Produced by Simon Gardner, Bryan Ness and the Online
Distributed Proofreading Team at http://www.pgdp.net (This
book was produced from scanned images of public domain
material from the Google Print project.)





Transcriber's Notes

In this Plain Text version, unicode characters are used: α[alpha],
β[beta], γ[gamma], λ[lambda], ν[nu], π[pi] & υ[upsilon], ♂[male],
♀[female] and ⇆ [left arrow over right arrow].

Italic typeface has been represented by the use of _underscores_. Small
capital typeface has been represented by the use of ALL CAPITALS.

Superscript characters are indicated by caret and braces, e.g. 10^{-8}
("ten to the power of minus eight"). Subscript characters are indicated
by underscore and braces, e.g. H_{2}O.

Uncommon forms for chemical names have been retained where they occur in
the text, e.g. "atropin" for "atropine"; "asparagin" for "asparagine",
etc. The spellings of "Sidot blend" and "Sidot blende" are used
interchangeably in the text.

Some inconsistencies in formatting and punctuation have been retained
from the original. "PH" or P_{H} (P subscript H) is retained as used in
the text for the scale of alkali-acidity where the more familiar modern
usage is "pH". Molar concentrations are indicated in various ways (lower
case m, italic lower case m, small capital M).

Changes to the text have been made only in the case of obvious spelling
or type-setting errors. These are listed at the end of the book.

       *       *       *       *       *


             MONOGRAPHS ON EXPERIMENTAL BIOLOGY

                         EDITED BY

            JACQUES LOEB, Rockefeller Institute
             T. H. MORGAN, Columbia University
           W. J. V. OSTERHOUT, Harvard University




THE NATURE OF ANIMAL LIGHT

BY

E. NEWTON HARVEY, Ph.D.

       *       *       *       *       *

_MONOGRAPHS ON EXPERIMENTAL BIOLOGY_


PUBLISHED

    FORCED MOVEMENTS, TROPISMS, AND ANIMAL CONDUCT
    By JACQUES LOEB, Rockefeller Institute

    THE ELEMENTARY NERVOUS SYSTEM
    By G. H. PARKER, Harvard University

    THE PHYSICAL BASIS OF HEREDITY
    By T. H. MORGAN, Columbia University

    INBREEDING AND OUTBREEDING: THEIR GENETIC AND SOCIOLOGICAL
    SIGNIFICANCE
    By E. M. EAST and D. F. JONES, Bussey Institution, Harvard
    University

    THE NATURE OF ANIMAL LIGHT
    By E. N. HARVEY, Princeton University

IN PREPARATION

    PURE LINE INHERITANCE
    By H. S. JENNINGS, Johns Hopkins University

    THE EXPERIMENTAL MODIFICATION OF THE PROCESS OF INHERITANCE
    By R. PEARL, Johns Hopkins University

    LOCALIZATION OF MORPHOGENETIC SUBSTANCES IN THE EGG
    By E. G. CONKLIN, Princeton University

    TISSUE CULTURE
    By R. G. HARRISON, Yale University

    PERMEABILITY AND ELECTRICAL CONDUCTIVITY OF LIVING TISSUE
    By W. J. V. OSTERHOUT, Harvard University

    THE EQUILIBRIUM BETWEEN ACIDS AND BASES IN ORGANISM AND ENVIRONMENT
    By L. J. HENDERSON, Harvard University

    CHEMICAL BASIS OF GROWTH
    By T. B. ROBERTSON, University of Toronto

    COÖRDINATION IN LOCOMOTION
    By A. R. MOORE, Rutgers College

OTHERS WILL FOLLOW

       *       *       *       *       *

Monographs on Experimental Biology




                 THE NATURE OF ANIMAL LIGHT

                             BY

                  E. NEWTON HARVEY, Ph.D.

        PROFESSOR OF PHYSIOLOGY, PRINCETON UNIVERSITY

[Illustration]

                  PHILADELPHIA AND LONDON
                 J. B. LIPPINCOTT COMPANY



        COPYRIGHT, 1920. BY J. B. LIPPINCOTT COMPANY

  _Electrotyped and Printed by J. B. Lippincott Company.
  The Washington Square Press, Philadelphia, U. S. A._




EDITORS' ANNOUNCEMENT


The rapid increase of specialization makes it impossible for one author
to cover satisfactorily the whole field of modern Biology. This
situation, which exists in all the sciences, has induced English authors
to issue series of monographs in Biochemistry, Physiology, and Physics.
A number of American biologists have decided to provide the same
opportunity for the study of Experimental Biology.

Biology, which not long ago was purely descriptive and speculative, has
begun to adopt the methods of the exact sciences, recognizing that for
permanent progress not only experiments are required but quantitative
experiments. It will be the purpose of this series of monographs to
emphasize and further as much as possible this development of Biology.

Experimental Biology and General Physiology are one and the same
science, in method as well as content, since both aim at explaining life
from the physico-chemical constitution of living matter. The series of
monographs on Experimental Biology will therefore include the field of
traditional General Physiology.

  JACQUES LOEB,
  T. H. MORGAN,
  W. J. V. OSTERHOUT.




PREFACE


Bioluminescence, the production of light by animals and plants, has
always excited the admiration of the layman and the wonder of the
scientist. It is not surprising that an enormous literature dealing with
the subject has grown up. A large part of this literature, however, is
made up merely of reports that a certain animal is luminous, or records
of especially brilliant phosphorescence of the sea. Among those who have
inquired somewhat more carefully into the nature and causes of light
production may be mentioned the names of Beijerinck, R. Boyle, Dahlgren,
Dubois, Ehrenberg, Krukenberg, Mangold, McDermott, Molisch, Panceri,
Pflüger, Phipson, Quatrefages, Spallanzani, and Trojan. Several of these
men have written comprehensive monographs on the subject.

It is not the purpose of this book to deal with every phase of
bioluminescence. Volumes could be written on the evolutionary side of
the problem and the structure and uses of luminous organs. These
questions can only be touched upon. Neither is it my purpose to discuss
the ultimate cause of the light, whether due to vibration of electrons
or to other causes. That problem must be left to the physicist, although
it is highly probable that a study of animal light will give important
information regarding the nature of light in general, and no theory of
light can be adequate which fails to take into account the extraordinary
powers of luminous animals.

We shall be concerned largely with the physical characteristics of
animal light and the chemical processes underlying its production.
Great advances have been made since the first early guesses that the
light was due to phosphorus and was a kind of oxidation. Although the
problem cannot be considered as solved, it has been placed on a sound
physico-chemical basis. Some material is oxidized. Exactly what this
material is and why light accompanies its oxidation are the two more
fundamental problems in the field of Bioluminescence. How far and with
what success we have progressed toward a solution of these problems may
be seen from a perusal of the following pages.

It gives me pleasure to acknowledge the kindness of Dr. W. E. Forsythe
of the Nela Institute, Cleveland, Ohio, in reading and criticizing the
manuscript of Chapter III, and of Professor Lyman of Harvard University
for a similar review of Chapter II. I am also deeply indebted to my wife
for reading the proof and to Dr. Jacques Loeb and Prof. W. J. V.
Osterhout for many suggestions throughout the book. My thanks are also
due to Prof. C. Ishikawa of the Agricultural College, Imperial
University of Tokio, Japan, for his generous assistance in providing
_Cypridina_ material. Finally I wish to acknowledge the support of the
Carnegie Institution of Washington, through its director of Marine
Biology, Dr. Alfred G. Mayor. Without this support much of the work
described in this book could not have been accomplished.

  E. N. H.

  PRINCETON, N. J.,
    October, 1919.




CONTENTS


  CHAPTER                                                          PAGE

  I. LIGHT-PRODUCING ORGANISMS                                        1

  Early records and theories. "Shining fish and flesh." "Burning
  of the sea." Distribution of luminous organisms in plant
  and animal kingdoms. Secondary luminosity. False luminosity.
  St. Elmo's fire. Ignis fatuus. Flashing of flowers.
  Luminosity in man. Use to man of photogenic organisms.


  II. LUMINESCENCE AND INCANDESCENCE                                 20

  The complete spectrum. Radiation and temperature. "Cold
  light." Thermoluminescence. Phosphorescence and fluorescence.
  Triboluminescence and piezoluminescence. Crystalloluminescence.
  Chemiluminescence.


  III. PHYSICAL NATURE OF ANIMAL LIGHT                               40

  Purkinje phenomenon. Color and spectra of animal light.
  Polarization. Efficiency of animal light. Infra-red radiation.
  Ultra-violet radiation. Luminous efficiency and visual sensibility.
  Production of radiation penetrating opaque objects.
  Intensity of animal light. Summary.


  IV. STRUCTURE OF LUMINOUS ORGANS                                   67

  Photochemical and chemiphotic changes. The eye and the
  luminous organ. Intracellular and extracellular luminescence.
  Continuous and intermittent luminescence. Periodicity of
  luminescence. Luminous bacteria. _Noctiluca_ and photogenic
  granules. _Chætopterus_ and luminous gland cells. _Cypridina._
  Luminous glands. The firefly. Luminous organs (photophores)
  with lenses, reflectors, opaque and color screens. Uses and
  purpose of animal light.


  V. THE CHEMISTRY OF LIGHT PRODUCTION, PART I                       85

  Boyle's and Spallanzani's experiments. Shining wood and burning
  coal. Oxygen and luminescence. Carbon dioxide and
  luminescence. Heat production during luminescence. Luminescence
  and respiration. Water and luminescence. Phipson's
  noctilucin. Luciferin and luciferase. Photogenin and photophelein.
  Proluciferin. Oxyluciferin. Pyrophorin or luciferescein.
  Chemiluminescent reactions. "Biozymoöxyluminescence."


  VI. THE CHEMISTRY OF LIGHT PRODUCTION, PART II                    114

  _Pyrophorus_ luciferin and luciferase. _Pholas_ luciferin and
  luciferase. _Cypridina_ luciferin; stability, hydrolysis by acid
  and enzymes, adsorption, precipitation, salting out, solubility,
  distribution. _Cypridina_ luciferin a proteose? _Cypridina_
  luciferase and properties. _Cypridina_ luciferase an albumin.
  Specificity of luciferase. Action of fat solvent anæsthetics.
  Action of cyanides. Oxyluciferin. Nature of oxidative reaction.


  VII. DYNAMICS OF LUMINESCENCE                                     143

  Minute amounts of material for luminescence. Reaction velocity
  and chemiluminescence. Temperature and chemiluminescence.
  Oxidation in steps. Concentration and bioluminescence. Temperature
  and bioluminescence. Oxidation with and without
  luciferase. Reaction velocity and color of bioluminescence.

       *       *       *       *       *

THE NATURE OF ANIMAL LIGHT




CHAPTER I

LIGHT-PRODUCING ORGANISMS


The fact that animals can produce light must have been recognized from
the earliest times in countries where fireflies and glowworms abound,
but it is only since the perfection of the microscope that the
phosphorescence of the sea, the light of damp wood and of dead fish and
flesh has been proved to be due to living organisms. Aristotle mentions
the light of dead fish and flesh and both Aristotle and Pliny that of
damp wood. Robert Boyle in 1667 made many experiments to show that the
light from all three sources, as well as that of the glowworm, is
dependent upon a plentiful supply of air and drew an interesting
comparison between the light of shining wood and that of a glowing coal.
Boyle had no means of finding out the true cause of the light and early
views of its nature were indeed fantastic. Even as late as 1800 Hulme
concludes from his experiments on phosphorescent fish that the light is
a "constituent principle of marine fishes" and the "first that escapes
after the death of the fish." It was only in 1830 that Michaelis
suspected the light of dead fish to be the result of some living thing
and in 1854 Heller gave the name _Sarcina noctiluca_ to the suspected
organism. In 1875 Pflüger showed that nutrient media could be inoculated
with small amounts of luminous fish and that these would increase in
size, like bacterial colonies, and we now know that the light of all
dead fish and flesh is due to luminous bacteria.

In the early part of the nineteenth century it was surmised that the
light of damp wood was connected with fungus growth because of a
similarity in smell. In 1854 Heller recognized minute strands, which he
called _Rhizomorpha noctiluca_, as the actual source of the light. We
now know that all phosphorescent wood is due to the mycelium of various
kinds of fungi and that sometimes the fruiting body of the fungus also
produces light.

The phosphorescence or "burning of the sea," which is described by so
many of the older explorers, is also due entirely to living organisms,
both microscopic and macroscopic. The latter are mostly jelly-fish
(_medusæ_) or comb jellies (_Ctenophores_) and give rise to the larger,
more brilliant flashes of light often seen in the wake or about the
sides of a steamer at night. The former are various species of
dinoflagellates or cystoflagellates such as _Noctiluca_ (just visible to
the naked eye) which collect at the surface of the sea and often
increase in such numbers that the water is colored by day (usually pink
or red) and shines like a sheet of fire when disturbed at night.
Although _Noctiluca_ was recognized as a luminous animal in 1753 by
Baker, the light of the sea was a mysterious phenomenon to the older
observers. MacCartney, speaking before the Royal Society in 1810,
outlines the various older theories as follows: "Many writers have
ascribed the light of the sea to other causes than luminous animals.
Martin supposed it to be occasioned by putrefaction; Silberschlag
believed it to be phosphoric; Prof. J. Mayer conjectured that the
surface of the sea imbibed light, which it afterwards discharged. Bajon
and Gentil thought the light of the sea was electric, because it was
excited by friction.... I shall not trespass on the time of the Society
to refute the above speculations; their authors have left them
unsupported by either arguments or experiments, and they are
inconsistent with all ascertained facts upon the subject. The remarkable
property of emitting light during life is only met amongst animals of
the four last classes of modern naturalists, viz., mollusca, insects,
worms, and zoöphytes." MacCartney recognized the true cause of the
light, although he had little idea of the vast number of marine forms
which are luminous and omits entirely any reference to the fishes, many
of which produce a light of their own when living, apart from any
bacterial infection.

A survey of the animal kingdom discloses at least 36 orders containing
one or more forms known to produce light and several more orders
containing species whose luminosity is doubtful. In the plant kingdom
there are two groups containing luminous forms. The distribution of
luminous organisms is brought out in the accompanying classification of
plants and animals. Those orders are printed in italics which contain
species whose self-luminosity is fairly well established. It will be
noted that further subdivisions into orders is not given in classes of
animals which lack luminous forms.


TABLE I

_DISTRIBUTION OF LUMINOUS ORGANISMS IN PLANT AND ANIMAL KINGDOMS_

  PLANT KINGDOM

  I. _Thallophyta_
    Algæ
      Cyanophyceæ (Blue-green Algæ)
      Chlorophyceæ (Green Algæ)
      Phæophyceæ (Brown Algæ)
      Rhodophyceæ (Red Algæ)
    Lichenes (Lichens, symbiotic growth of algæ and fungi)
    _Fungi_
      Myxomycetes (Slime moulds)
      _Schizomycetes_ (Bacteria)
        _Bacterium_, _Photobacterium_, _Bacillus_, Pseudomonas_,
          _Micrococcus_, _Microspira_, _Vibrio_.
      Phycomycetes (moulds)
      Ascomycetes (Sac fungi, yeasts, some moulds)
      _Basidiomycetes_ (Smuts, rusts, mushrooms)
        Ustilaginæ (Smuts)
        Uridineæ
        Auriculariæ (Judas ears)
        Tremellineæ (Jelly fungi)
        _Hymenomycetes_ (Mushrooms)
          _Agaricus_, _Armillaria_, _Pleurotus_, _Panus_, _Mycena_,
            _Omphalia_,
            _Locellina_, _Marasinium_, _Clitocybe_, _Corticium_.
        Gasteromycetes (Stinkhorns and puff-balls)

  II. Bryophyta
    Hepaticæ (Liverworts)
    Musci (Mosses)

  III. Pteridophyta
    Equisetineæ (Horsetails)
    Salviniæ (Salvinia, Marsilia, etc.)
    Lycopodineæ (Club Mosses)
    Filicineæ (Ferns)

  IV. Spermatophyta
    Gymnospermæ (Cycads, Ginkgo, Conifers)
    Angiospermæ (Mono- and Dicotyledonous flowering plants).

  ANIMAL KINGDOM

  I. _Protozoa._ (One-celled animals)
    _Sarcodina_
      Rhizopoda
      Heliozoa
      _Radiolaria_
        _Thallassicola_, _Myxosphæra_, _Collosphæra_, _Collozoum_,
          _Sphærozoum_.
    _Mastigophora_
      Flagellata
      Choanoflagellata
      _Dinoflagellata_
        _Ceratium_, _Peridinium_, _Prorocentrum_, _Pyrodinium_,
          _Gonyaulax_, _Blepharocysta_, _Amphidinium_, _Diplopsalis_,
          _Cochlodinium_, _Sphærodinium_, _Gymnodinium._
      _Cystoflagellata_
        _Noctiluca_, _Pyrocystis_, _Leptodiscus_, _Craspedotella._
    Sporozoa
    Infusoria

  II. Porifera (Sponges)
    Calcarea
    Hexactinellida
    Desmospongiæ

  III. _C[oe]lenterata_
    _Hydrozoa_ (Hydroids and Jelly-fish)
      _Leptomedusæ_ or _Campanulariæ_
        Medusa form--_Eutima_, _Phyalidium_ (_Oceania_).
        Hydroid form--_Aglaophenia_, _Campanularia_, _Sertularia_,
                      _Plumularia_,
          _Cellularia_, _Valkeria_, _Obelia_, _Clytia_.
      _Trachomedusæ_
        _Geryonia_, _Lyriope_, _Aglaura_
      _Narcomedusæ_
        _Cunina_
      _Anthomedusæ_ or _Tubulariæ_
        Medusa form--_Thaumantias_, _Tiara_, _Turris_, _Sarsia_.
        Hydroid form--?
      Hydrocorallinæ
      _Siphonophora_
        _Abyla_, _Praya_, _Diphyes_, _Eudoxia_, _Hippopodius._
    _Scyphozoa_ (Jelly-fish)
      Stauromedusæ
      Peromedusæ
      _Cubomedusæ_
        _Carybdia_
      _Discomedusæ_
        _Pelagia_, _Aurelia_, _Chrysaora_, _Rhizostoma_, _Cyanæa_,
          _Dianea_, _Mesonema_.
    _Actinozoa_ (Corals, Sea-fans, Sea-pens, Sea-anemones)
      Actinaria
      Madreporareia
      Antipatharia
      _Alcyonaria_
        _Alcyonium_, _Gorgonia_, _Isis_, _Mopsea_
      _Pennatulacea_
        _Pennatula_, _Pteroides_, _Veretillum_, _Cavernularia._
        _Funicularia_, _Renilla_, _Pavonaria_, _Stylobelemon_,
          _Umbellularia_, _Virgularia?_
    _Ctenophora_ (Comb-jellies)
      _Cydippida_
        _Pleurobranchia_.
      _Lobata_
        _Mnemiopsis_, _Bolinopsis_, _Leucothea_ (_Eucharis_).
      _Cestida_
        _Cestus_.
      _Beroida_
        _Beroë._

  IV. Platyhelminthes
    Turbellaria (Flat-worms)
    Trematodes (Parasitic flat-worms)
    Cestodes (Tape-worms)
    Nemertinea (Nemertines)

  V. Nemathelminthes
    Nematoda (Round worms)
    Gordiacea (Hair worms)
    Acanthocephala (Acanthocephalids)
    Chætognatha (Sagitta)

  VI. Trochelminthes
    Rotifera (Wheel animalcules)
    Gastrotricha (Chætonotus)
    Kinorhyncha (Echinoderes)

  VII. _Molluscoidea_
    _Bryozoa_ (Corallines)
      Entoprocta
      _Ectoprocta_
        _Membranipora_, _Scrupocellaria_, _Retepora?_ _Flustra?_
      Brachiopoda (Lamp shells)
      Phoronidea (Phoronis)

  VIII. _Annulata_
      Archiannelida (Primitive worms, including Dinophilus)
      _Chætopoda_ (True worms)
        _Polychæta_
          _Chætopterus_, _Phyllochaetopterus_, _Telepsaris_, _Polynoë_,
            _Acholoë_, _Tomopteris_, _Odontosyllis_, _Lepidonotus_,
            _Pionosyllis_, _Phyllodoce_, _Heterocirrus_, _Polyopthalamus?_
        _Oligochæta_
          _Lumbricus_, _Photodrilus_, _Allolobophora_ (_Eisemia_),
            _Microscolex_, _Nonlea_, _Enchytræus_, _Octochætus_.
      Gephyrea (Sipunculus)
      Hirudinea (Leeches)
      Myzostomida (Myzostomus)

  IX. _Echinodermata_
      Asteroidea (Star-fish)
      _Ophiuroidea_ (Brittle-stars)
        _Ophiurida_
          _Ophiopsila_, _Amphiura_, _Ophiacantha_, _Ophiothrix_,
            _Ophionereis_.
        Euryalida
      Echinoidea (Sea urchins)
      Holothuroidea (Sea Cucumbers)
      Crinoidea (Feather-stars)

  X. _Arthropoda_
      _Crustacea_ (Crabs, lobsters, shrimps, etc.)
        Phyllapoda
        _Ostracoda_
          _Halocypris_, _Cypridina_, _Pyrocypris_, _Conch[oe]cia_,
            _Cyclopina_.
        _Copepoda_
          _Metridia_, _Leuckartia_, _Pleuromma_, _Oncæa_, _Heterochæta_.
        Cirripedia
        Phyllocardia
        _Schizopoda_
          _Nyctiphanes_, _Nematoscelis_, _Gnathophausia_, _Euphausia_,
            _Stylochiron_, _Boreophausia_, _Mysis?_
        _Decapoda_
          _Sergestes_, _Aristeus_, _Heterocarpus_, _Hoplophorus_,
            _Acanthephyra_, _Pentacheles_, _Colossendeis_
        Stomatopoda
        Cumacea
        Amphipoda
        Isopoda
      Onychophora (Peripatus)
      _Myriapoda_ (Centipedes and Millepedes)
        Symphyla
        _Chilopoda_
          _Geophilus_, _Scolioplanes_, _Orya_.
        Diplopoda
        Pauropoda
      _Insecta_ (Insects)
        _Aptera_ (Spring-tails)
          _Lipura_, _Amphorura_, _Neanura_
        Orthoptera
        _Neuroptera_
          _Teleganoides and Cænis_ of the Mayflies? _Termites?_
        Hemiptera
        _Diptera_ (Flies)
          _Bolitophila_ and _Ceroplatus_ larvæ, _Thyreophora?_
        _Coleoptera_ (Beetles)
          _Pyrophorus_, _Photophorus_, _Luciola_, _Lampyris_, _Phengodes_,
            _Photuris_, _Photinus_, etc.
        Lepidoptera
        Hymenoptera
      Arachnida (Spiders)

  XI. _Mollusca_
      Amphineura (Chiton)
      _Pelecypoda_ (Bivalves)
        Protobranchia
        Filibranchia
        Pseudo-Lamellibranchia
        _Eu-lamellibranchia_
          _Pholas_
        Septibranchiata
      _Gasteropoda_ (Snails, periwinkles, slugs, etc.)
        Prosobranchiata
        _Ophisthobranchiata_
          _Phyllirrhoë_, _Plocamopherus_.
        Pulmonata
      Scaphopoda (Dentalium)
      _Cephalopoda_ (Squids and Octopus)
        Tetrabranchiata
        _Dibranchiata decapoda_
          _Onychoteuthis_, _Chaunoteuthis_, _Lycoteuthis_, _Nematolampas_,
            _Lampadioteuthis_, _Enoploteuthis_, _Abralia_, _Abraliopsis_,
            _Watasenia_, _Ancistrocheirus_, _Thelidioteuthis_,
            _Pterygioteuthis_, _Pyroteuthis_, _Octopodoteuthis?_,
            _Calliteuthis_, _Histioteuthis_, _Benthoteuthis_,
            _Hyaloteuthis_, _Eucleoteuthis_, _Chiroteuthis_,
            _Mastigoteuthis_, _Cranchia_, _Liocranchia_, _Pyrgopsis_,
            _Leachia_, _Liguriella_, _Phasmatopsis_, _Toxeuma_,
            _Megalocranchia_, _Leucocranchia_, _Crystalloteuthis_,
            _Phasmatoteuthis_, _Galiteuthis_, _Corynomma_,
            _Hensenioteuthis_, _Bathothauma_, _Rossia?_, _Heteroteuthis_,
            _Iridoteuthis_, _Sepiola_, _Rondeletia_, _Inioteuthis_,
            _Euprymna_, _Melanoteuthis?_.

  XII. _Chordata_
      _Adelochorda_ (Balanoglossus)
        _Balanoglossus_, _Ptychodera_, _Glossobalanus_
      _Urochorda_ (Ascidians)
        _Larvacea_
          _Appendicularia?_
        _Thaliacea_
          _Salpa_, _Doliolum?_
        _Ascidiacea_
          _Pyrosoma_, _Phallusia_
      Acrania (Amphioxus)
      Cyclostomata (Cylostomes)
      _Pisces_ (Fishes)
        _Elasmobranchii_
          _Centroscyllium_, _Spinax_, _Paracentroscyllium_, _Isistius_,
            _Læmargus_, _Euproctomicrus_, _Benthobatis?_
        Holocephalii
        Dipnoi
        _Teleostomi_
          _Stomias_, _Chauliodus_, _Melanostomius_, _Pachystomias_,
            _Bathophilus_, _Dactylostomius_, _Malacosteus_, _Astronesthes_,
            _Ophozstomias_, _Idiacanthus_, _Bathylychnus_, _Macrostomius_,
            _Gonostoma_, _Cyclothone_, _Photichthys_, _Vinciguerria_,
            _Ichthyococcus_, _Lychnopoles_, _Diplophos_, _Triplophos_,
            _Valenciennellus_, _Maurolicus_, _Argyropelecus_, _Sternoptyx_,
            _Polyipnus_, _Ipnops? Neoscopelus_, _Myctophum_, _Halosausus_,
            _Xenodermichthys? Macrurus? Photoblepharon_, _Anomalops_,
            _Porichthys_, _Leuciocornus_, _Mixonus? Bassozetus? Oneirodes_,
            _Ceratias_, _Gigantactis_, _Chaunax_, _Malthopsis_,
            _Halicmetus_, _Monocentris_, _Lamprogrammus._
      Amphibia (Frogs, Toads, Salamanders)
      Reptilia (Snakes, Lizards, Turtles)
      Aves (Birds)
      Mammalia (Mammals)

The only groups of the plant kingdom which are known to produce light
are some of the bacteria and some of the fungi and the dinoflagellates
(_Peridineæ_) if one is to include them among the plants. Many different
species of phosphorescent bacteria have been described, differing in
cultural characteristics and structural peculiarities and grouped in the
genera, _Bacterium_, _Photobacterium_, _Bacillus_, _Microspira_,
_Pseudomonas_, _Micrococcus_, and _Vibrio_. Specific names indicating
their light-producing power such as _phosphorescens_, _phosphoreum_,
_luminosum_, _lucifera_, etc., have been applied.

All the fungi which are definitely known to produce light belong to the
_Basidiomycetes_, the largest and most highly developed of the true
fungi. Either the mycelium alone or the fruiting body alone, or both,
may be luminescent.

Among animals the best known forms are the dinoflagellates; _Noctiluca_;
hydroids; jelly-fish; ctenophores; sea pens; _Chætopterus_ and other
marine worms; earthworms; brittle stars; various crustaceans; myriapods;
fireflies and glowworms, the larvæ of fireflies; _Pholas dactylus_ and
_Phyllirrhoë bucephala_, both molluscs; squid; _Pyrosoma_, a colonial
ascidian; and fishes.

Luminous animals are all either marine or terrestrial forms. No examples
of fresh water luminous organisms are known. Of marine forms, the great
majority are deep sea animals, and it is among these that the
development of true luminous organs of a complicated nature is most
pronounced. Many of the luminous marine animals are to be found in the
plankton, while the littoral luminous forms are in the minority. Some
members of all the above groups are found at one or another of our
marine laboratories with the possible exception of _Pholas_,
_Phyllirrhoë_ and squid. Although earthworms and myriapods which produce
light are found in the United States, they are rather rare and seldom
observed forms.

Not only adult forms but the embryos and even the eggs of some animals
are luminous. The egg of _Lampyris_ emits light within the ovary and
freshly laid eggs are quite luminous. The light does not come from
luminous material of the luminous organ adhering to the egg when it is
laid but from within the egg itself. _Pyrophorus_ eggs are also
luminous. The segmentation stages of _Ctenophores_ are luminous on
stimulation, as noted by Allman (1862), Agassiz (1874) and Peters
(1905), but the eggs themselves do not luminesce. _Schizopod larvæ_
(Trojan, 1907), _Copepod nauplii_ (Giesbrecht, 1895), _Chætopterus
larvæ_ (Enders, 1909), and brittle star _plutei_ (Mangold, 1907) also
produce light.

Apparently there is no rhyme or reason in the distribution of
luminescence throughout the plant or animal kingdom. It is as if the
various groups had been written on a blackboard and a handful of sand
cast over the names. Where each grain of sand strikes, a luminous
species appears. The _C[oe]lenterates_ have received most sand.
Luminescence is more widespread in this phylum and more characteristic
of the group as a whole than any other. Among the arthropods luminous
forms crop up here and there in widely unrelated groups. In the
mollusks, excluding the cephalopods, only two luminous species are
known. Several _phyla_ contain no luminous forms whatever. It is an
extraordinary fact that one species in a genus may be luminous and
another closely allied species contain no trace of luminosity. There
seems to have been no development of luminosity along direct
evolutionary lines, although a more or less definite series of
gradations with increasing structural complexity may be traced out among
the forms with highly developed luminous organs.

While the accompanying list of luminous genera aims to be fairly
complete, there are no doubt omissions and some inaccuracies in it.
Anyone who has ever tried to determine what animal is responsible for
the occasional flashes of light observed on agitating almost any sample
of sea water will realize how difficult it is to discover the luminous
form among a host of non-luminous ones, especially if the animal is
microscopic in size. It is not surprising, then, to find many false
reports of luminous animals in the literature of the subject and we
cannot be too careful in accepting as luminous a reported case. The
difficulty lies chiefly in the fact that all luminous organisms with the
exception of bacteria, fungi, and a few fish, flash only on stimulation,
and, while it is easy enough to see the flash, the animal is lost
between the flashes. The only safe way to detect luminous organisms is
to add a little ammonia to the sea water. This slowly kills the
organisms and causes any luminous forms to glow with a steady,
continuous light for some time, a condition accompanying the death of
the animal. Not all observers, however, have followed this method. One
must always be on guard against confusing the light from a supposed
luminous form with the light from truly luminous organisms living upon
it. The reported cases of luminosity among marine algæ are now known to
be due to hydroids or unicellular organisms living on the alga.

We know also that many non-luminous forms may become infected with
luminous bacteria, not only after death, but also while living, so that
their luminescence is purely secondary. Giard and Billet (1889-90)
succeeded in inoculating many different kinds of amphipod crustacea
(_Talitrus_, _Orchestia_, _Ligia_) and isopod crustacea (_Porcellio_,
_Philoscia_) with luminous bacteria, in some cases passing the infection
from one to the next through nine individuals. Curiously enough the
bacterium did not produce light on artificial culture media but did when
growing in the body of the crustacea, which were killed in about seven
days by the infection. The species of _Talitrus_ and _Orchestia_ might
easily have been taken for truly luminous animals if not carefully
investigated.

Tarchanoff (1901) has injected luminous bacteria into the dorsal lymph
sac of frogs with the result that the animals continued to glow for
three to four days, especially about the tongue. I remember once while
collecting luminous beetles in Cuba, I was astounded to find a frog
which was luminous. Expecting this animal to be of great interest, I
examined it further only to find that the frog had just finished a
hearty meal of fireflies, whose light was shining through the belly with
considerable intensity.

Infection with luminous bacteria is especially liable to occur in any
dead marine animal. The flesh is an excellent culture medium. I have
seen non-luminous species of squid, recently killed, covered with minute
growing colonies, quite evenly spaced, so as to closely resemble
luminous species whose light is restricted to scattered light organs
over the surface of the body.

Indeed Pierantoni (1918) has carried this idea to extremes. He believes
that in the luminous organs of fireflies, cephalopods and _Pyrosoma_,
luminous symbiotic bacteria occur which are responsible for the light
of these animals, and he claims in the case of cephalopods and
_Pyrosoma_ to have been able to isolate these in pure culture on
artificial culture media. In the firefly they can be seen but not grown
and in luminous animals where no visible bacteria-like structures are
apparent he believes we are dealing with ultra-microscopic luminous
bacteria similar to the pathogenic forms suspected in filterable
viruses. While the assumption of ultra-microscopic organisms makes the
refutation of Pierantoni's views a somewhat hazardous task, no one can
deny that even an ultra-microscopic organism will be killed by boiling
with 20 per cent. (by wt.) HCl for 6 hours. As we shall see, the
luminous material of _Cypridina_, an ostracod crustacean, can withstand
such prolonged boiling with strong acid. The light of one animal at
least, and I believe many others also, cannot be due to any sort of
symbiotic organism.

Apart from these cases where light is actually produced but is not
primary, not produced by the animal itself, there are many forms whose
surface is so constituted as to produce interference colors. This is
true in many cases among the birds and butterflies whose feathers and
scales are iridescent. Some of these have been erroneously described as
luminous. Perhaps the best known case among aquatic animals is
_Sapphirina_, a marine copepod living at the surface of the sea, and
especially likely to be collected with other luminous forms. Its cuticle
is so ruled with fine lines as to diffract the light and flash on moving
much as a fire opal. Needless to say no trace of light is given off from
this animal in a totally dark room.

It has often been supposed that the eye of a cat or of other animals is
luminous. The eyes of a moth, also, can be seen to glow like beads of
fire when it is flying about a flame. Both of these cases are, however,
purely reflection phenomena and due to reflection out of the eye again
of light which has entered from some external source. The correct
explanation was given by Prevost in 1810. The eye of any animal is quite
invisible in absolute darkness. The same explanation applies to the
moss, _Schistostega_, which lives in dimly illuminated places and whose
cells are almost spherical, constructed like a lens, so as to refract
the light and condense it on the chloroplasts at the bottom of the
cells. Some of this light is reflected out of the cells again and gives
the appearance of self-luminosity. The alga, _Chromophyton rosanoffii_,
is another example of apparent luminosity, due to reflection from almost
spherical cells.

There are several light phenomena known which have nothing to do with
living organisms. Commonest of these is St. Elmo's fire ("corposants" of
English sailors), a glow accompanying a slow brush discharge of
electricity, which appears as a tip of light on masts of ships, spires
of churches or even the fingers of the hand. It is best seen in winter
during and after snowstorms and is a purely electrical phenomenon.

Less well known is the _Ignis fatuus_ (Will-o'-the-Wisp,
Jack-o'-Lantern, spunkie), a fire seen over marshes and stagnant pools,
appearing as a pale bluish flame which may be fixed or move, steady or
intermittent. So uncommon is this phenomenon that its nature is not well
understood, but it is believed to be the result of burning _phosphine_
(PH_{3} + P_{2}H_{4}), a self-inflammable gas, generated in some way
from the decomposition of organic matter in the swamp. The difficulty
with this explanation is that phosphine is not known as a decomposition
product of organized matter. Methane (CH_{4}), a well-known
decomposition product of organic matter and abundantly formed in swamps,
will burn with a pale bluish flame and some have thought the _Ignis
fatuus_ to be the result of this gas. As methane is not self-inflammable
there remains the difficulty of explaining how it becomes lighted.
Although still a mystery, it is possible that this light is also of
electrical origin or that in some cases large clusters of luminous fungi
have been observed.

The flashing of flowers, especially those of a red or orange color, like
the poppy, which many observers have noticed during twilight hours, is a
purely subjective phenomenon due to the formation of after images in
eyes partially adapted to the dark. This flashing, first observed by the
daughter of Linnæus, is never observed in total darkness or in the
direct field of vision, but only in the indirect field as during a
sidelong glance at the plant.

There are some cases of luminosity on record in connection with man
himself. (See Heller, 1854). Before the days of aseptic and antiseptic
surgery, wounds frequently became infected with luminous bacteria and
glowed at night. The older surgeons even supposed that luminous wounds
were more apt to heal properly than non-luminous ones. We know that
luminous bacteria are non-pathogenic, harmless organisms and the
presence of these forms even on dead fish or flesh never accompanies but
always precedes putrefaction. As recorded by Robert Boyle, no harm has
come from eating luminous meat, unless it may also have become infected
with pathogenic forms.

A few cases of luminous individuals have been noted in which the skin
was the source of light, especially if the person sweated freely. It is
possible that here we are again dealing with luminous bacteria upon the
accumulations of substances passed out in the sweat, which serves as a
nutrient medium.

There are also on record, in the older literature, cases of luminous
urine, where the urine when freshly voided was luminous. If these
observations are correct and they may, perhaps, be doubted, we are at
present uncertain of the cause of the light. Bacterial infections of the
bladder are not inconceivable although luminous bacteria are strongly
aerobic and would not thrive under anaerobic conditions. I can state
from my own experiments that luminous bacteria will live in normal human
urine, but not well. In albuminous urines it is very likely that they
would live better, and it is possible that the luminous urines reported
are the results of luminous bacterial infection. On the other hand, the
light may be purely chemical, due to the oxidation of some compound, an
abnormal incompletely oxidized product of metabolism, which oxidizes
spontaneously in the air. We know that sometimes these errors in
metabolism occur, as in _alkaptonuria_, where homogentistic acid is
excreted in the urine and on contact with the air quickly oxidizes to a
dark brown substance. Light, however, has never been reported to
accompany the oxidation of homogentistic acid, although it does
accompany the oxidation of some other organic compounds. (See Chapter
II.)

Finally, we may inquire to what extent luminous animals may be utilized
by man. Leaving out of account the use of tropical fireflies for
adornment by the natives of the West Indies and South America and the
use for bait, in fishing, of the luminous organ of a fish,
_Photoblepharon_, by the Banda islanders, we find that luminous bacteria
are of value for certain purposes in the laboratory.

These methods are all due to Beijerinck (1889, 1902). He has, for
instance, used luminous bacteria for testing bacterial filters. If there
is a crack in the filter the bacteria will pass through and a luminous
filtrate is the result, but a perfect filter allows no organisms to pass
and gives a dark filtrate.

Luminous bacteria are also very sensitive to oxygen and cease to
luminesce in its absence. By mixing luminous bacteria with an emulsion
of chloroplasts (from clover leaves) in the dark, allowing the bacteria
to use up all the oxygen, and then exposing the mixture to light of
various colors, the effect of different wave-lengths in causing
photosynthesis could be studied. Only if the chloroplasts are exposed to
a color in the spectrum which decomposes CO_{2} with liberation of
oxygen do the bacteria luminesce, and when this oxygen is used up by the
bacteria, the tube again becomes dark. Beijerinck has also worked out a
method of testing for maltose and diastase with luminous bacteria, based
on the fact that a certain form, _Photobacterium phosphorescens_, will
only produce light in presence of maltose or diastase which will form
maltose from starch.

Although Dubois and Molisch have both prepared "bacterial lamps" and
although it has been suggested that this method of illumination might be
of value in powder magazines where any sort of flame is too dangerous,
it seems doubtful, to say the least, whether luminous bacteria can ever
be used for illumination. Other forms, perhaps, might be utilized, but
bacteria produce too weak a light for any practical purposes. The
history of Science teaches that it is well never to say that anything is
impossible. It is very unlikely that any luminous animal can be utilized
for practical illumination, but there is no reason why we cannot learn
the method of the firefly. Then we may, perhaps, go one step further and
develop a really efficient light along similar lines. To what extent our
inquiry into the "secret of the firefly" has been successful may be
gleaned from the following pages.




CHAPTER II

LUMINESCENCE AND INCANDESCENCE


Modern physical theory supposes that light is a succession of wave pulses
in the ether caused by vibrating electrons. The light to which we are
most accustomed--sunlight, electric light, gaslight, etc.,--is due to
electrical phenomena connected more or less directly with the high
temperature of the source of the light. Every solid body above the
temperature of absolute zero is giving off waves of different wave-length
(λ) and frequency (ν) but of the same velocity (υ), in vacuo, 180,000
miles, or 300,000 kilometres a second. In fact, υ (a constant)=λ_{ν}, so
that it is only necessary to designate the wave-length in order to
characterize the waves. This is radiant energy or radiant flux.

As everyone knows, the long waves given off in largest amount from
objects at comparatively low temperatures give the sensation of warmth.
As we raise the temperature, in addition to these longer heat waves,
those of shorter and shorter wave-length are given off in sufficient
quantity to be detected. At 525° C., rays of about λ=.76µ in length are
just visible as a faint red glow to the eye. As the temperature increases
still shorter wave-lengths become apparent, and the light changes to dark
red (700°), cherry red (900°), dark yellow (1100°), bright yellow
(1200°), white-hot (1300°) and blue-white (1400° and above). Above λ=.4µ
the waves again fail to affect our eye, and, although they are very
active in producing chemical changes, we have no sense organs for
perceiving them. Thus, a white-hot object liberates radiant energy or
flux of many different wave-lengths corresponding to what we know as
"heat, light and actinic rays." All can be dispersed by prisms of one or
another appropriate material to form a wide continuous spectrum, such as
that indicated in Fig. 1. Radiant energy of λ=.76µ to λ=.4µ, evaluated
according to its capacity to produce the sensation of light, is spoken of
as visible radiation or luminous flux.

