Jagadis Bose : Response in the Living and Non-Living

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**Jagadis C. BOSE**

***Response in the Living and Non-Living***

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**Jagadis
C. Bose**  
M.A.(Cantab.), D.Sc.(Lond.) , Professor, Presidency College,
Calcutta  

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**Source: Project Gutenberg [EBook #18986]**   
**Produced by Bryan Ness, Laura Wisewell and the Online
Distributed Proofreading Team at http://www.pgdp.net**

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**LONGMANS, GREEN, AND CO.**   
**39 PATERNOSTER ROW, LONDON**   
**NEW YORK AND BOMBAY**   
**1902**

All rights reserved

The real is one: wise men call it variously [ Rig Veda ]

To my Countrymen This Work is Dedicated

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**PREFACE**

I have in the present work put in a connected and a more
complete form results, some of which have been published in the
following Papers:

De la Generalite des Phenomenes Moleculaires produits par
lElectricite sur la matiere Inorganique et sur la matiere
Vivante. (Travaux du Congres International de Physique. Paris,
1900.)   
On the Similarity of Effect of Electrical Stimulus on Inorganic
and Living Substances. (Report, Bradford Meeting British
Association, 1900.Electrician.)   
Response of Inorganic Matter to Stimulus. (Friday Evening
Discourse, Royal Institution, May 1901.)   
On Electric Response of Inorganic Substances. Preliminary
Notice. (Royal Society, June 1901.)   
On Electric Response of Ordinary Plants under Mechanical
Stimulus. (Journal Linnean Society, 1902.)   
Sur la Reponse Electrique dans les Metaux, les Tissus Animaux
et Vegetaux. (Societe de Physique, Paris, 1902.)   
On the Electro-Motive Wave accompanying Mechanical Disturbance
in Metals in contact with Electrolyte. (Proceedings Royal
Society, vol. 70.)   
On the Strain Theory of Vision and of Photographic Action.
(Journal Royal Photographic Society, vol. xxvi.)   
 These investigations were commenced in India, and I take
this opportunity to express my grateful acknowledgments to the
Managers of the Royal Institution, for the facilities offered me
to complete them at the Davy-Faraday Laboratory.

J. C. Bose.   
Davy-Faraday Laboratory, Royal Institution,   
London: May 1902.

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**CONTENTS**

**[CHAPTER I](#1)**   
**THE MECHANICAL RESPONSE OF LIVING SUBSTANCES PAGE**

*Mechanical response --- Different kinds of stimuli ---
Myograph --- Characteristics of response-curve: period,
amplitude, form --- Modification of response-curves*

**[CHAPTER II](#2)**   
**ELECTRIC RESPONSE**

*Conditions for obtaining electric response  Method of
injury  Current of injury  Injured end, cuproid: uninjured,
zincoid  Current of response in nerve from more excited to
less excited  Difficulties of present nomenclature  Electric
recorder  Two types of response, positive and negative 
Universal applicability of electric mode of response 
Electric response a measure of physiological activity 
Electric response in plants*

**[CHAPTER III](#3)**   
**ELECTRIC RESPONSE IN PLANTS  METHOD OF NEGATIVE VARIATION**

*Negative variation  Response recorder  Photographic
recorder  Compensator  Means of graduating intensity of
stimulus  Spring-tapper and torsional vibrator  Intensity of
stimulus dependent on amplitude of vibration  Effectiveness
of stimulus dependent on rapidity also*

**[CHAPTER IV](#4)**   
**ELECTRIC RESPONSE IN PLANTSBLOCK METHOD**

*Method of block  Advantages of block method  Plant
response a physiological phenomenon  Abolition of response by
anaesthetics and poisons  Abolition of response when plant is
killed by hot water*

**[CHAPTER V](#5)**   
**PLANT RESPONSEON THE EFFECTS OF SINGLE STIMULUS AND OF
SUPERPOSED STIMULI**

*Effect of single stimulus  Superposition of stimuli 
Additive effect  Staircase effect  Fatigue  No fatigue when
sufficient interval between stimuli  Apparent fatigue when
stimulation frequency is increased  Fatigue under continuous
stimulation*

**[CHAPTER VI](#6)**   
**PLANT RESPONSEON DIPHASIC VARIATION**

*Diphasic variation  Positive after-effect and positive
response  Radial E.M. variation*

**[CHAPTER VII](#7)**   
**PLANT RESPONSEON THE RELATION BETWEEN STIMULUS AND
RESPONSE**

*Increased response with increasing stimulus  Apparent
diminution of response with excessively strong stimulus*

**[CHAPTER VIII](#8)**   
**PLANT RESPONSEON THE INFLUENCE OF TEMPERATURE**

*Effect of very low temperature  Influence of high
temperature  Determination of death-point  Increased
response as after-effect of temperature variation  Death of
plant and abolition of response by the action of steam*

**[CHAPTER IX](#9)**   
**PLANT RESPONSEEFFECT OF ANAESTHETICS AND POISONS**

*Effect of anaesthetics, a test of vital character of response
 Effect of chloroform  Effect of chloral  Effect of
formalin  Method in which response is unaffected by variation
of resistance  Advantage of block method  Effect of dose*

**[CHAPTER X](#10)**   
**RESPONSE IN METALS**

*Is response found in inorganic substances?  Experiment on
tin, block method  Anomalies of existing terminology 
Response by method of depression  Response by method of
exaltation*

**[CHAPTER XI](#11)**   
**INORGANIC RESPONSEMODIFIED APPARATUS TO EXHIBIT RESPONSE
IN METALS**

*Conditions of obtaining quantitative measurements 
Modification of the block method  Vibration cell 
Application of stimulus  Graduation of the intensity of
stimulus  Considerations showing that electric response is
due to molecular disturbance  Test experiment  Molecular
voltaic cell*

**[CHAPTER XII](#12)**   
**INORGANIC RESPONSEMETHOD OF ENSURING CONSISTENT RESULTS**

*Preparation of wire  Effect of single stimulus*

**[CHAPTER XIII](#13)**   
**INORGANIC RESPONSEMOLECULAR MOBILITY: ITS INFLUENCE ON
RESPONSE**

*Effects of molecular inertia  Prolongation of period of
recovery by overstrain  Molecular model  Reduction of
molecular sluggishness attended by quickened recovery and
heightened response  Effect of temperature  Modification of
latent period and period of recovery by the action of chemical
reagents  Diphasic variation*

**[CHAPTER XIV](#14)**   
**INORGANIC RESPONSEFATIGUE, STAIRCASE, AND MODIFIED
RESPONSE**

*Fatigue in metals  Fatigue under continuous stimulation 
Staircase effect  Reversed responses due to molecular
modification in nerve and in metal, and their transformation
into normal after continuous stimulation  Increased response
after continuous stimulation*

**[CHAPTER XV](#15)**   
**INORGANIC RESPONSERELATION BETWEEN STIMULUS AND
RESPONSESUPERPOSITION OF STIMULI**

*Relation between stimulus and response  Magnetic analogue 
Increase of response with increasing stimulus  Threshold of
response  Superposition of stimuli  Hysteresis*

**[CHAPTER XVI](#16)**   
**INORGANIC RESPONSE  EFFECT OF CHEMICAL REAGENTS**

*Action of chemical reagents  Action of stimulants on metals
 Action of depressants on metals  Effect of poisons on
metals  Opposite effect of large and small doses*

**[CHAPTER XVII](#17)**   
**ON THE STIMULUS OF LIGHT AND RETINAL CURRENTS**

*Visual impulse: (1) chemical theory; (2) electrical theory 
Retinal currents  Normal response positive  Inorganic
response under stimulus of light  Typical experiment on the
electrical effect induced by light*

**[CHAPTER XVIII](#18)**   
**INORGANIC RESPONSEINFLUENCE OF VARIOUS CONDITIONS ON THE
RESPONSE TO STIMULUS OF LIGHT**

*Effect of temperature  Effect of increasing length of
exposure  Relation between intensity of light and magnitude
of response  After-oscillation  Abnormal effects: (1)
preliminary negative twitch; (2) reversal of response; (3)
transient positive twitch on cessation of light; (4) decline
and reversal  Resume*

