Comparative electro-physiology, a physico-physiological study

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COMPARATIVE
ELEC LBR-O-P YSIOLOGY

WORKS BY THE SAME AUTHOR

RESPONSE IN THE LIVING AND NON-
LIVING. With 117 Illustrations. 8vo. 10s. 6d.
1902.

“PLANT RESPONSE; as a means of Physio-
logical Investigations. With 278 Illustrations.
8vo. 21s. 1906.

LONGMANS, GREEN & CO., 39 Paternoster Row, London,
New York, Bombay, and Calcutta

x ry

~? COMPARATIVE
ELECTRO-PHYSIOLOGY

A PHYSICO-PHYSIOLOGICAL STUDY

BY

JAGADIS CHUNDER BOSE, M.A., D.Sc.

PROFESSOR, PRESIDENCY COLLEGE, CALCUTTA

WITH ILLUSTRATIONS

LONGMANS, GREEN, AND CO.

39 PATERNOSTER ROW, LONDON
NEW YORK, BOMBAY, AND CALCUTTA

1907

All rights reserved

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PREFACE

THIs volume concludes the line of investigation on respon-
sive phenomena in general, which I commenced with the
publication of a Memoir’ at the International Congress of
Science, Paris, 1900. In this first of my publications on the
subject I undertook to show the similarities of response in
inorganic and living substances. The method which I[ at
that time employed for obtaining my response-records was
that of Conductivity Variation. With the object of showing
that the similarity of response here demonstrated to exist
was due to some fundamental molecular reaction, common
to matter in general, and therefore to be detected by any
method of recording response, I next undertook to record
the Electro-motive Variation under stimulus. Believing, as
I did, in the continuity of these responsive phenomena, I
used the same experimental devices by which I had already
succeeded in obtaining the electric response of inorganic sub-
stances, to test whether ordinary plants also, meaning those
usually regarded as insensitive, would or would not exhibit

excitatory electrical response to stimulus. The stimulation

' * De la Généralité des Phénoménes Moléculaires produits par 1|’Electricité
sur la Matiére Inorganique et sur la Matiére Vivante’ (7ravaux du Congres
International de Physique, Paris, 1900). See also ‘On the Similarity of Effects
of Electrical Stimulus on Inorganic and Living Substances,’ Xefort Brit: Assoc.,
Bradford, September 1900 (Z/ectrician). >

vi COMPARATIVE ELECTRO-PHYSIOLOGY

employed was mechanical and quantitative, thus obviating
many sources of complication. By this method I was able
to show that every plant, and every organ of every plant, gave
true excitatory electrical response. As observations similar
to these were subsequently made by another investigator,
I quote here the following summary of my results. from the
preliminary account which I communicated to the Royal
Society, May 7, and afterwards read, with accompanying ex- -
perimental demonstration, before the Society, on June 6, 1goI.
‘An interesting link, between the response given by inor-
ganic substances and the animal tissues, is that given by plant
tissues. By methods. somewhat resembling that described
above, I have obtained from plants a strong electric response
to mechanical stimulus. The response is not confined to
sensitive plants like Mimosa, but is universally present. I
have, for example, obtained such response from the roots,
stems, and leaves of, among others, horse-chestnut, vine,
white lily, rhubarb, and horse-radish. . ‘The “current of
injury” is, generally speaking, from the injured to the
uninjured part. A “negative variation ” is also produced. |
obtained both the single electric twitches and tetanus. Very
interesting also are the effects of fatigue, of temperature, of
stimulants, and of poison. Definite areas killed by poison
exhibit no response, whereas neighbouring unaffected portions
show.the normal response.’ ! | | ,
It may be well to point out here that at the time when this.
communication was made, the view that ordinary plants
were excitable, and responded to mechanical stimulus by

1A more complete: account: will be. found in the report of my ‘ Friday
Evening Discourse’ before the Royal Institution, May 10, 1901, and in the
Journal of the Linnean Society, vol. xxxv.. Pp. 275.

PREFACE vii

definite electro-motive changes, was regarded as highly
controversial. Indeed, in the discussion which followed
the reading of my Paper, on June 6, 1901, Sir John Burdon
Sanderson went so far as to state that this excitatory
response of ordinary plants to mechanical stimulation was
an impossibility.

My next investigation was directed towards the question
whether the responsive effects which I had shown to occur
in ordinary plants might not be further exhibited by means
of visible mechanical response, thus finally removing the dis-
tinction commonly assumed to exist between the ‘sensitive’
and supposed non-sensitive. These results were published
in my work on Plant Response,’ where the effects of various
environmental stimuli on the different plant organs were
demonstrated by means of responsive movements. Many
anomalous effects hitherto ascribed to specific sensibilities
were here shown to be due to the differential excitability

of anisotropic structures, and to the opposite effects of
external and internal stimuli. Among other things, it was

there shown that internal stimulus was in reality derived from
external sources, and that the term ‘autonomous response’
was a misnomer, since all movements were due, either to the
immediate effects of external stimulus, or to stimulus previously
absorbed and held latent in the plant, to find subsequent ex-
pression. It was further shown that not gross mechanical
movements alone, but also other invisible movements, were
initiated by the action of stimulus ; that external stimulus,
so far from invariably causing a run-down of energy, more
often brought about its accumulation by the plant ; and that

the various activities, such as the ascent of sap and growth,

' Plant Response as a Means of Physiological Investigation, 1906,

vill COMPARATIVE ELECTRO-PHYSIOLOGY

were thus in reality different reactions to the stimulating action
of energy supplied by the environment.

With regard to these points, my results have been in direct
opposition to current views, according to which the effect
induced by stimulus is always disproportionately greater
than the stimulus, From the plausible analogy of the
firing-off of a gun by the pulling of a trigger, or the action
of a combustion-engine, it has been customary to suppose
that all response to stimulus must be of the nature of an
explosive chemical change, accompanied by an inevitable
run-down of energy. This supposition, however, overlooks
the obvious fact that the plant is not consumed by the
incessant and multifarious stimuli of its environment.
Rather, as we all know, it is the energy of the environ-
ment which is the agent that fashions the microscopic
embryo into the gigantic banyan-tree. And it is clear
that, for this to be possible, the energy contributed by the
blow of external stimulus must have been largely conserved.

In the course of the present work, I have not only been
able to corroborate, by means of electrical response, the
various results which I had already established, with regard
to the plant, by mechanical response, but I have also ex-
tended the electrical method in various directions, so as to
include many more recondite problems in connection with
the irritability of living tissues. It was my original inten-
tion to confine this investigation to the Electro-physiology
of Plants. But, finding that in the results so obtained I pos-
sessed a key to that of the animal also, I proceeded to apply
the same methods of inquiry, and to use the same experi-
mental devices, in the one case as in the other. I have thus

been able to trace out the gradual differentiation of various

PREFACE ix

responsive peculiarities, characteristic of given tissues, from ©
their simplest types in the plant to their most complex in the
animal. The value of such a comparative method of study,
for the elucidation of biological problems in general, is
sufficiently obvious. Exception may be taken with regard
to the unorthodox point of view from which various ques-
tions in animal physiology have been approached. It must
be remembered, however, that in this work the attempt has
been to explain responsive phenomena in general on the
consideration of that fundamental molecular reaction which
occurs even in inorganic matter. My mode of investigation
has thus been determined by the necessary progression
from simple to complex, and by my conviction as to the
continuity which existed between them. And from. this
attempt it will be seen that various results, which, accord-

ing to the so-called vitalistic assumption were anomalous,

are, in fact, capable of an increasingly simple and _ satis-

factory explanation. It must also be understood that my
work deals mainly with the electrical response of plants,
and that its extension into the field of Animal Electro-
physiology was intended for the demonstration of the con-
tinuity between the two. It was therefore impossible, in
the short space at my disposal, to make more than the
brief necessary references to the different theories already
in vogue concerning the response of various animal tissues.
These will be found, in all their detail, in the excellent
account given in the standard work of Biedermann.'

For the sake of clearness, however, I shall at this point
enumerate a few only of the points of difference between

current views and the results, obtained from actual experi-
1 Biedermann, Ziectro-physiology (English translation), 1896.

x COMPARATIVE ELECTRO-PHYSIOLOGY

ment, which I have set forth in the present volume.
The reactions of different tissues have hitherto been re-
garded as specifically different. As against this, a continuity
has here been shown to exist between them. Thus, nerve
was universally regarded as typically non-motile; its re-
sponses were believed to be characteristically different from
those of muscle. I have been able to show, however, that
nerve is not only indisputably motile, but also that the
investigation of its response by the mechanical method is
capable of greater delicacy, and freedom from error, than
that by the electrical. The characteristic variations in the
response of nerve, moreover, are, generally speaking, similar
to those of the muscle. It has been customary, again, to
regard plants as devoid of the power to conduct true excita-
tion. But I have shown that this view is incorrect. Experi-
ments have been described, showing that the response of
the isolated vegetal nerve is indistinguishable from that of
animal nerve, throughout a long series of parallel variations
of condition. So complete, indeed, has that similarity
between the responses of plant and animal, of which this
is an instance, been found, that the discovery of a given
responsive characteristic in one case has proved a sure guide
to its observation in the other, and the explanation of a
phenomenon, under the simpler conditions of the plant, has
been found fully sufficient for its elucidation under the more
complex circumstances of the animal. ,

Many anomalous conclusions, with regard to the response
of certain animal tissues, had arisen from the failure to take
account of the differential excitability of anisotropic organs.
Now this is a subject which, in the case of the simple plant

organ, is capable of very exact investigation. I have been

ety

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PREFACE X1

able to show that this differential excitability is widely -
present as a factor in determining the character of special
responses, and that it finds its culminating expression in the
electrical organs of certain well-known fishes, —

Few conclusions in. Electro-physiology have been sup-

_posed to rest on securer foundations than the generalisation

known as Pfliiger’s Law of the polar effects of currents. I
have found, however, that this law is not by any means
of such universal application as had been supposed, since,
above and below a certain range of electromotive intensity,
the polar effects of currents are precisely opposite to those
enunciated by Pfliiger. ©

Finally, that nervous impulse, which must necessarily
form the basis of sensation, was supposed to lie beyond
any conceivable power of visual scrutiny. But it has here
been shown that this impulse is actually attended by change

of form, and is therefore capable of direct observation. This

wave of nerve-disturbance, moreover, instead of being single,
has been shown to’ be of two different kinds, in which fact,
as I have further explained, lies the significance of the two
different qualities or tones of sensation.

In the concluding portion. of the paper which I read
before the Bradford meeting of the British Association in
the year 1900, I said :— |

‘In the phenomena described above there is little
breach of continuity. It is difficult to draw a line and
say : “ Here the physical process ends, and the physiological
process begins”; or “That is a phenomenon of inorganic
matter, and this is a vital phenomenon, peculiar to living
organisms”; or “These are the lines of demarcation that
separate the physical, the physiological, and the beginning

xil COMPARATIVE ELECTRO-PHYSIOLOGY

of psychical processes.” Such arbitrary lines can hardly
be drawn. , :

‘We may explain each of the above classes of phenomena
by making numerous and independent assumptions ; or,
finding some property of matter common and persistent
in the living and non-living substances, attempt from this
common underlying property to explain the many phe-
nomena which at first appear so different. And for this
it may be said that the tendency of science has always
been to attempt to find, wherever facts justify it, an under-
lying unity in apparent diversity.’

It was for the demonstration of this underlying unity
that I set out on these investigations seven years ago.
And now, in bringing to its close another stage of their
publication, I may, perhaps, be permitted to express the
hope that by them not only may a deeper perception of
this unity have been made attainable, but also that many
regions of inquiry may prove to have been opened out, which
had at one time been regarded as beyond the scope of experi-
mental exploration.

I take this opportunity to thank my assistants for their
efficient help in these researches.

J. C. BOSE.

PRESIDENCY COLLEGE, CALCUTTA :
August 1906,

CONTENTS

CHAPTER I

THE MOLECULAR RESPONSIVENESS OF MATTER
PAGE
Response to stimulus by change of form—Permeability variation— Variation
of solubility— Method of resistivity variation : (a) positive variation ; (4)
negative variation—Sign of response changed under different molecular
modifications—Response of vegetable tissue by variation of electrical
resistance—Response by electro-motive variation in inorganic substances
—The method of block—Positive and negative responses—Similar
responses in living tissues—Effects of fatigue, stimulants, and poisons on
inorganic and organic responses-—-Method of relative depression, or
negative variation, so called ; : F ; - j ; : I

CHAPTER II

THE ELECTRO-MOTIVE RESPONSE OF PLANTS TO DIFFERENT
FORMS OF STIMULATION

Historical—Difficulties of investigation—-Electrical response of pulvinus of
Mimosa—Simultaneous mechanical and electrical records—Division of
plants into ‘ordinary’ and ‘sensitive’ arbitrary —Mechanical and
electrical response of ‘ ordinary’ plants—Direct and transmitted stimu-
Jation—All forms of stimulus induce excitatory change of galvanometric
negativily . ‘ ce , . : é : j i aE LR

CHAPTER III

THE APPLICATION OF QUANTITATIVE STIMULUS AND KELATION
BETWEEN STIMULUS AND RESPONSE

Conditions of obtaining uniform response—Torsional vibration as a form of
stimulus— Method of block— Effective intensity of stimulus dependent
on period of vibration—Additive action of feeble stimuli—Response

Xiv COMPARATIVE ELECTRO-PHYSIOLOGY

, PAGE
recorder—Uniform electric responses—List of suitable specimens—

Effect of season on excitability—Stimulation by thermal shocks —Thermal
stimulator—Second method of confining excitation to one contact—In-
creasing response to increasing stimulus—Effect of fatigue—Tetanus . 29

CHAPTER IV

OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE IN
PLANTS

Response-curve showing general time-relations—Instantaneous mechanical
stimulation by electro-magnetic release—Arrangement of the rheotome
—Tabular statement of results of rheotomic observations—Rhythmic
multiple responses. ; ; : ; ‘ : ; : - “5

CHAPTER V

THE ELECTRICAL INDICATIONS OF POSITIVE AND NEGATIVE
TURGIDITY-VARIATIONS

Motile responses of opposite signs, characteristic of positive and negative
turgidity-variations—Indirect hydrostatic effect of stimulus causes
expansion and erection of leaf-—Positive and negative work—Wave of
increased hydrostatic tension transmitted with relatively greater velocity
than wave of true excitation— Method of separating hydro-positive and
excitatory effects— Indirect effect of stimulus, causing positive turgidity-

variation induces galvanometric positivity—Antagonistic elements in the
electrical response—Separation of hydro-positive from true excitatory
effect by means of physiological block ; [ ; ‘ , - Sg

CHAPTER VI

EXTERNAL STIMULUS AND INTERNAL ENERGY

Hydraulic transmission of energy in plants—True meaning of tonic condi-
tion-—Opposite expressions of internal energy and external stimulus
seen in growth-response—Parallelism between responses of growing and
motile organs—Increased internal energy caused by augmentation o1
temperature finds expression in enhanced rate of growth; erection of
motile leaf ; curling movement of spiral tendril ; and galvanometric
positivity—External stimulus induces opposite eftect in all these cases—
Sudden variation of temperature, acting as a stimulus, induces transient
retardation of growth ; depression of motile leaf ; uncurling mevement
of spiral tendril ; and galvanometric negativity— Laws of mechanical
and electrical response ° : ‘ / : : 69

|
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.
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CONTENTS

CHAPTER VII

ABSORPTION AND EMISSION OF ENERGY IN RESPONSE

Sign of response determined by latent energy of tissue, and by intensity of

external stimulus—Sub-tonic, normal and hyper-tonic conditions—The.

critical level—Outward manifestation of response possible only when
critical level is exceeded—Three typical cases: response greater than
stimulus ; response equal to stimulus; and response less than stimulus
—lInvestigation by growth-response—The sum of work, internal and
external, performed by stimulus constant—Positive response of tissues
characterised by feeble protoplasmic activity or sub-tonicity—Enhance-
ment of normal excitability of sub-tonic tissue by absorption of stimulus

CHAPTER VIII

VARIOUS TYPES OF RESPONSE

Chemical theory of response—Insufficiency of the theory of assimilation and
dissimilation --Similar responsive effects seen in inorganic matter—
Modifying influence of molecular condition on response—Five molecular
stages, A, B, C, D, E—Staircase effect, uniform response, fatigue—No
sharp line of demarcation between physical and chemical phenomena—
Volta-chemical effect and by-productions—Phasic alternation —Alter-
nating fatigue—Rapid fatigue under continuous stimulation—In sub-
tonic. tissue summated effect of latent components raises tonicity and
excitability—Response not always disproportionately greater than
stimulus—Instances of stimulus partially held latent: staircase and

additive effects, multiple response, renewed growth . : ; °
CHAPTER IX
DETECTION OF PHYSIOLCGICAL ANISOTROPY BY ELECTRIC
RESPONSE

Anomalies in mechanical and electrical response—Resultant response deter-
mined by differential excitability—Responsive current from the more to
the less excitable—Laws of response in anisotropic organ—Demonstra-
tion by means of mechanical stimulation—Vibrational stimulus—Stimu-
lation by pressure—Quantitative stimulation by thermal shocks

CHAPTER X

THE NATURAL CURRENT AND ITS VARIATIONS

Natural current in anisotropic organ from the less to the more excitable—
External stimulus induces responsive current in opposite direction—
Increase of internal energy induces positive, and decrease negative,

XV

PAGE

76

86

107

xvi COMPARATIVE ELECTRO-PHYSIOLOGY

. PAGE
variation of natural current—Effect on natural current of variation of
temperature—Effect of sudden variation—Variation of natural current
by chemical agents, referred to physiological reaction—Agents which
render tissue excitable, induce the positive, and those which cause excita-
tion, the negative variation—Action of hydrochloric acid—Action of
Na,CO,—Effect modified by strength of dose—Effect of CQ, and of
alcohol vapour—Natural current and its variations—Extreme unrelia-
bility of negative variation so-called as a test of excitatory reaction—
Reversal of natural current by excessive cold or by stimulation—Re-
versal of normal response under sub-tonicity or fatigue . ; ; + eto

CHAPTER XI

VARIATIONS OF EXCITABILITY UNDER CHEMICAL REAGENTS

Induced variation of excitability studied by two methods: (1) direct
(2) transmitted stimulation—Effect of chloroform—Effect of chloral—
Effect of formalin—Advantage of the Method of Block over that of
negative variation—Effect of KHO—Response unaffected by variation
of resistance—Stimulating action of solution of sugar—Of sodium carbon-
ate—Effect of doses— Effect of hydrochloric acid—Diphasic response on
application of potash—Conversion of normal negative into abnormal
positive response by abolition of true excitability . ‘ ; ‘ « o129

CHAPTER XII

VARIATIONS OF EXCITABILITY DETERMINED BY METHOD OF
INTERFERENCE

Arrangement for interference of excitatory waves—Effect of increasing
difference of phase—Interference effects causing change from positive to
negative, through intermediate diphasic—Diametric balance—Effect of
unilateral application of KHO—Effect of unilateral cooling . ; - Iq!

CHAPTER XIII

CURRENT OF INJURY AND NEGATIVE VARIATION

Different theories of current of injury—Pre-existence theory of Du Bois-
Reymond—Electrical distribution in a muscle-cylinder—Electro-mole-
cular theory of Bernstein—Hermann’s Alteration Theory— Experiments
demonstrating that so-called current of injury is a persistent after-effect
of over-stimulation—Residual galvanometric negativity of strongly excited
tissue—Distribution of electrical potential in vegetable tissue with one
end sectioned—Electrical distribution in plant-cylinder similar to that in
muscle-cylinder—True significance of response by negative variation—-
Apparent abnormalities in so-called current of injury—‘ Positive ’
current of injury ; ‘ : ‘ eas ; ‘ . 149

CONTENTS Xvil

CHAPTER XIV

CURRENT OF DEATH—RESPONSE BY POSITIVE VARIATION
PAGE
Anomalous case of response by positive variation—Inquiry into the cause—
Electric exploration of dying and dead tissue: death being natural—
Determination of electric distribution in tissue with one end killed—
Dying tissue shows maximum negativity, and dead tissue, positivity to
living—Explanation of this peculiar distribution—Response by negative
or positive variation, depending on degree of injury—Three typical cases
—-Explanation by theory of assimilation and dissimilation misleading —
All response finally traceable to simple fundamental reactions é - 164

CHAPTER XV

EFFECT OF TEMPERATURE ON ELECTRICAL RESPONSE

General observation of effect of temperature on plant—Effect of fall and rise
of temperature on autonomous response of Desmodium—Effect of frost
in abolition of electrical response—A fter-effects of application of cold, in
Eucharis, Ivy and Holly—Effect of rise of temperature in diminishing
height of response—This not probably due to diminution of excitability
—Similar effect in autonomous motile response of Desmodium—En-
hanced response as after-effect of cyclic variation of temperature—Aboli-
tion of response at a critical high temperature. ‘ : ‘ . 180

CHAPTER XVI

THE ELECTRICAL SPASM OF DEATH

Different fost-mortem symptoms—Accurate methods for determination of
death-point—Determination of death-point by abolition or reversal of
normal electrical response —Determination of death-point by mechanical
death-spasm—From thermo-mechanical inversion—By observation of
electrical spasm : (a) in anisotropic organs: (4) in radial organs—Simul-
taneous record of electrical inversion and reversal of normal electrical
response—Remarkable consistency of results obtained by different
methods— Tabulation of observations . ; , 2 . 2 - 582

CHAPTER XVII

MULTIPLE AND AUTONOMOUS ELECTRICAL RESPONSE

Repeated responses under single strong stimulus—Multiple mechanical
response in Biophytwm—Multiple electrical responses in various animal
and vegetable tissues —Continuity of multiple and autonomous response
—Transition from multiple response to autonomous, and dice versa—

a

XVili COMPARATIVE ELECTRO-PHYSIOLOGY

PAGE
Autonomous mechanical response of Desmodium gyrans and its time-
relations—Simultaneous mechanical and electrical records of automatic
pulsations in Desmodium—Double electrical pulsation, principal and
subsidiary waves—Flectrical pulsation of Desmodium leaflet under
physical restraint— Growth- pulsation — So-called current of rest in grow-
ing plants . : ? MF Sette : ; ; ; ‘. . 207

CHAPTER XVIII

RESPONSE OF LEAVES

Observations of Burdon Sanderson on leaf-response in Déone@a—Leaf and
stalk currents—Their opposite variations under stimulus—Similar leaf-
and-stalk currents shown to exist in ordinary leaf of Ficus religiosa—
Opposite-directioned currents in Cztrus decumana—True explanation of
these resting-currents and their variations—Electrical effect of section
of petiole on Dzonea and Ficus religiosa—Fundamental experiment of
Burdon Sanderson on lamina of Dzone@a— Subsequent results—Expeti-
mental arrangement with symmetrical contacts—Parallel experiments on >
sheathing leaf of /usa—Explanation of various results : ‘ 1223

CHAPTER XIX
THE LEAF CONSIDERED AS AN ELECTRIC ORGAN

Electrical organs in fishes—Typical instances, Zorpedo and Malepterurus—
Vegetal analogues, leaf of Pterospermum and carpel of D¢llenia indica
or pitcher of Mefenthe—Electrical response to transmitted excitation
—Response to direct excitation—Uni-directioned response to homo-

- dromous and heterodromous shocks—Definite-directioned response
shown to be due to differential excitability—Response to equi-alternating
electrical shocks—Rheotomic observations—Multiple excitations—
Multiplication of terminal electromotive effect, by pile-like arrangement,
in bulb of Uric/zs lily : ‘ ‘ , ; ‘ , . . 241

CHAPTER XX

THE THEORY OF ELECTRICAL ORGANS

Existing theories—Their inadequacy—-The ‘ blaze-current’ so called—Re-
sponse uni-directioned, to shocks homodromous or heterodromous,
characteristic of electric organs—Similar results with inorganic specimens
—Uni-directioned response due to differential excitability— Electrical
response of pulvinus of A//mosa to equi-alternating electric shocks—Re-
sponse of petiole of AZ#sa—Of plagiotropic stem of Cucurdita—-Of Eel—

The organ-current of electric fishes—Multiple responses of electrical
organ—Multiple responses of Bzofhyium . — . > : : . 250

CONTENTS XIX

CHAPTER XXI

DETERMINATION OF DIFFERENTIAL EXCITABILITY UNDER ©
ELECTRICAL STIMULATION
| ) PAGE
Advantage of electrical stimulation, in its flexibility—Drawbacks due to~
fluctuating factors of polar effects, and counter polarisation-current—
Difficulties overcome by employment of equi-alternating © electric
shocks—Methods of the After-effect and Direct-effect—Experiment of
Von Fleischl on response of nerve—Complications arising from use of
make and break shocks—Rotating reverser— Motor transformer—Re-
sponse of Musa to equi-alternating shocks—Abolition of this response by
chloroform—Response records of plagiotropic Cucurbita and Eel—
Differential excitability of variegated leaves, demonstrated by electric
response. é ita : > ; - ; : : eee

CHAPTER XXII

RESPONSE OF ANIMAL AND VEGETAL SKINS

Currents of rest and action—Currents in animal skin—Theories regarding
these—Response of vegetal skin—Stimulation by Rotary Mechanical
_Stimulator—Response of intact human skin--Isolated responses of upper
and. lower surfaces of specimens —Resultant response brought about by
differential excitability of the two surfaces—Differences of excitability
between two surfaces accounted for—Response of animal and vegetal
skins not essentially different—General formula for all types of response
of skin—Response of skin to different forms of stimulation gives
similar results— Response to equi-alternating electric shocks : (1) Method
of the After Effect ; (2) Method of Direct Effect—Response of grape
skin—Similar response of frog’s skin—Phasic variation of current of
rest induced as result of successive stimulation in (a) grape skin ; (4) frog’s
skin; (¢c) pulvinus of Jimosa—Phasic variation in autonomous me-
chanical response of Desmodium gyrans—Autonomous variation of
current of rest—True current of rest in skin from outer to inner—This
may be reversed as an excitatory after-effect of preparation—Electrical
response of skin of neck of tortoise—Electrical response of skin of
tomato—Normal response and positive after-effect—Response of skin
of gecko—Explanation of abnormal response. . ; . . 287

CHAPTER XXIII

RESPONSE OF EPITHELIUM AND GLANDS

Epidermal, epithelial, and secreting membranes in plant tissues—Natural
resting-current from epidermal to epithelial or secretory surfaces —Current
of response from epithelial or secretory to epidermal surface:—Response

a2

XX COMPARATIVE ELECTRO-PHYSIOLOGY

; PAGE
of Dil/enza—Response of water-melon—Response of foot of snail—The
so-called current of rest from glandular surface really due to injury—
Misinterpretation arising from response by so-called ‘ positive variation ’
—Natural current in intact foot of snail, and its variation on section—
Response of intact human armpit—Response of intact human lip—
Lingual response in man—Reversal of normal response under sub-
minimal or super-maximal stimulation—Differential excitations of two
surfaces under different intensities of stimulus, with consequent changes
in direction of responsive currents, diagrammatically represented in
characteristic curves—Records exhibiting responsive reversals. rita. 3 Se

CHAPTER XXIV

RESPONSE OF DIGESTIVE ORGANS

Consideration of the functional peculiarities of the digestive organ—Alter-
nating phases of secretion and absorption—Relation between secretory
and contractile responses. [Illustrated by (a) preparation of Mimosa;
(4) glandular tentacle of Drvosera—General occurrence of contractile re-
sponse—True current of rest in digestive organs—Experiments on the
pitcher of Wepenthe—Three definite types of response under different con-
ditions—Negative and positive electrical responses, concomitant with
secretion and absorption— Multiple responses due to strong stimulation
—Response in glandular leaf of Drosera—Normal negative response
reversed to positive under continuous stimulation— Multiple response in
Drosera—Response of frog’s stomach to mechanical stimulation—Re-
sponse of stomach of tortoise—Response of stomach of gecko— Multiple

_ response of frog’s stomach, showing three stages—-negative, diphasic,
and positive —Phasic variations : : ; ‘ , 329

CHAPTER XXV
ABSORPTION OF FOOD BY PLANT AND ASCENT OF SAP

Parallelism between responsive reactions of root and digestive organ—Alter-
nating phases of secretion and absorption—Association of absorptive
process with ascent of sap—Electrical response of young and old roots—
Different phasic reactions, as in pitcher of /Vepenthe—Response to
chemical stimulation—Different theories of ascent of sap-——Physical
versus excitatory theories—Objections to excitatory theory—Assumption
that wood dead unjustified—Demonstration of excitatory electrical re-
sponse of sap-wood—Strasburger’s experiments on effect of poisons on
ascent of sap—Current inference unjustified . : : ‘ ; - 349

CONTENTS

CHAPTER. XXVI

THE EXCITATORY CHARACTER OF SUCTIONAL RESPONSE

Propagation of excitatory wave in plant attended by progressive movement of
water—Hydraulic response to stimulus—The Shoshungraph— Direct and
photographic methods of record—Responsive variations of suction under
physiological modifications induced by various agents—Effects of lower-
ing and raising of temperature—Explanation of maintenance of suction,
when root killed—Effect of poison influenced by tonic condition—Effect
of anzesthetics on suctional response—Excitatory versws osmotic action
—Stimulation by alternating induction-shocks—Terminal and sub-ter-
minal modes of application—-Three modes of obtaining response-records,
namely (1) the unbalanced, (2) the balanced, (3) the over-balanced—
Renewal of suction previously at standstill, by action of stimulus--Re-
ponsive enhancement of suction by stimulus—After-effect of stimulus—
Diminution of latent period as after-effect of stimulus—Response under
over-balance—Response under sub-terminal stimulation—Variation of
response under seasonal changes .

CHAPTER XXVII

RESPONSE TO STIMULUS OF LIGHT

Heliotropic plant movements reducible to fundamental reaction of contrac-
tion or expansion—Various mechanical effects of light in pulvinated and
growing organs—Electrical response induced by light not specific, but
concomitant to excitatory effects—Electrical response of plant to light
not determined by presence or absence of chloroplasts—Effect of
unilateral application of stimulus on transversely distal point— Positive
response due to indirect. effect and negative to transmission of true
excitation—Mechanical response of leaf of AM/¢mosa to light applied on
upper half of pulvinus—Mechanical response consists of erection or
positive movement, followed by fall or negative movement—FElectrical
response of leaf of A/zmosa to light applied on upper half of pulvinus ;
induction in lower half of pulvinus of positivity followed by negativity—
Longitudinal transmission of excitatory effect, with concomitant galvano-
metric negativity --Direct effect of light and positive after effect—
Circumstances which are effective in reversing normal response—Plants
in slightly sub-tonic condition give positive followed by negative response
—Exemplified by (a) electrical and (4) growth response—Examples of
positive response to light—Periodic variation of excitability— Multiple
mechanical response under light—Direct and after-effect— Multiple
electrical response under light, with phasic alterations of (— + — +) or
(+ — + —)--After-effects ; unmasking of antagonistic elements, either
plus or minus—Three types of after-effects

f

S

XXi

PAGE

365

392

xxii COMPARATIVE ELECTRO-PHYSIOLOGY

CHAPTER: XXVIII

RESPONSE OF RETINA TO STIMULUS OF LIGHT
PAGE
Response of retina—Determination of true current of rest—Determination _

of differential excitabilities of optic’ nerve and cornea, and optic nerve
and retina—The so-called positive variation of previous observers
indicates the true excitatory negative—Retino-motor effects—Motile
responses in nerve— Varying responsive effects under different conditions
—Reversal of the normal response of light due to (1) depression of
excitability below par ; (2) fatigue—The sequence of responsive phases
during and after application of light—Demonstration of multiple
responses in retina under light, as analogous fo those in vegetable
tissues — Three types of after-effect—Multiple after-excitations in human
retina—Binocular Alternation of Vision—Demonstration of pulsatory
response in human retina during exposure to light —. , ‘ - 415

CHAPTER XXIX

GEO-ELECTRIC RESPONSE

‘Theory of Hydrostatic Pressure and Theory of Statoliths—Question regarding
active factor of curvature in geotropic response, whether contraction or
expansion—Crucial experiment by local application of cold—Reasons for
delay in initiation of true geotropic response—Geo-electric response of
shoot —Due to active contraction of upper side, with concomitant gal-—
vanometric negativity—Geo-electric response of an organ physically
restrained . ; : ; : . , . : ; ; «5 @34

CHAPTER XXX

DETERMINATION OF VELOCITY OF TRANSMISSION OF
EXCITATION IN PLANT TISSUES ;

Transmission of excitation in plants not due to hydromechanical disturbance,
but instance of transmission of protoplasmic changes—Difficulties in
accurate determination of velocity of transmission—A perfect method—
Diminution of conductivity by fatigue—Increased velocity of transmission
with increasing stimulus—Effect of cold in diminishing conductivity —
Effect of rise of temperature in ‘enhancing conductivity— Excitatory
concomitant of mechanical and electrical response—Electrical methods
of determining velocity of transmission—Method of comparison of longi-
tudinal and transverse conductivities—Tables of comparative velocities in
animal and plant —Existence of two distinct nervous impulses, positive
and negative ; ; Saas , ° . ; ; ; » 444 «

CONTENTS atte xxiii

CHAPTER XXXI

ON x ‘NEW METHOD FOR THE QUANTITATIVE STIMULATION
OF NERVE

WA : PAGE
Drawbacks to use of electrical stimulus in nehenpading electrical response —
Response to equi-alternating electrical shocks—Modification of response
by. decline of injury—Positive after-effect—Stimulation of nerve by
thermal. shocks—Enhancement of normal response after tetanisation —
Untenability of theory of evolution of carbonic acid—Abnormal positive
response converted into normal negative after tetanisation—Gradual
transition from positive to negative, through intermediate diphasic—
Effect of depression of tonicity on excitability and conductivity—Con-
version of abnormal into normal response by increase of stimulus-intensity
—Cyclic variation of response under molecular modification . , - 456

CHAPTER XXXII

ELECTRICAL RESPONSE OF ISOLATED VEGETAL NERVE

Specialised conducting tissues—Isolated vegetal nerve—Method of ob-
taining electrical response in vegetal nerve—Similarity of responses of
plant and animal nerve: (a) action of ether—(4) action of carbonic
acid—(c) action of vapour of alcohol—(d) action of ammonia—(e) ex-

‘ hibition of three types of response, negative, diphasic and positive—
(/) effects of tetanisation of normal and modified specimens—Effect of
increasing stimulus on response of modified tissue ‘ ; : . 468

CHAPTER XXXIII

THE CONDUCTIVITY BALANCE

Receptivity, conductivity, and responsivity—Necessity for distinguishing
these—Advantages of the Method of Balance —Simultaneous comparison of
variations of receptivity, conductivity and responsivity—The Conductivity
Balance—Effect of Na,CO, on frog’s nerve—Effect of CuSO,—Effect
of chemical reagents on plant nerve—Effect of CaCl, on responsivity—
‘Responsivity variation under KCl—Comparison of simultaneous effects
of NaCl and NaBr on responsivity—Effects of Na,CO, in different
dilutions on conductivity—Demonstration of two different elements in
conductivity, velocity and intensity—Conductivity versus responsivily—
(a) effect of KI—(é) Effect of NaI—Effect of alcohol on receptivity,
conductivity, and responsivity Comparison of simultaneous effects of
alcohol—(a) on receptivity verses conductivity-~ (4) on receptivity Versus
responsivity... : : : , : ps reas , . -. 479

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XXIV COMPARATIVE ELECTRO-PHYSIOLOGY

CHAPTER XXXIV

EFFECT OF TEMPERATURE AND AFTER-EFFECTS OF STIMULUS

ON CONDUCTIVITY

Effect of temperature in inducing variations of conductivity : (@) by Method
of Mechanical Response ; (4) by Method of Electric Balance—Effect of
cold—Effect of rising temperature—The Thermal Cell—After-effect of
stimulation on conductivity—The Avalanche Theory—Determination of
after-effect of stimulus on conductivity by the Electrical Balance —After-
effects of moderate stimulation—After-effect of excessive stimulation

CHAPTER XXXV

MECHANICAL RESPONSE OF NERVE

Current assumption of non-motility of nerve—Shortcomings of galvano-
metric modes of detecting excitation— Mechanical response to continuous
electric shocks—Optical Kunchangraph—Effect of ammonia on the
mechanical response of nerve—Effect of morphia—Action of alcohol—
Of chloroform—Abnormal positive or expansive response converted into
normal contractile through diphasic, after tetanisation—Similar effects
in mechanical response of vegetal nerve—Mechanical response due to

- transmitted effects of stimulation—Determination of velocity of trans-
mission—Indeterminateness of velocity in isolated nerve—Kunchan-
graphic records on smoked glass—Oscillating recorder— Mechanical
response of afferent nerve—Record of mechanical response of nerve due
to transmitted stimulation, in gecko—Fatigue of conductivity —Conver-
sion of normal contractile response into abnormal expansive, through

- diphasic, due to fatigue

CHAPTER XXXVI

MULTIPLE RESPONSE OF NERVE

Great sensitiveness of the high magnification Kunchangraph—Individual
contractile twitches shown in tetanisation of nerve—Sudden enhance-
ment of mechanical response of nerve on cessation of tetanisation—
Secondary excitation— Multiple mechanical excitation of nerve by single
strong stimulation—Multiple mechanical excitation of nerve by drying .

CHAPTER XXXVII

RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY

Variation of resistance in Dionea, by ‘ modification’—Excitatory change,
its various independent expressions—Characteristic difficulties of investi-

PAGE

497

597

532

CONTENTS XXV

PAGE
gation—Morographic record by variation of resistivity—Inversion of
curves at death-point—-Similarities between mechanical, electro-motive
and resistivity curves of death—The true excitatory effect attended by
diminution of resistance—Response of plant nerve by resistivity varia-
tion—Independence of resistivity and mechanical variations—Responsive
resistivity variation in frog’s nerve, and its modification under anzesthetics 540

CHAPTER XXXVIII

FUNCTIONS OF VEGETAL NERVE

Feeble conducting power of cortical tissues—Heliotropic and geotropic
effects dependent on response of cortical tissues only— Phenomenon of
correlation—Excitability of tissue maintained in normal condition only
under action of stimulus—Physiological activities of growth, ascent of
sap, and motile sensibility, maintained by action of stimulus—Critical
importance of energy of light—Leaf-venation a catchment-basin-—Trans-
mission of energy to remotest parts of plants—Plant thus a connected
and organised entity . , ? : , , P ; ; . 551

CHAPTER XXXIX

ELECTROTONUS

Extra-polar effects of electrotonic currents on vegetal nerve —Electrotonic
variation of excitability— Bernstein’s polarisation decrement—Hermann’s
polarisation increment— Investigation into the law of electrotonic varia-
tion of conductivity—Investigation on variation of excitability--Con-
ductivity enhanced when excitation travels from places lower to higher
electric potential, and depressed in opposite direction—When feeble,
anode enhances and kathode depresses excitability—All electrotonic
phenomena reducible to combined action of these factors—Explanation
of apparent anomalies . > , ; ; : ; : , . 560

: CHAPTER XL
INADEQUACY OF PFLUGER’S LAW

Reversal of Pfliiger’s Law under high E.M.F.—Similar reversals under
feeble E.M.F.—Investigation by responsive sensation—Experiments on
living wounds— Under moderate E.M.F., intensity of sensation enhanced
at kathode, and depressed at anode—Under feeble E.M.F., sensation
intensified at anode and depressed at kathode Aas {apaeernre of electrical
currents in medical practice s : : ¢ : ; ‘ »'s 578

XXVi COMPARATIVE ELECTRO-PHYSIOLOGY

CHAPTER XLI

THE MOLECULAR THEORY OF EXCITATION AND ITS
TRANSMISSION : |

‘PAGE

Two opposite responsive manifestations, negative and positive—Such

opposite responses induced by polar effects of currents of different signs

—Arbitrary nature of term ‘ excitatory ’"—Pro-excitatory and anti-excita-

tory agents—Molecular distortion under magnetisation in magnetic sub-

stances—Different forms of response under magnetic stimulation—

Mechanical, magneto-metric, and electro-motive responses—Uniform

magnetic responses—Response exhibiting periodic groupings—TIneffec-

tive stimulus made effective by repetition—Response by resistivity-

variation— Molecular model—Response of inorganic substance to electric

radiation—Effect of rise of temperature in hastening period of recovery

and diminishing amplitude of response—Sign of response reversed under

feeble stimulation—Conduction of magnetic excitation—The Magnetic

Conductivity Balance—Effect of A-tonus.and K-tonus, on excitability

and conductivity—Conducting path fashioned by stimulus—Transmission

of excitation temporarily blocked in iron wire, as in bporisar 7 nerve—

Artificial nerve-and-muscle preparation ; ‘ : ‘ Mega 9

CHAPTER XLII

MODIFICATION OF RESPONSE UNDER CYCLIC MOLECULAR
VARIATION

Anomalies of response—Explicable only from consideration of antecedent
molecular changes—Continuous transformation from sub-tonic to hyper-
tonic .conditions—Two methods of inquiry, first by means of character-
istic curves, second by progressive change of response—Abnormal re-
sponse characteristic generally of A or sub-tonic state—Abnormal trans-
formed into normal, after transitional B state—B state characterised by
staircase response—Responses at C stage normal and uniform—At stages
D and E responses undergo diminution and reversal—Responsive pecu-
liarities seen during ascent of curve, repeated in reverse order during
descent—All these peculiarities seen not only in living but also in in-
organic substances, under different methods of observation—Elucidation
of effect of drugs—Response modified by tonic condition and past
history . F : 3 ; , : , ; é ; . OFS

CHAPTER XLIII

CERTAIN PSYCHO-PHYSIOLOGICAL PHENOMENA—THE PHYSICAL
BASIS OF SENSATION uf

Indications of stimulatory changes in nerve : 1, Electrical ; 2, Mechanical—
Transmission in both directions—Stimulatory changes in motor and

5
q
;

CONTENTS XXVii

: PAGE
sensory nerves similar— Responsive molecular changes and the correlated
tones of sensation—Two kinds of nervous impulse, and their character-
istics— Different manifestations of the same nervous impulse determined
by nature of indicator-—Electrical, motile, and sensory responses, and
their mutual relations—The brain as a perceiving apparatus—Weber-
Fechner’s Law—Elimination of psychic assumption from explanation of -
particular relation between stimulus and resultant sensation—Explana-
tion of the factor of quality in sensation—Explanation of conversion from
positive to negative tone of sensation after tetanisation—Various effects
of progressive molecular change in nerve—Effects of attention and inhibi-
tion—Polar variations of tonus, inducing acceleration and retardation . 644

CHAPTER XLIV

DISSOCIATION OF COMPLEX SENSATION

Conversion of pleasurable into painful sensation, and vice versa, by electro-
tonus—The Sensimeter—Mechanical stimulation—Stimulation by ther-
mal shocks—Chemical stimulation—Opposite effects of anode and
kathode—Normal effects reversed under feeble E.M.F. —Negative tone
of sensation blocked by alcohol and anzesthetics—Separation of positive
and negative sensations, by lag of one wave behind the other—Dissocia-
tion of sensation by depression of conductivity—A bolition of the negative
or painful element by block of conduction . ; : : ; . 666

CHAPTER XLV

MEMORY jos oe be - 677

CHAPTER XLVI

REVIEW OF RESPONSE OF ISOTROPIC ORGANS - . 687

CHAPTER XLVII

REVIEW OF RESPONSE OF ANISOTROPIC ORGANS _ + 700

CHAPTER XLVIII

REVIEW OF RESPONSE OF NERVE AND RELATED PSYCHOLOGICAL
PHENOMENA . : é ' S55

CLASSIFIED LIST OF EXPERIMENTS ‘ ‘ ‘ : « » 925

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FIG.

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ILLUSTRATIONS

Series of Contractile Responses in Muscle

Response of Indiarubber

Response of Selenium to the Siimulas of Light.

Negative Response of Galena to Hertzian Radiation

Positive Response of Ag’ to Electric Radiation...

Electric Response in Metals é

Uniform Electric Response in Tin ;

Fatigue in the Electric Response of Metals . ;
Stimulating Action of Na,CO, on Electric Response of Siatinum
Abolition of Response in Metal by Oxalic Acid

.. Response by Method of Relative Depression
12.

Arrangement for observing Simultaneous Mechanical aa Flectrical
Responses ;

Simultaneous Merhantcal aa Hlectrical tone | in Biophytum

Photographic Record of Electrical Response by Galvanometric
Negativity of Pulvinus of J/mosa, when leaf is_ physically
restrained from falling : . Se

Method of Transmitted Stimulation .

Excitation by Sudden Tension ’

Excitatory Response to Tension and Corspavarion

The Mechanical Tapper

The Torsional Vibrator

The Vibratory Stimulator P

Complete Apparatus for Method of Block a Nitcators Stinrulation .

Influence of Suddenness on the Efficiency of Stimulus . iets

Spring Attachment for obtaining Vibration of Uniform Rapidity

Additive Effect . ‘ ‘ ; : : :

Response Recorder . ; :

Photographic Record of Uniform 7 te (Radish)

Stimulation by Thermal Shocks

Photographic Record of Uniform Response in Peiiole Fe em to
transmitted excitation

Taps of increasing strength I : 2: 3: “4 sadectan ep obey Sibente |

in leafstalk of turnip

ba]
2
OO ON ANUP WWD SY GF

—
ons

XXX COMPARATIVE ELECTRO-PHYSIOLOGY

Increased Response with Increasing Vibrational Stimuli (Caulifiower-
stalk) ‘

Responses to Indicating Stimulus obtuined: with’ Two Rpeelneas of
Stalk of Cauliflower

Genesis of Tetanus in Muscle

Photographic Record of Genesis of Tetanus in Methaeieal Response
of Plants (Style of Datura alba) ‘ ee

Fusion of Effect of Rapidly Succeeding SGmuli : ; -

Response of (a) quickly reacting Amaranth ; (6) of iia Coletta

Arrangement for Instantaneous Stimulation . Fos

General Arrangement for Rheotomic Observation

Enlarged View of Balanced Keys

Curve showing Rise and Fall of Rc aesive E, M. Change: onder
moderate stimulation

Response Curve from Rheotomic ch eee in Sin sf tuarcith
under strong stimulation . :

Artificial Hydraulic Response of Minioss °

Experimental Arrangement for obtaining Records on Staoked Devas
of Responses given to Direct and Indirect Stimulation, by Leaf of
Mimosa .

Mechanical Responiies: of Eoat of ‘Mihasa.

Mechanical Response of Bzophytum to Thermal Stimuiation .

Record of Response of A/imosa Leaf, taken on a fast-moving drum

The Abnormal Positive preceding the Normal Negative in Mechanical
and Electrical Responses in Biophytum

Photographic Record of Electrical Response of Petiole 7 Ceutinwer

Photographic Record of Electrical Responses of Potato-tuber

Photographic Record of Electrical.Response of Petiole of Fern .

Longitudinal Contraction and Retardation of Growth under Light in

Hypocotyl of Szzapzs nigra
Record of Growth in Crinum at Pen petacats of 34° C. and 3 5° C.
Balanced Record of Variation of Growth in Flower-bud of Crinum
Lily under Diffuse Stimulation of Light
Diagrammatic Representation of the Tonic Level

Photographic Record of Abnormal Positive passing into Recoial

Negative Response in a Withered ica crie of Leaf-stalk of
Cauliflower . ‘

Photographic Record af Sesieade Reeaenae | in Vascioias Net erve

Staircase Increase in Electrical Response of Petiole of Pe
rendered sluggish by cooling . :

Photographic Record of Uniform Ronusaals: (Radic

Photographic Record of Uniform Response in Petiole of Fern

Record showing Diminution of Response, when sufficient Time is not
allowed for Full Recovery

Fatigue in Celery

Fatigue in Leaf-stalk of Caulidowse”

Photographic Record showing Fatigue in Tin Wire which had ids
continuously stimulated for Several Days . : : + ti

er”, = ee

Sl ee i

ea

78.

QI.
92.

ILLUSTRATIONS xXxxi

Effect of Over-strain in producing Fatigue

Rapid Fatigue under Continuous Stimulation in (a) Muscle’; (3) Beak.
stalk of Celery (Electrical Response) ~

Photographic Records of Normal Mechanical Gee of Mitiova to
Single Stimulus (upper figure), and to Continuous Stimulation
. (lower figure) < ‘ i ;

Effect of Continuous Vibration (dictieh 50°) i in Carrot .

Oscillatory Response of Arsenic -acted on Continuously by iertion
. Radiation :

Mesusia Fatigue (a) in "Electrical Radpohies of Petiole of Cauli.
flower; (4) in Multiple Electric Responses of Peduncle of

. Biophytum ; (c) in Multiple Mechanical Responses of Leaflet of

. Biophytum ; and (d@) in Autonomous Responses of Desmodium .

Photographic Record of Periodic rio in the Automatic Pulsation

. of Desmodium Eyraus . ‘ ‘ : ; ;

Periodic . Fatigue in Pulsation of Frog’s s Heart (Pembrey and
Phillips) .

Photographic Record at Peisdie: F sae sete Continous: Sitiala:

. tion in.Contractile Response (Filament of Uric/is Lily) .

Fatigue in the.Contractile Response of Indiarubber

Reversed Response of Fatigued Nerve

PAGE
94
96
od
97

98

98
99
99
100

Iol
102

Preliminary Staircase, followed by iigiey in the Responses Br

Muscle (Brodie) . .

Preliminary Staircase, Riteeeics followed = ueasn: in we Rediolae
of Galena to Hertzian Radiation ;

Photographic Record of Responses of Style of Datura alba in oes
Growth had come to a Temporary Stop ‘ : cae

Differential Contractile Response of Artificial Strip

Responses of AZzmosa to Sunlight. of not too long Duration

Transverse Response of Pulvinus of Mimosa. ‘

Diametric Method of Stimulation of-an Anisotropic Crab

The Thermal Variator

Responsive Current in. Petiole of Musa frou Concave to Comvis Side

Parallelism of Natural Current in Pulvinus of AZmosa and Sheathing
Petiole of W/usa 2 got

Effect of Variation of Tuapeecuse on Natural Cotrene: \; which in
Petiole. of MZusa flows from Convex to Concave Side ‘

Photogiaphic Record showing effect of Sudden, followed by steady
Rise of Temperature on Natural Current, |, in A/usa

Action of 7 per cent. Solution of Na,CO, on Natural Current of Musa

Effect of CO, on Natural Current of Musa . :

Variation of the Transverse Natural and icapalaee Curfents: in
. Pulvinus of JZ@mosa.

Photographic Record of Effect of @hidroform on ecnbaak of Chae

Photographic Record showing Action of Chloral Hydrate on the
. Responses of Leaf-stalk. of Cauliflower . ; ‘

Photographic Record showing Action of Formalin (Radish) .

Abolition of Response at both A and B Ends "7 yg Action of
NaOH ‘ : : , ;

103
103

104
108
109
110
III
113
115

118
119
120
122
122

127
130

131

-132

134

XXXii COMPARATIVE ELECTRO-PHYSIOLOGY

FIG,

116.

118.

119.

Photographic Record showing the nearly complete Abolition of
Response by strong KOH

Photographic Record showing the Siieiilataky Aisin of Sdhition of

Sugar : Ne

Photographic Record Dowie Coctinens Actes wae 2 per seat:
Na,CO, Solution . ‘

Photographic Record showing the Depressing Action af 5 per ceil
HCl Acid . ‘

Photographic Record deeine Effect of I per oat KHO.

Photographic Record of Effect of 5 per cent. KHO. :

Striking-rods for stimulation of two ends of specimen and inducing
phase-difference .

Isolated and diphasic responses weit one aihesence of shins ;

Photographic Record showing Negative, Diphasic, and Positive
Resultant Responses in Tin ;

Photographic Records of Response of Bryphyltin

Photographic Record of ee of Petiole of Cauliflower by ‘the
Diametric Method F : , ;

Distribution of Electrical Tension in Maecte> oylinder .

Photographic Record showing Persistent Electrical After- Effect i in
Inorganic Substance under Strong Stimulation .

Photographic Record exhibiting Persistent Galvanometric Negativity
in Plant Tissue after Strong Stimulation

Experimental Arrangement for ier Electrical Effect due to
Section ‘

Records showing increasing Poe Galvansmeuie ‘Regativiey;
according as injury is caused nearer to proximal contact .

Curve showing the Electrical Distribution in Stem with one Sectioned ©

End. ‘ : ‘ ‘ . : ‘ : ‘ é

Electrical Distribution in Plant-cylinder with Opposite Ends
Sectioned

Record of es wnces | in Plant (Leaf: stalk | Coulifiowes by Method
of Negative Variation : - d

Response by Positive Variation of Reasina Current

Distribution of Electric Potential in Lamina of Colocasia along a enciial
line from dead to living through intermediate stages

Straight Form Potentiometer °

Distribution of Electric Potential in Penal of Nymphica ott one
end of which has been killed

Photographic Records of Responses of Vereinbie N erve, one end of
which has been injured . ‘

Typical Cases of Variation of Current of Rest and ction: Corsent,
Specimen originally isotropic ,

Typical Cases of Variation of Current of Rest and ‘Actiow: Cunrent:;
intermediate point naturally less or more excitable than either of
terminal

Typical Cases of Vor aeon of Guceat of Het and Acton: Comeonit
Anisotropic organ, B end originally more excitable than A

PAGE
135
136

136

w= =—- 7

Ve ee ee ee

eS SS Oe

' FIG,

120.
121.
122.
123.
124.
125.
126.
527.

128.
129.

130.

131.
132.

133.

134..

135.

136.

137.

138.

139.

140.
I4I.
142.

143.
144...

145.

ILLUSTRATIONS | xXXxXi

b

—e
me

PAGE
Photographic Record showing Effect of Rapid Cooling, by Ice-cold
Water, on Pulsations of Desmodium gyrans 181
Photographic Record of Pulsations of Desmodium during Continuous
Rise of Temperature from 30° C. to 39° C. f . 182
Diminution of Response in Zucharis by Lowering of Tesh peretavé «+883
_After-effect of Cold on Ivy, Holly, and Zucharis Lily . 184
Photographic Record of Responses in Zucharis Lily during the Rise
and Fall of Temperature - 185
Diminished Amplitude of Response with Rising Temperature (Stem
‘of Amaranth) .. .- “ght 186
Photographic Records of AenblaGiindeas Dibleanie in Driiahisaes,
showing Increase of Amplitude and Decrease of Frequency, with
Lowering of Temperature 188
Photographic Record showing Effect of Sieant 3 in shicliabitinie ihiehoaes 190
Record of Electric Responses of Amaranth at various Temperatures. 195
Photographic Record of Thermo-mechanical Curve given by Coronal
Filament of Passiflora 198
Thermo-mechanical Curve of Two Different nineciaiee of Style of
Datura alba, obtained from Flowers of the same Plant 198
The Thermal Chamber 200
Photographic Record exhibiting Bicetsie Spades in the Petiole of
Musa 202
Photographic Réecond showed Electric Taversion at Death siecle
59°5°, in the Petiole of Amaranth . 203
Record showing Inversion of Electric Curve and ‘Siti Nalepsises
Reversal of Electric Response in Stem of Amaranth. 204
Multiple Mechanical Response of Aiophytum, due to a Single
Strong Thermal Stimulus . 208
Multiple Electro-tactile Response in ‘Stem of Wenosa due # Bite
Strong Thermal Stimulus . ; 209
Photographic Record of Multiple Electrical Ripon: in Lae a
Biophytum . 209
Multiple Electrical ieasheses ade Different Bonus val Siiehlies | in
Different Organs 210
Photographic Record of Multiple Electrical Response to Siteie
Thermal Shock in Frog’s Stomach : 210
Induction of Autonomous Response in Siophytum ‘a Moderately
High Temperature of 35°C. . 211
Initiation of Multiple Response in Ester Leaflet of ‘iceman
originally at Standstill . : : ‘ 212
Photographic Record of Autonomous Mechanical Pislestion in
Desmodium Leaflet . 213
Spark-record of Single Pulsation in . Leaflet of Detwotiiuats . 214
Photographic Records of Simultaneous Mechanical and Electrical
Pulsation of Desmodium Leaflet é ; 218
Photographic Record of. Simultaneous Mathaniont tnd Electrical
Pulsation in Leaflet of Desmodium, before and after Physical |
Restraint of Leaflet . é : ; ; ‘ :

« 220

“‘Xxxiv COMPARATIVE ELECTRO-PHYSIOLOGY

FIG.
146. ~
147...
148. .
149.
150. .
I5I.
152. :
153.
154. .

155:

156. |
187.
7858...
159.
160.
161.
162.

163...
164.

165.
166.
167.
168.
169...
$70.
St.

172.
7%

PAGE
Crescographic Record of ee Growth- “responses in Peduncle of .
Crocus. .« ‘ : ‘ 221
Natural and db co nonctet Guuveeste 3 in Teavek cp 2284
Burdon Sanderson’s Fundamental Experiment on Dioian Leaf 229°
_ Parallel Experiment in Sheathing Petiole of A/usa » «2229
Positive Response of certain Leaves of Dionea — 230
Diphasic Response of Leaf of Dzonea ‘ in Hapa Positive followed
. by negative. . . . ; 230
Positive Response of same bet when ‘ modified ? by" peeiiiies ae"
stimulation. .. .. ” : 230
. Experimental Connections with Piosive asicviinn to the second
‘Experimental Method of Burdon Sanderson’... ioe RO Bam ©
Response. of Under-surface of, Leaf of Dionea, with Electrical
Connections as in Fig. 153: Wee: iss
- Photographic Records of Positive, Tiphasie, ee Megative Rape
of. Petiole of J/Zusa depending on the Effective antensity OF <3 35
. Transmitted Stimulus .. . ° ° 238.
Electrical Response of Lamina of Nymphaea alba due to Pamelor. ;
Excitation from Petiole . / 246
Diagrammatic Representation by Du fois: Reymond for Explanation
_ of Electrical Response in Organ’of Zorpedo . : i gaz
Photographic Records of Responses given by Leaf of Coleus wromae ais:
when both Surfaces are Excited Simultaneously by cigars
VSRGGK To ye~ 4 Apa 248
Experimental Adan deiace ig Mhovicant Ghicteniices 252
Records of Two Successive Responses in Leaf of Soph lies
calycinum under Equi-alternating Electrical Shocks. . ° - 253
. Response-curve from Rheotomic Observation on Leaf of Nymphaea
alba . ; : : es |
Series of Responses ees i hast a Fidrosferamum subtrifolium to
Stimulus of Equi-alternating Electrical Shocks . : 0 255
Photographic Record of Responses of Carpel of Dzl/enia nikita 256
Photographic Record of Normal Responses given by Pitcher of
Nepenthe, under Equi-alternating Electric Shocks . ‘ . 256
Responsive Currents in Lead Wire , 264
Flat Strip of Lead, of which lower Surface is omnittated:| . 265
Photographic Records of After-effect of Homodromous ¢ and Hetero-
dromous | Induction-shocks:in prepared Strip of Lead .. ¥- 6 Lee
Photographic Record of Responses to -Equi-alternating Electric °.
Shocks in Prepared Lead Strip. -. ae » 267
Response of Pulvinus of AMtmosa- to Equi alternating Electric ey:
Shocks .:+ . ; ; : 268
Experimental Arrangement. for Detantiination of Excitatory ‘Afver-
effect of Equi-alternating Electrical Shocks. 276
Method of Direct Effect of Excitation by Equi- caltamvating Shocks 280
Excitation by Equi-alternating Shocks 281
Photographic Record of Response of Petiole of Bis: to “Equi: “alee
nating Electric Shocks, before and after Application of Chloroform 284

A
:
’

~

ILLUSTRATIONS Tse XXXV

Photographic Record of Responses of ee Stem of Cac ‘bila
to Equi-alternating Electric Shocks. ¥:
Electrical Responses of Eel to Equi-alternating Electrical Shocks
Rotary Mechanical Stimulator. _.. - aes ea
Diagram Representing Different Levels - Excitability, ne ‘Leto,
and Minus .. . -
Electrical Response of Grape: arte to Rotary Méchanical Stimulation
Electrical Response of Frog’s Skin to Rotary Mechanical Stimulation
Photographic Record of Electrical Kesponses of Upper Surface of
Intact Human Forefinger to Rotary Mechanical Stimulation —
Photographic Record of Electrical’: Responses ee ork skin to
. Thermal Shocks .. }
Photographic Record of Electrical Rexpceseh of Grape-skin to Stimid
_ lation by. Equi-alternating Electrical.Shocks -
Photographic Record of Series of Electrical Responses of Frog’s s Skin
. to Equi-alternating Electrical Shocks .. -.
Photographic Record of Transverse Response of. Palvinus af Mimosa
. to Equi-alternating Electrical Shocks... ray
Continuous. Photographic Record of Autonomous Pulsation of Des-
_ modium gyrans from 6 P.M. to 6 A.M, an,
Photographic Record of Electrical Responses in Skin ‘of Neck of
. Tortoise.to Stimulus-of Equi-alternating Electrical Shocks .. - .
Isolated Responses of Upper and Lower Surfaces of Skin of Tomato
. to Rotary Mechanical Stimulus. ~
Photographic Record of Series of Wesncaaa: in Skin of Eatante er
. Equi-alternatin Electrical Shocks. .
A Single Response of Skin of Tomato to Equbslternating Shock
. recorded on Faster Moving Drum .
Photographic. Record of Series of Normal Responses in Skin ve
- Geckow’ :,
Photographic Riou of ‘AtiiGened Dipbasis aiienonecs in Skin of
Gecko, converted to Normal, after Tetanisation :
Transverse Section of Tissue of Hollow Peduncle of Diialis aly:
Photographic Record of. Responses of Water-melon to- meek
- nating Electric Shocks .
Photographic Rece d of- Electrical Responses ved Tnteet: Hiutaah
- Armpit’. . +. : ‘y
Experimental Arrangement ioe Ritepoiine of Hein’ Lip ey
Photographic Record of Electrical Response of Intact Human Lip
Possible Variations of Responsive Current, as. between. Two Surfaces
- A and R, shown by. Means- of "Diagrammatic. iss paca of

. Characteristic Curves. --.. - a ae y SLE ety
Photographic Record: showing Resariid of N ofmial 2 eee in
. Pulvinus of A/émosa due to Fatigue - 2 a A Ee 2 -

.. Photographic Record showing Reversal of Resconse in Carpe of

. Dillenia indica, wnder Sub-minimal Stimulation -
Pitcher of Vepenthe, with lid removed. - oo
Glandular Surface of a Portion of the aug Menibtaine: ofthe Pitcher
> Of Nepenthe-. -.0 2 were ie Se eee el

336-

XXXVi COMPARATIVE ELECTRO-PHYSIOLOGY

FIG,

202.
203.
204.
205.
206.
207.
208.
200.
210,
211.
212.
213.
214.
215.

216.
217.

218,
219,

220,
221.
222.
223.

224.
225.
226.
227.

228.
229.

230.

Transverse Section of Tissue of Pitcher of Vepenthe. ‘ ;

Photographic Record of Series of Normal Negative Responses of Glan-
dular Surface of Wefenthe in Fresh Condition to Equi-alternating
Electric Shocks

Photographic Record of Réspdmses nf Pitcher i in Intermediate Stage,
having Attracted a Few Insects . :

Photographic Record of Responses of Pitcher in Third Stags) the
whole Glandular Surface thickly Coated with Insects

Multiple Response of Pitcher of Vepenthe, in First or Fresh Stage, to
Single Strong Thermal Shock

Multiple Response of Pitcher pf Wideathe: 3 in Third Siage, to Single
Strong Thermal Shock .

Photographic Record of Responses in Fresh Dest of D osera to Bau
alternating Electrical Shocks

Photographic Kecord of Multiple Remniaas é asd of \ Detniesh in
Positive Phase

Photographic Record of N etstad Negative Riepooies of Frog’: s
Stomach to Mechanical Stimulation

Photographic Record of Normal Negative Responses of Stomach of
Tortoise to Stimulus of Equi-alternating Electric Shocks .

Photographic Record of Normal Response in Stomach of Gecko to
Equi-alternating Shocks, seen to be reversed after Tetanisation

Photographic Record of Multiple Responses in Stomach of Frog to a

_ Single Strong Thermal Shock

Photographic Record of Normal Negative Relpdanie of Voume Root
of Colocasia

Photographic Record of Dasities Riaponie’ in Older Root of Caberastn

Photographic Record of Electrical Response of Sap-wood

Photographic Record showing Normal Responses of Living Wood te
Vibrational Stimulus, and the Abolition of Response by a Toxic
Dose of Copper Sulphate . a, ‘

The Shoshungraph

Curve showing Normal Suction: at 23° Cy “Pricresisal Suction at 35°
C., and the After-effect persisting on Return to Normal Tempera-
ture .

Action of Ansehibeticn 3 in ; Aiohiien of Suetion

Effect of Strong KNO, Solution

Effect of Strong NaCl Solution .

Record of Blank Experiment showing Alwence of asiy Disturbenss
of Record from Induction-shocks as such

Terminal Mode of Application of Stimulus

Sub-terminal Mode of Application of Stimulus

Renewal of Suction, Previously at Standstill, by Action of Stineuies

Photographic Record of Effect of Stimulus in Enhancing Rate of
Suction -,. , ; ‘

Variation of Latent Peisad as Afar aie of Gitiaiie 5

Photographic Record showing Variation of Latent Period as After-
effect of Stimulus ;

Suctional Response under Over- Galaace

363
369

372

375
376
377

378
380
380

383

383
384

385
386

Se atl at ee

ILLUSTRATIONS ’ XXXVii-

Photographic Récord of Effect of Stimulus on Over-balance . :

Photographic Record of Response to Continuous Sub- terminal Stimu-
lation .

Experimental Arauigeasent a Bictection of Electrical Change

_ induced at the Point transversely Distal to Point stimulated .

- Record of Response to Moderate Unilateral Stimulation under the

Experimental Arrangement described . oles

Record of Different Specimen under same Experimental boca:
ment when Stimulus is first Moderate and then Increased

Mechanical Response of Pulvinus of A/imosa to Continuous Action
of Light from Above . : ° ,

Electrical Response in the Lower Half is the Pulvinus of Mimosa

due to Stimulation of Distal Upper Half by Light . ,

Photographic Record of Series of Negative Responses of Petiole of

. Bryophyllum to Stimuli of Sunlight . ‘ A :

Record. of Responsive Growth-variation taken under céniliteie of
balance in slightly Sub-tonic Flower-bud of Crz#zuwm Lily under
Diffuse Stimulation of Light . ,

Photographic Record of Positive Response of the Petiole of Cauli-
flower to Light . ‘ .

Multiple Mechanical Response of Leaflet of Biohytun aa the
Continuous Action of Light f :

Photographic Record of Multiple Electrical eonceee in oe, 6
Bryophyllum under Continuous Action of Light . .

Diagrammatic Representation of Phasic Alternations, and After- effect
in Type I. , . : :

Photographic Record of Pieaie Kisccnationk. showing Direct and
After Effects of Lightin Type I., represented by Bryophyllum .

Diagrammatic Representation of Phasic Alternations, and After
Effect in Type III. . ; .

Photographic Record of Phasic Aaveriatien, showing ‘Disect a

_ After Effects in Type III., represented by Petiole of Cauli-
flower .

Photographic Recut of Pals of Diiciecee dabei witha a Sicknd
Specimen of Cauliflower, representative of Type ITI. ‘ ‘

Experimental Arrangement for Determination of Differential Excita-
bility of Optic Nerve and Cornea .

Series of Photographic Records of Excitatory etieniore 3 in F vis ’s
Eye to Equi-alternating Electric Shocks

Experimental Arrangement for Demonstration of Differential Excita-
bility as between Retina and Optic Nerve .

Series of Photographic Records of Excitatory teauiies in F mt s
Retina to Equi-alternating Electric Shocks

Photographic Record of Multiple Response of Retina of Frog snide
Continuous Action of Light. ,

Response of petiole of Bryophyllum. Fighé: was cut off on sities

ment of maximum positivity in the second of the multiple

KespOnses, «.. ‘ : , ; , orig Ge

PAGE

386
388
397
398
399
400.
401

402
405

407

Xxxviii © COMPARATIVE ELECTRO-PHYSIOLOGY

FIG.

254.
255.

256.
257:
258.
259.
260.
261.
262.
263.
264...
265.
266.
267.

. 268.
260.

270..
\ 27

272.

273.
274.
275.
276.
277.

278,

279.

Similar effect in response of tetina of Ophiocephalus-fish’. = .

The same with another specimen. ‘Light was here‘cut ‘off after the
first oscillation

Response of retina of Ophistephalus whe slightly aid

Response of frog’s eye (Kiihne and Steiner) -. ‘

After-effect of Light on Silver Bromide. . yal he :

Response of petiole of cauliflower. Light was here cut off’ on attain.
ment of maximum negativity... .° . reve ise

Response of retina of Ophdocephalus fish hee ‘depneskeas te

Response of isolated retina of fish as.observed by Kiihne and Steiner

Inclined Slits for Stereoscope and Composite Image formed i in the
Two Eyes : :

Composite Indaaiphésable Word, “68 which Components iare . Seen
Clearly on Shutting the Eyes - 2. -~. é

Diagrammatic Representation: of a Multicellular. Organ laid ‘Hotei

_ tally and Exposed to Geotropic Stimulus: . -

Effect on Apogeotropic Movement of Temporary Application of Cold
on Upper and Lower Surfaces respectively.

Diagrammatic Representation of Experiment showing Curvature
. Induced by Unilateral Pressure Exerted by Particles . :

Record of Responsive Curvature Induced in Bud of Crinum ee by
Unilateral Pressure of Particles .° -..

Record of Apogeotropic Response in Scape of Bricks! Lily”

Photographic Record of Geo-electric Response in the Scape - of
Uriclis Lily laid horizontally. . ere:

Experimental Arrangement. for Sidijecting: Organ to Geetespie
‘Stimulus, Mechanical Response.being Restrained:

Geo-electric Response of the’ Physically. Restrained Scape of Uriclis
Labyet Ss: wae Lo .

Diagrammatic Representation af Electrical Consheann for Deter-
_mination of ‘Velocities of . Centrifugal and -Centripetal ‘Trans-
missions .- . | s A ¢: ae i a

Experimental Adregsinent fot coopster the Relative Conduc-
tivities in Transverse and Longitudinal Directions eis

Response of Frog’s Nerve under Simultaneous Excitation of both
Contacts, by Equi- aereee Electrical Shek: one. Contact
. being Injured e ;

Bahbaticement of Amplitude of agus as After- effect * Thermal
. Tetanisation, in Frog’s Nerve

Conversion of Abnormal Positive into Normal Negative Response
. after Thermal Tetanisation .. -. ia

Gradual Transition from Abnormal Boultvh tieoaish Diphasic, i
Normal Negative Responses. in Frog’s’ Nerve -

Abnormal Positive Response converted through Dipheate to grat
Negative under the increasingly Effective Intensity.of Stimulus,
brought about by Lessening the ssa between the ee
and Stimulated Points... ...: % é ;

Frond of Fern with Conducting Nerves akgaed ptha as sith.

PAGE .
427

427
428
428 .
429
430
430
430°
432 -
432-
435 -
436
437

437
438

440°
441
442°
447
454
457
462
463
464
466
469

’ FIG.
280.

281.
282.
283.
. 284. :

285.

286.

287.

288. °

- ILLUSTRATIONS: » ‘! XX XIX

Photographic Record of Effect of Ether on he Electrical Response of
Plant-nerve .

Photographic Ratants et Effect of Co, on Electrical Rescane of
Plant-nerve .

Photographic Record of Ripken of Response by Strong Apeicatton

_ of Alcohol

‘Photographic Record of Effect of Ammonia on 1 Ordinary ‘Tissue: sf

Petiole of Walnut .

Photographic Record of Effect. of. Similar Application of Socata .

. on Plant-nerve.

Photographic Resaca of Exhibition of Three Sues sf Response, .

Normal Negative, Diphasic, and Abnormal Positive, in Nerve
. of Fern under: Different Conditions :

Photographic Record of Effect of Tetanisation in ES Enhative:
ment of Normal Negative Response in Nerve of Fern .

Photographic Record of Conversion of the Abnormal Di-phasic hitn
. Normal Negative, after Tetanisation,.T, in. Nerve of Fern

Photographic Record showing how the Abnormal Positive Response
is converted through’ Diphasic into Normal Negative by the

' Increasing Effective Intensity of Stimulus, due to Lessening the
. Distance between the Responding and Stimulated Points.

. Diagrammatic Representation of the Conductivity Balance . :

Photographic Record made during Preliminary Adjustment fay
Balance of Nerve of Fern . ‘ ‘ é : ‘ ;

. Complete Apparatus of Conductivity Bitarice

Effect of Na,CO, Solution on Responsive Excitability a F Bee s Nerve

Effect of CuSO, on Frog’s Nerve

Photographic -Record showing iighsocemeat o Rimehivile by
Application of CaCl, .

. - Photographic Record showing Haviedslcn of Rendaastie Excitability

by Application of KCl .
Photographic Record exhibiting Comparative Effects of NaCl tad
NaBr on Responsivity

Photographic Record of Effect Fi Dilute (* 5 per cee. ) Sates of

Na,CO, on Variation of Conductivity

Giistageanis Record of Effect of Stronger Dobe: (2 per ents i) of

. Na,CO, Solution on Conductivity . ~- . é

. RESPONSIVITY versus CONDUCTIVITY under KI ~

RESPONSIVITY versus CONDUCTIVITY under Nal
. Effect of Alcohol on the Responsivity of Frog’s Nerve

Photographic Record of Effect of Alcohol Vapour on Receptivity:

- Photographic Record of Effect of Alcohof on Conductivity .

. . Photographic Record showing Effect. of Alcohol on Responsivity
- Diagrammatic Representation of Experimental Arrangement’ for

’ Demonstration. of RECEPTIVITY versus CONDUCTIVITY, or of
RECEPTIVITY versus RESPONSIVITY . ne haere
RECEPTIVITY versus RESPONSIVITY under Alcohol
Photographic Record aan Effect of spsiii on » Cohductivity of
PjJant-nerve. : . . .

PAGE
472
473
473
474

474

475
476

477

477
482

482
484
485
485 .

486
487
487
488

489
491
492
492
493
494
494

- 495

495

499

COMPARATIVE ELECTRO-PHYSIOLOGY

The Cork Chamber for Gradual Raising of the Temperature of one
Arm of the Balance .- :

Photographic Record Skiing Effect of Riau Tenipedsaded on
Conductivity i

Experimental Arrangement for Riadyiing ‘After- effect of Seances on
Conductivity and Excitability :

Photographic Record Showing Effect of ‘ Mosiaeate Siteaniatiend in
Enhancing Conductivity and Excitability

- Photographic Record showing Effect of Excessive Stimulation i in De-

pressing Excitability and Conductivity
Record of Contractile Response in Frog’s Nerve indi Contiawdus
Electric Tetanisation .

. . Optical Kunchangraph for Machsiticel Résponss of Hise

Diagrammatic Representation of meee for Obtaining Petes.
mitted Effect of Stimulus .

Photographic Record of Effect of aia on pivecbanines Resneiize
-of Frog’s Nerve . : .

Photographic Record showing Abobasis of Mechanics Response oa
Frog’s Nerve by Action of Solution of Morphia

Photographic Record showing Preliminary Exaltation in Mechsnical
Response of Frog’s Nerve after Application of Alcohol ‘

Photographic Record showing Effect of Chloroform on Mechanical
Response of Frog’s Nerve .

. . Photographic Record showing Mocornal hace commento’ into

‘Negative Response after Tetanisation

Photographic Records showing Gradual Dldatpéatanice oe Positive
‘Element in diphasic Mechanical Responses of Frog’s Nerve
and Plant-nerve

. . Photographic Record sional Sinairense Effect in Medalees Re-

sponse of Frog’s Nerve .

. . Photographic Reproduction of Recon of Méckanicat Rea ponus af

Frog’s Nerve and Plant-nerve obtained on Smoked Glass Surface
of Oscillating Recorder

324. Record of Mechanical Responses to Electrical Stamatis chaaiviell on.
Smoked Glass, and given by the Optic Nerve of Fish Ophiocephalus
325. Record, obtained on Smoked Glass, of Transmitted Effect of Stimu-
lation on Nerve of Gecko . , z ee
326. . Initiation of Multiple Response by Drying of Ne erve : .
‘327. . Diagrammatic Representation of Experimental Arrangement for Re-
: cording Response by Resistivity Variation .
328. . Photographic Record of the Morographic Curve takin by Method of
; Resistivity Variation in Pistil of Hibiscus. Critical point of in-
version at 60°8° C, . ‘
329. Photographic Record of the Morographic aes ken os Method of
Eléctromotive Variation in’ Petiole of JZusa. Critical point of
inversion at 59:6° C. .
330. Photographic Record of the Morgeaphie Cave ‘sane by Method of

Mechanical Response in Filament of Passifora. Critical point of

inversion at 59°6 .C. . ; ; ‘ ° ‘ + Dhue .

PAGE —

500
501
504
504
505

510
511

512
516
516
517
518

521

522

524

528
529
530
539
544
546

546

546

339-
341.
342.

343-
344.

345.

346.

347:
348.
349-

350.

351.

352.

353+

354:

ILLUSTRATIONS

Response Records by Resistivity Variation, in the Nerve of Fern

Effect of Chloroform seen in benim i of ee tg dk in
Frog’s Nerve .

Photographic Record of Effect of ali dienes in Enhancing Mechani-
cal Response of Plant-nerve .

Photographic Record showing Bekeucemeat of Excitability dndér
Action of Light in Nerve of Fern

Distribution of Fibro-vascular Elements in Siigle Sane of Stem df
Papaya

Extra-polar Kat- dccaponie Effect

Extra-polar An-electrotonic Effect »

Extra-polar Electrotonic Effects under an Maiae E. M. F, shins rises
from *6 to 1°4 Volts . :

Diagram illustrating Bernstein’s Dechanieat of Kat- cbiitioale Caiént

Diagram illustrating Bernstein’s Decrement of An-electrotonic Current

Diagram representing Hermann’s Polarisation-increment under
Tetanising Shocks, with reversed polarising Current

Diagram representing Hermann’s Polarisation-increment fades
Tetanising Shocks, with reversed polarising Current :

Experiment with Petiole of Fern demonstrating Variation of Cou
ductivity by Polarising Current, Excitation travelling electrically
Downhill :

Experiment with Petiole of Fern desisghstraliais Masten of Bex:
ductivity by Polarising Current, Excitation travelling electrically
Uphill é ‘

Photographic Records of Rassonaes salons in last inegariseents when
Excitation was transmitted with and against the Polarising Current.

Photographic Record of Modification of Conduction during Passage
of Excitation from Anodic to Kathodic Region, under Increasing
Intensity of Polarising E.M.F.

Photographic Record showing Eshanced Condectizin fie Kathodic
to Anodic Region .

Experimental Arrangement to Exhibit the eliccnmnent of xciat
bility at Anode, when the Acting E.M.F. is feeble

Experimental Arrangement to Exhibit Depression of Excitability a at
Kathode, when the Acting E.M.F. is feeble .

Photographic Records of Response, illustrating the Hevanchebiews: bf
Excitability at Anode, and Depression at Kathode, under Feeble
Acting E.M.F. in two Specimens of Nerve of Fern a and é. :

Experimental Arrangement demonstrating the Joint Effects of
Variation of Conductivity and Excitability by Polarising Current .

Experimental Arrangement demonstrating the Joint Effects of
Variation of Conductivity and Excitability by Polarising Current,
when Current is Reversed . ‘

Photographic Record of Response under the Kerapasenenis given in
Figs. 351, 352 in Nerve of Fern

Experimental Arrangements for Showing so- called Polatisn tan:
increment by the Joint Effect of Increased Excitability at Anode
and Enhanced Conduction of Excitation electrically Uphill .

Cc

xli

PAGE

548
55°
554
557
558
560
560
561
562
562
563

563
565 .

565

566

567
568
569

569

570

572

572

572

574

xlfi

FIG,

355:

356.
357:
359.

360.

365.

COMPARATIVE ELECTRO-PHYSIOLOGY

Experimental Arrangements for Showing so-called Polarisation-
increment by the Joint Effect of Increased Excitability at Anode
and Enhanced Conduction of Excitation electrically Uphill.
Direction of Current in this is Reversed :

Photographic Record of Responses in Nerve of Fern, andes Anite
and Kathodic Action as described in Figs. 354 and 355.

Photographic Record of Similar Effects in Nerve of Frog .

Make-kathode and Break-anode Effects in Biophytum :

Effect of Anode and Kathode on Responsive Sensation in er
Hand

Polar Effects of Cureate ia to Eoclned Aprile on ones
Half of Pulvinus of Erythrina indica 7

Experimental Arrangement for Magnetometric. Method of Recard

Photographic Record of Uniform Magnetic Responses of Iron

Photographic Record of Periodic Groupings in Magnetic Responses

Photographic Record of Response and Recovery of Steel under
Moderate and strong Magnetic Stimulus

Photographic Record showing Ineffective Stimulus made Effective by
Repetition

Molecular Model

Method of Resistivity Macaious

Photographic Record of Response of prin esiaaine Powder in Sugpish
Condition to Stimulus of Electric Radiation

Photographic Record Showing Uniform Response of -Ahenvbetocn
Powder to Uniform Stimulus of Electric Radiation .

Photographic Record of Response of Tungsten

Experimental Arrangement for obtaining Response in iro * i
duction Current : ;

Magnetic Conductivity Balance

Process of Balancing illustrated by Pivotopra pate Record af Reiponnes.

Effect of K- and a-Tonus on Magnetic Conduction :

Opposite Effects of K-Tonus when moderate and strong

Effects of k- and A-Tonus on Magnetic Excitability

Gradual Enhancement of Conductivity by the Action of Stiendies

Characteristic Curve of Iron under increasing Force of Magnetisation

. Characteristic Conductivity Curve of Sensitive Metallic Particles be-

longing to Negative Class, under increasing Electro-motive Force.

Cyclic Curves of Magnetisation and of Conductivity

Photographic Record of Magnetic Tetanisation of Steel, éthiblting
Transient Enhancement of aba Speed on Cessation .

Mechanical Response of Frog’s Nerve to successive equal Stimuli,
applied at Intervals of One Minute

Mechanical Response of Frog’s Nerve, showing Conversion of Ab-
normal Positive into Normal Negative Response after Tetanisation

. Photographic Record showing Conversion of Abnormal ‘ Down’ Re-

sponse in Tin to Normal ‘ Up,’ after Tetanisation

PAGE

574

575
575
579

582.

589

594
594
594
595
595
598
600

601

602

603

604
607
608
609
610
611
612
620

621
622

623
625
627

628

ee St is.

ILLUSTRATIONS

Gradual Transformation from <Abonrek: to Normal Response in
Platinum ;

Normal Electro-motive Resnse 3 in Tin, sakuiced after Tetkiteation

Photographic Record of Abnormal Response of Selenium Cel con-

. verted into Normal after Tetanisation

Photographic Record showing Moderate Normal Geshcees of Sclendigs
enhanced after Tetanisation

Photographic Record of Abnormal aN e unpeied to Electric
-Radiation, converted after Tetanisation into Diphasic and Normal .

Moderate Normal Response of Aluminium, enhanced after Tetanis-
ation

Photographic Record of Eahansemeat of ‘Mieneue neseouse aier
Tetanisation

Vertical Series of Recsds sowie Tensiorantion of iioecisl rao
Normal Response after Tetanisation in Living and Inorganic alike
in the A phase

Series showing how Delamighon etieecese: ee Ressnien' in ‘the
B Phase

. Photographic Racorit storing Responses niaadian with different

parts of characteristic curve in frog’s nerve

Photographic Record of Response of Tungsten zh as finkance-
ment of Response after moderate Tetanisation, and Reversal of
Response, due to Fatigue under stronger Tetanisation .

. Series showing reversal of Normal Response by mee due to cong

Tetanisation inducing the E phase .

Fatigue in Indiarubber giving rise to Dinkaue ana: Beveyied Re-
sponses

Fatigue age ss Diphasic Variation ana Reversal of N Scania Response
in Frog’s Nerve

Abnormal Response of ae ty Rieiasiobisens followed ii et
Response of Contraction

Record of Response in Nerve of Gecke showing the Effect of eat
metically increasing Stimulus : :

Response of Nerve of Bull-frog to Stimuli 1, 2, a peo Bs is Rn
in Arithmetical Progression .

Response of Optic Nerve of Ophioephalus e Arithmetically i sicenaiite
Stimuli 1, 2, 3, 4, 5,6, 7 . ‘

Mechanical Response of Nerve of Fern to Arithmetiealy i increasing
Stimulus

Photographic Record my Magretic “Responses in Steel t to Arith-
metically increasing Stimulus . : ‘ . - :

The Sensimeter

Revival of latent Image in Metal

xii
PAGE

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683

whew
Sas =
Py)

s2 Sk, hb git Tei, eC)

COMPARATIVE ELECTRO-PHYSIOLOGY

CHAPTER I
THE MOLECULAR RESPONSIVENESS OF MATTER

Response to stimulus by change of form—Permeability variation—Variation of
solubility — Method of resistivity variation: (a) positive variation ; (4)
negative variation—Sign of response changed under different molecular
modifications—Response of vegetable tissue by variation of electrical re-
sistance—Response by~electro-motive variation in inorganic substances—
The method of block—Positive and negative responses—Similar responses in
living tissues—Effects of fatigue, stimulants, and poisons on inorganic and

organic responses — Method of relative depression, or negative variation, so
called,

IN studying the properties of living tissues, we find one of
their most important characteristics is found in the fact
that they exhibit the state of excitation under the impact of
stimulus. On the cessation of stimulus, again, the excited
tissue returns to its original condition. The excitatory change
thus undergone is fundamentally due to the derangement, or
upset, of the molecules of the living tissue from their normal
equilibrium, recovery being brought about by their restoration
to that state. The excitatory condition is sometimes shown
by change of form, as in the case
of the shortened length of excited
muscle (fig. 1). This might be
compared with the shortening of
stretched india-rubber under ther- *'~ ees ei rirstheag
mal stimulus (fig. 2).

Now it is clear that the molecular change consequent
on excitation must occasion various concomitant physical

B

2 COMPARATIVE ELECTRO-PHYSIOLOGY

changes, and it should be theoretically possible to detect and
measure this induced molecular change by recording such
concomitant variations, Thus the stimulus of light, for
example, may induce a mole-
cular change which may in its
turn induce, say, a variation
in the permeability of the sub-
stance to liquid. Bichromated
gelatine becomes less perme-
able under the action of light.
The solubility of a substance
Fic. 2. Response of India-rubber may again undergo variation
sepsis ini ty nO at under external stimulus —sul-
phur, for example, usually
soluble in carbon disulphide, is rendered insoluble under
the action of light.

In order, then, to study the effect of a given stimulus
with accuracy, we should be able to detect and measure the
extent of the changes induced. The two effects which have
just been referred to are not, as will be seen, highly susceptible
of accurate measurement. But in the detection of molecular
changes by electrical means, we have at our disposal methods
-for the measurement of such changes, the ease and delicacy
of which leave nothing to be desired. Two such methods
may be used—that of Resistivity and that of Electro-motive
Variation. According to the method of resistivity variation,
the substance to be experimented on is placed in an electrical
circuit, including a delicate galvanometer and a suitable
electro-motive force, such as to cause a small deflection of
the galvanometer. The impact of the stimulus on the sub-
stance under examination now induces in it a molecular
change by which its resistance is made to undergo a variation,
which in the case of certain substances may be an increase,
or in that of others adiminution. On the cessation of external
stimulus, the substance shows recovery, with a corresponding
return to its original conductivity. Thus in the case of
selenium, for instance, the conductivity is increased, or the

THE MOLECULAR RESPONSIVENESS OF MATTER 3

resistance decreased, under the action of light. In fig. 3 is
shown a number of responses to light, given on a series of
separate exposures, each of one second’s duration, the inter-
vening periods allowed for recovery being of one minute each.

Fic. 3. Response of Selenium to the Stimulus of Light
(Resistivity variation method)

These responses were obtained by recording the increased
deflection due to decreased resistance under the impact of
light, and the subsequent recovery. Such responses, by means
of decreased resistance, we may arbitrarily distinguish as
negative. Similar responses are
also given by a mass of metallic
particles when acted upon by
electric radiation. In fig. 4 are
seen several of these negative
responses given by galena under
the action of this stimulus.
There are, on the _ other
hand, some substances: which _
give positive responses ; that is to aes ee SPORE oF Soul
say, their resistance is increased, (Resistivity variation method)
or conductivity decreased, under
the action of stimulus. The deflection of the galvanometer
under a constant electro-motive force now undergoes diminu-
tion during the impact of stimulus. Such positive responses

are obtained with potassium and sodium. ~That the sign
B2

4 COMPARATIVE ELECTRO-PHYSIOLOGY

of response does not depend on the electro-positivity or
negativity of the substance is seen in the fact that while
highly electro-positive potassium gives positive response,
the equally electro-negative dioxide of lead gives a response
of the same sign. Substances like magnesium, aluminium,
and iron give negative response.

It is found, again, that the same substance, under different
molecular conditions, will give responses of opposite signs.
For example, a particular molecular variety of silver, Ag’,
gives positive (fig. 5), whereas ordinary silver gives nega-
tive response. Again, while
Ag’ normally gives positive,
yet the sign of this response
is gradually reversed to nega-
tive, under the long-continued
action of very strong stimulus.
By the employment of the
same method of resistivity
variation, I have been able to
obtain excitatory response records from living tissues also.
Details of these will be given in a subsequent chapter.

The electric response, however, employed to obtain
the excitatory reaction of living tissues, depends upon the
electro-motive variation of the substance under stimulation.
This electric reaction has. been regarded as vitalistic in
contradistinction to physical. But I have shown that
similar responses are given by inorganic substances also.
That is to say, the molecular excitability on which the
phenomenon of response depends is not distinctive of animal
tissues alone, but is common to all matter, both organic and
inorganic. If, then, we desire to understand those funda-
mental reactions which underlie the response of living tissues,
it will be well to observe its occurrence in the much simpler
case of the inorganic body.'

If we take an inorganic substance, say a piece of metal

Fic. 5. Positive Response of Ag’ to
Electric Radiation

' For a detailed account cf, Bose, Aesponse in the Living and the Non-
Living.

THE MOLECULAR RESPONSIVENESS OF MATTER 5

wire, and if its molecular condition be the same throughout,
it is obvious that its physical properties will likewise be
uniform. Hence its electrical condition will also be the
same at every point; in other words, it will be iso-electric.
But if a portion of this wire should now be made to undergo
a molecular change, as, say, by hammering, the physical
condition of this portion will be made different from that of
the rest. There will, therefore, be an electrical difference,
and the wire will no longer be iso-electric. This fact can
be verified by making suitable connections between the
molecularly strained and unstrained portions of the wire,
and a galvanometer, when a current will be found to flow
through the galvanometer, showing that a difference of
electrical potential has been brought about by the induced

(2) (c)

Fic. 6. Electric Response in Metals

(a) Method of block; (4) Equal and opposite responses when the ends A
and B are stimulated ; the dotted portions of the curves show recovery ;
(c) Balancing effect, R, when both the ends are stimulated simultaneously.

inequality of molecular conditions in different parts of the
same wire.

I shall now describe the method by which electrical
responses to molecular disturbance may be obtained from
inorganic substances. For this purpose, two different methods
may be employed—first, the method of block, and, secondly,
the method of relative depression. According to the first
of these, the wire to be experimented on is held clamped
at the middle, electrical connections being made with a
galvanometer at two points, A and B, by means of two
non-polarisable electrodes (fig. 6). We may now produce

6 COMPARATIVE ELECTRO-PHYSIOLOGY

excitation of the A end of the wire, by imparting a torsional
vibration, the molecular disturbance being prevented from
reaching the B end by the intervening block. Using this
method of experiment, I have obtained with different sub-
stances two different types of response—namely, positive
and negative. In the positive, the responsive current flows
through the wire from the unexcited to the excited, or
towards the excited—that is to say, the excited point
becomes galvanometrically positive. Responses of this kind
are given by tin, zinc, platinum, and other metals. In fig. 7
is seen a uniform series of such responses
to uniform stimulus. The intensity of the
response, moreover, does not appear to
depend on the chemical activity of the
substance. For the response of the chemi-
cally inactive tin is much stronger than
that of the active zinc. The very inactive
platinum is also found to give a fairly
strong response, although the electrolytic
contacts are made with pure water.

The electro-motive response may also be obtained by other
modes of molecular excitation. Thus, instead of torsional,
we may use longitudinal vibration. A metallic rod of brass,
AC, is clamped in the middle. A thin copper wire is led
sideways from the clamp and connected with a piece of
brass, B. A and B are connected with a galvanometer by
means of non-polarisable electrodes. If now the C end of
the rod be rubbed with resined cloth, A may be thrown into
longitudinal vibration, B being little affected by this. It is
here interesting to observe the concomitance of the electrical
response with the sonorous tesponse of the rod, and the
dying of the electrical response with the waning of the musical
note. The stronger the molecular vibration, the stronger the
sound, and also the stronger the response. The direction of
the responsive current in the metal is from the less excited B
to the more excited A.

We found under the method of conductivity variation

Fic. 7. Uniform Elec-
tric Response in Tin

THE MOLECULAR RESPONSIVENESS OF MATTER 7

that when a substance is molecularly modified, the sign of
its response tends to be reversed. Thus, as already said,
ordinary silver gives positive, and modified silver, Ag’,
negative response. But the latter, under strong and long-
continued stimulation, has its response re-converted, as it
were, to the normal positive. In the same way, under the
method of electro-motive variation also, we find the normal
positive response of, say, tin, or platinum, becoming con-
verted by molecular modification into negative, to be again re-
converted under continuous stimulation to the normal positive.

There are, again, certain other substances, of which the
normal response is negative. Thus a wire of brominated
lead, for instance, when suitably prepared, is found to give an
electro-motive response in which the current flows from the
excited to the unexcited or away from the excited, the excited
point becoming galvanometrically negative.

These electro-motive responses of the inorganic have thus
the same characteristics as those which have been observed
in the case of animal tissues. Certain tissues, such as highly
excitable muscle and nerve, give negative response—that is
to say, the excited point
becomes galvanometrically
negative. Other tissues,
again, the skin for example,
give positive response. The
normal responses, moreover,
are sometimes found to be
reversed under molecular
modification, and to be re-
reversed to normal response
under long-continued stimu-
lation.

The electrical responses

; : Fic. 8. Fatigue in the Electric
of metals, again, are subject Response of Metals

to an increase or decrease
which is paralleled. by the same phenomenon in the response
of animal tissues under similar circumstances. That is to

8 COMPARATIVE ELECTRO-PHYSIOLOGY

say, fatigue is found to depress the response of the inorganic
as of the organic (fig. 8). As in the case of animal tissues,
again, so also in that of metals, certain chemical substances
act as excitants, enhancing the response (fig. 9), others as
depressors and still a third class—such as oxalic acid—as
poisons, abolishing response altogether (fig. 10).

By taking advantage of the last of these facts, we arrive
at a second means of obtaining response—that is to say, the
method of relative depression. If both the contact points

Before * After
Fic. 9. Stimulating Action of Na,CO, on Electric Response of Platinum

Records to the left exhibit response before, to the right after the
application of reagent.

A and B be equally excited—-that is to say, subjected to diffuse
stimulation—the responsive ‘currents will be opposed, and
there will be no resultant galvanometric effect. This was
overcome, according to the method of block, by localising
excitation at one point, say, A; we might, however, neutralise
altogether the counteracting excitatory effect at B by
abolishing the excitability of that point, as, say, by the
application of oxalic acid, A being left in its normal con-
dition. If now the wire be subjected to diffuse stimulation

THE MOLECULAR RESPONSIVENESS OF MATTER 9

by vibrating it as a whole, a resultant response will occur.
But by the application of oxalic acid to one contact, a resting
or permanent current has been induced in the circuit. The
responsive or action current
originated under stimulation
is now found to flow in a
direction opposite to that of
this resting current—that is
to say, it causes a negative
variation of it (fig. 11).
The method of response
by the so-called negative
variation, which is generally
employed in studying re-
sponsive phenomena in
animal tissues, is in reality,

After

as will be seen later, a form Before 4

: : : Fic. 10. Abolition of Response in
of this method of relative siétal by Oxélic Acid
depression. i

Various means have been described, in the course of this
chapter, for the detection and record of that excitatory change
which is brought about by the upsetting of molecular equi-
librium under stimulus,
and the subsequent re-
covery. The responsive 6
change may find expres-

sion in different ways.

This expression may, ; a

for instance, in the case

of living tissues, take the

form of mechanical con- Fic. 11. Response by Method of Relative
traction, or of the elec- Depression

trical variation of gal- _ * TePresents current of rest ; ¥ represents

vanometric negativity.

Or the opposite change, expressed mechanically as ex-
pansion, will be evidenced by galvanometric positivity. But
it must be borne in mind that neither of these expressions

10 COMPARATIVE ELECTRO-PHYSIOLOGY

is consequent on the other It would be as incorrect to
suppose that the electrical effect depended on the mechanical,
as to assume that the mechanical was brought about by the
electrical. The two are independent expressions of the same
fundamental molecular change, brought about by the shock
of stimulus.

Again, those various responsive phenomena and.their modi-
fications which are the subject of our inquiry, are such as are
induced by different external agencies. Under the influence
of certain conditions, the responses of living matter undergo
an abolition—the change which we associate with death. In
inorganic matter also, we find a similar change of responsive-
ness into irresponsiveness, to take place. The death-change
in the case of living matter is thus not due to a change from
the organic to the inorganic condition, but to some molecular
transformation. And the nature of this very obscure trans-
formation may one day be elucidated by a careful study of
the changes which take place in inorganic matter, when it
passes from responsivity to irresponsivity.

The word ‘ physiological’ is generally used to distinguish
phenomena which are believed to be exclusively characteristic
of the properties of living matter. Such phenomena, however,
- are found, as our power of investigation grows, to be increas-
ingly capable of analysis into physico-chemical processes.
In my own use of the term ‘physiological,’ therefore, it will
be understood as a convenient expression for describing the
response-phenomena of plant or animal tissues, but as in no
sense opposed to the word ‘ physical.’

We shall, in the following chapters, study excitatory
effects in living tissues, and their variations under different
conditions, using the methods of electrical response. These
phenomena will be studied with special detail in the case of
vegetable tissues, and it will be found that there is no
responsive reaction exhibited by any one amongst the various
types of animal tissues, which has not its exact corre-
spondence in the vegetable. Those anomalies, further, which
have been observed in the response of the animal, will be seen

THE MOLECULAR RESPONSIVENESS OF MATTER II

to be fully elucidated by the study of similar phenomena
under the simpler conditions of the plant. And finally an
attempt will be made to arrive at some generalisation which
will show the continuity between the simplest form of
response in the inorganic and the most complex which occur
in the highest type of animal tissue.

CHAPTER II

THE ELECTRO-MOTIVE RESPONSE OF PLANTS TO DIFFERENT
FORMS OF STIMULATION |

Historical—Difficulties of investigation—Electrical response of pulvinus of
Mimosa—Simultaneous mechanical and electrical records—Division of plants
into ‘ ordinary’ and ‘sensitive’ arbitrary—Mechanical and electrical response
of ‘ordinary’ plants—Direct and transmitted stimulation — All forms of
stimulus induce excitatory change of galvanometric negativity.

IT has been customary to divide plants, as regards their
responsiveness, into two distinct classes: ‘ordinary’ and
‘sensitive. Of these only the latter class, represented by
such plants as Wzmosa and Dionea, was regarded as excitable.
Hence the attention of observers desirous of investigating
excitatory electro-motive phenomena in vegetable tissues was
mainly attracted towards the reactions exhibited by these
plants. The experiments undertaken in this field by Kunkel,
Burdon Sanderson, and Munk are well known. Burdon
Sanderson and Munk worked on the sensitive leaves of Dzonega
and Kunkel on-those of W/zmosa.'

Electro-motive variations were observed to ‘ake place in
all these plants on stimulation, but the conclusions arrived
at by the investigators were not concordant. Burdon Sander-
son and Munk found out that the resting-current between
two selected points of Dzonza exhibited variation on applica-
tion of stimulus to the leaf. They thus obtained di-phasic
and sometimes even tri-phasic responses, consisting of positive
and negative variations. More definite results were obtained
by Burdon Sanderson, in the responsive variations of the
normal leaf-current, flowing between the proximal and distal

1 For a more detailed account cf. Biedermann, ZEéectro-physiology, English
translation, 1898, vol. il. pp. 1-31.

— =

ae

THE ELECTRO-MOTIVE RESPONSE OF PLANTS 13

points of the midrib of the leaf. On stimulation of the

lamina, this current was found to undergo a diminution, or

negative variation. But the current in the stalk, or petiole
was found to undergo the opposite change—that is to say, a
positive variation. Kunkel, in working with the pulvinus of
Mimosa, found that on excitation a series of opposite or
oscillatory electro-motive variations was induced. He also
found electro-motive differences to be induced as the result
of the flexure or injury of ordinary stems He believed all
these electrical phenomena to be consequent on hydrostatic
disturbance or water-movement.

By means of this ‘ migration of water’ Kunkel attempted
to explain all the electrical phenomena in vegetable organs.
The electro-motive difference between different parts of an
organ was due, according to him, to their different powers of
absorption of water. The greater absorptiveness of one
point, with its consequent greater movement of water, would
render that point relatively positive. As against this, how-—
ever, Haake pointed out that electrical differences between
different points were also to be found, even in submerged
plants, like Valisnaria and Nztella, in which there could not
possibly be any differences of absorptiveness. This difference,
therefore, he suggested, must be ascribed to some vital
process, inasmuch as the P.D. is seen to undergo a change
whenever the respiratory process is interfered with, as, say,
by the substitution of hydrogen for oxygen.

We shall study later in greater detail the conditions on
which this ‘current of rest,’ so called, actually depends
(Chapter X.). But more important is the excitatory variation
induced by stimulus. It has already been stated that
Kunkel found oscillatory variations of the current to occur

“on stimulation of the leaf of MMZzmosa. These alternating

variations were difficult to reconcile with his theory of the
active, single-phased displacement of water, as he did not
fail to see, and he suggested that the first negative swing
observed might be due to the disturbance of the diffusion-
process through alterations of the protoplasm. ~

14 COMPARATIVE ELECTRO-PHYSIOLOGY

Munk attempted to explain the complicated. electrical
effects which he observed in Dzon@a by assuming the existence
of two different kinds of electro-motive elements, affected in
opposite ways, the maximum changes being initiated in one
set earlier than in the other. In this way, he thought, it
might be possible to explain the occurrence of positive and
negative variations, holding that the upper parenchymatous
layer of the leaf, and the upper midrib, went through the
negative, and the under layer and the under midrib through
the positive change. |

Burdon Sanderson, in his ‘ fundamental experiment’ on the
lamina of Dzone@a, had his led-off circuit connected with the
upper and lower surfaces of one lobe, stimulus being applied at
the other. In the experiments described in the ‘ Phil. Trans.’
of 1882, he found that the upper or inner surface of the leaf
become positive on excitation. This he regarded as the
true excitatory change. The upper contact now, however,
after a certain interval became negative, a change which
Burdon Sanderson designated as the after-effect. This after-
effect he ascribed to the electrical variations caused by that
movement of water which had been observed by Kunkel.
But with regard to the preceding positive variation he says :

‘The excitatory disturbance which immediately follows
excitation is an explosive molecular change, which by
the mode of its origin, the suddenness of its incidence,
and the rapidity of its propagation is distinguished from
every other phenomena except the one with which I
have identified it, namely, the corresponding process in
the excitable tissues of animals... . The direction of
the excitatory effect in the fundamental experiment is
such as to indicate that in excitation excited cells
become positive to unexcited, whereas in animal tissues
excited parts always become negative to unexcited.’!

In a subsequent series of experiments, however, given in
‘Phil. Trans,’ for 1888 Burdon Sanderson finds the reaction

' Phil. Trans. vol. clxxiii.

ee eae es ee

a a

ee eee Se eae ee ee

THE ELECTRO-MOTIVE RESPONSE OF PLANTS 15

of leaves ‘in their prime’ to be somewhat different. A strong
negative phase was now observed on stimulation, but pre-
ceded by a short-lived positive reaction. These results will
be discussed in detail in a subsequent chapter, but it may be
said here that from the records given by Burdon Sanderson
it is difficult to know which of the various responsive phases
are to be regarded as those of true excitation, and which as
the results of some other cause.

It will thus be seen that the results arrived at and the
theories advanced by different observers in this field are some-
what at variance with eachother. This must have been due
to the difficulties met with in disentangling the fundamental
reaction from those various subsidiary effects which are apt
to be found in combination with it. Chief among these
difficulties was (1) the fact that positive and negative
variations are generally measured in terms of an existing
current of rest. But, as a matter of fact, these two
apparently opposite responsive variations, positive and
negative, are not always indicative of opposite reactions.
For an identical excitatory reaction, added algebraically to
the resting-current, might appear, according to circumstances,
as either of the two. There was also (2) the difficulty of
discriminating two opposed electrical effects, one of which
was due, as I shall show, to true excitation, and the other
to increase of internal energy brought about by mechanical
movement of water. Under different conditions, it may be
either the one or the other of these which becomes prominent.
I shall hope to show that each of them is definite and dis-
tinguishable from the other.

With regard to the response of plants in general, ae
it may be well to state here that the first fact to be demon-
strated in the course of the present work is that such
responsive phenomena as may be observed in the case of
sensitive plants like Dzon@a, are not unique, but occur
under similar circumstances even in ordinary plants, and are
characteristic of all plant organs. I shall be able to show,
moreover, that an explanation of these phenomena, much

16 COMPARATIVE ELECTRO-PHYSIOLOGY

simpler than the theory of electro-motive molecules, is
available. It will also be proved that the electrical response
due to true excitation is quite distinct from that which is
brought about by the hydrostatic disturbance, its sign being
in fact opposite. This true excitatory electrical response,
again, will be shown to be modified by all those conditions
which affect the physiological state of the tissue. And,
lastly, it will be proved that there is no breach of continuity
as between the electrical responses in plant and animal,
for not only is the sign of response in both cases the
same, but it is also true that every type of response and
modification of response, which occurs in the animal tissue, is
to be found under parallel circumstances in that of the
plant also.

In order to determine what is the electrical response
characteristic of excitation, we first select for experiment a
sensitive plant, say J/zmosa, because here, in the responsive
fall of the leaf, we have a visible indication of the excitatory
reaction. It is desirable at this point to say a few words re-
garding the use of the terms ‘ excitatory ’ and ‘true excitation.’
We are all familiar with the fact that, when muscle is excited
by stimulus, it responds in a conspicuous manner by con-
traction. This is universally accepted as the phenomenon of
excitation, its electrical concomitant being galvanometric
negativity. Having once applied the term ‘excitatory’ to this
particular aspect of molecular response in living tissues, it is
of course important that we should henceforth distinguish
carefully between it and its possible opposite, namely, ex-
pansion, with concomitant galvanometric positivity. Under
stimulation there is a contraction of, and expulsion of water
from, the excited pulvinus, which brings about the depression
of the leaf. It is generally. supposed that only the lower half
of the pulvinus is excitable. This, however, is an error, for
both upper and lower halves are excitable, and contract
under stimulation. If localised stimulus be applied on the
upper side, that side contracts, and, by the concavity thus
induced, the leaf is erected. But, though both halves are

+. eee

Pe — = ."*
CO ea eee

THE ELECTRO-MOTIVE RESPONSE OF PLANTS 17

sensitive, yet the excitability of the lower is, generally
speaking, greater, and diffuse stimulation therefore causes
greater contraction of that half. Hence the resultant fall is
due to the differential contraction of the two sides of the
organ. The excitatory reaction of the organ, then, consists
of a contraction ; expulsion of water with consequent diminu-

Fic. 12. Arrangement for observing Simultaneous Mechanical and
Electrical Responses

Leaf stimulated by electro-thermic stimulator. Mechanical record obtained
by excursion of spot of light reflected from Optic Lever, which falls on
the right of drum. Electric record obtained by excursion of galvano-
meter spot of light adjusted to fall on the left side of the drum.

tion of turgidity, or negative turgidity variation ; and fall of
the leaf. :

In order next to determine the electrical concomitant of
this reaction, we make suitable electrical connections by
non-polarisable electrodes, with a galvanometer. One of
these is made with the pulvinus, whose excitation is to be
observed, and the other with a distant indifferent point. In
this way we can obtain the excitatory effect at the pulvinus,
uncomplicated by that at the distal point. A spot of light,
reflected from the galvanometer mirror, is thrown on the

C

18 COMPARATIVE ELECTRO-PHYSIOLOGY

recording drum. This spot of light, hitherto quiescent, shows,
by its sudden deflection, the occurrence of the excitatory
change.

To show the concomitance of the mechanical and elec-
trical responses, and in order to detect with certainty the
exact moment of the initiation of the former, a magnifying
arrangement is obtained by attaching the end of the leaf to
an Optical Lever. The pull exerted by the falling leaf rotates
the fulcrum-rod, carrying a light mirror. The spot of light.
from this mirror moves in a vertical direction, and that —
of the galvanometer horizontally or laterally. For the
purpose of simultaneous record, it is necessary to have the
two in one direction. The up and down movement of
the spot from the Optic Mirror is therefore converted into
lateral, by means of reflection from a second mirror, suitably
inclined.

Stimulation may be effected in the neighbourhood of
the pulvinus by means of the electro-thermic stimulator,
which has the advantage of producing no mechanical dis-
turbance. This consists of a V-shaped platinum wire,
suddenly heated by the momentary passage of an electric
current. On applying stimulus in this manner it is found
‘that the two responses—mechanical and electrical—take
place at the same moment, the mechanical fall of the leaf
being practically coincident with the induced electrical
variation. As regards the sign of this electrical change, the
excited point is found to become galvanometrically negative :
that is to say, the electro-motive variation induced in the
excited vegetable, is the same as that observed in animal
tissues. I give below a series of these simultaneous records
of mechanical and electrical response (fig. 13), obtained from
Biophytum, whose lateral leaflets give motile indications. It
will be seen that the responsive fall of the leaflet, and the
subsequent recovery, are synchronous with the electrical
variation of galvanometric negativity, and its subsequent
recovery. For convenience of inspection. I shall always,
unless specially stated to the contrary, represent the normal

THE ELECTRO-MOTIVE RESPONSE OF PLANTS 19

responses of mechanical depression and galvanometric nega-
tivity by up-curves. The erectile movement and galvano-
metric positivity will, conversely, be represented as down.

A few words may be said here as regards the syn-
chronism between the two forms of response. The excitatory
molecular change takes place instantaneously, and the
electro-motive variation is, as far as can be judged, strictly
concomitant with it. This is shown by the rheotomic
method of observation, described in Chapter IV. It will there
be seen that a very considerable electro-motive change has
already been induced, in a period so short as ‘oI of a second
after the reception by the tissue of the stimulating shock.

Fic. 13. Simultaneous Mechanical (M) and Electrical (E) Responses in Biophyium

These responses are seen to take place at the same moment.

In the electrical response, then, of highly excitable tissues
there is practically no latent period. But if the same elec-
trical variation be recorded by the galvanometer, there will
be a lag in the response, owing to the inertia of the galva-
nometer needle. Similarly, in the mechanical response,
though the excitatory reaction is immediate, yet the motile
response is delayed, by the antagonistic actions of the upper
and lower halves of the pulvinus, the sluggishness of the
tissue, and the mechanical inertia of the indicating leaf.
The latent period of the mechanical response of a vigorous
Mimosa, owing to all these causes, I find to be about
twenty-four-hundredths of a second. But this may be still

further prolonged when the tissue is in a state of depressed
C2

20 COMPARATIVE ELECTRO-PHYSIOLOGY

excitability. It will thus be seen that even when the funda-
mental excitatory reaction is instantaneous, its outward
expression, whether mechanical or electrical, may nevertheless
appear to be subject to delay in consequence of the inertia
of the particular indicator concerned.

As regards these two forms of response, it should further
be remembered that the mechanical and electrical responses
are independent indications of the fundamental excitatory
reaction, and that neither is
dependent for its occurrence
on the other. Thus, when
the mechanical response is
physically restrained, the
electrical response takes
place unimpeded. I shall
here relate an experiment
in illustration of this point.

A leaf of Mimosa re-
sponds to strong stimulus
by complete collapse, and
the recovery from this state
is somewhat prolonged,
taking from five to eighteen
minutes, according to the

Fic. 14. Photographic record of Elec- :
trical Response by Galvanometric season. In order to obtain

Negativity of Pulvinus of Mimosa, . : :
when leaf is physically restrained from a series of FCSPONSe with

falling. The first series in response to these recoveries, within a
Series to stimuli twice as strong. Teasonable time, I find that
it is necessary to apply

moderate stimulus. There is then a moderate fall, without
complete collapse, and recovery under such circumstances is
found to take place within a minute or so. In order to show
that electrical response takes place, even when the leaf is
prevented from giving mechanical expression, I held the
petiole in a clamp, and obtained the set of electrical responses
seen in fig. 14. The first series of this record were taken
in answer to uniform stimuli of a given intensity, and the

THE ELECTRO-MOTIVE RESPONSE OF PLANTS 2I

second to stimuli twice as strong. We may here see how
response is increased by increased intensity of stimulus.
One peculiarity to be noticed in this figure is the trend of
the base-line downwards, showing the increasing positivity
of the pulvinus. In order to obtain a photographic record
the experiment had to be carried out in a dark room, and
under these circumstances the pulvinus undergoes an increase,
or positive variation, of turgidity. And we shall see later
that a positive turgidity variation is associated with galvano-
metric positivity in the same way as the negative turgidity
variation is found to be accompanied by galvanometric
negativity. |

In consequence of the impression produced by the con-
spicuous movements of the leaf of M/zmosa,it was assumed that
only plants showing such movements were to be regarded as
excitable. I have already shown elsewhere, however, that
this test of lateral motile responses, as a sign of sensitiveness,
is fallacious in the extreme. Such mechanical display is
possible only when the two halves of an organ are unequally
contractile, and there is consequently a greater expulsion of
water from one, in response to stimulus, than from the other.
If these conditions are not fulfilled, even the so-called ‘ sensi-
tive’ Mimosa would appear to be insensitive. Thus, when
we place a cut branch of J/zmosa in water, the pulvini of the
leaves, on account of vigorous suction at the cut end, are
rendered over-turgid, and the leaves become highly erected.
On now applying stimulation, no responsive fall is found to
take place ; this is due to the difficulty encountered in the
expulsion of water from the gorged tissue. An intact plant,
again, which in the light has been found highly sensitive,
will often be found insensitive after a short time spent in a
dark room. It will then be difficult to believe that the plant
is of the sensitive class, for the hardest blow will fail to
evoke any mechanical response. And not only does the
Mimosa cease to show responsive movement under these cir-
cumstances, which may perhaps be regarded as exceptional ;
but under perfectly normal conditions also, its sensitiveness

22 COMPARATIVE ELECTRO-PHYSIOLOGY

varies so much that its motile response would seem at times
almost to have disappeared. I have already pointed out
that it is by the unequal excitabilities of the upper and
lower halves of the pulvinus that that differential contrac-
tion is induced which brings about the lateral response of
the Mzmosa leaf. Now it is clear from this that if the
differential excitability should be reduced or abolished, by
any means whatsoever, there will then be a corresponding
diminution or abolition of response. We shall see later that
the excitability of a tissue depends upon its state of turgor,
and in Mzmosa, from internal causes, a periodic variation is
induced in the relative turgescence of the two halves of the
pulvinus. We might then expect, in consequence of this, to
find a periodic variation of motile sensibility. And certainly,
whatever may be the cause, a long course of observation
will convince the inquirer of the occurrence of great varia-
tions in the sensibility of MW/zmosa at different times of the
day. Thus, I had six specimens of this plant growing in
pots in the open, and I found, watching them in the month of
August, that at eight o’clock in the morning the pulvini of
the leaves of all these plants were sensitive in the highest
degree. Half an hour later, however, this sensitiveness had
so far waned that they would give hardly any motile indi-
cation. It is, perhaps, worth while to remark, in connection
with this, that-a constant observer is able to judge, by a
peculiar, though indescribable, attitude of the leaves, whether
or not this condition of insensitiveness has supervened. Thus
the mechanical movements of the belauded sensitive plants,
such as MJzmosa,on which depended the arbitrary assumption
that ‘ordinary’ plants were insensitive, rest on a basis which
is itself extremely unreliable. For by this standard one
identical plant ought to be classed as belonging to both the
sensitive and insensitive groups, according to the time of day
at which any particular observation is made.

The fact that when the mechanical response of the leaf of
Mimosa is physically restrained, excitatory electrical response
takes place unimpeded, shows that we have a criterion by

THE ELECTRO-MOTIVE RESPONSE OF PLANTS 23

which to test the excitability of a plant, independently of
any motile indication. On applying this test, I have found
that not the so-called sensitive plants alone, but all plants
and all organs of all plants, respond to stimulation. And
from this I was led to the discovery that ordinary plants also,
in spite of current misconceptions, exhibit motile response by
mechanical contraction. The common error of regarding
these plants as insensitive has arisen from the fact that in a
radial organ, diffuse stimulation induces equal contractions
on all sides. Hence those lateral movements, dependent on
differential contraction, which are seen so conspicuously dis-
played in Mimosa, cannot take place here. But that the
organ as a whole undergoes a responsive contraction has
been demonstrated by recording the consequent induced
shortening of its length. Such longitudinal contraction is
sometimes very considerable ; for instance, in the filamentous
corona of Passiflora it may sometimes be as much as 20 per
cent. of the original length.

Having thus shown that all plants are excitable, I shall
proceed to demonstrate the fact by means of electrical
response. In studying the excitatory effect on ordinary
plants, we must bear in mind that there are two different
ways of stimulating a given point: that is to say, locally or
directly, and by transmission of excitation from a distance.
Conducting tissues are capable of stimulation in either of
these ways, but the feebly conducting must be subjected to
local excitation, since the effect of stimulus applied at a
distance cannot, in their case, reach the responding point.
Organs containing fibro-vascular elements are fairly good
conductors, and stimulus applied on them at one or two
centimetres from the point to be stimulated will thus easily
reach it. It must, however, be remembered that stimulus
becomes enfeebled by transmission through a long tract, its
effect at a great distance being negligible. Parenchymatous
tissues are bad conductors of excitation, and in order to
excite them, stimulus must therefore be applied directly. ©

Turning first to the transmitted mode of stimulation,

24 COMPARATIVE ELECTRO-PHIYSIOLOGY

we take a petiole or stem, and making suitable electrical
connections (fig. 15), apply stimulus, say by contact of hot
wire at the point marked x. After a short interval, necessary
for the excitation to traverse the intervening distance, an
electrical response is obtained, of galvanometric negativity.
It is thus seen that the electrical response of ‘ ordinary’ is of
the same sign as that of ‘sensitive’ plants, and that in both,
again, it is like that of animal tissues.

I shall next proceed to demonstrate a very important _

proposition : namely, that all effective forms of stimulation
induce an identical excitatory response of galvanometric
negativity. Any sudden change of environmental conditions
may constitute an efficient stimulus. Such are: sudden rise

Fic. 15. Method of Transmitted Stimulation

Stimulus applied to the right at x. Excitation reaches right contact first,
causing galvanometric negativity of the point.

of temperature ; any variation of pressure, whether of tension
or compression ; mechanical blows or torsional vibration ; any
prick or cut; the application of a chemical agent, such as
acid ; the application of light ; the incidence or variation of
electrical currents; and, lastly, the action of gravity. The
stimulatory action of all these agents has already been
demonstrated in my work on ‘ Plant Response,’! the excita-
tion induced being there shown to find expression in
appropriate mechanical movements. In the present volume
I shall deal more particularly with the electrical reactions
which they induce. The effects of the stimulating action of

1 Bose, Plant Response as a Means of Physiological Investigation, 1906.

a

Se eee

RE hae 8 ce tla A al tnt ls YL

THE ELECTRO-MOTIVE RESPONSE OF PLANTS 25

electrical currents, of light and of. gravity, will be taken
up in special chapters devoted to their consideration, while
here I shall demonstrate the exci-
tatory effects of the other forms
of stimulus enumerated.

We have already observed the
responsive effect which results
from the sudden application of
heat, by means of a hot wire.
The effects of various forms of
mechanical stimulation may now
be subjected to demonstration,
and first we have to observe the
effect of the stimulus resulting from
sudden tension. The specimen is
clamped securely in the middle

(fig. 16), so that when a vertical pull Fic. 16. Excitation by Sudden
Tension

is given to the upper half, that Plant securely clamped. When
half alone is subjected to a sud- suddenly pulled, tension in-

. 4 duces galvanometric nega-
denly increased tension, the lower tivity of A.

being left entirely unaffected. |

Under these circumstances, there is an electrical response,
A becoming galvanometrically negative. A is next subjected
to mechanical compression, and for this purpose the piece of
moistened cloth surrounding the specimen, and making the
electrical connection at A, is placed between the two grooved
halves of a cork. The enclosed plant tissue at A may now
be made to undergo sudden compression, by squeezing the
pieces of cork together. This gives rise to the same electrical
response as before.

This fact, that both tension and compression will give rise
to similar excitatory responses of galvanometric negativity,
may receive independent demonstration by first making an
electric connection at A with the upper side of the speci-
men (fig. 17). When the tissue at A is now suddenly bent
down, this upper side becomes convex: that is to say, it is
subjected to tension. This gives rise to the excitatory

26 COMPARATIVE ELECTRO-PHYSIOLOGY

response of negativity. The electrical connection at A is
next removed to the lower side of the specimen, at a point A’.
On now repeating the sudden flexure, A’ undergoes com-

_ Fic, 17. Excitatory Response to Tension

and Compression

pression instead of ten-
sion. The result is a
similar negative elec-
trical response.
Excitation may,
again, be produced by
means of a sudden blow
at a point. This blow
may be delivered by
means of a spring-tapper
(fig. 18), in which S is

When E is connected with the upper point A x
a sudden bending down causes tension of the spr ing proper and

A. When connection is made with a’ the theattached rod Rcarries

same flexure causes compression of A’.
Both induce galvanometric negativity.

at its end the tapping
head T. A _ projecting

rod—the lifter L—passes through SR. It is provided with
a screw-thread, by means of which its length, projecting
downwards, is regulated. By means of this the height or

ee peed)

Fic. 18. The Mechanical Tapper

intensity of the stroke may
be varied. As one of the
spokes of the cog-wheel c
is rotated past L, the spring
is lifted and released, and
T delivers a sharp tap.
The height of the lift, and
therefore the intensity of
the stroke, is measured by
a graduated scale _ not
shown in the figure. We
can increase the intensity

of this stroke through a wide range, first, by augmenting the
projecting length of the spring by a sliding catch. We may
give isolated single taps, or superpose a series in rapid
succession according as the wheel is rotated slowly or quickly.

THE ELECTRO-MOTIVE RESPONSE OF PLANTS 27

Stimulation, again, may be effected by the prick of a needle
or pin in the neighbourhood of A. Response to this also
occurs by the normal galvanometric negativity. Successive
pricks may thus give rise to successive responses.

Or the specimen may be subjected to torsional vibration.
It is here held in the middle by a clamp, and stimulus of
torsional vibration is applied (2) @)
at one end. - The stimulation a
of A makes that end gal-
vanometrically negative, the
direction of the current
outside the circuit being
towards, and in the tissue
away from, A. Vibration of Blah op is 2 or es

3 j Current of response when
B induces responsive nega- 2B is stimulated >
tivity of B (fig. 19), the
current of response being

B

Fic. 19.. The Torsional Vibrator
(a) The plant is clamped at c, between

now reversed. In the cases 7 A pee B. Pig tee"
; : . : esponses obtained by alternately
just described, it will be stimulating the two ends. Stimula-
noticed that stimulus is ap- tion of A produces upward response ;

of B gives downward response.

plied directly. This method

is, therefore, specially applicable when we wish to study the
excitability of such tissues as are not good conductors of
excitation, the method of transmitted stimulation being here,
therefore, inapplicable.

In order to observe the effect of chemical sijinailabion, the
given agent—sulphuric or hydrochloric acid—is applied at
x at ashort distance from the proximal contact. The trans-
mitted excitation is now again demonstrated by the induced
galvanometric negativity of that contact. It will thus be seen
that, whatever be the effective form of stimulus employed,
it gives rise to a definite and invariable electrical response
whose sign is always one of galvanometric negativity.

It was shown, then, in the course of this chapter that
the excitatory change in ‘sensitive’ plants is characterised
by contraction, negative turgidity variation, mechanical
depression of the leaf, and by the electricals response of

28 COMPARATIVE ELECTRO-PHYSIOLOGY

galvanometric negativity, all these effects being concomitant.
It was further shown that electrical response is independent
of the mechanical, being unimpeded in its occurrence when
the leaf is physically restrained.

The same electrical response of galvanometric negativity
is also obtained from the tissues of the so called ‘ ordinary’
plants. And these electrical responses of plant tissues, it was
further noted, are identical in sign with the corresponding
responses given by animal tissues. |

All forms of stimulus, moreover—mechanical, thermal,
photic, chemical, and electrical—induce the same excitatory
response of galvanometric negativity.

CHAPTER III

THE APPLICATION OF QUANTITATIVE STIMULUS AND
RELATION BETWEEN STIMULUS AND RESPONSE

Conditions of obtaining uniform response—Torsional vibration as a form of
stimulus—Method of block—Effective intensity of stimulus dependent on
period of vibration—Additive action of feeble stimuli—Response recorder—
Uniform electric responses—List of suitable specimens—Effect of season on
excitability—Stimulation by thermal shocks—Thermal stimulator —Second
method of confining excitation to one contact—-Increasing response to increas-
ing stimulus— Effect of fatigue—Tetanus.

A QUALITATIVE demonstration has been given in the last
chapter of the induction of galvanometric negativity in plant
tissues, in response to the excitation caused by various forms
of stimulus. This galvanometric response is thus a sign or
indication of the state of excitation ; and under normal con-
ditions it will be of uniform extent, provided only that the
stimuli are also uniform. Assuming this ideal condition to
be secured, it is clear that the physiological modifications
induced by various agents will be manifested by a corre-
sponding modification of response. The conditions essential
to such application of stimulus are, then, (1) that it should be
capable of uniform repetition ; (2) that it should be capable
of increase or decrease by definite amounts; and (3) that it
should be of such a nature as to cause no injury, by which
the excitability of the tissue might be changed in some
unknown degree. These conditions, on which the success of
the electro-physiological investigation depends, are very
difficult to meet. Chemical stimulation, for example, cannot
be uniformly repeated. Electrical stimulation, again, which
has the advantage of being easy to render quantitative, is
open to the objection that by escape of current it may induce

30 COMPARATIVE ELECTRO-PHYSIOLOGY

galvanometric disturbance. Indeed, as the response is
electrical, it is obvious that if we are to obtain unimpugnable
results, a non-electrical form of stimulus is almost a necessity.
But it is only after providing against various sources of error
that the electrical form of stimulation can be used with con-
fidence. The stimulation caused by mechanical blows can be
repeated, it is true, with uniform intensity. But the point
struck is subjected to increasing injury, and its excitability
thus undergoes an unknown variation. |
I have, however, been able to devise two different modes
of stimulation, in which all these difficulties have been —

Ss

(a) (b)

L : )

Fic. 20. The Vibratory Stimulator

Plant P is securely held byavicev. The twoends are clamped by holders
cc’. By means of handles H H’, torsional vibration may be imparted
to either the end A or end B of the plant. The end view (4) shows
how the amplitude of vibration is predetermined by means of movable
stops, Ss’.

successfully overcome. rendering the results as perfect as
possible. These are (1) torsional vibration, and (2) the
application of thermal shocks. For the obtaining of perfect
responses, it must be said here that there is still another
condition to be fulfilled. If we wish to obtain the pure
effect of stimulus at one contact, say A, special care must be
taken that excitation does not reach the second contact, B;
for otherwise, unknown effects of interference will occur.
This may, it is true, be obviated by means of the method of
relative depression or method of negative variation, so called,
to be described in a subsequent chapter. But the experi-
mental mode which I am about to describe, in which a block

THE APPLICATION OF QUANTITATIVE STIMULUS 31

is interposed between A and B, is much more perfect.
According to this arrangement, the specimen is tightly
clamped in the middle, by which device the excitation’ of
either end is practically precluded from affecting the other.
Stimulation is brought about by means of torsional
vibration. The stem or petiole is fixed, at its middle, in a
vice, V, the free ends being held in tubes, C C’, each provided

:/

AZ
Fic, 21. Complete Apparatus for Method of Block and Vibratory
Stimulation

Amplitude of vibration which determines the intensity of stimulus is
measured by the graduated circle seen to the right. Temperature is
regulated by the electric heating coil R. For experiments on action
of anzesthetics, vapour of chloroform is blown in through the side tube.

with three clamping jaws. A torsional vibration may now
be imparted to the specimen at either end by means of the
handles H and H’ (fig. 20). The amplitude of vibration
which determines the intensity of stimulus can be accurately
measured by the graduated circle, and may be predeter-
mined by means of the sliding stops s Ss... The complete
vibrational apparatus, by means of which various experi-
mental investigations may be carried out, is given in fig. 21,

32 COMPARATIVE ELECTRO-PHYSIOLOGY

Moistened cotton threads in connection with the non-polari-
sable electrodes, E E, make secure electrical contacts with A
and B. For experimenting on the effects of temperature,
there is an electrical heating coil, R, inside the chamber.
For the study of the effects of different gases, there are inlet
and outlet tubes, which enable a stream of the required gas
or vapour to be circulated through the chamber.

If the A end of the specimen be now suddenly torsioned
through a given number of degrees, a responsive electro-

motive variation takes place, which after-

wards subsides gradually. If next the
torsioned end be suddenly brought back
to the original position, a second electro-
motive response is obtained, similar to the
first. Hence, in the case of a to-and-fro
ab e ad_ vibration, the responsive effects are addi-
a tive, and we have the further advantage
7 aa 22. Influence of that the tissue at the end of the operation is
uddenness on the F im ‘ a
Efficiency of Stimu- returned to its original physical condition.
his In order that successive stimuli may
The curves a, 4, ¢, d, 2 :
are responses to be equally effective, another factor besides

vibrations of the the constancy of the amplitude of vibra-

same amplitude, , : 2
30°. Ina the vi- tion has to be considered. It is to be

bration was. Very borne in mind that the effectiveness of the

slow; in 6 it was

less slow; it was

rapid in c, and very
_ rapid in @.

stimulus in evoking response depends also
on the rapidity of the onset of the dis-

turbance. In the application of vibratory
stimulation to plants, I find the extent of response to depend
to some degree on the quickness with which the vibration
is effected. I give below records of responses to successive
stimuli, induced by vibration through the same amplitude,
which were delivered with increasing rapidity (fig. 22). It
will be noticed that an increasing quickness of vibration
increased the response, but that this reached a limit. If
we wish, then, to maintain the effective intensity of stimulus
constant, we must meet two conditions. First, the amplitude
of vibration must be kept the same. This is done by means

Se ee ee er

So EL A TIA tatty, alas Batis sb:

THE APPLICATION OF QUANTITATIVE STIMULUS 33

of the graduated circle and movable stops: and, second, the
vibration period must be uniform. This last condition is
effected by an arrangement shown in fig. 23. The torsion-
head is kept tense by means of a stretched spiral spring, s,
made of steel. From this torsion-head there projects an
elastic brass piece, B. R is a striker which can be made to
give a quick stroke to B, by the rotation of the handle. A
quick to-and-fro vibration is thus produced, by the blow
given to B, acting against the tension of the antagonistic
spring S. The amplitude of the angular vibration is at the

E oc

Fic. 23. Spring Attachment for obtaining Vibration of Uniform Rapidity

same time predetermined by means of the stops P and qQ.
The arrangements described are as used in ordinary work.
But for certain experiments on differential excitability, a
second striker, R’, may be attached to the other end of the
apparatus, and by this means the opposite contacts in con-
nection with E and E’ may be excited simultaneously.

In order to obtain responses of great amplitude, it is now
necessary to increase the amplitude of vibration. But this
may give rise to fatigue. By way of avoiding this, therefore,
it is still possible to obtain enlarged response by the additive
effect of repeated feeble stimuli. In the electrical response
of plants a sub-minimal stimulus, singly ineffective, is found

D

34 COMPARATIVE ELECTRO-PHYSIOLOGY

to become effective by the summation of several. This is
seen in fig. 24, where a single vibrational stimulus of 3°,

b

a

—-.

1 1 '
+ JOsec>

Fic. 24. Additive
Effect

(z) A single stimulus
of 3° vibration pro-
duced little or no
effect, but the same
stimulus when
rapidly superposed
thirty times pro-
duced the large
effect (4). (Leaf
stalk of turnip.)

alone ineffective, was found to evoke a
large response when repeated with rapidity
thirty times in succession.

For the delivering of such equal and
rapidly succeeding stimuli, I substitute for
the single striker R an eight-spoked wheel,
a complete rotation of which, by means of
the handle, gives rise to a definite sum-
mated effect: and a series of responses to
such summated stimulations is found to
be uniform. The galvanometer used for
these experiments is a dead-beat instru-
ment of D’Arsonval type. The sensitive-
ness of this is such that a current of 10°
ampere causes a deflection of I mm. at
a distance of I metre. For a quick and
accurate method of obtaining. records, I

devised the following form of response-recorder. The
curves are obtained directly, by tracing the excursion of the

Fic. 25. Response Recorder

galvanometer spot of light on a revolving drum (fig. 25).
This drum, on which is wrapped the paper for receiving
the record, is driven by clockwork. Different speeds of

THE APPLICATION OF QUANTITATIVE STIMULUS) 35

revolution can be given to it by adjustment of the clock-
governor, or by changing the size of the driving-wheel. The
galvanometer spot is thrown down on the drum by the
inclined mirror M. The galvanometer deflection takes place
at right angles to the motion of the paper; a stylographic
pen attached to a carrier rests on the writing surface. The
carrier slides over a rod parallel to the drum. As has been
said before, the galvanometer deflection takes place parallel
to the axis of the drum, and as long as the plant rests un-
stimulated, the pen, remaining coincident with the stationary
galvanometer spot on the revolving paper, describes a
straight line. If, on stimulation, we trace the resulting
excursion of the spot of light, by moving the carrier which
holds the pen, the rising portion of the response curve will
be obtained. The galvanometer spot will then return more
or less gradually to its original position, and that part of the
curve which is traced during this process constitutes the
recovery. The ordinate in these curves represents the
electro-motive variation, and the abscissa the time.

_ We can calibrate the value of the deflection by applying
a small known E.M.¥., say of ‘1 volt, to the circuit, and
noting the deflection which results. This gives us the value
of the ordinate. The value of the abscissa which represents
time is determined by the distance through which the
recording surface moves, in unit time. In this simple
manner accurate records are obtained. It has the additional
advantage of enabling the observer to see at once whether
the specimen is suitable for the purpose of investigation. A
large number of records might be taken by this means, in a
comparatively short time.

It is also easy to take the records photographically by
wrapping a photographic film round the recording drum.

I give in fig. 26 a series of responses taken from the
root of radish (Raphanus sativus), in which the stimuli were
applied at intervals of one minute. This shows how ex-
tremely uniform the responses may be rendered, if proper
precautions are taken, It may here be once more pointed

D2

36 COMPARATIVE ELECTRO-PHYSIOLOGY

out, that for convenience of inspection, the records in this
book have been so taken that the normal electrical responses ©
of galvanometric negativity, unless specially stated to the
contrary, are seen as up-curves, galvanometric positivity being
represented by down-curves. These excitatory responses of

Fic. 26. Photographic Record of Uniform Responses (Radish)

galvanometric negativity are obtained with all plants, and
with every organ of the plant. I give here a table containing
a list of specimens which will be found on stimulation to give
fairly large electro-motive effects, occasionally as high as
‘rt volt.

Organ Specimen

Carrot (Daucus carota)
Radish (Raphanus sativus)

Geranium (Pelargonium)
Stem : : . | Vine (V7tds vinifera)
Amaranth (Amaranthus)

Horse Chestnut (4 sceulus hippocastanum)
Turnip (Brassica napus)

Petiole . , . | Cauliflower (4rasszca oleracea)

Celery (Apium graveolens)

| Eucharis lily (2ucharis amazonica)

Peduncle. ; . | Arum lily (Azcardia africana)

Fruit ° . | Egg-plant (Solanum melongena)

THE APPLICATION OF QUANTITATIVE STIMULUS 37

These responses, being physiological, vary in intensity
with the condition of the specimen. The same plant which
gives strong electrical response in spring or summer, may
exhibit but feeble responsiveness in autumn or winter. Again,
we shall see in a subsequent chapter that any agent which
depresses physiological activity will also depress the electri-
cal response; and, lastly, when the specimen is killed, the
normal response is abolished.

I shall next describe a second and equally perfect method
of stimulation, by means, namely, of thermal shocks. We
have seen that a sudden thermal variation acts as an efficient
stimulus. I have also shown in my ‘Plant Response’ that
thermal radiation acts as a stimulating agent, in inducing
excitatory contraction. Hence, if a tissue be surrounded by
a platinum wire, through which an electrical heating-current
can be sent, the enclosed tissue will be subjected to a sudden
variation of temperature, and also to the thermal radiation
proceeding from the heated wire. Now if in successive
experiments the duration and intensity of the current
flowing through the wire be maintained constant, the
stimuli also will thereby be rendered constant. The thermal
stimulator, as already said, surrounds the specimen, but is
not in actual contact with it. This is to prevent any injury
to the tissue, by scorching. The current is so adjusted as to
make the platinum wire red-hot and this heating-current is
closed for about half a second at a time. Should larger
response be desired, it-can be obtained by the summated
effect of a number of such shocks, or the thermal stimulator
may be put in direct contact with the tissue, if care be
taken that the rise of temperature is not so great as to
injure it. :

The difficulty of ensuring similarity of duration to each
individual shock is overcome by the use of a balanced key
actuated by a metronome (fig. 27). A second rod is attached
at right angles to the vibrating rod of the metronome, and
carries a bent piece of brass in the form of two prongs.
During the course of each vibration these prongs dip into

38 COMPARATIVE ELECTRO-PHYSIOLOGY

two cups of mercury, thus closing the electrical circuit for a
brief and definite time. When a second press-key, not shown
in the figure, is open, the circuit is incomplete, and there
is no thermal stimulation. The observer then presses this
key, and counts, say,
five strokes of the
metronome,. after

is again opened. In
this way, the sum-
mated effect is ob-
tained, of five equal
thermal shocks. This
Fic. 27. Stimulation by Thermal Shocks process is repeated
as often as desired,
at intervals of, say, one minute, by which time the tissue is
generally found to have completely recovered from its ex-
citatory electrical variation. :

In the case of the experimental arrangements of which
the diagram is given in fig. 27, stimulation is confined to one
contact of the responding circuit. The method by which
excitation was here prevented from reaching the distal
contact is important. I shall, in the course of the present
work, show that the parenchymatous tissue of the lamina of
a leaf or leaflet is a bad conductor of excitation. Hence if
the second contact of the circuit be made with this tissue,
the stimulus does not reach the distal point. It is true that
a certain small proportion might conceivably be conducted
through the attenuated fibro-vascular channel of the midrib.
But even so remote a contingency is provided against by a
transverse cut across the midrib on the hither side of the
contact.

The arrangements, then, being made in the manner de-
scribed, the tissue may be subjected to the action of successive
uniform stimuli. How regular the resulting responses may be
rendered will be seen from fig. 28, in which is given a series
of responses obtained from the petiole of a fern (fig, 28)

which the press-key ©

8 eee

THE APPLICATION OF QUANTITATIVE STIMULUS 39

under successive thermal shocks, imparted at intervals of one
minute. We have hitherto studied the responses caused by
uniform stimuli. We shall next observe the increase of
responsive effects brought about by increase of stimulus. In

Fic, 28. Photographic Record of Uniform Response in Petiole of Fern
to transmitted excitation

animal tissues it is found, speaking generally, that increasing
stimuli induce increasing effects, but that this process has a
limit ; and in plant tissues the same is found to be the case.
In order to obtain effects of the simplest type, not compli-
cated by any secondary phenomena,
it is necessary to choose specimens
which exhibit little fatigue. In the
first of these the stimulus was ap-
plied by means of the spring-tapper.
The first stimulus was given by a
fall of the striking-lever from the
height h; the second from 2h; and

; Fic.
the third from 3h. The response- ee
F Taps of increasing strength
curves (fig. 29) clearly show the in- 1:2:3:4 producing in-

crease of effect due to this increasing acheter eaiinat ees
stimulus.

In the second series, the stimulus applied was vibrational,
and increased from 2°5° to 12°5° by steps of 2°5° at a time.
Fig. 30 shows how the intensity of response tends under
these conditions to approach a limit. The following table
gives the absolute values of the responsive electro-motive
variations. ;

40 COMPARATIVE ELECTRO-PHYSIOLOGY

TABLE SHOWING THE INCREASED ELECTRO-MOTIVE VARIATION INDUCED
BY INCREASING STIMULUS.

Angle of vibration Induced E.M.F.
rg 044 volt.
5° "O75
7:5° "090 55
10° E0045
12°5° "106 ,,

In such normal cases an inerease of response is always
induced with increasing stimulation. A diminution of
response may, however, sometimes appear, with increasing

°

23° 5° 74° 10 12°

Fic. 30. Increased Response with Increasing Vibrational Stimuli
(Cauliflower-stalk)

Vertical line = +1 volt. Stimuli applied at intervals of three minutes.

stimulus. But this is merely a secondary effect, due to
fatigue. The following records (fig. 31) will show in what
manner this may be brought about. They were taken with
specimens of the petiole of cauliflower, in one of which (A)
fatigue was absent, while in the other (B) it was present. In
the first specimen the recovery from each stimulus was

THE APPLICATION OF QUANTITATIVE STIMULUS 4qI

complete. Every response in this series starts, therefore,
from a position of equilibrium, and the height of each single
response increases with increasing stimulation. In the
second case, however, the molecular derangement consequent
on stimulation is not completely removed after any single

40° so

FIG. 31. Responses to Increasing Stimulus obtained with Two Specimens
of Stalk of Cauliflower

In (a) recovery is complete, in (4) it is incomplete.

stimulus of the series. That the recovery is only partial is
seen in the gradual shifting of the base-line upwards. In
the former case the base-liné had been horizontal, represent-
ing a condition of complete equilibrium. Now, however, the
base-line, or line of modified equilibrium, is tilted upwards.
Thus, even here, if we measure the heights of successive

42 COMPARATIVE ELECTRO-PHYSIOLOGY

responses from the line of absolute equilibrium, they will be
found to increase with increasing stimulus. Ordinarily, how-
ever, no allowance is made for the shifting of the base-line,
the responses being measured instead from the -place of its
previous recovery, or point of modified equilibrium. In this
way these responses undergo an apparent diminution.

I have occasionally observed another curious phenomenon
in connection with the subject of response under increasing

stimulus. During the gradual increase of the stimulus from —

a low value, there would at first be no response. But on
reaching a certain critical value, a response would suddenly
be evoked which was maximum—that is to say, would not be
exceeded, even when the stimulus was further increased.
We have here a parallel case to what is known in animal
physiology as the ‘all or none’ principle. In the case of
cardiac muscle, for example, there is a certain minimal
intensity of stimulus which is effective in inducing response.
‘But further increase of stimulation causes no concomitant
increase of effect.

When a tissue is subjected to rapidly succeeding stimuli,
the excitatory effects are superposed upon each other. In

muscle, for example, the contractile effect of the second

stimulus is added to that of the first, before that has time to
disappear. The result is a summation of effects more or less
complete ; and these attain a maximum. With moderate
frequency of stimulation, such a tetanic effect is incomplete,
tending to become more and more complete, with the
progressive increase of frequency (fig. 52). I have obtained
results in every way similar to these, with the mechanical
response of ordinary plants. In fig. 33 is given a photo-
graphic record of tetanus, taken from the longitudinal motile
responses of the style of Datura alba. Similar tetanic effects
are also obtained in the electric response of plants, of which
the records seen in fig. 34 form an example.

The difficulties in the quantitative observation of electrical
response have thus been overcome by the employment of two
different methods of stimulation—namely, torsional vibration,
and stimulation by thermal shocks. In the case of the

EE -_ _

THE APPLICATION OF QUANTITATIVE STIMULUS 43

former, the intensity of stimulation was seen to depend on
the amplitude of vibration. In the latter, stimulus intensity
was determined by that of the thermal variation, which again
was regulated by the intensity and duration of the electrical
heating-current. It was also seen to be important that the

Fic. 32. Genesis of Tetanus in Muscle

Record to left shows incomplete tetanus, with moderate frequency of
stimulation. Record to right shows tetanus more complete, with
greater frequency of stimulation (Brodie).

excitation of one contact should be prevented from reaching
the other, and this was provided against in two different
ways. In the first of these, a physical block was interposed
between the two contacts. In the second, the distal contact
was made with the non-conducting tissue of a lateral leaf.

&
a es (b)
Fic. 33. Photographic Record Fic. 34. Fusion of Effect ot
of Genesis of Tetanus in Rapidly Succeeding Stimuli

Mechanical KResponse of

i scle ; (4) i t.
Plants (Style of Datura alba) wi stg aati | let tin

When these precautions were observed, it was found that
uniform stimuli induced uniform response. Stimuli which
were singly ineffective, were found on repetition to become
effective. A tetanic effect was obtained by the rapid super-
position of stimuli.

CHAPTER IV

OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE
IN PLANTS

Response - curve showing general time - relations — Instantaneous mechanical
stimulation by electro-magnetic release—Arrangement of the rheotome—
Tabular statement of results of rheotomic observations—Rhythmic multiple
responses.

IN taking records of the electric response of plants, a
galvanometer of fairly high sensitiveness is required. One
which gives a deflection of I mm. at a scale-distance of
I-metre, under a current of 10°° ampere is found, as already
said, to be suitable for practical purposes. I used for most of
the experiments in this work a dead-beat galvanometer of
the D’Arsonval type. The natural period of swing in these
galvanometers is somewhat long, however, and the response-
record thus lags behind the electro-motive changes induced
by stimulus.
In order, therefore, to investigate the time-relations of a
growing electro-motive reaction in a plant, after the recep-
tion of the stimulating shock, it is necessary to employ a
rheotomic mode of investigation. An account of this, and
of the results obtained, will be given in the course of the
present chapter. The after-effect of stimulus is found to
be somewhat persistent and to vary in duration in different
specimens. In some cases, recovery is complete in a very
short time; in others it takes very much longer. For the
purpose of forming a general idea of this difference two
response-records are given here, one of which was taken from
a stem of the quickly-reacting Amaranth (fig. 35), and the
other from the more sluggish Colocasza. It will be seen that

oe a ee

OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE 45

while in the first of these the recovery was completed in
fifteen seconds, in the latter, even after the lapse of forty
seconds, it was still far from complete. Indeed, in this case
it was not altogether accomplished till after several minutes.
The character of the tissue again is an important factor in
determining the time required for recovery. Thus it will be
shown that in a vegetable structure functioning as nerve,
recovery is much more rapid than in ordinary tissue. The
physiological modification induced by season, moreover, is
seen in the fact that response and recovery are quicker in

Fic. 35- Response of (a) quickly reacting Amaranth ;
(4) of sluggish Colocasia

summer than in winter. This difference is demonstrated by
mechanical response also, for in that of the leaf of Mzmosa,
as already stated, it is found that, whereas in summer the
period is six minutes, in winter it is as long as eighteen, or
three times as much.

In the study of the time-relations of response, we may
overcome the difficulty of the galvanometer-inertia by using,
as already said, some modification of the rheotome, originally
devised by Bernstein. The relative values of electrical
variation induced at various periods after the impact of
the excitatory shock may here be found by making brief

46 COMPARATIVE ELECTRO-PHYSIOLOGY

galvanometric contacts of equal period at the required
intervals. : 3

The difficulty in this investigation lies in the instan-
taneous application of a stimulus at a definite moment, and
in the successful adjustment of the subsequent interval at
which the resulting responsive current is to be led to the
gsalvanometer and recorded. Instantaneous stimulation can,
it is true, be effected by electrical shock. But polarisation,
and other disturbances caused by it, might give rise to
unknown variations in the responsive effect. Hence, it is
advisable when recording the electrical response to employ,
if possible, a non-electrical form of stimulus. And it is only
after the successful employment of such an unimpeachable
method, that we can feel any confidence in the use, after due
precautions have been taken, of the electrical stimulus itself,
as will be described ina later chapter. Another obstacle to
be overcome is the elimination of the unknown element of
time required for transmission when stimulus is applied at
a distance from the responding point. This uncertainty
can only be removed by applying the stimulus directly on
the responding point itself. All these difficulties I have
successfully met by employing the mechanical form of
stimulation, which I am now about to describe. We have
seen that a stimulus of definite intensity may be imparted
by a quick torsional vibration of either twist or un-twist, or
of the one followed by the other. The intensity of this
stimulus, as we saw, depends on the angle of torsion, and
remains constant as long as that angle is maintained the
same. For this-purpose I use the vibrational apparatus
already described, successive excitations being produced on
one side only, say the right. The torsion-head is set by
pulling a vertical thread by which the index is made to rest
against the stop P. This pull of the vertical thread is
against the antagonistic action of the spiral spring S (fig. 36).
During the process of the setting, which is carried out slowly,
there is a slight excitatory disturbance. But this is allowed
to subside, The vertical thread by which the torsion-head

OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE 47

is ‘set,’ is kept pulled up by an electro-magnetic arrangement
shown in fig. 37, where the electro-magnet is seen to hold

a soft iron armature at the
end of the thread. At the
moment when stimulation is
to be effected the current
which energises the electro-
magnet is interrupted by an
automatic arrangement which
will be described later. By
the break of the current the
armature is released and a
semi-vibration of the torsion-

Fic. 36. Arrangement for In-
stantaneous Stimulation
Torsion-head set by string against stop Q
is suddenly let go by electro-magnetic

release seen in fig. 37.

head is suddenly produced, the amplitude of which has been
predetermined by suitable adjustment of the stop P. Suc-

Fic. 37. General arrangement for Rheotomic Observation

A, B, striking rods attached to revolving rheotomic disc; K,, key for
electro-magnetic release of torsional stimulator ; K,, for unshunting the
galvanometer, G; E, electro-magnet with its armature by which the
vibration-head, Vv, is set at a definite torsion-angle; N,, N,, non-
polarisable electrodes making electric contacts with specimen ;?c, com-

pensator.

cessive stimuli of equal intensity may thus be applied on
the experimental tissue at whatever time may be desired.

48 COMPARATIVE ELECTRO-PHYSIOLOGY

The next point is to secure an automatic arrangement
by which galvanometric connections can be made with the
experimental tissue, for a short period of time, say, ‘o1 of a
second. In order to study the growing electro-motive changes,
these short-lived contacts are to be effected in successive
experiments at gradually increasing intervals of ‘oI, ‘02, ‘03
seconds, and so on after stimulation. It should be remem-
bered in connection with this subject that the reactions in
plant tissues are much more sluggish than those in the.
animal. The time-intervals here provided for, therefore, are
even smaller than would have been strictly necessary,

The general plan of the apparatus for carrying out this
investigation is seen in fig. 37. The revolving rheotome-disc —
carries two striking-bars, A and B, of which A is fixed, and
B capable of an increasing angular adjustment behind A.
The bar A, striking against the key K,, interrupts the electro-
magnetic circuit E, thus causing stimulation. All this time,
the galvanometer G is short-circuited by key K,, and it is
-only when the striker B unshunts the galvanometer, by
striking against K,, that the responsive current can act on the
galvanometer. C is the compensating potentiometer, the
object of which will be described presently. The rheotome-
disc is rotated by means of a motor, provided with a perfect
governor, the period of asingle rotation being adjusted to
one second. The circumference of the disc is 100 cm. One
centimetre of this circumference therefore represents an in-
terval of time of ‘o1 second. The breadth of the striker B is
also 1 cm. and it will therefore pass over a given point in the
course of ‘or second. These striking-rods attached to the
disc, impinge, as already said, against two electrical keys K,,
and kK, which are adjusted along the same radius of the disc.
K, is a balanced key, one end of which carries a two-pronged
brass fork, both prongs of which are normally dipped in cups
of mercury, thus completing the particular electric circuit.
By the blow given by the striker A on a projecting rod
attached to K,, this fork is tilted upwards, and the circuit is
broken. The striker B then impinges on the second key, K,.

OBSERVATIGN BY RHEOTOME ON ELECTRIC RESPONSE 49

Here, the prong is kept down by a spring S, the circuit being
re-made, as soon as the breadth of the striker B has passed
over the projecting rod—that is to say, in ‘oI second (fig. 38).
The interval of time be-
tween the actions on the
two keys, by which the
two different electrical cir-
cuits are broken in suc-
cession, can be gradually
increased, by increasing
the angle between A and B.

The key K,, as already
said, controls the electro-
magnet, which, on _ its

release, instantaneously
effects. the mechanical 7

“stimulation of the tissue. *'* 38. en Sian £3
The rotation of the rheo- K,, actuated by rod A, K, by B.

tome-disc does not at once

become uniform, on the Starting of the motor, but attains
this when one revolution has been completed. Therefore
the experimental observations are not made till the speed
has become steady. By pressing the key K, during the first
revolution (fig. 37), the break-action of A on K, is postponed.
K, is then opened, and during the next revolution, stimulation
is effected.

In order to obtain the galvanometric effect of excita-
tion at definite short intervals of time after the stimulus
has been applied, the galvanometer short circuit, as stated
before, is removed at those definite intervals. The adjust-
ment of the striking-rod: B, in relation to A, enables us to
open the short circuit, for ‘ol of a second, at increasing
intervals. When the rod B is at a distance of I cm. from 4,
the short circuit is removed after ‘ol second, when at 2 cm.
after ‘02 second, and so on. Thus, in the arrangement just
described, the galvanometer is short-circuited, except at those
definite intervals required for observation. In a second

E

50 COMPARATIVE ELECTRO-PHYSIOLOGY

arrangement, the galvanometer is kept open, and closed only
during ‘or of a second at the required increasing intervals of
time. Fe .

There may be a pre-existing difference of potential
in the plant, as between the two points of galvanometric
contact, N, and N, In order that this may not be a source
of disturbance, a compensating potentiometer arrangement,
C, is employed. The slider of the compensator is so adjusted
that it exactly balances the resting difference of potential
in the specimen. Under these circumstances, neither make
nor break of the galvanometer occasions any deflection. And
this balance is readjusted for each experiment of the series.

I give below two tables which. summarise rheotomic
observations on specimens of the petiole of cauliflower. By
successive intervals of a given length should always be under-
stood the mean interval: that is to say, the period between-the
application of stimulus and the mid-point in the removal of
the short circuit. Thus, for the mean interval of ‘02 of a
second, the middle of the .striking-rod 8B, whose breadth is
I cm., placed at a distance of 2 cm. from A. The galvano-
meter is therefore acted on for ‘oI of a second, throughout
‘the period from ‘o15 to ‘025 of a second, after stimulation.
In the first two sets of results here given, the observations will
-be seen to have been taken at the somewhat long intervals
of ‘1 of asecond. The stimulus applied in these cases was
moderate. In the case of a third specimen, the observations
on which will be given subsequently, the results were recorded
at intervals of ‘o1 of a second.