Below the infra-red comes a region of wave-length as yet uninvestigated,
and beyond this may be placed the Hertzian electric waves of long
wave-length used in wireless telegraphy. Above the ultra-violet comes
another region as yet uninvestigated, and then Röntgen rays (X-rays) and
radium rays, of exceedingly short wave-length. These last types need not
concern us except in that we may later inquire if they are given off by
luminous animals. The shortest of the ultra-violet are known as Schumann
and Lyman rays. These relations are brought out in Table 2.


TABLE 2.

_Wave-lengths of Various Kinds of Radiation_

Wave-lengths of light are usually given in Ångstrom units. One micron
(µ)=.001 mm.=1000 millimicrons (µµ)=10,000 Ångstrom units (Å) or tenth
metres=10^{-10} metres or 10^{-8} centimetres. The entire scale of
wave-lengths extends from 10^6 to 10^{-9} centimetres.

  Hertzian electric waves (upper limit not reached) above 12 km. to .16 cm.
  Unexplored region             .16 cm. to 310µ
  Infra-red                     310µ to .76µ
  Visible light                7600 Å to 4000 Å
  Ultra-violet                 4000 Å to 320 Å
  Unexplored region             320 Å to 12 Å
  X-rays                         12 Å to 0.2 Å
  Radium γ rays                 0.2 Å and shorter

[Illustration: FIG. 1.--Schematic representation of various types of
radiation to form a wide continuous spectrum.]

  .05Å  .2Å .8 3.2 12.8  50.  200.  800.    3200.        1.28µ
  --------+---------+------------+-------------+---------+-- ...
  RADIUM  |         |            |             |         |
  γ       | X RAYS  | UNEXPLORED | ULTRAVIOLET | VISIBLE |
  RAYS    |         |            |             |         |
  --------+---------+------------+-------------+---------+-- ...

                                 1.28µ 5.µ 20. 80. 320.    .128cm.  .5cm.
                           ... --+------------------+----------+---------
                                 |                  |          | HERTZIAN
                                 |  INFRA RED       |UNEXPLORED| ELECTRIC
                                 |                  |          | WAVES
                           ... --+------------------+----------+---------

The total radiant energy which a body emits is a function of its
temperature and for a perfect radiator, or what is known as a black body,
the total radiation varies as the fourth power of the absolute
temperature, T. (Stefan-Boltzmann Law). The radiant energy emitted at
different wave-lengths is not the same but more energy is emitted at one
particular wave-length (λ_{max.}) than at longer or shorter ones,
depending also on the temperature. If the various waves are intercepted
in some way, their relative energy can be measured by an appropriate
instrument and spectral energy curves can be drawn, showing the
distribution of energy throughout the spectrum. Fig. 2 gives a few of the
curves, and it will be noted that the maximum shifts toward the shorter
waves the higher the temperature. In fact, for a black body
λ_{max.}×T=2890, and at 5000° C. (about the temperature of the sun)
λ_{max.} lies within the visible spectrum. In gas or electric lights it
lies in the infra-red region. The area enclosed by these spectral energy
curves represents the total energy emitted, and, knowing this and the
area enclosed by the curve of visible radiation, it is easy to determine
how efficient a source of light is as a light-producing body. We shall
inquire more fully into this question in Chapter III, in considering the
efficiency of the firefly as a source of light.

[Illustration: FIG. 2.--Distribution of energy throughout the spectrum
of the sun, electric arc, and gas light (_after Nichols and Franklin_).
Ordinates show the relative intensities of different wave-lengths
emitted. The notches in the curve represent absorption bands and the
dotted line represents what the radiation from the sun would be if no
selective absorption occurred. V=violet and R=red end of visible
spectrum. (_Courtesy Macmillan Co._)]

A body which emits light because of its (high) temperature is said to be
incandescent and we speak of temperature radiation. We know, however, of
many cases where substances give off light at temperatures much below
525° C. They do not follow the Stefan-Boltzmann law. The light emission
is stimulated by some other means than heat. Such bodies we speak of as
_luminescent_, and in this category belong all luminous animals. The
distinction between light and luminescence was first pointed out by
Wiedemann (1888). It is usual to classify luminescences, according to
the means of exciting the light, into the following groups:

  Thermoluminescence
  Phosphorescence and Fluorescence
      Photoluminescence
      Cathodoluminescence
      Anodoluminescence
      Radioluminescence
  Triboluminescence and Piezoluminescence
  Crystalloluminescence
  Chemiluminescence

The luminescence which appears in a vacuum tube when an electric current
is passed through it is sometimes spoken of as _electroluminescence_. As
electroluminescence and also thermoluminescence are really special cases
of phosphorescence or fluorescence and tribo-and crystalloluminescence
are closely allied, the classification has only the merit of emphasizing
the means of producing light. Let us examine each kind in turn in order
that we may place the light of animals, _organoluminescence_ or
_bioluminescence_ (or _biophotogenesis_), in one of these classes. All
are examples of "cold light," light produced at temperature far below
those observed in incandescent solids. In this category should be placed
also the light from salts in the bunsen flame, for flame spectra and
line spectra in general, while only obtained at relatively high
temperatures, are not to be confused with the purely temperature
radiation from the incandescent particles of carbon in a gas or candle
light. The sodium or lithium flame, etc., is not a simple function of
temperature and has been spoken of as a luminescence,
_pyroluminescence_. As the luminescence of organisms could in no manner
be regarded as a pyroluminescence, occurring at temperatures far above
those compatible with life, a consideration of this form of luminescence
will be omitted. Some other low temperature flames are known, such as
that of CS_{2} in air, rich in ultra-violet rays, despite its relatively
low temperature. While these are of interest to the physicist and
chemist, they can have no direct bearing on the luminescence of animals
and their consideration will also be omitted. (See Bancroft and Weiser,
1914-1915.)

THERMOLUMINESCENCE.--Some substances begin to emit light of shorter
wave-length than red, well below 525°. This is thermoluminescence.
Diamond, marble, and fluorite are examples. Only certain varieties of
fluorite show the phenomenon well. A crystal of one of these varieties
heated in the bunsen flame on an iron spoon will give off a white light
long before any trace of redness appears in the iron. Other crystals may
luminesce in hot water. In all, this luminescence is dependent on a
previous illumination or radiation of the crystal. If kept in the dark
for a long time no trace of light appears when fluorite is placed at a
temperature of 100°, but after a short exposure to the light of an
incandescent bulb, although no light can be observed in the fluorite at
room temperature, quite a bright glow appears at 100°. Calcium, barium,
strontium, magnesium and other sulphates containing traces of manganese
sulphate, show a similar phenomenon after exposure to cathode rays
(Wiedemann and Schmidt, 1895 b). They emit light during bombardment, but
this soon ceases when the rays are cut off. If the sulphates are now
heated they give off light, red in the case of MgSO_{4} + MnSO_{4},
green in the case of CaSO_{4} + MnSO_{4}. The power to emit light on
heating may be retained for months after the exposure to cathode rays.
The emission of light by bodies after previous illumination or radiation
is called _phosphorescence_ and will be considered below. It would seem
that the cases of thermoluminescence with which we are acquainted are
really cases of phosphorescence intensified by rise of temperature. The
spectrum of thermoluminescent bodies, also, is similar to that of
phosphorescent ones. (See Fig. 3.) However, not all phosphorescent
materials are also thermoluminescent. The production of light by animals
is quite another phenomenon from thermoluminescence.

PHOSPHORESCENCE AND FLUORESCENCE.--Although the word phosphorescence has
been used in a very loose way to indicate all kinds of luminescence, and
particularly that of phosphorus or of luminous animals, to the physicist
it has a very definite meaning, namely, the absorption of radiant energy
by substances which afterwards give this off as light. Phosphorescence
does not strictly apply to the light of white phosphorus. If the radiant
energy is light (visible or ultra-violet) we speak of
_photoluminescence_, if cathode rays we have _cathodoluminescence_, if
anode rays, _anodoluminescence_, and if X-rays (Röntgen rays) we have
_radioluminescence_. Inasmuch as the α, β, and γ rays of radium
correspond to the anode, cathode, and X-rays, respectively, radium
radiation also produces luminescence in many kinds of material. If the
material gives off the light only during the time it is radiated we
speak of fluorescence; if the light persists we speak of
phosphorescence. The distinction is perhaps a purely arbitrary one, as
there are a great many substances which give off light for only a
fraction of a second (1/5000 sec. in some cases) after being illuminated
(_photoluminescence_). Some substances also, which fluoresce at ordinary
temperatures, will phosphoresce at low temperatures. Phosphorescence is
exhibited chiefly by solids, fluorescence also by liquids and vapors.

Special means must be used to observe a phosphorescence of short
duration. E. Becquerel has devised an apparatus for doing this, a
_phosphoroscope_. It consists of revolving disks with holes in them
between which the object to be examined is placed. The holes are so
arranged that the object is first illuminated and then completely cut
off from light. The observer looking at it through another hole sees it
at the moment it is not illuminated and can thus tell if it is
phosphorescing. By determining the rate of revolution of the disks it is
easy to calculate how long the phosphorescence persists.

While relatively few solids phosphoresce after exposure to light at
ordinary temperature a large number of these acquire the property at the
temperature of liquid air. Included in the list are such biological
products as urea, salicylic acid, starch, glue and egg shells. The
temperature also affects the wave-length and hence the color of the
light given off. Usually the higher the temperature the shorter the
wave-length, but in the case of some bodies (SrS) the wave-lengths
become longer at the higher temperature.

The best known cases of phosphorescence which occur at room temperature
and the group to which the word phosphorescence is commonly applied, are
those of the alkaline earth sulphides (BaS, CaS, SrS) and ZnS. An
Italian, Vicenzo Cascariolo, is said to have discovered the Bologna
stone (BaSO_{4}) which, by calcination with charcoal, gave an impure
phosphorescent BaS or _lapis solaris_. Canton's phosphorus (CaS) was
later prepared "by heating a mixture of three parts of sifted calcined
oyster shells with one part of sulphur to an intense heat for one hour."
Hulme spoke of it as the "light magnet of Canton," because of its power
of attracting and absorbing light. The pure sulphides do not show this
property. Only if small amounts of some other metal such as Cu, Pb, Ag,
Zn, Sb, Ni, Bi, or Mn are present, will the sulphide phosphoresce. One
part of impurity in a million is often sufficient. Such mixtures,
together with a flux of Na_{2}SO_{4}, Li_{3}(PO_{4})_{2} or some other
fusible salt constitute a "phosphor." A "phosphor" is in reality an
example of a solid solution and is the basis of some kinds of luminous
paints.

The intensity and duration of a phosphorescent light depend chiefly on
the nature of the exciting rays, the color chiefly on the impurity
present but the alkaline earth metal also exerts an influence. Rise in
temperature increases the intensity but diminishes the duration, so that
the total amount of light emitted is about constant at different
temperatures.

The spectrum of most phosphorescent substances is made up of one or more
continuous bands having _maxima_ at different wave-lengths. In the light
incident on a phosphorescent substance are also bands of light rays
which are absorbed and whose wave-lengths are more efficient than others
in stimulating phosphorescence. These bands in the phosphorescent light
are usually of longer wave-length than those in the light which excites
the phosphorescence. This fact is known as Stokes' Law, but it has been
found not to be universally true. Curiously enough, red and infra-red
rays have the power of annulling phosphorescence after a momentary
increase in brightness and phosphorescing materials have been used to
determine if infra-red rays are given off in the light of the firefly.
Ives (1910) showed that infra-red radiation had no power of quenching
the light of the firefly as it does the phosphorescent light of Sidot
blende (ZnS), one fact tending to show that the firefly's light is not
due to phosphorescence. Fig. 3 is a reproduction of a photograph of the
phosphorescence spectrum of ZnS.

[Illustration: FIG. 3. Spectrum of zinc sulphide phosphorescence (_after
Ives and Luckiesh_). Photographs were taken by a special device one
minute (middle) and fifteen minutes (bottom) after exposure to the light
of the mercury arc and compared with a helium spectrum (top). In the
middle photograph, the mercury exciting lines are visible. It will be
noted that the narrow band of phosphorescent light does not shift its
position during decay of phosphorescence.]

Other facts show that the light of luminous animals is in no sense a
phosphorescence and is quite independent of previous illumination of the
animal. Luminous bacteria will continue to luminesce although they are
grown in the dark for many weeks. Indeed strong light has a bactericidal
action on these forms similar to that with ordinary bacteria. With some
marine forms light has an inhibiting effect. They lose their power of
luminescence during the day and only regain it at dusk or when kept in
the dark for some time. Indeed, ordinary light never has the effect of
causing luminescence in the same sense as it causes phosphorescence of
CaS.

Fluorescence is most efficiently excited by the cathode rays of a vacuum
tube. They not only cause the residual gas in the tube to glow
(_electroluminescence_) by which their path may be followed with the
eye, but also a vivid fluorescence of the glass walls of the tube,
yellow green with sodium glass, blue green with lead and lithium glass.
LiCl_{2} in the path of cathode rays gives off a blue light; in the path
of anode rays a red light; NaCl a blue cathodoluminescence and a yellow
anodoluminescence. The spectrum of the latter is a line spectrum of Li
or Na, showing the characteristic red or yellow lines similar to those
observed where Li or Na is held in the bunsen flame. The spectrum of the
salts under excitation of cathode rays is a short continuous one in the
blue region. Fluorescent spectra in general are of this nature, made up
of short bands of light in one or more regions.

Diamonds, rubies and many minerals fluoresce brilliantly in the path of
cathode rays. Some specimens of fluorite (CaF_{2}) show the phenomenon
especially well, whence the name _fluorescence_. Fluorescent screens of
barium platinocyanide, willemite (Zn_{2}SiO_{4}), Sidot blend (ZnS) or
Scheelite (Ca tungstate) are frequently employed to render visible
X-rays. The luminous paint most used at the present time is ZnS
containing a trace of radium salt. The rays of the radium continually
emitted cause a steady fluorescence of the ZnS. Indeed, if one examines
the paint on the hands of a watch with a lens the flash of light from
the impact of alpha particles on the ZnS can be distinctly seen, as in
the _spinthariscope_.

Some animal tissues and fluids, especially the lens of the eye, will
luminesce in the path of radium rays, as shown by the experiments of
Exner (1903), but there is no evidence that luminous animals are
especially active in this respect. Ultra-violet rays have the same
action.

The luminous material of practically all luminous forms, if dessicated
sufficiently rapidly, can be obtained in the form of a dry powder which
will give off light when moistened with water. Coblentz (1912) has
exposed this dry material to light, to the ultra-violet spark, and to
X-rays and in no case has a phosphorescence or fluorescence ever been
observed. I have examined the action of radium upon _Cypridina_ light.
There was no intensifying or diminishing effect of twenty milligrams of
radium (probably the bromide) on a luminous solution of _Cypridina_
material, nor was phosphorescence or fluorescence excited in a
non-luminous extract of the animal. We must conclude that animal light
is not a fluorescence of any substance due to radiation produced by the
animals themselves.

Many solutions show fluorescence in strong lights. This is especially
marked in quinine sulphate, mineral oils, eosin, fluorescein, esculin,
rhodamin, chlorophyll, etc. The fluorescence of eosin in 10^{-8} grams
per cubic centimetre is visible in daylight and 10^{-15} grams per cubic
centimetre in the beam from an arc lamp. It is difficult to realize that
the bluish fluorescence of quinine sulphate is really an emission
rather than a reflection of light. But a test tube of quinine sulphate
solution held in the ultra-violet region of a spectrum will glow with a
pale blue light, although it is not illuminated with any rays that are
visible to our eyes. Concerning this, Stokes, to whom the word
fluorescence and much of our knowledge of the subject is due, says, "It
was certainly a curious sight to see the tube" (containing quinine
sulphate solution) "instantaneously lighted up when plunged into the
invisible rays; it was literally 'darkness visible.'" Quinine sulphate
absorbs the ultra-violet converting these rays into visible blue ones.
Its spectrum is a short continuous one. Most fluorescent substances
convert short into longer wave-lengths (Stokes' Law), but some may cause
the reverse change.

A substance, fluorescent in solution, has been found in a few luminous
animals, notably in several species of fireflies and also in a
non-luminous beetle. It is called _pyrophorine_ or _luciferesceine_.
Dubois (1886) has ascribed to pyrophorine the power of absorbing
invisible rays and transforming them into visible ones, thus increasing
the animal's light. That this is not the case has been shown by the work
of Coblentz (1909). He photographed the spectrum of the firefly's light
and the fluorescent spectrum of luciferesceine. The latter is almost
complementary to the former (see Fig. 4) and no trace of the fluorescent
spectrum appears in the spectrum of the light of the firefly. McDermott
(1911 _a_) has studied the properties of luciferesceine and regards it
merely as an incidental material found in many animals of the
_Lampyridæ_ (in some non-luminous forms) and having no connection with
the light production. A trace of alkali usually increases and acid
inhibits the fluorescence of solutions.

[Illustration: FIG. 4.--Spectrum of fluorescent substance found in
fireflies below (2) and of firefly luminescence above (2) compared with
helium vacuum tube (1) (_after Coblentz_).]

TRIBOLUMINESCENCE AND PIEZOLUMINESCENCE.--Under this head are grouped a
number of light phenomena which at first sight may appear to be
electrical in nature but in reality are not. The light is produced by
shaking, rubbing, or crushing crystals, and only crystalline bodies
appear to show _triboluminescence_ or _piezoluminescence_. A striking
case is that of uranium nitrate. Gentle agitation of the crystals is
sufficient to give off sparks of light which much resemble the
scintillations of dinoflagellates when sea-water containing these
animals is agitated. If Romberg's phosphorus, which is fused CaCl_{2},
is rubbed on the sleeve, it glows with a greenish light. Lumps of cane
sugar rubbed together will glow. Saccharin crystals will also light if
shaken and Pope (1899) found that the bluish light of saccharin was
bright enough to be visible in a room in daytime. It only appeared from
impure crystals and freshly crystallized specimens. Other crystals,
also, have been found to lose their power of lighting after a time.

Among biological substances, cane sugar, milk sugar, mannite, hippuric
acid, asparagin, _r_-tartaric acid, _l_-malic acid, vanillin, cocaine,
atropin, benzoic acid, and many others show triboluminescence. A long
list is given by Tschugaeff (1901), by Trautz (1905), and by Gernez
(1905). The spectrum is a short continuous one, the waves emitted
depending on the kind of crystal. Thus the color of the light varies
among different santonin derivatives from yellow to green. In saccharin
it is blue.

Although the light produced by some living organisms resembles
triboluminescence in that it may be evoked by rubbing or shaking the
animals, it is in reality fundamentally different since it is dependent
on the presence of oxygen whereas triboluminescence is not.

CRYSTALLOLUMINESCENCE.--Crystalloluminescence is observed when solutions
crystallize. It was described by Bandrowski (1894, 1895) in arsenious
oxide, in NaF, or if HCl or alcohol is added to hot saturated NaCl
solution. A bluish light with sparkling points appeared. All well
authenticated cases are exhibited by simple inorganic salts and these
are also all triboluminescent. The reverse is not true, however; many
triboluminescent substances are not crystalloluminescent.
Crystalloluminescence is much less widespread than triboluminescence.
Trautz (1905) has studied the matter in a number of compounds and comes
to the conclusion that the light is really a special case of
triboluminescence in which the growth of individual crystals causes them
to rub together. The light becomes much brighter on stirring a mass of
crystals which exhibit crystalloluminescence. While in some cases
crystalloluminescence is unquestionably due to the triboluminescence of
crystals rubbing against each other it is not in every case, as has been
clearly shown by the work of Weiser (1918 _b_). He studied luminescence
of saturated aqueous alkali halide solutions (NaCl, KCl, etc.,) upon
addition of alcohol or of HCl. The salt crystallizes out under these
conditions and Weiser found that the light is brightest when the
conditions of concentration of alcohol or of HCl are such as to cause
heaping up of Na and Cl ions. He believes that the bluish light which
appears is due to the combination of ions in the reaction, Na^+ + Cl^- =
NaCl. Only if this proceeds rapidly enough does luminescence occur.
Weiser studied also the crystalloluminescence and triboluminescence of
AsCl_{3} and of K_{2}SO_{4}. By photographing the luminescence through
color screens of different absorptive power (Weiser, 1918, _a_) a
spectrum of the light could be obtained, and it was found to be
identical in both the tribo- and crystalloluminescent light; in the case
of AsCl_{3}, a band in the green-blue, blue and violet. Weiser believes
the light in this case also to come from recombination of the ions,
As^{+++} + 3Cl^- = AsCl_{3}, and that crystalloluminescence in general
is due to rapid reformation of molecules from ions broken up by
electrolytic dissociation while triboluminescence is due to rapid
reformation of molecules from ions broken up by violent disruption of
the crystal. Of course in triboluminescent organic crystals which do not
dissociate into ions, some other reaction must be responsible for the
light. One thing seems certain, that the two types of luminescence are
similar. As Bigelow[1] remarks, "It is altogether probable that the
cause of this" (crystalloluminescence) "whatever it may be, is the same
as the cause of triboluminescence, whatever that may be."

[1] Theoretical and Physical Chemistry, 1912, p. 516.

Crystals are not found in the luminous organs of animals with the
exception of the fireflies. In these a layer of cells occurs (see
Chapter IV) filled with minute crystals of one of the purine bodies
(xanthin or uric acid). One might surmise that the light of the animal
was a crystalloluminescence accompanying the formation of these
crystals. It is easy to show, however, that the light comes not from the
crystal layer but from another layer of cells containing large granules.
It is also dependent on the presence of oxygen while
crystalloluminescence takes place in the absence of oxygen. The crystal
layer possibly serves as a reflector. Its significance will be
discussed in a later chapter.

[Illustration: FIG. 5.--Dubois's figures showing transformation of
photogenic granules to crystals (_after Dubois_).]

The light of luminous organisms is quite generally associated with
granules. In one of the centipedes (_Orya barbarica_), which produces a
luminous secretion, Dubois (1893) has described the transformation of
these granules into crystals and at one time he supposed the light to be
a crystalloluminescence. He later reversed this opinion and, certainly,
examination of his drawings which are reproduced in Fig. 5 does not
convince one of the actuality of crystal formation.

The phenomenon of _lyoluminescence_, described by Wiedemann and Schmidt
(1895) as a light accompanying the solution of colored (from exposure to
cathode rays) crystals of Li, Na, or K chlorides, is probably due to a
triboluminescence from stirring of the crystals during solution.

CHEMILUMINESCENCE.--As the name implies, chemiluminescence is the
production of light during a chemical reaction at low temperatures. This
does not mean that the other types of luminescence are not connected
with chemical reactions--using the word _reaction_ in a broad sense--for
we have reason to believe that in some cases spectra are not
characteristic of the element as such but are rather characteristic of a
particular reaction in which the element takes part (dissociation into
ions, changes from monovalent to bivalent condition, etc.) and that this
is the reason one element may show various spectra under different
conditions (Bancroft, 1913). The chemiluminescences are rather oxidation
reactions involving the absorption of gaseous or dissolved oxygen and
may be very easily distinguished from all the previously mentioned
luminescences by this criterion. They should, perhaps, more properly be
called _oxyluminescences_.

The glow of phosphorus is the best known case, recognized since
phosphorus was first prepared by Brandt in 1669. It is interesting to
note that when first prepared phosphorus was regarded as a peculiarly
persistent type of phosphor, _i.e._, a material akin to the impure
alkaline earth sulphides.

Fresh cut surfaces of Na and K metal will glow in the dark for some
time, especially if warmed to 60°-70° (Linnemann, 1858). A film of oxide
is formed over the surface, showing definitely that oxidation has
occurred. Ozone oxidizes organic matter with an accompanying glow
(Fahrig, 1890; Otto, 1896). The light from ozone acting on pyrogallol
solution is especially bright under certain conditions.

Radziszewski (1877, 1880) gives a long list of substances, chiefly
essential oils, which luminesce if slowly oxidized in alcoholic
solutions of alkalis. Formaldehyde, dioxymethylen, paraldehyde,
metaldehyde, acroleïn, disacryl, aldehydeammonia, acrylammonia,
hydrobenzamid, lophin, hydroanisamid, anisidin, hydrocuminamid,
hydrocinamid, besides waxes, and such biological substances as glucose,
lecithin, cholesterin, cholic, taurocholic, and glycocholic acids, and
cerebrin, all luminesce on oxidation. Radziszewski himself and many
other authors have compared the light of organisms to this type of
luminescence. Indeed the incorrect identification of granules found in
the cells of practically all luminous tissues as oil droplets, is
largely due to the influence of Radziszewski's work. Dubois (1901 _b_)
has added esculin, and Trautz (1904-5) many aldehydes and phenol
derivatives, including vanillin, papaverin, tannic and gallic acids,
besides glycerol and mannite to the list of biological substances
oxidizing with light production. Guinchant (1905) has described
oxyluminescence of uric acid and asparagine, Weitlaner (1911) of
substances in humus and McDermott (1913) of substances in urine and the
anaerobic alkaline hydrolysis products of glue and Witte's peptone.
Pyrogallol is especially prone to luminesce, as was first noticed by
Lenard and Wolf (1888) in developing a photographic plate with
pyrogallol developer. Later the luminescence was studied in some detail
by Trautz and Schloringin (1904-5) who developed the well-known
luminescent mixture of pyrogallol, formaldehyde, K_{2}CO_{3} and
H_{2}O_{2}. As I have shown, pyrogallol can be oxidized in a great many
different ways, and some of these are of great interest, for they very
closely imitate the mechanism for the production of light in organisms.
These are recorded in Table 3, which also includes various other types
of oxyluminescence of general or biological interest.


TABLE 3

_Types of Oxyluminescent Reactions_

   1. Oxidation in air spontaneously.

      (_a_) At ordinary temperatures. [Phosphorus. Fresh-cut surfaces of Na
        or K. Thiophosgene and Thio-ethers (RCS.OR).]

      (_b_) At melting or vaporizing points. (Fats, terpenes, sugars,
        resins, gums, ether, silk and others.)

   2. Oxidation in aqueous or alcoholic alkalies. (Many organic
      substances.)

   3. Oxidation in hypoiodites, hypobromites, or hypochlorites. (Many
      organic substances.)

   4. Oxidation in peroxides (H_{2}O_{2} or Na_{2}O_{2}). (Many organic
      substances.)

   5. Oxidation in ozone. (Many organic substances.)

   6. Oxidation in acid permanganate. (Pyrogallol.)

   7. Oxidation in persulfates and perborates. (Formaldehyde,
      paraformaldehyde.)

   8. Oxidation in perchlorates, periodates, and perbromates. (Palmitic
      acid.)

   9. Combination of 2 and 4. (Many organic substances.)

  10. Combination of 3 and 4. (Many organic substances.)

  11. Oxidation with H_{2}O_{2} and hæmoglobin or vegetable oxidases.
      (Pyrogallol, gallic acid, lophin, esculin.)

  12. Oxidation with H_{2}O_{2} and MnO_{2}, Fe_{2}Fe(CN)_{6} Mn(OH)_{2} +
      Mn(OH)_{3} Ag_{2}O, chromium oxide, cobalt oxide. (Pyrogallol.)

  13. Oxidation with H_{2}O_{2} and ferrocyanides, chromates, bichromates,
      permanganates, Fe salts, and Cr salts. (Pyrogallol, esculin.)

  14. Oxidation with H_{2}O_{2} and collodial Ag. Pt. Pd. Au.
      (Pyrogallol.)

The spectrum of chemiluminescent reactions has been described in a few
instances as continuous but no definite measurements of its extent have
been made. Radziszewski (1880) found the light of lophin oxidized in
alcoholic caustic alkali, examined with a two-prism spectroscope, to
give a continuous spectrum, brightest at _E_, with the red and violet
ends lacking. Trautz (1905, p. 101) states that the
pyrogallol-formaldehyde-Na_{2}CO_{3}-H_{2}O_{2} reaction gives a
continuous spectrum from the red to the blue green with maximum
brightness in the orange. Weiser (1918 _a_) has studied the spectra of
some chemiluminescent reactions by photographing the light behind a
series of color screens. He finds also that the spectra are short, with
maximum intensity in various regions. Thus, _amarin_ oxidized by
chlorine or bromine, extends from the yellow to greenish blue with a
maximum in the green while _phosphorus_, dissolved in glacial acetic
acid and oxidized with H_{2}O_{2}, luminesces from yellow green to
violet.

The spectra of luminous animals are quite similar to those of
chemiluminescent reactions. Moreover, as we have seen, chemiluminescence
is essentially an oxyluminescence, since oxygen is necessary for the
reaction. All luminous animals also require oxygen for light production.
Therefore, bioluminescence and chemiluminescence are similar phenomena
and they differ from all the other forms of luminescence which we have
considered. The light from luminous animals is due to the oxidation of
some substance produced in their cells, and when we can write the
structural formula of this photogenic substance and tell how the
oxidation proceeds, the problem of light production in animals will be
solved.




CHAPTER III

PHYSICAL NATURE OF ANIMAL LIGHT


Interest in the light of animals from a physical standpoint has centred
around questions of quality, efficiency and intensity, but in only one
group of luminous animals, the beetles, have accurate measurements of
these characteristics been made. This is due in part to the abundance of
these forms and their appeal to human interest and in part because they
are among the brightest of luminous organisms. Weak lights are not only
difficult to measure but, when dispersed to form spectra, give bands so
faint that their limits are very difficult to see and more so to
photograph. Very few organisms produce light visible to the fully
light-adapted eye. Although their light may seem quite bright to the
dark-adapted eye, the dark-adapted eye is a poor judge of the quality,
_i.e._, the color of a light. This is because of the Purkinje
phenomenon, a change in the region of maximum sensibility of the retina
with change in intensity of the light. For an equal energy spectrum, to
the normal, completely light-adapted eye, yellow-green light of
wave-length, λ = .565µ, appears the brightest, but when the light is
made fainter the maximum shifts first to the green and then to the blue.
The dark-adapted eye can see green or blue better than yellow and for
this reason weak lights will appear more green or blue than stronger
ones of the same energy distribution. Also two weak lights of the same
spectral composition may appear different in color if they differ much
in intensity. This is illustrated in Fig. 6.

[Illustration: FIG. 6.--Visibility curves for three illuminations
showing the shift in region of maximum visibility, or Purkinje
phenomenon (_after Nutting_).]

The shift in sensibility of the eye occurs in illuminations of between
0.5 and 50 metre-candles and represents a change from central cone
vision (high intensities) to peripheral rod vision (low intensities).
The _fovea centralis_ lacks rods and this part of the eye becomes
practically color blind at very low intensities of light. Below 0.5 and
above 50 metre-candles visibility varies but little with change in
intensity. It is clearly necessary then to distinguish between the
physical objective phenomenon of light and the physiological subjective
sensation of light.

It is a fact that different luminous animals produce light of quite
different colors as judged by our eye. A range of spectral tints has
been described which extends from red to violet but "yellowish,"
"greenish" and "bluish" tints are commonest. Indeed one or two animals
possess several luminous organs emitting lights of different colors.
This is true in a South American firefly, _Phengodes_, whose lights are
red and greenish yellow, and in the deep sea squid, _Thaumatolampas
diadema_, which produces lights of three colors, two shades of blue and
red. The red light in the case of the squid appears to be due to a red
color screen formed by the chromatophores, but in _Phengodes_ no screen
is present.


TABLE 4

_Wave-lengths of Fraunhofer Lines and Prominent Lines in Line Spectra_


  FRAUNHOFER LINES

  ========================================================================
        Line        |Color |    Wave-lengths     |      Source
                    |      |    (µµ = µ/1000)     |
  ------------------+------+---------------------+------------------------
          A         |Red   | 759.4 (band)        |Oxygen in atmosphere.
          a         |Red   | 718.5 (band)        |Water vapor atmosphere.
          B         |Red   | 686.7               |Oxygen vapor atmosphere.
          C         |Red   | 656.3               |Hydrogen in sun.
     D_{1} D_{2}    |Yellow| 589.6, 589.0        |Sodium in sun.
          E         |Green | 527.0               |Calcium in sun.
  b_{1} b_{2} b_{4} |Green | 518.4, 517.3, 516.8 |Magnesium in sun.
          F         |Blue  | 486.1               |Hydrogen in sun.
          G         |Violet| 430.8               |Calcium in sun.
         H K        |Violet| 396.9, 393.4        |Calcium in sun.
  ------------------+------+---------------------+------------------------


  BUNSEN FLAME LINES

  ===============================================
    Source  | Color  | Wave-lengths (µµ = µ/1000)
  ----------+--------+---------------------------
  Potassium | Red    | 769.9, 766.5 (double)
  Lithium   | Red    | 670.8
  Sodium    | Yellow | 589.6, 589.0 (double)
  Thallium  | Green  | 535.1
  Magnesium | Green  | 518.4
  Strontium | Blue   | 460.7
  ----------+--------+---------------------------


  PLÜCKER TUBE LINES

  ===============================================
    Source  | Color  | Wave-lengths (µµ = µ/1000)
  ----------+--------+---------------------------
  Mercury   | Yellow | 579.0, 576.9
            | Green  | 546.1
            | Blue   | 491.6, 435.8
            | Violet | 407.8, 404.7
  Hydrogen  | Red    | 656.3
            | Blue   | 486.1, 434.1
  Helium    | Red    | 728.2, 706.5, 667.8
            | Yellow | 587.6
            | Green  | 504.8, 501.6, 492.2
            | Blue   | 471.3, 447.2
            | Violet | 438.8, 402.6, 388.8
  ----------+--------+---------------------------

As we have seen, difference in color of the light does not necessarily
indicate difference in spectral composition because of the Purkinje
effect. However, examination of the spectrum of various luminous forms
has very clearly indicated that the different colors are really due to
light rays of different wave-length and are not the result of any
subjective phenomena. To facilitate comparison, spectral lines and
colors are given in Table 4. The first adequate observations on the
spectra of luminous animals were made by Pasteur (1864), who studied
_Pyrophorus_ and found a continuous spectrum unbroken by light or dark
bands. Lankester (1868) discovered a similar continuous spectrum in
_Chætopterus insignis_ and placed its limits from line 5 to 10 on
Sorby's Scale (about λ = 0.55µ to λ = 0.44µ). Young
(1870) first recorded the limits of the firefly spectrum as a little
above _C_ (λ = .6563µ) to _F_ (λ = .4861µ). Since then a
number of luminous forms have been examined and all are found to give
short continuous spectra (not crossed by light or dark bands or lines)
lying in different color regions. Thus, Conroy (1882) examined the
glowworm (_Lampyris noctiluca_) light and observed a band extending from
λ = 0.518µ to λ = 0.656µ. Dubois (1886) states that the
spectrum of _Pyrophorus noctilucus_, the West Indian "Cucullo," extends
from slightly further than the Fraunhofer _B_ line to the _F_ line,
while Langley and Very (1890), working on the same form, placed the
limits at λ = 0.468µ to λ = 0.640µ. It consists, then, of
a broad band chiefly in the green and yellow. But, "would the light not
extend farther were it bright enough to be seen?... if the light of the
insect were as bright as that of the sun would it not extend equally far
on either side of the spectrum?" "It is impossible to increase the
intrinsic brilliancy by any optical device, but if it be impossible to
make the light of the insect as bright as that of the sun, it is on the
other hand quite possible to make the light of the sun no brighter than
that of the insect ..." Langley and Very investigated this question,
forming a solar spectrum from sunlight of the same intensity as that of
_Pyrophorus_ and a _Pyrophorus_ spectrum together in the same field of
the spectroscope. The latter was very much shorter than the solar
spectrum, showing that its length was not due to weakness of the red and
blue rays but to their absence. Later Ives and Coblentz (1910)
photographed the spectrum of a firefly (_Photinus pyralis_), together
with that of a carbon glow lamp, on plates sensitive to all wave-lengths
of visible rays under conditions which would have recorded all visible
radiations given off. They found the spectrum to extend only from
λ = 0.51µ to λ = 0.67µ (Fig. 7). Another species of
firefly (_Photuris pennsylvanica_) was found by Coblentz (1912) to give
a spectrum extending from λ = 0.51µ to λ = 0.59µ (Fig. 8).
The _Photinus_ light extends much further into the red and it is easy to
distinguish between _Photinus_ and _Photuris_ in nature, merely by the
reddish tint of the light of the former. These photographic records show
conclusively that the color of the light of luminous animals is not a
subjective phenomenon due to the Purkinje effect and the low intensity
of the light, but is real, an actual difference in spectral
composition of the light emitted. Neither is it due, at least in the
fireflies examined, to the existence of color screens which absorb
certain rays, allowing only those of a definite color to pass. The
spectra of forms thus far investigated are reproduced in Fig. 9 and
recorded in Table 5. It will be noted that they vary considerably in
position but are all of the same type. The spectrum of _Cypridina
hilgendorfii_ is the longest thus far investigated (λ = .610µ to
λ = .415µ), extending well into the blue, and the light of this
form is very blue in appearance.

[Illustration: FIG. 7.--Spectra of carbon glow lamp, A, firefly
(_Photinus pyralis_); B, and helium vacuum tube, C (_after Ives and
Coblentz_).]

[Illustration: FIG. 8.--Spectra of helium vacuum tube (1); carbon glow
lamp (2); the firefly, _Photinus pyralis_ (3); and the firefly _Photuris
pennsylvanica_ (4) (_after Coblentz_).]

[Illustration: FIG. 9.--Spectra of various luminous animals (_after
McDermott_). 1. Portion of the visible solar (grating) spectrum showing
Fraunhofer lines. 2. _Pyrophorus noctilucus_ (Langley and Very.) 3.
_Lampyris noctiluca_ (Conroy). 4. _Photinus pyralis_ (Ives and
Coblentz). 5. _Photinus consanguineus_ (Coblentz). 6. _Photuris
pennsylvanica_ (Coblentz). 7. _Phengodes laticollis_ (McDermott). 8.
_Bacterium phosphoreum, B. phosphorescens or Bacillus photogenus_
(Molish). 9. _Photobacterium indicum_ (Barnard). 10. _Mycelium X_
(Molish). 11. _Luminous bacteria_ (Förster). 12. _Agaricus sp._?
(Ludwig). 13. Fluorescent spectrum of luciferesceine of _Photinus
pyralis_ (Coblentz). Only the extreme ends of the bands are shown and no
attempt is made to indicate the relative density of different portions
of the spectra.]


TABLE 5.--_Limits of Spectra of Various Luminous Organisms_

  ============================================================================
    Light         | Spectrum (µ)   |Emission |Observer   |Method and remarks
                  |                |maximum  |           |
  ----------------+----------------+---------+-----------+--------------------
  Cypridina       | 0.610-0.415    |         |Harvey,    |Eye observation,
    hilgendorfii  |                |         |  1919     |  Zeiss comparison
                  |                |         |           |  spectroscope.
  Chætopterus     | 0.55-0.44      |         |Lancaster, |Eye observation.
    insignis      | (approximately)|         |  1868     |
  Pyrophorus      | 0.72-0.486     |         |Dubois,    |Eye observation.
    noctilucus    |                |         |  1886     |
  Pyrophorus      |  .640 - .468   | 0.57    |Langley    |Eye observation
    noctilucus    |                |         |  and Very,|  and comparison
    (thoracic     |                |         |  1890     |  with solar
    light)        |                |         |           |  spectrum of
                  |                |         |           |  equal intensity.
  Pyrophorus      |  .663 - .463   |         |           |
    noctilucus    |                |         |           |
    (abdominal    |                |         |           |
    light)        |                |         |           |
  Photinus        |  .67 - .51     |         |Ives and   |Photographic
    pyralis       |                |         |  Coblentz,|  comparison with
                  |                |         |  1909     |  carbon glow lamp
                  |                |         |           |  of equal
                  |                |         |           |  intensity.
  Photuris        |  .59 - .51     |  .552   |Coblentz,  |Photographic
    pennsylvanica |                |         |  1912     |  comparison with
                  |                |         |           |  carbon glow lamp
                  |                |         |           |  of equal
                  |                |         |           |  intensity.
  Photinus        |  .65 - .52     |  .578   |Coblentz,  |Photographic
    consanguineus |                |         |  1912     |  comparison with
                  |                |         |           |  carbon glow lamp
                  |                |         |           |  of equal
                  |                |         |           |  intensity.
  Phengodes       |  .65 - .52     |         |McDermott, |Eye observation.
    laticollis    |                |         |  1911 e   |
  Lampyris        |  .656- .518    |         |Conroy,    |Eye observation.
    (glow worm)   |                |         |  1910     |
  Photinus        |  .670- .487    |         |Young,     |Eye observation
                  |                |         |  1870     |  direct vision
                  |                |         |           |  spectroscope.
  Bacteria        |G to F extending|         |Barnard,   |  Photographic.
                  |  toward D for  |         |  1902     |
                  |  long exposure |         |           |
  Bacteria        |Somewhat beyond |         |Fisher,    |Eye observation.
                  |  G to D        |         |  1888     |
  Bacteria        |  .58 - .43     |         |Förster,   |Eye observation
                  |                |         |  1887     |  Zeiss. Abbe
                  |                |         |           |  microspectral
                  |                |         |           |  ocular.
  Bacteria        | >.500 to .350  | Bright  |Forsyth,   |Photographic,
                  |                |   band  |   1910    |  quartz
                  |                |   at .4 |           |  spectroscope.
  Agarious        | 0.56-0.48      |         |Ludwig,    |Eye observation,
    melleus       | (approximately)|         |  1884     |  Sorby Brown
                  |                |         |           |  microspectroscope.
  Xylaria         |  .54 - .46     |         |Ludwig,    |Eye observation,
    hypoxylon     | (approximately)|         |  1884     |  Sorby Brown
                  |                |         |           |  microspectroscope.
  Micrococcus     |b into the      |         |Ludwig,    |Eye observation,
    Pflugeri      |  violet        |         |  1884     |  Sorby Brown
                  |                |         |           |  microspectroscope.
  Mycelium X      |  .570 - .480   |         |Molish,    |Eye observation,
                  |                |         |  1904,    |  Zeiss comparison
                  |                |         |  book     |  spectroscope.
  Bacterium       |  .570 - .450   |         |Molish,    |Eye observation,
    phosphoreum   |                |         |  1904,    |  Zeiss comparison
                  |                |         |  book     |  spectroscope.
  Bacterium       |  .570 - .450   |         |Molish,    |Eye observation,
    phosphorescens|                |         |  1904,    |  Zeiss comparison
                  |                |         |  book     |  spectroscope.
  Bacillus        |  .570 - .450   |         |Molish,    |Eye observation,
    photogenes    |                |         |  1904,    |  Zeiss comparison
                  |                |         |  book     |  spectroscope.
  Pseudomonas     |  .570 - .450   |         |Molish,    |Eye observation,
    lucifera      |                |         |  1904,    |  Zeiss comparison
                  |                |         |  book     |  spectroscope.
  ----------------+----------------+---------+-----------+--------------------

As first shown by Dubois (1886) for _Pyrophorus_, and confirmed by
myself for _Cypridina_, the light is not polarized in any way. I may add
that the _Cypridina_ light like any other light may be polarized by
passing through a Nicol prism.

