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EXPERIMENTAL MORPHOLOGY

THE MACMILLAN COMPANY

NEW YORK + BOSTON - CHICAGO
ATLANTA + SAN FRANCISCO

MACMILLAN & CO., Limitep

LONDON + BOMBAY * CALCUTTA
MELBOURNE

THE MACMILLAN CO. OF CANADA, Lrtp.
TORONTO

_ EXPERIMENTAL MORPHOLOGY

. j \\
BY

CHARLES BENEDICT DAVENPORT, Pu.D.

INSTRUCTOR IN ZOOLOGY IN HARVARD UNIVERSITY

Neto Bork
THE MACMILLAN COMPANY
LONDON: MACMILLAN & CO., Lrp.

1908

All rights reserved

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——— Copyrremn, 1896, 1899,
By THE MACMILLAN COMPANY.

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n, two parts in one volume, April, 1908,

Dedicated

‘

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

dae - MY MOTHER

Die morphologische Betrachtung setzt also eine genaue
chemisch physikalische Kenntniss, 1. des betreffenden
Korpers selbst, und 2. aller der bei seiner Entstehung auf
ihn einwirkenden Stoffe und Korper voraus.— JAEGER,
Zoologische Briefe, p. 9.

La vie ne se concoit que par le conflit des propriétés
physico-chimiques du milieu extérieur et des propriétés
vitales de l’organisme réagissant les unes sur les autres. —
BERNARD, Rapport sur les progres de la physiologie générale
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 the 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. 2

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 well 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: How 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.
Vil

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 ; 3, den-
sity of the medium; 4, molar agents; 5, 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 qualities
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 VERWORN and
LorB 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. Sasrng, Dr. G. W.
CoGGESHALL, and Dr. H. E. Sawyrr. Of my zodlogical
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. MArxk, who has
read parts of the manuscript and proof and has made important
suggestions and emendations. I am also greatly indebted to
Mr. CHARLES BULLARD 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 CROTTY
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 thatsiich-
licher exacter biologischer Forschung ist erwacht”; and the
greatest problem of morphology is ever more and more the
object of this biological experimentation.

CHARLES BENEDICT DAVENPORT.

CAMBRIDGE, MaAss., Dec. 1, 1896.

—————

PREFACE TO PART II

DEVELOPMENT consists of growth and differentiation, accom-
panied in the larger organisms by nuclear- and cell-division.
The present Part deals with, growth.

The importance of the study of growth cannot be over-
estimated, and it is a cause for wonder that the treatment of
the subject has been so much neglected by text-books. Indeed,
it is a surprising fact that it has not been thoroughly and sys-

tematically investigated. For, in last analysis, the maintenanee——

of the human race depends upon that property which protoplasm
among all substances alone displays of increasing itself for an
indefinite time and to an indefinite amount. And the possibil-
ity of increasing the-human race beyond limits that are not
far off depends upon a better knowledge of the conditions of
growth. ‘The reader has only to consider that the world’s
supply of 2500 million bushels of wheat, 2000 million bushels
of maize, 90 million tons of potatoes, and its untold millions
of tons of beef, pork, and fish are reproduced each year by
growth. The mineral matters of the soil are being washed out
into the sea and are largely lost, but the capacity of growth
under appropriate conditions is never lost; it redoubles as the
amount of the growing substance is increased. The only thing,
then, which limits growth is the limitations in the conditions
of growth. \What are these conditions? This is the important
question to which attention has been directed in this Part.
Aside from this practical interest, the study of growth is

important as bearing on the question of the dependence of vital
activities, and especially development, upon external conditions,
xa

oe PREFACE

and the possibility of the control of development by appropri-
ately altering those conditions. Growth phenomena show them-
selves, indeed, particularly susceptible to this control, and are
consequently especially valuable for experimental study.

In the preparation of the Second Part, I have been put again
under heavy obligations to my friend and colleague, Dr. G. H.
PARKER, who has read most of the manuscript and made
important suggestions. I am also indebted to Dr. H. E. SAw-
YER for reading Chapter XI in the manuscript, and to my wife
for much painstaking work on the manuscript and proofs and
for compiling the index.

Cc. B. D.

CamBRiIDGE, Mass., Dec. 11, 1898,

CONTENTS

PREFACE

CHAPTER I
AcTION OF CHEMICAL AGENTS UPON PROTOPLASM

§ 1. Modification of Vital Actions
Oxygen .
Hydrogen .
Oxides of Carbon .
Ammonia ‘ ‘
Catalytic Poisons . : :
Poisons which form Salts.
a. Acids ‘ ’
b. Soluble Mineral ae : ‘ :
c. Salts of Heavy Metals . : -
7. Substitution Poisons .
8. Sodic Fluoride.
9. Special Poisons .
§ 2. Acclimatization to Shimiout Reverie
§ 3. Chemotaxis . : ‘ ;
Summary of the Chapter
Appendix to Chapter I
Literature . ;

Sh ae

CHAPTER II
EFFECT OF VARYING MOISTURE UPON PROTOPLASM

§ 1. On the Amount of Water 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 Pockoninan
8. Desiccation-rigor and Death . ‘
§ 3. On the Acclimatization of Organisms to Henioration
§ 4. The Determination of the Direction of Movement by Moisture —
Hydrotaxis . , . : ‘ F : . ° .
Literature . . ‘ : . ‘ ° ‘ ‘ ° . °

PAGE

58
59
59
60
60
65

66
67

xli CONTENTS

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 Sieuitans atid Genarel
Functions of Protoplasm : 74
§ 8. Acclimatization to Solutions of Greater or an Density then the
Normal . : ‘ oa
§ 4. Control of the Direction of Lasomades by Fasatey «oT oaotaicia . 89
Literature . : ° ; . : ; ; ° : e - 98
CHAPTER IV

AcTIon oF MoLtar 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 eterhivin g ie Dixsotion: of Locate:
tion — Thigmotaxis (Stereotaxis) and Rheotaxis . : - 105
Literature . : : : : 5 ‘ ‘ ; ; ; 2 AAO
CHAPTER V

EFFECT OF GRAVITY UPON PROTOPLASM

§ 1. Methods of Study ‘ : : - 112

§ 2. Effect of Gravity upon the Strhoturs af Brogantaans ; : » 118:

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

Literature . ‘ ; ‘ : , 3 : ‘ ; : - 124
CHAPTER VI

Errect OF ELECTRICITY UPON PROTOPLASM

§ 1. Concerning Methods . ‘ 126
§ 2. The Effect of Electricity upon the Strnctare snd General Fisis!
tions of Protoplasm ; : : : : : ° - 129
§ 3. Electrotaxis . : ; ; : ‘ Papi é : . 140
Summary of the Chapter . ; ; ° ° ‘ ; , ae | |

Literature . "1 ‘ : ; d - ‘ ‘ ; 4 - 152

. tear wi
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ed a

CONTENTS

CHAPTER VII
AcTION oF LIGHT UPON PROTOPLASM

§ 1. The Application and Measurement of Light :
§ 2. The Chemical Action of Light upon Non-living Substauioes:
1. The Synthetic Effects of Light : ‘ ,
2. Analytic Effect of Light
8. Substitution Effects of Light .
4. The Isomerismic and Polymerismic Changes prodused by Light
§ 3. The Effect of Light upon the General Functions of Organisms
1. Effect of Light upon Metabolism . ;
a. The Thermic Effect of Light on Métsbolisin
b. The Chemical Effect of Light on Metabolism
2. Vital Limits of Light Action on Protoplasm
8. Effect of Light upon the Movement of Protoplasm
a. Effect of Low Intensity of Light.on Movement — Dark-

rigor . é

b. Effect of High Tateuatty of Light on Biseaiient a
Light-rigor

§ 4. Control of the Direction of Lain btion by Tae _ Phetitatia

and Photopathy ; é : : ¢ ;

1. False and True Phitotasis
2. Distribution of Phototaxis and Photopathy -
a. Protista : ; :
b. Cells and Cai oxeaeh
‘ a. Chlorophyll Bodies
8. The Rearrangemepvt of Piguet 3 in Aninal Cells
in Response to Light ;
_y- The Migration of Pigment Cells in the Motasoan
Body : ‘ . ;
c. Metazoa
3. The General Laws of Phototaxts and Photopathy
a. The Sense of the Response
b. The Effective Rays
c. Phototaxis vs. Photopathy :
d. The Mechanics of ane to room
Summary of the Chapter : :
Literature . : ° ° : ° . : ;

Xili

PAGE

154
161
162
163
164
164
166
166
166
170
171
175

175
178

130
181
182
182
189
189

192:

193
194
196
196
201
203
207
210
212

Xiv

§ 3.

§ 4.

§ 5.

CONTENTS

CHAPTER VIII

ACTION OF HEAT UPON PROTOPLASM

. Nature of Heat and the General Methods of its Application
. The Effect of Heat upon the General Functions of ve

1. Effect of Heat upon Metabolism .
2. Effect of Heat upon the Movement of Protoplasm ad ale
Irritability — . : ; : : , :
Temperature-Limits of Life
1. Temporary Rigor and Death at the Hisher Lizoit of ‘Tee.
perature, Maximum and Ultramaximum . ‘
2. Temporary Rigor and Death at the Lower Limit of Toupee
ture, Minimum and Ultraminimum . ‘ . ;
Acclimatization of Organisms to Extreme Tenagecabinns
1. Acclimatization to Heat
2. Acclimatization to Cold :
Determination of the Direction df Tadseiobion by Heat _— ‘Ther-
motaxis .

Notes to Table X XT
Literature

CHAPTER IX

GENERAL CONSIDERATIONS ON THE EFFECTS OF CHEMICAL
AND PuysicAL AGENTS UPON PROTOPLASM

. Conclusions on the Structure and Composition of Protoplasm
. The Limiting Conditions of Metabolism
. The Dependence of Protoplasmic Movement on Metabolism

and upon External Stimuli

. The Determination of the Direction of Lakeantaan

PAGE

219
222
222

225
231

231

239
249
249
257

258
263
267

274
275

277
278

“CONTENTS

ee eee ee

CHAPTER X

. ; ‘ PAGE
INTRODUCTION: On NorMAL GROWTH : Fr : Z ; »- 281

a _

CHAPTER XI

\
EFFECT oF CHEMICAL AGENTS UPON GROWTH

§ 1. Effect of Chemical Agents upon the Rate of Growth . . . 293
1. The Materials of which Organisms are composed . : . 294
a. Analysis of the Entire Organism . 296

b. Detailed Account of the Various Scant se as Food 304
~ Oxygen, 304; Hydrogen, 306; Carbon, 306; Nitro-
gen, 307; Phosphorus, 313; Arsenic, Antimony,
and Bismuth, 314; Sulphur, 314; Chlorine, 316;
Bromine, 316; Iodine, 317; Fluorine, 317; Lith-
ium, 318; Sodium, 318; Potassium, 318; Rubidium
and Cesium, 320; Strontium, 321; Manganese, 321;
Iron, 321; Magnesium, 323 ; Silicon, 324; Copper,

324.
2. The Organic F ood used by agacaoeeh in Growth . 2 . 324
a. Fungi. ‘ : ‘ ‘ : - 324
5 b. Green Plants . i ; , 3 = . 3826
r c. Animals . ; ; : : ‘ , eM gee nie: PR
Aimeeba, 328; Amphibia, 329; Mammals, 330.

3. Growth as a Response to Stimuli . : ‘ . del
a. Acceleration of Growth by Chemical Sanaa . . 331
6. The Election of Organic Food ; 333

§ 2. Effect of Chemical Agents upon the Direction of Growth — Ganda
tropism. : . 339
1. Chemotropism in the Penthelés of Fisietitonciia Plants - 335
2. Chemotropism of Roots . .. j i ? ; ‘ . 336
3. Chemotropism of Pollen-tubes 2s a Se ein hg en ain Sy Woh | +
4. Chemotropism of Hyphe : ee se
5. es of nieces Tuten’ in Revers . - 3842
Literature ; PoUMGe oe, Ss,

xV

Xvi CONTENTS

CHAPTER XIi
THE EFFECT OF WATER UPON GROWTH

§ 1. Effect of Water upon the Rate and Quantity of Growth
§ 2. Effect of Water on the Direction of Growth — Hydrotropism

1. Roots ‘ én ae

2. Rhizoids of Higher Cryptogams

3. Stems ; . ;

4. Pollen-tubes . 3 : j - . - ‘ ;

5. Hyphee of nas ‘ : ; : ° ea eee
Literature ; ; ; ; . : ‘ 3 . ©

CHAPTER XIII

EFFECT OF THE DENSITY OF THE MEDIUM UPON GROWTH

§ 1. Effect of Density upon the Rate of Growth . . . .
' Literature ; ‘ . : ‘ . ginine : ;

CHAPTER XIV
Evezct oF MoLtar AGENTS UPON GROWTH

§ 1. Effect of Molar Agents SL Ai the Rate of Growth. . .
1. Contact . ‘ : : : . . .
2. Rough Movements .
3. Deformation ;
4. Local Removal of Tissue

§ 2. Effect of Contact upon the Direction of Grow ilies Filpmotroninn

1. Twining Stems

to it ‘
7. Explanation of Thigtneronlees

§ 3. Effect of Wounding upon the Direction of Growth — Prauthe-

tropism . .
1. False Traumatropism
2. True Traumatropism

§ 4. Effect of Flowing Water upon the (Direotion of Growth oa ihe.

tropism . : : . : . : . .
Summary of the Chapter ° Pesan ; a i Siete
Literature ° ° : : : . . . . : ;

2. Tendrils . ; : : : :

3. Roots ‘ :

4. Cryptogams . ;

5. Animals .

6. The Accumulation of Contest otandin sua eidinablhation

PAGE

350
355
356
357
358
358
358
360

362
369

370
370
370
372
3875
376
376
377
380
381
382

382
383

384
384
384

387
388
389

i,
}
a

“ie CONTENTS

CHAPTER XV
EFFECT oF GRAVITY UPON GROWTH

§ 1. Effect of Gravity upon the Rate of Growth . ‘
§ 2. The Effect of Gravity upon the Direction of Growth — Gedksdpioe
1. False Geotropism ; ‘ ; ‘ - - ‘
2. True Geotropism : Pts ‘
a. Roots. ‘ P ‘ : $

b. Stems. ‘ : / : F ‘ ‘ .

c. Rhizoma . ‘ ‘ : ‘ P ° > :

d. Cryptogams . Sir ae eat Oe te Ra eae te

e. Animals . : ‘ : . .

f. After-effect in Geotropism ee ore ae
Summary "gee lta ale Bi ener Ne Sy nat? ee
Literature : - ; - : : A fed) ut

CHAPTER XVI
Errect or ELEectTricity upon GRowTH

§ 1. Effect of Electricity upon the Rate of Growth
§ 2. Effect of Electricity upon the Direction of Growth—Electro-
tropism F
1. False and True Blackrotropien
2. Electrotropism in Phanerogams

3. Electrotropism in Other Organisms

4, Magnetropism .

5. Explanation of Blectrotropism and ‘Baneaty a ws
Literature * er se ee oe se eh Alco inet eee

CHAPTER XVII
Errect or Ligut upon GRowTH

§ 1. Effect of Light on the Rateof Growth. . . . .
1. Retarding Effectof Light . . . . .
2. Accelerating Effectof Light . . . . .
3. The Effective Rays. .
a. The Effective Raysin the Retardation of Growth by Light
b. The Effective Rays in the Acceleration of Growth by Light
4. The Cause of the Effect of Light on the Rate of Growth
§ 2. Effect of Light upon the Direction of Growth — Phototropism
SiR OR ee Ls ‘ : Reeth ce. 2
2. Animals . : Oe a? eee ee
a. Serpalides. : ‘ ? ° . . :
b. Hydroids . ; : : - Ap ee

xvii

PAGE

391
391
392
392
392
397
398
398
398
401
402
403

405
409
409
409
411
412
413
413
414

416
416
423
427
427
432
436
437
437
442
442
443

XVili CONTENTS

PAGE
3. General Considerations .. - : 4 y ‘ ; . 444

a. Persistence of Stimulation . . . arnt . 444
6. Acclimatization to Light : ‘ : : ‘ . 444
c. Mechanics of Phototropism . . . . . . 444
Literature : Ne YOM a me ta es i

CHAPTER XVIII.
EFFECT OF HEAT ON Gaowrn

§ 1. Effect of Heat on the Rate of Growth . : ; ss » 400

1. Plants. : : . ; ; ‘ : ‘ ° . 450

2. Animals . ° ‘ . 457

3. Some General rE accompanying Heat Effects. . 460

a. Latent Period . . , ; ‘ : - 460

b. Sudden Change of Tampareties wm tN (Snes a

c. Cause of Acceleration of Growth by Heat. ; . 461

§ 2. Effect of Heat on the Direction of Growth—Thermotropism . 463
1. Effect of Radiant Heat ... ; ; ‘ : : - 463

2. Conducted Heat. ities ‘ ; : , - «+ 464

8. Causes of Thermotropism . : : ; » eae GS
Summary of the sipaciecs RE RAR : vl Ue - ee BOF
Literature , range ; ‘ : ar). ah)? lee oor

CHAPTER XIX

EFFECT oF COMPLEX AGENTS UPON GROWTH, AND GENERAL
CONCLUSIONS

§ 1. The Coéperation of Geotropism and Mansi) oes : : - 470

§ 2. Effect of Extent of Mediumoon Size . ; 473
§ 3. General Considerations relating to the Action ia Growth of

External Agents : ‘ ‘ . : , . 478

1. Modification of Rate of Growth ; : ; ; . 478

2. Modification of Direction of Growth — Pioeiath ; : - 480
3. Adaptation in Tropisms . : : . : ; Bog
4. Critical Points in Tropism ~5 > 6 7-"s) 92°.) «Se 484
' Literature fo Ee i eS i.

List oF TABLES IN Parts I anp II . ‘ ; - : ;. . 489

InpEx TO Parts I anp II . A - ; r . git ee, SOS

;

EXPERIMENTAL MORPHOLOGY

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EXPERIMENTAL MORPHOLOGY

CHAPTER I
| ACTION OF CHEMICAL AGENTS UPON PROTOPLASM

In this chapter it is proposed to consider (1) 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. MoprricaTion or Virau 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 (N,H,) and hydroxylamine
(NH, — 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, much use has been made of the admirable
work of Loew (’93). Not only is the adopted classification of poisons for the
most 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 no other authority is given have been taken from Lorw’s book.

B 1

2 CHEMICAL AGENTS AND PROTOPLASM [Cu. I

certain indirect means for determining its constitution. Since
death is due to chemical change, we ought to determine what
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 shown, for example, by RicHeET (’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 anzerobic 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 down of O-containing compounds
in the nutritive medium. (Cf. Lorw, ’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. |

DeEMooR* 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 EnceLMANN’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 promptly regained its nor-
mal activity. Cells immobilized during 24 hours regain their
movements in less than 5 muBD tes, 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, ’94, pp. 192, 218.) In Ciliata the
rate of the contractile vesicle does not, however, seem to be
altered. (RossBACH, ’72, p. 40.)

Ozone and hydrogen peroxide produce atomistic “active” oxy-
gen by becoming split up in the plasma. Ozone (Q,) is said
to kill quickly bacteria in water, if the latter does not contain
too much organic substance; in the dry state, however, bacte-
ria are injured only slowly by it. COHLMULLER, ’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 (H,O,).— PANETH (89) added one part
of neutralized H,O, 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. Algz survived
only 10 to 12 hours in a completely neutral. 0.1% solution.
A 10% solution is fatal in a few minutes. (Cf. Bokorny,
"86, 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.

ee CHEMICAL AGENTS AND PROTOPLASM [Cu, I

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

Sodic chromate (Na,CrO,).— Many anerobic Schizophytes
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 alge. (LOEW, 93, p. 16.)

Potassice dichromate (K,Cr,0O,).—A 0.1% solution kills alge
(Spirogyra) in a few hours.

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

Chlorine, bromine, and iodine, as well 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 —

C,H,,0, + Br, + H,O — C.H,,0, + 2 HBr.

glucose.

(LorEw, ’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
Cl, Br, I. (Compare the osmotie effects of the halogens, p. 72.)

Potassic chlorate (KC1O,)— 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 anaérobic forms are affected by a 0.5% solution;
the aérobic withstand up to 3%. Alge (Spirogyra) die after -
a few days ina 0.01% solution of the salt. (LoEw, ’93, p. 17.)
_ Arsenious acid (H,AsO,) and to a less degree arsenic acid
(H,AsO,) are poisons which Binz and ScHULZ (’79) believe

§ 1) MODIFICATION OF VITAL ACTIONS 5

to act by oxidizing the protoplasm. Thus H,AsO, 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 9.1%
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.) Algz (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 alge
(Zygnema, Diatomacea), upon Infusoria, and upon tadpoles
showed themselves, uniformly, more powerful agents than the
corresponding arsenic salts. The lower fungi are only slightly
affected by arsenious salts; not at all by those of arsenic acid.

2. Hydrogen. — Kine (64, p. 52) subjected Ameeba 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.

DrEMoor (’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-
iH pears uniformly granular. If, on the contrary, the cell possesses
7 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 Krpp’s apparatus, and
should pass through a series of washing flasks containing, e.g., solutions of potash
and acetate of lead. See Verworn: Allgemeine Physiol., p. 285. DEmoor
kept his stamen hairs in sugared water in an ENcGELMANN’s chamber.

——_-

6 CHEMICAL AGENTS AND’ PROTOPLASM [Cu. 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, CO, and CO, have very dif-
ferent effects upon protoplasm. Thus DEeMmoor (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 endosare in a
number of completely hyaline fragments ; the endosarc becomes
vacuolated, and death ensues in from 20 to 60 minutes. Many
bacteria are only slightly affected by CO.

4. Ammonia (NH,). — A 10% solution provokes vacuolli-
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 anesthesia. (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 T

by alkaline (0.001%) silver solutions. Other basic substances,

like potash and organic amine bases, and ‘various alkaloids,

produce the same effect. (Cf. Lozw and Bokorwny, ’89.)
Azoimid. — LoEW (91) has studied the effect upon proto-

; N
plasm of this somewhat close ally of ammonia, || NE. The
N
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 produces the characteristic granulations. Infusoria are
killed in 2 to 2} hours by a 0.1% solution of N,Na, and the
water-living Nematodes, Planaria, Ostracoda, Copepoda, and
young Planorbis and Lymnea are killed by a 0.05% solution in
30 to 40 minutes. Alge 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 anesthetics — 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 Lozw
(798). :

8 CHEMICAL AGENTS AND PROTOPLASM | [Cu. 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 between molecular
composition and strength of action. We may begin with the
methan series. ‘This series, which has CH, —as its base, runs

as follows :—
CH,
CoH,
C,H,, ete.

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

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 poisonous qualities
encrease, —

CH,Cl is slightly anesthetic,
CHCl, = chloroform,
CCl, is very dangerous, stupefying involuntary muscles.

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

In ethan (Cc, Hy) also, when Cl replaces H, the substance be-
comes a more active poison; e.g. C,H,Cl,, methal 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 Cl atoms to the molecule; thus, —

sulphur ethyl, C,H;—S—C,H;, is a weak poison.
monochlorsulphurethyl, C,H,—S—C,H,Cl is a stronger poison.
dichlorsulphurethyl, C,H,C1—S—C,H,Clisa very powerful poison.

In the more complex sulphonic hydrocarbons of the methan
series, where the alkyls CH, —, C,H; —, etc., are introduced,
the rule holds that the more pnd in "the alkyl the more active
the substance as a poison; thus, —

§ 1] MODIFICATION OF VITAL ACTIONS 9

PNG. re SO.CH,

CH, Pei \go,CH,

is not poisonous ;

sulphonal : is poisonous ;
5 cH,/ Neca
CH S$0.C,H
trional : Se le oie is poisonous; and
CH, /°\so,.H,
C,H. S0,C,H
tetronal : ‘ Ne Zh sifiae is more poisonous.

a \g0.C.H;
The same holds for the acetals; thus, —

H O.CH, H O.C,H
1 Ae CH, is grr lucen sultan wy As oe OH.

We find the same thing in the ethyl group, —

CH C.F

CH,—C — OH is less active than CH,—C — OH.

CH, CH,
trimethalearbinol. dimethalethylearbinol.

And also in the alcohols, —

methyl aleohol, CH,OH, weak actiou;
ethyl] alcohol, C.H;OH, weak action ;
isopropyl alcohol, C;H,OH, 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 anes-
thetically, that of the higher plants as well as that of the
higher animals. (BERNARD, C., 78, and Eurine, F., 86.)
KUHNE (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.
} chloroform 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 (Cu. 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. (ScHtRMAYER, ’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
anesthetized. (DEMooR, 94, P. an |

Chloral hydrate, CCl, — ae which is closely related to

4 H
| sol
chloroform, Cl — ae acts similarly as a protoplasmic anes-
| H

thetic. A 0.1% solution kills Infusoria, Rotifera, and diatoms
in 24 hours, but filamentous algze 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.

* Evrine, F. (’86, pp. 47-51). The swarm-spores employed belonged to the
species Chlamydomonas 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) oF Resistance or TappoLes or Buro Vurearis, Laur.
(Hixp LEGS HAD JUST APPEARED) TO VARIOUS ALCOHOLS

STRENGTHS. 0.01%| 0.1%| 0.3% | 0.5% | 0.7% |1.0%) 1.5% | 2.0%| 25%
methylic* .... 0.3-0.8) 0.07-0.3
ORBTOC. wo) 0s stupor] 0.16
propylic, norm. . 0.6 0.3 | 0.15
propylic, iso... . 05 | 0.2-0.3 | 0.15
butylic, norm... 1.0 0.08
butylic, iso. ... 0.15-0.25/0.05-0.15
butylic, tertiary. 0.15-0.33 0.05-0.25
amylic, norm.. . 0.2-0.5
| aa ae 4-5 |1.5-2.0

TABLE II
Ture (in Hours) or Resistance OF InrusORIA AND OsTRACODA TO VARIOUS

ALCOHOLS

STRENGTHS. 0.005% 9.1% | 0.5% | 1.0% | 3.0%

ES WO fs Stes apie talelMe: oad od badass «aj 20
SE, REN gr ae aa +
ITEM a A: oss do, oa 08 0 72T
NEOTEL 100s, id decals. sow o bEA) oid ce ee 18
SE nr er eee 48 |18
EINES fan ars 6. Siig oe ke we: hee, ue 8 o 72 |48T
BEMIMC MORMON US Fi os. eee ee ed oS 48 +T
SS EE Sar a doe eae 2+) w#
LESSIG NEE = SPA a ey ig 24

_* The structural formulas of these alcohols are given here for reference : —
Dewy sie Sg Ge eg a Se OE — CHO

CPG Beets ie sale sr CH — CHAO
propylic, norm. .... . . . CH 3.CH,—CH.OH
propylic, iso. . . . ...... . . (CHs)s— CHOH

butylic, MOREE ea a ee CHzs e CHe . CHe = CH.OH

butylic, iso. ro > CH — CH.OH
3
butylic, tertiary . . . . .. 1. . CH. > COH — CHs

amylic,norm.. . . . CH3.CH2,.CH2.CH»,—CH.,OH
SOs waded ois. fer nile es sine ke Ole CH — CHO

t Ostracoda only ; the Infusoria died after 18 hours.

12 CHEMICAL AGENTS AND PROTOPLASM [Cu. I

TABLE III

Time (1n Hours) oF Resistance PER1I0D or Sprrocyra ComMMUNIS TO
Various ALCOHOLS

STRENGTHS. 0.005% | 0.01% | 0.05% | 0.1% | 0.5% | 1.0% | 2.0% | 3.0% | 4.0%
methylic..... 120 96 48
ethylic.*.). 5 <0 72 72 48
propylic, norm. . 72
propylic, iso... . 48
butylic, norm.. . 42 48
butylic, iso. ... ; 96 48
butylic, tertiary. 48
amylic, norm.. . 24
BMVHC 8d ely 66 72 24. 24

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 the most poisonous; the tertiary, least.

Carbonic disulphide (CS,) is one of the more powerful cata-
lytic poisons. A saturated aqueous solution, which contains
only a trace of CS,, nevertheless kills quickly alge, bacteria,
and the lower water animals. (LOEW, 793, 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;
6. the soluble mineral bases; ¢. salts of heavy metals.

a. Acids. —The strong inorganic acids act, in general, more
powerfully than the organic. Most bacteria, alge, 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% 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% H,SO,. (CLOEw.)

To organic acids many alge are little resistant. Thus Spiro-
gyra and Spheroplea 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.

b. 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. FROMANN, ’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 alge
like Spirogyra.

K,CO, kills bacteria in 0.8% to 1.0% solutions.

Na,CO, 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 Na,CQ,.

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 Na,CO,, for example, as described by FROoMANN,
is very similar to that of NaCl, whose action is probably solely
osmotic.

e. 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 | [Cu. I

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 0.00005%. CLockg, ’95, p. 327.) Among mer-
curic salts, splenic fever bacteria do not develop in 0.0003%
HgCl, in nutritive bouillon, nor 0.0125% in blood. Lactie 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
NAGE. (793), ** 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 (CuH2Q2).
Similarly produced solutions of other metals, Ag, Zn, Fe, Pb, Hg, had a simi-
larly fatal effect upon Spirogyra. NAGeEu1 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 ina
comparatively resistant organism, like Stentor, a solution of 1 : 80,000,000 HgCly
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. (See p. 30.) Even in NAGELI’s experiments
solutions of less than 1: 100,000,000 had little action.

ESS

iad

§ 1] MODIFICATION OF VITAL ACTIONS 15

0.1%. NeAu and I have found that Stentor cceruleus is killed
by a 0.001% solution HgCl, 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 zine 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 zine 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 Lorw 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 (H,N — OH); which
justifies at the same time the term “substitution poisons.”

O N —OH
Go 2 NOH BOF + H,0.
Nu Nu
any aldehyde. hydroxylamine. an aldoxim.

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. (Lorw, ’85*, p. 523.)

0.005% kills in 36 hours Infusoria which withstand a similar con-
centration of strychnine. (LOoEw.)

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 Rotifera in 10 to 15 minutes; those
of Nais in 20 to 30 minutes. (Horer, ’90, pp. 324, 325.)

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

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

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

16 CHEMICAL AGENTS AND PROTOPLASM [Cu. I

Diamid, or hydrazin (H,N — NH,) 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. (Lorw, 93.)

Phenylhydrazin

‘ DN = NH, is more powerful. A
solution of —

0.0067% kills Infusoria and algz within 18 hours.
0.05% prevents the development of bacteria and mucors.

As free ammonia (NH,) is a far weaker poison than diamid
(H,N — NH,), so anilin (C,H,NH,) is far weaker than phenyl-
hydrazin (C,H,.NH.NH,).

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 (7.e. groups which
can be derived from ammonia by the substitution for two H
atoms of bivalent acid radicals); thus, —

CH = CH CH; — CH
cH SN oHx NH
CH — CH CH, — CH;
pyridin (weaker poison). piperidin (stronger poison).
HC = HC H,C — H,C
oH \N cHX ie NH
CH — © CH, — CH
|
CH CH,
Ayam
CH, CH, CH,
collidin (weak). |
CH,

coniin (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
(NH,) unreplaced by an alkyl, the substance is poisonous.

§ 1) MODIFICATION OF VITAL ACTIONS 17

ONLY sLiGHTLy Porsonovs. - VIOLENT Porsons.
C,H, —CH = N C,H; - CH —NH\
OH au. DCH — CH,
C,H; — CH = N C.H;—C =. N
hydrobenzamid. amarin.
CH = CH CH = CH\.
cH > | NH
CH — CH CH = CH
pyridin. pyrrol.*

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.CH,), the poisonous qualities of the substance are con-
siderably diminished ; thus, —

More Porsonovs. Less Poisonous.
C,H;N H, C,H;NH . CO — CH,
anilin. antifebrin.t
C,H;NH . NH, -C,H,NH .NH.CO.CH;
phenylhydrazin. pyrodin.
NH NH
: HN = oe HN = ae ;
; NH, NH .CO. NH,
F guanidin. dicyandiamidin.

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

* While a 0.07 % solution of pyrrol kills Isopods, Rotifers, Planaria, ete., in
about 1 hour, these organisms withstand a solution of pyridin of the same
strength. (Lorw, ’87, p. 444.)

+ ScotrMayer (790, 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.

c

18 CHEMICAL AGENTS AND PROTOPLASM [Cu. ]

NH — CH N .CH, — CH
| I
CO C—NH | CO C—N.CH, °
| Yoo | No
NH —C=N NH — clin
xanthin. theobromine.
N.CH,— CH
| |
CO C—N OH,
| Neo
N.CH,—C=N ae
coffein.

are successively less poisonous. (LOEW, ’93, p. 46.)

H ~€ H
Noe EE,
While benzol is rather inactive, 8 grammes
C C
HS ONG ON

|
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. (LorEw, ’87, p. 440.) Thus there fol-
low in order of poisonousness : —

H H H
| | |

C C C
HO”. Soon. a0” SO OH eee a | On
| | |

HC CH HC CH ' HC CH
Ne Gok bg
| | |
H OH 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. Alge die in a1% solution after 20 to 30

§ 1) MODIFICATION 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.

Resorcin (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 alge in a few hours; while,
with resorcin, Infusoria, diatoms, and green alge 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.

Hydrocyanie 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, —

R R CN

No =0+4 NH = \cXon :
HZ ees

aldehyde.

The degree and variety of its action may be inferred from
the following data, taken from Lorw (793): Infusoria die
quickly in a 0.1% solution, but Ascaris resists a 83% 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; eg. (CN),Hg,
Na,Fe(CN),NO.

Hydric sulphide acts as a poison either by deoxidizing the

lasma,
£ HS + 0 = H,0+5,

20 CHEMICAL AGENTS AND PROTOPLASM [Cu. I

or by acting on the aldehydes,

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

Sulphurous oxide (SO,) attacks members of the aldehyde

group, —

R\ Bw sO k
a =0+S80,KH = NoXon
H HZ H

aldehyde.

0.1% kills lower fungi in a few minutes, 0.01% in a few hours.

Selenous oxide (SeOQ,), which acts chemically much like SO,
and has a much greater molecular weight (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 (TeO,, mol. wt. = 157) is non-poisonous,
although chemically closely allied to the two preceding.
(Boxorny, 793.) }

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. —

C,H, © NH, + CH,O — C,H;N CH, + H,0O.

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, ’98, p. 58.) Hence the
poisonousness of aldehydes for living albumens.

Formaldehyde. —'This substance (H —CH:QO) 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. , (Conn, ’94, p. 5.)

A weak solution seems to act anesthetically 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 (CH,—CHO) is anesthetic; and paraldehyde
(CH, — CHO), kills alge 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 NH, — CH, — CH: (OC,H,;),, amidoacetal, Infu-
soria, and diatoms die within 15 hours, and, somewhat later,
filamentous alg.

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

C.H,. NH, + HO. NO = ¢,H,.0H + N,+ H.0,

amine, alcohol.
and
C,H, .NH,. HNO; + HO. NO = C,H;.N;ONO, + 2 H,0.
aniline nitrate. diazobenzene nitrate.

Thus a solution of 0.001% of free nitrous acid is poisonous
to alge, 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 alge, 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 alge
‘(Oscillaria, Cladophora, Gidogonium, diatoms) within 24 hours,

22 CHEMICAL AGENTS AND PROTOPLASM (Cu. 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.

Lorw 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 [Cu. I

causes Medusz 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; Palemon (after temporary
stimulation) is paralyzed by a 0.01% solution in 30 minutes ;
Sepiola is killed by 0.005% in less than a minute. (GREEN-
woop, ’90.)

Veratrin, Atropin, 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, RosssAcH (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. KiHne, 64,
pp. 47, 65, 100.)

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

Its action upon Protista has been studied by CHARPENTIER
(85), Appuco (90), SCHURMAYER (790, pp. 4388-448), AL-
BERTONI (791, p. 318), DANILEWSKI (’92), and MAssART
(93, p. 66); upon sexual cells, by O. and R. Hertwie (87,
p. 159) and ALBERTONI (91, p. 809); 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- 489). Cocaine acts similarly upon the nerve centres and
muscles of the more differentiated animals.

§ 1] MODIFICATION OF VITAL ACTIONS 25

Morphin 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: C,,H,,N,O,; 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 ScHURMAYER (90, pp. 423-433). KRUKENBERG
(80) has studied its effects upon higher Invertebrates. Its
action upon sexual cells has been studied by the brothers
HERTWIG (87, pp. 1538-156, 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-
eroscope. A 0.02% or 0.01% solution can be withstood for
a few minutes (0.01% solution was withstood for 5 minutes,
ScHURMAYER). As for the weakest solution that will kill,
ScHURMAYER found that a Paramecium resisted for only 16
to 20 minutes so weak a solution as 0.0005%, while RossBAcH
found Stylonychia little affected by a 0.0055% solution. The
spermatozoa of Echinoids, according to the HERTWIcs (87,
p- 164), so resist a 0.01% solution that after 180 minutes the
movement is only somewhat retarded. LEchinoid 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 codrdination, and
a rotation takes place about the axis of progression. Next,

26 CHEMICAL AGENTS AND PROTOPLASM [Cu. 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. 4238-426.) 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 85 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, Ascaridz have a considerable resistance,
which SCHRODER (895, 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 (C,)H,,N,O,). — 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 TEN BoscH
(780) on leucocytes; by O. and R. Hertwie (87) on sexual
cells; and by KRUKENBERG (80) on higher Invertebrata.

§ 2] ACCLIMATIZATION TO CHEMICAL AGENTS 27

Ameeba, 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, KRUKENBERG, ’80,
p- 10), and it affects the cerebrum and heart ganglia of
mammals. |

Antipyrin, 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
iy) | oc . /N-CH,

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. Lorw, ’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 [Cu. 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% Na,CO,, and even the extremely resistant Ascaris
lives only 5 to 6 hours in a 5.8% solution of this salt, Lomw
CTT, p. 187) has found in Owen’s Lake, California (an alkaline
water containing among other things 2.5% Na,CO,), numerous
living Infusoria, Copepoda, larve 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. a
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 H,SO, 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, 7.e. as much as 0.4 gramme. (Bryz 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

y

a
a
+

§ 2] ACCLIMATIZATION TO CHEMICAL AGENTS 29

rattlesnake poison (Crotalophorus 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 EHRLICH (91). This
investigator fed white mice (which are killed by 54, 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 EHRLICH’s paper, shows
the gradual increase of immunity as a result of feeding on the .
poison : —

TABLE IV
STRENGTH OF NuMBER OF INDI- Maximum In-
No. or EXPERIMENT DEGREE OF
Last DOSE GIVEN,| VIDUALS EXPERI- | JECTED SOLUTION
Day. = IMMUNITY.
IN MG. MENTED ON. BORNE, %'S.
Die in
SDS seb oda 4 8 1 0.0005 1
er tree ae 5 16 0.0007 1.3
RE a eae 6 23 0.0066 13.3
PEE ehh oneal 7 5 0.005 10
a RA 8 18 0.01 20
BS Sg ac ailar'e Sa 12 9 0.02 40
DME. a akete. is ait 20 3 0.033 66.6
BBEN ton 6! 33s ve oabte 50 1 0.05 100
WARE ore ewe 80 + 0.1 200
04 Gee a cee 80 1 0.2 400

Thus after the first 4 or 5 days the immunity rapidly in-
creased; so that, while the solution of 559557 Kills normal

30 CHEMICAL AGENTS AND PROTOPLASM (Cu. I |

mice, those acclimatized during 21 days resist qo0y tO sty
occasionally 345, 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 MARMIER (’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% HgCl,. After the
lapse of two days both were put into a killing solution of
0.001% HgCl,, 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
132 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 arenano 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.

———————<—— eee

§ 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.

90 sEcs.
a
Ne 80
\
a8
. n=
| 2
3
2
80 3
Ba ir
eg
te Mi
aNd
Pe
= — = = 40 SECS.
: : ‘Bees

STRENGTH OF CULTURE SOLUTIONS

Fic. 1.— Curve of resistance periods to a 0.00125 % solution of HgCl, of Stentors
reared in various solutions of HgClg 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 toa 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 (Cu. 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? Exuruiicn found that mice acclimated to ricin were
just as sensitive to abrin as the normal animals, and the same
is true, mutat?s mutandis, for mice which resist abrin.

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

EHRLICH (791) 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. <3

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.

§ 8. CHEMOTAXIS

ENGELMANN (’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

ar

§ 3] CHEMOTAXIS BB

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 CO, in place of oxygen. If green
algw are introduced, the bacteria move towards them so long
as they, under the influence of sunlight, are producing oxygen.
In the dark the alge have no effect.

During the decade and a half which have elapsed since En-.
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, zodspores, Flagellata, Infusoria, and
bacteria; ADERHOLD (788), of Euglena viridis; VERWORN
(89, p. 107), of Cryptomonas ; STANGE (90), of zodspores 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 ;
BucuHnER, 791; 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 spermatozodids. It can hardly be questioned that.
the phenomena shown by these organisms are of the same order
as those seen in Metazoa—1in those ants which LuBBocxk (’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 larve of flies with which Lors (’90, p. 79) has experi--
mented. Lors found that these crept towards a piece of flesh:
brought nearer to them than the distance of 1.5 cm. Even just
hatched larve (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 larve strongly. While decaying flesh

and cheese allure, neither fat, asafcetida, nor ammonia do so.
D

34 CHEMICAL AGENTS AND PROTOPLASM (Cu. 1

Returning now to the simple organisms, let us 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 zodspores and bacteria to the edges of
the cover-glass, to the open end of a capillary tube (ADERHOLD,

A Air bubble
esa terete eet eo” :
Pn at mth Boece die et eek toy
bt ow" eee re
¢ ay" ae SPS. wee 8 ‘ae? te ee nie
.° Pa ae ae ie “Se *
ee Reh ae ; : avk\ Q oe
i * ta ae aah po ae
ei eae *.. Zone of Spirillum -':8 33 4%
2 ier ~ oS
oe ay cae eae
aN oe Zone of Anophrys ..¢3 % me
o%, “\ o -v ont ae o
oe tt aa * = ve ow
ae ee sit
_ & Be: >
“ hd 4%,
eid vf. oe o° cy
e? Ma ie ve Sree ey
“4 ‘ie les 0508? 200% She? a
oat pa Rt Aa Haw A.
CL. “Oe IW tat * atetets Te-

Fic. 2.— a. Corner of the glass slip covering a drop of liquid containing Spirillum
and Anophrys, showing their aggregation with reference to the aerated bound-
ing film of the drop. 0b. 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.)

ENGELMANN (794) 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. 8).

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

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Semel. ie ” Sot fad Pedy ;

5 5a

Fies. 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 affected by the small oxygen tension resulting
from the dim light (Fig. 5a).

36 CHEMICAL AGENTS AND PROTOPLASM [Cu. 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, cesium, 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 zodspores of a Saprolegnia belonging to the ferax
group of DE BAry.+ Sodic, ammonic, lithic phosphate, calcic
phosphate held in solution by CO,, as well as phosphoric acid
were employed and found to act attractively. Other salts,
KNO,, K,SO,, KCl, HKCO,, BaClO,, SrCO,, MgSO,, had
either a negative or indifferent action upon the zodspores.

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 zoéspores 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 Prerrer 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.

+ 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.

CHEMOTAXIS 37

§ 3]

organisms pass only into the first part of the tube; a,7,, such
a balancing of the opposing forces that the organisms stand

before the mouth of the capillary tube.

ie aw Be weerate Sopic Drpuos- | Porasstc Mono- | AMMonIUM PuHos- | PHOSPHORIC
%’s. 5 PHATE PHOSPHATE PHATE Actp

(HNa,PO,). (HK PO,). (H,NH,4P0O, ?). (HgP0O,).

morte 04... . AsIo Adfy Ass n

04 to 0.08 ... Ayr; Aer,

0.08 to 0.04 ... ay dy a, Ayr,

BOs tp)0.02 - v6 0 ay, a, ay’;

0.02 to 0.008... 0 0 ay

0.008 to 0.004... . a,

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 (785, pp. 222, 223) states that mammalian
spermatozoa are attracted by KHO. !

Organic Compounds.— Alcohol, in grades between 10% and 1%,
-acts repulsively towards bacteria. Glycerine is neutral to the
same organisms and to zodspores 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 PFEFFER (’84) 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 0.14 mr.
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 [Cu. I

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

STANGE (90, p. 155) has experimented much more fully
- with the action of organic acids upon zodspores of Saprolegnia
and upon myxameebe. 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 amcebe of
Axthalium, its repellent action being about equal to the attrac-
tive action of an equal amount of butyric acid.

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

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 zodspores to phosphates, as well as the
cases of attraction of bacteria (PFEFFER, ’88, p. 605) and of fly
larve (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.

General Remarks on the Relation between Molecular Composi-
tion and Response. — PFEFFER (’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. (PFEFFER, ’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 (C,H,,0,)
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 between the Strength of the Stimulus and that of the
Response. — 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

* Staut (’84, p. 164) called the attraction of plasmodium of myxomycetes to
bark extract ‘* Trophotropism.”’

40 CHEMICAL AGENTS AND PROTOPLASM (Cu. 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 “ Reizumfang.”’

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 (788, p. 599)
has employed the nomenclature which we have used above
(p. 86) — a, to a, 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 (a) in Bodo saltans: KCl, 0.02%; KsPO4, 0.002%; KH2POx,,
0.0035%; KNOs, 0.26%; KeSO4, 0.22%; KCl0s, 0.3%; K4(CN)6Fe, 0.235% ;
Ke - CgHOo, 0.02%; RbCl, 0.14%; LiCl, 0.6%; LiNOs, 3%; NH,Cl, 0.8%;
neutral ammonium phosphate, 0.08%; SrCle, 0.2%; Sr(NOg)e, 0.4%; BaCle,
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

RESPONSE OF
GRADE OF SOLUTION.
BACTERIUM TERMO. SPIRILLUM,
9.53 % KCl = 5% K ay 31s
1.906 % KCl = 119K as sr;
0.191 ¥, KCl = 0.1% K as dy
0.019 % KCl = 0.01% K ay a,
0.0019 % KCl = 0.001% K a, 0
Bopo SALTans,
3.48% KH,PO, =10%K asf";
0.348% KH,PO, = 0.1%K Ayr,
0.0354, KH,PO, = 0.01% K a,
0.0035 ¥% KH,PO, = 0.001% K a,
0.00067 %, KH,PO, = 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 (Cu. 1
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 threshold stimulations but also the
concentrations necessary to produce the response indicated
by a, a, etc. The following table, from PFEFFER (88,
p. 634), gives some of such determinations: —

CAPILLARY FLurip — MgEaAT EXTRACT.
CuLtuRE Fiuip—

Megat ExtTrRActr.

8 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 % (a)
0.5 % (a,)
5% (4)

0.08 % (ay)
0.8% (42)
8% (42)

0.1% (a,)
1% (42)
10% (a2)

§ 3] CHEMOTAXIS 43

From this table it appears that the 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 may be defined as the minimum increase of a preéxisting
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 preéxisting (culture)

stimulus, and this is true whatever the degree of the preéxist-
ing stimulus; and it is shown by experiment that, in general,
as the preéxisting 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
WEBER 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 7’. 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 stimulation 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 (31s), the solution in the capillary tube must
be 30 times stronger (30 x 31s) 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-

+4 CHEMICAL AGENTS AND PROTOPLASM [Cu. I

tions may be shown by the following table, following one given
by PFEFFER (8, p. 401) :—
s corresponds to 7’.
s+ 303s = 31s corresponds to r'+r.
313+ 30x 31s= 31 x 31s corresponds to r/+r+r.
31 x 31s+30 x31 x 31s = 31x31 x 31s corresponds to r'+r+r+r.

That is to say, while the stimulation increases geometrically,
the reaction increases arithmetically. 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 (7) 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 ¢ 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 Retz (initial R), and since the re-
action is usually indicated by the initial letter in Empfindung, in German text-
books this formula usually runs H=c-log R, which differs from the above
equation only in the symbols employed.

ve
ty
4
7+
ma d

SUMMARY 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 amceboid, 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, p. 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 [Cu. I

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 Borr (90, p. 479), it takes of gold
chloride to kill —

TABLE V
Anthrax bacillus . .. . . . 0.0125%
Cholera spirillum . . ... . 01%
Diphtheria bacillus ... . . 01%
Typhoid bacillus . . . . . . 0.2%

Glanders bacillus . . . . . . 0.25%

x?
é)
iP
4,
'
,
i
:

y
‘|
,
“*
i
7
7

az
<
“
as
'
’

SUMMARY OF THE CHAPTER 47

Thus the weak solution, 0.0125%, of AuCl,, 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-
eal 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 kinds
of molecules, or the proportions 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 AuCl, upon anthrax
and typhoid may be accounted for by assuming that the amido-
acids are dissimilar in anthrax and typhoid 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 AuCl, 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
Borer (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). 60. eae
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 [Cu. I

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

TABLE VII

CAUSTIC CARBOLIC | MuRIATIOC SULPHURIC METHYL

SUBSTANCES. Sopa AcID AcIp AcIp VIOLET,
(NaHO). (CgH,0). (HCl), (H,S0,).
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 GoLp MALACHITE | OXYOYANIDE
SUBSTANCES. NitRATE | CHLORIDE GREEN. or Hg. AVERAGE.

‘(AgNOs). | (AuCl3).

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% HCN
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 H,SO,-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; 0. salt-forming poisons; ¢. 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-
E

50 CHEMICAL AGENTS AND PROTOPLASM [Cu 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.

b. 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.

ce. 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, anesthesia. The poisonous action seems here
proportional to the complexity and instability of the compound.
Thus, in many groups, when the alkyls CH,—, C,H;—, 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 Cl for H increases the poisonous action.

‘=
¢
+
7
a,
A
=)
ih
=

, << ne a!

a

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 anes-
thetic or paralyzing agents—e.g. chloroform and some alka-
loids, veratrin, atropin, cocaine, strychnin, and antipyrin—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 lecomotion is’ interfered with by strychnin and co-
caine. Their stimulating action produces accelerated move-
ments, and these are accompanied by loss of codrdination.

Since many catalytic poisons (anesthetics) destroy ?trrita-
bility, 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 exeretory function results from the action
of CO, NH,, chloroform, cocaine, strychnin; at least, an ex-
cessive vacuolation of the protoplasmic body occurs under the
action of these agents.

52 CHEMICAL AGENTS AND PROTOPLASM [Cu. I

Experiments on chemotaxis 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 (= Cytotropism)

Roux (9+) has given the latter name to a phenomenon which
is probably only a special case of chemotaxis, but which may be
better considered apart. He isolated, in an indifferent medium,
two or three cells from the egg 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 slowly,
and that the direction of the movement of any one cell was,
under certain conditions, determined by the position of the
other cell or cells.

In order to perform the experiment a proper medium in which to study
the movement of the cells must be prepared as follows: a small quantity —
5 to 10 cem.—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 ;

' pair, the path of migra-

APPENDIX — CYTOTAXIS 53

and when several pairs of cells were in the field, this movement
took place in various directions, indicating that their move-
ment was not determined by conditions outside the approaching
cells. To get further light on the migration of the cells, their
distance apart was meas- a -
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 \
points 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 p)
in about 10.5 minutes.
The rate of migration
is, however, extremely
variable. In some cases %

the cells seem even to

move apart (negative Fics. 6, 7. — Two sets of curves, showing the

“9 course of ‘‘cytotactic’’ movements of the

cytotaxis ?) cleavage cells of the frog. In each figure

Certain special eases the dotted line represents a diameter of the

: cell. The full line represents the successive

me? worthy of considera- positions of the extremities of the diameters

tion. When a third cell as the cells approach. The distances between

lies near an approachin horizontal lines = 4 ; between vertical lines,
PP 8 75 seconds. (From Roux, ’94.)

we mel te el me me fe oe le te el

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-

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tion of the pair may become convex towards the third cell.
Two cell-complexes, each composed of three or four cells,
may approach and connect. But masses composed of a
larger number of cells form “closed complexes” which
show no eytotactic activity. The isolated cells of differ-

54 CHEMICAL AGENTS AND PROTOPLASM [Cu. I

ent eggs of the same species behave like cells 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.

LITERATURE

Appvuco, V. 790. Sur l’existence et sur la nature du centre respiratoire
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ALBERTONI, P. 91. Wirkung des Cocains auf die Contractilitit des Proto-
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BERNARD, C. 778. Lecons sur-les phénomenes de la vie communs aux ani-
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Boer, O.’90. Ueber die Leistungsfahigkeit mehrerer chemischer Desin-
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Boscu, C. TEN °80. De physiologische werking van chinamine. Onder-
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Bryz, C. ’67. Ueber die Einwirkung des Chinin auf Protoplasma-Bewe-
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Binz, C. and Scuuuz, H.’79. Die Arsengiftwirkungen vom chemischen
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Boxorny,.T. 86. Das Wasserstoffsuperoxyd und die Silberabscheidung
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88. Ueber die Einwirkung basischer Stoffe auf das lebende Protoplasma.
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93. Ueber die physiologische Wirkung der tellurigen Siure. [Abstr. in]
Bot. Centralbl. LVII, 16.

Bourne, A. G.’87. The Reputed Suicide of Scorpions. Proc. Roy. Soc.
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Bucuner, H.’91. Die chemische Reizbarkeit der Leukocyten und deren
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92. Die keimtodtende, die globulicide und die antitoxische Wirkung
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CatmetTrTeE, A.’94. L’immunisation artificielle des animaux contre le venom
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eae yt es

LITERATURE 55

CHARPENTIER, A. ’85. Action de la cocaine et d’autres alcaloides sur cer-
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184.

Criark, J. 89. Protoplasmic Movements and their Relation to Oxygen
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Coun, F. 94. Formaldehyd und seine Wirkung auf Bacterien. Bot.
Centralbl. LVI, 3-6.

DaniLewskI, B. ’92. Ueber die physiologische Wirkung des Cocains auf
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DAREMBERG, G. 91. Sur le pouvoir destructeur du serum sanguin pour les
globules rouges. C. R. Soc. Biol. XLIII, 719-721.

Darwin, C.’75. Insectivorous Plants. 462 pp. New York: Appleton & Co.

Davenport, C. B. and Near, H. V., 96. On the Acclimatization of
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Demoor, J. 94. Contribution 4 l’étude de la physiologie de la cellule (in-
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Dewirz, J. 85. Ueber die Vereinigung der Spermatozoen mit dem Ei.
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Euruicsg, P.’91. Experimentelle Untersuchungen iiber Immunitat. I Ueber

Ricin. II Ueber Abrin. Deutsche med. Wochenschr. 976-979; 1218,
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Exrvine, F.’86. Ueber die Einwirkung von Ather und Chloroform auf die
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ENGELMANN, T. W. ’81. Neue Methode zur Untersuchung der Sauer-
stoffauscheidung pflanzlicher und thierischer Organismen. Arch. f.
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82. Ueber Licht- und Farbenperception niederster Organismen. Arch.
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94. L’émission d’oxygeéne sous l’influence de la lumiére, par les cellules
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Fayrer, J. 74. The Thanatophidia. 2d ed., 178 pp., 31 pls. London:
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FRoMANN, C. ’84. Untersuchungen iiber Struktur, Lebenserscheinungen
und Reaktionen thierischer und pflanzlicher Zellen. Jena. Zeitschr.
XVII, 1-349. Taf. I-III. 19 Jan. 1884.

GREENWOOD, M.’90. On the Action of Nicotin upon Certain Invertebrates.
Jour. of Physiol. XI, 573-605. Dec. 1890.

HEIDENSCHILD, W. ’86. Untersuchungen iiber die Wirkung des Giftes der

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Hertwie, O. and R. ’87. Ueber den Befruchtungs- und Teilungsvorgang
des tierischen Eies unter dem Einfluss dusserer Agentien. Jena.
Zeitschr. XX, 120-241. 8 Jan. 1887.

56 CHEMICAL AGENTS AND PROTOPLASM [Cn. I

Horer, B.’90. Ueber die lahmende Wirkung des Hydroxylamins auf die
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Kantuack, A. A. 92. The Nature of Cobra Poison. Jour. of Physiol.
XIII, 272-299. May, 1892.

KRUKENBERG, C. F. W.’80. Vergleichend-physiologische Studien. 1 Reihe,
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Ktune, W.’64. Untersuchungen iiber das Protoplasma und die Contrac-
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LreBeR, T.’88. Ueber die Entstehung der Entziindung und die Wirkung
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Locks, F. 8. 95. Ona Supposed Action of Distilled Water as such on Cer-
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1895.

Logs, J.’90. Der Heliotropismus der Thiere und seine Uebereinstimmung
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Loew, O. ’77. Lieutenant Wheeler’s Expedition durch das siidliche Cali-
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’83. Sind Arsenverbindungen Gift fiir pflanzliches Protoplasma? Arch.
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85°. Ueber die Giftwirkung des Hydroxylamins verglichen mit der von
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30 Jan. 1885.

’87. Ueber Giftwirkung. Arch. f. d. ges. Physiol. XL, 437-447.
18 May, 1887.

’°88. Physiologische Notizen iiber Formaldehyd. Sb. Ges. f. Morpol. u.
Physiol. Miinchen. IV, 39-41.

791. Die chemischen Verhialtnisse des Bakterienlebens. Centralbl. f.
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792. Ueber die Giftwirkung des Fluornatriums auf Pflanzenzellen.
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93. Ein naturliches System der Gift-Wirkungen. 136 pp. Miinchen,
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Loew, O. and Boxorny, T.’89. Ueber das Verhalten von Pflanzenzellen zu
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Marmier, L. ’95. Sur la toxine charbonneuse. Ann. de |’Inst. Pasteur.
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LITERATURE 57

Massart, J. 93. Sur Virritabilité des Noctiluques. Bull. Sci. France et
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Nixotsk1, W.and Doeret, J.’90. Zur Lehre iiber die physiologische Wirkung
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OHLMULLER, 92. Ueber die Einwirkung des Ozons auf Bacterien. Chem.
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Ricuet, C.’89. Lachaleur animale. 307 pp. Paris: Alcan.

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Rosssacn, M. J. ’72. Die rythmischen Bewegungserscheinungen der ein-
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Tsuxamoto, M. ’95. On the Poisonous Action of Alcohols upon Different
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VeRWwoRN, M.’89. Psycho-physiologische Protisten-studien. 218 pp. 6 pls.
Jena: Fischer.

CHAPTER II
EFFECT OF VARYING MOISTURE UPON PROTOPLASM

In this chapter it is proposed to speak (1) 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. ON 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 OF WEIGHING. % WATER.
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] st fromcentralcavity | 83.2
Aleyonium palmatum (K)..... Weighed when fresh, 73.5 g. 84.3
Asteracanthion glacialis (K). . .. | Weighed 850 g. 82.3
Lumbricus complanatus (K)... . | 2 large specimens 87.8

58

.

>.
id
7

ale Mien (=
0 an

§2] DESICCATION AND PROTOPLASMIC FUNCTIONS 59

SPECIEs. ConDITIONS OF WEIGHING. % Water.
Oniscus murarius (B)........ 200 young individuals 68.1
Squilla mantis (K) ......... 1 individual 81.9
Astacus fluviatilus (B)....... 3 individuals weighing from 16.6 to
27.4 g. 71.1
Doris tuberculata (K)........ 88.4
Doriopsis limbata (K) ....... 3 individuals 86.5
Arion empiricorum (B)....... 6 individuals weighing from 4.5 to
7.1 g. 86.8
Limax maximus (B) ........ 4 individuals weighing from 0.1 to
17.1 g. 82.1
MEE VEITS (0S) 6 os wk ko a ss 4 individuals weighing from 111.2
to 35.2 g. 93.6
Various Vertebrates (B)...... 58.4 to
80.1
REINS ital ss Se aie oun ee
PRMIPOME Sant ta aah o, 050, 4-3 Embryo only, yolk removed 92.8
DENN MIME sca <y owl o 6, , 2 w Embryo only, ready to hatch 80.4
PRY ATOOR)) oof se eb oe es 3 From Goodale’s Physiolog. Bot., p.
236 91.0

These determinations suffice to show that water immensely
predominates over any other 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 FuUNC-
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 [Cu. IT

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
Kocus’ (’90, p. 685), who placed seeds, which had been dried
in a vacuum, in a receptacle connected with a GEISSLER’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 GEISSLER’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 Prétista, 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 adry 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. 446) in the case of the spermatozoa of the
frog, and the ciliated epithelium of the frog’s cesophagus 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 PREYER (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 was
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, by 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, 794.) Among nematodes, Tylenchus devastatrix,
KUHN, 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 certain species may be
subjected to desiccating influences, and that those same indi-
viduals may resist them so as to reéxhibit 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 valuable report of Broca (’61).

62 MOISTURE AND PROTOPLASM [Cu. 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. 817) 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 with 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

4
e°
AR

§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
Hupson (‘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 Kocus (790) 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 (791), 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 (Cu. 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 Kocus (790), 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, the 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
MUnTER (747), and more especially of Kocus (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, Kocus
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, z.¢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 Rai.uret (’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 Anguillulide.”’’

§ 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.

§ 8. ON THE ACCLIMATIZATION OF ORGANISMS 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.
(94) 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) has found.
that, although marine Ciliata cannot, in general, withstand.
desiccation, those from the chotts 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.
F

66 MOISTURE AND PROTOPLASM [Cu. II

§ 4. THE DETERMINATION OF THE DIRECTION OF MOvyE-
MENT BY MOISTURE, — HYDROTAXIS

This phenomenon has been described by STAHL (’84) in
Aithalium. 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 overit. 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’sS 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 Aithalium is in the fruit-
ing stage, it retreats from the moister part of the substratum,
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

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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 probably 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. pe ’26. Sur quelques petits Animaux qui, aprés avoir
perdu le mouvement par la dessication, le reprennent comme aupara-
vant quand on vient a les mettre dans l’eau. Ann. des Sci. Nat. IX,
104-110.

BEzoLp, A. von ’57. Untersuchungen iiber die Vertheilung von Wasser.
organischer Materie und anorganischen Verbindungen im Thierreiche,
Zeitsch. f. wiss. Zodl. VIII, 487-524. 26 Feb. 1857.

Bos, R. ’88. Untersuchung iiber Tylenchus devastatrix, Kiiun. Biol. Cen-
tralb. WII, 646-659. 1 Jan. 1888.

Broca, P. ’61. Rapport sur la question soumise 4 la Société de Biologie
par MM. Poucuet, PENNETIER, TrnEL et Doykre au sujet de la révi-
viscence des animaux desséchés, lu par M. Paut Broca au nom d’une

68 MOISTURE AND PROTOPLASM © (Cu. I

commission comp. de MM. Basrani, BERTHELOT, BRown-SEQUARD,
DARESTE, GUILLEMIN, CH. Rosin et Broca. Mém. Soc. de Biol.
(3), 1-139.

Biscuit, O. ’89. Protozoa (part). Bronn’s Klass. u. Ord. d. Thier-reichs.
I Bd. 1585-2035. 1889.

Crertes, A. 92. Sur la vitalité des germes des organismes microscopique
des eaux douces et salées. Bull. Soc. Zool. France. XVII, 59-62.

Davis, H. 738. A New Callidina: with the Result of Experiments on the
Desiccation of Rotifers. Monthly Micr. Jour. IX, 201-209. 1 May,
1873.

DrEHNECKE, C. 81. Einige Beobachtungen iiber den Einfluss der Pripa-
rationsmethode auf die Bewegungen des Protoplasma der Pflanzenellen.
Flora. LXIV, 8-14, 24-30. 1, 11 Jan. 1881.

Dorére, M. P. L. N. 42. Mémoire sur les Tardigrades. Ann. des. Sci.
Nat. (2) XVIII, 5-35.

ENGELMANN, T. W. ’68. Ueber die Flimmerbewegung. Jena. Zeitschr.
IV, 321-479.

Faaarout, F.’92. De la-prétendu reviviscence des Rotiféres. Arch. Ital.
de Biol. XVI, 360-374. 31 Jan. 1892.

FROMENTEL, E. pe ’77. Recherches sur la revivification des rotiféres, des
anguillules et des tardigrades. C. R. Assoc. franc. l’avanc. des sci.
VI (Le Havre), 641-657.

GAVARRET, J. ’59. (Quelques expériences sur les rotiféres, les tardigrades et
les anguillules des mousses des toits. Ann. Sci. Nat. (Zool.). (4), XI,
315-330.

Hupson, 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.

Kocus, W. ’90. Kann die Kontinuitat der Lebensvorginge zeitweilig vol-
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.
Vergl.-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. XLII, 71-157. 7 Apr. 1888.

Munter, J. 47. Flora. XXX, 478.

Poucnuet, F. A. ’59. Recherches et expériences sur les animaux ressusci-
tants. Paris: J. B. Balliére et fils. 92 pp. 1859.

Preyer, W. ’91. Ueber die Anabiose. Biol. Centralbl. XI, 1-5. 1 Feb.
1891.

RariueT, A. 92. Observations sur la resistance vitale des embryons de
quelques Nématodes. C. R. Soc. de Biol. XLIV, 703, 704.

LITERATURE 69

rwoscH, D. ’89. Einige Beobachtungen an Tardigraden. Sb. Naturf.
- Ges. Dorpat. IX, 89-92.

zANI, L. 1787. Oeuvres: Opuscules de physique, animale et vege-

tale, etc. Trans. Jean SeneBier. 3 tomes. Pavia and Paris.

" TAHL, E. ’84. (See Chapter I, Literature.)

_Zacuarias, O.’86. Kommen die Rotatorien und Tardigraden nach vollstin-

___ diger Austrocknung wieder aufleben oder nicht? Biol. Centralb. 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; (11) 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. InTRopucTORY REMARKS UPON THE STRUCTURE OF
PROTOPLASM 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 Burscuui, 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.+ Such a mem-

* Excellent treatises on the physical and chemical nature of solutions, in-
cluding a discussion of osmosis, are: Ostwa.p, ’91, and Wuernam, ’95,

+ 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 confined, 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 KNO, 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 K,SO,, 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 (84) 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 have

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

72 SOLUTIONS AND PROTOPLASM [Cu. III

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 VRIEs 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 DE 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 the
solution (molecular-weight solutions +) : —

(1) All salts of alkalis with one atom of metal to the molecule are
isotonic (formula, R'A' [composed of a monad metallic
radicle, #, and a monad acidic radicle, A});

(2) All organic compounds with no metal radicle have two-thirds the
osmotic action of the first group; e.g. cane sugar, C,.H..0,).¢

* 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.)

+ I shall use the phrase ‘ rdlaculayemelsit 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 MW Y% sol. Chemists frequently use as a unit
solution, called ‘‘normal’’ solution, the molecular weight in grammes dissolved
in 1000 g. of water. Our MW % sol. is therefore equal to one-tenth of a ‘‘normal”’
solution.

t 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 pe Vrizs (’88), who,
by the use of slowly absorbing plants, has found the isotonic coefficient 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, R,'A"); e.g.
K;SO,.

(4) Salts of alkalis with three atoms of the metal to the molecule
have five-thirds the osmotic action of (1) aan R,'A");
e.g. K,(C,H;0;).

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 Jsotonie Coefficients of DE VRIES. In addition to
these substances, DE VRIES determined that the isotonic coeffi-
cient is, in the case of —

salts of earthy alkalis with 1 acid radicle; eg. MgSO, . . 2
salts of earthy alkalis with 2 acid radicles; eg. CaCl, . . 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

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

oOo eR bb

while of the compounds the isotonic coefficients are —

KCl =1+2=8, MgSO, = 0+ 2 = 2,
K;(C,H;0;) = 3 x 1 + 2 — 5, etc.

The determination of isotonic coefficients has subsequently
been extended by several authors, especially by HAMBURGER
(86 and ’87) and by MAssart (89).

The work of HAMBURGER was done upon blood corpuscles.
The method employed by him was as follows: In certain weak
solutions the hemoglobin 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.

T4 SOLUTIONS AND PROTOPLASM 3 (Cu. III

The work of MAssArt was done chiefly upon bacteria. He
made use of the fact demonstrated by PFEFFER (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 coefficient 2 just begins to repel bacteria, a substance
which just begins to repel ina 5 MW % concentration has an
isotonic coefficient of 4.* ;

§2. ErrecT 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; (0) the modification of gen-
eral functions, and (c) the production of death.

* Starting from the observations of Prmerrrer and pg Vrixs the modern school
of physico-chemists has greatly extended our knowledge of solutions. As a
result of their work it appears that the validity of pk 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
CaCle, 53% (each into 8 ions) ; of MgCle, 40%; of KI, 79%; of MgSOx, 19%;
of Na2SO,4, 35.6 % (each into 3 ions); and soon. Valuable and extensive tables
for the determination of the percentage of dissociation at different concentrations
will be found in WuerTuam, ’95.

§ 2] EFFECT ON STRUCTURE AND 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.

Fic. 8.—1. Young, not more than half-grown, cells from the cortical parenchyma
of Cephalaria leucantha. 2. The same cell in a 4% solution of potassium nitrate..
3. The same cellina6% solution. 4. The same cellina10%solution. 1 and 4.
from nature, 2 and 3 diagrammatic, all in optical longitudinal section. h, cell
membrane; 7p, lining layer of protoplasm; &, cell nucleus; c, chlorophyll bodies ;
8, cell-sap; e, salt solution which has penetrated within the cell-membrane. (From:
Sacus: Pflanzenphysiologie, 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 Amceba
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 Ameweba and Myxomycetes
changes. They become more numerous and attenuated, so that

76 SOLUTIONS AND PROTOPLASM [Cu. IIL

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 spermatozoén 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 MAssAart (789) 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. MAssarv has,
indeed, obtained a rough quantitative expression of this state-
ment, which is given in Tables X and XI, p. 87. HAmBuR-

Fic. 9.— Blood corpuscles of the frog. 1, 2, normal; 3, 4, 5, various degrees of
plasmolysis by solutions. a, nucleus and shrunken plasma; 06, water-filled
spaces. (From HAMBURGER, ’87.)

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

Again, GRUBER (89) has found those individuals of the
heliozodn 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. Ifa 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 Ameeba 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 TT

water flagellate Anisonema acinus, BUTSCHLI, 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. Brrt (’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.

6. 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 Amceba
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 cesophagus 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.
(KUuNE, 64, p. 48; ENGELMANN, 68, p. 343.)* Ata certain

* A similar cessation of movement occurs when the lower organisms are sub-
jected in water to very great pressures. Experiments upon this phenomenon
have been made chiefly by Reanarp (’84, ’849-’844, and ’86), Certes (84,
*84*), and Rocer (’95). RrGNnarp 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 alge, 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 (Cu. Il

strength, however, varying for different individuals (ENGEL-
MANN, CZERNY), death rapidly ensues. Thus Amceba 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, RIcHTER (°92, pp. 37-40) found that while normal
Tetraspora swarm-spores move at the rate of about 60m 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 Rosspacu (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 a1% 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., 8342) is much less than in a 1%
solution of NaCl (mol. wt., 58.5), and their relative osmotic

2 4
3x 3423x585" or as 0.002: 0.017, or as 2: 17.

The phenomenon of contracting vacuoles seems not to be
confined to Protozoa. It occurs in the embryos of some Mol-
lusea, especially the stages of fresh-water Pulmonates, upon
which my friend, Dr. Kororp, performed some density experi-
ments. The early cleavage and blastula stages of many fresh-
water Pulmonates contain a central fluid-filled vacuole, which

action is as

300 atmospheres loses its contractility, and at 400 atmospheres becomes rigid
and hard. It also increases immensely in weight by the addition of water.
Rocer 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. Korormp (795, 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 BERT (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 stinauli, and, finally,
pass into complete paralysis. The action is slower upon
Crustacea and fish; but here, too, fresh water acts as an an-
esthetic. The respiratory movements become deep and rapid,
bivalves extend their branchiz, and Crustacea beat the water
rapidly with their appendages in order to renew the supply.
Animals ordinarily transparent, like meduse, 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 Gocorza, I am indebted to the kindness of
Mr. F. C. Waite.

80 SOLUTIONS AND PROTOPLASM 3 (Cu. IT

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 Seyllium canicula, placed in fresh water.

AFTER 2 Hours. Arter ?4 Hours.
% Increase in | % Increase in || % Increasein | % Increase in
Weight. Volume. Weight. Volume.
Muscular tissue... . 15 50 20 200
Glandular tissue ... 12 0 19 100
Nervous tissue .... 20 50 60 250

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 (66), PLATEAU (71), CouTANCE (’83), RINGER and
.Buxton (85), DE VARIGNY (’88), MAsSSART (’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 Sparus 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 both 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 skin (and cuticula) diminished. Thus, when plunged

_into sea water (3.046% salts) adult water insects resisted in-

definitely ; insect larve 6 to 4 hours; Entomostraca less than
an hour; Nephelis, 5 to 7 minutes; Planaria, 4 minutes; and
Hydra only 1 minute. GoGorzaA (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, ccelenterates. ‘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,
MgCl, 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
or Sea Satt. TEMPERATURE NOT GIVEN

(Numbers indicate minutes elapsing before death occurred)

8% NaCl. 8% MgClp. 3% MgSO,.

Mot. Wr., 58.5; | Mot. Wr., 95; | Mot. Wr., 120; Gira.
SPECIES. 1 C., 8; Osmotic | L.C., 4; Osmotic | LC., 2; Osmorte | wire

’ INDEX, a. A INDEX, 4s INDEX, 2

58.5 95 120
Gammarus roeselii. . 105 131 520 © 230
Asellus aquaticus .. 155 1162 2000 160
Daphnia sima .... 7.8 19.5 87 22
Cyclops quadricornis 12.1 37 690 257
Cypris fusca ..... 26.7 223 460 36

Although from this table it seems clear that there is an
inverse relation between resistance period and osmotic index,

PLATEAU did not believe that the death of the animals experi-
G

82 SOLUTIONS AND PROTOPLASM (Cu. 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,
MgCl,, 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 Bert (71). The work of the latter was done chiefly
upon fresh-water fishes; incidentally, upon frogs and some
fresh-water 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 BERT in observing that the
resistance period varies with the temperature; thus, the
European minnow (Phoxinus levis) 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. GoGoRZA
(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.* GoGorza’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 2 3 4 5 6 7
¥, of salt in solution....]| 3.7 | 2.8 | 2.5 | 19 | 12 | 09 | 0.00
Rel. resist. per... ...%. Indef.| 50.0 | 28.3 | 10.83| 5.44) 3.46) .1.84
Log. of rel. res. per... . . 1.7 | 145] 1.04] 0.73] 0.54]
Log. rel. res. per. x 1.7 .. aU Va hes |: Le TOD

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

84 SOLUTIONS AND PROTOPLASM — (Cu. III

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, z.e. as the ordinates increase the abscissz increase
as the logarithms of the ordinates. In line 4 are given
the (Briaes’) loga-
rithms of the num-
| bers in line 3,.and
|
|

50 50

in line 5 these loga-

49 Yithms are each mul- |

tiplied by a constant,

1.7, which gives a

| series of numbers

m ] 30 closely similar to

that of line 2. The

/ relation between

- density and_ resist-

ance period can thus

be expressed by the
/ equation

2 a ee hae

= in which D stands for
density; &, for re-
0 : : : By cota ;
0 9 12 19-25 BB 3.7 sistance period; and
Fig. 10.—Curve showing relation between the per- is aconstant whose
centage of salt in mixtures of fresh and salt water value depends upon
(abscissze) and the mean resistance periods in hours
of various organisms plunged therein (ordinates). the system of loga-

Constructed from the table. (After data of Go- rithms employed.
GORZA, ’91.)

This formula may be

ue m ,
transformed into the equivalent: =e, in which e is the
base of the NAPERIAN system of logarithms. Since the
osmotic pressure is proportional to the concentration (p. 71),

O

it follows also that R =e’ where O 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

§ 38. 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 (116)
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
V ARIGNY (’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 Mollusca (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,
are able to migrate from fresh to salt water and back, with impunity. On the
other hand, 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. (Lerpy, ’72, p. 165.)

86 SOLUTIONS AND PROTOPLASM . (Cu. Ill

Turbo, Arca, 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 aquaticus 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 Protasea
may become acclimated. Ror# 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 Amceba to a 4%
solution of NaCl, although Ameba 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 alge, by RICHTER (92); upon Myxomycetes, by
STAHL (’84); upon Actinospherium, by VERWORN (’89, p. 10);
upon bacteria, Flagellata, Ciliata, and Hydra, by MAssArRT
(89); upon Ciliata, by FABRE-DOMERGUE (788); upon Crus-
tacea, by PLATEAU (71), SCHMANKEWITSCH (75 and ’77),
and Bert (’83); upon the tadpoles of frogs, by Yune (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 87

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 GoGoRZA (91, p. 270), acclimatization is more
easily effected at a low temperature than at a high one.

Of the papers mentioned above, that of MASSART is especially
worthy of extended notice from its quantitative nature. He
subjected cysts of Ciliata to various concentrations of KNO,
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; p, 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 toa 3 MW {&% solution of
KNO, respectively. The observations were made immediately
after immersion of the cysts. No mention is made of the
temperature.

TABLE X— VortTICELLA

HuNDREDTHS OF MOLECULAR WEIGHT. | 0.5/1.0) 1.5 | 2.0) 2.5 | 3.0 | 3.5 | 4.0} 5.0

Unacclimated .......... vi vivplvp| p| P P
Acclimated to 1.8%....... v |vopivp| p|P|P
Acclimated to 3.0%....... vp|p|iP|\P

TABLE XI—Cotpopa

HuNDREDTHS OF MOLECULAR WEIGHT. | 0.5/1.0/ 1.5 | 2.0 | 2.5 | 3.0 | 3.5 | 4.0) 5.0

Unacclimated ........../0/v|v] ov v |v
Acclimated to 1.8 MW%.... 0 |v | vo | vp
Acclimated to 3.0 MW%.... v | p

ys ic
~'y

83 SOLUTIONS AND PROTOPLASM (Cu. III

If we take as our unit in Table X the concentration repre-
sented by vp, and in Table XI the concentration represented
by v, we may conclude that the subjection for 22 hours to a
1.8 MW % orto 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 has been argued
by MAssArT (’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 VRIES,
’°88 and ’89) have been observed to penetrate protoplasm.+
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
C71, 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 cultures 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 ; Anabena and Tetraspora, 0.018 MW %,
added monthly ; Ciliata, 0.0083 MW %, daily ; Hydra viridis, 0.001 MW %, daily
for 6 days; Tubifex, 0.02 MW 9%, daily; tadpoles, 0.004 to 0.014 MW %, daily.

+ 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,
MaAssArt 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 KNO,,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 KNO,. 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 RicHTER (’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
DeEnsITy: TONOTAXIS

Three authors only, so far as I know, have concerned them-
selves with this phenomenon,—STAHL (’84), PFEFFER (84,88),
and MAssArT (’89, 91). Srau (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 repulsively, 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 (Cu. III

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 MAssART brought evidence against PFEFFER’S
conclusions, and added many important data. His studies
were made chiefly upon bacteria, to a less degree upon Flagel-
lata, 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 MAssArtT 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 55,555
MW % (0.00691 gr. %) K,CO, for the purpose of attracting
the bacteria. When a tube containing only this dilute solution
of K,CO, 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
K,CO,, 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 ;
a, that they merely gathered about its mouth; 0, that they

;
3
4
j
7

§ 4] TONOTAXIS 91

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

the different values of » in the formula, Sos 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. Corr. 3 1 2 3 zo 5 6 7 8 9 10
NH,Cl (er. On ey. en aa a 0 0 0 0 0
reer wha GS. A A A A a a 0 0 oO 0
OS ea Se 0 o 0 0 0 0 0 0 0 7)
ES cost. A A A A a a 0 0 0 0
NH,NO, A A A A a a 0 0 0 0
NaNO, eee we | a a a 0 0 0
Le aS A A A A a a 0 0 7) wy)
(tee ae A A A A a 0 0 0 7) 0
KCl1O, A A A A a 0 ) 7) 0 0
Ms et Ber, A A A A a a 0 0 0 0

From this table it appears that, as a rule, solutions of 55
MW % and over are repelled, while those of iovoy OF 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 coefficient is
4, solutions of itso MW % and over always repel, and those of
iooo in the majority of cases permit free migration. In the
case of those substances whose isotonic coefficient is 2, solutions
of over 3335 MW % repel, and those of under ;,8,5. 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 (Cu. Il

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 was 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 water. Distilled water. Distilled water.

Fic. 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 Massarrt, ’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

Fic. 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.)

such that they are repelled by either hyperisotonice 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

Bert, P. 66. Note sur la mort des poissons de mer dans l’eau douce.
Mém. Soe. Sci. phys. et nat. Bordeaux. IV, 47-49.

71. Sur les phénomenes et les causes de la mort des animaux d’eau
douce que l’on plonge dans l’eau de mer. Comp. Rend. LXXIII,
382-385; 464-467. Aug. 1871.

73. La mort des animaux d’eau douce que |’on immerge dans ]’eau de
mer. C. R. Soc. de Biol., Paris. XXIII, 59-61.

’83. Sur la cause de la mort des animaux d’eau douce qu’on plonge dans
eau de mer et réciproquement. Comp. Rend. XCVII, 133-136.
16 July, 1883.

Brupant, F. §S. ’16. Mémoire sur la possibilité de faire vivre des Mol-
é. lusques fluviatiles dans les eaux salines, etc. Jour. de Phys. LXXXIII,
. 268-284. 1816.

7 Birscuut, 0. ’92. Untersuchungen iiber mikroskopische Schiiume und das
Protoplasma. Leipzig. 232 pp. 1892.

ee re

94 SOLUTIONS AND PROTOPLASM —_[Cu.. IIT.

CertTEs, A. ’84. Note relative 4 l’action des hautes pressions sur la vitalité
des micro-organismes d’eau douce et d’eau de mer. C. R. Soc. de Biol.
XXXVI, 220-222.

842, De l’action des hautes pressions sur les phénomenes de la putri-
faction et sur la vitalité des micro-organismes d’eau douce et d’eau de
mer. Comp. Rend. XCIX, 385-388. 25 Aug. 1884.

Coutrancr, H. A. ’83. Action biologique des sels de l’eau de mer au point
de vue de l’entretien des animaux marins. Bull. de la Soc. d’ Acclimat.
(3) X, 98-106. Feb. 1883.

Czerny, V.’69. Einige Beobachtungen iiber Amoben. Arch. f. mik. Anat.
V, 158-163.

Emery, H. 69. Notes physiologiques. Ann. des Sci. Nat. (Zool.). (5)
XI, 305-325.

ENGELMANN, T. W. ’68. (See Chapter I, Literature.)

FaBRE-DOMERGUE ’88. Recherches anatomique et physiologiques sur les
infusoires ciliés. Ann. des Sci. Nat. (7) V, 1-140.

Freperica, L. ’85. Influence du milieu ambient sur la composition du
sang des animaux aquatiques. Arch. de Zool. (2) III, xxxiy-—
XXXViii.

GoGorza y GONZALEZ, D. J.’91. Influencia del aqua dulce en los Animales
Marinos. Annales de la Soc. Esp. Hist. Nat. XX, 220-271. 1891.

GrusB_er, A.’89. Biologische Studien an Protozoen. Biol. Centralbl. IX,

14-23. 1 March, 1889.

HamburGe_er, H. J. ’86. Ueber den Einfluss chemischer Verbindungen auf
Blutkorperchen im Zusammenhang mit ihren Molecular-Gewichten.
Arch. f. Anat. u. Physiol., Physiol. Abth. Jahrg. 1886. 476-487.

’°87. Ueber die durch Salz- und Rohrzucker-Losungen bewirkten Ver-
ainderungen der Blutkorperchen. Arch. f. Anat. u. Physiol., Physiol.
Abth. Jahrg. 1887. 31-50.

JANSE, J. M. 87. Plasmolytische Versuche an Algen. Bot. Centralbl.
XXXII, 21-26. |

Kororp, C. A. 95. On the Early Development of Limax. Bull. Mus.
Comp. Zool. XXVII, 35-118.

Ktune, W.’64. (See Chapter I, Literature.)

Leipy, J.’72. On Artemia from Salt Lake, Utah. ene, Acad. Nat. Sci.
Philad. 1872. 164-166.

Massart, J. 89. Sensibilité et adaption des organismes 4 la concentra-
tion des solutions salines. Arch. de Biol. IX, 515-570.

91. (See Chapter I, Literature.)

OstwaLp, W. ’91. Solutious. Translated by Murr. 316 pp. London:
Macmillan. 1891.

PLATEAU, F.’71. Recherches physico-chemiques sur les articulés aquatiques.
Mém. cour. |’Acad. Roy. Belgique. XXXVI, 68 pp. |

PrerFrerR, W.’77. Osmotische Untersuchungen. Leipzig. 1877.

84. (See Chapter I, Literature.) 3

88. (See Chapter I, Literature.)