**[CHAPTER XIX](#19)**   
**VISUAL ANALOGUES**

*Effect of light of short duration  After-oscillation 
Positive and negative after-images  Binocular alternation of
vision  Period of alternation modified by physical condition
 After-images and their revival  Unconscious visual
impression.*

**[CHAPTER XX](#20)**   
**GENERAL SURVEY AND CONCLUSION 181**

**INDEX**   
[ Not included here ]

**ILLUSTRATIONS**

1. Mechanical Lever Recorder   
2. Electric Method of Detecting Nerve Response   
3. Diagram showing Injured End of Nerve Corresponds to Copper in
a Voltaic Element   
4. Electric Recorder   
5. Simultaneous Record of Mechanical and Electrical Responses 13
  
6. Negative Variation in Plants 19   
7. Photographic Record of Negative Variation in Plants 20   
8. Response Recorder 21   
9. The Compensator 22   
10. The Spring-tapper 23   
11. The Torsional Vibrator 24   
12. Response in Plant to Mechanical Tap or Vibration 25   
13. Influence of Suddenness on the Efficiency of Stimulus 26   
14. The Method of Block 28   
15. Response in Plant completely Immersed under Water 29   
16. Uniform Responses in Plant 36   
17. Fusion of Effect under Rapidly Succeeding Stimuli in Muscle
and in Plant 36   
18. Additive Effect of Singly Ineffective Stimuli on Plant 37   
19. Staircase Effect in Plant 37   
20. Appearance of Fatigue in Plant under Shortened Period of
Rest 39   
21. Fatigue in Celery 40   
22. Fatigue in Cauliflower-stalk 41   
23. Fatigue from Previous Overstrain 41   
24. Fatigue under Continuous Stimulation in Celery 42   
25. Effect of Rest in Removal of Fatigue in Plant 43   
26. Diphasic Variation in Plant 46   
27, 28. Abnormal Positive Responses in Stale Plant transformed
into Normal Negative Under Strong Stimulation 48, 49   
29. Radial E.M. Variation 50   
30. Curves showing the Relation between Intensity of Stimulus
and Response in Muscle and Nerve 52   
31. Increasing Responses to Increasing Stimuli (Taps) in Plants
52   
32. Increasing Responses to Increasing Vibrational Stimuli in
Plants 53   
33. Responses to Increasing Stimuli in Fresh and Stale Specimens
of Plants 54   
34. Apparent Diminution of Response caused by Fatigue under
Strong Stimulation 57   
35. Diminution of Response in Eucharis Lily at Low Temperature
61   
36. Records showing the Difference in the Effects of Low
Temperature on Ivy, Holly, and Eucharis Lily 62   
37. Plant Chamber for Studying the Effect of Temperature and
Anaesthetics 64   
38. Effect of High Temperature on Plant Response 64   
39. After-effect on the Response due to Temperature Variation 66
  
40. Records of Responses in Eucharis Lily during Rise and Fall
of Temperature 67   
41. Curve showing Variation of Sensitiveness during a Cycle of
Temperature Variation 68   
42. Record of Effect of Steam in Abolition of Response at Death
of Plant 69   
43. Effect of Chloroform on Nerve Response 72   
44. Effect of Chloroform on the Responses of Carrot 74   
45. Action of Chloral Hydrate on Plant Responses 75   
46. Action of Formalin on Radish 75   
47. Action of Sodium Hydrate in Abolishing the Response in Plant
78   
48. Stimulating Action of Poison in Small Doses in Plants 79   
49. The Poisonous Effect of Stronger Dose of KOH 79   
50. Block Method for obtaining Response in Tin 83   
51. Response To Mechanical Stimulation in a Zn-Cu Couple 85   
52. Electric Response in Metal by the Method of Relative
Depression (Negative Variation) 88   
53. Method of Relative Exaltation 89   
54. Various Cases of Positive and Negative Variation 90   
55. Modifications of the Block Method for Exhibiting Electric
Response in Metals 93   
56. Equal and Opposite Responses given by Two Ends of the Wire
95   
57. Top View of the Vibration Cell 96   
58. Influence of Annealing in the Enhancement of Response in
Metals 101   
59. Uniform Electric Responses in Metals 102   
60. Persistence of After-effect 105   
61. Prolongation of Period of Recovery after Overstrain 106   
62. Molecular Model 107   
63, 64. Effects of Removal of Molecular Sluggishness in
Quickened Recovery and Heightened Response in Metals 109, 110   
65. Effect of Temperature on Response in Metals 111   
66. Diphasic Variation in Metals 113   
67. Negative, Diphasic, and Positive Resultant Response in
Metals 115   
68. Continuous Transformation from Negative to Positive through
Intermediate Diphasic Response 116   
69. Fatigue in Muscle 118   
70. Fatigue in Platinum 118   
71. Fatigue in Tin 119   
72. Appearance of Fatigue due to Shortening the Period of
Recovery 120   
73. Fatigue in Metal under Continuous Stimulation 121   
74. Staircase Response in Muscle and in Metal 122   
75. Abnormal Response in Nerve converted into Normal under
Continued Stimulation 124   
76, 77. Abnormal Response in Tin and Platinum converted into
Normal under Continued Stimulation 125   
78. Gradual Transition from Abnormal to Normal Response in
Platinum 126   
79. Increase of Response in Nerve after Continuous Stimulation
127   
80, 81. Response in Tin and Platinum Enhanced after Continuous
Stimulation 127, 128   
82. Magnetic Analogue 132   
83, 84. Records of Responses to Increasing Stimuli in Tin 134,
135   
85. Ineffective Stimulus becoming Effective by Superposition 135
  
86. Incomplete and Complete Fusion of Effects 136   
87. Cyclic Curve for Maximum Effects showing Hysteresis 137   
88. Action of Poison in Abolishing Response in Nerve 139   
89. Action of Stimulant on Tin 141   
90. Action of Stimulant on Platinum 142   
91. Depressing Effect of KBr on Tin 143   
92. Abolition of Response in Metals by Poison 143   
93. Molecular Arrest by the Action of Poison 145   
94. Opposite Effects of Small and Large Doses on the Response in
Metals 146   
95. Retinal Response to Light 150   
96. Response of Sensitive Cell to Light 152   
97. Typical Experiment on the E.M. Variation Produced by Light
154   
98. Modification of the Photo-sensitive Cell 155   
99. Responses in Frogs Retina 156   
100. Responses in Sensitive Photo-cell 157   
101. Effect of Temperature on the Response to Light Stimulus 159
  
102. Effect of Duration of Exposure on the Response 159   
103. Responses of Sensitive Cell to Increasing Intensities of
Light 161   
104. Relation between the Intensity of Light And Magnitude of
Response 162   
105. After-oscillation 163   
106. Transient Positive Increase of Response in the Frogs
Retina on the Cessation of Light 164   
107. Transient Positive Increase of Response in the Sensitive
Cell 165   
108. Decline under the Continuous Action of Light 166   
109. Certain After-effects of Light 168   
110. After-effect of Light of Short Duration 172   
111. Stereoscopic Design for the Exhibition of Binocular
Alternation of Vision 176   
112. Uniform Responses in Nerve, Plant, and Metal 184   
113. Fatigue in Muscle, Plant, and Metal 185   
114. Staircase Effect in Muscle, Plant, and Metal 186   
115. Increase of Response after Continuous Stimulation in Nerve
and Metal 186   
116. Modified Abnormal Response in Nerve and Metal Transformed
into Normal Response after Continuous Stimulation 187   
117. Action of the same Poison in the Abolition of Response in
Nerve, Plant, and Metal 189

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***RESPONSE IN THE LIVING AND NON-LIVING***

**CHAPTER I**

**THE MECHANICAL RESPONSE OF LIVING SUBSTANCES**

*Mechanical response -- Different kinds of stimuli --
Myograph -- Characteristics of response-curve: period,
amplitude, form -- Modification of response-curves.*

One of the most striking effects of external disturbance on
certain types of living substance is a visible change of form.
Thus, a piece of muscle when pinched contracts. The external
disturbance which produced this change is called the stimulus.
The body which is thus capable of responding is said to be
irritable or excitable. A stimulus thus produces a state of
excitability which may sometimes be expressed by change of form.

