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EXPEEIMENTAL MORPHOLOGY

'J^^^^f^o

Experimental Morphology

BT

CHARLES BEInEDICT DAVENPORT, Ph.D.

INSTRUCTOR IN ZOOLOGY IN HARVARD UNIVERSITY

PART FIRST

EFFECT OF CHEMICAL AND PHYSICAL AGENTS
UPON PROTOPLASM

r) •

THE MACMILLAN COMPANY

LONDON: MACMILLAN & CO., Ltd.
1897

All rights rencrved

Copyright, 1896,
By the MACMILLAN COMPANY.

NortaooD ^ress

J. S. Gushing & Co. — Berwick & Smith
Norwood Mass. U.S.A.

DeDicateD

TO THE MEMORY OF THE FIRST AND MOST IMPORTANT
OF MY TEACHERS IN NATURAL HISTORY

MY MOTHEE

Die morphologische Betrachtung setzt also eine genaue
cheniisch physikalische Kenntiiiss, 1. des betreffenden
Korpers selbst, und 2. aller der bei seiner Entstehuiig auf
ihn einwirkeiiden Stoffe und Korper voraus. — Jaeger,
ZoologiscTie Brief e^ p. 9.

La vie ne se con^oifc que par le conflit des pvoprietes
physico-cliimiques du milieu exterieiir et des proprietes
vitales de rorganisuie leagissant les unes sur les autres. —
Bernard, Rapporl sur les progres de la physiulogie generale
en France, 1867, p. 5.

There can be little doubt, indeed, that every science as
it progresses will become gradually more and more quan-
titative. Numerical precision is doubtless tlie very soul of
science, as Herschel says. — Jevons, Principles of Science,
chap. xiii.

PREFACE

The problem which, since the time of Aristotle, has stood
first in interest and importance among the great questions of
Biology is that of the causes which direct the development of
the individual — that marvellous process by which the germ
is built up into the complex organism, by which the embryo
clothes itself with the characters peculiar to its species, by
which even minute individual traits of form and action are
exactly reproduced in the offspring from its parents.

The burden of clearing up this problem has fallen, naturally
enough, upon the shoulders of students of morphology. For
since morphologists deal with form, they are properly especially
concerned with the interpretation of form — they may Avell be
asked to account for it. Thus the problem of development is
an acknowledged morphological problem.

Several distinct steps can be recognized in the progress
which has been made in the interpretation of form. The
earlier studies were concerned chiefly with answering the ques-
tion. What are the differences between the various adult forms ?
The results of observations and reflections relating to this
question constitute the sciences of descriptive and comparative
anatomy. Next, a more fundamental inquiry was entered
upon : Hoiv are these forms produced or developed ? The
results of observations and reflections upon this subject con-
stitute the science of comparative embryology. Finally, in
these later days a still more fundamental question has come to
the front : Why does an organism develop as it does ? What
is that which directs the path of its differentiation ? This is
the problem which the new school of " Entwicklungsmecha-
nik " has set for itself — it is likewise the problem with which
this book is concerned.

viii PREFACE

The causes which determine the course of an organism's
development are numerous, but fall into two general categories ;
namely, internal causes, which include the qualities of the devel-
oping protoplasm ; and external causes, which include the
chemical and physical properties of the environment in which
the protoplasm is developing. The internal and external causes
may be studied separately, and in order to disentangle their
effects they must needs be studied separately. It is the pur-
pose of the present work to consider the effects resulting from
external causes.

When we wish to isolate the separate effects in any complex
of causes, we must resort to the well-known procedure of
experimentation, — and we find, indeed, that these external
causes lend themselves readily to this method of treatment.
Accordingly we call in experiment to get an insight into the
causes of organic form, and thus justify the name which we
have applied to our study, — Experimental Morphology.

The primary subdivision of the subject is based upon the
morphogenic processes to be treated of ; and of these, four
principal classes may be recognized. The first includes those
processes which are characteristic of all living protoplasm;
the second, those connected with growth ; the third, those
involved in cell-division ; and the fourth, those producing
differentiation. It is proposed to devote one part of the work
to each of these four classes of processes.

The secondary subdivision may be based upon the chemical
and physical agents whose effects we wish to isolate. These
may be grouped into eight categories, determined largely by
convenience ; namely, 1, chemical substances ; 2, water ; 8, den-
sity of the medium ; 4, molar agents ; 6, gravity ; 6, electri-
city ; 7, light ; and 8, heat. It is proposed to devote one
chapter to a consideration of the effects of each of these agents
upon protoplasm, upon growth, upon cell-division, and upon
differentiation.

Two words should be said about the point of view from
which this book has been written. In the first place, the
developing organism is regarded as a living organism, and as
such endowed with irritability and capacity of response ; con-
sequently, at the outset, we must especially consider the phe-

PREFACE ix

nomenon of response to external stimuli. Again it is with
living organisms that we have to deal, and, accordingly, no
distinction should be made between animals and plants. I
have, indeed, made no such distinction ; nevertheless, tastes
and training have led me to lay especial stress upon animals.
Even this is unfortunate, for the problem with which we are
concerned is precisely the same problem in all living organisms.

In the second place, much stress is laid upon the quantitative
measurement of agents and effects. The lack of precision in
many investigations can hardly be too strongly decried ; for it
often results in confusion and useless disputes. On the other
hand, there is good reason for believing that exact measure-
ment is the key to many of the most puzzling of our problems,
and important results are to be expected from its use.

As for the aim of the book, it is twofold. I have hoped on
the one hand that it might be readable to those who are inter-
ested in the general matters of which it treats — matters of
importance for philosophy, for psychology, and for pedagogy^
For man is an organism, and the development of his qualitids
is modified by just those agents which guide the development
of other organisms. My primary aim, however, has been a dif-
ferent one. It is this aim to which other purposes have been
made subservient, which justifies the historical treatment that
has been often adopted, and justifies also the detailed descrip-
tions of methods which the , lay reader will, naturally, omit.
This aim is so to exhibit our present knowledge in the field
of experimental morphology as to indicate the directions for
further research.

A few words of explanation and acknowledgment are neces-
sary : It was planned at the first to issue all four parts of the
work at once ; but the task grew in the doing, while the need
of its publication became more pressing. So it was decided
to issue the work in parts as soon as each should be done.
Even under this arrangement it has not been possible to
include some of the papers of the last six months ; especially
I regret the omission of important papers by Verw^orn and
LoEB upon Galvanotaxis. In writing a book of this sort,
which draws upon several sciences, I have had recourse to the
kind assistance of several of my colleagues in the physical and

X PREFACE

chemical departments of the University. I must especially
thank for favors Professor W. C. Sabine, Dr. G. W.
CoGGESHALL, and Dr. H. E. Sawyer. Of my zoological
associates, I am greatly indebted to Dr. G. H. Parker, who
has read nearly the entire manuscript and has offered valuable
criticisms on it, and to Professor E. L. Mark, who has
read parts of the manuscript and proof and has made important
suggestions and emendations. I am also greatly indebted to
Mr. Charles Bollard for his kindness in making photo-
graphs of figures from which most of the illustrations of the
First Part were reproduced. Finally, I cannot forbear to men-
tion the painstaking work of my wife, Gertrude Grotty
Davenport, in preparing the manuscript for the press and
revising the proofs.

As I send out this work I do so with the hope that it may
stimulate to even greater activity in the field of experimental
morphology. The subject is new, its importance hardly yet
generally recognized, its needs incompletely appreciated. In
its scope it embraces much of physics and chemistry, for life
and development are to be studied as the physicist studies light
and heat, or as the chemist studies solutions and combustion.
They are phenomena which must be analyzed by the use of
instruments of precision to determine the quality and quantity
of the acting agents, and to measure the change in the phe-
nomena resulting from a change in these agents. No other
field offers a better opportunity for the utilization of a broad
scientific training. The times, too, are auspicious. Biology
has never before attracted so many enthusiastic workers as it
does to-day. As Driesch has said, " Die Lust an thatsach-
licher exacter biologischer Forschung ist erwacht"; and the
greatest problem of morphology is ever more and more the
object of this biological experimentation.

CHAKLES BENEDICT DAVENPORT.

Cambridge, Mass., Dec. 1, 1896.

CONTENTS

Preface

PAGE

vii

CHAPTER I

Action of Chemical Agents upon Protoplasm

§ 1. Modification of Vital Actions

1 . Oxygen

2. Hydrogen

3. Oxides of Carbon

4. Ammonia

5. Catalytic Poisons

6. Poisons wliich form Salts

a. Acids ....

b. Soluble Mineral Bases .

c. Salts of Heavy Metals .

7. Substitution Poisons

8. Sodic Fluoride

9. Special Poisons

§ 2. Acclimatization to Chemical Agents
§ 3. Chemotaxis .....
Summary of the Chapter
Appendix to Chapter I ...

Literature ......

12
12
13
13
15
21
22
27
32
45
52
54

CHAPTER II

Effect of Varying Moisture upon Protoplasm

§ 1. On the Amount of AVater in Organisms ....
§ 2. On the Effect of Desiccation upon the Functions of Protoplasm

1. Effect of Dryness on Metabolism .....

2. Effect of Dryness upon the Motion of Protoplasm

3. Desiccation-rigor and Death ......

§ 3. On the Acclimatization of Organisms to Desiccation .

§ 4. The Determination of the Direction of IMovement by Moisture -

Hydrotaxis

Literature . . . . . . . . . . •

58
59
59
60
60
65

66
67

xii CONTEXTS

CHAPTER III
Action of the Density of the Medium upon Protoplasm

PAGE

§ 1. Introductory Remarks upon the Structure of Protoplasm and the

Physical Action of Solutions .... = .. 70

§ 2. Effect of Varying Density upon the Structure and General

Functions of Protoplasm ....... 74

§ 3. Acclimatization to Solutions of Greater or Less Density than the

Normal 85

§ 4. Control of the Direction of Locomotion by Density — Tonotaxis . 89

Literature ............ 93

CPIAPTER IV
Action of Molar Agents upon Protoplasm

§ 1. Effect of Molar Agents upon Lifeless Matter .... 97

§ 2. Effect of Molar Agents upon the Metabolism and Movement of

Protoplasm .......... 98

§ 3. Effect of Molar Agents in Determining the Direction of Locomo-
tion — Thigmotaxis (Stereotaxis) and Rheotaxis . . . 105

Literature ............ 110

CHAPTER V

Effect of Gravity upon Protoplasm

§1. Methods of Study . 112

§ 2. Effect of Gravity upon the Structure of Protoplasm . . . 113

§ 3. Control of the Direction of Locomotion by Gravity — Geotaxis . 114

Literature ...■.......•• 124

CHAPTER VI

Effect of Electricity upon Protoplasm

§ 1. Concerning Methods ......... 126

§ 2. The Effect of Electi-icity upon the Structure and General Func-
tions of Protoplasm ........ 129

§ 3. Electrotaxis 140

Summary of the Chapter ......•■• 151

Literature ........•••• 152

CONTENTS xiii

CHAPTER VII

Action of Light upon Protoplasm

PAGE

§ 1. The Application and Measurement of Light .... 154

§ 2. The Chemical Action of Light upon Non-living Substances . 161

1. The Syntlietic Effects of Light 162

2. Analytic Effect of Light 163

3. Substitution Effects of Light ...... 164

4. The Isomerismic and Polymerismic Changes produced by Light 164
§ 3. The Effect of Light upon the General Functions of Organisms . 166

1. Effect of Light upon Metabolism 166

a. The Thermic Effect of Light on Metabolism . .166

h. The Chemical Effect of Light on Metabolism . . 170

2. Vital Limits of Light Action on Protoplasm . . . 171

3. Effect of Light upon the Movement of Protoplasm . . 175

a. Effect of Low Intensity of Light on Movement — Dark-
rigor 175

6. Effect of High Intensity of Light on Movement —

Light-rigor . . . . . . . .178

§ 4. Control of the Direction of Locomotion by Light — Phototaxis

and Photopathy 180

1. False and True Phototaxis . . . . . . .181

2. Distribution of Phototaxis and Photopathy .... 182

a. Protista 182

h. Cells and Cell-organs 189

a. Chlorophyll Bodies 189

j8. The Rearrangement of Pigment in Animal Cells

in Response to Light ..... 192
y. The Migration of Pigment Cells in the Metazoan

Body 193

c. Metazoa 194

3. The General Laws of Phototaxis and Photopathy . . 196

a. The Sense of the Response ...... 196

h. The Effective Rays 201

c. Phototaxis vs. Photopathy ...... 203

(/. The Mechanics of Response to Light .... 207

Summary of the Chapter ......... 210

Literature ............ 212

xiv CONTENTS

CHAPTER Vm

Action of Heat upon Protoplasm

PAGE

§ 1. Nature of Heat and the General Methods of its Application . 219

§ 2. The Effect of Heat upon the General Functions of Organisms . 222

1. Effect of Heat upon Metabolism . . . . . . 222

2. Effect of Heat upon the Movement of Protoplasm and its

Irritability 225

§ 3. Temperature-Limits of Life ....... 231

1. Temporary Rigor and Death at the Higher Limit of Tem-

perature, Maximum and Ultramaximum .... 231

2. Temporary Rigor and Death at the Lower Limit of Tempera-

ture, Mininmm aiid Ultraminimum ..... 239

§ 4. Acclimatization of Organisms to Extreme Temperatures . . 249

1. Acclimatization to Heat ....... 249

2. Acclimatization to Cold ....... 257

§ 6. Determination of the Direction of Locomotion by Heat — Ther-

motaxis ........... 258

Notes to Table XXI 263

Literature 267

CHAPTER IX

General Considerations on the Effects of Chemical
AND Physical Agents upon Protoplasm

§ 1. Conclusions on the Structure and Composition of Protoplasm . 274

§ 2. The Limiting Conditions of Metabolism ..... 275

§ 3. The Dependence of Protoplasmic Movement upon Metabolism

and upon External Stimuli ....... 277

§ 4. The Determination of the Direction of Locomotion . . . 278

EXPERIMENTAL MORPHOLOGY

CHAPTER I

ACTION OF CHEMICAL AGENTS UPON PROTOPLASM

In this chapter it is proposed to consider (I) the effect of
the various chemical agents upon the chemical constitution of
protoplasm, as revealed by the results of their application, —
death, modification of the metabolic processes, and of rate of
movement ; (II) the phenomena of acclimatization to chemi-
cal agents ; and (III) the effect of such agents in determining
the direction of locomotion, — chemotaxis.

§ 1. Modification of Vital Actions*

The vital processes are chemical processes, taking place in a
highly complex, very unstable, constantly changing substance,
whose activities we call life. It is not easy to study this
living substance chemically by the ordinary methods ; for
these usually, first of all, kill the substance. That the living
substance and the dead are quite different is illustrated, for
example, in the action of diamid (N2H2) and hydroxylamine
(NH2 — O — H), which show no action upon dead protoplasm,
but are powerful poisons for all living plasm. The instability
of protoplasm enables us, on the other hand, to make use of

* In the preparation of this section, mucli use has been made of the admirable
work of LoEw ('93). Not only is the adopted classification of poisons for the
niost part his, but also, in a few cases, passages from his book have been translated
in toto here. Most of the determinations of killing strengths of the various re-
agents for which uo other authority is given have been taken from LoEw'sbook.
B 1

2 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

certain indirect means for determining its constitution. Since
death is due to chemical change, we ought to determine wliat
substances are fatal poisons to protoplasm ; and since every
activity of protoplasm is a chemical process, we ought to
study the modifications of these processes by the action of
various chemical reagents.

In studying the behavior of protoplasm in .the presence
of various reagents, we shall make use especially of observa-
tions upon Protista, sexual cells, and tissue cells. In cases
where sufficient observations on isolated plant or animal cells
are wanting, use will be made of observations upon Metazoa.

At the outset, attention should be called to the necessity
of a more quantitative study of the subject. A quantitative
study demands, especially, a careful noting of the conditions
of the experiment ; for the various physical conditions under
which the reagent is applied modify the result. Thus, it has
been shoAvn, for example, by Richet ('89, p. 212) that with
various poisons the toxic dose diminishes in amount with the
elevation of the temperature of the body.

1. Oxygen. — It is almost certain that no protoplasm can
long survive in the absence of oxygen. Apparent exceptions
are found in the case of the anaerobic bacteria, some of which
are killed in the presence of free oxygen, but multiply rapidly
when the oxygen supply is cut off. It has been suggested that,
in the case of these and some other parasitic organisms, oxygen
is derived from the breaking clown of O -containing compounds
in the nutritive medium, (Cf. LoEW, '91, p. 760.)

The effect of diminished oxygen upon protoplasm is described
by Clark ('89, pp. 370, 371) and by Demoor ('94, p. 191).
Clark determined the minimum oxygen pressure necessary for
the vital movements of the plasmodia of Myxomycetes and the
protoplasm of plant hairs and tissue cells. This he found to
range from 1 mm. (plasmodia of Myxomycetes) to 3 mm. (leaf
hairs of Urtica) of mercury.

Demoor*" subjected Tradescantia stamen hairs, in water, to a

* In studying the effect of a vacuum, Demoor employed a piece of apparatus
constructed essentially on the plan of an Engelmann's chamber. This consists
of a box whose top is a centrally perforated metallic diaphragm and whose
bottom is a circular glass. The vertical walls consist of an outer cylinder, at

§ 1] MODIFICATION OF VITAL ACTIONS 3

pressure of 6 to 8 cm. of Hg, or 0.08 to 0.1 of an atmosphere
(p. 71). In one hour, on the average, the protoplasmic move-
ments were affected, and in most cells ceased in 2 to 3 hours,
slight oscillations only of granules occurring. Thus, not death,
but arrest of activity, occurred during this period as a result
of reduction of atmospheric pressure — upon which the amount
of oxygen held in the water depends. That death did not
occur is shown by the fact that when air was readmitted at
the normal pressure the protoplasm j)romptly regained its nor-
mal activity. Cells Immobilized during 21 hours regain their
movements in less than 5 minutes, and these become normal in
from 10 to 20 minutes.

Pure oxygen acts in an opposite fashion from diminished oxy-
gen tension, exaggerating the activity of protoplasm. Under
its action the protoplasmic movements are much accelerated,
but preserve, meantime, their normal character. (Tradescantia
hairs, leucocytes; Demoor, '91, pp. 192, 218.) In Ciliata the
rate of the contractile vesicle does not, however, seem to be
altered. (Rossbach, '72, p. 10.)

Ozone and hydrogen peroxide produce atomistic "active" oxy-
gen by becoming split up in the plasma. Ozone (O3) is said
to kill quickly bacteria in Avater, if the latter does not contain
too much organic substance ; in the dry state, however, bacte-
ria are injured only slowly by it. (Ohlmuller, '92, p. 861.)

Other substances which, with a greater or less degree of
probability, may be said to act through oxidation of the pro-
toplasm, may be treated of here.

Hydrogen peroxide (H2O2). — Paneth ('89) added one part
of neutralized H2O2 to 10,000 (0.01%) of hay infusion, and
found that all Ciliata were dead within 15 to 30 minutes.
Stronger solutions act more rapidly ; and even in a 0.005%
solution, only part of the animals survived. Algte survived
only 10 to 12 hours in a completely neutral 0.1% solution.
A 10% solution is fatal in a few minutes. (Cf. Bokoeny,
'8G, p. 355.)

Salts of chromic^ manganic, permanganic, and hypochlorous

the periphery of the diaphragm, and an inner cylinder at the inner margin of
the diaphragm. An inlet and an outlet tube communicate with each of the
spaces, — the central space and that between the two cylinders.

4 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

acids act as intense poisons, apparently by directly yielding
oxygen atoms to the plasma proteins.

Sodic chromate (NagCrO^). — Many anserobic Scliizophytes
are killed even by a 0.05% solution of this salt. Splenic fever
bacteria do not develop in a 0.05% solution in bouillon; in
an agar-agar solution, they do not cease to develop until a con-
centration of 0.5% is reached, although they no longer produce
spores in a 0.05% solution. Sodic chromate also acts strongly
on alga3. (Loew, '93, p. 16.)

Potasdc dichromate (K2Cr207). — A 0.1'% solution kills algse
(Spirogyra) in a few hours.

Potassic permanganate (KMnO^) is an energetic poison for
alga3 and Infusoria. A 0.2% solution kills Infusoria (Para-
mecium) in one minute.

Chlorine, bromine, and iodine, as v^ell as hypochlorous acid
salts, act, even in very considerable dilution, fatally upon
all organisms, by splitting water, forming hydro-halogen com-
pounds, and leaving the oxygen to unite with the living proto-
plasm. The action of bromine upon glucose may be written — •

CeHiaOs + Bro + H,0 = CeHi^O, + 2 HBr.

glucose.

(Loew, '93, p. 15.)

BiNZ has pointed out that (on Infusoria) the poisonous
action of these three halogens, like their other chemical prop-
erties, diminishes with increase of atomic weight, in the series
CI, Br, I. (Compare the osmotic effects of the halogens, p. 72.)

Potassic chlorate (KClOg) — also similar salts of I and Br —
oxidizes in an essentially different fashion from the permanga-
nates. For the latter oxidize even dead organic matter, but
the former does not. This reagent may be considered a pas-
sively oxidizing one. Concerning its visible effects, we find
that bacteria in general are injured by a 2% solution; with
weaker solutions in nutrient media the bacteria reduce it to
KCl. The anaerobic forms are affected by a 0.5% solution;
the aerobic withstand up to 3%. AlgtB (Spirogyra) die after
a few days in a 0.01% solution of the salt. (Loew, '93, p. 17.)

Arsenious acid (HgAsOg) and to a less degree arsenic acid
(HgAsO^) are poisons which Binz and Schulz ('79) believe

§ 1] MODIFICATION OF VITAL ACTIONS 5

to act by oxidizing the protoplasm. Tlius HgAsOg can take
up free oxygen as it would be found in water, and it can part
with it readily to the protoplasm, thus oxidizing and eventually
wholly consuming it. Such is one theory of its action. A few
words as to effects upon Protista: Infusoria survive in 0.1%
potassic arsenite in spring water only a short time, but live
for weeks in a 0.1% solution of the potassic arsenate. (Loew,
'83, p. 112.) Algse (Spirogyra) are killed by a 0.1% solution
of potassic arsenite in six days, — the protoplasm contracts and
shows formation of granules, the death of the chlorophyll bands
preceding that of the cytoplasm. The same solution of potassic
arsenate, meantime, shows no injurious action, (Loew, '87,
p. 445.) Still other arsenious acid salts tried upon other algse
(Zygnema, Diatomacea), upon Infusoria, and upon tadpoles
showed themselves, uniformly, more powerful agents than the
corresponding arsenic salts. The lower fungi are only slightl}^
affected by arsenious salts ; not at all by those of arsenic acid.

2. Hydrogen. — Kuhne ('64, p. 52) subjected Amoeba to H
for 24 minutes. At the end of that time, some individuals
had assumed a spherical shape, others appeared unchanged in
form, but were motionless. Similar results were obtained with
Actinophrys, the plasmodium stage of Myxomycetes, and with
the stamen hairs of Tradescantia.

Demoor ('94, p. 190) also experimented upon the latter
object, and his results are worth giving in detail.* During
the first moments of the passage of the gas, the protoplasmic
movements are slightly accelerated. Soon the protoplasm be-
comes very granular, and, after a variable time, 15 to 40 minutes,
is quiet. The aspect of the protoplasm at this time varies
with the character of the cell. If it is young, having a large
nucleus and without a primordial utricle, the protoplasm ap-
pears uniformly granular. If, on the contrary, the cell possesses
a great reserve of water, with long, protoplasmic filaments,
the protoplasmic granules become more refringent, increase in
volume, and accumulate around the nucleus, — the peripheral

* Method : The hydrogen gas may be generated in a Kipp's apparatus, and
should pass through a series of washing flasks containing, e.g., solutions of potash
and acetate of lead. See Vkuwoun : Allgemeine Physiol., p. 285. Dejiook
kept his stamen hairs in sugared water in an Engelmann's chamber.

6 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

protoplasm appearing hyaline. The living substance is in
repose. The hydrogen may be passed through the apparatus
containing the stamen hairs for from 1 to 5 hours without any
movement or other change appearing in the protoplasm. Air
is now admitted. The protoplasmic movements rapidly return ;
the granules at first oscillate in their places, then gradually
extend the range of their movement. In 5 to 6 minutes the
cell has regained all of its anatomical and physiological charac-
ters. A similar immobility affects also leucocytes subjected to
hydrogen. This occurs in about an hour ; but there is great
individual variation in this respect. Upon substituting air,
the activity of the protoplasm is resumed in from 10 to 20
minutes. Protoplasm which has been subjected to the action
of hydrogen thus appears not to be permanently modified, since
normal movements recur rapidly upon readmitting air. It
seems probable, therefore, that the temporary cessation in move-
ments in the presence of hydrogen is due to the exclusion of
oxygen from the protoplasm.

3. The two Oxides of Carbon, COg and CO, have very dif-
ferent effects upon protoplasm. Thus Demoor ('94, pp. 191,
,202, 219) found that whereas the former immobilizes quickly,
but kills very slowly, perhaps chiefly by asphyxia, the latter
seems in some cases actively to attack the protoplasm. In
leucocytes, the ectosarc is separated from the endosarc in a
number of completely hyaline fragments ; the endosarc becomes
vacuolated, and death ensues in froip 20 to 60 minutes. Many
bacteria are only slightly affected by CO.

4. Ammonia (NHg). — A 10% solution provokes vacuoli-
zation, partial coagulation, and irregular movements in the
protoplasm of the Tradescantia hair. The cell finally enters
into repose, all the granules accumulating around the nucleus.
Washing the preparation with water restores the original char-
acters of the protoplasm. Thus, ammonia at first energetically
excites protoplasm, later producing anaesthesia. (Demoor, '94,
p. 193.) Even with very weak aqueous solutions (0.005%),
which do not kill the protoplasm, Bokorny ('88) has observed
the production in Spirogyra cells of granules, which process
does not, however, seem to modify the normal activities of the
cell. These granules, " proteosomes," are intensely blackened

§ 1] MODIFICATION OF VITAL ACTIONS 7

by alkaline (0.001%) silver solutions. Other basic substances,
like potash and organic amine bases, and various alkaloids,
produce the same effect. (Cf. Loew and Bokorny, '89.)
Azoimid. — LoEW ('91) has studied the effect upon proto-

plasm of this somewhat close ally of ammonia, || ^NH. The

poisonous action of this substance seems to depend upon its
excessively unstable structure, for it easily disintegrates with
violent explosion and production of ammonia. This latter
then iDroduces the characteristic granulations. Infusoria are
killed in 2 to 2|- hours by a 0.1% solution of NgNa, and the
water-living Nematodes, Planaria, Ostracoda, Copepoda, and
young Planorbis and Lymnsea are killed by a 0.05% solution in
30 to 40 minutes. Algse are more resistant.

5. Catalytic Poisons. — There is a large number of unstable
C-compounds which are neither acid nor basic nor characterized
by chemical energy, which are, nevertheless, intense poisons
for all living cells. Here belong the anaesthetics — ethylether,
chloroform, chloral, carbontetrachlorid, methylal, alcohols, car-
bon disulphide, etc.*

Nageli believes these to act as poisons by virtue of an in-
herent lively condition of molecular movement, which disturbs
the normal condition of movement in the living plasma body,
and, on that account, produces death. Loew believes, more
precisely, that the transmitted condition of violent movement
leads to chemical transformations in the unstable albumen of
the protoplasm.

As examples of the effect of the mere presence of many un-
stable carbohydrates upon chemical processes, it has been found
that HCl and prussic acid, which unite alone only at a high
temperature, unite in the presence of various ethers at —15°.
Again, the mere presence of some CH compounds transforms a
substance into its isomeric condition. Thus, thiourea is trans-
formed by an alcoholic solution of amylnitrite into its isomer
rhodanammonium. Such poisons, which change the protoplasm
by transmission of molecular movements, may be called cata-

* This paragraph and the two following are largely translated from Loew

('1)3).

8 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

lytic poisons ; the process which they inaugurate being known
as catalysis (apparently produced by mere contact).

First will be considered the laws of relation betiveen molecular
composition and strength of action. We may begin with the
methan series. This series, which has CHg — as its base, runs

as follows : —

CH4
C2HB
CsHg, etc.

In the members of this series, the poisonous action increases
up to a certain limit, with the number of O atoms ; above that
limit the compounds are more stable and are more indifferent ;
e.g. paraffine (C21H44 to C27H5Q).

Beginning with methan, CH^, we find this substance — marsh
gas — innocuous when mingled with air. As the H atoms become
replaced by one or more chlorine atoms., the poiso7ious qualities
increase, —

CH3CI is slightly anaesthetic,

CHCI3 = chloroform,

CCI4 is very dangerous, stupefying involuntary muscles.

If the H atoms are replaced by any other halogen, — e.g. I, —
anaesthesia is produced among some Vertebrates. Thus, 0.5 to
1 grain of CH2T2 kills a rabbit.

In ethan (C2Hg) also, when CI replaces H, the substance be-
comes a more active poison; e.g. C2H3CI3, lethal chloroform,
acts like chloroform.

Also, among the sulphur hydrocarbons we observe the same
fact of increase of poisonous action with increase in the number
of CI atoms to the molecule ; thus, —

sulphur ethyl, C2H3— S — C2H5 is a weak poison,

monochlorsulphurethyl, C2H5— S — C2H4CI is a stronger poison,
dichlorsulphurethyl, C2H4CI — S — C2H4CI is a very powerful poison.

In the more complex sulphonic hydrocarbons of the methan
series, where the alkyls CHg—, C2H5— ,etc., are introduced,
the rule holds that the more atoms in the alkyl the more active
the substance as a poison ; thus, —

§ 1] MODIFICATION OF VITAL ACTIONS

CHsV /SO2CH3

/ C \ is not poisonous ;

CH3/ \SOoCH3

sulphonal : / C \ is poisonous ;

CH3/ \SOAH5

CHgy /SOAH5
trional : / C \ is poisonous ; and

tetronal : / C \ is more poisonous.

CoH/ ^SOoC^H,

The same holds for the acetals ; thus, —

[\ /O.CH3 H\ /

H\ /O.CH3 Hv /O.CoK

/ C \ is half as active as / C \

H/ \O.CH, CH3/ \o.aH,

We find the same thing in the ethyl group, —

CH3\ G.^,\

CH3 — C - OH is less active than CH3— C - OH.

CH3/ CH3/

trimethalcarbinol. diinethalethylcarbinol.

And also in the alcohols, —

methyl alcohol, CH3OH, weak action ;
ethyl alcohol, C2H5OH, weak action ;
isopropyl alcohol, C3H7OH, stupefying.

A few words now concerning the morphological changes ob-
served in protoplasm subjected to the action of poisons belonging
to this group. Here belong especially the various anesthetics.

Chloroform and ether seem to affect all protoplasm aues-
thetically, that of the higher plants as well as that of the
higher animals. (Bernard, C, '78, and Elfing, F., '86.)
KiJHNE ('64, p. 100) first studied the effect of chloroform vapor
upon Tradescantia hairs, but Demoor ('94, p. 193) has since
described the action of this reagent in much more detail.
l cliloroform water at first (2 to 5 minutes) produces a very
intense excitement in the movements of the protoplasm, a
strong vacuolization occurs, and then the cytoplasm gradually

10 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

becomes immobile and dies in from 15 to 30 minutes. The
nucleoplasm is less energetically acted upon than the cyto-
plasm. Upon swarm-spores, which are highly responsive to
light (p. 182), weak solutions of ether and chloroform have
such an effect that without preventing locomotion they destroy
the power of responding to the stimulus of the external agent.
So, too, the migrations of the chlorophyll in Metaphyta * under
the influence of light (see p. 189) is prevented. Ciliata are
slightly paralyzed, for the period of the contractile vacuole is
diminished. The whole cell body becomes distended with water,
and the trichocysts are exploded. (Schurmayer, '90, p. 453.)

When chloroform water is slowly applied to leucocytes they
acquire a spherical form ; when quickly applied they become
immobile without change of form. The first effect is a very
intense increase in movements, especially of the ectosarc.
Ultimate washing in serum suffices to restore the leucocyte
to its wonted activity ; so that it has not been killed, but only
ansesthetized. (Demoor, '94, p. 217.)

/OH

Chloral hydrate^ CClg — C^OH, which is closely related to

\h

yd
chloroform, CI — C — CI, acts similarly as a protoplasmic anses-

\h

thetic. A 0.1% solution kills Infusoria, Rotifera, and diatoms
in 24 hours, but filamentous algse and Nematoda withstand it.

Sulphonal in 0.1% solution is less injurious than the pre-
ceding, since during 24 hours the above-mentioned organisms
are uninjured. (Loew, '93, p. 25.)

Upon the effect of alcohols on protoplasm, extended experi-
ments have recently been made by Tsukamoto ('95). These
reveal in much detail the peculiarities of action of the different
kinds. I give three tables showing the time of resistance in
hours of various organisms to the various alcohols, constructed
from data furnished by his paper.

* Elfing, F. ('86, pp. 47-51). The swarm-spores employed belonged to the
species Clilamydomonas pulvisculus. The strengths of the solutions which
inhibit their response without stopping locomotion are : of ether, 1% to 5% ; of
chloroform, 12% to 25%. The migration of chlorophyll in Mesocarpus is in-
hibited by a 1% to 2% ether solution.

§1]

MODIFICATION OF VITAL ACTIONS

11

TABLE I

Time (in Hours) or Resistance of Tadpoles of Bufo Vulgaris, Laue.
(Hind Legs had just appeared) to Various Alcohols

Strengths.

0.01%

0.1%

0.3%

0.5%

0.7%

1.0%

1.6%

2.0%

0.3-0.8

stupor

0.16

0.6

0.3

0.15

0.5

0.2-0.3

0.15

1.0

0.08
0.15-0.25

0.05-0.15
0.15-0.33

0.05-0.25

0.2-0.5

4-5

1.5-2.0

3.5%

methylic* . . . .

ethylic

propylic.norm. .
propylic, iso. . . .
butylic, norm. . .
butylic, iso. . . .
butylic, tertiary,
amylic, norm. . .
allylic

0.07-0.3

TABLE II

Time (in Hours) of Resistance of Infusoria and Ostracoda to Various

Alcohols

methylic . .

ethylic

propylic.norm. .
propylic.iso . . .
butylic, norm.. .
butylic, iso . . .
butylic, tertiary,
amylic, norm. . .
allylic

Stkkngtiis.

0.005%

0.1%

0.5%

1.0%

72 1

18

48

18

72

48 1
48 + t

24 +

24

24

3.0%

20

4

* The structural formulas of these alcohols are given here for reference : ■

methylic H - CH.2OH

ethylic CH3 - CH.2OH

propylic, norm CH3 . CHo - CHcOH

propylic, iso (CH3)2 - CHOH

butylic, norm CH3 . CHo . CH2 - CH«OH

butylic, iso.

CH
CH

3 > CH - CHoOH

butylic, tertiary ^JJ^^COH-CHs

amylic, norm. .
allylic

CII3 . CHo . CHo . CHo - CHoOH
CHo. CH- CHoOH

t Ostracoda only ; the Infusoria died after 18 hours.

12

CHEMICAL AGENTS AND PROTOPLASM

[Ch. I

TABLE III

Time (in Hours) of Resistance Period of Spirogtra Communis to
Various Alcohols

Stkengtiis.

0.005%

0.01%

0.05%

o.i%

0.5%

1.0%

3.0%

3.0%

4.0%

methylic

ethylic

propylic, norm. .
propylic, iso. . . .
butylic, norm. . .
butylic, iso. . . .
butylic, tertiary,
amylic, norm. . .
allylic

66

72

24

24

72
96

24

72
48
48
48
48

120
72

96
72

48
48

From these experiments it appears that allylic alcohol is more
injurious than the others, so that Tsukamoto ('95, p. 281)
believes it to attack the protoplasm directly rather than to act
merely catalytically. We see also that the rule enunciated
above about the greater activity of substances with more com-
plex alkyls holds true in general. Of the butylic alcohols the
normal is tlie most poisonous ; the tertiary, least.

Carbonic disulphide (CS2) is one of the more powerful cata-
lytic poisons. A saturated aqueous solution, which contains
only a trace of CSg, nevertheless kills quickly algse, bacteria,
and the lower water animals. (Loew, '93, p. 29.)

6. Poisons which form Salts. — This is the third group recog-
nized by Loew. In this case we have to do with acids and
bases which unite with the protein substances of the pro-
toplasm-producing salts. Thus disturbances leading to death
are produced. In addition this group comprises the poisonous
metallic salts. So we may recognize three groups: a. acids;
b. the soluble mineral bases ; c. salts of heavy metals.

a. Acids. — Tne strong inorganic acids act, in general, more
powerfully than the organic. Most bacteria, alga?, and Infusoria
are very sensitive to inorganic acids (see Migula, '90), but
splenic fever bacteria resist 1% HCl for 24 hours, and their
spores 2<fo HCl for 48 hours. Mold withstands 1% phos-
phoric acid. Certain tissues have gained a high resistance
capacity to inorganic acids. Thus, the gland cells of marine

§ 1] MODIFICATION OF VITAL ACTIONS 13

Gastropoda (Dolium, Cassis, Tritonium, Natica heros) secrete
2% to 3% H2SO4. (LoEW.)

To organic acids many algae are little resistant. Thus Spiro-
gyra and Spliceroplea die in 0.1% malic or tartaric acid after
30 minutes ; in 0.05% malic or tartaric acid after 24 hours ; in
0.01% of these same acids in a few days. Formic acid pre-
vents development of bacteria even in small percents — 0.05%
to 0.006%. On the other hand, some protoplasm has acquired
a resistance to organic acids. The vinegar eel — Rhabditis
aceti — lives in 4% acetic acid. The protoplasm of the Dro-
sera tentacle resists 0.23% tartaric, citric, and other organic
acids.

h. Soluble mineral bases ^ including those of corrosive alkalies
and the alkaline earths : Ca, Ba, and Sr. The corrosive alka-
lies cause a swelling of the protoplasm, but the primary effect
is rather a chemical one. (Cf. Fromaxn^, '84, p. 90.)

The lower water animals and plants are quickly killed by
0.1% potassic or sodic hydrate. Thus, the movements of
Chara cease in 0.05% KOH in 35 minutes. Bacteria are more
resistant ; the limit for the typhus bacilli being between 0.10%
and 0.14%, and for the cholera bacillus, between 0.14% and
0.18%. Ascaris is still more resistant, living for 20 minutes
in a 2% solution of NaOH.

CaO is still more powerful. A 0.007% to 0.025% solution
in bouillon kills bacilli. A 0.013% solution is fatal to algaj
like Spirogyra.

K2CO3 kills bacteria in 0.8% to 1.0% solutions.

NagCOg kills Ascaris in a 5.8% solution after 5 to 6 hours.
(LoEW, '93, pp. 33, 34.) Fromann has discussed the histo-
logical changes in protoplasm after treatment in Na2C03.

It is difficult to say whether the action of some of these re-
agents may not be an osmotic, rather than a chemical one.
The action of Na2C03, for example, as described by Fromann,
is very similar to that of NaCl, whose action is probably solely
osmotic.

c. Salts of Heavy Metals. — The method of action of these
poisons has been accounted for upon the following grounds :
When amido-acids (which are found as disintegration products
of all animal tissues) are treated with salts of the heavy metals.

14 CHEMICAL AGENTS AND PROTOPLASM [Cii. 1

the hydrogen in either the carboxyl-group or the amido-
group can be replaced by the metal. Likewise the hydrogen
of the amido-group in urea derivatives and many bases are
replaceable by metals. In the still more complicated protein
stuffs the H bound to the N or O can be replaced. Many
metals, indeed, like silver or mercury replace preferably the H
of the amido-groups, and on this account, perhaps, their salts
are especially poisonous. (Loew, '93, p. 34.)

Salts of Hg, Ag, and Cu cause death to Spirogyra even in
a dilution of 1 : 1,000,000 ; the chlorophyll bodies being first
affected.* Upon the bacteria of splenic fever the double
cyanides of Ag, Hg, and Au are the most injurious, next those
of Cu, Pb, and Zn, and, finally, those of Pt, Ir, and Os. Tad-
poles and Tubifex are killed in 24 hours by solutions of CuSO^
weaker than 0.00006%. (Locke, '95, p. 327.) Among mer-
curic salts, splenic fever bacteria do not develop in 0.0003%
HgClg in nutritive bouillon, nor 0.0125% in blood. Lactic acid
bacteria do not reproduce in 0.0007%. Mold spores are killed in

* In this connection reference must be made to the posthumous paper of
Nageh ('93), " Ueber oligodynamische Erscheinungen in lebenden Zellen."
This author found that water distilled in copper vessels or 1 litre of water in
which 12 clean copper coins had stood for four days acted fatally upon Spiro-
gyra. The water was found in one such case to contain 1 part Cu in 77,000,000 of
water. It was believed to be in solution in the form of the hydroxyd (CUH2O2).
Similarly produced solutions of other metals, Ag, Zn, Fe, Pb, Hg, had a simi-
larly fatal effect upon Spirogyra. Nageli believed that the effect of the metals
was not a chemical one, but was due to a new force — " oligodynamic." Besides
the fact of the action of very dilute solutions, the only evidence he adduced for
the new force was based on the difference of action on the chlorophyl bands of
solutions of 1:1000 or 1:10,000 and 1:10,000,000. In the weaker solutions
("oligodynamic" action) the bands alone were drawn away from the cell-wall,
in the stronger solution (chemical action) the whole peripheral protoplasm was
shrunken away. It does not seem necessary to invoke a new force to explain
the action of weak solutions: first, because the two actions are not sharply
separated, according to Nageli's own data ; secondly, because the chlorophyll
bands are in general more sensitive than the rest of the protoplasm (p. 5) ;
and, thirdly, because the action of so weak a solution is not surprising in view of
the fact that Spirogyra is one of the least resistant of organisms. Even in a
comparatively resistant organism, like Stentor, a solution of 1 : 80,000,000 HgCla
produces acclimatization to the poison and 1 : 10,000,000 has an injurious effect.
Yet between the action of such solutions and those of 1 : 1000 there is a complete
graduation in increasing effect. (Seep. 30.) Even in Nageh's experiments
solutions of less than 1 : 100,000,000 had little action.

§ 1] MODIFICATION OF VITAL ACTIONS 15

0.1%. Neal and I have found that Stentor cceruleus is killed
by a 0.001% solution HgCl2 in a few seconds. (Cf. p. 30.)
Ascarids die in a 0.1% solution in an hour. (Schroder, '85.)

Silver salts occasionally act upon bacteria more energetically
that those of Hg. Cadmium and zinc salts are poisonous — the
former more so than the latter. Thus, whereas 0.015% of cad-
mium sulphate inhibits reproduction of lactic acid bacteria,
0.1% of zinc sulphate is not injurious. Many salts of thallium
are likewise active. Thus Loew ('93, p. 37) found that in
0.1% thallium sulphate Spirogyra died in 4 to 6 hours.

7. Substitution Poisons. — In this group Loew places cer-
tain nitrogenous substances which attack the amido and alde-
hyde groups of living protoplasm. These are extremely unstable
substances and may therefore be transformed by agents which
have no effect upon dead protoplasm. The supposed method
of action of a poison upon an aldehyde may be illustrated in
the case of the poison hydroxylamine (H2N — OH); which
justifies at the same time the term "substitution poisons."

■R-Cf +H,= N-OH=:Il-Cf + HoO.

any aldehyde. hydroxylamine. an aldoxiin.

Hydroxylamine. — This is a general and powerful poison.
Thus, among the lower organisms, a solution of neutral hy-
droxylamine of —

0.001% kills diatoms within 24 hours. (Loew, '85^ p. 523.)

0.005% kills in 36 hom-s Infusoria which withstand a similar con-
centration of strychnine. (Loew.)

0.01% kills diatoms in something less than 15 hours; Planaria and
leeches in 12 to 16 hours. (Loew.)

0.1% paralyzes the muscles of Eotifera in 10 to 15 minutes ; those
of Nais in 20 to 30 minutes. (Hofer, '90, pp. 324, 325.)

0.2% kills Rotifers, Copepoda, and Isopods in 1 hour (Loew);
stupefies Vorticella in from 2 to 10 minutes. (Hofer,
'90, p. 325.)

0.25% stupefies Stentor in 10 to 20 minutes. (Hofer.)

Benzenylamidoxim and acetoxim., more complex derivatives of
hydroxylamine, are somewhat less poisonous.

16 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

Diamid, or hydrazin (HgN — NHg) in the form of neutral
solutions of the sulphate is a rapid poison. A solution of —

0.01% kills various alga species in 1 to 2 days.

0.02% is injurious to bacteria.

0.05% kills various water animals within 12 hours. (Lobw, '93.)

Phenylhydrazin yN — NHg

H

is more powerful.

solution of —

0.0067% kills Infusoria and algae within 18 hours.

0.05% prevents the development of bacteria and mucors.

As free ammonia (NHg) is a far weaker poison than cliamid
(H2N — NH2), so anilin (CgHgNHg) is far weaker than phenyl-
hydrazin (CgHg . NH . NH2).

Passing now to the more complex nitrogenous compounds,
we find, first, that bodies which possess slight or no poisonous
power, and contain tertiary N, can become strong poisons by
addition of H and formation of imido-groups (i.e. groups which
can be derived from ammonia by the substitution for two H
atoms of bivalent acid radicals) ; thus, —

/CH = CH\ /CHo - CH.,\

CH^ ^N ch/ )nH

^CH - CH^ \CHo - ch/

pyridin (weaker poison). piperidin (stronger poison).

/HC = HC\ /H.,C - H.C\

CH< >lsr CHo( )nh

^CH - C^ \CH, - CH/

I " I

CH CH2

/ \ I

CH3 CH3 CH2

collidin (weak).

CH,.,

comln (violent).

In the preceding and the two following cases it is seen that,
in general, when there is a hydrogen atom of the amid radical
(NH2) unreplaced by an alkyl, the substance is poisonous.

§ 1] MODIFICATION OF VITAL ACTIONS

Only slightly Poisonous
CeH, - CH
CqH.5 — CH

17

/CH — CfiHg

hydrobeczamid

/CH = CH\

CH^ >

^CH - CH-^

pyridin.

CfiH.

Violent Poisons
CH - NH\^

CfiH.r — C

: N
amarin.

./

CH - C,H,

CH = CH\
CH = CH^

pyrrol.*

NH

This increased poisonousness, correlated with the presence
of H joined to N, may be accounted for by the union of
this H with the O of the ketons or aldehydes of the living
substance.

Likewise when one or more H atoms of the amido-group
are replaced by an acid radical (e.g. that of acetic acid,
CO . CHg), the poisonous qualities of the substance are con-
siderably diminished ; thus, —

tloRE Poisonous.

Less Poisonous.

CeH^NH^

CeHsNH . CO - CHg

anilin.

antifebrin.t

CeHsNH . NHo

CeH^NH . NH . CO . CH,

Iihenylhydrazin.

pyrodin.

/NH.
HN = C(

^NHa

/NHo
HN = C(

\nH . CO . NH.

giianidin.

dicyandiamidin.

In like manner when, in an imido-group, the H (of the NH
radical) is replaced by alkyls {e.g. CHg), the substances become
less poisonous ; thus, —

* "While a 0.07 % solution of pyrrol kills Isopods, Rotifers, Planaria, etc., in
about 1 hour, these organisms withstand a solution of pyridin of the same
strength. (Loew, '87, p. Hi.)

t SciiiJRMAYER ('90, p. 445) finds that upon Ciliata (Carchesium) a 0.1%
solution slightly accelerates at first the action of the cilia, diminishes the rate of
succession of the phases of the contractile vacuole, and leaves the protoplasm
permanently more or less paralyzed.

18 CHEMICAL AGENTS AND PROTOPLASM [Ch. ]

NH-CH N.CH3-CH

I II I II

CO C - NH CO C - N . CH3

I I ^CO I I \co

xanthin. theobromine.

N.CH3-CH

1 II

CO C - N . CH3

I 1 ^co

N . CH3 - C = N /

eotfeiii.

are successively less poisonous. (Loew, '93, p. 46.)

H

While benzol \ \ is rather inactive, 8 grammes

h/^\c/''\h

I

H

per day being withstood by the human organism, with the
replacement of the H atoms by OH the substance becomes
more poisonous in direct proportion to the number of H
atoms thus replaced. (Loew, '87, p. 440.) Thus there fol-
low in order of poisonousness : —

H

H

1

H

1

iC^ \c-OH

HC/^ \c-OH

HO-C^ \c-0

iL\ /CH

\c/

HC\ /CH

HC. /CH

\c/

1

H

OH

1
OH

phenol (monoxybenzole).

resorcin (dioxybenzole).

phloroglucin (trioxybenzole).

Phenol (or carbolic acid) and its derivatives attack unstable
substances, especially aldehydes, forming insoluble products.

Phenol itself produces in the higher animals a paralysis of
the nerve centres. Algte die in a 1% solution after 20 to 30

§ 1] MODIFICATIOX OF VITAL ACTIONS 19

minutes; in a 0.1% solution after 3 days. Infusoria die
quickly in a 1% solution. Ascaris lives only 3 hours in a
0.5% solution.

Resojxin (0.5 g.) is hypnotic to man ; 0.085 g. per kg. is
fatal to dogs. Its isomer — pyrocatechin — is more active.
0.1% of it in spring water kills diatoms and Infusoria after
a few minutes, and filamentous algce in a few hours ; while,
with resorcin, Infusoria, diatoms, and green algse live several
hours — even as long as 18 hours.

By replacing one of the H atoms of phenol by COOH (or
carboxyl), thus producing salicylic acid, the poisonous qualities
are reduced.

Hydrocyanic Acid, CNH. — The action of this substance is
peculiar in that, acting on the central nervous system, it is
in small quantities a more violent poison for Vertebrates than
for Invertebrates. Hydrocyanic acid acts upon aldehydes —
in dilute solutions upon the most unstable compounds only ; in
stronger concentration upon all aldehydes. Its peculiar work-
ing may be hypothetically explained by assuming the aldehydes
of the ganglion cells to be more unstable than those of other
cells, so that traces of CNH which do not injure other cells
destroy quickly the nerve cells. (LoEW.)

The action may be shown by the equation, —

)c = o + CNH=r ;c— OH.

H/ H/

aldehyde.

The degree and variety of its action may be inferred from
the following data, taken from Loew ('93): Infusoria die
quickly in a 0.1% solution, but Ascaris resists a 3% solution
for 75 minutes. The resistance of the hedgehog to CNH is
remarkable ; five times the dose which killed, in 4 minutes, a
cat weighing 2 kg. produced in the hedgehog only a slight
sickness. A myriapod (Fontaria) excretes CNH when irri-
tated. Certain salts of CNH act as poisons ; e.g. (CN)2Hg,
Na2Fe(CN)5NO.

Hydric sulphide acts as a poison either by deoxidizing the

plasma,

HoS + O =r H,0 + S,

20 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

or by acting on the aldehydes,

)c = 0 + H.s = ;c - s + H2O.

It acts rather energetically upon algae and Infusoria. In Ver-
tebrates, the central nervous system is attacked and the oxy-
htemoglobin of the blood is altered.

Sulphurous oxide (SOg) attacks members of the aldehyde

group, —

R\ E\ /SO3K

)C = 0 + SO3KH = )C — OH
H/ H/ \h

aldehj'de.

0.1% kills lower fungi in a few minutes, 0.01% in a few hours.
Selenous oxide (Se02), which acts chemically much like SOg
and has a much greater molecular Aveight (64 : 111), acts less
energetically as a poison. A 0.1% solution kills Spirogyra
and Zygnema in 3 hours, while 0.01% is scarcely injurious.
Tellurous oxide (Te02, mol. wt. = 157) is non-poisonous,
although chemically closely allied to the two preceding.

(BOKORNY, '93.)

Aldehydes. — The poisonous action of these substances de-
rived from oxidation of alcohol is dependent upon their insta-
bility. So we find that an aldehyde, which, like grape sugar,
is fairly stable, is likewise non-poisonous ; while formaldehyde,
which is very unstable and active, is correspondingly poisonous.
Aldehydes attack especially the unstable amides, affording ni-
trogenous compounds ; e.g. —

CfiH^ • NH2 + CH2O = CeHsNCHo + H2O.

Now, even in passive albumens, part of the N is in the form
of amido-groups ; for, in treating with nitric acid, much nitro-
gen is set free, which would not occur were all of the N second-
arily or tertiarily bound up. (LoEW, '93, p. 58.) Hence the
poisonousness of aldehydes for living albumens.

Formaldehyde. — This substance (H — CH : O) acts upon
propeptones and upon albumen, affording compounds which are
not readily soluble. An aqueous solution of —

§1] MODIFICATION OF VITAL ACTIONS 21

0.01 % is fatal to bacteria.

0.05% kills worms, molluscs, and isopods in 2 hours. (Loew, '88,

p. 40.)
1.00% kills Spirogyra very quickly. (Cohn, '94, p. 5.)

A weak solution seems to act ansesthetically upon Noctiluca.
(Massart, '93, p. 65.)

When various radicals are substituted in H — CH : O, the
substance acts more like a catalytic poison. Thus, ethyl-
aldehyde (CHg — CHO) is anaesthetic ; and paraldehyde
(CH3-CHO)3 kills algce in a solution of 0.002% in 24
hours and causes protoplasm to become immobile either (leuco-
cytes) after momentary stimulation (Demoor, '94, p. 218) or
(Noctiluca) at once (Massart, '93, p. 66}.

Several derivatives of ethylaldehyde are poisonous. Loew
('93, p. 60) has shown that in a 0.1% solution of the neutral
sulphate of NHg — CH2 — CH : (002115)2, amidoacetal, Infu-
soria, and diatoms die within 15 hours, and, somewhat later,
filamentous algcje.

Nitrous acid^ as is well known, produces, even in great dilu-
tion, OH-compounds from amido-compounds (R — NH2) ; or
else, under certain conditions, especially with aromatic amido-
compounds, diazo-compounds result ; e.g. —

C2H5 . NH2 + HO . NO = C2H5 . OH + ^2 4- HoO,

amine. alcohol.

and

CgHs . NH, . HNO3 -K HO . NO = CgH^ . NoONO. + 2 H,,0.

aniline nitrate. diazobenzene nitrate.

Thus a solution of 0.001% of free nitrous acid is poisonous
to algiB, and more so than nitric acid. The lower fungi are
also very sensitive to nitrous acid. Its action as an acid is
weak, so that its salts are set free in the presence of even the
weaker organic acids. On this account, even neutral nitrates
kill such plants (some algaj, e.g. Spirogyra) as have an acid
cell-sap.

8. Sodic Fluoride. — The poisonous action of the fluorides
of the light metals, and especially sodium, has not hitherto
been explained. A 0.2% solution of NaF kills various algae
(Oscillaria, Cladophora, (Edogonium, diatoms) within 24 hours,

22 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

producing a change in size of the nucleus. (Loew, '92.) A
1% solution kills the nerves of a frog in 2 hours.

9. Special Poisons. — Toxic Protein Compounds. Little need
be said here concerning the recent discoveries of poisonous
albuminoids excreted by disease-producing bacteria, or of those
secreted by the parasitized body (alexines). Similar compounds,
highly poisonous to Vertebrates, have been extracted from the
seeds of some Phanerogams, e.g. ricin, from the seeds of Rici-
nus communis (castor-oil bean); abrin, from the seeds of the
leguminous Abrus precatorius, L. ; and phallin, from the toad-
stool Agaricus phalloides, Fr. Finally, in this group may be
placed a large number of protein substances derived from
animals, which are more or less poisonous to a greater or
smaller number of kinds of protoplasm. The poison of the
rattlesnake (Crotalus) and of the cobra (Naja) is fatal to
Vertebrates in small, hypodermically injected, doses. Hydra,
Turbellaria, Rotifera, and Crustacea are also affected by it ;
but Infusoria and Flagellata are apparently unaffected. (Hei-

DENSCHILD, '86, p. 330.)

It is important that, according to the experiments of several
investigators, among the earlier of whom may be mentioned
Daremberg ('91) and Buchner ('92), the various species of
Vertebrates possess protein substances in their blood serum
which are to a certain extent injurious to other species, since
the blood serum of any one species will destroy the red and
white blood corpuscles of another. The poisonous action of
these animal protein substances seems to be due to their un-
stable character, whereby they easily form unions with the
unstable groups of the protoplasm, frequently producing
thereby violent poisons which work as substitution poisons.
(LoEW, '93, pp. 81-84.)

Alkaloids. — These basic, nitrogenous compounds have, for
the most part, very complex molecules, so that their structure
has, in many cases, not been determined. Consequently the
nature of their chemical action upon protoplasm is, in general,
unknown.

LoEW suggests ('93, p. 85) the following theory of action of
alkaloids. The bases unite with the active protein substances
of the cell, and thereby introduce a disturbance of equilibrium

§ 1] MODIFICATION OF VITAL ACTIONS 23

in the plasma body — a disturbance which is especially mani-
fest in their action upon the protoplasm of ganglion cells. The
capacity of this union is influenced by various factors : by
the configuration and degree of dilution of the poison ; by the
degree of instability of the kind of protoplasm acted upon ;
by the configuration of the molecule of the active protein
substance in the cells ; and by the specific (micellar) structure
of the plasma body. That organic bases can unite with active
albumen is known from observations upon plant cells contain-
ing stored-up active protein substances. If the configuration
of the albumen molecule and the general texture of the pro-
toplasm favor the attack by the base, a disturbance of the
equilibrium of the protoplasm will result, even in considerable
dilution of the poison.

The alkaloids affect chiefly the nervous tissue in the higher
animals, producing, in some cases, paralysis ; in others, increased
activity. Thus, curarin is paralytic in its action, while the
closely allied strychnin is (in dilute solutions) stimulating
upon nerve cells. Since action is almost confined to nerve
tissue, additional evidence is afforded of the extraordinary
instability of the nervous protoplasm.

The dissimilar effect of an alkaloid upon the different sub-
stances constituting nerve protoplasm gives an idea of the
complexity of the latter. Thus, an alkaloid may stimulate
nerves with certain functions to increased activity, and may
reduce nerves in the same body, having other functions, to
depression and paralysis; e.g. nicotin excites sensory nerves,
and depresses the activity of the cardio-motor nerves.

It is important that many of these alkaloids act also upon
Protozoa and the lowest plants, in which nervous substance is
still undifferentiated. Other of these alkaloids, however, do
not act upon Protista.

We will now proceed to an examination of the action of the
principal vegetable alkaloids, arranged according to the sys-
tematic position of the plants from which they are obtained.

Nicotin. — The effect produced by nicotin is directly pro-
portional to the differentiation of nervous substance ; thus, it
is almost inoperative on Protozoa and Actinia. Hydra is not
very sensitive, 0.5% being a fatal dose. A solution of 0.05%

24 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

causes Medusoe to become quiet in 30 minutes, and is fatal to
the earthworm in a few hours ; Echinoderms are paralyzed by
a 0.05% solution in 30 minutes ; Palsemon (after temporary
stimulation) is paralyzed by a 0.01% solution in 30 minutes ;
Sepiola is killed by 0.005% in less than a minute. (Gkeen-
WOOD, '90.)

Veratrin, Afropin, and Cocaine act upon Vertebrates so as
to excite the central nervous system at first, and then to
paralyze it. All act, however, as poisons upon undifferenti-
ated protoplasm (Protozoa). Thus, Rossbach ('72) found
that when Ciliata were subjected to veratrin chloride and
to atropin sulphate, a peculiar rotary movement took place
about one end as a fixed axis. Then imbibition of water
with great vacuolation of the protoplasm occurred. Later,
the contractile vacuole fails to contract, and protoplasmic
movements cease a few seconds after. (Cf. Kuhne, '64,
pp. 47, 65, 100.)

Cocaine is apparently a benzol derivative, closely related,
chemically, to atropin. Its formula is thus given: —

/ I ".
H,C CH„ CH,

I I I^CO . CeH,.

N CHO^H,

C-COO.CH3

Its action upon Protista has been studied by Charpentier
('85), Adduco ('90), ScHtJRMAYER ('90, pp. 438-448), Al-
BERTONi ('91, p. 318), Danilewski ('92), and Massart
('93, p. 66); upon sexual cells, by O. and R. Hertv^ig ('87,
p. 159) and Albbrtoni ('91, p. 309); and upon tissue cells
by Albertoni. The result has been to show that cocaine
first stimulates for a very short time to excessive activity, and
then stupefies and paralyzes. With the paralysis, a strong
vacuolation of the protoplasm occurs, since the excretory func-
tion of the contractile vacuole is inhibited (Schurmayer, '90,
p. 439). Cocaine acts similarly upon the nerve centres and
muscles of the more differentiated animals.

§ 1] MODIFICATION OF VITAL ACTIONS 25

MorpJiin acts less violently upon the nervous tissue of Ver-
tebrates. It has a very weak action upon Protista.

Strychnin^ chemically considered, is an alkaloid with the
formula: €211^22^2^2' specific gravity, 1.359 at 18°; soluble
to about 0.025% in water at 14.5°; has a very bitter taste.
The nitrate is generally employed. The action of strychnin
upon Protista is known through the studies of Max Schultze
('63, p. 32), BiNZ ('67, pp. 384-389), Rossbach (72, pp.
52-54), and Schuemaybr ('90, pp. 423-433). Keukenberg
('80) has studied its effects upon higher Invertebrates. Its
action upon sexual cells has been studied by the brothers
Heetwig ('87, pp. 153-156, 164) «

Although not fatal to bacteria and only in strong solutions
fatal to the large fungi, strychnin is a nearly universal proto-
plasmic poison. It kills the protoplasm of the Drosera ten-
tacles and hinders the development of peas, corn, and lupines.
The amount of strychnin that Protozoa can withstand has been
variously stated, while all authors admit considerable individ-
ual variation in this respect. Probably Protozoa cannot ordi-
narily resist a saturated solution for one minute. Rossbach
('72, p. 52) found that no infusorian of his cultures survived
a "0.1% solution" long enough to be placed under the mi-
croscope. A 0.02% or 0.01% solution can be withstood for
a few minutes (0.01% solution was withstood for 5 minutes,
Schuemayer). As for the weakest solution that will kill,
ScHUEMAYEE found that a Paramecium resisted for only 15
to 20 minutes so weak a solution as 0.0005%, Avhile Rossbach
found Stylonychia little affected by a 0.0055% solution. The
spermatozoa of Echinoids, according to the Hertwigs ('87,
p. 164), so resist a 0.01% solution that after 180 minutes the
movement is only somewhat retarded. Echinoid eggs are in-
jured in a few minutes by 0.005%.

The injurious action of strychnin on Protozoa varies in the
different groups, the resistance capacity increasing, in general,
with the height of systematic position of the group. The
first effect in Ciliata is an increased activity of the cilia ; if
cirri are present, these strike more powerfully; locomotion is
abnormally rapid ; but the movements lack coordination, and
a rotation takes place about the axis of progression. Next,

26 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

the movements become so disorganized that locomotion is im-
possible, despite accelerated cilia-motion. Finally, the move-
ments suddenly cease, death intervening. (Schurmayer, '90,
pp. 423-426.) The process of excretion seems to be especially
affected. Immediately after the addition of a 0.02% solution,
the contractile vesicle increases to from 4 to 10 times its normal
diameter, and loses its spheroidal form. In a slightly greater
dilution, 0.014%, the contractile vesicle momentarily constricts,
but in diastole gains twice its normal diameter, and the time
between phases of contraction is greatly increased. Thus, the
normal rate of contraction for Euplotes at 15° C. is between
30 and 35 seconds ; but in a 0.014% solution of strychnin
this is diminished to 1 in 500 seconds. Frequently, several
vacuoles are formed, and, eventually, the whole body becomes
greatly vacuolated, and death intervenes. (Rossbach, '72,
pp. 52, 53.) Many higher organisms are not very sensitive
to strychnin. Thus, Ascaridse have a considerable resistance,
which Schroder ('85, p. 307) ascribes to their not opening
their mouths in the solution, the poison being thus obliged
to pass through the skin. So, too, snails were found by
Krukenberg ('80, p. 100) to be very resistant to strychnin.