Se.

LITERATURE 95

REGNARD, P.’84. Recherches expérimentales sur l’influence des trés hautes
pressions sur les organismes 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 4 l’action des hautes pressions sur quelques phéno-
meénes vitaux (mouvement des cils vibratiles, fermentation). C.R. Soc.
de Biol. XXXVI, 187-188.

84°. Sur la cause de la rigidité des muscles soumis aux trés hautes
pressions. C. R. Soc. de Biol. XXXVI, 310-311.

’844. Effect des hautes pressions sur les animaux marins. C. R. Soc. de
Biol. XXXVI, 394-395. .

°86. Action des hautes pressions sur les tissues animaux. Comp. Rend.
CII, 173-176.

Ricuter, A. ’92. Ueber die Anpassung der Siisswasseralgen an Kochsalz-
lésungen. Flora. L, 4-56.

Rincer, S. and Buxton, D. W. ’85. Concerning the Action of Small
Quantities of Calcium, Sodium, and Potassium Salts upon the Vitality
and Function of Contractile Tissue and the Cuticular Cells of Fishes.
Jour. of Physiol. VI, 154-161. July, 1885.

Rocer, H. ’95. Action des hautes pressions sur quelques bacteries. Arch.
de Physiol. (5) VII, 12-17. Jan. 1895.

Rosspacu, M. J. ’72. (See Chapter I, Literature.)

Roru, M. 66. Ueber einige Beziehungen des Flimmerepithels zum con-
tractilen Protoplasma. Arch. f. path. Anat. u. Physiol. XXXVII,
184-194. Oct. 1866.

ScCHMANKEWITSCH, V.’75. Ueber des Verhiltniss der Artemia salina Miln.
Edw. zur Artemia Miihlhausenii Miln. Edw. und dem Genus Bran-
chipus Schaeff. Zeitschr. f. wiss. Zool. XXV, Suppl., 103~116.

77. Zur Kenntniss des Einflusses der iusseren Lebensbedingungen auf
die Organisation der Thiere. Zeitsch. f. wiss. Zool. XXIX, 429-494.
6 Sept. 1877.

79. ([Abstr. in Nature. XXTIX, 274. 1884.]

Sra, E. ’84. (See Chapter I, Literature.)

Varicny, H. pe ’88. Beitrag zum Studium des Einflusses des siissen
Wassers auf die Seethiere. Centralbl. f. Physiol. I, 566-568. 21
Jan. 1888.

VERwoRN, M. ’89. (See Chapter I, Literature.)

Vries, H. pe 84. Eine Methode zur Analyse der Turgorkraft. Jahrb. f.
wiss. Bot. XIV, 427-601.

’88. Le Coefficient Isotonique de la Glycerine. Arch. Néerland. XXII,
384-391.

’89. Ueber die Permeabilitat der Protoplaste fiir Harnstoff. Bot. Ztg.
XLVI, 309.

Wuetuam, W.C.D.’95. Solutions and Electrolysis. Cambridge Nat. Sci.
Man. Cambridge, Eng. 296 pp. 1895.

96 SOLUTIONS AND PROTOPLASM . (Cu. IL

Yune, E. ’85. De l’influence des variations du milieu physico-chemique sur
le développement des animaux. Arch. Sci. phys. et nat. (8) XIV,
502-522. 15 Dec. 1885.

ZACHARIAS, OQ. ’84. Ueber die amceboiden Bewegungen der Spermatozoen
von Polyphemus pediculus de Geer. Zeitschr. f. wiss. Zool. XLI,
252-258.

88. Ueber Pseudopodien und Geisseln. Biol. Centralbl. VIII, 548,
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: (1) The:.
effect of molar agents upon lifeless matter; (11) effect upon
the metabolism and movement of protoplasm; and (III) effect.
in determining the direction of locomotion, — thigmotaxis.
(stereotaxis) and rheotaxis.

§ 1. Errect or MoLtArR AGENTS UPON LIFELESS MATTER.

Mechanical disturbance can induce in certain lifeless com-
pounds violent chemical changes. Compounds which are so-
affected are preéminently 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 suffices 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 | [Cu. 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, explosion 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, yolume, and timbre. }

§ 2. ErrectT 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 MAssart (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 Actinospherium and Thalassi-

§ 2] EFFECT ON METABOLISM AND MOVEMENT ‘99

cola. When Actinospherium 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 Darwtn’s (75, p. 393) work on
the gland cells of insectivorous plants. In many species, to
be sure, e.g. Drosera, Dionza, 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
alands 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. HorvARTH (’78) and MELTZER (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
amceba, 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 [Cu. IV

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
ge | 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
a b © A : following changes occur:
Fic. 13. — Pseudopodium of Orbitolites, re- the protoplasm lying next

tracting as a result of local stimulation. .
The arrows give the direction of the the cut directly collects

_ streaming of protoplasm. At the left is into small spherical or
orn ae nonin of the exsation s+ fusiform masses which be
gin to migrate’ centripe-

tally (Fig. 138, 6). This movement meets with the normal
centrifugally migrating plasm and turns the latter towards the
centre again (Fig. 13, ¢). 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

§ 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 Difflugia (Fig. 15) be slightly
shaken, the pseudopodium contracts into the shell; if it be

Fic. 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 0, 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 unite 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 MOLAR AGENTS AND PROTOPLASM [Cu. IV

U

Fic. 16.—A series showing seven phases in the contraction of a pseudopodium of
Difflugia 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. — Actinospherium Eichhornii, unirritated. Natural size about 0.5 mm.
(From VERWORN, ’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 ;

§ 2] EFFECT ON METABOLISM AND MOVEMENT 103

Fic. 18.— Actinospherium Ejichhornii, at the beginning of irritation. The proto-
plasm is accumulated along the pseudopodia in drops and spindles. (From
VERWORN, ’89.) |

says HOFMEISTER (’67, p. 50), “The threads become knotty,
tear apart, draw together into short clubs or balls, and fuse

Fic. 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 VERWORN, ’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 well known

104 MOLAR AGENTS AND PROTOPLASM [Cu. IV

that 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 contraction in Protista.

A few words 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 amcba becomes a
spherical mass, Actinospherium 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. Errect oF MoLAR AGENTS IN DETERMINING THE
DIRECTION OF LOCOMOTION— THIGMOTAXIS (STEREOTAXIS)
AND RHEOTAXIS *

We have already seen that when a pseudopodium of an
amceba 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 ameba 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 amceba 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 amcba
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 6lyua,
**contact’’) was first applied to these phenomena by VeRworn (789, p. 90);
stereotaxis, under the form ‘‘stereotropism’’ (from crepedés, ‘‘solid’’), was intro-
duced by Lors (’90, p. 28), and is practically synonymous with thigmotaxis.

i

106 MOLAR AGENTS AND PROTOPLASM [Cu. IV

pseudopod gradually extends itself, and new ones are formed,
until at last the whole substance of the’ amceba 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 VERWORN (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 thespreading 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 (788, 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 soluble substances, the effect produced is doubtless
due to contact.

The aggregated organisms tend, in moving, to keep upon the
surface 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. 481),
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 an 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

a SS) eS
nS Se Ose iy

SRE AL
Sas N48 8 *

JT. ee

4, iy

Fic. 20.— A, Oxytricha seen from below; B, from the side; C, crawling over the
egg of Anodonta. (From VERWORN, ’95.)

by a water-film. Ifa spherical grain be placed in the drop of
water, aggregation takes place about that also. A similar
experiment, with similar results, was made by MASSART (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 with solids,
indicates that we are here dealing with irritability to contact.
The quality of the 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 | [Cu. IV

they may no longer cling to the glass, but wander, undirected,
through the water. 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 would 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 DEwitTz (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 (795) 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.
Prerrer (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 Rheotaris, which may
be regarded provisionally as a form of thigmotaxis, although
the possibility of its being rather a case of chemotaxis is not
excluded.

ROSANOFF (68) was the first to notice the rheotaxis of the
large plasmodium of A‘thalium septicum, but he ascribed it
to geotaxis. The correct interpretation was first given by
STRASBURGER (78, p. 62), and has been confirmed by JOnN-
SON (83), and STAHL (’84). When Athalium 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

lata il lia

§ 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 they 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, frequently 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 [Cu. 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 water 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 PeLiet, H. ’72. Sur la théorie de l’explosion des com-
posés détonants. Compt. Rend. LXXYV, 210-214.

DanTEC, F. LE ’95. Sur l’adhérence 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 Ki.
Arch. f. d. ges. Physiol. XXXVII, 219-223. 29 Oct. 1885.

’°86. Ueber Gesetzmissigkeit in der Ortsveranderung der Spermatozoen
und in der Vereinigung derselben mit dem Ei. Arch. f. d. ges. Physiol.
XXXVITI, 358-385. 31 March, 1886.

Dutrocuet ’37. (See Chapter VIII, Literature.)

Hormerster, W. 67. Die Lehre von der Pflanzenzelle. Leipzig: Engel-
mann. 664 pp. 1867.

Horvatu, 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 stro6menden Wassers auf wachsende
Pflanzen und Pflanzentheile (Rheotropismus). - Ber. .D. bot. Ges.
I, 512-521.

Logs, J.’90. (See Chapter VII, Literature.)

Massarvt, J. 88. Sur Virritabilité des spermatozoides de la grenouille.
Bull. ?Acad. roy. Belg. (3) XV, 750-754.

91. La sensibilité tactile chez les organismes inférieurs. Jour. de
Médecine de Bruxelles. 5 Jan. 1891. [Abstract only seen in Centralb.
f. Bacteriol. XI, 566.]

93. (See Chapter I, Literature.)

Me tzer, S. J. 94. Ueber die fundamentale Bedeutung der Erschiitterung
fiir die lebende Materie. Ztschr. f. Biol. XXX, 464-509.

Prerrer, W.’88. (See Chapter I, Literature.)

LITERATURE 111

Rosanorr, S. ’68. De l’influence de l’attraction terrestre sur la direction
des plasmodia des myxomycétes. Mém. Soc. Sci. nat. Cherbourg,
XIV, 149-172, Tab. I.

Sraut, E. ’84. (See Chapter I, Literature.)

STRASBURGER, E. ’78. (See Chapter VII, Literature.)

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: (1) Methods
of Study; (ID) Effect of Gravity upon the Structure of Proto-
plasm; (IID) Control of Locomotion by Gravity — Geotaxis.

§ 1. METHODS oF 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

tow

ty)
J

Fic. 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 ; 7.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 arabic. 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
affixed 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 rapidly rotating
either about a horizontal or a vertical axis. By varying the
rate of rotation the centrifugal force will vary, in accordance

with the formula, f= ai

(in meters) and ¢@ 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.

, in which r is the rotating radius

§ 2. EFFECT oF GRAVITY UPON THE STRUCTURE 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
I

114 GRAVITY AND PROTOPLASM | [Cu. V

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 HERRICK (95) 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

nucleus of a young ovum
(; mm. in diameter) showing
the nucleolus, which has, ap-
parently, caused a distention
of the nuclear membrane by

Fic. 22.— Section through the ovary of a lobster the pressure of its own weight.
hardened with its dorsal surface (D) upper- Arrow shows the direction of
most. The nucleoli lie against the ventral the earth’s centre. Magnified
surface of the nucleus. Magnified 50 diame- _ 248 diameters. (From HER-
ters. (From HERRICK, ’95.) 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).

§ 8. CONTROL OF THE DIRECTION OF LOCOMOTION BY
GRAVITY — GEOTAXIS *

The control of the movements of Protista has been investi-
gated chiefly by four naturalists: ScHwWARzZ (784), who studied
Euglena and Chlamidomonas; ADERHOLD (’88), who studied

* So called by Scuwanrz (’84, p. 71).

§ 3] 'GEOTAXIS 115

Euglena and desmids; MaAssart (91), who worked upon
bacteria, and ciliate and flagellate Infusoria; and JENSEN (793),
who experimented with Euglena, Chlamydomonas, and eight
species of Ciliata.

The observation that led ScHwArz 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 algz or to currents in the water ?
To get an answer to this question SCHWARZ heated the sand
to 70° C —a fatal temperature — and no aggregation occurred.
Again, the alge were subjected to vapor of chloroform; no
aggregation. Again, to a low temperature (5° to 6°); 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 alge 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 alge. 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 [Cu. 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 SCHWARZ
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 which 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 e -4 when e equals the acceleration

of centrifugal force in the required units; f, 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 SCHWARZ 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.

MAssArtT (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 117

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 15° to 20° C.,
and positively geotactic at 5° to 77°C. The other species men-
tioned above are negatively geotactic —7.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 ee
carefully into the cause of the phe-
nomenon than previous authors. The ford
new forms which JENSEN worked aS

$ én . See? ty ey
with were these Ciliata: Paramecium,

Urostyla, Spirostomum, Colpoda, Col- i ' ‘
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

Fic. 24.— Glass tubes, about 0.5
em. in diameter and 20 cm.
long, fused at one end, and
filled with water containing ~
Paramecium (represented
by points). a@ shows aggre-
gation of the Paramecium
at upper end of tube; }b,
aggregation of Paramecium
around bacteria suspended

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
veiling geotaxis; ec shows
that occasionally the Para-
mecia avoid the uppermost
layer of the water. (From
JENSEN, ’93.)

in the water, — chemotaxis (Fig. 24,

b),— 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

* JensEN used glass tubes of 0.5 to 1 cm. diameter, and 5 to 100 cm. length,
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 | [Cu. 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, Lozs (90 and ’91) showed that the
holothurian Cucumaria cucumis, the starfish Asterina gibbosa,
and the lady-bird beetles (Coccinellide) 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 PER-
KINS 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

atany 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 40°
the lapse of a constant 9° as
time (45 seconds). The | Vie
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 = 35° 80°
inclination. The re-
sults obtained indicated
that the deviation of — * 90° a0° 70° 60° 50° 40° 30° 20° 10° 0°

, ANGLE OF INCLINATION OF SURFACE TO HORIZONTAL
the slug from vertical- irk
Fig. 25.— Curves showing relation between the

ity diminished with the sine of the angle of inclination of a glass plate
cosine of the angle and the angular position of a slug which was
first placed on it in a horizontal position and

mad . by the P late. then left for 40 seconds in the dark. Curve A
The relation between is constructed by drawing ordinates from the
the angular deviation heavy horizontal line, 0°-45°, corresponding to
3 ‘ each angle of inclination of the surface (laid

from ver ticality and off as abscisse). The lengths of the ordinates
the sine of inclination are determined by 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

™
@

IZ.

DEVIATION OF SLUG FROM 45°
é
or

°
>
s
°

of the glass plate is

graphically represented the mean angular deviation from the initial
in Figo. 25. The con- position of a slug crawling undirected upon a

: 8 horizontal plate. Curve B is constructed by
clusion from the ex- drawing down from the base ordinates propor-
periments is that the tional to the natural sines of the different an-

lower limit ‘of the sen gles of inclination of the glass plate.

sitiveness of Limax 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: §=a-sin @, in which

120 GRAVITY AND PROTOPLASM [Cu. V

6 is the angular deviation of the slug from 45° towards 90°,
expressed in degrees; 6 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
Fic. 26.—Spirostomum ambi- numbers in ordinary aquaria, sus-
guum, side view. a2,ado- jended almost motionless in mid-
ral zone of cilia; 0, mouth;
os, gullet; n, nucleus; ck, Water, having a distinctly vertical
contractile canal; cv, con- position and with the head end
Bae cn oh a ee oe upward. They cannot be
Magnified about 120 diam-
eters. (From Birscutr said to be strictly motionless, since
Bios agus eae)" Pro- 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 Jut1A B. Piatt, 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.

§ 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 VERWORN (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. VERWORN 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 ScHwARz (84,
p- 68) says that both Euglena and Chlamidomonas assume all
positions in falling; MAssart (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 this 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 Prarr has used solutions of gum arabic 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 9.6 mm. had a sp. gr. of 1.044, while those 12 mm. long had a sp. gr.
of 1.017.

122 GRAVITY AND PROTOPLASM — [Cu. 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 greaier 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.

Fic. 27.— Hypothetical line

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

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 JENSEN.

The arrow at p indicates
the direction of the pull
of gravity; 1, 2, 3, 4, 5,
successive positions occu-
pied by the Paramecium.

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 (irom Juneau, 98.)
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.

124 GRAVITY AND PROTOPLASM (Cu. 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
arabie 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 acelimatiza-
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.)

DeEHNECKE, C.’80. Ueber nicht assimilirende Chlorophyllkérper. Inaug. Diss.
Koln. Abstr. in Bot. Ztg. XXX VIII, 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. LIIT, 428-480. 5 Jan. 1893. .

93". Die absolute Kraft einer Flimmerzelle. Arch. f. d. ges. Physiol.

LIV, 537-551. 24 June, 1893.

LITERATURE 125

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

(Thierischer Geotropismus.) Sb. Wiirzb. Phys.-med. Ges.

90. (See Chapter VII, Literature.)

91. Ueber Geotropismus bei Thieren. Arch. f. d. ges. Physiol. XLIX,
175-189. 1891.

Massart, J. 91. Recherches sur les organismes inférieurs. III. La
sensibilité a la gravitation. Bull. PAcad. roy. Belg. (3) XXII,
158-167. 1891.

Scuwarz, F.’84. Der Einfluss der Schwerkraft auf die Bewegungsrichtung |
von Chlamidomonas und Euglena. Ber. bot. Ges. II, 51-72.

Verworn, M.’89. (See Chapter I, Literature.)

CHAPTER VI
EFFECT OF ELECTRICITY UPON PROTOPLASM

_In this chapter we shall consider (1) 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 VERWoRN, ’95,
Chapter V, and in OSTWALD, ’94, Chapter XV.

Since 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 batteries, 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 DANTELL 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-zine 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 rheochord 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
pU Bors-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 | [Cu. 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 MArTrutas (94, p. 394)
propose for physiological purposes a unit one-millionth as great,
to be designated as 6. 6 then indicates a current of 9/55 milli-
ampere per square millimeter of cross-section. It is very de-
sirable that, when practicable, currents should hereafter be
expressed in 6’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 ErrectT 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 (Actinospherium), 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 begitis, 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 Actinospherium 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-
spherium to the constant curreat are gathered from the observa-
tions of KUHNE (64, p. 59) and VERWoRN (89%, pp. 8, 9).
Fundamentally similar observations have been made by KiHNE
(C64, p. 79) and VERWorRN (’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.)

K

/

130 ELECTRICITY AND PROTOPLASM (Cu. VI

2%
i ip ih,
alli.

. ou a; i

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

2

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 Actinospherium 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 Ameeba, 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 VERWORN (’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

Fic. 29.— Peranema. a, quietly swimming; ), irritated by an induction stroke.
(From VERWORN, ’95.)

Fig. 30.— Actinospherium eichhornii, StetN. Showing effect of the alternating
current. At both poles the pseudopodia are undergoing a disintegration, which
proceeds equally at the two poles. (From VERWORN, ’89.)

which alternately reverse their direction. Thus, each pole of
the organism subjected to such a current receives alternately
the making (or breaking) effects at anode and kathode. The
maximum action is thus obtained. When an Actinospherium
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 [Cu. 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 amceba 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. (KUHNE, ’64,
pp. 80, 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,
finally, disintegration (Fig.

Fic. 31.— One of the cells of a stamen hair

of Tradescantia virginica. A, unstimu-
lated; B, stimulated by an induction
current. At a, b, c, d, the protoplasm
has aggregated into drops and clumps.
(From VERWORN, ’89, after KUHNE,
64.)

31).

After having studied the
effect of the electric current
upon 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 ameboid Pelomyxa is subjected
to the constant current, a contraction appears, at the time of

134. ELECTRICITY AND PROTOPLASM [Cu. 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. (VERWORN, ’89*, p. 19.) This relation
may be expressed in tabular form as follows : —

At ANODE. At KATHODE.
Upon making........ excitation rest
Upon breaking....... rest excitation —

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

Actinospherium, the following reaction : — :
At ANODE. AT KATHODE.

Upon making. ....... excitation rest

Upon breaking....... 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 Actinospherium : —

AT ANODE. At KATHODE.
Upon making... <3. xs */5 excitation excitation
Upon breaking....... rest 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 desirable. 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 KaATHODE.
Upon making........ rest excitation
Upon breaking....... 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
whole 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 when 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 weaker contraction. Upon break-
ing the current, there was some excitation of the parts of the

136 ELECTRICITY AND PROTOPLASM [Cu. 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 MAKING. Upon BREAKING.
At ANODE. Atv Kartuopg, || At ANODE. At KATHODE.

Limneus......-. excitation rest rest excitation
Planorbis....... excitation rest rest excitation
Aplysia punctata . . | excitation > | excitation rest | excitation
Scheeurgus (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
Mollusca) 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

Upon MAKING. Upon BREAKING.

At ANODE. At Katuope. || AT ANODE. At KatTHopE,
Pagurus striatus rest excitation ||excitation rest
Triton cristatus. . . | excitation < | excitation

* 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, A’schurea.
Its formula is excitation = excitation; rest, rest. NAGEL says,
however, that these results were uncertain and variable.

In some other groups studied — Celenterata 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 VERWORN (’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. 341.) 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 (’894, p. 24).

138 ELECTRICITY AND PROTOPLASM [Cu 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 KUHNE (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 fluid, 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.
(BLAsStIus 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 produced
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 KUHNE (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 Actinospherium

140 ELECTRICITY AND PROTOPLASM (Cu. VI

and Amceba 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.

§ 38. 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 Amceba; then pass to the
more complex forms of Protista, especially the Ciliata, and after

Fia. 32.— Galvanotaxis of Amceba diffluens. A, Amceba creeping, unstimulated ;
B, after closing of the constant current. The arrow indicates the direction of
locomotion. (From VERWORN, ’95.)

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

When such an amceba 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 amceba must grad-
ually move from the anode (Fig. 32, B), and if several Amcebee
are under the cover-glass, they will eventually aggregate about
the kathode. Here we 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 amcba, we watch a free swimming
flagellate Infusorian, — 'Trachelomonas hispida (Fig. 33), — we

a

———EEEE——EeE——————— ee lee lh

ee ee

OO — |

a

§ 3] ELECTROTAXIS 141

see the long flagellum which 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

Fic. 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 ccerulens 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
_ Telative intensity.* He found that the precision with which

* LupLorr 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 Marruias (p. 128), namely, 1 one-millionth of

142 ELECTRICITY AND PROTOPLASM [Cu. V1

the Paramecia aggregated at one pole was determined by the
strength of the current, as follows: A current of 38 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 65 and 156 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

oO
—
for)

“S
|
or

or
“
«
———

~

-~

Vaal
=

oo
Jf,
a
oo

[
]
val

RELATIVE RATES OF MIGRATION
VA
RELATIVE RATES OF MIGRATION

_
—

0

oO

10d 206 306 406 506 606 00
STRENGTHS OF CURRENTS ;

Fia. 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 abscisse, by
the strength of current in 6’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 36 to
216 the rapidity of aggregation increased, but as the current
increased still further this rate diminished until locomotion
nearly ceased at above 606. The intensity, therefore, of 216
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 Lupiorr’s galva-
nometer readings (given in milliamperes) by +395, or (which is the same thing)
multiply them by 60. That will give us the current in 6’s persq. 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

t a,

Fic. 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
VERWORN, ’95.)

after the current is broken, and the time is independent of the
strength of,the preéxisting 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

Fic. 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 (Cu. VI

creased, however, this spiral becomes shorter, 7.e. has more
turns per centimeter of progression from one pole to the other

Be a ea en a

Fia. 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. 387), until at 606, in making one turn of the spiral, the
organism progresses hardly more than its own length.

Finally, the effect of the current
wl upon the movement of the cilia must
ae) be considered.* In the resting Para-
ee mecium the cilia rise perpendicularly
ae. RY from the surface of the body (Fig. 38).
and ae If an individual stands with its ante-
i Mee rior (blunt) end towards the anode,
eed and a current of 88 passes through,
beer the cilia at the posterior (kathode)
AD) end begin to vibrate. If the individ-
NR ual lies transverse to the current and

ey the current is closed, the cilia on the

kathode side vibrate, those on the

ee er coh cegioess sa anode side being quiet. With a cur-
vrctimulated. The blunt rent of 168 one can see that the kath-
end is anterior. (From ode stimulation increases the forward
eran Phaaky (anteriad) phase of. the cilium move-
ment (the “recovery”). With an intensity of 246, vibration

of cilia occurs at both kathode and anode. It is, however, more

* LupLorr 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 (’98, p. 556).

*

a.

§ 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 backward 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 oceur. The excess in effectiveness of the
stroke may be designated by the quantity z. 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
z+m. ‘The stimulus received at the kathode or anterior end
diminishes the effectiveness of the stroke by a quantity which
we may call n, which is larger than m. Here the excess energy
of stroke over recovery is x—n. If at any intensity of cur-
rent n exceeds 2, the anterior cilia will work to oppose the
forward motion of the individual, and when n — 2 = z + 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 608.

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 we are observing a Paramecium lying in

the axis of a current of medium intensity, with its anterior
L

146 ELECTRICITY AND PROTOPLASM [Cu. VI

end towards the anode. Since nm is here supposed to be less
than z, 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 energy of the stroke
is x + m, while on the kathode side itisz—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. VERWORN
(89°), however, has found that some Protista are positively
electrotactic; namely, the flagellata, Polytoma uvella, Crypto-

monas ovata, and Chilomonas paramecium; the ciliate, Opalina;
and some bacteria. Finally, Verworn (795, 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
VERWORN ) transverse electrotaxis. |

Passing now to the Metazoa, we find investigations concern-
ing electrotaxis among Invertebrates by NAGEL (92 and ’92*

2" ee Ser

§ 3] ELECTROTAXIS 147

and 795), and BuLAsrius and SCHWEIZER (’93); and among
Vertebrates by these authors and also HERMANN (’85 and ’86),
EwA.p (94, 94°, and 794°), 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-
stus and ScHweEIzER. The numbers which follow give the
year of publication and the page.

TABLE XV
Sprcirio NAME. Pree oF Lee ve AUTHORITY.
CURRENT. RESPONSE.
Mollusca :
Limnea stagnalis........... weak - N. 95
Var. other Gastropoda (probably) . — N. 7928; 795
Annelida:
1 tig tig) | gas ae ae oe _ N. 795, 626
Pubifex rivuloram)! esse. 60. — N. ’95,°631
Hirudo medicinalis.......... 0.88 — B.S. 792, 516
Branchiobdella parasitica ...... — B.S. 92, 516
Crustacea :
oh ee A a aoe strong ~ N. 792, 629
Asellus aquaticus ........... strong . + N. 95, 633
Astacus fluviatilus .......... 0.48 + B.S. 792, 518
Insecta :
DIOUMUNGES ion Cane Oa oceat es 4 Ws a es +? N. 795, 636
COPIA NiTIRtA ae See ee + N. 795, 636
Dytiscus marginalis.......... 1.98 + B.S. ’92, 519
Hydrophilus piceus....... eee p C108 ~ 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 [Cu. VI

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 (795, 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,
z.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 HERMANN
(85, °86). He used frog larve 14 days old, held in a shallow
rectangular porcelain trough, along the two small sides of which
thick zine 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 larve, 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 zine 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 0.356 to 0.47 6, 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 was 1.586. With this current a marked orientation of

§ 3] ELECTROTAXIS 149

the fish with their heads to the anode was noticed. With
Salamandra larve currents of 2.36 to 4.76 were chiefly em-
ployed. In the experiments of BLAsIus and SCHWEIZER the
organisths 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 EWALpD (’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 larve 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 0.36 and 1.56 frog tadpoles of from 1 to 3 weeks old
did face the kathode, as EwAxLp found, and did move towards
it. But HERMANN and MArratas (’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 paralysis 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 (which has the broadest
range) is that by which the organisms are irritated as it flows

150 ELECTRICITY AND PROTOPLASM [Cu. V1

cephalad, so that they come to lie with head towards anode;
the weakest current is that by which (following Ewa.p)
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 electrotactie organisms exhibit the katex type of
irritability; and negatively electrotactic organisms exhibit the
anez type or, in general, the electrotactie organism turns tail to
the exciting pole.

EwALp ('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.. EWALp 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 EwAxp,
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. Nowif 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 +
-_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 (Cu. VI

LITERATURE

BIEDERMANN, W.’83. Ueber rythmische Contraction quergestreifter Mus-
keln unter dem Einflusse des constanten Stromes. Sitzb. Wien. Akad.,
Math.-Nat. Cl. LXXXVII, Abth. 3, pp. 115-136. Taf. I-II, 1883.

Buasius, E. and Scuweizer, F. 93. Electrotropismus und verwandte
Erscheinungen. Arch. f. d. ges. Physiol. LILI, 493-543. 10 Feb.
1893.

ENGELMANN, T. W. 69. Beitrige zur Physiologie des Protoplasma. Arch.
f. d. gés. Physiol. I, 307-322.

"70. Beitrige zur allgemeinen Muskel- und Nervenphysiologie. Arch. f.
d. ges. Physiol. ILI, 247-326.

Ewa.p, J. R. ’94. Ueber die Wirkung des galvanischen Stroms bei der
Lingsdurchstromung ganzer Wirbelthiere. Arch. f. d. ges. Physiol.
LV, 606-621. 10 Feb. 1894. !

948, 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. 380 Nov. 1894.

Fick, A. ’63. Beitrage zur vergleichenden Physiologie der irritablen Sub-
stanzen. Braunschweig. 1863. (Not seen.)

Gotusrew, A. ’68. Ueber die Erscheinungen, welche elektrische Schlage
an den sogenannten farblosen Formbestandtheilen des Blutes hervor-
bringen. Sitzb. Wien. Akad., Math.-Nat. Cl. 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 Marratas, 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 Gelatinelésung. Biol. Centralbl. XII, 556-560. 1 Oct. 1892.
Krart, H. ’90. Zur Physiologie des Flimmerepithels bei Wirbelthieren.

Arch. f. d. ges. Physiol. XLVII, 196-235. 9 May, 1890.

Ktune, W. ’64. Untersuchungen iiber das Protoplasma und die Con-
tractilitat. Leipzig: Engelmann. 1864.

Luptorr, K. ’95. Untersuchungen iiber den Galvanotropismus. Arch. f.
d. ges. Physiol. LIX, 525-554. 5 Feb. 1895.

NaGet, 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. LIII, 332-347. 24 Nov.
71892.

LITERATURE 153

Naget, W. A.’95. Ueber Galvanotaxis. Arch. f.d. ges. Physiol. LIX, 603-
642. 5 Feb. 1895.

OstwaLp, 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 March,
1889.

’89>. The same (continued). Arch. f. d. ges. Physiol. XLVI, pp. 267-
303. 18 Noy. 1889.
95. (See Chapter IV.)

Wa ter, 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 (1) the application
and measurement of light; (II) its chemical action; (III) 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. ‘T'o 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 (FRAUENHOFER’S lines) which cross
the solar spectrum. The largest of these are lettered, begin-
ning with A in the visible red and ending with H 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 encyclopedias 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

Red Orange Yellow Green Blue Indigo Violet
tee ett |
75 70, 165 GO| ! yy 45 40
; ! | 1
t | § i
aBC D Eb F G h

Fria. 40.— Diagram of the-solar spectrum showing the main absorption bands and the
range of the 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, =~) in the following table, and also
the number of waves per second in 10"ths.

TABLE XVI
ABSORPTION | WAVE LENGTH, | VIBRATIONS PER || ABSORPTION} WAVE LENGTH, | VIBRATIONS PER
Bann. SAG SECOND 7 x 102. Banp. A. SECOND x 102,
aN ane) aie 0.760 392 E. 0.527 uw 566
a utes 0.687 433 FE; 0.486 p 613
(RINE 0.656 pw 454 G. 0.431 pw 692
2 WA 0.589 pu 506 H. 0.397 p 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 [Cu. VIL

Extreme ultra-violet » = 0.295 w; 1010 x 10” 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 spectrum. 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

of the rays in it.
next to heliostat; O, pro-
jecting lens; P, prism; S,
S,, scale marked with wave
lengths; D, D,, diaphragm,
including a variable slit; c,
¢;, collecting lens; E, posi-
tion of object subjected to
the rays. The spectrum
ranges from A=0.75 4 to A=
40. (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 FRAUENHOFER’S lines by interpolation from Fig. 40.* To in-
clude rays whose wave lengths differ by exactly 0.05 u 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, an@ 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.

* Tf 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 #’) 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 \=0.67 » and »=0.61 4, sodium salts
give a pure yellow light of \=0.59 yw, thallium salts (poisonous
vapor) a green at about A=0.54 yw, and indium salts a blue and
a violet, both beyond A=0.46yu. 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 fuchsin *
(vermilion)
aw | a See ee Minium .
’( golden yellow .. . | Litharge, PbO
ls a WOW 5 ine ota ots Chrome yellow, | Concen. Sol. potassic chromate
> { yellow-green. ... PbO.CrO, (a little red and green)
Eto On» BOG a pec cists cupric arsenite,| Nickel nitrate, NiO.(NO,),
ScHEEL’S green
b to F, transition from
blue-green to blue
F to FiG, cyanite blue... . | Berlin blue Bleu de Lyon (a little V) ¢
F}G to G, indigoblue..... Ultramarine
G to OS Oo eS e 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. (PrincsHerm, ’80, p. 409.)
+ F to H is given by ammoniated copper sulphate, CuSo,-4 NH; + H2O
(PRINGSHEIM).

158 LIGHT AND PROTOPLASM [Cu. VIL

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 RAayuereu (’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 waves. 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 (7.e. such as is given by a
diffraction grating, where all rays differing in wave length by
0.1 are equally distant) and when it is prismatic (in which
there is a crowding of rays at the redend). 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 prismatie 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 D and H, at X\=0.59 w;* the
warmest part is, in the normal spectrum, near )=0.60 yw, but
in the prismatic spectrum, beyond the visible red, at about
A=1.00y. 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 uw.

§ 1) APPLICATION AND MEASUREMENT OF LIGHT 159

Eee el EC bree re hE LET EE
Curve of Relative Warmth in Normal Spectrum.
Curve of Relative Warmth in Prismatic Spectrum.
Curve of Relative Brightness in Prismatic Spectrum.
= Curve of Relative Actinic Effect in Prismatic Spectrum.
i
—
Ail ~~
A I 1
vk tla
v tT TH
Z 4 1
v/ ‘ '
\ ' 1
\ I :
v i
\ : ‘ a
\ ' H
4 / 4 1 BS inl
WA Ka ' cd
+ 4 T A
ea 1 -
TAX 4 - 4
A _\' m ‘ar A
Eg 4
y, \ H - Pa \
i \ ‘ a :
/ ' : sa
VA y ‘
/ ‘ ! eB \
Hi a 3
re T Le v
ys ue ‘
VA BEG
Sa \ is
tr 7 \ \
LT \ 3
an ’ SP "
| | 4044 50 u 60 TO u
H G F E D C B A

Fic. 42.— Seale 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
(°84, p. 233) ; the curve of brightness is constructed from the data of VIERORDT
(’73, p. 17); that of actinism is taken from BuNsEN and Roscok (’59, p. 268) and
indicates the relative efficiency of the different 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 action ;
at about A=0.42 w this action reaches a maximum.

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 (Cu. 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
VreRorRDT (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 NiIcHoL prism, until equality
of brightness is obtained. A modified form of VIERORDT’sS
convenient instrument is made by H. Kriss of Hamburg,
Germany. A modified form of GLAN’s photometer is de-
scribed by VOGEL (77).

VoGeEt’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 (8) 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

CHEMICAL ACTION OF LIGHT 161

§ 2]
rays now pass through (4) a Nicnot 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
Nicuou 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

:

l
|

I

F
ll

2

of Lea (’85),

Fic. 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 gq; (C, colli-
mating lens. D, doubly refract-
ing quartz prism; m, m, the
holder of the NicHot prism JN,
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’, O, 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

reference to a third (con--
stant) is as the squares of
the tangent of the angle
through which the NicnHot.
prism has been rotated.
Other modifications of

GLAn’s photometer are those of Lord RaYLeriex (’81) and.

upon which the spectrophotometer of the:

Cambridge (Eng.) Scientific Instrument Co. is based..

§ 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-
larly among organic compounds.
The effects are mainly due to the
blue and violet rays, hence are

162 LIGHT AND PROTOPLASM [Cu. 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; 8. 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, (8) of chlorine or bromine, or
(y) of another organic compound.

Among the compounds which take up oxygen is bilirubin,
C,,H;,N,0,, a solution of which, in sunlight, even when air is
excluded, oxidizes to biliverdin, C,.H,,N,O,. In the absence
of sunlight this change requires air (B. III, 418). Ducnaux
C87, p. 353) finds that vegetable oils, such as olive or palm
oils, are rapidly oxidized if exposed to ight. 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, COCI,
(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
FRANZ, 70). Likewise, when chlorine is passed, in sunlight,
through a solution of C,H,Cl,O, in CS,, there is formed
C,H,Cl,0,, two atoms of Cl having been added. Finally,
C,Cl, may be made by uniting C,Cl, and Cl, in sunlight (B. I,
158); and the compound C,H,-FeBr,-2H,O may be made by
passing, in sunlight, C,H, through a concentrated aqueous
solution of FeBr, (B. I, 113).

* Most of these cases were obtained by searching through BEILsTEIn (’86-’95),
References to this book will be made throughout 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: C,,H,O, + C,H;CHO = C,,H, (OH)
(O-CO C,H;). Again, chinon (benzochinon) and benzaldehyd
may unite in the sunlight to form benzohydrochinon, according
to the formula: C,H,O, + C,H;CHO = C,H,CO C,H,(OH),.
Finally, benzochinon and isovaleraldehyd may similarly unite
to form isovalerochinhydron, thus: C,H,0, + C,H,CHO =
C,H,CO C,H,(HO),. 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 C,H,,,0, break up in the sunlight and in the
presence of a small quantity of uranium oxide, into CO, and
an acid C,H,,O, (B. I, 63). For example, oxalic acid, C,H,O,,
breaks up thus into formic acid, CH,O, and CO,. Also an
aqueous solution of butyric acid, C,H,O,, in the presence of
uranyl nitrate, breaks up, in the sunlight, into CO, and
C,H, (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
(C,H,,NO-HCl),PtCl,, an ammoniacal derivative of acetone,
becomes (C,H,,NO - HCl), PtCl,; and (C,H,,NO - HCl),PtCl,
becomes (C,H,,NO - HCl), PtCl, (B. I, 982, 983). Again, chlo-
rine acetate, Cl- O-C,H,O, undergoes slow decomposition in
the light (B. I, 462); C,H,Cl,, a derivative of pentine, C,H,,
does the same; and ethylester, ClO - C,H,, 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 [Cu. 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 swnliyht, 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 which they assume their
red form have been ascribed to sunlight. Elwomargin acid,
C,,H3)0,, is a compound found in connection with glycerine
in the oil of the seeds of Eleococea (Aleurites) vernica —
Chinese oil tree —one of the Euphorbiacee. This acid erys-
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, eleostearin 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. III, 180). Again, among the
derivatives of ethylene, C,H,, is chlorethylene, C,H,Cl, 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,H,Br, 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 by fermentation
are produced by light. Thus Nrteece DE SAINT VicTOoR and
CoRVISART (759) 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 (794) 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 Sacus (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 Onrmus (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 by 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 months 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.
AXENFELD (Centralbl. f. Physiol. X, 147) 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 tlie
rays have resulted negatively.

166 LIGHT AND PROTOPLASM [Cu. VII

§ 3. THE Errect or LIGHT UPON THE GENERAL FUNCTIONS
OF ORGANISMS

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. 3

a. The Thermice 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 (C,H,,O,) 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 to this process. Just what rays are
the essential ones has been a point of some dispute. The
earlier studies on the subject, made chiefly by DRAPER (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 this is a fundamental matter, for it has
been shown, for instance by REINKE (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
(ef. Fig. 40).

Z Later investigations with improved methods have shown
quite conclusively that it is especially the rays with X = 0.68 p,
or those very close to the absorption band B, which are most

yv

oul
ea
pf
ws

vd

7
Be i i Ls i 2 4 8 16
16 8 4 2 1 1 i: i =:

Fic. 44. — Curve showing the relation between intensity of light (abscissz) 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
CTT) 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

[Cu. VI.

per minute by the submerged, illuminated plant. As is shown
in Fig. 45, the maximum of gas production occurred at about
absorption line B— and this
is the more marked of the
absorption bands of chloro-
phyll.

A similar result was reached
by ENGELMANN and set forth
in a long series of papers (81,
Iv "82, °82%, °83, ’83*, 84, ’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-

400 430 460 500 540 600 660 750

GIRS D EbD|F Gh

SSS

II} Il

oaAantavtrwwnreH &

se et et
Ca a)

= Re eS eet
SaeR&B a ke &

| I
700) 650 600 500] 450
1

aBc Dike SOR

Fic. 45.— Curve whose ordinates are pro-
portional to the number of gas bubbles
eliminated per minute by leaves illumi-
nated by the various rays whose wave
lengths are given at the bottom of the

550

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 Alc 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.)

ratus especially designed by
ENGELMANN 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

§ 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
A = 0.85 4, most oxygen is produced at this point. (ENGEL-
MANN, *83, p. 709.)

Finally, by an ingeniously devised experiment, TIMIRIAZEFF
(90) has settled this matter in the most direct and indubitable

a@-B Cc D E db F

—_.——
—_—
4
; f
‘

Fic. 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 KF 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 FRAUENHOFER’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 Band 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 [Cu. 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 (i.e. below
the D line).*

In conclusion it may be said that the greater proportion of
the radiant energy entering the plant tissue is absorbed. Thus
MAYER (793) 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.

b. The Chemical 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 shows 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 (HreLMHoLTz, 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 Downers and BLuuntT (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 FRANKLAND:
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 H, and exposed to a November sun-

172 LIGHT AND PROTOPLASM [Cu. 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 H-shaped
area sterilized by the light (Fig. 47). Compare the, earlier
results of BUCHNER (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.

Fic. 47. — Appearance of a gelatine culture of Bacillus anthracis, exposed to the light
over only the area #, and then incubated for 48 hours. In the area £ no colonies
have developed. (From WARD, 93.)

Not all rays have this bactericidal property. Downers and
Buiunt (78) found that only the blue rays were thus active,
for behind red or yellow glass the bacteria readily developed.
W ARD (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 w) 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 the 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

~" 7
* ~~
“AE Ton

in
August, and 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 Warp, 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 DowNnzs and
BLUNT, is that light has no effect upon bacteria when they are
ina 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 [Cu. 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, WETTSTEIN (85) found that the conidia of
Rhodomyces Kochii, a human intestinal parasite, did not de-
velop in the light. KLErN (’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. ELviIne (90, p.
105) gained similar results with Aspergillus, although several
days or weeks of insolation did not kill the fully ripe spores.
WARD (793) determined that insolated spores, cultivated on
agar or gelatine plates, of Oidium lactis (5 cases), Saccharomyces
pyriformis (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 PRINGsS-
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

“Ss, 20 min. in H.

d atmosph. air.

- \ 6 to 6 min. in

Fic. 49. — Piece of a sprout of Nitella mucronata

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:

which was subjected in 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 filled 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 6 minutes.
(From PRINGSHEIM, ’81.)

(a) effect of low intensity of light upon movement; (4) effect
of high intensity of light upon movement; and (ce) effect of
change of intensity on contraction.

a. Effect of Low Intensity of Light on Movement — Dark-rigor.
— We have 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 immobility, which may
be called dark-rigor, since return of light brings a return of
movements. Dark-rigor is very marked in the sensitive plant.

176 LIGHT AND PROTOPLASM (Cu. VII

If this plant is kept for several days 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
ENGELMANN (783 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 ight. 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, LANKESTER). But
that it is not merely oxygen which induces movement is shown
by the fact that when an abundant oxygen supply is artificially
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 calls phototonus. +

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 photometricum, 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 Sacus
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-red 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. Sorokin (’78) found that protoplasmic
streaming in the plasmodium of Dictydium ceases at night,
being awakened to movement by the light. Finally, VEr-

ee : an ws D E b F g
80] ‘75| 70 65

Fic. 50.— a. Spectrum of the chromophyll of bacterio-purpurin, showing absorption
bands at A= 0.594 and A=0.534. An (invisible) absorption band has been deter-
mined by means of the bolometer at A= 0.854. 0b. 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 ENGELMANN, ’833.)

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 updén 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
N

178 LIGHT AND PROTOPLASM [Cu. VIL

chlorophyll, nearly or quite essential to movement. Phototo-
nus is a convenient name for the condition induced by light.

b. Effect of High Intensity of Light on Movement — Light-

rigor. —We have just seen that in some organisms the. most
vigorous movements occur at an optimum intensity of light,
which produces phototonus. Ata 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), which 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 (782, 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 13
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 by Change in Intensity of Lllumina-
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 the Myxomycetes, ENGELMANN (’79)
has found that the amceboid 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 Hzematococcus 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, LoresB (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 branchiz seem to be the sensitive organs. Adult barnacles
show a similar sensitiveness to light; for PoucHET (72, p. 111)
found that momentary cutting off of the light, as by 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 (Cu. VII

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 organisins, 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 their existence; but very powerful light, long
continued, proves fatal to most protoplasm.

§ 4. CONTROL OF THE DIRECTION OF LOCOMOTION BY
Ligut — PHOTOTAXIS AND PHOTOPATHY *

In 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, SAcuHs (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-

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
light (Fig. 51). .

There is at least one other kird 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
GRABER. STRASBURGER used photometry for what I here call photopathy, but
Ottmanns (92, p. 206) 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 [Cu. 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 schizomycete — 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 Swarm-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 zodspores
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, FAmmNTZIN (’67) had discovered that swarm-

Le | — O_O

ee ema rea mee a el AE AT = SENT MF NAT A Ape ey tight as Mt ma en A
, = eek a ties “ A MaRS ae

§ 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 STRASBURGER’S
(78) epoch-making paper appeared.

SfRASBURGER worked with swarm-spores of various species
of alg, and with the flagellate Chilomonas and Euglena. He
observed again the phenomenon that the sense (+ 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.
STRASBURGER 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- 896); and Volvox, by CIENKOWSKI (’56), VERWORN
(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. (STRASBURGER, 78, p. 568.)

Desmids, especially Closterium, have been experimented with
by STAHL (’78 and °79), KuEBs (’85), and ADERHOLD (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 ADER-
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
head-over-heels motion, since the free end bends down to the

184 LIGHT AND PROTOPLASM [Cu. 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 VERWORN
(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, rotdtion
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.

Myzxomycetes. —In its ameeboid form and when subjected to
strong sunlight A{thalium 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

,
|
.
.
tf
ty

§ 4] PHOTOTAXIS AND PHOTOPATHY 185

the illuminated region. (BARANETZKI,’76, p. 328, and STAHL,
*84, p. 167.)

BARANETZEKI 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 Fs
plasmodium had become very
thin, owing to the retreat of the
protoplasm from under the slit
to the darker region (Fig. 52).

fthizopoda.—Although,
Fic. 52.— Plasmodium of Athalium septicum,

Be. WS have : BOOR, Pelo- after having been kept in the dark for some
myxa 1S irritated by a time and then illuminated, for half an hour,

sudden illumination. a over a cross-shaped area, only. The illumi-
; nated area is on the upper part of the figure.

phototactic or photo- The protoplasm has retracted from it, leaving
pathic response has not a partially clear region in the form of a cross.

hitherto been certainly i dbbcontg pape tater ars ae

observed in this group. VERWORN (’89, pp. 40, 41), indeed,
experimented, but with negative results, upon Ameeba limax,
Amoeba princeps, Actinospherium, 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.

yBe

VeERWORN’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, finally, the laterally

186 ' LIGHT AND PROTOPLASM [Cu. 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 Amceba is phototactic or not.

I have experimented with Ameceba proteus, using methods
resembling VERWORN’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
amoeba 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 amoeba 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 amceba 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
2mm. 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 water, 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 window, —a west window, —a beam of
direct sunlight, or of reflected light from the morning sky, was
admitted to the amceba. 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 in temperature or of
illumination at the two poles of the ameeba is scarcely conceiy-
able. The rays of radiant energy were the only directing agent.
Under these conditions the amceba 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 amceba 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.
54, for the phenomenon of acclimatization comes in and the
responses become irregular. But, despite such irregularities,
my studies lead me unhesitatingly to conclude that Ameeba,
although not at all photopathic, is strongly phototactic. This
result is important, for, since Amceba 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 (alge) — 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 water they
move from the light. The conclusions to which ENGELMANN
arrived from these and other facts were that these 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.

LIGHT AND PROTOPLASM [Cu. VII

b, (3). 14:20 to 14:34
13:57

Prior | i
;. Fig. 53.—Camera drawing, showing
7 the successive positions assumed
! by an ameeba subjected to light
' falling upon it from one side. The
; arrow lies in a horizontal projec-
: tion of the sun’s rays. The ameba
i retreats from the source of light.
: The numbers to the right of the
f outlines of the ameba give the
t
'
4
[
[
!

Interval
not observed

observed times between 10:28 and
11:22 a.m. Magnified 16 diameters.

Fig. 54. — Camera drawing, showing
the successive positions assumed
by an ameeba retreating from the
light. The position of the infalling
ray was successively changed from

Ban ) (1) to (2), (3), and (4). The arrow

labelled “‘ First direction of migra-
tion ’’ shows the direction of loco-

90-5 4(U po at - motion of the amceba before the

light fell upon it at the beginning of
the experiment. The numbers indi-
cate hoursand minutes. During the
interval from 13:06 (=1:06) P.M. to

13:57, the amceba was not under di-

| rect observation, since I was called

538 away. Magnified 16 diameters.

First direction
of migration

(1). 12:48 to 14:00

Cases that can be explained only on the ground of the imme-
diate effect of light upon the direction of movement are cer-
tainly rare. EntTz (88), indeed, has intimated that Opalina
flees from light, but VERWORN (’89, pp. 53-57) was not able
to confirm him in this point. VERWORN’S method was here,
as in the case of Amceba, 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-

§ 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 rceselii, St. eceruleus, Carchesium polypi-
num, and Uroleptus musculus. On the other hand, we have
often noticed here in Cambridge that our Stentor cceruleus is
(rather indefinitely) negatively phototactic 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, Amceba, plasmodia of Myxomycetes, and
swarm-spores of Chytridium. The phenomenon is thus wide-
spread, if it is not universal.

b. 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 (vy) 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 intensity 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 [Cu. 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 epistrophe; 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, Moore), and upon
prolonged standing in the
dark (negative apostro-
phe). (Fig. 55.)

It appears, then, that
epistrophe occurs’ only
within certain limits of
Fie. 55. — Cross-section through the leaf of light intensity - The in-

Lemna trisulea. A. Position of the chlo- tensities included between

rophyll grains in diffuse daylight — epis- sk :
trophe. #8. Position of the chlorophyll these limits constitute
grains in intense light — positive apos- What Moore calls the

trophe. CC. Position of the chlorophyll epistrophic interval. The
grains in darkness — negative apostrophe. J ae R

(After STAHL.) 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

* The limits were determined by Moore, in a roughly quantitative way, by
means of his photrum, 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 j, 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).

§ 4] PHOTOTAXIS AND 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
aérophytes in an intermediate position (Fig. 56, 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. ;

ai

Fic. 56.— A diagram of Moore’s photrum, showing for six spaces the epistrophic
interval (shaded region). 1. Anacharis (Elodea) canadensis, ‘‘ water-weed.”’
2. Lemna trisulea. 3. Saxifraga granulata (position of positive critical point).
4. Oxalis acetosella (position of negative critical point only approximate).
5. Pteris critica (positive critical point). 6. Pyrethrum sinense (garden Chry-
santhemum). -+ indicates the brighter 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 be
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. H1zronyMus (’92, p. 466) considers them to
be for the purpose of screening the nucleus. Moore (p. 222),

192 LIGHT AND PROTOPLASM _ [Cu. VII

however, chiefly 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.”’

B. 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 (795, pp. 144, 162). He has found that
the dark color of the (illuminated) skin is due to the rich

er eee a
Aeon

ance
aon
wee

Ae Ae Sent eS
Xi ay

“anit

Fic. 57.— Vertical section through a black dermal papilla of Chameleo vulgaris.

ep, epidermis; cu, cutis; p, black pigment cells; p’, 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 STEINACH (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 193.

we find this capacity for rearrangement of pigment granules,
as EXNER (89 and 91, p. 104), SreraANowska (’90), Szcza-
“WINSKA (91), PARKER (795), 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 level 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:

Ses EHS NS
———— aS Sieits’ “4

NL Sg py

cu. ep.
Fic. 58. — Vertical section of a whitish-yellow dermal papilla; lettering as in Fig. 57..
p’, 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.

y- The Migration of Pigment Cells in the Metazoan 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 [Cu. VIL

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 centripetally 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.

ce. 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. 66) 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 TREMBLEY 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 Ce-
lenterata to light. The larve 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 (DRIESCH,
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. ‘ennenstl Auruority REMARKS.
RESPONSE.
i
Fresh-water planaria. .. . — Logs, ’90, p. 95
muenoe BP. 6s. 5 ss 8 en _ DrieEscu, ’90, p. 155
Polygordius, larva ..... — LoEB, ’93, p. 90 see p. 200
f Darwiy, ’81, p. 21
MARE WOKTL: "ss se ce Roe _ GRABER, ’83, p. 210 photophob
( HEsskE, 96
io a Pay _— LoEB, ’90, p. 96
TREMBLEY, 1744, p. 96
+ BERT, ’78, p. 989 ! photophil ( ?)
MERIC S98. o. Sowce wy, a LUBBOCK, ’82, ’83
; + DAVENPORT and CANNON| phototactic
Many marine copepoda ..j|—(or+)} Logs, ’93, p. 96 see p. 200
Balanus, larva ....... —(or+)}| Groom and Logs, ’90, p.| see p. 200
160
Banaue. Jarva ® os. sss es — LoEB, ’93, p. 83
Idotea tricuspidata..... -+- GRABER, ’85, p. 141 photophil
Diastylis (Cuma) rathkii . + Logs, ’90, p. 91 mud-inhabiting
Carcinus menas....... ~- DRIESCH, ’90, p. 156 photophob
Homarus americanus, larva + HERRICK, ’96, p. 189
el ae aes ae + Logs, ’90, p. 55
Blatta germanica (blinded) i GRABER, ’83, p. 235 photophob
Musca dom. (?), larva... or Logs, ’90, p. 69
Musea, adult ........ + Loes, ’90, p. 81
Musca vomitoria, larva .. —_ Davipson, ’85, p. 160
Musca cesar, larva..... — PoucHET, ’72, p. 113
Eristalis tenax, larva ... —: POUCHET, ’72, p. 129
- SEITz, ’90, p. 337
Lepidoptera, adult ..... _ Loz, ’90, p. 46 see p. 197
: Lore, ’90, p. 51
Lepidoptera, larva ..... + Pounron, ’87, p. 315
Ants, after gaining wings . a Lors, ’90, p. 63
Melolontha vulgaris. (May
DOOGIG) .-).-. bata na ots ~ Logs, ’90, p. 86
Tenebrio molitor, larva . . — Loes, ’90, p. 84
Dertalium., ouch Se0-% a LACAZE-DUTHIERS, ’57, photophob
p. 25
Rissoa octona........ _ GRABER, 85, p. 144 photophil
Littorina rudis ....... _ DRIESCH, ’90, p. 155 photophob
Gasterosteus spinachia. . . — GRABER, *85, p. 148
SEROMA ici praca tate tet _— GRABER, ’83, p. 221 photophob
WLOG ie) oer Reh Sek a _— Logs, ’90, p. 90

196 LIGHT AND PROTOPLASM [Cu. VIL

A study of this table reveals the fact that, in general, organ-
isms which live in shady places or in the dark are negatively
phototactic or photopathic, while those living in the light are
positively phototactic or photopathic. ‘Thus most fresh-water
planarians and leeches are inhabitants of shady pools. ' Polynoé |
is generally found in dark retreats, the earthworm and fly
larvee are lovers of the dark, and shell-molluses are for the
most part enclosed in cases impervious to light. On the other
hand, Daphnia is found largely in open pools, larve 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 +
phototactic.

3. The General Laws of Phototaxis and Photopathy. — Under
this head we shall consider: (a) the sense of the response;
(6) the effective rays; (¢) prototaxis vs. photopathy; (d) 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 internal conditions. 7

We find that, under similar external conditions, different
organisms respond differently. For example, many Oscillarie
(p. 184) are positively phototactic even in direct sunlight;
whilst even moderately strong light will repel many diatoms.
In fact, we find that a positively phototactic 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 phototactic 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.
Lors (90, p. 46) has performed some experiments with these
insects, which I will cite in detail.

EXPERIMENT 1.— (a) Sphinx, Bombyx, and other moths were kept in a
large glass cage in a room illuminated only by daylight. As darkness came
on, the moths began to fly towards that side of the cage which was next the
window. Again (b), pup of nocturnal moths, left in a room, emerged during
the night, and were always found in the morning at the closed window of
theroom. 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 the point where
the moth was liberated. Thus, there is no preference for artificial light.

The conclusion at which LOEB arrived was that these moths
undergo a diurnal variation in responsiveness to light, which
corresponds to the change from day to night. But the fact
that, in experiment 1 c, 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 high 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, Lorep (90, p. 56) has found that, at the intensities

198 LIGHT AND PROTOPLASM [Cu. 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.

Tight can modify the response to light; thus, Groom and
LorsB (’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 larve 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 Ulothrix spores, which are
positively phototactic 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 Hematococcus 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 intensity. 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 by 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 STRASBURGER
(78, p. 605) in the swarm-spores of Heematococcus, 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 opposite 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 change is not due to

200 LIGHT AND PROTOPLASM (Cu. VII

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 80° 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 STRASBURGER have been in part
confirmed by other authors in other species.

Groom and Loes (’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 phototaxis] 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. Massart (’91, p. 164) remarks, incidentally, that the flagellate
Chromulina is + phototactic at 20°C., but — phototactic at 5°C. Lorn
(793, pp. 90, 96) obtained a result with Polygordius larve and Copepoda
which seems, at first sight, the opposite of SrRASBURGER’s. Polygordius
larvee, negatively phototactic at 16°, were gradually cooled to 6°, at which
temperature they began to move rapidly towards the + side of the vessel.
As the temperature 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 Lors 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] PHOTOTAXIS AND PHOTOPATHY 201

(93, pp. 94, 96) for information on this subject. Negatively
phototactic Polygordius larve were placed in sea water to
which 1% to 1.8% NaCl had been added. ‘They now appeared
positively phototactic. Positively phototactic individuals, on
the other hand, placed in sea water diluted with 40% to 60%
fresh water 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
Polygordius and Copepoda, according to Logs, 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 phototaxis is modi-
fied by previous subjection to light, by temperature, and by
concentration. ‘These agents modify the attunement of the
organism. Any quantitative experiments upen 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 range 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. :

6. The Effective Rays. — We have hitherto considered chiefly
the action of white light, merely referring casually to the

202 LIGHT AND PROTOPLASM [Cu. VII

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 Conn (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= 0.47n tor’ =0.49 4; that is, rays very near FRAUEN-
HOFER’S line #. ‘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 ight. 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. LuBBocKk (82,

§ 4] PHOTOTAXIS AND PHOTOPATHY 203

p- 127; °84, p. 187) 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 Brert’s (’78, p. 989)
conclusions, that “the animals see . . . only those rays which
we ourselves 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 prevailingly photopathic.
Thus both Bert (’68, p. 381) and LusBock (’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.

e. Phototaxis vs. Photopathy. — We have hitherto assumed.
the existence of two dissimilar sorts of locomotor response to.
light — phototaxis and photopathy. Phototaxis we defined as.
migration in 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 the same as STRASBURGER’S. It con-.
sisted of a hollow prism P, containing a dark solution and.
placed over the trough 7, with its organisms. STRASBURGER.
(78, p. 585). put swarm-spores of Botrydium and Bryopsis into:
the trough, and reflected the light perpendicularly through 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 [Cu. VII

of light, as in the.figure. The spores now moved towards.
the source of light, ¢.e. in the direction of the infalling rays
but constantly into a region of less intensity of light.

Loot a,
one
Patt
WS
oe yi

” il a 3

pu iy °

6o"L-- a ae 4 4 m4

aie: ed L 9

Pal A: Fo -

i oo > |

“~ Ff <<
yo ee
ee RE SE KS

[ T é )

Fia. 59.— Diagram showing the position of apparatus and the direction of the rays
in an experiment in phototaxis. 7’, trough of water containing organisms, A and
B its two ends, M its middle. P, a prismatic box containing a solution of India
ink. SS, screen to cut off extraneous light. JZ, gas-lamp having a WELSBACH
burner. Drawn to scale.

Loxs’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, ¢;
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 larvee with which
he experimented moved into the darkened chamber and thus
towards the source of light (Fig. 60). Again, a clear test tube
containing larve (Fig. 61) was placed so that its closed end
6 was directed towards the window FF. A bundle of sun’s
rays SS struck nearly perpendicularly the mouth of the tube a,
when the larve were aggregated at the beginning. Neverthe-
less the larvee, 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

Fu

§ 4] ' PHOTOTAXIS AND PHOTOPATHY 205

organisms is determined by the direction of the light rays.
There is, then, such a thing as phototaxis.

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 followed unequal illumination by rays
perpendicular to the trough. Thus Lussock found that

60 61 S

Fic. 60.— Two test tubes a and b, containing Porthesia larve c, which move towards
the window FF, although in doing so they pass from a brighter to a darker region.
_ (Lozs, ’90.)
Fic. 61.— Diagram to show how Porthesia larve move in the test tube ab towards
the window FF, although in doing so they leave the part of the tube more brightly
illumined by the sun’s rays SS. (Loxrs, ’90.)

Daphnias, placed in a trough nearly perpendicular to the rays
dispersed by a prism, moved towards the brighter part of the
spectrum. GRABER employed screens of diverse translucency
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 [Cu. VIL

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, Loes (93, pp. 100-103)
has found that fresh-water 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.
Fic. 62.— Diagram showing position So it comes about that when

taken by Planaria torva in a shal- these Planaria are in a shallow

low cylindrical glass vessel a, %, evlindrical, vessel (Fig..62, a, 6,

c, d, placed opposite a window 3 ;

AB. (Lox, '93.) ec, d) in front of a window AB,

they accumulate neither at the
side towards the window nor that away from it, but at ¢ 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 CANNON’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.

At 1B

§ 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 amceba. 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 flagellum 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. 233), 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 (NAGEL, ’96, p. 58). Blinded Helix are said by
WILLEM (91, p. 248) and Nace (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 skin (NAGEL,
"96, p. 22; GRABER, ’83, p. 233; Dusors, 90, p. 858). 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 dermatoptic reaction, see Nace, 796.

208 LIGHT AND PROTOPLASM [Cu. VIL

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
“highly 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
LorB (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. CANNON 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 Lors 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-

ee:

LOW LIGHT ATTUNEMENT

A<

LOW LIGHT ATTUNEMENT

Fie. 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 ; z.e. until it is in the

light ray. Subsequent locomotion will carry the organism in a
is

210 LIGHT AND PROTOPLASM (Cu. 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 phototaxis.

Such an explanation can serve only for elongated organisms.
The case of the ameeba 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 ight 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

—————— er

rs

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 processes 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 = 40u to 49u 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 intensity 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 widely 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 [Cu. VII

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=)
%

Fe

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1859.

OLTMANNS, F.’92. Ueber die photometrischen Bewegungen der Pflanzen.
Flora. LXXV, 183-266. Taf. IV.

~

216 LIGHT AND PROTOPLASM [Cu. VII

Onimus, E. 95. Pénétration de la lumiére dans les tissus vivants. C: R.
Soc. de Biol. Paris. XLVII, 678, 679. 26 Oct. 1895.

ParkeER, G. H. 795. The Retina and Optic Ganglia in Decapods, espe-
cially in Astacus. Mitth. Zool. Stat. Neapel. XII, 1-73, Pls.
I-III.

Prerrer, W.’71. Die Wirkung farbigen Lichtes auf die Zersetzung der
Kohlensiure in Pflanzen. Arb. bot. Inst. Wiirzburg. I, 1-76.

Poucuet, G. ’72. De Vinfluence de la lumiére sur les larves de diptéres
privées d’organs extérieurs de la vision. Rev. et Mag. de Zool. (2)
XXII, 110-117; 129-138; 183-186; 225-231; 261-264; 312-316.
March-August, 1872.

Poutton, E. B.’87. Notes in 1886 upon Lepidopterous Larve, etc. Trans.
Ent. Soc. Lond. for 1887. pp. 281-321, Pl. X. Sept. 1887.

PrinesHeErM, N. ’80. Ueber Lichtwirkung und Chlorophylifunction in der
Pflanze. Jahrb. f. wiss. Bot. XII, 288-437. Taf. XI-XXVI.

81. Ueber die primiren Wirkung des Lichtes auf die Vegetation.
Monatsber. Akad. Wiss., Berlin, Jahre 1881. pp. 504-534.

Raum, J. ’89. Die gegenwirtige Stand unserer Kenntnisse tiber den Ein-
flusse des Lichtes auf Bacterien und auf den thierischen Organismen.
Zeitschr. f. Hygiene. VI, 312-368.

RayYLeieH, Lorp, ’81. Experiments on Color. Nature. XXYV, 64-66.
17 Nov. 1881.

REInkE, J. ’83. Untersuchungen iiber die Einwirkung des Lichtes auf die
Sauerstoffausscheidung der Pflanzen. I. Mitt. Bot. Ztg. XVI, 697-
707; 7138-723; 732-738. |

’84. The same. II. Mitt. Bot. Ztg. XLII, 1-10; 17-29; 33-46; 49-59.
Jan. 1884.

Sacus, J. 76. Ueber Emulsionsfiguren und Gruppirung der Schwarm-
sporen im Wasser. Flora. LIX, 241-248; 257-264; 273-281.

60. Ueber die Durchleuchtung der Ptapsendbvelie: Sb. K. Akad. Wiss.,
Wien. XLIII, Abth. 1. 6 Dec. 1860. [Also in his Gesammelte
Abh. iiber Pflanzeu-physiol. I, 167.]

64. Wirkungen farbigen Lichts auf Pflanzen. Bot. Ztg. XXII, 353-
358, 361-367, 369-372. Nov., Dec. 1864. [Also in his Ges. Abh.
I, 261-292.] .

92. Gesammelte Abhandlungen iiber Pflanzenphysiologie. I Bd. Leip-
zig, Engelmann.

Sertz, A. 90. Allgemeine Biologie der Schmetterlinge. Zool. Jahrb.
Abth. f. Syst. V, 281-343. 19 July, 1890.

Soroxin, N. 78. Grundziige der Mykologie mit Uebersicht der Lehre
iiber die Infectionskrankheiten. Bd. I, Hft. 1,511 pp. Kasan [Rus-
sian. Only the Abstract in Botan. Jahresber. VI (1878), 1 Abth.,
p- 471, has been seen. ]

Srant, E. ’78. Ueber den Einfluss des Lichtes auf die Bewegungserschein-
ungen der Schwiirmsporen. Verh. phys.-med. Ges. Wiirzburg. XII,
269, 270.

LITERATURE 217

Sta, E.’79. Ueber den Einfluss des Lichtes auf die Bewegungen der
Desmidien nebst einigen Bemerkungen iiber den richtenden Einfluss
des Lichtes auf Schwirmsporen. Verh. phys.-med. Ges. bicbeaasycd.
XIV, 24-34.

’80. “Ueber den Einfluss von Richtung und Stirke der Beleuchtung
auf einige Bewegungserscheinungen im Pflanzenreiche. Bot. Ztg.
XXXVITI, 297 et folg. April-June, 1880.

84. Zur Biologie der Myxomyceten. Bot. Ztg. XLII, 145-155, 161-
175, 187-191. March, 1884.

STEFANowsKA, M. 90. La disposition histologique du pigment dans les
yeux des Arthropodes sous l’influence de la lumiére directe et de
Yobscurité complete. Recueil Zool. Suisse. V, 151-200. Pls. VII,
IX. 15 July, 1890.

Sremacn, E.’91. Ueber Farbenwechsel bei niederen Wirbelthieren bedingt
durch directe Wirkung des Lichtes auf die Pigmentzellen. Centralbl.
f. Physiol. V, 326-330. 12 Sept. 1891.

92. Untersuchungen zur vergleichenden Physiologie der Iris. Arch. f.
d. ges. Physiol. LI, 495-525. 28 July, 1892.

STRASBURGER, E. 78. Wirkung des Lichtes und der Wirme auf Schwirm-
sporen. Jena. Zeitschr. XII, 551-625.

Streit, G. and Franz, B.’70. Einwirkung von Chlor auf absoluten Al-
kohol bei Sonnenlicht. Jour. prakt. Chem. CVIII, 61, 62. 13 Jan.
1870.

SzczAwinskKA, V.’91. Contribution & l’étude des yeux de quelques Crus-
tacés et recherches sur les mouvements du pigment granuleux et des
cellules pigmentaires sous l’influence de la lumiére et de l’obscurité
dans les yeux des Crustacés et des Arachnides. Arch. de Biol. X,
523-566. 31 March, 1891.

TrmiriazerF 77. Recherches sur la decomposition de l’acid carbonique
dans le spectre solaire par les parties vertes des végétaux. Ann. de
Chim. et de Physiq. (5) XIT, 335-396.

90. Enregistrement photographique de la fonction chlorophyllienne par
la plante vivante. Comp. Rend. CX, 1346-1347. 23 June, 1890.

TReMBLEY, A. 1744. Mémoires pour servir 4 V’histoire d’un genre de polypes
d’eau douce, & bras en forme de cornes. Leyden. 324 pp., 13 pls.
1744. [The reference is to the end of the first memoir.]

VeRworn, M. ’89. (See Chapter I, Literature.)

95. (See Chapter IV, Literature.)

Vierorpt, K. ’73. Die Anwendung des Spectralapparates zur Photometrie
‘der Absorptionspectren und zur quantitativen chemischen Analyse.
169 pp., 6 Taf. Tiibingen: Laupp.

VocEL, H. C. 77. Spectral-photometrische Untersuchungen insbesondere
zur Bestimmung der Absorption der die Sonne umgebenden Gashiille.
Monatsber. Akad. Wiss., Berlin. Jg. 1877, pp. 104-142, Taf. I.

Warp, H. M. ’93. Experiments on the Action of Light on Bacillus anthra-
cis. Proc. Roy. Soc., London. LII, 393-400. 10 Feb. 1893.

218 LIGHT AND PROTOPLASM [Cu. VIL

Warp, H. M.’93%. Further Experiments on the Action of Light on Bacillus
anthracis. Proc. Roy. Soc. LITT, 23-44.
04. The Action of Light on Bacteria. III. Proc. Roy. Soc. LIV,
472-475.
948, Further Experiments on the Action of Light on Bacillus anthracis
and on the Bacteria of the Thames. Proc. Roy. Soc. LVI, 315-394.
WertstTEIn, R. y. ’85. Untersuchungen iiber einen neuen pflanzlichen
Parasiten des menschlichen Korpers. Sb. K. Akad. wiss. Wien. XCI,
1 Abth., 33-58.
WittreM, V. ’91. La vision chez les Gastropodes pulmonés. Comp. Rend.
CXII, 247, 248. 26 Jan. 1891.
Witson, E. B. 91. The Heliotropism of Hydra. Am. Nat. XXV, 413-433.
Winoeranpsky, S. 87. Ueber Schwefelbacterien. Bot. Ztg. XLV, 489 et
folg. Aug.—Sept. 1887.
Yuna, E. ’78. Contributions & V’histoire de l’influence des milieux physiques
sur les étres vivants. Arch. de Zool. VII, 251-282.

a

CHAPTER VIII
ACTION OF HEAT UPON PROTOPLASM

In this chapter it is proposed to consider (1) briefly, the
nature of heat and the general methods of its application ;
(II) the action of heat upon the general functions of organ-
isms; (II]) the temperature-limits of life; (IV) the aceli-
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
Irs 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
219

220 HEAT AND PROTOPLASM [Cu. 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 z« (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 (¢) with the object of ex-
perimentation. The whole is coy-
ered over by a half globe of glass
(7), 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

Fic. 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 bell g; u, support for
the flower-pot; d, tripodal
iron stand carrying the spirit-
lamp /. (From SAcus, 792.)

horizontal microscope (lig. 65), like.
those devised by Cort (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 — 83°; and cal-
cium chloride and snow, in the proportion of 2 to 1, give — 42°,

§ 1] METHODS 221

the initial temperature being always supposed to be 0°. Far
lower temperatures than these have been obtained by phy-
sicists, notably PicrET, to whose work we shall refer again

male iN

‘yom DUM

Fic. 65.— Cori’s stage aquarium. A, the aquarium proper; 7, holder for the
aquarium; R, R, slides, with springs. (From Cort, ’93.)

(p. 240). The organisms to be acted upon may be kept in an

apparatus (Fig. 66) like that employed by PoucHert (66).
Throughout this chapter, as indeed throughout the whole

book, thermometric readings are given in Centigrade scale,

Soa
Te D eet
aE

Fic. 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 PoucHETt, ’66.)

222 HEAT AND PROTOPLASM [Cu. 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 Errect or 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. 3872) for the organisms of the
sea, that light begins to appear shortly above 20°, reaches its
maximum intensity at 40° in the fireflies and 85° in the water
organisms, and entirely disappears at 59° to 62° in the first
case, and 438° 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 Wueat SEEDLINGS.
~Totat Amount or O ar Lieiaea tees 01: ToraL AMOUNT OF O edie nthe 1.
ABSORBED PER 0.C. ABSORBED.

0.60 22.4° 0.10 15.6°
0.77 re Fy 0.038 4.4°
0.76 30.5° 0.067 9.8°
0.77 30.0° 0.088 15.4°
1.04 35.0° 0.022 0.3°
0.91 38,.2° 0.010 0.1°

§ 2] EFFECT ON GENERAL FUNCTIONS 223

Likewise MoissaAn (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

at 0°C., 0.32c.c.
Pinus pinaster (30 grammes) . . . | at 13°, 1.30 c.c.
(at 15°, 1.90 ¢.¢.
at 11°C., 0.54c.¢.

Agave americana (70 grammes) at 40° 5.56 &.c
: .56 @.¢.

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 TRE-
VIRANUS (31, p. 23) 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 oxygen 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 CO, evolved by seedlings varies with the tempera-
ture. On this point we have data by DEHERAIN and MoIssan
C74, p. 827), RiscHawi (’77), and others. DEHERAIN 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 CO, produced per
100 grammes of leaves : —

TEMP. Gas. CO,. Temp. Gas. COs. Temp. | Gms. CO,. || Temp. | Gas. CO,.

7 | 0.031 15 | 0.165 90 | 0263 | 40 | 0.961
13 0.139 18 | 0.178 21 | 0.289 41 | 1.189
14 0.157 19 | 0.193 32 | 0.514 42 | 1.395

When plotted (with the temperatures as abscisse) the relation
between temperature and weight of CO, produced is expressed

224 . HEAT AND PROTOPLASM (Cu. 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 RiscHAwlI, where the following series was obtained: —

TEMPERATURE. Weieut CO, In Ma. TEMPERATURE. Weicut CO, in Mea.
5° 3.30 Oy 17.82
10° 5.28 30° 22.04
15° 9.90 35° 28.38
20° 12.54 40° 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 SAcus (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 Cat 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 13 hours; in B after 2 to 5
hours ; whilst in (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, Rosspacu (’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 ON GENERAL FUNCTIONS 225

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. TTT,
778; NAGeELI, *60, p. 7;
SAcHS, 64; HOFMEISTER, ’67,
pp- 53, 54; and Coun, ’71, for
plant cells; and KUHNE, 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

DEGREES
13 5 7 9 1118 15 17 19 21 23 25 27 29 31 33 3%

1 1
3 3
~/
_—
5
: = z
9 |-LI1 Z 9
oI zm i nu
/
.
agees .
17 7
19 ig:
a Il “a 1
23 a 23:
25 25 -
27 aT
29 29°
31 31
33 33-
8 f 6.
37 aT
39 39:
4 4
a J as
45 45-
47 / 47
49 rd 49
51 51
58 53:
55 [ ss
57 7 - St
59 59
61 T ol
63 63

Fic. 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 Chilodon cucul-
lulus. The abscisse indicate degrees.
of temperature, Centigrade, in two-.
degree intervals; the ordinates give
the number of seconds elapsing
between successive contractions of
the vesicle, in two-second intervals..
(From SEMPER, ‘Animal Life.’’)

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
through 0.1 mm. of the granules floating in the stream of

protoplasm seen in the end cells of Nitella syncarpa.

Q

Some

226 HEAT AND PROTOPLASM - (Cu. VITI

measurements were made, also, by SCHULTZE, on Tradescantia
hairs. 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

60 mm TT 60 mm
tT
\
\
\
50 mm 50 mm
ia \
va \
]
40 mm 4 i \ 40 mm
]
/
I
L
30 mm 30 mm
/
cas 2 aa ‘
Py o
mA ‘
20 mm aug 4 20mm
a7 4 \
4 \
6 Ohi . D
4 Sy ¢
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Z ad ; 1
\
10 mm Vi aoe = ‘ : 10 mm
VA ‘ \ A
im dent ODE la \ ‘
, a ee V
| Lee
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A
Pi A

°

0° 5 10” F469 BO" REF eR Rae ee 45°C.
Fia. 68.— Curves showing the relation between temperature (abscissz) 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 abscisse

*§ 2] EFFECT ON GENERAL FUNCTIONS 227

represent temperatures (Centigrade) from 0° on the left to 44°
on the 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 reached, 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 CALLIBURCES. He placed a bit of
ciliated membrane from the frog’s cesophagus 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°to19°C. . . . . 22 minutes, 3 seconds;
at 28°C. . . . . . 8 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 cesophagus.- 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 (Ca. VII

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 80
Y
"0 7 ta 70
60 d 60
|
i \ AG
\
rN l
29 | Fa
10 V 10
ol 0
0 10’ 20’ 30’ 40’

Fic. 69.— Curves showing relation between temperature (curve 7'7') and rapidity
of movement of the cilia of the mouth and cesophagus of the frog. The abscisse
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, 777.)

and SCHURMAYER (’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 coédrdinated. Towards 40°, the progres-

§ 2] EFFECT ON GENERAL FUNCTIONS 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
optimum 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, ameeboid organisms,
and ciliated cells thus agree in demonstrating a close relation be-

80 80
naa |
70 70
\
\
50 \ ? 50
“0 7} 0
30 30
\ yi tt
=
20 20
py RG i
— ae
10 Seiko 10
0 0
0’ 10’ 20’ 30” 40’ 50° 60’

Fic. 70.— A set of curves having the same meaning as those of Fig. 69. In this case,
however, the temperature first falls and then rises, instead of rising 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-

s

230 HEAT AND PROTOPLASM (Cu. VIII

Above this temperature, the rate of protoplasmic movement
rapidly decreases. |

That temperature influences the irritability of protoplasm
is demonstrated by many facts. Thus, STRASBURGER (’78, p.
611) found that, at a high temperature, the light attunement
of swarm-spores changes. For example, swarms of Heematococ-
cus and Ulothrix, which are — phototactic, move at 30° C. from
the — to the + side of the drop. Lors (90, p. 48) has
found that Prothesia larve do not respond to light at a tem-
perature below + 138°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. 1830) has
shown that the response of muscles to electric stimulus varies
with the temperature. Thus, with the neck muscles of the
tortoise at —

See ey NuMBER OF es binygis REQUIRED
4°C. 1
9° C, 5
21° C7, 25
28°C. 34

isms of the experiment have been taken are, unfortunately, rarely given in
experiments on heat. From observations made by the Massachusetts State
Board of Health (Report on Water Supply and Sewage, 1890, Part I, p. 660), it
appears that the various ponds and reservoirs in the state, having a depth varying
from 19 to 5 metres, had a mean August (maximum) temperature ranging (in
the different ponds) from 24° to 21°C. Various rivers, mostly not of mountain
origin, had, in 1887, amean July (maximum) temperature, 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 82°C. (Red Sea, Gulf of
Mexico.) See A. Acassiz, ‘‘Three Cruises of the Blake,’’ Bull. Mus. Comp.
Zooél., 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.

a ee a a ee

§ 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 todiminish. 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. (ENGELMANN, 779,

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
sensitiveness to touch. Thus, the high temperature of 37° had
produced 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 PickrorD (51). He states
that, at a high temperature, muscle went into a rigid con-

232 HEAT AND PROTOPLASM [Cu. VII

dition (“‘Scheintodtenstarre”) 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. (48.8° C.) for 1 minute. I will now add some additional
cases of production 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
Actinophrys, which retracts its pseudopodia and appears as a lifeless mass
at 35° to 38°, but is not killed until 48° is reached. In the same year Sacus
(63, p. 453) repeated more fully the experiments of P. p—E CANDOLLE on
Mimosa pudica. He found that a temperature of 30° C. for 3 hours did not
produce rigor. A temperature of 40° for 1 hour 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. Sacus clearly distinguishes a “voriiber-
gehende Wirmestarre ” from death.

Ktune (’64, pp. 45, 67, 87, 103) drew a sharp contrast between the
rigidity of death, which he calls “ Warmestarre,” and the transitory immobile
condition or “ Wirmetetanus.” He found this latter condition to occur in
Ameceba 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 brought to that temperature. In all cases there is such a relation
between temperature and time of subjection that the greater the one is the
less need be the other in order to produce heat-rigor.

Very instructive also are the observations of HormrisTER (’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 similar 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), SAmMKOowyY (’74), MorieerA (91), GoTSCHLICH
(’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-LIMITS OF LIFE 233

lengthening again as the temperature falls. If, however (Gor-
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 SAcus. 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 (793, p. 154), “Die thermische
Dauerverkurzung ist also eine qualitative unvollendete Starre”
(z.e. death-rigor). 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 death 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

TABLE XIX

ReEsuLts OF EXPERIMENTS TO DETERMINE THE ULTRAMAXIMUM TEMPERATURE
OF ORGANISMS IN WATER, OR THE TEMPERATURE AT JUST ABOVE WHICH
ORGANISMS REARED UNDER NoRMAL Conpirions wiLt Die

[Cu. VII

MaxIMuM CONDITIONS OF
SPECIES. AUTHORITY,
TEMPERATURE, EXPERIMENT.
Cryptogams.
Bgctarsa ss yes a piel ohne 45°C. Maximum temperature) COHN, ’77, p. 253;
of growth in liquid |- ’94, p. 150
TRGGR SS 95 ora a ‘ 53° Moist; average max. | SCHUTZENBERGER,
"79, p. 162
Oscillatorie «. 6 23 62 5s 45° 7}
PROMI 2° oe tea es 4 42° |
SPIPOC VTA. i Se 44° t| Death point DE VRIES, ’70, p.
CEdogonium } | 388
Hydrodictyon....... 46° J
Cladophora. 4 6043? 45° to 60° Sacus, ’64, p.5
Nitella flexilis....... 45° Gradually raised DUTROCHET, ’37,p. °
TTT "
Funaria hygrometrica . . 43° DE VRIES, ’70, p.
388
Marchantia polymorpha \ 46° bs uy
Lunularia vulgaris J
Phanerogams.
Vallisneria spiralis. ...}| 45°to50° | Gradually raised
Ceratophyllum demersum | 45° to 50° | Suddenly immersed }| Sacus, ’64, p. 5
for 10 minutes
Various plant cells. ...| 47° to 48° | Died (suddenly sub-| ScHULTZE, ’63, p.
jected) 48
Protozoa.
AXthalium sept....... 40° Plasmodium died after | KUHNE, ’64, p. 87
2 minutes
PADDR: .6)'6 5 6.9 wile edbes 40° to 45° —s | Death point + 6
Actinophrys.......:.. 42° Death point. Activity | ScHULTZE, ’63, p.
lost at 38° 34
DEON once sae hes 43° Death point SCHULTZE, ’63, p.
38
Various Flagellata and 45° to 60° most usual. | BiirscuHui, ’84, p.
swarm-spores...... 40° to 60° Heat-rigor usually 860; 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-
peratures for the
motile stage
Various Infusoria..... 45° Can withstand only a | ScHURMAYER, ’90,

short time

p. 412

TEMPERATURE-LIMITS OF LIFE 235
MAXIMUM ConDITIONS
SPECIES. AvTHoriry.
TEMPERATURE. OF EXPERIMENTS.
Paramecium........ 42° to 46°C.| Gradually subjected | MENDELSSOHN,’95,
p-19 /
ee eae 44° to 50°. «|| Heat-rigor point, tem-| DAavENPORT and
| peratureraisedgrad-| CASTLE, 95, p.
ually. From apool; 229
kept warm by boiler
waste
Vorticellide........ 41° to 42° ScHULTZE, ’63, p.
; 49
Celenterata.
ST ore la bate ss cus: » 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°to40° | Suddenly immersed FRENZEL, ’85, p
461-466
Pleurobranchea ..... 33° Temp. gradually raised < ms
0 OS J 33° Died in 3 hours aS “
NOR i pc fa. 9 ew 35° Died eee *E
Young squids . . ; 37° Heat-rigor ; died at 41° | BERT, ’67, p. 135
Vermes. -
Warbellaria ........ 44.5° Death point SCHULTZE, 63, p.
49
SPALLANZANI,
Anguillulide ..... 44.5° belt AM 1787, Tom. I., p. 56-
ScHULTZE, ’63, p..
7 49
Rotifera } ee ee 45° to 48° =| Moist DovERE, 42, p. 29
Tardigrada 98° Dried Broca, ’61, p.4446
BMGDRETS.. 5. ew es : 40° Suddenly immersed, | FRENZEL, ’85, pp-
died quickly; at 30°} 461-465
lived indefinitely
ae ae 27° to 30° +=| Suddenly heated; < A
slowly warmed, re-
sisted 30°
PP ree ‘ 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 he f ‘a
Cypris F 36° ‘ ce 317
Gammarus roselii.... . 36° “ 5 big ** 316
Asellus aquaticus..... 43.5° ” - 7 “« 316

Argyroneta aquatica...