*Mechanical response to different kinds of stimuli.*This
reaction under stimulus is seen even in the lowest organisms; in
some of the amboid rhizopods, for instance. These lumpy
protoplasmic bodies, usually elongated while creeping, if
mechanically jarred, contract into a spherical form. If, instead
of mechanical  disturbance, we apply salt solution, they
again contract, in the same way as before. Similar effects are
produced by sudden illumination, or by rise of temperature, or
by electric shock. A living substance may thus be put into an
excitatory state by either mechanical, chemical, thermal,
electrical, or light stimulus. Not only does the point
stimulated show the effect of stimulus, but that effect may
sometimes be conducted even to a considerable distance. This
power of conducting stimulus, though common to all living
substances, is present in very different degrees. While in some
forms of animal tissue irritation spreads, at a very slow rate,
only to points in close neighbourhood, in other forms, as for
example in nerves, conduction is very rapid and reaches far.

The visible mode of response by change of form may perhaps be
best studied in a piece of muscle. When this is pinched, or an
electrical shock is sent through it, it becomes shorter and
broader. A responsive twitch is thus produced. The excitatory
state then disappears, and the muscle is seen to relax into its
normal form.

*Mechanical lever recorder*. In the case of contraction
of muscle, the effect is very quick, the twitch takes place in
too short a time for detailed observation by ordinary means. A
myographic apparatus is therefore used, by means of which the
changes in the muscle are self-recorded. Thus we obtain a
history of its change and recovery from the change. The muscle
is connected to one end of a writing lever. When the muscle
contracts, the tracing point is pulled up in one 
direction, say to the right. The extent of this pull depends on
the amount of contraction. A band of paper or a revolving
drum-surface moves at a uniform speed at right angles to the
direction of motion of the writing lever. When the muscle
recovers from the stimulus, it relaxes into its original form,
and the writing point traces the recovery as it moves now to the
left, regaining its first position. A curve is thus described,
the rising portion of which is due to contraction, and the
falling portion to relaxation or recovery. The ordinate of the
curve represents the intensity of response, and the abscissa the
time (fig. 1).

**Fig. 1.Mechanical Lever Recorder**

![](fig001.jpg)

The muscle M with the attached bone is securely held at one
end, the other end being connected with the writing lever. Under
the action of stimulus the contracting muscle pulls the lever
and moves the tracing point to the right over the travelling
recording surface P. When the muscle recovers from contraction,
the tracing point returns to its original position. See on P the
record of muscle curve.

*Characteristics of the response-curve: (1) Period, (2)
Amplitude, (3) Form.*  Just as a wave of sound is
characterised by its (1) period, (2) amplitude, and (3) form, so
may these response-curves be distinguished from each other. As
regards the period, there is an enormous variation,
corresponding to the functional activity of the muscle. For
instance, in tortoise it may be as high as a second, whereas in
the wing-muscles of many insects it is as small as 1/300 part of
a second. It is probable that a continuous graduated scale
might, as suggested by Hermann, be drawn up in the animal
kingdom, from the excessively rapid contraction of  insects
to those of tortoises and hibernating dormice.[1] Differences
in form and amplitude of curve are well illustrated by various
muscles of the tortoise. The curve for the muscle of the neck,
used for rapid withdrawal of the head on approach of danger, is
quite different from that of the pectoral muscle of the same
animal, used for its sluggish movements.

Again, progressive changes in the same muscle are well seen in
the modifications of form which consecutive muscle-curves
gradually undergo. In a dying muscle, for example, the amplitude
of succeeding curves is continuously diminished, and the curves
themselves are elongated. Numerous illustrations will be seen
later, of the effect, in changing the form of the curve, of the
increased excitation or depression produced by various agencies.

Thus these response records give us a means of studying the
effect of stimulus, and the modification of response, under
varying external conditions, advantage being taken of the
mechanical contraction produced in the tissue by the stimulus.
But there are other kinds of tissue where the excitation
produced by stimulus is not exhibited in a visible form. In
order to study these we have to use an altogether independent
method, the method of electric response.

**FOOTNOTES:**

[1] Biedermann, Electro-physiology, p. 59.

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**CHAPTER II**

**ELECTRIC RESPONSE**

*Conditions for obtaining electric response  Method of
injury  Current of injury  Injured end, cuproid: uninjured,
zincoid  Current of response in nerve from more excited to
less excited  Difficulties of present nomenclature  Electric
recorder  Two types of response, positive and negative 
Universal applicability of electric mode of response 
Electric response a measure of physiological activity 
Electric response in plants.*

Unlike muscle, a length of nerve, when mechanically or
electrically excited, does not undergo any visible change. That
it is thrown into an excitatory state, and that it conducts the
excitatory disturbance, is shown however by the contraction
produced in an attached piece of muscle, which serves as an
indicator.

But the excitatory effect produced in the nerve by stimulus can
also be detected by an electrical method. If an isolated piece
of nerve be taken and two contacts be made on its surface by
means of non-polarisable electrodes at A and B, connection being
made with a galvanometer, no current will be observed, as both A
and B are in the same physico-chemical condition. The two
points, that is to say, are iso-electric.

If now the nerve be excited by stimulus, similar disturbances
will be evoked at both A and B. If, further, these disturbances,
reaching A and B almost simultaneously, cause any electrical
change, then,  similar changes taking place at both points,
and there being thus no relative difference between the two, the
galvanometer will still indicate no current. This null-effect is
due to the balancing action of B as against A. (See fig. 2, a.)

*Conditions for obtaining electric response.*  If then
we wish to detect the response by means of the galvanometer, one
means of doing so will lie in the abolition of this balance,
which may be accomplished by making one of the two points, say
B, more or less permanently irresponsive. In that case, stimulus
will cause greater electrical disturbance at the more responsive
point, say A, and this will be shown by the galvanometer as a
current of response. To make B less responsive we may injure it
by means of a cross-sectional cut, a burn, or the action of
strong chemical reagents.

**Fig. 2.Electric Method of Detecting Nerve Response**

![](fig002.jpg)

(a) Iso-electric contacts; no current in the galvanometer.   
(b) The end B injured; current of injury from B to A:
stimulation gives rise to an action current from A to B.   
(c) Non-polarisable electrode.

*Current of injury.*  We shall revert to the subject of
electric response; meanwhile it is necessary to say a few words
regarding the electric disturbance caused by the injury itself.
Since the physico-chemical conditions of the uninjured A and the
injured B are now no longer the same, it follows  that
their electric conditions have also become different. They are
no longer iso-electric. There is thus a more or less permanent
or resting difference of electric potential between them. A
current  the current of injury  is found to flow in the nerve,
from the injured to the uninjured, and in the galvanometer,
through the electrolytic contacts from the uninjured to the
injured. As long as there is no further disturbance this current
of injury remains approximately constant, and is therefore
sometimes known as the current of rest (fig. 2, b).

A piece of living tissue, unequally injured at the two ends, is
thus seen to act like a voltaic element, comparable to a copper
and zinc couple. As some confusion has arisen, on the question
of whether the injured end is like the zinc or copper in such a
combination, it will perhaps be well to enter upon this subject
in detail.