SPECIMEN I SPECIMEN II
Mean interval Galvanometric Mean interval Galvanometric .-
after excitaton deflection after excitation deflection
‘I second 70 divisions — “I second 26 divisions
‘2 ” 100 29 | 2 ” ifele) 95
3 se 310 $9 ey 7° ”
"4 iy 220 99 “4 ” 64 9
Hh sas 104 ee ae 56 2
I°O ” 7° re) i ie) ne) 42 $9
2°0 29 15 re) 2°O 55 24 <7

OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE 51

It will be seen from the observations made on the first of
these two specimens that the maximum electro-motive effect
was attained in three-tenths of a second after excitation. In
the second case, the maximum was reached in two-tenths
of a second. The curve given in fig. 39 shows how quickly
the electro-motive variation attains a maximum, and how
rapid is its decline after reaching this point. There apppears
to be practically no latent period, the induction of the electro-
motive effect being apparently immediate. This will be
made evident by the results given in the next series.

Fic. 39. Curve showing Rise and Fall of Responsive E.M. Change,
under moderate stimulation

Ordinate represents galvanometric deflection ; abscissa, time. Large
division = 1 second. (Petiole of cauliflower. )

For the next experiment, I took the stem of Amaranth,
which I find to be more excitable and more quickly reacting -
than the petiole of cauliflower. The intensity of stimulus
was here greater than in the last case. I may state now what
will be demonstrated in full later, that a strong stimulus
often gives rise, not to a single, but to multiple responses.
I had previously detected these multiple responses by means
of both mechanical and galvanometric indications, and found
them to have periodicities varying from some I5 seconds to
several minutes. . Indeed, had they been much*quicker than
they were, they could not have been detected, owing to the

E2

§2 COMPARATIVE ELECTRO-PHYSIOLOGY

inertia of the motile leaflets or of the galvanometer needle.
By the employment of the rheotomic method, however, I was
able to detect multiple responses having periodicities of the
order of one-tenth or so of a second. All the experiments
carried out on Amaranth gave two or three waves of electro-
motive variation, the character of which will be understood
from the following table and curve (fig. 40).

Mean interval after excitation | Galvanometric deflection

|

‘OI second 63 divisions

"05 29 77 29 ‘ |
7S eee | 82 55 |
“20 Fs; | 68 -
"30 | 765 |
*40 rr 75 re) |
60s; | ce ea |
70 55 86 oe) |
80, | OF 555 |

It will here be seen that even after so short an interval as
‘ol of a second, a considerable electromotive change had

Fic. 40. Response Curve from Rheotomic Observation in Stem of
Amaranth under strong stimulation

Note occurrence of multiple response. Large division of abscissa = *1 second.

already been induced. The first maximum occurred after
y5, the second after *3, and the third after ‘6 of a second.

Nea

ce eae ee. ee ee eae ee ee

OBSERVATION BY RHEOTOME ON ELECTRIC RESPONSE 53

We thus see that there is a rhythm in these multiple
responses, the successive maxima being here found to
occur at periods which constitute multiples of ‘15 second.
The third of these rhythms may be presumed to be missing,
owing to the fact that no observation was taken at ‘45 second,
as, at the time when these experiments were carried out,
I was unaware of the existence of such rhythmicities. It was
by the curves plotted from these data that my attention was
first drawn to their occurrence.

It will thus be seen that the electro-motive variation is
initiated practically simultaneously with the impact of
stimulus on the organ. With moderate stimulus, the maxi-
mum variation is reached within two-tenths of a second, or
this period may be made still shorter by the employment
either of a more quickly reacting tissue, or of a greater

_intensity of stimulus. Strong stimulation is apt to give rise

to rhythmic multiple responses.

CHAPTER'..V

THE ELECTRICAL INDICATIONS OF POSITIVE AND
-NEGATIVE TURGIDITY VARIATIONS

Motile responses of opposite signs, characteristic of positive and negative
turgidity-variations—Indirect hydrostatic effect of stimulus causes expansion
and erection of leaf—Dositive and negative work—Wave of increased hydro-
static tension transmitted with relatively greater velocity than wave of true
excitation — Method of separating hydro-positive and excitatory effects—In-
. direct effect of stimulus, causing positive turgidity-variation’ induces galvano-
‘metric positivity—Antagonistic elements in the electrical response —Separation
of hydro-positive from true excitatory effect by means of physiological block.

~HAVING now described that fundamental electrical response
of galvanometric negativity which is characteristic of excita-
tion, I shall next proceed to deal with an opposite type
of response—namely, that of galvanometric positivity. The
combination of these two factors, in varying degrees of each,
in the electrical response of plants, has been a source in the
past of the greatest perplexity, leading investigators to con-
tradictory results. And it can only be by disentangling them,
and by ascertaining the conditions under which each invari-
ably occurs, that precision will be arrived at in the field of
electrical response.

We have seen that excitation of the pulvinus of Mimosa
induces negative turgidity-variation, with fall of the leaf, and
galvanometric negativity. What, then, would be the out-
ward expression of an increase of turgidity—that is to say, of
the positive turgidity-variation ?

With regard, first, to the mechanical expression, we may
subject the question to an experimental test. The cut end
of a branch of Mimosa, bearing leaves, is fixed watertight
in one end of a U-tube, filled with water, and the other

POSITIYE AND NEGATIVE TURGIDITY-VARIATIONS 55

end is connected alternately with a vacuum and a force
pump, by means of which a diminution or increase of hydro-
static pressure may be induced at will. In this way it is
possible to suck water away from, or force it into, the plant
and its organs, thus producing negative and positive turgidity-
variations at will. When turgidity is thus diminished the
indicating leaf is seen to fall. This is what happens also
under the ordinary negative turgidity-variation induced by
excitation. When turgidity is increased, on the other hand,
the leaf is erected (fig. 41). In the case of the negative
variation of turgidity, the pulvinus as a whole loses water,

10° 20° 30° 40° 50’ 60’ 70’ 80° 90°

Fic. 41. Artificial Hydraulic Response of AZimosa

The plant was subjected to diminished pressure up to a, and to normal
pressure to 4, after which the pressure was increased. The effect
of diminished pressure, in the depression of the leaf, continues for a
while. The ordinate represents movement of tip of leaf in cm.,
abscissa represents time.

but more from the lower and more excitable half than
from the upper. In the case of the positive turgidity-
variation, also, it is again the more excitable lower half
which absorbs the greater quantity of water. Thus, in Mzmosa,
and in Bzophytum, the mechanical indication of increased
turgidity is an erection of the leaf or leaflet. The
characteristic electrical indication of this will be observed
presently.

It has already been mentioned that the direct application
of stimulus at a point causes a negative turgidity-variation
of that point. We shall now see whether, under any

56 COMPARATIVE ELECTRO-PHYSIOLOGY

circumstances, stimulus will induce a positive turgidity-
variation. If we now apply moderate stimulus on the
stem of J/zmosa, at a certain distance below the pulvinus, an
excitatory expulsion of water will occur at the point directly
stimulated. Such an expulsion of water will then cause, it
is clear, a hydrostatic disturbance of increased pressure.
And this hydro-mechanical disturbance will be transmitted
with relatively great velocity. Now such an increase of
pressure, as we have seen, causes an increase of turgidity at
the puivinus, in consequence of
which the leaf ought to be erected.
And although this hydrostatic
disturbance is transmitted very
quickly, yet a certain time is con-
sumed in the process of forcing
water into the pulvinus, by which
to bring about the erection of the
leaf. After the passage of the
hydrostatic wave, there follows
Fic. 42. Experimental Arrange- the wave of true excitation, passing
sea arn ares from cell to cell, and inducing the
given to Direct and In- Characteristic reaction, of negative
eee eee by Leaf of tyroidity - variation. And when
Thermal stimulator at s produces this excitatory wave reaches the
trey smlstion my gene pulvinus, the previous erectile
stimulation, at a distant point, Movement should give place ~ to
Sys eterna to indirect effect excitatory depression, or fall of
the leaf. In fig. 42 are seen the

arrangements for an ptoknehiueiit on Mimosa by which these
inductions may be verified. Moderate thermal stimulus is
applied at S, at a certain distance below the indicating leaf.
This latter is attached by a thread to a writing-lever, which
traces the response-record on a smoked revolving drum.
When the stimulus is applied at a point S very near the
pulvinus, the response takes place by a negative turgidity-
variation, with a concomitant fall of the leaf, seen in fig. 43
(a) as an up-curve. When a moderate stimulus is applied

a lla le i

POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 57

at a greater distance S,,, the hydrostatic wave causing the
positive turgidity-variation brings about an erectile twitch.
This is followed by a responsive fall, when the true excitation
reaches the organ (fig. 43, 0).

It has thus been shown that by separating the responding
point from the point stimulated, or the receptive point, it is
possible to discriminate two
different effects which are both
brought about by stimulus. It
is most important, moreover, to
distinguish between these two
factors : namely, the direct effect
of stimulus causing contraction,
and its indirect effect, causing
expansion. We have seen that
direct excitation and transmitted
excitation both induce contrac-
tion, negative turgidity-variation
and fall of the leaf. Unfor-
tunately, in animal physiology, Fic. 43. Mechanical Responses

it has been customary to apply Reet eaaesmesa
eee (a) record of responsive fall when
the term zuzdirect to that form stimulus applied near the re-
of stimulation which is applied sponding organ; (4) response
. : * when stimulus is applied on
at a distance. And it has not same side, but at greater dis-
. . tance, s,,. A preliminary erectile
been noticed that such stimulus seuliocie ins bere: fallowed.” bey
is capable of inducing diametri- the true excitatory depression.
: ' This is due to the indirect effect
cally opposite results, according first transmitted being succeeded
as the true excitatory effect by the direct. Had the stimulus
applied been feebler, or more
reaches, or does not reach, the distant, there would have been
responding organ. When the ons first, or indirect erectile

intervening tissue is highly
conducting, the transmitted effect induces exactly the same
result as if stimulus were applied directly. But we shall
see that when the intervening tissue is non-conducting or
feebly conducting, true excitation is not transmitted, and the
effect which makes its appearance at the responding point
is then due to increase of hydrostatic tension, causing positive

58 COMPARATIVE ELECTRO-PHYSIOLOGY

turgidity-variation, with the concomitant effect of expansion,
and, in the case of J/zmosa, of erection of the leaf. This
latter effect of positive turgidity-variation and expansion,
I shall therefore distinguish as the INDIRECT EFFECT of
stimulus, in contradistinction to the term INDIRECT STIMU-
LATION, as it is generally used. The last-named, however,
I shall myself always refer to under the title of TRANS-
MITTED STIMULATION. If the intervening tissue be of

Fic. 44. Mechanical Response of Biophy/um to Thermal Stimulation

Stimulus was applied at some distance from the responding leaflet. And
the preliminary erectile twitch is due to the prior arrival of the
hydrostatic disturbance. Thick dot represents moment of application
of stimulus.

moderate conducting power, we shall, as in the case of the
experiments on J/zmosa, obtain a preliminary erectile twitch,
due to the indirect effect of stimulus, followed by a fall, in
consequence of the transmission of the true excitatory effect.
In fig. 44 is seen this twofold expression of the indirect
and transmitted effects of stimulus, given by the leaflet of
Biophytum.

These two waves, then, of increased hydrostatic tension

ah a hh ll al ee ee
’

“Me as tare,

POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 59

and of true excitation, induce, as we have now seen, opposite
responsive reactions. But of these, that due to true excita-
tion is, generally. speaking, greatly predominant. Hence,
when these two waves reach the responding organ in close
succession, as is the case when the point of stimulation is
very near, the excitatory effect masks the hydrostatic. In
order, then; to ‘separate them, we may employ various
methods. First, in the case of highly conducting tissues, the
stimulus must be applied at a sufficient distance to make the
slow excitatory wave lag adequately behind the quickly
travelling hydrostatic wave. Or we may choose a direction
of transmission of excitation which will be relatively slow.
Thus I have found that transmission across a stem, for
example, is very much slower than along its length. Hence,
on applying moderate stimulus at S, (fig. 42) ata point on the
stem diametrically opposite the pulvinus, of the given leaf, it
is found that the excitation reaches the pulvinus only after a
measurable interval, the hydrostatic effect inducing erectile
response much earlier. Thus in a given experiment, whose
record was taken on a fast-moving drum (fig. 45), the erectile
response took place ‘6 second after the application of stimu-
lus, whereas the true excitatory fall did not occur till 3:45
seconds had elapsed—that is to say, 2°85 seconds later. It is
to be borne in mind that’ a certain interval of time passes,
even after the arrival of the respective waves, before the tur-
gidity-variation is able to give rise to the motile indication.
Let us next examine the results at the responding tissue
of the indirect effect of stimulus. The distant receptive point
contracts on stimulation, and sends to the responding organ
a wave of increased hydrostatic tension. This, as we have
seen, forces water in, and expands the tissue.. Work is thus
done ox the tissue which increases its store of energy. In
this the indirect is unlike the typical direct effect of stimulus.
For the latter causes the impulsive fall of the leaf, which
represents work done dy the tissue, and an expenditure of
energy. We must, therefore, recognise two distinct respon-
sive effects, according as the work done is fosétive—done on

60 COMPARATIVE ELECTRO-PHYSIOLOGY

the tissue—or negative: that is to say, done by the tissue.
The outward manifestations of these two processes are
respectively expansion and contraction. The positive, as we
shall see, is not the result of hydrostatic disturbance as such,
but is the effect of energy transmitted hydraulically.

The indirect effect of stimulus, then, gives rise to positive
turgidity-variation, and increases the internal or -potential

Fic. 45. Record of Response of A/zmosa Leaf, taken on a fast-
moving drum

Stimulus applied at moment @, on point of stem diametrically opposite to
responding leaf. Hydro-positive erectile response occurs at 4, *6 second
after application of stimulus. True excitatory response of fall takes
place at c, 3°45 seconds after application of stimulus. Time-marks
represent fifths of a second.

energy of the organ. A positive turgidity-variation is thus
concomitant with an increase of internal energy and
a negative turgidity-variation with the reverse. In observing
the mechanical response, we saw that the expression of
positive turgidity-variation, due to the indirect effect of
stimulus, consisted of an erection, and was therefore of
opposite sign to that of the negative turgidity-variation,
caused by true excitation, and expressing itself in a fall, of

POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 61

the leaf. We shall now see whether a similar difference
exists between the electrical expressions of the positive and
negative turgidity-variations.

In carrying out this experiment, I took a specimen of
Biophytum and applied stimulus at a distance from the par-
ticular leaflet whose responses were to be observed, arranging,
at the same time, for a simultaneous record of the mechanical
and electrical responses. It will be seen from fig. 46 that the
preliminary erectile twitch, due to the positive turgidity-
variation, has, as its concomitant, galvanometric positivity.
And this is followed in both records by its opposite: namely,
the contractile fall and the galvanometric negativity of true
excitation.

It will thus be seen that the increase of internal energy, with
its positive turgidity-variation, has, as its electrical expression,
galvanometric positivity. Besides this, the mere physical
movement of water in
the tissue gives rise to
a certain electrical varia-
tion of positivity, and
this can still be detected,
even after the tissue is
killed. The question of
how to discriminate what
proportion of the electro-
positivity was due to this
mere water - movement,
and what to the increase
of turgidity, associated
with the. increase of in-

Fic. 46. The Abnormal Positive preceding
the Normal Negative in Mechanical and
ternal energy, I at first Electrical Responses in Biophytuni
found it very difficult to * represents the moment of application of
; , stimulus. The upper is the mechanical
decide. But I ultimately and the lower the’ electrical record.

The records downward indicate erection

succeeded in doing this of the leaf or galvanometric positivity.

by bringing a plant to
a condition just short of death, and thus abolishing its
true excitatory reaction. In this condition, the responsive

62 COMPARATIVE ELECTRO-PHYSIOLOGY

indication was found to be one of considerable electro-
positivity. On finally killing the-plant, however, the positive
change due to water-movement was found to represent so
insignificant a proportion of the whole as to be negligible,

In order to exhibit the electrical expression of the
excitatory and hydro-positive effects of stimulation, in
ordinary plants, I took a petiole of cauliflower and made
one connection, the proximal,
with a point on it, and the other
with an indifferent point on the
surface of the lamina. In order
to obtain the unmistakable hydro-
static effect, the petiole was sud-
denly squeezed, at a distance of
6.cm. from the proximal contact,
and this gave rise, as will be seen
(fig. 47, a), to a positive response,
represented downwards. This
was repeated once more, and the
same effect observed. I next
applied thermal stimulus at a dis-
tance of 4 cm. from the respond-
ing point. In this case hydro-
static and excitatory disturbances

reached the contact, the hydro-

PIG, ty vical Reponse of Peticle Static shortly followed by the

of Cauliflower excitatory, as in the case of the

a, hydro-positive ; 2, di-phasic; experiment on Mimosa. This

c, excitatory negative responses. : :

is seen in the record, as a di-

phasic response, the hydrostatic positive being followed by
the excitatory negative (fig. 47, 0).

Reference has already been made to the observation of
Burdon Sanderson, that in the lamina of the Dzonea leaf the
immediate response was one of galvanometric positivity. Mis-
taking this for the true excitatory effect, he concluded that
the response of the plant was of opposite sign to that of the

POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 63

animal. From the experiment just described, however, it will
be seen that the effect observed by him was in reality due,
not to true excitation, but to the hydrostatic disturbance, or
indirect effect of stimulus.

In the next record (fig. 47, ¢) we see the effect of stimulus
applied nearer: that is to say, at a distance of 2 cm. from the
proximal contact. Owing to the propinquity of the point of
stimulation, the two disturbances are not now sufficiently
separated, and the excitatory negative reaction completely
masks the hydrostatic positive effect.

It is thus seen that, as has been said, one method of
exhibiting these two effects separately is to apply stimulus
at a point so distant from the proximal contact that there
is an interval between the arrival of the two waves of hydro-
static and excitatory disturbance respectively. It is obvious,
then, that if the tissue under experiment be a good con-
ductor of excitation, we must place the point of stimulation
at a long distance from the first electrode, in order that
the effect of excitation may lag sufficiently behind the
hydrostatic wave. Similarly, in a bad conductor of excita-—
tion, it will be the indirect effect alone which will reach
the proximal contact, unless the stimulus applied be very
near, and very strong.

In order to distinguish these two opposite effects from
each other, I shall in future refer to that hydrostatic
effect which causes expansion and galvanometric positivity
as ‘the hydro-positive effect, by way of differentiating it
from ‘the true excitatory. effect, of negative turgidity-
variation and galvanometric negativity.

It has already been said that tissues which exhibit
a high degree of. conduction are characterised by more
or less of protoplasmic continuity. Hence, fibro-vascular
elements are relatively good, and parenchymatous. tissues
bad, conductors of excitation. The cells of the potato tuber
for this reason exhibit very little power of transmitting
excitation. When, therefore, in experimenting with this

64 COMPARATIVE ELECTRO-PHYSIOLOGY

tissue, stimulation was caused by application of a hot wire
so near as I cm. to the proximal contact, it was the hydro-
positive effect alone which reached it, giving rise to posi-
tive response. It was only, indeed, by applying the stimulus
very near, at a distance of 3 mm., that the true excitatory

response of galvanometric nega-

tivity was in this case . obtained
. (fig. 48).

From what has been said, it
will be seen that when a given
point is excited by transmitted
stimulation, two antagonistic elec-
trical effects are induced—one of
positivity, due to hydro-positive
action, and the other of negativity,
due to true excitation. When
the stimulator is near to, or co-
incides with, the responding point,
the tissue is subjected to rapidly
succeeding positive and negative
turgidity-variations, and the elec-
trical indication of the latter being
the more intense, it masks the

Fic. 48. Photographic Record former, and the resulting response
of Electrical Responses of . : A
Potato-tuber is determined by an _ algebraical

a, Positive response to stimulus summation of the two. In a

applied at distance ; 4, Negative yjgorous specimen, whose excit-
response to stimulus applied tan :

near. ability is great, the excitatory gal-

vanometric negativity masks the
positivity. The resultant electrical response in general is
expressed by the formula N,z—P,, where N, is the galvano-
metric negativity due to the true excitatory effect,and P,, the
positivity due to the hydro-positive effect, which immediately
precedes it. From this, it is clear that, as regards the
resultant galvanometric response of vegetable tissues under
stimulation, there may occur the two typical cases displayed
in the following table :

POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 65

TYPICAL CASES OF RESULTANT RESPONSE

Conditions . Constituent Factors Resultant Response
Excitability great Nez >Pu Galvanometric negativity
Excitability diminished Ng <Pxy Galvanometric positivity

or nearly abolished

We thus see how, under the physiological modifications
induced by various agents, the normal negative response of
a tissue may undergo diminution, or even reversal. We
have, for the sake of simplicity, assumed that the two
antagonistic effects act on the specimen simultaneously.
But, asa matter of fact, under certain circumstances, their
time-relations may be subjected to change. Hence various
effects of interference may be seen, giving rise to diphasic
responses, such as positivity followed by negativity, or the
reverse. Or, instead of diphasic, there may even be multi-
phasic responses, since it will be shown that very strong
stimulus may cause not a single but repeated responses.
Some of these effects will be described in detail in a sub-
sequent chapter.

I shall here meanwhile describe another method, in which,
by means of a selective physiological block, we can unmask
the contained hydrostatic effect of positivity, from the
ordinary response of galvanometric negativity. The oc-
currence of the excitatory contraction, in J/zmosa for
example, as shown by the fall of the leaf, depends on a
favourable excitatory condition of the tissue. If this ‘motile
excitability should be in any way depressed or abolished as,
say, by application of ice-cold water on the pulvinus, the
true excitatory response could not take place. But if, under

these circumstances, we applied stimulus at the diametrically

Opposite point S, (fig. 42), the hydrostatic wave alone would

be found to reach the organ. and, vz e¢ armzs, to produce

expansion there, with a consequent erection of the leaf.

It will thus be seen that the hydrostatic transmission of the

indirect effect of stimulus is not to any great extent affected
F

66 COMPARATIVE ELECTRO-PHYSIOLOGY

by the loss of excitability of the tissue. Similarly, the
transmission of true excitation may be selectively blocked,
in a tissue, by the application of various depressing agents,
such as anesthetics, without appreciably affecting the
passage of the wave of increased hydrostatic tension.

For the present experiment I took a leaf of fern, and
made the proximal electrical connection with the petiole, and
the distal with an indifferent point on a leaflet. By means
of the thermal stimulator (p.38), I now applied successive ©
uniform stimuli at intervals of one minute, on a point
15 cm. below the proximal .contact. The first. three

Fic. 49. Photographic Record of Electrical Response of Petiole of Fern

First part of record shows normal negative responses ; second part shows
positive response unmasked by selective physiological block of chloro-
form ; in the third part is seen the abolition of response when stimulus
is applied on anzsthetised area itself.

responses of the series are seen (fig. 49) to be more or less
uniform, and negative. Such resultant response is, as has
been pointed out, due to the summation of two antagonistic
effects, of which the excitatory is predominant. In order
therefore to eliminate from this resultant response its excita-
tory component, I applied chloroform on a narrow belt inter-
mediate between the point of stimulation and the proximal
contact. From the next three responses it will be seen that
the hydrostatic effect of positivity, represented by down-
responses, was thus successfully unmasked. The application
of chloroform is thus seen to act here as a selective block,

POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 67

the wave of increased tension being transmitted across its
area, whereas the wave of true excitation is arrested.

But the hydrostatic disturbance itself was caused by the
excitatory contraction of the distant point. The abolition of
the excitability of an intermediate point did not, as we have
seen, block the hydrostatic wave. If now the stimulator be
brought nearer, and placed over the strongly anzsthetised
area, the expulsion of water dependent on true excitation
can no longer take place. On doing this, therefore, we find
that neither the true excitatory negative, nor its consequent
hydrostatic positive effect, is exhibited at the responding
point. Response is thus totally abolished.

We thus see that incident stimulus gives rise in the plant
to two distinct responsive expressions. In that which we
shall consider first—namely, the direct, or true excitatory
effect—there is an expenditure of energy, which is indicated
by a contraction, negative turgidity-variation, mechanical
fall, and galvanometric negativity. In the second, or indirect,
of these two effects, we have the opposite of ali these. That
is to say, we have here an increase of internal energy, expan-
sion, positive turgidity-variation, erection of leaf, and galvano-
metric positivity. The galvanometric negativity, due to
negative turgidity-variation, is generally speaking of much
greater intensity than the galvanometric positivity, due to
positive turgidity-variation. Hence, when the two effects
act on a tissue in rapid succession, that of electro-negativity
masks the positive. The wave of increased hydrostatic tension,
by which the indirect effect of stimulus is transmitted, has a
greater speed of transmission than that of true excitation. It
may be transmitted even across tissues of which the excita-
bility has been depressed or abolished, whereas the trans-
mission of true excitation is arrested by the intervention of
such a physiological block.

The occurrence of these opposed effects of galvanometric
negativity and positivity has long been regarded as a pheno-
menon of a highly perplexing nature. It was too hastily
assumed that wherever these opposed electrical changes took

F.2

65 = COMPARATIVE ELECTRO-PHYSIOLOGY

place, they were necessarily to be ascribed to opposite or
antagonistic chemical processes—namely, of assimilation and
dissimilation. That this, however, cannot be universally true,
has here been proved by tracing the two effects to their
definite respective origins, in positive and negative turgidity-
variations. I shall enter into this subject in greater detail in
the subsequent chapters.

CHAPTER VI

EXTERNAL STIMULUS AND INTERNAL ENERGY

Hydraulic transmission of energy in living tissue ~True meaning of tonic con-
dition—Opposite expressions of internal energy and external stimulus seen in
growth-response— Parallelism between responses of growing and motile organs
—Increased internal energy caused by augmentation of temperature finds
expression in enhanced rate of growth ; erection of motile leaf; curling move-
ment of spiral tendril ; and galvanometric positivity—External stimulus induces
opposite effect in all these cases—Sudden variation of temperature, acting as a
stimulus, induces transient retardation of growth; depression of motile leaf ;
uncurling movement of spiral tendril ; and galvanometric negativity—Laws of
mechanical and electrical response.

We have seen in the last chapter that external stimulus,
directly applied, induces in an excitable vegetable tissue a
contractile response, with concomitant galvanometric nega-
tivity. An increase of internal energy, on the other hand,
was there seen to give rise to expansion, and galvanometric
positivity. These two factors of external stimulus and internal
energy are thus seen to be antagonistic in their general
expressions.

But while stimulus from outside, impinging on an excit-
able area, thus caused an expenditure of energy at that area,
by inducing excitatory response there, yet it was also found
that, by its indirect effect, it brought about an increase of
energy in neighbouring tissues. By the sudden contraction,
and expulsion of water from the excited area, energy was ©
transmitted hydraulically, and the consequent positive tur-
gidity-variation caused an erectile response of a neighbour-
ing motile organ. In the simple case in which the point of
receptivity was at a distance from that of response, it was
seen that these two effects of stimulus, direct and indirect,
were easily discriminated from one another. But as the

7O COMPARATIVE ELECTRO-PHYSIOLOGY

stimulator was brought nearer and nearer, the two effects
became superposed, and one was masked by the other.
Even in this case, however, on careful examination, it is
possible to infer the results due to the action of the internal
factor.

Thus, we may suppose stimulus to be applied directly on
the pulvinus of M/zmosa, bringing about a responsive fall of

the leaf. The expelled water from the excited pulvinus will —

‘now be forced into the neighbouring tissues, making them
over-turgid, and raising their energy above par. On the

cessation of stimulus, the water that has been forced away -

will flow back from the region of heightened, to that of
lowered tension, and re-establish the normal turgidity of the
pulvinus, which had undergone a negative variation, The
erectile recovery of the leaf is thus seen to be, not a merely
passive process, but an effect dependent on the internal energy
of the plant.. This is also shown by the fact that in autumn
and winter, when the internal energy is low, the period of
recovery is very long, being sometimes as much as eighteen
minutes ; whereas in summer, on the other hand, with the
increased internal energy of the plant, it takes place nearly
three times as quickly. I have elsewhere shown that it is
this internal energy which is vaguely referred to as the tonic
condition of the tissue, and that it consists of the sum total
of energy derived from external stimuli previously absorbed
and held latent by the plant. The different forms of stimulus
may be very various. We have for instance tonicity, as
imparted by light, or phototonus ; by favourable temperature,
thermotonus ; by electrical current, edectrotonus; by internal
hydrostatic pressure, hydrotonus ; or by the presence of favour-
able chemical substances, chemotonus.

We have seen that, as a general rule, external stimulus
and internal energy find responsive expressions of opposite
sign, the former inducing a negative, and the latter, a positive
turgidity-variation. It is, nevertheless, important to demon-
strate the extensive applicability of this law, by many different
results and different modes of manifestation. And such a

ee ea a ne

ne A aut RE ip rt ee Se Be

EXTERNAL STIMULUS AND INTERNAL ENERGY oe oe

demonstration would undoubtedly become still more con-
vincing, if we should succeed in discovering some mode of
response in which the antagonistic effects of internal energy
and external stimulus found opposite expressions.

-- Such an example, of a very striking character, I have in
my work on ‘ Plant Response’ shown to be found in growth-
response. But the same opposition, between the effects of
external stimulus and internal energy, I shall now proceed to
demonstrate not only by means of growth-response, but also
through mechanical and electrical responses. In the case of
srowth, the responsive expression of the growing organ, under
increased turgidity, consists of an expansive elongation. If
the organ be growing at a uniform rate, an increase of internal
energy will enhance that rate. But when external stimulus
acts directly on the growing organ, the normal rate of growth
is retarded during the action of stimulus. Thus it will be seen
that though the mechanical response of a motile organ, and
the movement of a growing organ, appear so different, yet
these two expressions are not fundamentally distinct. For
while in one, the application of direct stimulus, causing nega-
tive turgidity-variation and contraction, induces depression of
the leaf, in the other, the same negative turgidity-variation
and contraction under external stimulus causes a depression
of the rate of growth. And, on the other hand, indirect effect
of stimulus, er increase of internal energy, inducing positive
turgidity-variation, brings about in the one case the erection
of the leaf, in the other an enhancement of the normal rate
of growth. This parallelism is displayed in detail in the
table given below.

It is thus understood that the indication of response to
external stimulus is the depression of the motile leaf, or
depression of the rate of growth, while the effect of increased
internal energy is the erection of the motile leaf, or enhance-
ment of the rate of growth.

We shall first deal with the responsive expression to
that positive turgidity-variation which is due fo the increase
of internal energy. One mode of increasing the internal

72 COMPARATIVE ELECTRO-PHYSIOLOGY

TABULAR STATEMENT SHOWING COMPARATIVE EFFECTS OF EXTERNAL
STIMULUS AND INTERNAL ENERGY ON PULVINATED AND GROWING ORGANS

| Mechanical response Growth response
Effect of normal turgidity : Effect of normal turgidity :

Normal horizontal position of leaf. Uniform rate of growth.

Local action of external stimulus : Local action of external stimulus :

Contraction ; Contraction ;

Diminution of turgidity ; Diminution of turgidity ;

and concomitant depression of leaf. and concomitant depression of rate

of growth.
Action of internal energy exhibited by | Action of internal energy exhibited by
(a) Recovery ; (az) Recovery:

Re-establishment of turgidity and Re-establishment of turgidity and
gradual return of leaf to normal gradual return of organ to normal
horizontal position. rate of growth.

(4) Increased hydrostatic pressure : (4) Increased hydrostatic pressure :

Erection of leaf. Increased rate of growth. -

energy of a plant is by a moderate rise of temperature. And
this finds expression in the case of a motile organ, by the
erection of the leaf. Thus, when J/zmosa is raised in tem-
perature, all its leaves become highly erect. A diminution
of energy, on the other hand, by cooling, brings about a
depression of the leaves.

In the same way, the rate of growth is exalted by rise of
temperature. Thus in a growing flower of Crinum lily the
normal rate of growth at 30° C. was ‘oo4o mm. per minute,
and this was exalted to ‘o113 mm. per minute, or nearly
three times, when the temperature was raised*to 35°5° C.
Lowering of temperature, on the other hand, greatly de-
presses the rate, and may even, if it proceed far enough,
cause arrest of growth.

As regards external stimulus, on the contrary, we have
seen that its effect on the motile organ is one of depression.
The following record (fig. 50) shows that it has a similar
influence on the rate of growth. The first part of the curve
shows the normal rate of elongation. But after the applica-
tion of stimulus of light, growth is not only retarded, but
there is an actual shortening of the organ. On the cessation
of stimulus, the normal rate of growth is gradually re-
established.

EXTERNAL STIMULUS AND INTERNAL ENERGY 73

I shall next give examples in which the opposite effects
of external stimulus and internal energy are exhibited in
growth response, motile response, and electrical response.
To take first the response of growth: we have seen that
a steady rise of temperature brings about an increase of
internal energy, while a sudden variation of temperature
acts as a stimulus. Thus, if we effect a sudden augmenta-
tion of temperature, this will act on the organ, during the
period of variation, as a stimulus; but afterwards, when
the temperature itself, or its rate of rise, has become

mm,
“|

“2

|

= =. ee eS ! {

Be) Seas SESE Le ve = Oe SES. ! parsed WEISEL"
10° 15° 20’ 25° 30\35’ 40° 45’ 50’ 55’ 60’ 65° 70’

Fic. 50. Longitudinal Contraction and Retardation of Growth under
Light in Hypocotyl of Smaps nigra

The first part of the curve shows the normal rate of growth. Arrow (1)
indicates moment of application of diffuse light, which is seen not only
to retard growth, but also to induce a’ marked contraction. The
second arrow indicates moment of withdrawal of light, and dotted
portion of the curve shows recovery.

steady, the condition will act by increasing the internal
energy of the organ. These opposite results are seen to
be strikingly illustrated by growth response in the case of
the following record (fig. 51),

The normal rate of growth at 34° C. was here ‘o15 mm.
per two minutes. By a sudden application of heat, raising
the temperature of the chamber ultimately by 1° C., a respon-
sive contraction was caused, as is seen in the record. But,
on the attainment of a steady augmented temperature of
35° C., an increased rate of growth, which now amounted to
024 mm. per two minutes, was observed, owing to the
increase of internal energy.

74 COMPARATIVE ELECTRO-PHYSIOLOGY

Or the same difference may be demonstrated by means
of mechanical response. A Mzmosa is placed in a small
chamber and subjected to a sudden rise of temperature.
In consequence of this there is a preliminary excitatory
depression, followed, on the attainment of a steady rise, by
gradually increasing erectile re-
sponse, which carries the leaf
above its original level.

These opposed motile effects
can be shown, moreover, even
in the case of ordinary plants.
We take a_ spiral tendril of
Passiflora. In this, the outer
or convex surface is more ex-
citable than the inner or con-
cave, and external stimulus,
causing greater contraction of
this more excitable outer side,
induces a movement of un-
curling. This movement corre-

» sponds to the excitatory fall

Fag, St, gpa cf Groth of Mimosa. The response by
and 35° C. increase of internal energy is,
The dotted line represents the however, the opposite of this,

variable period of temperature

change. Note the contractile and consists of a movement of
twitch and transient highly ac- : “1.
celerated growth which follows. curling. When the tendril is

The rate of growth became con- placed in a vessel of water, of

stant when the temperature be- bch 4h b

came permanent at 35° C. which the temperature can be

varied at will, a sudden rise of

temperature causes a preliminary excitatory movement of

uncurling, followed by a movement of curling, when the
higher temperature has become steady.

The electrical expressions of external stimulus and in-
ternal energy are similarly opposed. In fig. 85 (Chapter X.)
will be seen a record showing that sudden variation of
temperature, acting as an external stimulus, induced a

responsive galvanometric negativity, whereas steady rise of

EXTERNAL STIMULUS AND INTERNAL ENERGY 75

temperature had the opposite effect—that, namely, of.
inducing galvanometric positivity.

It is thus seen that while the characteristic effect of
external stimulus on an excitable tissue is to cause a nega-
tive turgidity-variation, that of increased internal energy
is to induce a positive turgidity-variation. The former of
these, or negative turgidity-variation, finds electrical expres-
sion in galvanometric negativity ; in a motile organ by the
fall of the leaf, and in a growing organ by retardation of the
rate of growth. The latter, or increase of internal energy,
on the other hand, is expressed electrically by galvanometric
positivity ; mechanically, by erection of the leaf; and in a
growing organ by an acceleration of the normal rate of
growth.

We thus arrive at the following laws of response of
isotropic organs :

1. Effective stimulation induces contraction and galvano-
metric negativity.

_ 2. Increase of internal energy induces expansion and
galvanometric positivity.

CHAPTER VII

ABSORPTION AND EMISSION OF ENERGY IN RESPONSE

Sign of response determined by latent energy of tissue, and by intensity of
external stimulus— Sub-tonic, normal and hyper-tonic conditions — The
critical level—Outward manifestation of response possible only when critical
level is exceeded— Three typical cases: response greater than stimulus;
response equal to stimulus ; and response less than stimulus—Investigation by
growth-response—Instance of sum of work, internal and external, performed
by stimulus constant—Positive response of tissues characterised by feeble
protoplasmic activity or sub-tonicity—Enhancement of normal excitability
of sub-tonic tissue by absorption of stimulus.

WE shall find, in this and succeeding chapters, that the
nature and intensity of response are determined not merely
by the intensity of stimulus, but also by the molecular con-
dition of the responding substance. The excitatory mani-
festation is dependent upon the occurrence of a particular
directioned molecular distortion. Hence, if by the action of
the stimuli of the environment, an incipient distortion in this
direction has already been induced in the tissue, the incidence
of even moderate stimulus will then prove sufficient to
precipitate visible excitatory manifestation. A tissue in this
condition is said to be highly excitable or fully tonic. If, on
the cther hand, the tonic condition be less favourable, long-
continued stimulation will be necessary to evoke the excita-
tory effect. Here, during the first part of application,
stimulus will appear to be ineffective. As a matter of fact,
however, it is at work to give such a predisposition to the
molecules that the action of subsequent stimulus shall be
rendered effective.

In the simple case in which the tonic condition is favour-
able, a given stimulus will induce a given responsive expres-

Py Ee Pe PL Re

el aT FS

ee

ABSORPTION AND EMISSION OF ENERGY IN RESPONSE 77 |

sion. If further, the tissue, on recovery, return to its original
condition, then a second similar stimulus will induce the
same responsive expression as the first. These responses
will thus be uniform. But if, owing to the after-effect of
stimulus, the condition of the tissue itself be changed, the
responses will be found to exhibit either staircase increase or
fatigue decline, according to the particular molecular con-
siderations involved, which will be described in detail in the
following chapter.

It will be interesting here, however, to take an extreme
case of a tissue in the opposite condition—namely, of great
sub-tonicity. It is clear that since the excitability of the
tissue is here feeble, there will be little or no outward
manifestation of ercztatory response. The incident stimulus
will thus be absorbed, and entirely held latent. And the
increase of internal energy thus brought about may find
expression mechanically by expansion, or electrically by
galvanometric positivity.

In the case which we have selected, the excitability of the
tissue is too low for the ordinary excitatory expression to occur.
Hence the incident stimulus will be entirely absorbed, and
there will be a gain of energy without any loss. The whole
responsive expression will in this case consist, not of con-
traction but of expansion. In other words, it will be exactly
opposite to that which is usually consequent upon external
stimulus. In order to demonstrate this, I took a seedling of
Tamarindus indicus which had been cut off from its supply
of external energy, and was consequently sub-tonic. Owing
to the insufficiency of internal energy, its growth had, in
fact, come to a standstill. On now subjecting this seedling
to thermal stimulation, the absorbed stimulus raised the
internal energy and found expression in growth expansion.
We have seen that the effect of external stimulus on a growing
organ in normal tonic condition was the retardation or arrest
of growth. But here, in a tissue which is sub-tonic, we find
that the effect is exactly opposite. :

Without, however, taking so extreme a case, as that in

78 COMPARATIVE ELECTRO-PHYSIOLOGY

which sub-tonicity is manifested by arrest of growth, we may
select a specimen in which, while the tissue is not fully tonic,
there is still, nevertheless, a feeble rate of growth. In such
a case we may expect the income from the absorption of
stimulus to prove greater than the expenditure in the form of
true excitatory response. Hence, if we subject such a tissue
to the constant action of an external stimulus, we shall in
the first stage obtain the predominant effect of the internal
factor, with its positive turgidity-variation and enhanced rate
of growth.

But by the continued action of this accumulating income,
the tonic condition of the tissue will be raised to the normal,
with a concomitant increase of excitability. It will now
therefore be the excitatory component which becomes pre-
dominant, resulting in the negative turgidity-variation, con-
traction, and retardation of growth.

In order to detect these variations of the normal rate of
growth, under the action of stimulus, it is necessary to have
at our disposal some very delicate means of record. This
need I have, however, been able to meet, by devising the
Balanced Crescograph, more fully described in my book
on ‘ Plant Response.’ Here, the uniform rate of elongation
of a growing organ causes a rotation of the recording Optic
Lever. The spot of light from this lever falls upon a second
mirror, which is subject to a compensating movement. When
the balance is exact, the spot of light, reflected from the two
mirrors, remains quiescent. When, however, the normal rate
of growth, under the action of any agent, undergoes varia-
tion, the balance is upset. Thus, when growth is accelerated,
there is a movement of the recording spot of light in one
‘direction, say up, and when retarded, a movement in the
opposite, say down.

In order to study the effect of external stimulus on a
tissue in a slightly sub-tonic condition, I took a flower-bud
of Crinum lily,and first obtained a balanced record, seen as a
horizontal line (fig. 52). Stimulus of light was now applied,
and it will be seen that after a short latent period the

QE

ABSORPTION AND EMISSION OF ENERGY IN RESPONSE 79

absorbed stimulus induced a positive turgidity-variation, with
enhanced rate of growth, as seen by the up-curve. But by
this absorption of the stimulus itself, the tonic condition
of the specimen was raised, with consequent increase of ex-
citability, and the response became normal. That is to say,
it now consisted of contraction and retardation of growth
as seen by the downward curve. The external stimulus was
now cut off and the

dotted portion of the
curve shows the after-
effect. The after-effect
is thus not a mere re-
covery, but an enhanced
rate of growth, due to the
increased energy which
remains latent. It was
only when this was ex-
hausted that the normal
rate of growth was re- Fic. 52. Balanced Record of Variation of
established, as seen in Growth in Flower-bud of Crinum Lily

eo £ under Diffuse Stimulation of Light
the horizontal part o the Continuous lines represent the effect during

curve. And as the tissue application of light, the dotted line on

: f ‘ withdrawal of light. The plant was
was now in full tonic originally in a sub-tonic condition, and

ia

5 es re 1 { ars. _S
10’ 15° 20’ 25’ 40° 35’ 40° 45

condition the renewed application of light at x, after short
aged ; latent period, induces preliminary ac-
application of stimulus celeration of growth. After this follows
. : . the normal retardation. On withdrawal
of light did : “ gs hers of light, in the dotted portion of the curve
induce a preliminary en- is seen the after-effect, followed by

be Sith ty f return to the normal rate of . growth.
ancement of the rate o A second and long-continued application

growth, but the normal of light induces retardation, followed by
A oscillatory response.

contraction and retarda-

tion. Its long-continued application gave rise to the further

phenomenon of multiple response, a subject which will be

fully dealt with in a future chapter.

Now owing to this fact that the response of growth gives
us by means of the enhancement or depression of its rate,
effects which correspond to the positive and negative, we are
able clearly to perceive :

80 COMPARATIVE ELECTRO-PHYSIOLOGY

(1) That when the tonic condition or the excitability of
the tissue is low, the predominant effect will be the positive.
This has been shown during the course of the present chapter
in the case of a very sub-tonic tissue of Zamarindus indicus,
where the positive or growth-expansion effect was initiated
by the action of stimulus.

(2) That when the sub-tonicity of a tissue is not very
great, incident stimulus will at first give the positive effect of
an enhanced rate of growth. But with the absorption of the
stimulus itself, the tonic condition of the tissue will be raised,
and we shall then obtain the true excitatory reaction of con-
traction and retardation of growth. Thus, in this intermediate
case, the positive response will be seen to pass into normal
negative. ,

(3) And, lastly, that when the tonic condition is already
high, the excitatory negative response will predominate and
we shall obtain normal contractile response. Both this and
the previous intermediate cases are illustrated by the experi-
ment described on Crinum lily. It was there seen that the
first effect of incident light was positive, the tissue being
sub-tonic ; subsequently, the tonic condition being raised,
this response was converted into the excitatory negative.
And on renewed application of stimulus thereafter the
immediate response continued to be negative.

The fact that by means of growth-response, it is possible
to obtain indications of the external and internal work per-
formed by absorbed stimulus, enables us to demonstrate a
proposition of great importance, that, namely, under certain
conditions, the sum of the work done, internally and
externally, by a given stimulus, is constant. This will be the
case where there is little or no dissipation of energy in the
course of transformation. In considering the question of the
relative proportions of the incident stimulus utilised for in-
ternal and external work respectively, we find it clear, from
considerations already adduced, that the lower the tonic con-
dition the greater will be the proportion of stimulus held
latent for the performance of internal work. The nearer is

4
F
>

wat “Se = ee

ie oy -

414. 4t4 >. a A

ee ae ee

ABSORPTION AND EMISSION OF ENERGY IN RESPONSE 81

the tonic condition, on the other hand, to the critical level,
the greater will be the excitatory overflow, and the smaller
the latent component. The internal and external factors
will thus be complementary to each other. pia
‘On subjecting this inference to experimental demon-
stration by means of growth-response, I fully succeeded in
verifying it. According to this method of growth-response,
it will be remembered, the true excitatory effect is measured
by retardation of the normal rate of growth, the internal
factor of increased latent energy being represented, on the
other hand, by a corresponding enhancement of the rate of
growth. This being understood, it was found that in a
particular specimen of growing tissue, whose tonic condition
was somewhat low, the external and internal effects caused
by a given stimulus were in the proportion of 32 to 13'5.
When the tonic condition of the specimen was raised, how-
ever, and the same stimulus was applied, the external effect
was found to be enhanced to 38 at the expense of the internal,
which was now found to be lowered to 8°5. The sum of the
work done, both internally and externally, is seen to be in
both these cases approximately the same, being in the former
experiment 455, and in the latter 46's. .
~ We have seen that, of the two antagonistic factors of
response, the positive will predominate if the excitability
of the tissue be in any way diminished. Such a loss of
excitability may occur in either of two ways: (1) by the
sub-tonicity of the tissue itself; (2) by the depression con-
sequent on fatigue. Under either of these conditions then
we may expect to obtain the exhibition of the positive effect.
The exhibition of the positive effect. under fatigue will be
described in the course of the next chapter. We shall here
consider instances in addition to those already given, of the
occurrence of the positive effect in a tissue which is sub-tonic.
We have to bear in mind that the work which incident
stimulus is called upon to perform is two-fold, both internal
and external, and that there is a certain critical excitatory
level, above which only is the normal responsive expression
G :

So COMPARATIVE ELECTRO-PHYSIOLOGY

possible. The actual potential or excitatory level of a tissue
depends on its tonic condition and the intensity of the
incident stimulus. Now this existing potential of the tissue -
may be anything within a wide range, S T, when sub-tonic,
N when normal, or H T when hyper-tonic or above the
ordinary normal degree (fig. 53). Since
wb Roes Ph FeRAt ara it is necessary that the incident stimulus
should cause the critical level C to
be slightly exceeded, if there is to
be an excitatory overflow, we can see
that the intensity of the stimulus re-
oh. ee. quisite to evoke response will be greater
eg Poe in proportion as the tonicity of the tissue
itself is low. Thus when the tissue is
extremely sub-tonic, a stimulus of or-
dinary intensity could never avail to
raise the energy of the system above
See rad fa se the critical point, and the response
Tonic Level must then therefore be positive. Under
N,normal;sT,sub-tonic; these circumstances it will only be by
HT, hyper-tonic ; and » : ; z
c, the critical level | the impact of excessively strong sti-
mulus, or by the cumulative action of
a series of moderate stimuli, that the critical point can be
reached and passed, and the normal negative response
evoked.

Thus the intensity of the minimally-effective stimulus in
evoking normal response will afford us a measure of the
tonicity of the tissue. If the latter be high, then the feeblest
stimulus will precipitate outward response, and indeed, if
excessive, response will occur on little or no provocation, and
such movements we call‘autonomous.’ It must be remem-
bered, however, that it was by the previous absorption of
stimuli that the tissue was brought to this point of unstable
equilibrium at which the added impact of an infinitesimal
stimulus causes it to bubble over, as it were, into apparently
spontaneous activity.

The predominant expression of the highly tonic tissue

ee ee eT

ABSORPTION AND EMISSION OF ENERGY IN RESPONSE 83

being thus negative, we must go to the other extreme of great
sub-tonicity if we are to be successful in demonstrating the
occurrence of the unmixed positive response. This considera-
tion leads us to expect that positive response will be evoked
on moderate stimulation from tissues that are either not
highly tonic or protoplasmically defective. I shall show in
Chapter XXII. that in cells of epidermis, where the proto-
plasmic contents have been reduced to a minimum, response
to moderate stimulus tends in general to be positive, Even
highly excitable tissues like nerve, as will be shown later,
when cut off from their supply of energy, often become so
sub-tonic as to give positive response. I shall here show
how ordinary tissues exhibit this effect, when the tonic con-
dition is allowed to fall to such an extent as to render the
tissue extremely sub-tonic. For this purpose I took a cut
specimen of petiole of cauliflower, and kept it without water
for a couple of days. By this process the specimen, became
somewhat withered. I next proceeded to take records of its
electrical responses under increasing stimuli. The intensity
of these stimuli rose from I to 10 units. It will be seen
from the record (fig. 54) that each stimulus up to 9 evoked
positive response, and that it was the strong stimulus of |
10 which gave rise to the normal response of negativity.
This constitutes the first instance of a phenomenon which
I shall show later to be of very extended occurrence—the
induction, namely, of one effect under moderate, and its
opposite under very feeble stimulation. It is not so easy to
demonstrate this fact with a highly excitable, as with a some-
what sub-tonic tissue, where the critical intensity of stimulus
for the evoking of normal response need not be impracticably
low. A point to be taken into account here is the after-effect
of sub-minimal stimulus in enhancing subsequent normal
excitability. Thus it is found in taking the record of
responses to a succession of feeble stimuli, that though they
are at first abnormal positive, they are afterwards converted
into ‘normal negative. That it is the after-effect of the.
previous stimulation which thus enhances previous excitability.
G2

84 COMPARATIVE ELECTRO-PHYSIOLOGY

may also be demonstrated by subjecting the tissue to con-
tinuous stimulation or tetanisation, when the abnormal
positive is found to pass into normal negative.

From the experiments that have been described, it would
appear that the several kinds of response characteristic of
various tissues are relatively rather than absolutely different.
The true excitatory reaction of an excitable tissue, is one
of galvanometric negativity. Any diminution of the ex-—
citability—whether by lowering of tonic condition or other

Fic. 54. Photographic Record of Abnormal Positive passing into Normal Nega-
tive Response in a Withered Specimen of Leaf-stalk of Cauliflower

Stimulus was gradually increased from I to 10, by means of spring-tapper.
When the stimulus intensity was 10, the response became reversed into
normal negative. (Parts of 8 and 9 are out of the plate.) This record
is to be read from right to left. _Down-records stand for positive, and
up-curves for negative responses.

causes—will bring about a decrease of this negativity, which
may culminate in actual positivity. Thus negative is not
separated from positive response by any break of continuity ;
but we are able, on the contrary, to trace a gradual transition
from one to the other. Moreover, in every response we
have the two antagonistic elements, positive and negative,
either actually or potentially present. The form taken by
the resultant response is entirely determined by the question
of what proportion of the stimulus impinging upon the tissue
becomes latent ; and this in its turn depends upon the tonic

See? poe,

ABSORPTION AND EMISSION OF ENERGY IN RESPONSE 85

condition of the tissue. When the absorbed stimulus is
wholly retained, response is positive, but by this absorption
the tonicity of the tissue and its excitability are both raised.
When the tonic condition of the tissue, on the other hand, is
already high, and its excitability great, a large proportion of
the energy finds outward expression, and we obtain the
normal negative response. Between these two extremes, we
may observe many effects of interference, due to the play
of the two antagonistic elements. If, then, the time-relations
be not coincident, variations will be induced which will find
expression in different types, diphasic response, positive
followed by negative, and vzce versa.

The question considered in the course of the present
chapter has been that of the energy received and given out
by the tissue, and the molecular work, positive and negative,
performed during these processes. Such work, however, is
itself the result of molecular distortions brought about by
stimulus, and the question of the amplitude of response, as
related to the degree of distortion, will be discussed in the
following chapter.

CHAPTER VIII

VARIOUS TYPES OF RESPONSE

Chemical theory of response—Insufficiency of the theory of assimilation and dis- |

similation—Similar responsive effects seen in inorganic matter—Modifying in-
fluence of molecular condition on response— Five molecular stages, A, B, C, D, E
—Staircase effect, uniform response, fatigue—No sharp line of demarcation
between physical and chemical phenomena—Volta-chemical effect and by-
products—Phasic alternation—Alternating fatigue—Rapid fatigue under con-
tinuous stimulation—In sub-tonic tissue summated effect of latent components
raises tonicity and excitability—Response not always disproportionately greater
than stimulus—Instances of stimulus partially held latent : staircase and ad-

ditive effects, multiple response, renewed growth— Bifurcated responsive ex-
pression.

ACCORDING to current theories, living matter is maintained
in a state of equilibrium by the two opposed chemical pro-
cesses of assimilation and dissimilation. It is supposed that
stimulus causes a down or dissimilatory change, which is
again compensated during recovery by the building-up or
assimilative change. In the case of uniform responses, again,
these two processes are regarded as balancing each other.
On this theory, when the down change is the greater of the
two, the potential energy of the system falls below par ; for
the building-up process cannot then sufficiently repair the
chemical depreciation caused by it. Hence occurs dimi-
nution of response, or fatigue, which is supposed to be further
accentuated by the accumulation of deleterious fatigue-stuffs.
The disappearance of fatigue after a period of rest is ex-
plained by the renovating action of the blood-supply, which
is also regarded as the means of carrying away the fatigue-
stuffs.

A serious objection to these explanations lies, however,
in the fact, that even excised and bloodless muscles exhibit
recovery from fatigue after a period of rest. In isolated

Se ee a a a el te te

ee ee ee ee

VARIOUS TYPES OF RESPONSE 87

vegetable tissues, again, where there is no active circulation
of renovating material, the same effect, and its removal after
a period of rest, are observed. Thus the difficulties en-
countered in explaining fatigue, on purely chemical ‘con-
siderations, are great enough; but still greater are those
difficulties which arise when we come to deal with the stair-
case effect—typically shown in cardiac muscle—in which
successive responses to uniform stimuli exhibit a gradual
enhancement of amplitude. The results obtained here are
in direct opposition to the theory described; for in this
particular case we have to assume that the same stimulus
which is usually supposed to cause a chemical breakdown,
has become efficient to induce. an effect exactly the reverse.

Of the two antagonistic elements in the electrical response,
moreover, it is the positive which is supposed to be associated
with the assimilative, and the negative with the dissimilative
change. If this supposition were correct, however, it would
be natural to expect that the positive response would be
manifested predominantly in vigorously growing tissues, in
which assimilation must be at its greatest. Fatigued tissues
on the other hand, in which dissimilatory changes are sup-—
posed to be predominant, should manifest negativity as their
characteristic response ; moribund tissues, in contrast with the
actively growing, might also be expected to exhibit respon-
sive negativity. In actual fact, however, the very reverse is
the case. For in vigorous tissues, normal response is by
galvanometric negativity ; and it is the over-fatigued or
- moribund which characteristically exhibit the positive re-
sponse.

It would be difficult again to conceive of assimilation
and dissimilation in the case of inorganic matter. Yet even
in inorganic matter we find reproduced all the various types
met with in the response of living tissues: namely, uniform
response, the staircase effect, and fatigue. Response being
really due to molecular upset from a condition of equilibrium,
we can see how different forms of responsive expression will
occur, according to the various molecular conditions of the

88 COMPARATIVE ELECTRO-PHYSIOLOGY

substance at the time being. One of the most important
factors, then, in determining the character of response is the
molecular condition of the substance itself. The numerous
anomalies hitherto encountered in our interpretation of
responsive phenomena are all traceable to our failure to take
this factor of molecular condition into account. For a full
exposition of the modifying influence which it exercises on
response, however, though I shall here state some of the
principal conclusions which I have arrived at, the reader is —
referred to Chapter XLII.

From the fact, that every type of response is to be
obtained from inorganic matter, where chemical assimilation
and dissimilation are obviously out of the question, it is clear
that the fundamental phenomenon must be dependent on
physical or molecular, and not on such hypothetical chemical
changes. It must, however, be remembered that though re-
sponse phenomena and their modifications are undoubtedly
in the first place physical or molecular, yet in the borderland
between physics and chemistry there is no sharp line of
demarcation. For example, yellow phosphorus becomes
converted, under the stimulus of light, into the red, or
allotropic, variety. This molecular change, however,cis also
attended by a concomitant change in the chemical activity,
phosphorus in its allotropic condition being less active than
in the yellow. Under certain circumstances, further, it is
possible to have a secondary series of chemical events follow-
ing upon a condition of unequal molecular strain. A homo-
geneous living tissue, when unstimulated, is iso-electric.
When stimulated, however, an electro-motive difference is
induced, as between the stimulated and unstimulated parts of
the tissue. . The result is an electrical current attended
by electro-chemical changes. As a consequence of such
volta-chemical action, when prolonged, by-products (fatigue
stuffs?) may be accumulated, and these may have a de-
pressing effect on the activity of the tissue. Hence, just
as, after very prolonged activity of a voltaic combination, it
is necessary to renew the active element and change the

VARIOUS TYPES OF RESPONSE 89

electrolyte, surcharged with by-products, so after sustained
activity of a living tissue, the process of renewal, or renova-
tion, will be necessary. It is thus seen how upon the funda-
mental molecular derangement, a chain of very various
chemical events may follow, as its after-effect. And it is
only by going in this way to the very root of the pheno-
menon that we can avoid the many contradictions with
which we are confronted by the chemical theory.

In studying various response phenomena, our conclusions
are necessarily based upon the observation of the amplitude
of responses. It is therefore important at this point to draw
attention to the danger of hasty inferences. On finding, for
instance, that the amplitude of response in a given case is
diminished, we are apt to infer that the responding tissue
has undergone depreciation. But this is not invariably the
case. In the entire process of response, while stimulus
induces molecular upset, we must remember that there is
also an internal factor, which brings about molecular restitu-
tion. Now, if this force of restitution be inany way enhanced,
it is easy to see that the responsive distortion of the mole-
cules will find itself opposed, with consequent diminution of
amplitude. We shall thus often find that a rise of tem-
perature, by enhancing the force of recovery, actually causes
a diminution of response. That this is not due, however, to
any depreciation of the tissue is seen from the fact that the
same rise of temperature enhances another excitatory pro-
perty of the tissue—namely, the speed of its conduction.

I shall now give a brief account of the modifying influence
exercised on response by the molecular condition. It will be
shown, in the Chapter (XLII) on the Modification of Response
under Cyclic Molecular Variation, that a given response is
not determined merely by the nature of the responding
substance, but also by the amount of the energy which it
possesses. Starting from the lowest condition of sub-tonicity,
a substance undergoes progressive molecular transformation
by the action of the impinging stimulus itself. Five stages
may be roughly distinguished in this transformation. In the

gO COMPARATIVE ELECTRO-PHYSIOLOGY

first, or A, stage of extreme sub-tonicity, we have absorption
without excitatory response. By this absorption the sub-
stance passes into the next, or B, stage, which is the stage of
transition, where response is converted from the abnormal to
normal. Above this stage the rate of molecular transforma-
tion is very rapid. From the residual after-effect of stimulus,
the substance now passes from the stage B to the stage 0,
which is a condition of more or less stability. Further |
stimulation carries the substance to stages D and E. Here
the molecular distortion from the normal equilibrium is very
great. Stimulation applied in this condition has little
further effect in inducing response. That is to say, excit-
ability is here reduced to a minimum. In this extremely
distorted position, moreover, the substance has a strong
tendency to revert to the position of normal equilibrium.

In the A condition of extreme sub-tonicity, since there
‘is absorption without excitation, the response which we
obtain is abnormal positive. Intense or long-continued
stimulation carries the substance into the B stage, with its
normal negative response often preceded by diphasic. An
example of this has already been given in fig. 54, obtained
from the sub-tonic petiole of cauliflower. We shall meet,
however, with numerous other examples in a great variety
of tissues. Arriving at the B stage, the substance is still
somewhat sub-tonic, and the rate of molecular transformation
here is rapid. From the after-effect of stimulus the mole-
cules of the somewhat inert substance become incipiently
distorted in the same direction as that of normal response.
A proportion of the incident stimulus is thus utilised in
inducing a favourable molecular disposition. A repetition of
the original stimulus will now give rise to a greater excitatory
reaction than before. Thus at the B stage we obtain a stair-
case increase of response. This fact—that by the after-effect
of previous stimulation the molecules may be incipiently dis-
torted in a direction favourable to excitatory response—finds
‘illustration in stimuli individually ineffective being made
effective by repetition, The result here is evidently made

VARIOUS TYPES OF RESPONSE QI

conspicuous by the summation of the after-effects of all the
preceding stimuli with the direct effects of their successors.
The staircase effect is seen in the two accompanying records.
In fig. 55 is given a photographic record of the staircase
increase.in the electrical response of a vegetable nerve! in
somewhat sub-tonic condition, In fig. 56 we have a second
example of this effect, seen in the electrical response of the
petiole of Sryophyllum, rendered artificially sub-tonic by
cooling.

We next arrive at the C stage, which is, as has been said,
one of more or less stability. Expenditure is here, for a
certain length of time, balanced by
income. The molecular condition
of the tissue being thus constant,
the responses are uniform. I give
below records of such uniform re-
sponses to uniform stimuli, ex-

Fig. 56. Staircase Increase
in Electrical Response of

Fic. 55. Photographic Re- Petiole of Bryophyllum,
cord of Staircase Response rendered sluggish by
in Vegetable Nerve cooling

hibited by different tissues. In fig. 57 are seen uniform
electrical responses to uniform mechanical stimuli, given
by the root of radish. Fig. 58 shows uniform electrical
responses to uniform thermal stimuli, given by the petiole
of fern.

The C€ is succeeded by stages D and E, representing
a condition of over-strain. In fig. 59, a, are shown uni-
form responses to uniform stimuli, applied at intervals

" An account of the discovery of certain vegetable tissues, with the function of
nerves, will be found in Chapter XXXII,

92 COMPARATIVE ELECTRO-PHYSIOLOGY

of one minute. An inspection of the record shows that
there is in such cases a complete recovery, at the end of
which the molecular condition is the same as before stimula-
tion. Hence, successive responses are exactly similar to each
other. The stimulation-rhythm was now changed, to intervals

Fic. 57. Photographic Record of Uniform Responses (Radish)

of half a minute instead of one, while the stimuli were main-
tained at the same intensity as before. It will be noticed
(fig. 59, &) that these responses are now of much smaller

Fic. 58. Photographic Record of Uniform Response in Petiole of Fern

amplitude, in spite of the equality of stimulus. An inspec-
tion of the figure also shows that, when greater frequency of
stimulation was introduced, the tissue had not had time to
effect complete recovery from previous strain. The mole-
cular swing towards equilibrium had not yet abated, when

VARIOUS TYPES OF RESPONSE 93

the new stimulus with its opposing impulse was received.
There is thus a diminution of height in the resultant

(a) (4) (<)
Fic. 59. Record showing Diminution of
Response, when sufficient Time is not

allowed for Full Recovery : :
ake ed : ; Fic. 60. Fatigue in
In (a) stimuli were applied at intervals of one Celery

minute ; in (4) the intervals were reduced ; - :
to half a minute ; this caused a diminution Vibration of 30° at in-
of response. Jn (c) the original rhythm: is tervals of half a minute.
restored, and the response is found to be

enhanced (Radish).

response. The original rhythm of one minute was now
restored, and the succeeding records (fig. 59, c) at once show
increased response.

Residual strain is thus seen to
be one of the principal reasons of
reduced response or fatigue. This
is also shown in a record which
I have obtained with a petiole of
celery (fig. 60). It will be noticed
there that, owing to imperfect
molecular recovery, during the

Fic. 61. Fatigue in Leaf-stalk of

time allowed for rest, the heights Cauliflower

of succeeding responses undergo Stimulus : 30° vibration at interval
; rier . ‘ f one minute.

acontinuous diminution. Fig. 61

gives a photographic record of
fatigue in the petiole of cauliflower, and fig. 62 of fatigue in
inorganic response. !

It is evident that residual strain, other things being equal,
will be greater if the stimuli have been excessive. This is

94

COMPARATIVE ELECTRO-PHYSIOLOGY

seen in fig. 63, where the first set of these responses, A, is for
an intensity of mechanical stimulation of 45° vibration, and
the second set, B, of augmented amplitude, for an intensity
of go° vibration.

Fic. 62. Photographic Record showing
Fatigue in Tin Wire which had been
stimulated for

continuously
Days

On reverting, in C, to the first stimulus-

intensity of 45°, the re-
sponses are seen to undergo
a great diminution, as com-
pared with the first set, A.
This change is due to the
over-strain of the previous
excessive stimulation. But
we should expect that the
effect of such over-strain »
would disappear with time,
and the responses regain
their former height, after a
period of rest. In order to
verify this, therefore, I re-
newed stimulation (at the
intensity of 45°) fifteen

‘minutes after c. It will be seen from the record D how far
fatigue had been removed in this interval.

45

Os

a

Fic. 63.

90

B

Effect of Over-strain in producing Fatigue

45 45

C , D

Successive stimuli applied at intervals of one minute. The intensity of
stimulus in C is the same as that of A, but response is feebler owing to

previous over-stimulation.

Fatigue is to a great extent removed after

fifteen minutes’ rest, and the responses in D are stronger than those in
c. The vertical line between arrows represents ‘05 volt. (Turnip

leaf-stalk. )

One peculiarity that will be noticed in these curves is
that, owing to the presence of comparatively little strain, the
first response of each set is relatively large. The succeeding

VARIOUS TYPES OF RESPONSE 95

responses are approximately equal, where the residual strains
are similar. The first response in fig. 63, A, shows this, because
there had been long previous rest. The first of B shows it,
because we are there passing for the first time to an increased
intensity of stimulus. The first of C does not show it, because
of the strong residual strain from the preceding excessive
stimulation. And the first of D, again, does show it, because
the strain has now been removed, by the interval of. fifteen
minutes’ rest.

Of the antagonistic elements of positivity and negativity
which are present in response, we have seen that the positive
becomes predominant when the excitability of the tissue is
in any way depressed. And since a tissue under fatigue has
its excitability lowered, it follows that in this condition it
may be expected to exhibit a tendency towards positive
response : that is to say, expansion in the case of mechanical.
and galvanometric positivity in the case of electrical, response.
Thus, when a tissue is subjected to continuous stimulation,
the first effect will be the maximum negative response,
contraction and galvanometric negativity. But on the setting-
in of fatigue, the positive effect will predominate, inducing
a fatigue-reversal of the response. In cases where such
fatigue is very great, as, for instance, in certain muscles,
the top of the tetanic curve undergoes rapid decline (fig. 64, a).
The normal contraction now exhibits a reversal, or relaxation.
In the sensitive plant, 1/zmosa, similarly, continuous stimula-
tion by electrical shocks gives rise to results which are essen-
tially the same. It will be noticed that after the responsive
fall of the leaf it returns to its former erect position, in spite
of the fact that stimulus is still being continued. Here also,
as in the corresponding case of muscle, we have the usual
sequence, of (1) normal contraction and (2) fatigue relaxation
(fig. 65).

In electrical response, also, under continuous stimulation,
the normal galvanometric negativity, owing to the increasing
positive effect, undergoes decline or abolition. © This is seen
in fig. 64, 6, which exhibits the decline of electrical response

96 COMPARATIVE ELECTRO-PHYSIOLOGY

under continuous stimulation in the petiole of celery. The
fatigue in the mechanical response of muscle under similar
conditions is given in @ for the purpose of comparison. The
effect of rest in inducing molecular recovery, and hence in
the removal of fatigue, is illustrated in the following set of
photographic records (fig. 66). The first of these shows the
curve of electrical response, obtained with a fresh plant. It
will be seen that under a continuous stimulation of two minutes
the response first attains
a large amplitude, after
which it declines, in a
fatigue-reversal. Another
two minutes were now

(a)

(6)

Fic. 65. Photographic Records of
Normal Mechanical Response of
Mimosa to Single Stimulus: (upper

’ ‘ figure), and to Continuous Stimu-

Fic. 64. Rapid Fatigue under Con- gt s
tinuous Simutation in (az) Muscle ; lation (lower, agure) ‘ }
(6) Leaf-stalk of Celery (Electrical In the latter case the leaf is erected in
Response) spite of continuous stimulation.

allowed for recovery, and we observe that a partial recovery
takes place. Stimulation was now repeated throughout
the succeeding two.minutes, to be followed once more by
two minutes’ rest. The response in this case is seen to be
decidedly smaller than at first. The same effects are seen
in the third response. A period of rest of five minutes was
next given, and the curve subsequently obtained: under the

VARIOUS TYPES OF RESPONSE 97

same two minutes’ stimulation as before shows greater
response than the preceding, owing to the partial removal
of residual strain. |

There is one aspect of the subject of fatigue-reversal
which now demands our attention. Wehave seen that under
continuous stimulation, a maximum contraction is induced,
which is attended by the depression of the leaf of A/zmosa.

Fic. 66. Effect of Continuous Vibration (through 50°) in Carrot

In the first three records, two minutes’ stimulation is followed by two
minutes’ recovery. The last record was taken after the specimen had
a rest of five minutes. The response, owing to removal of fatigue by
rest, is stronger.

This is followed, however, by a reversal—namely, expansion,
with re-erection of the leaf. According to the chemical
theory of assimilation and dissimilation, the fatigue-effect
is assumed to be due to an explosive dissimilatory change,
with consequent run-down of energy. Inthe case of Wzmosa,
however, it is difficult to understand how, by a mere run-
down of energy and consequent passivity of the tissue, an
active movement of erection—involving the performance of
work in lifting the weight of the leaf—could be brought

H

98 COMPARATIVE ELECTRO-PHYSIOLOGY

about. Now we have seen that the diminution of normal
response may be brought about by the augmentation of the
internal factor, tending to enhance the force of restitution,
and the necessary augmentation of
the internal factor may be the result
of an increase of internal energy.
Thus while the plant is the recipient
of a continuous income, its responsive
expression is alternately one of emis- —
sion and absorption of energv. Thus
negative and positive succeed each
Fic. 67. Oscillatory Re- other or vice versa. Such a phasic

sponse of Arsenic acted ; : pe

-on Continuously by alternation is widely present, as we

Hertzian Radiation -

shall see, in the response, not only

Taken by method of con- * oe ‘

‘ ductivity variation. of various living tissues, but also of

inorganic substances. The follow-

ing record (fig. 67) exhibits this oscillatory response in arsenic
under the continuous stimulation of electric radiation. In

the case of Wzmosa, under continuous stimulation, we obtain

Fic. 68. Alternate Fatigue (2) in Electrical Responses of Petiole of
Cauliflower; (4) in Multiple Electric Responses of Peduncle of
Biophytum ; (c) in Multiple Mechanical Responses of Leaflet of Bio-
phytum ; and (ad) in Autonomous Responses of Desmodium

a single alternation, and a certain period must then elapse,
before the response can be repeated. In other cases, how-
ever, continuous stimulation may give rise to two, or three, or
a large number of similar alternations.

VARIOUS TYPES OF RESPONSE 99

In connection with this subject of phasic alternation I
may describe a certain curious phenomenon, which I have
often noticed ; I refer to the periodic waxing and waning of
both mechanical and electrical responses. The simplest
example of this will be a case in which the responses are
alternately large and small. But others are to be found in
which the groupings are more complex. In fig. 68a@ is seen
such a simple alternation, in the electrical response of the
petiole of cauliflower, under successive uniform stimuli. In
6, c, and d@ are shown similar alter-
nations in multiple and autonomous
responses. I give alsoa photographic
record (fig. 69) of a similar alterna-
tion in the automatic pulsations of
the leaflet of Desmodium gyrans.

IANA ATAVATANLE

Fic. 69. Photographic
Record of Periodic

Fatigue in the Auto- Fic. 70. Periodic Fatigue in
matic Pulsation of Des- Pulsation of Frog’s Heart
modium gyrans (Pembrey and Phillips)

Similar alternations are sometimes observed in the beating
of frog’s heart (fig. 70). |

In the following record of mechanical response (fig. 71),
taken from the style of Datura alba, we find that fatigue, as
already understood, would not explain the phenomenon
observed. For here, under the continuous action of stimulus,
without any intervening period of rest for the so-called
‘assimilatory’ recuperation, we see that a second response
occurs. I shall later give other instances in which pulsating
responses, with their alternating negative and positive phases,
are given, under the action of continuous stimulation. We
pass here imperceptibly from the ordinary phenomenon of

H2

TOO COMPARATIVE ELECTRO-PHYSIOLOGY

individual response to individual stimulus, into that of
multiple response, either to continuous, or to a single strong
stimulation. The excess of energy derived from impinging
stimulus is in the latter case held latent in the tissue to find
subsequent expression in phasic alternations of negative and
positive variations in series (cf. Chapter XVII).

There can be no doubt that these effects of periodic
alternation of phase are due to two antagonistic reactions,
becoming effectively predominant by turns. Thus the con-—
tinuous impact of stimulus on a tissue may first give rise to
the negative phase of response. But by the continuous
absorption of incident stimulus, the internal energy is in-
creased, with its. opposite
reaction of _ positivity.
Hence, the negativity will
be gradually diminished,
and the _ positive phase
become predominant. The
existence of these’ two
antagonistic factors will be
understood, from an inspec-
“Fre. 71. Photographic Record of tion of the top of a tetanic

Periodic Fatigue under Continuous curve. Here, the more or

Stimulation in Contractile Response ‘ ,

(Filament of Uriclis Lily) less horizontal line repre-

| sents a state of balance
between the two opposite forces of excitatory response by
contraction, with galvanometric negativity and recovery or
expansion, with galvanometric positivity. When this state
of balance is disturbed, by a sudden cessation of the
hitherto continuously acting stimulus, a brief overshooting
of the response in the negative direction is sometimes seen,
followed by recovery. We shall meet with examples of
this in, among others, the responses of retina and certain
vegetable tissues under light. Such facts it has been
suggested afford a demonstration of the two antagonistic
processes of assimilation and dissimilation, characteristic of
living tissues. But that they are really to be accounted for

VARIOUS TYPES OF RESPONSE IO!

from molecular considerations will be seen from the fact
that effects exactly similar are met with in the response of
inorganic matter (cf. figs. 258 and 383.)

In the case of responses exhibiting fatigue from over-
strain, we have a diminution of normal response, which may
ultimately culminate in reversal. We may imagine a spiral
spring, undergoing increasing compression from a gradually
augmenting force. The responsive compression will at first
be considerable. But this will soon reach a limit, beyond
which added force will seem to have but little power to induce
further responsive distortion. In a somewhat similar way,
we may visualise the condition of the responding molecule at
the stage D or E. Here, molecular distortion has almost
reached its limit. It follows that added stimulus can induce

Fic. 72. Fatigue in the Contractile Response of India-rubber
Note the periodic alternation and the reversal at the end.

little further distortion. But the maximally distorted mole-
cule has now a great tendency to revert to the position of
equilibrium, and the shock of stimulus, instead of inducing
excitatory action, induces the reverse. That this is to be ex-
plained by molecular rather than chemical considerations,
is seen in the following record (fig. 72) of the contractile
response of india-rubber to thermal stimulation. This
represents the last part of a long series of responses, whose
amplitude was already undergoing a progressive decline.
Further symptoms of growing fatigue are seen in the periodic
alternations of amplitude, and in the final reversal of response
to one of expansion. I shall later give another record in
which the normal negative response is seen reversed to
positive through an intermediate diphasic.

102 COMPARATIVE ELECTRO-PHYSIOLOGY

The fact that the normal response of living tissues may be
reversed under fatigue, I am here able to show by an
experiment of an unexpected character. It is usually
supposed that fatigue is typical of such tissues as muscle,
and absent from nerve. But I shall show with regard to all
the various types of response, that there is none of these
which is distinctive of any one tissue. The difference is one
of degree and not of kind. The same intensity and duration
of stimulus which is efficient to cause
fatigue in muscle will not be enough to
do so in the case of nerve. But even
nerve will display fatigue when ex-
cessively stimulated. In the record given
in fig. 73, a particular nerve of frog
had been previously fatigued, by over-
stimulation, and on now taking individual
responses to individual stimuli, it was
found that they had become reversed to
positive.

Thus a particular type of response is
the result of a particular condition of
the responding substance, and there is
none which is exclusively characteristic

. ' of any one tissue. Were it otherwise,
Fic. 73. Reversed Re- ordinary muscle, in which the explosive
sponse of Fatigued ;

Neve molecular change is supposed to be so

predominant, should typically show only
the fatigue, and never the staircase effect. But the following
record (fig. 74) shows that this is not the case. For at first
it exhibits a characteristic staircase effect ; the responses are
then for a time uniform; and lastly, we see fatigue, in a
manner exactly corresponding to the theoretical considera-
tions which we have anticipated in stages B,C, and D. The
staircase response is thus not peculiar to cardiac muscle, but
is to be seen, under appropriate conditions, in skeletal
muscle, in nerve, and even in inorganic substances. In
fig. 75 is given a series of responses of Galena to Hertzian

VARIOUS TYPES OF RESPONSE 103

radiation, which in its various phases of staircase, uniform
and fatigue-decline, is parallel to that just seen in muscle.
The phasic change, due to molecular transformation, which
I have already pointed out under continuous stimulation, is
seen in both these records in the shifting of the base-line. In
fig. 64. under continuous stimulation, we see the mechanical
response of muscle passing from a condition of growing
contraction into one ofrelaxation. In the record of individual
responses given in fig. 74, the same is seen to take place:
A similar phenomenon is ob-
served in the mechanical re-
sponse of Mimosa (fig. 65).
When the mode of record,
however, is electro-motive, in-

Fic. 75. Preliminary Staircase, In-
crease, followed by Fatigue, in the

Fic. 74. Preliminary Staircase, Response of Galena to Hertzian
followed by Fatigue, in the Radiation
Responses of Muscle (Brodie) (Resistivity variation method)

stead of mechanical, the increasing galvanometric negativity
which corresponds to increasing contraction, is found gradually
to give place to positivity (fig. 64 4). | And finally, when the
mode of record is by resistivity-variation, we find, by the
shifting of the-base line in fig. 75, that the residual negative
variation of resistance at first waxes and then wanes.
Instances have been given, in which a portion of the in-
cident stimulus has been seen to be held latent to do internal
work. And from this it is clear that the current assumption that
response must always be larger than stimulus is quite un-

104 COMPARATIVE ELECTRO-PHYSIOLOGY

tenable. There are cases, again, in which a large portion of the
incident stimulus is held latent for a time, to find subsequent
manifestation externally. This I have been able to demon-
strate by the discovery of multiple response in plants. Thus
while a single moderate stimulus in such cases evokes a
single response, a single strong stimulus is found to give
repeated or multiple responses. This I have shown, not
only in mechanical, but also
in electrical response, and the
latter subject will be taken
up in detail in a subsequent
chapter.

And, lastly, it follows
from what has been. said,
that incident stimulus need
not always cause depreciation
of the energy of the tissue,
but that, on the contrary,
it may actually raise it above
par. I shall now describe an

example in which incident
-Fic. 76.- Photographic Record of .
' Responses of Style of Datura alba stimulus was seen to find

in which Growth had come toa bifurcated expression. In
Temporary Stop f 63 : h

The up curve shows contraction. As 8 ps fey ees ee rien
long as the base-line is horizontal, graphic record of contractile
growth is seen to be at standstill. ; ; ‘ ty] £
Renewal of growth at sixth re- responses in the style o
sponse, after which growth-elon- Datura alba, in which growth
gation is shown by the trend of : 5
the base-line downwards. had previously been in a state

of standstill. The first five
responses of this series are seen to be uniform. A portion
of the stimulus applied must, however, from the first
have been absorbed and held latent in the organ, thus
increasing that internal energy, or tonic condition, on
which growth depends. For at the sixth response we
find that growth recommences, and the stimulus now
finds bifurcated expression, in maintaining response and in
renewing growth, as seen in the trend downwards of the

oe ty ee ee ee ‘a di tale

_

VARIOUS TYPES OF RESPONSE TO5

hitherto horizontal base-line. This bifurcation causes the
first contractile response of the now growing organ—sixth of

the series—to be smaller than usual. But, as a favourable

tonic condition is gradually established by the absorption of
energy and the molecular mobility of the responding organ
is increased, the contractile response becomes larger, and
growth goes on at a certain steady rate. This constitutes
an instance in which stimulus, so far from lowering the
energy of the responding system, has actually raised it
above par.

It would thus appear that while the theory of assimilation
and dissimilation is insufficient for the explanation of the
various characteristics of response, the difficulties there en-
countered are, on the contrary, satisfactorily explained, on
taking full account of the influence on response of the
molecular condition of the responding substance. From
the chemical hypothesis of an explosive molecular change,
with its attendant dissimilation and run-down of energy, it
would follow that previous stimulation should always induce
a depression of the subsequent responses. Instead of this,
however, it is found that previous stimulation sometimes
exalts, and at other times depresses, the subsequent re-
sponses. This apparent anomaly we have seen to be ex-
plained by the consideration of molecular transformation.
From the sluggish condition A, we have seen tissues trans-
formed, by the impact of moderate stimulus, to condition B,
with its greater excitability. It is only when the molecular
condition has been brought to D or E, that the responses
undergo a diminution or reversal.

The molecular condition, then, undergoes a continuous
transformation, in consequence of the action of stimulus, from
the extreme of sub-tonicity A to the overstrained molecular
conditions D and E. In the A stage, there is no true ex-
citatory expression, response to stimulus being here by the
abnormal positive variation. The substance is next trans-
formed into stage B, where response exhibits a staircase
character. In the next stage C, the responses are uniform.

106 COMPARATIVE ELECTRO-PHYSIOLOGY

Under over-stimulation, the stages D and E are reached,
characterised by diminished amplitude of response, or actual
reversal into positive. There are thus two conditions under
which we obtain abnormal positive responses. One of these
is that of sub-tonicity, and the other, the reversal due to
fatigue.

There is, again, no tissue which is exclusively characterised

by any specific type of response. All these—staircase,

uniform, and fatigue—will occur in muscle, nerve, plant,
and even inorganic matter, under certain definite and ap-
propriate conditions. In a future chapter, we shall study in
detail the characteristic molecular curve, from which light
will be thrown on the internal molecular condition of the
tissue, and the influence of that condition on response.

Ne fi teat tn Oo el

os

CHAPTER IX

DETECTION OF PHYSIOLOGICAL ANISOTROPY BY ELECTRIC
RESPONSE

Anomalies in mechanical and electrical response—Resultant response determined
by differential excitability—Responsive current from the more to the less
excitable—Laws of response in anisotropic organ—Demonstration by means
of mechanical stimulation—Vibrational stimulus—Stimulation by pressure—
Quantitative stimulation by thermal shocks.

IT has been customary, as we know, to ascribe the varied
movements of plant-organs under external stimulus, to the
presence of different specific sensibilities ; and, indeed, it
would seem at first sight impossible to reduce such highly
complex and apparently unrelated phenomena, to the terms
of a single fundamental reaction, common to all alike. There
is no denying, for instance, that certain plant-organs, when
acted on by light, bend towards it, and others away. I have
elsewhere shown,' however, that all these diverse movements
are clearly traceable to one fundamental excitatory reaction,
and that the different effects observed are due merely to the
differential excitabilities of various parts of the structure ;
and that the resultant movement is in all cases brought
about by the greater contraction of the more excited side.
Passing next to the electrical response of living tissues,
animal and vegetable, we encounter many anomalies. Not

only will one tissue give positive, and another negative

response, but we find also that the same tissue will give

sometimes one and sometimes the other. ‘These apparent

inconsistencies are often due, as we shall find, to the dfferentzal

excitability of anisotropic structures—a factor in the problem

which has not hitherto been recognised. An investigation on
1 Bose, Plant Response.

108 COMPARATIVE ELECTRO-PHYSIOLOGY

this subject, then, demands that we first discover some means
of determining the relative excitabilities of different parts of
a tissue.

As the simplest example of an anisotropic structure, we
may take a compound strip of ebonite and stretched india-
rubber, glued firmly together throughout their length. Of
these, the india-rubber is the more contractile, and when the
strip as a whole is subjected to periodic thermal stimulation,
response takes place by the greater contraction induced in >
the india-rubber. Ifthe strip be held, with the india-rubber
below, response will be by the induced concavity of the
lower side. -In fig. 77 is shown a series of these responses of
the compound strip, taken on a smoked
surface by means of a recording lever.

In anisotropic motile organs, such as
the pulvinus of J/zmosa, response takes
place by differential contraction, the more
excitable side being that which under
diffuse stimulation becomes concave.
If we apply very moderate stimulus
AG 21. DiRerenge locally on the upper half of the pulvinus,

sponse of Artificial we shall find that, by the excitatory con-

sh traction of this half, the leaf is raised.
A. similar contractile effect, though of greater intensity, is
induced when the lower half of the pulvinus is stimulated
locally, the leaf in this case undergoing a depression. When
both upper and lower halves, then, are excited simultaneously,
the resulting fall of the leaf shows that the contraction of the
lower half must in this case be the greater, or, in other words,
that this half is the more excitable of the two. This experi-
ment may be carried out very easily by using the stimulus of
light. Fig. 78 gives the results observed (a), showing the up
movement consequent on stimulation of the upper half; (¢)
that caused by equal stimulation of the lower half; and (c) the
resultant fail when the two are excited simultaneously. In the
case of mechanical response, then, we find it true that response
is by the greater contraction of the more excitable.

DETECTION OF PHYSIOLOGICAL ANISOTROPY fore

We shall next observe what is the electrical mode of
response for.a tissue which is anisotropic, or unequally ex-
citable on two sides. For this purpose we may again take
the pulvinus of A/zmosa, and make electrical connections at
two diametrically opposite points on the upper and lower
halves of the pulvinus respectively. It is to be remembered
that electrical response takes place on excitation, whether
the leaf be free to move, or physically restrained. We may,
therefore, hold it in a fixed position; and indeed this is
advisable, in order to avoid that shifting of the electrical
contacts which might
possibly take place if
it were allowed to fall.

The two contacts
are made with two
fine straws filled with
kaolin paste, moistened
in normal saline. On
now applying a series
of thermal stimuli, on
the petiole, near the

pulvinus, I obtained the
responses given in fig. Fic. 78. Responses of AZ/mosa to Sunlight of

; not too long Duration
79. It will be seen
: (a) Light acting on pulvinus from above ; (64) light
that the responsive acting on pulvinus from below ; (c) light acting
current flows in the simultaneously from above and below. Dotted

3 line represents recovery on cessation of light.
tissue from the rela-

tively more excited lower, to the less excited upper, half
of the organ.

We thus arrive at a comprehensive law of the mechanical
and electrical response of anisotropic organs:

Diffuse stimulation induces greater contraction and
galvanometric negativity of the more excitable side.

The laws of electric response in the anisotropic organ
may then be detailed ‘as follows :—

1. On simultaneous excitation of two points, A and B, the
responsive current flows in the tissue from the more to the less
excited.

IIo COMPARATIVE ELECTRO-PHYSIOLOGY

2. Conversely, if under simultaneous excitation the responsive
current be from B to A, then B is the more excitable of these
two points.

These form only an instance of the general law that the
responsive current always flows from the more to the less
excited. For when a point, B, is excited locally—-this point,
that is to say, being the more excited—the responsive
current is found to flow away from it to a neutral or in-
different point, A, for which any distant point will serve,
provided the tissue be non-conducting. Should it be con-
ducting, the neutrality of A is maintained by interposing a

Fic. 79. Transverse Response of Pulvinus of AZimosa

The petiole is securely held to prevent movement, and diametric electric
contacts made in the upper and lower surfaces of pulvinus. Re-
sponsive current is from lower to upper surface.

block. Should the stimulus, however, not be local, but diffuse,
a resultant response may still be obtained by injuring or
killing the point A, and thus diminishing or abolishing its
excitability. On stimulation, the point B is now necessarily
the more excited, and the responsive current is still away
from B, towards A. And finally, owing to physiological
anisotropy, B may be naturally more excitable than A, and
6n stimulation the responsive current will then be found
to flow from the more excited B to the less excited A.

The comparison of the excitabilities of the two points
A and B, therefore, reduces itself to the application of similar

DETECTION OF PHYSIOLOGICAL ANISOTROPY III

stimuli to the two points simultaneously, and then ascertaining
the direction of the responsive current.

For this purpose we might employ any form of stimulus,
and it is extremely interesting to find that, however diverse
the. stimuli, the results obtained by them are always
identical And here we have not merely a means of
qualitative demonstration, but in some cases one of quanti-
tative also. i

If we take an erect stem of Cucurbita, it being radial
and isotropic, all its flanks will be found equally excitable.
Hence, if two diametrically opposite contacts are made, there

Fic. 80. Diametric Method of Stimulation of an Anisotropic Organ

Diametrically opposite contacts are made at A and B, and tissue subjected
to vibrational stimulus.

will, on diffuse stimulation, be no resultant response. But
when such a stem becomes recumbent, the upper side, being
now constantly exposed to light, becomes fatigued by over-
stimulation, with consequent diminution of its excitability.
This is true only when the stimulus has been excessive and
long continued ; for we have seen moderate stimulus may
sometimes enhance the excitability. By the unilateral action
of light, then, the organ has been converted from radial into
anisotropic, the lower side being that which we shall expect
to find the more excitable.

On mounting such a stem in the vibratory apparatus
(fig. 80), and making diametrically opposite contacts on the
two anisotropic surfaces, we find that on applying vibration

112 COMPARATIVE ELECTRO-PHYSIOLOGY

both sides are subjected to similar stimulus simultaneously ;
and the responsive current is now found to flow across the
tissue, from the lower to the upper side. The lower is thus,
as we expected, the more excitable. Since we can by means
of vibration apply measured stimuli, it will be seen that we
have here a quantitative method of investigation. Moreover,
as the stimulus is applied directly, it is applicable not only
to conducting but also to non-conducting tissues.

If we next take a radial stem or petiole of Cucurbita, and

slit it longitudinally, we obtain, in either of the halves, a
specimen having an inner and an outer surface. As one of
these has been exposed to light and the other protected
from it, we should expect to find, on examination, that there
has been an induction of physiological anisotropy. As such
a specimen is not very well adapted for vibrational stimula-
tion, we may use that of pressure. Two moistened rags, in
_ connection with non-polarisable electrodes, pass through two
pieces of cork, adjusted on the two surfaces—outer and
inner—at diametrically opposite points. When the inter-
posed tissue is now subjected to sudden pressure its two
surfaces are excited simultaneously, and the responsive
- current is found to flow from the inner concave to the
outer convex surface, proving that the former was the more
excitable. |

We might again use the chemical form of stimulation,
and the results obtained by this method will be described in
the course of the next chapter. But these forms of stimulus
—by pressure, or by chemical means—are not capable of
exact measurement. For quantitative observations, then, it
is necessary to employ some other form of stimulus, and the
electrical offers us in this respect many advantages. There
are, however, in this case many possible disturbing influences
to be considered, all of which must be carefully eliminated
before the method can be used without misgiving. How this
may be done will be shown in a future chapter. For the
present I shall describe another method of stimulation which
I have been able to bring to great perfection, by which

ee

DETECTION OF PHYSIOLOGICAL ANISOTROPY 113

two points of an anisotropic organ may be simultaneously
excited, under a series of stimuli of uniform or increasing
intensity.

This mode of excitation, by thermal shocks, will be found
in every way satisfactory and convenient. The Thermal
Variator, by which stimulation is effected, consists of a spiral
of german-silver wire, the diameter of the spiral being about
3 cm. The electrical circuit, through which the heating-
current is sent, is closed periodically for a definite length of

Fic. 81. The Thermal Variator

The anisotropic tissue-petiole of J/wsa is held in ebonite clip, c. 8, &’,
electrodes connected with opposite sides. Specimen after adjustment
pushed inside heating-spiral, T, by slide, s. Spiral heated periodically
by closure of electric circuit by metronome, M.

time, by means of a metronome (fig. 81). The thermal
variation within the coil can be controlled by a suitable
adjustment of the battery-power, or by the duration of
closure, or both. The experimental tissue is held in an
ebonite clip, C, fixed on a slide, S, on the same stand as the
heating-spiral. This slide is pulled out for the purpose of
adjustment. Square or circular pieces of wetted muslin make
contacts with equal areas on two opposite sides of the
experimental tissue, these pieces of cloth being connected
with non-polarisable electrodes, E and E’ After the adjust-

y

IIl4 COMPARATIVE ELECTRO-PHYSIOLOGY

ment is made, the slide is pushed in, till the tissue is well in
the centre of the coil. When the circuit is completed, for a
brief period, both the sides A and B are subjected to the same
sudden variation of temperature, which, as we know, acts as
a stimulus. As the two contacts are thus in practice raised
to the same temperature, there will be no thermo-electrical
disturbance. The responsive current, therefore, will be
determined by any difference of excitability which may exist

as between A and B. The spiral also gives out heat-radia-

tion, which acts as a contributory stimulus. That it is the
thermal variation, and not the temperature, which acts as
the efficient external stimulus, is seen from the fact that
when the tissue is subjected to the higher temperature con-
tinuously, the galvanometric deflection obtained is opposite
in direction to that induced by the thermal shock. This is
because the absorption of heat, as such, increases the internal
energy, and thus induces an electrical effect opposite to that
caused by external stimulation.

As experimental tissue, we may use the sheathing
petiole of Musa. The required piece is cut and mounted in
the apparatus, the concave surface being taken, say, as B,
and the convex as A. I have mentioned J/usa as suitable
for this purpose, because I find it, when fresh, to show
practically no sign of fatigue in its responses. There are
many other sheathing petioles, which would doubtless answer
the same purpose more or less perfectly. |

In obtaining records with this specimen, it is found that
the responsive current flows across the petiole, from the inner
concave surface B to the outer convex surface A, showing
that it is the inside which is more excitable. Uniform
stimuli of short duration were applied at intervals of one
minute, and the responses obtained are seen to be fairly
uniform (fig. 82). The specimen was next subjected to the
anesthetic action of chloroform. This, it will be seen, in-
duced a very great depression of the response.

It has thus been shown that just as the greater contrac-
tion and concayity of a motile organ enables us to discrimi-

DETECTION OF PHYSIOLOGICAL ANISOTROPY I15

nate which side of two is the more excitable, so here also the
more excitable side is that which, on diffuse stimulation,
exhibits galvanometric negativity relatively to the other.
From this it becomes possible to determine the relative
excitabilities of any anisotropic organ, even though it be
non-motile, and therefore incapable of exhibiting any con-
spicuous mechanical response. The difficulty of applying
equal and quantitative stimulus on two sides simultaneously

Fic. 82. Responsive Current in Petiole of Musa from Concave to
Convex Side

First series, normal ; after application of chloroform subsequent
depression.

has now been overcome by vibrational stimulation, and by
the perfection of the method of thermal shocks. Thus a
definite resultant response has been shown to be determined
by the differential excitabilities of two parts of an experi-
mental tissue. And that from this consideration it becomes
further possible to resolve many of the remaining anomalies
of electrical response will be fully demonstrated in a sub-
sequent chapter.

CHAPTER X
THE NATURAL CURRENT AND ITS VARIATIONS

Natural current in anisotropic organ from the less to the more excitable—External
stimulus induces responsive current in opposite direction—Increase of internal
energy induces ‘positive, and decrease negative, variation of natural current—
Effect on natural current of variation of temperature—Effect of sudden
variation—Variation of natural current by chemical agents, referred to
physiological reaction—Agents which render tissue excitable, induce the
positive, and those which cause excitation, the negative variation—Action of
hydrochloric acid—Action of Na,CO,—Effect modified by strength of dose—
Effect of CO, and of alcohol vapour—Natural current and its variations—
Extreme unreliability of negative variation so-called as test of excitatory
reaction— Reversal of natural current by excessive cold or by stimulation —
Reversal of normal response under sub-tonicity or fatigue.

WE have seen that when the pulvinus of A/zmosa is excited
by an external stimulus, there is a relatively greater expulsion
of water from the more excitable lower half, with a con-
comitant greater contraction. Conversely, the lower half of
the pulvinus is capable of absorbing more water, and of
expanding to a greater extent, than the upper. Increased
internal energy, in contrast to the action of external stimulus,
has the effect of causing a greater expansion of the lower
half of the pulvinus, and thus raising the leaf. This we saw
exemplified when the plant was subjected to a gradually
rising temperature, so as to increase its internal energy, its
leaves being thereby made to show increased erection (p. 72),
Hence the more excitable tissue in the pulvinus of Wzmosa
is characterised, both by greater power of absorption and by
greater emission of energy, according to circumstances. In
this we see a close analogy to the action of inorganic bodies,
in which also we find the greatest power of emission to be
associated with a correspondingly great power of absorption of

energy.

THE NATURAL CURRENT AND ITS VARIATIONS I17

We have thus seen that in order to maintain a high state
of excitability, absorption of energy is necessary. On

excitation, emission of energy occurs. In this latter case, of

emission, we observe a concomitant galvanometric negativity
of the more excited lower side. Since to have maintained its
excitability the opposite process of absorption would have
been necessary, it follows that the more excztable lower side
must under normal conditions be galvanometrically positive.
This is found to be the case. For when the leaf is in an
excitable condition, there is an electro-motive difference
between the upper and lower halves of the pulvinus, in con-
sequence of which a current flows across the tissue, from the
less excitable upper to the more excitable lower half, which
is thus galvanometrically positive, in relation to the upper.
We have here, then, an additional instance of the opposite
effects of internal energy and external stimulus. Internal
energy, maintaining a greater excitability of the lower half
of the pulvinus, induces in it a relative galvanometric positivity.
External stimulus, on the other hand, gives rise to precisely
the opposite effect—namely, the relative galvanometric
negativity of the lower half. Under typical conditions, then,
we may expect the more excitable point to be galvano-
metrically positive; and the more excited to be galvano-
metrically negative.

Turning next to non-motile tissues, we find the same
conclusions to hold. good. We saw that in the case of the
sheathing petiole of M/usa, the concave was more excitable
than the convex side. The concave is thus normally positive
to the convex side, and the natural current flows across the
tissue from the convex to the concave. While the natural
current flows from the more excitable to the less excitable,
external stimulus gives rise to a responsive current in the
opposite direction, from the more excited to the less excited,
constituting a negative variation of the current of rest. .

Let us next consider what would be the effect of an
increase of internal energy on the natural current. Since the

action of internal energy is opposite to that of external

stimulus, we should expect it to induce a positive variation of

118 COMPARATIVE ELECTRO-PHYSIOLOGY

the natural current. Diminution of internal energy on the
other hand might be expected to cause a negative variation.
These effects are diagrammatically represented in fig. 83,
which also exhibits the parallelism between the electric
responses of motile pulvinus and non-motile anisotropic
organ. :

We next proceed to subject the question of the effect of

increased or diminished internal energy on the natural
current to experimental verification. As regards the increase ~

of internal energy, we have already seen that this can
be secured by a gradually

id Than rising _ temperature, its
¥ diminution being, con-
eas 2G, trariwise, secured by a
2 falling temperature. In

the case of Mzmosa, we

Fic. 83. Parallelism of Natural Current .
in Pulvinus of Mimosa and Sheathing 54W that the former in-

Petiole of Musa duced an erection of the

Upper and less excitable surface of former Jeayes and the latter a
corresponds with outer or convex sur- ‘

face of latter. The natural current, N, gradual depression. In

is in both from the less to the more ex-
citable. In both excitatory current, E, order, then, to observe the

is in opposite direction, z.e. from the effect of increase or de-
more to the less excitable. In Musa ae

increase of internal energy (+ }) in- Crease O internal energy
duces a positive; and diminution of on the existing current of

internal energy (— *) a negative, varia-
tion of the natural current. rest, we have only to sub-
ject the specimen to gradual
thermal ascent or descent, and record the consequent
variation of current.

The specimen of Zusa is placed in a chamber and two
diametrically opposite contacts are made, with the internal
and external surfaces, and led off to the galvanometer. To
take first the effect of cooling: a stream of ice-cold water is
sent through a hollow tube in the chamber: this gradually
lowers the temperature, say from 30° C. to 27° C. It will be
seen from left-hand curve of fig. 84 that this has the effect
of diminishing the natural current of rest in the tissue, as
represented by the dotted arrow |}. When the chamber is

THE NATURAL CURRENT AND ITS VARIATIONS I1I9Q

allowed to’ return to the temperature of the room, this
diminution of current is annulled.

To study the effect, on the other hand, of a rising tempera-
ture, the chamber is gradually heated, by means of the
electric heating-coil already described. In thus raising the
temperature, it is found (fig. 84, right-hand curve) that the
natural resting-current undergoes an increase. On cooling
again to the original =
temperature, this in-
crease is annulled.
That these effects are
due to induced elec-
tro-motive variations,
and not to any
changes of resistance,
is demonstrated from
the fact that the effect
described takes place
even when the original
E. M. F. is exactly
balanced by a poten-

tiometer. Fic. 84. Effect ot Variation of Temperature
It ‘all on Natural Current, {, which in Petiole of
was specially Musa flows from Convex to Concave Side
stated that these ob- Effect of cooling from 30° C. to 27° C., seen
servations with regard on left, induces negative variation of natural
current. Restoration to original value on
tothe effect of varying return to surrounding temperature. Warm-
t | ing induces positive variation (see record to
emperatures apply right). In this and subsequent figures in
only to steady varia- the present chapter { indicates the direction
of the natural current of rest.

tions. In the case of

thermal ascent, we

have seen that a steady rise brings about an increase of
the existing current. But since sudden variation of tempera-
ture acts as a stimulus, we shall, in the preliminary stage,
obtain an excitatory reaction, which will cause a transient
diminution of the current of rest. This will be followed,
when the rise of temperature is steady, by am increase of
the current of rest. I give here (fig. 85) a photographic

120 COMPARATIVE ELECTRO-PHYSIOLOGY

record of these contrasted effects. In the first part of the
curve we observe a sudden movement of the record upwards
corresponding to the sudden rise of temperature. This is so
great as to carry the curve out of the photographic field. We
have here, then, a sudden excitatory diminution of the natural
current. In the next stage, while
the temperature is steadily ascending,
we find a reversal of the curve, and
the natural current is enhanced above.
the normal. On now allowing the
chamber to cool down to the original
temperature of the room, the natural
current was found to return more or
less to its normal value.

We shall next study the effect
of chemical agents on the natural
current. The mode of procedure
is to apply the given agent on both
the contacts at the same time. If

Fic. 85. Photographic
Record showing effect of
Sudden, followed by

steady Rise of Tem-
perature on Natural Cur-
rent, ¥, in A/usa

the substance be liquid, it can be
applied by a pipette. If it be gaseous,

the specimen is placed in a chamber
through which the gas or vapour is
allowed to stream.

' During sudden variation of
temperature an excitatory
negative variation of
natural current: takes
place, as shown by first
up curve; when rise of

- temperature becomes
steady there is a positive
variation, as shown by
the down curve ; on re-
turn to surrounding tem-
perature, the normal cur-
rent is restored to its
original value.

In observing
the effects of various agents we
obtain results which are at first
sight very perplexing. For example,
certain substances will be found to
induce a diminution of the natural
current, and others an increase. The
effect, moreover, is found to be modi-
fied by the strength of the dose. Thus an agent which,
in a given strength, will cause a diminution of the natural
current, may often be found to cause an increase, when
sufficiently diluted. This inquiry is of great importance,
since it is directly connected with many equally obscure
problems in medical practice, where the effect of a drug

THE NATURAL CURRENT AND ITS VARIATIONS I12I

is well known to be modified by the amount of the
dose.

Much light appears to be thrown on this subject, when
we consider the electrical reactions of the chemical agents as
due to their physiological action. If a drop of hydrochloric
acid be applied to the pulvinus of J7/zmosa, the leaf falls,
showing that the more excitable side has undergone a greater
excitatory contraction. We have also seen that when a drop
of this acid is applied on any tissue in the neighbourhood of,
but not directly touching, an electrical contact, it induces an
excitatory galvanometric negativity. If now we apply it in
solution, say, of 10 per cent. on the two diametrically opposite
contacts of J/usa, we shall expect that the greater excitatory
reaction induced on the concave side will give rise on that
side to a relative galvanometric negativity, resulting in a
negative variation of current of rest. On the application of
the reagent this is found to be the case, the responsive
current flowing in a direction opposite to that of rest: that
is to say, it flows from the more excited concave to the less
excited convex.

It is by considering chemical agents from the point of
view of their physiological reaction, that we are able to
explain their diversity of effects, according to the strength of
the dose and the duration of application. We have seen that
while a strong stimulus induces the excitatory effect of
negativity, a feeble stimulus will bring about the opposite,
or positivity. This abnormal positive response, however, by
the continued action of moderately feeble stimulus becomes
converted into normal negative. Now a chemical substance
which in a certain strength acts as an efficient excitatory
agent, may, when sufficiently diluted, act as a feeble stimulus,
inducing a positive response. If the same agent again were
applied in a slightly greater concentration, its immediate.
effect might be positive, to be succeeded under continued
application by the normal negative.

We might thus expect, using a strong salon of a given
chemical reagent, to obtain a negative variation of the current

122 COMPARATIVE ELECTRO-PHYSIOLOGY

of rest; using a dilute solution, to obtain a positive varia-
tion ; and, lastly, applying a dose of intermediate strength,
to discover the very interesting case in which the reagent
would give rise immediately to a positive variation, and after
a longer or shorter continuance of its action, to a reversed, or
negative variation, of the current of rest. These inductions
are found fully verified in the experiment which I am now
about to describe.

1

|
i

‘

‘
Vv

Fic. 86. Action of 7 per cent. Solution Fic. 87. Effect of CO, on

of Na,CO, on Natural Current of M/zsa Natural Current of AZwsa
Preliminary positive variation represented Preliminary positive seen to be’
by down curve followed by reversal, succeeded by negative variation
50 seconds after application. 5 minutes after application. ;

Applying a strong solution of sodium carbonate —10 per
cent. or above—at the electrical contacts on Musa, the result
is a negative variation of the natural current. If nowa dilute
solution of I per cent. be applied on a similar specimen, we
obtain a response by positive variation. And if, lastly, we
use a 7 per cent. solution, we obtain, as will be seen from the
record (fig. 86) the preliminary positive, succeeded, under the
continued action of the agent, by reversal to the negative,
variation.

We pass next to the question of the effect of gases. In
fig. 87 is given a record of the action of carbonic acid on

i MN i a

THE NATURAL CURRENT AND ITS VARIATIONS 123

the natural current in /usa. It will be seen here that in the
first stage there was an enhancement, or positive variation,
of the existing current. In a later stage, however, this is
followed by a reversal, the resting-current now undergoing a
diminution. We have here an effect parallel to that of the
intermediate dose of sodium carbonate. Vapour of alcohol
also exerts an effect very similar ; that is to say, it induces a
preliminary exaltation, followed by a depression of the natural

current.

In connection with this subject, of the changes induced
in the natural electro-motive difference between the two
surfaces, by the action of a chemical reagent, it is well to
distinguish between the effects of two different factors:
namely, the electrical variation caused by the chemical sub-
stance as such, and that brought about by the excitatory
reaction. Let us suppose both the electrical contacts to be
made on iso-electrical surfaces, with normal saline solution;
there will then be no difference of potential, as between the
two. But this state of things will be disturbed, by the appli-
cation of another chemical solution, say acid, on either one
of the two contacts. The resulting disturbance may be dis-
tinguished as due to heterogeneity of chemical application.
But if the same chemical agent be applied at both the
contacts, no such chemical heterogeneity will ensue. If,
then, any electro-motive difference be induced, it must be due
primarily to some induced physiological change. The contact
which has been rendered more excitable will become increas-
ingly positive ; that which is more excited, on the other. hand,
will become increasingly negative. That the induced electro-
motive variation under such circumstances is indicative ot
a variation of excitability or excitation, was seen in the fact
that the same chemical agent—for example, Na,CO,— caused
a positive variation when dilute, a negative when strong, and
positive followed by negative under the continued action of
an intermediate dose. This conclusion—that the variation
of the existing current, by the simultaneous application
at the two contacts of the same chemical reagent, is due

124 COMPARATIVE ELECTRO-PHYSIOLOGY

to a physiological reaction, the positive variation being a
sign of relatively increased, and the negative of decreased,
excitability—will be verified by an independent mode of in-
quiry, to be described in the following chapter. |

It follows from the experimental demonstration which has
just been given that the phenomena of the natural current
and its variations may be summarised in general as follows :

1. Under normal conditions, the current of rest flows in

the tissue from the less to the more excitable. In other

words, the more excitable is galvanometrically positive to the
less excitable.

2. Increase of internal energy induces an increase or.
positive variation of the existing current ; and diminution of
internal energy induces a negative variation.

3. External stimulus induces a negative variation of the
true or natural current of rest.

The natural current and its variations under normal con- .

ditions have now been studied. We shall next proceed to trace
out those conditions under which abnormal results may occur.
Excessive cooling, by diminishing internal energy, may thus
reverse the normal current, which reversal may become more
or less persistent. It has been shown, moreover, that in an
anisotropic organ, external stimulus gives rise to a current
opposite in direction to the natural current. . By this excita-
tory reaction the more excitable side, hitherto positive, is
rendered negative, and if the excitatory reaction be great, it
may remain fora considerable period in this reversed condition
of galvanometric negativity.

We have seen that under normal conditions, the direction
of the natural or true current of rest is from the less to the
more excitable, and that external stimulus causes a responsive
current in the opposite direction, which thus constitutes a
negative variation of the current of rest. This state of
things we shall distinguish as the primary condition. It
frequently happens, however, in consequence of previous
stimulation, with its after-effect, that extremely varied effects,
appearing at first very anomalous, occur, with regard to the

‘Le

ee

THE NATURAL CURRENT AND ITS VARIATIONS 125

direction, not only of the current of rest, but also of the
current of response. We shall be able. to obtain a clear
understanding of these effects, on subjecting the underlying
phenomena to close analysis. As a concrete example, we
may take for our investigation the various effects to be
observed in the pulvinus of Mzmosa.

In this anisotropic organ, the directions of the resultant
current of rest and the current of response are determined,
as we have seen, by the differential excitability and differential
excitation of the two sides of the organ. We shall fix our
attention, however, for the sake of simplicity, on the changes
which occur in the more effective lower half. I shall here
succinctly describe the various post-primary phases in the

changing effect, culminating in the onset of fatigue from over-

stimulation. In the primary condition, as we have seen, the
lower half of the pulvinus is positive to the upper, the
direction of the resting-current being down ¥. On stimula-
tion, the lower half becomes negative and. the response
current is up t. Response thus takes place by a negative
variation of the resting-current.

We may now suppose the pulvinus to be in a state of
slight excitation, its molecular condition at or about the B
stage. This existing state of moderate excitation will annul
the previous positivity, and the current of rest will now be
zero. At this stage, however, as we have seen, the excit-
ability of a tissue is enhanced. Hence, on stimulation, the
lower half of the pulvinus will exhibit responsive negativity,
and the direction of the response current will be up ft: We
are, however, unable to describe this variation in terms of the
current of rest, since that, as we have already seen, is zero.

A condition of still stronger excitation, bringing the
tissue to the C condition, will induce galvanometric negativity
of the lower half. The so-called current of rest is thus
upwards t. But as the excitability of the lower half is. still
relatively greater than that of the upper, it follows that
external stimulus will bring about a responsive current whose
direction is upwards t, This normal excitatory response,

126 COMPARATIVE ELECTRO-PHYSIOLOGY

then, in this particular case, appears as a positive variation of
the resting-current.

And, finally, we may imagine the pulvinus to have been
strongly excited, so as to be in the condition Dor E. The
resting-current will in this case be upwards ft. But the ex-
citability of the lower half, owing to fatigue, has now become
depressed, a condition which, as we have seen, tends to give
rise to the abnormal positive response, the responsive current

being thus downwards ¥. As the modified current of rest |

is upwards, this abnormal current of response will appear as
a negative variation of it.
All these cases are conveniently tabulated as follows :

TABULAR STATEMENT OF THE RELATIVE DIRECTIONS OF THE CURRENT
OF REST AND THE RESPONSIVE CURRENT UNDER VARIOUS CONDITIONS.

Current of rest. Current of re- | Variation of current of rest.

ndition.
Co sponse.

Negative variation

Primary condition , |
Feebly excited
Moderately excited
Strongly excited and
| fatigued . :

*

t fi. :,
+ Positive variation
1

Negative variation

| > -o<

The various conditions mentioned may be induced
accidentally in the responding organ, or may be brought
about by the excitatory effect of experimental prepara-
tion. I give here the records of certain experiments
performed on J/zmosa, in which some of these changes were
seen to occur as the result of stimulation (fig. 88). The
normal natural current is seen to be from above to below, as
represented by the dotted arrow. The first strong stimulus,
applied at the moment represented by the thick dot, gives
rise to a responsive current whose direction is from below to
above, Owing to the strong intensity of the stimulation,
there is here a slight indication of multiple response. As an
after-effect of stimulus, we observe that the normal resting-
current has undergone a reversal, the lower surface, which
was formerly positive, having now become relatively
negative, A second stimulus now gave rise to a response

— oe

——

THE NATURAL CURRENT AND ITS VARIATIONS 127

similar to the first. But after this, owing to the greater
fatigue with loss of excitability induced in the lower half of
the pulvinus, the succeeding responses are seen to be reversed,
the responsive current being henceforth from above to below.

From the table given on the previous page, it will be
seen that hardly could any standard have been devised for
the study of excitatory reaction, so likely to be prolific of
confusion as this, of the so called variation of the resting-
current. For in the first
three cases displayed, we
see one identical excitatory
effect, appearing now as a
negative, again as doubtful,
and a third time as a positive
variation of the current of
rest. In the fourth case,
again, it is actually the
abnormal response’ which
appears as the normal nega-
tive variation! But while
these responses appear to
be so various, the underlying

Fic. 88. Variation of the Transverse
Natural and Responsive Currents in
Pulvinus of Wzmosa

Natural current } which -is normally
down, reversed in consequence of
strong external stimulus. The first
two responses are normal, z.¢. current
being from below to above. Strong
stimulus is here seen to induce mul-

reaction is nevertheless con-
stant. The direction of the
responsive current is always
from the more to the less

tiple responses. After the second
response on account of the greater
fatigue induced in the lower half of
the pulvinus, the direction of the
responsive current is seen to be

reversed. Thick dots represent

excited. moment of application of stimulus.

It has thus been shown |
in the course of the present chapter that under normal
conditions the current of rest flows in the tissue from
the less to the more excitable; that increase of internal
energy causes a positive variation of the current of rest ,
while its diminution gives rise to a negative variation ; that
reagents which increase excitability induce a positive, and
those which cause excitation a negative, variation of the
resting-current ; and, finally, that external stimulus induces
a negative variation of the resting-current. While these are

128 COMPARATIVE ELECTRO-PHYSIOLOGY

the normal reactions, however, under abnormal conditions,
they may be reversed. Thus, excessive cooling or strong

external stimulation may reverse the normal current of rest. .

There are, moreover, two different conditions, those, namely,
of sub-tonicity (cf p. 106) and fatigue, which may be effective
in bringing about a reversal of the normal direction of the
responsive current. In this way, by means of induced varia-
tions of the resting-current and of the responsive current,
many very varied effects become possible.

Al ett i od

_— Te eee

—o

CHAPTER XI

VARIATIONS OF EXCITABILITY UNDER CHEMICAL
REAGENTS com :

Induced variation of excitability studied by two methods: (1) direct (2) trans-
mitted stimulation—Effect of chloroform—Effect of chloral— Effect of formalin
—Advantage of the Method of Block over that of negative variation—Effect
of KHO—Response unaffected by variation of resistance—Stimulating action
of solution of sugar—Of sodium carbonate— Effect of doses—Effect of hydro-
chloric acid— Di-phasic response on application of potash—Conversion of normal
negative into abnormal positive response by abolition of true excitability.

IT has been said in a previous chapter that the electrical
response is a true physiological response. This is demon-
strated by the fact that, while a vigorous specimen gives
strong electrical response of galvanometric negativity, the
same specimen, when killed, whether by heat or by poison,
ceases to respond. This particular electrical response is
thus seen to be a concomitant of physiological efficiency.
It follows that, whatever diminishes physiological activity
will, parz passu, modify the amplitude of the response. But
in cases in which the death of the tissue is brought about by
steam or by poison, it is the last stage only, namely the
abolition of response, that can be observed. It is also impor-
tant, however, to be able to trace the growth of physiological
changes through the concomitant modification of response.
In this way it is possible not only to study the gradual onset
of death, as induced by a poison, but also the action of other
chemical agents, some of which might be of such a nature
as to induce exaltation, others depression, and still others,
like the narcotics, a temporary abolition of the electrical
response.
K.

130 COMPARATIVE ELECTRO-PHYSIOLOGY

An essential condition of this investigation is first to obtain
a uniform series of responses. Having once done this, those
subsequent changes in the response which are due to the appli-
cation of a given reagent can be demonstrated in an unmis-
takable manner. I have already explained in Chapter III.
that this may be done by either of two different methods:
namely, those of direct and of transmitted stimulation. Inthe
first of these we employ vibrational stimulus, using the Method

ql
i

Before 4 After

Fic. 89. Photographic Record of Effect of Chloroform on Responses of Carrot

Stimuli of 25° torsional vibration at intervals of one minute.

of Block. In the second, the stimulus of thermal shocks is
used, the excitation of the proximal contact being due to
transmitted stimulation.

We shall investigate the effect of chemical reagents by
both these methods. And first I shall give results obtained
by the employment of the Method of Block, the tissue being
subject to direct stimulation. In cases where the effect of
gaseous reagents, like chloroform, is to be studied, the
vapour is blown into the plant-chamber (see fig. 21). In

EXCITABILITY UNDER CHEMICAL REAGENTS 131

cases of liquid reagents, they are applied on the points of
contact A and B, and in their close neighbourhood. The
experiment is carried out by first obtaining a series of
normal responses to uniform stimuli, applied at~ regular
intervals of time, say one minute, the record being taken the
while on a photographic plate. Then, without interrupting
this procedure, the given agent—say, vapour of chloroform—
is applied, by being blown into the chamber. It will be seen
from fig. 84 how rapidly chloroform induces depression of
response, and how the effect grows with time. If the speci-
men be subjected for a short time only to the anesthetic,
the depressing action proves transient, passing off on
the reintroduction of fresh air. But too strong or too pro-
longed an application induces a permanent abolition of
response.

I give below (figs. 90, 91), two sets of records, one of
which shows the effect of chloral and the other formalin.

:

A A
— \ ' \ \ A £ a
Ne NAA

Before + After

Fic. 90. Photographic Record showing Action of Chloral Hydrate on the
Responses of Leaf-stalk of Cauliflower

Torsional vibration of 25° at intervals of one minute.

These reagents were applied as solutions on the tissue at

the two leading contacts and adjacent surfaces. Both

are scen to induce a rapid decline of the response. In the
K 2

I 32 COMPARATIVE ELECTRO-PHYSIOLOGY

normal responses, shown in fig. QI, is seen a very interesting
instance of alternating fatigue.

In order to bring out clearly the main phenomena, I
have postponed till now the consideration of a point of some
difficulty. To determine the influence of a reagent in
modifying the excitability of a tissue, we rely upon its effect
in exalting or depressing the responsive E.M. Variation, and
we read this effect by means of changes induced in the
galvanometric deflection. Now as long as the resistance of
the circuit remains constant, an increase or decrease of
galvanometric deflection will accurately indicate a heightened
or depressed E.M. Variation, due to augmented or lowered

AAA

Sy Me,

a

Before t After
Fic. 91. Photographic Record showing Action of Formalin (Radish)

excitability, induced by the reagent in the tissue. But by
the introduction of the chemical reagent the resistance of
the tissue may undergo a change, and, owing to this cause,
modification of response, as read by the galvanometer, may
be induced without any E.M. Variation; The observed
variation of response may thus be partly owing to some
unknown change of resistance, as well as to that of the
E.M. Variation.

This difficulty may, however, be obviated by interposing
a very large and constant resistance in the external circuit.
The variation in the tissue then becomes negligible, the
galvanometric deflections being now proportional to the
electro-motive variation, An actual experiment will make

EXCITABILITY UNDER CHEMICAL REAGENTS 133

this point clear. Taking a carrot as a specimen, I found its
resistance f/us the resistance of the non-polarisable electrodes
to be 20,000 ohms. The application of a chemical reagent
reduced this to 19,000 ohms. The resistance of the galva-
nometer used was 1,000 ohms, and the high constant external
resistance interposed was I million ohms. The variation of
resistance induced in the circuit by the application of the
reagent was thus 1,000 in 1,020,000, or less than one part in
a thousand. :

In studying the variation of excitability in animal tissues,
the method of negative variation is employed. But I may
here draw attention to the advantage which is afforded by
the employment of the Method of Block instead. For,
in the method of negative variation, one contact being
injured, the chemical reagents act on injured and uninjured
unequally. It thus happens that by this unequal action the
resting difference of potential is indefinitely altered. But the
intensity of response in this method of injury may to a
certain extent be dependent on the resting difference. It is
thus seen that, when this method is employed, a factor is
introduced which may give rise to complications.

According to the Block Method, however, the two contacts
are made with uninjured surfaces, and the effect of the
reagents on both is similar. Thus no advantage is given to
either contact over the other. The changes now detected in
the response are therefore due to no adventitious circum-
stance, but to the reagent itself. If further proof be desired
of the effect ascribed to the action of the reagent, we can
now obtain it by the alternate stimulation of the two ends
A and B. I give below (fig. 92) a record of responses
obtained in this way from the petiole of turnip. This petiole
was somewhat conical in form, and owing to this difference
between the A and B ends, the responses given by one were
slightly smaller than those given by the other, though the
stimuli were equal in the two cases. A few drops of a
10 per cent. solution of NaOH were applied at both ends.
The record shows how quickly this reagent abolished the

134 COMPARATIVE ELECTRO-PHYSIOLOGY

response of both. In the next figure (fig. 93) is given a photo-
graphic record, showing the marked depression of response
induced by a strong solution of KOH, and in order to show
that under the given experimental conditions, the variation
of resistance does not in any way affect the responses, the
deflection produced in the galvanometer by the application
of an E.M.F. of ‘1 volt to the circuit is shown at the
beginning and end of the record. The equality of these two
deflections shows that the resistance in the circuit has
remained practically the same throughout the experiment.

Before t After

Fic. 92. Abolition of Response at both A and B Ends by the Action

of NaOH
Stimuli of 30° vibration were applied at intervals of one minute to A and
B alternately. Response was completely abolished twenty-four

minutes after application of NaOH.

Therefore, the change in the amplitude of the E. M.
responses recorded may be taken as due entirely to the
variation in the excitability of the tissue.

In the experiments just described, the stimulus was
applied directly at the responding point. By the application
of a chemical reagent, not only was the responsive excitability
of the tissue modified, but its receptivity, or power of
receiving stimulus, also underwent a change. It will be
shown later that the receptive excitability and the responsive
excitability are not necessarily the same. The records which
have just been given show what is, strictly speaking, the

EXCITABILITY UNDER CHEMICAL REAGENTS — 135

effect of the reagent on both receptivity and responsivity
jointly.

If, however, we wish to study the effect of the reagent on
responsive excitability alone, it will be necessary to separate
the receptive from the responding point, and apply the reagent
on the latter. This may be done by the method of trans-
mitted stimulation described previously. Successive uniform

Before + Afier

Fic. 93. Photographic Record showing the nearly complete Abolition
of Response by strong KOH
The two vertical lines are galvanometer deflections due to ‘1 volt, before

and after the application of reagent. It will be noticed that the total
resistance remains unchanged.

stimuli applied at a given point cause excitatory response at
the separate responding point, the record of which is taken ;
after this, the chemical reagent is applied locally at the
responding point. It will be seen that the receptive
excitability and the conductivity of the intervening tissue
remain unaffected, changes being induced at the responding
area alone.

I shall now describe effects obtained by this method.

I 36 COMPARATIVE ELECTRO-PHYSIOLOGY

The specimen employed was the petiole offern. The thermal
stimulator was at a distance of 1°5 cm. from the proximal
electrode. In fig. 94 is shown the stimulating action of a

Fic. 94. Photographic Record showing the Stimulatory Action
of Solution of Sugar

2 per cent. solution of sugar, inducing a continuous enhance-

ment of response for some time.
Another stimulating agent is a dilute solution of Na,Co,.

This when applied in 1 per cent. solution induces an

Fic. 95. Photographic Record showing Continuous Action of
2 per cent. Na,CO, Solution

Preliminary exaltation followed by depression.

enhancement of amplitude of response, but when given in
strong solution, induces depression. An intermediate strength
of solution shows preliminary enhancement followed by de-

pression (fig. 95).

EXCITABILITY UNDER CHEMICAL REAGENTS 137

While pursuing another line of inquiry on the effect of
various strengths of solution of Na,Co, on the natural
current, I obtained results which were parallel (p. 122).
It was there shown that dilute solution of Na,Co, induced
a positive variation of the natural current ; a strong solution,
a negative variation, and that a solution of intermediate
strength induced a preliminary positive followed by a negative
variation. Thus the positive variation in the last-named
experiments, already shown to be indicative of increased
excitability, was here seen to correspond with heightened
amplitude of response, while the negative variation on the
other hand is seen to coincide with depression of excitability.
The application of a strong solution inducing excitation,
carries the molecular condition of the tissue to the stage
E, where, as we know, the excitability is depressed.

Another fact elucidated by this and similar inquiries,
which I have pursued elsewhere,' lies in the fact that the
difference between stimulants and poisons, so called, is often
one merely of degree. Thus a stimulatory reagent, if given
in large quantities, will be found to induce a profound
depression, whereas a poisonous reagent in minute quantities
may be found to act as a stimulant. In carrying out a
similar investigation with regard to growth response, | found
that sugar, for instance, which is stimulating in solutions of,
say, I to 5 per cent., becomes depressing when the solution
is very strong. Copper sulphate again, which is regarded as
a poison, is only so at 1 per cent. and upwards, a solution of
‘2 per cent. being actually a stimulant. The difference
between sugar and copper sulphate is here seen to lie in the
fact that in the latter case the range of safety is very narrow.
Another fact, which must be borne in mind in this connec-
tion, is that a substance like sugar is used by the plant for
general metabolic processes, and thus removed from the
sphere of action. Thus continuous absorption of sugar could
not for a long time bring about sufficient accumulation to
cause depression. With copper sulphate, however, the case

1 Bose, Plant Response, p. 488.

i138 COMPARATIVE ELECTRO-PHYSIOLOGY

is different. Here, the constant absorption of the minimal
stimulatory dose would cause accumulation in the system,
and thus ultimately bring about the death of the plant.

Fic. 96. Photographic Record showing the Depressing
Action of 5 per cent. HCl Acid

The effect of very dilute acids is often to induce an
enhancement of excitability, while strong solutions induce
depression and abolition. In fig. 96 is shown the depression

Fic. 97, Photographic Record showing Effect of I per cent. KHO

Note the preliminary positive twitch at the fourth response after application.

and abolition induced by the rene. of a 5 per cent.
solution of hydrochloric acid.

In dealing with the question of electrical response, we
have seen that two opposed electrical effects occur in the

EXCITABILITY UNDER CHEMICAL REAGENTS 139

tissue subjected to stimulation. One of these is the positive
effect, and the other, the true excitatory change of galvano-
metric negativity. As the latter is, under normal conditions,
predominant, the simultaneous effect of both is a resultant
negativity. The positive effect may, however, be unmasked,
as we have seen, by abolishing the true excitatory effect
of negativity (p. 66). This positivity may also be un-
masked, if, by the action of a chemical reagent, the time-

Fic. 98. Photographic Record of Effect of 5 per cent. KHO

Note the complete reversal of response to positive at the beginning,
and its subsequent abolition.

relations of the two responses are changed, so that instead of
occurring simultaneously, the one is made to lag behind the
other. This case will be seen very strikingly illustrated in
fig. 97, which exhibits the effect of a 1 per cent. solution of
KHO, on response to transmitted stimulation in the petiole
of fern. In the normal responses here given, we observe
the resultant response of galvanometric negativity. The
application of KHO is first seen to reduce the excit-
ability, as indicated by the reduced height of the responses.
Later, we observe that the true excitatory effect is delayed.

140 COMPARATIVE ELECT RO-PHYSIOLOGY

Hence the positive effect is no longer completely masked.
Its existence is now seen as a preliminary downward
twitch in a di-phasic response, in the case of the fourth
and succeeding records, after the application of KHO. In
fig. 98, a stronger, namely a 5 per cent. solution of KOH, was
used. And here, by the almost complete abolition of the
excitatory factor, the response has undergone an apparent
conversion to positive; this positive response is, however,
subsequently abolished by the death of the plant.

os

Seer ae -

CHAPTER XII

VARIATIONS OF EXCITABILITY DETERMINED BY METHOD
OF INTERFERENCE

Arrangement for interference of excitatory waves—Effect of increasing difference
of phase—Interference effects causing change from positive to negative,
through intermediate di-phasic—Diametric balance—Effect of unilateral
application of KHO—Effect of unilateral cooling.

I HAVE explained how the variations of excitability brought
about by various agencies may be determined, by recording
the corresponding amplitudes of response, I shall now pro-
ceed to describe a new and interesting method of making
such determinations, by means of which it will be found
possible to elucidate certain questions which without it must
remain obscure. This method is, moreover, of extreme
delicacy, enabling the investigator to detect the slightest
variation of excitability, induced by any agent.

Let two points in the experimental tissue, say A on the
right, and B on the left, be suitably connected with the galva-
nometer, and let the occurrence of excitation at A on the
right be represented by an ‘up’ response record, the excita-
tory effect at B, on the left, being represented as ‘down.’
If now the two points, A and B, be excited simultaneously,
the resultant electrical response will be due to the algebraical
summation of the two excitatory electro-motive effects E, and
Ey, these standing for the individual electrical effects at the
two points A and B, Now if the intensities of the two effects
be the same, and if their time-relations be also the same,
it is evident that these two excitatory electrical waves, being
of equal amplitude and having the same ‘phase but of
opposite signs, will, by their mutual interference, neutralise

142 COMPARATIVE ELECTRO-PHYSIOLOGY

each other. Under such balanced conditions, therefore, on
simultaneous excitation of A and B, the resultant response
will be zero. If now, under the modifying action of any
external agency, the excitability of A be enhanced, it is clear
that the resultant response will be ‘up, showing the greater
excitability of the right-hand point. A similar effect will
also be produced if the excitability of B be depressed. |
Similarly the depression of the excitability of A, or enhance-
ment of B, would cause a resultant response which would be
‘down.’ If, again, the two waves of excitation be not of the
same phase, we shall obtain various di-phasic effects resulting
from the algebraical summation of the constituent response-
curves. The resultant zero-response may thus be converted
into di-phasic, by the action of any agency which is capable
of changing the time-relations of either of the constituent
responses.

_ I shall now proceed to describe the experimental arrange-
ments by which two points in connection with E and E’ may
be excited, and the resulting electrical disturbances made to
interfere with each other. For this purpose we may use the
vibrational stimulation which has already been described,
with certain necessary additions .(fig. 99). The angle of
torsional vibration which regulates the intensity of excitation
is determined by two stops, P and Q. An elastic piece of
brass, B, projects from the torsion-head. When a single
stroke is given to this, a quick to-and-fro vibration is induced,
the backward pull being supplied by the attached spring, s.
The amplitude of this vibration remains always the same, as
determined beforehand by the setting of the stops P and Q.
The stroke is given by the striking-rod R, set in motion by
the turning of a handle. What has already been said about
the excitation of the right-hand side of the specimen applies
equally to the left-hand, arrangements for the purpose being
a duplicate of those just described. After deciding on a
suitable angle of torsional vibration for the right, and taking
the response at that point, we proceed to adjust the torsional
angle on the left, so that the response there may be exactly

EXCITABILITY DETERMINED BY INTERFERENCE 143

the same as that on the right. If the excitability of the two
points had been exactly the same, equal amplitudes of vibra-
tion would have resulted in the equal stimulation of both.
But in practice the excitabilities are found to be slightly
different and the angle of vibration of the one must, therefore,
be so adjusted as to induce an excitatory effect exactly equal
to that of the other.

The two striking-rods, one on the right, R, and the other
on the left, R’, can be adjusted so that both are in the same

E
a

a

us

rt ie
B
\

4 P

ee

<

=
Nee” :
Fic. 99. R, R’, striking-rods for stimulation of two ends of specimen ;

B, elastic brass tongue projecting from torsion-head. For producing
phase-difference R is adjustable in azimuth. .

vertical plane, or so that one is in advance of the other.
The left rod is permanently fixed to the rotating axis, but
the right can be set at any angle that is desired, with the
other. When the right striking-rod is set, pointing to zero of
the scale, the two rods are in the same vertical plane, and the
rotation of the handle causes equal vibrational stimulus by
the two at the same moment. The excitatory reactions on
right and left are now, therefore, of the same phase and of
equal intensity, but opposed to each other. In fig. 100, a,
are reproduced the two separate and equal constituent
responses given by a specimen of stem of Amaranth. The

144 COMPARATIVE ELECTRO-PHYSIOLOGY

‘down’ curve was given by the individual excitation of the
left, and the ‘up’ by the right. On the simultaneous excita-
tion of the two points, the resultant response was zero (6).
But if the excitation of one—say, the right—be increased by
increasing the angle of vibration, the resultant differential
response is found to be ‘up.’ It is obvious that’ a similar
effect would have been observed had the stimulation of the
right been kept the same, while its excitability was increased .
by any external agent. In these cases we have two opposed
excitatory waves of similar phase, and of the same or unequal
intensities, interfering with each other.

Fic. 100. (a) Isolated response of left side (down) and right side (up) ;
(4) null-effect when excitations are simultaneous ; (c), (d@), (e) di-phasic
responses obtained with increasing difference of phase.

We shall next take some simple instances in which, while
the stimulation is maintained constant, there is an increasing
difference of phase. If the right-hand striking-rod R, instead
of being set at zero, be set to the right, or at a p/us angle,
the rotation of the handle will cause a slightly earlier excita-
tion of the right than of the Jeft. If, on the other hand, the
rod be set at a mznus angle, the excitation of the right will
be later than that of the left. Under these circumstances,
instead of the null-effect due to continuous balance, we shall
have a di-phasic response. It is also clear that as the phase
difference is increased, the neutralisation of -effects will
become. less and less perfect, the separate constituent respon-
ses being thus rendered increasingly apparent, In fig. 100, ¢,

EXCITABILITY DETERMINED BY INTERFERENCE 145

is seen the di-phasic effect which was induced when the
excitation of the right was made to lag slightly behind that
of the left, by the adjustment of the striking-rod at a
small mznus angle. The first of the two twitches, which is
downwards, indicates the relatively earlier excitation of the
left-hand contact. As the phase-difference was increased
progressively as in (d) and (e), it is seen that the constituent
elements of the di-phasic response are increased corre-
spondingly. It is also clear from this that, having obtained
the null-effect, if any agents were afterwards applied locally
which would make the excitation of the one point earlier
than that of the other, we must then expect the null-effect
to be modified to di-phasic. An earlier ‘up’ twitch would
now indicate that the right-hand contact, having had its re-
action quickened, was the first to respond ; an earlier ‘down’?
twitch the opposite. 3

We thus see how the conversion of the null-effect into a
resultant ‘down’ negative or ‘up’ positive, could .be utilised
as a test of the excitatory or depressing nature of a given
reagent. We alsosee how the conversion of this null into a
di-phasic effect would give us indications as to the change
of time-relations induced by the reagent. I shall here,
before going on to describe the results obtained with plants,
give a photographic record (fig. 101) of certain positive, nega-
tive, and di-phasic effects obtained in the electrical response
of the inorganic substance, tin, under appropriate modification
of the excitability of its two contacts by various chemical
reagents.’

Turning now to the question of the determination of
the effects of the various reagents by the Method of
Interference, we may, as we have seen, cause simultaneous
excitation of right and left, by means of the apparatus which
has just been described, and which I shall distinguish as the
Longitudinal Balance. There is, again, another and simple
method of accomplishing the same object, by means, namely,
of the Diametric Balance, the diagram of which has already

1 Bose, Response in the Living and Non-Living, p. 115.
L

146 ' COMPARATIVE ELECTRO-PHYSIOLOGY

been given in fig. 80. Using this arrangement, the specimen
is clamped at one end, the vibration-head being at the other.
Electrical connections are now made with the two dia-
metrically opposite points, A and B, of which one, say A, is
the upper, and B the lower. Ina tissue -which is isotropic,
vibrational stimulus will induce equal and simultaneous
excitation at the two points A and B. The effect of any
given agency is tested by applying it locally, say at A, and
observing the resultant variation of the response. I shall

(a) (4) (c)
Fic. 101. Photographic Record showing Negative, Di-phasic, and
Positive Resultant Responses in Tin under appropriate modifications
of excitation of the two contacts

here give examples of results obtained by both these methods,
thus affording an indication of the extent of their applicability
in various investigations. ,

We have seen in the previous chapter that the application
of strong solution of potash will abolish the excitability of
a tissue. Using the Longitudinal Balance, I took a petiole
of Bryophyllum and first made such adjustments that the
right ‘up’ and left ‘down’ responses were almost equal.
On now producing simultaneous excitation of the two ends,
a di-phasic response was obtained, due to the fact that the
left-hand point was the quicker to respond. Strong solution

EXCITABILITY DETERMINED BY INTERFERENCE 147

of potash was next applied on the right-hand point, and
from the record it is seen that the ‘up’ part of the di-phasic
response, due to the excitation of the right-hand side, was
thus completely abolished, the ‘down’ response being at the

| same time increased. by the
suppression of this opposing
response (fig. 102).

In order to demonstrate the
use of the Diametric Balance
Method, I undertook to investi-
gate by its means the influence
of the lowering of tempera-
ture on excitability. For this

Fic. 103. Photographic Record of
Response of Petiole of Cauliflower
Fic. 102. Photographic Records. by the Diametric Method
(a) Di-phasic response of petiole A contact was naturally more excitable,
of Bryophyllum, the up compo- hence resultant ‘up’-response. Ex-

nent being due to the excitation citability of A being depressed by
of right side. Strong application local application of ice, the re-
of KHO on the right abolished sultant response became converted
this responsive component, giving to ‘down’; normal ‘up’-response
rise in (4) to enhanced down was restored on allowing the tissue

response to return to surrounding temperature.

purpose, I took a petiole of cauliflower. In this instance,
the natural excitability of the upper contact, A, was greater
than that of the lower, B. Hence the resultant response was
not zero, but ‘up.’ The point A was now cooled locally by
ice. This process so lowered its excitability that that of B
was now relatively the greater, hence the resultant response
was found to be reversed or ‘down. The point A was next

L:2

148 COMPARATIVE ELECTRO-PHYSIOLOGY

allowed to return to the surrounding temperature of the room,
records of the response being taken meanwhile, at intervals
of one minute. It will be seen how, by means of the gradual
restoration of the original excitability of A, the resultant
response changes gradually from negative to zero, and then
again from zero back to positive, indicating the restoration
of the naturally greater excitability of A (fig. 103).

We have thus studied two different methods, both of
which depend on interference, for the determination of the
variations of excitability induced by different external agents.
In a subsequent chapter we shall study a modification of this
method, by means of which it is possible to demonstrate the
variations not only of excitability but also of conductivity
under various reagents.

e

CHAPTER XIII
CURRENT OF INJURY AND NEGATIVE VARIATION

Different theories of current of injury—Pre-existence theory of Du Bois-
Reymond—Electrical distribution in a muscle-cylinder—Electro-molecular
theory of Bernstein—Hermann’s Alteration Theory—Experiments demon-
strating that so-called current of injury is a persistent after-effect of over-
stimulation—Residual galvanometric negativity of strongly excited tissue—
Distribution of electrical potential in vegetable tissue with one end
sectioned—Electrical distribution in plant-cylinder similar to that in muscle-
cylinder—True significance of response by negative variation—Apparent
abnormalities in so-called current of injury—‘ Positive’ current of injury.

IF a section be made of an uninjured nerve or muscle, the
transverse contact will be found to be galvanometrically
negative, as compared with an uninjured longitudinal contact.
I shall have occasion in the present chapter to give a simple
explanation of this phenomenon and of the excitatory nega-
tive variation of the current of injury. It is, therefore, only
necessary to recapitulate briefly the three theories which have
hitherto been proposed on this subject.

The Pre-extstence Theory of Du Bois-Reymond supposed
that the smallest particle had the same electro-motive
characteristics as the entire tissue, each such electro-motive
molecule consisting of two bi-polar portions, the positive
poles of any two molecules being always face to face with
each other. This theory was based upon the fact that a
muscle-cylinder, for example, exhibited a peculiar distribu-
tion of electrical tension. There are in such a cylinder, one
longitudinal and two transverse surfaces. Midway in the
cylinder is the equatorial zone of the longitudinal surface,
and this zone is positive to all the rest. Thus the electro-
motive difference between one electrode placed on the

I50 COMPARATIVE ELECTRO-PHYSIOLOGY

equator, and the other, is increased as the latter is moved
further and further away, say towards the right transverse
section. The distribution
of electrical tension on
the left side of the
equator is symmetrical
with this (fig. 104). On
these facts was based the
theory of Du _ Bois-
Reymond; but this has

Fic. 104. Distribution of Electrical : me ‘nite hed
Tension in Muscle-cylinder. since been found to be in-

adequate. I skall later
return to the explanation of the particular distribution of
electrical tension involved.

According to the theory of Bernstein, known as the
Electro-chemical Molecular Theory, the fundamental attribute
of the molecule is chemical. Its poles are supposed to attach
to themselves electro-negative groups of atoms, while its
sides attach oxygen, and stimulation is supposed to be
attended by explosive chemical changes.

According to Hermann’s A/teration Theory, finally, all the
_ electro-motive activities of living tissues are supposed to be due
to chemical rather than molecular changes of the substance.
In amplification of this theory, Hering attributes all electro-
motive phenomena to the disturbance of equilibrium by
up and down chemical changes.

It is my intention to show in the course of the present
chapter that the current of injury is an after-effect of
over-stimulation. And since excitation is fundamentally
due to molecular upset, we shali best understand the
electro-motive changes concomitant with it, if we first study
it and its after-effect under the simplest conditions, namely
those of inorganic substances. For here the action of such
complicating factors as assimilation and dissimilation is
clearly out of the question.

We have found for example that a piece of well-annealed
wire was iso-electric throughout its length. In the first

CURRENT OF INJURY AND NEGATIVE VARIATION I5I

place, when a portion of it was subjected to any molecular
disturbance, an electro-motive difference was induced, as
between the molecularly disturbed or excited and the un-
disturbed areas. The intensity of this electro-motive change,
in the second place, was seen to increase with intensity
of excitation. And, thirdly, the recovery from excitation
was seen to be delayed, where the intensity of stimulus
was strong (fig. 105). This is shown in the electrical

°

° ° me) ° -o -°
5 Io Is 20 25 30 35 45

Fic. 105. Photographic Record showing Persistent Electrical After-Effect
in Inorganic Substance under Strong Stimulation. Note the tilt of
base-line upwards

The vertical line to the right represents ‘1 volt.

response of tin as a persistent after-effect, the sign of
which is the same as that of the excitatory electro-motive
change.

A similar state of things is exhibited mechanically in a
torsioned wire. When the torsion is moderate, and the
molecular distortion slight, the released wire quickly re-
covers its original position of equilibrium. But when the
torsion is excessive and the wire strained beyond a certain
limit, it remains for a long time in a torsioned condition,

152 COMPARATIVE ELECTRO-PHYSIOLOGY

even after it has been set free. Recovery is thus, in such
a case, indefinitely delayed. In other words, a molecularly
over-strained substance exhibits a persistent after-effect.
Turning next to plant response, we find a similar per-
sistence of the after-effect to occur in consequence of over-
stimulation. And first we shall take the simplest case—
that in which the tissue is directly stimulated. Here the
specimen was petiole of cauliflower, and increasing stimuli

24° eC 74° 10° 123°

Fic. 106. Photographic Record exhibiting Persistent Galvanometric
Negativity in Plant Tissue after Strong Stimulation

Stimuli applied at intervals of three minutes. Vertical line = ‘1 volt.

were applied, at intervals of three minutes, by means of a
gradually increasing angle of torsional vibration. It will be
noticed that whereas the electrical recovery from moderate
stimulation—as seen in the first of the series—is complete,
it becomes, with increasing stimulus, more and more in-
complete (fig. 106). In other words, the tissue, after strong
stimulation, is seen to exhibit an after-effect of residual
galvanometric negativity, which is really due to incomplete
molecular recovery, in consequence of over-strain.

In the cases just given, stimulation was applied directly.

CURRENT OF INJURY AND NEGATIVE VARIATION 153

We shall now, however, take an instance in which excitation
is transmitted and observe the persistent negative after-effect,
due to strong stimulation. We know that a cut (mechanical
section) or the application of a hot wire (thermal section)
acts as a strong stimulus, and the effective intensity of such
stimulation will obviously decrease with increasing distance
from the point of stimulation. Hence, if we observe the
persistent excitatory change of galvanometric negativity,
which is induced as between an indifferent point—say, the
surface of a leaf—and points increasingly near to the zone
of section, we shall find that the electro-motive change
is greatest at the point of section, and is progressively
lessened as we recede from it. This induction may be
verified experimentally by taking readings of the persistent
negativity, as between an indifferent point, B, and points
such as the contacts a, 0, c, d, A (fig. 107), which are further
and further removed from the point of section. For this
purpose we may employ a capillary electrometer, whose indica-
tions are independent of the varying resistance of the interposed
tissue. The magnifying power of the observing microscope
was so adjusted that ‘1 volt gave a reading of 100 divisions
of the micrometer. In carrying out an experiment on the
leaf of Colocasza I found the electrical distribution, as between
an indifferent point on the lamina and points on the
sectioned petiole, at increasing distances from the section,
to be as shown in the following table :

TABLE SHOWING ELECTRICAL DISTRIBUTION IN SPECIMEN OF Co/ocasia.

[The sectioned end was negative. 100 divisions = ‘1 volt. |

Tiintaie thom section E.M. difference between indifferent
and given points

*5 cm. 50 divisions
I 99 40 ”
2 9 33 99
3 9° 29 99
4

99 27 cd

It will thus be seen that points near the sectioned end are
more negative than others further away.

154 COMPARATIVE ELECTRO-PHYSIOLOGY

I shall next describe the more sensitive galvanometric

method of investigation. The resistance is here maintained
constant by having the permanent. contacts at A and the
indifferent point B (fig. 107). The specimen is a stem of
Calotropis gigantea. A thermal section is made at first, say,
at a distance of 3 cm. from A. The persistent galvanometric

negativity of A will now be due to the after-effect of stimula-
tion by section. The thermal injury is now repeatcd at |

LL

of ih
cai 5

3 2 15 3
Fic. 107. Experimental Arrange- Fic. 108. Records showing in-
ment for determining Electrical creasing Persistent Galvano-
Effect due to Section metric Negativity, according

as injury is caused nearer to
proximal contact A, z.e. moved
from 3 to'5 cm, distance

decreasing distances from A. I give a series of records
(fig. 108), from which it will be seen that when the stimulus
of thermal section occurs at some distance, there is no

persistent after-effect, recovery being complete. But as the

injury is made nearer and nearer A, the permanent after-

effect becomes greater and greater. From observations made .

in the course of a similar experiment, I obtained the following
results, given in tabular form, which show the increasing
value, with lessening distance, of this persistent galvano-
metric negativity.

eee

CURRENT OF INJURY AND NEGATIVE VARIATION 155

TABLE SHOWING PERMANENT GALVANOMETRIC NEGATIVITY AT
DIFFERENT DISTANCES FROM POINT OF INJURY,

Distance from section Galvanometric negativity
25 cm. 220 divisions
5» 180;
IO ,, 120 os
| 5% FINS |
2°0 35, 49 ” |
| 370 5, inst Sb |

In fig. 109 we have a curve which illustrates these results,
and explains why the maximum negativity is at the zone
of section, diminishing rapidly as we recede from it. It is
obvious that if these sections had been made to the right as

Fic. 109. Curve showing the Electrical Distribution in Stem with
one Sectioned End

Ordinate represents galvanometric negativity ; abscissa, the distance
from sectioned end.

well as to the left of A, the result would have been a duplicate
series of changes of galvanometric negativity in reference
to A, on. that side also. Such a series is represented in
fig. 110, by means of dotted lines. It will also be seen from
this figure that the greatest electro-motive difference exists

156 COMPARATIVE ELECTRO-PHYSIOLOGY

as between the equatorial point A and the two terminal
sections a and a’; that symmetrical points cc’, 0 0’, a a’, are
equipotential ; and that a point relatively nearer the terminal
section is galvanometrically negative, in reference to one
further away from it. It will also be seen that this electrical
distribution is exactly the same as that seen in a muscle-
cylinder, with terminal sections, as given in fig. 104.

Thus, without the postulation of any electro-motive mole-
cules so-called, these experimental results afford a simple
and direct explanation of the so-called current of injury, as
the excitatory after-effect of strong stimulation.

Fic. 110. Electrical Distribution in Plant-cylinder with Opposite
Ends Sectioned

The Current of Injury is simply therefore an excitatory
after-effect, due to incomplete recovery from over-strain.
But even after strong stimulation a slow recovery may occur,
and the Current of Injury will thus undergo a progressive
diminution. This will probably account for Engelmann’s
observation that in medullated nerves the E.M.F. of the
artificial cross-section fell, by as much as from 25 to 60
per cent., in the first two hours after section, and disappeared
altogether within twenty-four. The renewal of the cross-
section he found to renew the original difference. This is
an obvious case of renewal of the effect by re-stimulation.

The disappearance of negativity, owing to recovery, only

CURRENT OF INJURY AND NEGATIVE VARIATION 157 |

takes place when the injury has not been excessive. If,
however this has been too great, the injured tissue will then
pass gradually into a condition of permanent death. But
the electrical change concomitant with death is one of
positivity, as I shall show in the next chapter. Thus the
subsidence of the galvanometric negativity of an injured point
may be brought about by either of two processes, which are
exactly opposite—namely, recovery or death.

Turning next to the subject of the Negative Variation
of an existing current of rest, as a reliable index to the state
of excitation, two different questions arise. First: why, in
order to obtain response to diffuse stimulation, is it necessary
previously to subject one of the contacts to injury? And
secondly: why is the responsive action-current opposite in
direction to the resting-current, thus constituting a negative
variation of it?

With reference to the first of these questions, we have
already seen that when two points, A and B, are simul-
taneously excited, the resultant electro-motive response is
equal to E,—E,. If, then, the excitabilities of these two
points are the same, it is clear that the resultant response
will be zero. From this we can see that, in order to obtain
a resultant response, we must depress or abolish the excita-
bility of one of the two contacts.

This inference may be verified by the employment of the
Method of Block and of longitudinal balance. Two equal
and opposite responses are first obtained at A and B. Then
one end, say B, is injured by thermal section. The specimen
being now replaced in the vibratory apparatus, it is found
that, whereas the A half gives strong response, the end B
gives none. Or the B end of the specimen may be injured
by a few drops of strong potash, the other end remaining
uninjured. The end A is then stimulated, and a strong
response is obtained. The end B is next stimulated, and
there is little or no response. The block between A and B is
now removed, and the specimen stimulated throughout its
length. Though the stimulus now acts on both contacts,

158 COMPARATIVE ELECTRO-PHYSIOLOGY

yet, owing to the irresponsive condition of B, there is a
resultant response, and the direction of this action-current
is found to be from A to B. We have thus experimentally
verified the assumption that in the same tissue an uninjured
portion will be thrown into a greater excitatory state than
an injured, by the action of the same stimulus. ;

When the point B is injured, there is generally speaking
a more or less persistent current set up which flows from |
Bto A. But we saw that the direction of the action-current
was opposite—that is to say, from Ato B. This will explain
the reason why the action-current causes a diminution or
negative variation of the current of injury, so called. One
method of doing this is to cause injury to one of the two
points. If this be such as to kill the tissue, then its
excitability is permanently abolished. Or by causing the
excessive stimulation of injury, we may simply depress the
excitability of the tissue for a longer or shorter time.

I shall now give a few instances of response in plants by
negative variation, Taking the petiole of turnip, we injure an
area on its surface, say B. A current is now observed to
flow in the petiole from the injured B to the uninjured A.
The induced difference of potential depends on the condition
of the plant, and the season. In the experiment here
described, its value was ‘13 volt. A sharp mechanical tap
was now given to the petiole, between A and B, and a sudden
diminution, or negative variation, of current occurred, the
resting potential difference being decreased by ‘026 volt. A
second and stronger tap induced a second response, causing
a greater diminution of potential difference by ‘047 volt.

In another experiment, the specimen employed was a
petiole of cauliflower (Brassica oleracea). ‘The first up-line
to the right indicates the current of injury. The three re-
sponses which succeed are induced by a given intensity of
stimulus, the next series of six, being in response to stimulus
nearly twice as strong, exhibit signs of fatigue (fig. 111).

The current of injury generally undergoes a diminution
with time. This is often, as has been explained, on account

CURRENT OF INJURY AND NEGATIVE VARIATION 159

of slow recovery from the excessive stimulation of injury.
Response by negative variation is then found to undergo a
decline. It is in general vaguely accepted that, in order to
obtain a response by negative variation an‘antecedent current
of injury is necessary, by whose induced variation we may
be able to record responsive effects. In cases of the dis-
appearance of the current of injury, it is supposed that
response must necessarily vanish, since its antecedent con-
dition no longer exists. But I have already shown, and shall

sayy

Fic. 111. Record of Responses in Plant (Leaf-stalk of Cauliflower)
by Method of Negative Variation

The first three records are for stimulus intensity I ; the next six are for in-
tensity twice as strong; the successive responses exhibit fatigue. The
vertical line to the left represents ‘I volt. The record is to be read
from right to left.

have occasion again to show in the next chapter, that these
suppositions are altogether erroneous. For we may obtain the
usual response when the current of. injury is zero, or even
positive. In fact, the only essential condition for the obtaining
of resultant response is that at one contact the excitability
should be in a state of relative depression.

In that case in which response becomes enfeebled, with
the gradual decline and vanishing of the current of injury,
a simple explanation is often applicable. When the tissue is
injured, it does not necessarily die. In fact, I have often

160 COMPARATIVE ELECTRO- PHYSIOLOGY

found that, in order to ensure death—in the case for instance
of thermal section—a prolonged application of the fatal
temperature is necessary. In ordinary cases of injury caused
by the application of heat, I find that we have merely exces-
sive stimulation of the point, with depression of excitability.
But after a long interval, excitability is more or less restored,
with the gradual passing away of the effect of injury. The
subsidence of the current of injury thus also denotes the
restoration of excitability to a greater or less extent. Hence
that differential action between the uninjured and injured
contacts, which determines the amplitude of the resultant
response, will become correspondingly diminished. And
when response has undergone diminution from this cause,
a fresh injury is found to renew its amplitude. This is due
to the reduction of excitability now freshly brought about at
one of the contacts. €

There are, however, two other additional factors which
may further contribute to the enhancement of response after
a recent injury. We have seen that, as a general rule, the
resultant response will be E,—£E, where E, means the
excitatory electrical change induced at A, and E, that induced
at B. It would therefore appear that this value will be at its
maximum when the excitability of B is totally abolished by
reason of injury, the resultant effect being due to the
unopposed electrical excitation at A. But we have seen
that when the true excitatory negative variation of a point
is abolished, it may nevertheless exhibit a positive electrical
variation, due to hydro-positive action. When this happens
to be the case, this positive effect at B, conspiring with the
true excitatory effect at A, may bring about a response larger
than we should have supposed to be maximum.