Hydrachna cruenta....

Insecta.
Potaran shat 2p ee

Agabus bipustulatus...
Hydaticus transversalis .
Culex pipiens, larva...
Hydrophilus caraboides .
Hydroporus dorsalis ...
Nepa cinerea 7}
Notonecta glauca f see
Cloé diptera, larva
Musca vom. (?)......
Musca vom., larva....
Musca vom., pupa ....
Silk worm larva .....
‘Butterfly’? larva....
Culex larva...s 5, +. %

Echinodermata.
Te sO Se RG a

PIGIOUNLTIA: o-fas ea ete

Vertebrata.
Many fresh-water fishes .

44° to 45°

37.5°
42.5°
43.7°
42.5°
42.5°
43.7°

80°

30° to 40°

40°

86°

83°

27° to 38°

Suddenly subjected

Submerged (?)

Suddenly subjected;
died slowly. At 36°
died at once

Death point

Death point

Died rapidly (sud-
denly subjected)

Died in several hours
(suddenly subjected)

Survived only a few
seconds
In pond out of doors.

Temperature elevated
gradually

236 HEAT AND PROTOPLASM (Cu. VUI
MaxImMuM CONDITIONS OF
pinnae TEMPERATURE, EXPERIMENT, AEROS:
Paleamon ... eee 26° C. Died in 2 hours (sud-| FRENZEL, ’85, p.
denly subjected) 463
Soyllaris is its! eee sie 30° Died in 1 hour (sud- * af
denly subjected)
Pagurus prideauxii. ... 36°
Dromia vulgaris ..... 38°
Pisa gibbosa. oo... 's a's» 36° F DE VARIGNY, ’872,
‘Portunus puber. ..... 34° peach po p. 173
Carcinus 6D) si.:5 «25-5. 38°
Grapsus BP... sss es 38°
Arachnida.

PLATEAU,
316

sé sé

"Tai. De

NICOLET, ’42, p. 11

PLATEAU,
316

42, p.

SPALLANZANTI, 1787,
Tom. I, pp. 56-58

FRENZEL, ’85, pp.
460-463

&é sé

EDWARDS, ’24, p.
114

KNAUTHE, 95, p.
752

BERT, ’76, p. 169

Davy, ’63, p. 125

a Zz
aa» '

§ 3] TEMPERATURE-LIMITS OF LIFE 237
SPECIES. T - sameusebi Veees Of AUTHORITY.
EMPERATURE. EXPERIMENT. *
Hippocampus ...... 30°C. | Lived half an hour FRENZEL, ’85, p.
462
Salamander....... 44° Death point SPALLANZANI,
1787, Tom. I, p. 56
MOMs wis s cic eo oe 40° to 42° | Suddenly subjected in | Epwarps, 24, p.
: water;deathatonce| 374
Frog, adult (summer) 42° to 43° =| Death-rigor in 7 to 14| Moriaara, ’91, p.
o minutes 385
Seomrog, adult ..... ; 43,8° SPALLANZANI,
1787, p. 55
Frog, tadpoles ..... 41° Raised in from 5 to 10 | See p. 253
wo: minutes ;
Rabbit Death point when | OBERNIER, 66, p.
j | Gatais gos es 44° to 45° raised gradually; 22
convulsions at 42°
ee 45° In water; giddinessin | Epwarps, 24, p.
5): a few seconds 374
Human spermatozoa... 50° Died in 10 minutes MANTEGAZZA, ’66,
p. 186
Vertebrate muscle ....}| 40° to 50° Ktune, 759, pp.
784-804
Vertebrate muscle (frog) 45° to 50° «| Raised in 30seconds | GorTscHLIcH, 93,
We 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 individuals 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 the

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 [Cu. VIII

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, Naidide,
Nepa (water-scorpion), Notonecta (water-boatman), Cloé 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 high

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. KitHne (’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-

ee

ae ee ie ee oe ee ee i

ss

§ 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
KUHNE’s great service to show that there 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 StrRasBURGER (°78, p. 611) found that Chilo-
monas curvata was uniformly killed at 45° C. by the explosion of the body, and
_ Dr. W. E. Casrwe 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 [Cu. VIII

which 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 PlorteT (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, ProTeT (’93%, cf. also C. DE CANDOLLE, ’84) 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 upon
raising the temperature. Some Rotifera and Infusoria were
frozen in their native water at — 60°, and kept at that tem-
perature, apparently, for nearly 24 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 Picter’s paper is, I 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] TEMPERATURE-LIMITS OF LIFE 241

later. Asa 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 VELTEN) 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 DeEmoor, ’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 Grrosa, 89). Among animals, KUHNE
(64, p. 46) found Amceba cooled to near 0° almost motionless.
PURKINJE 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 Picret’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 (Cu. 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 KUHNE (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
HERMANN (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 codperation 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 chemical 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.¢ 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 X min-
utes will resist a lower temperature, —(A + a)°, for a shorter time, X — z.

Thus, Clepsine complana resists — 8°C. for 15 minutes ; — 5°C. for 90 minutes.
So Planorbis corneus resists — 7° for 5 hours, but — 5° for 48 hours. Again,
Musca domestica can resist — 12° for 5 minutes; — 8°for 20 minutes; and

— 65°C. for 40 minutes. (Rorepet, ’86.) Since many authors have little re-
garded the duration of action of the cold, their determinations have little
scientific value.

+ The importance of this is illustrated: by some experiments of Sacus
(’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

DETERMINATIONS OF THE

HEAT AND PROTOPLASM

TABLE XxX*

[Cu. VIII

ULTRAMINIMUM OF ORGANISMS REARED UNDER
NorMaL Conpirions

MINIMUM ConDITIONS
et TEMPERATURE. OF EXPERIMENT. AUTRARENE:
Plant cells.
Tradescantia ..... —14°+ In water, rapidly
frozen .
Hair colle: «4: 6:j3s0je 353 —14°— In air, rapidly tro- | RURRy eae
zen )
Swarm-spores..... — j° Fully frozen, cautious-| STRASBURGER, °78,
ly thawed p. 612
Swarm-spores (Proto- Coun, 50, p. 720
fasens) <4 as 0° to —1°
Protozoa.
PaO? 685 on Sh ra ie 0° — Rapidly frozen on| KUHNE,’64, pp.46-47
slide over ice and
salt
Animal tissues.
White blood corpuscles: : ;
( — 2° to —3° | During8hours; warm-| SCHENK, ’69, p. 26
sss d rapidly
f Amphibia. .... '
of ambit | — AS For a_ short time; se eee
, warmed rapidly
Of FAB ah ne — 3 During 15 minutes ra “ 626
Saliva corpuscle....| —6° to —8° | Over 60 minutes + iar 7 §
Red blood corpuscle — 15°+ PoucHET, ’66, p. 18
Spermatozoa:
of Amphibia. .... — 4° to —7° ScHENK, ’69, p. 29
of Mammalia .... — §— Returned to activity od oy
on thawing
WE SPOR Sy eeu — 8°to —10°—| Frozen in testis Prevost, ’40,
OE THOR Souk sca. ha — 10° to — 12° QUATREFAGES, ’53,
: p. 353
OP RIA FS 6b a 1 nue 17° Gradually thawed MANTEGAZZA, ’66, p.
183
Eggs of Amphibia. . . — 9? During 1 hour SCHENK, ’69, p. 28
— GF Subjected a very short | Roru, ’66, p. 189
Ciliated epithelium of | - time
Anodonta ...... be he Seer Subjected during 6 45 189
minutes
* Temperatures all in degrees Centigrade. — before a number indicates below

zero, — or + after a number indicates that the true lethal temperature lay

slightly below or above that number.

(W), in water.

(A) indicates that the organism was in air ;

is

bil

§ 3]

TEMPERATURE-LIMITS OF LIFE

245

MInIwuM ConDITIONS
SPECIES. AUTHORITY.
TEMPERATURE. or EXPERIMENT.
Platyhelminths.
Dendroceelum lacteum 0° to —1° | Suddenly or gradually | ROEDEL, ’86, p. 207
subjected, till ice
forms
Mollusca.
Helix hispida ..... — §8 During 30 minutes ~ pada? |) |
Helix pomatia..... —10° During 600 minutes es “192
Helix pomatia..... (—14° to —18°)+| Gradually frozen for | PouCHET, ’66, p. 28
180 minutes, and
then thawed
Helix hortensis . |(—14° to —18°)+/ During 180 minutes 7 43
Helix aspera...... (—14° to —18°)+ eS Se = o
id Evy 2) — 7 * 300 = ** (A) | ROEDEL, 86, p. 212
ae — Jo i 88 EAS “313
Pulmonate embryos 0° to —1° | ‘‘ Died upon freezing ”’ re 212
(W and A)
S'S eee nese —17°+ During 2 hours (A) POUCHET, ’66, p. 26
Annelida.
Aulastomum gulo... — 2 During 12 to 15 hours | ROEDEL, ’86, p. 206
(W)
Clepsine complanata . — 5° During 90 minutes( W) iy? “< 6213
Renita s. h. ea es — & ‘“* “some min- | DOENHOFF,’72, p.725
utes” (W)
Insecta.
Apis mellifica ..... —1.5° During 210 minutes | 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
Pelopzus (chrysalis) — 28° — Out-of-doors, with- | WYMAN, ’56, p. 157
stood this tempera- |"
ture
EE Des ba) 5 ees. nid — & During 30 minutes ROEDEL, ’86, p. 197
Peederus riparius ; — 4 - = = ae
Phytonomus sp..... —12° ae PS We ar oe Pe risig PS |!
Melolontha ...... 18" +> * 120 =“ (A) | PoucHET, ’66, p. 26
Melolontha (larva) . . — 15° -+- of ey ree 7 Rae
Cetonia ols ale \« , ‘ se “ce se
Hydrophilus A Wins Mi tae (4) a.
ON SIBGUN Sho 55 aki. — 4° “« 60 ‘* (A) | Kocns, ’90, p. 682
Vanessa cardui, larva — 15° * 600 rs ROEDEL, ’86, p. 212
Vanessa io, larva... —17°+ s* 120 25: PoucHET, ’66, p. 27
Smerinthus populi . . — 10° ** 150 “ ROEDEL, ’86, p. 212
Ocneria dispar. .... — 4 SDR oH ” "So Se
Culex pipiens, larva . — 4 ete. ARS hs - “< -213
PEUOCE. ey hats cds aruis wk — 6° to — 10° © 180 es DoENHOFF,’72, p.725
Musca dom. ...... — 5° ae 3 ROEDEL, 86, p. 201
Various insects . . 0° ‘* 2 to 30 minutes | PLATEAU, "72, p. 98

(on ice)

246 HEAT AND PROTOPLASM [Cu. VIII

MINIMUM CoNnDITIONS
praaee TEMPERATURE, oF EXPERIMENT. POR OREET:
Arachnida.
Phalangium opilio .. a GP During 60 minutes ROEDEL, ’86, p. 201
Tegenaria domestica . 1G? ‘ . ti ae
Argyroneta aquatica . wee ye Soe a Son
Hydrachna cruenta. . = seen " af oe ae
PEBOAGON ST 5 phe aly 5 — 2° to —3° > GBG 3 DOENHOFF,’72, p.724
Crustacea.
Cyclops quadricornus. 0°? iam ‘““(W) | PLATEAU, ’72, p. 300
Cyclops spirillum... — 6° ** 120 ‘“(W) | ROEDEL, ’86, p. 201
&é 6“ 201
Daph WOK ee st ses e
saat ge arte , WA PLATEAU, 772, p. 300
Gammarus pulex ... 0° toe ‘“(W) | ROEDEL, ’86, p. 205
Asellus aquaticus... 0° (W) em
Astacus fluviatilus .. —11.5° ‘ -aday (A) | PoucHET, ’66, p. 32
Vertebrata.
Rana esculata..... — 4° to — 10° ** 180 minutes (A) es Sao

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:
Amceba, 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, Pelopzeus 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

ee Se ee ee

§ 3] TEMPERATURE-LIMITS OF LIFE 247

can withstand almost any temperature.* MULLER-THURGAU
(80) found that the “succulent labellum 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 —4°.” (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, what 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.; 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. Thus, WELTNER (°93, p. 276) 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 6, and from March 12
to 24; the intervals 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 (Brarem, 90,
p. 83) and the eggs of the silk-worm (Ducravx, ’71).

+ Poucuet (’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. e

248 HEAT AND PROTOPLASM (Cu. VII

says KUHNE, “ 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

ee

ee

——

§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 Celenterata, marine Mollusca, 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. +

* 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 Dutrocuer (’37, p. 777) and HormeistTeR (’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 VELtTNER (’76, p. 214) for Nitella and
other plant cells.

+ 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

TABLE XXI

(Cu. VIII

List oF Specites Founp 1n Hor Springs, with THE CONDITIONS UNDER
WHICH THEY OccuR

LocALITY AND CONDITION OF

No.* SPECIES. Temp. C, te AUTHORITY.
1 | Chroococcus 51° to 57° | Benton’s Hot Springs, Cal. | Woop, ’74, p. 34
2 | Nostoes or Pro- 93° Geysers, Lake Co., Cal.; not | BREWER, ’66, p. 391,
tococcus abundant at this tem-| also WyMAN, ’67,
perature p. 155
3 | Nostocs 51° to 57° | Benton’s Hot Springs, Cal. | Woop, ’74, p. 34
4 |Anabeena ther- 57° Dax, warm springs SERRES, ’80, pp.13-23
malis
5 | Leptothrix 44° to 54° | Carlsbad Springs Coun, ’62, p. 539
6 |Oscillaria or | 54° to 68° | Yellowstone Nat. Park, | WHEp, ’89, p. 399
‘** Confervee ”’ U.S.A.
4 . 54.4° Springs, Bernandino Sierra, | BLAKE, ’53, p. 83
Cal.
8 + 57° Algeria, Constantine proy-| GeRvaIs, ’49, p. 12
ince, waters of Hammam-
Meskhoutin
9 1 57° Hot Springs, Taupo, New | SPENCER, ’83, p. 303
Zealand 6
10 60° to 65° | Geysers, Lake Co., Cal.,| BREWER, ’66, p. 392
U.S.A.
11 4 60° to 65° | Hot Springs, Ark., U.S.A. | Jamzs, ’23, II, p. 291
(Long)
12 se 71° Hot Springs at Bafios Luzon, | Dana, ’38-’42, p. 543
Philippines
13 a 75.5° Soorujkoona Hot Springs | Hooker, J.D. ’55, I,
. p. 24
14 3 81° to 85° | Ischia EHRENBERG, 759, p.
493.
15 ¥ 98° Iceland FLOURENS, 746, p.
934
16 i z Outlet of Lake Furnas, | Dymr, ’74, p. 324

Azores.

selves with a hand lens, bottles of alcohol for preserving organisms for further

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

“No. SPECIES, Temp. C. LpALES “ encagrete a Avrunority,
Diatoms Frequently associated with
other alg in hot springs
17 ‘| Physa acuta 33° to 35° | Sources of Dax, St. Pierre, | DuBALEN, 73, p. iv
France
18 | Paludina sp. 50° Thermal waters, Abano,|DE BLAINVILLE, ’24,
Padua p. 141
19 | ‘‘Bivalve testa- ? Hot Springs, Ark. MITCHILL, ’06, p. 306
ceous animal ’”’
20 | Rotifera and An-| 44° to 54° | Carlsbad Springs, Bohemia | Conn, ’62, p. 539
guillulidz
Anguillulide 45° Aix, springs DE SAUSSURE, 1796,
V, p. 13, § 1168
22 rs 81° Ischia, in hot springs EHRENBERG, ’59, p.
494
25 | Cypris balnearia | 45° to50.5°|; Hammam-Meskhoutin Montez, 93, p. 140
24 | Stratiomys larva 69° In hot spring, Gunnison | GRIFFITH, ’82, p. 599
Co., Col.
25 rs ? In hot spring, Uinta Co.,| BRUNER, ’95
Wyo.
26 | ‘‘ Water beetle ”’ 44.4° |In warm spring, India;|} Hooker, J. D.’55, p.
abundant 24
27 " 2 Hot spring, Port Moller,| Dart, W. H. (per-
Alaska 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 93° (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 Hoppre-SEYLER’s inability to confirm EHRENBERG’S observa-
tions, the case seems established of Cypris thriving at 45° to
50.5°. Very extraordinary are the observations Nos. 24 and
25 on Stratiomys larve, 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 organisms can live and thrive

252 HEAT AND PROTOPLASM [Cu. 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. TTT) 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, HormEiIsTer (’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 recovered.

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.
236-240) 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°
higher, no tadpole died under 43°, the average increase of
resistance being 3.2°. This increased capacity of resistance
was not produced by the dying off of the less resistant indi-
viduals, for no deaths occurred in these experiments during

254 HEAT AND PROTOPLASM (Cu. 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 the 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 83 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 which 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 EXTREME TEMPERATURES 255

Since experiments have proved the fact of acclimatization, it
now remains to determine, if possible, its cause; to answer the
question, by virtue of what property can organisms which, 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° and 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 : —

Eee 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 that 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 (ScHUTZENBERGER, °79, p. 162). Damp
uredo-spores are killed at 58.5° to 60° C., but dry ones with-
stand up to 128° (HorrMAn, °63); and dry spores of some
molds up to 120° (Pasteur, ’61, p. 81). According to DAL-
LINGER (780, 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 (742, 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 [Cu. 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° (Lewirn, ’90).
DALLINGER and DRYSDALE (74, p. 101) and DALLINGER
(80, pp. 18, 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 181° 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. Lewiru, ’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 BUTSCHLI (’89, pp. 1652-1654). 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 Actinospherium the change from the richly vacuolated
motile form to the encysted condition is even more marked.
As BrAvER (794, p. 193) has 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

1 ie ee” ee

2 Oe Sere ae

§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 coagulable 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,”
Frrcu, °46, p. 10), and other species of Trichocera and Podura.
-Cf. also Boreus hiemalis and B. brumalis (FircH). 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 thrown 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 Euglene gathered in the swmmer time were:
not responsive below + 5° to + 6° C., ADERHOLD (’88, p. 320):
found that Euglene gathered in the winter would respond.
even at 0°. We may say, the 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
8

258 ' HEAT AND PROTOPLASM (Cu. 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 (783 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
/&thalium 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. WoORTMANN (’85) added the observation that when
the warmer temperaturé rose above 36° a repellent action of
the warmer water was discernible.

VERWORN experimented chiefly with Ameba. 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

lr oe ———

a

a

> poe

§ 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 ameeba in a drop of water. The light
from the mirror was cut off until the ameba, 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 the line of demarcation; then for a moment
movement ceased and a few seconds after the protoplasm of the
amceba began to flow backwards. In from 10 to 30 seconds
the amceba was wholly in the dark again. Similarly, when the
cover-glass was moved so that the ameeba 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., whilst 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 passing the light through a solution of iodine in CS,
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 — Ameba is positively
thermotactic towards that temperature.

Similar results were obtained by VERWORN with the shelled
Rhizopod Echinopyxis aculeata, and later (see JENSEN, 793,
p- 440) with Paramecium. More complete studies on the
latter were, however, made by MENDELSSOHN, who worked in
VERWORN’S laboratory. MENDELSSOHN devised an excellent
method of study. A brass plate 20 cm. x 6 cm. and 4 mm.
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 [Cu. VIII

desired. Starting now with the trough filled with infusion
water, the Paramecia are seen to be uniformly distributed
(Fig. 71, a4). 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

10? —_ 2
Fic. 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, ¢).

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 tem-

7
1
:
q
*
;
j
d

§ 5] THERMOTAXIS 261

perature ranges from 24° to 28°C. This temperature is thus

the optimum temperature for Paramecium, the 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 WILDEMANN (’94)
from Euglenze 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. Lors (790, p. 43) enclosed the larve 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 larve
wandered thither. Similarly some ants (Formica sanguinea)
are thermotactic according to WASMANN (791, p. 22); and the
cockroach (GRABER, ’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 body; 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
currents in the water.

262 | HEAT AND PROTOPLASM [Cu. 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
Ameba 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 Amceba. 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 8°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 irritability cease as a result of excessive stimulation, and

—S Se Oe ee

és

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, while 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 Chroécoccus 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 they were most abundant in waters of the temperature 52° to 60° (125° to
140°F.). In the hotter springs the plants appeared to be of the simplest 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-
ferve formed considerable masses of a very bright green color.”’ In a letter to
Wyman, however, Brewer 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 Protococcus, intensely green and rather dark.”

f

264 HEAT AND PROTOPLASM [Cu. VIII]

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
which flows a creek. ‘‘In the basin,’? says Mrs. Partz, ‘‘are produced the
first forms [Nostoc] partly at a temperature of 124° 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 algez,”’ etc.

4. Not seen by me.

5. Coun states: ‘* Thermometerbeobachtungen zeigten in verschiedener Tem-
peratur des Wassers verschiedene, schon durch die Farbe erkennbare Arten ;
zwischen 48° und 35°R., 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 tiber 44° enthalt keine lebenden Organismen. Ganz dasselbe fand AcarpH
1827.”

6. No statement as to the method of determining temperature. The meas-
urements were made in the outlet toa 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 conferve 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 l’eau au moment ou elle s’échappe des sources avait donné
a notre thermométre + 95° cent.’’ [It cooks eggs, meat, beans, etc.] ‘‘ Il est
inutile de dire qu’on ne trouve en cet endroit aucun animal ne aucun végétal
aquatique vivant. Cependant on voit cpurir sur les cénes d’ot jaillit l’eau
bouillante, et en des points ot le pied éprouve, méme & travers la chaussure, un
sentiment de vive chaleur, de petites Araignées qui m’ont paru étre du genre
Lycose. Quelques-unes s’aventurent méme et cela sans inconvénient a travers la
surface des petits cratéres remplis d’eau chaude que présentent les cénes dont il
‘s’agit. Dans la substance calcaire également fort chaude d’un de ces cénes que
nous percions & coups de pioche pour en faire sortir l’eau bouillante par le flanc,
nous avons trouvé plusieurs exemplaires vivants d’un petit Coléoptére de le fa-
mille des Hydrophiles, 1’ Hydrobius orbicularis, qui y avaient fixé leur demeure.

‘‘T’eau & + 95° qui sort de différents points d’ Hammam-Meskhoutin perd assez
rapidement cette température élevée. Elle n’a déja plus que 57° dans les vas-
ques du second tiers de la cascade, dans lesquelles on commence & trouver des
productions cryptogamiques. Celles-ci sont en partie couvertes d’un enduit
ferrugineux assez épais.”’

9. Plants found in samples of water from Taupo, ‘‘ growing in water the
temperature of which varied from 105° F. 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.”’

13. Data concerning temperature incomplete. ‘‘Conferve 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; the 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, réthlichen 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 Schlecht
der Acqua della Rita 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 driickte. Es war sehr voll von vielartigen
lebenden kleinen Thieren. Darunter war 4 Arten munter bewegter Rader-
thiere, niimlich Diglena Catellus, Conurus uncinatus, die Abanderung des
Brachionus Pola mit kleinen Stirnzihnen am Schilde, auch Philodina erythro-
phthalma, ausgebildete Eier im Innern fiihrend. Von Polygastern fanden sich
in frischer Lebensthitigkeit 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, EHRENBERG’s Observations have not been confirmed by Hopre-
Serer (’75, pp. 119, 120), who examined Ischia, but found no alge living at a
temperature much above 60°.

15. The entire reference is this: ‘‘M. FLtourens met sous les yeux de 1’ Aca-
démie des conferves recueillies en Islande par M. DescLo1zEavx, qui les a trouvées
végétant dans la source thermale de Gréf, & une température de 98 degrés”’ [of
course, 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 few 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 limosa 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 (Cn. VII

16. The temperatures were not taken on the spot. Moseiey says: ‘‘ The
water from which the Alge were gathered was in the pools from which the
. Chrodcoccus was collected as far as I can now [7.e. many months after (?)] 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 4 35 degrés, les Physa acuta, Drap. sont en nombre
si considérable qu’elles forment un véritable fond mouvant dans les canaux.’?
These hot water molluscs, as experiment showed, were killed at about 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, espéce de paludine sans doute, vit
dans celles d’Abano, dont la température 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 mesuré plusieurs fois & en diverses saisons, la chaleur de ces eaux,
& je l’ai toujours trouvée 4 trés-peu prés la méme; savoir, de 35 degrés dans
celle du soufre, & de 86} ou 36.7 [R. from context] dans celle de St. Paul.
Malgré la chaleur de ces eaux, on trouve des animaux vivans dans les bassins
qui les regoivent ; j’y ai reconnu des rotiféres, des anguilles & d’autre animaux
des infusions. J’y ai méme découvert en 1790, deux nouvelles especes de
tremelles douées d’un mouvement spontané.’’

22. See note No. 14.

23. Many individuals collected by R. Buancuarp ‘‘dans les eaux de thermes
du Hamman-Meskhoutine, prés Guelma, dans les premiers jours d’avril; l’eau
des thermes, au point de la récolte, a une température de 45° et de 50.5° C.
Les Cypris formaient une sorte de zone continue, de couleur chocolat, sur le
bord de l’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. Warp of the Uni-
versity of Nebraska, I have now before me. The larve were sent to Professor
Bruner by Joun C. Hamm, of Evanston, Wyoming, upon whom this statement
of the conditions of life of the organisms depends. The larve 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.

OO ae

ot 5) re

: LITERATURE 267

The larve were actively moving. Mr. Hamm» writes to Mr. Bruner: ‘I did
not have a thermometer with 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 more 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. Paut Berra.
yu des barbellons dans de l’eau a 34° C.””

29. **Mon ami Mr. Coccui,’’ says SPALLANZANI, ‘‘ raconte que les Grenouilles.
ne soufirent point dans les bains de Pise, quoiqu’elles soient exposées & une:
chaleur indiquée par le 111° du Thermometre de FaHRENHEIT qui correspond au.
37° du Thermometre de REaumur [! sic].”’

LITERATURE

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414, —

268 HEAT AND PROTOPLASM (Cx. VIL

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270 HEAT AND PROTOPLASM [Cu. VIII

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272 HEAT AND PROTOPLASM [Cu. VIII

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— -
a

aie.

LITERATURE 273

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VeELTEN, W. 776. Die Einwirkung der Temperatur auf die Protoplasma-
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Verworn, M. ’89. (See Chapter I, Literature.)

Vines, 8. H.’86. Lectures on the Physiology of Plants. Cambridge [Eng.]
Univ. Press. 710 pp. 1886.

Vries, H. pe "70. Materiaux pour la connaissance de linfluence de la
temperature sur les plautes. Arch. Néerl. V, 385-401.

Wasmanwn, E. 91. Parthenogenesis bei Ameisen durch kiinstliche Tem-
peraturverhaltnisse. . Biol. Centralbl. XI,.21-23. 1 Feb. 1891.
Weep, W. H. ’89. The Vegetation of Hot Springs. Am. Nat. XXIII,

394-400.

WELTNER, W.’93. Spongillidenstudien, II, Arch. f. Naturg. pp. 245-284.

Wevyt, T.’77. Beitrige zur Kenntniss thierischer und pflanzlicher Eiweiss-
korper. Zeitsch. f. Physiol. Chem. I, 72-110.

Witpemanny, E. pr 94. Sur le thermotaxisme des Euglénes. Bull. Soe.
Belg. Micros. XX, 245-258. 6 Aug. 1894.

WoLkorr, von and Mayer 74. Landwirthsch. Jahrb. I[II. 1874.

Woop, H. C. ’74. A Contribution to the History of the Fresh-water Alge
of North America. Smithsonian Contributions to Knowledge. XIX,
Art. HI. 1874.

Wortmann, J. 85. Der Thermotropismus der Plasmodien von Fuligo
varians (Aethalium septicum d. Aut.). Ber. D. Bot. Ges. III, 117-:
120.

Wyman, J. 56. [Observations on the Cold endured by Hibernating In-
sects.] Proc. Bost. Soc. Nat. Hist. V, 157.

67. Observations and Experiments on Living Organisms in Heated —
Water. Am. Jour. Sci. XLIV, 152-169.
Yuna, E. ’85. (See Chapter III, Literature.)

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, (1) the structure and composition of
protoplasm; (II) the limiting conditions of metabolism ;
(IIT) the dependence of protoplasmic movement upon metabo-
lism and external stimuli; and (IV) the doveriaaias of the
direction of locomotion:

§ 1. CONCLUSIONS ON THE STRUCTURE AND COMPOSITION
OF PROTOPLASM

The question of the séructure of protoplasm is preéminently

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 constitution of protoplasm is, on the other
hand, preéminently 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

4 A yiig pliant FC cep ye Sbeey tn yy et pe oy

= ig 2
‘

a

$2] -—~«XLIMITING 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 may 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 different 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 Limitrine ConpiTIons or METABOLISM

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-
quently, to place our limits very far out.

276 GENERAL CONSIDERATIONS [Cu. 1X

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 eaused
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 be 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 processes 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
optimum 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 (Cu. 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 DETERMINATION 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’
amoeba 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 amceba 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
reproduced in Fig. 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

10:58

11:02

Fic. 72.—Camera drawing, showing the successive positions assumed by Amceba
proteus when acted upon by external agents uniformly in all directions. Mag-
nified 16 diams.

-¥

Fic. 73.—Tracks made on paper by larve of Musca cesar moving in the dark from
a central spot of colored fluid. (From PoucHeEt, ’72. Revue et Mag. de Zool.
(2) XXIII.) ,

280 GENERAL CONSIDERATIONS [Cn. IX

fact that whereas the amceba responding to light is constantly
elongated in the direction of the infalling ray, the ameba
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 larve of Musca (Lucilia) cesar, kept in the
dark (Fig. 73;:compare Fig. 74, where the same larve 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 larve, 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 PovucHET, ’72.)

protoplasm of whatever sort in the organism. The sense of
that migration depends in part upon the internal condition of
the protoplasm. The mechanism by which locomotion is effected
—that is wholly 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.* 3

* There are several other important matters upon which the results of this
First Part throw light, such as the Mechanics of Response 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.

PART It

THE EFFECT OF CHEMICAL AND PHYSICAL
| AGENTS UPON GROWTH

—_0-9500—_.

CHAPTER X
INTRODUCTION: ON NORMAL GROWTH

ORGANIC growth is increase in volume.* It is not develop-
ment; it is not differentiation; it is not increase in mass,
although the latter may often serve as a convenient measure
of growth.

In analyzing the processes of growth in organisms we must
recognize at the outset that organisms are composed of living
matter and formed substance, and that growth may therefore
result from the increase in volume of either of these. The
living matter, in turn, is composed of two principal substances :
the plasma and the enchylema or cell sap; so growth may be
due to the increase of either of these substances, — may result
either from assimilation, or more strictly from the excess of

* Growth has been variously defined. Thus Huxtey has called growth
‘* increase in size,’’ which is essentially the same as my definition. Sacus (’87,
p. 404) defines growth as an increase in volume intimately bound up with
change of form (‘‘eine mit Gestaltveranderung innig verkniipfte Volumen-
zunahme’’); and he illustrates the definition by the example of the growth of
a sprout from its beginning to its full development. In this case two phenom-
ena are distinguishable: first, increase in volume, and, second, the filling out of ©
the details of form. As Sacus says, these phenomena taken together are gen-
erally denominated ‘‘development’’; and it seems decidedly advantageous to
retain this word with its usual signification, and to distinguish the two compo-
nent processes by the terms growth and differentiation.

PFEFFER’S (’81, p. 46) definition differs still more widely from the one pro-
posed above. He defines growth as change in form in the protoplasmic body
(‘* die gestaltliche Aenderung im ProtoplasmakGrper’’) ; and he goes on to say
that increments of volume and mass are not proper criteria of growth. Prerrer
illustrates this statement by the following example: A plant stem or a cell mem-

281

282 INTRODUCTION [Cu. X.

the constructive over the excretory processes of the plasma, or
from the taking in of water.* | ,
Of the three factors involved in growth— increase of formed
substance, of plasma, and of enchylema—the part played by the
last seems to me to have been underestimated. Plant physiol-
ogists have been in the best position to acquire the facts.

brane can be permanently elongated by extension beyond the limits of elasticity
without the volume necessarily increasing;—-and he apparently means to
include such an artificial deformation in his definition of growth. ‘‘And,’’ he
continues, ‘‘ under certain circumstances a diminution of volume of a plant seg-
ment can indeed occur as a result of growth, when, for example, the elasticity
of the wall is increased by growth and water is pressed from the cell until equi-
librium is restored.’’ It may be doubted, however, if Prerrer would say that
in this case the cell, as a whole, had grown ; but if he would, then his definition
is a wide departure from ordinary usage.

Also, Vines (’86, p. 291) offers a definition, which is intermediate between
that of Sacus and that of Prerrer. ‘‘ By growth,’’ he says, ‘‘ we mean per-
manent change of form, accompanied usually by increase in bulk.’? But then
he goes on to say, ‘‘ Nor does this increase even of the organized structures of
an organ, that is of the protoplasm and the cell wall, necessarily imply that it is.
growing. Thus, an increase of the cell wall may take place without any appre-
ciable enlargement of the cell, as, for instance, when a cell wall thickens.”’
But since the thickening is a ‘‘ permanent change of form,’’ it should be consid-
ered by the author a growth process were not increase in size of the cell after
all, in the author’s mind, the most important criterion of its growth. Finally,
Frank (’92, p. 855) finds no other criterion for growth than an increase in vol-
ume (dependent, however, upon the increase of a particular substance). Thus,
with these different plant physiologists, we see the word growth bearing the
ideas of increase of volume and differentiation, then of differentiation alone,
and, finally, of increase of volume alone.

* Various analyses of the process of growth have been made by different
authors. Let us look at afew of these opinions. Says Huxiey (’77, p. 2),
‘* growth is the result of a process of molecular intussusception.’’ According to
_ N. J. C. Mitier (’80, p. 100), ‘‘ all phenomena of growth depend, in last analy-
sis, upon this, that the molecule of the solid substance is introduced into the
region of growth.’’ Frank (’92, p. 355) understands by growth that increase
of volume which consists of the apposition or intussusception of new solid mole-
cules of similar matter (‘‘ welche auf der An- oder Einlagerung neuer fester
Molekule gleichartigen Stoffes beruhen’’). According to VERworwn (’95, p. 475),
growth is due to the excess of assimilation over disassimilation. These defi-
nitions include what I regard as only half the process of growth.

On the other hand, Driescn (’94, p. 37) distinguishes two kinds of cell
growth: (1) passive growth, due to imbibition of water, and (2) active growth,
resulting from assimilation. This classification agrees with the one I have pro-
posed, but I think the term passive growth very inapt, since the imbibition of
water is as truly an active process as any other vital activity.

Int. ] ON NORMAL GROWTH 283

They have recognized in the tip of the plant three growth
regions. At the extreme tip of the stem (or radicle) is the
region of rapid cell division but comparatively slow growth ;

next below is the
mM. zone exhibiting the
Grand Period of
growth; and still

below is the zone of
histological differ-

Pg entiation (Fig. 75)..
tas In the first zone
ces growth of plasma

is occurring ; in the
Fie. 75. — Curve of daily growth in length of a disc, second zone growth
originally 1 mm. long, and taken immediately behind ;
the vegetation point of a radicle of Phaseolus. It of the enchylema is
comes to occupy in successive days the three zones chiefly taking place;
referred to in the text. From Sacus, Lectures on
Plant Physiology.

1 % 3 4 s) v 7 8 v 10 DAYS

in the third zone
there is growth of
formed substance. The immense preponderance of the growth
of the second period (at 7 days) is an index to the preponderat-
ing influence in growth of the imbibition of water.

3.0
2.8

4, >
0.2 pes N . a
° Tae Bi as ~ 4 besece= NS)
05 1.0 15 200 = 25 30 635.4000 CG iGO CCC

Fic. 76.— Curve representing the intensity of growth of roots of Pisum sativum,
; Vicia sativa, -------- ; and Lens esculenta, —-—-—-— , the time being

assumed to be constant. The length of the abscissz in the direction from left to
right corresponds to the distance, in millimeters, of the marked spaces on the root
from the root apex. The ordinates correspond to the amount of growth, in milli-
meters, of the corresponding piece of the root after 20 hours. From CIEsIELSKI (’72.)

That which occurs with one and the same piece of the stem
on successive days takes place simultaneously at the different
zones of the growing organ. Thus in the radicle (Fig. 76)

284 INTRODUCTION [Cu. X.

we find during a period of 20 hours little growth occurring at
the root tip, a maximum of growth at 3 or 4 millimeters from
the tip, and further up less growth, until a zone of almost no

growth is reached.
An analysis of the substance of the stem at different levels
below the tip reveals the same thing —a sudden increase in the
amount of water

from 73% at the

ig = tip to 88% at the
first internode (II),

: reaching a maxi-
7 mum at 93% in the
Va second internode
10°, CII), then falling

I I UI IV ¥ slightly (92.7) to

Fic. 77. — Curve showing the percentage of water in suc- the fifth internode
cessive internodes of hothouse plants of Heterocen- }
tron roseum Hook. et Arm., about 4 decimeters high. (VI, Fig. TE The
The ordinates indicate the percentage of water at experiments and ob-
each internode from the terminal bud (I) to the fifth

(VI). (From Kraus, ’79.) servations upon

which these conclu-
sions rest thus agree in assigning the chief réle to water in the
growth of plants.

While the fact that water constitutes a large proportion of
the growing animal was made known by the classical researches
of BAUDRIMONT and MARTIN SAINT-ANGE (51), the impor-
tance of the part which it plays in the growth of animals seems
first to have been appreciated by LoEB (92, p. 42), who
showed how in the withdrawal of water by plasmolytic meth-
ods growth was interfered with. Later I made a series of
determinations of the relative part played by water and dry
substance in the growth of an animal (tadpole). Eggs and
embryos at various ages were weighed after removal of super-
ficial water. Then they were kept in a desiccator from which
air had been pumped and which contained a layer of sulphuric
acid to absorb moisture. After repeated weighings a condition
was found in which the drying mass lost no more water (con-
stant weight). The total diminution in weight indicated .the
mass or volume of free water contained in the organism at the
beginning of the experiment. Numerous weighings were

Int. ] ON NORMAL GROWTH 285

made during two seasons upon Amblystoma, toads, and frogs.
All series showed the same thing; the most complete series is
that given in the following table : —

TABLE XXII

Empryos or Frogs. 1895*

WEIGHT oF Dry
Tixe Days AFTER | AVERAGE SUBSTANCE, WEIGHT OF %o oF
" HatTcHInc. | WEIGHT, IN Me. us: Mo. WATER IN Me.| WATER.
May 2 1 1.83 .80 1.03 56
AR 2 2.00 .83 1.17 59
mn G 5 3.43 -80 2.63 77
"Ss 7 5.05 . .54 4.51 89
cae |) 9 10.40 12 9.68 93
Be 1S 14 23.52 1.16 22.36 96
June 10 41 101.0 9.9 91.1 90
July 23 84 1989.9 247.9 1742.0 88

These results are graphically represented in Fig. 78. The

curve and table show that, exactly as in plants, there is a
100% in

Citas tee te
eA

7o%

ay

So%

Days, 1 20 30 40 so 60 7o 60 EY)

Fic. 78.— Graphic representation of last column of Table, showing percentage of
water in frog embryos from 1 to 84 days after hatching. Compare with Fig. 77.

period of slow growth accompanied by abundant cell division
—the earliest stages of the egg. Then follows, after the first

* Compare with the less complete table of BaupRrimont and Martin Sarnt-
AnGE, ’51, p. 532.

286 INTRODUCTION [Cu. X

few hours, a period of rapid growth due almost exclusively to
imbibed water, during which the percentage of water rises
from 56 to 96; lastly comes the period of histological differen-
tiation and deposition of formed substance, during which the
amount of dry substance increases enormously, so that the per-
centage of water falls to 88 and below. But the growth is due
chiefly to imbibed water.

The foregoing facts thus unite in sustaining the conclusion
that at the period of most rapid growth of organisms growth
is effected by water more than by assimilation.

In later development the proportion of water slowly falls.
This fact is well brought out in the following tables : —

TABLE XXIII

SHOWING THE PERCENTAGE OF WATER IN CHICK EmBpryos AT VARIOUS STAGES
up To Harouine, FROM Ports, ’79

Hours or Broopine. ABSOLUTE WEIGHT IN GRAM, Yo WATER.
48 0.06 83
54 0.20 90
58 0.33 88
91 1.20 83
96 1.30 68
124 2.03 69
264 6.72 59
TABLE XXIV

SHOWING THE PERCENTAGE OF WATER IN THE HumMAN EMBRYO AT VARIOUS
Staces up To Birt, FROM FEHLING, ’77

AGE IN WEEKS. ABSOLUTE WEIGHT IN GRAM. % Water. .

6 0.975 97.5
17 36.5 91.8
22 100.0 92.0
24 242.0 89.9
26 569.0 86.4
30 924.0 83.7
35 928.0 82.9
39 1640.0 74.2

lll tay Sia, “ian aaa aia, ileal

a

Int. ] ON NORMAL GROWTH 287

These results indicate that during later development growth
is largely effected by excessive assimilation or by storing up
formed substance.

From another standpoint we can recognize two kinds of
growth: one a transitory growth, after which the enlarged
organ may return again to its former size, and the other a per-
manent or developmental growth, which is a persisting enlarge-
ment, and plays an important part in development. As an
example of transitory growth may be cited the case of the Sen-
sitive Plant, whose leaflets when touched turn upwards as a
result of the growth of cells on the convex side; but this
enlargement is only temporary—it is transitory growth.
This phenomenon is indeed usually not included in the idea of
growth ; yet it is well-nigh impossible to draw a sharp line of
distinction between it and permanent growth. For example,
when a tendril of .the Passion Flower is touched it may curve
as a result of growth of the cells on the convex side, and this
curvature may later become obliterated, as in the case of the
Sensitive Plant; but the longer the contact is continued the
more the cells enlarge, and the more their walls become perma-
nently modified. Thus the condition of temporary growth
shades insensibly into that of permanent growth. So far as
possible we shall consider in this book only developmental
growth.

Still another classification may be made of the phenomena of
growth. We may distinguish between diffused and localized
growth. In diffused growth the entire individual or many of
its parts are involved. In localized growth the process is con-
fined to'a limited region. Thus in the early development of
the frog diffused growth occurs, while in the formation of the
appendages we have an example of localized growth. Since
localized growth is an important factor in differentiation, many
of the data concerning this phenomenon will be first considered
in the Part dealing with Differentiation.

Normal growth may or may not be accompanied by cell-divi-
sion. But usually cell-division occurs sooner or later in the
growing mass. ‘The act of cell-division seems to retard the
process of growth. ‘This conclusion follows from some experi-
ments of WARD (795, p. 300) on the growth of bacteria, which

288

INTRODUCTION

are summarized in the curve, Fig. 79.
growth in length of the bacterial rods is delayed at intervals

(Cu. X

This shows how the

MOMENT WHEN 4TH SEPTUM
WAS CLEARLY VISIBLE,
GROWTH s. MAXM,
MOMENT|WHEN 8D SEPTUM |
WAS VISIBLE,
GROWTH MAXM, 70-03
LA
70 yl MOMENT WHEN 2D SEPTUM
WAS FIRST, VISIBLE,| Je 4
GROWTH AT MAXM.
ff
my MOMENT WHEN 1ST SEPTUM L—— 59-86
WAS DISTINCTLY VISIBLE, Ane
GROWTH AT MAXM, Y 64-6
“45 (it 50°76
45°3
40 ee 43-48 t PERIOD OF MINM! GROWTH,
fr ¥ | —_ 39°84 & 4TH CELL DIVISION.
30 32:56 34°38 THIRD PERIOD OF MINM, GROWTH,
i 29-12 WHEN 8D DIVISION
27-30 TOOK PLACE.
20 ft 2—_g
So * - i)
tec! Suulumtvamtumer 26 eee
ral or win onowin, OND cemod.or Mmonowrn? =H OR ORR
& WHEN FIRST CELL DIVISION OCCURRED.

OCCURRED.

Fia. 79. — Curve of growth of a bit of a filament of Bacillus ramosus, 27.30 # long at
the beginning and 70.88 ™ at the end of the period of observation. The curve
shows certain periods of diminished growth (indicated by the arrows below the
curve), which correspond to cell-division. From Warp (’95, p. 300).

by the nuclear divisions and the accompanying formation of

transverse septa.*

2 fs

oes

y

MM.

20 40

Semper, Animal Life, p. 163.

60

Fie. 80. — Curve of length of shell of Lymnea stagnalis
at intervals from hatching up to 85 days.

80

100

From

The course of
normal growth may
now be studied in

* Attention may here
be called to aphenomenon
which has_ repeatedly
been observed when a
single growing mammal
has been weighed at
regular intervals. This is
a sort of alternation of
periods of unusually rapid
growth with periods of
diminished growth, the
interval being a day or
two. There is an irregu-
larity in the length of
these periods. See Sarnt-
Loup, ’93; compare also
Minor, ’91, Table XIV.

ee EEE

=

Ivt.] ON NORMAL GROWTH 289

the case of certain selected, typical organisms. This may be most
quickly done by the use of curves whose abscisse represent
time intervals and whose ordinates represent size or weight.
Figures 80, 81, and 82 are such curves. In all cases excepting
that of guinea pig (in which the curve represents the growth
of only a comparatively late developmental period, namely,
from birth onward) the curves exhibit one characteristic shape.

The absolute increments are not, however, shown directly by
these curves. ‘To obtain them one must transform the curves
into others in which the

. : 8

successive ordinates shall _—
represent the absolute incre-
ment of weight over the
last preceding. Underthese -
circumstances the absolute .
increments rapidly reach a
maximum from which they
decline to zero.* me

Why does the growth de-
cline to zero? Thetheory , 2%
has been suggested} that \
there is a “certain impulse \
given at the time of im- wife

pregnation which gradually 5 10 mos.

Fie. 81.— The continuous line (a) represents:
fades out, so that from the weights in fractions of a kilogramme.

the beginning of the new attained by guinea pigs from birth until
growth there occurs a 12 months old. The broken line (6) rep--

a. 4 E resents the daily percentage increments
diminution in the rate of (%’s at the right) of the same guinea pigs.

growth.” The facts of up to7 months. After Minor (’91).

4%

KILOGRAMS
~

* Another method of representing curves of growth has been proposed by
Professor Minor (’91, p. 148), who argues that for a given period the rate of
growth should be expressed as the fraction of weight added during that period ;:
for, he says, ‘‘the increase in weight depends on two factors: first, upon the
amount of body substance, or, in other words, of growing material present at a.
given time ; second, upon the rapidity with which that amount increases itself.’”
Such a curve of percentage daily increments is given for the guinea pig in Fig.
81. Since, however, the greater part of the ‘‘ body substance’’ at its period of
greatest growth is not ‘‘ growing material,’’ as assumed, but water, the peculiar
value of the curve of percentage increments is doubtful.

¢ By Minor, ’91, p. 151.

U

290 INTRODUCTION [Cu X

growth in the tip of the plant do not, however, support this
theory, for the protoplasm at this point may go on growing
. for centuries, as we see in the

1, case of trees. Some of the
a protoplasm at the tip is, how-
| / ever, constantly falling back
ms to form part of the stalk:
1; Sata this part soon ceases to grow,
ce A undergoing histological dif-
ry ferentiation. The reason
if / why the animal ceases at
$s v length to grow is the same
ey VA as the reason why the differ-
10 a entiated tissue below the tip
J of the epicotyl ceases to grow

0 at i
rs a 70 —not because there is a nec-

Fic. 82.—Curves of growth of Phaseolus e€SSary limit to growth force
multiflorus (continuous line) and Vicia gt g certain distance from
faba (broken line). The ordinates rep- . ; } :
resent actual lengths attained on the impregnation, ut because it
respective days by a bit of stem origi- is in the nature of the species
nally 1 mm. long. After Sacus, Lect- that the individual should
ures on Plant Physiology. ’ :

cease to grow at this point.

The indefinite growth of this part, the limited growth of that,

are as much group characters as any structural quality.

To recapitulate briefly :_ Growth is increase in size, and may
result from increment of either the formed substance through
secretion, the plasma through assimilation, or the enchylema
through imbibition. This increment may be either transitory
or permanent; the latter class chiefly concerns us_ here.
Growth may be either diffused throughout the entire organism,
or local, forming a factor of differentiation. In normal growth
the increase is at first slow, then rapidly increases to a maxi-
mum, and, finally, in most animals, diminishes to zero. This
final cessation is a special quality of certain organisms, to be
explained like structural qualities, on special grounds.

tt) 5 et ae 88 co

Co -

Int. ] ON NORMAL GROWTH 291

0 1 2 3 4 5 6 7 8
/
Pa
|
VA
Yo
ee
Ya
"a
a
PA
By,
if
/
[
|
/
‘ss 7
0 1 2 3 4 5 6 7 8 YEARS

Fic. 83.— Curve of growth of man. The ordinates represent weight in kilogrammes.
The prenatal part of the curve is constructed from the data of FEHLING (’77);
the postnatal part from QUETELET (’71) for the male. The curve of the first
twelve months of postnatal life is adapted from GALTon (’84).

LITERATURE

Bavuprimont, A., and G. T. Martin Satnt-AnGE, ’51. Recherches anato-
miques et physiologiques sur le développement du foetus et en parti-
culier sur |’évolution embryonnaire des oiseaux et des batrachiens.
Mém. presentés par divers savants & l’Acad. des Sci. de l’Inst. Nat. de
France. XI, 469-692. 18 pls.

292 INTRODUCTION [Cu. X

Driescu, H. ’94. Analytische Theorie der organischen Entwicklung. Leip-
zig. Engelmann, 185 pp. 1894.

Freuuine, H. 77. Beitrage zur Physiologie der placentaren Stoffverkehrs.
Arch. f. Gynikologie. XI, 523-557.

Frank, A. B.’92. Lehrbuch der Botanik nach dem gegenwirtigen Stand
der Wissenschaft bearbeitet. I. Band. Leipzig. 1892.

Gatton, F. ’84. Life History Album. 172 pp. London. 1884.

Huxtey, T. H.’77. A Manual of the Anatomy of Invertebrated Animals.
698 pp. London. 1877.

Kraus, G. ’79. Ueber die Wasservertheilung in der Pflanze. Festschr. z.
Feier des Hundertjahrigen Bestehens d. Naturf. Ges. in Halle. pp.
187-257.

Logs, J.’92. Untersuchungen zur physiologischen Morphologie der Thiere.
II. Organbildung und Wachsthum. 82 pp. 2 Taf. Wiirzburg. 1892.

Minot, C. 8. 91. Senescence and Rejuvenation. Jour. of Physiol. XII,
97-153. Plates 2-4.

Miter, N. J. C. ’80. Handbuch der allgemeinen Botanik. I. Theil.
Heidelberg. 1880.

PFEFFER, W.’81. Pflanzenphysiologie. Engelmann. Leipzig. 2 Bde.
383 +474 pp.

Pott, R. 79. Untersuchungen iiber die chemischen Veranderungen im
Hiihnerei wahrend der Bebriitung. Landwirth. Versuchs-Stat. XXIII,
203-247.

QUETELET, A. "71. Anthropométrie ou mesure des différentes facultés de
Vhomme. 479 pp. 2 pls. Bruxelles and Paris. 1871.

Sacus, J. 87. Vorlesungen iiber Pflanzenphysiologie. Leipzig. Engel-
mann. 884 pp. 1887.

Sarnt-Loup, R.’93. Sur la vitesse de croissance chez les Souris. Bull. Soc.
Zool. de France. XVIII, 242-245.

Verworn, M. ’95. Allgemeine Physiologie. 584 pp. Jena: Fischer.
1895.

Vines, S. H.’86. Lectures on the Physiology of Plants. Cambridge [Eng.]
Univ. Press. 710 pp. 1886.

Warp, H. M.’95. (See Chapter XVII, Literature.)

——————— ee ee

oe

———

OO PE eS eS

bd

ee a ES
\

CHAPTER XI
EFFECT OF CHEMICAL AGENTS UPON GROWTH

WE shall consider this subject under two heads: (1) Effect
upon the rate of growth, and (2) Effect upon the direction of
growth.

§ 1. Errect oF CHEMICAL AGENTS UPON THE RATE OF
GROWTH

Organic growth, occurring in a material composed of water,
plasma, and formed substance, consists in the increment of.each
of these components. The means and results of varying the
quantity of water in the organism will be discussed in the next
chapter ; here we are to consider the results of assimilation,
including the production of formed substance. ‘The scope of
our work may be more precisely defined as the answer to the
question, What role do the various chemical substances (exclud-
ing water) play in the metabolic changes involved in growth?

There are two réles played by chemical substances in the
body ; and, accordingly, we may distinguish two kinds of
chemical agents having diverse effects upon growth. These
agents — foods, in the widest sense of the word — must supply
the material—the atoms—from which the molecules of the
plasma, or of its formed substance, are made up; and, sec-
ondly, they must supply energy for metabolism. Foods, then,
yield to the organisms matter and motion; they are hylogenic
(plastic) and thermogenic (respiratory).

These two offices of chemical agents in growth are only in
certain cases exerted by distinct kinds of food. In the case of
animals, sodium chloride and iron compounds are examples of
wholly plastic foods, while the free oxygen taken into the body
is chiefly thermogenic. In the case of the free oxygen, how-
ever, it is quite probable that it is sometimes used in the con-

struction of the molecule of active albumen which, according
293

294. EFFECT OF CHEMICAL AGENTS [Cu XI

to LoEw, constitutes the essential living substance. For exam-
ple, oxygen performs this office in LOEw’s (’96, p. 39) hypoth-

esis of the formation of albumen in plants from the nitroge-—

nous products which result from the action of an enzyme upon
the reserve proteids, z.e. leucine. Thus

leucine formaldehyd
C,Hi,N O, +- 7 O = 2 CO, fe H,O + 4 CH,O f- NHs3.
formaldehyd asparagin

4CH,O + 2NH,+ 0,= C,H;N,0,+ 3 H,0.

Now since, as LOEW makes probable, asparagin is a stage in
the production of albumen, the free oxygen molecule may be
essential to the synthesis of the living substance.

The facts indicate that the plastic and thermogenic functions
of foods are inextricably intermingled —that both are exhib-
ited in the mutations of the living substance as well as in the
respiratory processes. Thus, on the one hand, assimilation is
accompanied not only by endothermic (energy-storing) but
also by exothermic (energy-releasing) processes ; while, on the
other hand, the partial oxidation of the food proteids may be
a necessary step towards assimilation. It is because the net
result is the storing or the release of energy that we may speak
of any complex of processes as enthodermic or exothermic, and
certain foods as plastic or thermogenic.

The source of energy in organisms is not, however, solely
food. Energy may likewise be derived directly from energy
in the environment. This source is of greatest importance in
the case of chlorophyllaceous organisms, but it is probably not
of importance for them alone. * For the heat and light of the
environment aid, as we have seen (pp. 166-171, 222-225),
various metabolic processes in all kinds of protoplasm.

1. The Materials of which Organisms are Composed.—To
determine the sorts of materials which plastic food must supply
to the body, it will be instructive to consider the proportional
composition of the body out of water and dry substance, both
organic and inorganic. Such data, gathered from various
animals and plants, are given in the following table : —

4
:
:

§ 1] UPON THE RATE OF GROWTH 295

TABLE XXV
ANIMALS
m=] : a a
3 ee ee a
m SS Re << ~s
‘ . 3 = > = = = 5 =o
SPEcIEs. SE Voe SS Soke SAz AUTHORITY.
- z & Re % D 2
3 5 3 S = =
6 - < 6 A 2
Sponges, average ..../|79.4} 11.0 9.7 54.1 45.9 | KruKensere, '80
Meduse:
Rhizostoma cuvieri. . .| 95.4 1.6 3.0 34.8 65.2 ss
Actiniaria :
Anthea cereus...... 87.6 10.7 1.6 87.0 13.0 ss
Actinia mesembryanth. | 83.0; 15.4 17 90.0 10.0 se
Sagartia troglodytes ..| 76.8; 20.9 2.3 81.1 18.9 “6
Cerianthus membran. .| 87.7| 11.6 1.7 87.2 12.8 “6
Alcyonium palmatum .| 84.3; 10.8 4.9 68.8 31.2 “
Asteroidea:
Astercanthion glacialis.| 82.3} 14.1 3.6 79.6 | 20.4 6
Annelida:
Lumbricus complanatus | 87.8 9.7 2.4 80.2 19.8 ee
Crustacea:
Oniscus murarius. ...| 68.1| 21.2 10.6 66.6 33.4 BEzo.p, ’57
Squilla mantis ..... 10D S28 5.9 78.9 21.1 | Krvxensere, 80
Astacus fluviatilus ...| 74.1| 16.8 9.1 64.9 35.1 BeEzop, °57
Mollusca:
Doris tuberculata. . . .| 88.4 9.0 2.6 77.6 22.4 | KrvKxensere, 'S0
Doriopsis limbata. . . .| 86.5} 12.4 | 91.9 8.1 6
Arion empiricorum. . .| 86.8; 10.1 3.1 76.5 23.5 BEzop, 57
' Limax maximus ... .| 82.1} 16.4 1.5 91.6 8.4 ‘“

Ostrea virginiana... .| 88.3| 10.8 0.9 92.3 rye
(without shell)

Tunicata:
21 a a a oe 93.6 31°} 3.8 48.4 51.6 | Keuxensere, '80
Vertebrata:
Cyprinus auratus. ...|77.8| 17.6 4.6 79.1 20.9 BeEzoxp, ‘57
Triton igneus ...... 80.2; 16.1 3.7 81.1 18.9 es
| Triton cristatus..... 79.6 | 17.0 3.4 82.9 17.1 ee
: Bombinator igneus .. .| 77.3} 19.4 3.3 85.2 14.8 ae
: Bufo cinereus ...... 79.2} 14.8 6.0 71.1 28.9 és
Rana esculenta ..... 82.7} 14.2 3.0 82.2 17.8 66
Angius fragilis ..... 55.0} 32.1 12.9 71.5 28.5 ss
Lacerta viridis. ..... 71.4} 23.2 5.4 81.3 18.7 ee
SDAITOW:) 64: boa xh eit ea 67.0} 27.8 5.2 84.3 15.7 66
MASS <c)eia, diet ieieeeh Orel} Rie 5.0 85.2 14.8 ss
PROMO) 2.45. Meera 70.8 | 25.7 3.5 88.0 12.0 ‘6
MEAN es ope aie ee 65.7 | 29.6 4.7 86.3 13.7 | Vorxmann, °74

296 EFFECT OF CHEMICAL AGENTS [Cu. XI

PLANTS
Oats, in blossom ... .| 77.0 6.4 16.6 27.8 72.2 Wo rr, °65
Wheat, in blossom , . .| 69.0 9.3 21.7 30.0 70.0 66
Vea vines, green ... .| 81.5 4.8 13.7 26.0 74.0

a. Analysis of the Entire Organism.— We are now ready to
consider the atomic composition of the dry substance of organ-
isms. VOLKMANN (74) has contributed data on this subject
in the case of man. Thus the dry substance gives : —

Cc ASH

0 H N :
52.9% 185% 47% Ga tee

In the case of a plant (stems and leaves of dry clover) we |

have, according to JOHNSON : —

C 0 H N bs) P REMAINING ASH

ATA%, 37.8% 50% 21% 012% 0.30% 20%

These two determinations, fairly typical of the higher plants
and the higher animals respectively, run nearly parallel. The
greatest difference is shown by the nitrogen, which is more than
three times as abundant in animals as in plants. Oxygen, on
the other hand, is more abundant in plants.

The ash, in turn, must be further analyzed. The following
table gives the percentage composition of the ash of various
organisms : —

TABLE XXVI
ANIMAL, New-sporn Doe. MENHADEN (FIsH). Oat PLANT.
AUTHORITY. Buneg, ’89. Cook, ’68, p. 498. AVENDT (VINES, ’86, p. 129).
CaO 29:5 40.0 12.1
P05 39.4 35.8 8.8
K.0 11.4 ae: A 45.9
Cl 8.4 3.1 6.1
Na,O 10.6 4.7 2.32
MgO 1.82 8.1 4.12
Fe,03 0.72 a 0.54
SiO, mene 6.1 17.2
SO3 we oa 2.86

a

ee A

§ 1) . UPON THE RATE OF GROWTH 297

It would be valuable to know the relative number of atoms
of each of the metalloids and metals named in the preceding
table. This may be determined in the following way: Find
the proportion by weight of each metallic radical (excluding
the oxygen) in the entire ash and divide this percentage by the
molecular weight of the metal. The varying weights of the
elements are thus eliminated, and a set of numbers which indi-
cate relative abundance of atoms is obtained. We multiply
these small fractions by 1000 for convenience. The results
are as follows :—

TABLE XXVII

New-sorn Doe. MENHADEN (FISH). Oat PLaAnt.
Ca 528 715 216
P 555 506 124
K 2438 151 974
Cl 24 174 1738
Na 343 150 60
Mg 45 77 114
Fe 9 ae 6
Si oa 101 287
Ss — — 36

These examples may suffice to show how diverse is the com-
position of different organisms and how diverse therefore must
be their requirements in the way of food to build up the adult
body. The examples serve also to indicate what are the
important elements for organisms. ‘They appear to be the
same for animals and plants, and are : —

*Carbon *Calcium Sodium *Sulphur
*Oxygen *Potassium Chlorine Silicon
*Hydrogen *Phosphorus *Magnesium “*Iron
*Nitrogen

While this list does not pretend to exhaust the elements found
in organisms, it contains those which are usually present.

In the organism the atoms just named are, of course, found
in combination. The carbon, oxygen, hydrogen, and nitrogen
are contained in the organic matter of the organism — the

* Those elements which are starred (*) are essential to all organisms.

298 EFFECT OF CHEMICAL AGENTS [Cu, XI

greater part of the entire dry matter. The relations of the
remaining elements are largely obscure. Some of them form
inorganic acids in the body, such as hydrochloric and sulphurie
acids.. Others form inorganic compounds deposited in the body
as supporting or protective substances, such as the calcic phos-
phate and: calcic carbonate of bone and spicules and the silicic
oxide of plants. But there can be little doubt that a large and
highly important part of these elements is built up into organic
molecules and in this position plays a weighty and varied part
in metabolism and growth. As examples of the way in which
the metals and metalloids occur in the organic molecule I may
cite a few cases in which the molecular structure has been deter-
mined more or less satisfactorily. Thus we have sulphur in albu-
men, C,,Hj;.Njg5O0,,3; iron in hematin, C,,H,,N,FeO,; phos-
phorus in lecithin, CyH,,NPO,, and nuclein, C,,H,)N,P 30905
magnesium in chlorophyllan, and various halogens in_ the
urates of sodium, calcium, and lithium. In discussing as we
shall immediately the importance of each of these elements for
the formation of the body we shall find additional facts con-
cerning the importance of the metallic atoms in the organic
molecules. ‘There is good reason for believing that the pecul-
iar properties of hemoglobin depend upon its iron and that
the characteristic properties of nuclein depend largely upon its
phosphorus and (as the later investigations indicate) its iron
-also. As our knowledge develops, the importance to many
organic molcules in the living body of metallic or metalloid
elements becomes clearer; the “ash” of the body is not some-
thing accidental, secondary, or superfluous, but is an essential
part of the organism.

We must now consider the source of the various elements
necessary to nutrition. Botanists early determined that C, H,
and O enter the organism through the carbonic acid and water
which green plants absorb. Concerning the source of nitrogen
there has been less certainty ; it is generally believed to come
from nitrates in the soil, but that matter will be considered
later in more detail. Another source of the more characteris-

tically organic elements, C, H, N, and O, is, without doubt,

organic compounds of various sorts. Although it has long
been known that insectivorous plants absorb the organic mat-

—————

— =<

ee eS pa ee eee

—

§ 1] UPON THE RATE OF GROWTH 299

ters they digest, still it is only recently that the fact that green
plants in general can make use of organic compounds has been
recognized. BokoRNY (97) has lately brought together the
evidence which makes this conclusion certain. It appears that
in the presence of organic solutions some alge may grow for
half a year in the absence of carbon dioxide; and the potato
plant may, even in the dark, store up starch in its tubers in the
presence of rich organic food. Nitrogen may also be gained
from amido-bodies ; thus, BASSLER (’87) found that his maize
cultures grew better in asparagin,

CO,H - CH(NH,) - CH,: CO(NH,),

than in potassium nitrate. Thus plants may gain their C, H,.
QO, and N from either organic or inorganic sources.
Non-chlorophyllaceous organisms, on the other hand, have:

long been known to gain their

C, H, N, and O from organic if ee
compounds ; indeed, it has gen- ° EOS
erally: been believed that they f

can gain those elements from a b ,

organic compounds only. Cer-
tain observations, however, Fyo.s4.—a, Nitrosomonas europea (ni-
throw doubt u pon the entire trite bacteria from Ziirich) ; b, Nitro-.

\ - - of. somonas javensis (nitrite bacteria.
correctness of this belief; these —g,om Java): c, Nitrobacter (nitrate-

are especially the remarkable __ bacteria from Quito). Magnified 1050.

results gained by W INOGRAD- After WINOGRADSKY, from FISCHER,.
Vorlesungen iiber Bakterien, 1897.

SKY (90) from nitrifying bacte-

ria (Fig. 84). This author found that the bacteria abla’

grow in a mixture of inorganic salts free of organic matters.

Solutions free from organic matter were prepared by the following
means: The-culture vessels were cleaned by boiling in them sulphuric.
acid and potassium permanganate. The water used in the cultures and in
washing the vessels was twice distilled in vessels without joints of organic:
material — the second time with the addition of sulphuric acid and potassium.
permanganate. The magnesium sulphate and potassium phosphate, used as:
food, were calcined; the calcium carbonate, used in excess, was likewise
calcined and saturated with carbon dioxide; finally, the ammonium sul-
phate was especially prepared to avoid organic impurities. The culture
flasks were plugged with calcined amianthus, not with cotton. The solu-
tions were inoculated with a mere trace of the culture containing nitrifying

300 EFFECT OF CHEMICAL AGENTS [Cu. XI

organisms. The cultures were then reared either in complete darkness or
in dim light. The precautions taken to eliminate organic matters would
seem to be complete; but those who know the difficulties of such experi-
ments seem willing to admit the possibility “that exceedingly minute quan-
tities of organic nitrogen and carbon are actually present” (JoRDAN and
Ricuarps, ’91, p. 880). On the other hand, “exceedingly minute quanti-
ties” of organic matter could hardly account for the vigorous growth of bac-
teria; and, in general, a priori objections cannot be permitted to overthrow
results gained by the use of methods which are beyond reproach.

The organisms placed in this water, deprived of the last
traces of organic matter, developed rapidly, but not quite so
rapidly as organisms placed in natural water to which the
necessary salts had been added. Analysis showed that not only
nitrates but also organic carbon compounds had been formed.
Thus the careful experiments of WINOGRADSKY demonstrate
what the less critical experiments of HErR&us (86) had
already rendered probable, that a complete synthesis of organic
matter may take place through the action of living beings and
independently of the solar rays. These noteworthy observa-
tions, then, obliterate the last sharp line of distinction between
the nutritive processes of chlorophyllaceous and non-chloro-
phyllaceous organisms. We may now state that the elements
C, H, N, and O may be gained from complex organic food
materials by all organisms, and from simple compounds, such
as carbonic acids, ammonia, and water, by all chlorophyllaceous
organisms, and, very probably, by certain non-chlorophylla-
ceous ones also.

The elements other than C, H, nN, and O are probably
gained by chlorophyllaceous and non-chlorophyllaceous organ-
isms alike, from either inorganic or organic compounds con-
caining the necessary elements; although, possibly, animals
make use of the metals more readily when they are in organic
compounds. Suitable proportions of the different metals in a
nutritive solution for green plants are given in the following
tables, showing various standard solutions employed by differ-
ent experimenters : —

§ 1) UPON THE RATE OF GROWTH 301

TABLE XXVIII

Nourritive SoLuTions FOR PHANEROGAMS

Sacus’ Solution Gramues.
MURETEOL WOAOE oe es RR? ey 1,000.0
Potanin nitrate, KINO, 2. 6 ee ks 1.0
Calcium sulphate, CaSOQ,. ....... 0.5
Magnesium sulphate, MgSO, ..... . 0.5
Calcium phosphate, CaHPO, ...... 0.5
Ferrous sulphate, FeSO, . . . . ... . trace

Scurmper’s Solution (’90)

Distilled water . . . She ae restier of 600.0
Calcium nitrate, Ca(N 0, tN GE rey nae 6.0
ore Us Si 6 eer 1.5
Magnesium sulphate, MgSO, . ..... 1.5
Neutral potassium phosphate, K,PO, . . . 1.5
Puete ODIOFIGS, NOON. se ee ek 1.5

FraAnk’s Solution

Water, =}, distilled; 29 Berlin reservoir water. 1,000,000.0

Calcium nitrate, Ca(NO;), . ..... .- 267.4

POusetim Chiorige, BOL. vie ee 121.5

Potassium phosphate, K,PO, . .... . ee LS

Magnesium sulphate, MgSO,-7H,O. . . . ~ 100.2

Perric CnlOrige) Bein. os Se Re eS trace
The first differs from the others chiefly in the absence of chlo-
rine.

_ How fit ordinary waters may be to provide all these salts is
shown by this analysis of the ordinary drinking water of Bos-
ton (JORDAN and RIcHARDs, ’91) :—

e
. TABLE XXIX

shams BY Weicut or InorGanic Matters 1n 1,000,000 Parts or
PoTaBLE WATER

PINES BONG eis its ek ei ene: 458

Chlorine vk: ; antic me bb ait + QOD,
Alumina and oil of i CN ae i SoA iM | iy 6
Ole ORIG lah eis asic de ee s O4D

DIMM Sioa toa. a, wy nara cies acces +. 260
RE are, ea, fie ee es) 0, Se
PEMD Paes ate 5g he See eT ase, O00
Me ee aed See OR ae eh se Oe
DUISEMMINI RE otis ata ke ae ase alse OG

302 EFFECT OF CHEMICAL AGENTS (Cu. XL

All of the elements mentioned above, except phosphorus,
appear in this list. Thus, ordinary drinking water is clearly
well adapted to the nutrition of plants.

For alge, MouiscH (95) used the solution given in the fol-
lowing table : —

TABLE XXX
Nurritive Sovution ror ALG#

GRAMMES,
Water. 330, do eS) ee
(NH) HPO, | tore. sinlas eat ae 0.8
(KA SPO, 4.6! a. og ee 0.4
MgSO, 5 NSF ce eres 0.4
FeSO, fe ie eas ws) ee a

(2 drops of a 1% sol.)

Here we note an absence of the calcium used in the solutions
for phanerogams. |
Fungi likewise require a mixture of salts, according to
NAGELI (80, p. 854) and BENECKE (95), in the following
proportions:— | |
TABLE XXXI

Nutritive So.utions For Funet
NAgeEtt’s Solution BENECKE’S Solution

GRAMMES. GRAMMES.

Water. tw es «OCCT Water: ra) ane
CNP Oe aos 06°) KH PO wae og ee meas 5.0
MgSO,+7H,O .. . 0.5 | MgSOQ,+7H,O.. . 0.01
KCl, aha Se ee ay 0.5} EX BOLE Seti ariet oe 0.5
OOS 5 es ate ares 0.05-; NH Gini rect ica ea 10.0
Organic Compounds . Pesos ye skcue Sass trace
Giyverma yea. 1. 50.0

The solutions differ principally in the proportion of the salts.
Finally, all animals likewise require a certain quantity of
salts. What the proportions are can be shown in the case of
young mammals, which live during part of their growing
period exclusively upon milk. A wonderfully closé relation
exists, indeed, between the proportions of the mineral con-
stituents of milk and of the young mammal before it has begun
to suck. This is shown in the analyses made by BUNGE (89)
upon the milk of a dog and the body of its newly-born pup.

.
———————

re

—_—— «= =

ae =a

— ee,

a a ee
;

§ 1) UPON THE RATE OF GROWTH 303

TABLE XXXII

CoMPARISON OF AsH IN NEW-BORN DoG AND IN THE MILK OF ITS MOTHER

vps In MILE: In New-sorn Doe:
{ J or Asu. % or Asa.
P20; 34.2 39.4
CaO 27.2 29.5
Cl 16.9 8.4
K,0 15.0 11.4
Naz,O : 8.8 10.6
MgO 1.5 1.8
r Fe,03 0.12 0.72

The quantities in the two columns are fairly similar. The
greatest proportional difference occurs in the case of tron, and
this fact requires a special explanation, which is briefly this,
that iron is more important for the rapidly growing embryonic
stages than for later life.

So likewise in the eggs of birds we find stored up all the
mineral matters which are necessary for their development.
Thus the yoke of the hen’s egg contains phosphoric acid, lime,
chlorine, potassa, soda, magnesia, iron oxide, and silica in the
relative abundance indicated in this descending series. ‘This
series closely agrees with that given for milk.

In the case of marine animals, also, certain inorganic elements
are a necessary food. The following list of such elements is
based upon the results of thorough experiments by HERBST
(97) upon developing eggs of sea-urchins, starfishes, hydroids,
ctenophores, and tunicates ; the most favorable proportions of
the elements were not, however, determined: calcium (in the
form of carbonate, sulphate, or chloride), chlorine, iron (trace),
magnesium, phosphorus (as Ca,P,O, or CaHPQO,), potassium,
sodium, and sulphur. Now all these elements are found in sea
water, which in the Mediterranean Sea near Naples contains in
1000 parts of water *

* After ForcHHAMMER (’61), p. 383.

304 EFFECT OF CHEMICAL AGENTS (Cu. XI

30.292 parts NaCl
3.240 “ MgCl,
2.638 “ MgSO,
1.605 “ CaSO,

OTTO 300 Aa
0.080 “ silicic acid, calcium phosphate, and insolu-
Total . 38.634 ble residue, including CaCO, and Fe,Qx.

From the foregoing tables it appears that mineral substances,
and essentially the same mineral substances, are required by
all organisms. ‘The differences in this respect between the
different organisms are slight. Thus while sodium is not
included among the necessary elements of either chlorophyl-
laceous plants or fungi, its occurrence in considerable quantity
in milk, probably associated with chlorine as common salt, indi-
cates that it is important for some animals.

The important conclusion seems warranted that all organisms
may use as hylogenic food any sort of compound which will
furnish the appropriate elements, but that among animals, and
to a less degree among fungi, organic combinations have the
preference because they fulfil at the same time the thermogenic
function.

b. Detailed Account of the Various Hlements used as Food. —
We may now consider the part which each element plays in the
growth of the body as a whole, reserving for the Fourth Part a

consideration of the specific réle which the element plays in ~

organs of the body. We may, in general, consider first the
share taken by the element in the constitution of the body, then
the form in which the element gains access to the body, and
finally what general effect it has upon the growth of the
organism.

Oxygen.— Excepting carbon, oxygen constitutes a greater
part of the body, by weight, than any other element. Between
20% and 25% of the dry substance of the human body and
between 85% and 45% of that of green plants is oxygen.
The oxygen used as hylogenic food comes to land-animals
from the organic compounds and the air consumed by the
developing young; the oxygen of water-animals may come
from their food or from the oxygen dissolved in water ; finally,

a

TP kale ia ar aie

§ 1) UPON THE RATE OF GROWTH 305

that of phanerogams is believed to be gained chiefly from the
air at all parts of the body, roots as well as stems and leaves.

Since oxygen is of great importance for metabolism (p. 2),
it is naturally essential to growth. It is well known that the
lower the oxygen tension is, the more slowly do seeds germinate
and pass through their early stages of growth: Thus in an
experiment performed by BERT (’78, pp. 848-853) barley grains
which germinated and were reared at various pressures had
in six days the following dry weights : —

ATMOSPHERIC PRESSURE. RESULTING WEIGHT.
76 cm. mercury (normal atmosphere) 8.8 mg.
50 Bf (0.66 $e ) ye
25 9 (0.33 se ) 6.2
7 ri (0.1 iy ) No growth

On the contrary, as the oxygen pressure increases up to about
twice the normal, growth is accelerated, but beyond that point
growth is retarded until at about 7 atmospheres growth hardly
occurs.

In older seedlings, observations upon which have been made
by WIELER (83), JENTYS (788), and JACCARD (93), atmos-
pheric pressure below the normal, even down to one-fourth or
one-eighth of the normal, appears to induce accelerated growth ;
likewise in pure oxygen at the atmospheric pressure growth is
as rapid as or somewhat more rapid than in the ordinary at-
mosphere. When, however, the oxygen tension is above the
atmospheric pressure or below one-eighth of the normal, growth
is retarded. It thus appears that an abnormal oxygen pressure
may accelerate growth, and as we shall see later, the same effect
is produced by other abnormal conditions.

Among animals, also, the oxygen tension exerts an important
effect upon growth. This is shown by the experiments of
RAUBER (784, pp. 57-65) upon the eggs of the frog.

To get a variable atmospheric pressure RAUBER used champagne flasks
in which were put the eggs and a little water. Through the air-tight cork
of the inverted flask one end of a U-shaped glass tube of proper length and
strength was passed. To the other end was fixed a funnel through which

x

506 EFFECT OF CHEMICAL AGENTS [Cu. XI )

mercury could be poured into the tube. The column of mercury produced
the increased pressure in the flask, and the difference in height of the
mercury in the two arms of the tube was a measure of this pressure. To
get a pressure below the normal a partial vacuum was produced by a water-
pump and the flask was then sealed. We assume (with Brrr, ’78, p. 1153)
that the chief effect of the variation in the atmospheric pressure was the
variation in the amount of oxygen absorbed by the water. Pure oxygen
was also used in the flask. .

At a pressure of three atmospheres no growth occurred. At
a pressure of two atmospheres growth was slower than at the
normal pressure. At three-fourths of an atmosphere also
growth was retarded and at one-half. an atmosphere death
generally occurred. ‘Thus the optimum condition of oxygen
tension is near the normal for the atmosphere.

The same thing is indicated in a qualitative way by the
experiments of Lozs (92). The stems of the hydroid Tubu-
laria possess in ordinary water a high regenerative capacity,
but in water deprived of oxygen by boiling no regeneration
takes place, although, after the water has been aerated again by
shaking, rapid growth occurs.

Hydrogen.—This element forms, in its various compounds,
between 5% and 10%, by weight, of the dry substance of
organisms. How is it acquired? In the case of plants it is
believed that it is taken into the organism as a constituent of
water, which combines with carbon or carbonic acid in the plant,
forming either starch directly or some other compound from
which starch is later derived. Other possible sources of
hydrogen are ammonia and its compounds, also the organic
compounds absorbed. The hydrogen of fungi and animals has
clearly been derived from the latter compounds alone. The
effect of hydrogen gas upon growth seems to be merely that
due to the replacement of oxygen; it has no active effect.

Carbon is the largest constituent of dry organic matter, of
which it forms between about 44% and 60%. In green plants
it is obtained for the most part from the carbon dioxide or
carbonic acid of the air which is absorbed by the leaves. Other
sources of carbon for green plants are found in many organic
compounds, such as urea, uric acid, hippuric acid, glycocoll,
kreatin, guanin, asparagin, lucin, tyrosin, and acetamid. ‘These
afford nitrogen also. Certain green plants make use of animal

Se a -
ae

§ 1) UPON THE RATE OF GROWTH 307

matter, e.g. insects, as food. Fungi and animals obtain their
carbon from carbon compounds elaborated by plants. The
indispensableness of carbon for the life of all organisms as well
as for their growth requires no illustration.

Nitrogen. — Of the importance of nitrogen as a hylogenic
food nothing more need be said than that it is essential to the
formation of albumen. ‘The ordinary form in which nitrogen is

Ny
tL y

\

Wie AY ay

i>
Sits
fe

Fic. 85.— Cultures of Sinapis alba in pure quartz sand, to which have been added
equal amounts of a nutritive solution, but unequal quantities of nitrogen in the
form of calcic nitrate, as follows: A, without nitrogen: B, 0.1 gramme calcic
nitrate in each vessel; (’, 0.6 gramme calcic nitrate in each vessel. After a photo-
graph. From FRANK (’92).

obtained by the seedling is, as already stated (p. 298), that of

the nitrates or ammonia in the soil (Fig. 85). Growing fungi

gain it chiefly from nitrogenous organic compounds, but many
fungi can make use of ammonium nitrate for this purpose.
Growing animals gain nitrogen chiefly, if not exclusively, from
organic compounds, especially albumen and allied substances.
Free nitrogen is found wide-spread in nature. It forms
about 79% of the volume of the air; penetrates into water,
though in a smaller proportion than in the air, and even into
the soil. Thus for organisms living in any of these media free

308 EFFECT OF CHEMICAL AGENTS [Cu. XI

nitrogen is a possible food. Is it actually made use of ? This
question has until recently usually been answered in the nega-
tive, and this conclusion was the more readily accepted since
nitrogen is a notoriously inert gas.

Another view, however, has within recent years come to
obtain. It developed in this wise. It had long been known
that land which has lain fallow or on which clover or other
leguminous crops have been reared is in a way strengthened as
if fertilized, and it was also known that this strengthening is
due to the fact that the soil acquires nitrogen from the air
and “ fixes” it in the form of nitrates. While the studies of
PASTEUR on fermentation, since 1862, had paved the way for
the interpretation of the process, the fact that it is due to organ-
isms was first proved by ScHLOsine and Muntz (77, ’79).
This proof they made by chloroforming a certain mass of nitri-
fying earth and finding that the nitrifying process thereupon
ceased. Later, they isolated a form of bacteria which had
the nitrifying property. Their results were quickly confirmed
and extended by others, notably BERTHELOT (85, ’92, etc. ), in
a long series of investigations, so that there is now no question
that the nitrification of the earth is brought about by the
activity of bacteria, perhaps of several species.

The results thus gained were extended to some of the higher
fungi by FRANK (92, p. 596).

Spores of Penicillium cladosporioides were sown in a nutritive solution of
pure grape sugar and mineral salts, completely free of nitrogen, and in the
presence of air which had been freed from ammonia by passing through
sulphuric acid. The fungi grew, but not so rapidly as those in a solution
containing nitrogenous compounds, and produced a mass of hyphe. These
hyphe, when tested, yielded ammonia. One such culture solution of 65 ce.
volume became filled with the fungus mass in ten months and yielded 0.0035
gramme of nitrogen, which must have been derived from the air.

As similar results have been gained for other molds by
BERTHELOT (’93) and for Aspergillus and Penicillium glau-
cum by PuRIEWITSCH (95), we seem almost justified in pre-
dicting that the capacity for assimilating free, atmospheric
nitrogen will prove to be a characteristic of all fungi.

Now if it is conceded that some organisms can make use of
the nitrogen of the air, it is clear that the a priori objection to

_ ee ee
le Ne nt oe or =

%

OA ae ee

es ee ee ee ee ee ee ee eae
|

§ 1) UPON THE RATE OF GROWTH 309

all organisms doing so, the objection, that is, on the ground of
the inertness of nitrogen, is disposed of. The question is now
merely one of fact. Do the alge, the higher plants, and the
animals make nitrogenous compounds out of free atmospheric
nitrogen?

Of these groups, the alge first claim our attention because
of the inherent probability that they will act more like bacteria
than any other group, since they pass over into the bacteria
through such connecting forms as the Oscillarize and Nostocs.
SCHLOSING and LAURENT (’92), FRANK (93), KocH and
KossowitTscH (’93), experimented with various species of Nos-
toc, Oscillaria, Lyngbya, Tetraspora, Protococcus, Pleurococ-
cus, Cystococcus, Ulothrix, etc., and found that, when supplied
with a non-nitrogenous food, these plants produced nitrogenous
compounds in the substratum, evidently gaining their nitrogen
from the previously purified air.