If we take two rods, of zinc and copper respectively, in
metallic contact, and further, if the points A and B are
connected by a strip of cloth s moistened with salt solution, it
will be seen that we have a complete voltaic element. A current
will now flow from B to A in the metal (fig. 3, a) and from A to
B through the electrolyte s. Or instead of connecting A and B by
a single strip of cloth s, we may connect them by two strips s
s?, leading to non-polarisable electrodes E E?. The current will
then be found just the same as before, i.e. from B to A in the
metallic part, and from A through s s? to B, the wire W being
interposed, as it were, in the electrolytic part of the circuit.
If now a galvanometer be interposed at O, the current will flow
from B to A through the galvanometer, i.e. from right to left.
But if we interpose the galvanometer in the electrolytic part of
the circuit, that is to say, at W, the same current will appear
to flow in the opposite direction. In fig. 3, c, the
galvanometer is so interposed, and in this case it is to be
noticed that when the current in the galvanometer flows from
left to right, the metal connected to the left is zinc.

Compare fig. 3, d, where A B is a piece of nerve of which the B
end is injured. The current in the galvanometer  through
the non-polarisable electrode is from left to right. The
uninjured end is therefore comparable to the zinc in a voltaic
cell (is zincoid), the injured being copper-like or cuproid.[2]

**Fig. 3.Diagram showing the Correspondence between injured
(B) and uninjured (A) contacts in Nerve, and Cu and Zn in a
Voltaic Element**

![](fig003.jpg)

Comparison of (c) and (d) will show that the injured end of B
in (d) corresponds with the Cu in (c).

If the electrical condition of, say, zinc in the voltaic couple
(fig. 3, c) undergo any change (and I shall show later that this
can be caused by molecular disturbance), then the existing
difference of potential between A and B will also undergo
variation. If for example the electrical condition of A approach
that of B, the potential difference will undergo a diminution,
and the current hitherto flowing in the circuit will, as a
consequence, display a diminution, or negative variation.

*Action current*.  We have seen that a current of injury
 sometimes known as current of rest  flows in a nerve from
the injured to the uninjured, and that the injured B is then
less excitable than the uninjured A. If now the nerve be
excited, there being a greater  effect produced at A, the
existing difference of potential may thus be reduced, with a
consequent diminution of the current of injury. During
stimulation, therefore, a nerve exhibits a negative variation.
We may express this in a different way by saying that a current
of action was produced in response to stimulus, and acted in an
opposite direction to the current of injury (fig. 2, b). The
action current in the nerve is from the relatively more excited
to the relatively less excited.

*Difficulties of present nomenclature.*  We shall deal
later with a method by which a responsive current of action is
obtained without any antecedent current of injury. Negative
variation has then no meaning. Or, again, a current of injury
may sometimes undergo a change of direction (see note, p. 12).
In view of these considerations it is necessary to have at our
disposal other forms of expression by which the direction of the
current of response can still be designated. Keeping in touch
with the old phraseology, we might then call a current
negative that flowed from the more excited to the less
excited. Or, bearing in mind the fact that an uninjured contact
acts as the zinc in a voltaic couple, we might call it
zincoid, and the injured contact cuproid. Stimulation of the
uninjured end, approximating it to the condition of the injured,
might then be said to induce a cuproid change.

The electric change produced in a normal nerve by stimulation
may therefore be expressed by saying that there has been a
negative variation, or that there was a current of action from
the more excited to the less excited, or that stimulation has
produced a cuproid change.

The excitation, or molecular disturbance, produced by a
stimulus has thus a concomitant electrical expres sion. As the
excitatory state disappears with the return of the excitable
tissue to its original condition, the current of action will
gradually disappear.[3] The movement of the galvanometer needle
during excitation of the tissue thus indicates a molecular upset
by the stimulus; and the gradual creeping back of the
galvanometer deflection exhibits a molecular recovery.

This transitory electrical variation constitutes the
response, and its intensity varies according to that of the
stimulus.

*Electric recorder*.  We have thus a method of obtaining
curves of response electrically. After all, it is not
essentially very different from the mechanical method. In this
case we use a magnetic lever (fig. 4, a), the needle of the
galvanometer, which is deflected by the electromagnetic pull of
the current, generated under the action of stimulus, just as the
mechanical lever was deflected by the mechanical pull of the
muscle contracting under stimulus.

The accompanying diagram (fig. 4, b) shows how,  under the
action of stimulus, the current of rest undergoes a transitory
diminution, and how on the cessation of stimulus there is
gradual recovery of the tissue, as exhibited in the return of
the galvanometer needle to its original position.

**Fig. 4.Electric Recorder**

![](fig004.jpg)

(a) M muscle; A uninjured, B injured ends. E E? non-polarising
electrodes connecting A and B with galvanometer G. Stimulus
produces negative variation of current of rest. Index
connected with galvanometer needle records curve on travelling
paper (in practice, moving galvanometer spot of light traces
curve on photographic plate). Rising part of curve shows effect
of stimulus; descending part, recovery.

(b) O is the zero position of the galvanometer; injury produces
a deflection A B; stimulus diminishes this deflection to C; C D
is the recovery.

*Two types of response  positive and negative*.  It may
here be added that though stimulus in general produces a
diminution of current of rest, or a negative variation (e.g.
muscles and nerves), yet, in certain cases, there is an
increase, or positive variation. This is seen in the response of
the retina to light. Again, a tissue which normally gives a
negative variation may undergo molecular changes, after which it
gives a positive variation. Thus Dr. Waller finds that whereas
fresh nerve always gives negative variation, stale nerve
sometimes gives positive; and that retina, which when fresh
gives positive, when stale, exhibits negative variation.

The following is a tabular statement of the two types of
response:

I. Negative variation.  Action current from more excited to
less excited  cuproid change in the excited  e.g. fresh muscle
and nerve, stale retina.

II. Positive variation.  Action current from less excited to
more excited  zincoid change in the excited  e.g. stale nerve,
fresh retina.[4]

From this it will be seen that it is the fact of the electrical
response of living substances to stimulus that is of essential
importance, the sign plus or minus being a minor consideration.

*Universal applicability of the electrical mode of response.*
 This mode of obtaining electrical response is applicable to
all living tissues, and in cases like that of muscle, where
mechanical response is also available, it is found that the
electrical and mechanical records are practically identical.

The two response-curves seen in the accompanying diagram (fig.
5), and taken from the same muscle by the two methods
simultaneously, clearly exhibit this. Thus we see that
electrical response can not only take the place of the
mechanical record, but has the further  advantage of being
applicable in cases where the latter cannot be used.

*Electrical response: A measure of physiological activity.*
 These electrical changes are regarded as physiological, or
characteristic of living tissue, for any conditions which
enhance physiological activity also, pari passu, increase their
intensity. Again, when the tissue is killed by poison,
electrical response disappears, the tissue passing into an
irresponsive condition. Anaesthetics, like chloroform, gradually
diminish, and finally altogether abolish, electrical response.

**Fig. 5.Simultaneous Record of the Mechanical (M) and (E)
Electrical Responses of the Muscle of Frog. (Waller.)**

![](fig005.jpg)

From these observed facts  that living tissue gives response
while a tissue that has been killed does notit is concluded
that the phenomenon of response is peculiar to living
organisms.[5] The response phenomena that we have been studying
are therefore considered as due to some unknown, super-physical
vital force and are thus relegated to a region beyond physical
inquiry.

It may, however, be that this limitation is not justified, and
surely, at least until we have explored the whole range of
physical action, it cannot be asserted definitely that a
particular class of phenomena is by its very nature outside that
category.

*Electric response in plants.*  But before we proceed to
the inquiry as to whether these responses are or are not due to
some physical property of matter, and are to be met with even in
inorganic substances, it will perhaps be advisable to see
whether they are not paralleled by phenomena in the transitional
world of plants. We shall thus pass from a study of response in
highly complex animal tissues to those given under simpler vital
conditions.