Several writers [Dubois (1914 book)], Fischer (1888), Molisch (1904
book) have noticed that the light of luminous bacteria changes in color
if grown on different culture media. Light which is "silver white" on
dead fish becomes "greenish" on salt-peptone-gelatin media and more
yellow on salt-poor media. Peron (1804) and Panceri (1872) describe the
light of _Pyrosoma_ as yellow to greenish after death of the animal and
reddish on stimulation; then fading out through orange, yellow, greenish
and azure blue. Polimanti (1911) describes the normal light of
_Pyrosoma_ as greenish, and states that as the animals die, or if they
are kept at temperatures above the optimum, the light becomes more red.
McDermott (1911, _b_) noticed that the light of fireflies placed in
liquid air became decidedly reddish just before going out and on
rewarming the first light to appear was reddish followed by the proper
shade at higher temperatures. I have frequently observed a more
reddish color from luminous tissues of the firefly upon the addition of
coagulants such as alcohol, and have noted that the light of _Cypridina_
becomes weaker and more yellow at both low (0°) and high (50°)
temperatures. The meaning of these color changes will be discussed in
Chapter VII.

The efficiency of any light may be defined in several different ways:
(1) By the percentage of visible wave-lengths in the total amount of
radiation emitted, _i.e._, visible radiation divided by total (heat,
visible, actinic) radiation; (2) by considering, in addition to visible
radiation ÷ total radiation, the sensibility of the eye to different
wave-lengths, visible radiation × visual sensibility ÷ total radiation.
Visible radiation × visual sensibility is spoken of as luminosity; (3)
by the amount of light (expressed in candles) produced in relation to a
given expenditure of energy or in relation to the cost of the energy
expended. Thus, of the radiation emitted from an incandescent electric
lamp only a small per cent. is light, the rest being heat and actinic
rays. It is therefore very far from being 100 per cent. efficient. If
there were no infra-red or ultra-violet in the radiation from an
incandescent lamp its efficiency would be 100 per cent. if we
disregarded visual sensibility. But if we take into account the fact
that the eye is most sensitive to yellow green, a source of light, even
though emitting only visible radiation, would not be 100 per cent.
efficient unless its maximum of emission corresponded also with the
maximum of visual sensibility. We shall return to this question in a
later paragraph. Looking at the question from the standpoint of energy
consumption, the carbon incandescent lamp gives one mean spherical
candle for 4.83 watts (watt = 10^7 ergs per sec.), while the tungsten
lamp gives one mean spherical candle for 1.6 watts, about one-third the
energy, and the latter is consequently more efficient.

As we know practically nothing of the energy transformations occurring
during the process of light production in organisms, all statements
regarding the efficiency of their light are based on relations between
the visible radiation and total radiation. This involves a measurement
of rays in the infra-red region (heat rays) and ultra-violet region
(actinic rays) as well as the light rays proper, and any other radiant
energy produced. While all spectroscopic investigations show that the
spectrum of luminous animals never extends to the limits of the visible
spectrum in either the red or violet, it is possible that bands occur in
the infra-red or ultra-violet, and special methods must be employed to
detect these. Radiations of all kinds, if converted into heat on
striking the blackened surface of a thermopile, bolometer, or radiometer
can be measured by changes in temperature and the relative amounts of
energy represented be compared in a common unit, the calorie. By proper
screening, all rays except the visible light rays can be cut off from
the measuring instrument and the amounts of energy represented in light
and in total radiation thus be determined.

Dubois (1886) first studied this problem in _Pyrophorus_ by the use of a
thermopile and galvanometer and found a small amount of radiation from
the luminous region in excess of that from a non-luminous region. It
amounted to a galvanometer deflection of 0.95° and was increased 0.3°
during the flash of the insect on electrical stimulation. This increase
of 0.3° is possibly due to heat produced on muscular contraction. In any
case the amount of heat radiated in comparison with that of the candle
is very small indeed. A more careful study has been made by Langley and
Very (1890) with the bolometer. They point out first of all that the
total radiation from the most powerful luminous organ (the abdominal
one) of _Pyrophorus_ which affected their bolometer slightly, would, in
the same time (10 seconds), be sufficient to raise the temperature of an
ordinary mercurial thermometer having a bulb 1 cm. in diameter by rather
less than 2.3 × 10^{-6}° C. We may thus gain some idea of the magnitude
of the measurements to be made. The radiation from _Pyrophorus_ which
affected their bolometer was shown to be due merely to the "body
heat"[2] of the insect, and it is largely cut off by a plate of glass
which is opaque to all wave-lengths of 3µ or more. These waves are given
off by bodies at temperatures below 50° C. and belong "to quite another
spectral region to that in which the invisible heat associated with
light mainly appears." Langley and Very then compared the radiation from
a non-luminous bunsen flame and the _Pyrophorus_ light, interposing a
plate of glass in each case to cut off the waves longer than 3µ, and
found several hundred times more radiation in the case of the bunsen
burner but, nevertheless, perceptible radiation from _Pyrophorus_. The
former consisted of radiant heat shorter than λ = 3µ and extending up to
the visible light rays (λ = 0.7µ since the bunsen flame emitted no
light). The very slight effect of the _Pyrophorus_ radiation must be due
to wave-lengths between λ = 3µ and λ = 0.468µ, the limit of the
_Pyrophorus_ spectrum in the blue. Langley and Very assumed it to be due
entirely to the band of visible light, λ = 0.640µ to λ = 0.468µ, and
assumed that no invisible heat rays were produced. All of the energy of
_Pyrophorus_ light would therefore lie in the visible region and its
efficiency (light rays ÷ heat + light + actinic rays) would be 100 per
cent. Later, Langley (1902) reinvestigated the radiation of _Pyrophorus_
and could detect no heating whatever with the bolometer. "A portion of
the flame of a standard sperm candle, equal in area to the bright part
of the insects, gave under the same circumstances, a bolometric effect
of such magnitude that had the heat of the insect been 1/80,000 as great
as that from the candle, it would certainly have been recognized."
Coblentz (1912) also, using a vacuum thermopile of Pt and Bi, was unable
to detect any infra-red radiation from _Photinus pyralis_, but found
that the temperature of this firefly is slightly lower than the air.
These temperature measurements will be discussed in a later chapter.

[2] Langley and Very evidently supposed that the body temperature of the
firefly, like the mammal or bird, is higher than its surroundings.

The assumption of Langley and Very that the small amount of _Pyrophorus_
radiation passing glass is all light has been called into question by
Ives (1910), who points out that Langley and Very failed to use a screen
which would cut off either the visible rays or the invisible rays
between 3µ and 0.7µ. They really left the question open as to whether
the effect of _Pyrophorus_ light on their bolometer was due to the
visible band of rays or to this plus another band in the infra-red. "The
firefly's actual efficiency as a light source is dependent to a large
degree on the radiation being confined to the visible region. If there
should be found infra-red of quantity comparable to the visible, the
firefly, while still a very efficient source would not be, as usually
supposed, the example of an ideally efficient light produced by
nature."

Ives investigated the question further by the phosphor-photographic
method. "In brief it consists of this: Phosphorescence, which is excited
in various substances by exposure to short waves (blue, violet or
ultra-violet), is destroyed by exposure to longer waves (orange, red,
infra-red). Thus, a surface of Balmain's paint or of Sidot blende,
excited to phosphorescence and then exposed in a spectrograph, will have
areas of reduced brightness wherever long-wave energy has fallen upon
it. If this surface is then laid on a photographic plate for a short
period, a permanent record is obtained on the plate after development."
Preliminary tests showed that the method was applicable in the case of
weak light such as the firefly spectrum and also if the light is
intermittent like the firefly. With Sidot blend (ZnS) the extinguishing
action extends from λ = 0.6µ to λ = 1.5µ. A sheet of deep ruby glass,
which cut off all the visible rays of the firefly but allowed infra-red
to pass, was placed between the firefly light and a surface of
phosphorescent Sidot blend which was exposed to the firefly flashes for
three and a half hours. No extinction of phosphorescence occurred, while
without the ruby glass, extinction, due to the orange rays of the
_visible_ firefly light was noticeable in 20 minutes. There is thus no
infra-red of an intensity at all comparable to the visible as far as λ =
1.5µ, the lower limit of the phosphor-photographic method. Coblentz
(1912) had examined the transparency of the dry chitinous integument of
various fireflies (Fig. 10) in the infra-red and reports it to be fairly
transparent down to λ = 2.8µ, opaque between λ = 2.8µ and λ = 3.8µ,
transparent again to λ = 6µ, and opaque beyond that. The infra-red
could, then, if it were emitted, largely pass through the integument
which is similar in absorption properties to complex carbohydrates.
Transparency of the integument to the ultra-violet was not studied.

[Illustration: FIG. 10.--Transmissivity of the integument of fireflies
to infra-red radiation (_after Coblentz._)]

Although photographs of the spectrum of firefly (_Photinus_) light show
that it extends only to the beginning of the blue, Forsyth (1910)
reports ultra-violet radiation in luminous bacteria. He exposed a plate
for 48 hours to the spectrum of bacterial light dispersed by a quartz
prism and got a continuous band from λ = 0.50µ (the lower limit of
sensitivity of the plate) to λ = 0.35µ. However, McDermott (1911 _d_)
was unable to observe fluorescence of p-amino-ortho-sulpho-benzoic acid,
which responds to the ultra-violet light. Molisch (1904, book)
photographed bacterial and fungus light through glass and through a
piece of quartz and found no difference in density on the plate. As the
exposure was brief, to avoid saturation, and as the ultra-violet, which
passes quartz but not glass, has a much greater action on the plate
than visible light, we must conclude that ultra-violet is absent. Ives
(1910) investigated the spectrum of _Photinus pyralis_, using a quartz
spectroscope, and found no evidence of ultra-violet radiation, at least
as far as λ = 0.216µ.

It will thus be seen that the radiation from the firefly has been very
carefully studied and that no waves are given off from λ = 1.5µ to λ =
0.216µ with the exception of the short band (λ = 0.67µ to λ = 0.51µ) in
the visible, and it is highly probable that no radiation is given off
with wave-lengths longer than λ = 1.5µ. The firefly light remains, then,
100 per cent. efficient, differing from all our artificial sources of
light, the best of which does not approach this value. As Langley and
Very express it in the title to their paper, it is "the cheapest form of
light," not cheapest in the sense of that we can reproduce it
commercially at less cost than other lights, but cheaper in the sense
that it is the most economical in the energy radiated. This energy is
all light and no heat. "Cold light" has actually been developed by the
firefly and concerning which "we know of nothing to prevent our
successfully imitating."

[Illustration: FIG. 11.--Spectral energy curves of various fireflies and
the carbon glow lamp (_after Coblentz_).]

I have already pointed out that we may also consider the efficiency of a
light in relation to the sensibility of our own eye. That is, we take
into account not only the energy distribution in the spectrum of the
light but also the fact that different wave-lengths of an equal energy
spectrum affect our eye very differently. As the normal light-adapted
eye is most sensitive to yellow green of λ = 0.565µ, monochromatic light
of this wave-length will appear much brighter than monochromatic light
of any other wave-length with the same energy. Monochromatic light of λ
= 0.565µ will then be the theoretically most efficient possible, when we
consider the energy radiated in relation to the sensitivity of our eye.
This is the usual method of determining the luminous efficiency of
artificial lights and is obtained from a knowledge of the radiated
energy and the visual sensibility. Reduced luminous efficiency = light
(_radiated energy_ × _visual sensibility_) or luminosity ÷ total
radiated energy.

[Illustration: FIG. 12.--Visibility curves of various investigators
obtained by different methods (_after Hyde, Forsyth and Cady_).]

[Illustration: FIG. 13.--Luminous efficiency of the 4-watt carbon glow
lamp, shaded area ÷ total area (_after Ives and Coblentz_).]

[Illustration: FIG. 14.--Luminous efficiency of the firefly, shaded area
÷ total area (_after Ives and Coblentz_).]

The spectral energy curve for the firefly has been worked out by Ives and
Coblentz (1910), using a photographic method in which the intensities of
different wave-lengths of the firefly (_Photinus pyralis_) light is
compared with that of a carbon glow lamp by measuring theamount of
photochemical change produced on panchromatic photographic plates. Fig.
11 gives the energy curves of various fireflies and the carbon glow lamp
in the same spectral region. The visual sensibility curve used by Ives
and Coblentz is that of Nutting (1908, 1911), based on Konig's data. It
is reproduced in Fig. 6. The latest visibility curve is that of Hyde,
Forsyth and Cady (1918), reproduced in Fig. 12. It is based on
observations of twenty-nine individuals. As individuals vary considerably
in their sensibility to different wave-lengths, the visibility curve
represents an average, but it is the only standard we have with which to
evaluate the energy we call light. Color-blind individuals would have a
visibility curve very different from normal individuals. Composite curves
showing the luminous efficiency of the 4-watt carbon glow lamp and the
firefly, both in relation to visibility, are given in Figs. 13 and 14,
respectively. In these figures the luminous efficiency is the shaded
area ÷ total area, 0.43 per cent. for the carbon glow lamp and 99.5 per
cent. for the firefly, "these numbers representing the relative amounts
of light (measured on a photometer) for equal amounts of radiated
energy--a striking illustration of the wastefulness of artificial methods
of light production. From the specific consumption of the tungsten lamp
(1.6 watts per spherical candle) and the mercury arc (.55 watts per
spherical candle) we obtained by comparison with the carbon filament that
their luminous efficiencies are 1.3 and 3.8 per cent. The most efficient
artificial illuminant therefore has about 4 per cent. of the luminous
efficiency of the firefly." This is calculated to be .02 watts per
candle. More recent determinations (Coblentz, 1912), using a new
sensibility curve of Nutting's (1911) for a partially light-adapted eye,
give the reduced luminous efficiency as 87 per cent. for _Photinus
pyralis_, 80 per cent. for _Photinus consanguineus_ and 92 per cent. for
_Photuris pennsylvanica_.

[Illustration: FIG. 15.--Spectral energy, luminosity and visibility
curves (_after Gibson and McNicholas_)
  A. Spectral energy curve of Hefner lamp.
  B. Spectral energy curve of acetylene flame.
  C. Spectral energy curve of tungsten (gas-filled) glow lamp.
  D. Spectral energy curve of black body at 5000° absolute (sunlight).
  E. Spectral energy curve of blue sky.
  H_g_. Spectral energy curve of Heræus quartz mercury lamp.
  L_v_. Visibility curve for human eye.
  L_a_. Luminosity of Hefner lamp.
  L_e_. Luminosity of blue sky.
]

The luminous efficiencies of various forms of artificial illuminants
have been calculated by Ives (1915) and are given together with that of
the firefly in Table 6. Fig. 15 gives spectral energy curves for
various illuminants reduced to 100 at λ = .590µ, luminosity curves for
the Hefner lamp and blue sky, and a visibility curve worked out by
Coblentz and Emerson (1917) from observations on 130 individuals.


TABLE 6

_Luminous Efficiencies of Various Illuminants_

  ------------------------+------------------------+--------+----------------
                          |                        |        |Efficiency
   Illuminant and         |   Commercial           | Lumens |(visible
   commercial description |   rating               | per    |radiation ×
                          |                        | watt   |visual
                          |                        |        |sensibility ÷
                          |                        |        |total radiation)
  ------------------------+------------------------+--------+----------------
  Carbon incandescent lamp| 4 watts per mean       |   2.6  |   0.0042
   oval anchored (treated)|  horiz. c.             |        |
   filament               |                        |        |
                          |                        |        |
  Tungsten incandescent   | 1.25 watts per mean    |   8.0  |    .013
   lamp, vacuum type      |  horiz. c.             |        |
                          |                        |        |
  Mazda, type c           | 600 C. P. 20 amp.,     |  19.6  |    .032
                          |  0.5 w. p. c. Series   |        |
                          |  type C.               |        |
                          |                        |        |
  Carbon arc (open)       | 9.6 amp. clear globe   |  11.8  |    .019
                          |                        |        |
  Open arc, yellow flame, | 10 amp. D. C.          |  44.7  |    .072
   inclined trim          |                        |        |
                          |                        |        |
  Quartz mercury arc      | 174-197 volt, 4.2 amp. |  42.0  |    .068
                          |                        |        |
  Glass mercury arc       | 40-70 volt, 3.5 amp.   |  23.0  |    .037
                          |                        |        |
  Nernst lamp             |                        |   4.8  |    .0077
                          |                        |        |
  Acetylene               | 1 L per hr. consumption|    .67 |    .0011
                          |                        |        |
  Petroleum lamp          |                        |    .26 |    .0004
                          |                        |        |
  Open flame gas burner   | Bray 6 high pressure   |    .22 |    .00036
                          |                        |        |
  Incandescent gas lamp,  | .350 lumens per        |   1.2  |    .0019
   low pressure           |  B. T. U. per hr.      |        |
                          |                        |        |
  Incandescent gas lamp,  | .578 lumens per        |   2.0  |    .0032
   high pressure          |  B. T. U. per hr.      |        |
                          |                        |        |
  Firefly                 |                        | 629.0  |    .96
  ------------------------+------------------------+--------+----------------

The firefly light by the above method of calculating efficiency is not
100 per cent. efficient because its maximum (λ = 0.567µ) does not
correspond with the maximum sensibility of the eye (λ = 0.565µ), but
taking into consideration also other effects of color, the firefly light
would be a still more inefficient and trying one for artificial
illumination, as all objects would appear a nearly uniform green hue.
Indeed the distortion would be even greater than with the mercury arc,
whose objectionable green hue is so well known. "We may say, therefore,
that the firefly has carried the striving for efficiency too far to be
acceptable to human use; it has produced the most efficient light known,
as far as amount of light for expenditure of energy is concerned, but
has produced it at the (inevitable) expense of range of color. The most
efficient light for human use, taking into account both color and
energy-light relationships, would be a light similar to the firefly
light containing no radiation beyond the visible spectrum, but differing
from it by being white." (Ives, 1910.) Although the spectral energy
curve for _Cypridina_ light has not been worked out, it will be noted
that the _Cypridina_ spectrum is much longer than that of the firefly,
more nearly approaching the spectrum of an incandescent solid giving
white light. It approaches, but does not attain the ideal.

Although Muraoka (1896) and Singh and Maulik (1911) have described
radiations coming from fireflies which would pass opaque objects and
affect a photographic plate, and Dubois reports the same from bacteria,
the existence of such radiation has been denied by Suchsland (1898),
Schurig (1901) and Molisch (1904 book). The experiments of Molisch on
luminous bacteria are of greatest interest, for they are very carefully
controlled and show without a doubt that black paper or Zn, Al, or Cu
sheet will allow no rays from these organisms to pass that will affect a
photographic plate, even after several days' exposure. The _visible_
light of luminous bacteria will affect the plate after one second
exposure. Moreover, Molisch has pointed out the errors of those who
claim to have found penetrating radiation in luminous forms. It seems
that certain kinds of cardboard, especially yellow varieties, or wood,
will give off vapors that affect the photographic plate. The action is
especially marked with damp cardboard at a temperature of 25°-35° C.,
and Dubois and Muraoka must have used such cardboard to cover their
plates. A piece of old dry section of beech or oak trunk, placed on a
photographic plate for 15 hours in a totally dark place, will register a
beautiful picture of the annual rings of growth, medullary rays,
junction of bark and wood, etc. Russell (1897) had previously found that
many bodies, both metals and substances of organic origin (gums, wood,
paper, etc.), placed in contact with photographic plates, would affect
them, and concluded that vapors and not rays were the active agents. As
a dry piece of wood has a very definite smell, there is something given
off which can affect our nose and there is no reason why it should not
change, by purely chemical action, the photographic plate. This action
of wood on the plate is prevented by interposing a sheet of glass.
Frankland (1898) has described similar vapors coming from colonies of
_Bacillus proteus vulgaris_ and _B. coli communis_ which affect a
photographic plate laid directly over the colonies in an open petri
dish. There is no effect if the glass cover of the petri dish is between
plate and bacteria. There is, then, no specific emission of X-rays or
similar penetrating radiation from luminous tissues which will affect
the photographic plate through opaque screens.

A similar conclusion is reached if we attack the problem in another way.
X-rays and radium rays (Becquerel rays) cause fluorescence of ZnS,
barium platinocyanide, willemite (Zn_{2}SiO_{4}), and calcium
tungstate. Coblentz (1912) showed that the firefly will cause no
fluorescence of a barium platinocyanide screen and I have been unable to
detect fluorescence of zinc sulphide, barium platinocyanide, zinc
silicate (willemite) or calcium tungstate shielded from _Cypridina_
light by black paper, although the light of this organism is quite
bright enough to cause phosphorescence of zinc sulphide without the
black paper. The samples of the above four substances all showed
fluorescence in presence of radium rays, but only the ZnS phosphoresces
after exposure to light rays, although the willemite was phosphorescent
after exposure to the ultra-violet.

While photometry at low intensities is a difficult procedure at best, if
the light varies in intensity or is a flash, accurate measurements
become well-nigh impossible. The figures given for intensity of animal
luminescence must, therefore, be accepted with a realization of the
difficulties of measurement. By candle is meant the international
candle, unless otherwise specified, equal to 1.11 Hefner candles (H. K.)
0.1 pentane lamp and 0.104 carcel units. It is a measure of intensity.

Amount of light, or light flux, measured in lumens, is that emitted in a
unit solid angle (area/_r_^2) by a point source of one candle-power. One
candle-power emits 4π lumens. The latest figure for the mechanical
equivalent of light at λ = .566 is .0015 watt (Hyde, Forsyth and Cady,
1919), _i.e._, 1 lumen = .0015 watt. One watt is 10^7 ergs (one joule)
per second.

The illumination (of a surface) is that given by one candle at one
metre, the candle metre (C.M.) or lux. The surface then receives one
lumen per square metre. A metre kerze (M.K.) is the illumination given
by one Hefner candle at one metre distance.

The brightness of a surface is measured in lamberts or millilamberts. A
lambert is "the brightness of a perfectly diffusing surface radiating or
reflecting one lumen per square cm." A millilambert is 1/1000 lambert.
For further definitions the reader is referred to the reports of the
committee on nomenclature of the Illuminating Engineering Society.

Dubois (1886) states that one of the prothoracic organs of _Pyrophorus
noctilucus_ has a light intensity of 1/150 Ph[oe]nix candle of eight to
the pound (probably about equivalent to 1/150 candle) and that 37 or 38
beetles (each using all three light organs) would produce light
equivalent to one Ph[oe]nix candle. Langley (1890) found that to the eye
the prothoracic organ of _Pyrophorus noctilucus_ gave one-eighth as much
light as an equal area of a candle and the actual candle-power of the
insect was 1/1600 candle. It may be remarked in passing how widely
divergent these observations are.

For the flash of the firefly (_Photinus pyralis_) Coblentz (1912) found
variation from 1/50 to 1/400 candle, the predominating values being
around 1/400 candle. A continuous steady glow is sometimes obtained from
this insect and it proved to be of the order of 1/50,000 candle.

Steady sources of light can be more easily measured and we have two
records of the light intensity from luminous organisms with continuous
light. One of these is a fish, _Photoblepharon palpebratus_, with a
large luminous organ under the eye, of flattened oval shape, 11 × 5 mm.,
which glows continuously without change of intensity. The organ can be
darkened by a screen similar to an eyelid which pulls up over it. Steche
(1909) reports the intensity to be .0024 M.K.[3]

[3] The metre-kerze is a unit of illumination, not of intensity, and is
incorrectly used by Steche.

Luminous bacteria probably glow with less intensity than any other
organism. The light from a single organism cannot be seen but that from
a colony is visible to the dark-adapted eye. Even so we must remember
that the eye is an exceedingly delicate instrument which can detect very
small energy changes. The "minimum radiation visually perceptible" has
been calculated by Reeves (1917) to be in the neighborhood of 18 ×
10^{-10} ergs per second and the light from a small colony of luminous
bacteria represents little more radiation than this.

Lode (1904, 1908), by a modified grease spot photometer method,
ascertained that the light of his brightest bacterial colony of _Vibrio
rumple_ had an intensity of 7.85 × 10^{-10} H.K. per sq. mm. or 0.785
H.K. per 1000 sq. metres (=0.562 German-normal candles per 1000 sq.
metres). In round numbers this is about one German-normal candle per
2000 sq. metres, or two to three times this area for the light from an
ordinary stearin candle. Lode calculated that the dome of St. Peter's at
Rome, if covered with bacteria, would give little more light than a
common stearin candle. An ordinary room of 50 sq. metres wall and
ceiling area would give out only 0.039 German-normal candle. It does not
seem likely that luminous bacteria will ever come into vogue for
illuminating purposes. Friedberger and Doepner (1907) by a photographic
method, not entirely free from error, found that one square millimetre
of lighting surface of a bouillon culture of photobacteria gave 6.8 ×
10^{-9} German-normal candles, about ten times Lode's value. Even at
this rate commercial lighting by luminous bacteria does not appear a
promising field for investors.

To sum up, we may say that light from animal sources is in no way
different from light of ordinary sources, except in intensity and
spectral extent. It is all visible light, containing no infra-red or
ultra-violet radiation or rays which are capable of penetrating opaque
objects. It is not polarized as produced, but may be polarized by
passing through a Nichol prism. Like ordinary light, animal light will
also cause fluorescence and phosphorescence of substances, affect a
photographic plate, cause marked heliotropism of plant seedlings
(Nadson, 1903) and stimulate the formation of chlorophyll (Issatschenko,
1903, 1907). Because of the weakness of bacterial light, etiolated
seedlings do not become green to the eye (Molisch, 1912 book), but a
small amount of chlorophyll is formed which can be recognized by the
spectroscope because of its absorption bands.




CHAPTER IV

STRUCTURE OF LUMINOUS ORGANS


The production of light is the converse of the detection of light. In
the first case chemical energy is converted into radiant energy; in the
second case radiant energy is converted into chemical energy. The
lantern of the firefly is an organ of _chemi-photic_ change; the eye is
an organ of _photo-chemical_ change. While it is theoretically probable
that all reactions which proceed in one direction under the influence of
light, will proceed in the opposite direction with the evolution of
light, the formation of luciferin from oxyluciferin (described in
Chapter VI) is the only one definitely known. Perhaps we may place in
this category also the instances of photoluminescence, but the chemical
reaction involved cannot be pointed out.

We know of no animal whose eyes, the organs, _par excellence_, of
photochemical change, give off light in the dark. All cases of luminous
eyes have been conclusively shown to be purely reflection phenomena. The
eyes of a cat only glow if some stray light is present which may enter
and be reflected out again. Photochemical reactions and chemiluminescent
reactions do have this in common, however, that they are largely but not
exclusively oxidations. Whether all photochemical changes in the eyes in
animals require oxygen or not, is unknown, but all animal
light-producing reactions, without exception, are oxidations, and light
is only produced if oxygen is present. Some material is oxidized.

In general, we may divide luminous organisms into two great classes
according as the oxidizable material is burned within the cell where it
is formed or is secreted to the exterior and is burned
outside--intracellular and extracellular luminescence. Many animals with
intracellular luminescence have quite complicated luminous organs. It is
an interesting fact that a great similarity may be observed between the
evolution of the complex organs of vision and of these complicated
organs. In the simplest unicellular forms certain structures within the
cell serve as the photochemical detectors of light, while in luminous
protozoa, similarly, granules scattered throughout the cell are oxidized
with light production. In the higher forms the eye contains groups of
photosensitive cells connected with afferent nerves, lenses, and
accessory structures for properly adjusting the light, while luminous
organs contain groups of photogenic cells in connection with efferent
nerves, lenses, and accessory structures for properly directing the
light. It is interesting to note that in the two groups where the eye
has attained its highest development, the cephalopods and vertebrates,
here also the luminous organ is found in greatest complexity and
perfection. In intermediate stages of evolution the eye and luminous
organ so closely approach each other in structure that it is still a
mooted question whether certain organs found in worms and crustacea are
intended for receiving or producing light.

We may also divide luminous forms into two groups according as the
oxidation of luminous material goes on continuously, independently of
any stimulation of the organism; or is intermittent, oxidation and
luminescence occurring only as a result of stimulation, using the word
"stimulation" in the same sense in which it is used in connection with
nerve or muscle tissue. Bacteria, fungi, and a few fish produce light
continuously and independently of stimulation. Its intensity varies only
over long periods of time and is dependent on the nature of the nutrient
medium or general physiological condition of the organism. All other
forms give off no light until they are stimulated. Stimulation may of
course come from the inside (nerves) or outside. Only under unfavorable
conditions, such as will eventually lead to the destruction of the
luminous cells, do these forms give off a continuous light. This has
often been spoken of as the "death glow," and is to be compared with
_rigor_ in muscle tissue.

Some of the fish which produce a continuous light possess a movable
screen similar to an eyelid which can be drawn across the organ, thus
shutting off the light, so that the animal appears to belong to the
group which flashes on stimulation. This is true of _Photoblepharon_,
while _Anomalops_ can rotate the light organ itself downward, so as to
bring the lighting surface against the body wall and thus cut off the
light (Steche, 1909). Other fish (_Monocentris_) are unable to "turn
off" their light.

Animals which flash spontaneously on stimulation through nerves from
within, possess a very varied rhythm. The different species of fireflies
can be distinguished by the character of their flashing (McDermott,
1910-17; Mast, 1912). Fig. 16 shows the method of flashing of some
common eastern North America species. The glowworm light lasts for many
seconds and then dies out. This interval of darkness persists for some
minutes and is then followed by another period of glowing. Some
fireflies have a light which may be described as partially
intermittent. It lasts for hours, but may become more dim or be
intensified on stimulation.

[Illustration: FIG. 16.--Chart showing relative intensities and
durations of flashes of American fireflies (_after McDermott_). One cm.
vertically = approximately 0.02 candle power; one cm. horizontally =
approximately one second. The flash of the males (♂) is at the left;
that of females (♀) at right of chart.]

Some forms only produce light at certain seasons of the year. According
to Giesbrecht (1895) this is true of the copepods, which only light in
summer and autumn, and according to Greene (1899) in the toad-fish;
_Porichthys_, which can only be stimulated to luminesce during the
spawning season in spring and early summer.

Some animals possess a periodicity of luminescence. They only luminesce
at night and fail to respond to stimulation or are difficult to
stimulate during the day. Bright light has an inhibiting effect. Perhaps
correlated with this is the fact that most luminous forms are strongly
negatively heliotropic. Fireflies lie hidden in the day, to appear about
dusk and the ostracod crustacean, _Cypridina_, is difficult to obtain on
moonlight nights.

The Ctenophores were the first forms in which the inhibiting effect of
light was noticed. This was described by Allman (1862) and has been
confirmed by a number of observers, especially Peters (1905). Massart
found that _Noctiluca_ was difficult to stimulate during the day and
_Ceratium_, according to both Zacharias (1905) and Moore (1908), only
luminesces at night, or if kept in darkness, for some little time.
Crozier[4] finds a persistent day-night rhythm of light production when
_Ptychodera_, a balanoglossid, is maintained for eight days in continued
darkness. The animal is difficult to stimulate during the period which
corresponds to day and luminesces brilliantly and at the slightest touch
during the period which corresponds to night.

On the other hand, a great many forms are able to luminesce quite
independently of previous illumination. According to Crozier[4]
_Chætopterus_ luminescence is not affected by an exposure to 3000
metre-candles for six hours.

[4] Private communication.

In the case of animals with extracellular luminescence we may speak of
luminous secretions and true luminous glands. A large number of forms
possess luminous glands or gland cells, including some of the _medusæ_,
the hydroids (probably), the pennatulids (?), the molluscs (_Pholas_ and
_Phyllirhoë_) (probably), some cephalopods (_Heteroteuthis_ and
_Sepietta_), most annelids, ostracods, copepods, some schizopods
(_Gnathophausia_) and decapod (_Heterocarpus_ and _Aristeus_)
crustaceans, all myriapods, and the balanoglossids. The remaining
organisms burn their material within the cell. These include the
bacteria, fungi, protozoa, some medusæ (?), ctenophores (probably), most
cephalopods, a few annelids (_Tomopterus_ (?)), ophiuroids (?), some
schizopod (_Nyctiphanes_, _Euphasia_, _Nematocelis_, _Stylochiron_) and
decapod (_Sergestes_) crustacea, all(?) insects, _Pyrosoma_, and fishes
(_selachians_ and _teleosts_). It is among this latter type that the
most complicated luminous organs have been developed. While a
description of all the types of luminous organs and luminous structures
cannot be attempted here (excellent descriptions have been given by
Dahlgren and Mangold) it is necessary to understand the structural
conditions in a few of the forms whose physiology has attracted most
attention.

Luminous bacteria are so small that the light from a single individual
cannot be seen. It is almost impossible to make out structural
differences within the cell and we cannot definitely state in just what
special region, if any, the luminescence is produced. We do know that
the light is intracellular and that filtration of the bacteria from
their culture medium gives a dark sterile filtrate absolutely free from
any luminous secretion.

Among protozoa, in certain forms at least, it is easy to observe that
luminescence is connected with globules or granules which were
considered by the earlier observers to be oil droplets. Thus, in
_Noctiluca_ (Figs. 17 and 18), when the animal is violently stimulated
or in the presence of reagents which slowly kill it, the whole interior
appears a mass of starry points of light which can be traced to minute
granules along the strands of protoplasm (Quatrefages, 1850).

[Illustration: FIG. 17.--_Noctiluca miliaris_, showing photogenic
granules in cytoplasm. _n_, nucleus; _c_, cytoplasmic strands containing
photogenic (large) and other (small) granules; _p_, pharynx; _f_,
flagellum; _o_, oral groove; _t_, tentacle; _s_, spines at base of
tentacle; _v_, vacuoles. _Drawn by E. B. Harvey._]

[Illustration: FIG. 18.--_Noctiluca miliaris_ as it appears during
luminescence (_after Quatrefages_). Upper left and middle, low power;
below, high power; upper right, a crushed fragment still luminescent.]

Turning to the multicellular forms, we find the simplest development of
luminosity in those animals which possess gland cells producing a
luminous secretion. These cells may be scattered over the surface of the
animal as in _Chætopterus_ (Fig. 19) or _Cavernularia_, or restricted to
certain areas [_Pholas_, (Fig. 19),] or more definitely localized to
form an isolated group of gland cells as in _Cypridina_. True
multicellular glands also occur. In every case, however, we find that
the luminosity of these uni- or multicellular glands is connected with
the presence of granules. They are often spoken of as _luciferine
granules_, although it is not certain whether they are made up of
luciferin or luciferase (see Chapter IV) or both. They are most similar
to the zymogen granules found so abundantly in gland cells and thought
to be the precursors of various enzymes. According to Dahlgren (1915),
the luciferine granules stain blue-black by iron hæmatoxylon after
fixation at the boiling point, and photogenic cells can be detected by
this method of selective staining. Dubois (1914, book), who regards them
as examples of _bioprotein_, comparable to the chondriosomes and handed
on from one generation to another, gives them the name of _vacuolides_
or _macrozymases_. In some forms he has described their transformation
into crystals and believed at one time that animal light was a
crystalloluminescence. His figures of the crystal transformation are
not very convincing. Pierantoni (1915) has considered the granules to be
_symbiotic_ luminous bacteria, but this is certainly not the case.

[Illustration: FIG. 19.--Diagram of _Pholas_ (right) and _Chætopterus_
(left) to show distribution of luminous areas (_after Panceri_).]

The light of _Chætopterus_ comes from a material mixed with a mucous
secretion formed over almost the whole body surfaces of the animal. A
section of the epithelium shows large mucous-producing cells and smaller
granule-containing light cells (Fig. 20). These appear to be under
nervous control, as a strong stimulation in one part of the body causes
luminescence which spreads over the whole surface of the worm. The
animal becomes fatigued rather readily, however. In the pennatulids,
such as _Cavernularia_, we have also the formation of a luminous
secretion over the whole surface of the body and the individual animals
in this colonial form are also connected with nerves. A stimulation in
any local region, as Panceri (1872) first showed (Fig. 21), will cause a
wave of luminosity to spread from this point until it extends over the
whole surface of the colony. In _Pennatula_ the rate of this luminous
wave is about 5 cm. per second.

[Illustration: FIG. 20.--Sectional view of the luminous epithelium of
_Chætopterus_ (_after Dahlgren_). _cu_, cuticle; _l. c._, light cells,
some showing discharge of secretion; _d. l. c._, discharged and emptied
light cells; _m. c._, mucous cells.]

[Illustration: FIG. 21.--Diagram of _Pennatula_, showing by arrows the
course of a wave of luminosity which spreads over the colony from the
point stimulated (s) (_after Panceri_).]

_Pholas dactylus_ possesses similar light cells to those of
_Chætopterus_, but they are restricted to narrow bands on the siphon and
mantle and a pair of triangular spots near the retractor muscles. Nerves
pass to the luminous regions.

In many luminous animals the light secretion formed over the surface of
the body is small in amount and adheres to the animal because it is
embedded in the mucous skin secretions. In those forms which possess a
true localized light gland the luminous secretion when expelled into the
sea water (if the animal be a marine form) may persist as a luminous
streak for some time and exhibit diffusion and convection
movements. The most beautiful examples of luminous secretions are found
among the ostracod crustacea.

[Illustration: FIG. 22.--Luminous gland of _Cypridina hilgendorfii_
(_after Yatsu_). 2, longitudinal section. 4, transverse section.]

[Illustration: FIG. 23.--Single enlarged gland cell of _Cypridina_
(_after Dahlgren_). P, nucleus and plasmasome; C, cytoplasm; F,
secretion fibrils; D, reservoir duct filled with large yellow granules;
O, valve-like outer opening of cell at surface of body.]

In _Cypridina hilgendorfii_ the luminous gland is situated on the upper
lip near the mouth. It is made up of elongate (some 0.7 mm. in length),
spindle-shaped cells, each one of which opens by a separate pore with a
kind of valve. The openings are arranged on five protuberances. Muscle
fibres pass between the gland cells in such a way that by contracting
the secretion can be forced out. In the sea water the secretion
luminesces brilliantly and the Japanese call these forms _umi hotaru_,
or marine fireflies. Fig. 22 is a diagram showing the structure.
Watanabe (1897), who first studied this form, and also Yatsu (1917) have
described two kinds of granule-containing cells, one with large yellow
globules, 4-10µ in diameter (Fig. 23), the other with small colorless
granules 0.5, in diameter. I have observed in the living form these two
types and also large colorless globules of the same size as the yellow
globules. All dissolve when extruded into the sea water. Dahlgren[5] has
described from sections four types of cells containing (1) large
globules, (2) small granules, (3) a fat-like material, (4) a mucous
material. Just what the significance and nature of these types of
substance is cannot be stated at present. At least one, probably two,
are concerned in light production. The others may possibly form
digestive fluids which act on the food of the animal.