Doubt exists, however, as to whether the free nitrogen is
taken in directly by the alge or only after having been assimi-
lated by bacteria associated with the alge and by them made
into nitrogenous compounds. For the latter alternative speak
the experiments of KossowirscH (’94) and Mo.uiscuH (795).
KossowitscH, who with Kocu had previously found that alge
gain nitrogen from the air when reared in impure cultures,
now took special pains to get algal cultures free from bacteria.
To this end he reared alge on potassium silicate permeated by
a nutritive solution. The pure cultures thus gained were then
grown in a sterilized flask to which air, freed from ammonia,
was admitted. The nutritive solution was made of salts free
from nitrogen but containing the other essential elements.
The results of this experiment were striking. The pure cult-
ures of alge grew for a time, but then ceased. New non-
nitrogenous food did not revive them, but the addition of
nitrates caused rapid growth.

Other evidence was gained from analyses. When the cult-
ures of alge were pure there was no increase in the amount of
nitrogen in the dry matter of the alge. But when bacteria
were mingled with the alge, the quantity of nitrogen was
increased. This is shown in the following typical analy-
sis : —

310 EFFECT OF CHEMICAL AGENTS [Cu. XI

MILLIGRAMMES OF N IN CULTURE,

CONTENTS OF CULTURE.

AT THE BEGINNING. AT THE END,
Cystococcus, pure culture 2.6 2.7
, . ¢ no sugar . 2.6 3.1
Cystococcus, with bacteri 4
y ; aoe) with sugar 2.6 8.1

These results, abundantly confirmed by Mo.uiIscH (’95), seem
to show that unless bacteria are present algze can build up free
N into nitrogenous compounds only slowly, if at all.*

While ScCHLOSING and MUntz, BERTHELOT, and others were
gaining an explanation of the enrichment of fallow ground,
HELLRIEGEL (°86) and WILFARTH were making their investi-
gations upon the cause of the enriching action of leguminous
crops, which led them to the conclusion that it was due to the
fixation of nitrogen in plants with root-nodosities containing
bacteria, the compounds thus formed by the symbiotic bacteria
being directly assimilated by the plant. This conclusion has
been repeatedly sustained for leguminous plants (Fig. 86).

The question whether green phanerogamous plants other
than legumes can make use of free atmospheric nitrogen is one
which is still in hot debate, and it is not an easy one to answer.
The calm conviction, based chiefly upon the excellent work of
BoUSSINGAULT (760), and LAWES, GILBERT, and PuecH (61),
that nitrogen is not thus obtained was rudely shaken by the
paper of FRANK (93) in which that author stated that he finds
that nitrogen is removed from the air by non-leguminous
plants— plants, moreover, which are not known to have
bacteria living in their roots. Consequently he is of opinion
that perhaps the fixation of free nitrogen may be carried
on by any living plant cell.

The difficulties in the solution of the problem may thus be
set forth. It is recognized that all growing plants make use

* One ‘crucial test’? of Franx still requires an explanation. If the free
nitrogen is ‘‘ fixed” by the aid of bacteria, the process should go on in the dark.
Experiment shows that it does not do so. This difficulty Kossowirscn over-
comes by the assumption that the activities of the bacteria are dependent upon
certain carbohydrates which the plant can afford them only in the light.

, EE

— ee ee ~~

§ 1) UPON THE RATE OF GROWTH 311

of nitrogen, but the nitrogen is usually obtained from the soil
in the form of nitrates. It is feasible to determine by analysis
the amount of nitrogen in the soil at the beginning of the ex-
periment and the amount in the seed planted, and then after
the experiment to determine the quantity in the soil and in
the plant. But the difficulty comes in interpreting the results

Fic. 86. — Parallel cultures of peas in the symbiotic and the non-symbiotic conditions.
Each series comprises three culture vessels: B, the symbiotic plants in soil with-
out nitrogen; C, the non-symbiotic plants in like soil; A, for comparison, non-
symbiotic plants after addition of nitrate tothe soil. Aftera photograph. (From
FRANK, ’92.)

of the analyses. Thus the fact that the sum of nitrogen in the
plant and the soil is greater at the end than at the beginning
of the experiment does not prove that the plant has taken in
free nitrogen ; for, as we have seen, the soil contains nitrifying
bacteria, which intermediate between the free nitrogen of the
air and the nitrates absorbed by the green plants. This diffi-

312 EFFECT OF CHEMICAL AGENTS (Cu. XI

culty may be partly met by sterilizing the soil, but this prob-
ably produces also other changes than the death of the bacteria.

The most careful observations of the last five years have not
supported FRANK’s generalization. Here and there there
have been observers who, like LIEBSCHER (’92) and STOKLASA
(96), believe they have evidence for the direct assimilation of
free nitrogen by the cells of phanerogams. But the evidence
for the contrary opinion is predominant.

The experiments which speak for the theory that green
plants cannot directly make use of free nitrogen are not in
unison. Thus, some indicate that in non-leguminous as well
as leguminous plants nitrogen of the air is indirectly made use
of through the action of the bacteria of the soil, while accord-

ing to others it would seem not to be made use of at all. To

the first class belong the experiments of PETERMANN (91, ’92,
and ’93) with barley, of Nospspe and HiILttNerR (795) with
mustard, oats, and buckwheat, and of PFEIFFER and FRANKE
(96) with mustard. ‘To the second class belong the experi-
ments of ScHLOsING and LAURENT (792 and 792) with
various plants, DAy (’94) with barley, and AEBy (96) with
mustard. In the second class, however, the experimental con-
ditions did not favor the development of the bacteria of the
soil. The experiments of PETERMANN were, however, carried
out upon a very large scale and under practically normal con-
ditions and showed a marked difference between the acquisi-
tion of nitrogen by barley growing in an unsterilized soil and
in a sterilized one. Likewise NoBBE and HILTNER, and
PFEIFFER and FRANKE, were careful to rear plants under
normal conditions, so that their results are worthy of especial
consideration. They agree that there is an acquisition of
nitrogen by the plant growing in normal soil and that this
occurs only when the soil is unsterilized. We conclude then
that probably phanerogams, like alge, can use the free nitro-
gen of the air as food only after it has been converted into
nitrates by the action of the nitrifying organisms —the bac-
teria of the soil.

Turning now to animals, whose nutrition is often compared
with that of fungi, we find an absence of knowledge on the
subject of the nutritiveness of free nitrogen. It is clear that

§ 1) UPON THE RATE OF GROWTH 313

land animals are in a favorable position for making use of it,
since it penetrates with the oxygen to all parts of the body..
It is found in the blood of mammals, but still as free nitrogen.
Whether it eventually becomes fixed in the body is entirely
unknown. The a priori argument against such fixation — the
argument of inertness— has lost much of its force since the
discovery of the nitrifying organisms.

Phosphorus. —This element is of constant occurrence in
organisms. It has been found in yeast, mucors of the most
diverse kinds, seeds, plant tissues, and animal tissues of all
kinds. It is indeed one of the first among the mineral ele-
ments of most organisms, as shown on pages 296 and 297. Of
the dry substance of a fish, about 7% is phosphoric acid, and
the dry substance of many seeds yields 15%. Phosphorus
occurs in organisms as phosphoric acid compounds. Of these
the most important organic compounds are nuclein, which has
albuminoid properties, and occurs chiefly in all nuclei and in
deutoplasm; lecithin, of a fatty nature, occurring in yeast,
plasmodium of Aithalium, seeds, milk, yolk of eggs, and
nervous tissue; and glycerin-phosphoric acid, a product of
decomposition of lecithin and found wherever the latter occurs.
As examples of inorganic salts we have the sodium and potas-
sium phosphates of the blood and tissues and the calcium phos-
phate deposited in bone.

So important an element as phosphorus would naturally form
an essential part of the food of all growing organisms. It is
supplied at first in the germ,—seed or egg,— but later must
come from without. Plants gain phosphorus from the disinte-
grating rocks. Animals derive it chiefly from plants, directly
or indirectly, or from the calcic phosphate of the sea; in mam-
mals it is supplied to the developing young through the milk,
which, as we have seen on page 303, is rich in phosphates.

The abundance of phosphorus in the body indicates that its
office in the organism is an important one, and its peculiar
abundance in seeds, yolk, and milk indicates that it is especially
important in growth. Experiments have been directed towards
this point. The fact has long been established that plant
growth cannot occur in the absence of phosphates, and this is
true not only for green plants, but also for molds and yeast

314 EFFECT OF CHEMICAL AGENTS (Cu. XI

(RAULIN, 69). Embryos of various marine animals also will
not develop in the absence of phosphorus (HERBsT, 97). The
peculiar importance of phosphorus for growth is also indicated
by the fact that HArtIa and WEBER (’88) found more phos-
phoric acid in the ash of the growing ends of the plant than in
its fully differentiated parts. Again, Lozw (91*) found that
Spirogyra kept in a nutritive solution of salts in which phos-
phorus alone was lacking, continued to live and, indeed, to
form starch and albumen, but its cells did not grow or divide ;
so that LoEw concludes that an important use of phosphorus
is to nourish the cell-nucleus, and this fact is easily understood
from the known importance of the phosphorus-containing
nuclein of chromatin in cell-division. All these facts go to

show that phosphorus is of prime importance in the growth of —

organisms.

Arsenic, Antimony, Boron, and Bismuth, and their compounds,
are apparently all injurious to organisms, so that sublethal
solutions strong enough to be active, interfere with or even
inhibit growth.

Sulphur. — This element is, without doubt, of constant oc-
currence in organisms of all sorts, for it constitutes between
0.3% and 2% of all proteids, out of which organic bodies are
largely composed. Sulphur forms between 0.6% and 1% of
various (dry) organs of man, and nearly 1% of the dry sub-
stance of a month-old seedling of Sinapis alba.

In the growth of a plant (Sinapis alba) the amount of its
sulphur increases from 0.02 mg. in the seed to 84.4 mg. in the
adult plant, and, indeed, it has been shown in one case
(ARENDT, 59, for the oat plant) that the percentage of sul-
phuric acid in the ash increases from 2.9 to 4.2 as the plant
develops from a seedling to maturity. Since the sulphur goes
chiefly into the composition of the living substance, its hylo-
genic importance for growth is evident.

The form in which sulphur may be taken into the body is
very varied. It is well known that green plants usually
absorb it in the form of sulphates, especially sulphates of
potassium, calcium, and magnesium; marine animals take it
chiefly from the calcic sulphate of sea water, and land animals
gain it largely from organic sulphur compounds produced in

————EE—

SEE ee ee

§ 1) UPON THE RATE OF GROWTH 315

plants. Whether non-chlorophyllaceous plants can make use
of it has been much discussed, and is worthy of further inves-
tigation. WINOGRADSKY (’88, ’89) has, indeed, shown that
the sulpho-bacteria store up pure sulphur from sulphuretted
hydrogen (H,S), and Prescu (’90) has concluded, as a result
of feeding himself with pure sulphur and analyzing the sulphur
of the urine, that about one-fourth of the sulphur taken into
the body in an elementary form becomes built up into organic
molecules. Recently HEersst (97) has shown that embryos

f

Py
ke
‘op
;
aks

as)
SERS
ape SS

_

sD RSC ANE AT
5 &, (ga

Fic. 87.— Right, Larva of Echinus reared for 72 hours in water containing all the
necessary salts; the sulphur being in the form of 0.26% magnesium sulphate and
0.1% ealecic sulphate, and the phosphate in the form of CaHPO,. The larva is
normal. Left, Larva reared for 68 hours in a solution containing no sulphur nor
CaCl,. The typical larva without sulphur, but with CaCl, differs from this chiefly
in the presence of rudimentary spicules; kr, spicule-forming cells. (From HERBST,
97.)

of sea-urchins and other marine animals do not develop in the

absence of sulphur (Fig. 87). These facts indicate that not

green plants merely, but all organisms, can use elementary
sulphur as a hylogenic food.
The Halogens, chlorine, bromine, iodine, and fluorine, are

elements which are closely similar in their chemical reactions

316 EFFECT OF CHEMICAL AGENTS [Cu. XI

outside of organisms, and carry a part of that peculiarity with
them into organisms. All of them are of physiological interest ;
but so far as we know chlorine and iodine are most important.

Chlorine. — This element is probably of constant occurrence
in organisms, and indeed in rather large quantities, as Table
XXVII, p. 297, shows. It is not strange that it should be so,
since this element is very widely distributed in alli waters.
This very fact, however, renders it possible that chlorine is
merely an accidental constituent of organisms, being unessential
to growth, and precisely this conclusion has been maintained.

Of green plants it was early asserted that growth occurs as
readily in solutions containing no chlorine as in ordinary
potable water, but of late years evidence opposed to this view
has been accumulating. Thus, while it appears that growth
may occur in the absence of chlorine, AscHorr (90) and
others have found that growth is not so vigorous as in solutions
containing this element. It has been thought that chlorine
makes an advantageous combination with the potassium neces-
sary for the plant, but the true significance of the favorable
properties of chlorine remains undetermined.

Turning to animals, we find that chlorine occurs in the milk
of mammals, and is therefore probably necessary to them.
According to HERBST (’97, p. 709) it is a necessary food for
young echinoids. Certainly in the form of sodium chloride
it is an essential food of the higher animals, and some of them,
especially the herbivora, require large quantities of it, as “ salt-
licks” testify. The function of chlorine is not altogether
plain. It must be used in the production of the hydrochloric
acid of the digestive juices. In addition, sodium chloride is
found widely distributed in the tissues. It has often been
asserted that it goes through the tissues unchanged; but
NENCKI and ScHOUMOW-SIMANOWSKY (794) believe that it is
probably disintegrated and the chlorine built up into organic
molecules.

Bromine. — The normal occurrence of traces of this element
has lately been demonstrated by Hotrer (90) for a great
variety of plants. It occurs most abundantly in various
fruits, apple, pear, peach, and also in the leaves and twigs of
many plants, as well as in various berries. Its normal occur-

a

ee

$1] UPON THE RATE OF GROWTH 317

rence permits us to believe that it has an importance, if not for
growth, at least for development; there is, however, no direct
evidence that it is generally necessary to organisms. Since it
is closely allied to chlorine, the question whether it may replace
chlorine in growth has been tested. NENCKI and SCHOUMOW-
SmMANOWSKY (’94) have found that in the higher animals
the bromides can replace the chlorides to a limited extent, but
are clearly less advantageous. Altogether the importance of
bromine for growth is slight.

Iodine. — This element is of wide-spread occurrence in organ-
isms, probably as a constituent of organic molecules, for it is
found in plants, especially in some species of Fucus and Lami-
naria (cf. ESCHLE, ’97); in invertebrates, especially in sponges
and the stem of Gorgonia; and in vertebrates, especially in
mammals, where it has recently been shown to be most im-
portant for growth. It has long been known that mammals
which have been deprived of the thyroid gland acquire a weak
condition of body known as myxceedema. ‘This effect has been
accounted for by the loss, to the organism, of a substance
elaborated in the thyroid gland; for when the thyroid gland,
or a docoction of it, is fed to the animal it recovers to a certain
extent its normal condition. The nature of this substance has
been investigated by BAUMANN and Roos (96), who find that
it is a compound of iodine —thyroiodine; for when thyro-
iodine is fed to the myxedema patient, the same favorable
result ensues as follows feeding upon the gland.

Fluorine is found rather widely distributed among verte-
brates in very minute quantities. It forms about 1.3% of the
total ash of bone. It is present also in the hen’s egg, being
more abundant in the yolk than in the albumen (TAMMANN,
°88). Since it is chiefly found in the body as a constituent of
bone, possibly in the form of the mineral apatite, Ca,,F, (PO,),
it may very well be that its chief importance is in the consti-
tution of this formed substance. According to BRANDL and
TAPPEINER (792) the normal amount in the body may be
greatly increased by feeding small quantities of sodium fluoride
during a long period. Altogether, we have no reason for
thinking that fluorine is essential to the growth of organisms
in general.

318 EFFECT OF CHEMICAL AGENTS [Cu. XI

Salts of Alkalis.— This group contains one or two of the
most important elements of which organisms are composed.
The elements are only slightly replaceable by one another.

Lithium seems normally to have little importance for growth,
although slight traces of it have been found spectroscopically
in the blood (HoOPPE-SEYLER, ’81, p. 453).

Sodium is probably of constant occurrence in organisms.
The quantity of it in the body is widely different in different
species; and as our table on page 297 shows, it may vary in its
position from one of the most abundant of the elements to one
of the least. Whereas sodium is not essential to the nutrition
of plants, it is necessary in the form of sodium chloride to
certain higher animals. Sodium is also found in all the tissues
of the body, and perhaps enters into the albuminoid molecule
(NENCKI, 94). The fact that, as we have seen on page 303,
soda is a prominent constituent of milk, indicates its impor-
tance in the growth of mammals. Finally, HeERBstT (797) has
been able to demonstrate its indispensability for the growth of
marine animals.

Potassium constitutes an important part of all organisms.
It forms the largest part of the ash of nearly all phanerogams
(see page 297) and is markedly abundant in yeast and in many
invertebrates. It occurs in the body as chloride and as sul-
phate, and probably also in combination with albumen and
various organic acids (VINES, p. 134).

That it is an essential and unreplaceable food for all organ-
isms is indicated by trustworthy experiments upon fungi, alge,
phanerogams, invertebrates, and vertebrates. RAULIN (769)
first showed that only culture-solutions containing this metal
permit the growth of fungi.

The experiments of BENECKE (796) upon the growth of
certain molds, e.g. Aspergillus, are worth citing in detail as an
illustration of the method.

He sowed spores in culture-vessels made of a glass which analysis had
shown to be free from potassium. Two of these vessels contained a nutri-
tive aqueous solution consisting of 3% cane sugar and 0.25% magnesium
sulphate. To the one of these solutions was added 1.2% potassium nitrate,
and 0.26% potassium phosphate; and to the other 1% sodium nitrate and

0.5% sodium phosphate. After four days the first culture was covered by a
sheet of fungi and in five weeks the whole surface was black with spores; in

§ 1) UPON THE RATE OF GROWTH 319

the second culture, on the other hand, little growth had occurred even at
the end of five weeks. The crop from each of the cultures was then
harvested and its dry weight determined. That of the first culture was
0.3 gramme, that of the second 0.03 gramme.

By a somewhat similar procedure MoLiscH (95) has been
able to show that potassium is essential to the growth of alge ;
and NoBBE and others (’71) that it is necessary for the growth
of phanerogams.

The experiments upon animals have been rather less satisfac-
tory on account of the greater difficulties in experimentation.

ANY

SAN . be
\)

Z
a
veal
is =
a,
=
a

|
ay AL

Fie. 88. — Two embryos of Spherechinus from parallel cultures. a, reared in a solu-
tion containing all the necessary salts; embryo normal. 06, reared in the same
solution, but without potassium; blastula wall abnormally dense, and embryo of
small size. (From HErsst, ’97.)

Nevertheless we have some trustworthy data upon this matter.
On the side of the invertebrates. we have the experiments of
LorB (92), who placed a hydroid, Tubularia, in fresh water
to which solutions of various combinations of the salts found
in sea water were added so as to give approximately the nor-
mal osmotic effect. Under these circumstances regeneration
of the hydroids occurred only in the solutions containing
potassium. Again, Herpst (97) finds potassium essential to
the growth of embryos of echinoids (Fig. 88). Thus the
potassium compounds seem necessary to the processes upon
which growth depends. On the side of vertebrates we have
the somewhat inconclusive results of KEMMERICH (’69), who
fed two young dogs of the same age and of nearly the same
size upon meat boiled until a large portion of its salts was
extracted. To the food of one dog he added only sodium chlo-

320 EFFECT OF CHEMICAL AGENTS [Cu. XT

ride; to that of the other, both sodium chloride and potassium
salts. After 26 days the dog fed on the potassium salts as well
as the sodium chloride was about 30% heavier than the other,
and this difference was reasonably ascribed to the beneficial
effects of the potassium.

The particular part which potassium takes in growth is still
somewhat doubtful. The recent observations of COPELAND
(97) with seedlings reared in water cultures in which sodium
replaces potassium, lead him to the conclusion that potassium
is necessary to turgescence. The potassium salts become
lodged in the eell-sap, as analysis shows, and are therefore,
perhaps, one of the principal causes of imbibition.

Rubidium and Cesium. — These rather rare metals are
important only because of the fact that they may replace
potassium in the growth of some fungi. WINOGRADSKY (84)
recognized this to be the case with rubidium in yeast cultures.
NAGELI (80) found that in molds rubidium and cesium gave
even greater growth of dry substance than potassium cultures,
a conclusion abundantly confirmed by the studies of BENECKE
(95). Whatever, therefore, is the significance of potassium
for growth, rubidium and cesium seem to have the same
significance.

Earthy Metals. — Under this head are included the elements
calcium, strontium, and barium, which form compounds having
closely similar molecular structure and properties. We might
therefore expect them to be in some degree mutually replace-
able. 3

Calcium shares with potassium and phosphorus the position
of one of the most abundant elements of organisms. It is found
in every tissue and seems to be a constant accompaniment of
protoplasm.

Its constant occurrence is indicative of its importance as
food for both plants and animals. It is apparently indispensa-
ble and unreplaceable by any other element in phanerogams ;
but MoniscH (794) finds that growth can take place in certain
molds (Penicillium, Aspergillus) as well in its absence as in
its presence, and in some algz, but not in all (Momiscu, ’95),
calcium is apparently of little importance. In animals, calcium
can be replaced by other elements only to a very slight extent.

jigd ne

, i,
Pen? 5
ce :

.§1) UPON THE RATE OF GROWTH 321

Its absence from the water in which echinoid larve are
developing produces dwarfs. In vertebrates, owing to the
need of this metal for the skeleton, large quantities of calcium
are taken in by the growing organism. In normal growth,
then, the food of animals and phanerogams must contain
calcium.

Strontium, although closely allied to calcium, is rather rarely
found in considerable amount in organisms. In certain plants,.
as e.g. Fucus, it is constantly present. It can be stored up in
the animal organism when supplied abundantly in the food, but

in general is believed to be of little importance for growth.

Manganese, likewise, is not of general importance, although.
it is found abundantly in certain plants, e.g. Trapa natans,
Quercus robur, and Castanea vesca, and in the excretory organ
of the molluse Pinna squamosa (KRUKENBERG, ’78).

Iron. — This most.abundant of the heavy metals occurs so
frequently in organic substances, especially those related to the
compounds found in protoplasm, that it is little wonder that
iron has been found to be an essential ingredient of all proto-
plasm, hardly less important than oxygen itself. Although its
occurrence has been demonstrated, especially by SCHNEIDER
(89), in all the large groups of animals, its amount in any
individual or organ is always very small. Iron oxide (Fe,O,)
forms between 1% and 2% of the ash of muscle, about 5% of
the ash of blood, and rarely rises to 5% in plants.

It is found in the body, for the most part, as in yolk
(BUNGE, ’85), in organic union. It occurs thus in the chro-
matin of the nucleus of all cells (MAcALLUM, 792, ’94;.
SCHNEIDER, 795).

That chromatin contains iron has been demonstrated by Macattum
(91) by means of a microchemical method whose general validity has never,,.
so far as I know, been questioned. It was shown by BunGgE, in 1885, that.
when tissue is put into ammonium sulphide the iron, even in an organic:
molecule, is separated from its compound, and uniting with the sulphur
forms ferrous sulphide (FeS). This ferrous sulphide appears in the proto-
plasm as green granules (black in large quantity); and the fact that these
granules appear abundantly in the nucleus shows that iron is especially
abundant there. Additional evidence is given if after several weeks the
chromatin loses its stained appearance and becomes rusty. This result is
interpreted as due to the formation of ferric oxide, Fe,O,; for when the

¥

322 EFFECT OF CHEMICAL AGENTS [Cu. XI

nuclei are subjected to hydrochloric acid and potassium ferricyanide they
immediately assume a deep azure-blue color, clearly due to the formation
of “Prussian blue” or Fe,(FeC,N,),. This series of reactions can only be
explained on the ground that there is iron in the nucleus.

Iron has shown itself to be essential to the growth of all
organisms. Its importance for growth is indicated by its rela-
tive abundance in the yolk of birds’ eggs, and by the fact of
its occurrence in larger proportion in a mammal just born than

he
vee
ASL
SEIT aD
& ~
= 2.

Fia. 89. — Echinus larve from parallel cultures, all 53 days old. a, reared in a solu-
tion containing all salts, including iron as FeCl; 6 and c¢, from solutions contain-
ing all salts excepting iron. (From HERBST, ’97.)

in later stages. When excluded from a nutritive solution
which is otherwise complete, growth is imperfect (Fig. 89).
This may be associated with the facts that in plants the chloro-
phyll granules are not developed in its absence, that in the
higher animals hemoglobin cannot be formed, and that the
chromatic substance of all cells requires it.

The question in what form iron is absorbed by the organism
has been the subject of an extensive discussion. Although
doses of metallic iron have long been used with favorable

ee eee

os

§ 1) UPON THE RATE OF GROWTH 323

results in medical practice, BUNGE (785) concluded that only
organic iron compounds are assimilable. The studies of
KUNKEL (791 and ’95) and WOLTERING (95) have, however,
shown in the clearest manner that inorganic iron is assimilated,
stored in the liver, and made use of in the construction of such
organic compounds as the hemoglobin of the blood. At the
same time, as SOCIN (91) and others have shown, iron may
be gained from organic compounds. Apparently, iron com-
pounds of any sort may be made use of by the organism.
Magnesium. —This metal is closely associated with calcium,
the two usually occurring together in organisms just as they
do in the inorganic world. As the table on page 297 shows,
magnesium is of constant occurrence among organisms, although
never present in great quantity. The magnesium is gained by
green plants at the same time with the calcium from mineral
salts (chiefly magnesium carbonate and sulphate) derived from

disintegrating rocks. Fungi can also make direct use of the

salts of magnesium (excepting always the chloride) ; and ani-
mals, although no doubt chiefly gaining their magnesium from
plants or the waters in which they live, may make use of min-
eral salts, especially in the construction of the mineral parts of
various formed substances, such as those of bone.

So constant an element is presumably necessary to the organ-
ism, and numerous observations make it quite certain that this
is true for green plants in general. Indeed, the fact that mag-
nesium occurs in chlorophyllan of chlorophyll makes it prob-
able that it functions in assimilation. Concerning its indis-
pensableness for fungi there can likewise be no doubt, since
BENECKE’S (95, p. 519) experiments show it to be replaceable
neither by calcium, barium, or strontium. While some investi-
gators, like HOPPE-SEYLER, believed it to have little signifi-
cance for the animal body,—to be an accidental accompaniment
of calcium, —later study has shown that it is of importance
for regeneration of hydroids (LoxEB, ’92), and, according to
HERBST (°97), a constituent of the sea water which is necessary
to the normal growth of various marine larve. Also its occur-
rence, although slight, in milk, as well as its very abundant
occurrence in seeds, indicate that it plays an important, if an
unknown, part in growth.

324 EFFECT OF CHEMICAL AGENTS (Cu. XI

Silicon. — This element is of wide occurrence among organ-
isms. In many plants, especially the grains and grasses, it is
exceeded in abundance only by potassium. Among the lower
organisms whole groups, e.g. diatoms, Radiolaria, and glass
sponges, are characterized by the great amount of silica made
use of. Even in vertebrates it is found wide-spread in the
blood, gall, bones, feathers, and hair. ‘The silicon required for
the body is gained by plants and lower organisms from the
soluble silicates or silicic acid of the soil and waters ; by verte-
brates, probably from plants.

Although Sacus (87, p. 271) was able in 1862 to show that
growth even of maize (about one-third of whose ash is silica)
continues in the absence of silicon, yet some grains do better,
according to Wourr (81), when that element is abundant.
It is significant, likewise, that, as Poteck (750) found, 7% of
the ash in the albumen of the hen’s egg is silicon.

Copper. — Brief mention may be made of the fact that this
metal occurs in a great variety of organisms, but usually in
minute quantity. It occurs as a physiologically important con-
stituent of the hemocyanine of the blood of the squid (FRED-
ERICQ, 78, p. 721), of crabs and lobsters, and of certain gas-
tropods and lamellibranchs (FREDERICQ, ’79).

2. The Organic Food used by Organisms in Growth. — All
organisms may use organic compounds as food; all organisms
which contain no chlorophyll, certain bacteria excepted, must
doso. This organic food may consist of solutions of definite
composition or it may consist of solid masses of plant and
animal tissue composed of varied and indeterminate kinds of
organic molecules. The former are made use of chiefly by
plants; the latter, by the higher animals. This distinction is,
however, not a necessary and constant one, for on the one hand
insectivorous plants and many fungi live upon solid masses
which they digest, and on the other hand some of the Protozoa
can be. fed upon known solutions, and doubtless some of the
higher animals could be likewise fed, although few experiments
seem to have been made in this direction. Even in methods
of nutrition there is no sharp line to be drawn between the
different groups of organisms.

a. Fungi. — Our knowledge of the effect of known chemi-

§ 1) UPON THE RATE OF GROWTH 325

cal compounds used as food has been much more advanced
by studies upon this group than upon any other. Yeast
and bacteria have been especially investigated, but valuable
results have been obtained upon the higher fungi also. Con-
sidering all these results together, it appears that the nutritive
value of an organic compound is perhaps chiefly determined by
its assimilability; that is, the less the energy required to attack
and transform the compound by the various chemical means at
hand, the more favorable it is as a food. This assimilability
depends in turn upon the molecular structure — upon a certain
molecular instability or lability — upon the possession of that
quality which is found in its extreme expression in many
organic poisons. As Lorw (91, p. 761) has expressed it:.
Poison action, like nutritive action, is a relative conception.
An indifferent body can become, by entrance of one atom-group,
a nutritive substance; by entrance of an additional atom
group, a poison. While a certain lability—that is, a certain
degree of ease of decomposition— is a condition of the nutritive
quality of a substance, a slight increase of this lability can
give it a poisonous character, especially when the loosely
arranged atoms can link into that atom-grouping upon which
the vital movement in the protoplasm depends. Thus methan
is indifferent for bacteria, methylalcohol is a nutritive sub-
stance, formaldehyd is a poison, and its combination with sodic
sulphate again a nutritive material.*

Additional laws of nutritive value which hold true in many
cases are as follows: The assimilable carbon compounds con-
tain the group CH, or at least CH. Under otherwise similar
conditions, compounds with one carbon atom are assimilated
with great difficulty (methylamin) or not at all (formic acid,
chloral); and, in general, but with important. exceptions in the
case of certain classes of substances, the assimilability increases
as the number of carbon atoms in the molecule increases. The

* The graphic formulas of these substances are : —

OH OH

4 rs

CH, CH;-OH CH, san
Nox SO3Na.

methan, methylalcohol. formaldehyd. formaldehyd-sodic sulphate.

326 EFFECT OF CHEMICAL AGENTS [Cu. XI

radical HO- is usually easily released, consequently we find |

compounds containing this radical in general more assimilable

than allied. compounds in which the HO- is replaced by H. ~

Especially is this true when the HO- is joined with radicals
containing carbon and hydrogen atoms. For example, foods
with the radical -CH,-OH are more nutritive than those with
-CH,. Hydroxylized acids are better food for bacteria than
non-hydroxylized — lactic acid, C,;H,Os3, is better than pro-
pionic acid, C,H,O,. It is, perhaps, a special case under this
rule that multivalent alcohols —?.e. those containing several
HO groups—are better foods than the univalent ones; for
instance, glycerine, CH,OH-CHOH-CH,OHU, is better than
propylalcohol, CH,-CH,-CH,OH. Finally, the entrance of
the extremely unstable aldehyd (-CH:O) and keton (-CO-)
groups increases the nutritive capacity of the food; for
example, glucose, -CH,OH - (CH -OH),CHO, or fructose,
CH,OH - (CH -OH), -CO-CH,OH, is better than mannit,
CH,OH.(CH-OH),-CH,OH. But all substances containing
the group CHOH are good foods, since this compound can be
used directly in the construction of carbohydrates, and eventu-
ally of albumen.

As an example of the application of these general principles
may be given this series of substances arranged in the order of
their decreasing nutritive value for yeast and molds (NAGELI
and LorEw, ’80): 1, sugars; 2, mannit, glycerine, the carbon
groups in leucin; 3, tartaric acid, citric acid, succinic acid, the
carbon groups in asparagin; 4, acetic acid, ethylalcohol, kinic
acid; 5, benzoic acid, salicylic acid, the carbon groups in pro-
pylamine; 6, the carbon groups in methylamin, phenol.

In conclusion may be mentioned a food for bacteria which,
although inorganic, resembles organic compounds in that it
may serve as a source of energy. ‘This is the hydrogen disul-
phide employed by the sulphur bacteria and allied forms
(WINOGRADSKY, ’87, ’89).

b. Green Plants. —It has already been shown that organic
compounds can be assimilated by green plants. The experi-
ments which have shown this have been made upon both alge
and phanerogams, especially by Bokorny, Loew, A. MEYER,
and LAURENT. It appears that, in the absence of carbon

—— a

—<. 7

Z

§ 1) UPON THE RATE OF GROWTH 327

dioxide, Spirogyra may form starch from methylalcohol, -for-
maldehyd, glycol, methylal, acetylethylesteracetat, acetic acid,
lactic acid, butyric acid, succinic acid, phenol, asparaginic acid,
citric acid, acid calcium tartrate, ammonium tartrate, calcium
bimalate, glycocoll, tyrosin, leucin, urea, hydantoin, kreatin,
and peptones.* Phanerogams form starch from glycerine, cane
sugar, levulose, dextrose, lactose, maltose, mannit, dulcit, and

lecithin. While daylight favors assimilation it can be in some

cases dispensed with. Thus the potato plant can accumulate
starch in the dark when glycerine is used as food.

An attempt to gain a deeper insight into the conditions of
formation of albumen from organic matter has been made by
HANSTEEN (796), who reared Lemna in solutions of grape sugar
or cane sugar, on the one hand, and amids, like asparagin, urea,
glycocoll, leucin, alanin, or kreatin, on the other; also on grape
sugar and inorganic nitrogenous bodies such as potassium
nitrate, sodium nitrate, ammonium sulphide, and ammonium
sulphate. Asa result of feeding on grape sugar alone at 20°C.
during 24 hours, much starch was stored in the cells; when
grape sugar and inorganic nitrogenous bodies were combined
little starch and much albumen were produced. Much albumen
was also gained when the nutritive solution contained cane
sugar and urea, or asparagin and ammonium chloride, or
asparagin and ammonium sulphate. The production of albu-
men in green plants is favored by nitrogenous organic com-
pounds.

e. Animals. —These organisms are distinguished from the
foregoing by an immense requirement of energy for their
muscular processes, much of which is continually lost to the
organism in the form of motion communicated to the environ-
ment. On the other hand, growth is generally slower than in
plants. Consequently in animal nutrition thermogenic foods
are the more important and the nutritive processes are prevail-
ingly exothermic. The plastic processes are the less striking ;
nevertheless, it is they which chiefly concern us in our study
of growth.

Among the organic compounds ingested, carbohydrates are

* The reagents were employed in about 0.1% solution, and whenever acid were
neutralized with lime-water.

328 EFFECT OF CHEMICAL AGENTS [Cu. XI

believed to have little importance as plastic foods —we have
chiefly to consider the use of the complex fats, albuminoids, and
other organic compounds. We can make little use of the
extensive tables of calorific properties of foods which, however
important for determining capacity for supplying energy,
afford little insight into the plastic properties of the food —
its importance for the growth of dry substance or the imbi-
bition of water.

The difficulties in the way of feeding animals upon known
nutritive solutions are great, both because solutions are not
their normal food, and because, in the case of water organisms,
the bacteria introduced with the animals thrive better than
they. Consequently the observations on nutritive compounds
for animals are meagre. It will be best to consider them
under the types upon which they have been made.

Ameba. — We owe important studies on the foods of Ameeba
to the fact that some species have a pathogenic importance.

Cultures of them have therefore been made by bacterio-
logical methods. It is found that various, even innocuous

kinds, will grow upon egg albumen in distilled or phenylated
water kept at about 15° C. (CrIvELLI et Mager, ’70, ’71;
Montl, ’95), upon agar-agar sheets from which the soluble
substances have been removed by repeated washing in distilled
water (BEYERINCK, ’96), upon “ Fucus [Chondrus?] crispus”
(CELLI, *96), or upon slices of potato (GORINI, ’96). ‘It is
thus clear that, in addition to salts, Amceba needs only a very
simple nitrogenous diet. It is, however, uncertain whether
the amceba feeds directly from the organic food stuff, or indi-
rectly upon the bacteria which grow
upon the food supplied.

Infusoria.— A beginning has been
made in the study of this group by
Fic. 90.— Polytoma uvella, OGATA (93), who reared pure cultures

a flagellate infusorian. of the flagellate Polytoma uvella (Fig.

hk) (natch i 90) on plates of nutrient gelatine
(which is extremely rich in protein) and also upon a medium
composed of 500 ccm. meat bouillon, 12.5 grammes grape
sugar, and 250 grammes of a Japanese mixture of alge called
“yori,” derived mostly from the species Porphyra vulgaris.

ee

ee ee

§ 1] UPON THE RATE OF GROWTH 329

The mixture was cooked, neutralized, filtered, sterilized, and
infected with the flagellates, which had been isolated by means
of capillary tubes. Here again growth was supported by
simple, definite foods.

Amphibia. — It is a great leap from Protozoa to vertebrates,
but precise feeding experiments are almost lacking in the
invertebrate Metazoa. In the present group come the pioneer
experiments of Yune (783). This author fed a number of

_ tadpoles derived from the same batch of eggs upon: foods of

various kinds in unlimited quantity and under otherwise
similar conditions. After forty-two days the size of the tad-
poles in each lot was measured and the following results were
obtained : — |

TABLE XXXII

Resvutts oF FeepInG TADPOLES ON VARIOUS SUBSTANCES

No. or VESSEL. 1 2 3 4 5 6
f ae sees ALBUMINOUS
PLANTS: PIECES OF ALBUMEN PIEcES PIECES
KInpDs OF Ege ENVE-
1 ANACHARIS YOLK OF or HEN’s or FIsH or BEEF
Foop LOPE OF ;
| AND Wenn Hen’s Eee, Eee, FLESH. FLEsuH.
\| Sprroeyra. 5
Length of
tadpole 18.3 23,2 26.0 33.0 38.0 43.5
Breadth of
tadpole 4.2 5.0 5.8 6.6 8.8 9.2

It will be observed that the importance for growth was not
proportional to the calorific properties of the respective foods,
for the yolk of the hen’s egg has about 40% higher fuel value
than dry egg albumen or dry flesh. The least growth occurred
with a plant food which is relatively rich in carbohydrates, and
has some protein and little fat; the third greatest growth

occurred with the yolk, which has more fat than protein ; next

comes egg albumen, with more protein than fat; and, finally,
fish and beef flesh, characterized by their high percentage of
nitrogenous matter. The tadpole grows fastest on a highly
nitrogenous diet. :

330 EFFECT OF CHEMICAL AGENTS [Cu. XI

Additional experiments upon the frog’s egg have been made
by DANILEWSKyY (795), who found that such eggs placed in
water containing zs}o, Of lecithin gained in 54 days 300%
greater weight than those reared in pure water. The author
believes, however, that this small quantity cannot act in a
directly nutritive manner but, rather, that it favors in some
way the assimilation of food.

Mammals. —'The requirements of agriculture have led to
numberless experiments upon the feeding of domesticated mam-
mals. Yet they are for the most part of little value for our
purpose. A few of the better class of experiments from our
point of view may be given, together with such conclusions as
they permit. )

Years ago, LAWES and GILBERT (’53), from extensive feed-
ings of sheep and pigs, upon diverse foods, reached the conclu-
sion that those “apparently grew more where, with no defi-
ciency of other matters, the nitrogenous constituents were very
liberally supplied. Hence, the gross increase obtained might
be somewhat more nitrogenous with the large supply of nitrog-
enous food; but it would in that case, according to some
experiments of our own, contain a larger proportion of water,
and less of solid matter, than where more fat had been pro-
duced.” More recent studies made on various domesticated
animals tend to confirm these results. A mixed diet with an
abundance of nitrogenous food permits of greater growth than
an equal quantity of food of one kind, or mixed food in which
the nitrogenous constituent is scant. Growth tends to
increase with the quantity of nitrogenous food rather more
closely than with that of the non-nitrogenous food devoured.

This conclusion is sustained by the striking results gained
by PrOsHER (797) in investigating the cause of the varying
percentage rate of growth of different mammals. ‘The rela-
tion between growth and the percentage of the different
organic and certain mineral constituents of milk is given in the
following table : —

§ 1)

UPON THE RATE OF GROWTH

TABLE XXXIV

331

SHOwING FOR VARIOUS MAMMALS THE TIME REQUIRED TO DOUBLE THE BIRTH-

WEIGHT, THE PERCENTAGE OF DIFFERENT ORGANIC CONSTITUENTS IN THE
~ MILK, AND THE RELATIVE QUANTITY OF ALBUMEN, CALCIUM OXIDE, AND
PuospHoric Acip IN THE MILK OF THE DIFFERENT SPECIES—THE QUAN-
TITY IN MAN BEING TAKEN AS THE STANDARD

1 2 3 4 5 6 7 o::
RELATIVE
RELATIVE} RELATIVE! RELATI¥E
SPEcIEs. slags % % To QUANTITY | QUANTITY | QUANTITY
DouUBLE Far, Suear. |ALBUMEN.
ALBUMEN.| Ca0. POs.
WEIGHT.
Man. 1 3.5 6.6 1.9 1.0 1 1
Horse i 1.1 6.1 2.3 1.2 4 3
Ox . 2 4.5 4.5 4.0 2.2 5 4
‘Pig. ay 6.9 2.0 6.9 3.7 — —
‘Sheep ty 10.4 4.2 7.0 3.8 8 9
Dog . oy 10.6 3.1 8.3 4.45 14 10
Cat . ds 3.3 4.9 9.5 5.1 oe be

From this table it is clear that there is a close relation.
between rate of growth and the percentage of albumen only
among the organic substances of milk. This relation is best.
brought out by comparing columns 2 and 5. The last two col-.
umns show a close relation between growth and the quantity
of calcium and phosphorus in the milk. But of the organic:
substances the quantity of the nitrogenous compound deter-.
mines the rate of growth.

3. Growth as a Response to Stimuli. — Hitherto we have-
regarded the process of growth in too mechanical a way, as.
though certain nutritive compounds, passing into a chemical.
mill, were inevitably transformed, at a certain rate, into proto--
plasm or formed substance. We have now to recognize that.
the growth processes are essentially vital processes, and, as:
such, characterized by all that complexity which we find in:
such a vital process as response to stimuli.

a. Acceleration of Growth by Chemical Stimulants. — Many
chemical agents which are not themselves food may stimulate
the growth processes. We have already seen (p. 51) how
certain poisons cause, in dilute solutions, accelerated move-

332 EFFECT OF CHEMICAL AGENTS [Cu. XI

ments and heightened metabolism. To the cases previously
given may be added the experiments of ScHuLz (°88), who
found that various poisons, such as corrosive sublimate, iodine,
bromine, and arsenious acid, increase the activities of yeast in
fermentation. It is not strange, therefore, to find that poisons
may, at a certain concentration, accelerate growth. That they
do so follows from the experiments of RicHARDs (’97), who
reared the molds Aspergillus, Penicillium, and Botrytis in
nutritive solutions to which had been added small quantities
of zinc sulphate, other metallic salts, cocaine, morphine, and
other alkaloids. After five to seven days Aspergillus, reared in
nutritive solutions in which sugar was the organic compound,
had gained the following dry weights (in milligrammes).
In all the experiments, except those in the column headed
*“ Control,” the solution contained certain non-nutritious sub-
stances in from 0.002% to 0.033% concentration.

TABLE XXXV

SHow1ne THE ToTtaL Dry WeiIcuT In MILLIGRAMMES OF A Crop or ASPER-
GILLUS REARED IN THE ABSENCE AND IN THE PRESENCE OF VARYING
QUANTITIES OF IRRITATING SUBSTANCES

SUBSTANCE. ConTROL. | 0.002% 0.004% 0.008% 0.016% 0.033%
Zn8O4 335 730 760 765 770 715
NaFl 250 565 405 — 840 270 245
NaeSiOs 350 520 575 450 435 380
CoSOx4 245 405 350 235 170 75
Cocaine 280 410 320 350 390 540
Morphine 160 155 170 140 210 215

It is clear from this table that the addition of even small quan-
tities of innutritious and poisonous substances may so excite
the hylogenic processes as to cause twice or even far more than
twice the normal formation of dry substance in a given time,
and that this excessive growth increases with the concentration
of the salt up to a certain optimum, beyond which growth
declines again to below the normal. Similarly TowNsEND
C97) has observed that a scedling living under a bell jar
whose atmosphere contains a small quantity of ether grows

§ 1) UPON THE RATE OF GROWTH 333

faster than one under similar conditions but without ether. If
the plant is subjected to an increased quantity of ether, growth
is retarded. The effect of these poisons is thus very different
from that of nutritive substances; it is due to the irritating
properties of the poison. .

b. The Election of Organic Food.—Not all of the food-stuff
presented to the organism is utilized by it—neither, on the
one hand, all of the kinds of food, nor, on the other, all of the
food of the most acceptable kind if offered beyond a certain
amount. There is an election of kind and of amount. A
study of an election of kind has been made by DucLAUx (’89),
and, especially, PFEFFER (95). The method employed was
this: To the organisms (various molds, Aspergillus, Penicil-
lium, etc.) were offered two compounds ; one more nutritious,
the other less so. Under these circumstances, the more nutri-
tious compound was usually taken by the organism, while the
less nutritious was often left entirely alone; thus, dextrose

' was preferred to glycerine, peptone to glycerine, and dextrose

to lactic acid, even when, in each case, the quantity of the
latter substance was in excess of the former. The election
was not, however, always of the more nutritious material, so
far as we can judge of relative nutritiveness. Thus, when
Aspergillus was sown on a nutritive fluid, containing 8% dex-
trose and 1% acetic acid, proportionally far more of the latter
was assimilated than of the former, although the latter is of
less value as food, as was shown by the fact that the plant had
also to devour a considerable quantity of the dextrose. This
extensive assimilation of a slightly nutritive substance is not,
so far as we can see, an adaptive process. |

The character of the election may change with age, so that
what is favorable for growth at one time is not at another.
Thus DucLtaux (’89) found that alcohol restrains or arrests
the germination of the spores of molds, whereas it is made use
of almost as abundantly as sugar by the adult plant; so, like-
wise, lactose and mannit cannot nourish young plants when
they replace sugar in the nutritive solution, whereas they are
a good food for the older plants.

So, also, among vertebrates, the food of the young, supplied
in the egg or in the milk of the parent, is very unlike that

834 EFFECT OF CHEMICAL AGENTS (Cu. XI

which is most favorable for growth in later stages. So impor-
tant is this difference of food at different ages that agriculturists
persistently change the ratio of the different foods supplied as
their animals increase in age. The reason for this change in
food required lies doubtless in this, that the chemical processes

of growth change with the age of the animal; at first imbi- .

bition of water predominates, then comes the secretion of the
various formed substances of the organism and the constant
maintenance and increase of the plasma. The most favorable
food of an organism at any time is dependent upon the
metabolic processes going on at that time.

The election of quantity is not less striking. It is well
known that an increase above a certain limit in the amount of
food presented to an organism or even actually taken into its
body does not result in any increase in growth. There is a
certain amount, fixed within broad limits, which corresponds
to a maximum of nutritiveness. This amount, this feeding
capacity, is not, however, necessarily constant at all stages of
the adult growth of the organism. For it has been observed
in certain animals, e.g. pigs, that as they grow older there is
a steady increase in the amount of food required to produce a
pound of gain in weight. Such facts serve to indicate that the
rate of growth is largely determined by internal factors.

Let us now summarize the results of this study of the effect
of chemical agents upon the rate of growth. Of foods, those
used in the plastic processes are chiefly to be considered. The
substances serving as plastic food must contain all the elements
normally occurring in the organism. ‘These are found in di-
verse proportions in different organisms, and hence the neces-
sity of dissimilar foods. Not only carbon, oxygen, hydrogen,
and nitrogen are necessary, but a whole series of other elements,
such as phosphorus, sulphur, chlorine, iodine, sodium, potas-
sium, calcium, iron, and magnesium are more or less essential.
The organic plastic food varies with the group of organisms.
Of relatively little importance for green plants, it becomes
essential to fungi. In this group we find the most important
character of a nutritive substance to be a certain degree of
lability. Among animals a mixed diet is especially beneficial,
but nitrogenous food favors growth more than non-nitrogenous

= I ee he eee

§ 2] UPON THE DIRECTION OF GROWTH 335

food. Finally, growth must be studied as a response to chem-
ical agents which may stimulate the protoplasm to absorb and
assimilate them to the degree required by the organism, or
which may stimulate the protoplasm to absorb some other sub-
stances, as we have seen in the case of zine sulphate. The
quantity and quality of food needed will, moreover, vary with
the age and other qualities of the organism. The consumption
of food both in quantity and in quality will be closely deter-
mined by the demand. All these complexities in the process
of nutrition indicate that it, like other processes in organisms,
can only be explained on the assumption of a vastly complex
molecular organization of the protoplasm.

§ 2. EFFECT OF CHEMICAL AGENTS UPON THE DIRECTION
OF GROWTH — CHEMOTROPISM

One of the most common processes in the early development
of organisms is the turning or bending of a filament, tubule, or
lamella. The cause of this turning is clearly an unequal
growth of the two sides of the organ. When the bending
organs are internal, their movements are largely removed from
experimental study; when external, as in plants, they more
easily lend themselves to our investigation. The object of
this investigation is always to find in how far the direction of
these tropic movements is determined or is determinable by
external agents.

In the present section it is proposed to consider in how far
tropic movements are determined by chemical agents. At the
outset it must be said that the growth which gives rise to these
bendings is frequently due to imbibition of water; and in such
cases it may be only temporary. Yet these temporary bendings
pass by such insensible gradations into permanent ones that a
sharp distinction between the two is impracticable and unim-
portant. Rejecting such a classification of the subject, we may
adopt one based on the tropic organ.

1: Chemotropism in the Tentacles of Insectivorous Plants. —
This case of chemotropism was the earliest to be observed ;
was DARWIN (75, p. 76) who first called attention to it. sii
found that when drops of water or solutions of non-nitrogenous

336 EFFECT OF CHEMICAL AGENTS [Cu. XI

compounds are placed upon the leaves of the sundew, Drosera,
the tentacles remain uninflected; but when a drop of a nitroge-
nous fluid, such as milk, urine, albumen, infusion of raw meat,
saliva, or isinglass, is placed on the leaf, the tentacles quickly
bend inwards over the drop. DARWIN now set to work sys-
tematically to determine which salts and acids cause and
which do not cause inflection. Of nine salts of ammonia tried,
all caused inflection of the tentacles, and of these the phosphate
of ammonia was the most powerful. Sodium salts in general
cause inflection while potassium salts do not. The earthy
salts are in general inoperative, as are likewise those of lead,
manganese, and cobalt. ‘The more or less poisonous salts of
silver, mercury, gold, copper, nickel, platinum, and chromic
and arsenious acids produce great inflection with extreme quick-
ness. Other substances which caused inflection were nitric,
hydrochloric, iodic, sulphuric, phosphoric, boracic, and many
organic acids; gallic, tannic, tartaric, citric, and uric acids
alone being inoperative. In all these cases, where a bending
of the tentacles over the drop occurs, the turning must be
regarded as a response to the stimulus of the chemical sub-
stance. An excitation proceeds from the irritated region to
the protoplasm upon whose imbibitory activity the turning of
the tentacles depends.

2. Chemotropism of Roots. — Attention was directed to the
fact that roots turn towards or from chemical substances by
MouiscH (84), who experimented with gases. When grains
of maize or peas are sprouted in water, their roots will turn

Fic. 91.—Seedling of Zea, whose radicle originally was just touching the water
obliquely with its apex and thereafter nutated in characteristic fashion, keeping
close to the air. (From Mo.iscu, 784.)

ee a

a

§ 2] UPON THE DIRECTION OF GROWTH 337

upwards towards the surface of the water —in response to the
more abundant oxygen supply there (Fig. 91), and will grow
along the surface of the water. MoLiscH undertook a: sys-
tematic investigation of the action of various gases in con-
trolling this growth.

The method employed was as follows: The gases were enclosed in glass
vessels whose mouth was closed by a plate of hard rubber perforated by
slits, 2 cm. long by 2mm. broad. The vessel being laid on its side so that
the slits were vertical, the rootlet of a germinating grain was placed in front
of it. As the gas diffused from the vessel, it was for some time in excess
upon one side of the rootlet. The gases experimented with were pure
oxygen, pyrogallic acid, nitrogen, carbon dioxide, chlorine, hydrochloric
acid gas, illuminating gas, ammonia, nitrous oxide, ether, chloroform, and
oil of turpentine. :

In all cases there occurred, generally after about an hour, a
turning of the root towards the gas (positive aérotropism,
MotuiscH), followed by a marked curvature from the slit (neg-
ative aérotropism). Since decapitated roots respond in the
Same way as intact ones, but in less degree, MOLISCH con-
cluded that the gases affect the growing region directly and do
not require the intervention of the root-tip.

3. Chemotropism of Pollen-tubes.— The suggestion was early
made by PFEFFER (’83), as a consequence of his discovery of
chemotaxis in swarm-spores, that perhaps the bending of the
antheridium-tube of Saprolegnia towards the odgonium was a
case of response to a chemical agent. STRASBURGER (’86)
offered a similar suggestion for phanerogams. PFEFFER (’88)
then made experiments, but was unable to control the direction
of growth of pollen-tubes. MoxiscH (’89 and ’93) was next
led to undertake further study in this direction by the obser-
vation that, when various pollen-grains are germinating in a
nutritive drop and a cover-glass is placed over them, the pollen-
tubes, after approaching near to the edge of the cover-glass,
turn away towards the centre again (Fig. 92,a,6). The move-
ment from the margin of the cover-glass cannot be ascribed to
a difference of density produced by evaporation at the margin,
for it occurred in a saturated atmosphere; nor can it be due to
surface tension of the bounding film of water, for the turning
occurred before the surface film was reached. These results

Z

>

338 EFFECT OF CHEMICAL AGENTS [Cu. XI

were abundantly confirmed by Miyosur (’94*), so we must
conclude that the pollen tube is negatively aerotropic to oxy-
gen: However, this negative aérotropism does not occur in all
pollen, for that of Orobus vernus and various other legumes, of
Primula acaulis, Viola odorata, V. hirta, etc., were indifferent.
a
a —b

TA

ie
VY

Fic. 92.—TIllustrates chemotropism of pollen-tubes. a. Negative chemotropism with

reference to the air (aérotropism) of pollen-tubes of Narcissus tazetta; the tubes
are growing under a cover-glass in a 7% sugar solution and turn at the edge, a, b,
from the air; magnified about 20. 6. Negative aérotropism of pollen-tubes of
Cephalanthera pallens, after 20 hours; a, 6, edge of cover-glass. cc. Stigma of
Narcissus tazetta in 7% sugar solution; pollen-tubes grow towards the stigma;
magnified about 10. (From Mo.iscH, ’93).

A second class of chemotropisms is seen in the turning of
pollen-tubes towards the stigma of a flower.* When pollen is
sown upon a plate of agar-agar or gelatine on which the upper
end of a ripe pistil has been placed, the tubes are sent out in

* Mouiscu accounts for the failure of some of the earlier experiments with
pollen-tubes on the ground that certain pollen-tubes do not exhibit this class of
chemotropism. Among these are Viola odorata, V. hirta, Orobus vernus, etc. —
species which are likewise not aérotropic.

§ 2] UPON THE DIRECTION OF GROWTH 339

all directions at first, but quickly grow towards the pistil
(Fig. 92, ¢). “ Mrvosui ('94*) found that the top of the pistil was
most attractive and that lower sections were less so until the
ovary is nearly reached, when the attraction is high again. If
the ovules of Scilla are placed on the plate of agar with its own
pollen, the pollen-tube will even grow into the micropyle of
the ovule. Pollen-tubes of a different species-or even genus,
e.g. Diervilla rosea, Ranunculus acer, etc., may likewise enter
the Scilla ovule, and even hyphe of Mucor stolonifer will turn
towards the ovules and penetrate into them. Thus the attract-
ing stuff is not a specific stimulant confined in its activity to
one kind of pollen-tube nor even to pollen-tubes in general.

The nature of the attracting substance has been studied by
Mryosur. Glucose is certainly present in the fluid excreted
by the ripe stigma of many phanerogams; and, if the agar-agar
substratum contain a 2% solution of cane sugar, there is no
longer chemotropism with reference to the ovule, since now the
attraction is not confined to a particular point. So it may be
concluded that it is the sugar of the ovule or stigma which
attracts the pollen-tube and that the excreted fluid contains
about a 2% solution. Consequently, the chemotropism of
pollen-tubes may be only a special case of chemotropism to
sugar.

Further experimentation confirmed Mryosut (94) in this
conclusion. Using the method employed by him in the case of
hyphe (p. 340), he injected Tradescantia leaves with various
solutions and sowed pollen of Digitalis purpurea upon the
leaves. When pure water was injected there was no effect,
but the substances named in the following list attracted the
pollen-tubes so that they grew down through the stomata into
the leaf : —

cane sugar . 2-8% levulose . 1% (slight action)
grape sugar, 48% lactose . 1-2% (“slight”)

dextrin . . 1-2%

The following solutions were neutral :—
maltose. . . . . 1% asparagin . . . 2%
meat extract... . glycerine . . . 205%

peptone. 8s gum arabic .. 2%

340 EFFECT OF CHEMICAL AGENTS [Cu. XI

The following were repellent : —

BICOBON | wear Oe potassium sulphate. 1%
ammonium sulphate, 1% sodium malate . 0.5-2%

It will be observed that all the attracting substances are
sugars.

4. Chemotropism of Hyphea.— While various authors had
noticed an apparent movement of hyphe towards certain
chemical agents or towards their hosts, the earliest systematic
observations upon this subject are those of WORTMANN (’87).
He placed fly-legs and other nutritive substances in Saprolegnia
cultures and noticed that the hyph left their original direc-

Fic. 93. — Negative chemotropism of a hypha of Peziza trifoliorum from the secre-
tions of a mycelium of Aspergillus niger. (From REINHARDT, ’92.)

tions to grow straight towards the food substance. Later
REINHARDT (’92) showed that hyphe of Peziza may be lured
out of their straight direction by spores of Mucor placed near
them; or, again, if a plate of gelatine rich in sugar be placed
above a plate of pure gelatine upon which hyphe of Peziza are
growing, all hyphe will send up branches to meet the more
nutritive surface; or, again, if Aspergillus niger, whose secre-
tions are fatal to Peziza, is placed near the latter, the hyphe
cease to grow at a distance of about 2 mm. from the Aspergillus
and then send out shoots which grow away from the injurious
substance (Fig. 93).

The most exhaustive studies on this subject are, however,
those of Mryosu1.(’(94), who worked with germinating spores
of Mucor mucedo and M. stolonifer, Phycomyces nitens, Peni-
cillium glaucum, Aspergillus niger, and Saprolegnia ferox.
Perforated membranes were employed, either in the form of
plant epidermis with stomata or of collodion films perforated

a a

Sa = -

§ 2] UPON THE DIRECTION OF GROWTH 341

by a fine needle point. The solutions were injected into the
leaf of Tradescantia, spores were sown upon its stoma-bearing
surface, and the whole was kept in a moist chamber. If the
solution was attractive, the growing hyphe penetrated into the
stomata, whereas in the absence of the solution they showed no
tendency to do so. Similarly, spores sown on the perforated
plate sent hyphze downwards through the holes when the plate
was floating on attractive solutions, but not otherwise. Mole-

Fic. 94.— Upper figure: Piece of the under side of a leaf of Tradescantia discolor
injected with 2% ammonium chloride, and sown with spores of Mucor stolonifer.
The young hyphze show chemotropic turnings, and have eventually penetrated
into the stomata. Drawn 27 hours after sowing the spores ; magnified 100. Lower
Jigure: Penicillium glaucum growing on a leaf of Tradescantia, which has been
injected with a 2% solution of cane sugar. The hyphz have branched, and the
branches have penetrated into the stomata. Drawn 25 hours after sowing the
spores; magnified 70. (From Mryosnut, ’94.)

cules diffusing out from the solution through the openings
determine the direction of the growing hyphe, so that from all
directions hyphe grew radially towards the openings in the
membranes (Fig. 94). ?

To prove that the result gained was truly chemotropism,
and not something else, a series of experiments was made.
That it was not a response to gravity was shown by sowing
the spores below as well as on top of a leaf; that it was nota
response to light or moisture was shown by keeping the cult-

342 EFFECT OF CHEMICAL AGENTS [Cu. XI

ures in a dark, moist chamber ; in both cases, the chemotropic
responses occurred. That contact was not the determining
factor was shown by placing above and below sheets of perfo-
rated collodion a layer of 5% gelatine, deprived of calcium
salts, which are attractive. One of these layers was fertilized
with grape sugar, the other remained sterile. The spores were
sown sometimes in the sterile, sometimes in the fertile layer of
gelatine; in the former case, the hyphe always grew (up or
down) into the sterile layer; in the other case, they remained
in the fertile layer. If both gelatine layers were sterile, or if
both were equally fertile, the hyphez did not grow through the
holes in the membranes. Not the holes, but the stuff diffusing
from them, determined the direction of growth of the hyphe.
There is a close relation between the chemical constitution
of the agents and their effects. The following substances
are attractive: compounds of ammonium (ammonium nitrate,
chloride, malate, tartrate), phosphates (of potassium, sodium,
ammonium), meat extract, peptone, sugar, asparagin, lecithin,
etc. The fcllowing are neutral: glycerine and gum arabic (1
to 2%). The following are repellent :- all free inorganic as
well as organic acids, alkalis, alcohol, and certain salts, e.g.
potassium-sodium tartrate, potassium nitrate, calcium nitrate,
potassium chloride (2%), potassium chlorate (8%), magne-
sium sulphate, sodium chloride (2%), ferric chloride (0.1%),
phosphoric acid, etc. Comparing this list with that which
PFEFFER and STANGE tried on swarm-spores (Pt. I, pp. 36-
38), we find that there is a rather close correlation. In both
cases, glycerine (a good food) is neutral, alcohol repellent,
phosphates attractive. As in the reaction of swarm-spores, so
in those of hyphe, WEBER’s law is followed.
_ 5. Chemotropism of Conjugation Tubes in Spirogyra. —
This case is closely allied to chemotropism of pollen-tubes.
Attention was first called to it by OvERTON (788), who
observed that at the point where the tubes were about to arise
bacteria accumulated from the surrounding water. From this
phenomenon, and on other grounds, he was led to conclude
that a substance is excreted at this point which exercises a
directive influence upon the conjugation tubes, insuring their
meeting. This conclusion has been confirmed by HABERLAND

.

at se oe

LITERATURE 343

(90), who finds additional evidence for it in the character of
the turnings which the two tubes from the opposite cells
undergo in order successfully to impinge upon each other.

The results of experimentation upon chemotropism show
that various substances may direct the growth of such elon-
gated organs as the tendrils, roots, and hyphe of plants; so
that greater growth takes place on the side turned from the
region of greatest concentration or towards it, as the case may
be. In many instances it can be shown that the direction of
growth is on the whole an advantageous one for the organism
—so that the directed growth may be considered an adaptive
one. In other cases, however, the response seems to have no
relation to adaptation.

If that which controls direction is the unequal concentration
of chemical agents in the medium, the immediate cause is
excessive growth on one side, due to excessive imbibition or
to excessive assimilative activity. The relation between these
causes is doubtless complicated. The chemical agent acts
upon the protoplasm, changing its molecular structure; the
changed protoplasm exhibits changed growth activities. Thus
we say the chemical agents act as stimuli.

LITERATURE

Arsy, J. H.’96. Beitrag zur Frage der Stickstoffernihrung der Pflanzen.
Landwirthsch: Versuchs-Stat. XLVI, 409-439.

Ascnorr, C. ’90. Ueber die Bedeutung des Chlors in der Pflanze. Landw.
Jahrbiicher. XVIII, 113-141.

BAssteR, P. 87. Die Assimilation des Asparagins durch die Pflanze.
Landwirthsch. Versuchs-Stat. XX XIII, 231-240.

BauMANN, E. ’95. Ueber das normale Vorkommen von Jod im Thier-
korper. (I. Mitth.) Zeitschr. f. physiol. Chemie. XXI, 319-330.
28 Dec. 1895.

BavuMany, E. and Roos, E. ’96. Idem (II. Mitth.), ibidem. XXI, 481-493.
2 Apr. 1896.

Baumann, E.’96. Idem (III. Mitth.), ibidem. XXII, 1-15. 16 May, 1896.

Benecke, W.’95. Die zur Ernahrung der Schimmelpilze nothwendigen
Metalle. Jahrb. f. wiss. Bot. XXVIII, 487-530.

"96. Die Bedeutung des Kaliums und des Magnesiums fiir Entwickelung

und Wachsthum des Aspergillus niger v. Th., sowie Einiger anderer
Pilzformen. Bot. Ztg. LIV.

344 EFFECT OF CHEMICAL AGENTS [Cu. XI

BERTHELOT, ’85. Fixation directe de l’azote atmosphérique libre par cer-
tains terrains argileux. Comp. Rend. CI, 775-784. 26 Oct. 1885.
92. Nouvelles recherches sur la fixation de l’azote atmosphérique par les
microbes. Comp. Rend. CXV, 569-574. 24 Oct. 1892.
93. Recherches nouvelles sur les microorganismes fixateurs de l’azote.
Comp. Rend. CXVI, 842-849. 24 Apr. 1893.
Bert, P. ’78. La pression barométrique. Recherches de physiologie ex-
perimentale. 1168 pp. Paris, 1878. .
BrYERINCK, M. W.’93. Bericht tiber meine Kulturen niederer Algen auf
Niahrgelatine. Centralbl. f. Bakteriol. u. Parasitenkunde. XIII, 368-
373. 23 Mar. 1893.
96. Kulturversuche mit Amoében auf festem Substrate. Centralbl. f.

Bakteriol. u. Parasitenk. XIX, 257-267. 28 Feb. 1896.

Brzoup, A. von ’57. (See Chapter I, Literature.)

Boxorny, T. 97. Ueber die organische Ernahrung griiner Pflanzen und
ihre Bedeutung in der Natur. Biol. Centralbl. XVII, 1-20; 33-48.
Jan. 1897.

BovussinGAu_t, J. B. J. D. 60. Agronomie, chemie agricole et physiologie. -

2 tomes. Paris, Mallet-Machelier, 1860. .
BrANDL, J., and Tappemmer, H. ’92. Ueber die Ablagerung von Fluor-
verbindung im Organismus nach Fiitterung mit Fluornatrium. Ztschr.
f. Biol XXVIII, 518-539.
Bunar, G.’73. Ueber die Bedeutung des Kochsalzes und des Verhalten der
Kalisalze im menschlichen Organismus. Ztschr. f. Biol. IX, 104-148.
74. Der Kali-, Natron-, und Chlorgehalt der Milch, verglichen mit dem
anderer Nihrungsmittel und das Gesammt-Organismus der Sauge-
thiere. Ztschr. f. Biol. X, 295-835. .
85. Ueber die Assimilation des Eisens. Ztschr. f. physiol. Chem. IX,
49-59.
’89. Ueber die Aufnahme des Eisens in den Organismus des Sauglings.
Ztschr. f. physiol. Chem. XIII, 399-406.
Ceut, A. ’96. Die Kultur der Amoében auf festem Substrate. Centralbl. f.
Bakteriol. XTX, 536-538. 25 Apr. 1896.
CopELANnD, E. B. ’97. The Relation of Nutrient Salts to Turgor. Bot.
Gazette. XXIV, 399-416. Dec. 1897.
Cook, G. H. ’68. Geology of New Jersey. Newark, 1868.
CRIVELLI, G. B. and Maaet, L. 70. Sulla produzione delle Amibe. Rend.
R. Inst. Lombardo. (2), III, 367-375. Plate.
91. Ancora sulla produzione delle Amibe. Ibidem. (2), IV, 198-203.
Danitewsky, B.’95. De l’influence de la lécithine sur la croissance et la
multiplication des organismes. Comp. Rend. CXXI, 1167-1170. 30
Dec. 1895.
96. De Vinfluence de la lécithine sur la croissance des animaux a sang
chaud. Comp. Rend. CXXIII,195-198. 20 July, 1896.
Darwin, C.’75. Insectivorous Plants. London: Murray. 462 pp. 1875.
Day, T. C. 94. The Non-Assimilation of Atmospheric Nitrogen by Germi-
nating Barley. Trans. and Proc. Bot. Soc. Edinburgh. XX, 29-34.

LITERATURE 345

Ductaux, E.’89. Sur la nutrition intracellulaire. Ann. de |’Inst. Pasteur.
III, 97-112. March, 1889.

Escuie 97. Ueber den Jodgehalt einiger Algenarten. Zeitschr. f. physiol.
Chemie. XXIII, 30-37. 27 Mar. 1897.

ForcHHAMMER, G.’61. Resultater af sine Undersogelser, saavel over Salt-
mengden i Middelhavets Vand. Overs. K. danske Vidensk Selskabs
Forhangl. Aaret. 1861. 379-391.

Frank, A. B.’88. Die Ernahrung der Pflanzen mit Stickstoff. Berlin, 1888.

92. Lehrbuch der Botanik, I. 669 pp. Leipzig: ENGELMANN.
93. Die Assimilation des freien Stickstoffs durch die Pflanzenwelt. Bot.
Ztg. LI, 139-156.

Frepericg, L. 78. Sur l’organisation et la physiologie du Poulpe. Bull.
de l’Acad. roy. de Belg. XLVI, 710-765.

79. Note sur le sang du Homard. Ibid. XLVII, 409-413.

Gortnt, C. 96. Die Kultur der Amében auf festem Substrate. Centralbl.
f. Bakteriol. XIX, 785.

HaBERLAND, G. ’90. Zur Kenntnis der Conjugation bei Spirogyra. Sitz-
ungsber. d. Akad. d. wiss. Wien. Math.-Nat. Cl. XCIX}, 390-400.
1 Tafel.

HAnsTEEN, B. ’96. Beitrige zur Kenntniss der Eiweissbildung und der
Bedingungen der Realisirung dieses Processes im phanerogamen Pflan-
zenkérper. Ber. deutsch bot. Ges. XIV, 362-371. 28 Dec. 1896.

Hartic, R. and Weser, R. ’°88. Das Holz der Rotbuche. Berlin, 1888.
[Quoted from Loew, ’91, p. 270.]

HELLRIEGEL, H. ’86. Welche Stickstoffquellen stehen der Pflanze zu
Gebote? Tageblatt des 59. Versammelung, Deutscher Naturforscher
und Aerzte. Berlin, 1886. p. 290.

HeNsEN, V. and ApsTreen, C. ’97. Die Nordsee-Expedition, 1895, des
Deutschen Seefischerei-Vereins. Ueber die Eimenge der im Winter
laichenden Fische. Wiss. Meeresuntersuchungen, herausgegeben von
der Kommission zur wiss. Unters. d. deutschen Meere in Keil, N. F.
Band II, Heft. 2, pp. 1-98.

Hersst, C.’97. Ueber die zur Entwickelung der Seeigellarven nothwendigen
anorganischen Stoffe, ihre Rolle und ihre Vertretbarkeit, I. Theil.
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Entwickelungsmechanik d. Organismen. V. 649-793. Taf. XITI-XIV.
9 Noy. 1897.

Heraeus 86. Zeitschr. f. Hygiene. I.

Hoppe-SEY Ler, F. ’81. Physiologische Chemie. Berlin, 1881.

Hotter, E. 790. Ueber das Vorkommen des Bor im Pflanzenreich
und dessen physiologische Bedeutung. Landw. Versuchs-Station.
XXXVI, 437-458. 1890.

JACCARD, P. ’93. Influence de la pression des gaz sur le développement des
vegetaux. Comp. Rend. CXYVI, 830-833. 17 April, 1893.

JENTYsS, S. ’88. Ueber den Einfluss hoher Sauerstoffpressungen auf das
Wachsthum der Pflanzen. Unters. a. d. bot. Inst. Tiibingen. II.
419-464.

346 EFFECT OF CHEMICAL AGENTS [Cu. XI

JOHNSON, S. W. ’68. How Crops grow. 394 pp. New York.

JORDAN, E. O. and Ricwarps, KE. ’91. Investigations upon Nitrification
and the Nitrifying Organism. From Report, Mass. State Board of
Health, Water Supply, and Sewage. Part II. pp. 865-881. [Dated
1890.]

Kemmerici, E. 69. Untersuchungen iiber die physiologische Wirkung der
Fleischbriihe, des Fleischextracts und der Kalisalze des Fleisches.
Arch. f. d. ges. Physiol. II, 49-93.

Kocn, A. and Kossowrtscn, P. 93. Ueber die Assimilation von freiem
Stickstoff durch Algen. Bot. Ztg. LI, 321-325. Nov. 1, 1893.

Kossowitscu, P. 94. Untersuchungen iiber die Frage, ob die Algen freien
Stickstoff fixiren. Bot. Ztg. LII, 97-116. 16 May, 1894.

- KruKENBERG, C. F. W.’80. (See Chapter II, Literature.)

78. Mangan ohne nachweisbare Mengen von Eisen in der concretionen
aus dem Bojanus’schen Organe im Pinna squamosa Gm. Unters.
Physiol. Inst. Univ. Heidelberg. II, 287-289.

‘Kunxet, A. J. 791. Zur Frage der Lisenresorption. Arch. f. d. ges.
Physiol. L, 1-24. 25 June, 1891.

95. Blutbildung aus .anorganischen Eisen. Arch. f. d. ges. Physiol.
LXI, 595-606. 25 Sept. 1895.

LAuRENT, E. ’88. Sur la formation d’amidon dans les plantes. Bruxelles,
1885.

Lawes, J. B. and Giipert, J. H. 53. On the Composition of Foods,
in Relation to Respiration and the Feeding of Animals. Rept. 22d
Meet. British Ass. Adv. Sci. for 1852, 323-353.

Lawes, J. B., Gitpert, J. H. and Puan, E. ’61. On the Sources of the
Nitrogen of Vegetation, with Special Reference to the Question whether
Plants assimilate Free or Uncombined Nitrogen. Philos. Trans. Roy.
Soc. London. CLI, 481-577.

LiesscHEer 93. Beitrag zur Stickstofffrage. Jour. f. Landwirtschaft.
XLI. [not seen. ]

Logs, J. ’92. (See Chapter X, Literature.)

Lorw, O. ’91. Die chemische Verhiltnisse des Bakterienlebens. Centralbl.
f. Bakteriol. IX, 659-663.

91°. Ueber die physiologischen Functionen der Phosphorsiure. Biol.
Centralbl. XI, 269-281. 1 June, 1891.

96. The Energy of the Living Substance. 116 pp. London. 1896.

Loew, O. and Boxorny, T. ’87. Chemisch-physiologische Studien iiber
Algen. Jour. f. prakt. Chem. XXXVI, 272-291.

Lupxg, R. ’89. Ueber die Bedeutung des Kaliums in der Pflanze. Landw.
Jéihrb. XVII, 887-913.

Macatuvum, A. B. ’91. On the Demonstration of the Presence of Iron in

Chromatin by Micro-chemical Methods (Abstract). Proc. Roy. Soe.

XLIX, 488-489. July 10, 1891.

92. Idem. Proc. Roy. Soc. XL, 277-286. Jan. 20, 1892.

94. On the Absorption of Iron in the Animal Body. Jour. of Physiol.
XVI, 268-297. 17 April, 1894.

LITERATURE 347

Meyer, A. ’85. Ueber die Assimilations-producte der Laubblitter angio- »
spermer Pflanzen. Bot. Ztg. XLIII, 417 et seq.

Mryrosur, C. 94. Ueber Chemotropismus der Pilze. Bot. Ztg. LIU,
1-27. 1 Taf.

948, Ueber Reizbewegungen der Pollenschliuche. Flora. LXXVIII,
76-93. 24 Jan. 1894.

Motiscu, H. ’84. Ueber die Ablenkung der Wurzeln von ihrer normalen
Wachsthumsrichtung durch Gase ( Aérotropismus). Sb. k. Akad. d.
Wiss. Wien. XC}, 111-191.

89. Ueber die Ursachen der Wachsthumsrichtungen bei Pollen-
schliiuchen. Sitzungsanzeiger k. Akad. Wiss. Wien. 1889, No. II.

92. Die Pflanze in ihren Beziehungen zum Eisen., Jena, 1892.

93. Zur Physiologie des Pollens, mit besonderer Riicksicht auf die
chemotropischen Bewegungen der Polleuschliuche. Sb. k. Akad. d.
Wiss. Wien.. CII}, 423-448.

94". Ueber Chemotropismus der Pilze. Bot. Ztg. LI}, 1-27.

94%, Ueber Reizbewegung der Pollenschliuche. Flora. LXXVIII,
76-93. 24 Feb. 1894.

94°. Die mineralische Nahrung der niederen Pilze. Sb. Wien. Akad.
CIII}, 554-574.

95. Die Ernahrung der Algen. Siisswasser Algen. I. Abhandl. Sb.
Akad. Wiss. Wien. CIV}, 783-800.

96. The same. II. Abhandlung. Sb. Akad. Wiss. Wien. CV}, pp.
633-648.

Montr, R. ’95. Sur les cultures des amibes. Arch. Ital. de Biol. XXIV,
174-176.

Nacet, K. v. [with Loew, O.]. 80. Ernahrung der niederen Pilze durch
Kohlenstoff- und Stickstoffverbindungen. Sb. Miinchen Akad. X,
277-367.

Nencxt, M. 94. Note sur les prétendues cendres des corps albumenoides. _
Arch. des sci. biol. St. Petersburg. III, 212-215.

Nenckx1, M. and Scuoumow-Simanowsky, E. O. 94. Etudes sur le chlore et
les halogenes dans l’organisme animale. Arch. des sci. biol. St.
Petersburg. IIT, 191-211.

Nosse, F., Scuroper, J. and ErpmMann, R. 71. Ueber die organische
Leistung der Kaliums in der Pflanze. Landw. Versuchs-Stat. XIII,

321-399; 401-423.

Nossg, F. and Hittner, L. 95. Vermégen auch Nichtlegumenosen freier
Stickstoff aufzunehmen? Landw. Versuchs-Stat. XLV. 155-159.

Oaata, M.’93. Ueber die Reinkultur gewisser Protozoen (Infusorien).
Centralbl. f. Bakteriol. XIV, 165-169. 7 Aug. 1893.

Overton, C. E. 88. Ueber den Conjugationsvorgang bei Spirogyra. Ber.
D. bot. Ges. VI, 68-72. =

PETERMANN, A. ’91. Contribution a la question de l’azote. Premiére note.
Mém. cour. et autres mém. de l’acad. Roy. de Belg. Collection in 8vo.
XLIV. 23 pp.1 pl. Jan. 1891.

"92. Seconde note. Same Mémoires. XLVII, 1-37, 1 pl.

he a feererie

- 848 EFFECT OF CHEMICAL AGENTS [Cu. XI

PFEFFER, W.’83. (See Chapter I, Literature.)

’88. Ueber chemotactische Bewegungen von Bakterien, Flagellaten und
Volvocineen. Unters. a. d. bot. Inst. Tiibingen, IT. 582-661,

95. Ueber Election organischer Nihrstoffe. Jahrb. f. wiss. Bot. XXVIII,
205-268. 4

PFEIFFER, T. and Franke, E. ’96. Beitrag zur Frage der Verwertung ele-
mentaren Stickstoffs durch den Senf. Landw. Versuchs-Stat. XLVI,
117-151. Taf. I.

Poteck, T. ’50. Analyse der Asche von Eiweiss und Eigelb der Hiihnereier.
Ann. de Physik und Chemie. LXXVI, 155-161. 7 Feb. 1850.

Prescu, W. ’90. Ueber das Verhalten des Schwefels im Organismus und
den Nachweis der unterschwefligen Siure im Menschenharn. Arch. f.
path. Anat. u. Physiol. CXIX, 148-167. 2 Jan. 1890.

ProscHeER ’97. Die Beziehungen der Wachsthumsgeschwindigkeit des
Siuglings zur Zusammensetzung der Milch bei verscheidenen Sauge-
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PuriewiTscH, K. ’95. Ueber die Stickstoffassimilation bei den Schimmel-
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RavuBeEr, A. 84. Ueber den Einfluss der Temperatur, des atmosphirischen
Druckes und verschiedener Stoffe auf die Entwicklung thierischer Eier.
Sitzungsber. d. naturf. Gesell. Leipzig. X, 55-70.

Ravin, J. 69. Etudes chimiques sur la végétation. Ann. des Sci. Nat.
(Bot.). (5), XI, 93-299.

REINHARDT, M. O. 92. Das Wachsthum der Pilzhyphen. Jahrb. f. wiss.
Bot. XXIII, 479-599.

Ricuarps, H. M.’97. Die Beeinflussung des Wachsthums einiger Pilze durch
chemische Reize. Jahrb. f. wiss. Bot. XXX, 665-688.

Roos, E. 96. Ueber die Wirkung der Thyrojodins. Zeitschr. f. physiol.
Chem. XXII, 16-61. 16 May, 1896.

Sacus, J. v.’87. Vorlesungen iiber Pflanzenphysiologie. Leipzig, Engelmann.

Scuimpkr, A. F. W.’90. Zur Frage der Assimilation der Mineralsalze durch
die griine Pflanze. Flora. LX XIII, 207-261.

Scuiosine, T. fils et Laurent, E. ’92. Recherches sur la fixation de
Vazote libre par les plantes. Ann. de |’Inst. Pasteur. VI, 65-115.
Feb. 1892.

92. Sur la fixation de l’azote libre par les plantes. Ann. de I’Inst.
Pasteur. VI, 824-840. Dec. 1892.

Scuia@sine, T., and Mintz, A. ’77. Sur la nitrification par les ferments
organisés. Comp. Rend. LXXXIV, 301-303. 12 Feb. 1877.

79. Recherches sur la nitrification. Comp. Rend. LXXXIX, 891-894.
24 Nov. 1879.

ScHNEIDER, R.’89. Verbreitung und Bedeutung des Eisens im animalischen
Organismus. Humbolt. VIII, 337-345. Sept. 1889.

95. Die neuesten Beobachtungen iiber naturliche Eisenresorption in
thierischen Zellkernen und einige charakteristische Fille der Eisen-
verwerthung im Korper von Gephyreen. Mitth. a. d. Zool. Stat. zu
Neapel. XII, 208-215. 6 July, 1895.

a

LITERATURE r 349

Scnuuz, H.’88. Ueber Hefegifte. Arch. f. ges. Physiol. XLII, 517-541.
20 March, 1888.

93. Ueber den Schwefelgehalt menschlicher und thierischer Gewebe.
Arch. f. d. ges. Physiol. LIV, 555-573. 7 July, 1893.

Socry, C. A. 91. In welcher Form wird das Eisen resorbirt? Zeitschr. f.
physiol. Chem. XV, 93-193. 10 Jan. 1891.

Sroxiasa, J. ’96. Studien iiber die Assimilation elementaren Stickstoffs
durch die Pflanze. Landw. Jahrb. XXIV, 827-863.

STRASBURGER, E.’86. Ueber fremdartige Bestaubung. Jahrb. f. wiss. Bot.
XVII, 50-98.

TaMMANN, G. ’88. Ueber das Vorkommen des Fluors in Organismen.
Zeitschr. f. physiol. Chem. XII, 322-326.

TappPEINER, H. 93. Ueber Ablagerung von Fluorsalzen im Organismus
nach Futterung mit Fluornatrium. Sb. Ges. Morph. u. Physiol.
Munchen. VIII, 22-26.

TownsEnND, C. O. ’97. The Correlation of Growth under the Influence of

eInjuries. Ann. of Bot. XI, 509-532.

Vines, S. H. ’86. (See Chapter VIII, Literature.) j

Vorxmann, A. W.’74. Untersuchungen iiber das Mengenverhiiltniss des

} Wassers und der Grundstoffe des menschlichen Kérpers. Ber. d. Sachs.
Ges. d. Wiss., Leipzig. XXVI, 202-247.

Wie ter, A.’83. Die Beeinflussung des Wachsens durch verminderte Par-
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189-232.

Wrnocrapsky, S. ’84. Ueber die Wirkung dusserer Einfliisse auf die
Entwicklung von Mycoderma vini. Arb. St. Petersburger Naturf. Ges.
XIV, 132-135 [Russian]. Abstr. in Bot. Centralbl. XX, 163-167.