Curare^ or urare, is an alkaloid, derived from Strichnos
species. The commercial substance is very variable in com-
position. NiKOLSKi and Dogiel ('90) have studied the effects
of this drug upon various organisms. Upon adding a few
drops of a 0.8% solution of curare to water containing an
amoeba, the first effect is a shrinking towards a spherical form
and a cessation of all movements. Subsequent washing in
water ultimately restores the normal movements. As is well
known, it paralyzes also the protoplasm of the nerve endings.

Quinine^ or chinin (C2QH24N2O2). — The "sulphate," which
is first produced in the process of extraction, is commonly
employed. This is, moreover, more soluble than the pure
alkaloid, 1 part dissolving at 9.5° in 788 parts of water. In-
vestigations on the action of this poison upon protoplasm have
been made especially by Binz in a series of papers beginning
with '67; by Rossbach ('72) on Protozoa; by teist Bosch
('80) on leucocytes; by O. and R. Hertwig ('87) on sexual
cells; and by Krukenberg ('80) on higher Invertebrata.

§ 2] ACCLIMATIZATION TO CHEMICAL AGENTS 27

Amoeba, Actinophrys, and various Infusoria are killed by a
0.1% solution in a few minutes, and leucocytes and eggs of
Echinoids are paralyzed even by a 0.005% solution. Its action
is thus more powerful than that of strychnin. The proto-
plasm at first contracts, then gradually dissolves and streams
away. Upon the higher animals, quinine so acts as to paralyze
the central nervous tissue (in Mollusca, Krukeisiberg, '80,
p. 10), and it affects the cerebrum and heart ganglia of
mammals.

Antipi/rin, or phenyldimethylpyrazolon, is an alkaloid de-
rived from and belonging clearly to the benzol type, in which
one atom of H is replaced by a complex atom-group, as may be
seen from the formula —

/CH\ HC == C - CH,

I I 0C\ /N-CH3

The effect of this agent upon Protozoa has been studied by
ScHURMAYER ('90, pp. 434-437) and Massart ('93, p. 64).
A solution of 0.1% acting for 80 minutes, caused Oxytricha
at first to move more rapidly, but eventually to become
transformed into a shapeless mass, whose protoplasm disinte-
grates. Acting upon Noctiluca, a 0.25% solution causes a
bright glimmer immediately after applying, followed by dark-
ness again. Thus there is here a momentary hyperesthesia.

§ 2. Acclimatization to Chemical Agents

It is clear that the protoplasm of different organisms is dis-
similar. We see this in the different reactions to the same
chemical agent. Not only is the reaction of the various spe-
cies unlike, but individuals of the same species from different
localities differ widely. (Cf. LoEW, '85.)

We are, naturally, most familiar with this phenomenon in
the case of man. Thus, the common North American poison
ivy (Rhus toxicodendron) produces, in some persons, extensive
inflammation in parts which have come even indirectly in con-

28 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

tact with it ; while, by other persons, it may be taken into the
mouth with impunity.

The phenomenon shown by man is found in other animals
also. Thus, among Invertebrates, although few bacteria can
resist 1% NagCOg, and even the extremely resistant Ascaris
lives only 5 to 6 hours in a 5.8% solution of this salt, Loew
('77, p. 137) has found in Owen's Lake, California (an alkaline
water containing among other things 2.5% NagCOg), numerous
living Infusoria, Copepoda, larvse of Ephydra, and molds.
Again, the vinegar eel, Rhabditis aceti, lives in a 4% solution
of acetic acid, although this strength is usually fatal ; e.g. <k
0.23% solution of acetic acid kills the tentacles of Drosera.
(Darwin, '75, p. 191.)

What is true of the whole organism is true also of its parts.
The gland cells of some marine Gasteropoda (Dolium, Cassis,
Tritonium, Natica heros) secrete HgSO^ of a strength (2% to
3%) which is fatal to most protoplasm; the myriapod Fontaria
excretes, when irritated, the extremely poisonous CHN; and,
according to LoEW ('87, p. 438), the plant Oxalis produces
potassic oxalate, which is a violent poison to most protoplasm.

One general law of high resistance is worthy of notice: an
organism which produces an albuminoid poison is strongly
resistant to that poison. Thus, Fayrer ('74) has shown that
venomous serpents are not destroyed by the secretion of their
poison glands when it is injected into them ; and Bourne
('87) has shown that scorpions are not injured by their own
venom.

An explanation of the facts of varied resistance capacity is
first gained through experiment. We all know that, among
men, a high resistance capacity to a poison may be acquired by
taking a small quantity of it at frequent intervals. Thus,
users of tobacco, alcohol, and various alkaloids become, in time,
capable of taking, without apparent injury, quantities which
would at first have proved fatal. Arsenic eaters may eventu-
ally swallow without injury four times the ordinarily lethal
dose, i.e. as much as 0.4 gramme. (BiNZ and Schulz, '79.)

Results similar to those observed in man have been obtained
by experiment upon other animals. Thus, Sewall ('87)
inoculated a pigeon hypodermically with sub-lethal doses of

§^]

ACCLIMATIZATION TO CHEMICAL AGENTS

29

rattlesnake poison (Crotalopliorus tergeminus). While no
unacclimatized pigeon could resist 1 drop of a 6.8% solution of
venom in glycerine, pigeons inoculated with at first weak, then
gradually increasing solutions, came at last (after 178 days) to
resist 4 drops of the glycerine venom mixture. Likewise Kan-
THACK ('92) succeeded in acclimatizing two rabbits and a hen
to serpent's venom.

Very similar are the experiments of Ehrltch ('91). This
investigator fed white mice (which are killed by i^\ of their
weight of a 0.0005% solution of ricin, hypodermically in-
jected) upon food cakes soaked in a weak solution of the poison.
After feeding them for a varying length of time upon constantly
increasing solutions, he determined the maximum solution
which, hypodermically injected, they would withstand. If we
call the maximum solution which the unacclimatized organism
will withstand our unit of immunity, we can express the degree
of immunity of the acclimatized organisms by the strength of
solution (expressed in terms of that unit) which they can resist.

The following table, taken from Ehelich's paper, shows
the gradual increase of immunity as a result of feeding on the
poison : —

TABLE IV

No. or Experiment
Day.

Strength of
Last Dose given,

IN MG.

Number op Indi-
viduals EXPERI-
MENTED ON.

Maximum In-
jected Solution

BORNE, %'s.

Degree ok

LmM UNITY.

IV

V

VI

VII

VIII

X

XII

XV

XVIII

XXI

4

5
6

(

8
12
20
50

80

80

8

16
23

5

18
9
3
1
4
1

j Die in
1 0.0005
0.0007
0.0066
0.005
0.01
0.02
0.033
0.05
0.1
0.2

1

1.3

13.3

10

20

40

66.6
100
200
400

Thus after the first 4 or 5 days the immunity rapidly in-

creased ; so that, while the solution of

2 0 0 0 0 0

kills normal

30 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

mice, those acclimatized during 21 days resist yoVo *° "soo"'
occasionally 2io' corresponding to a grade of immunity of 200
to 800.

By fundamentally similar procedures Calmette ('94) has
rendered rabbits immune to the action of strong doses of the
venom of Naja tripudians (cobra) and of Pelias berus.

Still more recently Makmier ('95) has isolated a toxin
produced by anthrax bacteria reared in a peptone-glycerine
solution. Inoculated into an animal sensitive to anthrax,
this toxin produces, in certain doses, death by cachexy. By
employing suitably graduated doses, however, one can obtain
immunity of the organism to anthrax, as one does to the venom
of serpents.

Some attempts to produce acclimatization in lower organisms
have been made by Dr. H. V. Neal and myself. Stentor was
employed as the object of experimentation. We reared two
lots of Stentors under similar conditions except that Lot 1 was
cultivated in water and Lot 2 in 0.00005% HgCl2. After the
lapse of two days both were put into a killing solution of
0.001% HgClg, and the second lot was found to survive longer
than the first. The mean resistance period to the killing solu-
tion of the lot reared in water was 83 seconds ; of that reared
in 0.00005% corrosive sublimate, 304 seconds. Similar results
were obtained in other experiments. In Fig. 1 a curve is
given showing the relation between strength of culture solu-
tion and period of resistance. From this curve, based upon
182 determinations, it appears that the resistance period varies
directly with the strength of the solution in which the protoplasm
has been cultivated.

This law holds good, however, only within certain limits.
If the culture solution is too strong, above 0.0001%, the
organism will be weakened by it so that it cannot resist the
killing solution so long as those reared in water can.

A similar effect of heightened resistance to quinine is ob-
tained by cultivating organisms in quinine.

Experiment shows that a slight increase of the resistance
period follows subjection to the culture for one hour only; and
that the degree of acclimatization varies directly as the time
of subjection.

§2]

ACCLIMATIZATION TO CHEMICAL AGENTS

31

The facts obtained by us clearly indicated, then, that, without
selection, — for no deaths occurred in our culture solutions, —
the protoplasm may become modified merely by subjection to the
poison, so as to gain an increased resistance to it. Hence
the acclimatizations that we find in nature need not have
been brought about by natural selection — must have occurred,
indeed, even without selection, if the organisms had been
gradually subjected to their environment.

gOsECS.

80

GO

50

10 SECS.

Fig. 1.-

STRENQTH OF CULTURE SOLUTIONS

-Curve of resistance periods to a 0.00125% solution of HgCU of Steutors
reared in various solutions of HsrClo during 20 to 96 hours.

We did not determine for how long a time the acclimatized
Protozoa retained their heightened resistance capacity. The
only data we have upon the subject of persistence of acclima-
tization is derived from studies on Vertebrates.

Thus it is the familiar experience of arsenic eaters that, after
they have broken off their habit, the body does not quickly
return to a normal condition. Even after a considerable period
of self-denial the taking of large doses may be recommenced —
must be recommenced, indeed, or illness sets in.

Ehrlich ('91) has studied experimentally the phenomenon

32 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

of acclimatization to ricin. Mice which had gained an immu-
nity of over 200, and were then kept for 6.5 months on normal
food, had still a resistance, although not precisely determined,
certainly far above 50.

It is an important question : Is an organism acclimated to
one poison thereby rendered more resistant to poisons in gen-
eral, or only to the specific poison to which it has been accli-
mated? Ehelich found that mice acclimated to ricin were
just as sensitive to abrin as the normal animals, and the same
is true, mutatis mutandis^ for mice which resist abrin.

Concerning the changes in the protoplasm brought about by
acclimatization little is known.

Ehrlich ('91) and Calmette ('94) have shown that in the
blood of the immunized animal a substance, antitoxic to the
specific substance employed, is produced, and this apparently
prevents the action of the strong poison by transforming its
molecules. The antitoxic substance is of such a nature that
when blood containing it (from an acclimatized animal) is
injected into an unacclimatized one, the latter becomes immune
to the poison.

For Protista another hypothesis is admissible ; namely, that
the weak solution of the poison, which is used in acclimatiza-
tion, gradually destroys those compounds upon which the
strong solution would have acted suddenly and, therefore,
fatally. The gradual destruction is not fatal because of its
slowness. At the same time it prevents the violent action of
the strong poison, since it leaves it nothing to be acted upon.

The parallelism between the results of experiments upon
acclimatization to poisons and those upon immunization through
vaccination, leads to the suspicion that, at bottom, the two
processes are closely akin.

§ 3. Chemotaxis

Engblmann ('81) seems to have been the first to show that
the direction of locomotion of simple protoplasmic masses is de-
terminable by chemical agents in the environment. He found
that Bacterium termo is thus acted upon by oxygen which is
not uniformly distributed. Like many Infusoria, these bacteria

§ 3] CHEMOTAXIS 33

gather at the margin of the cover-glass, where oxygen is more
abundant than elsewhere. If oxidized blood is introduced
under the cover-glass, they move toward it, but not toward
blood containing much COg in place of oxygen. If green
alsrae are introduced, the bacteria move towards them so long-
as they, under the influence of sunlight, are producing oxygen.
In the dark the algse have no effect.

During the decade and a half which have elapsed since Ex-
gelmann's first paper appeared, chemotactic phenomena have
been observed among nearly all kinds of motile organisms and
with reference to the most diverse kinds of chemical substances.
Engelmann ('82) has studied the chemotactic movements of
diatoms ; Stahl ('84), of Myxomycetes ; Pfeffer ('84, '88),
of plant spermatozoids, zoospores, Flagellata, Infusoria, and
bacteria ; Aderhold ('88), of Euglena viridis ; Verwoex
('89, p. 107), of Cryptomonas ; Staxge ('90), of zoospores and
Myxomycetes ; and Massart ('91), of Spirillum, Heteromita,
and Ciliata.

Within the last five years a voluminous literature has grown
up on the medical side relating to chemotaxis in leucocytes and
pathogenic bacteria. Into this literature we cannot penetrate
deeply, but refer to some of the principal papers : Leber, '88 ;
BucHNER, '91 ; RoEMER, '92 ; Metschnikoff, '92.

It thus appears that chemotactic phenomena show themselves
among all the groups of lower motile organisms : Rhizopoda
(Myxomycetes), Flagellata, Ciliata, bacteria, diatoms, zo-
ospores, and spermatozooids. It can hardly be questioned that
the phenomena shown by these organisms are of the same order
as those seen in Metazoa — in those ants which Lubbock ('84,
p. 233) has shown to move from chemical agents (essence of
cloves, lavender water, and other scented stuffs), saturating a
camel's-hair brush placed about |- inch above their path ; and
in the larvas of flies with which Loeb ("90, p. 79) has experi-
mented. Loeb found that these crept towards a piece of flesh
brought nearer to them than the distance of 1.5 cm. Even just
hatched larviB (which had therefore never been stimulated by
meat) reacted in this way. Not meat only, but a trace of meat
juice on glass attracted the larvce strongly. While decaying flesh
and cheese allure, neither fat, asafcetida, nor ammonia do so.

34 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

Returning now to the simple organisms, let ns consider the
kinds of chemical substances which incite to a response.

Oxygen is for almost all organisms a means of attraction.
Various methods of demonstrating this have been used. Thus
Stange ('90, p. 139) filled capillary tubes with pure oxygen,
under an air-pump, and brought them to the water containing
zoospores, which then penetrated into them.

The aggregation of zoospores and bacteria to the edges of
the cover-glass, to the open end of a capillary tube (Aderhold,

Air bubble

;;.• " ^ . Zone of Spirillum, y .-v

;• '-^ lone of Anophrys . . '^A *

CC. '•'v.-:v::,,:,.;.,.::P>^"

Fig. 2. — a. Corner of the glass slip covering a drop of liquid containing Spirillum
and Anophrys, showing their aggregation with reference to the aerated hound-
ing film of the drop. h. An air-bubble in the drop, showing aggregation of the
organisms about it. (From Massart, '91.)

'88, p. 314), or to an enclosed air-bubble, are well-known phe-
nomena. (Cf. Massart, '91, p. 159 ; Verworn, '89, p. 107 ;
and see Fig. 2.)

EiSTGELMANN ('94) has employed a still more refined method
of studying attraction towards oxygen. A drop of foul water
is put on a glass slide with an alga cell in the centre, and is
covered by a cover-glass whose edges are hermetically sealed
by vaseline. The bacteria are uniformly distributed in the
water, moving in a lively manner, since they gain oxygen
everywhere. If the slide thus prepared is kept in the dark,
the oxygen is gradually consumed and the bacteria become
quiescent, showing no distribution with reference to the cen-
tral chlorophyllaceous body (Fig. 3).

If the slide is now exposed to the light, oxygen is produced
by the alga and a regular distribution of the bacteria in two
distinct regions — in a mass around the central alga, and in a

§ 3] CHEMOTAXIS 35

peripheral zone — is apparent (Fig. 4). The peripheral zone
contains bacteria which are beyond the tactic action of the
oxygen. The central mass of bacteria have emigrated from
what is now a clear ring between the centre and the peripheral
zone. If the light be temporarily cut off, the central bacteria

:ji^*;

O * 0 ft • * * " • * " .

3

y • ,

■ ' • '! . •* o 7 *• ' -o'"' : . '. .

=•.*';'•*"!

•Jf..:'' «•"•;•-• s . .•■5:. •1>^;.

5 5a

Figs. 3-5 a. — Bacteria surrounding an algal cell. Fig. 2 shows the uniform distribu-
tion of the bacteria when the drop of water is kept in the dark. Fig. 3 shows the
aggregation of the bacteria towards the algal cell when this has emitted oxygen
rapidly in the strong light for two minutes. Fig. 4 shows the same preparation
shortly after the light has been cut off. Fig. 5 shows the same preparation when
a fainter light is now permitted to fall upon the green cell. Magnified about 170
diameters. (From Engelmann, '94.)

begin to disperse (Fig. 5). If, a minute after, a dim light be
let through, the radius of its activity will be relatively small, so
that a central aggregation will be found and also an inner
peripheral zone, comprising those dispersing central bacteria
which are not aifected by the small oxygen tension resulting
from the dim light (Fig. 5a).

36 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

Inorganic Salts. — Pfeffer* ('88, p. 601) tried various salts
of potassium; viz. chloride, phosphates, nitrate, sulphate, car-
bonates, chlorate, ferrocyanide, and tartrate, and found that
all attracted various bacteria (B. termo. Spirillum undula),
and the flagellate Bodo saltans with greater or less strength,
when the solution in the capillary tube contained 0.1% K. So,
likewise, various salts of sodium, rubidium, csesium, lithium,
ammonium, calcium, strontium, barium, magnesium, especially
the chlorides, were employed. All of these solutions at a
concentration of 0.5% exhibited a marked attractive influ-
ence upon Bacterium termo ; a weaker one, upon the two
other species.

Stange ('90) experimented with the action of various phos-
phates upon zoospores of a Saprolegnia belonging to the ferax
group of De BARY.f Sodic, ammonic, lithic phosphate, calcic
phosphate held in solution by COg, as well as phosphoric acid
were employed and found to act attractively. Other salts,
KNO3, K2SO4, KCl, HKCO3, BaClOg, SrCOg, MgSO^, had
either a negative or indifferent action upon the zoospores.

The attractive action of the phosphates is correlated with
the fact that phosphates are abundant in the muscles of insects.
The following table shows the effect of the different strengths
of solutions of four phosphates upon zoospores of Saprolegnia.
In this table, constructed from Stange, the symbol r indicates
repulsion ; 0, no action ; a, attraction ; a^ indicates a slight
attraction ; a^, a strong attraction ; a^r^, an attraction which
is partly balanced by a repulsion due to density, so that the

* The method employed by Ppeffer in his experiments was as follows :
Glass capillary tubes with a lumen of from 0.03 to 0.14 mm. diameter and a
length of 7 to 12 mm., and sealed by fusion at one end were employed. To fill
the capillary tube, it was placed in a watch-glass containing the experiment solu-
tion, and the whole was placed in a vessel from which air was pumped. Under
the diminished atmospheric pressure, 2 to 4 mm. of fluid entered the capillary
tube ; the rest of the tube contained air, which kept the fluid oxidized. After
rinsing, the free end of the tube was plunged into the drop culture, whence the
solution diffused out.

t The species were cultivated upon carcasses of flies thrown into glasses filled
with bog water. After good colonies were obtained, the carcasses were washed,
to rid of Infusoria. Such colonies may be employed to infect sterilized flies'
legs placed in sterilized bog water, or they may be transferred directly to wounds
in flies' legs.

§3]

CHEMOTAXIS

37

organisms pass only into the first part of the tube ; a^r^^ such
a balancing of the opposing forces that the organisms stand
before the mouth of the capillary tube.

Strength of Solution,

SoDio Diphos-
phate

Potassic Mono-
phosphate

Ammonium Phos-
phate

Phosphoric

Acid

(IINaaPOi).

(H2KPO4).

(H,NH4P04?).

(H3PO4).

0.8 to 0.4 ... .

«3'-2

a^To

«.3'-3

r

0.4 to 0.08 . . .

«2''l

rt,?-,

0.08 to 0.04 . . .

^2

a.y

a^

a^r.

0.01 to 0.02 . . .

0

^'1

«i

«i''i

0.02 to 0.008 . . .

0

0

0,

0.008 to 0.004 . . .

'"'i

0.004 to 0.002 . . .

0

It will be noticed that the various substances produce dif-
ferent effects in the same strength of solution ; and it is
interesting to observe (a point to which further reference will
be made) that the strength of solution required to produce a
given response is roughly proportional to the molecular weight
of the substance employed.

Inorganic acids and hydrides seem, in general, to act repul-
sively, but phosphoric acid is an important exception to this
rule. Dewitz ('85, pp. 222, 223) states that mammalian
spermatozoa are attracted by KHO.

Organic Compounds. — Alcohol^ in grades between 10% and 1%,
acts repulsively towards bacteria. Crlycerine is neutral to the
same organisms and to zoospores of Saprolegnia. (Stange, '90.)
The sugars, etc., dextrose, milk sugar, dextrin, act attractively
upon Bacterium termo in 10% or weaker solutions. Many or-
ganic acids are among the most attractive reagents. It was with
malic acid that Pfeffee, ('81) tried his earlier fundamental
experiments upon the spermatozoids of ferns. The attraction
exerted is very great, so that a capillary tube of 0.1 to 0.11 mm.
calibre, containing a 0.05% solution of malic acid, attracts
from a drop of water full of spermatozoids at the rate of 100
individuals in one hour. Even a 0.001% solution acts chemo-
tactically. Now, malic acid is of very wide distribution among
plants, and it occurs in the fern prothalli upon which the sexual

38 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

organs arise, so that it seems probable that it occurs in the
mouth of the archigonium, and that by its presence sperma-
tozoids are attracted towards the egg cell.

Stange ('90, p. 155) has experimented much more fully
with the action of organic acids upon zoospores of Saprolegnia
and upon myxamoebye. To the former, acetic acid (0.01%) and
tartaric acid (0.0125%) act attractively. Upon the latter, still
other acids were tried ; butyric, lactic, and valeric acids cause
response in concentrations between 0.2% and 4% ; malic acid,
between 0.5% and 4%. Other attracting acids are : propionic,
citric, tartaric, and tannic. Acetic acid repels the amoebse of
^thalium, its repellent action being about equal to the attrac-
tive action of an equal amount of butyric acid.

Nitrogenous Oompounds. — Urea, asparagin, kreatin, taurin,
hypozanthin, carnin, and peptone have been found by Pfeffek,
('88) to exert an attractive influence, especially in the case of
the reagents italicized.

Benzol Derivatives. — Pfeffer found that sodium salicylicate
and (commercial) sulphate of morphine are clearly attractive to
Bacterium termo in 1% solutions.

From the foregoing list of organic compounds whose effect
upon Protista has been tested by Pfeffer and Stange, it
appears that except alcohol and sometimes acetic acid, none
acts repulsively, and that glycerine alone is neutral to all proto-
plasm. It is further true that we do not find here any strict
relation between the chemotactic action of a substance and its
advantage to the organism. Substances which have a nutri-
tive value for the organism, such as glycerine has for bacteria,
may be wholly neutral, while solutions which act fatally, like
1% sodic salicylicate and 1% morphine, attract. In the same
way, many of the organic salts which act attractively cannot
be considered as of importance to the organism. On the other
hand, as already pointed out, the attraction of most Protista to
oxygen, of Saprolegnia zoospores to phosphates, as well as the
cases of attraction of bacteria (Pfeffer, '88, p. 605) and of fly
larvse (Loeb, '90, p. 79) to meat extract, and of Myxomycetes
to bark extract (Stahl, '84 ; Stange, '90), is advantageous.
Chemotaxis is, therefore, in some cases, a response to the
stimulus afforded by substances which can be employed by

§ 3] CHEMOTAXIS 39

the organism as food ; under which circumstances it can be
called " Trophotaxis." * In other cases it is a response to
chemical substances which have no significance as food, and
have no other importance for the organism.

It is clear that we cannot assume that response to injurious
substances is an adaptation which has been brought about by
natural selection. If a response occurs in one case independent
of the action of selection, we should hesitate to ascribe to this
cause the origin of other, even favorable, responses.

G-eneral Remarks on the Relation between Molecular Comjyosi-
tion and Response. — Pfeffek, ('88, pp. 608-612) has pointed
out that the capacity of any substance to stimulate cannot be
inferred from its chemical constitution and relationships. Thus,
the minimum concentration of milk sugar which will produce
a response is 1 % , while in the case of the closely allied grape
sugar it is 10% ; but in the very different kreatin it is also 1%.
Also, the action of any chemical compound is determined not
by the elements, such as C, H, O, which it contains, but by the
entire molecule ; in other words, the atomic composition is less
important than the structure of the molecule or the arrange-
ment of its atoms. Thus, malic acid and its compounds with
neutral ammonium, sodium, barium, and calcium containing
0.001% parts of the acid, have an equal action upon the sperma-
tozoids of ferns, which do not react to the diethylester of
malic acid, even in strong solutions. (Pfeffee, '88, p. 655.)
Again, nitrogenous organic compounds are, in general, more
active than the non-nitrogenous ones ; but this cannot be held
to be due alone to the presence of N ; for dextrin (CgHjoOg)
is nearly as active as the nitrogenous peptone, and, on the other
hand, the nitrates of metals are not more active than their
chlorides, while the ammonia salts are relatively weak.

Relation hetiueen the Strength of the /Stimulus and that of the
Ret^punse. — When we say that malic acid attracts sperma-
tozoids we mean that under certain physical conditions of
the water which we may call normal it does so. And under
normal conditions of the water, it is only within certain limits

* Rtatil ('84, p. 104) called the attraction of Plasmodium of myxomycetes to
bark extract " Trophotropism."

40 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

that malic acid attracts. The strengths of solutions which
attract under such conditions lie between 0.001% and 10%.
The weaker solution may be designated the minimum ; the
stronger, the maximum concentration which provokes a re-
sponse. The minimum solution provoking response is also
often called by the Germans the " Reizschwelle," or "stimula-
tion threshold " ; * the optimum, the " Reizhohe," or " stimu-
lation acme"; the range, the " Reizumf ang. "

The character of the responses observable at the two limits
is very different ; at the minimum, attraction is very feeble ;
thus, while a capillary tube containing 0.01% neutral sodic
malate, plunged into water at 14°-20° C, swarming with
spermatozoids, attracts 400 of them in 10 minutes, a 0.001%
solution attracts only 10-25 individuals during the same time,
and a 0.0008% exerts little attractive effect, the spermatozoids
remaining undirected in their movements. At the maximum,
on the contrary, repulsion is observed. The spermatozoids
move from the mouth of the capillary tube. Between the
two extremes lies the concentration of greatest attraction —
the acme. As we pass from the acme towards the minimum,
the attraction becomes less and less. As we pass towards the
maximum, the attraction remains the same, or increases ; but
repelling influences are now at work, which eventually entirely
counteract the attractive influences.

A satisfactory method of expressing quantitatively the facts
just mentioned has not been invented. Pfeffer ('88, p. 599)
has employed the nomenclature which we have used above
(p. 36) — a^ to (Xg being combined with r^ to r^ to indicate
the coworking in varying proportions of attraction and repul-
sion. Using this nomenclature, we may illustrate the state-
ments made in the last paragraph with examples taken from
Pfeffer's work: —

* The following substances at the solutions named produce the threshold
attraction (ai) in Bodo saltans: KCl, 0.02%; K3PO4, 0.002%; KH2PO4,
0.0035%; KNO3, 0.26%; K2SO4, 0.22%; KCIO3, 0.3%; Iv4(CN)6Fe, 0.235%;
K2-C4H406, 0.02%; RbCl, 0.14%; LiCl, 0.6%; LiNOs, 3%; NH4C], 0.3%;
neutral ammonium phosphate, 0.08%; SrCl2, 0.2%; Sr(N03)2, 0.4%; BaCl2,
0.17%; dextrin, 0.1%; urea, 1%; asparagin, 0.1%; taurin, 1%; sarkin,
0.33%; pepton, 0.01%; meat extract, 0.01%.

§3]

CHEMOTAXIS

41

Kespoxse

OF

Bacterium tekjio.

Spikillum.

9.53 % KCl

_

5%K

«3

"3^3

1.906% KCl

=

1%K

«3

Vl

0.191 % KCl

=

0.1 % K

«3

Qg

0.019% KCl

=

0.01 % K

«2

«1

0.0019 % KCl

0.001 % K

1.0 %K

«1

0

BODO SALTANS.

3.48 % KH2PO4

«3''3

0.348% KH2PO4

=

0.1 % K

Ggr,

0.035 % KHoPO,

=

0.01 % K

«2

0.0035% KH2PO4

=

0.001 % K

«1

0.00067 % KH2PO4

=

0.0002 % K

0

Compare also the table on p. 37.

For all reagents which exert an attractive influence there
exists the maximum (repelling) and minimum (indifferent)
limits referred to. In the case of reagents, which, like alco-
hol, repel bacteria at between 1% and 10%, there is doubtless
an indifferent limit, but it is not necessary that there should be
a degree of concentration at which attraction takes place. In
the one case, then, the phenomena of indifference, attraction,
repulsion, follow each other with increasing concentration ; in
the other case, only indifference and repulsion. The difference
in action of the two cases is due, in part at least, to the fact
that all solutions, independently of their chemical constitution,
become repellent when they become concentrated enough.
The repulsion, then, of high grades of chemical solutions is
purely an osmotic phenomenon, and, as such, will come under
discussion in the third chapter. It follows, also, from what has
been said, that, in the case of those reagents which exert no
attraction at any concentration, the acme and maximum coin-
cide and lie at the saturation point of the solution.

Finally, we may discuss the third case in which the reagent
acts indifferently, as glycerine does upon bacteria between 17%
and 0.86%. It is clear, that if the density of the solution can

42

CHEMICAL AGENTS AND PROTOPLASM

[Ch. I

be rendered great enough, a repulsion due to osmosis must
occur. If the substance is, however, only soluble slightly or
miscible, it may be that repulsion will never occur. Whether
or not attraction will occur before the repulsion point is reached
will have to be determined experimentally for each reagent.

Thus the action of an untried substance upon any organism
may be any one of three kinds : (1) It may be indifferent at
all grades ; (2) it may be indifferent at lower and repellent
at higher grades ; (3) it may be indifferent, attractive, and
repellent at successive grades. Of two substances belonging
to the second or third class, one may act upon an organism at
a certain concentration with indifference, the other at the same
concentration with repulsion. Likewise the same solution of a
substance may attract one kind of protoplasm and repel another,
under otherwise similar conditions.

We have seen above that the same reagent acts upon the
same kind of protoplasm similarly only when the other con-
ditions of the experiment are also the same. Among the
varying conditions which have been especially investigated is
that of the chemical constitution of the medium. The experi-
ment has generally been made as follows : A particular species,
let us say Bacterium termo, is to be subjected to the action of
a particular reagent, e.g. meat extract. The bacteria are reared
in cultures containing a varying quantity of the meat extract,
and the concentration of the capillary fluid producing the
threshold stimulation is measured in each case. We may
compare not only the thresliold stimulations but also the
concentrations necessary to produce the response indicated
by a^y ^2' 6tc. The following table, from Pfeffee ('88,
p. 634), gives some of such determinations: —

Culture Fluid —

Capillary Fluid — Meat Extract.

Meat Extract.

3 X cult. cone.

5 X cult. cone.

8 X cult. cone.

10 X cult. cone.

0.01 %
0.1 %

1%

0.03% (?)

0.3%(?)

3%(?)

0.05% («0

0.5%(ai)

5%(«i)

0.08% (a,)

0.8% (a,)

8%(«2)

0.1% (a^)

1 % («2)

10% (a^)

§ 3] CHEMOTAXIS 43

From this table it appears that tlie strength of solution
necessary to provoke a certain response depends upon the
strength of solution to which the protoplasm has been pre-
viously subjected and increases proportionately with it. It is
clear that the capillary solution of 0.1%, which produces a
marked chemotaxis in bacteria reared in a culture solution of
0.01%, would awaken no response in bacteria reared in 0.1%.

We are now in a position to appreciate the importance of
still another addition to our terminology of stimuli — the dif-
ferential threshold stimulation (Reizunterscheidsschwelle) —
which ma}' be defined as the minimum increase of a preexisting
stimulus which is capable of calling forth a just noticeable
reaction. In the case just cited, the differential threshold
stimulation lies just above 3. times the preexisting (culture)
stimulus, and this is true whatever the degree of the preexist-
ing stimulus ; and it is shown by experiment that, in general,
as the preexisting stimulus increases, the differential threshold
stimulation increases in the same proportion. This observa-
tion is in perfect accord with the law formulated long ago by
Webek with especial reference to sight. This law runs : The
smallest change in the magnitude of a stimulus which will call
forth a response (differential threshold stimulation) always
bears the same proportion to the whole stimulus. We may
express this law mathematically, as Fechner has done, by the
following considerations : Let us take the case of a protoplas-
mic body, as, for example, that of a spermatozoid, living in a
stimulating medium (s) of a certain concentration and experi-
encing a certain reaction r' ; then s corresponds to r' . In
order just to get a chemotactic response (threshold stimulation),
a solution of say 30 times the concentration must be brought
to the solution affording the stimuhxtion s. This will give a
reaction which is greater than r' by a quantity which we may
designate r, so that the quantity of the whole reaction may be
designated as r' + r. If the organisms are now placed in this
stronger solution (31 ,s), the solution in the capillary tube must
be 30 times stronger (30 x 31 s) in order to give the differential
threshold stimulation. The reaction following this stimulation
may be designated, according to Fechner's conception, as
r' -{- r -\- r. The relation of the successive stimuli and the reac-

44 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

tions may be shown by the following table, following one given
by Pfeffer ('84, p. 401) : —

s corresponds to r'.
s-\- 30 s = 31 s corresponds to r'+r.

31 s+ 30x31s= 31 X 31s corresponds to ?-'+7-+?\

31 X 31 s+30 X 31 X 31 s = 31 X 31 X 31 s corresponds to r'+r+r+r.

That is to say, while the stimulation increases geometrically,
the reaction increases arithmetica^3^ In the preceding table
the second term of the left-hand member of the equation is
always the differential threshold stimulation.

The most important objection that can be urged against this
formula of Fechner is that there is not sufficient reason for
believing that the various reactions (r) to the differential
threshold stimulations of various strengths are equal, nor that
the stronger reaction to the strong stimulus is composed of
many weak reactions. If these assumptions were true, it would
follow that when the successively higher stimuli increase as a
series of numbers the reactions increase as the logarithms of
these numbers. If now we adopt as a unit in this phenomenon
the quantity of the threshold stimulation (estimated in units of
concentration of solution, of mass, light intensity, heat inten-
sity, etc.), which we may call s, the strength of any stimulus
{S} may be estimated in those units, and the strength of the
corresponding reaction (.R) will be indicated by the equation
R = c ' log S, in which c is a constant to be determined empiri-
cally, and S the strength of the stimulus expressed in units of
the threshold stimulation.*

While we are not yet in a position to understand the signifi-
cance of Weber's law, we cannot fail to be struck with the
resemblance of the phenomena with which it concerns itself to
those of acclimatization referred to in the second section of
this chapter. We there showed that organisms subjected for a
while to a chemical agent no longer reacted as at first to that
reagent. We have here shown that organisms subjected for

* Since the German word for stimulus is Beiz (initial i?), and since the re-
action is usually indicated by the initial letter in Empfindung^ in German text-
books this formula usually runs E = c ■ log B, which differs from the above
equation only in the symbols employed.

SUMMAEY OF THE CHAPTER 45

a while to the action of a certain stimulating agent respond no
longer to a concentration which would at first have provoked
a reaction. In both cases it is the action of the chemical agent
which modifies the subsequent action of the protoplasm, without
doubt by changing the chemical constitution of the protoplasm.

Mechanics of Response. — Having considered the general
relation between strength of stimulus and of reaction, it now
becomes necessary to examine more in detail into the way in
which the reaction takes place.

A variety of kinds of locomotion exists among chemotactic
organisms — that of the Myxomycetes is amoeboid, that of
Infusoria is by flagella or cilia. In all cases the first and
perhaps the only effect of the acting reagent is to determine
the position of the axis of the body, in the case of bodies with
fixed form ; or to determine the pole of outflow in the case of
amoeboid organisms. The axis lies in the line of flow of the
diffusing solution or perpendicular to the isotonic lines, or lines
of equal concentration. Whatever movement now occurs must
be either towards or from the source of stimulus.

I have said above that the axis orientation is perhaps the
only effect of the acting reagent. Pfeffer ('84, j). 463 ; '88,
p. 631), indeed, maintains that the stimulus does not directly
cause a markedly more rapid locomotion in the case of bacteria
and Flagellata ; but in the case of plasmodia it seems possible
that such a hastening of movements occurs. (Stahl, '84.)
However, it is necessary that measurements should be made in
this matter. Further observations on the mechanics of taxis
must be deferred to the general treatment of the subject in
Chapter IX.

Summary of the Chapter

We attempted in the first section to bring together observa-
tions relating to the action of various chemical substances upon
protoplasm with the aims of discovering the general laws of
poison-action on protoplasm and of gaining an insight into the
chemical structure of protoplasm and the chemical operations
involved in the elementary vital processes. We ought now,
therefore, to attempt to draw such conclusions as the imperfect
and often confusing data we have collected will permit.

46 CHEMICAL AGENTS AND PROTOPLASM [Ch. 1

All the reagents with which we have dealt have been sub-
stances capable of absorption by, mixture with, or solution
in, water ; and the reason for this is that almost all proto-
plasm is itself enveloped by water and largely composed of
water.

For the most part we have dealt with mixtures or solutions.
Now the action of these is a double one. They exhibit, first,
an osmotic action, and, secondly, they may attack the molecules
of the protoplasm, transforming them. The osmotic action we
will consider in the third chapter ; the transforming one alone
concerns us now. It is not easy, without experiment, to say
to which of these two categories of action the change wrought
by any substance is due. To determine between the two
possible causes it would be desirable in each case to treat the
protoplasm to a control solution having the same osmotic action
as the first, but no transforming effect. If such a solution
produces no modification of the protoplasm, then the effect
wrought by the first reagent is due purely to molecular trans-
formations. It is not easy to find a reagent of which we may
be certain that it acts only osmotically. NaCl is probably more
generally useful in this way than any other substance. In the
experiments which have hitherto been made, this double action
of solutions has not been sufficiently considered. Hence, a
doubt concerning the immediate cause hangs about many of
the phenomena described in the first section.

The first principle which the data collected establish is
that the protoplasm of different organisms is dissimilar. This
is shown by the diversity in their chemical reactions ; by the
fact that whereas, in one case, a certain percent solution
causes so extensive a molecular transformation as to result in
death, in another, no injurious effect is produced.

Thus, according to Boer ('90, p. 479), it takes of gold
chloride to kill —

TABLE V

Anthrax bacillus 0.0125%

Cholera spirillum 0.1%

Diphtheria bacillus 0.1%

Typhoid bacillus 0.2%

Glanders bacillus 0.25%

SUMMARY OF THE CHAPTER 47

Thus the weak solution, 0.0125%, of AuClg, which is fatal to
anthrax, does not injure the glanders bacillus, which requires
a solution 20 times as strong ; and we conclude that the chemi-
cal constitution of the glanders bacillus must be different from
that of anthrax.

The dissimilarity of the different protoplasms may be either
a qualitative or a quantitative one. That is to say, the kmds
of molecules, or the pj-oportions of the different molecules, may
differ in the two cases. If we assume that gold chloride acts
upon protoplasm by the Au replacing some of the H in an
amido-acid, then the diversity in action of AuClg upon anthrax
and typhoid may be accounted for by assuming that the amido-
acids are dissimilar in anthrax and tj^phoid or that the propor-
tion of the kinds especially affected is different in the two cases.
To which of these two causes the diverse reactions to AuClg are
due cannot yet, in any given case, be determined.

A second principle which we may draw from our data is this :
Some kinds of protoplasm have a general high resistance to all
chemical agents, while other kinds have a high or low resistance
to particular agents only (^specific high or low resistance).
Thus, in the case of pathogenic bacteria, the experiments of
Boer ('90) show that, in general, the anthrax bacillus has a
low resistance, and glanders a high one. His experiments were
made with 10 reagents upon five kinds of bacteria. Table VII
gives in modified form the results obtained by Boer. His
results are given in the form of Table V; the present table
is constructed from the original by making the mean of the
five observations in each column unity and reducing the sepa-
rate observations proportionately. Thus Table V becomes —

TABLE VI

Anthrax bacillus 0.09

Cholera spirillum 0.75

Diphtheria bacillus 0.75

Typhoid bacillus 1 .51

Glanders bacillus 1.88

All the other determinations have been treated in like manner.
Throughout the table the numbers in each column stand for

48

CHEMICAL AGENTS AND PROTOPLASM

[Ch. I

relative resistance capacity. The reagents are placed with the
weakest-acting first.

TABLE VII

Caustic

Carbolic

Muriatic

Sulphuric

Methyl

Substances.

Soda

Acid

Acid

Acid

Violet.

(NaHO).

(CeHeO).

(HCl).

(H2SO,).

Molecular "Weights.

40

94

37

98

Anthrax bacillus ....

0.46

0.95

0.40

0.37

0.07

Cholera spirillum . . .

1.38

0.71

0.32

0.37

0.33

Diphtheria bacillus . .

0.69

0.95

0.63

0.94

0.17

Typhoid bacillus ....

1.09

1.43

1.46

0.94

2.22

Glanders bacillus ....

1.38

0.95

2.19

2.36

2.22

Silver

Gold

Malachite

Oxtcyanide

Substances.

Nitrate
(AgNOa).

Chloride
(AUCI3).

Green.

OP Hg.

Average.

Molecular Weights.

170

304

Anthrax bacillus ....

0.20

0.09

0.02

0.93

0.388

Cholera spirillum . . .

1.04

0.75

0.17

0.62

0.632

Diphtheria bacillus . .

1.67

0.75

0.11

0.93

0.760

Typhoid bacillus ....

1.04

1.51

1.75

1.25

1.415

Glanders bacillus ....

1.04

1.88

2.92

1.25

1.802

From this table we see that the bacillus of glanders is more
resistant than that of anthrax (except in one instance, in which
the resistance is equal in the two cases) whatsoever be the
poison employed. The bacillus of glanders affords, thus, a
good illustration of an organism with a general high resistance
capacity.

The diversity in general resistance capacity which is found
among bacteria exists also among other organisms. Thus, the
parasitic Ascaris has shown itself highly resistant in all cases
in which the action of a poison on it has been compared with
that on another species; for instance (p. 10) 0.1% chloral
hydrate kills Infusoria, Rotifera, and diatoms in 24 hours, but
Ascaris withstands this solution. Again, while 0.1% HON
kills Infusoria quickly, Ascaris resists 3% for 75 minutes. The
general higher resistance may be due to one of three causes :

SUMMARY OF THE CHAPTER 49

either to the fact that the protoplasm is protected from attack,
as is the case with the encysted forms of Protozoa, which are
very resistant; or to the fact that the protoplasm is not so
readily acted upon by reagents brought actually in contact
with it, due to diminished amount of water or other structural
modifications ; or, finally, that the protoplasm has a different
composition, certain unstable molecules found in other kinds
of protoplasm being absent.

We will now consider the phenomena of diversity in specific
resistance of protoplasm. A case of specific low resistance is
found in the nervous tissue. Thus many of the alkaloids, e.g.
nicotine and cocaine, are almost indifferent to the protoplasm
of Protista, but act towards the nervous system as powerful
poisons. Hence we are led to conclude that nervous protoplasm
contains especially unstable compounds, upon which its action
depends. When they are subjected to the action of very weak
— towards most substances, indifferent — reagents, extensive
and fatal transformations occur.

Cases of specific high resistance are apparently found in some
glands which secrete intense poisons, or in some organisms
which live in solutions of some usually poisonous agent. Ex-
amples of this class are the HCl-secreting glands of the
Vertebrate alimentary tract, the poison-glands of venomous
serpents, and the H2S04-secreting glands of Gasteropoda;
also the vinegar eel, which lives in 4% acetic acid. It ought
to be said that it is largely an inference based upon experi-
ments on acclimatization, that these glands or organisms will
not show a general high resistance. Experiments are needed
to determine this point. As to the cause of specific high resist-
ance, I believe that much light is gained from the facts of
acclimatization, and that any sufficient theory of the latter
would serve also to explain the former (see p. 30).

Under the general poisons we have distinguished four main
groups : a. oxidizing poisons ; b. salt-forming poisons ; c. sub-
stitution poisons ; d. catalytic poisons. I will comment briefly
upon the action of the poisons of each of these groups.

a. Oxidizing Poisons. — The ordinary oxidation processes in
living protoplasm involve the consumption not of the proto-

50 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

plasm itself, but of the thermogenic substances stored therein
(sugar, yolk). After these have been consumed in starvation,
or when the organism is subjected to the action of oxidizing
poisons, the molecules of the protoplasm become oxidized.
All protoplasm which is readily accessible must be injured by
the direct attacks of " active " oxygen.

h. Salt-forming Poisons. — The facility with which an acid
or a base forms salts with the protein substances of the proto-
plasm must depend, in large part, upon the quality of the
protein molecules. It is well known that certain protein sub-
stances, such as keratin, chitin, and fibrin, are not readily acted
on by acids or bases, and it seems necessary to suppose that
some such resistant proteids are the essential parts of glands
which secrete these reagents. Into this group fall the salts of
heavy metals characterized by their extraordinary fatalness.

c. Substitution Poisons. — This group comprises, besides a
few sulphur compounds, almost exclusively nitrogenous sub-
stances, and among these a large proportion of compounds
with closed chains. As many of these are indifferent to dead
albumen, but violent poisons to living protoplasm, it is clear
that the latter must contain certain extremely unstable groups
(amido-, aldehyde-, and keton-groups, LoEW, '80). Among
these poisons the relation between molecular structure and
poisonous action is very marked, especially in the nitro-com-
pounds. Thus, bodies containing H united with N are poison-
ous in direct proportion to the number of H atoms so combined.
It seems probable that H so combined is very easily given up
to the molecules of the living substance, destroying them.
H in the hydroxyl radical seems also more easily parted with
than H joined to C.

d. Catalytic Poisons. — Chiefly organic compounds of the
fat series, which have little chemical energy and produce, for
the most part, anaesthesia. The poisonous action seems here
proportional to the complexity and instability of the compound.
Thus, in many groups, when the alkyls CHg — , C^Hg — , etc.,
are successively introduced, the substance grows more poison-
ous as the number of atoms in the alkyl increases. In the
methan series and among sulphureted compounds the substi-
tution of CI for H increases the poisonous action.

SUMMARY OF THE CHAPTER 51

The study of the action of poisons upon protoplasm gives us
an insight into the extreme complexity of the living substance
— its composition out of numerous kinds of compounds, many
of which are extremely unstable. Not all protoplasm contains
the same compounds, hence it must be a very dissimilar thing
in different organisms. Not all of the compounds in any pro-
toplasmic body are essential to life, for we may act upon a
protoplasmic body by a weak reagent, and gradually change
its composition so that it will no longer be killed by the strong
solution, and all of this without perceptible injury — at least,
this is the conclusion to which the study of acclimatization of
Protista leads us. The altered chemical constitution will be
transmitted in the division of the individual, and thus the
composition of the protoplasm of a race will have been deter-
mined by the medium in which it and its ancestors have been
living.

Finally, we may consider what light the action of reagents
throws upon the processes involved in the elementary vital
functions. The normal movement of protoplasm is profoundly
modified by interfering with the oxygen supply. Thus, when
the oxygen pressure is diminished, movements are retarded ; in
the presence of pure oxygen they are accelerated. Some ances-
thetic or paralyzing agents — e.g. chloroform and some alka-
loids, veratrin, atropin, cocaine, strychnin, and antipja-in — give
rise first to acceleration, then to disappearance of movements
in the protoplasm. Protoplasmic movement is, consequently,
closely associated with oxidation, and it does not occur in the
absence of irritability.

Normal locomotion is interfered with by strychnin and co-
caine. Their stimulating action produces accelerated move-
ments, and these are accompanied by loss of coordination.

Since many catalytic poisons (anaesthetics) destroy irrita-
hility., one may conclude from the action of these chemical
agents that (p. 7) stability of molecular movement is essential
to the performance of this function.

Disturbance of the excretory function results from the action
of CO, NHg, chloroform, cocaine, strychnin; at least, an ex-
cessive vacuolation of the protoplasmic body occurs under the
action of these„ asrents.

52 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

Experiments on cliemotaxis show that many substances
brought near to protoplasmic bodies control their locomotion.
The effect upon locomotion depends both upon the kind of
protoplasm and the strength of the reagent. In many cases,
a certain strength of reagent attracts an organism, while a
stronger solution repels, and a weaker solution is indifferent.
In such a case we may speak of the protoplasm as being attuned
to the attracting strength of the reagent. We find great diver-
sity in the strength of solution of a reagent to which different
protoplasms are attuned. This difference of attunement to
chemotactic reagents is parallel to the difference in strength of
the killing solution of various protoplasms. As the latter is
probably due to the past action of chemical agents upon the
protoplasm, so is also the former.

APPENDIX TO CHAPTER I

Cytotaxis (= Cytotropisni)

Roux ('94) has given the latter name to a phenomenon which
is probably only a special case of cliemotaxis, but which may be
better considered apart. He isolated, in an indifferent medium,
two or three cells from the Qgg of a frog (Rana fusca) at the
morula or blastula stage of development. These he placed near
each other upon a glass slide, and found that they moved sloAvly,
and that the direction of the movement of any one cell Avas,
under certain conditions, determined by the position of the
other cell or cells.

In order to perform the experiment a proper medium in "wliicli to study
the movement of the cells must be prepared as follows : a small quantity —
5 to 10 ccm. — of fresh egg albumen (not cut up, but with the albumen
threads intact) is filtered through clean wadding, and the completely clear
filtrate is used. In other cases a more or less strong salt solution is
employed. The cleavage cells are isolated in the filtrated albumen, on a
glass plate, by means of needles. To diminish evaporation the glass plate
is put into a shallow glass vessel containing several drops of water.

When two cells were placed near each other (about one-fourth
of their diameter apart), the distance between them diminished.
The approach took place along a line joining .the two cells ;

APPENDIX— CYTOTAXIS

53

and when several pairs of cells were in the field, this movement
took j)lace in various directions, indicating that their move-
ment was not determined b}^ conditions outside the approaching
cells. To get further light on the migration of the cells, their
distance apart was meas-
ured at short intervals
of time. The results of
two series of such meas-
urements are represented
graphically in Figs. 6 and
7. In both of these dia-
grams the heavy lines
indicate the successive
positions assumed by
four points ; namely, the
j)oints of the two cells
which are nearest each
other and those which
are most distant. In
the first case the cells
traverse the distance of
their diameters (58 /x.)
in about 10.5 minutes.
The rate of migration
is, however, extremely
variable. In some cases
the cells seem even to
move apart (negative
cytotaxis ?).

Certain special cases
are worthy of considera-
tion. When a third cell
lies near an approaching
pair, the path of migra-
tion of tlie pair may become convex towards the third cell.
Two cell-complexes, each composed of three or four cells,
may approacli and connect. But masses composed of a
larger number of cells form " closed complexes " which
show no cytotactic activity. The isolated cells of differ-

\ ^ ^

XI *-Z^

N^ r^

tA ,^ -/r -

L '\^ A /- -

' ^ ^^ V : X

"4 t ^ 3r

I ^ ^ ' -^-^

l^ I ' ^^.

^- I ^ 4 -4N

r ' -^ t I -\-

--I- T- -'r- 4 P4^

\ ' ^ I ' ' r

V' ' ^ I J '

\l I ' I+-X.-

!b t i se vi

\ ' i ^\

A I ' -A >-Xt

^^N ■ f\ ^^>^\

^tf 1- 3_ '

'S 4-- 4 "

f -i-.t 2 '

Z^L t Z I

-,.J^X- -1 - ^ t

ai , /-^- I it 4 I

Nfes^ I L^^ti 1 r

' ■ I ^J J .L

1 1 1 t-l 4 L

.;_ 1 1 T_ ^ .L

^ 1 +J-i- 4 ^

tp -N' ^ J -

-r-\ -|y i^^ ""^

T lu

'A ^_X

: ' / 6 7

.ZVjS^

Figs. G, 7. — Two sets of curves, showing the
course of "cytotactic" movemeuts of the
cleavage cells of the frog. In each figure
the dotted line represents a diameter of the
cell. The full line represents the successive
positions of the extremities of the diameters
as the cells approach. The distances hetweeu
horizontal lines = 4/ix ; hetweeu vertical lines,
75 seconds. (From Roux, '9i.)

54 CHEMICAL AGENTS AND PROTOPLASM [Ch. I

ent eggs of the same species behave like ceils from the
same egg.

By these important experiments it is established that, inside
of the body, parts may act upon parts, determining the direc-
tion of motion. The importance of this fact will be discussed
in a later Part of this book.

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TsuiCAMOTO, M. '95. On the Poisonous Action of Alcohols upon Different

Organisms. Jour. Coll. Sci. Japan. VII, 269-281.
Verworn, M. '89. Psycho-physiologische Protisten-studien. 218 pp. 6 pis.

Jena : Fischer.

CHAPTER II

EFFECT OF VARYING MOISTURE UPON PROTOPLASM

In this chapter it is proposed to speak (I) of the amount of
water in organisms ; (II) of the effect of desiccation upon the
functions of protoplasm ; (III) of the acclimatization of organ-
isms to desiccation, and (IV) of the control of the direction
of locomotion by moisture — hydrotaxis.

§ 1, Oisr THE Amount of Water in Organisms

Any theory of the structure of protoplasm must recognize
that water forms the greater part of the whole mass ; between
60% and 90%. In the case of dry seeds and grains, however, it
may fall below 15%. Many determinations have been made of
the proportion of water in the body of entire organisms and in
their organs. I give in tabular form some of these determina-
tions, which were made by Bezold ('57), designated by (B);
Krukenberg ('80), designated by (K); and Liebermann
('88), designated by (L).

TABLE VIII

Species.

Conditions op Weighing.

% VVATElt.

Various sponges (K)

In most cases, kept a short time in

fresh sea water ; dried on surface

84.0 to

and weighed.

74.5

Medusa : Rhizostoma Cuvieri

(K).

Whole animal, directly from water

95.4

Piece of disc.

95.0

Various Actinia (K)

A few minutes after removal from

sea.

87.7 to

A little water lost from central cavity

83.2

Weighed when fresh, 73.5 g.

84.3

Asteracanthion glacialis (K).

Weighed 850 g.

82.3

Lmnbricus complanatus (K) .

2 large specimens

87.8

§ 2] DESICCATION AND PROTOPLASMIC FUNCTIONS

59

Species.

Conditions of Weighing.

% Water.

Oniscus murarius (B). .
Squilla mantis (K) . . .
Astacus fluviatilus (B) .

Doris tuberculata (K) . .
Doriopsis limbata (K) .
Arion empiricorum (B) .

Limax maximus (B) . .

Botryllus (K) ..... .

Various Vertebrates (B)

Chick (L)

7 days old

21 days old

Turnip (root)

200 young individuals
1 individual

3 individuals weighing from 16.6 to
27.4 g.

3 individuals

6 individuals weighing from 4.3 to
27.1 g.

4 individuals weighing from 0.1 to

17.1 g.
4 individuals weighing from 111.2
to 35.2 g.

Embryo only, yolk removed
Embryo only, ready to hatch
From Goodale's Physiolog. Bot., p.
236

68.1
81.9

71.1

88.4
86.5

86.8

82.1

93.6
58.4 to
80.1

92.8
80.4

91.0

These determinations suffice to show that water immensely
predominates over any otlier substance in active organisms,
and indicate that it plays an important role.

The role played by water is, in fact, extremely varied. It
serves to maintain that unstable, foam-like structure of the
protoplasm upon which its capacity for movement depends ; it
acts as a solvent for matter taken into the protoplasmic body;
and it serves to transport dissolved substances from place to
place in the organism. In a word, it is essential to movement
and to those chemical processes which constitute metabolism.

§ 2. On the Effect of Desiccation upon the Func-
tions OF Protoplasm

We may consider this topic under the following heads :
(1) effect upon metabolism ; (2) effect upon the motion of
protoplasm; and (3) the production of desiccation-rigor and
death.

1. Effect of Dryness on Metabolism. — Since water is so
essential to metabolism, we should expect that a diminution of
metabolism would accompany dryness. And this is clearly the
case. Thus dry seeds, in. which the water is reduced to only 10

60 MOISTURE AND PROTOPLASM [Ch. II

to 15%, when placed under conditions of temperature favor-
able to metabolism, show almost no change in the course of
days. This has been indicated also by an experiment of
KocHs' ('90, p. 685), who placed seeds, which had been dried
in a vacuum, in a receptacle connected with a Geisslee's tube,
such as is used in the spectroscopic study of gases. The air
was completely pumped out of both vessels, and after some
months a spectroscopic study of the gases in the Geisslee-'s
tube showed no trace of nitrogen or carbon, yet the seeds later
germinated. This experiment can hardly be considered to
demonstrate KocHs' point, however, since the seeds were
deprived of oxygen, as well as moisture.

The act of drying may, on the contrary, induce the manu-
facture and elimination of certain secretions. This occurs
apparently in many Protista, which form cysts in the drying
pools. This phenomenon is seen again in some of the higher
animals, — such as our garden slugs, — which secrete slime in
large amount when kept for a short time in a dry place. In
both cases the result is of immense importance for the con-
tinued life of the organism, — in both cases it is to be consid-
ered a response to the stimulus afforded by evaporation of water.

2. Effect of Dryness upon the Motion of Protoplasm. — We
have seen that water plays an important role in the movement
of protoplasm. When by any means the water is partly with-
drawn, the protoplasmic currents will be slowed. When, on
the contrary, protoplasm, which is lying in an " indifferent "
medium, such as blood serum, is placed in distilled water,
unusually active movements occur. This has been shown by
Engelmann ('68, p. 4:4:6) in the case of the spermatozoa of the
frog, and the ciliated epithelium of the frog's oesophagus just
removed from its body. Similarly, Dehnecke ('81) found that
protoplasm of the tissue cells of the higher plants exhibited
abnormally rapid movements upon adding water. These obser-
vations indicate that water may act as a stimulus to the move-
ment of protoplasm.

3. Desiccation-rigor and Death. — It is a familiar fact which
has been established by over a hundred and fifty years of
experimentation, that some organisms, when gradually dried,
may cease from movements. This immotile condition has

§ 2] DESICCATION AND PROTOPLASMIC FUNCTIONS 61

sometimes been regarded as death. By Preyee, ('91) it has
been called "anabiosis." I shall call it desiccation-rigor, and
correlate it with phenomena, produced by various other agents,
which cause the cessation of a movement that is restored again
when the action of the untoward agent is withdrawn.

And these are just the conditions we meet with here, — ces-
sation of activity without loss of power of revival. This Avas
very evident from the work of Spallanzani (1787, Tom. II,
pp. 212, 213). This author showed clearly that one and the same
adult rotifer can be observed in the evaporating drop, until all
the water is gone, and it has lost all movement and its normal
form. If, after an hour, the slide is moistened again, the
rotifer reassumes, b}^ degrees, its natural form and activities.
Spallanzani noticed, what has been the nearly unanimous
testimony of subsequent observers, that a rotifer dried for
hours on clean glass does not revive ; revivification occurs
only when the rotifers have crawled into sand. As for the
length of time during which desiccation-rigor may persist
in rotifers without death occurring, we know only that it may
be considerable, extending through months, and even years.

Similar phenomena to those observed in rotifers have been
described for tardigrades and certain nematodes, although these
organisms have not been studied in so much detail. Among
the tardigrades only those species which live in moss, and
are thus especially liable to desiccation, withstand drying.
(Lance, '94.) Among nematodes, Tylenchus devastatrix,
KiJHN, which lives in grains of wheat, is a classic object of
study. Strongylus rufescens is, according to Railliet ('92),
capable of resisting dryness for 68 days or more. We may
thus conclude that adult organisms of certaiii species may be
subjected to desiccating influences, and that those same indi-
viduals may resist them so as to reexhibit activities after the
return of favorable conditions.*

While the results of these drying experiments are scarcely
doubted, much difference of opinion has arisen concerning the
interpretation of the results. The first moot point is the
degree of desiccation which the protoplasm of the organisms

* See in connection with this the vakiable report of Broca ('61).

62 MOISTURE AND PROTOPLASM [Ch. IT

experiences. Many writers have assumed that this has been
rendered in their experiments very great or nearly perfect.
Thus DoYERE ('42, p. 28) says: "What is the condition of
the animalcules in the dried sand of the gutters? I have
never seen them, at such times, in any other condition than
reduced to spangles as fragile and more deformed than when
dried free on the glass. I have never discovered a single one
which manifested any traces whatever of life, or which did not
present all the appearances of a complete desiccation. Never-
theless, I do not pretend by this to invalidate all contrary asser-
tions ; the principal fact, that of the return to life after an
absolute desiccation, is not affected thereby." The physicist
Gavarret ('59, p. 317) subjected, for 34 days, moss contain-
ing rotifers to a vacuum having a pressure of only 4 mm. of
mercury, and other experimenters have likewise employed a
similar "chemically drying" device, which they believed capa-
ble of extracting all water from the protoplasm.

The evidence that all water is withdrawn from the body of
the organism is often very slight. The fact that the seeds or
plant tissues in which nematodes or tardigrades are living,
have been dried until they lose no appreciable weight, is not
sufficient evidence that their inhabitants are completely dried.

On the other hand, there is positive evidence that one, at
least, of the organisms which has been considered as having
been absolutely dried, can protect itself from this condition.
It is especially Davis ('73) who has shown this. This author
has experimented with the rotifer Philodina roseata. When
dried on a glass plate with sand, it assumes a spherical form.
At the same time, however, it secretes a gelatinous envelope.
Thus encapsuled it may rest for days until upon the addition
of water it reassumes its active, adult form. That a layer
of such gelatinous substance is sufficient to resist the drying
action of a vacuum-chamber Avith sulphuric acid, was illus-
trated by putting grapes varnished with gelatine in such a dry
chamber for one week. They emerged in a fresh, juicy con-
dition. One of the encapsuled rotifers was crushed after
"desiccation" and yielded under the cover-glass a drop of fluid.
In this case then the rotifer was not fully dried. Davis
accounts for the fact that isolated rotifers dried on a clean

§ 2] DESICCATION AND PROTOPLASMIC FUNCTIONS 63

slide will not survive desiccation, on the ground that the sand
forms a necessary retreat in which the organism can quietly
encapsule itself. Of the fact of such encapsuling there can be
no doubt ; it is abundantly substantiated by the testimony of
Hudson ('73 and '86). There is a doubt, however, whether
this encapsuling is a phenomenon common to all organisms
which can resist desiccating influences, and, therefore, whether
Davis's explanation is generally applicable. To sum up : I
believe there is no sufficient evidence that an adult organism
or active protoplasm of any sort can rapidly lose all of its " free
water " without such a destruction of its finer structure as
would make it incapable of exhibiting vital activities upon
moistening again.

A much greater capacity undoubtedly inheres in spores and
seeds. Thus Kochs ('90) subjected perforated seeds of Zea
mais, Phaseolus, and Triticum vulgare to an almost perfect
vacuum (made by a mercury pump) for 8 days, and they nearly
all germinated. Even the small radish seed, with part of the
cuticula removed, subjected to a vacuum for three weeks ger-
minated perfectly. Probably there is no limit to the amount
of desiccation which seeds and other masses of protoplasm
especially adapted to resist desiccation can withstand.