Again, though over-stimulation of a point diminishes its
excitability, yet moderate stimulation often enhances it.
The effect of this, in enhancing resultant response, is well seen
in the case of conducting nerves. Thus, when the point B is
injured, the excitation caused by injury reaches A, and causes
moderate stimulation of that point. As an after-effect of this

CURRENT OF INJURY AND NEGATIVE VARIATION IOI

moderate stimulation, A often becomes more than normally
excitable.! It is thus seen how, after a recent injury, these
two factors—of a hydro-positive effect at the injured, and of
increased excitability at the uninjured contact, in consequence
of moderate transmitted stimulation—may act to enhance the
response.

We have seen that the common effect of injury is to
induce a galvanometric negativity of the point injured. We
have further seen that in such a case the response to external
stimulus is by a negative variation of the current of injury.
We have next, then, to take up various instances which appear
highly anomalous, cases, that is to say, in which the injured
point, relatively to the uninjured, is, for some hitherto
unknown reason, galvanometrically positive. As a result
of this and other causes, there are, in addition to the cases
already described in a previous chapter, instances in which
response is found to take place, not by a negative, but by
a positive, variation of the current of rest or of injury as
the case may be.

The first point to be considered in connection with such
abnormal responses is whether the experimental tissue is
physiologically isotropic, that is to say, of equal excitability
throughout, or anisotropic, possessed of unequal excitabilities
at different points. The discussion of the first of these
cases, the isotropic, I propose to defer to the following chapter.
The anisotropic will be touched upon here, though its detailed
consideration will be entered upon in the next.

As an example of the anisotropic organ, we may take
the pulvinus of MWzmosa, in which the lower side is more
excitable than the upper. In animal tissues also, such aniso-
tropy is not uncommon. For example, we may have a
_ muscular tissue terminating in a glandular. Owing to this
anisotropy, the muscular and glandular surfaces are unequally
excitable, and it will be shown in a later chapter that,
generally speaking, it is the glandular which exhibits more
intense excitatory galvanometric negativity. When such a

‘ For further details, see Chapter XLII.
M

162 COMPARATIVE ELECTRO-PHYSIOLOGY

preparation is made, by cutting across the muscle, it is found
that an electrical current flows from the uninjured gland to
the injured muscle. From this it has been supposed that
such a current was not the current of injury at all, but
something of an unknown nature, essentially different. The
consequent perplexity is the result of a failure to understand
on the one hand that there is no such thing as a current of
injury fer se, except as the after-effect of strong stimulation,
and on the other, that the current induced in the tissue is
always from the more excited to the less excited. In the
present case of muscle-and-gland preparation, the excessive
stimulation due to section becomes diffused all over the
tissue, and since the glandular surface is the more excitable,
its excitatory galvanometric negativity is greater than that
of the sectioned muscle, which thus becomes relatively positive.
We have here a striking demonstration of the necessity for
regarding the electrical reaction as the sign, not of injury, but
of the excitation caused by injury. In the case described,
for instance, the physical injury is obviously incapable of
transmission, and it is the consequent excitation which is con-
ducted to the gland.
_ The account of an experiment on a sensitive leaf of
Mimosa will serve to elucidate the foregoing argument. If
one contact, A, be made with the upper half of the pulvinus,
and the other, C, with a distant and indifferent point, then, on
giving a prick near A, we shall find that that contact, owing
to excitation by injury, becomes galvanometrically negative.
If, next, we make two contacts at diametrically opposite
points of the pulvinus, A on the upper, and B on the lower,
surfaces, it will then be found, on causing injury at the upper
point A, that that point, relatively to B, becomes galvano-
metrically positive. This is because the stimulus caused bv
the injury has become diffused throughout the pulvinus, witn
the effect of causing greater excitation and consequent
sreater galvanometric negativity at the more excitable B.

It has been seen that a mechanical or thermal section
acts as a strong stimulus. It has also been shown that

CURRENT OF INJURY AND NEGATIVE VARIATION 163

recovery from a strong stimulus is very protracted. Hence,
after such stimulation, there is persistent galvanometric
negativity as an after-effect. As the intensity of this after-
effect depends upon the intensity of stimulation, it will be
seen that the galvanometric negativity near the section will
be greater than at a distant point, where the transmitted
effect of stimulation is feeble. From this it follows, that the
so-called current of injury will flow in the tissue from the
neighbourhood of the cut, to the distant and relatively un-
excited end. The current of injury is thus an after-effect of
strong stimulus. The peculiar electrical distribution which
occurs in a muscle-cylinder is also found in a plant-cylinder,
and both are equally explicable from the fact that the
greatest excitatory after-effect occurs at the two sectioned
ends, and that this decreases progressively towards the
equator. The over-stimulated area of injury has its excit-
ability depressed or abolished ; diffuse stimulation, causing
sreater excitation of the uninjured contact, induces in it a
greater excitatory effect of negativity, and this gives rise to a
diminution of the existing difference of potential, as between
the injured and uninjured. This is the explanation of
response by the so-called negative variation.

In an anisotropic tissue the excitation caused by injury,
when diffused, induces greater galvanometric negativity of
the more excitable part. If this be the distal end, the re-
sultant persistent current will be from the distal uninjured to
the proximal injured. An apparently anomalous case: will
thus arise of a ‘ positive’ current of injury, so-called.

CHAPTER XIV

CURRENT OF DEATH—RESPONSE BY POSITIVE VARIATION

Anomalous case of response by positive variation—Inquiry into the cause—
Electric exploration of dying and dead tissue : death being natural—Determi-
nation of electric distribution in tissue with one, end killed—Dying tissue
shows maximum negativity, and dead tissue, positivity to living —Explanation
of this peculiar distribution—Response by negative or positive variation,
depending on degree of injury—Three typical cases—Explanation by theory of
assimilation and dissimilation misleading— All response finally traceable to
simple fundamental reactions.

WE have seen in the last chapter that, in order to obtain
response by negative variation, it is customary among
investigators on animal physiology to kill one end of the
experimental tissue, say by scalding. It is generally sup-
posed also that dead tissue is negative to living. On stimu-
lation, the induced negativity of the living contact, now
superposed on the existing P.D. of the unilaterally killed
tissue, causes a negative variation of it. This mode of investi-
gation, by means of the negative variation, is one which has
hitherto, as we have seen, been universally regarded as reliable.

In the course of my investigations on the response of
vegetable tissues, by this mode of negative variation, however,
I have sometimes found response to take place by the positive
variation. Taking, for example, a stem of Lalsam, I killed
one end by immersion in boiling water. On now subjecting

this to diffuse vibrational stimulus, the responsive action was-

found to induce a positive variation of the existing current.
On further investigation, I found that the excitatory electrical
variation at the living contact had remained normal; that is
to say, the direction of the responsive current was away
from the excited living, and towards the killed end. I next

a

ee ee a

Lt gO ae ee

I
Nae

RESPONSE BY POSITIVE VARIATION 165

found that the so-called ‘current of injury’ had in this case,
owing to some hitherto unknown cause, undergone a reversal,
and was now from the living to the dead, the latter being
galvanometrically positive to the former, to the extent of
‘08 volt. The abnormality of the response lay, then, in this
fact, that the current of reference had become reversed, and
that the responsive current, due to excitation, was now con-
cordant with it, instead of antagonistic, thus constituting a
positive variation (fig. 112). Later
on, I discovered many instances in
which the killed end was positive
to the unkilled. Since, then, it is
possible for the current of reference
itself to undergo such obscure and
spontaneous reversals, from un-
known causes, it is easy to see
how uncertain the study of re-
sponsive phenomena must become,
if we are to depend upon the
negative variation as our only Fic, 112. Response by Positive
reliable means for their investiga- Variation of Resting Current
tion. I next, therefore, turned my acti a aaeys howe Py
attention towards an inquiry into reversed, the killed end having
the causes of these anomalous Dans cathe a aise si
reversals. »

The subject therefore resolved itself into an investigation
as to what conditions determined the negativity or positivity
of a tissue at the onset of death. My first attempt, then, was
to study a case in which the approach of death was natural,
and not the result of any sudden or violent change, such as
might conceivably give rise to abnormal reactions. And in

‘ my search for suitable specimens, I noticed that often, owing

to local mal-nutrition or other causes, the leaves of plants
exhibited spots or areas, from which, as centres, death pro-
ceeded in constantly widening circles. Thus, in the leaves
of Colocasia, for example, we find such dead and dying areas
in otherwise fairly healthy leaves. The innermost of these

166 COMPARATIVE ELECTRO-PHYSIOLOGY

patches may be quite dark and discoloured, while, as the
living tissue is approached, this dark passes imperceptibly
into yellow colour. And beyond this, again, we find the
discolouration of yellow passing into the vivid green of living
tissue. Proceeding thus in a radial direction inwards, towards
the centre of such a patch from the living green, we shall
find all possible stages of death, from its initiation, somewhere
on the border-line between green and yellow, to its phase of
completion, in the dark central area. On testing the electrical
conditions of these different parts, I found that the border
between green and yellow was negative to the living green
surface. But the same point was also negative to the dead
central area, and more negative to this than to the living
tissue. Hence the dead was relatively positive to the living.
Or if we make one fixed contact on the living tissue, and
if the second exploring contact be made with various points

_ successively on a radial line passing from this to the centre

of the dead area, these contacts will pass in succession through
the living, the dying, and the dead. The variation of elec-
trical potential will be found to be at its greatest along this
line. The electro-motive difference between the point which
has been fixed on the living tissue, and the exploring second
contact, will at first be found to increase. The maximum
difference is attained on reaching the border-line between
green and yellow, or very little beyond this, this point being
galvanometrically the most negative. On now passing further
inward from this point, the maximum difference is found to
decrease, till we come to a point in the dead tissue which is
iso-electric with the living. On now again passing inwards,
to the still more completely dead tissue of the central area,
we find that we are approaching points which are more and
more galvanometrically positive, as compared with the living
tissue. The dying point on the border-line between green
and yellow is thus the most negative, and points to the right
or left of this are positive in comparison with it, the dead,
however, being more positive than the living. It has been
said that the electro-motive variation is most rapid along the

CURRENT OF DEATH 167

radial line. On the other hand, we obtain series of equi-
potential surfaces whose outlines closely follow those of the
boundaries of the different degrees of discolouration.
[shall next proceed to give quantitative measurements.
The first point to be considered is that of the choice of a
definite electrical level, which is to be used as a standard.
If this point be selected in the living tissue, we shall find that
our standard of comparison is extremely variable, since the
tonic condition, on which its electrical level depends, is itself
subject to change. The only condition which cannot be
modified in any way is that of complete death. This may
be taken, then, as the standard level. The method of experi-
ment will thus consist in selecting a series of equidistant points,
abcd,and so on, 5 mm. apart, along a radial line, passing
outwards from the central area, which is completely dead, to
the green tissue. The non-polarisable contacts E and E’ are
first placed on a and 4, then on @ and ¢, ¢c and d, and so forth.
The external circuit contains a high resistance, compared with
which any difference of resistance, as between any 5 mm. of
interposed tissue, becomes negligible. Hence, the successive
deflections of the galvanometer indicate the electro-motive
difference that exists between a and @, 0 and «¢, and so on.

One difficulty which is experienced, in these measure-
ments of small electro-motive differences, lies in securing the
iso-electric condition of the non-polarisable electrodes them-
selves. Whatever precautions are taken in the construction of
these, a small electro-motive difference will sometimes be
found to exist between them. The existence of such a
difference is easily tested by bringing the kaolin ends of the
two electrodes in contact, or by dipping both of them close
together in a vessel of normal saline solution. Any electro-
motive difference of the electrodes, however small, will now
give rise to a large galvanometric deflection.

This difficulty may be overcome by first taking special
precautions as to the purity of zinc rods and the chemicals
employed, and secondly, by keeping the electrodes for
a long time short-circuited, with their ends dipped in normal

168 COMPARATIVE ELECTRO-PHYSIOLOGY

saline. In very obstinate cases, however, I succeeded in
eliminating all differences by subjecting the electrodes to
cyclic variations of alternating electro-motive force. By
means of a Pohl’s commutator, without cross-bars, the
electrodes were put in connection with an alternating source
of E.M.F., and with the galvanometer intended to test
the resulting variation in the E.M. difference, by turns. —
A small hand-driven alternating-current generator was used
for this purpose. The speed of rotation of this machine
was gradually raised to a maximum, and afterwards as
gradually slowed down. Thus at each cycle the electrodes
were subjected to ascending and descending intensities of
alternating electro-motive variations. The effect of such cyclic
changes, in diminishing the existing electro-motive difference
between a pair of electrodes, specially selected for carelessness
of preparation, will be clearly seen from the following tabular

results:

Condition at starting Galvanometric deflection E.M. difference
Original difference . , 360 divisions 009 volt
After first cycle : F 40 Js 52?)
After second cycle . ; fe) ie One,
After third cycle. ; fe) - ee

It will thus be seen that, after a very short time of this treat-
ment, the two electrodes were rendered iso-electric.

I next proceeded to determine the distribution of elec-
trical potential in the various portions, living and dead, of
the leaf, In order to remove any accidental strain, the leaf
was placed in tepid water, and kept there for about half an
hour, till the water was cooled to the surrounding temperature.
The experiment was then carried out, in the manner already
described, and the following tabular statement shows the
results obtained. The electrodes, it will be remembered, were
placed successively at points 5 mm. apart from each other,
along a radial line proceeding from the dead tissue to the
living, the first point being taken as zero;

CURRENT OF DEATH 169,

* Position of Electrodes | Calapaner Deflection
| o— 5mm. e) division
5 ane ei E. =~ 1D 9
IO i568 5 igs e520. 1 255
15 — 20 55 ® i 45 9
20— 25 ,, 225400055
25— 39 5, — 140 29
30 — 40 ,, | + TIO +95
40 — 45 9 ‘+ 20 5)

It will be observed that as we proceed from the dead to
the dying, the negativity of the latter rapidly increases, the
maximum being at 30 mm. from the zero-point taken on the

5 10 15 20 25 30 35 40 45

|
: HM vr
Wh

te

tI

400 ee

Fic. 113. Distribution of Electric Potential in Lamina of Co/ocaséa along
a radial line from dead to living through intermediate stages. Ab-
scissa gives distance in mm. from chosen centre in dead tissue, ordinate
represents galvanometric negativity in divisions. Dead tissue repre-
sented dark, dying shaded, and living white.

dead tissue. This point of maximum-negativity almost
coincides with the visible border-line between the yellow
and the green. Beyond this, however, there is an electrical

170 COMPARATIVE ELECTRO-PHYSIOLOGY

reversal, the living becoming increasingly positive, as com-
pared with the dying. An inspection of the curve (fig. 113)
shows that while there is a point in the tissue between the
dying and the dead, which is equipotential with the living,
the completely dead tissue is positive to the living.

I next carried out an experiment in which death was
artificially induced, by immersing a portion of the tissue in
boiling water. In connection with this, I may say that it is
extremely difficult to ensure the complete death of a thick —
tissue. It is only the outside layers which undergo death
easily, but the interior tissues, from their protected position,
are extremely resistant, and it is only after prolonged
immersion in boiling water that death can really be ensured
throughout. In the present experiment, however, where
only a part of the tissue is to be killed, such prolonged
immersion would cause death to encroach upon those
portions of the tissue which were intended to be kept
alive. This difficulty was met by choosing a specimen,
the inside of which was accessible to boiling water. The
peduncle of the water-lily (Nymphea alba) in transverse
section appears extremely reticulated, and there is thus no
difficulty in exposing all its parts to the direct action of the
hot water.

The upper end of the peduncle was kept surrounded by
a cloth moistened in ice-cold water, the lower end being
immersed in boiling water for ten minutes. The specimen
was then placed.in tepid water, and allowed to cool down
slowly. In this way a length of the peduncle was ob-
tained, in which one end was completely killed, whereas
the other remained fully alive, the intermediate portions
showing all stages of the transition from the living to
the dead condition. In order to determine the electrical
distribution in its different parts, I now employed the
potentiometer method of balance. One electrode was per-
manently connected with that dying point which by a
previous test had been found to exhibit maximum nega-
tivity. The second electrode was placed at successive points,

I eS Ee oS

CURRENT OF DEATH 171

each of which was nearer than the last by 5 mm. to the dead
end, which was to the left. The same process was now re-
peated, the successive |
readings however being
taken towards the right
or living end. At each
point, the electro-motive
difference was balanced
by the potentiometer.
This straight form of
potentiometer had a

Fic. 114. Straight Form Potentiometer
scale divided into one x8 isa stretched wire with added resistances,

Rand R’. Sis a storage cell. When the
thousand parts (fig. 114), key, K, is turned to the right, one scale

and when its terminal division = ‘ooI volt, when turned to the
. left one scale division = ‘or volt. P is the
electro-motive force was plant.

adjusted to 1 volt, each }
division of the potentiometer was equal to ‘oor volt. The
following table gives the results obtained :

Distance from maximum . *

Towards left or dead end, : : Towards right or living end
; ; t t = ; ; ,
E.M. difference in yo55 volt “ee ee, iene C + (—) or E.M. difference in y;55 volt

I*2 *5 cm 9

5"0 FO 5, 2°5

18°2 I"5 55 4°7

22°0 rig! ae 6°8

23°0 HES 10°0

23°3 7 hee 12°8

ee 3°55» I 5 6

—— 4°O' 754 16°8

a: 4°55 17°5

— BD igs 18°'0

Here, also, as in the case of natural death, we find a point
in the dying tissue which is most negative. From the curve
given in fig. 115, it will also be seen that as we pass away
from this point in either direction towards the living or dead
area, we find an increasing positivity ; the curve for the dead
portion is, however, much steeper than that for the living.
Thus two points, one 1'5 cm. to the left in the dead tissue,
and another 5 cm. to the right in the living tissue, are
iso-electric. But while the maximum positivity of the living

172 COMPARATIVE ELECTRO-PHYSIOLOGY

is ‘O18 volt, that of the dead is 0233 volt. Hence the
dead tissue is here positive to the living, to the extent of
0053 volt.

We have seen that the prevailing idea is that the dead is
negative to the living. But from the results here shown, we
can see that this is not a complete statement of the case.
Since then the electro-motive variation, instead of showing a

25°

'
‘
t
i
!
i
Pi ——— + -\ 1. Lesne=
i]
i
i
i
i
{
j

he ee ee

ew ee Rn ee we we ee oes = oe a «.

2 ee me ee ee fe me me me ee ee ee

oe ee ee ee ee es ee ee ee ee ee ee ee es eee ee es es

he a a ee ee ee

ee a Ca

2 3 4 +e)
Fic. 115. Distribution of Electric Potential in Petiole of Vymphea alba,
one end of which has been killed.

The point of maximum negativity is taken as zero, distances to the left
or towards the dead taken as mznws, to the right or living, as Aplus.
Ordinate represents potential difference in thousandths of a volt.

progressive change from the living to the dead, exhibits a
maximum difference, followed by a reversal, it may be asked,
what is the reason of this anomaly ?

Much light is thrown on this subject from the results
given by another line of inquiry, to be explained in detail in
Chapter XVI. _ It is there shown that the plant-tissue on the
first onset of death exhibits a sudden contraction, indicative

CURRENT OF DEATH B73

of a strong excitatory reaction. This corresponds with the
rigor mortts of the animal, and by means of suitable
apparatus, the concomitant mechanical response can be
recorded. An electrical record of the same phenomenon
may also be obtained, in the form of an electrical spasm of
galvanometric negativity. Succeeding to this rigor of the
dying tissue, a post-mortem relaxation takes place, with
a concomitant change from galvanometric negativity to
positivity.

Now in a tissue which has been killed unilaterally only,
it will be understood that all possible gradations are to be
expected. Passing from the completely dead to the fully
_alive, we must necessarily pass through various zones,
beginning with the abnormally relaxed, through the inter-
mediate highly contracted. and rigored tissue on the death-
frontier, to the living, which is not so contracted as the
dying, and not so relaxed as the dead. At the point
where the onset of death-.is recent, the rigor, or excitatory
contraction and galvanometric negativity, are at their
maximum, Compared with:this, the slightly tonically con-
tracted living is positive, but not so positive as the abnormally
relaxed dead. :

The death-frontier, however, is not fixed. It is con-
tinually encroaching on-the living. The line of maximum
rigor and galvanometric negativity is thus also shifting in
the same direction. Along with this, however, the opposite
process of post-mortem relaxation is proceeding; so that a
point which was, in consequence of rigor, maximally negative,
becomes gradually converted to positive.

This positivity of dead tissue as compared with living,
which has here been demonstrated in the case of the plant,
I find to be also true of animal tissue, in those cases which
I have investigated. ‘Thus, while an injured.and dying area
in a frog’s nerve is negative, an already dead area is
positive, relatively to the living nerve. There is, moreover,
an intermediate area, between the dying and dead portions
of the nerve, which is iso-electric to the living,

174 COMPARATIVE ELECTRO-PHYSIOLOGY

Hence, having one contact fixed on a living area and
the other on (1) the dying, (2) the intermediate, and (3)
the dead tissue, we shall obtain three different types of
what is known as the ‘injury-current.’ In the first of these
the second contact will be negative, a condition which has
hitherto been assumed to be the sole characteristic of the
current of injury. But there are two other cases to be
considered. Of these, when the second contact is made at
a point intermediate between the dying and dead tissues,
we shall find it to be iso-electric with the first, or living
contact. And thirdly, when the second contact is on a
dead area, the latter will be positive to the first, or living
contact. We thus find three cases of the current of injury—
the first being negative, the second zero, and the third
positive.

Taking the first of these—that in which the injured
contact is negative—the action-current, in response to
stimulus, will bring about a negative variation of the so-
called current of injury. In the second, the result will be
indeterminate, since the injury-current is zero. In the third,
the response will be by a positive variation of the current of
injury.

I give below three photographic records in illustration of
these three cases, obtained with vegetable nerve. I may state
here that I have often observed results precisely similar in
the case of frog’s nerve also. In the first record, in fig. 116,
the thermal injury was moderate. The injured point was
thus negative, and the current of injury is represented here
by an up-line. The responses are seen to be by negative
variation. In the second record the injury was greater, and
the injured point was almost neutral; that is to say, on
making contact there was a slight up-twitch, which subsided
to zero. There is here, then, no current of injury. The
subsequent responses are, however, down, the action-current
being away from the living contact. In the third record
the injury was so great as completely to kill the injured
point, which thus became positive to the living. The

RESPONSE BY POSITIVE VARIATION 175

reversed injury-current is represented as down, the subse-
quent excitatory responses are also down, and constitute a
positive variation of the current of injury.

It will thus be seen that an identical excitatory reaction
of the living tissue appears to give rise to directly opposite

Fic. 116. Photographic Records of Responses of Vegetable Nerve,
one end of which has been injured

In the first injury was slight; current of injury represented up, response
by negative variation. In the second, injury greater; injured point
neutral, response down. In the third, injured point killed; injury
current reversed down, response by positive variation.

effects—namely, a negative or a positive variation of the
injury-current. :

I give below a short summary of the diversities of
response which may occur when either the natural, or the
injury-current, is taken as the current of reference.

(a) (6)
< Cc >C
B— m , Br —iD pj
>R —>R

Fic. 117. Typical Cases of Variation of Current of Rest and Action-
Current. Specimen originally isotropic

(a) A, end slightly injured and negative; Cc, current of injury; R, action-
current, a negative variation of Cc. (4) A, end killed and positive ;
C, current of injury; R, action-current, a positive variation of c.

First—we take the case where the point A is slightly
injured (fig. 117,@). The current of injury, Cc, is A> B, and
the responsive current, Rk, is B- A, constituting a negative
variation.

176 COMPARATIVE ELECTRO-PHYSIOLOGY

But when A is killed, the current of injury C is B> A, the
responsive current is also BA, constituting a positive
variation (fig. 117, 0).

Second —we take an instance where, owing to some physio-
logical difference, an intermediate point A is less excitable
than B or B’ (fig. 118, a). The primary natural current will
here be from the less to the more excitable : that is to say, C will

be A>B’ and A+B. If stimulus be now applied at x onthe

right, an identical excitatory current R, flowing away from the
excited point from right to left, will cause seemingly opposite
effects: that is to say, a negative variation of A+B’ and a
positive variation of A> B.

(a) (6)
~< c a >C <
Bop al ‘sas Xp!

Fic. 118. Typical Cases of Variation of Current of Rest and Action-
Current ; intermediate point naturally less or more excitable than
either of terminal.

(a) Intermediate A, less excitable, shown by vertical shading ; current or
rest A>B and A->B’; when right-hand point x excited, action-current
R from right to left, gives rise to negative variation of As’, and
positive variation of A>B. (4) Intermediate B, more excitable, shown
by horizontal shading ; current of rest A>B and A’->B ; action-current
on excitation at x, from right to left, giving rise to positive variation
of a’/—>B and negative variation of AB.

_ Again, we ‘may have the intermediate point B naturally
more excitable than A’ or A. The natural current C will
be A>B and A’>B (fig. 118, 4). Stimulation at x will now
give rise to an excitatory current R, from right to left. The
results here will, however, appear to be exactly the reverse
of those in the last case: that is to say,.an identical current,
R, will give rise to a positive variation of A’ > B, and negative
variation of A>B. Instances of these effects will be given
in Chapter XVIII.

And, lastly, we may have a typically anisotropic tissue,
composed of two halves, which are unequally excitable—as,
for instance, the upper and lower halves of the pulvinus of
Mimosa, or the muscle and gland in a muscle-and-gland

-RESPONSE BY POSITIVE VARIATION 177

preparation. Under normal conditions the primary or natural
current C is from the less excitable A to the more excitable B,
represented by A > B (fig. 119, a). The action-current R, being
in the opposite direction B > A, constitutes a negative variation.
- But owing to the after-effect of excitation, such as may
occur in isolating the specimen by section, the normal resting
current C is reversed toB > A (fig. 119, 4). Here the end B may
still be the more excitable of the two, hence the action-current
B- A will constitute a positive variation of the current of rest.
But when B becomes fatigued, its excitability is reduced
below that of A; hence the action-current is from the
relatively more to less excitable, ze. A>B. In this case,

(a) (6) : (c)
——_>C es ta F
A B A oon - ae LIB
R<——_ R <———- ———>R

Fic. 119. Typical Cases of Variation of Current of Rest and Action-
Current. Anisotropic organ, B end originally more excitable than A

- (a) Current of rest A->B ; action-current, R, in opposite direction ; response
by negative variation. (4) Owing to excitatory after-effect, current of
rest reversed to B—>A; B nevertheless more excitable than A; action-
current, R, is B—>A; response by positive variation. (c) Current of
rest reversed BA; action-current also reversed AB, by depression
of excitability of B, owing to fatigue ; response by negative variation.

on account of the reversal of both the current of rest and
action-current, the latter appears to constitute a negative
variation of the former (fig. 119, c).

It will thus be seen how intricate and diverse are the
responsive variations of the resting current, induced by
stimulus. Sometimes negative, sometimes positive, it would
appear as if there were no guiding principle to regulate these
phenomena. The so-called explanations hitherto attempted
have consisted in assigning the positive variation to a
hypothetical process of assimilation, and the negative to
dissimilation. Such explanatory phrases:reach the climax
of absurdity when we find ourselves compelled to ascribe |
one identical excitatory reaction now to assimilation and
then to dissimilation.

N

178 COMPARATIVE ELECTRO-PHYSIOLOGY

Indeed it must be said that, however suggestive the
general theory of assimilation and dissimilation may have
been found, its abuse has often stood in the way of physio-
logical inquiry. The inquirer, when faced with any difficulty,
instead of attempting to surmount it by patient inquiry, was
tempted rather to evade it by invoking the aid of an hypothesis
which could be made with equal ease to explain a given
fact or its direct opposite. We must remember that in the —
investigation of obscure problems, the danger is always,
instead of seeking an underlying law, to become satisfied
with the mere registration of phenomena, and by naming
these to imagine that they have been explained. The
resulting chaos in the present case has served to deepen
the impression that vital phenomena must always remain
capricious and mystical.

But when we come to survey the facts that have been
described, we find the phenomena of response, however
diverse they may at first sight appear, to be in no way
governed by chance or caprice. ‘They are, on the contrary,
definite and uniform under definite conditions.

As regards the so-called current of rest in a naturally
isotropic tissue, of which one end has been subjected to
injury, we must remember that the effect of injury is one of
excitation, its sign, within limits, being contraction and
galvanometric negativity. But we have seen that when a
point is over-stimulated, fatigue-changes appear which give
rise to a reversal of its normal sign of response, from con-
traction to expansion, from negative to positive (cf fig. 64)
The change at death, in which contractile rigor passes into
post-mortem relaxation, is analogous to this. ‘Thus when one
end of the specimen is merely injured, that end becomes
more or less persistently galvanometrically negative, the
current flowing away from it. But when the same end is
actually killed, the electrical change may be reversed, to one
of galvanometric positivity.

In an isotropic tissue, then, we may, by moderate injury,
bring about a state of anisotropy, under which the uninjured

RESPONSE BY POSITIVE VARIATION 179 _

end is rendered relatively the more excitable, and galvano-
metrically positive, compared with the inexcitable injured end.
In a naturally anisotropic organ, we have a state of things
which is analogous. In this case, in the primary condition,
the more excitable surface is galvanometrically positive. But
under the excitation due to preparation, or accidental dis-
turbance, this more excitable surface becomes the more excited,
and, relatively to the other, gaivanometrically negative. These
varying changes in the direction of the so-called resting
current, or current of reference, are the cause of the existing
anomalies in the interpretation of response by the positive
or negative variation.

But the direction of the action-current under normal
conditions is always the same. On diffuse stimulation it is
always from the more excited B to the less excited A.
The differential excitability or anisotropy, may be either
natural, or artificially induced, as by injuring one end of an
isotropic tissue. There are two different conditions under
which the normal effect may undergo reversal, those, namely,
of great sub-tonicity or excessive fatigue. But the statement
that the responsive current is always from the more excited to
the less excited, remains universally true. Numerous illustra-
tions, in verification of the cases laid down, will be met with
in the course of subsequent chapters.

CHAPTER XV
EFFECT OF TEMPERATURE ON ELECTRICAL RESPONSE

General observation of effect of temperature on plant—FEffect of fall and rise of
temperature on autonomous response of Desmodium —Effect of frost in abolition
of electrical response—After-etfects of application of cold, in EZucharis, Ivy
and Holly—Effect of rise of temperature in diminishing height of response—
This not probably due to diminution of excitability—Similar effect in auto-
nomous motile response of Desmodium—Enhanced response as after-effect of
cyclic variation of temperature—Abolition of response at a critical high
temperature.

WE have now seen that the physiological activity of a living
tissue may be gauged by means of its electrical response.
We know further that the influence of temperature is of
importance in the maintenance of a proper physiological
_condition. There is a certain range of temperature which is
favourable to this, and above or below these limits physio-
logical efficiency is diminished. If the plant be kept too long
at or above a certain maximum temperature, it is liable to
undergo death. Similarly, there is a minimum point at which
physiological activity is arrested,and below which death is apt
tooccur. The plant has thus two death-points, one above the
maximum and the other below the minimum temperature.
Some can resist these extremes better than others, and
length of exposure is also a factor which should not be for-
gotten in the question of the ultimate survival of the plant
under the given unfavourable conditions. Certain species
are hardy, while others succumb easily.

An unmistakable indication of the effect of temperature
on physiological activity is found in the variations induced
by it in the autonomous motile pulsations of the telegraph
plant, Desmodium gyrans. Here, too great a lowering of the

OE OO EE

EFFECT OF TEMPERATURE ON ELECTRICAL RESPONSE 181

temperature abolishes the pulsation. In fig. 120 are seen
(1) the records of normal pulsations ; (2) their arrest under
the application of ice-cold water; and (3) their revival, as
the plant regains the temperature of the room. In fig. 121
is shown the effect on similar pulsations of a rising tempera-
ture. The records in this case were obtained with a different

Fic, 120. Photographic Record showing Effect of Rapid Cooling, by
Ice-cold Water, on Pulsations’of Desmodium gyrans

Normal pulsations recorded to the left. Effect of application of ice-cold
water is seen in the production of diminished amplitude and abolition
of pulsation. Gradual return to the temperature of the room revives
the pulsation in a staircase manner, the period remaining approximately
constant. Note that cooling displaces the pulsation in a downward or
contracted direction. Gradual warming, conversely, is seen to produce
the opposite displacement towards expansion. Up-records represent
the fall of the leaflet, down-records its rise.

specimen, and it is seen that the pulsations are diminished |
in amplitude while their period is quickened, with rise of
temperature. When the temperature is raised still higher,
they come to a stop altogether.

_ We shall next proceed to observe the effect of temperature
on the electrical response of plants. As regards the influence
of cold, for example, I have found, during the course of a
research carried out in England, that after frosty weather,

182 COMPARATIVE ELECTRO-PHYSIOLOGY

the electrical responses undergo an almost complete aboli-
tion. During a certain week, for instance, the temperature
was 10° C., and the electrical responses then obtained from
radish (Raphanus sativus) were considerable, giving an E.M.
response which varied from ‘o5 to ‘1 volt. Two or three
days afterwards, however, as the effect of frost, I found the
electrical response of this plant to have practically dis-
appeared. A few specimens were found nevertheless which
were somewhat resistant. But even in these the average
E..M. response had only a value of ‘003 volt, instead of the
normal mean of ‘075 volt. That is to say, their average
sensitiveness had been reduced to one twenty-fifth. On now

Fic. 121. Photographic Record of Pulsations of Desmodium during
Continuous Rise of Temperature from 30° C. to 39° C.

warming these radishes to 20° C. there was an appreciable
revival, as shown by their increasing response. But in those
specimens which had been frost-bitten, warming effected no
restoration. From this it would appear that frost killed some,
which could not be subsequently revived, whereas others
were reduced to a condition of torpidity from which, on
warming, there was a revival.

I have also investigated the effect of an artificial lowering
of temperature on the electrical response of plants. The
Eucharis lily is particularly sensitive to cold. In this case I
took the petiole, and obtained response at the ordinary
temperature of the room, which was at the time 17°C. I
then placed it for 15 minutes in a cooling chamber at a

EFFECT OF TEMPERATURE ON ELECTRICAL RESPONSE 183 .

temperature of —2°C. On now again trying to obtain
response, it was found that it had practically disappeared.
The same specimen was next warmed to 20° C., and this
induced a revival of response (fig. 122).

I was next desirous of studying the after-effect of lowered
temperatures on different plants. For this purpose I chose
three specimens (1) the
petiole of Eucharts Lily,
(2) the stem of Ivy,
and (3) Holly. I took
their normal responses
at 17° C.,, and after-
wards placed them in
an ice-chamber at a
temperature of o° C.
for 24 hours. The
specimens were then
taken out, and their
responses under stimu-
lation once more re-
corded (fig. 123). From
these it will be seen
that while the respon-
siveness of the delicate (h)
Eucharis Lily was com- | |
pletely abolished, that eagnss
of the hardier plants, 110,128, Diminuton of Response in
Holly and Ivy, exhibited (z) Normal response at 17° C.
complete revival. (6) The response almost disappears when plant

; : f is subjected to —2° C. for fifteen minutes.
One interesting fact (c) Revival of response on warming to 20° C.

which I have noticed

is that when a plant approaches its death-point, by reason
of excessively high or low temperature, not only is its re-
sponse, of galvanometric negativity, diminished to zero, but
it is even occasionally reversed to positive. This effect
is due to the unmasking of the positive, by the abolition
of the true excitatory component.

(a) (Cc)

184 COMPARATIVE ELECTRO-PHYSIOLOGY

We shall next study the effect on the electrical response
of the plant of a rise of temperature. The great difficulty of
this investigation lies in raising the plant-chamber to the
various determinate temperatures required. I was able,
however, to accomplish this by means of electric heating. <A
spiral of german silver wire was placed in the plant-chamber
(cf. fig. 21), and by varying the intensity of the current
the temperature was then regulated at will. In the process —
of this electric heating a complicating factor was found in the
excitatory action of any sudden variation of temperature. But
no such excitatory disturbance occurs if the rise of tempera-
ture be not fluctuating, but gradual .and continuous. I was
able to secure this, by selecting at the beginning of the

aL

\ a o b
} KA be

Holly Eucharis
Fic. 123. After-effect of Cold on Ivy, Holly, and Zucharis Lily

_ a, The normal response ; 4, response after subjection to freezing temperature
for twenty-four hours.

experiment, a suitable strength of current, such as to raise
the temperature of the chamber continuously, at an approxi-
mately uniform rate. Care had also to be taken that thermal
radiation from the wire should not strike the specimen, since
such radiation, as we shall see later, acts as a stimulus. The
interposition of a sheet of mica, however, obviated this diff-
culty, mica being opaque to thermal radiation.

While, under these conditions, the temperature was being
raised, uniform vibrational stimuli were applied at intervals,
and responses recorded, the temperature of the chamber at
the moments of stimulation being carefully noted. In this
way I obtained the following photographic record, with
a petiole of Hucharis lily, affording a general idea of the
effect of temperature on response. It will be seen that

EFFECT OF TEMPERATURE ON ELECTRICAL RESPONSE 185

while the temperature was rising from 20° C. to 22° C. the
amplitude of the response was increased. After this, however,
it fell rapidly in height with rise of temperature and became
very small, at or near 60° C.- On allowing the temperature
to: fall, however, the responses revived, with this peculiarity,
that during the cooling, as compared with those given during
the ascent of temperature,
they were markedly en-
hanced (fig. 124).

The heating arrange-
ments in this case were
such that the temperature
was made to rise some-
what rapidly. It will be
noticed that response had
not here disappeared,
even at 65° C., though,
as we shall see in the
next chapter, the death-
point is at about 60° C.,

This apparent anomaly
is due to the fact that
the plant, which is a bad
conductor, was not al-
lowed time fully to attain
the temperature of its
surroundings. We shall

Fic. 124. Photographic Record of Responses
in Hucharis Lily during Rise and Fall of
Temperature

Stimulus constant, applied at intervals of
one minute. The temperature of plant-
chamber gradually rose on starting current
in the heating coil; on breaking current,
the temperature fell gradually. Tem-
perature corresponding to each record is
given below.

see that when the tem- Temperature rising: (1) 2 0 °, (2) 20°, (3) 22°,

perature is raised at a RE ATL Y (765 51°, (To)

slower rate—about 1° C. 45°, (11) 40°, (12) 38°.

in I1°5 minute—and when

the specimen is not too thick, excitatory response disappears

with the approach of death, at a temperature very near 60° C,
I give below a record of the effect of temperature

varying from 30° C. to 50° C. on the response of the stem

of Amaranth (fig. 125). In order to obtain perfect results,

it is necessary that the specimen should not exhibit any

186 COMPARATIVE ELECTRO-PHYSIOLOGY

fatigue, and I have found that this plant is but little subject
to it. It will be noticed how the response is continuously
depressed, as the temperature rises from 30° C. upwards.
In this case, the thermal ascent took place at the rela-
tively slow rate of 1° C. in 1I°5 minute, so that there was
time for the plant to attain the temperature of its sur-
roundings. A tabular statement is given below, showing
the effect of temperature on amplitude of response, in two -
different specimens of Amaranth :

SPECIMEN I, SPECIMEN II.
Temperature 1 Height. ofresponse || Temperature. Height of respotise |
|" |
30° age Ce | 200 divisions || 30° C. 110 divisions |
35° I * 2» | a5. go ”»
40° | re) | 40 40 ”
45° | 2 ”» 45° 25 »
50° 43 "99 50° IO vA

The same fall in amplitude of response, when a certain
point has been reached in the thermal ascent, to which |
have already referred, in the
case of Eucharzs lily, has
also been noticed in that of
muscle. From this it might
be concluded that rise of
temperature beyond 30° C.
or so, induced depression of
excitability. But here we

40°

are met by an anomaly.
45° For growth, which I have
50° shown to be a phenomenon
of excitatory response, in-
- ad : creases, in the case of .
Fic. 125. Diminished Amplitude of the plant, throughout the
Response with Rising Temperature. thermal ascent up to an

(Stem of Amaranth) ; Sarr
optimum point at or near

35° C. Conductivity, again, which is, to a certain extent,
correlated with excitability, undergoes enhancement with

40°

35°

EFFECT OF TEMPERATURE ON ELECTRICAL RESPONSE 187 ©

rising temperature. Thus in a certain specimen of Szo-
phytum, for example, while the velocity of transmission
at 30° C. was 3°77 mm. per second, it became enhanced to
9'I mm.—that is, nearly three times—when the temperature
was raised to 37°C. From these considerations, it would
appear that the diminution in amplitude of electrical response,
under a rising temperature below the rigor-point, might not
always be due to a diminution of excitability, but to some
other cause. |

In connection with this, it must be borne in mind that
two factors are included in the process of response: namely,
the external stimulus which induces contraction, or galvano-
metric negativity, and the internal factor which brings about
recovery. For I have already shown that whereas the action
of stimulus induces one effect—the contraction, for example, of
an excited tissue with galvanometric negativity—an increase
of internal energy causes exactly the opposite —that is to say,
the expansion of the tissue and galvanometric positivity.
External stimulus and internal energy thus act antagonisti-
cally. A steady rise of temperature causes, as we have seen,
an increase of internal energy. Hence, increased energy
due to rise of temperature, enhancing the force of recovery,
may cause a diminution of response, which is not due to
diminution of excitability.

The inference that it is the increased internal energy due
to rise of temperature which, by augmenting the force of
recovery, diminishes the amplitude of response, appears the
more probable from certain characteristics observed in the
autonomous pulsation of Desmodium gyrans. If rise of
temperature increased the force of recovery, we should
expect, conversely, that a fall of a few degrees would have
the effect of diminishing this force of recovery, and con
sequently enhancing the response. That this actually occurs
will be seen in fig. 126, in the first part of which is given
a series of responses at the temperature of the room, which ©
was 29° C. When the temperature of the plant-chamber
was now lowered to 25° C., the force of recovery would appear

188 COMPARATIVE ELECTRO-PHYSIOLOGY

to be diminished, since the amplitude of response was con-
siderably enhanced. That the general excitability of the
plant was not increased by the lowering of temperature,
is seen from the fact that the frequency of pulsation was
reduced on cooling to about two-thirds of its original value.
The diminution of response with rising temperature may
thus be due to an increase of internal energy, which tends

Fic. 126. Photographic Records of Autonomous Pulsations in Des-
modium, showing Increase of Amplitude and Decrease of Frequency,
with Lowering of Temperature

The pulsations to the left were recorded at the ordinary temperature of
the room, 29° C. Those to the right, when the temperature had been
lowered to 25° C.

to cause antagonistic expansion and consequent galvano-
metric positivity. This view finds support from the records
seen in figs. 129 and 133, given in the next chapter. The
first of these (fig. 129) shows the expansion, with consequent
physical elongation, of the filament of Passzfora under a
rising temperature. In the second (fig. 133) is seen the in-
creasing galvanometric positivity of a specimen of Amaranth
under similar circumstances.

It is now clear that when the temperature of the tissue

EFFECT OF TEMPERATURE ON ELECTRICAL RESPONSE 189

is below a certain thermotonic minimum, the effect of a rise
of temperature will be to enhance the amplitude of response
by removing molecular sluggishness. This fact has been
illustrated in the gradually heightened mechanical response
of the autonomous pulsation of Desmodium gyrans when a
plant artificially cooled was allowed to return to the normal
temperature of the room (fig. 120). If similarly a plant
tissue be first cooled and then allowed to return to the
surrounding temperature, its electrical responses to suc-
cessive uniform stimuli being recorded throughout, a stair-
case increase of response will be observed during the return.
When the temperature, however, is raised above a certain
optimum, a depression of the amplitude of response begins,
not by the depression of excitability, but by the increasing
force of recovery due to an augmentation of the internal
factor. True depression only takes place when the plant
is approaching a condition of heat-rigor.

One very curious effect of temperature-variation which
has been touched upon is the marked increase of sensi-
tiveness which often makes its appearance as its after-effect.
This is seen exemplified in the record given in fig. 124,
showing the effect of a cyclic variation of temperature
on Eucharzs lily. In another experiment with Scotch kale,
the response at the temperature of 30° C. was eleven
divisions, and at 50° C. eight divisions, during the thermal
ascent. During the descent, however, the amplitude at
50° C. was sixteen, and at 30° C. twenty-three divisions.
The sensitiveness was thus doubled. This enhancement
may be due in part to the increased molecular mobility
consequent on the annealing effect, as it were, of temperature-
variation. But it may also be regarded as partly due to the
difference of the antagonistic forces which the excitatory
response has to overcome during ascent and descent. During
the thermal ascent, the opposing expansive force is being
rapidly accelerated. During the thermal descent, on the
other hand, this is no longer the case, for the force of re-
covery is now undergoing a diminution.

190 COMPARATIVE ELECTRO-PHYSIOLOGY

When the temperature is raised above a certain critical
point, the plant is killed, and its electrical response dis-
appears at the same time. This is demonstrated visually in
the accompanying photographic record (fig. 127). In this
case, normal responses were first obtained at the usual tem-
perature of the room. Steam was next introduced into the

Before * After

Fic. 127. Photographic record showing effect of Steam in abolishing
Response

The two records to the left exhibit normal response at 17° C. Sudden
warming by steam induced at first an inorease of response, but five
minutes’ exposure to steam killed the plant (carrot) and abolished the
response.

Vibrational stimulus of 30° applied at intervals of one minute; vertical
line = ‘I volt.

plant-chamber, and kept streaming in during the course ot
the experiment, electrical responses being recorded mean-
while at intervals of one minute. It will be seen that at first
a transitory augmentation ot excitability was induced. But
this quickly disappeared, and in five minutes the plant was
effectively killed, as is shown in the waning and final aboli-
tion of response. This experiment affords us a qualitative
demonstration of the abolition of response at death under

EFFECT OF TEMPERATURE ON ELECTRICAL RESPONSE I9QI

the influence of high temperature. In the next chapter we
shall enter upon an exact determination of this critical point
of death. cate

It is thus seen that temperature modifies the electrical
response of plants. There isa temperature-minimum below
which response is abolished. If the plant be kept too long
at this temperature it is apt to be killed. In the case of a
delicate species like Eucharis, which is highly susceptible of
the injurious effect of cold, the electrical response is per-
manently abolished by long exposure. But hardier plants,
like Holly and Ivy, show revival of electrical response, on a
return to a favourable temperature. The electrical response
disappears also at a certain maximum temperature con-
stituting the death-point.

CHAPTER XVI
THE ELECTRICAL SPASM OF DEATH

Different fost-mortem symptoms—Accurate methods for determination of death-
point— Determination of death-point by abolition or reversal of normal elec-
trical response—Determination of death-point by mechanical death-spasm—
From thermo-mechanical inversion—By observation of electrical spasm : (a) in
anisotropic organs: (4) in radial organs—Simultaneous record of electrical
inversion and reversal of normal electrical response—Remarkable consistency
of results obtained by different methods—Tabulation of observations.

IT will be seen from the last chapter that there is in the case
of every plant a certain high temperature which is critical,
since above it life passes into death. Much difficulty has
been experienced in the exact determination of this critical
point, because no sure criterion of death was hitherto avail-
able, such as would furnish an immediate and reliable indica-
tion of its occurrence. The various symptoms of death, such
as drooping, withering, discoloration and the escape of
coloured cell-sap, do not manifest themselves at the onset of
death, but at some time indeterminately later. Even when a
plant has been subjected to a temperature in excess of the
fatal degree, it continues to appear fresh and living ; and it is
not till after some longer or shorter interval that the death
symptoms are seen.

To take, for example, the symptom of drooping, it is
clear that the loss of turgidity on which this depends cannot
at once make itself visible. In a thick tissue, again, death
may take place in the superficial layers of the plant, the
interior tissues, owing to feeble thermal conductivity, remain-
ing comparatively unharmed. Or, if we employ the test of
discoloration, which we shall find to occur some time after
the initiation of death we find that the exact moment at

THE ELECTRICAL SPASM OF DEATH 193

which discoloration begins cannot be detected with sufficient
precision. When we place the specimen in a thermal bath
under a rising temperature, the beginning of discoloration
- after death is so slight as to be impossible of detection, and
by the time it becomes marked, the temperature has already
passed several degrees above the fatal point. I have found,
for example, that the colour of the milk-white style of Datura
_ .alba has changed to brown by the time that the temperature

of the bath has risen to about 64° C. In the petals of
Sesbania coccineum, again, a striking change of colour is
detected, under similar conditions. Rich crimson here turns
into pale blue at a temperature of about 67° C.. The fila-
mentous corona of Passiflora quadrangularis, finally, in which
the filaments are barred by purple rings, loses its colour
normally at about 68° C. In all these cases, the initiation of
the loss of colour must have been imperceptible. Hence, all
that can be determined from such experiments is that the
death-changes must have commenced at some. temperature
~ lower than 64° to 68° C.

Before proceeding further, it is necessary to obtain a clear
idea of what is meant by the death-point. In animals, an
early symptom of death consists in the setting in of rigor
mortts. But this does not synchronise throughout the
body, certain parts of the organism undergoing the death-
change earlier than others. Thus the only definition of the
death-point which can be made at all precise is that which
regards it as the point of initiation of some unmistakable
sign of death. I shall next proceed to describe several
death-symptoms and the modes by which they may be de-
tected with certainty.

With regard to such detection, I Siti pointed out else-
where that, theoretically, it should be possible to make such
a determination by watching the waning of some effect
characteristic of the living condition, the death-point being
known by its cessation at a given moment. Such a test, as
we shall presently see, is afforded by the electrical responses.
The ideally perfect method, however, would be by the

O

194 COMPARATIVE ELECTRO-PHYSIOLOGY

detection of some effect which at the moment of death under-
went a sudden reversal to its opposite. There would not
here be even that minor degree of uncertainty which is in-
cidental to the determination of the exact vanishing-point of
a waning effect. And such methods are afforded by my
discovery of the occurrence of mechanical and electrical
spasms at the moment of death.

Turning now to the method of the waning effect, we have

seen that response to stimulus by galvanometric negativity is _

distinctive of the living condition. When the plant is killed,
this normal response disappears. At the moment of death
from high temperature, therefore, we may expect to see the
abolition of this normal excitatory response of negativity.

For this investigation I took a batch of six radishes.
The specimens were kept for five minutes previous to each
experiment in water at a definite temperature (say of 17° C.),
and were then mounted in the vibration-apparatus and
their responses observed. Each specimen was next dis-
mounted and replaced in the bath at a higher tempera-
ture (say of 30° C.) for another five minutes. After this, a
second set of responses, to the same stimulus as before, was
taken. In this way observations were made with each plant,
till the temperature at which response almost or altogether
ceased was reached. I give below (p. 195) a table of the
results obtained with the six radishes.

From these experiments it would appear that in these
cases the responses disappeared at about 55° C. It should
be stated here that this investigation was carried out in the
winter season in England, and it will be shown later that
the incidence of cold has the effect of lowering the normal
death-point by about 4° or 5° C.

I was next desirous of substituting, for this method of
discontinuous observations, one which should be continuous.
I, therefore, subjected the specimen—a stem of Amaranth—
to a continuous rise of temperature, and took records of
responses to uniform stimuli after every few degrees of the
ascent. I found here that not only was there a gradual

i Ge ties Ee

THE ELECTRICAL SPASM OF DEATH 195

TABLE SHOWING EFFECT OF HIGH TEMPERATURE IN ABOLISHING
RESPONSE OF RADISH (Raphanus sativus)

‘Dien vt te 6" see Re et a tl i te i ee

Specimen Temperature penis ensinp papa é

: 178-6, 70
53° C. 4
aie & oot OF 160.
i Sg I

17° CG; 100

3 50° C. 2
1 ee OF 80

4 55° C. fe)
17° C. 40

5 | 60° C, fe)
6 a7? C, 60
55°.C. oO

decrease of response, tending towards its abolition, with
rising temperature, but also that, at the death-point, it under-
40

43

50

60°
Fic. 128. Record of Electric Responses of Amaranth at various temperatures
The response undergoes reversal to positive at the critical temperature of 60° C.

went actual reversal from the normal galvanometric nega-

tivity to positivity (fig. 128). This was due to the fact that
02

196 COMPARATIVE ELECTRO-PHYSIOLOGY

on reaching the death-point, the contained positive com-
ponent in response was unmasked by the abolition of the true
excitatory effect. But this positive response disappears also
after a short time. It will thus be seen that by this method
the death-point is capable of determination within very narrow
limits, having been, in the present case, near 60° C. When
the tissue is thin, this temperature soon proves fatal. But

should it be thick, a very much longer exposure to it

is necessary, if the interior of the tissue is to be killed
effectively.

I have also discovered another method of obtaining the
death-point with precision, in the symptoms afforded by
mechanical responses. For I found thata death-spasm occurs
at a certain critical moment in a plant, which is analogous
to the death-throe of the animal. The experimental plant—
Mimosa, for instance—was placed in a bath of water, whose
temperature was being raised gradually, at a uniform rate of,
say, 1° C, per one minute and a half, until the death-point was
reached. During all this time there was no responsive fall
of the leaf, for, we have seen, it isa sudden variation, and not
a gradual rise of temperature, which acts as an excitatory
stimulus. This gradual rise, on the other hand, increases the
internal energy of the plant, by which the turgidity of the
pulvinus is continuously augmented. In this process the
increase of turgidity is more energetic in the more excitable
lower half than in the upper. The greater expansion of the
lower side of the pulvinus thus raises the leaf continuously.
But immediately on reaching the death-point, there is a
reversal of thls movement, and an abrupt fall of the leaf.
This spasmodic movement is sudden and well-defined. In
a vigorous J/zmosa the death-spasm is found to occur at
or very near 60°C. This contraction of death is followed
after some time by a fost-mortem relaxation.

That the death-response is an excitatory phenomenon
is seen from the fact that any circumstance which lowers
physiological activity lowers the death-point also. Thus,
after a spell of cold weather, I found that the death-point

ee ee

THE ELECTRICAL SPASM OF DEATH 197

of Mimosa was lowered from the normal 60° C. to about
53° C. This latter value, it will be remembered, was ap-
proximately the same as that obtained with radish, in winter,
by the method of electrical response. Again, I find fatigue
to induce a lowering of the death-point, the extent of which
depends upon the degree of fatigue. When this was moderate,
I have found the death-point of MW/zmosa to be lowered to
56° C.

This spasmodic contraction, indicative of the initiation of
death, may express itself in diverse ways. For example,
if the tubular peduncle of Ad/zum be filled with water, and
raised gradually in temperature, there comes a moment at
which a sudden expulsion of the contained water occurs. A
spiral tendril of Passzfora, under the same circumstances,
exhibits a sudden uncurling. The florets of the ray, in certain
Composite, show characteristic movements, either up or down.
In all these cases alike, under normal circumstances, the
death-point is found to be at or near 60° C.

Turning next to the radial organs of ordinary plants,
these also exhibit a sudden longitudinal contraction at the
onset of death. I have shown elsewhere how, by means
of the Morograph, an instrument which I devised for this
purpose, a thermo-mechanical curve is recorded by the
specimen, while it is being subjected to the continuous rise of
temperature, culminating in the death-point. The ordinate
of this curve represents the induced variation of length, and
the abscissa the temperature. The expansion described in
the case of MWimosa is seen here in the form of a gradual
elongation, up to the moment of reaching the death-point.
When this point is reached, however, a sudden contraction
takes place, giving rise to an inversion of the curve. This
turning point is very abrupt. The curve as a whole is
thus one of life-and-death, in which the point of inversion
separates the two. I give below a photographic record of
this thermo-mechanical curve, obtained with the coronal
filament of Passtfora. The death-point occurred here at
59°6° C. (fig. 129). The thermo-mechanical curve is very

198 COMPARATIVE ELECTRO-PHYSIOLOGY

similar in similar specimens under normal conditions.
Fig. 130 gives two records of two different styles of Datura
alba, obtained from flowers of the same plant. The death-
point is seen to have occurred at 60°C. In recording the
thermo-mechanical curve, there is found to be, normally
speaking, a continuous expansion up to the death- point.
In the case of vigorous specimens, in a good tonic condition,
the inversion does not take place
till about 59°6° or 60° C. But in
less vigorous specimens, a certain
hesitation, as it were, is seen to
occur in the record at or near
55° C. With vigorous specimens,

Fic. 129. Photographic Record
of Thermo-mechanical Curve
given by Coronal Filament
of Passiflora

The first or down part of the so 30° gee oe S* S0° 55° 60° 6S°
curve shows expansion, but

on reaching death-point, at Fic. 130. Thermo-mechanical Curve of «
59°6° C., there ska sudden Two Different Specimens of Style of
inversion, due to spasmodic Datura alba, obtained from Flowers
death-contraction. of the same Plant

there may be the merest indication of this hesitation ; in other
cases, with less favourable tonic condition, the hesitation is
prolonged, but the expansion finally proceeds, ahd the death
inversion takes place at the usual temperature of about
60° C. When the specimen, however, is enfeebled, or has
been subjected to unfavourable circumstances, the point of
transient instability becomes fatal, and the inversion takes
place there. As an example of what has just been referred
to—namely, the influence of unfavourable external circum-

THE ELECTRICAL SPASM OF DEATH . 199 —

stances in lowering the death-point—it may be mentioned here
that the sudden incidence of cold weather will lower it by
some 4° or 5° C. Intense fatigue will lower it by as much
as 19° C.

_ [have already said that this spasm, taking place at the
moment of death, is an excitatory response. On this theory
it occurred to me that it should also be possible to determine
the onset of death by an electrical spasm. It may be well
at this point, therefore, to examine some of the conditions
under which such a spasm, supposing it to take place, might
be displayed most conspicuously. We may suppose a radial
organ, with the usual electrical contacts, A and B, to have
its temperature raised gradually up to the death-point.
The excitatory effect of death may now be expected to
cause the galvanometric negativity of a given point. But
since these excitatory effects are equal and similar at
A and B, they will balance each other, and there will be
little or no resultant galvanometric response. In order to
obtain a marked resultant effect, then, we must have an
organ in which the excitabilities of the two points A and B
are different. This difference of excitability, necessary to the
exhibition of a resultant response, may be either natural or
artificially induced. For the former, we may take a specimen
which is not radial, but anisotropic, thus affording us two points
of galvanometric contact, possessed of unequal excitabilities.

We have seen that the inner surface of the petiole of
Cucurbita maxima was more excitable than the outer.
The same is true of the hollow peduncle of Uvzcits lily.
There is also a great difference of excitability as between the
upper and lower sides of the scale of the bulb of the same
lily, in the season of flowering, the concave surface of this
scale being more excitable than the convex. Any of these
specimens described I find to answer asmizably for the purpose
of this investigation.

Taking the petiole of Cucurbita, then, I divided it longi-
tudinally, and rejected one-half, ‘thus obtaining a half-tube,
of which the inner concave surface was more excitable than

200 COMPARATIVE ELECTRO-PHYSIOLOGY

the outer convex. Electric contacts were now made
through non-polarisable electrodes with equal and opposite
areas on the two sides. These adjustments were made in a
heating chamber containing electrical arrangements by which
the temperature could be raised continuously. This was
satisfactorily accomplished by an incandescent electrical
lamp which was placed in a second chamber, vertically below |
the plant-chamber. There was a wooden partition between
the two, by which the light of the lamp was excluded from
the specimen (fig. 131). For the radiation itself will be

y
E Ro Rx

| an
et || sa
[A625 My
|

Fic. 131. The Thermal Chamber

Electric lamp in the lower compartment raises temperature of the upper.
E, E’, electrodes making contacts with the specimen ; T, thermometer.

shown to constitute stimulus, and the object in the present
case was to eliminate all exciting factors except death itself.
By means of side-openings, the heated air was enabled to
pass into the plant-chamber, thus raising the temperature. A
rheostat included in the lamp-circuit made it possible to
adjust the rate of this rise of temperature, its average being
about 1° per minute.

The natural current through the petiole is, under normal
circumstances, from the less excitable outer to the more
excitable inner surface: that is to say, the inner is galvano-

THE ELECTRICAL SPASM OF DEATH ZO}

metrically positive. This is true when the excitation, due
to section made for the purpose of preparation, has subsided.
This stimulation, by causing greater excitation of the inner
surface, is liable to induce there a temporary negativity.
A gradual rise of temperature, as we saw, caused an increased
turgidity of the more excitable lower side of the pulvinus
of Mimosa, and this increased turgidity was exhibited
mechanically by the erection of the leaf. But the electrical
sign of increased turgidity is galvanometric positivity. We
have also seen that electrical responses occur equally in
motile and non-motile tissues. In the petiole of Cucurbita
then, on its more excitable inner surface, we obtain, during
the gradual rise of temperature, an increasing galvanometric
positivity. This is true only, as has been said before, when
the rise is continuous, and not marked by fluctuation. For
any sudden variation will act as a stimulus, causing galvano-
metric negativity of the more excitable inner side. For this
reason it is necessary that the rheostatic resistance inter-
posed in the lamp-circuit, for the adjustment of the uniform
rate of rise of temperature, should be made at the beginning
of the experiment, such tissue being very sensitive to this
particular stimulatory action. At the commencement of my
investigation I experienced much trouble from the erratic
movement of the galvanometer spot of light, and the
obtaining of a steady electrical curve seemed at that time
almost hopeless. Later on, however, I found that these
fluctuations were traceable to temperature-variations, unavoid-
ably associated with the attempt to regulate the rise of
temperature by movement of the rheostatic slide. It is for
this reason, then, that the adjustment must be made, once for
all, at the beginning.

Carrying out the experiment in this manner, I obtained,
with various anisotropic organs, a sudden inversion of the
electric curve at the death-point. This death-point was
found, in all vigorous specimens, from which traces of injury
had been removed by previous rest, to occur accurately
at 59°6° or 60° C._ In these electrical curves, the same

202 COMPARATIVE ELECTRO-PHYSIOLOGY

point of instability, already noticed in the thermo- mechanical
curve, was often found to occur at or about 55°C. And
if the specimen were not in favourable tonic condition, or
had been suffering from injury, the death-point was lowered
to this degree. 3
I give below an electrical curve showing the point of
inversion at death (fig. 132). It was obtained with the
sheathing petiole of Musa. The
inner or concave side of this petiole
is more excitable, as we have seen,
than the outer. These responsive
electrical variations were very large,
and could not be represented within
the limits of the photographic plate.
I therefore took a photographic
record between the temperature of
54° C. and 67° C. only. The first
part of the curve represents the
increasing galvanometric posi-
tivity of the more excitable inner
surface of the specimen. The
same process of increasing posi-
tivity under the continuous rise of
temperature, had been going on
Hieltae whctourerkak Reacont previously, it is to be understood,
exhibiting Electric Spasmin before arrival at 54° C., at which
he Fe Hole oh Ae the photographic record was com-
Sudden electric inversion takes ee
place at the death-point, menced. This increasing galvano-
59°5°. Record was com- metric positivity corresponds to
menced at 54° C., and suc- : .
cessive gaps in the record the gradual erection of the leaf in
cae C. rise of tem- Yy0sa, and to the expansion of
a radial organ, such as a coronal
filament of Passzflora, all alike being due.to the positive
variation of turgidity. In order to give an indication of the
particular temperature at each portion of the curve, the re-
cording light was obscured for about 15 seconds after each
degree of temperature. The successive gaps, then, are one

THE ELECTRICAL SPASM OF DEATH 203

degree centigrade of temperature apart. These interruptions,
however, were not made after the occurrence of the inversion.
As soon as the death-point was reached, in the present case
at 59°5° C., there was a sudden inversion of the electrical
curve (fig. 132), corresponding with the point of inversion of
the thermo-mechanical curve (fig. 129). Each of these
curves is seen to bear a striking resemblance to the other.
In both cases, the inversion was due to the same fact of
sudden excitation, finding expression in the one, in induced
galvanometric negativity, and in the other, in mechanical
contraction.

In the case of organs which are more or less radial, and
in which there is little differential excitability, it is necessary
to abolish the excitability of one
contact, as, say, by previous scalding.
For this experiment I took a leaf of
Amaranth, and injured a portion of
the lamina by immersion in boiling
water. The two contacts were
made, one with the petiole, and the
other with the injured lamina. On
raising the temperature continuously,
the more excitable petiole became
increasingly positive. The photo-
eraphic record in this case was com-
menced only on reaching 55° C., and
the death-inversion took place at date Pitre, saree
59°5° C. (fig. 133). version -at Death-point,

We have already seen that, besides 525» Patrice. a
this electrical reversal, there is another
means of detection of the death-point, afforded by the con-
version of the response to external stimulus from the normal
negative into positive. Now it occurred to me that it would
be interesting, if in the same specimen, both these tests could
be applied at the same time. We could then see whether
two methods so independent of each other furnished mutual
corroboration or not. For this purpose I took a stem of

204 COMPARATIVE ELECTRO-PHYSIOLOGY
Amaranth, and abolished the excitability of one of the two
contacts—a lateral leaf—by scalding. The electrical curve,

under a continuously rising temperature, was now taken in
The existing electro-motive difference

the usual manner.
between living and injured contacts underwent the usual

40°
fe]
45
Oe é
‘ 4
f
S H
oe !
. 50°
MA. 59°
‘
55}
: \ ‘|
‘ ' 58
‘ !
Vv
57°

Fic. 134. Record showing Inversion of Electric Curve (represented
by dotted line) and Simultaneous Reversal of Electric Response in

Stem of Amaranth
{ indicates current of injury from injured to uninjured contact, which,
Normal

reaching a maximum, undergoes reversal at death-point.
response up, also becomes reversed to down after death-point.

increase, reaching a maximum at the death-point. Meanwhile
electrical responses to uniform vibrational stimuli were taken
at intervals a few degrees apart. It will be seen (fig. 134)
that the electrical inversion took place at 57° C., this
moderate lowering of the death-point being due, in all
probability, to the slight depression caused by scalding at

THE ELECTRICAL SPASM OF DEATH © 205

the distal contact, which had not had time to pass off. The
test-responses to uniform mechanical stimulation which
were being taken meanwhile show a continuous diminution
towards the death-point. When this, however, had been
passed, the response is seen to be reversed in direction to
positive. As has been said before, this positive response also
disappears after a time. We thus obtain a very striking
demonstration of the fact that the reversal of the electrical
curve and the reversal of the sign of response are concomitant.

It may be mentioned here, in anticipation of a future
chapter, that the death-point may also be obtained by the
sudden inversion of the curve of electrical resistivity, and
that the value obtained in this way coincides with those
already given.

I give below a table showing the death-points deter-
mined by various methods:

TABLE SHOWING DEATH-POINTS OBTAINED BY DIFFERENT METHODS

Specimens Method pac
Cc.
1. Flower of French Marigold . | Opening or closing of flower 59°
2 Peduncle of Aliium . . | Expulsion of contained water 59°
3. Spiral tendril of Passifora . | Movement of uncurling . Z
4. Pulvinus of AZ@imosa . . | Spasmodic lateral movement | 59°-60°
5-8. Style of Datura (four speci-
mens). Each gave . . | Morograph : : e} , '60?
9-12. Style of Azbzscus (four speci-
mens). Each gave . : ” , ; ‘ 60°

13-18. Coronal filament of Pass¢flora

(six specimens). Each gave » ‘ 60°
Anisotropic organs . | Electric inversion

19. Petiole of Cauliflower . . es os : ; 60°
20. Scale of Uriclis bulb. ; ae rey : ¥ 60°
21. Petiole of Musa . , . 43 ve 60°
22. Radial organ: petiole of

Amaranth : 4 ‘ ss a : - | 59°6°
23. Petiole of Amaranth . . | Reversal of sign of electrical | 59°6°

response

24. Style of Hzbéscus . ‘ . | Resistivity variation . : 60°

It is thus seen that employing different methods and
using plant-organs which are equally diverse—flowers, bulbs,
petioles, and others—a death-point is determined which

206 COMPARATIVE ELECTRO-PHYSIOLOGY

is very definite and practically the same for all phanero-
gamous plants. Among the mechanical methods, that
which depends on the thermo-mechanical curve, giving
the death-point by a sudden inversion, is specially accurate.
Of an equally precise character is the death-point obtained
by the inversion of an electrical curve, and also that which
is given by reversal of the electrical response. And it is in

the highest degree remarkable that the points of inversion —

in the mechanical and electrical curves respectively, together
with the point of reversal of the electrical response itself,
should so exactly coincide.

ate Lars

CHAPTER XVII
MULTIPLE AND AUTONOMOUS ELECTRICAL RESPONSE

Repeated responses under single strong stimulus—Multiple mechanical response
in Biophytum-—Multiple electrical responses in various animal and vegetable
tissues— Continuity of multiple*and autonomous response—Transition from
multiple response to autonomous, and vice versa—Autonomous mechanical
response of Desmodium gyrans and its time-relations — Simultaneous
mechanical and electrical records of automatic pulsations in DVesmodium—
Double electrical pulsation, principal and subsidiary waves—-Electrical
pulsation of Desmod7um \eaflet under physical restraint—Growth- ema
—So-called current of rest in growing plants.

WE have seen that when a plant organ is acted on by a
single stimulus of sufficient intensity, it exhibits a single
excitatory effect, which may show itself in two independent
ways, as mechanical and electrical response. We have also
seen that part of the impinging stimulus may become latent,
to find appropriate expression later. It was also shown
that with increasing intensity of stimulus the amplitude of
response reaches a limit. It may thus happen that a very
strong stimulus, not finding adequate expression in a single
response, will exhibit itself by means of repeated responses.
The incident energy in such cases is held latent for a
time,’ to manifest itself later in a rhythmic manner.

I have been able to demonstrate the occurrence of this
multiple excitation, in response to a single strong stimulus,
by several different and independent methods. The simplest
and most striking of these depends on the recording of the
motile effects in the leaflets of Bzophytum. In fig. 135 are seen
no less than sixteen multiple pulsations resulting from a single
strong thermal stimulation of the petiole bearing the leaflets.

1 For more detailed account see Bose, Plant Response, pp. 2779-357.

208 COMPARATIVE ELECTRO-PHYSIOLOGY

The average period of each pulsation is here about thirty
seconds ; but this may vary in different cases from half of this
toone minute. I have also been able to detect these multiple
excitatory waves, during their transit through non-motile con-
ducting tissues such as stems. ‘The imperceptible volumetric
changes which occur on the arrival of excitation were here
detected electrically by variations of pressure induced in an
enclosing microphonic contact. In fig. 136 is seen such

Fic, 135. Multiple Mechanical Response of Biophytum, due to a Single
. Strong Thermal Stimulus

multiple electro-tactile response in the stem of MW/zmosa, due
to a single thermal stimulus.

I have also been able to record such multiple excitatory
effects by means of electro-motive response. In fig. 137 is
seen a photographic record of a series of such responses,
given by the leaf of Bzophytum, the individual thermal
stimuli being here applied at intervals of five minutes. It will
here be noticed that each single stimulus gave rise to
from five to eight responses, the average period of which
was thirty seconds. From the corresponding mechanical

MULTIPLE AND AUTONOMOUS ELECTRICAL RESPONSE 209

responses, it will be remembered that the average period of
these had also this value.

These multiple responses to
a single strong stimulus, while
very strikingly manifested by
such plant-tissues as the pul-
vinules of Azophytum, and in
the animal, by the cardiac
tissue, are also exhibited by
almost all kinds of tissues
under favourable circumstances.
In fig. 138 will be seen records
which show this in the case
of different vegetable organs
under diverse forms of stimu- ge

A . 3 Fic. 136. Multiple Electro-tactile
lation. In fig. 139 1S given Response in Stem of AZ/mosa,
a series of multiple responses Savi Single Strong. ’Thermal
which I have obtained from
frog’s stomach. I have also
detected the occurrence of multiple responses in nerves of
animals, which will be described in a later chapter.

(Original record reduced to }.)

Fic. 137. Photographic Record of Multiple Electrical Response in
Leaf of Biophytum

First series of eight responses to a single thermal stimulus ; second stimulus,
after interval of five minutes, evoked five responses ; third stimulus, after
second interval of five minutes, gave six responses. Average period of
each response, thirty seconds nearly.

We have seen that multiple response takes place in

consequence of some sufficient increase of internal energy.
P

210 COMPARATIVE ELECTRO-PHYSIOLOGY

In the cases. mentioned,

this was derived from impinging

stimulus. The internal energy of a tissue may, however, be

Fic. 138. Multiple Electrical Responses under Different Forms of
Stimulus in Different Organs

(a) In Mimosa due to thermal, and (4) to chemical stimulation ; (c) in
peduncle of Azophytum, due to thermal stimulus ; [N.B.— This ‘series
persisted for two honrs.] (d) in hypocotyl of Zamarindus indica, due

to stimulus of cut.

increased, and multiple

initiated in other ways, as,

Fic. 139. Photographic Record
of Multiple Electrical Re-
sponse to Single Thermal
Shock in Frog’s Stomach

response may consequently be
for instance, by adequately raising
the temperature of the plant.
This is seen in the following
record of pulsatory responses as
induced in a young leaflet of
Biophytum, when the temperature
was raised to 35° C. With the
increase of internal energy, the
turgidity of. the tissue was en-
hanced, and the excessive hydro-
static tension thus brought about
induced autonomous. pulsations
(fig. 140), as in a quiescent snail’s
heart similar pulsations are in-
duced by increase of the internal
hydrostatic pressure. I have else-
where shown that the energy
which expresses itself in pulsatory

movements may be derived by the plant, either directly from
immediate external sources; or from an excess of such

MULTIPLE AND AUTONOMOUS ELECTRICAL RESPONSE 2II

energy already accumulated and-held latent in the tissue,
aided by the incidence of external stimulus; or from the
excessive accumulation of such latent energy alone. There
is thus a continuity between multiple and autonomically
responding plants. Azophytum, which under ordinary cir-
cumstances belongs to the former of these classes, becomes
converted into the latter under exceptionally favourable
tonic conditions. That is to say, it responds by a single
response to a single moderate stimulus, and by multiple

Fic. 140. Induction of Autonomous Response in Biophy/um
at Moderately High Temperature of 35° C.
Note the diminution of amplitude of response with falling temperature.
The pulsations came to a stop below 29° C.

responses. to a strong stimulus. Under exceptionally favour-
able tonic conditions, however, it exhibits spontaneous or
autonomous responses. Desmodium gyrans, on the other hand,
which ordinarily exhibits autonomous response, will, under
unfavourable circumstances, cease to exhibit spontaneous
movements. It then exhibits a single response to a single
moderate stimulus, and multiple responses to a single strong
stimulus :

When the leaflet of this plant, owing to deficit of internal
energy, is in a state of standstill, a renewal of the supply of
stimulus will restore it to a condition of autonomous response.
This is seen in the following record (fig. 141) of the response

P.2

212 COMPARATIVE ELECTRO-PHYSIOLOGY

of the leaflet of Desmodium. The leaflet was in a quiescent
condition, but under the action of stimulus of light, it ex-
hibited multiple responses ; and these, owing to the increasing
absorption of energy, showed a staircase enhancement of
amplitude. On the cessation of light, the energy absorbed
maintained the pulsation for some time.

It is thus the absorption of energy which is the cause of the
so-called autonomous movements. The energy, as already
stated, may be derived by the plant either directly from ex-
ternal sources ; or from the excess already accumulated and
held latent in the tissue, aided by incident external stimulus ;
or from an excess of latent energy previously accumulated.

Fic. 141. Initiation of Multiple Response in Lateral Leaflet of
Desmodium originally at Standstill

Light applied at x and continued till the end of the sixth response, as
shown by the thick line. The responses show a staircase increase
with increase of absorbed energy. Pulsations persist for a short time
even on the cessation of stimulus.

It. would be impossible to conceive of movement without
an exciting cause. Only under the action of stimulus
can a living tissue give responsive indications. An ex-
ternal stimulus may either give rise to an immediate
responsive expression, or be partly or wholly reserved

latent form for subsequent manifestation. ‘Inner stimuli’
are simply external stimuli previously absorbed and _ held
latent. A plant or animal is thus an accumulator which
is constantly storing up energy from external sources, and
numerous manifestations of life—often periodic in their
character—are but responsive expressions of energy which |
has been derived from external sources and is held latent in

the tissue.

MULTIPLE AND AUTONOMOUS ELECTRICAL RESPONSE 213

In Desmodium gyrans, as is well known, we have the typical
example of autonomous response, its secondary leaflets
executing periodic up and down or elliptical movements.
The movement of the leaflet in some instances takes place by
jerks, in others it is more uniform. The period of a com-
plete up-and-down movement varies between two and four
minutes. The length of this period is much affected by
temperature, being less when this is moderately high. From
the normal, or highest position, the leaflet sinks somewhat
rapidly ; having reached its maximum depressed position, it
rests fora while. There
is next a rather slow
rise to its original posi-
tion. This up-and-down
motion is in some cases
approximately straight.
In others, the pulvinule
of the leaflet is slightly
twisted after its descent,
and the corresponding
curve described becomes
more circular.

In view of certain Fic. 142. Photographic Record of Autonomous
peculiarities to be ob- Mechanical Pulsation in Desmodium Leaflet

Bs , Period of each complete pulsation

served in the electrical =. 2°7 minutes.

response of Desmodium,

it is necessary here to enter into some detail regarding the
time-relations of its mechanical response during the two
phases of down and up movements. The great difficulty
in recording the pulsatory movements of Desmodium lies
in the extreme slenderness of the lateral leaflets. This
is such that the friction of a light recording-lever against
the recording surface is sufficient to bring these movements
to a stop. This difficulty has, however, been overcome, as
stated elsewhere, by means of the Optical Lever.! Fig. 142

‘ See also Bose, Plant Response, p. 5.

214 COMPARATIVE ELECTRO-PHYSIOLOGY

gives a photographic record of a series of autonomous
pulsations exhibited by a leaflet of Desmodium.

For the accurate observation of the rate of movement of
the Desmodium \eaflet during its different phases I have
also been able to make records by means of a series of
punctures produced by electrical sparks on a recording-
surface. The sparks occur at the short gap between the
end of the recording arm of a very light aluminium lever
and the drum, these being connected respectively with the
two electrodes of a Ruhmkorff’s coil. The electrical dis-
turbance does not affect the
plant, as the pulsating leaflet
is separated from the other
arm of the lever by a long
silk thread. The primary
current in the Ruhmkorff’s
coil is broken at intervals of
five seconds. Hence succes-
sive punctures in the record

Fic. 143. Spark-record of Single | represent intervals of five
| ci cia in pene of Desmodium seconds each. I give here
Showing time-relations of down- and .

up-movements in single pulsation (fig. 143) a record obtained
of leaflet of Desmodium. Up- in this manner, of a single

curve represents down-movement ‘ 5

of leaflet and wce versa. In- Mechanical pulsation of a

i has successive dots Jeaflet of Desmodium. It is

to be understood that the
up-movement in the record represents the down-movement
of the leaflet.

These movements are produced by excitatory con-
tractions of the lower and upper halves of the pulvinus
alternately. An inspection of the record given shows that
after a pause in the highest position a sudden excitatory
impulse is developed in the lower half, which is gradually
exhausted as the lowest position is reached. The maximum
rate of movement to which this excitation gives rise is in
this particular case ‘7 mm. per second. After the lowest
position is attained there is a pause. The up-movement

ble ee a

+e i

i Dt Sie El ae ae al

MULTIPLE AND AUTONOMOUS ELECTRICAL. RESPONSE 215.

then takes place more gradually and at a much slower rate.
This movement is due to natural recovery, aided by a
moderate excitatory contraction of the upper half of the
pulvinus. 1 give herewith a table showing the characteristic
rates of movement in the different phases of the entire
pulsation.

TABLE SHOWING RATES OF MOVEMENT AT DIFFERENT STAGES OF
PULSATION IN DESMODIUM. —

Down-movement Up-movement |

Total period. : 70 seconds
Average rate . ‘61 mm. per second | Average rate . ‘4 mm. per second |
Praximiim tte. "F* 5, nS gs Maximumy rate. *5 5, 53 55

Duration of pause 40 seconds | Duration of pause. 35 seconds |

Total period. ‘ 45 seconds

Several facts are brought out in this table which are of
special importance, and first we observe that the excitatory
impulse which causes the down-movement is brief and quickly
exhausted. -This is seen by the great distance covered

during the first ten seconds, after which the movement

gradually slows down. This indicates a short-lived impulsive
action, the subsequent movernent of the leaflet being mainly
due to inertia. There is then a pause in the down-position, after
which the up-movement commences. It will be noticed here
that this movement is more gradual and prolonged than the

down-movement. From the indications given by these

characteristic movements, we may conclude that the excita-
tory reaction by which the down-movement is caused is
relatively more intense and more quickly exhausted than
that which brings about the up-movement. We may gauge
the relative intensities of the two impulses approximately,
either from the maximum or the average rates of the down

and up motions. The former gives the ratio of a0 the

latter gives Ohar52, The intensity of the downward

impulse may therefore be taken to be roughly one and a-half
times as great as that which occasions the up-movement.

216 COMPARATIVE ELECTRO-PHYSIOLOGY

The total duration of the down-movement is again much less
than that of the up.

We have seen that a single excitation has a single con-
comitant electrical pulsation. We have also seen the multiple
electrical responses corresponding to multiple excitations.
It remains, then, to find out whether autonomous pulsations
have any electrical concomitant, and if so, of what nature.
I shall here, therefore, describe experiments for the recording
of the electrical pulsation of the Desmodium leaflet. For this
purpose I selected specimens in which the movement of the
leaflet was not spasmodic, but gradual and continuous, and
where the up and down movements were pebromicnatcly ina
straight line.

In order to obtain those responsive electro-motive changes
which might accompany the automatic movements of the
leaflets, it was necessary to make one of the electric contacts
at a point on the tissue which was free from excitation, the
second contact being made at a place where the excitatory
reaction was at its maximum. I have shown elsewhere! that
the seat of autonomous excitation in Desmodium is neither
central nor peripheral, but localised at the slender pulvinated
joints to which the leaflets are attached, the latter thus serving
merely as indicating flags. Acting on these considerations, I
made one contact with the slender pulvinule of a lateral
leaflet, the other being made with the common petiole.
These electrical connections were made securely by means of
cotton threads moistened with normal saline solution, and
attached to non-polarisable electrodes. The electro-motive
variations induced in the plant now gave rise to correspond-
ing deflections in the galvanometer in circuit. On taking
records of these electrical responses, I was surprised to find
that, corresponding with each complete mechanical vibration,
there was a double electrical pulsation—a large principal
followed by a smaller subsidiary wave. In a given case,
where the period of the complete mechanical vibration was
about 3°5 minutes, the period of the principal of these two

' Bose, Plant Response, p. 299.

MULTIPLE AND AUTONOMOUS ELECTRICAL RESPONSE 217

waves of electrical response was slightly less than I minute,
and that of the subsidiary wave a little over 2°5 minutes.
These double electrical pulses, corresponding to a single
mechanical vibration, are at first very puzzling, and I under-
took special investigations to ascertain the reason of this
peculiarity. In order to obtain an insight into the relation
between these mechanical and electrical responses it was
necessary to take simultaneous records of the two on the
same recording drum. This was accomplished by having
the two recording spots of light—one from the galvanometer
and one from the optic lever—thrown on the same horizontal
slit, in front of the revolving drum, round which was wrapped
a sensitive photographic film. The galvanometer spot of
light, and consequently the electrical response record, was
the lower of the two. The vertical movement of the spot of
light which records the mechanical response is to be under-
stood as converted into horizontal by reflection from a
second mirror suitably inclined. This experimental arrange-
ment is similar to that employed for simultaneous mechanical
and electrical records in the case of Mimosa, as shown in
fig. 12.

The record given in fig. 144 exhibits the simultaneous
mechanical and electrical responses thus obtained. It will
be seen that the minor electrical wave took place while the
leaflet was moving up from (a) and coming to its highest
position at (6). This was followed by a wave of higher
amplitude but shorter period, which coincided with the
movement of the leaflet again from its highest to its lowest
positions. It will thus be seen that the subsidiary electrical
wave of small amplitude and relatively long period coincided
with the slow up-movement of the leaflet, and that the
principal wave, characterised by large amplitude and short
period, corresponded with the quick down-movement of the
leaflet. These galvanometric deflections indicated, it must be
understood, a condition of galvanometric negativity of the
pulvinule at the moments of its excitatory up and down
movements. The following considerations make it easy to

218 COMPARATIVE ELECTRO-PHYSIOLOGY

understand why two electrical waves correspond to one
mechanical pulsation. First, we know that an excitatory
change at a given point will have, as its concomitant, an
electro-motive variation of galvanometric negativity. Second,
the intensity of this electro-
motive variation depends
on the intensity of the
excitatory change. And
lastly, on the cessation of
excitation there is an elec-
trical recovery.

Now we have seen from
the spark-record (fig. 143)
that the leaflet during one
complete mechanical pul-
sation is subjected to two
excitatory impulses, occur-
tring in the upper and
lower halves of its pul-
vinule alternately. It is
these two excitations
which give rise to the two
electrical disturbances of
galvanometric negativity.
And the different ampli-
Fic. 144. Photographic Records of tude and period in the two

etenliapos Merten] yd, Pies” canes ‘ace. fully’ abooitted
ab (upper figure) represents up-movement for by the different period

of leaflet; a 4 (lower figure) corre- gnd intensity of the two

sponding electrical subsidiary wave ; : ;
6 a’ (upper figure) down-movement €xCitatory impulses. It

of leaflet; 4 a' (lower figure) corre- yj] be remembered that
sponding principal electrical wave. ; ;
the excitatory impulse
which produced the up-movement was the feebler and more
protracted of the two. It is consequently attended by an
electrical disturbance of moderate intensity and correspond-
ing persistence. On the cessation of the up-movement, as we
have seen, there is a pause, and during this time we find that

MULTIPLE AND AUTONOMOUS ELECTRICAL RESPONSE 219

electrical recovery takes place; but before this is complete,
and while there is still a certain residual galvanometric
negativity, there occurs that more intense and short-lived
excitatory reaction which finds mechanical expression in the
downward-movement. The same reaction finds electrical
expression in a brief and intense response of. galvanometric
negativity ; on the expenditure of this excitatory impulse
there is again an electrical recovery, which becomes prac-
tically complete. 2

In the instance given in the spark-record, it was found
that the relative intensity of the down to the up impulse was
approximately as I'5 is to 1. And it is interesting to see
that in the photographic record of the electrical responses
(fig. 144), the ratio of the amplitudes of the corresponding
electrical waves is also the same. In other instances, the
relative intensity of the principal wave is still higher. I give
below two tables showing the absolute. values of the electro-
motive variations in two different cases.

TABLE I. TABLE II.
Syren rim variation. | E.M. variation. Deere | E.M. variation. | E.M. variation.
ation rincipal wave Subsidiary wave ations Principal wave Subsidiary wave
I ‘0014 volt | ‘odds 5 volt I | ee: folt "0016 volt |
Ee 0k, ep 00051 re 2 "0025. 55 “OOI5, 55
3 ‘OOI4 ,, 00054 5, 3 Lege ot, | oo16 ,,
4 "OOI5 , "00054 5, 4 "0025 5, | O07. 55
§ 54 "0016 4; — 5 | ‘0026 ,; | —

It might: be thought that these two electrical waves had
been induced by the mechanical movement of the leaflet as
such. We have seen, however, that the electrical response
is a concomitant of the excitatory condition, whether such
excitation be followed by any mechanical response or not.
This we saw in the absence of mechanical movement in the
case of ordinary plants. The same was found also in the

220 COMPARATIVE ELECTRO-PHYSIOLOGY

case of sensitive plants when responsive mechanical move-
ments were prevented from taking place by physical
restraint (p. 20). The mechanical and electrical responses
are thus independent modes of expression of a single funda-
mental excitatory process. In order to demonstrate this in
the case of the autonomous pulsation of Desmodium, | first
obtained simultaneous mechanical and electrical responses of

Fic. 145. Photographic Record of Simultaneous Mechanical and
Electrical Pulsation in Leaflet of Desmodium, before and after Physical
Restraint of Leaflet.

The first part of this record shows both mechanical and electrical pulsa-
tion. In the second part, leaflet was physically restrained, as seen
in the mechanical record, becoming horizontal. Electrical pulsation
now seen to persist with even greater vigour than before.

the leaflet (ig. 145). In the next part of the same record the
mechanical movement of the leaflet was restrained, as seen in
the upper mechanical record, which here becomes a straight
line. But the lower record, which gives the electrical re-
sponse, still shows the double electrical pulsation unimpeded.
Indeed, so far from the mechanical response having been
the cause of the electrical, we find that on its arrest, at
least in this particular case, the latter becomes very

MULTIPLE AND AUTONOMOUS ELECTRICAL RESPONSE 221

much enhanced. In fact, it appears as if the fundamental
excitatory reaction, being now deprived of one of its two
modes of expression, exhibited the other with the greater
energy. .

We thus see that not only does the electrical response
sive us a means of detecting the action of external stimulus
on a tissue, but that
the same mode of
indication enables us
further to demon-
strate the existence
of those internal ex-
citations which may
find mechanical ex-
pression in the so-
called ‘autonomous’
movements,

One such autono-
mous pulsation pre-
‘sent in all plants is
that of growth, and
by means of the
highly magnified re-
cord given by the
Crescograph. I have
eee ue to: conaest Fic. 146. Crescographic Record of Multiple
of the additive effects Growth-responses in Peduncle of Crocus

of multiple minute The ordinate represents the extent of responsive
elongations in mm. ; the abscissa, time in
seconds.

20” 40"

pulsatory movements.
Wesee this in fig. 146,
which gives a series of records of multiple growth responses
obtained with the peduncle of Crocus at different times of
the day. In the present case, the average period of each
pulsation is twenty seconds. In the case of relatively slow
pulsations like these, if one electrical connection be made
with the growing-point, where such movements are in pro-
gress, and the other with an old leaf in which they have

222 COMPARATIVE ELECTRO-PHYSIOLOGY

ceased, the galvanometer-spot of light is thrown into a state
of oscillation, indicative of the local excitatory reactions at |
the growing-point.

These. multiple pulsations of growth consist of alternating
positive and negative turgidity-variations. In dealing with
the concomitant electrical response, however, we have seen
(p. 64) that the induced galvanometric negativity, owing to
its greater intensity, always overpowers the galvanometric
positivity, if the two occur in rapid succession. In growth-
pulsation, the constituent pulses are often extremely rapid.
Hence a growing-point may be expected to exhibit, galvano-
metrically, a resultant negativity. This consideration may
explain the observation of Johannes Miiller-Hetlingen, other-
wise unexplained, that the growing-points of both shoot and
root, in the seedling of Pzsum sativum, are negative, as
compared with the indifferent cotyledons.

CHAPTER XVIII
- RESPONSE OF LEAVES

Observations of Burdon Sanderson on leaf-response in Dionea—Leaf-and-
stalk currents—Their opposite variations under stimulus—Similar leaf-and-
stalk currents shown to exist in ordinary leaf of F2cus religiosa—Opposite-
directioned currents in Czt¢rus decumana—True explanation of these resting-
currents and their variations—Electrical effect of section of petiole on Dzonca
and Ficus religtosa—Fundamental experiment of Burdon Sanderson on
lamina of Dzonea—Subsequent results—Experimental arrangement with
symmetrical contacts—Parallel experiments on sheathing leaf of A/usa—
Explanation of various results.

IT was pointed out in Chapter II. that progress in the in-
vestigation of the subject of excitatory phenomena in plants
had been long delayed, in consequence of the prevalent idea
that only motile plant-organs were ‘excitable.’ The atten-
tion of investigators was thus mainly confined within the
narrow range of the so-called ‘sensitive’ plants, such as
Dionea. It was also shown, in the same place, that the
results already arrived at by observers in this field had not
been altogether concordant, and presented many anomalies,

As it has now been demonstrated, however, in the course
of previous chapters, that ordinary plants are fully sensitive, it
will be well to proceed to show that the various effects
observed in the ‘sensitive’ Dzong@a may be still better studied
in ordinary leaves. It will be possible, moreover, by follow-
ing this line of inquiry, to determine those general laws, of
which the peculiarities observed in Dzonga are only instances ;
and thus we shall be the better able to offer an explanation
of such cases as now appear anomalous. Se

Before doing this, I shall briefly recapitulate the principal
effects observed by Burdon Sanderson in the leaf of Dzonea.

224 COMPARATIVE ELECTRO-PHYSIOLOGY

These observations relate firstly to the existing current of
rest in the petiole and midrib, and the variations of this
resting-current, whether under excitation of the lamina, or by
section of the petiole, or again, by the action of electro-
tonus; and secondly, to the induction of variations of a
transverse current between the upper and lower surfaces, of
the lamina. As regards the current in the petiole and its
prolongation the midrib, which I shall distinguish as ‘the
longitudinal petiolar current, Burdon Sanderson found this

Fic. 147. Natural and Responsive Currents in Leaves

(a) Leaf- and stalk-currents in Dzonga. Natural current, N, flows out-
wards < A-, s being stalk-current, and L leaf-current. Stimulation
of lamina at x gives rise to responsive current, R, from right to left,
inducing negative variation of leaf-current and positive variation of
stalk-current. When stimulus, however, is applied on left at x,
responsive current, R, is from left to right, inducing ¢ffects exactly
opposite of former, viz. negative variation of stalk-current and positive
variation of leaf-current; (4) Leaf- and stalk-currents in Ficus rel-
giosa similar to those of Déowea. Natural current flows outwards
<A->. Stimulation of lamina at x gives rise to responsive current,
R, inducing negative variation of leaf- and positive variation of stalk-
currents; (c) Leaf- and stalk-currents of C7ztrus decumana, opposite
to those of Ficus and Dionea, > A<-. Stimulation at x induces
positive variation of leaf and negative variation of stalk-currents.

to flow in the midrib, from the end proximal to the stalk to
the distal end. This he designated as the ‘normal leaf-
current.’ He further found that if electrical connections were
made, so that one contact was near the lamina, and the other
away from it, the stalk-current was opposite in direction to
the leaf-current (fig. 147 (a) ).

On stimulation of the lamina, these resting leaf-and-stalk
currents were found to undergo responsive variations. But
these changes were exactly opposite to each other. That is
to say, the leaf-current underwent a negative, and the stalk-

RESPONSE OF LEAVES ik eee

current a positive, variation. No explanation has as yet been
offered, regarding either the existence of these opposite-
directioned currents of rest, or the. apparently anomalous
result, that an identical stimulus would induce, in one case
a-negative, and in the other a positive, variation of them.

As regards these peculiar currents of rest we have

seen (p. 176), that if an intermediate point be physio-
logically less excitable than either of the two terminal
points, then a resting current will flow from the less to the
more excitable. This is the particular current-distribution
in the leaf of Dzonga. It is not a unique phenomenon, for I
have noticed other such instances in ordinary leaves. The
point of junction of the petiole with the lamina of Ficus
religiosa, for example, is galvanometrically the most negative
point in that petiole-and-midrib. _The currents here also,
then, as in the case of Dzon@a, flow outwards from the point
of junction—the leaf-current towards the tip of the leaf, and
the stalk-current in the opposite direction (fig. 147 (0) ).
_ We also saw, however, in the same place, that there may
be instances in which an intermediate point is more excitable
than either of the two terminal. When this is so, the
currents of rest will be reversed in direction, and flow
inwards. This I find to be the case in the leaf of Cztrus
decumana (fig. 147 (c) ).

Next with regard to the excitatory variation of these
resting-currents in leaf and stalk, we must remember
that the effect of stimulation is to give rise to a true
excitatory current, flowing away from the excited. If then
there be already a resting-current, the responsive current will
be added to this algebraically. When the lamina to the
right is excited, the responsive current flows from right to
left. This would naturally, in the case of Dzonea, induce a
negative variation of the leaf-current, and a positive variation
of the stalk-current (fig. 147 (a) ). The same thing is seen
on stimulating the lamina of Ficus religiosa, where also the
excitatory current, being of opposite sign to the leaf-current,
and of the same sign as the stalk-current, induces a negative

Q

226 COMPARATIVE ELECTRO-PHYSIOLOGY

variation of the former, and positive variation of the latter
(fig. 147 (6) ). The same stimulus thus induces effects which
are apparently opposite. Or an interesting variation of the
phenomenon may be obtained, on repeating the experiment
with the leaf of Cztvus. Here, on stimulating the lamina,
we observe a positive variation of the leaf-current, and a
negative variation of the stalk-current (fig. 146 (c)). This is
because the currents of reference or resting-currents are the
_ opposite of those in Dzonea and Ficus religiosa.

Another series of variations exactly the reverse of these,
and therefore at first sight anomalous, is caused by simply
changing the point of application of stimulus, from the right
end on the lamina, to the left end on the stalk. The direc-
tion of the excitatory current is thus reversed, being now
from left to right (fig. 147 (a) ). By algebraical summation,
there now occurs a negative variation of the stalk-current,
and a positive variation of the leaf-current, in Dzon@a and
Ficus religtosa, while the very opposite takes place in Cztrus.

I shall here draw attention once more to those errors to
which an investigator becomes liable when he infers that
positive and negative variations must necessarily be the
expression of assimilatory and dissimilatory processes. For
we have just seen that the same responsive current, by alge-
braical summation with two opposite-directioned resting-
currents, may appear to be both positive and negative, at
one and the same time. Again, with a single resting-current,
it is possible to obtain either a positive or a negative varia-
tion, according as the same stimulus is applied to the right
or the left. It is now abundantly clear that the one uni-
versal effect of stimulus is to give rise to a responsive current
which flows from the more to the less excited portions of the
tissue. If there be already an existing current, the responsive
current is added to this algebraically, and induces, according
to circumstances, either a positive or a negative variation.
Much confusion, and many erroneous inferences would be
avoided, if instead of looking at these variable indications
attention were centred on the one constant criterion, namely

RESPONSE OF LEAVES 227

that the excitatory current always flows from the more to the
less excited portions of the tissue.

Another effect observed by Burdon Sanderson was, that
on cutting the petiole across, the existing normal leaf-current
was increased, the amount of this increase being determined
by the length of the petiole cut off, in such a way that the
shorter the petiole left, the stronger the leaf-current became.
In Nature (vol. x. p. 128), he suggested an explanation of this
phenomenon. In the leaf of Dzonga, as already said, there
is a resting-current in the stalk, opposed in direction to that
in the leaf. Thus ‘the electrical conditions on opposite sides
of the joint between stalk and leaf are antagonistic to each
other ; consequently, so long as the leaf and stalk are united
each. prevents or diminishes the manifestation of electro-
motive force by the other.’ He thus inferred that the pro-
gressive removal of the antagonistic element, by section of the
stalk, would serve to enhance the intensity of the leaf-current.

Taking the ordinary leaf of Fzcus religiosa, | have myself
been able to obtain results precisely similar to those described
in Dzonea, by making successive sections of the petiole, at
shorter and shorter distances from the point of junction.
The leaf-current at each section underwent an increment.
The parallelism of the two sets of effects will be seen from
the following table.

Ficus LEAF. DION#A LEAF (BURDON SANDERSON).

=e eh Sy a ae
' Length of stalk Galvanometric deflection | Length of stalk | Galvanometric deflection

om. | 16 divisions 2°5 cm. 40 divisions

ty Stee
4 >» 36 re) | 1°25 5, ; 50 2”
2 » 5° ” | 06 ,, 65 ”
|
I 5, | 60 ;; bid AOS 5 opal re 90 5;

Burdon Sanderson’s suggested explanation that the suc-
cessive augmentations of the leaf-current were due to suc-
cessive removals of the antagonistic element, by section, is

Q2

228 COMPARATIVE ELECTRO-PHYSIOLOGY

quite untenable. He failed to see that the effect was, on the
contrary, due to the increasing excitatory action of the
sections themselves. Similar results may be obtained, even
without the bodily removal of the supposed antagonistic
element, if, instead, we apply an increasing intensity of
stimulus, as say, by contact of a hot wire at points nearer
and nearer to that of junction. In the case of the trans-
verse section, the cut acts as a stimulus, and the respon-
sive current flows from the left to the right... Algebraical
summation of this with the existing leaf-current, which is
also from left to right, causes an increase, or positive variation
of it, ina manner exactly the converse of the negative varia-
tion induced in the leaf, when the stimulus was applied on
the lamina. - As the section is made nearer and nearer to the
point of junction, the degree of stimulation, and the con-
sequent positive variation of the resting-current, must become
greater and greater.

And lastly, in the case of the longitudinal lesfieasPauk
Burdon Sanderson found that if a current from a battery
were directed through a leaf-stalk, at the same time that the
two ends of the midrib were led off to the galvanometer, the
difference previously existing between the ends of the midrib
would be increased, if the current led through the leaf-stalk
were in the same direction with the leaf-current, and
diminished, if it were in the opposite direction. A similar
effect, as seen in the conducting tissues of ordinary plants,
will be studied in detail, when we take up the question of
the extra-polar effects’ induced by electrotonic currents
(Chap. XXXIX.). |

We have already seen that, by means of induced varia-
tion of the longitudinal stalk-current, under the stimulation
caused by section of the petiole, it is easy to obtain an un-
mistakable indication of the nature of the true excitatory
electrical change. Burdon Sanderson, however, laboured
under the disadvantage, as already said, of having failed to
recognise that a section acts as a stimulus. His _ investi-
gation, therefore, on the character of the excitatory variation,

RESPONSE OF LEAVES 229.

was chiefly carried out by means of experiments on electrical
variations induced in the lamina. These depended (1) on
variations in the cross-difference of existing potential between
the upper and lower surfaces, according to his ‘fundamental
experiment, and (2) on electrical variations in the led-offs of
symmetrical surfaces of contact on the under-side of opposite
lobes. The results which he obtained, however, by these
methods, appear to the reader to have been very conflicting,
and in fact the experimental methods described by him
would seem to have been open to many sources of complica-
tion of which he himself was unaware.

Fic. 148. Burdon Sanderson’s Funda- Fic. 149. Parallel Experiment in
mental Experiment on Dzonea Leaf Sheathing Petiole of Musa
Electrical stimulus applied on distal Thermal stimulus applied on distal
lobe, 7, induces responsive effect side induces responsive effect on
on led-off circuit fw. Upper or led-off circuit. Upper or ‘internal’
internal surface, f, more excitable surface more excitable than lower.

than lower, 772.

I shall deal first with Burdon Sanderson’s ‘fundamental
experiment, of which the excitatory electrodes are seen on the
left lobe, and the led-off on the right in fig, 148, In fig. 149
is given a diagram of a parallel experiment carried out by
myself on the petiole of Musa. ‘According to Burdon-
Sanderson, as the result of excitation, a + current is induced
in the right lobe of Dzonea (fig. 150). This means, of
course, that the upper or more excitable surface of the right
lobe has become positive to the lower. This current, how-
ever, he termed ‘excitatory,’ regarding it as the analogue of
the ‘action-current’ known to animal physiology. After
this first phase, when a certain interval had elapsed, he

230 COMPARATIVE ELECTRO-PHYSIOLOGY

observed a second phase to set in, in which the upper surface
became relatively negative to the lower. This negative
change, which he called the ‘after-effect,’ he described as
taking place at that moment at which the mechanical effect
of excitation also made itself evident.

This negative phase—called by him the ‘after-effect’—
Burdon Sanderson regarded as connected with those electrical
changes which had been observed by Kunkel to be induced
by movement of water in the tissues. The first effect on the

‘an

Fics. 150,151,152. Recordsjof Electrical Responses of Different Leaves
of Dionea according to Fundamental Experiment of Burdon Sanderson

HATTA

|

|

Fig. 150. Positive response of certain leaves of Dzonea. Time-marks
20 per second (Burdon Sanderson).
Fig. 151. Diphasic response of leaf of Droxea ‘in its prime.’ Positive
followed by negative. Time-marks Io per second (Burdon Sanderson).
Fig. 152. Positive response of same leaf when ‘ modified’ by previous
stimulation. Time-marks Io per second (Burdon Sanderson).
The above récords were obtained with capillary electrometer.

contrary, which immediately preceded this, and was charac-
terised by relative positivity of the upper surface, he regarded,
as already mentioned, as the true excitatory or action-effect.
The following is from his summary :

‘The first phase of the variation--the effect which
immediately follows excitation, and has an opposite
sign to the after-effect, and a much higher electro-motive
force—does not admit of a similar explanation: for it
cannot be imagined that a change which spreads over
the whole lamina in less than one-twentieth of a second
can be dependent on migration of water. The excita-
tory disturbance which immediately follows excitation

RESPONSE OF LEAVES 231

is an explosive molecular change, which by the mode of
its origin, the suddenness of its incidence, and the
rapidity of its propagation, is distinguished from every
other phenomenon except the one with which I have
identified it—namely, the corresponding process in the
excitable tissues of animals. Of the nature of this
preliminary disturbance (to which alone the term ex-
citatory variation ought to be applied, it alone being
the analogue of the ‘action-current’ of animal physio-
logy) we know nothing. ... The direction of the ex-
citatory effect in the fundamental experiment is such as
to indicate that in excitation, excited cells become
positive to unexcited, whereas in animal tissues excited
parts always become negative to unexcited. The ap-
parent discrepancy will probably find its explanation in
the difference of the structural relations of the electro-
motive surfaces.’ }

_ From this quotation it will be seen that Burdon
Sanderson had fallen into the basic error of mistaking what
I have demonstrated to be the hydro-positive, for the true
excitatory effect, and wece versa.

In a subsequent Paper again (Phz/. Trans. vol. 179, 1889)
Burdon Sanderson published certain results, which differed
from those referred to above. He had previously found that
usually speaking the upper surface of each lobe was negative
to the lower. Later, however, he came to the conclusion
that in the leaf of Dzonga in its ‘prime, the upper surface
was positive to the under. On repeating his ‘fundamental
experiment’ moreover, with these vigorous leaves, he found
that instead of the pronounced positive response which he had
previously observed, he now obtained a short-lived positive
effect succeeded by a strong negative (fig. 151). He was
unable to offer any definite explanation of this difference
between the two sets of results, but suggested that it might
arise, in some way, from changes of the resting-current.

’ Phil, Trans. 1882, vol. 173, p- 55:

232 COMPARATIVE ELECTRO-PHYSIOLOGY

‘In the leaf, observed facts show most conclusively
that the two sets of phenomena—those of the excited
and those of the unexcited state—are linked together
by indissoluble bands: that every change in the state
of the leaf when at rest conditionates a corresponding
change in the way in which it responds to stimulation,
the correspondence consisting in this, that the sign, that
is the direction, of the response is opposed to that of the
previous state, so that, as the latter changes sign in the
direction from + to |, the former changes from | to +.’ }

In making this statement, Burdon Sanderson was _ prob-
ably guided by the prevalent opinion that response takes
place by a negative variation of the existing current of rest.
We have seen, however, that this supposition is in fact
highly misleading. For, owing to such fluctuating factors as
age, season, previous history, or excitation due to prepara-
tion, the so-called current of rest may and frequently does
undergo reversal. Thus a single excitatory effect might, as we
have seen (pp. 175-177) under different circumstances, appear
either as a positive or a negative variation of the existing
current. The assumption of the universality of response by
negative variation is thus seen to be unjustifiable.

Indeed, it would appear from the description of some of
the experiments actually related by Burdon Sanderson him-
self, that response did not, even in these cases, always take
place by negative variation of the existing current. For
instance, while in the leaf of Dzon@a in its ‘prime’ (upper
surface positive) the response is negative, and while this
latter becomes reversed to positive, as he tells us, in conse-
quence of ‘ modification’ due to previous excitation (fig. 152),
yet headmits that even in these circumstances the upper surface
had first returned to positivity (zbzd. p. 447). Thus, though
the responses of the leaf in its ‘prime, and of the ‘ modified ’
leaf are opposed, yet the antecedent electrical condition of
the modified leaf has not in this case undergone reversal.

Phil. Trans. 1889, vol. 179, p. 446.

RESPONSE OF LEAVES 233

The suggestion, therefore, that the reversal. of response is
due, in some way unexplained, to a reversal of the electrical
condition of the leaf, cannot hold good. Nor does the use of

the term ‘ modification’ in any way
of the phenomenon. A satisfactory
explanation of this reversal of
response, then, still remains to be
found.

So much for the ‘fundamental
experiment. The next experi-
mental arrangement employed by
Burdon Sanderson consists of a leaf
which is led off by symmetrical
contacts on the under surfaces of
its two lobes (fig. 153). If now the
right lobe was excited, by touching

assist in the elucidation

FIG, 153. Experimental Con-
nections with Dzonea ac-
cording to the Second
Experimental Method of
Burdon Sanderson

one of the sensitive filaments (on the upper surface) with a
camel’s-hair pencil, in the neighbourhood of the leading-oft
contact, it was found that the under-surface of the right lobe
became first positive, and subsequently negative (fig. 154),

relatively to the left (zdzd. p. 440).

Mn

i

Fic. 154. Response of Under-surface of Leaf of Dzon@za, with Electrical
Connections as in Fig. 153

{I

Mechanical excitation of upper surface of right lobe. shows relative

positivity of under surface of same right
its relative negativity (down curve).
(Burdon Sanderson).

lobe (up curve), followed by
Time-marks 20 per second

Summarising these various observations, then, we find
results which are very much at variance. First, according
to the ‘fundamental experiment,’ certain leaves are seen to
give rise to the positive response; other leaves, in their

prime, give diphasic response, the

upper surface becoming

234 COMPARATIVE ELECTRO-PHYSIOLOGY

first positive and then negative. These latter again, after
previous excitation, become so modified as to show only
positive changes. And lastly, using the experimental
arrangement of symmetrical contacts, a diphasic variation
is obtained—positive followed by negative—on the under-
surface, instead of the upper, of the lobe excited. No theory
is advanced, however, by which a comprehensive explanation
might be afforded of these apparently anomalous results.

But from the generalisations which I have already esta-
blished, regarding the electrical signs of the hydro-positive
and true excitatory effects respectively, and from the results
of certain experiments on ordinary leaves which I shall
presently describe, it will be found easy to arrive at a true
explanation of the various observations related by Burdon
Sanderson, which would otherwise have appeared inexplic-
able. The fact that hydrostatic disturbance induces galvano-
metric positivity, and that true excitation induces negativity,
has already been clearly demonstrated under conditions from
which all possible sources of complication had been elimi-
nated (p. 61). The experimental arrangement adopted by
Burdon Sanderson, however, laboured under the double dis-
advantage, not only of a liability to confuse the hydro-
positive and true excitatory effects, but also of the com-
plexity arising from the differential excitability of the
responding organ. It is only indeed by the closest analysis
that it is possible to discriminate, in his results, between such
as are due to true excitation and those arising from the hydro-
positive effect.

The various electrical phenomena which are possible in
an anisotropic organ in consequence of the hydro-positive
and excitatory effects respectively, may be clearly exhibited,
as I have already shown, by means of the mechanical
response of the leaf of MW/zmosa. With regard to this, we
have seen (pp. 59, 60) that direct stimulation of the pulvinus
induces a negative mechanical response, or fall of the leaf,
by the greater contraction of the more excitable lower half
of the organ. The corresponding electrical variation would

RESPONSE OF LEAVES 235

thus consist in the greater galvanometric negativity of this
more excitable lower, in relation to the less excitable upper half.
If the stimulus, however, be applied at some considerable
distance, so that true excitation cannot reach the responding
point, then we have an erectile or positive mechanical
response of the leaf. This is brought about by the relatively
greater expansion of the more excitable. The corresponding
electrical response will be the galvanometric positivity of
this more excitable, in relation to the less excitable half of
the organ. Between these two extremes lies that experi-
ment in which stimulus is applied at some intermediate
point, the consequence of which is that the hydro-positive
wave, with its greater velocity, reaches the responding organ
earlier than true excitation, thus bringing about a pre-
liminary erectile or positive response, followed by the ex-
citatory negative or fall of the leaf. The corresponding
electrical response would therefore be diphasic, positive
followed by negative.

But the occurrence of this second or negative phase is
only possible when the conductivity is so great as to allow
the wave of true excitation to reach the organ. We may
imagine that in a very vigorous plant, with its great con-
ductivity, we have found a point, at the maximum distance
from which the true excitatory effect of a given stimulus is
capable of transmission to the organ. With such a speci-
men, in its ‘prime,’ we shall observe a diphasic effect—pre-
liminary positive followed by negative. But if we took a
less vigorous specimen, and applied the stimulus at the same
distance from the responding point, the true excitatory wave
would fail to reach the responding organ, and we should see
there, only the positive effect due to hydro-positive action.
Hence, two different specimens, treated in exactly the same
way, may exhibit two different effects, one diphasic, and the
other positive alone; this difference being due to their
unequal vigour, and concomitant inequality of excitability
and conductivity. This will account for the diphasic and
positive responses which were exhibited by the more and

236 COMPARATIVE ELECTRO-PHYSIOLOGY

less vigorous leaves respectively of Dzonga, when stimulation
was applied on the distal lobe, according to the fundamental
experiment of Burdon Sanderson.

We must next refer to the reason why a leaf that origin-
ally gives diphasic response—positive followed by negative
—undergoes such ‘ modification, in consequence of: previous
excitation, as thereafter to give only positive response. We
have seen that the negative element of the diphasic response
is due to the arrival at the responding point of the true
excitatory wave originated at the distant point of stimula-
tion. Now it has been shown (p. 65), that if by any
means the conductivity of an intervening region should
become diminished, we may expect that the hydro-positive
effect will continue to be transmitted, although the passage
of true excitation is partly or wholly blocked. By-means of
this selective block, I was able to unmask the hydro-positive
component present in resultant response (cf. fig. 49).

I have shown elsewhere! that the conducting power of a
tissue will be impaired by the fatigue consequent on previous
stimulation. Thus, in the petiole of Bzophytum, | found that
while the plant, when fresh, had a conductivity measured
by the velocity of transmission of excitation, at a rate of
1°88 mm. per second, the same plant, when partially fatigued
by four successive stimulations, had its conductivity dimi-
nished, the velocity of transmisson being now only 1°54 mm.
per second. The diminution in this case, then, was about
18 per cent. I shall moreover show in a later chapter
that in consequence of growing fatigue the passage of true
excitation may at a certain stage be arrested, the hydro-
positive effect alone being then transmitted. It is thus easy
to explain how it was that in Burdon Sanderson’s experi-
ment, of stimulus applied on the distal lobe, the wave of
true excitation became blocked, and the ‘ modified’ leaf gave
positive response alone. These considerations will be found
as I think, to offer a satisfactory explanation of the conflicting
results arrived at by Burdon Sanderson,

1 Plant Restonse, Pp. 244.

RESPONSE OF LEAVES 237

I shall now, however, proceed to describe a series of ex-
periments exactly parallel to the ‘fundamental experiment’
on Dionea, carried out on ordinary plants. We have seen
that the inner or concave surface of the sheathing petiole of
Musa is relatively more excitable than the outer or convex.
Thus it corresponds with the ‘internal’ or upper surface of the
leaf of Dzonga. The more excitable internal surfaces of both
these, again, correspond with the more excitable lower half
of the pulvinus of AZzmosa. In fig. 149 is shown an experi-
mental arrangement with a specimen of JZusa which will be
seen to be parallel to that of Burdon Sanderson’s funda-
mental experiment on Dionea. In order to avoid any such
disturbance as might conceivably arise from current-escape, if
the electrical form of stimulus were used, I employed the
thermal mode of stimulation. A momentary heating-current
passed through a thin platinum wire gave the thermal varia-
tion required, and was found to furnish a very satisfactory
form of stimulus. The led-off circuit was at first placed at a
distance of 16 mm. from the point of stimulation. As the
stimulation was moderate, and as the conductivity of the
tissue was not great, the effect induced at the respond-
ing circuit was hydro-positive, the more excitable concave
surface becoming positive (fig. 155 (a) ). This response is the
same as the positive responses given by the ‘unmodifiable
leaf’ of Dzonea (fig. 150), as well as that of a vigorous leaf
which had been ‘modified’ by fatigue (fig. 152). On next
taking a second pair of led-off points, at the shorter distance
of 8 mm., the hydro-positive effect reached the led-off points
earlier, and was followed by the true excitatory wave. This
is seen as a preliminary positive response, followed by the
excitatory negative (fig. 155 (2)). This again is the same
as the di-phasic response of a Lzonea leaf in its ‘prime’
(fig. 151). Inthe experimental arrangement with J/usa the
led-off circuit was now brought still nearer to a distance of
4 mm. There was now little interval between the arrival
at the led-off points of the hydro-positive and true excitatory
effects; and since the latter is of predominant electrical

238 COMPARATIVE ELECTRO-PHYSIOLOGY

expression, the former is masked by it, and we obtain here
only the excitatory negative variation (fig. 155 (¢) ).

It only remains to consider the responses which Burdon
Sanderson obtained with symmetrical contacts (fig. 152) on the
under-surfaces of the two lobes. In the next figure (fig. 153)
is reproduced his record of electrical response, obtained on
mechanical stimulation of a sensitive filament situated on
the upper surface of ‘the right lobe, vertically above the
right-hand led-off. This response is, as will be seen, di-

Fic. 155. Photographic Records of Positive, Diphasic, and Negative
Responses ot Petiole of A/usa depending on the Effective Intensity
of Transmitted Stimulus

(az) Here stimulus was applied at a distance and hydro-positive effect
alone transmitted ; (6) Stimulus was applied nearer, and the positive
effect was succeeded by the true excitatory negative; (c) Stimulus was
applied very near, with the result of true excitatory negative response.

phasic, its first phase being one of relative positivity of
the under-surface of the excited lobe, and the second
representing its subsequent relative negativity. This first
phase is clearly due to the earlier transmission of the
hydro-positive or indirect effect of excitation, from the
stimulated point on the upper surface. It was supposed
by Burdon Sanderson that the second phase of this re-
sponse represented the later arrival of the same positive
effect at the distal second contact, which would thus induce
reversal. But it appears much more probable that this
second phase of negativity is due to the arrival at the

RESPONSE OF LEAVES 239

under-surface of the wave of true excitation, initiated
vertically above. This relative negativity of the under-
surface may or may not be helped by the induction of
positivity at the distal, due to the transmission of the hydro-
positive effect. This view is supported by the fact that in a
corresponding experiment on an ordinary leaf, in which the
second contact was at a distance too great to allow of the
effective transmission of any hydro-positive wave, the
stimulation of the upper surface induced a similar diphasic
response at a point diametrically opposite, on the under side.
In this case the second or negative component of the
response could not be due to anything but the subsequent
arrival of the true excitatory wave with its concomitant
negativity.

It is now clear that among the various results
obtained from the study of the electrical responses of the
leaf of Dzonga, there are some which do not represent
true excitation at all, while in others it is only one of the two
phases which is significant of this, the other being due to the
hydro-positive effect. We have also seen that Burdon
Sanderson at starting fell into the error of wrongly identify-
ing the true excitatory electrical effect with that which was
due to the hydro-positive effect, and vice versa. We have seen
that there is not a single response given by the so-called
excitable leaf of Dzong@a, which cannot be obtained under
similar conditions from the leaves of ordinary plants also.
In fact it has been by means of experiments carried out on
the latter that we have been enabled to unravel all the
intricacies which were offered by the recorded responses of
the lamina of Dzonea. :

It has further been shown in the course of the present
chapter that the leaf and stalk currents observed in Dzonga
are also found in, for instance, the leaf of Ficus religiosa.
These have been shown, moreover, to be due to physiological
differences between an intermediate and the terminal points.
The negative variation of the leaf-current, and the positive
variation of the stalk-current, on the stimulation of the

240 COMPARATIVE ELECTRO-PHYSIOLOGY

_ lamina, were both alike shown to be the result of the alge-
braical summation of a definite excitatory current with the
two opposite-directioned resting-currents. The positive
variation of the leaf-current, again, on section of the petiole,
has been traced to the same cause, namely the stimulatory
action of mechanical section, giving rise to an excitatory
current which was summated with the existing leaf-current.
Finally the positive response of the concave surface of
Dionega has been shown to arise, not from any specific
difference between plant and animal response, but from the
fact that in this particular case it was the indirect hydro-
positive effect of stimulus that was transmitted, inducing an
action opposite to that of true excitation.

CHAPTER XIX
THE LEAF CONSIDERED AS AN ELECTRIC ORGAN

Electrical organs in fishes—Typical instances, Zorfedo and Malepterurus—
Vegetal analogues, leaf of Pterospermum and carpel of Déllenta indica or
pitcher of Mefenthe—Electrical response to transmitted excitation — Response
to direct excitation—Uni-directioned response to homodromous and hetero-
dromous shocks—Definite-directioned response shown to be due to differential
excitability— Response to equi-alternating electrical shocks—Rheotomic ob-
servations-—Multiple excitations—Multiplication of terminal electromotive
effect, by pile-like arrangement, in bulb of Uyzc/zs lily.

IT has been shown that by a study of the peculiarities of
electrical response in plants, it is possible to obtain an
insight into the obscurities of similar responses in the animal
tissue. Among animal structures, there is one—the elec-
_trical organ of certain fishes—the explanation of whose action
offers unusual difficulties to the investigator. But I shall
attempt to show in the course of the present chapter, that
there are also, on the other hand, vegetable structures, the
study of which will be found to elucidate the electro-motive
action here involved. Taking that of the Torpedo as type,
we find that the electrical organ is disposed in the form of
columns, each column consisting of. numerous electrical
plates, arranged in series, one over the other, like the plates
in a voltaic pile. Each electrical plate consists of a rich
plexus of nerve-fibres imbedded in a gelatinous mass.
There are thus two surfaces, one nervous and the other non-
nervous. Each disc then becomes electro-motive under the
impulse from the nerve. Though the induced electro-motive
force in each plate is small, yet in consequence of their serial
arrangement in columns, the elements are coupled for inten-
sity, and the resulting E.M.F. of discharge becomes high,
R

242 COMPARATIVE ELECTRO-PHYSIOLOGY

Fritsch estimates the total number of these plates in some of
the Torpedos to be over 150,000.

From the point of view of their development, these
electrical organs in general constitute modified muscles,
containing nerve-endings, The electrical fish known as
Matepterurus of the Nile is an exception to this rule, inas-
much as morphological evidence goes to prove that in its
~ case it is glandular, rather than muscular, elements which
have been so modified.

The peculiar characteristic of the discharge of electrical
organs in general, is that it takes place in a definite direction
at right angles to the plates. It was Pacini who tried to
establish the generalisation that the direction of the dis-
charge would be found to be dependent on the morphological
character of the organ. He found that as a general rule
the discharge takes place in a direction from that surface of
the disc which receives the nerve (henceforth to be referred
to as the anterior surface) to the opposite non-nervous, or
posterior, surface. Thus in the Zorfedo, where the plates
are horizontal, and the anterior or nervous surface constitutes
the ventral aspect of the disc, the discharge is from the
ventral or anterior, to the dorsal or posterior surface. In
Gymmnotus again, the plates or discs are vertical to the long
axis, The anterior or nervous surface is here towards the
tail-aspect, and the discharge is from tail to head. If these
cases had been all, Pacini’s generalisation, as regards the
direction of discharge—from the anterior nervous to the
posterior non-nervous—would have been complete, and from
it some attempt might have been made to offer an explana-
tion of the phenomena. Unfortunately, however, this is not
so, since Malepterurus presents a hitherto inexplicable ex-
ception to the rule. In this fish, though the anterior or
nervous surface is towards the tail-aspect as in Gymnotus,
yet the discharge is in the opposite direction towards the
head : that is to say, from the posterior surface to the anterior.
The difficulties in the way of an explanation of the activity
of these electrical organs of certain fishes are thus seen to be

THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 243,

very great. Is the activity something specific occurring in
these fishes alone, and unrelated to other electro-motive
phenomena in the animal tissues? Or is it related to the
electromotive action already observed in excited muscles?
In support of the latter view, it is urged that most of the
electrical organs consist of modified neuro-muscular elements,
Against this argument, however, as we have just seen, is the
instance of Malepterurus, in which, from a morphological
standpoint, the organ is to be regarded as a modified gland,
and therefore not muscular in character,

There are certain peculiarities, further, about the action
of these organs which call for elucidation. Among these
is the question of the character of the natural current of rest,
about the significance of which there have been differences
of opinion. There is also the fact that the organ, under a
single strong excitation, gives rise not to one, but to a series
of electrical responses.

We have seen that the apparently unique character of
this group of organs constitutes an added difficulty in
arriving ata correct theory on the subject. But it is clear
that if we could succeed in discovering among vegetable
organs any cases which showed similar characteristics,
we should then be so much the nearer to the determination
of that fundamental reaction on which the phenomenon in
animal and vegetable alike depends,

In the typical case of Zorpedo, it has been seen that the
conducting nerve, when entering into an electrical plate,
breaks into an extensive ramification, and thus forms the
nervous surface, in contradistinction to the jelly-like sub-
stance in which it is imbedded, forming the opposite, and
here indifferent surface of the plate. Now this arrangement
is closely imitated by many ordinary leaves, in which the
vascular elements break, on reaching the lamina, into a pro-
fuse arborisation. |

I must here anticipate matters to say that I have discovered
in the fibro-vascular bundles of plants (see ei hap. XXXII.)
elements which are in every way peel eres to the nerves of

R2

244 COMPARATIVE ELECTRO-PHYSIOLOGY

animals. For an exact vegetal analogue to the electrical
plate of Zorpedo, we may take certain leaves in which the
ventral, or anterior, surface is formed of a prominent network
of highly excitable nervous elements, while the upper consists
of an indifferent and relatively inexcitable mass of tissue. An
example of this may be found in the leaf of Pterospermum
subertfolium (Rox.) whose lower surface is characterised by |
a remarkably perfect venation, while the upper or posterior
is dry and leathery. Thus the nerve passing into an elec-
trical plate of Zorvpedo corresponds with the petiole attached
to the leaf just described, since in the two cases alike, it is the
ventral surface which contains the highly excitable nervous

elements.
In the exceptional JMJalepterurus, on the other hand, -

it is, as we have seen, a modified gland, and not a modified
muscle, which forms the posterior surface of an individual
electrical element. Morphologically speaking, the vegetal
analogue is found in such organs as the carpellary leaf of
Dillenta indica, or the pitcher of Nepenthe, both of which
are glandular on their upper or inner surfaces. In point
of structure, then, these leaf-organs are analogous to single
discs or elements of the electrical organs of TZorgedo and
Malepterurus respectively. But we have still, in the course
of the present chapter, to inquire whether the electrical
reactions are equally correspondent—that is to say, whether,
on stimulation, the excitatory current in the type of vege-
table organ represented by the leaf of Pterospermum is or
is not, from the lower or anterior surface to the upper
posterior, as in the electrical plate of Zorpedo; and, con-
versely, whether in the type represented by the carpel of
Dillenia or the pitcher of Wefenthe the excitatory current is
from the posterior to the anterior surfaces, corresponding
with the discharge in the electrical element of MWalepterurus,
from the posterior glandular to the anterior non-glandular
surface.

While dealing with the theory of the action of electrical
organs, I shall be in a position to show that the characteristic

THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 245

reaction of each of these two types is governed entirely by
the question of the relative excitabilities of the two surfaces.
The physiological anisotropy on which the distinctive effect
of the type depends is very pronounced in the representa-
tive cases of the vegetal analogues which have been named. In
many other cases, however, though the results under normal
conditions are fairly definite, and approach one or other of
the two types, yet the characteristic responses are liable to be
reversed under the physiological modifications induced by
age and surrounding conditions. In this way it may be said
of the leaf of water-lily (Vymphea alba), of Bryophyllum
calcineum, and of Coleus aromaticus that when vigorous, and
in their proper season, their responses are of the first of these
two types, while those of the bulb-scale of Uviedis lily, with
its glandular inner surface, are of the second type.

The electrical organ of the fish may be excited indirectly
by means of stimulus transmitted through the nerve; or
direct stimulation may be applied, as by means of induction-
shocks. Under either of these conditions the excitatory
discharge is definite in its direction. In the case of Jorpedo,
as already mentioned, this is always from the ventral and
anterior to the dorsal or posterior surface. Turning then to
the corresponding vegetable organ of the first type, I shall
show that transmitted stimulus induces an effect exactly
similar ; and I shall demonstrate this experimentally by means
of the leaf of Vymphea alba. Suitable galvanometric connec-
tions were made with the ventral anterior and with the dorsal
posterior surfaces of the lamina. Thermal shocks, by means
of the electro-thermic stimulator, were applied on the petiole,
close to the lamina, at intervals of one minute, records being
taken photographically of the resulting responses. It should
be remembered here that excitation is transmitted to the
lamina by the conducting nerve-like elements present in the
petiole. The records (fig. 156) show that the effect of this
periodically transmitted stimulation was a series of respon-
sive currents, whose direction was like that of the discharge
in Torpedo, from the anterior surface to the posterior.

246 COMPARATIVE ELECTRO-PHYSIOLOGY

Of great importance was the investigation carried
cut by Du Bois-Reymond on the effects induced in the
electrical organ by the passage of currents in different
directions. Polarising-currents in the direction of the natural
discharge of the organ are distinguished, in the terminology
introduced by Du Bois-Reymond, as homodromous, and
those in the opposite as heterodromous. Polarisation-effects
in the direction of the natural discharge he distinguishes as
‘absolutely positive polarisation, and
against that direction ‘as absolutely
negative.’ A polarisation-current in
the same direction as the polarising-
current he calls ‘relatively positive,’
and in the opposite direction ‘rela-
tively negative’ polarisation. It
was found by him that polarising-
currents of fair intensity and short
duration, whether homodromous or
heterodromous, would always give
rise to polarisation-currents in the
same direction as the natural dis-
mea, re6. Mice charge. He believed this to be due

of Lamina of Vympheaalba to the occurrence in the electrical
due to Transmitted Excita- % . ors.
ah an Prole organ of two different polarisation-
Direction of responsive current effects, positive and negative. This
incaat ttl avper serace will be understood from his own dia-
grammatic representation (fig. 157)
of the effect which he supposed to take place immediately
on the passage of the polarising-current. In the upper
figure the ascending arrow represents the homodromous
polarising-current. This gives rise, according to Du Bois-
Reymond, to two opposite polarisation-effects. The de-
flection seen in the galvanometer is the resultant of these,
represented by the shaded part of the figure. The resultant
of a homodromous current, then, is positive polarisation,
both absolute and relative. The heterodromous current, on
the other hand, induces absolutely positive and relatively

THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 247

negative polarisation.

According to Du_ Bois-Reymond,

further, heterodromous shocks induce no relatively positive
polarisation, or only infinitely little (see down curve in lower

part of figure).
from Saxton’s. machine, he
obtained only the absolutely
positive _ polarisation - effect.
This he accounted for by
supposing the relatively nega-

tive polarisations in both
directions to cancel each
other; the heterodromous

positive to be so small as
to be practically negligible ;
and the homodromous posi-
tive. therefore to be alone
effective.

Du Bois-Reymond failed

to recognise the element of

excitation. in. these
nomena. . What he
positive polarisation has been
shown by subsequent workers
to be due to local polar ex-
citation. But the question
as to how polarising-currents
in both directions could give
rise to a_ single-directioned
responsive effect has not up
to the present, so far as I am
aware, been explained fully
and satisfactorily. The ex-

phe-
calls

On sending congruent wireless currents

Fic. 157. Diagrammatic Representa-
tion. by Du Bois-Reymond for Ex-
planation of Electrical Response in
Organ of Torpedo.

- The natural discharge is here supposed

to be from below to above. A

’ homodromous current + (upper half
-of figure) is supposed to, induce
two opposite polarisations, positive

» and negative. The resultant, repre-
sented by shading in "figure, is
absolutely and relatively positive.
A heterodromous current |, on the
other hand, is regarded as inducin
a resultant absolutely positive and
relatively negative polarisation
(lower part of BEUrE ja:

periments carried out on leaves, which I am sidan to
describe, will, however, throw much light on this subject.

It has already been shown, from anatomico-physiological
considerations, that there are certain leaves which approxi-
mate to the character of single plates of such electrical organs

248 COMPARATIVE ELECTRO-PHYSIOLOGY

as that of Zorpedo. One such leaf, already mentioned, was
that of Pferospermum. When induction-shocks are sent in
both homodromous and heterodromous directions through
such a leaf, between upper and lower surfaces, the leaf being,
it is understood, in a normal condition, a responsive current
is found to be evoked, always in one direction—that is to say,
from the lower or anterior to the upper or posterior surface.
This is strictly parallel to the electrical reaction observed by
Du Bois-Reymond in Zorfedo.

That this result is really due to the excitatory effect
is proved by the fact that the same is found to occur
when other forms of stimulation
are used. Thus, if we place the
leaf of Coleus aromaticus within
a surrounding thermal helix, suc-
cessive thermal shocks, acting
simultaneously on both surfaces,
give rise to responsive currents
which are, as in the last case,
Fic. 158. Photographic Records from the lower anterior to the

pete silat Site se Seat upper posterior surface. Fig. 158

ae te Thema Pee gives a series of such responses.
Resultant responsive current from From the fact which has already

more excitable anterior toless been fully established, that on

sa rca a the simultaneous excitation of
two points the responsive current is always from the more to
the less excitable, it is quite clear that in the present case it
is the lower or anterior surface of the leaf which is the more
excitable. These responsive currents, obtained under a non-
electrical form of stimulus, and similar to those evoked by
electrical shocks, completely demonstrate the fact that the
result is brought about, not by polarisation, either positive
or negative, but by the afferential excitability of the tissue
itself. The response of electrical organs in general, then
may be summarised in the following law:

The excitatory discharge is determined by the physiological
anisotropy of the organ, its definiteness of direction being deter-

THE LEAF CONSIDERED AS ‘AN ELECTRIC ORGAN 249

mined by the fact that the responsive current is always from the
more to the less excitable of the two surfaces.

Referring once more to the definite-directioned _after-
current which we have seen to be induced as the result of
polarising-currents, whether homodromous or heterodromous,
it is now clear that these currents act as an _ electrical
form of stimulus. The intensity of the after-current
here seen in the galvanometer, however, is not wholly due
to the excitatory electro-motive change, but in part also to
physical polarisation, which is added to it algebraically. Thus,
an exciting homodromous shock gives rise to an electrical
after-effect, in which the excitatory current is opposed by
a counter-current of negative polarisation. Under a hetero-
dromous shock, on the other. hand, the excitatory electrical
change becomes summated with the negative polarisation,
which is now in the same direction as itself. In these cases,
though the preponderating nature of the excitatory effect
determines the definite direction of the after-effect, yet it is
difficult to know how much of the latter is actually due
to excitatory action as such, and how much to ordinary
polarisation helping or opposing this.

Very much greater complexities ensue again in practice
rom the difference between anodic and kathodic actions
on the two unequally excitable surfaces. In Torpedo, for
instance, according to Du Bois-Reymond, the electrical organ
responds better to a homodromous than to a heterodromous
exciting current, while in J/alepterurus, according to Gotch,
the reverse is the case, the heterodromous being more efficient
than the homodromous. Such diversity of results is prob-
ably to be accounted for by the considerations to which I
have referred.

If we take, tor example, the simplest case, that in which
the anterior surface is more excitable than the posterior, and
if we suppose an induction-current of moderate intensity
to be sent in a homodromous direction, we may assume that
Pfliiger’s Law—the kathode excites at make, and the anode
at break—will hold good. We shall here, for the sake of

250 . COMPARATIVE ELECTRO-PHYSIOLOGY

simplicity, neglect any effects that may accrue from anode-
make and kathode-break. Under a homodromous induction-
shock, then, two different excitatory electrical changes will
be induced, on the lower and upper surfaces respectively, the
consequent currents through the tissue being in opposite
directions. On these, moreover, will be superposed again the
polarisation-current. Calling the effect induced by anode-
break as A, and that of kathode-make as K,, we shall obtain
a resultant consisting of A,on the more excitable anterior
surface, mznus K,, on the less excitable posterior, mznxus the
negative polarisation-effect. Under a heterodromous shock,
on the other hand, we shall have K,, on the more excitable
anterior surface, mznus A’ on the less excitable posterior, plus
the negative polarisation-effect.

Even this, however, does not exhaust the possibilities
of complication. _ For I shall show in a subsequent Chapter,
and have already shown elsewhere, that under a high E.M.F.
Pfliiger’s Law does not apply. The relative excitatory
values of anode and kathode may indeed undergo one or
more reversals, according to the intensity of the acting
electro-motive force. Thus, under a moderately high E.M.F.
in what I have designated the A stage, both the anode and
kathode are found to excite at make, and either kathode or
anode at break. In the B stage, under a still higher E.M.F.,
it is the anode which excites at make, and the kathode at
break.

It will thus be seen what a number of complicating
factors may be present when an organ is excited by currents
of varying direction and intensity. If, then, we wish to study
the purely excitatory reaction of an organ, as dependent
solely upon its individual characteristics, uncomplicated by
defects inherent in the method of excitation, we must see
first that the applied stimulus is equal on both surfaces, and,
secondly, that such factors as are not excitatory—that is to say,
negative or counter-polarisation—are eliminated. These ends
may be accomplished by subjecting the responding organ
to symmetrical and alternating equal and opposite shocks,

THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 25I

following each other in rapid succession. For the resultant
negative polarisation will in practice be neutralised, if the
primary polarising currents are similar, equal, and opposite.
The stimulus applied on the two surfaces, moreover, will be
equal, if the two rapidly succeeding and opposite-directioned
shocks be so symmetrical as to be interchangeable. Which-
ever may. be the factor of excitation will then act equally on
both surfaces. The response, therefore, will now be determined
solely by the natural difference of excitability as between the -
two surfaces. |

It has been said that in order to accomplish these experi-
mental conditions, the two opposite shocks should be equal in
intensity and in point of time-relations. An ordinary make-
and-break Ruhmkorff’s shock does not fulfil this condition, since
the break-shock is there the quicker'and more intense of the
two. Moreover, owing to the varying residual magnetisation
in the iron core, successive shocks may not be equal. These
defects are overcome by sending round the primary, with
a constant rapidity, two equal and opposite currents in
alternation. During one semi-cycle, then, the primary current
varies from + C to — C,and during the next from — C to
+ C, and since these two changes are effected with the same
rapidity, the induced currents are. symmetrical, equal, and
opposite. |

Such reversal of current is accomplished by means ofa
rotating reversing-key. The key R is wound up against the
tension of a spring S, being maintained in this set position
by the electro-magnet E, acting on the armature. When the
current in the electro-magnet is broken, the alternating
double shock from the induction coil I is passed through the
experimental leaf L, by means of non-polarisable electrodes
N, N,. In the case just described the sequence of the
current through the. primary coi] was, say, right-left-right.
In the next experiment, by means of the Pohl’s commutator,
K,, this sequence may be made left-right-left (fig. 159).

Empioying this method, I have carried out rheotomic
observations for determining the time-interval after the shock

fr
}
\

{

252 COMPARATIVE ELECTRO-PHYSIOLOGY

at which the E.M.F. attained its maximum. The general
arrangement here is similar to that described in Chapter IV.
(cf. fig. 37). C is the compensator by which any existing
electro-motive difference is compensated at the beginning of
each experiment. The striking-rod A breaks the current
in the electro-magnet E, by which the rotating reverser R is
actuated, which brings about equal and opposite shocks to
the leaf. The galvanometric after-effect, at any short

All lis

= Tc =

bt
> Sh on See

Fic. 159. Experimental Arrangement for Rheotomic Observations

A, B, striking-rods attached to revolving rheotomic disc; K,, key for
electro-magnetic release of rotating reverser R; K,, key for unshunting
the galvanometer when pressed by rod, B, for a definite period; ky,
key for preliminary adjustment ; E, electro-magnet with its armature
by which rotating reverser, R, is set against antagonistic spring, S ;
K,, Pohl’s commutator; Cc, compensator; P, primary, and 1, the
secondary, of the exciting induction-coil ; N,, N,, non-polarisable elec-
trodes, making electrical contacts with posterior and anterior surfaces
of leaf.

interval after excitation, is obtained by the un-shunting of
the galvanometer, caused by the striker B impinging against
the key K, (fig. 159). We have seen that, owing to the
presence of various complicating factors, as well as to the
occurrence of negative polarisation, successive responses to
homodromous and heterodromous shocks are unequal. By
the employment of equi-alternating induction-currents, how-

THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 253

ever, we obtain true excitatory effects, unmodified by any
such elements of uncertainty. In order to show how perfect
the results obtained by this method become, I give here
(fig. 160) the records of two successive excitatory responses
obtained from a leaf of Bryophyllum calycinum, the responsive
current being from the lower or anterior surface to the upper
or posterior. In this mode
of stimulation, by equal
and opposite shocks, as
already said, no advantage
is given to either surface
over the other. Neverthe-
less, I thought it well to
take two successive records
under shocks, in which the
alternating currents in the
primary circuit were first
right-left-right, and then left-
right-left.

In the electrical organ
of TZorpedo Gotch found
the maximum electromotive
change to be attained in
about ‘oI second after the
application of the excitatory
shock. In leaves, again, I
find the rapidity with which
the maximum effect is at-

. Fic. 160. Records of Two Successive
tained to depend on the Responses in Leaf of Bryophylium
nature of the tissue. and calycinum under Equi-alternating

‘ Electrical Shocks

also on the intensity of the

exciting shock. In sluggish specimens this may be as long
as ‘2 second. It should be remembered that in the case
of mechanical stimulation of moderate intensity also, this
period was, similarly, about *2 second (p. 51). With very
vigorous leaves of Vymphaea alba, however, and employing
a stronger electrical stimulus, the maximum effect was

254 COMPARATIVE ELECTRO-PHYSIOLOGY

attained in a much shorter time —that is to say, in about
‘03 second. I give below a table showing the rheotomic
observations made on such a leaf at gradually increasing
intervals after the exciting shock. It should be remembered

TABLE OF RHEOTOMIC OBSERVATIONS.

Mean interval after the shock | Galvanometric deflection
|
‘ol of a second ‘20 divisions |
°03 9° 99 | 63 99 |
"O§ 9° > I 7 Je |
°O7 3° +] I 5 9 |
I 99 39 20 99
°2 9° bi] 9 23 |
‘ 99 ” 8 oe) |
*h 29 rm) 5 ?

that the recording galvanometer was un-shunted for ‘ol
second, The curve given in fig. 161 has been plotted from
these results. The maximum
electro-motive change took place,
as already pointed out, in ‘03
second after the application of
stimulus. This curve shows
multiple apices, as was also the
case, it will be remembered, after
a strong mechanical stimulation
(cf. fig. 40). This point will be
referred to in greater detail in
the next chapter. In the course
of half a second after the shock,
the . excitatory electro-motive
change had subsided to about
one-twelfth of the maximum,
Fic. 161. Response-curve from It has been said that the
scp teeer epee onLeaf excitatory current depends for
Ordinate represents galvanometer its definiteness of direction on
deflection; abscissa,: time in the physiological anisotropy of
hundredths of a second.
the organ. In_ those leaves
in which the physiological differentiation of the upper and
lower surfaces is not strongly marked, the differential

I CU

THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 255

excitability of the two is liable to undergo reversal, under
the changing conditions of age, season, and fatigue induced
by previous stimulation. In the leaf of Pzerospermum,
however, which I have here taken as the type corresponding
with Zorpedo, the normal differential excitability is generally
very persistent. Here the excitability of the posterior
surface, which is leathery, is slight, and practically negligible.
But the anterior surface, with its rich and prominent venation,
is highly excitable, The excitatory discharge of such a leaf
is thus from the anterior to the posterior. I give in fig. 162
a series of its responses to equi-alternating electric shocks,
It will be seen that these are
very uniform, and exhibit
practically no signs of fatigue.
We have thus found a
vegetable organ whose re-
sponses are exactly parallel
to those of a single plate of
the electrical organ of Zorpedo
and its type. We shall next ens
study the responsive pecu- TiC; 162. Series of Responses, given
liarities of the vegetable organ folium to Stimulus of Equi-alternat-
Base responses correspon d ng eectneal Shocks at Intervals ot
with those of the organ of
Malepterurus. \t has been mentioned that the posterior surface
of each single element of this electrical organ is regarded as
consisting of a glandular, rather than a muscular, modification.
Among corresponding leaf-organs, then, the carpellary leat
of Dzllenta indica might, as we also saw, be taken as the

‘type, its posterior surface: being glandular. Or the analogy

will be still more perfect if we take as the vegetal type the
pitcher of Vepenthe. Here the internal or posterior surface
is richly provided with glands. -The next point to be deter-
mined is whether, in these cases also, on excitation the
responsive current is from the posterior surface to the anterior,
as in the electrical element of Madepterurus. And on sub-
jecting them to equi-alternating electrical shocks, I found

256 COMPARATIVE ELECTRO-PHYSIOLOGY

this to be the case. The responsive current here flowed from
the glandular posterior to the non-glandular anterior surface.
From this experiment we see that a glandular surface is
exceptionally excitable, a conclusion which will be found to
be supported by the numerous experiments on glandular
organs in general, to be described in Chapter XXIV. I give
in fig. 163 a series of photographic records, obtained on
excitation of Dzllenza indica. In the next record (fig. 164)
are seen the responses given by the pitcher of Wepenthe.

Fic. 164. Photographic Record
of Normal Responses given by

; ic Record of Re- ; saat
Fic. 163. suis ge Gy rae Pitcher of Mepenthe, under Equi-
sponses 0 a alternating Electric Shocks
Natural current from posterior to an- ‘ ene
terior, and responsive current from sie scare aca woes harden
anterior to posterior surfaces. hg nae he donee
glandular surface. Note ten-

dency to multiple response.

An interesting fact to be noticcd in the latter is the tendency
to multiple response. '

Similar results were also obtained on taking any single
scale of the bulb of Uvzclzs lily about the time of flowering.
In each of these the lower or outer surface is invested with a
more or less dry and glistening membrane, while the upper
or concave is moist and glanduloid. The moisture observed
inside each scale is in fact exuded from this inner surface.
On subjecting one of these scales, then, to the electrical

THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 257

excitation already described, it is found that a very strong
responsive current is obtained, whose direction is, as in the
last case, from the glanduloid to the non-glanduloid surface.

The effect of the serial arrangement, again, in enhancing
the electro-motive force—as seen in the pile-like arrangement
of the electrical organ of fishes—may be exemplified, in
the parallel instance of the plant-organ, by means of the
superposed scales of the bulb, as found in nature. The bulb
may be divided longitudinally into halves, of which the
right-hand half is mounted, for experiment, with the scales
vertical. It will be understood that all the glanduloid
surfaces here face the left, while the non-glanduloid are
turned to the right. Thus the left aspect of this pile
corresponds to the head aspect of the organ of JZalepterurus.
The latter, on excitation, responds by a current in the
direction of head to tail—that is to say, from glandular to
non-glandular ; and similarly, in the pile-like half-bulb of
Uricls lily, the responsive current is from glanduloid to non-
glanduloid—that is to say, from left to right.

Another interesting way to perform the same experi-
ment is without making any section of the bulb. We
take a bulb of Uvzclzs, with the peduncle rising out of the
middle. When this hollow peduncle is cut across, it allows of
an electrical connection being made with the centre of the
interior of the bulb. An equatorial belt makes the second,
or outer, connection. On subjecting this to equi-alternating
shocks, the resulting response will be found to be from the
inner surface to the outer, through the numerous intermediate
scales, the individual effect in each being concordant and
additive: .

We have thus seen how the response of a leaf gives us an
insight into the action of a plate of an electrical organ ; how
the differential excitabilities of the two surfaces give rise on
stimulation to an induced E.M.F. as between the two; how
a nervous and indifferent-tissued surface will give rise toa
response in one direction, and a glandular and non-glandular

S

258 COMPARATIVE. ELECTRO-PHYSIOLOGY

in the other; and finally how, by a serial arrangement, the
terminal electro-motive effect becomes enhanced. The light
thus thrown on the two types of response, known to occur in
the electrical organs of fishes, is evident. Further con-
siderations, relating to the theory of electrical organs, will be
given in detail in the next chapter.

EE a i

et EA

ee

CHAPTER XX

THE THEORY OF ELECTRIC ORGANS

Existing theories—Their inadequiacy—The ‘blaze-current’ so called— Response
uni-directioned, to shocks homodromous or heterodromous, characteristic of
electric organs—Similar results with inorganic specimens — Uni- directioned

_response due to differential excitability—Electrical response of pulvinus of

| Mimosa to equi-alternating electric shocks—Response of petiole of Musa—
Of plagiotropic stem of Cucurbita—Of Eel—The organ-current of electric
fishes—- Multiple responses of electrical organ — Multiple responses of
Biophytum.

ONE of the most perplexing problems in connection with

the phenomena of electrical organs is the question as to

whether the activity of such organs is specific—that is to say,
peculiarly characteristic of them—or-falls into line with the
other electro-motive reactions observed in animal tissue.
Many arguments have been brought forward for and against
the identity of these phenomena with the excitatory reactions
of the nerve and muscle. :

From the experimental results which I have Aéecribert

however, it would already appear that such reactions as these

of the electrical organ are not specifically characteristic, even
of the animal structure, but may equally well be observed in
plant tissues. It is therefore essential, if we are to determine
that basic reaction which is common to all alike, that we
should find a wider generalisation than has hitherto been
contemplated. This basic reaction, as we have already seen,
depends upon the differential excitability of an anisotropic
organ, and this aspect of the case we are now. about to study
in greater detail. Before doing this, however, we shall briefly
glance at various theories which have been suggested, but are
generally admitted to be inadequate. |
$2

260 COMPARATIVE ELECTRO-PHYSIOLOGY

Bell, for example, thought it might be possible to explain
‘the discharge of the electrical organ solely by the negative
variation of the nerve-current, concomitant with innervation.
In this arrangement the dorsal surface of the electrical plate
(of Zorpedo) would, at the moment of innervation, become
positive, the ventral surface negative, as actually occurs.’

As against this, it was pointed out by Du Bois-Reymond
that this hypothesis in the first place predicates the existence
of a current of rest, caused by the ‘natural’ cross-sections
(acting like artificial sections) of the nerves in the plates, and
accordingly heterodromous to that of the discharge. Instead
of this permanent current—which must correspond in E.M.F.
with the discharge, if the nerve-current is to disappear in the
negative variation—there is only an inessential P.D. during
rest, and the resulting ‘organ-current’ is always homodromous
with the discharge.! |
Even had these objections not existed, however, Bell’s
hypothesis would have failed to explain the electrical action
of Malepterurus. Du Bois-Reymond himself tried to explain
the action of the electrical organ, ‘not by the negative
variation of the nerve current, but by a process in the
electrical plates transformed from muscles, comparable with
the negative variation of the muscle-current, as set forth from
the standpoint of the pre-existence theory.’ Here, however,
it is perhaps sufficient to point out that the pre-existence
theory, on which the hypothesis was based, is now held to be
invalidated.

There remains only the Chemical, or Alteration Theory,
which associates all electrical changes with the corresponding
chemical processes of assimilation and dissimilation. But
it has not been made clear in what way these can bring about
the characteristic discharge of the electrical organ.

There is another point, not altogether unrelated to this
subject, which may be dealt with on the present occasion,
I allude to the so-called ‘blaze current’ of Dr. Waller. By
this is meant an after-current in the same direction as the

' Biedermann, Z/ectro-Physiology (English translation), vol. II. p. 462.

THE THEORY OF ELECTRIC ORGANS 261

exciting current. It is, in, fact a new name for that phe-
nomenon which Du Bois-Reymond indicated as ‘ positive
polarisation-current. Du Bois-Reymond had also shown
that this particular effect was most markedly exhibited when
the functional activity or ‘livingness’ was at its highest.
Under opposite conditions, again, it would disappear. The
intensity of this homodromous after-effect was thus dependent
on the degree of vitality of the tissue under experiment.
Hermann and Hering, however, afterwards showed that what
Du Bois-Reymond called ‘ positive polarisation’ was in reality
excitatory reaction. These excitatory effects are known to
be caused by either the anode or the kathode!; and I have,
in the course of the last chapter, demonstrated the fact that
it is the differential excitability of a tissue which determines
such uni-directioned response. It is difficult, therefore, to see
the necessity of a new name for these phenomena. Dr.
Waller himself, however, offers the following as an important
reason :

‘The great mass of living things, whatever else they
may give and take from their surroundings, take oxygen
and give carbonic acid ; they may live slowly or they
may live quickly—sluggishly smoulder or suddenly
blaze. A muscle at rest is smouldering: a muscle in its
contraction is blazing ; the consumption of carbohydrate
and the production of CO,, never absolutely in abeyance,
even in the most profound state of rest, are sharply
intensified when the living machine puts forth its full
power, and there is then a sudden burst of heat, and an
electrical discharge... .’?

This amounts to another way of saying that the cause of
the excitatory galvanometric effect is some explosive dis-
similatory change, a view which I have already shown in

1 ‘Within a given ‘ physiological ” range of strength of current the negative
kathodic must, equally with the positive anodic, be designated an ‘“‘irritative ”
after-current, due entirely to ‘‘ polar current-action.” ’—Biedermann, Zéctro-
Physiology (English translation), vol. I. p. 448. |

* Waller, Signs of Life, p. 74.

262 COMPARATIVE ELECTRO-PHYSIOLOGY

previous chapters to be quite untenable. I shall presently
describe experiments which will further show that galvano-
metric responses, not to be distinguished from this, take place
when there is no possibility of any consumption of carbo-
hydrates or production of CO,. ,

The fact, however, that the excitatory after-effects de-
scribed, disappear on the death of the tissue, has led Dr,
Waller to put forward the generalisation that this so-called
‘blaze-current’ is the final distinction between living and
non-living matter. His formula, with regard to this, is, ‘ If
the object of examination exhibits blaze in one or in both
directions, it is living.’ He admits, nevertheless, that a sub-
stance which is undoubtedly living will not always exhibit
the ‘blaze-current.’ -But it is contended that the occurrence
of ‘blaze’ is an undoubted ‘sign of life, and that thus
a strong distinction is to be made between vitalistic and
non-vitalistic, or physical, reactions. Hence, as there is
supposed to be no excitatory reaction possible in non-living
or inorganic matter, it would follow that electrical shocks
passed through such a substance, in either direction, should
give rise only to those counter-polarisation currents which
are known to physicists. In such cases, on reversing the
direction of the shock, the direction of the after-current
is also reversed ; but in the living substance, it is maintained,
the case is quite different. If the direction of the shock be
here reversed, the after-current will still appear, with direction
unchanged, because in this latter instance it is not generated
by the shock, but is, on the contrary, an inexplicable function
of the living material, set in action by it, in the same way as
a loaded gun is fired by pulling the trigger. The possibility
of obtaining from the given substance such a uni-directioned
after-current, independently of the direction of the shock, is
thus to be taken as the test and token of ‘ vitality.’

_ Now, while it is certainly true that.the domain of physio-
logical phenomena has not yet been so thoroughly explored
as that of the physical, it is nevertheless equally true that
no one could venture to claim that even physical phenomena

THE THEORY OF ELECTRIC ORGANS 263

had up to the present been exhaustively studied. It is, then,
somewhat hazardous to declare that because a particular
phenomenon has not yet been observed to occur in inorganic
matter, it is by that fact demonstrated to be hyper-physical
in its nature, and must be relegated to the different and
mystical category of the exclusively vitalistic. The very
foundation of such a statement would be swept from under
it, the moment it was shown that the same phenomenon
followed, under the same circumstances, in conditions which
were admitted to be purely physical.

