three
inches, its weight three sixteenths of an ounce; so that the materials of
the nest, and the weight of the bird, are not likely to draw down an
habitation so slightly suspended. A nest of this bird is preserved in the
British Museum, (Pennant's Indian Zoology). This calls to one's mind the
Mosaic account of the origin of mankind, the first dawning of art there
ascribed to them, is that of sewing leaves together. For many other curious
kinds of nests see Natural History for Children, by Mr. Galton. Johnson.
London. Part I. p. 47. Gen. Oriolus.

3. Those birds that are brought up by our care, and have had little
communication with others of their own species, are very defective in this
acquired knowledge; they are not only very awkward in the construction of
their nests, but generally scatter their eggs in various parts of the room
or cage, where they are confined, and seldom produce young ones, till, by
failing in their first attempt, they have learnt something from their own
observation.

4. During the time of incubation birds are said in general to turn their
eggs every day; some cover them, when they leave the nest, as ducks and
geese; in some the male is said to bring food to the female, that she may
have less occasion of absence, in others he is said to take her place, when
she goes in quest of food; and all of them are said to leave their eggs a
shorter time in cold weather than in warm. In Senegal the ostrich sits on
her eggs only during the night, leaving them in the day to the heat of the
sun; but at the Cape of Good Hope, where the heat is less, she sits on them
day and night.

If it should be asked, what induces a bird to sit weeks on its first eggs
unconscious that a brood of young ones will be the product? The answer must
be, that it is the same passion that induces the human mother to hold her
offspring whole nights and days in her fond arms, and press it to her
bosom, unconscious of its future growth to sense and manhood, till
observation or tradition have informed her.

5. And as many ladies are too refined to nurse their own children, and
deliver them to the care and provision of others; so is there one instance
of this vice in the feathered world. The cuckoo in some parts of England,
as I am well informed by a very distinct and ingenious gentleman, hatches
and educates her own young; whilst in other parts she builds no nest, but
uses that of some lesser bird, generally either of the wagtail, or hedge
sparrow, and depositing one egg in it, takes no further care of her
progeny.

As the Rev. Mr. Stafford was walking in Glosop Dale, in the Peak of
Derbyshire, he saw a cuckoo rise from its nest. The nest was on the stump
of a tree, that had been some time felled, among some chips that were in
part turned grey, so as much to resemble the colour of the bird, in this
nest were two young cuckoos: tying a string about the leg of one of them,
he pegged the other end of it to the ground, and very frequently for many
days beheld the old cuckoo feed these her young, as he stood very near
them.

The following extract of a Letter from the Rev. Mr. Wilmot, of Morley, near
Derby, strengthens the truth of the fact above mentioned, of the cuckoo
sometimes making a nest, and hatching her own young.

"In the beginning of July 1792, I was attending some labourers on my farm,
when one of them said to me, "There is a bird's nest upon one of the
Coal-slack Hills; the bird is now sitting, and is exactly like a cuckoo.
They say that cuckoo's never hatch their own eggs, otherwise I should have
sworn it was one." He took me to the spot, it was in an open fallow ground;
the bird was upon the nest, I stood and observed her some time, and was
perfectly satisfied it was a cuckoo; I then put my hand towards her, and
she almost let me touch her before she rose from the nest, which she
appeared to quit with great uneasiness, skimming over the ground in the
manner that a hen partridge does when disturbed from a new hatched brood,
and went only to a thicket about forty or fifty yards from the nest; and
continued there as long as I staid to observe her, which was not many
minutes. In the nest, which was barely a hole scratched out of the
coal-slack in the manner of a plover's nest, I observed three eggs, but did
not touch them. As I had labourers constantly at work in that field, I went
thither every day, and always looked to see if the bird was there, but did
not disturb her for seven or eight days, when I was tempted to drive her
from the nest, and found _two_ young ones, that appeared to have been
hatched some days, but there was no appearance of the third egg. I then
mentioned this extraordinary circumstance (for such I thought it) to Mr.
and Mrs. Holyoak of Bidford Grange, Warwickshire, and to Miss M. Willes,
who were on a visit at my house, and who all went to see it. Very lately I
reminded Mr. Holyoak of it, who told me he had a perfect recollection of
the whole, and that, considering it a curiosity, he walked to look at it
several times, was perfectly satisfied as to its being a cuckoo, and
thought her more attentive to her young, than any other bird he ever
observed, having always found her brooding her young. In about a week after
I first saw the young ones, one of them was missing, and I rather suspected
my plough-boys having taken it; though it might possibly have been taken by
a hawk, some time when the old one was seeking food. I never found her off
her nest but once, and that was the last time I saw the remaining young
one, when it was almost full feathered. I then went from home for two or
three days, and, when I returned, the young one was gone, which I take for
granted had flown. Though during this time I frequently saw cuckoos in the
thicket I mention, I never observed any one, that I supposed to be the
cock-bird, paired with this hen."

Nor is this a new observation, though it is entirely overlooked by the
modern naturalists, for Aristotle speaking of the cuckoo, asserts that she
sometimes builds her nest among broken rocks, and on high mountains, (L. 6.
H. c. 1.) but adds in another place that she generally possesses the nest
of another bird, (L. 6. H. c. 7.) And Niphus says that cuckoos rarely build
for themselves, most frequently laying their eggs in the nests of other
birds, (Gesner, L. 3. de Cuculo.)

The Philosopher who is acquainted with these facts concerning the cuckoo,
would seem to have very little _reason_ himself, if he could imagine this
neglect of her young to be a necessary _instinct_!

XIV. The deep recesses of the ocean are inaccessible to mankind, which
prevents us from having much knowledge of the arts and government of its
inhabitants.

1. One of the baits used by the fisherman is an animal called an Old
Soldier, his size and form are somewhat like the craw-fish, with this
difference, that his tail is covered with a tough membrane instead of a
shell; and to obviate this defect, he seeks out the uninhabited shell of
some dead fish, that is large enough to receive his tail, and carries it
about with him as part of his clothing or armour.

2. On the coasts about Scarborough, where the haddocks, cods, and dog-fish,
are in great abundance, the fishermen universally believe that the dog-fish
make a line, or semicircle, to encompass a shoal of haddocks and cod,
confining them within certain limits near the shore, and eating them as
occasion requires. For the haddocks and cod are always found near the shore
without any dog-fish among them, and the dog-fish further off without any
haddocks or cod; and yet the former are known to prey upon the latter, and
in some years devour such immense quantities as to render this fishery more
expensive than profitable.

3. The remora, when he wishes to remove his situation, as he is a very slow
swimmer, is content to take an outside place on whatever conveyance is
going his way; nor can the cunning animal be tempted to quit his hold of a
ship when she is sailing, not even for the lucre of a piece of pork, lest
it should endanger the loss of his passage: at other times he is easily
caught with the hook.

4. The crab-fish, like many other testaceous animals, annually changes its
shell; it is then in a soft state, covered only with a mucous membrane, and
conceals itself in holes in the sand or under weeds; at this place a hard
shelled crab always stands centinel, to prevent the sea insects from
injuring the other in its defenceless state; and the fishermen from his
appearance know where to find the soft ones, which they use for baits in
catching other fish.

And though the hard shelled crab, when he is on this duty, advances boldly
to meet the foe, and will with difficulty quit the field; yet at other
times he shews great timidity, and has a wonderful speed in attempting his
escape; and, if often interrupted, will pretend death like the spider, and
watch an opportunity to sink himself into the sand, keeping only his eyes
above. My ingenious friend Mr. Burdett, who favoured me with these accounts
at the time he was surveying the coasts, thinks the commerce between the
sexes takes place at this time, and inspires the courage of the creature.

5. The shoals of herrings, cods, haddocks, and other fish, which approach
our shores at certain seasons, and quit them at other seasons without
leaving one behind; and the salmon, that periodically frequent our rivers,
evince, that there are vagrant tribes of fish, that perform as regular
migrations as the birds of passage already mentioned.

6. There is a cataract on the river Liffey in Ireland about nineteen feet
high: here in the salmon season many of the inhabitants amuse themselves in
observing these fish leap up the torrent. They dart themselves quite out of
the water as they ascend, and frequently fall back many times before they
surmount it, and baskets made of twigs are placed near the edge of the
stream to catch them in their fall.

I have observed, as I have sat by a spout of water, which descends from a
stone trough about two feet into a stream below, at particular seasons of
the year, a great number of little fish called minums, or pinks, throw
themselves about twenty times their own length out of the water, expecting
to get into the trough above.

This evinces that the storgee, or attention of the dam to provide for the
offspring, is strongly exerted amongst the nations of fish, where it would
seem to be the most neglected; as these salmon cannot be supposed to
attempt so difficult and dangerous a task without being conscious of the
purpose or end of their endeavours.

It is further remarkable, that most of the old salmon return to the sea
before it is proper for the young shoals to attend them, yet that a few old
ones continue in the rivers so late, that they become perfectly emaciated
by the inconvenience of their situation, and this apparently to guide or to
protect the unexperienced brood.

Of the smaller water animals we have still less knowledge, who nevertheless
probably possess many superior arts; some of these are mentioned in Botanic
Garden, P. I. Add. Note XXVII. and XXVIII. The nympha of the water-moths of
our rivers, which cover themselves with cases of straw, gravel, and shell,
contrive to make their habitations, nearly in equilibrium with the water;
when too heavy, they add a bit of wood or straw; when too light, a bit of
gravel. Edinb. Trans.

All these circumstances bear a near resemblance to the deliberate actions
of human reason.

XV. We have a very imperfect acquaintance with the various tribes of
insects: their occupations, manner of life, and even the number of their
senses, differ from our own, and from each other; but there is reason to
imagine, that those which possess the sense of touch in the most exquisite
degree, and whole occupations require the most constant exertion of their
powers, are induced with a greater proportion or knowledge and ingenuity.

The spiders of this country manufacture nets of various forms, adapted to
various situations, to arrest the flies that are their food; and some of
them have a house or lodging-place in the middle of the net, well contrived
for warmth, security, or concealment. There is a large spider in South
America, who constructs nets of so strong a texture as to entangle small
birds, particularly the humming bird. And in Jamaica there is another
spider, who digs a hole in the earth obliquely downwards, about three
inches in length, and one inch in diameter, this cavity she lines with a
tough thick web, which when taken out resembles a leathern purse: but what
is most curious, this house has a door with hinges, like the operculum of
some sea shells; and herself and family, who tenant this nest, open and
shut the door, whenever they pass or repass. This history was told me, and
the nest with its operculum shewn me by the late Dr. Butt of Bath, who was
some years physician in Jamaica.

The production of these nets is indeed a part of the nature or conformation
of the animal, and their natural use is to supply the place of wings, when
she wishes to remove to another situation. But when she employs them to
entangle her prey, there are marks of evident design, for she adapts the
form of each net to its situation, and strengthens those lines, that
require it, by joining others to the middle of them, and attaching those
others to distant objects, with the same individual art, that is used by
mankind in supporting the masts and extending the sails of ships. This work
is executed with more mathematical exactness and ingenuity by the field
spiders, than by those in our houses, as their constructions are more
subjected to the injuries of dews and tempests.

Besides the ingenuity shewn by these little creatures in taking their prey,
the circumstance of their counterfeiting death, when they are put into
terror, is truly wonderful; and as soon as the object of terror is removed,
they recover and run away. Some beetles are also said to possess this piece
of hypocrisy.

The curious webs, or chords, constructed by some young caterpillars to
defend themselves from cold, or from insects of prey; and by silk-worms and
some other caterpillars, when they transmigrate into aureliae or larvae, have
deservedly excited the admiration of the inquisitive. But our ignorance of
their manner of life, and even of the number of their senses, totally
precludes us from understanding the means by which they acquire this
knowledge.

The care of the salmon in choosing a proper situation for her spawn, the
structure of the nests of birds, their patient incubation, and the art of
the cuckoo in depositing her egg in her neighbour's nursery, are instances
of great sagacity in those creatures: and yet they are much inferior to the
arts exerted by many of the insect tribes on similar occasions. The hairy
excrescences on briars, the oak apples, the blasted leaves of trees, and
the lumps on the backs of cows, are situations that are rather produced
than chosen by the mother insect for the convenience of her offspring. The
cells of bees, wasps, spiders, and of the various coralline insects,
equally astonish us, whether we attend to the materials or to the
architecture.

But the conduct of the ant, and of some species of the ichneumon fly in the
incubation of their eggs, is equal to any exertion of human science. The
ants many times in a day move their eggs nearer the surface of their
habitation, or deeper below it, as the heat of the weather varies; and in
colder days lie upon them in heaps for the purpose of incubation: if their
mansion is too dry, they carry them to places where there is moisture, and
you may distinctly see the little worms move and suck up the water. When
too much moisture approaches their nest, they convey their eggs deeper in
the earth, or to some other place of safety. (Swammerd. Epil. ad Hist.
Insects, p. 153. Phil. Trans. No. 23. Lowthrop. V. 2. p. 7.)

There is one species of ichneumon-fly, that digs a hole in the earth, and
carrying into it two or three living caterpillars, deposits her eggs, and
nicely closing up the nest leaves them there; partly doubtless to assist
the incubation, and partly to supply food to her future young, (Derham. B.
4, c. 13. Aristotle Hist. Animal, L. 5. c. 20.)

A friend of mine put about fifty large caterpillars collected from cabbages
on some bran and a few leaves into a box, and covered it with gauze to
prevent their escape. After a few days we saw, from more than three fourths
of them, about eight or ten little caterpillars of the ichneumon-fly come
out of their backs, and spin each a small cocoon of silk, and in a few days
the large caterpillars died. This small fly it seems lays its egg in the
back of the cabbage caterpillar, which when hatched preys upon the
material, which is produced there for the purpose of making silk for the
future nest of the cabbage caterpillar; of which being deprived, the
creature wanders about till it dies, and thus our gardens are preserved by
the ingenuity of this cruel fly. This curious property of producing a silk
thread, which is common to some sea animals, see Botanic Garden, Part I.
Note XXVII. and is designed for the purpose of their transformation as in
the silk-worm, is used for conveying themselves from higher branches to
lower ones of trees by some caterpillars, and to make themselves temporary
nests or tents, and by the spider for entangling his prey. Nor is it
strange that so much knowledge should be acquired by such small animals;
since there is reason to imagine, that these insects have the sense of
touch, either in their proboscis, or their antennae, to a great degree of
perfection; and thence may possess, as far as their sphere extends, as
accurate knowledge, and as subtle invention, as the discoverers of human
arts.

XVI. 1. If we were better acquainted with the histories of those insects
that are formed into societies, as the bees, wasps, and ants, I make no
doubt but we should find, that their arts and improvements are not so
similar and uniform as they now appear to us, but that they arose in the
same manner from experience and tradition, as the arts of our own species;
though their reasoning is from fewer ideas, is busied about fewer objects,
and is exerted with less energy.

There are some kinds of insects that migrate like the birds before
mentioned. The locust of warmer climates has sometimes come over to
England; it is shaped like a grasshopper, with very large wings, and a body
above an inch in length. It is mentioned as coming into Egypt with an east
wind, "The lord brought an east wind upon the land all that day and night,
and in the morning the east wind brought the locusts, and covered the face
of the earth, so that the land was dark," Exod. x. 13. The migrations of
these insects are mentioned in another part of the scripture, "The locusts
have no king, yet go they forth all of them in bands," Prov. xxx. 27.

The accurate Mr. Adanson, near the river Gambia in Africa, was witness to
the migration of these insects. "About eight in the morning, in the month
of February, there suddenly arose over our heads a thick cloud, which
darkened the air, and deprived us of the rays of the sun. We found it was a
cloud of locusts raised about twenty or thirty fathoms from the ground, and
covering an extent of several leagues; at length a shower of these insects
descended, and after devouring every green herb, while they rested, again
resumed their flight. This cloud was brought by a strong east-wind, and was
all the morning in passing over the adjacent country." (Voyage to Senegal,
158.)

In this country the gnats are sometimes seen to migrate in clouds, like the
musketoes of warmer climates, and our swarms of bees frequently travel many
miles, and are said in North America always to fly towards the south. The
prophet Isaiah has a beautiful allusion to these migrations, "The Lord
shall call the fly from the rivers of Egypt, and shall hiss for the bee
that is in the land of Assyria," Isa. vii. 18. which has been lately
explained by Mr. Bruce, in his travels to discover the source of the Nile.

2. I am well informed that the bees that were carried into Barbadoes, and
other western islands, ceased to lay up any honey after the first year, as
they found it not useful to them: and are now become very troublesome to
the inhabitants of those islands by infesting their sugar houses; but those
in Jamaica continue to make honey, as the cold north winds, or rainy
seasons of that island, confine them at home for several weeks together.
And the bees of Senegal, which differ from those of Europe only in size,
make their honey not only superior to ours in delicacy of flavour, but it
has this singularity, that it never concretes, but remains liquid as syrup,
(Adanson). From some observations of Mr. Wildman, and of other people of
veracity, it appears, that during the severe part of the winter season for
weeks together the bees are quite benumbed and torpid from the cold, and do
not consume any of their provision. This state of sleep, like that of
swallows and bats, seems to be the natural resource of those creatures in
cold climates, and the making of honey to be an artificial improvement.

As the death of our hives of bees appears to be owning to their being kept
so warm, as to require food when their stock is exhausted; a very observing
gentleman at my request put two hives for many weeks into a dry cellar, and
observed, during all that time, they did not consume any of their
provision, for their weight did not decrease as it had done when they were
kept in the open air. The same observation is made in the Annual Register
for 1768, p. 113. And the Rev. Mr. White, in his Method of preserving Bees,
adds, that those on the north side of his house consumed less honey in the
winter than those on the south side.

There is another observation on bees well ascertained, that they at various
times, when the season begins to be cold, by a general motion of their legs
as they hang in clusters produce a degree of warmth, which is easily
perceptible by the hand. Hence by this ingenious exertion, they for a long
time prevent the torpid state they would naturally fall into.

According to the late observations of Mr. Hunter, it appears that the
bee's-wax is not made from the dust of the anthers of flowers, which they
bring home on their thighs, but that this makes what is termed bee-bread,
and is used for the purpose of feeding the bee-maggots; in the same manner
butterflies live on honey, but the previous caterpillar lives on vegetable
leaves, while the maggots of large flies require flesh for their food, and
those of the ichneumon fly require insects for their food. What induces the
bee who lives on honey to lay up vegetable powder for its young? What
induces the butterfly to lay its eggs on leaves, when itself feeds on
honey? What induces the other flies to seek a food for their progeny
different from what they consume themselves? If these are not deductions
from their own previous experience or observation, all the actions of
mankind must be resolved into instinct.