The second moot point is this : Is the protoplasm, rendered
immotile by drying, living or not ? Spallanzani prejudiced
the question by the title of his chapter on this matter, —
" Observations and experiments on some marvellous animals
which the observer can at his will make pass from death to
life" ; and he and many of his successors argue that death has
truly occurred. Preyer ('91), however, prefers to reserve the
term "dead" for protoplasm which is at the same time lifeless
and incapable of life ; while to protoplasm which is lifeless but
capable of revivification he applies the term " anabiotic." The
question then is this, is life truly suspended during the immo-
tile state ? If we think of life as the sum of the chemical
changes occurring in the protoplasm, we shall realize that all
degrees of vitality, even to complete cessation of activity, may
occur without our being able anywhere to say at this point life
becomes extinct. We can hardly hope ever to deny that mini-
mum vital changes are occurring ; since the minimum changes

64 MOISTURE AND PROTOPLASM [Ch. II

must be beyond our ken. That these vital changes are some-
times exceedingly slight, is sufficiently indicated by the experi-
ments upon seeds performed by Kochs ('90), and referred to
on p. 60, That, however, slight changes are occurring even
in seeds is indicated by the fact that dessication-rigor cannot
continue indefinitely without loss of the power of revivifi-
cation.

In the case of the rotifers, tardigrades, and nematodes, months,
and even years, may elapse without complete loss of capacity
for revivification. It is generally admitted, however, that in
cases of long-continued drought, tlje chances of revitalizing
upon moistening are much diminished.* In the case of seeds
it has been maintained that under certain conditions, such as
are realized in the mummy -graves of Egypt, life may persist
for more than a thousand years. However, the experiments of
MiJNTER ('47), and more especially of Kochs ('90, p. 683),
throw doubt upon this assertion, since they found that the
ancient, charred seeds fell to pieces in water like lime. As
for seeds preserved above ground in the ordinary way, Kochs
was assured by seedmen that they could not remain capable
of germination over 10 years. These facts go to show that
gradual changes occur in the dry protoplasm which are prob-
ably metabolic changes, i.e. vital changes ; and that therefore
life is hardly extinct in the very dryest protoplasm.

The whole matter of desiccation-rigor is, after all, one with
which we are familiar in nature's larger laboratory. Many
Protista, when the ponds in which they live dry out, encyst
themselves and enter into a motionless condition in which they
resist the hot and dry summer winds. Thus, they may lie for
weeks, and, as experimentation has shown, they may be dried
for several years (see Butschli, '89, p. 1663, for references)
without loss of capacity for revivification. The same device

* Thus Railliet ('92) says of Strongylus rufescens : "I have seen them
regain their activity after 42 and even 68 days of desiccation. However, this
activity is much slower in manifesting itself. After the course of a month a
contact of 8 to 10 minutes is sufficient to bring them back to movement. . . .
After 68 days at least 50 minutes are required, and certain individuals have
shown activity only after 1 hour and 20 minutes. Moreover, the movements
were limited, and only a small number of cases contorted themselves like ordi-
nary Anguillulidse."

§ 3] ACCLIMATIZATION TO DESICCATION 65

for resisting desiccation is seen in the gemmules of sponges,
and Bryozoa, the eggs of many animals, and the spores of many
plants. Thus some protoplasm normally responds to the
stimulus of drought by going into desiccation-rigor.

While, as we have seen, some protoplasmic bodies may be
dried as far as possible by the ordinary methods used in chem-
istry without death ensuing, other bodies, especially the adult
forms of higher organisms, whose cellular respiration is de-
pendent upon a circulating fluid, are killed by desiccation.
For loss of this fluid or desiccation-rigor in the pumping
muscles will produce asphyxia. But these conditions do not
militate against the belief that there is no necessary lower
limit to the amount of water which must occur in quiescent
protoplasm in order that it may retain vitality during a lim-
ited period.

§ 3. On the Acclimatization of Okganisms to
Desiccation

We have seen in the last section that certain organisms are
more capable of resisting desiccation without fatal effect than
others; e.g. rotifers, tardigrades, and Tylenchus. Now it is
clear that these organisms are especially apt to become dried,
so that it is possible that their high capacity for resistance has
been produced by acclimatization without selection. I shall
here add certain other cases of resistance to dryness which I
believe, but cannot prove, to have been thus produced. Lance
('91) has mentioned, as already stated, that only those tardi-
grades which live in the moss of gutters (where they are
alternately wet and dried), and not those living in water, show
the phenomenon of revivification. Certes ('92) lias found
that, although marine Ciliata cannot, in general, withstand
desiccation, those from the cliotts and saline lakes of Algeria
may be dried like those from fresh-water ponds and swamps.
The difference in resistance between the forms dwelling in
the sea and in inland salt-water ponds is doubtless due to the
fact that the former are not regularly desiccated, while the
latter are ; consequently the latter alone have had a chance to
become acclimated to desiccation.

66 MOISTURE AND PROTOPLASM [Ch. II

§ 4. The Determination op the Direction of Move-
ment BY Moisture, — Hydrotaxis

This phenomenon has been described by Stahl ('84) in
J^thalium. When this Myxomycete is placed in the dark upon
a glass plate covered with several layers of moistened filter
paper, it expands uniformly over the homogeneously moistened
substratum. If, now, the plate be placed in a drying chamber,
the paper dries slowly, and one can see that the mass of the
Plasmodium draws towards those places which remain longest
damp. If a dilute gelatine jelly is smeared upon a glass slide
supported in a horizontal position about 2 mm. above the
Plasmodium, still in the dark chamber, the plasmodium sends
up branches, some of which may touch the gelatine and spread
out over it. If the water dries still further, the entire Myxomy-
cete may become transferred to the slide above. If, now, the
paper be moistened again, the plasmodium sends branches down
to it. Stahl's explanation is that of the old mechanical
school. He says, the peripheral protoplasmic layer lying next
the dryer region is poorer in water ; while that next the
damper part of the substratum contains much water. If it be
assumed that the internal streaming tends to occur uniformly
towards all points of the periphery, it is clear that the dryer,
more consistent part will offer greater resistance than the more
fluid part, and in this part, therefore, branches will tend to
arise. In correspondence with the interpretations which we
have hitherto placed upon similar phenomena I prefer to call
this a case of response to the stimulus of excessive moisture —
in any case it may be designated positive hydrotaxis.

When, however, the plasmodium of J^^thalium is in the fruit-
ing stage, it retreats from the moister part of the sabstratum,
and other Myxomycetes in the fruiting stage show the same
negatively hydrotactic tendency. Thus the same agent, water,
stimulates the same organism, at different stages, to reverse
movements.

I will now summarize the conclusions concerning the effect
of water upon protoplasm. Water constitutes by far the larger
part of protoplasm and of all active organisms. Metabolism is

LITERATURE 67

directly dependent upon it, and certain excretory processes are
stimulated by it. The motion of protoplasm is likewise de-
pendent upon water, which determines the unstable condition
of that substance. Desiccation, therefore, produces a rigor,
and this may continue, in the absence of water, for months, and
even years, the organism being, meanwhile, ready to awake
to activity upon the return of moisture. The degree of desic-
cation which organisms can resist varies. In the case of the
higher organisms, it is slight ; in the case of bodies especially
adapted to resist dryness (spores, seeds, statoblasts), there is,
perhaps, no practicably attainable limit to the dryness which
their protoplasm may undergo without loss of power of revivifi-
cation. The condition of desiccation-rigor is not known to be
one of death which is replaced by life upon return of moisture.
It is probably rather a condition of minimum metabolism.
The great resistance capacity exhibited by certain organisms is
correlated with their liability to desiccation in their natural
surroundings. Finally, Myxomycetes (and probabl}^ other or-
ganisms) respond to inequalities in the amount of moisture
in their environment, moving either towards or from greater
moisture. We recognize thus that the activities of protoplasm
are to a large extent dependent upon the existence of water in
it ; and that protoplasm reveals itself as sensitive to differences
in the amount of moisture, responding by secretions, by the
assumption of a quiescent condition, and by locomotion with
reference to water.

LITERATURE

Blainville, H. de '26. Sur quelques petits Animaux qui, apres avoir
perdu le mouvement par la dessication, le reprennent comme aupara-
vant quand on vient h les mettre dans I'eau. Ann. des Sci. Nat. IX,
104-110.

Bezold, a. von '57. Untersuchungen iiber die Vertheilung von Wasser.
organischer Materie und anorganischen Verbinduiigen im Thierreiche,
Zeitsch. f. wiss. Zool. VIII, 487-524. 26 Feb. 1857.

Bos, R. '88. Untersuchung iiber Tylenchus devastatrix, Kuhn. Biol. Cen-
tralb. VII, 646-659. 1 Jan. 1888.

Broca, p. '61. Rapport sur la question souraise :\ la Societe de Biologie
par MM. Pouchet, Pennetier, Tinel et DovfeRE au sujet de la revi-
viscence des animaux desseches, lu par M. Paul Broca au nom d'une

68 MOISTURE AND PROTOPLASM [Ch. II

commission comp. de MM. Balbiani, Berthelot, Brown-Sequard,

Dareste, Guillemin, Ch. Robin et Broca. Mem. See. de Biol.

(3), 1-139.
BtJTSCHLi, O. '89. Protozoa (part). Bronn's Klass. u. Ord. d. Thier-reichs.

I Bd. 1585-2035. 1889.
Certes, a. '92. Sur la vitalite des germes des organismes microscopique

des eaux douces et salees. Bull. Soc. Zool. France. XVII, 59-62.'
Davis, H. '73. A New Callidina: with the Result of Experiments on the

Desiccation of Rotifers. Monthly Micr. Jour. IX, 201-209. 1 May,

1873.
Dehnecke, C. '81. Einige Beobachtungen liber den Einfluss der Pr'apa-

ratioiismethode auf die Bewegungen des Protoplasma der Pflanzenellen.

rio-ra. LXIV, 8-14, 24-30. 1, 11 Jan. 1881.
DoYiiRE, M. P. L. N. '42. Memoire sur les Tardigrades. Ann. des. Sci.

Nat. (2) XVIII, 5-35.
Engelmann, T. W. '68. Ueber die Flimmerbewegung. Jena. Zeitschr.

IV, 321-479.
Faggioli, F. '92. De la pretendu reviviscence des Rotiferes. Arch. Ital.

de Biol. XVI, 360-374. 31 Jan. 1892.
Fromentel, E. de '77. Recherches sur la revivification des rotiferes, des

anguillules et des tardigrades. C. R. Assoc, fran^. I'avanc. des sci.

VI (Le Havre), 641-657.
Gavarret, J. '59. Quelques experiences sur les rotiferes, les tardigrades et

les anguillules des mousses des toits. Ann. Sci. Nat. (Zool.). (4), XI,

315-330. i'

Hudson, C. T. '73. Remarks on Mr. Henry Davis' Paper "On the Desic-
cation of Rotifers." Monthly Micr. Jour. IX, 274-276. 1 June,

1873.
'86. [Desiccation of Rotifers.] Jour. Roy. Micr. Soc. (2) VI, 79.
KocHS, W. '90. Kann die Kontinuit'at der Lebensvorgange zeitweilig vbl-

lig unterbrochen werden? Biol. Centralbl. X, 673-686. 15 Dec.

1890.
Krukenberg, C. F. W. '80. Ueber die Vertheilung des Wassers, der organ-

ischen und anorganischen Verbindungen im Korper wirbelloser Thiere.

Vergi.-Physiol. Stud. I, 2 Abth. 78-106.
Lance, D. '94. Sur la reviviscence des Tardigrades. Comp. Rend. CXVIII,

817, 818. 9 Apr. 1894.
Liebermann, L. '88. Embryochemische Untersuchungen. Arch. f. d. ges.

Physiol. XLIII, 71-157. 7 Apr. 1888.
MuNiiER, J. '47. Flora. XXX, 478.
PoucHET, F. A. '59. Recherches et experiences sur les animaux ressusci-

tants. Paris : J. B. Balliere et fils. 92 pp. 1859.
Preyer, W. '91. Ueber die Anabiose. Biol. Centralbl. XI, 1-5. 1 Feb.

1891.
Railliet, a. '92. Observations sur la resistance vitale des embryons de

quelques Nematodes. C. R. Soc. de Biol. XLIV, 703, 704.

LITERATURE 69

Rywosch, D. '89. Einige Beobachtungen an Tardigraden. Sb. Naturf.

Ges. Dorpat. IX, 89-92.
Spallanzani, L. 1787. Oeuvres : Opuscules de physique, animale et vege-

tale, etc. Trans. Jean Senebier. 3 tomes. Pavia and Paris.
Stahl, E. '84. (See Chapter I, Literature.)
Zacharias, O. '86. Kommen die Rotatorien und Tardigraden nach vollstan-

diger Austrocknung wieder aufleben oder nicht? Biol. Centrg,lb. VI,

230-235. 15 June, 1886.

CHAPTER III

ACTION OF THE DENSITY OF THE MEDIUM UPON
PROTOPLASM

In this chapter we shall consider (I) the structure of proto-
plasm and the physiological action of solutions ; (II) the effect
of density upon the structure and general functions of proto-
plasm ; (III) acclimatization to solutions of greater or less
density than the normal ; and (IV) control of the direction of
locomotion by density — tonotaxis.

§ 1. Inteoductoey Remaeks upon the Steuctuee of
Peotoplasm and the Physical Action of Solutions

It is now generally recognized that protoplasm consists of
two substances closely interwoven : the living plasma and a
watery chylema. The relation of the plasma and the chylema
is still a debated matter. Since the only theory of the struct-
ure of protoplasm which has been experimentally tested is that
of Butschli, his theory is especially worthy of recognition.
According to this theory, the relation of plasma and chylema is
that of water and air in a foam-work. The whole protoplasmic
mass is bounded and penetrated through and through by plasma
films which envelop watery globules. It is with membranes
constructed of such protoplasm that the physical phenomena
of osmosis are exhibited.*

Osmosis occurs when two aqueous solutions of different
density are separated by an animal membrane. f Such a mem-

* Excellent treatises on tlie physical and chemical nature of solutions, in-
cluding a discussion of osmosis, are : Ostwald, '91, and Whetham, '95.

t Osmosis occurs likewise when such solutions are separated by inorganic
walls containing pores of extreme fineness ; e.g. a wall of porous clay in which
copper ferrocyanide has been precipitated.

70

§ 1] PHYSICAL ACTION OF SOLUTIONS 71

brane permits the free passage of water, but not of the dissolved
substance, or rather, of the dissolved substance but slowly.
Under these conditions, the water flows more rapidly towards
the solution containing the greater number of molecules (per cc).
The theory of this movement is that upon the side containing
the greater number of molecules of salt fewer water molecules
will in a given time strike the membrane than upon the other
side ; and since the number passing through is proportional
to the number striking, relatively fewer molecules of water
will consequently pass out, and so there will be a resultant flow
of water to that side ; and if the mass of water is conflned, it
will exert great pressure.

This phenomenon of osmosis plays an important part in
organic life. Thus, under certain conditions, cells take in the
surrounding water, so that their walls are put under tension
(turgescence). The tension thus gained may be considerable,
amounting to 6 or 7 atmospheres. Under other conditions the
cells give up their water to the surrounding medium, thus
losing their turgescence. This occurs when they are put into
certain solutions of KNOg or NaCl. The relation between the
density of the internal and external fluids thus determines the
internal pressure experienced by the cell.

A quantitative method of determining this pressure in the
presence of various solutions has been employed by Pfeffer
('77). Solutions of different dry salts in different proportions,
enveloped by a semi-permeable membrane, were placed in pure
water, and the pressure upon a column of mercury determined.
It was found, for example, that with a 1% solution of cane
sugar a pressure of 47.1 cm. of mercury* was produced ; with
a 1% solution of K2SO4, a pressure of 193 cm. of Hg. He
concluded, as a result of his various experiments, (1) that the
pressure is proportional to the concentration of the solution,
and (2) that as the temperature rises the pressure increases.

De Vries ('81) made a noteworthy advance, using plant
cells as objects of experimentation and subjecting them to
various solutions of substances freed of water. He determined
the degree of concentration which a solution of KCl must liave

* The pressure of 76 cm. of mercury equals that of 1 atmosphere.

72 SOLUTIONS AND PROTOPLASM [Ch. Ill

in order that no endosmosis or exosmosis should occur through
the cell wall.* He next determined the same thing for some
other substances, e.g. KI, and found that the degree of con-
centration which produces no osmosis is, for two different
solutions, proportional to the molecular weights of the salts
dissolved in them. Solutions which produce the same osmotic
effect DE Veibs called isotonic. A solution of 0.746% KCl is
isotonic with a solution of 1.661% of KI, for the molecular
weight of KCl is 74.6, and that of KI is 166.1. Thus the first
result which db Vries gained was that the osmotic effect of
solutions of salts of similar structure depends upon the number
of their molecules in the solution.

The second conclusion of de Vries was that salts of dis-
similar structure have different osmotic properties, even when
the number of molecules in the two solutions is the same.
Thus, he found that with an equal number of molecules to thfe
solution (molecular-weight solutions f ) : —

(1) All salts of alkalis with one atom of metal to the molecule are

isotonic (formula, R'A' [composed of a monad metallic
radicle, R, and a monad acidic radicle, -4]);

(2) All organic compounds with no metal radicle have two-thirds the

osmotic action of the first group ; e.g. cane sugar, C12H22O11. %

* As is well known, when a fully developed plant cell is put into a strong
saline solution the living plasma sac separates from the cell wall and contracts,
eventually, into a ball, — the result of the chylema flowing out of the protoplasm
(plasmolysis). The weaker the concentration, the less marked the plasmolytic
phenomena. Finally, a concentration is reached so weak that the separation of
the plasma sac hardly occurs or is limited to a single corner. This concentra-
tion may be regarded as equal to that of the cell-sap — as that at which no
osmosis occurs. (See Fig. 8.)

t I shall use the phrase "molecular-weight solution " to indicate solutions in
the making up of which the molecular weight of the substance in grammes, dis-
solved in 100 g. of water, is used as the unit of concentration. It will often be
convenient to abbreviate it as MVV% sol. Chemists frequently use as a unit
solution, called "normal" solution, the molecular weight in grammes dissolved
in 1000 g. of water. Our M W % sol. is therefore equal to one-tenth of a "normal ' '
solution.

X The fact that glycerine can be absorbed by some plants has introduced a
complexity into the determination of its isotonic coefficient. This determina-
tion has been made the subject of a special investigation by de Vries ('88), who,
by the use of slowly absorbing plants, has found the isotonic coefBcient to be 1.78,
which agrees approximately with the number given above for organic compounds.

§ 1] PHYSICAL ACTION OF SOLUTIONS 73

(3) All salts of alkalis with two atoms of metal to the molecule have

four-thirds the osmotic action of (1) (formula, i^a'^") 5 ^■9'-
K2SO4.

(4) Salts of alkalis with three atoms of the metal to the molecule

have five-thirds the osmotic action of (1) (formula, Bs'A'");
e.g. K3(CoHA)-.

In other words, the osmotic action of groups (2), (1), (3),
and (4) are in the proportions of 2, 3, 4, 5. These last num-
bers are the Isotonic Coefficients of de Veies. In addition to
these substances, de Veies determined that the isotonic coeffi-
cient is, in the case of —

salts of earthy alkalis with 1 acid radicle ; e.g. MgS04 . . 2
salts of earthy alkalis with 2 acid radicles ; e.g. CaCl2 ... 4

In the third place de Vries established the law that each
acid group and each metal has, in all compounds, the same par-
tial isotonic coefficients ; the coefficient of any salt is the sum
of these partial coefficients of the constituent components.
These partial coefficients are : —

for each atom-group of an acid .• . . 2

for each atom of an alkaline metal (Li, Na, K, Rb, Os) . . 1
for each atom of an earthy metal (Ca, Sr, Ba, Mg) .... 0

while of the compounds the isotonic coefficients are —

KCl = 1 + 2 = 3, MgS04 = 0 + 2 = 2,

K2SO4 = 2x1 + 2 = 4, MgCl, = 0 + 2x2 = 4,

-K3(CcH50;) = 3x1+2 = 5, etc.

The determination of isotonic coefficients has subsequently
been extended by several authors, especially by Hamburger
('86 and '87) and by M assart ('89).

The work of Hamburger was done upon blood corpuscles.
The method employed by him was as follows : In certain weak
solutions the hsemoglobin passes out of the red blood corpuscles
of ox blood. The concentration at which it just began to ex-
trude was determined for various salts, and it was found that
these concentrations were usually proportional to the molecular
weights of the substances divided by certain whole numbers,
which are the same as the isotonic coefficients of de Vries.

74 SOLUTIONS AND PROTOPLASM [Ch. IH

The work of Massaet was done chiefly upon bacteria. He
made use of the fact demonstrated by Pfepfbr (see p. 41)
that substances, which at a low concentration attract bacteria
chemotactically, at a higher concentration repel them. He
found that, in general, the repulsions exercised by the various
dissolved substances are proportional to their isotonic coef-
ficients, when the solutions are made up as MW solutions.
Thus, when a 10 MW % concentration of a substance with iso-
tonic coefQcient 2 just begins to repel bacteria, a substance
which just begins to repel in a 5 MW % concentration has an
isotonic coefficient of 4.*

§ 2. Effect of Varying Density upon the Structure
AND General Functions of Protoplasm

Under this head we may consider, (a) the effect upon the
general structure of protoplasm ; (5) the modification of gen-
eral functions, and (c) the production of death.

* Starting from the observations of Pfeffer and de Vries tlie modern school
of physico-chemists has greatly extended our knowledge of solutions. As a
result of their work it appears that the validity of de Vries' law will not hold
strictly for all solutions at all concentrations. For the number of effective
particles in every solution of electrolytes, namely, of salts, bases, and acids, is
greater than the number of molecules put into the solution ; because a certain
proportion of the dissolved molecules break up or dissociate into their constitu-
ent ions, and the osmotic pressure is determined by the number of both
molecules and free ions in the solution. In the case of sugar, the alcohols and
non-electrolytes in general, no dissociation occurs. In a normal solution of
potassic chloride, on the other hand, 75.5% of the molecules dissociate, each
forming two free ions. Since 24.5% of the molecules are intact and there are
151 free ions percent of the molecules introduced, the total number of mole-
cules and free ions in the solution is 175.5% of the molecules introduced and
the osmotic effect of a normal solution of KCl is 1.755 times that of a normal
solution of sugar. The percentage of molecules of any electrolyte, as for
instance KCl, which dissociate in solution increases as the strength of the
solution diminishes, eventually becoming 100. Thus, in one-half the normal
solution, 78 % of the molecules of KCl dissociate ; at 0. 1 times the normal solu-
tion, 86%; at 0.01, 94%; at 0.001, 98%. Also, the percentage of molecules
dissociated in normal solutions of different electrolytes varies. Thus, in such a
solution of NaCl, 67.5% of the molecules are dissociated; of LiCl, 61%; of
CaClo, 53% (each into 3 ions) ; of MgCls, 40%; of Kl, 79%; of MgSO*, 19%;
of Na2S04, 35.6 % (each into 3 ions); and so on. Valuable and extensive tables
for the determination of the percentage of dissociation at different concentrations
will be found in Whetham, '95.

§2]

EFFECT OX STRUCTURE AXD FUNCTIONS

75

a. Since a protoplasmic mass is bounded by a film, permit-
ting osmosis, it is clear that its characters may be greatly
altered by varying the degree of concentration of the solution
in which it lives ; and we have already seen that they are so
altered.

When plant cells, with a rigid cell-wall, are put into dense
solutions, the water is drawn from the protoplasmic sac which,
contracting, is torn from the cell-wall. The salt solution pene-
trates through the latter, but cannot enter the bounding plasma-
film, which continues to contract around the diminishing glob-
ule of water until only a small ball remains.

Fig. 8. — 1. Young, not more than half-srown, cells from the cortical parenchyma
of Cephalaria leucantha. 2. The same cell in a 4% solution of potassium nitrate.
3. The same cell in a 6% solution. 4. The same cell in a 10% solution. 1 and 4
from nature, 2 and 3 diagrammatic, all in optical longitudinal section, h, cell
membrane; p, lining layer of protoplasm: k, cell nucleus; c, chlorophyll bodies;
s, cell-sap ; e, salt solution which has penetrated within the cell-membrane. (From
SjVchs: Pflauzenphysiologie, after de Vries.)

Put into pure water, on the contrary, the protoplasmic sac
becomes distended, provided the cell sap contains an appro-
priate solution, generally a plant-acid. Thus turgescence is
brought about.

The same effect of varied density upon the structure of pro-
toplasm is observable among animals also. Thus, Kuhne
('64, p. 48) and Czerny ('69, pp. 158, 161) found that AuKeba
shrinks into a spherical mass when put into a 1% to 2% NaCl
solution, and, when returned to fresh water, swells. Also, the
character of the pseudopodia of AmiBba and Myxomycetes
changes. They become more numerous and attenuated, so that

76 SOLUTIONS AND PROTOPLASM [Ch. Ill

the whole form of the organism has been likened to a horse-
chestnut with its shell on. (Kuhne, '64, pp. 48, 83 ; Czerny,
'69, p. 159.) Zacharias ('84, p. 254, and '88) has described a
similar phenomenon in the spermatozoon of Polyphemus pedicu-
lus. When put into a 3% NaCl solution the spermatozoa lost
their cylindrical form and protruded long pseudopodia. A
remarkable fact about the pseudopodia, moreover, was that in
locomotion they were used like flagella. Likewise, Fabre-
DoMERGUE ('88, p. 102) and Massart ('89) have observed
that the protoplasm of encysted Ciliata swells or contracts
according as it is placed in a less or more dense medium ; the
cyst thus being perfectly permeable by water. Massart has,
indeed, obtained a rough quantitative expression of this state-
ment, which is given in Tables X and XI, p. 87. Hambur-

v-'i Cy

/

Fig. 9. — Blood corpuscles of the frog. 1, 2, normal; 3, 4, 5, various degrees of
plasmolysis by solutions. a, nucleus and shrunken plasma; h, water-filled
spaces. (From Hamburger, '87.)

GER ('87) has found that dense solutions produce the same
modifications upon blood-corpuscles (see Fig. 9).

Again, Gruber ('89) has found those individuals of the
heliozoon Actinophrys sol which live in fresh water different
from those which live in the sea, and he has produced that dif-
ference artificially. In the marine variety the plasm is dense,
granular, free from vacuoles ; while that of the fresh-water
kind is extraordinarily rich in vacuoles, and has even a foamy
appearance. If a marine form is gradually accustomed to fresh
water its protoplasm soon acquires a vacuolated structure which
renders it indistinguishable from the fresh-water one. Gruber
also accustomed fresh-water Actinophrys to sea water, when it
acquired the structure of the normal marine form. Likewise
the marine Amoeba crystalligera, which has a dense protoplasm,
becomes vacuolated after being accustomed to fresh water.
Also, ScHMANKEWiTSCH ('79) has found that when the fresh-

§2] EFFECT ON STRUCTURE AND FUNCTIONS 77

water flagellate Anisonema acinus, Btjtschli, is cultivated for
many generations in water to which sea salt is gradually added,
its structure is modified with the increasing density. The in-
dividuals become smaller and their feeding canal is not well-
formed. Another change, which has been studied only in
Vertebrates, is loss of weight. Bert ('71) found that a gold-
fish plunged into sea water loses 67% of its weight, and that
young eels lose 10% to 17%. This fact also is clearly what
we should expect from the theory of action of solutions, accord-
ing to which the weak solutions of the body cavity should lose
water. Thus, the changes produced in the structure of proto-
plasm by more or less dense solutions are chiefly the results of
osmosis.

h. Among the functions of protoplasm, general movements
(with locomotion) and excretion seem to be most markedly
affected by density. Thus, Kuhne ('64, p. 48) found that, when
first subjected to a 1% NaCl solution, the movements of Amoeba
became more lively for a moment. Engelmann ('68, p. 343)
noticed the same acceleration in movement in the cilia of the
epithelium lining the frog's oesophagus when subjected to pure
water — hence, to a weaker solution than the normal cell fluid.
Even after death, fresh water causes a transitory activity in
the cilia. In all cases, after a minute or two (1% solution) the
movements begin to diminish, until at last they cease. This
cessation of movement, whether due to loss or imbibition of
water, is not necessarily death. For, if the abnormal con-
centration has not acted for too long a time, the movements
return when the protoplasm is placed again in its normal fluid.
(KiJHNE, '64, p. 48; Engelmann, '68, p. 343.)* At a certain

* A similar cessation of movement occurs when tlie lower organisms are sub-
jected in water to very great pressures. Experiments upon this phenomenon
have been made chiefly by Regnard ('84, '84»-'84<i, and '86), Ckrtes ('84,
'84a), and Roger ('95). Regnard was able, by the use of a special apparatus,
to subject beer yeast, in water, during 1 hour, to a pressure of 1000 atmospheres
(about 1000 kilograms per sq. cm.). When yeast so subjected was then placed in
sugared water, it showed at first no activity. It was not dead, however, but had
fallen into a latent life ; for 1 hour after it had been relieved from pressure it
revived and fermentation set in. Some algse, Infusoria, and actinians, subjected
to 600 atmospheres during 10 to 60 minutes, or to 300 atmospheres for 24 hours
(Certes, '84), exhibited a similar temporary rigor. Likewise muscle at 200 to

78 SOLUTIONS AND PROTOPLASM [Ch. Ill

strength, however, varying for different individuals (Engel-
MANN, Czeiiny), death rapidly ensues. Thus Amoeba quickly
breaks up in a 10% solution, and the ciliated epithelium of a
frog's throat in a 2.5% solution. Four phases in the action of
concentrations may thus be observed : stimulation, retardation,
density-rigor, and death. Even in concentrations at which
motion is not entirely inhibited, locomotion may be interfered
with. Thus, RiCHTBR ('92, pp. 37-40) found that while normal
Tetraspora swarm-spores move at the rate of about 60/u. per
second, or else rotate about 100 times per minute, those in an
11% solution hardly move from their place, or sometimes
move one-eleventh as fast as the normal swarm-spores. While
it is possible that the dense water affords a mechanical obstacle
to locomotion, it seems more probable that it is the general
diminution of activities which causes the slow migration.

The modification of excretion by abnormal concentrations
has been studied especially by Rossbach ('72). This experi-
menter worked upon fresh-water Ciliata (which alone possess a
contractile vacuole) by subjecting them to a 0.5% solution of
NaCl. The contractile vacuole became diminished almost to
invisibility, and the interval between contractions was in-
creased. In a 1% solution of sugar a reduction in size of the
contractile vacuole occurred, but this was not so marked as in
the case of the 1% NaCl solution. This is what we should
expect according to theory, for the number of molecules in a
1% solution of sugar (mol. wt., 342) is much less than in a 1%
solution of NaCl (mol. wt., 58.5), and their relative osmotic

action is as -^^Arrr. = o L ^^ ^^ ^s 0.002 : 0.017, or as 2 : 17.
3 X 342 3 X 58.5
The phenomenon of contracting vacuoles seems not to be
confined to Protozoa. It occurs in the embryos of some Mol-
lusca, especially the stages of fresh-water Pulmonates, upon
which my friend. Dr. KoFOiD, performed some density experi-
ments. The early cleavage and blastula stages of many fresh-
water Pulmonates contain a central fluid-filled vacuole, which

300 atmospheres loses its contractility, and at 400 atmosplieres becomes rigid
and liard. It also increases immensely in weight by the addition of water.
Roger pointed out that, subjected for 2 minutes to a pressure of 3000 kilograms
per sq. cm. , certain bacteria (Streptococcus) are even killed.

§ 2] EFFECT ON STRUCTURE AND FUNCTIONS 79

undergoes periodic enlargement and discharge as in the case of
the contractile vacuole. Kofoid ('95, p. 104) found that
when eggs of Physa and Amnicola were placed in a 0.19% or
0.10% NaCl solution, the contents of the central cavity, once
extruded, were not so quickly restored as in the control eggs,
and that the maximum volume attained by the vacuole in the
salt solution was less than that attained in fresh water. For
example, " the cavity of the control eggs attained a diameter of
5 to 7 units, while that of the eggs in the salt solution was
only 3 to 4 at the time of elimination. There were, however,
a very few cases in which the cavity reached a diameter of 5
units."- Of interest is the additional fact that marine Gastro-
poda do not seem to have a " cleavage " cavity, but that this is
confined to eggs developing in fresh water or moist situations.

The effect of density upon the higher animals is very com-
plex, according to the observations of Beet ('71) upon the
gold-fish. Plunged into sea water it shows violent, unco-
ordinated movements ; then it becomes immobile, and rises to
the surface by virtue of its relatively lower specific gravity.

The effect of fresh water upon marine organisms is equally
striking, as GoGORZA* ('91) has shown. They go immediately
to the bottom and move with difficulty. Swimming animals
swim badly if at all, and small fishes have to make much exer-
tion to rise to the surface. The sensibility also undergoes
great changes. Many animals soon become lethargic. Echino-
derms and molluscs act as if anesthetized, since they do not
respond as quickly as usual to external stimuli, and, finally,
pass into complete paralysis. The action is slower upon
Crustacea and fish; but here, too, fresh water acts as an an-
aesthetic. The respiratory movements become deep and rapid,
bivalves extend their branchige, and Crustacea beat the water
rapidly with their appendages in order to renew the supply.
Animals ordinarily transparent, like medusffi, become opaque ;
first externally, then internally. The cornea of fish becomes
opaque and the external slime coagulates. The tissues become
swollen, so that soft-bodied animals are visibly deformed — in

* For an abstract of the work of Gogokza, I am indebted to the kindness of
Mr. F. C. Waite.

80

SOLUTIONS AND PROTOPLASM

[Ch. Ill

fishes the eyes are forced out, the foot of gastropods swells, the
blood corpuscles swell up and burst, and muscular tissue may-
increase as much as 6 times in volume. The enlargement of
the different tissues is exhibited in the following table, which
shows the percentage increase in weight and volume of organs
of Scyllium canicula, placed in fresh water.

After 2 Houks.

Aftek ?4 Hours.

% Increase in
Weight.

% Increase in
Volume.

% Increase in
Weight.

% Increase in
Volume.

Muscular tissue ....
Glandular tissue . . .
Nervous tissue ....

15
12
20

50

0

50

20
19
60

200
100
250

All of these phenomena are clearly explicable upon the assump-
tion of their production by endosmosis.

c. The pressure due to dense solutions may become very
great, amounting, as I have said, to many atmospheres. So it
is not surprising that a change of medium may rend cells or
at any rate kill organisms. This result may be brought about
either when the denser solution is inside of the body or outside ;
the former case is realized when marine animals are plunged
into fresh water, the latter when fresh-water animals are
plunged into solutions of salts. Studies upon the fatal effects
of varying the concentration of solutions have been made by
Bert (^'o'o). Plateau ('T1), Coutancb ('83), Rixgee and
Buxton ('85), de Varigny ('88), Massart ('89), Gogorza
('91), and Richter ('92).

Bert's ('66) studies were made upon marine fish which he
plunged into fresh water. In a vessel holding 4.8 litres of
fresh water, a mullet died in 44 minutes, and a Spams in 86
minutes. Since the fishes lived longer in a sugar solution,
Bert concluded that death was due to diminished density of
the medium. In this conclusion he was nearer the truth than
his immediate followers in this work.

Plateau's ('71) observations were made upon all classes of
Invertebrates, but especially upon Arthropods. He subjected

§2]

EFFECT ON STRUCTURE AND FUNCTIONS

81

them to solutions botli more and less dense than the normal,
and determined their resistance periods. As a result of sub-
jecting fresh- water animals to salt solutions, he found that
their resistance period diminished approximately as the thick-
ness of the shin Qand cuticula} diminished. Thus, when plunged
into sea water (3.046% salts) adult water insects resisted in-
definitely ; insect larvae 6 to 4 hours ; Entomostraca less than
an hour ; Nephelis, 5 to 7 minutes ; Planaria, 4 minutes ; and
Hydra only 1 minute. Gogorza ('91) got similar results, find-
ing the resistance capacity of the different groups to diminish in
this order : molluscs, crustaceans, fish, worms, tunicates, echino-
derms, ctElenterates. So we may consider this relation between
resistance period and thickness of covering a general law of
resistance ; and it is what we should expect upon the theory
that the solutions act osmotically.

By subjecting organisms to separate solutions, each contain-
ing 3% of the various salts found in sea water. Plateau was
able to show that NaCl produced the most important effect,
MgCl2 the next most important effect, and MgSO^ still less.
This is shown by the following —

TABLE IX

Resistance Periods of Fresh-water Crustacea to Various Constituents
OF Sea Salt. Temperature not given

(Numbers indicate minutes elapsing before death occurred)

Species.

3%NaCl.
MOL. Wt., 58.5;
I.e., 8 ; Osmotic

Index, — — .
58.5

MoL. Wt., 95;
I.e., 4; Osmotic

Index, — .
95

3%MgS04.
MoL. AVt., 120;
I.e., 2; Osmotic

Index, -^.
120

Sea
Water.

Gammarus roeselii. .
Aselkis aquaticus . .
Daphuia sima ....
Cyclops quadricornis
Cypris f usca

105

155
7.8
12.1
26.7

131

1162

19.5

37

223

520

2000

87

690

460

230
160

22
257

36

Although from this table it seems clear that there is an
inverse relation between resistance period and osmotic index,
rLATEAU did not believe that the death of the animals experi-

82 SOLUTIONS AND PROTOPLASM [Ch. Ill

mented upon was due alone to the osmotic action of the salts.
To this conclusion he was led by an unfortunately devised
experiment. He compared the action of several pairs of solu-
tions, one of the members of the pair being a salt, and the
other member sugar, the dissolved substance of each having
the same gross- weight. In all cases the action of the salt
was the more powerful. But this is what we should expect
upon the theory that death is caused by osmosis, since the
osmotic index of sugar is far lower than that of any of the salts
with which comparison was made.

Let us now ascertain the relation between the resistance
period and the "osmotic index." To determine the relative
resistance periods for any species in the different salts, we may
take as our unit the average resistance period to all the salts,
and express the separate resistance periods in terms of that
unit. To determine the osmotic index, we divide the isotonic
coefficient by the molecular weight. The resistance periods
will vary inversely as the osmotic indices. For the salts, NaCl,
MgClg, MgSO^, the reciprocals of the osmotic indices are : 19.6,
23.8, 58.8 ; and the mean relative resistances are : 19, 63, 217.
From this comparison it is seen that while the reciprocals of
the osmotic indices increase roughly from 1 to 3, the relative
resistance period increases from 1 to 11 ; or the resistance
period increases more rapidly than the reciprocals of the osmotic
indices, and roughly as the squares of those reciprocals.

At about the same time with Plateau's work was published
that of Beet ('71). The work of the latter was done chiefly
upon fresh-water fishes ; incidentally, upon frogs and some
fresh-Avater Arthropoda. These were plunged directly into
sea water, and their resistance periods determined. Some
species showed an extraordinary variability in their resistance
period ; sticklebacks (Gasterosteus leiurus) from the same
locality (about Paris) resisting for from 2 hours to 1 month
or more.

A decided advance was made by Beet in observing that the
resistance period varies with the temperature ; thus, the
European minnow (Phoxinus Isevis) died in sea water —

at 9° C. in 30 minutes, at 22° C. in 14 minutes,

at 14° C. in 25 minutes, at 28° C. in 9 minutes.

§2]

EFFECT ON STRUCTURE AND FUNCTIONS

83

Thus, in this case there is a diminution in the resistance period
of approximately 1 minute for every degree of increase in the
temperature.

Similar observations have been made by others. Gogoeza
('91, p. 242) finds that in all animals, at a low temperature, the
resistance period is 2 to 3 times as long as at a high temperature.

In connection with these facts, it is to be noted that osmotic
pressure increases with temperature, indeed, is proportional to
the absolute temperature. (Ostwald, '91, p. 114.) But as
we are not able to say what relation exists between osmotic
pressure and resistance period, we cannot say whether the above
table agrees with the physical law.

Finally, we may discuss the question of the relation between
the strength of the solution and the length of the resistance
period. Data for this discussion are afforded by the extensive
observations of GoGORZA. This author disclaims having found
any mathematical relation, but his tables, properly treated, do
show such a relation. The resistance periods depend upon so
many factors that the times obtained by subjecting one animal
to different concentrations of a salt cannot be directly compared
with those obtained from another animal. It is the relative
resistance periods only that can be thus compared.* Gogoeza's
concentrations were obtained by subjecting marine animals to
mixtures of marine and fresh water. No. 1 contained 100%
sea water; No. 2, 75%; No. 3, 66%; No. 4, 50%; No. 5, 33%;
No. 6, 25%; No. 7, 0%. Averaging the relative lengths of
life of 22 species which died in 75%, or weaker percents of
sea water, and comparing with the percentage of salts in various
concentrations (the density of Mediterranean sea water being
taken as 1.037), we get —

No. OF Solution :

1

3

3

4

5

6

7

% of salt in solution ....

Rel. resist, per

Log. of rel. res. per. ...
Log. rel. res. per. x 1.7 . .

3.7
Indef.

2.8

50.0

L7

2.9

2.5
28.3
1.45
2.5

1.9

10.83

1.04

1.7

1.2
5.44
0.73
1.2

0.9
3.46
0.54
0.9

0.00
1.84

* The relative resistance periods are calculated by the method described
on p. 82.

84

SOLUTIONS AND PROTOPLASM

[Ch. Ill

The curve shown in Fig. 10 is constructed from the second
and third lines of this table. The table shows that, within the
limits of 2.8% and 0.9% concentration, the curve is a logarith-
mic one, i.e. as the ordinates increase the abscissae increase

as the logarithms of the ordinates.

50

40

30

20

10

40

30

30

10

0

1.3

1.9

3.8

3.7

0

Fig. 10. — Curve showing relation between the per-
centage of salt in mixtures of fresh and salt water
(abscissae) and the mean resistance periods in hours
of various organisms plunged therein (ordinates).
Constructed from the table. (After data of Go-
go bza, '91.)

In line 4 are given
the (Briggs') loga-
rithms of the num-
bers in line 3, and
in line 5 these loga-
rithms are each mul-
tijjlied by a constant,
1.7, which gives a
series of numbers
closely similar to
that of line 2. The
relation between
density and resist-
ance period can thus
be expressed by the
equation

D=k. log. B,

in which D stands for
density ; Ji, for re-
sistance period; and
^ is a constant whose
value depends upon
the system of loga-
rithms employed.
This formula may be

transformed into the equivalent: E=e^, in which e is the
base of the Napeeian system of logarithms. Since the

osmotic pressure is proportional to the concentration (p. 71),

o
it follows also that H = e^' where 0 stands for the osmotic
pressure and k' for a new constant. The same relation holds
when we compare the reciprocals of the relative resistance
periods — or the relative rapidity of killing — and the abso-
lute diminution of concentration.

§3] ACCLIMATIZATION 85

§ 3, Acclimatization to Solutions of Greater or Less
Density than the Normal

In the preceding section we saw that different organisms had
a diverse resistance period to the same density of solution. In
part, this may be accounted for, as we have seen, on the ground
of a difference in the rapidity of osmotic action — thick-skinned
animals resisting longer than thin-skinned ones. All diversity
in the effect of solutions, cannot, however, be accounted for on
this ground. Thus, the molluscs of the sea and those of fresh
water appear to have an equally pervious epidermis, yet the
former will, of course, withstand a much stronger solution of
salt than the latter. This difference in resistance capacity
seems closely correlated with the conditions of the medium in
which the organism has been reared. Thus, Beudant ('16)
found that littoral species (living, therefore, in a part of the sea
where the water is much diluted by rivers), e.g. Ostrea, ^Mytilus,
Patella vulgata, resist fresh water better than deep-sea species;
and this discovery has been abundantly confirmed by de
Varigny ('88).*-

That the conditions of density of the culture medium deter-
mine the resistance capacity is proven by experiment, for, by
varying the density of the culture solution, we may vary the
resistance period of the individuals experimented on. Beudant
('16) was the first to show this. He used Lymnea, Physa,
Planorbis, Ancylus, Paludina, and some other fresh-water Mol-
lusca. He began in April by putting these organisms into a
1% NaCl solution, and, continuing to add salt slowly, by Sep-
tember many of these withstood a 4% solution — a solution
which kills animals suddenly subjected to it. He performed
likewise the reverse experiment upon marine MoUusca (Patella,

* The extremes of density in which organisms are capable of living are often
considerable. On the one hand, the individuals of some species, especially fish,
nre able to migrate from fresh to salt water and back, with impunity. On the
other liand, many species of a family, the other members of which are marine,
have become accustomed to fresh water. Examples of this last case are the
hydroid Cordylophora lacustris, the mollusc Dreissena, and the endoproctan
bryozoan Urnatella. Likewise, some marine species have come to live in exces-
sively salt water. Such, for example, is the case with Artemia salina which
lives in Salt Lake, Utah, containing over 22% of salts. (Leidv, '72, p. 165.)

86 SOLUTIONS AND PROTOPLASM [Ch. Ill

Turbo, Area, Cardium edule, Mytilus edulus, etc.) bringing
them to live in fresh water by gradually diluting the medium.

Plateau ('71) gradually accustomed the fresh-water Asel-
lus aquations to pure sea water, so that even in mixtures con-
taining between 20% and 80% of sea water they laid eggs and
produced a second generation. The second generation lived
108 hours in pure sea water, while Asellus freshly taken and
plunged into sea water live only about 5 hours.

Not only the larger organisms, but also tissues and Protozoa
may become acclimated. Roth observed in '66 (p. 190) that
cilia become " accommodated " to gradually increasing densi-
ties ; Engelmann ('68, p. 343), however, denied, though with-
out critical experiments, the validity of this conclusion for the
case of the ciliated epithelium of the frog's throat. Later,
CzERNY ('69, -p. 161) succeeded in acclimating Amoeba to a 4%
solution of NaCl, although Amoeba rarely resists 1% when sud-
denly subjected to it.

These early experiments have since been greatly extended,
observations having been made upon nearly all groups of organ-
isms — upon algse, by Richter ('92) ; upon Myxomycetes, by
Stahl ('84); upon Actinospherium, by Verworn ('89, p. 10);
upon bacteria, Flagellata, Ciliata, and Hydra, by Massart
('89); upon Ciliata, by Fabre-Domergub ('88); upon Crus-
tacea, by Plateau ('71), Schmankewitsch ('75 and '77),
and Bert ('83); upon the tadpoles of frogs, by Yung ('85,
p. 520) ; and upon representatives of almost all of the principal
groups, by de Varigny ('88) and Gogorza ('91).

The aims and methods of these experimenters have been
very diverse. Some have sought merely to illustrate how
marine organisms may have come to live in fresh water, or the
reverse. Such have usually made mixtures of fresh and salt
water, the proportions of the one gradually increasing (de
Varigny, Schmankewitsch, Gogorza), or they have added
sea salt, dry or in solution, to the normal fresh-water medium
of the organism (Yung). Massart, on the other hand, having
in mind the more fundamental problem of the action of density
upon protoplasm, has employed solutions of a single salt at a
time — solutions, moreover, based usually upon the osmotic
index of the salt as a unit of concentration.

§3]

ACCLIMATIZATION

8T

Athough there has been a gradual improvement in methods,
the conditions other than that of concentration have too often
been omitted from consideration. The omission of the tempera-
ture of the experiment solutions is especially unfortunate, for
according to Gogoeza ('91, p. 270), acclimatization is more
easily effected at a low temperature than at a high one.

Of the papers mentioned above, that of Massaet is especially
worthy of extended notice from its quantitative nature. He
subjected cysts of Ciliata to various concentrations of KNO3
and noted the effect upon the protoplasm. In the following
tables, the first line of numbers names the solution in parts of
the molecular weight expressed in grammes. The symbols in
the columns headed by these numbers have the following signifi-
cations: 0, no effect; v, the cysts possess a large vacuole whose
pulsations are infrequent; v p^ the vacuole is still prominent
but plasmolysis is occurring ; jp, the plasmolysis is more marked
and the vacuole is gone; P, the plasmolysis is so marked that
the form of the infusorian is lost. The results given in the
third and fourth lines were obtained from individuals acclimated
for 22 hours to a 1.8 MW % and to a 3 M\V % solution of
KNO3 respectively. The observations were made immediately
after immersion of the cysts. No mention is made of the
temperature.

TABLE X — VORTICELLA

Hundredths of Molecclae Weight.

Unacclimated ...
Acclimated to 1.8%
Acclimated to ^3.0 %

0.5

1.0

1.5

3.0

3.5

3.0

3.5

4.0

(.'

V

vp

vp

P

P

P

V

vp

vp
vp

P
P

P
P

TABLE XI — CoLPOD.A.

Hundredths or Moleoitlar Weight.

0.5

1.0

1.5

3.0

3.5

3.0

3.5

4.0

5.0

Unacclimated

0

('

V

V

(7

V

V

Acclimated to L8M\V%. . . .

0

V

V

vp

p

P

Acclimated to 3.0 MW%. . . .

V

p

p

P

88 SOLUTIONS AND PROTOPLASM [Ch. Ill

If we take as our unit in Table X tlie concentration repre-
sented by V p, and in Table XI the concentration represented
by V, we may conclude that the subjection for 22 hours to a
1.8 MW % or to a 3 MW % solution of the salt has given a
resistance capacity of between 2 and 3 times the normal.*

The question now arises, what is the cause of this increased
resistance capacity ? It is not merely apparent, resulting from
the selection of the more resistant individuals, thus elevating
the mean. It is clearly due to a diminution in the intensity of
osmosis; and this must be due to the establishment of an equi-
librium between internal and external osmotic pressures.

Now, this equilibrium can only be brought about by the
density of the internal fluids becoming equal to that of the
external medium; and this requires that the salt held in solu-
tion shall traverse the bounding protoplasmic films, gaining
the interior. That such a traversing occurs lias been argued
by Mass ART ('89), who has himself produced new evidence for
this conclusion. As is well known numerous pigments in
solution penetrate to the nucleus of the living protist. Potassic
nitrate (Janse, '87, p. 22), glycerine, and urea (de Vkies,
'88 and '89) have been observed to penetrate protoplasm. f
That NaCl does the same thing has been shown by many
observers. Thus, Emery ('69) found that when a frog is
placed in a salt solution and is left there for some time, then
rinsed in water until no salt appears in the washings, and,
finally, put into pure water, salt is given forth from the epider-
mis (precipitation on adding silver nitrate). Likewise Plateau
('71, p. 20) found that various fresh-water Arthropods reared
in a salt solution excreted an unusual amount of salt ; and
Frederic ('85) has determined that the quantity of salt in the
blood of Carcinus varies from 3.1% to 1.5%, according to the

* A few data concerning proper acclimatization cultui-es to NaCl may be
found useful. To acclimate bacteria 0.003 to 0.009 MW % may be added daily ;
Oscillaria, 0.01 MW %, added monthly ; Anabajna and Tetraspora, 0.018 MW %,
added monthly ; Ciliata, 0.003 MW %, daily ; Hydra viridis, 0.001 MW %, daily
for 6 days ; Tubifex, 0.02 MW %, daily ; tadpoles, 0.004 to 0.014 MW %, daily.

t A fact observed by Bert (71) suggests that some solids are taken into the
body in acclimatization ; for, he says, fresh-water fishes acclimatized to sea
water gain in weight, and when placed in fresh water fall to the bottom. The
fact that they fall to the bottom indicates that their specific gravity is increased.

§ 4] TONOTAXIS 89

density of the salt solution in which it has been reared. Finally,
Massakt has shown, by a new method, that several soluble
organic compounds can permeate the bounding cell-film of
Flagellata. Thus, if after permanently plasmolyzing Polytoma
uvella by a 0.02 MW % solution of KNO3, a 0.01 MW % solu-
tion of saccharose be added to the solution, the protoplasm soon
regains its normal form, apparently by absorption of saccharose,
since the cell-wall is impermeable to KNOg. By the same
method, potassium acetate, calcium butyrate, calcium phosphate,
glycerine, ammonium tartrate, asparagine, glycose, sodium
benzoate, salicin, and phloridzin can be shown to permeate the
protoplasm of this flagellate. All these facts point to the con-
clusion to which physicists had arrived concerning dead animal
membranes, that protoplasm admits the slow penetration of the
dissolved salts, and thus effects the eventual equilibration of
internal and external densities.

In conclusion, a word may be said concerning variability in
capacity of acclimatization. The data afforded, upon this sub-
ject by RiCHTEE. ('92) are the most valuable. He was able to
acclimatize Tetraspora to 16% (0.27 MW %) NaCl, while
Spirogyra would not withstand, under like treatment, 0.5%
(0.0085 MW %). It is clear then that, just as the resistance
capacity varies, so also does the acclimatization capacity.

§ 4. Control of the Direction of Locomotion by
Density : Tonotaxis

Three authors only, so far as I know, have concerned them-
selves with this phenomenon, — Stahl ('84), Pfeffer('S4, '88),
and Massart ('89, '91). Stahl ('84) observed that plasmodia
of Myxomycetes withdrew from solutions either denser or less
dense than the normal, and concludes that the action is not a
simple, directly explicable one, but is rather a highly compli-
cated irritability phenomenon. The observations of Pfeffer
were incidental to his study of chemotaxis. He found that
high concentrations of many substances acted repulsivel}', and
he was at first ('84, p. 455) inclined to attribute this repulsion
to osmotic action, but later ('88, p. 624) he believed this view
disproved. The disproof he considered to lie in this, that

90 SOLUTIONS AND PROTOPLASM [Ch. Ill

the repulsive quality varies with the quality of the substance
— may occur even in substances which are not attractive at
any concentration. Pfeffer is, therefore, inclined to regard
strong, repelling solutions as acting in a different fashion from
attractive ones. Just as strong sunlight may repel organisms
attracted by weak light, — both phenomena being light phe-
nomena, — so the repulsion and attraction of solutions may
both be regarded as chemical phenomena.

The work of Massaet brought evidence against Pfeffee's
conclusions, and added many important data. His studies
were made chiefly upon bacteria, to a less degree upon Flagel-
iata. Hydra, the frog, and the human conjunctiva. The results
of the studies showed that neutral solutions of a certain con-
centration repel, and that the repulsion is proportional to their
isotonic coefficients and inversely proportional to their molecu-
lar weights, and, therefore, that the repulsions are purely
osmotic phenomena.

The conclusions of Massart thus summarized were obtained
by the use of special methods, which gave quantitative results.
So they are worth detailed consideration. A drop of liquid
containing bacteria is suspended from the under side of a
cover-glass in a moist chamber whose side walls are formed of
cardboard, and whose top is the cover-glass. Into the drop,
glass capillary tubes similar to those used by Pfeffer are in-
troduced, filled with the solution whose action is to be studied.
In addition to this solution all the tubes should contain ^q oVoo
MW % (0.00691 gr. %) K2CO3 for the purpose of attracting
the bacteria. When a tube containing only this dilute solution
of K2CO3 is put into the drop, bacteria crowd into it and liter-
ally fill it in from 20 to 30 minutes. But when a series of
increasing solutions of a neutral salt like NaCl is added to the
K2CO3, the organisms at first do not crowd in so rapidly, then
remain at the mouth, and, finally, are repelled from the tube
opening. Massart has tabulated the results obtained with
Spirillum upon using tubes containing different chemical sub-
stances in different degrees of concentration. One of these
tables, in slightly modified form, is reproduced here. In this
table, A indicates that the bacteria entered the tube readily ;
«, that they merely gathered about its mouth ; 0, that they

§4]

TONOTAXIS

91

were repelled. The numbers at the heads of the columns are

the different values of n in the formula,

1000

MW %. Since

the different solutions were made up on the basis of molecular
weights, all solutions of a given concentration contained the
same number of molecules.

TABLE XII

ISOTON. COEF. 3.

1

3

3

4

5

6

7

8

9

10

NH4CI ....

A

A

A

a

a

0

0

0

0

0

NaCl . .

A

A

A

A

a

a

0

0

0

0

KCN . .

0

0

0

0

0

0

0

0

0

0

KCl. . .

A

A

A

A

a

a

0

0

0

0

NH4NO3

A

A

A

A

a

a

0

0

0

0

NaNOg .

A

A

A

A

a

a

a

0

0

0

KNO3. .

A

A

A

A

a

a

0

0

0

0

KBr . .

A

A

A

A

a

0

0

0

0

0

KCIO3 .

A

A

A

A

a

0

0

0

0

0

KI ...

A

A

A

A

a

a

0

0

0

0

From this table it aj)pears that, as a rule, solutions of y^^
MW (fo and over are repelled, while those of y^^q or under,
except in the case of KCN, permit the free migration of the
bacteria into the tube.

In the case of those substances whose isotonic coefiicient is
4, solutions of ^ q'Vo MW % and over always repel, and those of
YoVo ^^^ ^^^ majority of cases permit free migration. In the
case of those substances whose isotonic coefficient is 2, solutions
of over i\^-Q MW % repel, and those of under YQit'Q usually
permit free migration. The solutions at which repulsion just
occurs in the three cases are in the ratio 10 : 7 : 6 ; which is
nearly the same ratio as the reciprocals of the isotonic coef-
ficients, which, multiplied by 2 run, 10 : 6.6 : 5. Thus the
conclusion seems justified that the repelling action of these
substances is proportional to their isotonic coefficients, and is,
therefore, probably osmotic in its nature.

In a second work, Massart ('91) has studied this matter
with the aid of new methods. A drop of sea water containing
bacteria is prepared as before, on a cardboard ring, but, in place

92

SOLUTIONS AND PROTOPLASM

[Ch. Ill

of a capillary tube containing a dense solution, grains of NaCl
are placed at one point of the margin of the drop. These
grains gradually dissolve, their molecules gradually diffuse
through the drop, and as they do so the bacteria retreat before
them, remaining in the zone of least concentration. Again, a
drop of distilled water Avas placed alongside of the drop of sea
water containing Spirillum, and the two drops were connected
by a communicating canal of water (Fig. 11). As the dis-

Distilled iKater.

Distilled water.

Distilled water.

Fig. 11. — A drop of sea water connected with a drop of distilled water (in lower part
of diagrams) . The marine bacteria of the former retreat before the encroachment
of the latter. (From Massart, '91.)

tilled water mingles with the sea water at one mouth of
the communicating canal, the bacteria retreat further and fur-
ther from that mouth, keeping in the most concentrated part
of the drop. Finally, when a drop of sea water is connected
with one of distilled water, and granules of NaCl are placed
in the drop of sea water, the bacteria, retreating from the zone
of too great concentration penetrate into the drop of distilled
water (Fig. 12), where they now find the proper concentration.
Thus, Spirillum is sensitive both to solutions denser and to
those weaker than the normal (hyperisotonic solutions and
hypisotonic solutions, Massart).

In summing up the observations of this section, we notice
that some organisms (for Massart found some non-sensitive
bacteria) are sensitive to concentration. This sensitiveness is

LITERATURE 93

ClNa CESTa ClNa ClNa ClNa

Fig. 12. — A drop of sea water joined by a canal with a drop of distilled water. The
density of the sea water is being gradually increased in the successive figures by
the dissolution of grains of salt placed at one edge. As the solution thickens, the
organisms (marine Anophrys, represented by dots) retreat towards the distilled
water. (From Massart, '91.)

sucli that they are repelled by either hyperisotonic or hypiso-
tonic solutions ; only in a certain concentration do they come
to rest. We may speak of these organisms as attuned to
this concentration. Different organisms are attuned to dif-
ferent concentrations, and there can be no doubt that the
degree of concentration to which they are attuned is deter-
mined by the past experience of the organisms, as the facts
of acclimatization indicate.

LITERATURE

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382-385; 464-467. Aug. 1871.
'73. La niort des animaux d'eau douce que Ton immerge dans I'eau de

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I'eau de mer et reciproquement. Comp. Rend. XCVII, 133-136.

16 July, 1883.
Beudant, F. S. '16. Memoire sur la possibilite de faire vivre des Mol-

lusques fluviatiles dans les eaux salines, etc. Jour, de Phys. LXXXIII,

268-284. 1816.
BuTsciiLi, O. '92. Untersuchungen liber mikroskopische Schaume und das

Protoplasma. Leipzig. 232 pp. 1892.

94 SOLUTIONS AND PROTOPLASM [Ch. Ill

Certes, a. '84. Note relative k Taction des hautes pressions sur la vitalite

des micro-organismes d'eau douce et d'eau de mer. C. E,. Soc. de Biol.

XXXVI, 220-222.
'84^ De Taction des hautes pressions sur les phenomenes de la putri-

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V, 158-163.
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infusoires cilies. Ann. des Sci. Nat. (7) V, 1-140.
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Gogorza y Gonzalez, D. J. '91. Influencia del aqua dulce en los Animales

Marines. Annales de la Soc. Esp. Hist. Nat. XX, 220-271. 1891.
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Blutkorperchen im Zusammenhang mit ihren Molecular-Gewichten.

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LITERATURE 95

Regnard, p. '84. Recherches esperimentales sur I'influence des tres hautes

pressions sur les orgaiiismes vivants. Comp. Rend. XCVIII, 745-

747. 21 March, 1884.
'84^ Note sur les conditions de la vie dans les profondeurs de la mer.

C. R. Soc. de Biol. XXXVI, 164-168.
'84''. Note relative a Taction des hautes pressions sur quelques pheno-

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de Biol. XXXVI, 187-188.
'84". Sur la cause de la rigidite des muscles soumis aux tres hautes

pressions. C. R. Soc. de Biol. XXXVI, 310-311.
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Biol. XXXVI, 394-395.
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96 SOLUTIONS AND PROTOPLASM [Ch. Ill

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549. 15 Nov. 1888.

CHAPTER IV

ACTION OF MOLAR AGENTS UPON PROTOPLASM

This subject is so ill-defined that it is impossible to draw
any line of distinction between contact on the one hand and
a crushing pressure, or wounding, on the other. The molar
agents may be solid or fluid. The methods of application may
vary from a blunt contact or a sharp cut or puncture to the
impact of flowing liquid. All these agents have this in common,
however, that they act in a gross, mechanical way. The sub-
ject will be discussed under the following heads : (I) The
effect of molar agents upon lifeless matter ; (II) effect upon
the metabolism and movement of protoplasm ; and (III) effect
in determining the direction of locomotion, — thigmotaxis
(stereotaxis) and rheotaxis.

§ 1. Effect of Molar Agents upon Lifeless Matter

Mechanical disturbance can induce in certain lifeless com-
pounds violent chemical changes. Compounds which are so
affected are preeminently unstable. This instability, however,
varies greatly in degree. In some cases, the blow of a hammer
is required to upset the molecules ; the result being often a
violent explosion. In other cases (^e.g. chloride or iodide of
nitrogen), the slightest touch of a feather suSices to produce
an explosion. Now, most of the substances which explode
upon impact, and which are used in the arts, are organic com-
pounds,— fulminate, nitro-glycerine, gun-cotton, and picric-
acid derivatives, — and therefore it is not surprising that we
find the notoriously unstable protoplasm violently affected by
contact.

Especially important for biology is the fact that undulatory
motions and other periodic disturbances produce very important
H 97

98 MOLAR AGENTS AND PROTOPLASM [Ch. IV

molecular changes in chemical compounds. Certain substances
have a specific rate of vibration, so that when this is reproduced
by a vibrating cord or plate, exjDlosion of the substance may
occur. Iodide of nitrogen is one of these substances which is
exploded by a high note. (Champion and Pellet, '72, p. 212.)
Upon this property of explosive compounds depends, apparently,
the efficacy of "detonators," the explosion of a small quantity
of which is capable of producing the explosion of a great mass
of a second compound. Living protoplasm is, likewise, espe-
cially affected by periodic disturbances, and it is doubtless due
to the peculiarities of its chemical structure that the auditory
epithelium is so affected by sound waves in all their modifica-
tions of pitch, volume, and timbre.

§ 2. Effect of Molar Agents upon the Metabolism
AND Movement of Protoplasm

We shall first consider the effect on metabolism, and then on
movement. The principal metabolic effects that will be con-
sidered are phosphorescence and secretion.

The phosphorescence of organisms is usually regarded as a slow
combustion (oxidation) of organic substances. This chemical
process is apparently accelerated by mechanical irritation, as
every one must have noticed who has rowed a boat on a quiet
summer's evening upon the sea. At every stroke of the oar,
a gleam is sent along its length. An analytical study of this
phenomenon has been made by M assart ('93, p. 62). When
a drop of water containing Noctiluca is put on filter paper, and
the liquid is absorbed, there comes a moment when the surface
film of the water flattens the spherical body of Noctiluca. At
that moment of pressure light is emitted. If, however, the
water is put into a slight vibration by a needle attached to a
tuning-fork, and if the agitation is insufficient to deform the
body, no light will be given forth. Deformation of the body,
but not slight agitation, is, consequently, accompanied by those
metabolic processes which result in the production of light.