[5] Private communication soon to be published.

Turning now to the animals possessing light cells with intracellular
luminescence we find in general that such light cells are localized to
form definite light organs and that these may be single, as in the
common fireflies, paired, as the prothoracic light organs of
_Pyrophorus_, or scattered over the surface of the body, as in so many
shrimps, cephalopods and fishes, when they are often called photophores.
The light cells proper are often associated with reflectors, lenses,
opaque screens and color screens.

[Illustration: FIG. 24.--Distal portion of malpighian tubule of
_Bolitophila_, showing modification to form photogenic organ (_after
Wheeler and Williams_). _MT_{1}_, _MT_{4}_, malpighian tubules forming
photogenic organ; _R_, reflector; _M_, muscle; _T_, trachea.]

The insects possess the simplest types of intracellular light organs, a
mass of photogenic cells, which, in the common firefly (_a lampyrid
beetle_) of Eastern North America, has probably been developed from the
fat body, while in the New Zealand glowworm, the larva of a tipulid fly
(_Bolitophila luminosa_), part of the Malpighian tubule cells have
acquired photogenic power (Wheeler and Williams, 1915). This is
illustrated in Fig. 24.

The photogenic organ of the firefly is made up of two kinds of cells, a
dorsal mass of small cells several layers deep, the reflector layer, and
a ventral mass of large cells with indistinct boundaries, the photogenic
layer (Fig. 25). The photogenic cells contain a mass of granules,
spherical in the male and short rods in the female. The photogenic cells
are divided into groups by large tracheal trunks which pass into the
light organ and branch to form tracheoles connected with tracheal end
cells. The exact distribution varies in different species, but in all
the arrangement is such as to give a very abundant oxygen supply. Each
group of photogenic cells is surrounded by a clear ectoplasm containing
no granules. The tracheoles pass through this and either end openly
within the photogenic cells or anastomose with tracheoles from
neighboring tracheæ. Nerves, but no blood-vessels--which are absent in
insects--enter the organ. It is difficult to determine if the nerves
supply the tracheal end cells or the photogenic cells.

[Illustration: FIG. 25.--Sectional view of photogenic organ of the
firefly (_after Williams_), showing reflector or crystal layer (_U_)
above and photogenic cells (_P_) below. _C_, cuticula; _T_, trachea;
_c_, capillaries of tracheal end cells; _H_, hypodermis; _EC_, tracheal
end cells; _N_, nerve.]

The dorsal reflecting layer is made up of cells containing numerous
minute crystals of some purin base, either xanthin or urates, or both.
They have a white milky appearance and while they are certainly not good
reflectors in the optical sense, they do act as a white background,
scatter incident light, and partially prevent its penetration to the
internal organs of the firefly. Although a few crystals similar to those
of the reflector layer are found in the photogenic cells and in other
cells of the body, it is known that the photogenic cells are not
transformed into the reflector cells. The two layers are distinct and
permanent from an early stage in development.

Curiously enough, the light organ of the larva of the firefly (glowworm)
is quite distinct from that of the adult. Like so many other structures
in insects, the adult organ is developed anew from potential photogenic
cells during the pupal period. Even the egg of the firefly is luminous
and glows with a steady light, and during the pupal period light may
sometimes be seen coming from the thoracic region.

In the firefly there is no true lens, the light merely shining through
the cuticle which is transparent over the light organ, whereas over the
rest of the body it is dark and pigmented. In the deep sea shrimp,
_Acanthephyra debelis_, with light organs scattered over the surface of
the body, the cuticle covering the light organ forms a concavo-convex
lens, behind which are the photogenic cells (Kemp, 1910). As may be seen
from Fig. 26, the lens is made up of three layers which suggests that it
may be corrected for chromatic aberration--a veritable "achromatic
triplet." In an allied form, _Sergestes_ (Fig. 27), the lens is of two
layers and double convex. Optical studies of these lanterns have been
made by Trojan (1907). The course of the light rays is shown in Fig. 28.
The lens of these organs is also bluish in color which suggests that
they may serve also as color filters. Behind the photogenic cells is a
mass of connective tissues through which enters the nerve, for the
light of these organs is under the control of the animal and may be
flashed "at will."

[Illustration: FIG. 26.--Sectional view of photogenic organ of
_Acanthephyra debilis_ (_after Kemp_). _n_, nerve; _s. l._, sheathing
layer of cells; _g_, cone of refractive granules at end of nerve strand;
_c_, cellular layer; _i. l._, _m. l._, _o. l._, inner, middle and outer
layer of lens.]

[Illustration: FIG. 27.--Sectional view of photogenic organ of
_Sergestes prehensilis_ (_after Terao_). _bm_, basement membrane; _cs_,
connective strands of photogenic layer; _hy_, hypodermis; _l_{1}_,
_l_{2}_, _l_{3}_, layers of lens; _le_, lens epithelium; _n_, nerve;
_ph_, photogenic cells; _pi_, pigment layer; _r_, reflector; _th_,
theca.]

[Illustration: FIG. 28.--Diagram of photogenic organ of _Nyctiphanes
Conchii_, to show pathways of light rays arising in the light cell layer
(_after Trojan_). _p_, pigment; _ri_, inner reflector; _lp_, light
cells; _rf_, refractor; _f_, focus; _l_, lens; _A-A_, axis;
_a_{1}-a_{4}_, _b_{1}-b_{4}_, light rays reflected from _ri_;
_c_{1}-c_{4}_, light rays passing directly outward; _d_{1}-d_{9}_ and
_e_{1}-e_{9}_, light rays which have passed refractor and lens
respectively.]

All gradations in complexity of light organs may be found from the
condition in the shrimp just described to that found among the squid and
fish. Figs. 29 and 30 are sections of two of the more complicated types
found in squid. The explanation given to the various structures is that
of Chun (1903) to whom we are indebted for a careful histological
investigation of these forms. It will be noted that in addition to
photogenic and lens tissues there are various types of reflector cells
and a line of pigment about the whole inner surface of the organ to
effectively screen the animal's tissues from the light. In one form
(Fig. 30) chromatophores are found about the region where the light is
emitted and these no doubt serve as color filters. There are also an
abundant blood supply and nerves passing to the organ. Figs. 30 and 31
are sections through light organs of fishes.

We thus see that light organs may be very simple and also very
complicated. The latter must have evolved from the former, although it
is not always possible to point out the intermediate stages. It is not
within the scope of this book to discuss bioluminescence in its
evolutionary aspects. It may be worth while, however, to point out
briefly what is known concerning the use of the light to the animal.
There are four possibilities.

[Illustration: FIG. 29.--Sectional view of photogenic organ of a squid,
_Abraliopsis_ (_after Chun_.) _refl^1_, _refl^2_, reflectors; _lac._,
lacunar spaces; _chr._, pigment screen of chromatophores; _chr.^1_,
chromatophore; _phot._, photogenic cells; _l_, lens; _co._, cuticle;
_v_, blood vessel; _fibr._, connective tissue.]

(1) The light may be of no use whatever, purely fortuitous, an
accompaniment of some necessary or even unnecessary chemical reaction.

This appears to be the case in the luminous bacteria and fungi and
perhaps the great majority of forms which make up the marine plankton,
_Noctiluca_, dinoflagellates, jelly-fish, ctenophores and even the
sessile sea pens.

[Illustration: FIG. 30.--Sectional view of photogenic organ of a squid,
_Calliteuthis_ (_after Chun_). _phot._, photogenic cells; _l_, _l^1_,
lens; _n_, nerve; _spec._, "Spiegel"; _pg._, pigmented screen; _c.
fusif._, spindle-shaped reflector cells; _chr._, chromatophore color
screen.]

[Illustration: FIG. 31.--Sectional view of photogenic organ of a fish,
_Stomias_ (_after Brauer_). _p_, pigment screen; _dr_, _dr^1_,
photogenic gland cells; _l_, lens.]

We know that luminous bacteria occasionally lose the power of lighting
and that on certain culture media they develop as non-luminous forms.
Luminescence is not indispensable to them. The same is true of some of
the fungi but _Noctiluca_ and other animals are not known in a
non-luminous condition, although we can see no definite value to the
organism of this power of luminescence.

[Illustration: FIG. 32.--Sectional view of photogenic organ of a fish,
_Argyrophelecus affinis_ (_after Brauer_). _p_, pigmented screen; _dr._,
photogenic cells; _r_, _r^1_, reflector?; _l_, lens?; _s_, sclera; _g_,
connective tissue.]

In the case of sea pens, however, we might suppose that the light acts
as an attraction to small organisms on which the sea pen feeds, although
these creatures only luminesce when stimulated in some way, which rather
detracts from the above suggestion.

(2) The light may act as a warning to scare away predacious animals
which would otherwise feed on the luminous organism. Perhaps this is the
case in the sea pens, although these forms possess nematocysts which
should serve as adequate protection. The marine worm, _Chætopterus_, is
brightly luminous and lives its whole life in an opaque parchment tube.
If this tube were torn open by a predacious form we might conceive that
the attacking animal would be alarmed by the light and refrain from
destroying the worm. The _Chætopterus_, however, could not rebuild
another tube and its light would only protect it in the night time.
These cases will suffice to indicate the difficulties and perplexities
of the problem. Perhaps we may add one more guess and suppose that the
light of certain fishes is actually for blinding or distracting their
enemies or blinding the forms on which they feed. Until this use of
luminous organs has actually been observed, we can give little credence
to it.

(3) The light may serve as a means of recognition or a sex signal to
bring the sexes together for mating. It would seem from the work of Mast
and of McDermott that this is the case in the common fireflies and it
may be the case in the toad-fish, _Poricthys_, which is only luminous in
the spawning season and in the worm, _Odontosyllis_, of Bermuda, which
is brilliantly luminous while swarming when the eggs and sperm are shed.
It is non-luminous at other times (Galloway and Welch, 1911.)

(4) Finally, it is possible that animals with complex luminous organs,
such as squid, fish and shrimp, actually use these as lanterns. It is
significant that most of them are deep sea forms, living in a region of
perpetual darkness, and it is perfectly logical to suppose that they
make use of their light organs for illuminating purposes.

The whole problem of the use and purpose of luminous organs is an
exceedingly complex and difficult one. We have, perhaps, said enough to
indicate this and may add that in most cases, so far as opinion is based
on actual evidence and observation, that of the layman is of as great
value as that of the scientist.




CHAPTER V

THE CHEMISTRY OF LIGHT PRODUCTION, PART I


Two experiments, both performed very early in the history of
Bioluminescence, are of great importance in understanding the nature of
animal light. Boyle (1667), as already mentioned, proved the necessity
of air for the luminescence of wood and fish and Spallanzani (1794)
showed that parts of luminous medusæ gave no light when dried but if
moistened again would emit light as before. We see then, that air
(oxygen), water, and some photogenic substance are necessary for the
light production. Spallanzani's experiment, which has been confirmed for
a great many luminous forms, shows also that animal luminescence is not
a _vital_ process, in the same sense that the conduction of a nerve
impulse is a vital process. A nerve loses its characteristic property of
conduction on drying or maceration while luminous cells still possess
the power to luminesce after drying or maceration. Using the terminology
of the older physiology we may say that "living protoplasm" is not
necessary for light production.

The experiments of Boyle (1626-91) are of great interest, especially
those in which he studied the behavior of shining wood under the
receiver of his air pump. On October 29, 1667, he wrote:

"Exp. I.: Having procured a Piece of _shining Wood_, about the bigness
of a groat or less, that gave a vivid Light, (for _rotten Wood_) we put
it into a middle sized _Receiver_, so as it was kept from touching the
Cement; and the _Pump_ being set a-work, we observed not, during the 5
or 6 first Exsuctions of the Air, that the splendor of the included Wood
was manifestly lessened (though it was never at all increased;) but
about the 7th Suck, it seemed to glow a little more dim, and afterwards
answered our Expectation, by losing of its Light more and more, as the
Air was still farther pumped out; till at length about the 10th
Exsuction, (though by the removal of the Candles out of the Room, and by
black Cloaths and Hats we made the place as dark as we could, yet) we
could not perceive any light at all to proceed from the _Wood_.

"Exp. II.: Wherefore we let in the outward Air by Degrees and had the
pleasure to see the seemingly extinguished Light revive so fast and
perfectly, that it looked to us almost like a little Flash of Lightning,
and the Splendor of the Wood seemed rather greater than at all less,
than before it was put into the Receiver."

Boyle proved that light from the wood was able to pass a vacuum and
later showed that "shining fish" behaved as the "shining wood," but that
a piece of white hot iron would not regain its light on readmitting air
to the exhausted receiver and that the iron lost its glow under the
air-pump merely because it cooled off. A piece of glowing coal, however,
did lose its light in the absence of air and regained it on again
admitting air, provided the air had not been removed for too long. Boyle
was apparently impressed with the similarity of the light giving process
in glowing coal and shining wood as he draws a comparison between the
two which brings out the fundamental similarity of combustion
processes.

"Resemblances:

VII. The Things wherein I observed a Piece of _shining Wood_ and a
_burning Coal_ to agree or _resemble_ each other are principally these
_five_:

    1. Both of them are _Luminaries_, that is, give _Light_, as having
    it (if I may so speak) _residing in them_; and not like
    _Looking-glasses_, or _white Bodies_, which are conspicuous only by
    the _incident Beams_ of the _Sun_, or some other _luminous Body_,
    which they _reflect_....

    2. Both _shining Wood_ and a _burning Coal_ need the Presence of the
    Air (and that too of such a _Density_ to make them continue
    _shining_)....

    3. Both _shining Wood_ and a _burning Coal_, having been deprived,
    for a Time, of their _Light_, by the withdrawing of the contiguous
    _Air_, may presently recover it by letting in fresh _Air_ upon
    them....

    4. Both a _quick Coal_ and _shining Wood_ will be easily quenched by
    _Water_ and _many other Liquors_....

    5. As a _quick Coal_ is not to be _extinguished_ by the Coldness of
    the _Air_, when it is greater than ordinary; so neither is a Piece
    of _shining Wood_ to be deprived of its _Light_ by the same Quality
    of the _Air_....

Differences:

    1. The first Difference I observed betwixt a _live Coal_ and a
    _shining Wood_ is, that whereas the _Light_ of the _former_ is
    readily _extinguishable_ by _Compression_ (as is obvious in the
    Practice of suddenly _extinguishing_ a piece of _Coal_ by treading
    upon it), I could not find that such a _Compression_ as I could
    conveniently give without losing sight of its operation, would _put
    out_, or much injure the _Light_, even of small Fragments of
    _shining_ Wood....

    2. The next _Unlikeness_ to be taken notice of betwixt _rotten Wood_
    and a _kindled Coal_ is, that the latter will, in a very few
    _Minutes_, be totally _extinguished_ by the withdrawing of the
    _Air_; whereas a Piece of _shining Wood_, being eclipsed by the
    Absence of the _Air_, and kept so for a Time, will immediately
    _recover_ its _Light_ if the _Air_ be let in upon it again within
    half an hour after it was first withdrawn....

    3. The next _Difference_ to be mentioned is, that a _live Coal_,
    being put into a small close Glass, will not continue to _burn_ for
    very many _Minutes_; but a Piece of _shining Wood_ will continue to
    shine for _some_ whole _Days_....

    4. A _fourth Difference_ may be this: that whereas a _Coal_, as it
    _burns_, sends forth Store of _Smoke_ or _Exhalations_, _luminous
    Wood_ does not so.

    5. A _fifth_, flowing from the former, is, that whereas a _Coal_ in
    _shining_ wastes itself at a great Rate, _shining Wood_ does not....

    6. The last Difference I shall take notice of betwixt the bodies
    hitherto compared is, that a _quick Coal_ is actually and vehemently
    hot; whereas I have not observed _shining Wood_ to be so much as
    sensibly _lukewarm_."

It should be clearly borne in mind that if we place luminous organisms,
say bacteria or fungi, in an atmosphere devoid of oxygen and find that
no light is produced, this may merely mean that certain functions of the
cell are interfered with, including light production, but does not
necessarily indicate that oxygen is actually used up in the photogenic
process. If we find, however, that extracts of luminous cells or
luminous secretions devoid of cells cease to light when the oxygen is
removed and again luminesce when it is returned, we may be quite certain
that the photogenic process itself requires free oxygen. As luminous
extracts of fireflies, pennatulids, ostracods, _Pholas_ and others give
off no light when the oxygen is removed, we may safely conclude that for
these luminescences, oxygen is necessary. Bacteria, fungi, and
_Noctiluca_, whose light also disappears in absence of oxygen, although
they are whole cells, we may by analogy also assume to require oxygen in
the photogenic process.

Some of the earlier workers on fireflies and _Noctiluca_ obtained light
even after placing these organisms in absence of oxygen, but they did
not realize how low is the amount of oxygen necessary to produce light.
It is difficult to remove traces of oxygen from the water, traces which
are nevertheless sufficient to cause luminescence. If the organisms are
numerous, as in an emulsion of luminous bacteria, they will themselves
use up all the oxygen and the liquid soon ceases to glow except at the
surface in contact with air. We may gain an idea of the amount of oxygen
necessary for luminescence from an experiment of Beijerinck (1902). He
mixed luminous bacteria with an emulsion of clover leaves containing
chloroplasts and kept the two in the dark until all the oxygen was used
up and the bacteria ceased to glow. If now a match was struck for a
fraction of a second, sufficient oxygen was formed by photosynthesis to
cause the bacteria to luminesce for a short time.

Exact figures on the minimal concentration of oxygen for luminescence
cannot be given. The luminescent secretion of _Cypridina hilgendorfii_
will still give off much light if hydrogen containing only 0.4 per cent.
of oxygen is bubbled through it, _i.e._, a partial oxygen pressure of
1/250 atmosphere (3.04 mm.Hg). However, addition of a fresh emulsion of
yeast cells to a glowing _Cypridina_ secretion is sufficient to rapidly
extinguish the light, because the yeast is capable of utilizing the last
trace of oxygen in the mixture. Light only appears when, by agitation,
we cause more air to dissolve. The minimal concentration of oxygen for
luminescence of _Cypridina_ lies somewhere between 3.04 mm. and the
amount which living yeast fails to extract from solution, a
concentration approaching zero. It is probably nearer the latter figure.

As the oxygen pressure is increased from 0 to about 7 mm., the intensity
of the _Cypridina_ luminescence increases and at the latter figure the
light is just as bright as if the solution were saturated with air (152
mm.O_{2}). Thus, the luminescence requires only a low pressure of oxygen
and the similarity to the saturation of hæmoglobin with oxygen is
obvious. Just as hæmoglobin is nearly saturated with oxygen at low
pressures and becomes bright red in color, so the luminous material
becomes saturated with oxygen at low pressures and glows intensely.

Boyle also made many experiments to show that air was necessary for the
life of animals and the germination of seeds and showed that repeatedly
respired air was unfit for further breathing. About the same time R.
Hooke discovered the true meaning of respiratory movements and by
forcing a blast of air continuously through the lungs with bellows, was
able to keep animals alive. He concludes "that as the bare Motion of the
_Lungs_, without fresh air, contributes nothing to the life of the
Animal, he being found to survive as well as when they were not moved as
when they were; so it was not the Subsiding or Movelessness of the
_Lungs_ that was the immediate cause of death, or the stopping of the
circulation of the Blood through the _Lungs_, but the Want of a
sufficient Supply of fresh Air." The cause of death on collapse of the
lungs could not be better stated to-day. Thus combustion, respiration
and luminescence of flesh or wood were early recognized as related
phenomena.

Although the "gas sylvestre" (CO_{2}) of burning charcoal and
fermentation of wine was known to van Helmont (1577-1644) and Mayow
(1646-1679) in 1674 showed that "spiritus nitroærens" (oxygen) was
responsible for the life of animals and for combustion, a century
elapsed before the true significance of these gases became known. In the
meantime the phlogiston theory of combustion had been developed, Black
(1728-1799) in 1755 had rediscovered carbon dioxide ("fixed air") in the
expired air and Priestley (1733-1804) and Scheele (1742-1786) had both
rediscovered oxygen ("dephlogisticated air") in 1774. About the same
time Lavoisier overthrew the phlogiston doctrine and showed that in the
combustion of organic substances water and CO_{2} are formed.

Later it was realized that this slow combustion did not take place in
the lungs, or in the blood, but in the tissues cells themselves and
respiration in the chemical sense has come to mean this universal slow
combustion in the cells of the body rather than the breathing movements
of the lungs themselves. In anaerobic respiration, CO_{2} is given off,
but no oxygen absorbed. In aerobic respiration, oxygen is absorbed and
CO_{2} given off. In addition we know of many substances which oxidize
by taking up oxygen without giving off CO_{2}. We have seen that oxygen
must be absorbed for luminescence of animals and we may now inquire
whether CO_{2} is given off and the relation between respiration and
light production.

To determine if CO_{2} is given off during luminescence it is necessary
to work with fairly pure luminous materials, obtained from luminous
organisms. It is impossible to use the living organisms themselves as
the CO_{2} continually respired becomes a very disturbing factor. From
_Cypridina_, a small crustacean, two materials soluble in water may be
prepared (_luciferin_ and _luciferase_), which will give a brilliant
luminescence on mixing. It is possible to determine the H-ion
concentration of the two solutions separately and of the mixture of the
two after the luminescence has occurred.

If CO_{2} is produced during luminescence the H-ion concentration of the
luminous solution should increase. Measurements made electrometrically
with the hydrogen electrode have failed to demonstrate any increase in
acidity. The PH of both solutions and of a mixture of the two is 9.04.
This would indicate that CO_{2} is not produced. As both luminous
solutions contain proteins and the luminous substances themselves are
probably proteins, which have a high buffer value, a method of this kind
is none too sensitive. However, we can definitely state that not enough
CO_{2} is produced to be detected and that this may be due to the buffer
action of the luminous substances themselves. After all, unless
luminescence is connected with respiration, we should hardly expect
CO_{2} to be produced.

Another method of testing CO_{2} production is to measure the amount of
heat produced during luminescence. Substances burned during respiration
give off considerable heat, one gram of glucose to CO_{2} and H_{2}O, as
much as 4000 calories. We have seen in Chapter III that no infra-red
radiation is produced in the light of the firefly. This does not mean,
however, that no heat is produced by the reaction which produces the
luminescence. A temperature change of a few thousandths or hundredths of
a degree would evolve no measurable radiation. Coblentz (1912) first
studied the problem of heat production in the firefly, using a
thermocouple as the measuring instrument. He came to the conclusion that
the temperature of the insect was slightly lower than the temperature of
the air and that the luminous segments were slightly hotter than the
non-luminous segments, whereas a dead firefly is of the same temperature
as its surroundings. No definite increase or decrease in temperature
could be established during the flash of the firefly. However, further
work on the firefly is much to be desired.

The use of a living animal for such measurements introduces a possible
source of error in that any contraction of the muscles of the animal
will produce heat which may add to an increase or mask a decrease of
temperature during luminescence. Utilization of extracts of luminous
animals containing the luciferin and luciferase mentioned above avoids
the complications due to muscular contraction. By bringing the solutions
of luciferin and luciferase to the same temperature and then mixing
them one can measure any increase or decrease of temperature which
occurs during the luminescence which results from mixing. We can thus
gain some idea of the heat of oxidation of luciferin.

As a determination of heat production is of considerable interest the
method will be given in some detail. Although the experiment sounds very
simple, it is actually somewhat difficult to carry out. The attainment
of temperature equilibrium between two solutions is very slow when one
wishes to obtain them to within 0.001° C. of the same temperature. After
many attempts, the following arrangement of apparatus (Fig. 33) was
found most satisfactory. About 10 c.c. luciferin solution was placed in
the inner tube (_D_) of a special non-silvered thermos bottle (_A_).
About 1 c.c. of luciferase solution was placed in a very thin-walled
glass tube (_E_) which was immersed in the luciferin solution and
connected with a small motor so that it could be slowly but constantly
rotated, thus stirring the solutions. Thermocouples (_L_ and _M_) of
advance (.008 in)--copper (No. 30, _B_ and _S_, enamel insulated) wire
were paraffined and placed in each tube and the copper wires connected
through a copper double throw switch (_C_) with a Leeds and Northrup
d'Arsonval wall galvanometer (No. 34637, silver strip suspension) of 35
ohms resistance and 310 megohms sensitivity. The constant temperature
junctions (_N_) were placed in a large Dewar flask (_B_) filled with
water at approximately the same temperature as the luciferin solution.
One mm. galvanometer scale division represented 0.003° C. and the
division readings could be estimated to tenths. By means of a glass rod
(_F_) placed in the tube containing luciferase solution, this tube
could be broken and the luciferase and luciferin solution mixed.

[Illustration: FIG. 33.--Apparatus for determining heat production
during luminescence of luciferin. A, special thermos tube. B, Dewar
flask for constant temperature junctions. C, double throw switch. D,
tube containing luciferin solution. E, tube containing luciferase
solution. F, glass rod for breaking E. G, rubber stopper with groove, K,
for pulley cord. H, cork closing thermos tube. J, brass sleeve in H
allowing rotation of E. L, thermojunction in luciferase solution. M,
thermojunction in luciferin solution. N, constant temperature
junctions.]

[Illustration: FIG. 34.--Curve showing temperature change when two tubes
containing water at the same temperature are mixed. 0.1 galvanometer
scale division = 0.003° C. Dots represent readings of thermocouple in
tube D; crosses readings of thermocouple in tube E.]

It was found that even after the luciferase and luciferin solutions
came to the same temperature within the thermos bottle, this was not
necessarily the same as that of the room and a slow rise or fall
occurred as indicated by a slow drift of the galvanometer coil. Readings
of each thermocouple on the galvanometer scale were therefore taken at
one-minute intervals for some time before and after mixing the luciferin
and luciferase solutions and plotted as curves. Control experiments were
also carried out in exactly the same manner as the luciferin-luciferase
experiments, but water was placed in the two tubes instead of luciferin
and luciferase. Figs. 34 and 35 give typical experiments with water and
with luminescent solutions, respectively.

[Illustration: FIG. 35.--Curve showing temperature change when luciferin
and luciferase solutions at the same temperature are mixed. 0.1
galvanometer scale division = 0.003° C. Dots represent readings of
thermocouple in luciferin solution; crosses, readings of thermocouple in
luciferase solution.]

With both control (water) and luciferin experiments there was a slight
rise in temperature on mixing the liquids in the two tubes. The average
rise of five control (water) experiments was .0054° C. and the average
rise of five luciferin experiments was .0048° C.

The average rise in temperature is no doubt due to heat from friction in
mixing of the liquids and breaking of the glass tube. The difference in
the average rise of control and of luciferin experiments is so small
(.0006° C.) as to have little significance. We may therefore conclude
that if any temperature change occurs during the luminescent reaction it
is certainly less than 0.001° C. and probably less than 0.0005° C., too
small to be measured by this method.

To prepare the luciferin solution, two grams of dried _Cypridina_ were
dissolved in 20 c.c. hot water and 10 c.c. of this 10 per cent. solution
was used in the thermos bottle in the above experiments. If we assume
that 1 per cent. of the dried _Cypridina_ is luciferin, 0.01 gram of
luciferin on oxidation was not able to raise the temperature of the 10
c.c. (in reality 11 c.c., since 1 c.c. luciferase solution was mixed
with the 10 c.c. luciferin solution) .001° C. This means that 1 gram
luciferin liberates _at least less_ than 10 calories during the
luminescence accompanying oxidation.

Since 1 gram glucose liberates 4000 calories on complete oxidation to
CO_{2} and H_{2}O, it will be seen that the oxidation of luciferin is a
very different type of reaction from the oxidation of glucose. As we
shall see, it is probably similar to the oxidation of reduced hæmoglobin
or the oxidation of leuco methylene-blue to methylene blue. According to
Barcroft and Hill (1910), 1.85 calories are produced per gram of
hæmoglobin oxidized. I have been unable to find figures for the heat
exchange during oxidation of leuco-dyes, but it is no doubt also small.
Since luciferin evolves no measurable amount of heat on oxidation, we
have very good evidence in support of that obtained by electrometric
measurements of H-ion concentration, that no carbon dioxide is produced
during luminescence of luminous animals.

In most animal cells it is perfectly clear that luminescence does not
accompany respiration, since respiration is a continuous process,
whereas light is only produced on stimulation. It is true that on
stimulation respiration is accelerated, and we might suppose that
luminescence is an accompaniment of accelerated respiratory oxidations;
but this is not the case, for in luminous animals a rise in temperature
of ten degrees centigrade will accelerate the respiratory oxidations 250
per cent. without necessarily causing the production of light.

In fungi and bacteria, on the other hand, which continually emit light,
it is quite natural to suppose that the light is an accompaniment of
respiration, just as we know the heat of these forms to be. This view
was accepted by such of the earlier workers as Fabre in 1855, who found
that luminous portions of a mushroom, _Agaricus olearius_, gave off more
CO_{2} (4.41 c.c. CO_{2} per gram in 36 hours at 12° C.) than
non-luminous portions (2.88 c.c. CO_{2} per gram in 36 hours at 12° C.).
This experiment has never been repeated and there are many reasons
besides luminescence why one piece of fungus might have a more rapid
respiratory rate than another piece. It is not true that rapidly
respiring plant tissues, such as germinating seeds or the spadix of
_Araceæ_, are luminous, although they produce considerable heat.

On the other hand, it is very easy to prove that luminescence, even in
bacteria, is not connected with respiration. Thus, Beijerinck (1889 _c_)
found that of several species of luminous bacteria studied by him, one,
_Bacterium phosphorescens_, was a facultative anaërobe and would grow,
_i.e._, multiply, but not luminesce in the absence of oxygen. Some
forms, ordinarily producing light, will grow, but fail to luminesce at
high temperatures. Beijerinck (1915) has recently found that these
individuals may, by continued cultivation at high temperatures, form
non-luminous strains which fail to luminesce when again brought into
lower temperatures, favorable for luminescence. These non-luminous
mutants occasionally give rise to atavistic brilliantly luminous forms.
Beijerinck also finds that after exposure of _Photobacter splendidum_ to
ultra-violet or strong sunlight, radium or mesothorium rays,
luminescence continues but no growth occurs. There is thus ample
evidence that growth and respiration are properties quite distinct and
separable from luminescence. Indeed, respiration increases continuously
up to a relatively high maximum whereas luminescence falls off rapidly
above a relatively low optimum. McKenney (1902) found also that _Bacillus
phosphorescens_ could grow rapidly in 0.5 per cent. ether without
producing light.

Luminescence has been compared in bacteria to pigment formation, as
rather definite cultural conditions are necessary for realization of
both chromogenic and photogenic function. Some pigment-formers, as
_Bacillus pyocyaneus_, which produces a water-soluble green pigment,
remain colorless under anaërobic conditions. A colorless chromogen is
formed, which oxidizes to the green pigment in the air. If this
colorless chromogen produced light during its oxidation as well as green
pigment, we would have a case of both chromogenic and photogenic
function combined in one species of bacterium. Luminescence involves
something more than respiration, an oxidation of a very definite and
particular kind.

Since Spallanzani's observation that the luminous material of medusæ
could be dried, and upon moistening would again give light, many
confirmatory observations have been made on other forms. _Pyrosoma_,
_Pholas_, _Phyllirrhoë_, fireflies, _Pyrophorus_, copepods, ostracods,
pennatulids, fungi, and bacteria can all be dessicated and the
photogenic material preserved for a greater or less time. In a
dessicator filled with CaCl_{2}, dried luminous bacteria lose, after a
few months, their power to give light on being moistened. On the other
hand, ostracods and copepods will still luminesce after years of
dessication. The luminous material in the latter case appears capable of
indefinite preservation, but it is possible that the quick loss of
photogenic power with dried luminous bacteria is merely an indication
that they contain very little photogenic substance and that the dried
ostracods would also in time lose their power to luminesce. It is
certainly a fact that the amount of luminous material in a single gland
cell of an ostracod is vastly greater than that in the same mass of
bacterial colony.

When the dried powdered luminous material of an ostracod is sprinkled
over the surface of water, it goes into solution and leaves luminous
diffusion and convection trails plainly visible in the water. Many
luminous marine forms give off a phosphorescent slime when they are
handled, which adheres to the fingers. It is not surprising that this
luminous matter should have early received a name. In 1872, Phipson
called it _noctilucin_ and described some of its properties. He regarded
the luminous matter which can be scraped from dead fish (luminous
bacteria) and the mucous secretion of _Scolopendra electrica_ or the
luminous matter of the glowworm to be this material, noctilucin, which,
"in moist condition, takes up oxygen and gives off CO_{2} and when dry
appears like mucin." Phipson says that it forms an oily layer over the
seas in summer (he probably refers to masses of dinoflagellates), is
liquid at ordinary temperatures and less dense than water, smells a
little like caprylic acid, is insoluble in water but miscible with it,
insoluble in alcohol and ether, dissolves with decomposition in mineral
acids and alkalies and contains no phosphorus. We can see from this
description that the word "noctilucin" does not indicate a chemical
individual, but it is the earliest attempt to definitely designate the
luminous substance.

The idea of a definite substance oxidizing and causing the light has
been upheld by a number of investigators, and many years later Molisch
called this substance the _photogen_. He contrasts the "photogen theory"
with certain other views of light production, which may be spoken of as
"vital theories," notably those of Pflüger (1875), who looked upon
luminescence as a sign of intense respiration, and of Beijerinck (1915),
who regarded the light as an accompaniment of the formation of living
matter from peptone.

Fortunately biological science has advanced beyond the stage where a
living process can be explained by calling it a vital process, and we
must fall back upon the idea of a photogen oxidizing with light
production. Indeed, it is now possible to go much further than this and
describe the properties of the photogen, but we must not lose sight of
the fact that it was recognized very early in the history of
Bioluminescence, that water, oxygen, and a photogenic substance were
necessary for light production.

A very great advance in our knowledge of the chemistry of the problem
was made by Dubois in 1885. He showed that if one dips the luminous
organ of _Pyrophorus_ in hot water, the light disappears and will not
return again. Also if one grinds up a luminous organ the mass will glow
for some time but the light soon disappears. If one brings the
previously heated organ in contact with the unheated triturated organ it
will again give off light. Later, Dubois showed that the same experiment
could be performed with the luminous tissues of _Pholas dactylus_. A
hot-water extract of the luminous tissue, and a cold-water extract of
the luminous tissue, allowed to stand until the light disappears, will
again produce light if mixed together. Dubois (1887 _b_) advanced the
theory that in the hot-water extract there is a substance, luciferin,
not destroyed by heating, which oxidizes with light production in the
presence of an enzyme, luciferase, which is destroyed on heating. The
luciferase is present together with luciferin in the cold-water extract,
but the luciferin is soon oxidized and luciferase alone remains. Mixing
a solution of luciferin and luciferase always results in light
production until the luciferin is again oxidized. Similar substances
have been found by me in the American fireflies, _Photinus_ and
_Photuris_, the Japanese firefly, _Luciola_, and in the ostracod
crustacean, _Cypridina hilgendorfii_. Crozier[6] reports that they exist
also in _Ptychodera_, a balanoglossid. I have been unable to demonstrate
their existence in luminous bacteria; in the annelid, _Chætopterus_; the
pennatulids, _Cavernularia_ and _Pennatula_; the squid, _Watasenia_;
and the fish, _Monocentris japonica_. E. B. Harvey (1917) could not
demonstrate them in _Noctiluca_. There are several reasons why the
existence of such bodies might be difficult to demonstrate, but these
reasons cannot be considered here. We thus see that the photogen is in
reality of dual nature, that two substances are necessary for light
production and that they may be very readily separated because of
difference in resistance to heating. In this respect Bioluminescence is
similar to some other biological processes, notably to certain immune
reactions and to certain enzyme actions.

[6] Private communication.

Thus, for the hæmolysis of foreign red blood corpuscles, a specific
immune body (_amboceptor or substance sensibilatrice_) not destroyed by
moderate heating, and a thermolabile complement (_alexin_) are
necessary.

For the alcoholic fermentation of glucose by the zymase of yeast juice
two substances are also necessary. The zymase is made up of a heat
resistant, dialyzing component, the co-enzyme, and a non-dialyzing
substance, destroyed on boiling, the enzyme proper. Both must be present
for alcoholic fermentation of glucose to proceed and the two may be
separated by dialysis or by their difference in resistance to heating.
Several other characteristics of living cells are known to depend on the
joint action of two substances, one thermolabile, the other
thermostable. The reducing action of tissues, according to Bach,
requires a reducing enzyme proper or perhydridase and some easily
oxidizable substance, such as an aldehyde. The aldehyde has been spoken
of as the co-enzyme.

Because of the necessity of thermostable and thermolabile substances for
light production in luminous animals and because I was unable to oxidize
the thermostable material of _Cypridina_ with such oxidizing agents as
KMnO_{4}, H_{2}O_{2}, blood and H_{2}O_{2}, BaO_{2}, etc., I called the
heat resistant substance of _Cypridina_, "_photophelein_" (from _phos_,
light and _opheleo_, to assist), comparable to co-zymase, and the heat
sensitive substance of _Cypridina_, "photogenin" (from _phos_, light and
_gennao_, to produce), comparable to the zymase proper of yeast. In mode
of preparation and properties, the photophelein of _Cypridina_ was also
comparable to the luciferin of _Pholas_ and the _photogenin_ of
_Cypridina_ to the luciferase of _Pholas_. I also regarded photogenin as
the source of the light (hence the name), because a solution of
_Cypridina_ photogenin (=_Pholas_ luciferase) will give light on mixing
with crystals of salt and other substances which could not possibly be
oxidized. I later found, however, that this result was due to the fact
that the photogenin solution contained some of the thermostable
substance (luciferin) bound (combined or adsorbed), and that this was
freed by the salt crystals and oxidized with light production. I have
consequently abandoned the view that the system of substances concerned
in light production is similar to the zymase--co-zymase system of
yeast--and have adopted Dubois' term, luciferase (=_photogenin_) for the
thermolabile material, and luciferin (=_photophelein_) for the
thermostable material.

The luciferin of _Cypridina_ differs from that of _Pholas_ in that it
will not oxidize with light production with any oxidizing agents that I
have tried, and will give no light with luciferase from _Pholas_. It
does, however, oxidize spontaneously in solution, although no light
accompanies this oxidation.

I believe that for accuracy and definiteness we must designate the
luciferins and luciferases from different animals by prefixing the
generic name of the animal and speak of _Pholas_ luciferin, _Cypridina_
luciferase, _Pyrophorus_ luciferase, etc. In extracts of many
non-luminous animals Dubois has found oxidizing agents which can oxidize
_Pholas_ luciferin with light production and I have confirmed this for
_Pholas_, but I have not found any such substances in non-luminous
animals which will oxidize _Cypridina_ luciferin with light production.
I have found in extracts of non-luminous animals substances which will
liberate the bound luciferin in a concentrated _Cypridina_ luciferase
solution. The luciferin can then be oxidized by the luciferase and light
appears. Their effect is similar to that of salt crystals and I suggest
that they be called _photopheleins_, substances that assist in the
luciferin-luciferase reaction by liberating bound luciferin. One of the
best ways of freeing a solution of luciferase from bound luciferin is to
shake with chloroform. We can then do away with the disturbing effects
of bound luciferin.

It is obvious that luciferin must be formed from some precursor in the
cell and following the usual biochemical terminology, Dubois has called
it _proluciferin_ or _preluciferin_, and believes that it is converted
into luciferin by an enzyme co-luciferase. The experiments to prove the
existence of proluciferin were first made by Dubois on _Pholas_ in 1907
and have since been amplified (1917 _a_; 1918 _a_ and _b_).

In order to understand these experiments it must be borne in mind that
Dubois prepares luciferin from _Pholas_ in three ways: (1) By
precipitating the viscid luminous fluid from the siphons with 95°
alcohol and dissolving the precipitate in water (1901_a_, 1907). (2) By
extracting the luminous organs with 90° alcohol in a closed vessel for
twelve hours and filtering (1896). (3) By heating the viscid luminous
fluid to 70° C. Apparently _Pholas_ luciferin is sparingly soluble in
alcohol as it can be obtained either in an alcoholic extract (method 2)
or by precipitation with alcohol (method 1). Proluciferin (called
_preluciferine_ in a later paper, 1917 _a_, 1918 _a_), is prepared by
methods 1 or 2 except that fatigued siphons, from which luciferin has
been removed by washing, are used (1907, 1917 _a_, 1918 _a_).
Preluciferin can also be obtained on boiling an extract of the luminous
organ of _Pholas_ because luciferin (at 70°), luciferase (at 60°) and a
co-luciferase are all destroyed below the boiling point (1917 _a_).

Co-luciferase is prepared (1) by heating a luciferase solution to 65°
(1917 _a_) or (2) by extracting with water portions of the siphon of
_Pholas_ which have previously been macerated and well extracted with
alcohol (1918 _a_). Long-continued treatment with alcohol apparently
destroys the luciferase without affecting the co-luciferase. On mixing a
solution of preluciferin with one of co-luciferase and allowing them to
stand for 8-10 hours, luciferase is formed and can be recognized by the
fact that it will give light with a crystal of KMnO_{4}. Preluciferine
does not do this.