Electric response has been found by Munck, Burdon-Sanderson,
and others to occur in sensitive plants. But it would be
interesting to know whether these responses were confined to
plants which exhibit such remarkable mechanical movements, and
whether they could not also be obtained from ordinary plants
where visible movements are completely absent. In this
connection, Kunkel observed electrical changes in association
with the injury or flexion of stems of ordinary plants.[6] My
own attempt, however, was directed, not towards the obtaining of
a mere qualitative response, but rather to the determination of
whether throughout the whole range of response phenomena a
parallelism between animal and vegetable could be detected. That
is to  say, I desired to know, with regard to plants, what
was the relation between intensity of stimulus and the
corresponding response; what were the effects of superposition
of stimuli; whether fatigue was present, and in what manner it
influenced response; what were the effects of extremes of
temperature on the response; and, lastly, if chemical reagents
could exercise any influence in the modification of plant
response, as stimulating, anaesthetic, and poisonous drugs have
been found to do with nerve and muscle.

If it could be proved that the electric response served as a
faithful index of the physiological activity of plants, it would
then be possible successfully to attack many problems in plant
physiology, the solution of which at present offers many
experimental difficulties.

With animal tissues, experiments have to be carried on under
many great and unavoidable difficulties. The isolated tissue,
for example, is subject to unknown changes inseparable from the
rapid approach of death. Plants, however, offer a great
advantage in this respect, for they maintain their vitality
unimpaired during a very great length of time.

In animal tissues, again, the vital conditions themselves are
highly complex. Those essential factors which modify response
can, therefore, be better determined under the simpler
conditions which obtain in vegetable life.

In the succeeding chapters it will be shown that the response
phenomena are exhibited not only by plants but by inorganic
substances as well, and that the  responses are modified by
various conditions in exactly the same manner as those of animal
tissues. In order to show how striking are these similarities, I
shall for comparison place side by side the responses of animal
tissues and those I have obtained with plants and inorganic
substances. For the electric response in animal tissues, I shall
take the latest and most complete examples from the records made
by Dr. Waller.

But before we can obtain satisfactory and conclusive results
regarding plant response, many experimental difficulties will
have to be surmounted. I shall now describe how this has been
accomplished.[7]

**FOOTNOTES:**

[2] In some physiological text-books much wrong inference has
been made, based on the supposition that the injured end is
zinc-like.

[3] The exciting cause is able to produce a particular
molecular rearrangement in the nerve; this constitutes the state
of excitation and is accompanied by local electrical changes as
an ascertained physical concomitant.

The excitatory state evoked by stimulus manifests itself in
nerve fibres by E.M. changes, and as far as our present
knowledge goes by these only. The conception of such an
excitable living tissue as nerve implies that of a molecular
state which is in stable equilibrium. This equilibrium can be
readily upset by an external agency, the stimulus, but the term
stable expresses the fact that a change in any direction must
be succeeded by one of opposite character, this being the return
of the living structure to its previous state. Thus the
electrical manifestation of the excitatory state is one whose
duration depends upon the time during which the external agent
is able to upset and retain in a new poise the living
equilibrium, and if this is extremely brief, then the recoil of
the tissue causes such manifestation to be itself of very short
duration.  *Text-book of Physiology*, ed. by Schafer,
ii. 453.

[4] I shall here mention briefly one complication that might
arise from regarding the current of injury as the current of
reference, and designating the response current either positive
or negative in relation to it. If this current of injury
remained always invariable in directionthat is to say, from the
injured to the uninjuredthere would be no source of
uncertainty. But it is often found, for example in the retina,
that the current of injury undergoes a reversal, or is reversed
from the beginning. That is to say, the direction is now from
the uninjured to the injured, instead of the opposite. Confusion
is thus very apt to arise. No such misunderstanding can however
occur if we call the current of response towards the more
excited positive, and towards the less excited negative.

[5] The Electrical Sign of Life ... An isolated muscle gives
sign of life by contracting when stimulated ... An ordinary
nerve, normally connected with its terminal organs, gives sign
of life by means of muscle, which by direct or reflex path is
set in motion when the nerve trunk is stimulated. But such nerve
separated from its natural termini, isolated from the rest of
the organism, gives no sign of life when excited, either in the
shape of chemical or of thermic changes, and it is only by means
of an electrical change that we can ascertain whether or no it
is alive ... The most general and most delicate sign of life is
then the electrical response.Waller, in *Brain*, pp. 3
and 4. Spring 1900.

[6] Kunkel thought the electric disturbance to be due to
movement of water through the tissue. It will be shown that this
explanation is inadequate.

[7] My assistant Mr. J. Bull has rendered me very efficient
help in these experiments.

---

  
**CHAPTER III**

**ELECTRIC RESPONSE IN PLANTSMETHOD OF NEGATIVE VARIATION**

*Negative variation  Response recorder  Photographic
recorder  Compensator  Means of graduating intensity of
stimulus  Spring-tapper and torsional vibrator  Intensity of
stimulus dependent on amplitude of vibration  Effectiveness
of stimulus dependent on rapidity also.*

I shall first proceed to show that an electric response is
evoked in plants under stimulation.[8]

In experiments for the exhibition of electric response it is
preferable to use a non-electrical form of stimulus, for there
is then a certainty that the observed response is entirely due
to reaction from stimulus, and not, as might be the case with
electric stimulus, to mere escape of stimulating current through
the tissue. For this reason, the mechanical form of stimulation
is the most suitable.

I find that all parts of the living plant give electric
response to a greater or less extent. Some, however, give
stronger response than others. In favourable cases, we may have
an E.M. variation as high as *1 volt.  It must however be
remembered that the response, being a function of physiological
activity of the plant, is liable to undergo changes at different
seasons of the year. Each plant has its particular season of
maximum responsiveness. The leaf-stalk of horse-chestnut, for
example, exhibits fairly strong response in spring and summer,
but on the approach of autumn it undergoes diminution. I give
here a list of specimens which will be found to exhibit fairly
good response:

Root.  Carrot (Daucus Carota), radish (Raphanus sativus).

Stem.  Geranium (Pelargonium), vine (Vitis vinifera).

Leaf-stalk.  Horse-chestnut (AEsculus Hippocastanum), turnip
(Brassica Napus), cauliflower (Brassica oleracea), celery (Apium
graveolens), Eucharis lily (Eucharis amazonica).

Flower-stalk.  Arum lily (Richardia africana).

Fruit.  Egg-plant (Solanum Melongena).

*Negative variation.*  Taking the leaf-stalk of turnip we
kill an area on its surface, say B, by the application of a few
drops of strong potash, the area at A being left uninjured. A
current is now observed to flow, in the stalk, from the injured
B to the uninjured A, as was found to be the case in the animal
tissue. The potential difference depends on the condition of the
plant, and the season in which it may have been gathered. In the
experiment here described (fig. 6, a) its value was *13 volt.

**Fig. 6.  (a) Experiment for Exhibiting Electric Response in
Plants by Method of Negative Variation. (b) Responses in
Leaf-stalk of Turnip to Stimuli of Two Successive Taps, the
Second being Stronger.**

![](fig006.jpg)

A and B contacts are about 2 cm. apart, B being injured. Plant
is stimulated by a tap between A and B. Stimulus acts on both A
and B, but owing to injury of B, effect at A is stronger and a
negative variation due to differential action occurs.

A sharp tap was now given to the stalk, and a sudden
diminution, or negative variation, of current occurred, the
resting potential difference being  decreased by *026 volt.
A second and stronger tap produced a second response, causing a
greater diminution of P.D. by *047 volt (fig. 6, b). The
accompanying figure is a photographic record of another set of
response-curves (fig. 7). The first three responses are for a
given intensity of stimulus, and the next six in response to
stimulus nearly twice as strong. It will be noticed that fatigue
is exhibited in these responses. Other experiments will be
described in the next chapter which show conclusively that the
response was not due to any accidental circumstance but was a
direct result of stimulation. But I shall first discuss the
experimental arrangements and method of obtaining these graphic
records.

**Fig. 7.  Record of Responses in Plant (Leaf-stalk of
Cauliflower) by Method of Negative Variation**

![](fig007.jpg)

The first three records are for stimulus intensity 1; the next
six are for intensity twice as strong; the successive responses
exhibit fatigue. The vertical line to the left represents *1
volt. The record is to be read from right to left.