Secondly, contact may induce the production and discharge
of secretions. Verworn ('89, p. 81) has called attention to
this phenomenon in the cases of Actinosphserium and Thalassi-

§ 2] EFFECT ON METABOLISM AND MOVEMENT 99

cola. When Actinosphserium is subjected to a slight stimula-
tion, such as would be produced by other Protozoa wandering
among its pseudopodia, it shows no response. But when an
infusorian or a rotifer swims against the pseudopodia with
force, they discharge a sticky substance which holds the dis-
turbing organism fast. The same result follows the irritation
of one of the pseudopodia by touching it with a fibre of cloth
or filter paper. Like effects follow the irritation of Thalas-
sicola. Thus, some Protista respond to particular kinds of
contact by the excretion of a sticky substance.

In the higher animals, also, contact may call forth secretions ;
thus, the stolons of many hydroids secrete a cement from the
surface applied to the substratum.

Among the higher plants, also, contact has sometimes a similar
effect. Examples appear in Darwin's ('75, p. 393) work on
the gland cells of insectivorous plants. In many species, to
be sure, e.g. Drosera, Dionsea, Drosophyllum, mere contact of
inorganic bodies has no effect upon the secretions of the glands
of the leaves. In the case of Pinguicula lusitanica, however,
fragments of glass, as well as seeds and albumen, caused the
glands with which they came in contact to secrete more freely
than before.

This response to contact by secretion is, for the most part,
an advantageous one. It enables the Protista and the insec-
tivorous plants to hold their prey or their enemy, as the case
may be ; and it enables the stolon to hold fast to the sub-
stratum.

The change in metabolism may be so profound as to lead
to death. PIorvaeth ('78) and Meltzee ("94) have shown
that when bacteria are violently shaken, not only is growth
interfered with, as we shall see in the second part of this
book, but death may ensue, so that cultures of bacteria may
be sterilized.

We now turn to consider the modification, of movement by
molar agents. The general phenomena are familiar. An
amoeba, any other rhizopod, or a white blood corpuscle con-
tracts when the cover-glass over it is disturbed. The stream-
ing in the plasmodia of Myxomycetes is retarded or inhibited

100

MOLAR AGENTS AND PROTOPLASM

[Ch. IV

(L*

upon shaking. When alga cells, such as those of Chara or
Vallisneria, are freshly transferred to the slide, the disturbance
causes cessation of movements (Hofmeister, '67, p. 50).
When the stamen hairs of Tradescantia are crushed, the stream-
ing of the plasma ceases. When Chara is cut across or punct-
ured, rotation stops for a longer or shorter time (Dutrochet,
'37, p. 780). Even when a stem of Chara is pricked at the
node by a needle, without penetrating into the cavity, move-
ment ceases for a minute
or two. Thus, mechanical
disturbance profoundly af-
fects protoplasm.

Let us now consider
more in detail the changes
which take place in the
protoplasm. Verworn"
('92, p. 24) has given
us data on this matter.
Orbitolites is a rhizopod
having extremely deli-
cate, filamentous pseudo-
podia. If one of these
pseudopodia be cut across
as at a;. Fig. 13, a, the
following changes occur :
the protoplasm lying next
the cut directly collects
into small spherical or
fusiform masses which be-
gin to migrate centripe-
tally (Fig. 13, 6), This movement meets with the normal
centrifugally migrating plasm and turns the latter towards the
centre again (Fig. 13, c). Gradually the thickenings elongate
until, before they have reached the central body, they are no
longer visible (Fig. 13, d). In about 2 minutes normal move-
ments are completely restored (Fig. 13, e). Slightly different
results are gained from Cyphoderia (Fig. 14). When the
large pseudopodium of this organism is touched with a needle
near its distal end, it thickens (as in the case of Obitolites) and

CL t> ^ "■ ^

Fig. 13. — Pseudopodium of Orbitolites, re-
tracting as a result of local stimulation.
The arrows give the direction of the
streaming of protoplasm. At the left is
shown the beginning of the excitation; at
the right, its end. (From Verworn, '92).

§2]

EFFECT ON METABOLISM AND MOVEMENT

101

the thick region, together with all the proximal lying proto-
plasm, begins to flow towards the centre. The whole plasma
thread retracts.

Again, if an individual of Diiflugia (Fig. 15) be slightly
shaken, the pseudopodium contracts into the shell ; if it be

Fig. 14. — Cyphoderia margaritacea, showing the retraction of its pseudopodium as a
result of irritation at the point indicated by the arrow. (From Verworn, '92.)

Fig. 15. — Difflugia urceolata ; at a, stimulated by a weak local irritation ; at b, by a
somewhat stronger one. (From Verworn, '89.)

violently shaken, the following changes occur : drops of a less
highly refractive substance seem to gather on the surface of
the filamentous pseudopodium and unit^ to form a sheath sur-
rounding a more highly refractive axis. At the same time,
axis and sheath retreat into the central mass. In this case,
then, we have a segregation of dissimilar protoplasmic sub-
stances, and a tendency to collect about centres along the

102

MOLAE AGENTS AND PROTOPLASM

[Cii. IV

u

<

o

1^

^

Fig. 16. — A series showing seven phases in the contraction of a pseudopodium of
Diiflugia lobostoma, following total stimulation. The series passes from left
to right. (From Verworn, '92.)

pseudopodium and in the whole mass. The same thing is seen
in the widely dissimilar Actinospherium (Fig. 17). Here is

Fig. 17. — Actinosphserium Eichhornii, unirritated. Natural size about 0.5 mm.
(From Verwokn, '89.)

especially noticeable (Figs. 18, 19) the tendency to produce
fusiform or spherical aggregations, and to retract the pseudo-
podia. So, too, in the irritated stamen hairs of Tradescantia ;

EFFECT ON METABOLISM AND MOVEMENT

103

Fig. 18. — Actinosphserium Eichlioriiii, at the beginning of irritation. The proto-
plasm is accumulated along the pseudopodia in drops and spindles. (From
Verwobn, '89.)

says HoFMEiSTER ('67, p. 50), "The threads become knotty,
tear apart, draw together into short clubs or balls, and fuse

Fig. 19. — Three pseudopodia of the same individual, much enlarged, a, normal
condition; the axial thread is seen, surrounded by protoplasm. 6, the pseudo-
podia at the beginning of stimulation, c, d, the stimulation is continuing, and
the axial thread is shortening, e, the three pseudopodia are almost completely
retracted. (From Verwoun, '89.)

partly with the collection of protoplasm lying about the cell-
nucleus and partly with the peripheral protoplasmic layer."

These similar phenomena from various organisms are funda-
mental ; how are they to be interpreted? It is Avell known

104 MOLAR AGENTS AND PROTOPLASM [Ch. IV

tliat non-vital semi-fluid substances tend to assume a spherical
form by virtue of the property of surface tensions. That pro-
toplasm does not always assume this form is due to special
causes. When a Protist or one of its pseudopodia is irritated
by contact, it tends to assume a spherical form or a thread tends
to aggregate into spherical drops. It seems probable, we can-
not say more than that, that this aggregation is due to a dimi-
nution in the activity of those causes which oppose the action
of surface tension; and so the latter reasserts itself. It is
likewise possible that new attractive centres arise. That a
thread should break up into drops indicates, moreover, a loss
in cohesion. Loss of cohesion, formation of new centres of
attraction, and diminution of the form-maintaining forces, —
these seem to be the effects of contact. They must be due to
the chemical changes wrought by contact.

The changes just referred to constitute the essence of con-
traction, a phenomenon of widespread occurrence not only among
Protista, but among the higher plants and animals ; for ex-
ample, in the sensitive plant and in Vertebrate muscle. Into
these contraction phenomena which follow contact in the higher
organisms we cannot go ; their study belongs to the field of
plant and animal physiology. At bottom, however, we must
believe many of these phenomena in the higher organisms to
be due to the same causes as contrastion in Protista.

A few Avords concerning rhythmically repeated disturbances.
A single disturbance gives rise, as we have seen, to a series of
phenomena producing contraction; but in a few seconds the
effects of the disturbances are past and the protoplasm returns
to its uncontracted form. If, however, the shock is repeated
before relaxation has fully occurred a new contraction is super-
imposed on the first, and the resulting contraction is more
violent than a single one. If now shock follow shock in quick
succession, a violently contracted condition, known as tetanus,
results. Under the condition of tetanus the amoeba becomes a
spherical mass, Actinosphserium retracts all of its pseudopodia,
a branching Carchesium stock forms a little ball, and muscle
fibres are greatly shortened. In a word, rhythmically repeated
shocks are accompanied by an exaggeration of those changes
which result from a single shock.

§ 3] THIGMOTAXIS 105

§ 3. Effect of Molar Agents in determixing the
Direction of Locomotion — Thigmotaxis (Stereotaxis)

AND RhEOTAXIS *

We have already seen that when a pseudopodimn of an
amoeba is touched by a solid body it retracts. In this retrac-
tion the centre of mass is transferred to a new point. If the
stimulation is often repeated upon the same side, contraction
continues on that side, until eventually the amoeba will have
migrated a considerable distance. In this case the determina-
tion of the direction of locomotion is closely allied to the phe-
nomena of contraction as a result of stimulation, considered in
section 2. The retraction of the protoplasm which follows its
irritation is the cause of the migration of the amoeba in a defi-
nite direction. This direction is away from the touching body.
The response may consequently be called negative thigmotaxis.

The phenomenon of negative thigmotaxis is widespread.
There are almost no free-moving organisms which do not move
away from contact or molar disturbance of an unusual or vio-
lent sort. Thus you may very definitely control the direction
of movement of a planarian or a slug by touching the body
upon the side opposite the direction in which you wish it to
move. In such cases, also, there is first a contraction of the
body upon the irritated side.

The opposite phenomenon of movement towards, or clinging
to, the irritating body — positive thigmotaxis — is less common
and therefore more striking. It has long been known, I imag-
ine, — it certainly is an observation easily made, — that an
amoeba which has come in contact with a solid body clings
close to it and moves over its surface. Le Dantec ('95,
p. 211) has described the action in much detail. An anift'ba
descending in the drop touches the glass slide first by a single
protruding pseudopodium. Next, the pseudopod elongates hori-
zontally, and at the same time affixation takes place, so that the
organism does not roll about when the water is agitated. The

* Thigmotaxis, under the different form " thigmotropism " (from dly/xa,
"contact") was first applied to these ijhenomena by Vekwoun ('89, p. 90);
stereotaxis, under the form " stereotropism " (from crrepeds, "solid"), was intro-
duced by LoEB ('90, p. 28), and is practically synonymous with thigmotaxis.

106 MOLAR AGENTS AND PROTOPLASM [Ch. IV

pseuclopod gradually extends itself, and new ones are formed,
until at last the whole substance of the amoeba is spread out
parallel to the glass, over whose surface it moves. That there
is a considerable adherence is shown by the fact that the
amoeba is not disturbed by an appreciable current. If, how-
ever, it is made to contract, it looses its hold at once.

Very similar phenomena occur, according to VERWORisr ('95,
p. 429), in Orbitolites also. Such an organism lying in a watch
glass begins to send out pseudopodia which, so long as they
move free in the water, are simple straight threads ; but when
they touch the glass they adhere to it, stream out along it, and
send out branches. In these Rhizopoda, consequently, the
presence of a solid body is a stimulus to the spreading out of
the pseudopodia and to those changes by which close adhesion
is effected.

We now pass to the other simple organisms. Among Infu-
soria, Pfeffer ('88, pp. 618-621) has found that Glaucoma
scintillans and, to a less degree, Colpidium colpoda, Parame-
cium aurelia, and Stylonychia mytilus aggregate about solid
bodies in the water, such as fragments of soaked filter paper
or particles of barium sulphate. Since these cannot supply
oxygen or solubl^ substances, the effect produced is doubtless
due to contact.

Thfe aggregated organisms tend, in moving, to keep upon the
surfa^^e of the solid. Thus Pfeffer ('88, p. 619) found that
Urostyla weissii, coming in contact with glass threads, moved
along them on their ventral surfaces ; and Massart ('91)
observed some Chlamydomonades remain hanging to objects
with which they came in contact. Verworn ('95, p. 431),
likewise, finds that Oxytricha travels over the surface of Ano-
donta eggs or particles of detritus which it happens upon in
the water. In one instance, the organism ran for some time
over the surface of aii egg of Anodonta without being able to
leave it. After four hours, it was able, by the aid of a- piece
of slime which came in contact with the egg, to free itself from
that body.

Phenomena similar to the above-described for bacteria and
Infusoria are found in spermatozoa also. Dewitz ('85 and
'86) first noticed this in the case of the cockroach, Periplaneta

§3]

THIGMOTAXIS

107

orientalis. When an 0.8% or 0.9% NaCl solution contain-
ing spermatozoa was put under a cover-glass, the spermatozoa
arranged themselves in two layers, one in contact with the
cover-glass, the other in contact with the slide. By isolating
some of the spermatozoa at the upper surface and putting them
under a cover-glass, he found that they likewise distributed
themselves at both upper and lower surfaces. Hence the segre-
gation into two layers was not due to a difference in kind
between the spermatozoa occupying the two positions, but to
the fact that there were here two surfaces of contact, separated

Fig. 20. — A, Oxytricha seen from below; B, from the side; C, crawling over the
egg of Anodonta. (From Verworn, '95.)

by a water-film. If a spherical grain be placed in the drop of
water, aggregation takes place about that also. A similar
experiment, with similar results, was made by ]Massaiit ("88)
with frog spermatozoa. Here, too, the active spermatozoa kept
in contact with the upper and lower glass surfaces, whilst the
weak forms lay midway between. The fact that only active
spermatozoa show this tendency to keep in contact Avith solids,
indicates that we are here dealing with irritability to contact.

The quality of tlie surface influences its capacity for stimu-
lating to positive thigmotaxis. Thus, while mere roughness
has no effect, if the surface of glass be smeared with a slimy
mass, so thick that the spermatozoa can hardly penetrate it,

108 MOLAR AGENTS AND PROTOPLASM [Ch. IV

they may no longer cling to tlie glass, but wander, undirected,
through the Avater. Again, while the surface film of water
often acts thigmotactically, if the surface tension is reduced
by a thin covering of oil, it no longer holds the organisms.
It v/ould seem that a certain minimum difference in rigidity,
between any surface and the medium, is necessary in order
that the surface should act thigmotactically.

Once in contact with a sufficiently attracting surface, the
organism may move to and fro over it, but it can hardly leave
it. It is, as Dewitz ('86, p. 366) says, as though the sperma-
tozoa were attracted by a magnet. This close adhesion of the
organism to the irritating surface is a remarkable phenomenon.
Le Dantec ('95) suggests that the amoeba adheres to the
glass by molecular attraction. On the other hand, it may be
doubted whether the close adhesion signifies anything else
than the absence of a sufficient stimulus to leave the surface
of contact.

When an organism has been stimulated by contact for some
time, it at last becomes changed so that it no longer responds
as it did at first. Thus Dr. W. E. Castle has informed me
that he has seen a colony of Stentors, in an aquarium, being
constantly struck by Tubifex waving back and forth, yet the
Stentors did not contract as they usually do when struck.
Pfeffee ('88, p. 619) has observed that Urostyla retreats,
after a time, from the surface with which it was in contact.
These facts indicate that protoplasm can become acclimatized
to contact so as to be no longer stimulated by it.

We now turn to the consideration of Hheotaxis, which may
be regarded provisionally as a form of thigmotaxis, although
the possibility of its being rather a case of chemotaxis is not
excluded.

EosANOFF ('68) was the first to notice the rheotaxis of the
large plasmodium of ^thalium septicum, but he ascribed it
to geotaxis. The correct interpretation was first given by
Steasbuegeb, ('78, p. 62), and has been confirmed by Jonn-
SON ('83), and Stahl ('84). When iEthalium is placed on a
strip of saturated filter paper, the upper end of which is
dipped in a beaker of water, it is subjected to a current
of water in the substratum. At the same time it moves

§ 3] RHEOTAXIS 109

against the current. The current controls the direction of
locomotion.

The evidence that it is indeed the current is partly gained
by exclusion. It cannot be geotaxis, for if the current is
flowing upwards on any arm of the strip, the plasmodium
flows down. It can hardly be hydrotaxis, for the strip is uni-
formly saturated throughout. The action of light may be
excluded by shutting the whole apparatus in the dark, when
the same response occurs. When the direction of the current
in the strip is reversed, the movement of the plasmodium is
reversed also. Thus no other cause will explain the result but
that of the moving water.

Satisfactory evidence that it is the current as such which acts
will not be forthcoming until it has been shown that other
fluids than water, e.g. oil, provoke a similar response. Until
such an explanation has been tried, it must remain uncertain
whether the phenomenon is not perhaps due to a difference in
the quality of the afferent and the efferent water.

Finally, it must be mentioned that higher organisms, espe-
cially fish, are rheotactic. Whoever has seen fish ascending
streams from the sea in the spring has had this vividly
impressed upon him. Before some dam thousands of fish will
be seen, all facing the torrent of water against which th.Qj can
hardly hold their own. It is the current which determines
their position. They are responding to the direction of flow
of the waters.

To recapitulate : In many non-living substances, especially
organic compounds, violent chemical changes (explosions) are
brought about by contact and especially by repeated vibra-
tions. So, too, in protoplasm, chemical change, exhibiting
itself in modified metabolism, frequent!}'" follows contact. The
explanation adapted to the non-living series of phenomena is
adapted to the living series also, — the molecules of the sub-
stance are complex, loosely associated, very unstable, so that
even a slight mechanical disturbance will serve to dissociate
their atoms. Protoplasm is a mixture of so many substances
that the whole mass does not become changed at once ; but
continued stimulation may eventually produce such wide-
spread changes as to lead to death. One of the most evident

110 MOLAR AGENTS AND PROTOPLASM [Ch. IV

results of contact upon protoplasm is modification of move-
ment, — momentary quiet, followed by contraction. Rapidly
repeated shocks lead to a summation of responses called teta-
nus. Slowly repeated shocks may lead to acclimatization to
contact. Finally, the direction of locomotion is in some cases
controlled by contact ; many organisms move from the touch-
ing body — negative thigmotaxis ; others may face the impact
of flowing Avater or keep close, as though attached, to the rigid
surface — positive thigmotaxis. If the changed chemical con-
dition following contact be called the " response," then all
changes wrought by contact on protoplasm may be considered
as responses.

LITERATURE

Champion, P. and Pellet, H. '72. Sur la theorie de I'explosion des com-
poses detonants. Compt. Rend. LXXV, 210-214.
Dantec, F. le '95. Sur I'adherence des amibes aux corps solides. Compt.

Rend. CXX, 210-213. 28 Jan. 1895.
Darwin, C. '75. (See Chapter I, Literature.)
Dewitz, J. '85. Ueber die Vereinigung der Spermatozoen mit dem Ei.

Arch. f. d. ges. Physiol. XXXVII, 219-223. 29 Oct. 1885.
'86. Ueber Gesetzmassigkeit in der Ortsveranderung der Spermatozoen

und in der Vereinigung derselben mit dem Ei. Arch, f . d. ges. Physiol.

XXXVIII, 358-385. 31 March, 1886.
Dutrochet '37. (See Chapter VIII, Literature.)
HoFMEiSTER, W. '67. Die Lehre von der Pflanzenzelle. Leipzig: Engel-

niann. 664 pp. 1867.
HoRVATH, A. '78. Ueber den Einfluss der Ruhe und der Bewegung auf

das Leben. Arch. f. d. ges. Physiol. XVII, 125-134. 21 May,

1878.
JoNSSON, B. '83. Der richtende Einfluss stromenden Wassers auf wachsende

Pflanzen und Pflanzentheile (Rheotropismus). Ber. D. bot. Ges.

I, 512-521.
LoEB, J. '90. (See Chapter VII, Literature.)
Massart, J. '88. Sur I'irritabilite des spermatozoides de la grenouille.

Bull. I'Acad. roy. Belg. (3) XV, 750-754.
'91. La sensibilite tactile chez les organismes inferieurs. Jour., de

Medecine de Bruxelles. 5 Jan. 1891. [Abstract only seen in Centralb.

f. Bacteriol. XI, 566.]
'93. (See Chapter I, Literature.)
Meltzer, S. J. '94. Ueber die i'undamentale Bedeutung der Erschiitterung

fiir die lebende Materie. Ztschr. f. Biol. XXX, 464-509.
Pfeefer, W. '88. (See Chapter I, Literature.)

LITERATURE 111

RosANOFF, S. '68. De I'influence de I'attraction terrestre sur la direction
des Plasmodia des myxomycetes. Mem. Soc. Sci. nat. Cherbourg,
XIV, 149-172, Tab. I.
Stahl, E. '84. (See Chapter I, Literature.)
Strasburger, E. '78. (See Chapter VII, Literatui-e.)
Verworn, M. '89. (See Chapter I, Literature.)

'92. Die Bewegung der lebendigen Substanz. 103 pp. Jena : Fischer.

1892.
'95. Allgemeine Physiologie. 584 pp. Jena : Fischer. 1895.

CHAPTER V

EFFECT OF GRAVITY UPON PROTOPLASM

We shall consider this subject under three heads: (I) Methods
of Study ; (II) Effect of Gravity upon the Structure of Proto-
plasm ; (III) Control of Locomotion by Gravity — Geotaxis.

§ 1. Methods op Study

Under normal circumstances gravity acts upon organisms
continuously, uniformly, and in one direction only at a time.
In this respect it is widely different from most of the agents

jO

Fig. 21. — Diagram of the essential part of a klinostat. A rotating block or drum,
to which tubes containing the geotactic organisms may be attached in the position
indicated.

which we have to consider. Since its action is uniform it can
be varied only in an indirect way ; i.e. by turning the organism
or by replacing gravity in part by a force working in another
direction. One of the simplest ways of turning the organism
so as to eliminate gravity is by means of the klinostat (Fig. 21).
This is made in various forms, and consists essentially of a
horizontal rod supported near the ends and made to revolve
about its long axis by clockwork. Towards the middle of the
rod, or at one end, is rigidly affixed a block to which may be

112

§ 2] EFFECT ON STRUCTURE 113

fastened, radially, the vessels containing the objects of experi-
mentation. When the rod revolves, all sides of the object
are brought successively and equally under the influence of
gravity's pull. By this means the directive action of gravity
is eliminated.

In the case of organisms living in water, the effect of gravity
may be overcome by the buoyancy of the medium. It is clear
that an organism floating in a medium of its own weight can-
not be affected by gravity. This condition can be brought
about by increasing the specific gravity of water by adding
soluble substances such as gelatine and gum arable. Since
the specific gravity of the organism tends gradually to change
with that of the medium, this method does for rapid experi-
ments only.

In dealing with larger organisms, which, like slugs, can keep

aflixed to glass or other smooth surfaces, the inclination of the

surface may be varied from a vertical position to a horizontal

one, thus varying the active component of gravity. Finally,

gravity may be replaced by centrifugal force by rapidl}^ rotating

either about a horizontal or a vertical axis. By varying the

rate of rotation the centrifugal force will vary, in accordance

2 Trh-
with the formula, /— ~' ^ , in which r is the rotating radius

(in meters) and t"^ the square of the time of a rotation (in
seconds). This varying centrifugal force will act exactly in
the same way as gravity, only from the centre of rotation.

§ 2. Effect of Gravity upon the Stefctuee of
Protoplasm

Very few observations have been made upon this subject,
and yet indications are not wanting that the field would well
repay working. Thus, where the cell contains specifically
heavier and lighter substances the two will be separated by
the action of gravity. This occurs in plant cells in which,
according to Dehnecke ('80), various contained bodies, e.g.
chlorophyll granules and starch grains, tend to sink to the
lower side of the cell. This result is produced in from a few
minutes to several hours. This effect is likewise seen in many

114

GRAVITY AND PROTOPLASM

[Ch.Y

ova in which the yolk sinks to the lower pole and the proto-
plasm floats on top, in whatever position the egg may be held.
This fact undoubtedly has an important effect upon develop-
ment, as we shall see later.

Of the specifically heavier bodies above referred to, the
nucleolus is a striking example, as Hekrick ('96) has recently

shown. Thus, when the
ovary of a lobster is
killed, the nucleoli of
all the nuclei are found
in contact with that part
of the nuclear membrane
which was the lowest at

^W6@

Fig. 22. — Section through the ovary of a lobster
hardened with its dorsal surface (D) upper-
most. The nucleoli lie against the ventral
surface of the nucleus. Magnified 50 diame-
ters. (From Herrick, '95.)

Fig. 23. — Section through the
nucleus of a young ovum
(J mm. in diameter) showing
the nucleolus, which has, ap-
parently, caused a distention
of the nuclear membrane by
the pressure of its own weight.
Arrow shows the direction of
the earth's centre. Magnified
248 diameters. (From Her-
rick, '95.)

the moment of killing (Fig. 22). The weight of the nucleolus
is relatively so great as sometimes to cause a depression in the
part of the nuclear membrane upon which it rests (Fig. 23).

§ 3. Control of the DiRECTioisr of Locomotion by
Gravity — Geotaxis *

The control of the movements of Protista has been investi-
gated chiefly by four naturalists : Schwarz ('84), who studied
Euglena and Chlamidomonas ; Aderhold ('88), who studied

* So called by Schwarz ('84, p. 71).

§ 3] GEOTAXIS 115

Euglena and desmicls ; Massart ('91), who worked upon
bacteria, and ciliate and flagellate Infusoria ; and Jensen ('93),
who experimented with Euglena, Chlamydomonas, and eight
species of Ciliata.

The observation that led Schwaez to his study was that
Euglena and Chlamidomonas, shaken up with sand and covered
by it, constantly, even in the dark, rose to the surface. The
experiments now made by Schwarz to determine the true
cause of the phenomenon were a model of experimental investi-
gation. In the first place only fresh and actively moving
individuals were used, and light was carefully excluded, either
by enveloping the culture vessel in black paper, or by working
in a dark chamber. I shall now give in detail the experiments
and their results.

When the Flagellata were placed in water they responded
like those in sand — they soon came to the upper surface. But
may not this upward movement be purely passive due to the
small specific gravity of the algse or to currents in the water ?
To get an answer to this question Schwaez heated the sand
to 70° C — a fatal temperature — and no aggregation occurred.
Again, the algse were subjected to vapor of chloroform ; no
aggregation. Again, to a low temperature (5° to G°) ; no
aggregation. An aggregation occurred, however, when the
temperature of the same culture was raised to 22**. Finally,
Lycopodium spores and Euglena in the resting stage do not
move upwards ; hence no currents are passing in this direction.
On the contrary, these experiments show that the upward
movements of the algse are the results of its own active loco-
motion.

Nor can it be that anything else than gravity determines the
direction of the locomotion. That the greater amount of oxy-
gen at the upper level is not the controlling agent was shown
by smearing the sides of a glass cylinder with a thin layer of
sand containing the algte. In this thin layer, permeated by
oxygen, they still accumulated at the upper margin. That the
locomotion was not directed by currents in the water (Rheo-
taxis, p. 108) was indicated by the fact that whether the free
end of the tube, at which evaporation is occurring, be up or
down, migration is always upwards. Thus, since the stimulus

116 GRAVITY AND PROTOPLASM [Ch. V

of chemical agents and currents was eliminated, gravity seemed
to remain as the only directing force.

It Only remained to show that the attractive force of the
earth can be replaced by centrifugal force, and this Schwaez
was able to do by means of the klinostat. By varying the
rate of rotation of this machine he varied the centrifugal force
and was able to determine the limits within whicli the Infusoria
move against an opposing force. The acceleration of the rota-
tion-force may be expressed in terms of the attraction of gravity

/
as a unit by the formula c — -, when c equals the acceleration

g

of centrifugal force in the required units; /, the centrifugal
force found, as on p. 113 ; and g the acceleration due to gravity.
It appeared from the experiments that, in both living Euglena
and Chlamidomonas migration took place towards the central
end, thus against the centrifugal force, when the latter was
over 0.5 g., and under 8.5 g. Under the lower limit no migra-
tion occurred ; near the upper limit aggregation occurred at
both ends ; above the upper limit aggregation took place at the
peripheral end — that is to say, with the centrifugal force.
Clearly, then, geotaxis is in these cases a movement against an
opposing force, provided that force is considerable (over 0.5 g.}
but not too great (over 8.5 g.).

The workers in this field who followed Schwaez advanced
our knowledge of geotaxis in two principal ways : first, by
increasing the number of organisms known to be geotactic, and,
secondly, by revealing the fact that closely allied species may
have geotaxis of opposite sense.

Massakt ('91, pp. 161-167) employed a simple but satisfac-
tory method. He placed Protista in a capillary tube which was
open, hence equally oxygenated at the two ends. By invert-
ing the tube the ends were brought into different relative posi-
tions with respect to the earth, causing the geotactic organisms
to migrate throughout its length. As a result of his experi-
ments it appeared that Spirillum ; the flagellata, Polytoma,
Chlamydomonas, and Chromulina ; and the ciliata, Anophrys
and Euplotes, are geotactic. The sense of geotaxis may be
different between individuals of the same genus ; thus, under
similar conditions Spirillum separated into a lot lying at the

§3]

GEOTAXIS

IIT

upper part of the tube and a lot at the lower part ; and the
individuals of both the upper and lower lot were active. The
sense of response depends upon temperature also. Thus Chro-
mulina woroniniana is negatively geotactic at 16° to 20° C,
and positively geotactic at 5° to 7° C. The other species men-
tioned above are negatively geotactic — i.e. move in the direc-
tion opposite to that in which the
force tends to carry them.

Jensen* ('93) finally has greatly
extended our knowledge of the spe-
cies responsive to gravity, has shown
the necessity for regarding carefully
the other agents acting during the
experiment, and has entered more
carefully into the cause of the phe-
nomenon than previous authors. The
new forms which Jensen worked
with were these Ciliata : Paramecium,
Urostyla, Spirostomum, Colpoda, Col-
pidium, Ophryoglena, and Coleps ;
also the more commonly used species,
Euglena and Chlamydomonas. The
other agents whose action may mod-
ify that of gravity are chemical stuffs,
density, warmth, light, etc. Light
may be easily excluded. On warm
days the typical geotactic phenomena
are often absent, the Paramecia sink-
ing to the deeper, cooler layers. The
Infusoria aggregate around bacteria
in the water, — chemotaxis (Fig. 24,

^), — and they shun the uppermost layer, apparently because,
owing to evaporation, this layer is denser — tonotaxis (Fig.
24, c). Whether light inhibits the geotactic response was
one of the questions asked and answered by Jensen. When

<; b c

Fig. 24. — Glass tubes, about 0.5
cm. in diameter and 20 cm.
long, fused at one end, and
filled with water containing
Paramecium ( represented
by points) . o shows aggre-
gation of the Paramecium
at upper end of tube ; h,
aggregation of Paramecium
around bacteria suspended
in the water — chemotaxis
veiling geotaxis; c shows
that occasionally the Para-
mecia avoid the uppermost
layer of the water. (From
Jensen, '93.)

* Jensen used glaas tubes of 0.5 to 1 cm. diameter, and 5 to 100 cm. leugtb,
fused at one end. To prevent the free end becoming richer in oxygen, a layer
of oil 2 to 3 cm. high was poured over that end, or, air being carefully excluded,
it was sealed by an impermeable plug of wax.

118 GRAVITY AND PROTOPLASM [Ch. V

the centrifugal machine was used in the sunlight, movements
towards the centre clearly appeared. It was thus proved
that negative geotaxis (which is the same as centrotaxis) may-
occur in the sunlight.

The data of geotaxis are incomplete without a consideration
of this phenomenon in the higher animals. LoEB is one of the
first investigators in this field. In 1888, he found that flies,
deprived on both sides of the free ends of the balancers or the
wings, and placed upon a board, move always upwards upon it.
If the plane of the board is held oblique to the horizontal, the
fly always moves along that line which makes the smallest
angle with the vertical. Likewise cockroaches seem to be
stimulated by gravity when this acts perpendicularly to their
ventral surface, so that they tend to move off from a horizontal
surface and do not come to rest until they are on a more or less
nearly vertical one. Thus, Loeb put twenty-one cockroaches
into a truncated, pyramidal box, one of whose sides made an
angle of 80° with the horizontal ; another 60°, the third 45°,
and the fourth 25°. After an hour, the number of individuals
on each face of the box was counted at intervals of 10 minutes.
Adding together the results of 10 such counts he found on the
steepest wall 94 cases ; on the wall inclined at 60°, 61 cases ;
on that inclined at 45°, 28 cases ; on that at 25°, 25 cases ; and
on the horizontal surfaces, 2. After several hours 75 to 80%
of the animals were found on the steepest side, although it had
the smallest area. Later, Loeb ('90 and '91) showed that the
holothurian Cucumaria cucumis, the starfish Asterina gibbosa,
and the lady-bird beetles (Coccinellidse) are likewise geotactic.
Finally, it may be mentioned that several species of the slug,
Limax, are geotactic.

There is in Protista, as already mentioned, a limit to the
intensity of the attractive force below which no response will
occur. Is there such a limit in Metazoa likewise ? Experi-
ments upon this point have been made by Miss Helen Pee,-
Kiisrs and myself in connection with my experimental course at
Radcliffe College. We have also been able to answer the ques-
tion, what difference in effect is produced by different intensi-
ties of gravity's action. We experimented with the great slug,
Limax maximus, which crawls readily upon a glass plate placed

3]

GEOTAXIS

119

at any angle. As explained on p. 113, the intensity of gravity's
action will diminish as the sine of the angle of inclination of
the plate is diminished from 90° to 0°. We determined the
deviation of the slug
from a vertical position
upon plates at various
inclinations, and after
the lapse of a constant
time (45 seconds). The
experiments were per-
formed in a dark box.
The number of tests
made at each inclina-
tion was sixty. The
time required to re-
spond fully to gravity
did not vary appreci-
ably with the angle of
inclination. The re-
sults obtained indicated

A

j

1

B-

_

0°

j

/

5°

//

/^

/

/

15°

/

/

'/

V

//

f

J

[y

/

.^

P

__

-^

'

^

^

L-"

B

35°

,~c

iO°

45°

50°

60

80

that the deviation of
the slug from vertical-
ity diminished with the
cosine of the angle
made by the plate.
The relation between
the angular deviation
from verticality and
the sine of inclination
of the glass plate is
graphically represented
in Fig. 25. The con-
clusion from the ex-
periments is that the
lower limit of the sen-
sitiveness of Liraax to gravity is extremely small, below
0.13 g., and that as the angle of inclination of the plate
diminishes the deviation from 45° towards verticality dimin-
ishes in accordance with the relation : S = a- sin ^, in which

'"90° 80° 70° 60° 50° 40° 30° 20° 10° 0°

ANGLE OF INCLINATION OF SURFACE TO HORIZONTAL

Fig. 25. — Curves showing relation between the
sine of the angle of inclination of a glass plate
and the angular i^osition of a slug which was
first placed on it in a horizontal position and
then left for 40 seconds in the dark. Curve A
is constructed hy drawing ordinates from the
heavy horizontal line, 0'^5^, corresponding to
each angle of inclination of the surface (laid
off as abscissa?) . The lengths of the ordinates
are determined hy the number of degrees of de-
viation of the axis of the slug from 45° towards
90°. 45^^ is taken as a base, since it would be
the mean angular deviation from the initial
position of a slug crawling undirected upon a
horizontal plate. Curve B is constructed by
drawing down from the base ordinates propor-
tional to the natural sines of the different an-
gles of inclination of the glass plate.

120

GRAVITY AND PROTOPLASM

[Ch.V

S is the angular deviation of the slug from 45° towards 90°,
expressed in degrees ; 0 is the angle of inclination of the plate
to the horizontal, and a is a constant.

In inquiring into the cause of geotaxis in animals it seems
best to consider chiefly the phenomenon as exhibited in Protista,

for in the higher animals this capacity
seems bound up with the possession of
special organs of orientation. In this
group the first and apparently most
important part played by gravity is
the determination of the axis of the
individual, which comes to lie vertical
and with the head end up or down
according to the conditions of the
protoplasm. After the positions of
the axis and poles are determined, or-
dinary locomotion produces the geo-
tactic phenomena. That gravity may
determine a vertical position without
locomotion occurring is shown in the
ciliate infusorian Spirostomum (Fig.
26), which at times occurs in large
numbers in ordinary aquaria, sus-
pended almost motionless in mid-
water, having a distinctly vertical
position and with the head end
directed upward. They cannot be
said to be strictly motionless, since
by carefully attending to them one
can see them slowly rising or falling
or alternately, perhaps, rising and falling in their almost im-
perceptible movements. Miss Julia B. Platt, who has
studied carefully the movements of Spirostomum, found that
of 78 individuals observed all but 7 had the anterior extrem-
ity directed upwards and the 7 exceptional individuals were
all moving downwards. It therefore seems quite certain that
Spirostomum tends in water to orient itself with reference to
gravity, although without aggregating at the upper surface.

Fig. 26. — Spirostomum ambi-
guum, side view, az, ado-
ral zone of cilia ; o, mouth ;
OS, gullet ; 71, nucleus ; cJc,
contractile canal; cv, con-
tractile vacuole; a, anus.
Magnified" about 120 diam-
eters. (From BuTSCHLi
[Bronn's Tliier-reicb : Pro-
tozoa], after Stein.)

§ 3] GEOTAXIS 121

To explain the phenomenon of axis-orientation, two principal
theories have been advanced. The first may be called the
mechanical theory; the second the response-to-stimulus theory.
The first theory is that once suggested by Vekwoei^ ('89, p.
122). It appeared to him that it was self-evident from purely
physical grounds that, in complete quiescence of the flagellum,
the hinder end of the protist should be directed downwards,
and not the anterior flagellum-bearing end. If one conceives
such an individual to move its flagellum, which precedes in
locomotion, it must move towards the surface of the water;
thus against gravity. Veeworn finds the stimulation theory
inconceivable, since gravity cannot even be compared with
stimuli. In falling, the body of the protist might rub against
the water particles, which would offer a stimulus, but this
would be more allied to rheotaxis.

It might seem an easy thing to determine whether geotactic
Protista artificially rendered quiescent (e.g. killed or stupefied)
would stand with their anterior ends uppermost; but the
killing is apt to distort the form, and the organisms being
heavier than water * fall to the bottom. Something might be
gained from an observation of how they fall, but there is very
great discordance among authors upon this point, probably in
part due to difficulties of observation. Thus Schwauz ('84,
p. 68) says that both Euglena and Chlamidomonas assume all
positions in falling; M assart ('91, p. 164) finds that Chlamido-
monas falls with flagellum directed upwards and Jensen ('93,
p. 451) declares that Euglena viridis killed by iodine falls

* Few determinations seem to have been made of the specific gravity of living
Protista. Jensen ('93'') attempted to do tliis for Paramecia, but his method was
bad and his results bad likewise. He made solutions of potassium carbonate,
of varying specific gravity, and found that Paramecium just floats in a solution
whose sp. gr. is 1.25. The difficulty of the method is that solutions of salt
having a relatively small molecular weight act so powerfully in withdrawing
water from the organism as to cause it to shrink and increase in relative
weight. Miss Platt has used solutions of gum arable whose osmotic action
is so slight that organisms live in it for hours. In such solutions, paralyzed
but living Spirostoma and Paramecia neither sank nor rose when the specific
gravity was between 1.016 and 1.019 ; so that it seems probable that the specific
gravity of Infusoria lies near 1.017. Tadpoles recently hatched and having a
length of 9.5 mm. had a sp. gr. of 1.044, while those 12 mm. long had a sp. gr.
of 1.017.

122 GRAVITY AISTD PROTOPLASM [Ch. V

almost without exception with the broader flagellate pole down-
wards. Both from the fact that it can be easily demonstrated
that when a body heavier than water falls in that medium its
larger end will precede, and from the fact that Jensen was
especially careful that the killed organism should not be
deformed, his results must be considered the best established.
Now, since the dead Euglena tends to sink with flagellum
downwards whereas the active Euglena stands flagellum
upwards, we must conclude that the orientation of Euglena
and probably other Protista is not passive but due to their
activity and must be regarded as a response more or less directly
due to gravity.

But just how does gravity act as a stimulus to determine the
direction of orientation of the body? We have two principal
theories to examine. First, that of Jensen, that gravity acts
indirectly on the organism by directly causing a difference in
pressure in the water at different levels. This difference in
water pressure, at various levels, affects directly the two poles
of the organisms, which stand at different levels, and the
organism responds to this difference in pressure. The second
theory, which I adopt, is that the organism, owing to its specific
gravity being greater than the medium, experiences greater
resistance (friction + weight) in going upwards even to the
slightest extent than in going downwards (friction — weight).
Another stimulus, which is probably associated with this, de-
pends upon the fact that an unsymmetrical body, heavier than
water, tends to fall with its larger end down. Those nega-
tively geotactic organisms, which stand with their larger end
up, will be consequently in a condition of unstable equilibrium ;
those organisms which stand with their larger end down will
be in stable equilibrium. In the first case a deviation from
verticality would be accompanied by relatively diminished
resistance on one side ; in the second by relatively increased
resistance on one side. In either case, the distribution of the
mass of the animal may give the organism the means of deter-
mining, but not in a mechanical way, the position of its axis.

The evidence for the first theory Jensen finds especially in
a fact which he believes opposes the second. Negatively
geotactic organisms, placed in an inclined tube, move towards

§3]

GEOTAXIS

123

the upper side and then travel obliquely, not vertically, along
it toward the upper part of the tube, thus into strata of con-
stantly diminishing pressure. If weight controlled in any way
their movements, they should move vertically as from 1 to 2
(Fig. 27) until they meet the side of the glass. Then they
should move off, as to 3, then vertically to 5, and so on. Since
they do not so move, gravity, Jensen thinks, cannot be said to
act directly. In criticism of this conclusion it may be urged
that it is without proper foundation, for
if an organism whose irritability (in-
stincts) would lead it to move verti-
cally is mechanically unable to do so
exactly, it will do so as far as practi-
cable. This observation cannot, there-
fore, be said to militate against the
second theory. Finally, there is this
positive objection to Jensen's theory
that it is applicable only to geotaxis in
water animals, and can therefore be
only a special explanation of geotaxis.
On the other hand, there is evidence
which is opposed to the first theory and
favors directly the second. And Jen-
sen has himself contributed some of
this evidence. He put Urostyla into
a glass tube containing a 0.5% aque-
ous gelatine solution. They showed
no tendency to go upwards. At the
expiration of 20 hours many deaths
had occurred, but some normally ac-
tive individuals were still at the lower end of the tube. Why
this loss of geotaxis ? Jensen believes it due to the fact that
the difference in pressure of the successive layers did not
increase proportionally to the increase in resistance of the
solution. I would suggest that it may be due to the fact
that the weight of the body of the Protista is now relatively
less than that of the solution, so that the organism, tending
to move against resistance, comes to lie at the bottom of the
buoyant fluid, hence appears positively geotactic.

Fig. 27. — Hypothetical line
of migration of Parame-
cium in an inclined tube,
upon the assumption that
gravity acts directly to
determine direction of
locomotion, according to
the conception of Jexsen.
The arrow at p indicates
the direction of the pull
of gravity; 1, 2, 3, 4, 5,
successive positions occu-
pied by the Paramecium.
(From Jensex, '93.)

124 GRAVITY AND PROTOPLASM [Ch.V

Geotaxis in the higher organisms, especially Vertebrates,
cannot here be discussed at length. It is sufficient to state
that as LoEB ('91, p. 189) concludes, it is probably dependent
upon the internal ear. Miss Platt has, at my suggestion, sub-
jected young negatively geotactic tadpoles to solutions of gum
arable of the same specific gravity as themselves, and has found
that they still migrate upwards. This result makes it probable
that here also orientation is effected by the internal ear, and
hence is independent of the action of gravity upon the entire
body.

Finally must be mentioned the phenomenon of acclimatiza-
tion to a central pressure. This has been observed by Jensen
('93, p. 470), who says, when Paramecium or Urostyla has been
strongly " centrifugated " towards the peripheral end of the
tube, where it is subjected to a high pressure, it shows, when
the tube is then placed vertically, a much livelier geotaxis
than it would have done without " centrifugating." Clearly
the temporary action of the high pressure has increased the
irritability to gravity.

To recapitulate : Gravity affects the structure of protoplasm
by separating the lighter and heavier substances. It may
determine the direction of locomotion by determining the ver-
ticality of the axis of the body. Varying the intensity of
gravity's attraction diminishes the precision with which this
determination takes place. The determination of the vertical
position is, in the lower organisms, probably due to difference
in ease of movement when going up and going down.

LITERATURE

Aderhold, R. '88. (See Chapter I, Literature.)

Dehnecke, C. '80. Ueber nicht assimilirende Chlorophyllkbrper. Inaxig. Diss.

Koln. Abstr. in Bot. Ztg. XXXVIII, 795-798. Also in Bot. Centralbl.

I, 1537.
Herrick, F. H. '95. Movements of the Nucleolus through the Action of

Gravity. Anat. Anz. X, 337-340. 8 Jan. 1895.
Jensen, P. '93. Ueber den Geotropismus niederer Organismen. Arch, f .

d. ges. Physiol. LIII, 428-480. 5 Jan. 1893.
'93^. Die absolute Kraft einer Flimmerzelle. Arch. f. d. ges. Physiol.

LIV, 537-551. 24 June, 1893.

LITERATURE 125

LoEB, J. '88. Die Orientirung der Thiere gegen die Schwerkraft der Erde.

(Thierischer Geotropismus.) Sb. WUrzb. Phys.-med. Ges.
'90. (See Chapter VII, Literature.)
'91. Ueber Geotropismus bei Thieren. Arcb. f. d. ges. Physiol. XLIX,

175-189. 1891.
Massart, J. '91. Recherches sur les organismes inferieurs. III. La

sensibilite a la gravitation. Bull. I'Acad. roy. Belg. (3) XXII,

158-167. 1891.
ScHWARZ, F. '84. Der Einfluss der Schwerkraft auf die Bewegungsrichtung

von Chlamidomonas und Eugiena. Ber. bot. Ges. 11, 51-72.
Verwtorn, M. '89. (See Chapter I, Literature.)

CHAPTER VI
*

EFFECT OF ELECTRICITY UPON PROTOPLASM

In this chapter we shall consider (I) some methods em-
ployed in the investigation of this subject ; (II) the effect
of electricity upon the structure and general functions of pro-
toplasm ; and (III) the effect of electricity in determining
direction of locomotion — electrotaxis.

§ 1. Concerning Methods

While the phenomena of magnetism and electricity are closely
allied, their effects upon protoplasm seem to be widely dis-
similar. Thus no certain action of magnetism has hitherto
been observed, but electricity, however produced, causes nearly
uniformly an effect.

Any experimental work with the electric current involves
apparatus for its production, application, and measurement ;
namely, batteries or other sources of electricity ; electrodes for
applying the current to the organism ; troughs to contain the
free swimming animals used for experimentation ; a galvanom-
eter for measuring the current ; a rheochord for varying the
intensity of the current ; a reversing key ; and, for interrupted
currents, an induction machine with interrupter, and an elec-
trometer for measuring such currents. A description of the
principal forms of these instruments and the methods of con-
structing some of them will be found in Veeworn, '95,
Chapter V, and in Ostwald, '94, Chapter XV.

ISince the works just named are easily accessible, it will be
unnecessary here to describe these instruments in detail. A
few additional suggestions, the result of my experience, may,
however, be found helpful. Concerning batte^-ies, first ; accumu-
lators are without doubt to be preferred, where practicable, on

126

§ 1] METHODS 127

account of the strength and continuance of their currents. In
other cases, Clark or Daniell elements, if enough of them
are united in series, will meet the requirements. The character
of the electrodes^ next, will depend upon the nature of the in-
vestigation. Nonpolarizable ones of hair (camel's-hair brush),
clay, or paper (plug of filter paper in glass tubing drawn out
to a cone) are usually employed, but all of these offer consider-
able resistance. The troughs will vary in form and size with
the organisms to be contained in them ; some of them will be
described in connection with the experiments in which they have
been employed. They are all rectangular enclosures having
clay ends when it is desirable that these should be nonpolariz-
able. For large troughs, sheet-zinc electrodes are used, cover-
ing the smaller sides of the trough. Although some of the
reflecting galvanometers are more sensitive, a " millammeter "
such as that made by the Weston Electrical Works is a much
more convenient instrument and sensitive enough for most
work of this sort. The rlieochord is practically a low-resistance
box, capable of indefinitely fine gradations. This is introduced
into the short branch of a divided circuit, so that by varying
its resistance a varying share of the current shall be forced into
the longer circuit. A very simple and excellent device for
altering the strength of current is the "• Compression-rheostat "
of Blasius and Schweizer ('93). This consists of a piece of
rubber tubing filled with zinc sulphate, stopped at the ends
and introduced into the circuit. By means of a thumbscrew
the walls of the middle of the tube may be pressed together, the
lumen correspondingly reduced, and the resistance increased.
The induction apparatus usually employed is one invented by
DU Bois-Reymond. In this the secondary coil may be with-
drawn from the primary coil to any desired distance, thereby
diminishing the intensity of the induced current. Through
the action of such an instrument the current is alternately
made and broken, and each electrode becomes in quick suc-
cession anode and kathode. Since alternating currents cannot
be measured by an ordinary galvanometer, an electrometer
must be employed. So much concerning apparatus.

A word should be said about the method of stating the cur-
rent employed. Very many authors have been satisfied with

128 ELECTRICITY AND PROTOPLASM [Ch. VI

saying that the current was strong or weak, others have given
the kind and number of elements employed. Such statements
are wholly inadequate to give an accurate idea of the strength
of current to which the organisms under experimentation were
subjected. Even merely to state the galvanometer reading in
milliamperes is insufficient. We must know as nearly as pos-
sible what strength of current is passing through the organism,
and this involves knowing the density of the current passing
through the water in the trough. Now it is obvious that a
current passing through a mass of water of small cross-section
is stronger per square millimeter than an equal current dis-
tributed over a large cross-section. It is necessary, conse-
quently, to know the cross-section of the mass of water through
which the stimulating current is passing, in order to determine
the " density " or strength at any point. For technical pur-
poses the unit of current-density is taken at 1 ampere to the
square millimeter. Hermann and Matthias ('94, p. 394)
propose for physiological purposes a unit one-millionth as great,
to be designated as S. 8 then indicates a current of j-^^ milli-
ampere per square millimeter of cross-section. It is very de-
sirable that, when practicable, currents should hereafter be
expressed in S's. More than one useless discussion has been
precipitated by not giving a sufficiently accurate quantitative
expression to the current employed. (See, for illustration,
below, p. 149.)

Finally, the strength of current necessary to produce a
certain result depends upon the relative conductivity of the
organism and the surrounding water. If, through the presence
of substances in solution, the conductivity of the water is
abnormally great, one must use a greater current (as read off
from the galvanometer) than otherwise to produce a certain
effect. (Waller, '95, p. 97.) It would probably be best,
when possible, to use in the trough the water in which
the organism has been living, since the quantity of salts
in the organism has been shown to vary with that of its
medium. (See p. 88.)*

* See Kaiser, Wien Akad. CIV, p. 17, 1895, for a new trough adapted to the
stage of the microscope.

§ 2] EFFECT ON STRUCTURE AND FUNCTIONS 129

§ 2. The Effect of Electricity upon^ the Structure
AND General Functions of Protoplasm

The fundamental phenomenon of the action of an electric
current upon protoplasm may be seen while watching a helio-
zoan (Actinosphserium), lying in a drop of water, through
which a weak, constant current is "made." We find that the
filamentous pseudopodia begin quickly to retract at the two
poles lying in the axis of the current ; and as the current
continues, this contraction continues likewise. The primary
effect of a weak constant current is thus a centripetal flowing
of the protoplasm. The current stimulates to contraction.

If, now, the current be increased, or be longer continued,
further changes occur. The pseudopodia lying in the current
become varicose, and break up into a chain of drops; the
vacuoles on the periphery begin to burst, emptying out their
fluids; and in these regions the protoplasm collapses. Thus,
the stronger current produces continued contraction, accom-
panied by collapse of the protoplasmic foam-work.

Finally, the plasma itself begins, upon the anode side, to dis-
integrate, and the loose particles to move towards the positive
electrode. As the plasma of this side is gradually eaten away,
the outline of the Actinosphoerium passes through phases like
those of the waning moon, until, finally, the last thin crescent
fades away. The particles of the mass have wholly lost their
cohesion (Fig. 28).

The facts just given concerning the behavior of Actino-
spha^rium to the constant current are gathered from the observa-
tions of KtJHNE ('64, p. 59) and Verworn ('89", pp. 8, 9).
Fundamentally similar observations have been made by Kuhne
('64, p. 79) and Verworn ('89\ p. 274) on Myxomycetes,
and by Verworn ('89% pp. 13, 17) on the rhizopods, Poly-
stomella and Pelomyxa. So these data may be considered as
of general worth for naked protoplasm.

Also upon ciliated epithelium, the constant current acts
as a very strong excitant, producing an active movement in
cilia which had previously nearly ceased to beat. This excita-
tion occurs, especially about the two poles, immediately upon
" making " the current. (Kraft, '90, pp. 234, 235.)

130

ELECTRICITY AND PROTOPLASM

[Ch. VI

Fig. 28. — Actinosphserium eichhornii in four successive stages of polar excitation
by means of the constant electric current. Disintegration begins at the anode
(+) pole. (From Verworn, '95.)

Allied, apparently, to the foregoing phenomena are the pro-
toplasmic changes which follow the sudden breaking of the
current. Unless the current has been very feeble, the pseudo-
podia of Actinosphserium begin, at the moment of breaking, to
contract and become varicose upon the kathode side, while the
formerly irritated anode side is quiet. Thus, the breaking of
the current also acts as a stimulus, but this is, in general,
weaker than that caused by making.

If, now, a current which endures for only an instant — if a
single induction shock — is sent through, the making and break-
ing stimuli are practically coincident, and a violent response
may be called forth. Thus, Engelmann ('69, p. 317) found
that Amoeba, subjected to a strong shock, retracted its pseudo-
podia, and assumed a spherical form within two seconds ; and
GoLUBEW ('68, p. 557) has described a similar response in
leucocytes. Under similar circumstances, the flagellum of the
flagellate Peranema (Fig. 29) made an energetic stroke. (Ver-
worn, '95, p. 414.) I have spoken above as though there were
both a making and a breaking stimulus ; but this is not known
to be the case. It. is generally recognized from experiments

§2]

EFFECT ON STRUCTURE AND FUNCTIONS

131

on muscle, that it is the " making " only of a single induction
shock which produces the response ; but Verwoen ('89% pp.
19-22) has found that in the rhizopod Pelomyxa it is, on the
contrary, the breaking excitation which causes the response.
The subject deserves further study.

Finally, the effect of an alternating current must be con-
sidered. This current is characterized by the fact that it is
composed of a series of rapidly repeated instantaneous shocks

T ..

.;-■'.. ±

irritated by an induction stroke.

Fig. 29. — Peranema. a, quietly swimming;

(From Verworn, '95.)
Fig. 30. — ActinosphiErium eiclihornii, Stein.

current. At both poles the pseudopodia are undergoing a disintegration, which

proceeds equally at the two poles. (From Verworn, '89.)

Showing effect of the alternating

which alternately reverse their direction. Thus, each pole of
the organism subjected to such a current receives alternatelj^
the making (or breaking) eifects at anode and kathode. The
maximum action is thus obtained. When an Aetinosphcerium
is stimulated by such a current, the pseudopodia at both poles
contract and become varicose ; and, finally, the protoplasmic
substance begins to disintegrate and to flow out from the cell
towards the two electrodes, until the body acquires a biconcave
form. (Verworn, '89% p. 11.) In this case the disintegra-

132

ELECTRICITY AND PROTOPLASM

[Ch. VI

tion takes place at both poles, since both are, alternately,
anodes (Fig. 30).

Similar effects have been observed in other cases. Thus,
when an amoeba is subjected to an alternating current, it be-
comes spherical ; the protoplasmic streaming of the plasmodia

of a myxomycete ceases, and,
with stronger currents, the
whole mass contracts, water
being forced out. Finally,
an attempt at a similar re-
sult is seen in the stamen-
hair cells of Tradescantia, in
which, under stimulation, the
protoplasmic threads segre-
gate into irregular or sphe-
roidal clumps. (KtJHNE, '64,
pp. 30, 31, 75, 99.) In all
these cases we see that the
action of a violent current,
like repeated contact, leads
(as Engelmann, '69, p. 321,
has suggested) to results
which can be accounted for
on the ground of reduced
cohesion, — first, tendency to
spherical aggregation, and.

Fig. 31. — One of the cells of a stamen hair finally, disintegration (Fig.

of Tradescantia virginica. ^4, unstimu- 31).

lated; i? stimulated by an induction ^^^^^ j^^^- ^^^^-^^^ ^he

current. At a, b, c, a, the protoplasm '^

has aggregated into drops and clumps. effect of the elcctric Current

(From Verworn, '89, after Kuhke, ^^pQ^ Protista and simple

, cells, it remains to consider,
very briefly, its effect upon muscle and upon nerve. Since
Caldani discovered, in 1756, that frogs, shortly after death,
could be stimulated to movement by frictional electricity, and
Galvani and Volta, towards the end of the last century,
discovered, by the same response, the phenomenon of galvan-
ism, these tissues have frequently been made the subject of
careful experimentation. It has been shown, not merely that

§ 2] EFFECT ON STRUCTURE AND FUNCTIONS 133

the nerve can be stimulated to its functions, but that muscle
from which the activity of the nerve has been excluded by the
use of curare (which inhibits the action of the nerve, but not
of the muscle), will contract upon the passage of a current.

Upon the character of the current, however, depends that
of the response ; thus, although, as we have seen, a closed
constant current continues to stimulate Protista, it has been
said not to stimulate nerve or muscle. A contraction follows,
it has been maintained, only upon considerable variations in the
electrical condition, such as result from making or breaking
the current. It is probable, however, that there is not so great
a difference in responsiveness of muscle and Protista as would
seem to be implied, for Biedermann ('83) has shown that the
constant current produces a whole series of slight contractions
in muscle which cannot be regarded merely as a secondary
result of the making shock ; and FiCK ('63) has observed
contraction due to the constant current in muscles of Lamel-
libranchia. So that even in muscles, there is an actual, though
weak, response to a steady, constant current.

There are two phenomena following momentary shocks ap-
plied to muscles which deserve notice in passing. First, when
a single induction shock is passed directly through a muscle,
we notice that the contraction is not simultaneous with the
shock, but follows only after the lapse of a certain "latent
period." This latent period represents, it is believed, time
spent in transformations going on in the plasma preparatory to
contraction. Secondly, when we pass (especially in a muscle-
nerve preparation) a series of induction shocks, closely following
one another, as in the alternating current, a very violent con-
traction is produced, since the new shock comes to the muscle
before it has had time fully to relax, and causes a contraction of
the already contracted tissue. Thus stimulus is superimposed
upon stimulus, and a summated response (tetanus) takes place.

"We must now consider more carefully a subject to which
we have hitherto merely alluded, namely, the relation to the
electrodes of the point of the organism at which the response
first appears. Thus, when the amoeboid Pelomyxa is subjected
to the constant current, a contraction appears, at the time of

134

ELECTRICITY AND PROTOPLASM

[Ch. VI

making the current, at that pole only which is turned towards
the anode. When the current is broken, on the contrary, a
contraction occurs at the kathode, the pseudopodia next the
anode becoming quiet. (Verwoeist, '89% p. 19.) This relation
may be expressed in tabular form as follows : —

At Anode.

At Kathode.

Upon making

Upon breaking

excitation

rest

rest
excitation

All Protista do not, however, according to Verwokn, respond
in the same way as Pelomyxa ; thus, with the constant current
of a certain intensity, he got in both Polystomella crispa, and
Actinosphserium, the following reaction : —

At Anode.

At Kathode.

Upon making

Upon breaking

excitation
rest

rest
rest

It must be said, however, that the reactions obtained in any
case are dependent upon the strength of current employed ;
thus, with a stronger current, the following result was obtained
with Actinosphterium : —

At Anode.

At Katuode.

Upon making

Upon breaking

excitation
rest

excitation
excitation

A comparison of the last two tables seems to indicate that, very
probably, with a current intermediate between the weak and
the strong current employed, we should get a result like that
obtained with Pelomyxa. At any rate, we may say that all
these cases tend to group themselves about the Pelomyxa for-
mula ; — making : anode, excitation ; kathode, rest ; breaking :
anode, rest ; kathode, excitation. A brief designation of this
type is desi]^ble. Since the condition at the anode upon

§2] EFFECT ON STRUCTURE AND FUNCTIONS 135

making is distinctive, we may call this the anode-excitation
type, or, briefer still, anex type.

Turning, now, to nerve and muscle tissue, we meet with a
type of response, on making and breaking the current, alto-
gether irreconcilable with this. As is well known, when a
constant current is made or broken, all the tissue lying between
the electrodes is not stimulated at one time, but the excitation
makes its appearance at the anode or kathode, and thence is
transmitted to the other pole. One can demonstrate this on
slow-moving (e.g. extremely tired or dying) muscle at the
extremities of which the electrodes are placed. The contrac-
tion begins at one electrode, and travels towards the other.
By using more refined methods, this relation, which holds for
nerves, striated and smooth muscle (cf . Engelmann, '70, p. 302)
has been formulated as follows : —

At Anode.

At Kathode.

Upon making

Upon breaking

rest
excitation

excitation
rest

This is seen to be the very opposite of the response given by
Pelomyxa. It may be called the kathode-excitation type, or,
in brief, the katex type.

Having now seen that two fundamentally different types exist
in the response of the two extreme groups of the animal king-
dom, the question arises, what is the distribution of these types
amongst the intermediate forms — the Invertebrate Metazoa?
Fortunately, through the investigations of Nagel ('92 and '92"),
we have data upon this subject. In Nagel's experiments, the
Avhole animal was employed, the two electrodes were placed at
the opposite ends of its long axis, the metallic circuit was then
made or broken as required, and the pole (anode or kathode)
at which contraction first occurred was noted. Thus, Nagel
found that Avhen the current was made through the sea-hare,
Aplysia, there was strong excitation and momentary retraction
of the parts next to the anode, while next to the kathode the
body showed a considerably Aveaker contraction. Upon break-
ing the current, there was some excitation of the parts of the

136

ELECTRICITY AND PROTOPLASM

[Ch. VI

body next to the kathode, but none at the anode end. The
result that one obtains depends, however, to a certain extent,
upon the strength of the current that one employs. But Nagel
did not, apparently, measure his currents, so there is no cer-
tainty that his results can be at once duplicated. Taking the
results for various Invertebrates as they are given, however
they are instructive.

TABLE XIII

Upon MAKCfG.

Upon Bp.eaking.

At Anode.

At Kathode.

At Anode.

At Kathode.

Limnseus

excitation

rest

rest

excitation

Planorbis

excitation

rest

rest

excitation

Aplysia punctata . .

excitation >

excitation

rest

excitation

Schseurgus (octopod)

excitation >

excitation

rest

excitation

Helix hortensis . . .

excitation >

excitation

rest

slight excitation

Ciona intestinalis . .

excitation >

excitation

rest

rest

Janus cristatus . . .

excitation =

excitation

rest

slight excitation

Pleurobranchia . . .

excitation =

excitation *

rest

slight excitation

Nassa reticulata . . .

weak excit.

rest

rest

rest

All the species in this table (all of which, except Ciona, are
MoUusca) show in their response a more or less close approach
to the type of Pelomyxa (excitation, rest ; rest, excitation) ; and
we may believe that with appropriate stimulus they would re-
spond in precisely that way.

In a second class of cases the response of the whole animal
belongs to the katex type ; thus two species examined by
Nagel showed the following responses : —

TABLE XIV

Pagurus striatiis .
Triton cristatus . .

Upon Making.