3. The dormouse consumes but little of its food during the rigour of the
season, for they roll themselves up, or sleep, or lie torpid the greatest
part of the time; but on warm sunny days experience a short revival, and
take a little food, and then relapse into their former state." (Pennant
Zoolog. p. 67.) Other animals, that sleep in winter without laying up any
provender, are observed to go into their winter beds fat and strong, but
return to day-light in the spring season very lean and feeble. The common
flies sleep during the winter without any provision for their nourishment,
and are daily revived by the warmth of the sun, or of our fires. These
whenever they see light endeavour to approach it, having observed, that by
its greater vicinity they get free from the degree of torpor, that the cold
produces; and are hence induced perpetually to burn themselves in our
candles: deceived, like mankind, by the misapplication of their knowledge.
Whilst many of the subterraneous insects, as the common worms, seem to
retreat so deep into the earth as not to be enlivened or awakened by the
difference of our winter days; and stop up their holes with leaves or
straws, to prevent the frosts from injuring them, or the centipes from
devouring them. The habits of peace, or the stratagems of war, of these
subterranean nations are covered from our view; but a friend of mine
prevailed on a distressed worm to enter the hole of another worm on a
bowling-green, and he presently returned much wounded about his head. And I
once saw a worm rise hastily out of the earth into the sunshine, and
observed a centipes hanging at its tail: the centipes nimbly quitted the
tail, and seizing the worm about its middle cut it in half with its
forceps, and preyed upon one part, while the other escaped. Which evinces
they have design in stopping the mouths of their habitations.

4. The wasp of this country fixes his habitation under ground, that he may
not be affected with the various changes of our climate; but in Jamaica he
hangs it on the bough of a tree, where the seasons are less severe. He
weaves a very curious paper of vegetable fibres to cover his nest, which is
constructed on the same principle with that of the bee, but with a
different material; but as his prey consists of flesh, fruits, and insects,
which are perishable commodities, he can lay up no provender for the
winter.

M. de la Loubiere, in his relation of Siam, says, "That in a part of that
kingdom, which lies open to great inundations, all the ants make their
settlements upon trees; no ants' nests are to be seen any where else."
Whereas in our country the ground is their only situation. From the
scriptual account of these insects, one might be led to suspect, that in
some climates they lay up a provision for the winter. Origen affirms the
same, (Cont. Cels. L. 4.) But it is generally believed that in this country
they do not, (Prov. vi. 6. xxx. 25.) The white ants of the coast of Africa
make themselves pyramids eight or ten feet high, on a base of about the
same width, with a smooth surface of rich clay, excessively hard and well
built, which appear at a distance like an assemblage of the huts of the
negroes, (Adanson). The history of these has been lately well described in
the Philosoph. Transactions, under the name of termes, or termites. These
differ very much from the nest of our large ant; but the real history of
this creature, as well as of the wasp, is yet very imperfectly known.

Wasps are said to catch large spiders, and to cut off their legs, and carry
their mutilated bodies to their young, Dict. Raison. Tom. I. p. 152.

One circumstance I shall relate which fell under my own eye, and shewed the
power or reason in a wasp, as it is exercised among men. A wasp, on a
gravel walk, had caught a fly nearly as large as himself; kneeling on the
ground I observed him separate the tail and the head from the body part, to
which the wings were attached. He then took the body part in his paws, and
rose about two feet from the ground with it; but a gentle breeze wafting
the wings of the fly turned him round in the air, and he settled again with
his prey upon the gravel. I then distinctly observed him cut off with his
mouth, first one of the wings, and then the other, after which he flew away
with it unmolested by the wind.

Go, thou sluggard, learn arts and industry from the bee, and from the ant!

Go, proud reasoner, and call the worm thy sister!

XVII. _Conclusion._

It was before observed how much the superior accuracy of our sense of touch
contributes to increase our knowledge; but it is the greater energy and
activity of the power of volition (as explained in the former Sections of
this work) that marks mankind, and has given him the empire of the world.

There is a criterion by which we may distinguish our voluntary acts or
thoughts from those that are excited by our sensations: "The former are
always employed about the _means_ to acquire pleasureable objects, or to
avoid painful ones: while the latter are employed about the _possession_ of
those that are already in our power."

If we turn our eyes upon the fabric of our fellow animals, we find they are
supported with bones, covered with skins, moved by muscles; that they
possess the same senses, acknowledge the same appetites, and are nourished
by the same aliment with ourselves; and we should hence conclude from the
strongest analogy, that their internal faculties were also in some measure
similar to our own.

Mr. Locke indeed published an opinion, that other animals possessed no
abstract or general ideas, and thought this circumstance was the barrier
between the brute and the human world. But these abstracted ideas have been
since demonstrated by Bishop Berkley, and allowed by Mr. Hume, to have no
existence in nature, not even in the mind of their inventor, and we are
hence necessitated to look for some other mark of distinction.

The ideas and actions of brutes, like those of children, are almost
perpetually produced by their present pleasures, or their present pains;
and, except in the few instances that have been mentioned in this Section,
they seldom busy themselves about the _means_ of procuring future bliss, or
of avoiding future misery.

Whilst the acquiring of languages, the making of tools, and the labouring
for money; which are all only the _means_ of procuring pleasure; and the
praying to the Deity, as another _means_ to procure happiness, are
characteristic of human nature.

       *       *       *       *       *

SECT. XVII.

THE CATENATION OF MOTIONS.

    I. 1. _Catenations of animal motion._ 2. _Are produced by irritations,
    by sensations, by volitions._ 3. _They continue some time after they
    have been excited. Cause of catenation._ 4. _We can then exert our
    attention on other objects._ 5. _Many catenations of motions go on
    together._ 6. _Some links of the catenations of motions may be left out
    without disuniting the chain._ 7. _Interrupted circles of motion
    continue confusedly till they come to the part of the circle, where
    they were disturbed._ 8. _Weaker catenations are dissevered by
    stronger._ 9. _Then new catenations take place._ 10. _Much effort
    prevents their reuniting. Impediment of speech._ 11. _Trains more
    easily dissevered than circles._ 12. _Sleep destroys volition and
    external stimulus._ II. _Instances of various catenations in a young
    lady playing on the harpsichord._ III. 1. _What catenations are the
    strongest._ 2. _Irritations joined with associations from strongest
    connexions. Vital motions._ 3. _New links with increased force, cold
    fits of fever produced._ 4. _New links with decreased force. Cold
    bath._ 5. _Irritation joined with sensation. Inflammatory fever. Why
    children cannot tickle themselves. 6. Volition joined with sensation.
    Irritative ideas of sound become sensible._ 7. _Ideas of imagination,
    dissevered by irritations, by volition, production of surprise._

I. 1. To investigate with precision the catenations of animal motions, it
would be well to attend to the manner of their production; but we cannot
begin this disquisition early enough for this purpose, as the catenations
of motion seem to begin with life, and are only extinguishable with it; We
have spoken of the power of irritation, of sensation, of volition, and of
association, as preceding the fibrous motions; we now step forwards, and
consider, that conversely they are in their turn preceded by those motions;
and that all the successive trains or circles of our actions are composed
of this twofold concatenation. Those we shall call trains of action, which
continue to proceed without any stated repetitions; and those circles of
action, when the parts of them return at certain periods, though the
trains, of which they consist, are not exactly similar. The reading an epic
poem is a train of actions; the reading a song with a chorus at equal
distances in the measure constitutes so many circles of action.

2. Some catenations of animal motion are produced by reiterated successive
irritations, as when we learn to repeat the alphabet in its order by
frequently reading the letters of it. Thus the vermicular motions of the
bowels were originally produced by the successive irritations of the
passing aliment; and the succession of actions of the auricles and
ventricles of the heart was originally formed by successive stimulus of the
blood, these afterwards become part of the diurnal circles of animal
actions, as appears by the periodical returns of hunger, and the quickened
pulse of weak people in the evening.

Other catenations of animal motion are gradually acquired by successive
agreeable sensations, as in learning a favourite song or dance; others by
disagreeable sensations, as in coughing or nictitation; these become
associated by frequent repetition, and afterwards compose parts of greater
circles of action like those above mentioned.

Other catenations of motions are gradually acquired by frequent voluntary
repetitions; as when we deliberately learn to march, read, fence, or any
mechanic art, the motions of many of our muscles become gradually linked
together in trains, tribes, or circles of action. Thus when any one at
first begins to use the tools in turning wood or metals in a lathe, he
wills the motions of his hand or fingers, till at length these actions
become so connected with the effect, that he seems only to will the point
of the chisel. These are caused by volition, connected by association like
those above described, and afterwards become parts of our diurnal trains or
circles of action.

3. All these catenations of animal motions, are liable to proceed some time
after they are excited, unless they are disturbed or impeded by other
irritations, sensations, or volitions; and in many instances in spite of
our endeavours to stop them; and this property of animal motions is
probably the cause of their catenation. Thus when a child revolves some
minute on one foot, the spectra of the ambient objects appear to circulate
round him some time after he falls upon the ground. Thus the palpitation of
the heart continues some time after the object of fear, which occasioned
it, is removed. The blush of shame, which is an excess of sensation, and
the glow of anger, which is an excess of volition, continue some time,
though the affected person finds, that those emotions were caused by
mistaken facts, and endeavours to extinguish their appearance. See Sect.
XII. 1. 5.

4. When a circle of motions becomes connected, by frequent repetitions as
above, we can exert our attention strongly on other objects, and the
concatenated circle of motions will nevertheless proceed in due order; as
whilst you are thinking on this subject, you use variety of muscles in
walking about your parlour, or in sitting at your writing-table.

5. Innumerable catenations of motions may proceed at the same time, without
incommoding each other. Of these are the motions of the heart and arteries;
those of digestion and glandular secretion; of the ideas, or sensual
motions; those of progression, and of speaking; the great annual circle of
actions so apparent in birds in their times of breeding and moulting; the
monthly circles of many female animals; and the diurnal circles of sleeping
and waking, of fulness and inanition.

6. Some links of successive trains or of synchronous tribes of action may
be left out without disjoining the whole. Such are our usual trains of
recollection; after having travelled through an entertaining country, and
viewed many delightful lawns, rolling rivers, and echoing rocks; in the
recollection of our journey we leave out the many districts, that we
crossed, which were marked with no peculiar pleasure. Such also are our
complex ideas, they are catenated tribes of ideas, which do not perfectly
resemble their correspondent perceptions, because some of the parts are
omitted.

7. If an interrupted circle of actions is not entirely dissevered, it will
continue to proceed confusedly, till it comes to the part of the circle,
where it was interrupted.

The vital motions in a fever from drunkenness, and in other periodical
diseases, are instances of this circumstance. The accidental inebriate does
not recover himself perfectly till about the same hour on the succeeding
day. The accustomed drunkard is disordered, if he has not his usual
potation of fermented liquor. So if a considerable part of a connected
tribe of action be disturbed, that whole tribe goes on with confusion, till
the part of the tribe affected regains its accustomed catenations. So
vertigo produces vomiting, and a great secretion of bile, as in
sea-sickness, all these being parts of the tribe of irritative catenations.

8. Weaker catenated trains may be dissevered by the sudden exertion of the
stronger. When a child first attempts to walk across a room, call to him,
and he instantly falls upon the ground. So while I am thinking over the
virtues of my friends, if the tea-kettle spurt out some hot water on my
stocking; the sudden pain breaks the weaker chain of ideas, and introduces
a new group of figures of its own. This circumstance is extended to some
unnatural trains of action, which have not been confirmed by long habit; as
the hiccough, or an ague-fit, which are frequently curable by surprise. A
young lady about eleven years old had for five days had a contraction of
one muscle in her fore arm, and another in her arm, which occurred four or
five times every minute; the muscles were seen to leap, but without bending
the arm. To counteract this new morbid habit, an issue was placed over the
convulsed muscle of her arm, and an adhesive plaster wrapped tight like a
bandage over the whole fore arm, by which the new motions were immediately
destroyed, but the means were continued some weeks to prevent a return.

9. If any circle of actions is dissevered, either by omission of some of
the links, as in sleep, or by insertion of other links, as in surprise, new
catenations take place in a greater or less degree. The last link of the
broken chain of actions becomes connected with the new motion which has
broken it, or with that which was nearest the link omitted; and these new
catenations proceed instead of the old ones. Hence the periodic returns of
ague-fits, and the chimeras of our dreams.

10. If a train of actions is dissevered, much effort of volition or
sensation will prevent its being restored. Thus in the common impediment of
speech, when the association of the motions of the muscles of enunciation
with the idea of the word to be spoken is disordered, the great voluntary
efforts, which distort the countenance, prevent the rejoining of the broken
associations. See No. II. 10. of this Section. It is thus likewise
observable in some inflammations of the bowels, the too strong efforts made
by the muscles to carry forwards the offending material fixes it more
firmly in its place, and prevents the cure. So in endeavouring to recal to
our memory some particular word of a sentence, if we exert ourselves too
strongly about it, we are less likely to regain it.

11. Catenated trains or tribes of action are easier dissevered than
catenated circles of action. Hence in epileptic fits the synchronous
connected tribes of action, which keep the body erect, are dissevered, but
the circle of vital motions continues undisturbed.

12. Sleep destroys the power of volition, and precludes the stimuli of
external objects, and thence dissevers the trains, of which these are a
part; which confirms the other catenations, as those of the vital motions,
secretions, and absorptions; and produces the new trains of ideas, which
constitute our dreams.

II. 1. All the preceding circumstances of the catenations of animal motions
will be more clearly understood by the following example of a person
learning music; and when we recollect the variety of mechanic arts, which
are performed by associated trains of muscular actions catenated with the
effects they produce, as in knitting, netting, weaving; and the greater
variety of associated trains of ideas caused or catenated by volitions or
sensations, as in our hourly modes of reasoning, or imagining, or
recollecting, we shall gain some idea of the innumerable catenated trains
and circles of action, which form the tenor of our lives, and which began,
and will only cease entirely with them.

2. When a young lady begins to learn music, she voluntarily applies herself
to the characters of her music-book, and by many repetitions endeavours to
catenate them with the proportions of sound, of which they are symbols. The
ideas excited by the musical characters are slowly connected with the keys
of the harpsichord, and much effort is necessary to produce every note with
the proper finger, and in its due place and time; till at length a train of
voluntary exertions becomes catenated with certain irritations. As the
various notes by frequent repetitions become connected in the order, in
which they are produced, a new catenation of sensitive exertions becomes
mixed with the voluntary ones above described; and not only the musical
symbols of crotchets and quavers, but the auditory notes and tones at the
same time, become so many successive or synchronous links in this circle of
catenated actions.

At length the motions of her fingers become catenated with the musical
characters; and these no sooner strike the eye, than the finger presses
down the key without any voluntary attention between them; the activity of
the hand being connected with the irritation of the figure or place of the
musical symbol on the retina; till at length by frequent repetitions of the
same tune the movements of her fingers in playing, and the muscles of the
larynx in singing, become associated with each other, and form part of
those intricate trains and circles of catenated motions, according with the
second article of the preceding propositions in No. 1. of this Section.

3. Besides the facility, which by habit attends the execution of this
musical performance, a curious circumstance occurs, which is, that when our
young musician has began a tune, she finds herself inclined to continue it;
and that even when she is carelessly singing alone without attending to her
own song; according with the third preceding article.

4. At the same time that our young performer continues to play with great
exactness this accustomed tune, she can bend her mind, and that intensely,
on some other object, according with the fourth article of the preceding
proportions.

The manuscript copy of this work was lent to many of my friends at
different times for the purpose of gaining their opinions and criticisms on
many parts of it, and I found the following anecdote written with a pencil
opposite to this page, but am not certain by whom. "I remember seeing the
pretty young actress, who succeeded Mrs. Arne in the performance of the
celebrated Padlock, rehearse the musical parts at her harpsichord under the
eye of her master with great taste and accuracy; though I observed her
countenance full of emotion, which I could not account for; at last she
suddenly burst into tears; for she had all this time been eyeing a beloved
canary bird, suffering great agonies, which at that instant fell dead from
its perch."

5. At the same time many other catenated circles of action are going on in
the person of our fair musician, as well as the motions of her fingers,
such as the vital motions, respiration, the movements of her eyes and
eyelids, and of the intricate muscles of vocality, according with the fifth
preceding article.

6. If by any strong impression on the mind of our fair musician she should
be interrupted for a very inconsiderable time, she can still continue her
performance, according to the sixth article.

7. If however this interruption be greater, though the chain of actions be
not dissevered, it proceeds confusedly, and our young performer continues
indeed to play, but in a hurry without accuracy and elegance, till she
begins the tune again, according to the seventh of the preceding articles.

8. But if this interruption be still greater, the circle of actions becomes
entirely dissevered, and she finds herself immediately under the necessity
to begin over again to recover the lost catenation, according to the eighth
preceding article.

9. Or in trying to recover it she will sing some dissonant notes, or strike
some improper keys, according to the ninth preceding article.

10. A very remarkable thing attends this breach of catenation, if the
performer has forgotten some word of her song, the more energy of mind she
uses about it, the more distant is she from regaining it; and artfully
employs her mind in part on some other object, or endeavours to dull its
perceptions, continuing to repeat, as it were inconsciously, the former
part of the song, that she remembers, in hopes to regain the lost
connexion.

For if the activity of the mind itself be more energetic, or takes its
attention more, than the connecting word, which is wanted; it will not
perceive the slighter link of this lost word; as who listens to a feeble
sound, must be very silent and motionless; so that in this case the very
vigour of the mind itself seems to prevent it from regaining the lost
catenation, as well as the too great exertion in endeavouring to regain it,
according to the tenth preceding article.

We frequently experience, when we are doubtful about the spelling of a
word, that the greater voluntary exertion we use, that is the more
intensely we think about it, the further are we from regaining the lost
association between the letters of it, but which readily recurs when we
have become careless about it. In the same manner, after having for an hour
laboured to recollect the name of some absent person, it shall seem,
particularly after sleep, to come into the mind as it were spontaneously;
that is the word we are in search of, was joined to the preceding one by
association; this association being dissevered, we endeavour to recover it
by volition; this very action of the mind strikes our attention more, than
the faint link of association, and we find it impossible by this means to
retrieve the lost word. After sleep, when volition is entirely suspended,
the mind becomes capable of perceiving the fainter link of association, and
the word is regained.