I have shown, it will be remembered, in the previous
chapter, that the uni-directioned response to electrical
shocks in either direction was due to the differential
excitability of the structure. The response of any aniso-
tropic organ would always be from the more to the less
excitable, the more excitable becoming relatively galvano-
metrically negative. There may here be various cases of
excitation, all giving results of the same type, say, a respon-
‘sive current from B to A. The first is that in which, on
excitation, both B and A become galvanometrically negative,
A being the less so of the two. In the second case, the excit-
ability of A being slight, or negligible, B alone becomes
negative. And in the third ‘case, excitation induces
positivity of A and negativity of B. In all these cases the
relative negativity of B being greater, the responsive current
will flow from B to A. The resultant current is made up, :
in the first case, by subtracting the galvanometric negativity
of A from that of B; in the second case, it consists of the
galvanometric negativity of B, that of A being zero; and in
the third case, it is produced by the addition of the effect
at A to that at B. Examples of the last of these will
be found in certain animal and vegetable skins, described
in Chapter XXII.

These being the conditions, then, for the induction of
the uni-directioned responsive current, it appeared to me
probable that the same result could be obtained with
inorganic substances, provided that the specimen were so

264. COMPARATIVE ELECTRO-PHYSIOLOGY

prepared as to be anisotropic, one side having a greater
potentiality of galvanometric negativity under excitation
than the other. In that case, further, it was clear that the
strongest resultant current would be obtained, if one surface
of the structure became galvanometrically positive, and the
other negative, on excitation. I have already stated, in
Chapter I., that different inorganic substances give electrical
responses of opposite signs. Thus the response of lead is
positive, while that of brominated lead is negative. If, then,
we take a lead wire A B,
clamped in the middle
at C, as represented
in the upper diagram
(fig. 165), and stimulate
the right-hand end B,
say by mechanical
vibration, a responsive

- current will be induced,
Fic. 165. Responsive Currents in Lead Wire which will flow. to-

Upper figure—Excited wire, galvanometrically :
positive. Simultaneous excitation of both wards the stimulated,

ends balance each other ; resultant response B thus becoming gal-
‘-Z6ro. . : :
Lower figure—Left portion, lead wire, right vanometrically posi-
portion, brominated lead wire, shown as tive. The same will
shaded. Response of first positive, of second A
negative. Simultaneous excitation of the be the case with 4,

erg andes, fella reponse which“ on stimulation. When
both A and B are simul-

taneously stimulated, it is evident that the two responsive
currents, being antagonistic, will cancel each other. But
if the right-hand half B’ of the wire consist of brominated
lead (lower diagram, fig. 165), while the left-hand half a’ is of
lead like that used in the first case, then stimulation of B’ will
cause a responsive current to flow away from the right-hand
excited end, B’ thus becoming galvanometrically negative ;
A’, on the other hand, will give rise to a positive response
towards the excited. Simultaneous excitations of A’ and B’
will not then be antagonistic, but additive in their effects.
The resultant response will thus be from the negative b’ to

<n

THE THEORY OF ELECTRIC ORGANS 265

the positive A’. We may next take a flat strip of lead, of
which the lower surface B is brominated... On mechanical
stimulation of both surfaces by vibration it will now be
found that the resultant responsive current flows across the
strip, from the negatively-responding B to the positively-

_responding A (fig. 166). It will be seen that here—as the

molecular disturbance
on which excitation
depends is caused by a
non-electrical form of
stimulus—the electrical
character of the response

obtained is unexcep- Fic. 166, © Flat Strip of Lead, of which

tional in its freedom lower Surface is Brominated

from any complication Response of upper surface positive, of lower
y Pi : surface negative. Resultant response

by the polarisation- from lower to upper.

factor.

Let us next consider what would be the effect of sending
induction shocks across such a strip. If inorganic bodies
be really inexcitable, then we can here obtain only the
counter-polarisation current as the after-effect. That is to
say, on sending a shock from below to above in an ascending
direction, we should observe only negative polarisation as
an after-effect, or a descending current from above to below.
A descending shock should, on the other hand, give rise to
an ascending after-current. But if inorganic substances
should prove to be excitable, and if B were to become on
excitation relatively negative to A, as we found in the
experiments on mechanical stimulation, then, whatever the
direction of the shock, we should have a uni-directioned
response, from below to above, exactly like the excitatory
discharge of the electrical organ of Zorpedo, from the ventral
surface to the dorsal.

‘ In order to brominate this surface as required, it may be held exposed to
vapour of bromine. Or an electrical deposit may be made by electrolysis, in a
bath of potassium bromide solution. A certain depth of deposit and time of
formation are important to the successful preparation of the plate. When these
are secured, the proper condition of responsiveness is found to be long-enduring
as will be seen from the photographic records.

266 COMPARATIVE ELECTRO-PHYSIOLOGY

I give below (fig. 167) photographic records of the
responsive after-effects actually obtained on carrying out
this experiment on the lead strip prepared as described. It
is here seen that whatever had been the direction of the
‘shock, homodromous + or heterodromous |, the responsive
current was always one-directioned : that is to say, from the
more negatively-excitable lower to the positively-excitable
upper surface. If the test of the ‘blaze-current’ is to be
accepted, then we shall be compelled to refer this. metallic
strip to the category of organic matter in a living condition !

Fic. 167. Photographic Records of After-effect of Homodromous *¢ and
Heterodromous | Induction-shocks in Prepared Strip of Lead

Note uni-directioned response, whatever be direction of induction-shock.

Since it is admitted that the electrical response of living
tissues is due to molecular excitation, and since we obtain
similar electrical effects, as just seen, from the inorganic, it
is clear that excitability is the property, not of the organic
alone, but of all matter. It is also clearly seen that the one.
directioned response of an anisotropic structure—so charac-
teristic, among other things, of the electrical organ of
certain fishes — depends on its differential molecular excit-
ability. “The phenomenon is thus reduced to what are almost
its last terms—namely, the molecular. It is therefore un-
necessary to call in the aid of such indeterminate factors as
vitalism, or assimilation and dissimilation,

THE THEORY OF ELECTRIC ORGANS 267

In taking these responses to homodromous and hetero- .
dromous shocks, the counter-polarisation-current is super-
posed upon the excitatory effect. For this reason we see,
in fig. 164, that the homodromous response, in which
negative polarisation was an opposing factor, is smaller than
the heterodromous, in which polarisation conspires with the
excitatory current. We have seen, in our experiments on
the leaf-organ, that when this negative polarisation is
annulled by taking responses under equi-alternating elec-
trical shocks, successive responses, giving the true excitatory
effect, become equal. ~ I
give here (fig. 168) a series
of responses of the pre-
pared lead strip, under
these conditions of equi-
alternating shocks, in
which they are seen to
have become equal, the
resulting responsive cur-
rent being from the lower
surface to the upper, as
before.

Fic. 168. Photographic Record of Re-

Having thus demon- sponses to Equi-alternating Electric
strated in various ways See et Si of One Minute in
epared Lead Strip
the nature of that funda- Responsive Current as before from lower
mental condition, which to upper surface.

determines the excitatory discharge of the electrical, organ,
we may next take other organs which are known to be
differentially excitable, and observe whether they also,
under electrical excitation, give definite uni-directioned
responses.

The differential excitability of the upper and lower
surfaces of the pulvinus of J/zmosa are well known. On
subjecting this organ, then, to equi-alternating electrical
shocks, I obtained uni-directioned responsive currents, their
direction being from the more excitable lower to the less
excitable upper half, of which a photographic record is given

268 COMPARATIVE ELECTRO-PHYSIOLOGY

in fig. 169. In this particular specimen, owing to growing
fatigue, the responses are seen to undergo diminution. In the
sheathing petiole of Musa also, we found, as will be remem-
bered, that the inner or concave surface was more excitable
than the outer or convex. In taking records of the responses
of such a specimen to equi-alternating electrical shocks, the
direction of the responsive current was found to be from the
more excitable inner to the less excitable outer surface.

It is now evident that in the
structure of any single element of
an electrical organ, the essential
question is not ‘as to the corre-
spondence of one part or another
with muscle, nerve, or gland; but
merely that of anisotropy. Any
tissue which is anisotropic is
potentially an electrical element.
Thus a stem of Cucurbita origin-
ally radial, becomes physiologically
anisotropic when it happens to
assume the recumbent posture,
owing to the a-symmetrical action
Fic. 169. Response of Pulvinus of environmental stimuli. Such

of Mimosa to Equi-alternating __ : ,

Flectric Shocks an anisotropic organ, when elec-
Responsive current from more trically excited, gives a one-

Srna gad to less excit- Girectioned responsive current

from the lower or ventral to the
upper or dorsal surface. A similar reaction is, curiously enough,
shown by the body of the Eel, which also, on excitation, gives
a responsive current from the ventral surface to the dorsal.

The responsive peculiarity of the constituent elements of
the electrical organ is thus not unique. The extraordinary
character of the organ depends merely upon the serial
arrangement of innumerable such elements, connected with
a nerve-trunk, by means of which a voluntary impulse is
enabled to bring about the excitatory discharge of the
electrical pile, and so convert it into a weapon of offence.

THE THEORY OF ELECTRIC ORGANS 269

The most difficult problem with regard to these electrical
organs having thus been solved, it remains to say a few
words concerning two other points: namely, the natural
current of rest and the repeating character of the excitatory
discharge.

As regards the first of these, Du Bois-Reymond found
the current of rest—which he designated as the organ-current
—to be in the direction of the electrical discharge. We have
found, however, that, as a general rule, in the primary
condition, the true natural current flows in the opposite
direction to that of excitation, that is to say, from the less
to the more excitable. In agreement with this, I find, in
the leaf of Pterospermum, the electrical reaction of which
is similar to that of the plate of Zorpedo, that while its
excitatory current is from the more excitable ventral to
the less excitable dorsal, its resting-current is opposite to
this—that is to say, from dorsal to ventral. With regard
to the electrical organ, then, there can be little doubt that
here also the true resting-current would have been found
to be opposite in direction to the excitatory, if it could
have been observed and recorded under an absolute con-
dition of physiological rest. In a highly excitable struc-
ture, however, the shock of preparation, as we have seen
and shall further see, leaves an after-effect which reverses
the natural current of rest. For this reason, the current
of rest observed in preparations of the electrical organ
has not, in all probability, represented the true current, but
rather the excitatory reversal of it. This view is supported
by the fact that while in the organ-preparation of
Torpedo, this reversed, or ingoing-current of rest is con-
siderable, in the intact fish it is negligible. It must be borne
in mind that the fish is spontaneously excitable, and also
that there must remain a certain residual effect from the
organ-discharges. Nevertheless Zantedeschi found a resting-
current to occur in the intact fish in the reverse direction to
that of the excitatory discharge. This was evidently the
true resting-current. This view of the organ-current, of

390; COMPARATIVE ELECTRO-PHYSIOLOGY

Du Bois-Reymond, as, in reality, a persistent after-effect of
excitation, gathers confirmation from an observation made
by Gotch, that it is considerable in 7 orpedo, in which the
excitatory effect also is known to be very persistent ; but in
Malepterurus, where recovery from excitation is rapid, this
particular organ-current is practically absent from excised
preparations. | | 7

We may turn now to the repeated or oscillatory character
observed in the electrical discharge by both Gotch and
Schénlein. This is seen in the multiple apices ‘of its
rheotomic curve. Multiple apices are also found, as we have
seen, in the rheotomic observations on vegetable organs,
given in fig. 40. Gotch attempts to explain these repeated
responses of the electrical organ—which he calls ‘auto-
excitation ’—by the passage through the tissue of the intense
current due to the response; this he regards as exciting the
tissue again, and bringing about the repetition of the same
effect. With regard to this hypothesis, however, it is un-
necessary to suppose that it is the intense electrical current
of the first response which is the exciting cause of the
second, and so on. For we must bear in mind that multiple
response is not exclusively characteristic of these electrical
organs, with their high intensity of discharge-current, but
is exhibited by tissues of various kinds. These, as we have
seen in Chapter XVII., may be thrown into a condition of
rhythmic or multiple excitation by any form of stimulus,
provided that its intensity be beyonda certain value. It thus
happens, as we have seen, that while a single moderate stimulus
induces a single response, a single strong stimulus induces
multiple responses.

Indeed this fact—that it is not the intensity of the
first responsive current, causing a new excitation of the
tissue, which is accountable for the second, and so on—
becomes quite clear, as soon as we make quantitative obser-
vations of response, in those cases in which it receives
undoubted visible manifestation, by the orderly fall of leaflets
serially arranged—that is to say,in such plants as Biophyium.

THE THEORY OF ELECTRIC ORGANS 271

The sensitiveness of these leaflets is of that order which
requires on an average an E.M.F. of 12 volts to cause excita-
tion by kathode-make or anode-break. And this value is
considerably higher for anode-break than for kathode-make.
The lowest E.M.F. which I have found with highly excitable
Biophytum to be effective in causing excitation, was 4 volts,
and in less sensitive specimens it might be as high as
20 volts. )

Now, on applying a strong stimulus, say by contact of
hot wire, on the petiole bearing the sensitive leaflets, an
excitatory wave is initiated, which, during its progress, brings
about depression of the leaflets in serial order. After an
interval of about half a minute, a second wave is found to
be initiated from the original point of excitation, causing a
second series of responses, shown by the same serial depres-
sion of the leaflets as before. And such recurrent excitations
may take place from a single stimulus, as often as twenty times.
On determining the E.M.F. value of each of these excitatory
waves, however, I have found it to be of the order of ‘or volt.
This, it will be seen, is only about four one-hundredths
of the minimum E.M.F. necessary to induce excitation of
the leaflet. It clearly follows that here the original stimulus
is the cause of these multiple excitations, and not the first
response the cause of the second.

The phenomenon of multiple response then, is, as we have
seen, of very extensive occurrence, and not confined to elec-
trical organs. We have seen it exhibited even by ordinary
tissues, and we shall find in subsequent. chapters that
such repeated responses are actually induced in nervous
and glandular tissues, under the action of an intense stimulus.
This is interesting in view of the fact that the electrical
organs of fishes are made up of either neuro-muscular or
neuro-glandular elements.

CHAPTER 3X1

DETERMINATION OF DIFFERENTIAL EXCITABILITY
UNDER ELECTRICAL STIMULATION

Advantage of electrical stimulation, in its flexibility—Drawbacks due to
fluctuating factors of polar effects, and counter polarisation-current—Difficulties
overcome by employment of equi-alternating electric shocks—Methods of the
After-effect and Direct-effect—Experiment of Von Fleischl on response ot
nerve —Complications arising from use of make and break shocks-—Rotating
reverser—Motor transformer—Response of A/wsa to equi-alternating shocks—
Abolition of this response by chloroform— Response records of plagiotropic
Cucurbita and Eel—Differential excitability of variegated leaves, demonstrated
by electric response.

WE have seen, in Chapter IX. that the differential excitability
of any two points in a tissue can be detected, by observing
the direction of resultant response, when both the points are
simultaneously excited by an identical stimulus. It was
seen in the same place also that the more excitable point
becomes, under diffuse stimulation, relatively galvanometrically
negative. I further described the various forms of quanti-
tative stimulus which might be employed for this purpose,
those, namely, of mechanical vibration and of stimulation by
thermal shocks. By employing these non-electrical forms of
stimulus the fundamental law of differential response was
firmly established, in such a way as to exclude every source
of uncertainty.

The electrical form of stimulation is characterised never-
theless by many advantages. Its intensity, for instance,
is easily graduated. But its principal superiority lies in its
sreat flexibility of application. Any two points, however
remote or difficult of access they may be, may by this means
be subjected to a required stimulus, if we can only apply two

DETERMINATION OF DIFFERENTIAL EXCITABILITY 273

electrodal points to them. These qualities, however, are
counterbalanced by many serious drawbacks. For the re-
sultant electrical change, induced at a given point by an
electrical shock, is the sum of a number of changing factors,
which may be broadly classified as excitatory and polarising.
Let us suppose the induction shock to enter at a point. We
shall there have the physiological polar effects of anode-make
and anode-break. There is again, on the cessation of the
current, a counter-electro-motive force due to polarisation.
The physiological reaction, moreover, will depend on the
excitability of the point.

Next, as regards the second or kathodal point, where the
shock-current leaves the tissue. We have here the physiological
effects of kathode-make and break, the factor of the ex-
citability of the point, and the counter electro-motive force
due to polarisation, all contributing to the resulting electrical
change at that point. That relative electrical difference
induced between the points A and Bb, which determines the
observed electrical variation, thus equals the sum of the
fluctuating factors acting on A, mznus the sum of the
fluctuating factors acting on B. These elements of variation
are sufficiently complicated ; but still another, as already
said, is added to them, in the fact that, with regard to the
excitatory polar effects of currents themselves, we have not
to deal simply with the law enunciated by Pfliiger, that the
kathode excites at make and the anode at break. The com-
plete law, as will be shown in a later chapter, is complicated by
the fact that the result depends on the intensity of the electro-
motive force. With feeble and again with excessive E.M.F.,
the actual facts are the opposite of conclusions arrived at by
Pfliiger. Under these circumstances it would appear at first
sight impossible that any reliable results could be obtained by
the employment of the electrical form of stimulation. I shall
now, however, proceed to show in what manner all these
difficulties may be overcome, and the electrical form of
stimulus made extremely reliable. This will perhaps be best
understood if we take a concrete example. Let us suppose

T

274 COMPARATIVE ELECTRO-PHYSIOLOGY

that a single electrical shock of moderate intensity enters an
isotropic tissue at the point A, and leaves it at B ; A will then
be the anode, and B the kathode. Here the true excitatory
effect is found to take place only at the kathode, probably
because the anode-break excitation takes place at much
higher intensities of E.M.F. than the kathode-make. At these
higher intensities, then, the anode-break effect also will occur.
At an excessively high E.M.F. again, these relations, for
reasons already explained, may undergo reversal. The point
of such reversal would depend on the nature and excitability
of the tissue. Though, for all these reasons, the relative
excitations of A and B remain a matter of doubt, yet we may
be sure of the excitation of both points, if two, or any equal .
number, of exactly equal shocks be sent through the tissue in
opposite directions, in rapid alternation. If, again, instead of
two alternate shocks only, we give z alternating shocks, abso-
-lutely equal, and if, further, the natural excitability of the two
points A and B have been the same, then there will be nothing
to distinguish the excitatory effect induced at A from that at B.
In other words, the two excitations will be exactly equal.
These strictly equal and opposite alternating currents, more-
over, can have no resultant polarisation-effects, for the effect
arising from an induction shock, in either direction, will be
counteracted by that caused by the opposite.

We thus see that by the employment of this method
the only change induced at the two electrodes will be the
excitatory change, the physical polarisation-factor being
eliminated. Thus, on subjecting two points, A and B, to
equal stimulation, the induced galvanometric negativity, at
both the points, will be equal, if the natural excitabilities of
. the two have been the same. But if the tissue be anisotropic,
and the natural excitability of one point, say b, greater than
that of A, then we shail obtain a resultant responsive current,
which will flow in the tissue from the more excited B to the
less excited A, the induced galvanometric negativity of B
being relatively the greater. We have here what is merely
a repetition, by electrical stimulation, of the results which

DETERMINATION OF DIFFERENTIAL EXCITABILITY 275

were described in Chapter IX., as obtained by thermal and
mechanical stimulus. How perfect and how consistent, due

precautions being taken, these results may be rendered, will

be seen from the numerous records in this and the following
chapters.

I have postponed till now the consideration of the mode
of application of these alternating shocks. The usual alter-
nating current from a Ruhmkorff’s coil would be entirely
unsuitable for delicate and crucial experiments ; first, because
the excitatory values of the slow make- and quick break-shocks
are unequal ; and, secondly, because such currents leave their
residual polarisation effects.

These defects I have been able, as stated in the last
chapter to avoid, by quick reversals of the primary current
which actuates an induction-coil. When the primary
current is reversed from the js/us to the mznus direction,
we obtain an induction-current due to magnetic varia-
tions of lines of force, from, say, plus n to minus n. When
the primary current is re-reversed, from mznus to plus,
we obtain an opposite induction-current, due to magnetic
variation, from mznus n to plus n. It will be seen that if
these reversals of the primary current are made with equal
rapidity, the alternating induced currents will be equal
and opposite. The reversals are accomplished by means of
a Pohl’s commutator, worked up and down by a crank, in
connection with an electric revolving motor (fig. 170). The
intensity of the induction-shock may be varied by sliding
the secondary nearer to, or further away from, the primary.
Having now described the general means of producing equi-
alternating electric shocks, it still remains to explain two
distinct methods of applying them, for the determination of
the differential excitability of the tissue. These may be
distinguished as: (1) the Method of the AFTER-EFFECT ; and
(2) the Method of DirRECT-EFFECT. According to the first
of these—the method of the after-effect—the tissue is excited
for a definite length of time, and the excitatory effect
observed, by connecting it immediately afterwards with the

"3

276 COMPARATIVE ELECTRO-PHYSIOLOGY

galvanometer-circuit. The manner in which this is done will
be understood from fig. 170. We have a highly insulating
electrical key, K, of ebonite. P and Q are connected with two
points A and B of the tissue, whose relative excitabilities are
to be determined. A spiral spring keeps the key down, con-
necting the two points in the specimen with the galvanometer.
Any existing difference of potential, as between the two points

al

M

Fic. 170. Experimental Arrangement for Determination of Excitatory
After-effect of Equi-alternating Electrical Shocks

M, electrical moter working Pohl’s commutator for alternate reversal of
current in primary, P. Note that the connecting-rod, A, works simply
up and down, causing reversals of current ; $s, secondary coil; k,
ebonite key kept down by elastic spring, the two surfaces of the
specimen being thus in circuit with galvanometer, G. When key is
pressed, these are put in circuit with exciting coil, s. When key is
released, after-effect of excitation on specimen exhibited by galvano-
meter deflection. C, the compensator.

is balanced by the compensating potentiometer c. Under these
circumstances, the galvanometer spot of light would remain
steady, whether the key was up ordown. By pressing the key
K, the galvanometer-circuit is broken, and the tissue is put in
series with the exciting circuit S, which forms the secondary
of the induction-coil. When the key is again released, the
galvanometer-circuit is rapidly made, at a definite short
interval after the cessation of the exciting shock, and the
resulting deflection of the galvanometer indicates the differ-

ale ee Va ee ee ies ©

DETERMINATION OF DIFFERENTIAL EXCITABILITY 277°

ential excitation as between A and B. In this way records
may be taken af a series of the after-effects of brief
excitations, at intervals of, say,a minute. The direction of
this responsive current, which in the tissue is from the more
to the less excitable, enables us to determine the relative
excitabilities of the two points, A and B.

Much more delicate is the second method, that, namely,
which depends on the record of the Direct-Effect of equi-
alternating shocks; but for its perfect working, certain
difficulties have to be overcome. One of the first conditions
to be fulfilled lies in the perfect equality of the alternating
shocks. The importance of this will be understood on
observing the effect of the alternating shocks given by a
Ruhmkorff’s coil, when actuated by a vibrating hammer.
Here, the make- and break-shocks are of unequal intensity
and duration, and the following sources of disturbance come
into play: (1) a galvanometric drift in one direction or the
other ; (2) a resultant inequality of polarisation-effects ; and
(3) the inequality of the excitatory values of the two shocks.

The galvanometer-drift, owing to the inequality of the
induction shocks, becomes very troublesome, when we have
to employ, as is necessary, an instrument of high sensibility.
If the differential excitability of the specimen be very great,
this drift may be masked by the predominant excitatory
effect. In other cases, however, the excitatory effect itself
may be overpowered by the drift. The difference of
intensity as between the make- and break-shocks in the
Ruhmkorff’s coil described, thus becomes a strongly dis-
turbing element. The necessity to make the two shocks
absolutely equal will be understood when we find that
alternating telephonic currents, which are generally re-
garded as equal and opposite, induce a drift of the
galvanometer in one direction or the other, on account of a
slight difference of intensity between the two alternating
currents. 4

The difficulty arising from inequality of polarisation-
effects is tao obvious to require further elucidation. Still

278 COMPARATIVE ELECTRO-PHYSIOLOGY

more important, moreover, is the disturbing factor last
mentioned, that of the inequality of excjtatory values as
between the make- and break-shocks themselves. This
element of uncertainty is very clearly seen in the experi-
ments of Von Fleischl on the response of nerve. The
resulting deflection he found to be in the direction of the -
break-shock. The explanation of this phenomenon has
hitherto been regarded as a matter of great difficulty,
authorities being much divided on the subject. In these
experiments, alternating currents from a Ruhmkorff’s coil
are sent through the galvanometer and the nerve, in series.
The two points on the nerve, A and B, are presumably of
equal excitability. A make-shock of relatively lower E.M.F.
passes, say, from A to B, followed by a break-shock of higher
E.M.F..in the opposite direction, from B to A. Confining
our attention to the excitatory effects of these shocks, we
have at A, during make and break, the following four effects :
(a) feeble anode-make; (4) feeble anode-break ; (c) strong
kathode-make ; and (d@) strong kathode-break. At B, on the
other hand, at the same time, we shall have: (a’) feeble
kathode-make ; (6’) feeble kathode-break ; (c’) strong anode-
make ; and (@’) strong anode-break. Now, since the excitatory
value of anode-break is probably the stronger and more
persistent, and since the intensity of this effect will depend,
within certain limits, on the intensity of the anodic shock, it
follows that the (@’) or strong anode-break effect at B will, as
a general rule, be the most conspicuous of these. That is to
say, as a result of all these excitatory effects in combination,
greater galvanometric negativity will be induced at B than at
A, the responsive current being thus from B->A, in the same
direction as the break shock, which was the actual result. In
any case, whatever may have been the cause of this, it is
clear that the employment of such unequally exciting shocks
of make and break would be fatal to any attempt to
determine accurately the natural difference of excitability as
between the two points. I may state here, that when I have
employed absolutely equal alternating shocks on a specimen

DETERMINATION OF DIFFERENTIAL EXCITABILITY 279

of nerve, I have obtained no resultant deflection whatever,
showing that such shocks induce exactly equal excitations
in an isotropic tissue. But if the excitability of one of the
two points be first abolished by killing, then a definite
resultant responsive current is obtained, from the excitable
living to the inexcitable dead. So perfect were in fact the
results secured by means of these equi-alternating electric
shocks, that I was desirous not only to detect, but also to
record photographically, the responses thus obtained. In
this a certain difficulty is experienced, inasmuch as the
alternating shocks are apt to render the recording spot of
light tremulous, and thus to spoil the photographic im-
pression. This may, however, be overcome by making the
alternation frequency so high, in reference to the period of
the needle or suspended coil of the galvanometer, that the
unsteadiness of the deflection ceases.

I shall now describe the practical means employed to
obtain equi-alternating shocks of any frequency that may be
desired. This I have been able to do in several ways, and,
among others, by using a Rotating Reverser. This consists
of an ebonite disc, on the periphery of which there are strips
of metal of equal breadth, and separated from each other by
equal distances. The odd strips (1, 3, 5, and so on) are
connected together and led to a metallic ring on the left of
the disc. The same is done with the even strips, which are
led to the right. The two electrodes of a battery are led
through a key, K, to these two metallic rings and are con-
nected with them by means of brushes. Thus one ring, with
all the odd strips, is connected, say, with the positive, and the
other, with all the even strips, with the negative pole of the
battery. The current is led off by a second pair of brushes,
placed diametrically opposite to each other on the disc, in
the primary circuit, P, of an induction coil (fig. 171). Let us
suppose the upper brush to be connected with an odd strip,
the lower will then be connected with an even. The current
in the primary coil now flows in one direction. When the
disc is rotated, so as to bring the next pair of strips in

280 COMPARATIVE ELECTRO-PHYSIOLOGY

contact with the brushes, the upper will then be connected
with the even strip and the lower with the odd. Thus the
direction of the current will be reversed, and rapid rotation
of the disc will give rise to equi-alternating currents in the
primary of the induction coil. This will in turn induce
equi-alternating induction currents in the secondary, the
intensity of which can, as already said, be varied within wide
limits by appropriate changes of distance between the
primary and the secondary. The number of strips in the
apparatus used is fifty, and when the disc is rotated, by

Fic. 171. Method of Direct Effect of Excitation by Equi-
alternating Shocks

R, rotating reverser, in circuit with primary coil, P. Duration of stimula-
tion determined by metronome, M._ 8, secondary coil in series with
' specimen and galvanometer.

means of an electrical motor, at a rate of one revolution
per second, there will be fifty alternations of current in a
second. The duration of the application of the stimulating
shock to the tissue is regulated by a metronome, which
completes the primary circuit for a definite short length of
time. When the metronome, M, is so adjusted as to complete
the circuit for *5 second, then a stimulus of that duration will
be imparted at each stroke. A second interrupting key, not
shown in the figure, is included in the circuit. When this
key is closed, a single beat of the metronome gives a stimu-
lating shock of *5 second’s duration. ‘The key is now opened

DETERMINATION OF DIFFERENTIAL EXCITABILITY 281

for one minute for recovery. In this way, records of response
and recovery are obtained, at intervals, say, of one minute.
Another very effective means of producing equi-alter-
nating shocks is by the employment of an alternating-
current dynamo, driven by an electrical motor, M (fig. 172).
The alternating current is led to the primary of a Ruhm-
korffs coil in the usual manner. The motor is driven by an
electrical supply from the street mains, its speed being
adjusted by a regulation of the current, which is effected by

TO THE MAIN

Fic. 172. Excitation by Equi-alternating Shocks

M, motor, rotating armature of alternating-current dynamo, D; R, liquid
rheostat, in circuit with street-mains, for regulating speed of rotation
of motor; Pp’, idle coil; P, primary coil; I, resonating index; s,
secondary coil, in series with specimen and galvanometer. Duration
or excitation determined by pressure of key, K.

an electrolytic rheostat, R. As the dynamo is provided with
a permanent horse-shoe magnet, the intensity of the alter-
nating current is determined by the speed of rotation of
its armature. If the speed be kept always constant, the
number of alternations will also be constant, and the ex-
citing value of the electric shocks will depend simply upon
the distance of the primary from the secondary. It is thus
possible day after day to use the same intensity of stimu-
lation, and thus to compare the relative excitabilities of

282 COMPARATIVE ELECTRO-PHYSIOLOGY

different tissues. The constancy of the speed of rotation of
the alternating-current dynamo is secured by means of the
resonating index, I. This consists of a short steel spring
with a long index. When the frequency of alternation is
the same as the natural period of vibration of the spring, the
resonator is thrown into strong sympathetic vibration. At
first the rheostatic resistance, which determines the speed of
the motor, is made slightly too large. The movable plate is
now gradually brought nearer, till the proper speed has been
arrived at, and this point is at once indicated by the induced
vibration of the resonator. | .

A further difficulty has to be overcome in the main-
tenance of the uniformity of speed. When the open circuit
of the alternating dynamo is closed, by the interposition of
the primary of the Ruhmkorff’s coil, the speed undergoes
a sudden diminution, owing to the work which the dynamo
has now to perform. In order to avoid this fluctuation,
then, the dynamo circuit is kept closed by means of an idle
primary coil, P’, which is a duplicate of the primary, P, of the
Ruhmkorff’s coil. When the key, K, is pressed, the alter-
nating current is transferred from P’ to P. There is thus no
fluctuation in the speed of the dynamo, and the duration of the
closure determines that of the stimulus. I may mention
here, that instead of employing a separate motor to drive
the alternating-current dynamo, I have sometimes used, with
equal success, a motor transformer, giving rise to alter-
nating currents. It is easy to construct a very compact and
portable form of this latter apparatus.

In this manner we may apply uniform stimuli of equi-
alternating shocks at regular intervals of time, say of one
minute. The usual preliminary test of the successful
elimination of all sources of disturbance may here be made
in the following way. The kaolin ends of the non-polaris-
able electrodes are connected with each other, without the
interposition of a specimen, and alternating shocks from the
secondary are passed through the circuit. These should
give rise to no deflection in the galvanometer. It may be

Seg ON ee

ie ae

a.

DETERMINATION OF DIFFERENTIAL EXCITABILITY 283

said here that I use a D’Arsonval type of galvanometer, in
which, instead of a suspended needle, we have a suspended
coil. There is thus here not even the remote contingency
of disturbance which might arise from the demagnetisation
of the magnetic needle. Having thus tested, by null action,
the symmetry of the electrodes and the galvanometer, the
differentially excitable tissue, say the sheathing petiole of
Musa, is interposed, with its concave and more excitable
surface upwards. On now: applying excitation by equi-
alternating shocks, the responsive current will be found to
flow downwards, from concave to convex, giving a deflection
of the galvanometer, say to the right. And this deflection
will continue to be to the right, even if the battery current
(fig. 171) be reversed by means of key K. The direction of
the excitatory current, moreover, depending solely, as it does,
on the relative excitabilities of the two surfaces of the
specimen, will remain constant, even if the connections with
the secondary coil, S, be reversed. The zinc rod, N, of the
non-polarisable electrode in connection with the concave
surface (fig. 172) has thus, up to the present, shown induced
galvanometric negativity, the galvanometric deflection being
to the right. But if we exchange the zinc rods of the non-
polarisable electrodes, it will then be N’ which will be con-
nected with the more excitable concave surface, and it will
now be this electrode N’ which will show galvanometric nega-
tivity. This reversal of the galvanometer deflection with the
reversal of the electrodes affords additional confirmation of
the greater excitability of the concave surface of the specimen
of Musa. |

In these experiments the existing current of rest may
be balanced previously by a potentiometer. But this is not
absolutely necessary. I give below a series of records
obtained with a specimen of the sheathing petiole of Musa
(fig. 173), in which we know the inner or concave surface
to be more excitable than the outer or convex. The
responsive current is seen under this form of electrical
stimulus, as we found to be the case under mechanical and

284 COMPARATIVE ELECTRO-PHYSIOLOGY

thermal stimulation, to flow from the more excitable concave
to the less excitable convex. In order next to demonstrate
the physiological character of these responses, I subjected
the tissue to the action of chloroform, and the record in the
second part of the figure shows the consequent Bepresion
of the response.

The great delicacy and pliability of this mode of applica-
tion of stimulus enable us to attack many difficult problems,
on the difference of excit-
ability between two points in
a tissue, with perfect ease.
To how many distinct in-
vestigations it can be suc-
cessfully applied will be set
forth in detail in succeeding
chapters. As there is nothing
to prevent the two exploring .
electrodes from being applied
on any two points, however
distant, of the same organism,

‘Fic. 173. Photographic Record of Re-
sponse of Petiole of usa to Equi-
alternating Electric Shocks, before
and after Application of Chloroform.

it is seen that we have here
a means of determining, not
only the differential excit-

ability of any two points of
the same organ, but also that of any two organs of the same
specimen. For the present I shall, however, content myself
with giving a few instances only in illustration of the ex-
treme delicacy of this method in detecting physiological
differences as between two points.

We shall first turn our. attention to those physiological
modifications which are due to the a-symmetrical action of
the environment on the organism, and here we shall select
the case of the plagiotropic stem of Cucurbita. We have
seen that in the recumbent stem of this plant the tissue of
the upper side is rendered relatively fatigued by the con-
tinuous action of sunlight, and thus becomes permanently
less excitable than the lower side. We have also found that

DETERMINATION OF DIFFERENTIAL EXCITABILITY 285

while the natural resting-current was from the less excitable
upper to the more excitable lower side, the responsive cur-
rent under mechanical stimulation was in the opposite direc-
tion—namely, from the lower to the upper (p. 112). Using
now the electrical form of stimulus, we obtain results which
are identical. Fig. 174 gives a series of such responses
under equi-alternating electrical shocks. Curiously enough,
as pointed out in the last chapter, I have detected a similar
plagiotropy in the case of the eel. The head of the fish
was cut off, and voluntary action thus eliminated ; electrical
connections were then made, after a period of rest, with the
dark dorsal upper surface, and the
colourless skin of the ventral or
lower. A natural current was now
found to flow from the upper

Fic. 174. Photographic Record

of Responses of Plagiotropic Fic. 175. Electrical Responses of
Stem of Cucurbita to Equi- Eel to Equi-alternating Electrical
alternating Electric Shocks Shocks

Direction of responsive current from Current of response from ventral
ventral to dorsal surface. surface to dorsal.

surface to the lower, as in the case of the plagiotropic stem
of Cucurbita. Electrical excitation was now applied, and
the result was a responsive current from the more excitable
lower to the less excitable upper surface again, as in the
case of Cucurbita. In fig. 175 is seen a series of records in
illustration of this.

Another investigation which I thought might be interest-
ing had reference to the variegated colouring of certain
foliage leaves, A striking example of this is found in the

286 COMPARATIVE ELECTRO-PHYSIOLOGY

tropical elephant creeper (Pothos), the rich green of which is
barred by longitudinal streaks of milk-white. This dis-
tribution of colour is found even in the youngest and most
vigorous leaves. The question whether such colouring was
accidental or associated with physiological differences could,
I thought, be determined by the delicate mode of investiga-
tion which was now at my disposal. On making electrical .
connections, then, with the green and white portions of a leaf,
I found that the natural current of rest was from white to
green through the tissue, and, on further testing the differ-
ential excitability in the usual manner, the responsive current
was observed to flow from the green to the white. This
showed that pallidity was here associated with a depressed
physiological condition, |

CHAPTER XXII
RESPONSE OF ANIMAL AND VEGETAL SKINS

Currents of rest and action—Currents in animal skin—Theories regarding these
—Response of vegetal skin—Stimulation by Rotary Mechanical Stimula-
tor—Response of intact human skin—Isolated responses of upper and
lower surfaces of specimens—Resultant response brought about by differ-
ential excitability of the two surfaces—Differences of excitability between
two surfaces accounted for— Response of animal and vegetal skins not
essentially different—General formula for all types of response of skin—
Response of skin to different forms of stimulation gives similar results—
Response to equi-alternating electric shocks : (1) Method of the After Effect ;
(2) Method of Direct Effect—Response of grape skin—Similar response of
frog’s skin—Phasic variation of current of rest induced as result of
successive stimulation in (a) grape skin ; (4) frog’s skin ; (c) pulvinus of
Mimosa—Phasic variation in autonomous mechanical response of Des-
modium gyrans—Autonomous variation of current of rest—True current of
rest in skin from outer to inner—This may be reversed as an excitatory
after effect of preparation—Electrical response of skin of neck of tortoise —
Electrical response of skin of tomato —Normal response and positive after-
effect — Response of skin of gecko—Explanation of abnormal response,

IN this and the next few chapters it is my intention to make
an inquiry into the responsive peculiarities of the skin,
epithelium, and glandular tissues, alike in plant and animal.
By the study of such simple cases as are found in plants, it
should be possible to obtain’a clear insight into the various
factors which go to make the corresponding phenomena
in animal tissues so complicated and obscure as to be
difficult of reconciliation with each other.

It is not possible in a short space to give any but the
briefest summary of the work hitherto done on this extended
subject in animal physiology. All that can be attempted is
to indicate some of the leading theories and_results, at the
same time drawing attention to those outstanding questions
which still remain open. Some of the methods which I have

288 COMPARATIVE ELECTRO-PHYSIOLOGY

employed in the investigation of plant phenomena, moreover,
have proved so highly satisfactory that records will be given
of the results obtained by their means in the case of
animal tissues also. And this will, I hope, show the great
reliability and simplicity which it is thus possible to intro-
duce into the investigation as a whole.

With regard to the electrical effects in animal skin,
epithelium, and glands, the inquiry resolves itself into the
determination of, (1) the direction of the current of rest ; (2)
that of the excitatory current ; and, lastly, (3) a consideration
of theories regarding these. The first of these, the current
of rest, was found by Du Bois-Reymond and Engelmann in
the skin of frog to be ‘ingoing ’—that is to say, passing from
the outer surface to the inner. Hermann also found a
similar current in the skin of eel. He regarded the source of
electro-motive action as lying in the partial mucin-metamor-
phosis of single cells. From the fact that in the toad, where
the ingoing current is specially strong, the skin glands are
vigorously developed, and from the discovery by Rosenthal
that in the mucous glands of the stomach the current is also
ingoing, it was assumed that the observed electro-motive
forces were due to the glandular nature of the tissues. The
skin current of the frog and of the fish, and the glandular
current of the stomach, are thus usually regarded as due to
the same cause.

There is, however, a serious discrepancy in this view,
_ inasmuch as, while local stimulation of the upper surface of
the frog’s skin induces.a positive change, a similar stimula-
tion of an unmistakably glandular surface is found to bring
about a negative. If then the electrical effect on the skin
of frog be the same as on a glandular surface, the dis-
crepancy of their responsive reactions becomes inexplicable.

As regards the excitatory change, very diverse results
have been recorded when stimulus has been applied indi-
rectly —that is to say, through the nerve. This fact is not to
be wondered at, since the responsive effects are subject, as will
be shown, to numerous modifying influences. It is generally

Fo a ee ee

RESPONSE OF ANIMAL AND VEGETAL SKINS 289 —

supposed, in the preparations made for these experiments,
that it is one surface only which is electro-motive. I shall
show, however, that the responsive effects are brought about
by the differential excitability of the two. This response,
again, is modified by relative changes induced in the two
surfaces. And, in addition to these, still further compli-
cations are introduced when the stimulus is indirect—that is
to say, applied through the nerve. In this case, the relative
excitations of the two surfaces will be determined by the
particular distribution of the nerve-endings. Again, we
shall see that, in an isolated preparation, the nerve itself
is liable to undergo certain changes by which its trans-
mitted effect may be modified even to reversal (p. 530).
Thus, so long as it remains highly excitable, the transmitted
effect is one of true excitatory galvanometric negativity. But
with physiological depression, the conductivity of the nerve
is very much lowered, and the effect transmitted becomes
reversed to positivity.

For all these reasons, if we wish to study the specific
reactions of skin, epithelium, and gland preparations, it is
better to do so by observing them under direct stimulation.

Engelmann, in studying the responsive reactions to
direct stimulation of frog’s skin, found a negative variation of
the current of rest. Since the latter was naturally ‘ingoing,’
as regards the upper or’ epidermal surface, this meant that
the responsive current was ‘outgoing.’ Reid, again, work-
ing on the skin of the eel, obtained ingoing response, or
positive variations of the resting-current, by single induction
shocks in either direction. Biedermann, in the mucous
membranes of the tongue and stomach, obtained both
positive and negative variations of the current of rest,
Waller, using single induction shocks in either direction,
found in the digestive mucosa both ingoing and outgoing
responses, the former being much predominant.

Even under the simple conditions imposed by direct
stimulation, then, the results obtained are seen to be in-
consistent. They would appear to show both that the

U

290 COMPARATIVE ELECTRO-PHYSIOLOGY

responsive effects in the different preparations are different
and that, even in the same preparation, they may be reversed
under unknown changes of circumstances.

It appeared to me, as already said, that much light might
be thrown on the questions thus raised by means of an
investigation carried out on plants. The most perfect
method of experiment here would consist in observing the

separate responsive effects on upper and lower surfaces of

the preparation. Waller employed single induction shocks
for this purpose, observing the after-effect. But in this
case, the action of polarisation was not excluded. It
would thus be more satisfactory, in order to eliminate
this unknown element, to employ either a non-electrical
mode of stimulus or an electrical form which would leave
no resultant polarisation effect. The latter condition, as
we have seen, was fulfilled by the employment of rapidly
alternating currents, whose alternating components were
absolutely equal.

As regards the application of a non-electrical form of
stimulus, both thermal and mechanical forms may theoreti-
cally be employed. Engelmann and others used heated
metals in the proximity of one of the electrodes, for the
production of thermal stimulus. This, however, has the
disadvantage of thermo-electrical variation, due to unequal
heating of the two contacts. Besides this, there is also the
effect of a rising temperature, which, as we have seen, is
opposite to that of sudden variation, the latter alone consti-
tuting the excitatory effect. I have already explained
how these difficulties may be overcome by using thermal
shocks in which a sudden thermal variation is made to act
on both contacts at once. The resultant response thus
obtained was shown to be determined by the differential
excitability of the two contacts under examination. As
regards the mechanical mode of stimulation, previous
observers have employed pressure or friction. Such stimulus,
however, is at best merely qualitative. If it be applied at
the contact itself, objections may be taken to the effect, as

Rae a A meh

RESPONSE OF ANIMAL AND VEGETAL SKINS 291

due to, or modified by, the variation of contact resistance.
‘And if to avoid this the mechanical stimulus be applied, not
at the electrode, but at a neighbouring point, the results will
be quite different, according as the conductivity of the
intervening tissue is great or slight. In the former case
they will consist of the transmitted effect of true excitation ;
in the latter of the indirect effect, whose electrical sign is
the exact opposite.

Fic. 176. Rotary Mechanical Stimulator

Specimen of skin pinned on hinged platform which is pressed against
electrodes by elastic india-rubber. Electrodes rotated by cord, c c’.
S, antagonistic spring, made of elastic. Enlarged view of electrode
seen to the right. T, outer fixed brass tube ; T', inner rotating tube,
holding non-polarisable electrode. P, pumice-stone.

A perfect method of direct mechanical stimulation has
been described in Chapter III., the stimulus being vibrational.
But for investigations on limp structures, such as skin, this
method is not practicable, and the modification which I am
now about to describe is necessary, in order to meet the
difficulties of the case. The apparatus consists of a hinged
platform, P (fig. 176), on which the specimen is securely
pinned. The two electrodes, E and E’, rest with a definite
pressure on the two points A and B, whose excitatory re-
actions are to be studied. These electrodes have at their

U2

292 COMPARATIVE ELECTRO-PHYSIOLOGY

lower ends projecting pumice-stone cylinders of equal sec-
tions, soaked in normal saline. When the electrode E is
rotated, the mechanical friction induces local excitation of
the point A. B may also be subjected to similar isolated
excitation in the same way. In order that such successive
excitations may be quantitative and uniform, it is necessary
first that a definite area at A or B should be stimulated. In.

other words, there must be no lateral slip. For this reason |

the electrodes are passed through tubular holders which, from
the description presently to be given, will be seen to allow
rotation about a definite vertical axis. The extreme bases
of the pumice-stone cylinders are, as has been said, of equal
section. The glass electrode tube is tightly fixed, by means
of a cork, inside a brass rotating tube. The latter, again,
plays inside an outer brass tube, which is fixed. The inner
brass tube is provided with two collars, one below and one
above, by means of which rotation can take place without
up or down movement. A string is also wound round it, by
pulling which rotation is produced. The electrodes are
perpendicular to the plane of the platform which carries the
-specimen. It will thus be seen that any variation of the
surface subjected to stimulation is prevented.

The next difficulty to be overcome is that of liability
to variation in the pressure of the contact. It will be
remembered that the platform is hinged. It is further held
up against the electrodes by the tension of an elastic piece
of india-rubber or a spiral spring of steel. This pressure can
be regulated to a suitable value, and kept constant.

The final difficulty is to apply successive stimuli of equal
value, and to render them capable also of graduation from
low to high values. This could be secured by rendering the
successive rotations of the exciting electrodes equal in number
and ‘in time of execution. The intensity of stimulus might
then be increased by increasing the number of rotations or
the pressure of the electrodes on the specimen.

In order to apply successive rotations of definite number,
one end of the string wound round the ‘inner brass tube is

a

a

Sea hile A rea

RESPONSE OF ANIMAL AND VEGETAL SKINS 293 —

attached to a piece of stretched india-rubber, which is fixed
by its other end to the apparatus. The second end of the
string is tasselled, after being passed through a fixed ring.
This position of the string is adjusted by means of a knot, so
that the india-rubber at its other end is already in a state
of tension. When the tassel is now suddenly pulled and let
go, it gives rise to a number of rotations in the positive,
followed by an equal number of rotations in the opposite
direction, the latter work being performed by the stretched
antagonistic spring. It should be remembered that a
mechanical rotation, whether p/us or mznus, gives rise to the
same excitatory reaction. Next, to make the number of
rotations definite, let us suppose the inner brass tube to have
a circumference say of I cm. If the string be now pulled
through a distance of 5 cm., and let go, there will be five
rotations in the positive, followed by five rotations in the
negative direction. A second knot in the string, at the
distance of 5 cm. from the first, exactly limits the length of
the pull; and increase or decrease in the intensity of the
stimulus.can be brought about by a change in the distance
of the regulating knot.

The distance between the two electrodes being always
the same, the resistance of the interposed tissue remains
approximately constant. To nullify any accidental variation,
a high and constant external resistance is interposed in the
galvanometer circuit. When the excitatory electro-motive
variation of the specimen is very great, it is possible to use
an external resistance as high as one million ohms. It should,
however, be remembered that even if there be any unavoid-
able variation of resistance, it will not in any way affect the
discrimination of sign of the characteristic electro-motive
response. For the excitatory effect at either electrode may
be tested by repeating the experiment with the other. The
experiments which will be described afforded definite and
characteristic records, which were found capable of repetition.
The physiological character of such responses was further
demonstrated by repeating the experiment, after killing the

294. COMPARATIVE ELECTRO-PHYSIOLOGY

tissue with boiling water, when these electro-motive variations
were found to disappear. How very reliable these responses
can be rendered is shown by the photographic record in
fig. 180, which is of very special interest, giving as it does the
record of responses afforded by the intact human skin.
Turning now to the nature of the response of. the skin,

it has been found by Engelmann and others, as already said,
that in the frog, while the natural resting current is from the —

outer surface to the inner, the responsive current is from
inner to outer. Dr. Waller, again, undertook to analyse the
constituent elements of this response, by passing induction
shocks along each of the surfaces, first upper and then lower,
and in both directions. He then observed the after-effect
at one of the excited points, in relation to an indifferent
point. In this way he found that an excited point on the
upper surface becomes galvanometrically positive, the current
being thus outgoing. The inner surface, however, he found
to be ineffective. When an induction shock is passed across
the tissue, the resultant response from lower to upper is thus,
according to Dr. Waller, due to induced positivity of the
upper surface.

With vegetable specimens, however, such as the outer
skin of apple, the results obtained by him were opposite to
those of the frog’s skin. ‘The responsive currents were here
found to be ingoing, the excited point being galvanometrically
negative. The explanation offered, in regard to these results,
is that living tissues have the peculiarity of responding by
‘blaze currents’ to electrical shocks. The use of this phrase,
however, as already said, offers no real explanation ; but even
apart from this point, the question remains, Why should the
blaze currents, so called, be directly opposed in the cases of
frog’s skin and of the particular vegetable skins which are
mentioned, respectively? In answer to this, the hypothesis
put forward by Dr. Waller is, that the difference arises from
the different natures of animal and vegetable protoplasms.'

' ¢ Vegetable protoplasm is in major degree an instrument of synthesis and
accumulation, in minor degree the seat of analysis and emission, Animal

a =
BOS Ae hk Pe ESS Satna, yt

RESPONSE OF ANIMAL AND VEGETAL SKINS 2905 —

I shall, however, be able to adduce facts and considera-
tions from which it will be possible to arrive at a simpler and
more conclusive explanation of these phenomena, on the
basis of the differential physiological excitability of the two
surfaces. I shall show, moreover, that the difference between
animal and vegetable protoplasm, thus assumed to exist, has
nothing to do with the question.

We have seen that when the physiological activity of a
tissue is in any way impaired, its normal excitatory re-action
of galvanometric negativity is depressed. This may even go
so far as to cause an actual reversal of the response, to
galvanometric positivity, as we found in the case of depressed
tissues (p. 84). Taking a vegetable specimen, then, say a
hollow petiole or peduncle, we find that the outer surface,
which is habitually exposed to the manifold influences of the
environment, becomes histologically modified, being much
more cuticularised than-the inner. Thus these outer and
exposed cells generally become reduced in size, and thick-
walled, with little protoplasmic contents. Hence, as regards
functional activity, these epidermal cells are in a_physio-
logical sense very much degraded. We should then expect
their excitability to be proportionately lowered in comparison
with, say, the inner surface of the same tube, protected as
that has been from outside influences. And the variation of
physiological excitability thus induced may involve not only
the surface, but also the subjacent layers to a certain extent.

Theoretically, then, the induced galvanometric negativity
of the outer would be less than that of the inner surface,!
and simultaneous excitation of both, by whatever means
produced, should give rise to a resultant responsive current

protoplasm is in major degree an instrument of analysis and emission, in minor
degree the seat of synthesis and accumulation. The vegetable, in most immediate
contact with inert things, combines, organises, and accumulates, The animal,
in less immediate contact with inert matter, disrupts, utilises, and dissipates
in their fragments organic compounds that it has received ready made from
other animals and from plants.’—Waller, Signs of Life, p. 85.

1 This refers to normal skin, and not to that in which the surface is typically
glandular.

296 COMPARATIVE ELECTRO-PHYSIOLOGY

from inner to outer. The degree of this diminution of
excitatory negativity in the outer surface, moreover, cul-
minating as this may in actual positivity, will depend upon
the extent of its transformation. In connection with this
it should be remembered that, in order to bring out the
differential excitabilities of the two surfaces, it is necessary
to apply localised stimuli of an intensity not too excessive.
For, if the stimulus be very strong, there is always a
possibility of its affecting deeper layers of the tissue and
thus causing complications in the resultant excitatory
changes. The intensity of stimulus which may be safely

used without bringing about

3 y such complications will depend
b- a zl on the conductivity of the
Pd A creme tissue. Epidermal cells are,

ee Gar pas generally speaking, feeble con-
os | ductors, but in this matter it
ee must be understood that the

; differences in this respect be-
Fic. 177. Diagram Representing ‘ :
Different Levels of Excitability, tween different tissues are not
Pika: sels ease eee ' absolute, but a question of
Diagram to right of figure shows ;
degree, and may to a certain

how resultant up response (inner
to outer) may be obtained when extent be modified under dif-

induced change at A is plus, and
at B minus, or when induced ferent circumstances. Thus a
eee less negative than feebly conducting tissue, under
a favourable condition of tem-
perature and strong intensity of stimulation, will become to
a certain extent conducting. Highly conducting tissues like
nerve, on the other hand, under unfavourable circumstances

may, as I shall show later, be converted into very feeble

conductors.
Returning now to the question of the responsive reactions

of skin, we see the theoretical possibility of the following
typical reactions. Let the scale of excitabilities be repre-
sented by diagram to the left of fig. 177. Now, if the trans-
formation of the outer epidermal surface, A, be maximum, the
sign of its reaction will exhibit the greatest extent of deviation

ee

RESPONSE OF ANIMAL AND VEGETAL SKINS 267

from the normal negativity. That is to say, its response will
become absolutely positive, as represented by a above the zero
line. The response of the inner surface, B, may be normal and
strongly negative, as represented by e below the zero line.
When both these surfaces, then, are simultaneously excited,
the excitatory positive variation, or ‘outgoing’ current at A,
will conspire with the ‘ingoing’ current at B and the
resultant electro-motive difference will be B, + A,, the direction
of the responsive current being thus from inner to outer.
But the same resultant up-response will also be induced, even
if the reaction of both surfaces be negative, provided only
that that of the outer, A,, be less negative than that of the
inner, B,, as explained by the diagram to the right of fig. 177.
The responsive current will then be represented as B,—A,,
that is to say, as proceeding from the more negative B to
the less negative A. We have thus examined the two
extreme cases possible under the following formula, in which
the arrows show the direction of the responsive current, from
the more to the less induced negative:

end>-co> boa.

I shall next proceed to demonstrate the existence of
these two extreme types, taking vegetable skins as the
experimental specimen. It was supposed by Dr. Waller, as
will be recalled here, that owing to characteristic differences
between animal and vegetable protoplasm the response of
vegetable skin was opposite to that of animal skin: that is to
say, the former was ‘ingoing’ and the latter ‘outgoing.’ That
this generalisation is not, however, justified, will be seen from
the experiments which I am about to describe, carried out
on the skin of grape.

These results, it should here be pointed out, are not
dependent upon any one method of inquiry, for each
problem was subjected to attack and analysis by four
different modes of experiment. The first of these (1) was by
the Rotary Method of Mechanical Stimulation. This
method has the great advantage that by it the absolute

298 COMPARATIVE ELECTRO-PHYSIOLOGY

response of each surface is displayed separately, without
either being affected by the other. There is here, moreover,
no complication due to the polarisation factor, inevitable
when uni-directioned induction shocks are employed for
excitation. Thus, after the individual responses of each
surface have been analysed, we are able to arrive at.a definite
conclusion as to what would be the character of the resultant

response if both the surfaces were simultaneously excited. |

This conclusion is then submitted to three other tests. Thus,
(2) the two surfaces of the specimen are subjected simul-
taneously to the same thermal shocks, according to the
method already described. Again, (3) the Method of
the After Effect under equi-alternating shocks is employed.
And, finally, (4) the Direct Effect of these equi-alternating
shocks of moderate intensity is recorded. The results
obtained by all these diverse methods are in complete
concordance with each other, and fully support the theo-
retical inferences which have already been made.

I took the skin of a ripe muscatel grape, such as are
available in Calcutta. On making the galvanometric con-
nections with the outer and inner surfaces, a resting current,
-C, was found to flow in the skin from the outer to the
inner, just as in the skin of the frog (right-hand diagram,
fig. 178). The grape skin was now mounted in the rotary
stimulating apparatus, first, for the stimulation of the outer
or epidermal surface, with the outer layer placed upwards.
The distance between the two electrodes was always the
same—namely, 2 cm. On now stimulating one of the two
contacts, response took place by the induced galvanometric
positivity of that point. That is to say, the current was
‘outgoing, into the galvanometer circuit, from the surface
of the skin. When the second point was now stimulated the
deflection previously obtained was reversed, the second contact
thus also exhibiting galvanometric positivity on excitation.

The position of the skin in the apparatus was now
changed, the inner surface being placed upwards. In this
way points diametrically opposite to those in the last case

eT ee

Pw a cn rt i i es ti.

RESPONSE OF ANIMAL AND VEGETAL SKINS 299 —

were subjected to excitation. It was now found that the
responses of the inner surface were normal—that is to say, of
galvanometric negativity. I give here (fig. 178, a) records
of two successive sets of responses obtained from the external
and internal points A and B. These records clearly demon-
strate that the resultant up-response, on simultaneous exci-
tation of the outer and inner surfaces, is brought about
by the induced galvanometric positivity of the outer added
to the induced negativity of the inner surface. As the resist-
ance of the circuit in the two successive experiments was
maintained approxi-

A B
mately the same, the
. + bs
amplitude of these re- Pile F
sponses gives a fairly el t
a . One
sf \

accurate idea of the ta oe
relative electrical effects F

4
induced on the two sur- Fic. 178. Electrical Response of Grape-
faces. The positive or skin to Rotary Mechanical Stimulation

(a) A, positive response of outer surface ;
B, negative response of inner surface ;

‘outgoing’ effect of the

outer surface is here (6) c, current of rest, from outer to inner ;

; R, excitatory response from inner to outer,
slightly greater than the consisting of summated results of positive
‘ ingoing’ effect. The pig aes of outer with negative response

diagram in fig. 178, 3,
shows how the individual effects conspire to give rise toa
responsive current from the inner to the outer.

In order to test the reality of the correspondence between
this response of the grape skin and that of the frog, I now
repeated these experiments, employing the same apparatus
for mechanical stimulation, on the skin of the frog. From
the records given in fig. 179 it will be seen that the isolated
response of the outer surface is positive, or ‘outgoing,’ that
of the inner being negative, or ‘ingoing. The amplitude
of the former was, however, much greater than that of the
latter. These responses disappeared altogether when the
tissue had been killed by immersion in boiling water. From
isolated responses obtained by means of induction shocks,
Dr. Waller had been led to regard the outer surface of frog’s

300 COMPARATIVE ELECTRO-PHYSioLOGY

skin as alone active, the inner being, to his thinking, in-
effective. This particular result may possibly be accounted
for by supposing that he used a stimulus intensity which
was not sufficiently strong. In my own experiments I
obtained clear demonstration of the effectiveness of both
surfaces in opposite ways electrically, though the effect
obtained from the outer was undoubtedly the more intense
of the two. By comparing these two experiments, then, on
the grape skin and skin of frog, it will be seen that the
inference that the vegetable protoplasm reacts in any way

A B
o =
c R
A B A ae
ee es B —e
v f
b
a a
Fic. 179. Electrical Response of Frog’s Skin to Rotary Mechanical

Stimulation

(a) A, positive response of outer ; B, negative response of inner; (a’) A
and B exhibit abolition of response in skin on boiling ; (4) Cc, current
of rest from outer to inner ; R, excitatory response from inner to outer,
being summated effect of positive response of outer and negative

response of inner.

essentially different from that of the animal is quite unjus-
tified. How widely applicable is the method of mechanical
excitation by rotary stimulus will be seen in an attempt,
successfully carried out, to determine the very difficult ques-
tion of the characteristic response of the intact human skin.
This will be seen in the following record of the results
obtained with the skin of a forefinger. The responsive elec-
trical changes represented by the down records, exhibit induced
galvanometric positivity of the excited surface (fig. 180).

I shall next describe the results obtained by simultaneous
excitation of the inner and outer surfaces of grape-skin.
The responses now given, under stiniulation by thermal

EE ee

RESPONSE OF ANIMAL AND VEGETAL SKINS 301

shocks, are seen in fig. 181, the resultant current being seen
to be ‘ up ’—that is to say, from the inner to the outer.

On observing the excitatory after-effect of equi-alternating
shocks, the results were found to be the same, the responsive
current being now once more from the inner to the outer.

I next took a series of records of the direct effect of
equi-alternating shocks, the results of which were precisely
the same as before. On applying stimulation, by exactly
equal and alternating shocks, we, as already explained,

Fic. 180. Photographic Record

of Electrical Responses of Fic. 181. - Photographic -Record of
Upper Surface of Intact . Electrical Responses of Grape-skin
Human Forefinger to Rotary to Thermal Shocks at Intervals of a
Mechanical Stimulation. Minute

Down responses here indicate Responsive current from inner to outer,
induced galvanometric posi-
tivity.

obtain a result which is due solely to the differential excita-
tion of the two opposite surfaces. This is not complicated
in any way by the factor of polarisation, although the latter
could not have failed to be present if the exciting shocks
had been one-directioned. Under the conditions of these
equi-alternating shocks, then, a certain effect is often
seen, in the phasic variation of the base-line, which is ex-
tremely characteristic. We have already seen (p. 98) that
when a tissue is subjected to repeated or continuous stimula-
tion, its condition undergoes a phasic or periodic variation.
Thus from a neutral or positive condition, it may pass into
one of maximum contraction or galyanometric negativity, to

302 COMPARATIVE ELECTRO-PHYSIOLOGY

be subsequently reversed to positive once more. Such phasic
changes, moreover, may be repeated. They find visible
indications in appropriate shiftings of the base line of the
record. Similar effects are also shown in the differential
response as seen in the records given in fig. 182; this feature
; is very noticeable. We here ob-
tain the resultant response of the
two surfaces of grape-skin, from
. the inner to the outer. As the
result of the series of stimuli
applied, the existing current of

FIG. 182. Photographic Re-
cord of Electrical Responses
of Grape-skin to Stimula-
tion by Equi-alternating
Electrical Shocks at In-
tervals of a Minute Fic. 183. Photographic Record of Series

of Electrical Responses of Frog’s Skin to

Equi-alternating Electrical Shocks applied

Responsive current from inner

to outer. Note periodic

variation of resting-current, at Intervals of One Minute

causing shifting of base-line, Direction of responsive current from inner to
down and up. outer. Note also variation of base-line.

rest undergoes a periodic variation. If this had remained
constant, the base-line would have been horizontal. In the
present case, the original current of rest was from outside
to inside. This, at first, underwent an increase; then a
decrease ; to be followed, later, by another increase. Thus,
in the course of about ten minutes, it exhibited an alterna-
tion of almost one whole cycle.

In the next figure (fig. 183) I give a series of results obtained

RESPONSE OF ANIMAL AND VEGETAL SKINS 303

with frog’s skin in direct response to equi-alternating shocks.
Here we find the usual ‘up’ responses, showing that, as
before, the direction of the responsive current is from within
to without ; and here also we see the existing current of rest
undergoing a periodic change.

It has now been fully demonstrated that the response
of skin is determined by the differential excitabilities of its
two surfaces, upper and lower, that of the lower being. the
greater. That the resultant responsive current from lower to
upper, is in such cases brought about by the greater excit-
ability of the lower, has been fully shown, in a previous
chapter, by experiments on
the pulvinus of J/zmosa.
I next made records of a
long series of responses
given by the last-named
specimen, with the object
of finding out whether or
not these also exhibited a
periodic variation of the
resting-current similar to
those just observed in the
anisotropic skins of grape

Fic. 184. Photographic Record of Trans-
and of frog. Electrical verse Response of Pulvinus of A/imosa

: to Equi-alternating Electrical Shocks
connections were made : ; . .
The direction of the responsive current is

with diametrically opposite from the more excitable lower to the
; less excitable upper. Note the cyclic
points on the Upper and variation of the current of rest.

lower surfaces of this

organ, and they were subjected to equi-alternating shocks.
Owing to the conducting power of the tissues, it was
not now the upper and lower skin surfaces merely, but
the upper and lower halves of the organ that became
excited. And the responsive current was from the lower
to the upper, as already demonstrated. In the particular
record seen in fig. 184, the general resemblance to the
responses of skin is sufficiently obvious. The interesting
feature of this record is the periodic changes in the resting-

304 COMPARATIVE ELECTRO-PHYSIOLOGY

current, which exhibit a complete cycle in the course of
thirteen minutes. Thus, as a consequence of the after-effect
of stimulus, a cyclic variation of relative conditions is
induced, as between any two anisotropic surfaces, such as
those of skin or pulvinus. This cyclic variation of relative
conditions is indicated by the concomitant variations induced
in the resting-current, shown in the shiftings of the base line.

I have been able, further, to demonstrate the interesting
fact that such phasic variations are capable of exhibition |
even through mechanical response. I have already ex-
plained that autonomous pulsations, such as those of the
lateral leaflets of Desmodium gyrans, may be regarded as
the after-effect of stimuli previously absorbed and held
latent by the tissue. In taking the record of a series
of such pulsations, I have often found phasic variations
to occur, similar to those obtained with long-continued
response of skin or pulvinus. If, for example, the lower
half of the pulvinus of the lateral leaflet of Desmodium
undergoes an increase of turgidity above the average, that
half will become more convex, and the base-line of the
record will be correspondingly tilted. The converse will
take place under the opposite change. Thus the phasic
variations shown in the record (fig. 185) clearly indicate
that the relative turgidities of the two surfaces of an
anisotropic organ may undergo a periodic change. The
corresponding electrical expression of this we have seen in
the variation of the current of rest. This variation may
sometimes be so great as actually to reverse the normal

current of rest. Thus, while under normal standard con-
ditions the resting-current in the pulvinus of Mzmosa is from
the upper half to the lower, across the organ, this normal
direction may sometimes be found to be reversed.

It may now be asked, What is it, in the case of the skin,
which determines the respective directions of the resting-
current and the current of response? We have seen that
the current of rest in the frog’s skin, from outer to inner, is
generally attributed to the possession of glands by the outer,

RESPONSE OF ANIMAL AND VEGETAL SKINS 305

a supposition seemingly supported by Rosenthal’s discovery,
already referred to, that an apparently similar ‘ingoing’
current was to be observed in the mucous coat of the frog’s
stomach. Against this may be urged the conclusion, to
which Hermann drew attention, that the skin glands are nor-
mally nearly closed to the external surface, and cannot there-
fore have any external galvanic relation. There are, moreover,
other arguments. First, a similar current is observed in the
case of grape-skin, where there is no special glandular layer.
Second, the specific response of a glandular surface is

HE MH

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Wi iH if! Hii yy iii TAA),
}!

itt ALE My
Hill Ih)

Nyy AWE Mii Wi

6 P.M. 9 P.M. I2

nA AAV

aaa wt WW) iyo

WV VV"

12 3 A.M. 6 A.M.

Fig. 185. Continuous Photographic Record of Autonomous Pulsaticn of
Desmodium gyrans from 6 P.M. to 6 A.M.

The lower record is in continuation of the upper. Note phasic variation.

definite, and is by galvanometric negativity, whereas the
response of the outer surface of frog or grape skin on
excitation is by galvanometric positivity. And, thirdly, we
shall see that the current observed in the mucous membrane
of stomach is most probably not the natural current of rest,
but the excitatory after-current.

It will be remembered, however, that we have always
found the natural current to flow ‘in the tissue from the less
to the more excitable, and the current of response in the
opposite direction. In the skin, owing to physiological and

iS

306 COMPARATIVE ELECTRO-PHYSIOLOGY

histological modifications, the outer surface is reduced in
excitability. The epidermal layers have little protoplasmic
contents, and may be transformed in various ways, becoming
corneated or cuticularised. The extent of such transforma-
tion may be small or great, but the external layer will as
a general rule become less excitable than the inner tissue.
Hence, under normal conditions, we have a current of rest
from without to within.

If the inner layer be only moderately excitable, or if its
power of recovery from excitation be great, then the dis-
turbance caused by the prepara-
tion of the specimen will be
slight, or will pass off quickly.
It is to be remembered that as
the inner surface is the more
excitable, the responsive current
due to the mechanical stimulus
of preparation wil! be from
inner to outer; and therefore
its after-effect, proving in certain

Fic. 186. Photographic Record cases persistent, may give rise
of Electrical Responses in Skin to g current apparently the re-
of Neck of Tortoise to Stimulus PP y
of Equi-alternating Electrical verse of the true normal current.
aera at Intervals of One Thus the direction of the current

The direction of the responsive of rest, which we should have
current was from inner to inferred theoretically to be from
outer. The so-called current ‘
of rest was also in this case, the less to the more excitable,
owing to the excitatory after- may occasionally be found re-
effect of preparation, from inner ; ;
to outer. versed, owing to the excitatory

after-effect of preparation. The
current of rest, moreover, is liable to autonomous periodic
variation, as we have seen.

The most satisfactory method of determining the relative
excitabilities of two surfaces, then, lies in subjecting them to
simultaneous excitation, and observing the direction of the
responsive current. In the skin, unless the tissue was

fatigued, I have always found this to be from the more

RESPONSE OF ANIMAL AND VEGETAL SKINS 407

excitable inner to the less excitable outer, even in those
cases where the normal direction of the resting-current had
been reversed, as an excitatory after-effect of preparation.
This fact is well illustrated in the following record, taken
with the skin of the neck of tortoise. As an after-effect of
preparation, the resting-current so called was here reversed,
flowing from inner to outer. But the excitatory responsive
current was nevertheless from the more excitable inner
to the less excitable outer (fig. 186).

It was stated at the beginning of this chapter that the
resultant response from inner to outer merely expresses the
general fact that the vs
excitability of the inner
is greater than that of
the outer. And this will a
still remain true, even A :
when the transformation ae
of the external layer is — iN Se 3
not so great as actually e : 4

to reverse its individual
g Fic. 187. Isolated Responses of Upper and
galvanometric response Lower Surfaces of Skin of Tomato to Rotary

from negativity to posi- Mechanical Stimulus

an - (a) A, negative response of feeble intensity in
tivity. The experi- rs outer ahce : “ negative response of iach
mental results obtained greater intensity in inner surface ; (4) Cc, cur-
‘ : ‘ rent of rest from outer to inner. Resultant
with the skin of ripe excitatory response from inner to outer, due

tomato form a case in to greater induced galvanometric negativity
point. The natural ndeoat |

current of rest is here, as usual, from the outer to the
inner, and the excitatory responsive current in the opposite
direction. But from the analysis of individual responses,
on the outer and inner surfaces, obtained by means of
the rotary apparatus for mechanical stimulation, it will be
seen (fig. 187) that both the surfaces alike give the
normal excitatory response of galvanometric negativity.
This responsive negativity of the inner, B, is, however,
very much greater than that of the outer. The resultant

response, then, representing as this does the difference in
; b dy

308 COMPARATIVE ELECTRO-PHYSIOLOGY

degree between two negativities, is still from inner to
outer, owing to the greater excitatory reaction of the
inner.

That the direction of the resultant response is actually
from the inner to the outer is seen in the series of records
given in fig. 188. The stimulus consisted of equi-alter-
nating electrical shocks, applied at intervals of one minute.
The record shows negative responses, followed appa-
rently by the positive after-effect. In order to observe the
peculiarities of this response in greater detail, the record
was taken on a faster-moving drum (fig. 189). From this
figure it will be seen that
there was a short latent period
of no responsive reaction.
Response then rose to a
maximum, and again sub-
sided. After now reaching
the zero position, the record
proceeded in the positive
direction, and again reverted
back to zero. In_ similar
records, the occurrence of

Fic. 188, Photographic Record of
Series of Responses in Skin of

Tomato under Equi-alternating
Electrical Shocks applied at In-
tervals of One Minute

Direction of resultant current from
inner to outer followed by feeble
opposite after-effect.

this latent period, and _ posi-
tive after-variation, has been
adduced by certain physio-
logists as affording visible
demonstration of the exist-

ence of opposite processes of assimilation and dissimilation.
It has been supposed that the various features of the response
were the outcome of a sort of tug-of-war between the two
opposed forces, the preliminary pause being the expression
of a short-lived balance, while the subsequent negative and
positive variations were to be regarded as indicating the
predominance, now of the one process, and then of the other.
That in the present case such an assumption is unwarranted
will be evident when we observe the isolated responses of the
upper and lower surfaces separately (fig. 187). In each of

RESPONSE OF ANIMAL AND VEGETAL SKINS 309

these we see the normal response of galvanometric negativity,
followed by recovery, without evidence of any antagonistic
process, such as might give rise to subsequent positivity.
The difference between these two responses lies simply in
their time-relations. On simultaneous excitation of the two,
the predominant negativity of the inner gives the first half
of the negative response. The persistence of the excitatory
reaction of the outer, on the other hand, after the subsidence
of the effect on the inner, gives rise to the apparently

Fic. 189. A Single Response of Skin of Tomato to Equi-alternating
Shock recorded on Faster Moving Drum

positive after-effect. Thus, here the supposed tug-of-war
between two opposite processes of assimilation and dis-
similation is, in reality, between two normal responses
having ‘different time-relations. It is from a failure to
recognise the fact that the excitatory reaction is not con-
fined to one, but takes place on both surfaces, that such
erroneous assumptions as that referred to have often been
occasioned,

310 COMPARATIVE ELECTRO-PHYSIOLOGY

The result which I have described—namely, a greater
responsive negativity of the inner than of the outer, giving
rise to a resultant responsive current from inner to outer—is
that which occurs in the majority of cases with tomato.
But, as establishing a continuity between this response and
that of grape-skin, | may mention the interesting fact that
in a few instances I obtained records in which, while the
inner surface on excitation exhibited a strong negativity,
the outer, under the same stimulus, exhibited a feeble
positivity.

The normal response of skin is sometimes, however,
found to be reversed, and no explanations have yet been

Fic. 190. Photographic Record of Series of Normal Responses
in Skin of Gecko

Responsive current from inner to outer surface.

offered to account for this. But I have shown two definite
conditions of universal application, which are liable to bring
about the reversal of normal response. These are, on the
one hand, sub-tonicity, and, on the other, fatigue. Should
the condition, in a given case, be the former of these, then
the impact of stimulus will of itself, by raising the tonic
condition, restore the normal response. ‘Thus in a case of
abnormal positive response due to sub-tonicity, an inter-
vening period of tetanisation will tend to convert the ab-
normal response to normal. An abnormal positive will thus
pass into diphasic, and thence into the normal negative.

RESPONSE OF ANIMAL AND VEGETAL SKINS 311

For the following experiments, I took the skin of gecko,
which can be detached from the body with very little injury.
This animal offers remarkable facilities for many electro-
physiological experiments. Its isolated tissues can be main-
tained in a living condition for a very long time. Its sciatic
nerve affords us a specimen about 15 cm.in length. Thus
for electro-physiological investigation, it provides much
greater advantages than the frog.

Fic. 191. Photographic Record of Abnormal Diphasic Responses in Skin
of Gecko, converted to Normal, after Tetanisation

Taking a specimen of gecko skin, which was in a favour-
able tonic condition, I obtained the series of normal responses
to equi-alternating shocks, which is given in fig. 190. The
responsive current here flowed from the inner to the outer
surface. I next took another specimen, which was in a less
favourable tonic condition, and obtained records of its
responses, here seen (fig. 191) to be diphasic. An intervening
period of tetanisation is seen, however, to restore the normal
response.

CHAPTER XXIII
RESPONSE OF EPITHELIUM AND GLANDS.

Epidermal, epithelial, and secreting membranes in plant tissues—Natural
resting-current from epidermal to epithelial or secretory surfaces—Current of
response from epithelial or secretory to epidermal surfaces—Response of
Dillenia—Response of water-melon—Response of foot of snail—The so-
called current of rest from glandular surface really due to injury—
Misinterpretation arising from response by so-called ‘positive variation’
—Natural current in intact foot of snail, and its variation on section —
Response of intact human armpit—Response of intact human lip—Lingual
response in man—Reversal of normal response under sub-minimal or super-
maximal stimulation—Differential excitations of two surfaces under different
intensities of stimulus, with consequent changes in direction of responsive
currents, diagrammatically represented in characteristic curves—Records ex-
hibiting responsive reversals,

HAVING now seen how the responsive peculiarities of the
epidermis may be elucidated by the responses of similar
tissues in the plant, we shall next take up an inquiry as to
the parallelism between the responses of epithelium and
glands in animal and in vegetable tissues. And here, as in
the last case, we shall find the obscurities of the one made
clear by the study of the other.

If we take the hollow peduncle of a Uviclis lily, and,
cutting this into longitudinal halves, take a portion from the
upper end of one, we shall observe noticeable differences
between the investing membranes of the outer and inner
surfaces. On the outer, as we have seen elsewhere, the cells
are dry, thick-walled, and cuticularised. This surface then
is naturally distinguished as epidermal. The internal mem-
brane of the hollow tube, however, is very thin, and its cells
very little differentiated (fig. 192). The internal membrane
may thus be distinguished as epithelial.

If now we examine this inner membrane continuously

A ote ate 34K =]

RESPONSE OF EPITHELIUM AND GLANDS 313

from the top to the bottom, at the point where the peduncle
rises from the bulb, we shall find that the epithelial layer of
the upper end passes imperceptibly into a markedly secret-
ng (glandular?) layer at the lower. By this, secretion is
constantly taking place, filling up the hollow tube with fluid.
In one instance which I measured, the amount of this
secretion was as much as IO grammes in the course of the
day. These secreting cells in this, which may be called the
glanduloid layer, are very thin-
walled and excessively turgid,
and, from an evolutionary point
of view, these gradual transitions
from epidermal to epithelial, and
from epithelial to secretory layers,
observed under conditions of such
great simplicity, are extremely
interesting. |

When we come to test the
electrical reactions of these tissues,
we find, on making electrical con-
nections with the external epi-
dermis and the internal epithelium,
that a natural current flows in the
tissue from the external surface yc, 192, Transverse Section of
to the internal: This would indi- tissue of Hollow Peduncle of

: ‘ Uriclis Lily
cate that the internal was the Cells of epidermis are small and
more excitable of the two. This thick-walled, those of inner

: . surface large and thin-walled.
conclusion is confirmed on the
application of simultaneous excitation to outer and inner ;
for the direction of the responsive current is found to be from
the internal surface to the external. _

If, next, electrical connections be made with the.epidermal
and secretory layers, a current of rest is once more observed
from the external to the internal. On excitation, a very
strong electrical response is given, its direction being from
the highly excitable secreting layer to the less excitable
epidermal. From these experiments we see that the

314 COMPARATIVE ELECTRO-PHYSIOLOGY

epidermal cells are, generally speaking, the least, and the
secreting cells the most, excitable.

I shall show, moreover, that all the responsive character-
istics of these secretory cells are to be found repeated in those
admittedly glandular layers which occur in the lining of the
pitcher of Vepenthe, and cover the upper surface of the leaf of
Drosera. Before, however, entering upon the consideration of
these highly differentiated organs of Nepenthe and Drosera, -
which are further characterised by some of the digestive
functions, I shall first discuss in detail the reactions of a
simpler type of vegetable organ. This is exemplified by
a single unripe carpel of Dz/lenia indica, already referred to,
When this is carefully removed from the inside of the
pseudocarp, and opened, the inside is found to be filled with
a gelatinous secretion. This is gently removed, and electrical
connections are made with the inner and outer surfaces. It
must be borne in mind that these vegetable organs, being not
highly excitable, admit of experimental preparations being
made with little or no excitatory effect of injury. Allowing
now for a period of rest after making the preparation, it will
always be found that the current of rest is from the outer
layer to the secreting inner layer, which latter is thus,
relatively speaking, galvanometrically positive. From the
fact which we have generally observed, that the natural
current of rest is from the less to the more excitable, it would
appear, then, that the inner layer is here the more excitable.
This conclusion, moreover, is in agreement with the inference
already arrived at, in connection with the tissues of the
Uriclis lily, that secreting cells as a rule are relatively the
most excitable. This inference may, however, be subjected
to the test of direct experiment.

I first tested the response of the same specimen by means
of thermal shocks, applied to both surfaces simultaneously.
The definite direction of the responsive current, from the
inner to the outer, across the tissue, proved conclusively that

* the inner surface was the more excitable, becoming as it did,
galvanometrically negative in relation to the outer, A similar

RESPONSE OF EPITHELIUM AND GLANDS 315

effect was obtained as an after-effect of equi-alternating
shocks. I next took records of the direct effect of equi-alter-
nating shocks. The direction of the responsive current was
found, as before, from the inner to the outer.

In the fruit of water-melon we obtain another specimen
whose interior cavity is filled with secretion. On making a
suitable preparation of this specimen, and arranging electrical
connections with the outer epidermal and inner secretory
surfaces, I found the responsive current, under equi-alter-
nating electrical shocks, to be from the inner secretory to the
outer epidermal. Fig. 193 gives a photographic record of
these responses.

From the typical responsive effects thus obtained with
vegetable specimens under the simplest conditions, we are
enabled to see that the effect of
localised stimulus depends on
the characteristic response of
the surface layers of the organ.
When dealing with this question
of the electrical reaction of epi-
thelium and glands in animal
tissues, Biedermann rightly Fic. 193. Photographic-Record of

: , Responses of Water-melon to
came to the conclusion that it Equi-alternating Electric Shocks
was the surface epithelial layer Responsive current from internal
which was, in an electro-motive stale to external epidermal
sense, most effective, the term,
in its widest sense, including the epithelium of glands and
papillz.

One complicating factor present in the electrical reactions
of animal epithelia and glands, but relatively absent under
the simpler conditions of the plant, is the effect of injury caused
by the process of isolation. The very fact of making the neces-
sary section involves a stimulus of great intensity, and unless
the effect of this has thoroughly subsided, the after-effect of
such stimulation may be so strong as to reverse the normal
current of rest, and otherwise modify the excitability of the
tissue, This is seen, for example, in an experiment carried

316 COMPARATIVE ELECTRO-PHYSIOLOGY

out by Dr. Waller,’ on the isolated paw of a cat. The
current of rest was found by him to flow from the surface
of the pad to the section. From this he was led to the
conclusion that this current could not have been due to
injury, since in that case it would have flowed from the
sectioned to the uninjured surface, and not in the opposite
direction, as was found to be the case.

This misconception arises from a failure to realise that.

the so-called ‘current of injury’ is, in fact, an after-effect of
excitation. In the case under consideration, the section,
acting as an intense stimulus, simply induces greater excita-
tory reaction of the more excitable, which in this case
happens, as we should have expected, to be the glandular
surface. The injury-current here, then, is necessarily from
the more excited glandular to the less excited non-glandular.

A precisely similar result was obtained in the case of
anisotropic plant-organs, where excitation caused by injury
of the less excitable side, becoming internally diffused,
induced greater galvanometric negativity of the more ex-
citable distal point (p. 162). For a typical experiment on
a glandular preparation, showing the principal effects, and
the complications that may arise owing to injury, we may
take the detached foot of the pond-snail, the lower surface of
which, as is well known, secretes a slimy fluid. On allowing
‘for the necessary period of rest, and then making electrical
connections, we observe a current of rest, so-called, which
flows from the glandular to the sectioned end. This is not
to be mistaken for the true natural current of rest, being in
fact the after-effect of a greater galvanometric negativity at
the more excited glandular surface, consequent on section.
An independent experiment, in support of this induction,
will be described presently. On now simultaneously ex-
citing the two surfaces, by equi-alternating shocks, the
responsive current is found to flow from the gland inwards,
the more excitable gland becoming thus galvanometrically
negative. The responsive current is in this case in the same

' Waller, Signs of Life, p. 101,

RESPONSE OF EPITHELIUM AND GLANDS 317

direction as the so-called current of rest, constituting a
positive variation of it.

From these experiments it is clear that the responsive
current is due to the greater intensity of the induced gal-
vanometric negativity at the more excitable glandular
surface. It must, however, be noted here that this definite
understanding of the phenomenon has been arrived at by
fixing our attention on the relative excitatory reactions at
the two contacts. If, instead of this, we had regarded it from
the usual point of view, of variations of the resting-current
only, we must have interpreted it as apparently an abnormal
positive variation ;! for the so-called resting-current, in such
a case, on account of the excitatory after-effect of injury,
must also, as we have seen, flow from the more excited gland
to the less excited muscle. Great confusion, and resultant
misinterpretation of observations, have arisen from not
sufficiently recognising these facts, that the resting-current
may be originated in either of two distinct ways, and that
the excitatory effect may consequently be summated with
it in different manners. The resting-current in the primary
condition is, as I have demonstrated elsewhere, the natural
current. This originates in the natural differences of ex-
citability between different points, and is, in the intact
specimen, through the tissue from the less to the more ex-
citable. External stimulus now gives rise to a responsive
current, which is in the opposite direction, and therefore
constitutes a negative variation of this, This takes. place
because the more excitable point, which was naturally
positive, has now become negative. But we may have a
current of rest which is due to previous excitation, or
injury, such as may be caused by the shock of the pre-
paration. This current, though usually regarded as the
resting-current, is not the true natural current of rest. It
is really, as it were, the responsive current. become persis-
tent. Succeeding stimuli, inducing responsive galvanometric

1 We shall find in Chapter XX VII. that similar misinterpretations have arisen
with regard to the responsive current in the retina, p. 417.

218 COMPARATIVE ELECTRO-PHYSIOLOGY

negativity of the more excitable, will now give rise to a current
in the same direction as this resting-current, thus constituting
a positive variation of it. It is only when fatigue has set in
at the more excitable, and induced great depression of
excitability there, that the response-current may undergo a
reversal, its direction now being from what was. originally
the less excitable, to the originally more excitable (p. 177).

An example of this I found in the sectioned foot of the large

Indian garden-snail. Here the excitatory action on the
glandular surface, due to the shock of preparation, was ex-
tremely great, as evidenced by the profuse secretion which
occurred iinmediately. Owing to this over-stimulation,
fatigue was induced, with consequent great depression of ex-
citability. Hence the responsive current was now found
to be reversed, having, with reference to the glandular
surface, become outgoing instead of ingoing.

It has been stated above that the ingoing current of rest,
observed at the glandular surface under preparation, was not
the true natural current, but due to the excitatory after-effect
of injury. ‘This I was able to verify by observing the current
of rest under natural conditions, without excitation. The
snail was allowed to crawl on a glass surface, in the middle of
which was a strip of linen moistened in normal saline. This
brought the glandular surface into electrical connection with
one of two non-polarisable electrodes. When the snail had
of its own accord come to a temporary standstill on this piece
of linen, the other electrode was quietly placed against the
skin of the upper side of the protruding body. The natural
current of rest was now found to be outgoing, as regards
the glandular surface of the foot, the more excitable being
thus galvanometrically positive. The absolute electro-motive
difference was found to be + ‘0013 volt. The foot was now
sectioned, and the difference of potential between the same
points was found to have undergone a reversal. The
supposed resting-current was now ingoing, through the
glandular surface. Thus, owing to the excitation consequent
on preparation, the more excitable surface, originally positive,

7). ee ee ee

4064 cee (

RESPONSE OF EPITHELIUM AND GLANDS 319

had become negative. The induced variation from the
original condition, in the present case, was from + ‘OoI3
volt to — ‘0020 volt. It will thus be seen that any irritation
is liable to change the natural positivity of a highly excitable
glandular surface to negativity. The supposed similarities
between the ingoing responsive currents of frog’s skin, and
the glandular surface of the stomach, are therefore not real.
That the two cases are quite different is proved indeed by
the fact that local stimulation of the surface of the skin
induces galvanometric positivity, whereas a similar stimulation
of the glandular surface induces negativity.

In experimenting on animal tissues, it is therefore ad-
visable, wherever possible, to use intact specimens. The
numerous experimental difficulties with which we are in that
case confronted, may be overcome by the method of simul-
taneous and equi-alternating shocks which has been described.
How practicable this method has been
rendered will appear from the experi-
ments which | have yet to describe on
human subjects.

We have seen that a protected sur-
face is likely, other things being equal,
to be more excitable than an exposed
one. Partly owing to this fact, and
partly also to its richer possession of
imbedded glands, it appeared to me
probable that the inner surface of the
armpit would prove electrically more pig. 194. Photographic
excitable than a corresponding area, on, Record of Electrical

Responses of Intact
say, the upper and outer surface of the Human Armpit
same shoulder. In the records which I Responsive current from
succeeded in obtaining (fig. 194), this “Pit to shoulder.
supposition was fully borne out. Equi-alternating shocks of
one second’s duration were applied at intervals of one minute,
and the direct effect photographically recorded. The re-
sulting responses were found to be ingoing as regards the
armpit, thus proving that that surface was the more excitable.

320 COMPARATIVE ELECTRO-PHYSIOLOGY

In order next to show that epithelial cells in the animal
are relatively more excitable than epidermal, as we have
already found to be the case in vegetable tissues, I performed
the following experiment on the human lip. Here it was
important that the electrical connections should be main-
tained steady. A light spring-contact key was therefore

made, as seen in the lower part of fig. 195. The lower.
contact of this spring-clip consisted of an amalgamated plate .

of zinc leading to the lower electrode. Over this were tied
four thicknesses of blotting-
paper soaked in zinc sulphate
solution. On this again were
placed three more thicknesses of
blotting-paper, soaked in normal
saline. The zinc plate which
formed the upper limb of the
clip, in connection with the
second electrode, was similarly
covered with separate layers of
blotting-paper, soaked in zinc
sulphate and normal saline re-
spectively. The protruded lower
lip was now placed in the clip,
as shown in the upper figure, in
| such a way that the latter made
: ee eS of Towne a gentle but secure contact. A

Lip. galvanometer and a source of
Lower figure gives an enlarged view equi-alternating currents were

oe also placed in the circuit. Of
the two electrodes, the upper was in connection with the
epithelial, and the lower with the epidermal surfaces. The
natural current was now found to flow in the tissue, as in the
corresponding cases of plant specimens, from the epidermal
to the epithelial. The perfect steadiness of the contact was
evidenced by the stillness of the deflected galvanometer spot
of light. On now applying the alternating excitatory
shock, the responsive current was found to be in the oppo-

RESPONSE OF EPITHELIUM AND GLANDS 321

site direction to the natural current, thus demonstrating the
fact that the epithelial layer was here, as in the plant, the
more excitable of the two. The regularity of this effect will
be seen from the series of photographic records given below
(fig. 196), in which is exhibited a slight staircase effect.

We next proceed to deal with the response of the glan-
dular organ, the tongue. The tongue of the frog has formed
the subject of a very extended series of researches, by
Engelmann and Biedermann. On_ very
careful isolation, entailing as little injury
as possible, it was found by these workers
that the natural current was ‘entering’
that is to say, it flowed across the tongue
from the upper surface to the lower. Both
electrical and mechanical stimulation was
found by these observers to cause a negative
variation of this natural current.

As isolation of such a highly excitable
organ as the tongue may, however, give rise
to unknown excitatory after-effects, it ap-
peared to me very desirable that an investi-
gation on this subject should be carried out * pei Se prides
on the intact human tongue. In connection Electrical Response
with this, I must point out that both the Sere pen
surfaces of the tongue are excitable. Our Responsive current
inquiry, therefore, is into the relative excit- ‘Tom epithelial to

epidermal surface.
abilities of its upper and lower surfaces. Here
the experimental difficulty lies in this very high excitability
of the organ, on account of which—except when in a quies-
cent state and with a very steady contact—the galvanometer
spot of light is apt to be erratic in its movements. Much
of this difficulty is overcome, however, by holding the pro-
truded tongue lightly clamped between the teeth. The upper
and lower surfaces may then easily be held in the clip-key
already described. From this double support of the clip and
the teeth it is, with a little practice, possible to arrange
matters in such a way that the galvanometer spot is

Y

322 COMPARATIVE ELECTRO-PHYSIOLOGY

practically stable. The current of rest in the intact human
tongue is then found to be from the upper to the lower surface,
as in the frog. This, according to our previous results, would
indicate that the upper surface is the less excitable. This
inference finds independent verification, when we subject the
organ to the stimulus of equi-alternating shocks. A very

strong responsive current is now found to flow through the

tongue, from the lower to the upper surface.

The tongue is so extremely sensitive that its characteristic

response can be evoked even with very feeble stimulus. I
have already explained that the alternating currents induced
by speaking before a telephone are not exactly equal and
opposite, the current being slightly stronger in one direction.
Hence, if such currents be made to play upon an organ in
which the excitability is only moderately differential, the
preponderance of one of the two elements of the alternating
shocks is then likely to mask the true excitatory effect. But
the differential excitability of the tongue is so great that the
responsive current is always from below to above, whether
the exciting current be made to act in a favourable or
unfavourable direction. Thus, if one speak, even in a very
ordinary voice, into an exciting telephone, which is in series
with the rest of the circuit, with its poles direct or reversed,
a definite lingual current. is induced in response. This, as
already said, is always in direction from the lower surface to
the upper—surely a curious instance of the speech of one
inducing lingual response in ariother, by direct, and not by
provocative action !

The results which have been described are the normal
effects given in response to stimulus of moderate intensity.
By moderate stimulus is here meant that intensity of current
which is obtained when the primary coil is slightly within
the secondary. By feeble, on the other hand, is meant the
intensity produced when the primary is at a distance from
the secondary. Excessively strong stimulus again occurs
when the primary is pushed fully within the secondary. I
shall now proceed to describe occasional variations which

a ee

RESPONSE OF EPITHELIUM AND GLANDS 333

may be observed when the stimulus is either very feeble or
excessively strong.

We have seen (p. 83) that when the intensity of stimulus
is below the critical degree which is sufficient to induce
response, its effect is to increase the internal energy of
the tissue. We have also seen that the sign of this
increased internal energy is galvanometric positivity, being
thus opposite to the excitatory effect. Hence, in a dif-
ferentially excitable tissue, we may expect to find instances
in which stimulus that falls below the threshold of true
excitation will act by inducing a greater galvanometric
positivity of the more excitable, whereas, under normal
intensity of stimulus, the more excitable would have
become galvanometrically negative. We can thus see the
possibility of response being reversed under very feeble
stimulus.

It must be remembered that the excitability of both
the contacts is a factor in the response, which has hitherto
been overlooked. A second very important factor, which
has not yet been taken into consideration, is the difference
between the characteristic curves of the tissues at the
two different surfaces. By characteristic curve is here meant
the curve which shows the relation between intensity
of stimulus and response. This difference will be better
understood from the diagram of the theoretical curves given
below (fig. 197). This exhibits all the cases that can possibly
exist. : .

Let the curve A aa’ a" represent the characteristic curve
of the surface A. Let the curve B 0 0’ 6” similarly represent
the characteristic curve of the surface B. Of these two
surfaces, B is under moderate stimulation, normally the more
excitable. In the middle portion of the curve, representing
response under moderate intensity of stimulus, the induced
galvanometric negativity of B is thus greater than that of A.
Under moderate excitation, therefore, the current is d’>a!
through the tissue in the direction from B to A. But below
the threshold of true excitation, B would be positive, and A

¥2

324. COMPARATIVE ELECTRO-PHYSIOLOGY

relatively negative to it. Hence there would here be
a reversal of response, the direction of the responsive current
a> through the tissue being now from A to B. This current
will be recorded by the galvanometer, provided the induced
difference between A and B be sufficiently great.

Having thus inferred the different effects possible under
sub-minimal and moderate stimuli, we shall next consider

the differential effect which may sometimes be induced by |

excessively strong stimulus. In the middle part of the curve,

| - ie
4 |
o , b
é b
z
“1
a
A @
ped STIMULUS
| 6

Fic. 197. Possible Variations of Responsive Current, as between Two
Surfaces A and B, shown by Means of Diagrammatic ‘Representations of
Characteristic Curves

A, a, a’, a”, characteristic curve of surface A; B, 4, 6’, 6", that of B.
Under moderate stimulation, B is the more excitable, its induced
galvanometric negativity being greater, and the direction of current
from 4’ Zo a', as in the middle part of the curve. Under sub-minimal
and super- -maximal stimulation the direction of the responsive current
is reversed to a > 6 and a" - 6” respectively.

B40! b” is seen to be very much steeper than Aad a’

tae

that is to say, the excitatory effect increases very rapidly
with the stimulus, in the more excitable of the two surfaces.
But this increase may sooner or later reach a limit, that curve
tending to become horizontal, aided in this process, possibly,
by growing fatigue. The curve A a@a' a’, however, though
not so steep, may yet continue to rise throughout a longer
abscissa, representing increasing intensity of stimulus. In
such a case, there would be a second crossing-point, and

Mint thas do rn MMe 2 gee ae m .

RESPONSE OF EPITHELIUM AND GLANDS 325

a second reversal of normal response into a@’’>0", under
excessively strong stimulation. We are thus enabled to see
the theoretical possibility of the reversal of normal response
under the two conditions of sub-minimal and super-maximal
stimulation. All these phases may not be displayed in the
same specimen; but it may be possible to find different
specimens exhibiting one or the other.

In some cases the difference a—d is too small to allow
of an appreciable galvanometric effect, and in their higher
parts the curves do not cross. In such specimens, then,
there is no response under sub-minimal stimulus, and only
normal response under increasing intensities, however strong.
The only exception to this will take place when fatigue
supervenes, a case which will be dealt with presently. I find
that this type of response is the most common.

We have next to consider those cases in which in the -
sub-minimal region, the difference a—é is appreciable, the
reversal to normal 6’>a’ taking place under higher in-
tensities of stimulus. There need not in such an instance,
be any second reversal. Here, then, the normal response
under moderate or strong stimulus is reversed when the
stimulus is sub-minimal. An example of this will be given
presently.

Lastly, there may be a type of response in which in the
sub-minimal region the difference a—Jd is slight, and the
normal 6’-<a' is reversed to a''+6" in the region of excessive
stimulation. I shall be able to give an example of this also.

I have been able, by taking different specimens, to
demonstrate the occurrence of these theoretical reversals of
response, under sub-minimal and super-maximal stimulation.
I have not yet been able to find a single specimen ex-
hibiting both reversals, but it is not impossible that this
exists. | |

The type in which response remains normal throughout
a wide range of stimulus-intensity is too numerous to
require special illustration. But this normal response may
be reversed under fatigue. Generally speaking, a highly

320 COMPARATIVE ELECTRO-PHYSIOLOGY

excitable tissue may be expected to show earlier or greater
fatigue, than, other things being equal, a less excitable
tissue.' Thus, under strong or long-continued stimulation,
the excitability of the originally more excitable B may be
depressed, so as to fall below that of A, with consequent
reversal of response. This will be seen clearly ina typical
experiment on the pulvinus of Mzmosa. Electrical con-
nections were here made with the upper and less excitable
surface A and the more excitable lower surface B, records
being then taken of normal responses to equi-alternating

Fic. 198. Photographic Record showing Reversal of Normal Response
in Pulvinus of AZzmosa due to Fatigue

(az) Series of normal responses, direction of current being from more
excitable lower to less excitable upper; (4) Reversed responses in
same specimen, due to previous tetanisation, causing fatigue.

electric shocks, The stimulus employed was of moderate
intensity, the secondary being placed slightly overlapping
the primary. The responses (fig. 198, a) are seen to be
normal, the responsive current being from the lower to
the upper. They also show signs of slight fatigue, their
amplitude undergoing diminution. The secondary was then
pushed over the primary, and the tissue subjected to the
consequent intense stimulus for two minutes continuously.

' In this matter, the nature of the tissue must be taken into consideration,
nerve, for example, being less subject to fatigue than muscle.

RESPONSE OF EPITHELIUM AND GLANDS 327

The secondary was next brought back to its original position
and a record once more taken of its successive responses
to stimuli of the same intensity as before. It will be seen
(fig. 197, 6) that the response is completely reversed by the
relative depression of the excitability of the lower surface
B. Similar reversal under fatigue will be shown in the
glandular organ of Drosera in the next chapter (fig. 208).
I have obtained other interesting variations of normal
response induced by fatigue. Thus, taking the carpel of
Dillenia indica, and making electrical contacts with its inner
and outer surfaces, the responses under moderate stimulus
were found to be normal—that is to say, from inner to outer
—the secondary being here understood to be partially over-
lapping the primary at a distance of six divisions of the
scale. The secondary was now pushed home, and the tissue
subjected for a short time to strong and continuous stimula-
tion. Moderate fatigue was thus induced. When the
secondary was now brought back to the distance of six
divisions of the scale the response was found to be reversed.
Thus, moderate fatigue had here been sufficient to bring
about the reversal of the relative excitabilities of the two
surfaces of the carpel of Dz/lenia indica, when the testing
stimulus was of original intensity. But when the intensity
of stimulus was increased, by pushing in the secondary to a
position marked three divisions on the scale, the response
became once more normal. Thus, fatigue had in this case
modified the excitability of the two surfaces in such a way
that an intensity of stimulus, which was formerly effective to
induce greater excitation of the originally more excitable, was
now ineffective ; and its greater excitation, with the restoration
of normal response, could now only be evoked under stronger
stimulus.

We shall next describe the reversal ot normal response
under sub-minimal stimulation. For this we shall once
more select the carpel of Dzd/enia indica. A record of its
normal response—the direction being from inner to outer—is
given in the first series of records in fig. 199. After taking

328 COMPARATIVE ELECTRO-PHYSIOLOGY

this record the intensity of stimulus was reduced by pulling
out the secondary further away from the primary. The
responses were now found reversed, as seen in the subsequent
series. |
We have last to consider the reversal induced by intense
stimulation. Such instances must not be confused with the
effect of fatigue. The two
can be distinguished by the:
fact that the fatigue-reversal
takes place after a series of
normal responses, whereas
the true reversal, due to
strong intensity of stimulus,
which we are now discuss-
ing, is exhibited at the very
beginning. Such an effect
I have observed in the
response of the human
Fic. 199. Photographic Record showing lip. The direction of
Reversal of Response in Carpel of the responsive current was

Dillenia indica, under Sub-minimal
Gisiawbatins normally, under moderate

The first series show normal electrical stimulus, from the epi-
responses under moderate stimulus, 41,1; .
responsive current from internal to thelial to : the epidermal

- external surface; the second series surfaces. Under very strong

exhibit reversed response under sub- ° :
minimal stimulation, current from stimulus, however, this
external to internal surface. normal direction was found
to be reversed.

But the employment of excessively strong stimulation
introduces other complicating factors. ‘The applied stimulus
may be supposed to be localised only when it is of moderate
intensity. With intense stimulus the subjacent tissues are
liable to be involved in giving rise to excitatory response ;
and it then becomes a difficult problem to discriminate how
much of the observed effect is due to the superficial layer,
and how much to others more deeply situated,

CHAPTER XXIV
RESPONSE OF DIGESTIVE ORGANS

Consideration of the functional peculiarities of the digestive organs— Alternating
phases of secretion and absorption—Relation between secretory and con-
tractile responses. [Illustrated by (a) preparation of AM/zmosa; (6) glandular
tentacle of Drosera—-General occurrence of contractile response—True current
of rest in digestive organs—Experiments on the pitcher of Mepenthe—Three
definite types of response under different conditions-—Negative and positive
electrical responses, concomitant with secretion and absorption—Multiple
responses due to strong stimulation— Response in glandular leaf of Drosera—
Normal negative response reversed to positive under continuous stimulation
—Multiple response in Drosera—Response of frog’s stomach to mechanical
stimulation — Response of stomach of tortoise—Response of stomach of gecko ,
—Multiple response of frog’s stomach, showing three stages—negative,
diphasic, and positive—Phasic variations.

HAVING now dealt with the responsive characteristics of the
skin, epithelium, and glands, alike in plant and animal, the
next subject to be taken up is that of the response of the
digestive mucosa. And here we have to determine, first,
whether or not there is, broadly speaking, any continuity
between the responses of digestive organs and those which
we have just been studying ; and, secondly, to what extent
the functional specialisation of the tissue has acted in
accentuating certain of its responsive peculiarities.

Surveying the function of digestion as a whole, we see
that it consists, briefly, of two different processes—those,
namely, of a previous secretion, by which food is rendered
soluble, and of a subsequent absorption, by which the dis-
solved foodstuffs are absorbed. In the membrane of the
simplest digestive organ, then, the epithelial ‘lining, using
that term in its most inclusive sense, must be endowed with
the two properties of secretion and absorption under different

330 COMPARATIVE ELECTRO-PHYSIOLOGY

circumstances. The question then suggests itself, what are
the circumstances which determine this outflow or inflow ?
In the digestive processes, moreover, in plant and animal
alike, each of the reactions referred to, whether of secretion
or absorption, must be more or less long-continued. Thus
these responsive actions, instead of being single and spas-
modic, are likely to be multiple and long-sustained. The

characteristic response to stimulus of a secreting organ is.

understood to be by secretion. Is this reaction essentially
different from those fundamental processes which underlie
the responses of contractile organs, or are we to regard con-
traction and secretion as but different expressions of a single
responsive phenomenon ? |

In order to test this question, of the connection between
responsive secretion and contraction, it will be well here to
draw attention to certain experiments of Sachs, on the
response of J/zmosa, though our inferences will be somewhat
. different from those which their author intended. If we take
a longitudinal slice of the lower half of the pulvinus of
Mimosa and keep it in a moist chamber for some time till
_ the tissue has recovered from the excitation due to section,
and if we then subject it to fresh excitation, water will be
found to ooze out, or undergo secretion from the excited
tissue. We may explain this occurrence in either of two
ways: first, that, in consequence of the molecular changes
induced by stimulus, contraction and permeability-variations
take place in the cells, the expulsion of water being an
expression of the active process of contraction ; or, secondly,
that the oozing-out of the water is a passive process, due to
permeability-variation of the turgid cells alone, without con-
traction.

The two theories may be distinguished broadly as those
of active contraction and passive secretion. In the thin
section of the Mzmosa pulvinus it is the exudation of water
that is noticeable, and not any marked movement character-
istic of contraction. But in the intact pulvinus, owing to,its
anisotropic structure, the greater contraction of the more

ea bad _

ht Li

aaa aii i

pan”
PRBS

RESPONSE OF DIGESTIVE ORGANS 331

excitable lower half is exhibited in a marked manner by
downward mechanical movement, magnified as this is by the
long petiolar index. The intact organ, moreover, is invested
with an impervious skin, hence the excitatory exudation, or
expulsion, of water, being internal, is not seen outwardly.
Thus a single identical reaction may appear from different
points of view, as either secretory or contractile.

The occurrence of contraction is thus most easily demon-
strable when it is accompanied by conspicuous movement.
This, however, demands considerable physiological aniso-
tropy, the differential contraction then giving rise to a very
marked lateral movement, as in J/zmosa. Ih radial organs
of plants, on the other hand, owing to balanced contractions
of opposite sides, there is no marked responsive movement.
Hence ordinary plant-organs have hitherto been regarded as
non-contractile and insensitive. But I have shown that all
these radial organs exhibit longitudinal contraction, to be
detected and recorded by means of suitable magnifying
devices. All motile responses are brought about, it must be
remembered, by transference or redistribution of fluids. Now,
in organs invested with impervious membranes the effect of
fluid-transference is. manifested by mechanical movement ;
whereas, in naked tissues, the fluid-transference is directly
visible as secretion. |

From the very important series of researches carried out
by Darwin, on the excitatory reactions in the tentacles of
Drosera, we know that the pedicel, carrying the gland on its
summit, is somewhat flattened, and that it is this anisotropic
lower part which is alone capable of movement. The gland-
cells on the head of the tentacle have been shown by
Gardiner to be provided with delicate uncuticularised cell-
walls, which are curiously pitted on their upper or free
surfaces. The terminal organ, or head, which is radial,
would thus seem to be peculiarly fitted for the exudation of
liquid on excitation. In the anisotropic motile portion of
the pedicel, on the other hand, the responsive reaction mani-
fests itself by bending. It would thus appear that the same

332 COMPARATIVE ELECTRO-PHYSIOLOGY

excitatory reaction may exhibit itself in different parts, even
of the same organ, by mechanical movement and secretion
respectively, according to the facilities which one or the other
portion offers.

That the phenomenon of contraction is behind the ex-
citatory expulsion of water in a vegetable organ, would

appear highly probable from certain results obtained in the |

electrical response. The stimulation of an ordinary vegetable
tissue gives rise to two distinct electrical effects at a distance.
The first of these is the arrival of the hydro-positive effect of
galvanometric positivity, with positive turgidity-variation.
The second is the wave of true excitation, with its character-
istic of negative turgidity-variation and concomitant gal-
vanometric negativity. The first, consisting, as this does,
of a hydrostatic blow delivered at a distance, can only, it
appears to me, be ascribed to an active process of contrac-
tion, causing the squeezing-out of water in the excited region.
A passive escape of fluid, due to mere permeability-variation,
could not, as I think, originate that impulsive hydrostatic
shock which is transmitted to a distance. For such a result
to take place an active expulsion would seem to be
requisite.

In view of these facts, is it necessary to hold the doctrine
of discontinuity, or, when there is evidence in its favour, are
we to believe in the continuity of these apparently different
reactions? The excitatory reactions of different classes of
tissues have hitherto been regarded as different, chiefly
because some were looked upon as motile, and others as
non-motile ; muscle, for example, was held to be typical of
the first, and nerve of the second, of these classes. In this
case of the nerve, it has been believed that there was no
visible manifestation of the excitatory change. I shall,
however, be able to show that even this supposition is
incorrect, since the excitatory reaction in the nerve is in fact
attended by contraction. The electrical indication of gal-
vanometric negativity which is concomitant with contraction
in contractile tissues, is also obtained in the case of excited

al i kk

« bb SD WAL et OF ee Ser

Tet!

RESPONSE OF DIGESTIVE ORGANS 333

glands. The visible changes which occur under stimulation
in these three types of tissues would thus appear to differ
only in degree. ae Io

We may now turn more especially to the question of the
electrical reactions of the digestive mucosa. As regards the
natural current of rest, we have seen that Rosenthal and
others found that this current was ingoing—that is to say,
the mucous layer was negative, as compared to the muscular
coat of the stomach. Biedermann had also noticed a strong
current of rest between the glandular surface of Drosera and
the stalk. But it will be shown that the glandular coat of
the stomach is more excitable than the muscular layer.
Hence we should have expected that the natural current of
rest would have been from the less excitable to the more
excitable, the mucous layer in a state of rest being thus
relatively galvanometrically positive. The opposite direc-
tion of the current which has been observed, would rather
appear to be ascribable to the excitatory after-effect of pre-
paration. I have already described how the glandular foot
of the snail, under conditions of perfect rest, is galvano-
metrically positive. But the excitation caused by prepara-
tion renders this highly excitable glandular surface negative
That the fact of cutting open the stomach, to make the
experimental preparation, similarly, would cause intense
excitation with galvanometric negativity, was to have been
expected. I shall be able, indeed, to show, by means of
experiments to be described presently, that the shock con-
sequent on this preparation is to give, not one, but a pro-
longed series of multiple electrical responses.

I have almost invariably found, in making electrical
contacts after section, with the inner and outer surfaces of
frog’s stomach, that the multiple responses caused by section,
persisted for more than an hour; and until these had
subsided no fresh experiment could be undertaken, to
obtain records of the response of the stomach to external
stimulus. I have also found that many of these frogs were
in the habit of swallowing stones and pebbles, the persistent

334 COMPARATIVE ELECTRO-PHYSIOLOGY

mechanical irritation of which would contribute to the
negativity of the mucous lining.

Finding, then, that it would be impossible to obtain the
natural current, in a stomach which had to be cut open, I
next turned my attention to stomachs which are naturally
open. These are seen in the upper concave surface of the
leaf of Drosera, for instance, which is provided with glandular
tentacles. I here made electrical connections with the upper
and lower surfaces respectively. But the tentacles excited by
the contact of the electrode bent and clasped it round, an
excitation which was seen in the galvanometer as negativity
of that surface. From this may be gauged the difficulties
which attend the observation of the true natural current of
rest in such an excitable organ as the stomach. The
demonstration, however, of the galvanometric positivity of
the snail’s foot, and of the inner glandular surface of the
carpel of Dzllenza indica, lead to a strong presumption in
favour of the true resting-current in the stomach being from
the non-mucous layers to the mucous.

Having thus seen the difficulties imposed by the high
motile excitability of the tentacles of Drosera, 1 next turned
my attention to other specimens. We have seen that there
is a secretion of fluid at the lower end of the hollow interior
of the peduncle of Uvzcls lily, and that the secreting inner
layer is here galvanometrically positive in a state of rest.
As this tube, however, is closed, it cannot be regarded as
subserving the absorption of food-material. But the same
limitation does not apply to those modified foliar structures,
the pitchers of Vepenthe ' (fig. 200). These, as is well known,
are open. They have a histological differentiation, moreover,
of their lining membrane, actual glands being present
(figs. 201, 202), which are admitted to be comparable to those
of the animal digestive organ, though of a much simpler type.
A fluid is secreted by these glands, and insects entrapped in
the pitcher are in it dissolved or decomposed. The products

1 I have to thank the authorities of the Botanical Garden, Sibpur, for
supplying me with these valuable specimens.

— , a

Og WO pee er

RESPONSE OF DIGESTIVE ORGANS : 335

are subsequently absorbed by the tissue, as in corresponding
cases, by the stomach of animals. From the study of the
responsive peculiarities of so primitive a type of stomach, we
might then expect to gain much light on the action of more
complex and highly specialised digestive organs. In order
first to obtain the true current of rest,
I took a young pitcher which had
previously been kept free from all 16
disturbance. I next made electrical INN
; yl
connections, by means of non-polaris- Ly ans
able electrodes, with the inner (glan- i Bt ha
dular) and outer surfaces of this iy
pitcher respectively. As some excita- ianuil
tory reaction may be induced in a 1 Mm ZN
highly excitable organ, even by the wo BE
contact of normal saline, the cotton ]
threads in connection with these non- F
polarisable electrodes were moistened Vy WE
with the natural secretion of the Woe
pitcher itself. On carrying out the
experiment under these ideal condi-
tions, I found, as I had expected,
that the current of rest flowed from
the outer non-glandular to the inner glandular surface, the
latter thus being galvanometrically positive.

In investigating next the excitatory reaction, I obtained
three different types of responses—negative, diphasic, and
positive—characteristic of certain definite conditions. Before
entering upon the details of these experiments, it is advisable
to discuss here the probable significance of the negative and
positive electrical reactions observed.

We have seen that a slice of tissue from the’ pulvinus of
Mimosa excretes water under excitation. The electrical
reaction under these circumstances is one of galvanometric
negativity. But during the process of recovery, when the
tissue is absorbing water, this negativity diminishes, a change
that is tantamount to that increase of positivity with which

Fic. 200. Pitcher of Ve-
penthe, with lid removed.

336. COMPARATIVE ELECTRO-PHYSIOLOGY

we are already familiar, as the invariable accompaniment of a

positive turgidity-variation.

Thus, if galvanometric negativity is to be taken as the
concomitant of the expulsion or secretion of fluid, it would

x ieee
q\ S EN

AD
PSS)

ay 08 ges
of: - e<

\
an {gee we ue i

Fic. 201. Glandular Surface of a iin
of the Living Membrane of the Pitcher

appear that the opposite
process of absorption would
be indicated by the respon-
sive galvanometric
tivity.

Again the fresh pul-
vinus of J7Zzmosa responds,
when excited, by. a me-
chanical fall, a negative
turgidity-variation, and by
galvanometric negativity.

posi-_

of Nepenthe.
But after long-continued

stimulation, these normal responses are found to undergo
reversal. The pulvinus expands; water must be re-absorbed,
and the leaf is re-erected. The normal galvanometric nega-
tivity is now reversed to positivity. It will thus be seen that

while, in a fresh tissue, stimulus gives rise to expulsion of
fluid—the electrical indi-

cation of this
being galvanometric nega-
tivity—in a tissue which
has already, on the other
hand, been under con-
tinuous stimulation there
will be a tendency towards
the phasic reversal of re-
sponse to galvanometric
positivity, indicative of the
process of absorption.

In the case of motile
tissues, these excitatory
reactions of the outflow and inflow of fluids appear to us of
little consequence, except in the form of those appropriate

Transverse Section of Tissue of

FIG. 202.
Pitcher of Mepenthe.

wu, outer surface; L, inner surface; g, glands
present in the internal surface.

process ©

i WR

RESPONSE OF DIGESTIVE ORGANS 337

motile responses which they occasion. But in glandular
organs, they become possessed of much greater significance,
since they constitute the main function of such structures.

Electrical responses, in every way analogous to those
which have been described, are obtained from the glandular
surfaces of digestive organs. That is to say, the glandular
surface when fresh exhibits responsive galvanometric nega-
tivity on excitation. In Drosera, for example, under these
conditions secretion is seen to take place. Thus the negative
phase of response, in this as in the case of Mzmmosa, is asso-
ciated with expulsion of fluid or secretion. After continuous
stimulation, again, the responsive phase here, as in MWzmosa, is
found to be reversed to positive, indicative, as there is every
reason to believe, of absorption. From a consideration of
the functions of the digestive organ, we should be prepared,
as already pointed out, to expect the occurrence of two
alternating processes. In the fresh state, ingestion of food,
acting as a stimulus, would naturally induce excitatory
secretion; and this excitatory secretion must be followed
later by the absorption of dissolved food. These alternating
phases of secretion and absorption indubitably occur. We
shall also find, in the electrical response-records, a phasic alter-
nation of negative and positive under appropriate conditions.

We have seen that. there is a continuity between the
different reactions of non-glandular and glandular tissues. We
have also seen that, as in the one case, so too in the other,
a phasic change takes place from negative to positive. Inthe
digestive organ, however, we have to deal mainly with the
fluctuations of fluids—secretion and absorption—and the
attendant electrical variations, which consist of two opposite
phases, positive and negative. As far as I have found it
possible to test the matter experimentally, it has invariably
been the case that the negative electrical phase was associated
with secretion ; and everything points to the probability that
the converse of this—the association, namely, of. the positive
electrical phase with the process of absorption—-holds equally
good.

338 COMPARATIVE ELECTRO-PHYSIOLOGY

We now return to the question of the normal response of
the pitcher in its three different conditions. Of these, in the
youngest, no flies are present; such a specimen will be
known as ‘fresh.’ Jn others, somewhat older, are a few
insects. These pitchers may be regarded as moderately
excited, owing either to the struggles of the insects or to the
supply of food, or to both. Still another class is found, in
which the glandular part of the inner surface of the pitcher is
practicaily coated with captured insects, and has thus already
been subjected to long-
continued stimulation.
The responses of these
three classes of specimens
are in each case, as I shall
show, very characteristic.

I shall first describe
experiments carried out
on fresh = specimens.
Records were made of
their responses to equi-
alternating shocks of
moderate intensity, at

Photographic Record of Series

F1G. 203.

of Normal Negative Responses of Glan-
dular Surface of Wepenthe in Fresh Con-

dition to Equi-alternating Electric
Shocks given at Intervals of Two Minutes

Responsive current from internal glandular
to external non-glandular surface. Note
occurrence of multiple response and trend

intervals of two minutes.
The responsive current
was here found to flow
from the internal glan-
dular to the external non-

of base-line upwards. if
glandular surface. Fig.

203 gives a series of such responses. It was said at the
beginning that the responses of digestive organs were likely
to be multiple. This is seen to be true even under the
moderate stimulus applied in the present case. But under
the action of stronger stimulus, such as that of a thermal
shock, the response is found to consist of a long and multiple
series, records of which will be seen later.

Another peculiarity to be noticed, in the series of re-
sponses given in fig. 203, is that the base-line of the record

~RESPONSE OF DIGESTIVE ORGANS. 339

trends upwards. This indicates that the glandular surface,
by the residual effect of stimulation, is being rendered more
and more galvanometrically negative. This explains why
the internal surface of the stomach has been found by
different observers to be negative, a condition of more or
less persistent negativity being thus clearly due to the ex-
citatory after-effect of preparation. Had it not been for the
exceptional opportunity afforded by the open pitcher of
Nepeuthe, it would have been impossible to make galvano-
metric connections with the intact inner glandular surface
and thus to ascertain that such a surface is naturally gal-
vanometrically positive.

I may here point out the very interesting medics
tion of response which occurs in the same specimen under
a long-continued series of stimulations. This modification,
due to fatigue so-called, makes its appearance first in dimi-
nution of the height of the responses. Some of the con-
stituent multiple responses due to a single stimulus are
then found to be reversed to positive, and after this they
show a tendency to become more or less completely
reversed.

It is also interesting to find that the same modifications
make their appearance, in the same order, in those pitchers
which have been subjected to continuous stimulation, to a
greater or less extent, by the supply of insects. That is
to say, a pitcher containing a few insects is found to give
responses, the multiple constituents of which are sometimes
positive and sometimes negative. This intermediate phase is
seen well illustrated in the record given in fig. 204. But in
the pitcher whose inner surface is already thickly coated with
insects, and which has long been exposed to the continuous
action of such stimulation, the characteristic response is
found to be the reverse of that of the fresh specimen. — It
will be seen from the record in fig. 205 that in such a case
the individual effect of a single stimulus is a series of mul-
tiple responses which are positive. In this record a curious

effect is again seen, that of the shifting om the base-line, now
ae

340 COMPARATIVE ELECTRO-PHYSIOLOGY

downwards. This indicates an increasing positivity of the
glandular surface.

The results which have thus been described, in the case
of the fresh pitcher, and of one subjected for a long period to
the stimulus of food, are fully compatible, it will be observed,
with the theory of digestion as a diphasic process, in which
galvanometric negativity is associated with a predominant
secretion, and the subsequent galvanometric positivity with a.
predominant absorption by
the glandular membrane.

Fic. 205. Photographic Record of Re-
sponses of Pitcher in Third Stage, the
whole Glandular Surface thickly

Fic.. 204. Photographic Record Coated with Insects. Stimuli applied
of Responses of Pitcher in at Intervals of two Minutes
Intermediate Stage, having
Attracted a Few Insects

The response here is in the positive phase,
direction of current being from non-

Note here the occurrence of two glandular to glandular. Notealso the
phases in constituent responses, multiple character of responses to
positive being predominant. single stimuli.

It is also important to notice that while in the fresh
condition the glandular surface is positive, and in the
moderately stimulated condition negative, yet positivity of
the glandular surface is not always to be taken as a sign of
its fresh condition. For we have here seen that under long-
continued stimulation, the electrical condition is apt to be
reversed to one of positivity,

RESPONSE OF DIGESTIVE ORGANS 341

It has been stated that on account of the highly excitable
nature of the digestive organ, a single stimulus, if strong,

Fic. 206. Multiple Response of Pitcher of Mefenthe, in First or Fresh
Stage, to Single Strong Thermal Shock

The constituent responses are both negative and positive, the former being stronger.

would give rise in it to a multiple series of responses. The
two following records (figs. 206 and 207) illustrate this fact
in two different speci-
mens which were in
somewhat different con-
ditions. The stimulus
employed in each case
was a _ single strong
thermal shock, and the
multiple responses were
found to persist, in both,
for quite an hour. In
the first of these figures,
the constituent responses
of the series were both
negative and positive, ye, 207, Multiple Response of Pitcher of
the former being pre- Nepenthe, in Third Stage, to Single Strong
dominant. In the second gna ae

The constituent responses are here - pre-
record (fig. 207 ) the dominantly positive.
positive phase is pre-
dominant in the responses, and the trend of the base-line down-
wards shows increasing positivity of the glandular surface.

342 COMPARATIVE ELECTRO-PHYSIOLOGY

In taking up this investigation on the pitcher of Vepenthe
it appeared to me that much light would be thrown, by the
study of this simple organ, on the many: difficulties connected
with the response of the more complex digestive organs of
the animal. This surmise has proved to be fully justified,
for in the experiments which I have carried out in the latter
field, the results are a mere repetition of these typical effects
seen in Wepenthe under corresponding circumstances.

Before passing from
Nepenthe to the study
of digestive tissues in
animals, it will be well
to deal here with the
more complex type of
vegetal digestive organ
seen in the plant
Drosera. 1 took for my
experiment a specimen
of the Indian Dvrosera
longifolia, the upper
surfaces of whose leaves
are covered, as is well

known, with glandular
Fic. 208. Photographic Record of Responses :
in Fresh Leaf of Drosera to Equi-alternating tentacles. Here, as ‘5
Electrical Shocks the case of the pitcher
The first series show normal responses. Current J h
from upper glandular to lower non-glandular of Nepentne, the re-

surface. In the second series normal response sponse of leaves which
is reversed to positive, after tetanisation, T.
are fresh and have not

been subjected to previous excitation, is by induced negativity
of the glandular surface, and this is reversed to positive under
long-continued stimulation. These two phases are seen in
figure 208, in which the first series is a record of normal
responses of galvanometric negativity, to equi-alternating
shocks applied at intervals of one minute; and the second,
the reversed responses exhibited by the same leaf, to the
same stimulus, when it has, in the meantime, been subjected
to tetanising shocks for three minutes continuously. It is

RESPONSE OF DIGESTIVE ORGANS 343

curious and interesting to note here, as in the case of
Nepenthe, the trend of the base-line up, when the response
is the normal negative, and down when it is the reversed
positive, indicating in the one case increasing negativity, and
in the other increasing positivity.

As in the Mepenthe, so also in the leaf of Drosera,
specimens which are not fresh—that is to say, previously
unexcited——are apt to exhibit the positive phase of response.
I give below a series of multiple
responses (fig. 209) induced in such
a leaf by a strong stimulation. The
stimulus was in this case given by
sectioning the leaf, and the response
therefore illustrates the fact that
preparation itself acts as a stimulus.
In the present case, electrical con-
nections with the galvanometer,
were made with the upper and
lower surfaces of the leaf on the
plant, intact. On now cutting the
petiole across, a long series of
multiple responses, lasting for about
45 minutes, was found to be set
up. These pulsations were at first
rapid, and then slowed down
gradually, the average period of a r pae, Pestommpnic Bacol
single pulsation being about 30 of Drosera in Positive Phase
seconds. Only a portion of the ‘Stimulus was caused here by

: : section of the petiole.
record is shown in fig. 209.

Having thus seen the typical responses exhibited by
the digestive organs of plants, we shall now pass to the
consideration of the reactions induced in animal stomachs.
Here, again, two different subjects of inquiry arise, the
direction, namely, of the natural current of rest, and that of
the action or responsive current. As regards the first of
these, it will be remembered that Rosenthal found it to be
strongly ‘ingoing’—that is to say, from the mucous to the

344 COMPARATIVE ELECTRO-PHYSIOLOGY

muscular coats of the stomach. From this it was supposed,
as we have seen, that the mucous coat of the stomach of the
frog had the same electro-motive reaction as its outer skin.
We shall find, however, that there is in reality no such
similarity between the two, inasmuch as, while the excitatory
reaction makes the outer skin galvanometrically positive, its
effect on the mucous surface under normal conditions is to
induce galvanometric negativity. In the case of Nepenthe,
further, we have seen that the natural current of rest is from
the non-glandular outer to the glandular inner surface, and
that this is liable to reversal, as an excitatory after-effect of
preparation. The i ingoing current, therefore, observed in the
preparation of frog’s stomach, is to be regarded, not as the
natural current of rest, but as the excitatory after-effect due
to isolation.

With regard, next, to the current of action, Biedermann
states that direct electrical excitation, by rapidly alternating
shocks, induces a negative variation usually preceded by a
positive swing. Since the so-called current of rest is ingoing,
a ‘negative variation’ of it evidently means an outgoing
current—that is to say, galvanometric positivity of the
mucous coat. Hence the responsive action of the mucous
coat, as described by Biedermann, is a transient negativity
followed by positivity.

In dealing with this question of the electrical response
of the digestive organ, we must be prepared, as the result of
previous experiments on plants, to meet with variations of
the excitatory effect, due to the phasic condition of the tissue.
And first, for the clear demonstration of the effect of ex-
citation on the mucous surface, uncomplicated by changes
induced at the second contact, I employed the Rotary
Method of Mechanical Stimulation of the given area. The
rotating electrodes were applied to the inside of a properly
mounted frog’s stomach, and experiment commenced some
time after the cessation of the multiple response due to
preparation. The following record (fig. 210) exhibits the
first four of these responses to individual mechanical stimuli,

ee

DL we and Oh, cocaine arth lh ee

RESPONSE OF DIGESTIVE ORGANS 345

applied at intervals of one minute. The responsive variation
took place by the induced galvanometric negativity of the
excited area. Under long-continued stimulation fatigue was
found to be induced, the responses becoming diminished
and even tending to a reversal from the normal to
positive.

In order to show that the inner mucous surface is
relatively more excitable than the muscular coat, I next
subjected the two to simultaneous excitation by equi-alter-
nating electrical shocks, And for the sake of establishing a

Fic, 210, Photographic Fic. 211, Photographic Record
Record of Normal of Normal Negative Re-
Negative Responses sponses of Stomach of Tor-
of Frog’s Stomach to toise to Stimulus of Equi-
Mechanical Stimula- alternating Electric Shocks
tion applied at Intervals of One

Minute

generalisation as to the reaction of the stomach, I now took
a different specimen—namely, the stomach of tortoise. The
responses in the figure (fig. 211) showed relative galvano-
metric negativity of the inside of the stomach.

We have seen that fresh vegetable stomach responds by
normal negativity, but that, under continuous stimulation,
a phasic change is induced, by which response is reversed to
positive (cf. fig. 208). I shall next demonstrate the corre-
sponding effect in the animal stomach. Taking.a preparation
of the stomach of gecko, I obtained normal responses, whose
direction was from the glandular internal to the muscular

346 COMPARATIVE ELECTRO-PHYSIOLOGY

external surface. After an intervening period of tetanisation,
however, the responses are seen to be reversed (fig. 212).

The next record has been selected for the purpose of
showing the gradual process of transition from the normal
negative to the reversed positive response. The specimen
taken was frog’s stomach. At the commencement of the
experiment the galvanometer spot was quiescent, but when
the specimen was subjected to a single strong thermal shock,
a prolonged series of multiple responses was initiated, per-
sisting for more than an hour, Of this series I here re-
produce four different
portions (fig. 213). The
first of these (a) con-
sists of pulses of gal-
vanometric negativity
of the internal surface.
The recoveries are here
incomplete, and _ the
base-line shifts upwards,
showing an increasing
negativity of that sur-
face. The negative
pulses are then reversed
Fic. 212, Photographic Record of Normal to positive, through an

Response in Stomach of Gecko to Equi- intermediate di-phasic

cient aaa seen to be reversed after (6). Tn the: first part

of this pronouncedly
positive response (c) the base line is horizontal. It then
begins to shift downwards (@), thus exhibiting a decreasing
negativity—or increasing positivity—of the internal surface.
In this periodic variation of the electrical condition we have
a significant parallel to the records which we have already
seen in Wepenthe and in Drosera (figs. 203, 205, 208, and 209).

It has already been pointed out that, in view of the
functional peculiarities of the digestive organ, it might be ex-
pected that the alternate reactions of secretion and absorption
would neither of them be single and spasmodic, but each long-

RESPONSE OF DIGESTIVE ORGANS 347

sustained. In this connection it is suggestive that the digestive
organs should show so strongly marked a characteristic of
multiple response. It would thus appear, as already said, that
mechanical stimulation during ingestion of food gives rise to
the responsive reaction of secretion, evidenced electrically by
response of galvanometric negativity of the internal surface.
There then sets in the opposite phase, associated with the

Fic. 213. Photographic Record of Multiple Responses in Stomach of
Frog to a Single Strong Thermal Shock

Four parts are given of this long series. (a) Negative series; (4) Alter-
nating negative and positive constituent responses ; (c) Positive series ;
(Z) Positive series. Note trend of base-line upwards in negative a,
and downwards in positive d.

reversal of electrical response, probably indicating the ab-
sorptive process. This reversal of response, to galvanometric
positivity, may be the work of three different factors, which
may or may not be mutually dependent. In the first place,
we have seen that long-continued stimulation was apt of
itself, other things being equal, to give rise to a reversal of
response. Secondly, after secretion has reached its maxi-
mum, the empty mucous cells in contact with fluid would
naturally tend to reabsorb. And, lastly, we have seen that
an increase of internal energy, in whatever way produced,

348 COMPARATIVE ELECTRO-PHYSIOLOGY

tends to give rise to a responsive reaction, whose sign is
opposite to that of excitation—expansion instead of con-
traction. Now such an increase of internal energy could not
fail to be the result of the absorption of the chemically-
dissolved food.

Another interesting consideration to be remembered in
connection with digestive organs is that periodically-acting

forces give rise to an induced periodicity, which persists for |

a time, even in the absence of the periodically-exciting cause.
A well-known illustration of this is met with in the nycti-
tropic movements, so-called, of plants, induced as these are
by the periodic variation of night and day. These move-
ments persist for a certain length of time, even when the
plant is kept in continuous darkness. Similarly, animals
accustomed to the supply of food at regular intervals would
undoubtedly exhibit alternating phasic changes apparently

spontaneous, in the condition of the digestive organ in

consequence of the original periodicity of the exciting cause.
Such an organ, therefore, must necessarily exhibit periodic
electrical variations.

OO a

~~. fT) ce ee ee

CHAPTER XXV

ABSORPTION OF FOOD BY PLANT AND ASCENT OF SAP

Parallelism between responsive reactions of root and digestive organ— Alternating
phases of secretion and absorption—Association of absorptive process with
ascent of sap—Electrical response of young and old roots—Different phasic
reactions, as in pitcher of Mepenthe—Response to chemical stimulation—
Different theories of ascent of sap—Physical versus excitatory theories—
Objections to excitatory theory—Assumption that wood dead unjustified—
Demonstration of excitatory electrical response of sap-wood—Strasburger’s

experiments on effect of poisons on ascent of sap—Current inference unjus-
tified. :

WE have seen in the last chapter that in the digestive pro-
cess as a whole there must be alternating phases of secretion
and absorption. The secretion of dissolving fluids, by which
insoluble substances are rendered soluble, we found to take
place under stimulation, and to be succeeded by a process
of absorption, by means of which the now dissolved food-
material found access into the organism. These functions,
though seen characteristically in the digestive organs of
animals, are also to be observed in some plants, such as the
pitcher of Nepenthe, or the leaf of Drosera. Here, situated
externally, we find what are practically open stomachs,
digesting, as do those of animals, solid organic food. But
plants in general have to depend on the supply of inorganic
food-material, often presented in solid or insoluble forms, for
their nourishment. In this case also it is obvious that the
same sequence of solution by dissolving fluids, and subse-
quent absorption, must be gone through. And the organ by
which this takes place must evidently be the root. In this
regard the well-known experiments on the corrosion of
marble by the root of a growing plant are sufficient to show

350 COMPARATIVE ELECTRO-PHYSIOLOGY

that these organs secrete acids, by means of which insoluble
substances are made soluble. It is equally clear, further, that
the inorganic solids so dissolved are afterwards absorbed by
the plant. Thus it will be seen that these alternating pro-
cesses of secretion and absorption of food-material, as they
take place in the vegetable organism, are not very different
in their essential features from the ordinary phenomenon of
digestion as known to us. The chief distinction between the
two would now seem to lie in the fact that in the animal the
supply of food is in the main organic, and in the plant inor-
ganic. Even here, however, we meet with connecting links
in the form of insectivorous plants, in whose case the organic
supply is obtained by means of the digesting leaf, and the
inorganic through the roots. We may regard digestion,
therefore, in its widest sense, as a process of absorption of
insoluble food rendered soluble, whether such food be organic
or inorganic. Apparently, then, in the case of the plant the
root functions as a digestive organ. But whether or not this
analogy is merely superficial can only be determined by an
experimental inquiry into the parallelism which may or may
not exist between the various excitatory reactions of the
root on the one hand and a typical digestive organ on the
other.

In order to obtain the large quantity of inorganic material
which is necessary to the nutrition of a tree, for instance, it
is clear that fresh quantities of charged fluid must be con-
stantly taken up. In order further that this process may be
maintained continuously it must be possible to get rid of the
useless water, which is accordingly passed off, chiefly from the
transpiring leaves, in the form of vapour. The absorption of
food and the ascent of.sap, or transpiration-current, would
appear therefore to be related phenomena. I shall, in the
course of the present and following chapters, then, take up in
detail the consideration of these two aspects of the problem,
which will thus constitute two main lines of inquiry:

(1) Whether or not the excitatory reaction of the root has
any similarity to that of digestive organs in general; and

ABSORPTION OF FOOD BY PLANT 351

(2) whether or not the ascent of sap is fundamentally due to
similar excitatory reactions.

With regard to the latter of these questions it may be
stated here that the nature of the efficient cause of the
ascent of sap is universally regarded, in plant physiology,
as constituting a problem of the greatest obscurity. The
various non-physiological theories which have hitherto been
advanced are admitted to be inadequate, as we shall see later.
We are thus confronted either with an insoluble problem or
with the necessity of finding physiological reactions which
will account for the ascent of sap.

As regards the latter of these alternatives, haurcaes. ob-
jections apparently very serious have been brought forward.
Against the physiological character of the action it has
been urged (a) that wood, being supposed to be dead,
could take no part in the ascent. of sap. It is known
moreover (4) that killing the roots with boiling water does
not prevent the ascent of sap. And, lastly (c), in the well-
known experiments of Strasburger it was found that strongly
poisonous solutions can be carried to the tops of trees. From
these facts it has been held to be proved that the ascent of
sap cannot be dependent on the livingness of the tissues
concerned. ~* .

But if, on the other. hand, it could be shown that these
objections were not valid, and if, further, some crucial experi-
ment were devised to demonstrate that excitatory action was
attended by a concomitant responsive movement of water in
the tissue, it might then be claimed that the physiological
theory of the ascent of sap had been established on a firm
basis. The attempt to do this will form the subject of the
next chapter.

The first question that falls within the scope of our
investigation, then, is as to whether the reactions of the root
are or are not similar to those of digestive organs in general.
We have seen, in the case of the latter, that as there are two
opposite activities, of secretion and absorption, so also there
are two opposite responsive phases, negative and positive, the

352 COMPARATIVE ELECTRO-PHYSIOLOGY

former being the more characteristic of the fresh condition,
and the latter of a specimen which has been previously sub-
jected to continuous stimulation. Before giving any account,
however, of these electrical responses, it will be interesting
to demonstrate here the occurrence of secretion in young or
fresh specimens, when subjected to excitation. . The fact
that young rootlets secrete, on excitation by contact, has

already been seen in the well-known experiment on the

corrosion of marble, mentioned above. But I shall now
describe a new experiment, in which this fact is even more
convincingly demonstrated. I took a specimen of Colocasza,
srowing in marshy soil. The plant was lifted bodily, with
earth adhering, and placed in water, so as to expose the
roots gradually, without causing injury. It was then kept
overnight, with the roots in normal saline solution, which
was slowly absorbed by the tissues. Next morning, again,
it was carefully washed till there was no trace of salt ad-
hering. One of the very young roots was now immersed
in very dilute solution of silver nitrate. If the previous
washing haa oeen effective, there ought now to be no white
precipitate, or only the merest trace, formed in the silver
solution. The two electrodes of a Ruhmkorff’s coil were
next connected, one with the silver solution,*and the other
with the stem of the plant. On now passing tetanising
shocks, the immersed root became excited, and secreted its
contained salt solution, this being seen in the silver nitrate as
streams of white precipitate.

Turning next to the electrical mode of investigation, we
have found that in the digestive organs, the galvanometric
negativity, which is the characteristic response of a specimen
in the fresh condition, becomes reversed to positivity under
continuous stimulation. In the case of Mepenthe, very young
pitchers exhibited this normal response of negativity, which
was converted, under continuous stimulation, into diphasic,
tending towards positivity. Older specimens, again, pre-
viously stimulated by the presence of excitatory food-material,

Diane tN He line odes Py

ABSORPTION OF FOOD BY PLANT 353

were found to be in the positive phase, giving rise to response
by galvanometric positivity. 3 |
In the case of the root, it is interesting to find that
there is a similar alternation of responsive phases. For
this demonstration I again took the root of Colocasia, and
recorded its responses to equi-alternating electric shocks.
Among the mass of roots there are naturally some which
are dead and decaying. One of these was selected for one
electrical contact, while the other was made with a young
and vigorous root. The responsive reaction, under these
conditions, was found to take place
by galvanometric negativity (fig. 214).
Under long-continued stimulation,
however, I have often found this
normal response by galvanometric
negativity to be reversed to its
opposite, positivity. From this we
may pass to the consideration of
response in older roots, where the
phasic reaction is typically positive. a ee ae
Now we have seen in previous Record of Normal Nega-
chapters, as will be remembered, that ns Response..of Young
oot of Colocasia
there are two different conditions
under which the positive may be substituted for the normal
negative response. The first is that of reversal under long-
continued stimulation, which we ,have just seen. And the
second occurs when the stimulus falls below the critical
level which is necessary to the evoking of true excitation.
In this latter case, as we saw further, the incident stimulus
increases the internal energy, and causes expansion, positive
turgidity-variation, and galvanometric positivity. It would
thus appear that one identical stimulus may induce one effect,
that of galvanometric negativity, in a highly excitable tissue,
and the opposite, or galvanometric positivity, in a tissue that
is less excitable. In connection with this question the ex-
perimental results which I am about to describe are very
significant.

AA

354 COMPARATIVE ELECTRO=PHYSIOLOGY

We have seen that a young root of Colocasia, when fresh,
gives the normal response of. galvanometric negativity.
Taking next an older root of the same plant, and employ-
ing the same intensity of stimulus as before, I found the
responses to take place, generally speaking, by galvanometric
positivity (fig. 215). This would appear to suggest a ten-
dency towards specialisation of fufction, galvanometric nega-
tivity being associated, as we have seen, with secretion, and |
positivity, in all probability, with the opposite—namely,
absorption. A similar specialisation of certain cells for
secretion and others for absorption is manifested more
unmistakably in the digestive organs
of the higher animals. |

Thus in the young roots the pre-
dominant reaction would seem to be
secretion, reversed under continuous
stimulation to absorption. In the older
roots, on the other hand, the pre-
dominant reaction must be supposed
to be absorptive. Here, then, judging
from the electrical indications, we
Fic. 218. Photographic would seem to have proof of that

Pe One Rea physiological activity in virtue of which

Colocasia water is taken up by the root, thus

! giving rise to the so-called ‘root-
pressure. We can also see how, by the summated activities
of numerous roots, this ‘ root-pressure ’ is kept approximately
constant for a certain length of time. Taking longer periods
into account, further, we can see that this physiological
activity is likely to undergo periodic change, a fact which is
evidenced by the known periodic variation of root-pressure.
The question, however, of the actual influence of excitation
on the process of the ascent of sap will be dealt with in the
next chapter.

One form of stimulus to whose action the roots must often
be subjected is that of the chemical substances present in
the soil, and I undertook to test the electrical variations

--ABSORPTION OF FOOD BY PLANT | 355

induced by these. The results obtained, at least with the
specimens which I have tried, are in general parallel to those
obtained by the electrical form of stimulation. Thus, in
young roots, in the majority of cases, when subjected to the
action of so dilute a solution as ‘5 per cent. of sodium car-
bonate, an electrical change of galvanometric negativity was
induced. The continued action of this solution, however,
tended to induce a reversal to galvanometric positivity. But
the reactions of older roots were different—that is to say, in
the greater number of the latter cases, a solution of °5 per
cent. induced galvanometric positivity ; and it required a
much stronger solution, of from 5 to 10 per cent., to bring
about the reaction of galvanometric negativity.

We have thus seen that in the root, as in the digestive
organ, there are alternating phases of secretion and absorp-
tion, and that it is by means of the secreted fluid that solid
inorganic substances are rendered soluble, for subsequent
absorption as food. We have seen moreover that the elec-
trical reactions in the two cases are similar; that in the
young root, as in the young glandular organ of Wepenthe, the
characteristic response is by galvanometric negativity ; and
that long-continued stimulation induces diphasic variation,
with a tendency towards the reversal to positive. We saw
further that older roots, like the glands in the older pitchers
of epenthe, have a phasic reaction which is predominantly
positive. And now, having thus completed our first line of
inquiry, we shall turn to the second---the question, namely,
as to whether the ascent of sap is or is not essentially due to
physiological reaction.

The possible explanations of the ascent of sap may be
grouped broadly under two different heads, as either physical
or physiological. Under the former of these must be named
such theories as those of atmospheric pressure, capillarity,
osmosis, and evaporation from leaves. Under the latter,
the physiological, the movement of water is regarded as
mainly due, in some hitherto undefined way, to excitatory
actions by which the sap is propelled in a uni-directioned

AA2

356 COMPARATIVE ELECTRO-PHYSIOLOGY

manner, this primary movement being aided by accessory
factors.

Afnong the physical theories which have been pro-
pounded for the explanation of the ascent of sap those of
atmospheric pressure and of capillarity are admitted to be
inadequate. But that of osmosis and transpiration, put
forward by Dixon, Joly, and Askenasy, is of much greater

weight. According to this, the ascent is brought about by —

transpiration from leaves. The fluid in the mesophyll cells
of the leaves becomes concentrated by evaporation; thus
osmotic attraction is set up by the leaves, and the suction
thereby exerted is supposed to be transmitted backwards as
far as the roots, through cohering columns of water. The
difficulties in the way of this theory lie (1) in explaining how
a slow osmotic action could produce so rapid a water-current ;
and (2), in the absence of any conclusive proof that, under
actual conditions within the plant, the water-column could
have sufficient tensile strength. Even apart from these
objections, however, the fact remains that energetic water-
movements take place in the plant in the entire absence of

transpiration. For example, sap exudes from the cut end of

a tree which may exert a pressure as great as that of a
column of liquid 13 metres in height.

It is thus seen that there is an independent activity o:
some kind which maintains the movement of water through
the plant. That this activity, moreover, is not resident in the
root merely is seen from the fact that exudation of water
takes place from the tips of grass-blades when their cut stems
have been placed in water. Criticising the theory of trans-
piration, Strasburger rightly remarks that transpiration only
makes a place for inflowing water, but cannot furnish the
force necessary to convey a large volume of fluid rapidly for
a considerable distance through wood. From the considera-
tion of these and other facts, Pfeffer, in his summary, was
led to the conclusion which he states as follows: ‘A satis-
factory explanation of the means by which the transpiration-
current is maintained has not yet been brought forward. If

a ae

ET: he gece

wb Sc 5 Whe) So en

ABSORPTION OF FOOD BY PLANT bi? ae

no vital actions take part in it, then it is obvious that we
have only an incomplete knowledge of the causes at work
and of the relationship of the different factors concerned.’ *

The inadequacy of these theories to explain the ascent
of sap has, then, been freely admitted. With special refer-
ence, further, to that of osmosis, I shall myself be able to
show that the movement of water often takes place in the
plant, in a direction contrary to what it would be if osmosis
alone were involved. The fact that the absorption of water
is not a merely passive process, but a phenomenon connected
with irritability, will be further shown in the depression of
the rate of water-movement by such conditions as depress
irritability, whereas the opposite circumstance will be found
to enhance it. :

We are thus driven to examine the possibility of a
physiological explanation of the ascent of sap. On such
a theory it must be supposed to be brought about by the
action of stimulus, inducing reactions expressed in the re-
sponsive movement of water. The objections made to the
physiological explanation have already been recapitulated.
They are (1) that the movement of water is known to take
place rapidly, and by preference, through woody tissues
which are supposed to be dead; and (2) that when the roots
have been killed by hot water, or when poison is supplied,
the transport of sap continues to take place. I shall now
proceed to examine these arguments, and to show that the
objections raised, though apparently so strong, are not really
valid.

We shall first refer to the argument which has been
based upon the fact that in trees conduction takes place
very rapidly through woody portions which are regarded as
dead. It is not, it must be noted, implied by this that
the presence of wood is essential to the ascent of sap, in-
asmuch as even in trees there are tracts of living cortical
tissue in the roots which have to be traversed before the
water can reach the woody tissues. In seedlings of Gramine

’ Pfeffer, Physiology of Plants (English translation), 1903, p. 224. |

358 COMPARATIVE ELECTRO-PHYSIOLOGY

only one or two days old, again, water ascends, and is ex-
creted at the tip of the yet unopened leaf. Transpiration
is here at its minimum, and the fibro-vascular elements at
this early stage cannot be regarded as ‘dead wood.’ Finally,
in herbaceous plants, where woody elements are ee Ane
the ascent of sap is seen to take place.

Assuming, for the sake of argument, that in the case of

the tree, the mass of wood in the interior were dead, it might.

still conceivably be of use in the irrigating system as a
central reservoir. This would certainly be advantageous to
rapidity of transit. At the lower end of the tree, the wood
abuts upon the delicate parenchymatous tissues of the root,
and at the upper upon those of the leaves. According to
the physiological theory, then, it might be supposed that it
was by the multiple activity of the cells of the root that
water was pumped into the wood ; and that at the other end
the central reservoir was able to furnish a supply to make
up for the constant loss by transpiration. Laterally also, in
the stem itself the cortical tissues could draw upon this
central supply. Under such an arrangement no part of the
_ plant could be very far away from the reservoir.

As a matter of fact, this sketch corresponds roughly to
the working of the tree as an hydraulic machine. The
system is, however, somewhat more complex than has been
indicated. Besides the central, we have also to remember
the presence of lateral reservoirs, in the parenchymatous
tissues of the cortex. But the transport of water through
these is not, of course, so rapid as through the central, more
specifically conducting, system. In the case of herbaceous
plants, where the quantity of wood is insignificant, we may
regard the central channels as abolished. Here we have
soft cortical tissues extending continuously from root to
leaves through the stem, and it is obviously through these
that the ascent of water takes place. In woody trees, then,
there is no reason to suppose that the cortical tissues could
not play a similar part in the conveyance of water. The
difference is, that in this case there is also an added and

F ried ¢ ral ” al
ae Bee De ee ee ee tr Vee oe

Ses | le

ABSORPTION OF FOOD BY PLANT 359

better channel available, which will naturaily come into
requisition where quick transit is required.

In a woody trunk, then, we have (1) the outer cortical
cylinder of water-conducting tissues, by which the ascent of
sap takes place slowly. We have (2) the highly-conducting
central woody tissue, which not only allows of water ascend-
ing rapidly through it, but is also (3) in lateral communi-
cation with the outer cylinder. The hydraulic system thus
consists of a large central canal, as it were, connected with
innumerable lateral reservoirs, which are the cells of the
cortex. When a demand arises for rapidity of water-supply
on account of transpiration, we can now see that no less than
three different factors are brought into requisition. First
there is the rapid upward transit through the wood ;
secondly, the slow ascent through the cortex ; and thirdly,
the lateral supply from the cortex by way of the nearest
wood. :

As regards the last of these, the cortical tissues in contact
with the wood act ina manner not very unlike that of the
roots towards the soil. That is to say, under different cir-
cumstances, they absorb water from it, and excrete water
into it, these alternating processes being by no means
accidental, but guided by appropriate excitatory reactions.

Turning our attention for a moment to the movements
of Mimosa \eaf, we find that on excitation the expelled water
makes its way to the fibro-vascular tissue. There is here, in
the excitable tissue, unlike the case of secretory organs, no
external vent, and we see the necessity of a central reservoir
to which water excitatorily expelled may find access. On
the subsidence of excitation, the water is re-absorbed by the
organ, causing expansion and re-erection of the leaf. Such
movements of inflow and outflow evidently take place in the
trunk of the tree itself. Under the stimulus of sunlight,
the excited cortical tissue will squeeze water inwards into the
central reservoir. If this takes place, the effect will be seen
in a diametric contraction. At the time when transpiration
is most rapid, under the action of sunlight, there is thus

360 COMPARATIVE ELECTRO-PHYSIOLOGY

besides the water coming from the roots, an additional
supply available from the lateral reservoirs. The loss of
water thus sustained by the cortex during the day is made
up again at night, when it will suck water outwards from the
central reservoir. We have here a case analogous to the
action of the excitatory tissue of the pulvinus of J/imosa

expelling water into the wood on excitation, and re-
absorbing it on the cessation of excitation. The occurrence |

of these reactions in the cortex explains the observation
made by Kraus that the organs of the plant diminish in bulk
from morning to afternoon, the reverse seo taking place
from afternoon to morning.

We have thus seen how important a factor is excitatory
reaction in the observed movements of water, even on the
supposition that the woody tissue, being dead, is a merely
passive agent. The question has still to be attacked,
however, whether this assumption, so generally made, is
correct, that the wood used for conduction of water is dead.
This supposition has arisen from the chemical transformation
undergone by the protoplasm in woody vessels. We have
seen, however, in the case of the epidermal cells of the skin,
that it is possible for chemical transformation to occur,
without necessarily being accompanied by the death-change.

Before proceeding to inquire whether the conducting
woody channels are really dead, it is desirable to say a few
words as to the particular tissues in the wood, which are
most effective for this purpose. Many experiments have
been carried out to determine this. Among other things
various staining fluids have been employed. But an objec-
tion raised in the case of some of these has been that the
water of such solutions travels faster than the dye dissolved
in it. For my own part, I have found the employment of
dilute solution of phenolpthaline to be exceedingly delicate
and useful for the purpose of this investigation. It is
perfectly colourless, and the staining appears only after
appropriate development. ‘The cut end of the stem is placed
in this dilute solution and left for some time. Transverse

<7. ae

i.

~ " - = »
PRAT SO te bee

“* eee eee ee ee ee ee ee ee lr Cll

ABSORPTION OF FOOD BY PLANT 361

sections of the stem at different heights are then made and
placed in the field of a microscope. There is now nothing
distinguishing to be seen, as the solution sucked up by the
stem was colourless. Dilute solution of potash, however, will
act on this as a developer. The particular tissues, therefore,
through which the solution has been conducted, on now
being subjected to the action of this agent, become of a rich
crimson colour. By this means it is easy to see, as already
determined by various observers, that it is the younger, or
‘sap-wood, which is concerned in the work of the rapid
conduction of water, the older, or ‘heart-wood,’ being
ineffective for this purpose. If, however, the wood taking
part in the ascent of sap had been dead, and acted as a
passive agent merely, it is difficult to understand the reason
of this selective action of the younger, and presumably more
living, woody tissues. |

It occurred to me, finally, that as electrical response is an
indubitable concomitant of the excitatory reaction of living
tissues, the question as to whether sap-wood was alive or
dead could be subjected to a decisive test. For this purpose
I took various strips of sap-wood from different woody plants.
The cortical tissue was in each case carefully removed, and
the specimens were placed in water, allowing them a period
of rest. The first experiment was to observe whether local
stimulation by the Rotary Mechanical Stimulator did or did
not evoke electrical response. I found from this, that mecha-
nical excitation of the sap-wood induced considerable excita-
tory response of galvanometric negativity. I then subjected
the same tissue to the action of boiling water for: a length of
time, and again tested its electrical reaction by the same
method. The wood was found to be very resistant to the
action of heat, and it was only after long immersion that
the responses were entirely abolished. Drying was in fact
found, significantly enough, to be an easier method than the
application of heat, to kill, and therefore to. abolish the
responsiveness of, the wood. If the wood be first dried, and
then soaked in water, it entirely ceases to manifest electrical

362 COMPARATIVE ELECTRO-PHYSIOLOGY

response. The ordinary wood of commerce exhibits no
response. The familiar fact that the cut end of a woody
stem, when not placed in water immediately, ceases to
suck up water, has been supposed to be due solely to
the intervention of air-bubbles. From the experiment which
I have described, however, it would appear that the death
of the exposed tissue by drying must be included here as a
factor in this abolition of suction.