At Anode.

rest
excitation <

At Kathode.

excitation
excitation

Upon Breaking.

excitation

At Kathode.

rest

* Inconstant in occurrence.

§2] EFFECT ON STRUCTURE AND FUNCTIONS 137

These are representatives of the groups Crustacea and Ver-
tebrata.

Among all the species studied by Nagel there was only one
which gave results not easily assignable to either of the two
types. This organism is the larva of a dragon-fly, ^-Eschurea.
Its formula is excitation = excitation ; rest, rest. Nagel says,
however, that these results were uncertain and variable.

In some other groups studied — Coelenterata and Echinoder-
mata — the current used provoked no response at either pole ;
while with Amphioxus the current employed produced excita-
tion at both poles on both making and breaking the circuit.
Such variations as these, are, however, easily accounted for on
the ground that different species require currents of different
strengths to call forth what may be termed the typical response.

Not merely between different groups do we find a difference
in the type of response, but even inside the group of Protozoa
dissimilarity has been shown to occur. Thus Verwoen ('89*,
p. 301) has given reasons for believing that three flagellate
species, the ciliate Opalina, and some bacteria belong to the
katex type, although as just stated (p. 133) other Protozoa
exhibit the anex type of response.

Finally it appears that individuals of one and the same species
subjected to different intensities of current may give rise to
responses belonging to the opposite types. Thus when a
medium current is " made " through Triton cristatus the exci-
tation is greater at the kathode than at the anode ; but when
the weakest current is employed a making response occurs at
the anode only, and when a slightly greater intensity is used the
continuance of the current provokes a continuance of the exci-
tation at the anode. (Nagel, '92% p. o-tl.) Likewise the
reaction of Vertebrate muscle varies with its internal condition.
Thus degenerated or over-stimulated muscle shows predominat-
ing anode stimulation on making the current ; and transverse
stimulation of the muscle fibre gives the same result.*

To sum up, two principal types of response to the electric
current may be distinguished : the first or anex type character-
izing most Protozoa, Mollusca, Vertebrates (slightly stimulated),

* For a discussion of these cases see Verworn ('80", p. 24).

138 ELECTRICITY AND PROTOPLASM [Ch. VI

and weak muscle fibres ; the second or katex type found espe-
cially among some Flagellata, Arthropoda, and Vertebrata. A
third possible type (katanex type) is certainly of very limited
distribution. Between the two types we notice this connecting-
link, that in some Vertebrates a weak current produces one
type of response ; a strong current the other. The reason for
the existence of these two distinct types — one of which char-
acterizes animals with less differentiated, the other those with
more differentiated, muscular and nervous systems — is still
greatly in need of investigation.

The nature of the protoplasmic change wrought by the
current is an important matter. We have already accounted
for the effect that we see in the Protista, on the ground of re-
duced cohesion. It is probable also that the current gives rise
in the cytoplasm to chemical changes which are different at the
two poles. It is well known that when a current is passed
through a neutral solution of a salt there is produced an acid
at the anode, and an alkali at the kathode. Since in the higher
animals, at least, the body contains such solutions, it seems
probable that acid and alkaline substances are here likewise
produced by the passing current. This probability is supported
by an observation of KiJHNE ('64, p. 100), who found that the
violet coloring matter of the stamen hairs of Tradescantia
become changed by the action of a very strong induction shock.
He says that a change in the violet jfluid, like that which occurs
at the anode, can be brought about by dilute hydrochloric acid ;
while a change like that appearing at the kathode can be pro-
duced by potassic hydrate. An observation of Nagel ('92% p.
346) suggests also that the current acts by producing a chemi-
cal change. He finds that that part of the body of the snail
and the leech which shows most markedly the anode-making
excitation is coincident with that which is most sensitive to
chemical substances. So that the reaction to a galvanic, still
more to a faradic, stimulation resembles that to a strong, dis-
agreeable taste (quinine). In this case the response may
result either from the chemical substance acting directly on
the muscles or attacking first the sense organs. In the latter
case the response would occur through the mediation of the
nervous system.

§ 2] EFFECT ON STRUCTURE AND FUNCTIONS 139

So far then we have distinguished two chief effects of the
current on protoplasm — a dissociation effect and a chemical
effect. It may now be worth while to mention that there is
good reason for believing that in the more highly differentiated
animals, like Vertebrates, not all protoplasm is affected to the
same degree nor in the same way. Thus a nervous and a
muscular effect can be clearly distinguished in frogs, for ex-
ample. The principal effect is exerted upon the central nervous
system, for Hermann ('86, p. 415) found that the tail of
tadpoles is responsive only so long as it contains a piece of
spinal nerve ; and upon frogs subjected to curare, which inhib-
its the action of the nerve alone, the current produces a much-
diminished effect, giving rise merely to muscular twitchings.
(Blasius and Schweizer, '93, p. 528.) Very little progress
has been made, however, upon the determination of the action
of different intensities upon the different tissues of which the
Vertebrate body is composed.

We have seen that the electric current provokes a response,
and we have seen also that organisms vary in their responsive-
ness so that a current strong enough to call forth a response in
one species is not sufficient to excite another species. We may
say that the one species is attuned to a different strength of
current from the other. This difference in responsiveness indi-
cates, of course, a corresponding difference in composition of
the protoplasm. Such a difference may, moreover, be i)roduced
in a single individual by artificial means. These means are
the subjection for a considerable period to the electric current.
Suppose we subject an organism to a current of a strength only
slightly greater than that just necessary to provoke a response.
After the current has acted for some time we find that it no
longer excites. This phenomenon of acclimatization to the
galvanic current was first observed among the Protista, so far
as I know, by KuriNE ('64, pp. 76, 78), who found that in
Myxomycetes, after a few induction shocks had been sent
through the plasmodium, additional shocks of the same intensity
were without effect, and stronger shocks had to be sent through
to cause contraction. Similar results were obtained by Ver-
WORN ('89", p. 10 ; '89^ p. 272) in subjecting Actinosphrerium

140 ELECTRICITY AND PROTOPLASM [Ch. VI

and Amoeba to a weak constant current. At first the pseudo-
podia on the anode side plainly retracted, but later ceased to
do so, and, finally, the current still passing, the retracted
pseudopodia began to extend again. The action of the current
so modified the protoplasm as to change the attunement of the
organism.

§ 3. Electrotaxis

In studying the subject of aggregation with reference to the
electric current, we shall consider first the simplest case of this
phenomenon as it is exhibited in Amoeba ; then pass to the
more complex forms of Protista, especially the Ciliata, and after

^j^^m

A B

Fig. 32. — Galvanotaxis of Amoeba diffluens. A, Amoeba creeping, unstimulated;

B, after closing of the constant current. The arrow indicates the direction of
locomotion. (From Verwokn, '95.)

that to the Metazoa. After dealing with the phenomena we
must attempt to explain them.

When such an amoeba as that shown in Fig. 32, A, is sub-
jected in a drop of water to the action of a weak constant
current, as already indicated (p. 129), it contracts, especially
upon the face turned towards the anode. If the current is not
strong enough to produce disintegration at that pole, but only
repeated contraction, and if meanwhile the kathode pole retains
its power of throwing out pseudopodia, the amoeba must grad-
ually move from the anode (Fig. 32, 5), and if several Amoebae
are under the cover-glass, they will eventually aggregate about
the kathode. Here Ave have, then, in its simplest form, a case
of electrotaxis, and, since the organism moves toward the
negative electrode, we may call it negative electrotaxis.

If now, instead of an amoeba, we watch a free swimming
flagellate Infusorian, — Trachelomonas hispida (Fig. 33), — we

§ 3] ELECTROTAXIS 141

see the long flagellum wliich precedes in locomotion coming to
lie in the current and directed towards the kathode, so that the
animal migrates in that direction. The following explanation
of the observed fact that the flagellum becomes directed towards
the kathode has been offered by Verworn ('89^ p. 298). The
flagellum and the pole from which it arises constitute the most
sensitive end of the body. When the flagellum is stimulated
it beats violently, and since it is stimulated most when turned
towards the anode, it beats most violently when in this attitude.
A position 180° from this is one of comparative rest. In interme-
diate positions the degree of stimulation is intermediate. After
a few strokes the body will " naturally " come to assume and to
retain that position in which the flagellum is least stimulated.
More detailed still is our knowledge of electrotaxis among

Fig. 33. — Trachelomonas hispida, swimming towards the kathode (— ) upon closure
of the current. The arrow shows the direction of locomotion. (From Ver-
WORN, '89.)

the ciliate Infusoria. The authors who have worked upon
this group are chiefly Verworn ('89" and '89^) and Ludloff
('95). The work of the former shows that the phenomenon
of electrotaxis is exhibited by many species, especially Para-
mecium aurelia and P. bursaria, Stentor coerulens and S.
polymorpha, Pleuronema chrysalis, Opalina ranarum, Bursaria
truncatella, Halteria grandinella and Stylonichia mytilus.
Ludloff employed only Paramecium, but studied it much
more completely, especially using various currents of known
relative intensity.* He found that the precision with which

* Ludloff employed a trough with wax walls, clay ends, and glass bottom,
and used brush electrodes. The intensities of current given by him are the
readings of the galvanometer. The cross-section of the water mass in which
the Paramecia were, and over which the current spread itself, is not exactly
given, but was probably about 20 sq. mm. If we employ the unit of strength
recommended by Hermann and Matthias (p. 128), namely, 1 one-millionth of

142

ELECTRICITY AND PROTOPLASM

[Ch. VI

the Paraniecia aggregated at one pole was determined by the
strength of the current, as follows : A current of 3 S caused
in general a movement towards the kathode, although many
individuals appeared not to be affected by it. In 20 seconds
the anode end of the fluid was almost free from Infusoria,
With currents of 6 S and 15 B the aggregation at one pole be-
came more complete and took place in a short time. Indeed,
there was a relation found between the time required for

r^

r

\

\

)

\

y

\

/

\

L

t

\,

1

\

^.

I

\

N

"^

^

35

10(5

206 30(5 40(5 50c5

STRENGTHS OF CURRENTS

60(5 70^

Fig. 34.^ — Curve showing relation between strength of currents and relative time
elapsing before Paramecia have aggregated at the kathode. The ordinates are
measured by the reciprocals of the number of seconds elapsing ; the abscissae, by
the strength of current in 5's.

aggregation at the kathode and the strength of current
employed, which is instructive, and is given above in graphic
form (Fig. 34).

This curve shows that as the current increased from 3 S to
21 8 the rapidity of aggregation increased, but as the current
increased still further this rate diminished until locomotion
nearly ceased at above 60 8. The intensity, therefore, of 21 8
produced the most rapid movements.

Upon opening the current, the Infusoria in all cases swim,

1 ampere per sq. mm. (designated 5), then we must divide Ludloff's galva-
nometer readings (given in milliamperes) by xf §o' ^^ ("which is the same thing)
multiply them by 50. That will give us the current in 6's per sq. mm. All of
the numerical data given in the text have undergone this operation.

§3]

ELECTROTAXIS

143

rapidly for a moment, towards the opposite pole (anode), but
then quickly begin to redistribute themselves throughout the
water. This redistribution has occurred in about 20 seconds

Fig. 35. — Apparatus for studying electrotaxis of Paramecium. A rectangular trough,
whose ends are of clay and sides of wax, is built upon a glass plate. The current
is applied by means of brush electrodes. The direction of the migration of the
paramecia is indicated by the arrow. They move towards the kathode. (From
Vekworn, '95.)

after the current is broker^, and the time is independent of the
strength of the preexisting current.

The movement of the Infusorian from one pole to the other
takes place along the lines of flow of the current. If the ter-
minals are two parallel plates, these lines are about parallel
(Fig. 35); if they are two points near the opposite sides of

A B

Fig. 36. — Curves made by Paramecia in its galvanotactic response when pointed
electrodes are used in the drop of water. A, beginning of migration ; B, com-
plete aggregation. (From Verworn, '95.)

a water drop, the lines have the direction of the lines made
by iron filings scattered on a plate over the two poles of a
magnet (Fig. 36).

Besides this path of general migration, the form of the path
followed by individuals varies with the current. Normally
Paramecium moves in a long spiral. As the current is in-

144

ELECTRICITY AND PROTOPLASM

[Ch. VI

creased, however, this spiral becomes shorter, i.e. has more
turns per centimeter of progression from one pole to the other

Fig. 37. — Form of the path of Paramecium under different conditions, a, when not
subjected to the constant current; b, when subjected to a slight current; c, when
subjected to a still stronger one. (From Ludloff, '95.)

(Fig. 37), until at 60 S, in making one turn of the spiral, the
organism progresses hardly more than its own length.

Finally, the effect of the current
upon the movement of the cilia must
be considered.* In the resting Para-
mecium the cilia rise perpendicularly
from the surface of the body (Fig. 38).
If an individual stands Avith its ante-
rior (blunt) end towards the anode,
and a current of 8 S passes through,
the cilia at the posterior (kathode)
end begin to vibrate. If the individ-
ual lies transverse to the current and
the current is closed, the cilia on the
kathode side vibrate, those on the
anode side being quiet. With a cur-
rent of 16 S one can see that the kath-
ode stimulation increases the forward
(anteriad) phase of the cilium move-
ment (the "recovery"). With an intensity of 24 S, vibration
of cilia occurs at both kathode and anode. It is, however, more

* Ludloff was enabled to make a careful study of the effect of the current
on the cilia by making use of gelatine solutions such as have been recommended
by Jensen ('93, p. 556).

Fig. 38. — Paramecium, show-
ing position of cilia when
unstimulated. The blunt
end is anterior. (From
Ludloff, '95.)

§ 3] ELECTROTAXIS 145

intense at the kathode and is also in opposite directions at the
two poles. This law is important, and may be thus formulated:
The current intensifies at the anode the hackivard movements and
at the kathode the forward movements of the cilia, and the latter
are more intensified than the former ; or, in other words, the
anode stimulation increases the effectiveness of the normal
stroke, the kathode stimulation diminishes the effectiveness of
the normal stroke, and the diminishing effect is the greater of
the two.

On the basis of these observed facts, Ludloff has proposed
a theory which accounts for several of the electrotactic phe-
nomena in the Ciliata, especially the fact that with strong
currents there is a diminution in the rate of locomotion, and
that at a lower intensity the axis of the organism is placed in
the axis of the current, with its anterior end towards the
kathode. This theory may be stated as follows: In every com-
plete swing of a cilium two phases may be distinguished —
the backward "stroke" and the forward "recovery." Nor-
mally the stroke is the more effective, otherwise forward loco-
motion would not occur. The excess in eff'ectiveness of the
stroke may be designated by the quantity x. Let us assume a
Paramecium lying in the axis of the current with its anterior
end towards the kathode. Then the stimulus received at the
anode or hinder end increases the effectiveness of the stroke by
a quantity which we may designate m. Thus the excess
energy of the stroke over recovery is for these hinder cilia
X + on. The stimulus received at the kathode or anterior end
diminishes the effectiveness of the stroke by a quantity which
Ave may call ?i, which is larger than m. Here the excess energy
of stroke over recovery is a; — 7i. If at any intensity of cur-
rent n exceeds .r, the anterior cilia will work to oppose the
forward motion of the individual, and when n — x = x + m loco-
motion will not occur. Such a strength of current probably
occurred in the experiment given on p. 142, where locomotion
ceased at above 60 S.

To account for orientation of the axis and its anterior
end, we have merely to apply the general law given above.
Let us suppose that Ave are observing a Paramecium lying in
the axis of a current of medium intensity, with its anterior

U6

ELECTRICITY AND PROTOPLASM

[Ch. VI

end towards the anode. Since n is here supposed to be less
than X, the resultant effect is to move the animal forward. In
moving forward in its spiral course, one side becomes presented
to the anode. On this side the excess of energj^ of the stroke
is a; + m, while on the kathode side it is a; — n. The resultant
effect of the cilia on the two sides forms a couple which revolves
the organism about one of its short axes until it comes again
into the axis of the current, but with its anterior end towards
the kathode. The beating of its cilia must now carry it towards
the kathode (Fig. 39).

Fig. 39. — Diagram showing the successive attitudes (a, b, c, d, and e) assumed by
Paramecium when its head is turned towards the anode at the beginning (a). It
rotates till its head is next the kathode (e) . (From Ludloff, '95.)

Before leaving the Protozoa, we ought to look over the whole
field. We have hitherto considered only cases of migration
towards the kathode — negative galvanotaxis. Verwokn
('89''), however, has found that some Protista are positively
electrotactic ; namely, Mie flagellata, Polytoma uvella, Crypto-
monas ovata, and Chilomonas paramecium; the ciliate, Opalina;
and some bacteria. Finally, Veeworn ('96, p. 446) describes
one of the elongated Ciliata — Spirostomum ambiguum — which
places its long axis across that of the current and migrates
towards neither pole, a condition which may be called (after
Verwoen) transverse electrotaxis.

Passing now to the Metazoa, we find investigations concern-
ing electrotaxis among Invertebrates by Nagel ('92 and '92^

§3]

ELECTROTAXIS

147

and '95), and Blasius and Schweizer ('93); and among
Vertebrates by these authors and also Hermann ('85 and '86),
EwALD ('94, '94% and '94''), Hermann and Matthias ('94), and
Waller ('95). The number of species investigated has been
considerable. I give below a table of the Invertebrate genera
studied and the sense (+ or — ) of their response at the given
intensity of currents. Barely rough quantitative expression
of strength of current can 'be deduced from Nagel's paper.
Where no data are given the currents are supposed to be of
intermediate strength. N. stands for Nagel, B.S. for Bla-
sius and ScHWEiZER. The numbers which follow give the
year of publication and the page.

TABLE XV

Specific Name.

Mollusca :

Limnsea stagnalis

Var. other Gastropoda (probably)

Annelida :

Lumbrieus

Tubifex rivulorum

Hirudo medicinalis

Branchiobdella parasitica

Crustacea :

Cyclops

Asellus aquaticus

Astacus fluviatilus

Insecta :

Notouecta

Corisa striata

Dytiscus margin alis

Hydrophilus piceus

Strength of

Sense of

CUKRENT.

Response.

weak

-

0.8 8

-

strong

+

strong

+

0.4 8

+

+ v

+

1.9 8

+

L9 8

-

Authority.

N. '95

N. '92"; '95

K '95, 626
N. '95, 631
B.S. '92, 516
B.S. '92, 516

N. '92, 629

N. '95, 633
B.S. '92, 518

N. '95, 636
N. '95, 636
B.S. '92, 519
B.S. '92, 519

From this table it appears that Mollusca and Annelida are
usually negatively electrotactic to a current of medium inten-
sity, while Arthropoda are mostly positively electrotactic to
such a current. It is noteworthy, however, that two quite

148 ELECTRICITY AND PROTOPLASM [Ch. YI

closely allied beetles like Dytiscus and Hydrophilus should
by the same observers be found to react in different ways.

In addition to the species named, some have been studied
which have given no results. Thus Nagel ('95, p. 639) ob-
tained no response from the larva of Libellula depressa, even
with a wide range of current-intensities.

Passing now to the Vertebrata, we enter a region in which,
as a result of more numerous studies, the data are more volu-
minous, but at the same time less in accord. Since many mat-
ters are here still in dispute, we may best consider historically,
i.e. in chronological sequence, what has hitherto been done in
this field.

The first person to describe the phenomenon of electrotaxis
in Vertebrates — as, indeed, in any organism — was HERMAisrisr
('85, '86). He used frog larvse 14 days old, held in a shallow
rectangular porcelain trough, along the two small sides of which
thick zinc wires were placed, connected with a chain of 20 small
zinc-carbon elements. No mention of the strength of the cur-
rent except such as can be gained from these facts was made.
This omission of quantitative details is to be regretted, since
had the strength of current to which the organisms were sub-
jected been given, much subsequent confusion might have been
avoided. With this current, then, of unknown intensity, flow-
ing through the water containing the larvse, all of the latter
were seen to place themselves in the axis of the current with
their heads directed toward the anode. This orientation was
the consequence of the fact that a current passing cephalad
through the larva acted as a violent stimulus ; but while
passing caudad it brought stupefaction or even (temporary)
paralysis.

The results obtained by Hermann were now confirmed and
extended by Blasius and Schweizer ('93). They employed
a wooden trough with sheet zinc electrodes of nearly the cross-
section of the smaller ends of the trough, and experimented
upon fishes, Salamandra, and the frog. The weakest current
employed was 0.35 S to 0.47 S, which merely affected the char-
acter of the swimming of the fish subjected to it, without
determining its direction. The next stronger current men-
tioned M'^as 1.58 8. With this current a marked orientation of

§3] ELECTROTAXIS 149

the fisli with their heads to the anode was noticed. With
Salamandra larvse currents of 2.3 S to 4.7 S were chiefly em-
ployed. In the experiments of Blasius and Schweizer the
organisms sometimes migrated toward the anode, if the cur-
rent was not so strong as to stupefy, but they lay stress upon
the point that the migration is a secondary phenomenon — that
the orientation is the primary effect of the current.

Next came the observations of Ewald ('94), who used very
young tadpoles (5 days) and non-polarizable points as elec-
trodes. Thus he was not able to give the strength of current
to which the individuals were subjected. His results seemed
directly to oppose those of the two preceding authors, for
with his (unknown) current, the tadpoles were stimulated
when the current passed caudad and stupefied by one passing
cephalad ; also they placed themselves in the axis of the cur-
rent with their heads towards the kathode. The larvae did
not seem to find this position as a direct response to stimulus,
but whenever an individual, in its turnings to the right and
left, fell into this — electrotactic — position it was no longer
stimulated, but stupefied, and so came to rest.

These discordant results of Ewald led Hermann, with his
student Matthias, again into the discussion. By careful
measurements of the strength of current, they found that
between 0.3 S and 1.5 S frog tadpoles of from 1 to 3 weeks old
did face the kathode, as Ewald found, and did move towards
it. But Hermann and Matthias ('94) believed this result
to be due to the fact that only cephalad-flowing currents of this
intensity excite, and thus only such currents are able to pro-
duce locomotion.

Ewald ('94^), however, cannot accept their idea that a
caudad-passing current of small intensity produces no excita-
tion, for, he says, he has seen small fish, lying with face to the
anode, made to move towards the kathode by the action of the
weak current. Since Hermann and others have shown that
very strong currents cause paralj'sis even when flowing cepha-
lad, Ewald concludes that we must recognize the existence of
three different effects at three intensities; weakest, medium,
and strongest. The medium current (Avhich has the broadest
range) is that by which the organisms are irritated as it flows

150 ELECTRICITY AND PROTOPLASM [Ch. VI

cephalad, so that they come to lie with head towards anode ;
the weakest current is that by which (following Ewald)
the organisms are irritated as it flows caudad, so that they
come to lie facing the kathode ; finally, the strongest cur-
rent is that at which a violent stimulation leading to paraly-
sis is produced by the cephalad-flowing current (as well as
the caudad ?).

In seeking for an explanation of electrotaxis in Metazoa, it is
necessary, first of all, to notice that there is a close relation
between response to the make-shock (as described on pp. 136,
137) and the direction of orientation of the body in electro-
taxis. Thus all gastropods studied are, upon making, excited
chiefly at the anode, and, correspondingly, all gastropods hitherto
studied when subjected to the current face the kathode ; so on
the other hand, such Crustacea as have been studied are stimu-
lated at the kathode, and they accordingly come to face the
anode. In regard to Vertebrates, we have apparently a double
electrotactic orientation varying with the current, and corre-
spondingly we have, as Nagel has shown (p. 137), a double
irritability depending on the current. A medium current pro-
duces a kathode excitation and an anode orientation ; while
the weakest current produces an anode excitation and a
kathode orientation. So we may lay it down as a general
law : Positively electrotactic organisms exhibit the katex type of
irritahility ; and negatively electrotactic organisms exhibit the
anex type or^ in general^ the electrotactic organism turns tail to
the exciting pole.

Ewald ('94, pp. 611-615) accounts for this difference of
response of Vertebrates to weak and strong currents, by the
aid of certain observations that he made upon the excitation
of the nerve cord. We have already seen that the making
of the medium constant current stimulates at the kathode, so
that an animal turns tail to the kathode. Ewald found that
the two parts of the dorsal nerve were differently stimulated
by the current ; the brain was stimulated chiefly by a caudad-
passing current ; the spinal cord chiefly by a cephalad-passing
current. This conclusion was established by two experiments.
First, the two electrodes, placed a few millimeters apart, are
brought into contact with different parts of the body of a fish.

SUMMARY OF THE CHAPTER 151

Let the current be passing through the fish from the anterior to
the posterior electrode. At the tail end we get no excitation ;
and, as we pass forward, the body remains quiet until, pass-
ing the region of the medulla oblongata, an excitation appears.
If the operation is repeated with a reverse current, we get
excitation behind the head and quiet on the head. Secondly,
if a frog larva be cut in two transversely at the root of the
tail, the head end is irritated only by a caudad-flowing cur-
rent ; the tail end only by a cephalad-flowing current ; while
in both cases the opposite current quiets. (Cf. also Ewald,
'94^ p. 162.) These observations were now made use of to
explain the opposite orientation of the tadpole in the presence
of weak and strong currents. Nagel assumed that the weak-
est currents can affect the brain only. Now if that current
runs caudad, it will strongly stimulate the body so that it turns
tail to the anode. The medium currents, however, stimulate
the whole dorsal nerve, but the spinal cord to a preponderating
degree, so that a cephalad-passing current irritates more than a
caudad current, and the animal will turn tail to the kathode.
Thus weaker or stronger current will determine — or -h
electrotaxis.

Summary of the Chapter

Electricity affects protoplasm in two principal ways : first,
by causing contraction ; second, by determining orientation.
We can distinguish two principal types of contraction phe-
nomena and, corresponding to and dependent upon these, two
types of orientation phenomena. The first type of contraction
is that which is produced, upon making the constant current,
chiefly at the anode ; the second is produced chiefly at the
kathode. The corresponding orientation or migration types
are, facing the kathode and facing the anode. Since the orien-
tation phenomena are dependent upon the contraction phe-
nomena, the most important causes to be investigated are, first,
that of contraction, and second, that of the difference in type
of contraction exhibited by different organisms. The funda-
mental teaching of this chapter is that the electric current acts
as a stimulus upon protoplasm, and may determine the charac-
ter of its activities.

152 ELECTRICITY AND PROTOPLASM [Ch. VI

LITERATURE

BiEDERMANN, W. '83. Ueber rythmische Contraction quergestreifter Mus-

keln unter dem Einflusse des constanten Stromes. Sitzb. Wien. Akad.,

Math.-Nat. CI. LXXXVII, Abth. 3, pp. 115-136. Taf. I-II, 1883.
Blasius, E. and Schweizer, F. '93. Electrotropismus und verwandte

Erscheinungen. Arch. f. d. ges. Physiol. LIII, 493-543. 10 Feb.

1893.
Engelmann, T. W. '69. Beitrage zur Physiologie des Protoplasma. Arch.

f. d. ges. Physiol. II, 307-322.
'70. Beitrage zur allgemeinen Muskel- und Nervenphysiologie. Arch. f.

d. ges. Physiol. Ill, 247-326.
Ewald, J. R. '94. Ueber die Wirkung des galvanischen Stroms bei der

Langsdurchstromung ganzer Wirbelthiere. Arch. f. d. ges. Physiol.

LV, 606-621. 10 Feb. 1894.
'94^ Berichtigung. Arch. f. d. ges. Physiol. LVI, 354. 11 Apr. 1894.
'94**. Ueber die Wirkung des galvanischen Stroms bei der Langsdurch-
stromung ganzer Wirbelthiere. II Mitth. Arch. f. d. ges. Physiol.

LIX, 153-164. 30 Nov. 1894.
FiCK, A. '63. Beitrage zur vergleichenden Physiologie der irritablen Sub-

stanzen. Braunschweig. 1863. (Not seen.)
GoLUBEW, A. '68. Ueber die Erscheinungen, welche elektrische Schlage

an den sogenannten farblosen Formbestandtheilen des Blutes hervor-

bringen. Sitzb. Wien. Akad., Math.-Nat. CI. LVII, Abth. 2, 555-572.
Hermann, L. '85. Eine Wirkung galvanischer Strome auf Organismen.

Arch. f. d. ges. Physiol. XXXVII, 457-460. 2 Dec. 1885.
'86. Weitere Untersuchungen iiber das Verhalten der Frochlarven im

galvanischen Strome. Arch. f. d. ges. Physiol. XXXIX, 414-419.

21 Oct. 1886.
Hermann, L. and Matthias, F. '94. Der Galvanotropismus der Larven

von Rana temporaria und der Fische. Arch. f. d. ges. Physiol. LVII,

391-405. 20 July, 1894.
Jensen, P. '93. Methode der Beobachtung und Vivisektion von Infusorien

in Gelatinelosung. Biol. Centralbl. XII, 556-560. 1 Oct. 1892.
Kraft, H. '90. Zur Physiologie des Flimmerepithels bei Wirbelthieren.

Arch. f. d. ges. Physiol. XL VII, 196-235. 9 May, 1890.
KuHNE, W. '64. Untersuchungen iiber das Protoplasma und die Con-

tractilitat. Leipzig : Engelmann. 1864.
LuDLOFF, K. '95. Untersuchungen iiber den Galvanotropismus. Arch. f.

d. ges. Physiol. LIX, 525-554. 5 Feb. 1895.
Nagel, W. a. '92. Beobachtungen iiber das Verhalten einiger wirbelloser

Thiere gegen galvanische und faradische Reizung. Arch. f. d. ges.

Physiol. LI, 624-631. 26 March, 1892.
'92^ Fortgesetzte Beobachtungen iiber polare galvanische Reizung bei

Wasserthieren. Arch. f. d. ges. Physiol. LIH, 332-347. 24 Nov.

1892.

LITERATURE 153

Nagel, W. a. '95. Ueber Galvanotaxis. Arch, f . d. ges. Physiol. LIX, 603-

642. 5 Feb. 1895.
OsTWALD, W. '94. Manual of Physico-chemical Measurements. Translated

by J. Walker. 255 pp. London : Macmillan. 1894.
Verworn, M. '89*. Die polare Erregung der Protisten durch den galva-

nischen Strom. Arch. f. d. ges. Physiol. XLV, pp. 1-36. 23 jMarch,

1889.
'89''. The same {continued). Arch. f. d. ges. Physiol. XLVT, pp. 267-

303. 18 Nov. 1889.
'95. (See Chapter IV.)
Waller, A. D. '95. Galvanotropism of Tadpoles. Science Progress. IV,

96-103. Oct. 1895.

CHAPTER VII

ACTION OF LIGHT UPON PROTOPLASM

In this chapter it is proposed to discuss (I) the application
and measurement of light ; (II) its chemical action ; (HI) the
effect of light upon the general functions of organisms; and
(IV) the control of locomotion by light — phototaxis and
photopathy.

§ 1. The Application and Measurement of Light

Light, which as a form of radiant energy is closely related to
radiant heat, is always accompanied by a certain quantity of
heat, whose action (in at least one control experiment in every
set) should be eliminated. To cut out heat without great loss
of light, we must employ transparent adiathermal media. Of
these, a plate of ice is the most effective, but alum, on account
of its higher melting point, is more convenient. A parallel-
sided vessel full of distilled water, or, still better, a saturated
aqueous solution of alum, forms an inexpensive, highly adi-
athermal screen.

The quality of the light used in any experiment should be
carefully determined. If any other light than that of the sun
or incandescent solids is employed, it should be subjected to
spectroscopic analysis. For biological purposes a direct-vision
hand spectroscope, such as Browning's, is convenient and
adequate.

Often monochromatic light or a definite range of the spectrum
is desired. This may be obtained in various ways. The
purest monochromatic light can be got by making a long spec-
trum and using the desired part of it. To make such a spec-
trum one may employ, in a dark room, a "lamp, followed in
succession by a slit and a lens to form an image of the slit

154

§1]

APPLICATION AND MEASUREMENT OF LIGHT

155

on a prism of bisulphide of carbon,* which gives very great
dispersion of the rays.

In defining the regions of the solar spectrum which are
employed in any study, it is usual to make reference to the
dark absorption bands (Featjenhofer's lines) which cross
the solar spectrum. The largest of these are lettered, begin-
ning with A in the visible red and ending with M in the
visible violet. At other times it may be more convenient to
define any part of the spectrum by means of the extreme
wave lengths between which it lies. Lithographs showing the
spectral colors and the wave lengths corresponding thereto
are given in encyclopaedias and most of the text-books on
physics. A crude attempt is made to show the relation be-
tween color and wave length in Fig. 40. The wave lengths at

Eed Orange

Telle

\\

Green

Blue

Indlf

"■o

Violet

75 |70; li

5

G

0

^

5

5

0

i

5

10

aBC

D

E b

h

Fig. 40. — Diagram of the solar spectrum showing the main absorption bands and the
range of tlie various spectral colors. The numbers are wave lengths in hundred-
thousandths of a millimeter. (From Reinke, '84.)

the different absorption bands are given more exactly (in thou-
sandths of a millimeter, = /a) in the following table, and also
the number of waves per second in lO^^ths.

TABLE XVI

Absorption

Wave Length,

Vibrations per

Absorption

Wave Length,

Vibrations per

Band.

A.

Second n x IQi-.

Band.

A.

Second n x 10".

.1

0.700^

392

E. . . .

0.527 /A

566

/>'

0.GS7 fx

433

F. . . .

0.486 fjL

613

c

O.0.")()/A

454

(}....

0.431 fi

692

D

0.589^

50G

II . . . .

0.397 fi

751

* The bisulphide prism may be made as follows : Upon a thick glass plate
three rectangular pieces of glass of equal size are placed perpendicularly, so as

156

LIGHT AND PROTOPLASM

[Ch. VII

Extreme ultra-violet A, — 0.295 /a; 1010 x lO^^ vibrations per
second.

To obtain monochromatic light from the spectrum, Reinke's ('84) spec-
trophor will be found useful (Fig. 41). In this instrument a beam of sun-
light cast by a heliostat through a slit at H is converged by means of an
interpolated lens, O, upon a prism, P, set at the angle of minimum devia-
tion. Passing through this prism the rays are dispersed and a spectrum is
formed upon a diaphragm D, D^ composed of halves bounding a second slit
whose position and width may be varied at will so as to include any desired
part of the specti'um. A large lens C known as the collector brings the
rays which have passed through the second slit to a focus at E. Just in

Fig. 41. — Diagram showing the
construction of Eeinke's
spectrophor and the path
of the rays in it. H, slit
next to heliostat ; 0, pro-
jecting lens; P, prism; S,
Si, scale marked with wave
lengths ; D, Di, diaphragm,
including a variable slit ; c,
Cj, collecting lens ; i', posi-
tion of object subjected to
the rays. The spectrum
ranges from A = 0.75 /i to a =
40 /i. (From Reinke, '84.)

front of the diaphragm is placed a scale S, S^ of wave lengths fitted to the
spectrum obtained. Such a scale may be constructed with reference to the
position of Frauenhofek's lines by interpolation from Fig. 40.* To in-
clude rays whose wave lengths differ by exactly 0.05 fx the slit must be wider
when at the blue end than when at the red end of the spectrum (Fig. 40).

to form a hollow, triangular (60°) prism. The plates are fixed to each other
and to the glass base by a pasty cement made by mixing plaster of paris and
liquid glue. This cement soon hardens, and is not attacked by the carbon
disulphide. The hollow prism is now filled with fluid, and a triangular glass
plate is cemented on as a cover.

* If artificial light is used, two points on the scale can be obtained as follows :
Volatilize in a Bunsen flame, temporarily replacing the lamp, a salt of barium
and one of calcium, and note the position of the extreme blue band on the former
(line F) and the yellow band of the latter (line D). After determining these
two points the remaining lines can be plotted upon the scale.

§1]

APPLICATION AND MEASUREMENT OF LIGHT

157

A second method of getting monochromatic light is by the
use of flames tinged with various volatilized metals. Of these,
lithium salts give reds at A, = 0.67/i and \ = 0.61/x, sodium salts
give a pure yellow light of A, = 0.59/i, thallium salts (poisonous
vapor) a green at about X = 0.54/a, and indium salts a blue and
a violet, both beyond X = 0.46/z. The number of metallic
vapors which give even nearly monochromatic light is, however,
not large.

A third method for producing monochromatic light is found
in the use of solutions of pigments. Such solutions may be
held in deep glass vessels whose back and front glass surfaces
are parallel and near together. In the following table are given
in the first column the names which may be applied to differ-
ent parts of the spectrum, following Helmholtz (Handbuch,
p. 251); in the second column the pigments which while dry
give corresponding spectral colors in diffuse daylight and which
may also be used in making solutions ; and in the third column
certain pigments which in solution Yung ('78, p. 251) found to
transmit almost exclusively the part of the spectrum named in
the first column.

TABLE XVII

From outer limit to line C, red . . .

Cinnibar, HgS

Alcoholic solution f uchsin *

(vermilion)

C to

^ j orange

' i golden yellow . . .

Minium

Litharge, PbO

jj to

^ j yellow

' / yellow-green ....

Chrome yellow,

Concen. Sol. potassic chromate

PbOXrOo

(a little red and green)

E to

b, green

cupric arsenite,
Scheel's green

Nickel nitrate, NiO^CXO^).

b to

F, transition from
blue-green to blue

F to F

s G, cyanite blue ....

Berlin blue

Bleu de Lyon (a little V) f

F\ G to

(r, indigo blue

Ultramarine

G to

H, violet

Violet de Parme

Solutions made up from these pigments should, however, be
examined spectroscopically before using to make sure of the
purity of the color.

* Also a solution of iodine in carbon disulphide. (Pringsheim, '80, p. 409.)
t i^ to H is given by ammoniated copper sulphate, CuSo4'4NH3 -|- HoO
(Pringsheim).

158- LIGHT AND PROTOPLASM [Ch. VII

Finally, a fourth and decidedly practical way of obtaining
pure colors is by the use of transparent plates of colored glass or
other transparent solids. It is very difficult to get monochro-
matic glasses of certain colors in the market. A pure red is
easily obtainable; the blue is apt to contain some red also ; and
the green, both blue and yellow. Lord Rayleigh ('81, p. 64)
has used "films of gelatine or of collodion, spread upon glass
and impregnated with various dyes, gelatine being chosen when
the dye is soluble in water and collodion when the dye is soluble
in alcohol." This method seems to me to be of wide applica-
bility in our light experiments. For solid media are, after all,
far less troublesome than fluids, vapors, or spectra ; and con-
venience is one of the most valuable qualities of a method.

A brief statement must be made concerning the physical
properties of the different light Avaves. An inspection of any
prismatic solar spectrum shows that certain parts are brighter
to our eyes than others, and a thermometer placed in different
parts of the spectrum indicates a higher temperature towards
the red end. Curves are given in Fig. 42 which show the
relative warmth of different parts of the visible spectrum both
when the spectrum is a normal one (i.e. such as is given by a
diffraction grating, where all rays differing in wave length by
0.1 yL6 are equally distant) and when it is prismatic (in which
there is a crowding of rays at the red end). Curves of relative
brightness and of relative chemical (actinic) activity, so far as
can be judged from the union of chlorine and hydrogen, are
also given, for the prismatic spectrum. Being laid off on the
" normal " scale the curves last mentioned are somewhat dis-
torted. From these curves it appears that the brightest part
of the spectrum lies between lines I) and E^ at X=0.59/x;* the
warmest part is, in the normal spectrum, near A,=:0.60/a, but
in the prismatic spectrum, beyond the visible red, at about
X = 1.00/A. Finally, the .chemical activity of the rays increases
towards the blue end of the spectrum, but the relative activity
is different for the different substances acted upon. Measured
by their ability to unite chlorine and hydrogen, the rays having

* Mengarini ('89, p. 135) finds the point of maximum brightness to lie at
about 0.57 /x.

§1]

APPLICATION AND MEASUREMENT OF LIGHT

159

1 M 11 1 M 1 1 11 1 1 1 1 1 1 1 1 1 1 1 M 1 1 1 1

_ Curve of Relative Warmth in Prismatic Spectrum.

Curve of Relative Brightness in Prismatic Spectrum.

Curve of Relative Actinic Effect in Prismatic Spectrum.

-r\

—

^

; 1

■"-

-J

^

A

/

1 \

■V

/

\

/

.'

\

/

! \

"*>

/

\

/

\

/

\

/

/

\

/

/

(

'

\

/

<^'

\

/

1

/

^

/

/

,<

\

/

,/

/I

t

/

y

/

\

/

'

y

/

\

/■'

/

/

•'

/

\

1

/

\

1

y

(

f

I

^'

/

\

y

>

/

\

/'

\

/

\

/

y

/

\

f'

1

/

/

\

f

/

.-*

•!

,-•

■

\

\

y'

'

/

\

,^

/

\

^•

■^

/

\_

\

...

_.

—

—

—

~~

■-

—

—

--1 —

^^

.4ofj

.'iQ/f

.6

Oil

.70 (i

\

H

G

F

E

D

C

B

/

\

-

i 1

Fig. 42. — Scale of normal solar spectrum, above which is drawn the normal curve
of relative warmth ; also the curves of relative warmth, brightness, and actinism
of the prismatic solar spectrum. The curves of warmth are taken from Langley
('Si, p. 233) ; the curve of brightness is constructed from the data of Vierordt
('73, p. 17) ; that of actinism is taken from Bunsen and Roscoe ('59, p. 2GS) and
indicates the relative efficiency of the dii?erent rays of the midday sun in caus-
ing the union of chlorine and hydrogen. The absolute value of the ordinates is
entirely arbitrary.

a longer wave length than 0.51^ have feeble chemical actiou ;
at about \ = 0.42//, tliis action reaches a maximmu.

Not only the quality but also the intensity of the light with
which we experiment must be known. It is, fortunately, quite

160 LIGHT AND PROTOPLASM [Ch. VII

easy to determine the intensity of white light in terms of a
recognized unit ; namely, a paraffine candle burning at the rate
of 7.78 grammes per hour. A paraffine candle burning at this
rate has one candle power (C. P.) ; burning at twice this rate,
2 candle power, and so on. A comparison of any other light
with this standard may be made by means of any of the well-
known photometers, of which text-books of physics give a
description.

The determination of the intensity of a colored light requires
an additional piece of apparatus ; namely, a spectrophotometer.
The two principal types of spectrophotometer are that of
ViERORDT ('73) and that of Glan ('77), both of which
have undergone important improvements. The principle in
both types is the same. A spectrum of both the unmodified
(standard) light and that which has passed through the colored
screen are made side by side, so that their corresponding colors
can be compared. Since the source of light is the same, every
part of the spectrum of the unmodified light will be brighter than
the corresponding part of the spectrum of the colored light.
To bring the corresponding colors in the two spectra to the
same intensity, the unmodified light must be made less intense
to a measurable extent. In Vierordt's spectrophotometer
this result is brought about by narrowing that half of the slit
through which the unmodified light passes to get to the prism.
In Glan's apparatus the diminution in intensity is gained by
the polarization of both lights and the obscuring of the brighter
by the rotation of its analyzing Nichol prism, until equality
of brightness is obtained. A modified form of Vierordt's
convenient instrument is made by H. IvRtiss of Hamburg,
Germany. A modified form of Glan's photometer is de-
scribed by VoGEL ("77).

Vogel's apparatus (Fig. 43) consists essentially of a collimator contain-
ing (1) a slit of changeable width, separated by a band q into an upper and
a lower part to receive respectively the modified and the normal light ; (2) a
lens to render the rays parallel before they impinge upon (3) a doubly refract-
ing quartz prism, by which both upper and lower rays are broken into two
polarized rays. Of these four rays the uppermost and the lowest are cut
off by a diaphragm near F, so that only the middle two, which lie near
together, pass eventually to the eye. These two rays are oppositely polar-
ized and come, one from the upper, the other from the lower slit. The two

§2]

CHEMICAL ACTION OF LIGHT

161

rays now pass through (4) a Nichol prism (capable of being rotated along-
side a graduated arc) set at 45°, in which position both rays pass through
without changed relative intensity. The rays emerging from
the collecting telescope are now dispersed by
passing through the vertically placed prism,
and the adjacent parallel spectra are observed
through a telescope. By a rotation of the
NiCHOL prism through an
observed number of degrees
the stronger light may be
brought to the intensity of
the weaker. The relative
intensity of two lights with
reference to a third (con-
stant) is as the squares of
the tangent of the angle
through which the Nichol
prism has been rotated.
Other modifications of
Glan's photometer are those of Lord Rayleigh ('81) and
of Lea ('85), upon which the. spectrophotometer of the
Cambridge (Eng.) Scientific Instrument Co. is based.

Fig. 43. — Diagrams showing con-
struction of Vogel's spectropho-
tometer. 1. Horizontal section
through the optical axis. M,
mirror to reflect standard light,
by aid of a totally reflecting
prism p, into the optical axis.
S, shutter with slit divided into
an upper and a lower half by
means of a band q ; C, colli-
mating lens. D, doubly refract-
ing quartz prism ; m, in, the
holder of the Nichol prism iV,
which can be rotated through an
arc that can be read off from a
graduation on m, m; P, a flint
glass prism ; B, F, 0, observing
telescope, in which, at the focal
point, near F, is a diaphragm
cutting out the two outermost of
the four spectra coming through
B. 2. Front view of the shutter.
(From VoGEL, '77.)

M

§ 2. The Chemical Action of
Light upon Non-living Sub-
stances

The process of photography has
made us familiar with the fact
that daylight acts upon the halo-
gen salts of silver, gold, platinum,
and other metals, although the
nature of the chemical change
wrought by the light is uncer-
tain. It is not, perhaps, gener-
ally appreciated, but it is well
known to chemists, that light
can produce or further very
many chemical changes, particu-
larlj^ among organic comjiounds.
The effects are mainly due to the
blue and violet rays, hence are

162 LIGHT AND PROTOPLASM [Ch. VII

not the results of the heat of sunlight. Most of these chemi-
cal effects may be grouped under four heads. 1. Synthetic ;
2. Analytic ; 3. Substitutional ; and 4. Isomerismic and Poly-
merismic. A few others may be classed (5) as fermentative.
Let us now consider each of these five classes.*

1. The Synthetic Effects of Light will be considered chiefly
with reference to organic compounds. All the cases I have
gathered fall into three groups : addition to the organic com-
pound either (a) of oxygen, (/3) of chlorine or bromine, or
(7) of another organic compound.

Among the compounds which take up oxygen is bilirubin,
CggHggN^Og, a solutiou of which, in sunlight, even when air is
excluded, oxidizes to biliverdin, C32HggN^Og. In the absence
of sunlight this change requires air (B. Ill, 418). Duclaux
('87, p. 353) finds that vegetable oils, such as olive or palm
oils, are rapidly oxidized if exposed to light. Chastaign ('77,
p. 198) believes this oxidizing action of light upon organic com-
pounds to be of very wide-spread occurrence ; the blue-violet
part of the spectrum being, in this respect, the most active.

The direct combination by means of light of a halogen and
another substance is also not rare. Thus, in daylight, hydro-
gen unites with chlorine explosively. It unites with bromine
also, although with difficulty. Similarly, equal volumes of
chlorine and carbon monoxide unite quickly in the sunlight or
magnesium light to form carbon monoxid chloride, COClg
(B. I, 546). Again, when chlorine is passed through alcohol
under the influence of strong sunlight or magnesium light the
two substances unite and produce chloral hydrate (Street and
Fkaistz, '70). Likewise, wlien chlorine is passed, in sunlight,
through a solution of C3H2CI2O2 in CS2, there is formed
C3H2CI4O2, two atoms of CI having been added. Finally,
C2Clg may be made by uniting CgCl^ and CI2 in sunlight (B. I,
158) ; and the compound CgH^ • FeBrg • 2H2O may be made by
passing, in sunlight, C^H^ through a concentrated aqueous
solution of FeBr2 (B. I, 113).

* Most of these cases were obtained by searching through Beilstein ('86-'93).
Eeferences to tliis book will be made tliroughout this section by the letter B,
followed by the number of the volume and page upon which the statement may
be found.

§ 2] CHEMICAL ACTION OF LIGHT 163

Important cases of the direct synthesis of organic compounds
are given by Klinger and Standke ('91). These authors
have shown that in sunlight (and not in the dark) phenanthren-
chinon unites directly with benzaldehyd to form a third com-
pound phenanthrenhydrochinonmonobenzoat, in accordance
with the formula : (\^U^C\ + CgHgCHO = C-^^U^ (OH)
(O • CO CgHg). Again, chinon (benzochinon) and benzaldehyd
may unite in the sunlight to form benzohydrochinon, according
to the formula: CgH^O^ + CgHgCHO = CgHgCO C6H3(OH)2.
Finally, benzochinon and isovaleraldehyd may similarly unite
to form isovalerochinhydron, thus : CgH^Og + C^HgCHO =
C^HgCO CgHg(H0)2. These cases, then, are examples of
organic compounds which are wholly indifferent in the dark,
but which, subjected to strong sunlight, lose their identity by
uniting directly ; they may suffice to illustrate the important
synthetic effect of sunlight on non-living, organic compounds.

2. Analytic Effect of Light. — Cases of this effect are nu-
merous, varied, and striking. I will cite a few. The organic
dibasic acids CuH2n_204 break up in the sunlight and in the
presence of a small quantity of uranium oxide, into COg and
an acid CJri^^O^ (B. I, 63). For example, oxalic acid, C2H20^,
breaks up thus into formic acid, CH2O2 and CO2. Also an
aqueous solution of butyric acid, C4Hg02, in the presence of
uranyl nitrate, breaks up, in the sunlight, into COg and
Cglig (B. I, 422). We have seen that chlorine will unite
directly with organic compounds under the influence of light ;
on the other hand, compounds containing chlorine may lose it
in the sunlight. Thus under these conditions the ketone
(CgHj^NO • HCl)2PtCl4, an ammoniacal derivative of acetone,
becomes (CgHi^NO • HCl)2PtCl2; and (CgHj^NO • HCl)2PtCl4
becomes (CgHi^NO • HCl)2PtCl2'^(B. I, 982, 983). Again, chlo-
rine acetate, CI • O • CgHgO, undergoes slow decomposition iu
the light (B. I, 462) ; CgHgCl2, a derivative of pentine, CgHg,
does tlie same ; and ethylester, CIO • CgHg, explodes in sunlight.
Similarly explosive in sunlight is the greenish oil distilled when
absolute alcohol is poured over dry calcium chloride (B. I, 223).
Finally, sugar (Duclaux, '86, p. 881) and oxalic acid (Downes
and Blunt, '79, p. 209) are oxidized and break up into water,
carbon dioxide, and other compounds. These cases may serve

164 LIGHT AND PROTOPLASM [Ch. VII

to show the important chemical effects of sunlight in the dis-
integration of organic compounds.

3. Substitution Effects of Light. — The principal substitu-
tion effect of light is the replacement of hydrogen in an organic
compound by either chlorine or bromine. This occurs so fre-
quently that examples are superfluous. The substitution takes
place most rapidly and completely in direct sunlight, and it has
been shown that the rays at the blue end of the spectrum are
the most active in this process. The compounds affected
belong to the most varied groups of both the fatty and aro-
matic series — carbohydrates, acids, aldehydes, ketones, and
sulphides.

4. The Isomerismic and Polymerismic Changes produced by-
Light are among the most interesting. I will cite some exam-
ples. In the first place, it may be said that the changes in the
elements phosphorus and sulphur by wliich they assume their
red form have been ascribed to sunlight. Ela3omargin acid,
C^^^Hg^O^, is a compound found in connection with glycerine
in the oil of the seeds of Elseococca (Aleurites) vernica —
Chinese oil tree — one of the Euphorbiacege. This acid crys-
tallizes in rhombic plates which melt at 48°. When an alco-
holic solution of this acid is placed in a bright light, leaf -like
crystals of its isomere, elseostearin acid, which melt at 71°,
are produced (B. I, 535). Again, thymochinon forms yellow
crystals, which are soluble in alcohol. Subjected to a strong
light, opaque, whitish-yellow crystals are produced, which are
insoluble in alcohol. This substance, which does not arise in
the dark, and is hence not merely the result of oxidation, is
called polythymochinon (B. Ill, 180). Again, among the
derivatives of ethylene, C^H^, is chlorethylene, C^HgCl, a gas.
When placed in the sunlight this passes into a polymere, which
forms a viscous, amorphous, insoluble mass (B. I, 158). In
like fashion, bromethylene, C^HgBr, a fluid, is rapidly trans-
formed in the sunlight into a polymere, which is solid, amor-
phous; and insoluble in water, alcohol, or ether (B. I, 181), and
bromacetylen, C^HBr, a gas, is gradually transformed, in the
light, into a solid polymere. Finally, very many substances
undergo a gradual change of color in the sunlight, but the
nature of the accompanying molecular change is unknown.

§2] CHEMICAL ACTION OF LIGHT 165

5. Changes resembling those brought about hj fermentation
are produced by light. Thus Niepce de Saint Victor and
COKVISAET ('59) have found that a 0.1% solution of starch,
exposed during 6 to 18 hours to the summer sun, becomes trans-
formed into sugar, while in the dark no such change occurs.
The change is favored by a small quantity of uranium nitrate.
In a similar fashion glycogen is transformed into sugar more
rapidly in the light than in the dark. On the other hand,
Green ('94) finds that the ferment which normally transforms
starch into sugar is destroyed by subjection to a strong light,
the violet rays being especially active in this process. Like-
, wise, ptyalin, the ferment of saliva, is destroyed by light.

To sum up, light affects organic compounds in very varied
and important ways. We are, accordingly, prepared to find
that light exerts a very important influence on the activities
of protoplasm. Nor is the influence necessarily confined to
the surface, for most protoplasmic bodies are more or less
translucent. Thus Sachs ('60) found by looking through
a tube with one end fitted to the eye and the other directed
towards the sunlight, that considerable layers of plant tissue,
for example over 32 mm. of the tissue of the potato tuber, did
not cut out all the light, and that red had the greatest pene-
trating power, violet the least. Even the epidermis of man
permits light to pass, and Onimus ('95) asserts that light can
pass through the hand to such an extent as to affect during
26 to 30 minutes an orthochromatic plate kept in a tight wooden
box perforated only by the opening which is covered b}* the
hand. Whether the " Rontgen rays," which have so striking
a power of penetrating organic matters, are more of the
nature of light than of other physical agents, is still a subject
of debate. Whether they produce any important chemical
changes in protoplasm has not yet been fully determined.*

* During the six mouths which have elapsed since the above was written,
accounts of marked physiological effects of the Rontgen rays have been pub-
lished. Thus, exposure of the skin to them for an hour frequently causes loss
of hair and finger nails, and produces symptoms resembling those of sunburn.
AxENFELi) (Centralbl. f. Physiol. X, 1-47) finds that many insects and a crusta-
cean, Porcellius, kept in a box only one-half of which is penetrated by the rays,
aggregated in this part. Several experiments upon the tropic influences of the
rays have resulted negatively.

166 LIGHT AND PROTOPLASM [Ch. VII

§ 3. The Effect of Light upon the Genbeal Functions

OF OllGANISMS

In this section we shall consider in succession (1) the effect
of light upon metabolism ; (2) the vital limits of light action
on protoplasm ; and (3) the effect of light upon the movement
of protoplasm.

1. Effect of Light upon Metabolism (including Assimilation).
— Metabolism is a complex of chemical processes. Since, as
we have already seen, light has important chemical effects, we
are not surprised to find that it plays an important role in
metabolism. The effects of light are, however, of two distinct,
kinds. One is a thermic effect, due to the heat rays of white
light ; the other is a chemical effect due to the " actinic rays "
of the spectrum.

a. The Thermic Effect of Light on Metabolism is shown chiefly
in the assimilative processes of chlorophyllaceous plants. The
facts of this assimilation are chiefly these : various simple com-
pounds, water, carbon dioxide, salts of ammonia and nitrates,
are used as food by plants. For every volume of the gas —
carbon dioxide — taken in, one volume (nearly) of oxygen is
excreted. Starch (CgH^QOg) is the first visible product of the
water and carbon dioxide taken in. Chlorophyll is essential to
the absorption of carbon dioxide, to the giving forth of oxygen,
and to the formation of starch. Finally, chlorophyll can as-
similate only in the presence of sunlight and at a proper tem-
perature.

Now, not all the rays of sunlight with their varied wave
lengths are essential tX) this process. Just what rays are
the essential ones has been a jDoint of some dispute. The
earlier studies on the subject, made chiefly by Dhaper, ('44),
Sachs ('64), and Pfeffer ('71), were unanimous in declaring
that the most active rays in assimilation were those occupying
the yellow part of the spectrum at about line D — the region
of maximum brightness to our eyes (Fig. 42). But these ob-
servers were at fault in that, while they carefully determined
the quality of light and the corresponding quantity of assimila-
tion, none of them gave, in the experiments with color screens,
any adequate data upon the intensity of the diversely colored

§3] EFFECT UPON GENERAL FUNCTIONS 167

lights employed ; and tins is a fundamental matter, for it has
been shown, for instance by Reixke ('83 and '84), that, within
certain limits, the rate of assimilation increases with the inten-
sity of the light (Fig. 44). Even in experiments with the
colors of prismatic spectra one must remember that the rays
are crowded together at the red end, so that a given length of
the spectrum contains more rays at that end than at the other
(cf. Fig. 40).

Later investigations with improved methods have shown
quite conclusively that it is especially the rays with X = 0.68 /u.,
or those very close to the absorption band B^ which are most

16 8121111

Fig. 44. — Curve showing the relation between intensity of light (abscissfe) and quan-
tity of oxygen set free by Elodea canadensis. -} indicates the unit intensity of the
light from the heliostat. (From Reinke, '84.)

active in assimilation. The methods employed have been most
diverse, but they have yielded the same result. Timiriazeff
('77) studied the assimilative power of the different parts
of the solar prismatic spectrum, determining by gasometric
methods the quantity of gases decomposed in a given time.
Reinke ('84) also used the spectrum, but by means of his
spectrophor was able to get more strictly monochromatic light,
to use more nearly comparable extents of the spectrum, and,
especially, to get a more exactly comparable (in this case,
optimum) assimilative intensity for each part of the spectrum
than his predecessors. (See p. 156.) As the measure of
assimilation, Reinke used the number of gas bubbles set free

168

LIGHT AND PROTOPLASM

[Ch. VII

per minute by tlie submerged, illuminated plant. As is shown
in Fig-. 45, tlie maximum of gas production occurred at about

absorption line B — and tliis
is the more marked of the
absorption bands of chloro-
phyll.

A similar result was reached
by ENGELMAiiTN and set forth
in a long series of papers ('81,
'82, '82% '83, '83% '81, '86, and
'87). He found that certain
bacteria are extremely sensi-
tive to oxygen, moving in the
direction of small increments
of the oxygen density. Now,
by putting a thread of alga in
the same water with bacteria
and subjecting the thread to
a "microspectrum," that part
in which assimilation is pro-
ceeding most rapidly, and in
which, therefore, oxygen is
being most rapidly excreted,
will be indicated by the great-
est aggregation of bacteria.
The microspectrum was pro-
duced by means of an appa-
ratus especially designed by
ExGELMANN for his work and
now manufactured by the
Zeiss firm in Jena. The
appearances seen under the
microscope when the spec-
trum falls upon the alga in
the bacterium - water are
shown in Fig. 46. The max-
imum aggregation (hence,
maximum assimilative activ-
ity) at the red end occurs

Fig. 45. — Curve whose ordiuates are pro-
portional to the number of gas bubbles
eliminated ]Der minute by leaves illumi-
nated by the various rays whose wave
lengths are given at the bottom of the
diagram, and whose number of vibra-
tions per second are given at the top.
The background of the figure is com-
posed of the absorption spectra of the
chlorophyll in living leaves. 1, 2, etc.,
at the left, indicate the number of leaves
of Impatiens parviflora, which, when
superimposed, give the corresponding
spectrum at the right of these numbers.
The absorption at 0 is from a fern pro-
thallus, that at Ale is derived from an
alcoholic solution of chlorophyll. I to
IV indicate absorption bands. Beyond
F there is very general absorption
of the highly refractive rays. (After
Reinke, '84.)

§3]

EFFECT UPON GENERAL FUNCTIONS

169

close to the absorption band of chlorophyll , Observations
upon the chlorophylls of brown, blue-green, and red cells,
which, as Engelmann's microspectro-photometer indicated,
have a maximum absorption at other points, showed a maxi-
mum of assimilative activity at these other absorption points.
In bacterio-purpurin also, in which some of the most active
assimilative rays are those of the invisible red at about
\ = 0.85/x, most oxygen is produced at this point. (Exgel-
MANN, '83, p. 709.)

Finally, by an ingeniously devised experiment, Timieiazeff
('90) has settled this matter in the most direct and indubitable

^

, --

/ >f

- - •

> '

-- 7 -'.<:

,

•\.,\

f^

, -

-.—

,' ^

"

y

J.

ni

II

^^^

g

'■

- '.'

- /

'\.

■

r

-^

^ 1

Fig. 46. — Piece of Cladophora with swarming bacteria in the microspectrum (gas-
light) . The chlorophyll grains which fill the cells very uniformly are omitted ;
and, instead, the absorption band between B and C, and the tolerably pro-
nounced band at the violet end between E and F, are indicated by shading.
(From Engelmann, '82.)

fashion. He kept "a plant for two or three days in the dark,
until the starch in its leaves had gone; then, in a dark room, a
prismatic spectrum was thrown upon the leaf and the position
of Fraxjenhofer's lines indicated on the leaf. After from
three to six hours, starch had formed, under the influence of
the light, only in the region of the absorption bands of chloro-
phyll lying between B and D. This was determined by plung-
ing the leaf into boiling alcohol, thus decolorizing it, and then
staining in tincture of iodine, which combines especially with
the starch. The deeply dyed places, where starch had been
formed, reproduced the absorption spectra of chlorophyll.

The concurrent testimony of these and other observers work-
ing upon so diverse material and with such excellent methods

170 LIGHT AND PROTOPLASM [Ch. VII

justifies the conclusion that it is the rays absorbed by the plant
pigments which enable them to do their work in the decompo-
sition of carbon dioxide. The effective absorbed rays are,
moreover, chiefly those towards the red end of the spectrum,
those having over 525 x 10^^ vibrations per second (z'.e. below
the I) line).*

In conclusion it may be said that the greater proportion of
the radiant energy entering the plant tissue is absorbed. Thus
Mayer ('93) has shown that of dark radiant heat at 100°
about 80% is absorbed by a leaf through which it passes, and
this proportion is about the same whether the leaf is thick or
thin. Of this absorbed heat perhaps less than 10% is absorbed
by the chlorophyll. The rest must be used up in the vital
processes other than assimilation.

h. The Ohemical Effect of Light on Metabolism must now be
considered ; and of this we must notice at the outset two
degrees. The greater effect, which is a fatal one and the better
known, will be treated of further on. The lesser effect is less
striking, yet it must be included in the greater. It shows
itself in a disturbance of metabolism.

This disturbance of metabolism is evinced in some green
plants by heightened production of carbon dioxide and the
formation of chlorophyll ; and it is noteworthy that a similar
result occurs among Infusoria, according to the observations of
Fatigati ('79), who finds the violet rays more active than the
green in this process. Among the Metazoa light produces im-
portant chemical changes in the retina of the eye, and especially
in the skin, facilitating the production of pigment. That im-
portant chemical changes take place in the illuminated retina
follows from the experiment of placing the electrodes at oppo-
site surfaces of the frog's retina. The galvanometer sliows in
the darkened eye a slight " current of rest " flowing from the
front face to the deeper-lying part, containing the cones. If
now the retina be suddenly illuminated by blue, green, yellow,
red, or white light, a current, the result of chemical action,
appears flowing in the opposite direction ; this continues for

* Other, less important, thermal effects of light on plants are found in the
formation of chlorophyll and in the quickening of transpiration, which seem
chiefly due to the red and ultra-red rays.

§ 3] EFFECT UPON GENERAL FUNCTIONS 171

some time, slowly diminishing, however, in intensity. Certain
chemical changes in the living retina may, indeed, be studied
optically. These especially concern the visual purple. This
is a substance lying in the outer ends of the rods of the retina,
which, under the action of light, becomes bleached, but regains
its color in the dark (Helmholtz, Handb., pp. 265-273).
These facts serve to indicate that light may influence metabo-
lism even in organisms destitute of chlorophyll.