Recently Dubois (1918 _a_) states that preluciferine is nothing but
taurine and that taurine occurs in large quantities in _Pholas_ and is
transformed into luciferine by the action of co-luciferase. Not only
taurine, but also Byla's peptone, egg lecithin, and esculin can be
converted into luciferine by co-luciferase, and since esculin, a
glucoside, is so transformed, Dubois believes this proves that
co-luciferase belongs to the hydrolases. Indeed, it proves too much.
Luciferin must have an extraordinary chemical structure if it can be
formed by hydrolysis of such diverse compounds as peptone, lecithin,
esculin and taurine. A glance at the structural formula of esculin and
taurine is sufficient to emphasize the diverse nature of these two
substances.

[Illustration: Taurine]

[Illustration: Esculin]

I believe that in these experiments Dubois has been working with an
oxidation product of luciferin, what I have called _oxyluciferin_,
rather than a pro-substance. The mode of preparation of _Pholas_
preluciferin and _Pholas_ co-luciferase is such as could be used in the
preparation of _Cypridina_ oxyluciferin, and it seems more logical to
look for the presence of _Pholas_ oxyluciferin in one or both of Dubois'
extracts rather than believe that luciferin can be formed from both
taurine and esculin. When the co-luciferase solution stands with the
preluciferin solution we would in reality have not the formation of
luciferin from preluciferin, but the formation of luciferin from
oxyluciferin, by some reducing agent in the mixture. Indeed, in a very
recent paper Dubois (1919 _c_) takes the view that his co-luciferase is
a reducing enzyme which forms luciferin by reduction (presumably from
oxidized luciferin) and no mention is made of preluciferin.

It is, of course, obvious that when luciferin oxidizes, some oxidation
products must be formed. Most observers have assumed the oxidation
products of luciferin to be relatively simple and to represent a rather
complete breaking down of the luciferin molecule. Carbon dioxide was
mentioned by Phipson (1872) as being formed. We have just seen that no
carbon dioxide is formed during the oxidation of _Cypridina_ luciferin
and there is evidence that no fundamental change at all occurs. It is
for this reason that I have called the oxidation product of luciferin
_oxyluciferin_.[7] As we shall later see, the change luciferin
oxyluciferin is to be compared to the oxidation of colorless dyes
(leuco-compounds) to the colored dye. The chemical properties of
oxyluciferin are similar to those of luciferin and the oxyluciferin can
be readily reduced to luciferin again.

[7] It is unfortunate that Dubois (1918 b) has used the term
oxyluciferine in a quite different sense from the present use. He
regards oxyluciferine as a substance still capable of giving light by
autoöxidation, and represents the steps in luminescence as follows:

  "Co-luciférase + preluciférine = luciférine.

   Luciférase    + luciférine    = oxyluciférine.

   Oxyluciférine + oxygéne       = lumiérè."

I should represent them as follows:

  Luciferin + oxygen ⇆ oxyluciferin.

The reaction proceeds to right with light production only in presence of
luciferase.

Finally, we have the fluorescent substance of _Pyrophorus_ and
fireflies, which Dubois first called _pyrophorin_, but later, adopting
McDermott's terminology, speaks of as _luciferesceine_. This Dubois
regards as a substance intensifying the light and modifying its color by
changing invisible into visible rays. As we have seen, this theory,
while attractive, will not stand the test of critical examination.

Phipson's noctilucin, while the first name for the photogen of luminous
animals, is too vague a substance, chemically, to warrant a retention of
the term. Of the names, luciferin, luciferase, preluciferin or
proluciferin, co-luciferase, photogenin, photophelein, oxyluciferin,
luciferesceine, I believe that only proluciferin, luciferin,
oxyluciferin, luciferase and photophelein stand for substances which are
really significant for the theory of light production. _Luciferin_ is
the heat resistant, dialyzable substance which takes up oxygen and
oxidizes with light production in the presence of the heat sensitive,
non-dialyzing, enzyme-like _luciferase_. The luciferin must come from
some precursor, _proluciferin_, but I have been unable to demonstrate
the existence of this body in _Cypridina_ and know nothing definite of
its properties. The luciferin oxidizes to _oxyluciferin_ which has the
same chemical properties as the luciferin itself and may be reduced to
luciferin again by reducing substances in luminous and other animals or
by inorganic reducing agents. _Photophelein_ is a name for substances in
various animal or plant extracts which are capable of liberating
luciferin from some bound condition in solutions containing luciferase.
Under this term are included a number of unknown, probably quite
different substances, some of which are thermostable and others
thermolabile.

We have seen that Bioluminescence is an oxyluminescence, that the light
is probably due to the oxidation of a compound, luciferin, in presence
of air and water and that the oxidation is accelerated by an enzyme-like
substance, luciferase. We also saw in Chapter 2 that light production is
of fairly common occurrence during the oxidation of many organic
compounds, provided the oxidation is carried out in the proper way. Many
of these organic compounds must be oxidized by relatively strong alkali
or such strong oxidizing agents as would have a very deleterious action
on living cells. In 1913, Ville and Derrien, in a short note to the
French Academy, "Catalyse Biochemique d'une Oxydation Luminescente,"
show that _lophin_ could be oxidized by vertebrate blood in the presence
of H_{2}O_{2}. In the same year Dubois (1913) found that esculin, the
glucoside from horse chestnut bark, would also oxidize and luminesce in
presence of blood and H_{2}O_{2}. In these cases the hæmoglobin of the
blood acts as a catalyst, transferring oxygen from the H_{2}O_{2} to
esculin or lophin and is to be compared to luciferase, except that
luciferase does not require the presence of H_{2}O_{2}.

As the hæmoglobin does not lose this power on boiling, whereas
luciferase does, the analogy is far from perfect. Many oxygen carriers
are known, however, which may be destroyed on boiling their solutions,
namely, the peroxidases of plant juices. Esculin will not luminesce with
peroxidase and H_{2}O_{2}, but pyrogallol or gallic acid will. If one
mixes a test tube containing pyrogallol solution + H_{2}O_{2} with
potato or turnip juice or almost any plant extract, a yellowish
luminescence appears. The plant extract loses the power to cause such
luminescence on boiling and the peroxidase will not dialyze. It is, of
course, comparable to luciferase and acts on the thermostable,
dialyzable pyrogallol-H_{2}O_{2} mixture, which is comparable to
luciferin. Curiously enough, although many hydroxyphenol and
amino-phenol compounds can be oxidized by peroxidase and H_{2}O_{2},
only pyrogallol and gallic acid will oxidize with light production. Many
other oxidizers can take the place of the peroxidase. A list of these is
given on page 151. No other peroxide can take the place of H_{2}O_{2}
with peroxidases as oxidizers, but a few can replace H_{2}O_{2} with
other oxidizers. This is brought out in Table 7.


TABLE 7

_Peroxides Giving Light with Pyrogallol and Oxidizers_

  Key to column headings:
   [A]: Oxidizer. (Equal parts added to a mixture of M/100 pyrogallol and the
          peroxide)
   [B]: H_{2}O_{2} 3 per cent.
   [C]: Benzoyl hydrogen peroxide (insoluble powder)
   [D]: Ozonized turpentine (one drop)
   [E]: Na_{2}O_{2} (powder)
   [F]: BaO_{2} (powder)
   [G]: MnO_{2} (insoluble powder)
   [H]: PbO_{2} (insoluble powder)
   [I]: K persulfate M/10
   [J]: Na perborate M/20
   [K]: K perchlorate M/10
   [L]: Quinone (insoluble crystals)


  -----------------------------------------------------------------------------
         [A]               |[B]|[C]|[D]| [E] | [F] |[G]|[H]| [I] | [J] |[K]|[L]
  -------------------------+-- +---+---+-----+-----+---+---+-----+-----+---+---
  Turnip juice             | + | - | - |  -  |  -  | - | - |  -  |     |   | -
  1 percent blood extract  | + | - | - |Faint|  -  | - | - |  -  |  -  | - | -
                           |   |   |   |flash|     |   |   |     |     |   |
  M 20 K_{4}Fe(CN)_{6}     | + | - | - |  -  |  -  | - | - |  -  |  -  | - | -
  M 100 KMnO_{4}           | + | - | - |  -  |  -  | - | - |Faint|Fair | - | -
                           |   |   |   |     |     |   |   |flash|flash|   |
  M 10 FeCl_{3}            | + |   |   |     |     |   |   |     |  -  | - |
  M 100 CrO_{3}            | + |   |   |     |     |   |   |     |  -  | - |
  Na hypobromite           | + | - | - |Faint|Faint| - | - |Fair |Fair | - | -
                           |   |   |   |flash|flash|   |   |flash|flash|   |
  Ca hypochlorite          | + | - | - |  -  |  -  | - | - |Faint|Fair | - | -
                           |   |   |   |     |     |   |   |     |flash|   |
  MnO_{2}                  | + |   |   |     |     |   |   |     |     |   |
  Mn(OH)_{3} sol in peptone| + |   |   |     |     |   |   |     |  -  | - |
  Colloidal Ag             | + |   |   |     |     |   |   |     |     |   |
  -------------------------+---+---+---+-----+-----+---+---+-----+-----+---+---

Our knowledge of the existence of such analogous, purely organic
chemical oxidations, which proceed with light production, greatly
strengthens Dubois' theory that the luciferin-luciferase reaction
really represents a catalytic oxidation of similar nature. As Dubois
(1914 _a_) expresses it, we are dealing in luminous organisms with "1°
une luminescence; 2° une chemiluminescence; 3° une oxyluminescence; 4°
une zymoluminescence.

"Ou si l'on bien admettre que les zymases sont encore quelque chose de
vivant, une Biozymoöxyluminescence." Perhaps it is not really necessary
to admit that the enzymes are living in order that we may adequately
visualize the nature of the photogenic process.

In the next chapter the properties of the three principal substances,
luciferin, oxyluciferin and luciferase, will be studied more carefully.




CHAPTER VI

THE CHEMISTRY OF LIGHT PRODUCTION, PART II


Since Radziszewski's experiments on the oxidation of oils in alcoholic
solutions of alkali, most of the early workers on Bioluminescence
tacitly assumed that the oxidizable material was fat or a fat-like
substance. Support was given to this view by the occurrence in cells of
granules or globules from which the light was seen to come. We now know
that these bodies are not fat droplets and that neither luciferin nor
luciferase are soluble in such fat solvents as ether, chloroform, benzol
or benzine. Phipson's description of the properties of noctilucin are
too crude and inaccurate to be considered. Dubois did not study the
chemical properties of luciferin and luciferase from _Pyrophorus_, the
first form with which he worked, except to point out that _Pyrophorus_
luciferase was destroyed on heating and was precipitated by alcohol
while the _Pyrophorus_ luciferin was not so affected. Luciferin was
found only in the luminous organ of _Pyrophorus_, not in the blood;
luciferase probably exists throughout the animal.[8]

[8] Private communication from R. Dubois.

PHOLAS LUCIFERIN.--In a series of papers since 1887 Dubois has studied
the chemical properties of _Pholas_ luciferin and _Pholas_ luciferase.
He finds the luciferin to be destroyed above 70° C., to dialyze slowly,
to oxidize with light production in the presence of _Pholas_ luciferase,
KMnO_{4}, H_{2}O_{2}, hæmatine and H_{2}O_{2}, BaO_{2}, PbO_{2},
hypochlorites, and the blood of various marine mollusks and crustacea.
It is insoluble in fat solvents but forms a colloidal solution in water
from which it is precipitated unchanged by picric acid, alcohol at 82°,
and (NH_{4})_{2}SO_{4}. It is not precipitated by NaCl, MgSO_{4} or
acetic and carbonic acids, except in presence of neutral salts. It forms
an insoluble alkali albumin with NH_{4}OH. Dubois (1887 _a_) stated at
one time that it could be crystallized and has spoken of it as belonging
to several different classes of substances, proteose, nucleoprotein,
albumin. Most recently he describes luciferin as a natural albumin
having acid properties. It occurs only in luminous, not in non-luminous
animals, and is found in all parts of the mantle, especially the
siphons. It does not occur in non-luminous parts of the mollusk. No
photographs of luciferin crystals have ever been published.

PHOLAS LUCIFERASE.--_Pholas_ luciferase has all the properties of an
enzyme, is destroyed at 60° C., is non-dialyzable, insoluble in fat
solvents, but forms a colloidal solution in water. It is not affected by
1 per cent. NaF but its activity is suspended in saturated salt
solutions, sugar or glycerine, and it may be preserved in this way, its
activity returning on dilution. It is digested by trypsin and slowly
destroyed by the fat solvent anæsthetics, such as chloroform. For this
reason Dubois regards it as an oxidizing enzyme similar to the oxydones
of Batelli and Stern. Because he found iron in an extract of _Pholas_
dialyzed for a long time against running water, Dubois considers that it
is associated with iron, and reports that it will oxidize the ordinary
oxidase reagents, such as pyrogallol, gum guaiac, a-naphthol and
para-phenylene-diamine, etc. It remains to be proved, however, that
luciferase and not the oxidizing systems such as occur in all cells are
responsible for the coloration of these reagents. Dubois has found
luciferases or substances capable of giving light with _Pholas_
luciferin in the blood of many non-luminous crustacea and mollusks (in
_Barnea candida_, _Solen_, _Cardium edulis_, _Ostræa_ and _Mytilus_).

CYPRIDINA LUCIFERIN.--Despite the large amount that has been written on
luminous animals, Dubois' work on _Pholas_ and my own on _Cypridina_ and
the firefly are the only truly chemical studies that give us any idea of
the nature of the photogenic substances in any luminous animal. In many
ways _Cypridina_ luciferin is similar to _Pholas_ luciferin, but the two
differ in a sufficient number of points to make certain that they are
not identical substances. As I have emphasized above, we should speak
not of luciferin and luciferase but of the _luciferins_ and the
_luciferases_. The luciferins, as the oxidizable substances, must claim
first attention. They are more simple substances than the luciferases.
If we are to produce light artificially in the same way that animals do,
the luciferins must be synthesized. The luciferin of _Pholas_ will
luminesce with KMnO_{4} and other oxidizing agents, and, although I have
not yet succeeded in oxidizing _Cypridina_ luciferin with oxidizing
agents, I have no doubt but that some inorganic catalyzer will be found
to take the place of luciferase and accelerate oxidation of _Cypridina_
luciferin with light production.

The most remarkable peculiarity of _Cypridina_ luciferin is its
stability. In my first paper on _Cypridina_ I stated that luciferin was
not destroyed by momentary boiling but would be destroyed if boiled four
or five minutes; also, that it was unstable at room temperatures and
would disappear from solution in the course of a day or so. The reason
for this is that luciferin oxidizes even in absence of luciferase and
will then no longer give light with luciferase. This spontaneous
oxidation, which occurs without light production, can be prevented by
keeping the luciferin in a hydrogen atmosphere or by the addition of
acid. Under these conditions the luciferin can be boiled without
destruction or preserved for months without deterioration. The rapid
disappearance of luciferin from neutral or alkaline solution on boiling
in the air is entirely due to the more rapid oxidation at the boiling
point. As the oxidation product, oxyluciferin, can be readily
reconverted into luciferin again, we can not consider luciferin unstable
in the sense that its molecule is actually destroyed as is the case when
luciferase is boiled.

Not only is luciferin stable on boiling but it will actually withstand
boiling for 10 hours with 20 per cent. HCl (by weight, sp. gr. = 1.1) or
with 4 per cent. H_{2}SO_{4}. After one day of boiling with 20 per cent.
HCl the luciferin was completely destroyed and with 4 per cent.
H_{2}SO_{4} destruction was almost complete. In these cases there was no
question of a mere oxidation to oxyluciferin, as no oxyluciferin could
be demonstrated after boiling with such strong acids. An actual
destruction, probably an hydrolysis of the luciferin molecule, occurred.
We shall have occasion to refer to this again in considering the protein
nature of luciferin. It must be borne in mind that many proteins require
four or five days' boiling with 20 per cent. HCl for complete hydrolysis
to amino-acids. Luciferin forms a solution in water, probably colloidal,
although the luciferin will dialyze through parchment or collodion
membranes. It is rather readily adsorbed by various finely divided
materials such as bone black, Fe(OH)_{3}, kaolin, talc and CaCo_{3}. It
is not destroyed by any of the enzyme solutions which I have tried.
These include such as are widely divergent in action: pepsin HCl,
trypsin, erepsin, salivary and malt diastase, yeast invertase, urease,
rennin and the enzymes of dried spleen, kidney and liver substances.

By extracting the dried Cypridinas ground to a powder, the solubility of
luciferin in non-aqueous solvents could be easily studied, and by adding
such reagents as dilute acids, alkalies, neutral salts and the
alkaloidal reagents to an aqueous solution of luciferin the general
biochemical behavior of luciferin can be quite accurately stated. For
convenience the results of this study are given in Table 8.


TABLE 8

_Properties of Photogenic Substances from Cypridina_

  =========================================================================
            Property      |     Luciferase        |   Luciferin
  ------------------------+-----------------------+------------------------
  _Salting out_           |                       |
    By saturation NaCl    |Not precipitated       |Not precipitated.
    By half saturation    |    Do.                |    Do.
      MgSO_{4}            |                       |
    By saturation MgSO_{4}|Nearly completely      |Partially
                          |  precipitated         |  precipitated.
    By saturation MgSO_{4}|    ...                |    Do.
      + acetic acid       |                       |
    By half saturation    |                       |
      (NH_{4})_{2}SO_{4}  |Slightly precipitated  |Not precipitated.
    By saturation         |Completely precipitated|Nearly completely
      (NH_{4})_{2}SO_{4}  |                       |  precipitated.
    By saturation         |                       |
      (NH_{4})_{2}SO_{4} +|    ...                |Nearly completely
      acetic acid         |                       |  precipitated.
                          |                       |
  _Solubility in_         |                       |
    Methyl alcohol        |Insoluble              |Soluble.
    Ethyl alcohol         |    Do.                |    Do.
            90 per cent.  |    Do.                |    Do.
            70 per cent.  |    Do.                |    Do.
            50 per cent.  |Slightly soluble       |    Do.
    Propyl alcohol        |Insoluble              |    Do.
    Isobutyl alcohol      |    Do.                |Fairly soluble.
    Amyl alcohol          |    Do.                |Slightly soluble.
    Benzyl alcohol        |    Do.                |Soluble.
    Acetone               |    Do.                |Fairly soluble.
            90 per cent.  |    Do.                |Soluble.
            70 per cent.  |Slightly soluble       |    Do.
            50 per cent.  |Fairly soluble         |    Do.
    Ethyl acetate         |Insoluble              |    Do.
    Ethyl propionate      |    Do.                | Fairly soluble.
    Ethyl butyrate        |    Do.                |    Do.
    Ethyl valerate        |    Do.                |Slightly soluble.
    Ethyl nitrate         |    Do.                |Very slightly soluble.
    Glycerine             |    Do.                |Soluble.
    Glycol                |    Do.                |    Do.
    Ether                 |    Do.                |Insoluble.
    Chloroform            |    Do.                |    Do.
    Carbon disulfide      |    Do.                |    Do.
    Carbon tetrachloride  |    Do.                |    Do.
    Benzol                |    Do.                |    Do.
    Toluol                |    Do.                |    Do.
    Xylol                 |    Do.                |    Do.
    Petroleum ether       |    Do.                |    Do.
    Anilin                |    Do.                |    Do.
    Glacial acetic acid   |    Do.                |Fairly soluble.
                          |                       |
  _Alkaloidal Reagents_   |                       |
    Phosphotungstic acid  |Completely precipitated|Very nearly completely
                          |                       |  precipitated.
    Phosphotungstic and   |    ...                |Very nearly completely
      acetic acids        |                       |  precipitated.
    Phosphotungstic acid  |    ...                |Completely precipitated.
      and HCl             |                       |
    Tannic acid           |Nearly completely      |Nearly completely
                          |  precipitated         |  precipitated.
    Tannic and acetic     |    ...                |Nearly completely
      acids               |                       |  precipitated.
    Tannic acid and HCl   |    ...                |Nearly completely
                          |                       |  precipitated.
    Picric acid           |Nearly completely      |Not precipitated.
                          |  precipitated         |
    Picric and acetic acid|    ...                |    Do.
    Picric acid and HCl   |    ...                |    Do.
    K_{4}Fe(CN)_{6} and   |    ...                |
      acetic acid         |                       |    Do.
                          |                       |
  _Heavy Metal Salts_     |                       |
    Basic lead acetate    |Completely precipitated|Not completely
                          |                       |  precipitated.
    Neutral lead acetate  |Nearly completely      |Not completely
                          |  precipitated.        |  precipitated.
    Neutral lead acetate  |    ...                |Not precipitated.
      and acetic acid     |                       |
    Mercuric chloride     |Not precipitated       |Not completely
                          |                       |  precipitated.
    Mercuric chloride and |    ...                |Almost completely
      acetic acid         |                       |  precipitated.
    Uranyl nitrate and    |    ...                |Not completely
      acetic acid         |                       |  precipitated.
                          |                       |
  _Acids and Alkalies_    |                       |
    NaOH                  |Not precipitated       |Not precipitated.
    NH_{4}OH              |    Do.                |    Do.
    Acetic acid           |    Do.                |    Do.
    H_{2}CO_{3}           |    Do.                |    Do.
    Trichloracetic acid   |    Do.                |    Do.
  ------------------------+-----------------------+------------------------

Because the luciferin is almost completely precipitated by saturation
with (NH_{4})_{2}SO_{4}, we may conclude that it occurs in water in the
colloidal state. This excludes it from belonging to one of the numerous
groups of biochemical compounds occurring in true solution and places it
among the known groups of colloidal substances, the soaps, proteins,
polysaccharides, phospholipins, galactolipins (_cerebrosides_), tannins
or saponins. It is not a polysaccharide because nearly completely
precipitated by phosphotungstic acid, nor a soap because not
precipitated by calcium salts, nor a phospho- or galactolipin because
insoluble in benzine, hot or cold. It gives no tannin or saponin tests.
Only the protein group remains, and of the eighteen protein classes
recognized by the American Society of Biochemists, the general
properties of luciferin indicate that it should be placed among the
natural proteoses, somewhere on the borderland between the proteoses and
peptones. The fact that luciferin will dialyze, although almost
completely salted out by (NH_{4})_{2}SO_{4}, is strong evidence in favor
of placing it in such a position.

On the other hand, luciferin has two properties which to say the least
are unusual for proteins. I refer to its solubility in alcohols,
acetone, esters, etc., and non-digestibility by trypsin or erepsin,
which have almost universal proteolytic power.

The best known class of proteins soluble in alcohol is the prolamines of
plants, but the prolamines are insoluble in water and in absolute
alcohol. Zein, the prolamine of corn, is soluble in 90 per cent. ethyl,
methyl, and propyl alcohols, in glycerol heated to 150° C., and in
glacial acetic acid. Recently Osborne and Wakeman (1918) have described
a protein from milk having solubilities similar to those of gliadin, the
prolamine of wheat. Welker (1912) has described a substance, obtained
from Witte's peptone, giving the biuret, Millon, and Hopkins-Cole tests,
which is soluble in water and absolute alcohol but not in ether, and it
is possible that others of the peptones are soluble in absolute alcohol.
On the other hand, some proteins in the absence of salts form colloidal
solutions in strong alcohol from which they may be precipitated by an
appropriate salt. As the absolute alcohol extract of _Cypridinæ_ was
made from dry material containing the salts of sea water, some salt was
present, but there is always the possibility of sol formation.

If we extract dried _Cypridinæ_, which have previously been thoroughly
extracted with benzine or ether, with 800 c.c. of boiling absolute
alcohol for an hour, filter the alcohol extract through blotting paper
and hardened filter paper, quickly evaporate the filtrate to dryness on
the water bath, and dissolve the residue in a small quantity of water
saturated with CO_{2},[9] we obtain a yellow opalescent solution which
gives a bright light with luciferase. This solution contains some
protein or protein derivatives as it gives a very faint Millon
reaction, a good positive ninhydrin test, reddish blue in color, but no
biuret reaction. It precipitates with tannic and phosphotungstic acids
but not with picric, acetic, trichloracetic, or chromic acids. The
extract gives a faint Molisch reaction for carbohydrates. As the
evidence points to the presence of some protein products in the absolute
alcohol extract of _Cypridinæ_, it is possible that this protein is
luciferin. It should be emphasized, however, that the Millon reaction
was very faint, although the ninhydrin was quite marked and the biuret
negative.

[9] To make the solution slightly acid and prevent oxidation of the
luciferin.

Although luciferin is not digested by trypsin, even after five days at
38° C., it does hydrolyze with mineral acids after about 16 hours'
boiling. Some proteins, the albuminoids and racemized proteins, resist
tryptic digestion but yield to acid hydrolysis. We know also that some
NH-CO linkages of proteins are broken down with great difficulty by
trypsin as it is difficult to obtain a tryptic digest of protein which
does not give the biuret reaction, and the work of Fischer and
Abderhalden has shown that certain artificial polypeptides are not
digested by pure activated pancreatic juice.

We have, then, three possibilities: Luciferin is (1) either a natural
proteose not attacked by trypsin, or (2) if attacked by trypsin its
decomposition products (presumably amino-acids) still contain the group
oxidizable with light production, or (3) it is not protein at all. I
have been unable to oxidize with light production various mixtures of
amino-acids (from tryptic digestion of beef and casein, or the acid
hydrolysis products of luciferin itself) by means of luciferase, and
consequently am led to believe that _Cypridina_ luciferin is either a
new natural proteose, soluble in absolute alcohol and not digested by
trypsin or that it belongs to some other group than the proteins. The
absence of a biuret reaction would point in that direction and the
question must await further study.

_Cypridina_ luciferin is found in the luminous gland of the animal and
possibly in parts non-luminous as well as in the luminous organ. This is
true of the luciferin from fireflies which is found throughout the body
of _Luciola_, _Photuris_ and _Photinus_.

CYPRIDINA LUCIFERASE.--Luciferase, on the other hand, has _all_ the
properties of a complex protein. It will not dialyze through collodion
or parchment membranes, is soluble only in aqueous solvents, and hence
precipitated by alcohol and acetone, digested by proteolytic enzymes,
readily changed by contact with dilute acid and alkali and irreversibly
coagulated on boiling. It is completely salted out of solution by
saturation with (NH_{4})_{2}SO_{4} and nearly completely precipitated by
the alkaloidal reagents. Its other properties are given in Table 8.
Taken together, they point to the group of albumins as the class of
proteins with which luciferase most closely agrees.

If luciferase is not a protein it is so closely bound up with protein
that it cannot be separated. This is characteristic of many enzymes and
luciferase is also an enzyme. We can determine this by finding out
whether luciferase will accelerate the oxidation of a large amount of
luciferin, for such is the test of a catalytic substance. If we take 1
c.c. of a dilute solution of luciferase (1 _Cypridina_ to 50 c.c. water)
and add to it successive 1 c.c. portions of concentrated luciferin (1
_Cypridina_ to 2 c.c. solution) as soon as the light from the preceding
addition has disappeared, after four 1 c.c. additions, no more light is
produced. The luciferase is therefore used up and cannot oxidize more
than a certain quantity of luciferin. In this experiment, however, we
added a concentration of luciferin from one _Cypridina_ 100 times that
of the luciferase from one _Cypridina_, i.e., four additions each 25
times as concentrated. We have, of course, no way of telling what the
absolute amount (in milligrams) of luciferin or luciferase is in a
single _Cypridina_, but we do know that the luciferase from one
_Cypridina_ cannot oxidize luciferin from more than 100 Cypridinas. If
the ratio of luciferin to luciferase in a single animal is 100:1, it
would mean that luciferase could oxidize 10,000 times its weight of
luciferin. A large excess of luciferin but not an indefinite quantity
can be oxidized by luciferase, and I believe this is sufficient
justification for considering luciferase an enzyme, although it is not
an ideal example of an organic catalyzer. Quite a number of enzymes are
known to be diminished during the course of the reaction they accelerate
or to be poisoned by their reaction products. Enzyme reactions inhibited
by the formation of reaction products again proceed if these are removed
or diluted. However, light does not again appear in a mixture of weak
luciferase with excess of luciferin upon dilution with water, so that
the luciferase cannot have been merely inhibited by some reaction
product but must have been actually used up during the reaction. It
should be noted in passing that the peroxidases, ordinarily spoken of as
oxidizing enzymes, are used up in the reaction and can only oxidize
limited amounts of oxidizable substances, a quantity almost in
proportion to the concentration of peroxidase present.

Whether luciferase is an oxidizing enzyme made up of an albumin
associated with some heavy metal as iron, copper or manganese is
uncertain. From analyses of whole _Cypridina_, kindly made for me by
Prof. A. H. Phillips of Princeton University, all three of these metals,
which we know to be associated with biological oxidations, are present,
and it is quite possible that one of them is concerned with the
oxidation of luciferin.

Although I have tested a great many oxidizers, organic and inorganic,
and a large number of oxidizing enzymes from blood and tissue extracts
of animals rich in iron, copper and manganese, I have found no material
which is capable of taking the place of _Cypridina_ luciferase.
Peroxidases or oxidases of plants, hæmoglobin, hæmocyanin, extracts of
mussels, manganese containing blood of various marine crustacea and
mollusks will give no light on mixing with luciferin. Such active
oxidizers as KMnO_{4}, H_{2}O_{2}, BaO_{2}, and many others, will not
oxidize _Cypridina_ luciferin with light production, although they can
oxidize _Pholas_ luciferin with light production.

The action of _Cypridina_ luciferase is very highly specific. It is
found only in the luminous organ of _Cypridina hilgendorfii_, not in
non-luminous parts and not in a non-luminous species of _Cypridina_
closely related to _hilgendorfii_.

Luciferins and luciferases from closely allied luminous forms will
mutually interact to produce light, but no light appears if these
substances come from distantly related forms. Thus firefly (_Photuris_)
luciferin will give light with _Pyrophorus_ luciferase and _vice versa_,
but _Cypridina_ luciferin will give no light with firefly (_Luciola_)
luciferase or _vice versa_, nor with _Pholas_ luciferase or _vice
versa_. The faint luminescences sometimes observed on mixing firefly or
_Cypridina_ luciferase with boiled extracts of non-luminous forms, or of
distantly related luminous forms, are probably caused by photophelein in
the boiled extract.

Like the plant peroxidases, _Cypridina_ luciferase is not readily
affected by the action of chloroform, toluol, etc. Unlike the plant
peroxidases, it will not oxidize (_i.e._, produce coloration) in either
presence or absence of H_{2}O_{2}, any of the hydroxyphenol or
aminophenol compounds, such as pyrogallol, a-naphthol,
para-diamino-benzine, gum guaiac, etc., commonly used as peroxidase
reagents. Neither will luciferase produce light with any substances,
such as oils, lophin, pyrogallol, gallic acid, esculin, etc., which we
know to be capable of oxidation with light production by other means.
The luciferases are very highly specific and act only upon the
luciferins of the same or closely related species. They must be placed
by themselves in a new class of oxidizing enzymes.

According to Dubois, _Pholas_ luciferase is rather readily destroyed by
chloroform and my own observations indicate that this is true also of
firefly luciferase, so that a certain amount of variation exists in the
group of luciferases.

None of the luminescent animals which I have studied are at all affected
by cyanides. The luminescence continues in extracts of _Cypridina_,
firefly, and _Cavernularia_, or in _Noctiluca_ and luminous bacteria
after addition of small or high (_m_/40) concentrations of KCN. In this
respect the luciferases are very different from many types of oxidizing
enzymes which are inhibited by exceedingly weak concentrations of
cyanide. It should be borne in mind, however, that while KCN inhibits
catalase and the catalytic decomposition of H_{2}O_{2} by Pt or Ag, it
does not affect the catalytic decomposition of H_{2}O_{2} by thallium.

OXYLUCIFERIN.--When luciferin is oxidized it must be converted into some
substance or substances and I believe this change involves no
fundamental destruction of the luciferin molecule as it is a reversible
process. I shall speak of the principal (if not the only) product formed
as _oxyluciferin_.

If we assume that the oxidation of luciferin changes the molecule but
slightly, we at once think of comparing the change luciferin ⇆
oxyluciferin with the change reduced hæmoglobin ⇆ oxyhæmoglobin. The
condition is, however, not so simple as this, for oxyhæmoglobin will
again give up its oxygen providing the partial pressure of oxygen is
made sufficiently low, whereas oxyluciferin will not do this, at least
in the dark. We can not reduce oxyluciferin solution by exhausting the
oxygen with an air-pump.

There is another oxidation-reduction system which can also be easily
reversed, but not by merely removing the oxygen from the solution--that
is, the reduction of a dye such as methylene blue to its leuco-base. I
believe the change which occurs when luciferin is oxidized is similar to
that which occurs when the leuco-base of methylene blue or sodium
indigo-sulphonate is oxidized to the blue dye. Oxidation of leuco-dye
bases occurs spontaneously in presence of oxygen and appears to consist
in the removal of hydrogen from the leuco-base with formation of water.
Reduction of these dyes may be effected in the same ways that
oxyluciferin can be reduced. In the case of methylene blue, reduction
consists in the addition of two hydrogen atoms. Whether a similar change
occurs when oxyluciferin is reduced or whether oxygen is actually added
as in formation of hæmoglobin cannot be definitely stated at present. We
may write equations representing these possibilities as follows:

  C_{16}H_{20}N_{3}SCl + O ⇆ C_{16}H_{18}N_{3}SCl + H_{2}O
  (leuco-methylene blue)     (methylene blue)

  Hæmoglobin + O ⇆ oxyhæmoglobin.

Let us now turn to the methods which may be used in reduction of
oxyluciferin. We may then endeavor to write an equation which will
represent the fundamental changes in the luminescence reaction.

My attempts to reduce the oxidation product of luciferin started from
the observation that if one places a clear solution of luciferase in a
tall test tube, although it may give off no light at first when shaken,
after standing a day or so a very bright light would appear on shaking.
This was especially true when the luciferase had become turbid and
ill-smelling from the growth of bacteria. Thinking that the bacteria
produced a substance which could be oxidized by the luciferase, I tried
growing bacteria and also yeast on appropriate culture media, and after
some days of growth mixing the culture media containing the products of
bacterial or yeast growth with luciferase, expecting to obtain light;
but no light appeared. However, if a little crude luciferase solution
was added to the bacterial or yeast cultures and then allowed to stand
for some hours, light appeared whenever they were shaken. Indeed such
cultures behaved much as a suspension of luminous bacteria which has
used up all the oxygen in the culture fluid and will only luminesce
when, by shaking, more oxygen dissolves in the culture medium.
Realizing that in bacterial cultures in test tubes, anaërobic
conditions soon appear, and also the strong reducing action of bacteria
upon many substances (for instance, nitrates or methylene blue) under
anaërobic conditions, it struck me that the bacteria might be reducing
the oxidation product of luciferin to luciferin again. We must remember
that since crude luciferase solution is a cold-water extract of a
luminous animal allowed to stand until all the luciferin has been
oxidized, it must contain oxyluciferin as well as luciferase and will
give light if the oxyluciferin is again reduced and oxygen admitted.
This appears to be the correct explanation of the above experiments.

Oxyluciferin may also be readily reduced by the use of the blood of the
horse-shoe crab (_Limulus_) allowed to stand until bacteria develop.
This experiment is of special interest because the blood contains
hæmocyanin, which is colorless in the reduced condition and blue in the
oxy-condition. The color change thus serves as an indicator of the
oxygen concentration in the blood. A sample of foul-smelling _Limulus_
blood full of bacteria will become colorless on standing in a test tube
for 10 to 15 minutes, but the blue color quickly returns if shaken with
air. Such a blood has the power of reducing oxyluciferin through the
activity of the bacteria which it contains. Fresh blood has very little
if any reducing action.

Not only bacteria but also tissue extracts have a strong reducing action
in absence of oxygen. Thus, muscle tissue stained in methylene blue will
very quickly decolorize (reduce) the methylene blue if oxygen (air) is
kept away, but the blue color immediately returns if air is admitted.
Oxyluciferin (_i.e._, a solution of luciferin which has been completely
oxidized by boiling or standing in air until it no longer gives light
with luciferase) if mixed with a suspension of ground frog's muscle and
kept in a well-filled and stoppered test tube for some hours, is reduced
to luciferin and gives a bright light if now poured into luciferase
solution. Frog muscle suspension alone, or oxyluciferin alone, give no
light with luciferase, nor will a mixture of frog muscle suspension and
oxyluciferin, if shaken with air for several hours. Only if this last
mixture be kept under anaërobic conditions is the oxyluciferin reduced.

The reducing action of tissues is said to be due to a reducing enzyme
(_reducase_ or _reductase_), itself composed of a perhydridase and some
easily oxidized body such as an aldehyde. In the presence of the
perhydridase the oxygen of water oxidizes the aldehyde and the hydrogen
set free reduces any easily reducible substance which may be present.
There is a perhydridase in fresh milk, spoken of as _Schardinger's
enzyme_, which is destroyed by boiling. If some aldehyde is added, fresh
milk will reduce methylene blue to its leuco-base or nitrates to
nitrites, upon standing a short time. If shaken with air the blue color
returns. There is no reduction unless an aldehyde is added or unless
some boiled extract of a tissue such as liver is added. The boiled-liver
extract has no reducing action of its own, but supplies a substance
similar to the aldehyde which has been spoken of as _co-enzyme_. The
aldehyde is oxidized to its corresponding acid. Milk will reduce
methylene blue without aldehyde if bacteria are present in large
numbers. There is no reduction if the milk, methylene blue, and aldehyde
are agitated with air. The temperature optimum is rather high, 60° to
70° C.

I find that milk is a favorable and convenient medium for the reduction
of oxyluciferin and that it acts without the addition of an aldehyde or
the presence of bacteria. There is probably a substance acting as the
aldehyde in the luciferase-oxyluciferin solution. No light appears if
milk is added to a luciferase-oxyluciferin solution, but if the mixture
is allowed to stand in absence of oxygen light will appear when air is
admitted. The air can be conveniently kept out by filling small test
tubes completely with the solution and closing them with rubber
stoppers.

As almost all animal tissues contain reductases it is not surprising to
find that a freshly prepared and filtered extract of _Cypridina_
containing oxyluciferin and luciferase, which gives no light on shaking,
will, on standing in a stoppered tube for 24 hours at room temperature in
the dark give light when air is admitted. While this may be due to the
development of bacteria with a reducing action, it does not seem likely,
as under the same conditions methylene blue is not reduced in 24 hours,
and there is no turbidity or smell of decomposition in the tube. In 48
hours bacteria appear and methylene blue is also reduced. If we add
chloroform, toluol or thymol to the tubes of _Cypridina_ extract to
prevent the growth of bacteria, and allow them to stand 48 hours, upon
admitting air the tube with chloroform gives no light but the tubes with
toluol and thymol do give light, although it is not so bright as if they
were absent. I believe that these substances have a destructive action on
the reductases, most complete in the case of chloroform. Dubois (1919_c_)
also has recorded the occurrence of a reducing enzyme in _Pholas_, a
"hydrogenase," which is able to form hydrogen from cane sugar, and
luciferin from a boiled extract of _Pholas_. He now regards it as
identical with his co-luciferase.

I have not been able to demonstrate that a _Cypridina_ extract will
reduce methylene blue, or nitrates to nitrites, either with or without
the addition of acetaldehyde. This may be due to the fact that
oxyluciferin, which is also present, may be reduced more readily than
either nitrates or methylene blue, and so is reduced first.

We can also reduce oxyluciferin by means which do not involve the use of
animal extracts. Perhaps the best of these is reduction by palladium
black and sodium hypophosphite. The latter is oxidized in presence of
palladium and nascent hydrogen is set free. The nascent hydrogen reduces
any easily reducible substance which may be present, such as methylene
blue or oxyluciferin. Oxyluciferin is not reduced by palladium alone or
hypophosphite alone, but methylene blue is reduced by palladium black
alone.

If hydrogen sulphide is passed through a solution of methylene blue the
dye is very quickly reduced and becomes colorless. If the H_{2}S is
driven off by boiling the colorless methylene-blue solution, the blue
color again returns on cooling. Oxyluciferin can also be reduced by
H_{2}S.

If one adds some Mg powder to oxyluciferin and then dilute acetic acid
in successive additions as the acetic acid is used up in formation of Mg
acetate, the oxyluciferin will be reduced relatively quickly. Nascent
hydrogen is produced in the reaction and is no doubt the active reducing
agent.

Dilute acid favors the reduction of oxyluciferin. If one saturates an
oxyluciferin solution with CO_{2} or adds a little dilute acetic acid,
HCl, HNO_{3} or H_{2}SO_{4}, to it, a certain amount of reduction will
occur. No reduction occurs if the solution is saturated with pure
hydrogen, even if allowed to stand 24 hours. The action of the acid
begins when the solution of oxyluciferin, ordinarily slightly alkaline
(PH = 9), is made neutral (PH = 7.1) as indicated in Table 9. The action
of the acid must be on the oxyluciferin, as no luciferin or other
enzymes destroyed on boiling are present.