On this circumstance depends the impediment of speech before mentioned; the
first syllable of a word is causable by volition, but the remainder of it
is in common conversation introduced by its associations with this first
syllable acquired by long habit. Hence when the mind of the stammerer is
vehemently employed on some idea of ambition of shining, or fear of not
succeeding, the associations of the motions of the muscles of articulation
with each other become dissevered by this greater exertion, and he
endeavours in vain by voluntary efforts to rejoin the broken association.
For this purpose he continues to repeat the first syllable, which is
causable by volition, and strives in vain, by various distortions of
countenance, to produce the next links, which are subject to association.
See Class IV. 3. 1. 1.

11. After our accomplished musician has acquired great variety of tunes and
songs, so that some of them begin to cease to be easily recollected, she
finds progressive trains of musical notes more frequently forgotten, than
those which are composed of reiterated circles, according with the eleventh
preceding article.

12. To finish our example with the preceding articles we must at length
suppose, that our fair performer falls asleep over her harpsichord; and
thus by the suspension of volition, and the exclusion of external stimuli,
she dissevers the trains and circles of her musical exertions.

III. 1. Many of these circumstances of catenations of motions receive an
easy explanation from the four following consequences to the seventh law of
animal causation in Sect. IV. These are, first, that those successions or
combinations of animal motions, whether they were united by causation,
association, or catenation, which have been most frequently repeated,
acquire the strongest connection. Secondly, that of these, those, which
have been less frequently mixed with other trains or tribes of motion, have
the strongest connection. Thirdly, that of these, those, which were first
formed, have the strongest connection. Fourthly, that if an animal motion
be excited by more than one causation, association, or catenation, at the
same time, it will be performed with greater energy.

2. Hence also we understand, why the catenations of irritative motions are
more strongly connected than those of the other classes, where the quantity
of unmixed repetition has been equal; because they were first formed. Such
are those of the secerning and absorbent systems of vessels, where the
action of the gland produces a fluid, which stimulates the mouths of its
correspondent absorbents. The associated motions seem to be the next most
strongly united, from their frequent repetition; and where both these
circumstances unite, as in the vital motions, their catenations are
indissoluble but by the destruction of the animal.

3. Where a new link has been introduced into a circle of actions by some
accidental defect of stimulus; if that defect of stimulus be repeated at
the same part of the circle a second or a third time, the defective motions
thus produced, both by the repeated defect of stimulus and by their
catenation with the parts of the circle of actions, will be performed with
less and less energy. Thus if any person is exposed to cold at a certain
hour to-day, so long as to render some part of the system for a time
torpid; and is again exposed to it at the same hour to-morrow, and the next
day; he will be more and more affected by it, till at length a cold fit of
fever is completely formed, as happens at the beginning of many of those
fevers, which are called nervous or low fevers. Where the patient has
slight periodical shiverings and paleness for many days before the febrile
paroxysm is completely formed.

4. On the contrary, if the exposure to cold be for so short a time, as not
to induce any considerable degree of torpor or quiescence, and is repeated
daily as above mentioned, it loses its effect more and more at every
repetition, till the constitution can bear it without inconvenience, or
indeed without being conscious of it. As in walking into the cold air in
frosty weather. The same rule is applicable to increased stimulus, as of
heat, or of vinous spirit, within certain limits, as is applied in the two
last paragraphs to Deficient Stimulus; as is further explained in Sect.
XXXVI. on the Periods of Diseases.

5. Where irritation coincides with sensation to produce the same
catenations of motion, as in inflammatory fevers, they are excited with
still greater energy than by the irritation alone. So when children expect
to be tickled in play, by a feather lightly passed over the lips, or by
gently vellicating the soles of their feet, laughter is most vehemently
excited; though they can stimulate these parts with their own fingers
unmoved. Here the pleasureable idea of playfulness coincides with the
vellication; and there is no voluntary exertion used to diminish the
sensation, as there would be, if a child should endeavour to tickle
himself. See Sect. XXXIV. 1. 4.

6. And lastly, the motions excited by the junction of voluntary exertion
with irritation are performed with more energy, than those by irritation
singly; as when we listen to small noises, as to the ticking of a watch in
the night, we perceive the most weak sounds, that are at other times
unheeded. So when we attend to the irritative ideas of sound in our ears,
which are generally not attended to, we can hear them; and can see the
spectra of objects, which remain in the eye, whenever we please to exert
our voluntary power in aid of those weak actions of the retina, or of the
auditory nerve.

7. The temporary catenations of ideas, which are caused by the sensations
of pleasure or pain, are easily dissevered either by irritations, as when a
sudden noise disturbs a day-dream; or by the power of volition, as when we
awake from sleep. Hence in our waking hours, whenever an idea occurs, which
is incongruous to our former experience, we instantly dissever the train of
imagination by the power of volition, and compare the incongruous idea with
our previous knowledge of nature, and reject it. This operation of the mind
has not yet acquired a specific name, though it is exerted every minute of
our waking hours; unless it may be termed INTUITIVE ANALOGY. It is an act
of reasoning of which we are unconscious except from its effects in
preserving the congruity of our ideas, and bears the same relation to the
sensorial power of volition, that irritative ideas, of which we are
inconscious except by their effects, do to the sensorial power of
irritation; as the former is produced by volition without our attention to
it, and the latter by irritation without our attention to them.

If on the other hand a train of imagination or of voluntary ideas are
excited with great energy, and passing on with great vivacity, and become
dissevered by some violent stimulus, as the discharge of a pistol near
one's ear, another circumstance takes place, which is termed SURPRISE;
which by exciting violent irritation, and violent sensation, employs for a
time the whole sensorial energy, and thus dissevers the passing trains of
ideas, before the power of volition has time to compare them with the usual
phenomena of nature. In this case fear is generally the companion of
surprise, and adds to our embarrassment, as every one experiences in some
degree when he hears a noise in the dark, which he cannot instantly account
for. This catenation of fear with surprise is owing to our perpetual
experience of injuries from external bodies in motion, unless we are upon
our guard against them. See Sect. XVIII. 17. XIX. 2.

Many other examples of the catenations of animal motions are explained in
Sect. XXXVI. on the Periods of Diseases.

       *       *       *       *       *

SECT. XVIII.

OF SLEEP.

    1. _Volition is suspended in sleep._ 2. _Sensation continues. Dreams
    prevent delirium and inflammation._ 3. _Nightmare._ 4. _Ceaseless flow
    of ideas in dreams._ 5. _We seem to receive them by the senses. Optic
    nerve perfectly sensible in sleep. Eyes less dazzled after dreaming of
    visible objects._ 6. _Reverie, belief._ 7. _How we distinguish ideas
    from perceptions._ 8. _Variety of scenery in dreams, excellence of the
    sense of vision._ 9. _Novelty of combination in dreams._ 10.
    _Distinctness of imagery in dreams._ 11. _Rapidity of transaction in
    dreams._ 12. _Of measuring time. Of dramatic time and place. Why a dull
    play induces sleep, and an interesting one reverie._ 13. _Consciousness
    of our existence and identity in dreams._ 14. _How we awake sometimes
    suddenly, sometimes frequently._ 15. _Irritative motions continue in
    sleep, internal irritations are succeeded by sensation. Sensibility
    increases during sleep, and irritability. Morning dreams. Why
    epilepsies occur in sleep. Ecstacy of children. Case of convulsions in
    sleep. Cramp, why painful. Asthma. Morning sweats. Increase of heat.
    Increase of urine in sleep. Why more liable to take cold in sleep.
    Catarrh from thin night-caps. Why we feel chilly at the approach of
    sleep, and at waking in the open air._ 16. _Why the gout commences in
    sleep. Secretions are more copious in sleep, young animals and plants
    grow more in sleep._ 17. _Inconsistency of dreams. Absence of surprise
    in dreams._ 18. _Why we forget some dreams and not others._ 19.
    _Sleep-talkers awake with surprise._ 20. _Remote causes of sleep.
    Atmosphere with less oxygene. Compression of the brain in spina bifida.
    By whirling on an horizontal wheel. By cold._ 21. _Definition of
    sleep._

1. There are four situations of our system, which in their moderate degrees
are not usually termed diseases, and yet abound with many very curious and
instructive phenomena; these are sleep, reverie, vertigo, drunkenness.
These we shall previously consider, before we step forwards to develop the
causes and cures of diseases with the modes of the operation of medicines.

As all those trains and tribes of animal motion, which are subjected to
volition, were the last that were caused, their connection is weaker than
that of the other classes; and there is a peculiar circumstance attending
this causation, which is, that it is entirely suspended during sleep;
whilst the other classes of motion, which are more immediately necessary to
life, as those caused by internal stimuli, for instance the pulsations of
the heart and arteries, or those catenated with pleasurable sensation, as
the powers of digestion, continue to strengthen their habits without
interruption. Thus though man in his sleeping state is a much less perfect
animal, than in his waking hours; and though he consumes more than one
third of his life in this his irrational situation; yet is the wisdom of
the Author of nature manifest even in this seeming imperfection of his
work!

The truth of this assertion with respect to the large muscles of the body,
which are concerned in locomotion, is evident; as no one in perfect sanity
walks about in his sleep, or performs any domestic offices: and in respect
to the mind, we never exercise our reason or recollection in dreams; we may
sometimes seem distracted between contending passions, but we never compare
their objects, or deliberate about the acquisition of those objects, if our
sleep is perfect. And though many synchronous tribes or successive trains
of ideas may represent the houses or walks, which have real existence, yet
are they here introduced by their connection with our sensations, and are
in truth ideas of imagination, not of recollection.

2. For our sensations of pleasure and pain are experienced with great
vivacity in our dreams; and hence all that motley group of ideas, which are
caused by them, called the ideas of imagination, with their various
associated trains, are in a very vivid manner acted over in the sensorium;
and these sometimes call into action the larger muscles, which have been
much associated with them; as appears from the muttering sentences, which
some people utter in their dreams, and from the obscure barking of sleeping
dogs, and the motions of their feet and nostrils.

This perpetual flow of the trains of ideas, which constitute our dreams,
and which are caused by painful or pleasurable sensation, might at first
view be conceived to be an useless expenditure of sensorial power. But it
has been shewn, that those motions, which are perpetually excited, as those
of the arterial system by the stimulus of the blood, are attended by a
great accumulation of sensorial power, after they have been for a time
suspended; as the hot-fit of fever is the consequence of the cold one. Now
as these trains of ideas caused by sensation are perpetually excited during
our waking hours, if they were to be suspended in sleep like the voluntary
motions, (which are exerted only by intervals during our waking hours,) an
accumulation of sensorial power would follow; and on our awaking a delirium
would supervene, since these ideas caused by sensation would be produced
with such energy, that we should mistake the trains of imagination for
ideas excited by irritation; as perpetually happens to people debilitated
by fevers on their first awaking; for in these fevers with debility the
general quantity of irritation being diminished, that of sensation is
increased. In like manner if the actions of the stomach, intestines, and
various glands, which are perhaps in part at least caused by or catenated
with agreeable sensation, and which perpetually exist during our waking
hours, were like the voluntary motions suspended in our sleep; the great
accumulation of sensorial power, which would necessarily follow, would be
liable to excite inflammation in them.

3. When by our continued posture in sleep, some uneasy sensations are
produced, we either gradually awake by the exertion of volition, or the
muscles connected by habit with such sensations alter the position of the
body; but where the sleep is uncommonly profound, and those uneasy
sensations great, the disease called the incubus, or nightmare, is
produced. Here the desire of moving the body is painfully exerted, by the
power of moving it, or volition, is incapable of action, till we awake.
Many less disagreeable struggles in our dreams, as when we wish in vain to
fly from terrifying objects, constitute a slighter degree of this disease.
In awaking from the nightmare I have more than once observed, that there
was no disorder in my pulse; nor do I believe the respiration is laborious,
as some have affirmed. It occurs to people whose sleep is too profound, and
some disagreeable sensation exists, which at other times would have
awakened them, and have thence prevented the disease of nightmare; as after
great fatigue or hunger with too large a supper and wine, which occasion
our sleep to be uncommonly profound. See No. 14, of this Section.

4. As the larger muscles of the body are much more frequently excited by
volition than by sensation, they are but seldom brought into action in our
sleep: but the ideas of the mind are by habit much more frequently
connected with sensation than with volition; and hence the ceaseless flow
of our ideas in dreams. Every one's experience will teach him this truth,
for we all daily exert much voluntary muscular motion: but few of mankind
can bear the fatigue of much voluntary thinking.

5. A very curious circumstance attending these our sleeping imaginations
is, that we seem to receive them by the senses. The muscles, which are
subservient to the external organs of sense, are connected with volition,
and cease to act in sleep; hence the eyelids are closed, and the tympanum
of the ear relaxed; and it is probable a similarity of voluntary exertion
may be necessary for the perceptions of the other nerves of sense; for it
is observed that the papillae of the tongue can be seen to become erected,
when we attempt to taste any thing extremely grateful. Hewson Exper.
Enquir. V. 2. 186. Albini Annot. Acad. L. i. c. 15. Add to this, that the
immediate organs of sense have no objects to excite them in the darkness
and silence of the night, but their nerves of sense nevertheless continue
to possess their perfect activity subservient to all their numerous
sensitive connections. This vivacity of our nerves of sense during the time
of sleep is evinced by a circumstance, which almost every one must at some
time or other have experienced; that is, if we sleep in the daylight, and
endeavour to see some object in our dream, the light is exceedingly painful
to our eyes; and after repeated struggles we lament in our sleep, that we
cannot see it. In this case I apprehend the eyelid is in some degree opened
by the vehemence of our sensations; and, the iris being dilated, the optic
nerve shews as great or greater sensibility than in our waking hours. See
No. 15. of this Section.

When we are forcibly waked at midnight from profound sleep, our eyes are
much dazzled with the light of the candle for a minute or two, after there
has been sufficient time allowed for the contraction of the iris; which is
owing to the accumulation of sensorial power in the organ of vision during
its state of less activity. But when we have dreamt much of visible
objects, this accumulation of sensorial power in the organ of vision is
lessened or prevented, and we awake in the morning without being dazzled
with the light, after the iris has had time to contract itself. This is a
matter of great curiosity, and may be thus tried by any one in the
day-light. Close your eyes, and cover them with your hat; think for a
minute on a tune, which you are accustomed to, and endeavour to sing it
with as little activity of mind as possible. Suddenly uncover and open your
eyes, and in one second of time the iris will contract itself, but you will
perceive the day more luminous for several seconds, owing to the
accumulation of sensorial power in the optic nerve.

Then again close and cover your eyes, and think intensely on a cube of
ivory two inches diameter, attending first to the north and south sides of
it, and then to the other four sides of it; then get a clear image in your
mind's eye of all the sides of the same cube coloured red; and then of it
coloured green; and then of it coloured blue; lastly, open your eyes as in
the former experiment, and after the first second of time allowed for the
contraction of the iris, you will not perceive any increase of the light of
the day, or dazzling; because now there is no accumulation of sensorial
power in the optic nerve; that having been expended by its action in
thinking over visible objects.

This experiment is not easy to be made at first, but by a few patient
trials the fact appears very certain; and shews clearly, that our ideas of
imagination are repetitions of the motions of the nerve, which were
originally occasioned by the stimulus of external bodies; because they
equally expend the sensorial power in the organ of sense. See Sect. III. 4.
which is analogous to our being as much fatigued by thinking as by labour.

6. Nor is it in our dreams alone, but even in our waking reveries, and in
great efforts of invention, so great is the vivacity of our ideas, that we
do not for a time distinguish them from the real presence of substantial
objects; though the external organs of sense are open, and surrounded with
their usual stimuli. Thus whilst I am thinking over the beautiful valley,
through which I yesterday travelled, I do not perceive the furniture of my
room: and there are some, whose waking imaginations are so apt to run into
perfect reverie, that in their common attention to a favourite idea they do
not hear the voice of the companion, who accosts them, unless it is
repeated with unusual energy.

This perpetual mistake in dreams and reveries, where our ideas of
imagination are attended with a belief of the presence of external objects,
evinces beyond a doubt, that all our ideas are repetitions of the motions
of the nerves of sense, by which they were acquired; and that this belief
is not, as some late philosophers contend, an instinct necessarily
connected only with our perceptions.

7. A curious question demands our attention in this place; as we do not
distinguish in our dreams and reveries between our perceptions of external
objects, and our ideas of them in their absence, how do we distinguish them
at any time? In a dream, if the sweetness of sugar occurs to my
imagination, the whiteness and hardness of it, which were ideas usually
connected with the sweetness, immediately follow in the train; and I
believe a material lump of sugar present before my senses: but in my waking
hours, if the sweetness occurs to my imagination, the stimulus of the table
to my hand, or of the window to my eye, prevents the other ideas of the
hardness and whiteness of the sugar from succeeding; and hence I perceive
the fallacy, and disbelieve the existence of objects correspondent to those
ideas, whose tribes or trains are broken by the stimulus of other objects.
And further in our waking hours, we frequently exert our volition in
comparing present appearances with such, as we have usually observed; and
thus correct the errors of one sense by our general knowledge of nature by
intuitive analogy. See Sect. XVII. 3. 7. Whereas in dreams the power of
volition is suspended, we can recollect and compare our present ideas with
none of our acquired knowledge, and are hence incapable of observing any
absurdities in them.

By this criterion we distinguish our waking from our sleeping hours, we can
voluntarily recollect our sleeping ideas, when we are awake, and compare
them with our waking ones; but we cannot in our sleep _voluntarily_
recollect our waking ideas at all.

8. The vast variety of scenery, novelty of combination, and distinctness of
imagery, are other curious circumstances of our sleeping imaginations. The
variety of scenery seems to arise from the superior activity and excellence
of our sense of vision; which in an instant unfolds to the mind extensive
fields of pleasurable ideas; while the other senses collect their objects
slowly, and with little combination; add to this, that the ideas, which
this organ presents us with, are more frequently connected with our
sensation than those of any other.

9. The great novelty of combination is owing to another circumstance; the
trains of ideas, which are carried on in our waking thoughts, are in our
dreams dissevered in a thousand places by the suspension of volition, and
the absence of irritative ideas, and are hence perpetually falling into new
catenations. As explained in Sect. XVII. 1. 9. For the power of volition is
perpetually exerted during our waking hours in comparing our passing trains
of ideas with our acquired knowledge of nature, and thus forms many
intermediate links in their catenation. And the irritative ideas excited by
the stimulus of the objects, with which we are surrounded, are every moment
intruded upon us, and form other links of our unceasing catenations of
ideas.