2. Vital Limits of Light Action on Protoplasm. — We have
seen above (p. 167) that the rate of assimilation diminishes in
chlorophyllaceous plants with a diminution in the intensity of
the light. At last a point is reached where the intensity is so
low that no further assimilation can occur, and after the con-
sumption of the stored-up food-stuffs, starvation and death must
eventually ensue. For non-chlorophyllaceous organisms, how-
ever, no such lower limit exists. Many, as parasites or cave
dwellers, live in complete darkness, even through many genera-
tions. A lower vital limit to the action of light exists only in
the case of chlorophyllaceous plants.

With the upper vital limit, it is, however, quite different.
This is found in the most diverse groups. Its occurrence in
bacteria being of especial hygienic importance, these organisms
have been made the object of exhaustive studies. Monte-
GAZZA (see NiCKLES, '65) was perhaps the first to discover that
strong light kills bacteria, but Downes and Blltkt (78 and
'79) were the first to study the matter thoroughly. Since their
time, numerous experiments have been made upon bacteria, as
well as the higher fungi. For literature, see Feaxkland
and Ward ('92), and Ward ('93, p. 309). Even the earliest
observers found that, while cultures of bacteria reared in the
dark rapidly flourished, they not merely did not thrive when
subjected to sunlight, but actually became sterilized. That the
sterilization was complete was shown by the fact that when the
culture was placed again in the dark, no bacteria developed in
it. This result is most striking when certain bacteria, say of
the species Bacillus anthracis, are mixed with gelatine or agar-
agar, poured uniformly over a glass plate. If the glass plate
is then covered by a black paper stencil containing some
character, e.g. the letter ^, and exposed to a November sun-

172

LIGHT AND PROTOPLASM

[Ch. VII

light for 6 hours, and if then the whole plate is placed in a dark
incubator at 20° C. for 48 hours, the bacteria will be found to
have developed in all parts of the plate except in the JtZ-shaped
area sterilized by the light (Fig. 47). Compare the earlier
results of BucHNEE, ('92). That in these cases it is the light
and not a high temperature which induces the sterilization in
the illuminated region is shown by the fact that Buchner ('92)
obtained even more striking results when parts of the culture
plate were exposed under 50 cm. of water, which cuts off the heat.

Fig. 47. — Appearance of a gelatine culture of Bacillus antliracis, exposed to the light
over only the area E, and then incubated for 48 hours. In the area E no colonies
have developed. (From Ward, '93.)

Not all rays have this bactericidal property. Downes and
Blunt ('78) found that only the blue rays were thus active,
for behind red or yellow glass the bacteria readily developed.
Ward ('94) threw a solar spectrum upon an agar film in which
bacteria were developing in a dark chamber. He found that
the bactericidal effect was greatest in the region of the blue-
violet rays (about \ = 0.43 /x) and diminished towards the
extreme violet and the yellow, where it had almost disappeared.
These facts were ascertained by incubating the bacteria for 48
hours after insolation, when certain parts affected by the spec-
trum were found to remain clear (Fig. 48). When an electric

§3]

EFFECT UPON GENERAL FUNCTIONS

173

spectrum (obtained by tlie use of a quartz prism) was em-
ployed, a bactericidal effect was obtained (provided no glass
intervened) in the ultra-violet. That the action of the light
was not in these cases primarily upon the food-film was shown
by the fact that a plate of sterile agar, exposed behind a stencil
plate, and then laid flat on a film of dried unexposed spores,
permitted the uniform growth of the spores, in the illumined as

Fig. 48. — Plate of anthrax spores, exposed for 5 hours to the solar spectrum in
August, aud incubated for 48 hours. The horizontal line shows the length of
the spectrum. The vertical lines are not Frauenhofer'.s lines, but serve to
show the limits of the principal regions, of the spectrum. The clearest area is
that where fewest spores have developed in the incubation— where, consequently,
the bactericidal effect was greatest. (From Ward, '94.)

well as in the unillumined region. All these observations show
that the bactericidal action of light is due to the action of the
chemical rays on the protoplasm.

Another fact of importance, first discovered by Downes and
Blunt, is that light has no effect upon bacteria when they are
in a vacuum. This abundantly confirmed observation indicates
that death only secondarily results from light. The primary
cause of death is an oxidation process, — a process rendered
possible by the mediation of light. As we have seen (p. 162),
many organic compounds undergo oxidation in the highly
refracted light rays. Probably there are in bacteria such com-

174 LIGHT AND PROTOPLASM [Ch. VII

pounds, the rapid oxidation of which is incompatible with life.
In any case it is clear that the bactericidal effect of light is a
chemical one.

Concerning the range of organisms which are thus affected,
it must be said that chiefly pathogenic species, such as the
bacteria of anthrax, of typhus fever, and of cholera have been
experimented with and have shown themselves most suscep-
tible. Other bacteria are, however, likewise affected. Among
the other fungi, Wettsteik ('85) found that the conidia of
Rhodomyces Kochii, a human intestinal parasite, did not de-
velop in the light. Klein ('85) found' the same thing to be
true for the conidia of Botrytis cinerea, and showed that the
blue-violet rays were the most effective ones. Elving ('90, p.
105) gained similar results with Aspergillus, although several
days or weeks of insolation did not kill the fully ripe spores.
Ward ('93) determined that insolated spores, cultivated on
agar or gelatine plates, of Oidium lactis (5 cases), Saccharomyces
pyriforrais (4 cases), and " a ' Stysanus ' conidial form " found
as a saprophyte on the screw-pine, Pandanus, (2 cases) became
injured. These are all hyaline and colorless except Stysanus,
which is nearly so. Certain colored spores which Ward experi-
mented with gave negative results, and Ward concluded that
this is because the blue end of the spectrum is cut off before
reaching the deeper protoplasm. However this may be, we
actually find that in many, but not all, fungi the metabolic
processes of the spores are disturbed and even death is pro-
voked by intense light.

Why the spores should be especially susceptible to the action
of light is an important inquiry. Ward believes the answer
to be that the spores contain oily substances, which are espe-
cially liable to oxidation in light, as we have already seen.

Finally, we have to consider the experiments which demon-
strate that a strong sunlight may be injurious even to green
plants. This result follows clearly from the work of PrijSTGS-
HEIM ('81). When strong sunlight is focussed for a short time
upon cells of Spirogyra, Nitella, Mesocarpus, or Tradescantia
stamen hairs in atmospheric air (5 to 15 minutes), they are
killed. No result occurs, however, when the same light falls
upon green cells in which the atmosphere has been replaced by

§3]

EFFECT UPON GENERAL FUNCTIONS

175

hydrogen (Fig. 49). That it is here also the oxygen (and not
the carbon dioxide) of the air which is the destructive agent
is shown by subjecting the plants to air freed of carbon dioxide,
when they are killed by light as before.

The most important results following from the "conclusions
of this sub-section are : a minimum vital limit of light action
exists only in the case of
those organisms (chloro-
phyllaceous plants) which
depend upon light for as-
similation ; a maximum
limit is found among the
most diverse organisms,
those with chlorophyll
and those without. The
rays which have the more
rapid vibrations are the
more active. They pro-
duce chemical changes to
which death is primarily
due.

3. Effect of Light upon
the Movement of Proto-
plasm.— Under this head
we shall consider only
those protoplasmic move-
ments which may not be
grouped under Locomo-
tion, and shall discuss
three classes of cases :
(a) effect of low intensity of light upon movement ; (6) effect
of high intensity of light upon movement ; and (c) effect of
change of intensit}^ on contraction.

a. Effect of Ltnv Intensity of Light on Blovement — Dark-rigor.
— We liave already seen that chlorophyllaceous plants must
eventually die if kept in the dark. Some time before death
occurs the plants go into a condition of immobilitj^ Avhich may
be called dark-rigor, since return of light brings a return of
movements. Dark-rigor is very marked in the sensitive plant.

Fig. 49. — Piece of a sprout of Nitella mucronata
which was subjected iu a gas chamber to a
green light in three successive experiments
A, B, C In experiment A the insolation
lasted 2 to 3 minutes, the gas chamber be-
ing tilled with atmospheric air. In experi-
ment B the insolation lasted 20 minutes in
the presence of hydrogen. In experiment C
the insolation occurred again in the presence
of atmospheric air and lasted 5 to (i minutes.
(From Pringsheim, '81.)

176 LIGHT AND PROTOPLASM [Ch. VII

If this plant is kept for several clays in darkness, the usual
response to touch does not occur. From some observations of
Bert ('70, p. 338), it appears that it is the absence of the
blue-violet and orange-red rays which brings about this dark-
rigor ; for it occurs nearly as rapidly in green light as in the
dark. In these cases the absence of movement in the dark
might seem to be the result of diminished assimilation.

But dark-rigor occurs under conditions which destroy the
general validity of this conclusion ; for example, in the reddish-
purple bacteria * whose reactions have been studied chiefly by
EiSTGELMANN ('83 and '88). It appears that in these organisms
light is essential to movement ; for, after having been kept
over night in the dark, they are found in the morning at first
motionless ; only later, after 5 to 10 minutes of illumination,
do they awaken to activity. If now, after keeping for a time
in the light, the organisms are brought again into the dark,
their movements gradually diminish until, in a few hours, they
have ceased. We have seen above (p. 51) that oxygen is nec-
essary to movement, and we know that many plants excrete
oxygen in the light. We might expect that the quiescence of
these organisms in the dark is a consequence of their failure to
produce the oxygen necessary to locomotion, and indeed they
do produce in the light a slight quantity of oxygen, by virtue
of their chromophyll (bacterio-purpurin, Lankestek). But
that it is not merely oxygen which induces movement is shown
by the fact that when an abundant oxygen supply is artihcially
furnished, no movement occurs in the dark. Thus light, in the
presence of oxygen, is essential to movement ; it seems to be
necessary to the irritable condition upon which locomotion
depends. This irritable state of the protoplasm conditioned
upon a certain intensity of light Engelmann colls phototonus.-f

The analysis of this matter has been carried further. It has
been found that a perceptible time (latent period) elapses

* This term includes bacteria known as Bacterium photoraetricum, Bacterium
roseopersicinum, rubescens, etc., Monas okeni, Spirillum violaceum, and by other
names.

t The term was applied to this phenomenon by Engelmann on account of its
resemblance to that already described for the higher plants, and to which Sachs
had previously given this name.

§3]

EFFECT UPON^ GENERAL FUNCTIONS

177

between the illumination of the organism and the occurrence
of movement. Also, the ultra-reel rays produce most rapid
locomotion, next the orange-yellow, and weakest the violet-blue
and violet-red. Spectrum analysis shows that the most active
rays are the ones absorbed by the chromophyll (Fig. 50).

This phenomenon of phototonus is not confined to the purple
bacteria. Thus, Famintzin ('67, pp. 29-31) has shown that
the movements of the closely related Oscillaria are dimin-
ished in the dark.. Sokokin ('78) found that protoplasmic
streaming in the plasmodium of Dictydium ceases at night,
being awakened to movement by the light. Finally, Ver-

aBCD EbF g

80

75

70

65 GO

55

50

1

:.«

m

•

'

•a

1

:• ' '"

=

M

^

=

Fig. 50. — a. Spectrum of the chromophyll of bacterio-purpurin, showing absorption
bands at A = 0.59 m and A = 0.53 m. An (invisible) absorption band has been deter-
mined by means of the bolometer at A = 0.85 m. b. The bacteria are seen aggre-
gated chiefly in the regions of the absorption bands. The accumulation of bacteria
in these regions of absorbed energy seems due to the fact that the moving bacteria
cannot pass from a region of high energy to one of low without a violent stimulus
which impels them back again. (From Engelmanx, '83''.)

WORN ('89, Nachschrift, and '95, p. 393) finds that, in the
dark, the ciliate Pleuronema chrysalis rests quietly in the
water, only occasionally making its peculiar spring. But
when diffuse daylight is focussed upon it, for instance by the
mirror of a microscope, it springs rapidly by the movement of
its long cilia ; and this movement is often repeated, so long as
light continues to fall. The movement is produced by blue or
violet rays ; red rays have little or no effect. A latent period
of from 1 to 3 seconds elapses before the response occurs.

These cases serve to show that light, in the presence of other
suitable conditions, is, both for some chlorophyllaceous organ-
isms and plant tissues and for some organisms destitute of

178 LIGHT AND PROTOPLASM [Ch. VII

chlorophyll, nearly or quite essential to movement. Phototo-
nus is a convenient name for the condition induced by light.

h. Effect of High Intensity of Light on Moveynent — Light-
rigor. -—Wq have just seen that in some organisms the most
vigorous movements occur at an optimum intensity of light,
Avhich produces phototonas. At a lower intensity there is no
movement. It appears, furthermore, that there is for many or-
ganisms a maximum intensity of light, below that which produces
death (ultramaximum), Avhich causes a cessation of movement
that may be called light-rigor. This condition is distinguished
from that of death by the fact that diminished light brings
return of activity. Engelmann ('82, p. 109) observed this
condition in his Bacterium photometricum, and remarks that
it is common to all bacteria. Similar light-rigor has been
observed in green plants also. Pringsheim ('81, p. 516)
found that when, in the presence of oxygen, strong sunlight
was let fall upon Nitella, the movements ceased after 1|-
minutes. If the insolation was now interrupted, normal move-
ments were resumed.

Summing up the effects of varied intensities of light, it
appears that for many organisms there is an optimum, which
produces a condition of phototonus, in which the organism
moves and responds regularly to stimuli. As the light inten-
sity falls below, or rises above this optimum, the activity of
movement diminishes,' ceasing at certain points in the condi-
tions of dark-rigor and light-rigor. Beyond each of these
points, again, is the point of death.

e. Contraction produced hy Change in Intensity of Illumina-
tion. — ■ We here consider a number of cases not closely related
except in this, that quick movements are produced after stimu-
lation by change in the intensity of the light. The cases are
found both among Protista and Metazoa.

Among the sulphur-bacteria Engelmann ('88, p. 665 ; 88*)
has noticed that a sudden diminution in the intensity of the
light, produced by shading the mirror of the microscope, is
followed by a spring backwards, often to the distance of 10
to 20 times the organism's length. This reaction Engel-
MANN has called " Schreckbewegung." When the light is sud-
denly increased, a forward movement takes place, but this is

§ 3] EFFECT UPON GENERAL FUNCTIONS 179

less marked. Among tlie Myxomycetes, Engelmann ('79)
has found that the amcjeboid Pelomyxa, when suddenly sub-
jected to a strong light, contracts into a spherical mass.
Sudden darkening or gradual illumination produces no such
contraction. Among swarm-spores, Strasburger ('78, pp. 575,
576) has noticed that a sudden diminution of the light puts
the quiet Hsematococcus spores again in motion, and makes the
Botrydium spores start as though disturbed. Such violent
movements of the protoplasm indicate that a very considerable
chemical change has taken place in it.

Passing, next, to the Metazoa, we find that certain smooth
muscle fibres are made to contract by the direct action of light ;
thus, Steinach ('92) has offered most convincing evidence
that the contraction of the iris, in the lower vertebrates at
least, may occur as a direct reaction to illumination, even when
the eyeball is cut out, and the iris, indeed, separated from
connection with the ciliary part of the eye.

Some of the higher animals react strikingly like Engel-
mann's bacteria. Thus, Loeb ('93, p. 103) found that Serpula
uncinata retracts into its tube when the hand is passed between
it and the light ; but sudden increase of illumination has no
effect. Nagel ('96, p. 76) finds the same thing in Spirographis,
and Andrews ('91, pp. 285, 296) has observed the same phe-
nomenon in the eyeless Hydroides dianthus. In these cases
the branchicB seem to be the sensitive organs. Adult barnacles
show a similar sensitiveness to light ; for Pouchet ('72, p. Ill)
found that momentary cutting oft' of the light, as b}' the shadow
of the hand, caused arrest, for several seconds, of the rhythmic
movements of protrusion of the appendages from the shell. In
this case, the sensitive region has not been located. Some
lamellibranchs (Nagel, '96, p. 50) react similarly to increased
light. These are examples of a phenomenon which we shall
meet with again in considering growth. They serve to show
that there is a wide-spread irritability of protoplasm to changes
in intensity of light.

Let us now review the conclusions of this section. Light —
especially the thermic rays — is essential to the decomposi-
tion of carbon dioxide by chlorophyllaceous plants. The only
effective rays are those absorbed by the chlorophyll. The rate

180 LIGHT AND PROTOPLASM [Ch. VTI

of assimilation is increased by increased intensity of light. The
chemical rays act to increase metabolic changes, and the output
of carbon dioxide. As these rays become more intense, the
metabolic changes go on with abnormal rapidity, until, finally,
death ensues ; thus, intense light is fatal to many, perhaps to
all, organisms. Absence of light, however, is injurious only as
preventing assimilation in chlorophyllaceous organisms ; but
these supply the food for other organisms, so that continued
darkness in any environment must likewise be eventually fatal
to all life. All organisms, before succumbing to darkness or
to light, enter into a condition of rigor, from which they may
return to activity if favorable conditions are restored. Sudden
change of intensity often produces violent protoplasmic changes,
awakening quiescent organisms to activity, or causing, in the
higher organisms, violent contractions.

All of these effects of light, whether produced by the thermic
or chemic rays, probably give rise to great chemical changes
by which disturbances of metabolism, and eventually death,
may be produced. Not all organisms find light immediately
necessary to tlieir existence ; but very powerful light, long
continued, proves fatal to most protoplasm.

§ 4. Control of the Direction of Locomotion by
Light — Phototaxis and Photopathy *

Li this section we shall (1) distinguish between false and
true phototaxis ; (2) consider the observed cases of phototaxis
among Protista, the parts of higher organisms, and the Metazoa
as entire organisms ; and (3) discuss the general laws of photo-
taxis and photopathy.

* In this section we shall deal with two sets of phenomena which very likely
are different, but which, in our ignorance, we cannot always distinguish. The
first includes that active migration of organisms whose direction is determined
by that of the rays of light. This is phototaxis. The second includes the
wandering of organisms into a more or less intensely illuminated region, the
direction of locomotion being determined by a difference in intensity of illumina-
tion of the two poles of the organism. This is photopathy. According as the
migration is towards or from the source of light, we can distinguish positive ( + )
and negative ( — ) phototaxis. According as the migration is towards or from
the more intensely illuminated area, we can distinguish positive ( + ) and negative

§ 4] PHOTOTAXIS AND PHOTOPATHY 181

1. False and True Phototaxis. — It must certainly be a very
old observation that when small organisms are placed in a
vessel in front of a window, they are soon found arranged with
reference to the window ; some lying on the nearer side, some
on the further side, and others swimming indifferently back
and forth through the vessel. The conclusion is near at hand
that this arrangement of the organisms is determined by the
light. This conclusion is, however, not necessarily correct.
Thus, Sachs ('76) showed that, under certain conditions,
wholly passive substances — oil drops, in a mixture of water
and alcohol — might exhibit a similar aggregation towards the
window or away from it. These conditions are that the vessel
should be cooler next the window. Then, on the cooler side,
there will be a descending current ; on the warmer side, an
ascending current ; on the surface, a current towards the win-

A
a

Fig. 51. — Vertical section through a dish showing distribution in water of passively
suspended bodies, as a result of difference of temperature at the two sides of the
vessel. A, warmer side ; B, cooler side. Arrows show the direction of movement
of currents in the water. The objects lighter than water are grouped at b ; those
heavier than water, at a.

dow ; and on the bottom, a current from the window. If
the passive bodies are such as float, they will thus be carried
towards the window, and will exhibit a false phototaxis (in
the positive sense); if, on the contrary, they tend to sink, they
will be carried from the window, and show false negative pho-
totaxis. Now this appearance, due to passive transportation
by currents, may likewise, under the given conditions, be
exhibited by organisms — but the phenomenon is not due to
liglit (Fig. 51).

There is at least one other kind of pseudophototaxis. This

( — ) photopathy ; and correspondingly we can in this second case speak of the
organisms themselves as photophil or photophob. In this nomenclature I follow
Graheu. Strasburgek ttsed photometry for what I here call photopathij, but
Oltmanns ('92, p. 20(5) has employed photometry to indicate the capacity of
organisms to perceive different degrees of intensity of light. So, perhaps, the
terminology here employed may lead to the least confusion.

182 LIGHT AND PROTOPLASM [Ch. VII

may occur when there are in the vessel chlorophyllaceous
organisms producing oxygen in the sunlight. The oxygen,
more abundantly formed on the sunny side of the vessel, becomes,
then, a means of attraction to other (chemotactic) organisms,
whose position seems thus to be determined directly by relative
brightness.

A good example of this kind of pseudophototaxis is described by Engel-
MANN ('81*). He found that the Schizomycetes in a certain drop of water,
partially illuminated, were aggregated toward the illuminated side. Exami-
nation revealed the presence of a chlorophyllaceous schizoraycete — Bacte-
rium, chlorinum — in the drop, and the apparent phototactic appearances were
easily accounted for as follows : Under the influence of light the Bacterium
chlorinum secreted oxygen, and this acted chemotactically to attract the
bacteria, which thus moved, at the same time, towards the illuminated
area. That it was the oxygen produced in the sunlight rather than the
light itself which attracted, was evinced by the fact that, when the supply
of oxygen is abundant in all parts of the drop, or if the Bacterium chlorinum
is removed, no aggregation takes place at the bright point.

2. Distribution of Phototaxis and Photopathy. — a. Protista.
— We now come to the consideration of the cases of true pho-
totaxis and photopathy, and shall first discuss the distribution
of the phenomenon in the different groups of Protista. Of the
Protista we may take up first the chlorophyllaceous forms.

Flagellata and iSw arm- Spores. — In no other group does
phototaxis show itself more clearly than in this. The earliest
studies were made here, but despite the ease of gaining results
they were mostly fragmentary and uncritical. A simple ex-
periment of Nageli ('60) had, indeed, showed conclusively
that swarm-spores are responsive to light. A glass tube three
feet long and held vertically was filled with alga- water. When
the upper end of the tube was enveloped by black paper the
organisms moved to the lower end, and conversely. A diffi-
culty was encountered, however, in the fact that when zoospores
were placed in a plate by a window, the organisms gathered
at the edge next the window, which, since the edge of the plate
threw a shadow there, was the darkest part of the surface. In
consequence some authors had concluded that swarm-spores
shun the light ; whereas Cohn asserted, all too briefly, that
they move in the direction of the rays and toward the source
of light. Finally, Famintzin ('67) had discovered that swarm-

§4] PHOTOTAXIS AND PHOTOPATHY 183

spores which moved towards a light of a certain intensity would
move from light of a certain greater intensity. That was the
condition of knowledge on this subject when Steasbukgee's
('78) epoch-making paper appeared.

Steasbueger worked with swarm-spores of various species
of algse, and with the flagellate Chilomonas and Euglena. He
observed again the phenomenon that the sense (-f or — ) of
response depends upon the intensity of the light. He also
showed that the rate of movement is quicker in stronger light
on account of the fact that the path taken by the organism is
straighter ; and (p. 586) that phototaxis is the result of the
organism putting its long axis in the axis of the infalling rays.
Steasbueger found also that, in general, the smaller species
of swarm-spores and the smaller individuals are more respon-
sive than the larger ones.

Later studies have extended our knowledge of the distri-
bution of phototaxis in this group. Swarm-spores have been
studied by Stahl (78, '80) ; Euglena, by Engelmann ('82%
p. 396) ; and Volvox, by Cienkowski ('56), Veewoen
('89, p. 45), and Oltmanns ('92). Especially interesting
is the fact that colorless swarm-spores, like those of Chytri-
dium, which are parasitic upon chlorophyllaceous forms, respond
like the green organisms. (Steasburgee, "78, p. 568.)

Desmids^ especially Closterium, have been experimented with
by Stahl ('78 and '79), Klebs ('85), and Adeehold ('88).
All are markedly phototactic in moderate, diffuse daylight.
This phototaxis is the more striking since the method of loco-
motion of these forms is peculiar. The crescentic Closterium
moniliferum, for example, stands inclined and glides along, one
extremity touching the substratum, the free extremity in ad-
vance. The gliding seems to result from the secretion of a
stream of mucus along the substratum. Now Stahl believed
that the angle of inclination of the Closterium is dependent
upon the direction of the infalling rays of light, being parallel
thereto. This relation has been denied by Klebs, but Adee-
hold, by varying the direction of the infalling rays, has shown
that the azimuthal position is determined by light. Under
certain conditions Closterium moniliferum moves by a sort of
liead-over-heels motion, since the free end bends down to the

184 LIGHT AND PROTOPLASM [Cii. VII

substratum and becomes attached, and the former attached end
becomes free. Stahl explains this on the ground that the
ends of Closterium periodically exchange their tendency to
point towards the light. The appearances just described are
found in diffuse daylight. In stronger light the azimuthal
position is 90° from the infalling light. If direct sunlight
falls upon desmids, they move from the light (negative pho-
totaxis).

Diatoms have been studied by Stahl ('80) and Veewoen
('89, p. 47). Locomotion is effected in these organisms as in
desmids by the secretion of mucous threads. The movement
towards diffuse daylight (Navicula, Stauroneis) takes place
slowly, but it often affects nearly all the individuals. The
long axis does not seem to be clearly oriented in the direction
of the infalling rays, which may be partly accounted for by
the normal zigzag method of locomotion. Under strong sun-
light diatoms appear negatively phototactic. Occasionally a
culture will be found whose individuals are separated into two
groups — one next the positive side, the other next the nega-
tive side of the vessel.

Oscillaria. — Verworn ('89, p. 50) has made experiments
on the reaction of these organisms, whose method of locomotion
is probably similar to that of desmids. They are markedly
positively phototactic from half darkness to direct sunlight ;
only in intense sunlight do they fail to accumulate at the posi-
tive end of the vessel. The aggregation at the positive pole
takes place by the threads assuming a direction parallel to the
rays of light and creeping forward thus, side by side. Ver-
worn states that after all have attained the -}- edge, rotation
of the slide or vessel through 180° does not cause a prompt
transfer of all individuals towards the light side — at least
during the time of his observation only a few had crawled
towards the light in its new position. According to Wino-
GRADSKY ('87), Beggiatoa is generally negatively phototactic.

Myxomycetes. — In its amoeboid form and when subjected to
strong sunlight jEthalium septicum retreats into the substratum,
but while in the dark it comes to the surface (Hofmeister, '67,
p. 625 ; Strasburger, '78, p. 620). Also, when the Plasmo-
dium is partially illuminated, the protoplasm tends to flow from

§4]

PHOTOTAXIS AND PHOTOPATHY

185

the illuminated region. (Baean^etzki, '76, p. 328, and Stahl,
'84, p. 167.)

Baranetzki proceeded as follows : a glass plate was placed in a saucer so
that its surface was 2 or 3 mm. below the rim. The plate was covered by-
filter paper which extended
over the rim and here dipped
into water, by which means
it was kept moist. Over the
saucer was laid an opaque
cover, blackened below and
provided with a narrow slit.
The Plasmodium was placed
on the filter paper and diffuse
daylight was thrown upon the
slit by means of a plane mir-
ror. In less than half an hour
the illuminated threads of the
l^lasmodium had become very
thin, owing to the retreat of the
protoplasm from under the slit
to the darker region (Fig. 52).

Rhizopoda. — Although,
as we have seen, Pelo-
myxa is irritated by a
sudden illumination, a
phototactic or photo-
pathic response has not

Fig. 52. — Plasmodium of .^thalium septicum,
after having been kept in the dark for some
time and then illuminated, for half an hour,
over a cross-shaped area, only. The illumi-
nated area is on the upper part of the figure.
The protoplasm has retracted from it, leaving
a partially clear region in the form of a cross.
(From Baranetzki, 75.)

hitherto been certainly
observed in this group. Verworn ('89, pp. 40, 41), indeed,
experimented, but with negative results, upon Amceba limax,
Amoiba princeps, Actinosphserium, and Actinophrys. Only
in Polystomella crispa did he notice a slow wandering
towards the source of light ; but he was uncertain whether
this was due to light.

Verwoun's method was not well devised, however, for bringing out
phototactic response. The Protista were placed on the slide, and, after cut-
ting out heat rays by means of a plate of ice, were subjected to the light or
to the Engelmann microspectrum, and illuminated at different intensities
either over the whole body or over only a part. All disturbing influences,
he says, were as far as possible eliminated : gravity, by an exact horizontal
position of the microscope on a table with three screw-feet ; the action of
the edge of the drop, by using a very broad drop; and, iinally, the lateraUy

186 LIGHT AND PROTOPLASM [Ch. VII

impinging rays of light, by means of a black cardboard box placed over the slide.
Thus it is clear that all of his light fell upon the organism in perpendicular
rays from below. This method of experimentation would clearly not show
whether Amoeba is phototactic or not.

I have experimented with Amoeba proteus, using methods
resembling Verworx's, and likewise dissimilar ones, and have
reached new results. In the first place, I have proceeded some-
what after the fashion of Verworn to determine whether the
amceba in a field illuminated from below, and separated by a
sharp line into a light and dark half, showed any change of
movement in passing from dark to light or from light to dark ;
also, whether an amceba moving in a uniformly illuminated
field changed its direction when half of its body was dark-
ened. Nearly all such experiments were negative. No effect
resulting from the change from light to dark or the reverse
could be detected. Thus far my results agreed with Ver-
worn's.

In a second set of experiments, I proceeded differently.
Usually one amoeba was isolated by means of a capillary tube.
It was then introduced, with a drop of clear water, between
two slips of glass, each about 25 by 50 mm., which were kept
2 mm. apart, and at the same time cemented together, by glass
strips of equal thickness placed near the ends. By this means a
broad field for movement with uniformity of conditions of con-
tact was ensured. The whole space between the two glass plates
being now filled with clear Avater, the entire apparatus was sub-
merged in a vessel which contained water about 2 cm. deep,
and which was slightly smaller than the stage of the micro-
scope. Finally, the entire stage, but not the substage optical
apparatus, was kept in the dark by means of a cone made of
several thicknesses of dense black cloth fastened by a slip-noose
to the objective, and folded below the stage so as completely to
exclude all extraneous lateral light. Light from the mirror
was cut off by an interposed card. Through a slit in the cloth
on the side next the v\dndow, — a west window, — a beam of
direct sunlight, or of reflected light from the morning sky, was
admitted to the amoeba. The plates of glass being as nearly as
possible horizontal and occasionally rotated, the directive action
of gravity was eliminated. Since, so far as could be seen with

§ 4] PHOTOTAXIS AND PHOTOPATHY 187

the microscope, no local sources of food or oxygen occurred in
the water between the plates of glass, chemotactic influences
were uniformly distributed. From the conditions of the ex-
periment already described, a difference iji temperature or of
illumination at the two poles of the amoeba is scarcely conceiv-
able. The rays of radiant energy were the only directing agent.
Under these conditions the amoeba nearly uniformly showed
itself negatively phototactic to light of an intensity varying
from strong diffuse light to direct sunlight. The absence of
uniformity is to be ascribed to the accidental presence of some
disturbing agent. The movements made by the amoeba were
represented graphically by making at intervals a camera drawing
of its outline. Two such graphic representations are repro-
duced in Figs. 53 and 54. It must be said that it is difficult to
get so extended a series of changes in light as is shown in Fig.
64, for the phenomenon of acclimatization comes in and the
responses become irregular. But, despite such irregularities,
my studies lead me unhesitatingly to conclude that Amoeba,
although not at all photopathic, is strongly phototactic. This
result is important, for, since Amoeba is responsive to light, it
may very well be that such responsiveness is a general property
of protoplasm.

Ciliata. — A double action of light must be here taken into
account. Engelmann ('82% pp. 391-395) states that those
Ciliata which contain chlorophyll (algse) — e.g. Paramecium
bursaria, Stentor viridis, Bursaria — move towards the light,
but only when the oxygen tension in the water is low. Also
when the water drop is illuminated by a microspectrum, instead
of white light the organisms aggregate towards the red end.
Here are the rays by which most oxygen is produced from the
chlorophyll, since assimilation takes place fastest here. When
the organisms are placed in excessively oxidized Avater they
move from the light. The conclusions to which Engelmann
arrived from these and other facts wei'e that tliese species have
a very delicate sensitiveness to variations in oxygen tension, and
that it is through this sensitiveness that light influences move-
ment. Accordingly, it would seem that the apparent photo-
taxis is truly a case of chemotaxis ; but this conclusion requires
better evidence.

188 LIGHT AND PROTOPLASM [Ch. VII

V"

h

14:42

(3). 14:20 to 14:34

13:00

/Av.02

' Fig. 53. — Camera drawing, showing

the successive positions assumed
by an amoeba subjected to light
falling upon it from one side. The
arrow lies in a horizontal projec-
tion of the sun's rays. The amceba
retreats from the source of light.
The numbers to the right of the
outlines of the amoeba give the
observed times between 10:28 and
11:22 a.m. Magnified 16 diameters.
Fig. 54. — Camera drawing, showing
the successive positions assumed
by an amoeba retreating from the
light. The position of the infalling
ray was successively changed from
^3.oe}!) (1) to (2), (3), and (4). The arrow

labelled " First direction of migra-
tion " shows the direction of loco-
motion of the amoeba before the
light fell upon it at the beginning of
First direction the experiment. The numbers indi-

of migration cate hoursandmiuutes. Duringthe

^ interval from 13:06 ( = 1:06) p.m. to

12:48 to i4:oo 13:57, the amoeba was not under di-

rect observation, since I was called
53 54 away. Magnified 16 diameters.

Cases that can be explained only on the ground of the nume-
diate effect of light upon the direction of movement are cer-
tainly rare. Entz ('88), indeed, has intimated that Opalina
flees from light, but Verworn ('89, pp. 53-57) was not able
to confirm hiin in this point. Verwoen's method was here,
as in the case of Amoeba, not satisfactory. Instead of having
the light fall from one side only upon the drop containing the
Opalinas, he let the light pass vertically from below through a
small hole, and could observe no tendency to avoid the illu-

L-^'

§4] PHOTOTAXIS AND PHOTOPATHY • 189

minated spot. The light in this case clearly did not act from
one side, and the test of phototaxis can therefore hardly be said
to have been critically made. Likewise, even with unilateral
illumination, Verworn was unable to gain a phototactic re-
sponse with Stentor roeselii, St. cceruleus, Carchesium polypi-
num', and Urolej)tus musculus. On the other hand, we have
often noticed here in Cambridge that our Stentor cceruleus is
(rather indefinite!}^) negatively p)hototactic to diffuse daylight.
Thus, an individual swimming free in a bit of glass tubing
pointing horizontally towards the window only very slowly
wanders away from the light. In conclusion, then, we must
admit that Ciliata are not markedly phototactic, but more
refined methods must be used before we can say of any of
them that they exhibit no trace of this response.

Let us summarize briefly the results obtained from Protista.
Phototaxis is most marked among actively motile, chlorophyl-
laceous forms. Many colorless forms are, however, also photo-
tactic — Beggiatoa, Amcsba, plasmodia of Myxomycetes, and
swarm-spores of Chytridium. The phenomenon is thus wide-
s|)read, if it is not universal.

h. Cells and Cell-organs. — Under this head will be consid-
ered, (a) the rearrangement of chlorophyll corpuscles, (^8)
the rearrangement of pigment in animal cells, and (7) the
migration of pigment cells in the metazoan body.

a. That the chlorophyll bodies of the higher plants change
their position in the cell according to the intensit}' of the light
to which they are subjected has been made known chiefly
through the labors of Famintzin ('67), Borodin ('69),
Frank ('72), Stahl ("80), and Moore ('87). If one fastens
a strip of black paper upon a leaf on which the sun's rays are
falling, one will find, upon removing the paper after a time,
that the darkened part is dark green whilst the brightly illu-
minated part is considerably lighter, so that an image of the
form of the dark paper is produced upon the leaf. This image
is, however, only temporary, A few hours after the removal
of the paper the leaf is of a uniform green again. Sections
through a leaf thus affected show that in the dark green
(shaded) part of the leaf the chlorophyll lies on those walls
of the cells which are perpendicular to the incoming rays.

190

LIGHT AND PROTOPLASM

[Ch. VII

whilst in the light green (illuminated) part of the leaf the
chlorophyll lies upon the walls parallel to the rays. When

the grains are upon the
superficial face of the
cells they are said to be
in epistropJie; when they
have turned away from
this face they are in apos-
trophe. This apostrophic
position is found under
two opposite conditions
of illumination : under
intense light, as we have
just seen (positive apos-
trophe, Mooeb), and upon
prolonged standing in the
dark (negative apostro-
phe). (Fig. bS.^

It appears, then, that
epistrophe occurs only
within certain limits of
light intensity. The in-
tensities included between
these limits constitute
what Moore calls the
epistrophic interval. The
epistrophic interval varies
in position and in extent
in different species.* It has been found that in the case of
plants which normally live in the bright sun the epistrophic

Fig. 55. — Cross-section through the leaf of
Lemna trisulca. A. Position of the chlo-
rophyll grains in diffuse daylight — epis-
trophe. B. Position of the chlorophyll
grains in intense light — positive apos-
trophe. C. Position of the chlorophyll
grains in darkness — negative apostrophe.
(After Stahl.)

* The limits were determined by Moore, in a roughly quantitative way, by
means of his pliotrum^ constructed as follows. A room with a single window
illuminated by the sun was chosen and 12 feet spaced off from the window back
into the darkness. The intensity of the light diminished of course as one re-
treated from the window. Plants of various species were allowed to stand,
simultaneously, at varying distances from the window, and the distance back at
which epistrophe began to appear, and, finally, at which negative apostrophe
came in, were noted. Then a diagram Jg the actual scale was made (Fig. 56),
showing the position of the points of beginning and ending of epistrophe (so-
called positive and negative critical points).

§1]

PHOTOTAXIS A]S"D PHOTOPATHY

191

interval is a region of relatively high intensity (Fig. 56, 6) ;
in aquatic plants the epistrophic interval occurs in a region
of low intensity (Fig. 56, 1 and 2) ; and in shade-loving
aerophytes in an intermediate position (Fig. 5Q, 4 and 5).
One may say that every species is attuned to a certain intensity
and range of light, in which epistrophe occurs, just as in
swarm-spores there is a certain intensity and range of light in
which positive phototaxis occurs, and that attunement depends
upon the conditions to which the organism has adjusted itself
through living in them.

— +

Fig. 56. — A diagram of Moore's photrum, showing for six sjiaces the epistrophic
interval (shaded region). 1. Anacharis (Elodea) canadensis, '"water-weed."
2. Lemna trisulca. 3. Saxifraga granulata (position of positive critical point).

4. Oxalis acetosella (position of negative critical point only approximate).

5. Pteris critiea (positive critical point). 6. Pyrethrnm sinense (garden Chi-y-
santheraum). -|- indicates the hrighter end of the photrum.

Concerning the question of the mechanism of the movement
of the chlorophyll grains, there is much difference of opinion.
It is urged on the one hand that the chlorophyll grains move
actively to attain their new positions, and, on the other, that
they are passively carried by the cell currents. Of these two
views analogical reasons are perhaps the strongest for preferring
the second.

As to the question in how far these movements can ho
regarded as adaptive, we may say that Stahl believed that
they regulate the relation between intensity of sunlight and
assimilating area, so that the quantity of assimilation shall not
become too great. Hieronymus ('92, p. 466) considers them to
be for the purpose of screening the nucleus. IMooke (p. 222),

192

LIGHT AND PROTOPLASM

[Ch. VII

however, cliiefly from a consideration of vegetative apostro-
phe, has been led to the conclusion "that the movements of
chlorophyll have no relation whatever to benefit or injury
experienced by the grains, nor necessarily to the well-being of
the protoplasm."

/8. The Rearrangement of Pigment in Animal Cells in Response
to Light. — One of the striking cases of this effect of light is
seen in the pigment cells of the skin of the chameleon, as
described by Keller ('95, pp. 144, 162). He has found that
the dark color of the (illuminated) skin is due to the rich

Fig. 57. — Vertical section through a black dermal papilla of Chamseleo vulgaris.
ej3, epidermis; cu, cutis; p, black pigment cells; j}', processes of the cells con-
taining pigment ; y', yellow pigment cells. (After Keller, '95.)

branching at the base of the epidermis of black pigment cells
lying deep in the cutis (Fig. 57). In the dark, the pigment
granules stream out of the branches into the cell body, but the
branches themselves are undisturbed (Fig. 58). So long as
the black pigment has this central position, the skin appears
whitish. The light, on the contrary, causes the pigment, which
is probably carried passively in the plasma, to move centrifu-
gally. Whether the direct response to light of the pigment
cells of the frog, as described by Stehstach ('91), is of the
same nature, or due to contractions of the pigment cells, re-
mains to be determined.

Again, in the retina of the compound eyes of Arthropoda,

§4]

PHOTOTAXIS AND PHOTOPATHY

19^

we find this capacity for rearrangement of pigment granules,
as ExNER ('89 and '91, p. 104), Stefanowska ('90), Szcza-
wiNSKA ('91), Parker ('95), and others have shown. In the
higher Crustacea, for example, the pigment granules of the
pigment cells surrounding the rhabdome (or " spindle ") are, in
the dark, below the leyel of the spindle. Upon illumination,
however, these granules migrate (or are carried) upwards, and
partly envelop the rhabdomes. I believe it has not been deter-
mined what rays are involved in producing this result. This
response to light is considered to be an advantageous one, since

IP

' '^ cu. ep.

Fig. 58. — Vertical section of a whitish-yellow dermal papilla ; lettering as in Fig. 57.
pf, processes of black pigment cells containing no pigment. (After Keller, '95.)

the pigment thus cuts off side rays from the perceptive organ
— the rhabdome.

It is interesting that we should find cells containing two so
diverse kinds of pigment as chlorophyll and the retinal pig-
ment responding to light in so similar a fashion. In most of
the cases, if not all, this response is an adaptive one.

7. The Migratio7i of Pigment Cells in the 3Ietazoan Body. —
It has been shown, apparently first by Engelmann ('85), that
the pigment cells of the retina vary their movements with the
light. Thus, when a strong light is thrown upon the retina
of the frog, the pigment cells send out pseudopodium-like
processes between the rods and cones, whereas in the dark the

194 LIGHT AND PROTOPLASM [Ch. VH

pigment lies behind all these elements. Also, among the Crus-
tacea, the protoplasm of the outer pigment cells, surrounding
the cones of the compound eye, migrates centripetallj in a strong
light, to return again to its peripheral position in darkness.
These movements may also be considered adaptive. They are,
in addition, movements which are discharged only by light.

c. Metazoa. — We may treat of the control by light of the
movements of the higher animals somewhat more summarily
than we have the preceding classes. The facts will be arranged
by groups in systematic order.

Among radial animals, Hydra has perhaps been for the
longest time an object for photopathic study. Trembley
(1744, p. QQ^ had noticed that Hydra viridis, and even muti-
lated pieces of it, came to the light side of the vessel. When
the light was admitted only through a chevron-shaped slit, the
Hydras were later found aggregated opposite the slit in the
form of a chevron. That it was not the warmth of the sunlight
that attracted was shown by turning the slit towards the cooler
air, whereupon the same response occurred. The observations
of Teembley showed that the Hydras did not move in as straight
a line as possible towards the light (they must, of course, follow
a firm substratum), but gradually wandered towards it. The
response of Hydra must therefore be considered as photopathy.
More extensive studies were made upon Hydra by Wilson ('91),
who found that Hydra fusca is likewise responsive to light, and,
indeed, photophil with reference to diffuse daylight, and photo-
phob to direct sunlight. And it can be shown that it is an
advantage to Hydra to be photophil, since many of the Ento-
mostraca upon which it feeds are phototactic.

Besides Hydra, I know of only one case of response by Coe-
lenterata to light. The larvse of the sponge Reniera are said
(Marshall, '82, p. 225) to flee from the light, — probably
negative phototaxis.

Among Echinodermata^ Asteracanthion rubens (Graber, '85,
p. 155) appears to be photophil, and Asterina gibbosa (Dribsch,
'90, p. 155) to be photophob.

Although, as we have seen, some radial animals may respond
to light, the phenomenon is more wide-spread in the bilateral
groups, — flatworms, annelids, crustaceans, insects, molluscs,

§4]

PHOTOTAXIS AND PHOTOPATHY

195

and Vertebrates. The results of experiments may here be
given in tabular form. Unless otherwise stated, the light is sup-
posed to be diffuse daylight, and the response to be phototactic.

TABLE XVIII

Organism.

Sense op
Response.

AUTHOEITY

Remarks.

Fresh-water planaria ....

_

LoEB, '90, p. 95

Polynoe sp

—

Driesch, '90, p. 155

Polygordius, larva

—

LoEB, '93, p. 90
/ Darwin, '81, p. 21
1 Graber, '83, p. 210

see p. 200
1

Earthworm

-

> photophob

' Hesse, '96

)

Leech

r

—

LoEB, '90, p. 96
/ Trembley, 1744, p. 96

)

Daphnia •

+

} Bert, '78, p. 989
( Lubbock, '82, '83

V photophil ( ?)

)

+

Davenport and Gannon

phototactic

Many marine copepoda . .

-(or+)

LoEB, '93, p. 96

see p. 200

Balanus, larva

-(or +)

Groom and Loeb, '90, p.
KiO

see p. 200

Limulus, larva

—

Loeb, '93, p. 83

Idotea tricuspidata

+

Graber, '85, p. 141

photophil

Diastylis (Ciima) rathkii .

+

Loeb, '90, p. 91

mud-inhabiting

Carciuus majnas

—

Driesch, '90, p. 156

photophob

Homarus americanus, larva

+

Herrick, '96, p. 189

Plant lice

+

Loeb, '90, p. 55
Graber, '83, p. 235

Blatta germanica (blinded)

photophob

Musca dom. (?), larva . . .

—

Loeb, '90, p. 69

Musca, adult

+

Loeb, '90, p. 81

Musca vomitoria, larva . .

—

Davidson, '85, p. 160

Musca cfEsar, larva

—

Pouchet, '72, p. 113

Eristalis tenax, larva . . .

—

Pouchet, '72, p. 129

Lepidoptera, adult

+

( Seitz, '90, p. 337
1 Loeb, '90, p. 46

see p. 197

Lepidoptera, larva

+

J Loeb, '90, p. 51

1 PouLTON, '87, p. 315

Ants, after gaining wings .

+

Loeb, '90, p. 63

beetle)

—

Loeb, '90, p. 86

Tenebrio molitor, larva . .

—

Loeb, '90, p. 84

Dentalium

—

Lacaze-Duthiers, '57,
p. 25

photophob

Rissoa octona

+

Gkabeb, '85, p. 144

photophil

Littorina rudis

—

Driesch, '90, p. 155

photophob

Gasterosteus spinachia. . .

™

Graber, '85, p. 148

Triton

—

Graber, '83, p. 221

photophob

Prog

—

Loeb. '90, p. 90

196 LIGHT AND PROTOPLASM [Ch. VII

A study of this table reveals the fact that, in general, organ-
isms which live in shady places or in the dark are negatively
pliototactic or photopathic, while those living in the light are
positively pliototactic or photopathic. Thus most fresh-water
planarians and leeches are inhabitants of shady pools. Polynoe
is generally found in dark retreats, the earthworm and fly
larvse are lovers of the dark, and shell-molluscs are for the
most part enclosed in cases impervious to light. On the other
hand, Daphnia is found largely in open pools, larvce of Lepi-
doptera and many adult insects live in the sun. Into this
general rule there are some cases which do not so obviously fall.
But we have little data concerning the habits of the races em-
ployed and the absolute intensity of light used, so that these
cases may perhaps be only apparent exceptions. One clear
exception is that of the mud-inhabiting Diastylus, which is 4-
phototactic.

3. The General Laws of Phototaxis and Photopathy. — Under
this head we shall consider : (a) the sense of the response ;
(5) the effective rays ; (c) prototaxis vs. photopathy ; (c?) the
mechanics of response to light.

a. The Sense of the Response. — In considering, now, more
generally, the effect of daylight upon the direction of loco-
motion of organisms, we must recognize that the sense of
response (whether + or — ) depends upon internal conditions
and external conditions — upon the quality of the protoplasm
and the nature of the environment. Let us consider, first, the
dependence upon interyial conditions.

We find that, under similar external conditions, different
organisms respond differently. For example, many Oscillarise
(p. 18i) are positively pliototactic even in direct sunlight ;
whilst even moderately strong light will repel many diatoms.
In fact, we find that a positively pliototactic or photopathic
organism is such only in the presence of a certain intensity of
light. When the intensity is diminished below a certain point,
no response will occur. When, on the other hand, the intensity
is increased above a certain point, the organism moves away
from the source of light. There is a certain range of intensity
in which alone the positive responses occur. The position and
the extent of this positively pliototactic range vary for the

§4] PHOTOTAXIS AND PHOTOPATHY 197

different species, — they are closely correlated with the condi-
tions of light in which the organism has been reared. As a
result of these conditions, we may say that each organism is
attuned to its peculiar range and intensity of light.

Upon the ground of this difference in attunement may be
explained the remarkable difference in behavior of butterflies
and moths to light. It is well known that butterflies fly
towards even the strongest sunlight, whilst moths are secluded
during the daytime, but at night fly towards the candle-light.
LoEB ('90, p. 46) has performed some experiments with these
insects, which I will cite in detail.

Experiment 1. — («) Sphinx, Bombyx, and other moths were kept in a
large glass cage in a room illuminated only by daylight. As darkness came
01:1, the moths began to fly towai'ds that side of the cage which was next the
window. Again (&), pupse of nocturnal moths, left in a room, emerged during
the night, and were always found in the morning at the closed window of
the room. Finally (c), a nocturnal moth, made to fly in the daytime, directed
its way to the window. Thus, nocturnal moths are positively phototactic
to diffuse daylight as well as candle-light.

Experiment 2. — Hawk-moths were brought into a room with the single
window at one end, and a petroleum lamp at the opposite end. It was
found that, as twilight came on, the moth flew to the window, or to the light,
according to the relative intensity of the one or the other at tlie point where
the moth was liberated. Thus, there is no preference for artilicial light.

The conclusion at which Loeb arrived was that tliese moths
undergo a diurnal variation in responsiveness to light, which
corres^ionds to the change from day to night. But the fact
that, in experiment 1 <?, nocturnal moths flew, in the daytime,
towards the diffusely lighted window, throws a doubt upon this
interpretation. All the facts are equally well explained upon
the following ground: Butterflies are attuned to a higli intensity
of light, moths to a low intensity ; so that bright sunlight,
which calls forth the one, causes the other to retreat. On the
other hand, a light like that of a candle, so weak as not to
stimulate a butterfly, produces a marked response in the moth.
We shall consider, in a moment, the cause of these differences
in light attunement.

We have seen that one internal condition modifying response
is the racial quality of attunement. A second is that of period
of life. Thus, Lokp. ("90, p. 56) has found that, at the intensities

198 LIGHT AND PROTOPLASM [Ch. VII

employed, the wingless plant lice were hardly responsive to
light. The winged form was markedly positively phototactic.
So, likewise, in the case of ants (Loeb, '90, p. 63), during the
period of the marriage flight the males and females (but not
the workers) are strongly positively phototactic, but after that
period they show themselves neutral. The case of the house-
fly, Musca, is interesting, since the larva and adult are photo-
tactic in opposite senses (see table). In most of these cases,
the difference in responsiveness is associated with a difference
in habit.

The sense of response depends, also, as we have seen, upon
external conditions. In this regard, the immediately preceding
conditions of light, the temperature, the concentration, and the
supply of oxygen have important effects. We shall consider,
in order, the action of these conditions.

Light can modify the response to light ; thus, Groom and
Loeb ('90) have shown that the nauplii of Balanus, as well as
other pelagic animals, come to the surface of the sea during
the night, but descend before the strong sunlight. This does
not indicate merely a low light-attunement of the race ; for
nauplii exposed to sunlight in the early afternoon are all posi-
tively phototactic, and only gradually, as the day progresses,
move from the sunny window, until, finally, even as dusk
approaches, all are found on the side away from the window.
Nor have we here to do with a diurnal change in the sense of
the response. For if a culture is kept in the dark, it is found
to be at first positively phototactic at whatever time of day it
is exposed ; only later acquiring the negative phototaxis. In
the same way, when the young Balanus larvse leave the interior
of the shell of the parent, they are at first positively phototactic ,•
but after being in the light for from | to 2 hours, they become
negatively phototactic. The more intense the light, the quicker
its effect.

Another observation upon the nauplii is representative of a
new class of light effects. When nauplii which have become
negatively phototactic through exposure are covered for a few
minutes, and then suddenly again exposed to light, they move
momentarily towards the light, and then begin their negative
movement again. Somewhat similar are the results obtained

§4] PHOTOTAXIS AND PHOTOPATHY 199

by Strasburger ('78, p. 574) on Ulotlirix spores, which are
positively pliototactic in a weak light. While responding to
such a light, they do not, however, turn at once when a light
of repelling intensity is thrown upon them. So, also (p. 600),
when Hseraatococcus is responding to indigo light, the inter-
position of red glass does not at once cause it to turn from its
path. In all these cases, the immediately preceding condition
of light continues to exert an action which modifies the response.

Closely allied are the results obtained by Verworn ('89,
p. 50) upon the diatom, Navicula brevis, which is attuned to
only the faintest light. When, however, a culture had been
reared by a window for two weeks, the attunement to light
had been so raised that now a slight degree of positive photo-
taxis took place in diffuse light. We have in these facts
examples of a phenomenon which we have observed in the
action of other agents. It is one expression of the acclimatiza-
tion of organisms to the peculiar conditions of their environ-
ment. We have just seen that every organism has its optimum
intensity of light for metabolism and response, and that this
optimum is very varied ; but, throughout, one law holds.
Organisms which are accustomed to live in strong light have
a high optimum intensity; and those accustomed to live in
a weak light have a low optimum intensit}^ This relation
is, indeed, so close as to raise the suspicion that the normal
intensity of the light has determined the optimum. And this
suspicion is confirmed bj^ the experimental evidence just cited.
Now, since the position of the optimum is usually advantageous,
we may conclude that light can so modify protoplasm as to
adapt it for the conditions in which it is living.

We now pass to the consideration of the effect of tempera-
ture upon response. This effect was noticed by Strasbctrgek
('78, p. 605) in tlie swarm-spores of Hiiematococcus, Ulothrix,
etc., which, at a temperature of 16° C. to 18° C, gather at the
side of the drop next to the window. If, now, they are sub-
jected to a temperature of 40° C, the intensity of the light
being constant, they migrate to the opi:)osite side. On the
other hand, at a temperature of 35°, the -|- aggregation is more
complete than at 16° to 18°. Control experiments with emul-
sions satisfied Strasburger that this chancre is not due to

200 LIGHT AND PROTOPLASM [Ch. Vll

currents in the water, but is a truly vital phenomenon. That
it is such is indicated also by the following curious behavior.
If swarm- spores which normally aggregate at 18° towards the
positive side of the drop, are suddenly brought to 18° from 30°,
they appear, for a moment, negative. Conversely, if swarm-
spores which normally aggregate at 30° towards the negative
side of the drop are suddenly brought from 8° to 30°, they ap-
pear, for a moment, positive. Thus, the immediately preceding
culture-temperature affects the sense of the response.

The results obtained by Stkasburgee, have been in part
confirmed by other authors in other species.

Groom and Loeb ('90, pp. 166, 172) state that in the case of the nauplii
of Balanus — "at a higher temperature, for instance 25° C, the phenomena
[of phototaxisj are run through more sharply and quickly than at a tempera-
ture of about 15°"; and again, "we often succeeded in suddenly changing
the sense of the heliotropism of the larva by a sudden change, of only a few
degrees, in the temperature of the water." This statement is unfortunately
so vague as to say little more than this, that temperature influences the
response. Massaut ('91, p. 164) remarks, incidentally, that the flagellate
Chromulina is + phototactic at 20° C, but — phototactic at 5°C. Loeb
('93, pp. 90, 96) obtained a result with Polygordius larvae and Copepoda
which seems, at first sight, the opposite of Strasburger's. Polygordius
larvse, negatively phototactic at 16°, wei'e gradually cooled to 6°, at which
temperature they began to move rapidly towards the + side of the vessel.
As the ten)perature gradually rose they became — phototactic again. Indi-
viduals which were (abnormally) + phototactic at 17° to 24°, when raised
gradually to 29° became — phototactic. Sudden diminution of temperature
within the limits at which response occurs did not change the sense of their
response. Thus, negative individuals brought suddenly from 23° to 13°
remained negative. Exactly parallel results concerning the relation of
temperature and response were obtained by Loeb from Copepoda.

All results may be harmonized in the expression : Diminu-
tion of temperature below the normal causes reversal of the
normal response ; elevation of the temperature to near the
maximum accelerates the normal response. The point of
light attunement varies with the temperature.*

Not only light and heat, but also the concentration of the
medium affects light attunement. We are indebted to Loeb

* It follows from these experiments that it is necessary in any phototac-
tic investigation to regard not only the intensity of the light, but also the
temperature.

§4] PHOTOTAXTS AND PHOTOPATHY 201

('93, pp. 94, 96) for information on this subject. Negatively
phototactic Polygordius larvae were placed in sea water to
which \ojo to 1.3% NaCl had been added. They now appeared
positively phototactic. Positively phototactic individuals, on
the other hand, placed in sea water diluted witli 40% to 60%
fresh Avater became negatively phototactic. Similar results
were obtained with Copepoda. Thus increased concentration
rendered + phototactic (raised light attunement), while dimin-
ished concentration rendered — phototactic (lowered light at-
tunement). Increased concentration works, therefore, upon
Polygdrdius and Copepoda, according to Loeb, like diminished
temperature.

Finally, the chemical condition of the medium has an impor-
tant effect on photopathy, as can be judged from certain
observations of Engelmann ('82% p. 391). Various chloro-
phyllaceous Ciliata, e.g. Stentor viridis and Paramecium bur-
saria, are photopathic only when the oxygen supply in the
medium is below the normal. In such media they are strongly
photophil. This case is clearly not a case of phototaxis, as we
have just seen (p. 187). The response is advantageous since it
brings these organisms into the sunlight, where chlorophyll can
produce oxygen.

To recapitulate : the sense of response in phatotaxis is modi-
fied by previous subjection to light, by temperature, and by
concentration. These agents modify the attunement of the
organism. Any quantitative experiments upon phototaxis
must therefore take all of them into account. Certain chloro-
phyllaceous organisms exhibit + photopathy, but only in an
insufficiently oxygenated medium.

From the foregoing considerations we conclude that for
every phototactic organism there are three ranges of intensity
to be distinguished : the positively phototactic I'ange in which
the organism moves towards the light ; below this, the indiffer-
ent range extending to darkness ; above it, the negatively
phototactic range extending up nearly or quite to the point of
light-rigor. The limits of these ranges vary with both external
and internal conditions.

h. The Effective- Rays. — We have hitherto considered chiefly
the action of white light, merely referring casually to the

202 LIGHT AND PROTOPLASM [Ch. Vll

action of the different rays of which it is composed. We
must now answer the question : What different effects do the
different rays have ?

The effect of the different rays in phototaxis is very clearly
seen in the various groups of Protista and among the Fla-
gellata and the swarm-spores, there is entire uniformity of
response according to the testimony of CoHN ('65, p. 36),
Strasburger ('78, pp. 593-599), Engelmann ('82% p. 398, in
Euglena), and Verworn ('89% p. 49, in Navicula). Here the
more actinic rays with shorter and more rapidly vibrating wave,
act exactly like white light, whilst the rays from the opposite
end of the spectrum have no more effect than darkness. More
precise determinations were made by Strasburger ('78, p.
597), who found that the swarm-spores of the alga Botridium
responded to the blue and violet, but especially to the indigo,
whilst the green and ultra-violet were alike without effect.
And Engelmann, by means of his microspectral apparatus,
was able to determine that Euglena responded chiefly to the
rays X = 0.47/a to A, =0.49 /a ; that is, rays very near Frauen-
hofer's line F. The colorless Myxomycetes agree with the
chlorophyllaceous forms, according to Baranetzki ('76, p.
332), in responding to blue rays only.

Among the higher organisms, Hydra, according to Wilson,
accumulates especially behind blue glass, to a small extent
behind green glass, and is entirely indifferent both to the upper
violet rays and those below the green. The photophil starfish
Astracanthion rubens, even when deprived of its eyes, was
found by Graber to be "cyanophil"; even, though in slight
degree, to a low intensity of light. Among Mollusca, Graber
found that the photophil Rissoa moved towards the blue even
when the intensity of the blue light was less than that of the red,
and Driesch asserts that the photophob Littorina rudis shuns
only blue rays. Thus, without multiplying cases, the results
of experiments may be summed up as follows : positively pho-
totactic or positively photopathic organisms are such only in
the presence of the blue rays.

There are some few observations which are in apparent dis-
cord with this conclusion. Whether the ultra-violet rays are
ever active is a fairly debatable question. Lubbock ('82,

§4] PHOTOTAXIS AND PHOTOPATHY 203

p. 127 ; '84, p. 137) showed that Daphnia and some ants are
very sensitive to the violet rays, and Graber ('83, p, 214)
found that the photophob earthworm withdraws from ultra-
violet rays. This result is unusual, however, for most experi-
menters have agreed with this much of Bert's ('78, p. 989)
conclusions, that " the animals see . . . only those rays which
we oui'selves see," or, better, that the range of irritability of
the protoplasm of our retina is as great as that of any other
protoplasm.

Below the blue, some authors have believed the yellow rays,
the brightest of the spectrum, to be prevailingl}^ photopathic.
Thus both Bert ('68, p. 381) and Lubbock ('83, p. 214) find
that Daphnia accumulates especially in the yellow and green
parts of the spectrum. Regarding these results I have only
the comment that they need further confirmation.

c. Phototaxis vs. PJiotopathy. — We have hitherto assumed
the existence of two dissimilar sorts of locomotor response to
light — -phototaxis and photopathy. Phototaxis we defined as
migration ih the direction of the light rays, and photopathy as
migration towards a region of greater or less intensity of light.
Are we justified in making this distinction ?

The chief ground for this distinction is the existence of two
sorts of phenomena which, not having been generally recog-
nized as different, have led to extensive discussion. The best-
established of these phenomena is phototaxis, which was proved
to exist by certain crucial experiments of Strasburger on
Protista, and of Loeb on Metazoa. Mr. W. B. Cannon and
I have used Strasburger's methods on Daphnia, and con-
firmed his results. Figure 59 gives a view of our apparatus,
which was essentially tlie same as Strasburger's. It con-
sisted of a hollow prism P, containing a dark solution and
placed over the trough T^ with its organisms. Strasburger
('78, p. 585) put swarm-spores of Botrydium and Br3-opsis into
the trough, and reflected the light perpendicularly througli the
prism upon the trough. There was now a perfect gradation in
intensity from the thick end to the thin edge of the prism.
Yet the organisms showed no tendency to aggregate at the
clearer end. The light was now permitted to enter the trough
obliquely, the thicker end of the prism being next the source

204

LIGHT AND PROTOPLASM

[Ch. VII

of light, as in the figure. The spores now moved towards
.the source of liglit, i.e. in the direction of the inf ailing rays
but constantly into a region of less intensity of light.

o<^>-'

^^e^

Fig. 59. — Diagram showing the position of apparatus and the direction of the rays
in an experiment in phototaxis. T, trough of water containing organisms, A and
B its two ends, M its middle. P, a prismatic box containing a solution of India
ink. S, screen to cut off extraneous light. L, gas-lamp having a Welsbach
burner. Drawn to scale.