TABLE 9

_Effect of Acid on Reduction of Oxyluciferin_

  =============================================================================
      Solution                   | P_{H}|Luminescence|    Remarks
                                 |      |   with     |
                                 |      | luciferase |
  -------------------------------+------+------------+-------------------------
  20 c.c. Oxyluciferin alone     | 9.01 |  Negative  |
  20 c.c. Oxyluciferin + .05 c.c.| 8.8  |  Negative  |
    5 per cent. acetic acid      |      |            |
  20 c.c. Oxyluciferin + .15 c.c.| 7.1  |  Fair      |
    5 per cent. acetic acid      |      |            |
  20 c.c. Oxyluciferin + .30 c.c.| 5.9  |  Good      |Acid forms precipitate in
    5 per cent. acetic acid      |      |            |  this oxyluciferin sol.
  20 c.c. Oxyluciferin + .50 c.c.|      |  Good      |Acid forms precipitate in
    5 per cent. acetic acid      |      |            |  this oxyluciferin sol.
  20 c.c. Oxyluciferin + .75 c.c.|      |  Good [10] |Acid forms precipitate in
    5 per cent. acetic acid      |      |            |  this oxyluciferin sol.
  -------------------------------+------+------------+-------------------------

[10] Light disappears quickly because of the effect of the acidity on
the luciferase.

It is possible that the action of bacteria (which produces CO_{2}),
muscle tissue (which contains lactic acid), milk (in which lactic acid
may be formed by bacteria), or Mg + acid, in forming luciferin, is not
the result of their reducing power but of their acidity. Fortunately we
can test this matter by the use of reducing fluids which are not acid.
If they also form luciferin from oxyluciferin, a reduction must occur.
Nascent H can be generated by the action of NaOH on Al, or when finely
divided Mg or Zn or Al is placed in water. With Mg the water becomes
only slightly alkaline from formation of almost insoluble Mg(OH)_{2}. If
we add some Al powder and dilute NaOH to an oxyluciferin solution, H is
given off and luciferin is formed. As oxyluciferin cannot be formed by
the addition of alkali alone we must have in this experiment a reduction
of oxyluciferin in alkaline medium by the nascent H produced. Luciferin
can also be formed by merely adding Al or Zn or Mg dust to an
oxyluciferin solution. Methylene blue can also be readily reduced to its
leuco-base by Zn dust or Al + NaOH.

Indeed, if one adds some Al or Zn or Mg powder to a solution of
luciferase, light will appear whenever the solution is shaken.
Luciferase solution must always contain the oxidation product of
luciferin, oxyluciferin. In presence of nascent H this is reduced to
luciferin, and since the reaction of the medium is alkaline and
luciferase is present this is oxidized with light production, when, by
shaking, air is dissolved. The light can never become very bright except
at the surface because of the deficiency of oxygen in the solution. It
would seem, then, that the action of bacteria, yeast, muscle cells,
etc., on oxyluciferin must be due not entirely to their acid reaction
but to their reducing power as well.

The above experiment is a very striking and instructive one. Given a
test tube of luciferase solution containing, as it does, oxyluciferin,
add some Zn dust or Mg powder, and the evolution of hydrogen begins.
Conditions are now favorable for the reduction of oxyluciferin and this
occurs. Shake the contents of the tube to dissolve oxygen and light
appears. Allow the tube to stand and the light soon disappears. Shake
again and the light reappears. The luminescence reduction and oxidation
process can be demonstrated many times.

A similar experiment can be performed with luciferase and oxyluciferin
solution by addition of NH_{4}SH. This will serve also as another
example of the reduction of oxyluciferin in an alkaline medium. Whenever
we shake a tube of luciferase, oxyluciferin and NH_{4}SH, light will
appear. When the tube is at rest it becomes dark. Even the merest touch
is sufficient to agitate the tube contents, cause solution of oxygen and
appearance of light. It is just as if we stimulate the tube to produce
light and I believe the phenomenon has a deeper significance and a more
fundamental similarity to the phenomena of stimulation than may at first
appear. What more simple means of controlling a process can we think of
than by admission or withdrawal of oxygen? The firefly turns on its
light by stimulation through nerves of the luminous organ. _Noctiluca_
flashes on stimulation of any kind, even the slightest agitation causing
a brilliant emission of light. If the stimulation process means merely
the admission of oxygen to the photogenic cells we have a mechanism in
the cell itself for automatically producing the light. The admission of
oxygen results in aërobic conditions and luciferin in presence of
luciferase can then oxidize to oxyluciferin with luminescence. When the
oxygen is used up, the light ceases, anaërobic conditions prevail, and
the oxyluciferin is reduced to luciferin again. Thus, luciferin is
reformed during the rest period of _Noctiluca_ or between the flashes of
the firefly. What more efficient type of light than this is to be
desired?

Again, methylene blue offers an interesting parallel to oxyluciferin. A
little NH_{4}SH added to methylene blue solution will reduce
(decolorize) it to the leuco-base. If the tube is now shaken the blue
color returns. On standing reduction again occurs. The process can be
repeated a number of times, the reaction going in one or the other
direction, depending on the oxygen content of the mixture.

As methylene blue contains no oxygen, its reduction consists in the
addition of two atoms of hydrogen. When leuco-methylene blue oxidizes,
water is formed by the union of these two atoms of hydrogen with oxygen,
thus:

  C_{16}H_{20}N_{3}SCl + O ⇆ C_{16}H_{18}N_{3}SCl + H_{2}O
    (leuco-methylene blue)       (methylene blue)

  Briefly--MH_{2} + O ⇆ M + H_{2}O

To reduce methylene blue we can add the two hydrogen atoms directly from
nascent hydrogen formed in the solution or we can split up water by a
catalyzer in the presence of some substance, which will take up the
oxygen of water, thus:

  NaH_{2}PO_{2} + H_{2}O + Pd = NaH_{2}PO_{3} + H_{2} + Pd
   (Sodium hypophosphite)         (Sodium phosphite)

This reaction occurs in presence of finely divided palladium. Methylene
blue can be reduced by the H_{2} and the hypophosphite oxidized.

Since oxyluciferin can be reduced by palladium and sodium hypophosphite
(Harvey, 1918), it is probable that we can write the equation for
reduction of oxyluciferin and oxidation of luciferin in a similar manner
to that of methylene blue:

  Luciferin + O ⇆ Oxyluciferin + H_{2}O

  Briefly--LH_{2} + O ⇆ L + H_{2}O.

Just as in the case of methylene blue the reaction proceeds in the right
hand direction spontaneously if the pressure of O is sufficiently high.
If luciferase is also present we have luminescence.

  LH_{2} + O + luciferase ⇆ L + H_{2}O + luciferase (luminescence)

The reaction proceeds in the left hand direction under low oxygen
pressure, in the presence of nascent hydrogen or with some catalyzer
which is able to split water, transferring the H_{2} to oxyluciferin and
the O to an acceptor (A). NaH_{2}PO_{2} plays the part of the acceptor.

  L + H_{2}O + A + Pd = LH_{2} + AO + Pd.

This appears to be the way in which the reducing enzymes or
perhydridases (comparable to the Pd) of living tissues act (Bach,
1911-13) and the action of yeast cells, bacteria, muscle suspensions,
etc., in reducing oxyluciferin must occur in the same manner.

If we assume that the LH_{2} (luciferin) compound is dissociated to even
the slightest extent into L and hydrogen, the hydrogen ion will shift
the equilibrium toward the formation of that substance which involves
the taking up of hydrogen. Consequently we may obtain a partial
formation of luciferin by adding an acid to oxyluciferin. Reduction of
the H-ion concentration tends to shift the equilibrium in the opposite
direction. Consequently, addition of alkali favors the oxidation of
luciferin, and it is quite generally true that biological oxidations are
favored by an alkaline reaction. In addition oxygen in alkaline medium
has a higher oxidation potential than in neutral or acid media. I
believe this is the explanation of the action of acid in formation of
luciferin from oxyluciferin.

Addition of acid is not the only means of favoring the formation of
luciferin from oxyluciferin. Any reaction which proceeds in one
direction with evolution of light should, theoretically, proceed in the
opposite direction under the influence of light. So far as I know the
case of a reaction, photogenic in one direction and photochemical in the
other direction, has never been described, unless we are to accept the
cases of phosphorescence, for instance, the absorption of light by CaS
and its emission in the dark. However, the reaction which occurs during
phosphorescence cannot be stated.

It is a fact that light will cause the reduction of oxyluciferin. A tube
of oxyluciferin exposed to sunlight for six hours, or the mercury arc
for two hours, will be partially converted into luciferin. It will
luminesce when luciferase is added, while a control tube kept in
darkness shows no trace of luciferin. The action is more marked with the
ultra-violet as a solution of oxyluciferin in a quartz tube showed more
reduction than one in a glass tube when exposed for the same length of
time to the quartz mercury arc. The reduction is not dependent on the
formation of acid under the influence of light since two tubes of
oxyluciferin, one kept in darkness and the other exposed to sunlight for
six hours, had the same reaction, PH = 9.3. Of course some reducing
substance might be formed under the influence of light but this is not
very probable.

We may therefore write the reaction for luminescence in the following
way:

                            darkness
                            alkali
                            luciferase
  luciferin (LH_{2}) + O ⇆  oxyluciferin (L) + H_{2}O (luminescence)
                            perhydridase
                            acid
                            light

Acid and light favor reduction while alkali and darkness favor oxidation
in the luciferin ⇆ oxyluciferin reaction. Whether the luciferin be really
oxidized by removal of H_{2} or whether by addition of oxygen is, of
course, uncertain, but the analogy with methylene blue is striking and
may serve as a working hypothesis until the composition of luciferin and
its oxidation product are known.

While I have not studied the properties of oxyluciferin as fully as
those of luciferin, so far as I can judge, both substances give the same
general reactions and possess identical properties. Both crude luciferin
and crude oxyluciferin solution are yellow in color, but I do not
believe that either pure luciferin or oxyluciferin are yellow in color,
because an ether or benzine extract of _Cypridina_ is also yellow,
although luciferase, luciferin, and oxyluciferin are insoluble in ether
and benzine. The yellow pigment which can be observed to make up part of
the luminous gland of _Cypridina_ is not luciferin or luciferase. It may
be a pigment related to _urochrome_.

When tests are applied and precipitating reagents are added to crude
luciferin and crude oxyluciferin solution, they give identical results
in each case. A more complete account of the chemistry of luciferin has
been given in this chapter, and there is no need of duplicating these
statements regarding oxyluciferin. Like luciferin, the oxyluciferin will
pass porcelain filters, dialyze through parchment or collodion
membranes, and is undigested by salivary diastase, pepsin HCl, Merck's
pancreatin in neutral solution, and erepsin. The salivary diastase and
the pancreatin (containing amylopsin, trypsin, and lipase) were allowed
to digest for four days at 38° C. without showing any evidence of
digestive action.

As luciferin is so easily oxidizable a substance, we should expect to
find that it will reduce just as glucose will reduce. However, a
concentrated solution of luciferin has no reducing action on Fehling's
(alkaline Cu), Barfoed's (acid Cu), Nylander's (alkaline Bi) or Knapp's
(alkaline Hg) reagent. Glucose will reduce methylene blue in alkaline
(not in neutral solution), but luciferin will not reduce methylene blue
in alkaline or neutral solution. It would seem, then, that luciferin
must contain no aldehyde group. If so, we should expect to obtain
reduction of some of the above reagents. Just what group is concerned in
the oxidation is unknown at the present time, and in the absence of more
experimental data, speculation regarding it can be of little value.


SUMMARY

In summing up we may say that the luminescence of at least three groups
of luminous animals, the beetles, _Pholas_, and _Cypridina_, has been
definitely shown to be due to the interaction of two substances,
luciferin and luciferase, in presence of water and oxygen. Luciferin and
luciferase have quite different properties and may be easily separated
from each other by various chemical procedures. As the luciferins and
luciferases from different luminous animals have somewhat different
properties, they may be designated by prefixing the generic name of the
animal from which they are obtained.

_Cypridina_ luciferin differs from _Pholas_ luciferin in that it can not
be oxidized with light production by KMnO_{4}, H_{2}O_{2}, with or
without hæmoglobin, or similar oxidizing agents. _Cypridina_ luciferase
differs from _Pholas_ and firefly luciferase in that it is not readily
destroyed by the fat-solvent anæsthetics, such as chloroform, ether,
etc.

When _Cypridina_ luciferin is oxidized, no fundamental splitting of the
molecule occurs, because the product, oxyluciferin, can be readily
reduced to luciferin again. This reduction is brought about under
conditions similar to those necessary for the reduction of dyes, such as
methylene blue. Oxyluciferin can be reduced to luciferin, which will
again give light with luciferase, by the reductases of muscle tissue,
liver, etc., or by bacteria; by Schardinger's enzyme of milk; by H_{2}S;
by the nascent hydrogen from the action of acetic acid on magnesium or
of water or NaOH on aluminium, zinc or magnesium; and by palladium black
and sodium hypophosphite, all well-known reducing methods. Reduction of
oxyluciferin no doubt occurs even in presence of luciferase if oxygen is
absent, and reduction of oxyluciferin no doubt occurs in animals which
burn luciferin within the cell, thus tending for conservation of
material. Dilute alkali favors oxidation and dilute acid favors the
reduction. Light favors the reduction of oxyluciferin.

Apparently luciferin and oxyluciferin have identical chemical
properties. Neither is digested by the enzymes: malt diastase, ptyalin,
yeast invertase, pepsin, trypsin, steapsin, amylopsin, rennin, erepsin,
urease or enzymes occurring in the water extracts of dried spleen,
kidney, or liver. Luciferase is destroyed only by pepsin (probably),
trypsin, erepsin, and something in spleen and liver extract.

Luciferase is unquestionably a protein and all its properties agree with
those of the albumins. Although used up in oxidizing large quantities of
luciferin, it behaves in many ways like an enzyme and may be so
regarded.

Luciferin, on the other hand, is not digested by proteolytic enzymes, is
dialyzable, almost but not completely precipitated by saturation with
(NH_{4})_{2}SO_{4}, and is soluble in absolute alcohol, acetone, and
some other organic solvents, but not in the strictly fat-solvents like
ether, chloroform, and benzol. There are, however, certain CO-NH
linkages which are not attacked by proteolytic enzymes and some peptones
soluble in absolute alcohol, so that these two characteristics do not
bar it from the group of proteins. Luciferin, in fact, has many
properties in common with the proteoses and peptones but its chemical
nature cannot be definitely stated at present.




CHAPTER VII

DYNAMICS OF LUMINESCENCE


One of the most extraordinary things regarding luminescence in general
is the small amount of material necessary to cause a visible emission of
light. To take an extreme case, the flash of light resulting from the
impact on ZnS of a single α particle, a helium atom, is visible to the
naked eye. Addition of one part in a million of some heavy metal to pure
CaS will confer phosphorescent properties on the latter. We are forced
to believe that the heavy metal enters into some reaction during
illumination which is reversed with light emission after illumination
and a very small amount of heavy metal is necessary. Pyrogallol in
water, 1:5,000,000 (m/512,000), can be oxidized with light production by
K_{4}Fe(CN)_{6} and H_{2}O_{2} (Harvey, 1917) and m/100 pyrogallol +
H_{2}O_{2} will give a visible light with colloidal platinum in
1:250,000 concentration (Goss, 1917).

Luciferin and luciferase from _Cypridina_ will also luminesce in
exceedingly small concentration. If one grinds a single _Cypridina_ in a
mortar with water and dilutes the extract to 25,600 c.c., light can be
observed if luciferin is added to this dilute luciferase solution. By
determining the volume of the luminous gland of _Cypridina_ and even
assuming that this volume is all luciferase, one can calculate that one
part of luciferase in 1,700,000,000 parts of water will give light when
luciferin is added. Likewise, a similar dilution of luciferin will give
visible light when luciferase is added.

The sensitivity of our eye is largely responsible for the detection of
so small an energy change. As we have seen, recent determinations have
proved that the dark adapted eye can detect 18 × 10^{-10} ergs per
second. From the heat of complete oxidation of pyrogallol it is possible
to calculate the amount of pyrogallol necessary to give 18 × 10^{-10}
ergs if completely oxidized. This quantity is infinitesimally small.
When pyrogallol is oxidized by K_{4}Fe(CN)_{6} and H_{2}O_{2}, it is not
completely oxidized and probably only a small amount of the energy is
converted into light; otherwise we should be able to see the
luminescence of a very much weaker concentration of pyrogallol. As the
reaction luciferin ⇆ oxyluciferin is so easily reversible, very little
energy must be liberated, and, as experiments indicate, very little
heat, if any, accompanies light production. Even though this be true, it
is still possible for a very small amount of luciferin to produce a very
large amount of light.

A very small amount of luciferase only is necessary because it behaves
as an enzyme and follows the general rule that catalysts act in minute
concentrations.

On the assumption that luciferase is an enzyme, an organic catalyst
oxidizing luciferin with light production, we may appropriately inquire
into the relation between the concentration of luciferin and luciferase
and intensity and duration of luminescence. Oxygen tension, hydrogen ion
concentration and temperature must be maintained constant as these all
affect both intensity and duration of luminescence. Before considering
luciferin and luciferase, however, let us study a few well-known
chemiluminescent oxidations with special reference to concentration of
reacting substances and temperature.

The effect of temperature on luminescence is of special interest because
it gives us a means of analysis for determining if the luminescence
depends on reaction velocity. We know that photochemical reactions are
very little affected by temperature because the reaction is dependent on
the absorption of light, a physical process, and this increases only a
small per cent. for a rise of temperature of 10° C. To put it in the
usual way, its temperature coefficient (Q_{10}) for a 10° interval is
usually less than 1.1. On the other hand, we should expect photogenic
reactions, in which some of the chemical energy is converted into
radiant energy, to give off much more light the greater the reaction
velocity. As reaction velocity increases so rapidly with temperature
(Q_{10} = 2 to 3), luminescence intensity should rapidly increase with
increase in temperature.

Trautz (1905), from his extensive study of the chemiluminescence of
phenol and aldehyde compounds came to the conclusion that luminescence
intensity was proportional to reaction velocity. He based his
conclusions largely on the effects of temperature and concentration of
reacting substances and went so far as to declare that any reaction
would produce luminescence if the reaction velocity were sufficiently
increased. It is quite true that increasing the temperature does
increase the intensity of chemiluminescence, but this is only within
certain limits. As we raise the temperature, chemiluminescence becomes
more intense but we soon reach a temperature for maximum luminescence
and above this the intensity diminishes. This is especially well seen in
the action of various oxidizers on pyrogallol and H_{2}O_{2} recorded in
Table 10. At 100° C. practically no light is produced by many
oxidizers which are themselves unaffected at 100°. If we are to connect
reaction velocity with intensity of luminescence we must conclude that
the evolution of light is dependent rather on an optimum than a maximum
reaction velocity.


TABLE 10

_Temperature and Light Production. The Oxidizer is Mixed with an Equal
Amount of M/100 Pyrogallol + 3 per cent. H_{2}O_{2}_

  =========================================================================
                        |                   Temperatures
        Oxidizer        +----------+---------+---------+--------+----------
                        |   0-2°   |   20°   |   50°   |   75°  |  98-100°
  ----------------------+----------+---------+---------+--------+----------
  Turnip juice          | Faint    | Good    | Good    |        | Negative.
  1 per cent.           |          |         |         |        |
    blood extract       | Faint    | Fair    | Good    |        | Fair.
  M/20 K_{4}Fe(CN)_{6}  | Negative | Good    | Bright  | Bright | Good.
  M/100 KMnO_{4}        | Fair     | Good    | Bright  | Bright | Faint
                        |          |         |         |        |   flash.
  M/50 K_{2}Cr_{2}O_{7} | Negative | Fair    | Faint   | Fair   | Negative.
  M/100 CrO_{3}         | Negative | Good    | Bright  | Bright | Faint.
  M/10 KCr alum         | Negative | Faint   | Faint   | Faint  | Negative.
  M/10 NH_{4}Fe alum    | Negative | Faint   | Faint   | Faint  | Very
                        |          |         |         |        |   faint.
  MnO_{2}               | Negative | Fair    | Fair    | Fair   | Negative.
  NaClO                 | Bright   | Bright  | Bright  |        | Fair
                        |   flash  |   flash |   flash |        |   flash.
  ----------------------+----------+---------+---------+--------+----------

Quite a number of instances are known in which increasing the mass of
reacting substances leads not to an increase but to an actual cessation
of luminescence. This fact does not confirm the theory that reaction
velocity is a determining factor in luminescence. The conditions for the
luminescence of white phosphorus are most interesting and unusual. (See
van't Hoff, 1895; Ewan, 1895; Centnerszwer, 1895; Russell,1903; Scharff,
1908.) Phosphorus will only begin to luminesce at a certain small
pressure of oxygen. This "minimum luminescence pressure" of oxygen is
very low, so low that earlier observers, failing to remove traces of
oxygen, thought that luminescence might occur in absence of oxygen.
Curiously enough there is also a "maximum luminescence pressure" of
oxygen above which no luminescence occurs. Phosphorus will not luminesce
in pure oxygen. Between the minimum and maximum is an "optimum
luminescence pressure" where luminescence of the phosphorus is
brightest. The exact values of these pressures vary with degree of water
vapor present and with temperature. According to Abegg's _Handbuch der
anorganischen Chemie_, the maximum luminescence pressure with water
vapor present, is 320 mm. Hg at 0° and increases 13.19 mm. Hg for each
degree rise in temperature. This means that for a definite temperature,
say, 20°, phosphorus will not luminesce with an oxygen pressure of 583
mm. Hg, but will luminesce with pressures under this. If, however, we
raise the temperature, luminescence will occur with an oxygen pressure
of 583 mm. Hg.

A somewhat analogous case is presented by the oxidation of pyrogallol
solution in contact with ozone, except that in this reaction too high a
concentration of pyrogallol will hinder the oxidation. I have not
studied the effect of varying concentrations of ozone. If oxygen, passed
through an ozonizer (the silent electric discharge tube), is bubbled
through m/100 pyrogallol, no luminescence occurs at 0°, a fair
luminescence at 20°, a good luminescence at 50°, and a bright
luminescence at the boiling point. If the pyrogallol is of _m_
concentration, no luminescence occurs at 0° or 20°, a fair luminescence
at 50°, and a bright luminescence at the boiling point. For a definite
temperature, say 20°, no light appears if the pyrogallol is of _m_
concentration, but if we raise the temperature, luminescence can occur.
The similarity to phosphorus is obvious. Thus the "maximum luminescence
pressure" of pyrogallol increases with increase of temperature.

We have already seen that pyrogallol can also be oxidized, if H_{2}O_{2}
is present, by a great variety of substances, such as peroxidases of
potato or turnip juice, hæmoglobin, KMnO_{4}, K_{4}Fe(CN)_{6}, CrO_{3},
MnO_{2}, hypochlorites and hypobromites, or colloidal Pt and Ag. For
convenience we may collectively speak of these as oxidizers. They are
recorded in Table 13. No light occurs if H_{2}O_{2}is absent. In the
case of some of these oxidizers pyrogallol will luminesce in dilute
concentrations but not in strong. Also, dilute pyrogallol will luminesce
with a dilute solution of oxidizer but not with a concentrated solution
of oxidizer. The effect of rise in temperature in these cases also is to
increase the "maximum luminescence concentration" of pyrogallol and the
"maximum luminescence concentration" of oxidizer. Table 11 shows this
effect of temperature with K_{4}Fe(CN)_{6} and varying concentrations of
pyrogallol, and Table 12 shows the effect of temperature with pyrogallol
and varying concentrations of K_{4}Fe(CN)_{6}. Table 10 shows the
relation between temperature and intensity of luminescence with
pyrogallol and various oxidizers. The terms _faint_, _fair_, _good_, and
_bright_ are purely relative designations of brightness as estimated by
the eye, for accurate measurements of weak intensities are very
difficult to make.

From Table 10 it should be noted that the intensity of luminescence of
pyrogallol oxidized with most oxidizers is actually less at the boiling
point, a fact which I have repeatedly verified. Let us now see how these
facts are to be explained. If we assume that luminescence is dependent
on reaction velocity, the intensity of luminescence should increase with
increasing temperature. Up to a certain limit this is what we find, but
at temperatures above this limit the intensity of luminescence actually
decreases. The duration of luminescence also decreases. There is an
optimum temperature for luminescence in many cases and we can only
conclude that luminescence depends not on a very rapid reaction velocity
but on a certain definite reaction velocity. Assuming that this is true,
how can we account for the anomalous fact that in high concentrations of
oxygen, phosphorus will not luminesce or that in high concentrations of
pyrogallol, there is no luminescence in presence of ozone or of oxidizer
and H_{2}O_{2}. Of course with high active mass of oxygen (in case of
phosphorous luminescence) or of pyrogallol (in case of pyrogallol
luminescence) the reaction velocity must be greater than the
optimum. If that is the case, then lowering the temperature should
reduce the reaction velocity to the optimum and light should appear.
However, as we have seen, not lowering but raising the temperature
causes luminescence with high oxygen concentration or high pyrogallol
concentration.


TABLE 11

_Temperature, Concentration of Pyrogallol, and Light Production. An
Equal Amount of M/20 K_{4}Fe(CN)_{6} is Mixed with Pyrogallol + 3 per
Cent H_{2}O_{2}_

  A = Concentration of pyrogallol (after mixing)

  =========================================================================
          |                       Temperatures
     A    +---------+---------+-------+--------+--------+--------+---------
          |   0-2°  |   10°   |  20°  |  30°   |  50°   |  75°   |  98-100°
  --------+---------+---------+-------+--------+--------+--------+---------
  M/4     | Negative| Negative| Good  | Very   | Faint  | Fair   | Faint
          |         |         |       |   faint|        |        |
  M/40    | Negative| Faint   | Faint | Faint  | Good   | Bright | Good
          |         |         |       |        |        |        |
  M/400   | Faint   | Fair    | Good  | Good   | Good   | Bright | Bright
          |         |         |       |        |        |        |   flash
  M/4,000 | Bright  | Bright  | Bright| Bright | Bright | Fair   | Negative
          |         |         |       |        |   flash|   flash|
  --------+---------+---------+-------+--------+--------+--------+---------


TABLE 12

_Temperature, Concentration of Ferrocyanide and Light Production. An
Equal Amount of K_{4}Fe(CN)_{6} is Mixed with M/100 Pyrogallol + 3 Per
Cent H_{2}O_{2}_

  A = Concentration of K_{4}Fe(CN)_{6} exposed to light (after mixing)

  ========================================================================
                      |                     Temperatures
           A          +---------+-----+-----+-----+------+--------+-------
                      |   0-2°  | 10° | 20° | 30° |  50° |  75°   |98-100°
  --------------------+---------+-----+-----+-----+------+--------+-------
  Half saturated      |Negative |Faint|Fair |Fair |Good  |Good    |Faint
    at 20° C          |         |     |     |     |      |        |  flash
  One-sixth saturated |Very     |Fair |Good |Good |Bright|Very    |Good
    at 20° C          |  faint  |     |     |     |      |  bright|  flash
  --------------------+---------+-----+-----+-----+------+--------+-------


TABLE 13

_Substances Giving Light with Pyrogallol and Hydrogen Peroxide_


  Key to column headings:

  A = Equal volume added to mixture of 1 part M/100 pyrogallol or 1 part 3
      per cent H_{2}O_{2} + 1 part M/100 pyrogallol; hence, concentrations
      final mixture are one-half that given

  B = Light with pyrogallol

  C = Light with pyrogallol + H_{2}O_{2}

  D = Blueing of gum guaiac

  E = Blueing of gum guaiac + H_{2}O_{2}

  F = Liberation of oxygen from H_{2}O_{2}

  =============================================================================
     A                                         |  B   |  C   |  D  |  E  |  F
  ---------------------------------------------+------+------+-----+-----+-----
   1 Potassium ferrocyanide                    |  -   |Bright|  +  |     |  +
      (K_{4}Fe(CN)_{6} M/10-M/20)              |      |      |     |     |
   2 Potassium ferricyanide                    |  -   |Very  |  -  |  -  |Very
      (K_{3}Fe(CN)_{6} M/10-M/1,250)           |      | faint|     |     | slow
                                               |      | to - |     |     |
   3 Potassium chromate                        |  -   |Good  |  +  |     |  +
      (K_{2}CrO_{4} M/20-M/100)                |      |      |     |     |
   4 Potassium bichromate                      |  -   |Good  |  +  |     |  +
      (K_{2}Cr_{2}O_{7} M/50-M/100)            |      |      |     |     |
   5 Potassium permanganate                    |  -   |Bright|  +  |  -  |  +
      (KMnO_{4} M/50-M/200)                    |      |      |     |     |
   6 Potassium hydroxide                       |  -   |  -   |  -  |  -  |Very
      (KOH M-M/6,250)                          |      |      |     |     | slow
   7 Potassium chlorate                        |  -   |  -   |  -  |  -  |  -
      (KClO_{3} M/10)                          |      |      |     |     |
   8 Potassium persulfate                      |  -   |  -   |  -  |  -  |  -
      (K_{2}S_{2}O_{8} M/10-M/128)             |      |      |     |     |
   9 Potassium chromium alum                   |  -   |Faint |Very |Very |  -
      (Cr_{2}(SO_{4})_{3}.K_{2}SO_{4} M/10)    |      |      | slow| slow|
  10 Ferric ammonium alum                      |  -   |Faint |  +  |     |Very
      (Fe_{2}(SO_{4})_{3}.(NH_{4})_{2}SO_{4}   |      |      |     |     | slow
      M/10)                                    |      |      |     |     |
  11 Ferric chloride                           |  -   |Fair  |  +  |     |Slow
      (FeCl_{3} M/10-M/250)                    |      |      |     |     |
  12 Ferrous sulfate                           |  -   |Fair  |  -  |  +  |Slow
      (FeSO_{4} M/10-M/6,250)                  |      |      |     |     |
  13 Copper sulfate                            |  -   |  -   |  -  |  +  |Very
      (CuSO_{4} M/5-M/125)                     |      |      |     |     | slow
  14 Chromic acid                              |  -   |Bright|  +  |     |  +
      (CrO_{3} M/100)                          |      |      |     |     |
  15 Chromic sulfate                           |  -   |Faint |  -  |  +  |Slow
      (Cr_{2}(SO_{4})_{3} 2 per cent)          |      |      |     |     |
  16 Chlorine water                            |  -   |  -   |  +  |     |  +
  17 Bromine water                             |  -   |  -   |  +  |     |  +
  18 Iodine in KI                              |  -   |  -   |  +  |     |  +
  19 Sodium hypochlorite                       |Faint |Bright|  +  |     |  ++
      (Cl water + NaOH)                        | flash|      |     |     |
  20 Sodium hypobromite                        |Faint |Bright|  +  |     |  ++
      (NaOBr, bromine water + NaOH)            | flash|      |     |     |
  21 Sodium hypoiodite                         |  -   |Faint |  +  |     |  +
      (I in KI + NaOH)                         |      |      |     |     |
  22 Calcium hypochlorite                      |  -   |Good  |  +  |     |  ++
      (Ca(OCl)_{2} saturated solution)         |      |      |     |     |
  23 Turnip juice                              |  -   |Bright|  -  |  +  |  ++
  24 Turnip juice heated to 70°                |  -   |Faint |  -  |  +  |Very
                                               |      |      |     |     | slow
  25 Turnip juice boiled                       |  -   |  -   |  -  |  -  |  -
  26 Albumin solution                          |  -   |  -   |  -  |  -  |  -
  27 Albumin solution + KMnO_{4}               |  -   |Good  |  +  |  -  |  ++
  28 Albumin solution + KMnO_{4} boiled 1 min. |      |      |     |     |
          and filtered (no precipitate forms)  |  -   |Good  |  +  |  -  |  ++
  29 Gelatin solution                          |  -   |  -   |  -  |  -  |  -
  30 Gelatin solution + KMnO_{4}               |  -   |Good  |  -  |  -  |  ++
  31 Gelatin solution + KMnO_{4} boiled 1 min. |      |      |     |     |
          and filtered (no precipitate forms)  |  -   |Good  |  +  |  -  |  ++
  32 Colloidal Ag                              |  -   |Bright|  +  |     |  +
  33 Colloidal Pt                              |  -   |Bright|  +  |     |  +
  34 Colloidal Fe(OH)_{2} (dilute)             |  -   |  -   |  -  |  +  |  -
  35 Sodium nucleoproteinate (liver)           |  -   |  -   |  -  |  +  |  -
  36 Sodium nucleoproteinate (mammary gland)   |  -   |  -   |  -  |  -  |  -
  37 Sodium nucleate (yeast)                   |  -   |  -   |  -  |  -  |  -
  38 Squid blood (Sepia esculenta).            |      |      |     |     |
          Contains hemocyanin                  |  -   |Fair  |     |     |  ++
  39 Squid blood (Sepia esculenta) boiled      |  -   |Good  |     |     |  -
  40 Lobster blood (Palinurus japonicus).      |      |      |     |     |
          Contains hemocyanin and              |      |      |     |     |
          tetronerythrin, a lipochrome         |  -   |Faint |     |     |  ++
  41 Lobster blood (Palinurus japonicus)       |      |      |     |     |
          boiled                               |  -   |Fair  |     |     |  -
  42 Annelid blood (Laonome japonica).         |      |      |     |     |
          Contains chlorocruorin               |  -   |Good  |     |     |
  43 Annelid blood (Laonome japonica) boiled   |  -   |  -   |     |     |
  44 Luminous pennatulid extract               |      |      |     |     |
          (Cavernularia haberi)                |  -   |  -   |  -  |  +  |  ++
  45 Luminous ostracod extract                 |      |      |     |     |
          (Cypridina hilgendorfii)             |  -   |  -   |     |     |  +
  46 Luminous protozoan extract                |      |      |     |     |
          (Noctiluca miliaris)                 |  -   |  -   |  -  |  -  |  -
  47 Firefly (Luciola viticollis) extract,     |      |      |     |     |
          luminous organs                      |  -   |  -   |     |     |  ++
  48 Ferrous ferrocyanide (Fe_{2}Fe(CN)_{6})   |  -   |Faint |  +  |     |  +
  49 Zinc ferrocyanide (Zn_{2}Fe(CN)_{6})      |  -   |  -   |  +  |     |Very
                                               |      |      |     |     | slow
  50 Chromic oxide (Cr_{2}O_{3})               |  -   |  -   |  -  |     |Slow
  51 Chromic hydroxide (Cr(OH)_{2})            |  -   |  -   |  -  |Slow |  +
  52 Manganese dioxide (MnO_{2})               |  -   |Good  |Slow |Slow |  ++
  ---------------------------------------------+------+------+-----+-----+-----

I believe the explanation of these phenomena lies rather in another
direction and that the effect of the temperature and concentration of
reacting substances affects not only the reaction velocity but also the
reaction products. While intensity of luminescence undoubtedly increases
with increasing reaction velocity, the luminescence itself probably
accompanies only one stage in the formation of a series of oxidation
products. This stage is favored at a definite temperature and mass of
reacting substances. Thus, in the oxidation of phosphorus several
intermediate oxides are said to be formed. The oxidation takes place in
steps and probably the luminescence is connected with only one of the
steps in a chain of reactions. It is probable that a certain oxygen
pressure and temperature favors that particular step at the expense of
the others and so this oxygen concentration and temperature correspond
to the optimum for luminescence.

The supposition that certain definite oxidation products of pyrogallol
must be formed in order to produce light is borne out by the fact that
pyrogallol must be oxidized in a particular way to obtain luminescence.
The blackening of pyrogallol with absorption of oxygen in presence of
alkali is a very well-known reaction, but luminescence does not
accompany this type of oxidation. I have tried mixing all concentrations
of pyrogallol and all concentrations of alkali in an endeavor to obtain
some light, but always with negative results. Likewise my attempts to
obtain light during the electrolysis of salt solutions containing
pyrogallol by means of the nascent oxygen at various kinds of anodes
have met with negative results. A similar case is presented by luciferin
which oxidizes spontaneously (most rapidly in presence of alkali)
without light production and only produces light when oxidized in
presence of luciferase.

To sum up the results of the dynamics of chemiluminescence we may say
that certain oxyluminescences occur only if the substance is oxidized in
a particular way under definite conditions of temperature and
concentration and that this is probably due to a favoring of one step
(with which the luminescence is associated) in a chain of oxidations.
Providing temperature and concentration are such as to favor the step
responsible for luminescence, then higher temperature and greater
concentration result in increased intensity of luminescence.

Let us now turn to luminous organisms and consider the effect of
temperature and of concentration of reacting substances (oxygen,
luciferin and luciferase) on the luminescence. We have already seen that
luminescence of a luciferin-luciferase mixture begins with an
extraordinarily low oxygen tension and increases in intensity with
increasing tension of oxygen, but that very soon an oxygen tension is
reached where a maximum luminescence is obtained and further increase of
oxygen tension gives no brighter light. In this respect the luminescence
intensity--oxygen tension curve is no doubt very similar to the
hæmoglobin saturation--oxygen tension curve. Hæmoglobin is about 50 per
cent. saturated at 10 mm. oxygen pressure, 80 per cent. saturated at 20
mm. oxygen pressure and completely saturated at pressures of oxygen
well below the pressure of oxygen in air (152 mm. Hg). As the optimum
oxygen tension for luminescence of luciferin is also well below that of
air, mixtures of luciferin and luciferase luminesce with equal
brilliancy whether air or pure oxygen is bubbled through them. To obtain
an excess of oxygen it is only necessary to keep the solution saturated
with air and statements regarding concentration of luciferin and
luciferase and intensity or duration refer to excess of oxygen.
Investigators who have studied the effect of increase in oxygen pressure
on luminous animals have come to the same conclusions. High pressures of
air or oxygen do not increase the intensity of luminescence (Dubois and
Regnard, 1884).

The hydrogen ion concentration of crude solutions of luciferin and
luciferase, made by extracting whole Cypridinas with hot or cold water
is fairly constant, about PH = 9, determined electrometrically. Such
solutions have a high buffer value and the PH does not change during
oxidation of luciferin so that this variable is automatically
controlled.

Because of difficulties in measuring low intensities of light which are
constantly changing, no figures on light intensities can be given, but
it is easy to establish the following facts: The greater the
concentration of luciferin or luciferase the more intense the
luminescence. The greater the concentration of luciferin the longer the
duration of luminescence and the greater the concentration of
luciferase, the shorter the luminescence lasts. Thus, if we mix
concentrated luciferin and weak luciferase we get a bright light which
lasts for a half hour or more, gradually growing more dim. Concentrated
luciferase and weak luciferin give a bright flash of light which
disappears almost instantly. Concentrated luciferase and concentrated
luciferin give a brilliant light which lasts for an intermediate length
of time and weak luciferin and weak luciferase give a faint luminescence
which lasts for an intermediate length of time.

These facts can all be explained by regarding luciferase as a catalyzer
which accelerates the oxidation of luciferin and by assuming that
intensity of luminescence is dependent on reaction velocity, _i.e._, on
rate of oxidation. Contrary to the condition for phosphorus and for
pyrogallol there appears to be no optimum concentration of luciferase or
luciferin, but the luminescence intensity increases gradually with
increasing concentration of luminous substances up to the point where
pure (?) luciferin and pure (?) luciferase, as secreted from the gland
cells of the animal, come in contact with each other. This, the maximum
brightness, is not to be compared with the light of an incandescent
solid, but is nevertheless visible in a well-lighted room, out of direct
sunlight.

The effect of temperature on _Cypridina_ luminescence also bears out the
preceding conclusions. For a given mixture of luciferin and luciferase
the light becomes more intense with increasing temperature up to a
definite optimum and then diminishes in intensity. The diminution in
intensity above the optimum is due to a reversible change in the
luciferase so that its active mass diminishes. This change becomes
irreversible in the neighborhood of 70° (depending on various
conditions), where coagulation of luciferase occurs. Light will appear
at 0° but it is far less intense than light at higher temperatures and
it is more yellow in color. The light of optimum temperatures is quite
blue. The weaker light at temperatures above the optimum is also more
yellow in color. I believe this difference in color is a function of the
slowed reaction velocity, for a mixture of luciferin and luciferase
which gives a bluish luminescence at room temperature, will give a
weaker and yellowish luminescence if diluted with water. Dilution with
water will slow the reaction velocity. If the difference in color were
not real but due to change in color sensitivity of the eye with
different intensities of such relatively weak light (Purkinje
phenomenon), the weaker light should appear more blue. As the weaker
light appears more yellow, I therefore believe the color difference is
actual and not subjective.

A minimum, optimum, and maximum temperature for luminescence is observed
in all luminous organisms. The minimum is usually very low. Luminous
bacteria will still light at -11.5° C. The power to luminesce under
ordinary conditions is not destroyed by exposure to liquid air, for, on
raising the temperature, light again appears (Macfayden, 1900, 1902).
Almost all organisms will luminesce at 0° C., and the luminescence
minimum probably represents the point at which complete freezing of the
luminous solution occurs. It is very low with bacteria because they are
solutions in capillary spaces of very small size, a condition tending to
lower the freezing point.