10. The absence of the stimuli of external bodies, and of volition, in our
dreams renders the organs of sense liable to be more strongly affected by
the powers of sensation, and of association. For our desires or aversions,
or the obtrusions of surrounding bodies, dissever the sensitive and
associate tribes of ideas in our waking hours by introducing those of
irritation and volition amongst them. Hence proceeds the superior
distinctness of pleasurable or painful imagery in our sleep; for we recal
the figure and the features of a long lost friend, whom we loved, in our
dreams with much more accuracy and vivacity than in our waking thoughts.
This circumstance contributes to prove, that our ideas of imagination are
reiterations of those motions of our organs of sense, which were excited by
external objects; because while we are exposed to the stimuli of present
objects, our ideas of absent objects cannot be so distinctly formed.

11. The rapidity of the succession of transactions in our dreams is almost
inconceivable; insomuch that, when we are accidentally awakened by the
jarring of a door, which is opened into our bed-chamber, we sometimes dream
a whole history of thieves or fire in the very instant of awaking.

During the suspension of volition we cannot compare our other ideas with
those of the parts of time in which they exist; that is, we cannot compare
the imaginary scene, which is before us, with those changes of it, which
precede or follow it: because this act of comparing requires recollection
or voluntary exertion. Whereas in our waking hours, we are perpetually
making this comparison, and by that means our waking ideas are kept
confident with each other by intuitive analogy; but this companion retards
the succession of them, by occasioning their repetition. Add to this, that
the transactions of our dreams consist chiefly of visible ideas, and that a
whole history of thieves and fire may be _beheld_ in an instant of time
like the figures in a picture.

12. From this incapacity of attending to the parts of time in our dreams,
arises our ignorance of the length of the night; which, but from our
constant experience to the contrary, we should conclude was but a few
minutes, when our sleep is perfect. The same happens in our reveries; thus
when we are possessed with vehement joy, grief, or anger, time appears
short, for we exert no volition to compare the present scenery with the
past or future; but when we are compelled to perform those exercises of
mind or body, which, are unmixed with passion, as in travelling over a
dreary country, time appears long; for our desire to finish our journey
occasions us more frequently to compare our present situation with the
parts of time or place, which are before and behind us.

So when we are enveloped in deep contemplation of any kind, or in reverie,
as in reading a very interesting play or romance, we measure time very
inaccurately; and hence, if a play greatly affects our passions, the
absurdities of passing over many days or years, and or perpetual changes of
place, are not perceived by the audience; as is experienced by every one,
who reads or sees some plays of the immortal Shakespear; but it is
necessary for inferior authors to observe those rules of the [Greek:
pithanon] and [Greek: prepon] inculcated by Aristotle, because their works
do not interest the passions sufficiently to produce complete reverie.

Those works, however, whether a romance or a sermon, which do not interest
us so much as to induce reverie, may nevertheless incline us to sleep. For
those pleasurable ideas, which are presented to us, and are too gentle to
excite laughter, (which is attended with interrupted voluntary exertions,
as explained Sect. XXXIV. 1. 4.) and which are not accompanied with any
other emotion, which usually excites some voluntary exertion, as anger, or
fear, are liable to produce sleep; which consists in a suspension of all
voluntary power. But if the ideas thus presented to us, and interest our
attention, are accompanied with so much pleasurable or painful sensation as
to excite our voluntary exertion at the same time, reverie is the
consequence. Hence an interesting play produces reverie, a tedious one
produces sleep: in the latter we become exhausted by attention, and are not
excited to any voluntary exertion, and therefore sleep; in the former we
are excited by some emotion, which prevents by its pain the suspension of
volition, and in as much as it interests us, induces reverie, as explained
in the next Section.

But when our sleep is imperfect, as when we have determined to rise in half
an hour, time appears longer to us than in most other situations. Here our
solicitude not to oversleep the determined time induces us in this
imperfect sleep to compare the quick changes of imagined scenery with the
parts of time or place, they would have taken up, had they real exigence;
and that more frequently than in our waking hours; and hence the time
appears longer to us: and I make no doubt, but the permitted time appears
long to a man going to the gallows, as the fear of its quick lapse will
make him think frequently about it.

13. As we gain our knowledge of time by comparing the present scenery with
the past and future, and of place by comparing the situations of objects
with each other; so we gain our idea of consciousness by comparing
ourselves with the scenery around us; and of identity by comparing our
present consciousness with our past consciousness: as we never think of
time or place, but when we make the companions above mentioned, so we never
think of consciousness, but when we compare our own existence with that of
other objects; nor of identity, but when we compare our present and our
past consciousness. Hence the consciousness of our own existence, and of
our identity, is owing to a voluntary exertion of our minds: and on that
account in our complete dreams we neither measure time, are surprised at
the sudden changes of place, nor attend to our own existence, or identity;
because our power of volition is suspended. But all these circumstances are
more or less observable in our incomplete ones; for then we attend a little
to the lapse of time, and the changes of place, and to our own existence;
and even to our identity of person; for a lady seldom dreams, that she is a
soldier; nor a man, that he is brought to bed.

14. As long as our sensations only excite their sensual motions, or ideas,
our sleep continues sound; but as soon as they excite desires or aversions,
our sleep becomes imperfect; and when that desire or aversion is so strong,
as to produce voluntary motions, we begin to awake; the larger muscles of
the body are brought into action to remove that irritation or sensation,
which a continued posture has caused; we stretch our limbs, and yawn, and
our sleep is thus broken by the accumulation of voluntary power.

Sometimes it happens, that the act of waking is suddenly produced, and this
soon after the commencement of sleep; which is occasioned by some sensation
so disagreeable, as instantaneously to excite the power of volition; and a
temporary action of all the voluntary motions suddenly succeeds, and we
start awake. This is sometimes accompanied with loud noise in the ears, and
with some degree of fear; and when it is in great excess, so as to produce
continued convulsive motions of those muscles, which are generally
subservient to volition, it becomes epilepsy: the fits of which in some
patients generally commence during sleep. This differs from the night-mare
described in No. 3. of this Section, because in that the disagreeable
sensation is not so great as to excite the power of volition into action;
for as soon as that happens, the disease ceases.

Another circumstance, which sometimes awakes people soon after the
commencement of their sleep, is where the voluntary power is already so
great in quantity as almost to prevent them from falling asleep, and then a
little accumulation of it soon again awakens them; this happens in cases of
insanity, or where the mind has been lately much agitated by fear or anger.
There is another circumstance in which sleep is likewise of short duration,
which arises from great debility, as after great over-fatigue, and in some
fevers, where the strength of the patient is greatly diminished, as in
these cases the pulse intermits or flutters, and the respiration is
previously affected, it seems to originate from the want of some voluntary
efforts to facilitate respiration, as when we are awake. And is further
treated of in Vol. II. Class I. 2. 1. 2. on the Diseases of the Voluntary
Power. Art. Somnus interruptus.

15. We come now to those motions which depend on irritation. The motions of
the arterial and glandular systems continue in our sleep, proceeding slower
indeed, but stronger and more uniformly, than in our waking hours, when
they are incommoded by external stimuli, or by the movements of volition;
the motions of the muscles subservient to respiration continue to be
stimulated into action, and the other internal senses of hunger, thirst,
and lust, are not only occasionally excited in our sleep, but their
irritative motions are succeeded by their usual sensations, and make a part
of the farrago of our dreams. These sensations of the want of air, of
hunger, thirst, and lust, in our dreams, contribute to prove, that the
nerves of the external senses are also alive and excitable in our sleep;
but as the stimuli of external objects are either excluded from them by the
darkness and silence of the night, or their access to them is prevented by
the suspension of volition, these nerves of sense fall more readily into
their connexions with sensation and with association; because much
sensorial power, which during the day was expended in moving the external
organs of sense in consequence of irritation from external stimuli, or in
consequence of volition, becomes now in some degree accumulated, and
renders the internal or immediate organs of sense more easily excitable by
the other sensorial powers. Thus in respect to the eye, the irritation from
external stimuli, and the power of volition during our waking hours,
elevate the eye-lids, adapt the aperture of the iris to the quantity of
light, the focus of the crystalline humour, and the angle of the optic
axises to the distance of the object, all which perpetual activity during
the day expends much sensorial power, which is saved during our sleep.

Hence it appears, that not only those parts of the system, which are always
excited by internal stimuli, as the stomach, intestinal canal, bile-ducts,
and the various glands, but the organs of sense also may be more violently
excited into action by the irritation from internal stimuli, or by
sensation, during our sleep than in our waking hours; because during the
suspension of volition, there is a greater quantity of the spirit of
animation to be expended by the other sensorial powers. On this account our
irritability to internal stimuli, and our sensibility to pain or pleasure,
is not only greater in sleep, but increases as our sleep is prolonged.
Whence digestion and secretion are performed better in sleep, than in our
waking hours, and our dreams in the morning have greater variety and
vivacity, as our sensibility increases, than at night when we first lie
down. And hence epileptic fits, which are always occasioned by some
disagreeable sensation, so frequently attack those, who are subject to
them, in their sleep; because at this time the system is more excitable by
painful sensation in consequence of internal stimuli; and the power of
volition is then suddenly exerted to relieve this pain, as explained Sect.
XXXIV. 1. 4.

There is a disease, which frequently affects children in the cradle, which
is termed ecstasy, and seems to consist in certain exertions to relieve
painful sensation, in which the voluntary power is not so far excited as
totally to awaken them, and yet is sufficient to remove the disagreeable
sensation, which excites it; in this case changing the posture of the child
frequently relieves it.

I have at this time under my care an elegant young man about twenty-two
years of age, who seldom sleeps more than an hour without experiencing a
convulsion fit; which ceases in about half a minute without any subsequent
stupor. Large doses of opium only prevented the paroxysms, so long as they
prevented him from sleeping by the intoxication, which they induced. Other
medicines had no effect on him. He was gently awakened every half hour for
one night, but without good effect, as he soon slept again, and the fit
returned at about the same periods of time, for the accumulated sensorial
power, which occasioned the increased sensibility to pain, was not thus
exhausted. This case evinces, that the sensibility of the system to
internal excitation increases, as our sleep is prolonged; till the pain
thus occasioned produces voluntary exertion; which, when it is in its usual
degree, only awakens us; but when it is more violent, it occasions
convulsions.

The cramp in the calf of the leg is another kind of convulsion, which
generally commences in sleep, occasioned by the continual increase of
irritability from internal stimuli, or of sensibility, during that state of
our existence. The cramp is a violent exertion to relieve pain, generally
either of the skin from cold, or of the bowels, as in some diarrhoeas, or
from the muscles having been previously overstretched, as in walking up or
down steep hills. But in these convulsions of the muscles, which form the
calf of the leg, the contraction is so violent as to occasion another pain
in consequence of their own too violent contraction; as soon as the
original pain, which caused the contraction, is removed. And hence the
cramp, or spasm, of these muscles is continued without intermission by this
new pain, unlike the alternate convulsions and remissions in epileptic
fits. The reason, that the contraction of these muscles of the calf of the
leg is more violent during their convulsion than that of others, depends on
the weakness of their antagonist muscles; for after these have been
contracted in their usual action, as at every step in walking, they are
again extended, not, as most other muscles are, by their antagonists, but
by the weight of the whole body on the balls of the toes; and that weight
applied to great mechanical advantage on the heel, that is, on the other
end of the bone of the foot, which thus acts as a lever.

Another disease, the periods of which generally commence during our sleep,
is the asthma. Whatever may be the remote cause of paroxysms of asthma, the
immediate cause of the convulsive respiration, whether in the common
asthma, or in what is termed the convulsive asthma, which are perhaps only
different degrees of the same disease, must be owing to violent voluntary
exertions to relieve pain, as in other convulsions; and the increase of
irritability to internal stimuli, or of sensibility, during sleep must
occasion them to commence at this time.

Debilitated people, who have been unfortunately accustomed to great
ingurgitation of spirituous potation, frequently part with a great quantity
of water during the night, but with not more than usual in the day-time.
This is owing to a beginning torpor of the absorbent system, and precedes
anasarca, which commences in the day, but is cured in the night by the
increase of the irritability of the absorbent system during sleep, which
thus imbibes from the cellular membrane the fluids, which had been
accumulated there during the day; though it is possible the horizontal
position of the body may contribute something to this purpose, and also the
greater irritability of some branches of the absorbent vessels, which open
their mouths in the cells of the cellular membrane, than that of other
branches.

As soon as a person begins to sleep, the irritability and sensibility of
the system begins to increase, owing to the suspension of volition and the
exclusion of external stimuli. Hence the actions of the vessels in
obedience to internal stimulation become stronger and more energetic,
though less frequent in respect to number. And as many of the secretions
are increased, so the heat of the system is gradually increased, and the
extremities of feeble people, which had been cold during the day, become
warm. Till towards morning many people become so warm, as to find it
necessary to throw off some of their bed-clothes, as soon as they awake;
and in others sweats are so liable to occur towards morning during their
sleep.

Thus those, who are not accustomed to sleep in the open air, are very
liable to take cold, if they happen to fall asleep on a garden bench, or in
a carriage with the window open. For as the system is warmer during sleep,
as above explained, if a current of cold air affects any part of the body,
a torpor of that part is more effectually produced, as when a cold blast of
air through a key-hole or casement falls upon a person in a warm room. In
those cases the affected part possesses less irritability in respect to
heat, from its having previously been exposed to a greater stimulus of
heat, as in the warm room, or during sleep; and hence, when the stimulus of
heat is diminished, a torpor is liable to ensue; that is, we take cold.
Hence people who sleep in the open air, generally feel chilly both at the
approach of sleep, and on their awaking; and hence many people are
perpetually subject to catarrhs if they sleep in a less warm head-dress,
than that which they wear in the day.

16. Not only the sensorial powers of irritation and of sensation, but that
of association also appear to act with greater vigour during the suspension
of volition in sleep. It will be shewn in another place, that the gout
generally first attacks the liver, and that afterwards an inflammation of
the ball of the great toe commences by association, and that of the liver
ceases. Now as this change or metastasis of the activity of the system
generally commences in sleep, it follows, that these associations of motion
exist with greater energy at that time; that is, that the sensorial faculty
of association, like those of irritation and of sensation, becomes in some
measure accumulated during the suspension of volition.

Other associate tribes and trains of motions, as well as the irritative and
sensitive ones, appear to be increased in their activity during the
suspension of volition in sleep. As those which contribute to circulate the
blood, and to perform the various secretions; as well as the associate
tribes and trains of ideas, which contribute to furnish the perpetual
dreams of our dreaming imaginations.

In sleep the secretions have generally been supposed to be diminished, as
the expectorated mucus in coughs, the fluids discharged in diarrhoeas, and
in salivation, except indeed the secretion of sweat, which is often visibly
increased. This error seems to have arisen from attention to the excretions
rather than to the secretions. For the secretions, except that of sweat,
are generally received into reservoirs, as the urine into the bladder, and
the mucus of the intestines and lungs into their respective cavities; but
these reservoirs do not exclude these fluids immediately by their stimulus,
but require at the same time some voluntary efforts, and therefore permit
them to remain during sleep. And as they thus continue longer in those
receptacles in our sleeping hours, a greater part is absorbed from them,
and the remainder becomes thicker, and sometimes in less quantity, though
at the time it was secreted the fluid was in greater quantity than in our
waking hours. Thus the urine is higher coloured after long sleep; which
shews that a greater quantity has been secreted, and that more of the
aqueous and saline part has been reabsorbed, and the earthy part left in
the bladder; hence thick urine in fevers shews only a greater action of the
vessels which secrete it in the kidneys, and of those which absorb it from
the bladder.

The same happens to the mucus expectorated in coughs, which is thus
thickened by absorption of its aqueous and saline parts; and the same of
the feces of the intestines. From hence it appears, and from what has been
said in No. 15. of this Section concerning the increase of irritability and
of sensibility during sleep, that the secretions are in general rather
increased than diminished during these hours of our existence; and it is
probable that nutrition is almost entirely performed in sleep; and that
young animals grow more at this time than in their waking hours, as young
plants have long since been observed to grow more in the night, which is
their time of sleep.

17. Two other remarkable circumstances of our dreaming ideas are their
inconsistency, and the total absence of surprise. Thus we seem to be
present at more extraordinary metamorphoses of animals or trees, than are
to be met with in the fables of antiquity; and appear to be transported
from place to place, which seas divide, as quickly as the changes of
scenery are performed in a play-house; and yet are not sensible of their
inconsistency, nor in the least degree affected with surprise.

We must consider this circumstance more minutely. In our waking trains of
ideas, those that are inconsistent with the usual order of nature, so
rarely have occurred to us, that their connexion is the slightest of all
others: hence, when a consistent train of ideas is exhausted, we attend to
the external stimuli, that usually surround us, rather than to any
inconsistent idea, which might otherwise present itself; and if an
inconsistent idea should intrude itself, we immediately compare it with the
preceding one, and voluntarily reject the train it would introduce; this
appears further in the Section on Reverie, in which state of the mind
external stimuli are not attended to, and yet the streams of ideas are kept
consistent by the efforts of volition. But as our faculty of volition is
suspended, and all external stimuli are excluded in sleep, this slighter
connexion of ideas takes place; and the train is said to be inconsistent;
that is, dissimilar to the usual order of nature.

But, when any consistent train of sensitive or voluntary ideas is flowing
along, if any external stimulus affects us so violently, as to intrude
irritative ideas forcibly into the mind, it disunites the former train of
ideas, and we are affected with surprise. These stimuli of unusual energy
or novelty not only disunite our common trains of ideas, but the trains of
muscular motions also, which have not been long established by habit, and
disturb those that have. Some people become motionless by great surprise,
the fits of hiccup and or ague have been often removed by it, and it even
affects the movements of the heart, and arteries; but in our sleep, all
external stimuli are excluded, and in consequence no surprise can exist.
See Section XVII. 3. 7.

18. We frequently awake with pleasure from a dream, which has delighted us,
without being able to recollect the transactions of it; unless perhaps at a
distance of time, some analogous idea may introduce afresh this forgotten
train: and in our waking reveries we sometimes in a moment lose the train
of thought, but continue to feel the glow of pleasure, or the depression of
spirits, it occasioned: whilst at other times we can retrace with ease
these histories of our reveries and dreams.

The above explanation of surprise throws light upon this subject. When we
are suddenly awaked by any violent stimulus, the surprise totally disunites
the trains of our sleeping ideas from these of our waking ones; but if we
gradually awake, this does not happen; and we readily unravel the preceding
trains of imagination.