”_

With sap-wood I was
also able to obtain the in-
dication of galvanometric
negativity in response to
thermal stimulation. Hot
platinum wire was applied
at a distance of 5 mm.
from the proximal contact.
Response was thus due to
the transmitted effect of
excitation.

I was next desirous
to obtain photographic

records of the normal

Fic. 216. Photographic Record of +s

Electrical Response of Sap-wood ied Sells of living wood
The normal negative responses seen in the and its variations under

| first series are depressed after application chemical agents. For this

of chloroform in the second.

purpose I employed both
the electrical and vibrational modes of stimulation. For the
first of these, the strip of sap-wood was cut in the form
of a two-pronged fork, of which one prong was killed by
exposure to the drying influence of the air, while the other
was kept alive by immersion in water. The specimen was
now placed in water as a whole, in order to moisten the dried
half. After this, electrical connections were made in the
usual manner with the killed and unkilled ends of the speci-
men. On next subjecting it to equi-alternating shocks’
response was obtained as induced galvanometric negativity
of the living prong. These responses are seen in fig. 216 in
the first series of records to the left. Chloroform was next

ABSORPTION OF FOOD BY PLANT 363

applied, and we observe the consequent depression of re-
sponse; when the chloroform was blown off the responses
were found to undergo revival.

In the next experiment, a specimen of living wood was
mounted in the vibrational apparatus, and its normal re-
sponses taken. I next applied copper sulphate, and the
record shows the consequent abolition of response (fig. 217).
I have thus been able to establish the fact that the woody
vessels of the sap-wood are not dead but living, and hence
fully susceptible of physiological reaction. This will, I think,
be found to dispose of one of
the difficulties raised in regard
to the physiological theory of
the ascent of sap.

We come, secondly, to the
objections that have been based
on the ground of the ascent of
sap through a tree whose roots
have been killed by boiling

Fic. 217. Photographic Record

water, and, further, on the ex- showing Normal Responses ot
: * Living Wood to Vibrational
periments of Hartig and Stras- Stimulus, and the Abolition of

burger. These observers set cut Response by a Toxic Dose of
ends of trees in tubs of poisonous Wei eee

solutions, such as copper sulphate, which were found, in spite
of their toxic character, to ascend to the leaves. It is clear
that if such violent protoplasmic poisons ascend the trunk,
they must kill all the cells lying in their path. And from
this it was inferred that the living cells in the stem could
not be necessary to the rise of sap. Strasburger was thus
led to the conclusion that ‘the supposition that the living
elements in any way co-operate in the ascent of the
transpiration current is absolutely precluded.’’

It does not, however, appear that this inference on the
part of Strasburger was justified, for we must remember the
fact that any cut piece of stem when placed in water is found
to exhibit suctional activity. Hence the active cells con-
cerned—if the process is to be regarded as due to such—

' Strasburger, Zext-dook of Botany (English translation), 1903, p. 188.

364 COMPARATIVE ELECTRO-PHYSIOLOGY

must be distributed throughout the plant. Death of a given
zone, then, would arrest the activity of that particular zone
but not that of another zone higher up. Thus a poisonous
solution would only abolish activity in those cells which it
had already reached. The activity of cells above would
remain unaffected. That the death of cells below offers no
resistance to the passage of water, when suctional activity is

maintained above I have demonstrated elsewhere, and shall |

again show in the course of the next chapter, in cases in
which the lower part of the plant was killed by boiling
water. Under the action of poisons, similarly, I have been
able to show that a poison can: pass easily through killed
tissues owing to the suctional activity of cells higher up.
This was demonstrated by means of experiments on Des-
modium gyrans, where the cut end of the petiole was placed
in copper sulphate solution. It is fortunate that in this case,
during the ascent of poison, we have areas whose activity
is manifested visibly by the rhythmic motile indications of
the pulvini of the inserted lateral leaflets. That copper
sulphate solution arrests rhythmic activity, and induces
death, is seen by the rapid stoppage of pulsation when
we apply it directly on the pulvini of the pulsating leaflets.
When it is applied, however, at the cut end of the petiole, the
arrest of pulsation only takes place after sufficient time has
elapsed for the poison to ascend through the intervening
distance. This shows clearly that successive zones are killed
one after another, and that the death of a point below does
not stop the suction above. From this experiment it is evi-
dent that the application of poison, at the root, or the cut end
of a stem, need not be expected to arrest suction until the
whole plant has been killed, and from Strasburger’s account of
his experiment it is evident that the movement of water did
come to a stop when the poison reached the top of the tree.

We thus see that the objections which have been raised,
with regard to the physiological nature of the ascent of sap,
are not valid. I shall therefore proceed in the next chapter
to describe crucial experiments in demonstration of the fun-
damentally excitatory character of this process,

Aw yi he et Rie aah tent ti ae)

ih ieee)

SS ee ee eee ee

CHAPTER XXVI
THE EXCITATORY CHARACTER OF SUCTIONAL, RESPONSE

Propagation of excitatory wave in plant attended by progressive movement of
water — Hydraulic response to stimulus—The Shoshungraph—Direct and photo-
graphic methods of record—Responsive variations of suction under physiological
modifications induced by various agents—Effects of lowesing and raising of
temperature—Explanation of maintenance:of suction, when root killed—
Effect of poison influenced by tonic condition—Effect of anzesthetics on
suctional response—Excitatory verszs osmotic action—-Stimulation by alter-
nating induction-shocks—Terminal and sub-terminal modes of application—
Three modes of obtaining response-records, namely (1) the unbalanced,
(2) the balanced, (3) the over-balanced—Renewal of suction previously at
standstill, by action of stimulus—Reponsive enhancement of suction by
stimulus—After-effect of stimulus —Diminution of latent period as after-effect

of stimulus—Response under over-balance—Response under sub-terminal
stimulation —Variation of response under seasonal changes.

IN the last chapter it was shown that the various objections
hitherto urged against the excitatory nature of the ascent of
sap were not justified. In the course of the present chapter,
therefore, I shall adduce proofs that the water-movement in
the plant is the result of stimulatory action. Instead of
vaguely referring the phenomenon to physiological activity,
moreover, we shall attempt, proceeding from the ‘basis
of other excitatory reactions, already clearly established,
first to see whether inferences based on these are capable of
explaining the present problem, and secondly, to subject
those inferences themselves to the test of experimental in-
vestigation.

We cut a certain length of the stem of M/zmosa, and keep
it immersed for some time ina very dilute solution of common
salt, until the tissue has become charged with this. The
specimen is then taken out, and thoroughly rinsed with clean
water. It is now held vertically, with the lower end dipped

366 COMPARATIVE ELECTRO-PHYSIOLOGY

in a highly dilute solution of silver nitrate. A portion of the
tissue higher up is now excited by contact with a hot wire.
The excitation thus induced is then found to travel through
the intervening distance, with a velocity characteristic of the
conducting power of the tissue. The arrival of the excita-
tory wave at the lower end is attended by an expulsion of
the cell-sap containing the salt solution previously absorbed..

This expulsion is instantly made visible by the formation of |

a dense white precipitate of silver chloride. From this
experiment it is seen that the passage of excitation is at-
tended by a forward movement of water in the direction of
propagation. |

The next point to be realised is that a strong or a long-
continued stimulus will give rise in the tissue, not to one,
but to a multiple series of propagated waves. If the tip of
a leaf of Biophytum be strongly excited, we see successive
waves of excitation, marked by the serial fall of the motile
leaflets, proceeding again and again in the centripetal
direction, from the terminal excited point. If, similarly, the
end of theroot be excited, by any means, an excitatory move-
ment of water will be induced, proceeding away from this
end, in an upward direction. It must be remembered, how-
ever, that excitation proceeds in all directions from the
excited point. If then the point of excitation be terminal, it
is evident that the direction of propagation, being away from
this, will be upwards. But if the tip of the root be highly ex-
citable, then, owing to local excitation, there will also be a
certain amount of secretion into the soil. Even highly
excitable tissues, however, after continuous stimulation, show
a tendency, as we have seen, to the reversal of their character.
istic response. This secretion at the terminal point of the
root will tend to become changed into absorption. Again,
looking at the succession of excitatory waves propelling
water upwards, we can see that these will leave a deficit of
cell-sap behind, which will further act rather for the absorp-
tion than for the secretion of fluid. And in addition to
these, if there be any other directive influences, such as

a a a a ii i i a i

Pad

Sev apie

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 367

evaporation from the leaves, they will tend to help the
particular uni-directioned flow. We have seen that these
conclusions are confirmed by the results obtained in the
electrical response of the roots. We there saw that very
young roots give at first negative responses, which are after-
wards reversed to positive, under continuous stimulation.
Older roots, as we also saw, give response by positivity. We
saw, further, that there was much reason for regarding
negative response as associated with the secretion, and
positive with the absorption of fluid.

Thus the serial propagation of excitation from cell to
cell, with the concomitant movement of water, will normally
be upwards. In this connection it is very significant that the
younger portion of the fibro-vascular bundle is the preferential
channel for the conduction, at once of water and of excitation.
It is thus seen that a one-directioned movement of water
may be produced by the multiple excitatory activity
of the tissue. And just as the multiple activity of certain
tissues, say, for instance, the leaflets of Desmodium, may
be gauged by their multiple mechanical movements, so
in the rate of the water-movement we have a means of
measuring the intensity of the multiple rhythmic activity of
those which are concerned in the ascent of sap. This would
be analogous to the measurement of the rhythmic activity of
the heart, by a determination of the rate of flow of the
circulating blood. In the case of the plant, however, this rate
of movement might be measured, either by means of the pro-
pulsion of water forwards, or by the suction exerted behind.

In order to demonstrate the fact that the water movement
in the ascent of sap is mainly dependent on excitatory
reactions, it is necessary to have at our disposal some means
of rapidly observing and recording the variations induced by
physiological changes in the rate of ascent. For this pur-
pose I was successful in devising the Shoshungraph or
suction-recorder, described in detail in my book on ‘ Plant
Response.’ ! :

' Bose, Plant Response, pp. 364-371.

368 © ‘COMPARATIVE ELECTRO-PHYSIOLOGY

-° This instrument consists of (1) an arrangement by which
the specimen may be subjected rapidly to the action of
different excitatory or depressing agents ; (2) a potometric
tube for the measurement of changes of suctional activity,
under different external conditions ; and (3) a contrivance by
tmneans of which the movements of the water-index, with
their time-relations, are recorded. The principal parts of the
apparatus are seen in fig. 218. V is the plant-vessel, in
which the specimen is mounted, with or without roots, by
means of a watertight india-rubber cork. R is the
reservoir, which may be filled with hot or cold water, or with
the required chemical solution. By appropriate manipula-
tion of stopcocks, by means of key K, the water in the plant-
vessel may be replaced quickly by any of these, and the
effect of the changed condition on the rate of water-move-
ment observed.

A direct record of the rate of movement may be made on
the revolving drum, actuated by clockwork, as shown in the
figure. For this purpose, a pen, P, is fitted over the
potometric tube, by means of a brass collar, which has a
rectangular opening, kept always coincident with the water-
index. The collar, carrying the pen, is attached to a thread,
which passes round small pulleys. One end of this thread
carries a counterpoise, M, and the other is wound round a
wheel, W, which can be so manipulated as to make the pen
follow the movements of the water-column. When the
water-index is followed in the way described, a direct record
of the water-movement in the plant is obtained. A curve
is thus traced, the ordinate of which represents the quantity
of water sucked up, and the abscissa the time. The slope of
the curve thus gives the rate of movement. As long as
suction is uniform, this slope remains constant. If, however,
any exciting agent increases the rate of suction, there is an
immediate flexure in the curve, which thus becomes steeper.
A depressing agent lessens the slope, and when suction is
abolished, the record becomes horizontal. For the detection
of the slightest variation in the rate of suction, the Method of

Se a

a

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 369

Balance is employed, which depends upon an application of
compensation, by which, under normal conditions, the water-
index is kept stationary, though the suctional movement in

Fic, 218. The Shoshungraph

V, plant-vessel ; R, reservoir ; C, compensator, whose balancing height is
adjusted by rack and pinion, s; kK, key for manipulation of four-way

stop-cock ; P, recording pen, with counterpoise M, manipulated by
wheel, w. The drumjis rotated by the clock at uniform speed.

BB

370 COMPARATIVE ELECTRO-PHYSIOLOGY

the plant is in no way disturbed. The balance is obtained
by allowing water to enter the plant-vessel, from the com-
pensator, C, at a rate exactly equal to that of its withdrawal
by suction. Thus, under a condition of balance, the record
‘becomes horizontal. An exciting agent now produces an
inclination of the record upwards, or a depressing agent a

declination downwards. This was the instrument employed.
by me for the obtaining of records in a simple manner of.

‘suctional response and its variations, under different physio-
logical modifications. A fuller account of the method and
the results obtained by it will be found in my book on
‘Plant Response.’ As the subject of the ascent of sap is, how-
ever, of extreme importance, I thought it desirable to see to
what extent the sensitiveness of this instrument could be
raised, and also to devise means, in connection with it, for the
automatic record of results obtained. For the latter purpose
I employed photography. As the water-index, whose ex-
cursions in the potometric tube are to be recorded, is trans-
parent, it is necessary to provide an additional opaque index,
which shall move in and out with it. This consists of a
short length of mercury, lying in contact with the end of the
“water-column. The potometer tube is placed in the field of
a magic lantern, and the index is focussed on a moving
photographic plate by means of an objective. The sensitive-
ness of this method of record may be increased in two ways.
First, the bore of the capillary tube may be made finer and
finer. But this cannot be carried to an extreme, as the
capillary offers great resistance to the free movement of the
index. Secondly, the sensitiveness may be increased to any
extent by the employment of a highly-magnifying and
short-focus objective. By the combination of both these
devices, we are able in practice to arrive at an extraordinary
degree of sensitiveness, qualifying us to attack some of the
most difficult problems with the greatest ease. For our
present purpose, however, it is not by any means necessary
to approach the limit of this sensitiveness. The photo-
graphic records given in the course of the present chapter

a a

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 37I

were obtained with a tube having a bore I square mm. in
section, and employing an ordinary magic lantern objective,
which casts an image without any magnification. The
Method of Balance again, as we have seen, affords us another
opportunity of arriving at an experimental adjustment of
creat sensitiveness.

The experimental delicacy obtained by high tiouihen
tion can only be used to the greatest advantage when
coupled with the Method of Balance, if we have means at
our disposal for securing the utmost possible perfection of
the balance. We have seen that the balance is adjusted
when the rate at which water is removed from the plant-
vessel by suction is exactly equal to the rate of its inflow
from the compensating vessel, Cc. This compensation is
roughly effected by the rack and pinion, Ss, which serves to
regulate the flow by raising or lowering the compensating
vessel (fig. 218). For the purpose of the final adjustment
the narrow bore of the thick india-rubber tubing, which con-
nects the compensator with the plant-vessel, is capable of
gradual constriction. This must be accomplished by equal
compression on all sides, as bilateral compression alone
would act to induce a discontinuous closure and sudden
arrest of flow. If the compressing arrangement be something
after the model of the iris-diaphragm, then the bore, which
regulates the flow, may be constricted gradually and con-
tinuously. With such an arrangement it is easy to arrive at
a balance so perfect that the index appears to be quite
stationary. Under-balance would now make it move, say to
the right ; and over-balance to the left.

We shall now proceed to show that those agents shih
exalt physiological activity also act to enhance suction; and
that those which induce physiological depression will also
depress suction. One of those which enhance the multiple
activity of the tissue is, as we know, the rise of temperature ;
whereas cooling, or lowering of temperature, tends to depress
it, even to the extent of abolition. Thus an automatically
vibrating leaflet of Desmodium has its vibration-frequency

BB2

372 COMPARATIVE ELECTRO-PHYSIOLOGY

enhanced by a rise, and depressed or arrested by a fall, of
temperature. A similar effect is seen to occur in the suctional
response of plants. Thus, in a given specimen of Cvoéon,
application of cold water at 4° C. to the root was found to
arrest the suction in-the course of 8 minutes. This arrest
by cold was not permanent, for the normal rate of suction re-
appeared on the return of the water to a normal temperature.
On applying water of raised temperature to the root, on the
other hand, the rate of suction was immediately found to
be enhanced. This is illustrated in the following record
(fig. 219), in which the normal rate of suction at 23° C. was
7 cubic mm. in volume, or 7 mg.
in weight per minute. The ap-
plication of water at 35° C. now
induced a steep rise of the curve,
indicating an enhanced rate of
suction of 58 mg. per minute, or
more than eight times the rate at
23° C. On now once more sub-
stituting water at 23° C., the rate
is seen to become lowered, but
not to fall so low as at the
ere ttn at oso C, factesed beginning. It now fell from 58
Suction at 35° C., and the to 14 mg. per minute, instead of
io ideal Pee Ketur returning to the original 8 mg.
This is due to the fact that
the internal energy of the tissue has been raised in the
meantime by the absorption of warm water, the enhancement
of the normal rate being a persistent after-effect of this.

We shall next take up the apparently anomalous case,
in which, when the root has been killed by pouring boiling
water over it, the suction of the plant is nevertheless main-
tained. In such an experiment the normal record was first
taken, and boiling water was then passed through the plant-
vessel continuously for some time till the roots were killed.
On allowing the water in the vessel to return to the tempera-
ture of the room, it was found that suction was taking place

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 373

at an even greatcr rate than ordinary. This result would
at first appear to show that protoplasmic activity had
nothing to do with the ascent of sap, and the objection
would have been fatal if the activity which produces suction
had been confined to the roots alone. But in reality, as we
have already seen, such activity is present, to a greater or
less extent, throughout every zone of the plant. The only
part which is killed, however, in the experiment - just
described, is that which is actually immersed in, or in
immediate contiguity with, the boiling water; and the
unkilled tissues above continue their suctional activity
unabated. The increase in the rate of suction is to be ex-
plained by the fact that the entrance of water, instead of
being effected through the extremely attenuated channels
of the root-hairs, now takes place through the whole mass of
the root, acting virtually as a wet rag tied round the base
of the living stem. The mass of water which it is thus
possible to suck up directly through the broad-sectioned
stem is evidently much greater than could have been taken
in through the resistant, organically-conducting channels of
the rootlets. |
The fact thus demonstrated, that the local death of a
given zone does not fer se arrest the suctional activity of the
tissues above it, explains why a poison may be carried to the
top of atree. It is evident that only when it has thus been
conveyed, and when all the tissues have thus been killed,
could a permanent arrest take place. And Strasburger him-
self admits that arrest under these conditions does occur.
With reference to the effect of poison, again, it is im-
portant to bear in mind that its toxic effect depends, toa
certain extent, on the tonic condition of the tissue. Thus a
Desmodium \eaflet which was moderately vigorous had its
pulsatory movement arrested soon after the local application
of the copper sulphate solution. In more vigorous leaflets,
however, the arrest did not take place till after a considerable
length of time. Indeed, in some cases, after a preliminary
arrest, the leaflet is able to shake off the effects of the poison

374 COMPARATIVE ELECTRO-PHYSIOLOGY

absorbed, by some process of accommodation. I have shown
elsewhere! that the effect of poison on the response of
growth is modified to a remarkable extent by the different
tonic conditions of the tissue. The experiments in question
were carried out on similar specimens of Crinum lily, in
which the only difference induced depended on the fact that
one set had been kept at a temperature of 30° C., and were

thus in moderate tonic condition, while the others had been.

maintained at 34° C., bringing about, as I have shown, an
optimum tonic condition. The application of a 5 per cent.
solution of copper sulphate to one of the first of these was
found to induce the rapid decline and final arrest of growth,
while a similar application, on a specimen in the optimum
condition of the second set, induced a preliminary exaltation
followed by a slow depression and ultimate arrest of growth,
the last-named, however, being reached only after the lapse
ofa considerable time.

The difference of effect under different tonic conditions
was still more strikingly exhibited by the application of a
smaller dose—namely, of a I percent. solution. This was
found to induce a depression of growth, which was ultimately
fatal to the plant, in the case of specimens kept at 30° C.
But when the same dose was applied to a plant which had
been kept at 34° C, the effect was seen in a marked
exaltation of the rate, for a fairly long time, after which it
shook off the effect of poison altogether, resuming its normal
rate of growth.

Thus the effect of poison on the various activities of the
plant is seen to depend not only on the amount of the
agent, and the duration of application, but also on the
tonic condition of the tissue. Strong and prolonged applica-
tions will abolish all active processes, by inducing the death
of the plant. In accordance with this, I find that in certain

plants under the action of copper sulphate the arrest of

suction is more rapid than in others. All alike, however,
exhibit permanent arrest sooner or later.
1 Bose, Plant Response, pp. 487-488.

~— ST ae |, ae

wethcept

—"
EN

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 375

The question of the excitatory nature of the ascent of
sap may again. be tested by the application of anzsthetic
agents, such as solution of ether. The record is first taken
of the actual rate of suction, and then by quick manipulation
_of the double key, the water in the plant-vessel down to the
base of the specimen is replaced by ether solution. The
original rate of suction had in a particular case been 40
cubic mm. per minute. After
the application, however, this
became depressed, and in the
course of four minutes under-
went a preliminary arrest.
This short arrest was suc-
ceeded by reversal, or expul-
sion, which lasted for fourteen
minutes, and then gave place
to what was practically per-
manent arrest (fig. 220).

I have occasionally ob-
served an interesting variation
in the arrest of suction induced
by ether. Shortly after the
application just described an
arrest of suction is induced.
This, however, is only pre-
liminary, suction after an
interval being renewed at a_ Fic. 220. Action of Anesthetics in

: Abolition of Suction
very slow rate. When this 3
Seca : Solution of ether substituted for water
has proceeded for some time, at point marked with dots... Suc-
the process undergoes a tion abolished within fifteen minutes.

eradual and final arrest.

It has already been said that though the excitatory
reaction is to be regarded as the fundamental cause of the
transport of water in the plant, yet there are other factors
which undoubtedly contribute to that result, One of these
may be the favourable disposition of osmotic substances—
for example, the concentration of cell-sap consequent on

376 COMPARATIVE ELECTRO-PHYSIOLOGY

evaporation, in the leaves. That this osmotic effect is,
however, merely secondary, and that the ascent is chiefly
due to excitatory action, is seen in certain experiments
which may be mentioned here, in which the ascent takes
place with even greater vigour than before, when it is opposed
by an osmotic influence. .

The various solutions of salts are very unequal in their
physiological action : some, like potassium nitrate, are neutral,’
but others, as strong solutions of sodium chloride, are ex-
citatory. Thus the action of
a strong solution of potassium
nitrate is physiologically more
or less neutral, while its osmotic
action, at the same time, is
pronounced. A strong solution
of common salt, on the other
hand, is both excitatory and
osmotic.

If then we apply KNO,
solution to the cut end of a
stem, water will be osmotically
withdrawn from the plant, in
| opposition to the normal ascent
Fic. 221. Effect of Strong KNO, of se ; There. will thus be .

Solution depression of the rate of suction

The first record shows the normal after the application, as seen in
and the second the depressed rate .
the following record (fig. 221),

of suction caused by the reagent.

which I obtained with a cut
branch of Cvoton. If, however, in a similar experiment,
a strong solution of NaCl be applied, two antagonistic
reactions will be set up. One, due to the osmotic action,
will oppose suction, and the other, due to the excitatory
nature of the reagent, will accelerate it, while the resultant
effect will be modified by the excitability of the experimental
plant. In fig. 222 is shown the effect of NaCl solution in

' It should be mentioned here that even such neutral salts, in strong solution,
induce physiological depression.

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 377

increasing the suction of a specimen of ‘Croom in a favourable
condition of excitability. We have here a very great en-
hancement of the ascensional movement caused by this solu-
tion, which would, acting osmotically, have retarded the
normal rate. The physiologically excitatory action of strong
sodium chloride, however, is not permanent, and the enhanced
excitability is followed by depression. The effect on suctional
response in such cases, then, is modified by the factor of time,
the. first enhancement being
followed by a fall below the
original normal rate of suction.

The experiments which I
have here described show how
intimately suctional response is
connected with excitatory re-
action. Having thus seen that
any physiological modification
of the tissue is attended by an
appropriate change in the rate
of suction, it only remains to
demonstrate finally the fact that
stimulation is attended by a
responsive movement of water Fic. 222. Effect of Strong NaCl
in a tissue. In order to do this, Solution

we should have at our disposal The first record shows the normal
. and the second the exalted rate
mens means of applying of suction caused by the reagent.

stimulus which is capable of |

measurement, capable of graduation, and not in itself of
a nature to disturb the delicate balance of the shoshun-
graphic record. The end sought after was first to record
the normal rate of suction, and then to observe the
effect immediately induced in this by the application of the
stimulus, the process of record being uninterrupted mean-
while. The only form of stimulus which would comply
with these conditions is the electrical, given by tetanising
induction shocks, of longer or shorter duration. The possible
objections to the use of this form of stimulus are as follows :

378 COMPARATIVE ELECTRO-PHYSIOLOGY

1. The water in the plant-vessel may be supposed to undergo
decomposition by electrolysis. There may also be a certain
evolution of heat in the plant-vessel. 2. In a sluggish
tissue, such as that of the plant, the excitatory value of
induction- shocks may not prove sufficient to Soles suctional
response.

With regard to the first of these objections, it is to be
borne in mind that the shocks, being alternate, will produce |
but little polarisation effect. Fhe heating effect of a current
so small in quantity, moreover, is also likely to be very
slight. ~The extent of
the disturbance from
these causes can, how-
ever, be determined by
a blank experiment.
The electrodes, by
whose proper applica-
tion the plant is ex-
cited, are allowed to
hang down in the plant-
vessel without direct

Fic. 223. Record of Blank Experiment showing
Absence of any Disturbance of Record from attachment to the plant

Induction-shocks as such itself. The alternating

Photographic record of excursion of .mercury t AT
index in Shoshungraph. The thick white CUrrent will now pass

line shows duration of application of shock. through the water, only
Time-marks in this and other photographic :
records represent intervals of five minutes. a very small fraction of
it, incapable of pro-
ducing effective excitation, passing through the plant.
The Shoshungraph is adjusted for the balanced condition,
given as we have seen, a horizontal line of record, and
that intensity of induction-current which is to be used
in subsequent experiments is now passed through the
plant-vessel for twenty minutes continuously. It will be
seen from the record (fig. 223), that no disturbance was
induced by this in the balanced line, thus proving that such
disturbing effects, if they exist, are in practice negligible. In
actual experiments, where the excitatory effect is to be studied,

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 379.

the duration of application is often less than a minute, and
seldom exceeds five minutes. It should also be borne in
mind that individually and collectively the effects of the dis-
turbing causes enumerated would, if anything, be towards
expulsion from the plant-vessel. We shall see, however,
that the typical responsive effect is movement in the opposite
direction, indicative of an enhancement of suction. With
regard to the second cause of misgiving, as to whether plant-
tissues may or may not be made to exhibit excitatory varia-
tion by means of induction-shocks, I have found that some
specimens, notably those of Cvofon, are sufficiently suscep-
tible to this form of stimulation. For this purpose it is
necessary to use very strong induction-shocks from a large
coil, This necessity is further increased by the fact that
much of the induction-current is uselessly and unavoidably
shunted by the water in the vessel. |
This electrical stimulation may be applied to the cut end
of the branch, immersed in the water of the plant-vessel, in
either of two different ways. The first of these may be
described as the Zerminal Mode of Application, its object
being to localise the excitation more or less at the lower
end of the specimen. This is done by tying two small
pieces of platinum, in connection with the electrodes, to
diametrically opposite sides of the base of the stem by means
of a thread. Or two pins, in connection with the electrodes,
may be pricked into the lower section of the specimen near
its circumference. This transverse mode of stimulation,
across the diameter of the stem, is not, theoretically, so
effective as longitudinal stimulation would be, but under
the particular experimental conditions nothing better could
be devised (fig. 224). The second mode of applying this
electrical stimulus I shall distinguish as Swd-terminal. Here,
two pins in connection with the electrodes pierce through the
stem, one above the other, in planes at right angles to each
other (fig. 225). After arranging the electrical connections
in any one of the ways enumerated, the specimen is adjusted
in the Shoshungraph, and allowed a period of rest for the

380 COMPARATIVE ELECTRO-PHYSIOLOGY

passing off of excitatory effects of preparation. The record
of normal suction is then taken by means either of the ordi-
nary recorder or of photography. The variation induced in
the record after the application of stimulus, then, exhibits the
effect of excitation.

In order to test the results in as many ways as possible, I

arranged for three different methods of record. The first
was without balance. Here the slope of the suction-curve |

indicates the normal rate of suction, the enhanced rate under
stimulus being indicated by flexure and increased steepness.

Fic. 224. Terminal Fic, 225. —Sub-terminal

Mode of Applica- Mode of Application
tion of Stimulus of Stimulus

A diminution in the rate of suction, or an expulsive effect,
would, on the other hand, be indicated by a corresponding

diminution of the slope, or reversal of the curve.
The second method of record is carried out under exact

balance, and is, as already explained, an extremely delicate
means of detecting variations in the rate of suction. If this
rate be enhanced the curve rises suddenly from the balanced
horizontal line, a depression inducing, on the contrary, a
downward movement. The last method is that of Over-

balance, where, owing to a supply of water from the com-

— ee a

Piaget oe

ee

= LS ee,

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 381

pensator at a uniform rate in larger quantity than necessary,
a movement of the index is induced in a direction opposite
to that of suction. Here the slope of the curve, due to over-
balance, is down, and should the stimulus cause any enhance-
ment of suction, the steep down-curve must be replaced by a
less steep, or horizontal, or up-curve. The Method of Balance
is, as I have said, the most delicate, but this Method of Over-
balance enables us to detect the after-effect of stimulus in a
striking manner.

As regards the form of this response by movement of
water, reference has already been made to previous results,
in which we saw that the excitatory effect in the plant, as
studied by electrical response, was of two different types,
according to certain phasic conditions. Highly excitable
roots, we found, gave response by galvanometric negativity,
indicating secretion or expulsion of water. Less excitable
roots, on the other hand, gave response by positive variation,
most probably indicating responsive absorption. These two
opposite effects actually occur, as I find, under. different
phasic conditions, in the suctional responses which I am
about to describe. :

I shall deal first with the results which I invariably
obtained in carrying out experiments on Crofom and certain
other plants during the month of February. The Indian
winter was just over, and the spring had not yet fully set in.
The nights were still cold, though the days were growing
warmer. The plants, therefore, owing to these peculiar
climatic conditions, must be regarded as having been some-
what sub-tonic. My first experiment related to the initiation
of suctional activity in a specimen which, in this respect,
had been previously at standstill. Stimulus might here be
expected to renew that multiple activity on which suctional
response, according to our theory, depends. We may here
refer once more to the initiation of multiple activity by
stimulus in a leaflet of Desmodium previously at standstill.

I have shown that when this plant is deprived of its
store of latent energy by unfavourable conditions, then the

382 COMPARATIVE ELECTRO-PHYSIOLOGY

multiple movement ofits leaflets is arrested. If the plant,
for instance, be kept for some time in a dark room, the leaf-
lets cease to pulsate. But if now an electrical shock of
moderate intensity be given to the pulvinus, the incident
stimulus, by its excitatory action, gives rise to a number of
responsive movements, which again come to a stop as soon
as the imparted energy is exhausted. Or we may, in such a
case, employ the stimulus of light. A record of the subse-
quent effect has already been given on a. previous page
(cf. fig. 141).

It will there be noticed He that the quiescent leaflet is
thrown into pulsatory movements after the lapse of a short
latent period ; (2) that the increasing absorption of stimulus
has the effect of augmenting the amplitude of response ; and
lastly (3) that, owing to the presence of latent energy derived
from the impinging stimulus, the activity of the leaflet con-
tinues for some time, even on the cessation of stimulus itself.
It is, in. fact, by that enhancement of the tonic condition,
which comes about by the continuous absorption of energy
from the’ environment, that the apparently autonomous
response of the leaflet is maintained. There is, as has been
said ‘before, no essential difference between multiple and

autonomous response. A tissue, which was responding

autonomously, comes to a state of standstill when its store
of latent energy falls below par. Conversely, by the acces-
sion of energy from external stimulus, activity is resumed,
multiple passing into autonomous response.

Returning, then, to the hydraulic mode of response, as
observed in variations of suction, we might expect that the
irapact of stimulus would initiate this in a tissue at suctional
standstill. For this experiment I took a specimen of Croton
and mounted it, with terminal electrodes, in the Shoshun-
graph, At this time it showed a moderate rate of suction.
It was then kept undisturbed in a dark room for forty-eight
hours, at the end of which time, owing to the run-down of its
latent energy, the suctional activity was found to be arrested.
But on the application of electrical stimulation, the suctional

a a

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 383

activity was again renewed, after a latent period of two
minutes, and found to persist for a considerable time, even
on the cessation of stimulation (fig. 226). We have: here,
theny an exact parallel to the renewal of the so-called
autonomous response of Desmodium leaflet referred to
above, ee

We have thus studied the phenomenon of the variation of
suction by renewal when found at zero. We shall next con-

A
2 Uaioe Geer sagt ee ee ea * Fic, 227. Photographic

: Record of Effect of
Stimulus in Enhancing
Rate of Suction

Fic. 226. Renewal of Suction, Pre-
viously at. Standstill, by Action of
Stimulus This record was. taken

under balanced con-
ditions. Vertical line
represents moment of

, application of stimulus

for 30 seconds.

The half-shaded portion of figure repre-
sents time of application. of stimulus.
Suctional response is seen to be
initiated after a latent.period of one
minute, and to persist after the cessa-
tion of stimulus,

KA

sider the case of a variation induced in the existing rate by
the action of stimulus. The normal rate is exactly balanced,
a condition which is represented in the photographic record by
the straight line which results from the stationary position of
the mercury index. Stimulus of 5 seconds’ duration was now
applied, and the responsive acceleration is seen as a steep rise
in the record (fig. 227). This responsive acceleration persists

' Ifa cut branch of any plant be kept in water for several days, its suctional
activity, as is well known, disappears. This is commonly attributed to the
blocking of the cut end by mucilage and bacterial growths, since the making of
a fresh section is found to renew the activity. This making of a fresh section,

384 COMPARATIVE ELECTRO-PHYSIOLOGY

during a period that depends on the intensity of stimulus and
the condition of the tissue, after which it declines slowly.
After recovery, however, the rate is generally somewhat
higher than at first. This is due to the persistent after-
effect of stimulus absorbed, If
the enhanced suctional rate be
now again balanced, and
stimulus. applied once more,
there will be a still further
enhancement of the rate. In
this way, owing to the succes-
sive increase of latent energy,
the suctional activity is enhanced
till it reaches a limit, after which
there is but little additional effect
to be induced by stimulus.
There is another and _ in-
teresting effect which is often
observed, in consequence of

Variation of Latent
Period as After-effect of Stimulus

Fic. 228.

The record was taken under balanced
conditions. Half-shaded portion

represents application of stimulus
for 30 seconds. Lower record
shows latent period to be 45
seconds. After _re-balance,
stimulus of 30 seconds was once
more applied. -Upper record
now shows reduction of latent

energy absorbed from previous
stimulation. This is the diminu-
tion of the latent period, after
which response takes place.
This will be seen in the following

period to 30 seconds.

| record (fig. 228). The initial
rate of suction was in this case balanced, as usual, and
stimulus of thirty seconds’ duration was applied. The
responsive acceleration is seen to take place forty-five
seconds after the cessation of stimulus. The enhanced rate
was balanced, and a stimulus of thirty seconds’ duration

however, does not decide the question; for in making it, is involved the
strong mechanical stimulus of a cut. The outgrowths may, no doubt, obstruct
the passage of water, and yet the total abolition of suction not be due to this
cause alone. The more effective cause is, in fact, the run-down of energy, as
proved by the experiment described above. In another experiment I took a cut
stem in which suction had come to a standstill, and, without disturbing the
mucilaginous end, I supplied it with water somewhat above the ordinary tem-
perature. This thermal stimulation at once initiated renewed suctional_ activity
with great vigour.

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 385

was applied once more. It is here seen that this stimulus
induces a further acceleration. The latent period, however,
of this second response is reduced from forty-five seconds,
which was its value in the first case, to thirty seconds.

This variation of latent period is brought out still more
clearly by the application of a stimulus of shorter duration,
in which case the latent period is more prolonged, and its
variations, therefore, more easily observed. In order to show
this, I took a fresh specimen of Cyvof¢on, and, after the initial
balance, applied stimulus of five seconds’ duration. It will
be seen from the photographic record (fig. 229) that the

Fic, 229. Photographic Record showing Variation of Latent Period
as After-effect of Stimulus

Stimulus applied was for 5 seconds. Moment of application represented
by vertical line. Lower record shows latent period to be 25 minutes.
After re-balance, stimulus of 5 seconds was again applied. Upper
record now shows reduction of latent period to 20 minutes,

latent period was here very long, being as much as twenty-
five minutes. After re-balance stimulus was once more
applied, lasting, as before, for five seconds. The latent
period in the second case is seen to be reduced to twenty
minutes. |

As an interesting and independent verification of the
enhancement of suction by stimulus, I now took a number
of response-curves, using the Method of Over-balance. Here,
it will be remembered, the normal over-balance is indicated
by a down-curve, and acceleration of suction by diminution
of the slope, or even by reversal, of this curve. In fig. 230
is seen a record obtained in this manner the first down part

CC

386 COMPARATIVE ELECTRO-PHYSIOLOGY

of which shows the curve of over-balance. Stimulus of halt
a minute’s duration was now applied, and it will be noticed

t {Fic. 230. Suctional Response
under Over-balance

Stimulus of 30 seconds neutralises
over-balance and reverses curve,

that on account of the re-
sponsive acceleration the
slope becomes increasingly
diminished, till,- after an
interval of one minute and
a half, the curve becomes
horizontal. After this it is
reversed to the upward direc-
tion. It will thus be seen
that the responsive accelera-
tion has here, induced a rate
of suction which is not merely
sufficient to compensate the
over-balance, but greatly ex-
ceeds it. .In the next photo-

eraphic record (fig. 231) I have been successful in showing
the immediate and persistent after-effects. In order to do

Fic. 231. Photographic Record of Effect of Stimulus on Over-balance

First stimulus for 2 seconds, represented by first vertical line, neutralises
and reverses over-balance. Horizontal record after reversal represents
persistent after-effect. Second stimulus for 2 seconds, represented
by second vertical line, gives risejto up-record, the persistent after-
effect being represented by a curve of diminished slope.

this within the limited range of a photographic plate, I
employed stimulus of the short duration of two seconds.

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 387

The first part of the record shows the normal down-curve of
over-balance. Stimulus of two seconds’ duration was now
applied, at the place marked in the record with a vertical
line. This is seen to induce a growing diminution, in the
slope of the curve culminating in reversal; and afterwards,
owing to the persistence of the after-effect of stimulus, the
record becomes horizontal. A second stimulus of two
seconds’ duration was now applied. ‘This is seen to induce a
further enhancement of the rate, which is shown by the up-
curve. The slope of this curve undergoes a slow decline with
the waning of the immediate effect of stimulus. But on |
account of that component of the stimulus which remains
latent in the tissue, there is induced a more or less persistent
after-effect, which is greater than the after-effect due to the
first stimulus. For while the after-effect of the first stimulus
was seen to make the record horizontal, the second after-
effect renders the curve slightly ascending. From these
and other facts previously enumerated it will be under-
stood that the effect ot latent stimulus derived from external
sources is to increase suctional activity up to a certain
limit.

Having now described the various effects induced in
a slightly sub-tonic tissue, under the simplest mode of
stimulation, namely, the terminal, we shall proceed to inquire
as to what are the effects induced under a somewhat more com-
plex mode of stimulation. This is the case with sub-terminal
stimulus, where the point stimulated is not on the external
extremity, but within the tissue, though near the lower end.
Under these conditions the excitatory wave will proceed in
two opposite directions, upwards and downwards. The
short terminal zone, however, being close to the directly
stimulated area, will be more intensely affected than the
extended upper region. For this reason there is likely to
be a predominant expulsion of water from the lower end.
Under continued strong stimulation, however, the more
intensely excited lower zone may become fatigued. The

natural upward suction, probably enhanced by the action of
cc2

388 COMPARATIVE ELECTRO-PHYSIOLOGY

stimulus, may now be expected to reassert itself, thus con-
verting expulsion into renewed suction.

In any case, whatever the explanation, I find that the
result of this mode of stimulus is, first, a movement of
expulsion, followed, under continued intense stimulus, by
renewal of the upward suction. These various effects
are seen in the following photographic record, where
the up-curve represents the normal unbalanced -suction
(fig. 232). Continuous
stimulation was now applied
at the point marked with a
verticalline. It will be seen
that normal suction is here
diminished, and afterwards
reversed into expulsion.
This expulsive movement
continues, as I already knew
from previous experiments,
for a considerable length of
time, before the second re-
versal to suction is brought
Fic. 232. Photographic Record of about by fatigue of the lower

. 4 i b- i l .
cat ee Continuous Sub-termina zone. In order to expedite

Response was taken without balance the reversal, so that the

Continuous stimulation applied from cyrye might remain within
. moment represented by vertical line.

This induced diminution, arrest, and the plate, I applied a still
reversal of response to expulsion. : :

Stronger stimulation applied at second SLrenges stimulation, at the
vertical line. This induced a second point marked by the second

reversal to suction. Thin white line . ‘ A
shows duration of application of vertical line. This was done
stimulus of moderate intensity; and by increasing the voltage
subsequent thick line, of greater ; 4a ae
intensity. which worked the primary
of the induction coil from
six to eight volts. It will be seen how this reversed the
expulsion, converting it into renewed suction.
We have seen, as already stated in the electrical response
of roots, that while less excitable old roots will generally

give positive response, highly excitable young roots give

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 389

negative. We saw, further, that there was reason to
associate this positive response with the process of absorp-
tion, and the negative, conversely, with that of expulsion
or secretion. With various kinds of tissues, moreover, we
have found, and shall see further, that as a general rule
positive response is obtained, either when the tissue is
sub-tonic, and very slightly. excitable, or when the stimulus-
intensity is feeble, and when the tissue is fatigued by over-
stimulation. Negative response, on the other hand, is
characteristic of highly excitable tissues. Under natural
conditions, then, when the roots are subjected to the
moderate stimulation of such factors as contact with soil,
water, and food, we might expect their response to be
positive or absorptive. In cut branches, also, in which the
tissue is not extremely excitable, a simple terminal applica-
tion of stimulus induces, as we saw, the absorpto-positive
effect, either by initiating suction, or by enhancing that
which was already taking place.

But in highly excitable young roots, in contact with a
stimulating supply of inorganic food, the characteristic
response, as we have seen, is by secretion. The electrical
response also of young roots we found to be negative.
Between these two extremes of positive and negative, then,
there must be an intermediate case in which the responsive
action to external stimulus will be zero.

Applying this to the parallel case of suctional response
in cut branches, we should expect to meet with. two
different cases besides that already given. In one, where
the tissue is very highly excitable, the response under simple
terminal stimulation will be negative or expulsive. In
tissues, however, which are not so highly excitable, but more
excitable than those sub-tonic specimens whose characteristic
responses I have already described, it might be possible to
find cases in which the suctional response to stimulus will
be zero. In the sub-tonic tissues referred to, we have already
seen that in consequence of increase of internal energy by
external stimulus, the suctional response tends to reach a

390 COMPARATIVE ELECTRO-PHYSIOLOGY

limit, after which further stimulation would produce little or
no effect. 7

Thus we see that if a tissue from any cause be sub-tonic,
even moderately strong stimulus will induce positive or
absorptive response. If it, on the other hand, be highly
excitable, the response may be expected to be negative or
expulsive. Between these two, in the intermediate state of
excitability, the effect will be neither one nor the other, that
is to say, zero. These results concern the application of
somewhat strong stimulus, such as that of electrical shocks.
Feeble stimulus will generally evoke response by absorption.
We can also clearly see that the tonic condition, and there-
fore the excitability, of a tissue will vary with the seasons,
being low at the end of winter, and high in spring or summer.
Thus the same strong stimulus which in the one season will
induce absorption, might be expected in the other to provoke
expulsion. In experimenting on suction during the period
of seasonal variation, I obtained results which verified these
inferences,

These experiments, as will be remembered, were begun
_ in February, when the spring had scarcely commenced, and
the plants were in a sub-tonic condition. Under these
circumstances, we saw that the terminal application ot
stimulus uniformly evoked positive response, by enhance-
ment of suction. By the end of February, however, when
warmer weather prevailed, and the vigour of the plants was
evidently greater, I was surprised to find that the same
stimulus, applied in the same way, to similar specimens of
Croton evoked little or no response. A week later—that is
to say, in the beginning of March, when the Indian spring
was well advanced, and the physiological activity of the
plants high—I found that the response which had thus seemed
to disappear was renewed, but had become reversed in sign.
Strong terminal stimulation now, as a rule, evoked responsive
expulsion.

From the considerations enumerated at the beginning of
these investigations, it was seen that the various physical

EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 391

theories brought forward to account for the ascent of sap
were admittedly inadequate. The further objections, urged
against the fundamentally excitatory nature of the processes
involved, on the ground of the important part played in the
ascent by sap-wood, generally regarded as dead, I have also
shown to be untenable. The sap-wood I have shown to be
not dead, but living, and to exhibit the normal response of
living tissues to excitation. The long persistence of: suction,
when the roots are killed with hot water, or the cut
specimen placed in poison, was shown to be accounted for
by the fact that the death of any individual zone does not
arrest suction in those above. I have shown, moreover, that
those agents, such as rising temperature, which exalt the
general physiological activity of the tissue, enhance suctional
activity also. Those which, like cold or anzsthetics, act, on
the other hand, to depress the general physiological activity,
will depress and arrest its suctional activity also. And,
finally, the fact. that the water-movement is a form of
excitatory response has been fully demonstrated by the
experiments described and the records given in the course
of the present chapter. The physiological theory of the
ascent of sap may thus be regarded as established.

CHAPTER XXVII
RESPONSE TO STIMULUS OF LIGHT

Heliotropic plant movements reducible to fundamental reaction of contraction
or expansion—Various mechanical effects of light in pulvinated and growing
organs—Electrical response induced by light not specific, but cencomitant to
excitatory effects—Electrical response of plant to light not determined by
presence or absence of chloroplasts—Effect of unilateral application of stimu-
lus on transversely distal point—Positive response due to indirect effect and
negative to transmission of true excitation—Mechanical response of leaf of
Mimosa to light applied on upper half of pulvinus—Mechanical response
consists of erection or positive ovement, followed by fall or negative move-
ment—Electrical response of leaf of A/¢mosa to light applied on upper halt
of pulvinus ; induction in lower half of pulvinus of positivity followed by
negativity—Longitudinal transmission of excitatory effect, with concomitant
galvanometric negativity—Direct effect of light and positive after-effect—
Circumstances which are effective in reversing normal response—Plants in
slightly sub-tonic condition give positive followed by negative response—
Exemplified by (a) electrical and (6) growth response—Examples of positive
response to light—Periodic variation of excitability—Multiple mechanical
response under light—Direct and after effect—Multiple electrical response
under light, with phasic alternations of (— + — +) or (+ — + —)—After
effects; unmasking of antagonistic elements, either A/ws or minus—Three
types of after-effects.

THE first important point that arises, in connection with the
response of living tissues to light, is the question whether
such response is peculiar in its character, or fundamentally
similar to that which is evoked by other forms of stimulus.
The mechanical movements of plants under light are
apparently so diverse that it would at first sight appear
almost impossible to derive them all from any common
fundamental reaction. Thus, some plant organs are found
to turn towards the light, others away from it, and
others again to remain perpendicular to it. Thus three
different typical effects—positive, negative, and dia-helio-

RESPONSE TO STIMULUS OF LIGHT 393

tropic—are induced in different cases by the same
stimulus. These effects, moreover, are found to occur in
growing as well as in pulvinated organs. This incon-
sistency of effects has been a source of great perplexity,
inclining observers to the belief that the action of any given
plant organ under light is determined, not by some definite
reaction, but by its own power to decide what is for its
individual advantage.

I have shown elsewhere, however,! that as regards
mechanical response, the reaction of plant organs to the
stimulus of light is extremely definite. This, like other
forms of stimuius, induces negative turgidity variation and
contraction, as well as consequent retardation of growth in
growing organs. Such excitatory effects, moreover, if the
tissue be of fair conducting power, may be transmitted in
either a transverse or a longitudinal direction. The intensity
of this transmitted excitatory effect is thus dependent, as I
have shown, on the intensity and duration of stimulus and
on the conductivity of the tissue. If neither the intensity of
the stimulus nor the conductivity of the tissue be great, it
will be the indirect or hydro-positive effect which will reach
the distant point, there to induce a positive turgidity
variation and expansion. The foregoing observations relate
to tissues in a normal condition of excitability. When the
tissue is sub-tonic, however, the absorbed stimulus, as we have
seen, increases the internal energy and brings about a re-
sponsive expansion.

I have also shown that the various mechanical move-
ments induced by the unilateral action of light, depend (1)
upon whether the stimulus remains localised on the proximal
side of the organ or is conducted to the distal ; and (2) on
the relative excitabilities of proximal and distal. I have
shown, moreover, that all the diverse effects induced by light
are demonstrably traceable to the action of these various
factors in varying combination. And, finally, certain highly
excitable tissues, owing to excess of energy derived from

1 Plant Response, pp. 551 to 685.

304 COMPARATIVE ELECTRO-PHYSIOLOGY

continuous stimulation, exhibit alternations of phase, negative
and positive, or vice versa, constituting multi-phasic or
oscillatory response. On these considerations it is possible
to summarise the principal effects caused by light, as

follows:

MECHANICAL EFFECTS OF LIGHT ON PULVINATED AND

GROWING ORGANS.

II. | Normally — ex-
citable organ
subjected to |
unilateral
light.

A. Organ radial.

|
|
|
|

| B. Organ aniso-
| | tropic or dorsi-
ventral.

of internal energy.

A 1. Moderate light,
causing excitatory
contraction of proxi-
mal and hydro-posi-

tive expansion of |

distal.

A 2. Strong light. Ex-
citatory effect trans-
mitted to distal, neu-
tralising first.

A 3. Intense and long-
continued light.
Fatigue of proximal
and excitatory con-
traction of distal.

Description .
Case of Hate Action Effect observed
-|
I. | Tissuesub-tonic. | Stimulus causesincrease | Expansion or enhanced

rate of growth, e.g.
Pileus of Coprinus
drooping in dark-
ness, made re-turgid
by light. Renewed
growth of dark-
rigored plant ex-
posed to light.

. Curvature towards

light, e.g. positive
curvature of seed-
lings of Sinapis;
positive curvature of
Lepidium seedlings
(Oltmanns). .

Neutral effect, e.g.
Sinapis and Lepfi-
dium (Oltmanns)
under strong and
long-continued light.

- Reversed or nega-

tive response, e.g.
Sinapis and Lept-
dium (Oltmanns).

BI. Excitatory con-
traction of proximal
predominant, owing
either to greater ex-
citability of proximal
or feeble transverse
conductivity of tissue.

B 2. Transmission of
excitation through
highly conducting
tissue to more ex-
citable lower or
distal. Greater con-

traction of distal.

_

N

. Positive response,

e.g. upward folding
of leaflets in so-called
‘diurnal sleep’ of
Robinia, Erythrina
indica, and Clitorta
ternatea.

. Negative response,

e.g. downward fold-
ing of leaflets in so-
called ‘ diurnal sleep’
of Oxalis, Biophy-
tum, and Averrhoa.

RESPONSE TO STIMULUS OF LIGHT 395 |

Case

Description Action Effect observed
of tissue

III. | Tissues -which | Considerable absorp- “Initiation of multiple

exhibit mul- tion of energy, im-- response in Desmo-
tiple or auto- mediate or prior. dium gyrans_pre-
nomous _re- _ viously at standstill ;
sponse. multiple response

| under continuous

|

| | action of light in

| Biophytum; photo-

| tactic movements

| of swarming spores ;
cf. multiple visual im-
pulses in retina.

Turning now to the electrical responses induced by light,
our investigation is resolved into the inquiry whether these
are not the electrical concomitants of those excjtatory effects
which we have already been able to analyse through
mechanical response. But, before proceeding to this question,
I shall first briefly refer to certain ‘electrical effects of light
upon green leaves’ which have been observed by Dr. Waller.'
- His experiments were performed by making galvanometer
connections with two halves of the same leaf, one being
strongly illuminated and the other unilluminated. With leaves
of different plants he obtained opposite electrical effects under
the action of light. From the leaves of Iris, for example, during
illumination, he obtained response of galvanometric negativity,
with reversal, or positivity, on the cessation of light as its after-
effect. With leaves of Zrope@olum and Mathiola, on the con-
trary, he obtained positive response during illumination and
subsequently negative. Beyond the suggestion that negativity
may be associated with dissimilation and positivity with
assimilation, Dr. Waller offers no explanation of this opposi-
tion of effects observed by him. He states, however, that he
regards the presence of ‘chloroplasts’ as essential to these
electrical reactions under light, inasmuch as petals, he found,
gave no response. Even in the case of the green leaves ‘of
ordinary garden shrubs and trees,’ moreover; he found no

' Waller, Proc. Roy. Soc. vol. \xvii. pp. 129-137.

396 COMPARATIVE ELECTRO-PHYSIOLOGY

response. This he ascribes to their ‘low average metabolism.’
It will thus be seen that no satisfactory explanation is offered
either of the mutual opposition of the electrical effects ob-
served or of the way in which the presence of ‘chloroplasts’
acts as a determining factor.

To turn now to the subject of my proper inquiry, it has
to be determined whether those electrical responses which
may be observed in vegetable tissues under the action of -
light are or are not another expression of the same excita-
tory reactions under light which I have already demonstrated
by means of mechanical response. And it may be as
well to say at the outset that it is the excitability of the
tissue, and not the presence or absence of ‘chloroplasts,’ that
is the critical factor in determining this electrical response.
For I have obtained strong responses under light from pul-
vini, stems, and other tissues which are relatively deficient in
‘chloroplasts’; and again, while the lamina of a plant rich
in ‘chloroplasts’ would give but moderate response to light,
the petiole of the same plant, characterised by less ‘chloro-
plasts,’ would often give much stronger response. The etio-
lated stem of celery, moreover, gives strong electrical response.
And, finally, it is an error to suppose that petals of flowers
are irresponsive to light, for I have obtained strong response
from petals of Seshania coccineum and from Eucharis lily.
Animal nerve, again, in which there is no chlorophyll, gives
response to light.

As I have already shown the typical heliotropic effects
exhibited by plants to be brought about by differential
excitatory action on the proximal and distal sides of the
same organ, I shall now proceed to exhibit the electrical
counterparts of these experimentally. As I wish, moreover,
to show that the general electrical response to the unilateral
action of light is fundamentally the same as that induced by
other forms of stimulus, the first experiment to be described
will be one depending on the unilateral application of a non-
luminous stimulus, say thermal.

If on one side of a growing organ we apply a series of

RESPONSE TO STIMULUS OF LIGHT 397

thermal shocks, by means of the electro-thermic stimulator,
the proximal side will undergo contraction, while the ex-
pelled water, by its hydro-positive effect, will induce expan-
sion on the distal side. By means of these two conspiring
actions the organ will be bent towards the source of
stimulus. The electrical variation on the distal side will
therefore be positive ; but if the stimulus applied be suffi-
ciently strong and long-continued, true excitation will be
transmitted across the tissue to the distal side. This will
neutralise the first mechanical movement, and the corre-
sponding electrical effect will be a reversal of the previous

Fic. 233. Experimental Arrangement for Detection of Electrical Change
induced at the Point transversely Distal to Point stimulated

Upper point stimulated by thermal shocks from electro-thermic stimulator,
the lower being the transversely distal point.

positive into the excitatory negative. Similar electrical
effects will also be observed if the organ be restrained from
movement, or if it be so old as to have lost its power of
motility.

Taking now a young stem of 4ryophyllum, 1 applied a
series of thermal stimuli at the proximal point (fig. 233).
Periodic closure of the electrical circuit by means of a metro-
nome caused rapidly succeeding thermal shocks to act on the
upper or proximal side. By adjusting the heating current
the stimulus was at first made moderate. It will be seen

398 COMPARATIVE ELECTRO-PHYSIOLOGY

from the photographic record (fig. 234) that this gave rise
electrically to an increasing positive effect at the diametrically
opposite point. This clearly shows that the latter under-
went a positive turgidity variation, in consequence of the
forcing-in of water expelled by excitatory contraction from the
upper side. It is at this stage the indirect and not. the true
excitatory effect of stimulus that is being transmitted to B.
By this experiment it is
also demonstrated that the
positive curvature induced
by the unilateral applica-
tion of any stimulus is the
joint effect of the direct
excitatory contraction of
the proximal side and the
indirect or hydro-positive
expansion of the distal.!

Another interesting
F1G. 234. Record of Kesponse to Moderate h b b
Unilateral Stimulation under the Experi- P®¢nomenon to © Cn

mental Arrangement described served in this curve is that,
Response of distal point by increased after the maximum effect
galvanometric positivity due to hydro-
positive effect. Note initiation of multi: has been reached, there
ple response. . , .
is a series of oscillatory
multiple responses. In this result there may possibly be two
factors in operation: first, after the maximum hydro-positive
tension has been set up there may be a gradual percolation
of the true excitatory effect, with its opposite reaction, the
unstable balance thus produced manifesting itself in oscilla-
tions; and, secondly, we know that increased hydrostatic

tension has the effect of initiating multiple responses, as seen

1 In records of such a response as I have just described, when exhibited by
highly excitable tissues, a preliminary negative twitch, of momentary duration,
may sometimes be observed. This is not due to the conduction of true excitation,
but to pseudo-conduction. The sudden blow delivered by the hydrostatic wave
on its arrival at the distal point is, in a highly excitable structure, sufficient of
itself to induce a short-lived excitatory effect. Thus this does not represent the
true transmission of excitation, but its initiation de novo by a secondary mecha-
nical cause (p. 446).

RESPONSE TO STIMULUS OF LIGHT 399

in the snail’s heart, under a sufficiently high degree of
internal hydrostatic pressure.

As regards conduction in general, we know that a
strong stimulus is transmitted to a greater distance than a
weak. In the next record (fig. 235) this may be seen in an
interesting manner. At first a moderate stimulus was em-
ployed, and this gave rise to (2) a maximum positive varia-
tion of the distal point B. The stimulus was then increased
and we observe that (0) the
excitatory effect, now reach-
ing B, causes a reversal of
the curve, owing to induced
galvanometric negativity. If
at the beginning we had used
a stimulus of fairly strong
intensity the first effect would
have been a positivity of B,
due to the indirect effect of
stimulus ; and, secondly, the
excitatory effect would have
reached the point gradually,
neutralising and afterwards

reversing the first. I shall FIG. 235. Record of Different Specimen

now describe the correspond- under same Experimental Arrange-
: ‘ ment when Stimulus is first Moderate
ing effects, both mechanical and then Increased

and electrical, which are in- (a) Positive response, due to hydro-
positive effect ; this is converted to

duced by stimulus of light. negative in (6) due to transmission of
Wetake a Winiosa plant, and excitatory effect under stronger stimu-
lation.

subject only the upper half of

one of its primary pulvini to the action of sunlight. The
effects thus induced are (1) the local contraction of the excited
upper half, and the expansion of the lower half by the hydro-
positive effect ; (2) the gradual percolation of true excitation
to the lower half, and consequent initiation of excitatory con-
traction there; and (3) the continued action of excitation
and increasing contraction on the more excitable lower half.
All these effects. are exhibited in the mechanical response

400 - COMPARATIVE ELECTRO-PHYSIOLOGY

shown in fig. 236, where the first is seen in the up-curve,
which thus indicates the joint action of contraction in the
upper and expansion in the lower, giving rise to an erectile
movement. After an interval of one minute the excitatory
effect is seen to have reached the lower half, giving rise now
to a reversed or down movement, which, on account of the
greater excitability of the lower, is seen to carry the leaf
downwards, much below its original position. The dotted
portion of the curve shows the after effect on the cessation of
the stimulating light. It is
here interesting to observe
that it is possible to obtain
an after-effect which is posi-
tive and of opposite sign to
the true excitatory effect, this
positivity being due to the
increased internal energy
consequent on the absorption
Fic. 236. Mechanical Response of Of stimulus.

Pulvinus of AZmosa to Continuous
Action of Light from Above applied In fig. 237 are shown the
at Moment marked | electrical effects consequent

- Positive heliotropic movement caused on _ stimulation by light in
by excitation of upper half neu- ;

tralised by transmission to distal another specimen of the
side, and ultimately reversed owing ulvinus of Mimosa The
to greater excitability of lower half. : , :

Dotted line represents recovery on electrical contacts are made

cessation of light. Note final erec- ; : :
tion of leaf above original position in this case, one with the

as after-effect of absorbed stimulus. lower half of the pulvinus and
the other with a distant in-

different point. Stimulus of light is applied, as in the
last case, on the upper half. This experimental method
is free from the objection which has been urged against
Dr. Waller's experiments on green leaves, that the result
was complicated by the direct action of light on the electrode
itself. It should be pointed out, however, that the presence
of such photo-electric action is more important theoretically
than practically, being of relatively small amount. A further
complication which arises from the direct action of light on

RESPONSE TO STIMULUS OF LIGHT 401

one of the electrodes lies in rise of temperature. Though in
all such experiments the incident light should pass to the
organ through a thick stratum of water, which absorbs its
heat-rays, yet the absorption of light by the tissue must
necessarily occasion a slight rise of temperature. In con-
nection with this should be remembered the fact I have
elsewhere demonstrated, that though sudden variation of
temperature acts as an excitatory agent, yet a slow and
gradual rise, enhancing the internal energy, brings about
only a slight positivity, opposite to the effect of true excita-
tion. In this particular ex-
periment, however, as the
electrical contacts are not
directly acted on by light,
we obtain results uncom-
plicated by such disturbing
factors.

The first electrical effect
brought about in the lower
half of the pulvinus by yy. 237. Electrical Response in the

icati : Lower Half of the Pulvinus of
sd plication of light ii the Mimosa due to Stimulation of
distal upper half is seen in Distal Upper Half by Light

fig. 237 as an increasing gal- Observe the first phase of positivity,
; ee ‘ due to hydro-positive effect, con-
vanometric positivity. This verted subsequently into negative
is concomitant to the hydro- NF ae transmission of true ex-
positive effect at the lower
half, which, conspiring with the contraction of the upper,
produces that up-movement of the leaf seen in the previous
figure. The excitatory effect next reaches the lower half,
and we there obtain increasing galvanometric negativity in
consequence. This corresponds with the mechanical move-
‘ment of depression. From this experiment it is clear that
light, like other forms of stimulus, induces, as its true excita-
tory reaction, galvanometric negativity, the indirect or hydro-
positive effect being one of galvanometric positivity.
In the last case, then, we obtained a transverse trans-
mission of the true excitatory effect. Similar effects are
DD

402 COMPARATIVE ELECTRO-PHYSIOLOGY

also obtainable by longitudinal transmission. In order to
do this an organ must be selected which is a fairly good
conductor. I have thus been able to observe a series of
responses to transmitted stimulus of light, using such speci-
mens as the petiole of Bryophyllum. Light was here applied
at a distance of 5 mm. from the proximal contact, and this
gave rise to a series of true excitatory responses of galvano-
metric negativity.

Having thus established unmistakably the negative sign
of the excitatory electrical variation induced and transmitted
under stimulus of light, I shall
next proceed: to give records of
experiments in which light was
applied directly. The effect ob-
served in these cases is naturally
much larger, as there is no
enfeeblement by _ transmission.
Fig. 238 shows a series of such
responses, obtained at intervals of
two minutes, by the application
of sunlight — previously passed
through a stratum of water—
during five seconds only in each
Hie eA? Phaeatic Be. ~case, on the petiole of a vigorous
“cord of Series of Negative leaf of Bryophyllum. It will be

Responses of Petiole of noticed that after each response

Bryophyllum to Stimuli of : nee

Sunlight of Five Seconds?’ Of galvanometric negativity there

Dt eee ee Inter- is an after-effect of positivity, in
Observe the positive after-effect, consequence of which the base

due to increase of internal line of the series, instead of re-

energy, which causes down- site :

ward trend of base-line. maining horizontal, trends down-

wards. This power of holding

stimulus latent, for the increase of internal energy, we shall
later see to be important, as heralding the initiation of
multiple response. The exhibition of these after-effects, due
to increase of latent energy, is also to be observed in the
record given already of the mechanical response of Jzmosa

RESPONSE TO STIMULUS OF LIGHT ~ 403

(fig. 236), where the leaf, after its excitatory fall, was re-
erected, on cessation of stimulus, above its original height.
This, as we saw, was due to a certain portion of the incident
stimulus becoming latent, and thus increasing the internal
energy.

We shall next take up the subject of the occurrence of
positive response, as sometimes induced by light. This may
be the result of various different causes. There is one fact,
however, in connection with the action of light which it is
important to bear in mind. Thus, if we subject the lower
half of the pulvinus of A/zmosa, for instance, to the action of
sunlight, its responsive fall will be gradual, unlike the sudden
depression caused by thermal or mechanical stimulation.
This is because light, usually speaking, constitutes a stimulus
of only moderate intensity. We have seen that a stimulus
which falls below a certain critical level of excitatory intensity
will evoke positive, instead of negative response. We have
also seen that from a sub-tonic tissue the positive response is
more easily obtained than from one which is highly ex-
citable. Now, as the excitatory efficiency of a mechanical
stimulus is very great, and as that stimulus is also incapable
of finely graduated decrease, it follows that, in order to ex-
hibit positive response under such stimulation, it is necessary
that the tissue stimulated should be extremely depressed, or
even moribund. Under such conditions I have shown
(p. 83) that it is possible under feeble stimulus to obtain
positive response, which, under stronger, will pass into the
normal negative.

The stimulus of light, then, whose action is very moderate,
discriminates more finely between tonic gradations of the
tissue than can other forms of stimulus. If this tonic con-
dition be very favourable, and the excitability high, the re-
sponse will be by normal galvanometric negativity. If the
tonic condition, however, be less favourable, the response is
liable to be positive. This latter fact will be very strikingly
demonstrated, in a later chapter, by experiments carried out
on nerves, It will there be shown that while highly excitable

DD2

404 COMPARATIVE ELECTRO-PHYSIOLOGY

nerve gives the normal negative response, the same tissue,
if its tonic condition be below par, gives a more or less per-
sistent positive response. It is only when the tonic condition
of the nerve has again been raised, by long-continued
stimulation, that it will once more give normal response.
Fatigue is another condition which is liable to give rise to
the abnormal positive response.

The use of the stimulus of light carries with it, also, a
further limitation. A mechanical stimulus, say vibrational,
throws into activity the whole mass of tissue, not only in its
superficial, but also in its deeper lying strata. Now we have
seen that the epidermal layer of living tissues is less excitable
than those which are deeper seated. It may even, in fact, on
loca! excitation, give positive response (p. 298). It is to be
noticed, moreover, that light acts from outside, its excitatory
influence affecting the outmost tissue first, and only by
gradual percolation passing to the subjacent. Owing to
these two facts, then, of the moderateness of this stimulus
and the superficial character of its action, the tissue, if not
highly excitable, is apt, under its application, to give positive
_ response. We have seen, further, that various circumstances,
such as age and season, have an important effect in varying
the excitatory reaction of a tissue. We saw the effect of
age exemplified in the responses given by two different
specimens of roots (p. 353), in which a young root gave nega-
tive and an older positive responses. Again, we shall see
presently that there is a diurnal period, on account of which
the state of turgor, the excitability, and the sign of response,
are all alike liable to undergo periodic variations. Under
the stimulus of light these varying excitabilities may be ex-
pected to find varying expressions.

That sub-tonicity tends to make the response, under
moderate stimulation, positive, is seen in the fact that an
etiolated petiole of celery gives positive response under light
Again, I have noticed that leaves of Bryophyllum, which
usually give normal negative responses, sometimes exhibit
positive, if the plant, during the previous night, have been

RESPONSE TO STIMULUS OF LIGHT 405

subjected to unusual cold. Even in such a case, however,
though the first responses are positive, successive exposures
to light, by raising the tonic condition, are found to restore
the response to the normal negative.
The same facts receive interesting illustration in the re-
sponse of growth. If the growing organ be in a normally
excitatory condition, the
stimulus of light, inducing
negative turgidity varia-
tion, causes retardation
of growth. If the tissue, "|s° w0" 1s" 20" 25° 80° 35° 40°45
however, be in an ex-
tremely sub-tonic con-
dition, light stimulus, by
increasing the internal
energy, gives rise to the
positive effect, that is to
say, the initiation, or en-

Fic. 239. Record of Responsive Growth-
variation taken under condition of balance

hancement, of the rate in slightly Sub-tonic Flower-bud of
Cri ; : enuha tian Gf
at growth. If the erow- rane Lily under Diffuse Stimulation o

ing tissue, again, be only Continuous lines represent the effect during

; 3 : application of light, the dotted line on
slightly sub sek gie ‘ = withdrawal of light. The plant was
shall have a preliminary originally in a sub-tonic condition, and

+4 ° application of light at x, after short
positive, or enhancement, latent period, induces preliminary ac-

followed by the negative celeration of growth. After this follows
: the normal retardation. On withdrawal

response, or retardation of light, in the dotted portion of the
of the rate of growth. curve is seen the negative after-effect,
eT - followed by return to the normal rate of
This is seen in the fol- growth. A second and long-continued

application of light induces retardation,

lowing record, which I followed by oscillatory response.

obtained from a slightly

sub-tonic flower-bud of Crzzum lily, in the induced variations
of the normal rate of growth under the stimulus of light
(fig. 239). This record was made with the Balanced Cresco-
graph, where the normal rate of growth is recorded as a
horizontal line, enhancement or positive variations of the
rate being represented by up-curves, and retardation, or
negative variations, by down-curves. It will be noticed that

406 COMPARATIVE ELECTRO-PHYSIOLOGY

the first effect of light on this sub-tonic tissue was to induce
a positive response, followed subsequently by the normal
negative. Continuous stimulation is seen later to give rise
to oscillatory responses.

Having thus shown the continuity between the normal
negative and positive responses, I give below a record of the
response to light of a petiole of
cauliflower (fig. 240), a specimen
which usually, though not always,
exhibits galvanometric positivity.
Each stimulus, by exposure for
five seconds, was in this case
applied after an interval of two
minutes. It should be mentioned
here that the same tissue which
gives positive response to the
moderate stimulus of light will
Fic. 240. Photographic Re. Show the normal negative when

cord of Positive Response sybjected to a stronger stimulus,

of the Petiole of Cauliflower er
to Light of Five Seconds’ Such as the mechanical.

OE Honea ee ana The effects studied up to the
present have consisted of single

responses induced by light. But this stimulus also induces
multiple response, as we saw in the oscillatory variations
of growth in the Crinum lily in fig. 239. The same
phenomenon is observed in the case of motile response.
For example, I took a plant of Bzophytum, in which the leaf-
lets are outspread, in the presence of diffuse light, and threw
upon it direct sunlight. A series of multiple responses was
now induced, under the continuous action of stimulus, a
record of which is given in fig. 241. The up-curves here
represent excitatory downward movements, and the down-
curves their partial recoveries. Owing to the incomplete
character of these recoveries, the leaflets, as the result of a
series of such responses, are finally closed downwards. In the
outspread diurnal position the lower half of the pulvinus of the
leaflet is somewhat more turgid than the upper half, and in

RESPONSE TO STIMULUS OF LIGHT 407

consequence of repeated responses there is also a relatively
greater contraction and loss of turgidity in that lower half.
The leaflets are thus closed by the additive effect of multiple
normal negative responses or downward movements.

When a Szophytum plant is kept in the dark the leaflets
undergo a closure which is outwardly similar to that induced
by light, but actually arises from a cause precisely opposite.
Under strong stimulus of light a general contractile effect
drives the water inwards to the interior of the plant, and, the
loss of turgor in the lower halves of the pulvini being, as we
have just seen, greater than in the
upper brings about the closure
of the leaflets. But in complete
darkness the reverse process is set
up. The water returns to the
pulvini, making them over turgid.
Under this condition of excessive
turgor, however, the upper half of
the pulvinus becomes more turgid
than the lower, and, being thus
rendered more convex, closure of
the leaflets is brought about. Ex-
posure to light in this condition
: Fic. 241. Multiple Mechanical
induces a greater loss of turgor by Response of Leaflet of
the upper than by the lower half, Biophyium under the Con.

: tinuous Action of Light

and we consequently obtain the

outspread or erected position of the leaflets by a series of
small positive movements. Thus, as the result of internal
changes, the response of an organ may undergo reversal
from the ordinary negative to positive. The change from
light to darkness, by which we have here seen the character
of response to be so greatly modified, occurs in the diurnal
periodic alternation. And we can see that, in consequence
of such an imparted periodicity, an alternation of phase is
impressed upon the organism, which will carry with it a
periodic variation of excitability. If this diurnal periodicity
acted alone its after-effect would be comparatively simple,

408 COMPARATIVE ELECTRO-PHYSIOLOGY

but it is complicated by other periodicities, such as that of
temperature variation, which do not always coincide in
maxima and minima with these variations of light.

We have seen from mechanical indications that multiple
excitations are induced by light. We have, therefore, to
determine whether similar multiple excitations can be detected
electrically. Fig. 242 is a photographic record of a series of
such electrical responses ob-
tained from the lamina of
a leaf of Bryophyllum sub-
jected to the continuous
action of light. We see here
an alternation of phase in
the response, negative being
followed by positive in each
case throughout the series.
This constitutes a parallel

case to that of the mechanical
Fic. 242. Photographic Record of ; ;

Multiple Electrical Response in FeSponse in fig. 241, inasmuch

ue keer Con- as, owing to incomplete re-

covery from each negative
phase, the base line is gradually tilted upwards. But this
need not always occur, for the two phases may be equal, and
in that case the base line remains horizontal.

We have seen, in the chapter on Multiple and Autono-
mous Response, that these effects are due to the absorption
of an excess of energy. When this absorption is great the
energy may find an outward expression, even after the
cessation of the stimulus. An example of this was seen in
the mechanical response of a Desmodium \eaflet (fig. 141):
The plant was at first in a sub-tonic condition, and the auto-
nomous pulsation of its lateral leaflets had come to a stand-
still. One of these was now exposed to the continuous
action of light and its record taken. It will be noticed that
under this stimulus of light multiple responses were initiated,
which persisted for a time as an after-effect, even on the ces-
sation of light. In taking electrical records of the after-effect

RESPONSE TO STIMULUS OF LIGHT 409

of stimulation by light, I have obtained similar multiple
after-effects. And in this connection I have discovered certain
characteristic peculiarities of the electrical after-effect which
would appear to throw much light on the obscure subject
of after-effects in the retina. The electrical after-effect of
stimulus of light varies greatly in different conditions of the
tissue, but is capable of classifica-
tion under three different types. ‘ /

The first of these types refers -
to those multiply responding tis-
sues which give the usual single
response of galvanometric nega-

tivity under short exposure to |

light. When such specimens are a ‘a at
subjected to the continuous action \

of this stimulus they give multiple \
responses whose phases alternate e\

in the sequence of *mznus-plus-
minus-plus (—+—-+). Confining

Fic. 243. Diagrammatic Repre-

our attention to the first two pairs
of such phasic alternations under
continuous stimulation of light
(fig. 243), we observe that, in the
first period, excitatory . negativity
attains its maximum at J, after
which the phase becomes reversed
to positive, in which process the
curve may arrive at the original
base line, or stop short of this or
go beyond it. The maximum of

sentation of Phasic Alter-
nations, and After-effect in
Type I.

During action of light, the

phasic. alternations are a 4,
ba',a' b’,o'a' (—+—+);
6 is here the maximum
negative, and a’ the maxi-
mum positive. Withdrawa
of stimulus at point of re-
versal a’ causes unmasking
of positive component, which
is exhibited by overshooting
of the curve in the positive

_ direction, @’ c.

this phase, a’, we shall designate as maximum positivity.
Under the still-continued action of the stimulus the phase
now changes once more to negative, and so on.

It has already been stated (p. 100) that these periodic
alternations in phase were brought about by antagonistic

reactions becoming effectively predominant by turns.

Thus,

as was there pointed out, in those cases which normally give

410 COMPARATIVE ELECTRO-PHYSIOLOGY

negative response, the internal energy may be so increased
by the continuous absorption of impinging stimulus as to
induce a continuously increasing antagonistic reaction of
positivity. Hence, in such cases, negativity is gradually
diminished, and ultimately reversed. After the attainment
of maximum positivity, however, the negative element once
more becomes predominant.

With a fresh specimen, exhibiting multi-phasic responses
under the continuous action of light, I find it easy to obtain
a convincing demonstration of the presence of the positive
factor by a sudden cessation of stimulus at an appropriate
moment. If the stimulus be stopped at 4, the increasing
internal energy and natural tendency to recovery will con-
spire with each other, and the after-effect will, generally
speaking, be 6a’. That is to say, this effect is the same as
that of natural recovery.

When the second or positive phase has reached its maxi-
mum a’, the response under the continued action of stimu-
lation is once more reversed to negative a’ J’, as we have
seen. At this point of reversal a’, the positive, is balanced
by the negative. If then at this point the impinging stimu-
lus be suddenly withdrawn, the positive element, finding
itself unopposed, will overshoot the line of balance, and the
curve will proceed in the positive direction towards c (fig. 243).
This phasic sequence (Type I.) then, during stimulation, and
as an after-effect of it, should thus be (— + -:-), the dotted
sign representing the after-effect. That this is actually so,
is seen in the following series of photographic records
(fig. 244), where the dotted portion of the record exhibits
the after-effect. The intensity of this positive after-effect
varies with the freshness and vigour of the specimen. The
influence of fatigue, in the gradual diminution of the effect,
is seen in the two subsequent series (4) and (c) obtained
from the same specimen. This diminution culminates in
the gradual diminution of the positive after-effect, and its
conversion into a negative after-effect, as seen in (d).

We thus arrive at an intermediate case (Type II.), exem-

RESPONSE TO STIMULUS OF LIGHT 411

plified by specimens which are not very fresh. The sequence
ishere(— + ...). In some instances, if the stimulus be stopped
at the end of the first negative phase, we obtain a small
increment of negativity as the after-effect. The sequence
here, then, is (— ...).

Fic. 244. Photographic Record of Phasic Alternations, showing Direct
and After Effects of Light in Type I., represented by Bryophyllum

a: First record of the series. Positive after-effect represented by. dotted
curve is here strong. 4andc: Less strong positive after-effects due to
fatigue. Inc light was stopped slightly beyond the second phase of
maximum positivity; d, owing to fatigue, after-effect converted into
negative. Dotted portions of curve represent, as usual, the after-effect
on cessation of light.

Turning to Type III., we take specimens whose charac-
teristic response to short-lived stimulus of light is by
galvanometric positivity, the multiple phases in which, under
its continuous action, may be expected to_be in the se-
quence represented in figure 232, that is tosay(+ — + —)
As the responses here are the exact opposite of those in

412 COMPARATIVE ELECTRO-PHYSIOLOGY

Type I., we may expect to obtain the unmasking of the nega-
tive element in the response, as the after-effect, on the with-
drawal of stimulus. Here there should be cessation of stimulus
at the end of the second phase, in this case, maximum mznus.
The negative element, thus freed from its opposing positive,
will demonstrate its presence by over-shooting. in the
negative direction (fig. 245). This
is seen in the next two figures
(246 and 247). The specimen
; taken was the petiole of cauli-
flower, in that particular condition
which gives the positive as its
immediate response. The _alter-
nation of plus-minus-plus-minus,
under continuous stimulation, is
seen in the first part of fig. 246.
Stimulus was now stopped ata
point short of the maximum nega-
tivity, and we see the consequent
overshooting in the negative
direction. In the next figure
(fig. 247), is seen a single alter-
nation of p/us-minus during stimu-
lus, in a different specimen, with

ue eS

FIG. 245. Diagrammatic Repre-
sentation of Phasic Alter-
nations and After Effect in
Type III.

During action of light the phasic
alternations are a 0, b a’,
a’ b', b’ a" (+—+-—);3 is
here the maximum positive,

and a’ the maximum nega-
tive. Withdrawal of stimulus
at point of reversal a’
causes unmasking of negative
element, which is exhibited
by the overshooting of the
curve in the negative direc-
tion, a’ ¢.

its after-effect and recovery from
that effect. The impinging stimu-
lus was in this second case stopped
at the exact point of maximum
negativity, and the overshooting

curve shows, by its abrupt steep-
ness, its sudden freedom from the restraint imposed by the
opposite element of positivity. Thus, in this instance of
Type III., we arrive at the typical formula of (+ — ...).
It may then be said that under this head, of alternation of
phase, we have examined representative cases of the two ex-
treme Types I. and III., between which lie many variations,
classified as intermediate, or Type II.

RESPONSE TO STIMULUS‘*OF LIGHT 413

It has thus been seen that the electrical response of

plants to light is not essentially different from their response

to other forms of stimulus. The various effects observed
are the electrical concomitants of

those excitatory effects which we
had already seen to be exhibited
in mechanical response. In a

ft

ae se
ee ee ee

re te spe see ee en te A ne en ao
i
Sa
-
entice

i

|

|
/

som pga saCe é

Fic. 246. Photographic Record of Phasic
Alternation, showing Direct and After
Effects in Type III., represented by with a Second Specimen of
Petiole of Cauliflower Cauliflower, representative of

Continuous line represents effect during appli- Type III.
cation of light. Stimulus was withdrawn
slightly before the attainment of the second
maximum negativity, resulting in over-
shooting of curve in negative direction.
Dotted portion of record represents after-
effect on cessation of light,

FiG. 247. Photogiaphic Record
of Pair of Responses obtained

The stimulus of light was in
these cases withdrawn exactly
on the attainment of the
negative maximum. Dotted
portions of the record ex-
hibit the after-effect.

highly excitable tissue the direct effect gives rise to galvano-
metric negativity. The indirect effect of stimulus, however,
is one of galvanometric positivity. Positive response may
also be obtained from a tissue which is not highly ex-

414 COMPARATIVE ELECTRO-PHYSIOLOGY

citable or in a sub-tonic condition or fatigued. The pre-
sence or absence of chlorophyll is not a determining factor
in electrical response. As in the case of mechanical and
growth responses, so also in the electrical, continuous stimu-
lation gives rise to multiple responses, as its direct or after-
effect. ‘The sequence of phases, under the direct action of
continuous stimulation, may be (— + — +) or(+ — + —).

Taking into account both the direct and after-effect, the
observed results may be classified under three types. In.
the first type, that of fresh and highly excitable tissues, the
formula is(— + -i-). In the second or intermediate type, it
is (— + ...) or (— ...). And in the third type we have
the formula (+ -— ...).

CHAPTER XXVIII
RESPONSE OF RETINA TO STIMULUS OF LIGHT

Response of retina—Determination of true current of rest—Determination o:
differential excitabilities of optic nerve and cornea, and optic nerve and
retina —The so-called positive variation of previous observers indicates the
true excitatory negative—Retino-motor effects—Motile responses in nerve—
Varying responsive effects under different conditions—Reversal of the normal °
response of light due to (1) depression of excitability below par ; (2) fatigue—
The sequence of responsive phases during and after application of light—
Demonstration of multiple responses in retina under light, as analogous to
those in vegetable tissues—Three types of after-effect—Multiple after-
excitations in human retina—Binocular Alternation of Vision—Demonstra-
tion of pulsatory response in human retina during exposure to light.

THE nature of the electrical reaction of the retina under
stimulus of light constitutes a problem which has attracted
many investigators, chief and earliest among these being
Holmgren, Kiihne and Steiner, Dewar and McKendric. The
results obtained by these workers have been confirmed by
the later researches of others; but while their general observa-
tions are fairly concordant, the way in which the phenomena
they have described are related to the excitatory reaction is a
question which has hitherto remained undetermined.
Observed results, in fact, would seem to show that the
electrical reactions of the retina are of a nature quite different
from those exhibited by other animal tissues. For whereas
nerve or muscle, for example, responds on excitation by
negative variation, the retina, under the same normal con-
ditions, is said to exhibit a positive variation. The subject
is very. much complicated, moreover, by the confusion which
has unfortunately arisen as to the meaning of the terms
positive and negative. These positive and negative varia-
tions are so named in reference to the existing current ot

416 COMPARATIVE ELECTRO-PHYSIOLOGY

rest, which, as we have already seen, does not constitute a
very definite or unvarying standard. A still further source
of complication is introduced again when, under certain
internal changes in the retina itself, the normal response is
found to be reversed.

The present inquiry, then, resolves itself into the follow-
ing questions :—(1) What is the true current of rest, and do
the various currents which have been observed really fall
under this head or not? (2) What is the galvanometric
character, positive or negative, of the excitatory reaction of
the retina—that is to say, is the excitatory phenomenon in
the eye similar to, or different from, that of other tissues?
' (3) May we not discover, in the case of the retina, those mul-
tiple excitatory reactions which we have already found to be
induced by light in vegetable tissues? (4) And, lastly, what
are the after-effects of this particular stimulus in the retina?

Of these we shall deal first with the question of the direction
of the current of rest. In an eyeball which is isolated entire
it has been found that the nerve is negative to the cornea,
and the current of rest is therefore believed to flow through
the eye from nerve to cornea. In an isolated nerve-retina
preparation, on the other hand, the rod-surface of the retina
is negative to the nerve, the current of rest being thus from
retina to nerve. These observed currents, however, may not
be true currents of rest, but rather excitatory after-effects,
due to injury in preparation. In such cases we have seen
that the naturally more excitable becomes persistently nega-
tive. We have also found that the true current of rest flows
from the less to the more excitable, the latter being thus
galvanometrically positive. In order, therefore, to determine
the true nature of the resting-current, we have first to deter-
mine which of each two surfaces, nerve and cornea, and
nerve and retina, is the more excitable.

I have already described how, by means of equi-alter-
nating electrical shocks, the differential excitability of a
preparation can be determined. We saw also that under
such conditions the resulting responsive current flows from

RESPONSE OF RETINA. TO STIMULUS.OF LIGHT 417

the more to the less excitable. The experimental arrange-
ment used in this investigation is shown in fig. 248. In such
an experiment, equi-alternating shocks are given to the’ pre-
paration by means of a secondary coil included in the circuit.
The existing current, from nerve to cornea, may be balanced
previously by a potentiometer. Whether the record be taken
under balanced or under ordinary conditions, it is found that
in anormal eyeball the responsive current is from the nerveto
the cornea, showing that the nerve
is relatively the more excitable of
the two. Fig. 249 gives a series
of such responses. It will also
be noticed that the excitatory
current is in the same direction

>» {

>R
Fic. 248. Experimental
'. Arrangement for Deter-
mination of Differential ©
_. Excitability of Optic — ;
Nerve and Cornea Fic. 249. Series of Photographic Records of
‘Excitatory Responses in Frog’s Eye to

Equi-alternating Electric Shocks at Inter-
_ vals of One Minute

C, injury current, or so-called
current of rest; R, re-
sponsive current.

Current of response from nerve to cornea.

as the existing current, and thus constitutes a positive varia-
tion of it. Thzs positive variation of the current in the eyeball
thus indicates a true excitatory reaction of the optic nerve.
From the fact that the nerve is more excitable than the
cornea, it is clear that the sectioning of it for isolation of the
eyeball, acting as an intense stimulus, will result in its excita-
tory negativity, which will persist for a time and slowly dis-
appear. Owing to this fact, a current flows from the more
excited nerve to the less excited cornea. That this current
E E

—A18 COMPARATIVE ELECTRO-PHYSIOLOGY

is not the true resting-current, but rather an excitatory effect
consequent on preparation, is supported by the known fact
that it undergoes a decline more or less rapid. On the other
hand, from the fact just demonstrated that the nerve is the
more excitable, we should expect that, under natural or
primary conditions—that is to say, inthe absence of excitatory
disturbance—the resting-current would be from the less to the
more excitable, or in other words, from cornea to nerve, This |
conclusion I was able to verify by carefully dissecting away
the socket of the frog’s eye, and
making connections with the
longitudinal surface of the un-
detached nerve and the cornea.
Under these ideal conditions
the true resting-current was
detected, and was, as expected,
from the cornea to the nerve.

In order, next, to determine
whether the current, observed to
flow, in a nerve-retina prepara-
< tion from retina to nerve, is a
‘ee true: resting-current, or merely

C
R
Fic. 250, Experimental Arrange- an excitatory after-effect, I pro-

ment for Demonstration of ‘ i
Differential Excitability as bee ceeded to determine, in the

tween Retina and Optic Nerve — manner already described, which

c, so-called current of rest; R, re-

sponsive current. of the two surfaces was the more

excitable. Under the excita-
tory effect of equi-alternating shocks, the responsive current
was found to flow from the retina to the nerve, thus
proving that the retina was the more excitable (fig. 250).
The first series of responses in fig. 251 gives a record of these
effects with a moderate intensity of stimulation, while the
second series shows the responses under an intensity nearly
twice as great. The so-called current of rest observed in the
nerve-retina preparation is thus to be taken as due to that
after-effect of preparation which is inseparable from the
isolation of such a highly excitable tissue. /¢ well also be

RESPONSE OF RETINA TO STIMULUS OF LIGHT 4I9

noticed that the true excitatory effect on the retina ts tn the same
direction as the existing injury-current, and thus constitutes
a positive variation of tt. .
Thus, as regards forms of stimulus other than light, such
as, for example, the electrical, the responsive reaction of the
retina is by induced galvanometric negativity. This at once
disposes of the doubt that the general reaction of the retina
might be of a different sign from that of any other tissue.
But we have still to determine whether or not the stimulus
of light, in particular, induces the same normal negative
change, The next question to be taken up, then, is that of
the true nature of the responsive variation induced in the

Fic. 251. Series of Photographic Records of Excitatory Responses in Frog’s
Retina to Equi-alternating Electric Shocks at Intervals of One Minute

Responsive current from retina to nerve. First series show response to
stimulus of moderate intensity ; the second series to stimulus of intensity
nearly twice as great.

retina by light. We have seen that the effect recorded as
normal by numerous observers, whether in the eyeball or in
the isolated retina (Kiihne and Steiner) was a positive varia-
tion. But since we now know that retinal response to stimu-
lation in general is not unlike that of other tissues, and since,
with regard to the stimulus of light'in particular, we have
seen it induce true excitation in vegetable tissues, we might
expect the responsive reaction of the retina to light to take
place by galvanometric negativity. We must then accept
one of two conclusions. Either the positive change is a
misnomer for the phenomenon observed in the eye, or the
inference which we have drawn from the analogy of vegetable
tissues is not justified.

420 COMPARATIVE ELECTRO-PHYSIOLOGY

As, in reference to this latter point, however, it may be
urged that the retina is exceptionally sensitive to light,
while the reactions of vegetable tissues are generally slug-
gish, it may be worth while to point out here that vegetable
tissues are not so insensitive as is generally supposed, but
are often, on the contrary, highly susceptible to the: action of
light. It. was, for instance, found by Darwin that the coty-
ledons of Phalaris canariensts were, in the course of some _
hours’ exposure, curved towards a small lamp, placed ata
distance from them of 12 feet.. The intensity of the stimulus
of light was in this case extremely feeble. I have myself
observed, again, the remarkable sensitiveness to light of the
terminal leaflet of Desmodztum,.which, on the mere striking
of a match in its vicinity, was thrown into a state of pulsatory
movement.

I shall, in the course of the present chapter, describe
certain definite effects on the retina, which will prove, in an
- unmistakable manner, that, when exposed to light, it under-
goes a change of galvanometric negativity. It is now there-
fore necessary to show clearly that what has been described
as the positive variation is really due to the excitatory nega-
tive change of the retina. What has to be demonstrated,
then, is the way in which this simple underlying reaction of
negativity comes to appear as a positive variation of the
opposite-directioned currents of rest in the a and
isolated retina respectively.

As regards experiments on the eyeball, with contacts at
nerve and cornea, we have seen that. the existing injury-
current is from nerve to cornea, and that this undergoes a
positive variation when the nerve is stimulated in any way.
This is because the added. negativity induced in the nerve
gives rise to an increase, or positive variation of, the existing
current (fig. 248). Now, when light falls on the eye it -acts
on both the cornea andthe retina. The former, however,
is relatively inexcitable, especially to so moderate a stimulus
as that of light. But the retina is excited, and its excitatory
condition is rapidly transmitted to the optic nerve, which

eee

RESPONSE OF RETINA TO STIMULUS OF LIGHT 421.

thus becomes galvanometrically negative. The so-called
positive» variation observed under such an experimental
arrangement, then, is really the result of the true excitation
of the retina conducted to the optic nerve.

In experiments- on nerve-and-retina preparations, with
contacts on the nerve and the retina, the existing injury-
current is from retina to nerve.- When do¢/ nerve and retina
are excited simultaneously, by equi-alternating electrical
shocks, we have seen that, on account of the greater ex-
citability of the retina, the resultant responsive current, here
differential. is from retina to nerve, constituting a positive
variation of the existing injury-current (p. 419). In the case
of stimulation by light, however, it is the retina which is directly
excited. The added negativity thus induced in the retina
gives rise to an increase or positive variation of the existing
injury-current (fig. 250). Hence, in all these cases, the so-
called positive variation really indicates the normal excitatory
negative effect. The apparent anomaly involved in the
supposition that the response of the retina to light was
positive, and thus of opposite character to that of other ex-
citable tissues, is thus seen to be due to a misinterpretation
of observed results. It is unfortunate that, as a consequence
of this misinterpretation, the effects described by different
observers, of the response of the eye as ‘ positive,’ are really
to. be understood as ‘negative, and vice versa. When
quoting these results, therefore, I shall always give the actual
effect indicated in italics and in parentheses,

Another observation which lends independent support
to the view that the retina exhibits the true excitatory re-
action, is found in the fact—noted by Van Genderen-Stort
and Engelmann—that the cones exhibit a motile effect by
retraction under light. It has. been supposed from this that
the optic nerve contains not merely sensory, but also retino-
motor fibres. But I shall show that it.is not that the endings
only of the optic nerve, but also that nerve itself, which
exhibit true excitatory contraction under stimulation (cf.
figs. 324,404). All nerves, in fact, will be shown in a later

422 COMPARATIVE ELECTRO-PHYSIOLOGY

chapter to exhibit normal excitatory contraction, and it will
be by the study of these motile responses in nerves, and their
variations under different condition, that we shall be able
unerringly to relate the abnormal responses sometimes seen
in the retina to those changes of condition to which they are
due. :
With regard to these abnormal responses, I have already
shown that various tissues exhibit them under the two
different conditions of sub-tonicity and fatigue. With regard
to nervous tissue in particular, however, I may refer here,
by anticipation, to results which will be given in detail
in Chapter XXXV. concerning the mechanical response
of nerve and its variations. In normal conditions of ex-
citability the nerve gives response by contraction, and this
is its true excitatory response, concomitant to the electrical
response of galvanometric negativity. This excitatory re-
sponse, then, whether by contraction or by negativity, will
here, as in preceding chapters, be designated ‘negative.’
We have seen that the maintenance of the normal condition
of a highly excitable tissue depends on its supply of energy.
Hence, when such a tissue is isolated from the organism of
which it forms a part, it is liable to fall below its normal
tonic level. This depressed condition, however, does not
connote any permanent chemical depreciation, but only a
temporary depression of its fund of energy. Under such
an induced lowering of the tonic condition, the response is
reversed to positive. But under continuous stimulation,
excitability is again enhanced, and the abnormal positive is
converted to normal negative.

Thus we obtain, in a somewhat sub-tonic tissue, the
following results :

(1) Under a short-lived or instantaneous stimulus, whose
effective value falls below the true excitatory level, response
is positive (expansion),

(2) Under the continuous action of stimulus the effective
value is at first below, but after a time rises above, excitatory
efficiency. In consequence of this we obtain a first phase of

RESPONSE OF RETINA TO STIMULUS OF LIGHT 423 .

response which is positive, followed by a second which is
negative (expansion followed by contraction).

The second condition to induce a reversal of the normal
response occurs in consequence of the fatigue due to previous
over-stimulation.

(3) A reversed positive response (expansion) in conse-
quence of fatigue. | |

The various anomalies which occur in the response of the
eye will all be found resolvable into one or other of these
cases. I shall first describe certain experiments which will
demonstrate the reversal that is brought about by induced
sub-tonicity. We have seen that the normal response of an
eyeball, with two contacts at nerve and cornea, consists
of a current from the nerve to the cornea. I have already
given records of such normal responses, obtained by sub-
jecting the preparation to equi-alternating electric shocks
(fig. 249). In certain cases, however, in which the isolated
eyeball of the frog had fallen into a sub-tonic condition, the
response was found to be reversed, the nerve, under excita-
tion, becoming relatively positive instead of normally nega-
tive. It has already been said that such a reversal is due to
great depression in the condition of the nerve. In dealing
with these cases, therefore, it occurred to me that it ought to
be possible to restore the normal response by the application
of some exciting reagent—say, dilute Na,CO,—to the nerve
in its depressed condition. As the result of this application
I found the reversed response to be restored to the normal.

I obtained results precisely similar to these with isolated
retina of the frog. The normal responses—a current from
retina to nerve (fig. 238)—under equi-alternating shocks,
were here found, in a depressed specimen, to be reversed.
But the application of Na,CO, solution on the retinal surface
brought the responses back to the normal. These abnormal
responses, then, rectifiable to normal, are those due to sub-
tonicity. And under fatigue finally, induced by long-
continued, or over stimulation, I find the normal response
of the eye to be reversed.

a2a COMPARATIVE ELECTRO-PHYSIOLOGY

This is the place in which to refer to various anomalous
effects observed. by previous investigators, and to offer satis-
factory explanations of them from the results which I have
already demonstrated. I shall therefore give a brief sum-
mary of these from the admirable account of Biedermann.

(a) ‘In light, frogs—z.e, such as have been exposed for
hours to the full effect of daylight—the positive fore-swing

of the negative variation concomitant~with the impact of ©

light is entirely wanting, or appears as a trace only.’ ‘ Since
this posztzve varzation of the existing current really means, as
I have already shown, the ‘true excitatory negative, and the
negative variation conversely, the occurrence of positive
response, this observation means that a frog’s eye, previously
exposed for a long time to light, gives positive response.

This, then, is a simple instance of the reversal of response
from negative to positive under fatigue, which I have already
dealt with above as case (3).

(0) ‘The fact that the three phases of the retinal action
current, due to transitory illumination, appear in sensitive
preparations, even when, as with the electric spark, the
impact of light is momentary, shows that the medium nega-
tive (fosttzve) phase must not be regarded merely as the
consequence of permanent illumination, since it is just this
phase which alone appears in less excitable preparations with
instantaneous light stimuli.’

‘With regard to this it may be said that the medium
positive phase here referred to, as given by. the excitable
retina under continuous stimulation, is not the same as that
positive response which ‘alone appears in less excitable pre-
parations with instantaneous light stimuli. The former is
due to fatigue-reversal, while the latter is an instance of the
abnormal positive response of a sub-tonic tissue to feeble
stimulus. This will be understood from the following con-
siderations. In the retina, under continuous stimulation, the
first phase of response is the true excitatory negative. This
gives place to a second, or positive, due to _fatigue-decline.

' Biedermann, Zéectro- Physiology (English translation), vol. ii. pp. 474-477.

RESPONSE OF RETINA TO STIMULUS OF LIGHT 425 - i g
And this is again succeeded bya transitory negative effect

on the sudden cessation of: light. These constitute the three

phases of retinal action-current just referred to, under con-

tinuous stimulus. This sequence is wrongly represented in
symbols as (+ — +), since the actual changes concerned are
(—+-—). ; .

Now in highly excitable. tissues, under instantaneous
stimulation, we observe a sequence of response apparently
similar, the first being normal_ negative, the second positive,
owing- partly to recovery and: partly to the positive after-
effect ; and the last phase representing a return from this
positive. These three phases, therefore, though apparently
similar, are not really the same as those just referred to
under continuous stimulation, where the ‘medium negative
(postteve) phase’ was the result of fatigue-reversal. The so-
called negative (fosztive) effect which alone appears on the
instantaneous stimulation of relatively inexcitable tissues is,
again, the positive response of a sub-tonic tissue to a stimulus
deficient in true excitatory value, already described (p. 422)
as case (1). Similar positive responses of vegetable tissues
in a sub-tonic condition under the action of light were seen
in fig. 240.

We come next to the question whether or not we may
discover multiple responses in the retina analogous to those
which have already been demonstrated in the case of vege-
table tissues. The occurrence of such an effect has not
hitherto been suspected. We have seen that, under the
continued action of light, vegetable tissues exhibit multiple
responses ; and since we have found a general close analogy
to exist between the responses to light of the retina and of
these, we should expect that similar multiple responses would
be found in the eye also. The reason why these were not
hitherto detected lay in the inevitable depression of excit-
ability in the isolated retina or eyeball. In the retina of certain
fishes, where the excitability does not appear to decline so
rapidly, I have often obtained records of multiple responses
For example, in the retina of Wallago attu fish the stimulus of °

nee’ COMPARATIVE ELECTRO-PHYSIOLOGY

light applied for three seconds gave as its after-effect multiple
responses which lasted for ten minutes, the average period of
each oscillation being twenty seconds. I have also obtained
such multiple responses from the eye of vigorous bull-frogs,
a photographic record of one of these results being given in
fig. 252. We shall also see at the end of this chapter that
it is quite easy to detect the occurrence of these multiple
responses in the intact human eye under stimulus of light.

As we have seen that multiple response is the expression
of energy previously absorbed, and held latent in the tissue
for a time, and since, as has been stated, the retina itself
exhibits multiple response, it is easy to see that this organ,
on the cessation of light, will show after-effects.

In my experiments on the effects
of light on vegetable tissues I found,
as has already been said, three
different types of direct- and after-
effect. The first of these related to
those highly excitable tissues which
under continuous stimulation gave

normal responses (—~+—+). In
Fic. 252.—Photographic Re- gych cases, if the stimulus was
cord of Multiple Response ;

of Retina of Frog under stopped on the attainment of

Continuous Action of Light 14.imum positivity the immediate
after-effect was an increase of positivity. The formula
was thus (—+ ++). In the third type, with sub-tonic
tissues, the sequence, under continuous stimulation, was
(+ —-+-—), and on the stoppage of stimulation at maximum
negativity this negativity became suddenly augmented. The
formula here was thus (+ —---). In the second or inter-
mediate type, again, the formula of the direct and after-
effects was either (— + -+-) or (— -:-).

I shall now discuss in some detail the various types of
after-effects met with in the retina, corresponding, as I shall
be able to show, with those met with in vegetables tissues.
After-effects like those of Type I., had not hitherto been
noticed in the retina for the reason that their demonstration

‘RESPONSE OF RETINA TO STIMULUS OF LIGHT —<— |

can only be obtained in a tissue of normal high excitability,
and not in one which has undergone depression in con-
sequence of isolation. I was fortunate enough, however, to
meet with a species of fish, Ophiocephalus marulius, whose
vitality is so exceptional that it lives for days when taken
out of water. When the fish is pithed, its heart continues
beating vigorously for many hours. I made a preparation
of the eye of this fish and carried out experiments on it
under the action of light. |

In fig. 254 is given a record obtained with this specimen
during the application of light and on its cessation. It will

FIG. 253. FIG. 254. FIG. 255.

FIGs. 253, 254, 255. Parallel Records of Responses given by Plant and
Retina, during and after Illumination, illustrative of Type I
(— + +). In all these cases up-curve represents induced galvano-
metric negativity ; down-curves, positivity. White background in this
and following records represent light, and shaded, darkness.

Fig. 253. Response of petiole of Aryophylium. Light was cut
off on attainment of maximum positivity in the second of
the multiple responses.

Fig. 254. Similar effect in response of retina of Ophzocephalus fish.

Fig. 255. The same with another specimen. Light. was here
cut off after the first oscillation.

be seen that during the application of light the sequence was
(—+—+). It will be noticed that, after completing two
oscillations, and after the response-curve was even slightly
reversed at its maximum positive phase the light was with-
drawn. The immediate effect was a sudden increase of posi-
tivity, followed by a series of after-effect oscillations. In the
next figure (255), obtained with a different specimen of the
same fish, light was withdrawn at the exact moment of
maximum positivity, and the result is seen to be similar to
the last—namely, an immediate enhancement of positivity,

-

ageiRfe. 428 COMPARATIVE ELECTRO-PHYSIOLOGY

followed by an after-oscillation. The essential similarities
between these and corresponding records obtained on a fast-
moving drum, of the response of the petiole of Sik wi det
under light (fig. 253), are sufficiently obvious.

When the excitability of the tissue is not so high, we
may obtain after-effects of Type II., in which the formula is
—-+-+--) or (—---). This was exemplified in vegetable
tissues (cf. fig. 245 @).. In Ophziocephalus, 1 was able to obtain —
this result also, when the specimen was slightly fatigued
(fig. 256). With the eye of the frog, Kiihne and Steiner
obtained .the record given in fig. 257, which is seen to be
parallel to that given in fig. 256, its true significance being
shown in the formula (— +---).

|
Fic. 256. FIG. 257.

Fics. 256, 257. Parallel Records given by Plant and Eye; during and
after Illumination, as illustrative of Intermediate Type II. (— + ---)

Fig. 256. _ Response of retina of Ophzocephalus when slightly
fatigued.
Fig. 257. Response of frog’s eye (Kiithne and Steiner).

A sub-case of Type II. is represented again, by (—-+--),
where on the sudden cessation of light, there is a transient
increase of excitatory response, This, as we saw, was due to
the abrupt withdrawal of the antagonistic influence of a
reversing force. I may state here that I have been able to
demonstrate an exactly parallel effect with nerve of frog,
where the excitatory negative effect during stimulus under-
goes a brief and sudden augmentation on its cessation (p. 5 36).
This sudden augmentation on the stoppage of stimulus has
been taken as a proof of the existence of antagonistic pro-
cesses of assimilation and dissimilation, rather than as due to
molecular-derangement by external stimulus and its after-effect.

RESPONSE OF RETINA TO STIMULUS OF LIGHT 429

That, for its explanation, however, it is not necessary to
postulate the two processes of assimilation and dissimilation is
clearly seen from the fact that I have obtained: an exactly
similar effect in inorganic. substances,
suchas silver bromide, a record of whose
response is seen in fig. 258. |
We next turn to what has been-
designated as Type III.,-in which the
sequence of responses, owing to the
depressed. condition of the -tissue, is.
reversed, the formula here. being
(+—+-—), while the direct and after-
effects are represented by (+ —--:). asiecih ——
This result was already obtained in the f
sub-tonic tissue of the petiole of
cauliflower, a record of this being given
in fig. 259. Iwas able to detect similar
effects in a, retina of Ophzocephalus, in

=>

oom ee we wee eee eee

—_—_—_—

which response had become reversed
under the sub-tonicity- due to long
isolation (fig. 260). These results will
explain the somewhat anomalous re-
sponse which Kiihne and _ Steiner
obtained with the isolated retinz of
certain fishes (fig. 261).

Returning now from the question

. rieet . Fic. 258. After-effect
of multiple excitations during and after OF bight “on “Silver
the exposure to light—in prepared speci- Bromide

mens, where results must. be modified The thick line represents

response during light
to.an unknown extent by the effects ~ (half a minute’s ex-

'

\

'

t

'

'

'

'

'

'

1

\

\
{
\
‘
‘

\
\
\
\

<a

i i Een Ne posure), and dotted

- pasate — i cade to that line the recovery dur-

of the responses of the intact. eye, ing darkness. Note
= t t s ] as ©

where alone we may expect to obtain igh Be eect

the truly normal effects, we may attack 7

the problem by means of visual sensation itself. Multiple
excitation, as the after-effect of strong luminous stimulation,
is here somewhat easy of demonstration. But its exhibition

430 COMPARATIVE ELECTRO-PHYSIOLOGY

during the action of light presents unusual experimental
difficulties.

It is a well-known fact that if, after looking at a bright
object for some time, we close the eyes, we see the image
repeated many times, The occurrence of these after-images
is somewhat different under a transitory flash of illumination,
and with more persistent exposure to light. As the visual
sensation is to be regarded as the excitatory effect, there
will—owing to the fact that this excitation must reach its
maximum some time after the cessation of an instantaneous
exposure—be a persistence of the excitatory after-effect, with

FIG. 259. FIG, 260, | Fic. 261,

FIGS. 259, 260, 261. Parallel Records of Responses given by Plant and
Retin, during and after Illumination, illustrative of Type III.
(+ —...)

Fig. 259. Response of petiole of cauliflower. Light was here cut
off on attainment of maximum negativity.

Fig. 260. Response of retina of Ophiocephalus fish when de-
pressed.

Fig. 261. Response of isolated retina of fish as observed by
Kiihne and Steiner.

N.B.—The true excitatory negative response was by these
observers described as the ‘ positive variation.’

its corresponding visual sensation. This is not so, however,
when the eye is closed after looking at a bright object for a
considerable time. In this case there is a positive rebound—
opposite to the true excitatory negative effect—with con-
comitant sensation of darkness. The next rebound is negative,
giving rise to a repetition of the original sensation ; and these
alternating phases may be repeated manytimes. With the eyes
closed, the negative or luminous phases are the more prominent.

The same phenomenon may be observed in a somewhat
different manner when, after: staring at a bright object, we

RESPONSE OF RETINA TO STIMULUS OF LIGHT 431 —

look towards a well-lighted wall. The dark phases will now
become the more noticeable. If, however, the wall be dimly
lighted, both the dark and bright phases will be noticed alter-
nately. It has been suggested that these phenomena might
be due to some obscure form of fatigue, but the regular alter-
nations observed clearly demonstrate them to be a case of
oscillatory changes and multiple response. _

The demonstration of multiple responses in the human
retina, as an after-effect, is thus seen to be easy. But their
occurrence during continuous exposure of the eye to light is
more difficult to prove, This arises from the fact that the
waxing and waning of the effect are so gradual: as not to be
noticeable, unless against some definite standard of com-
parison. I shall now prove that, during the continuance of
constant light, pulsatory visual effects are produced. These
pulsations go unnoticed in visual sensation, not only for want
of a standard of comparison, but also because of the remark-
able fact which I have discovered, that while the impressions
of each individual retina undergo variation, the sum total of
the two remains always approximately constant. I have
been able to provide the necessary comparison-standards by
having two distinguishable images produced in the two eyes,
the fluctuation of the visual excitation in one eye being thus
capable of detection, by comparison with that in the other.
It would have been impossible to detect this fluctuation, had
the excitatory variation taken place in the two eyes simulta-
neously, ze. if the maximum excitation in the one had
occurred at the same moment as the maximum excitation in
the other. But I have found that, as regards excitation
there is a relative difference of phase, of half a_ period,
between the two retinz, so that the maximum effect at a
given moment in one eye corresponds to the minimum in
the other. This constitutes the phenomenon which I have
designated the Binocular Alternation of Vision. It is owing
to this fact that the periodic excitations in each retina are
unmistakably brought out by the following experiment,
which consists in looking through a stereoscope that holds,

432 COMPARATIVE. ELECTRO-PHYSIOLOGY

instead of photographs, incised plates with two inclined cuts,
the right eye seeing the slit ‘inclined to the right, while the
left sees that inclined to the left. When. the. observer looks
through the stereoscope turned to the bright sky, his two
eyes are acted on by strong stimulus of light through these
divergently-inclined slits... The resultant sensation: forms the
image of an inclined cross (fig. 262).. On now closing the
eyes the multiple after-effect is observed as recurring images. ©
The relative difference of half a period, already referred to, is
here perceived in a very interesting manner, for the after-
image is not now the complete inclined cross. Instead of this,
each of the two arms is seen in regular sequence alternately.

4 ; | 0)

. . FIG. 263. Composite Indecipherable
Inclined Slits ‘Word, of which Components are
Seen Clearly on Shutting the Eyes

Fic. 262.
for Stereoscope and Com-
posite Image formed in
the Two Eyes

That is to say, when the one is at its brightest the other has
completely disappeared, and vice versa. The impression in
each eye thus undergoes a periodic fluctuation. Some yery
curious effects can thus be exhibited, when, instead of the
two inclined bars, the incisions to be looked through com-
pose a word. For instance, two letters forming half of the
word may be seen by one eye, and the other two by the
other. The result of this is that, as long as the eyes are
open, we obtain an indecipherable image, due to super-
position, like the following (fig. 263). »

But when the eyes are closed, then, owing to dznocular
alternation of the multiple after-effect, the blur disappears,
and the word is spelt out in repeated succession in the field

RESPONSE OF RETINA TO STIMULUS OF LIGHT 433,

of dark vision, as RO ME RO ME, and so on. In this
curious instance one sees better with eyes closed than open!

The next problem that presents itself is that of demon-
strating the pulsatory nature of the visual sensation in each
eye, under the constant action of light. The stereoscope,
with its two inclined slits, is now taken and turned towards
the bright sky, and when the design is looked at steadily it
will be found that, owing to pulsatory excitation in each eye,
and the binocular alternation of vision, when one bar of the
cross begins to be dim the other becomes bright, and vce
versa. The success of this experiment is determined by the
fact that the image in each eye forms a comparison-standard
for the other. And as the changes in the two eyes proceed
in opposite directions, the visual fluctuations during the con-
tinuous action of light, are brought out with the greatest
distinctness. It may be stated here that the period of this
visual oscillation has an average value of about four seconds.
It is, generally speaking, shorter with young people, and
longer with old. Even in the same individual, again, it is
modified, according as the previous condition has been one of
rest or activity. I give here a set of readings given by an
observer :

| Time of day | Period Time of day | Period
SAM. . , - 3 seconds 6 P.M. ; | 5°4seconds |
I2noon . ‘ page OFM ay RG: 755
3PM. . : | eat II P.M. Z | 6b

In this connection it may be interesting to mention that
the period of a single oscillation in a multiple response,
measured in frog’s retina, under experimental conditions, was
ten secands. In the case of the retina of Wadllago, the aver-
age period was twenty seconds.

CHAPTER XXIX
GEO-ELECTRIC RESPONSE

Theory of Hydrostatic Pressure. and Theory of Statoliths—Question regarding
active factor of curvature in geotropic response, whether contraction or ex-
pansion— Crucial experiment by local application of cold—Reasons for delay
in initiation of true geotropic response—Geo-electric response of shoot—
Due to active contraction of upper side, with concomitant galvanometric
negativity—Geo-electric response of an organ physically restrained.

IN the case of the action of external stimulus on plant
organs it is possible, given the direction of incident uni-
lateral stimulus, to predict the nature of the responsive
movement. I have shown elsewhere, in my work on Plant
Response, that all the actual movements of a plant organ
can be deduced from the simple law that it is the more
excited side that becomes concave. But though this law is
sufficient guide in dealing with the action of a known ex-
ternal stimulus, yet the problem becomes much more obscure
when we have to account for any movement which occurs in
response to a stimulus whose seat is internal. An example
of this class is afforded in the responsive curvature associated

with gravity. Thus, a shoot laid horizontally will curve up-.

wards till the free end becomes vertical. In connection with
this subject there are two different points to be elucidated.
First, is the question as to the mode in which gravity exer-
cises stimulation ; and second, that of the method by which,
in answer to this stimulus, a definite responsive curvature
takes place. As regards the first of these, it may be said
that the only conceivable way in which gravity could produce
stimulation is by some differential effect of weight acting on
the responding cells. According to this, the necessary dif-
ferential weight-effect may be due to the weight of cell-

. ee oe

eee | a ey

GEO-ELECTRIC RESPONSE 435.

contents, whether of the sap itself or of those heavy particles
like starch-grains, which are contained in it. The former, or
Theory of Hydrostatic Pressure, was suggested by Pfeffer
and supported by Czapek ; the other, or Theory of Stato-
liths, has been advocated by Noll, Haberlandt, and Nemec.
In the case of a multicellular plant laid horizontally
(fig. 264), E and E’ may be regarded as areas in which stimu-
lation is caused by the
weight of the particles.
It is obvious that the
effects produced on the E Pe ee a eee
upper and lower sides of
the shoot are antago-
nistic;. yet, in spite of
this, we obtaina resultant &'

oecvclecceclecocelessosl.,

: ! 1

curvature upwards. This P a
- shows that the excitation Fic. 264. Diagrammatic Representation of
of one side must be a Multicellular Organ laid Horizontally

and Exposed to Geotropic Stimulus.
greater than that of the On the upper side the statoliths act on the
other, the particular direc- inner, and on the lower side on the

tioneditapedeaieal a eee, age poe wall (after Francis
being due to this fact.

It is clear, then, that the induced curvature upwards of the
horizontally-laid shoot is due to the effective action of the
weight particles on either the upper or the lower side of the
shoot. We can see that if it is the upper which is the more
effective, then curvature must take place by excitatory con-
traction ; if, on the contrary, the lower be the more effective,
the curvature is then to be regarded as the result of respon-
sive expansion. There has been considerable uncertainty as
to which of these is actually the case, the prevailing view
being that it is the expansion of the lower surface which is
the active factor.'

That it is, however, the excitatory contraction of the
upper side which is the active factor in this curvature I have
already demonstrated by alternate unilateral applications of

1 For more detailed account see Plant Response, pp. 495 to 511.
’ ; : FF2

436 COMPARATIVE ELECTRO-PHYSIOLOGY

cold. It is known that the continuous application of cold
diminishes or abolishes the excitability of a tissue. If, then,
it is by excitatory action on the upper side that curvature is
induced, it will be found that the local application of cold on
that side will retard or arrest this responsive curvature, the
application of cold on the lower side producing practically no
effect. If, on the contrary, this curvature should be mainly
due to some excitatory action on the lower side, we may then
expect to find that the application of cold on that side has

FIG. 265. Effect'on Apogeotropic Movement of Temporary Application
of Cold on Upper and Lower Surfaces respectively

Application above is seen to produce arrest of movement, while application
below has no perceptible effect. Ordinate of curve represents up-move-
ment of tip of organ in mm ; abscissa represents time.

the effect of arresting the growing curvature, its application
on the upper being more or less ineffective. On carrying out
these experiments it was found that cold had the effect of
arresting curvature only when it was applied on the upper
side of the shoot (fig. 265). This conclusively proved that
gravitational stimulus, acting on the horizontally-laid shoot,
induced response by excitatory contraction of the upper side.
This fact, of response by contraction, is fully concordant with
what we know of the effect on the plant of other forms of
stimulation. This question I intend, however, in the course

GEO-ELECTRIC RESPONSE 437

of the present chapter, to submit to independent examina-
tion by means of electrical response. __
I have already shown that . F

the unilateral pressure of par-
ticles on the growing organ is
effective in inducing curvature set |
in such a way that the side
acted upon becomes concave.
This experiment was carried
out by subjecting one side of
a growing organ to the pres-
sure of iron particles, which
were pressed against it by the pig 266.

ETE
LUT
uu

Diagrammatic Repre-

action of an electro-magnet on sentation of Experiment showing
‘ ‘ Curvature Induced by Unilateral
the opposite side (fig. 266). Pressure Exerted by Particles

The magnetic particles in this. F, flower-bud of Crinum; s, india-

f ti d ; | rubber strip studded with iron
case tunctione as virtua particles attracted by electro-

statoliths, and a curvature was magnet, M, causing palate
: . ° pressure on growing region ; 1,
induced by the excited side iodux attached to Hower

becoming concave (fig. 267).

There is, however, one difficulty in connection with the
statolithic theory of stimulation. When the stem is held
erect the particles rest on the bases of the cells, and their
general distribution on
the two sides of the
organ is symmetrical.
Asymmetry of distri-
bution is induced, how-
ever, when the shoot is
laid . horizontally, and
stimulation might beex- Fic. 267. Record of Responsive Curvature

-.4.-- -Induced in Bud of Crinum Lily by Uni-
pected to follow within lateral Pressure of Particles
a very short time, since
the. displacement of particles from base to side cannot take
long. This being so, the geotropic curvature of the shoot
upwards should take place within a short time. But, instead
of this, we find that the curvature is at first downwards; and |

438 COMPARATIVE ELECTRO-PHYSIOLOGY

it is not till after the lapse of a period, which is sometimes
as much as an hour in duration, that there is a reversal of this
downward movement into the normal apo-geotropic move-
ment. Fig. 268 gives a curve which exhibits this prelimi-
nary movement persisting for nearly forty minutes before its
ultimate reversal into the usual normal apogeotropic curva-
ture upwards.

This delay in the appearance of the characteristic response
may, however, be explained from the known fact that steady
tension increases, whereas compression retards, the rate of
growth. Thus, in a horizontally-laid shoot, there is a ten-
dency to curve down by its own weight, the upper side being

Fic, 268.. Record of Apogeotropic Response in Scape of Uriclis Lily’

The up-curvature due to apogeotropic action proper commenced forty
minutes after the specimen was laid horizontally.

in this way subjected to tension, and the lower to compression.
The effect of these is an increased rate of growth on the
upper, associated with a decreased rate on the lower, sides of
the specimen, giving rise to a downward curvature. The fact
that geotropic stimulus has to overcome this action before its
own characteristic effect can be exhibited may account for
the observed delay in its appearance. A crucial experiment
in support of this explanation will be given presently.

We have seen in the last chapter that the presence of
internal excitation is capable of detection by electrical indi-
cations, and by taking advantage of this fact we have an
independent means of coping with the obscurities of the
present problem. I have demonstrated, by means of experi-
ments already referred to, that it is the upper side which,

GEO-ELECTRIC RESPONSE 439

under the action of gravity, undergoes excitatory contraction.
It follows that, as an indirect effect of such contraction, the
water expelled from the upper will reach the lower side of
the shoot, and cause an increased turgidity and expansion of
that side. The apogeotropic curvature is thus brought about
directly by the contraction of the upper, and indirectly by the
expansion of the lower, side of the horizontally-laid shoot.
This being so, we may expect, in accordance with our pre-
vious investigations on the true excitatory and hydrostatic
effects respectively, that that side will become galvano-
metrically negative which is excited by geotropic stimulus.
And it is found that it is in fact the upper side of the hori-
zontally-laid shoot which exhibits galvanometric negativity ;
the lower, in which the positive turgidity-effect had been
indirectly induced, being found to show galvanometric posi-
tivity. 3
But this result is only obtained simultaneously with the
induction of the normal apogeotropic curvature. And, before
this, other disturbing effects may occur. We take an erect
stem and make two galvanometric contacts, one on each side
of its growing region. The stem is next laid horizontally.
As regards the electrical effects which are now exhibited
three distinct phases are to be distinguished. First, in con-
sequence of the mechanical disturbance due to the laying of
the organ on one side, there will be an excitatory electrical
effect on both upper and lower sides, and the resultant re-
sponsive current will be determined by the difference of
excitability which may happen to exist, in this particular
individual, between the two. This variable stage is termi-
nated in the course of about ten minutes. We next have a
steady condition, brought about by the effects of tension and
compression already described as acting on the upper and
lower sides respectively. This gives rise, as we have seen, to
increased growth, with its attendant positive turgidity, on the
upper as compared with the lower side. |
Hence, during this stage, when the curvature is proceed-
ing downwards, we may expect that the upper side will

440 COMPARATIVE. ELECTRO-PHYSIOLOGY

be galvanometrically positive in relation to the lower, the
direction of the current in the horizontal shoot being from
below to above. And finally, in the third stage, we have the
geotropic stimulation effectively overpowering and reversing
this downward movement. And since it is the upper side
that is now geotropically excited to an effective extent, we
find that that side becomes galvanometrically negative.
Thus, the electrical indication, like the mechanical, gives
in this ultimate stage the characteristic response of the

Fic. 269. Photographic Record of Geo-electric Response in the Scape
of Uriclis Lily laid horizontally

In the first phase of response, the current is from the upper surface to the
lower, the upper being galvanometrically positive. After fifty minutes,
the excitatory geotropic effect reverses the current, which is now
ascending, or from below to above, the excited upper-surface being
galvanometrically negative. _ (Compare corresponding mechanical
record, fig. 268.)

plant-tissue to gravitational stimulus. The excitatory
effect is now exhibited mechanically by the contraction
and concavity, and electrically by the galvanometric
negativity of the upper side of the horizontally laid shoot
(fig. 269). These similarities between the mechanical and
electrical records will be seen on comparing this figure with
fig. 268. We have thus seen that, owing to secondary
mechanical disturbances, the proper exhibition of the true
geotropic response is delayed. And from this it is difficult
to say how quickly the geotropic response follows the dis-

GEO-ELECTRIC RESPONSE 441

placement of the hypothetical statolithic particles. I have
been able to overcome this difficulty, which at first appears
very great, in the following way. It has been shown that
the state of excitation, even when all mechanical expression
of it is restrained, may be detected by galvanometric nega-
tivity. Those secondary effects, due to mechanical dis-
turbance, which mask for a time the excitatory effect of
gravitational stimulus, may thus be eliminated completely by
restraining all movement of the shoot. The problem thus
resolves itself into the fixing of an experimental shoot, say
the peduncle of Uviclis lily—in such a way that mechanical

Fic, 270, Experimental Arrangement for Subjecting Organ to Geotropic
Stimulus, Mechanical Response being Restrained

response is completely restrained. The next point is to
subject the specimen, at a given moment, to the stimulus of
gravity, and record the consequent electric response.

I shall now describe the experimental method by which
these conditions were successfully met. It is clear that when
any two points are acted on symmetrically by the force of
gravity, there is no resultant geotropic action. This is the
case in regard to two diametrically opposite points, A and B,
situated laterally on an erect shoot. When the shoot is laid
horizontally, two lateral points are again acted on sym-
metrically by. the force of gravity, and there is thus xo differ-
ential action as. between the two. But if the shoot be now
rotated on itself,.so that one of these points is diametrically

442 COMPARATIVE ELECTRO-PHYSIOLOGY

above, and the other below, a differential action will be
induced as between the upper and lower sides, the upper
being relatively the more excited. In the following ex-
periment I took a specimen of Uvzclzs lily, and fixed the
entire plant horizontally, as seen in the figure (fig. 270). The
pivoted support allowed the responsive points A and B to
be at first lateral. Owing to symmetry there was now no

Fic. 271. Geo-electric Response of the Physically Restrained Scape
of Uriclis Lily

Up-curve represents responsive current from upper to lower surface during
action of geotropic stimulus, Down-curve represents recovery on
cessation of stimulus. Response commenced after latent period of one
minute ; after-effect persisted for two minutes. Breaks in curve are
due to obscuration of recording spot of light at brief intervals. .

differential action of gravity, nor consequent electrical varia-
tion, as between the two. The galvanometric record was
now a horizontal line. The specimen, on its support, was
next quickly rotated through 90°. The statolithic particles
were thus displaced, falling on the inner tangential wall of
the upper side, and outer tangential wall of the lower. An
electrical response was perceived in about one minute, which
went on augmenting with time, the upper side being in-
creasingly galvanometrically negative (fig. 271). The fact

GEO-ELECTRIC RESPONSE 443

already demonstrated by the alternate cooling of the upper
and lower surfaces is again seen here: namely, that it is the
upper surface which exhibits the true excitatory effect, by
induced concavity in the case of mechanical and by galvano-
metric negativity in that of electrical response. It will also
be seen that when secondary disturbing causes are removed,
the response to gravity is immediate, showing that there is
no anomalous delay between the displacement of the hypo-
thetical particles and the consequent response. By now
rotating the specimen back through 90°, the action of gravity
is virtually removed. The after-effect persists for two
minutes, and after this the response curve shows the usual
recovery,

CHAPTER: XXX

DETERMINATION OF VELOCITY OF TRANSMISSION OF
EXCITATION IN PLANT TISSUES

Transmission of excitation in plants not due to hydromechanical disturbance, but
instance of transmission of protoplasmic changes—Difficulties in accurate
determination of velocity of transmission—A perfect method—Diminution of
conductivity by fatigue—Increased velocity of transmission with increasing
stimulus—Effect of cold in diminishing conductivity—Effect of rise of tem-

- perature in enhancing conductivity—Excitatory concomitant of mechanical
and electrical response—Electrical methods of determining velocity of trans-
mission—Method of comparison of longitudinal and transverse conductivities
—Tables of comparative velocities in animal and plant— Existence of two
distinct nervous impulses, positive and negative.

WHEN a point in the tissue is stimulated the state of excita-
tion is often found to be transmitted to a distance. This is
well seen in the case of sensitive plants, where the excitation
applied at one point is found to give rise to motile responses
of the distant leaf or leaflets.

In this transmission of excitatory impulses to a distance
in the plant we have a phenomenon which would seem to be
analogous to nervous transmission in the animal. For certain
reasons to be given presently, however, it has usually been
supposed that there is actually nothing in common between
the two. ‘The nervous system belongs exclusively to the
animal organisation, and, indeed, to the more highly de-
veloped Metazoa only. Plants, unicellular animals, and the
lower Metazoa have no nerves, and if in exceptional cases
(as in the excitatory movements of many plants) there are
forms of activity which resemble the vital manifestations of
the animal organisation, as effected by nerves, it is easy to
prove that the resemblance is merely superficial.’ *

' Biedermann, Zlectro- Physiology, English translation, 1898, Vol. ii. p. 32.

VELOCITY OF TRANSMISSION OF EXCITATION 445

This assumption, that there could be nothing in common
between the transmission of excitatory impulses in plant and
animal, was thought to derive support from Pfeffer’s experi-
ment on the effect of anesthetics on conduction in J/zmosa.
The anzsthetisation of the pulvinus is found to abolish its
motile excitability. The effect of strong stimulus was never-
theless found by Pfeffer to be transmitted across the anzsthe-
tised area, giving rise to the depression of leaves beyond. It
was natural to infer from this that, as the motile excitability
of the pulvinus was abolished by the anesthetic, so must
the protoplasmic conductivity also have been abolished. It
was therefore inferred that—unlike the conduction of stimulus
in animal tissues, where such transmission is known to take
place by the propagation of protoplasmic changes—the ap-
parent conduction of excitation in a plant was purely hydro-
mechanical.

But I have shown elsewhere, and shal]! demonstrate again
in Chapter XX XIII. by different means, that though excita-
bility and conductivity are related phenomena, yet the varia-
tion of the one is not necessarily identical with that of the
other. Thus a certain degree of anzsthetisation may be
sufficient to induce arrest of motile excitability, and yet may
not always abolish conductivity.!

Another objection which has been urged against the
theory of the transmission of protoplasmic changes through
the plant is based on certain experiments of Haberlandt. In
these the excitation in J/zmosa is said to have been propa-
gated over dead tracts of the petiole, these portions having
been killed by scalding. But it is extremely difficult to
ensure the death of interior tissues by such means as super-
ficial scalding. I have found that a portion of a plant tissue
which had been subjected locally to the action of boiling
water afterwards exhibited signs of true excitatory electrical
response. It is only by prolonged immersion in boiling water
that the electrical response is. totally abolished. Only after
such treatment, therefore, can one be quite sure that the

' Bose, Plant Response, pp. 227-229. -

446 COMPARATIVE ELECTRO-PHYSIOLOGY

interior tissue is really killed by scalding, and unless this is
thoroughly done it is easy to see that the inner cells may
continue to conduct excitation.

There is, moreover, another possibility, that of pseudo-
conduction, by which the effect of stimulus might appear to
be transmitted across dead areas. In Haberlandt’s experi-
ment, even if the intervening tissues had been killed, there
would still be two masses of tissue, separated from each other |
by an intervening area of dead tissue. A strong stimulus
applied to either of these might then cause an excitatory
expulsion of water, capable, when transmitted across the
dead. area, of imparting a mechanical blow to the second
living tissue, sufficient to set up excitation de novo in that
portion of the petiole. ,

I shall, however, be able to show that conduction is
brought about in the plant by the same transmission of
excitatory protoplasmic changes which occurs in the animal ;
and that those agencies—such as cold, anesthetics, fatigue,
and the polar effects of currents—which induce its variation
in the one case, have the same identical effect in the other
also. The electrical responses, again, afford us a crucial
‘method of distinguishing between hydrostatic and excitatory
effects. For, had the transmission of excitation taken place
in plants by means solely of the propagation of hydrostatic
disturbance, its electrical sign would then have been one of
galvanometric positivity alone. But we have found, on the
contrary, that the sign of the true excitatory reaction is
always of galvanometric negativity. The distinct characters
of these true excitatory and hydrostatic waves have already
been demonstrated in various experiments, in some of which
the hydrostatic has been seen as a positive twitch preceding
the true excitatory negative, while in others the transmission
of the negative was abolished by the application of a selective
block, such as chloroform, thus bringing about the exhibition
of the positive alone (p. 66). So true indeed is it that
excitatory changes are propagated in the plant as in the
animal, that I have actually been able to isolate certain

VELOCITY OF TRANSMISSION OF EXCITATION 447

tissues whose responsive peculiarities are indistinguishable
from those of animal nerves. These must therefore be
regarded as vegetable nerves (Chapter XX XII.).

The determination of the velocity of transmission of
excitation in sensitive plants may be made by applying a
stimulus at any point and observing the interval which
elapses before motile effects are visible at a given distance.
It is, however, impossible by such means to obtain accurate
and consistent results until certain factors of variation are
successfully eliminated. These are (1) indefinite changes of
excitability owing to in-
jury caused by stimulus at
the point of application ;
(2) changes of conductivity
caused by fatigue; and
(3) the unknown effects
of varying intensities of
stimulus on velocity of
transmission.

As a result of investi-
gations on this subject I
found that the velocity of

Fic. 272. Diagrammatic Representation
of Electrical Connections for Deter-

transmission can only be mination of Velocities of Centrifugal
‘ and Centripetal Transmissions
regarded as a determinate Fe
: ‘ X A and B are exciting’ electrodes, and L the
quantity when the intensity indicating leaflet.

of stimulus has a definite

value. Excessive stimulation, again, is found, by causing
injury, to modify the excitability and conductivity of the
tissue. These difficulties, however, are overcome by the
employment of a stimulus which does not cause injury, and
which is capable of repetition at uniform intensity. One
such form of stimulation is obtained by the use of discharge
from a condenser previously charged to a known,voltage
(fig. 272). As regards those changes of conductivity which
are due to fatigue, I have found that fatigue is removed, and
conductivity fully restored, after the lapse of a definite period
of rest, varying in duration in different plants from four to

448 COMPARATIVE ELECTRO-PHYSIOLOGY

ten minutes. In the case of Azophytum, for instance, the
required interval was found to. be about five minutes. |
Taking a specimen of Szophytum, and employing the
method of determination which has been described, I found
successive values which were very consistent ; and, having
thus secured conditions which made it possible to obtain

exact results, I proceeded next to investigate the effects of

various factors—such as fatigue, intensity of stimulus, and

temperature—in modifying the velocity of transmission.

Before proceeding to describe these results in detail, how-
ever, it should be mentioned that, though the velocity of
transmission of excitation is constant in the same plant
under uniform conditions, yet this is not necessarily the case,

if the direction of conduction be reversed. In the petiole of

Biophytum, for example, the centrifugal velocity is always
higher than the centripetal, being about fifty per cent.
_ greater. .

Specimen I

Direction Distance | Time | Velocity

: | | |

Centripetal . ; . 22°5mm. | 11'2seconds 2 mm. persec.|
Centrifugal . : ‘ 45 mm. i ar 2°79 TMs. i ys

Specimen IL

Direction | Distance | Time | Velocity
|
|
|

15*2 seconds |1°84mm. persec.
17°5 a |2*2 mm. 99

Centripetal . : Bi 28 mm.
Centrifugal . : - 39°5 mm.

In order to study the effect on velocity of progressive
fatigue, we may gradually shorten the interval of rest. The
velocity of transmission in the petiole of Bzophytum when
fresh was found to be 1°88 mm. per second in the centripetal
direction. Before making a second experiment on the same
specimen, an intervening period of rest of three minutes was
allowed. This was found to reduce the velocity slightly, it
being now 1°86 mm. per second. The following table shows
the results obtained by a series of five experiments on the

4. >: eee

VELOCITY OF TRANSMISSION OF EXCITATION 449
same specimen. The distance through which the transmis-
sion was observed was 27 mm.

TABLE SHOWING VARIATIONS OF VELOCITY OF TRANSMISSION AND. OF
AMPLITUDE OF RESPONSE WITH INCREASING FATIGUE

Intervals of rest Time igen aenaae = Velocity
The plant fresh. . | 14°3 seconds 34 divisions 1°88mm. persec.
3 minutes . : or} BS SeL 55 20 a 1°86mm. ,,
2 minutes , , ta ye We See Oe eee I°72mm. ,,
I minute ; : Ag eh eee he SURI 1°64mm. ,,
= minute ; : SPSS Lr tes 154mm. ,,

It will thus be seen that the fatigue due to having only
half a minute’s rest reduced the normal velocity of the
specimen by 18 per cent.

The effect of intensity of stimulus on velocity of trans-
mission was next studied. The stimulus employed was that
of condenser discharge, increased intensity being obtained
by an increasing voltage of charge. In this way it was
found that velocity increased with increasing intensity
of stimulus. This fact is shown in the following table,
which gives the results of an experiment on a petiole of
Liophytum.

TABLE SHOWING INCREASE OF VELOCITY WITH INCREASING STIMULUS

Specimen I.—Centripetal T; ransmisston
The distance traversed by stimulus was 27 mm.

Stimulus Time | Velocity
‘o1 Microfarad charged to 8 volts 14°9 seconds | 1°8 mm. per second
> $9 I2 >> 14°4 29 I°9 mm. >?
en BULSIOL 5 TAB * 55 | 2° mm. Pe

Spectmen 11.—Centrifugal Transmission
The distance traversed by stimulus was 38 mm.

Stimulus Time Velocity
‘ol Microfarad charged to 8 volts 11°6 seconds 3'27 mm. per second |
» » 16 ,, 10'2 ;; 3°72 mm. 9
os Ps 24; ROE 25, 3°76 mm. = ee
” oo) 32 4 9°9 ” 3°83 mm. ”

450 COMPARATIVE ELECTRO-PHYSIOLOGY

With regard to the effect of temperature, I found that
cold reduced the velocity of transmission. Thus, in one
experiment, slight cooling reduced it to one-third, and when
carried still further, it abolished the conductivity altogether.
A rise of temperature, on the other hand, had the effect of
enhancing velocity of transmission. The following table
shows that a rise of temperature from 30° C. to 35° C.
doubled the velocity, and that at 37° C. the rate was.
almost three times that at the first temperature. The
velocity was in this case determined in the centrifugal
direction.

TABLE SHOWING THE EFFECT OF RISE OF TEMPERATURE ON VELOCITY.

Distance traversed by stimulus 41 mm.

Temperature Time | Velocity
307¢), II seconds 3°7 mm. per second
35° C. 5 33 7°4 mm »
37° C. 4°5 9 | g*t mm. ry)

Transmission of excitation, as I have shown elsewhere,
and shall show again, is depressed or abolished by the action
_of anesthetics. We shall also see, further, that the polar
effects of currents on the velocity of transmission are the
same in the plant as in the animal, being opposite, accord-
ing as it is the anode or kathode. In the case of a so-called
‘sensitive’ plant, by taking advantage of the motile indica-
tions afforded by the leaf or leaflet, it is possible to determine
the velocity of transmission of excitation and its modifica-
tions. With ordinary plants, however, no such indications
being available, it is obvious that we must find some other
means of detecting and observing the excitatory wave during
transit. Onesuch I have described elsewhere as the Electro-
tactile Method. It is found that the passage of the excitatory
wave, even through an ordinary tissue, brings about minute
form-changes. These give rise to pressure-variations as
between two enclosing contacts. And this variation of
pressure, in turn, can be recorded by means of a sensitive
electrical device.

VELOCITY OF TRANSMISSION OF EXCITATION 451.

There is, however, a more direct way of detecting the
excitatory wave during its passage through a vegetable
tissue. In this—the Electro-motive Method—the galvano-
meter takes the place of the motile leaflet. It has been
shown that. when the plant tissue is directly excited, the
state of excitation is invariably accompanied by an electro-
motive variation, the excited point becoming galvano-
metrically negative. Hence any excitatory wave which is
transmitted through the tissue will always have an electro-
motive wave as its strict concomitant. The moment, there-
fore, at which excitation reaches any given point, may
always be determined by observing the arrival at that point
of the excitatory electrical disturbance of galvanometric
negativity. In order to prove that the arrival of excitation
at the given point is attended by this specific electrical
response, we may perform an experiment on a plant such
as Biophytum, which is provided with motile leaflets. One
of the indicating leaflets is attached to the optic lever, its
base being connected with one of the electrodes of the
galvanometer, while the second is attached to a distant point
on the leaf. The two spots of light, one from the optic
lever indicating the mechanical response, and the other from
the galvanometer, indicating the electrical, are so adjusted
as to lie one above the other, on the same revolving-drum.
On now applying a stimulus, say thermal, at.a distant point,
it will be found, after the lapse of a definite interval; that
both spots of light are deflected at the same time, showing
that both alike give an outward indication of that state of
molecular disturbance which is synonymous with excitation.
These manifestations, of both kirids, would therefore take
place at an identical moment, if only the inertia of the
two indicators were absolutely the same. But, just as the
same impulse would be indicated at slightly different times,
if one indicating-lever were light, and the other heavy, so
here also there may be a slight difference as regards time
between the appearance of the mechanical and electrical

GG2

452 COMPARATIVE ELECTRO-PHYSIOLOGY

responses, according as the virtual inertia of the one indicator
exceeds that of the other.

In determining velocity of transmission by the Electro-
motive Method, a previous experiment gives us the loss of
time due to the inertia of the galvanometer. This, deducted
from the observed interval between the application of
stimulus and response, gives the time required for trans-
mission through the given distance. In this manner I have
been able to determine the rate of transmission of excitation
in ordinary plants. I give below a table which shows these
velocities as determined by me in the case of sensitive plants,
and of ordinary plants, and for the purpose of comparison,
those obtained by other observers, in the nerves of some of
the lower animals, from which it will be seen that all these
are more or less of the same order.

TABLES GIVING VELOCITIES OF TRANSMISSION OF EXCITATORY WAVE

(a) Animal.

Subject Velocity

Nerve of Anodon : . | IO mm. per second
|
|

Nerve of Eledone (observed by Uexkiill) ‘5 to 1 mm. Ms
(6) Sensitive Plants.
Subject | Velocity
| eens
Mimosa pudica: petiole. : : ; | 14 mm. per second
Neptunia oleracea: petiole . : ; . | I°I mm. ie
Biophytum sensitivum : |
Petiole of, direction centripetal . 7 2°I mm.
Petiole of, direction centrifugal . 3°38 mm. os
Peduncle of . F : : ; | 3°7 mm. ze
(c) Ordinary Plants.
Subject | Velocity
= = - po LiLE
Fern: isolated nerve of . , . 2 50 mm. per second
Ficus religtosa: stem. : ; ; a 9°4 mm. ‘3
Cucurbita : tendril ; ; | 5 mm. ¥3
Jute: stem P e ‘ : ‘ - | 3°5 mm. Pe
Artocarpus: petiole . ; ; ; Fae *54 mm. ae

VELOCITY OF TRANSMISSION OF EXCITATION 453.

Since the conduction of excitation takes place by the
transmission of protoplasmic changes, it is evident that it must
occur most easily along those paths in which there is greatest
protoplasmic continuity. It is clear, then, that certain
elements in the fibro-vascular bundles will furnish the best
conducting medium. Cells of indifferent tissue, on the other
hand, like the parenchyma of the leaf, are divided from each
other by more or less complete septa, the fine filaments, by
which neighbouring cells may be protoplasmically connected,
being so minute that the conduction of stimulus through such
imperfect channels must be comparatively feeble. Such
tissues are, therefore, indifferent conductors of excitation,
the stimulus remaining more or less localised in them.
Plant-organs, then, which contain fibro-vascular elements,
such as the stem, peduncle, and petiole, are for that reason
relatively good conductors. Conductivity in such an organ,
again, is,as we should expect, much greater along the length
than across.

I shall now describe an important method by which the
relative conductivity of a tissue in different directions may
be experimentally determined, verifying by its means the
difference in the power of a tissue to transmit stimulus
longitudinally and transversely. For this purpose I took
a thick peduncle of J/usa, and made two electrical con-
nections, of which one was at a fixed point B, transversely
situated as regards C, the point of application of stimulus.
The second point, A, was longitudinally above Cc, and its
distance from it could be varied in successive experiments
(fig. 273).

If we now take a point, A, in such a position that CA is
equal to CB, then, on account of the better conductivity along
CA, the excitation will reach the A contact earlier than that
at B, making that point galvanometrically negative. The
direction of the first responsive current, therefore, will be
from A->B in the tissue. If, next, the longitudinal contact
be moved to A”, that is to say, so far that the excitation
reaches the B contact first, then the responsive current. will

454 COMPARATIVE ELECTRO-PHYSIOLOGY

be reversed, flowing now from B>A”. A point of transition,
or of balance, A’, may now be found by searching, at which
the movement of the exploring contact, nearer or further,
will give rise to opposite responsive currents. The con-
ductivity along the longitudinal direction will then be, to
that in the transverse direction, as the balancing-distance
CA’ is to CB. With a given specimen of the peduncle
of Musa the transverse distance CB was 3°7 cm., and the
longitudinal balancing-distance CA” was determined at 10°4
cm. Hence the longitudinal velocity was 2°8 times that in
the transverse direction.

Fic. 273. Experimental Arrangement for Comparing the Relative
Conductivities in Transverse and Longitudinal Directions

C, point of application of stimulus ; B, permanent transverse contact ;
A, A’, A’, exploring points of longitudinal contact for obtaining
balance,

It has been shown that different tissues in the plant may
possess extremely different powers of conducting stimulus.
In animals there are specialised channels of conduction
known as nerves, and in plants also I have been able to
discover similar conducting tissues, which can be isolated
for the study of their responsive peculiarities. Experiments
on this subject will be related in detail in Chapter XXXII.
It may be said here, however, in anticipation, that the
velocity of transmission of true excitation through these
nervous channels is, generally speaking, fairly high, being at
the rate of about 50 mm. per second in the case of isolated

_ ——

VELOCITY OF TRANSMISSION OF EXCITATION 455 _

nerve of fern. This, for the relatively sluggish vegetable
tissue, is undoubtedly very high.

In connection with this question of velocity of trans-
mission, a fact not hitherto taken into account is, that there
are two distinct kinds of nervous impulses, travelling with
different velocities—namely, the hydro-positive and the true
excitatory negative. Of these the velocity of the former is
greater. In the nerves of higher animals, where the velocity
of transmission of true excitation is also great, it is not
generally easy to distinguish one from the other, so rapid
is their succession. But their occurrence as distinct waves,
even in animal tissues, I shall be able to demonstrate in
a subsequent chapter. In plants, however, where the velocity
of transmission of true excitation is not very high, it generally
lags perceptibly behind the positive wave (p. 59). Burdon
Sanderson, in his determination of the velocity of trans-
mission of excitation in Dzonea, arrived at the exceptionally
high result of 200 mm. per second. I have shown, however,
that the wave whose velocity he measured was not of true
excitation, but of hydro-positive disturbance (p. 231).

In the present chapter it has been my object to demon-
strate the reality of true excitatory propagation in plants
similar to that in the animal. The examples given will be
found more fully described on referring to my book on ‘ Plant
Response.’ I shall, however, in the course of the present
work describe new and extremely delicate means by which
the modifications of conductivity may be studied in plants
unde- varying physiological conditions, 7

CHAPTER XXXI

ON A NEW METHOD FOR THE QUANTITATIVE
STIMULATION OF NERVE

Drawbacks to use of electrical stimulus in recording electrical response— Response
to equi-alternating electrical shocks—Modification of response by decline of
injury—Positive after-effect—Stimulation of nerve by thermal shocks —
Enhancement of normal response after tetanisation—-Untenability of theory of
evolution of carbonic acid—Abnormal positive response converted into normal
negative after tetanisation—Gradual transition from positive to negative,
through intermediate diphasic—Effect of depression of tonicity on excitability
and conductivity—Conversion of abnormal into normal response by increase
of stimulus-intensity—Cyclic variation of response under molecular modifica-
tion.

IN the study of the electrical effects of excitation on the
nerve, the chief experimental difficulty lies in the selection
of a form of stimulus which can be made quantitative. In
such investigations it is usual to employ the electrical form
of stimulus, because of the great facilities which it offers.
A marked drawback to its use, however, lies in the fact that
unless extraordinary precautions are taken it is liable to lead
to serious error. It must be remembered that for the detec-
tion of responsive variations in the nerve an extremely
sensitive galvanometer has to be employed. The excitatory
effect which is to be detected being indicated by the relatively
feeble electrical response, and the form of stimulus being also
electrical and being of high intensity, the results are liable to
be disturbed in an unknown manner by leakage of the stimu-
lating current.

In some cases it is possible to take the bold step of
including the experimental nerve itself in a circuit in which
the exciting coil and the galvanometer are in series. Under
these circumstances, and employing strictly equi-alternating

QUANTITATIVE STIMULATION OF NERVE 457

shocks, we have seen that the resultant response is due to
the differential excitabilities of the two nerve-contacts A and
B. If, for instance, we wish to obtain the responsive reaction
of one point only, say A, uncomplicated by that of 8, it is”
only necessary to abolish the excitability of the latter. This
can be done to a greater or less extent by injury, as, say, by
making a transverse section, or by scalding. Response will
then take place by the induction of relative galvanometric
negativity at A. In fig. 274 is seen
a series of records obtained in this
manner. The responses here apparently
indicate growing fatigue of the nerve.
They also exhibit the positive after-
effect.

With reference to the method of
obtaining response by injuring one con-
tact, commonly employed, it may be
said that the assumption that the ex-
citability of the injured point is totally
abolished is not justified; for I have
found that though recent injury causes
a great depression of excitability, yet py. 274. Response of
after a lapse of time the injured point — Frog’s Nerve under

‘ F ‘ar Simultaneous Excita-
tends to recover its excitability to a tion of both Contacts,

greater or less extent. In such a case by Equi - alternating
. é Electrical Shocks, one
we may expect two different effects to Contact being Injured

be exhibited in the responses. The re- Note the positive after-
sultant response being due, as we have i 3

seen, to the differential excitability of A and B, the gradual
restoration of the excitability of B will progressively diminish
the amplitude of the resultant response, thus giving it the
appearance of fatigue. Under these conditions, and after
a sufficiently long interval, response may almost disappear.
This appears to me to be the true explanation of the gradual
fall in the amplitude of response, when the specimen is a
nerve, having one contact at the transverse section. It also
explains why, in such a nerve, a fresh section, causing

458 COMPARATIVE ELECTRO-PHYSIOLOGY

renewed depression of excitability, is necessary in order to
obtain renewed amplitude of response.

The second effect due to this depression, without abolition
of the excitability of B, is seen in the diphasic character of
the responses. The positive after-effect observed in the record
shown in fig. 274 may thus be ascribed to the later induction
of negativity at the depressed point B. The electrical re-
sponse of the nerve is apparently liable in this way to great _
variations, when the method of record employed is differential.
But it must be remembered that true characteristic variations
of the response as determined by physiological modification
can only be obtained by finding some means which shall
be strictly independent of this differential factor. With this
object, I have succeeded in devising a new mode of observing
and recording the direct effect of stimulus on the nerve,
uncomplicated by the differential factor. In a subsequent
chapter we shall, using this method, be able to determine
the conditions which induce the characteristic variations in
the response of nerve, from the staircase increase to the fatigue-
decline, or even reversal, through the intermediate phase of
uniform reponses.

The method which. has just been described, of exciting
the nerve at both contacts by equi-alternating shocks, is not
applicable, however, where the object of investigation is the
conductivity of an intervening tract of nerve between the
exciting and the led-off circuits. Here the employment of
electrical shocks as exciting stimulus gives rise to disturbing
unipolar effects, which persist even when the physiological
conductivity of the intervening tract is destroyed as, say, by
ligature or by crushing. Thus—

‘If the nerve of a frog’s leg is laid across two
electrodes connected with the poles of a secondary coil,
so as to close the induction circuit, a ligature being then
applied to the myopolar tract, tetanus may still be
observed in the isolated leg, on making the lead off from
it at a certain distance of coil... These unipolar effects

QUANTITATIVE STIMULATION OF NERVE 459

may obviously be very disturbing, and are indeed pro-
ductive of fallacies in vivisection and also in experi-
ments with the galvanometer, if not avoided by due
precautions. Hering has pointed out that in experiments
such as the investigation of the negative variation of
nerve-currents, in which galvanometers and exciting
circuits are separated by a long tract of nerve, the most
complete insulation of the two circuits is no guarantee
against the overflow of induced electricity through the
interpolar part of the nerve into the galvanometer
circuit... . This kind of unipolar stimulation is an
obvious danger in all experiments on action-currents and
negative variation in nerve, while it shows what narrow
bounds restrict the intensities of current that may be
safely used in these experiments.’ ?

From this it will be seen how important it is to have at
our command some non-electrical form of stimulation, when
the response to be recorded is electrical. Heidenhain. em-
ployed a mechanical form of stimulation, by which the nerve
was subjected to blows from an ivory hammer, which was
kept vibrating by means of an electro-magnetic arrangement.
The employment of this mode of stimulation would there-
fore eliminate all that uncertainty—arising from the possible
escape of current—which is inseparable from the use of
electrical stimulus. Though this method must be regarded
as one of great value, yet it is impossible to say how far the
excitability of a given point in a structure so delicate as
nerve will remain unmodified under the repeated action of
such blows. In any case, it appeared desirable to inquire
whether there was no other non-electrical form of stimulus
that could be rendered practicable.

Besides the mechanical, the only remaining non-electrical
forms of stimulus are the chemical and the thermal. Of
these, the former is obviously incapable either of repetition or

* Biedermann, Z/ectro- Physiology (English translation), 1898, vol. ii. pp. 222-
223.

460 COMPARATIVE ELECTRO-PHYSIOLOGY

of being rendered quantitative. As regards the latter, I~have
already shown its practicability for experiments on excitatory
phenomena in vegetable tissues. Thus a single loop of
platinum wire may be made closely to surround the experi-
mental tissue. A definite current sent through the platinum
loop for a given length of time will now subject the encircled
area to a sudden thermal variation, which acts as a stimulus.
Successive closures of the circuit for a definite length of
time are ensured by means of a key actuated by a metro-
nome. The intensity of stimulus may be graduated in a pre-
determined manner by the adjustment of the heating-current.
Excitation may then be caused either by one or by a
summated series of thermal shocks.

I was now desirous of determining whether this form of
stimulation would prove advantageous to experiments on
the nerve, and in the course of the investigation I found it to
be extremely convenient and appropriate. With good speci-
mens of nerve I have been able, using thermal stimulus, to
obtain long-sustained records of perfectly regular responses.
As regards its pliability and facility of application this form
of stimulus is quite unique. How many difficult problems
-are made possible of attack by its means will be realised in
the course of the two following chapters, where the responsive
variations of different conducting tissues under changing
conditions are subjected to investigation.