*Response recorder.*  The galvanometer used is a
sensitive dead-beat DArsonval. The period of complete swing of
the coil under experimental  conditions is about 11
seconds. A current of 10-9 ampere produces a deflection of 1 mm.
at a distance of 1 metre. For a quick and accurate method of
obtaining the records, I devised the following form of response
recorder. The curves are obtained directly, by tracing the
excursion of the galvanometer spot of light on a revolving drum
(fig. 8). The drum, on which is wrapped the paper for receiving
the record, is driven by clockwork. Different speeds of
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 drum,
and  as long as the plant rests unstimulated, 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 the
process constitutes the recovery. The ordinate in these curves
represents the E.M. variation, and the abscissa the time.

**Fig. 8.Response Recorder**

![](fig008.jpg)

We can calibrate the value of the deflection by applying a
known E.M.F. to the circuit from a compensator, and noting the
deflection which results. The speed of the clock is previously
adjusted so that the recording surface moves exactly through,
say, one inch a minute. Of course this speed can be increased to
suit the particular experiment, and in some it is as high as six
inches a minute. In this simple manner very accurate records may
be made. It has the additional advantage that one is able at
once to see 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.

*Photographic recorder.*  Or the records may be made
photographically. A clockwork arrangement moves a photographic
plate at a known uniform rate, and a curve is traced on the
plate by the moving spot of light. All the records that will be
given are accurate reproductions of those obtained by one of
these two methods. Photographic records are reproduced in white
against a black background.

*Compensator.*  As the responses are on variation of
current of injury, and as the current of injury may be strong,
and throw the spot of light beyond the recording surface, a
potentiometer balancing arrangement may be used (fig. 9), by
which the P.D. due to injury is exactly compensated; E.M.
variations produced by stimulus are then taken in the usual
manner. This compensating arrangement is also helpful, as has
been said before, for calibrating the E.M. value of the
deflection.

**Fig. 9.The Compensator**

![](fig009.jpg)

A B is a stretched wire with added resistances R and R?. S is a
storage cell. When the key K is turned to the right one scale
division = *001 volt, when turned to the left one scale division
= *01 volt. P is the plant.

*Means of graduating the intensity of stimulus.*  One of
the necessities in connection with quantitative measurements is
to be certain that the intensity of successive stimuli is (1)
constant, or (2) capable of gradual increase by known amounts.
No two taps given by the hand can be made exactly alike. I have
therefore devised the two following methods of stimulation,
which have been found to act satisfactorily.

**Fig. 10.The Spring-tapper**

![](fig010.jpg)

*The spring-tapper.*  This consists (fig. 10) of the
spring proper (S), the attached rod (R) carrying at its end the
tapping-head (T). A projecting rod  the lifter (L)  passes
through S R. It is provided with a screw-thread, by means of
which its length, projecting downwards, is regulated. This fact,
as we shall see, is made to determine the height of the stroke.
(C) is a cogwheel. As one of the spokes of the cogwheel 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 means of a graduated
scale. We can increase the intensity of the stroke through a
wide range (1) by increasing the projecting length of the
lifter, and (2) by shortening the length of spring by a sliding
catch. We may give isolated single taps or superpose a series in
rapid succession according as the wheel is rotated slow or fast.
The only disadvantage of the tapping method of stimulation is
that in long-continued experiment the point struck is liable to
be injured. The vibrational mode of stimulation to be presently
described labours under no such disadvantage.

*The electric tapper.*  Instead of the simple mechanical
tapper, an electromagnetic tapper may be used.

**Fig. 11.The Torsional Vibrator**

![](fig011.jpg)

Plant P is securely held by a vice V. The two ends are clamped
by holders C C?. 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 (b) shows how the amplitude of vibration is
predetermined by means of movable stops S S?.

*Vibrational stimulus.*  I find that torsional vibration
affords another very effective method of stimulation (fig. 11).
The plant-stalk may be fixed in a vice (V), the free ends being
held in tubes (C C?), provided with three clamping jaws. A rapid
torsional vibration[9] may now be imparted to the stalk by means
of the handle (H). The amplitude of vibration, which determines
the intensity of stimulus, can be accurately measured by the
graduated circle. The amplitude of vibration may be
predetermined by means of the sliding stops (S S?).

*Intensity of stimulus dependent on amplitude of vibration.*
 I shall now describe an experiment which shows that torsional
vibration is as effective as stimulation by taps, and that its
stimulating intensity increases, length of stalk being constant,
with amplitude of  vibration. It is of course obvious that
if the length of the specimen be doubled, the vibration, in
order to produce the same effect, must be through twice the
angle. I took a leaf-stalk of turnip and fixed it in the
torsional vibrator. I then took record of responses to two
successive taps, the intensity of one being nearly double that
of the other. Having done this, I applied to the same stalk two
successive torsional vibrations of 45 deg and 67 deg respectively.
These successive responses to taps and torsional vibrations are
given in fig. 12, and from them it will be seen that these two
modes of stimulation may be used indifferently, with equal
effect. The vibrational method has the advantage over tapping,
that, while with the latter the stimulus is somewhat localised,
with vibration the tissue subjected to stimulus is uniformly
stimulated throughout its length.

**Fig. 12.Response in Plant to Mechanical Tap or Vibration**

![](fig012.jpg)

The end B is injured. A tap was given between A and B and this
gave the response-curve a. A stronger tap gave the response b.
By means of the handle H, a torsional vibration of 45 deg was now
imparted, this gave the response c. Vibration through 67 deg gave
d.

Effectiveness of stimulus dependent on rapidity also. In order
that successive stimuli may be equally effective  another
point has to be borne in mind. In all cases of stimulation of
living tissue it is found that the effectiveness of a stimulus
to arouse response depends on the rapidity of the onset of the
disturbance. It is thus found that the stimulus of the break
induction shock, on a muscle for example, is more effective, by
reason of its greater rapidity, than the make shock. So also
with the torsional vibrations of plants, I find response
depending on the quickness with which the vibration is effected.
I give below records of successive stimuli, given by vibrations
through the same amplitude, but delivered with increasing
rapidity (fig. 13).

**Fig. 13.Influence of Suddenness on the Efficiency of
Stimulus**

![](fig013.jpg)

The curves a, b, c, d, are responses to vibrations of the same
amplitude, 30 deg. In a the vibration was very slow; in b it was
less slow; it was rapid in c, and very rapid in d.

Thus if we wish to maintain the effective intensity of stimulus
constant we must meet two conditions: (1) The amplitude of
vibration must be kept the same. This is done by means of the
graduated circle. (2) The vibration period must be kept the
same. With a little practice, this requirement is easily
fulfilled.

The uniformity of stimulation which is thus attained solves the
great difficulty of obtaining reliable quantitative values, by
whose means alone can rigorous demonstration of the phenomena we
are studying become possible.

**FOOTNOTES:**

[8] A preliminary account of Electric Response in Plants was
given at the end of my paper on Electric Response of Inorganic
Substances read before the Royal Society on June 6, 1901; also
at the Friday Evening Discourse, Royal Institution, May 10,
1901. A more complete account is given in my paper on Electric
Response in Ordinary Plants under Mechanical Stimulus read
before the Linnean Society March 20, 1902.

I thank the Royal Society and the Linnean Society for
permission to reproduce some of my diagrams published in their
Proceedings.J. C. B.

[9] By this is meant a rapid to-and-fro or complete vibration.
In order that successive responses should be uniform it is
essential that there should be no resultant twist, i.e. the
plant at the end of vibration should be in exactly the same
condition as at the beginning.

---

  
**CHAPTER IV**

**ELECTRIC RESPONSE IN PLANTSBLOCK METHOD**

*Method of block  Advantages of block method  Plant
response a physiological phenomenon  Abolition of response by
anaesthetics and poisons  Abolition of response when plant is
killed by hot water.*

I shall now proceed to describe another and independent method
which I devised for obtaining plant response. It has the
advantage of offering us a complementary means of verifying the
results found by the method of negative variation. As it is
also, in itself, for reasons which will be shown later, a more
perfect mode of inquiry, it enables us to investigate problems
which would otherwise have been difficult to attempt.