*87. Ueber Schwefelbacterien. Bot. Ztg. XLV, 493 et seq.

89. Recherches physiologiques sur les sulphobactéries. Ann. l’Inst. Pas-
teur. IIT, 49-60. Feb. 1887.

‘90. Recherches sur les organismes de la nitrification. Ann. |’Inst.
Pasteur. IV, 257-275. May, 1890.

95. Recherches sur l’assimilation de l’azote libre de l’atmosphere par les
microbes. Arch. des sci. biol. de St. Petersb. III, 297-352.

Wor rr, E. v.’81. Ueber die Bedeutung der Kieselsiure fiir die Haferpflanze
Landw. Versuchs-Stat. XXVI, 415-417.

65. Mittlere Zusammensetzung der Asche, aller land- und forstwirth-
schaftlichen wichtigen Stoffe. Stuttgart, 1865.

Worrerine, H. W. F. C. 95. Ueber die Resorbbarkeit der Eisensalze.
Zeitschr. f. physiol. Chem. XXI, 186-233. 26 Nov. 1895.

Wortmann, J. ’87. Zur Kenntniss der Reizbewegung. Bot. Ztg. 812.

Yune, E. 83. Contributions & l’histoire de l’influence des milieux physico-
chimiques sur les étres vivants. Arch. de Zool. (2). I, 31-52.

CHAPTER XII
THE EFFECT OF WATER UPON GROWTH

WE have already, in Chapter X, laid stress upon the impor-
tance of the imbibition of water for the growth of both plants
and animals. Here we may consider more in detail the rela-
tion between growth and water, both as concerns the rate or
quantity of growth and the direction of growth, or hydro-
tropism. | .

§ 1. Errect oF WATER UPON THE RATE AND QUANTITY
oF GROWTH

It naturally follows from what we know of the importance
of water for growth, that the rate of growth will be closely
dependent upon water supply. And as all growth-phenomena
have been better studied in plants than in animals, our further
illustration of this fact will be drawn chiefly from the former.

First, plant germination demands a certain minimal quantity
of water. What this quantity is may be determined either by
finding the least amount which will permit of normal germina-
tion, or by measuring the amount absorbed by different seeds
before protruding their radicles. This latter quantity has
been shown by the careful determinations of HOFFMANN (’65,
p- 52) to vary from between 40% and 60% of the original dry
weight, in the case of various cultivated grains, to over 100%
in the case of various Leguminose.

In fungi, likewise, LESAGE (795, p. 311) has found that
there is a hygrometric limit below which Penicillium spores
will not germinate ; and that the interval elapsing before ger-
mination begins is the shorter the moister the atmosphere.

The method employed by Lesage is of wide applicability. The tension
of the water-vapor formed above a saline solution is less than that formed
above distilled water; and it diminishes in proportion to the concentration

350

_s

—

Ve

§1j : RATE AND QUANTITY OF GROWTH 351

of the solution. Indeed, to a given solution of a particular salt, e.g. sodium
chloride, there corresponds a constant hygrometric state, however much the
temperature may vary. This hygrometric condition may be calculated by
the formula: 1—na, where saturation is taken as unity, n equals the number

_ of grammes of sodium chloride dissolved in 100 grammes of water, and a is

a constant factor, varying with the salt, and equal to 0.00601 in the case of
sodium chloride. The spores were reared in a moist chamber, whose
bottom was made by a plate full of the solution.

The results of LESAGE’s experiments are given in the fol-
lowing table : —
TABLE XXXVI

SHow1nec INTERVAL IN DAYS ELAPSING BEFORE GERMINATION WHEN SPORES
oF PENICILLIUM ARE KEPT IN Moist CHAMBERS OVER VARIOUS SOLUTIONS
or Sopium CHLORIDE

n | 0 21.5 | 23.6 | 26.5 30-33.5

Interval. .. | 1 6 9 | 11 No germination after 171 days

From these results it follows by calculation that the spores ger-
minate at the hygroscopic state of 0.82-0.84 or over, but not
below this limit.

The foregoing cases, taken from the two principal groups of
plants, agree in showing that a certain amount of water is
essential to the revival of the metabolic activities which are
preliminary to germination. The large quantity of water
absorbed by the seed or spore affords the mechanism or the
stimulus to growth.

Also, in the later stages of plant growth, the water both of
the atmosphere and of the soil is essential. The importance of
atmospheric moisture was shown by REINKE (76), who com-
pared the size of the leaf-stem in different hygrometric condi-
tions. :

The method of measuring was as follows: a young potted Datura (one
of the Solanacexz) was placed so that the lower half of one of its stems was
horizontal. A fine platinum wire, suspended from a standard above, hung
vertically near the stem, and made one turn around it. The lower end of
the wire carried a 2-gramme weight. That part of the wire which sur-
rounded the stem was protected by a layer of tinfoil. As the stem swelled

or grew thinner, the weight rose or fell. The vertical oscillation of the
weight measured the variation in circumference of the stem.

352 THE EFFECT OF WATER [Cu. XII

It appeared that as the atmospheric moisture increased, a
considerable increase in the cross-section of the stem followed ;
and as it diminished, the size of the stem diminished likewise.
The results are graphically given in Fig. 95.

| |
; ni
' FI i
\ _ A
nM ¥ ai!
A | \ ri ia
\F ri
“\ L 4 \
a % \ rm OD). a Q i
VY \ I \ Y Lv)
} ¥
4
\ ¥
eZ ge
ie BS —e ‘eee
ULa a t= ws Bs!
han, OE PA, han, PR “ ba ee
. s “a
= + Zi}
a FP Sond RS ‘. Fd
© — Z
10--12--§ 10-42 10-29" 17"
oc. sh
Cm eer bi O+ 0+ eo eT be o—-e!|!
|| oe eee
11

Fia. 95.— Curve of growth in thickness of a Datura stem, M-M, correlated with
variations in relative humidity, H-H, the temperature T7—T remaining nearly uni-
form. The part of the curve falling below O-O indicates loss of thickness below
the normal. The abscisse represent hours. (From REINKE, 76.)

These experiments have been repeated by Francis DARWIN
(93) upon the fruit of a gourd, Cucurbita, whose growth is
little influenced by variations in temperature. He determined,
by means of a delicate micronieter apparatus, the average incre-
ment in microns per minute; and, at the same time, by means
of a dewpoint thermometer, the moisture of the air. The
relation between rate of growth and psychometric readings is
best shown graphically, as in the curves of Fig. 96. The

‘
/ H
’
" bh, M. 3
a «
p Se eon i FE tw -
E “4 et -" Pp] 2
¢ x a
7 “7 Pha VY 2
ns | :
&
0 a?
11 12th 12 ne a 3 4 5 6 7 8 9 10

Fia. 96.— Curve of diameter of fruit of Cucurbita (full line) correlated with varia-
tion in humidity (broken line). The abscisse represent hours; the ordinates
represent growth in wz per minute (numbers on the left) and per cents of humidity
(numbers on the right). (From DARwIN, ’93).

§1] UPON THE RATE AND QUANTITY OF GROWTH 353

figure shows plainly how, in general, an increment or a decre-
ment in one of these quantities is accompanied by a corre-
sponding change in the other.

The cause of this relation between changes in volume and in
moisture is partially explained by considering the quickness
with which increased growth follows increased moisture. It
is undoubtedly due, as TSCHAPLOWITZ (’86) has suggested, to.
the diminution in the transpiration of the plant in moist air as
compared with dry air. The change in the rate of transpira-.
tion is, however, not to be conceived as an immediate physical
result of the change in moisture, but as a response to the s‘im-
ulus of greater or less water in the atmosphere.

The amount of water in the soil also has an important influ-
ence on the rate of growth. Quantitative studies on this well-
known fact were afforded by HELLRIEGEL, who reared barley
in soils which contained various fractional parts of the satura-
tion quantity. Giving his results in the form of a table, we:
have the following relation between the humidity of the soil
and the amount of dry matter produced, after a certain number

of days, in the grain and in the chaff : —.

TABLE XXXVII

PropvctTion, IN Dry MATTER.
Hvumipity or Sort.
Grains. Chaff.
80%, 8.77 9.47
60 9.96 11.00 (Max.)
40 10.51 (Max.) 9.64
30 9.73 8.20
20 7.75 5.50
10 0.72 1.80
5 — 0.12

The principal conclusion that one can draw from this table is
that there is an optimum humidity of the soil for growth,
which is not, however, the same for all organs.

More extensive researches upon this subject have been made
by JUMELLE (789), who studied chiefly the effect of water
upon the growth of the various organs of the plant, and by

2a x

354 THE EFFECT OF WATER UPON GROWTH [Cu. XII

GAIN (92, 95), who studied the effect upon the entire plant,
so that his results are of especial interest here.

Gain planted seeds of various species in sand to which a little garden
loam had been added. He was careful either to select seeds of equal size or,
after sprouting had occurred, to weed out all but the normal, medium-sized
ones. In one set of experiments, the soil contained from 3% to 6% of
water; in the other, from 12% to 16%.

GAIN found that the entire plant grew faster in the humid
than in the dry soil, as the accompanying diagram, Fig. 97,

mw’

fe ee ee ee ee ee ee ee ee ee me ewe eee ee ee ee es we we a es i ee ee ee

1 ros 1

1 r n
1-MAY 1 JUNE 1 JULY

Fia. 97. — Curves of fresh weight of two similar seedlings of flax, one growing in
moist, the other in dry, soil. The maximum weight (M) gained by the plant
differs in the two cases, and also the time of gaining that weight. /F’, time of
flowering ; fm, time of fructification. (From Gary, ’95.) ,

indicates. The aérial parts of the plant are more affected than
the subterranean. The ratio of growth of plants in moist soil
to those in dry varied from 1.12 (radish) to 2.83 (bean).

Ee

= [aaa
- a

eh) i-

§ 2] HYDROTROPISM 350

Among animals the importance of moisture for the growing
young is indicated by the fact that even in species living on
the land or in the air the eggs and larve are frequently con-
fined to moist situations, as in pulmonate gasteropods, in many
insects, and in reptiles. When this is not the case, the eggs
are provided with thick, water-containing envelopes, as in
birds, or are placed on succulent leaves, or in special fluid-
filled receptacles, as in many insects. Only rarely, as for
example in the case of the meal worm, Tenebrio, and the Der-
mestide, are the young found growing in a very dry medium.
Doubtless in such cases the amount of water required for
growth is less than in the cases where the larve develop in
moist situations. |

To summarize, a minimal quantity of water is essential to
germination and growth; and above this limit growth pro-
ceeds more rapidly with the increase in water up to a maxi-
mum which varies with the species.

§ 2. ErrectT oF WATER ON THE DIRECTION OF GROWTH
— HYDROTROPISM

A growing organ, such as a leaf, root, or stolon, is normally
in a condition of turgescence, as a consequence of the imbibi-
tion of water. So long as the turgidity is equal on the two
sides of the organ the latter retains its normal position. If
the turgidity is diminished on one side, the organ bends
towards that side; if it is increased on one side, the organ
bends from that side. Thus, variations in cell turgidity cause
changes in the position of organs.

This inequality of turgescence on the two sides of an organ
may arise in a homogeneous atmosphere; for certain organs
have the capacity in a dry atmosphere of losing water on one
side faster than on the other, and in a moist atmosphere of
becoming more turgescent on one side than on the other. Con-
sequently, the organ assumes a characteristic position accord-
ing as the hygroscopic condition of the atmosphere is high or
low. Such hygroscopic movements are of wide occurrence
among plants, and are often highly adaptive. We see them,
for example, in the folding of vegetative parts of the so-called
Resurrection Plant of California (Selaginella lepidophylla), by

356 THE EFFECT OF WATER UPON GROWTH [Cu. XII

which the whole plant is rolled into a ball capable of being
transported by the wind, perchance to a moister region.
These hygroscopic movements occurring in a homogeneous
medium are to be distinguished from true hydrotropism, for
they are not properly growth phenomena.

True hydrotropism occurs in growing elongated organs, such
as roots or stolons, which grow from or toward a region of
greater or less moisture. The observations on this phenom-
enon have not been numerous, and are difficult to bring under
one point of view ; consequently, we shall do best to classify
the cases studied on the basis of the organs considered.

1. Roots. — The first studies upon hydrotropism in roots
were made in the middle of the eighteenth century ; but they
were crude and uncritical. The first adequate experiments
were made by KniaHt (11). He half-buried some beans in a
flower-pot filled with earth, inverted the pot (in which the
earth and seeds were retained by a grating), and kept the
earth moist by adding water through the hole in the bottom of
the pot. The radicles, instead of growing vertically down-
wards as radicles normally do, ran horizontally along the sur-
face of the moist earth. The same results were got by JOHN-
SON (29), who found in addition that if the mouth of the
inverted flower-pot, or other seed receptacle, be placed in a
moist atmosphere, the roots grow vertically downwards; they
are no longer turned aside by dry air. ‘Then DUCHARTRE
(56) discovered that when a seedling was grown in relatively
dry earth, with its aérial part in a close, moist chamber, the
roots did not penetrate vertically into the soil, but grew out
horizontally, and even upwards. SAcHS (72) varied this
experiment by planting his seeds in a basket made of netting,
fixed to a metallic frame, and hung with its sides inclined at
an angle of 45° with the horizontal plane. When the appa-
ratus was placed in a damp chamber the radicles grew verti-
cally downwards ; but in dry air they turned back towards the
bottom of the sieve containing the damp earth, and ran along
its under surface. SACHS called especial attention to the fact
that it is the damper side which becomes concave; and this
shows that the turning is not due to direct physical causes.

The second epoch in the study of hydrotropism now began.

——e

a ee ey

patil bata

TDS AT EE ae ©

g2] - HYDROTROPISM 357

The fact of its existence being granted, the conditions of its
occurrence were carefully studied. Thus DARWIN (’80, Chap-
ter III) investigated the locus of the irritable protoplasm.
Some of the young bean-radicles were coated for the distance
of a millimetre or two from the apex with a mixture of olive
oil and lamp black in order to exclude the moist air. Such
showed almost no hydrotropic movements. Killing the tip by
caustic produced the same result. Thus the terminal two
millimetres or so include the irritable protoplasm.

This conclusion was disputed by WIESNER (’81, p. 133) and
DETLEFSEN (82) on the grounds that on the one hand coating
or killing the tip introduced abnormal conditions to which the
failure of hydrotropism might be ascribed, and, on the other
hand, after the tip of the root was cut off a curving might still
occur. However, a very careful review of the subject with
new experiments by MoLiscH (’84), a pupil of WIESNER, con-
firmed DARwIN’s conclusion. Thus MOoLiscH covered all of
the radicle excepting the terminal 1 to 1.5 mm. with wet
paper. ‘This upper part could then hardly be irritated by an
unequal distribution of moisture in the environment. Never-
theless, when a strip of moist filter-paper was placed opposite
the tip the hydrotropic response occurred. The response must
then have been due to a stimulus received exclusively at the
tip, and it may be concluded that the tip alone is stimulated
by moisture.

Now, although only a millimetre or two of the tip is irritable,
the response of bending takes place some distance, 7 to 28 mm.,
behind the tip, nearly in the region of maximum growth.
Thus sensitive and responsive regions do not coincide — there
is a transmission of stimuli. The facts that the hydrotropic
response occurs in the region of rapid growth and that at the
minimum temperature of growth response no longer occurs,
indicate clearly that the hydrotropism of roots is not the result
of mechanical loss of turgescence on one side, but that it is on
the contrary a growth phenomenon — a localized growth which
is a response to a stimulus.

2. Rhizoides of Higher Cryptogams.— While it is a priori
probable that the rhizoids of hepatics should react like the
roots of phanerogams, MoLiscuH desired to demonstrate the fact

358 THE EFFECT OF WATER UPON GROWTH ([Cu. XII

by experiment. Upon a glass dise was placed a piece of moist
filter-paper so large that its edges hung vertically downwards
as a flap beyond the margin of the disc. Thalli of various
Marchantiacez were placed in sand at the margin of the dise in
such a way that the young growing edge projected half a
centimetre beyond. ‘The dise and the object on it Were ex-
posed to daylight, but slowly rotated in a horizontal plane in
order to eliminate phototropic action. The young, positively
geotropic, rhizoids which developed beyond the margin of the
disc did not grow vertically downwards, but turned towards
the flap of moist filter-paper, thus proving that they are posi-
tively hydrotropic. ‘The same is doubtless true of the rhizoids
of ferns. do

3. Stems. — Very few studies seem to have been made upon
the hydrotropism of the stems of seedlings; the most impor-
tant are those of Moniscu. Several sets of experiments were
carried out upon seedlings of flax, pepper-grass (Lepidium
sativum), bean, Nicotiana camelina, etc. The method employed
was nearly that of WORTMANN (see below). Of these plants
the hypocotyls of the flax alone showed any hydrotropism ; it
may accordingly be concluded that stems are markedly hydro-
tropic in but few seedlings.

4. Pollen-Tubes. —The reactions to moisture of these organs
have been studied by Mryosur (’94). He placed pollen-grains
on the stigma of the same species and found that whereas in a
dark, moist chamber the pollen-tubes grew in all directions,
when dry air was admitted the pollen-tubes turned towards the
centre of the stigma. This turning is best explained as a
response to the greater moisture surrounding the mouth of the
stigma. It is clearly also an advantageous result, since it tends
to direct the pollen-tube to the ovary.

5. Hyphe of Fungi.— While Sacus (79) early suggested
that the sporangium bearer of Phycomyces nitens is negatively
hydrotropic, the first experimental evidence on this point was
offered by WORTMANN (’81).

Spores of Phycomyces were sown on bread kept in a moist chamber
whose walls were made opaque to prevent phototropism. When, after three
or four days, some of the sporangium-bearers had gained a height of one or
two centimetres all were bent to one side excepting one which protruded

§ 2] | HYDROTROPISM 359

through a small hole in the glass disc. Parallel to this hypha and close to
it was placed a piece of soaked card. After 4 to 6 hours the hypha turned
from the damp card; but when the card was dry no such turning occurred.

The extraordinary sensitiveness of the sporangium bearing
filaments of Phycomyces has been shown by the experiments of
ERRARA (93). He found that these organs turned toward
rusting iron, china-clay, agate (but not rock crystal), and sul-
phuric acid. He explained this result on the ground that
these substances absorb the moisture in their vicinity. Con-
sequently the hydrotropic filaments turn towards this rela-
tively dryer region. So sensitive, indeed, is this plant that it
may be used to detect a very slight difference in the hygro-
scopic properties of chemically related substances.

Not only do the hyphz of Phycomyces turn from moisture,
but, as MouiscH (’83) showed, those of Mucor stolonifer and
the relatively great trunk of the toadstool Coprinus velaris
respond in the same way. The spores are thereby carried
away from the moist situation.

In conclusion a word may be said concerning the cause of
hydrotropism. It is probable that two diverse phenomena are
confused under the term. One of these is seen when a multi-
cellular organ like the root of phanerogams is unequally
moistened on opposite sides; the moister side will lose water
less quickly than the other, or it may actually imbibe some.
Its cells will accordingly become more turgescent and the
whole moister side more convex. ‘This result is due to a
relatively direct, almost mechanical, cause; it simulates nega-
tive hydrotropism, but it is so different in kind from the true
phenomenon that it may be called false hydrotropism.

In the second class of cases we see multicellular organs, such
‘aS roots, becoming concave towards the slightly moister region,
or unicellular organs, such as rhizoids, pollen-tubes and hyphe™
—organs which cannot be supposed to become unequally tur-
gescent on the two sides — exhibiting a + or — turning.
These cases cannot be explained on direct mechanical grounds;
they are responses to stimuli, and, as such, examples of true
hydrotropism.

These two kinds of hydrotropism may occur in the same
organ under different conditions and thus cause turnings in

360 THE EFFECT OF WATER UPON GROWTH §[Cu. XII

opposite directions. Thus WoRTMANN (81, p. 374) finds that
a mycelium growing downwards towards water turns horizon-
tally before touching it and branches profusely. Similarly a
root growing towards water will not penetrate into it, but will
turn to one side. The greatly increased moisture causes the
reversal of the tropism, but this is probably due to the fact
that a false hydrotropism replaces the true response ; however,
as true hydrotaxis may take place in both directions, so there
may be a true negative as well as positive hydrotropism.

I now summarize our conclusions concerning the effect of
water upon growth. Water plays a part in growth second in
importance to no other agent, so that in its absence growth
cannot occur. As the quantity is increased, growth is increased
until an optimum is reached. ‘The amount imbibed does not,
however, depend directly upon the amount available, but rather
upon the needs or the habits of the species. Growth of elon-
gated organs may take place from or towards moisture, and the
turning may be a true response to the stimulus of higher or
lower aqueous tension, —a response which may show itself in
a bending at some distance behind the irritable tip. This
response is, moreover, often of an advantageous kind, directing
the rootlets towards water and the pollen-tube towards the
moist stigma or keeping the sporangium in the dry atmosphere
necessary for the production of dry spores. In a word, imbi-
bition of water and growth with reference to the source of
moisture are regulated to the advantage of the species.

LITERATURE

Darwin, C. ’80. The Power of Movement in Plants. London, 1880.
Darwin, F. ’93. On the Growth of the Fruit of Cucurbita. Ann. of Bot.
VII, 459-487. Pls. XXII, XXIII. Dec. 1893.

DETLEFSEN, E. ’82. Ueber die von Ch. Darwin behauptete Gehirnfunction
der Wurzelspitze. Arb. a. d. bot. Inst. Wiirzburg. II, 627-647.
DucHartTRE, P.’56. Influence de l’humidité sur la direction des racines.

Bull. Soc. bot. France. IIT, 583-691.
Errara, L. 93. On the Cause of Physiological Action at a Distance.
Rept. Brit. Ass. Adv. Sci. for 1892, 746, 747.

a LS le ee ee

‘
ea
.

LITERATURE 361

Gain, E. ’92. Influence de ’humidité sur la végétation. Compt. Rend.
CXYV, 890-892. 21 Noy. 1892.

795. Recherches sur la réle physiologique de l’eau dans la végétation.
Ann. Sci. Nat., Bot. (7), XX, 63-215. Pls. I-IV.

HorrMann, ’65. Beitrige zum Keimungsprocess. Landwirthsch. Versuchs-
Stat. VII, 47-54.

Jounson, H.’29. The Unsatisfactory Nature of the Theories proposed to
account for the Descent of the Radicles in the Germination of Seeds,
shewn by Experiments. Edinb. New Philos. Mag. VI, 312-317.

JUMELLE, H. ’89. Recherches physiologiques sur le développement des
plantes annuelles. Revue Générale de Bot. I, 101 et seq.

Knieut, F. A. ’11. On the Causes which influence the Direction of the
Growth of Roots. Phil. Trans. Roy. Soc. London. Pt. I; 209-219.

LzesaGe, P. 95. Recherches expérimentales sur la germination des spores
die Penicillium glaucum. Aun. Sci. Nat., Bot. (8), I, 309-322. Noy.
1895. ,

Mryosu1, M. ’94. Ueber Reizbewegungen der Pollenschlauche. Flora.
LXXVIII, 76-93.

Mouiscu, H. ’84. Untersuchungen iiber den Hydrotropismus. Sb. Wien.
Akad. LXXXVIII}, 897-942. Taf. I.

Reinke, J. 76. Untersuchungen iiber Wachsthum. Bot. Zig. XXXIV,
65-69, 91-95, 106-111, 113-134, 136-160, 169-171. Pls. IJ, III. Feb.,
Mar. 1876.

| Sacus, J.’72. Ablenkung der Wurzel von ihrer normalen Wachsthumsricht-

ung durch feuchte Korper. Arb. bot. Inst. Wiirzburg. I, 209-222.

79. Ueber Ausschliessung der geotropischen und heliotropischen Kriim-
mungen wiihrend des Wachsens. Arb. bot. Inst. zu Wiirzburg. II,
209-225.

TscuarLowi7z, F. C.’86. Untersuchungen iiber die Wirkung der klimat-
ischen Factoren auf das Wachsthum der Culturpflanzen. Forsch.
Agr. IX, 117-145. [Abstr. in Bot. Jahresber.] XIV, 57, 58.

WIeEsNeER, J.’81. Das Bewegungsvermégen der Pflanzen. 212 pp. Wien,
1881.

WortTMAnN, J.’81. Ein Beitrag zur Biologie der Mucorineen. Bot. Ztg.
XXXIX, 368-374, 383-387. June, 1881.

CHAPTER XIII

EFFECT OF THE DENSITY OF THE MEDIUM UPON
GROWTH

In this chapter we cannot, as hitherto, consider the effect
of density upon both the rate or quantity and the direction of
growth, for no studies seem to have been made upon the latter
subject.

§ 1. Errect or DENSITY UPON THE RATE OF GROWTH

We have seen in Chapter III (p. 77) that the increase or
decrease in the concentration of a solution produces, by osmosis,
changes in the structure of protoplasm, in its locomotion, and
in its excretory activity. It remains to be seen to what extent.
change in density can affect the metabolic activities concerned
in growth. |

The relation between the rate of growth of plants and con-
centration has been the subject of much study, e.g. by WIELER
(83), DEVRIES (77), JARIUS (86), JENTYS (788), ESCHEN-
HAGEN (789), and STANGE (92). It is agreed that, in general,
as the solution containing the plant becomes more concentrated
the seedling or the fungus (JENTYS, p. 455) grows more slowly.

The question now arises whether there is any maximum
concentration at which growth is completely inhibited. Data
on this subject are given by ESCHENHAGEN, who finds that
various fungi will not grow at a concentration above the
following limits :—

STARCH. GLYCERINE, Sopium NITRATE, Common SA.t.

CgH120¢- C3H,03. NaN0QOs3. NaCl.
Aspergillus... 53% 43%, 21% 17%
Penicillium... 55 43 21 18
Botrytis. .... 51 37 16 12

362

§ 1] EFFECT OF DENSITY UPON RATE OF GROWTH 363

Also RAcrBorRsKI (’96) found that Basidiobolus cultivated
in a nutritive solution containing 10% peptone, 1% glucose,
and the necessary salts, ceased to grow when the concentration
of the salts reached the following percents : —

sodium chloride, NaCl, 6%. glycerine, C,H,0,, 20%.
potassium chloride, KNO;,11%. glucose, C,H,,0,, 25%.

The foregoing maximum concentrations vary with the molec-
ular weights of the dissolved substances, indicating that their
effect is purely an osmotic one.

Germination is likewise affected by concentration, as a valu-
able series of experiments by VANDEVELDE (’97) clearly shows.

Seeds of the pea, Pisum sativum, were soaked for 24 hours in solutions
of common salt varying from 1% to 35%, then removed, planted, and the
percentage of seeds which germinated (G%) and the mean interval elapsing
before germination (I) determined. (I) was, more precisely, the time elaps-

ing (in days) before one half of the seeds had germinated. The results are
given as follows : —

TABLE XXXVIII

SHOWING THE RELATION BETWEEN THE CONCENTRATION OF THE SOLUTION IN
WHICH PEAS HAVE BEEN SOAKED AND THEIR GERMINATION

%|\| &% I %o G% % | G% I %o G% I

1 | 98.00 | 2:1 | 10 | 12.46 | 5.9 | 19 | 4.00 | 5.7 | 28 6.83 | 5.7
2 | 97.17 | 3.7 | 11 7.00 | 6.6 | 20 | 5.67 | 5.7 | 29 8.83 | 6.7
3 | 85.17 | 4.0 | 12 | 10.00 | 6.3 | 21 | 3.33 | 7.0 | 30 | 10.33 | 6.5
4 | 34.50 | 4.6 | 18 8.50 | 6.8 | 22 | 1.50 | 5.6 | 31 8.83 | 6.8:
5 | 32.66 | 4.8 | 14 7.19 | 6.3 | 23 | 1.838 | 6.2 | 32 | 10.67 | 7.2.
6 | 16.83 | 5.0 | 15 4.50 | 6.7 | 24 | 4.00 | 5.8 | 33 | 23.00 | 6.2
7 | 15.83 | 5.2 |] 16 6.83 | 7.1 | 25 | 0.83 | 5.8 | 34 | 31.33 | 6.5
8 | 14.83 | 5.3 | 17 4.76 | 6.6 | 26 | 4.50 | 6.3 | 35 | 56.83 | 7.0
9 | 12.66 | 5.4 | 18 3.383 | 6.2 | 27 | 8.17 | 6.8

This table yields some remarkable results. As the concen-
tration increases from 1% to 15%, the percentage of germina-
tions diminishes from 98 to 4.5, and the mean germination
interval increases from 2.1 days to nearly 7, near which point
it remains at all higher concentrations. From 15% to 29% the
percentage of germinations fluctuates so irregularly between
6.8 and 0.83 that within these limits it may be considered con-

364 EFFECT OF DENSITY OF THE MEDIUM [Cu. XIII

stant. As the concentration increases from 29%, instead of
the grains all being killed or failing to germinate, we have the
interesting result that the percentage of germinating individ-
uals rises rapidly from 4 to 56. WANDEVELDE hazards the
following explanation of this result: ‘Dilute solutions are
easily absorbed; the more concentrated the solution, the
smaller the power of diffusion; in a saturated solution the
seeds do not swell and the action of the surrounding solution

is less injurious.” But we need to know more of the condi- -

tions under which this result occurs before we can accept any
interpretation.

With animals we find growth similarly affected as with
plants. Lor (92) first showed this in his experiments upon
the regenerative growth of decapitated tubularian hydroids.
The regenerating hydroids were kept in water more and less
‘dense than, and equally dense with, sea water. At the end of
eight days the length of the regenerated piece was measured in
seven to nine individuals at each concentration. The results
may be given in the form of a curve (Fig. 98) by laying off as
abscisse the percents of sodium chloride in the water and as
ordinates the corresponding average growth in millimetres : —

- NORMAL SEA WATER

*)
T T “Tr + + . + ——f

1 ne 2 3 4 5 6
DILUTE SEA WATER ’ CONCENTRATED SEA WATER

or

Fig. 98.— Curve showing the relation between the density of the medium and the
proportional rate of growth of regenerating Tubularia. The maximum ordinate
indicates 10.5 mm. growth in 8 days. ‘ The numbers at the base of the curve are
per cents of density in excess of distilled water; thus “3” signifies a specific
gravity of 1.03. (From Logs, ’92.)

This curve shows that the optimum concentration for growth
is not, as might have been expected, the normal concentration,
but one considerably below the normal, namely 2.5% instead

UPON THE RATE OF GROWTH 365

§ 1]
of 3.8%. Anything which favors endosmosis seems, within
certain limits, to favor growth. .«

Regenerating annelids have also been studied at my labora-
tory by Mr. J. L. FRazEur. A large number of worms of a
species of Nais, all of approximately the same size, were cut into
two parts. Of these the anterior, consisting of twelve seg-
ments, was alone preserved for experimentation, and was placed
in water either pure or containing a variable amount of com-
mon salt in solution. At the end of ten days the anterior
piece had regenerated at its tail end a certain number of seg-
ments varying with the strength of the solution as shown in
the following :—

TABLE XXXIX

SHOWING THE AVERAGE NUMBER OF SEGMENTS OF NAIS REGENERATED PER Day
In Various Soitutions or Sopium CHLORIDE

Ave. No. or Ave. No. or
No. or | SEGMENTS No. or SEGMENTS
SoLurTion. SoLuTion,
INDIVIDUALS, | REGENERATED INDIVIDUALS. | REGENERATED
PER Day. PER Day.
Water 15 2.13 0.250% ¢ 1.19
0.125 % 5 1.72 0.375 5 1.18
0.188 16 1.42 0.500 © 5 1.14

The decrease in the number of regenerated segments was
thus, with increasing concentration, at first rapid, then slow.

Fission, which is so closely bound up with growth that we
may treat it as an index of growth, is also controlled by the
concentration of the medium. Mr. P. E. SARGENT has, at my
suggestion, studied this subject in the naid Dero vaga. This
species divides so rapidly that ordinarily it doubles its numbers
every ten days. The worms were kept in solutions of varying
concentration of various salts. ‘They were reared in similar
jars, supplied with similar food,* and kept under otherwise
similar conditions. A definite number of worms having been
put in each jar, the increment at the end of ten days was deter-

* 1 to 2 cc. of corn meal extract was added every day to the 200 cc. of water
in which the worms were living.

EFFECT OF DENSITY OF THE MEDIUM

366 (Cu. XI

mined by counting. The results of some of these countings are
given below for a number of salts : —:

TABLE XL

AVERAGE IncrEAsE Per Cent or InpivipuALs OF DERO VAGA REPRODUCING,
DURING TEN Days, IN SoLuTIONS OF DIFFERENT SALTS aT VaryinG Con-

CENTRATIONS. MINUS QUANTITIES INDICATE DiIMINUTION IN NUMBER OF
INDIVIDUALS
a Y a E =
a a a a a
STRENGTH oF Sotu- | 4 4 Ras 4 Ras
TION. Bibs cake} Bl ik ee tala see
S S Ae ee ee ee ae mn tee “as beh ib =
A A A a 4 'S) A a A 4
Mo ec. WriGuts, 58.5 120 111 95 74.6
Control: water | 787 | 1138:0%] 75] 134.0%
0.05 % 100 | 835.2 |50} 22.0 | 50 40% | 25) 12%|50;) 12%
0.10 350 | 77.0 |75)—106 |50|} —12 50.|—64
0.15 100 | 58.0 |75|/— 26 |25| —36 |25|/—28 | 25|/—92
0.20 550 | 40.8 | 75|)—35.3 |50/} —58 | 25|—68
0.25 100 | 21.5 |75|—65.5 |25| —72
0.30 350 3.2 |75|—84.0 |25| —84
0.35 25 |—24.0 25| —92
0.40 375 |—18.1 25 | —100
0.50 150 |—35.0

These columns, and especially the first one, show a close
relation between concentration and growth (as tested by mul-
tiplication of individuals). They show also that the diminished
growth falls off rapidly at first with slight increments of con-
centration, then less slowly at the higher grades (Fig. 99).
Finally they show that different salts have diverse osmotic
effects, for sodium chloride is less retarding than any other
salt at the same percentage of concentration. The effect of
the remaining salts is seen to increase as the molecular weight
diminishes, and therefore the osmotic effect increases (Fig. 99).
The fact that magnesium sulphate dissociates at these weak
concentrations only about two-thirds as much as calcium chlo-
ride does, would lead us to expect even a relatively smaller
effect as compared with calcium chloride than we find (see
p- 74, note); perhaps further experimentation would give facts

— oe a

§ 1) UPON THE RATE OF GROWTH 367

agreeing closer with theory. On the whole, Table XL indi-
cates that it is the osmotic effect which retards growth.

In tadpoles a similar retarding effect of solutions has been
observed by YUNG (85), who made solutions of 0, 2, 4, 6, and
8 grammes of sea salt in
1000 grammes of water, ™
and reared frog’s embryos = 10
in them. Otherconditions 100
excepting concentration 90
were believed to be alike 80 | \
in all experiments. In the 70 | \
0.2% solution the tadpoles
developed at nearly the
same rate as in pure water.
In the denser solutions
there was a retardation in
development. which in-
creased with the density
of the solution, so that in
the 0.8% solution the lar- ~°J
ve hatched out seventeen ~*?

CEETT

ee

Co
Zz
ie

Wa

: i
fi
A

\ N

days behind the normal ~—3% \\
time. iil a E- \\

The effect of a sudden -30;}—} Se)
change in the density of -0 aN
the solution has been es- = _1 ae ia
pecially studied by TRUE § ~49 . EAN
(95). Beans, Vicia faba, _,, ‘ : ‘
which had radicles from _,,, XN
17 to 35 mm. long, were
placed directly in the solu- 0 .05 10 15 .20 .25 .30 .35 .40 .45 .50

tions and held there so that Fig. 99.— Curves of average increase per cent

the cotyledons alone were of individuals (ordinates) of Dero vaga re-

ee : producing, during 10 days, in solutions of
ee. The cultures were different salts, whose strengths are laid

kept in the dark. When off as abscisse. The data are taken from
the transfer was made sud- Table XL.

denly to a 1% solution of
potassium nitrate, it was observed that a mechanical contraction
occurred, followed by a more or less prolonged period of retar-

368 EFFECT OF DENSITY OF THE MEDIUM [Cu. XIII

dation in the rate of growth. When, on the other hand, the
plant was transferred from a salt solution to which it had
become accustomed to pure water, a mechanical elongation
quickly occurred, but this too was followed by a retardation in
the rate of growth. Thus the reduction in the rate of growth
is not a mechanical result of change of medium, but is a
response to the stimulus of changed environment.

We have hitherto considered almost exclusively the effect of

aqueous solutions. We must now consider how a variation in
the pressure of the atmosphere affects the growth of plants.
Upon this subject experiments have been made by JACCARD
(°93), who found that when the pressure of the air was reduced
from 78 cm. to between 10 cm. and 40 cm. of mercury, growth
is two or three or even six times as rapid as in ordinary air.
Likewise when the air is compressed to between three and six
atmospheres acceleration in growth occurs, although not to the
same extent as in the depressed air. If, however, the rarefac-
tion is very great (below 10 cm.) or the pressure excessive
(over 8 atmospheres), growth is retarded. Experiments indi-
cate that this result is not wholly due to the concentration of
the oxygen in the air. We may therefore conclude that a

change in pressure from the normal accelerates growth by |

irritating the growing plasma up to a certain limit, beyond
which its injurious effects counterbalance its favorable ones.
Summing up this account of the effect of concentrated solu-
tions upon the growth of organisms, we find that in general as
the density increases beyond the normal’ the rate of growth
diminishes until, at a certain concentration, it ceases. In the
particular case of marine organisms a reduction in concentration
to a certain point causes excess of growth; below that point,
diminution. It is probable that the diminution in growth is
proportional to the osmotic action of the medium (Chapter ITI).
An explanation of the foregoing phenomena may be attained
by reference to the principles laid down in preceding chapters.
In Chapter X it has been shown that growth depends very
largely upon the specific imbibition of water. We do not
know the cause of the difference in imbibitory properties at
different times; but if, as has been suggested, it is purely an
endosmotic phenomenon resulting from the secretion of plant

ee eS ee eee ‘topes

§ 1) UPON THE RATE OF GROWTH 369

acids or salts in the cell sap, then we can understand how a
denser medium should diminish or destroy the imbibitory
tendency. On the other hand, a change in concentration may
act in a more indirect fashion to cause increased growth ;
namely, by calling forth a response to the irritation of changed
conditions of pressure.

LITERATURE

EscHENHAGEN, F. 89. , Ueber den Einfluss von Lésungen verschiedener
Concentration auf das Wachsthum von Schimmelpilze. Stolp, 1889.

JACCARD, P. 93. Influence de la pression des gaz sur le développement des
végétaux. Comp. Rend. CXVI, 830-833. 17 April, 1893.

Jarius, M. ’86. Ueber die Einwirkung an Salzlésungen auf den Keimungs-
process der Samen einiger einheimischer Culturgewiichse. Landwirths-
schaft. Versuchs-Stat. XXXII, 149-178. Taf. IT.

JenTys, S. 88. Ueber den Einfluss hoher Sauerstoffpressungen auf das
Wachsthum der Pflanzen. Unters. a. d. bot. Inst. Tiibingen. II,
419-464.

Logs, J. 92. (See Chapter X, Literature.)

Racrporski, M. 96. Ueber den Einfluss iusserer Bedingungen auf die
Wachsthumsweise des Basidiobolus ranarum. Flora. LXXXIII,
110-115.

Sranece, B. 92. Beziehungen zwischen Substratconcentration, Turgor und
Wachsthum bei einigen phanerogamen Pflanzen. Bot. Ztg. L, 253
et seq.

True, R. H.’95. On the Influence of Sudden Changes of Turgor and of
Temperature on Growth. Ann. of Bot. IX, 365-402. Sept. 1895.

VANDEVELDE, A. J. J. 97. Ueber den Einfluss des chemischen Reagentien
und des Lichtes auf die Keimung derSamen. Bot. Centralbl. LXIX,
337-342. 11 March, 1897.

DE Vries, H. 77. Ueber die Ausdehung wachsenden Pflanzen-zellen durch

; ihren Turgor. Bot. Ztg. XXXYV, 1-10.

Wre.eEr, A. 83. Die Beeinfliissung des Wachsens durch verminderte Par-
tiarpressung des Sauerstoffs. Unters. a. d. Bot. Inst. Tiibingen. I,
189-232.

Yune, E. ’85. De l’influence des variations du milieu physico-chimique sur
le développement des animaux. Arch. des Sci. Phys. et Nat. XIV,
502-522. 15 Dec. 1885.

2B

CHAPTER XIV
EFFECT OF MOLAR AGENTS UPON GROWTH

It is proposed in this chapter to consider, first, the effect of
contact; rough movements, deformations, and associated molar
agents upon the rate of growth, and, secondly, the effect of
such agents upon the direction of growth.

§ 1. Errect or MoLAR AGENTS UPON THE RATE OF
GROWTH

We have already (Chapter IV) seen that profound changes
in metabolism and the motion of protoplasm are induced by
various sorts of contact. We shall here consider how those
changes result in modifications of growth.

1. Contact.—In the case of organs which normally grow
upon a solid substratum the growth may take place more
rapidly after coming in contact than before. Thus Logs (91,
p. 29) says of the stolons of the hydroid Aglaophenia pluma,
that when they reach a solid surface they begin to grow
more rapidly than stolons which develop free in the water.
Evidently the stimulus of contact excites to extraordinary
growth.

2. Rough Movements.— Experiments with this agent have
been almost confined to bacteria, and have been made by shak-
ing. The first experimenter in this direction was HoRVATH
(78), whose method of work is worth giving in some detail.

Glass tubes about 20 cm. long and 2 cm. wide were half filled by a nutri-
tive fluid, inoculated with an infusion full of various bacteria, and sealed.
The tubes were then fixed on a board which was made to swing horizontally
to and fro by means of a motor through an are of about 25 em. length at
‘the rate of 100 to 110 times per minute. At the end of each excursion the
board received, by means of a special device, an extra blow. ‘The resulting
agitation was like that made in shaking a test-tube.

370

Ce

~v re Se Oe —_—

a

i

ar

$1) EFFECT OF MOLAR AGENTS UPON GROWTH 371

The results of HoRVATH’s experiments were these. Tubes
which were shaken for 24 hours were clear at the end of that
period, while similar tubes kept at rest had become muddy
with bacteria in the same time. If, now, the shaken tubes
were kept at rest during a day in a warm oven, they, too,
produced a rich growth of bacteria. When, however, the tubes
had been shaken for 48 hours they not only were found clear,
but they did not become cloudy upon subsequent warming
(1, p. 99). The shaking during the briefer period had thus
merely interfered with the normal growth processes, but the
more prolonged shaking had resulted in the death of the
bacteria.

Subsequent attempts by other workers to reproduce these
results, by the use, however, of other methods, partially or
completely failed. REINKE (80), indeed, found that in water
agitated for 24 hours bacteria had ceased to grow, but had not
been killed; in so far a confirmation of HorvatH. Other
investigators, however (BUCHNER, ’80; TuMAs, ’81; LEONE,
°85; Scumipt, *91; RussELL, 92; and others), have either
obtained no effect upon the growth of bacteria, or have found
it increased by motion. The results seemed hopelessly dis-
cordant.

The more recent work of MELTZER (94) has, however,
brought these conflicting observations under one general law,
and has thus offered an interpretation of the varied results.
He pointed out first that the diverse results of previous investi-
gators were due to the use of different species of bacteria and
of different kinds and degrees of shaking; in a word, to dis-
similar methods. MELTZER employed pure cultures of bacteria
of ascertained species, and counted the colonies by the well-
known bacteriological methods. Shaking was either violent,
being done in a machine somewhat like HorvAtnH’s; or slight,
being done by hand. The media used were neutral salt solu-
tions, Kocn’s bouillon, or pure water. The results showed
that a slight shaking is advantageous to the metabolism of
Bacterium ruber in water. Thus, while a culture containing
950 colonies, left quiet, was reduced after 8 days to 259
colonies; shaken, it had at the end of the same period 1366
colonies ; and shaken with glass drops rolling loose in the tube,

372 EFFECT OF MOLAR AGENTS [Cu. XIV

it had attained 16,200 colonies. When, however, the shaking
was longer continued the number of colonies began to fall off,
so that after 21 days the medium shaken with glass drops
exhibited only 5 colonies. ‘These facts enable us to distinguish
a minimum degree of movement which will permit of growth
(shaking for 6 days without glass drops); an optimum
(shaking for 8 days with glass drops); and a maximum (shak-
ing for 21 days with glass drops). The optimum is very
diverse in different species. ‘Thus in Bacterium megaterium it
is so low that shaking for a little over 1.5 days results fatally.
It is probable that the growth of every race of bacteria is
attuned to a particular optimum of movement.*

3. Deformation.— Under this head we may consider the
effects of pulling and bending upon the growth of an elongated
body. Data upon this subject have been obtained only from
plants.

The effect of pulling upon the growth in length of a plant
stem has been studied by BARANETZKY (79), SCHOLTZ (87),
and HEGLER (93). The results obtained are concordant and
-important. It appears that when a weight is attached, by
means of a cord running over a pulley, to the. epicotyl of
various seedlings—such as Helianthus, Tropzolum, Cannabis,
Linum, etc.,—the growth in length of the stem is, under
appropriate conditions, not accelerated but retarded. When,
for example, a pull of 13 grammes is exerted upon the epicotyl

* Concerning the cause of the increase of growth accompanying a slight molar
disturbance and the diminished growth and death accompanying a violent one,
MELTZER has something to say. He finds in those cultures in which no growth
of bacteria occurs, no fragment of cells but on the contrary nothing except a fine
‘‘dust ’? — the bacteria have experienced a molecular disintegration. In order
to explain this disintegration, Mrettrzer accepts NAGE I’s conception of the
structure of protoplasm, — micelle enveloped by water, — and supposes that a
molar disturbance modifies the normal movements of these micelle. A very
violent movement causes the micelle to separate completely ; a much less tur-
bulent movement causes an increase in the vibrations of the micelle by which
they are brought into more intimate contact with food material including
oxygen, and more easily get rid of the metabolic products. Without accepting
NAGELI’s micellar hypothesis, we may account for the beneficial effects of slight
movement upon the ground of an increased supply of oxygen afforded by it;
and we may regard the fatal effect as the result of disturbed metabolism or of
protoplasmic disintegration.

§ 1) UPON THE RATE OF GROWTH 373

of a Cannabis seedling there is a momentary elongation followed
for six hours by no growth whatever; then periods of growth
alternating with periods of retardation occur until, after
perhaps 24 hours, the hourly growth is nearly equal to that
of the unweighted plant. The least weight which will cause a
retardation is different for different plants. In the case of
Cannabis and Linum it is below 1.3 grammes, a result which
indicates that the weight of the index used in self-recording
auxanometers is sufficient to retard the growth of the plant and
thus to give an abnormal growth curve.

The diminution of growth is not the same at all periods of
the plant’s development. Thus the retarding effect is greatest
at the commencement of the grand period of growth, but begins _
quickly to diminish until at the maximum of growth there is
no retarding effect. Then, as the rate of growth decreases, the
retardation becomes more evident. The effect of the pull is
best seen in comparing the curves of daily fluctuation of growth
of the weighted and unweighted plants. The early morning is
the period of rapid growth, and at this time the growth of the
stretched plant is quite equal to or exceeds that of the un-

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Fic. 100. — Curves of hourly growth, measured in hundredths of a millimetre, — ver-
tical scale at the left. The full line gives the course of growth of a Cannabis seed-
ling subjected to a pull of 13 grammes. The dotted line gives, for comparison,
the course of nearly normal growth, the plant being subjected to a pull of only
3 grammes. The numbers at the bottom indicate hours of the day; the broken
line at the bottom indicates night-time. (From HEGLEr, ’93.)

weighted one. During the early night, on the contrary, when
growth is feeble, the stretched stem grows slowly (Fig. 100).
If an etiolated plant is used, the daily growth fluctuations are
eliminated and the effect of the larger growth cycle becomes

374 EFFECT OF MOLAR AGENTS [Cu. XIV

evident. Thus, in general, the more rapid the growth, the less
is the retardation provoked by pulling.

The direction in which we must look for an explanation of
these facts is indicated by the circumstance that, in the most
rapid period, growth is chiefly due to imbibition of water, while
in the preceding and succeeding periods it is due more to an
increase in the plasma. Thus not all kinds of growth are
equally affected by the irritation of pulling, but principally that
growth which is due to assimilation. Further insight into this
matter is gained from the circumstance that despite the fact
that growth is slower in the plant under tension the tur-
gescence in the stretching zone is greater in such a plant than
.ina normal one. This indicates again that it is not the imbib-
itory process which is interfered with but rather the assimila-
tive one. All these facts thus lead to one conclusion, that,
under tension, the plasma, especially that of the cell-wall,
grows in length less rapidly than under normal circumstances.
This diminution of growth can hardly be explained in a direct
mechanical way; we must consider it a response to the
stimulus of pulling.

A confirmation of this conclusion is found in the fact that
the effect of the pulling gradually wears off. Thus when one
of a pair of seedlings of Cannabis sativa is subjected to a pull
of 20 grammes, there is a retardation during the first day of
61% in the stretched plant as compared with the control plant;
during the second day of 51%; during the third day of only
9%. (HxEeLER, 93, p. 389.) In order that the retardation
should continue, additional weight must be imposed; then an
increased retardation occurs. ‘Thus in one case HEGLER sub-
jected one of two Helianthus seedlings to a pull of 50 grammes.
During the first day the retardation of the pulled plant was
20% ; during the second there was an excess of growth over
the control of 17%; then 150 grammes were added; on the
third day the retardation was 18%; on the fourth there was
an acceleration of 2%. This series of phenomena is clearly
like that which we have observed in locomotion — there is an
accommodation of the growing protoplasm to the stimulus.

There can be little doubt that in the cases of diminished
growth in length there is a thickening of the cell-walls and

§ 1] UPON THE RATE OF GROWTH non

probably an increase in cross-section of the whole stem. There
is indeed considerable experimental evidence for this con-
clusion. Thus ScHENCK (793) found that when stems are
irritated by twisting or bending, an excessive growth both
of cell-walls and of the wood as a whole follows. So, too,
NEWCOMBE (795) finds that roots become strengthened by
attaching weights to them. In fact, if stems are deprived of
their normal swaying movements, for instance by enclosing
internodes in plaster casts which inhibit lateral movements and
partly support the weight of the superior part of the plant,
their walls remain abnormally thin.

These effects of deformation are of especial importance
because they are so clearly not at all directly mechanical but
adaptive; they are, indeed, rather opposed to the direct
mechanical effects which would tend to stretch the cells, and
thus to diminish the thickness of their walls. Here again the
organism shows itself a highly irritable thing, capable of
responding in an adaptive fashion.

4. Local Removal of Tissue. — When a protist, for instance
a Stentor, is transsected, certain changes take plaee along the
cut surface. First, there is a warping of the edges towards
each other; secondly, rapid growth (differential growth, page
287) occurs. Similarly, if a Hydra be cut lengthwise, the free
edges may fold towards each other so as to form a smaller cyl-
inder, and the seam, by growth, will be healed over. So, too,
in the higher animals, the removal of a bit of tissue results usu-
ally in the closure of the wound and growth to fill the gap.
We may call these two processes warping and regenerative
growth.

The causes of these two processes are probably different.
The warping seems to result from the presence of tensions and
pressures in the tissues whose equilibrium is disturbed by the
cut. This process is probably grossly mechanical. The regen-
erative growth, however, must: have a less direct explanation.
It is apparently a typical response to the stimulus of cutting,
or of the new environment presented at the cut edge.

Here, too, may be mentioned an experiment by Lors (92,
p- 51), which throws light upon the cause of these internal
tensions. Below the crown of tentacles of a Cerianthus a

376 EFFECT OF MOLAR AGENTS UPON GROWTH ([Cu. XIV

horizontal slit was made in the side of the body-wall. The
tentacles over the slit contracted — there was a sort of negative
growth. The shortening was doubtless due,
as LOEB says, to the loss of water and con-
sequently of turgescence in this part of the
body-wall (Fig. 101). I have cut the body-
wall of a hydroid immediately below an
incipient bud, whereupon the bud at once
flattened out. These experiments show
how important water pressure is for the
maintenance of the size of the body and for
growth, and in so far explain the mechanical
effect of a cut or other similar wound.

tay § 2. EFFECT OF CONTACT UPON THE DIREC-
Fic. 101. — Cerianthus, - TION OF GROWTH — THIGMOTROPISM
from which a piece, :
a, b, c, has been cut, Having seen that molar agents can affect
causing a loss of tur-

the rate of growth, we are in a position to

gescence and conse- ;

quent shrinking of understand how a molar agent, acting upon

tentacles on thecut one side only of an elongated organ or

side. (From LOEB, ‘ ;

199.) plate of tissue, may induce a less or

greater growth upon that side, and, con-

sequently, a bending towards or from it. This turning
phenomenon may now be considered. Before taking up the
permanent growth turnings, however, we may consider a case of
transitory growth, which throws valuable light upon the true
nature of thigmotropism, and serves to connect it with thigmo-
taxis. This is the case of the pseudopodia of Orbitolites,
which, according to VERWORN (’95, p. 429), float at first free
in the water after being protruded through holes in the shell;
but as soon as they grow longer and heavier they sink in the
water, until their distal ends touch the substratum. ‘To this
they become attached by a delicate secretion, and grow out
along it by the streaming of the protoplasm. ‘The persistent
clinging to the substratum is a thigmotropic reaction, and one
which belongs clearly to the category of response.

1. Twining Stems.— The characteristic form of twining
plants, like the bean, has long excited the interest of natural-

ars <7

§ 2] THIGMOTROPISM 377

ists. A study of the cause of this form was made by PALM
(27), by Mont (27), and by Durrocuet (743, 44); and
from this early period to the present there have existed on this
matter great differences of opinion. On the one hand, there
has been maintained a view that had great inherent probability,
the view, namely, that the twining of plants is a response to
the contact-stimulus of the object about which they are coiled.
Against the general validity of this view certain experiments
of DARWIN (’82, p. 16) seem conclusive. For he found that
even the hard rubbing of the stalk caused no modification of
the normal spiral growth. Accordingly, the conclusion seems
generally accepted to-day that the peculiar form of growth of
most twining plants is the combined result of geotropism, by
which the stem grows upwards, and a special form of nutation,
by which it impinges against the supporting stick and bends
round it. The twining is thus mechanical, — depending upon
the structure of the stem,— rather than responsive.

An exception among twining plants is found in the dodder,
Cuscuta. This plant is a parasite, belonging to the Convol-
vulus family, and lives upon the flax and other plants. ‘It is
leafless, and twines closely about its host, into which it sends
the feeding organs—the haustoria. According to the careful
studies of PerrcE (’94), the stem, when not in contact with
any solid body, makes long, steep turns about the axis of the
spiral, as is the case with other twiners. If now the free stem,
during a period of slow growth, be brought into contact with a
wooden or glass rod or a thread at about 3 cm. from the tip, the
stem bends sharply, and in the course of 15 hours makes two
or three close turns around the vertical support. If the con-
tact be made at a distance of only about 1 cm. below the tip,
there will be little or no change in the character of the twining.
If the point of contact be too far below the tip,—6 to 7 cm.,—
there will also be no effect. The result is thus clearly depend-
ent upon a stimulus applied at a definite sensitive point; it is
a typical response.

2. Tendrils. — Very similar to the phenomena of close twin-
ing in Cuscuta is that of coiling in the tendrils of phanero-
gams—those most marvellously sensitive of all plant struct-
ures. DARWIN (’82) and PFEFFER (’85), particularly, have

3878 EFFECT OF MOLAR AGENTS UPON GROWTH [Cu. XIV

studied by experimental methods the movements of these
organs. The conditions which induce the twining of tendrils
are peculiar. It appears that tendrils are not irritated .by
mechanical shaking, such as is produced by a powerful current
of air issuing from a narrow tube; nor by a drop or strong cur-
rent of water, provided it contains no hard particles; nor even
by a stream of mercury, or the surface of pure mercury or oil.
All solid bodies, however, with the exception of moist gelatine,
when rubbed against the stem stimulate it so as to produce a
bending at the irritated point.

The behavior of moist gelatine is instructive. PFEFFER
first observed that it was exceptional, and PrrrcE has found
the same exception to hold for Cuscuta. PrFEFFER’s experi-
ments showed that, no matter how great the pressure or
strokes made by drops of 5 to 14% gelatine, or by glass rods
covered by a layer of moist gelatine, no response occurred ;
and PEIRCE (’94, p. 66) found that when the Cuscuta stem
came in contact with a rod covered with wet gelatine it made
only the long, steep turns characteristic of the free-growing
stem. Later, when it reached the part of the rod not covered
with gelatine, it formed at once a close, tight coil. That it is
not the chemical composition of gelatine which prevents the
twining is shown by the fact that dry gelatine, even to 25%,
irritates ; also, if some sand is mingled with the moist gelatine,
tropism occurs. The fact that wet gelatine does not irritate is
explained by PFEFFER upon the ground that the stimulus is
not given by mere contact, for a blow does not produce it. A |
certain degree of adhesion between the tendrils and the irritat-
ing substance is necessary. The moist surface of the gelatine
prevents such adhesion taking place. The effective irritation
is a sort of tickling.

The degree of this tickling may, however, be extremely
slight. Thus PFEFFER (85, p. 506) placed a rider of cotton
thread, weighing 0.00025 milligramme, on a tendril, and
found that no effect was produced so long as it was quiet;
whereas, when the rider was put in motion by a current of air,
a considerable bending occurred. Under similar conditions, a
thread weighing 0.00012 milligramme produced no reaction.
MacDoueGat (96, p. 376) finds that a spider’s web, 43 cm.

§ 2] THIGMOTROPISM 379

long, suspended above a tendril of Echinocystis, caused such a
reaction that the tendril coiled around and fastened to it.

Concerning the irritable region, it appears that in most ten-
drils there is an especially sensitive side and an especially
sensitive zone. ‘The presence of a more irritable side is not a
constant character of all tendrils, however. Thus, Cobza
scandens, Cissus discolor, and others, are irritable on all sides.
When a differentiation in this respect occurs, however, a bend-
ing takes place towards the more irritable side. The sensitive
zone lies either at the tip or immediately below.*

The period of development at which the tendril is most irri-
table must also be considered. Thus, DARwrn (’82, p. 174)
says: ‘“ Tendrils which are only three-fourths grown, and, per-
haps, even at an earlier age, but not whilst extremely young,
have the power of revolving and grasping any object which
they may touch. These two capacities . . . both fail when
the tendril is full grown.” PFEFFER (785, p. 485) and MUz-
LER (786, p. 104) likewise find tendrils irritable only in the
latter part of their growth-period.+

There are four periods in the response to a momentary
stimulus: (1) a latent period elapsing before the curvature
begins to take place; (2) a period of bending; (3) a period of
quiescence in the bent condition ; and, finally, (4) a period of

y, Sai pe

> er

1 2 3 4

Fic. 102.— Curve of contraction of a tendril. The distance of the curve from the
base represents the amount of displacement of the tip; one unit on the base-line
represents five minutes of time; 1 to 2, latent period and period of contraction;
2 to 3, period of maintenance; 3 to 4, period of relaxation. (From MacDouGa.,
95.)

* In Cuscuta, according to Peirce (’94, p. 64), the tip is non-irritable; the
most sensitive zone is 3 cm. below the tip.

t In Cuseuta, Perrce (94, pp. 63, 64) found that neither the stalk of seed-
lings nor of older plants, during the period of rapid growth which follows the
formation of haustoria, are sensitive. Irritability shows itself only when
growth becomes less rapid, as it does some time after forming haustoria.

380 EFFECT OF MOLAR AGENTS UPON GROWTH ([Cu. XIV

straightening again. These periods are represented graphically
in Fig. 102. The latent period is of variable length in differ-
ent species. Perhaps the shortest period is that of Cyclan-
thera, which MULLER (’86, p. 103) found to vary in the most
sensitive condition of the plant from 5 to 9 seconds. DARWIN
(°82, p. 172) found a latent period in Passiflora tendrils of 25
to 30 seconds, while in other cases (Dicentra smilax, Ampe-
lopsis) this period may be 30 to 90 minutes or more in length.
The entire time required for the plant to straighten completely
again is, according to MULLER (86, p. 104), for Cyclanthera
about 20 minutes. ‘These times depend, however, to a large
extent upon various external agents. ‘Thus a quick response
is favored by a temperature between 17° and 33° C:, sunlight
rather than shade, considerable humidity, and small size of ten-
dril. Thus this growth response resembles, in its dependence
upon various conditions, other responses, e.g. those of muscle,
to stimuli.

8. Roots. — Thigmotropism in roots was apparently first
investigated by Sacus (’78, pp. 437-439). He fastened ger-
minating seeds of various species in a moist chamber so that
their radicles, of about 10 to 30 mm. length, were horizontal.
A pin was now placed against the root near its tip so as to
exert considerable pressure. Usually within eight or ten
hours a turning of the root in the growing region occurred so
that it became concave towards the pin and finally made a
complete loop about it, or, if the needle was vertical, descended
along it in a spiral —a result of the double action of thigmo-
tropism and geotropism. This response was, however, rather
inconstant and appeared not to be very powerful.

The sense of the thigmotropic response was, in the foregoing —
example, positive; that is, the turning was towards the solid
body. DARwIN (81, p. 181) believed that he had evidence
that the response is sometimes negative. ‘Thus he says that
the radicle of a germinating bean, coming in contact with a
sheet of extremely thin tinfoil (0.003 to 0.02 mm. in thick-
ness), was in one experiment deflected without making a groove
upon it ; also, when a piece of paper was gummed to the root
near the tip, the root usually turned so that it became convex
to the gummed paper. But DARwIN’s conclusion has not been

eee SS —EeEeeeeelrrl ee Oe eee eee lel,

LO Ee

§ 2] THIGMOTROPISM 88]

sustained by later work. Thus DETLEFSEN (’82) found that
bean radicles plunged right through tinfoil 0.0074 mm. in
thickness, and WIESNER (’84) and SPAULDING (’94) have shown
that the turning from the gummed paper is the result of the
injurious action of the gum. Indeed, it is difficult to see how a
root, which must force its way through the earth, should turn
from a solid surface. Experience shows rather that it turns
towards it and tends to grow along it or through it.

4. Cryptogams. — Among Fungi a thigmotropic response has
been observed and studied in the mold Phycomyces nitens by
ERRARA (784) and WORTMANN (787). They find that rub-
bing the sporangiferous hypha lightly with a bristle or glass
thread for from three to six minutes will produce a response
more powerful even than that to light. As with tendrils, 7%

to 14% gelatine, almond oil, and water drops provoke no bend-_ .

ing; but, on the other hand, even the mutual rubbing of two
adjacent sporangiferous hyphe may incite a response. The
response will, however, appear only when the growing region
of the hypha is irritated ; if the hypha is fully grown, no thig-
motropism will take place. The sharpest part of the bend will
occur at the region of greatest growth, not necessarily at the
point of contact. However, WORTMANN finds that the turn-
ing commences at the point of contact, but becomes more and
more pronounced as the bend approaches the most rapidly
growing part of the hypha. ‘The response to a brief contact
is only tehporary. Thus when a sporangiferous hypha 2.3 cm.
long was touched for one minute with a glass thread a bending
began to appear after 15 minutes and disappeared 10 minutes
later. Thus Phycomyces follows closely the laws of response
of tendrils.

The rhizoids of the hepatic Marchantia and its allies have
been found by MouiscuH (’84, p. 933) to behave in a similar
way to the foregoing. When the hepatics are placed on damp
filter-paper, over a watch-glass, in a moist chamber and in the
light, one finds after 48 hours that rhizoids have penetrated
through the filter-paper. Since the paper reveals, even to the
microscope, no pores, and since grains of corn starch, of from 2
to 24 microns diameter, will not pass through it, we must con-
clude that the root hairs of 10 to 25 microns diameter, although

382 EFFECT OF MOLAR AGENTS UPON GROWTH ([Cu. XIV

consisting of only a single cell, have the power of forcibly
boring their way between the fibres of the paper. This phe-
nomenon is most easily accounted for on the ground of response
to contact.

5. Animals. — The phenomenon of thigmotropism is exhib-
ited among animals in the power of growing along an irregular
substratum. Thus the stolons of hydroids, Bryozoa, and some
compound ascidians, upon once gaining the surface of an appro-
priate substratum, cling closely to it without reference to the
direction, up or down, which the substratum may take. It is
not necessary that the surface should be a rough one; the sur-
face film of water may incite the response. More striking is
the direction of growth of regenerating hydroid stems, accord-
ing to the observations of LorB (91, p. 18). This experi-
menter found that when pieces are cut from a stem of Tubularia
and are so placed in a cylindrical glass vessel that the lower
end lies buried in the sand while the upper end is in contact
with the side of the vessel, then, regeneration of the hydranth
occurring, the new growth is perpendicular to the surface of
the vessel, z.e. horizontal. This direction is independent of the
direction of light rays, since it occurs at all parts of the circum-
ference of the vessel; nor is it a response to gravity, since the
stems normally assume a vertical position. The phenomena
are, in so far, exactly like those in plants.

The experiments made upon plants suggest a series which
might be made upon animals. Do stolons exhibit nutations to
aid in the finding of the solid substratum? What substances
call forth the thigmotactic response? Will a momentary irri-
tation cause turning? The field of thigmotropism, like that of
the other tropic phenomena of sessile animals, is an imperfectly
worked one.

6. The Accumulation of Contact-Stimulus and Acclimatization
to it.— These: two phenomena accompanying contact-stimu-
lation must be alluded to. PFEFFER (’85, p. 506) pointed out
that a soft blow which calls forth no response when given
once, will produce bending when given repeatedly for several
minutes. The basis for an explanation of this phenomenon is
given by an observation of DE VRIES (73, p. 307), who with-
drew the support from a tendril which had already turned

ee ee

\
|

NE ER Oe eR Ee I et La

—"

§ 2] THIGMOTROPISM 383

through 45° as a result of contact irritation. The tendril con-
tinued to bend at the previously irritated point even after the
irritant had been removed. Thus a stimulated condition per-
sists after the removal of its inciting cause, and this gives a
chance for the building up of a powerfully stimulated condition
by the accumulation of slight stimuli.

The persistence of the stimulated condition is revealed by
another set of changes. PFEFFER found that the tendrils of
Sicyos when repeatedly rubbed at short and regular intervals
first coil and then gradually straighten out. . DARWIN (782,
p- 155), who had previously shown this same thing, found also
that after a tendril of Passiflora gracilis had been stimulated 21
times in 54 hours it finally hardly responded at all. Similar
results have been obtained with Drosera hairs (PFEFFER, ’85,
p- 514). Thus the constantly repeated stimulation produces
such a modification of the protoplasm that it eventually fails to
respond. On the one hand, this phenomenon is the same as
that of fatigue; on the other, it resembles closely the condition
seen in stimulated Protista referred to in Chapter IV, § 3, and
there designated as acclimatization.

7. Explanation of Thigmotropism. — Concerning the cause of
the bending of plants as a result of contact, I know of no better
explanation than that offered by Sacus (87, pp. 697-699).
He ascribes the bending to a difference in the rate of growth
on the two sides of the bending cylindrical organ. This is
indicated by the fact that it is chiefly in the region of
“ stretching” that the response occurs; 7.e. shortly behind the
apex. At the very tip, growth by assimilation is chiefly occur-
ring; below the region of stretching, growth is occurring only
slowly. The measurements of DE VRIES (73) have, however,
shown directly that the convex side of the tendril grows faster
than the straight tendril and the concave side less rapidly.
The convex side thus pushes still farther over the concave, pro-
ducing the coiling. As the region of stretching is one of
imbibition of water, we conclude that more water is taken in on
the convex side than on the concave, where even a loss of water
may occur; or perhaps there is a movement of water from the
irritated towards the opposite side. The irritant then produces
a chemical change on one side of the organism such as to cause

384 EFFECT OF MOLAR AGENTS UPON GROWTH ([Cu. XIV

a movement towards that side or from that side according as
the organ is positively or negatively thigmotropic.

§ 3. Errect OF WOUNDING UPON THE DIRECTION OF
GROWTH — TRAUMATROPISM *

Under this head may be considered the effect of a special
class of molar agents, namely, those which produce a wound,
upon the direction of growth of roots. We may consider first
false and then true traumatropism.

1. False Traumatropism.— When the growing tissue of the
radicle of a seedling is destroyed on one side by caustic or heat,
the radicle turns towards that side (CIE-
SIELSKI, ’72; DARWIN, ’81; SPAULDING,
94). This result is satisfactorily ex-

1 plained on the ground that the killing
| of the growing tissue on one side causes
a retardation or cessation of growth on

7 that side; so that, while the points 2, y

Fic. 103.—Diagramofa (Fig. 103), remain nearly stationary, the
root tip, illustrating points 2, y', opposite to them, grow widely
false traumatropism: anart. It will be seen at once that this
xy ,region of wounding. ; 3
The line y-y’ ranorig- bending belongs to a wholly different
inally parallel to the category from the thigmotropic curva-
line x-x’, but by growth ; : ‘
has been brought to tures described in the last section. It
make an angle of 9° is, as DARWIN called it, a mechanical
idoatay bending ; it is a false traumatropism.+
2. True Traumatropism. — Of widely different cause from

the foregoing is the turning due to slight wounding which has

been investigated by CIESIELSKI (72), DARWIN (81), DET-

LEFSEN (’82), WIESNER (’84), and SPAULDING (94). DaArR-

WIN irritated the radicle of a bean by touching it near the

apex with dry caustic (nitrate of silver). The point of wound-

* From Greek, rpadua, a wound.

t A phenomenon allied to this is seen when at an early stage one half of a
frog embryo is killed and, consequently, remains of small size; the larger,
growing, side soon comes to bend around the smaller, dead, side. A fuller
account of these experiments, made by Roux and others, upon the frog’s egg,
must be postponed to the next Part of this work, since it is complicated by the
phenomenon of regeneration.

——

§ 3] TRAUMATROPISM 385

ing appeared as a small, dark spot on one side of the radicle.
The seedlings were then suspended in a moist chamber, over
water, and at a temperature of 14.4°C. After 24 hours almost
all of the radicles showed a marked curvature from the
wounded side. Other means can be used to produce this
result : a thin slice cut off obliquely from the tip of the radicle,
a drop of shellac, of copper sulphate, of potassium hydrate, or
steam at about 95°C. (SPAULDING) —in general, any agent.
which irritates strongly without killing.

Concerning the place on the root where the injury must be:
made in order that a response should appear, SPAULDING finds.
that if the branding is made further from
the apex than 1.5 mm. no traumatic curva-
ture will occur; or if an oblique cut at the
apex should not involve the growing root tip,
as at ab, Fig. 104, it is without effect. So
it seems that the pro-
liferating root tip is

the sensitive part. Wa. 10: +> Diana
The point of maxi- showing the rela-
mum curvature is, how- Hons. 0f the roas
: tip, r.t, and -the
ever, not at the root tip, root cap, 7.c.; a,b,
but lies in the region line of a cut which
f t - th involves only the
of most rapid growth. Sik ems:

The ‘length of time
elapsing between injury and response
varies with the species and with the tem-
perature. Thus, at a temperature of 18°C.
the curvature begins in from 45 to 55
minutes, and reaches a maximum within
| 24 hours ( WIESNER).
. it The long, latent period and the slowness.
of complete response give an insight into-
the reason for this separation of the per-
i 105.— Median longi- ceiving and responding zones. During the
udinal section through ‘ er : .
@ gypsum cast, bd, sur- latent period the irritated tissue is be-
rounding and repress- coming stretching tissue through the im-
da es hee bibition of water, while the root tip is
PFEFFER, '93.) becoming generated in advance, leaving

2c

386 EFFECT OF MOLAR AGENTS UPON GROWTH ([Cu. XIV

the irritated protoplasm behind. This can be demonstrated if
(following PFEFFER, ’93) the freshly irritated radicle is con-
fined in a plaster cast (Fig. 105). The growth of the tip is
slackened so that it does not leave the irritated tissue far
behind; at the same time, the zone of stretching encroaches
upon the root tip, so that, if the radicle is released after several
days, the curvature, although taking place, occurs abnormally
near the tip. If the response were transmitted a fixed dis-
tance backward from-the tip, we should expect that in the
confined plant either the turning would take place at the normal
position or would altogether fail to occur. Since neither of
these effects follows, the conclusion is strengthened that the
identical plasm which is irritated responds, producing the
traumatic curvature. |

Temperature, controlling as it does the rate of growth, con-
trols the length of the latent period. According to the obser-
vations of WIESNER, this is at —

TEMPERATURE, In Damp CHAMBER, In WATER.

8.0° C. 438 min. 393 min.
17.5° C., 87 52
25.0° C, 37 28
33.0° C. 58 70

Thus, 25° C. seems to be about the optimum temperature for
the traumatropic response; and this is a temperature 10° to
12° below the optimum for protoplasmic movements (Chap.
VIII, § 2).

The true explanation of traumatropism remains, after pro-
longed discussion, uncertain. DARWIN regarded it as a
response to stimulation, but DETLEFSEN and WIESNER sought
to show that it is the immediate mechanical result of the
injury. Thus, DETLEFSEN assumed tensions in the root cap,
which caused the root when cut on one side to shorten on the
other ; but this conclusion was disproved by SPAULDING, who
found that the usual results do not follow when the root cap is
injured without injuring the root tip. WEISNER’s explanation
was based on the observation that decapitated roots grow more

§ 4) RHEOTROPISM 387

rapidly in water than normal ones. In like manner, if the
root is, as it were, half decapitated, by cutting the tissue on
one side, an abnormally rapid growth will take place on that
side, proximal to the injury. The reason for this more rapid
growth, continues WIESNER, is that the nutritive fluids
intended for the tip are prevented by the injury from attaining
the tip, and, consequently, go to build up the cell-walls above
the wound. While the possibility of this explanation cannot
be denied, the facts are not opposed to another interpretation,
such as is offered by SPAULDING, and which is more in accord
with the explanations of other tropic phenomena. ‘This expla-
nation is that the wounding produces a chemical change in the
protoplasm of one side of the root, such that growth occurs
more rapidly upon that side, either as a result of increased

upbuilding of cell-walls or of increased imbibition of water, or
of both.

§ 4. ErrectT oF FLOWING WATER UPON THE DIRECTION
OF GROWTH — RHEOTROPISM

When the radicle of a bean is suspended by the cotyledons
above a stream of flowing water, so that it lies in the axis of
the current and points down stream, the free end, as it grows,
gradually turns, and becomes directed up stream. It turns ©
against the current.

This remarkable phenomenon, named rheotropism by its dis-
coverer, JONSSON (’83, p. 518), has been carefully studied by
him by the following method: The stream, whose rate could
be controlled at will, flowed in a trough. Over the current,
seedlings of maize and other grains, with well-developed rad-
icles, were suspended so that the radicles lay in the axis of the
current, and were directed either up stream or down as desired.
When the rootlets were directed down stream, a turning began,
after a latent period of several hours, and reached its final posi-
tion in the current in about twenty hours. If the rootlet was
originally directed up stream, it simply grew straight ahead
until mechanically bent out of position by the impact of the
water. By directing a rootlet alternately down stream and up
stream after each rheotropism has occurred, the whole root
may become very zigzag. These facts show clearly that cer-

388 EFFECT OF MOLAR AGENTS UPON GROWTH [Cu. XIV

tain radicles are sensitive to the impact of water, so that they
turn in such a way that the irritant shall affect their two sides
equally, and shall be directed against the tip. While the pre-
cise part of the radicle which is sensitive to the current has
not been determined, the responding part is in the region of
greatest growth, and the response is such that the root becomes
concave towards the irritant.

Among animals, a response which probably belongs to this
category has been observed by Logs (91, p. 36) in the grow-
ing stem of the hydroid Eudendrium. In a vessel of water in
which all other hydranths turned towards the light, there was
one which rose near the cloacal opening of an ascidian, from
which strong currents of water passed. ‘This individual was
turned with its concave side towards the impinging current.
It is probable that the current had induced a rheotropic
response. :

SUMMARY OF THE CHAPTER

The rate of growth of the entire organism or of its organs
is accelerated by contact, as in the stolons of hydroids; by
rough movement, as in bacteria; by cutting — when accelerated
growth occurs along the cut surface. Growth in length
may be retarded by pulling, as in stems and roots. Many
organisms show themselves very sensitive in their growth to
mechanical irritation.

The direction of growth is determined < external agents,
acting as irritants, in the cases of the twining dodder, tendrils
in general, roots, the hyphe of Phycomyces, the rhizoids of
hepatics, and the hydranths. of various hydroids. Wounding
may cause a turning from the wounded side in the radicle of a
seedling, and ridjeles and hydreids may even grow so as to
face the current. .

The sensitiveness to contact may be excessively great, a
swinging cotton rider weighing 0.00025 mg. causing a tendril
to bend. This sensitive region varies from near the tip in
roots to some distance behind the tip in the case of tendrils.
The response may occur after seconds, as in Cuscuta, or after
hours, as in traumatropism of radicles. The bending usually
reaches a maximum at the region of greatest growth. The

LITERATURE 389

stimulated condition persists for some time after irritation, so
that a summation of effects may occur. An acclimatization to
contact may appear, when no response is invoked by the irrita-
tion. The thigmotropic response may be explained, in general,
as due to a chemical change, wrought by the one-sided impact,
such as to cause a disturbance in the equality of the growth
processes — assimilation, secretion, or imbibition —on the two
sides of the organ.

LITERATURE

BaRANETZEY, J. "79. Die tagliche Periodizitat im Langenwachsthum der
Stengel. Mém. de l’Acad. de St. Petersb. XXVII. 91 pp.
Bucuner, H. ’80. Ueber die experimentelle Erzeugung des Milzbrand-
contagiums aus den Heupilzen. Sb. k. bayer. Akad. Miinchen. X,
368-413. |
CresretskI, T. 72. Untersuchungen iiber die Abwartskriimmung der
Wurzel. Beitrige zur Biologie der Pflanzen. Band I, Heft II. pp.
1-30. Taf. I.
Darwin, C.’65. On the Movements and Habits of Climbing Plants. Jour.
Linn. Soc. (Bot.). IX, 1-118.
82. The Movements and Habits of Climbing Plants. 208 pp. 3d
thousand. London, 1882. [Date of first edition, 1875.]
Darwin, C. and F.’81. The Power of Movement in Plants. 592pp. New
York, 1881.
DETLEFSEN, E. ’82. (See Chapter XII, Literature.)
DutrocHet, H. ’43. Des mouvements révolutifs spontanés qui s’observent
chez les végétaux. Ann. Sci. Nat. XX (Bot.), 306-329.
44. Recherches sur la volubilité des tiges de certains végétaux et sur la
cause de ce phénoméne. Ann. Sci. Nat. II (Bot.), 156-167.
Errara, L. 84. Die grosse Wachsthumsperiode bei den Fruchttragern von
Phycomyces. Bot. Ztg. XLII, Nos. 32 to 36. Aug., Sept. 1884.
Heeer, R. 93. Ueber den Einfluss des mechanischen Zugs auf das
Wachsthum der Pflanze. Beitrage z. Biol. d. Pflanzen. VI, 383-432.
Horvatn, A. ’78. (See Chapter IV, Literature.)
Jonsson, B. 83. (See Chapter IV, Literature.)
Leone, T. ’85. Sui microorganismi delle acque potabili. Atti della R.
Accad. Lincei (4) Rencond. I.
Logs, J. ’91. Untersuchungen zur physiologischen Morphologie der Thiere.
I. Ueber Heteromorphose. Wiirzburg, 1891.
92. (See Chapter X, Literature.)
MacDovaat, D. T. ’96. The Mechanism of Curvature of Tendrils. Ann.
of Bot. X, 373-402. April, 1896.
MEtTzeER, S. J. 94. (See Chapter IV, Literature.)

390 EFFECT OF MOLAR AGENTS UPON GROWTH ([Cu. XIV

Mont, H. v. ’27. Ueber den Bau und das Winden der Ranken und Schling-
pflanzen. Tiibingen, 1827.

Motiscn, H. ’84. (See Chapter XII, Literature.)

Miitier, O. ’86. Untersuchungen iiber die Ranken der Cucurbitaceen.
Reitrige z. Biol. d. Pflanzen. IV, 97-144. °

Nerewcomse, F. C. ’95. The Regulatory Formation of Mechanical Tissue.
Bot. Gazette. XX, 441-448. Oct. 1895. j

Pam, L. H.’27. Ueber das Winden der Pflanzen. 101 pp. 3 Tab. Stutt-
gart, 1827.

Perrcr, G. J. 94. A Contribution to the Physiology of the Genus Cuscuta.
Ann. of Bot. VIII, 538-117. Pl. VIII. March, 1894.

PFEFFER, W. ’85. Zur Kenntniss der Kontaktreize. Unters. a. d. bot.
Inst. Tiibingen. JI, 483-535.

93. Druck und Arbeitsleistung durch wachsende Pflanzen. Abh. siichs.
Ges. d. Wiss., Leipzig. XX, 235-474.

Reinke, J. 80. Ueber den Einfluss mechanischer Erschiitterung auf die
Entwickelung der Spaltpilze. Arch. f. d. ges. Physiol. XXIII,
434-446.

Russet, H. 8. ’92. The Effect of Mechanical Movement upon the Growth
of Certain Lower Organisms. Bot. Gazette. XVII, 8-15. Jan. 1892.

Sacus, J.’73. Ueber das Wachsthum der Haupt- und Nebenwurzeln. Arb.

_ Bot. Inst. Wiirzburg. I, 385-474.
’87. (See Chapter X, Literature.)

ScuEnck, H.’93. Ueber den Einfluss von Torsionen und Biegungen auf
das Dickenwachsthum einiger Lianen-Stimme. Flora. LXXVII,
313-326.

Scumipt, B. ’91. Ueber den Einfluss der Bewegung auf das Wachsthum
und die Virulenz der Mikroben. Arch. f. Hygiene. XIII, 247.

Scuoitz, M. ’87. Ueber den Einfluss von Dehnung auf das Langenwachs-
thum der Pflanzen. Beitr. z. Biol. d. Pflanzen. IV, 365-408.

SpauLpinG, V. M. 794. The Traumatropic Curvature of Roots. Ann. of
Bot. 423-452. Pl. XXII. Dec. 1894. |

Tumas, L. ’82. Ueber die Bedeutung der Bewegung fiir das Leben der
niederen Organismen. Medic. Wochenschr. 1882. No.18. St. Peters-
burg.

Verworn, M.’95. Allgemeine Physiologie [1st Aufl.]. 584 pp. Jena, 1895.

DE Vrigs, H.’73. Langenwachsthum der Ober- und Unterseite sich kriim-
mender Ranken. Arb.. Bot. Inst. Wiirzburg. I, 302-316.

Wiesner, J. 84. Untersuchungen iiber die Wachsthumsbewegungen der
Wurzeln. Sb. k. Akad. Wiss. Wien. LXX XIX}, 223-302.

WortTMANN, J. ’87. Zur Kenntniss der Reizbewegungen. Bot. Zig. XLV,
785 et seq. Dec. 1887.

CHAPTER XV

EFFECT OF GRAVITY UPON GROWTH
§1. Errect or GRAVITY UPON THE RATE OF GROWTH

Ir is a result of the sessility of the higher plants that they
and their parts are acted upon continuously in one direction by
gravity. It might consequently be suspected that the rate of
their growth would be affected if they were placed in an
abnormal position with respect to this agent. In the experi-
ments which have been made to test the correctness of this
suspicion various methods have been employed. When the
growth of Penicillium which is removed from gravity’s action
by being slowly revolved on a klinostat is compared with that
of a plant under normal conditions, the former is found to be
morerapid. The plant seems to reap an advantage from not hav-
ing to sustain its own weight (Ray, ’97). When Phycomyces
is inverted, its growth is slower than in the normal position
(ELFVING, 80). These two experiments upon fungi indicate
a considerable sensitiveness on their part to gravity. Experi-
ments made by Eirvine (80) and ScHwAkz (’81). upon the
growth of inverted phanerogams and those from which the
action of gravity had been eliminated by the slowly rotating
klinostat, as well as those which had been subjected to exces-
sive pressure by the centrifugal machine, yielded for the most
part only negative results. Upon the rate of growth of seed-
lings gravity has little effect.

§ 2. THE EFFECT OF GRAVITY UPON THE DIRECTION OF
GROWTH — GEOTROPISM

As with contact so with gravity two classes of effects may
be distinguished, which, while often producing similar results,
bring them about through very dissimilar processes. The first
of these is a mechanical effect due to gravity acting upon the

391

392 EFFECT OF GRAVITY UPON GROWTH [Cu. XV

growing organ as it might upon any other heavy body. The
second is a vital effect, having no immediate, direct, physical
relation to the cause. The first may be called false geotro-
pism; the second, true geotropism.