In order to obtain the electrical responses of animal
nerve—that of frog, for example—the distal contact is killed
and appropriate electrical connections made with the galvano-
meter. The heating current is then adjusted for the desired
amount of excitation.: The thermal variation, it must be
remembered, should not be so great as to injure the tissue
in any way. The platinum loop is not in this case in contact
with the specimen, and this is the mode generally employed.
Should a more intense stimulation be desired, however, the
nerve may be allowed to rest on the platinum loop. In
such a case care must be taken to see that the rise of
temperature is not so great as in any way to injure the

QUANTITATIVE STIMULATION OF NERVE 461

tissue. The nerve, as usual, must be enclosed in a moist
chamber, a convenient form of which, as employed i in 1 practice,
will be seen in fig. 291. |

I shall next give a few records in illustration of the ease
and efficiency with which this mode of stimulus may be
applied. These records will show the characteristic varia-
tions of response given by the nerve under different con-
ditions. When making records of electrical responses with
frog’s nerve, under electrical stimulus, Dr. Waller obtained
responses of three different types. The first of these was
the normal, and consisted of negative responses ; the second
was diphasic ; and the third was the abnormal positive. This
last he regarded as characteristic of stale nerve.

These normal negative responses of the first of the three
classes were found by him to undergo enhancement after a
period of tetanisation ; while the third, that of the abnormal
response of stale nerve, underwent a change into diphasic,
or a reversal to normal, after tetanisation.

From the fact that carbonic acid enhances the normal
negative response of nerve, Dr. Walier has suggested that
the enhancement of response in normal nerve after tetanisa-
tion, and the tendency of the modified nerve to revert to the
normal, are results of the hypothetical evolution ot carbonic
acid in the nervous substance, due to metabolism accompany-
ing excitatory reactions. It must be said, however, that no
trace of the presence of carbonic acid has yet been detected
in such cases. I shall be able to show, moreover, that these
effects are in no way due to the evolutions of carbonic acid,
but take place in consequence of molecular changes induced
in the responding tissue, which find concomitant expression
in changes of conductivity and excitability.

I shall now give records of responses of these various
types obtained under the action of thermal stimulus. In
order to exhibit the effect of tetanisation I give, in fig. 275,
a series of normal responses by induced _galvanometric
negativity, given by nerve of frog in its normal excitatory
condition. ‘This nerve was then subjected to tetanic thermal

462 COMPARATIVE ELECTRO-PHYSIOLOGY

shocks, after which its responses to individual stimuli of the
former intensity were recorded once more. The subsequent
responses show, as is seen in the record, an enhancement of
amplitude. .
The next series of responses, in fig. 276, exhibits abnormal
galvanometric positivity. It may be mentioned here that
; these abnormal responses are
not, as supposed by Dr.
Waller, exclusively character-
istic of the stale condition of
the nerve. For employing
other and more delicate
methods of record I have
found even fresh nerves,
under certain conditions, to
exhibit this effect. Neither
is this positive response due
in general to any chemical
degradation. Instead of this,
as we shall see in the present
and succeeding chapters, it
may be attributed to the
run-down of the latent energy
of the specimen, a process

Fic. 275. Enhancement of Amplitude

of Response, as After-effect of which becomes accelerated in
Thermal Tetanisation, in Frog’s . ;
Notice , 5° isolation. When such a de-

The first three responses are normal. pressed specimen is supplied

Brief thermal tetanisation is here again with the requisite
applied, and the responses subse-

quently obtained under original energy, it becomes normally,
stimulation are seen to be en-
added: or even supernormally, ex-
citable. The first part of the
following record (fig. 276) gives a series of abnormal positive
S §: #/9) § p
responses obtained from a specimen of frog’s nerve, which
was in a somewhat sub-tonic condition. After the appli-
cation of tetanic thermal shocks it will be noticed that the
responses in the second part of the figure have become

converted into normal. —

QUANTITATIVE STIMULATION OF NERVE 463

Between these two extremes of normal negative and
abnormal positive responses there lies the intermediate
diphasic. All these—positive, diphasic, and negative—may
be exhibited in the same specimen, in the course of a sus-
tained record of responses to single stimuli, without tetani-
sation. This fact is illustrated in fig. 277, where the first
series shows the unmixed abnormal positive.
then passes by a gradual
transition into diphasic—
positive followed by negative
—and this phase, lastly, is
succeeded by a series of
purely negative responses.

We come next to the ex-
planation of these phenomena.
We have seen that on account
of isolation the tonic condition
of a highly excitable tissue
will undergo a graduai decline.
On account of this its ex-
citability and conductivity
will fall below par. We have
also seen that in this de-
pressed condition the normal

The response

Fic.

Conversion of Abnormal

276.

response by negativity tends
to be reversed to positivity.
With regard to the con-
duction of excitation it may

Positive into Normal Negative Re-
sponse after Thermal Tetanisation

to left
into normal’ negative
on right, after intervening tetanisa-
tion.

Abnormal positive response
converted

be said that this condition of
depression will lower the power of the tissue to conduct true
excitation. Thus a stimulus of given intensity, capable under
normal conditions of transmission to a certain distance, will,
when the tissue is thus depressed, fail of conduction to the
same distance. It will now, therefore, be the hydro-positive
effect of stimulus which will make its appearance alone at
the distant responding point. And the electrical expression
of this will be galvanometric positivity.

464 COMPARATIVE ELECTRO-PHYSIOLOGY

We have also seen that a tissue which is not in the
highest tonic condition may have its tonicity increased by
the action of impinging stimulus, with consequent enhance-
ment of its excitability. I shall also demonstrate, in
Chapter XXXIV, that the effect of an impinging stimulus
on a sub-tonic tissue is a similar enhancement of con-
ductivity. The result of this will be either (1) that a tissue
which has already conducted a moderate intensity of

ot —

FIG. 277. Gradual Transition from Abnormal Positive, through
Diphasic, to Normal Negative Responses in Frog’s Nerve

Cf. similar effect in response of skin of gecko, fig. 191.

stimulus to a distant point will show, after continuous stimu-
lation, an enhanced power of conduction ; or (2) that in a
very sub-tonic tissue, in which true excitation has at first
failed to reach the responding point, the true excitatory
negative is subsequently transmitted instead of the hydro-
positive alone.

Under actual experimental conditions, where the stimulus
is applied at a distant point, the twofold effects of exaltation of
excitability and conductivity under tetanisation both come
into play. In normally responding nerve, the increased con-

QUANTITATIVE STIMULATION OF NERVE 465

duction of excitation, and the enhanced excitability of the
responding-point, give rise to an increased amplitude of
response after tetanisation, as already seen in fig. 275. Ina
depressed nerve, as the transmitted effect is positive, and the
tendency of the responding point itself, owing to sub-tonicity,
is to the abnormal positive, the record will exhibit the
‘abnormal positive alone, as in fig. 276. But under a series
of successive stimuli, the conductivity and excitability of the
tissue are both gradually raised, and the effect of this is seen
in the consequent gradual restoration of the normal negative
response, through the intermediate diphasic (fig. 277). Or, if
we do not wish to trace out the intermediate steps of transi-
tion, we may tetanise the depressed nerve for a certain
length of time, and record only the terminal change to
the restored normal negative, as is seen in fig. 276.

Taking one of the extreme cases—say that in which the
response to transmitted stimulus is positive, and is converted
into normal negative after tetanisation—we see that the first
result is due to inefficient conductivity, allowing only the
hydro-positive effect to cause response. After this, increasing
conductivity, making an increasing transmission of true exci-
tation possible, gives rise to a diphasic, and ultimately to
the normal negative response. This result is analogous to
the three types of responses—positive, diphasic, and negative
—which we have already obtained with the imperfectly con-
ducting tissue of the petiole of cauliflower and the tuber of
potato (figs. 47, 48). We there saw that where excitatory
efficiency of transmitted stimulus was sufficiently great, it
gave rise to the normal negative response. When this, how-
ever, was not so great, we obtained ‘the diphasic. Finally,
when the true excitatory effect could not be transmitted,
only the abnormal positive response appeared. That
gradation by which the transmitted stimulus was made
fully, partially, or non-effective, to induce true excitation,
was simply and most conclusively carried out in the case of
the potato, by removing the point of stimulation to an
increasing distance from the responding point. In the cases

H H

466 COMPARATIVE ELECTRO-PHYSIOLOGY

described, then, the three types of response are exhibited by
the same tissue, in indubitable relation to the variation of
its effective conductivity. If, then, results exactly parallel
can be demonstrated to occur in the case of nerve also, it.
follows that there is no necessity there to make any such
hypothetical assumption as that of the evolution of carbonic
acid, suggested by Dr. Waller, in explanation of the conver-
sion of abnormal response to normal.

In order to show how a varying conduction will give rise
to these three types of responses, I shall now describe an

Fic. 278. Abnormal Positive Response convérted through Diphasic
to Normal Negative under the increasingly Effective Intensity of
Stimulus, brought about by Lessening the Distance between the
Responding and Stimulated Points

experiment which I carried out with a frog’s nerve in some-
what subtonic condition. Here, when the stimulator was
placed at some distance from the responding point, the
response was the abnormal positive (fig. 278). When the
effective intensity of transmitted stimulus was now slightly
increased by moving the point of application a little nearer,
the response became diphasic ; and finally, when the stimu-
lator was placed still nearer, the response became normal
negative. Thus with an identical specimen we may obtain
at will either negative, diphasic, or positive response, by
making changes only in the effective intensity of stimulus
employed. We have also seen, moreover, that if we kept

QUANTITATIVE STIMULATION OF NERVE 467

the stimulator at a certain distance from the responding
point, such as at first to cause only positive response, succes-
sive stimulations would then act to enhance conductivity
gradually, and thus give rise to the appropriate changes,
diphasic and negative in the response.

The ultimate cause of these variations must therefore lie
in the molecular condition of the tissue. Under varying cir-
cumstances, this undergoes a cyclic change, the responsive
reaction at any given moment constituting an indication of
the particular molecular condition of the tissue. A more
complete demonstration of this, carried out by an altogether
different method, will be given in a subsequent chapter. My
principal object in this chapter has been to prove the
efficiency of the thermal shock as a mode of stimulation of
nerve. Its wider applicability, in the case of other related
investigations, will be treated in the two succeeding chapters,

HH 2

CHAPTER XXXII
ELECTRICAL RESPONSE OF ISOLATED VEGETAL NERVE

Specialised conducting tissues—Isolated vegetal nerve—Method of obtaining
electrical response in vegeta] nerve—Similarity of responses of plant and
animal nerve: (a) action of ether—(4) action of carbonic acid—(c) action
of vapour of alcohol—(d) action of ammonia—(e) exhibition of three types
of response, negative, diphasic and positive—(/) effects of tetanisation of
normal and modified specimens—Effect of increasing stimulus on response
of modified tissue.

IT has been shown in the previous chapter that the state of
excitation is transmitted to a distance in vegetable tissues.
It has also been proved that such transmission is not due to
the propagation of hydrostatic disturbance but to that of
protoplasmic changes, precisely as in the case of animal
tissues. It is obvious, further, that such transmission will be
the more perfect the less the interruption of protoplasmic con-
tinuity. Hence tissues like stems and petioles, which contain
fibro-vascular elements, are found to be good conductors
of excitation, whereas indifferent tissues, such as those of
leaves and tubers, are relatively feeble as regards this power,
excitation in their case remaining somewhat localised.

Even with regard to stems and petioles themselves, a
contrast is found to exist in this respect between the fibro-
vascular elements and the ground tissue. Thus, in the case
of a petiole of cauliflower, I made two experimental prepara-
tions. In the first, the ground tissue was cut away, leaving
the fibro-vascular elements ; and in the second, a column of
ground tissue was left outstanding, denuded of fibro-vascular
elements. The former of these was found to transmit
excitation to a certain distance, whereas in the latter the
transmission was practically absent. In the case of a third

RESPONSE OF ISOLATED VEGETAL NERVE 469

preparation I bifurcated the specimen, stripping away from
one of the two limbs the fibro-vascular elements, and from
the other most of the ground tissue. Galvanometric connec-
tions were now made with the free ends of the fibro-vascular
and ground tissues respectively, and stimulus was applied by
means of transverse cut, or by application of a hot plate
across the area of union. The transmitted effect was now
perceived as galvanometric negativity, at the end of that
strip which was composed of fibro-vascular elements.

In studying this |
subject of conduction,
I found the transmitted
effect of excitation to
be universally well ex-
hibited in the petioles
of ferns, successive re-
sponses, obtained at a
distance from the point
of stimulation, being
in their case singularly
perfect and uniform.

From this I was led
to the conclusion that
the disposition of the.
conductors must here fic. 279. Frond of Fern with Conducting
hie par ticularly uel} Nerves N exposed in Enlarged Figure to Right
adapted to their purpose. I had long been desirous of isolating
whatever elements in the vegetable tissue were to be regarded
as performing the function of nerves, and it appeared to me
that I had here found a good subject for this investigation ;
and accordingly, on carefully breaking the hard casing of the
petiole, and pulling it away in both directions, I was able
to isolate the conducting fibro-vascular threads, which were
long, soft, and white in colour, remarkably similar in their
appearance to animal nerves (fig. 279). These threads vary
in number with different species of ferns, and resemble
animal nerves in general appearance. It is sometimes

470 COMPARATIVE ELECTRO-PHYSIOLOGY

possible to detach one of them having a length of 20 cm.
or more.

Now the essential feature of a nerve is its protoplasmic
continuity, which is ensured by its fibrous structure. And
in what I have called the vegetable nerve we find.the same
characteristic to hold good. On viewing this structure, as
it appears on making a transverse section of the petiole,
we find it enclosed within sheath-like sclerenchyma. It ©
mainly consists in itself of a bundle of fine fibres with a
few vessels in the centre. But however remarkable these
external resemblances may seem, they are by no means so
startling as the more fundamental similarities which are
demonstrated so soon as we proceed to subject this vegetable
structure to those tests of electrical response which are
characteristic of animal nerve. It may be said that for the
following investigation the nerves of the common maiden-
hair fern (Adtantum) and Nephrodium molle were found most
suitable.

In obtaining a plant nerve for purposes of experiment
it is possible to dissect it out and at the same time to avoid
injury. It is then placed in normal saline solution for about
half an hour, so as to remove all traces of excitation due to
handling. When the external temperature is not high, the
excitability of the isolated plant nerve is found to remain
relatively unaffected for a considerable period, but in the hot
weather it undergoes rapid decline; and the only way in
which I could overcome this difficulty was by placing the
specimen in normal saline solution which was ice-cold. The
experimental precautions to be taken are precisely the same
as those observed in corresponding experiments with animal
nerve; that is to say, the specimen should be placed in a
moist chamber. For the process of drying is found to induce
a transient increase of excitability followed by a permanent
abolition of responsiveness, in the one case as in the other.
In order to obtain responses, one end of the specimen may
be killed by the local application of hot salt solution. The
galvanometric connections are then made, one with the killed,

RESPONSE OF ISOLATED VEGETAL NERVE 471

and the other with the unkilled portions of the specimen
higher up. In order to ensure that the electrical indication
be a true responsive reaction, it is well to use a non-electrical
form of stimulus. One of the most perfect forms—as we
have seen in the previous chapter, on excitation of animal
nerve—is the thermal, and this may be applied in precisely
the same manner, that is to say, by means of a platinum
wire, surrounding, but not necessarily in contact with, the
given area of the specimen, this wire being heated periodically
in the manner previously described, by means of a metro-
nome closing an electric circuit. With a good specimen,
a single thermal shock, lasting for less than a second, will be
found sufficient to induce a considerable electrical response,
or a response of still greater amplitude may be obtained by
the summated effects of several such stimuli. One of the
most noticeable differences between this plant nerve and
other vegetable tissues lies in its greater excitability. For
example, while a single thermal shock of less than one second’s
duration is sufficient, as has been said, to evoke immediate
and considerable response from the isolated nerve, we find that,
in order to evoke similar response from the petiole of the fern
as a whole, it is necessary to submit it to the same stimulus
some twenty times in succession, the response even after this
taking place with relative sluggishness. |

A still further characteristic is its indefatigability. A long
series of responses to uniform stimuli, such as would in the
case of ordinary tissues bring about marked fatigue, will in
that of nerve induce little or none. Rapidly succeeding
tetanising shocks, moreover, such as in other tissues induce
rapid’ decline, induce, generally speaking, but little of such
an effect on the response of nerve. In the case of this vege-
table nerve also the same statements hold good. A long
continued series of responses shows little fatigue. After
tetanisation, moreover, we find that the responses of nerve,
whether animal or vegetable, become enhanced.

In the matter of the effects induced by chemical re-
agents on animal and vegetable nerves, a further remarkable

A472 COMPARATIVE ELECTRO-PHYSIOLOGY

parallelism is to be observed. The completeness of this may
be seen in greater detail in the next chapter. I shall, at the
present point, confine myself to giving a few typical cases.
Ether, for example, when acting on animal nerve, induces a
preliminary exaltation of excitability, which is followed under
its long continued action by depression. On blowing off
the ether vapour again the original state of excitability is
restored. In fig. 280 are seen the similar effects of this
reagent on vegetable nerve, where (@) exhibits the normal
response, (0) the immediate exaltation due to ether, (c) the

Fic, 280, Photographic Record of effect of Ether on the Electrical
Response of Plant-nerve

(a) Normal response: application of ether at point marked with ¢;
(4) Enhanced response in first stage of action of ether; (c) Subse-
quent depression ; (2) Restoration of normal response after blowing-oft
of ether. .

subsequent effect of depression, which becomes marked after
continuous action during twenty-five minutes, and (d) the
restoration of the original condition on the blowing-off of
the ether.

Carbonic actd is known, in the case of animal nerve, to
have the effect, in the first stage, or in small quantities, of
inducing exaltation, which passes under its prolonged action,
or, in the case of a stronger application, into depression. A
similar effect is seen in fig. 281, where (a) shows the normal
response of a vegetable nerve, and (0) the preliminary exalta-
tion due to carbonic acid introduced into the vegetable nerve-

RESPONSE OF ISOLATED VEGETAL NERVE 473

chamber. This is seen to increase continuously for some
twenty minutes in (c). But after the expiration of half an
hour depression makes its appearance (¢). This becomes still
more marked, after the fortieth minute, in (e), |

Fic. 281. Photographic Record of Effect of CO, on Electrical
Response of Plant-nerve

a, normal responses ; 4 and ¢, enhanced response during first stage of
action ; @ and e, subsequent growing depression.

Alcohol vapour in strong, or long-continued applications,
induces marked decline of response in animal nerve. Parallel
effects are seen in the case of vegetable nerve in fig. 282.

The effect of ammonia on animal tissues is character-
istically different, according as the subject of experiment is

Fic. 282. Photographic Record of Abolition of Response by Strong
Application of Alcohol

nervous or ordinary tissue. While the excitability of the
muscle, for example, is but little affected by its application,
that of nerve is quickly abolished. In order to see whether
the same characteristic difference would be exhibited, as

A74 ~ COMPARATIVE ELECTRO-PHYSIOLOGY

between ordinary vegetable tissues and vegetable nerve, I
first studied its effect on the ordinary tissue of the petiole of

Fic. 283. Photographic Record of Effect of Ammonia on Ordinary
Tissue of Petiole of Walnut

Note that the effect of ammonia here is practically negligible.

walnut. It will be seen from fig. 283 that ammonia here
induced a Digs teayy no change in the excitability. But when
the same reagent was applied
to the isolated nerve of
fern the response underwent
depression, followed by total
abolition, in the course of
five minutes (fig. 284).

One very curious charac-
teristic of the _ electrical
response of frog’s nerve is
the occurrence, as referred
to in the last chapter, of
three distinct types of re-
sponses, according to its

Fic. 284. Photographic Record of aye :
Effect of Similar Application of condition. Thus, as_ has

Ammonia on Plant-nerve already been said, while
The response here is rapidly diminished highly-excitable nerve é€x-
and finally abolished. sae ;

hibits the normal negative
response, the same nerve, when it has become sub-tonic, will
give a mixed or diphasic response; and a nerve which is

RESPONSE OF ISOLATED VEGETAL NERVE A75

modified to a still greater extent will show a purely abnormal
or positive electrical response. Inthe case of vegetable nerve,
J find exactly the same three types of response repeated, under
the same conditions. This will be seen in the three sets of
records given in fig. 285. The normal responses, which are
negative, are here represented as ‘up, while the abnormal
positive is represented as ‘ down.’ :

Still more remarkable is the parallelism observed between
the effects of tetanisation, on animal and vegetable nerve,
both normal and modified. In the case of fresh frog’s
nerve the responses are, as we have seen, enhanced, after

Fic. 285. Photographic Record of Exhibition of Three Types of
Response, Normal Negative, Diphasic, and Abnormal Positive, in
Nerve of Fern under Different Conditions

a period of tetanisation. The effect of tetanisation on
vegetable nerve is precisely similar, as is seen in fig. 286.
In the case of the modified frog’s nerve, moreover, it is-found
that the abnormal positive response tends, after tetanisation,
to become normal. This is seen in the abnormal response,
whether positive or diphasic, being converted to the normal
negative type. I have obtained exactly parallel effects in
the case of modified vegetable nerve. In fig. 287 we see
the abnormal diphasic response of vegetable nerve converted,
after tetanisation, into normal negative.

Thus, as in the response of animal nerve, so also in that
of the vegetable, tetanisation is found to have the effect of
enhancing the normal, or converting the abnormal into

476 COMPARATIVE ELECTRO-PHYSIOLOGY

normal response. The abnormal response of nerve we found
to be due to the joint depression of conductivity and excita-
bility, on account of which the positive alone, instead of the
true excitatory negative, was exhibited. In experimenting
with frog’s nerve we saw that abnormal! response might, at
will, be converted into normal through the intermediate
diphasic by appropriately increasing the effective intensity
of stimulation. A simple means of effecting this was to
bring the stimulator gradually nearer the responding point.

Fic, 286. Photographic Record of Effect of Tetanisation in Inducing
Enhancement of Normal Negative Response in Nerve of Fern

The first series of responses seen to he enhanced after intervening tetani-
sation, T.

In the response of vegetable nerve effects exactly parallel are
to be observed.

With a given specimen of vegetable nerve, the stimulator
had at first been placed at a distance of 2 cm. from the
proximal galvanometric contact, and the responses then
taken were found to be of the abnormal positive type. The —
stimulator was now brought nearer, the distance being
reduced to I cm., and the next pair of responses is seen to
be diphasic, consisting of a positive twitch followed by the

RESPONSE OF ISOLATED VEGETAL NERVE 477

normal negative response. The distance was next reduced
still further, namely, to ‘5 cm., with the result that the

Fic. 287. Photographic Record of Conversion of the Abnormal
Diphasic into Normal Negative, after Tetanisation, Tr, in Nerve of
Fern

Fic. 288. Photographic Record showing how the Abnormal Positive

' Response is converted through Diphasic into Normal Negative, by
the Increasing Effective Intensity of Stimulus, due to Lessening the
Distance between the Responding and Stimulated Points

responses now became normal negative (fig. 288). It is thus
seen that there is a continuity of response in the same

478 COMPARATIVE ELECTRO-PHYSIOLOGY

tissue, as between the abnormal and normal, through the
intermediate diphasic.

From the various experiments, then, which have been
given in this chapter, it will be seen that the response of the
isolated vegetable nerve is in every respect similar to the
corresponding responses of animal nerve. And we shall also
see how, by means of the study of this vegetable nerve, we
are enabled to elucidate many obscurities in the responses
of the corresponding animal tissue. We shall in the next
chapter enter in detail into the question of the modifications
induced in the conductivity and excitability of vegetable
nerve under the action of various external agencies, and
these will be found to exhibit the strictest parallel with
corresponding variations induced in the animal. .

CHAPTER XXXIII

THE CONDUCTIVITY BALANCE

Receptivity, conductivity, and responsivity—Necessity for distinguishing these—
Advantages of the Method of Balance—Simultaneous comparison of variations of
receptivity, conductivity, and responsivity—The Conductivity Balance—Effect
of Na,CO, on frog’s nerve—Effect of CuSO,—Effect of chemical reagents on
plant nerve—Effect of CaCl, on responsivity—Responsivity variation under
KCl—Comparison of simultaneous effects of NaCl and NaBr on responsivity
—Effects of Na,CO, in different dilutions on conductivity—Demonstration of
two different elements in conductivity, velocity, and intensity—Conductivity
versus responsivity—(a) effect of KI—(4) Effect of Nal— Effect of alcohol on
receptivity, conductivity, and responsivity—Comparison of simultaneous effects
of alcohol—(a@) on receptivity versus conductivity—(2) on receptivity versus
responsivity,

WE know that when any point in a tissue is acted on by
external stimulus, it receives the stimulation and is thrown
into a state of excitation. This excitation is then conducted
along the length of the tissue, and may be made outwardly
manifest at some distant point by means of a suitable in-
dication such as motile or galvanometric response. There
are thus three different aspects of the excitatory effect to
be distinguished from each other, namely, first the excita-
tory effect at the point of reception of stimulus, which I
have elsewhere designated receptive excitability, or simply
Receptivity : secondly, the power of transmission of excita-
tion, or Conductivity: and thirdly, the excitatory effect
evolved at the distant responding region, which I shall
henceforth term Responszvity. ‘Though these three aspects of
the excitatory reaction are all alike dependent upon the
molecular derangement caused by stimulus, it is nevertheless
important to consider them separately, since their variation is
not always the same under the same circumstances. We

480 COMPARATIVE ELECTRO-PHYSIOLOGY

have seen, for example, that a rise of temperature, by in-
creasing molecular mobility, enhances conductivity. But
this increase of molecular mobility and internal energy also
goes to augment the force of recovery, and, owing to this,
the amplitude of excitatory response may be decreased.
Thus, while a rise of temperature increases conductivity, it
may appear to decrease responsive excitability. So much
for the necessity of a distinction between conductivity and |
responsivity. The term ‘excitability’ is commonly used for
receptivity and responsivity indifferently. But I shall show
in the course of the present chapter that it is important to
make a distinction between these, since ‘the same external
agent may effect the two differently.’ In the ‘following
investigation, receptive excitability, or receptivity, will be
represented by R, conductivity by cC, and responsive ex-
citability, or responsivity, by E.

In determining the effect of any external condition such
as the application of a chemical reagent on responsive ex-
citability, in the case of animal nerve, it is usual to take a
series of normal responses, and then to record the modified
responses after the application of the reagent. By com-
paring a number of such series of records, representing the
action of various reagents on different specimens, the relative
effect of each chemical may be inferred. The drawback to
this method lies, first, in the fact that by the addition of the
chemical reagent the resistance of the electrical circuit
undergoes an unknown change, thus inducing a variation in
the amplitude of response, which is not necessarily due to the
excitatory electromotive change fer se. It is true that this
difficulty may to a greater or less extent be obviated by
interposing a high external resistance in the circuit, but this,
by reducing the deflection, necessarily reduces the sensitive-
ness of the method also. Different specimens again cannot
but be characterised by slight individual peculiarities, and the
experimental arrangements therefore can only be considered
to be perfect when we are able to compare the effects of two

! See also Bose, Plant Response, pp. 215-230.

THE CONDUCTIVITY BALANCE 4381-

agents on an identical specimen. Again, in a series of
chemical compounds which differ but slightly in effect from
one another, an arrangement has to be devised by which
the most minute excitatory variations will be conspicuously
displayed. The same delicacy of experimental adjustment
also becomes necessary when we wish to investigate the
varying effects of time and quantity in the application.

Similar considerations are involved when we attempt to
observe the effects of various agents on conductivity and
receptivity ; and still more complicated are the difficulties to
be overcome when we have to study the property of con-
ductivity versus responsivity or receptivity, or of receptivity
versus responsivity, under the action of the same external
agent. The methods hitherto available are neither perfect
nor delicate enough for a complete and satisfactory determina-
tion by their means of the various problems which arise in
this connection. I' shall now, however, describe a very
perfect and delicate method carried out by an experimental
arrangement which I have devised, and shall designate as the
Conductivity-Balance, by which the variation of an affected
region may be continuously compared with a normal area
as regards each of the three different aspects of the ex-
citatory reaction, namely, receptivity, conductivity, and
responsivity. In this method, moreover, the result is un-
affected by any variation of resistance in the circuit that may
be induced by changed conditions. It also enables us to
solve the various difficulties encountered in comparing the
relative changes induced in conductivity with those induced
in receptivity or responsivity, or in the two last in respect to
each other, under the influence of a given reagent.

In fig. 289 is given a diagrammatic representation of the
principal parts of this Conductivity-Balance. The thermal
stimulator produces stimulation of the enclosed area of the
specimen. The excitatory wave travels along both arms of
the balance, through the conducting region C and c’, and
induces excitatory electromotive effects at the two responsive
points Eand E’. The excitatory electrical effects at E and E’

IT

482 COMPARATIVE ELECTRO-PHYSIOLOGY

are opposed, and when these are equal, and balance each
other, the galvanometer indication is then reduced to zero.
E and E’ are usually at a distance of about 4 cm. from each
other. When the stimulator is brought too near to the left
contact E’, the excitatory effect of
galvanometric negativity which is
induced there is relatively greater
than at E. The balance is thus dis-
turbed, and the resultant responsive
deflection is then, say, downwards.
When the stimulator is placed, on
the other hand, too near the contact
E, to the right, the resultant galvano-
metric deflection will be up.! By
suitable movement of the stimulator,
to and fro between these two ex-
tremes, a point may be found where
the excitatory effects at E and E’
will exactly balance each other. I
give here (fig. 290) a record taken

Fic. 290. Photographic Re-
cord made during Pre-
liminary Adjustment for
Balance of Nerve of Fern

The first two down-responses
show over-balance, when
S is too near the left,
E’ being relatively more

Fic. 289. Diagrammatic Representa-

tion of the Conductivity Balance excited. The up-responses

s, thermal stimulator; c and c’, the indicate over - balance
conducting arms of the balance ; caused by s_ being too
E and E’, responding points. Dif- much to the right. The
ferential excitatory electrical effects horizontal record shows
at E and E’ recorded by galvano- attainment of — exact
meter, G. balance.

during this preliminary stage of adjustment. The first two
down-responses were obtained when the stimulator was too
far away from the balancing-point to the left. The next two

1 It is to be understood that what is said here refers to nerve in a normal
condition of conductivity.

THE CONDUCTIVITY BALANCE. 483

up-responses were obtained when it-was contrariwise too far
to the right. More careful adjustment reduced this up-
movement, as seen in the next two responses, and finally,
when the exact balancing-point was reached, the effect was
null, as seen in the horizontal record.

In studying the question of the variation of responsive
excitability induced by any given reagent, the agent is
applied at the point E to the right. Any variation of excit-
ability will then upset the balance. If the reagent be of a
stimulatory character we shall obtain a resultant up-response,
but if it be of a depressing nature, E will be rendered rela-
tively the less excitable of the two points, and the response
will consequently be down. It will thus be seen that that
upsetting of the balance by which either up- or down-responses
are induced is due simply to the relatively excitatory or
depressing effect of the reagent, and is completely inde-
pendent of any variation of resistance which might be
brought about by its application. In the course of the
following investigation, it is to be understood that the elec-
trical connections are so made that the greater excitation of
the right-hand contact is always represented by up-response,
and vice versd. If it be desired to make a comparison
between the excitatory reactions of two reagents, then the
two are applied simultaneously, one at E and the other at E’.
The resulting record then affords us a continuous graphic
illustration of the relative and varying effects of the two.

If, again, it is the influence of any agent on conductivity
that is to be studied, we first take a balanced record and then
apply the given reagent on an area of about I cm. at Con
the conductingarm. In this case, the responsive excitabilities
of the two points E and E’ are the same, but if the effect of
the agent have been to induce increased conductivity of Cc,
then the excitation transmitted to the right-hand side, E, will
be greater, and the response caused by the upsetting of the
balance will be upwards. Conversely, a down-response will
indicate that the effect of the agent has been to depress the
conductivity. Again, we can compare the relative effects in

II2

484 COMPARATIVE ELECTRO-PHYSIOLOGY

conductivity-variation induced by two different agents which
are applied simultaneously, one on the arm C and the other
enc,

It is possible again to compare the variation of con-
ductivity with that of responsivity, by applying one agent at
a responding region, say E, and the other on the opposite arm
of the balance atc’. The mode of investigation of receptivity
changes will be described presently. :

In fig. 291 we have the complete apparatus. The animal
or vegetal nerve, N N, rests on non-polarisable electrodes of

E. E2 Es; E 4

Fic. 291. Complete Apparatus of Conductivity Balance

The nerve N supported on electrodes E,, E,;. The two other electrodes
E, E, are not used in this experiment, but are employed for experiments
on electrotonus; T, thermal stimulator, the relative lengths of the
arms of the balance being adjusted by the slide s.

a U-shape. For the present experiments, two electrodes, E,
and £,, are sufficient, their mutual distance being capable of
any variation by movement along a sliding-bar. The same
apparatus might be used for experiments on electrotonus, in
which two additional electrodes would be required. The
position of the electrothermic stimulator T is capable of very
careful adjustment for purposes of balance, by means of the
sliding-rod s. A glass cover, not shown in the figure, fits into
the groove which is represented by a double dotted line sur-
rounding the apparatus, and thus enables the chamber con-
taining the nerve to be kept in a properly humid condition.

THE CONDUCTIVITY BALANCE 485

In all these experiments by balance, it is to be borne in
mind that adjustment is always made for perfect balance
at the beginning of the record, and represented by a short,
more or less horizontal, line. te
In order to show the typical effects of induced variations
of excitability, in upsetting the balance, I shall first give
records of experiments carried out on the nerve of frog.
Dilute sodium carbonate is known to be an agent which
enhances excitability. A long-continued application, or the
application of a stronger dose,
may, however, bring about a
depression. When a dilute
solution of Na,CO, was ap-

Fic. 292. Effect of Na,CO, Solution
on Responsive Excitability of Frog’s
Nerve

In this and following records the hori-
zontal line at the beginning indicates
exact balance. The upsetting of the
balance in the up-direction repre-
sents either the enhanced respon-
sivity of the right-hand responding
eg _E, = the Leer a con-

uctivity of the right-hand arm c,
Riowascueeal eee ont correspond- Fic. ASS SEM Se SRR On Et0g's
ing absolute or relative depressions. Nerve
Na,CO, applied to E is seen to exalt The down record shows depression of
the responsivity of that point. excitability.

plied at the responsive point E on the right side, the up-
setting of the balance upwards immediately indicated the
greater excitability induced by the reagent. The long-
continued action of this reagent, however, showed that the
enhanced excitability was undergoing a gradual decline
(fig. 292).

In order to exhibit the characteristic upset caused by
a depressing agent, I employed on another specimen a
toxic solution of copper sulphate, applying it at E on the
right. The previous state of equilibrium is seen by the
horizontal line at the beginning of the record, and the

486 COMPARATIVE ELECTRO-PHYSIOLOGY

subsequent depression of excitability at E is shown by the
upsetting of the balance downwards (fig. 293).

I shall next take up the determination of the changes
induced by chemical agents on the excitability of plant nerve
and shall begin by describing the different effects which occur
on the application of calcium and potassium salts. For this
purpose, deci-molecular solutions were employed. Fig. 294

shows the effect of CaCl, on.
vegetable nerve, the solution
being applied at E on the
-right-hand side. It will be
noticed that this caused an
upset of the balance, showing
an increase of excitability
that becomes considerable
after the expiration of five
minutes. In the case of KCl,
however, this effect was re-
versed, that is to say, a de-
pression was induced. This
, is seen in fig. 295, where the
_ Fic. 294. Photographic Record show- balanced record gives way,
ing Enhancement of Responsivity Gat te diphasic, and :atter-

by Application of CaCl,
CaCl, applied to E is seen to exalt wards to a down-response,

the responsivity of that point. indicating an effect of de-

| pression at E. These two
experiments show the effect of the basic moiety in in-
ducing changes of responsive excitability.

I shall next describe experiments by which the simul-
taneous effects of two different reagents on the responsivity
of a given tissue may be compared. For this purpose, one
agent is applied at one end of the balance E, the other being
administered at E’. In the case of animal nerve, it was
shown by Griitzner, that both NaCl and NaBr induce ex-
citatory effects, that induced by NaBr being relatively the
greater. But the continued action of either of these reagents

THE CONDUCTIVITY BALANCE 487

induces depression, which sets in earlier in the case of NaBr.
The effect of these two reagents on vegetable nerve is pre-

Fic. 295. Photographic Record showing Depression of Responsive
Excitability by Application of KCl

cisely the same, as will be seen from an inspection of the
record given in fig. 296. The NaBr was applied on the

Fic. 296. Photographic Record exhibiting Comparative Effects of
NaCl and NaBr on Responsivity

NaCl was applied on E’ and NaBr on £, the formula being E’yaciEnapr-
The record shows the greater and earlier effect of NaBr at E in
causing relative excitation followed by relative depression.

right-hand side E, and NaCl on the left-hand E’,a process
which is expressed, for the sake of brevity, by the formula
E'wacil’wapr =0Lhe greater and earlier. excitatory effect of

488 COMPARATIVE ELECTRO-PHYSIOLOGY

NaBr, applied on the right-hand side, is shown by the
resultant up-responses. But after a time, E being now
depressed by. the continued, action of NaBr, the effect of
NaCl, applied on the left, becomes relatively predominant,
a fact demonstrated by the upset of the balance in the oppo-
site direction, with concomitant down-responses.

We shall next take up the subject of variations induced
in conductivity. We have seen that dilute solutions of
Na,CO, have the effect of exalting responsive excitability.

FIG. 297. Photographic Record of Effect of Dilute (+5 per cent.) Solution
of Na,CO, on Variation of Conductivity

Reagent applied on right arm c. Record shows immediate enhancement
of conductivity giving rise to up-curves, followed by depression, seen
in down-curves. Note the appearance of a down-twitch at the be-
ginning of the sixth response due to the later arrival of excitation at E.
Note further the replacement of up- by increasing down-responses.

Long-continued applications, or strong solutions, however,
have the effect of inducing a depression. Similarly, I find
that this reagent has the effect of enhancing conductivity,
provided the solution is sufficiently dilute. In the case of
the petioles of ferns, a 2 per cent. solution was found to
induce a preliminary exaltation of excitability, followed
by a depression (p. 136). In dealing with the conductivity-
variation in certain isolated vegetable nerves, however, a
2 per cent. solution was found to induce a depression of con-
ductivity, but a °5 per cent. solution caused an enhancement

THE CONDUCTIVITY BALANCE 489

of conductivity, followed, after long-continued action, by
depression.

These facts are illustrated in an extremely interesting
manner in the records given in figs. 297 and 298. In both
these cases the solution was applied on the right arm of the
balance at C, the difference being only that in the first experi-
ment the strength of solution was ‘5, and in the second 2 per
cent. An inspection of fig. 297 shows that the application
of the first induced a great and immediate enhancement of
conductivity, causing resultant up-responses, which were par-
ticularly marked during the first four minutes. This increased

Fic. 298. Photographic Record of Effect of Stronger Dose (2 per cent.)
of Na,CO, Solution on Conductivity.

The solution was applied on the right arm of the balance c. Note grow-
ing depression and appearance of diphasic effect.

conductivity is then seen to undergo a continuous decrease
and reversal into growing depression, as seen in the substi-
tution of increasing down-responses. This record deserves
special attention, inasmuch as it affords us an insight into a
phenomenon which could not otherwise have been suspected.
Greater conductivity is usually associated with increased
velocity of transmission. It would appear, however, that the
term conductivity really covers two different phenomena
which may not always be concomitant. That is to say,
an increase of conductivity may mean either a greater speed
of transmission of excitation or a greater intensity of the

490 COMPARATIVE ELECTRO-PHYSIOLOGY

excitation transmitted. In the first four records of the present
series the induced enhancement of conductivity is shown by
the occurrence of up-responses only. The fifth record, how-
ever, shows a marked preliminary twitch in the negative
direction, followed by an up-response of some amplitude.
This shows that the excitatory effect reached the. right end
E later than the left, though the intensity still remained
greater. The continued action of the reagent subsequently ~
reduced the intensity also, so that this diphasic ultimately
became converted into a purely monophasic down-response,
gradually increasing to a maximum. In fig. 298 we observe
the depression of conductivity by a stronger dose of 2 per
cent. solution of Na,CO,, applied on the right-hand side at C.
Here, again, we can see the separated effects of the two
elements of conductivity—that is to say, the intensity of the
effect transmitted and the speed of transmission. In the first
‘few responses of this series we see the diminished intensity
of transmission to the right giving rise to resultant responses
which are entirely downwards. Later, this transmission of
enfeebled excitation becomes delayed also, and by the phase-
difference thus induced we obtain the growing diphasic effects
which have already been fully explained on p. 144, fig. 100.
Owing now to this growing difference of phase, the two
opposed effects no longer neutralise each other to the same
extent as before, and we obtain increasing amplitude of both
the constituent phases. The down-curve in the diphasic
response represents the earlier arrival, and relatively greater
intensity, of effect at the left contact E’. And the up-curve
shows the later arrival of the less intense effect at the right-
hand contact: E. It is thus clearly seen that conductivity
includes two different elements of speed and intensity which
may not in all cases be coincident.

I shall next describe experiments which will demonstrate
the variation of conductivity versus that of responsive excit-
ability under the action of the same reagent. In animal nerve
responsive excitability is diminished by the action of strong
solutions of neutral salts, and potassium salts induce greater

THE CONDUCTIVITY BALANCE 491

depression than corresponding sodium salts. But neutral
salts, generally speaking, affect conductivity to a much
slighter extent than responsivity. There is, however, a very
curious exception to this rule in the case of animal nerve,
where 6'1 per cent. of Nal is found to affect the conductivity
to a much greater extent than the responsive excitability.
I find a remarkable parallelism to these effects in the case of
vegetable nerve, which
is capable of striking
demonstration by the
comparative method of
simultaneous variations
of conductivity and
excitability already de-
scribed. In order to
demonstrate these con-
trasted effects of KI
and Nal on conductivity
and excitability, I shall
here give an account
of two different experi-
ments. In the first,
after obtaining the pre-
liminary balance, KI
was applied at ton Fic. 299. KESPONSIVITY versus

ie pia ; CONDUCTIVITY under KI
SHE Sie eee, SOS saat This photographic record shows the effect of

reagent being also ap- KI on responsivity and conductivity when

Tiead th ee reagent applied at £’ and C simultaneously.
pile at € end E o The formula is E’x;Cx;. Record shows
the left arm, this pro- greater depression of responsivity than of

; conductivity.
cess being represented

by the formula E’,..C,,.. The record seen in fig.'299 shows,
by its resultant up-responses, that a greater depression of
responsivity at E’ than of conductivity at c has been induced.
In the next experiment (fig. 300) Nal was applied instead of
KI, on C to the right, and E’ to the left, the formula thus
being E’,..C.., The resultant responses were now down-
wards, showing that there was a relatively greater depression

492 COMPARATIVE ELECTRO-PHYSIOLOGY

of conductivity than of responsivity. In respect of conduc-
tivity and responsivity, therefore, the effects of these two
drugs, KI and Nal, are seen to be opposite.

In order to observe the effect of alcohol on nervous tissue,
by means of the conductivity balance, I first experimented
on the nerve of frog. A 5 per cent. solution was applied
at the responding point E. This is seen (fig. 301) to induce
a depression of responsivity.
A more dilute solution generally
induces a preliminary exaltation
followed by depression.

We said in the previous
chapter that when alcohol
vapour was passed into the
chamber of the vegetable nerve
the responses underwent a rapid
abolition. This result, however,

FIG. 300. RESPONSIVITY versus
CONDUCTIVITY under Nal

The formula in this case is E’ya1Cnar.
Photographic record shows an
effect opposite to that of KI as

Fic. 301. Effect of Alcohol on
the Responsivity of Frog’s

previously described, there being Nerve

now a relatively greater de- Upsetting of the balance in the
pression of conductivity than of downward direction shows
responsivity. depression.

was due to the joint action of the variations of receptivity,
conductivity, and responsivity, some of which may possibly
have been in the positive and others in the negative
direction. In order to determine the effect of each of these
we must, then, perform separate experiments. Such a deter-
mination I have made, using the method of the so-called
‘negative variation, in which the proximal galvanometric

THE CONDUCTIVITY BALANCE 493

contact was on an unkilled, and the distal on a killed
area. The first of these experiments was on variation of
receptivity. The thermal stimulator was provided with mica
shields, so that the receptive area was strictly circumscribed
at the centre of the thermal platinum loop. Normal responses
were first taken; the receptive area was next touched with
I per cent. solution of alcohol, and the modified responses
were recorded. The results are seen in fig. 302, which gives

Fic, 302, Photographic Record of Effect of Alcohol Vapour on
Receptivity

The three normal responses to the left are seen to be exalted after applica-
tion of ether onsthe receptive point.

a striking demonstration of the increased receptivity induced
by dilute alcohol.

The effect on conductivity, however, is in curious con-
trast to this, On applying I per cent. solution in the
conducting region between the stimulator and the proximal
contact, a very great diminution of the conducting power
is observed, as seen in fig. 303. It may be stated here
that a similar enhancement of receptive excitability, and
depression of conductivity, are found to be the result of the
action of alcohol in animal nerve also.. In the next ex-
periment, it is the variation of responsivity under the action
of dilute alcohol which is tested. After taking the normal

4904 COMPARATIVE ELECTRO-PHYSIOLOGY

a

responses as usual, a I per cent. solution of alcohol was
applied at the proximal contact. It will be seen from the
record in fig. 304 that the immediate effect was a depression

Fic. 303. Photographic Record of Effect of Alcohol on Conductivity

The three large responses to the left show the normal effect of transmitted
excitation. Responses almost abolished, as seen on the right, by
depression of conductivity.

of the amplitude of response. This subsequently becomes
converted into a diphasic response, consisting of a preliminary
positive followed by the normal negative; and finally the

Fic. 304. Photographic Record showing Effect of Alcohol on
Responsivity

a, normal responses, depressed, after application of alcohol, to d@; and
converted later to abnormal positive responses c.

response was totally reversed to positive, by the abolition of
the true excitatory effect.

It is thus seen that while dilute alcohol exalts the recep-
tive excitability, it induces a depression of both conductivity

THE CONDUCTIVITY BALANCE 495

and responsivity. I shall now describe further experiments
by which the. relative effects of alcohol are compared, as
between conductivity and receptivity, and as between recep-
tivity and responsivity. :

For the purposes of such a comparison, a new balancing
arrangement has to be employed (fig. 305). Here, two
electro-thermic stimulators
are in series, so that ex-
citations may be produced
at two different points
simultaneously. The gal-
vanometer contacts E’ and

Fic. 305. Diagrammatic Repre-
sentation of Experimental Ar-
rangement for Demonstration
of RECEPTIVITY versus CON- FIG. 306. RECEPTIVITY versus RESPON-
DUCTIVITY, or of RECEPTIVITY SIVITY under Alcohol
versus RESPONSIVITY

Alcohol was applied at the receptive point

s and s’ are exciting thermal loops to the left R’, and the responsive point
in series ; R and R’, the enclosed to the right E. The formula was
receptive points ; C and Cc’, con- R'aic.Eatc, The photographic record
ducting arms; E and E’, the shows the relative enhancement of
responsive points. receptivity.

E are made with two points intermediate between the stimu-
lators. The distance of one of the two stimulators is kept
constant, at, say, 2 cm. to the left of E’, while the other is
moved nearer to, or further from, E, until a balance is obtained.
A 1 per cent. solution of alcohol is then applied to the left
receptive point, R’, and the right conducting area, C, the
formula now being R’,.C,,... The fact that the receptive
excitability is heightened by this reagent, and conductivity
depressed, receives independent confirmation “from the upset
of the balance, giving rise to a downward response.

496 COMPARATIVE ELECTRO-PHYSIOLOGY

The next experiment consists of a comparison of the
simultaneous variations of receptivity and_ responsivity.
Alcohol is applied at R’ and E, the formula thus being
RlacEace .And we find here in confirmation. of our
previous results that, on account of the opposite effects of
this agent on the receptive and responsive excitabilities, the
resultant response is downwards (fig. 306), showing that the
receptivity has been relatively exalted. Thus the experi-
ments which I have here described show that the same agent
may have different effects on receptive and _ responsive
excitability, and thus accentuate the necessity of clearly
distinguishing between the two.

CHAPTER XXXIV

EFFECT OF TEMPERATURE AND AFTER-EFFECTS
OF STIMULUS ON CONDUCTIVITY

Effect of temperature in inducing variations of conductivity : (2) by Method of
Mechanical Response ; (4) by Method of Electric Balance—Effect of cold—
Effect of rising temperature—The Thermal Cell—After-effect of stimulation
on conductivity—The Avalanche Theory—Determination of the after-effect
of stimulus on conductivity by the Electrical Balance—After-effect of moder-
ate stimulation—After-effect of excessive stimulation.

IN studying the effect of temperature in inducing variations
of conductivity, we may use either of two different methods—
in the first place the method of mechanical, or in the second
that of electrical response. For the first of these it is neces-
sary to have what is generally known as a ‘sensitive’ plant,
the leaves or leaflets of which afford conspicuous motile
indications of the arrival of the excitatory wave from
a distance. In such a case the time-interval between the
application of stimulus and the response of a leaflet at a
known distance gives us a measure of the velocity of con-
duction ; and if we carry out successive experiments at
different temperatures we have a means of determining the
effect of temperature on conductivity. Employing this
method, I have elsewhere given a, determination of the
effect of temperature on the velocity of transmission in
Biophytum sensitivum. It was there shown that lower-
ing of temperature reduced the velocity of transmission
even to the extent of abolition, when the cooling was suf-
ficiently intense. With moderate cooling the velocity was
found to be decreased to about one-third. ‘The effect of
rise of temperature was, on the contrary, an increase of
KK

498 COMPARATIVE ELECTRO-PHYSIOLOGY

velocity. When it rose from 30° C. to 35° C., for example,
the velocity was doubled.

By employing the electrical method of response, however,
we are rendered independent of the use of sensitive plants,
and by means of the Conductivity Balance we are enabled to
demonstrate the slightest variation of conductivity, as between
the left arm of the balance, which is maintained at standard
temperature, and the right, which is subjected to the given |
change. ,

Thus in a definite experiment on a nerve of fern the
temperature of the room was 30°C. After first obtaining
the balanced record, the temperature of a portion of the
right arm of the balance was lowered. This one-sided
cooling was effected by supporting the right arm of the
nerve, through a certain length, in the concavity of a U-tube
through which cold water at 15° C. was passed. Stimuli
were now applied at intervals of one minute. Previously,
as will be understood, such stimuli, owing to balance, had
induced no resultant effect. But now, on account of the
depression of conductivity on the right side, brought about
by cooling, the balance was disturbed, and the resultant
down-response seen in fig. 307 shows the diminished con-
ductivity of the right arm. On the ‘gessation of the flow of
cold water the balance was gradually restored, in concomit-
ance with the return to the original temperature.

I next investigated the results of a rise of temperature, and
here I specially desired to observe the conductivity variations,
not at any one degree, but throughout a graduated and con+
tinuous rise. I was confronted at the outset of this investi-
gation by the difficulty arising from the fact that there was
no convenient and satisfactory means for the local variation
of the temperature of the nerve, in definite and known
degrees. In connection with this there was also the further
difficulty that a sudden variation of temperature will, in
itself, act as a stimulus. Hence, in studying the effects of
temperature per se, it is essential that there should be no
such sudden variation. These difficulties were overcome by

EFFECT OF TEMPERATURE ON CONDUCTIVITY 499

the employment of an electrical arrangement to bring about
the graduated and continuous rise of temperature.

A certain length of the vegetable nerve on the right arm
of the Conductivity Balance was thus raised continuously in
temperature, and its conductivity compared with that of the
left arm of the balance, the latter being maintained at the
temperature of the room, which happened at the time to be
33°C. The device by means of which this was accomplished

Fic, 307. Photographic Record showing Effect of Cooling on Con-
ductivity of Plant-nerve

Balance was obtained at starting, when temperature of both arms was
30° C. On cold being applied on right arm, the balance was dis-
turbed, showing diminished conductivity on that side. On restoration

of normal temperature, the balance is seen at the end of the record to
be again restored.

will be understood from fig. 308. A piece of cork has a
small chamber cut into it measuring I cm. each way. In
this is placed moist blotting-paper, which keeps it damp, and
across it passes a. length of 1 cm. of the right arm of the
vegetable nerve in the Conductivity Balance. This cork-
chamber has inlet and outlet tubes ¢ and #.. The first of
these contains a spiral, H, of platinum, which can be heated
to a suitable degree by means of an electrical current, the

KK 2

500 COMPARATIVE ELECTRO-PHYSIOLOGY

intensity of which is capable of careful adjustment. The
cork chamber is closed with a cover, through which passes
a thermometer, T, for the indication of the temperature
within, The tube Z’ is connected with an aspirator, and air
is thus sucked in by 4, and, passing through the platinum
spiral, is warmed, and raises the temperature of the nerve in
the chamber. This rise of tem-
perature is adjusted (1) by regu-
+ lating the electrical current which |
heats the spiral, and (2) by con-
trolling the inflow of air... As
regards the first of these two
processes, the electrical heating-
circuit has a carbon rheostat
interposed, by which the rate of
rise of temperature may be
regulated. The movement of the
current of air, on the other hand,
is controlled by adjusting the
stopcock of the aspirator. By the
joint manipulation of both these
the rate of rise of temperature
t inside the chamber may be made
perfectly uniform, and in my
yoga ee Rouing ate experiments this rate was approxi-
Temperature of one Armof mately 1° C. per minute.
ene As already said, I selected a
A and B, the two halves of the - ,
chamber ; T, thermometer ; piece of vegetable nerve and took
at ia cap aerate a balanced record. After this the
heating. temperature of the thermal cell
on the right-hand side was raised
continuously, the response-record being taken at each degree
of the rise, till a temperature of 50° C. had beenat tained.
From the record given in fig. 309 it will be seen that the
conductivity was always greater at temperatures up to 47° C.
than it was on the left-hand side, which was all the time
maintained at the constant temperature of 33°C. At 48°C,

EFFECT OF TEMPERATURE ON CONDUCTIVITY 501

however, the reversal of response showed that the conduc-
tivity was now being depressed. And at still higher tem-
peratures it was found to undergo a very great depression,
as is seen by the abrupt downward movement of the curve.
It is thus seen that, by means of the Method of Balance, this
very difficult problem of the variation of conductivity under
variation of temperature is made capable of exact study.

I shall next describe the results of an investigation into
the after-effects of stimulus on conductivity and excitability,

Fic. 309. Photographic Record Showing Effect of Rising Péapelatons
on Conductivity

Balance obtained at starting at 33° C. Successive responses recorded at
each degree C. of rise of temperature. Record shows increasing
conductivity up to 472 C. A depression of conductivity is seen by
reversal of curve to set in at 48° C., and this becomes extremely pro-
nounced at 50° €.

a subject of much difficulty and of considerable theoretical
importance. It has been found in Animal Physiology
that the sciatic nerve of a frog, for instance, is not equally
excitable throughout its length. When such a nerve, with
its attached terminal muscle, is cut off from the spinal cord, it
is seen to be more excitable the further from the muscle is
the point on the nerve that is subjected to stimulation.
From this fact that excitation increased with the distance of
the point excited from the motor organ, Pfliiger was led to

502 COMPARATIVE ELECTRO-PHYSIOLOGY

the ‘ Avalanche Theory,’ namely, that during the passage of
excitation down the nerve it. actually gathers strength. But it
is clear that this cannot be true, since we have seen that, other
things being equal, excitation is always greater the nearer the
point of stimulation to the responding region, and on this fact
have depended all those experiments already described, which
involved a delicate balance of equal excitations. It follows
that the observed enhancement of excitability of a point on the
nerve which is distal from the muscle, and in the neighbour-
hood of a section, must be ascribed to some other cause. In
reference to this Heidenhain, indeed, explained the greater
excitability of higher tracts of divided nerve by the proximity
of the artificial section. For the lower end of the nerve at
once exhibits the same marked activity as the upper end if
a section be made lower down. Excitability is, in fact,
raised near the section, wherever the section may be. The
distance travelled by the excitation could not, therefore, be
the determining factor in the magnitude of effect. For so far
from increasing it, this, as a matter of fact, causes diminution.
It is to be remembered that though the excitability is
increased near the point of section, yet at the section itself
it is almost abolished, otherwise there could not have been
any response by'so-called negative variation. The question
now arises, Why should the excitability be raised near: the
point of section ?

It has been supposed that this was due to certain electri-
cal changes induced by section, which in turn gave rise to
electro-tonic variations of excitability. We shall see, in
Chapter XL, that the passage of an electrical current through
a living tissue induces changes of excitability. And this
phenomenon is known as the electro-tonic effect.. Now any
‘injury, such as a mechanical or thermal section, is known
to induce galvanometric negativity, or anodic change, at or
near the point of section. But it is the kathode-effect which
is excitatory. And the observed greater excitability of the
nerve near a point of section is supposed to be due to kat-
electrotonus, produced within a certain tract from the cross-

OE i at ty ok de ie

AFTER-EFFECT OF STIMULUS ON CONDUCTIVITY 503

section by internal short-circuiting of the nerve-current.
That this explanation, however, does not meet all the
requirements of the case will appear from certain experi-
ments which I shall describe, where, under exactly similar
electrotonic changes due to section, a result directly the
opposite of this, that is to say, of depression, is seen to be
induced. .

All these various facts will be found fully reconcilable,
however, on the basis of a proposition which I shall establish,
namely that zz a nerve, moderate stimulation enhances ex-
citability and conductivity, while excessive stimulation has the
opposite effect of bringing about the depression of both. It is
indeed natural to expect that while moderate stimulation, by
increasing molecular mobility, would bring about one effect,
excessive stimulus, by inducing overstrain, would result in
exactly the opposite. Before proceeding to give an experi-
mental demonstration of this hypothesis, we shall first
consider the explanation which it affords of the peculiar
excitatory changes observed in the case of cross-sectioned
nerve. In the first place we know that a cut acts as a
stimulus. And since we found that the effect of stimulus
decreases with the distance from the point of stimulation, it
would appear that at the section itself the stimulation would
be excessive ; moderately strong at a certain distance from
it; and practically negligible when very far away. In
complete accordance with this is the resulting increase of
excitability which has been observed near the point of
section, while at the point itself the nerve is relatively
inexcitable.

The fact that stimulation, when not excessive, increases
the conductivity and excitability, we found illustrated in the
staircase increase of electrical response, and in the enhance-
ment of amplitude after tetanisation, in vegetable and animal
nerves (figs. 275 and 286). The same fact will be demonstrated
later by means of the mechanical response of nerve. I shall
now describe certain experiments which demonstrate it once
more in a new and interesting manner. 2

504 COMPARATIVE ELECTRO-PHYSIOLOGY

A vegetable nerve was adjusted for balance, with the
ends projecting some distance beyond the electrodes. In
order to show that the effect of injury is due to stimulus as
such, and not to any particular form of it, I now made a
thermal instead of mechanical section, by applying salt
solution heated to about 60° C. in the region A, at a distance
of I cm. to the right of E (fig. 310). The effect of this
stimulation was to induce a moderate excitation of the right |
arm of the balance, relatively to the left. If this moderate
stimulation were to induce
any increase of excitability
and conductivity, that fact
would be demonstrated by

Fic. 311. Photographic Record
Showing Effect of Moderate
Stimulation in Enhancing
Conductivity and Excita-

Fic. 310. Experimental Arrange-
ment for Studying After-effect of
Stimulus on Conductivity and

Excitability

The stimulator adjusted to obtain
balance between Eandk’. Stimulus
of moderate or strong intensity is
applied to a point on the right of E.
Upsetting of the balance in an
_upward direction shows an en-
hancement, and in a downward
direction, depression, of con-
ductivity and excitability.

bility

otted line at beginning shows
the resting-current, as a per-
sistent effect of stimulation.
The upsetting of the balance
upwards constitutes a positive
variation of the resting-
current, and indicates en-
hanced conductivity and
excitability.

the upsetting of the balance, the resultant response being
upwards. That this is what actually occurs will be seen
from the records in fig. 311. It will be noticed that in
consequence of stimulation to the right of E, that point
became, more or less permanently, galvanometrically negative.
This is represented by the dotted line upwards at the
beginning of the record. It must be remembered that before
the application of the thermal section, the right and left hand
excitations, proceeding from the electro-thermically stimu-

AFTER-EFFECT OF STIMULUS ON CONDUCTIVITY 505 —

lated point in the middle, were exactly equal and balanced.
The fact that after this application, however, there are
resultant responses which are upwards, shows, as already
said, that by the moderate stimulation of the right-hand
side, both excitability and conductivity have been increased.
The resultant upward response here is, then, in the same direc-
tion as the so-called ‘ current of injury, and forms, as it were,
a positive variation of it.

In another experiment, in which I wished to try the
effect of excessive stimulation, instead of applying a hot
solution at 60° C., I produced
greater injury and consequent
excessive stimulation, by scorch-
ing the nerve at the same point
as before, witha red-hot platinum
wire. In this case resultant
response was downwards, show-
ing that the excitability and
conductivity of the right-hand

Fic. 312. Photographic Record

side of the balance had been showing Effect of Excessive
; P Stimulation in Depressing Ex-
depressed by over-stimulation. citability and Conductivity

I was next desirous: of Up-line at starting shows the rest-

: . ing-current due to after-effect of
demonstrating that the excita- stimulation. The upsetting of

bility of the over-stimulated or balance in a downward direction

: ‘ constitutes a negative variation

excited point undergoes depres- of the resting-current, and shows

sion. For this purpose I took depression of conductivity and
excitability.

a fresh specimen and first ob-
tained a state of balance. Similar excitation of E’ and E
produced a balanced or null effect. The point E was then
injured by touching it with a hot platinum wire. On now
proceeding to take records, it is seen that the responses
were downwards, showing the depression of excitability at
the injured E (fig. 312).

The fact that galvanometric negativity had been induced
at E, by reason of injury, is demonstrated at the beginning
of the record as an up-line. The subsequent resultant
responses due to simultaneous excitation of E and E’ are

506 ~~. COMPARATIVE ELECTRO-PHYSIOLOGY

-seen to be a negative variation of the resting-current due
to injury. It is thus seen that while simultaneous-excita-
tions of two normally excitable points E and E’ are prevented
by balance from giving rise to any response, the excitatory
response becomes manifest when the balance is disturbed
by the injury of either point of galvanometric contact ; and
that, under these circumstances, the response is a negative
variation of the current of injury. This experiment is |
important as giving a theoretical insight into the so-called
response by negative variation. It also shows how limited
is the applicability of the assumption that response is always
by negative variation. For, in the similar experiment,
previously described, under moderate injury, the response was
by positive variation of the resting-current.

It is further seen from these experiments that the
enhancement of excitability, under the stimulation due to
moderate injury, could not be caused by the suggested
electrotonic effect. For the same anodic change induced
by injury at E causes, in the case of moderate injury, an
enhancement, and under greater injury a depression, of
excitability. It is thus clear that the modifying influence
is the effective intensity of stimulation. This fact, that
moderate stimulation enhances, and excessive stimulation
depresses excitability, will be further demonstrated ina future
chapter, by the independent method in which the effects of
electrotonus are completely eliminated. )

CHAPTER XXXV
MECHANICAL RESPONSE OF NERVE

Current assumption of non-motility of nerve—Shortcomings of galvanometric
modes of detecting excitation—Mechanical response to continuous electric
shocks—Optical Kunchangraph—Effect of ammonia on the mechanical
response of nerve—Effect of morphia—Action of alcohol—Of chloroform—
Abnormal positive or expansive response converted into normal contractile
through diphasic, after tetanisation—Similar effects in mechanical response
of vegetable nerve—Mechanical response due to transmitted effects of
stimulation—Determination of velocity of transmission—Indeterminateness
of velocity in isolated nerve—Kunchangraphic records on smoked glass—
Oscillating recorder—Mechanical response of afferent nerve—Record of
mechanical response of nerve due to transmitted stimulation, in gecko—
Fatigue of conductivity—Conversion of normal contractile response into
abnormal expansive, through diphasic, due to fatigue.

I HAVE already referred to the distinctions which are com-
monly insisted on, as between the reactions of different
animal tissues. Certain of these are regarded as motile
and others as. non-motile. From an evolutionary point of
view, however, it is difficult to conceive of such a hard-and-
fast distinction. It would be easier, believing -in continuity,
to suppose that a certain responsive reaction, characteristic
of the simplest living substance, had become accentuated
in some tissues, and not so accentuated in others, according
to their different functional requirements. Thus the belief
held so implicitly by physiologists that nerves exhibit no
motile response whatsoever’ becomes questionable, and is
seen to require investigation. After submitting it to this,
moreover, one finds it difficult to understand how such an

‘ ‘Nerves are irritable; when they are stimulated, a change is produced in
them ; this change is propagated along the nerve, and is called a nervous impulse ;

there is no change of form in the nerve visible to the highest powers of the-
microscope.’ (Kirke’s Handbook of Physiology, 15th edition, p. 105.).

508 COMPARATIVE ELECTRO-PHYSIOLOGY

idea ever gained currency, unless, indeed, it was due to the
tyranny imposed on our thought by these arbitrary classifi-
cations themselves.

Before entering, however, on the question whether the
excitatory reaction in nerve finds motile expression or not,
we shall first examine the only method at present available
for the detection of the condition of excitation. Since ex-

cited nerve has hitherto been supposed to exhibit no visible

change, it followed that the only method possible for the
detection of the excitatory change was the electrical. In-
vestigations on nerve, therefore, had perforce to be carried
out by this means, through the medium either of the capillary
electrometer or of the sensitive galvanometer. But the elec-
trical method labours under certain inherent disadvantages,
and first of these is the objection which it raises to the free
employment of the most convenient form of stimulus, that,
- namely, by induction shocks. For we have seen that unless
extraordinary precautions are taken, we have here, owing to
the possible escape of current, an element of error and un-
certainty in the results. If, on the other hand, it should
become possible to obtain mechanical response from the
_ nerve, this particular form of stimulation might be employed
without misgiving. |

The second limitation which the electrical mode of
detection imposes upon us is that arising from the differ-
ential character of the response which it indicates. For
stimulus induces electrical changes at both the contacts—
proximal and distal-—the record made being finally due to
the algebraical summation of the two. It is true that the
excitability of one contact is artificially depressed by injury.
But it is often difficult to say how far this injury has been
effective in completely abolishing the excitability of this
point. The depression of excitability, due to partial injury,
will sometimes disappear to a certain extent, with lapse of
time, and much uncertainty sometimes occurs as to whether
a certain curious variation in the response of the nerve—
negative followed by positive—is due to this or some other

edd A St at a

MECHANICAL RESPONSE OF NERVE 509

cause. With mechanical response, however, provided this
could be rendered practicable, no such difficulty need arise.
For in that case it would be the direct effect of the exci-
tatory change, uncomplicated by any other disturbance,
which would be recorded.

Finally, as regards the detection of the excitatory change
itself, the galvanometer is unable to indicate any change
below a certain high intensity of excitation. Thus it gives
no indication when excitation is due to one or to a few
shocks: it can only detect an excitatory effect which is much
stronger than this, having been brought about by the super-
posed effects of tetanic shocks of a certain duration. In
order to obtain even such effects, a galvanometer of very
high’ sensitiveness is necessary. That of a fairly delicate
instrument, detecting a current of about ‘ooI ampere, will
have to be exalted some ten millions of times before it can
give efficient indications of excitatory effects in nerves ; and
in such a degree of galvanometric sensitiveness we approach
a limit which cannot be very much exceeded.

Returning now to our original question, we have first to
determine whether excitation causes any motile effect in
nerve. Under observation, it is easily seen that when the
nerve is excited by tetanic electrical shocks it increases in
thickness and at the same time shortens in length. We
have here a phenomenon in every way analogous to the
thickening and shortening of muscle under excitation. The
contraction which occurs in nerve, moreover, is of an order
by no means microscopic. I give here a record (fig. 313)
of the contractile response of nerve under continuous
stimulation by fairly strong tetanising electric shocks. This
record was obtained by means of the ordinary lever-recor@er,
the magnification employed being only three times. The
induced contraction in this particular case was about 14 per
cent. It will also be seen that this contraction reached a limit,
at which state of maximum contraction the nerve remained
for a considerable time. After this we observe a tendency

5 £0 COMPARATIVE ELECTRO-PHYSIOLOGY

to decline, owing to fatigue. In some other cases, moreover,
I have obtained a contraction of as much as 20 per cent.

If we wish to obtain a series of successive responses,
however, it is desirable to avoid over-stimulation of the
tissue. In order, then, to obtain a response-record under
moderate stimulation, we have to employ a higher magni-
fication.. This magnification, if made about 200 times, is
more than sufficient for all practical purposes, and the photo-
graphic records given in the course of the present chapter
are of this order. With long ‘specimens of nerve, however,
a magnification of fifty times would be enough, and in the

Fic. 313. Record of Contractile Response in Frog’s Nerve under
Continuous Electric Tetanisation.

Magnification, three times.

course of the next chapters, I shall give certain records on this
scale, obtained directly on a smoked glass surface. The
apparatus used for the purpose was the Kunchangraph
(Sanskrit, Aunchan, contraction), which I had already devised
afd employed in recording the contractile responses of plant-
tissues. This apparatus, as adapted for the purpose of
recording mechanical response in nerves, consists of, first,
a nerve-chamber, N; secondly, a modified Optical Lever, 0 ;
and thirdly, a photographic recorder, D (fig. 314).

_ Of these, the nerve-chamber consists of a small rectangular
ebonite box, the front of which is closed by a semi-cylindrical

N, nerve chamber containing nerve with electrical connections, E E’,

MECHANICAL RESPONSE OF NERVE Sil

FIG, 314. Optical Kunchangraph for Record of Mechanical
Response of Nerve

Thread tied to lower end of nerve, and attached to short arm of optic
lever, O. Beam of light from L reflected from mirror of optical lever,
oO, falls on recording-drum, D. Adjustment of reflected spot of
light made by micrometer screw, Ss. Periodic electric stimulation at
intervals of one minute is automatically made by means of key regulated
by clock-work. Air bubbles through water at w, and is led on by
india-rubber tubing, T, to nerve-chamber, thus kept humid. By
proper manipulation of stop-cock any vapour—as chl oroform—con-
tained in vessel V, may be passed through nerve-chamb er, subsequent
responses showing effect.

S12 COMPARATIVE ELECTRO-PHYSIOLOGY

glass cover. The nerve is placed vertically within this, and
held, at its upper end, by a clamp. The lower end of the
nerve is connected with the short arm of the Optical Lever
by means of a thread, which passes through a hole in the
floor of the chamber. A second thread of cotton moistened
with saline solution hangs loosely from the end of the nerve,
and is connected with the electrode E’.. When the electrodes
E and E’ are put in connection with the secondary of an
induction coil R, the entire length of the nerve is subjected to.
direct excitation. When, on the other hand, we wish to study
the effect of transmitted excitation,
the nerve is lightly clamped at B
(fig. 315). Excitation is then induced
in the portion of the nerve A a, and
after transmission through the inter-
vening tract, causes the motile effect
in the responding portion of the
nerve B C, :

One precaution which I find to be
very necessary is the maintenance of
the properly humid condition in the
i ._,_nerve-chamber. This is_ specially

IG. 315. Diagrammatic , . ;

Representation of Ar- important in the warm weather which

rangonen irae characterises the greater part of the

Stimulus, 1, indicating year in India. The usual means of

Sai keeping the chamber moist, by a large
quantity of blotting-paper soaked in water, is not sufficient
to bring about the maintenance of the normal excitability of
the nerve for any length of time. This need was met by
keeping moist vapour in uniform circulation through the
nerve-chamber. An air-bag is kept under suitable pressure,
and the air, bubbling through water in the vessel W, is made
to enter the nerve-chamber through an entrance-pipe, and
to escape by an exit-pipe. In warm weather it is well to
keep fragments of ice in the water-vessel. By proper mani-
pulation of the stop-cock of the air-bag, a gentle stream of
cooled and humid air is kept in constant circulation through

MECHANICAL RESPONSE OF NERVE 513

the chamber. Observing these precautions, I have been
able to obtain responses from a given nerve for as much as
three hours continuously, whereas, without this care, they
would have come to a stop in a very short time. By a
modification of this arrangement, we are also enabled to
study the effect on the excitability of the nerve of various
gases and vapours contained in a second vessel, v. A series
of responses is first taken, under normal conditions—that
is to say, when the nerve is surrounded simply by a moist
atmosphere. On now turning a three-way tap in a given
direction, the water-vapour can be made to: pass through the
vessel V, filled with the given gas or vapour, before reaching
the nerve-chamber. The series of responses then obtained
will show either the immediate or the after-effect of the
reagent at will. For it is easy, by means of the three-way
cock, to shut off the gas and re-establish the first or normal
condition, after which the responses will afford an indication
of the nature of the after-effect.

_ The lower end of the nerve, as has been said, is attached
to the arm of the lever which passes through the fulcrum-rod.
A light .mirror is fixed on the fulcrum-rod, its face being
downwards. The pull caused by the excitatory contraction of
the nerve causes rotation of the fulcrum-rod, and this in turn
gives rise to a deflection of the spot of light reflected from
the mirror. A responsive relaxation of the nerve would
give rise, on the other hand, to a deflection of the spot of
light in the opposite direction. The long arm of the lever,
it will be noticed, is here the ray of light. The responsive
movement of the spot of light is recorded on a moving
photographic plate vertically below the mirror, and whose
movement, regulated by clockwork, is in a direction at right
angles to that of the spot of light. The photographic plate,
or the film wrapped round the drum, moves under a fixed
wooden cover, not shown in the figure, which is provided with
a narrow incised slit. The length of this is parallel to the
direction of the movement of light, and at right angles to that
of the plate or film. The advantage of having the plate

LL

514 COMPARATIVE ELECTRO-PHYSIOLOGY

vertically below the mirror lies in the fact that a lighted
candle may be placed in the dark room without spoiling
the record by diffuse illumination. The only way in which
such diffuse light could now find access to the plate would
be by reflection from the ceiling. But if the ceiling of the
experimental room is blackened, or a black cover placed over
the nerve-chamber at a certain height, even this possibility is
eliminated. The advantage which the observer enjoys, when,
instead of groping in semi-darkness, he can work in a fairly
well-lighted room is obvious. By making the arm of the
lever to which the nerve is attached sufficiently short, and by
placing the recording plate sufficiently far away, a wide
range of magnification, from several hundreds to several
thousands, may be obtained. It may sometimes be desirable
to subject the nerve to a certain amount of tension, and
this is secured by placing a small weight on the arm of
the lever. With high magnification, due adjustment, which
is very troublesome, lies in bringing the spot of light con-
veniently over the recording plate. This difficulty is obviated,
however, by means of a fine micrometer screw S which moves
the whole nerve-chamber up or down, in relation ‘to the
Optical Lever. The adjustment of this screw in a right-
handed manner then moves the spot of light in one direction,
say to the left, while its left-handed rotation moves it to the
right. This movement can be made very fine, and the spot
adjusted to any part of the photographic field.

It remains to deal with the possible disturbances inci-
dental to the high magnification employed. Apprehension,
in this matter, is often more fanciful than real. Disturbances
might no doubt occur, however, when proper conditions are
not secured for the experiment. If the nerve-chamber, for
example, be supported on a different stand from that of the
Optical Lever, then the slightest tremor of the common
pedestal would result in relative movements of the two
supports, causing constant disturbance of the spot of light.
Under these conditions, heavy stone pedestals, erected on
steady foundations, afford no security against the ground-

MECHANICAL RESPONSE OF NERVE 515

vibrations of a busy city. But when both the nerve-
chamber and the Optical Lever are fixed to the same
supporting-rod, relative movements, due to external disturb-
ance, are practically eliminated. This common supporting-
rod may be screwed securely to a wall. With these precautions,
I have been able to take records, without the least dis-
turbance from the adjacent electric tram line. Asa matter of
fact, when the magnification required is only of a few hundred
times, nothing but gross carelessness could allow any source
of disturbance to remain. It is only when the magnification
has to be pushed to the order of a hundred thousand that
unusual care is necessary to avoid errors of disturbance.
One precaution which should, however, be taken, is that
arising from disturbance of the mirror by convection
currents of air. The remedy for this is obvious, namely;
a suitable glass cover.

This is the order of magnification which is necessary for
the recording of response under a degree of stimulation
- usual in making observations of excitatory electrical variation
with a very sensitive galvanometer. But while the sensitive-
ness of the galvanometric method of detecting response is
here nearing its limit, that of the mechanical method is in its
first stage only, and how greatly the sensitiveness of the
latter may be exalted when required will be shown in the
next chapter.

I shall: ‘flow “explain how easy it is to study the aiisin:
logical variations induced in the animal nerve under various
agencies by means of the mechanical response. The following
experiments were performed on specimens of the sciatic
nerve of frog. A well-known reagent for abolition of ex-
citability of the nerve is ammonia. Its effect on mechanical
response is seen in fig. 316. In all the following experiments,
the stimulus applied was by fairly strong tetanising electrical
shocks, which were usually of two seconds’ duration. Two
series of records were taken, successive responses being
recorded at intervals of one minute, before and after the

application of the chemical reagent. In fig. 316, the normal
L L 2

516 COMPARATIVE ELECTRO-PHYSIOLOGY

responses seen in the first series are found to be abolished
when the nerve has been subjected to strong vapour of
ammonia for some time. It should be mentioned here that
this abolition takes place under the action of a strong dose.
When highly diluted with air, the vapour ey cause a
temporary exaltation.

In the next figure (fig. 317) is shown the effect of szorphia.
After the application of this solution for a certain length of
time, the response is seen to
‘be abolished. The strength
of application which brings
about this abolition I find to
vary according to the condi-

Fic. 316. Photographic Record
of Effect of Ammonia. on
Mechanical Response of Frog’s

Nerve FiG.. “317: Photographic
First series of responses are nor- Record showing Abolition
mal. Second series show effect of Mechanical Response
of ammonia in practical aboli- of Frog’s Nerve by Action
tion of response. of Solution of Morphia

tion of the nerve. Another agent by which the mechanical
response of the nerve is found to be abolished is aconite.
And it is of special interest to note that I have often found
this to act as an antidote, for the revival of response
previously almost completely abolished by morphia. ‘The
condition of the nerve here also appears to be a determining
factor in the mutually antidotal action of these two poisons.
A strong application of alcohol after long-continued action

MECHANICAL RESPONSE OF NERVE 517

abolishes the response of nerve. But its preliminary effect
is often one of exaltation, as seen in fig. 318.

I shall next describe the effect of chloroform, which dis-
plays many interesting features. We have seen that when a
tissue is excited by impinging stimulus, two opposite effects
are induced : one of these is the increase of energy, by the
absorption of stimulus, and the other is the expenditure
of energy by excitatory response. The former, as we have
seen, finds expression in galvanometric
positivity and expansion. The latter,
on the other hand, is exhibited: as
galvanometric negativity and contrac-
tion. In the record of excitatory
response, the former of these elements
is generally masked by the predominant
negative or contractile effect. We have
also seen that this hidden positive may
be unmasked. in either of two: ways:
first, by retarding the expression of one
effect in relation to the other ; or, second,
by abolishing the excitatory negative
altogether. In the first of these cases,
the negative response is converted into
diphasic, say positive followed by Fic. 318. Photographic

: Record showing Pre-
negative. In the latter, the response limitiary Bimaltation it
becomes positive, by the suppression Mechanical Response

: . of Frog’s Nerve after
of the negative. An example of this Application of Alcohol
unmasking of the positive element, by
suppression of the negative, we have already seen to occur
under the action of chloroform (cf. fig. 49). This demon-
stration was made on a vegetable tissue, the test employed
being electrical.

The experiment which I am now about to describe is
interesting from the fact that effects parallel to those there seen
in a vegetable tissue are in it shown to occur also in the highly
specialised animal nerve. The unmasked ‘electro-positive
effect, moreover, is here seen to correspond with an expansive

518 COMPARATIVE ELECTRO-PHYSIOLOGY

response of the tissue. A record of the various phases in
the effect of chloroform on the mechanical response of nerve
is found in fig. 319. It will be seen here that the first effect
of chloroform was to cause a great enhancement of ex-
citability, which in this case lasted for about a quarter of an
hour. I have given only two responses of this series. After
this, the responses began to decline, and another very

Fic. 319. Photographic Record showing Effect of Chloroform on
Mechanical Response of Frog’s Nerve

First pair of responses, normal; second pair, preliminary exaltation on
application of chloroform; last series exhibit subsequent effect of
chloroform in unmasking the positive component as diphasic response.
Expansion is here followed by contraction. Note regular waning of
both components with growing aneesthetisation.

interesting reaction made its appearance. The impinging
stimulus had hitherto induced only an immediate contractile
response. But by the action of the chloroform the excitatory
effect was delayed, and the positive, or mechanically ex-
pansive response was unmasked in the form of a preliminary
downward twitch. Response was now, therefore, diphasic—
positive followed by negative. Immediately on the applica-

MECHANICAL RESPONSE OF NERVE 519

tion of stimulus, as may be seen from the record, there is a
sudden expansive movement downwards, followed by an
equally rapid reversed movement of contraction upwards,
and this followed again by a slow recovery. Each of the
successive stimuli evokes the same diphasic responsive
sequence. It must be noted that the downward twitches are
the preliminary, and not the after-affect. It is also interesting
to note, as the tissue approaches death, under the continued
action of chloroform, how regularly in both negative and
positive directions the responses decrease in amplitude.

We shall next undertake an independent investigation
into the causes which bring about the three types of response
—abnormal positive, diphasic, and normal negative—known
to be exhibited in the electrical response of the animal, and
already demonstrated as occurring also in that of the vege-
tal nerve. While discussing these three types of electrical
response and their variations in Chapter XXXI. it was
stated that the differences of effect involved were due to
changes in conductivity and excitability, brought. about by
varying tonic conditions. It was also explained, in the same
place, that the continued isolation of so highly excitable a
tissue as nerve, from its accustomed supply of energy, would
be sufficient of itself to depress its tonic condition below
par, with concomitant depression of its conductivity and
excitability. The result of this depression of excitability
will be to render inefficient a stimulus which was formerly
efficient, to evoke the true excitatory reaction of galvano-
metric negativity. The absorbed stimulus will now induce
only a responsive positivity. The depression of conductivity
also would cause the transmission: of the hydro-positive,
instead of the excitatory negative, wave. Owing, then, to the
joint action of these two factors, stimulus induces a positive
response—the so-called ‘abnormal ’—at a distant responding
point, when the tonic condition of the tissue has become
depressed. Absorption of stimulus, however, by supplying
the requisite energy, raises the tonic condition, with con-
sequent restoration of conductivity and excitability. As

520 COMPARATIVE ELECTRO-PHYSIOLOGY

a result of this, the abnormal positive will pass into normal
negative response, through an intermediate diphasic, after
the impact of a series of stimuli, or after tetanisation. The
enhancement of conductivity and excitability thus conferred
on the tissue by the absorbed stimulus will now act by
still further tetanisation, to bring about the enhance-
ment of the normal negative response. Starting thus,
with the most depressed condition of the tissue, and sub-.
jecting it to continuous action of stimulus, we obtain four
typical stages : (1) the abnormal, passing after short tetanisa-
tion into (2) the diphasic ; this in its turn giving place to
(3) the normal negative alone ; which finally becomes (4) the
enhanced negative. |

In studying electrical response, both of animal and vege-
tal nerves, under appropriate experimental conditions, we
have already seen various examples of these different types
of response and their transformations. But under such modes
of experiment as have been described, the effects were, as
already stated, due to joint changes in excitability and con-
ductivity. I shall now, however, describe a still simpler
experimental arrangement, in which the stimulus is applied
directly on the tissue, and the responsive variations are,
therefore, due to variations in the excitability alone. These
changes, moreover, will be recorded by means of their direct
mechanical expression, namely, contraction, or its opposite
expansion.

With regard to abnormal response, I have already stated
that this is brought about, not by ‘staleness,’ or the moribund
condition, with its concomitant chemical changes, but by
the run-down of the energy of the tissue in isolation. On
investigating this subject, by means of mechanical response,
with its superior sensitiveness, this conclusion finds inde-
pendent support of the strongest character. On taking
even the freshest specimen, I generally find that its
responses at first are the abnormal positive. These gradually
pass into moderate negative through diphasic. This is due
to the raising of the tonic condition by the absorption of

MECHANICAL RESPONSE OF NERVE 521

the stimulus, and after a series of stimulations, the isolated
tissue, which was originally depressed, has its tonic condition
so much heightened, that the responses are enhanced to an
unprecedented magnitude. A specimen, in fact, which was
at first almost irresponsive, may generally be brought to
any state of exalted excitability desired, with concomitant
increase in amplitude of response, by merely subjecting it for
a certain length of time to the action of impinging stimulus.

Fic. 320. Photographic Record showing Abnormal Positive converted
into Negative Response after Tetanisation

First series, abnormal positive ; second series, persistence of this positive
after very brief tetanisation ; third series, conversion to negative, after
a tetanisation of longer duration.

I shall now describe in detail some of the principal
experiments, Selecting a specimen of frog’s nerve, I took
a series of responses to electrical shocks, of three seconds’
duration, at intervals, in each case, of one minute. The
testing stimulus was kept always the same throughout the
experiment, except for certain intervening periods of tetani-
sation. The variations seen in the responses thus give
a visual demonstration of the variations in excitability.
The record of these is given in fig. 320. The responses in

522 COMPARATIVE ELECTRO-PHYSIOLOGY

the first series are by the abnormal positive variation; that is
to say, by expansion. The tissue here being sub-tonic, the
impinging stimulus could not induce the true excitatory effect.
The tissue. was now subjected to short-lived tetanisation.
But the absorbed stimulus was not yet sufficient to induce
the normal responsiveness. The next series of. records,

= therefore, still exhibited the
abnormal positive response.
Tetanic shocks of longer
duration were next applied.
This gave rise to a short-
lived positive twitch down-
wards, succeeded by large
contractile response upwards,
After the cessation of the
second tetanisation, the
absorbed energy is seen to
have brought the tissue to
a condition of more or less
normal responsiveness. This
is seen in the third series,
where the first responses are
diphasic, but the positive
component (the downward
twitch) becomes perceptibly

Fic. 321. Photographic Records show- smaller and the negative

ing Gradual Disappearance of Positive larger, in each of the succeed-
Element in Diphasic Mechanical . Tt. wheal
Responses of Frog’s Nerve and INS responses. shou

Plant-nerve also be noticed that che

Note also the staircase increase. recovery from positive ts much
quicker than trom negative response. This fact is important,
in connection with certain psycho-physiological phenomena
to be described in a later chapter.

The effect of successive stimuli, in enhancing normal
response, when the nerve is not yet in maximum. tonic
condition is illustrated in a still more striking manner in the
record given in fig. 321, obtained with a different specimen

MECHANICAL RESPONSE OF NERVE 523

of frog’s nerve. In this, also, the first series of responses
was purely positive. But the record shown here begins at
the point where, in consequence of previous tetanisation,
response has become diphasic. Here it will be noticed that
the true excitatory effect of contraction is undergoing a con-
tinuous increase, while the abnormal positive is decreasing.
The excitatory response, indeed, becomes so great as to be
incapable of record within the plate. _

I have already shown how similar in every respec
are the responsive characteristics of the vegetal nerve to
those of the animal. This fact finds an interesting illus-
tration in the various phases of its mechanical response.
That is to say, plant nerve in a sub-tonic condition gives
positive, passing into diphasic and normal negative response,
under tetanisation. On arriving at this second stage of
diphasic response, successive responses undergo enhance-
ment in a manner precisely the same as holds good in the
corresponding cases with frog’s nerve. This is sufficiently
illustrated in the two records given side by side in
fig. 321, the first of which, as already said, is of frog’s nerve,
and the second, of nerve of fern. We see here again, as
already in numerous cases before, how the responsive pecu-
liarities and their modifications in the one are in every
respect paralleled by those of the other. The only differ-—
ence between them lies in the degree of their excitability,
that is to say, two stimuli of equal intensity will in general
induce a more intense excitatory effect in the nerve of frog
than in that of fern; or in order to obtain from both an
equal intensity of response, we must, in the case of fern,
employ. a stronger stimulus. We have seen that in con-
sequence of the absorption of stimulus, not only does the
abnormal positive phase disappear, giving place to the
normal negative, but the subsequent negative responses
themselves also show an enhancement in a staircase manner.
I give here (fig. 322) another record showing the mechanical
response of frog’s nerve to undergo this staircase enhance-
ment. From this effect then it is easy to understand that an

524 COMPARATIVE ELECTRO-PHYSIOLOGY

intervening period of tetanisation will markedly enhance the
negative response.

We have now seen that, by the direct mode of investiga-
tion afforded in mechanical response, we are able to trace
out the causes which determine the three types of response
found in nerves. It has been shown that all ‘these are
brought about by the varying tonic condition of the tissue.
From this it is easy to understand that the three types of |
electromotive responses in nerve are also due to the same
cause. In the experimental method
there employed, the variations of con-
ductivity appropriate to the tonic
condition are superposed on parallel
modifications of the excitability. Thus
not only is the responsive change of
a sub-tonic responding point positive,
but the effect which is transmitted to it
through sub-tonic conducting tissues is
also positive; after tetanisation, how-
ever, the tonic condition of the tissue is
raised. The power of transmitting
true excitation, previously in abeyance,
is now not only restored, but gradually

~ enhanced to a degree, depending within

aes pices ces limits, on the amount of tetanisation.

case Effect in Me- The excitability also undergoes a similar
chanical Response of :

Frog’s Nerve transformation, from the abnormal

positive to normal negative, which latter
again becomes enhanced to a degree that depends, within
limits, on previous excitation. These effects, seen in electrical
response to transmitted stimulation applied at a distance,
I find repeated also in the mechanical response of nerve,
under similar circumstances. That is to say, an isolated
nerve, by the very fact of its being cut off from its normal
sources of energy in the body of the intact animal, is apt
to be rendered sub-tonic, and under these conditions no
true excitation is transmitted, and it is only when the tonic

MECHANICAL RESPONSE OF NERVE 525

condition of the tissue has been raised, by the application
of fresh energising stimulus, that the conducting power can
be gradually restored. 2

This leads me to what is theoretically a very interesting
mode of determining the velocity of transmission in nerve,
by the mechanical response of the nerve itself, which will be
understood from the diagram already given (fig. 315). In
that figure, A B C is the nerve, so clamped at B as to prevent
any mechanical slip, but not tightly enough to obstruct the
transmission of excitation. The nerve, when brought to a
normal excitatory condition, is first excited at A a by a pair
of electrodes in connection with an induction coil. The
transmitted excitation, reaching B C, induces a contractile
mechanical response there, observed by the highly. magnify-
ing optic lever. Records of the transmitted effect of stimulus
obtained in this manner. will be given later in the chapter.
The interval of time, 7, between the application of stimulus
and the initiation of response is accurately determined by
the usual methods. Stimulus is next applied at B 4, and the
interval of time 7’ between stimulus and response again
determined. The difference (¢—7’) is the time required for
the stimulus to travel the intervening distance a 4. By this
means, I found the velocity of transmission in a certain
specimen of nerve of fern to be 50 mm. per second.

It is thus easy, by means of two successive experiments,
to eliminate from the observation the element of the latent
period. It is to be understood that the molecular change,
ultimately to be expressed as contraction, begins to be
initiated as soon as excitation reaches the responding area.
As the contractile effect exhibited by the nerve is relatively
small, we can see that a certain time will elapse before it
becomes sufficient to be perceptible, unless the magnification
employed is very high. With a magnification of the order
of 100,000 times, however—which, as I shall show, is quite
practicable—this loss of time is much lessened.

It was while working out this investigation that I realised
how indefinite must be any determination of the velocity of

526 COMPARATIVE ELECTRO-PHYSIOLOGY

transmission in an isolated nerve. The conductivity, even
in the intact organism, we have seen to be liable to modifica-
tion from various factors such as fatigue, and it is easy to
understand that it will become still more fluctuating when
the conducting tissue is isolated. The inevitable changes
consequent on separation from the natural sources: of energy
at once begin totake place. As the result of this sub-tonicity,
even a typically conducting tissue, like nerve, will cease to.
be the conductor of true excitation, and there will then be,
properly speaking, no physiological distinction between such
a structure and a non-conducting tissue. By the absorption
of stimulus, however, a transformation sets in, and the non-
conducting becomes gradually reconverted, first, into a
feebly, and then into a very highly conducting structure.
The possible variations in conductivity, therefore, are not a
matter of some few units per cent. quantitatively, but even
considered qualitatively range from non-conductivity to the
highest conductivity. And even, further, when the nerve
has been once more rendered conducting, its velocity of
transmission will vary greatly with the tonic condition
conferred by previous stimulation. Over-stimulation, again,
by inducing fatigue, diminishes the power of conduction of
true excitation. This fact I shall be able to demonstrate by
special experiments.

That such changes are not peculiar to the isolated nerve,
where the manifestation can be traced unmistakably to its
true cause, is seen in those cases of living animals where,
owing to mal-nutrition, or for other reasons, the tonic
condition of the nerve falls below par, with growing non-
conductivity and paralysis as the effect. And here it may
be said that the transformation again from non-conducting
or feebly-conducting to the normal state of conductivity
may in general be brought about by the same means as are
employed with the isolated nerve, namely, by the frequent
repetition of tetanising electric shocks.

The photographic method of recording the response of
nerve, employed in the Kunchangraph, has the advantage

~~ ee

MECHANICAL RESPONSE OF NERVE 527

that, as the record is made by the moving spot of light, the
recording-point, as it were, encounters no friction, and the
characteristic form of the response curve is thus unmodified.
But prolonged work in the photographic dark-room is very
fatiguing to the observer. I was, therefore, desirous of so
perfecting the ordinary mode of record by the movement of
the tracing-point of a lever over a smoked surface, that it
would be adequate for most purposes. The difficulties
involved in carrying this out lie, first, in the obtaining of a
sufficiently high magnification, and, second, in the overcoming
of friction at the writing point. A long lever, such as is
necessary for high magnification, entails a heavy weight.
But this can be obviated by employing a light and thin
aluminium wire, 50 cm. in length. The fulcrum-rod, to
which the lever-index is attached, has a diameter of 2 mm.
A thread attached to the contracting nerve is wound once
round this fulcrum-rod. The radius of the latter being 1 mm.,
the magnification produced by this arrangement is 500
times. The magnification may in this manner be raised as
high as 1,000, by taking a longer lever. For the tracing
point the end of the lever is bent at right angles, and a fine
bristle attached. Even this degree of magnification is not
always necessary, as I have already said. The records which
immediately follow have a magnification of only fifty times.
The next difficulty, as already stated, lies in the friction
to be overcome. The friction offered by a writing-surface of
smoked paper is too great to be employed. A surface of
plate-glass, coated with a thin and uniform layer of smoke,
offers considerably less resistance. But even this retards the
free movement of the tracing-point. I was therefore led to
the construction of my Oscillating Recorder. The glass
plate, on which the record is made, is carried on a primary
frame, which is moved at a uniform rate, regulated by clock-
work, on wheels, over rails. The plate is mounted on this
primary frame in a secondary frame, which is held away from
the primary, at a certain fixed distance, by means of spiral
springs. This secondary frame, by means of an electro-

528 COMPARATIVE ELECTRO-PHYSIOLOGY

magnetic arrangement, can be maintained in a state of to-
and-fro oscillation, always strictly parallel to the primary.
The recording-index moves in a vertical plane, and the
smoked plate backwards and forwards, at right angles to
this, the extent of its oscillation being about 1 mm. The
recording point is adjusted, barely to touch the smoked »
surface. Thus the oscillation of the plate brings it periodi-
cally in contact with the tracing-point, which is thus practi-
cally free to execute its movements unimpeded. When the
oscillation frequency of the plate is sufficiently high, and the
speed of the recording-surface low, the curve of record

Fic. 323. Pho ographic Reproduction of Record of Mechanical Re-
sponses of Frog’s Nerve (left-hand record) and Plant-nerve (right-hand
record) obtained on Smoked Glass Surface of Oscillating Recorder

appears as continuous. In other experiments, where the
determination of time-relations is important, a high speed
can be given to the plate by the regulation of the clockwork,
and the record will then appear as a succession of dots.
From these, and a knowledge of the oscillation-frequency
of the plate, the time-relations of different parts of the curve
can be determined with accuracy. I give here two different
series of uniform mechanical responses recorded with this
instrument, obtained from the nerves of frog and of fern
respectively (fig. 323).

I have also been able, by means of this instrument, to
demonstrate a very important fact, namely, that the responses

MECHANICAL RESPONSE OF NERVE 529

of the afferent or sensory nerves are in every way the same
as those of the efferent, or motor. The numerous records
already given are of the latter. For the demonstration of
the former I took the optical nerve of Ophzocephalus, and
recorded its responses to uniform electrical stimuli, on a
smoked surface. The following (fig. 324) is a photographic
reproduction of the record. Owing to sub-tonicity, the first
response is seen here to be abnormal positive. Successive
stiniulation converts this, through diphasic, into normal
negative, in a manner exactly the same as has already been
observed in the sciatic nerve of frog. Another interesting
record obtained with the optical 3
nerve is given later (fig. 404).

I also give in: the next figure
(fig. 325) a series of effects of
transmitted. stimulation, which
show.in avery interesting manner
the effect of fatigue in the modi-
fication of the conductivity of a
nerve. Itis customary to suppose

Fic. 324. Record of Mechanical

that the nerve is indefatigable. Responses to Electrical Stimu-
But I shall be able to show that lus obtained on Smoked Glass,

: gs ds and given by the Optic Nerve
not only is the conductivity of a of Fish Ophiocephalus

nerve liable to fatigue, but its Note the abnormal positive re-
_excitability also. The demon- natch a ree ed
stration of the latter will be given

in a succeeding chapter. For the demonstration of the
effect of fatigue on conductivity I selected a length of
10 cm. from the sciatic nerve of gecko. This was attached
for experiment to the Kunchangraph, in the manner
diagrammatically represented in fig. 315. The length Bc,
which showed contraction, in response to stimulus trans-
mitted from A, measured 5 cm. The two exciting elec-
trodes, A a, were 2 cm. apart. The intervening tract,
through which excitation was transmitted, was, therefore,
3 cm. At the beginning of the experiment, owing to the
depression of tone which the nerve had undergone, from

MM

530 COMPARATIVE ELECTRO-PHYSIOLOGY

isolation, its conductivity was below par, and the responses
obtained were positive. After a series of stimulations,
however, the true excitatory wave was transmitted, with the
concomitant negative or contractile responses. In order to
demonstrate the effect of fatigue on conductivity, the
recording of this series was commenced only after many
normal responses had already been given. In the series
recorded we can see that the responses at first exhibit
periodic fatigue. The accentuation of fatigue is then mani-
fested by a rapid decline in the amplitude of the responses.
A remarkable change next begins to appear. It has been

Fic. 325. Record, obtained on Smoked Glass, ot Transmitted Effect
of Stimulation on Nerve of Gecko

Note here the progressive effect of fatigue, seen first as periodic fatigue ;
second as diphasic effect ; and third as reversal into abnormal positive.

shown that the true excitatory negative response contains a
masked positive element. Owing now to growing fatigue, the
exhibition of the negative is delayed, and the positive thus
shows itself as a preliminary down-curve in a diphasic response.
Afterwards, the excitatory negative is completely abolished,
and the positive response by expansion alone remains, as
seen in the last of the series. Ultimately, when the nerve is
killed, by excessive stimulation, even the positive response
disappears.

We may notice here the interesting fact that nerve, which
is regarded as a conductor, par excellence, will sometimes

MECHANICAL RESPONSE OF NERVE 531

become a non-conductor. Conduction, therefore, is not
alone dependent on anatomical structure, but requires also
a certain molecular condition. A nerve, whose continuity
remains uninterrupted, may nevertheless undergo paralysis
and cease to conduct. Recovery may then, in many in-
stances, be brought about by tetanisation.

Thus, by means of mechanical response, obtained with
a magnification of only fifty times, we have been able to
demonstrate not only those results which may be observed
by the most sensitive galvanometer, but also others which
were never so detected. The magnification thus employed
in the Kunchangraph, however, is here, as already stated,
only in its lowest terms. When this is further exalted,
still further and important phenomena regarding the exci-

tatory changes in nerve are revealed, and some of these will
be described in the next chapter.

CHAPTER XXXVI
MULTIPLE RESPONSE OF NERVE

Great sensitiveness of the high magnification Kunchangraph—Individual con-
tractile twitches shown in tetanisation of nerve—Sudden enhancement of
mechanical response of nerve on cessation of tetanisation—Secondary excita-
tion—Multiple mechanical excitation of nerve by single strong stimulation —
Multiple mechanical excitation of nerve by drying.

WE have already seen that, in order to detect the excitatory
_ changes in nerve by the electrical method, the moderate
sensitiveness of an ordinary galvanometer has to be exalted
more than a million times. Galvanometric indications, more-
over, are liable, as we have seen, to be complicated by the
occurrence of differential effects at the two contacts. In
- the Kunchangraphic method of record, however, there is no
possibility of such complications, for the response curve here
represents the direct effect of stimulus. We also saw that,
according to this method, a very moderate magnification
would give us all the variations that could be detected by
the most sensitive galvanometer, and, besides this, owing to
its simplicity, it makes it possible to observe other phenomena,
whose occurrence the galvanometer could not satisfactorily
have demonstrated.

Such a magnification, however, as I have already said, is
in its first stage only. With due precautions it is possible
to obtain a Kunchangraphic magnification of a hundred
thousand times. It will easily be seen that this places at
our disposal an instrument of incomparable sensibility, by
whose aid many of the phenomena of the nervous change,
hitherto beyond our power of observation, may be brought
within the sphere of investigation.

a

21 et dhe Ot TS

i i, eee

——— a ae ee ee ee

MULTIPLE RESPONSE OF NERVE 533

This magnification, of the order of a hundred thousand
times, may be accomplished in either of two different
ways. A magnified image of the end of the long lever
may, in the first place, be thrown on a distant screen.
By this compound magnification the sensitiveness of the
record may be raised to the extent desired. Or, in the
second place, we may employ a battery of two levers in
series. The first of these gives a magnification, say, of
five hundred times, and is connected with a second optical
lever, by which a multiplying magnification of two hundred
times is easily obtained. It is unnecessary to point out that
special care should in this second case be taken to ensure
the steadiness of the support. With due precautions it is,
however, not difficult to secure the entire elimination of all
disturbing elements.

When the spot of light from the second lever is thus
thrown on a distant screen, it is very interesting to watch the
various changes induced in the nerve by the environmental
conditions. An isolated nerve in a moist chamber, cut off
from its natural sources of energy, becomes increasingly
sub-tonic. This process is attended by an abnormal relaxa-
tion, which causes a steady movement of the spot of light
in one direction. When the nerve has become very sub-
tonic, the effect of stimulus, as that of electric shocks, is to
enhance the tonic condition, and by this the downward
drift of the spot of light is retarded or arrested. In
cases of extreme sub-tonicity there is no further response,
beyond this arrest. But where the sub-tonicity is less
pronounced, stimulus will induce the abnormal positive
response by a sudden positive variation of the drift, which
is followed by recovery in the opposite direction. The
after-effect of absorption of stimulus is further effective in
causing the gradual retardation and final arrest of the
downward drift. By such absorption of stimulus the tonic

' The abnormal positive response is also obtained from ‘nerve in ordinary
tonic condition, it should be remembered, by the application of excessively
feeble stimulus.

534 COMPARATIVE ELECTRO-PHYSIOLOGY

condition is raised, and the normal excitability consequently
enhanced. From this point onwards the responses are con-
tractile or normal negative. At this stage the response of
the nerve exhibits the staircase increase, the nerve itself
showing a certain amount of tonic contraction. The
excitability of the nerve then attains a maximum, and the
successive responses become uniform. Long and intense
stimulation will, after this, bring on fatigue. This stage is
characterised, again, by a growing relaxation of the nerve as
a whole, and its responses may become, first, diminished in
amplitude, second, of a diphasic character, and, thirdly,
reversed to the abnormal positive, according to the amount
of fatigue which supervenes. We may thus, for the sake of
convenience, distinguish four stages in the response of
nerve. The first of these is the initial phase, SUB-TONIC
RELAXATION, and the characteristic response to individual
stimuli is here abnormal positive. The second phase
is that of the TRANSITION to normal response. The
characteristic responses to individual stimuli here show a
staircase increase, with more or less permanent contraction
as its after-effect. If at this stage the nerve is allowed to
remain long without stimulation, it slowly reverts to the
first stage of sub-tonic relaxation, with its growing relaxa-
tion and abnormal positive response. Stimulation, how-
ever, brings it back once more to the second or transition
stage. In the third stage of UNIFORM responsiveness, the
responses are normal and take place by equal contraction.
In the fourth, or FATIGUE stage, there is a tendency, as already
said, to relaxation on the part of the nerve as a_ whole,
and it thus outwardly mimics the stage of sub-tonicity.
The responses now, therefore, diminish in amplitude, and
show the diphasic or the abnormal positive character.
Further characteristics of these four stages, and_ their
relations to each other, will be treated in detail in
Chapter XLI.

A few words may be said about the mechanical response of
the nerve, when it is in a favourable condition of excitability.

MULTIPLE RESPONSE OF NERVE 535

We have seen that in order to obtain a galvanometric record
of the electrical response of nerve, one or even a few shocks
will not be sufficient to induce the necessary electromotive
change. For this, tetanic shocks of a certain duration are
necessary, and the responsive electromotive change is not
immediately perceptible. In consequence of this intensity of
stimulation, moreover, complete electrical recovery can only
take place after a perceptible interval. With the low magnifi-
cation Kunchangraph, too, tetanic shocks of something like
a second in duration are necessary, and complete recovery
here also requires a period of about one minute. But with
the greater sensitiveness available in the highly magni-
fying apparatus, response with a highly excitable specimen
of nerve is obtained with even so short-lived a stimu-
lation as that of two or three vibrations of the vibrating
interrupter of the secondary coil, lasting less than one-tenth
of asecond. The responsive contraction of this short-lived
stimulus, and its recovery, are also quick. It is in conse-
quence of the rapidity of this response and recovery that the
responsive contractions due to the rapidly intermittent
tetanising shocks do not become fused, but show themselves
in the response-curve as consisting of successive twitches,
corresponding to the component shocks. Owing to the high
amplitude of these responses, and the trend of the base-line
either up or down, it is difficult in practice to obtain photo-
graphic records of these effects. But it is easy enough to obtain
definite visual demonstration of various characteristic effects
in the response by the employment of the following device.
The spot of light from the optic lever is made incident on
a revolving mirror, and reflected from it to a large white
screen at some distance. During a period of repose the
quiescent spot traces a more or less horizontal line of light.
This may trend either in a downward or an upward direction
continuously, according as there is induced a continuous
sub-tonic relaxation or a growing contraction, due to the
after-effect of stimulus. Somewhere between these two
extremes may be obtained a condition of more or less

536 COMPARATIVE ELECTRO-PHYSIOLOGY

stability, where the record made by the spot of light appears
as a horizontal line. Under normal conditions, then, the
response to excitation is a sudden movement, due to con-
traction, say upwards, followed by recovery down. In
the response-curve projected on the screen, the vertical
movement or ordinate represents the amplitude of the re-
sponse, and the horizontal abscissa the time. Under tetani-
sation a series of curves corresponding in frequency to the |
frequency of the shocks is observed as serrations.

Another very interesting observation often made in the
mechanical response of nerve is that of the after-effect on
the cessation of continuous stimulation ‘by tetanic shocks.
It has been found, it will be remembered (p. 428), that the
response of the retina to the action of continuous light often
shows on its cessation a sudden transient increase. This
phenomenon has been regarded as peculiar tothe retina. But
I have found exactly parallel effects to occurin the mechanical
response of nerve. Under continuous stimulation there is a
tendency to the attainment of a maximum contraction, which
suddenly, on the cessation of stimulation, overshoots, to be
followed by the usual recovery. I have already referred to
the two different effects of an opposite character caused by
incident stimulus, namely, the effect of negativity, and its
converse positivity. In the case of mechanical response, it is
the former which is effective in inducing contraction, while
the latter is associated with expansion, and is a factor in re-
covery. It will also be seen, in a general way, that by the -
antagonistic action of these two elements, and by the differ-
ing relative intensities of their after-effects, many diverse
results may be exhibited. In the case of the after-effect in
question, which occurs by a sudden positive variation of the
contraction, the excitatory effect would appear to be pre-
dominant. Even when, after this brief positive variation,
recovery is taking place, the excitatory element, with its
contractile tendency, appears to persist; for if a second
stimulus be applied, some time before the recovery is com-
plete, the consequent contractile response takes place almost

MULTIPLE RESPONSE OF NERVE 537

instantaneously. But when the recovery is once complete,
a similar stimulation will not induce a similar immediate
response. Instead of this there will be a brief period of
hesitation or latency before its initiation.

Another interesting phenomenon, which I was first able
to observe by the help of the highly magnifying Kunchan-
graph, was the occurrence of multiple response in nerve
under intense stimulation. I was led to this discovery by
an investigation which I had undertaken for the demon-
stration of the identity of response in animal and vegetable
nerves. After showing the extended parallelism which
exists between the two, under similar conditions and varia-
tions of conditions, as already described, I was desirous of
seeing whether a plant nerve could be substituted in certain
experiments for the animal nerve. In accordance with this
I used the vegetal nerve in the experiment known as
secondary contraction. Here a nerve-and-muscle preparation
of frog is taken, and a second piece of frog’s nerve is suitably
laid, with one end lying upon the end of the other nerve.
On excitation of this second detached nerve, say by electric
shocks, excitatory electrical variation is found to cause
responsive contraction in the muscle of the first preparation.
In my own rendering of this experiment I employed, instead
of the second piece of: frog’s nerve, a length of nerve of
fern. In order that the experiment should not be open to
any objection arising from the escape of stimulating current,
I employed a non-electrical form of stimulus. This was
done by touching the plant nerve with a strongly heated wire.
The terminal muscle would then, under favourable conditions,
begin to respond by strong spasmodic contraction. When
this had subsided, a new series of tetanic contractions
began ; and this was repeated at short intervals, for nearly
half an hour. When this series of spasms had come to
a stop, I have often succeeded by a fresh application of the
hot wire to the vegetal nerve in obtaining a second series
of such repeated responses. It thus appeared that the
strongly excited plant nerve gave rise to a series of multiple

538 |. COMPARATIVE ELECTRO-PHYSIOLOGY

excitations, the indications of which were afforded by the
nerve-and-muscle preparation.

The only perplexing feature of these responses was the
abnormally long period of ten to fifteen seconds which was
generally found to elapse between the application of the
strong stimulus to the plant nerve, and the response subse-
quently given by the terminal muscle. Here it must be
remembered that the excitation applied at one end of the
plant nerve has to travel the entire length before its excita-
tory electrical variation can be communicated to the nerve
of the frog-preparation. The transmitted excitatory varia-
tion in the primary has, moreover, to reach a certain intensity
before it can effectively excite the secondary preparation. We
know, further, that an isolated piece of nerve is liable to fall
into a sub-tonic or depressed condition, in which its conducting
power is much lowered, to be gradually restored again under
strong or long-continued stimulation. These considerations
will probably be found to account for the delay in the occur-
rence of the first of these responses. It would thus appear from
the last experiment that a nerve, when subjected to a single
strong stimulus, will give a multiple series of responses. In
order to test this by direct experiment I employed the highly
magnifying Kunchangraph, and subjected an experimental
nerve of frog to a single strong thermal stimulation. This
gave rise, at first, either to an abnormal positive response or
to a moderate negative. But there followed, after a longer or
shorter pause, a series of multiple contractile responses, which
generally grew in intensity for a considerable time. There
were in the series a number of short pauses, each followed by
a veritable storm of excitation, in which individual responses
were so rapid that the up or down movement of the spot of
light appeared as brief flashes, in which all distinctness was
obliterated. This experiment conclusively shows that the
nerve, like certain other tissues, is susceptible of multiple
excitation.

If the nerve in a nerve-and-muscle preparation be
allowed to dry, the muscle is seen to be thrown into a series

MULTIPLE RESPONSE OF NERVE

of spasmodic contractions.

caused by multiple excitations induced in the nerve.

539

This also we may regard as

And

the correctness of this supposition I have been able to

verify by experiment. As
the individual responses in
these multiple series were of
fairly large amplitude, I ex-
pected to be able to obtain
a record of such a series
by an ordinary magnification
on smoked glass. In order
to* obtain this record under
normal conditions a stream’
of air, bubbling through
water, was passed through
the chamber at a uniform
rate. Owing to the run-
down of the latent energy
in the nerve, we are able
to observe a_ consequent
growing relaxation. By the
manipulation of a stop-cock
the air is passed through
a calcium chloride tube, in-
stead of a vessel containing
water. In this way the nerve
is quickly subjected to dry
air instead of moist vapour.
This substitution is repre-
sented in the record by an
upward arrow 7, and it will
be noticed how at this point

Initiation of Multiple Re-
sponse by Drying of Nerve

FIG. 326.

The nerve, owing to growing sub-
tonicity, was showing a growing
relaxation, as seen in the first part
of the record. Air passed through
CaCl, tube, and, thus dried, was
now passed through nerve-chamber
at point marked with upward arrow
*. This gave rise to a large con-
tractile response, followed by sub-
sequent multiple responses. Original
record on smoked glass here reduced
photographically to 4.

the relaxation is suddenly converted into excitatory con-

traction (fig. 326).

Under this process of drying, this single

contractile movement is followed by a long-continued series
of multiple responses, here seen to fall into a somewhat

irregular periodicity.

CHAPTER XXXVII
RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY

Variation of resistance in Dionea, by ‘ modification’—Excitatory change, its
various independent expressions—Characteristic difficulties of investigation—
Morographic record by variation of resistivity—Inversion of curves at death-
point—Similarities between mechanical, electro-motive and resistivity curves
of death—The true excitatory effect attended by diminution of resistance
— Response of plant nerve by resistivity variation—Independence of resistivity
and mechanical variations—Responsive resistivity variation in frog’s nerve,
and its modification under aneesthetics.

IT was noticed by Burdon Sanderson that leaves of Dionga

after ‘modification’ exhibited a diminished electrical resist-
ance; and this ‘modification’ he found to be most easily
induced after the passage of an electrical current through
the tissue. Subsequent observers have also noticed a diminu-
tion of resistance in many cases when a tissue has been
subjected to electric shocks. These diminutions of resistance
are observed as more or less permanent after-effects. The
experiments in these cases depend on obtaining the galvano-
meter deflections caused by a small E.M.F., before and after
the modification. The larger deflection due to the same
E.M.F. after modification shows that the resistance of the
tissue has undergone a diminution.

This method, however, is open to several objections.
The passage of constant or induction currents through the
tissue would not only give rise to polarisation effects, but
would also induce an unknown electromotive variation at
the two contacts on the surfaces of the tissue, to an extent
depending on their differential excitability. The observed
deflection by a small testing E.M.F. is thus affected, not

Oo ty ihe fan. BP

RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY 541

only by .the variation of resistance, but also by varying
polarisation and. excitatory electromotive effects.

The question still remains, What is the nature and
significance of this induced variation of resistance? As the
effects which have been referred to are generally seen to be
induced after excitation, and to constitute its after-effect,
does it follow that the diminution of resistance takes place
as a remote consequence of other excitatory changes?
Or is it but a different manifestation of that fundamental
molecular change, induced by excitation, of which the

electromotive variation and change of form are other and

independent expressions?

I showed in the first chapter of this book that one
identical molecular change may be detected in different
ways, according to the method of observation. Thus the
same excitatory change is shown both in change of form

-and in electromotive variation. That either manifestation

takes place in entire independence of the other is shown,
for instance, when the mechanical response of A/zmosa or
Desmodium is restrained, under which condition the electro-
motive response proceeds as before. Excitatory changes,
similarly, may express themselves independently either by
electromotive variations or by changes of electric resistance.
It was, in fact, by means of the latter method, that of the
variation of resistance, that I first demonstrated the responsive
molecular changes which take place in inorganic matter.!

If living tissues, therefore, really respond to excitation
in a manner similar to the inorganic, it should be possible
to obtain from them response-records by a new method,
that of Resistivity Variation alone. In order to demonstrate
this inference, it will be necessary to show that such varia-

tion of resistance takes place immediately on excitation,

and not as an after-effect. We ‘must, however, ascertain
whether this method of Resistivity Variation does or does

' Bose, De la Généralité des Phénomines Moléculaires produits par ? Elec-
tricité sur la matidre Inorganique et sur la Maticre Vivante. (Travaux du
Congrés International de Physique. Paris, 1900.)

542 COMPARATIVE ELECTRO-PHYSIOLOGY

not give us those two opposed effects, positive and negative,
which we have already seen to be exhibited by living tissues
in other forms of response whether mechanical or electro-
motive. Of these, again, supposing them to occur, it will
also be necessary to determine whether it is the increase or
decrease of resistance which corresponds to the negative and
positive mechanical and electromotive responses respectively ;

and finally it must be determined what are the effects of the.

various physiological modifications, induced by different
agencies, on the response by resistivity variation.

In this investigation many serious experimental difficulties
have first to be overcome. These will be dealt with in series
in the detailed description of the method to be employed.
It will be well, however, to see in what important respects
the conditions for the obtaining of response here are unlike
those of the electromotive variation. In the latter case, it
we employ an isotropic tissue, diffuse stimulation will induce
similar excitatory electromotive variations in every part of
the tissue. The differential electromotive variation, there-
fore, on which the recording of response depends, will, under
_ these circumstances, be impossible. In this case, therefore,
it is necessary to injure or kill the tissue at one of the two
contacts. Such artificial induction of anisotropy would not,
however, be necessary under an experimental method which
was not dependent on any differential action. Thus an
isotropic tissue would give response by longitudinal con-
traction when the stimulus was diffuse. Similarly, though
an isotropic tissue fails to give an electromotive response
under diffuse stimulation, yet we may expect it to exhibit
response by variation of resistance. The recording of
excitatory response by resistivity variation has thus one
advantage over that of the electromotive variation, inas-
much as the record is not affected by complications due to
differential action, but is the expression of the direct effect
of excitation. The question which we have next to deter-
mine, then, is whether or not the excitatory variation of the
living tissue is attended by any variation of its resistance,

i. ae os fe

RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY 543

and whether, if so, such variation is or is not of two opposite
signs, according to the tonic condition of the tissue con-
cerned. In subjecting this question to experimental investi-
gation, it is well to employ a non-electrical form of stimula-
tion, in order to avoid any possible disturbance of the
galvanometer record from polarisation or current escape.

The first point to be decided is the character, positive or
negative, of that resistivity variation by which the true
excitatory change finds expression. We have already seen
that when a tissue is subjected to a gradually rising tem-
perature it exhibits response, which is expressed mechani-
cally as increasing expansion, and electrically as increasing
positivity. When the temperature, however, has reached
the definite critical point. of death, we have seen that
there is a sudden excitatory effect induced, attended by
a reversal of the sign ‘of response. This is expressed
mechanically by a sudden contraction, and electrically by a
change to galvanometric negativity. I have already ex-
plained in Chapter XVI. that, in mechanical and electrical
morographic curves, the abrupt point of inversion represents
the death-point. I have also shown that this death-response
is a true physiological response; that the temperature at
which it takes place is definite in all phanerogamous plants,
being at, or very near, 60° C. in normal specimens; and that
it displays depression, by transposition te a lower tempera-
ture, when the tissue is physiologically depressed by such
influences as fatigue.'

From these facts we might expect, if a tissue sfioied
response by variation of resistivity, that up to 60° C., or so,
there would be a continuous one-directioned change of
resistance, succeeded on reaching 60° C. by an abrupt
reversal to the opposite-directioned change. In that case, it
would be the second of the two, which would be indicative
of true excitation. To carry out this experiment I took a
radial and physiologically isotropic pistil of, Wzb¢scus, and
mounted it on two non-polarisable electrodes. The specimen

1 Bose, Plant Kesponse, p. 177.

544 COMPARATIVE ELECTRO-PHYSIOLOGY

was now made the fourth arm of a Wheatstone’s bridge
(fig. 327), by which electrical resistance is usually determined.
The plant specimens employed generally possessed high
resistance, of the order of several hundreds of thousands of
ohms. In the Wheatstone’s arrangement employed by me,
P and Q represented the ratio-arms; R a standard. megohm,

lic. 327. Diagrammatic Representation of Experimental Arrange-
ment for Recording Response by Resistivity Variation

P Q, ratio arms of Wheatstone’s bridge; R, standard 1 or *5 megohm;
S, specimen.

or half-megohm; and s the specimen whose variations of
resistance were to be determined. It is now evident that

Cpa?
when the bridge is balanced, S = ~ R.
P

The ratio-arms, P and Q, consist of resistance-boxes,
which allowed a variation of from I to 10,000 ohms. In
order to obtain balance, of course, the ratio of the two had to
be suitably adjusted. A highly sensitive galvanometer was
used, and the electromotive force employed to obtain balance
was only ‘o5 volt. This low E.M.F. was obtained by the
use of a suitable potentiometer slide. It will be seen that,
owing to the very low E.M.F. and the high resistance in
the circuit, the current flowing through the specimen was
rendered extremely feeble. This was done in order to avoid

RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY 545

any complication such as might result from the passage of a
strong current. 7 4

In order to subject the specimen to a gradual and
continuous rise of temperature, it was placed in the thermal
chamber, which has already been described (fig. 131). Before
the gradual raising of the temperature is initiated, an exact
balance is first obtained, the galvanometer spot of light being
thus adjusted to zero. This position can be maintained for an
indefinite length of time, provided the specimen is subjected:
to no variation of temperature. We have already seen that no,
resultant electro-motive variation is induced, in consequence
of stimulus, in a physiologically isotropic tissue. Any
change now recorded under a gradual rise of temperature,
by the movement of the galvanometer spot of light, must,
therefore, be due toa resulting variation of resistance. The
movement of the galvanometer spot of light is recorded in
the usual manner, on a photographic plate, a down-record
representing an increase of resistance, and an up-record a
diminution. In order that the curve should also give indica-
tions of different temperatures, light is cut off for a short
time at every 2° C. of rise of temperature. Thus each of the
successive gaps in the record indicates a temperature-ascent
of 2° C.

Taking now the specimen of pistil of Wzdzscus, balanced as
described, it was seen, on beginning gradually to raise the
temperature, that the balance was upset, while the growing
deflection of the galvanometer spot indicated an incréasing
resistance. The method of experiment, which has been
described, proved now so delicate that it was impossible to
record the entire curve within the range of the photographic
plate. It was, therefore, necessary to choose for record only
that part of the deflection which included the interesting and
significant point of inversion. The photographic record
thus commences at 56° C., it being understood that there
has been, before this, a larger and continuously growing
deflection downwards, indicative of increasing resistance.
During record the deflection continues to increase, till the

NWN

546 COMPARATIVE ELECTRO-PHYSIOLOGY

critical point is reached. And here, though the temperature
still goes on ascending at the same rate as before, we see a
sudden reversal in the characteristic curve of resistivity,
showing that the hitherto increasing has suddenly become a
decreasing resistance. This abrupt inversion represents the

Fic. 328. FIG. 329. FIG. 330.

Fic. 328. Photographic Record of the Morographic Curve taken by
Method of Resistivity Variation in Pistil of Azdéscus. Critical point
of inversion at 60°8° C,

Fic. 329. Photographic Record of the Morographic Curve taken by
Method of Electro-motive Variation in Petiole of Musa. Critical point
of inversion at 59°6° C.

Fic. 330. Photographic Record of the Morographic Curve taken by
Method of Mechanical Response in Filament of 7ass¢flora. Critical

point of inversion at 59°6° C

excitatory effect which occurs at the point of initiation of
death, and is in the present case at 60°8° C. (fig. 328).

It is astonishing to find that the morographic curves
obtained from different specimens, by three methods so
different as the mechanical, the electro-motive, and that of

RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY 547

resistivity, should bear so strong a resemblance to each other,
as is here seen to be the case, in the three records given side
by side (figs. 328, 329, 330). The excitatory effect may thus
be manifested by contraction, galvanometric negativity, or
diminution of resistance. We have already seen that the
electromotive is not a consequence of the mechanical re-
sponse, but is exhibited independently, when physical move-
ment is restrained. The response by resistivity variation
likewise, is, as we shall see, an independent expression of the
fundamental molecular change due to excitation.

Having thus established the fact that true excitatory
response is exhibited by diminution of resistance, we‘ have
next to ascertain whether this method of resistivity-variation
is capable of being employed in the study of excitatory
phenomena in general, with as great facility as those
mechanical and electro-motive methods with which we are
already familiar. In order to determine this question I
employed the same Wheatstone’s bridge arrangement as
before. As it was important, for reasons previously given,
to use a non-electrical form of stimulus, I employed those
thermal shocks which we have already found to be so reli-
able. The thermal loop of platinum wire enclosed the
specimen as before, without being in contact with it. A
short-lived passage of heating-current, controlled by a metro-
nome, would now give rise to that sudden thermal variation
which we have seen to be effective in causing stimulation
It should be remembered that the rise of temperature, as
such, induces a responsive increase of resistance. But as, on
the other hand, the sudden thermal variation acts as a
stimulus, it should induce the excitatory response, by a
transient diminution of resistance. In the following experi-
ments, I employed the physiologically isotropic nerve of fern.
The resistance of this tissue, when balanced, was found to be
400,000 ohms. It should be stated here that this specimen
was in a very good tonic condition, and might be expected
therefore to give normal response. It was now subjected to
a series of stimuli of uniform intensity, at intervals of five

NN2

548 COMPARATIVE ELECTRO-PHYSIOLOGY

minutes. The consequent responses are seen to be uniform,
and to take place by that diminution of resistance which we
already know to constitute the normal mode of response
(fig. 331). In order to obtain some idea of the magnitude
of these resistance variations the balance was upset at the
end of the response record, to the extent of 4,000 ohms.
The deflection seen to the right of the figure represents the
effect of this variation of resistance. The normal resistance
of the tissue, including that of the non-polarisable electrodes
was, as stated before, 400,000 ohms. The resistance of the
electrodes themselves was 50,000 ohms. That of the tissue

FiG. 331. Response Records by Resistivity Variation, in the Nerve
of Fern ; Stimuli at Intervals of Five Minutes

Kesponse to stimulation is by the negative variation or diminution of
resistance. The record to the right shows deflection due;to variation
of resistance of 4,000 ohms.

alone was thus 350,000 ohms. The variation of resistance
induced by stimulus, therefore, was, in the present case,
approximately I per cent.

In order. next to determine whether the resistance
variation was a consequence of the responsive change of
form, or an independent expression of the fundamental
molecular change, I clamped a nerve of fern suitably, at
its two ends, to prevent any possible change of length, the
two non-polarisable electrodes being led off in such a way
as to include a certain length of the specimen. On
carrying out the experiment in this manner I obtained
response by diminution of resistance, exactly as in the last

RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY 549

case. It is thus seen that the response, by resistivity
variation, is an independent expression of the excitatory
variation. . a

In taking records of the responses of animal and vege-
table nerves, by the methods of mechanical and electro-
motive variations, we saw that, while the normal response
was negative, this was liable to become reversed to positive,
under two different conditions—namely, sub-tonicity and
the fatigue due to excessive stimulation. Similar reversals
are observed under similar conditions, when the method
of resistivity variation is employed. We saw, further, that
the abnormal positive response, due to sub-tonicity, could be
gradually converted into normal negative, through inter-
mediate diphasic, by tetanisation—further tetanisation acting,
moreover, to exalt this feeble into enhanced negative
response. Parallel results are observed in the case of
resistivity variation. The initial abnormal response, by
increase of resistance, is found, after short tetanisation, to
be converted into diphasic—an increase of resistance or
positive response preceding the true excitatory or negative
effect of diminution of resistance. Further tetanisation
brought about the disappearance of this preliminary positive,
and the enhancement of the negative, response. —

I used the same method, finally, for the observation of
response and its modifications, by means of anesthetics in
animal nerve. For this purpose I took a nerve of frog, and
subjected it to chloroform. It will be remembered that in
studying the effect of anzsthetics by the electro-motive
variation method, we found it, first, to reverse the normal
response to positive, and finally to’ induce an abolition,
which might prove to be either temporary or permanent.
The same thing is seen under the resistivity variation
method. In the first series of records, given in fig. 332, we
find normal responses by diminution of resistance, to a
series of stimuli applied at intervals of two minutes.
After the application of chloroform, the normal responses
are seen to have disappeared. Stimulus now evokes

550 COMPARATIVE ELECTRO-PHYSIOLOGY

either no response or an occasional flutter, in the positive
direction.

We have thus seen, in the course of the present chapter,
that, in addition to the mechanical and electro-motive modes
of response, there is also a third mode available—namely,
that by Resistivity Variation. We have also seen that the
results obtained under these three methods are identical.
It has been shown that the normal excitatory effect is in

AW WW Vi

FIG. 332. Effect of Chloroform seen in Modification of Resistivity
Variation in Frog’s Nerve

The normal responses seen to the left by diminution or negative variation
of resistance were evoked by stimuli at intervals of one minute.
Those to the right exhibit the effect of chloroform. The normal
response is thus abolished, and we have either no response or only an
occasional flutter in the positive direction.

all three cases negative, consisting of mechanical contraction,
galvanometric negativity, or diminution of resistance, as the
case may be. In recording the morographic curve by these
three methods, we find that up to the critical point of death,
at or near 60° C., we obtain expansion, galvanometric posi-
tivity, and increasing resistance. At that point, however,
there is a sudden reversal of the curve, indicating conversion
to negative, contraction, galvanometric negativity, and de-
crease of resistance.

CHAPTER XXXVIIi
FUNCTIONS OF VEGETAL NERVE

Feeble conducting power of cortical tissues—Heliotropic and geotropic eflects
dependent on response of cortical tissues only—Phenomenon of correlation
—FExcitability of tissue maintained in normal condition only under action of
stimulus—Physiological activities of growth, ascent of sap, and motile
sensibility, maintained by action of stimulus—Critical importance of energy of
light—Leaf-venation a catchment-basin—Transmission of energy to remotest
parts of plants—Plant thus a connected and organised entity.

IN the animal body, different kinds of tissues are possessed
of different degrees of conductivity, the nerve being specialised
for the rapid transmission of stimulus. And it is now seen
that in the plant also we have a similar state of things,
cortical tissue, for example, though excitable, having feeble
conductivity, whereas the vegetal nerve possesses this power
in high degree. The question next arises: What is the
function subserved in the economy of the plant by a tissue
so highly specialised for the rapid conduction of stimulus ?
The various growth curvatures, by means of which plants
place themselves under the directive action of light and
gravity, are of advantage to the organism. But in bringing
about these movements, the plant-nerve takes little or no
part. And this is the case, even when the responsive
curvature takes place at a certain distance from the point of
stimulus. Here the transmission takes place slowly, through
the feebly-conducting cortical tissues. For example, in
Avena, curvature in consequence of such transmitted effect is
observed, even when the fibro-vascular bundles have been cut
across. ,
If, indeed, the highly conducting nervous elements ha
been concerned, these curvatures in response to unilateral

552 COMPARATIVE ELECTRO-PHYSIOLOGY

stimulus could not well have taken place. This will be clear
if we consider the case of a radial organ, such as the stem,
unilaterally acted on by light. Here a positive heliotropic
movement is induced, by which the growing organ is placed
in the most favourable position as regards illumination. The
peculiarity of this phenomenon lies in the responsive
contraction of the side acted on by stimulus, with consequent
concavity and curvature towards light. This heliotropic |
movement continues until the organ has placed itself in the
direction of incident radiation. When this orientation has
become perfect there is no further movement, because the
proximal and distal sides are now equally stimulated. Had
the cortical tissue, on whose differential responsive action the
curvature depended, been as highly conducting as the
vegetable nerve, this particular-directioned movement would
have been an impossibility, for the stimulus, instead of
remaining localised on one side, would in that case have
become diffused, with the result of inducing antagonistic
effects on the proximal and distal sides, under which there
could have been no resultant curvature. Indeed this neutral-
ising action of conduction, in nullifying responsive curvature,
is seen even when unilateral stimulus is excessively strong.
For under these circumstances stimulus is conducted
transversely, through the imperfectly conducting tissue, with
the result of undoing the previous curvature. And it is
obvious that had the conductivity of the tissue been higher,
this neutralisation would have taken place, even under feeble
stimulation.

I have also shown elsewhere that, in the responsive
movements of leaves, conduction through nervous elements
plays little or no part. For the blade of the leaf may be
acted on by light without showing any responsive movement.
Hence the lamina is not to be regarded as the perceptive
organ. The organ by which, on the contrary, the responsive
movements of the leaves are determined is the pulvinus or
pulvinoid. This is at once perceptive and motile. When
such an organ, then, is acted on directly and locally by light,

FUNCTIONS’ OF VEGETAL NERVE 553

a responsive movement is\induced. These are facts which
can be demonstrated by shielding the lamina and pulvinus
alternately from the action of light. When the lamina alone
is exposed there is no action; but when it is the pulvinus
to which light is admitted, there is an immediate responsive
movement.

The lamina, it is true, is provided with a fine fibro-vascular
network containing the nervous strands. But the stimuli
received by this extensive system are ultimately conducted
along the thicker channels of which it forms the terminal
ramification, and serve to stimulate the plant as a whole.
When such stimuli reach the petiole, then, they cannot act in
that direct and unilateral manner in the motile organ which
is required for the responsive movement of the leaf. The
petiole, it is true, from its dorsiventral character, is unequally
excitable on its two sides. But since,in the process of the
transference of stimulus from the nervous to the ordinary
elements there is a great loss, and since, moreover, the motile
tissues in the case of most petioles are very sluggish, the
diffusely transmitted stimulus induces practically no directive
effect. Nor could there, in any case, have been any com-
parison between the effective strength of an external
stimulus acting directly and unilaterally, and a transmitted
stimulus acting diffusely.

It will thus be seen that conduction through specialised
nervous elements is by no means the essential factor in
bringing about those numerous directive curvatures which
subserve so many important functions in the life of the plant.
The question, therefore, as to what is the part in the economy
of the organism played by the vegetable nerve still remains
to be answered.

One very obscure problem in connection with Vegetable
Physiology is that of Correlation. Thus various complex
activities may be set up in one part of the plant, when
another part, more or less distant from it, is subjected to the
variation of some excitatory influence. In this way every
part of the plant-organism would appear to be ez rapport with

554 COMPARATIVE ELECTRO-PHYSIOLOGY

the rest, and this intimate connection between outlying areas
becomes comprehensible, when we are made aware of the
easy communication afforded by the existence of specialised
conducting elements.

I shall now proceed to deal with. the importance ot
stimulus, and its conduction to the interior of the plant, as
the essential factor in sub-
serving the various life-.
activities of the organism.
That the reception of stimu-
lus is important, in main-
taining the excitability of a
plant, is easily seen in the
case of Mzmosa, when de-
prived of light, for example.
Under these conditions, its
motile excitability is found
to disappear. And this is
only restored on re-exposure
to light. We have seen
again, in the course of the
last chapter, that the isolated
vegetable nerve, deprived, as
it is, of normal favourable
RiGcsrin Pilostanhins Recmdcc! conditions, becomes sub-tonic

Effect of Tetanisation in En- or moribund, and then its
hancing Mechanical Response of

Plant-nerve ordinary responsive power is

The first series of responses heightened abolished or even reversed.
to second series, after intermediate Under these ‘clvcumatantes
tetanisation.

the normal excitability is
found to be restored by the continued action of stimulus.
Abnormal positive response is thus found to be converted
into normal negative. Again, after an intervening period of
stimulation, response of ordinary amplitude is found, as
in fig. 333, to become enhanced. It is thus seen that a tissue,
when cut off from the supply of stimulus, loses its normal
excitability, and that a@ more or less continuous supply of

FUNCTIONS OF VEGETAL NERVE 555

stimulus ts essential to the maintenance of the proper excitatory
condition of a tissue. | |

It is known that in the animal, when the conduc-
tivity of a nerve is abolished by nerve degeneration, the
connected muscles also rapidly waste away. Thus the
maintenance of the proper excitability of various tissues is
dependent on their constant reception of stimulus or energy
through the mediation of the attached nerve. It is therefore
highly probable that the excitability of the indifferent vegetable
tissues is kept at its normal level by the reception of energy |
of stimulus through the conducting nerve. |

I shall next briefly refer to a fact which I have
demonstrated fully elsewhere, that all the principal physio-
logical activities of the plant, such as autonomous movement,
ascent of sap, and growth are fundamentally excitatory
phenomena. Thus, for example, the autonomous rhythmic
movements of the lateral leaflets of Desmodium gyrans come
to a standstill when their store of latent energy is exhausted.
And it is only by the accession of fresh stimulus from
outside that these multiple responses can be renewed. We
describe the state of the plant, when its internal energy is
below par, by saying that it is sub-tonic, the normal tonic
condition, or health of the plant, being dependent on the
sum total of stimulation previously absorbed by it. Turning
next to the question of the ascent of sap, I have shown that
the most important factor in bringing this about is the
multiple rhythmic activity of certain interior tissues of the
plant. Under such circumstances as cause the tonic condi-
tion of the tissues to fall below par, the rate of the ascent of
sap will be lowered, or it may possibly even be brought to a
standstill, owing to the depression of excitability induced.
On now supplying fresh stimulus, we find the excitability to
be renewed and the normal rate of ascent restored (p. 383).
Another instance of this is seen in the fzleus of Coprinus
which droops when kept too long in the dark, but recovers
its normal turgidity on exposure to light.

Growth, again, I have shown to be a result of multiple

5 56 COMPARATIVE ELECTRO-PHYSIOLOGY

rhythmic excitation. When the tonic condition of the plant
falls below par, growth is arrested, however large the amount
of formative material present. But if stimulus be applied,
while the plant is in this state of growth-standstill, there is a
renewal of responsive growth.

The importance of the absorption of stimulus of light to

the response of growth is seen in the development of certain
seedlings. These, when grown in the dark, become diseased |

and perish. The growth and the development of organs cease,
even though the cotyledons still contain considerable
quantities of unused formative substance. They become
moribund, as the expression of their loss of tonic condition,
which, as we have seen, depends upon the supply of stimulus
from outside. And in the present case the critical element
is the stimulus of light.

This fact that the stimulus of light may enhance the ex-

citability of a tissue, is shown in the following photographic
records of the mechanical response of vegetal nerve. The
first three responses show the extent of normal response to
a given electrical stimulus applied in the dark. The specimen
was then subjected to the light of an electrical arc lamp, and
the next series show the consequent enhancement of response,
under the same stimulus as before. Light was now cut off,
and after an interval response once more taken. This is seen
to have been of the same amplitude as at the beginning
(fig. 334). Thus light is seen to enhance excitability.

In the cases which we have just been considering we have,
for the sake of simplicity, confined our attention to a single
factor—namely the photo-tonic—among the many which
finally determine the general tonic condition of the plant.
And we have found that when the organism is deprived of
this source of stimulus, its motile activity, its suctional
activity, and its response of growth, all disappear. When
the plant, however, is restored to the direct action of light, all
these various activities reappear. Now it is clear that this
illumination cannot. directly penetrate to many of those
interior tissues, whose activity is nevertheless essential to the

oe

Pei Ba) Ras

FUNCTIONS OF VEGETAL NERVE 557

maintenance of life. How, then, is the external stimulus
conveyed to these? It is evident that this can only be
accomplished through the agency of the nervous elements.
This fact, of the transmission of the excitatory effect of
an external stimulus from one part of the plant to another at
a distance, there to maintain the tonic condition, is again
still more clearly seen in the well-known experiment on the
sensitiveness of Wzmosa when partially kept in the dark. If
one branch of this plant be covered by a dark box, while the
rest of it is exposed to light, it is found that the leaves of the

FIG. 334. Photographic Record showing Enhancement of Excitability
under Action of Light in Nerve of Fern

First series, normal mechanical responses to electrical stimuli, in dark ;
second series, the same, taken under light; third series, taken after
withdrawal of light.

first undergo no loss of motile sensitiveness. It is thus
evident that the photo-tonic stimulus has been transmitted
from the illuminated to the unilluminated portions of the
plant, through conducting channels, in order to maintain the
normal excitatory condition. |

Next comes @ie very interesting experiment of Sachs, in
which a long shoot of Cucurbita was made to grow inside a
dark box, the rest of the plant being exposed to light. The
covered part of the plant, under these circumstances, showed
normal growth of stem and leaves. Normal.flowers and a
large fruit were also produced in the same confinement.
The tendrils inside the box, moreover, were found to be fully

558 COMPARATIVE ELECTRO-PHYSIOLOGY

as sensitive as those outside. The transmission of stimulus
by the plant, in such a way as effectively to maintain such
complex life-activities as motility and growth, even in the
absence of direct stimulation, is. thus fully demonstrated.
And we may gather an idea from this fact of the funda-
mental importance, to the life of the plant, of those nervous
elements by which this is rendered possible.

One of the most important functions of the venation ot
the leaf, not hitherto suspected, is now made clear to us:
Among external stimuli, none
perhaps is so essential, or so
universally and easily available
to green plants, as energy otf
light. And we now see that
the fine ramification of fibro-
vascular elements over as wide
an area as possible in the leaf,
provides a virtual catchment-
basin for the reception of stimu-
lus. The expanded lamina is
Re Sages STistginurine ore Ties thus not merely a specialised

vascular Elements in Single structure, for the purpose of

Bevan heel ot hapaye photo-synthesis, but also a sen-
There are at least 20: such layers eb ‘

engirdling the stem. sitive area for the absorption

of stimulus, the effect of which
is gathered into larger and larger nerve-trunks, in the course
of its transmission downwards into the body of the plant.

And even in the interior of the plant the distribution o1
these is such that no mass of tissue is too remote to be ex-
cited by the stimulus conducted through the nervous ele-
ments buried in them. How reticulated they may be, even
in the trunk, is seen in the accompanying photograph of the
distribution of fibro-vascular elements in the main stem of
Papaya (fig. 335). This network, of which only a small
portion is seen in the photograph, girdles the stem through-
out its whole length, and in this particular case there were
as Many as twenty such layers, one within the other.

crawls,

‘aomsn mei; pooner STONE es

Pe ee le el

ae:

FUNCTIONS OF VEGETAL NERVE 559

It is thus seen how all parts of the plant are, by means of
nerve-conduction, maintained in the most intimate communi-
cation with each other. It is, then, in virtue of the existence
of such nerves, that the plant constitutes a single organised
whole, each of whose parts is affected by every influence that
falls upon any other. |

CHAPTER XXXATX

KLECTROTONUS

Extra-polar effects of electrotonic currents on vegetal nerve—Electrotonic
variation of excitability—Bernstein’s polarisation decrement —Hermann’s
polarisation increment—Investigation into the law of electrotonic variation
of conductivity —Investigation on variation of excitability—Conductivity en-
hanced when excitation travels from places of lower to higher electric potential,
and depressed in opposite direction—When feeble, anode enhances and kathode
depresses excitability—All electrotonic phenomena reducible to combined
action of these factors—Explanation of apparent anomalies.

WHEN an electrical current is Jed through a portion of a
nerve— entering, say, at A, and leaving by K—it is found that
electro-motive changes are induced by it in the extra-polar

AD aS =
FIG. 336. FIG. 337.
Extra-polar Kat- and An-electrotonic Effects

Fig. 336 shows kat-electronus, E near K being galvanometrically negative.
Fig. 337 shows an-electronus, E near A being now galvanometri-
cally positive.

regions. On the kathodic side, the electric potential near
K is found to be lowered in reference to a point further away.
On the anodic side similarly, the electric potential of a point
near A is found to be raised. These changes induced in the
electric potential are indicated by the galvanometric nega-
tivity of the point near the kathode, and positivity of that
near the anode (figs. 336, 337). In the tissue itself the
current is assumed to flow in a direction contrary to that in

>

ELECTROTONUS 561

the external galvanometric circuit, as indicated by the dotted
arrow.'

In the medullated animal nerve, the electrotonic currents
increase with the intensity of the polarising current. In the
vegetal nerve, I have obtained exactly similar results.
Taking afresh and vigorous specimen, the polarising elec-
trodes were placed at a distance of 2°5 cm. from each other,
the pair of extra-polar electrodes, where the electrotonic
effects are observed, being separated from these by 2 cm. and
divided from each other by 2 cm. also. The value of the
acting polarising E.M.F. could be varied by the use of a

Fic, 338. Extra-polar Electrotonic Effects under an Acting E,M.F.
which rises from °6 to 1°4 Volts

A, an-electrotonic deflections seen to left ; K, kat-electrotonic to right.

potentiometer arrangement. In order to induce in the extra-
polar electrodes, an-electrotonic and kat-electrotonic effects
alternately, the current in the polarising circuit can be sent
in one direction or the other by means of a reversing-key.
The record of the galvanometer deflection, in the extra-polar
circuit, gives a measure of the electrotonic effect induced.
In fig. 338 is seen such a record of. effects both an-electro-
tonic and kat-electrotonic, taken while the acting E.M.F. was
increased from ‘6 to 1°4 volt, by steps of ‘2 volt at a time.

' Certain considerations, which need only be referred to here, cast some
doubt on the validity of this assumption. But as it is so widely current in
physiological literature, I shall confine myself, in dealing with the subject of the
electrotonic current and its variations, to those indications in the external circuit
which are afforded by the galvanometer.

OO

562 COMPARATIVE ELECTRO-PHYSIOLOGY

I give here a table which shows the galvanometric deflection
corresponding to each particular E.M.F.

TABLE OF GALVANOMETRIC DEFLECTIONS AND CORRESPONDING E.M.F.

Volts | An-electrotonic effect Kat-electrotonic effect
6 _ §0 divisions 58 divisions -
8 65 9 78 9
| ae) 107 ) IIO -s
1‘2 126 ee 124 -
1°4 150°; | 148s,

In this particular experiment, it will be seen that the
an-electrotonic and kat-electrotonic effects are practically
equal. But, to be more accurate, the an-electrotonic are
slightly lower with low E.M.F., and slightly higher with
high, than the corresponding kat-electrotonic deflections. A
constant electrical current is thus seen to induce electro-
motive variations, outside its poles, in the vegetal nerve.

We next turn to the question of the variation of
excitability induced in a tissue, by the passage of a con-
stant current. On this subject the most important con-
tributions have been made by Bernstein and Hermann.
Bernstein, experimenting on the sciatic nerve of frog, found
that excitation induced a polarisation decrement. This
experiment is illustrated in the following diagram (figs. 339,

n
——
eceet
—o
<a
Siete

9
— . x — =? SSS
i EE Kk A j See eee ere
33 Kat~<--—- = 3300 An----> Tah
FIG, 339. FIG. 340.

Figs. 339, 340. Diagrams illustrating Bernstein’s Electrotonic Decrement

Fig. 339 shows decrement of kat-electrotonic, and fig. 340 of an-electro-
tonic currents, under stimulation at s. In this and following figures
the inside thin arrow indicates direction of polarising current, the
outside thick arrow the direction of responsive current.

340). In fig. 339 the kathodal effect is seen induced
in the extra-polar circuit. When the nerve is now excited

by tetanising electric shocks, a diminution of the extra-polar
current is induced. When the anodal effect is induced in

ELECTROTONUS ; 563.

the extra-polar circuit, by reversal of polarising current,
the an-electrotonic current, opposed in direction to the former
kat-electrotonic, also undergoes diminution on excitation
of the nerve (fig. 340). It has been suggested that this
diminution of electrotonic current was due to a supposed
diminution, during excitation, of the susceptibility of the nerve
to polarisation.

But this explanation is negatived by an experiment of
Hermann, showing the occurrence of polarisation increment
during excitation. In figs. 341 and 342 we havea polarising
_ and exciting circuit in series, excitation being caused by the

ot eh

= Yo a a aEEERRREaEned
A pea af K K <—__—_—_ A
Fic. 341. FIG. 342.

Figs. 341, 342. Diagrams representing Hermann’s Polarisation-
increment under Tetanising Shocks

Inside thin arrow indicates the direction of polarising current ; the
outside thick arrow, the direction of excitatory current.

secondary coil of an inductiorium. With such an arrange-
ment, the polarising current, whether from left to right or from
right to left, is found, during excitation, to undergo an
augmentation. Hermann refers these facts to alterations
of intensity in the negative wave of excitation, during its
passage through the nerve, when the latter is polarised. ‘ It is,
indeed, more pronounced at any point of the nerve, the more
strongly positive and weakly negative the polarisation of the
latter, ze. it increases when it is becoming algebraically
more positive, and diminishes when it advances upon more
negative points’ (Hermann’s Law of the ‘ Polarisation
Increment’ of excitation).!

It would thus appear that the observations hitherto made,
as to the effects of electrotonus on excitatory response, are of

! Biedermann, Blectro- -phystology (Engl. transl. ), vol, ii. p. 315.
002

564 COMPARATIVE ELECTRO-PHYSIOLOGY

a somewhat discordant character. I shall, however, be able
to show that their complexity is due to the combination of
the different effects of the polarisation current on conductivity
and on excitability. These separate effects may, according
to circumstances, either conspire or act antagonistically.
Hence the great variety of results, which appears at first
sight incapable of a consistent explanation.

In order, then, to discover the laws by which an electric.
current induces a variation of conductivity and excitability,
we must first determine the pure effect of the current on
conductivity, apart from any excitatory variation; and,
secondly, its effect on excitability, uncomplicated by any
variation of conductivity. | |

To take conductivity first: the ideally perfect arrange-
ment would be to have the polarising electrodes, in relation
to the region whose conductivity-variation is to be tested, at
a distance so great that they could exert no predominant
an- or kat-electrotonic influence upon it. In a led-off
circuit, moreover, a differential action, unless proper,pre-
cautions are taken, is exerted on two electrodes placed side
by side. It is, therefore, desirable to remove one of these
outside the sphere of action. Such, then, being the con-
ditions to be observed, in order to eliminate the effect of
the poles themselves, and thus determine the influence of the
direction of current on conductivity alone, I took a petiole
of fern 20cm. in length, and connected its ends through a
reversing-key with a Daniell cell (E.M.F.= 1 volt). The
responding galvanometer-circuit had one electrode about the
middle of the petiole, near the insertion of a certain lateral
leaflet, the other electrode being connected with the lamina
of the same leaflet, whose midrib, however, was cut across to
prevent transmission of the excitatory effect (figs. 343, 344).
It is thus seen that the led-off electrodes are at a relatively
great distance from the polarising electrodes, and further,
owing to one electrode being placed out of the way, on the
lateral leaflet, and the other symmetrically between anode
and .kathode, it is clear that anodal or kathodal action is

ee eS ee rae eee eee eee eee

ELECTROTONUS 565

reduced to wz. The excitation from the stimulator is
transmitted across the intervening conducting region, either
along the slope of a falling electrical potential, that is to
say, from-a galvanometrically positive to a galvanometrically
negative point, or against that direction, namely, in an
electrically uphill manner, from the galvanometrically
negative to the galvanometrically positive. Now, if the
direction of an electrical current have an effect on the
conduction of excitation, this fact will be detected by
the modification induced in the normal response during the
passage of the current. :

The results of the present experiment will be found to
determine this question. Excitation was induced by means

Fic. 343. : Fic. 344.
Figs. 343, 344. Experiment with Petiole of Fern demonstrating Variation
of Conductivity by Polarising Current

of the thermal stimulator, and the normal responses taken,
shown in fig. 345 a, as ‘up. The polarising current was
now sent from left to right; hence excitation will now be
transmitted through the intervening conducting region in an
electrically downhill manner, or in the direction of the falling
potential—that is to say, from the region of the anode to that
of the kathode. It will be seen presently that conduction is
retarded or abolished when excitation is made to travel elec-
trically downhill from the anode to the kathode.' If this be
so, we shall expect to detect the fact by the diminution of
the amplitude of the normal response, or even by its actual
reversal. For we have seen that when the excitatory re-
action of galvanometric negativity is sufficiently retarded, its
opposite, the positive effect, often makes its appearance alone.

1 These remarks apply to a feeble or moderate rate of fall of potential.

566 COMPARATIVE ELECTRO-PHYSIOLOGY

In fig. 345 4, this is seen to have actually occurred. There
will be other cases where, the depression of conductivity
induced being not too great, it will be possible to watch the
gradually lessening amplitude of response until it ends in
actual reversal. We have next to determine the effect on
conductivity, of the passage of excitation in an uphill
direction—that is to say, from the kathodic to the anodic
region. For this purpose the polarising current was reversed

Fic. 345. Photographic Records of Responses taken in last Experiment,
when Excitation was transmitted with and against the Polarising
Current

a, Normal response of petiole of fern to transmitted excitation; 4,
Reversal of response when excitation was travelling electrically downhill
or with the current; c, Normal response once more ; @, Enhanced
response due to increase of conductivity when excitation travels electri-
cally uphill, or against the polarising current. . Upward arrow 4
indicates that polarising current is in same direction as normal
response. Downward arrow { shows polarising current in opposite
direction. The same in the two following figures.

by means of a reversing key, the left-hand end of the petiole
being now made the kathode. Before doing this, however, I
stopped the current, and took a second set of records of
normal responses. It will be seen that by reason of the
cessation of the previously acting left-to-right current,
leaving an after-effect, these were slightly enhanced above
the first normal responses (fig. 345 ¢c). On now reversing
the current, conductivity was found to be enhanced, as seen
in the greater amplitude of response (fig. 345 @).

aan

ELECTROTONUS 567

I next undertook an investigation into the effect on
conductivity, of variations of intensity in a moderate polaris-
ing current. This is shown in fig. 346, in which excitation
travels electrically downhill—that is to say, from the anodic to
the kathodic region. In a we have the normal response
before the passage of the current. In 4 we have the re-
sponses reduced by the diminution of conductivity con-
sequent on the application of ‘1 volt for polarisation. On
the application of *5 volt in c, there was a tendency towards

Fic. 346. Photographic Record of Modification of Conduction during
Passage of Excitation from Anodic to Kathodic Region, under Increasing
Intensity of Polarising E.M.F.

a, Normal response ; 4, Diminished response where terminal E.M.F. was
"I volt; c, Response still further diminished and rendered diphasic
under *5 volt ; @, Response reversed under I volt.

reversal, the response being now diphasic, positive followed
by negative. Finally, on the application of 1 volt in -d, we
see the response reversed to positive, the conduction of the
true excitatory effect being here altogether abolished.

In a second set of experiments, carried out on a fresh
specimen, I investigated the effect of an increasing intensity
of the polarising current, when the excitation was made to
travel, electrically uphill, from the kathodic to the anodic
region. It will be seen, from figure 347, that the application
of a polarising E.M.F. of 1 volt increased the conductivity,
as seen in the heightened responses shown in 4, as compared

568 COMPARATIVE ELECTRO-PHYSIOLOGY

with the normal responses in a. The application of higher
polarising E.M.F. of °5, 1, and 1°5 volts respectively, now
- induced appropriate increments of conductivity, as seen in ¢,
d, and e. I was unable to use an E.M.F. of higher than
I'5 volts because the galvanometer spot of light became
unsteady. It is to be borne in mind that the specimens in
these experiments were 20 cm. long, and the maximum
potential gradient employed was only ‘07 volt per cm. In
experimenting on electrotonic effects, it must be remembered
that the E.M.F. employed is, generally speaking, feeble.

Fic. 347. Photographic Record showing. Enhanced Conduction from
Kathodic to Anodic Region

a, Normal responses; 4, c, d, ¢, Responses gradually enhancing under
increasing polarising current.

From the results described, then, we arrive at the follow-
ing law of the effect of a moderate or feeble constant electric
current on conductivity.