Loeb's ('90, p. 32) results were obtained by the use of quite
different methods. In one case he employed a chamber made
of two test tubes placed with their mouths together. One of
the tubes was darkened except for a clear streak at one end, c ;
and this darkened tube was pointed towards the light, so that
the rays fell through its axis. Although the clear chamber
was evidently the brighter, the Porthesia larvae Avith which
he experimented moved into the darkened chamber and thus
towards the source of light (Fig. 60). Again, a clear test tube
containing larvce (Fig. 61) was placed so that its closed end
b was directed towards the window FF. A bundle of sun's
rays SS struck nearly perpendicularly the mouth of the tube a,
when the larvae were aggregated at the beginning. Neverthe-
less the larvse, since their progress in the direction of the per-
pendicular rays was soon interrupted by the walls of the tube,
moved towards the window, from the region of greater intensity
of light in the direction of rays which passed more nearly in
the axis of the tube. That this is not negative photopathy to
strong light is indicated by the fact that the Porthesia larva is
attuned to a high intensity of light. The evidence would thus
seem satisfactory that the direction of migration of certain

§4]

PHOTOTAXIS AND PHOTOPATHY

205

organisms is determined by the direction of the light rays.
There is, then, such a thing as pliototaxis.

But is the direction of locomotion ever determined by a dif-
ference of intensity of light in adjacent regions, without refer-
ence to the direction of the light rays ? Whole series of obser-
vations make this probable ; for a migration to a definite part
of the trough has folloAved unequal illumination by rays
perpendicular to the trough. Thus Lubbock found that

p

Fig. go. — Two tost tubes a and h, containing Porthesia larvai c, which move towards

the window FF, although in doing so they pass from a brighter to a da river region.

(LOEB, '<)0.)
Fig. (il. — Diagram to sliow liow Porthesia larva? move in the test tube ah towards

the window FF, although in doing so they leave the part of the tube more brightly

illumined by the sun's rays SS. (Loeb, '90.)

Daphnias, placed in a trough nearly perpendicular to the rays
dispersed b}^ a prism, moved towards the brighter part of the
spectrum. Guaber employed screens of diverse traiislueenc}^
and color, which were placed adjacent to one another, and
found that the organisms tended to aggregate opposite the
one or the other. Oltmanns ('92, p. 195) has offered certain
new experiments pointing in the same direction. These experi-
ments were made upon Volvox minor and Volvox globator,
which were placed in a trough between which and the source

206 LIGHT AND PROTOPLASM [Ch. VII

of light a vertical screen was interposed. This screen formed
one side of a wooden box and consisted of two glass plates
making an angle of 2° with each other, the interspace being
filled with a solution of India ink in gelatine. When the sun-
light was let through this screen, the individuals in the trough
behind it sorted themselves into two groups ; the partheno-
genetic individuals, which collected opposite the clearer part
of the screen, and the female individuals, with fertilized eggs,
which collected behind the darker part of the screen, each suit-
ing itself to the intensity of light to which it was attuned.
When the intensity of the light was changed, the organisms
also changed their positions. Finally, Loeb ('93, pp. 100-103)

has found that fresh-Avater plana-
^^ " ' rians (Planaria torva) gradually

accumulate in the darker parts of
the vessel, since the light con-
stantly stimulates them to move-
ment, and in their wanderings
they gain the dark places by
accident and there are at rest.
„ CO T^- u ■ ■*• So it comes about that when

Fig. 62. — Diagram showing position

taken by Planaria torva in a shai- these Planaria are in a shallow
low cylindrical glass vessel a, b, cylindrical vcsscl (Fig. 62, a, 6,

c, d, placed opposite a window -in • <• p • i t r^

AB. (Loeb, '93.) ^' ^) ^^^ front of a wmdow AB,

they accumulate neither at the
side towards the window nor that away from it, but at c and
d, where the side walls of the vessel cut off much of the light.
All these cases, then, lead to one conclusion, that organisms
may move with reference to more or less intense light — that
there is such a thing as photopathy.

Indeed, a phototactic and a photopathic response may be
exhibited by the same organism. Thus in Cannoist's and my
experiments Daphnia was found to be phototactic, although
other observers have clearly shown it to be photopathic, a
result which we have not been able to disprove. We con-
clude, then, that some organisms have this double response
to light that they may move in the direction of its rays, and
that they may keep in a certain intensity of light to which
they are attuned.

§ 4] PHOTOTAXIS AND PHOTOPATHY 207

d. The Mechanics of Response to Light. — -Under this head
I shall speak of the part of the protoplasmic body most sensitive
to light, of the immediate effect of the light, and of the cause
of this immediate effect.

There can be no question that radiant energy with rapidly
vibrating waves produces upon all protoplasm a profound effect.
The question arises, however, to what extent in organisms a
special kind of protoplasm is differentiated for the reception of
rays which result in a discharge of the locomotor response.
Certainly such a differentiated protoplasm can hardly be con-
sidered necessary to the discharge of such a response, since
there is no morphological evidence of its existence in the
responsive amoeba. However, even in the swarm-spores and
Flagellata such a specialized protoplasm is clearly indicated.
Thus Engelmann ('82^, p. 396) found that when a dark band
fell across the body of a swimming Euglena, no reaction occurred
so long as the hinder chlorophyllaceous part alone was shaded.
When, however, the clear area at the base of the fiagellum was
shaded, a marked reaction occurred. Here, near the pigment
spot, if not at it, is the specialized light-perceiving protoplasm.

Similarly specialized protoplasm occurs extensively in the
higher groups in the form of retinas ; but there is much evi-
dence that in many eyeless Metazoa the whole surface contains
such light-perceiving substances. This is well known to be the
case in the earthworm (cf. Hesse, '96). According to Dubois,
('89, p. 283), the siphon of the boring mussel Pholas dactylus
contracts at the least variation of light intensity upon the skin.
Similarly, other Lamellibranchia (Ostea, Unio, Venus) close
their valves (Nag el, '96, p. 58). Blinded Helix are said by
WiLLEM ('91, p. 248) and Nagel ("96, p. 19) to be similarly
sensitive. The lamellibranch Psammobia, the blind Proteus
anguinus, and the blinded Triton cristatus are irritated by rays
of light, especially the blue rays, falling upon the ski]i (Nagel,
'96, p. 22 ; Graber, '83, p. 233 ; Dubois, *90, p. 358). Thus,
in many Metazoa, protoplasm sensitive to light is of widespread
occurrence, outside of the retina.*

The immediate visible effect of light upon the organism differs

* For an extended list of cases of such denuatoptic reaction, see Nagel, '96.

208 LIGHT AND PROTOPLASM [Cii. VII

according to the form of the organism. In elongate, antero-
posteriorly differentiated animals the first visible phototactic
response is the orientation of the organism's axis in the direc-
tion of the impinging ray, and with the head end directed
towards the source of light, or from that source, according as
the organism is positively or negatively phototactic. The
orientation is the more precise and the retention of the position
the more sure the nearer the light approaches the optimum
(attractive) or maximum (repellent) intensity, as the case may
be. If two rays of different intensities making an angle with
each other fall upon the organism, it apparently moves in the
direction of the intenser ray, if free to do so.*

In Amoeba, without differentiated axes, the effect of the ray
of light is to determine the position of the centrifugal stream-
ing by which a pseudopod is thrown out away from the light ;
and the streaming continues in this single direction so long as
conditions do not change. Thus the locomotion is in a straight
line, lying in the ray of light.

Light not merely determines the direction of the axis but
the position of the head end. As we have seen (p. 196) this
determination of the position of the head depends upon the
attunement of the organism, a quality which in turn varies
with certain internal and external conditions. Acting upon a
" higlily attuned " protoplasmic mass, light will cause orienta-
tion in one sense ; upon " lowly-attuned " protoplasm, an orien-
tation in the opposite sense.

Whether light has any other effect than that of orientation of
the body is a mooted question. Strasburger ('78, p. 577) and
LoEB ('90, p. 109) recognize that migration from one point to
another is more rapid in strong light than in weak, but believe
this difference in rate of migration is wholly explicable upon
the ground that the orientation is more precise in the stronger
light, that there is less wandering from side to side. Some ex-
periments made by Mr. CannojST and me upon Daphnia seem to
confirm this view and at the same time afford quantitative data
upon the degree of hastening. Thus in 18 trials Daphnia

* This statement is provisional only. It seems to follow from the experiments
of LoEB made upon moths and described on page 197. The point is worthy of
detailed comparative study.

§4] PHOTOTAXIS AND PHOTOPATHY 209

required, to travel 18 cm. in full light, 15% longer time than
the same individual required in light -^ as strong. Since the
increased time was only 15% instead of 300%, as it should be
were rate proportional to intensity, it seems probable — a con-
clusion confirmed by the direct observation of the organisms in
the trough — that the slower rate in the weaker light is due to
less precise orientation. How would the rate be influenced by
two lights of different intensities acting from opposite direc-
tions ? Upon this matter we have no experimental data.

Light, then, serves to orient the organism ; but how ? This
again leads us to the general question of the cause of the tactic
response, — a question which must be referred to a later chap-
ter. Certain special considerations may, however, be introduced
here. Let us first think of the way in which light acts on the
negatively phototactic (and photopathic ?) earthworm. Repre-

A-f-

LOW LIGHT ATTUNEMENT

LOW LIGHT ATTUNEMENT

Fig. 63. — Diagram, representing sunlight (SS) falling upon an elongated, bilateral
organism (represented by the arrow) whose head is at A. (Original.)

sent the worm by an arrow whose head indicates the head end
(Fig. 63, A^. Let solar rays SS fall upon it horizontally and
perpendicularly to its axis. Then the impinging ray strikes it
laterally, or, in other words, it is illuminated on one side and
not on the other. Since, now, the protoplasm of both sides is
attuned to an equal intensity of light, that which is the less
illuminated is nearer its optimum intensity. Its protoplasm is in
a phototonic condition. That which is strongly illuminated has
lost its phototonic condition. Only the darkened muscles, then,
are capable of normal contraction ; the brightly illuminated
ones are relaxed. Under these conditions the organism curves
towards the darker side ; and since its head region is the most
sensitive, response begins there. Owing to a continuance of
the causes, the organism will continue to turn from the light
until both sides are equally illuminated ; i.e. until it is in the
liglit ray. Subsequent locomotion will carry the organism in a

210 LIGHT AND PROTOPLASM [Ch. VII

straight line, since the muscles of the two sides now act simi-
larly. Thus orientation of the organism is effected. The same
explanation, which is modified from one of Loeb ('93, p. 86),
will account, mutatis mutandis, for positive pliototaxis.

Such an explanation can serve only for elongated organisms.
The case of the amoeba is quite different. Here we must think
of the protoplasm as being modified by a light ray so as to flow
centrifugally especially in that ray, perhaps through peculiar
molecular disturbance wrought by the ray.

As for photopathic response, that is probably to be accounted
for on the ground upon which Engelmann has explained the
arrangement of Bacterium photometricum in the microspec-
trum ; on the ground, namely, that increased brightness causes
a movement forwards, that a diminution in brightness causes a
movement backwards, or vice versa, thus resulting in the accu-
mulation of the organisms in the darker or lighter parts of the
field.

To summarize; then, light acts directly either through differ-
ence in intensity on the two sides of the organism, or by the
course the rays take through the organism. Difference in
intensity of light may also determine the position of organisms
with reference to light by virtue of the irritation produced by
rapid change of intensity.

Summary of the Chapter

The study of the effect of light on protoplasm must be made
quantitative as well as qualitative, and demands the use of appa-
ratus for determining the quality and intensity of the light
employed. The reactions produced by light upon protoplasm
are undoubtedly of a chemical character, and, indeed, experi-
ments with non-living organic compounds show that it has an
important effect in synthesis, in analysis, in substitution, in the
production of isomeric or polymeric conditions, and in fermen-
tation. Since protoplasm consists of a large number of kinds
of organic substances, we should expect light to produce far-
reaching results, the more so as it can penetrate deep into the
tissues of the organism.

The effect of light upon the general functions of organisms is

SUMMARY OF THE CHAPTER 211

revealed in modifications of metabolism and of movement, and
in the production of death. Upon metabolism we can distin-
guish an effect of the red rays, which are greatly absorbed by
chlorophyll and are chiefly active in assimilation, and an effect
of the blue rays, which seem to produce important chemical
changes, increasing the production of carbon dioxide in plants,
creating an electric current in the retina as it falls thereon,
and bleaching visual purple. These chemical changes become
more vigorous with increased intensity of light and may lead
to death ; while, at the opposite extreme, complete absence of
light may prove fatal by withdrawing the necessary thermic
and chemical energy. Again we find light sometimes necessary
to movement in protoplasm, at other times by its absence or
too great intensity inhibiting movement, or, again, by sudden
change in intensity, creating abrupt changes in movement.
Thus light undeniably has a great effect upon the processets of
metabolism and movement.

Finally, in those complex processes involved in locomotion,
light produces very widespread effects ; for the direction
(and, though only indirectly, perhaps, the rate) of locomotion
is influenced in so important a way that when light is with-
drawn the organism wanders aimlessly about. Of the various
rays, those with wave length — 40/^ to 49^i are the most active
in controlling locomotion. Movement towards the light takes
place at intensities of light varying greatly with the species
and also with the conditions other than light in which the indi-
vidual finds itself, — two factors upon which depends the degree
of attunement. Light having an intensitv above that to which
the organism is attuned repels the organism. Two kinds of
effects are produced by light : one by the direction of its ray
— phototactic ; the other by the difference in illumination of
parts of the organism — photopathic.

We thus see that organisms respond to light, and that this
response, exhibited in movements, is not of a widel}^ different
order from the disturbances produced in metabolism, which in
turn are of the same order as the chemical changes produced by
light in our laboratories upon non-living substances. In a word,
response to light is the result of chemical changes in the proto-
plasm wrought by light.

212 LIGHT AND PROTOPLASM [Ch. VII

LITERATURE

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LITERATURE 213

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214 LIGHT AND PROTOPLASM [Ch. VII

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LITERATURE 215

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'84. (See Chapter I, Literature.)
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216 LIGHT AND PROTOPLASM [Ch. VII

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LITERATURE 217

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218 LIGHT AND PROTOPLASM [Ch. VII

Ward, H. M. '93*. Further Experiments on the Action of Light on Bacillus

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CHAPTER VIII

ACTION OF HEAT UPON PROTOPLASM

In this chapter it is proposed to consider (I) briefly, the
nature of heat and the general methods of its application ;
(II) the action of heat upon the general functions of organ-
isms ; (III) the temperature-limits of life ; (IV) the accli-
matization of organisms to extreme temperature, and (V) the
determination of the direction of locomotion by heat — ther-
motaxis.

§ 1. Nature of Heat and the General Methods of
ITS Application

Heat is believed to be due to the vibrations of the molecules
of bodies. In any heated solid, fluid, or gaseous mass the
molecules are in constant motion. When the temperature
is increased, the motion is increased, and the impacts of the
flying molecules become more frequent. If a vessel containing
water is brought into contact with warmer air or warmer fluid,
its molecules fly faster, its temperature is raised. As the
motion of the molecules in the walls of the vessel increases,
the increased motion is transmitted to the contained water,
and finally to the objects in the water. Thus the motion of
the molecules of an organism in the water is increased with the
increase of the temperature of the water. Heat, as so-called
radiant heat, is transmitted through space in straight lines, and
follows all the laws of light, into which it passes when the rate
of wave vibrations becomes rapid enough to affect the retina.
The chief effects of radiant heat were considered in the last
chapter.

Heat is an important element in all chemical processes. The
state of cohesion — solid, liquid, gaseous — and the ease with

210

220

HEAT AND PROTOPLASM

[Ch. VIII

which molecular decomposition and synthesis occur, vary directly
with it. This is an important consideration in our study of pro-
toplasm, for most of its changes are chemical changes.

A word should be said concerning general methods of apply-
ing heat to protoplasm. In the case of the higher plants and

seedlings, the. device of Sachs ('92,
p. 117) may be employed. This
consists of two metallic vessels, a
and i (Fig. 64), of similar form,
one placed inside of the other, the
interspace being filled with water.
Within the inner vessel is placed
the pot (t) with the object of ex-
perimentation. The whole is cov-
ered over by a half globe of glass
(^), extending down to below the
level of the top of the pot. The
water is heated by a lamp (/) be-
low, by which means moisture and
warmth are carried to the plant. -

In the case of the lower organ-
isms, brief experiments may be con-
ducted in shallow aquaria for the
horizontal microscope (Fig. 65), like
those devised by CoRi ('93). It is
preferable to put inside of the outer
vessel a smaller glass vessel, which
shall contain the organisms and
the thermometer marking the tem-
perature of the water. For long-
continued experiments where con-
stant high temperature is required,
a warm oven, such as is used in bacteriological work, is essential.
The production of extremely low temperatures offers special
difficulties. For temperatures to — 40° or so, various freezing
mixtures can be employed. Of these chopped ice and common
salt in equal parts give a temperature of — 18° ; calcium chlo-
ride and snow, in proportions of 3 to 2, give — 33°; and cal-
cium chloride and snow, in the proportion of 2 to 1, give — 42°,

Fig. 64. — Apparatus for study-
ing the effect of heat upon
germination in phanerogams,
a, the external ; i, the inter-
nal vessel, between which is
a water space ; t, flower-pot
filled with earth and con-
taining a seedling of maize
p ; h, three supports for the
glass hell g ; u, support for
the flower-pot ; d, tripodal
iron stand carrying the spirit-
lamp I. (From Sachs, '92.)

§1]

METHODS

221

the initial temperature being always supposed to be 0°. Far
lower temperatures than these have been obtained by phy-
sicists, notably Pictet, to whose work we shall refer again

Fig. 65.

CoRi's stage aquarium. A, the aquarium proper; T, holder for the
aquarium ; E, R, slides, with springs. (From Coei, '93.)

(p. 240). The organisms to be acted upon ma}^ be kept in an
apparatus (Fig. 66) like that employed by Pouchet ('66).

Throughout this chapter, as indeed throughout the whole
book, thermometric readings are given in Centigrade scale,

Fig. 66. — Cold chamber seen in external view and in section. The wall is composed
of an inner cylinder containing the freezing mixture and the receptacle for the
object of experimentation, and an outer cylinder separated from the inner by a
packing of fragments of charcoal. The receptacle containing the organism is
provided with a thermometer and an air tube. (From Pouchet, '66.)

222

HEAT AND PROTOPLASM

[Ch. VIII

unless otherwise stated. All readings not designated by the
— sign are above the Centigrade 0 point. The point of abso-
lute 0, to which we may have occasion to refer, is — 273° C.

§ 2. The Effect of Heat upon the General Func-
tions OF Organisms

Under this topic will be considered (1) the effect upon
metabolism, and (2) the effect upon movement and irritability.

1. Effect of Heat upon Metabolism. — Within certain limits
the relative increase of temperature leads to a relative increase
in the activity of the various metabolic processes. This is well
seen in those chemical changes which produce so-called phos-
phorescence. Many years ago Macaire ('21, p. 157) showed
for fireflies, and Artaud ('25, p. 372) for the organisms of the
sea, that light begins to appear shortly above 20°, reaches its
maximum intensity at 40° in the fireflies and 35° in the water
organisms, and entirely disappears at 59° to 62° in the first
case, and 43° in the second. The temperature of these three
points — lowest temperature of metabolic activity, temperature
of greatest activity, and highest temperature permitting of
activity — may be called, respectively, the minimum, optimum,
and maximum temperatures for phosphorescence.

The effect of temperature on metabolism is seen in the
absorption of oxygen by organisms. Thus VON Wolkoff and
Mayer ('74) found that more oxygen is absorbed by seedlings,
as the temperature is increased, from 0° to about 35° C. This
is shown in the following table. (From Vines, '86, p. 198.)

Five Nasturtium Seedlings.

Four Wheat Seedlings.

Total Amount of 0
Absorbed per c.c.

Temperature C.

Total Amount of 0
Absorbed.

Temperature C.

0.60
0.77
0.76
0.77
1.04
0.91

22.4°
27.0°
30.5°
30.0°
35.0°
38.2°

0.10

0.038

0.067

0.088

0.022

0.010

15.6°
4.4°
9.8°

15.4°
0.3°
0.1°

§•2]

EFFECT ON GENERAL FUNCTIONS

Likewise Moissan ('79, p. 296) found that, in the dark, the
amount of oxygen absorbed by a branch of certain plants varied
with the temperature. Thus there was absorbed per hour by

Pinus pinaster (30 grammes)

Agave americana (70 grammes)

f at 0° C,
\ at 13°,
I at 15°,
f at 11° C,
i at 40°,

0.32 CO.
1.30 CO.
1.90 CO.
0.54 CO.
5.56 c.c.

These experiments serve to show clearly that in plants more
oxygen is absorbed as the temperature is raised to the optimum.

The same result is obtained from animals also. Thus Tee-
viRANUS ('31, p. 28) found that the honey bee Apis mellifica
absorbed at 14° C. 1.35 Paris cubic inches, and at 27.5°, 2.77
cubic inches of oxygen. At the higher temperatures the bee
was very active, so that the result seems here somewhat com-
plicated by the increased muscular activity accompanying a
higher temperature, which invokes a more rapid respiration.
Nevertheless, the phenomena of increased ox^^gen absorption
with higher temperature are fundamentally the same in plants
and animals.

Turning now to the process of excretion, it appears that the
amount of COg evolved by seedlings varies with the tempera-
ture. On this point we have data by Deheeain and MoisSAX
("74, p. 327), RiscHAWi ('77), and others. Dehekain and
MoissAN experimented with leaves of tobacco kept in the
dark. The same plant was used throughout the experiment,
and it remained throughout in good condition. In the follow-
ing table the temperatures are given in the first column, and,
in the second, the number of grammes of COg produced jier

100 grammes of leaves :

—

Temp.

Gms. COj.

Temp.

Gms. CO,.

Temp.

Gms. COj.

Temp.

Cms. COj.

7
13
14

0.031
0.139
0.157-

15

18
19

0.165
0.178
0.193

20
21
32

0.263
0.289
0.514

40
41
42

0.9G1

1.132
1.325

When plotted (with the temperatures as abscisste) the relation
between temperature and weight of CO3 produced is expressed

224

HEAT AND PROTOPLASM

[Ch. VIII

by a line which is slightly steeper at the higher temperatures
than at the lower. This change of steepness is, however, much
less striking in the case of the etiolated wheat seedlings studied
by RiscHAWi, where the following series was obtained: —

Tkmperatuke.

Weight CO2 in Mg.

Temperature.

Weight CO, in Mg.

5°
10°
15°

20°

3.30

5.28

9.90

12.54

25°
30°
35°
40°

17.82
22.04
28.38
37.60

The evidence from excretion thus also confirms the conclusion
that the metabolic processes are accelerated by raising the tem-
perature to a certain limit.

The effect of heat in the metabolic process of chlorophyll
formation is shown in some plants upon which Sachs ('64)
experimented. He prepared three culture chambers, all illu-
minated by a north light. A was kept at a high temperature,
namely, 30° to 34° C. ; B was kept at a temperature of 16° to
20° C, and (7 at 8° to 14° C. Into these chambers were put etio-
lated seedlings of Phaseolus multiflorus (bean) and Zea mais
(maize) which had been reared in the dark. The first traces of
turning green appeared in A after 1-| hours ; in B after 2 to 5
hours ; whilst in C no trace of greening appeared until several
days had passed. Thus it appeared that at the temperature of
8° to 14° C. chlorophyll is hardly produced.

We now pass to the consideration of some Protista. An
indication, at least, that the rate of metabolism is increased
with temperature is gained from the increased rapidity of
formation of the contractile (excreting) vacuoles of Ciliata
under these conditions. Thus, Rossbach ('72, p. 33) found
that the rapidity of the rhythmic movements of the contractile
vacuole is most intimately related with the temperature of the
body, so that one and the same species of animal under normal
conditions always has, at a given temperature, the' same number
of contractions. From the number of the rhythmic contrac-
tions one can therefore draw a certain conclusion concerning
the existing degree of temperature. This relation between

§2]

EFFECT OX GENERAL FUNCTIONS

225

DEGREES
1 3 5 7 9 11 13 15 17 19 21 23

27 29 31 33 35

temperature and interval between contractions is given in
Fig, 67. We cannot say that the increment of excretion is
exactly equal to that of con-
traction, but there is doubtless
a correlation between the two
activities.

From all these facts we may
conclude that, within certain
limits, an increase of tempera-
ture increases metabolism, and
a diminution of temperature
diminishes it. But the incre-
ment in metabolic processes
soon finds a limit at a tem-
perature above which the
metabolic processes begin to
diminish.

2. Effect of Heat upon the
Movement of Protoplasm and
its Irritability. — All observers
(DUTROCHET, '37, pp. 777,
778; Nageli, '60, p. 77;
Sachs, '64 ; Hofmeister, '67,
pp. 53, 54 ; and Cohn, '71, for
plant cells ; and KiJHNE, '59,
p. 821 ; and Schultze, '63,
p. 46, for Protozoa) agree
that a gradual increase in
temperature above that of the
ordinary living room results,
within certain limits, in an
increase in the rate of movement of the protoplasm. A
diminution in temperature, on the contrary, causes a decrease
in the movement. ,. ;-

For this acceleration with increased temperature, Nageli
sought to obtain a quantitative expression. He measured
the time consumed at different temperatures in the migration
tlirough 0.1 mm. of the granules floating in the stream of
protoplasm seen in the end cells of Nitella syncarpa. Some

Q

^

U-

«

J

-H-l

HI

— ■

^

r'

-1

w

V

r

y

— f

f

/

Y^

y

/

1

I

I^

^

f^

/'

/

/

/

J

;

/

/

1

f

1

1

/

1

1

/

-

J

/

Fig. 67. — The mean thermal curves de-
termined by RossBACH for the con-
tractile vesicle of Infusoria. I, for
Euplotes charon ; II, for Stylonychia
pustulata; III, for Cliilodon cucul-
lulus. The abscissre indicate degrees
of temperature, Centigrade, in two-
degree intervals ; the ordinates give
the number of seconds elapsing
between successive contractious of
the vesicle, in two-second intervals.
(From Semper, "Animal Life.")

226

HEAT AND PROTOPLASM

[Ch. VITI

measurements were made, also, by Schultze, on Tradescantia
liairs. But the work of neither of these equals in importance
the determinations of Velten ('76), which I propose to give
in some detail. He determined the time consumed by the

CO mm

50 mm

40 mm

30 mm

20 mm

.10 mm

1

1

"

'

—

""

~

1

h

r

y

s

^

\

\

\

s

s

-

J

1

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I

^

y

\

,

^

\

/

/

'

1

1

/

'

\

.

\

y

\

1

1

1

I

/

/

'

/'

1

\/

y

/

^

/

,

1

,^V-■

^

-'

'

V

1 c:n:^

y

'

'

/

/'

I

/

,'

'

f

r-

1

,

•'

/

^

•'

\

/

y

.N

r

,

,

^

A^'-

-

1

/

^ \

"-' \,'\

/

■^^

^

1

I

1'

^

I

/

I

'

^

_^

^

'

'

/

1

\

^

/

^-

— .

Fl

ODEA^

,

^

—

-*

\

,

^

—

'

t

,^

^

^

--

—

"

/

,.-

^

—

"

-

/

51

""

>

->

-

1

60 mm

50 mm

40 mm

30 mm

20 mm

10 mm

0° 5° 10° 15° 20' 25° 30° 35° 40 45 C.

Fig. 68. — Carves showins: the relation between temperature (abscissae) and rate of
movement per minute of the chlorophyll grains floating in the protoplasm of the
cells of three species of green plants. (Data from Velten, '76.)

floating chlorophyll grains in cells of Elodea canadensis and
Vallisneria spiralis, or the small granules near the wall of cells
of Chara in traversing 0.1 mm., at various temperatures. The
results in modified form are given graphically for these three
species in Fig. 68. In this figure, the ordinates represent
distance (in millimetres) traversed in 1 minute. The abscissse

§2] EFFECT ON GENERAL FUNCTIONS 227

represent temperatures (Centigrade) from 0° on the left to 44°
on tlie right. The rate of movement increases regularly up
to a maximum (the optimum), a rise of 1° C. being associated
with an increased rate of movement in Chara of 1.4 mm. ; in
Vallisneria of 0.62 mm. ; in Elodea of 0.26 mm. The rate of
increase is, in general, slightly greater near the optimum.
The optimum varies, in the three species, from 34° to 39°.
Beyond the optimum the rate rapidly decreases, cessation of
movement being readied, in the case of Elodea, in 3.7°, in
Vallisneria in 6.2°, in Chara in 8.4° beyond the optimum.
The curves exhibited in Fig. 68 are characteristic of other
vital functions besides motion, and illustrate this general law,
that the optimum temperature for the vital activities lies
much nearer to the maximum vital temperature than to the
minimum.

After having seen that the rate of flow of protoplasm is
dependent upon temperature, we should expect to find, as we
do, that that other form of protoplasmic motion, cilia vibration,
would be likewise dependent. Some quantitative data con-
cerning relation of temperature and rate of vibration were
gained as early as 1858 by Callibukces. He placed a bit of
ciliated membrane from the frog's oesophagus in a moist cham-
ber, and in contact with the cilia he laid a small glass cylinder,
horizontally supported, and provided with a dial by which its
revolutions could be counted. He found that the mean time
for a revolution was, —

at 12° to 19° C 22 minutes, 3 seconds ;

at 28° C. .... 3 minutes, 7 seconds ;

thus, in increasing the temperature from 15° to 28° C, the rate
of vibration is increased sevenfold.

Essentially similar results were obtained, through the use of
new methods, by Roth (^'66, pp. 185-189), upon the ciliated
epithelium of the frog's uterus, rabbit's trachea, and gill of
Anodonta, and by Engelmann ('68, pp. 381-384 ; 443, 444 ;
454, 455 ; and '77), upon the frog's oesophagus. The simplest
of these methods was to determine the rate of the transportation
of fine particles over the surface of the tissue. The result of
these studies showed that the optimum temperature for the

228

HEAT AND PROTOPLASM

[Ch.YIII

movements of Vertebrate cilia lies between 35° and 40° C,
and that a gradual elevation of temperature to this point is
accompanied by gradual increase in the rapidity of the stroke,
the law of which is exhibited in the curves shown in Figs. 69
and 70.

This variation in rate and regularity of cilia movement with
change in heat is marked in Infusoria, as Rossbach ('72, p. 312)

80

70

60

50

40

30

20

10

^ \ .i-C::?

10'

ro

50

40

30

20

10

0

20

30

40

Fig. 69. — Curves showing relation between temperature (curve TT) and rapidity
of movement of the cilia of the mouth and oesophagus of the frog. The abscissae
give, in minutes, the lapse of time from the beginning of the experiment. The
ordinates give, for the temperature curve, the degrees Centigrade, and, for the
other curve, the corresponding number of units of motor activity for the imme-
diately preceding 2 minutes as registered by Engelmann's apparatus. (From
Engelmann, 77.)

and ScHUEMAYEE, ('90, pp. 411, 412) have shown. The lower
the temperature falls below 15° C, the slower the locomotion,
almost ceasing at +4°. Upon raising the temperature above
15°, motion quickens, until, between 25° and 30°, motion
reaches a maximum, the Ciliata shooting back and forth with
the quickness of an arrow. Between 30° and 35°, the move-
ments become still more violent, and take on a new character.
They are no longer coordinated. Towards 40°, the progres-

§2]

EFFECT ON GENERAL FUXCTIONS

229

sive movement becomes slower, and finally ceases, while the
rotation continues, but in ever diminishing rapidity. A new
axis of rotation is assumed, running lengthwise and obliquely,
or running transversely, in the short axis of the body. Finally,
somewhere between 38° and 40°, motion ceases. Thus, the
ojDtimum temperature for the activities of the protoplasm lies
at about 30° C, and the maximum temperature is perhaps 10°
higher.

The experiments upon plant protoplasm, amoeboid organisms,
and ciliated cells thus agree in demonstrating a close relation be-

80

60

60

40

30

20

10

—

V

\

\

y

\

\

\

\

t

k

h

\

/

\

N

\

\

T

T

\

/

/

'--.^

\

V

/

/

■^

-^

^

i^.,

^

^

\

"^

80

GO

50

40

30

20

10

0

0

10

20

30

40

50

60

Fig. 70. — A set of curves having the same meaning as those of Fig. fiO. In this case,
however, Uie temperature tirst falls and then rises, instead of rlsiug first and then
falling. (From Engelmann, '77.)

tween temperature and protoplasmic movement. This relation
is such that, as the temperature is elevated above the freezing
point of water, the movements regularly increase, and reach
their greatest activity at about the temperature of slow-running
waters in the midst of summer, namely, about 25° to 30° C*

* The maximum temperature attained by bodies of ordinary water inhabited
by organisms seems to be close to the position of the optimum temperature of
organisms. Yet, temperature data concerning the waters from which the organ-

230 HEAT AND PROTOPLASM [Ch. VIII

Above this temperature, the rate of protoplasmic movement
rapidly decreases.

That temperature influences the irritahility of protoplasm
is demonstrated by many facts. Thus, Strasbueger ('78, p.
611) found that, at a high temperature, the light attunement
of swarm-spores changes. For example, swarms of Hfematococ-
cus and Ulothrix, which are — phototactic, move at 30° C. from
the — to the + side of the drop. Loeb ('90, p. 43) has
found that Prothesia larvse do not respond to light at a tem-
perature below -f 13° C. Similarly, in respect to geotaxis,
ScHWARZ ('84, p. 69) found that Euglena did not respond
at below 5° to 6° C. So, too, Campbell ('88, p. 130) has
shown that the response of muscles to electric stimulus varies
with the temperature. Thus, with the neck muscles of the
tortoise at —

Temperature.

Number of Shocks per Second Eequired
TO Tetanize.

4°C.

9°C.
21° C.

28° C.

1

5
25
34

isms of the experiment have been taken are, unfortunately, rarely given in
experiments on heat. From observations made by tlie Massachusetts State
Board of Health (Report on Water Supply and Sewage, 1890, Part I, p. 660), it
appears that the various ponds and reservoii's in the state, having a depth varying
from 19 to 5 metres, had a mean August (maximum) tenjperature ranging (in
the different ponds) from 24° to 21° C. Various rivers, mostly not of mountain
origin, had, in 1887, a mean July (maximum) temperatm-e, varying (in different
cases) from 26.5° to 24° C. Even in those ponds and streams in which the
surface temperature is over 25°, a lower temperature can be found below the
surface. Thus, from the report referred to, it appears that, while at 3.3 metres
below the surface we have nearly the surface temperature, at 6.6 metres below
the surface, we find a decrease of 3° to 10°, and at 10 metres a decrease of
from 9° to 17° below the surface temperature in different ponds. As for the sea,
the highest recorded surface temperature is about 32° C. (Red Sea, Gulf of
Mexico.) See A. Agassiz, "Three Cruises of the Blake," Bull. Mus. Comp.
Zool., XIV, p. 301. It would be a valuable piece of work to determine the
maximum summer temperature attained by the waters of shallow ponds, pools,
and marshes inhabited by organisms.

§3] TEMPERATURE-LIMITS OF LIFE 231

This shows that the muscle responds, and tends to return to
its uncontracted condition less quickly at a low than at a higher
temperature. In general, then, protoplasm is more responsive,
the closer we approach its optimum temperature.

§ 3. Temperature-Limits of Life

In the preceding sections we have seen that, as the tempera-
ture is raised above the optimum, or as it approaches 0° C,
the vital activities begin to diminish. Finally, we meet with a
higher or a lower limit, at which all movement and the processes
of metabolism cease. This point may be called, in the case of
the higher limit, the maximum, and in the case of the lower
limit, the minimum. The maximum and the minimum are not
points of death, but merely of cessation of activity, lasting
while the temperature endures, but being replaced by renewed
activity when the temperature is shifted towards the optimum.
This quiescent, or latent, condition of the protoplasm near
the vital limits of temperature may be called temporary rigor
(German " Starre ") to distinguish it from death. Death occurs
at a very few degrees beyond temporary rigor.

1. Temporary Rigor and Death at the Higher Limit of Tem-
perature, Maximum and Ultramaximum. (ExGELMANisr, '79,
p. 358.) — The occurrence, at a high temperature, of a con-
dition resembling death, except that the organism may revive
from it, seems first to have been noticed by P. de Candolle
('06, p. 346). He found that a Sensitive plant, kept 11 hours
at 37° C, lost all sensibility to touch, and did not close with
the coming on of night. Maintained, during the following
day and night, at a temperature of about 20°, it remained
insensitive during that period ; but on the succeeding night
it closed its leaves, and on the following day had regained its
sansitiveness to touch. Thus, the high temperature of 37° had
l)roduced an immotile state which was not death, since it was
only temporary. It may be called the state of temporary heat-
rigor.

The earliest record which I have found of a similar observa-
tion among animals is that of Pickford ('51). He states
that, at a high temperature, muscle went into a rigid con-

232 HEAT AND PROTOPLASM [Ch. VIII

dition (" Sclieintodtenstarre ") from which it might return to
a normal condition of sensitiveness. Such a rigid state was
brought about by subjecting a decapitated frog in water to
35° R. (43.8° C.) for 1 minute. I will now add some additional
cases of prod action of temporary heat-rigor in protoplasm which
I have found in the literature.

In 1863, Max Schultze (pp. 33, 34) found temporary heat-rigor in
Acfcinophrys, which retracts its pseudopodia and appears as a lifeless mass
at 35° to 38°, but is not killed until 43° is reached. In the same year Sachs
('63, p. 453) repeated more fully the experiments of P. de Candolle on
Mimosa pudica. He found that a temperature of 30° C. for 3 houi's did not
produce rigoi-. A temperature of 40° for 1 hoiu- produced loss of sensibility
during 20 minutes. Raised slowly even to 50°, sensibility was only tempo-
rarily lost, but 52° proved fatal. Immersed in water, heat-rigor occurred
at a temperature 5° to 10° lower. Sachs clearly distinguishes a "voriiber-
gehende Warniestarre " from death.

KuH>fE ('61, pp. 45, 67, 87, 103) drew a sharp contrast between the
rigidity of death, which he calls " W'armestarre," and the transitory immobile
condition or " Warmetetauus." He found this latter condition to occur in
Amoeba subjected to 35° for 1 minute, in Actinophrys subjected to 35°-40°
for several minutes, in motile Myxomycetes (Didymium serpula) subjected
to 30° for 5 minutes, in Tradescantia stamen hairs at over 45°, when gradu-
ally brougiit to that temperature. In all cases there is such a relation
between temperatiu-e and time of subjection that the greater the one is the
less need be the other in oider to produce heat-rigor.

Very instructive also are the observations of Hofmeister ('67, pp. 54,
55) which I briefly summarize: Hairs from the stem and leaf of Ecbalium
ageste showing lively movement were gradually raised from 16°-17° C. to
40° C. They became motionless at 40° C. After 1 to 2 hours, movement
returned, and was very violent. Cooled and raised again to 45° C, the proto-
plasm -was motionless at first, but after 17 minutes movements recurred but
were not rapid. Put again into 47.5° (after first cooling) heat-rigor occurred
in 5 minutes, but upon cooling, movements return.

Very si^^ilar experiences have befallen subsequent investiga-
tions which unite in supporting the conclusion that at a certain
temperature, slightly below the death point, protoplasm becomes
immobile, but retains the capacity for subsequent reacquisition
of movement upon lowering the temperature.

Finally, studies upon muscle, especially those of Chmule-
viTCH ('69), Samkowy ('74), Moriggia ('91), Gotschlioh
('93), and others, have shown that as the temperature is ele-
vated up to about 30° C, the muscle contracts more and more,

§3] TEMPERATURE-LBIITS OF LIFE 233

lengthening again as tlie temperature falls. If, however (Got-
schlich), the temperature is raised in about 60 seconds to 38°
and then lowered, the elongation of the muscle takes place only
very slowly. This is the condition of "thermische Dauerverk-
urzung," and is probably the same as the condition of tempo-
rary heat-rigor of Sachs. When, however, the temperature
is raised rapidly to 45° to 50° (or slowly to 35°), death-rigor
appears, accompanied by a coagulation of the protoplasm
which renders the whole mass opaque and permanently con-
tracted. The rapidly replaced contraction accompanying ele-
vation to about 30°, the slowly obliterated contraction of 38°,
and the permanent contraction of 45° are then three stages in
a series of effects of heat on muscle.

If now, contraction, heat-rigor, and death-rigor are merely
three stages in a series of effects of increasing temperature,
they probably have related immediate causes. Heat-rigor is
certainly a condition of tetanus, but the fact that the proto-
plasm in this condition is not sensitive and cannot quickly
return to the relaxed condition indicates that some of those
changes that, produce death-rigor have already occurred, but
not to such an extent that the organism cannot recover from
them. As Gotschlich says ('93, p. 154), "Die thermische
Dauerverkurzung ist also eine qualitative unvoUendete Starre"
(z.e. death-ri^or). From this point of view there is no exact
point at which heat-rigor occurs, since the period of persisting
rigidity varies in extent from 0 to many hours, and thus passes
by almost imperceptible gradations from a contraction in re-
sponse to heat on the one hand to death-rigor on the other.
The muscle increases in sensitiveness as the temperature rises
to the optimum, just as the movements of plasma in Chara do.
Beyond the optimum, sensitiveness diminishes, and this leads
to a condition of heat-rigor which becomes the more pronounced
the higher the temperature, until, through completed coagula-
tion, death occurs.

We must now consider this point at which d.eath occurs
from heat ; and, as an introduction to this discussion, we
may tabulate the results of experiments by numerous ob-
servers who have attempted to determine the ultramaximum
temperature.

234

HEAT AND PROTOPLASM

[Ch. VIII

TABLE XIX

Kesdlts of Experiments to Determine the Ultramaximum Temperature
OF Organisms in Water, or the Temperature at just above which
Organisms Reared under Normal Conditions will Die

Species.

Maximum
Temperatueb.

Conditions op

ExPEPvIMENT.

Authority.

Cryptogams.

Bacteria

45° C.

Maximum temperature

CoHN, '77, p. 253;

of growth in liquid

'94, p. 150

Yeast

53°

Moist; average max.

SCHTJTZENBERGER,

'79, p. 162

Oscillatoriae

45° 1

Nostoc

42° 1

Spirogyra |

CEdogoniura j

44° ■

Death point

DE Vries, '70, p.

388

Hydrodictyon

46°

Cladophora

45° to 60°

Sachs, '64, p. 5

Nitella flexilis

45°

Gradually raised

Dutrochet, '37, p.

777

Funaria hygrometrica . .

43°

DE Vries, '70, p.
388

Marchantia polymorpha 1

46°

It <(

Lunularia vulgaris J

Phanerogams.

Vallisneria spiralis ....

45° to 50°

Gradually raised "]

Ceratophyllum demersum

45° to 50°

Suddenly immersed }
for 10 minutes J

Sachs, '64, p. 5

Various plant cells ....

47° to 48°

Died (suddenly sub-

SCHULTZE, '63, p.

jected)

48

Protozoa.

.^thalium sept

40°

Plasmodium died after
2 minutes

KtJHNE, '64, p. 87

Amoeba

40° to 45°

Death point

« <i

Actinophrys

42°

Death point. Activity

SCHULTZE, '63, p.

lost at 38°

34

Miliolidse

43°

Death point

SCHULTZE, '63, p.

38
Butschli, '84, p.

Various Flagellata and

45° to 60° most usual.

swarm-spores

40° to 60°

Heat-rigor usually

8()0 ; Strasbur-

occurs between 40-' to

GER, '78, p. 611;

50° and is lower for

Dallinger, '80,

marine than for f . w.

p. 10

species. These tem-

jDeratures for the

motile stage

Various Infusoria

45°

Can withstand only a

SCHiJRMAYER, '90,

short time

p. 412

§3]

TEMPERATURE-LIMITS OF LIFE

235

Species.

Maximum
Tempekature.

Conditions
of expeeiments.

AtTTHOEITT.

Paramecium

42° to 46° C.

Gradually subjected

Mendelssohn, '95,
p. 19

Stentor

44° to 50°

Heat-rigor point, tem-

Davenport and

perature raised grad-

Castle, '95, p.

ually. From a pool

229

kept warm by boiler

waste

Vorticellidse

41° to 42°

SCHULTZE, '63, p.

49

Coilenterata.

Actinia

38°

Gradually raised (1

Frenzel, '85, p.

hour)

464

Beroe ovatus

40°

Death point, suddenly

de Varigny, '87,

subjected

p. 63

Mollusca.

Various Mollusca

30° to 40°

Suddenly immersed

Frenzel, '85, p.
461-466

Pleurobranchaea

33°

Temp, gradually raised

" "

Aplysia

33°

Died in 3 hours

" "

Eledoue

35°
37°

Died

Heat-rigor ; died at 41°

<i II

Young squids

Bert, '67, p. 135

Vermes.

Turbellaria

44.5°

Death point

SCHULTZE, '63, p.
49

f

Spallanzani,

Anguillulidae

44.5°

it ((

1787, Tom. I., p. 56

SCHULTZE, '63, p.

49

Rotifera 1

45° to 48°

Moist

DoYERE, '42, p. 29

Tardigrada J

98°

Dried

BROCA,'61,p.44-46

Diopatra

40°

Suddenly immersed,
died quickly ; at oO'

Frenzel, '85, pp.

461-465

lived indefinitely

Terebella

27° to 30°

Suddenly heated ;
slowly warmed, re-

II ((

sisted 30°

NaididsB

44.5°

SCHULTZE, '63, p.

49

"Bloodsucker"

44°

Death point

Spallanzani,
1777, Tom. I, p. 56

Crustacea.

Daphnia sima

33.5°

Suddenly subjected

PLATEAU,'72,p.316

Cyclops quadricornis 1

36°

<< <<

„ . 11 3J7

Cypris fusca

Gammarus roselii

30°

<( (1

" 316

Asellus aquaticus

43.5°

"

" 316

236

HEAT AND PROTOPLASM

[Ch. VIII

Maximum

Conditions op

Species.

Temperatckb.

Experiment.

AUTHOKITY.

Palsemon

26° C.

Died in 2 hours (sud-
denly subjected)

Frenzel, '85, p.
463

Scyll3.ris

30°

Died in 1 hour (sud-
denly subjected)

(( •(

Pagurus prideauxii ....

36°

Droinia vulgaris

38°

Pisa gibbosa

For tun us puber

36°
34°

Death point

DE VakIGNY, '87a,

p. 173

Carcinus sp

38°

Gi*apsus sp

38°

Araclmida.

Argyroneta aquatica . . .

38.5°

Suddenly subjected

Plateau, '72, p.
316

Hydrachna cruenta. . . .

46.2°

Submerged (?)

« <i

Insecta.

Podura

27°

Suddenly subjected;
died slowly. At 36°
died at once

NiCOLET, '42, p. 11

Agabus bipustulatns . . .

38° 1

Hydaticus transversalis .

39°

Culex pipiens, larva . . .

40°

Hydrophilus caraboides .

42°

Death point

Plateau, '72, p.

Hydroporus dorsalis . . .

42°

316

Nepa cinerea 1

Notonecta glauca 1- • ■ ■

44° to 45°

Cloe diptera, larva J

Musca vom. (?)

37.5° ■

Musea vom., larva ....

42.5°

Musca vom., pupa ....
Silk worm larva

43.7°
42.5°

Death point

Spallanzani, 1787,
Tom. I, pp. 56-58

" Butterfly " larva ....

42.5°

Culex larva

43.7°

Echinodermata.

Antedou

30°

Died rapidly (sud-

Frenzel, '85, pp.

denly subjected)

460-463

Holothuria

30° to 40°

Died in several hours
(suddenly subjected)

Vertehrata.

Many fresh-water fishes .

40°

Survived only a few

Edwards, '24, p.

seconds

114

f 36°

In pond out of doors.

Knauthe, '95, p.

752

Fish

\ 33°

Temperature elevated
gradually

Bert, '76, p. 169

27° to 38°

Davy, '63, p. 125

§3]

TEMPERATURE-LIMITS OF LIFE

237

Species.

Maxi.mum
Temperatuee.

Conditions of
expeklment.

AuTnOEITT.

Hippocampus

30° C.

Lived half an hour

Feenzel, '85, p.
462

Salamander

44°

Death point

Spallanzani,
1787, Tom. I, p. 56

Froa:

40° to 42°

Suddenly subjected in
water ; death at once

Edwards, '24, p.
374

Frog, adult (summer) . .

42° to 43°

Death-rigor in 7 to 14

MOKIGGIA, '91, p.

minutes

385

Frog, adult

43.8°

Spallanzani,
1787, p. 55

Frog, tadpoles

41°

Raised in from 5 to 10
minutes

See p. 253

Rabbit 1

Death point when

Obeenier, '66, p.

i.

44° to 45°

rai.sed gradually ;

99

(

Dog J

convulsions at 42^

Man

45°

In water ; giddiness in
a few seconds

Edwards, '24, p.
374

Human spermatozoa . . .

50°

Died in 10 minutes

Mantegazza, '66,
p. 186

Vertebrate muscle ....

40° to 50°

KtJHNE, '59, pp.
784-804

Vertebrate muscle (frog)

/ 45° to 50°

Raised in 30 seconds

GOTSCHLICH, '93,

i 35°

Raised in 18 minutes

p. 123

The determinations given in the above table may be compared
only with caution, for diverse conditions give results which
cannot be directly correlated. Thus individuate of the same
species, but reared under diverse environment, have a different
resistance period to heat. The lethal temperature varies accord-
ing as the organisms are suddenly or gradually subjected to the
high temperature. Also, the individuals of the same species
will die at different temperatures according as they are rap-
idly subjected to the high temperature or gradually accus-
tomed to it, and, as we have seen, a lower temperature, long
continued, often produces the same result as a higher tempera-
ture during a brief period. Finally, too little care has been
exercised in most cases to determine the temperature of tlie
water immediately upon, and a few minutes after, placing the
animals in it, — an operation which lowers the temperature
of the water. In the experiments cited, unless otherwise
stated, the conditions were gradual subjection continued for
a short time only. The quality of the water in which the

238 HEAT AND PROTOPLASM [Ch. YTTI

experiments were carried on is supposed to be, except for its
temperature, normal for the species. Summarizing the table,
we find that the Protista have the highest maximum tempera-
ture of any group, it being in extreme cases about 60° for active
organisms, but generally between 40° and 45°. Among the
Metazoa, the highest maxima recorded (excepting Rotifera and
Tardigrada) are 44° to 45° for Turbellaria, Anguillula, Naididse,
Nepa (water-scorpion), Notonecta (water-boatman), Cloe larva.
Salamander, and mammals. A water-mite (Hydrachna) is
said to have withstood up to 46.2°, and some vertebrate tissues
resist up to 50°. For the great majority of Metazoa, the maxi-
mum temperature lies below 45° and, in the case of marine
species, below 40°. The low maximum temperature of marine
species is probably due to the low maximum temperature of
the sea as compared with ponds. We may consequently con-
clude from the foregoing that the maximum temperature for
protoplasm lies generally between 35° and 50°, the lower limit
being characteristic of organisms living in a medium of low
temperature (the sea), the latter, of organisms reared in warm
pools or of organs (vertebrate muscle) in a body kept at a higli
temperature.

The question now arises, what is the cause of the death of
protoplasm at high temperatures? To get some insight into
this matter, let us examine the phenomena accompanying death
of protoplasm from overheating. Kuhne ('64, p. 44) thus
describes the appearance of an Amoeba subjected for a moment
to a fatal temperature (45°). The structure is entirely altered
since it has become transformed into a mass of knobbed, opal-
escent, solid lumps, which, even in transferring to the slide,
become easily broken apart. This appearance is clearly due
to a coagulation of the protoplasm. A similar coagulation
takes place in Actinophrys eichhornii (Kuhne, '64, p. 67) at
45°. "'- The sphere shrinks into a flat, hardly transparent, cake,
no longer reacts to the strongest induction shocks, and breaks
up after 24 hours into a heap of small granules and irregular
pieces." Likewise, in muscles a change is produced by heat
which is evidently a kind of coagulation. A coagulation then
seems to be the immediate cause of death at high temperatures.

But just what is the component of protoplasm which co-

§ 3] TEMPERATURE-LIMITS OF LIFE 239

agulates at the death point of organisms? As Kuhne ('64,
p. 1) pointed out, it cannot be ordinary egg albumen ; for,
excepting the contractile substance, we know of no native
albumen which coagulates between 35° and 50° C. It was
KiJHNB's great service to show that th.ere is a substance which
can be pressed out of frozen, triturated, and then thawed
muscle, which becomes quickly opalescent at 40°, through the
separation of the muscle plasma into myosin and a serum.
This serum, in turn, contains an albuminoid which coagulates
at 47° (Demant, '79 and '80). Now, since there are proteids
in muscle which coagulate at about the point at which muscle
goes into permanent heat-rigor, and since these proteids can
no longer be squeezed out of rigid muscles, the conclusion
seems justified that permanent heat-rigor in muscle is due to
the coagulation of these proteids.

Related, easily coagulable proteids occur in widely dissimilar
organisms. For example, myosin has been found in vegetable
protoplasm (Weyl, '77, p. 96), and Halliburton ('88) has
described a globulin from blood corpuscles which coagulates
at 48° to 50°. Their distribution in protoplasm is, therefore,
probably general, and so we are justified in concluding that the
death of protoplasm by heat is, in general, the result of the
coagulation of a proteid (globulin). Death occurs because
the vital machinery has been broken down.*

2. Temporary Rigor and Death at the Lower Limit of Tem-
perature, Minimum and Ultraminimum. — Whilst towards the
upper limit of ordinary terrestrial temperatures (35° to 40° C.)
molecular changes in organic compounds are hastened, towards
the lower limits (—40° to — 50°) molecular changes are slow,
being principally confined to the transformation from the liquid
or gaseous to the solid or liquid condition. This transforma-
tion does occur in the water of protoplasm, but the colloids,

* At this place reference may be made to the fact that protoplasm subjected
to a high temperature sometimes breaks to pieces with the suddenness and com-
pleteness of an explosion. Thus Stkasburger ('78, p. 611) found that Chilo-
monas curvata was uniformly killed at 45° C. by the explosion of the body, and
Dr. W. E. Castle tells me that he has observed the same phenomenon under
like conditions in Stentor. An investigation of this profound change in pro-
toplasm would be sure to throw valuable light upon the nature of the living
substance.

240 HEAT AND PROTOPLASM [Ch.VIII

wliicli constitute the living part, are not modified by even the
lowest of the terrestrial temperatures, except that the molecular
changes which they undergo are very slow. This being true,
protoplasm which contains no water, or very little, ought not to
be changed by low temperatures, — that is to say, the machine
will not be injured.

With the activities of the machine — with the vital processes
— it is, however, quite different. They are essentially chemical
processes, and hence we should expect them to be diminished
at a low temperature. If, as Pictet ('93) maintains from an
extensive and highly important series of. experiments, no chemi-
cal processes take place at temperatures below — 100° C, then
protoplasm ought to exhibit no vital processes at this tempera-
ture, and, indeed, experience shows that, as we have already
seen, as the temperature is lowered below^ the optimum, all
manifestations of activity diminish. It is clear that at a certain
point they must entirely cease. And at that point death,
following the usual definition of the word, would ensue.

But does the cessation of the vital processes, without injury
to the mechanism, necessarily preclude the possibility of a
return to activity ? Let us examine the experimental evidence
on this point. Schumacher ('74, p. 179) subjected yeast to
cold and found that, at the lowest temperature produced
(— 113.7°), the yeast cells were not completely killed. More
recently, Pictet ('93% cf. also C. de Candolle, '81) has sub-
mitted various dry seeds and spores of bacteria to a temperature
of nearly — 200°, at which temperature the atmosphere becomes
liquefied, but without fatal effects. Other results were still
more remarkable : vibratile cilia from the mouth of the frog
were cooled to — 90°, and recovered their movement uj3on
raising the temperature. Some Rotifera and Infusoria were
frozen in their native water at — 60°, and kept at that tem-
perature, apparently, for nearly 21 hours. Most have subse-
quently regained their activity. Eggs of the frog, lowered
slowly to — 60°, can revive. Eggs of the silk-worm can resist
to —40°. Other experiments of Pictet* will be referred to

* This general criticism of Pictet's paper is, 1 believe, valid. He does not
give us data enough upon time of subjection to the low temperature, time em-
ployed in reducing the temperature, and other details. Thus, concerning his

§3] TEMPEKATURE-LIMITS OF LIFE 241

later. As a result of these and others' investigations we may-
conclude : Protoplasm may under certain circumstances, of
which one of the most important is the absence of water, resist,
uninjured, the lowest temperatures. There is no fatal minimum
temperature for dry protoplasm.

We must now turn our attention to those cases in which the
phenomena of cessation of activity or death appear, and seek
to determine their causes ; and first concerning temporary
cold-rigor. We have already seen that as the temperature is
lowered, the rate of metabolic processes and protoplasmic
movements is lowered. What happens at the lower limit of
activity, and where does this lie? The chlorophyll granules
of Vallesneria move (according to Veltek) only about 1 mm.
per minute at 1° C. and not at all at 0°; the rotation of Nitella
ceases (Nageli, '60, p. 77) at 0°C.; in Tradescantia hairs,
movement is wholly arrested on freezing the cell sap (Kuhne,
'64, p. 100, and Demoor, '94, p. 194). Even in seeds and
bacteria, which are not killed by the lowest temperatures, all
vital activities have probably ceased at 0°, for de Candolle
('65) found that in only one species out of ten could he get a
seed kept at 0° to germinate, and even then germination was so
retarded that it took from 11 to 17 days as opposed to 4 days
at 5.7°. Likewise, bacteria do not multiply below + 5° to
+ 10° (BoNARDi and Gerosa, '89). Among animals, Kuhne
('64, p. 46) found Amoeba cooled to near 0° almost motionless.
PuiiKiNJE and Valentin ('35) first noticed that the ciliated

experiments on Scolopendra, he merely says : " I have frozen to — 40° three
Scolopendras which perfectly resisted the treatment and lived after thawing out.
Submitted to —50°, they have also resisted. Frozen a third time to — 90°, they
are all three dead." Now, in the absence of further data, it is quite possible
that the heat of metabolism kept the internal body temperature considerably
above that of the chamber, the thick cuticula preventing rapid loss of heat, very
much as a man's clothing enables him to withstand the — 40° of an arctic winter.
Another experiment of Pictkt's lends greater probability to this explanation of
some cases of great resistance. Three snails were subjected to a temperature of
from — 110° to — 120° during several days. The operculum of two of these was
not intact, so that it did not close the orifice. These two individuals died ; but
the third, which was completely sealed up, survived. Those which were not
sufficiently clad, so to speak, lost so much internal heat that their internal fluids
were frozen. Of course this criticism cannot apply in the case of those organ-
isms mentioned in the text which are without a thick cuticula.

R

242 HEAT AND PROTOPLASM [Ch. VIII

epithelium of the frog ceased its movements at 0°. Muscles
of the frog were found by Kuhne ('64, p. 3) to become at
— 3° to — 7° a solid lump which did not, however, wholly lack
irritability. The evidence of all these cases shows that activity
nearly ceases in protoplasm at or near 0° C.

Another effect produced on protoplasm by cold — an effect
which often immediately precedes quiescence — is violent con-
traction. This has been repeatedly observed. The protoplasm
of Tradescantia hairs, which has been in cold-rigor, was found
by KQhne ('64, p. 101) to lie in separated rounded drops and
lumps, — an appearance like that resulting from excessive stimu-
lation. The rapid freezing of muscle gives rise, according to
HERMANisr ('71, p. 189), to violent contractions. The sciatic
nerve of, the frog's leg when cooled to — 4° to — 8° causes clonic
contractions of the muscle, lasting two minutes. (Affana-
SIEFF, '65, p. 678, and others.) It is clear, then, that cold acts
as a violent stimulus to protoplasm.

The final result of temporary rigor is thus clearly brought
about by the cooperation of two causes : (1) the diminution in
the chemical processes upon which metabolism and movement
depend, and (2) the directly stimulating effect of the cold,
which acts like contact or excessive heat. Both causes work
to produce a quiescence which may be replaced by activity
when the causes are withdrawn.

The fact that cold-rigor usually occurs close to the zero-
point indicates that the activities of protoplasm are closely
determined by the fluid state of water. This fact is not to be
explained on the ground that freezing prohibits all chemical
change — many chemical changes take place below the freez-
ing point of water, but, apparently, few of those which are
involved in metabolism. Nor is the rigor due to the change
which the freezing of the protoplasmic fluids brings, because
as the temperature approaches the zero-point, but while the
water is still perfectly fluid, metabolism diminishes ; and it
diminishes at such a rate as to cease just where water begins to
freeze. The critical point for vital activity has been adjusted
to this critical point of water.

So, too, the composition of protoplasm is such that at a tem-
perature, lying below the normal and above the freezing point

§3] TEMPERATURE-LIMITS OF LIFE 243

of water, those cliemical changes rapidly occur which we desig-
nate response to the stimulus of cold. This composition of
protoplasm, upon which cold can work such important modifi-
cations, is a quality of immense importance in the economy of
the organism, as the changes of each autumn testify.

Below the point of temporary cold-rigor lies that of death,
if death point there be. The position of the death point is,
however, very diverse in different organisms. Part of the
diversity in the death points assigned by different authors is,
however, due to the fact that in the methods of determining
the death points there has been a lack of uniformity.

Five elements ought always to be regarded in experiments
on the ultraminimum temperature. (1) History of the tem-
perature conditions in which the individual or its race had
lived before experimentation ; (2) rate at which the organ-
ism has been cooled, — if possible, the temperature of the
organism itself rather than that of the medium ; (3) inten-
sity of cold just sufficient to kill; (4) duration of applica-
tion of the cold and the kind of medium in which the
organism is subjected to the cold ; * and (5) the rate of
thawing out.f These elements have been too much neg-
lected in the past.

I shall now present in tabular form some of the more
reliable determinations of the death point of organisms, pref-
acing with the caution that the results are not closely
comparable.

* The duration of application and intensity of the fatal cold stand in an
inverse relation, so that organisms which resist a temperature — A° for A' min-
utes will resist a lower temperature, —(A + a)°, for a shorter time, JC — x.
Thus, Clepsine complana resists — 8°C. for 15 minutes ; — 5°C. for 90 minutes.
So Planorbis corneus resists — )° for 5 hours, but — 5° for 48 hours. x\gain,
Musca domestica can resist — 12" for 5 minutes; —8° for 20 minutes; and

— 5°C. for 40 minutes. (Roisdel, '86.) Since many authors have little re-
garded the duration of action of the cold, their determinations have little
scientific value.

t 'I'he importance of this is illustrated by some experiments of S.vcns
('60, p. 177), who found that the leaves of the beet or cabbage frozen at from

— 4° to — 6° died if they were thawed in air at 2° or 3°, or in water at 6^ to
10° ; but lived when slowly thawed in water at 0°. In general, the more gradual
the thawing, the lower the fatal temperature.

244

HEAT AND PROTOPLASM

[Ch. VIII

TABLE XX*

Determinations of the Ultraminimum op Organisms Reared dnder
Normal Conditions

Minimum

Conditions

Species,

AUTHOKITY.

Temperatuee.

OP Experiment.

Plant cells.

Tradescantia

-U° +

In water, rapidly ]

frozen |

KuHNE, '64, p. 100

Hair cells

— 14° —

In air, rapidly fro- \

zen J

Swarm-spores

- 1°

Fully frozen, cautious-

Strasburger, '78,

ly thawed

p. 612

Swarm-spores (Proto-

CoHN, '50, p. 720

coccus)

0° to — 1°

Protozoa.

Amoeba

0°-

Rapidly frozen on
slide over ice and
salt

KtJHNE, '64, pp. 46-47

Animal tissues.

"White blood corpuscles :

|- - 2° to - 3°

During 8 hours; warm-

SCHENK, '69, p. 26

of Amphibia

1 -7°

ed rapidly
For a short time;
warmed rapidly

" 26

of rabbit

- 3^

During 15 minutes

« 26

Saliva corpuscle ....

- 6° to - 8°

Over 60 minutes

" 27

Red blood corpuscle .

-15° +

Pouchet, '66, p. 18

Spermatozoa :

of Amphibia

-4° to -7°

SCHENK, '69, p. 29

of Mammalia ....