1. False geotropism may be treated very briefly, since it is
not a true growth phenomenon. Asan example of such geotro-
pism may be cited the downward bending of the top of a stem
heavily laden with a head of seed or with fruit, or the upward
growth of the long fronds of kelp in the sea on account of the
buoyant effect of the dense sea water. In such cases the
direction of the growth can be accounted for upon well-known
principles of hydrostatics.

2. True Geotropism.— The biological effect, on the other
hand, which is seen in true geotropism is often opposed to
the gross physical one. It shows itself especially in various
groups of sessile plants and animals. Since, unfortunately, com-
paratively few experiments have been made upon geotropism
in animals, the great mass of our knowledge on this subject is
derived from studies on plants.

The general fact of geotropism strongly impresses one who
stands on the shore of a lake in our northern country and looks
across to the dense pine forest on the opposite side. The
landscape is composed of vertical and horizontal lines —
vertical lines below formed of close-set trunks of trees, hori-
zontal lines above formed of the great branches. If at one side
a steep slope ascends, its outline is obscured by the grill-work
of perpendicular lines formed by the vegetation which clothes
it. Here the effect —the dissimilar effect—of gravity in
determining the direction of growth of two organs, trunk and

branch, is seen. ‘There are, however, still other organs which .

may respond to the same stimulus. Among these are the
roots, flower stalks, and leaves of phanerogams; the vertical
parts of many vascular cryptogams; the sporiferous hyphe of
fungi and some vertical alge, e.g. Chara. There is no need to.
examine all these cases of geotropism, but only such of them as
will help us to get at the principles of the action of gravity in
determining the direction of growth.

a. Roots. — When a seedling is so placed that its radicle is
horizontal, the radicle does not continue to grow out in the

Oe eee

occur without growth.

§ 2] GEOTROPISM 393

same direction; but all additional growth is vertical so that
the radicle bends sharply downwards —it is positively geotropic.
The curvature does not take place at the very tip of the root,
—in the region of growth by assimilation, — but immediately
behind in the region of stretching or of growth by imbibition.
The precise region at which the curvature occurs was deter-
mined by CIESIELSKI (’72), by means of a method illustrated
in Fig. 106. It is here seen that
the maximum bending occurs in this
radicle at between 3 and 4 mm. from
the tip. It is also plain that the
geotropic curvature is in some way
connected with growth—could not

To show that the normal vertical
growth of a root is due to the press-
ure of gravity, KNIGHT, in 1806,
determined experimentally that the
direction of its growth can be deter-
mined by other pressures replacing
gravity, such as centrifugal force.

“ Fie. 106.— An originally straight
Thus when seedlings were attached RN tay Slat igile akc
to the rim of a wheel and this was in 0.5 mm. spaces and placed
made to rotate rapidly about a hori- _nearly vertically with its apex
zontal axis the radicles grew straight rit - iat ee . pi
outward from the axis; thus in the wards in the zone of greatest
sense in which the centrifugal press- Stw'h at _ between 3.5 and 4
mm. from the tip. (From CrE-
ure acted, as before they had grown _ grersxr, 72.)
in the sense of the pull of gravity.

A second method of proof, employed by SAcuHs (’79), consisted

in eliminating the effect of gravity by means of the klinostat

(Chapter V, § 1), under which circumstances the root grew
irregularly. Such results leave no room for doubt that it is

gravity which determines the verticality of the root.

The question now arises, in what way does gravity control
the direction of growth of this organ? An early suggestion
was that the action was direct, due to the relatively great
specific gravity of the root tip; but this idea was easily refuted
by a mass of evidence. Thus it is not, @ priori, easy to see

394 EFFECT OF GRAVITY UPON GROWTH (Cu. XV

how the mere weight of the tip of the plant, supported as it
is by the firm soil, should enable it to find its way down.
Experiments, also, have shown that the radicle will curve
downwards against considerable resistance such as is afforded
by the surface of a cup of mercury, by a weight which is lifted
by means of a thread passing over a pulley (JOHNSON, ’29),
or by a delicate spring which is compressed by the down-cury-
ing radicle (WACHTEL, 795). By these various methods it has
been demonstrated that the down-curving of the geotropic
radicle is an active process capable of overcoming resistance
amounting, in one case, to 150 milligrammes. Consequently
gravity does not act in a grossly mechanical way, but as a
stimulus inciting a growth response.

If now the down-curving of the root is a response the
question arises, where is the stimulus received; at the region
of curvature or at some other point? This is a question which
has excited much discussion, owing to apparent contradictions
in the experimental evidence. ‘The first attempt to answer
this question was made by CIESIELSKI* (’72), who cut off the
terminal one-half millimeter of the radicle, placed the rootlet

in a horizontal position, and found that, although growth con- —

tinued, no down-curving occurred until, after several days, the
root tip had regenerated. He concluded that the root tip
is useful or necessary in geotropism. Sacus (73, p. 433)
repeated CIESIELSKI’S experiments and likewise found an
incomplete exhibition of geotropism. But this he attributed
to the excessive irritation of the cutting, which led to exagger-
ated movements of nutation, tending to obscure geotropism.
DARWIN (80) confirmed CIESIELSKI’S results after both

cutting off the root apex and cauterizing it, and explained .

SACHS’ partial failure to get like results on the ground that he
did not amputate the radicles in a strictly transverse direction.
DARWIN concluded that the “tip of the radicle is alone sensi-
tive to geotropism, and that when thus excited it causes the ad-
joining parts to bend.” The exact length of the sensitive part
seems to vary with certain conditions, but it is generally less

* Hartie (’66, p. 53) had already stated that the decapitated root was not
geotropic.

—_——_ Tt

Le

2.0mm. long. The preparation was now

§ 2] GEOTROPISM 395

than 1 to 1.5 mm. This terminal millimeter or so, then, acts
like a sense organ in a vertebrate, which receives the sensation
at some distance, it may be, from the responding organ.

From this time on, two schools may be distinguished, of
which the first, following DARwty, regarded the stimulus as
received at the root tip and transmitted to the region of
growth; while the second conceived the stimulus to act di-
rectly upon the root in the bending region and to arise from
the difference in the pressures on the upper and lower surfaces
of the radicle. The second school persistently denied the:
validity of the decapitation experiments, WIESNER (781) in.
particular maintaining that decapitation inhibited growth and
consequently growth curvatures, but did not necessarily remove:
the sensitive organ. ‘The first school was forced to new experi-
ments. FRANcIS DARWIN (’82) maintained on the basis of
such experiments that it is not the cutting per se which
inhibits geotropism ; for the cutting of the root tip, as for
example, lengthwise, without its removal, permits the normal
response. But it was easy to reply to this that a transverse cut-
might well affect growth more seriously than a longitudinal
one.

The satisfactory solution of this difficulty required a method
by which, without mutilating the root, gravity should act
horizontally upon the chief growing part of the root without so
acting upon the root tip. A method for accomplishing this
was invented by PFEFFER (94). <A radicle of a bean or other
species, fixed to a klinostat, was made to grow into a small
glass tube, closed at its further end and bent so as to form two
arms, at right angles to each other, and each about 1.5 to

turned until the root tip was directed ver-
tically downwards, while the rest of the
root, and especially its chief growing re-
gion, was horizontal (Fig.107). Thisregion Fic. 107.—Diagram il-
was then subjected to the full transverse oe emer
ployed in PFEF-
action of gravity, while the tip was not so FER’s experiment.
acted upon. Meanwhile the normal growth
processes were not interfered with, for as the root lengthened

it backed out, so to speak, from the bent tube, the apex remain-

396 EFFECT OF GRAVITY UPON GROWTH [Cx. XV

ing at the blind end. Under these conditions no geotropic cur-
vature occurred; but such curvature always took place when
the root tip was placed horizontally or at any acute angle with
the horizon. This experiment seems, then, better fitted than
any previous one to prove that the geotropic sensitiveness of
the root resides in the apex.* Consequently, since, as an in-
spection of Fig. 106 will show, the curving part of the root can
contain none of the originally irritated cells, there must be a
transmission of stimuli from the root tip to the curving region.

Two associated phenomena remain to be considered. First,
geotropic response is more powerful, the bending becomes
stronger, as the angle made by the root with the vertical in-
creases, reaching a maximum when the root is’ horizontal
(Sacus, ’78, p. 454). Secondly, as’already indicated, response
does not take place immediately after the root is placed hori-
zontally. In one experiment of SAcus’ (’73, p. 440) a bean
radicle placed horizontally and growing in loose earth at 20° C.
_began to turn downwards in the second hour. There is thus a
considerable latent period.

The cause of geotropism in roots is indicated by the con-
ditions of its occurrence already mentioned. It is intimately
associated with growth, yet, as KIRCHNER (’82) has shown, it
may occur.at a temperature (2° to 3.5° C.) at which growth is
extremely slow. ‘The turning is clearly due to unequal growth
upon the convex and concave sides of the root. But is it due
to acceleration on the convex side over the normal, to retarda-
tion on the concave side, or to both? Measurements have been
made upon plants to decide this question. In one set of such
measurements made upon the bean radicle by Sacus (73,
p- 465) the growth was hastened about 3% on the convex side
and retarded 42% on the concave side, so that both accelera-
tion and retardation occur.

Finally, lateral roots which run more or less obliquely down-
wards have been shown by SAcus (’74) and others to be
influenced by gravity; for, if the plant be inverted, the roots
will turn until they assume their normal inclination to the
horizontal plane. :

* But species may differ in this respect as in phototropism (see page 441).

§ 2] GEOTROPISM 897

b. Stems. — The central fact that the upward growth of
stems is determined by gravity is established by the observa-

eo.

tions that on the klinostat no definitely
directed growth occurs, and that on the
centrifugal machine the stem turns in
the opposite sense to that of the cen-
trifugal pressure. The stem is nega-
tively geotropic. As with roots, so with
stems, a number of questions now arise:
Where is the sensitive region and where
the response? At what inclination of
the stem is the strongest geotropic cur-
vature called forth? What is the im-
mediate cause of the curvature?

As Fig. 108 shows, the response of
the stem of a seedling is fundamentally
different from that of the radicle. In-
stead of the tropism beginning at one
point, and continuing there as in the
root (Fig. 106), it begins close below
the cotyledons of the seedling and passes
downwards towards the base as far as
growth is still occurring. Response,
consequently, takes place along the whole
“stretching” region. ‘The sensitive re-
gion also, unlike that of the root, is not
confined to the tip, but extends along
the entire bending stem. _

The position in which the strongest
response is incited was believed by
SACHS (’79", p. 240) to be the horizontal
one, and BATESON and DARWIN (’88)
have confirmed this conclusion. Their

method depends upon the fact that a

stem placed horizontally and restrained
for several hours from taking the verti-
cal position will, upon being released,

\ :
CS

15

16

Fic. 108.— Course of geotro-

pism in a plumule. The
successive figures 1 to 16
indicate successive stages
in the geotropic turning of
a seedling growing in half
darkness. Placed at first
horizontal as at 1, the plant
has become completely erect
at 16. The most rapid growth
is just behind the cotyle-
dons and diminishes toward
the base. The temporary
bending beyond the vertical
is to be noted. (From StTRAs-
BURGER, NOLL, SCHENCK,
and ScHIMPER, Textbook
of Botany, Macmillan.)

suddenly spring upwards. In using this method it was found
that the stem springs through a greater are after having been

398 EFFECT OF GRAVITY UPON GROWTH (Cu. XV

restrained for two hours in a horizontal position than if re-
strained in any oblique position, whether the tip be directed up
or down.

Concerning the cause of the curvature there is little to add
to what was said under “ Roots.”” The remote cause is appar-
ently the dissimilar action of gravity on the upper and the
under sides of the stem; the immediate cause is the difference
in growth on the two sides of the stem. In the special case of
stems with knots, the knots show themselves especially respon-
sive to the geotropic stimulus.

e. Rhizoma. — These horizontally running, root-like, subter-
ranean stems are strikingly responsive to gravity, as ELFVING
(80), especially, has shown. He has reared various rushes in
a glass box with their axes making various angles with the
vertical. In their subsequent growth all the rhizomes of the
plants extended in a strictly horizontal direction. In this case
any component of gravity, however small, running in the direc-
tion of the axis of the rhizome seems to irritate. The curving
into a horizontal plane may be called transverse geotropism
(diageotropism, FRANK).

d. Cryptogams.— We have already seen (p. 891) that the
sporangiferous hyphe of Phycomyces nitens are negatively
geotropic. The same is true of certain alge. Thus RICHTER
(94) has found that when the stem of Chara is inverted the
youngest two or three internodes curve upwards in their
further growth so that the apex of the stem is now directed
zenithwards. On the other hand the rhizoids of this species
are positively geotropic. Rotation experiments show that in
the absence of the directive pressure of gravity there is no
definite orientation. Finally, some mosses are slightly geo-
tropic. Thus, Bastrr (91) reared Polytrichum juniperinum
in the dark in both air and water, some plants being placed right
side up, others inverted. In both cases new branches budded
from the roots and, although etiolated, grew irregularly up-
wards — there was a feeble negative geotropism.

e. Animals. —Since only sessile organisms can be expected
to show marked geotropism, this phenomenon among animals
must be confined to rather few groups. It has been studied
hitherto exclusively in the group of hydroids. Many repre-

CR eT ae ae

§ 2] GEOTROPISM 399

sentatives of this group show themselves, however, markedly
responsive.

The first observations upon geotropism in hydroids seem to
have been made by LoEB (91%, pp. 27, 28). He says: “When
a stolon was formed at the cut end of a vertical stem (of Ag-
laophenia) it grew (in case it did not come in contact with a
solid body) first a short distance horizontally, and then down-
wards. In horizontal stems the stolon grew directly down-

W,-- A hs
NP

~ \V ve
\ SA ARS
ee See
BSI AS
BU Sto OPS.
YZ

JN

7 a ae
Se ae

w A

Fic. 109. — Positive geotropism of regenerated stolons (W;, W2) and negative geotro-
pism of regenerated hydranths of Aglaophenia pluma. The original piece of the
stem is included between b and c. This piece was placed vertically, right end up,
in the aquarium. At the cut end, b, the stolon (W,) has arisen, but has soon begun
to grow downwards. It has produced a vertical hydranth ats. We, an adventi-
tious stolon. (From Logs, ’91*.)

Fie. 110.— Two bits of regenerating stems of Antennularia antennina. The one at
the left is in the normal position ; that at the right is inverted. From both, new
hydranths (S) have developed at the upper end, and new stolons (W) at the lower
end. (From Logs, ’92.)

400 EFFECT OF GRAVITY UPON GROWTH (Cu. XV

wards.” ‘ Adventitious stolons grew directly downwards
towards the earth. This was most noteworthy when such
adventitious stolons arose from a reversed stem (with the apex
down) sticking in the sand; under these circumstances the
stolon grew towards the apex. These descending stolons
showed occasionally twistings and curlings, such as are found
in tendrils. The newly arising sprouts [hydranths] behaved
in the reverse fashion from the stolons: they grew vertically

upwards” (Fig. 109). Subsequently, LozB (92, p. 8, ’94) -

b
a Re ne

* SITLL

Te a ee

W
111

Fia. 111.— A bit of regenerating stem of Antennularia antennina placed in the water
obliquely, with the basal end downwards. The new hydranths (S) and stolons (W)
arise vertically. (From Logs, ’92.)

Fia. 112. — A piece of the stem of Antennularia placed horizontally, and regenerating
stolons (7,7) downwards, and hydranths (b,c) upwards. (From Lors, ’94.)

found another hydroid, Antennularia, which, whether the stem
was held inverted, oblique, or horizontal, sent out new stems,
which grew vertically upwards, and stolons, which grew verti-
cally downwards (Figs. 110,111,112). The growing stolon,
if moved out of its first position, will curve until it acquires
again its vertical direction. The geotropism of stolons has
been likewise carefully studied by Driescn (792). This
author found in a species of Sertularella that, although the
main stolons are not geotropic, the daughter (secondary) sto-

‘

§ 2] GEOTROPISM 401

lons are markedly negatively geotropic. As the following
figure shows (Fig. 113), it is only the newly growing part
which exhibits this geotropism. ‘These geotropic movements

1

ey
2)
=

Fig. 113.— Diagrams of a Sertularella stock, showing how the direction of growth
is determined by gravity. The arrow points towards the earth’s centre. The stock
originally placed in the position a is subsequently reversed as at 5, and again as
atd. The asterisk indicates a hydranth. (From Drigscu, ’92.)

in animals, which occur near the growing apex, are clearly due
to unequal growth on the two sides of the inclined stem or
stolon.

Many untouched questions on geotropism in animals arise
for solution — questions about the location of the perceiving
and the responding portions of the stem, latent period and
after effect, and others.. Especially is it desirable to find how
wide-spread the geotropic phenomena are in sessile animals.

f. After-effect in Geotropism.— When a root or stem is
placed horizontally, and retained in that position for a part of
its latent period, and then, before tlfe curving has appeared, is
rotated on its long axis through 180°, the turning takes place
at about the time and towards the same side as it would had
the organ been left undisturbed ; in its new position the root
turns up, and the stem, for the moment, down. ‘The response,
once set in motion, works itself out, until finally annihilated
by an opposing response (HOFMEISTER, °63 ; CIESIELSKI, ’72).

This experiment has been variously modified in ways which
throw light on the meaning of the after-effect. It has repeat-
edly been observed that if the root tip be decapitated before

2D

402 EFFECT OF GRAVITY UPON GROWTH [Cu. XV

the end of the latent period the geotropism will occur in the
normal manner. ‘The impulse once transmitted, the geotropic
function of the root tip is finished. Again,.SAcus (’74*) laid
a stem in a horizontal position for an hour or two, until up-
curving had commenced near the tip. The tip was now held
horizontal, and for from one to three hours, during which
stretching took place, the horizontal part grew horizontally,

while the new tip turned zenithwards. ‘The tip in turning de-.

termines the direction of the incipient stretching zone, and the
stretching continues in this direction without regard to subse-
quent changes in position of the stem. The stretching is inde-
pendent of any control on the part of the tip.

Other conditions of geotropic after-effect have been deter-
mined by WorTMANN (’84). He treated a stem according to
Sacus’ method, and placed it in a chamber filled with hydro-
gen. Growth ceased. After oxygen was readmitted the tip
turned up at once, but no after-effect appeared. ‘This had
been annihilated by the absence of oxygen. If, however, the
stimulated sprout was placed vertically in de-aérated water,
there was an after-effect, but no geotropic response. So we
may conclude that, in the absence of oxygen, the geotropic
response will not occur; and that an after-effect may occur if
the stretching tissue is bathed with water for imbibition, but
not. under other conditions.

SUMMARY

The rate of growth seems to be little affected by the absence
of gravity or the abnormal condition of its action, except in
some of the higher fungi, where the removal of gravity hastens
growth, and its abnormal direction retards. Geotropism is
found only in sessile organisms. In roots the turning occurs
in the region of greatest growth, and the tip alone is sensitive
to gravity’s action. The response is preceded by a latent
period, and is strongest after the root has been placed hori-
zontal; it is due, in the case of both roots and stems, to an
acceleration of growth on one side and its retardation on the
other. In plumules the turning begins near the tip and pro-
ceeds towards its base; the whole bending region is responsive

—-

m —— nie i ee

a — ee ee

LITERATURE 403

as well as sensitive. Many cryptogams show negative geo-
tropism. Many branches and rhizomes show transverse geotro-
pism. Among animals, hydroids show negative geotropism.
A marked after-effect follows negative stimulation, by means
of it we can show that stretching or the geotropic curvature
are independent of any control from the tip after once the
stimulus has been transmitted to the stretching region. Like
other responses to stimuli, geotropism does not occur in the
absence of oxygen.

LITERATURE

Bastit, E. ’91. Recherches anatomiques et physiologiques sur la tige et la
feuille des mousses. Rev. Gén. de Bot. IIT, 255 et seq.

BaTeEson, ANNA, and Darwiy, F.’88. On a Method of Studying Geotro-

pism. Ann. of Bot. I, 65-68. June, 1888.

CresiEtskI, T.’72. (See Chapter XIV, Literature.)

Darwin, C.’80. (See Chapter XII, Literature.)

Darwin, F. ’82. On the Connection between Geotropism and Growth.
Jour. Linn. Soc. XIX, 218-230.

Driescu, H.’92. Kritische Erérterungen neuerer Beitriage zur theoretischen
Morphologie. II. Zur Heteromorphose der Hydroidpolypen. Biol.
Centralb. XII, 545-556. 1 Oct. 1892.

EtFvinG, F. ’80. Beitrag zur Kenntniss der physiologischen Einwirkung
der Schwerkraft auf die Pflanzen. Acta Soc. Scient. Fennice, Helsing-
fors. XII, 25-58.

80. Ueber einige horizontal wachsende Rhizome. Arb. Bot. Inst. Wiirz-
burg. II, 489-494.

Hartia, T. 66. Ueber das Eindringung der Wurzeln in den Boden. — Bot.
Ztg. XXIV, 49-54. 16 Feb. 1866.

HorMeIstTer, W. ’63. Ueber die durch die Schwerkraft bestimmten Richt-
ungen von Pflanzentheilen. Jahrb. f. wiss. Bot. LILI, 77-114.

Jounson, H.’29. The Unsatisfactory Nature of the Theories proposed to
account for the Descent of the Radicles in the Germination of Seeds
shewn by Experiments. Edinb. New Philos. Jour. April, 1829.
312-317.

Kircuner, O. 82. Ueber die Empfindlichkeit der Wurzelspitze fiir die
Einwirkung der Schwerkraft. Prog. zur 64. Jahresfeier d. k. Wiirt-
temb. Landwirths. Akad., Hohenheim. 53 pp. Abstr. Bot. Centralb.
XIII, 180-183.

Kniaut, T. A. 06. On the Direction of the Radicle and Germen during
the Vegetation of Seeds. Phil. Trans. London for 1806. pp. 99-108.

Lors, J. ’91. Ueber Geotropismus bei Thieren. Arch. f. d. ges. Physiol.
XLIX, 175-189.

404 EFFECT OF GRAVITY UPON GROWTH [Cn. XV

918. Untersuchungen zur physiologischen Morphologie der Thiere. I.
Ueber Heteromorphose. 80 pp. Taf. Wiirzburg, 1891.

92. Untersuchungen zur physiologischen Morphologie der Thiere. II.
Organbildung und Wachsthum. Wirzburg: G. Hertz. 81 pp.

704. On Some Facts and Principles of Physiological Morphology. Biol.
Lectures, Wood’s Holl Laboratory, 1893. pp. 37-61.

Prerrer, W. 794. Geotropic Sensitiveness of the Root-tip. Ann. of Bot.
VIII, 317-820. Sept. 1894.

Ray, J. ’97. Variations des champignons inférieurs sous l’influence du
milieu. Rev. Gén. de Bot. IX, 193-212, 245-259, 282-304. June-
Aug. 1897.

Ricuter, J. 94. Ueber Reaction der Characeen auf dussere Einfliisse.
Flora. LXXVIII, 899-423.

Sacus, J. ’73. Ueber das Wachsthum der Haupt- und Nebenwurzel. Arb.
Bot. Inst. Wiirzburg. I, 385-474. |

74. The same, continued. Arb. Bot. Inst. Wiirzburg. I, 584-634.

748, Ueber Wachsthum und Geotropismus aufrechter Stengel. Flora.
LVI, 320-331.

79. Ueber Ausschliessung der geotropischen und heliotropischen Kriim-
mungen wihrend des Wachsens. Arb. Bot. Inst. Wiirzburg. II, 209-
225.

79", Ueber orthotrope und plagiotrope Pflanzentheile. Ibid. pp. 226-
284.

87. Vorlesungen iiber Pflanzen-Physiologie. 2 Aufl. Leipzig: Engel-
mann. 884 pp. 1887.

Scuwarz ’81. Der Einfluss der Schwerkraft auf das Langenwachsthum der
Pflanzen. Unters. Bot. Inst. Tiibingen. I, 53-96.

WacnrTe., M.’95. Einige Versuche betreffend die Frage iiber die geotrop-
ischen Kriimmungen der Wurzeln. Abstr. in Bot. Centralb. LXIII,
309, 310. 7

WIeEsNeER, J. ’81. Bewegungsvermégen der Pflanzen. Wien, 1887.

WortMAnn, J.’84. Studien iiber geotropische Nachwirkungserscheinungen.
Bot. Ztg. XLII, 705-713. 7 Nov. 1884.

Se ee a

CHAPTER XVI

EFFECT OF ELECTRICITY ON GROWTH
§ 1. Errect or ELECTRICITY UPON THE RATE OF GROWTH

ELECTRICAL changes are so intimately associated with chem-
ical changes that we may reasonably expect not only to find that
the metabolic processes of growth are accompanied by the
development of electricity, but also to find that an electric.
current disturbs growth. It is indeed known that electricity,
is produced in seedlings, for MULLER-HETTLINGEN (83) has
obtained from a seedling of Vicia faba by connecting the two
extremities a maximum electro-
motive force of about one-tenth
of.a volt. (Fig. 114.) There is
thus in the living plant an elec-
tric stress. Will an outside cur-
rent, which must affect that of the
organism, disturb also its growth?

In the case of the growing
animal even a slight current of
electricity is usually injurious.
Thus LoMBARDINI (768) and
WINDLE (793 and ’95) have sub- Fre. 114.— Vicia seedling. The lines
jected the egg of the chick to uniting different points of the seed-

A ling may represent the wires run-
such a current running trans-

ning to the galvanometer; the points
versely through the embryo, with themselves are those from which

the result that the embryo either “he current was led off; the arrows
go with the currents in the wires.

soon ceased to develop or devel- (From MiLier-HEeTrLincEN, ’83.)
oped abnormally. Rusconi (40),

on the other hand, believed that a slight current accelerated
the development of the frog’s egg. More extended experiments
with known strengths of currents are much to be desired.*

* Certain unconfirmed results with a powerful magnet deserve to be noted.
Maaeiorrni (’84) found that developing hens’ eggs subjected to this agent pro-
duced four times the normal number of cases of arrested development.

405

EFFECT OF ELECTRICITY (Cu. XVI

406

Upon growing plants, on the other hand, numerous experi-
ments have been made. Nevertheless there is still a difference
of opinion even as to the occurrence of any effect. During the
middle of the last century much attention was paid to this
subject. BERTHELON (1783) and several others concluded
from extended researches that electricity favors plant growth ;
but their results, apparently having no practical value, were
largely forgotten. A century later GRANDEAU (79) revived
the idea of the beneficial effect for plants, not merely of cur-
rents of electricity, but also of those of the atmosphere. This
paper seems to have been the starting-point of the modern

discussion.
The methods employed in studying the action of electricity

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Fig. 115. — The effect of atmospheric electricity upon the growth of plants. A, To-

bacco plant reared under normal conditions. B, Similar plant reared under a
wire cage, by means of which it is isolated from the action of atmospheric elec-

tricity. (From GRANDEAU, ’79.)

$2) - UPON THE RATE OF GROWTH 407

have been of two general kinds. On the one hand the
seedling is electrified by passing a current through the soil in
which it is growing and after several days comparing it with
an untreated seedling. On the other hand the tension of the
atmospheric electricity is altered either by electrifying the air
of the chamber in which a plant is growing, or by isolating a
plant from the action of atmospheric electricity by means of a
cage made of fine wire and with meshes so wide that a minimum
amount of light is cut out (Fig. 115 4 and B).

The method of passing a current through the soil has been
employed by WARREN (’89), CHODAT ('92), McLEop (93 and
94), and by other investigators with results favorable to the
plants. McLrop passed the current transversely. He sunk
plates of metal on either side of the pea seeds employed in the
experiment and used a current from a single cell. While
the control seedlings germinated somewhat earlier than the
electrified ones, at the end of 45 days the latter had outstripped
the former. Again, a coil of wire, partly stripped of its insula-
tion, was imbedded in the ground, and from a lot of similar
mustard seeds some were placed next to the uncovered wire
and others about one inch away from the insulated part of the
wire. A constant current was sent through, and at the end of
seven days the seedlings planted near the uncovered wire were
_ one-third larger than the others. CHODAT used a current
passing lengthwise through the plant. Similar beans were di-
vided into two equal lots and each was reared in glass cylinders
under similar conditions, except that one was unelectrified
while the other was electrified by the following method. The
cylinder rested on one armature of tin-foil while the other was
suspended 1.8 meters over the first. The armatures were
connected with a Holtz machine and a current was passed
through the cylinder for about three hours each day. The
result was that on the fourth day leaves began to show on
the electrified seedlings but not on the control ones, and
on the seventh day all the electrified seedlings had attained
considerable size, whereas the control ones were just making
their appearance. The electrified seedlings were spindling,
however, much as if reared in the dark. WARREN’S experi-
ments are noteworthy in that he found the seedlings which

408 EFFECT OF ELECTRICITY [Cu. XVI

were nearer the positive electrode more advanced than those
which were nearer the negative electrode.

The method of electrifying the air over the plants was
employed by CELI (78), FREDA (788, on Penicillium), and
LemstrOmM (90). Their methods were somewhat dissimilar :
Cext discharged static electricity through a wire breaking up
into fine points over the growing seedlings and got increased
growth; FREDA used a similar method with Penicillium
reared on bread but obtained no favorable effect, LeEmstTr6OmM
conducted his experiments upon a larger scale, since he
covered a small part of a field of germinating barley with fine
parallel wires about a meter apart, provided with metal points
at intervals, and supplied with a current from a Holtz machine
during eight hours a day for over two months. In LEM-
STROM’S experiments the yield of the electrified field was
35% in excess of that of the unelectrified, and the quality of
the grain was better. These experiments, which extended
through several years, were carried on in various parts of
Scandinavia and in France, and generally resulted in a favor-
able effect upon the growth of malt crops.

The method of eliminating atmospheric electricity was used
with success by GRANDEAU (’79), who employed the method
of isolating seedlings in a wire cage referred to on p. 407.
The plants reared in the wire cage grew uniformly less rapidly
than similar plants reared outside. ALoI (795) has confirmed
these results with the same method, using maize and bean
seedlings.

On the other hand other investigators, preéminently
WOoOLLNY (’93), who used the methods both of increasing and
of eliminating atmospheric electricity, obtain only negative
results. Thus the whole matter stands, rejected on @ priori
grounds by many, denied as a result of negative experiments
by others, but still apparently demonstrated by three lines of
experimentation, none of them, however, free from criticism.
There prevails a cautious scepticism concerning the validity
of the positive results obtained.

Various explanations have been offered by those who accept
the positive results. FREDA, who found that Penicillium is
injured by the increased atmospheric electricity, attributed that

§ 2] UPON THE DIRECTION OF GROWTH 409

injury to the greatly increased amount of ozone that appeared
in his vessels. -In the open air, on the other hand, the increase
of ozone would be relatively so slight that it might well be
advantageous to growth. WARREN’S results would then be
accounted for by the fact that the ozone is especially produced
at the positive pole, thus favoring for a time the excessive
growth at that pole. On this explanation the electricity would
act only indirectly. Somewhat similar is the conclusion of
THOUVENIN (96), that the electric current aids the plant in its
decomposition of carbon dioxide. On the other hand there is
reason for believing that since plants are adjusted to an
(internal) electrical condition, a slight external one might
be advantageous rather than injurious.

§ 2. Errect oF ELECTRICITY UPON THE DIRECTION OF
GROWTH — ELECTROTROPISM

In 1882 the Finnish botanist ELFVING announced his dis-
covery that when the radicle of the seedling of a bean or of
certain other species was subjected in water to a transverse
current of electricity, it grew towards the anode. ‘This was the
introduction to a series of interesting studies on what has been
called electrotropism. In classifying the data which have been
acquired we may make use of the following heads: 1. False
and True Electrotropism; 2. Electrotropism in Phanerogams ;
8. Electrotropism in Other Organisms; 4. Magnetropism ; and
5. Explanation of Electrotropism and Summary.

1. False and True Electrotropism.— ELFVING himself ob-
served two opposing phenomena in the seedlings which he
subjected to the current. In most cases the radicles grew
towards the anode, but in one species, Brassica oleracea — the
wild cabbage —the radicle grew towards the kathode. ELrF-
VING was inclined, in consequence, to believe that some species
respond by growth in one direction and other species by the
opposite growth; that these are diverse responses to the same
agent, just as negative and positive chemotropism are. Gradu-
ally, however, it became evident, chiefly through the work of
MULLER-HETTLINGEN (’83) and especially BRUNCHORST (’84,
’89), that these results are due to dissimilar causes. Thus

410 EFFECT OF ELECTRICITY [Cu. XVI

BruNcHoRsT (’84, p. 209) found that the radicles of seedlings
of Brassica grow, under otherwise similar conditions, at a cur-
rent intensity * of 0.03 6 to 0.05 6, towards the kathode, and at
a current intensity of 3.0 6 towards the anode (Fig. 116).

TAGS

BRASSICA

f

Fig, 116.— Effect of different strengths of electric current on the radicle of Brassica.
At the right: strength of current, 1.16; all strongly negative and growing well.
At the middle: strength of current, 1.8 6; after a few hours negative at the apex
but positive higher up. At the left: strength of current, 3.16; all positive, weak,
and dead. (From BrRuNCHORST, ’84.) ‘e

If decapitation has occurred the kathode turning does not
follow, whereas the anode turning does occur as in the intact
root. A similar result having been obtained with seedlings of
various species, the conclusion was drawn that “the positive
galvanotropic curving is a simple chemico-pathological phenom-
enon which has only a superficial analogy with the directive
movements of roots, and therefore does not deserve the name
galvanotropism ” [electrotropism].

The cause of the positive turning effect, it has been sug-
gested, lies in the fact that certain substances, perhaps
hydrogen peroxide and ozone, produced in electrolysis act
more injuriously upon the positive than upon the negative
side. According to another explanation, offered by RiscHawit
(85), the positive curvature is due to the kathophoric action

* The current density (see Chapter VI, § 1) is calculated from the following
data: The amount of copper deposited in a voltameter was 0.14 mg. to 35 mg.
per hour during the course of experimentation. A current of one ampere
intensity deposits 0.000326 gramme of copper per second or 1.17 mg. per
hour per milliampere. Thus the strength of current varied from 0.12 to 30
milliamperes. The determination of the density requires a knowledge of the
cross-section over which the current spread itself. For this we may take the
given area of the electrodes, 6499 sq. mm., which is not far from the cross-
section of the trough.

§ 2] UPON THE DIRECTION OF GROWTH 411

of the current.* DuBo1s-REyMonpD had found that when a
current was passed through a cylinder of hard-boiled albumen
it became concave towards the anode owing to the passage of
water into the plant and its aggregation at the kathode side.
RiscHAWI found that a cylinder of plant tissue did the same,
and he attributed this result as well as that seen in the living
radicle to the accumulation of water at the kathode side. But,
as BRUNCHORST points out, this is not the whole explana-
tion, for the positive curving is generally accompanied by
death of the tissue, and death would not necessarily result from
the kathophorie action. By the use of a transverse partition of
porous clay BruncHoRST (’89) has been able to show that
the radicles in the positive T

half of the vessel are much
more seriously affected than
those in the negative half,
which fact the kathophoric
theory will not explain, but
the chemical theory will (Fig.

117). In accordance with the ae,
view that the positive reaction

is not a reaction to stimulus,

but is a false electrotropism,

it will be henceforth neg-

lected. The negative reaction, Fic. 117. — Radicles of Phaseolus on opposite

on the contrary, is a response sides of a partition, T, subjected to a

to stimulus —a true electro- transverse electric current, of 6.5 8 inten-
> sity, for two hours. * On the positive side
tropism.

of the partition all the roots are strongly
2. Electrotropism in Phane- positive; on the negative side, where the

rogams —We have seen that water is being continually renewed, the
; roots are slightly positive, being bent less

the transverse electric cur- than 40°. (From Bruncuorst, ’89.)
rent, when not too strong,

causes a turning of the tip of the seedling from the anode.
That this turning is a growth phenomenon is indicated by the
fact that it takes place a few millimeters behind the tip in the
region of maximum growth. This is then the region of response.

* The kathophoric action is seen when an electric current passes perpendicu-
larly through a porous partition submerged in water. The liquid moves through
the partition towards the kathode (hence called also electrical endosmosis).

412 EFFECT OF ELECTRICITY [Cu. XVI

The location of the sensitive region has been demonstrated
by various methods. MULLER-HETTLINGEN placed the tip only
of a radicle in contact with moist flannel through which the
current was passing; the radicle turned from the anode. Also
Bruncuorstr (’84) found that when merely the apex was in
contact with the electrified water there was a marked turning
from the anode, even when the current was so powerful as to
cause the submerged root to turn towards the anode. ‘The tip
is sensitive. Next BruncHorstT cut off the tip and found that
no response occurred when the current traversed the radicle.
Hence the tip is necessary to response, and it may be con-
cluded provisionally that as in geotropism so in galvanotropism
the root tip is the only sensitive part of the radicle.

The critical point at which the electrotropic effect passes
into the mechanical one is indicated by a sigmoid turning of
the radicle. According to BRUNCHORST’S observations this
critical point lies, at a temperature of 20°, for Phaseolus seed-
lings near 1.28; for Helianthus near 1.36; for Lupinus,
2.58; for Brassica, 36; for Lepidium, 3.56. These results
indicate that the different species have a diverse sensitiveness
to the electric current, so that an intensity which causes the
radicle of one species to turn from the anode will cause the
other to turn towards it (false electrotropism).*

3. Electrotropism in Other Organisms.— While the stolons
of hydroids, Bryozoa, and tunicates offer an excellent oppor-
tunity for experiments on electrotropism in animals, results
have been obtained, so far as I know, outside the group of
phanerogams only in the mold Phycomyces. HEGLER (’92)
has subjected this organism not to the ordinary electric current,
but to Hertz’ electric waves.t The result was that, after
exposing to the radiant electricity for from three to six hours,
the sporangiferous hyphz curved markedly from the source of

* We can now easily understand why Extrvine obtained, with approximately
the same current, a positive curvature in many species, but a negative one with
Brassica. As the list just given shows, the critical point in Brassica lies high.

+t These were obtained by reflecting, by means of a parabolic tin reflector,
the radiant energy upon the stems of the fungi. The latter were covered with
a pasteboard box, to keep out light, and the whole experiment was performed
in a darkened room. The fungi were experimented with when about 8 to 10
em. long, a period when they are most sensitive to light.

EE

NT ED tte en 9

a ee
a7

§ 2] UPON THE DIRECTION OF GROWTH 413

the rays in the same fashion, but not so powerfully, as they
would have curved from light. Thus, electric waves produce
in Phycomyces a negative electrotropism.

4. Magnetropism.—It was stated in an earlier chapter *
that magnetism has no clearly established effect upon proto-
plasm. The alleged effect on growth is, consequently, worthy
of attention. TOLOMEI (793) placed over a glass vessel con-
taining germinating peas a large horseshoe magnet, connected
with a battery composed of eight Daniell cells. The germi-
nating organs bent away from the centre of the magnetic field ;
by an appropriate position of the magnet the roots might be
forced to grow upwards. TOLOMEI also asserts that young
plants are diamagnetic, z.e. tend to place their long axes at
right angles to the lines of force of the magnet. These results
are interesting enough to deserve confirmation.

5. Explanation of Electrotropism and Summary. — Is elec-
trotropism the direct result of the current, or is it, like the
effect upon the rate of growth, an indirect result, due, for
instance, to chemical agents produced by the current? If the
action is indirect, it may be either of a mechanical or of a
chemical nature. RISCHAWI, who proposed the very clever
explanation of positive curvature on the ground of katophoric
action, offered a similar explanation for negative electrotro-
pism. He finds that a cylinder made of coagulated yolk, and
placed in the water transverse to the current, bends at first
convex to the anode, owing to the more rapid diffusion at first
of water into that side; but, later, when the whole mass
becomes permeated, it bends so as to be concave towards the
anode. So, in the root, a weak current can induce a weak dif-
fusion of the external water into the cells on the anode side.
This theory does not, however, meet the conditions ; for, first,
a long-continued weak current does not induce the positive
curvature, and, secondly, because the decapitated root does not
turn from the anode, and the irritation of the tip alone can
induce the result. The mechanical theory must be rejected.

There remains only the other theory, that the negative tro-
pism is a response to a stimulus of some sort applied at the tip.

* Chapter VI, § 1.

414 EFFECT OF ELECTRICITY UPON GROWTH _ [Cu. XVI

It is possible that the stimulus is due to a chemical agent pro-
duced by the current, or directly to the current itself. The.
first alternative is opposed by the fact that the reflected
HERTZ waves, which have little or no gross chemical effect,
still incite a response. There is every reason for concluding
that the electric current, like gravity, and, as we shall see,
light, acts in determining the direction of growth immediately.

The electric current appears to affect the rate of growth of
some plants, so that they grow more rapidly when lying in the
magnetic field or in a highly electrified atmosphere than other-
wise; but this effect is often slight and uncertain. The direc-
tive effect on the growth of elongated organs is more marked.
Apart from a false electrotropic effect produced by the injury
of the positive side of the root, so that growth ceases on that
side, there is a true electrotropic effect, which shows itself in a
turning of the root from the anode. This is a true response to
stimulus, depending for its consummation upon the presence of
the root tip. (The HEertz waves produce this effect in Phyco-
myces. Magnetism has an uncertain effect. The whole’ phe-
nomenon is closely like that of response to gravity and light.

LITERATURE

Axor, A. ’91. Dell’ influenza dell’ elettricita atmosferica. Malpighia. V,
116-125.
95. Dell’ influenza dell’ elettricita atmosferica sulla vegetazione delle
piante. Bull. Soc. Bot. Italiana. Oct. 1895. pp. 188-195.
BERTHELON DE St. Lazare 1783. De IJ’électricité des végétaux, ouvrage
dans lequel ou traite de l’électricité de l’atmosphére sur les plantes, etc.
Paris et Lyon: Didot. 468 pp. 8 Tab.
BruncuorstT, J. 84. Die Funktion der Spitze bei den Richtungsbewegungen
der Wurzeln. II. Galvanotropismus. Ber. D. Bot. Ges. II, 204-219.
’89. Notizen iiber den Galvanotropismus. Bergens Mus. Aarsberetning
for 1888. No.5. 35 pp.
CreLt 778. Appareil pour expérimenter l’action de l’électricité sur les plantes
vivantes. Comp. Rend. LXXXVII, 611-612. 22 Oct. 1878.
Cuopat, R. 92. Quelques effets de l’électricité statique sur la végétation.
Arch. Physiq. et Nat. (3), XXVIII, 478-481.
DuBois-Reymonp, E. ’60. Ueber den secundiren Widerstand, ein durch
den Strom bewirktes Widerstandsphinomen an feuchten pordsen
Kérpern. Monatsber. Berlin Ak. 1860. pp. 846-906.

LITERATURE 415

Erving, F.’82. Ueber eine Wirkung des galvanischen Stroms auf wiichs:
ende Keimlinge. Bot. Ztg. XL, 257-264, 273-278. Apr. 1882.
Frepa, P.’88. Sulla influenza del flusso elettrico nello sviluppo dei vegetali
aclorofillici. Le stazioni sperimentali agrarie ital. Roma. XIV, 39-

56. [Abstr. in Just’s Jahresber. XVI, 93, 94.]

Gautier, A. 95. [Comments on paper of FLAMMARION.] Comp. Rend.
CXXI, 960, 961. 16 Dec. 1895.

GRANDEAU, L. 79. De Vinfluence de l’électricité atmosphérique sur la
nutrition des végétaux. Ann. de Chim. et de Physiq. (5), XVI, 145-
226. Feb. 1879.

Heater, R. ’92. Ueber den Einfluss des mechanischen Zugs auf das Wachs-
thum der Pflanze. Beitrage zur Biologie der Pflanzen. Band VI.
Heft. III, 383-432. Taf. XII-XV.

LemsTroM, S. 90. Om elektricitetens inflytande pa vaxterna. Helsingfors,
1890. 67 pp. 4°. [Abstr. in Bartey. Trans. Mass. Horticult. Soc.
for 1894. 54~-79.]

LoMBARDINI 68. Forme Organiche Irregolari negli Ucelli e ne’ Batrachida.
Pisa, 1868.

Maaerorrnt, C. 84. Influenza del magnetismo sulla embriogenesi e sterili-
mento degli uovi. Atti Acad. Lincei. (3), Transunti, VIII, 274-279.

McLeop, H. M. ’93. The Effect of Current Electricity upon Plant Growth.
Trans. and Proc. New Zealand Inst. XXV, 479-482. May, 1893.

94. Thesame. Ibid. XXVI, 463, 464.

Miuier-Hettiincen, J. 83. Ueber galvanische Erscheinungen an kei-
menden Samen. Arch. f. d. ges. Physiol. XXXI, 193-214. 2 May,
1883.

Riscuawt, L. ’85. Zur Frage iiber den sogenannten Galvanotropismus.
Bot. Centralb. XXIT, 121-126.

Rusconr, M. 40. Ueber kiinstliche Befruchtungen von Fische und iiber
einige neue Versuche in Betreff kiinstlicher Befruchtung an Frdéschen.
Arch. f. Anat. Physiol. und wiss. Medicin (Miiller). 1840. 185-193.

THOUVENIN, M. ’96. De l’influence des courants électrique continues sur la
décomposition de l’acide carbonique chez les végétaux aquatique. Rev.
Gén. de Bot. VIII, 433-450.

Totomer, G. ’93. Azione del magnetismo sulla germinazione. Malpighia.
VII, 470-482. [Abst. Just’s Jahresber. XXI, 37.]

Warren, H. N.’89. The Effects of Voltaic Electricity toward Germina-
tion. Chem. News. LIX, 174.

Winp te, B. C. A. ’93. On Certain Early Transformations of the Embryo.
Jour. of Anat. and Physiol. XXVII, 436-453. July, 1893.

95. On the Effects of Electricity and Magnetism on Development. Jour.
of Anat. and Physiol. XXIX, 346-351. April, 1895.

Wottny, E. ,’93._ Electrische Culturversuche. Forsch. Agr. XVI, 243-

267. [Abstr. in Just’s Jahresber. XXI, 36.]

CHAPTER XVII
EFFECT OF LIGHT UPON GROWTH

WE have seen in Chapter VII that light profoundly affects
metabolism, not only by its heat rays, which are essential to
the process of starch formation in green plants, but also by its
more chemically active rays, which produce chemical changes
in organisms of all classes. We have now to see how, as a
result of these effects, light has an influence upon growth.

§ 1. Errect or LIGHT ON THE RATE OF GROWTH

Two fundamental principles, established in the First Part of
this work, must be recognized at the outset of this discussion,
or else the data which have been accumulated will appear con-
fused and meaningless. The first principle is that white light
is not a constant, definitely determined thing, but varies in its
intensity, and, as we saw in the case of phototaxis (I, p. 201),
at the different intensities produces diverse, even opposing,
effects. The second principle is that not all organisms are sim-
ilarly affected by the same intensity of white light. This is
because they are attuned to diverse intensities of light, so that
the same intensity will call forth a dissimilar response in differ-

ent organisms (I, p. 196). It is a consequence of these two

principles that, when we classify our data on the basis of the
intensity of the light, we shall find dissimilar effects in each
class ; or when, on the other hand, we classify on the basis of
results, we shall have to consider in each class apparently
diverse causes. Since, however, results are always more cer-
tain than causes, we adopt the method of treatment on the
basis of results.

1. Retarding Effect of Light.— We have already in the
First Part of this work seen that Protista are injuriously
affected by strong sunlight, cultures of bacteria becoming

416

ss

eee

§ 1) : EFFECT OF LIGHT UPON GROWTH 417

sterilized and ordinary aquaria being quickly deprived of
living occupants. To the higher organisms, on the other hand,
sunlight is generally not fatal, but is usually unfavorable to
growth. This result is most clearly seen in seedlings. Thus
WIESNER (79, p. 181) exposed seedlings of the vetch Vicia
sativa under a clear glass globe to sunlight, after having
marked off a centimeter’s distance upon its zone of strongest.
growth, and having placed it in a horizontal position so that it.
should get the full force of the sun’s rays. No growth occurred
during seven and a half hours, although the control, in a dark-.
ened globe, turned its tip upwards and grew from 2.5 to.
3.1 mm. during that period. A vertical seedling of the same:
age was so protected by its foliage that in the sunlight it grew
from 0.5 to 1.2 mm. on the different sides. Thus, when the
growing part of a seedling is exposed to sunlight, little or no-
growth occurs, and accordingly we find, as SAcHs (’63) first.
pointed out, that the growing tissue of vegetative points is.
usually protected from the sun’s rays.

In animals, likewise, it is noteworthy that embryonic tissue,
and indeed the entire embryonic individual, is usually sheltered.
from sunlight. In animals the embryo is sheltered in the dark-
ness of the maternal body ; in birds and reptiles the egg shells.
are not merely mechanically resistant, but more or less opaque,
and, moreover, the whole egg is usually hidden from light.*
The delicate, often externally pigmented, embryos of Amphibia.
are often buried by one of the parents or else develop among:
weeds in the water. More rarely, as sometimes in the case of
frogs, they occur in open ponds, but then imbedded in a thick:
envelope of albumen. Fishes usually bury their eggs} or affix
them to the under side of stones or place them in other shady
retreats. ‘To the general rule, however, pelagic fish eggs seem
to constitute an important exception ; but some of these, per-
haps all, can change their level in the water (HENSEN and.
APSTEIN, “97, p. 63). Among molluscs, embryos are oftem
retained in the shell of the parent or laid in capsules and then

* Bianc (’92) has indeed shown that the development of the hen’s egg is
much retarded when subjected in the incubator to daylight.
+ Mitret (’35) has shown that exclusion of light is the chief advantage
gained in this habit.
2=E

418 EFFECT OF LIGHT (Cu. XVII

attached to the under side of rocks, hidden in sand or secreted

in other shady places.

Insects affix their eggs to the under

side of leaves, provide nests for them, bury them in the earth,
in masses of food, in a hundred places hidden from direct sun-
light. Even the larve, which swarm on the surface of seas and

Fie. 118.— Two seedlings of
Sinapis alba of equal age.
EZ, reared in the dark, etio-
lated. N, reared in ordi-
nary daylight, normal.
Root hairs arising from
the roots. (From STRAS-
BURGER, Nout, SCHENCK,

and SCHIMPER, Textbook.

of Botany.)

lakes, sink before the rising sun and
find protection beneath the superin-
cumbent strata of water.* From these
facts we may conclude that, in general,
growth does not take place in nature
in full exposure to sunlight.

Diffuse daylight, even the light which
is essential to all healthy green plants,
markedly affects their growth. This
is a matter of every-day observation.
Who has not observed the contrast be-
tween the elongated, scraggy form of
plants grown in the dark and the re-
pressed, compact form characteristic of
the light? (Fig. 118.) Experiments
and comparative measurements give
us an insight into the degree of this
difference.. Take, for example, the
case of tubers. SAcHs (’63) planted
similar potato tubers in flower-pots.
One pot was covered with a clear bell-
jar and placed in the window; the
other, which served as a control, was
covered by a large flower-pot, thus re-
maining in the dark. Both pots were
kept equally moist. At the end of a
period of 53 days, while the control
tubers had produced sprouts from 150
to 200 mm. high, those which had been

* The degree of protection from light afforded by layers of water is indicated
by certain calculations of Wuirrte ('96), who finds that in a reservoir whose
color is slight (0.33, platinum standard), a layer of water one foot thick absorbs
25%, of the light falling upon it, so that only 0.752, or 56%, of the light at the sur-
face gets below two feet; 0.75%, or 42%, below three feet, and so on.

eee —y—————————_———<_ —“-.- -

§ 1) UPON THE RATE OF GROWTH 419

exposed to the spring sunlight were only 10 to 13 mm. high
—a reduction to one-fifteenth the height in the dark. Many
seedlings show the same thing; thus SAcus found that the
hypocotyl of the buckwheat (Fagopyrum), which attains a
height of 35 to 40 cm. in the dark, reaches only 2 to 3 em. when
freely exposed on a sunny day — here again a reduction in
height of about 94%. This diminution in length is accompanied
for a-while by a diminution in size of the plant asa whole. This
is shown by the measurements of KARSTEN (’71), who raised
kidney beans in the dark and in the light for a month or two,
and found that the entire individual reared during this period
in the light weighed less than that reared in the dark.

The proportionate weight in dark and light was as 12 to 10, fresh weight.
The only organs which were heavier in the seedlings grown in the light
were the roots (slightly) and the leaves (as 5.4 to1). This excess in the
growth of illuminated leaves as compared with those developed in the dark
is characteristic only of such as have broadly expanded blades. Such leaves
seem to require the light for their full development; they constitute a
special case, the peculiarities of whose development will be considered
together with that of other special cases in the last Part of this work. The
growth of leaves, like that of the rest of the plant, is relatively retarded in
the daytime, but this is probably due to the increased transpiration of that
period (PRANTL, ’73).

The effect of daylight upon the growth of stems is, as SACHS
has pointed out, unequal in the different plants. In extreme
cases (internodes of Bryonia, a wild gourd; of Dioscorea, the
yam; etc.) daylight has no evident effect, for the stems have
the scrawny, “etiolated” habit characteristic of plants grown
in the dark. Plants which are little repressed by light are
said by SAcus to be chiefly those whose rapidly growing parts
are sheltered from the sun’s rays by protecting coverings. We
may conclude that the growth processes of such plants are
little interfered with by strong light, because their protoplasm
has through long experience become attuned to it. Except
where such attunement has occurred, light tends to retard the
growth of phanerogams.

The germination of seeds and spores of fungi is accompanied
by processes akin to those of growth, and so may be treated
here. The germinating protoplasm of seeds is partly shielded
from light by a thick coat; nevertheless a series of careful

420 EFFECT OF LIGHT [Cu. XVII

observers in the early half of the century, and, more recently,
NoBBE (782), ADRIANOWSKY (788), and others, have shown
that germination of seeds takes place slightly earlier in the
dark than in daylight. Among fungi, also, we have the assur-
ances of HOFFMANN (’60, p. 821) that the spores of the mush-
room Agaricus campestris germinate more slowly in the light ;
and of DE BARY (’63, p. 40) that the spores of the potato
fungus, Peronospora infestans, and its allies do germinate with
difficulty in the daylight, and not at all in the sunlight. Thus
the germination of spores —
=~ even more than of seeds is
retarded by light (p. 174).
ogre Passing now tothe growth
A ens of fungi, we find numerous
and harmonious observations
\ on the effect of light. Fries
| (21, p. 502) first noticed
} that the growth of fungi is
* retarded in the light, and
SCHMITZ (43, p.512), KRAUS
(76, p.6), VINES (78), STA-
MEROFF (’97), and others
have confirmed this result
for hymenomycetes, the er-
got fungus, and molds.*
BREFELD (77, p. 90; 789,
p- 275) found that the toad-
stool Coprinus stercorarius
reared in the dark attains a
length of two feet or more,
while in the daylight it is

only an inch long (Fig. 119).

Fic. 119. — Coprinus stercorarius in reduced A gain, the sporan gifer ous
size. Fig. 1, typical young fruiting f

fungus reared in the light. Fig. 2, a, b, hypha of the dung mold Pi-

ce, d, fungus reared in weak illumination. ]obolus microsporus, which
Fig. 5, Coprinus reared in darkness.

1, sclerotium; 2, 6, stalk; 3, 4, fruit; 18 eight or ten inches long
5, roots; 6,hyphe. (From Breretp,’77.) in the dark, grows only half

* But Buiior (’97) denies it in the case of Phycomyces nitens. His experi-
ments are not, however, convincing.

§ 1] UPON THE RATE OF GROWTH 491

an inch long in the daylight. Bacillus ramosus, in one case,
grew during five hours, in the dark, 540; in the light, 200 y
(WARD, 95). These results demonstrate that the inhibiting
or retarding effect of sunlight, and even of diffuse daylight, is
probably unconnected with the chlorophyll function, but is due
to a more general effect of light upon growing protoplasm.
Even brief illumination has its marked.effect. Thus VINEs
(78, p. 137), who has made exact measurements of the hourly
growth of the sporangiferous hyphz of the mold Phycomyces
nitens, found that growth was diminished whenever the plant
wassubjectedforonly gs 9 » un wit 2 8 4

===

3 == =

an hour to sunlight ff TM i i i i

(Fig.120). Thesame 4 Ne e ee es al

is true for phanero- x NO i " f “Al

gams (GODLEWSKI, WE aa TN

ee sf fs

The great diurnal *| i e— é : i

period of darkness and col + rin ; : TNT ell

illumination to which | / | A

plants are subjected |) / | :

in nature likewisehas *| ae il | \

; : Le ill NA IN IO

its effect on growth. Ta i an ee ; a , an ae

Thefirststudiesmade 0 ul ee 22°

upon this subject were Fic. 120. — Diagram illustrating the retarding influence
3 of light upon the growth of a sub-aérial hypha of

by TREwW in 1727. Phycomyces. The thick line represents the course

Numerous observers of Lapses the thin ae of passa ee a8

: un spaces, peri of e ure to light; t

followed, but it was shaded Seeks sald of sich asaut The nents a

left to SACHS C72), the left indicate tenths of millimeters, those at the

by the aid of his aux- right, degrees of temperature; those at the top,

3 hours. (After Vinzs, '78.)

anometer, to obtain a

continuous curve of growth. This showed at a glance that dur-

ing the night the rate of growth gradually increases, reaches a

maximum at about daybreak, diminishes to a minimum a little

before sunset, and then begins to rise again.* This variation

in the rate of growth is opposed to the diurnal fluctuation of

temperature, since this is low at night and high during the day.
It is favored, on the other hand, by the circumstance that heat

* A similar periodicity has been detected among toadstools and puffballs by
Kravs (°83, p. 97).

422 EFFECT OF LIGHT [Cu. XVII

and light favor transpiration ; and this means loss of water
and, consequently, of growth. Just how far these opposing
effects neutralize each other cannot be said, but our compara-
tive study gives assurance that the effect may well be pro-
duced by light acting alone. While the diurnal periodicity in
growth can clearly be ascribed to no other cause than the alter-
nation of day and night, it is an important fact that this perio-
dicity may be exhibited for several days after the plant has been
placed in a room kept constantly dark. There is apparently a
persistence of an effect impressed by environment.

Among animals the evidence of a retarding effect upon
growth is not so clear. MAuvpas (’87, p. 1008), indeed, con-
cludes from actual experiment that various ciliate Infusoria
multiply with equal rapidity in the presence or the absence of
light. In the higher vertebrates, on the other hand, light,
acting through the retina, increases destructive metabolism, as
MOLESCHOTT (55) first pointed out, so that many vertebrates
undergo a greater loss of weight in the light than in the dark.
Indeed, a diurnal periodicity in the weight of animals was
described as long ago as 1852, by BIDDER and ScuHMrIpT, who
found that starving cats lost weight much faster in the day
than at night. These facts constitute a not unimportant par-
allel with the conditions in plant growth.

In summarizing the foregoing facts on the retardation of
growth by light, we see that strong sunlight usually com-
pletely inhibits growth, so that the growing parts of organ-
isms, or entire organisms during the period of growth, are usu-
ally concealed. Even diffuse light retards growth, especially
in the following organisms: most seedlings, many of the
higher aérial fungi, germinating seeds in general, and spores
of fungi. Also, light hastens destructive metabolism in the
higher vertebrates so as to diminish weight rapidly. The
organisms thus brought together are without exception aérial.
This fact suggests that in plants, at least, the restraint of
growth by light may be due to the rapid loss of water which
accompanies illumination. The illumination of seedlings and
fungi for only a brief period —an hour or so—retards their
growth. These organisms likewise exhibit a diurnal perio-
dicity in growth corresponding to the alternation of day and

§ 1] UPON THE RATE OF GROWTH 423

night. Not all seedlings and fungi are equally affected by
light ; the effect depends upon their normal conditions of illu-
mination —the conditions to which they have become attuned.

2. Accelerating Effect of Light.— Although certain species
of phanerogams are little affected in their growth by light,
actual acceleration probably rarely occurs in this group. The
parasitic mistletoe (Viscum album) seems to form an impor-
tant exception, however, since, according to WIESNER (’79, p.
183; °98, p. 506), it neither grows nor germinates in the dark.
This fact is correlated with a peculiarity in its phototropic
response, as we shall see later (p. 438). Among aquatic alge
several cases of acceleration of growth by light have been

T
NUMBER CIC. |
ee ee
WATENGITY OF cH,
0 20 40 ~—60 100
|
2 ae
‘ P 4
6 f DIAGRAM SHOWING THE

GROWTH OF DIATOMS
AND THE
INTENSITY OF LIGHT
il AT VARIOUS DEPTHS
@
5

DEPTH IN FEET
So leo
=

8

| LAKE COCHITUATE WATER LOCATED IN LAKE COCHITUATE
&— NOV. 29,1895. EXAMINED DEC. 9, 1895.
{s TEMPERATURE 40 = 44, COLOR 0.33

THE DIATOMS WERE CHIEFLY ASTERIONELLA AND
MELOSIRA,
THE INTENSITY OF LIGHT AT DIFFERENT DEPTHS WAS
CALCULATED ON THE ASSUMPTION THAT A LAYER OF
WATER ONE FOOT IN DEPTH ABSORBS 25°%o OF THE
LIGHT FALLING UPON IT.

i
LIGHT!

_
o

Fig. 121.

recorded. The flat, circular, green thallus of Coleochete scu-
tata, when obliquely illuminated, -grows, according to Kny
(84), faster on the side next to the light. Again, Spirogyra
which has been kept in the dark until all of its starch has been
consumed grows when placed in the light, but does not grow
in darkness (FAMINTZIN, ’67). Lately WHIPPLE (’96) has
given quantitative data on the relation between intensity of
light and of growth in diatoms. A known quantity of dia-
toms of one ,or two species was placed in a bottle of water,

424 EFFECT OF LIGHT [Cu. XVII

covered with bolting cloth, and suspended in the water of a
reservoir, at. the surface and at various depths below the sur-
face down to 20 feet. Experiments were made at a time
when the temperature of the reservoir water was almost the
‘ same at all depths. After several days the bottles were col-
lected and the number of diatoms in each determined. The
results of one series of experiments, shown graphically in Fig.
121, demonstrated that the growth of diatoms is directly pro-
portional to the intensity of light received by them.* We
may conclude that in general, excepting perhaps the mistle-
toe, those plants whose growth is accelerated by light normally
have their growing parts fully exposed to sunlight. Their pro-
toplasm is attuned to a high intensity of light—is not retarded
by it ; indeed, demands it for the normal exercise of its func-
tions.

Passing now to the subject of germination, we find that the
first development of the spores of the higher cryptogams usu-
ally requires or is: favored by light (HorrmManny, ’60, p. 321,
and others). The spores of many ferns, of the moss Poly-
trichum commune (BORODIN, *68), of the hepatics Duvalia and
Preissia (LEITGEB, ’77), and of Vaucheria do not germinate at
all in the dark. However, this result is not universal among
the higher green cryptogams, for MILDE (’52, p. 627) observed
that spores of Equisetum germinated in the dark as well as in
the light; and it is clear that certain fern spores (Ophioglos-
sum) can do so, for they germinate when covered by soil toa
depth of 3 to 5 em. It is somewhat unexpected to find
the spores of such dark-lovers as ferns and hepatics nor-
mally dependent for their germination upon light. One calls
to mind, however, the fact that it is the habit of such spores to
germinate on the surface, where their prothalli are found -—
hence at such times always subjected at least to a diffuse light.

Certain seeds, also, are said to germinate more readily in the
light than in the dark. We have already cited the case of the
mistletoe ; the same seems to be true of the meadow grass,
Poa, as is shown by the following experiments of STEBLER
(81). Two species were experimented with, and two experi-

* However, Wurprte found that growth at the surface, where full sunlight
fell upon the bottle, was less than at a few inches below the surface.

:

§ 1) UPON THE RATE OF GROWTH 425

ments were made upon each species. In each experiment two
lots of seeds were placed together in a thermostat; the one

_ being subjected to daylight, the other being kept in darkness.

The percentage of germination in the eight lots was as fol-
lows : —

Poa NEMORALIS, Poa PRATENSIS.
Lieut. Dark. LiGut. DakkK.
~ Experiment No.1... ....-..- 62 3 59
Meapermment NO.'2 ces eee we 53 1 61 0

The result seems decisive and has been fully confirmed by
LIEBENBERG (’84) and JONsson (’93), not only for Poa but
certain other small seeds.

According to LIEBENBERG the favorable action of daylight
is due rather to the alternation of high and low temperature on
the seed. Thus, while about 8% of Poa seeds germinate in
a dark chamber kept constantly either at 20° or 28° C., 91%
are germinated after 34 days in a dark chamber kept for 19
hours at 20° C. and for 5 hours at 28° C. In this case we have
to do clearly with a response to a particular stimulus of the
heat rays reminding us of the stimulus of alternating heat and
cold necessary for the germination of certain animal statoblasts
or gemmules (BRAEM, 795).

Among growing animals, studies on the effect of Light were
early made by Epwarps (21), who concluded that tadpoles
would not develop at all in the dark. In this he went as far
from the truth in one direction as HIGGENBOTTOM (750 and
63) and MAcDONNELL (’59), who denied any difference of
growth in the light and in the dark, did in the other. The
work of YuNG (’78) first revealed the exact truth of the
matter. This naturalist placed freshly laid frogs’ eggs in
vessels, each containing 4 liters of water and 60 eggs. One
lot was placed in front of a window, where, however, it
never received the direct rays of the sun. The other lot was
kept constantly in the dark. Otherwise the conditions of the

426 EFFECT OF LIGHT (Cu. XVII

two lots were very similar. After 30 days, and again after
60, 3 typical tadpoles of each lot were measured. Their
averages, together with those from a second series, are given
below :—

TABLE XLI

Suow1ne FOR Two Lots or TapPoLes THE RELATIVE SIZES ATTAINED IN THE
LIGHT AND IN THE DARK

REARED IN THE RELATIVE Size or
* Ligut’? TappoLes
COMPARED WITII
Lieut. Dark. “Dark.”
Lot 1: 80 days Length . . . . | 23.10 mm./| 19.66 mm. 117%

Breadth. ...4 « 5.50 4.66 118
Lot 1: 60 days Length . .. . | 82.16 30.30 106
Breadthis: . «0. 7.66 7.16 107
Lot 2: 25 days Length ... .| 19.83 15.83 125
Brean a 4.33 3.50 124

This table clearly shows that tadpoles grow faster in the light
than in the dark, and that the difference in the rate of growth
is more marked during the first than during the second month
of development.*

Other animals have been experimented upon by Yuna. He
placed recently fecundated eggs of the sea trout, Salmo trutta,
in 4-liter vessels, each of which contained 200 eggs. Those
lots which were reared in the light hatched a day earlier than
those reared in the dark. Also, the pond snails, Lymnea stag-
nalis, reared in the light hatched in 27 days, whereas those
reared in the dark required 33 days. Perhaps less weight is to
be given to the observation of HAMMOND (’73), who found
that 20-day-old cats, reared under similar conditions except as
concerns daylight, grew faster in the light than in the dark.

* With these experiments agree certain experiments of Lressona (’77) and
CaMERANO (’98) upon the size of tadpoles taken from ponds so thickly covered
with vegetation as to shut out the light, as compared with tadpoles from fully
exposed ponds. CameErano finds that, at the same stage of development, the
sizes are as 9 to 14, or the tadpoles reared in the light are 156% of the size of
those reared in the darker ponds. Such observations in which the other con-
ditions are not controlled are not, however, altogether satisfactory.

§ 1) UPON THE RATE OF GROWTH 427

There is thus a considerable body of evidence that a not too
intense light accelerates the growth of animals in general.

To sum up, we find that diffuse light accelerates growth in
the following organisms: Mistletoe seedlings, Coleocheta, etio-
lated Spirogyra, diatoms, germinating spores of many ferns,
mosses, hepatics, and Vaucheria, germinating seeds of Viscum
and small-seeded grasses, tadpoles, embryo snails, trout, and,
perhaps, young kittens; in brief, of a parasitic seedling, of
alge, of germinating spores in many higher cryptogams, of a.
few germinating seeds, and of some animals. The collection.
seems like a heterogeneous one; yet omitting germination
phenomena, the case of the parasitic mistletoe, and the doubtful
cat, all the organisms concerned are aquatic. The reason why
the growth of aquatic organisms is not restrained by light may
be that with them light does not produce increased trans-
piration.

3. The Effective Rays. — As we have seen in the First Part.
the various rays of which white light is composed affect proto--
plasm diversely. The question now arises, What part do the:
separate kinds of rays play in the retarding and accelerating
effect of light on growth — what are the rays upon which these:
effects especially depend?

At the outset it must be stated that a large part of the recorded observa-.

_ tions upon this subject is worthless because the methods were not quantita-

tive. Let us suppose we have a white light of known intensity which in-
hibits growth, and that we desire to know which of the component rays are
most effective in imbibition. The different component rays should have the
same intensity as they have in the given white light. For a more effective:
ray of weak intensity will produce a smaller result than a less effective ray
of great intensity; because not only quality but intensity of the light deter-.
mines its effect. Now, insufficient care has been taken to measure, by the:
methods given in Chapter VII, the intensity of the colored light employed;:
consequently it is little wonder that most contradictory statements are given.
as to the effect of red, green, and violet light upop related organisms, and.
that great caution is demanded in drawing conclusions from the data at
hand.

a. The Effective Rays in the Retardation of Growth by Lnght.
— We have already seen (p. 166) that experiments upon the
effect of the different rays upon metabolism occupied the atten-
tion of naturalists in the first half of the century. It was but

|
428 EFFECT OF LIGHT (Cu. XVII

a step to the study of the effect of these rays upon growth, and
this step was taken by SAcus in 1864.

The method of subjecting the plant to particular rays was as follows:
The apparatus consisted of a glass jar, placed inside of a larger glass jar, the
interspace being filled with a colored fluid. This apparatus stood behind a
southeast window. Orange light was obtained by 12 to 13 mm. of a satu- ©
rated solution of potassium dichromate, which transmitted red, orange, and
yellow, but no blue or violet; and blue light, by the same thickness of
ammoniated copper sulphate, which excluded all rays of shorter vibration
than the green, but, likewise, reduced the intensity of the violet end of the
spectrum. The relative chemical intensity of the light passing through the
solutions was determined by noting the time required to blacken photo-
graphic paper held in the inuer jar.

Under the conditions of the experiment young seedlings of
the white mustard, Brassica alba, and of flax, Linum usitatis- _
simum, grew more rapidly and vigorously in the orange rays,
which act thus like darkness, than in the blue, which act thus
like daylight. In orange light the leaves, although differen-
tiated, remain small, while the internodes are elongated; in
both of which respects the plants show themselves etiolated. .
In the blue rays the cotyledons, unlike the leaves, remain small;
since, in the absence of assimilation, which requires red rays,
they are drawn upon for food. Throughout, the less intense
blue rays acted more like white light than the more intense
orange rays.

Several confirmatory experiments upon other plants may
now be briefly considered. BERT (’78, p. 986) cultivated a
Sensitive Plant ina lantern made of red glass. It lived for
months, elongated considerably, and had small leaves; one
might have called it etiolated but for its remaining green,
owing to the formation of chlorophyll in the red rays (p. 170,
note). Behind blue glass it had the general form character-
istic of white light, but it did not grow as large as in day-
light — which includes also the warmer rays. The whole
habit of the plants in the red rays indicated greater turges-
cence than in the blue: a result which BERT suggests may be
due to the manufacture in the presence of the red-yellow rays
of a material (glucose) causing an endosmotic flow. This
explanation, however, seems negatived by the fact that plants
grown in darkness exhibit this same condition. WEISNER

a

§ 1) UPON THE RATE OF GROWTH 429

(93) finds that the stems of seedlings of Vicia faba grow
behind Sacus’ blue solution, which reduces the intensity from
one-third to one-half that of daylight, nearly as slowly as in
daylight, and much more slowly than in darkness, in the ratio
of: daylight, 141; blue, 155; darkness, 185. Again, FLAM-
MARION ((95) cultivated the Sensitive Plant in little conserva-
tories behind clear and colored glass.* From a lot of seedlings
reared under tformal conditions those were selected which were
most alike (all 27 mm. high), and placed, July 4th, in the
various conservatories. On October 22d the plants had the
following average heights: in the red, 420 mm.; green, 152
mm.; white, 100 mm.; blue, 27 mm. (Fig. 122). Thus, under

se
)

is

Pee SE 2 ge
Tm A TT ae
“ANNI
Green

Fic. 122. — Action of different solar rays upon the growth of the Sensitive Plant. On
August ist, placed as seedlings each 27 mm. high behind diversely colored glass
screens. Photographed Oct. 22. (From FLAMMARION, ’95.)

* The data concerning methods are as follows: The blue glass used trans-
mitted only the more highly refracting rays; the red was almost strictly mono-
chromatic ; the green was less satisfactory, but let through no red. The inten-
sity of illumination decreased considerably in the order: white, red, green,
blue. The conservatories were placed side by side, under similar conditions,
and a current of air was passed through, from one to the other, to maintain a
uniform temperature.

430 EFFECT OF LIGHT [Cu. XVII

red light, as in darkness, the greatest growth occurred ; under
-the blue light no growth had occurred, 7.e. less than under
the clear glass. The order of height was thus: blue, white,
green, red ; that of the vigor of vegetation was: blue, green,

white, red. ‘The peculiarly injurious effect of the violet and.

ultra-violet rays is shown also in the deleterious action of
electric light, which is rich in these rays (SIEMENS, ’80, ’80,
’82). All the foregoing observations are thus*in accord, and
indicate that the retarding action of white light upon seedlings
is the resultant of the accelerating and the inhibiting actions
of the different rays.

Among fungi we have observations by VINES (’78) which
show that Phycomyces nitens, subjected intermittently to the
action of darkness on the one hand, and of white light, blue
light, or yellow light, on the other, suffered a similar retarda-
tion in white and blue light, while in yellow light no marked
retardation occurred.* Bacillus ramosus (Fig. 123) grows
behind a red screen as in darkness; behind a blue screen (of
CuSO,) its growth is retarded as in daylight (Warp, 795,
p- 381).

Among alge FAMINTZIN ('67) has found that Spirogyra
which has been kept in the dark until all of the starch is con-
sumed grows more rapidly in the successive members of this
series: darkness (no growth), blue light, full lamplight, yellow
light. Here we see that, while a certain amount of light is
necessary to the metabolism of the etiolated alga, growth, as a
whole, is favored by the absence of blue rays.

Animals which are symbiotic with algz flourish or decline
with the latter. Accordingly, YuNe (92) has found that
Hydra viridis,} which has this kind of symbiosis, grows more
rapidly in the successive members of the series: darkness
(fatal), violet, green, white, and red. This series is essen-
tially that just given for alge living alone.

* Kraus (’76) says that Claviceps growing in daylight attains a length of
only 4to6 mm. ; in green rays, 17 mm.; in yellow and blue, each, 30 mm. ;
and, in the dark, 36 mm. Not much weight can be given to this statement,
since an account of methods is lacking.

+ A similar result was obtained with the green turbellarian Convoluta

Schultzii.

a es

ara

oS CSE

§1J UPON THE RATE OF GROWTH : 431

The foregoing concordant observations may be summed up
in the statements that the action of white light upon seedlings
is the resultant of the action of the component rays; that, of
these, the red tends to favor growth by rendering possible
starch formation; the blue, on the other hand, tends to

Ne
X

40 4 —
fe: No. 7 5 | OO

oe

715.4

L
Sees veer ame far, eee 28 Os A SR RE ce Sew BS

I

8
wits

\

Fic. 123.—Curves of growth of threads of Bacillus ramosus in blue light (Experi-
ment No. 75, of Warp) and in red light (Experiment No. 74). The numbers at
the left indicate microns; at the bottom, hours. The retardation due to blue
light is evident. (From WARD, 95.)

restrain growth, probably by introducing certain destructive
(or controlling) chemical changes ; that, in the dark, seedlings
being freed from the restraining action of the chemical rays,
grow rapidly so long as the stored food products permit; that,
in daylight, although the means of nutrition is provided, the
presence of the inhibiting blue rays tends to cause slow
growth. Upon other organisms whose growth is retarded by
light, the effect of white and blue light must be quite the same;
and the experiments of VINES and of WARD upon fungi show
that this is the case. The effective rays in retardation of
growth are clearly those at the blue end of the spectrum.

432 . EFFECT OF LIGHT . (Cu. XVII

6. The Effective Rays in the Acceleration of Growth by
Light. — We have seen that’ the effective rays in retardation
are the blue; the question now arises: Will the same rays
serve, in other cases, for acceleration, or must the latter be
due to the red rays? .

As concerns the germination of ferns we have the observa-
tions of BORODIN (’68, p. 435), in the case of Aspidium, that
germination did not take place in the blue any more than it
did in darkness, while the red rays produced nearly the whole
effect of white light. Germination in this case seems to
demand the red rays for its processes— processes consisting
largely of certain chemical changes favoring imbibition of
water. Probably those seeds which germinate more rapidly in
the light than in the dark make similar use of the red rays, as
JONSSON (93) has, indeed, found they do in the case of Poa.

Passing now to animals, we find the first critical work on
these organisms is that of BECLARD (’58). This experimenter
placed at one and the same time, under diversely colored glass
bells, eggs of the flesh-fly, Musca carnivora, taken from a
single laying. All the eggs produced larve; of these, the
largest were formed under the violet or blue glass, the small-
est under the green. The effect of the other colors was inter-
mediate and fell in the following order: violet, blue, red,
yellow, white, green. The larve reared under the violet rays
were three-fourths greater than those reared under the green.*
The apparent acceleration in violet, as compared with white
light, indicates that the green rays of white light retard. This
was the result actually obtained by SCHNETZLER (74, p. 251),
who found: that tadpoles developed more slowly behind green
glass (from which red and violet rays chiefly were cut out)
than behind clear glass.

* Yune (78) made more critical experiments upon tadpoles.
Screens of nearly monochromatic solutions were used (p. 157).
The size of the vessels and the number of tadpoles in each

* Exactly opposite results for blow-flies are given by Davipson (’85), whose
work, however, strikes one as crude. Fly larve reared in a bottle made of blue
glass had at the end of nine days only half the weight, on the average, of larve
reared either behind clear glass or in the dark. This subject needs careful
investigation.

Ԥ1) UPON THE RATE OF GROWTH 433 |

were the same. At the end of one month* three tadpoles
were taken at random from each vessel and measured. In the
following tables are given the average length and breadth of
these tadpoles (from series of 1876 and 1877), and also the
lengths compared with that in white light :—

TABLE XLII

AVERAGE Dimensions OF TADPOLES REARED BEHIND CLEAR AND COLORED
SCREENS DURING ONE MontTH

Cotor or LicuHT. AVERAGE LENGTH. AVERAGE BREADTH. I ee
Wtit@ sca. 24.43 mm. 5.37 mm. 100
6 re 28.58 6.75 117
MRE tbe es 4» 25.66 5.70 105
MOMOW 2%. « 24.37 5.46 * 99
MEMES: debrin ts < 20.37 4.66 83
Sa ae 16.99 3.91 70

Similarly, averaging the dimensions of the tadpoles at the
expiration of two months, we obtain : —

TABLE XLIla

AVERAGE DIMENSIONS OF TADPOLES REARED BEHIND CLEAR AND COLORED
ScREENS DURING Two MontTus

CoLor or Lieut. AVERAGE LENGTH. AVERAGE BREADTH. apogee gaa
eT. 6 ce 8 31.58 mm. 7.50 mm. — 100
MMOGs fr) d Gas 42.32 10.41 134
1 ane 33.92 8.00 107
Yellow ..... 32.24 7.50 102
OS aa er ey er 27.17 6.50 86
ree 6654s All died before two months

Tadpoles reared in the dark were uniformly slightly larger
than those reared in red light, while violet and blue light show
themselves especially favorable to the growth of the frog.

* During the first days of development in the cases of the frog, the snail Pla-
norbis, and the sea-urchin Echinus, there is, according to Driescn (’91), no
difference in the rate of growth behind various colored glasses. The diverse
effects of different rays appear only in later stages.

2F

45-4 EFFECT OF LIGHT [Cu. XVII

Upon Echinoderm larve VERNON (95) has made some
important experiments. He used YuNe’s methods of getting
colors; but relative intensity is not indicated. The following
table gives his results : —

TABLE XLIII

PERCENTAGE DEVIATIONS IN LENGTH OF LARV OF STRONGYLOCENTROTUS
LIVIDUS REARED BEHIND Various COLORED SCREENS, FROM LENGTH oF
LARV REARED IN WHITE LIGHT

Cotor. NuMBEE oF SETS OF MEAN CHANGE.
EXPERIMENTS.
Semi-darkness< .-.5 Was 3 + 2.5%
Complete darkness .......% 4 — 1.3
Blue (copper sulphate)....... 2 — 4.5
POOR Ge dees w i, ate rene ne Bae 4 — 4.8
BOL” 5 atin. ahs Ou bee set San op 2 — 6.9
Blue (Lyon’s blue) .....5....% 2 — 7.4
Vellow..: vy aleve twist Hedi Shae 2 — 8.9

All larvee reared in violet light soon died on account of the
development of bacteria. In this case the order of growth
followed the series: white, blue (of copper sulphate solution),
green, red, blue (of Lyon’s blue), yellow. This series differs so
much from BECLARD’s that the experiment demands confirmation.

Certain experiments of YUNG on the relative time of hatch-

ing may be given here, since the time of hatching depends”

upon rate of growth :—

TABLE XLIV

RELATIVE Time OF HATCHING OF ORGANISMS REARED BEHIND COLORED

ScREENS

LOLIGO VULGARIS. SALMO TRUTTA. LYMNAA STAGNALIS. AVERAGE.
Violet, 50 days Violet, 32 days Violet, 17 days Violet
Blue, be. Yellow, 34 ‘* Blue, 19 * Blue
apn ef Blue, \ 35 te Yellow, 25 ‘ Yellow
Red, White, White, 27 ‘ White
Green, —* Green, 36 ‘ Red, 36 * Red
White, all died . Green, all died Green

* Had not hatched by 62 days.

§ 1] UPON THE RATE OF GROWTH 435

These series run then in order of effect on growth exactly par-
allel to the series obtained from the growing tadpole, and are
very similar to the series obtained by BECLARD for the blow-
fly.

There are certain a priort grounds for believing that
BECLARD’s series is the more correct, not only for growing
flies, but for all animals. We would then get for a curve of
relative effect of the different parts of the spectrum upon
growth something like Fig. 126, J.* The conclusion to which
all these experiments point is this: the accelerating effect of
weak white light upon the growth of animals, contrary to the
case in plants, is due to the short-waved rays.

The alleged peculiar effects of the green rays cannot go
unnoticed. These seem to have been first insisted upon by
Bert (72, ’78), who found that in the green lantern the
young sensitive plant lost sensibility and died in three or four
days, which is about the time in which they would have died
in complete darkness. This observation has been confirmed
by several experimenters ; for example, by KrAus (’76, p. 8),
ADRIANOWSKY (783), VILLON (794, p. 461), and GAUTIER
(95) for plants, and by SCHNETZLER and by Yunge for tad-
poles. Yet, on the other hand, FLAMMARION (795) found no
peculiar action of green light upon the sensitive plant. In
the absence of precision in the opposing statements, we may
doubt whether green rays, as such, produce any positive harm.
It is probable that they are neutral in growth.

Summing up the results of our study on the effective rays in
the modification of growth by light, we find that retardation,
as it occurs in most aérial plants, is due to the chemically
active rays; that acceleration, as it occurs in animals, is like-
wise due to the same rays. Both effects must be due to chem-
ical, metabolic changes, induced by light: in the first class,

* The favorable effect of violet or blue rays was noticed also by ViLton (’94,
p. 463) upon silkworms. Here may be mentioned the ‘‘ blue glass”’ rage of
twenty years ago, which was largely due to the writings of General A. J.
PLEASONTON (’76), which, while containing a basis of truth experimentally
obtained by the author, were of a highly uncritical and even sensational char-
acter.

436 EFFECT OF LIGHT [Cu. XVII

these are of an injurious character; in the second, they favor
the metabolic growth processes. Long-waved light, on the
other hand, has usually no more effect than darkness, or the
absence of light. However, upon germinating ferns and
grasses long-waved light has a decided accelerating effect.
Since even in daylight growth occurs faster than in the dark
we must conclude that upon these organisms the blue rays do
not seem to exert an injurious effect; they are, as it were,
blind to the blue rays, and hence experience no freedom from
restraint in the dark, and, unlike seedlings, no excessive growth
there. |

4. The Cause of the Effect of Light on the Rate of Growth.
— The action of red rays upon growing phanerogams requires
no special explanation here. It is clear, from what we already
know, that an etiolated seedling, or alga, can develop only in
the presence of the red rays, which are ordinarily essential to
its nutrition. Consequently, we find that red rays do not
hinder the growth of ordinary seedlings, but cause etiolated
green plants as well as seedlings of ferns and grasses to grow
faster than they would in the dark.