19. There are various degrees of surprise; the more intent we are upon the
train of ideas, which we are employed about, the more violent must be the
stimulus that interrupts them, and the greater is the degree of surprise. I
have observed dogs, who have slept by the fire, and by their obscure
barking and struggling have appeared very intent on their prey, that shewed
great surprise for a few seconds after their awaking by looking eagerly
around them; which they did not do at other times of waking. And an
intelligent friend of mine has remarked, that his lady, who frequently
speaks much and articulately in her sleep, could never recollect her dreams
in the morning, when this happened to her: but that when she did not speak
in her sleep, she could always recollect them.

Hence, when our sensations act so strongly in sleep as to influence the
larger muscles, as in those, who talk or struggle in their dreams; or in
those, who are affected with complete reverie (as described in the next
Section), great surprise is produced, when they awake; and these as well as
those, who are completely drunk or delirious, totally forget afterwards
their imaginations at those times.

20. As the immediate cause of sleep consists in the suspension of volition,
it follows, that whatever diminishes the general quantity of sensorial
power, or derives it from the faculty of volition, will constitute a remote
cause of sleep; such as fatigue from muscular or mental exertion, which
diminishes the general quantity of sensorial power; or an increase of the
sensitive motions, as by attending to soft music, which diverts the
sensorial power from the faculty of volition; or lastly, by increase of the
irritative motions, as by wine, or food; or warmth; which not only by their
expenditure of sensorial power diminish the quantity of volition; but also
by their producing pleasureable sensations (which occasion other muscular
or sensual motions in consequence), doubly decrease the voluntary power,
and thus more forcibly produce sleep. See Sect. XXXIV. 1. 4.

Another method of inducing sleep is delivered in a very ingenious work
lately published by Dr. Beddoes. Who, after lamenting that opium frequently
occasions restlessness, thinks, "that in most cases it would be better to
induce sleep by the abstraction of stimuli, than by exhausting the
excitability;" and adds, "upon this principle we could not have a better
soporific than an atmosphere with a diminished proportion of oxygene air,
and that common air might be admitted after the patient was asleep."
(Observ. on Calculus, &c. by Dr. Beddoes, Murray.) If it should be found to
be true, that the excitability of the system depends on the quantity of
oxygene absorbed by the lungs in respiration according to the theory of Dr.
Beddoes, and of M. Girtanner, this idea of sleeping in an atmosphere with
less oxygene in its composition might be of great service in epileptic
cases, and in cramp, and even in fits of the asthma, where their periods
commence from the increase of irritability during sleep.

Sleep is likewise said to be induced by mechanic pressure on the brain in
the cases of spina bifida. Where there has been a defect of one of the
vertebrae of the back, a tumour is protruded in consequence; and, whenever
this tumour has been compressed by the hand, sleep is said to be induced,
because the whole of the brain both within the head and spine becomes
compressed by the retrocession of the fluid within the tumour. But by what
means a compression of the brain induces sleep has not been explained, but
probably by diminishing the secretion of sensorial power, and then the
voluntary motions become suspended previously to the irritative ones, as
occurs in most dying persons.

Another way of procuring sleep mechanically was related to me by Mr.
Brindley, the famous canal engineer, who was brought up to the business of
a mill-wright; he told me, that he had more than once seen the experiment
of a man extending himself across the large stone of a corn-mill, and that
by gradually letting the stone whirl, the man fell asleep, before the stone
had gained its full velocity, and he supposed would have died without pain
by the continuance or increase of the motion. In this case the centrifugal
motion of the head and feet must accumulate the blood in both those
extremities of the body, and thus compress the brain.

Lastly, we should mention the application of cold; which, when in a less
degree, produces watchfulness by the pain it occasions, and the tremulous
convulsions of the subcutaneous muscles; but when it is applied in great
degree, is said to produce sleep. To explain this effect it has been said,
that as the vessels of the skin and extremities become first torpid by the
want of the stimulus of heat, and as thence less blood is circulated
through them, as appears from their paleness, a greater quantity of blood
poured upon the brain produces sleep by its compression of that organ. But
I should rather imagine, that the sensorial power becomes exhausted by the
convulsive actions in consequence of the pain of cold, and of the voluntary
exercise previously used to prevent it, and that the sleep is only the
beginning to die, as the suspension of voluntary power in lingering deaths
precedes for many hours the extinction of the irritative motions.

21. The following are the characteristic circumstances attending perfect
sleep.

1. The power of volition is totally suspended.

2. The trains of ideas caused by sensation proceed with greater facility
and vivacity; but become inconsistent with the usual order of nature. The
muscular motions caused by sensation continue; as those concerned in our
evacuations during infancy, and afterwards in digestion, and in priapismus.

3. The irritative muscular motions continue, as those concerned in the
circulation, in secretion, in respiration. But the irritative sensual
motions, or ideas, are not excited; as the immediate organs of sense are
not stimulated into action by external objects, which are excluded by the
external organs of sense; which are not in sleep adapted to their reception
by the power of volition, as in our waking hours.

4. The associate motions continue; but their first link is not excited into
action by volition, or by external stimuli. In all respects, except those
above mentioned, the three last sensorial powers are somewhat increased in
energy during the suspension of volition, owing to the consequent
accumulation of the spirit of animation.

       *       *       *       *       *

SECT. XIX.

OF REVERIE.

    1. _Various degrees of reverie._ 2. _Sleep-walkers. Case of a young
    lady. Great surprise at awaking. And total forgetfulness of what passed
    in reverie._ 3. _No suspension of volition in reverie._ 4. _Sensitive
    motions continue, and are consistent._ 5. _Irritative motions continue,
    but are not succeeded by sensation._ 6. _Volition necessary for the
    perception of feeble impressions._ 7. _Associated motions continue._ 8.
    _Nerves of sense are irritable in sleep, but not in reverie._ 9.
    _Somnambuli are not asleep. Contagion received but once._ 10.
    _Definition of reverie._

1. When we are employed with great sensation of pleasure, or with great
efforts of volition, in the pursuit of some interesting train of ideas, we
cease to be conscious of our existence, are inattentive to time and place,
and do not distinguish this train of sensitive and voluntary ideas from the
irritative ones excited by the presence of external objects, though our
organs of sense are furnished with their accustomed stimuli, till at length
this interesting train of ideas becomes exhausted, or the appulses of
external objects are applied with unusual violence, and we return with
surprise, or with regret, into the common track of life. This is termed
reverie or studium.

In some constitutions these reveries continue a considerable time, and are
not to be removed without greater difficulty, but are experienced in a less
degree by us all; when we attend earnestly to the ideas excited by volition
or sensation, with their associated connexions, but are at the same time
conscious at intervals of the stimuli of surrounding bodies. Thus in being
present at a play, or in reading a romance, some persons are so totally
absorbed as to forget their usual time of sleep, and to neglect their
meals; while others are said to have been so involved in voluntary study as
not to have heard the discharge of artillery; and there is a story of an
Italian politician, who could think so intensely on other subjects, as to
be insensible to the torture of the rack.

From hence it appears, that these catenations of ideas and muscular
motions, which form the trains of reverie, are composed both of voluntary
and sensitive associations of them; and that these ideas differ from those
of delirium or of sleep, as they are kept consistent by the power of
volition; and they differ also from the trains of ideas belonging to
insanity, as they are as frequently excited by sensation as by volition.
But lastly, that the whole sensorial power is so employed on these trains
of complete reverie, that like the violent efforts of volition, as in
convulsions or insanity; or like the great activity of the irritative
motions in drunkenness; or of the sensitive motions in delirium; they
preclude all sensation consequent to external stimulus.

2. Those persons, who are said to walk in their sleep, are affected with
reverie to so great a degree, that it becomes a formidable disease; the
essence of which consists in the inaptitude of the mind to attend to
external stimuli. Many histories of this disease have been published by
medical writers; of which there is a very curious one in the Lausanne
Transactions. I shall here subjoin an account of such a case, with its
cure, for the better illustration of this subject.

A very ingenious and elegant young lady, with light eyes and hair, about
the age of seventeen, in other respects well, was suddenly seized soon
after her usual menstruation with this very wonderful malady. The disease
began with vehement convulsions of almost every muscle of her body, with
great but vain efforts to vomit, and the most violent hiccoughs, that can
be conceived: these were succeeded in about an hour with a fixed spasm; in
which one hand was applied to her head, and the other to support it: in
about half an hour these ceased, and the reverie began suddenly, and was at
first manifest by the look of her eyes and countenance, which seemed to
express attention. Then she conversed aloud with imaginary persons with her
eyes open, and could not for about an hour be brought to attend to the
stimulus of external objects by any kind of violence, which it was proper
to use; these symptoms returned in this order every day for five or six
weeks.

These conversations were quite consistent, and we could understand, what
she supposed her imaginary companions to answer, by the continuation of her
part of the discourse. Sometimes she was angry, at other times shewed much
wit and vivacity, but was most frequently inclined to melancholy. In these
reveries she sometimes sung over some music with accuracy, and repeated
whole pages from the English poets. In repeating some lines from Mr. Pope's
works she had forgot one word, and began again, endeavouring to recollect
it; when she came to the forgotten word, it was shouted aloud in her ear,
and this repeatedly, to no purpose; but by many trials she at length
regained it herself.

These paroxysms were terminated with the appearance of inexpressible
surprise, and great fear, from which she was some minutes in recovering
herself, calling on her sister with great agitation, and very frequently
underwent a repetition of convulsions, apparently from the pain of fear.
See Sect. XVII. 3. 7.

After having thus returned for about an hour every day for two or three
weeks, the reveries seemed to become less complete, and some of their
circumstances varied; so that she could walk about the room in them without
running against any of the furniture; though these motions were at first
very unsteady and tottering. And afterwards she once drank a dish of tea,
when the whole apparatus of the tea-table was set before her; and expressed
some suspicion, that a medicine was put into it, and once seemed to smell
of a tuberose, which was in flower in her chamber, and deliberated aloud
about breaking it from the stem, saying, "it would make her sister so
charmingly angry." At another time in her melancholy moments she heard the
sound of a passing bell, "I wish I was dead," she cried, listening to the
bell, and then taking off one of her shoes, as she sat upon the bed, "I
love the colour black," says she, "a little wider, and a little longer,
even this might make me a coffin!"--Yet it is evident, she was not sensible
at this time, any more than formerly, of seeing or hearing any person about
her; indeed when great light was thrown upon her by opening the shutters of
the window, her trains of ideas seemed less melancholy; and when I have
forcibly held her hands, or covered her eyes, she appeared to grow
impatient, and would say, she could not tell what to do, for she could
neither see nor move. In all these circumstances her pulse continued
unaffected as in health. And when the paroxysm was over, she could never
recollect a single idea of what had passed in it.

This astonishing disease, after the use of many other medicines and
applications in vain, was cured by very large doses of opium given about an
hour before the expected returns of the paroxysms; and after a few
relapses, at the intervals of three or four months, entirely disappeared.
But she continued at times to have other symptoms of epilepsy.

3. We shall only here consider, what happened during the time of her
reveries, as that is our present subject; the fits of convulsion belong to
another part of this treatise. Sect. XXXIV. 1. 4.

There seems to have been no suspension of volition during the fits of
reverie, because she endeavoured to regain the lost idea in repeating the
lines of poetry, and deliberated about breaking the tuberose, and suspected
the tea to have been medicated.

4. The ideas and muscular movements depending on sensation were exerted
with their usual vivacity, and were kept from being inconsistent by the
power of volition, as appeared from her whole conversation, and was
explained in Sect. XVII. 3. 7. and XVIII. 16.

5. The ideas and motions dependant on irritation during the first weeks of
her disease, whilst the reverie was complete, were never succeeded by the
sensation of pleasure or pain; as she neither saw, heard, nor felt any of
the surrounding objects. Nor was it certain that any irritative motions
succeeded the stimulus of external objects, till the reverie became less
complete, and then she could walk about the room without running against
the furniture of it. Afterwards, when the reverie became still less
complete from the use of opium, some few irritations were at times
succeeded by her attention to them. As when she smelt at a tuberose, and
drank a dish of tea, but this only when she seemed voluntarily to attend to
them.

6. In common life when we listen to distant sounds, or wish to distinguish
objects in the night, we are obliged strongly to exert our volition to
dispose the organs of sense to perceive them, and to suppress the other
trains of ideas, which might interrupt these feeble sensations. Hence in
the present history the strongest stimuli were not perceived, except when
the faculty of volition was exerted on the organ of sense; and then even
common stimuli were sometimes perceived: for her mind was so strenuously
employed in pursuing its own trains of voluntary or sensitive ideas, that
no common stimuli could so far excite her attention as to disunite them;
that is, the quantity of volition or of sensation already existing was
greater than any, which could be produced in consequence of common degrees
of stimulation. But the few stimuli of the tuberose, and of the tea, which
she did perceive, were such, as accidentally coincided with the trains of
thought, which were passing in her mind; and hence did not disunite those
trains, and create surprise. And their being perceived at all was owing to
the power of volition preceding or coinciding with that of irritation.

This explication is countenanced by a fact mentioned concerning a
somnambulist in the Lausanne Transactions, who sometimes opened his eyes
for a short time to examine, where he was, or where his ink-pot stood, and
then shut them again, dipping his pen into the pot every now and then, and
writing on, but never opening his eyes afterwards, although he wrote on
from line to line regularly, and corrected some errors of the pen, or in
spelling: so much easier was it to him to refer to his ideas of the
positions of things, than to his perceptions of them.

7. The associated motions persisted in their usual channel, as appeared by
the combinations of her ideas, and the use of her muscles, and the equality
of her pulse; for the natural motions of the arterial system, though
originally excited like other motions by stimulus, seem in part to continue
by their association with each other. As the heart of a viper pulsates long
after it is cut out of the body, and removed from the stimulus of the
blood.

8. In the section on sleep, it was observed that the nerves of sense are
equally alive and susceptible to irritation in that state, as when we are
awake; but that they are secluded from stimulating objects, or rendered
unfit to receive them: but in complete reverie the reverse happens, the
immediate organs of sense are exposed to their usual stimuli; but are
either not excited into action at all, or not into so great action, as to
produce attention or sensation.

The total forgetfulness of what passes in reveries; and the surprise on
recovering from them, are explained in Section XVIII. 19. and in Section
XVII. 3. 7.

9. It appears from hence, that reverie is a disease of the epileptic or
cataleptic kind, since the paroxysms of this young lady always began and
frequently terminated with convulsions; and though in its greatest degree
it has been called somnambulation, or sleep-walking, it is totally
different from sleep; because the essential character of sleep consists in
the total suspension of volition, which in reverie is not affected; and the
essential character of reverie consists not in the absence of those
irritative motions of our senses, which are occasioned by the stimulus of
external objects, but in their never being productive of sensation. So that
during a fit of reverie that strange event happens to the whole system of
nerves, which occurs only to some particular branches of them in those, who
are a second time exposed to the action of contagious matter. If the matter
of the small-pox be inserted into the arm of one, who has previously had
that disease, it will stimulate the wound, but the general sensation or
inflammation of the system does not follow, which constitutes the disease.
See Sect. XII. 3. 6. XXXIII. 2. 8.

10. The following is the definition or character of complete reverie. 1.
The irritative motions occasioned by internal stimuli continue, those from
the stimuli of external objects are either not produced at all, or are
never succeeded by sensation or attention, unless they are at the same time
excited by volition. 2. The sensitive motions continue, and are kept
consistent by the power of volition. 3. The voluntary motions continue
undisturbed. 4. The associate motions continue undisturbed.

Two other cases of reverie are related in Section XXXIV. 3. which further
evince, that reverie is an effort of the mind to relieve some painful
sensation, and is hence allied to convulsion, and to insanity. Another case
is related in Class III. 1. 2. 2.

       *       *       *       *       *

SECT. XX.

OF VERTIGO.

    1. _We determine our perpendicularity by the apparent motions of
    objects. A person hood-winked cannot walk in a straight line. Dizziness
    in looking from a tower, in a room stained with uniform lozenges, on
    riding over snow._ 2. _Dizziness from moving objects. A whirling-wheel.
    Fluctuations of a river. Experiment with a child._ 3. _Dizziness from
    our own motions and those of other objects._ 4. _Riding over a broad
    stream. Sea-sickness._ 5. _Of turning round on one foot. Dervises in
    Turkey. Attention of the mind prevents slight sea-sickness. After a
    voyage ideas of vibratory motions are still perceived on shore._ 6.
    _Ideas continue some time after they are excited. Circumstances of
    turning on one foot, standing on a tower, and walking in the dark,
    explained._ 7. _Irritative ideas of apparent motions. Irritative ideas
    of sounds. Battement of the sound of bells and organ-pipes. Vertiginous
    noise in the head. Irritative motions of the stomach, intestines, and
    glands._ 8. _Symptoms that accompany vertigo. Why vomiting comes on in
    strokes of the palsy. By the motion of a ship. By injuries on the head.
    Why motion makes sick people vomit._ 9. _Why drunken people are
    vertiginous. Why a stone in the ureter, or bile-duct, produces
    vomiting._ 10. _Why after a voyage ideas of vibratory motions are
    perceived on shore._ 11. _Kinds of vertigo and their cure._ 12.
    _Definition of vertigo._

1. In learning to walk we judge of the distances of the objects, which we
approach, by the eye; and by observing their perpendicularity determine our
own. This circumstance not having been attended to by the writers on
vision, the disease called vertigo or dizziness has been little understood.

When any person loses the power of muscular action, whether he is erect or
in a sitting posture, he sinks down upon the ground; as is seen in fainting
fits, and other instances of great debility. Hence it follows, that some
exertion of muscular power is necessary to preserve our perpendicular
attitude. This is performed by proportionally exerting the antagonist
muscles of the trunk, neck, and limbs; and if at any time in our
locomotions we find ourselves inclining to one side, we either restore our
equilibrium by the efforts of the muscles on the other side, or by moving
one of our feet extend the base, which we rest upon, to the new center of
gravity.

But the most easy and habitual manner of determining our want of
perpendicularity, is by attending to the apparent motion of the objects
within the sphere of distinct vision; for this apparent motion of objects,
when we incline from our perpendicularity, or begin to fall, is as much
greater than the real motion of the eye, as the diameter of the sphere of
distinct vision is to our perpendicular height.

Hence no one, who is hood-winked, can walk in a straight line for a hundred
steps together; for he inclines so greatly, before he is warned of his want
of perpendicularity by the sense of touch, not having the apparent motions
of ambient objects to measure this inclination by, that he is necessitated
to move one of his feet outwards, to the right or to the left, to support
the new centre of gravity, and thus errs from the line he endeavours to
proceed in.