A moderate polarising E.M.F. induces variations of conduc-
tivity. The conductivity is increased in the direction from the
kathodic to the anodic region, and depressed in the opposite,

Having thus demonstrated the pure effect of a constant
electric current on conductivity, we have next to study the
unmixed effect of polarisation on excitability. We. have
seen that when two equally excitable points in the same
circuit are simultaneously excited by an identical stimulus,
there is no resultant response, since the two excitatory

* eLECTROTONUS 569

effects balance each other. The galvanometric effect is
then zero. But if one of the two have its excitability en-
hanced in any way, this balance will be disturbed, and a
resultant current will flow through the circuit, the more ex-
citable contact becoming galvanometrically negative. I now
took a long piece of isolated vegetal nerve and connected
it with the galvanometer at E and E’,, a secondary coil,
giving equi-alternating electric shocks, being also in the
circuit (fig. 348). The
two longitudinal con-
tacts E’ and E being
more or less equally
excitable, there was at
first no. resultant re-
sponse to stimulation.
E’ was now made the
anode, an E.M.F. of +1
volt being used for the
purpose, and a perma-
nent current was found
to flow in the galvano-
meter in the direction
of E’GE shown by the
thin inner arrow, E’
being galvanometrically

FIG, 349.

Experimental Arrangement
to Exhibit the Enhancement of Excit-
ability at Anode, and its Depression at
Kathode, when the Acting E.M.F. is
feeble

Figs. 348, 349.

positive. On now ap-
plying equi-alternating
shocks, the balance was

Fig. 348 shows enhancement of excitability
at anode; Fig. 349, the depression of
excitability at kathode.

Inside thin arrow indicates direction of tantarins

ing current. Outside thick arrow, direction
of excitatory current. Note that in both
thereis a so-called polarisation-decrement.

found to have been dis-
turbed, and the re-
sponsive. current to be in the opposite direction, namely,
EGE’, as shown by the thick arrow; E’ now undergoing an
excitatory negative variation. This shows that the ex-
citability of E’ has become enhanced by being made
anode. E’ was next made kathode, in consequence of
which the permanent current in the galvanometer was now
in the direction of EGE’ (fig. 349). E’ is now the kathode, E

570 COMPARATIVE ELECTRO-PHYSIOLOGY

in relation to it being anode. On excitation the responsive
current was in the opposite direction to the permanent
current, in consequence of the induced depression of the
kathode E’ or the induced enhancement of excitability at
the relative anode E. In fig. 350 are given the records of
these effects. Two different experiments were carried out,
on two different specimens of plant nerve, whose records are
given in a and 4, fig. 350. In each of these we observe, first,

Fic. 350. Photographic Records of Response, illustrating the Enhance-
ment of Excitability at Anode, and Depression at Kathode, under
Feeble Acting E.M.F. in two Specimens of Nerve of Fern a and 6

Before application of polarising current there was no resultant response in
either case. When E’ was made anode, there was an up-response,
indicating enhanced excitability of that point.. The dotted arrow ¥
seen below shows the direction of polarising current. The responsive
current is then opposite in direction to the polarising current. When
E’ is made kathode the resultant response is down, showing depression
of the excitability of the point. The responsive current is here also
opposite in direction to the polarising current.

the enhanced excitability due to E’ being made anode,
which gives rise to up-responses, opposite in direction to the
permanent current, shown by the dotted arrow below. The
second pair of responses in each case shows the depression
of excitability at the kathodic point E’, which is tantamount
to enhancement of excitability at the relative anode E. An
inspection of figs. 348 and 349 will show that the responsive
current is always in a direction opposite to that of the existing
polarising current, thus constituting the so-called polarisation

+

FOO OO ee eee ee oe

TGR conse pL SS ee

Seb er aN ea

ee

nace -2t
WwW |

ELECTROTONUS S71

decrement. But we shall presently find that the direction of
the responsive current is the only constant factor here, de-
termined as this is by the relative excitabilities of the. two
electrodes. An identical variation of excitability may, as
I shall show, appear under different circumstances, either as
a polarisation-increment or as a decrement.

I have obtained results precisely like the foregoing, with
the sciatic nerve of frog. It should be mentioned here that
such effects are obtained without much difficulty in the first
stages of polarisation. But, if this be prolonged, there is
a certain liability to reversal.

From the experiments which have been described on
variations of excitability by the polar action of currents, we
arrive at the following law:

A feeble E.M.F. induces modifications in the excitability of a
tissue: the anode enhances and kathode depresses excitability.

This result is startling, contravening, as it does, Pfliiger’s
Law. A factor that had not been taken into account
was the range of E.M.F., within which this law might
be applicable. In the present case, the acting E.M.F. is
relatively feeble, and we shall see later that Pfliiger’s Law
does not apply above or below a certain medium range.

Having thus obtained the isolated effects of electric
currents on conductivity and excitability respectively, I
next took up those more complex cases in which both
effects were present in various combinations. This problem
was attacked by means of the Conductivity Balance. In
this experiment, carried out on the petiole of fern, the led-off
points E and E’ were at a distance of 6 cm. from each other.
The distance of each of the polarising electrodes A and K
outside the led-off circuit E’ and E was 2 cm. (figs. 351 and
352). The thermal stimulator S was so adjusted before
the passage of the current that the excitations at E’ and E
were exactly equal, as seen in the balanced horizontal record
n fig. 353a. It should be mentioned here thatthe galvano-
meter connections were so arranged that an _ increased
excitability of the left-hand contact E’, would be shown by

572

COMPARATIVE ELECTRO-PHYSIOLOGY

means of ‘down’ and that of the right hand contact E by

means of ‘up’ responses.

An E.M.F. of *5 volt was now

eens Gorrtey rep
fa = Ame fl
A E’ E K K; E E H
noe
FIG, 351. FIG. 352.

Figs. 351, 352.

Experimental Arrangement demonstrating the Joint Effects of

Variation of Conductivity and Excitability by Polarising Current

employed to induce polarisation, the anode being in the first

case to the left.

Fic. 353. Photographic Record of Response
under the Arrangements given in Figs. 351,
352 in Nerve of Fern

a, Balanced record before passage of polarising
current.

4, Resultant response downwards when polar-
ising current is from left to right, as shown
by arrow —. This shows excitability of
FE’ and conductivity in direction SE’ to be
relatively enhanced.

c, Resultant response upwards when polarising
current is from right to left <. This
shows excitability of E and conductivity in
direction SE to be relatively enhanced.

Here we have a greater excitability induced

at E’ by the proximity
of the anode, that of E
being depressed by the
proximity of kathode.
Of the two waves of ex-
citation, moreover, which
proceed in opposite di-
rections from the stimu-
lator S, that towards E’
is moving electrically
uphill, or towards the
anode, and owing to
increased conductivity
in that direction the
excitation is better con-
ducted than in the case
of the second wave,
which is _ proceeding
electrically downhill to-
wards the kathode at
E. It must also be

remembered that not only is the intensity of excitation
which reaches E’ greater than that which reaches E, but also
that the point E’ is itself rendered more excitable by the

ELECTROTONUS 573

contiguity of the anode, while E is depressed by that of the
kathode. Hence, by the concordant action, at each end of
the balance, of conductivity and excitability changes, and
owing to the opposite nature of these changes at opposite
ends, the original balance is disturbed, and we obtain
resultant down responses, showing the greater excitation and
galvanometric negativity caused at E’ than at E, when anode
is to the left and kathode to the right. This is exhibited in
the first pair of down responses in figure 353 4. When,
however, the polarisation current is reversed (fig. 352), the
excitation at the right-hand side, E being now near the anode,
is relatively the greater, and we find the resultant responses
to be upwards, as seen in the third record in fig. 353. To
go back to the question of the relative directions of electro-
tonic and responsive currents, we find in that case, when
the anode is to the left, that E’ is galvanometrically positive,
while the excitatory change makes it galvanometrically
negative. This means that the excitatory response takes
place by the so-called polarisation decrement. When the
anode again is to the right, the galvanometrically positive E
tends by excitation to become galvanometrically negative.
This will be clearly understood from the arrows which
accompany the diagram, in figs. 351, 352. The inner and thin
arrows represent the direction of the polarising current, and
the thick outer arrows the responsive current. These results
are tantamount to an example of the so-called polarisation-
decrement. In order to show, however, that the. same
excitatory reaction might appear as a polarisation-increment,
I shall describe another experiment.

The experimental tissue is here the isolated nerve of fern,
and the method employed is again that of the Conductivity
Balance. In this case, however, it will be noticed (figs. 354,
355), that the galvanometer is included in series with the
polarising E.M.F., instead of being placed as a shunt, as in the
lastcase. The stimulator was first adjusted at halance. The
left electrode was now made kathode, the right being anode,
the E.M.F. employed being °2 volt (fig. 354). On account

574 COMPARATIVE ELECTRO-PHYSIOLOGY

of the increased excitability of A at the anode, and also
of the greater intensity of excitation conducted towards it,
the balance was disturbed, and the resultant response ‘took
place by the enhanced galvanometric negativity of that
point. The responsive current thus constituted an increment
of the polarisation-current, as seen from the arrows; of which
the thin inner represents the polarisation and the thick outer
the responsive current. On now reversing the current again;
the right-hand end being made anode and more excitable,
the resultant response was found to take place by the
enhanced negativity of that point, thus again constituting
a polarisation increment (fig. 355). I give here two different

Fic. 354. T'IG. 355.
Figs. 354, 355. - Experimental Arrangements for Showing so-called
Polarisation-increment by the Joint Effect of Increased Excitability
at Anode and Enhanced Conduction of Excitation electrically Uphill

sets of photographic records, obtained with the nerves of
fern and frog respectively. Balance was first obtained at
the beginning of the record, but on the passage of the
polarisation current, this balance was found to be disturbed.
When the right end of the balance was made anode, the
resultant response on excitation was up, demonstrating the
enhanced excitability of the anodic point. When the right-
hand end, however, was made kathode, the balance was
upset in the opposite direction, that is to say, down, showing
that the left-hand anodic point was now the more excitable.
Fig. 356 gives a record of these responses as obtained from
the nerve of fern, and fig. 357 from the nerve of frog. The
responsive currents in these cases, it should be noted, are in
the same direction as the polarising current.

ELECTROTONUS - 575

On referring to the experiments on polarisation increment
and decrement which have just been described it will be noticed
that the excitatory reaction is the same in both cases, taking
place by the enhanced galvanometric negativity of the more
excitable anodic point. The seeming difference in the
electrotonic variation in the two cases lies simply in the fact
of the different dispositions of the galvanometer. This
occupied, in the first case, the position of a shunt in the
polarisation-circuit, while in the second it was placed in
series.

From the investigations which have been described, we
shall now find ourselves in a position to explain the various

FIG. 356. FIG. 357.

Fic. 356. Photographic Record of Responses in Nerve of Fern, under
Anodic and Kathodic Action, as described in Figs. 354 and 355.
The upsetting of the balance is upwards, when the right-hand end of
the balance is made anode, proving the enhanced excitability thus
induced. Resultant response downwards when the right-hand end of
the balance is made kathode.

Fic. 357. Photographic Record of Similar Effects in Nerve of Frog.

experiments of Hermann and Bernstein, and to show that
these, although apparently conflicting, are really mutually
consistent. First, then, to take Hermann’s experiment, and
referring back to figs. 341 and 342, in which the galvanometer
is placed in series in the polarisation-circuit, we find this to
be an instance in which we have to deal almost exclusively
with the effect of anode and kathode on excitability.
Simultaneous excitation of the anodic and kathodic points
by alternating induction currents, induces greater excitation,
and consequent enhanced negativity of A. The responsive

576 COMPARATIVE ELECTRO-PHYSIOLOGY

current, being thus concordant with the electrotonic current,
causes an increase of it, the so-called polarisation-increment.
In Bernstein’s experiment on polarisation-decrement, we
are confronted with a question of greater complexity, for
here we have to deal with changes of conductivity and
excitability at the same time. We shall first take the -case
(fig. 339) in which one electrode of the led-off circuit E is
under kat-electrotonus. EE’ is therefore relatively anodal,
and consequently more excitable. The excitation from the
stimulator S which reaches E’ is in this case impeded in
reaching E by the fact that it has to travel electrically
downhill—that is, from the anodal E’ to kathodal E. Thus,
owing to the greater excitation which reaches E’, and owing
also to the greater excitability induced in it by the fact that
it is relatively anode, excitation induces a relatively greater
galvanometric negativity of that point. The thick arrow in
the figure indicates the excitatory current, which is opposite
in direction to the polarisation current, which latter is
indicated by the thin arrow. In the second case, when the
polarisation current is reversed (fig. 340), E is anodal, and
_ therefore relatively more excitable, and E’ kathodal, and there-
fore less excitable. Unlike the last case, the excitation from
s, in order to reach FE, has now to travel electrically uphill
from the kathodal to the anodal points. The excitation of E
therefore is in this case not impeded. Hence greater excit-
ability of E makes that point, on stimulation, galvanometrically
negative, and the responsive current, represented by a thick
arrow, brings about a diminution of the polarisation-current.
It has thus been shown, in the course of the present
chapter, that the same electrotonic effects are exhibited in
the case of the plant, as in that of animal, nerves. It has
been shown that various apparently anomalous results may
be brought about by simple combinations of two different
factors. Thus, the so-called polarisation increment and
decrement are not mutually conflicting. They are, on the
contrary, due to the distinct and definite effects induced by
electrotonus on conductivity and excitability respectively,

ELECTROTONUS SGe-

As regards conductivity, it has been shown that excitation
travels best in the direction electrically uphill—that is to say,
from a place of low to one of high electric potential. In
consequence of this fact a moderate excitation becomes
enhanced when travelling from the kathodic to the anodic
region. Conductivity is depressed, on the other hand, from
anode to kathode. An excitatory impulse is thus retarded
in travelling electrically down-hill. For these reasons, a
normal negative excitatory effect may, during transmission,
undergo either diminution of intensity, or actual reversal to
positive.

With reference, again, to electrotonic variations of excita-
bility, we have seen that under feeble E.M.F. it is the anode
that exalts, and the kathode that depresses. This conclusion.
is obviously opposed to the generalisation known as Pfliiger’s
Law, the extent of the applicability of which will be discussed
in detail in the following chapter.

P,P

CAP LER
INADEQUACY OF PFLUGER’S LAW

Reversal of Pfliiger’s Law under high E.M.F.—Similar reversals under feeble
E.M.F.—Investigation by responsive sensation—Experiments on _ living
wounds—Under moderate E. M.F., intensity of sensation enhanced at kathode,
and depressed at anode—Under feeble E.M.F., sensation intensified at anode
and depressed at kathode—Application of electrical currents in medical
practice.

IN studying polar variations of excitability in nerves, in
the last chapter, we found that, during the passage of the
current, it was the anode which enhanced excitability and
the kathode which induced depression. Now this conclusion,
as will be remembered, is directly opposed to what is known as
Pfliigers Law, the universal applicability of which has
hitherto been regarded as beyond dispute. Pfliiger’s Law
lays it down that the kathode excites at make, and the anode
at break; and that, moreover, during the passage of a
constant current, excitability is raised at or near the kathode,
and depressed at or near the anode. We are next, then, led
to inquire: Under what conditions is this law applicable, and
when does it fail to hold good? Now, as regards the effects
at make and break, I have shown elsewhere, in the course of
experiments on plants, that these are not determined by
anode and kathode alone, but also by the intensity of the
acting electro-motive force. Thus, in the case of the sensitive
Biophytum, in a given experiment it was found that, using the
moderately strong E.M.F. of 24 volts, the excitatory wave at
make was found to be initiated at kathode, and to travel in
both directions, causing depression of nine pairs of leaflets.
The forward half of this wave of excitation, stopped only at

i i as

ET A A
_
' Sn
. —————
ST

INADEQUACY OF PFLUGER’S LAW 579

one pair of leaflets before the anode. There was no action
at the anode itself at make. After a suitable interval, during
which the leaflets re-erected themselves, the current was
interrupted. There was now no action near the kathode at
break; but excitation was induced at the anode, as was
shown by the fall of three pairs of leaflets in its vicinity (fig. 358),
The experiment was now repeated by reversing the direction
of the current. The poles being thus reversed, eight pairs of
leaflets fell at the new kathode, in and out. There was no
effect, however, at the new anode at make. But at break,
excitatory reaction was _ ini-
tiated at the anode, and none
at the kathode.

These are the normal
effects, falling under Pfliiger’s
Law, which holds good within
a certain medium range of
E.M.F. But when the E.M.F.
is much higher, I find that
these normal effects become Fic. 358. Make-kathode and Break-

reversed. Thus, employing anode Effects in Bzophytum
EMF. of lts-j Upper figure shows effect at make,
an i.M.I'. Of 220 volts, it was excitation being produced at
found that excitation took kathode. Lower figure shows
effect at break, excitation being
place at the anode at make, now produced at anode.

the excitatory depression of |

the leaflets passing slowly thence towards the kathode. At
break, excitatory action was initiated at the kathode, the
wave of excitation then passing towards the anode. I thus
found, by the employment of a very high E.M.F., that the
normal polar effects were completely reversed. Intermediate
between these two extremes of normal and reversed action,
I obtained a transitional phase, in which both anode and
kathode were seen to excite at make. At break also there
was here occasional excitation, at either anode or kathode.
Similar reversals and transitional effects have also been
noticed, in the case of certain protozoa by Kiihne and

Verworn. Thus Pelomyxa is excited by the anode at make,
PP2

580 COMPARATIVE ELECTRO-PHYSIOLOGY

and by the kathode at break. Actinospherium, again, shows
excitation on make, at both anode and kathode, and on break
at the kathode only.

Having thus demonstrated the fact that an excessively
strong E.M.F. induces a reversal of the normal polar effects,
it may not appear improbable that there should be a similar
reversal of these effects when the intensity of E.M.F. is
varied in the opposite direction, that is to say, when it is |
very weak. I have already drawn attention, in many places,
to the importance of this factor of intensity in determining
the excitatory effect of a stimulating agent. A chemical
reagent, for instance, when administered in moderate or very
dilute doses, will induce one effect, say that of exaltation,
and, in greater quantities, the very opposite, or depression.
A poisonous reagent, again, which usually induces depression,
will, if given in sufficiently minute quantities, have the effect
of exaltation. These reversals, under varying intensities of
the external agent, are noticeable again in different physico-
chemical phenomena. Thus it is well known that in the
formation of the photographic image, while a moderate
_ intensity of light gives us the normal ‘negative,’ a stronger
intensity will produce a ‘ positive,’ and a still more intense
light, bring about a re-reversal. We may thus have a series
of recurrent reversals.

- Returning, then, to the question of polar action on
excitability, we find that the typical results of Pfliiger with
nerve and muscle preparations, were obtained when using
a moderately strong E.M.F. In this, which is sometimes
distinguished as the third stage, excitatory contraction of the
muscle is induced, only on the closure of the descending
current, or opening of the ascending. In the former case,
the kathode is nearest the muscle, and as there is no inter-
mediate block the excitation is clearly due to the make-action
of the kathode. In the second case, similarly, the break of
the anode, which is now near the muscle, causes excitation.
With very weak E.M.F., however—that is to say, in his first
stage—Pfliiger found that excitation took place by the make

INADEQUACY OF PFLUGER’S LAW 581

of both ascending and descending currents, but not at the
break of either. Extending the clear inference of the
previous case to cover this, it was supposed that here, too,
the kathode—at one time near to, and at another far from, the
responding muscle—excited at make. But this is not so
conclusive, since the anode might equally well be regarded
here as causing the excitation at make. Indeed this
supposition that a very weak anode might cause excitation
at make derives some support from Heidenhain’s experi-
ments. For, using a weak E.M.F., he found make-excitation
to occur in the first stage only, when the current was
ascending—that is to say, when the anode was near the
responding muscle. This result would tend to show that
there was a possibility of the reversal of normal polar effects
when thé acting E.M.F. was weak. With regard to this
particular effect of minimal currents, there are considerable
differences of opinion. The obtaining of such an effect is
probably only possible when the nerve-muscle preparation is
in an exceptionally favourable condition of excitability, a
state of things not always possible to secure in the isolated
specimen. It therefore occurred to me that the effect of
a feeble anode in enhancing excitability might be demon-
strated conclusively in the case of the vigorous intact animal.
With this consideration in view, I carried out a number of
experiments on certain of my students and myself.

If we make a slight wound, say one square cm. in area, on
the back of the hand, and apply a solution of salt, which is
not too strong, a constant sensation is induced which cannot
be called painful, but may best be described as smarting or
irritating. If now we apply one non-polarisable electrode
on this wound, and the other on a distant and indifferent
point, then, on applying an E.M.F. to the circuit, charac-
teristic variations of sensation will be induced, depending
on whether the wound-spot is made anode or kathode
(fig. 359). Employing an E.M.F. of 2 volts, it will be found
that when the spot is made kathode, the sensation, which
was previously one of mere general irritation, becomes

582 COMPARATIVE ELECTRO-PHYSIOLOGY

intensely painful. This is because the kathode, at make and
during its continuation, induces an enhancement of the excit-
ability of the wound-spot. On the cessation of the current,
the painful sensation disappears, and the normal smarting is
restored. The wound-spot was next made anode, with

Fic. 359. Effect of Anode and Kathode on ROSES Sensation
in Human Hand

By means of reversing key, R, E in connection with the esha: -spot may be
made anode, and E' kathode, and wice versa. By alternately pressing
the keys, K’ and kK, feeble or moderately strong E.M.F. may be em-

ployed.
the same E.M.F. as before. The sensation now experienced
was one of soothing, the sense of smarting irritation having
disappeared. On the stoppage of this current the original
irritation was again restored.

In these experiments we have typical instances of the
kathode inducing increase of excitability, and the anode

INADEQUACY OF PFLUGER’S LAW 583.

depressing it, during the continuation of the current, a
verification, by means of responsive sensations, of Pfliiger’s
Law. Having thus, with moderate E.M.F. obtained the
excitatory effect at kathode, and depressing effect at the
anode, by means of the contrasted sensations of intense
irritation and soothing, I was next desirous of seeing
whether, with low E.M.F., these effects would be reversed.
I therefore undertook investigations on a dozen different
individuals, to determine the effect of anode and kathode,
as the E.M.F. was gradually increased from *3 to 2 volts.
It should be mentioned here that the subjects of the
experiments were totally ignorant of the object of the
investigations, and were simply asked to describe their
sensations at different points. Their ages varied from
eighteen to twenty-five. As the critical point may undergo
some variation with the season, it may be worth while also
to mention that the experiments were carried out in
summer, in the month of August.
The following case may be taken as typical :

PoLAR EFFECTS OF E.M.F. oF VARIOUS INTENSITIES ON RESPONSIVE

SENSATION
Acting E.M.F. | Effect on wound-spot when kathode Effect on wound-spot when anode
*3 volt Slightly soothing Marked increase of irritation
So _ Slightly soothing Marked increase of irritation
os eee Increase of irritation Indifferent
ES 155 Increase of irritation Slightly soothing
2°0 volts Painful Soothing

It will thus be seen that the kathode, which, at the
moderately intense E.M.F. of 2 volts, induced a painful
sensation, owing to the increase of excitability, induced the
very opposite effect of depressing excitability at the low
E.M.F. of -3 volt. Precisely the reverse, moreover, was the
case with the anode. Here, with ‘3 volt, excitability was
found to be enhanced, causing increase of irritation, while,
with the moderately strong E.M.F. of 2 volts, it induced the
opposite effect of soothing, by depression of excitability.

584 COMPARATIVE ELECTRO-PHYSIOLOGY

The critical point of reversal would in this instance appear
to be slightly below 1 volt, in the case of the kathode, while
in that of the anode, it was at 1 volt, or slightly above. The
effect observed at the extreme points were the same in all
cases. Individual differences were concerned only with the
exact point of reversal. Thus the point of reversal for the
kathode varied in different cases between ‘6 and 1 volt;
whereas with the anode it varied from 1 to 1°5 volt. Ina.
subsequent chapter, this phenomenon of reversal of sensation
under varying intensities of E.M.F., when other forms ot
stimulus are applied, will be studied in more detail. It may
be stated here, however, that though the critical point of
reversal varies to some extent with different individuals, and
under different forms of stimulation, yet the law holds good
that the excitatory effects induced by moderate E.M.F. are
exactly reversed under feeble.

The main results regarding this opposition of the effects
of feeble and strong E.M.F. may be still better demonstrated
by the method of successive contrasts. In the last experi-
ments, a long course of observations on the same individual,

would be liable to fatigue the tissue. Moreover, the fine
gradation of the changes induced is not calculated to exhibit
the contrasts involved in their full intensity. Having, then,
determined, from the previous experiments, that an E.M.F.
of ‘5 volt and another of 2 volts were opposed in their
excitatory effects, I now made special arrangements for
applying these two intensities of E.M.F. alternately. For
this purpose, I arranged a potentiometer which gave an
E.M.F. of 2 volts between L and N (fig. 359), and of
‘5 volt between Land M. The end, L, was connected with
the wound-spot by means of a non-polarisable electrode.
A distant indifferent point, say on the surface of the finger,
was connected with a double key KK’. When kK’ was
pressed, ‘5 volt was applied, and when K, 2 volts. Further,
by means of a reversing-key, P, the wound-spot could be
made either anode or kathode at will. In this way, first
making the wound-spot anode, I applied alternately the

INADEQUACY OF PFLUGER’S LAW 585 __

E.M.F. of ‘5 and of 2 volts respectively. The lower voltage
now gave rise to intense excitatory pain. On the cessation
of the current the normal smarting sensation, due to salt,
was restored, and on now applying 2 volts, this slight
irritation was superseded by a sensation of soothing. This
result was found to be repeated many different times.

The kathodic effect was next put to the test, and found
to induce responsive sensations exactly the reverse. The
application of *5 volt caused a soothing sensation, due to
depression of excitability. An E.M.F. of 2 volts, on the
other hand, induced an increase of excitability, with con-
sequent pain. |

These results are shown in the following table :

METHOD OF SUCCESSIVE CONTRASTS TO SHOW REVERSAL OF SENSATION
UNDER POLAR CURRENTS

Wound-spot anode Wound-spot kathode
E.M.F. ‘5 volt _ E.M.F. 2 volts E.M.F. of ‘5 volt E.M.F. of 2 volt
Intense pain Soothing Soothing Painful

From these experiments, then, it will be seen that during
the passage of the current, and when the E.M.F. is low, it
is the anode which increases the excitability, and the
kathode which depresses. Pfliiger’s Law is thus seen not
to be universally applicable, but to be true only within
certain limits, the very reverse of this law holding good, in
the case of excessively high, and in that of low E.M.F.
The demonstration which has just been given of the latter
of these two facts, is independently borne out by the results
of electrotonic variations of excitability in nerves, described
in the last chapter, where we saw that, with moderately
feeble E.M.F., excitability was enhanced by the anode and
depressed by the kathode.

It will thus be seen that polar variations ot excitability
are not always the same, but differ in character, according as
the intensity of the acting E.M.F. is moderate or low. The
great significance of this fact is apparent, with regard to the

586 COMPARATIVE ELECTRO-PHYSIOLOGY

medical application of electricity, since the failure to recog-
nise that reversal of effects which is to be expected under a
feeble E.M.F. might here lead to a result the very opposite
of that intended.

It has thus been shown that Pfliiger’s Law of the Polar
Variation of Excitability is not universally applicable. It
fails when the E.M.F. is either too high or too low, the
effects observed under these circumstances being precisely.
the opposite of those enunciated by Pfliiger. Under a low
E.M.F. then, it is the anode which enhances the excitability,
depression being induced by the kathode. This important
fact, and the further fact that with low E.M F. conductivity
is increased in the direction of the rising electrical potential,
and depressed in that of the falling potential, will be found
to explain all the varied electrotonic phenomena of nerves
described in the previous chapter.

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CHAPTER XLI

THE MOLECULAR THEORY OF EXCITATION AND ITS
TRANSMISSION

Two opposite responsive manifestations, negative and positive—Such opposite re-
sponses induced by polar effects of currents of different signs—Arbitrary nature
of term ‘excitatory ’—Pro-excitatory and anti-excitatory agents—Molecular
distortion under magnetisation in magnetic substances—Different forms of re-
sponse under magnetic stimulation—Mechanical, magneto-metric, and electro-
motive responses— Uniform magnetic responses—Response exhibiting periodic
groupings—Ineffective stimulus made effective by repetition—Response by
resistivity-variation—Molecular model—Response of inorganic substance to
electric radiation—Effect of rise of temperature in hastening period of re-
covery and diminishing amplitude of response—Sign of response reversed under
feeble stimulation—Conduction of magnetic excitation—The Magnetic Con-

- ductivity Balance—Effect of A-tonus and K-tonus, on excitability and con-
ductivity— Conducting path fashioned by stimulus—Transmission of excitation

temporarily blocked in iron wire, as in conducting nerve—Artificial nerve-
and-muscle preparation,

IT is admitted that the excitation of living tissues is brought
about by some kind of molecular disturbance, and that the
passage of this molecular disturbance from point to point zs
the transmission of excitation. As we do not possess the
power of molecular vision we have perforce to be contented
with the vagueness of the ideas which these terms connote,
complicated as they are by the concomitance of other
apparently mysterious properties of living tissues. If re-
sponse and its variations, however, be in truth mainly de-
pendent on the molecular condition of the tissue and its
upset, then, from molecular considerations alone, it must
be possible to explain why, under certain conditions, the
responding substance is increased in excitability, and under
others depressed. It has hitherto been found impossible to
determine what is the nature of the antecedent molecular

588 COMPARATIVE ELECTRO-PHYSIOLOGY

conditions to which these differences may be due: what it
is that so determines the Zone, that the excitability of a tissue
is made to undergo a profound change during the action of
a particular stimulus or on its cessation; and what finally
causes the fact that one identical stimulus, say that of
tetanising shocks, will sometimes act to exalt, and at others
to depress, the excitability of the same tissue. It is the
caprice which has seemed to preside over these phenomena.
that has forced observers upon the postulation of a hyper-
physical ‘vital force. In the course of the present work,
however, it has been shown that not only the simple pheno-
mena of response, but all their complex variations also, are
to be met with in the inorganic as in living matter, and that
their explanation, therefore, must be sought for in the nature
of antecedent molecular changes. As in the inorganic, the
conditions of investigation are less complex than in living
tissues, it follows that the study of molecular transformations
and their after-effects there, is likely to throw much light
upon that phenomenon of response which we have thus seen
to be universal.
| Taking first the response of living tissues, we find that
the responsive change is of two kinds. This may be illus-
trated by the following experiment, carried out on the
pulvinus of Erythrina indica during the season of its greatest
sensitiveness. The stimulus employed was that of a con-
stant electrical current. When the upper half of the pul-
vinus was made anode, response was found to take place by
local expansion. This is seen in the up-record of figure 360.
On the break of the anode, we observe a movement of
recovery in the opposite direction. The pulvinus was next
subjected to kathode-make, and we observe a_ responsive
contraction. At kathode-break, however, we have a recovery
by expansion. We have thus observed two opposite re-
sponsive effects, according to the different polarities of the
stimulating agent—namely, expansion at the make of anode,
and contraction at that of kathode.
Since responsive effects must be due to molecular upset,

THE MOLECULAR THEORY OF EXCITATION 589

or to new conditions of alignment, it is clear that contraction
must be brought about by a one-directioned, and expansion
by the opposite-directioned, change. This is evident in the
present case, since the polar stimulating agents are opposite
in their characters, and the opposition of their effects must
correspond to this. Now it is necessary to distinguish these
two responsive effects by opposite terms, which must needs
be somewhat arbitrary.
The contractile effect has
thus been taken as the
normal excitatory and
negative. Having once
adopted such a nomencla-
ture, it is of course im-
portant that it should be
strictly adhered to. Thus,
if contraction be the nor-
mal response, then any-

thing which tends to Up-curve represents expansion and con-
vexity. Down-curve represents con-

traction and concavity. Continuous
curve represents the action at make.

Fic. 360. Polar Effects of Currents due
to Localised Application on Upper
Half of Pulvinus of Zryihrina indica

enhance it must be re-

garded as excitatory, and
anything which opposes or
retards it as depressing.

The dotted curve shows the effect at
break. Am = convexity induced at
anode-make. Ad = responsive con-

cavity at anode-break. Km =induced
concavity at kathode-make. Ké =
expansion induced at kathode-break.
The time-marks represent minutes.

This word ‘depressing’ is,
however, unfortunate, since
by it might be indicated a
permanent depreciation of the tissue, while diminution of
the normal response is possible without such depreciation.
Moderate rise of temperature, for example, with its
expansive tendency, will lessen the contractile response
without necessarily depreciating the tissue (p. 187). Revert-
ing once more to the kathodic mode of stimulation, we
know that a certain intensity of kathode is necessary, for
the visible initiation of contractile response.’ Should the
intensity employed be just short of this, there will be an

1 These kathodic and anodic effects refer to the normal moderate range of
E.M.F, within which Pfliiger’s Law is applicable.

590 COMPARATIVE ELECTRO-PHYSIOLOGY

incipient molecular distortion, in the same direction as that
which precipitates the excitatory response, hence kat-electro-
tonus should prove to be excitatory. But a moderate
anode, with its incipient molecular distortion in the opposite
direction, will retard the normal response, and thus appear
to be depressory. I must here point out that these terms
excitatory and depressing have ordinarily speaking no ab-

solute meaning, and can only acquire a definite significance

when we have first fixed on that form of response which is
to be regarded as normal. If, instead of contraction, we had
regarded expansion as the normal response, then the effect
of anode would have been regarded as excitatory, and that
of kathode as depressing. We must therefore recognise that
the very fact of contractile response being taken as excita-
tory, entails as a consequence the designation of all agencies,
such as K-tonus, which predispose the tissue to contraction,
-as excitatory, or better pro-excitatory, while those which, like
an-electrotonus, oppose this, must be regarded as depressory,
or better anti-excitatory.

From what has been said, it will be understood that it is
the direction of the molecular derangement which determines
‘the character of the response. That molecular upset, which
expresses itself as excitatory contraction, we may call the
K-effect, and the reversed molecular movement, expressed
as expansion, the A-effect. ‘Thus, under anode, in fig. 360,
the molecular distortion in one direction induces the expan-
sive A-effect. On the cessation of this, the rebound of
recovery causes a movement in the opposite direction, which
may carry the molecules back, not merely as far as the
equilibrium position, but beyond this. This movement,
however, is in the same direction as that induced by K-make.
Hence we may understand how excitation is caused, not only
by K-make, but also by strong A-break. We may also
understand how it is that the excitatory effect is much

enhanced when A-break is immediately followed by K-make.

We also see, in a general way, that a particular-directioned
molecular movement would have the most intense excitatory

Ss

RO —— I enaataetiiar otal
Se al ea

THE MOLECULAR THEORY OF EXCITATION 591

value when the molecular distortion was proceeding at a
rapid rate, and not so much when a condition of permanent
distortion had been attained. It is for this reason that,
usually speaking, the excitatory effect is most pronounced
at either kathode-made or anode-break,! and not so much
during the continuation of kathodic action.

To recapitulate some of the principal facts enumerated
above, the term ‘excitatory’ being applied to a particular-
directioned distortion or K-effect, then anything which
induces an incipient molecular distortion in the same direc-
tion, tending to aid the K-effect, and therefore to enhance
that response, will be known as K-tonus. Anything, on the
other hand, which induces an incipient distortion in the
opposite direction, will oppose or retard the normal K-effect,
and will, therefore, be known as inducing A-tonus.

In the examples given, the opposite K- or A-effects -
observed were the outward manifestations of the aggregate
molecular effects induced. And from these we inferred the
opposite-directioned changes which must have been their
antecedent cause. In working with inorganic substances,
however, and particularly in dealing with magnetic bodies,
our power of molecular scrutiny is much keener. A rod of
iron, for example, is known to consist of magnetic particles,
each one of which is-a true magnet, possessed of polar
properties. Under ordinary circumstances these magnetic
molecules are in close chains, but under the action of
magnetising forces they become distorted in a directive
manner. Under north-magnetising force they are distorted
in one direction, and under south polar induction in the
reverse. The intensity of the induced magnetisation is a
measure of the degree of molecular distortion, and can be
gauged by the deflection of the freely suspended needle of a
magnetometer in the neighbourhood. Increasing magnetising
force is thus seen to induce greater magnetometric deflections,

! It is conceivable that there should be occasions in which the final condition
of distortion is not attained quickly, but slowly ; or where it is Huctuating instead

of stable. Under such circumstances the excitation induced would be more or
less persistent or tetanic.

592 COMPARATIVE ELECTRO-PHYSIOLOGY

and on the cessation of the inducing force there is usually a
molecular recovery, with a concomitant return of the magneto-
metric indicator to its original position.

Here, then, we have a means of recording the molecular
distortions induced in a substance under a given external
force. We are able also to study the relation between the
acting force and the distortion induced, while it is increased
or diminished in a known manner. And further, keeping
the acting force the same, we are here able to study the
effects of various modifying agents on the response, as
recorded by the magnetometer,

In all these cases, then, we have a strict parallel to the
excitatory molecular changes and their variations induced in
a living tissue under stimulus. But besides this local action
we have also, in the living tissue, nerves possessing the
property of transmitting the state of excitation—that is to
say, the molecular disturbance—to a distance ; and this trans-
mission is modified appropriately by the various modifica-
tions which may be induced in the conducting nerve. Simi-
larly I shall be able to show that, in an iron wire, excitatory
magnetic disturbance is propagated to a distance; this con-
duction likewise being modifiable by the molecular changes
induced in the conducting wire.

Thus, in those particular cases where molecular scrutiny
is possible, we are enabled to visualise with considerable
accuracy those molecular events on which excitation and its
transmission depend. Afterwards, discarding this illustrative
class of magnetic substances, I shall refer to other methods,
by which the responsive manifestations of ordinary substances
under stimulus, and the modifications of these responses
under various conditions, will be recorded. From so compre-
hensive a study we shall find that whatever be the mode ot
record, and whatever the experimental substance employed,
the fundamental reaction, and its variations under particular
conditions, are curiously similar. It will then be realised
that the response of living tissues is not alone of its own
kind, but falls under a wide generalisation,

THE MOLECULAR THEORY OF EXCITATION 593

But before proceeding further with the magnetic responses,
we must call to mind two different responsive manifestations
of living tissues. We have observed these under the polar
action of electric currents, one being the K- and the other the
A-effect. Similarly in magnetic substances also, under the
action of the magnetising forces, we observe two different
effects brought about by opposite polar changes. One of
these is the result of north and the other of south polar in-
duction ; and of these, for the sake of convenience, we shall
fix our attention on the effect induced by the north pole as
the normal negative or K-effect.

The fundamental molecular change induced may here,
as in the case of living tissues, be recorded in various ways.
In the present case, of the response of magnetic substances
under magnetic stimulation, the methods of record may be
classified as mechanical, magnetometric, and electro-motive.
Joule discovered that a rod of soft iron undergoes a change
of length on magnetisation. Though this variation is very
small, I find it comparatively easy to demonstrate and record
the responsive change concerned by means of the following
device. One end of the iron rod is fixed, and the free end,
carrying a wooden disc, rests on a tambour covered with
stretched indiarubber. The tambour chamber is closed
except at the point where a capillary tubing of glass enters
it. This tube contains a short index. On now suddenly
inducing magnetisation by a magnetising coil, the rod under-
goes instantaneous elongation, and the resulting expulsion
of air from the tambour causes a corresponding movement
of the index outwards. Cessation of the magnetising current
is attended by immediate recovery. It need only be men-
tioned here that by making the diameter of the tambour
sufficiently large, and that of the capillary tube sufficiently
small, and by optically magnifying the movement of the
index, it is easy to obtain for this mode of experiment a very
high degree of sensitiveness. 5

It is much easier, however, to record responsive molecular
changes by the usual magnetometric, or by the induction or

QQ

594. COMPARATIVE ELECTRO-PHYSIOLOGY

electro-motive method. According to the former of these,
the magnetising coil, C, is placed broadside on, in reference

Fic. 361. Experimental Arrangement

for Magnetometric Method of Record Fic. 362. Photographic

M, magnetometer ; C, magnetising coil ; Record of Uniform

B, balancing coil; A, ammeter; -R, Magnetic Responses
rheostat ; K, key actuated by metro- , of Iron

nome.

to a freely suspended magnetic needle with its attached

mirror (fig. 361).

Fic. 363. Photographic
Record of Periodic
Groupings in Mag-
netic Responses

A second balancing coil, B, is placed on

the other side, and so adjusted as to
nullify any disturbance of the needle
by the magnetising coil. The experi-
mental rod of iron is then introduced
inside C, and the responsive molecular
action induced by the exciting current
is recorded in the usual manner by the
deflected spot of light from the mag-
netometer, M, thrown on a revolving
drum. The intensity of the exciting
current, measured by the ammeter, 4,
is capable of adjustment by means of
the rheostat, R. The duration of appli-
cation of the exciting current is deter-

mined by a metronome, and thus kept uniform in successive
experiments. In fig. 362 is seen a series of records obtained
in this manner, employing stimulation of moderate intensity.
In fig. 363 is seen a curious instance of periodic groupings

THE MOLECULAR THEORY OF EXCITATION 595

in magnetic responses, similar to those obtained in living
tissues. In the next figure (fig. 364) is shown the effect of
strong stimulation, which gives rise to responses, not only
of greater amplitude, but also of prolonged recovery. Under
the strong stimulation here employed, owing to persistent
molecular strain, the recovery did not become complete.
This is analogous to the contracture in strongly excited
-muscle. Such persistent strain may be removed by miole-
cular vibration, the hastened recovery in the present record

4 being the result of a tap.
Magnetic stimuli, individually
ineffective, become effective
by repetition. In fig, 365 is

Fic. 364. Photographic Record or
Response and Recovery of Steel
under Moderate and Strong Mag-
netic Stimulus

First pair of records show response and

recovery under moderate stimulus. FIG. 365. spare sie ay Record
In the next two, stronger stimulus sabes: neffective Stimulus
induces response of greater ampli- made Effective by Repetition

tude and incomplete recovery.
Molecular vibration by tap, at point
marked by down-arrow |, hastens
recovery.

Asingle brief magnetic stimulation
induced little or no effect, but
when rapidly repeated thirty

times it became effective.
seen a record of this. Tetanisation also induces the maxi-
mum effect of fusion—as will be seen in the following chapter.
Tetanisation, again, induces interesting after-effects in mag-
netic responses, precisely the same as those seen in living
tissues. Under certain conditions, moreover, to be fully
described later, tetanisation, as we shall see, enhances the
subsequent responses, while under. other conditions, by in-
ducing fatigue, it brings about their depression.

I have already mentioned the fact that in addition to

QQ2

596 . COMPARATIVE ELECTRO-PHYSIOLOGY

the mechanical and magnetometric methods of studying
response in magnetic substances, there is also a third .means
available, in the Induction or Electro-motive Method, to be
fully described at the end of the present chapter.

I have now explained how the extent of molecular
distortion induced in a magnetic substance by an external
force can be gauged or measured by magnetometric or
electric indications. For the detection of similar changes,
however, in matter which is not pronouncedly magnetic, it
is necessary to devise a method of record of more universal
application. Such a method we have, as already said, in
the record by resistivity-variation. It is here desirable,
however, to give. a more detailed account of this and the
principle involved. | |

Our object being the detection of the molecular changes
induced by stimulus, let us briefly consider certain well-
known cases of molecular transformation induced by various
stimulating agencies. Thus, when sulphur is subjected for
a certain length of time to the action: of light, there is no
visible sign of any change. Its solubility in carbon
disulphide, however, has been altered, and we can dis-
criminate-the portions acted upon from those unacted, by
means of this ‘developing’ solution. But such discrimina-
tion is only possible when the molecular or allotropic
modification has gone so far as to be somewhat stable—that
is to say, when the after-effect of stimulus is persistent.
The development of any after-effect would have been
impossible had the substance in the meanwhile exhibited
self-recovery. Between the original condition A, again, and
the terminal modification D, the substance must have passed
through many gradations of condition, of a more or less
impermanent stability. This case is analogous to that of a
piece of iron under the action of magnetising forces, with
their consequent molecular modifications. When the acting
force is moderate, and the specimen has the power of self-
recovery, the induced molecular distortion—that is to say, the
induced ‘magnetisation—is fugitive, and there is no after-

THE MOLECULAR THEORY OF EXCITATION 597

effect on the cessation of the force. But, under intense
magnetisation, the molecular transformation is more or less
persistent, and we observe an after-effect in the induced
permanent magnetisation. To revert here to the illustration
of sulphur, it is only because the persistent terminal change
is the most easily distinguishable that we single it out for the
name of ‘allotropic change. As a matter of fact we see
that this is but the climax of a series of changes, and so
incomplete a view has been made current by the fact that
we had no means of recording the intermediate changes
while they were in progress.

The next question is as to the possibility of making such
records of molecular transformations, or of induced varia-
tions in the state of molecular aggregation, while they are
taking place. This may be accomplished, as I shall show,
by the concomitant variation of electrical conductivity. It
is to be borne in mind that the state of molecular aggrega-
- tion plays an important part in determining the conductivity
of a substance, and as an example we may take the case
of carbon, which exhibits wide differences of conductivity in
its two allotropic conditions of graphite and diamond. Let
us imagine a piece of carbon in an intermediate or neutral
state between these two. We-may suppose that an external
force distorts it to a small extent towards the more con-
ducting state of graphite. This distortion would be attended
by an increase of conductivity, from which latter the extent
of molecular distortion or upset involved might be inferred.
Now, during the distortion from the equilibrium position, a
force of restitution will tend to restore the carbon to its
original neutral condition. If the’ distortion does not
proceed beyond the elastic limit, then, on the cessation of
the external stimulus, it will recover its original state, and
this will be evidenced by the restoration of its original con-
ductivity. But if the distortion be of a sub-permanent or
permanent type, the recovery will be very much protracted,
or will not take place at all. Such more or less permanent
distortion, known as allotropic transformation due to stimulus

598 COMPARATIVE ELECTRO-PHYSIOLOGY

of light, is seen in the production of red phosphorus from the
yellow variety, and the insoluble from the soluble variety of
sulphur.

It will thus be seen that the conductive aspect of a given
substance is not definite, but variable, the conductivity being
dependent on the particular molecular condition of the sub-
stance. This peculiarity may be represented in the accom-
panying model (fig. 366), if we give the cylinder representing
the sensitive molecule three main-conducting aspects A B C.
The non-conducting aspect is represented by c. With the
sensitive substance in this
particular condition, inter-
posed in the electric circuit,
the current in the galvano-
meter would be zero. A is
the semi-conducting aspect
of the substance, under
which we may imagine the
corresponding deflection of
the galvanometer to be 50.
B is the highly conducting
aspect, the corresponding
galvanometer reading being
100.

Fic. 366. Molecular Model The model representing

the sensitive substance has
its surface divided into six parts, the opposite sextants being
put in electric communication. The opposite sextants CC
are coated with shellac to represent the non-conducting
aspect ; the sextants AA are coated with graphite to repre-
sent the semi-conducting aspect; and the highly conducting
aspect is represented by the sextants BB coated with tinfoil.
The three main aspects of the sensitive substance are thus
represented in the model; it is to be understood that with
sensitive substances, under the action of stimulus, the transi-
tion from one aspect to the next is gradual, and not abrupt,
as represented. ‘The sensitive substance is interposed between

THE MOLECULAR THEORY OF EXCITATION 599 —

two electrodes. The torsion of the wire by which the
cylinder is suspended represents the force of restitution.
The galvanometer coil, by its deflections, exhibits indirectly
the molecular strain produced in the substance by the action
of stimulus.

Let us suppose that we start with the substance in its
normal state A, with moderate conductivity, and let the corre-
sponding galvanometer deflection be 50. Let the substance
belong to the negative class which exhibits an increase of
conductivity, or diminution of resistance, under the action of
stimulus. The stimulus will therefore distort the substance
to a state of increased conductivity, the increased conductive
aspect BB being brought opposite the electrodes. The
enhanced current thus produced causes a deflection of,
say, 100 in the galvanometer. If the strain has not been
excessive, the substance will return, on the cessation of
stimulus, to its original position of equilibrium, and the
galvanometer deflection will fall from 100 to the original
value 50. If the substance belong to the positive class, the
distortion will be in the opposite direction, and the effect
of stimulus will be to induce a responsive increase of
resistance.

The coil of the indicating galvanometer thus moves in
perfect response to the varying molecular strain induced in
the sensitive substance by the action of stimulus. The
invisible molecular distortions are thus revealed by the
visible deflections of the galvanometric indicator—the effect
on one is merely the reflection of the effect on the other.
A curve of the molecular effect, induced by the action of
stimulus, may thus be obtained with the galvanometer de-
flection as ordinate, and the time as abscissa. It is thus
seen that these response-curves faithfully represent the in-
visible molecular strain-effect due to the stimulus, and the
subsequent recovery. =

I shall now describe how in practice, by this method of
resistivity variation, we obtain responses of various sub-
stances to the stimulus of visible or invisible radiation. The

600 COMPARATIVE EILECTRO-PHYSIOLOGY

sensitive substance may be made the fourth arm of the
Wheatstone’s bridge, and the responsive galvanometric de-
flection and subsequent recovery of the spot of light—by
the upsetting of the balance, under the action of stimulus
of radiation—is recorded in the usual manner, on a moving
photographic plate. Or the sensitive substance may be
placed in series with a galvanometer, a small E.M.F. giving
a steady permanent deflection. Taking first selenium as the.
sensitive substance, the molecular change induced by the
action of light, with its concomitant variation of resistance,
causes a deflection of the galvanometer spot of light. On
the cessation of the stimulus, molecular recovery takes place,
and the deflected spot of light returns to its original position.
A series of such responses will be found on referring to
page 3, fig. 3. The parallel method employed in recording
the responsive resistivity varia-
tion of masses of metallic par-
ticles of various kinds, under
the stimulus of electric radia-
: tion, will be understood from
Fic. 367. Method of Resistivity "8+ 367. On obtaining records
Variation of the responses given under
Sensitive metallic particles placed in this method, I find, as I pointed
tube in series with galvanometer 5
and E.M.F. This gives a steady out in the first chapter, that
permanent deflection. Stimulus the responding substances are

‘of electric radiation induces a ;
responsive variation of resistance of two different types. The

with. concomitant variation of first, of which aluminium may
galvanometric deflection.
be taken as the example, re-
spond by diminution, or negative variation of resistance. The
second, illustrated by potassium or arsenic, respond by an in-
crease, or positive variation of resistance. In living tissues
also, tested by various modes of response, we have seen two
opposite types to occur—highly excitable nerve giving one,
say, negative, while skin, on the other hand, gave the positive.
In the case of the inorganic substances referred to, we
have extreme types, whose response is generally either
positive or negative. There are, however, intermediate

at ane a

THE MOLECULAR THEORY OF EXCITATION 601

cases, where it is liable to change of sign according as the
stimulus is feeble or strong. Certain substances, again,
cannot quickly recover from the after-effect of stimulus ;
while, in others, recovery is fairly rapid. Recovery from
intense stimulation is generally, other things being equal,
more protracted than from feeble or moderate. Anything,
however, which enhances molecular freedom or mobility will
tend to hasten recovery.

I shall now give several typical records in illustration
of the peculiarities of this form of response by resistivity
variation, under various conditions. The first example

Fic. 368. Photographic Record of Response of Aluminium Powder in
Sluggish.Condition to Stimulus of Electric-Radiation. .

The first two responses exhibit incomplete recovery, which becomes com-
plete on application of warmth. Note that warmth, increasing force
of recovery, hastens recovery and also diminishes amplitude of
response, as seen in the two succeeding records.

given, that of aluminium powder, will» be of the negative
type, the response being by diminution of resistance. When
the substance tested happens to be in a sluggish condition,
recovery is very protracted. There is then a _ response-
remainder of persistent negative variation, corresponding to
the contraction-remainder in muscle, or persistent electro-
motive negativity in other living tissues. But we know that
a moderate rise of temperature is favourable to recovery ;
and on applying gentle heat, at the end of the second
response, with its incomplete recovery, the persistent effect is
seen to be removed, and -there is an immediate completion of
recovery (fig. 368).

This is the place to refer once more to an apparent

602 COMPARATIVE ELECTRO-PHYSIOLOGY

anomaly, in the response of living tissues, where a slight rise
of temperature increases conductivity, at the same time that
it appears to diminish excitability, inasmuch as it brings
about a lessened amplitude of response (Chapter XV.).
This latter, however, may not really be due to diminution of
excitability, since the same effect might equally well be
brought about by an enhancement of the force of recovery.
This view is supported by the further records given in
fig. 368. We see here that incomplete recovery became
complete, under the application of gentle heat. The next
response given by this slightly warmed substance is seen to

Fic. 369. Photographic Record Showing Uniform Response of Alu-
miniun Powder to Uniform Stimulus of Electric Radiation.

show complete recovery within a relatively short time, this
enhanced force of recovery bringing about at the same time
a diminution in the height of response. The temperature of
the substance was now again raised to a slightly higher
degree, and the next response shows a still further diminished
height and a considerably quickened recovery. When a
substance is in a normal condition of excitability, its succes-
sive responses to uniform stimuli are found to exhibit com-
plete recovery, and to be of equal amplitude. Figure 369
shows such a series obtained with powdered aluminium.

We have seen that the increased molecular mobility con-
ferred by warming hastens recovery. A similar hastening of
recovery may be brought about by a mechanical tap, as has
already been shown (fig. 364) in the case of magnetic response.

THE MOLECULAR THEORY OF EXCITATION 603

In fig. 370 is seen an example of the same thing in tungsten,
where recovery from the effect of electric radiation is hastened
by a tap.

It has been shown that the normal response by negativity
in living tissues is liable to reversal under very feeble
stimulation. This is better observed when the tissue is
not highly excitable; because in this case it is easy to
adjust the intensity of stimulation, so as to fall below the
critical value for excitation.
It is very interesting to ob-
serve similar opposed effects,
under feeble and moderately
strong stimulations, in the re-
sponse of inorganic substances.
For the reason just mentioned,
it is desirable to select a sub-
stance for this purpose, which
possesses a moderate degree
of sensibility. Using a mass
of tungsten particles, I found
that under strong intensity
of electric radiation—-brought
about by placing the radiator
within a short distance of the Fic. 370. Photographic Record

of Response of Tungsten
substance—the response was ; :
The incomplete recovery is hastened

by the normal negative varia- by application of tap at points,
tion, or diminution of resist- marked with downward arrow.
Cf. fig. 364.

ance. But when the intensity
of stimulus was dimfnished by placing the radiator at a
greater distance, then the response was converted to positive.
A record of this abnormal effect under feeble stimulation will
be given later.

Thus, having observed molecular response and its varia-
tions by the Magnetic and Resistivity Methods of record, we
now proceed to study the transmission of the state of
excitation. We have seen that the essential condition of the
transmission of excitation in living tissues lies in the

604 COMPARATIVE ELECTRO-PHYSIOLOGY

propagation of molecular disturbance from point to point.
The characteristics of such propagation must be—(1) that the
transmitted molecular disturbance becomes enfeebled with
distance, so that at a certain point the transmitted excitation
would be reduced to zero; (2) that while a moderate
stimulus is transmitted to a short distance, a stronger
stimulus would be carried further ; and (3) that the intensity
of excitation transmitted would depend on the conducting
power of the intervening tract, this conductivity being
capable of enhancement by certain agencies, and depressible
by others.

I shall now proceed to show that in an iron wire a
transmission of molecular disturbance takes place which is

Fic. 371. Experimental Arrangement for obtaining Response in Iron by
Induction Current

similar to that at the basis of the transmission of excitatory
changes, both, as I shall show, being modifiable by similar
circumstances in a similar manner. For these investigations
I have employed the Induction or Electro-motive Method of
observation. In the experimental arrangement—a diagram-
matic representation of which is shown in fig. 371—S is
the stimulating or exciting coil appliéd at the point to be
excited. The conducting region intervenes between S and R,
which is the responding point, over which is wound the
receiving coil, placed in series with either a telephone or a
galvanometer. When the excitatory molecular disturbance
reaches R, it gives rise to an induction current in the coil,
which in turn causes a sound in the telephone, or a
responsive deflection in the galvanometer. For the purpose
of simplicity, we shall take north polar or K-excitation as

THE MOLECULAR THEORY OF EXCITATION 605

normal, and the resulting deflection of the galvanometer to
the right as the normal response. ~The direct effect of the
coil S on the coil R may be regarded as negligible, when
they are separated from each other by a sufficient distance,
and this would be even more true if the intervening iron wire
were bent at an angle of 90 degrees.

Employing this mode of obtaining records of response to
K- or.A-excitation, we meet with several curious analogies
to the responsive effects seen in living tissues, under the
electrical mode of stimulation. Electrical excitation of
nerve and muscle, for example, is most effective when it is
longitudinal, and ineffective when transverse. The same is
true of magnetic excitation of iron, where longitudinal
excitation is effectively transmitted to a great distance,
whereas transverse excitation is relatively ineffective.

Again, in the case of the electrical excitation of living
tissues, it is at the instant of kathode-make, as we have seen,
that excitation is induced. Continued action exhibits in

general no effect. The same normal excitatory effect seen

at kathode-make, is induced again, but at anode-break.
Similarly, in the case of an iron wire, the normal galvano-
metric response is seen at the moment of K-magnetic
excitation, but not during its continuance. The same
excitation is also obtained, at break of A, or south polar
magnetisation. .

We are led from such close analogies, not only to visualise,
but also to obtain some insight into the sequence of
molecular events which is the concomitant of excitation.
I have already pointed out that excitation and its opposite,
depression, being phenomena of molecular. distortion, it
is to be expected that a particular-directioned distortional
movement should be associated with one of these, and the
opposite with the other. We also know the further
suggestive fact that it is the sudden change of the environ-
ment, inducing a sudden responsive molecular disturbance,
that is most effective in bringing about excitation. The
latent period, and a slowly-rising excitation, correspond to the

606 COMPARATIVE ELECTRO-PHYSIOLOGY

slow initiation of the molecular upset. After this the rate of
molecular distortion will be rapid, and in this second period
we find that the excitatory reaction also is at its maximum.
In any case, it is rather during the period of increasing
molecular distortion that we should expect to see the
most intense excitation, than when a static condition of
derangement has been attained. Thus it is at the moment
of K-make that we obtain the excitatory indication, and not
afterwards, when the molecules are being maintained in the
distorted position. ,

Returning once more to the iron wire, we find that when
the distorted molecules have been set free by the break of kK,
there is a sudden movement of recovery in the opposite
direction. If now the K-effect, with its particular-directioned
molecular movement, be termed the excitatory, then the oppo-
site movement must be regarded as one of depression, and it
is interesting to note that in a living tissue there is an after-
effect of depression at kathode-break. The anode-make, on
the other hand, with its opposite molecular distortion, is, as
' one would expect, depressory. But at the break, the
direction of the rebound of the released molecules being the
same as that brought about by K-make, must be excitatory.
The close parallelism which we have thus traced out, forces
upon us the conclusion that the molecular actions which
underlie the excitation of living tissues may be-polar in their
character.

The fact that magnetic excitation undergoes diminution
during transmission, can be shown by moving the receiving
coil R further and further away from S, when the responsive
sound in the telephone, or deflection in the galvanometer, will
be found to undergo a graduated diminution, till, with a given
stimulus, the effect, from being considerable, is reduced at a
certain distance to zz/, Keeping this distance the same,
however, a stronger stimulus will be found efficient to evoke
response, and the responding coil will now have to be moved
further, in order again to reduce the response to zero.

We shall next study the variation of conductivity induced

-_. =

THE MOLECULAR THEORY OF EXCITATION 607

by an external agent, as. modifying the intensity of the
transmitted effect. In order to study the phenomenon of
conduction and its modification, as will be remembered, a
delicate form of Conductivity Balance, fully described in
Chapter XX XIII. was used. Excitation was here caused by
S at a middle point, the transmitted excitatory effects at E’
and E being made to balance, This condition of balance
was obtained when one arm, say the left E’, was kept at a
fixed distance from Ss, and the other, or right, was moved
towards S, or away from it, as required. When E was too far
from S the excitatory effect would be smaller than at E’, and
this under-balance would be indicated by a response, say
downwards. When, again, E was too near to S, there would
be an over-balance, the resultant response being upwards.
Between these could be found a point of exact balance
where the record was horizontal (cf figs. 289, 290).

A high degree of delicacy in the study of: similar
phenomena in the case of iron wires may be obtained by

Fic. 372. Magnetic Conductivity Balance

S, magnetising coil, by which north-polar or K-impulses are sent out in
two directions as shown by arrows. E BE’, receiving coils, adjusted
at balance. M, permanent magnet, by ,which either A- or K-tonus
is induced at the responding ends of the iron rod. T, tonic coil,
by which A- or K-tonic molecular dispositions may be induced in
one arm of the balance.

the employment of the Magnetic Conductivity Balance
(fig. 372), which I shall now describe. The magnetic
stimulator, S, consists of a pair of similar coils wound in
opposite directions, When a magnetising current is suddenly

608 COMPARATIVE ELECTRO-PHYSIOLOGY

sent through these two coils, in a proper direction, two equal
north-polar impulses will be generated simultaneously, and
travel, one to the right, towards E, and the other to the left,
towards E’. [n order to obtain a balance of the excitatory
effects at E and E’, we keep E’ at a fixed distance, and move
E backwards and forwards till the balance is found. This
process of balancing will be found graphically illustrated in
the records given in fig. 373. E was placed at first too near
to S, and the over-balance is seen as up-responses. The coil
was then moved away very gradually, and the response of
over-balance is seen at each step to undergo a diminution or
approach towards balance. We next note the attainment
of exact balance, where the record is seen to be horizontal.
The coil is now moved still further to the right, and the con-

Fic, 373. Process of Balancing illustrated by Photographic Record
| of Responses

sequent increasing under-balance is exhibited by the gradually
increasing reversed down-responses.

Having thus obtained balance, we are able to record the
variations induced in conductivity by a given agent. This
is applied on the right arm of the balance, the subsequent
upset of which, in one direction or the other, indicates the
enhancement or depression of conductivity. Resulting up-
responses will indicate enhancement, and down-responses
depression. A well-known agent for the enhancement or
depression of the conductivity of the nerve is the polar
action of the kathode and anode. Moderate kat-electro-
tonus enhances conductivity, whereas the anode depresses
or inhibits it. The explanation which I have already offered,
regarding anodic and kathodic effects on excitability, will
also. be found applicable in the case of conductivity. An
excitatory or kathodic effect will be facilitated in trans-

THE MOLECULAR THEORY OF EXCITATION 609

mission, if the molecules in its path are already incipiently
orientated, so that the incident stimulus finds them pre-
disposed to respond in that direction and to transmit the
excitation. Hence the kathodic effect is more easily trans-
mitted through a tract which is in a state of K-tonus,
whereas it is retarded or inhibited under A-tonus. We shall
now study the corresponding effect in magnetic conduction.
Normal excitation in these experiments, it should be remem-
bered, is taken as that which is brought about by the north-
polar or K-effect. If there is a tonic coil, T, surrounding one
arm of the balance, then, by sending a permanent current of
moderate intensity round the coil, in one direction or the
other, we may induce at will, in that arm, either K-tonus
or A-tonus. The molecular disposition induced by the
stimulus, and by K- and A-tonus respectively, will be under-
stood from the diagrammatic representation given in fig. 372.
Local variation of excitability at E may be induced by
bringing near to’it either the north
or south pole of a permanent
magnet M.

I shall now exhibit the enhance-
ment or depression of magnetic
conductivity by K- or A-tonus. A
balanced record is first obtained,

Fic, 374. Effect of K- and

and K-tonus then induced in the A-Tonus on Magnetic Con-
right arm. Successive K-make ex- duction
aes . . The first series exhibit by
citations are now applied, starting resultant over-balance up-
from the centre of the balance at wards the effect of K-tonus
‘ ; -% in enhancing ‘conductivity
S, and proceeding onwards to left of right arm, The next
and right simultaneously. The — series, with resultant
down-responses, show de-
resulting responses are recorded, pression by A-tonus.

records of the break-effect being

avoided by timely interruptions of the galvanometer-circuit.

It will be seen (fig. 374) from the upsetting of the balance in

an upward direction, that K-tonus has induced enhancement

of conductivity in the right arm. On now causing A-tonus,

by reversing the current in the enclosing tonic coil, T, a de-
¢ RR

610 COMPARATIVE ELECTRO-PHYSIOLOGY

pression of conduction is induced, as shown by the upsetting
of the balance in a downward direction.

- We next turn to the question of the variation of conduc-
tivity induced by K-tonus, when moderate or excessively
strong ; and it is here important to forecast from theoretical
considerations what is to be expected under varying intensities
of the polarising force. It is easy to understand that moderate
K-tonus, inducing an incipient orientation of the molecules,
will predispose them to easy upset in a particular direction,
thus greatly facilitating the transmission of excitation from
point to point. Thus a moderate K-tonus will enhance con-
ductivity. But if the K-tonus in question be excessive, so that
the molecules are already distorted to their maximum position,
incident stimulus can then induce no further change, and under
such circumstances there can be little transmission. Hence,
under increasing intensity of K-tonus, we may expect to obtain
increasing conductivity up to a certain point. But, beyond
this, the conductivity will be decreased, or even actually
inhibited.

These anticipations are seen fully verified in the accom-
panying record (fig. 375), which shows the opposite effects
on conductivity of moderate
and strong K-tonus. The
upsetting of the balance
in an upward direction,
K, shows the effect of
moderate K-tonus. Strong
K-tonus was next applied,
with the effect of upsetting
the balance in the opposite
direction, K’. Thus we see that, while under moderate
K-tonus the conductivity is enhanced, under a much greater
intensity it becomes depressed. This will, I think, be found
to explain a somewhat anomalous occurrence, which has
been observed in regard to the conduction of excitation
through a kathodic region in nerve-and-muscle preparation.
A stimulus applied on the extra-polar region in nerve is

Fic. 375. Opposite Effects of kK-Tonus
when moderate and strong

THE MOLECULAR THEORY OF EXCITATION OI

found tobe transmitted through the kathodic area, inducing
enhanced response of the indicating muscle, if the polarising
current be weak. But when the intensity of the kathode is
made stronger, even the strongest stimulus will fail to induce
response. This is evidently due to the fact that a strong
kathode induces a depression or abolition of conductivity.

Moderate K-tonus, then; we have seen to induce enhanced
conductivity, because of the favourable molecular disposition
which it brings about. Even on the cessation of K-tonus
this disposition remains, owing to molecular ‘ retentiveness,
with its concomitant enhanced conductivity as an after-
effect. This induction of a favourable molecular disposition
or habit is an interesting phenomenon, which we shall meet
with again. :

We shall next study the enhancement or depression of local
excitability by K- or A-tonus. We saw, in Chapter XXXIIL,
that by means of the Con-
ductivity Balance we might
determine the variations, not
only of conductivity, but also
of local excitability. In mag-
netic experiments the responsive
area at the right-hand end of
the balance may be made either
K-tonic or A-tonic, by bringing
near it one or other pole of
a permanent magnet. Under
induced A-tonus, the molecular
excitability is depressed, and

Fic. 376. Effects of K- and

the balance upset in a down- A-Tonus on Magnetic Ex-
. ‘ ae citability
ward direction; while under
4 Ae From the resulting upset of the
K-tonus excitability is enhanced, balance, A is seen to induce de-

the resulting response being up- FF coun SNR EETER Es
wards (fig. 376).

A still more interesting case is that in which the stimulus
itself fashions,:as it were, the path for its own conduction.
The receiving coil is placed at such a distance from s

RR2

612 COMPARATIVE ELECTRO-PHYSIOLOGY

(fig. 371) that, owing to imperfect conductivity of the inter-
vening tract, but little excitation reaches it. Excitation at S,
however, distorts the molecules in its immediate neighbour-
hood, in a certain direction, incipiently distorting others at a
little greater distance in the same favourable way. A second
stimulus is therefore transmitted a little further, bringing
about the same predisposition still further on, Thus an im-

proved conducting-path is made, in a substance formerly but.

an indifferent conductor, by the action of the stimulus itself.
In this way transmitted excitation, at first relatively ineffec-
tive, becomes increasingly effective (fig. 377). It is very
interesting to note that I have obtained an effect exactly
parallel in the case of nervous tissues.
For example, when attempting to
obtain the transmitted effect of ex-
citation by mechanical response, in
a vegetable or animal nerve in de-
pressed tonic condition, the first series
Fic. 377. Gradual Enhance- Of tetanising shocks would induce no
RED oe Caen response. It would sometimes be
} only after long repetition that con-
ductivity would be gradually restored, as seen in the initiation
and subsequent enhancement of responses given at the distant
responding-point:
- It may be that few phenomena connected with the
response of living tissues, bring home to us, so effectively
aS an experiment on a nerve-and-muscle preparation, the
sense of the specific and mysterious character of the
responsive manifestations of the living. The nerve, at its
central termination, is locally excited by electric shocks,
and some obscure impulse then passes through the long
conducting tract to the muscle at the other end. Arriving
there, this invisible nervous impulse initiates a new Series
of events, which find expression in visible motile indications
The work performed at the responding end may be out of
all proportion to the strength of the stimulus imparted at the
centre. It is as if the nervous impulse tapped a relay, and

a

AR ee php ee EER Bee ae ee eT ee Ne ae a

rine nerf
mo

In pa ym ae |

eau

THE MOLECULAR THEORY OF EXCITATION 613

set free a local store of latent energy. The conductor,
moreover, is seemingly unlike the conductor in an electrical
circuit, where the line wire and return wire must be
periodically connected with terminals of an electro-motive
source, for any message to be transmitted. In the nerve
we have only a single conductor, without a return, an
arrangement by which it would appear as difficult to send
a message, as it would be to apply the two poles of a
battery at the end of a single wire, in the expectation of
a signal from the recorder at the far end. Inorganic matter
again, is popularly regarded as susceptible only of impulses
from the grosser physical forces, while the nerve—the
vehicle of psychic impulses—is conceived of as_ played
upon by forces of a finer order, ‘and as itself modifiable,
by subtler influences, notably that of its own previous
history,or memory. There are, as we know, some conditions
which induce such changes in the nervous channel itself,
that messages from outside, previously scarcely perceptible,
are accentuated. Under opposite influences, again, the
conduction of impulse is interrupted. Similar results are
brought about by certain agents of a polar character, like
the action of anode and kathode. Under electrotonic action
the transmission of impulses through the nerve may be
blocked, conduction being renewed as soon as the electric
block is removed. Or electrotonic action, again, may be
used for the opposite purpose, of accelerating the trans-
mission of impulses. Nothing more convincing than such
facts could have been urged in support of the hyper-physical
character of the phenomena in question.

But the experiments which I have described, relating
to the conduction of excitatory molecular changes in a
piece of iron wire, show that parallel phenomena occur in the
physical domain also; and in order to demonstrate this in
a striking manner, I cannot do better than describe an
arrangement which I have devised, and which may be
taken as an artificial nerve-and-muscle preparation. This
consists of a thin iron rod for the transmission of magnetic

614 COMPARATIVE ELECTRO-PHYSIOLOGY = -

excitation applied at one end, with a responding arrange-
ment, to give motile indications, at the other. This latter
consists of a secondary coil, which may be slipped over the
responding point, being in series with some sensitive metallic
powder in circuit with a galvanic recorder, and a voltaic
cell as source of energy. The excitatory molecular dis-
turbance transmitted through the conducting iron rod gives
rise, on reaching the responding-point, to an_ electrical
disturbance in the secondary coil connected with the motile
indicator. This electrical disturbance causes secondary
excitation of the sensitive substance, in consequence of
which the electric conductivity of the particles becomes
suddenly enhanced. By this ‘relay’ action the stored-up
energy of the cell is suddenly released, with a consequent
‘induction of motile response in the galvanic recorder. It
is thus seen that this motile response, initiated by the
transmitted stimulus, need not be proportionate to its
primary exciting cause, since it may possibly be much en-
hanced by the amount of energy set free in the responding
circuit itself. This transmission of excitation is liable,
moreover, as in nerve, to be modified by subtle molecular
changes induced in the conducting tract through which it
takes place. Excitation may be arrested in the one case
by an electrical block ; and in the other, similarly, we are
able to stop the transmission of a message, by means of a
magnetic block. It is by no gross physical restraint that
the impulse is so arrested, but by invisible molecular
distortion within the rod. Molecular freedom is next re-
stored by the removal of- the magnetic block, and we find
that the message, which, though constantly reiterated, was
hitherto inhibited, is suddenly allowed to rush onwards
and bring about the signal. ;

CHAPTER XLII os

MODIFICATION OF RESPONSE UNDER CYCLIC
MOLECULAR VARIATION .

Anomalies of response—Explicable only from consideration of antecedent
molecular changes— Continuous transformation from sub-tonic to hyper-tonic
conditions—Two methods of inquiry, first by means of characteristic curves,
second by progressive change of response—Abnormal response characteristic
generally of A or sub-tonic state—Abnormal transformed into normal, after

_ transitional B state—B state characterised by staircase response—Responses at
C stage normal and uniform—aAt stages D and E responses undergo diminution
and reversal— Responsive peculiarities seen during ascent of curve, repeated
in reverse order during descent—All these peculiarities seen not only in living
but also in inorganic substances, under different methods of observation—
Elucidation of effect of drugs—Response modified by tonic condition and past
history.

WE have seen that, normally, the phenomenon of response
in living tissues is very definite’ There are other con-
ditions, however, under which it is found to be modified or
even reversed. These abnormal effects may be brought
about, either by feeble stimulation, or by changes in the
responding tissue itself. Thus, though moderate stimulus
evokes normal negative response, a feeble stimulus will often
be seen to induce the abnormal positive, and this is most
easily observed in certain particular modifications of the
tissue associated with sub-tonicity. The fatigue-changes
due to excess of stimulation are also, curiously enough,
effective in bringing about the same abnormalities of response.

It is open to-us to regard these anomalies as the result of
obscure vital actions, and therefore incapable of further
analysis. Or,since the phenomenon of response itself is
admitted to be due to the molecular upset caused by
stimulus, their origin may be looked for in the antecedent

616 COMPARATIVE ELECTRO-PHYSIOLOGY

molecular condition of the responding substance. There is
a school of investigators, again, who, appearing to discard the
theory of vital action, in accounting for these changes, have
substituted for it the hypothetical anabolic, or up-building,
and catabolic, or down-breaking, chemical changes. And
such assumptions have certainly the advantage of meeting
every emergency, whether it be an expected effect or its
direct opposite which occurs, for by their means it is always _
possible to make a reference to the one process or the other,
whatever be the inconsistency involved.

- As regards the interminable controversy on the physical
versus chemical nature of response-phenomena, I have
already drawn attention to the fact that on the border-line
between Physics and Chemistry it is impossible to make any
sharp demarcation. Changes, in themselves undoubtedly
molecular or physical, may be attended by concomitant
changes of chemical activity. An example will perhaps
make this clear. We may take, for instance, the photo-
graphic action of light on a sensitive plate. This is re-
garded as due to chemical dissociation or break-down. If
this were so, however, the effect would be permanent. But,
instead of this, the latent image is liable to disappear, and in
a Daguerreotype plate the after-effect of light—that is to say,
the persistence of the image—has a duration of a few hours
only. Such images, moreover, due to the action of light,
have been found to form themselves even on elementary and
inert chemical substances like gold. Here, any chemical
break-down, in the ordinary sense of the word, is out of the
question.

Stimulus in general we have seen to induce molecular
distortion, the persistence of which is dependent on the
strength of the stimulus, and also on the power of self-
recovery characteristic of the given substance. We have
further seen a difference of electrical potential to be induced,
as between molecularly strained and unstrained areas.
When the substance, therefore, thus differentially acted upon,
is placed in a suitable electrolyte, volta-chemical actions are

CYCLIC MOLECULAR VARIATION 617

necessarily set up, by which material in one part may be
accreted, and in another dissolved. In this way a positive
or negative image may be developed.

We have also seen, in the responses of living tissues, that
while moderate stimulation induces one effect, the same
stimulation, long continued, may cause the so-called fatigue-
reversal, such reversals sometimes, in fact, becoming
recurrent. It is interesting to note that in a similar fashion
a photographic plate, subjected to various durations of
exposure, will give either negative or reversed positive
images, or recurrences of these." :

From such facts it is clear that for the elucidation of
response and its variations, we must look to its molecular
antecedents, and not to its secondary chemical or other
consequences. If response phenomena in general, then, are
determined by molecular conditions, as such, it follows that
in order to unravel the anomalies which occur in - the
response of living tissues, we must attempt to ascertain those
conditions which induce any given variation of response in
matter in general. That these phenomena are not peculiar
to the response of living tissues, but take place in all matter
under similar circumstances, is a fact which has been often
reiterated in the course of previous chapters, and which I
first pointed out in the course of my investigations on
‘Response in the Living and Non-Living,’ ?

In the work in question, referring to the occurrence of
abnormalities in response, I said :

‘Calling a// normal response negative, for the sake of
convenience, we observe its gradual modification, correspond-
ing to changes in the molecular condition of the substance.
Beginning with that case in which molecular modification is
extreme, we find a maximum variation of response from the
normal, that is to say, to positive. Continued stimulation,
however, brings the molecular condition to normal, as

* Bose, ‘On Strain Theory of Photographic Action,’. Proc. Roy. Soc.
1902.
See Response in the Living and Non-Living (1902), pp. 129, 130.

618 COMPARATIVE -ELECTRO-PHYSIOLOGY

evidenced by the progressive lessening of the positive
response, culminating in- reversion ‘to the normal negative.
This is equally true of nerve and metal. In the next class
of phenomena the modification of molecular condition is not
so great. It now exhibits itself merely as relative inertness,
and the responses, though positive, are feeble. Under
continued stimulation, they increasé in the same direction as
in the last case—that is to say, from less negative to more
negative, this being the reverse of fatigue. This is evidenced
alike by the staircase effect and by the increase of response.
after tetanisation, seen, not. only in nerve, but also in
platinum and tin. The substance may next be in what we
call the normal condition. Successive uniform stimuli now
evoke uniform and equal negative responses—that is to say,
there is no fatigue. But after intense or long-continued
stimulation, the substance is overstrained. The responses
now undergo a change from -negative to Jess negative:
fatigue, that is to say, appears. Again, under very much
prolonged stimulation, the response may decline to zero, or
even undergo a reversal to positive, a phenomenon which we
shall find instanced in-the reversed response of retina, under
the long continued stimulus of light.

‘We must, then, recognise that a substance may exist in
various molecular conditions, whether due to internal changes
or to the action of stimulus. .The responses give us indica-
tions of these conditions. A complete cycle of molecular
modifications can be traced, from the abnormal positive to
the normal negative, and then again to positive, seen in
reversal under continuous stimulation.’ !

It is the molecular cycle here referred to, with the con-
comitant cyclic variation of response, that forms the subject
of the present chapter.. I shall attempt to show that the
various anomalies in-the response of living tissues, which
were referred to in an earlier passage, may be elucidated

' In the above quotation I have, in accordance -with the convention which
I now uniformly oe referred to normal response as negative, and abnormal
as positive.—/. C. B _

CYCLIC MOLECULAR:VARIATION — 619

by this consideration. I explained, im the first chapter of
the present work, the fact that the molecular derangement
of matter under stimulus might be studied by recording
any one of several concomitant physical changes. -These
are: (a) the change of form—contraction or expansion ;
(3) the electro-motive change ; and (c) the variation of electric
resistivity. By means of the first of these we investigated
the responsive effects induced by stimulus in animal and
vegetable tissues, and in the inorganic substance indiarubber.
By the second, that of electro-motive variation, the excitatory
change and its variations were studied in living tissues, animal
and vegetable, and in inorganic bodies like metal wires.
And, lastly, by variation of resistivity, we have obtained
records of excitatory changes in living tissues, as also in
masses consisting of metallic particles. In the last chapter,
moreover, I have shown that the molecular responses of a
magnetic substance may be recorded by means of appropriate
magnetometric or galvanometric methods.

I shall now take up the question of the nature of those
obscure molecular modifications which the response of a
substance is found to undergo, and in consequence of which
it exhibits variations either of intensity or of sign. The
only conceivable reason for such changes would lie in some

unknown transformation of the antecedent molecular con-
dition. This being so, the next question is, whether we could
possibly discover what these transformations are.

The properties of a substance at any given moment, we
must remember, are not determined solely by the nature of
that substance, but also by the energy which it possesses.
It is obvious, for instance, that the responsive properties of
matter, when its energy is depleted or its condition-is a-tonic,
will be different from those of matter in a higher tonic-con-
dition, and that there will be many gradations intermediate
between the two. Thus, as a substance is gradually trans-
formed, from a state of depletion to one of excessive energy,
we~can see that, theoretically, there -might - be two possible
ways of obtaining an insight into the progressive molecular

620 ' COMPARATIVE ELECTRO-PHYSIOLOGY

changes occurring in it. First of these would be the con-
tinuous observation of the character of the replies made by
the changing substance to the shock of stimulus, with the
progressive modification of those replies. And the second
method would lie in taking a continuous record of some
property of the substance, as a whole, which was undergoing
a concomitant change. In the first of these modes of
scrutiny the information would be obtained by an inspec-
tion of the varying responses. In the second, it would be
arrived at by the examination of certain characteristic curves ;

z
=
fe es
+
oR)
eS
wi
ra
a)
<
=

MAGNETISING FORCE

Fic. 378. Characteristic Curve of Iron under increasing Force of
Magnetisation

and finally, if both these methods gave correct indications of
the molecular state at the time being, then each particular
response of the first method would be found to have its
own place in the characteristic curve of the second. This
characteristic curve will be best understood from a con-
tinuous record of the induced molecular change occurring
under the action of an increasing external force. The
simplest example of this is afforded by the curve which
shows the relation between induced magnetisation and
inducing magnetic force (fig. 378). This induced magne-
tisation, as will be understood, measures the amount of
molecular distortion. A characteristic curve, essentially

CYCLIC MOLECULAR VARIATION 621

similar, is obtained from filings of a substance belonging
to the negative class under increasing electro-motive force
(fig. 379). Taking first the substance in a low or indifferent
condition, we find the curve in its earliest stage, A, to be
almost horizontal. That is to say, the molecular distortion
induced is here very slight. We next arrive, however, at a
stage, B, which I shall call transitional, where increasing
force induces change at a rapid rate. In the third stage,
subsequent to this, there is a decline in the rate of change,
the molecules now approaching their maximum distortion,

fa
Pa
Lid
A
a
a
O

ELECTROMOTIVE FORCE

Fic. 379. Characteristic Conductivity Curve of Sensitive Metallic
Particles belonging to Negative Class, under increasing Electro-
motive Force

These principal features are common to characteristic curves
in general, slight deviations from the type being met with
occasionally. In the cases given, for example, the substance
starts from an indifferent condition. But it might have been
in a still lower, or a-tonic, condition at starting. Under such
circumstances I find that the tendency of the first part of
the curve is to fall below the zero-line, crossing it, however,
in an upward direction, at the transitional point B. When
the curve, again, has reached the highest point, c, it may
remain horizontal for a considerable time, or there may be a
decline, owing, as we shall see, to fatigue.

622 - COMPARATIVE ELECTRO-PHYSIOLOGY

If we take a cyclic curve, recording the effects. under
increasing, followed by those under diminishing, force, it will
be found that the forward and return portions of the curve do
not in general coincide (fig: 380 a). Thus, when an increasing
magnetising force starting from’ zero acts on an iron rod, and
is brought back to zero, the condition of the rod at the end
is not exactly the same as at the beginning. A certain
amount of- molecular work, which is not reversible, has been
done during the cycle.. A certain molecular distortion persists
as an after-effect in residual magnetisation. Similarly, when

Fic. 380. Cyclic Curves of Magnetisation (2) and of Conductivity (4)

metallic particles. are subjected to cyclic electro-motive varia-
tion, an after-effect is found to persist in a change of con-
ductivity. In substances belonging to the negative class
the after-effect is one of enhanced conductivity ! (fig. 380 4).

Referring again to that molecular condition of the
substance which is represented by @ in fig. 378, we find
that a new increment or accession of force will raise its
condition to 4’. In this case the acting force has been
continuously operative and continuously increasing. On
the cessation of the acting foree, a substance possessing
marked self-recovery will fall back from 6’ to 4 But
if. there be a certain persistence of after-effect, then a

1 Bose, ‘On the Change of Conductivity of Metallic Particles under Cyclic
Electro-motive Variation.’—7he Electrician, September 1901.

CYCLIC MOLECULAR VARIATION 623

stimulating force which had raised the substance to - 0’
would, when again applied, after a very brief interval,
raise it to J’, and so on. That is to: say, the molecular
effect would in this case be additive. Tetanisation - will
thus give a curve bearing a great resemblance to the charac-
teristic curve. This will be seen from the following record,
obtained by magnetic tetanisation of steel (fig. 381), which
bears so close a resemblance to the record of electrical
tetanisation of nerve (cf fig. 313). Both these curves, again,
resemble the typical characteristic curve seen in fig. 378. In

Fic. 381. Photographic Record of Magnetic Tetanisation of Steel,
exhibiting Transient Enhancement of Response on Cessation

In a tetanising shocks were moderate, in 4 strong.

all these we find that the curve rises, after a longer or shorter
horizontality, in an abrupt manner ; that its rate of rise then
undergoes a decline, the curve tending again to become
horizontal ; after which fatigue-decline may be initiated. In
the. photographic record of the magnetic tetanisation of
steel (fig. 331), a remarkably suggestive phenomenon is ob-
served. In that part of the tetanic curve which is horizontal
the one-directioned molecular distortion, due to stimulus, is
exactly balanced by the force of restitution. On the sudden
cessation of tetanisation the state-of balance is disturbed,
and we obtain here the remarkable occurrence of a_ brief
overshooting, Or positive variation, in the curve, followed

624 COMPARATIVE ELECTRO-PHYSIOLOGY

by recovery. This is exactly parallel to the sudden
enhancement of response in the retina on the cessation of
tetanising light, or to the enhancement of response in
the nerve when the tetanising electrical shock is suddenly
withdrawn (pp. 428, 536). From the present experiment it
will be seen that the suggested explanation of the pheno-
menon, as due to anabolic or katabolic changes, is gratuitous.

In responding substances, where the persistence of after-_
effect is relatively great, the successive shocks for the obtaining
of the tetanic curve need not be repeated so quickly as where
recovery is rapid. The shifting of the base-line of a series
of even such responses as indicate incomplete tetanus, will
give an indication of the form of the characteristic curve.
The progressive molecular modification of a substance may
thus be gauged, as already pointed out, in either of the two
different ways—by progressive changes in the character of
the response, or by means of the characteristic curve of the
substance, And if both these, again, represent correctly the
molecular condition of the material, we shall further find
that definite parts of the characteristic curve have each their
peculiar responsive features. In order to take these records
‘of the characteristic curve and corresponding responses of
a substance, moreover, we may adopt any method that is
convenient—mechanical, electro-motive, magnetic, or that of
the resistivity variation. The feasibility of such records is
obviously a matter of the extent of the change induced and
the sensitiveness of the recording apparatus. Of the various
methods here mentioned, it may be said that there are no
particular sources of uncertainty to be guarded against in
regard to variations of resistance, of magnetisation, or of
length. But in the method of electro-motive variation, as the
change to be recorded is relative, being measured against a
neutral or indifferent point, some difficulty occurs in securing a
point which is invariable. This may be done more or less per-
fectly, however, by choosing an injured or killed point on the
tissue for the second contact, in order that it may be subject
to as little variation as possible from environmental changes.

CYCLIC MOLECULAR VARIATION 625

‘We shall now proceed to the description of the distinctive
characteristics of certain. molecular states, We may take
first the case of ‘nerve, which gives different characteristic
responses under different’ conditions; and here, employing
the simplest mode of record—namély, the mechanical—we
find, as already said; that, when it is cut off from all sources
of energy, the specimen is apt°to fall into a condition of
stowing sub-tonicity,, This is indicated in the mechanical

Fic. 382. Mechanical Response of Frog’s Nerve to successive equal
Stimuli, applied at Intervals of One Minute

The sloping line at the beginning shows growing elongation due to sub-
tonicity, Stimulus here causes positive response. Fourth, fifth, and
sixth responses are distinctly diphasic. Responses become normal
and ‘increasingly negative’ after the seventh, with marked staircase
increases. Molecular transformation is seen to be very rapid, above the

B point of transition. Record is a photographic reduction, half original
size, of tracings obtained on smoked glass,

record by an increasing abnormal elongation, as in fig. 382,
given above. When the nerve is now subjected to the
action of stimulus, its. tonic condition is gradually restored,
progressing towards a normal excitatory condition. The
molecular transformation involved here is at first expressed
by growing retardation of the abnormal elongation, and
afterwards by gradual contraction. At the point of trans-
ition from positive to negative, or from elongation to

sS

626 COMPARATIVE ELECTRO-PHYSIOLOGY

contraction, that is’to’say, in stagé B,we shall find that the
rate of transformation becomes very rapid.

The second test, by which we may judge of the progress
of molecular transformation in the experimental specimen,
consists, as we have seen, in the nature of its reply to
stimulus. Thus, in the sub-tonic condition, with its tendency

to elongation, the responses are abnormal. positive. From
this they pass gradually, with the progress of molecular.

transformation, into the normal negative, the intermediate
responses being either diphasic or zero. As the process is
very rapid after passing the point of transition, the succeeding
responses near this point show a staircase increase.

Or if we do not wish to record the intermediate series,
but merely to observe the terminal transformation into
negative, or enhanced negative, due to the ascent of the
molecular curve above the transitional point, we may apply
a rapid series of stimuli, or tetanisation. We may here,
according to circumstances, and the point started from,
obtain either (1) abnormal positive transformed to normal
. negative responses; or (2) diphasic, passing into normal
negative; or (3) feeble, becoming enhanced, negative
response. The idea has been put forward, as already said,
that tetanisation enhances the responsiveness of the nerve,
by some supposed evolution of carbonic acid. That this,
however, is erronéous, has been shown by numerous experi-
ments already related, and by the fact that even in inorganic
substances, under given circumstances, tetanisation enhances
response. Nor is it invariably true, in any case, that its effect
is always to enhance response. Under certain conditions,
it may actually cause depression. The decisive ‘element in
the question of its effect lies in that part of the characteristic
curve at which it is applied. If this be immediately after
the point of transition its result will be an enhancement.
Should tetanisation, however,.be applied above the maximum
or highest point in the curve, its effect will be the diminution
of response by fatigue. ;

In order clearly to exhibit the fact that continuous

Ne ee

i - hs

CYCLIC MOLECULAR VARIATION 627

molecular transformation shows itself in two different ways—
by a progressive physical change of the substance itself as
exhibited’ by the characteristic curve, and also by a pro-
gressive variation in the character of the responses—I shall
here give a pair of records of the mechanical response of
frog’s nerve. In fig. 382 the continuous molecular trans-
formation caused by impinging stimulus is shown by the
growing contraction, or responsive mechanical negativity of
the nerve, as seen in the
shifting of the base-line
upwards. It is also in-
teresting to notice here
the continuous trans-
formation of the in-
dividual responses from
the abnormal positive
through diphasic to the
normal negative. There
is also the noticeable
additional fact that after
the point of transition

is passed the response Fic. 383. Mechanical Response of Frog’s

undergoes a marked Nerve, showing Conversion of Abnormal
. ; Positive into Normal Negative Response
staircase increase. In after Tetanisation

fig. 383 is given another Note also the shifting of the base-line up-

: : wards, and that the individual period of
record, obtained with positive is shorter than that of negative

frog’s nerve, where, after responses.
an intervening period of
tetanisation, the abnormal positive response is converted into
normal negative with staircase increase. The shifting of the
base-line upwards is also very noticeable here. Effects pre-
cisely similar are observed in the mechanical response of
vegetal nerve.

If we now turn to a different ae of observation—-say
that by the electro-motive variation—the records will. be
found to bear a remarkable resemblance, in every. particular,

to those which have just been given. We find here the same
SS 2

628 COMPARATIVE ELECTRO-PHYSIOLOGY

continuous transition, from abnormal positive to normal
negative, :as before, through intermediate diphasic, with: a
shifting: of ‘the base-line upwards, exhibiting an increasing
negativity. “The gradual transformation of the character of
the response may be seen when a long series of successive
responses to successive stimuli is taken (cf fig. 277). Or the
abnormal positive may be-séen’ transformed: into normal
negative, after an intervening period .of tetanisation. (cf
fig. 276). Or when the point of molecular transition is
passed, ‘the effect of intervening
tetanisation is to enhance the ampli-
tude of response (cf fig.275). It will
thus be seen that the characteristic
response in the sub-tonic condition A
is abnormal positive ; and that, when
the substance ‘is transformed by
stimulation, to a point above the
transitional B, the response is con-
verted into normal negative, and
lastly, since the rate of transforma-
tion is very rapid above the point B,
that successive responses in that
region exhibit a. staircase increase,
or moderate negative becomes the
| enhanced negative, after an_inter-
Fic. 384. Photographic Re- yening period of tetanisation.. The

cord showing~ Conversion ‘ : q

of Abnormal ‘Down’ Re- underlying transformation is thus

yee Re aeenites indicated by changes in the response,

and also by the shifting of the base-
line upwards, in exhibition of the characteristic curve. These
changes, which have now been described in the case of nerve,
will be found to apply in all other instances of melecular
transformation equally,

Results in every way parallel are obtained with inorganic
substances. In fig. 384 is seen the abnormal electro-motive
response, represented as ‘down,’ converted into normal
‘up’ after an intervening period of tetanisation. In the

CYCLIC MOLECULAR VARIATION 629

next figure (fig. 385) is shown how this abnormal response
in platinum, in consequence of successive ‘stimulation, is

Fic. 385. Gradual Transformation from Abnormal to Normal Response
in Platinum

The transition will be seen to have commenced at the third and ended at
the seventh, counting from the left.

eradually transformed-into a growing normal, through the
intermediate diphasic. In fig. 386 is seen how the normal

Fic, 386. Normal Electro-motive Response in Tin, enhanced after
Tetanisation

630 COMPARATIVE ELECTRO-PHYSIOLOGY

response is enhanced, after an intervening cet, in
a specimen of tin wire.

We pass next to the third mode of record, that, namely,
by the Conductivity or Resistivity Variation. A selenium

Fic. 387. Photographic Record of Abnormal Response of Selenium Cell
converted into Normal after Tetanisation

Stimulus applied was high frequency electric shocks,

cell I find to be sometimes in a certain molecular condition
in which it will respond to high frequency equi-alternating

FIG, 388, Photographic Record showing Moderate Normal Response of
Selenium enhanced after Tetanisation

Stimulus applied was light.

electrical shocks, of the order of a million times per second,
by an increase of resistance. ‘Tetanisation is found to induce
a transformation, attended by a diminution, or negative
variation, of resistance. After. this, the responses are found

es ie

Se NPE TY

ee ee ee

FPR RR NTE TT

CYCLIC MOLECULAR VARIATION 631-

to be converted into normal: that is to say, they now take
place by the diminution of resistance. Fig. 387. gives a
photographic record of these effects. Selenium cells, again,
under normal conditions, respond to light by a diminution
of resistance. After tetanisation, or continued application of
light, the normal responses, under certain circumstances,
undergo an enhancement. The transformation induced by
tetanisation, it is interesting to note, also shows itself by the
shifting of the base upwards (fig. 388).

I have found similar effects, again, to be exhibited by
various metallic powders, under the stimulus of electric
radiation. The record given in fig. 389 exhibits the

abnormal positive response, of increase of resistance, as

given by tungsten. After a short period of tetanisation the
base-line is. seen to be shifted upwards, the molecular
condition being transformed, in a negative direction, and

thus exhibiting a permanent diminution of resistivity. The

response in this particular transformed condition is seen to
be diphasic—positive followed by negative. A further
period of tetanisation carries this transformation still further
in the negative direction, and the individual responses now
seen are augmented normal negative. I give also a second
pair of records in which the normal response of moderate
amplitude in aluminium is enhanced, after an ee rsning
period of tetanisation (fig. 390). gf

We have seen, lastly, that molecular response may be
recorded by means of the magnetic variation. «And it is
interesting to see, by employing this mode of record, that
under certain conditions tetanisation will enhance erence
response (fig. 391). - 7

In order to make a striking demoristration of Hie fact
that the various phenomena described are not the result of
some specific property of living tissues, with their hypo-
thetical assimilation and dissimilation, but are determined
by molecular conditions common to matter both living and
inorganic; I shall now give in vertical. columns; several series
of records of responses, obtained, under parallel conditions,

632 COMPARATIVE ELECTRO-PHYSIOLOGY

from living tissues, animal and: vegetal, and from inorganic
bodies. As the methods also, by which these records were

Fic, 389. Photographic Record ot Abnormal Response of Tungsten to
Electric Radiation, converted after Tetanisation into Diphasic and Normal

obtained, were so different as those of the mechanical, the
electro-motive, the resistivity and the magnetic variations, it

Fic. 390. Moderate Normal Response of Aluminium, enhanced after
Tetanisation

follows that their similarities under parallel circumstances
can only be due to certain fundamental molecular reactions,
which are common to all alike. Further, since some of th

CYCLIC MOLECULAR VARIATION 633

responding substances were elementary, and the experimental

arrangements offered no. possibility
of chemical reaction, it follows that
similar responses, in other cases like-
wise, are determined, not» by some
antecedent chemical, but by molecular
action, though chemical action may
take place as a consequence of. their
responsive molecular derangement.,
_In the first of the series of records
in vertical columns (fig. 392) we
have: (a) a mechanical record of
abnormal response by expansion,

FIG. 391. Photographic Record of Enhancement
of Magnetic Response after Tetanisation

passing into normal response by con-
traction, after intervening tetanisation,
in frog’s nerve. In (0) we observe a
similar transformation, as seen in the
electro-motive response of frog’s nerve.
The abnormal response by galvano-
metric positivity is here converted by
tetanisation into the normal megazzve.
Turning next to inorganic substances,
and taking the method _ of Resistivity
Variation, we find in (c) the abnormal
postive response of tungsten converted
by tetanisation into normal negazzve,
Finally (d) where the specimen is tin
wire, and the record made by electro-

Fig, 392. Vertical Series of

a,

Records showing Trans-
formation of Abnormal
into Normal Response
after Tetanisation in
Living and Inorganic
alike in the A phase

Mechanical response of
frog’s nerve to electric
stimulation ; 4, Electro-
motive response of frog’s
nerve to thermal stimu-
lation; c, Response by
resistivity variation in
tungsten to electric radia-
tion; .d@, Electro-motive
response of tin wire to
mechanical stimulation.

634

FIG. 393.

COMPARATIVE ELECTRO-PHYSIOLOGY

motive variation, the abnormal response
is seen to be converted into normal after
tetanisation. It will be noticed, in all
these cases, that the antecedent molecular
transformation, on which the conversion
from abnormal to normal . response
depends, is also shown independently,
by the shifting of the base-line of the
record in the direction of the normal
response—that is to say, upwards,

In the next series, again, in fig. 393,
is shown the effect. of tetanisation in
enhancing feeble normal response. This
moderate normal response, it will be
remembered, is characteristic of the
molecular condition, just above the
point of transition from abnormal to
normal. In (a) is seen the enhancement
of mechanical response in nerve of fern.
In (6) we have the enhanced electro-
motive response of frog’s nerve. In (c)
a similar enhancement of electro-motive
response is shown in plant nerve. In (@)
we see the enhancement of response
after tetanisation in aluminium powder
by the method of resistivity variation,
the stimulus employed being Hertzian
radiation. In (e) the method of record
is also by resistivity variation, in a
selenium cell, under the stimulus of
light. And finally, in (7) are given the
responses of platinum wire, under the

Series showing how Tetanisation enhances Normal Response

in the B Phase

a, Mechanical response of frog’s nerve; 6, Electro-motive response of

frog’s nerve; c, Electro-motive’ response of plant-nerve; @, Response
by resistivity variation in aluminium powder; ¢, Response of selenium ;
f, Electro-motive response of tin.

CYCLIC MOLECULAR VARIATION 635

method of electro-motive variation, before and after mechanical
tetanisation. The antecedent molecular transformation to
which this enhancement is due may also be gauged, in all
these cases, by the shifting of the base-line upwards.

We have up to this time dealt with the first part only of
the characteristic curve, up to a point slightly above that of
transition. The responding substance, however, in con-
sequence of the after-effect of stimulation, now passes into

FIG. 394. Photographic Record showing Responses corresponding with
different parts of characteristic curve in frog’s nerve

a, Abnormal subtonic ; 4, Staircase ; c, Uniform ; d@, Fatigue decline ;
: ¢, Fatigue reversal,

various different phases of molecular condition, These may
be short-lived, or more or less persistent.

We shall next study all the responsive modifications dué
to these induced molecular conditions, from the subtonic A
to the post-maximum E conditions,-in order, Selecting as
our specimen for this purpose the nerve of frog, the different
phases through which this is capable of passing. may, for
convenience, be divided into five classes (fig: 394). . In the
first of thesé—the abnormal A phase—the nerve is sub-tonic.
It is here undergoing a relaxation, and its characteristic

636 COMPARATIVE ELECTRO-PHYSIOLOGY

response to -individual stimulus. is abnormal: positive. In
consequence- of stimulation, however; we have seen this
relaxation to be arrested, and to pass into growing con-
traction. ‘The characteristic’ of response at this transitional
stage is to be diphasic, passing gradually into the normal
negative. On reaching this, the B phase, the responses, as we
have seen, commence with feeble normal, and undergo a

staircase increase. We may arrive at an idea of the rate of

molecular transformation, in this and succeeding phases,
from the curve of the mechanical response of nerve under
tetanisation (cf fig. 313).. We there saw that in the B, or
transitional, phase, the rate of contraction was very rapid ;
we also found the individual responses at this stage to show
a staircase effect. The rate of contraction next became
slower, and the curve was afterwards more or less horizontal.
Beyond this, fatigue-relaxation set in.

We have now to observe the responsive variations
characteristic of these different phases. For this purpose, a
high magnification of three hundred times has to be em-
ployed. Records so obtained are given in fig. 394. The
method of procedure is as follows: We first take two or
three test-responses to individual stimuli of definite intensity,
at the A phase. This test-stimulus is subsequently main-
tained at the same intensity. When the record of the A
stage has thus been taken, continuous stimulation is applied
for a time, till we arrive at the B stage, when the record of
responses to individual stimuli is taken once more. The
contraction due to the previous tetanising stimulus employed
for the conversion of phase, is now so great that the record-
ing spot of light is carried out of the field. At the com-
mencement of each phasic record, therefore, the spot has to
be brought back to the plate by suitable adjustment of. the
reflecting mirror. Thus the first record of each series really
shows the effect of the termination of tetanisation, the sub-
sequent records showing response to individual stimuli. We
may, however, obtain some idea of the characteristic changes
occurring in the nerve as a whole, by joining the tops of the

a Ae ee

as) Noe ne Weer ae

Ee

CYCLIC MOLECULAR VARIATION. ~ 637

response records, Fromm the inclination of the line thus pro-
duced it is possible to. see whether the nerve at each ‘different
phase was contracting, had assumed a stable length, or was
relaxing. -In the B phase, as here shown, for instance, it will
be seen that the nerve, when undergoing an. increasing con-
traction, shows a staircase enhancement of response; at C
we observe this change to arrive at a climax,: with con-
sequent stability of condition and uniformity of response.

_ _ The characteristic curve, after this, undergoes a reversal :
that is to say, responsive contraction is now diminished, and
eventually gives place to relaxation ; and it is curious to find
that all the responsive phenomena observed during the
ascent are now repeated, but in the reverse order, That is
to say, during the ascent of the curve we obtained the se-
quence of abnormal positive, diphasic, and increasing normal
responses. And during the reversed process we obtain
diminishing normal, diphasic, and the culminating abnormal
positive response. The cycle of molecular phases, with their
attendant variations, is thus complete.

An inspection of D shows the change in the condition of
the nerve from the contracted to the relaxing state. The
onset of fatigue is also seen in the diminishing amplitude of
the responses, This process is seen accentuated, to the
actual reversal of response, in the last phase E, I shall later
give a special record exhibiting the diphasic responses inter-
mediate between D and E, |

The response of nerve has hitherto been supposed, as
already mentioned, to be specifically different from that of
ordinary tissues. One characteristic particularly’ insisted
upon was its indefatigability, or incapacity for fatigue, the
nerve in this respect differing essentially from the muscle.
On taking a general review, however, of nerve and muscle-
response, we find that there is no essential difference between
the two. During the first phase of contraction, both alike
show staircase increase. This is followed, in both, by a
series of uniform responses. And in the stage of fatigue,
in both, the process of contracture gives place to one of

638 COMPARATIVE ELECTRO-PHYSIOLOGY

relaxation. Theé’only difference lies in the fact that fatigue —
makes its appearance in the one case earlier than in the other.

When dealing with the subject of the enhancement of
response by tetanisation, I stated that here it was not
tetanisation, as such, which formed the determining factor in
bringing about the increase of response; this was rather due
to a phasic molecular transformation, induced by tetanisation.
If the substance happen to be in the transitional B phase,
then and then only will tetanisation enhance its response.
If, however, it should happen to be in the optimum C phase,
then the same tetanisation will have the effect of carrying
it into D and E, the phases of fatigue. The response here,

Fic. 395. Photographic Record of Response of Tungsten showing
Enhancement of Response after moderate Tetanisation, and Reversal
of Response, due to Fatigue under stronger Tetanisation

instead of being enhanced, will be decreased or reversed.
This is seen in the following record (fig. 395) obtained with
tungsten when moderate tetanisation enhances response,
whereas strong tetanisation, by bringing on fatigue, reverses
the normal response. |

How universal are these phenomena will be seen from
the accompanying series of records, obtained. not only with
various living tissues, but also with inorganic substances
under parallel conditions, the normal responses being in all
these cases reversed by tetanisation, in consequence of the
transformation from the C to the E phase. In fig. 396 (a)
is seen the normal contractile response of a frog’s nerve
reversed to the positive or expansional, after tetanisation.

CYCLIC MOLECULAR VARIATION

639

In (6) is seen the reversal of the normal electro-motive
response in the digesting leaf of Drosera, after tetanisation,
the stimulus here also being electrical.

reversal after tetanisation in the elec-
tro-motive response of the pulvinus
of Mimosa. And in (d) is given a
similar reversal after tetanisation, in
the response of tungsten powder, the

record being here of the resistivity

variation, under the stimulus. of
Hertzian radiation. These, and other
results already given, have _been
obtained by the employment. of
different forms of stimulation. We
may, therefore, regard these charac-
teristic transformations as: brought
about by all forms of stimulus alike.

We thus see that one identical
stimulus may give rise to opposite
effects, according to the molecular
condition of the responding tissue.
This molecular transformation, more-
over, may be brought about by the
previous action of the stimulus itself.
These considerations will, I think, be
found to elucidate the very obscure
question of the effect of drugs, with
special reference’ to the opposite
actions of large and small doses.

Since a chemical substance acts in-

a manner. not unlike that-of other
stimulating agents, a moderate dose
of a given reagent might be expected
to induce effects similar to that of
the action of moderate stimulation.

FI

a;

[In (¢) we have

G. 396. Series showing
reversal of Normal Re-
sponse by fatigue due to
strong Tetanisation in-
ducing the E phase

Mechanical response of
frog’s nerve; 4, Electro-
motive response of Dvo-
sera; ¢, electro-motive
response of pulvinus of
Mimosa; ad, Response
by resistivity variation
of tungsten powder.

Hence_its effect in
inducing molecular transformation will generally be to en-
hance excitability, as from B to ©. Too long-continued action,

640 COMPARATIVE ELECTRO-PHYSIOLOGY

‘however, carrying the substance acted upon ‘to the phase of
D or E, will cause depression, Or it is conceivable that the
same depression might be more rapidly induced by more
intense stimulation—that is to say, by a larger dose.
Now that this is what actually takes place has already
been shown in several experiments which have been
described, We saw, for example (fig. 95) that the continued
action of the moderately stimulating agent, sodium. car-
bonate, at first induced an exaltation of response, followed
later by depression. In the case of vegetal nerve, again
(ff. fig. 297), we found that the same agent, in smaller doses,
caused at first an enhancement of conductivity, followed
later by slow depression. A stronger dose of the same
reagent, however, was found to cause rapid depression
(fig. 298). Even in the case of poisons, so-called, the same
facts make their appearance. Here an agent which’ proves
toxic in large, appears as a stimulant when given in minute,
doses, Thus in studying the effect of various chemical
agents on growth-response, I found that while a one per cent.
solution of copper sulphate was toxic, the same reagent
proved stimulatory, if given in a solution of ‘2 per cent.
_ A more detailed account of these experiments will be found
in my work on ‘Plant Response,’ from which I quote the
following summing up: |
‘A survey of the effects of drugs, both stimulating and
poisonous, reveals the striking -fact that the difference
between them is [often] a question of quantity. Sugar, for
instance, which is stimulating. when given in solutions of,
say, I to 5 per cent., becomes depressing: when the solution
is very strong. Copper sulphate, again, which is regarded as
a poison, is only so at I per cent. and upwards, a solution of
‘2 per cent. being actually a stimulant, The difference
between sugar and copper sulphate is here seen to lie in the
fact that in the latter case the range of safety is very narrow.
Another fact which must be borne in mind in this connection
is that a substance like sugar is used by the plant for
general metabolic processes, and thus removed from the

ECR ene See ae el ee ee

Se IT Oe ee a a

i EY INR Peat

Pee,

CYCLIC MOLECULAR VARIATION 641

sphere of action. Thus, continuous absorption of sugar
could not for a long time bring about sufficient accumulation
to cause depression. With copper sulphate, however, the
case is different. Here, the constant absorption of the
sub-tonic stimulatory dose. would cause accumulation in the
system, and thus ultimately bring about the death of the
plant’? . =

From all this it is clear that the progress of medicine may
be greatly facilitated when the attention of investigators is
drawn to the importance of the molecular aspects of the
phenomena with which they have to deal. Thus, in examin-
ing the action of drugs, a threefold question is seen to arise.
It must first be determined what is the nature of the respon-

sive molecular change induced by the given reagent under

normal conditions. The second matter of inquiry is, What is
the critical dose, above and below which opposite effects may
be expected? And, finally, as the nature of the response has
been seen to be influenced by the part of the molecular curve,
at which the responding tissue has arrived, when the chemical
reagent is applied, it rollows that an important element in
the problem lies in the determination of the tonic condition
of the tissue. How important is this last factor will be seen
from an experiment to be described at the end of the present
chapter, where an identical course of treatment+‘in one
condition of the tissue revives it from inanition, and in
another hastens its death.

I have shown that when the condition of the substance
is transformed from C€ to E, the response ‘also/is reversed
from normal negative to abnormal positive. I shall now,
therefore, proceed to show that in the course of this
transition there is an intermediate stage of diphasic
response. Before exhibiting this in the case of nerve, I shall
give an interesting record in which the same thing is seen to
take place in the mechanical response of fatigued indiarubber.
Before the onset of fatigue, the normal'contractile responses
were large, but at that stage—that is to say before the record

1 Bose, Plant Response, p. 488.
yes iy

642 COMPARATIVE ELECTRO-PHYSIOLOGY

commences —they had begun to decline. In the series then
recorded (fig. 397) we see how the depressed contractile
responses are gradually transformed into’ abnormally expan-
sive, through an intermediate diphasic. : ;

Fic. 397. Fatigue in Indiarubber giving rise to Diphasic and Reversed
Responses

In the next series of mechanical records, obtained from
nerve of frog (fig. 398), we have results exactly similar. The
depressed contractile negative here passes through diphasic
to abnormal positive. Thus, during the descent of the
characteristic curve we obtain, as has been said before, a

Fic. 398. Fatigue inducing Diphasic Variation and Reversal of Normal
a Response in Frog’s Nerve
a, Diminished normal response; after tetanisation, enhanced fatigue in-
duces diphasic passing'into reversed positive response, 4 ; a period of rest
after this revived the normal response in c ; after long-continued tetani-
sation, response is seen to be abolished in.d, by the death of nerve.

repetition, but in reverse order, of all the phenomena seen
during the molecular ascent; the sequence of responsive
variation was from abnormal positive, through diphasic, to
increasing negative. During the descent the sequence is
diminishing normal response, diphasic, and abnormal positive.

ow wererter os Se SS ee ee ee ee eee

CYCLIC MOLECULAR VARIATION 643

The two halves of the cycle are thus strangely alike, one
being, as it were, a reflection of the other. The cycle begins
with sub-tonicity, due to a deficit of absorbed stimulus, and
ends with the abnormality caused by excess of stimulation.
The starting-point of the one may be supposed to meet the
end of the other in a common fatality. The tissue comes to
the same death by inanition on the one hand, through lack
of stimulation, and by fatigue, on the other, through over-
stimulation. But though the one half thus mimicks the other,
there is, as it were, a polar difference between the two, by
reason of the difference in their past histories. To revive the
dying tissue, in the beginning of the cycle, stimulation is
necessary ; to revive it afresh, at the termination of the cycle,
a period of rest is essential.

TT2

CHAPTER XLIII

CERTAIN PSYCHO-PHYSIOLOGICAL PHENOMENA—THE
PHYSICAL BASIS .OF SENSATION

Indications of stimulatory changes in nerve: 1, Electrical; 2, Mechanical—
Transmission in both directions—Stimulatory changes in motor and sensory
nerves similar—Responsive molecular changes and the correlated tones of
sensation—Two kinds of nervous impulse, and their characteristics— Different
manifestations of the same nervous impulse determined by nature of indicator
—Electrical, motile, and sensory responses, and their mutual relations —The
brain as a perceiving apparatus—Weber-Fechner’s Law—Elimination ot
psychic assumption from explanation of particular relation between. stimulus
and resultant sensation—Explanation of the factor of quality in sensation—
Explanation of conversion from positive to negative tone of sensation after
tetanisation—Various effects of progressive molecular change in nerve—FEffects
of attention and inhibition—Polar variations of tonus, inducing acceleration
and retardation.

IT is admitted that the molecular changes induced in the
nerve by stimulus, are followed by sensations perceived in
the brain. The question as to the nature of these antecedent
changes induced in the nerve, and the quality of the sensation
that succeeds them, falls properly, then, within the scope of a
physiological inquiry ; and it is certain aspects of this which
will be treated in the present chapter. I may here point out
that the results which I have to describe consist of deductions
drawn from direct experiment. They will in some cases
lend support to the psychological hypotheses already ad-
vanced ; while in others they will be found to be opposed.
In such cases, therefore, it is perhaps not too much to hope,
from their strictly experimental character, that they will

prove of use in deciding between rival theories; while in —
others they will be found to introduce facts and considera- —

tions which are entirely new.

———— ee,

o>
yp oer

PHYSICAL BASIS OF SENSATION 645

Referring to the excitatory changes on which sensation
depends, there has been much discussion as to whether the
effects of stimulus in efferent and afferent nerves are of the
same or of different natures. The difficulty in deciding this
point lay in the fact that the indications of the state of
excitation are different in the two cases, one exhibiting it
objectively by the motile effect, and the other subjectively
by sensation. It has been supposed, as we have seen, that
the excitatory changes transmitted by the nerves were un-
accompanied during their progress by any direct visible
indications. It has been shown, however, in the course of
previous chapters, that a change of form does in fact ac-
company the transmission of the wave of excitation along
the nerve. It was also shown that this mechanical indica-
tion could be rendered extremely delicate, ranking, in
degree of sensitiveness, between the galvanometer and the
brain. Employing this mode of investigation, then, we
found not only that the wave of excitation might be trans-
mitted in either direction in any given nerve, but also that
the changes induced by stimulus were similar in afferent and
efferent nerves (p. 529).

Regarding the nature of this molecular change, again,
it has been supposed that the nerve under excitation exhi-
bited a specific variation, known as the xeura/, totally unlike
those changes which take place, for instance, in muscle. We
have seen, however, that this is not the case, the mechanical
and electrical expressions of the molecular changes in excited
nerve being of a nature essentially similar to those observed
in muscle also.. Even in the matter of conduction, we have
seen that non-neural tissues transmit'the state of excita-
tion to a certain distance beyond the point of stimulation.

The difference in this respect is one of degree, and not of
kind.
We have next to deal with the question of sensation as

induced by molecular changes in the nerve. It is widely
admitted that the changes induced in the nerve by stimulus
will cause responsive sensations. But the relation between

646 COMPARATIVE ELECTRO-PHYSIOLOGY

the responsive sensation and the character of the molecular
change that induces it has been regarded as unascertainable.
‘That many of our feelings depend immediately upon the
condition of the nervous elements is beyond doubt... .
What is the peculiar nature of the excitation upon which
the different feelings depend ‘for their differences of
quality ? What is the characteristic change in the excita-
tion that gives rise to two kinds of tone which the feelings
possess, to pleasure and to pain? Physiological psycho-
logy can answer none of these questions with much con-
fidence.’ !

The fundamental contrast of tone in question raises the
inquiry, therefore, whether it may be possible to discover any
antecedent nervous changes of opposed character. Taking
an instance of response by some simple form of sensation, it
is well known that while moderate stimulus produces a feeling
which may be described in general as not unpleasurable, or
even distinctly pleasurable, an intense stimulus of the same
nature will cause a displeasurable or even painful, sensation.
These fundamental differences of quality are classified as
‘positive and negative Zones’ of sensation, the term ‘ positive’
being here associated with perceptions which are not un-
pleasant, or even actually pleasant, while ‘negative’ refers to
the reverse. While the sensations ensuing under moderate
stimulus, then, such as moderate pressure or moderate light,
are of ‘positive’ tone, those brought about by more intense
stimulus are apt to become converted into negative. The
positive sensation grows to a maximum, according to the rise
of stimulus-intensity within a certain limit. Beyond this
point, sensation becomes, first, less and less positive, and then
increasingly negative, as the intensity of stimulus continues
to be augmented. Ora simple stimulus, suchas a light blow,
which evokes a positive sensation, will, when often repeated—
that is to say, when employed tetanically induce a negative
or painful sensation. It is thus seen that the tone of sensation
is in some way associated with the intensity or duration of

* Ladd, Outlines of Phystological Psychology (1891), p: 387.

' rhe a i P -
cae ee ae ta 2 ab a) Shee ae

PHYSICAL BASIS OF SENSATION 647

stimulus. The question, however, remains, whether or not.
these opposite sensation-tones could be demonstrated to be
dependent upon characteristic nervous changes of opposed
characters. lf we should succeed in making such a demon:
stration a physico-physiological basis of. psychical effects
would have been established which would unquestionably
prove to be of great value,

Now we have seen, referring to previous investigations
on nerves, (1) that a feeble stimulus applied to the nerve is
transmitted as a pulse of expansion. This we have
designated the positive wave. The propagation of this
wave being more or less of the nature of a hydrostatic
disturbance, we have seen that its transmission is not affected
to any great extent, even when the conductivity of the tissue
is diminished. (2) A more intense stimulus we have found
competent to give rise to a disturbance of opposite or negative
sign—that is to say, toa pulse of contraction. The velocity with
which this second, or,as we have called it, the true excitatory
wave, was conducted, we found to increase with the intensity
of the stimulus. While with feeble stimulus the positive
wave alone was transmitted, with stronger, both negative and
positive were propagated, but the more intense negative was
liable to mask the feeble positive. As the negative wave
was dependent on the conductivity of the tissue for its
propagation, we have seen that it was possible to separate
the two by any means which would diminish the conductivity

"of the tissue. By such means the negative could be made to

lag behind the positive; or, by its complete suppression, it
was even possible to exhibit the positive alone. Thus a
tissue which normally gave only negative response, owing to
the masking of the positive, might, by the depression of its
conductivity, be made to give diphasic, or positive response
alone (p. 530).

So far then, as regards the detection of two nervous im-
pulses of opposite sign by means of the delicate mechanical
method. The same facts may also be demonstrated by the
less sensitive method of electrical response, according to

648 COMPARATIVE ELECTRO-PHYSIOLOGY

which we saw that the two nervous impulses were exhibited
by two opposite electro-motive variations—those of galvano-
metric positivity and negativity respectively. This reaction
of expansion and galvanometric positivity, however, may
also occur as the expression of the increase of internal
energy, in whatever way produced. Indeed, the positive
form of response under moderate stimulation may be

regarded as a case falling within this definition. Thus we .

see that, beginning with very moderate stimulus, we obtain
in the tissue a purely positive effect; and that, as the
stimulus is augmented, the true negative excitatory effect
also begins to make its appearance in increasing degree, the
positive component of the response being now more or less
masked. The energy that afterwards remains latent in the
tissue goes to enhance the tonic condition. The amount
thus held latent depends on the difference between income
and expenditure. As a general rule, it will be under
intense stimulation that the expenditure of energy will be
likely to exceed the income. Thus we have two extreme
cases, first, that in which moderate stimulus brings about
increase of energy ; secondly, that in which excessive stimulus
brings about run-down of energy ; and between the two a
large range of variation, within which either one condition or
the other may predominate. It must, of course, be under-
stood that anything which increases the tonic condition is for
the well-being or health of the organism, and is associated
with positivity. Similarly, any fall of the tonic condi-
tion below par makes for exhaustion and against healthy
tone.

We have next to take a rapid survey of the changes
induced by stimulus in the conducting nerve itself, or any of
its attached indicators. Such variations may, for purposes of
convenience, be classified as motile, electrical, and sensory.
In the nerve itself we have found, as has already been
pointed out, by means of the Kunchangraph, that the motile
change induced by feeble stimulus was one of expansion, the
same change being shown electrically by galvanometric

—_-

ee ee ee ee ee ee ee ee

——

PHYSICAL BASIS OF SENSATION 649

positivity. The change induced by strong stimulus, on the
other hand, was of contraction and galvanometric negativity.

In the terminal motile indicator also, there are two
different modes of response of opposite signs—namely,
expansion and contraction. -In the highly excitable muscle,
the occurrence of the former of these, brought about, as it is,
by very feeble stimulus, is not easy to demonstrate. Bearing
in mind, however, the fact that in nerve positive response is
more easily obtained when the excitability is depressed,
I succeeded in obtaining positive expansional response of the
muscle, in a nerve-and-muscle preparation of frog, which had
been depressed by the anzsthetic action of chloroform. At
a certain stage of anzsthetisation, the response of the muscle
under stimulation of the
nerve was found to take
place by expansion,
followed by recovery.
Just as in a nerve in
a somewhat depressed
condition, ee Fic. 399. Abnormal Response of Muscle by
stimuli evoke positive Relaxation, followed by Normal Response
response converted later af, Contraction

‘ 1 ; The first two responses by relaxation are
into normal negative, followed by two contractile responses.

so, in the muscle-pre-
paration described, the abnormal positive was followed by
the normal negative response. In fig. 399 I give a photo-
graphic reproduction of the myographic record obtained on
a smoked-glass surface.

In all these different effects we obtain, by means of the
mechanical response of the terminal organ, what is merely
a parallel expression of changes occurring in the nerve itself.
As in the nerve, so also in the muscle, there are two different
kinds of responsive expression—namely, expansion and con-
traction. Thus we see that the various manifestations
registered by different modes of indication are only so many
diverse expressions of the same fundamental molecular
changes.

650 COMPARATIVE ELECTRO-PHYSIOLOGY

We turn next to the sensory mode of indication, that is
to say, to the psychic effects registered in the central
perceiving organ by the positive and negative waves
conveyed to it along the afferent nerves. We have already
seen that the stimulatory changes induced in these sensory
nerves are precisely the same as those which occur in the
efferent. What, then, are the effects in the central apparatus

induced (1) by that positive impulse which is associated with .

expansion, and (2) by the negative impulse associated with
contraction ? :

It is a matter of universal experience, as already

mentioned, that feeble stimulus gives rise to sensations of
positive or pleasurable tone, while an intense stimulus of the
same kind will induce a responsive sensation which is negative
or painful. We have also seen, in the course of the present
work, that a feeble stimulus will give rise to a wave of
expansion and galvanometric positivity, while the same
stimulus, when intense, will give rise to a negative wave.
We are therefore justified in regarding the positive impulse,
associated with expansion and galvanometric positivity, as
_pleasure-bearing, and its, opposite as pain-bearing or dolori-
ferous. Numerous experiments—some being of a crucial
character—will be given, in the course of the present and
succeeding chapters, which will be found to lend full support
to this conclusion.

This fact, that the same stimulus may induce positive
sensation in the central and expansion in the motile organ,
or the negative painful sensation with muscular con-
traction, according only to the nature of the indicator,
will furnish grounds of reconciliation to those who
hold on the one hand that the motor reaction is secon-
dary to the mental, and on the other, that sensation
is merely an accompaniment of movements reflexly in-
duced.’

‘Many hold the motor reaction to be secondary to the mental. Of the
coarser emotions it has been argued by James that the feeling does not cause,

but is caused by, the bodily expression, The bodily changes, according to him,
follow directly the perception of the exciting fact, and our feeling of the same

Ue ed es ee eee ee eee

i pw eal a Eager

pment ns

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PHYSICAL BASIS OF SENSATION 651

If the sensation be in fact due to definite and ascertainable
physico-physiological changes in the nerve, then the various
modifications of sensation must, in like manner, be traceable
to corresponding modifications in the physico-physiological
process. In that case, the particular relation which is known
to exist as between stimulus and sensation—expressed as
Weber-Fechner’s Law — must be demonstrable as directly
dependent upon molecular changes induced, and not on the
existence of some assumed psychic factor. This molecular
theory, further, if it expresses a truth of universal applica-
tion, ought to be capable of explaining not only the
quantitative relation between stimulus and sensation, but
also that qualitative variation of which Weber-Fechner’s
Law is unable to take account. Should the Molecular
Theory prove adequate to this, its truth may be regarded as
demonstrated. |

We shall, however, subject this theory to further and still
more crucial tests. If it be true that our sensations,

‘painful and pleasurable, are due to nervous impulses of

opposite character, then any modification of either of these
impulses by any given agent should appropriately modify
the resultant sensation. We have seen, for instance, that
the negative wave is complex, and contains within it the
masked positive. We have also seen that by appropriate
means these two waves may be made to exhibit themselves
separately ; or the positive, by the total suppression of the
negative, may be displayed alone. I shall therefore show
that, by the employment of the same means, the subjective
sensation of painful or negative tone may also be analysed
into its component parts, which may thus be made to exhibit
themselves in succession; and, on the other hand, that by

changes as they occur zs the emotion. Certain experiments furnish evidence—
not highly satisfactory—that all pleasurable states of consciousness are accom-
panied by bodily movements of extension, and all painful by movements. of
flexion. These movements may be very slight. Miinsterberg concludes that
the feeling of agreeableness is the mental accompaniment and outcome of
reflexly-produced movements of extension, and disagreeableness of the move-
ments of flexion.’--Schafer, Zext-Book of Physiology, vol. ii. (1900), p. 975-

652 COMPARATIVE ELECTRO-PHYSIOLOGY

the complete obliteration of the negative element an already
painful sensation may be converted into pleasurable.

Of the scheme thus laid down, the first part will be
carried out in the present, and the second in the succeeding,

chapters.
Turning now to our sensations themselves, it may be well

to consider some of the characteristics of the central perceiving |

apparatus. Asa detector of nervous changes the brain is
undoubtedly the most delicate of instruments, surpassing in
this respect not only the galvanometer, but also the
Kunchangraph. It fails, however, strictly speaking, as an
accurate metrical apparatus. It is not able to discrimi-
nate quantitatively, for instance, by means of sensation,
through any wide range, between the finer differences of
intensity in the nervous impulses it receives. In the pain-
and-pleasure series, again, the distinctions which it is able to
make are, to a certain extent, of a merely qualitative
character, unmistakable only as between the two extremes
of the series, the intervening region tending to be somewhat
indefinite. The sensitiveness of the physical instruments,
Kunchangraph and galvanometer, is always constant and
reliable. For example, in the galvanometer, by adjusting
the controlling magnet, we can obtain varying degrees of
sensibility, which at any particular adjustment will remain
constant. But in the perceiving apparatus, not only is the
sensitiveness of different individuals widely different, but even
in a single individual it undergoes great variation under
different conditions.

By deliberate attention or inhibition, as by raising or
lowering of the controlling magnet in the galvanometer, the
sensitiveness of the perceiving field can be almost indefinitely
varied. Pursuing this analogy of the galvanometer further,
we find that in the brain, instead of a single coil, with its
one pair of terminals, there are many coils with many pairs
of terminals, receiving impulses from every part of the
organism. Confining our attention, moreover, to any single
circuit among these, we find again that the impulses it

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PHYSICAL BASIS OF SENSATION 65 3

conveys are varied in their character. There are, for
instance, the immediate effects of stimulus, whether positive
or negative, and also the persistent after-effects of stimuli
previously absorbed. The central apparatus, however, is not
acted on by these impulses from any single circuit alone,
but from many circuits at the same time, the whole resulting
in a ‘vague tremor of generalised consciousness. The
individual sensation evoked by any particular stimulus bears
to the rippling surface of this consciousness the relation of
a larger or smaller wave.

Thus we see that there are tele conditions which will
contribute to the intensity of the sensation evoked by an
jndividual stimulus. There will be, first—to revert to the
simile of the galvanometer-——the enhancement of the con-
ductivity of the particular circuit involved; and, secondly,
the suppression of all interference caused by the semi-
conscious activity of other circuits. By the action of the

will, producing the condition of attention or expectation,
the excitability of the receptive or responsive points, and the

conductivity of particular channels, may be exalted, while
they may be depressed in others by the reverse process of
inhibition. The extent to which it is claimed that this
power of inhibition may, with practice, be carried, would
appear almost unimaginable. -I have myself known of an
authenticated instance in which the pulsation of the heart was
arrested and renewed at will. In India, indeed, it has been
held, from very remote times, that such practices are capable
of reduction to a science. It is thus believed to be possible
that all nervous impulses due to external causes may one by
one be inhibited, until the attention is concentrated on a
given point, in complete isolation from any interference

whatever by the physical organism. Regarding the physical
aspects of these processes of inhibition and concentration,

more will be said at the end of this chapter. :

There are again other elements calculated to bring about
further variations in the sensitiveness of the instrument
which lie more or less beyond the control of the observer,

654 COMPARATIVE ELECTRO-PHYSIOLOGY

His previous habits and prepossessions all contribute, as is
well known, to modify it more or less permanently. The
principal reason for the constancy of the records made by
the physical indicators lies in the greater or less constancy
of the properties of those elements of which they are com-
posed. Even here there is a fluctuation of sensitiveness,
owing to changes in the properties of the material. But
these changes are neither so rapid nor so considerable as
in the neural apparatus, whose excitability is extremely
susceptible of modification under the influence of fatigue,
and of such varying factors as health and tonicity, as well as
by the action of the stimulus itself. 7 :
Looking now at the whole range of impulses generated
in the nerves under increasing stimulus, we shall see that
the positive effect is gradually augmented till it reaches a
maximum. It then undergoes a decline, passing into a
resultant negative. This resultant negative response con-
tains, as we know, a masked positive component, which
can be separated and exclusively demonstrated by appro-
priate methods. With increasing stimulus the negative
response undergoes an enhancement till a limit is reached.
Expressed in terms of sensation, then, the effect perceived
is at first of positive tone, and this, growing in intensity, is
pleasurable. This positive tone, however, afterwards under-
goes a diminution, and finally passes over thé zero-line ;
this constitutes the commencement of a somewhat extended
range, in which the resultant negative, with its masked
positive, undergoes increase. Referring to the curve at the
crossing of the zero-lirie, it must be said that we. have here
a neutral point. This is not, however, the same as
that absolute zero at which the curve of sensation was
initiated, for here the neutrality is not due to absence of
effect, but to the fluctuating equilibrium of two opposite
effects, one positive and the other negative. It is thus to
be understood that, while in the positive region the tone is
simple, in the region of the resultant negative it is complex,
the sensation here being.compounded of positive and nega-

PHYSICAL BASIS OF SENSATION 655 |

tive (pleasure-pain). In this region, then, it is theoretically
possible to bring out the positive element alone, by suppress-
ing the negative. It is the predominance of either one of
the two components which at any given moment determines
the pleasure-pain character of the complex sensation. At
a certain critical point it is the element of pain which will
begin to appear as relatively conspicuous, this proceeding
towards a climax with increasing stimulation.

It must be understood that we are dealing in general
with nervous response under normal conditions of excitability.
It will be sufficient here to make a cursory reference to
certain exceptional cases which may occur. We have found
that the character of the response given by a tissue is deter-
mined by the two factors of (1) the effective intensity of
stimulus, and (2) the excitability of the responding tissue.
If the nature of a given stimulus be such as to produce but
a moderate effect, there will be a greater likelihood of its
evoking only positive response. Or the responding tissue,
in another case, may possess exceptional excitability ; hence
the responsive indication here will tend from the beginning
to be negative. The different effects depending on the vary-
ing excitatory characteristics of the tissue, we have already
seen illustrated in several cases. The slightly excitable
epidermis was seen to give a predominantly positive response,
whereas nerve which had been rendered highly excitable
tended, on the other hand, to give negative response.

We shall now proceed further to consider the corre-
spondence between the responsive sensation and the degree
of nervous change induced by stimulus. And here the first
question that arises is that of the relation which sensation

bears to the intensity of the stimulus that provokes it. The

difficulty of this investigation lies in the generally unsatis-
factory character of the subjective standard, and in the
variations induced by stimulus itself in the sensitiveness of
the neurile elements. .

According to what is known as Weber-Fechner’s Law,
the strength of stimulus must increase in geometrical ratio

656 COMPARATIVE ELECTRO-PHYSIOLOGY

in order that the intensity of the sensation may increase
arithmetically. The method of experiment on which this
result was based is not, however, altogether unexceptionable.
Against the generalisation itself, many objections have been
urged, and even its supporters claim for it only a very
limited range of application. It has been pointed out that
Fechner starts with the assumption that the change of

sensation under varying intensities of stimulus is merely

quantitative ; he does not take into account that the quality
or sign of sensation is also liable to change.

Confining our attention to that range of sensation which
does not involve any change of quality, it is urged that,
starting from the minimally effective intensity of stimulus,
excitation at first increases very rapidly, and subsequently
more slowly, under successive equal increments of intensity.
This particular complexity led Fechner to suppose that such
complex phenomena as the quantitative relation between
stimulus and sensation were not determined by mere physical
or physiological factors. He therefore maintained that his
generalisation expressed an ultimate law concerning the
relation between physical stimuli and psychical reactions,
or, in other words, between body and soul.

It is now possible, however, turning away from specula-
tive hypotheses, to subject this question to direct and simple
experiment. We have seen how delicate and free from
complication is the record of the mechanical response of
nerve. In these tracings we have the record of the direct
effect of stimulatory action on the nerve itself. In order,
then, to study the effect of stimuli of varying intensities, I
first chose a specimen of the sciatic nerve of gecko. A
sliding electric inductorium was used for the purpose of
stimulation. From a previous experiment with a ballistic
galvanometer the absolute intensity of the electric shocks at
different distances of the secondary from the primary was
calibrated. Marks were then made on the sliding base,
which gave various intensities of stimulation—1, 2, 3, 4, 5—-
and so on. Thus, keeping the duration of the exciting

—— Sew

PHYSICAL BASIS OF SENSATION 657

primary current the same, and bringing the secondary nearer
and nearer the primary, the intensity of the stimulus could
be gradually increased quantitatively. The effective intensity
of stimulation might also. be increased in a graduated
manner by fixing the primary inside the secondary, and
gradually increasing the duration of stimulation.

The following record shows the effect of stimuli in-
creasing from one to ten, by increments of one at a time
(fig. 400). It will be seen that at the beginning, owing to
growing sub-tonicity, the nerve was undergoing a gradual
relaxation, the downward slope of the beginning of the record.
On application of stimulus of intensity as shown by 1, there
is a sudden responsive
relaxation, followed by
a partial recovery. As
the intensity of stimu-
lus is successively in-
creased, the positive
response undergoes an
increase, the maxi-
mum-positive response
being evoked when the FIG. 400. Record of Response in Nerve of

- : oye Gecko showing the Effect of Arithmetically
stimulus-intensity is 3. increasing Stimulus
After this the ampli-
tude of response undergoes a progressive decline, the response
to stimulus 8 being practically zero. This neutral point, as
was shown earlier, is not to be regarded as the true zero, being
in fact the balancing point of positive and negative. This
will be seen when we inspect the record of intensity 9, where
the increasing negative actually induces a minute diphasic
response—positive followed by negative. The next response
to stimulus 10 gives us a sudden large negative response.
Above this point of transition I find, as will be seen in the
following records, that there is a rapid enhancement of normal
negative response. Still later, this increase of rate would
decline, and later again, by the setting-in of fatigue, the
responses might undergo an actual diminution.. ‘Thus, in that

UU

658 COMPARATIVE ELECTRO-PHYSIOLOGY

part of the record which lies beyond the point of transition,
we can see that the excitatory change at first increases very
rapidly, and afterwards more slowly, under successive equal
increments of stimulus-intensity.

In order to test the universality of these characteristics of
nerve-responses, I obtained records with many different
specimens. The record just shown was taken, as already
said, with a sciatic nerve of gecko, which was in somewhat
sluggish condition. The next (fig. 401) was obtained from
the sciatic nerve of a vigorous bull-frog. On subjecting this
nerve to increasing stimuli, I, 2, 3, 4,.. . it was found that
the positive response reached
a maximum, after which it
declined, and the response be-
came diphasic. With gradu-
ally increasing stimulus, the
positive element in the re-
sponse now became smaller
and smaller, while the negative
grew larger. Above. this the
negative responses underwent

a very rapid increase.
Fic. 401.—Response of Nerve of ; ;
Bull-frog to Stimuli. 1, 2, 3, Up to this point, I have
. . . 12, increasing in Arithmetical peen describing the peculiari-
Progression : :
ties of response, as seen in
motor nerves. In order to show, however, that the same
characteristics hold good of the responses of sensory nerves,
I next took a specimen of the optic nerve of Ophzocephalus.
As I here wished to demonstrate the possibility of the response
after continuous increase, reaching a limit, I employed the very
moderate magnification of only thirty times, in the recording
Kunchangraph. With larger magnifications, the record
exceeds the recording-plate, and such a demonstration is
impossible. The object being thus to record the peculiarities
of response in the negative region only, that stimulus which
was taken as the unit was sufficiently strong to induce a
contractile response which, under the given magnification,

Ne anmenee

PHYSICAL BASIS OF SENSATION 659

appeared moderate. Records were then made under increas-
ing stimulus 1, 2, 3, 4, 5. ... It will be seen from these
(fig. 402) that increasing stimulus induces at first a rapid
augmentation of the negative response, after which a limit
is reached.

The same characteristics I find to hold good of the
response of plant-nerve (fig. 403). Here the response-records
were commenced at a point just above that of transition.
Now, if these particular relations between stimulus and
response be due, in the case
of man, to some specific
psychic reaction, then the
same must also be true not

Fic. 402.—Response of Optic Nerve FIG. 403. Mechanical’ Response
of Ophiocephalus to Arithmetically of Nerve of Fern to Arithmetic-
inereasing Stimuli 1, 2, 3, 4, 5, 6, 7 ally increasing Stimulus

only of the animal but also of the plant. And further, the
records themselves, being mechanical; were direct records
of undeniably physical changes. Even in the case of the
inorganic, again, the same characteristic relations obtain, as
we shall find in the next figure. Hence it is not true that
the relation between stimulus and the responsive reaction is
different in the inorganic from what it is in those living
nervous tissues whose changes we_ perceive .as_ sensation.
That is to say, it is determined, in all cases alike, by the
same underlying physical factors,
UU2

660 COMPARATIVE ELECTRO-PHYSIOLOGY

In fig. 404 we have a series of magnetic responses to arith-
metically increasing magnetic stimulation. The magnetising
current by which this was accomplished increased from :2
ampére to 2 amperes by steps of ‘2 ampere ata time. The
responses at first, as will be seen, increased at a very rapid
rate, and afterwards the rate declined. The remarkable
similarity between this record and that obtained with the
optic nerve of Ophzocephalus is at once apparent.

In the chapter on the modification of Response under Cyclic
Molecular Variation, I have already shown how the responsive
change differs in. intensity at different
parts of the characteristic molecular
curve. We there saw that just beyond
the point of transition, in the B state,
the rate of change was very rapid, and
that it became slower in the higher
part of the curve. The induced trans-
formations in the condition of the
nerve, by which it passes from the
phase B to @, and so on, are of them-
selves sufficient to elucidate not only
these, but also other obscure charac-
teristics of the phenomenon of sensa-
Fic, 404. Piciogta ht tion. They will, for example, explain

spied Mies sc ge the curious case in which an identical

Arithmeticallyincreas- stimulus given at regular intervals

sh is proves at first not unpleasant, and at
the end of the series actually painful. Here sensation has
become intensified, though the exciting stimulus remains the
same. I may quote here an account of an experiment by
Professor Sherrington, which exhibits this fact in a very
interesting manner :

‘I found that by focussing the heat rays from a lamp
upon a skin area of about 25 sq. mm. (on the back of the
hand), and allowing a perforated screen to intermittently
intercept the radiation, the heat-pain begins to be perceptibly
intermittent when, the times of play and of interception

PHYSICAL BASIS OF SENSATION 661

being equal, the intermittence falls below the rate of thirteen
per minute. An intensity of this intermittent radiation
stimuli, at first not painful, and yielding sensations strikingly
discrete, soon becomes dolorific, and then the sensations
remain discrete no longer, but are fused more or less to-
gether,’ ! i

This anomaly of gradual heightening of sensation, and
later, fusion of effects, appears at first sight inexplicable. I
shall give a satisfactory explanation of the latter point in the
next chapter ; but as regards the former of its two elements—
namely, the heightening of sensation under uniform intensity
of stimulus—we have seen that, owing to the after-effect of
stimulus, the condition of responding substances in general,
and nerve in particular, is gradually transformed, from a
point below the transition B to one above it. But, owing to
this transformation, the character of the response is changed
(cf. fig. 382). If the original response be positive, it will be

converted later into negative. If it be moderately negative,

it will be converted into more intense negative.

It will also be seen that the intensity of response is not
solely determined by the intensity of stimulus, but is modified
by the existing condition of the nerve. And this latter under-
goes a change by the action of stimulus itself. Thus there
are certain times of the day when, owing to sluggishness
of the tissues, our power of perception is dull. But acuity
of perception becomes enhanced with each successive stimulus
responded to. This is also true, more or less, of each indi-
vidual undertaking. These facts are easily understood from
a consideration of the different responses which are charac-
teristic of the ascent of the molecular curve above the point
of transition.

We have also to consider the fact that this progressive
molecular modification, under certain circumstances, imposes
the anticipation of the responsive maximum, with increasing
stimulus, or even, in other cases, the induction.of an actual
decline. The molecular variation, in consequence of the

1 Text-book of Physiology, edited by Schifer (1900), vol. ii. p. 998.

662 COMPARATIVE ELECTRO-PHYSIOLOGY

after-effect of previous stimulation, is seen by the shifting
upwards of the base-line. We may here refer back to fig. 31
where the responses of two different tissues to increasing
stimulus, show, in the one case complete recovery, and in
the other, a persistent after-effect. The base-line in the
former coincides with the line of absolute equilibrium ; and
increasing stimulus consistently shows an increasing response,
till, owing to molecular distortion reaching a maximum
value, a limit in the response was reached. In the second
of these records the persistent after-effect shifts the base-
line, which now becomes the line of modified equilibrium.
Owing to this fact, the relative maximum of variation
from the condition of modified equilibrium is reached much
earlier than would otherwise have happened. The extent
of individual response, after this, appears in fact to undergo
an actual diminution, though, measured from the line of
absolute equilibrium, this is not the case. In our sensation
we are unable to take cognisance of the absolute zero,
the changed condition of the nerve itself at any given
moment providing us with a relative zero, which is our
only standard of comparison, and our whole perception of
intensity depends upon induced variations from this chang-
ing zero,

The record which I have given in figs. 400 and 401, show-
ing the mechanical responses in the nerves of gecko and frog,
under increasing stimulus, not only explains the quantitative
change in the sensation, but also that change of quality or sign,
under appropriate conditions, which had not hitherto found any
explanation. We see in‘the curve of response, as has been
said, that with feeble stimulus response is foszdeve, and that
this positive response attains a climax, after which it diminishes
in amplitude, and then changes sign and passes over into
negative under increasing stimulation. In the corresponding
response by sensation, we find similarly, not only a difference
of quality or sign, but also a transformation from one to the
other, under increasing stimulation, from a climax where the
sensation attains a maximum of the pleasurable tone. After

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PHYSICAL BASIS OF SENSATION 663 ~

this the positive declines, and passes over the line of trans-
ition into the region of the negative or painful.

The fact, again, that a moderate stimulus, such as is
efficient to induce the positive sensation, will, if tetanically
applied, become negative or painful, finds satisfactory explana-
tion from the peculiar characteristics of the molecular curve.
For we have seen, under tetanisation, that the curve is raised
from the positive region, below the point of transition, into —
the negative, above it (cf fig. 383).

We have thus seen that by molecular transformation
the excitability of the nervous tissue may be enhanced or
depressed. There are other conditions also under which the
conducting power of the nerve, as well as its excitability,
appear to be modified by the exercise of will. Thus, by
attention, a stimulus which was previously scarcely per-
ceptible may be raised to sensory prominence. The reaction-
time, again, may be diminished by attention. The very
opposite of these effects, again, are induced by inhibition.
As an example of the latter may be mentioned the inhibi-
tion by the will of the muscular movements natural under a
given stimulus. It was at one time thought that this inhibi-
tion of movement was brought about by the in-nervation of
antagonistic muscles. This theory, however, is held to be
disproved by the fact that such inhibitory effects are seen,
even where antagonistic muscles are not present. It would
thus appear that the nerve is susceptible of being thrown
into certain conditions, in response to internal action, of an
unknown character, by which the transmission of excitation
through it is either accelerated or inhibited. This power
has been said to be ‘ unique and mysterious.’

That such opposite dispositions of the nerve may actually
result from opposite incipient distortions of the molecules is
well shown, however, by the action of electrotonus. Here
we have seen that by the influence of one pole an incipient
molecular distortion is brought about, which facilitates the
transmission of the true excitatory wave, while by the oppo-
site this transmission is hindered or blocked, Thus an

664. COMPARATIVE ELECTRO-PHYSIOLOGY

identical nerve will be rendered acceleratory or inhibitory
by the opposite.effects of the inducing tonus. |

If an external force be thus capable, according as it is
positive or negative, of inducing opposite molecular disposi-
tions, by which the conducting power of nerve is so pro-
foundly modified as to render it for the time being-either an
accelerator or an inhibitor, then it is not difficult to under-

stand that these molecular dispositions may also be yaried —

in a similar manner by impulses from an internal source.
The molecular dispositions themselves, by which these effects
are brought about, are no doubt curious, but they are neither
mysterious nor unique; for we have seen that by molecular
distortions of one sign or another, artificially induced in
magnetic substances, a given magnetic impulse may be either
accelerated or retarded.

We have seen that the transmission of excitatory changes
is facilitated,.if the nerve be subjected to incipient molecular
distortion in a favourable direction. Now in considering the
attitude of attention, we can see at once, if only from the
muscular indications which it induces, that the nervous
channel is probably thrown by it into a state of moderate
contraction. Inattention, on the other hand, must generally
be attended by an attitude of relaxation. We have again
found that while incipient contraction or K-tonus enhances
conduction, an intense contraction, or very strong K-tonus,
will inhibit, because the molecular distortion thus induced
is already maximum, and external stimulus can produce
little further effect (p. 610). It is here interesting to note
that the expression ‘steeling the nerves to pain’ is not
altogether fanciful or metaphorical. The attitude of pre-
paredness thus denoted is one of rigid contraction.

In the course of the present chapter, then, it has been
shown that there are two distinct nervous impulses, positive
and negative. The former, induced by feeble stimulus, gives
rise to a positive tone of sensation. The negative, on the
other hand, due to stronger stimulus, gives rise to a sensation

Pee ee

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PHYSICAL BASIS OF SENSATION 665

of painful or negative tone. The particular relation which
exists between stimulus and sensation has been shown to be
an expression of the peculiar characteristics of the molecular
curve. The ascent in the curve, being rapid immediately
above the point of transition, and slow later, equal increments
of stimulation cause in this region an increase of sensation
which is at first rapid and then slow. Below the point of
transition responses are positive. But tetanisation, inducing
a molecular transformation, carries the curve above the point
of transition. Hence moderate stimulus, inducing positive
sensation, is converted, when tetanically applied, into negative
or painful. The positive response is simple, but the negative
is complex, containing a masked positive; and we shall see
in the next chapter how this complex sensation can be
analysed into its component parts.

We have also seen that, in addition to moderate stimula-
tion, there are other agencies by which the tonus of nerves
may be altered. In a magnetic substance, the incipient
molecular distortions of one sign induced by K-tonus, enhance
the excitability and conductivity, while those due to A-tonus
depress them. Strong K-tonus, again, inhibits conduction.
By such polar actions, then, an impulse is either accelerated
or inhibited. Similar polar changes are seen in the nerve,
moreover, under the action of an- and kat-electrotonus. In
like manner, by the exercise of the internal stimulus of will,
the tonus of the nerve may be so varied that, under different
circumstances, the transmission of excitatory impulses is
accelerated or inhibited.

CHAPTER. XLIV
DISSOCIATION OF COMPLEX SENSATION

Conversion of pleasurable into painful sensation, and vice versa, by electrotonus—
The Sensimeter—Mechanical stimulation--Stimulation by thermal shocks—
Chemical stimulation—Opposite effects of anode and kathode--Normal effects
reversed under feeble E.M. F.—Negative tone of sensation blocked by alcohol
and anzesthetics—Separation of positive and negative sensations, by lag of
one wave behind the other—Dissociation of sensation by depression of con-
ductivity—-Abolition of the negative or painful element by block of conduction.

I SHALL next proceed to demonstrate, by means of decisive
experiments, the fact that sensation and its variations are
associated with certain physiological changes and _ their
appropriate modifications. In the mechanical and electrical
response of the nerve, we found that while moderate
stimulus gave positive response, a stronger stimulus gave
negative ; that while the positive was unmixed or elementary,
the negative contained a masked positive ; and further, that
the velocity of the transmission of the positive was greater
than that of the negative wave.

We shall now study the correspondence of the responsive
sensation with these various nervous changes induced by
stimulus, and their modifications under different agencies.
I shall next, therefore, show, in accordance with the chief aim
of this chapter, that the same conditions which determine the
exhibition of positive, mechanical, or electrical response, will
also, pari passu, determine positive tone in the responsive
sensation. Those conditions, on the other hand, which bring
about a negative mechanical or electrical change in the
nerve, will also induce a negative tone in the sensation. The
resultant transmitted effect recorded in the responding
apparatus, was, as we saw, determined by the receptive ex-

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DISSOCIATION OF COMPLEX SENSATION 667

citability of the stimulated point, and the conductivity of the
transmitting tissue. We shall, therefore, investigate separ-
ately the effects of various agents in the modification of
receptive excitability and of conductivity respectively. —

We saw, again, in the last chapter, that as the intensity of
stimulation is continuously increased, the response gradually
passes from the positive, through the point of transition, into
the negative. - This happens, as we have seen, immediately
above the point B. This region, therefore, may be referred
to as critical and indifferent, and must be regarded as having
the peculiarity that if, by any means, the molecular curve be
raised above it, the corresponding sensation tends to become
actually painful, or if carried below, becomes pleasurable.

It follows that, in this critical indifferent region, any
condition which tends to exalt the excitability of the tissue,
and thus the negativity of the response, will also accentuate
the negative tone of sensation, its mixed character thus
passing into the distinctly painful. Those conditions, on the

other hand, which lower excitability, and therefore responsive

negativity, will also act by detracting from the painful
element in the indifferent sensation in the critical region, and
rendering it to a greater or Jess extent positive, soothing, or
pleasurable. In this way, by depressing or raising the
excitability at will, a stimulus which had already caused a
painful sensation might be made not unpleasant, and an
indifferent or positive sensation could be made negative or
painful. We shall presently see how, by variations due to
the presence of internal or external modifying factors, the
positive tone of sensation is actually rendered negative, and
vice versa, under such transpositions.

Now we have at our disposal various well-known agencies
by which the excitability of the tissue can be raised or
lowered. In order to lower excitability, certain anzesthetic
agents may be employed, and their effect in the modification
of sensation-tones will presently be described. The ideally
perfect means, however, not only for the exaltation or
depression of excitability at will, but also for the rapid

668 COMPARATIVE ELECTRO-PHYSIOLOGY

interchange of the one effect with the other, is that of
electrotonus.

Under the normal condition of a medium intensity of
E.M.F., we know that it is the kathode which enhances excit-
ability, and the anode which depresses it. Hence an indifferent
sensation, however caused, will be rendered painful: when the
excited point is made kathode, or pleasurable when anode. If,

again, the stimulus be of sufficient intensity: to render the |

resulting sensation moderately painful, kat-electrotonus will
make it intensely painful, and an-electronus convert it into
soothing, by taking away from it the negative element.

The an- and kat-electrotonic effects referred to here are
those which fall under the generalisation made by Pfliiger.
I have shown, however, that the application of this law is
but limited. Under the action of a feeble E.M.F. these an-
and kat-electrotonic effects are exactly reversed, and it is
then the anode which renders the tissue excitable, the
kathode inducing relative depression. If, then, sensation-
changes are dependent, both qualitatively and quantitatively,
on antecedent physiological changes, we may expect corre-
sponding reversals to take place in sensation, according as
the anodic or kathodic applications are feeble or moderate.

And, lastly, we might expect to meet with other charac-
teristic changes in responsive sensation, due to the peculiar
differences shown in figs. 320 and 401, between the positive
and negative effects. We there saw that the positive
response was short-lived, whereas the negative was more
persistent. Even the negative response itself further was,
under moderate stimulation, of briefer duration than under

strong. In accordance with these facts there ought to bea _

difference in the fusion of sensation. Let us suppose that
the frequency of stimulus, for the induction of the indifferent
sensation, be adjusted in such a way as to cause a sensation
which is so fused as to be almost continuous. Under normal
kathode, this response, being converted into more persistent
negative, will now become completely fused and _ painful
Under normal anode, on the other hand, the individua

we ee 7 *

DISSOCIATION OF COMPLEX SENSATION 669

responses being converted into short-lived positive, the
resultant sensation will become discrete and pleasurable
Before proceeding to describe these experiments in detail, it
will be well to present these inferences in the form of a
tabulated summary :

EFFECT OF ELECTROTONUS ON INDIFFERENT SENSATION
IMPERFECTLY FUSED

Intensity of E.M.F. Anode Kathode
Moderate. Soothing and conspicuously | Painful and continuous.
discrete.
Feeble. Painful and continuous. . Soothing and conspicuously
discrete.

These generalisations I shall now demonstrate by means
of experiments carried out under, not one, but various forms
of stimulation. For experimental adjustment two conditions
have to be fulfilled. The first is so to regulate the intensity of
stimulus as to: cause the indifferent sensation. The second

is so to adjust its frequency as to induce a fusion of effects

all but complete. It may here be pointed out that in general
the degree of frequency necessary to bring about this semi-
fusion. will be a question of the effective intensity of
stimulation employed, and the excitability of the subject.
Having first decided on the intensity of stimulus to be
employed, it is easy to adjust its frequency by means of an
adjustable interrupter.