The luminescence maximum represents the point at which luciferase is
reversibly changed so as to be no longer active. If the temperature is
again lowered the luciferase again becomes active and light reappears.
Some degrees above this, and in all forms well below the boiling point,
luciferase is coagulated and destroyed. As the coagulation point of
proteins depends on many factors, such as time of heating, salt
content, acidity, etc., so the luciferases of different animals
coagulate at different temperatures depending on these conditions. Some
of the more reliable observations on these critical temperatures are
collected in Table 14.


TABLE 14

_Temperature Limits of Luminescence for Luminous Organism_

  -------------------------+---------------------+-------+-------+-------+
          Organism         |   Author and date   |Minimum|Optimum|Maximum|
  -------------------------+---------------------+-------+-------+-------+
  Pseudomonas javanica     | Eijkman, 1892       | -20°  | 25-33°|  45°  |
                           |                     |       |       |       |
  Bacterium phosphorescens | Lehmann, 1889       | -12°  |  ...  | 39.5° |
                           |                     |       |       |       |
  Bacterium phosphoreum    | Molish, 1904, book  |  -5°  | 16-18°|  28°  |
                           |                     |       |       |       |
  Light bacteria           | Tarchanoff, 1902    |  -7°  | 15-25°|  37°  |
                           |                     |       |       |       |
  Light bacteria           | Harvey, E. N., 1913 | -11.5 | 15-20°|  38°  |
                           |                     |       |       |       |
  Mycelium X               | Molish, 1904        |  ...  | 15-25°|  36°  |
                           |                     |       |       |       |
  Lampyrids                | Macaire, 1821       | -10   |   33° | 46-50°|
                           |                     |       |       |       |
  Pyrophorus noctilucus    | Dubois, 1886        |  ...  | 20-25°|  47°  |
                           |                     |       |       |       |
  Photuris pennsylvanica   | Lund, 1911          |  ...  |  ...  |  50°  |
                           |                     |       |       |       |
  Luciola viticollis       | Harvey, E. B., 1915 |  <0°  |  ...  |  42°  |
                           |                     |       |       |       |
  Cypridina hilgendorfii   | Harvey, E. N., 1915 |  <0°  |  ...  | 52-54°|
                           |                     |       |       |       |
  Cyclopina gracilis       | Lund, 1911          |  ...  |  ...  |  50°  |
                           |                     |       |       |       |
  Phylirrhoë bucephalum    | Panceri, 1872       |  44°  |  ...  |  61°  |
                           |                     |       |       |       |
  Pyrosoma                 | Panceri, 1872       |  <0°  |  ...  |  60°  |
                           |                     |       |       |       |
  Mnemiopsis Leidyi        | Peters, 1905        |   9°  |   21° |  37°  |
                           |                     |       |       |       |
  Noctiluca miliaris       | Quatrefages, 1850   |   1°  |  ...  |  40°  |
                           |                     |       |       |       |
  Noctiluca miliaris       | Harvey, E. B., 1917 |  <0°  |  ...  |  48°  |
                           |                     |       |       |       |
  Cavernularia haberi      | Harvey, E. N., 1915 |  <0°  |  ...  |  52°  |
                           |                     |       |       |       |
  Watasenia scintillans    | Shoji, R, 1919      |  ...  | 16-31°|  49°  |
  -------------------------+---------------------+-------+-------+-------+

We are thus led to the conclusion that intensity of luminescence is
dependent on the velocity of oxidation of luciferin and that with
lowered reaction velocity the spectral composition of the light changes.
The maximum emission shifts toward the yellow. I believe, however, that
in _Cypridina_ also, the luminescence intensity depends not only on
reaction velocity but on the particular manner in which luciferin is
oxidized. _Cypridina_ luciferin will luminesce only in presence of
_Cypridina_ luciferase and no light can be obtained from _Cypridina_
luciferin and a host of different oxidizers (with or without H_{2}O_{2})
such as are able to oxidize pyrogallol. Luciferin will also oxidize in
the air spontaneously but no light is produced. It is easy to show that
this spontaneous oxidation may be much more rapid than an oxidation with
luciferase and yet light appears only in presence of the latter. If a
concentrated solution of luciferin is kept near the boiling point it
will be completely oxidized to oxyluciferin in four or five minutes. No
light appears if air or even if pure oxygen is bubbled through it. The
same solution kept at 20° with a small amount of luciferase will
luminesce continuously and not be completely oxidized to oxyluciferin in
a half hour. We can, however, cause the luciferin to oxidize as rapidly
at 20° by adding concentrated luciferase as does the luciferin near the
boiling point without luciferase. A bright light is produced in the
former case, none in the latter case. The oxyluciferin formed from
spontaneous oxidation of luciferin appears to be the same as that formed
with luciferase present. Both give luciferin again on reduction. Perhaps
the reaction takes place in two stages, similar to those supposed to
occur in other enzyme actions:

  luciferin + luciferase = luciferinluciferase
  luciferinluciferase + O (or minus H_{2}) = oxyluciferin
    + luciferase.

We may then assume as a tentative hypothesis that luminescence only
occurs during oxidation (addition of O or removal of H) of the
luciferinluciferase compound.

We have just seen that the effect of cooling a _Cypridina_ extract
containing luciferin and luciferase and luminescing with a bluish light,
is to reduce the intensity and change the shade toward the yellow.
Velocity of oxidation must be lowered and with the same concentration of
luciferase lowered velocity means more light of the longer wave-lengths.
A very instructive experiment on color of the light can be carried out
with animals having different colored lights and so closely related that
their luciferins and luciferases will interact with each other. Such a
case is presented by the American fireflies, _Photinus_ and _Photuris_.
_Photinus_ emits an orange light, while _Photuris_ emits a greenish
yellow light. The difference in color is especially noticeable when the
luminous organs of the two forms are ground up in separate mortars. As
shown by Coblentz, the difference in color is real, the spectrum of
_Photinus_ extending farther into the red than that of _Photuris_ (see
Fig. 8). We can easily prepare luciferin and luciferase from the two
fireflies and make the following mixtures:

_Photinus_ luciferin × _Photinus_ luciferase = reddish light.

_Photinus_ luciferin × _Photuris_ luciferase = yellowish light.

_Photuris_ luciferin × _Photuris_ luciferase = yellowish light.

_Photuris_ luciferin × _Photinus_ luciferase = reddish light.

Thus the color of the light in these "crosses" is that characteristic of
the animal supplying the luciferase. To bring this fact in line with
what we have already said regarding reaction velocity and luminescence,
we must believe that the _Photinus_ luciferase oxidizes at a slower rate
than the _Photuris_ luciferase. In this connection it is of interest to
recall that the _Photuris_ light as emitted by the insect becomes
reddish at high temperatures, or if the insect is plunged into alcohol,
both conditions which bring about partial coagulation of the luciferase
and reduce its active mass.




BIBLIOGRAPHY


A few of the enormous number of papers on luminescence are included in
the list below. The attempt is made to list only those dealing with the
structure, chemistry or physiology of luminous animals and the physical
nature of their light, together with a small number of general interest.
More complete works on light and luminescence come first and original
articles follow. Authors' names are arranged alphabetically, their
papers chronologically. A fairly complete list of literature covering
the whole field of Bioluminescence is given by Mangold, 1910. The 1913
paper of Dubois gives a bibliography of his own contributions up to this
date so that only those papers to which special reference is made are
included below.


BOOKS AND GENERAL WORKS

BECQUEREL, E.: 1867, La Lumière.

DAHLGREN, U.: 1915, The Production of Light by Animals. _Jour. Franklin
Inst._, vols. 180 to date.

DUBOIS, R.: 1914, La Vie et La Lumière. Alcan, Paris.

GADEAN DE KERVILLE, H.: 1890, Les Vegetaux et les Animaux Lumineux.
Paris.

HARVEY, E. N.: 1917, The Chemistry of Light Production in Luminous
Organisms. Carnegie Inst., Wash., Pub. No. 251, pages 171-234.

HEINRICH, Pl.: 1811-1820, Die Phosphorescenz der Körper, etc. Nürnburg.

HOUSTOUN, R. A.: 1915, A Treatise on Light. London.

KAYSER, H.: 1908, Handbuch der Spectroscopie. Vols. ii and iv. Leipzig.

MANGOLD, E.: 1910, Die Produktion von Licht. Hans Winterstein's Handbuch
der vergleichende Physiologie, vol. iii, second half, pp. 225-392. Jena.

MOLISH, H.: 1904 and 1912, Leuchtende Pflanzen. Eine physiologische
Studie. Jena.

NUTTING, P. G.: 1912, Outlines of Applied Optics. Philadelphia.

PHIPSON, T. L.: 1870, Phosphorescence. L. Reeve and Co. London. 210
pages.

SHEPARD, S. E., 1914, Photochemistry. Longmans, Green and Co.


ORIGINAL PAPERS

ABEGG, R., and AUERBACH, F.: 1907, Handbuch der anorganischen Chemie.
Leipzig, vol. iii, pt. 3, p. 376.

AGASSIZ, A.: 1874, Embryology of the Ctenophoræ. _Mem. Am. Ac. Arts and
Science_, x, p. 371.

ALLMAN, G. I.: 1862, Note on the Phosphorescence of Beroë. _Proc. Roy.
Soc. Edinb._, iv, 518.

AUBERT ET DUBOIS, R.: 1884, Sur les propriétés de la lumière des
pyrophores. _Comp. rend. Acad. des Sc._, vol. xcix, p. 477.

BACH, A.: 1911-1913, Zur Kenntnis der Reduktionsfermente. _Biochem.
Zeit_, xxxi, 443; xxxiii, 282; xxxviii, 154; lii, 412-422.

BAKER, J.: 1743-1753, The Microscope Made Easy and Employment for the
Microscope.

BALLNER, F.: 1907, Ueber das Verhalten von Leuchtbacterien bei der
Einwirkung von Agglutinationsserum und anæsthesierenden chemischen
Agentien, etc. _Centralb. f. Bact._, 2 abt., xix, 572.

BANCROFT, W. D.: 1913, The Chemical Production of Light. _Journ. Frank.
Inst._, clxxv, 129.

BANCROFT, W. D., and WEISER, H. B.: 1914-1915, Flame Reactions, I, II,
III, IV. _Jour. Phys. Chem._, xviii, 213, 281, 762; xix, 310.

BANDROWSKI, E.: 1894-1895, Ueber Lichterscheinungen während der
Krystallisation. _Zeit. Phys. Chem._, xv, 323-326; xvii, 234-244.

BARCROFT, J., and HILL, A. V.: 1910, The Nature of Oxyhæmoglobin with a
Note on Its Molecular Weight. _Journ. Physiol._, xxix, pp. 411-429.

BARNARD, J. E.: 1902, Luminous Bacteria. _Nature_, _vol._ lxv, p. 536.

BEIJERINCK, M. W.: 1889a, Le photobacterium luminosum, bactérie
lumineuse de la mer du nord. _Arch. Néerlandaises_, T. 23, p. 104.

BEIJERINCK, M. W.: 1889b, L'auxanographie ou la méthode de
l'hydrodiffusion dans la gelatine appliquée aux recherches
microbiologique. _Arch. Néerlandaises_, vol. xxiii, p. 367.

BEIJERINCK, M. W.: 1889c, Les Bactéries lumineuses dans leur rapports
avec l'oxygène. _Arch. Néerlandaises_, T. 23, p. 416.

BEIJERINCK, M. W.: 1891, Sur l'aliment photogène et l'aliment plastique
des bactéries lumineuses. _Arch. Néerlandaises_, T. 24, pp. 369-442.

BEIJERINCK, M. W.: 1902, Photobacteria as a Reactive in the
Investigation of the Chlorophyll-function. _Proceedings of Section of
Sciences, Koninkl. Akad. van Wetenschappen te Amsterdam_, vol. iv, p.
45.

BEIJERINCK, M. W.: 1915, Die Leuchtbacterien der Nordsee im August und
September. Folia microbiologica, iv.

BLANCHETIÈRE: 1913, Oxydation et Luminescence. _C. R. Ac. Sc._, clvii,
118.

BONGARDT, J.: 1903, Beiträge zur Kenntnis der Leuchtorgane einheimischer
Lampyriden. _Ztsch. f. wiss. Zool._, Bd. 75, pp. 1 to 45.

BOYLE, R.: 1667, _Philo. Trans. Abridged Roy. Soc._, 5th Ed., vol. ii
(1722), p. 206, and iii (1749), p. 646.

BRAUER, A.: 1904, Ueber die Knochenfische. _Verhandl. Deutsch. Zool.
Ges._, vol. xiv, pp. 16-35.

BRAUER, A.: 1906, Die Tiefseefische. I. Systematischer Teil. II.
Anatomischer Teil. _Wiss. Ergeb. der Valdivia-Exped._ Jena.

CARRADORI, B.: 1798, Experiments and Observations on the Phosphorescence
of the Luciole, Lampyris italica. _Ann. d. Chemie_, xxiv, pp. 96-101;
_Philos. Magazine_, ii, pp. 77-80.

CARUS: 1864, Expériences sur la matière phosphorescente de la Lampyris
italica et action d'eau pour rendre à la matière dessechée cette
phosphorescence. _C. R. Ac. Sc._, lix, pp. 607-608.

CENTNERSZWER, M.: 1898, Ueber den Katalytischen Einfluss verscheidener
Gase und Dämpfe auf die Oxydation des Phosphors. _Z. Physik. Chem._, 26,
pp. 1-46.

CHUN, C.: 1893, Leuchtorgan und Facettenauge. Ein Beitrag zur Theorie
des Sehens in grossen Meerstiefen. _Biol. Ctbl._, Bd. xiii, pp. 544-571.

CHUN, C.: 1896, Atlantis. Biologische Studien über pelagische
Organismen, Chap. VI. Die Leuchtorgane der Euphausidén. _Biblioth.
Zool._, vol. vii, H. 19, pp. 196-212.

CHUN, C.: 1903, Ueber Leuchtorgane und Augen von Tiefsee-Cephalopoden.
_Verhandl. Dtsch. Zool. Ges._, pp. 67-91.

COBLENTZ, W. W.: 1909, Notiz über eine der Feuerfliege herrührende
fluorenzierende Substanz. _Physik Zeit._, x, pp. 955-956.

COBLENTZ, W. W.: 1912, A Physical Study of the Firefly. _Publication No.
164, Carnegie Inst., Wash., D.C._

COBLENTZ, W. W., and EMERSON, W. B.: 1917, Relative Sensibility of the
Average Eye to Light of Different Colors and Some Practical Applications
to Radiation Problems. _Bur. Standards, Scient. Pap. No. 303._

CONROY, J.: 1882, The Spectrum of the Light Emitted by the Glowworm.
_Nature_, vol. xxvi, p. 319.

DELEPINE, W. L.: 1910, Sur quelques composés organiques spontanement
oxydables avec phosphorescence. _C. R. Ac. Sc._, vol. cl, pp. 876-878.

DUBOIS, R.: 1885, Fonction photogénique des Pyrophores. _C. R. Soc.
Biol._, vol. xxxvii, 559-562.

DUBOIS, R.: 1886, Les Elatérides Lumineux. _Bull. Soc. Zool. de France_,
vol. xi, pp. 1-275.

DUBOIS, R.: 1887a, De la fonction photogénique chez le Pholas dactylus.
_C. R. Ac. Sc._, vol. cv, p. 690.

DUBOIS, R.: 1887b, Note sur la Fonction Photogenique chez les Pholades.
_C. R. Soc. Biol._, pp. 564-567.

DUBOIS, R.: 1892, Anatomie et Physiologie Comparées de la Pholade
Dactyle. _Ann. d. Univ. Lyon_, vol. ii, p. 1-155.

DUBOIS, R.: 1893, Sur le mécanisme de production de la lumière chez Orya
barbarica d'Algerie. _C. R. Ac. Sc._, Paris, July 17th.

DUBOIS, R.: 1896, Nouvelles Recherches sur la Production de la Lumière
par les êtres vivants. _C. R. Soc. Biol._, vol. xlviii, p. 995.

DUBOIS, R.: 1901a, Nouvelles recherches sur la Biophotogénèse. _C. R.
Soc. Biol._, vol. liii, p. 702.

DUBOIS, R.: 1901b, Luminescence obtenue par certains procédes
organiques. _C. R. Ac. Sc._, vol. cxxxii, p. 431.

DUBOIS, R.: 1907, Mécanisme Intime de la Formation de la Luciferine;
analogies et homologies des organs de Poli et la glande hypobranchiale
des Molluscs Purpurigenes. _C. R. Soc. Biol._, vol. lxii, p. 850.

DUBOIS, R.: 1913, Mécanisme Intime de la Production de la lumière chez
les Organismes Vivants. _Ann. Soc. Linn. de Lyons_, vol. lx, pp. 81-97.

DUBOIS, R.: 1914a, De la Place Occupée par la Biophotogénèse dans la
Series des Phénomènes Lumineux. _Ann. Soc. Linn. de Lyons_, vol. lxi,
pp. 247-256.

DUBOIS, R.: 1914b, Examen Critique de la Question de la Biophotogénèse.
_Ann. Soc. Linn. de Lyons_, vol. lxi, pp. 257-265.

DUBOIS, R.: 1916, Sur l'Anatomie de la glande Photogène de Pholas
dactylus. _Ann. Soc. Linn. de Lyons_, vol. lxiii, pp. 9-13.

DUBOIS, R.: 1917a, A propos de Quelques Recherches Recentes de M. Newton
Harvey sur la Biophotogénèse et du Rôle Important de la Preluciferine.
_C. R. Soc. Biol._, December 22d.

DUBOIS, R.: 1917b, Etude Critique de Quelques Travaux Resents Relatif à
la Biophotogénèse. _Ann. Soc. Linn. de Lyons_, vol. lxiv, pp. 65-118.

DUBOIS, R.: 1918a, Sur la Synthèse de la Luciferine. _C. R. Ac. Sc._,
vol. clxvi, p. 578.

DUBOIS, R.: 1918b, Nouvelles Recherches sur la Biophotogénèse. Synthèse
Naturelle de la Luciferine. _C. R. Soc. Biol._, vol. lxxxi, p. 317.

DUBOIS, R.: 1918c, Sur la Lumière Physiologique (Nouvelle reponse a M.
Newton Harvey). _C. R. Soc. de Biol._, vol. lxxxi, p. 484.

DUBOIS, R.: 1919a, b, Symbiotes, Vacuolides, Mitrochondries et Leucites.
_C. R. Soc. Biol._, vol. lxxxii, May 10th and July 26th.

DUBOIS, R.: 1919c, Reversibilité de la fonction photogénique par
l'hydrogénase de la pholade dactyle. _C. R. Soc. Biol._, vol. lxxxii, p.
840.

DUBOIS, R., et REGARD, P.: 1884, Note sur l'action des hautes pressions
sur la fonction photogénique du Lampyre. _C. R. Soc. Biol._, vol. xxxvi,
pp. 675-676.

EHRENBERG, C. G.: 1831, Ueber einen neuen, das Leucten der Ostsee
bedingenden, lebenden Körper. _Poggendorffs Ann. d. Phys. und Chem._,
Bd., vol. xxiii, p. 147.

EHRENBERG, C. G.: 1834, Das Leuchten des Meers. _Abhandl. d. Kgl. Akad.
d. Wiss. Berlin_, pp. 411-572.

EHRENBERG, C. G.: 1859, Ueber das Leuchten und ueber neue microskopische
Leuchthiere des Mittelmeeres. _Monatsber. d. Berliner Akad._, pp.
727-791.

EIJKMAN, C.: 1892, _Geneeskundig Tidschrift v. Ned. Ind._, Deel, 32 Abl.
4, p. 109.

ELIOT, C.: 1907-1915, Notes on a Collection of Nudibranchs from the Red
Sea. _Journ. Linn. Soc. London_, vol. xxxi, p. 102.

EMERY, C.: 1884, Untersuchungen ueber Luciola italica L. _Ztschr. f.
Wiss. Zool._, Bd. xl, pp. 338-355.

EMMERLING, O.: 1909, Hydrolyse der Meerleuchtinfusorien der Nordsee
(Noctiluca miliaris). _Biochem. Zt._, vol. xviii, pp. 372-374.

ENDERS, H. E.: 1909, A Study of the Life History and Habits of
Chætopterus variopedatus, Renier et Claparède. _Journ. Morph._, vol. xx,
pp. 479-532.

EWAN, T.: 1895, Ueber die Oxydationsgeschwindigkeit von Phosphor,
Schweifel und Aldehyde. _Zeit. physik. Chem._, vol. xvi, pp. 315-343.

EXNER, S.: 1903, Einige Beobachtungen ueber die durch Radiumstrahlen in
den tierischen Geweben erzeugte Phosphoreszenz. _Ctbl. f. Physiol._, Bd.
xvii, pp. 177-179.

FABRE, J. H.: 1855, Recherches sur la Cause de la Phosphorescence
d'Agaric de L'Olivier. _Ann. d. Sc. Nat._, 4 ser., vol. iv, p. 179.

FAHRIG, E.: 1890, The Phosphorescence Produced Upon the First Contact of
Ozone with Certain Fluids. _Chem. News_, vol. lxii, pp. 39-40.

FALGER, F.: 1908, Untersuchungen ueber das Leuchten von Acholoë
astericola. _Biol. Ctbl._, Bd. xxviii, pp. 641-649.

FISCHER, B.: 1888a, Ueber einen neuen lichtentwickelenden Spaltpilz.
_Ctbl. f. Bakt._, Bd. iii, pp. 105 and 137.

FISCHER, B.: 1888b, Bacterium Wachstum bei 0°. _Ctbl. f. Bakt._, Bd. iv,
p. 89.

FÖRSTER, J.: 1887, Ueber einige Eigenschaften leuchtender Bakterien.
_Ctbl. f. Bakt._, Bd. ii, p. 339.

FÖRSTER, J.: 1892, Ueber die Entwicklung von Bakterien bei niederer
Temperatur. _Centralbl. f. Bak._, vol. xii, pp. 431-436.

FÖRSTER, J.: 1914, Ueber die Leuctorgane und das Nervensystem von Pholas
dactylus. _Zeit. f. wiss. Zool._, vol. cix, pp. 349-393.

FORSYTH, R. W.: 1910, The Spectrum of Bacterial Luminosity. _Nature_,
vol. lxxxiii, p. 7.

FRANKLAND, P.: 1898, The Action of Bacteria on the Photographic Plate.
_Ctbl. f. Bakt._, 1st Abt. Bd. xxiv, pp. 609-612.

FRIEDBERGER, E., and DOEPNER, H.: 1907, Ueber den Einfluss von
Schimmelpilzen auf die Lichtintensität in Leuchtbacterienkulturen, etc.
_Centralbl. f. Bakt._, 1st Abt., xliii, p. 1.

FRIEND, H.: 1893, Luminous Earthworm. _Nature_, vol. xlvii, p. 462.

FUCHS, S.: 1891, Einige Versuche an der Leuchtorganen von Elater
noctilucus. _Centralbl. f. Physiol._, vol. v, pp. 321-325.

GALLOWAY and WELCH: 1911, Studies on a Phosphorescent Bermudan Annelid,
Odontosyllis enopla, Verrell. _Trans. Amer. Micros. Soc._, vol. xxx, pp.
13-39.

GEIPEL, E.: 1915, Beiträge zur Anatomie der Leuchtorgane tropischer
Käfer. _Zeit. Wiss. Zool._, vol. cxii, pp. 239-290.

GERNEZ, D.: 1905, Triboluminescence des composés Métalliques. _C. R. Ac.
Sc._, vol. cxl, pp. 1134, 1234, 1337.

GIARD, A.: 1890, Nouvelles recherches sur les bacteries lumineuses
pathogènes. _Comp. rend. soc. Biol._, T. xlii, pp. 188-191.

GIARD, A., and BILLET, A.: 1889, Observations sur la Maladie
phosphorescente des Talitres et Autres Crustaces. _Compt. rend. soc.
Biol._, vol. 1, Ser. 9, p. 593.

GIBSON, K. S., and MCNICHOLAS, H. J.: 1919, The Ultra-Violet and Visible
Transmission of Eye-protective Glasses. _Bureau of Standards. Tech.
Papers No. 119._

GIESBRECHT, W.: 1895, Ueber das Leuchten der pelagischen Copepoden und
das tierische Leuchten im allgemeinen. _Mitteil. d. Zool. St. Neapel_,
Bd. xi, pp. 648-694.

GIESBRECHT, W.: 1896, Ueber den Stiz der Lichtentwicklung in den
Photosphärien der Euphausiiden. _Zool. Anz._, Bd. xix, pp. 486-490.

GOSS, B. C.: 1917, Light Production at Low Temperatures by Catalysis
with Metal and Metallic Oxide Hydrosols. _Journ. Biol. Chem._, vol.
xxxi, pp. 271-279.

GREEF, R.: 1882, Ueber die rosettenförmigen Leuchtorgane der
Tomopteriden und zwei neue Arten von Tomopteris. _Zool. Anz._, Bd. v,
pp. 384-387.

GREENE, C. W.: 1899, The Phosphorescent Organs in the Toad Fish,
_Porichthys natatus_, Girard. _Jour. of Morph._, vol. xv, pp. 667-684.

GUINCHANT: 1905, Sur la triboluminescence de l'acide arsenieux. _C. R.
Ac. Sc._, vol. cxl, p. 1170.

HANDRICK, K.: 1901, Zur Kenntnis des Nervensystems und der Leuchtorgane
von Argyropelecus hemigymnus. _Zoologica_, Bd. xiii, Heft. 32, pp. 1-68.

HANKEL, W.: 1862, Notiz ueber Phosphorisches Leuchten des Fleisches.
_Ann. d. Phys. u. Chem._, Bd. cxv, p. 62.

HANSEN, H. J.: 1903, On the Crustaceans of the Genera Petalidium and
Sergestes from the "Challenger," with an Account of Luminous Organs in
Sergestes challengeri n. Sp. _Proc. Zool. Soc., London_, 1903, vol. i,
pp. 52-77.

HARVEY, E. B.: 1917, A Physiological Study of Specific Gravity and
Luminescence in Noctiluca, with Special Reference to Anæsthesia. _Pub.
No. 251, Carneg. Inst., Wash._, pp. 235-253.

HARVEY, E. N.: 1913, The Temperature Limits of Phosphorescence of
Luminous Bacteria. _Biol. Bull._, vol. ii, pp. 456-457.

HARVEY, E. N.: 1914, On the Chemical Nature of the Luminous Material of
the Firefly. SCIENCE N. S., vol. xl, pp. 33-34.

HARVEY, E. N.: 1915a, Experiments on the Nature of the Photogenic
Substance in the Firefly. _Jour. Am. Chem. Soc._, vol. xxxvii, pp.
396-401.

HARVEY, E. N.: 1915b, Studies on Light Production by Luminous Bacteria.
_Am. Jour. Physiol._, vol. xxxvii, pp. 230-240.

HARVEY, E. N.: 1915c, The Effect of Certain Organic and Inorganic
Substances Upon Light Production by Luminous Bacteria. _Biol. Bull._,
vol. xxix, pp. 308-312.

HARVEY, E. N.: 1916a, The Mechanism of Light Production in Animals.
_Science N. S._, vol. xliv, pp. 208-209.

HARVEY, E. N.: 1916b, Studies on Bioluminescence. II. On the Presence of
Luciferin in Luminous Bacteria. _Am. Jour. Physiol._, vol. xli, pp.
449-454.

HARVEY, E. N.: 1916c, Studies in Bioluminescence. III. On the Production
of Light by Certain Substances in the Presence of Oxidases. _Am. Jour.
Physiol._, vol. xli, pp. 454-464.

HARVEY, E. N.: 1916d, The Light-producing Substances, Photogenin and
Photophelein of Luminous Animals. _Science N. S._, vol. xliv, pp.
652-654.

HARVEY, E. N.: 1917a, Studies on Bioluminescence. IV. The Chemistry of
Light Production in a Japanese Ostracod Crustacean _Cypridina
hilgendorfii_, Muller. _Amer. Jour. Physiol._, vol. xlii, pp. 318-341.

HARVEY, E. N.: 1917b, V. The Chemistry of Light Production by the
Firefly, Id., pp. 342-348.

HARVEY, E. N.: 1917c, VI. The Light Production in a Japanese Pennatulid,
Cavernularia haberi, Id., pp. 349-358.

HARVEY, E. N.: 1917d, What Substance is the Source of Light in the
Firefly? _Science N. S._, vol. xliv, pp. 241-243.

HARVEY, E. N.: 1917e, Studies on Bioluminescence. VIII. The Mechanism of
the Production of Light during Oxidation of Pyrogallol. _Jour. Biol.
Chem._, vol. xxxi, pp. 311-336.

HARVEY, E. N.: 1918, Studies on Bioluminescence. VII. Reversibility of
the Photogenic Reaction in Cypridina. _Jour. Gen. Physiol._, vol. i, pp.
133-145.

HARVEY, E. N.: 1919a, Studies on Bioluminescence. IX. Chemical Nature of
Cypridina Luciferin and Cypridina Luciferase. _Jour. Gen. Physiol._,
vol. i, pp. 269-293.

HARVEY, E. N.: 1919b, Studies on Bioluminescence. X. Carbon Dioxide
Production during Luminescence of Cypridina Luciferin. _Jour. Gen.
Physiol._, vol. ii, pp. 133-135.

HARVEY, E. N.: 1919c, XI. Heat Production during Luminescence of
Cypridina Luciferin. _Id._, vol. ii, pp. 137-143.

HARVEY, E. N.: 1920, Studies on Bioluminescence, XII. _Id._, ii,
207-213.

HEINEMANN, C.: 1872, Untersuchungen ueber die Leuchtorgane der bei
Vera-Cruz vorkommenden Leuchtkäfer. _Arch. f. mikr. Anat._, Bd. viii,
pp. 461-471.

HEINEMANN, C.: 1873, Aschenanalyse von Leuchtorganen mexikanischer
Cucujos. _Pflüger's Arch._, Bd. vii, pp. 365-367.

HEINEMANN, C.: 1886, Zur Anatomie und Physiologie der Leuchtorgane
mexikanischer Cucujos. _Archiv f. Mikr. Anat._, Bd. xxvii, pp. 296-382.

HELLER, J. FLORIAN: 1853 u. 1854, Ueber das Leuchten im Pflanzen-und
Tierreiche. _Arch. f. Physiol. u. Pathol. Chem. u. Mikrosk., mit bes.
Rücksicht auf med. Diagnost. u. Therapie Wien._, N. F., Bd. vi, pp. 44,
81, 121, 161, 201, 241.

HENNEBERG, W.: 1899, Leuchtbacterien als Krankheitserreger bei
Schwammücken. _Centralbl. f. Bakt._, 1st Abt. xxv, pp. 649-650.

HOYLE, W. F.: 1902, The Luminous Organs of Ptergioteuthis margaritifera,
Mediterranean Cephalopod. _Manchester Mem._, vol. xlvi, No. 16.

HULME, N.: 1800, Experiments and Observations on the Light Which is
Spontaneously Emitted with Some Degree of Permanency from Various
Bodies. _Phil. Trans. Roy. Soc._, pp. 161-187.

HYDE, E. P., FORSYTH, W. E. and CADY, F. E.: 1918, The Visibility of
Radiation. _Astrophys. Journ._, vol. xlviii, pp. 65-88.

HYDE, E. P., FORSYTH, W. E., and CADY, F. E.: 1919, A New Experimental
Determination of the Brightness of a Black Body and of the Mechanical
Equivalent of Light. _Physical Review_, vol. xii, pp. 45-58.

ISHIKAWA, C.: 1913, Einige Bemerkungen ueber den leuchtenden
Tintenfisch, Watasenia Nov. Gen. (Abraliopsis der Autoren) scintillans,
Berry, aus Japan. _Zool. Anz._, 1913, vol. xliii, pp. 162-172.

ISSATSCHENKO, B.: 1903, Quelques expériences avec la lumière
bactérienne. _Ctbl. f. Bakt._, Abt. 2, Bd. x, pp. 497-499.

ISSATSCHENKO, B.: 1907, Zur Erforschung des Bakterienlichtes. _Centralb.
f. Bakt._, Bd. xix, pp. 116-117.

ISSATSCHENKO, B.: 1911, Erforschung des bakterielle Leuchten des
Chironomus (Diptera). _Bull. d. jard. imp. botan. St. Petersburg_, vol.
xi, p. 42.

IVES, H. E.: 1910, Further Studies of the Firefly. _Physical Rev._, vol.
xxxi, pp. 637-651.

IVES, H. E.: 1915, The Total Luminous Efficiencies of Present-day
Illuminants. _Physical Rev._, Ser. 2, vol. v, p. 390.

IVES, H. E., and COBLENTZ, W. W.: 1910, Luminous Efficiency of the
Firefly. _Bull. Bur. Stand., Wash., D. C._, vol. vi, pp. 321-336.

IVES, H. E., and LUCKIESH, M.: 1911, The Effect of Red and Infra-red on
the Decay of Phosphorescence in Zinc Sulphide. _Astrophys. Journ._, vol.
xxxiv, pp. 173-196.

JOHANN, L.: 1899, Ueber eigentümliche epitheliale Gebilde (Leuchtorgane)
bei Spinax niger. _Ztschr. f. wiss Zool._, Bd. lxvi, pp. 136-160.

JOUBIN, L.: Note sur l'appareil photogène d'un cephalopode
(Histioteuthis Rupelii). _Compt. rend. soc. Biol._, 1893, pp. 142-146.

JOURDAN, ET.: 1885, Structure des élytres de quelques Polynoës. _Zool.
Anz._, Bd. viii, pp. 128-134.

JOURDAN, ET.: 1887, Structure histologique des téguments et des
appendices sensitifs de l'Hermione hystérix et du Polynoë Grubiana.
_Arch. Zool. Expér._, 1887, 2nd ser., T. v, pp. 91-122.

JOUSSET, DE BELLESME: 1880, Recherches expérimentales sur la
phosphorescence du lampyre. _Jour. de l'anat. et de la Physiol._, T.
xvi, pp. 121-169.

KASTLE, J. H., and MCDERMOTT, F. A.: 1910, Some Observations on the
Production of Light by the Firefly. _Amer. Jour. Physiol._, vol. xxvii,
pp. 122-151.

KATZ, O.: 1891, Zur Kenntnis der Leuchtbakterien. _Centralb. f. Bak._,
pp. 9, 157, 199, 229, 258, 311, 343.

KEMP, S.: 1910, Notes on the Photophores of Decapod Crustacea. _Proc.
Zool. Soc., London_, pp. 639-651.

KNAB, F.: 1909, Luminous Termite Hills. _Science_, vol. xxx, pp.
574-575.

KÖLLIKER, A. V.: 1858, Ueber die Leuchtorgane von Lampyriden. _Verh. d.
Phys. Med. Ges., Würzburg_, Bd. viii, pp. 217-224.

KÖLLIKER, A. V.: 1859, Ueber die Leuchtorgane der amerikanischen
Pyrophorus-Arten. _Verh. d. Phys. Med. Ges., Stiz. ber., Würzburg_, Bd.
ix, p. 28.

KRUNKENBERG, F. C. W.: 1887, Neue Tatsachen für eine vergleichende
Physiologie der Phosphorescenzerscheinungen bei Tieren und bei Pflanzen.
_Vergl. Physiol. Studien, Heidelberg_, II Reihe, 4th Abt., pp. 77-142.

KUTSCHER, F.: 1897, Zur Physiologie der Phosphorescenz. _Ztschr. f.
Physiol. Chem._, 1897, Bd. xxiii, pp. 109-113.

KUTSCHER, F.: 1909, Die Leuchtorgane von Archoloë astericola. _Ztschr.
f. wiss. Zool._, Bd. xcii, pp. 75-102.

LANGLEY, S. P., and VERY, F. W.: 1890, On the Cheapest Form of Light
from Studies at the Allegheny Observatory. _Amer. Jour. of Sc._, 3rd
series, vol. xl, p. 97. Also Smiths. Miscell. Coll., xli, 1901.

LANGLEY, S. P.: 1902, _Ann. Astrophys. Obs._, vol. ii, p. 5.

LANKESTER, E. RAY: 1867, Preliminary Notice of Some Observations with
the Spectroscope on Animal Substances. _Jour. of Anat. and Physiol._,
vol. ii, p. 116.

LEHMANN, K. B.: 1889, Studien ueber Bacterium phosphorescens, Fischer.
_Ctbl. f. Bakt._, Bd. v, p. 785.

LENARD, P., and WOLF, M.: 1888, Lumineszenz der Pyrogallussaüre. _Ann.
Phys. u. Chem._, 1888, N. F. xxxiv, pp. 918-925.

LENDENFELD, R.: 1887, Die Leuchtorgane der Fische. _Biol. Ctbl._, Bd.
vii, pp. 609-621.

LINNEMANN, E.: 1858, Phosphorescenz des Kaliums und Natriums. _J. f.
Prac. Chem._, vol. lxxv, p. 128.

LODE, A.: 1904, Versuche, die optische Lichtintensität bei
Leuchtbakterien zu bestimmen. _Ctbl. f. Bakt._, I Abt., Orig., Bd. xxxv,
pp. 524-527.

LODE, A.: 1908, Experimente mit Leuchtbakterien. Referate. _Centralb. f.
Bakt._, 2nd Abt., vol. xxii, p. 421.

LUDWIG, F.: 1874, Ueber die Phosphorescenz der Pilze und des Holzes.
_Diss. Göttingen_, 30 pages.

LUDWIG, F.: 1884, Ueber die Spektroskopische Untersuchung photogener
Pilze. _Zeit. wiss. Mikr._, vol. i, pp. 181-190.

LUDWIG, F.: 1887, Die bisherigen Untersuchungen ueber photogene
Bakterien. _Centralb. f. Bakt._, vol. ii, pp. 372 and 401.

LUDWIG, F.: 1901, Phosphorezierende Tausendfüssler und die Lichtfäule
des Holzes. _Centralb. f. Bakt._, Abt. II., Bd. vii, pp. 270-274.

LUND, E. J.: 1911, On the Structure, Physiology and Use of Photogenic
Organs, with Special Reference to the Lampyridæ. _Journ. Exp. Zool._,
vol. xi, pp. 415-467.

MACAIRE, J.: 1821, Mémoire sur la phosphorescence des Lampyres. _Ann. d.
Chimie et Phy._, T. xvii, pp. 151-167.

MACAIRE, J.: 1822, Ueber die Phosphorescenz der Leuchtkäfer. _Gilbert's
Annal. d. Physik._, T. lxx, pp. 265-280.

MACAIRE, J.: 1822, On the Phosphorescence of Luminous Insects.
_Quarterly Journ. Science, Lit. and Art_, vol. xii, pp. 181-182.

MACARTNEY, J.: 1810, Observations on Luminous Animals. _Philos.
Transact._, vol. c, pp. 258-293.

MACFADYEN, A.: 1900, On the Influence of the Temperature of Liquid Air
on Bacteria. _Proc. Roy. Soc., London_, vol. lxvi, p. 180.

MACFADYEN, A.: 1902, On the Influence of the Prolonged Action of Liquid
Air on Micro-organisms and the Effect of Mechanical Trituration at the
Temperatures of Liquid Air on Photogenic Bacteria. _Proc. Roy. Soc._,
vol. lxxi, p. 76.

MACÉ: 1887, Les glandes préanales et la phosphorescence des géophiles.
_Comp. rend. soc. Biol._, pp. 37-39.

MANGOLD, E.: 1907a, Ueber das Leuchten der Tiefseefische. _Pflüger's
Arch._, Bd. cxix, pp. 583-601.

MANGOLD, E.: 1907b, Leuchtende Schlangensterne und die Flimmerbewegung
bei Ophiopsila. _Pflüger's Arch._, Bd. cxviii, pp. 613-640.

MASSART, J.: 1893, Sur l'irritabilité des Noctiluques. _Bull.
scientifique de la France et de la Belgique_, T. 25.

MAST, S. O.: 1912, Behavior of Fireflies (Photinus ardens?), with
Special Reference to the Problem of Orientation. _Jour. Animal
Behavior_, vol. ii, pp. 256-272; also _Science_, vol. xxxv, p. 460.

MATTEUCI, C.: 1843, Sur la phosphorescence du lampyre d'Italie (L.
italica). _C. R. Ac. Sc._, vol. xvii, pp. 309-312.

MCDERMOTT, F. A.: 1910-1917, Observations on the Light Emission of
American Lampyridæ. _Canad. Entomol._, 1910, vol. xlii, pp. 357-363;
1911, vol. xliii, pp. 399-406; 1912, vol. xliv, p. 73; 1912, vol. xliv,
p. 309; 1917, vol. xlix, pp. 53-61.

MCDERMOTT, F. A.: 1911a, Luciferesceine, the Fluorescent Material
Present in Certain Luminous Insects. _Jour. Amer. Chem. Soc._, vol.
xxxiii, pp. 410-416.

MCDERMOTT, F. A.: 1911b, The Stability of the Photogenic Material of the
Lampyridæ and Its Probable Chemical Nature. _Journ. Amer. Chem. Soc._,
vol. xxxiii, pp. 1791-1796.

MCDERMOTT, F. A. and CRANE, C. G.: 1911c, A Comparative Study of the
Structure of the Photogenic Organs of Certain American Lampyridæ. _Amer.
Nat._, vol. xlv, pp. 306-313.