For the same reason many people become dizzy, when they look from the
summit of a tower, which is raised much above all other objects, as these
objects are out of the sphere of distinct vision, and they are obliged to
balance their bodies by the less accurate feelings of their muscles.

There is another curious phenomenon belonging to this place, if the
circumjacent visible objects are so small, that we do not distinguish their
minute parts; or so similar, that we do not know them from each other; we
cannot determine our perpendicularity by them. Thus in a room hung with a
paper, which is coloured over with similar small black lozenges or
rhomboids, many people become dizzy; for when they begin to fall, the next
and the next lozenge succeeds upon the eye; which they mistake for the
first, and are not aware, that they have any apparent motion. But if you
fix a sheet of paper, or draw any other figure, in the midst of these
lozenges, the charm ceases, and no dizziness is perceptible.--The same
occurs, when we ride over a plain covered with snow without trees or other
eminent objects.

2. But after having compared visible objects at rest with the sense of
touch, and learnt to distinguish their shapes and shades, and to measure
our want of perpendicularity by their apparent motions, we come to consider
them in real motion. Here a new difficulty occurs, and we require some
experience to learn the peculiar mode of motion of any moving objects,
before we can make use of them for the purposes of determining our
perpendicularity. Thus some people become dizzy at the sight of a whirling
wheel, or by gazing on the fluctuations of a river, if no steady objects
are at the same time within the sphere of their distinct vision; and when a
child first can stand erect upon his legs, if you gain his attention to a
white handkerchief steadily extended like a sail, and afterwards make it
undulate, he instantly loses his perpendicularity, and tumbles on the
ground.

3. A second difficulty we have to encounter is to distinguish our own real
movements from the apparent motions of objects. Our daily practice of
walking and riding on horseback soon instructs us with accuracy to discern
these modes of motion, and to ascribe the apparent motions of the ambient
objects to ourselves; but those, which we have not acquired by repeated
habit, continue to confound us. So as we ride on horseback the trees and
cottages, which occur to us, appear at rest; we can measure their distances
with our eye, and regulate our attitude by them; yet if we carelessly
attend to distant hills or woods through a thin hedge, which is near us, we
observe the jumping and progressive motions of them; as this is increased
by the paralax of these objects; which we have not habituated ourselves to
attend to. When first an European mounts an elephant sixteen feet high, and
whose mode of motion he is not accustomed to, the objects seem to undulate,
as he passes, and he frequently becomes sick and vertiginous, as I am well
informed. Any other unusual movement of our bodies has the same effect, as
riding backwards in a coach, swinging on a rope, turning round swiftly on
one leg, scating on the ice, and a thousand others. So after a patient has
been long confined to his bed, when he first attempts to walk, he finds
himself vertiginous, and is obliged by practice to learn again the
particular modes of the apparent motions of objects, as he walks by them.

4. A third difficulty, which occurs to us in learning to balance ourselves
by the eye, is, when both ourselves and the circumjacent objects are in
real motion. Here it is necessary, that we should be habituated to both
these modes of motion in order to preserve our perpendicularity. Thus on
horseback we accurately observe another person, whom we meet, trotting
towards us, without confounding his jumping and progressive motion with our
own, because we have been accustomed to them both; that is, to undergo the
one, and to see the other at the same time. But in riding over a broad and
fluctuating stream, though we are well experienced in the motions of our
horse, we are liable to become dizzy from our inexperience in that of the
water. And when first we go on ship-board, where the movements of
ourselves, and the movements of the large waves are both new to us, the
vertigo is almost unavoidable with the terrible sickness, which attends it.
And this I have been assured has happened to several from being removed
from a large ship into a small one; and again from a small one into a man
of war.

5. From the foregoing examples it is evident, that, when we are surrounded
with unusual motions, we lose our perpendicularity: but there are some
peculiar circumstances attending this effect of moving objects, which we
come now to mention, and shall hope from the recital of them to gain some
insight into the manner of their production.

When a child moves round quick upon one foot, the circumjacent objects
become quite indistinct, as their distance increases their apparent
motions; and this great velocity confounds both their forms, and their
colours, as is seen in whirling round a many coloured wheel; he then loses
his usual method of balancing himself by vision, and begins to stagger, and
attempts to recover himself by his muscular feelings. This staggering adds
to the instability of the visible objects by giving a vibratory motion
besides their rotatory one. The child then drops upon the ground, and the
neighbouring objects seem to continue for some seconds of time to circulate
around him, and the earth under him appears to librate like a balance. In
some seconds of time these sensations of a continuation of the motion of
objects vanish; but if he continues turning round somewhat longer, before
he falls, sickness and vomiting are very liable to succeed. But none of
these circumstances affect those who have habituated themselves to this
kind of motion, as the dervises in Turkey, amongst whom these swift
gyrations are a ceremony of religion.

In an open boat passing from Leith to Kinghorn in Scotland, a sudden change
of the wind shook the undistended sail, and stopt our boat; from this
unusual movement the passengers all vomited except myself. I observed, that
the undulation of the ship, and the instability of all visible objects,
inclined me strongly to be sick; and this continued or increased, when I
closed my eyes, but as often as I bent my attention with energy on the
management and mechanism of the ropes and sails, the sickness ceased; and
recurred again, as often as I relaxed this attention; and I am assured by a
gentleman of observation and veracity, that he has more than once observed,
when the vessel has been in immediate danger, that the sea-sickness of the
passengers has instantaneously ceased, and recurred again, when the danger
was over.

Those, who have been upon the water in a boat or ship so long, that they
have acquired the necessary habits of motion upon that unstable element, at
their return on land frequently think in their reveries, or between
sleeping and waking, that they observe the room, they sit in, or some of
its furniture, to librate like the motion of the vessel. This I have
experienced myself, and have been told, that after long voyages, it is some
time before these ideas entirely vanish. The same is observable in a less
degree after having travelled some days in a stage coach, and particularly
when we lie down in bed, and compose ourselves to sleep; in this case it is
observable, that the rattling noise of the coach, as well as the undulatory
motion, haunts us. The drunken vertigo, and the vulgar custom of rocking
children, will be considered in the next Section.

6. The motions, which are produced by the power of volition, may be
immediately stopped by the exertion of the same power on the antagonist
muscles; otherwise these with all the other classes of motion continue to
go on, some time after they are excited, as the palpitation of the heart
continues after the object of fear, which occasioned it, is removed. But
this circumstance is in no class of motions more remarkable than in those
dependent on irritation; thus if any one looks at the sun, and then covers
his eyes with his hand, he will for many seconds of time, perceive the
image of the sun marked on his retina: a similar image of all other visible
objects would remain some time formed on the retina, but is extinguished by
the perpetual change of the motions of this nerve in our attention to other
objects. To this must be added, that the longer time any movements have
continued to be excited without fatigue to the organ, the longer will they
continue spontaneously, after the excitement is withdrawn: as the taste of
tobacco in the mouth after a person has been smoaking it.

This taste remains so strong, that if a person continues to draw air
through a tobacco pipe in the dark, after having been smoking some time, he
cannot distinguish whether his pipe be lighted or not.

From these two considerations it appears, that the dizziness felt in the
head, after seeing objects in unusual motion, is no other than a
continuation of the motions of the optic nerve excited by those objects and
which engage our attention. Thus on turning round on one foot, the vertigo
continues for some seconds of time after the person is fallen on the
ground; and the longer he has continued to revolve, the longer will
continue these successive motions of the parts of the optic nerve.

    _Additional Observations on _VERTIGO.

    After revolving with your eyes open till you become vertiginous, as
    soon as you cease to revolve, not only the circum-ambient objects
    appear to circulate round you in a direction contrary to that, in which
    you have been turning, but you are liable to roll your eyes forwards
    and backwards; as is well observed, and ingeniously demonstrated by Dr.
    Wells in a late publication on vision. The same occurs, if you revolve
    with your eyes closed, and open them immediately at the time of your
    ceasing to turn; and even during the whole time of revolving, as may be
    felt by your hand pressed lightly on your closed eyelids. To these
    movements of the eyes, of which he supposes the observer to be
    inconscious, Dr. Wells ascribes the apparent circumgyration of objects
    on ceasing to revolve.

    The cause of thus turning our eyes forwards, and then back again, after
    our body is at rest, depends, I imagine, on the same circumstance,
    which induces us to follow the indistinct spectra, which are formed on
    one side of the center of the retina, when we observe them apparently
    on clouds, as described in Sect. XL. 2. 2.; and then not being able to
    gain a more distinct vision of them, we turn our eyes back, and again
    and again pursue the flying shade.

    But this rolling of the eyes, after revolving till we become
    vertiginous, cannot cause the apparent circumgyration of objects, in a
    direction contrary to that in which we have been revolving, for the
    following reasons. 1. Because in pursuing a spectrum in the sky, or on
    the ground, as above mentioned, we perceive no retrograde motions of
    objects. 2. Because the apparent retrograde motions of objects, when we
    have revolved till we are vertiginous, continues much longer than the
    rolling of the eyes above described.

    3. When we have revolved from right to left, the apparent motion of
    objects, when we stop, is from left to right; and when we have revolved
    from left to right, the apparent circulation of objects is from right
    to left; yet in both these cases the eyes of the revolver are seen
    equally to roll forwards and backwards.

    4. Because this rolling of the eyes backwards and forwards takes place
    during our revolving, as may be perceived by the hand lightly pressed
    on the closed eyelids, and therefore exists before the effect ascribed
    to it.

    And fifthly, I now come to relate an experiment, in which the rolling
    of the eyes does not take place at all after revolving, and yet the
    vertigo is more distressing than in the situations above mentioned. If
    any one looks steadily at a spot in the ceiling over his head, or
    indeed at his own finger held up high over his head, and in that
    situation turns round till he becomes giddy; and then stops, and looks
    horizontally; he now finds, that the apparent rotation of objects is
    from above downwards, or from below upwards; that is, that the apparent
    circulation of objects is now vertical instead of horizontal, making
    part of a circle round the axis of his _eye_; and this without any
    rolling of his eyeballs. The reason of there being no rolling of the
    eyeballs, perceived after this experiment, is, because the images of
    objects are formed in rotation round the axis of the eye, and not from
    one side to the other of the axis of it; so that, as the eyeball has
    not power to turn in its socket round its own axis, it cannot follow
    the apparent motions of these evanescent spectra, either before or
    after the body is at rest. From all which arguments it is manifest,
    that these apparent retrograde gyrations of objects are not caused by
    the rolling of the eyeballs; first, because no apparent retrogression
    of objects is observed in other rollings of the eyes: secondly, because
    the apparent retrogression of objects continues many seconds after the
    rolling of the eyeballs ceases. Thirdly, because the apparent
    retrogression of objects is sometimes one way, and sometimes another,
    yet the rolling of the eyeballs is the same. Fourthly, because the
    rolling of the eyeballs exists before the apparent retrograde motions
    of objects is observed; that is, before the revolving person stops. And
    fifthly, because the apparent retrograde gyration of objects is
    produced, when there is no rolling of the eyeballs at all.

    Doctor Wells imagines, that no spectra can be gained in the eye, if a
    person revolves with his eyelids closed, and thinks this a sufficient
    argument against the opinion, that the apparent progression of the
    spectra of light or colours in the eye can cause the apparent
    retrogression of objects in the vertigo above described; but it is
    certain, when any person revolves in a light room with his eyes closed,
    that he nevertheless perceives differences of light both in quantity
    and colour through his eyelids, as he turns round; and readily gains
    spectra of those differences. And these spectra are not very different
    except in vivacity from those, which he acquires, when he revolves with
    unclosed eyes, since if he then revolves very rapidly the colours and
    forms of surrounding objects are as it were mixed together in his eye;.
    as when, the prismatic colours are painted on a wheel, they appear
    white as they revolve. The truth of this is evinced by the staggering
    or vertigo of men perfectly blind, when they turn round; which is not
    attended with apparent circulation of objects, but is a vertiginous
    disorder of the sense of touch. Blind men balance themselves by their
    sense of touch; which, being less adapted for perceiving small
    deviations from their perpendicular, occasions them to carry themselves
    more erect in walking. This method of balancing themselves by the
    direction of their pressure against the floor, becomes disordered by
    the unusual mode of action in turning round, and they begin to lose
    their perpendicularity, that is, they become vertiginous; but without
    any apparent circular motions of visible objects.

    It will appear from the following experiments, that the apparent
    progression of the ocular spectra of light or colours is the cause of
    the apparent retrogression of objects, after a person has revolved,
    till he is vertiginous.

    First, when a person turns round in a light room with his eyes open,
    but closes them before he stops, he will seem to be carried forwards in
    the direction he was turning for a short time after he stops. But if he
    opens his eyes again, the objects before him instantly appear to move
    in a retrograde direction, and he loses the sensation of being carried
    forwards. The same occurs if a person revolves in a light room with his
    eyes closed; when he stops, he seems to be for a time carried forwards,
    if his eyes are still closed; but the instant he opens them, the
    surrounding objects appear to move in retrograde gyration. From hence
    it may be concluded, that it is the sensation or imagination of our
    continuing to go forwards in the direction in which we were turning,
    that causes the apparent retrograde circulation of objects.

    Secondly, though there is an audible vertigo, as is known by the
    battement, or undulations of sound in the ears, which many vertiginous
    people experience; and though there is also a tangible vertigo, as when
    a blind person turns round, as mentioned above; yet as this
    circumgyration of objects is an hallucination or deception of the sense
    of sight, we are to look for the cause of our appearing to move
    forward, when we stop with our eyes closed after gyration, to some
    affection of this sense. Now, thirdly, if the spectra formed in the eye
    during our rotation, continue to change, when we stand still, like the
    spectra described in Sect. III. 3. 6. such changes must suggest to us
    the idea or sensation of our still continuing to turn round; as is the
    case, when we revolve in a light room, and close our eyes before we
    stop. And lastly, on opening our eyes in the situation above described,
    the objects we chance to view amid these changing spectra in the eye,
    must seem to move in a contrary direction; as the moon sometimes
    appears to move retrograde, when swift-gliding clouds are passing
    forwards so much nearer the eye of the beholder.

    To make observations on faint ocular spectra requires some degree of
    habit, and composure of mind, and even patience; some of those
    described in Sect. XL. were found difficult to see, by many, who tried
    them; now it happens, that the mind, during the confusion of vertigo,
    when all the other irritative tribes of motion, as well as those of
    vision, are in some degree disturbed, together with the fear of
    falling, is in a very unfit state for the contemplation of such weak
    sensations, as are occasioned by faint ocular spectra. Yet after
    frequently revolving, both with my eyes closed, and with them open, and
    attending to the spectra remaining in them, by shading the light from
    my eyelids more or less with my hand, I at length ceased to have the
    idea of going forward, after I stopped with my eyes closed; and saw
    changing spectra in my eyes, which seemed to move, as it were, over the
    field of vision; till at length, by repeated trials on sunny days, I
    persuaded myself, on opening my eyes, after revolving some time, on a
    shelf of gilded books in my library, that I could perceive the spectra
    in my eyes move forwards over one or two of the books, like the vapours
    in the air of a summer's day; and could so far undeceive myself, as to
    perceive the books to stand still. After more trials I sometimes
    brought myself to believe, that I saw changing spectra of lights and
    shades moving in my eyes, after turning round for some time, but did
    not imagine either the spectra or the objects to be in a state of
    gyration. I speak, however, with diffidence of these facts, as I could
    not always make the experiments succeed, when there was not a strong
    light in my room, or when my eyes were not in the most proper state for
    such observations.

    The ingenious and learned M. Sauvage has mentioned other theories to
    account for the apparent circumgyration of objects in vertiginous
    people. As the retrograde motions of the particles of blood in the
    optic arteries, by spasm, or by fear, as is seen in the tails of
    tadpoles, and membranes between the fingers of frogs. Another cause he
    thinks may be from the librations to one side, and to the other, of the
    crystalline lens in the eye, by means of involuntary actions of the
    muscles, which constitute the ciliary process. Both these theories lie
    under the same objection as that of Dr. Wells before mentioned; namely,
    that the apparent motions of objects, after the observer has revolved
    for some time, should appear to vibrate this way and that; and not to
    circulate uniformly in a direction contrary to that, in which the
    observer had revolved.

    M. Sauvage has, lastly, mentioned the theory of colours left in the
    eye, which he has termed impressions on the retina. He says,
    "Experience teaches us, that impressions made on the retina by a
    visible object remain some seconds after the object is removed; as
    appears from the circle of fire which we see, when a fire-stick is
    whirled round in the dark; therefore when we are carried round our own
    axis in a circle, we undergo a temporary vertigo, when we stop; because
    the impressions of the circumjacent objects remain for a time
    afterwards on the retina." Nosolog. Method. Clas. VIII. I. 1. We have
    before observed, that the changes of these colours remaining in the
    eye, evinces them to be motions of the fine terminations of the retina,
    and not impressions on it; as impressions on a passive substance must
    either remain, or cease intirely. See an additional note at the end of
    the second volume.

Any one, who stands alone on the top of a high tower, if he has not been
accustomed to balance himself by objects placed at such distances and with
such inclinations, begins to stagger, and endeavours to recover himself by
his muscular feelings. During this time the apparent motion of objects at a
distance below him is very great, and the spectra of these apparent motions
continue a little time after he has experienced them; and he is persuaded
to incline the contrary way to counteract their effects; and either
immediately falls, or applying his hands to the building, uses his muscular
feelings to preserve his perpendicular attitude, contrary to the erroneous
persuasions of his eyes. Whilst the person, who walks in the dark,
staggers, but without dizziness; for he neither has the sensation of moving
objects to take off his attention from his muscular feelings, nor has he
the spectra of those motions continued on his retina to add to his
confusion. It happens indeed sometimes to one landing on a tower, that the
idea of his not having room to extend his base by moving one of his feet
outwards, when he begins to incline, superadds fears to his other
inconveniences; which like surprise, joy, or any great degree of sensation,
enervates him in a moment, by employing the whole sensorial power, and by
thus breaking all the associated trains and tribes of motion.

7. The irritative ideas of objects, whilst we are awake, are perpetually
present to our sense of sight; as we view the furniture of our rooms, or
the ground, we tread upon, throughout the whole day without attending to
it. And as our bodies are never at perfect rest during our waking hours,
these irritative ideas of objects are attended perpetually with irritative
ideas of their apparent motions. The ideas of apparent motions are always
irritative ideas, because we never attend to them, whether we attend to the
objects themselves, or to their real motions, or to neither. Hence the
ideas of the apparent motions of objects are a complete circle of
irritative ideas, which continue throughout the day.