When electrolytic contacts are made on the uninjured surfaces
of the stalk at A and B, the two points, being practically
similar in every way, are iso-electric, and little or no current
will flow in the galvanometer. If now the whole stalk be
uniformly stimulated, and if both ends A and B be equally
excited at the same moment, it is clear that there will still be
no responsive current, owing to balancing action at the two
ends. This difficulty as regards the obtaining of response was
overcome in the method of negative variation, where the
excitability of one end was depressed by chemical reagents or
injury, or abolished by excessive tempera ture. On stimulating
the stalk there was produced a greater excitation at A than at
B, and a current of action was then observed to flow in the
stalk from the more excited A to the less excited B (fig. 6).

But we can cause this differential action to become evident by
another means. For example, if we produce a block, by clamping
at C between A and B (fig. 14, a), so that the disturbance made
at A by tapping or vibration is prevented from reaching B, we
shall then have A thrown into a relatively greater excitatory
condition than B. It will now be found that a current of action
flows in the stalk from A to B, that is to say, from the excited
to the less excited. When the B end is stimulated, there will be
a reverse current (fig. 14, b).

**Fig. 14.The Method of Block**

![](fig014.jpg)

(a) The plant is clamped at C, between A and B.

(b) Responses obtained by alternately stimulating the two ends.
Stimulation of A produces upward response; of B gives downward
response.

We have in this method a great advantage over that of negative
variation, for we can always verify any set of results by making
corroborative reversal experiments.

By the method of injury again, one end is made initially
abnormal, i.e. different from the condition which it maintains
when intact. Further, inevitable changes will proceed unequally
at the injured and uninjured ends, and the conditions of the
experiment may thus undergo unknown variations. But by the 
block method which has just been described, there is no injury,
the plant is normal throughout, and any physiological change
(which in plants will be exceedingly small during the time of
the experiment) will affect it as a whole.

**Fig. 15.Response in Plant (from the Stimulated A to
Unstimulated B) Completely Immersed Under Water**

![](fig015.jpg)

The leaf-stalk is clamped securely in the middle with the cork
C, inside the tube T, which is filled with water, the plant
being completely immersed. Moistened threads in connection with
the two non-polarisable electrodes are led to the side tubes t
t?. One end of the stalk is held in ebonite forceps and
vibrated. A current of response is found to flow in the stalk
from the excited A to the unexcited B, and outside, through the
liquid, from B to A. A portion of this current, flowing through
the side tubes t t?, produces deflection in the galvanometer.

*Plant response a physiological or vital response.*  I
now proceed to a demonstration of the fact that whatever be the
mechanism by which they are brought about, these plant responses
are physiological in their character. As the investigations
described in the next few chapters will show, they furnish an
accurate index of physiological activity. For it will be found
that, other things being equal, whatever tends to exalt or
depress the vitality of the plant tends also to increase or
diminish its electric response. These E.M. effects are well
marked, and attain considerable value, rising sometimes, as has
been said before, to as much as *1 volt or more. They are
proportional to the intensity of stimulus.

It need hardly be added that special precautions are taken to
avoid shifting of contacts. Variation of contact, however, could
not in any case account for repeated transient responses to
repeated stimuli, when contact is made on iso-electric surfaces.
Nor could it  in any way explain the reversible nature of
these responses, when A and B are stimulated alternately. These
responses are obtained in the plants even when completely
immersed in water, as in the experimental arrangement (fig. 15).
It will be seen that in this case, where there could be no
possibility of shifting of contact, or variation of surface,
there is still the usual current of response.

I shall describe here a few crucial experiments only, in proof
of the physiological character of electric response. The test
applied by physiologists, in order to discriminate as to the
physiological nature of response, consists in finding out
whether the response is diminished or abolished by the action of
anaesthetics, poisons, and excessively high temperature, which
are known to depress or destroy vitality.

I shall therefore apply these same tests to plant responses.

*Effect of anaesthetics and poisons.*  Ordinary
anaesthetics, like chloroform, and poisons, like mercuric
chloride, are known to produce a profound depression or abolish
all signs of response in the living tissue. For the purpose of
experiment, I took two groups of stalks, with leaves attached,
exactly similar to each other in every respect. In order that
the leaf-stalks might absorb chloroform I dipped their cut ends
in chloroform-water, a certain amount of which they absorbed,
the process being helped by the transpiration from the leaves.
The second group of stalks was placed simply in water, in order
to serve for control experiment. The narcotic action of
chloroform, finally  culminating in death, soon became
visually evident. The leaves began to droop, a peculiar
death-discolouration began to spread from the mid rib along the
venation of the leaves. Another peculiarity was also observed.
The aphides feeding on the leaves died even before the
appearance of the discoloured patches, whereas on the leaves of
the stalks placed in water these little creatures maintained
their accustomed activity, nor did any discolouration occur. In
order to study the effect of poison, another set was placed in
water containing a small quantity of mercuric chloride. The
leaves here underwent the same change of appearance, and the
aphides met with the same untimely fate, as in the case of those
subjected to the action of chloroform. There was hardly any
visible change in the appearance of the stalks themselves, which
were to all outer seeming as living as ever, indications of
death being apparent only on the leaf surfaces. I give below the
results of several sets of experiments, from which it would
appear that whereas there was strong normal response in the
group of stalks kept in water, there was practically a total
abolition of all response in those anaesthetised or poisoned.

Experiments on the effect of anaesthetics and poisons. A batch
of ten leaf-stalks of plane-tree was placed with the cut ends in
water, and leaves in air; an equal number was immersed in
chloroform-water; a third batch was placed in 5 per cent.
solution of mercuric chloride.

Similarly a batch of three horse-chestnut leaf-stalks was put
in water, another batch in chloroform-water, and a third batch
in mercuric chloride solution.

**I. Leaf-stalk of Plane-tree**

The stimulus applied was a single vibration of 90 deg.

A. After 24 hours in water --- B. After 24 hours in chloroform
water --- C. After 24 hours in mercuric chloride   
[ All leaves standing up and freshaphides alive] [Leaves began
to droop in 1 hour and bent over in 3 hoursaphides dead]
[Leaves began to droop in 4 hours. Deep discolouration along the
veins. Aphides dead ]

Electric response  Electric response  Electric
response

(1) 21 dns. (1) 1 dn. (1) 0 dn.   
(2) 31 "  (2) 1 "  (2) 0*25 "   
(3) 26 "  (3) 2 "  (3) 0*25 "   
(4) 15 "  (4) 0 "  (4) 0 "   
(5) 17 "  (5) 1 "  (5) 0*25 "   
(6) 23 "  (6) 1*5 "  (6) 0*25 "   
(7) 30 "  (7) 2 "  (7) 0 "   
(8) 27 "  (8) 1 "  (8) 0*25 "   
(9) 29 "  (9) 1 "  (9) 0*25 "   
(10) 17 "  (10) 0*5 "  (10) 0*5 "   
Mean response 23*6 Mean 1 Mean 0*15   
II. Leaf-stalk of Horse-chestnut   
(1) 15 dns. (1) 0*5 dn. (1) 0 dn.   
(2) 17 "  (2) 0*5 "  (2) 0 "   
(3) 10 "  (3) 0 "  (3) 0 "   
Mean 14 Mean 0*3 Mean 0

These results conclusively prove the physiological nature of
the response.

I shall in a succeeding chapter give a continuous series of
response-curves showing how, owing to progressive death from the
action of poison, the responses undergo steady diminution till
they are completely abolished.

*Effect of high temperature.*  It is well known that
plants are killed when subjected to high temperatures. I took a
stalk, and, using the block method, with torsional 
vibration as the stimulus, obtained strong responses at both
ends A and B. I then immersed the same stalk for a short time in
hot water at about 65 deg C., and again stimulated it as before.
But at neither A nor B could any response now be evoked. As all
the external conditions were the same in the first and second
parts of this experiment, the only difference being that in one
the stalk was alive and in the other killed, we have here
further and conclusive proof of the physiological character of
electric response in plants.