MCDERMOTT, F. A.: 1911d, Some Observations on a Photogenic
Microörganism, Pseudomonas Lucifera, Molish. _Proc. Biol. Soc., Wash._,
vol. xxiv, pp. 179-184.

MCDERMOTT, F. A.: 1911e, Recent Advances in Our Knowledge of the
Production of Light in Living Organisms. _Smithsonian Rep._, pp.
345-362; also _Sci. Amer. Suppl._, No. 1842, pp. 250-251.

MCDERMOTT, F. A.: 1913, Chemiluminescent Reactions with Physiologic
Substances. _Journ. Am. Chem. Soc._, vol. xxxv, pp. 824-826.

MCDERMOTT, F. A.: 1915, Experiments on the Nature of the Photogenic
Processes in the Lampyridæ. _Journ. Amer. Chem. Soc._, vol. xxxvii, pp.
401-404.

MCKENNEY, R. B.: 1902, Observations on the Conditions of Light
Production in Luminous Bacteria. _Proc. Biol. Soc., Wash._, vol. xv, pp.
213-234.

MCINTOSH, W. C.: 1885, Address on Phosphorescence of Marine Animals.
_Nature_, vol. xxxii, pp. 476-481.

MEYER, W. TH.: 1906, Ueber das Leuchtorgan der Sepiolini. _Zool. Anz._,
Bd. xxx, pp. 388-392.

MICHAELIS, G. A.: 1830, Ueber das Leuchten der Ostsee nach eigenen
Beobachtungen. Hamburg.

MOLISCH, H.: 1905, Luminosity in Plants. _Ann. Rept. Smithsonian Inst._,
pp. 351-362 (No. 1685).

MOORE, B.: 1908, Observations on Certain Organisms of (_a_) Variations
in Relation to Light and (_b_) a Diurnal Periodicity of Phosphorescence.
_Biochemical Jour._, vol. iv, pp. 1-29.

MURAOKA, H.: 1896, Das Johanniskäferlicht. _Wiedemann's Ann. d.
Physik._, N. F., Bd. lix, pp. 773-781.

MURAOKA, H.: 1897, Das Johanniskäferlicht. _Journ. of the Coll. of
Science, Univ. Japan_, vol. ix, p. 129.

NADSON, G.: 1902, Sur la phosphorescence des Bacteries. _Rapport fait à
la Soc. Microbiologie, St. Petersbourg_, March 29th.

NADSON, G.: 1903, Sur la phosphorescence des Bacteries. _Bull. du jardin
Imper. botan. de St. Petersbourg_, T. iii, pp. 110-122.

NADSON, G.: 1908, Zur Physiologie der Leuchtbacterien. _Bull. Jard. Imp.
Bot. de St. Petersbourg_, vol. viii, p. 144.

NICHOLS, E. L., and MERRITT, E.: 1912, Studies in Luminescence. _Pub.
Carneg. Inst., Wash._, No. 152, pp. 1-223.

NUTTING, C. C.: 1907, The Theory of Abyssal Light. _Proc. Seventh
Internat. Zool. Cong., Boston_, pp. 889-899.

NUTTING, P. G.: 1908, The Luminous Equivalent of Radiation. _Bull. Bur.
Standards, Washington, D. C._, vol. v, pp. 261-039.

NUTTING, P. G.: 1911, The Visibility of Radiation, a Recalculation of
Konig's Data. _Bull. Bur. Standards, Washington, D. C._, vol. vii, pp.
235-243.

OSBORNE, T. B. and WAKEMAN, A. J.: 1918, Some New Constituents of Milk.
A New Protein Soluble in Alcohol. _J. Biol. Chem._, vol. xxxiii, p. 243.

OSHIMA, H.: 1911, Some Observations on the Luminous Organs of Fishes.
_Jour. Coll. Sc., Tokio_, vol. xxvii.

OTTO, M.: 1896, Sur l'ozone et les phénomènes de phosphorescence. _C. R.
Ac. Sc._, vol. cxxlii, p. 1005.

OWSJANNIKOW, P.: 1864-1868, Zur Kenntnis der Leuchtorgane der Lampyris
noctiluca. _Mem. Ac. St. Petersb._, Ser. 2, vol. xi; also _Bull. Ac.
So._, 1864, vol. viii.

PANCERI, P.: 1872, Etudes sur la phosphorescence des animaux marins.
_Ann. d. Sc. Nat._, 5 Ser. Zool., T. xvi.

PANCERI, P.: 1877, Luminous Campanulariæ. _Nature_, vol. xvi, p. 30.

PASTEUR: 1864, Sur la lumière phosphorescente des Cucujos. _Comp. rend.
Acad. Sc._, T. lix, p. 509.

PERON, F.: 1804, Mémoire sur le nouveau genre Pyrosoma. _Ann. du Mus.
d'hist. Nat._, vol. iv, 437-446.

PETERS, A. W.: 1905, Phosphorescence in Ctenophores. _Journ. of Exper.
Zool._, vol. ii, p. 103

PFLÜGER, E.: 1875a, Die Phosphorescenz lebendinger Organismen und ihre
Bedeutung für die Principien der Respiration. _Arch. f. die ges.
Physiol._, vol. x, p. 275.

PFLÜGER, E.: 1875b, Ueber die Phosphorescenz verwesender Organism.
_Arch. f. d. ges. Physiol._, Bd. xi, pp. 222-263.

PHIPSON, T. L.: 1860, Sur la matière phosphorescente de la raie. _Compt.
rend. Acad. d. Sc._, T. li, p. 541.

PHIPSON, T. L.: 1872, Sur la noctilucine. _C. R. Ac. Sc._, T. lxxv, p.
547.

PHIPSON, T. L.: 1876, On Noctilucine, the Phosphorescent Principle of
Luminous Animals. _Journ. Franklin Inst._, vol. ci, pp. 68-72.

PIERANTONI, UMBERTO: 1918, Les microörganismes physiologiques et la
luminescence des animaux. _Scientia_, vol. xxiii, p. 43.

POLIMANTI, OSWALD: 1911, Ueber das Leuchten von Pyrosoma elegans Les.
_Zeitschrift f. Biol._, vol. lv, pp. 505-529.

POPE, W. J.: 1899, On Triboluminescence. _Nature_, vol. lix, p. 618.

PREVOST, BÉNÉDICT: 1810, Considérations sur le brillant des yeux du chat
et de quelques autres animaux. _Bibl. Britt. Sc. et Arts_, vol. xlv, pp.
196-212.

PÜTTER, A.: 1905, Leuchtende Organismen. _Ztschr. f. Allg. Physiol._,
Bd. v, Sammelreferate, pp. 17-53.

QUATREFAGES, A. DE: 1843, Note sur un nouveau mode de phosphorescence
observé chez quelques Annelides et Ophiures. _Ann. d. Sc. Nat._, 2nd
ser., Zool., T. xix, pp. 183-192.

QUATREFAGES, A. DE: 1850, Observations sur les noctiluques. _Ann. d. Sc.
Nat._, 3rd Ser., Zool., T. xiv, pp. 226-235.

QUATREFAGES, A. DE: 1850, Mémoire sur la phosphorescence de quelques
invertébrés marins. _Ann. d. Sc. Nat._, 3 ser., Zool., T. xiv, pp.
236-281.

QUATREFAGES, A. DE: 1862, The Phosphorescence of the Sea. _Popular Sc.
Rev._, vol. i, pp. 275-298.

RADZISZEWSKI, B.: 1877, Untersuchungen ueber Hydrobenzamid, Amarin und
Lophin. _Ber. d. d. chem. Ges._, vol. x, pp. 70-75 and pp. 321-322.

RADZISZEWSKI, B.: 1880, Ueber die Phosphorescenz der organischen und
organisierten Körper. _Liebigs Ann._, Bd. 203, pp. 305-336.

RADZISZEWSKI, B.: 1883, Zur Theorie der Phosphorescenzerscheinungen.
_Ber. d. d. Chem. Ges._, vol. xvi, pp. 597-601.

REEVES, P.: 1917, The Minimum Radiation Visually Perceptible. _Commun.
No. 51, Research Lab. Eastman Kodak Co._, pp. 167-174.

REICHENSPERGER, A.: 1908, Ueber Leuchten von Schlangensternen. _Biol.
Ctbl._, Bd, xxviii, p. 166-169.

REINELT, J.: 1906, Beiträge zur Kenntnis einiger Leuchtbacterien.
_Centralb. f. Bakt._, vol. xv., pp. 289-300.

REINKE, J.: 1898, Ueber das Leuchten von Ceratium tripos. _Wiss.
Meeresunters., herausgeg. V. d. Kommiss. z. wiss. Unters. d. deutsch.
Meers. in Kiel u. d. Biol. Station auf Helgoland_, N. F., Bd. iii, Abt.
Kiel, p. 37.

RICHTER, O.: 1906, Chlorophyllbildung im Bakterienlichte. _Sitz. ber. d.
k. k. Akad. d. Wiss. Wien. Math. nat. Kl._, Bd. 115, i, p. 298.

ROBIN, CH. et LABOULBENE, A.: 1873, Sur les organes phosphorescents
thoraciques et abdominals du Cocuyo de Cuba (Pyrophorus noctilucus, L.).
_Compt. rend. Acad. d. Sc. Paris_, T. lxxvii, pp. 511-517.

RUSSELL, W. J.: 1897, On the Action Exerted by Certain Metals and Other
Substances on a Photographic Plate. _Proc. Roy. Soc._, vol. lxi, pp.
424-433.

RUSSELL, E. J.: 1903, The Reaction between Phosphorus and Oxygen, Part
I. _Jour. Chem. Soc._, vol. lxxxiii, pp. 1263-1284.

SASAKI, M.: 1914, Observations on Hotaru-ika, Watasenia scintillans.
_Jour. Coll. Agric. Sapporo_, Japan, vol. vi, pp. 75-105.

SCHARFF, E.: 1908, Ueber das Leuchten des Phosphors und einiger
Phosphorverbindungen. _Zeit. physik. Chem._, vol. lxii, pp. 179-193.

SCHMIDT, P.: 1894, Ueber das Leuchten der Zuckmücken (Chironomidæ).
_Zool. Jahrb. Abth. Syst._, 8 Bd., pp. 58-66. Trans. in _Ann. Mag. Nat.
Hist._, (6), vol xv, pp. 133-141.

SCHULTZE, C. A. S.: 1886, Beobachtungen an Noctiluca. _Arch. f. Mikrosk.
Anat._, Bd. ii, p. 163.

SCHULTZE, MAX: 1865, Zur Kenntnis der Leuchtorgane von Lampyris
splendidula. _Arch. f. mikrosk. Anat._, Bd. i, pp. 124-137.

SCHURIG, W.: 1901, Biologische Experimente nebst ein Einhang
Microscopische Technik. Leipzig, p. 131.

SHOJI, R.: 1919, A Physiological Study on the Luminescence of Watasenia
scintillans (Berry). _Amer. Jour. Physiol._, vol. xlvii, pp. 534-557.

SINGH, P., and MAULIK, S.: 1910, Nature of Light Emitted by Fireflies.
_Nature_, vol. lxxxviii, p. 111.

SOKOLOW, IWAN: 1909, Zur Frage Ueber das Leuchten und die Drüsengebilde
der Ophiuren. _Biol. Ctbl._, Bd. xxix, pp. 637-648.

SPALLANZANI, LAZZARO: 1794, Memoria sopra le Meduse fosforiche. _Mem.
Soc. Ital. Verona_, vol. vii, pp. 271-290.

STECHE, O.: 1908, Beobachtungen ueber das Leuchten tropischer
Lampyriden. _Zool. Anz._, Bd. xxxii, pp. 710-712.

STECHE, O.: 1909, Ueber die Leuchtorgane von Anomalops katoptron und
Photoblepharon palpebratus, zwei Oberflächenfischen aus dem Malaysichen
Archipel. Ein Beitrag zur Morph. u. Physiol. der Leuchtorgane der
Fische. _Ztschr. f. wiss. Zool._, Bd. xciii, pp. 349-408.

STERZINGER, I.: 1907, Ueber das Leuchtvermögen von Amphiura squamata,
Sars. _Ztschr. f. wiss. Zool._, Bd. lxxxviii, pp. 358-384.

STÜBEL, H.: 1911, Die Fluorescence tierische Gewebe in ultra-violett
Licht. _Arch. f. d. ges. Physiol_, vol. cxlii, pp. 1-14.

SUCHSLAND, E.: 1898, Physikalische Studien ueber Leuchtbakterien.
_Festschr. d. 200-jähr. Jubelfeier der Franckeschen Stiftungen, Halle_,
p. 87. Ref. in _Zentralb. f. Bact._, II Abt. iv, pp. 713-715.

TARCHANOFF, J.: 1901, Lumière des bacilles phosphorescents de la mer
Baltique. _Compt. rend. Acad. d. Sc. Paris_, 1901, T. cxxxiii, pp.
246-249.

TARCHANOFF, J.: 1902, Biologisch-chemische Untersuchungen der
Phosphorescierenden Bakterien. (Russ.). _Journ. med. chim. St.
Petersbourg_, Bd. xxv-xxvi, pp. 56-74.

TERAO, A.: 1917, Notes on Photophores of Sergestes prehensilis, Bate.
_Annot. Zool. Japan_, vol. ix, pp. 299-316.

THOMAS, R. H.: 1902, A Luminous Centipede. _Nature_, vol. lxv, p. 223.

TOLLHAUSEN, P.: 1889, Untersuchungen ueber Bacterium phosphorescens
Fischer. _Diss. Würzburg._

TOMMASINO, TH.: 1904, Constatation d'une radioactivité propre aux êtres
vivants, vegetaux et animaux. _Compt. rend. Acad. d. Sc._, Bd. cxxxix,
pp. 730-731.

TOWNSEND, A. B.: 1904, Histology of the Light Organs, of Photinus
marginellus. _Amer. Nat._, 1904, vol. xxxviii, pp. 127-151.

TRAUTZ, M.: 1904, Ueber neue Lumineszenzerscheinungen. _Zeit. wiss.
Photogr._, vol. ii, pp. 217-223; also, _Zeit. f. Electrochem._, vol. x,
pp. 593-597.

TRAUTZ, M.: 1905, Studien ueber Chemilumineszenz. _Ztschr. physikal.
Chem._, vol. liii, pp. 1-111.

TRAUTZ, M., and SCHORIGIN, P.: 1905a, Kristallolumineszenz und
Tribolumineszenz. _Zeit. wiss. Photog._, vol. iii, pp. 80-90.

TRAUTZ, M., and SCHORIGIN, P.: 1905b, Ueber Chemilumineszenz. _Zeit.
wiss. Photog._, vol. iii, pp. 121-130.

TROJAN, E.: 1906, Neuere Arbeiten ueber die Leuchtorgane der Fische.
_Zool. Ctbl._, Bd. xiii, pp. 273-284.

TROJAN, E.: 1907, Zur Lichtentwicklung in den Photosphärien der
Euphausien. _Arch. f. mikr. Anat._, Bd. lxx, pp. 177-188.

TROJAN, E.: 1909, Leuchtende Ophiopsilen. _Arch. f. mikr. Anat._, Bd.
lxxiii, pp. 883-912.

TROJAN, E.: 1910, Ein Betrag zur Histologie von Phyllirhoë bucephala.
Peron und Lesueur. mit besonderer Berücksichtigung des Leuchtvermögens
des Tieres. _Arch. microscop. Anat._, vol. lxxv, pp. 473-517.

TROJAN, E.: 1913, Ueber Hautdrüsen des Chætopterus variopedatus, Clap.
_Sitz. ber. d. Kais. Ac. d. wiss. Wein._, vol. cxxii, Abt. 1.

TROJAN, E.: 1915, Die Leuchtorgane von Cyclothone Signata, Garman.
_Sitz.-ber. d. K. Akad. der wiss. Wien._, Bd. cxxiv, Abt. 1.

TSCHUGAEFF, L.: 1901, Ueber Tribolumineszenz. _Ber. d. d. chem. Ges._,
vol. xxxiv, pp. 1820-1826.

VALLENTIN, R., and CUNNINGHAM, J. T.: 1888, The Photospheria of
Nyctiphanes Norvegica. _Quart. Journ. of Micr. Sc._, N. S., vol. xxviii,
pp. 319-341.

VAN'T HOFF, J. H.: 1895, Ueber die menge und die Nature des sogen. Ozons
das sich bei langsamer Oxidations des Phosphors bildet. _Zeit. physik.
Chem._, vol. xvi, pp. 411-416.

VERRILL, A. E.: 1884, Evidences of the Existence of Light at Great
Depths in the Sea. _Nature_, vol. xxx, pp. 280-281.

VERWORN, M.: 1892, Ein automatisches Zentrum für die Lichtproduktion bei
Luciola italica L. _Ctbl. f. Physiol._, Bd. vi, pp. 69-74.

VIGNAL, W.: 1878, Recherches histologiques et physiologiques sur les
Notiluques. _Arch d. Physiol. Norm. et Patholog._, 2nd ser., T. v, pp.
415-454.

VILLE, J., and DERRIEN, E.: 1913, Catalyse biochemique d'une oxydation
luminescente. _C. R. Ac. Sc._, vol. clvi, p. 2021.

VOGEL., R.: 1915, Beitrag zur Kenntnis des Baues und der Lebensweise der
Larve von Lampyris noctiluca. _Zeit. wiss. Zool._, vol. cxii, pp.
291-432.

WATANABE, H.: 1897, The Phosphorescence of Cypridina hilgendorfii.
_Annot. Zool. Japan_, vol. i; also, _Zool. Jahrs._, 1897.

WATASÉ, S.: 1895, On the Physical Basis of Animal Phosphorescence.
_Biol. Lect. Marine Biol. Lab. Woods Hole_, pp. 101-119.

WATASÉ, S.: 1898, Protoplasmic Contractility and Phosphorescence.
_Biolog. Lect. Marine Biol. Lab. Woods Hole_, pp. 177-192.

WEISER, H. B.: 1918a, Color Determination of Faint Luminescence. _Journ.
Phys. Chem._, vol. xxii, pp. 439-449.

WEISER, H. B.: 1918b, Crystalloluminescence, I, II. _Journ. Phys.
Chem._, vol. xxii, pp. 480-509, and pp. 576-595.

WEITLANER, F.: 1909, Etwas von Johannis-Käferlicht. _Verh. d. Zool. Bot.
Ges. Wein._, vol. lix.

WEITLANER, F.: 1911, Weiteres vom Johanniskäferlicht und von
Organismenleuchten uberhaupt, etc. _Verh. d. Zool. Bot. Ges. Wein._,
vol. xli, p. 192.

WELEMINSKY, F.: 1895, Die Ursachen des Leuchtens bei Choleravibrionen.
_Prager med. Wochenschr._, Bd. xx, pp. 263-264.

WELKER, W. H.: 1912, Diffusibility of Protein Through Rubber Membranes
with a Note on the Disintegration of Colloidian Membranes by Common
Ethyl Ether and Other Solvents. _Biochem. Bull._, vol. ii, p. 70.

WHEELER, W. M., and WILLIAMS, F. X.: 1915, The Luminous Organ of the New
Zealand Glowworm. _Psyche_, vol. xxii, pp. 36-43.

WEIDEMANN, E.: 1888, Ueber Fluorescenz und Phosphorescenz. _Wied. Ann.
d. Phy. u. Chem._, vol. xxxiv, pp. 446-469.

WIEDEMANN, E., and SCHMIDT, G. W.: 1895a, Ueber Luminescenz. _Wied. Ann.
d. Phy. u. Chem._, vol. liv, pp. 604-625; 1895b, vol. lvi, pp. 201-254.

WIELOWIEJSKI, H. R. V.: 1882, Studien ueber die Lampyriden. _Ztschr. f.
wiss. Zool._, Bd. xxxvii, pp. 354-428.

WILLIAMS, F. X.: 1916, Photogenic Organs and Embryology of Lampyrids.
_Journ. Morph._, vol. xxviii, pp. 145-186.

YATSU, N.: 1917, Note on the Structure of the Maxillary Gland of
Cypridina hilgendorfii. _Journ. Morph._, vol. xxix, pp. 435-440.

YOUNG, C. A.: 1870, The Spectrum of the Firefly. _Amer. Nat._, vol. iii,
p. 615.

ZACHARIAS, O.: 1905, Beobachtungen ueber das Leuchtvermögen von Ceratium
tripos. _Biol. Ctbl._, Bd. xxv, pp. 20-30.




INDEX


  Abegg, R., 147

  _Acanthephyra_, 78

  _Agaricus_, 99

  Agassiz, A., 11

  Alkaptonuria, 17

  Allman, G. I., 11, 71

  Ammonia, 12

  Anodoluminescence, 26, 29

  _Anornalops_, 69

  Aristeus, 72

  Aristotle, 1


  Bach, A., 137

  Bacteria, luminous, 2, 10, 13, 14, 16, 18, 28, 45, 53, 61, 65, 69, 72,
    74, 81, 82, 89, 99, 101, 103

  Bacterial lamps, 18

  Baker, J., 2

  Bancroft, W. D., 36

  Bancroft and Weiser, 24

  Bandrowski, E., 33

  Barcroft and Hill, 98

  _Barnea_, 116

  Batelli and Stern, 115

  Becquerel, E., 26

  Beijerinck, M. W., 18, 89, 99, 100, 102

  Bigelow, S. L., 34

  Black, 91

  _Bolitophila_, 77

  Boyle, R., 1, 16, 85 ff

  Brandt, 36

  Brittle stars or ophiuroids, 10, 11, 72


  Canton's phosphorus, 27

  Carbon dioxide and luminescence, 91 ff

  _Cardium_, 116

  Cascariolo, V., 27

  Cathodoluminescence, 26, 29

  _Cavernularia_, 74, 103

  Centnerzwer, M., 147

  Cephalopods or Squid, 10, 11, 13, 68, 72, 84, 104

  _Ceratium_, 71

  _Chætopterus_, 10, 17, 42, 71, 73, 74, 83, 103

  Chemiluminescence, 36 ff, 45 ff

  Chlorophyll formation by animal light, 66

  _Chromophyton_, 15

  Chun, C., 79

  Coblentz, W. W., 30, 31, 44, 51, 52, 59, 60, 62, 64, 93, 160.

  Co-enzyme, 104, 130

  Co-luciferase, 107 ff

  Color of animal light, 41 ff, 157 ff

  Concentration and luminiscence, 145 ff

  Conroy, J., 43

  Crozier, W. J., 71, 103

  _Crustacea_, 10, 14, 68, 70, 72, 89, 101 ff

  Crysalloluminescence, 33 ff, 74

  _Ctenophores_, 2, 10, 11, 71, 72, 82

  Cyanides and luminescence, 126

  _Cypridina_, 14, 30, 45, 48, 63, 71, 73, 75 ff, 90, 92, 98, 103,
    105 ff, 155 ff


  Dahlgren, U., 72, 73, 75

  "Death Glow," 69

  Dinoflagellates, 2, 10, 32, 82

  Dubois, R., 31, 35, 37, 43, 45, 49, 61, 64, 73, 103 ff, 111, 114 ff,
    131, 155


  Earthworms, 10

  Efficiency of animal light, 48 ff

  Eggs, luminous, 11

  Electroluminescence, 24, 29

  Embryos, luminous, 11

  Euphasia, 72

  Ewan, T., 147

  Exner, S., 30

  Extracellular luminescence, 68, 71

  Eyes, luminous, 15 ff


  Fabre J. H., 99

  Fahrig, E., 37

  Fireflies, 10, 31, 34, 43, 69, 71, 77 ff, 89, 93, 101, 103, 135, 160

  Fishes, 1, 3, 10, 18, 64, 69, 72, 84, 85

  Flowers, flashing of, 16

  Fluorescence, 25 ff, 62

  Fluorescent screens, 29

  Forsyth, R. W., 53

  Frankland, P., 62

  Friedberger & Doepner, 65

  Frogs, luminous, 13

  Fungi or Basidiomycetes, 10, 69, 72, 81, 89, 99, 101


  Galloway and Welch, 84

  Gernez, D., 32

  Giard and Billet, 13

  Giesbrecht, W., 11, 70

  Glowworms, 1, 10, 43, 77

  _Gnathophausia_, 72

  Goss, B. C., 143

  Greene, C. W., 70

  Guinchant, 37


  H-ion concentration and luminescence, 92, 138, 155

  Heat production and luminescence, 93 ff

  Heliotropism by animal light, 66.

  Heller, J. F., 1, 2, 16

  _Heterocarpus_, 72

  _Heteroteuthis_, 72

  Hooke, R., 91

  Hulme, N., 1

  Hyde, Forsyth and Cady, 57, 63

  Hydrogenase, 131

  Hydroils, 10, 72


  "Ignis fatuus," 15

  Immune bodies, 104

  Infection, with luminous bacteria, 13

  Infra red rays in animal light, 48 ff

  Intensity of animal light, 63

  Intracellular Luminescence, 68, 71

  Interference colors, 14

  Issatschenko, B., 66

  Ives, H. E., 28, 44, 51 ff, 59, 61


  Kemp, C., 78


  Langley and Very, 43, 50 ff, 64

  Lankester, E. R., 42

  Lavoisier, 91

  Lenard and Wolf, 37

  _Ligia_, 13

  _Limulus_, 129

  Linnemann, E., 36

  Lode, A., 65

  Luciferase, 103 ff. Chap VI (properties);
    of _Pholas_, 114;
    of _Cypridina_, 123 ff

  Luciferesceine, 31, 110

  Luciferin, 103 ff. Chap. VI (properties);
    of _Pholas_, 114;
    of _Cypridina_, 116 ff

  _Luciola_, 103, 125.

  Luminescence, 23 ff

  Luminosity, distribution in plant and animal kingdom, 3 to 12

  Luminosity, false, 12 ff

  Luminous animals, habitat, 10

  Luminous animals, uses of to man, 17 ff

  Luminous granules, 73, 75

  Lyman rays, 21

  Lyoluminescence, 35


  MacCartney, J., 2, 3

  Macfayden, A., 157

  Macrozymases, 73

  Man, luminosity of, 16

  Mangold, E., 11, 72

  Massart, J., 71

  Mast, S. O., 69

  Mayow, 91

  McDermott, F. A., 31, 37, 45, 53

  McKenney, R. B., 100

  Medusæ or jelly fish, 2, 10, 72, 82

  Methane, 15.

  Michaelis, G. A., 1

  "Minimum radiation visually perceptible," 65, 144

  Molisch, H., 45, 53, 61, 66, 102

  Molluscs, 10, 72

  _Monocentris_, 69, 104

  Moore, B., 71

  Muraoka, H., 61

  Myriapods, 10, 35, 72

  _Mytilus_, 116


  Nadson, G., 66

  _Nematocelis_, 72

  _Noctiluca_, 2, 10, 71, 73, 82, 83, 89, 104

  Noctilucin, 101

  Nutting, P. G., 57, 59

  _Nyctiphanes_, 72, 80


  _Odontosyllis_, 83

  _Orchestia_, 13

  _Orya_, 35

  Osborne and Wakeman, 121

  _Ostræa_, 116

  Otto, M., 37

  Oxygen and luminescence, 1, 67, 85 ff, 147 ff

  Oxyluciferine, 108 ff, 127 ff, 158

  Oxyluminescence, 36 ff, 111 ff


  Paint, luminous, 28, 29

  Panceri, P., 45, 74

  Pasteur, 42

  Penetrating radiation in animal light, 61 ff

  _Pennatula_, 74, 103

  Pennatulids or sea pens, 10, 72, 74, 82, 83, 89, 101, 103

  _Peridineæ_, 10

  Periodicity of luminescence, 71

  Peron, F., 45

  Peroxidases, 11, 126, 148

  Peters, A. W., 11, 71

  Pflüger, E., 1, 102

  _Phengodes_, 41, 42

  Phillips, A. H., 125

  _Philoscia_, 13

  Phipson, T. L., 101, 109, 110

  _Pholas_, 10, 11, 72, 73, 74, 89, 101, 103, 105 ff, 114 ff, 131

  Phosphine, 15

  Phosphorescence, 24, 25 ff, 138, 143

  Phosphoroscope, 26

  Phosphor-photographic method, 52

  Phosphorus and luminescence, 38, 39, 147 ff

  _Photinus_, 44, 51, 53, 56, 59, 64, 103, 125, 160 ff

  _Photoblepharon_, 18, 64, 69

  Photochemical reactions, 67, 68, 138, 145

  Photogen, 102

  Photogenin, 105

  Photoluminescence, 26, 67

  Photophelein, 105, 106, 110

  Photosynthesis by animal light, 18

  _Photuris_, 44, 59, 103, 125, 160 ff

  Pierantoni, V., 13, 14, 74

  Piezoluminescence, 32 ff

  Polarization, 45

  Polimanti, O., 45

  Pope, W. J., 32

  _Porcellio_, 13

  _Porichthys_, 70, 83

  Preluciferine or proluciferine, 106 ff

  Prevost, B., 15

  Priestly, 91

  _Ptychodera_, 71, 103

  Purkinje phenomenon, 40, 44, 157

  Pyrogallol and luminescence, 37, 111, 148 ff

  Pyroluminescence, 24

  Pyrophorine, 31, 109

  _Pyrophorus_, 11, 43, 45, 49 ff, 64, 76, 101, 103, 114, 125

  _Pyrosoma_, 10, 13, 45, 72, 101


  Quatrefages, A. de., 73


  Radiant energy, 20 ff

  Radioluminescence, 26

  Radium rays or Becquerel rays, 21, 26, 30, 62

  Radziszewski, B., 37, 39

  Reaction velocity and luminescence, 145 ff

  Reductase, 130 ff

  Reeves, P., 65, 144

  Respiration and luminescence, 91, 92, 99

  _Rhizomorpha_, 2

  Romberg's phosphorus, 32

  Russel, E. J., 147

  Russel, W. J., 62


  _Sapphirina_, 14

  _Sarcina_, 1

  Scharff, E., 147

  Scheele, 91

  _Schistostega_, 15

  Schizopod larvæ, 11

  Schumann rays, 21

  Schurig, W., 61

  _Scolopendra_, 102

  Sea, phosphorescence of, 2

  _Sepietta_, 72

  _Sergestes_, 72, 78

  Singh and Maulik, 61

  Solen, 116

  Spallanzani, L., 85, 101

  Spectrum of chemiluminescence, 39

  Spectrum of luminous organisms, 42 ff

  Spectrum of phosphorescence, 28

  Spectrum, range of, 21 ff

  Spinthariscope, 30

  Steche, O., 65, 69

  Stefan-Boltzmann Law, 22, 23

  Stimulation and luminescence, 68 ff, 135

  Stoke's Law, 28, 31

  _Stylochiron_, 72

  Suchsland, E., 61

  Sulphides, phosphorescence of, 27

  Sweat, luminous, 17


  _Talitrus_, 13

  Tarchanoff, J., 13

  Temperature and luminescence, 145 ff, 156 ff

  Temperature radiation, 23

  _Thaumatolampas_, 42

  Thermoluminescence, 24 ff

  _Tomopterus_, 72

  Transparency of chitin to infra-red, 52

  Trautz, M., 32, 33, 37, 39, 145

  Triboluminescence, 32 ff

  Trojan, E., 11, 78

  Tschugaeff, L., 32


  Ultra violet rays in animal light, 53 ff

  Urine, luminous, 18

  Uses of luminous organs, 81 ff


  Vacuolides, 73

  van Helmont, 91

  van't Hoff, J. H., 147

  _Vibrio_, 65

  Ville and Derrien, 111

  Visual sensibility, 54 ff


  Watanabe, H., 75

  Watasenia, 104

  Water and luminescence, 85, 101

  Weiser, H. B., 33, 34, 39

  Welker, W. H., 121

  Wheeler and Williams, 77

  Wiedemann, E., 23

  Wiedemann and Schmidt, 25, 36

  "Will-o'-the-wisp," 15

  Wood, phosphorescent or shining, 1, 2, 85

  Worms or annelids, 3, 72


  X-rays or Röntgen rays, 21, 26, 30, 62


  Yatsu, N., 75

  Young, C. A., 43


  Zacharias, O., 71

  Zymogen granules, 73

       *       *       *       *       *

Transcriber's Notes

Uncommon forms for chemical names have been retained where they occur in
the text, e.g. "atropin" for "atropine"; "asparagin" for "asparagine",
etc.

The spellings of "Sidot blend" and "Sidot blende" are used
interchangeably.

"PH" or P_{H} (subscript H) is used throughout for the scale of
alkali-acidity where the modern usage is "pH".

On page 173, the citation for NUTTING, P. G.: 1908 has page range pp.
261-039. This is as it appears in the original, but is probably in
error.

Minor corrections to formatting and missing punctuation (mostly in the
bibliography) have been regularised without an explicit note.

Where changes to the text have been made in the case of spelling or
type-setting errors, these are listed as follows:

Page ix: changed "Phoshorescence" to "Phosphorescence" (II. LUMINESCENCE
AND INCANDESCENCE ... Phosphorescence and fluorescence.)

Page ix: changed "Biozymoxyluminescence" to "Biozymoöxyluminescence" (V.
THE CHEMISTRY OF LIGHT PRODUCTION, PART I ... "Biozymoöxyluminescence.")

Page x: changed "chemi-luminescence" to "chemiluminescence" in two
instances (Reaction velocity and chemiluminescence. Temperature and
chemiluminescence.)

Page 4, Table 1: changed period "_Bacillus_." to comma "_Bacillus_," in
list(_Bacterium_, _Photobacterium_, _Bacillus_, _Pseudomonas_, ...)

Page 5, Table 1: removed comma after "_Cunina_".

Page 15: changed "th" to "the" (Less well known is the _Ignis fatuus_)

Page 21, Table 2: changed "16" to ".16" (... above 12 km. to .16 cm.)

Page 26: re-positioned period outside of parentheses "after being
illuminated (_photoluminescence_)."

Page 29: changed "platino-cyanide" to "platinocyanide" (Fluorescent
screens of barium platinocyanide)

Page 29: added missing comma (willemite (Zn_{2}SiO_{4}), Sidot blend)

Page 34: added missing closing quotation mark ("It is altogether probable
that the cause of this" ...)

Page 39: superscript "2" changed to subscript "2" in Na_{2}CO_{3} (the
pyrogallol-formaldehyde-Na_{2}CO_{3}-H_{2}O_{2} reaction)

Page 41: "50-metre candles" changed to "50 metre-candles" (Below 0.5 and
above 50 metre-candles visibility varies ...)

Page 42, Table 4: changed "Fraünhofer" to "Fraunhofer" in the caption and
table heading (Fraunhofer Lines)

Page 47, Table 5: changed "Forster" to "Förster" (Bacteria ... Förster,
1887)

Page 56, Fig 12 caption: "Forsythe" changed to "Forsyth" (_after Hyde,
Forsyth and Cady_)

Page 72: added missing closing parenthesis "the molluscs (_Pholas_ and
_Phyllirhoë_)"

Page 74: "secretion" changed to "section" (A section of the epithelium
shows large mucous-producing cells ...)

Page 75: added missing closing punctuation (At least one, probably two,
are concerned in light production.)

Page 75: changed "intra-cellular" to "intracellular" (animals possessing
light cells with intracellular luminescence)

Page 81; Fig. 29 caption: added missing comma (_chr.^1_, chromatophore;
...)

Page 87: added missing closing parenthesis "(and that too of such a
_Density_ to make them continue _shining_)"

Page 90: "necesary" changed to "necessary" (Boyle also made many
experiments to show that air was necessary for the life of animals ...)

Page 93: changed "thermo-couple" to "thermocouple" (using a thermocouple
as the measuring instrument)

Page 94: "_D_" changed to "_B_" (placed in a large Dewar flask (_B_)
filled with water)

Page 97: "thermo-couple" changed to "thermocouple" (Readings of each
thermocouple on the galvanometer scale ...)

Page 94: "Thermo-couples" changed to "Thermocouples" (Thermocouples (_L_
and _M_) of advance...)

Page 100: changed "McKenny" to "McKenney" (McKenney (1902) found also ...)

Page 102: changed "misceable" to "miscible" (insoluble in water but
miscible with it)

Page 103: "demontrate" changed to "demonstrate" (I have been unable to
demonstrate their existence in luminous bacteria;)

Page 104: "thermolable" changed to "thermolabile" ( ...and a thermolabile
complement (_alexin_) are necessary.)

Page 104: "thermolable" changed to "thermolabile" (Because of the
necessity of thermostable and thermolabile substances for light
production ...)

Page 105: "thermolable" changed to "thermolabile" (luciferase
(=_photogenin_) for the thermolabile material ...)

Page 111: "preslence and H_{2}O_{3}" changed to "presence of H_{2}O_{2}"
(_lophin_ could be oxidized by vertebrate blood in the presence of
H_{2}O_{2}.)

Page 116: "or" changed to "of" ( ... and would disappear from solution in
the course of a day or so.)

Page 116: changed "oxidizible" to "oxidizable" (The luciferins, as the
oxidizable substances, must claim first attention.)

Page 123: "contrated" changed to "concentrated" (1 c.c. portions of
concentrated luciferin)

Page 132: "coluciferase" changed to "co-luciferase" (He now regards it as
identical with his co-luciferase)

Page 151, Table 13: corrected duplicate numbering "10" to "11" (11 Ferric
chloride)

Page 151, Table 13: corrected duplicate numbering "14" to "15" (15
Chromic sulfate)

Page 151, Table 13: abbreviated "minute" to "min." in two entries (boiled
1 min. and filtered)

Page 158: changed "appear" to "appears" (... and yet light appears only
in presence of the latter.)

Page 162: added missing closing punctuation (More complete works on light
and luminescence come first and original articles follow.)

Page 165: added missing comma (DUBOIS, R.: 1918a, Sur la Synthèse de la
Luciferine.)

Page 165: changed "Biophotogénesis" to "Biophotogénèse" (Recherches
Recentes de M. Newton Harvey sur la Biophotogénèse)

Page 165: changed "Biophotogénèsis" to "Biophotogénèse" (Nouvelles
Recherches sur la Biophotogénèse)

Page 166: changed "Oxydations geschwindigkeit" to
"Oxydationsgeschwindigkeit" (Ueber die Oxydationsgeschwindigkeit von
Phosphor ...)

Page 166: changed "Radiumstrahlem" to "Radiumstrahlen" (Einige
Beobachtungen ueber die durch Radiumstrahlen in den tierischen Geweben
erzeugte Phosphoreszenz.)

Page 166: changed "neiderer" to "niederer" (Ueber die Entwicklung von
Bakterien bei niederer Temperatur.)

Page 167: changed "nueue" to "neue" (Ueber die rosettenförmigen
Leuchtorgane der Tomopteriden und zwei neue Arten von Tomopteris.)

Page 169: added missing hyphen to "Pflanzen-" (Ueber das Leuchten im
Pflanzen-und Tierreiche.)

Page 169: changed "Rucksicht" to "Rücksicht" (mit bes. Rücksicht auf.
med. Diagnost. u. Therapie Wien.)

Page 170: changed "jord." to "jard." (Bull. d. jard. imp. botan. St.
Petersburg)

Page 171: changed "Lichtfaüle" to "Lichtfäule" (Phosphorezierende
Tausendfüssler und die Lichtfäule des Holzes)

Page 172: changed "Pfluger's Arch" to "Pflüger's Arch." (_Pflüger's
Arch._, Bd. cxix, pp. 583-601.)

Page 174: changed "Bedentung" to "Bedeutung" ( ... ihre Bedeutung für die
Principien der Respiration)

Page 175: changed "Lazaro" to "Lazzaro" (SPALLANZANI, LAZZARO: 1794, ...)

Page 176: changed "Leuchtvermogen" to "Leuchtvermögen" (Ueber das
Leuchtvermögen von Amphiura squamata, Sars.)

Page 177: changed "Triboluminescenz" to "Tribolumineszenz" (TSCHUGAEFF,
L.: 1901, Ueber Tribolumineszenz.)

Page 179: changed "Bandromski" to "Bandrowski" (Bandrowski, E., 33)

Page 179: changed "Baelli" to "Batelli" (Batelli and Stern, 115)

Page 179: changed "Centnerswer" to "Centnerzwer" (Centnerzwer, M., 147)

Page 179: changed "Fire-flies" to "Fireflies" (Fireflies, 10, 31, 34,...)

Page 180: changed "Forsythe" to "Forsyth" (Hyde, Forsyth and Cady, 57,
63).

Page 180: changed "Flankland" to "Frankland" (Frankland, P., 62)

Page 180: changed "Glow-worms" to "Glowworms" (Glowworms, 1, 10, 43, 77)

Page 181: changed "Piezolumisescence" to "Piezoluminescence"
(Piezoluminescence, 32 ff).

Page 182: changed "Stefan-Boltzman" to "Stefan-Boltzmann"
(Stefan-Boltzmann Law, 22, 23)

Page 182: changed "infrared" to "infra-red" (Transparency of chitin to
infra-red, 52)

Page 182: added missing page references (Weiser, H. B., 33, 34, 39)






End of Project Gutenberg's The Nature of Animal Light, by E. Newton Harvey