Also during all our waking hours, there is a perpetual confused sound of
various bodies, as of the wind in our rooms, the fire, distant
conversations, mechanic business; this continued buzz, as we are seldom
quite motionless, changes its loudness perpetually, like the sound of a
bell; which rises and falls as long as it continues, and seems to pulsate
on the ear. This any one may experience by turning himself round near a
waterfall; or by striking a glass bell, and then moving the direction of
its mouth towards the ears, or from them, as long as its vibrations
continue. Hence this undulation of indistinct sound makes another
concomitant circle of irritative ideas, which continues throughout the day.

We hear this undulating sound, when we are perfectly at rest ourselves,
from other sonorous bodies besides bells; as from two organ-pipes, which
are nearly but not quite in unison, when they are sounded together. When a
bell is struck, the circular form is changed into an eliptic one; the
longest axis of which, as the vibrations continue, moves round the
periphery of the bell; and when either axis of this elipse is pointed
towards our ears, the sound is louder; and less when the intermediate parts
of the elipse are opposite to us. The vibrations of the two organ-pipes may
be compared to Nonius's rule; the sound is louder, when they coincide, and
less at the intermediate times. But, as the sound of bells is the most
familiar of those sounds, which have a considerable battement, the
vertiginous patients, who attend to the irritative circles of sounds above
described, generally compare it to the noise of bells.

The peristaltic motions of our stomach and intestines, and the secretions
of the various glands, are other circles of irritative motions, some of
them more or less complete, according to our abstinence or satiety.

So that the irritative ideas of the apparent motions of objects, the
irritative battements of sounds, and the movements of our bowels and glands
compose a great circle of irritative tribes of motion: and when one
considerable part of this circle of motions becomes interrupted, the whole
proceeds in confusion, as described in Section XVII. 1. 7. on Catenation of
Motions.

8. Hence a violent vertigo, from whatever cause it happens, is generally
attended with undulating noise in the head, perversions of the motions of
the stomach and duodenum, unusual excretion of bile and gastric juice, with
much pale urine, sometimes with yellowness of the skin, and a disordered
secretion of almost every gland of the body, till at length the arterial
system is affected, and fever succeeds.

Thus bilious vomitings accompany the vertigo occasioned by the motion of a
ship; and when the brain is rendered vertiginous by a paralytic affection
of any part of the body, a vomiting generally ensues, and a great discharge
of bile: and hence great injuries of the head from external violence are
succeeded with bilious vomitings, and sometimes with abscesses of the
liver. And hence, when a patient is inclined to vomit from other causes, as
in some fevers, any motions of the attendants in his room, or of himself
when he is raised or turned in his bed, presently induces the vomiting by
superadding a degree of vertigo.

9. And conversely it is very usual with those, whose stomachs are affected
from internal causes, to be afflicted with vertigo, and noise in the head;
such is the vertigo of drunken people, which continues, when their eyes are
closed, and themselves in a recumbent posture, as well as when they are in
an erect posture, and have their eyes open. And thus the irritation of a
stone in the bile-duct, or in the ureter, or an inflammation of any of the
intestines, are accompanied with vomitings and vertigo.

In these cases the irritative motions of the stomach, which are in general
not attended to, become so changed by some unnatural stimulus, as to become
uneasy, and excite our sensation or attention. And thus the other
irritative trains of motions, which are associated with it, become
disordered by their sympathy. The same happens, when a piece of gravel
sticks in the ureter, or when some part of the intestinal canal becomes
inflamed. In these cases the irritative muscular motions are first
disturbed by unusual stimulus, and a disordered action of the sensual
motions, or dizziness ensues. While in sea-sickness the irritative sensual
motions, as vertigo, precedes; and the disordered irritative muscular
motions, as those of the stomach in vomiting, follow.

10. When these irritative motions are disturbed, if the degree be not very
great, the exertion of voluntary attention to any other object, or any
sudden sensation, will disjoin these new habits of motion. Thus some
drunken people have become sober immediately, when any accident has
strongly excited their attention; and sea-sickness has vanished, when the
ship has been in danger. Hence when our attention to other objects is most
relaxed, as just before we fall asleep, or between our reveries when awake,
these irritative ideas of motion and sound are most liable to be perceived;
as those, who have been at sea, or have travelled long in a coach, seem to
perceive the vibrations of the ship, or the rattling of the wheels, at
these intervals; which cease again, as soon as they exert their attention.
That is, at those intervals they attend to the apparent motions, and to the
battement of sounds of the bodies around them, and for a moment mistake
them for those real motions of the ship, and noise of wheels, which they
had lately been accustomed to: or at these intervals of reverie, or on the
approach of sleep, these supposed motions or sounds may be produced
entirely by imagination.

We may conclude from this account of vertigo, that sea-sickness is not an
effort of nature to relieve herself, but a necessary consequence of the
associations or catenations of animal motions. And may thence infer, that
the vomiting, which attends the gravel in the ureter, inflammations of the
bowels, and the commencement of some fevers, has a similar origin, and is
not always an effort of the vis medicatrix naturae. But where the action of
the organ is the immediate consequence of the stimulating cause, it is
frequently exerted to dislodge that stimulus, as in vomiting up an emetic
drug; at other times, the action of an organ is a general effort to relieve
pain, as in convulsions of the locomotive muscles; other actions drink up
and carry on the fluids, as in absorption and secretion; all which may be
termed efforts of nature to relieve, or to preserve herself.

11. The cure of vertigo will frequently depend on our previously
investigating the cause of it, which from what has been delivered above may
originate from the disorder of any part of the great tribes of irritative
motions, and of the associate motions catenated with them.

Many people, when they arrive at fifty or sixty years of age, are affected
with slight vertigo; which is generally but wrongly ascribed to
indigestion, but in reality arises from a beginning defect of their sight;
as about this time they also find it necessary to begin to use spectacles,
when they read small prints, especially in winter, or by candle light, but
are yet able to read without them during the summer days, when the light is
stronger. These people do not see objects so distinctly as formerly, and by
exerting their eyes more than usual, they perceive the apparent motions of
objects, and confound them with the real motions of them; and therefore
cannot accurately balance themselves so as easily to preserve their
perpendicularity by them.

That is, the apparent motions of objects, which are at rest, as we move by
them, should only excite irritative ideas: but as these are now become less
distinct, owing to the beginning imperfection of our sight, we are induced
_voluntarily_ to attend to them; and then these apparent motions become
succeeded by sensation; and thus the other parts of the trains of
irritative ideas, or irritative muscular motions, become disordered, as
explained above. In these cases of slight vertigo I have always promised my
patients, that they would get free from it in two or three months, as they
should acquire the habit of balancing their bodies by less distinct
objects, and have seldom been mistaken in my prognostic.

There is an auditory vertigo, which is called a noise in the head,
explained in No. 7. of this section, which also is very liable to affect
people in the advance of life, and is owing to their hearing less perfectly
than before. This is sometimes called a ringing, and sometimes a singing,
or buzzing, in the ears, and is occasioned by our first experiencing a
disagreeable sensation from our not being able distinctly to hear the
sounds, we used formerly to hear distinctly. And this disagreeable
sensation excites desire and consequent volition; and when we voluntarily
attend to small indistinct sounds, even the whispering of the air in a
room, and the pulsations of the arteries of the ear are succeeded by
sensation; which minute sounds ought only to have produced irritative
sensual motions, or unperceived ideas. See Section XVII. 3. 6. These
patients after a while lose this auditory vertigo, by acquiring a new habit
of not attending voluntarily to these indistinct sounds, but contenting
themselves with the less accuracy of their sense of hearing.

Another kind of vertigo begins with the disordered action of some
irritative muscular motions, as those of the stomach from intoxication, or
from emetics; or those of the ureter, from the stimulus of a stone lodged
in it; and it is probable, that the disordered motions of some of the great
congeries of glands, as of those which form the liver, or of the intestinal
canal, may occasion vertigo in consequence of their motions being
associated or catenated with the great circles of irritative motions; and
from hence it appears, that the means of cure must be adapted to the cause.

To prevent sea-sickness it is probable, that the habit of swinging for a
week or two before going on shipboard might be of service. For the vertigo
from failure of sight, spectacles may be used. For the auditory vertigo,
aether may be dropt into the ear to stimulate the part, or to dissolve
ear-wax, if such be a part of the cause. For the vertigo arising from
indigestion, the peruvian bark and a blister are recommended. And for that
owing to a stone in the ureter, venesection, cathartics, opiates, sal soda
aerated.

12. Definition of vertigo. 1. Some of the irritative sensual, or muscular
motions, which were usually not succeeded by sensation, are in this disease
succeeded by sensation; and the trains or circles of motions, which were
usually catenated with them, are interrupted, or inverted, or proceed in
confusion. 2. The sensitive and voluntary motions continue undisturbed. 3.
The associate trains or circles of motions continue; but their catenations
with some of the irritative motions are disordered, or inverted, or
dissevered.

       *       *       *       *       *

SECT. XXI.

OF DRUNKENNESS.

    1. _Sleep from satiety of hunger. From rocking children. From uniform
    sounds._ 2. _Intoxication from common food after fatigue and
    inanition._ 3. _From wine or of opium. Chilness after meals. Vertigo.
    Why pleasure is produced by intoxication, and by swinging and rocking
    children. And why pain is relieved by it._ 4. _Why drunkards stagger
    and stammer, and are liable to weep._ 5. _And become delirious, sleepy,
    and stupid._ 6. _Or make pale urine and vomit._ 7. _Objects are seen
    double._ 8. _Attention of the mind diminishes drunkenness._ 9.
    _Disordered irritative motions of all the senses._ 10. _Diseases from
    drunkenness._ 11. _Definition of drunkenness._

1. In the state of nature when the sense of hunger is appeased by the
stimulus of agreeable food, the business of the day is over, and the human
savage is at peace with the world, he then exerts little attention to
external objects, pleasing reveries of imagination succeed, and at length
sleep is the result: till the nourishment which he has procured, is carried
over every part of the system to repair the injuries of action, and he
awakens with fresh vigour, and feels a renewal of his sense of hunger.

The juices of some bitter vegetables, as of the poppy and the laurocerasus,
and the ardent spirit produced in the fermentation of the sugar found in
vegetable juices, are so agreeable to the nerves of the stomach, that,
taken in a small quantity, they instantly pacify the sense of hunger; and
the inattention to external stimuli with the reveries of imagination, and
sleep, succeeds, in the same manner as when the stomach is filled with
other less intoxicating food.

This inattention to the irritative motions occasioned by external stimuli
is a very important circumstance in the approach of sleep, and is produced
in young children by rocking their cradles: during which all visible
objects become indistinct to them. An uniform soft repeated sound, as the
murmurs of a gentle current, or of bees, are said to produce the same
effect, by presenting indistinct ideas of inconsequential sounds, and by
thus stealing our attention from other objects, whilst by their continued
reiterations they become familiar themselves, and we cease gradually to
attend to any thing, and sleep ensues.

2. After great fatigue or inanition, when the stomach is suddenly filled
with flesh and vegetable food, the inattention to external stimuli, and the
reveries of imagination, become so conspicuous as to amount to a degree of
intoxication. The same is at any time produced by superadding a little wine
or opium to our common meals; or by taking these separately in considerable
quantity; and this more efficaciously after fatigue or inanition; because a
less quantity of any stimulating material will excite an organ into
energetic action, after it has lately been torpid from defect of stimulus;
as objects appear more luminous, after we have been in the dark; and
because the suspension of volition, which is the immediate cause of sleep,
is sooner induced, after a continued voluntary exertion has in part
exhausted the sensorial power of volition; in the same manner as we cannot
contract a single muscle long together without intervals of inaction.

3. In the beginning of intoxication we are inclined to sleep, as mentioned
above, but by the excitement of external circumstances, as of noise, light,
business, or by the exertion of volition, we prevent the approaches of it,
and continue to take into our stomach greater quantities of the inebriating
materials. By these means the irritative movements of the stomach are
excited into greater action than is natural; and in consequence all the
irritative tribes and trains of motion, which are catenated with them,
become susceptible of stronger action from their accustomed stimuli;
because these motions are excited both by their usual irritation, and by
their association with the increased actions of the stomach and lacteals.
Hence the skin glows, and the heat of the body is increased, by the more
energetic action of the whole glandular system; and pleasure is introduced
in consequence of these increased motions from internal stimulus. According
to Law 5. Sect. IV. on Animal Causation.

From this great increase of irritative motions from internal stimulus, and
the increased sensation introduced into the system in consequence; and
secondly, from the increased sensitive motions in consequence of this
additional quantity of sensation, so much sensorial power is expended, that
the voluntary power becomes feebly exerted, and the irritation from the
stimulus of external objects is less forcible; the external parts of the
eye are not therefore voluntarily adapted to the distances of objects,
whence the apparent motions of those objects either are seen double, or
become too indistinct for the purpose of balancing the body, and vertigo is
induced.

Hence we become acquainted with that very curious circumstance, why the
drunken vertigo is attended with an increase of pleasure; for the
irritative ideas and motions occasioned by internal stimulus, that were not
attended to in our sober hours, are now just so much increased as to be
succeeded by pleasurable sensation, in the same manner as the more violent
motions of our organs are succeeded by painful sensation. And hence a
greater quantity of pleasurable sensation is introduced into the
constitution; which is attended in some people with an increase of
benevolence and good humour.

If the apparent motions of objects is much increased, as when we revolve on
one foot, or are swung on a rope, the ideas of these apparent motions are
also attended to, and are succeeded with pleasureable sensation, till they
become familiar to us by frequent use. Hence children are at first
delighted with these kinds of exercise, and with riding, and failing, and
hence rocking young children inclines them to sleep. For though in the
vertigo from intoxication the irritative ideas of the apparent motions of
objects are indistinct from their decrease of energy: yet in the vertigo
occasioned by rocking or swinging the irritative ideas of the apparent
motions of objects are increased in energy, and hence they induce pleasure
into the system, but are equally indistinct, and in consequence equally
unfit to balance ourselves by. This addition of pleasure precludes desire
or aversion, and in consequence the voluntary power is feebly exerted, and
on this account rocking young children inclines them to sleep.

In what manner opium and wine act in relieving pain is another article,
that well deserves our attention. There are many pains that originate from
defect as well as from excess of stimulus; of these are those of the six
appetites of hunger, thirst, lust, the want of heat, of distention, and of
fresh air. Thus if our cutaneous capillaries cease to act from the
diminished stimulus of heat, when we are exposed to cold weather, or our
stomach is uneasy for want of food; these are both pains from defect of
stimulus, and in consequence opium, which stimulates all the moving system
into increased action, must relieve them. But this is not the case in those
pains, which arise from excess of stimulus, as in violent inflammations: in
these the exhibition of opium is frequently injurious by increasing the
action of the system already too great, as in inflammation of the bowels
mortification is often produced by the stimulus of opium. Where, however,
no such bad consequences follow; the stimulus of opium, by increasing all
the motions of the system, expends so much of the sensorial power, that the
actions of the whole system soon become feebler, and in consequence those
which produced the pain and inflammation.

4. When intoxication proceeds a little further, the quantity of pleasurable
sensation is so far increased, that all desire ceases, for there is no pain
in the system to excite it. Hence the voluntary exertions are diminished,
staggering and stammering succeed; and the trains of ideas become more and
more inconsistent from this defect of voluntary exertion, as explained in
the sections on sleep and reverie, whilst those passions which are unmixed
with volition are more vividly felt, and shewn with less reserve; hence
pining love, or superstitious fear, and the maudling tear dropped on the
remembrance of the most trifling distress.

5. At length all these circumstances are increased; the quantity of
pleasure introduced into the system by the increased irritative muscular
motions of the whole sanguiferous, and glandular, and absorbent systems,
becomes so great, that the organs of sense are more forcibly excited into
action by this internal pleasurable sensation, than by the irritation from
the stimulus of external objects. Hence the drunkard ceases to attend to
external stimuli, and as volition is now also suspended, the trains of his
ideas become totally inconsistent as in dreams, or delirium: and at length
a stupor succeeds from the great exhaustion of sensorial power, which
probably does not even admit of dreams, and in which, as in apoplexy, no
motions continue but those from internal stimuli, from sensation, and from
association.

6. In other people a paroxysm of drunkenness has another termination; the
inebriate, as soon as he begins to be vertiginous, makes pale urine in
great quantities and very frequently, and at length becomes sick, vomits
repeatedly, or purges, or has profuse sweats, and a temporary fever ensues
with a quick strong pulse. This in some hours is succeeded by sleep; but
the unfortunate bacchanalian does not perfectly recover himself till about
the same time of the succeeding day, when his course of inebriation began.
As shewn in Sect. XVII. 1. 7. on Catenation. The temporary fever with
strong pulse is owing to the same cause as the glow on the skin mentioned
in the third paragraph of this Section: the flow of urine and sickness
arises from the whole system of irritative motions being thrown into
confusion by their associations with each other; as in sea-sickness,
mentioned in Sect. XX. 4. on Vertigo; and which is more fully explained in
Section XXIX. on Diabetes.

7. In this vertigo from internal causes we see objects double, as two
candles instead of one, which is thus explained. Two lines drawn through
the axes of our two eyes meet at the object we attend to: this angle of the
optic axes increases or diminishes with the less or greater distances of
objects. All objects before or behind the place where this angle is formed,
appear double; as any one may observe by holding up a pen between his eyes
and the candle; when he looks attentively at a spot on the pen, and
carelessly at the candle, it will appear double; and the reverse when he
looks attentively at the candle and carelessly at the pen; so that in this
case the muscles of the eye, like those of the limbs, stagger and are
disobedient to the expiring efforts of volition. Numerous objects are
indeed sometimes seen by the inebriate, occasioned by the refractions made
by the tears, which stand upon his eye-lids.

8. This vertigo also continues, when the inebriate lies in his bed, in the
dark, or with his eyes closed; and this more powerfully than when he is
erect, and in the light. For the irritative ideas of the apparent motions
of objects are now excited by irritation from internal stimulus, or by
association with other irritative motions; and the inebriate, like one in a
dream, believes the objects of these irritative motions to be present, and
feels himself vertiginous. I have observed in this situation, so long as my
eyes and mind were intent upon a book, the sickness and vertigo ceased, and
were renewed again the moment I discontinued this attention; as was
explained in the preceding account of sea-sickness. Some drunken people
have been known to become sober instantly from some accident, that has
strongly excited their attention, as the pain of a broken bone, or the news
of their house being on fire.