I shall first describe the Sensimeter, by means of which
these experiments were carried out. Mechanical stimula-
tion, when required, was caused by a tapper, actuated by an
electro-magnetic arrangement (fig. 405). When an electrical
current is sent round the electro-magnet, the soft iron arma-
ture is pulled down against an antagonistic spring. When
the current is stopped the armature is released, and the
tapper delivers a blow. The height from which the tapper
falls determines the intensity of the blow, the former being
dependent on the strength of the electro-magnetic pull,
which is determined in its turn by the intensity of the

670 COMPARATIVE ELECTRO-PHYSIOLOGY

current. This latter is adjusted by means of a carbon
rheostat. In order to adjust the frequency of stimulation,
a toothed-wheel is fixed on clock-work, the normal period of
rotation of the axle being once in four seconds. This
speed, however, may be continuously adjusted within a
certain range by means of a regulating governor. When
the toothed wheel has sixteen teeth, the frequency of stimu-
lation is four times in a second. By inserting wheels with
different numbers of teeth, and by means of the regulating

Fic. 405. The Sensimeter

governor, it is possible to obtain any desired graduation of
frequency.

The same experimental arrangement, with slight modi-
fications, may be employed to give a series of thermal shocks,
For this purpose the electro-magnetic tapping arrangement
is removed from the apparatus, and the electro-thermic
stimulator attached to the circuit, instead of the tapper. The
frequency of the thermal shocks may be regulated in the
usual manner, their intensity being dependent on that of
the heating current, which is adjusted by the rheostat.

DISSOCIATION OF COMPLEX SENSATION Crt

In experimenting on the effect of mechanical stimulation,
the intensity and frequency were so adjusted as to bring
about a neutral and imperfect fusion. In a_ particular
experiment, for example, the frequency of stimulus was four
times in a second. The receptive point for this experiment
was the very sensitive back of the end joint of the human
fore-finger—that is to say, the space immediately adjacent to
the quick of the nail. In order to study the electrotonic
effect, one electrode was applied by means of a piece of
cotton, moistened in normal saline, and placed on the
receptive area, the second being on a different finger. After
so adjusting the intensity and frequency of stimulus as to
sive the required semi-continuous and indifferent sensation,
the receptive point was made kathode, the E.M.F. employed
being moderate—that is to say, of 1°5 volt. The resulting
sensation was distinctly painful and continuous. By now
reversing the electrotonic current, the receptive point was
made anode, and the resulting sensation was not only
| positive or soothing, but also strikingly discontinuous. In
order to exhibit the reversal of these effects under feeble
; E.M.F., I employed an E.M.F. of ‘2 volt. The initial
indifferent sensation was now found to be converted under
anode, to negative and continuous, the kathode inducing a
soothing and discontinuous sensation. The effect under
a feeble E.M.F. is thus found to be in every way the opposite
of that under strong. When frequent experiments are
catried out on the same finger, the result is apt to be blurred
in consequence of fatigue. It is therefore advisable to carry
out the preliminary adjustment with one, and to repeat the
experiment on another finger. The normal opposite effects
of anode and kathode may in general be easily demonstrated
by an E.M.F. of 1°5 volt. But the value of the feeble
E.M.F. which induces the reversal of these, varies with
different individuals and with different modes of stimulation.
It is, therefore, advisable to start with the lowest possible
E.M.F. of the order of about ‘or volt, and increase it
gradually, till the reversal of effects is most pronounced. On

672 COMPARATIVE ELECTRO-PHYSIOLOGY

increasing the E.M.F. still more, the reversed effect passes
first into neutral and then back to the normal, characteristic
of ‘a moderate E.M.F.

Similar effects are also obtained on employing the
stimulus of thermal shocks. The electro-thermic stimulator
is now inserted in the Sensimeter, in place of the mechanical
tapper. The indifferent and incompletely fused sensation
becomes. continuous and painful, on making the receptive
point kathode, under a moderate E.M.F. of 2 volts. On now
making the receptive point anode, the sensation becomes
converted into a markedly discrete positive. The reversal of
these normal effects under a feeble E.M:F. was obtained in
a given experiment by thermal shocks, when the polarising
E.M.F. was ‘03 volt.

Turning next to the chemical mode of stimulation, it will
be remembered that an experiment has already been
described (p. 582) where a continuously irritating sensation
was caused by the application of salt on a wounded spot,
this moderate sensation of pain being rendered soothing
~when the spot was made normal anode, and intensely painful
when normal kathode. Effects precisely opposite resulted
from the application of a feeble E.M.F. It will thus be seen
that those same conditions which depressed the normal
negative response, also acted to obliterate the negative tone
from the resulting sensation. Those conditions, on the other
hand, which exalted the negativity of the response, would
convert the positive tone of sensation into negative or
painful. These general facts have been demonstrated by
the employment of different forms of stimulation, the neces-
sary depression or exaltation of excitability having been
brought about by electrotonus. So far we have dealt with
the modifications induced in the responsive sensation by
the variation of the receptivity of the excited point. We
shall next briefly discuss the effects which ensue on the
variation of the excitability and conductivity of the nerve by
different agents. In order to induce depression, there are
various anesthetic agents which might be used.

DISSOCIATION OF COMPLEX SENSATION 673

In investigating the influence of alcohol (p. 493) we saw
that three distinct effects were induced by it on the
receptivity, responsivity, and conductivity of a tissue
respectively, these effects themselves being further modifiable
by the duration and intensity of the application. It was
shown that, in the first stage of its application, alcohol exalted
the power of receptivity. But its effect on conductivity and
responsivity, especially after a certain duration of application,
was one of great depression. The total effect of alcohol is
thus somewhat complex. At an early stage of its applica-
tion there is an effect of exaltation. After a while, however,
the conducting power becomes increasingly depressed by its
action. This means that the passage of the true excitatory
or negative wave is progressively impeded or even blocked,
the positive alone continuing to be transmitted for a time.
At a certain stage of alcoholisation, therefore, the negative
tone of an existing sensation, normally painful, will, as it
were, be erased. And this withdrawal of the painful element,
by causing sudden relief, together with the actual trans-
mission of the positive wave, may induce a tone of sensation
which might even perhaps be regarded as pleasurable. In
any case the abolition of conductivity must eliminate the
element of pain, and it was undoubtedly this which, in
pre-anzesthetic medicine, caused its employment for certain
minor operations. Long and intense alcoholisation will, of
course, obliterate all sensation. On the after-effects of so
depressing a reagent it is unnecessary to dilate.

Effects, in some respects parallel, may be observed under
etherisation, where, at a certain stage in the action of the
narcotic, there is a cessation, not of all sensation, but of its
painful element alone. Thus, by depression of conductivity,
and’ consequent suppression of the negative wave, the positive
may be ‘dissociated’ from the negative sensation. Sustained
pressure on a nerve is also known to depress conductivity,
and it is interesting to note here that pressure.on the ulnar
nerve-trunk will abolish painful sensation, the positive, or
mere contact-sensibility remaining practically undiminished.

X X

674 COMPARATIVE ELECTRO-PHYSIOLOGY

We shall next study the various effects induced by the
variation of conductivity. We have already seen that a
moderately intense stimulus gives rise to two waves, one
positive and the other negative, the former having the
greater velocity of the two. Thus these two waves, starting
from the receptive and reaching the distant responding point,
will give rise to two different responsive effects, separated

from one another by an appreciable interval. The separation

depending on the lag of one wave behind the other, will be
greater the greater the length of the conducting tract. The
first to arrive at the perceiving centre being the positive
impulse, we shall have there a positive sensation of mere
touch or contact. The later-arriving negative wave gives
rise, according to the nature of the indicator, to mechanical
contraction, galvanometric negativity, or a painful sensation,
as the case may be. If the conducting tract be not
sufficiently long, the two waves will be superposed, or
indistinguishable, one masking the other. But they may be
analysed, or separated, by anything which diminishes the
conductivity of the intervening tract, and this is rendered
possible by the fact that the positive wave is not much
affected by changes of conductivity. On the other hand, the
velocity and intensity of the negative wave are both
diminished by anything that diminishes the conductivity.
Hence a diphasic response—the sensation of touch followed
by pain—may be expected, wherever the intervening con-
ducting tract between receptive and responsive points is
sufficiently long. In other cases, where the tract is shorter,
a sufficiently strong stimulation will give rise to a single
sensation of negative or painful tone. This negative
sensation, however, is complex in its character, masking as it
does, a contained positive element. If then the conductivity
of this transmitting nerve be in any way diminished to a

moderate extent, the complex sensation will be found to be

analysed, the negative being made to lag behind the positive.
There will thus be a dissociation of the dual elements of the
complex sensation, and the result will be a diphasic response

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DISSOCIATION OF COMPLEX SENSATION 675

—the positive or sensation of contact, followed by that of
pain. With: still greater depression of conductivity, the
normally painful sensation, by the blocking of its negative
element, will be turned into one of positive tone.

We shall now proceed to verify these theoretical inferences.
The fact that there are actually two distinct nervous impulses,
and that of these the positive travels faster than the negative,
is demonstrated by the well-known experiment in which a
smart tap is applied on the ball of the foot, with the result
that we perceive, first, the sensation of touch, and then, at an
appreciable interval afterwards, that of pain. The possibility
of this demonstration in a normal nerve is due to the length
of the conducting nerve here concerned.

In other cases the same dissociation is seen to be effected
under varying degrees of loss of conductivity, in different
forms of nervous paralysis. The considerations which I have
advanced, will, however, I believe, offer a satisfactory explana-
tion of those curious instances of ‘dissociation’ and ‘ delayed

pain’ which are known to pathology. In such cases, a prick

with a pin, for instance, is first perceived as mere contact,
and then, after an appreciable interval, as the sense of pain.
Other cases are known in which, the loss of conductivity
being very great; the patient could handle burning coal with-
out pain, the resultant perception being entirely positive.
From the diverse phenomena described in this and the
previous chapters, it is clear that a sensation of positive tone
is associated with that particular responsive change in the
nerve, which is expressed as expansion and galvanometric
positivity. We have also seen that such effects are brought
about by a feeble intensity of stimulus, which acts to increase
the internal energy without inducing the true excitatory
negative effect. Of anything which thus increases the
internal energy, it may be said in general that it will induce
positive mechanical and electrical expressions with concomi-
tant positive sensation, With stronger stimulus, as we have
seen, the negative mechanical and electrical responses are
induced. But such negative responses contain, as we have
XX2

676 COMPARATIVE ELECTRO-PHYSIOLOGY

also seen, the masked positive component, and from the point
of view of energy, they represent the algebraical summation of
income and expenditure, positive and negative, increase and
diminution. Considered as sensation, then, this particular
effect will be composed of dual elements, a mixture of positive
and negative tones. With very strong stimulation, finally,
the negative effect will be very great; expenditure will be
greater than income; and the sensation will assume a pre-
dominantly and persistently negative tone.

The complex negative, moreover, containing a masked
positive, is capable of dissociation into its component
elements. By the partial or complete block of conductivity,
it is exhibited as dual response of ‘dissociation, or by the
total suppression of the negative, as positive alone. In this
way, a sensation, originally painful, may be rendered not
unpleasurable, or even pleasurable. It was further shown,
employing electrotonus and the sensimeter, that an indif-
ferent and semi-fused tone of sensation can, by merely exalting
the excitability of the tissue, be converted at will into one

which is continuous and painful. By depressing the excit-

ability, on the other hand, this indifferent sensation may be
made pleasurable and strikingly discrete.

|
‘
|

CHAPTER XLV
MEMORY

Memory an after-effect of stimulus— Persistence dependent on strength of stimulus
—Rate of forgetting—Multiple after-effects in retina—Spontaneous revival of
after-images— Theories of memory— Latent images and their revival—After-
effect of stimulus on excitability and conductivity—Differential effect of diffuse
stimulus—Revival of latent image in metal—Revival of latent image on phos-
phorescent surface—Negative or reversed memory-image—Psycho-physio-
logical version of this experiment—Differential excitation under diffuse
stimulus, internal or external—Continuity of this seen in mechanical response
of plagiotropic stem and pulvinus of A/cmosa, in the electrical discharge of
certain fishes, and in psychic response of memory.

Up to the present we have considered only the immediate
effects of stimulus. We know, however, that excitation
entails, not only an immediate, but also an after-effect.. We
are thus led to the question of the physical aspects of the
phenomenon known as memory, which is admittedly a
matter of after-effects. Even with the somewhat insensitive
apparatus for the detection of nervous changes which is at
our disposal—the galvanometer or the Kunchangraph—we
find that the after-effect of strong is more persistent than
that of feeble stimulus. In the very sensitive neurile
apparatus, nervous changes and their after-effects are more
distinctly perceived. The psychological retention of an
impression follows, in general, the curve of response and
recovery. The fact that physiological recovery from the effect .
of strong stimulus is less rapid than from feeble, has its
correspondence in the period required for the fading of
sensory impressions, of which also it may be said that the
stronger persist longer than the weak.

This fact that the after-effect of strong stimulus siteitls

678 COMPARATIVE ELECTRO-PHYSIOLOGY

for a longer time than that of feeble, may be exhibited in.an
interesting manner as follows. A simple design is made
with magnesium powder and fired in a dark room. A
second observer, unacquainted with the design, observes the
flash and closes his eyes. The instantaneous flash,
obscured as it is by dense smoke, does not at once produce
any definite impression. In the retina, however, the ob-
scuring image of the smoke, being of little luminosity,
quickly passes off, and the after-effect of the brilliant flash,
thus separated from the obscuring smoke, grows into perfect
distinctness. In this manner I have often been able, by sub-
sequent closure of the eyes, distinctly to observe luminous
phenomena of brief duration, which, while the eyes were
open, had been indistinguishable. :

We have thus touched upon the question of the time
required for the obliteration of a mental impression.
Another interesting aspect of this subject lies in the rate at
which fading takes place, or, in other words, the rate of
molecular recovery. In the curve of recovery we find that
this rate is at first very rapid, and becomes increasingly slow
with the descent of the curve. This is also the characteristic
of the process of forgetting, Ebbinghaus, for instance, found
that the forgetting of a series of ‘nonsense syllables, at first
quick, became increasingly slower with time.

Certain excitable tissues, such as nerve and cardiac
muscle, give responses to strong stimulus, which, as we have
seen, are multiple in character. The retina, again, under
intense stimulus of light, exhibits multiple after-excitations,
which may be detected by a galvanometer (p. 426). This
fact explains the multiple after-image often seen on closing
the eyes after strong light. Another proof that these
multiple after-images are physiological lies in the fact that
their periodicity is modified by a previous condition of rest
or activity. Thus, early in the morning, when fresh from
rest, this period I find to be at its shortest, and later in the
day to become gradually longer, owing to growing fatigue.
In a given instance, the period at 8 A.M. was 3 seconds,

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MEMORY 679

which had lengthened to 5 seconds by 3 P.M.; and was
further prolonged to 6°5 seconds by II P.M. |

One way of exhibiting the after-images in the retina is,
as we have already seen, by means of a stereoscope con-
taining two incised slits inclined to each other, instead of
photographs. On looking through this at the bright sky for
ten seconds, or longer, a composite image is formed of an
inclined cross. The eyes are now closed, and the first. effect
noticed is one of darkness, due to the molecular rebound.
By reason of the Binocular Alternation of Vision, already
referred to, one luminous arm of the inclined cross now
projects itself aslant the dark field, and then slowly disap-
pears, after which the second, perceived by the other eye,
shoots out suddenly in a direction athwart the first. This
multiple alternation proceeds for a long time, and produces
the curious effect of two luminous blades crossing and re-
crossing each other. At first the after-images of the cross,
seen with the eyes closed, are very distinct, so distinct that
any unevenness in the design at the edges of the slanting
cuts can be made out clearly. There is here no doubt of
the ‘objective’ nature of the strain impressed on the retina,
which, on the cessation of direct stimulus of light, gives rise
to after-oscillations with concomitant visual recurrences.
This recurrence may be taken as a proof of the existence of
physical strain in the retina. The recurrent after-image is
very distinct at the beginning, but becomes fainter with each
repetition. A time comes when it is difficult to tell whether
the image is the objective after-effect due to previous strain,
or merely an effect of ‘memory.’ There is, in fact, no hard-
and-fast line of demarcation between the two—one merges
simply into the other. In connection with this, it is
interesting to note that some of the phenomena of memory
also are admitted to be recurrent.

Visual impressions and their recurrence often persist
for a very long time. It usually happens that, owing to
weariness, the recurrent images disappear, but in some in-
stances, long after this disappearance, they will spontaneously

680 COMPARATIVE ELECTRO-PHYSIOLOGY

appear at most unexpected moments. Thus in a given case
of the present experiment, performed in the afternoon, the
subject perceived this recurrence for some time, after which
the alternating impressions seemed to disappear, and were
completely forgotten. On retiring at night, however, these
recurrent images suddenly reappeared. Thinking the matter
to be an effect of light, the observer hastily extinguished his
lamp. But the recurrent images now became only the more ©
intense.

In another case the recurrence was observed in a dream,
about three weeks after the original impression was made,
and in this case it was seen as the crossing and recrossing
of bright swords. These instances of the revival at night of
impressions made in the daytime, when the interference o
distracting influences is withdrawn, is significant. Since an
intense stimulation of nerve is liable to recur spontaneously,
‘without the action of the will, or even in spite of it, it follows.
that any single impression, when very intense, may become
dominant, and persist in recurring automatically. Examples
of this are only too familiar.

We have hitherto dealt with that aspect of memory in
which it isa more or less immediate after-effect of sensory
stimulation. But we encounter a much more difficult pro-
blem when we come to the question of the revival of an
image long after it has apparently faded. It has been sug-
gested that this process of revival depends upon the existence
of some ‘scar, or fixed impression, in the brain, or on a
certain persistent disposition or tendency to movement
created there. It is perhaps worth while to point out here,
however, that though when a blow is recent, the smarting
effect will persist for some time, yet; when once healed, no
scar could of itself reproduce the original excitation. It is of
course recognised that such expressions are merely figurative,
and that the entire process is not clearly understood. We
are more likely, however, to arrive at a true explanation of
the phenomenon if we recognise in it two distinct factors,
first, that of molecular change, with concomitant change of

MEMORY 681

properties ; and, second, the effect of an internal stimulus,
delivered as a blow from within, by an impulse of the will,
upon the sensitive surface in which the image is latent. _

We shall now first observe in some detail those changes
which remain as an after-effect of previous stimulation. The
differential effect caused by primary stimulus fixes the latent
image, and it is only by the reproduction of the same differen-
tial excitation, that the memory-image can subsequently be
revived.

We must here recall briefly the results which were estab-
lished in Chapter XLII., on the modification of response
under cyclic molecular variation. It was there shown that,
under the action of stimulus, the molecular condition of a
substance undergoes a progressive variation, exhibited in its
characteristic curve ; that the forward and return curves do
not exactly coincide, because the history behind the two
half-cycles has not been the same; and, finally, that on the
cessation of stimulus, the original molecular condition is not
exactly restored, a certain effect being residual. Owing to
this residual effect, the properties of the responding sub-
stance are changed. We also saw that, in consequence of
this impressed change, the conductivity and excitability of’
the substance might be enhanced. A frequent repetition
of a stimulus was thus shown to create a habit or disposition
by which the mass of a substance, formerly almost non-con-
ducting, might be made a conductor of excitation.

These impressed molecular changes may not leave any
visible impression behind. But let us look at the responding
properties of a given substance at different points on the
characteristic curve. In a sluggish A condition, that is to
say, before it has even been excited, the power of response of
the substance to a given stimulus will be slight or negligible.
Let us suppose next that by the action of stimulus the sub-
stance is raised above B. On the cessation of stimulus a slow
recovery will then take place, whose completion may be
indefinitely prolonged. The substance will thus approach
very near the point B in the curve, without actually reaching

682 COMPARATIVE ELECTRO-PHYSIOLOGY

it. This difference between B and the point actually reached
may be so small as to be undetectable by any ordinary
mode of inspection. We therefore term the impression
latent. But the properties of this B area, formerly acted
upon, have been profoundly changed, being rendered more
excitable by the impressed effect of previous stimulus. In
this sensitive impression-surface will be certain areas in the

A and certain others in the B condition, the former sluggish.

and the latter characterised by enhanced excitability. By
the shock of an internal diffuse stimulus, a differential excita-
tion may now be induced, exactly similar to that caused by
primary stimulus. This zs.the revival of the memory-image.

_ We may carry out a physical experiment exemplifying
this process of the rise of a latent impression into vividness
under the action of diffuse stimulus. We may take a sensi-
tive surface, in which different areas, in consequence of pre-
vious excitation, have impressed on them latent variations of
excitability. Thus indifferent portions of the surface A, A,,
may have their excitability represented by zero, another
portion B, whose excitability has been exalted as the after-
_effect of stimulatory agents previously applied, will have its
normal excitability enhanced. In still a third portion, C, the
excitability is artificially depressed or abolished. The
responding substance was a tin wire; dilute solution of
sodium carbonate, which is an exciting agent, was applied
on the area B. The depressing or poisonous reagent, oxalic
acid, was applied at c. After a short period of this applica-
tion the wire was washed, and there was no outward indica-
tion of any difference between the areas A, Bandc. Elec-
trically also there was little or no permanent difference
between them. One non-polarisable electrode connected
with a galvanometer was kept permanently applied on the
indifferent surface A,. The second exploring electrode was

now moved along the wire, and while it rested on any point.

the wire was excited as a whole by vibration. The galvano-
meter, under this arrangement, would detect differential
excitability. As long as the exploring wire moved over

ae

MEMORY 683

indifferent areas there was no effect detected in the galvano-
meter. But as soon as the exploring electrode rested on the
area B, the latent enhancement of excitability there showed
itself by a sudden responsive up-movement of the galvano-
meter. When the electrode again passed over B and reached
an indifferent area, A,, response disappeared. But when it
reached C, with its depressed excitability, there was another
responsive movement, this time in the reversed or down
direction. It is thus seen that the impress made by the

Fic. 406. Revival of latent Image in Metal

action of stimulus, though it remain latent and invisible, can
be revived by the impact of a fresh excitatory impulse
(fig. 406).

Again, this revival of the latent image by a subsequent
stimulation may be exemplified ina simpler and more striking
way. We take a card and coat it with some so-called phos-
phorescent material, such as luminous paint. This is kept
a long time in the dark, till the whole is reduced to a uniform
A condition. From a previous experiment we have deter-
mined what is that duration of exposure, T, to a given

684 COMPARATIVE ELECTRO-PHYSIOLOGY

intensity of light, which will evoke a luminous or phosphor-
escent response. A stencilled pattern is now placed on the
prepared card, and the whole is exposed to light for the time T.
On now cutting off the light and removing the stencil a
luminous pattern is seen, which is the primary response.
This impression slowly fades out. But the cardboard now
contains a latent image, whose revival will be analogous to

that of memory. The stimulated areas which have now

ceased to respond are still, in virtue of previous stimulation,
in the B condition, which is more excitable than the indif-
ferent A. A feeble diffuse stimulus should now, by its
differential action, prove efficient to revive the latent image.
We now expose the whole card to diffuse stimulation of light,
of a duration shorter than T. The excitation of the indifferent
background will by this means be ineffective, whereas it will
be effective wherever the image proper has been impressed.
We shall, therefore, obtain a revival of the positive image—
that is to say, an image of the same kind as the original.

An interesting case occurs here, showing the theoretical
possibility of obtaining a negative or reversed ‘memory
image.” The possibility of this will be understood, from an
inspection of the characteristic curve. We saw that in the
region B the substance rises in excitability. But in the
region of D and E, where the maximum molecular distortion
has already been reached in consequence of over-stimulation,
fatigue changes are induced, by which the excitability is
depressed below the normal. It follows from what has
already been said that an impressed image of this character
will be revivable, under subsequent diffuse stimulation, but as
a negative, or reversed memory-image.

I shall now describe a psycho-physiological version of this
experiment. Let the observer stare at the incandescent fila-
ment of an electric lamp, preferably with one eye, say the
right, the left being kept closed all the time. The right eye
is next closed, and is further covered by the hand. Multiple
after-images will now be seen for some time, till the impression
seems to have completely disappeared. No trace of the

ae Se

. oe

ee, Se Sie eee

MEMORY 685

latent image is now perceivable in the field of dark vision.
When this point has been reached, the hand is suddenly
withdrawn from its position over the closed right eye. The
light in the room now percolates through the semi-translucent
eye-lid, and suddenly gives a moderate diffuse stimulus to
the retina. Under these circumstances, the latent image is
revived, as a negative—that is to say,as a very dark filament
against a brighter background. Thus the essential condition
for reviving the latent impression of stimulus would seem to
be the subjecting of the unequally impressed tissue to diffuse
stimulation. The revival of the image as positive or negative
will then be a question of whether the stimulus have been
moderate or intense.

I have already shown, by actual experiment on nervous

tissues themselves, that the differential excitability induced

as an after-effect of moderate stimulus (memory-impression)
will give rise, on diffuse stimulation, to one kind of response,
and the after-effect induced by strong stimulus to the reverse
(cf. figs. 311, 312). In the former case, the moderately
stimulated area, on diffuse re-stimulation exhibits induced
galvanometric negativity, as compared with the indifferent
contact, this being the sign of its relatively greater excitation.
In the second case, the sign of response is reversed, the
over-stimulated area, on re-stimulation, becoming galvano-
metrically positive.

The revival of memory-images is thus seen to be due to
differential response, evoked by diffuse stimulus, in an organ
rendered anisotropic, by the unequal impressions which it
contains of previous stimulation, A similar differential effect
under diffuse stimulation has been seen in plagiotropic stems.
Here the upper surface has a deep impression or memory of
over-stimulating sunlight, and on diffuse stimulation this
upper surface becomes galvanometrically positive, a respon-
sive current flowing from below to above. It will thus be
seen that there is a continuity between the impressions made
on the sensitive neurile elements, and the physiological
anisotropy induced by the differential action of past stimulus.

686 COMPARATIVE ELECTRO-PHYSIOLOGY

Diffuse stimulus, moreover, whether internal or external,
acting on the differentially excitable tissue, gives rise to a
marked indication, which may be either motile, electrical, or
psychic. A stimulus is applied to the stem of JM/zmosa.
This is transmitted as an excitatory impulse, and reaches the
differentially excitable organ, the pulvinus. As-‘far as this
organ is concerned, the transmitted stimulus may be re-
garded as internal. This internal stimulus, then, gives rise
to a conspicuous differential effect, shown in the fall of the
leaf. In electrical fishes, similarly, the internal stimulus,
delivered by the will of the animal upon the differentially
excitable organ, becomes evident as an excitatory discharge
In man, again, the revival of memory constitutes a psychic
response, due to the play of the diffuse internal stimulus of
will upon a sensitive surface rendered differentially excitable .
by the presence of a latent image.

It will thus be seen that various after-effects of stimulus
find expression as the phenomena of memory. The effect
of primary stimulus does not disappear at once, but fades
gradually, with a concomitant fading of the sensory impres-
sion. From the fact that the after-effect of feeble, is less
persistent than that of strong, stimulus, we understand that
the sensory or memory impression also lasts longer in the
latter case than in the former. Very intense stimulation,
again, is apt to give multiple responses as its after-effect, and
the corresponding psycho-physiological phenomenon is seen
in the recurrent after-images in the retina.

When a considerable interval has elapsed after the
primary stimulus, there is apparently no trace left of the
latent image. But the properties of the impressed portions
of the sensitive surface have undergone a more or less
permanent change in consequence of stimulation. Certain
channels have been rendered more conducting, and certain
areas more excitable. By an internal diffuse impulse it
is now possible to cause differential excitation, and thus to
revivify the latent image.

CHAPTER XLVI
REVIEW OF RESPONSE OF ISOTROPIC ORGANS

Laws of response—Opposite responsive expressions of true excitation and
increase of internal energy—-Separation of the positive and negative waves—
Position in molecular cycle determines character of response—Abnormal
sub-tonic positive and reversed fatigue positive—Effect of tetanisation—
Similar effects in the inorganic—Phasic alternations—Multiple and auto-
nomous response—Unmasking of antagonistic element by overshooting —
Different expressions of a single fundamental molecular change —Response
by change of form, by secretion or absorption, by variation of electric
resistivity, or by electro-motive change—For the last, induction of anisotropy
necessary—Perfect modes of stimulation : (a) Torsional vibration ; (¢) Rotary
mechanical stimulation ; (c) Thermal shocks; (@) Equi-alternating electric
shocks—Accurate determination of the death-point by mechanical and
electrical spasms—Current of injury due to after-effect of stimulus—
Explanation of characteristic electric distribution in plant and muscle
cylinders—Relative positivity of dead tissue—Reversal of current of injury
so-called—Unreliability of response by negative variation.

IT has been shown, in the foregoing chapters, that all the
diverse phenomena of response may be summarised in the
two following formule :

1, Excitatory response takes place by contraction and
galvanometric negativity.

2. Increase of internal energy induces the opposite effect,
of expansion and galvanometric positivity.

The first of these effects is simply demonstrated by direct
excitation of an excitable tissue. In order to demonstrate
the second, stimulus is applied at a distance from the
responding point. In consequence jof sudden local con-
traction at the receptive area, a wave of increased hydrostatic
tension is transmitted with great rapidity. Energy is thus
conveyed hydraulically, and at the distant responsive point
the transmitted effect induces expansion and galyanometric

688 COMPARATIVE ELECTRO-PHYSIOLOGY

positivity. This is followed by the more slowly transmitted
wave of true excitation, which on its arrival gives rise to the
normal response of contraction and galvanometric negativity.
The two responsive effects can thus be exhibited separately,
when one lags behind the other. When the intervening
tract is short, or the conductivity great, the excitatory
negativity masks the hydro-positive effect. But this hydro-

positive may again be unmasked, by various forms of.

selective physiological block, which depress the conduction
of the true excitatory, without interfering to any appreciable
extent with the passage of the hydraulic wave. In this way,
the positive may be separated from the contained negative,
the response being thus rendered diphasic— positive followed
by negative. Or, by the complete suppression of the
excitatory negative wave, a response originally negative may
be converted into purely positive (figs. 45, 47, and 49).

As response is an expression of molecular derangement,
it is the extent of this which determines its amplitude. The
character of response is also modified by the molecular
condition of the responding substance, and the different
molecular conditions through which a substance may pass
are indicated by the characteristic curve. From the study of
such a characteristic curve we find that these molecular
transformations are not specific, but of general occurrence—
alike in inorganic and living tissues. When the energy of
the ‘responding substance is for any reason below par, that is
to’ say, when it is in the extremely sub-tonic A condition,
external stimulus will be absorbed without evoking the
normal excitatory expression. Response will then be
abnormal, or of opposite sign to the true excitatory effect.
By the absorption of impinging stimulus the substance now
passes into the next stage B, where molecular transformation
proceeds at a rapid rate. At this stage, the previous
abnormal response is not only reversed to normal, but
successive responses exhibit a staircase increase. At the
next or C stage, the responses are uniform. Following this,
we arrive at the maximally distorted position D, Stimulus

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SE ——EE—E———=—— se CUreO

REVIEW OF RESPONSE OF ISOTROPIC ORGANS 689 |

at this stage induces little further excitatory distortion, while
the tendency to recovery is great. In this fatigue-state the
amplitude of response undergoes a decline, and in. the
succeeding stage E an actual reversal. :

_ The various corresponding types of response—sub-tonic
abnormal, staircase, uniform, fatigue-decline, and fatigue-
reversal—are not exhibited by any one particular kind, but
by all forms of tissues. Thus muscle may exhibit a short-
lived staircase effect, and nerve, supposed to be indefatigable,
not only shows decline, but even reversal of normal response,
under extreme fatigue.

There are two definite conditions ander which the normal
negative response is converted into abnormal positive, with
an intermediate diphasic. These are (1) the condition of
extreme sub-tonicity, and (2) that of fatigue brought on by
over-stimulation. As regards the first, it is to be remem-
bered that the normal excitability of a tissue is maintained
by the supply of energy from the rest of the organism of

which it forms a part. Under isolation, the latent energy or

tonic condition of the tissue is liable to fall below par, under
which circumstances the response becomes abnormal positive.
By the absorption of the energy of stimulus, the substance is
transformed from the A to the B condition, with restoration
of its normal response. The process of gradual .trans-
formation may be seen in a series of records to successive
stimuli, when the abnormal gradually passes into the normal,
through an intermediate diphasic.. Or, an intervening
tetanisation will serve to convert response from the abnormal
to the normal. Abnormal or reversed response is also seen
to occur under fatigue, but its genesis in the molecular curve
is here in reversed order to that of the abnormal response of
sub-tonicity. In the latter, during the continuous trans-
formation from the A to the © phase, stimulation converted
the abnormal response into normal, through diphasic. But
now, during transformation induced by stimulus from C to E,
the normal negative passes into abnormal positive, through
intermediate diphasic. To transform the abnormal positive
¥-Y¥

690 COMPARATIVE ELECTRO- PHYSIOLOGY

into normal negative in the first case, stimulation is necessary.
To do the samein the second case, rest is necessary. In
the records obtained from different animal tissues, various
anomalies are met with, of which there has not hitherto been
any satisfactory explanation. Thus the same tissue at
different times will be found to give either the normal
negative, or di-phasic, or abnormal positive response. Thus
it has been shown that in the two extreme cases alike, of sub-.
tonicity and fatigue, the response of nerve is abnormal positive
(p. 636). Numerous other examples of this fact have been met
with in the course of this work, in, for example, the response
of skin (p. 311), that of the glandular and digestive organs
(pp. 342, 346), and that of retina (p. 423). It will thus be
seen how important is the molecular condition of the tissue
in determining the nature of response. This is strikingly
shown in the fact that the same tetanisation which in the A
condition converts the abnormal to normal, in the D will
convert the normal into abnormal. Again, if tetanisation be
applied at the beginning of the B stage, the subsequent re-
sponses are enhanced, whereas the same tetanisation at the
_end of C induces a fatigue reversal (figs. 394, 395, and 398).
That the explanation of these various results is to be
sought for in molecular considerations, and not in that hypo-
thetical assimilation and dissimilation which really explain
nothing, is fully demonstrated by the fact that precisely
similar responsive variations are obtained, in the same cir-
cumstances, in the case of inorganic matter, under different
forms of stimulus and different methods of record. As an
example, may be cited the transformation of abnormal
response into normal, in tungsten, after tetanisation (fig.
391), the stimulus employed being electric radiation, and
the mode of record, resistivity-variation. Parallel effects have
been shown in the case of tin, the response being recorded
by the electro-motive variation, and the stimulus employed
mechanical (fig. 386). The enhancement of normal response
also under tetanisation, when at the B stage, has been shown
in tin (fig. 388); and finally, the reversal of normal response

REVIEW OF RESPONSE OF ISOTROPIC ORGANS 691

by fatigue was shown in tungsten under electric radiation,
while in the contractile response of indiarubber under thermal
stimulation it took place with intermediate diphasic: (fig.
397). The characteristic curve has been shown to exhibit
the history of molecular transformation under continuous
stimulation. In the first part of this curve a progressive
change is shown to be manifested outwardly by increasing
contraction or galvanometric negativity. In the second part
a reversal of this process is seen to occur. This is illustrated
in records of response under continuous stimulation. Thus
muscle shows increasing contraction, to be followed by
fatigue-relaxation (fig. 64). The same thing is observed in
Mimosa, as a fall of the leaf, followed by its re-erection
(fig. 65). Electrically, this is observed as increasing galvano-
metric negativity, followed by reversal to positivity. These
phasic alternations may in some cases be exhibited only
once, and in others repeatedly. Thus, in a certain style of
Datura such phasic alternation is seen to occur twice (fig.
76); and again, in leaflets of Desmodium gyrans, at first
quiescent, continuous stimulus of light gives rise to those
repeated alternations of negative and positive which consti-
tute multiple response (fig. 141). The distinction between
the tissue which gives only one such alternation, and others
which display it in repeated succession, is not, it should be
borne in mind, rigid. Even skeletal muscle, under certain
circumstances,.is found to give rise to rhythmic excitations.
The fact that multiple response is a phenomenon of wide-
spread occurrence, and not specifically characteristic of any
particular kind of tissue, has been fully demonstrated in the
course of the present work,

It would appear that there is a tendency of the incident
stimulus, when applied continuously, to find an expression
whose predominant characteristics are alternating. We may
first have the exhibition of excitatory molecular distortion.
But when this has reached a maximum, no further excitatory
expression being possible, the incident energy becomes
relatively effective in increasing the internal factor,- with

YY2

692 COMPARATIVE ELECTRO-PHYSIOLOGY

attendant expansion, galvanometric positivity, and enhanced
power of recovery. At the maximum point—that is to say,
at the top of the tetanic curve—the two forces are balanced ;
and at this point, if the stimulus be suddenly withdrawn, the
particular state of unstable balance is often manifested by a
brief overshooting in one or other direction. This effect’ is
often noticed in the retina and in certain vegetable structures

under the action of light (figs. 244, 247, 254, and 260), and

in nerve under electric tetanisation (p. 536). That it is not
primarily dependent on assimilation and dissimilation, but
on the molecular factor, is seen in the fact that similar effects
are also to be observed, under corresponding circumstances,
in the response of inorganic substances (figs. 258 and 383).

The phasic molecular alternation so conspicuously ex-

hibited under continuous stimulation may also be seen in the
record of responses to successive stimuli. . The phenomenon
is then regarded as an after-effect and shown by the shifting
of the base-line of the record (figs. 208 and 396).

Since the effect of stimulus is to induce a molecular
upset, the change in question must be attended by various
concomitant physical changes. It will therefore be possible
to record the excitatory effect by recording the attendant
variations of any one of these. The effect of stimulus may
thus be recorded by (1) the accompanying change of form,
in: contraction or expansion; (2) an attendant secretion or
absorption; (3) a variation of electric resistivity by dimi-
nution or increase of resistance; and (4) electro-motive

changes of galvanometric negativity or positivity. The

changes in the responding substance as a whole, may be
recorded by any one of the first three methods. But in the
last, or that by the electro-motive variation, the method
depends on the relative variations of the electric potential at
two different points. -For if the substance be isotropic and

subjected to diffuse stimulation, the electro-motive change at

the two contacts being similar, there will be no resultant
effect to record. For the recording of electro-motive response,
then, it is necessary to obtain an effect which is differential.

REVIEW OF RESPONSE OF ISOTROPIC ORGANS 693

The first way of doing this is to localise the stimulus at one
of the two contacts. This may be done by interposing a
physiological block between the two, so that the excitation
of one does not reach the other. The second method is to
select an experimental specimen which is anisotropic, whether
naturally or artificially. Artificial anisotropy is induced by
injuring one of the two contacts, and so bringing about a
relative depression of excitability at that point.

The method of resistivity variation which I had pre-
viously employed, in observing the response of inorganic
substances, proved capable of sufficient perfectibility for the
study of similar phenomena in living tissues also. The
main difficulty in applying this method had hitherto lain
in the disturbing electro-motive variation, consequent on
a-symmetrical excitation, or the differential excitability
of the structure. A detailed account of the means by
which this method was rendered reliable will be found in

' Chapter XXXVII., where it will be seen that records of

the excitatory variation obtained by it are in every way
similar, to those made by other methods. All the different
modes of taking records which have been enumerated are, it
must be remembered, independent expressions of a common
fundamental molecular change. Thus, on physically restrain-
ing that mechanical movement in a motile organ which. is
due to excitatory change, the electromotive response of
galvanometric negativity continues to be given. Similarly,
in a tissue in which, under the experimental arrangements,
there can be no resultant electro-motive change and no con-
tractile movement, the excitatory change may, nevertheless,
be observed by means of the resistivity variation (p. 548).

For the obtaining of the electromotive response, the
electrical mode of stimulation, unless special precautions
are taken, is subject to various disturbing influences, such as
current-escape and the occurrence of polarisation. For this
reason it was desirable to devise sore non-electrical form of
stimulation which should be capable of quantitative appli-
cation ; and this I have been able to secure by no less than

604 COMPARATIVE ELECTRO-PHYSIOLOGY

three distinct methods. I found that torsional to-and-fro
vibration constituted an effective form of stimulus, the
amplitude of which could be increased by increasing the
angle of vibration. The intensity of stimulus was found
to remain constant so long as the period and amplitude
vibration were kept constant. The tissue, moreover, was
not subject to injury by the use, within limits, of this method

(p. 31). My second method was that of Rotary Mechanical

Stimulation, in which friction of the terminal area of a pumice-
stone electrode constituted the stimulus, whose intensity was
determined by the number of rotations (p. 291). The third
non-electrical mode of stimulation employed was that of
thermal shocks. The area to be stimulated was, in this case,
enclosed within a thermal loop of platinum or german-silver
wire, the requisite thermal variation being produced by the
passage of a heating electrical current round the loop. The
intensity of the stimulus could in this case be varied by
increasing the intensity or duration of the heating current
(p. 38). And finally I have shown that the drawbacks inci-
dental to the electrical mode of stimulation might be over-
come by the use of equi-alternating shocks, the indefinite
polarisation factor being thus neutralised (p. 251).

As the intensity of stimulus is gradually increased, it
is found that the amplitude of response reaches a limit.
Beyond this, increase of stimulus evokes no increase of
response. On the application of a very strong stimulus,
then, there is an amount of energy which is unable to
find expression in the single response given by the tissue.
Under such circumstances, the excess of energy is held
latent, and often finds responsive expression later in a
series of multiple responses. This phenomenon of multiple
response to a single strong stimulus I find to be of very
extensive occurrence. As examples of the different kinds of
tissues in which this may be observed, may be mentioned
the stems and petioles of various plants (fig. 138), the
digesting leaves of Drosera (fig. 209), the pitcher of Mepenthe

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REVIEW OF RESPONSE OF ISOTROPIC ORGANS 695

(fig. 206), the animal stomach (fig. 213), nerves of animals,
and the retina (fig. 252).

I have also shown that thers is no strict line of
demarcation between the phenomena of such multiple
response and autonomous response so-called. Bzophytum, for
example, which, usually speaking, exhibits a single response
to a single moderate stimulus, and multiple response to a
strong stimulus, will, under exceptionally favourable tonic
conditions—that is to say, when it has absorbed from its
surroundings an excess of energy—exhibit responses which
are apparently autonomous. A typically autonomous plant
like Desmodium gyranus, again, when deprived by unfavour-
able circumstances of that excess of energy which it
requires, will be reduced to the condition of a multiply
responding plant. merely. It then responds by a single
response to moderate, and by multiple responses to strong,
stimulus. When the energy imparted by strong stimulus is
exhausted, these multiple responses come to a stop, to be
once more renewed, on a fresh accession of strong stimulus.
Or a lateral leaflet of Desmodium, originally quiescent, may
be put into, and maintained in, a state of pulsation by the
action of sunlight.

It is from the stored-up energy derived from _ its
surroundings that the tonic condition of the plant is so
raised as to maintain its so-called autonomous activity.
From this it will be seen that, strictly speaking, there is no
such thing as automatism. Movement can only be produced
by the immediate action of stimulus, or by energy previously
absorbed.

In recording the autonomous pulsation of the lateral
leaflets of Desmodium gyrans, it is found that while the
down-movement brought about by the contractile action of
the lower half of the pulvinule is very rapid, the up-move-
ment due to recovery, and to contraction of the upper half
of the organ, is relatively slow. The two alternating
excitatory impulses, in the lower and upper halves respec-
tively, are in the ratio approximately of 1°5 to 1, This

696 COMPARATIVE ELECTRO-PHYSIOLOGY

explains the peculiar electrical responses of Desmodium
gyrans, which are concomitant with the autonomous
mechanical pulsations of the leaflet. I find that, corre-
sponding with one complete mechanical pulsation, there are
two electrical pulses. Of these the principal electrical wave
coincides with the down-movement of the leaflet, and the
smaller with the up. The electro-motive intensity of the

principal wave is nearly 1°5 times that of the subsidiary. |

In a particular experiment, for example, while the value of
the former was ‘0024 volt, that of the latter was, ‘oo16 volt.
These electro-motive variations are expressions of funda-
mental excitatory effects, and not dependent on the
mechanical movement of the leaflets. For when the
responding leaflet is physically restrained, the electro-motive
responses exhibit even greater intensity than before. This
will be seen in the simultaneous records of mechanical and
electrical pulsations given in fig. 145.

An important subject of inquiry lay in the accurate
determination of the death-point. This investigation afforded
striking demonstration of the fact that it is a single
excitatory reaction which is expressed in different ways
under different modes of record. It has been shown that
when the experimental tissue is subjected to a gradual rise
of temperature, there is a definite point at which an
excitatory spasm occurs, marking the initiation of death.
If a continuous record be taken of the concomitant variation
of length, increasing expansion is found to be converted at
this point into a sudden contraction. In an anisotropic
organ like the pulvinus of Mzmosa the erectile movement of
the leaf is abruptly transformed into one of fall. A curled
tendril exhibits at this point a sudden uncurling. Taking,
again, the electro-motive method of record for the detection
of the death-point, the increasing positivity of .the
specimen is spasmodically reversed to negativity. Finally,
on employing for the record the method of resistivity
variation the increasing is seen to become suddenly
changed into a diminishing resistance. It is found,. how-

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REVIEW OF RESPONSE OF ISOTROPIC ORGANS 697 —

ever, employing numerous specimens, that these mechanical
and electrical spasms take place, under normal conditions,
at the same point. In the case of phanerogamous plants,
this is found to be at or very near 60° C. (figs, 328, 329,
330). That these mechanical and electrical spasms, further,
constitute a true case of excitatory response, is proved
by the fact that induced physiological depression also
induces depression of the death-point. Fatigue may thus
lower the death-point by as much as 19° C. :

The response of contraction, initiated at the death-point,
is later converted into fost-mortem relaxation, and galvano-
metrically the negativity initiated at the same moment
becomes subsequently a post-mortem positivity.

With regard to the so-called Current of Injury it. was
shown that this arises as the after-effect of strong stimulus.
It should be remembered that a cut, or the application of a
heated wire, constituting mechanical and thermal sections
respectively, will act as a strong stimulus, and, further, that
the after-effect of excitatory galvanometric. negativity is
persistent when the stimulus is strong.. The excitatory
effect, moreover, is transmitted from the point of application
to greater or less distances, according to the strength of
stimulus and the conductivity of the tissue. As this trans-
mitted effect undergoes diminution with distance, it is
obvious that the most intense negativity will be induced at
the point of section, undergoing a gradual diminution as
we move further away from it. If, taking a given length of
isotropic tissue, we make two opposite terminal sections, we
shall clearly have a symmetrical. distribution of electrical
potential as regards the middle or equatorial zone, the two
ends being most negative, while the equator is relatively
most positive (fig. 110). . Two points symmetrically situated
as regards this equator would thus be equi-potential, while
a-symmetrical points would show appropriate differences of
potential, a zone near the equator being relatively positive
to one which is further away from it, or nearer to the
terminal section. These considerations, supported as they

698 © COMPARATIVE ELECTRO-PHYSIOLOGY

are by experimental results, account satisfactorily for the
particular electrical distribution in a muscle-cylinder.

It is often supposed that dead tissue is negative to
living. But I have shown that this is not the case, the
dead being actually positive to the living. It has already
been mentioned, in connection with experiments described,
on the mechanical and electrical spasms of death, that at

the initiation of death, a tissue exhibits excitatory con-.

traction and negativity, while the post-mortem effect is one
of relaxation and positivity. This explains the peculiar
electrical distribution which I have observed, in the explora-
tion of tissues, of which some parts were dead, others
dying, and still others, again, fully alive. It was there shown
(figs. 113, 115) that the greatest negativity occurred on the
death-frontier. Proceeding in either direction from this
point, whether towards the living or towards the dead,
it is found that these points are increasingly positive, or
decreasingly negative. But the maximum positivity of the
dead portion is greater than that of the living. From this
it is clear that the dead is positive to the living.

From these facts, that the dying is negativé, and the
dead relatively positive to the living, it is clear that the
so-called current of injury is liable to reversal. In the case
of the former, the current of injury will be from the
dying to the living; in the latter, from the living to the
dead. This demonstration of the occurrence of a hitherto
unsuspected reversal, demonstrates to us the possibility of
many complications, and wrong theoretical inferences, For
response by the negative variation of the current of injury
is usually taken as the concomitant of the chemical process
of dissimilation, while the positive variation is held to be
associated with assimilation. Now, by the reversal of the
so-called current of injury, one identical excitatory reaction
may be made to appear, now as a negative, and again
as a positive variation. This is. sufficient to indicate the
unreliability of the so-called Method of Negative Variation,

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REVIEW OF RESPONSE OF ISOTROPIC ORGANS 699 _

an unreliability of which we shall further meet with many
glaring instances. Pe ;

An assumption more or less current is, that in order to
obtain response, there must be an antecedent current, by
whose negative variation it can be detected. Hence the
supposed necessity of a current of injury prior to response.
The real reason, however, for thus injuring one of the
contacts is so to depress its excitability that, on diffuse
stimulation, the excitatory response of the uninjured may
remain unbalanced, and therefore unannulled. That it is
this depression of excitability, and not the current of injury
as such, which is the essential condition for obtaining
resultant response, is seen from the fact that excitatory
response may still be obtained, even when the so-called
current of injury is zero, or reversed positive (fig. 116).

CHAPTER XLVII

REVIEW OF RESPONSE OF ANISOTROPIC ORGANS

Anisotropic organs—Laws of response in anisotropic organs—Natural current of
rest and current of response— Reversal of natural current of rest-—Unreliability
of positive and negative variations of current of rest-—Determination of the
differential excitability of a tissue—Resultant response of skin due to induced
stronger negativity of inner surface and feebler negativity (tomato skin) or
positivity (skins of grape and frog) of outer—Response of intact human skin —
Response of intact human lip—High excitability of secretory and glandular
surfaces—Response of glandular foot of snail—Response of intact human
tongue—Response of digestive organs—Phasic alternations of secretion and
absorption—Multiple response of digestive organs—Phasic changes induced
by previous activity—Response of digestive organs of Mepenthe and Drosera
—Electro-motive peculiarities of skin and mucous coat of stomach not similar
—Normal response by galvanometric negativity in mucous coat of stomach of
frog, gecko, and tortoise— The root as a digestive organ—Excitatory secretion
and galvanometric negativity of young roots—Phasic alternations of secretion
and absorption — Cognate subject of ascent of sap—.Sap-wood not really dead—
Proofs of physiological character of suctional response—Water-movement a
mode of excitatory response—Response of electrical organs—Two types,
Torpedo and Malepterurus—Vegetal analogues to electric plates of two types,
Torpedo and Malepterurus, in Pterospermum and pitcher of MWepenthe—-
Multiple character of response of electric organs—Response of electrical
organs constitutes an extreme case of differential excitability of anisotropic
structures--Similar effects with inorganic structures—Excitatory effect of
light on plant tissues—Phasic alternations—Initiation of multiple and autono-
mous response by light—Three types of direct and after-effects—Response of
retina like, and not different from, that of other tissues—Error introduced by
method of negative variation—Multiple responses in retina and their visual
correspondences —Binocular Alternation of Vision—Three types of direct and
after-effects in retina under light—Geo-electric response.

I SHALL next pass in review another class of phenomena,
the want of a clear understanding of which is at the root of
many supposed anomalies in the response of animal tissues.
I allude to the natural anisotropy, with consequent differential
excitability, of various organs,

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REVIEW OF RESPONSE OF ANISOTROPIC ORGANS /7oT ~

_ As an example of a differentially excitable organ we may
take the pulvinus of J/tmosa, in which the lower half is more
excitable than the upper. In this case, strictly localised
stimulation of either the upper or the lower evokes con-
traction and galvanometric negativity of that particular half,
the effect in the lower half being the greater. But if the
stimulus be diffused, whether internally or externally, the
response will be differential, by the greater contraction or
galvanometric negativity of the more excitable. From this
we arrive at the general law of the electrical response of
anisotropic organs.

1. On simultaneous excitation of two points A and B, the
responsive current flows in the tissue from the more to the less

~ excited.

2. Conversely, if under simultaneous excitation, the responsive
current be from B to A, B is the more excitable of these two
points.

The second of these two laws enables us to determine
the relative excitabilities of any two points. As a simple
example of the anisotropy induced in a tissue by the unequal
action of the natural stimuli of the enviroment, we may take
a tubular organ, such as the hollow peduncle of Uriclis lily.
Here the exposed outer surface, constantly subjected to
external stimuli such as light, becomes as it were fatigued,
and reduced in excitability. Other histological modifications
follow on this, the external cells becoming thus cuticularised
and protoplasmically defective. Owing to the depression of
excitability on this epidermal surface, the intensity of its
normal excitatory change by galvanometric negativity is
decreased, a change which, in the case of certain skins,
culminates in responsive positivity. The inner surface of the
hollow peduncle, which may be regarded as epithelial, being,
on the other hand, protected, remains normally excitable
and is thus more so than the outer surface. The outer sur-
face, however, probably by reason of the action of the external
stimuli to which it is constantly exposed, is naturally
negative, relatively to the protected and more excitable inner

702 COMPARATIVE ELECTRO-PHYSIOLOGY

surface. And it will generally be found true that while this
natural cnrrent of rest is from the less excitable A to the
more excitable B, the current of response, on the other hand,
which occurs on excitation, is from the potentially more
excitable, and therefore now more excited B, to the less
excitable and therefore less excited A.

Such is the course of events in the normal or primary
condition. But under the excitation due to preparation, or -
accidental disturbance, the more excitable surface becomes
the more excited, and relatively to the other, galvanometri-
cally negative. In consequence of this, the natural current
is reversed, and we have a resting-current due to the after-
effect of injury or accidental excitation, flowing from the
more to the less excitable. Thus, while the natural current,
in the primary condition, was from the less excitable A to
the more excitable A, that is to say, A > B, this reversed
current of rest, due to accidental excitation or injury, is from
B->A. Even now, however, & may be more excitable
than- A, hence fresh stimulation will induce a responsive
current from B to A. In the primary condition, such a
responsive current would have appeared as a negative varia-
tion of the natural current AZ. But when the primary
condition has been so modified that the natural current is
reversed, and has become B-A, the normal responsive
current B-+A will appear as a positive variation. Still
another variation is possible, when the normal response itself
undergoes reversal owing to fatigue, under which condition
this abnormal response, relatively to the reversed current of
rest, appears as if it were the normal negative variation
(fig. 119). It has, however, been shown that if we discard
this unreliable test of response, by the variation induced in
an antecedent current of rest—the so-called negative varia-
tion—it will be found that the responsive current always
flows from the more to the less excited.

In order to determine which of two points in an anisotropic
tissue is the more excitable, it is necessary, as now under-
stood, to determine the direction of resultant response, under

REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 703

stimulation which is equal and simultaneous. In order to do
this, we may employ such a non-electrical form of stimu-
lation as the mechanical or the thermal. For this it is
possible to employ (1) the Vibratory Stimulator; (2) the
Rotary Mechanical Stimulator ; or (3) stimulation by thermal
shocks. When results are obtained according to these
methods, there can be no uncertainty as to those compli-
cations of effects which might conceivably arise when the
electrical form of stimulus is employed. The last-named
may, however, be used without misgiving, when stimu-
lation is effected by equi-alternating shocks, The ordinary
Ruhmkorff’s make- and break-shocks are not suitable for
this purpose, inasmuch as the effective intensity is unequa]
for make and break, besides which the polarisation-effect may
not be exactly neutralised. The equi-alternating shocks,
from which these defects have been eliminated, are obtained
by means of (1) a rotary reverser in the primary coil (fig. 170),
or (2) a motor-dynamo (fig. 172). The responses again,
under these electrical forms of stimulation, may be photo-
graphically recorded as either the direct or the after-effect of
stimulus. It was shown, by the employment of all these
various methods of stimulus, mechanical, thermal, and elec-
trical, that the responsive current to be obtained with an
anisotropic organ was definite in direction, being always,
under normal conditions, from the more excitable B to the
less excitable A. I shall now proceed to recapitulate briefly
the results obtained by these methods in various cases of
anisotropic tissues, such as skin, epithelium, glands, animal,
and vegetal digestive organs, and electric organs generally.
Taking first the skin of tomato it has been shown that
the separate responses of the outer and inner surfaces are
unequal. The outer, owing to cellular modification under
the stimuli of the environment, gives only a feeble negative
response, whereas the internal surface gives a much stronger
normal response by galvanometric negativity. On simul-
taneous excitation of both inner and outer surfaces, the
responsive current is found to flow from the inner to the

704 ~ COMPARATIVE ELECTRO-PHYSIOLOGY

outer. Here the resultant’ current’ is ‘brought about~ by
the difference between the stronger responsive negativity of
the inner, and the feebler responsive negativity of the outer

surface, which © may be represented as” 4 With certain

specimens of tomato skin, however, the modification of the
outer surface is so great that its individual response is
reversed to positive, that of the inner being the normal

strong negative. The resultant response, then, is still from

inner to outer, but equals the summated effect of the two ne
From this we pass to the response of grape-skin, which
resembles the latter of these two cases. The response of
the skin of frog is also of this type, and it may be said
of skins in general that their response is from the. more
excitable inner surface to the less excitable outer. This
conclusion has been verified by experiments on various
skins, both vegetable and animal. Among the latter of these
may be mentioned the skin of the neck-of tortoise, and that
from various parts of the body of gecko.-

When the skin is isolated with very great care, so as to
reduce to a minimum the excitatory effect of preparation, it
is found-that the natural current of rest is from the less
excitable outer to the more excitable inner surface; the
excitatory current being in,the opposite direction. Owing to
the excitatory effect of preparation; the current of rest of the
skin of tortoise-was found reversed. The responsive current,
however, was found to flow from inner to outer, thus proving
that the inner surface was the more excitable. In illustration
of the great practicability of the methods employed, I may
refer to the photographic records obtained of the response of
the skin of the intact human forefinger (fig. 180). .

In describing the differential excitability of the hollow
peduncle of Uviclts lily, it was shown that protected surfaces
are, as a rule, more excitable than those which are exposed,
and have thus undergone a greater degree of modification.
On taking the plagiotropic stem of Cucurbita, the lower
surface of which is protected from light, it is. found that,

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REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 705

while the current of rest flows from the exposed upper to
the protected lower surface, the direction of the responsive
current is opposite, namely from the lower to the upper,
proving that the protected lower is the more excitable of
the two. Similarly, in the case of the intact human lip, I
found that the resting current was from the epidermal to
the epithelial, the responsive current being in the opposite
direction (fig. 196). . Again, on testing the differential
response of armpit and shoulder, I found that the respon-
sive current was from armpit to shoulder, the former being
thus the more excitable of the two (fig. 194).

We have seen that the lining membrane of the inner
surface of the peduncle of Uvric/zs lily is very thin, and that,
in distinction to the outer or epidermal membrane, it may be
regarded as epithelial. As we approach the bulb-end of the
peduncle, this inner layer of cells is found to be highly turgid,
and secretion is found to take place into the hollow tube.
The inner surface of the carpellary leaf of Dzllenta indica,
again, secretes a mucilaginous substance. In these two cases
there are no definite glands, But definite glands are found to
occur on the inside of the pitcher of Wepenthe. In all these
cases the secreting layer, whether provided with glands or
not, is found to be very highly excitable, and to respond
by strong galvanometric negativity. Taking a carpel of
Ditllenia indica, it is found that the natural current is from
the outer epidermal to the inner secreting surface, the respon-
sive current being in the opposite direction. On making very
careful connections, with the skin of the protruded body of
the snail, and the glandular under-surface of its foot, it is
found that the natural current is from the non-glandular to
the glandular, but the responsive current from glandular to
non-glandular. As an example of the way in which the
true natural current of rest may be reversed by the excitatory
effect of preparation, I showed that, while in the intact snail
the natural current was from non-glandular to glandular—
the gland being in this case relatively positive, to the extent
of -0013 volt—after the sectioning of the foot, the original

ZZ

706 COMPARATIVE ELECTRO-PHYSIOLOGY

natural current was reversed, owing to the greater relative
excitation induced at the glandular surface, which now
became relatively negative, to the extent of —-‘0020 volt.
With the intact human tongue, further, I found that a
very strong responsive current was induced on excitation,
from the lower to the upper surface, thus showing that the
lower was the more excitable of the two.

The response of digestive organs may now be passed in
review. In these, as in glandular organs, excitatory response
is supposed to take place by secretion. In connection with
this, it must be borne in mind that in the tissue of the
pulvinus of J/zmosa, on the removal of the impervious skin,
excitation induces secretion of the contained fluid, which,
again, is re-absorbed on the cessation of excitation. We
know the pulvinus to be contractile, and may therefore
regard this secretion as an effect of contraction, causing
expulsion of water. Apart from the differential action of
the upper and lower halves of the organ, and the magnifying
petiolar index, the fundamental contractile action would, in
the case of J/zmosa, as in others, have passed unnoticed.
This goes to show that it is not impossible that the phe-
- nomenon of secretion through a permeable membrane may
be associated with excitatory contraction. In favour of such
continuity, it may be urged that tissues, hitherto regarded as
non-motile, have been shown to exhibit excitatory contrac-
tion. In digestion, as a whole, we have to recognise two
different processes, those, namely, of secretion, and of sub-
sequent absorption. Parallel to these, we find that the
electrical response of digestive organs exhibits phasic alter-
nations of negativity and positivity.

It was shown that the pitcher of Wepenthe—which may
be regarded as an open stomach—affords us unique facilities
for the observation of the normal responses of digestive
organs. In experimenting with the animal stomach, the
specimen has to be cut open, in order to make the necessary
connections ; and, owing to the highly excitable character of
the organ, this gives rise to intense excitatory action, the

REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 707 |

after-effect of which is necessarily to reverse the normal
current of rest, With a pitcher of Mepenthe in a fresh
condition, the natural current of rest is from the outer to
the inner, the responsive current being in the opposite
direction, and the glandular surface, on simultaneous exci-
tation of the two, becoming galvanometrically negative
(fig. 203). Digestive organs, moreover, tend to -exhibit
multiple responses, the response to a single strong stimulus,
say thermal, or of mechanical section, consisting, whether in
animal or vegetable organs, of a series that may persist for
nearly an hour (figs. 206, 209, and 213), When the pitcher
of Nepenthe contains a large number of captured flies, that is
to say, when it has been subjected to long-continued stimu-
lation, it exhibits a phasic change, the responses now
becoming reversed to positive (fig. 205). This, as pointed
out above, is probably significant of absorption. In Drosera,
the normal response of the glandular surface is by induced
negativity, but on long-continued stimulation, this is reversed
to positivity (fig. 208).

In the animal stomach, the sine current of rest is
generally from the glandular to the non-glandular surface.
From the fact that the skin of the toad, which is also
possessed of imbedded glands, gives a current of rest from
the outer surface to the inner, it has been supposed that the
mucous coat of the stomach of the frog had the same electro-
motive reaction as its outer skin, That this, however, is not
the case is seen from the fact that on excitation the skin
becomes galvanometrically positive, while the mucous mem-
brane of the stomach becomes galvanometrically negative.
The observed current of rest in the stomach would appear,
from WVepenthe, to be, not the natural current of rest, but the
reversed current, due to the excitatory effect of preparation.
The normal effect of excitation in the stomach, I uniformly
find, in such different instances as frog, gecko, and tortoise, to
be by galvanometric negativity of the mucous surface (figs.
210, 211, and 212). On applying a strong thermal stimulus

to the stomach of frog, I obtained an interesting series of
ZZ2

708 COMPARATIVE ELECTRO-PHYSIOLOGY

responses, of which the first were negative, the second part
diphasic, and the last portion reversed positive (fig. 213).
Looking at the phenomenon of digestion, we see that it
consists first of a secretory process, by which certain solid
substances are dissolved, and secondly of the absorption of
these dissolved substances. Similar functions are subserved
in vegetable life by the root, by which solid inorganic food-

materials are first dissolved by secreted acids, and then

absorbed. The proof of the former is seen in the well-
known corrosion-figures produced by growing rootlets on a
marble surface. I have also been able to demonstrate the
phenomenon of excitatory secretion in young roots by allow-
ing them to absorb dilute salt solution, and then under exci-
tation to secrete it into highly dilute silver nitrate solution:
This last was attended by the visible formation of a white
precipitate. The electrical response of young roots of
Colocasia, moreover, I found to be by induced galvanometric
negativity (fig. 214), which, under long-continued stimulation,
was apt to show reversal to positivity. The older roots, on
the other hand, under the same intensity of stimulation, gave
response by galvanometric positivity (fig. 215). The former
of these responses, there is every reason to believe, is as-
sociated with secretion, and the latter with absorption.

This question of the absorption of inorganic food materials
by the plant is naturally connected with the subject of the
Ascent of Sap, which is regarded as one of the most difficult
problems in plant physiology. The non-physiological theories
advanced are admittedly inadequate to the explanation of
this phenomenon. That the ascent, nevertheless, could not
be due to physiological action was held to have been proved
by the facts (1) that water-conduction takes place pre-
ferentially through sap-wood, assumed to be dead ; and (2)
that poisonous solutions, such as would kill a living tissue,
have been found to be transported through the roots, or the
cut ends of their trunks, to the tops of trees.

I have, however, been able to show that these objections
are not valid. For in the first place, the supposed dead

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REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 709 |

wood, concerned in the transport of sap, through the trunks
of trees, can be proved, by electrical tests, to be fully
alive. This living wood responds to stimulation by in-
duced galvanometric negativity, such response disappearing
on the death of the tissue, as, say by drying, after which
it cannot be restored. The response of living wood is
also depressed by anesthetics, and abolished by poisons
(figs. 216, 217). As regards the argument based on the
transport of poison, it has been shown that as the active
elements concerned in the transport of sap are diffused
throughout the length of the trunk, the death of one indi-
vidual zone, to which the poison has ascended, does not
abolish the suctional activity of the zone above. It is only
when the plant has been killed throughout, by the arrival
of the solution at its top, that the complete arrest of suction
could be expected to take place. And this is found to be
the case. Various agents, on the other hand, which are
known to induce changes, whether of exaltation or depres-
sion, in the physiological activity, are found to induce corre-
sponding modifications in the rate of suction. A very
delicate means of investigating this question has been
shown to be that afforded by the records obtained with
the Shoshungraph (fig. 218). Here, under the ordinary
method of record, the slope of the curve indicates the
normal rate of suction, and the effect of various agencies
is immediately shown by the resulting flexure of the curve.
This method of record, again, becomes extremely sensitive,
when it is carried out under balanced conditions. By means
of these records, it has been shown that depressing agents,
such as cold or anesthetics, depress or arrest suction,
whereas warmth exalts it. It has been shown, further, that
just as the multiple activity of the Desmodium leaflet is
arrested, when the latent energy of the plant falls below
par, so also, under similar circumstances, the suctional activity
falls into abeyance, and that, as in the one case, so also in
the other, the activity is renewed, by the application of an
external stimulus. It has also been shown that the latent

710 COMPARATIVE ELECTRO-PHYSIOLOGY

period which elapses, before the initiation of this responsive
variation to external stimulus, is longer when the plant is in
a sub-tonic condition than in the same plant when its tonic
condition has been slightly raised by previous stimulation.
Crucial experiments, finally, have been described, showing
that water-movement is a mode of excitatory response.

A difficult problem in connection with electrical response
is that of the discharge from the electrical organs of certain .
fishes. In a large number of cases, of which Torpedo may
be taken as the type, the discharge takes place in a direction
from the anterior or nervous to the posterior and non-
nervous surface. Pacini’s generalisation that the responsive
discharge is always from the anterior to the posterior surface
is negatived by the instance of Malepterurus, in which it is
from the modified glandular posterior to the anterior surface.
Another peculiarity of the response of electric organs in
general is that the responsive current is always in the same
direction—that, namely, of the organ-discharge — whether
the exciting shock be homo- or hetero-dromous. No theory
has yet been found which will fully explain all these
peculiarities.

I have shown, however, that this phenomenon is not alone
of its kind ; nor is it dependent on any specific characteristic
of the animal nerve-and-muscle, or gland, of which different
electric organs are modifications. The response of the electric
organ simply constitutes an extreme case of differential
excitability, and follows the general law of response in
anisotropic organs—namely, that on diffuse stimulation the
responsive current flows from the more to the less excitable.
The peculiarity of the organ simply depends upon the fact
that owing to the serial arrangement of its elementary aniso-
tropic plates the terminal electro-motive effect becomes very
large by summation. We find vegetal analogues to the two
types of electrical plates of Zorpedo and Malepterurus, in
the leaves of Pterospermum, and the pitcher.of Vepenthe. In
the first of these, Pzerospermum, as in Torpedo, the anterior
nervous surface is relatively more excitable than the mass

REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 7II

of indifferent tissue on the posterior surface. Hence the
current of response is from the more excitable anterior to
the less excitable posterior. In the second type—the pitcher
of Nepenthe and the electrical plates of Malepterurus—the
posterior surface being glandular and therefore exceptionally
excitable, the responsive current is from posterior to anterior.

In taking rheotomic observations on the response to
electrical stimulation in various anisotropic leaves—virtually
acting, as has been shown, like electrical plates—it was found
that in sluggish specimens the maximum electro-motive value
was attained ‘2 second after the exciting shock. This was
also the value of the period which elapsed after the applica-
_tion of moderate mechanical stimulation. With vigorous
specimens, however, such as the leaves of Vymphea alba,
the maximum effect was attained in a much shorter time,
that is to say, in about ‘03 second. In the electrical organ
of Yorpedo the corresponding period has been found to be
‘o1 second. The response of electrical organs is found to be
repeated or multiple. In the rheotomic records obtained
with leaves, further, the multiple apices of the curve show
that the response of vegetable organs also has this multiple
character Multiple response, however, is not the peculiar
characteristic of the electrical organ, but has been shown to
take place in various kinds of animal and vegetable tissues.

Again, that this peculiarity—of definitely uni-directioned
response, whether the excitation be homodromous or hetero-
dromous—is not distinctive of life, with its specific powers
of assimilation and dissimilation, but of anisotropy in
general, with its consequent differential excitability, was
shown by the fact that similar uni-directioned responses to
homo- or hetero-dromous shocks were given by an inorganic
structure, consisting of prepared lead (fig. 167).

We have next to pass in review the question of the
response of plant and animal tissue to stimulus of light
The various motile responses, induced by light in plants, are
so diverse and so apparently incapable of being explained
by any single reaction of fundamental excitation, that it

712 COMPARATIVE ELECTRO-PHYSIOLOGY

was thought that the effect of this stimulus was different
in different cases, the specific reaction in each organ being
determined by the ultimate advantage of the plant. But I
have been able to show that the excitatory effect of light is
normal and like that of any other form of stimulus. The
various results induced by it depend, first, on the question
whether stimulus has remained localised at the point of

application, or been transmitted to distant areas. The effect |

is thus modified by the intensity of the stimulus and the
conductivity of the tissue. These results, however, may be
further modified by the differential excitability of the organ.
Here, as in other cases of stimulation, the general rule holds
good that response is by greater contraction and galvano-
metric negativity of the more excited. As a concrete example
may be mentioned the case of the pulvinus of MW/zmosa,
when the upper surface alone is subjected to the stimulus
of light. Here, owing to local excitatory contraction of
the upper, the expelled water reaches the lower half of the
pulvinus and induces there the hydro-positive effect of
expansion, both of these effects conspiring, in this first stage
of response, to erect: the leaf. The electrical variation at
the lower half is here, then, found to be positive. But as
the excitatory effect itself is gradually conducted to the
lower half, it induces there an increasing contraction. The
mechanical response is now therefore reversed, from one of
erection to one of depression, the electrical variation of the
lower half of the pulvinus undergoing at the same time a
corresponding change from positivity to negativity (fig. 237).
From this experiment it is clear that the electrical response
under light exhibits the same stimulatory changes which are
also visibly demonstrated by mechanical response. We see,
moreover, from this experiment that light in general acts
as a moderate stimulus. For while mechanical or thermal
stimulus induces a sudden collapse of the leaf of AZzmosa, the
application of light brings about only a gradual fall.

Owing to this moderateness of the stimulus of light, and
to the fact that its application is strictly local, it is easy to

eet ne ox eel

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ee gree ee

REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 713

understand the possibility of certain modifications occurring
in the response. Thus, in highly excitable and conducting
tissues, the responses will be by galvanometric negativity,
and the state of excitation will be conducted to a certain
distance. But we have seen that in tissues which are not
highly excitable, stimulus, falling below the excitatory value,
gives rise to positive response. Thus, under the action of
light, we obtain in plants two types of response, negative
and positive. Moreover, under continuous stimulation of
light, these may undergo phasic alternations (— + — +) or
(+ — +.—). Asan example of negative response to direct
or transmitted stimulation of light may be seen the response
of Bryophyllum (fig. 238), the positive response being exem-
plified in the record obtained with a petiole of cauliflower
(fig. 240).

It has been explained how these alternating phasic
responses lead us to the phenomenon of multiple and
autonomous response. |

A leaflet of Bzophytum, or a Desmodium \eaflet in a state
of standstill, under the continuous action of strong light, will
exhibit multiple mechanical responses. The corresponding
multiple electrical responses are seen in the response of the
lamina of Bryophylum under the action of continuous light
(fig. 242). It has also been shown that these phasic alterna-
tions are brought about by the fact that the antagonistic
elements in the response become effectively predominant by
turns. Either of these antagonistic factors may be unmasked
more effectively by the arrest of external stimulus at a
particular phasic maximum, Thus, in the case where the
normal alternation is (— + -— +), if the stimulus be sud-
denly withdrawn at the end of the second phase, or positive
maximum, the response overshoots in the positive direction
(figs. 243, 244). The characteristic direct and after-effects
in this Type I., then, during the application of light and its
remoyal are ((— + +). In specimens whose characteristic
response under continuous stimulation is (+ — + —), if
stimulus be again withdrawn at the end of the second

714 COMPARATIVE ELECTRO-PHYSIOLOGY

phase—here negative maximum—the response overshoots
in the negative direction (figs. 245, 247). The direct and
after-effects in this Type III., therefore, may be represented
by the formula (+ —...). Between these two extremes
lie instances of an intermediate Type II., which has cases (a)
and (6), according as the stimulus is removed at maximum
of the first or negative phase, or at maximum of the second

or positive phase. The formula of Type II. (a) is thus

(— + «.), while that of Type II. (0) is(—... ).

The response of the retina furnishes us with the most
striking examples of the action of stimulus of light. The
true character of this response has been supposed hitherto
to be unlike that of other tissues, for while excited nerve
and muscle were said to show response by ‘ negative
variation, the response of the retina was referred to as by
‘ positive variation.’ This furnishes us with an instance of
the confusion which is apt to result from making the
so-called resting-current the standard of reference. On
testing for the natural current, by making connections with
the longitudinal surface of the optic nerve, and with the
cornea, in an undetached eyeball of frog, I found that it
flowed from the cornea to the nerve. But when the eye is
detached, by section of the optic nerve, the after-effect of
excitation on the more excitable nerve reverses this current,
the nerve becoming relatively galvanometrically negative.
The normal effect of transmitted excitation from the retina
would now make the nerve still more galvanometrically
negative, and this would appear as a positive variation of the
reversed natural current. Hence, the responsive positive
variation, met with in the eye under light, is in reality the same
normal excitatory response, by galvanometric negativity, with
which we are already familiar.

I have also shown, by means of equi-alternating electric

shocks, that under normal conditions the optic nerve is more.

excitable than the cornea, and that the retina is more
excitable than the optic nerve. The eyeball and retina
have often been found by different observers to exhibit

pinot Aided ser sommes ee

ee ee ed

a

REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 715

abnormal or reversed response. Now, with regard to reversed
response in general I have shown it to be due to either of
two different conditions which hold good for all responding
tissues. These are in the first place sub-tonicity, and
secondly, fatigue. The abnormal response caused by the first
has been shown to be converted into normal, in the case of
the retina, by the action of an agent which enhanced the
excitability.

Another phenomenon which I discovered in the response
of retina was that of multiple response, induced by the
application of strong or of continuous stimulation. These
multiple responses have visual correspondences in the
multiple after-images seen in the retina, and in the visual
fluctuations which occur under the constant stimulus of
light. The latter of these facts was demonstrated by a
specially devised stereoscope (p. 432). In this connection
may be mentioned the interesting phenomenon of Binocular
Alternation of Vision. 3

The various types of direct and after-effects observed in
vegetable tissues under light I find to have their close
correspondences in the responses of the retina. Just as in
the highly excitable lamina of Bryophyllum, constituting
Type I., we have the formula of (— + -i-), so also, in the
highly excitable retina of Ophzocephalus, the same sequences
of direct and after-effects is observed. In less highly
excitable vegetable tissues, such as the petiole of cauli-
flower, affording us Type III., the sequence was shown
to be (+ —...). In correspondence with this may be
mentioned the response of the isolated retina of fish,
observed by Kiihne and Steiner. In this case, as the effect
of isolation, the retina must have become sub-tonic, which
supposition is borne out by the fact that its response to the
immediate action of light was abnormal positive instead of
negative. I found a similar sequence to occur in an isolated
sub-tonic retina of Ophiocephalus (figs. 260, 261).

Finally, in somewhat fatigued specimens, an intermediate
Type II. was found, in which the sequence was (— + ...)

716 - COMPARATIVE ELECTRO-PHYSIOLOGY

or (—...). Examples of these are afforded by the eye of
the frog. These correspondences, between the effects of
light in vegetable tissues and in the retina, will be clearly
understood from the series of figs. 253 to 261.

The next subject to be summarised is that of the
electrical response of plants to gravitational stimulus. In
an apogeotropic organ like the stem, when laid horizontally,
the mechanical response is such as to make the shoot once
more vertical. The active factor in this curvature might
obviously be, either the responsive contraction of the upper
side, or the responsive expansion of the lower. The question
to be decided here was whether the response of the plant,
to geotropic stimulus, was or was not of the same nature as
its response to other effective forms of stimulation—that is
to say, by excitatory contraction. An experiment has been
described (p. 436) in which this question was subjected to
tests. The local application of cold is known to bring
about the temporary abolition of the excitatory effect, and
in the present case, its application on the lower side of a
horizontally laid shoot was not seen to induce any effect on
the response, while, when applied on the upper, it retarded
- and arrested response to gravitation. This shows that in
this response it is the contraction of the upper side which is
the active factor. This is independently verified by the
test of electrical response, where I find that the upper
side, when subjected to gravitational stimulus, exhibits the
sign of true excitation—namely, by induced galvanometric
negativity.

The important Theory of Statoliths offers us a suggestive
explanation of the manner in which gravity exercises stimu-
lation upon the responding tissue, by the weight of solid
particles. When the stem is vertical, in consequence of the
symmetry of distribution of the particles on all sides, there
is no resultant action; and as soon as this symmetry is
disturbed by laying the stem horizontally, response might be
expected to be initiated. This, however, is not the case.
The shoot first bends down, and it is not until after the

is on

REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 717

expiration of nearly three-quarters of an hour that the first sign
of apogeotropic action appears. This anomaly is probably due
to the induced mechanical curvature caused by weight which
has first to be overcome. We may, however, regard ourselves
as independent of the mechanical indications, when recording
the effect of gravitational stimulus by geo-electric response.
The excitatory electric effect, as we have seen in other cases,
takes place as before, when all responsive mechanical
indications are restrained. Proceeding on this principle,
therefore, I found that the geo-electric response was initiated
within so short a time of subjecting the specimen to gravi-
tational stimulus as one minute (fig. 271). This experiment
shows of what widespread application is the electrical mode
of detecting the excitatory response of tissues, to many
different forms of stimulus,

CHAPTER XLVIII

REVIEW OF RESPONSE OF NERVE AND RELATED
PSYCHOLOGICAL PHENOMENA

Transmission of excitation in plants—Vegetal nerve—Similar variations of
receptivity, conductivity, and responsivity, under parallel conditions in plant
and animal nerves—Conductivity balance—After-effect of section on con-
ductivity and excitability—Function of vegetal nerve in plant-economy—
Laminz of plant form a catchment-basin for stimulus—Motile response of
nerve— Molecular cycle and characteristic changes in response of nerve—
Effect of fatigue on transmitted excitation—Similarity of excitatory molecular
changes in both afferent and efferent nerves—Multiple response induced by
strong stimulus in nerve—Multiple excitations in nerve during drying —
Individual contractile responses to constituent tetanising shocks—Negative
after-effect on abrupt cessation of tetanisation—Extra-polar effects similar in
plant and animal nerve —Inadequacy of Pfliiger’s Law— Under feeble E.M.F.
excitability enhanced by anode and depressed by kathode—Demonstration by
subjective response—Under feeble current excitation travels better against
than with it—Response by variation of electrotonic current due to algebraical
superposition of excitatory effect—Physico-physiological basis of sensation—
Identification of positive tone of sensation with hydro-positive wave and
negative tone of sensation with negative wave—Natural and artificial induc-

tion of dissociation of sensation—Physical explanation of Weber-Fechner’s —

Law—Quality of sensation also a factor—Conversion from painful to pleasur-

‘able and vice versa at will by electrotonus—Memory as an after-effect of
stimulus—-Persistent after-sensation— Revival of latent memory-image through
differential excitation induced by diffuse stimulation—-Same effects demon-
strated in the inorganic.

THE next subject to be reviewed is that of the conduction
of stimulus. It has been supposed that plants do not con-
duct excitation by the transmission of protoplasmic changes,
as certain animal tissues are known to do. Even in the well-
known case of Mimosa, where stimulus is seen to induce move-
ment at a distance, this was supposed to be the result of hy-
dro-mechanical disturbance. This conclusion has been shown,
however, to be erroneous, for pure hydrostatic disturbance

Pa

RESPONSE OF NERVE 719

has been proved to occasion an erectile movement of the
leaf with galvanometric positivity (figs. 44, 45, and 46). The
transmission of true excitation, on the other hand, gives rise
to a fall of the leaf and the electrical response of galvano-
metric negativity. Again, the transmission of excitation in
the plant is modified similarly by those varying physiological
conditions- which influence it in the case of the animal.
Thus, a strong stimulus is transmitted more quickly, other
things being equal, than a feeble. Fatigue, on the other
hand, is found to depress the velocity. The application of
cold reduces or temporarily abolishes the transmission, while
warmth enhances its velocity. Anzsthetics, again, are found
to depress conductivity. And lastly, the polar effect of
currents, in the plant as in the animal, is to induce opposite
changes, according as anode or kathode is applied. I have,
moreover, been able to isolate certain tissues specially fitted
for the conduction of excitation. These are found in the
soft parts of the fibro-vascular bundles, and are particularly
easy to isolate in the case of fern. They here possess the
relatively high velocity of about 50 mm. per second. It
may be said, in view of their peculiar responsive charac-
teristics, and the modifications of their response under given
conditions, that these structures are indistinguishable from
animal nerves, and may therefore be rightly designated
vegetal nerves. On isolation, for example, these highly
excitable vegetal nerves, like the animal nerve, when isolated,
are liable to fall into a state of sub-tonicity, on account of
which their conducting power is temporarily impaired. The
transmitted effect of stimulus, then, as in the corresponding
case of animal nerve, becomes one of abnormal galvano-
metric positivity. Continuous stimulation when in this state,
however, by carrying the tissue out of the A into the
B condition, converts the abnormal positive response into
normal negative, through an intermediate diphasic, in the
plant as in the animal nerve. When in the B stage, again,
tetanisation -has the effect of enhancing response in both,
The effects of ether, carbonic acid, alcohol vapour, and

720 COMPARATIVE ELECTRO-PHYSIOLOGY

ammonia are the same.in the one case as in the other. The
effects of various drugs on the receptivity, conductivity, and
responsivity of the vegetal nerve are the same as on those
of the animal, and finally, in the action of different salts, the
acid and basic moieties exhibit the same characteristic effects
in plant and animal nerves alike (Chapters XXXII. and
XXXITI.).

In order to study the variation of excitatory effects in.

nerves I was able to devise a very delicate instrument, the

Conductivity Balance: (fig. 291). This apparatus not only

enables us to study the modifications of conductivity, excit-
ability, and responsivity, induced by a given agent separately,
but also to compare relative variations as between any two
of these, say, for instance, conductivity against excitability,
or receptive excitability against responsivity. It also enables
us to compare and contrast the action of two different
reagents applied simultaneously in different parts of the
same nerve. In this way the factor of uncertainty introduced
by the unknown individual differences between two nerves is
eliminated.

_ The principle on which the Method of Conductivity
Balance depends is that of applying stimulus at a point
which, in the excitatory sense, is exactly midway between
the electrodes E and E’; the excitatory effects at E and E’
exactly balance each other, and the galvanometric deflection
is then zero. When the excitability of the right hand, E, or
the conductivity of the right arm, C, of the balance is
enhanced, the balance is upset and the resultant response
is, say, up ; depression, on the other hand, upsets it in the
opposite direction. Not only may the effects of various
chemical agents be determined by this method, but it is
easy also to study by its means the effects of temperature
on conductivity. Cold is thus found to depress, and warmth
to enhance it (figs. 307, 309). Another important investi-
gation carried out by this means was on the curious
phenomenon presented by the effect of section in enhancing
the excitability of adjacent points. It was shown that this

— a

Ss re

RESPONSE OF NERVE 721

was due to the molecular transformation caused by the
stimulus of the mechanical or thermal section. The effect
of such stimulus on neighbouring points is to induce moderate .
excitation, raising them to the higher excitability of the
condition B (fig. 311).. At or very near the section point
itself, on account of over-stimulation, the transformation is
to condition D or E, and the result should be one of loss of
excitability. In accordance with this, it is found that at
such points there is depression of excitability (fig. 312).

As regards the place of the vegetal nerve in the plant
economy, it may be said that the normal excitability of
a tissue, by which its proper functions are discharged, can
only be maintained fully by a supply of energy, which must
be received from the environment. Both animal and vegetal

’ nerves have been shown, when isolated, to lose their normal

conductivity and excitability, their response becoming ab-
normal or being abolished. It is only by the accession of
fresh energy of stimulus that the normal conductivity and
excitability are restored. It is known, further, that when the
nerve loses its excitability, undergoing consequent degenera-
tion, the attached muscle also exhibits rapid decay. It will
thus be seen that the various tissues of the organism are
maintained in their normal functional activities by means of
energy conveyed to them through the nerves.

One of the principal forms of energy in maintaining the
tonic condition of a green plant is sunlight; when deprived
of this, its various normal activities come gradually to a stop,
and the plant ultimately dies. But if any portion of the
plant be exposed to light even its shaded parts will be found
to continue in natural vigour. This is exemplified by the
experiment of Sachs, in which an undetached branch of
Cucurbita was kept in a dark box, and was found to grow,
and produce flowers and fruits, as if under normal conditions.
The fact that a plant, when totally deprived of sunlight, dies,
shows how essential to its tonic condition is energy of light.
The fact that so long as a portion of it is kept in light the
whole flourishes, proves the transmission of energy from one

3 A

722 COMPARATIVE ELECTRO-PHYSIOLOGY

part to another, a transmission which is now made com-
prehensible, being effected through the intervention of the
plant-nerves, whose existence I have demonstrated. In
the case of trees, again, the interior tissues whose: functions
are of great'importance in various ways, are inaccessible to
such external energy as that of light. But no part of
them:is far removed from the vegetal nerves, whose outer
endings are found in the ramified venation of the leaves.
The lamine of the plant thus in their aggregation form an
extensive catchment-basin for the reception of energy from
‘outside and its ultimate transmission within the plant. An
experiment has been described which shows the enhancement
of the excitability of the plant-nerve by energy of light

(fig. 334).

I have next to summarise a new method for the study of’

excitatory reactions in nerves. It has been supposed that in
certain respects the reaction of the nerve is specifically
different from that of the muscle. It has been regarded as
typically non-motile, the highest power of the microscope
being incapable, it was said, of detecting any effect in respon-
sive change of form. I have shown, however, that this
- conclusion was erroneous, there being in this respect a con-
tinuity between the responses of muscle and nerve. In
a particular case of frog’s nerve the responsive contraction
under strong stimulation was as much as 14 per cent. of the
original length, and in others, it was as much as 20 per cent.
or more. With a magnification of about 200 times, which is
afforded by my moderately sensitive Kunchangraph, the
observer is able to study all the excitatory phenomena in
nerve with as great ease, and much greater accuracy, as
by the employment of a very highly sensitive galvanometer.
Records of the electrical responses of nerve are obtained by
the differential effects of excitation at the two contacts, when
one of these has been subjected to injury. It has been
shown that such injury does not always completely abolish
the excitability of the second contact, for which reason there
may be induced a local reaction of feeble negative or reversed

RESPONSE OF NERVE 3 723

positive response. The interference of this with the normal
response at the uninjured contact is thus apt to give rise to
various complications. In contrast with this we have the
reliability of the mechanical response of the nerve, in which
the effect recorded is direct, and not differential. Again, the
electrical form of stimulus, which is almost universally
employed for the excitation of nerve, is liable by leakage,
unless very great precautions are taken, to vitiate the results
obtained by the electrical mode of response. When the
response observed, however, is not electrical but mechanical,
this source of error is obviously eliminated. } :
By means of mechanical response, the molecular trans-
formations through which the nerve passes, under the action
of stimulus itself, may be observed with the greatest clearness.
An isolated nerve, cut off from its natural supply of energy,
generally falls into a sub-tonicity indicated in the mechanical
record, as an increasing abnormal relaxation; and the
application of stimulus induces at this point an abnormal
positive response, of sudden expansion. Successive or con-
tinuous stimulations, however, transform the nerve from
condition A to condition B; the abnormal expansion being
arrested and converted into increasing contraction. . During
this stage, then, the responses to individual stimuli are trans-
formed from the abnormal expansive positive to the normal
contractile negative, through an intermediate diphasic.
Molecular transformation is here very rapid and the re-
sponses show a staircase increase (fig. 382)... An intervening
period of tetanisation will now have the effect of enhanc-
ing the response (fig. 383). In the clear demonstration
thus obtainable of a progressive molecular transformation,
with corresponding variations of response at its different
stages, we arrive at the true explanation of the change from
the abnormal positive to the normal negative, in electrical
response, and also of the enhancement of the normal negative
after an intervening period of tetanisation (figs. 275-278).
The next stage to be reached is C, where the responses
are uniform. After this, we arrive at D, where fatigue-decline
3 A 2

724 COMPARATIVE ELECTRO-PHYSIOLOGY

begins to make its appearance. Up to this point, the nerve
as a whole has been undergoing increasing contraction, the
base-line of the series of records being thus tilted upwards.
But after D, it begins to show relaxation, and at the stage E,
the responses to individual stimuli are actually reversed,
the region of transformation from diminishing to reversed
response being often marked by the appearance of diphasic
(figs. 396 and 400). The entire responsive cycle may thus be
viewed as consisting of two halves of which one is the reverse
of the other. From the state of extreme sub-tonicity at A
with its abnormal positivity, the responses are transformed
through diphasic to feeble normal negative at B. They here
increase in a staircase manner, till they become uniform at C.
After this begins the reversing process, due to fatigue,
brought on by overstrain, with its diminishing normal re-
sponses at D, through diphasic, to abnormal positive once

more,at E. Excessive sub-tonicity and excessive stimulation

alike find their extreme case in the abolition of all response
at death. The difference between the abnormal positive
response of sub-tonicity and the abnormal positive response of
fatigue lies in their previous history. The one is due to lack
of stimulation and the other to itsexcess. For the restoration
of normal response, the treatment in the two cases must be
opposite. In the first, the application of stimulus is necessary ;
in the second, it is its cessation, or rest, which is required.

_ Similar effects are also met with, in the case of trans-
mitted excitation. In the sub-tonic condition, conductivity
is depressed, and the transmitted effect is abnormal positive.
By the action of stimulus, however, the conductivity is
gradually restored, and the response to transmitted stimu-
lation is converted from abnormal. positive to normal
negative through the intermediate diphasic. After this,
under increasing fatigue the diminishing responses are con-
verted to abnormal positive through an intermediate diphasic
(fig. 325). Another important demonstration was that of the
perfect similarity of the molecular changes induced by
stimulus in the afferent and efferent nerves respectively.

RESPONSE OF NERVE 725

The experiments which have just been described were carried
out on the efferent gastrocnemius of frog and gecko. With
the afferent optical nerves of certain fishes I obtained
mechanical responses which were exactly the same as these
(figs. 324, 402). That is to say, in a sub-tonic condition the
optic nerve gave the abnormal positive or expansive re-
sponse, and this was subsequently converted into the normal
contractile responses, through an intermediate diphasic.

The mechanical response of nerve just described, may be
recorded either photographically, by a reflected spot of light,
or directly on a smoked-glass surface by means of a writing-
point. The difficulties due to friction in the latter case are
obviated by the use of the Oscillating Recorder. By means,
however, of a battery of levers, and using the optical method
of record, it is possible to have a magnification by the
Kunchangraph of one hundred thousand times or more, the
sensitiveness of the record being correspondingly enhanced.
By this means many new phenomena may be brought under
observation, one of these being the multiple response induced
by strong stimulus in nerve. It is known, again, that nerve
becomes highly excitable during the setting-in of ‘drying, and
under these conditions, in a nerve-and-muscle preparation,
repeated mechanical spasms are exhibited by the attached
muscle. In taking the mechanical record of nerve, it is found
that the substitution of dry for moist air at once induces a
visible contraction. Now this state of partial contraction,
bringing the nerve, as it does, into condition B, we know to
be significant of enhanced excitability. If the drying of the
nerve be now allowed to continue, it is found that there is
induced a series of multiple responses (fig. 326). And the
multiple spasms seen during drying in the muscle of a
muscle-and-nerve preparation undoubtedly have, as one of
their factors, these multiple excitations thus demonstrated
to take place in the nerve. ;

With the highly magnifying Kunchangraph, again, the
individual effect of a single shock is demonstrated with the
greatest clearness. Under rapidly succeeding tetanising

726 COMPARATIVE .ELECTRO-PHYSIOLOGY

shocks, the response shows a serration of the apical line,
proving that the individual responses are not completely
fused. On the abrupt cessation of tetanising shocks a
sudden enhancement of.the contractile effect occurs, followed
by the usual recovery. : This is analogous to the sudden

enhancement. of response on the cessation of tetanisation,

seen in the retina, in magnetic response, and in the response
of certain sensitive inorganic preparations under similar
circumstances (pp. 536, 428, 383).

The next subject to be surveyed is that of electrotonus,
and the variations in excitatory effects induced by it. It has
been shown that the polarising currents induce extra-polar
currents in the plant nerve, exactly as in that of the animal
(fig. 338). As regards the effect of electrotonic currents
generally on excitability, the results obtained by Bernstein
are described as polarisation-decrement, whereas those of
Hermann are known as polarisation-increment. That is
to say, with one experimental arrangement the induced
electrotonic current is seen to undergo a diminution under
excitation, and with a different arrangement an. increase.
These and other electrotonic variations appear to be very
anomalous, and incapable of mutual reconciliation.

I have, however, been able to show that all these effects
may be regarded as combining the variations of two distinct
factors, namely conductivity and excitability, under the
influence of an electrical current. One of the principal
difficulties in the correct explanation of these phenomena
has hitherto lain in the assumption that Pfliiger’s Law,
relating to the polar effects of currents, was of universal
application. I have shown, however, to the contrary, that
it applies only to a certain middle range of electro-motive
intensity, the excitatory effect at anode and kathode being,
at a very high E.M.F., exactly reversed. Going, again, to the
other extreme, of a low electro-motive force, I have shown
that, in opposition to Pfliiger’s generalisation, it is the anode
that enhances the excitability of a nerve, while the kathode
depresses it. This I have been able to demonstrate by

a ee ee

“pS aa as el Pal a al i ah lt ral a Re ar ON a solr ey,

“RESPONSE OF NERVE | 727

numerous experiments (figs. 350 and 353). The fact that
under feeble E.M.F. the variation of excitability is opposite
to that under moderate E.M.F. can be demonstrated with
great simplicity by means of the subjective response of
sensation. A wound was made on the back of the hand, and
the application of a dilute solution of salt caused a moderate
irritation. The application of kathode to this wound now
rendered the irritation intolerably painful, while that of the
anode at once made it soothing, removing: even the normal
discomfort due to the salt. These effects—coming under
Pfliiger’s generalisation that kathode enhances excitability,
while anode depresses—held good so long as the acting
E.M.F. was about 1°5 volt. But when the acting E.M.F.
was reduced to ‘5 volt, the kathode was found to induce
a soothing sensation, whereas the anode. became painful.

I have also found that the passage of a current pro-
foundly modifies the conduction of excitation in a directive
manner, according as the excitation has to travel with or
against it. In the simplest cases, where the polarising elec-
trodes are so far apart as to eliminate the direct excitatory
effect of the poles, and using a feeble current, I have shown
that excitation travels better electrically uphill, that is to say,
against the current, than down, or with it. Thus the normal
responses to transmitted stimulation are found to be enhanced
when the polarising current is against the ‘direction of trans-
mission. A polarising current in the same direction as that
of excitation, has, on the other hand, the effect of retarding
it. The normal responses are then diminished, or even
reversed to positive, by the diminution or abolition of the
power of true conduction (figs. 345, 346, 347).

The various effects described as polarisation-increment
and decrement have been shown further to be due to the
increased galvanometric negativity of the more excited of
two points, the responsive current being algebraically sum-
mated with the existing electrotonic current. The greater
excitation of one of these two points was also shown to be
due to the greater intensity of excitation conducted to it, or

728 COMPARATIVE ELECTRO-PHYSIOLOGY

to the greater excitability induced by the action of the anode,
or to both.

This summary of results will conclude with a brief
account of the demonstration of the physico-physiological
nature of the basis of sensation. The effect of a single
stimulus has been shown to consist of two different waves
sent out from the point stimulated, of which the hydro-

positive travels with a greater velocity than the true excita- .

tory or negative. If the stimulus applied, moreover, be
feeble, the positive wave alone will be transmitted. If the
stimulus, again, be very strong and the path of conduction
short, one wave will be superposed over the other, the nega-
tive masking the positive. The two waves, however, may
be separated from each other by inducing a depression of the
conductivity of the nerve, when the negative will be made to
lag behind the positive. By the suppression of the negative,
owing to sufficient reduction of conductivity, the positive
may be made to arrive at the responding point alone.
Nervous impulses have thus been shown to be of two
different kinds, positive and negative, and contrary to the
universal assumption that the nerve gives no visible indication
of its state of excitation, it has been shown that these are
accompanied by waves of expansion and contraction respec-
tively. In addition to these visible mechanical expressions,
we have also the concomitant electrical expressions of
galvanometric positivity and negativity. I have been able,
moreover, to identify the wave of expansion as the vehicle
of that change which gives rise to the positive tone of
sensation, which may be described as pleasurable or at
least not unpleasurable. The negative or contractile wave,
similarly, has been shown to be doloriferous. These two
waves we saw to be separable from each other, whenever the
conducting nerve was sufficiently long. Thus, when the sole
of the foot receives a smart stroke from a rod, two different
impulses are sent out, first the positive or sensation of con-
tact, which is not unpleasurable, followed by the negative,
with its different and painful tone of sensation. In various

AES Sea See Ree ee ee

RESPONSE BY SENSATION 729

well-known cases of nerve-disease, bringing on diminished
conductivity, this dissociation of sensation is met with patho-
logically. In paralysis, again, burning coals may be held in
the hand and induce only the feeling of contact, without any
sensation of pain.

One very difficult problem in connection with psycho-
logical response is that of the peculiar relation between the

intensity of stimulus and that of response. The generalisa-

tion known as Weber-Fechner’s law, asserts that stimulus
must increase in geometrical, for sensation to increase in
arithmetical, progression. Fechner, moreover, regarded this
relation, not as due to any physical or physiological factor,
but as a particular case of some specific psychological law.
On an inspection of the mechanical responses of animal
nerve, given in figs. 400, 401, and 402, however, we see that
the peculiar relation between stimulus and sensation follows
inevitably on the physiological character of those responses.
We there see that under feeble stimulus the response is
positive, connoting, as we know, a positive tone of sensation.
After this, as stimulus increases, the sign of response under-
goes a reversal into normal negative. From this point
onwards, for some time, the response to increasing stimulus
shows a rapid rate of increase; but this increase tends to
reach a limit as the maximum molecular distortion is
approached. These facts follow naturally from the mole-
cular theory of response which has been described, and in
such considerations we obtain an explanation of those
changes in the tone or quality of sensation of which Weber-
Fechner’s law was unable to take account. That these
responsive characteristics, again, are not peculiar to the
animal nerve, has been seen in the fact that vegetal nerves
also show a similar relation between stimulus and response
(fig. 403). That this relation indeed is universal, will be
understood from the response of an inorganic substance to
increasing stimuli, as given in fig. 404. |

Another interesting proof of the dependence of the
psychological upon physico-physiological changes is afforded

730 COMPARATIVE ELECTRO-PHYSIOLOGY

by the ‘polar action of currents. It has been shown that
the positive response is short-lived, whereas the negative is
relatively more persistent, its persistence increasing with the
intensity of the response. Now, by means of the Sensimeter
(fig. 405), we can apply a series of stimuli of measured
intensity in such a way as to induce the neutral sensation
which is neither pleasurable nor painful. The frequency of

this stimulation is so adjusted as to appear all but continuous.

If we now render the excited point moderately anode, and
thus reduce its excitability, the neutral will be converted to
the positive tone, and the sensation, moreover, will be rendered
strikingly discrete. If, next, the excitability of the stimu-
lated point be enhanced by the application of moderate
kathode, the neutral sensation will become converted into
painful, becoming, further, fused and continuous.
It will thus be seen that in the determination of sensation
the internal plays as important a part as the external. By
the peculiar molecular disposition of the nerve, it is indeed
possible, as we have seen, to convert one quality of sensation
into another, and such dispositions are to a greater or less ex-
tent under the control of the will. It is not external circum-
stances, then, which are the dominant factor psychologically,
for the impression created by these is capable of indefinite
modification in any direction, by the action of habitual
induced dispositions, The reader will see for himself what
illimitable possibilities are opened up by the line of thought
here suggested. Ee) |
The last subject to be reviewed is the phenomenon ot
memory, which is an after-effect of stimulus. The after-
effect of strong stimulus is in general more persistent than
that of feeble. Similarly, the memory of a strong sensation
is more¥enduring than of a weak one. Very strong stimulus,
again, gives rise, as we have seen, to multiple responses. In
the retina these are perceived as multiple after-images, which
sometimes appear to be renewed spontaneously. This fact
will often be found a sufficient explanation of visual phantoms
and hallucinations. ' This, however, is not the usual method

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RESPONSE BY SENSATION ~ 731.

of reviving memory-images. Long after every trace of the
primary stimulation has disappeared we can revive it by an
impulse of the will. Memory-impressions are often likened
to scars. Of this metaphor, however, it may be said, that
though, no doubt, when the blow is recent the smarting effect
will persist for some time, causing an ever-diminishing after-
sensation, yet, when the scar has healed, how could it, of
itself, reproduce the original sensation? To do this, the
original excitation would require to be reproduced, in the
absence of the primary exciting cause. If, then, instead of
regarding it as a scar, we translate the original impression
into shades of light and darkness, we see that such a picture
was produced by different intensities of the primary stimulus
acting on the sensitive surface—in other words, by means of
induced differential excitation. To bring back the picture we
have to reproduce, in the absence of prirnary stimulus, the
same state of differential excitation as was at first induced
by it.

Such a revival is possible, as already shown, under the
combined action of two different factors. It has been shown
that when an isotropic tissue is locally acted upon by stimulus,
the excitatory manifestation thus induced disappears after a
time. There is now nothing visible by which to. distinguish
the stimulated from the unstimulated areas. In consequence
of this stimulation, however, there has been a transformation
of the molecular condition of the portions acted upon. The
tissue, which was originally isotropic, has now become an-
isotropic, by the impression of this latent image. On diffuse
stimulation, the differentially excitable structure will now
exhibit the latent image, by various forms of differential
excitation, of which some one particular manifestation will,
in the case of any given organ, be the most conspicuous.

Thus, in a metallic plate containing latent positive and
negative chemical impressions, we shall obtain, on the appli-
cation of diffuse stimulus, corresponding positive and negative
galvanometric responses. In a phosphorescent plate, again,
a small area may be subjected to the action of light. On the

732 COMPARATIVE ELECTRO-PHYSIOLOGY

cessation of stimulus this will give luminous response, which
may be taken as the immediate effect of primary stimulus.
On the fading of this image, if the whole plate be subjected
to feeble diffuse illumination for a short time, the latent image
will once more appear as a bright patch against a dark back-
ground. This is because, as the after-effect of stimulus, the
area B has been rendered more excitable. Hence, diffuse

stimulation evokes more intense response from it than from |

its more inert background. Similarly, the memory-image
is capable of revival by the internal impulse of the will,
acting as a diffuse stimulus to evoke a differential sen-
sation, which reproduces the light and shade of the primary
picture. |

The responsive phenomena seen in living matter are,
_undoubtedly, wonderful and mysterious ; but those shown
by the inorganic are no less wonderful. By-ascribing all
physiological occurrences to specific reactions, and by con-
stantly postulating the intrusion of forces of a new order,
the road to the further advancement of knowledge is closed.
By the conception of matter itself, on the other hand, as
possessed of sensibility—that is to say, of molecular respon-
siveness—we attain an immediate accession of insight into
those physical interactions which must furnish the terms of
any ultimate analysis. We are led by it to the discovery
of the impressive fact of continuity as existent between the
responses of the most complex living, and the simplest
inorganic matter. Limiting ourselves, again, to the realm of
living matter, we are impelled to recognise parallelisms, in
the response of plant and animal, whose extent could never
otherwise have been suspected. All the responsive phe-
nomena of the animal are thus found to be foreshadowed in
the plant, and this to such a degree that in the common
script of the response-record the one is indistinguishable
from the other. In both we observe a similar series of
excitatory effects, whether these be exhibited mechanically
or electrically. Both alike are responsive, and similarly
responsive, to all the diverse forms of stimulus that impinge

ost SAE

Pike CeO te 2 Sere ed ts We

RESPONSE BY SENSATION rates

upon them. We ascend, in the one case as in the other,
from the simplicities of the isotropic to the complexities of
the anisotropic ; and the laws of these isotropic and aniso-
tropic responses are the same in both. The responsive
peculiarities of epidermis, epithelium, and gland; the re-
sponse of the digestive organ, with its phasic alternations ;
and the excitatory electrical discharge of an anisotropic
plate, are the same in the plant as in the animal. The
plant, like the animal, is a single organic whole, all its
different parts being connected, and their activities co-ordi-
nated, by the agency of those conducting strands which are
known as nerves. As in the plant-nerve, moreover, so also
in the animal, stimulation gives rise to two distinct impulses,
exhibiting themselves by twofold mechanical and electrical
indications of opposite signs. It is the nature of the indica-
tor, again, which determines in any given instance the form
of the responsive expression. A single molecular derange-
ment may thus find manifestation as change of form, alteration
of electrical condition, and subjective sensory variation. The
dual qualities or tones known to us in sensation, further, are
correspondent with those two different nervous impulses, of
opposite signs, which are occasioned by stimulation. These
two sensory responses—positive and negative, pleasure and
pain—are found to be subject to the same modifications,
under parallel conditions, as the positive and negative
mechanical and electrical indications with which they are
associated. And finally, perhaps, the most significant
example of the effect of induced anisotropy lies in that
differential impression made by stimulus on the sensory
surfaces, which remains latent, and capable of revival, as the
memory-image.
In this demonstration of continuity, then, it has been found
that the dividing frontiers between Physics, Physiology, and
Psychology have disappeared.

2

a

a

CLASSIFIED. LIST OF EXPERIMENTS

MOLECULAR RESPONSIVENESS OF MATTER .

Mechanical response :

PAGE
1. Contractile response in indiarubber ; . : > . ‘ 2
Electromotive response :
2. Response of tin . ‘ . 6
3. Fatigue in inorganic response : 7
4. Action of sce on response of batirnast : - d are 8
5. Action of ‘ poison’ in abolishing response of metal . 9
6. Response in metal by method of negative variation 9
Response by resistivity variation :
7. Response of selenium to light 3
8. Response of galena to electric radiation 3
g. Response of allotropic silver Ag’ to electric vailission 4
FUNDAMENTAL PHENOMENON OF RESPONSE IN PLANTS
10. Simultaneous record of mechanical and electrical response 19
11. Electrical response of pulvinus of Mimosa when physically re-
strained . ; 2 . 20
12. Response to sudden sailation of tension 25
13. Response'to sudden compression . ; 25
14. Response to tension and compression . 2
15. Response to mechanical blow ‘ . . : - : e726
16. Response to vibrational stimulus 27
17. Response to chemical stimulus : : : ; 2. 27
18. Response to thermal shock ‘ : : ‘ee ae
19. Influence of sudden variation on efficiency or siirialation * 32
20. Additive effect . ‘ ‘ : ‘ : ; 34.
21. Genesis of tetanus in mechanical response of plants . 43
22. Genesis of tetanus in electrical response of plants 43
23. Rheotomic observation of time relation . ‘ é 48
24. Response to increasing intensity of stimulus of mechanical blows 39
25. Response to increasing intensity of vibrational stimulus ae gies
26. Response to increasing stimulus, with or without complete recovery. 41

COMPARATIVE ELECTRO-PHYSIOLOGY

POSITIVE. AND NEGATIVE RESPONSE

. Hydraulic response in Mimosa

. Positive mechanical response followed by anlative in 5 Wioshysas ¢

. Positive mechanical response followed by negative in AZzmosa. .

. Simultaneous record of positive and ign mechanical and electrical

response in Bzophytum .

. Positive, diphasic and negative Seanoues in petiolé of cauliieer

. Positive and negative responses in tuber of potato

. Unmasking of positive element in response by selective block :

. Effect of stimulus of light on growth .

. Effects of steady and sudden variation of Pome on a prowth

response

VARIOUS TYPES OF RESPONSE

. Abnormal positive response in sub-tonic tissue

. Staircase response in tissue originally sluggish

. Staircase response in vegetal nerve

. Staircase response in galena

. Uniform response in plant

. Fatigue due to rapidly succeeding Tre oem

. Fatigue due to overstrain . ‘ ae
. Fatigue-decline under continuous stimulation, i in medhanical response

of Mimosa.

. Fatigue-decline under continuoas ecmueaens in tecnica! response

of celery

. Oscillatory response in arsenic

. Phasic alternation in mechanical dessonne of style of Diiave

. Periodic fatigue in electric response of plants . ‘

. Periodic fatigue in autonomous response of Desmodium an

. Reversal of normal response in fatigued nerve . : .
. Bifurcated expression of response as growth and mechantesl response

DETECTION OF PHYSIOLOGICAL ANISOTROPY

. Differential response of compound strip . :
. Isolated responses of upper and lower halves of ihe inus af Mitosa,

with resultant differential response .

. Transverse differential electrical response of eee af Mian
. Transverse differential electrical response of plagiotropic stem of

Cucurbita

. Transverse differential dlectrical: reponse i cetiole of Musa

NATURAL CURRENT OF REST AND ITS VARIATIONS

. Effect of rise of temperature on current of rest

. Effect of falling temperature on current of rest

. Effect of Na,CO, solution on current of rest

. Effect of CO, on current of rest ‘
. Reversal of natural current of rest as after- stint of esimuladion

103

102
104

108

109
1@ fe)

III
114

119
119
122
122
127

CLASSIFIED LIST OF EXPERIMENTS 737

EFFECT OF CHEMICAL AGENTS ON EXCITABILITY

PAGE
61. Effect of chloroform : : ‘ : ‘ é ; ; - 130
62. Effect of chloral hydrate . ; : ‘ ; RIM faerie an BSE
63. Effect of formalin . : : ; : ; ‘ ; ; . +932
64. Effect of NaOH. ; , ‘ ; : : , , na 5."
65. Effectof KOH . ‘ . i a é ; a : 835
66. Effect of sugar solution . “ ; ; ee ‘ 2. oe ae
67. Effect of Na,CO, solution. ° : ; : ; ; . 136
68. Effect of HCl . ; ‘ ; ; (on Ea
69. Effect of moderate and rong aa of KOH : . P i - 139
METHOD OF INTERFERENCE
70. Responsive effect of variation of phase ; F : ‘ 5 enh el
71. Diphasic response and its variation 4 : ; : : a EAS
72. Diametric method of recording response. ‘ , e . » 147
CURRENT OF INJURY AND NEGATIVE VARIATION

73. Electrical after-effect in inorganic substances under strong stimu-
lation . : ‘ I51

74. Resistant saicuaomnisis saath: in vegetable tinea cases sti
stimulation . : ‘ , Las oa
75. After-effect of persistent negativity ise to section 2), i aig
5 76. Electrical distribution in plant cylinder. : ; d Sf. age
77. Response by negative variation . : : : : d . 158

CURRENT OF DEATH AND RESPONSE BY POSITIVE VARIATION

78. Response by abnormal positive variation . : : g OS
79. Electric exploration of dying and dead tissue . : ’ ‘ . 169
80. Electric exploration of tissue one end of whichis killed . . . 171
81. Response by negative and positive variations of current of injury . 174

EFFECT OF TEMPERATURE

82. Effect of cold in arresting autonomous pulsation in Desmodium . . 181

83. Effect of warmth on autonomous pulsation of Desmodium : . 182
84. Effect of cold in pezmanent abolition of response , ‘ ote SZ
85. Effect of cold in temporary abolition of response. ‘ - 184
86. Effect of cyclic variation of temperature on electric response site EBS
87. Effect of rising temperature on amplitude of response ; . 186
88. Effect of rising temperature on conductivity pe , o Avca BOF
89. Abolition of response by high temperature ~ . e258 190
90. Effect of cooling on frequency and amplitude of pulsation a Des- :
modium , ‘ , : : ‘ : . ° jet OSS
3 8

738 COMPARATIVE ELECTRO-PHYSIOLOGY

DETERMINATION OF DEATH-POINT

91. Determination of death-point by abolition of electrical response . 195
92. Determination of death-point by means of thermo-mechanical curve 198
93. Determination of death-point ie means of inversion of electro-
motive curve . . : - + 202
94. Simultaneous reversal of fectital curve ea Seen ‘ : . 204

MULTIPLE AND AUTONOMOUS RESPONSE

95. Multiple mechanical response in Biophytum . ; : ae ae a
96. Multiple electrotactile response in Mimosa . : ; ; . 208
97. Multiple electromotive response in Biophytum . : , oe ROO
98. Multiple electric response in various tissues . ; , ‘ . 210
99. Multiple electric response in stomach of frog. j ; ae 8 Ie,
100. Autonomous response in Biophyium - ; eT
101. Initiation of multiple response in Deiwiutint cider light - eee ee
102. Spark record of autonomous pulsation in Desmodium . : 214
103. Simultaneous record of mechanical and electrical response of pul
sating Desmodium leaflet . : : 217 ;
104. Record of electrical responses in are ee leaflet nena movement
is restrained . : ‘ ; : : : : Shea
105. Multiple response of Seine ; : : : : } gee +f

RESPONSE OF LEAVES

106. Effect of section of petiole of /zcus on ihe current of rest : a: Bay
107. Effect of section of petiole of C7¢7ws on the current of rest . S96
108. Effect of stimulation of lamina. : . 225
109. Parallelism between response of J/usa aiid that of es eae

OO“. ee

ELECTRIC DISCHARGE IN ANISOTROPIC ORGAN

110. Response of leaf of Vymphea to transmitted stimulation ‘ + =2a5
111. Response of leaf of Co/ews to thermal shocks . A ; <4 She 4
112. Rheotomic observations. a ee
113. ‘ Blaze current,’ so-called, in lament pence : : ices etn

Response to equi-alternating shocks in :

114. Carpellary leaf of Didlenza . 3 . ; : . 256
115. Leaf of Plerospermum . : : ; : ‘ : Re
116. Pitcher of Nepenthe . , : : ; , : : . 256
117. Pulvinus of AZzmosa : : : : . : : ~ 4 ams
118. Bulb of Mriciis lily. : ‘ . : ‘ ‘ : i SY
119. Prepared strip oflead_. ; ; : : : : < i. Oe
120. Petiole of Alusa . : , : : ‘ .- (283
‘121. Plagiotropic stem of [ome f : : : : buts eos
$22, er. . . ; : : : ; ey ees
123. Variegated leaf of Pothos . . . . ; : ; ~ -« 206

124.
125.

‘126.
127.
128.
129.
130.
131.
132.
133.
134.
135.

136.

137.
138.

139.
140.
I4I.
142.
143.
144.
145.
146.
147.
148.

149.

150.
151.
152.
153-
154.
155-
156.

157:

CLASSIFIED LIST OF EXPERIMENTS

RESPONSE oF SKIN

Current of rest in vegetal skin :

Isolated responses to mechanical stimulus of id ali tower porbiecs
of grape skin . : : : ‘

Isolated responses of frog’s an?

Isolated responses of skin of tomato

Response of grape-skin to thermal shocks . ‘

Response of grape-skin to equi-alternating shocks

Response of frog’s skin to equi-alternating shocks .

Response of tomato-skin to equi-alternating shocks

Exhibition of positive after-effect .

Response of skin of tortoise

Response of intact human skin . ‘

Illustrative response of pulvinus of AZmosa waniae sei? variation

Illustrative autonomous senanee of Desmodium exhibiting cyclic
variation :

Normal response of skin of ake: ; A

Abnormal diphasic response of skin of gecko, ceerieds to aaian |
after tetanisation

RESPONSE OF EPITHELIUM AND GLANDS

Resting current in foot of snail

Reversal of true resting current by injury .

Response of water-melon F

Response of glandular foot of snail

Response of human arm-pit .

Response of human lip

Response of human tongue . :
Normal response of pulvinus of eee révened sue eigntaation
Response of Dz//enia and its reversal after tetanisation

Reversed response of Dz//enza under feeble stimulation .

RESPONSE OF DIGESTIVE ORGAN

Determination of natural current of rest in digestive organ of
Nepenthe .

Excitatory electric deagolise of fash vibe of Nepenthe

Response of Wefenthe at intermediate stage —

Response of pitcher of Vefenthe with entrapped iseets

Normal response of digestive leaf of Drosera and its reversal éter
tetanisation

Response of frog’s atitibeuth to iiebhaniéed pildautadion

Response of stomach of tortoise to electric stimulation

Normal response of stomach of ee and its reversal after eebht:
sation °

Multiple response to trou Sith ule in sf piteher of Wepenilic thes:
fresh . - ‘ :

3B2

739°

PAGE

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3097
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311

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319
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322

326
328

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338
339
339

342
345
345
346

341

749

158.

159.
160.

161.
162.
163.
164.
165.

166.
167.
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T 72:
‘$93.
174.
175.

176.
i or
178.
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180.
181.
182.
183.
184.
185.
186.
187.
188.

189.
190.

gl.
192.

193.

COMPARATIVE ELECTRO-PHYSIOLOGY

Multiple response in pitcher of Wepenthe with entrapped insects
Multiple response in Drosera . ,
Multiple response in stomach of frog

ASCENT OF SAP AND SUCTIONAL RESPONSE

Electrical response of young root

Electrical response of older root

Responsive secretion by root

Response of root to chemical stimulation : ;

Electrical response of sii wood and its lepresson aniter anses-
thetic .

Abolition of gedit: pepenae a weed by poison

Hydraulic response to stimulus .

Effect of cold on suctional response

Effect of rise of temperature on suctional responsé

Effect of anzesthetic on suctional response

Excitatory versus osmotic action

Initiation of suctional response and enhanceiient under atcaatite

Diminution of latent period as after-effect of stimulus

Responsive variation of suction under overbalance.

Response to sub-terminal stimulation

RESPONSE TO STIMULUS OF LIGHT

Transverse transmission of effect of moderate stimulus
Transverse transmission of effect of strong stimulus
Mechanical response of Mimosa to unilateral light .
Electrical response of A/imosa to unilateral light
Transmitted effect of stimulus of light

Electrical response of Bryophy/lum to light

Electrical response of petiole of cauliflower

Multiple growth response under light

Multiple mechanical response of Biophytum under hone
Multiple electrical response in Bryophyl/um under continuous light
Normal negative and positive after-effect under light
Influence of fatigue on after-effect .

Third type of direct and after-effects in alae bac light .

RESPONSE OF RETINA

Determination of differential excitability as between optic nerve and
cornea ‘

Determination of differential away as orcas Gina aoe opéle
nerve .

Determination of true current 96 ea in ae S aes . ‘

Conversion of abnormal retinal response to normal by escitatocy
agents

Normal retinal response of Ophiocephatus.

397

401
402
402

405
407
408
409
4II
412

417

419
418

423
427

194.
195.

196.

BOP
198.
199.
200.
201.

202.
203.
204.
205.

206.
207.
208.
209.
210.
211.
212.

213.
214.
215.

216.

217.

218.

219.

220.

221.
222.

223.
224.

225.

CLASSIFIED LIST OF EXPERIMENTS 741.

PAGE
Reversed retinal response and after-effect in Ophiocephalus Fecctady
Three parallel types of direct and after-effect of light in plant and

animal . ; Pau Rab aaas ~ 5p Si 430
Multiple response in hoe’ S aoe , : , , ; 426
Multiple response in retina of Wallago. + . : : ‘ - 433
Multiple response in human retina . : ie ep ae
Pulsating response in human retina under juiiaueam Tight : 592
Binocular alternation of vision . , ; : ; “ae i!
Analysis of composite image by after- shect ‘ F i . +: 432

GEO-ELECTRIC RESPONSE

Response to unilateral pressure of particles : ‘ ; 7 = 37
Determination of excited area under geotropic stimulus . ‘ - 436
Geo-electric response . ; S ~ Sye§40
Geo-electric response of an oad Ghesicaite ae F : - 442

VELOCITY OF TRANSMISSION >

Determination of velocity of transmission by mechanical response . 447
Determination of centripetal versus centrifugal velocity . : . 448
Effect of fatigue on velocity of transmission — . ; ; . « 449
Effect of intensity of stimulus on velocity . ‘ ‘ : - 449
Effect of temperature on velocity. .; . 450
Determination of velocity of transmission by pleetroniutive wiethoul 452
Longitudinal versus transverse conduction < : i . eee

ELECTRIC RESPONSE OF NERVE TO THERMAL STIMULUS

Electrical response of frog’s nerve to equi-alternating shocks . . 457
Normal response of animal nerve to thermal stimulation . . 460 .
Enhancement of normal response after thermal tetanisation . . 462
Abnormal positive converted to normal negative after thermal

tetanisation . . ‘ 463
Gradual transition oe {honda ester : sonal Woeative

through diphasic . P 465
Conversion of abnormal positive to sired eis faust Sige

by increasing intensity of stimulus : ; ° : . . 466

ELECTRIC RESPONSE OF PLANT NERVE

Effect of ether on electric response of plant nerve . : ; of eaQye:
Effect of carbonic acid . 5 ‘ : : . ; a: Cae
Effect of alcohol . ; : ‘ 5 F ‘ < «tae Oe
Effect of ammonia . - P : spt WEA
Effect of ammonia on response of indifferent iSueale:: : ; - 474
Three parallel types of response in plant and animal nerve Ae iak 7A.

Effect of tetanisation on enhancement of normal negative response. 475

742

226.
227,

228.
229.
230.
231.
232,
233.
234.
mae.
236.
237.
238.
239.
240.
241.
242.
243.
244.
245.

246.
247-
248.
249.
250.
25%.
252.

253:

254.
255.
256.
257:
258.

259.
260.
261.

COMPARATIVE ELECTRO-PHYSIOLOGY

Abnormal diphasic converted into normal negative after tetanisation
Conversion of abnormal positive to normal negative through inter-
mediate diphasic under increasing intensity of stimulation .

CONDUCTIVITY BALANCE

Effect of Na,CO, solution on responsivity of frog’s nerve

Effect of CuSO, solution on responsivity of frog’s nerve .

Effect of CaCl, on responsivity of ai nerve

Effect of KCl ;
Comparative effects of NaCl ant N ae on deeds

Effect of dilute solution of Na,CO,

Effect of stronger solution of Na,CO,

Excitability versus conductivity under KI

Excitability versus conductivity under NaI

Effect of alcohol on responsivity of frog’s nerve

Effect of alcohol on receptivity of plant nerve

Effect of alcohol on conductivity of nerve

Effect of alcohol on responsivity of nerve .

Receptivity verses responsivity under alcohol

Effect of cold on conductivity .

Effect of warmth on conductivity . ;

After-effect of moderate stimulation on peaduclivits and excitability
After-effect of strong stimulation on conductivity and excitability

MECHANICAL RESPONSE OF ANIMAL NERVE

Mechanical response of frog’s nerve under electric tetanisation .

Effect of ammonia on mechanical response

Effect of morphia

Effect of aconite .

Effect of alcohol

Effect of chloroform

Conversion of abnormal positive to ‘Homial peace ‘heough sisbacies
by tetanisation

Occurrence of staircase seer

Comparison of mechanical responses in accanl and slit nerve .

Mechanical response of optic (sensory) nerve .

Fatigue of conductivity in nerve of gecko. ‘ :

Transient enhancement of contraction on cessation of tetanisation

Multiple mechanical response in nerve as effect of drying .

MECHANICAL RESPONSE OF PLANT NERVE

Enhancement of excitability after tetanisation
Effect of light in enhancing excitability of plant nerve
Determination of velocity by mechanical response of plant nerve

PAGE

476

477

485

485.
486 ©

486
487
488
489
491
492
492
493
493
494
495
499
$01
504
595

509
516
516
516
517
518

521
524
528
529
530
536
539

554
556
525

.
.

262.

263.
264.

265.
266.
267.
268.
269.
270.
271.

272.

273:
274.

are.

CLASSIFIED LIST OF EXPERIMENTS

RESPONSE OF LIVING TISSUE BY RESISTIVITY VARIATION

Determination of death-point by inversion of curve of goles
Excitatory response by resistivity variation

Action of anesthetics on response by resistivity iivintod in fido%s s
nerve . . . . . . Oo . . *. e
ELECTROTONUS

Extra-polar effects in plant nerve

Variation of conductivity in plant nerve by piece of suse

Conduction of excitation with the current 5

Conduction of excitation against the current .

Modification of excitability by anode

Modification of excitability by kathode .

Variation of excitability and conductivity with pélacitiie sisesindes
in shunt ‘

Variation of excitability st cinddeivity $ith patiniateg Medtrblen
in series .

INADEQUACY OF PFLUGER’s LAW

Normal effects of anode and kathode on plant .

Reversal of normal effect under high E.M.F.

Demonstration by subjective response of opposite effects cotaeed by
moderate and feeble E.M.F.

MOLECULAR THEORY OF EXCITATION

Mechanical Response :

276.

Mechanical response of pulvinus of Zrythrina indica, by make of
kathode and anode

Magnetic Response :

277.
278.

279.

280.
281.

282.
283.
284.

285.
286.

287.

Uniform magnetic responses

Periodic groupings in magnetic response

Incomplete magnetic recovery after strong aieniation

Additive effect of magnetic stimuli, individually ineffective

Magnetic tetanisation, with transient enhancement of effect on
cessation .

Demonstration of anes raeoene balenas

Effects of A-tonus and K-tonus on magnetic comico .

Opposite effects of moderate and strong K-tonus on esagrnnite con-
duction .

Effects of A-tonus and k K- ewe on rielgrietic excitability

Enhancement of magnetic G-menen: by successive fongnetic
stimuli. ‘ ‘ : ° . :

Blocking of trainee of magnetic excitations

743 ©

PAGE
546
548

549

561
566
567
568
569
579

- 572

574

579
579

582

7A4 COMPARATIVE ELECTRO-PHYSIOLOGY

PAGE
Response by resistivity variation :

288. Response of aluminium powder to electric radiation . . * <3, OL
289. Persistent after-effect on strong stimulation . : : : . 603
290. Effect of warmth in hastening recovery . > ; gag? at one, OE
291. Uniform responses to electric radiation . apes 602

292. Cyclic molecular variation and concomitant snodification a response
—characteristic curves . ‘ ; : ‘ ; : 5: ce GRD

Effect of tetanisation at A stage, conversion of abnormal positive to

normal negative seen in :

293. Mechanical response of frog’s nerve. ; ; , , « 627
294. Electromotive response of tin . : . 628
295. Conversion of abnormal to normal thioagh dighaiivs in 7 caaioae - 629
296. Response by resistivity variation in selenium. — . : ‘ - 631
297. Response by resistivity variation in tungsten. : ; : «eee

Effect of tetanisation at B stage, enhancement of normal response

seen in :

298. Mechanical response of frog’s nerve. : : : : - 634
299. Responsive resistivity variation in selenium ; : . . woe
300. Responsive resistivity variation in aluminium powder . . < 63
301. Electromotive response of tin . : ; . : : ~' «O30
302. Magnetic response of iron. ‘ ; ; ‘ ‘ - | 633

Effect of tetanisation in inducing E stage, diminution or reversal of normal
response seen in :

303. Mechanical response of frog’s nerve . , : : * . ted. 98
304. Mechanical response of nerve of gecko . ‘ ‘ ‘ é - “he
305. Mechanical response of india-rubber. : ° ; : eh 16GS
306. Responsive resistivity variation in tungsten . ‘ ‘ : . 638

CORRELATION OF PSYCHIC AND PHYSIOLOGICAL RESPONSE

307. Expansive and contractile response in muscle . : . 649
308. Relation between stimulus and response in sciatic nerve ar seks «) g?
309. Relation between stimulus and response in sciatic nerve of bull-frog 658
310. Relation between stimulus and response in sensory optic nerve of

Ophiocephalus . ; : : . 659
311. Relation between stimulus anid fespolise in plant i nerve. » s B59
312. Relation between stimulus and response in magnetic substance . 660

EXPERIMENTS WITH SENSIMETER ON ELECTROTONIC VARIATION OF
SENSATION

313. Conversion of pleasurable sensation to painful under kathode
(mechanical stimulation) . ; ‘ : . . 670
314. Conversion of painful to pleasurable Scaaeepe ar anode (mechani-
cal stimulation) . ; : i ; , ; y ae, ST

315.
316.

317.
318.

319.
320.

321.

CLASSIFIED LIST OF EXPERIMENTS

Positive tone of sensation due to thermal stimulus converted to
negative under kathode .

Negative tone of sensation due to thermal ainalas. eoaneeed to
positive under anode . : ‘

Reversal of normal effects under feeble E. M. F. : ; 671, 672

745 ©

PAGE
672

672

Differences of fusion in sensation according as it is modified to
positive or negative . 5 F : : ; : 671, 672
MEMORY

Revival of latent impression in metal under diffuse stimulation é

Revival of latent or ‘memory image’ in phosphorescent screen under
diffuse stimulation

Reversed or negative image .

683

684
685

INDEX

ADDITIVE effect, 34, 595
After-effect, persistence of, under strong stimulation, 151-154
Anesthetics, effect of, on excitability, 130
on response of nerve, 472, 518, 673
on response of wood, 362
~ re on responsive resistivity variation, 549
Sa on suctional response, 375
eieoazons induced by stimulus, in memory image, 686
in metallic plate, 683
bd "e b in phosphorescent screen, 684
3 PR in plagiotropic stem, III
Arm-pit, sckpouiee of human, 319 ©
Ascent of sap, various theories of, 356
Assimilation and dissimilation, 68, 87, 308
Autonomous response, continuity with multiple, 211
* a in Biophytum, 211
is in Desmodium, 212
Reslenche theory, 502

bP) 99 29

BERNSTEIN on polarisation decrement, 562
Biedermann on response of glands, 289 ase riff
“ > of stomach, 289

Binocular alternation of vision, 431
Biophytum, mechanical response of, 58

aS multiple response of, 209

Pe positive and negative response in, 59
Blaze current, so-called, in lead, 266
Block, advantages of method of, 133

» method of, 5

Burdon Sanderson, on response of Dione@a, 12 ©

CHARACTERISTIC curves of conductivity, 621

3 », Of differentially excitable surfaces, 324
pr », of magnetisation, 620
Complex sensation, dissociation of, by lag, 674, 675
‘4s », obliteration of negative element in, by selective block, » 073s 675

Composite image, analysis of, by after-effect, 432
Conduction of true excitation in plants, 446

748 COMPARATIVE ELECTRO-PHYSIOLOGY

Conductivity balance, experiments with :
+ = sy on condectivny versus receptivity sek alcohol,

495
Wa - ~ on conductivity versus receptivity under KI and
Nal, 491-492
- cs - on receptivity under alcohol, 493
ee a me case versus responsivity under alcohol,
495
PP > a on responsive variation under alcohol, 494
re sy rs on variation of conductivity under alcohol, 494
Conductivity balance, experiments with :
si », Variation of responsivity by alcohol on frog’s nerve, 492
a * Py re by CaCl, on plant nerve, 486
$5 re ne . by CuSO, on frog’s nerve, 485
‘“e Fi Pe te by KCI on plant nerve, 487
& Pe ‘ys te by Na;CO, on frog’s nerve, 485
5 ms ‘6 es contrasted effects of NaCl and
NaBr, 487
a Pe ‘i conductivity by Na,CO, on plait ne ve, 488-
489
Conductivity balance, experiments with :
% effect of cold on conductivity, 499
+3 »» Of electric current, 565-568
- », Of excessive stimulus, 505
ae »» Of moderate stimulus, 504 ‘

», Of warmth, so1
el oa: 553
Corrosion figures, 349
Crescograph, 221
Cucurbita, electric response of plagiotropic stem of, 111, 285
Current of death, 166
Current of injury : anomalous variation in, 165

mA », diminution of response with diminution of, 159
ear i explanation of, 156
= op its decline, 158
a 33 positive and negative variation of, 161
ee various theories of, 149
Current of Reet, effect of CO, on, 122
oe », effect of fall of temperature on, 119
i », effect of Na,CO, on, 122
5 », effect of section of petiole on, 225-227
os », effect of steady rise of temperature on, 119
‘5 »» effect of sudden variation of temperature on, 120
- »» in animal skin, 288
a o> ©6in Citrus, 224
a », in Dionea, 224
"ys »» in Ficus, 224
9 », in foot of snail and its variation on injury, 318

” », in frog’s eye, 418

INDEX | 749

Current of rest, in Mepenthe, 335

iz », in vegetal skin, 298

ef ,, natural, and its variations, 317

Bs: »» phasic changes in, 302, 303

se », physiological condition determining, 117
aoe ,» positive and negative variations of, 126

% ,, reversal of, as after-effect of stimulus, 124

“ »» variation of, 175-177

DARWIN on excitatory reaction in Drosera, 331
Dead tissue, positivity of, 170

Death, different Jost-mortem symptoms of, 192
Death-point, accurate methods of determining, 194

ss determination of, by abolition or reversal of response, 195

od = by electric spasm, 202

a 36 by inversion of curve of electric resistivity, 546
a x by thermo-mechanical inversion, 198

Depression, response by method of relative, 9
Desmodium pulsation, electro-motive response of free leaflet, 218

»” » » “ leaflet physically restrained, 220

» ” > ” principal and subsidiary waves it;
; 219

<5 sy initiation of, under stimulus, 212

” » » Yate of, 215

a ss spark record of, 214

Bens: and McKendrick on retinal current, 415
Differential excitability, determination of: in eel, 285

Yr) $9 ee in Musa, 114, 284

>» 2 Pe in plagiotropic stem, III, 285
” 2” ” in pulvinus, 303

an. » % in retina, 419

” » 2 in variegated leaves, 286

Differential excitation, in memory revival, 680
Differential response, of compound strip, 108

e $3 of Mimosa, 108, 303
+ laws of, 109
Dicesinie organ, alternating phasic reactions in, 329
i »» current of rest in, 335, 344
Z », multiple response in, 333, 341, 343, 347
¥5 5, response of, in Drosera, 342, 343
9 99 » in frog, 345, 347
» 99 9 in gecko, 346
a : 5 in Nepenthe, 339-341
sa a Je in tortoise, 345
Digestive organ, response of, :
is iy i reversal of, in Dvosera after tetanisation, 342
ia = 4 3 in gecko after tetanisation, 346

Dillenia indica, normal response of, 256
» » » y9 reversal of, under fatigue, 327

750° COMPARATIVE ELECTRO-PHYSIOLOGY

Dillenia indica, reversal of normal response, under feeble stimulation, 328
Direct and after-effect, methods of, 275

x 5 of light, in plant, 409-414
ss »5 in retina, 427-430
asoeis tia and delayed pain, 675
ne of complex sensation, by depression of conductivity, 674
2” oe) 29 by lag, 675

Dose, effect of, on excitability, 136
Drosera, response in digestive leaf of, 342, 343
Drugs, modification of effect by tonic condition, 641
», significance of effect of dose, 639, 640
Drying, effect of, on nerve, 539
Du Bois-Reymond on current of rest in frog’s skin, 288

ee “4 on organ current, 260

a se on positive and negative polarisation, 246

- ¥ pre-existence theory of, 149 ;
Dying tissue, negativity of, 169, 173 a :
EBBINGHAUS, on rate of forgetting, 678 }
Eel, electric response of, 285 %
Electric discharge under excitation in leaf organ : ;

»» In Bryophyllum, 253 F

»» in bulb of Uriclés lily, 257. 1

»» in Coleus, 248 3

» in Mimosa, 268

», in Musa, 284 ‘

» in Mymphea, 246 3

in pitcher of Vepenthe, 256
in Pothos, 286

in Pterospermum, 255
Electric distribution, explanation of, in dying and dead tissue, 173

ic. “ in plant and muscle cylinder, 150, 156
Electric organ, anterior and posterior surfaces, 242
= », laws of response in, 248
is », theories of, 260
Electrical response, in absence of mechanical, 20, 220
ey ne laws of, in anisotropic organs, 109
a3 af »» in isotropic organs, 75
Electrotonus, Bernstein’s polarisation decrement, 562
i conversion of qualities of sensation by, 670-672
KA extrapolar effects in plant nerve, 561
ie Hermann’s polarisation increment, 563 ;
Ws law of variation of conductivity under, 568
oe ‘ excitability under, 571
Pe iodiication of conductivity by, 566-568
i variation of excitability by, 569

Energy, hydraulic transmission of, 69
Engelmann on current of rest in skin, 288
Equi-alternating shocks: their advantage, 274

INDEX

Excitability, variation of, by chloral, 131

9?

9)

29

chloroform, 130
formalin, 132
HCl, 138

KHO, 138
NaHO, 134
Na,CO,, 136
sugar solution, 136

BacBakion: true caoe of, 16

FATIGUE, alternating, 98
in response of metal, 7
reversal of normal response in D2//enza under, 327

9

99

93

99

“= on

93

93

be)

_ in Drosera under, 342
in Mimosa under, 326
in nerve under, 102
in stomach of gecko under, 346

transmitted effect in nerve under, 530
under continuous stimulation, 95

under overstrain, 96

Fibro-vascular bundles, distribution of, in stem, 558
Forgetting, rate of, 678
Frog, response in retina of, 418, 426
in skin of, 300, 302

in stomach of, 345, 347
Functions of vegetal nerve, 559

GALENA, response of, 3
Gecko, fatigue of conductivity in nerve of, 530,

response in nerve of, 657

in skin of, 310, 311

in stomach of, 346

Geo-electric response, in apogeotropic organ, 440

in organ physically restrained, 442
Gdotrenic action, hydrostatic theory of, 435

statolithic theory of, 435

Geotropic stimulus, determination of area excited by, 436
Gotch on oscillatory character of electric discharge, 270
Growth, effect of stimulus on, 73

; temperature on, 73

33

be]

9?

59

99

9?

99

Growth pulsation, 221
Gymnotus, electrical discharge in, 242

HAAKE on electromotive difference in plants, 13
Hartig on ascent of poison, 363
Heidenhain on enhancement of excitability by section, 502

Hermann on current of rest in skin, 288

2)

on polarisation increment, 563
Holmgren on retinal current, 415

751

:
—--- = '

752 COMPARATIVE ELECTRO-PHYSIOLOGY

Human lip, response of, 321

», skin, response of, 300

», tongue, response of, 322
Hydraulic response, 55

INJURY, degree determining sign of action current, 175 _
see Current of Injury .
Interference, induced difference of phase causing, 142

af method of: effect of chemical agents determined by, 147
* Be effect of cold determined by, 147
Inversion of thermo-mechanical curve, 198
“f of electro-motive curve, 202
Pr. of curve of resistivity, 546

KUHNE and Steiner on retinal current, 415

Kiihne on polar effects in Protozoa, 579

Kunchangraph, 511

Kunkel on electro-motive variation due to water movement, 13
», on electric reaction in plants, 13

LATENT image, revival in phosphorescent screen, 684 |
_ Latent impression, revival of, in metal, 683 : |
Laws of differential response, 109 |
s» 5, electrical response of isotropic tissue, 75 |
s» 3, response in electric organs, 248

+» 9, variation of conductivity under electrotonus, 568

rey) 9 ,», excitability under electrotonus, 571
Leaves, electric response of Bryophyllum, 253
oes 7 i »» bulb of Uriclis, 257 4
” ” re) », Coleus, 248
» » >». 3, Déllenia indica, 256
% 2 or », Mimosa, 268
” ” - », Musa, 284
le oe » », Wymphea alba, 246
9 » 3 »» pitcher of Wepenthe, 256
fe 5 a », Lothos, 286
a 5 », LPterospermum, 255
Light, stimulus of : clecticel response of A/zmosa under, 401
Ae ‘ mechanical response of Mzmosa under, 400
op ic: mechanical response under, in pulvinated and growing
organs, 394
A a multiple electrical response induced by, in plant, 406, 408
‘9 19 multiple mechanical response induced by, 407
> » » ” » ” in retina, 426
. multiple visual impulse induced by, 430

transmitted effect due to, 402
Libs influence of fatigue on after-effect of, 411
»» negative and positive responses to, 402, 406
»» phasic responsive alternations under, 408

INDEX 3 753

Light, positive and negative after-effects under, 409, 412
,», three types of direct and after-effect in plant under, 409-414
,, three types of direct and after-effect in retina under, 427-429
Lip, response of human, 321

MAGNETIC balance, 607
Magnetic conduction, blocking of, 614

<, 93 effect of A- and K-tonus on, 609

<3 aye enhancement of, by successive stimuli, 612

> cs opposite effects of moderate and strong K-tonus on, 610
3 response, additive effect in, 595

a fe direct effect of tetanisation and transient after- effect, 623
+5 s3 effect of A- and K-tonus on excitability, 611

xe =F induction record, 604

= magnetometric record of, 594

ye ie mechanical record of, 593

Re xi periodic, 594

.* . uniform, 594

Malepterurus, electrical organ of, 242
Mechanical and electrical response, simultaneous record of, 17, 19
Mechanical stimulator, rotary, 291
Melon, electrical response of, 315
Memory, an after-effect of stimulus, 677

4 explanation of revival of, 685

ee persistence, dependent on strength of stimulus, 677

a5 spontaneous revival of, 680
Memory image, negative, 684
P Metal, abolition of response by poison, 9
1 : »» fatigue in response of, 7

»» response of, 6

Mimosa, electrical response of, 20, 110, 127, 268, 326

re electrical response under light, 401

»» hydraulic response in, 55

», hydro-positive and negative response of, 56, 59

»» | mechanical response under light, 400

5, phasic changes in response of, 303

»» teversal of response by fatigue, 326

5, Variation of motile sensibility of, 21

differential response of, 108
etecaiae model, 598 ;
Molecular modification, reversal of normal response due to, 7
Molecular response, persistent after-effect in, 597, 601, 603
Molecular theory of excitation, 590
Molecular transformation, external tests of, 620
Morograph, 197
Morographic record by electro-motive response, 202
vs », by mechanical response, 198 ae
43 »» by resistivity variation, 546

Motor transformer, 281

754 COMPARATIVE ELECTRO-PHYSIOLOGY

Munk on response in Dionea, 12

Musa, electrical response of, parallel to Dionea, 237
Muscle cylinder, electrical distribution in, 150
Multiple response, electrical in Biophytum, 209

9» wi oe in Desmodium, 218, 220
>» » ” in Drosera, 343

és » - €lectro-tactile in Mimosa, 209

~ electrical in pitcher of Wefenthe, 341
% $5 re in stomach of frog, 347
re x mechanical, in Biophytum, 208

93 95 se in Desmodium, 212
” ” 9 in nerve, 539

mf oe rheotomic record showing, 52

re 9 under light in Bzophytum, 407

» »» ” in Bryophyllum, 408
4 as “ in cauliflower, 406

on re ‘5 in frog’s retina, 426

» % 5 in human retina, 430
. és of growth, 221

Nepenthe, current of rest in, 335
a multiple response in, 341
- three types of response in, 338-340
Nerve, excitatory electrical changes in, 508
me sg mechanical changes in, 509
,, failure to conduct, 530
Nerve of animal, electrical response of,

me ay oa . conversion of positive to negative after
~ thermal tetanisation, 463

" % . - conversion of positive to negative by in-
creasing intensity of stimulus, 466

* +3 Ra y»» ° employment of electrical stimulus, errors
due to, 458

” . os Pr enhancement of normal response after
thermal tetanisation, 462

re 7 e sa gradual transformation from positive to
negative through diphasic, 464

> » » 7 to equi-alternating shocks, 457

- 5a e a to injury of one contact, complications
arising from, 458

ge +3 “ ay under stimulation by thermal shocks, 460
see also Conductivity Balance. ;
Nerve of animal, mechanical response of,

» ” +s i constituent twitches during tetanisation
in, 535

oe) ry) 2 99 effect of drying on, 539

” ” ” ” effect of alcohol on, 517

» » » 99 », Of ammonia on, 516

» » » 9 »» Of chloroform on, 518

+

|
.
|
.
|
|

INDEX Lip SF

Nerve of animal, mechanical response of, effect of morphia on, 516

» ” » » Sg ee tetanising electric shocks, 510
» e 3 ss five stages in, 89, 635

” » a -3 multiple response in, 538° |

os 0» 33 re relation between stimulus and, 657-659
et - e a similarities of, in plant and animal, 528
» ” ” ” % in motor and sensory, 529

” y *” * three types of, 519

ox a 2 *F transient enhancement of, on cessation

of tetanisation, 536
Nerve of plant, discovery of, 470

oe »» response of, conversion of abnormal to normal after tetanisation,
475 ;
»» » a conversion of abnormal to normal by increasing in-
tensity of stimulus, 476
| a ” >» a3 effect of alcohol on, 473
i 9 > $s effect of ammonia on, 474
‘ ss st effect of CO, on, 472
9 ¥ 3 effect of ether on, 472
me fe “4 effect of tetanisation in enhancing, 476
$9 ee 4 three types in, 475 F
a 5, Similarities of response in, and in animal, 471-478
Nerve at plant, mechanical response of, 528
% » 2 » determination of velocity by, 525
» » ” % effect of light on, 557
» > >» 9 enhancement after tetanisation, 554
Nervous impulse, two kinds of, 647
PS various direct and indirect manifestations of, 648

Noll, Haberlandt, and Nemec, statolithic theory of, 435
5 Nymphea alba, response of leaf of, 246

Ophiocephalus, mechanical response of optical nerve of, 529
$5 response in retina of, 427-429

Oscillating recorder, 527

Optic nerve and cornea, differential excitability between, 417

PAcINI, law of, 242
Pfeffer and Czapek on theory of geotropism, 435
Pfliiger, avalanche theory of, 502
Pfliiger’s law ; its failure with high E.M.F., 579

5 aS oa with low E.M.F., 581

5 », Of polar effects of currents, 578
Phasic reactions, alternating, 100

,» Variations of current of rest, 302, 303
ns turgidity, 305

Phenoipthalines detection of transport channels by, 360°
| Polar effects of currents, demonstration of : s
i ay oe os by motile response in plants, 579
“= sy oa “3 . by subjective sensation, 582

g

756 - COMPARATIVE ELECTRO-PHYSIOLOGY

Poison, action of, modification of, by dose and tonic condition, 640, 641
a on inorganic response, 9
Positive response of sub-tonic tissue, 83
a unmasking of, from resultant negative, 66
Pterospermum, analogy with Torpedo, 255
Pulvinated and growing organs, similarities of response in, 394

REID, on response of skin of eel, 289
Resistivity variation, determination of death-point by, 546

3 +3 response by, and its correspondence in the other modes of
response, 549
v bs s3 experimental difficulties of, 540
~ a », of metallic particles by, 3, 600-603
a ag », Of frog’s nerve by, 549
ae », of selenium by, 3
Response, bifurcated expression of, 104
- considered as molecular derangement, 590
rs law of differential, 109
= law of isotropic, 75
‘3 positive, diphasic, and negative in cauliflower, 62
” =a 29 ” in potato, 64
‘5 simultaneous record of mechanical and electrical, 17, 19
re various forms of, 2 .
Response recorder, 34
Retina, determination of differential excitability of, and optic nerve, 418 . ;
5» excitatory after-effect in, 427-430 - 7
», multiple response in human, 430 :
29 2 9 in frog, 426 .
bere es Wallago, 425
Pe raion of, in Ophiocephalus, 427-429
= oy in frog, 418

5, so-called positive response of, .419
Retino-motor effect, 421
Retinal response, conversion of abnormal to normal, 423
oY ue explanation of abnormal, 423
ae ae three types of after-effect in, 427-429
Reverser, oscillating, 276
53 rotating, 280
Rheotome, observations with, 47, 254
Root as digestive organ, 349
», response of young and old, 353, 354
5» responsive secretion of, 352
Rosenthal on currént of rest in stomach, 288
Rotary Mechanical Stimulator, 291

SACHS on growth of Cucurbita in darkness, 557
Schonlein on oscillatory character of electric discharge, 270
Season, influence of, on recovery from stimulus, 45

es o on suctional response, 390

INDEX ; TBR

Selenium, response of, 3
Sensation, conversion from positive to negative by tetanisation a 66 5
+ different tones of, 646

ks dual elements in, 674
F effect on, of attention and inhibition, 652
are effect on, of molecular disposition, 663, 664
ss effect on, of progressive molecular change in nerve, 661
is identification with opposite nervous changes, 650
4. interchange of pleasurable and painful under electrotonus, 670- Oe
», - negative element in, blocked by anesthetics, 673 |
a3 positive and negative, 664 ;
ny positive simple, negative complex, 665

Sensimeter, 670

Shoshungraph, 368

Skin, abnormal response converted to normal after Seeanie ols, 31 3
», response of, in frog, 300, 302 '

+r A in gecko, 310, 311
Re By in grape, 299, 301, 302
a Ss in intact human, 300
rs - in tomato, 397, 308, 309
i in tortoise, 307
Snail, foot of, response in, 316
aS ets resting current and its variation in, 318

Staircase response, 91, 103, 522,524, 625, 635
Stimulants, action of on inorganic response, 8
Stimulation, by chemical agents, 27

ae by equi-alternating electric shocks, 277
% by taps, 26
“4 by tension and compression, 25
‘i by thermal shocks, 24
© effect of moderate, on conductivity, 504
a », of strong, on conductivity, 505

a instantaneous mechanical, 47

en response to various forms of, 24-27

re », to increasing intensity of, 40

ae rotary mechanical, 291
$3 vibratory, 27

Stimulator, electro-thermic, 38 ‘
“ vibratory, 30
Stimulus, effect of, on growth, 73

8 importance of, seen in ascent of sap, 382, 555

” 99 9 autonomous response, 212, 555
29 ” 9 growth, 556

» » »» motile excitability, 554

- opposite effects of, on highly tonic and sub-tonic’ G'tissues, 77
4g relation between, and response :

” » in plant-tissue, 40, 41

2 ‘* in nerve of bull-frog, 658

» 2 in nerve of fern, 659

|

e

758 COMPARATIVE ELECTRO-PHYSIOLOGY

Stimulus, relation between, in nerve of gecko, 657

9 * in optic nerve, 659

.; ig magnetic, in iron, 660
Strasburger on ascent of poisons, 363
Suctional response, diminution of latent period of, 384

» 3 effect of anzesthetics on, 375

* . effect of poison on, 374:

. »» effect of season on, 390

a 4 effect of variation of temperature on, 372

Pe =f initiation of, by stimulus, 382

a9 om osmotic versus excitatory action, 376, 377

x es persistence of, particular zone being killed, 373
= oe under method of balance, 383 -

$s ‘5 aa »» * overbalance, 386

= i: », unbalanced method, 388

TABULAR statement :

a is electro-motive variation in Desmodium leaflet, 219
9 . heliotropic effects, 394

Be determination of death-point, 205

$9 velocity of transmission in living tissues, 452

Tapper, the mechanical, 26

Temperature, different effects of, on conductivity and excitability, 187

‘a effect of cold on electric response, 183

ae effect of cyclic variation of, on electric response, 189
9 effect of high, in abolishing response, 190

% effect of low, on autonomous response, 181

» effect of, on growth, 74

* effect of rise of, on autonomous response, 182

¥ effect of rise of, on conductivity, 450, 501

93 effect of rise of, on electric response, 186

i effect of steady and sudden variation of, 74

Tetanus, genesis of mechanical and electrical, 43
Tetanisation, transient enhancement of response on cessation of :

os » ‘3 in brominated silver, 429
» 9 99 in frog’s nerve, 536
» ” 3 in frog’s retina, 428
” » 9 in magnetic response, 623

Tetanisation, effect of :
A stage—conversion of abnormal to normal response,
Electromotive response,

+ - continuous transformation from abnormal to normal
in platinum, 629
‘5 in nerve of fern, 475
1 zi in nerve of frog, 463
5 55 in skin of gecko, 311
Pn ‘ in tin, 628
Mechanical response,
an os conversion from abnormal expansive

contractile response in frog’s nerve, 627

to normal

INDEX a 759

Tetanisation, effect of :
Response by resistivity variation, ;
as Ai 3 in selenium, 629
aK fe a in tungsten, 630 ’
B stage—enxhancement of normal response,
. | Electro-motive response,

ot i in nerve of fern, 475
‘a »» in nerve of frog, 462
= = in response of tin, 630
Mechanical response,
58 ss in frog’s nerve, 634
Pe we in nerve of fern, 554
Response by resistivity variation,
sf me in aluminium powder, 632
re Bn in selenium, 630
Magnetic response,
3 $s in response of iron, 632

D stage—/fatigue reversal of normal response,
Electro-motive response,

9 ‘ reversal of normal response in Drosera, 342
” 4 38 a in stomach of gecko, 346
Mechanical response,
z ee reversal of normal contractile response in frog’s nerve,
635, 642
9 9 rr rs <3 in indiarubber,
642
oe) ” > ” 9 in nerve of

gecko, 530
Response by resistivity variation,
a », fatigue reversal in tungsten, 638

Thermal chamber, 200
os cork chamber, 500
¥ shocks, quantitatiye stimulation of nerve by, 460

3 »» stimulation by, 38
variator, 113
Time-relations, difference of, in different tissues, 45
+s rheotomic observations on, 50

Tongue, response of human, 322
Torpedo, electrical organ of, 241
Tortoise, response of skin of, 307
a me of stomach of, 345
Transportation channels, detection of, by phenolpthaline, 36

VELOCITY of transmission :
determination of, by electro-motive Inethed, 452

oe by mechanical method, 447
ss centrifugal versus centripetal, 448
” effect of fatigue on, 449

*”

760 COMPARATIVE ELECTRO-PHYSIOLOGY

Velocity of transmission :
determination of, effect of intensity of stimulus on, 449

+ effect of temperature on, 450
2 longitudinal versus transverse, 454

Verworn on polar effects of currents on Protozoa, 579

Vibratory stimulator, 30

Vision, binocular alternation of, 431

Visual impulse, pulsatory character, 432

Von Fleisch] on response of nerve, 278

WALLER on ‘blaze current,’ 260
7 on response of green leaves to light, 395
ss on response of skin, 294
oe on three types of response in nerve, 461
Waves, positive and negative : their characteristics, 67
Weber-Fechner’s law : its inadequacy, 656
Wood, demonstration of living characteristics of, 361
»» effect of anzsthetics and poison on pane of, 362, 36
»» effect on, of drying, 361
», normal response of, 361

ZANTEDESCI on organ current, 269

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