The action of the blue ray does, on the other hand, demand
more detailed consideration, for it seems at first as if its
diverse effects upon plants and animals constitute a great diffi-
culty. Why should the same rays retard the growth of aérial
organisms and accelerate that of water animals? In inventing
an hypothesis to fit the case, we have first to recognize that the
action of the blue ray is a chemical one, and is probably of the
same kind upon all organisms. It must, consequently, be that
the degree of the effect is different. This difference may be
due either to a difference in the quality of the different proto-
plasms or to a dissimilarity of the external conditions under
which the effect is produced. We may say that, either on
account of the presence of abundant free oxygen in the air, or,
perhaps, on account of a greater lability of plant protoplasm,
the blue rays effect such extensive transformations (oxidations,
QuINCKE, 94) in aérial plants as to interfere with growth,
possibly, by promoting loss of water. Upon water organisms,
on the other hand, only slight metabolic changes occur, which,
on the whole, favor the imbibitory or assimilative processes.

satie EEE eee —

§ 2] UPON THE DIRECTION OF GROWTH 437

§ 2. Errecr or LIGHT UPON THE DIRECTION OF GROWTH
— PHOTOTROPISM *

Under this topic will be considered, first, the effect upon
plants; secondly, upon animals; and, after that, certain gen-
eral matters concerning phototropism.

1.» Plants. — The fact that seedlings reared in a room near a
window all have their tops directed towards the source of light
instead of vertically can
scarcely have escaped any
one’s notice. References to
the phenomenon are found
in the literature of the an-
cients ; its scientific study
was begun in the early part
of the last century by HALES
(1727). Not only the stems
of seedlings but many other
plant-organs show this n n
growth with reference t0 =z
the direction of the infalling a
rays of light. Among these =
are tips of many stems, many
leaves, cotyledons, roots (es-
pecially aérial ones), tendrils, =
the fruit-bearing hyphe of ee
cryptogams, and certain or-
gans of the bryophytes and
pteridophytes.

The sense of the turning
: : . : Fie. 124. — Seedling of Sinapis alba exhibiting
ao ordinary day light 1s not positive phototropism of the stem, ab, and

always the same. Whilethe negative phototropism of the root, de. nn,
stems of. most seedlings of surface of the water in which the plant is

h: d germinating. The arrow indicates the di-
phanerogams turn towards rection of the infalling light rays. (From

the light (positive photo- Frayx, ’92.)

My NWI

PSION TAT |
|

rny

6

* On some accounts it is unfortunate to accept this word rather than the
older, more familiar term ‘‘ heliotropism”’; but as the latter is obviously unfitted
to our broader view of the subject, and encourages the introduction of new
special terms, such as selenetropism or turning towards the moon (Musser, ’90),
I think it is desirable to adopt the newer term.

438 EFFECT OF LIGHT [Cu. XVII

tropism), the following turn from it (negative phototropism):
the hypocotyl of the seedling mistletoe; the roots of many
plants, e.g. Sinapis (Fig. 124), Helianthus, Vicia faba, Zea
mais, etc.; stems of some recumbent dicotyledons, e.g. the
moneywort; the root hairs of the prothalli of ferns and hepat-
ics; the tendrils of the vinés Vitis and Ampelopsis. As we
shall see later, however, the sense of turning is, within limits,
dependent upon the intensity of the light.

Finally, we observe that plants differ greatly in the degree
of their phototropism. ‘Thus aquatic plants and non-chloro-
phyllaceous phanerogams are only very slightly phototropic
(compare HOCHREUTINER, °96).

The general phenomena of positive phototropism are seen
when a seedling which has been growing in the dark is illu-
minated upon one side by a horizontal ray. The tip of the
seedling, which is normally constantly “nutating” about the
vertical line passing through its axis, now begins to move
towards the light side of the vertical. The quickness with
which it does so seems to vary with the species and with the
intensity of illumination of the plant and other conditions of
the environment; the turning may be evident in 15 minutes*
or it may be delayed for several hours. ‘There is apparently a
certain, not precisely determined, latent period elapsing be-
tween illumination and response. ‘The curvature first appears
eh behind the tip of the seedling, but later almost the whole

stem above the ground becomes in-
) ff volved, so that after several hours
it points straight towards the
source of light (Fig. 125).

The intensity of light necessary
Cis Daa to provoke the maximum response
Bee Se or phototropie Varies with the species. WIESNER

curving of the cotyledon of (93) especially has made accurate

Avena sativa. a, before illu: determinations on this subject.
mination; 0, after 14 hours; c,
after 34 hours; d, after 74 hours. The unit of measurement is a normal

(From RoTHERT, ’94.) candle (p. 160) burning at a distance

* Darwin (’81, Chapter IX) found with the aid of a microscope that the tip
may begin to turn in from 3 to 10 minutes,

§ 2] UPON THE DIRECTION OF GROWTH 439

of one meter from the organism: (meter-candle). A flame of one candle
power at a distance of five meters has, therefore, an effective intensity
of 1+ 5?= 0.04 “meter-candles.” An ordinary flame of gas, kept at
constant pressure by means of a manometer, was employed in the earlier
experiments; a “ microburner” in the later ones.

The following table gives the optimum intensity in the case
of various seedlings, in units of the meter-candle, at a tempera-
ture of 20° to 27° C. and at a humidity of 75 to T7% :—

TABLE XLV
Tue Optimcm INTENSITY FOR PHOTOTROPISM IN VARIOUS SPECIES OF PLANTS
Lepidium sativum, hypocotyl . . . . 0.25-0.11
Pisum sativum, epicotyl . .... . 0.11
Phaseolus multiflorus, epicotyl . . . . 0.11
Vicia faba, epicotyl. . . poearstty 0.16
Helianthus annuus, leructotyi BPO Gisc v% 0.16
Vicia sativa, epicotyl . ...... 0.44
Salix alba, etiolated sprout . . .. . 6.25

This table shows also the effect of preceding conditions of illu-
mination; the etiolated plant has.a very high optimum.

At an intensity of light above the optimum the phototropic
response is less pronounced until, finally, at between 100 and
800 meter-candles it disappears. At an intensity below the
optimum a similar diminution in response occurs; but the
minimum lies often remarkably low. Thus Fiepor (793) has
found the minimum to lie for the different species at or just
below the following intensities (in meter-candles). The tem-
perature was 15° to 24° C., and the humidity between 58 and

80%.
TABLE XLVI

Tae Minimum Intensity FoR PHotrotropic RESPONSE IN VARIOUS SPECIES OF

PLANTS
Lepidium sativum, Amaranthus melancholicus ruber, * Papa-
ver peoniflorum, and tLunularia biennis . limit below 0.00033
*Vicia sativa. . . es 3 at Oa

Salpiglossus sinuata, Pet aadig seers Sass Ne catier! 0.004 to 0.16
Mirabilis jalappa, * Helianthus annuus, * Dianthus chinensis 0.016
* Xeranthemum annuum, *Raphanus sativus, * Helichrysum
monstrosum, *Capsicum annuum, Cynoglossum offici-
NAG a eee ee eee sg Sts en et} 0018 TONG

440 EFFECT OF LIGHT [Cu. XVII

This list shows that different plants have diverse photo-
tropic sensitiveness. Since in this list species preceded by an
asterisk (*) live in the sunlight, that preceded by a dagger (+)
is a shade-loving plant, while the others live in an intermediate
habitat, we may conclude that, in general, sun-loving plants
are less sensitive to light than those not markedly sun loving.
The former exhibit a sort of acclimatization to light.*

The effective rays have been determined by WIESNER (79,
p- 191) for seedlings of several species as a result of experi-
ments in which colored solutions were employed. His results
are summarized in Fig. 126, which shows that the phototropic
effect is greatest at the violet end of the spectrum, and that as
we pass towards the D line, lying between the yellow and the
orange, the effect diminishes, becoming null at D. In the red,
again, there is a considerable effect. Beyond the visible red,

Lr
Y

Leeks ren PP axns
“7 -

- be es eas
eit 1
Nae
ae Va oe |
PN “By
‘rele N\ A ed yes 3
Dye ele ri
hk. 4-65) 6 E H

Fic. 126.— A-H, positions of FRAUENHOFER’s lines in the spectrum.

, curves of phototropic effect of the various rays; the ordinates have only
relative values. J, J, curve for the seedling of the vetch, Vicia; IJ, IJ, for cress
seedlings; JZI, for etiolated willow shoots, upon which latter the more strongly
refractive rays only act phototropically.

----, curve of retardation of growth i in length of Helianthus seedlings reared
in the various rays. The ordinates give the increment in length of the seedling
subjected to the ray under consideration; thus the retardation is least at x, and
is greatest at y. (From WIESNER, .’81.) :

* Certain plants are so sensitive to differences of illumination on their two
sides as to make very delicate photometers. Thus Wiresner determined as
nearly as possible by Bunsen’s photometer the point of equal illumination
between two flames, but a seedling still detected a difference between their
intensities. Massart (’88) has made use of this method to demonstrate for
phototropism the validity of Wrxser’s law. He found that in Phycomyces a
difference of intensity of 18% between two sources of light could be detected ;
and this held true for all intensities of light.

§ 2] UPON THE DIRECTION OF GROWTH 441

in the region of the dark heat rays, we find an effect still pro-
duced. This effect of dark heat rays will be referred to again °
in the next chapter.

The Responding Region. — We have already seen that the
curvature begins a short way below the tip of the stem of the
seedling. Further study shows that this region of first curva-
ture is also that of maximum growth. The response does not,
however, end here, but passes basalwards even after the seed-
ling is transferred to the dark. Also in roots, the region of
maximum negative curvature is that of most rapid growth
(MULLER, ’76).

The Perceptive Region. —In most cases the region of re-
sponse is also that of perception. But DARwtn (’81) found
that in some organs this is not the case. When, for example,
the phototropic cotyledons of the seedlings of grasses and
grains were deprived of their tips for a distance of 2.5 to 4
mm., they exhibited no phototropism; but when only 1.3
mm. of the tip was cut off, the curving occurred, although
in diminished degree. Again, when the tips of some of the
cotyledons were covered with opaque caps made of glass
thickly painted with India ink, while others were covered with
transparent glass, the first lot remained straight or nearly so,
whereas the second curved normally. From such results DAR-
WIN concluded that the tip of the cotyledon is the chief per-
ceptive region. That it is not the only perceptive part, even
in cotyledons, follows from the observations of ROTHERT (’94),
who finds that a sight curvature succeeds the illumination of
the basal part alone of the cotyledon. In some seedlings of
dicotyledons, indeed, the perceptive region exists nearly equally
developed along the whole stem.

In those cases where the tip of the plant is alone percep-
tive there must be the transmission of an impulse from the per-
ceptive to the bending region. The rate of this transmission
is variable; in favorable cases it is about 2 cm. per hour
(RoTHERT, ’94, p. 209). If we define “ irritation ” or “ stimu-
lation” as the condition of the protoplasm immediately ante-
cedent to its response, —as the chemical transformation lying
behind the visible result, — then, since in these plants the
response occurs some distance from the perceptive region, we

442 EFFECT OF LIGHT [Cu. XVII

must conclude, with RorHeErt, that here, as in animals, stimu-
lation is a process distinct from perception.
2. Animals. — Phototropism among animals will naturally

be limited to elongated, sessile forms. It has hitherto been

detected only among hydroids and worms of the family Serpu-
lide. 3

a. Serpulide.— A type of response to light intermediate
between phototaxis and phototropism is described by Lorn
(90) for Spirographis spallanzanii. This worm (Fig. 127)

41
a
ve d
ar
Yo LA
4 iy
“/ ia
rs
ar —_ =——— _—— ———<— sid
¢ = = a ee
a = _—_ === = ———
v4 2 le ee sae = SS H
/ SS =a | a ———
atage —S_-——“=a“<€n’ =a a eet a —
—s— Se a ar paeecetes 2] -
c Sen sei oo eae = ae
= SS ss —
== SSS S82 SSS Y,
== = —_— y= = | y
— SX See Vy — Yj
i == SS . ee if
—— = = = al
—— — =
——
a = ee ——_
————— oo —-

Fia. 127. — Persisterit phototropic curvature in Spirographis spallanzanii. The ani-
mals were originally placed horizontally on the bottom of the aquarium, the
majority with their heads towards the side, efgh, of the aquarium away from
the window. In their further growth the animals curve until their heads are
turned towards the light side, abcd, of the aquarium, and the axes of their
gills stand in the direction of the rays of daylight. (From Logs, ’90.)

builds, from a secretion of the body, cylindrical tubes of some-
what elastic nature which are attached at their base to a solid
substratum. When these worms, in their tubes, are illumi-
nated from one side by a pencil of rays, the upper part of the
tube comes, within a few hours, to lie in the axis of the pencil,
and the gills, which surround the head, are stretched out
towards the source of light. This result seems to be due to
a sort of phototactic response modified by the sessile habit of

§ 2]

the organism.

UPON THE DIRECTION OF GROWTH

443

Since the tube is tough and elastic, its bending

towards the light must be due, at first, to muscular action of

the animal inhabiting it.

Additional secretions are, however,

constantly poured forth so that the new position soon becomes

in turn the permanent one.

Serpula, which has a tube con-

taining lime, likewise turns its head end towards the light ;
but, since its tube is firm and inelastic, the bending which it

finally exhibits must be ascribed alone
to growth of the shell by additions to
its free upper margin.

b. Hydroids. —'These have been.

made the object of study by DRIEScCH
(90) and Lors (790 and ’91, p. 36).
In stocks of Sertularella polyzonias,
reared in an aquarium, one often finds
a stolon (primary stolon) growing out
from the distal end, at first straight,
so as to prolong the axis of the stock,
then turning and growing from the
source of light. From the convexity
of this primary stolon a secondary one
buds forth. It grows towards the
light for a time, until it in turn buds
off a (tertiary) stolon; then it becomes
negatively phototropic. Tertiary and
succeeding generations of stolons fol-
low the same law. We have here the
remarkable phenomenon of change in
the sense of response depending upon
the condition of development of the sto-
lon (DriescH), In Eudendrium the
hydranths, in contradistinction to the
stolons, grow towards the light — they
are positively phototropic (Fig. 128).

Fic. 128.— Phototropism in re-

generation of Sertularia (poly-
zonias?). The stock was cut
near the stolon at 6 and in-
serted reversed in the sand,
being buried from @ to ec.
From the upper end 0, botha
stolon, Wj, and hydranths, S,
regenerated, and both grew
in the axis of the infalling
ray of light, indicated by the
arrow. The hydranths are di-
rected toward the source of
light; the stolon tip in the
opposite direction. Magnified
2 diameters. (From Logs,
’90.)

The effective rays in animal phototropism have not been

determined.
the more highly refractive ones.
hydroids is the growing region.
not turn in response to light.

It is highly probable that, as in plants, they are

The responding region in
The fully formed stolon does
The perceiving region is still

444 EFFECT OF LIGHT UPON GROWTH (Cu. XVII

unknown; the subject has not been investigated. Is it at the
tip or at the responding region, or do these regions exactly
coincide? ‘The essential identity of phototropism in sessile
animals and plants is striking, and indicates how closely simi-
lar needs are met by similar capacity for response in the two
groups.

3. General Considerations. —a. Persistence of Stimulation.
If a seedling, after momentary illumination on one side, be
placed in the dark before any turning has occurred, phototro-
pism will follow after the same interval as would have elapsed
had the plant remained in the light. Even if the irritated
seedling be placed in the dark in a horizontal position, no geo-
tropic curvature will interfere with the working out of the
stimulus already given. This persistence of an effect wrought
by light has been called by WIESNER photomechanical induc-
tion: it is, however, only a particular case of persistence of
an effect, of which we have seen other examples. As a result
of this phenomenon a seedling, intermittently illuminated for

one second and kept in the dark for two seconds, will respond.

phototropically as completely and as quickly as if it had been
kept continuously in the light.

b. Acelimatization to light is a process closely related to
the foregoing. As early as 1827 Mout observed that plants
reared in a weak light, or in the dark, became, after a time,
phototropically more sensitive than plants which had been con-
stantly exposed to full daylight. The observation has been
several times confirmed (cf. DARw1n, ’81, Chapter IX); so we
may conclude that the constant subjection to light diminishes
the sensitiveness towards light.

e. Mechanics of Phototropism. —It is clear that phototropic
curvature, as seen in the seedling, the mold, or the hydroid, is
the result of unequal growth upon the two sides of the cylin-
drical organ; and, indeed, that the positive phototropism is
due to a relative diminution of growth on the side next the
source of light, and the negative phototropism to a relative
increase of growth on that side. Experiments have shown
that in positive phototropism growth is excessively rapid upon
the convex side of the organ, and excessively slow upon the
concave side. These results are reasonably attributed to an

— ————E EO = -

LITERATURE 445

increased turgescence on the one side and a decreased turges-
cence on the other.

In unicellular organisms, on the other hand, this mechanism
cannot be called upon; and great difficulty has been met with
in explaining how an elongated cell, for instance, of a hypha, -
ean curve itself. Some authors have suggested that the
cell-wall on the convex side becomes excessively extensible, on
the concave side excessively rigid. Again, it has been sug-
gested that this change takes place rather in the protoplasm
inside the wall than within the wall itself. If, however, with
many plant physiologists we regard the cell-wall as the truly
living, only considerably modified, protoplasm, then we may
accept both of these views, and, uniting with them the expla-
nation advanced for phototropism in multicellular organs, say :
The curving of the unicellular organ is probably due to the
increased extensibility, gained through imbibition of water, of
the whole protoplasm (including cell-wall) of the convex side,
together with a corresponding diminution on the concave side.
In a word, then, the mechanism of phototropism may be stated
to be the excessively rapid imbibition of water by the proto-
plasm on the convex side.

But what starts the mechanism? This is the same question
that arises with other growth responses. Its anSwer must be
deferred to a later chapter.

LITERATURE

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Apucco, V.’89. Action de la lumieére sur la durée de la vie, la perte de
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Bary, A. pg, ’63. Recherches sur le développement de quelques cham-
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446 EFFECT OF LIGHT UPON GROWTH [Cu. XVII

Bipper, F. H., and Scumipt, K. ’52. Die Verdauungssifte und der Stoff-
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Borop1y, J.’68. Ueber die Wirkung des Lichtes auf einige héhere Krypto-

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Braem, F.’95. Mittheilung iiber den Einfluss des Gefrierens auf die Ent-
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BREFELD, O. 77. Botanische Untersuchungen iiber Schimmelpilze. III.
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89. Untersuchungen aus dem Gesammtgebiete der Mykologie. Fort-
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Buxtot, G.’97. Sur la croissance et les courbures du Phycomyces nitens.
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CAMERANO, L. 93. Dell’ azione dell’ acqua corrente e della luce sullo svi-
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Darwin, C. and F. ’81. (See Chapter XIV, Literature.)

Davipson, J. ’85. On the Influences of Some Conditions on the Metamor-
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Fiapor, W. ’93. Versuche iiber die Heliotropische Empfindlichkeit der
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FLAMMARION, C.’95. Etude de l’action des diverses radiations die spectre

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Fries, E. M.’21. Systema Mycologicum, etc. I. 520 pp.

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Gop.LewskI, E.’90. Die Art und Weise der wachsthumretardirenden Licht-
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21 March, 1891.]

~ SO

LITERATURE 447

Goptewskt, E. ’93. Studien iiber das Wachsen der Pflanzen. Abh. Krakauer
Akad. d. Wiss. XXIII, 1-157. [Polish.] Abstr.in Bot.Centr. LV, 34-40.

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pp- 19 Tab. London.

Hammonp, 73. Some Points relative to the Sanitary Influence of Light.
The Sanitarian, II.

Hensen, V. and Apstern, C. 97. Ueber die Eimenge der im Winter
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HicGGeNnsBottom, J. ’50. Influence of Physical Agents on the Development
of the Tadpole, of the Triton, and the Frog. Phil. Trans. Roy. Soc.
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63. Influence des agents physiques sur le développement du tétard de la
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HocureEvTINER, G.’96. Physiologie des plantes aquatiques du Rhone et du
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15 Apr.—15 June, 1896.

HorrMann, H. ’60. Untersuchungen iiber die Keimung der Pilzsporen.
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Jonsson, B. ’93. Iakttogelsen 6fver ljusets betydelse for fréns groning.
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Karsten, H. ’71. Die Einwirkung des Lichts auf das Wachsthum der
Pflanzen, beobachtet bei Keimung der Schminkbohnen. Landw. Ver-
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Kny, L. 84. Das Wachsthum des Thallus von Coleochete scutata in
seinen Beziehungen zur Schwerkraft und zum Lichte. Ber. Bot. Ges.
II, 93-96.

Kraus, G. ’76. Versuche mit Pflanzen im farbigen Licht. Ber. Sitzungs
d. Naturf. Ges. Halle. Jahre 1876. 4-8.

’83. Ueber das tiigliche Wachsthum der Friichte. Ber. d. Naturf. Ges.
zu Halle. 1883. 92-121.

Leitces, H. 77. Die Keimung der Lebermoossporen in ihrer Beziehung
zum Lichte. Sb. Wien. Akad. LXXIV, 1 Abth. 425-436. 1 Taf.

Lessona,’77. Studé sugli amfibi anuri del Piemonte. R. Accad. dei Lincei
Atti. (8) Mem. Sci. I, 1019-1098. 5 Tav.

LIEBENBERG, A. RITTER von, ’84. Ueber den Einfluss intermittender
Erwirmung auf die Keimung der Samen. Bot. Centralb. XVIII,
21-26.

Logs, J. ’90. Weitere Untersuchungen iiber den Heliotropismus der Thiere
und seine Uebereinstimmung mit dem Heliotropismus der Pflanzen.
Arch. f. d. Ges. Physiol. XLVII, 391-416. Taf. IX. 9 May, 1890.

91. Untersuchung zur physiologischen Morphologie der Thiere. I.
Ueber Heteromorphose. Wiirzburg: G. Hertz. 1891.

McDonnett, R.’59. Exposé de quelques expériences concernant l’influence
des agents physiques sur le développement du tétard de la grenouille
commune. Jour. dela Physiol. II, 625-632.

448 EFFECT OF LIGHT UPON GROWTH (Cu. XVIL

Massart, J. ’88. Recherches sur les organismes inférieurs. 1. La loi de
Weber vérifiée pour Li valine oases du champignon. Bull. Belg. Acad.
(3), XVI, 590-597.

Maupas, E. ’87. Sur la puissance de multiplication des Infusoires ciliés.
Comp. Rend. CIV, 1006-1008. 4 Apr. 1887.

Mipr, J.’52. Zur Entwicklungsgeschichte der Equiseten und Rhizokarpen.
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57-59.

Mittet, C. ’55. Influence nuisible de la lumiére sur les ceufs de certaines
especes de Poissons. L’Institut. XXII, 55. 14 Feb. 1855.

Mout, H. v. ’27. Ueber den Bau und das Winden der Ranken-und Schling-
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MotescuottT, J. ’55. Recherches sur l’influence de la lumiére sur la pro-
duction de l’acide carbonique par les animaux. Ann. d. Sci. Nat.
(Zool.). (4), IV, 209-224.

Mitturr, H. 76. Ueber Heliotropismus. Flora. LIX, 65-70, 88-95.

Musset, C. 90. Sélénétropisme. Comp. Rend. CX, 201-202. 27 Jan.
1890.

Nosskg, F. ’82. Uebt das Licht einen vortheilhaften Einfluss auf die Kei-
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Pieasonton, A. J.’76. The Influence of the Blue Ray of the Sunlight and
of the Blue Color of the Sky in developing Animal and Vegetable Life,
in arresting, and in restoring Health in Acute and Chronic Disorders
to Human and Domestic Animals. Philadelphia, 1876.

PrAntTL, K. 73. Ueber den Einfluss des Lichts auf das Wachsthum der
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QuinckE, H. ’94. Ueber den Einfluss des Lichtes auf den Thierk6rper.
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RotHert, W. ’94. Ueber Heliotropismus. ey 2 zur Biol. der Pflanzen.
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Sacus, J. 63. Ueber den Einfluss des Tageslichts auf Neubildung und
Entfaltung verschiedener Pflanzenorgane. Bot. Ztg. XXI, Suppl.
30 pp.

64. Wirkungen farbigen Lichts auf Pflanzen. Bot. Ztg. XXII, 353
et seq.

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’*80*. Some Further Observations on the Influence of Electric Light upon
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a i, es i

se Cheeni aaa a iit at i ii

LITERATURE 449

Sremens, C. W.’82. On Some Applications of Electric Energy to Horticultural
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Trew, C. T. 1727. Beschreibung der grossen Amerikanischen Aloe, wobei
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14 Oct. 1895.

Vitton, A. M.’94. La culture sous verres colorés. Rey. Sci. (4), I, 460-
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Warp, H. M.’95. On the Biology of Bacillus ramosus (Fraenkel), a Schizo-
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’81. Thesame. Theil II. Denkschr. Wien. Akad. XLII, 1-92.
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2¢@

CHAPTER XVIII
EFFECT OF HEAT ON GROWTH

As in other cases, so in describing the effect of heat we shall
consider separately its effect on the rate and on the direction
of growth.*

§ 1. Errrect oF HEAT ON THE RATE OF GROWTH

The descriptive fact that the rate of growth —of develop-
ment in general—in both animals and plants is dependent
upon temperature, has long been known. ‘The work upon
plants was begun earlier than that upon animals, and has been
carried further. We may consider, first, the results gained in
that group. |

1. Plants. — As an introduction to the study of the effect
of heat upon growing plants, we may consider the results of
measurements made upon phanerogams, showing, for various
temperatures, the increase in length of the plant after 48
hours : —

* The methods to be employed in subjecting organisms to heat have already
been discussed on pp. 219-222. The constant-temperature oven, of the kind
employed in bacteriological laboratories, may be used for rearing growing plants
or aquatic animals at a high temperature. An ordinary refrigerator will serve
for temperatures from near 0° to 8° or 10°C. The methods employed in thermo-
tropic experimentation are referred to on p. 464.

To test the question of the dependence of the optimum for growth upon the
temperature to which the organism is normally subjected it would be necessary
to rear a species attuned to a warm climate at a constantly low temperature for
several generations, or the reverse, and then compare the optimum of the normal”
race with that subjected to the new conditions. To test the question of the
dependence of the range of the growing temperatures upon the range of tem-
peratures in the environment, one lot of individuals of a species should be
reared in a constant-temperature room, and another in a very fluctuating
temperature.

450

Se

§ 1)

(EXPRESSED IN DEGREES CENTIGRADE).

EFFECT OF HEAT UPON GROWTH

TABLE XLVII

SHow1ne THE AveRAGE ToTaL INCREMENTS IN LENGTH (IN MILLIMETERS) OF

THE Plumules oF SEEDLINGS SUBJECTED TO DIFFERENT TEMPERATURES
THE OBSERVATIONS MARKED §
WERE MADE BY Sacus (60); THOSE MARKED K, By KOppeN (’71); AND
THOSE MARKED V, BY DE VRIES (’70).

451

Tue Time InrervVAL 1s 48 Hours

S a : = @ g re, = = 3 A
TEMPERATURE. 2 = 2 =) = = = 5 2S 2c = 2 =
SH 132/48) 2&|286)84)24] 88) EE
Ba |Ral|Saled [es | Az las}| As] as
14-15.9 5.0 9.1 38 5.9 1.5
16-17.9 TA*| 4.6* 3.0*
18-19.9 tH 8.3 | 11.6
20-21.9 9.3 25.5 | 25.0 | 24.9 | 38.0 | 20.5
22-23.9 10.8 30.0 | 31.0
24-25.9 20.1 45.8 | 33.9
26-27.9 11.0 | 56 | 296 | 10.0 | 53.9 | 54.1 | 52.0 | 71.9 | 44.8
28-29.9 26.5 ? 40.4 | 60.1
30-31.9 64.6 38.5 | 43.8 | 44.1 | 44.6 | 39.9
32-33.9 10.5 | 11.0 | 69.5 5.7 | 238.0 | 14.2
34-35.9 15.0 | 13.0 5.0 30.2 | 26.9 | 28.1
36-37 .9 20.7 8.7 | 12.6 | 10.0 0.0 9.2
38-39.9° 10.2 |. 9.1 5.5
42.5 7.5 4.6

TABLE XLVIII

SHOWING THE AVERAGE INCREMENTS IN LENGTH IN MILLIMETERS OF THE
Radicle or Various SEEDLING PLANTS SUBJECTED TO DIFFERENT TEM-

PERATURES. TEMPERATURES IN DEGREES CENTIGRADE. ALL FROM SACHS
(60). THe Time Inrervat ts 48 Hoors.

°C.” ZEA MAIS, ReAseoLNS CUCURBITA PEPO. | PISUM SATIVUM.

MULTIFLORUS.

17.0 2.5* 4.0*

25.7 39

26.3 24.5 47

28.5 34 41.0

33.2 39.0 30 17.0

34.0 55.0 28 30

38.2 25.2 22 14 12.2

42.5 5.9 7 11

* Growth during 96 hours,

452 EFFECT OF HEAT (Cu. XVITT

Data from the higher fungi have been afforded by the
studies of WIESNER (’73) upon Penicillium. I give all of
WIESNER’S data, although not all are strictly concerned with
growth. These data show the relation between temperature,
on the one hand, and the interval, in days, between sowing
and (1) germination, (2) formation of visible mycelium, and
(3) spore formation, on the other : —

TABLE XLIX

TIME, IN DAYS, REQUIRED FOR SPORES OF PENICILLIUM TO GERMINATE, PRODUCE
VisisLe MYCELIUM, AND TO FORM Spores, aT VARIOUS TEMPERATURES

TEMPERATURE °C, TIME TO GERMINATION. FINE RO -FROny arias bath 0 > 7p
OF VISIBLE MYCELIUM. ForMATION,

1.5 5.80.

2.0 5.50

2.5 3.00 6.00

3.0 2.50 4.00 9.00

3.5 2.25 . 3.50 8.00

4.0 2.00 3.00 7.75

5.0 1.50 2.90 7.00

7.0 1.20 3.00 6.25
11.0 1.00 2.30 4.00
14.0 0.75 2.00 3.00
17.0 0.75 2.00 - 3.00
22.0 (Opt.) 0.25 1.00 1.50
26.0 0.50 0.99 2.00
82.0 0.70 LOLs* 2.10
38.0 0.55 2.25 2.60
40.0 0.70 2.50 3.50

The law of growth of bacteria at various temperatures is
illustrated in the observations of WARD (95, p. 458). His
results are epitomized in the curves of Fig. 129.

The curve (Fig. 130) of the phanerogams Zea mais and Pisum
sativum, which is constructed somewhat differently from that of

Fic. 129.— Curve of relation between rate of growth of Bacillus ramosus and the
temperature. The growth is measured by the period, expressed in minutes («),
required for the bacillus to double its length. The relative duration of these
periods is expressed by the ordinates. The abscissw# are temperatures. (From
WARD, 95.)

Fic. 130. — Curves of absolute growth in 48 hours of Zea mais and Pisum sativum at
different temperatures. (Data from Table XLVII.)

7,

§ 1] -- UPON THE RATE OF GROWTH 453

6
220
200
te
160
roe 137
120
Qos
100 N
80 StH
” 52H
40 ni
at 33/2 3 33 [sit ap 0; s0/4
0

13° 14° 15° 16° 17° 18° 19° 20° 21° 22° 23° 24° 25° 26°27° 28° 29° 30° 31° 32° 33° 34° 35° 36° 37° 38° 39° 40° 41° |
Fic. 129

‘ Ts a

~ /_\\f

40 ; Ko

j Je eT OS ALS ae

a Bia

‘ ane Mest

2 l Nei

3 l \
aS ee he

Be aii A

454 EFFECT OF HEAT [Cu. XVIII

Fig. 129, shows, more graphically than the tables from which
they are drawn, that, as the temperature rises, growth increases
up to a certain point, and then diminishes again. The falling
off is more rapid than the increase —a condition which we
found also in the curves (Fig. 68; p. 226) giving the rate of
movement of protoplasm at different temperatures. We have
thus three critical points to distinguish: the minimum, or
lowest temperature at which growth occurs; the optimum, or
the temperature of greatest growth ; and the maximum, or the
highest temperature at which growth can take place. These
critical points, then, are to be considered comparatively ; and
as an introduction to this consideration I present, in a table,
the points as they have been determined for various species : —

TABLE L
SHowine Criticat Points FoR Various PLANT ORGANISMS, ARRANGED
ACCORDING TO THE OPTIMUM €
TEMPERATURE FOR GROWTH.
NAME OF PLANT. AUTHORITY.
Optimum, | Minimum. | Maximum.
Bacillus phosphorescens . . .| 20.0° 0.0° 87.0° | Forster, °87
Poniciliigm ~: oo. 85.4.4. Rees 22.0 1.6 43.0 WIESNER, ’73
Phaseolus multiflorus (Radicle) . 26.3 — — SacHs
Pisum sativum (Plumule) . .| 26.6 65 | — Koépren
Sinapis alba (Plum.) . .. . 27.4 - 0.0 37.2+ | DE VRIES
Lepidium sativum (Plum.) . . 27.4 1.8 87.2+ ae
Linum usitatissimum (Plum.) . 27.4 1B™: 87.2+ af
Lupinus albus (Plum.). . . .| 28.0 7.5 — K6pren
Hordeum vulgare (Plum.) . . 28.7 5.0 37.7 Sacus
i 28.7 5.0 42.5 Me
Triticum vulgare (Plum.). . { 29.7 7.5 an KoprEn
Yeast... see 6 + 6 ol] 62684 0.04 38.0
Bacillus subtilis . . . .. . 30.0 6.0 50.0
Bacterium termo. . .. . .| 80-85 5.0 40.0+ | Erpam, °75
; 32.4 9.6 — K6PPEN
gp teens hy {Ll gg 9.5 46.2 | Sacus
Phaseolus multiflorus (Plum.) . 83.7 9.5 46.2 a
Cucurbita pepo (Plum.) .. . . 33.7 13.7 46.2 a
Zea mais (Rad.). . . «i. . 84.0 — =e ‘
Bacillus ramosus. .... . 37.0 13.0 40.0 Warp, ’95
a GNENTOCIS®. “G..5;, 4 es 87.0 14.0 45.0 Fiscuer, ’97
WAS DORI RIORIB ir ne es 88.0 80.0 42.0 Be
‘¢ thermophilus . . . .| 63-70 42.0 72.0 ee

VS ee ee ee

=. ee re

§ 1) UPON THE RATE OF GROWTH 455

This table shows, first, that the optimum, minimum, and
maximum are correlated; that when one is high or low the
others are, in general, high or low also. It shows, moreover,
that the position of the optimum varies greatly ; so that the
minimum of one species, Bacillus thermophilus, lies higher
than the maximum of another, Bacillus phosphorescens. We
see, also, that the bacteria have, among all organisms, the great-
est variation in the optimum, for this ranges from 20° to 63°—
70° C., or through 43°-50° C. In the various phanerogams the
extreme range of the optimum is from 26.6° to 33.7°C., or
through 7°. Again, the range of temperatures at which
growth occurs in any one species varies greatly. The most
striking feature of this table—the one which most needs
accounting for—is its variety.

In respect to the optimum we find a certain relation between
the degree of temperature of most rapid growth and that to
which the organism is normally subjected. Taking the case of
an organism with a low optimum, we find Bacillus phosphores-
cens living in the North Sea, and normally subjected to a low
temperature ; for, even in its southern part, the mean temper-
ature of the North Sea is 17.5° at the surface. Taking the
case of organisms with a high optimum, we find Bacillus an-
thracis and Bacillus tuberculosis living in the mammalian body
at a normal temperature of 35° to 38° C. These numbers lie near
the optima of the species. Bacillus thermophilus lives in fer-
menting manure and in other situations attaining a temper-
ature of 60° to 70°. Likewise, among phanerogams, we find a
relation between the optimum and the normal temperature —
the maize and gourd are of tropical origin, while the white
mustard (Sinapis) belongs to the temperate zone. That this
agreement between optimum and normal temperature is not
always close may be partly ascribed to the fact that many spe-
cies of plants, especially cultivated plants which are usually
employed in experimentation, have lived at different times
under dissimilar environmental conditions. What, now, is the
reason for this general parallelism between the optimum and
the normal temperature? As in other cases, it can clearly be
ascribed only to an attunement gained by the organism as a
result of its subjection to the temperature.

456 EFFECT OF HEAT (Cu. XVII

As for the minimum we find that, while it varies somewhat
with the optimum, it never falls below 0°C. The reason for
tis is clear ; for, as we have already seen (p. 241), 0° C. is the
minimum for most vital activities. The fact that the minimum
for phanerogams is given some distance above 0° is partly due
to the fact that, since growth becomes very slow towards 0°, the
absolute minimum for growth is hard to find. KIRCHNER (83),
who paid particular attention to this matter, concluded that
the minimum temperature of both radicles and plumules of
many seedlings lies between 0° and 1°C. However, we cannot
ignore the fact that Cucurbita, for example, has a minimum for
growth considerably above the point of cold-rigor, nor that,
in pathogenic bacteria, the minimum is near the optimum of
some free-living organisms. ‘These facts teach us that the con-
ditions for growth may be surpassed before metabolism has
wholly ceased.

The maximum temperature tends to be rather constant ;
inside of the group of phanerogams the range is only from 37°
to 46°, or 9°. But 45° to 46° is a fatal temperature for most
plant protoplasm (p. 234), and 50° is the outside limit ;
hence the death-point (ultra-maximum) lies very close to—
only slightly beyond —the maximum temperature for growth.
It is probable that growth ceases where heat-rigor comes in.
The extraordinarily high resistance of Bacillus thermophilus
can create no surprise after our study of the capacity of organ-
isms for acclimatization to temperatures near the boiling-point
of water (p. 250). It is merely another striking case of the
capacity of protoplasm for self-adjustment.

The range of growing temperatures varies, as we have seen,
with the species. The greatest range in our table is that of
Bacillus subtilis, 44°. It is tolerably uniform for phanerogams
(37° to 32°); but in bacteria we have a range of 388° in the
case of Bacillus phosphorescens to only 12° in the case of
Bacillus tuberculosis. Here, again, we see a relation between
the vital peculiarities and the environment of the organism.
B. phosphorescens lives on the surface of the sea, whose tem-
perature varies with that of the air; whereas B. tuberculosis
lives in the mammalian body, whose temperature is nearly con-
stant. It is interesting that the temperature of 42°, which is

§ 1] UPON THE RATE OF GROWTH 45T

the maximum for B. tuberculosis of man, is likewise about the
human ultra-maximum ; and 30°, the minimum for B. tubercu-
losis, is just below the human ultra-minimum. Thus the
range of vital temperatures of this parasite is practically the
same as that of its host.

To sum up, the critical temperatures of plants are wonder-
fully adjusted to their environment, not only in respect to
the optimum for growth, but also in respect to the range
within which growth is possible. The origin of this adjust-
ment is, as the phenomena of acclimatization show, not to be
sought in any process of selection, but in the modification
wrought on the protoplasm by the temperature itself.

2. Animals.— We may begin our account of the effect of
heat on the rate of growth of animals by a table, necessarily
drawn from more limited data, but otherwise resembling
Table XLVII.

TABLE LI

SHOWING FOR DIFFERENT TEMPERATURES THE ABSOLUTE INCREASE IN LENGTH,
MEASURED IN MfFLLIMETERS, FROM THE 24TH TO THE 48TH HoUR AFTER
HartcHinc. MEASUREMENTS MADE ON YOUNG TADPOLES OF THE FRrRoc,
RANA VIRESCENS, AND THE ToapD, Buro LENTIGINOSUS, BY LILLIE AND
Know ton, ’98

AVERAGE GROWTH. AVERAGE GROWTH.
TEMPERATURE. 5 TEMPERATURE.
Froe. Toap. Froe. Toap.
9-10.9° 4.5 8.0 23-24.9° 41.3

11-12.9 5.3 5.3 25-26.9 31.5 39.0
13-14.9 4.3? 15.5 27-28.9 40.0
15-16.9 16.3 29-30.9 47.5 56.8
17-18.9 / 9.5 31-32.9 40.2 55.3
19-20.9 19.8 21.2 33-34.9 43.5
21-22.9

Oscar HERTWIG (’98) has determined the curves of growth
for Rana fusca, and these are given in Fig. 131. These curves
have not been carried beyond the optimum. (Compare Fig. 129.)

This table and the curves show plainly that the growth of
organisms so remote as the maize plant and tadpoles are simi-
larly affected by heat. In both cases there is a slow and con-

458 EFFECT OF HEAT (Cu. XVIII

stantly diminishing increment to the optimum, and then a
rapid decline to the maximum.
Although many ob-

30 me

. [ {| servations upon the
28 f effect of heat on the
os IT] growth of animals have
ye i | been made, they have
24 f been mostly fragmen-
= ] ] tary. I have gathered
o / / | certain cases from the
: , TOO literature which it may
ci 3 Ama meal not be useless to repro-
i718 fi | | duce here.
As} f aM ig Echinodermata. —
. i R TT TA TTT According to VERNON
13 E y, / aml (95) the optimum for
z E 3 Ss VANE the development of
oe DAVEY, / V4 Echinoid larve is 7°
; VA As Z 7 VA 99°,
se i an A oA ss A 7 Crustacea.— Nauplii
es LL, s te r vA of Branchipus and
MB oo re ee) — my Apus hatch out at a
Age: AO] a el = temperature of 30° in
he ae a Ei a OE 3 less than 24 hours,
2 ain an ne abaaruRle Cee: whereas at 16°-20° they
WeP VF Al WWI 17 1G IS 1 IFW 10 YP EF PSS Ls 21 require some weeks

Fig. 131. — Curves showing the relation between the num- (Semper, ’81, p. 129).
ber of days (ordinates, indicated at left) required for Lobster larve reared
the frog tadpole to reach a certain definite stage, and at 23° to 27° C. passed
the temperature to which it is subjected during devel- the fourth molt in
opment. Stage I is that of a gastrula whose blastopore about 10 days, or 3
is just closing; II, edges of medullary plate rising; %.
III, medullary tube completely closed; IV, tail evi- ;
deat, but gills not formed; V, embryo 5 mm. long; V® reared at 19° C.
VI, embryo 7.5 mm. long; VII, 9mm.long; VIII,11 (Herrick, ’96, p. 190).
mm. long; IX, 11.5 mm. long. (From HErtwie, ) Insecta. — The mi-

gratory locust is as-
serie to require at different temperatures the following times for hatching.

The figures are suspiciously regular. (From Curnor, 94, p. 18, after

“« CLEVELAND.” )

DSP TOOS oo a wis) atc, et ae a 20 15 10
DRE sa eR ae Bee ae ee 55 60 65

days earlier than lar-

Fishes. — Many experiments have been made with these animals for com-
mercial reasons, as it is sometimes desirable to retard growth during trans-
portation or to delay hatching until the season of the natural enemies shall
have been passed. Some of the results are summarized in

§ 1) UPON THE RATE OF GROWTH 459

TABLE LII

SHowinc FoR THREE Species or Fish tHe InTervat, IN Days, ELAPSING
BETWEEN FERTILIZATION AND HartcHinG, aT Various TEMPERATURES

TEMPERATURE OF WATER. Cop (Ear1t1, ’80). Hereine (Meyer, 78).| Sap (Rice, °84).

—2-— 0.0 ; 30.0

0- 1.9 32.5

2— 3.9 22.0 40

4- 5.9 - +. ¥-46.0

6- 7.9 ' 13.0 15

8— 9.9

10-11.9 11

13.5 . 11

20-23.0 . — 3-5

RavuBeER (’83) states that eggs of minnows and salmon, which develop:
during the winter season, will not grow at much above 12°-15°, but will do so:
at 0°. On the contrary, eggs which normally develop during the summer
grow better at the higher temperatures.

Amphibia. — The European. Rana is said not to develop at 0° (ScHuLTzE,
_’94), and the same is true of the Amblystoma tigrinum of the United States.
(LILi1e and Know Ton, 98). The time required to attain a definite stage,
at which the chorda is well developed and head and tail are sharply marked,
is for Rana temporaria: at 15°, 6 days; at 33°, 1 day (Herrwie, ’96). If
brought gradually to it tadpoles may develop at 37°, or even for a few hours
at 40°, but they do not thrive long at this temperature. The great effects of
temperature on rate of development of the frog are illustrated by Fig. 132.

Birds develop only at a high temperature and within narrow limits.
The normal for the chick is 38°, the minimum is 25°, the maximum near
42° (RAUBER, ’84). F£r£ (’94) has determined the rate of development of
the chick’s egg incubated at different temperatures. One lot at an abnor-
mal temperature and a second at 38° were reared synchronously; after a.
time the eggs were opened and the average stage of development (in hours.
of a standard series) determined. The following numbers express the ratio.
of the stage of development at the abnormal temperature to the stage at the:
normal temperature of 38°: —

Temperature. . . . 34° 35° 36° 37° ss°. 39° 40° 41°
Index of Development 0.65 0.80 0.72 ?* (1.00) 1.06 1.25 1.51

In summarizing these scattered observations on growing animals we e may
exhibit in one table their critical temperatures.

* The stage at 37° is taken from too few observations to be trustworthy. The
stages at 35° and 36° are irregular, doubtless because of too few observations.
As we go beyond 41° the ratio must decline again with great suddenness to 0.

460 EFFECT OF HEAT (Cu. XVIII

TABLE LHI

CriticaL Points For VARIOUS ANIMALS, ARRANGED ACCORDING TO THE

OpTiIMUM
SPECIES. Optimum. | Minimum. | MAximuM. AUTHORITY,

Minnows ° 0_1n0 :

. © e ° . . rc 0 12 —15 RAvuBER, 84
Salmon
CHITIGB oe ie ew eee | OR Dee oo —~ Vernon, ’95
Rana virescens. . . ... 30 3 — Livre and K., °98
Bufo lentiginosus. . . . 32 6 — Ag As e
Gallus domesticus. . . . 38 25 42 RAvuBeErR, ’84

These critical points for animals show the same variations with reference
to optima, minima, maxima, and range that those of plants do, and here
also these variations are clearly adjusted to the temperatures normally
experienced by the species.

3. Some General Phenomena accompanying Heat Effects. —
a. Latent Period. — We have seen that a change in the rate
of growth is produced by a change in temperature. If, how-
ever, the times of the two changes be carefully noted, it will
_be found that a considerable interval elapses between them.
This interval, the latent period, varies with the temperature.
Thus ASKENASY (’90, p. 75) found that, in the case of maize
seedlings cooled to 1°-5°, two or three hours elapsed before
decreased growth occurred ; whereas, when the seedling was
cooled to 0°, five hours elapsed. A similar effect follows a
change in the reverse direction.

b. Sudden Change of Temperature.—If the radicle of a
seedling is suddenly transferred from water at or near 0°C.
to water at between 18° and 21°, two effects follow. The first
appears immediately after the transference, and consists in the
sudden elongation of the radicle. The second appears later,
and consists in a growth which is slower than that of the
normal radicle. These facts have been determined by TRUE
(95), who concludes that the first effect is of a physical nature,
and is due to the fact that, at the higher temperature, osmotic
pressure is greater ; hence the tension in the tissues is greater
and, consequently, they become stretched. The second effect
TRUE regards as a response to the stimulus of the change, since

UPON THE RATE OF GROWTH 461

$1]
it is not constant for a given difference between the two tem-
peratures, but is greater in raising the temperature from 5° to
18° than in raising from 17° to 80°. The more abnormal one
of the pair of temperatures is, the greater is the response.

e. Cause of Acceleration of Growth by Heat. —The accel-
eration of growth may be due either to increased assimilation,
imbibition, or production of formed substance. Is it princi-
pally due to any one of these or are all increased in the same
proportion? Data on this subject are afforded by certain
measurements made by BIALOBLOCKI (’71).

Seeds of rye, barley, and wheat were planted in soil which was fertilized
by nutritive solutions and heated by a surrounding bath of water. The
average absolute weight of the whole plant of each species was determined
after the lapse of twenty days. The proportions of water, organic matter,
and ash in the entire plant were likewise determined. Some of the results
are givenin Table LIV. It is to be noted that the high temperature was
applied only to the soil in which the roots of the plant were imbedded.

TABLE LIV

Givinc THE AVERAGE WEIGHT (IN MILLIGRAMMES) AND THE PERCENTAGE OF
WaTER IN PLANTS WHOSE ROOTS ARE MAINTAINED IN SOIL, aT VARIOUS
TEMPERATURES, FOR 20 Days (BIALOBLOCKI)

RYE. BARLEY. WHEAT.
TEMPERATURE FRESH FRESH FRESH
Weient | % Warer.| Weient | % Warter.| Wetcut | % Water.
IN Me. In Me. IN Me.
10° 176 87.1 156 88.4 131 84.1
15 269 87.9 383 91.0 241 87.8
20 459 89.1 409 91.0 261 88.2
25 376 88.7 435 90.4 342 87.2
30 408 88.4 365 90.0 402 88.3
40 240 87.0 231 88.6 296 86.4
88 192 87.5 152 88.7 98 83.9

This table shows that the percentage of water increases slightly
but constantly as the growth is accelerated by increased tem-
perature, reaching a maximum near the optimum temperature.
Other data (not reproduced here) show that the percentage of
ash remains about constant, while that of dry organic sub-

462 - EFFECT OF HEAT (Cu. XVII

stance diminishes slightly towards the optimum temperature for
growth. We conclude, consequently, that in the acceleration
of growth by heat all three processes are accelerated, but the im-

Ho oi -bibitory process

28d

‘25TH

60° EAH.

56 FAHR.

53 FAHR.

5{ FAHR.

@

©

®

co)

+

27TH

28TH

3187

ae)

APRIL 4TH

6TH

70TK

MAY 22p

AUG, 1875

=
ae

28TH

ts

more than the
others.
Apparently con-
tradictory are the
results gained by
COPELAND (’96),
who found that
the cells in the
foliage of a moss
which was trans-
ferred from a cold
room at 2° to a
room at 18° to 20°
lost, in from one
to two weeks, a
degree of turges-
cence measured
by a 1 to 3% so-
lution of potassic
nitrate (p. 72).

When returned to

the cold room the
- cells gained an

increased turges-

cence. ‘The nearer

the temperature
lay to the optimum, the more rapid therefore the plant growth,
the lower was the turgescence. This seeming paradox can be
explained upon the hypothesis that just because the whole tissue
is expanding, just because the superficial increase of the organic
walls keeps pace, or more than keeps pace, with that of the
included water, there is less osmotic pressure in the rapidly
growing plants than in the slow-growing ones where the plasma
walls are not expanding as fast as the imbibitory process would
~ demand.

OCT. 31sT

}

Fic. 132.— A chart showing the correlation between the
stage of development of the frog on suecessive days
and the temperature at which it has developed. (From
HIGGENBOTTOM, ’50.)

§2] +. UPON THE DIRECTION OF GROWTH 463

We may now gather together the results of our study of the
effect of heat on the rate of growth of organisms. The relation
between temperature and rate of growth may be expressed by
a curve which, starting near 0°, reaches its highest point at a
temperature varying with the species, and falls to a maximum
temperature generally not far from the lethal temperature for
the race. ‘lhree critical points are thus distinguishable, — the
minimum, the optimum, and the maximum. In both animals
and plants these points are correlated. The optimum lies
close to the normal temperature for the species, the minimum
lies usually only a little above the point of cold-rigor, and the
maximum only slightly below the point of heat-rigor. The
optimum lies nearer the maximum than the minimum, but the
curve is not so unsymmetrical as that of metabolism. Any
change in temperature leads to a change in the rate of growth,
but this does not take place completely at once: there is a
latent period of an hour or so. A sudden rise in temperature,
especially from 0° to the ordinary summer temperature, is
accompanied not only by a mechanical (elongating) effect, but
also by a physiological response, showing itself in accelerated
growth. Finally, in the acceleration of growth by heat, the
imbibition of water is slightly more accelerated than the other
growth processes.

§ 2. Errect oF HEAT ON THE DIRECTION OF GROWTH—
THERMOTROPISM *

Two sorts of heat are to be here distinguished —radiant and
conducted. ‘The former is a form of radiant energy and allied
to light, consisting, indeed, of the rays lying beyond the visible
red of the spectrum. The latter is due to molecular vibrations
of the medium.

1. Effect of Radiant Heat. When Phycomyces nitens or
seedlings of Lepidium sativum, Zea mais, etc., are reared on a

* The first suggestion of this phenomenon was based upon an analogy with
the action of light and was made by van TreGHeEmM (’82), who gave it the name
Thermotropism. Wortmann (’83 and ’85) first published extensive critical studies
on the subject. Others who have contributed data are BarTHELEMY (’84),
working on the roots of bulbous plants ; Vocutine (’88), upon flower bade: and
AF KLERCKER (’91) upon radicles.

464 EFFECT OF HEAT (Cu. XVII

klinostat whose axis of rotation is parallel to the window, and
are subjected to rays of heat from a warmed plate of iron held
in the axis of rotation, they turn with reference to the source
of heat. Thus WorTMANN found that, at a distance from
the iron plate of 10 cm., corresponding to a temperature of
27° C., all the spore-bearing hyphze of Phycomyces turned in
seven hours from the source of heat; they were negatively
thermotropic. Under the same conditions the plumule of ‘a
seedling maize was positively thermotropic. The roots of the
hyacinth when growing in water turn towards the adjacent
stove-pipe. The flower-buds of Magnolia turn, in the field,
from the dark heat-rays of the sun (VOCHTING).

2. Conducted Heat. — The methods employed in working with
this agent have been as follows: WoORTMANN used a box
divided into two compartments by a diathermous partition.
Through one compartment there passed a constant current of
cold water; the second was filled with sawdust in which seeds
were imbedded. In front of this second compartment, on the
opposite side from the cold-water chamber, was a gas flame, the
source of energy. ‘The seeds were scattered through the saw-
dust, so that some were nearer the flame, others nearer the
cold hinder wall. The temperature of the sawdust near each
seedling was determined. KLERCKER used essentially the same
apparatus, excepting that a box of hot water replaced the flame.

The results of the experiments are summarized in

TABLE LV

SHOWING FOR THE RADICLES OF SEEDLINGS OF VARIOUS SPECIES THE RELATION
BETWEEN THE TEMPERATURE AND THE SENSE OF THERMOTROPIC RESPONSE

PHASEOLUS
TEMPERATURE. ZEA MAIS. ERVUM LENS. MULTIFLORUS.

50.0° — _ <<
40.0 — ie on
87.5 —
35.0
30.0
27.5
25.0
22.5
20.0
15.0

“f
|

++++4+4+4°

§ 2] UPON THE DIRECTION OF GROWTH 465

This table shows that the sense of thermotropism is not con-
stant for all temperatures, but is positive at the lower tempera-
tures, negative at the higher ones, and neutral at a certain
intermediate one. Also, just as different species vary in their
optimum so also do they vary in the temperature of neutrality.
As the optimum for growth
is high in maize radicles
(34°), and low in the pea
radicle (26°.3), so also is
the neutral point. The
neutral temperature is thus
also probably related to
the attunement of the or-

ganism and is an advan-
tageous response. Fic. 133. — Caloritropic curve of Sinapis alba,
: Se ; f showing the relation between the inclination
Within the range 0 of the radicle and the surrounding tempera-
ositive or of negative ture. The numbers on the left give the in-
p of

3 . clination in degrees; the horizontal series of
turning there is a correla numbers are the temperatures to which the

tion between the temper- plant is subjected, the temperature diminish-

ature and the angle of ing 4° for every centimeter of departure from
; “ ‘ the source of heat. (After Ar KLERCKER,
inclination of the organ. 91.)

KLERCKER has paid par-

ticular attention to this fact. His results aré summarized in
the following table and curves, showing for each species the
average inclination at each range of temperature : —

pg
s

°
N\
a

+
~
NN

INCLINATION FROM VERTICAL
"A

15° 20° 25° Cc.

TABLE LVI

Tue Sense (+ or —) aND THE AVERAGE EXTENT (EXPRESSED IN DEGREES OF
ANGULAR DEVIATION FROM VERTICALITY) OF THERMOTROPISM AT DIFFER-
ENT TEMPERATURES

Pisum sativum | —8.9 | —12.9] —27.2| —38.4|—43.9|
Sinapis alba| +10.5 | +190 | 424 | (See Fig. 133.)
Faba vulgaris | —438 | —65 | -98 | —191 | -—289 |

°C. . . « 18,14,15,16,17,18, 19,20, 21,22, 23, 24, 25, 26, 27, 28, 29, 30, 31,382,383, 34, 35, 36,37,38, 39,40, 41

We see here that the angle of inclination (whether + or—)
increases regularly as we depart from the temperature of

neutrality or that of 0° curvature.
* oe

466 EFFECT OF HEAT UPON GROWTH (Cu. XVII

3. Causes of Thermotropism.— VAN TIEGHEM suggested, in
his a priori account of thermotropism, that it was due to an
unequal growth on the two unequally heated sides of the
organ, the side whose temperature was nearest the optimum
making the greater growth. This explanation is not a
direct mechanical one, the turning stem does not act merely
like a metallic rod. The curvature is rather the result of

unequal growth at unequal temperatures. In accordance with

the theory just outlined we should find organs subjected on
one side to the optimum temperature growing on that side
faster than on the other, and hence turning from the optimum
—but they turn towards it. Again, plants subjected on one
side to a temperature slightly below the optimum will have a
still lower temperature on the opposite. side, and should be
negatively thermotropic — but they are positive. Finally,
plants subjected on one side to a temperature above the opti-
mum will have a lower temperature, one nearer the optimum,
on the opposite side, and should be positively thermotropic —
but they are negative. In a word, according to the theory,
plants should turn from the optimum; they turn, however,
towards the optimum, hence VAN TIEGHEM’Ss theory is exactly
opposed to the facts.

WoORTMANN, on the other hand, believed that the sense of
thermotropism is due to a self-regulation of growth in the
organism leading it to make this advantageous turning. The
stem tends to place itself in the axis of the heat rays just as in
phototropism it places itself in the. axis of the rays of light.
To this theory we must, however, add that plant organs may
respond to conducted heat as well as to radiant heat, since
they turn in a direction which, although opposed to the ordi-
nary law of growth, tends to bring the tip into its optimum
temperature. Such a result indicates clearly that thermotro-
pism is a response to stimulus.

If thermotropism is a response, where is the perceptive
region? Suspecting that it was at the apex, WORTMANN de-
capitated the root tip, but the response occurred as before.
Evidently the whole growing part is sensitive to temperature.

Thermotropism is thus seen to be such a response to the stimu-
lus of either radiant or conducted heat that the organ — plumule,

ee

= —aer Ut eee a

LITERATURE 467

radicle, flower-bud or sporangiferous hypha— tends to place
itself in the axis of the heat rays, if there are any, or to bend
towards or from the source of heat. Whether the organ shall
bend towards or from the source of heat depends both upon the
external temperature and the protoplasm of the plant. The
turning is such that it will tend to keep the organ at the opti-
mum temperature for its protoplasm, or bring it into such a
temperature. The response is thus, on the whole, an advan-
tageous one.

SUMMARY OF THE CHAPTER

There is in all organisms a close relation between tempera-
ture and rate of growth, such that growth is most rapid at that
temperature at which the chemical changes of metabolism pro-
ceed most quickly. The position of this optimum varies with
the normal thermal environment of the race; it is attuned, we
may say, to that normal temperature. Certain organisms or
their parts grow in a definite direction with reference to the
source of heat: away from the source when its temperature is
too high; towards the source when the temperature is low.
The neutral point varies in the different species in much the
same way as the optimum for growth varies. We may say
that the different attunements of organisms determine their
different neutral points. At the same time these responses are
advantageous. In some way the advantageous response of
the organism is bound up with its attunement.

LITERATURE |

ASKENASY, E. ’90. Ueber einige Beziehungen zwischen Wachsthum und
Temperatur. Ber. deut. Bot. Ges. VIII, 61-94. 23 April, 1890.
Bartuitemy, A. ’84. De l’action de la chaleur sur les phénoménes de
végétation. Comp. Rend. CXVIIT, 1006, 1007. 21 April, 1884.
BraLoswockt, J.’71. Ueber den Einfluss der Bodenwirme auf die Entwick-

lung einiger Culturpflanzen. Landw. Versuchs-Stat. XIII, 424472.
CopEeLAND, E. B. 96. Ueber den Einfluss von Licht und Temperatur auf
den Turgor. Inaug. Diss., 59 pp. Halle. Bot. Centralb. LXVILI,
177-180. 4 Nov. 1896. ‘
Curenot, L. ’94. L’influence du milieu sur les animaux. Encyclopédie
' scientifique des Aide-Mémoire. Paris: [1894].

468 EFFECT OF HEAT UPON GROWTH (Ca. XVII

Ear, R. E. ’80. A Report on the History and Present Condition of the
Shore Cod-fisheries of Cape Ann, Mass., etc. Rept. U. S. Fish Com.
for 1878. 685-740. ‘

Erpam, E. 75. Untersuchungen iiber Bacterien, III. Beitrage zur Biologie
der Bacterien. 1. Die Einwirkung verschiedener Temperaturen und
des Eintrocknens auf die Entwicklung von Bacterium Termo, Duj.
Beitrage z. Biol. d.-Pflanzen. I, 208-224.

Fre, C. 94. Note sur l’influence de la température sur l’incubation de l’ceuf
de poule. Jour. de l’Anat. et de la Physiol. XXX, 352-365.

Fiscuer, A. 97. Vorlesungen iiber Bakterien. Jena: Fischer, 1897.

Forster, J. 87. Ueber einige Eigenschaften leuchtender Bakterien. Cen-
tralb. f. Bacteriol. u. Parasitenk. LI, 337-340.

Herrick, F. H.’96. The American Lobster. Buil. U.S. Fish Com. XY,
1-252. 64 plates.

Hertwie, O. ’96. Ueber den Einfluss verschiedener Temperaturen auf die
Entwicklung der Froscheier. Sitzungsb. Berlin Akad. Jan. 1896.
105-108. 6 Feb. 1896. st |

98. Ueber den Einfluss der Temperatur auf die Entwicklung von Rana

fusca und Rana esculenta. Arch. f.mik. Anat. LI,319-381. 8 Jan. 1898.
HiGGENBOTTOM, J. ’50. (See Chapter XVII, Literature.)

KIRCHNER, O. ’83. Ueber das Langenwachsthum von Pflanzenorganen bei

niederen Temperaturen. Beitraige z. Biol. d. Pflanzen. III, 335-364.

KLERCKER, JOHN AF, 91. Ueber caloritropische Erscheinungen bei einigen
Keimwurzeln. Ofversigt af Kongl. Vetenskaps. Akad. Férh. XLVII,
765-790.

Kopren, W.’71. Waerme und’ Pflanzenwachsthum. Bull. Soc. Impér. des:

Naturalists, Moscow. XLIII, Part 2, 41-110.

Lituir, F. R., and KNow.Ton, F. P. 97. On the Effect of Temperature on
the Development of Animals. Zodélogical Bulletin. I, 179-193. Dec.
1897.

Meyer, H. A. ’78. Beobachtungen iiber das Wachsthum des Herings im |

westlichen Theile der Ostsee. Jahresber. der Commission zur wiss.
Unters. d. Deutschen Meere in Kiel. IV—VI, 227-251.

Rauser, A. ’84. Ueber den Einfluss der Temperatur, des atmosphiarischen
Drucks und verschiedener Stoffe auf die Entwicklung thierischer Eier.
Sb. Naturf. Ges. Leipzig. X. 55-70.

Rice, H. J. ’84. Experiments upon Retarding the Development of Eggs
of the Shad, made during 1879, at the U. S. Shad Hatching Station
at Havre de Grace, Md. Report U.S. Fish Com. for 1881. 787-794.

Sacus, J. 60. Physiologische Untersuchungen iiber die Abhangigkeit der
Keimung von der Temperatur. Jahrb. f. wiss. Bot. II, 338-877.

Scuu.tzg, O. ’94. Ueber die Einwirkung niederer Temperatur auf die
Entwicklung des Frosches. Anat. Anz. X, 291-294. 19 Dec. 1894.

Semper, C. ’81. Animal Life as affected by the Natural Conditions of
Existence. 472 pp. New York, 1881.

TrrGHeEM, P. van, ’82. Traité de Botanique. Paris, 1884. [First part
issued in 1882.]

= ee

-
be,

ee se ee ee ee ee

4

\

LITERATURE 469

True, R. H.’95. On the Influence of Sudden Changes of Turgor and of
Temperature on Growth. Ann. of Bot. IX, 365-402.

Vernon, H. M. 95. (See Chapter XVII, Literature.)

Voécutine, H. ’88. Ueber den Einfluss der strahlenden Wirme auf die
Bluthenentfaltung der Magnolia. Ber. deut. Bot. Ges. VI, 167-178.

Vries, H. pe, ’70. Matériaux pour la connaissance de l’influence de la
température sur les plantes. Arch. Néerlandais. V, 385-401.

Warp, H. M.’95. (See Chapter XVII, Literature.)

Wiesner, J.’73. Untersuchungen iiber den Einfluss der Temperatur auf die
Entwicklung des Penicillium glaucum. Sb. Wien. Akad. LXVIID,
5-16.

WorTMANN, J. ’83. Ueber den Einfluss der strahlenden Wirme auf wachs-
ende Pflanzentheile. XLI, 457-470, 473-479. July, 1883.

85. Ueber den Thermotropismus der Wurzeln. Bot. Ztg. XLII, 193

et seq.

CHAPTER XIX

EFFECT OF COMPLEX AGENTS UPON GROWTH, AND
GENERAL CONCLUSIONS

In the foregoing chapters we have examined the effect upon
growth of various agents considered as acting separately. ‘This
treatment has been necessary for purposes of analysis, but it
has the disadvantage that it does not reveal the normal
action of these agents. For, in nature, we find many agents
working together upon the growing organism. For example,
gravity is constantly acting in one direction, upon sessile

organisms at least, and at the same time the chemical character |

and the density of the surrounding medium, contact and im-
pact, light and heat, are exerting their specific influences. ‘The
rate of ‘growth of an organism and the direction of growth of
its organs are determined by the resultant of some half dozen
controlling factors which, in their totality, constitute environ-
ment.

Again, some of the factors influencing growth are so complex
that they are not yet amenable to analysis into the chemical,
molar, and physical agents whose effects we have considered in

foregoing chapters. For instance, the reaction of an organism.

to its own activity is still too complex an effect for us to be
able to resolve it into its elemental reactions to pressure, chem-
ical change, etc. The effect of exercise upon growth may con-
sequently form a subject for special consideration.

§ 1. THE COOPERATION OF GEOTROPISM AND PHOTOTROPISM

When light falls from one side upon a seedling in the ground,
the seedling is influenced by both gravity and light, and tends
to respond to both. In responding to both, the apex of the
seedling tends to point upwards on account of gravity’s action,
and laterally towards the source of illumination on account of

470

I es

— =~

§ 1) ‘GEOTROPISM AND. PHOTOTROPISM 471
w

the light. As a result of this combined response the plant
comes to occupy an oblique position.

The exact angle assumed by the plant is variable. It varies
in a given species with the intensity of the light, and, the in-
tensity of the light remaining constant, the angle varies with
the species. For example, seedlings of Lepidium sativum sub-
jected to a unilateral horizontal illumination for 48 hours ©
showed at different intensities of the light the following —
inclinations from the vertical (WIESNER, ’79, p. 196): —

DISTANCE OF SEEDLING FROM FLAME. INCLINATION FROM VERTICALITY,
0.25 meter 30°
0.30 « 35
Uys eee! 55
3b" 70
2.50 “ (optimum) 80
3.00 65
Se a 30

‘This table shows that the inclination from verticality in-

creases with the intensity of illumination to a certain maximum
degree, beyond which it diminishes again. This maximum
inclination is called the phototropic limiting angle.

More extended determinations of the limiting angle have
been made by CZAPEK (95), who finds that it is the same for
a given intensity of horizontal light whether the plant is verti-
cal or horizontal, having its apex directed towards the source
of light.

TABLE LVII

Givinc THE PHoTorropic Limiting ANGLE FOR VARIOUS SPECIES OF PLANTS

Phycomyces nitens . . . 90°| Sinapus alba (plumule). . 60°
Pilobolus crystallinus . . 90 | Pisumsativum. . .. . 60
WiGiaMttVO es dived te TO | VACIR faba. 6 ek oe 8 OD
Avena sativa . . . . . 70 | Phaseolus multiflorus . . 60
Phalaris canariensis. . . 70 | Sinapisalba(radicle) . . 50
Linum usitatissimum . . 70 | Helianthusannus. .. . 49
Brassica napus. . . . . 70 | Ricinuscommunis.. . . 45
Datura stramonium . . . 70 | Cucurbitapepo. . .. . 40
Lepidium sativum . =: . 60

472 EFFECT OF COMPLEX AGENTS ON GROWTH ([Cu. XIX
€

The phototropic limiting angle is constant for all cases in
which gravity and light act at a right angle, whether the plant
axis be originally placed vertically upright, inverted, or hori-
zontal. When the direction of the light ray makes some other
angle with that of gravity, the resulting position of the plant
may be quite different, as CZAPEK (’95) has shown.

If the light falls upon the plant vertically from below, in such
a way therefore as directly to oppose gravity, the resulting
position of the plant varies according to its original position, in
a way generally explicable on the ground that one of the two
tropic influences has come to prevail, but with diminished
power. ‘Thus, when the axis of the seedling is horizontal it
will, if like Avena it is very sensitive to light, turn its tip
slightly upwards for a time, and then definitely down. A
slightly phototropic plant, like Helianthus, assumes its limiting
angle of 45° from the zenith. When the seedling is exactly
inverted, plants highly ‘sensitive to light grow down, but
Helianthus places itself at 135° from the zenith, hence no longer
at. the limiting angle. When the axis of Helianthus is placed
obliquely downwards its tip becomes inclined at 45° from the
zenith.

If the ray of light falls upon the plant obliquely from below,
the result on the erect, horizontal, or inverted seedling is a
response to the active component of the light ray. The erect
seedling is affected in the same way as by the horizontal ray;
the horizontal seedling responds as though the light came verti-
cally from below, and all inverted plants place themselves in
the axis of the infalling ray.

If the ray of light falls obliquely from above, all plants, even
Helianthus, place themselves in the axis of the ray. This is
what might have been anticipated, since gravity affects the
inclined plant much less than the horizontal one, and so the
active component of the light ray is relatively more effective
in this oblique position than in the horizontal one.

The foregoing experiments show that, in general, the geo-
tropic reaction is modified by the simultaneous action of light.
I have hitherto assumed that the final position of the plant is
the resultant of the action of two tropic agents; that the pho-
totropic and geotropic reactions interlock. Another cause of

——e SS OOO

a oe
t-

§ 2] EFFECT OF EXTENT OF MEDIUM ON SIZE 473

the modified position is, however, possible. ‘The stimulating
action of light may interfere with the sensibility of the plant
to gravity. An early experiment made by CZAPEK seemed to
indicate that this is the case. A vertical plant was illumined
upon one side and then placed horizontally with the former
illumined side facing the nadir. ‘The geotropic curvature was,
as might be inferred from the experiment described on p. 444,
greatly retarded. The retardation of geotropism by a pre-
vious photic stimulation occurs, however, only in species which
are much more phototropic than geotropic. That the result
just described is not due to a diminution in geotropic sensitive-
ness follows from two considerations: first, a plant previously
geotropically stimulated is not retarded in its subsequent pho-
totropic response, as we should expect if the, irritated state
interfered with the reception of a new stimulus; secondly, the
retardation in response to light after geotropic stimulation
is most directly explained on the ground that a response
which is being actually worked out interferes with an incipient
response.

The conclusion may, consequently, be drawn that there is no
reason for believing that the modified response resulting either
from the simultaneous or successive action of two tropic agents
is due to an alterhation of geotropic or phototropic sensitive-
ness, but rather to a modification of the response. The modifi-
cation of the response is due to the interlocking effect or the
mutual interference of the phototropic and geotropic reactions
to stimuli.

§ 2. Errect oF EXTENT OF MEDIUM ON SIZE

The quantity to which an organism shall grow —the size
that it shall attain—is a specific character which is, within
limits, independent of the amount of food consumed by the
organism. In how far this character is dependent upon other
environmental conditions is an interesting question. It is clear
that size is relative, and among other things it is related to the
extent of the space in which the organism can move. An ant
can lose its way in a cage in which an elephant can hardly find
room to move. The ant is small, the elephant large, in relation
to their common room.

474 EFFECT OF COMPLEX AGENTS ON GROWTH [Cu. XIX

Now it is a common observation of naturalists that there is
frequently a relation between the size attained by a developing
organism and the extent of the medium in which it is develop-
ing. Animals reared in aquaria rarely attain the size of their
fellows developing in out-of-door ponds. Even in nature, fishes
of a given species living in small or densely inhabited ponds
are smaller than fishes of the same species inhabiting large or
sparsely populated ponds. According to SEMPER (’74) the
experiment was tried of transplanting the very small chars
from a small lake in the Maltathal, Carinthia, Austria, where
they were very abundant, to another lake where there were few
fish. The transplanted chars soon became three times the size
of the parent stock. }

In other eXperiments it has often been observed that tadpoles
reared in the laboratory, although well fed, never attain the
_ size of those living free. SrzBOLD* found that Apus reared in
a small vessel grew no longer than 7 or 8 mm. instead of 50
or more. The pond-snail, Limnza stagnalis, has been made
the special object of experimental dwarfing. Hoae (54)
found that when confined to a small, narrow cell they ac-
quire, even after six months, only the size of normal animals
two or three weeks old. Hoae’s conclysions no doubt ap-
peared crude to the physiologist of the last decade. He said
that the snail. grows “to such a size only as will enable it
to move about freely, thus adapting itself to the necessities of
its existence.” 7

SEMPER (’74) next undertook a more thorough set of experi-
ments upon these animals. He kept the snails in vessels con-
taining different quantities of water to each individual, and
found that as the quantity of water is diminished from 4000 cc.
or 2000 cc. to 100 cc., a diminution in the rate of growth occurs.
Increasing the number of individuals in a vessel has the same
effect as diminishing the volume of water. The relation of
volume of water per individual to length of shell at the end of
eight or nine weeks is given in Fig. 184. This curve shows
that as the volume increases from 100 ce. to 800 cc., the average
length of the shell of the snail doubles. The result SEMPER

* Cited from Sempnr (’74).

EE Oe ee

roe Sr
Se

§ 2] EFFECT OF EXTENT OF MEDIUM ON SIZE 475

explains on the hypothesis that water contains some substance
necessary to the growth of the snails, which becomes used up
before full size is acquired: the more quickly, of course, the
smaller the amount of water.

Instigated by SEMPER’s experiments YUNG (’85) now under-
took similar ones upon tadpoles. Twenty-five just-hatched
tadpoles were put into each of three vessels, A, B, and C, contain-
ing about 1200 cc. of water, but of different forms, so that A,

which measured 7 cm. diameter, had a depth of 30 cm. of water ;

aie

49 >

\
\

a

LENGTH OF SHELL
IN MILLIMETRES
S

Hyd

0 200 400 600 800 1000 1200 1400 1600 1800 2000
CUBIC CENTIMETRES OF WATER

Fic. 134.— Curve of relation between length of shell of Limnza stagnalis and
quantity of water in which it is reared. (From SEMPER, ’74.)

B, whose diameter was 11 cm., had 13 ecm. of water; and C,
whose diameter was 14.5 cm., had 6.5 cm. of water. At the
end of one and a half months measurements were made of the
length and the breadth of each tadpole with the following
average results : —

=

VESSEL A. VESSEL B. VESSEL C.
Length. 26.20 34.2 41,2
Breadth Roe 6.15 7.8 8.8
Date of first metamorphosis. August 4 July 22 June 18

Yune concluded that the larger size of the animals in the
shallower water (C) was due to its absorbing oxygen more
thoroughly. .

Finally, DE VARIGNy (94) has attacked even more. system-
atically this problem of effect of extent of medium on size. He
has found that Limnzas kept for eight months in similar
vessels, each containing 550 cc. of water and about 500 ec. of

476 EFFECT OF COMPLEX AGENTS ON GROWTH [Cu. XIX

air, but differing in that one was stoppered and the other not,
had attained about the same size (Fig. 185). Since the oxygen
supply of the snails in the two vessels was evidently very dis-
similar, YUNG’S explanation is shown to be inadequate. Next
DE VARIGNY tested the effect of differences in volume. He
reared Limneas in different quantities of water, in vessels of
dissimilar proportions, such that in all there was the same free
surface area of water. ‘The differences in volume had only a
slight.effect on the size of the snails (Fig. 186). On the other
hand differences in surface, with constant volume of water, have
an important influence on size. ‘The greatest growth occurs in
the broader vessel (Figs. 137, 188). The number of individuals
in the vessel influences the average size, as SEMPER found.

To test SEMPER’S theory that the small size of the animals in
the small vessel is due to its having exhausted the necessary
_ substance in the water, DE VARIGNY partitioned a vessel of
water into two unequal compartments and reared a Lymnea in
each. One of the compartments was made by partly submerg-
ing a test-tube, from which the bottom had been removed, in a
beaker of water. A piece of muslin, tied over the bottom of
the test-tube, permitted an interchange of water, but not the
intermigration of the Limnzas between the test-tube and the
main vessel of water. The latter constitutes the second com-
partment in which the snails lived. After several months the
individuals kept in the two vessels usually showed a marked
difference in,size, those reared in the roomier vessel being the
larger (Fig. 139). When, however, the two similar snails
were kept in similar tubes plunged in beakers of water of
unequal volume, they attained about the same size.

A second test of SEMPER’s theory applied by DE VARIGNY
consisted in comparing the growth of Limneas in fresh water
with their growth in water in which snails had for some time
been developing. The snails in the latter showed a slight but
nearly constant inferiority in size. It may well be that some of
the salts necessary to growth had been extracted from the water
by the development of snails therein, making it less fit for growth.
Nevertheless, even the most marked differences in the size of
the snails in the two kinds of water was not sufficient fully to
account for SEMPER’S result by means of SEMPER’S theory.

al
7

: >
tf

§ 2] EFFECT OF EXTENT OF MEDIUM ON SIZE 477

Fig. 135. — Two individuals of Limnza stagnalis, which have lived from May, 1891, to
January, 1892, in two flasks nearly alike in respect to surface and volume of water.
In the one case (shell at left) the flask, enclosing 500 cc. of air, was sealed; in the
other case (shell at right) the flask remained unsealed throughout the 8 months
of experimentation.
(From DE VARIGNY,

94.)

Fic. 136. — Limneza auri-
cularis, reared in dif-
ferent masses of water
having the same sur-
faces but different
volumes. The speci-
mens, taken in order 1
from left to right,

were reared in vessels
having surface areas
_ of 100, 200, 400, and
500 cc. respectively. by )
Experiments extended 5
1

7

35. -
VS

36

from 15 November to
5 April. (From DE
VARIGNY, 9.)

Fig. 137. — Limnza stag-

nalis. The individual 4
at the left lived from
18 November to 20
April in. a liter of
water having a sur-
137 138

face of only 2cm.diam-

eter; that at the right

lived during the same §
period in an equal vol-

ume of water having

a surface of 18 cm.

diameter. (From DE

VARIGNY, ’94.)

Fic. 138.— The Limnza
stagnalis at the left Cy
lived from 21 Novem- ‘4 eet
ber to 6 January in
1350 ec. of water hay- Fs Y Y Y fh
ing a surface of 3.5cem. = S d
as 2 5

diameter; that at the 3 4 6
left, somewhat larger, 13)

lived during this pe-

riod in 600 ce. of water having a surface of 16cm. diameter. (From DE VARIGNY,
94.)

Fic. 139. — Limnea 1 lived from 18 November to 5 April in a glass without a bottom
(capacity 250 ce.), suspended in the beaker (capacity 4200 cc.), in which 2 lived.
Limnza 3 lived from 20 November to 7 February in a tube, suspended in a vessel
in which 4 was reared. Limnza 5 lived from 9 April to 24 June in a tube, sus-
pended in the vessel in which 6 lived. (From pE Varieny, ’94.)

478 GENERAL CONSIDERATIONS (Cu. XIX

The conclusion to which DE VARIGNY arrived was that the
nanism provoked in the small vessels is caused by a diminution
of movement and consequently of exercise, for in the restricted
~ medium the movements are fewer and slighter, since the food is
near at hand. Also, the snails will exercise more in a body of
water with a broad, exposed surface than in a narrower one,
because they crawl so much on the surface films.

This interpretation is sustained by all the results excepting
those obtained from a varying number of individuals in masses
of water of the same volume and form. The fact that the
individuals grow larger the fewer they are, may be accounted
for, thinks DE VARIGNY, on psychological grounds; for, in the
crowded room, movements will be restricted from very much
the same cause that makes one move less rapidly in a street
containing impediments than in one which is quite clear.

It may well be doubted whether the bottom of this matter
has yet been reached. Probably nanism is produced by several
causes: such as insufficient supply of mineral constituents in
the water, especially of calcium salts, products of excretion in
the water, and exercise. ‘There is, however, much reason for
believing that Hoage’s conclusion is one which, with our fuller
knowledge, we can hardly improve upon —that, in respect to
the size attained as in other qualities, the snail has the power
of “adapting itself to the necessities of its existence.”

§ 8. GENERAL CONSIDERATIONS RELATING TO THE ACTION
UPON GROWTH OF EXTERNAL AGENTS

1. Modification of Rate of Growth. — Protoplasm is composed
of three kinds of substances: the living plasma, the formed sub-
stance, and the watery chylema. Accordingly, growth involves
three processes: that of the formation of new plasms, assimila-
tion; that of the manufacture of formed substance, secretion; and
that of the absorption of water, ¢mbibition. Anything which
affects these three processes will affect the rate of growth.

The action of external agents upon the rate of growth is of
two general kinds. There is, first, the general effect; and,
secondly, the specific effect. The general effect is more or less
similar in all protoplasmic masses (organisms) subjected to the
agent ; it is the result of some immediate and necessary modifi-

Se

~ a Po

eS —

§3] EFFECT OF EXTERNAL AGENTS UPON GROWTH 479

cation of the protoplasm depending upon its very structure.
This general effect may be of two sorts: a grosser mechanical
one and a more refined. The grosser general effect is seen in:
the osmotic action of dense solutions; in the elongation of an
organ consequent upon pulling it with a considerable force; in
the interference with vital actions by poisons, by intense light,
or by high temperatures. The more refined general effect is due
to the acceleration of growth by the acceleration of the essen-
tial metabolic processes involved in growth; hence come the
effects, within limits, of favorable foods, of electricity, of
radiant energy, and of warmth. We can explain the effect of
such refined agents by known chemical laws.

The grosser and the finer effects pass over into each other at
certain intensities. Thus the acceleration of growth produced
by summer temperature passes over at a higher temperature
into the gross retardation due to coagulation.

The specific effects, in contradistinction to the general, appear
only in certain organisms or their parts, and have no such evi-
dent and explicable relation to the cause as the general effects
have to their causes. Such is the increased growth resulting
from certain slight poisons, from the deformations of the stems
of certain plants, from a wound which leaves a defect to be
filled by growth. These effects cannot at present be accounted
for satisfactorily by known chemical processes; they result
from peculiarities of the specific protoplasms which depend
largely upon the past history of each kind of protoplasm.

The same agent may have at different intensities, at one time,
the specific ; at another, the general effect... Thus the slight pull-
ing of the stem of a seedling may induce the specific shortening
effect, whereas a stronger pull will cause a gross elongation.

The gross general effect, the refined general effegt, and the
specific effect form a series of results brought about by pro-
cesses which are quite intelligible in the first case, much more
complex in the second, and still further removed from our ken
in the last; we might speak roughly of these effects as due to
physical, chemical, and vital processes respectively, without
meaning to imply a qualitative difference between these pro-
cesses. The most complex of these three processes may also
be designated as response to stimulus.

480 GENERAL CONSIDERATIONS [Cu. XIX

Let us now consider the mechanics of the acceleration of
growth by various agents. ‘The mechanics of the effect of
food on growth varies of course with the food; some supply-
ing the energy or the material for assimilation, other kinds
furthering secretion, and still others going to build up the
molecules which do the work of vital imbibition. Whether
the poisons which, like zinc sulphate, stimulate growth affect
chiefly the assimilatory or the imbibitory process, is unknown;
but the slowness of the result suggests a modification of assimi-
lation. The effects of water and of solutions seem to be chiefly
upon imbibition; that of deformation and wounding chiefly
upon assimilation ; that of electricity is uncertain; that of
light is probably chiefly upon assimilation; and that of heat
upon imbibition. These conclusions are, however, tentative;
experiments are needed to test them further: this is one of the
next tasks in the investigation of growth.