9. Sometimes the vertigo from internal causes, as from intoxication, or at
the beginning of some fevers, becomes so universal, that the irritative
motions which belong to other organs of sense are succeeded by sensation or
attention, as well as those of the eye. The vertiginous noise in the ears
has been explained in Section XX. on Vertigo. The taste of the saliva,
which in general is not attended to, becomes perceptible, and the patients
complain of a bad taste in their mouth.

The common smells of the surrounding air sometimes excite the attention of
these patients, and bad smells are complained of, which to other people are
imperceptible. The irritative motions that belong to the sense of pressure,
or of touch, are attended to, and the patient conceives the bed to librate,
and is fearful of falling out of it. The irritative motions belonging to
the senses of distention, and of heat, like those above mentioned, become
attended to at this time: hence we feel the pulsation of our arteries all
over us, and complain of heat, or of cold, in parts of the body where there
is no accumulation or diminution of actual heat. All which are to be
explained, as in the last paragraph, by the irritative ideas belonging to
the various senses being now excited by internal stimuli, or by their
associations with other irritative motions. And that the inebriate, like
one in a dream, believes the external objects, which usually caused these
irritative ideas, to be now present.

10. The diseases in consequence of frequent inebriety, or of daily taking
much vinous spirit without inebriety, consist in the paralysis, which is
liable to succeed violent stimulation. Organs, whose actions are associated
with others, are frequently more affected than the organ, which is
stimulated into too violent action. See Sect. XXIV. 2. 8. Hence in drunken
people it generally happens, that the secretory vessels of the liver become
first paralytic, and a torpor with consequent gall-stones or schirrus of
this viscus is induced with concomitant jaundice; otherwise it becomes
inflamed in consequence of previous torpor, and this inflammation is
frequently transferred to a more sensible part, which is associated with
it, and produces the gout, or the rosy eruption of the face, or some other
leprous eruption on the head, or arms, or legs. Sometimes the stomach is
first affected, and paralysis of the lacteal system is induced: whence a
total abhorrence from flesh-food, and general emaciation. In others the
lymphatic system is affected with paralysis, and dropsy is the consequence.
In some inebriates the torpor of the liver produces pain without apparent
schirrus, or gall stones, or inflammation, or consequent gout, and in these
epilepsy or insanity are often the consequence. All which will be more
fully treated of in the course of the work.

I am well aware, that it is a common opinion, that the gout is as
frequently owing to gluttony in eating, as to intemperance in drinking
fermented or spirituous liquors. To this I answer, that I have seen no
person afflicted with the gout, who has not drank freely of fermented
liquor, as wine and water, or small beer; though as the disposition to all
the diseases, which have originated from intoxication, is in some degree
hereditary, a less quantity of spirituous potation will induce the gout in
those, who inherit the disposition from their parents. To which I must add,
that in young people the rheumatism is frequently mistaken for the gout.

Spice is seldom taken in such quantity as to do any material injury to the
system, flesh-meats as well as vegetables are the natural diet of mankind;
with these a glutton may be crammed up to the throat, and fed fat like a
stalled ox; but he will not be diseased, unless he adds spirituous or
fermented liquor to his food. This is well known in the distilleries, where
the swine, which are fattened by the spirituous sediments of barrels,
acquire diseased livers. But mark what happens to a man, who drinks a quart
of wine or of ale, if he has not been habituated to it. He loses the use
both of his limbs and of his understanding! He becomes a temporary idiot,
and has a temporary stroke of the palsy! And though he slowly recovers
after some hours, is it not reasonable to conclude, that a perpetual
repetition of so powerful a poison must at length permanently affect
him?--If a person accidentally becomes intoxicated by eating a few
mushrooms of a peculiar kind, a general alarm is excited, and he is said to
be poisoned, and emetics are exhibited; but so familiarised are we to the
intoxication from vinous spirit, that it occasions laughter rather than
alarm.

There is however considerable danger in too hastily discontinuing the use
of so strong a stimulus, lest the torpor of the system, or paralysis,
should sooner be induced by the omission than by the continuance of this
habit, when unfortunately acquired. A golden rule for determining the
quantity, which may with safety be discontinued, is delivered in Sect. XII.
7. 8.

11. Definition of drunkenness. Many of the irritative motions are much
increased in energy by internal stimulation.

2. A great additional quantity of pleasurable sensation is occasioned by
this increased exertion of the irritative motions. And many sensitive
motions are produced in consequence of this increased sensation.

3. The associated trains and tribes of motions, catenated with the
increased irritative and sensitive motions, are disturbed, and proceed in
confusion.

4. The faculty of volition is gradually impaired, whence proceeds the
instability of locomotion, inaccuracy of perception, and inconsistency of
ideas; and is at length totally suspended, and a temporary apoplexy
succeeds.

       *       *       *       *       *

SECT. XXII.

OF PROPENSITY TO MOTION, REPETITION AND IMITATION.

    I. _Accumulation of sensorial power in hemiplagia, in sleep, in cold
    fit of fever, in the locomotive muscles, in the organs of sense.
    Produces propensity to action._ II. _Repetition by three sensorial
    powers. In rhimes and alliterations, in music, dancing, architecture,
    landscape-painting, beauty._ III. 1. _Perception consists in imitation.
    Four kinds of imitation._ 2. _Voluntary. Dogs taught to dance._ 3.
    _Sensitive. Hence sympathy, and all our virtues. Contagious matter of
    venereal ulcers, of hydrophobia, of jail-fever, of small-pox, produced
    by imitation, and the sex of the embryon._ 4. _Irritative imitation._
    5. _Imitations resolvable into associations._

I. 1. In the hemiplagia, when the limbs on one side have lost their power
of voluntary motion, the patient is for many days perpetually employed in
moving those of the other. 2. When the voluntary power is suspended during
sleep, there commences a ceaseless flow of sensitive motions, or ideas of
imagination, which compose our dreams. 3. When in the cold fit of an
intermittent fever some parts of the system have for a time continued
torpid, and have thus expended less than their usual expenditure of
sensorial power; a hot fit succeeds, with violent action of those vessels,
which had previously been quiescent. All these are explained from an
accumulation of sensorial power during the inactivity of some part of the
system.

Besides the very great quantity of sensorial power perpetually produced and
expended in moving the arterial, venous, and glandular systems, with the
various organs or digestion, as described in Section XXXII. 3. 2. there is
also a constant expenditure of it by the action of our locomotive muscles
and organs of sense. Thus the thickness of the optic nerves, where they
enter the eye, and the great expansion of the nerves of touch beneath the
whole of the cuticle, evince the great consumption of sensorial power by
these senses. And our perpetual muscular actions in the common offices of
life, and in constantly preserving the perpendicularity of our bodies
during the day, evince a considerable expenditure of the spirit of
animation by our locomotive muscles. It follows, that if the exertion of
these organs of sense and muscles be for a while intermitted, that some
quantity of sensorial power must be accumulated, and a propensity to
activity of some kind ensue from the increased excitability of the system.
Whence proceeds the irksomeness of a continued attitude, and of an indolent
life.

However small this hourly accumulation of the spirit of animation may be,
it produces a propensity to some kind of action; but it nevertheless
requires either desire or aversion, either pleasure or pain, or some
external stimulus, or a previous link of association, to excite the system
into activity; thus it frequently happens, when the mind and body are so
unemployed as not to possess any of the three first kinds of stimuli, that
the last takes place, and consumes the small but perpetual accumulation of
sensorial power. Whence some indolent people repeat the same verse for
hours together, or hum the same tune. Thus the poet:

  Onward he trudged, not knowing what he sought,
  And whistled, as he went, for want of thought.

II. The repetitions of motions may be at first produced either by volition,
or by sensation, or by irritation, but they soon become easier to perform
than any other kinds of action, because they soon become associated
together, according to Law the seventh, Section IV. on Animal Causation.
And because their frequency of repetition, if as much sensorial power be
produced during every reiteration as is expended, adds to the facility of
their production.

If a stimulus be repeated at uniform intervals of time, as described in
Sect. XII. 3. 3. the action, whether of our muscles or organs of sense, is
produced with still greater facility or energy; because the sensorial power
of association, mentioned above, is combined with the sensorial power of
irritation; that is, in common language, the acquired habit assists the
power of the stimulus.

This not only obtains in the annual, lunar, and diurnal catenations of
animal motions, as explained in Sect. XXXVI. which are thus performed with
great facility and energy; but in every less circle of actions or ideas, as
in the burthen of a song, or the reiterations of a dance. To the facility
and distinctness, with which we hear sounds at repeated intervals, we owe
the pleasure, which we receive from musical time, and from poetic time; as
described in Botanic Garden, P. 2. Interlude 3. And to this the pleasure we
receive from the rhimes and alliterations of modern verification; the
source of which without this key would be difficult to discover. And to
this likewise should be ascribed the beauty of the duplicature in the
perfect tense of the Greek verbs, and of some Latin ones, as tango tetegi,
mordeo momordi.

There is no variety of notes referable to the gamut in the beating of the
drum, yet if it be performed in musical time, it is agreeable to our ears;
and therefore this pleasurable sensation must be owing to the repetition of
the divisions of the sounds at certain intervals of time, or musical bars.
Whether these times or bars are distinguished by a pause, or by an
emphasis, or accent, certain it is, that this distinction is perpetually
repeated; otherwise the ear could not determine instantly, whether the
successions of sound were in common or in triple time. In common time there
is a division between every two crotchets, or other notes of equivalent
time; though the bar in written music is put after every fourth crotchet,
or notes equivalent in time; in triple time the division or bar is after
every three crotchets, or notes equivalent; so that in common time the
repetition recurs more frequently than in triple time. The grave or heroic
verses of the Greek and Latin poets are written in common time; the French
heroic verses, and Mr. Anstie's humorous verses in his Bath Guide, are
written in the same time as the Greek and Latin verses, but are one bar
shorter. The English grave or heroic verses are measured by triple time, as
Mr. Pope's translation of Homer.

But besides these little circles of musical time, there are the greater
returning periods, and the still more distant choruses, which, like the
rhimes at the ends of verses, owe their beauty to repetition; that is, to
the facility and distinctness with which we perceive sounds, which we
expect to perceive, or have perceived before; or in the language of this
work, to the greater ease and energy with which our organ is excited by the
combined sensorial powers of association and irritation, than by the latter
singly.

A certain uniformity or repetition of parts enters the very composition of
harmony. Thus two octaves nearest to each other in the scale commence their
vibrations together after every second vibration of the higher one. And
where the first, third, and fifth compose a chord the vibrations concur or
coincide frequently, though less to than in the two octaves. It is probable
that these chords bear some analogy to a mixture of three alternate colours
in the sun's spectrum separated by a prism.

The pleasure we receive from a melodious succession of notes referable to
the gamut is derived from another source, viz. to the pandiculation or
counteraction of antagonist fibres. See Botanic Garden, P. 2. Interlude 3.
If to these be added our early associations of agreeable ideas with certain
proportions of sound, I suppose, from these three sources springs all the
delight of music, so celebrated by ancient authors, and so enthusiastically
cultivated at present. See Sect. XVI. No. 10. on Instinct.

This kind of pleasure arising from repetition, that is from the facility
and distinctness, with which we perceive and understand repeated
sensations, enters into all the agreeable arts; and when it is carried to
excess is termed formality. The art of dancing like that of music depends
for a great part of the pleasure, it affords, on repetition; architecture,
especially the Grecian, consists of one part being a repetition of another;
and hence the beauty of the pyramidal outline in landscape-painting; where
one side of the picture may be said in some measure to balance the other.
So universally does repetition contribute to our pleasure in the fine arts,
that beauty itself has been defined by some writers to consist in a due
combination of uniformity and variety. See Sect. XVI. 6.

III. 1. Man is termed by Aristotle an imitative animal; this propensity to
imitation not only appears in the actions of children, but in all the
customs and fashions of the world: many thousands tread in the beaten paths
of others, for one who traverses regions of his own discovery. The origin
of this propensity of imitation has not, that I recollect, been deduced
from any known principle; when any action presents itself to the view of a
child, as of whetting a knife, or threading a needle, the parts of this
action in respect of time, motion, figure, is imitated by a part of the
retina of his eye; to perform this action therefore with his hands is
easier to him than to invent any new action, because it consists in
repeating with another set of fibres, viz. with the moving muscles, what he
had just performed by some parts of the retina; just as in dancing we
transfer the times of motion from the actions of the auditory nerves to the
muscles of the limbs. Imitation therefore consists of repetition, which we
have shewn above to be the easiest kind of animal action, and which we
perpetually fall into, when we possess an accumulation of sensorial power,
which is not otherwise called into exertion.

It has been shewn, that our ideas are configurations of the organs of
sense, produced originally in consequence of the stimulus of external
bodies. And that these ideas, or configurations of the organs of sense,
referable in some property a correspondent property of external matter; as
the parts of the senses of light and of touch, which are excited into
action, resemble in figure the figure of the stimulating body; and probably
also the colour, and the quantity of density, which they perceive. As
explained in Sect. XIV. 2. 2. Hence it appears, that our perceptions
themselves are copies, that is, imitations of some properties of external
matter; and the propensity to imitation is thus interwoven with our
existence, as it is produced by the stimuli of external bodies, and is
afterwards repeated by our volitions and sensations, and thus constitutes
all the operations of our minds.

2. Imitations resolve themselves into four kinds, voluntary, sensitive,
irritative, and associate. The voluntary imitations are, when we imitate
deliberately the actions of others, either by mimicry, as in acting a play,
or in delineating a flower; or in the common actions of our lives, as in
our dress, cookery, language, manners, and even in our habits of thinking.

Not only the greatest part of mankind learn all the common arts of life by
imitating others, but brute animals seem capable of acquiring knowledge
with greater facility by imitating each other, than by any methods by which
we can teach them; as dogs and cats, when they are sick, learn of each
other to eat grass; and I suppose, that by making an artificial dog perform
certain tricks, as in dancing on his hinder legs, a living dog might be
easily induced to imitate them; and that the readiest way of instructing
dumb animals is by practising them with others of the same species, which
have already learned the arts we wish to teach them. The important use of
imitation in acquiring natural language is mentioned in Section XVI. 7. and
8. on Instinct.

3. The sensitive imitations are the immediate consequences of pleasure or
pain, and these are often produced even contrary to the efforts of the
will. Thus many young men on seeing cruel surgical operations become sick,
and some even feel pain in the parts of their own bodies, which they see
tortured or wounded in others; that is, they in some measure imitate by the
exertions of their own fibres the violent actions, which they witnessed in
those of others. In this case a double imitation takes place, first the
observer imitates with the extremities of the optic nerve the mangled
limbs, which are present before his eyes; then by a second imitation he
excites to violent action of the fibres of his own limbs as to produce pain
in those parts of his own body, which he saw wounded in another. In these
pains produced by imitation the effect has some similarity to the cause,
which distinguishes them from those produced by association; as the pains
of the teeth, called tooth-edge, which are produced by association with
disagreeable sounds, as explained in Sect. XVI. 10.

The effect of this powerful agent, imitation, in the moral world, is
mentioned in Sect. XVI. 7. as it is the foundation of all our intellectual
sympathies with the pains and pleasures of others, and is in consequence
the source of all our virtues. For in what consists our sympathy with the
miseries, or with the joys, of our fellow creatures, but in an involuntary
excitation of ideas in some measure similar or imitative of those, which we
believe to exist in the minds of the persons, whom we commiserate or
congratulate?

There are certain concurrent or successive actions of some of the glands,
or other parts of the body, which are possessed of sensation, which become
intelligible from this propensity to imitation. Of these are the production
of matter by the membranes of the fauces, or by the skin, in consequence of
the venereal disease previously affecting the parts of generation. Since as
no fever is excited, and as neither the blood of such patients, nor even
the matter from ulcers of the throat, or from cutaneous ulcers, will by
inoculation produce the venereal disease in others, as observed by Mr.
Hunter, there is reason to conclude, that no contagious matter is conveyed
thither by the blood-vessels, but that a milder matter is formed by the
actions of the fine vessels in those membranes imitating each other. See
Section XXXIII. 2. 9. In this disease the actions of these vessels
producing ulcers on the throat and skin are imperfect imitations of those
producing chanker, or gonorrhoea; since the matter produced by them is not
infectious, while the imitative actions in the hydrophobia appear to be
perfect resemblances, as they produce a material equally infectious with
the original one, which induced them.

The contagion from the bite of a mad dog differs from other contagious
materials, from its being communicable from other animals to mankind, and
from many animals to each other; the phenomena attending the hydrophobia
are in some degree explicable on the foregoing theory. The infectious
matter does not appear to enter the circulation, as it cannot be traced
along the course of the lymphatics from the wound, nor is there any
swelling of the lymphatic glands, nor does any fever attend, as occurs in
the small-pox, and in many other contagious diseases; yet by some unknown
process the disease is communicated from the wound to the throat, and that
many months after the injury, so as to produce pain and hydrophobia, with a
secretion of infectious saliva of the same kind, as that of the mad dog,
which inflicted the wound.

This subject is very intricate.--It would appear, that by certain morbid
actions of the salivary glands of the mad dog, a peculiar kind of saliva is
produced; which being instilled into a wound of another animal stimulates
the cutaneous or mucous glands into morbid actions, but which are
ineffectual in respect to the production of a similar contagious material;
but the salivary glands by irritative sympathy are thrown into similar
action, and produce an infectious saliva similar to that instilled into the
wound.

Though in many contagious fevers a material similar to that which produced
the disease, is thus generated by imitation; yet there are other infectious
materials, which do not thus propagate themselves, but which seem to act
like slow poisons. Of this kind was the contagious matter, which produced
the jail-fever at the assizes at Oxford about a century ago. Which, though
fatal to so many, was not communicated to their nurses or attendants. In
these cases, the imitations of the fine vessels, as above described, appear
to be imperfect, and do not therefore produce a matter similar to that,
which stimulates them; in this circumstance resembling the venereal matter
in ulcers of the throat or skin, according to the curious discovery of Mr.
Hunter above related, who found, by repeated inoculations, that it would
not infect. Hunter on Venereal Disease, Part vi. ch. 1.

Another example of morbid imitation is in the production of a great
quantity of contagious matter, as in the inoculated small-pox, from a small
quantity of it inserted into the arm, and probably diffused in the blood.
These particles of contagious matter stimulate the extremities of the fine
arteries of the skin, and cause them to imitate some properties of those
particles of contagious matter, so as to produce a thousandfold of a
similar material. See Sect. XXXIII. 2. 6. Other instances are mentioned in
the Section on Generation, which shew the probability that the extremities
of the seminal glands may imitate certain ideas of the mind, or actions of
the organs of sense, and thus occasion the male or female se