- 6°-

Returned to activity
on thawing

" 30

of frog

— 8°to-10° —

Frozen in testis

Prevost, '40.

of frog

-10° to -12°

Quatrefages, '53,
p. .353

of man

— 17°

Gradually thawed

Mantegazza, '66, p.
183

Eggs of Amphibia . . .

- 7°

During 1 hour

Schenk, '69, p. 28

f - 6°

Subjected a very short

Roth, '66, p. 189

Ciliated epithelium of

time

Anodonta

■j - 3°

Subjected during 6

" 189

I

minutes

* Temperatures all in degrees Centigrade. — before a number indicates below
zero, — or + after a number indicates that the true lethal teinpernture lay
slightly below or above that number. (A) indicates that the organism was in air ;
( W) , in water.

§3]

TEMPERATURE-LIMITS OF LIFE

245

Species.

Minimum
Temperatcke.

Conditions
of experlment.

AUTHOEITT.

Platy helminths.

Dendrocoelum lacteum

0° to - 1°

Suddenly or gradually
subjected, till ice
forms

Roedel, '86, p. 207

MoUusca.

Helix hispida

- 8°

During 30 minutes

" 191

Helix pomatia

-10°

Daring 600 minutes

" 192

Helix pomatia

(-li° to -18°)+

Gradually frozen for
180 minutes, and
then thawed

POUCHET, '66, p. 28

Helix hortensis ....

(—14° to —18°)+

During 180 minutes

" "

Helix aspera

(—14° to —18°)+

" 180

" "

Planorbis

— 7°

" 300 " {A)

Roedel, '86, p. 212

Limnsea

- 7°

" 180 " (A?)

" " 212

Pulmonate embryos .

0° to - 1°

" Died upon freezing "
(IF and A)

" 212

Limax

-17°+

During 2 hours (^)

PoucHET, '66, p. 26

Aimelida.

Aulastomum gulo . . .

- 2°

During 12 to 15 hours
(W)

Roedel, '86, p. 206

Clepsine complanata .

- 5°

During90minutes( W)

" 213

"Leech"

- 6°

" "some min-
utes" (W)

DOENHOFF,'72,p.725

Insecta.

Apis mellitica

-1.5°

During 210 minutes 1 Roedel, '86, p. 212

Apis mellifica

— 1.5°

" a few minutes

Doenhoff, '72, p. 724

Formica rufa

-1.5°

" 180 minutes

Roedel, '86, p. 196

PelopjBus (chrysalis) .

— 28° —

Out-of-doors, with-
stood this tempera-
ture

Wyman, '56, p. 157

Lema sp

- 6°

- 4°

During 30 minutes
•' 45

Roedel, '86, p. 197

PjEderus riparius . . .

" 197

Phytonomus sp

j2°

" 90

" 197

Meloloiitha

-18° +

" 120 " (A)

PoucHET, '66, p. 26

Meloloiitha (larva) . .

-15° +

" 180 " (A)

" 26

Cetoiiia |
Hydrophilus 1

-17° +

" 120 " {A)

" 26

Dytiseus

- 4°

" 60 " (A)

KocHS, '90, p. 682

Vanessa cardni, larva

-15°

" 600

Roedel, '86, p. 212

Vanessa io, larva . . .

-17° +

" 120

POUCHET, '66. p. 27

Sinerinthtis populi . .

-10°

" 150

Roedel, '86, p. 212

Ocneria dispar

- 4°

" 30 "

" " 212

Culex pipiens, larva .

- 4°

" 60

" 212

Musca

- 6° to - 10°

- 5°

" ISO
" 20

Doenhoff, '72, p.725

Miisca dom

Roedel, '86, p. 201

Various insects ....

0°

" 2 to 30 minutes

Plateau, '72, p. 98

(on ice)

246

HEAT AND PROTOPLASM

[Ch. VIII

Species.

Minimum

Temperature.

Conditions
OP Experiment.

Authority.

Arachnida.
Phalangium opilio .
Tegenaria domestica
Argyroneta aquatica
Hydrachna cruenta .
" Spider "

- 9°

- 6°

- 4°

- 4°
-2°to-

■3°

During 60 minutes
" 60
" 180
" 30
« 480

Crustacea.
Cyclops quadricornus
Cyclops spirillum .

Daphnia pulex . . .

Gammarus pulex .

Asellus aquations .

Astacus fluviatilus

Vertehrata.
Rana esculata . . .

OP

- 6°

0°
0°
0°
- 11.5°

-4° to— 10°

1

120

30

a day

■■{W)
■■{W)

■{W)

(Tr)|

{A)

180 minutes {A)

EOBDEL, '86, p. 201
" 201
" 201
" 201

DOENHOFF, '72, p. 724

Plateau, '72, p. 300
ROEDEL, '86, p. 201
" 201
Plateau, '72, p. 300
RoEDEL, '86, p. 205
Plateau, '72, p. 299
RoEDEL, '86, p. 205
PoucHET, '66, p. 32

19

Summarizing these conditions, we find that the following
organisms, even when thawed out carefully, are killed by sub-
jecting to a temperature of between 0° and — 5° for 60 minutes:
Amoeba, swarm-spores, white blood corpuscles of Amphibia,
planarians, pulmonate embryos, small leeches, certain entomos-
tracans, and some insects and spiders. These organisms are all
either soft bodied or of small size, and, excepting animals which,
like the bees, live in protected situations, they do not winter
over in our northern temperate countries. The following
species, on the other hand, resist — 10° for at least 60 minutes;
some snails (possibly), the beetles Melolontha (perhaps) and
Phytonomus, the Vanessa larva, Pelopieus chrysalis, and the
crayfish, — all protected by a thick covering, or of rather large
size. The reason why large size and thick covering should
increase resistance is not far to seek, — both conditions tend
to prevent the rapid loss of heat, — to defend the body from
freezing through and through.

Another cause of variation in resistance to cold is, doubtless,
the amount of water in the protoplasm. I have already referred
to this cause as explaining the fact that dry seeds and spores

§3] TEMPERATURE-LIMITS OF LIFE 247

can withstand almost any temperature.* MtiLLER-THURGAU
('80) found that the "succulent lahellum of Phajus freezes at
— 0.56° C. ; the succulent leaf of Sempervivum, at —0.7°;
the potato tuber, at — 1° ; the leaf of Tradescantia mexicana,
at — 1.16° ; the ivy leaf, at — 1.5°; the leaves of Pinus austri-
aca, at — 3.5°; young shoots of Thujopsis, at — 1°." (Vines.)
In this series of plant tissues, we see that the more succulent
the tissue, the higher its ultraminimum. Possibly the reason
why spermatozoa have so low an ultramaximum, despite their
small size, is on account of the denseness of their protoplasm.

Not all variations in ultraminimum temperature are, however,
explicable upon the ground of difference in size, body-covering,
or density of plasm. The interpretation of the difference in
sensitiveness to cold of the honey bee (Apis melifica) and the
red ant (Formica rufa), between Bombyx on the one hand and
Smerinthus and Vanessa on the other, must wait for further
knowledge.

The question now arises, Avhat is the cause of death in organ-
isms and protoplasm which succumb to low temperatures ?
With the higher animals the immediate cause is doubtless in
part asphyxia resulting from a stoppage in the flowing of the
frozen blood plasma, and in part the destruction of the red
blood corpuscles, as well as the white. f With the simpler
organisms, like planarians. Protozoa, or Tradescantia hair-cells
the case is different. An insight into the changes which pro-
duce death in such organisms may be gained from Kuhne\s
('64, p. 101) description of the effect of a temperature of — 14°
on Tradescantia hair-cells. The frozen hairs were placed in
water and observed under the microscope. " The appearance,''

* Striking cases are on record of the resistance of gemmules, or "animal
spores," to cold. Tims, Whltner ('93, p. 27(5) saw gemmules of Spongilla
fragilis frozen in an aquarium from December 26 to January 24, from the end
of January to February 5, from February 20 to March G, and from March 12
to 24 ; the intei'vals being occupied by thawings. Yet these gemmules produced
young sponges. In other cases, a certain amount of freezing favors the subse-
quent development of gemmules, e.g. those of fresh-water Bryozoa (Buaem, '90,
p. 83) and the eggs of the silk-worm (Duclaux, '71).

t PouciiET ('66, p. 18) found that when blood of the frog was let fall into a
capsule at a temperature of — 15° few of the red corpuscles were uninjured. In
most the nuclei had been cast out into the plasma.

248 HEAT AND PROTOPLASM [Ch. VIII

says KiJHNE, " was very remarkable, for there was no trace of
the protoplasmic network; but the violet cavity of the cell con-
tained, in addition to the naked nucleus, a large number of
separate round drops and lumps." In this case, the separate
pieces eventually became active again, so that the protoplasm,
though nearly killed, was not quite so.

The phenomena seen by Kuhne so closely resemble those
produced in the same kind of cells by the galvanic current and
other strong irritants as to indicate that cold acts as an intense
irritant. We cannot, however, conclude that cold acts in no
other way. It is clear that the expansion of forming ice in the
vacuoles of the protoplasm must seriously disturb the structure,
and, since the whole matter has received little attention, it is
possible that a molecular change of some sort takes place when
there is much water in the freezing protoplasm. To summarize:
Death by freezing results in the higher animals largely from
asphyxia, and in the simpler organisms from excessive irritation,
mechanical rupture, and, perhaps, other causes.

I shall now sum up this section on the effect of extremes of
heat and cold. As the temperature is elevated above the opti-
mum, molecular changes occur in the protoplasm leading to its
contraction. The contraction becomes more violent as the tem-
perature is still raised, until, finally, a new series of molecular
changes occur by which the protoplasm begins to coagulate.
At this point the protoplasm begins to lose its irritability. If
this process has not proceeded far, the vital activities may,
under favorable conditions, return (temporary heat-rigor) .
Beyond a certain point (death point) recovery is impossible.
The death point varies with the species, but lies not far from
the maximum natural temperature attained by the medium in
which they live. On the other hand, as the temperature is
diminished from the optimum, the chemical processes of
metabolism decrease in vigor and come to a standstill at about
the freezing point of water. Violent contractions accompany
the cooling process, concomitantly with which the protoplasm
breaks down. From this condition of temporary cold-rigor
recovery is still possible; but a little below, at a point dependent
upon the size of the body and the diathermous qualities of its

§4] ACCLIMATIZATION TO EXTREME TEMPERATURES 249

covering, the water of the body begins to freeze, and in that
process, or the subsequent thawings, the protoplasm undergoes
a (partly mechanical) change resulting in death. If the body,
however, contains no water, freezing cannot kill it.

Thus the effect of high temperatures is principally chemical,
involving the living plasma ; that of low temperatures is prin-
cipally mechanical, involving the water of the body. Both
raising and lowering the temperature act also as irritants.*
Finally, the positions of the maximum and minimum stand in
most intimate relation to the inorganic environment of the
organism and have been molded to that environment.

§ 4. Acclimatization of Organisms to Extreme
Temperatures

The phenomena to be discussed in this section fall naturally
into two subsections: (1) acclimatization to heat and (2) accli-
matization to cold. They will be considered in that order.

1. Acclimatization to Heat. — Our study of the maximum
temperature which organisms reared under ordinary circum-
stances can withstand, led us to the conclusion that few active
organisms can resist a temperature of over 45°, and for whole
groups like Coelenterata, marine MoUusca, and Crustacea, and
the fishes, 40° is a point of death. Yet, on the other hand, it
has long been known that there are organisms living in certain
hot springs in waters of considerably higher temperature. I
shall now give in tabular form some cases which I have
collected of organisms living at or above the normally lethal
temperature of the species, f

* Whether sudden change of temperature has an especial effect upon the
movement of protoplasm is a disputed question, which has been answered posi-
tively by DuTROCHET ('37, p. 777) and Hofmeister ('67, p. 53) for Nitella, and
DE Vries ('70, p. 394) for root hairs of Hydrocharis, but has since, as a result
of careful experiments, been denied by Veltner ('76, p. 214) for Nitella and
other plant cells.

t It is desirable that accurate data concerning the temperature of organisms
in hot springs should be made, and we have, in this country, unusually favorable
conditions offered for this study, especially in Arkansas, California, and the
Yellowstone National Park. It is to be hoped that persons who have had the
proper training should, when contemplating a visit to hot springs, provide them-

250

HEAT AND PROTOPLASM

[Ch.VIII

TABLE XXI

List of Species Eound in Hot Springs, with the Conditions under
WHICH they Occur

No*

Species.

Temp. C.

Locality and Condition op

Life.

AUTIIOKITY.

1
2

Chroococcus
Nostocs or Pro-

51° to 57°
93°

Benton's Hot Springs, Cal.
Geysers, Lake Co., Cal. ; not

Wood, '74, p. 34
Brewer, '66, p. 391,

tococcus

abundant at this tem-

also Wyman, '67,

3

Nostocs

51° to 57°

perature
Benton's Hot Springs, Cal.

p. 155
Wood, '74, p. 34

4

Anabtena ther-
malis

57°

Dax, warm springs

SERRES,'80,pp.l3-23

5
6

Leptothrix
Oscillaria or

44° to 54°
54° to 68°

Carlsbad Springs
Yellowstone Nat. Park,

CoHN, '62, p. 539
Weed, '89, p. 399

7

" Confervge"

54.4°

U.S.A.
Springs, Bernaudino Sierra,
Cal.

Blake, '53, p. 83

8

57°

Algeria, Constantino prov-
ince, waters of Hammam-
Meskhoutin

Gervais, '49, p. 12

9

«

57°

Hot Springs, Taupo, New
Zealand

Spencer, '83, p. 303

10

"

60° to 65°

Geysers, Lake Co., Cal.,

U.S.A.

Brewer, '66, p. 392

11

12

,j

60° to 65°

71°

Hot Springs, Ark., U.S.A.

(Long)
Hot Springs at Baiios Luzon,

James, '23, II, p. 291
Dana, '38-'42, p. 543

13
14

«

75.5°
81° to 85°

Philippines
Soorujkoona Hot Springs

Ischia

Hooker, J. D. '55, 1,
p. 24

Ehrenberg, '59, p.
493.

15

98°

Iceland

Flourens, '46, p.
934

16

?

Outlet of Lake Furnas,
Azores.

Dyer, '74, p. 324

selves with a hand lens, bottles of alcohol for preserving organisms for farther
study, and an accurately calibrated thermometer. A source of error to be
guarded against lies in the precise determination of the temperature of the water
immediately surrounding the organism observed; for in some warm springs or
their outlets the surface water is said to be much warmer than the deeper layers
in which the organisms are found. Finally, if possible, it would be desirable to
determine on the spot, experimentally, the maximum temperature which these
organisms can withstand. For this determination some of the methods referred
to on p. 220 should be used.

* Notes on each of these cases will be found at the end of this chapter, pp.
263-267.

§4] ACCLIMATIZATION TO EXTREME TEMPERATURES 251

Locality and Condition or

No.

Species.

Temp. C.

Life.

Adthoeitt.

Diatoms

Frequently associated with
other algae in hot springs

17

Physa acuta

33° to 35°

Sources of Dax, St. Pierre,
France

DUBALEN, '73, p. iv

18

Pal.udina sp.

50°

Thermal waters, Abano,
Padua

DE Blainville, '24,
p. 141

19

"Bivalve testa-
ceous animal "

?

Hot Springs, Ark.

MiTCHiLL, '06, p. 306

20

Rotifera and An-
guillulidflB

44° to 51°

Carlsbad Springs, Bohemia

CoHN, '62, p. 539

21

Anguillulidae

45°

Aix, springs

DE Saussure, 1796,
V, p. 13, § 1168

22

81°

Ischia, in hot springs

Ehrenberg, '59, p.
494

23

Cypris balnearia

45° to 50.5°

Hammam-Meskhoutin

Moniez, '93, p. 140

24

Stratiomys larva

69°

In hot spring, Gunnison
Co., Col.

Griffith, '82, p. 599

25

?

In hot spring, Uinta Co.,
Wyo.

Bruner, '95

26

"Water beetle"

44.4°

In warm spring, India;
abundant

Hooker, J. D. '55, p.
24

27

?

Hot spring, Port MoUer,
Alaska

Dall, W. H. (per-
sonal letter)

28

Barbels

34°

?

Bert, '77, p. 169

29

Frogs

38°

"Baths of the Pise"

Spallanzani, 1787,
Tom. I, p. 55

To summarize : Protista are stated to have been found in
nature in water at temperatures far above 60° C. The most
striking cases are of Oscillaria and " Conferva " from several
localities, which resist nearly up to the boiling point of water.
The closely allied Nostocs are, perhaps, next most abundant
and resistant, reaching 9;')° (possibly Protococcus) in the Cali-
fornia geysers. Metazoa are stated to live at temperatures
far above 45°. Although some doubt has been cast on No. 22
by Hoppe-Seyler's inability to confirm Ehrenberg's observa-
tions, the case seems established of Cj^pris thriving at 46° to
50.5°. Very extraordinary are the observations Nos. 24 and
25 on Stratiomys larvae, which, however, are sadly in need of
confirmation by competent observers. Leaving out of account,
for the moment, the less well established cases, there still
remains abundant evidence that orcfanisms can live and thrive

252 HEAT AND PROTOPLASM [Ch. VIII

in hot springs at a temperature near or above that which proves
fatal to their close allies.

No one doubts that in all the cases cited above the individuals
living in hot springs have been derived from ancestors which
lived in water whose temperature rarely exceeded 40° C. The
race has therefore become acclimatized, and the question arises :
How has that acclimatization been effected ?

Now experiments have shown that organisms, when gradually-
accustomed thereto, may resist a temperature which would have
killed them if they had been suddenly subjected to it. There-
fore it seems probable that the acclimatization of organisms to
hot springs has been a slow, long-continued process, during
which they have become gradually accustomed to higher and
higher temperatures, probably attaining the hot springs by
slowly advancing up their effluent streams.

This adaptation may have taken place without selection,
purely by the capacity of individual adaptation which organ-
isms possess. That individual adaptation is sufficient to account
for the vitality of organisms in hot springs has been shown by
experiment. Dutrochet ('37, p. 777) observed, long ago,
that an organism which at first seemed injured by a high
temperature gradually regained activity while still subjected
thereto.

Thus, he found, that the current of Nitella was at first diminished by-
raising' it to 27° C, but it soon became rapid again ; raised, now, to 34°, the
circulation began to fall off again, but in a quarter of an hour, the same
temperature continuing, the circulation became very rapid. This phenome-
non was repeated, also, at 40°. Similarly, Hofmeister ('67, p. 53) brought
Nitella flexilis suddenly from + 18.5° to + 5°C. The streaming movements
ceased. After staying 15 minutes in the cooler room, however, the rotation
of protoplasm recovei-ed.

Much more important, however, are the remarkable experi-
ments of Dallinger ('80). He kept Flagellata in a warm
oven for many months. Beginning with a temperature of
15.6° C, he employed the first four months in raising the tem-
perature 5.5° ; this, however, was not necessary, since the rise
to 21° can be made rapidly, but for success in higher tempera-
tures it is best to proceed slowly from the beginning. When
the temperature had been raised to 23°, the organisms began

§4] ACCLIMATIZATION TO EXTREME TEMPERATURES 253

dying, but soon ceased, and after two months, the temperature
was raised half a degree more, and eventually to 25.5°. Here
the organisms began to succumb again, and it was necessary
repeatedly to lower the temperature slightly, and then to
advance it to 25.5°, until, after several weeks, unfavorable
appearances ceased. For eight months, the temperature could
not be raised from this stationary point a quarter of a degree
without unfavorable appearances. During several years, pro-
ceeding by slow stages, Dallinger succeeded in rearing the
organisms up to a temperature of 70° C, at which the experi-
ment was ended by an accident.

In this case it is plain that the high temperature acted upon
the same protoplasm at the end of the experiment as it did
at the beginning. But while the protoplasm at the beginning
of the experiment was killed at 23° C, at the end it withstood
70°. It will be seen that, by gradual elevation of the tempera-
ture, Flagellata may become acclimated to a temperature of
water far above that which they can withstand when taken
directly from out of doors, and approaching that of the hottest
springs containing life.

A series of experiments, less extensive than that of Dal-
linger, was carried on by Dr. Castle and myself ('95, pp.
236-2^:0) upon the tadpoles of our common toad, Bufo lentigi-
nosus. Recently laid eggs were divided into two lots : one
lot was kept in a warm oven at a constant temperature of 24°
to 25°, others at about 15° C. Both lots developed normally,
but the former much the more rapidly. At the end of 4
weeks the point of heat-rigor was ascertained for each lot, by
gradually heating (in from 5 to 10 minutes) the water contain-
ing them, until the tadpoles showed no response to stimulus,
but, upon cooling, regained activity. The result was that the
toad tadpoles had gained an increased capacity to heat. For
when they were reared at a temperature of about 15° C, every
tadpole went into heat-rigor at 41° C, or below; whereas,
when they were reared at 24° to 25°, a temperature 10°
higlier, no tadpole died under 43°, the average increase of
resistance being 3.2°. This increased capacity of resistance
was not produced by tlie dying off of the less resistant indi-
viduals, for no deaths occurred in these experiments during

254 HEAT AND PROTOPLASM [Ch. VIII

the gradual elevation of the temperatures in the cultures. The
increased resistance was due, therefore, to a change in the
protoplasm of the individuals.

The question now arose : In how far is this change in the
protoplasm permanent? Will a return of tlie individuals to
cool water cause a return to the old point of heat-rigor ? We
made a few experiments on this subject which showed that
tadpoles which during 33 days in warm water have acquired
an increased resistance of 3.2° lose part of that acquired resist-
ance during 17 days' sojourn in cooler water. But the loss
is a very slow one. The effect of the high temperature on the
tadpoles is not, therefore, transitory, but persists — we have
not been able to determine how long — after the cause has been
removed.

So we may conclude : Individual organisms have the capacity
of becoming adapted to a high degree of temperature, so that a
temperature Avhich normally is fatal may be withstood. This
adaptation of the individual accompanies the subjection of
organisms to temperatures higher than those to which they
have already become accustomed. This capacity exists among
both Protozoa and Metazoa. The effect of the elevated tem-
perature persists (though in diminished degree) a considerable
time after the individual has been restored to a lower tempera-
ture.

Acclimatization may show itself not only in the change of
the maximum temperature, but also in the elevation of the
optimum. This is shown by the following experiments of
Mendelssohn ('95, p. 19). When Paramecia are placed in a
trough whose temperature is 24° to 28° at one end and 36° to
38° at the other, they are found to collect at the cooler end,
which indicates that the temperature of that end lies nearer
their optimum. If, however, the Paramecia, while uniformly
distributed in the trough, are subjected to a uniform tempera-
ture of 36° to 38° for from 4 to 6 hours, and then, in the same
trough, to a temperature varying from 24° at one end to 36° at
the other, they no longer collect at the usual optimum of 24° to
28°, but at 30° to 36°. Thus in 4 to 6 hours, by the action of
a temperature of 36° to 38°, the optimum has been raised 6°
to 8°.

§4] ACCLIMATIZATION TO EXTEEME TEMPERATURES 255

Since experiments have proved the fact of acclimatization, it
now remains to determine, if possible, its cause; to ansv/er the
question, by virtue of what property can organisms whi:h, like
Flagellata, normally perish at 45° C. come to live at 70° or
even higher temperatures ? We have seen that death at high
temperatures is apparently due to coagulation of certain proteids
in the protoplasm which undergo a chemical change at between
45° Mid 50° C Now, although the matter has not yet been
studied in these proteids, it has been shown for egg albumen
that in proportion as it is dried its coagulation point rises, as
the following table from Lewith ('90) shows : —

Egg Albumen.

Coagulation Temperature.

In aqueous solution

56° C.

With 25% water

74° to 80° C.

With 18% water

80° to 90° C.

With 6 % water

145° C.

Without water

160° to 170° C.

Since the coagulation point of egg albumen is raised by dry-
ness, it is very probable that a similar cause may act to raise
the coagulation point of protoplasm in organisms of hot springs.
Experimental studies are much needed upon this point. Mean-
while it can be said that one of the qualities which gives ca-
pacity of resistance to high temperatures is dryness. I shall now
cite some cases tliat I have collected, which prove this point.
It has been found that while moist yeast is killed at a tempera-
ture below 60°, dry yeast may be heated to 100° C. without
losing its vitality (SchOtzenberger, '79, p. 162). Damp
uredo-spores are killed at 58.5° to 60° C, but dry ones with-
stand up to 128° (Hoffman, '63); and drj^ spores of some
molds up to 120° (Pasteqii, '61, p. 81). Accordhig to Dal-
LTNCxER ('80, pp. 11-14), the dry spores of various Flagellata
are capable of withstanding a temperature from 10° to 27° C.
higher than that which these spores can resist in fluid. Accord-
ing to DoYERE ('42, p. 29), various animalcules (Rotifers,
Tardigrades) which cannot in water withstand a temperature
of 50° C. may, after long drying, be heated in air to 120° C.

256 HEAT AND PROTOPLASM [Ch.VIII

(rarely to 125°) without all dying. The foregoing cases show
clearly that increased resistance capacity is frequently gained
by subjecting the protoplasm of the organism to dryness.

But there are other conditions under which the living sub-
stance shows extraordinary resistance capacity. In general, as
is well known, the spores of organisms withstand higher tem-
peratures than the motile stage, when both are in water. This
rule holds for many cases : The spores of some bacteria may be
heated for a time above 100° C. without killing them, although
their motile stage is killed by 50° to 52° (Lewith, '90).
Dallinger and Drysdale ('74, p. 101) and Dallinger
('80, pp. 13, 14) have determined maximum temperatures for
several Flagellata and their spores in water. While none in
the motile stage could withstand a temperature higher than 61°,
the spores in water withstood maximum temperatures varying
between 65.5° and 131° for the different species.

Have the high resistance capacity of dry protoplasm and that
of spores a common cause ? Or, in other words, is the proto-
plasm of spores especially free from water ? Many observations
make it appear probable that this is so.

Thus in the case of bacteria, the protoplasm of the spore
stage is optically denser and occupies less space than in the
motile stage. (Cf. Lewith, '90.)

In the case of the ciliate Infusoria, the larger size of the
protoplasmic mass makes the comparison of the condition of
the protoplasm in the two stages easier. We glean the facts
from BiJTSCHLi ('89, pp. 1652-1651). As the process of encyst-
ment proceeds, the contractile vacuole continues to function,
the intervals between its contractions gradually increase, and
finally it disappears some time after the encystment is com-
pleted. Hand in hand with these changes goes a gradual con-
densation of the protoplasm. This condensation Butschli
believes to be due to an excretion of water from the proto-
plasm.

In Actinosphserium the change from the richly vacuolated
motile form to the encysted condition is even more marked.
As Brauer, ('94, p. 193) lias shown, the protoplasmic mass
becomes, during the process of encystment, smaller and denser.
The loss of water from the protoplasm is without doubt due to

§4] ACCLIMATIZATION TO EXTREME TEMPERATURES 257

the continued activity of the contractile vacuole at a time when
no fluids are being taken into the protoplasmic body.

From the foregoing considerations it appears probable that
one of the important characters of " spores " is the diminished
amount of free water held in the protoplasm; or, in other
words, its dryness. This dryness of the eoagulable substance
would seem to be cause of its higher resistance.

So far the evidence seems complete. Whether, however, loss
of water is the ultimate cause of the high resistance capacity
of hot-spring organisms or of those gradually acclimatized is
still uncertain. Analogy renders it highly probable that such
is the case.

2. Acclimatization to Cold. — Just as organisms may become
acclimatized to high temperatures, so also may they live in very
cold regions. I cite a few examples : Several species of Pro-
tista are said to live in the Alps above the snow line, coloring
the snow red. (Shuttleworth, '40.) A tardigrade is found
in the same locality. Certain insects live on or in the snow or
ice. Thus Desoria glacialis (or glacier flea) lives on the Swiss
glaciers, and on the snow live Podura hiemalis, Trichocera
brumalis (when the temperature is " below the freezing point,"
Fitch, '46, p. 10), and other species of Trichocera and Podura.
Cf. also Boreus hiemalis and B. brumalis (Fitch). Although
swarm-spores are usually extremely sensitive to cold, Stras-
BURGER ('78, p. 613) cites a case of a marine alga in which
they were being formed and tlirown out when the temperature
of the water was between —1.5° and — 1.8°C.

Increased resistance to cold seems often the result of the
action of cold on the organism. Thus, while Schwarz ('84,
p. 69) found that Euglense gathered in the summer tiiiie were
not responsive below + 5° to + 6° C, Aderhold ('88, p. 320)
found that Euglente gathered in the winter would respond
even at 0°. We may say, tlie winter cold had in some way
lowered the heat attunement of these Protista.

In seeking for an explanation of acclimatization to cold we
should recall that the cause of death from cold is chiefly the freez-
ing of water in the protoplasm, and the irritation of excessive
cold. Accustomed to great cold, protoplasm would doubtless
be no longer irritated by it ; whether under these circumstances

258 HEAT AND PROTOPLASM [Ch. VIII

it would contain less water is a question which lacks an experi-
mental answer.

The conclusion from the results offered in this section is
this : protoplasm may become so modified through the action
of excessive heat or cold that it is no longer killed at the ordi-
nary fatal temperatures. This result is partly due to the fact
that it is then not so strongly irritated by these extreme tem-
peratures, and partly owing to the fact that the coagulation
and freezing points have been shifted, possibly through loss
of water.

§ 5. Determination of the Direction of Locomotion
BY Heat — Thermotaxis

Our knowledge of this subject is still in its infancy and de-
pends chiefly upon the observations of Stahl ('84), Ver-
WORN ('89, pp. 67-68), Graber ('83 and '87), Loeb ('90, p. 43),
DE WiLDEMANN ('94), and Mendelssohn ('95). The first
two and the last two mentioned have employed Protista, and
we may consider their work first.

Stahl's studies were made upon Myxomycetes. He used
two beakers, of which one was filled with water at 7°; the
other with water at 30°. These were placed near each other,
and a strip of filter-paper, on which lay the plasmodium of
TEthalium septicum, was stretched between them. The two
ends of the strip with the corresponding ends of the plasmo-
dium hung into the two glasses. The result was that the
Plasmodium moved from the colder water toward the warmer,
although before the experiment it was moving in the opposite
direction. Wortmann ('85) added the observation that when
the warmer temperature rose above 36° a repellent action of
the warmer water was discernible.

Verworn experimented chiefly with Amoeba. The difficulty
in this operation depended upon the necessity of warming only
a part of the body of so small an animal. He used a glass plate
of 5 sq. cm. area, to the upper surface of which was glued a
piece of black paper, in which had been cut a rectangular open-
ing, 3 sq. mm. large, and with very sharp edges. This plate
was placed on the stage of the microscope so that the hole lay

§ 5] THERMOTAXIS 259

in the rays of the infalling, concentrated light of midsummer,
reflected from the mirror. Upon the black paper was placed
the cover-glass with the amoeba in a drop of water. The light
from the mirror was cut oif until the amoeba, in its migrations,
lay half-way over the edge of the orifice. Then concentrated
light was let through the slit. A small part of the body was
still moved across tlie line of demarcation; then for a moment
movement ceased and a few seconds after the protoplasm of the
amoeba began to flow backwards. In from 10 to 30 seconds
the amoeba was wholly in the dark again. Similarly, when the
cover-glass was moved so that the amoeba was brought half-way
over the open orifice it retreated into the dark. Direct measure-
ment showed that the temperature at the illuminated part was
40° to 50° C, Avhilst over the black paper it was 15° to 20° less.
That the movement was not due to the light was shown first
by cutting out, by means of ice, the heat rays only. No reac-
tion occurred. Secondly, by cutting out the light but not the
heat, by j)assing the light through a solution of iodine in CSg
so that only the ultra-red rays (which act like darkness to all
organisms) went through; the typical reaction occurred when
the temperature over the slit was 35°. From all of these ex-
periments the conclusion seems justified — Amoeba is positively
thermotactic towards that temperature.

Similar results were obtained by Verworn with the shelled
Rhizopod Echinopyxis aculeata, and later (see Jensen, '93,
p. 440) with Paramecium. More complete studies on the
latter were, however, made by Mendelssohn, who Avorked in
Verworn's laboratory. Mendelssohn devised an excellent
method of study. A brass plate 20 cm. x 6 cm. and 4 ram.
thick is properly supported in a horizontal position, and to its
under face are affixed, transversely, tubes through which hot
or cold water may be run from a reservoir placed at a high
level. In the middle of the plate a space 10 cm. x 2 cm. and
2 mm. deep is cut out and into it is fitted a glass or ebonite
trough. Special thermometers whose bulbs are coiled in the
plane of the trough, and hence perpendicularly to the stem,
serve to measure the temperature of the water in the trough at
any point. By means of water running through the transverse
tubes either end of the trough may be heated or cooled as

260

HEAT AND PROTOPLASM

[Ch. VIII

desired. Starting now with the trough filled with infusion
water, the Paramecia are seen to be uniformly distributed
(Fig. 71, a). Hot water is run through tubes under the right
end of the trough. After 10 minutes the thermometers show
the temperature of the water at the right end to be 38°, at the
left end 26°. At this moment, all Paramecia are in the left
third of the trough (Fig. 72, 6). If now the hot water be
passed through the left tube only, the temperature rises at
that end to 36° or 38°, falling to 27° or 28° at the other, and

1

■

73"

73 S

'1\

"

26-

38^

' ,7 '

10^

25?

Fig. 71. — Distribution of Paramecium in a trough of water with variable temperature
at the ends. (From Mendelssohn, '95.)

the Paramecia swim to the right end. Thus, with reference to
a temperature of 38°, Paramecia are negatively thermotactic.

If, now, cold water be passed through the left tube so that
the temperature of the left end of the trough falls to 10°,
while the right end is at 25°, the Paramecia migrate to the
right end. Towards a temperature of 25° Paramecium is thus
positively thermotactic (Fig. 72, c).

Finally, if cold water be passed through the tube at one end
of the trough and hot water at the other, the organisms will be
found accumulated in the middle of the trough where the tern-

§ 5] THERMOTAXIS 261

perature ranges from 24° to 28° C. This temperature is thus
the optimum temperature for Paramecium, tlie temperature
towards which it tends to move when the extremes are offered
to it. Using another nomenclature, we may say, Paramecium
is attuned to a temperature of 24° to 28° C.,* and tends to keep
in the temperature to which it is attuned.

Similar results have been obtained by de Wildemanx ('94)
from Euglense which were kept in damp sand and in the dark,
in a horizontal test-tube warmed at one end. Under these
conditions they migrated towards the temperature of 30° rather
than that of 15 to 22°.

Finally, we may consider thermotaxis as it is revealed in the
higher animals. Loeb ('90, p. 43) enclosed the larvse of the
bombycid moth Porthesia in an opaque box, one end of which
was next the stove. The animals moved to the warmer end of
the box. The migration differed, however, from migrations
with reference to light in that the body was not definitely
oriented with reference to the source of heat, but the larvse
wandered thither. Similarly some ants (Formica sanguinea)
are thermotactic according to Wasmann ('91, p. 22); and the
cockroach (Gkaber, '87, p. 254) moves towards that tempera-
ture which is more nearly normal for it. Graber ('83, p. 230)
has likewise shown that the salamander Triton is similarly
responsive. Thus some Metazoa as well as Protista are clearly
thermotactic.

Looking now for the cause of thermotaxis, we see at the out-
set that it is necessary to distinguish between two possibilities :
a movement towards a greater or less intensity of heat, and a
movement with reference to the direction of the heat rays in
radiant heat. Now we have seen in earlier chapters, in con-
sidering the action of gravity, the electric current, and light,
that these agents determine the direction of locomotion by
determining the orientation of the axis of the bod}-; and since
radiant heat passes in lines, it might be possible to have a
similar effect here. But there is no evidence that radiant
heat acts here. In the case of the Myxomycete, it is clear that

* Adequate control experiments with dead Paramecia and fine suspended
particles demonstrated that the movement was not purely passive ; i.e. due to
cnrronts in the water.

262 HEAT AND PROTOPLASM [Ch. VIII

a difference in the temperature of the two ends is sufficient
to determine direction of locomotion. In the case of Para-
mecium, it is improbable that radiant heat acted, since this
passes with difficulty through water. Finally, in the case of
the insects enclosed in a box there is evidence of no axis ori-
entation, and in the case of Verworn's experiments with the
Amoeba the action of direction is clearly shut out. We must
therefore conclude that direction of locomotion in thermotaxis
is not usually, if ever, determined by direction of heat rays.

Since it is not direction of heat rays, it is probably difference
of intensity of the agent at the two poles of the organism
which is the determining factor. This is clearly so in the case
of the Myxomycete and Amoeba. In the case of insects also, it
is clear that one part of the body being appreciably nearer the
source of heat would be appreciably warmer than the other,
and this difference in temperature might serve as an indication
to the organism of the direction of the source of heat. But
when we come to consider Mendelssohn's experiments on
Paramecium, we pause to think of the organism being so
sensitive as to be affected differently at the two poles by so
slight a difference of intensity as these poles must experience.
Mendelssohn has found that the least difference of intensity
at the ends of his 10 cm. long trough which will call forth a
thermotactic response is 3° C. The length of a Paramecium
is about 0.2 to 0.25 mm., which corresponds to a difference
of 0.01° C. of temperature at its two poles. This is the minimal
temperature-difference which acts as a stimulus to Paramecium
and calls forth a thermotactic response. Although this differ-
ence is small, we must, with Mendelssohn, in the absence of
opposing data, consider it the determining factor in thermo-
taxis, and conclude that, in general, the thermotactic response
is a response to differences in the intensity of heat to which
the two poles of the body are subjected.

Let us now sum up the results of our study of the effect of
heat on protoplasm. The rates of the metabolic processes and
of protoplasmic movements are controlled by temperature, since
they diminish from the optimum slowly towards the minimum
and rapidly towards the maximum. At these points movement
and irritabilitv cease as a result of excessive stimulation, and

NOTES TO TABLE XXI 263

either the beginning of coagulation (maximum) or the cessa-
tion of chemical change (minimum) appears. Finally, death
takes place at the ultramaximum through coagulation of the
proteids, Avhile it may occur beyond the minimum also, if the
protoplasm contains much water. The optimum temperature
is unlike in the different species, and certain individuals even
may gain a very high or low optimum (lying even beyond the
normal extremes) through the process of gradual acclimatiza-
tion. The acclimatization seems to be due to the direct action
of the varying environment upon the constitution of protoplasm.
Finally, many simple organisms (probably all protoplasm) re-
spond to heat by a locomotion which is adapted to keep them
at the temperature to which they are attuned. The movement
seems to be determined by the difference in intensity of heat at
the different parts of the body. This whole chapter reveals
protoplasm as a substance whose integrity is limited by chemico-
physical conditions. Within those limits, however, it is highly
sensitive to changes in temperature, becoming so altered by an
untoward temperature as not to be injured by it, or migrating,
if possible, so as to keep in the temperature to which it is
already attuned. In a word, protoplasm shows itself to be a
highly irritable, automatically adjustable substance.

NOTES TO TABLE XXI (p. 250)

1. The Chroococcus was found in some of the fronds of Nostocs from Owen's
Valley (see No. 3) ; but it is not stated whether they were in those Nostocs
which were derived from the hottest springs.

2. No details are given by Brewer concerning the method of determining
temperature. " In these warm mineral waters low forms of vegetation occur.
The temperatures were carefully observed in many cases. The highest tem-
perature noted, in which the plants were growing, was 93^ C. (about 200° F.).
But tliey were most abundant in waters of the temperature 52° to ()0° (125° to
1 10° F.). In the hotter springs the plants appeared to be of the simjjlest kind,
apparently, simple cells of a bright green color; but they were examined only
with a pocket lens. In the water below, about 60° to 65° C, filamentous Con-
fervpe formed considerable masses of a very bright green color." In a letter to
WvMAN, however, Bueweu says, concerning the same locality and determina-
tions: "The temperatures given here were carefully observed with a standard
Centigrade thermometer, with a naked elongated bulb," and "at the higher
temperature [93° C] they [the vegetable forms] were not abundant and existed
as grains like Nostoc or rrotococcus, intensely green and rather dark."

264 HEAT AND PROTOPLASM [Ch. VIll

3. The temperature determinations, like the organisms, came from a Mrs.
Partz, who is vouched for as reliable. No details concerning the method of
obtaining temperatures are, however, given. The springs form a basin from
vfhich flows a creek. "In the basin," says Mrs. Partz, "are produced the
first forms [Nostoc] partly at a temperature of 121° to 135° Fahr. Gradually
in the creek, and to a distance of 100 yards from the spring, are developed, at a
temperature of 110"-120°Fahr., the algae," etc.

4. Not seen by me.

5. CoHN states : " Therm ometerbeobachtungen zeigten in verschiedener Tem-
peratur des Wassers verschiedene, sclion durch die Parbe erkennbare Arten ;
zwischen 43° und 35° H., die hellgriine Leptothrix, zwischen 35° und 25° die
Oscillarien, Mastichocladen, etc., gesellt mit Raderthieren, Infusorien und Was-
seralchen ; in noch abkiihlterem Wasser die farblose Hygrocrocis nivea ; Was-
ser iiber 44° enthalt keine lebendeu Organismen. Ganz dasselbe fand Agardh
1827."

6. No statement as to the method of determining temperature. The meas-
urements were made in the outlet to a hot spring. In this outlet Hypeothryx
laminosa flourished at 68° and occurred at even a higher temperature.

7. This account also leaves something to be desired as to definiteness:
" Small springs rise at intervals of 10 to 20 feet along a distance of 30 to 40
rods. Their waters unite and form a little stream that empties into a brook a
short distance below. ... A dense mass of beautiful green confervse grew
about the bottom and sides of the channel, and floated in rich waving masses in
the hot water. In the immediate vicinity of the springs, however, no vegetable
growth appears. . . . The temperature of the hot stream, below all the springs,
was found to be 130°."

8. Gervais' account is detailed, but the method employed in determining
temperature is not given. The principal sections of interest are as follows :
" Nous avons dit que I'eau au moment ou elle s'^chappe des sources avait donn^
k notre thermomfetre + 95° cent." [It cooks eggs, meat, beans, etc.] " II est
inutile de dire qu'on ne trouve en cet endroit aucun animal ne aucun v^g^tal
aquatique vivant. Cependant on voit courir sur les cones d'ou jaillit I'eau
bouillante, et en des points ou le pied ^prouve, meme k travers lachaussure, un
senlimenL de vive chaleur, de petites Araign^es qui m'ont paru etre du genre
Lycose. Quelques-unes s'aventurent meme et cela sans inconvenient h travers la
surface des petits cral6res remplis d'eau chaude que presentent les cones dont 11
s'agit. Dans la substance calcaire ^galemeut fort chaude d'un de ces cones que
nous percions k coups de pioche pour en faire sortir I'eau bouillante par le flanc,
nous avons trouv^ plusieurs exemplaires vivants d'un petit Col^optfere de le fa-
mille des Hydrophiles, V HydroMus orMcularis, qui y avaient fix6 leur demeure.

"L'eauk +95° qui sort de diff^rents points d'Hammam-Meskhoutinperdassez
rapidement cette temperature eievde. Elle n'a (\€]k plus que 57° dans les vas-
ques du second tiers de la cascade, dans lesquelles on commence a trouver des
productions cryptogamiques. Celles-ci sont en partie couvertes d'un enduit
ferrugineux assez ^pais."

9. Plants found in samples of water from Taupo, "growing in water the
temperature of which varied from 105° P. to 131°." Two individuals are given
as occurring at "temp. 136°"; two at "temp. 116°."

10. See note 2.

NOTES TO TABLE XXI 265

11. The reference reads : " Not only confervas and other vegetables grow in
and about the hottest springs, but great numbers of little insects are constantly
sporting about the bottom and sides." The temperature of the various springs
runs from 92° to 151° F.

12. Dana says: "A species of feathery vegetation occurs also upon them
[the stones of the brook], bordering the streamlets where the temperature is
160° F., and presenting various shades of green and white."

1.3. Data concerning temperature incomplete. "Confervse abound in the
warm stream from the springs, and two species, one ochreous brown, and the
other green, occur on the margins of the tanks themselves, and in the hottest
water; tl*e brown is the best salamander, and forms a belt in deeper water than
the green ; both appear in luxuriant strata, wherever the temperature is cooled
down to 168°, and as low as 90°."

14. This seems a carefully observed case. Hot water flowed from the clefts
of the rock. "Die flache und schroffe Felswand worauf das heisse Wasser
rieselnd und tropfend herabfloss war mit 2 fingerdicken hell und dunkelgriinen
Oder auch gelben, rothlichen und braunen Filzen iiberdeckt. In diese Filze an
den Spalten eingesenkt zeigte das Thermometer 65 bis 68° R., entfernter von
der Spalte schnell abnehmend weniger. Die organischen Filze waren so heiss,
dass sie mit den Fingern nicht fassbar waren." Examined microscopically, the
mass was found to consist partly of dead, partly of living " Eunotia forms"
overgrown with Oscillaria. A similar condition was found also " in der Sclilecht
der Acqua della Kita bei eine Temperatur von 59° R. . . . Ich untersuchte in Serra-
valle aufgefangenes Wasser von 65° R. Warme, welches ich in ein Glas laufen
liess, wahrend ich die felzige Masse druckte. Es war sehr voU von vielartigen
lebenden kleinen Thieren. Darunter war 4 Arten munter bewegter Rader-
thiere, namlich Diglena Catellns, Conurus uncinatus, die Abanderung des
Brachionus Pola mit kleinen Stirnzahnen am Schilde, auch Philodina erythro-
phthalma, ausgebildete Eier im Innern fiihrend. Von Polygastern fanden sich
in frischer Lebensthatigkeit eine noch unbekannte eigenthiimliche, kleine Nas-
sula, Formen von Enchelys und Amphileptus von weniger sich auszeichender
Gestaltung. Besonders auffallend war die lebende Eunotia Sancta Antonii der
Capverdischer Inseln, deren Lebenszustand und Lebensbedingungen hierdurch
zum erstenmale bekannt werden." Despite the evident care taken to obtain
accurate results, Ehrenherg's observations have not been confirmed by Hoppe-
Seyler ('75, pp. 119, 120), who examined Ischia, but found no algae living at a
temperature much above 60°.

15. The entire reference is this : "M. Flourens met sous les yeux de I'Aca-
d^miedes conferves recueillies en Islande par M. Descloizeaux, qui lesa trouv^es
v^g^tant dans la source thermale de Grof, k une temperature de 98 degrds" [of
cour.se, C.]. Hooker ('13, p. 160) is often quoted as having obtained vegeta-
tion in Icelandic hot springs. Unfortunately, he gives no temperature deter-
minations. He says: "Close to the edge of many of the hot springs [vicinity
of the Great Geyser], and within a /e?o inches of the boiling water, in places
that are, consequently, always exposed to a considerable degree of heat, arising
both from the water itself and the steam, I found Conferva iimosa Dillw. in
abundance." Again, " In water, also, of a very great degree of heat, were, both
abundant and luxurious, Conferva flavescens of Roth and a new species allied
to C. rivularis.''*

266 HEAT AND PROTOPLASM [Ch. VIII

16. The temperatures were not taken on the spot, Moselet says: "The
water from which the Algae were gathered was in the pools from which the
Chroococcus was collected as far as I can now [i.e. many months after (V)] judge
after testing water of successive temperatures with my finger, about 149°-
158" F. The water of the sulphur-springs, in the area splashed by which the
Oscillatoria are found, is quite scalding to the hand, and probably between 176°
to 194° F."

17. The reference reads: "Dans celle [source chaude] de Saint Pierre, dont
la temperature varie de 33 k 35 degrfe, les Physa acuta, Drap. sont en nombre
si considerable qu'elles forment un veritable fond mouvant dans les canaux."
These hot water molluscs, as experiment showed, were killed at {Jaout 43°,
while Physa from ordinary sources die at once at 35°. They perished after a
few hours at 5° or 6°.

18. Merely the note: "On en [living mollusca] trouve aussi dans des eaux
thermales : par exemple le turbo thermalis, espfece de paludiue sans doute, vit
dans celles d'Abano, dont la temperature est de 40° R."

19. The statement is not critical: "Their heat [hot springs] is too great
for the hand to bear; the highest temperature is about 150°." "In the hot
water of these springs a green plant vegetated, which seemed to be a species of
conferva growing in such situations: probably the fontenalis. But what is more
remarkable, a bivalve testaceous animal adhered to the plant, and lived in such
a high temperature too."

20. See note 5.

21. " J'ai mesure plusieurs fois & en diverses saisons, la chaleur de ces eaux,
& je I'ai toujours trouv6e k tr^s-peu pr6s la meme ; savoir, de 35 degr^s dans
celle du soufre, & de 36^ ou 36.7 [R. from context] dans celle de St. Paul.
Malgre la chaleur de ces eaux, on trouve des animaux vivans dans les bassins
qui les regoivent ; j'y ai reconnu des rotifdres, des anguilles & d'autre animaux
des infusions. J'y ai meme d6couvert en 1790, deux nouvelles especes de
tremelles dou6es d'un mouvement spontan^."

22. See note No. 14.

23. Many individuals collected by R. Blanchard "dans les eaux de thermes
du Hamman-Meskhoutine, prfes Guelma, dans les premiers jours d'avril ; I'eau
des thermes, au point de la r^colte, a une temperature de 45° et de 50.5° C.
Les Cypris formaient une sorte de zone continue, de couleur chocolat, sur le
bord de I'eau."

24. Found "in a hot spring, temperature 157° F., attached to the rock by
the long end at about an angle of 45° and continually moving. . . . The rocks
were covered with them."

25. The note in "Insect Life" is abstracted from a longer article by Bruner
in the newspaper called the Lincoln (Nebraska) "Evening Call," for April 6,
1895. The article, through the kindness of Professor H. B. Ward of the Uni-
versity of Nebraska, I have now before me. The larvae were sent to Professor
Bruner by John C. Hamm, of Evanston, Wyoming, upon whom this stat' ment
of the conditions of life of the organisms depends. The larvae were found in a
cup-shaped depression in the top of a small isolated cone about 20 inches high,
situated about a few feet from a large sulphur mound or "dune," under which
one could hear the rumbling of boiling water. Through apertures in the bottom
the almost boiling water came up into the cup and ran over the edge of the pot.

LITERATURE 267

The larvae were actively moving. Mr. Hamm vsrrites to Mr. Bruner : "I did
not have a thermometer V7ith which to take the temperature, but . . . the water
was so hot when I saw them that I could not hold my hand in it. My best
judgment is and was at the time that the water was not moi'e than twenty or
thirty degrees [Fahr., of course] below the boiling point."

26. "A water beetle abounded in water at 112° " [F.].

27. Too hot for the hand to bear more than a moment or two.

28. The reference is to a discussion of a paper by Bert. " M. Paul Bert a
vu des barbellons dans de I'eau h 34° C."

29. " Mon ami Mr. Cocchi," says Spallanzani, " raconte que les Grenouilles
ne souffrent point dans les bains de Pise, quoiqu'elles soient expos^es k une
chaleur indiqji^e par le 111° du Thermometre de Fahrenheit qui correspond au
37° du Thermometre de Reaumur [! sic]."

LITERATURE

Aderhold, R. '88. (See Chapter I, Literature.)

Affanasieff, N, '65. Untersuchungen iiber den Einfluss der Warme und

der Kalte auf die Reizbarkeit der motorischen Froschnerven. Arch.

f. Anat. u. Physiol. 1865. pp. 691-702.
Artaud, J. B. L. '25. Essai sur la phosphorescence de I'eau de la mer.

Bull. sci. nat. (Ferussac). VI, 130, 131.
Bert, P. '67. Memoire sur la physiologie de la Seiche (Sepia officialis Linn.).

Mem. Soc. Sci. Bordeaux. V, 115-138.
'67". Sur la mort des animaux k sang froid par Taction de la chaleur.

Mem. Soc. sc. phys. efc nat. Bordeaux. V, xxii.
'76. Sur I'influence de la chaleur sur les animaux inferieurs. C. R. Soc.

de Biol. Paris. XXVIII, 168.
Blainville, de '24. Article Mollusques in Diet, des Sci. Nat. T. XXXII,

141.
Blake, W. P. '53. Geological Report, in Explorations and Surveys for a

Railroad Route to the Pacific Ocean. Vol. V. War Dept. U.S.A.
BoNARDi, E. and Gerosa, G. G. '89. Nouvelles recherches par rapport k

I'influence de certaines conditions pliysiques sur la vie des microorga-

nismes. Arch. Ital. de Biol. XII, 89-93. 28 July, 1889.
Braem, F. '90. Untersuchungen iiber die Bryozoen des siissen Wassers.

Biblioth. Zool. II. 134 pp.
Braukr, a. '94. Ueber die Encystirung von Actinosphaerium Eichhorni

Ehrhg. Zeitschr. f. wiss. Zool. LVIII, 189-221, Taf. x, xi.
Brewer, W. H. '66. Observations on the Presence of Living Species in

Hot and Saline AVaters in California. Am. Jour. Sci. XLI, 391-

394.
Broca, p. '61. (See Chapter II, Literature.)
Bruner, L. '95. Animal Life in Thermal Springs. Insect Life. VII, 413-

414.

268 HEAT AND PROTOPLASM [Ch. VHI

BiJTSCHLi, O. '84. Protozoa. Bronn's Klassen u. Ord. d. Thierreichs.

I Bd., II Abth. 785-864.
'89. The same. Ill Abth., Infusoria, pp. 1585-2035.
Callibukces, p. '58. Recherches experimentales sur I'influence exercee

par la chaleur sur les manifestations de la contractilite des orgaues.

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LITERATURE 271

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272 HEAT AND PROTOPLASM [Ch. VIH

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LITERATURE 273

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T

CHAPTER IX

GENERAL CONSIDERATIONS ON THE EFFECTS OF CHEM-
ICAL AND PHYSICAL AGENTS UPON PROTOPLASM

In the present chapter it is proposed to consider certain
general matters upon which the facts given in this First Part
throw light : namely, (I) the structure and composition of
protoplasm ; (II) the limiting conditions of metabolism ;
(III) the dependence of protoplasmic movement upon metabo-
lism and external stimuli ; and (IV) the determination of the
direction of locomotion.

§ 1. Conclusions on the Structure and Composition
OF Protoplasm

The question of the structure of protoplasm is preeminently
a histological one. Microscopical study must eventually be re-
lied upon to settle it. However, the results of experimental work
seem to favor, as we have already pointed out (p. 70), Butschli's
view of a honeycomb, or foam structure, of protoplasm.

The problem of the constitutioii of protoplasm is, on the other
hand, preeminently a chemical one, and it must be solved by
experimental methods. Our results can lead us to certain
qualitative statements on this matter.

The chemical composition of protoplasm is immensely com-
plex. Just as the geologist is forced by the facts to assume a
vast, but not infinite, time for earth building, so the biologist
has to recognize an almost unlimited complexity in the consti-
tution of protoplasm.

The evidence that protoplasm is so complex is gained partly
from the results of micro-chemistry. Many staining fluids act
upon only a small part of the protoplasm of a single cell, so
that a mixture of stains may be used, each component of which

274

§ 2] LIMITING CONDITIONS OF METABOLISM 275

attacks a different constituent of the protoplasm. In this way
the dissimilar substances in protoplasm are made strikingly
apparent. Not only does the protoplasm of one cell show this
differentiation, but that of different cells of the body stains very
diversely. Another line of evidence for the complexity of pro-
toplasm is gained from the study of the effect of poisons. We
have seen that the same poisonous substance acts very differently
upon allied species of organisms (e.g. of bacteria) and upon the
various organs of the body, — a fact which in many cases can
only be accounted for on the ground of dissimilar composition.
Again, most protoplasm must contain substances which are
acted upon specifically by the different agents ; for instance,
certain highly explosive compounds which are set off by contact,
certain others which are disturbed by light, and still others
which are especially changed by heat. Each compound, again,
must form an inconsiderable part of the whole, for (if the
action be not too intense or prolonged) the "stimulus" of the
agent results in no disturbance of the activities in general.
Likewise, the facts of acclimatization, according to which, ap-
parently, certain substances in the protoplasm vnay be destroyed
without other important change in activities, give additional
insight into protoplasmic complexity. Finally, the same agent
acts in varying degree on closely related protoplasm, and this
indicates that, even when the general composition is the same,
the proportions of the dift'erent substances vary. From the
facts of protoplasmic staining and of the varied effects of poi-
sons, from the diverse effects of other stimulating agents, and
from the facts of acclimatization of organisms, we conclude
that in dealing with protoplasm we are not always dealing with
the same thing, but, on the contrary, with very diverse combi-
nations, which have this in common, that they exhibit life.

§ 2, The Limiting Conditions of Metabolisim

Metabolism is life. To know the limits within which it can
occur is to know the vital limits. It is impossible to define
these limits closely, however, for, at either extreme, metabolism
graduates insensibly into inaction. It will be necessary, conse-
(juently, to place our limits very far out.

276 GENERAL CONSIDERATIONS [Ch. IX

The limiting conditions at which inaction occurs are of two
sorts. These may be termed respectively structural and dynami-
cal. These two sorts of limiting conditions may be illustrated
by comparing the protoplasmic mass to a factory, with many
boilers and engines, much shafting and belting, and countless
machines doing the most varied work. The amount of energy
developed in the boilers and the efficiency of the engines and
machines varies with certain conditions, such as the amount of
heat applied to the former, and the friction and waste in the
latter. The limiting mechanical conditions are reached when
the boiler is rent by the steam pressure, a break-down is caused
by friction, or a part rusts through and crumbles away. The
limiting dynamical conditions are reached when the heat no
longer suffices to form steam in the boiler, or the power is
insufficient to run the machines. In either case, at the structu-
ral, or at the dynamical limit, work ceases. It may be the
work of a small part of the factory, so that the cessation is
hardly noticed ; or it may involve all the machines, producing
complete cessation of activity.

To return to the protoplasm : the structural limiting condi-
tions are of two main sorts, — mechanical and chemical. The
mechanical limiting conditions are those in which the gross
structure becomes broken down, while the chemical limiting-
conditions are those in which the composition becomes changed.
To the mechanical group belongs the breaking down of the
plasma films, either by drawing out the water of the protoplasm
(by osmosis or by drying) or by the expansion due to the
freezing of the chylema. To the chemical group belong, for
example, the reactions upon protoplasm of the halogen salts
of the heavy metals, and of complex nitrogenous organic com-
pounds in whose molecules hydrogen is unstably joined to
nitrogen, also the coagulation of the plasma by high tempera-
tures and the destruction of molecules by contact, by the
electric current, or by light. The dynamical limiting condi-
tions, on the other hand, are the absence of oxygen or other
food-stuffs, the absence of the water necessary to the solution
and circulation of the food, absence of light, in the case of
chlorophyllaceous organisms, and a temperature much below
0° C. Thus, the conditions essential to metabolism are the

§ 3] PROTOPLASMIC MOVEMENT 277

absence of causes mechanically rupturing the machine, the
absence of agents of such intense activity as to change pro-
foundly its molecular constitution, and the presence of those
agents — food, heat, light, and water — which supply or dis-
tribute the energy of metabolism.

Given protoplasm under these conditions, and normal me-
tabolism must occur ; without them, there is no metabolism.
Vary the dynamical conditions quantitatively, and a quantita-
tive variation in metabolism will ensue. Approach a struct-
ural limiting condition, and metabolism begins to cease.
This conclusion, important for experimental morphology, is
now reached : A vital phenomenon occurring in a given proto-
plasmic mass can he reproduced only when the dynamical condi-
tions are reproduced^ and the structural limiting conditions are
in no wise closely approached.

§ 3. The Dependence of Protoplasmic Movement
UPON Metabolism and upon External Stimuli

I do not propose to enter the debated ground of the cause
of protoplasmic motion; but shall merely summarize the re-
sults of our studies on this subject. First, protoplasmic
movement is closely related to metabolism and is probably
dependent upon it. This is indicated by the fact that ces-
sation of movement always occurs before the vital limit is
reached. Rigor always precedes death. A second series of
facts indicating the same thing is found in the closeness
with which the optimum for metabolism agrees with the
optimum for movement. Thus at about 35° C. both the
metabolic j)rocesses and the movements of protoplasm find
their optimum. These two results, then, that movement is
impossible in dead protoplasm even when its structure is
seemingly unaltered, and the close approximation of the
oi)timum points for metabolism and for movement, are the
best justification for the belief that movement is dependent
upon metabolism.

But are the conditions essential to metabolism the only con-
ditions necessary for movement ? In other words, will move-
ment always accompany metabolism, or are external stimuli

278 GENERAL CONSIDERATIONS [Ch. IX

essential to its production? There is in biology no question
more important than this, and the answer is not so certain as
it ought to be. The fact that rigor occurs at a point at which
recovery of movement is still possible is not sufficient evidence
that metabolism has not ceased with the motion ; for I think it
has not been shown that with rigor " latent life " does not come
in. On the other hand, the fact that some bacteria are motion-
less in the absence of light (which can hardly be essential to
metabolism) would seem to indicate that conditions other than
those of metabolism are necessary to movement. This single
fact cannot, "however, lead us to a definite answer, and our
inquiry, whether or not "stimuli" are essential to protoplasmic
movement, must still be regarded as unanswered.

§ 4. The Determlnation of the Direction of
Locomotion

As we watch an animalcule swimming across the field of view,
or as we see a larger organism moving, perhaps in a broken
line, towards any point, we think of its movements as controlled
from inside. Yet it is clear that if an organism is moving
definitely towards a point, it must be on account of some influ-
ence emanating from that point and falling upon the organism.
Without external directive influences of some sort there can be
no directed movements.

This conclusion is confirmed by experiment. I have put an
amceba into the apparatus already described (p. 186), so that
the chemical conditions of its environment were uniform ; con-
tact and temperature were also similar on all sides ; the direc-
tive action of gravity was annulled and all light was cut off.
At intervals the position of the amoeba was platted by the aid
of light reflected momentarily from below the stage of the
microscope and by means of a camera. Thus the path of the
amoeba was traced. A typical tracing made in this way is
r-eproduced in E'ig. 72. Compare the devious path made under
these conditions with the straight path taken in response to
light (Fig. 53). The curious spiral twists and the turning of
the line upon itself are characteristic of all the tracings which
I have made under these conditions. Important also is the

§4]

DIRECTION OF LOCOMOTION

279

Fig. 72. — Camera drawing, showing the successive positions assumed by Amoeba
proteus when acted upon by external agents uniformly in all directions. Mag-
nified 16 diams.

Fig. 73. — Tracks made on paper by larva; of Musca ceesar moving in the dark from
a central spot of colored fluid. (From Pouchet, '72. Revue et Mag. de Zool.
(2) XXIII.)

280

GENERAL CONSIDERATIONS

[Ch. IX

fact that whereas the amcEba responding to light is constantly
elongated in the direction of the infalling ray, the amoeba
which is not stimulated from one direction exhibits, most of
the time, a stellate appearance. The wandering of the undi-
rected organism is illustrated again in the experiment of
Pouchet on the larvse of Musca (Lucilia) csesar, kept in the
dark (Fig. 73 ; compare Fig. 7-i, where the same larvae are
migrating under the directive influence of light).

From these experiments we make the deduction that external
agents play a role of the utmost importance for morphology, —
of the utmost importance because by them alone is determined
the direction of migration of the motile cells or the migrating

Fig. 74. — Tracing made like that of Fig. 73 by fly larvse, when the light falls upon
them in the direction of the arrow. A, the first direction of the light; B, the
second direction. To be compared with the undirected movements of Fig. 73.
(From Pouchet, '72.)

protoplasm of whatever sort in the organism. The se7ise of
that migration depends in part upon the internal condition of
the protoplasm. The mechanism by which locomotion is effected
— that is Avholly internal. The mechanism and the energy
necessary to make it go are alone impotent to determine any
adaptive movement or any other predictable result. To mech-
anism and energy must be added a stimulus external to the
responding protoplasm in order that an adaptive or orderly
result should occur.*

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First Part throw light, such as the Mechanics of Eesponse and the Origin of
Adaptation in Response. Since additional facts for the discussion of these
topics will be gained from the succeeding Parts, that discussion will be deferred.

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