2. Modification of Direction of Growth —Tropism. — The
tropic effect of an external agent occurs only when the agent
does not act uniformly from all sides upon the growing organ-
ism, but constantly from one side. Hence this effect will be
marked only in organisms which for a considerable period
present the same surface to the action of the agent. Such an
effect is characteristic therefore of sessile plants and animals.

The turning of an organ with reference to an external agent
may be either a gross effect or a specific response effect of the
agent. As examples of the gross effect may be cited the cases
of false traumatropism and false electrotropism, in which the
turning is due to the death or injury of the tissue on the con-
cave side of the organ. All cases of true tropism are cases of
response to stimuli: such are, chemotropism, hydrotropism,
thigmotropism, traumatropism, rheotropism, geotropism, elec-
trotropism, phototropism, and thermotropism.

The mechanics of these tropic responses may now be briefly
considered. In general the tropisms are growth phenomena,
for they are due to enlargement of the bending organ on one
side. The growth seems to be due either to assimilation or
imbibition, or both, secretion playing no part. It is not easy
to say whether in any case assimilation or imbibition is the
more important. An inference can be drawn, however, from

§3] EFFECT OF EXTERNAL AGENTS UPON GROWTH 481

the quickness of response, for growth by imbibition is more
rapid than that by assimilation. Also a histological study of
the curving region should throw light upon this question.
Among the rapid tropisms are chemotropism, especially as
seen in the tentacles of Drosera and in pollen-tubes, and thig-
motropism, as exhibited in tendrils. Such are probably due
to differential imbibition. Among slow tropisms are hydro-
tropism and rheotropism, v
which are probably due — :
largely to differential as- ep ——
similation. Traumatro-
pism, geotropism, and the
response to radiant en-
ergy, namely, electrotro-
pism, thermotropism, and
phototropism, are inter-
mediate in their rate, and
are probably due to the
combined action of assim-
ilation and imbibition.
Sections through the
responding region show g\¥
the importance of imbi-
bition in certain tropisms,
as, for example, geotro-
pism. In such sections it
is seen that the cells on
the convex side are en- ; 2
larged in all axes and full DB Gj
of water, while those of Fie. 140. — A section of a tropic fadlale taken im
the concave side arecom- the plane of curvature, at the region sg, Fig.

pressed so that the cells 1°. © epidermis; 7p, parenchyma; gbs,
sheath of the fibro-vascular bundle ; /zb, fibro--

are shoved into one an- vascular bundle; h, wood-cells; g, vessels.

other, are diminished in Those cells which lie next the nadir (a) are

; smaller than those turned toward the zenith
FIZC, and : have a dense (b). The latter appear stretched with water,
plasma (F 1g. 140). A typ- while the former, are dense and of small size.

ical set of measurements (ftom Cresrersxy, ’72.)
of the dimension of the cells in the curving region, compared
with normal cells, is given by CIESIELSKI (’72) as follows :—

TMM te —
TIT Dm —
svi Ce
say —

> © se
yay 194)

482 _ GENERAL CONSIDERATIONS [Cu. XIX

LENGTH. BREADTH. _ THICKNESS,
Cells of convex side . . .... 0.125mm. | 0.045 mm. 0.042 mm.
Cells of concave side . ... . . 0.020 0.025 0.026
Cells in normal condition ... . 0.099 0.035 0.032

The importance of imbibition for geotropism is also shown by
the experiment of cutting a slice off from the upper part of the
horizontal root, which then curves only slowly ; whereas, if
the cut surface is placed down, the curving takes place with
abnormal rapidity.

It being admitted that tropisms are, for the most part,
largely, if not chiefly, due to differential imbibition, the ques-
tion arises, How can this produce a turning? It is easy to see
. how it might be possible in the case of a multicellular plant,
but tropism also occurs in animals and unicellular organs, as
e.g. the hyphe of Mucor. It has been suggested, to meet this
difficulty, that the unequal growth affects primarily the cell-
walls; but this explanation does not quite meet the case of
hydroids. A general statement, applicable to multicellular
plants and animals and. to unicellular organs, may be made, if
the cell-wall be recognized as living, as follows: The imbibi-
tion distends the living substance on the convex side, the
water probably being in part drawn from the concave side.

Going a step farther, the tropic agent produces such a
change in the molecules of the curving region as to cause them
to imbibe water with abnormal rapidity. This change may,
however, be produced by the agent either directly or indi-
rectly. In all cases in which the sensitive part of the organ
‘becomes the curving part, the action of the agent is direct.
Examples are found in the thigmotropism of tendrils, in the
phototropism and thigmotropism of stems, and, probably, in
traumatropism. In cases in which the curving part is remote
from the sensitive part, as in geotropism, the action of the
agent is indirect. In these cases there must ‘be a transmission
of a stimulus from the sensitive part (the tip) to the respond-
ing part, producing the required molecular change there.

Concerning the nature of the changes induced by the tropi-

§5] EFFECT OF EXTERNAL AGENTS UPON GROWTH 483

cally stimulating agent, we have recently gained valuable data
from the studies of CZAPEK (98). He has found that the
stimulated protoplasm, for instance, of a geotropic radicle
exhibits no visible movements or negative electrical variation,

as in the nerve cells of animals, but does exhibit a chemical

change. Thus, when the root tip of the seedling of a bean or
other species is boiled in a solution of ammoniacal silver
nitrate, there is a marked reduction of the silver, especially in
the cells of the periblem. This reduction is stronger in the
cells of stimulated root tips than in those of unstimulated
ones. A second change consists in the diminution in the
amount of a substance of the root tip which easily loses oxy-
gen. Such a substance is indicated by such changes as these
in the normal root tip: blue coloration (oxidation) of a sec-
tion of the tip when placed in an emulsion of guaiac gum in
water; deep blue coloration of sections by indigo white*;
strong violet reaction (indophenal reaction) in sections sub-
jected to an aqueous solution of a-naphthol to which paraphe-
nylendiamin has been added. Now all such reactions are less
marked in the root after stimulation. We conclude that stim-
ulation results in increased capacity for reduction and dimin-

' ished capacity for oxidation— an increase in the avidity for

oxygen.

These changes occur long before the response of turning
shows itself ; they occur earlier in the non-sensitive roots,
and they are less marked after a slight stimulus, such as
results from a slight inclination of the root from the vertical
position.

The isolation of the two substances, the reducing and the oxidizing, was
now attempted. The former is not changed by boiling or by the action of
chloroform, and is soluble in alcohol; the latter is destroyed by heat, is
unchanged by chloroform, is insoluble in alcohol, and may be extracted
from the triturated cells by water. A large number of root tips of Vicia
faba were rubbed up with water until no fragments remained. This aque-
ous extract was filtered, and to the filtrate aleohol was added. A precipi-
tate occurred, which had all the properties of the oxidizing substance. It
is highly probable that it belongs to the category of oxidation ferments.

* This is made by the cautious reduction of indigo carmine by dilute hydro-
chloric acid and zine.

484 GENERAL CONSIDERATIONS [Cu. XIX

To get the reducing substance, the preceding solution was filtered to
eliminate the alcoholic precipitate. The filtrate had all of the qualities of
the reducing substance. A further study of its properties indicated that it
belongs to the aromatic organic substances, many of which have an intense
reducing action and are hence used in photography.

We may conclude that geotropic stimulation of the root tip
induces chemical changes leading to the increase of a reducing
substance of aromatic nature, and to the diminution in amount
of an oxidizing ferment.

3. Adaptation in Tropisms.— The capacity for bending is
usually associated with an advantage accruing to the part by
that bending. Thus, the upward tropism of the stem and the
downward tropism of the root; the positive phototropism of
the stem and the positive thigmotropism of the root and of
the climbing Dodder; negative traumatropism; and positive
and negative thermotropism, depending upon whether the
source of heat is of a less or greater temperature than the opti-
mum —all these responses tend to preserve the normal enyi-
ronment for the organism; they are adaptive. At least one

tropic response cannot be shown to be advantageous, namely,

electrotropism. Electric currents of such intensity as roots
respond to certainly do not exist in the soil. . The response has
no conceivable advantage in the ordinary life of the plant, and
yet it occurs with as much precision as does aresponse to light
or heat. If only there were, in the ground, such electric cur-

rents as we apply to the plant, we might be able to show an |

advantage of the response in this case also!

4. Critical Points in Tropism.—It has been shown repeat-
edly in the foregoing chapters that the sense of tropism
depends upon the degree of the stimulating agent. Thus
Mucor stolonifer is strongly positively chemotropic with refer-
ence to 2% cane sugar; becomes less so as the concentration
approaches 80% ; and is negatively chemotropic to a 50% solu-
tion. So, likewise, the radicle of Zea mais is

+ thermotropic at 12°— 36°
+ thermotropic at 37°-38°
— thermotropic at 40°- 49°.

In these cases, as in the tactic phenomena, there is recognizable
an optimum intensity of the agent, to which the organism is

eS ee

ee

§ 3] EFFECT OF EXTERNAL AGENTS UPON GROWTH 485

attuned, so that, if the intensity rises above that optimum, neg-
ative tropism will occur, and, if the intensity falls below that
optimum, positive tropism may be expected. This optimum —
this intensity to which the organism is attuned — differs, how-
ever, in different species. Thus, according to WORTMANN, as
we have seen, the turning-point of the radicle is fopr—

Zea mais, 37°;
Ervum lens, 27°;
Phaseolus multiflorus, below 22°.

But why is the turning-point so different in different species, —
or why are species attuned to different intensities? This dif-
ference is for the most part more or less closely correlated with
the usual intensity of the agent to which the growing organ-
ism is subjected. To certain minds the phrase “ Natural Selec-
tion” will be considered sufficient to stifle further inquiry ;
the known facts of self-adjustment, however, have thrown the

‘burden of proof that Natural Selection has acted in any case

upon those who assert it. Meanwhile we may seek for a
cause more consistent with sound physiology.

In the first place, the facts of “ after-effect” may be consid-
ered. It has been shown, with reference to the effect of many
of the agents considered, that this effect does not endure only
so long as the agent acts, but that it persists for a longer or
shorter period after the stimulus has ceased to be applied.
Thus, if a stem is placed horizontally, so that gravity stimu-
lates it and causes it to grow up, and it is then placed verti-
cally, the growth continues for a time in the former (now hori-
zontal) direction; or, a horizontally placed root, decapitated
after the lapse of one hour, curves geotropically, whereas a
root placed horizontally and decapitated at once does not do
so. Again, if a tendril is irritated by contact and the irri-
tating body is then removed, a thigmotropic curvature of as
much as 45° may occur. Still again, in an experiment of
DARWIN (81, p. 463), a seedling of canary grass was placed
before a window for nearly two hours, during which the coty-
ledon turned towards the glass; the light was now cut off, but
the cotyledon continued to bend in the same direction for one-
fourth to one-half an hour. It was kept in the dark for an

486 GENERAL CONSIDERATIONS [Cu. XIX

hour and forty mimutes (during which time it acquired an
upright position through the action of gravity), and then
exposed again to diffuse light from one side for an hour, show-
ing the phototropic curvature. Light was now excluded, but
the cotyledon continued to bend for 14 minutes towards the
window.» In these experiments there was a persistence of the
response to light after light had been cut off. Finally, if a
plant organ, which has been growing slowly at a low temper-
ature, is quite rapidly subjected to the optimum, the increased
growth is slow in making its appearance; it may be delayed
for an hour or two.

What is the significance of. this after-effect? It seems
clearly to show that an agent acting on protoplasm not merely
modifies the constitution of the protoplasm, but produces a
change which is more or less permanent, and is only slowly
obliterated upon removal of the agent, or becomes only slowly
overshadowed by a new stimulus. ‘This permanency of the
change wrought permits the acewmulation of extremely slight
effects. An instance of such accumulation is seen in tendrils,
which exhibit no response to a single soft blow but show evi-
dent thigmotropism to a series of such blows.

When, however, the repeated stimuli are each great, it is
not an accumulation of effect which is noticed, but rather
an absence of any response whatever. ‘Then appears the phe-
nomenon of acclimatization, or accustoming to the stimulus.
Examples of this have been given in the foregoing chapters.
Thus, in the case of thigmotropism, DARWIN found that
after repeatedly stimulating the tendril of the passion flower
(twenty-one times in 54 hours), it responded only slightly. In
the case of traumatropism, DARWIN (81, p. 193) observed
that the radicle, to one side of which a card had been fixed by
shellac, eventually became so accustomed to the stimulus that
it no longer bent away from it, but grew vertically downwards.
In the case of phototropism, WIESNER noticed that after a
growing organ had,been for some time subjected to daylight,
its growth was less markedly controlled by a unilateral illumi-
nation.

Any general explanation of acclimatization, whether of meta-
bolic or of growth processes, to repeated irritants must, at the

§3] EFFECT OF EXTERNAL AGENTS UPON GROWTH 487

present time, be hypothetical. The attempt to picture to our-
selves the probable processes which bring about this condition
should, nevertheless, be undertaken. It is generally accepted
that a stimulus of any kind produces a chemical change in the
protoplasm, and this leads to a change in the activity of the
protoplasm — the response. The different kinds of stimuli
usually induce different kinds of responses, and this is probably
because each kind of stimulus affects a particular kind of mole-
cule — a kind capable of being transformed by the stimulus in
question. If we assume that the reception of any stimulus is
due to the transformation of a specific kind of molecule capable
of being acted upon by the stimulus in question, then it is not
difficult to see how, by repeated, violent stimulations of the
same kind, nearly all of the molecules upon which sensation
depends should become transformed, so that, thenceforth, the
protoplasm should be incapable of receiving that kind of
stimulus until such time as the sensitive substance shall have
been reproduced. Let us imagine 100 molecules (a,, a, a3, a,
— og, Aoq, Ao) ) in the root tips which are capable of being
decomposed by daylight and as a result setting in motion a
series of changes resulting in the phototropic response. Let
us imagine that the irritation of light during the first half hour
decomposes 50 of them; during the second, 25 of the remain-
der; during the third, 12 of the remainder, and so on; then,
eventually, the sensation will grow weaker if the substance is
not renewed, so that the response will diminish in intensity
and finally fail altogether. ‘Then we say the organ is accli-
mated to the reagent, for the application of the agent produces
no response.

This explanation of acclimatization to violent agents may
‘now be easily extended to cover the case of attunement. Let
us imagine a plant which, living in the dark, is negatively pho-
totropic to ordinary daylight. It is attuned to a low intensity
of light. If, however, the plant comes gradually to change its
habitat so that it is repeatedly subjected to the sunlight, then,
as a result of repeated stimulation, those sensitive molecules
which are affected by the light are destroyed, so that the plant
no longer turns from the light. It is attuned to it. The same
theory, mutatis mutandis, will account for attunement to tem-

488 GENERAL CONSIDERATIONS [Cu. XIX

perature or to chemical agents. It is to be observed that this
hypothesis is not an hypothesis to account for response to stimuli
or of the usual adaptive nature of that response ; but to account
only for that phase of ‘adaptation ” which is seen in attunement.
The hypothesis is an attempt to explain an adaptive result
independently of selection, but rather as a necessary result of
the constitution of protoplasm.

The adaptive acclimatized or attuned condition may be in-
herited. It has. been shown that the acclimated condition
may long persist, only eventually apparently disappearing. It
may well: be doubted, however, if the acclimated protoplasm
ever returns exactly to its primitive condition. If it does not,
progeny developed from the acclimated protoplasm will neces-
sarily be different and respond differently from their parents.
Individual attunement will initiate a race attunement.

LITERATURE

Cresigtskt, 72. (See Chapter XIV, Literature.)
CzapEk, F.’95. Ueber Zusammenwirkung von Heliotropismus und Geotro-
pismus. Sb. Wien. Akad. CIV}, 337-875.
98. Ueber einen Befund an geotropisch gereizten Wurzeln. Ber. deut.
Bot. Ges. XV, 516-520. Jan. 1898.
Darwin, C. and F.’81. (See Chapter XIV, Literature.)

Hoae, J. 754. Observations on the Development and Growth of the Water-
snail (Limneus stagnalis). ‘Trans. Micr. Soc. London. © I, 91-103.
Semper, C. ’74. Ueber die Wachsthums-Bedingungen des Lymneus stag-

nalis. Arb. Zool.-Zoot. Inst. Wiirzburg. I, 138-167.
VariGny, H. px, ’94. Recherches sur le nanisme expérimentale. Contribu-

tion 4 l'étude de l’influence du milieu sur les organismes. Jour. de

Anat. et Physiol. XXX, 147-188.
WIrEsNER, J. ’79. (See Chapter XVII, Literature.)
Yuna, E. ’85. (See Chapter XIII, Literature.)

.
Ee

«XS ee

— | ol oo

LIST OF TABLES

IN PARTS I AND II

Time of Resistance of Tadpoles to Various Alcohols .
Time of Resistance of Infusoria and Ostracoda to Various
Alcohols . ; ; : , ‘
Time of Resistance Period of Spirogyra communis to Wark
ous Alcohols . ‘ ; ‘
Increase of Immunity resulting rae fending on Ricin
Lethal Solutions of Gold Chloride for Various Bacteria
Relative Resistance Periods of Various Bacteria to Gold
Chloride . :
Relative Resistance Period of Vari ious ‘Pacteba iis ‘Fabtuoa
Poisons .

. . Percentage of Water in Or ganisms

Resistance Periods of Fresh-water Crustaess to Vaiions
Constituents of Sea Salt.

Plasmolysis of Vorticella by Solutions

Plasmolysis of Colpoda by Solutions

Tonotaxis of Spirillum to Various Solutions

List of Animals showing the Anex Type of I critability

List of Animals showing the Kater Type of Irritability

Electrotactic Response of Various Invertebrates .

Wave Lengths and Vibration Times of Different Parts of
Spectrum . , ?

List of Solutions giving sails Mbncclnomatis Golérs

Phototactic Response of Various Animals . ;

Results of Experiments to determine the Ghsadaataans
Temperature of Organisms in Water,

Determinations of the Ultraminimum of Organisms soned
under Normal Conditions

List of Species found in Hot Springs, with the Gaui dibinis
under which they occur .

Percentage of Water and Dry Gabasenes in “ites Rmbipos
at Various Ages ;

The Percentage of Water in Chick Baibeyos at Vanious
Stages upto Hatching...

The Percentage of Water in the Piaieén Binbeas ah Varies
Stages up to Birth " : :

Percentage Composition of Animals end Planin :

489

PAGE

490

TABLE NO.

XXVI.
XXVIL.

XXVIII.
X XIX.
XXX.
XXXII.
XXXII.
XXXII.
XXXIV.
XXXYV.
XXXVI.

XXXVI.

XXXVITI.

XXXIX.
XL.

XLI.

XLII.

XLII.

XLIV.

XLV.

XLVI.

ALVIT.

XLVIII.

XLIX.

LIST OF TABLES

Percentage Composition of the Ash of Various Organisms

Relative Abundance of Various Elements in the Ash of
Organisms . - : :

Nutritive Solutions for Phanerogams

Inorganic Matters in Potable Water .

Nutritive Solutions for Algze

Nutritive Solutions for Fungi

Comparison of Ash in New-born Dog sna in the Milk of
its Mother . .

Results of feeding Tadpoles on Varian Shivstadeany

Showing for Various Mammals the Time required to
double the Birth-weight correlated with the Chemi-
cal Composition of the Milk of the Species

The Total Dry Weight of a Crop of Aspergillus rane
in the Absence and in the Presence of Various Quan-
tities of Irritating Substances

Interval elapsing before Germination when ieptns ai
Penicillium are kept in Moist Chambers over Vari-
ous Solutions of Sodium Chloride

Relation between the Humidity of the Soil and the Anibal
of Dry Substance produced : :

Relation between Concentration of the Soludth ne Ger-
mination of Peas

Relation of Regeneration of Nats to Strength of Soliton

Relation of Reproduction by Fission of Dero to the
Strength of the Solution ;

Relative Size of Tadpoles reared in the Light ane in the
Dark : : ‘
Average Dimensions of Tat voles reared bebiiid Clear anil

Colored Screens .

Percentage Deviations in Eeieth of Tanne of ‘Stiosevie
centrotus reared behind Various Colored Screens,
from Length of Larve reared in White Light .

Relative Time of Hatching of Organisms reared behind
Colored Screens .

The Optimum Intensity for Phowagiaay t in Va arious
Species of Plants : ; : ‘

Minimum Intensity for Phototropic Teapohse 3 in Various
Species of Plants

Average Total Increments in Lapet of the Ptittiiles of
Seedlings subjected to Different Temperatures .

Average Increments in Length of the Radicles of Various
Seedlings subjected to Different Temperatures .

Time required for Spores of Penicillium to germinate,
produce Visible Mycelium, and to form Spores, at
Various Temperatures

a a

TABLE NO.

L.
LI.

LI.

LITI.
LIV.

LV.

LVI.

LVII.

LIST OF TABLES

Critical Points for Various Plants

The Absolute Increase in Length of Tadpoles ak Different
Temperatures

The Time Required for Various Specie ‘ot Fish hatch 2
Various Temperatures ;

Critical Temperature Points for Visiow Miimiais ;

Average Weight and Percentage of Water in Plants risrad
at Various Temperatures .

The Relation between the iP sivciiaea nit the Bina of
Thermotropic Response in Various Seedlings .

The Sense and the Average Extent of Thermotropism at
Different Temperatures

Phototropic Limiting Angles for Various Plants

491

PAGE

454
457

459
460

461
464

465
471

=

INDEX

Acclimatization to solutions; 87; to
heat and cold, 249, 255, 257; to
contact-irritation, 382; to stimuli,
484.

Acetic acid, attracts zodspores, 38; re-
pels amceba, 38.

Acetoxim, 15.

Acids, inorganic, as poisons, 12; pro-
voking response, 37. ~

Acids, organic, as poisons, 13; chemo-

- taxis towards, 37.

Actinia, action of nicotin on, 23.

Actinophrys, action of hydrogen on,
5; of quinine, 27; of varying den-
sity, 76; heat-rigor of, 232.

Actinospherium, response to density,
86; contact, 98, 102; alternating
current, 131; galvanic current, 139.

Appuwco, action of cocaine, 24.

ADERHOLD, chemotaxis, 33, 34; grav-
ity, 114; phototaxis, 185; acclima-
tization to cold, 257.

ApriAnowsky, light and seed germi-
-nation, 420; green rays on plants,
435.

Assy, free nitrogen as food, 312.

/Ethalium, rheotaxis of, 108; photo-
taxis, 185.

AFFANASIEFF, cold on muscle, 242,

Agaricus, light on germination of, 420

ALBERTONI, cocaine on protoplasm, 24.

ALCOHOL, on protoplasm, 10; struct-
ural formulas, 11; resistance of or-
ganisms to, 11; chemotactic action,
37.

Aldehydes, 20.

Alge, effect on, of hydrogen peroxide,
3; sodic-chromate, 4; potassic per-

manganate, 4; potassic chlorate, 4;

potassic dichromate, 4 ; potassic ar-
senite and arsenate, 5; arsenious
acid, 5; azoimid, 7 ; chloral hydrate,
10 ; carbonic disulphide, 12 ; organic

492

acids, 13; calcic oxide, 13; diamid,
phenylhydrazin, 16; nitrous acid,
21; paraldehyd, 21; sodic fluoride,
21; oxygen, 34; changing density,
86; molar agents, 100; growth of
A. and salts, 302; nitrogen, 309;
potassium, 318, 319.

Alkaline salts and growth, 318.

Alkaloids, as poisons, 22.

Ammonia, effect on Tradescantia and
Spirogyra, 6.

Ameeba, effect on, of hydrogen, 5;
curare, 26 ; quinine, 27 ; chemotaxis,
38; varying density, 75, 86; molar
agents, 99; thigmotaxis, 105; elec-
tric irritation, 130, 132; electric ac-
climatization, 139 ; electrotaxis, 148 ;
phototaxis, 186; heat-rigor, 232;
coagulation, 238 ; cold, 241; thermo-
taxis, 258 ; foods of A., 328.

Ampelopsis, phototropism, 438.

Amphibia, foods of, 529; temperature
and growth, 459.

Amphioxus, electric excitation, 137.

Ancylus, acclimatization to changed
density, 85.

ANDREWS, photic irritability of Hy-
droids, 179.

Anex type of electric response, 137.

Animals, toxic protein compounds, 22 ;
salts necessary for, 502; organic foods
of, 327; thigmotropism, 382; geotro-
pism, 398; phototropism, 442; growth
of, at various teinperatures, 457.

Anisonema, change of structure with
density of solution, 77.

Annelida, negatively electrotactic, 147 ;
ultramaximum, 234, 246.

Antimony, effect on growth, 514.

Antipyrin, on protoplasm, 27.

Ants, chemotaxis, 33 ; phototaxis, 198;
thermotaxis, 261.

Apostrophe, conditions of, 190.

494

ApsTEIN, light on pelagic eggs, 417.

Apus, heat on growth of, 458.

Arca, acclimatization to changed den-
sity, 86. ;

ARENDT, sulphur and growth, 314.

Arsenic and growth, 314.

Arsenic acid, oxidization by, 5.

Arsenious acid, oxidization by, 5.

ARTAUD, temperature and metabolism,
222.

Arthropoda, effect of varying density,
81, 82; salt absorption by, 88; posi-
tively electrotactic, 147.

Ascaride, strychnin, 26.

Ascaris, sodic carbonate, 18 ; sodic hy-
drate, 13; phenol, 19; hydrocyanic

~ acid, 19.

Ascidia, thigmotropism, 382.

Asellus aquaticus, acclimatization to
changing density, 86.

Ash, of organisms, 295, 296; of dog
and dog’s milk, 303.

ASkENASY, latent period, 460.

Asparagin, chemotaxis towards, 38.

Aspergillus, nitrogen food, 308.

Atmospheric pressure and growth, 368 ;
electricity, 408.

Atropin and protoplasm, 24.

Azoimid, effect on protoplasm, 7.

”

Bacilli, calcic oxide and caustic potash
poisonous to, 15.

Bacillus ramosus, growth in colored
light, 480; critical points, 454.

Bacteria, effect on, of oxygen, 2, 168;
ozone, 3; potassic chlorate, 4; sodic
chromate, 4; carbonic disulphide,
12; organic acids, 13; potassic car-
bonate, 18; salts of heavy metals,
14; diamid, 16; formaldehyde, 21;
chemotactic, 33, 45; towards oxy-
gen, 34; inorganic salts, 36 ; alcohol
and glycerine, 37 ; to determine iso-
tonic coefficients, 74; acclimatiza-
tion to density, 86; tonotaxis, 90;
effect of violent shaking, 99, 371;
of light, 169, 171, 174; dark-rigor,
175; change of light intensity, 178 ;
light-rigor, 178 ; cold, 241; growth,
288 ; nitrifying, 299, 308-312 ; food,
324, 325; growth in light, 430; heat
and growth, 452; critical tempera-
tures, 454-457.

INDEX

Bacterium termo, chemotaxis, 32, 38.

Balanus larve, chemotaxis, 198.

BARANETZKI, negative phototaxis, 185; °
response of Myxomycetes to light,
202; effect of pulling on growth,
372.

Bark extract, attracts Myxomycetes,
88.

Barnacles, respond to shadow, 179.

DE Bary, light and seed germination,
420,

Bases, effect on protoplasm, 13.

BAss er, nutrition of plants, 299.

Bastit, geotropism, 398.

Bateson, geotropism, 397.

Bavuprimont, role of water in growth,
284.

Baumann, iodine and growth, 367.

Bean, effect of changing density, 367 ;
traumatropism, 384.

BecriarpD, colors and growth of fly,
432.

Beetles, geotaxis, 118.

Beggiatoa, negative phototaxis, 184.

BENECKE, solutions for fungi, 302 ; po-
tassium and growth, 318; rubidium
and cesium and growth, 820; mag-
nesium and growth, 323.

Benzenylamidoxim, poison, 15.

Benzol derivatives, chemotaxis towards,
38.

Bernarp, chloroform on protoplasm, 9.

Bert, effect of dense solutions on fish,
79, 80, 82; acclimatization to den-
sity, 86; dark-rigor, 176; range of
visible spectrum in animals, 203;
effective rays in phototaxis, 203;
oxygen and plants, 305; effective
rays in plant growth, 428; green
rays and growth, 435.

BERTHELON, electricity and plant
growth, 406.

BerTHELOT, nitrifying organisms, 308 ;
enrichment of fallow ground, 310.

-Beupant, acclimatization to density,

85. ‘
Breyerinck, food of Amoeba, 328. .
BezoxpD, water in animals, 58, 295. ‘
BIALoBLock1, heat and growth, 461.
BIEDERMANN, electric response of
muscle, 133.
Bryz, theory of arsenical poisoning,
4, 5; effects on protoplasm of halo-

eo ket ee

INDEX

gens, 4; strychnin, 25; quinine, 26 ;
acclimatization to arseni¢, 28.

Birds, effect of temperature on growth,
459.

Bismuth, effect on growth, 314.

Biasivus, compression-rheostat, 127 ;
electric irritation, 139; electrotaxis,
147-149.

Blood-corpuscles, to determine isotonic
coefficients, 73 ; effect on, of density,
76; and molar agents, 99.

Brunt. See Downes.

Body, composition, 294.

Boer, gold chloride, 46.

Boxorny, hydrogen peroxide a poison,
3; ammonia, 6; nutrition of plants,
299.

Bonarpi, minimum temperature for
bacteria, 241.

Boropt1y, light and chlorophyll arrange-
ment, 187; light on spores, 424;
effective rays in fern growth, 482.

Boron, and growth, 314.

TEN Boscu, quinine and protoplasm,
26.

Bourne, scorpions acclimated to own
poison, 28.

BovusstnGawtt, free nitrogen as food,
310.

Braem, heat and cold on statoblasts,
425.

Branchipus, heat and growth, 458.

Branpt, fluorine and growth, 317.

Brassica, light on growth, 428.

Braver, encystment, 256.

BREFELD, light and growth of toad-
stools, 420.

Bromine, and protoplasm, 4;
growth, 316.

Brouncuorst, electrotropism, 409-412.

Bryonia, light and growth, 419.

Bryozoa, desiccation of, 65; thigmo-
tropism, 382.

Bucuner, toxic protein compounds,
22; chemotaxis, 33 ; light and bac-
teria, 172; movement and growth,
371.

Bufo lentiginosus, acclimatization to
heat, 253 ; heat and growth, 457-460.
Bunce, iron and growth, 321-323.

' Burscuxr, encystment, 256.

Butyric acid, chemotaxis towards, 38.

Buxton. See RINGER.

and

495

Cesium and growth, 320.

Calcium and growth, 320.

Cavan, frictional electricity and
growth, 132.

CaLiipurceEs, heat and protoplasmic
movement, 227.

CaLMETTE, immunization, 30. See also
EBRLICH.

CAMPBELL, temperature and _ proto-
plasmic irritability, 230.

DE CANDOLLE, heat-rigor, 231; cold-
rigor, 240, 241.

Cannon, phototaxis of Daphnia, 203,
204.

Carbon, as food, 306; oxide of, and
protoplasm, 6.

Carbonic disulphide, and protoplasm,
12.

Carcinus, absorption of salt, 88.

Cardium edule, acclimatization to
density, 86.

Carnin, chemotaxis towards, 38.

Cassis, acclimated to sulphuric acid, 28.

CasTLe, acclimatization to contact,
108; to heat, 253.

Cat, light on growth of, 426.

Catalytic poison, action of, 7-9.

Ce 1, electrified air and plant growth,
408.

Cell-division and growth, 287.

Cex, food of Ameeba, 328.

CeErRTES, desiccation of Ciliata, 65.

Chameleon, pigment response to light,
192.

Chara, and caustic potash, 13.

CHARPENTIER, cocaine and protoplasm,
24.

CHASTAIGN, oxidizing action of light,
162.

Chemical agents, effect on vital ac-
tions, 1; acclimatization to, 27 ; and
growth, 293.

Chemotaxis, 32-54.

Chemotropism, 335; in insectivorous
plants, 335 ; of roots, 336 ; of pollen-
tubes, 337; of hyphe, 340; of con-
jugation tubes of Spirogyra, 342.

Chick, water in growth of, 286; elec-
tricity and growth of, 405 ; heat and
growth, 459.

Chilomonas, phototaxis and photo-
pathy, 183.

} Chlamydomonas, thigmotaxis of, 106.

496

Chloral hydrate, poison, 10.

Chlorine, poison, 4; effect on growth,
316.

Chloroform, action on protoplasm, 9,
10.

Chlorophyll, effect of light on position,
189; temperature and movements,
226.

CumuteEvitcnu, heat-rigor, 232.

Cuopat, electricity and plants, 407.

Chromic acid, as poison, 3, 4.

Chytridium, phototaxis, 183.

CrenkowskI, phototaxis, 183.

CIESIELSKI, traumatropism, 384; geo-
tropism, 393, 394; after-effect, 401 ;
tropism, 481.

Cilia, effect of density on movement,
77; electric stimulation, 145; tem-
perature, 227.

Ciliata, effect on, of oxygen, 3; hydro-
gen peroxide, 3; chloroform and
ether, 10 ; strychnin, 26 ; chemotaxis,
33; of saline lakes, 65; density ef-
fect, 76, 78, 86; phototaxis, 187.

CLARK, oxygen, 2

Cobra poison, 30.

Cocaine, effect on protoplasm, 24.

Cockroach, geotaxis, 118 ; thermotaxis,
261.

Coelenterata, electric response, 137;
phototaxis, 194,

Coun, phototaxis, 202 ; heat and proto-
plasm, 226.

Cold, 242 ; resistance to, 246 ; extreme,
248 ; acclimatization, 257.

Cold-rigor, 239.

Colored light, 482-436, 440, 441.

Crab, copper in blood of, 324.

Critical temperatures, 460.

Crivetuxi, food of Amoeba, 328.

Crustacea, density, 79, 81; optimum
temperature, 458.

Cryptogams, water and growth, 350;
geotropism, 378; thigmotropism, 381.

Cryptomonas, chemotaxis, 33.

Ctenophora, inorganic food, 303.

Cucurbita, moisture, 352.

Curnot, temperature and growth, 458.

Curare, Amoeba, 26.

Cyphoderia, molar agents, 100.

Cytotaxis, 52.

CzarreK, phototropism, 471; tropism,
482, 483.

INDEX

Czrrny, density, 75, 76, 78, 86.

Da uinGeR, heat and Infusoria, 252-
256.

DANILEWSKY, cocaine, 24;
330.

Daphnia, phototaxis, 203-206.

DarEmMBRAY, blood serum, 22.

Dark-rigor, 175, 176.

Darwin, C., insectivorous plants, 99;

- chemotropism, 835; hydrotropism,
357; tendrils and twining, 377; thig-
motropism, 379, 380, 383; trauma-
tropism, 384-386; geotropism, 394;
phototropism, 441, 485.

Darwin, F. , moisture and growth, 252,
geotropism, 397.

Davis, desiccation of rotifers, 62, 63.

Day, nitrogen, 312.

Death, 1; by poisons, 2-24; desicca-
tion, 60-65; density, 80-83; light,
171-175; heat, 231-249; limits, 275-
277.

DEHNECKE, gravity, 113.

DEHERAIN, temperature and secretion,
223.

Demoor, oxygen, 2,3; hydrogen, 5, 6;
ammonia, 6; oxides of carbon, 6;
chloroform, 9; paraldehyde, 21;
cold-rigor, 241.

Density of the medium, effect on pro-
toplasm, 70-93; on growth, 362-
369.

DerMANT, heat-rigor, 239.

Dero, fission and density, 365, 366.

Desiccation, protoplasm, 59; rigor and
death, 60, 61; acclimatization to, 65.

Desmids, phototaxis, 183.

Detiersen, hydrotropism, 257; trau-
matropism, 384.

DewitTz, chemotaxis, 37; thigmotaxis,
106, 107.

Diamid, poison, 1, 16.

Diatoms, effect on, of chloral hydrate,
10; hydroxylamine, 15; ethylalde-
hyde, 21; phototaxis of, 184, 199;
silicon food of, 324.

Differential threshold stimulation, 43.

Difflugia, molar agents, 101.

Dionza, response to contact, 99.

Dioscorea, light, 419.

Dodder, twining, 377, 484.

DoaIEL, curare, 26.

lecithin, ©

INDEX 497

Dogs, potassium and growth of, 319.

Dolium, and sulphuric acid, 28.

Downes, analytic effect of light, 163;
bactericidal effect of light, 171-173.

DoyéreE, desiccation, 62; heat on
Rotifera, 255.

‘Dragon-fly larve, electric stimulation,

137.
Draper, assimilation in plants, 166.
Driescu, phototaxis, 202; growth,
282 ; geotropism, 400 ; phototropism,
443.

Drosera, organic acids, 13; thigmo-
taxis, 99; thigmotropism, 383, 481.
Drosophyllum, and contact, 99.
Dryness and protoplasm, 59, 60.
DryspDaLeE, heat and protoplasm, 256.
Dusots, response to light, 207.
Ducuartre, hydrotropism, 256.
Ducravx, chemical effect of light, 162,
163 ; election of food, 333.
Durrocuer, molar agents, 100; tem-
perature on protoplasm, 225 ; accli-
matization to heat, 25%; twining,
377.
Duvalia, germination, 424.

Earthworm, nicotin, 24; phototaxis,
203.

Echinodermata, nicotin, 24; density,
79 ; electric current, 137 ; phototaxis,
194; light on growth, 484 ; optimum
temperature for growth, 458.

Echinoids, strychnin, 26.

Epwarps, light on growth, 425.

Effective rays in growth, 427-436 ; in
phototropism, 440.

Egg, food materials in, 303 ; shcueiias
rus, 313; iron, 322; electricity, 403.

Monexnuns. heat, 251.

EuR icy, ricin, 31; acclimatization to
poison, 32.

Electricity, 126 ; protoplasm, 129-153 ;
electrotaxis, 140-151; growth, 408-
414; electrotropism, 409-414.

Electrotaxis, 140-151.

Ervine, chloroform, 9; light, 174;
gravity and growth, 391; geotro-
pism, 398.

Embryos, phosphorus, 314 ; light, 417;
418.

Emery, salt absorption, 88.

Encystment, 256.

2K

ENGELMANN, chemotaxis, 32, 34; den-
sity, 86; electricity, 130, 132, 135;
bacteria and spectrum, 163; dark-
and light-rigor, 176, 178; changing
light intensity, 179 ; phototaxis, 182,
185, 187, 202, 207; retinal move-
ments, 195; photopathy and chem-
ical agents, 201; temperature, 227,
231.

Entomostraca, density, 81.

Entz, photopathy, 188.

Ephydra, acclimatization, 28.

Epistrophe, 190.

Epithelium, ciliated, 129, 227.

Ervacu, acclimatization, 29, 30.

Errara, hydrotropism, 359; thigmo-
tropism, 381.

EscHENHAGEN, growth and density,
362.

Escu.e, iodine and growth, 317.

Ether, 9, 10.

Ethylaldehyde, protoplasm, 21.

Euglena, chemotaxis, 33; phototaxis,
183; acclimatization to cold, 257;
thermotaxis, 261.

Ewa p, electrotaxis, 147-150.

Excretion and poisons, 51.

EXNER, pigment and light, 193.

Extent of medium and size, 473.

FaBRE-DoMERGUE, density, 76, 86.

Fallow ground, enrichment, 310.

False, phototaxis, 181; traumatro-
pism, 384 ; geotropism, 392 ; electro-
tropism, 409.

Famintzin, phototonus, 177; photo-
taxis, 182; chlorophyll position,
189 ; light and growth, 430.

Fatigati, rays which disturb metabo-
lism, 170.

FayYreEr, serpent poison, 28.

Fecuner, threshold stimulation, 434.

FEre£, temperature and chick’s growth,
459.

Fick, electric stimulation, 133.

Fiapor, phototropic limit, 439.

Fish, density-effects, 79-82 ; rheotaxis,
109 ; temperature and growth, 458,
459 ; medium and size, 474. See also
Gold-tish.

Flagellata, chemotaxis, 33, 36, 45;
salt-absorption, 86, 89; phototaxis,
182; acclimatization to heat, 252, 255.

498

FiamMarion, effective rays in growth,

429.

Fly larve, chemotactic, 38 ; geotactic,
118.

Fluorine, and growth, 317.

l‘ood, 309-330 ; response to, 39; elec-
tion, 334.

¥ormaldehyde, poison, 20, 21.

Frank, chlorophyll position, 189;
growth definition, 282 ; nitrogen as
food, 308-310.

Franke. See PFEIFFER.

FRANKLAND, light and bacteria, 171.

FrazEuR, regeneration and density,
365.

Frepa, electricity and growth, 408.

FREDERICQ, salt-absorption, 88 ; oe

per and growth, 824.

Fresh water absorbed by marine or-
ganisms, 79, 80.

Friss, light and fungi, 420.

Frog, sodic fluoride, 22; density, 82 ;
salt-absorption, 88; electric stimu-
lus, 182, 1389; pigment and light,
192; water in developing, 285; size
and medium, 474, 475.

Frog’s egg, cytotaxis, 52; cold-rigor,
240 ; oxygen and growth, 305 ; elec-
tricity, 405.

Fromann, soluble mineral bases as
poisons, 138.

Fungi, salts of arsenic, 5; sulphurous
oxide, 20; nitrous acids, 21; nutri-
tive solutions, 302 ; hydrogen as food,
306; potassium, 318; iron, 323;
organic foods, 324-326; water and
growth, 350; hydrotropism, 358; light
and growth, 420; colored light, 480.

Gain, water and growth, 254.

Galvanic current, acclimatization to,
139.

Gastropoda, copper in blood, 324.

GAUTIER, green rays and plants, 435.

GAVARRET, desiccated rotifers, 62.

Geotaxis, 114-124.

Geotropism, 391-403 ;
pism, 470.

Gerosa, cold, 241.

Germination, and solutions, 363; and
light, 424.

GILBERT. See LAWES.

GLAN, spectrophotometer, 160.

and phototro-

INDEX

Glucose, reaction, 4.

Glycerine, chemotactic, 37.

Gocorza, density, 79-83 ; acclimatiza-
tion, 86, 87.

Gold chloride, poison, 46, 47.

Gold-fish, density, 77,79.

GoLuBEW, electricity stimulus, 130. “

Gorin1, Amceba, 328.

Gorscuiicu, heat-rigor, 232, 233.

GraBER, phototaxis, 203, 205, 207;
thermotaxis, 258, 261.

GRANDEAU, electricity, 406, 408.

Gravity, methods, 112; protoplasm,
118, 114; direction of locomotion, .
114-124 ; growth, 391-403.

Green plants, light, 174 ; organic food,
826, 327.

GREENWOOD, nicotin as poison, 24.

Groom, phototaxis and temperature,
200.

Growth, analysis of processes, 281 ;
three factors, 282 ; regions in plants,
283; cell-division, 287; kinds of,
287; normal, 288, 289; chemical
agents on, 293 ; as response to stim-
ulus, 331; directed, 335, 355, 376,
384, 387, 391, 409, 437, 460; water,
3850; density, 862; molar agents,
370; wounding, 384; gravity, 391 ;
electricity, 405; light, 416; heat,
450 ; optimum, 454 ; maximum tem-
perature, 456 ; range, 456; modifi-
cation of rate, 478-480 ; modification
of direction, 480-483..

GRUBER, density, 76.

HABERLAND, chemotropism, 242.
Hemoglobin, properties, 298.
Hates, phototropism, 437.
HA.tuipurtTon, heat-rigor, 239.
Halogens and growth, 315.
HampvurG_Er, isotonic coefficient, 73;
density, 76.
Hammonp, light and growth, 426.
HANSTEEN, organic food of plants, 327.
Harrie, phosphorus and growth, 314.
Heat, absorption by plants, 170; nat-
ure of, 219; action on protoplasm,
222-268 ; chlorophyll formation, 224 ;
irritability, 225; acclimatization to,
249, 251; extremes, 248; direction
of locomotion, 258; growth, 450-
467 ; latent period, 460.

INDEX

Heat-rigor, 231, 239.

Hedgehog, hydrocyanic acid, 19.

HEGteER, pulling and growth, 372, 374;
electrotropism, 412.

HEIDENSCHILD, toxic proteids, 22.
Helianthus, pulling, 374; phototro-
pism, 438 ; phototropic angle, 471.

- HELLRicGEL, nitrogen fixation, 310.

HELMHOLTZ, light on retina, 171.

Hen, mineral matter in egg, 303; flu-
orine, 317.

HeEnseEvy, light and pelagic eggs, 417.

Hepatics, thigmotropism, 381.

Herzvs, nutrition, 300.

Herbivora, chlorine, 316.

Hersst, salts of marine animals, 303 ;
phosphorus and growth, 314; sul-
phur, 315 ; chlorine, 316 ; potassium,
319; magnesium, 328.

HERMANN, electrical measurements,
128 ; electric stimulation, 139 ; elec-
trotaxis, 147-149; cold, 242.

HERRICK, gravity and nucleus, 114;
temperature and growth, 458.

Hertwice, O., growth of frogs, 458, 459.

Hertwiec, O, and R., cocaine, 24;
strychnin, 25; quinine, 26; chemo-
taxis, 33.

Hieronymus, chlorophyll movements,
191.

Hiecensorrom, light and growth, 425.

Hittner, nitrogen and growth, 312.

Horer, hydroxylamine, 15.

HoFrrMann, water and growth, 250;
dryness and resistance to heat, 255 ;

_ light and germination, 420, 424.

-Hormeister, molar agents and proto-
plasm, 100, 102; phototaxis, 184;
temperature and protoplasm, 225;

heat-rigor, 232; geotropism, 401.

Holothuroidea, geotaxis, 118.

Honey bee, temperature and metab-
olism, 223.

Hopre-Ser ter, acclimatization to heat,
251; lithium on growth, 318; mag-
nesium, 323.

Horvatu, shaking protoplasm, 99 ; bro-
mine and growth, 316 ; rough move-
ment on growth, 370.

Hupson, desiccation, 63.

Human embryo, water in growth, 286.

Humidity of soil and growth, 253.

Hvuxtey, definition of growth, 282.

499

Hydra, nicotin, 23; density, 81, 86;
phototaxis, 194, 202; light waves
and growth, 430.

Hydrachna, maximum temperature,
238.

Hydrazin and protoplasm, 16.

Hydric sulphide, protoplasm, 19, 20.

Hydrides, chemotactic, 37.

Hydrocyanic acid, poison, 19,

Hydrogen on protoplasm, 5; in organ-
isms, 306.

Hydrogen peroxide, poison, 3.

Hydroidea, inorganic food, 303 ; iron,
323 ; density and regeneration, 364 ;
thigmotropism, 382 ; geotropism, 398,
399 ; phototropism, 443.

Hydroides dianthus, responds to
shadow, 179.

Hydrotaxis, 66.

Hydrotropism, 255.

Hydroxylamine, poison, 1, 15.

Hyphe, chemotropism, 340; hydro-
tropism, 358.

Hypochlorous acid, poison, 3, 4.

Hypozanthin, chemotactic stimulus,
38.

Indifferent chemical agents and proto-
plasm, 41, 42.

Induction apparatus, 127.

Infusoria, and potassic permanganate,
4; halogens, 4; arsenious acid salts,
5; azoimid, 7; chloral hydrate, 10;
hydroxylamine, 15 ; phenylhydrazin,
16; hydrocyanic acid, 19; ethylalde-
hyde, 21; quinine, 27; acclimatiza-
tion, 28; chemotaxis, 33; thigmotaxis,
106; katex response, 137; electro-
taxis, 140; wave-lengths which dis-
turb metabolism, 170; heat and
movement, 228; cold-rigor, 240; or-
ganic foods, 328; multiplication and
light, 422.

Injurious substances, response to, 39.

Inorganic salts and protoplasm, 37.

Insecta, hatching and temperature, 458.

Insectivorous plants, chemotropism,
335.

Invertebrates, quinine, 26; sodic car-
bonate, 28; water in, 58, 59; elec-
tric response, 136 ; electrotaxis, 147 ;
ultramaximum temperatures, 234-
237 ; ultraminimum, 244-246 ; in hot

500

springs, 250, 251; potassium as food,
318.

Iodine, protoplasm, 4; growth, 317.

Iron, and growth, 321-328.

Irritable period in development, 379;
region in tendrils, 379.

Isopoda, hydroxylamine, 15; formalde-
hyde, 21.

Tsotonic coefficients, 238.

JACCARD, oxygen on plant growth, 305;
pressure and growth, 368.

JANSE, Salt-absorption, 88.

JaRius, growth and density, 362.

JENSEN, geotaxis, 114-118, 121-124,

JENTYS, oxygen and growth, 305; den-
sity and growth, 362.

Jounson, hydrotropism, 256; geotro-
pism, 394.

Jonsson, rheotaxis, 108; rheotropism,
387; light and germination, 425.

JORDAN, analysis of water, 301.

JUMELLE, Water and growth, 253.

Karsten, light and plants, 419.

Katex type of electric response, 138.

KELLER, retinal pigment and light, 192.

Kuxss, phototaxis, 185.

Kew, light fatal to fungi, 174.

Kuincer, synthesis of organic com-
pounds, 163.

Knicut, hydrotropism in roots, 256;
geotropism, 393.

Know ron, temperature and growth,
459.

Kny, light and growth, 423.

Kocu, free nitrogen as alge food, 309.

Kocus, desiccation and seed vitality,
63, 64.

Kororp, blastula cavity, 78, 79.

Kossowitscn. See Kocu.

Krart, electricity on epithelium, 129.

Kravs, light on growth, 420; green
rays and growth, 430.

Kreatin, chemotactic, 38.

KRUKENBERG, Strychnin, 25; quinine,
26; water in organism, 58, 295;
iron and growth, 321.

Kin, desiccation of nematodes, 61.

Kiune, effect on protoplasm of hydro-
gen, 5; chloroform, 9; veratrin, 24;
varying density, 75-77 ; electric cur-
rent, 129, 132, 188, 189; tempera-

INDEX

ture and movement, 225 ; heat-rigor,

231, 252; fatal temperature, 238;

cold-rigor, 241; cold, 242, 247, 248,
KuNKEL, iron as food, 323,

Lactic acid, chemotactic, 38.

Lamellibranchiata, electric stimula-
tion, 135 ; light reaction, 179.

Lance, desiccation of tardigrades, 61,
65.

Land animals, acquisition of oxygen,
304 ; sulphur, 314. 7

Larve, food, 323 ; light, 418.

Laurent, nitrogen food of plants, 309,
312.

Lawes, nitrogen as plant food, 310;
food of mammals, 330.

LebeEr, chemotaxis, 33. .

Lr Danrec, thigmotaxis, 105, 107.

Leeches, poison, 18.

Legumes, enriching action of, 310.

Le1TcGep, light and spores, 424.

Lemna, organic food of, 327.

LemstrOm, electricity favors plant
growth, 408.

Leong, agitation of water and growth,
371.

Lesace, moisture and germination
350, 351.

Leucocytes, oxygen and protoplasm, 3 ;
chloroform, 10 ; quinine, 26 ; chemo-
taxis, 33; electric stimulation, 1380.

Lewirn, heat and coagulation, 255,
256.

LIEBENBERG, light and germination,
425.

LIEBERMANN, water of organism, 58.

LiesscueEr, free nitrogen as plant food,
312.

Life, temperature-limits, 231.

Light, methods, 154; monochromatic,
156-158 ; physical properties of dif-
ferent wave-lengths, 158, 159; in-
tensity, 160; chemical action, 161-
165; thermic’ effect on metabolism,
166-170 ; chemical effect, 170, 171;
vital limits, 171; and movement,
175; light-rigor, 178; and carbon
dioxide production in plants, 179;
phototaxis and photopathy, 180-210 ;
of chlorophyll, 189 ; of pigment, 192 ;
racial attunement, 197; period of
life, 197, 198 ; mechanics of response

INDEX

to, 207-209; retarding effect on
growth, 416-423 ; accelerating effect,
423-427 ; phototropism, 436-445.

Litte, temperature and growth of
tadpoles, 459.

Limax, geotaxis, 118-120.

Limneza, poisoned by azoimid, 7 ; ac-
climatization to density, 85 ; light on
growth of, 426; extent of medium
and size, 474.

‘Linum, light and growth, 428.

Lithium and growth, 318.

Lobster, copper in blood, 324; heat
and growth, 458.

Locker, metallic salts as poisons, 14, 15.

Locomotion, interference with normal,
51; determination of direction, 32,
66, 89, 105, 114, 140, 180, 258.

Locust, heat and growth of, 458.

Logs, chemotaxis, 33 ; oxygen attracts
fly larve, 38; gravity and inverte-
brates, 118 ; effect of light intensity,
179, 197; phototaxis, 198; photo-
taxis and temperature, 200; light
attunement, 200; phototaxis, 204,
206, 208 ; temperature and irritabil-
ity, 230 ; thermotaxis, 258-261 ; réle
of water in growth, 304; oxygen
and growth, 306; potassium and re-
generation, 319; magnesium and
growth, 323; growth and density,
364 ; contact and growth of stolons,
370; cutting and rate of growth,
376 ; thigmotropism in hydroids, 382 ;
rheotropism, 388 ; geotropism in hy-
droids, 399, 400; phototropism in
animals, 442, 443.

Loew, effect on protoplasm of oxy-
gen, 2; potassic chlorate, halogens
and sodic chromate, 4; arsenical
salts, 5; catalytic poisons, and azoi-
mid, 7; sulphonal, 10; carbonic di-
sulphide and inorganic acids, 12;
soluble mineral bases, 13; salts of
heavy metals, 14, 15; hydroxyla-
mine, substitution poisons, 15; com-
plex nitrogenous compounds, 16; hy-
drocyanic acid, 19; aldehydes, 20;
ethylaldehydes, 21; sodic fluoride,
21, 22; alkaloids, 22, 23; acclimati-
zation to poisons, 27; oxygen and
growth, 294 ; phosphorus and growth,
314. :

501

LomBarDINI, effect of electricity on
development of chick, 405.

Luppockx, chemotaxis, 33; effective
wave-lengths in phototaxis, 203, 205.

Lupvorr, electrotaxis, 141; theory of
electrotaxis in Ciliata, 145.

Macarre, heat and metabolism, 222.

Maca.tuM, iron in growth, 321.

MacDonrneE -t, light on frog’s growth,
425,

MacDovueat, contact response of ten-
dril, 378, 379.

McLeop,,electricity and plant growth,
407.

Mager, food of Amceba, 328.

Magnesium, and growth, 323.

Magnetropism, 413.

Maize, silicon in, 324. See Zea.

Malic acid, chemotactic, 37, 38.

Mammals, quinine, 27 ; foods of, 330.

Man, acclimatization to poisons, 28;
sulphur as food, 315.

Manganese, and growth, 521.

Manganic acid, poison, 3, 4.

Marine organisms, effect of fresh water
on, 79; foods of, 303.

MarRMIER, immunity, 30.

MaRsHALL, phototaxis, 194.

Martin Sarnt-AnGe, réle of water in
growth, 284.

Massart, effect on protoplasm of par-
aldehyde and formaldehyde, 21;
cocaine, 24 ; antipyrin, 27; chemo-
taxis, 33, 34; isotonic coefficients,
73, 74; density and protoplasmic
structure, 76, 80; acclimatization to
density, 86-88; tonotaxis, 89-92;
phosphorescence, 98; thigmotaxis;
106, 107 ; gravity and Protista, 114-
116, 121; phototaxis, 200.

Martruias. See HERMANN.

Mauvpas, light and growth of Infuso-
ria, 422. :

Mayer, absorption of heat by plants,
170; temperature and metabolism,
222.

Mechanics of response, 45.

Met7zer, shaking bacteria, 99, 371.

MENDELSSOHN, change of optimum,
254; thermotaxis, 258, 259.

Metabolism, modification by poisons,
1-27 ; by dryness, 59; molar agents,

502 INDEX

98; by light, 166-175 ; by heat, 222-
225; limiting conditions of, 275.

METSCHNIKOFF, chemotaxis in bacte-
ria, 33.

Mice, acclimatized to ricin, 29-32.

Mieuta, inorganic acids on protoplasm,
12.

Micpe, light and spores, 424.

Minor, growth, 289.

Mistletoe, light and growth, 425, 438.

Mryosui1, chemotropism, 388, 340 ; hy-
drotropism, 358.

Montz, twining stems, 377; acclimati-
zation to light, 444.

Moissan, temperature and metabolism
in plants, 225.

Moist gelatine, no thigmotropic re-
sponse to, 278.

Moisture and protoplasm, 58.

Molar agents, and lifeless matter, 97 ;
and protoplasm, 97 ; movement, 98,
99; metabolism, 98; direction of
locomotion, 105; and growth, 370.

Molds, and sodic carbonate, 28 ; nutri-
tive. solutions for, 302; and free
nitrogen, 308 ; potassium and growth,
318; rubidium, 320; election of or-
ganic foods, 333; thigmotropism,
381; electrotropism, 412 ; light, 420.

Molecular composition and effect on
metabolism, 39.

Mo escuort, effect of light on verte-
brates, 422.

Mouiscu, hydrotropism, 257; potas-
sium and calcium in growth, 319,
3820; chemotropism, 336, 337; hy-
drotropism, 359; thigmotropism,
381.

Mollusca, formaldehyde, 21; quinine,

27; changed density, 79; electro-

taxis, 147; phototaxis, 202, 207;
ultramaximum temperature, 235;
ultraminimum, 245; species living
in hot springs, 251; composition,
295; light and growth, 426.

MontecGazza, effect of strong light on
bacteria, 171.

Monrtt, food of Amoeba, 328.

Moors, light and chlorophyll arrange-
ment, 189, 191, 192.

Morieera, heat-rigor, 232.

Morphine, and protoplasm, 25.

Moths, phototaxis, 197.

Mucor, phenylhydrazin a poison, 16;
tropisms in, 482.

Mittier, H., responding region in
phototropism, 441.

Mutter, N.J.C., definition of growth,
282.

Mi ter, O., thigmotropism, 379, 380.

Mu.LierR-HETTLINGEN, electric stress
in seedlings, 405; electrotropism,
409.

Mivier-Tuurcav, freezing-point in
plants, 247.

Minter, vitality of dried seeds, 64.

Mintz, nitrifying organisms, 308, 310.

Musca, light and growth, 432. See
also Fly.

Muscle, electric stimulus, 183, 135;
cold-effect, 242.

Myriapoda, hydrocyanic acid secreted,
19.

Mytilus, acclimatization to density, 85,
86.

Myxomycetes, hydrogen, 5; chemo-
taxis, 38, 38, 45; varying density,
75, 86; molar agents, 100; electric
stimulation, 129; light stimulus,
179; phototaxis, 184, 202.

Nacer, electric stimulus, 135-138;
electrotaxis in invertebrates, 146,
150, 151; light stimulus, 179; me-
chanics of light response, 207.

NAGELI, catalytic poisons, 7; salts of
metals as poisons, 14; phototaxis,
182; temperature and movement,
225; cold-rigor, 241 ; nutritive solu-
tion for fungi, 302; cesium and
growth, 320.

Nais, regeneration and solutions, 365.

Naja tripudians, acclimatization to
poison of, 380.

Natica, acclimated to sulphuric acid,
28.

NEAL, corrosive sublimates as poison,
15; acclimatization to poison, 30, 31.

Nematoda, azoimid, 7 ; chloral hydrate,
10 ; desiccation, 61.

Nenckt, chlorine and growth, 316;
sodium and growth, 318.

Nephelis, effect of varying density, 81.

Nereis, effect of cocaine, 24.

Nerve, electric stimulation, 138, 135.

Nicotin, and protoplasm, 23, 24.

— —— =

ee ee eee eee ee

bee,

EE ey, a ee ee
.

INDEX 003

Niepce pe Saint Victor, chemical
action of light on starch, 165.

NIkOLskI, curare and protoplasm, 26.

Nitella, cold-rigor, 241.

Nitrogen, source of, in organisms, 307 ;
free N. as food, 308, 513.

Nitrogenous compounds, as poisons,
16-21; chemotactic, 38.

Nitrous acids, and protoplasm, 21.

Nosse, free nitrogen as plant food,
312 ; potassium as food, 319.

Noctiluca, effect of paraldehyde, 21;
formaldehyde, 21; antipyrin, 27;
deformation, 98.

Nuclein, composition, 298.

Nutritive solutions, for alge, 302; for
fungi, 302; light and seed germina-
tion, 420.

Nutritive values, laws of, 325.

Ocata, food of Infusoria, 328.

OHLMULLER, Ozone and bacteria, 3.

OxttmManns, phototaxis, 183, 205, 206.

Onimus, penetrability of tissues by
light, 166.

Optimum, 40; change of, 254; con-
centration for growth, 364; move-
ment for growth, 372; temperature
for growth, 454-456, 460, 461.

Orbitolites, molar agents, 100; thig-
motaxis, 106; thigmotropism, 376.

Organic, compounds chemotactic, 37;
food used in growth, 324; food,
election of, 333.

Organisms, atomic composition of dry
substance, 296 ; elements important
for, 297, 298; food of non-chloro-
phyllaceous O., 209.

Oscillaria, phototaxis, 184.

Osmosis, réle in organic life, 71;
quantitative measure of, 71-78.

Osmotic index, 82.

Ostracoda, azoimid, 7.

Ostrea, acclimatization to changed
density, 85.

OstwaLp, temperature and osmosis,
83 ; electrical methods, 126.

Overton, chemotropism, 242.

Oxygen, effect on anerobic bacteria, 2 ;
on protoplasm, 2-5; antipyrin, 27;
chemotactic, 34; thigmotactic, 106 ;
as food, 304; and growth, 305.

Ozone, and bacteria, 3.

Palemon, nicotin, 24.

Pam, cause of twining, 377.

Paludina, changing density, 865.

PanetH, hydrogen peroxide and Cili-
ata, 3.

Paraldehyde, protoplasm, 21.

Paramecium, strychnin, 26; electro-
taxis, 142, 144, 145; change of
optimum, 254; thermotaxis, 259,
260.

Parasites, oxygen, 2.

PARKER, response of pigment to light,
193.

PasTEvR, ultramaximum of dry spores,
255,

Patella, acclimated to diminished tem-
perature, 85.

Pathogenic bacteria, chemotaxis, 33.

PeEIRcE, twining in dodder, 377.

Pelias berus, rabbits acclimated to
poison of, 30.

Pelomyxa, electric stimulus, 129, 133,
134.

Penicillium, fixes free nitrogen, 308.

Peptone, chemotactic, 38.

Peranema, electric response, 130.

Perceptive ‘region, in phototropism,
441.

PERKINS, gravity and Limax, 118-120.

Permanganic acid, poison, 3, 4.

Peronospora, does not germinate in
light, 420.

PETERMANN, free nitrogen as plant
food, 312.

PFEFFER, chemotaxis, 33, 36-45;
measure of osmosis, 71; tonotaxis,
89, 90; thigmotaxis, 106, 108 ; wave-
length active in assimilation, 166 ;
growth, 281 ; election of food, 333;
chemotropism, 337 ; method of iso-
lating the root tip, 395; cause of
twining, 377; irritable period in

_ thigmotaxis, 379; contact stimulus,
382, 383, 386.

PreirFER, free nitrogen and plants,
312.

Phanerogamia, free nitrogen as food,
312 ; potassium, 318 ; calcium, 320 ;
electrotropism, 411; red rays and
growth, 436.

Phenol, as poison, 18.

Phenylhydrazin, poison, 16.

Phosphorescence, 98.

504 INDEX

Phosphorus, and growth, 313.

Photopathy, 180; distribution, 182;
laws of, 196; and chemical constitu-
tion of medium, 201.

Phototaxis, 180, 195; true and false,
181; distribution, 182; effect on P.
of strong light, 196; laws of, 196;
effective rays, 201; P. vs. photo-
pathy, 203.

Phototonus, 177.

Phototropism, 437, 488; optimum in-
tensity in, 439; effective rays, 443 ;
mechanics of, 444; limiting angle,
471, 472; after-effect, 484.

Phycomyces, water and spores, 358 ;
heat and growth, 464.

PickFrorp, heat-rigor, 231.

Pictert, cold-rigor, 240.

Pigeon, acclimatization to poison, 29.

Pigs, food of growing, 330.

Planaria, azoimid, 7; hydroxylamine,
15; density, 81; thigmotaxis, 105;
photopathy, 206.

Planorbis, azoimid, 7; density, 85.

Plastic foods, 293.

PLaTEAY, density, 80-82, 86; absorp-
tion of salt, 88.

Pratt, geotaxis, 124.

Poa, light on seeds, 424. .

Poisons, oxidizing, 3, 49; catalytic, 7,
50; salt-forming, 12, 50; substitu-
tion, 15, 50; acclimatization to, 29.

Po.eck, silicon in hen’s egg, 324.

Pollen-tubes, chemotropism, 337, 338 ;

- hydrotropism, 358.

Polygordius, phototaxis, 200.

Polyphemus, density effect, 76.

Polystoma, salt-absorption in, 89.

Polystomella, electric stimulus, 129.

Polytrichum, light and germination,
424,

Porthesia, thermotaxis, 261.

Potassium, growth, 318; regeneration,
319.

Potassium salts, poisons, 4, 5.

Poucuet, light-stimulus, 179.

Preissia, light and germination, 424.

Prescu, sulphur and growth, 315.

Preyer, anabiosis, 61, 63.

PrRINGSHEIM, light on green plants,
174 ; light-rigor, 178.

Propionic acid, 38.

PROsHER, growth of mammals, 330, 331.

Protein poison compounds, 22.

Protista, cocaine, 24; morphine, 25;
desiccation, 64; contact response, 99 ;
geotaxis, 114, 115, 118, 121-128;
electric stimulus, 134; acclimatiza-
tion to electricity, 139 ; electrotaxis,
146; photopathy and phototaxis,
182, 203; heat, 224, 228; thermo-
taxis, 258, 261; growth of P. and
light, 416.

Protoplasm, hydroxylamine, 1; oxy-
gen, 2, 3; substitution poisons, 15;
nicotin, 23; strychnin, 25; quinine,
26; antipyrin, 27; acclimatization
to poisons, 82; specific resistance of,
49; structure of, 70; varying den-

sity, 74; acclimatization to change ~

of density, 86 ; contact, 97 ; periodic
disturbances, 98; electric stimulus,
188; temperature, 241; chemical
agents: and growth, 274; structure
and composition, 274, 275; struct-
ural limiting conditions, 276.

Pseudophototaxis, 181, 182.

Pueu, free nitrogen, 310.

Pulmonates, fresh-water, varying den-
sity, 78.

Puriewitscu, free nitrogen, 308.

PurRKINJE, cold, 241.

Pyrocatechin, poison, 19.

QuinckE, effect of blue rays on growth,
436.
Quinine on protoplasm, 26, 27.

Rabbit, acclimatization to snake poi-
sons, 380.

RacrBorsklI, growth and density, 363.

Radiant heat and growth, 463.

Radiolaria and silicon, 324.

RAILLET, desiccation-rigor, 61.

Rana, heat and growth, 457-459.

RAvBER, Oxygen on frog’s eggs, 305;
temperature and growth, 459.

Ravin, phosphorus and growth, 314.

Ray, gravity and growth, 391.

RAYLEIGH, monochromatic light, 158.

Regeneration and potassium, 319:
density, 364, 365.

Rernunarpt, chemotropism, 340.

Reinke, light and plant assimilation,
167; moisture and growth, 251;
agitation of water and growth, 871.

——

- ee eo

INDEX

Removal of tissue, and growth, 375.

Repulsion, by chemical agents, 38; by
dense solutions, 91.

Resistance capacity, to poisons, 48; to
dense solutions, 83; to heat, 249.

Resorcin, poison, 19.

Response to injurious substances, 39;
mechanics of R., 45, 277; 480-484.

Rheostat, 127.

Rheotaxis, 105-108.

Rheotropism, 387, 388.

Rhizoids, hydrotropism of, 257.

Rhizoma, geotropism, 398.

Rhizopoda, thigmotaxis, 106; electric
stimulus, 129; phototaxis, 185; ther-
motaxis, 259.

Ricwarps, E. See Jorpan.

Ricuarps, H. M., growth and chemi-
cal irritation, 332.

Ricuet, toxic dose and temperature, 2.

RicHTER, varying density, 78, 80, 86,
89; geotropism, 398.

Rigor, cold-R., 242;
desiccation-R., 61;
light-R., 178.

Rincer, density, 80.

RiscHawl, temperature and excretion,
223; electrotropism, 410.

Roemer, chemotaxis, 33.

Roos, iodine and growth, 317.

Roots, chemotropism, 336; hydrotro-
pism, 256 ; thigmotropism, 380; geo-
tropism, 393.

Rosanorr, chemotaxis, 108.

Rossspacnu, 24; strychnin, 25, 26; qui-
nine, 26; varying density, 78; heat
and excretion, 224; heat and cilia
movement, 228.

Rots, temperature.and cilia move-
ment, 227.

Roruert, transmission of light stimu-
lus, 441.

Rotifera, chloral hydrate, 10; hydroxyl-
amine, 15; desiccation-rigor, 61, 62 ;
cold-rigor, 240; heat and dryness,
255.

Rough movements and growth, 370.

Roux, cytotropism, 52, 53.

Rubidium, effect on growth, 320.

Ruscont, electricity on frog’s egg, 405.

RussELL, movements and growth, 371.

dark-R., 175;
heat-R., 231;

Sacus, penetration of light into plant

505

tissue, 165; active rays in plant as-
similation, 166; false phototaxis,
181; temperature and protoplasmic
movement, 225; hydrotropism, 256 ;
growth, 281; silicon and growth,
324; hydrotropism, 358; thigmotro-
pism, 380, 383; geotropism, 393-
397, 402 ; light and growth, 417, 418;
curve of growth, 421; effective rays
in growth, 428.

Salmo trutta, light on eggs of, 426.

Salts as poisons, 14, 15; chemotactic, 36.

SamKowy, heat-rigor, 232.

SarGENT, fission and density, 365, 366.

Schizomycetes, pseudotaxis, 182.

Scuenck, effect of twisting on plant
growth, 375.

Scuioésine, nitrifying organism, 308,
310; alge and nitrogen, 309; free
nitrogen and phanerogams, 312.

ScHMANKEWITSCH, changed density on
Flagellata, 76, 77, 86.

Scnumipt, movements and growth, 371.

Scumitz, light and growth, 420.

ScHNEIDER, iron and growth, 321.

ScHNETZLER, rays affecting growth of
tadpoles, 432, 435.

Scuo.tz, pulling on plant growth, 372.

Scuoumow-Smanowsky. See NENCKI.

Scuroper, strychnin, 26.

Scuuttzez, M., strychnin, 25 ; temper-
ature and protoplasmic movement,
225 ; heat-rigor, 232.

Scuuttze, O.,temperature and growth,
459.

Scuutz, salts of arsenic, 4,5; acclima-
tization to poison, 28; poisons and
cell activity, 332.

Scuiirmayer, chloroform and ether,
10 ; cocaine, 24; strychnin, 25, 26;
antipyrin, 27 ; heat and cilia move-
ments, 228 ; cold-rigor, 240.

ScutiTzENBERGER, dry protoplasm re-
sists heat, 255.

Scuwarz, gravity and Protista, 114-
116, 121; temperature and irritabil-
ity, 230; acclimatization to cold,
257 ; gravity and growth, 391.

ScHwEIZER, compression rheostat, 127 ;
electric current, 139; electrotaxis,
147-149.

Scyllium, effect of changed solution
on, 80.

506

Sea-urchin, inorganic food, 303.

Secretion, contact stimulus, 99.

Seed, vitality, 64; phosphorus in, 303;
light on germination, 419, 422.

Seedling, oxygen and growth, 305;
ether and growth, 353, pulling stim-
ulus, 372, 378; rheotropism, 387 ;
electricity and growth, 405-410.

Selenous oxide and Spirogyra, 20.

Semper, extent of medium on size of
snails and fish, 474.

Sensitive plant, light on growth, 429;
temperature and growth, 458.

Sepolia, nicotin, 24.

Serpula uncinata, sudden change of
intensity, 179.

Serpulidz, phototropism, 442.

SEWALL, acclimatization to poison, 29.

Sexual cells, cocaine, 24; quinine, 26.

Sheep, food of growing, 330.

SHUTTLEWORTH, acclimatization to
cold, 257.

Silkworm, cold-rigor in eggs, 240.

Silicon and growth, 324.

Sinapis, phototropic, 438.

Slug, thigmotaxis, 105.

Snails, strychnin, 26; extent of me-
dium on size, 474, 475.

Socrn, iron and growth, 328.

Sodium, salts on protoplasm, 4, 21, 22;
and growth, 318.

Solutions, physical action of, 70.

Soroxin, phototonus, 177.

SPALLANZANI, desiccation-rigor in roti-
fers, 61, 65.

Sprautpine, false and true thigmotro-
pism, 384, 385.

Specific rate of vibration, 98.

Spectrophor, Reinke’s, 156.

Spectrophotometer, 160.

Spermatozoa, chemotaxis, 37 ; thigmo-
taxis, 106, 107.

Spermatozoids, chemotaxis, 33.

Spirillum, chemotaxis, 33.

Spirographis, sudden change of light,
179.

Spirogyra, ammonia, 6; salts of heavy
metals, 14; selenous oxide, 20;
formaldehyde, 21; phosphorus on
growth of, 314; effective rays in
growth, 430.

Sponge, silicon and growth, 324.

Sponge gemmules, 65.

INDEX

Spores, desiccation of, 65; heat, 256,
chemotropism, 341 ; light and germi-
nation, 419, 422, 424; heat and ger-
mination, 452.

Squid, copper in blood of, 324.

Sraux, chemotaxis, 33, 38, 45; hydro-
taxis, 66 ; acclimatization to changed
density, 86 ; tonotaxis, 89 ; rheotaxis,
108 ; light and chlorophyll arrange-
ment, 181, 191; phototaxis, 183-
185; thermotaxis, 250.

STaMEROFY, light and growth, 420.

STanDKE. See Kiincer.

Stance, chemotaxis, 33-38; growth
and density, 362.

Starfish, geotaxis, 118 ; phototaxis, 202 ;
inorganic food and growth, 303.
Statoblasts, changing temperature
necessary to development of, 425,
STEBLER, light and germination, 424.
STEFANOWSKA, light response of pig-

ment, 193.

Sre1nAcH, direct action of light on iris
movements, 179; light response of
pigment, 192.

Stems, hydrotropism, 358 ; gravity on
growth, 397; curvature, 398; day-
light and growth, 419.

Stentor, salts as poisons, 15; accli-
matization, 30, 31 ; ; photopathy, 189 ;
thigmotropism, 375.

Stimulus, relation between intensity
and response, 39, 40.

Sroxasa, free nitrogen and plants,
312.

Stolons, geotropism, 400; phototro-
pism, 445.

STrrRaAsBuRGER, rheotaxis, 108; light-
response, 179; phototaxis, 183, 184,
199, 202, 208 ; light and temperature
on locomotion, 199 ; temperature and
irritability, 230; high temperature,
239; acclimatization to cold, 257;
chemotropism, 537.

Strongylus rufescens, desiccation-rigor,
61.

Strontium, growth, 321.

Structure of protoplasm, 70.

Strychnin, 25, 26.

Sugar, attracts Bacterium termo, 37.

Sulphonal, 10.

Sulphur, on growth, 314; oxide and
growth, 20.

|
:

INDEX 507

Swarm spores, protoplasm, 10; photo-
taxis, 182, 183.

Szozawinska, light response of pig-
ment, 193.

Tadpoles, salts of arsenic, 5; of heavy
metals, 14; varying density, 86;
geotaxis, 124; electrotaxis, 149;
growth and density, 367; light and
growth, 425, 426, 432, 433; extent
of medium and size, 475, 478.

TAMMANN, fluorine and growth, 317.

Tannic acid, chemotaxis, 38.

TAPrPEINER, fluorine and growth, 317.

Tardigrades, desiccation, 61, 65; dry-
ing and heat resistance, 255.

Tartaric acid, chemotactic, 38.

Taurin, chemotactic, 38.

Temperature, effect on toxic dose, 2;
increases osmosis, 83; T.and metab-
olism, 222, 223; and protoplasmic
activity, 229, 230; ultromaximum,
231, 234-237; ultraminimum, 239;
sudden change of, 460, 461 ; thermo-
tropism, 464.

Temporary rigor, 242.

Tendrils, twining, 377.

Tension, effect on plasma, 374.

Tetraspora, and density, 78, 89.

Thalassicola, contact-response, 98, 99.

Thermogenic food, 293.

Thermotaxis, 105, 258, 261.

Thigmotropism, 376, 388, 463, 465,
466.

THOUVENTN, electricity and plants, 409.

Threshold stimulus to chemical agents,
42.

TrmiriszerFr, plant assimilation and
wave-lengths, 167, 169.

ToLomeEtI, magnetropism, 413.

Tonotaxis, 89-91.

Tradescantia hairs, oxygen, 2, 3; hy-
drogen, 5; ammonia, 6; chloro-
form, 9; molar agents, 102; electric
current, 182; cold-rigor, 241, 242;
cold, 247.

Traumatropism, 384, 386.

TREMBLEY, phototaxis, 194.

TREVIRANUS, temperature and metab-
olism, 223.

TrEw, light and growth, 421.

Triton, electric stimulation, 157 ; ther-
motaxis, 261.

Tritonium and sulphuric acid, 28.

Trophotaxis, 39.

Tropism, 484,

Trout, light and growth, 426.

TrvE, traumatropism, 384; electro-
tropism, 410.

TscHAPLOWI1z, moisture and growth,
253.

TsuKamoro, alcohols, 10-12.

Tubers, light and growth, 418.

Tubifex, poisons, 14.

Tubularia,. oxygen and regeneration,
506; potassium and regeneration,
319.

Tumas, molar agents and growth, 371.

Tunicates, inorganic food of, 303.

Turbo, acclimatization to changed
density, 56.

Twining stems, 376.

Ulothrix, prototaxis of spores, 199.
Ultramaximum temperature, 234,
Ultraminimum temperature, 244,
Urea, attractive, 38.

Urostyla, thigmotaxis, 106.

VALENTIN, cold, 241.

Valeric acid, chemical response, 38.

Vallisneria, cold-rigor, 241.

VANDEVELDE, germination and con-
centration, 363.

DE VaRiGNy, varying density, 80; ac-
climatization to density, 85, 86; ex-
tent of medium and Size of Limnza,
475-478.

VELTEN, cold-rigor, 241 ; temperature
and chlorophyll movements, 226,
227.

Veratrin, poison, 24.

VERNON, temperature and growth of
Echinoidea, 458.

Vertebrates, chemicals, 25; electro-
taxis, 150; potassium on growth,
318; calcium as food, 321; organic
foods of, 334.

VeRworn, chemotaxis, 33, 34; accli-
matization to changed density, 86;
phosphorescence, 98, 99; molar
agents, 100; thigmotaxis, 106; geo-
taxis, 121-123 ; electrical apparatus,
126; electric stimulation, 129-131,
134, 187 ; acclimatization to electric
current, 139, 140; electrotaxis, 141,

508

146, 148; phototaxis, 183-185, 188,
199, 202 ; growth, 282; thermotaxis,
258, 259.

Vicia, phototropism, 438.

ViERORDT, spectrophotometer, 160.

VILLON, green rays and light, 435.

Vinegar eel, organic acids, 13; accli-
mated to sodic carbonate, 28.

Vines, temperature and metabolism,
222 ; freezing point for plants, 247 ;
growth, 282 ; potassium and growth,
318 ; light and growth, 420, 421, 423 ;
effective rays in growth, 430.

Vitis, phototropism, 438.

Volvox, phototaxis, 183; light attune-
ment, 206.

DE VRIES, quantitative studies in os-
mosis, 71-73; salt-absorption, 88 ;
growth and density, 362; contact
stimulus, 382; thigmotropism, 383.

WacutTeEL, geotropism, 394.

Water, electric response, 128; elec-
trotaxis, 147.

Warp, bactericidal effect of strong
light, 171-174; cell division and
growth, 287; light and growth, 421.

Warren, electric current on plant
growth, 407.

Wasmann, thermotaxis, 261.

Water, amount in organisms, 58; réle
in organisms, 59; effect on proto-
plasm, 67; analysis of, 301; effect
on growth, 360. .

Water animals, hydrazin a poison, 16;
source of oxygen for, 304. _

Weser, phosphorus and growth, 314.

WEBER’s law, 43-45, 440.

WertsTEIN, light on development, 174.

Wert, heat-rigor, 239.

Wuiprrpte, light accelerating growth,
423.

WieLER, oxygen and plant growth,
305 ; growth and density, 362.

Wiesner, hydrotropism, 257; trau-
matropism, 384, 385; light and
seedlings, 417; mistletoe, 423;
Vicia faba, 429; intensity of light

INDEX

- and response, 488; effective rays
for seedlings, 440; heat and spore
germination, 452; phototropism and
geotropism, 471.

DE WILDEMANN, thermotaxis, 258, 261.

WitrartH, enriching action of le-
gumes, 310. _

WILLEM, light response, 207. .

Wi son, phototropism of Hydra, 202.

WINDLE, electricity and development
of chick, 405.

WInoGRADSKY, phototaxis, 184; nu-
trition of bacteria, 299; sulphur
and bacteria, 315; rubidium and
growth, 320; hydrogen disulphide
and bacteria, 326.

Wo rrr, silicon and growth, 324.

v. WoLKoFF, temperature on metabo-
lism, 222.

Wo tyy, atmospheric electricity, 408.

Wotterrne, iron and growth, 328.

‘Worms, formaldehyde, 21; electro-
taxis, 147; phototaxis, 195; ultra-
maximum, 235; ultraminimum, 245;
acclimatization to high temperatures,
251.

WorrtMann, chemotropism, 340; hydro-
tropism, 358, 360; thigmotropism,
381; geotropism, 402.

Wounding, and traumatropism, 384.

Yeast, phosphorus and growth, 313;
potassium and growth, 318.

Yune, acclimatization to changed den-
sity, 86; food of Amphibia, 329, 330 ;
density and growth, 367; light and
growth, 425, 426; light and growth
of hydra, 430; different wave-lengths
on growth of tadpoles, 433-435; ex-
tent of medium and size of tadpoles,
475.

ZACHARIAS, varying density on proto-
plasm, 76.

Zea, silicon and growth, 324; phototro-
pism, 438; temperature and growth,
451-455; thermotropism, 463-465.

Zooéspores, chemotaxis, 34, 36, 37.

:

ERRATA AND ADDENDA

PaGcE

¢

10, note, Etrrne should read ELFvine.

21, last sentence in next to last paragraph, should read: “On this account
even neutral nitrites kill such plants as have an acid cell-sap, but not
such as have a neutral cell-sap (some alge, e.g. Spirogyra).”

35. See the valuable paper of H. S. Jennines, Jour. of Physiology, XXI,
258-322, 1897, where it is shown that carbon dioxide in weak solu-
tions is attractive; in strong solutions, repellent.

59, line 3, 81.94, water should be 71.9%; line 4, 71.1% water should be 74.1%,

64. See Witt, Centralbl. f. Bakteriol. (2), III, 17; latent life of yeast.

72, second note, next to last line, one-tenth of should read ten times.

88, second line from bottom, FrepeEric should read FREDERICQ.

108, fifth line from bottom, JO6NNson should read Jonsson. |

113, line 9, should read, “cannot be affected, as a whole, by gravity.”

127, fourth line from the bottom, electrometer should read electrodynamometer.
146, line 13, galvanotaxis should read electrotazis.

157, Table XVII. Other solutions are suggested by W1EsNER, ’79, Wien.

Denkschrift, XX XIX, 187.

160. For measurement of chemical intensity see WIESNER, 93. Sitzungsber.

Wien. Akad. CII, 298.

170, line 5, over should read under.

174, line 13, Etvine should read ELFVING; so, too, on p. 213.

191, description of Fig. 56, line 1, spaces should be species.

196, first paragraph. Dr. A. D. Meap informs me that at Wood’s Holl

Diastylus swims free at night so that it is taken in the tow. Con-
sequently these crustaceans are not exclusively mud-inhabiting, and
may constitute no exception to the rule.

209, first two lines should read, “ migrated in travelling 18 cm. in full light,

15% faster than the same individual migrated in light } as strong.”

224. A fuller table than that of Riscnawi is given by CLAUSEN, ’89,

Landw. Jahrbiicher, XTX, 907, 911.

230. Compare with Campbell’s table the similar results of Epwarps,

Studies Biol. Lab., Johns Hopkins Univ., July, 1887; and those of
Hunt, ’97, Science, V, 907.

247, line 15, dele words “ between Bombyx.”
251. Trustworthy observations on organisms in hot springs have lately

been made by Davis, Science, July 30, 1897, and SercHELL, Univer-
sity (of California) Chronicle, I, 110-119.
509

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