The same facts may be demonstrated in a still more striking
manner by first obtaining two similar but opposite responses in
a fresh stalk, at A and B, and then killing one half, say B, by
immersing only that half of the stalk in hot water. The stalk is
replaced in the apparatus, and it is now found that whereas the
A half gives strong response, the end B gives none.

In the experiments on negative variation, it was tacitly
assumed that the variation is due to a differential action,
stimulus producing a greater excitation at the uninjured than at
the injured end. The block method enables us to test the
correctness of this assumption. The B end of the stalk is
injured or killed by a few drops of strong potash, the other end
being uninjured. There is a clamp between A and B. The end A is
stimulated and a strong response is obtained. The end B is now
stimulated, and there is little or no response. The block is now
removed and the plant stimulated throughout its length. Though
the stimulus now acts on both ends, yet, owing to the
irresponsive condition of B, there is a resultant response,
which from its direction is found  to be due to the
responsive action of A. This would not have been the case if the
end B had been uninjured. 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.

---

  
**CHAPTER V**

**PLANT RESPONSEON THE EFFECTS OF SINGLE STIMULUS AND OF
SUPERPOSED STIMULI**

*Effect of single stimulus  Superposition of stimuli 
Additive effect  Staircase effect  Fatigue  No fatigue when
sufficient interval between stimuli  Apparent fatigue when
stimulation frequency is increased  Fatigue under continuous
stimulation. --- Effect of single stimulus.*

In a muscle a single stimulus gives rise to a single twitch
which may be recorded either mechanically or electrically. If
there is no fatigue, the successive responses to uniform stimuli
are exactly similar. Muscle when strongly stimulated often
exhibits fatigue, and successive responses therefore become
feebler and feebler. In nerves, however, there is practically no
fatigue and successive records are alike. Similarly, in plants,
we shall find some exhibiting marked fatigue and others very
little.

**Fig. 16.Uniform Responses (Radish)**

![](fig016.jpg)

**Fig. 17.Fusion of Effect of Rapidly Succeeding Stimuli**

![](fig017.jpg)

(a) in muscle; (b) in carrot.

*Superposition of stimuli.*  If instead of a single
stimulus a succession of stimuli be superposed, it happens that
a second shock is received before recovery from the first has
taken place. Individual effects will then become more or less
fused. When the frequency is sufficiently increased, the
intermittent effects are fused, and we find an almost unbroken
curve. When for example the muscle attains its maximum
contraction (corresponding to the frequency and strength of
stimuli) it  is thrown into a state of complete tetanus, in
which it appears to be held rigid. If the rapidity be not
sufficient for this, we have the jagged curve of incomplete
tetanus. If there is not much fatigue, the upper part of the
tetanic curve is approximately horizontal, but in cases where
fatigue sets in quickly, the fact is shown by the rapid decline
of the curve. With regard to all these points we find strict
parallels in plant response. In cases where there is no fatigue,
the successive responses are identical (fig. 16). With
superposition of stimuli we have fusion of effects, analogous to
the tetanus of muscle (fig. 17). And lastly, the influence of
fatigue in plants is to produce a modification of response-curve
exactly similar to that of muscle (see below). One effect of
superposition of stimuli may be mentioned here.

**Fig. 18.Additive Effect**   
    
 

![](fig018.jpg)

(a) A single stimulus of 3 deg vibration produced little or no
effect, but the same stimulus when rapidly superposed thirty
times, produced the large effect (b). (Leaf-stalk of turnip.)   
 Additive effect.It is found in animal responses that
there is a minimum intensity of stimulus, below which no
response can be evoked. But even a sub-minimal stimulus will,
though singly ineffective, become effective by the summation of
several. In plants, too, we obtain a similar effect, i.e. the
summation of single ineffective stimuli produces effective
response (fig. 18).

*Staircase effect.*  Animal tissues sometimes exhibit
what is known as the staircase effect, that is to say, the
heights of successive responses are gradually increased, though
the stimuli are maintained constant. This is exhibited typically
by cardiac muscle, though it is not unknown even in nerve. The
cause is obscure, but it seems to depend on the condition of the
tissue. It appears as if the molecular sluggishness of tissue
were in these cases only gradually removed under stimulation,
and the increased effects were due to increased molecular
mobility. Whatever be the explanation, I have sometimes observed
the same staircase effect in plants (fig. 19).

**Fig. 19.Staircase Effect in Plant**

![](fig019.jpg)

*Fatigue.*  It is assumed that in living substances like
muscle, fatigue is caused by the break down or 
dissimilation of tissue by stimulus. And till this waste is
repaired by the process of building-up or assimilation, the
functional activity of the tissue will remain below par. There
may also be an accumulation of the products of dissimilation 
the fatigue stuffs  and these latter may act as poisons or
chemical depressants.

In an animal it is supposed that the nutritive blood supply
performs the two-fold task of bringing material for assimilation
and removing the fatigue products, thus causing the
disappearance of fatigue. This explanation, however, is shown to
be insufficient by the fact that an excised bloodless muscle
recovers from fatigue after a short period of rest. It is
obvious that here the fatigue has been removed by means other
than that of renewed assimilation and removal of fatigue
products by the circulating blood. It may therefore be
instructive to study certain phases of fatigue exhibited under
simpler conditions in vegetable tissue, where the constructive
processes are in abeyance, and there is no active circulation
for the removal of fatigue products.

It has been said before that the E.M. variation caused by
stimulus is the concomitant of a disturbance of the molecules of
the responsive tissues from their normal equilibrium, and that
the curve of recovery exhibits the restoration of the tissue to
equilibrium.

*No fatigue when sufficient interval between successive
stimuli.*  We may thus gather from a study of the
response-curve some indication of the molecular distortion
experienced by the excited tissue. Let us first take the case of
an experiment whose record is given  in fig. 20, a. It will
be seen from that curve that one minute after the application of
stimulus there is a complete recovery of the tissue; the
molecular condition is exactly the same at the end of recovery
as in the beginning of stimulation. The second and succeeding
response-curves therefore are exactly similar to the first,
provided a sufficient interval has been allowed in each case for
complete recovery. There is, in such a case, no diminution in
intensity of response, that is to say, no fatigue.

We have an exactly parallel case in muscles. In muscle with
normal circulation and nutrition there is always an interval
between each pair of stimuli, in which the height of twitch does
not diminish even after protracted excitation, and no fatigue
appears.[10]

**Fig. 20.Record Showing Diminution of Response when
Sufficient Time is not Allowed for Full Recovery**

![](fig020.jpg)

In (a) stimuli were applied at intervals of one minute; in (b)
the intervals were reduced to half a minute; this caused a
diminution of response. In (c) the original rhythm is restored,
and the response is found to be enhanced. (Radish.)

*Apparent fatigue when stimulation frequency increased.* 
If the rhythm of stimulation frequency be now changed, and made
quicker, certain remarkable modifications will appear in the
response-curves. In fig. 20, the first part shows the responses
at one minute interval, by which time the individual recovery
was complete.

**Fig. 21.Fatigue in Celery**

![](fig021.jpg)

Vibration of 30 deg at intervals of half a minute.

The rhythm was now changed to intervals of half  a minute,
instead of one, while the stimuli were maintained at the same
intensity as before. It will be noticed (fig. 20, b) that these
responses appear much feebler than the first set, in spite of
the equality of stimulus. An inspection of the figure may
perhaps throw some light on the subject. It will be seen that
when greater frequency of stimulation was introduced, the tissue
had not yet had time to effect complete recovery from previous
strain. The molecular swing towards equilibrium had not yet
abated, when the new stimulus, with its opposing impulse, was
received. There is thus a diminution of height in the resultant
response. The original rhythm of one minute was now restored,
and the succeeding curves (fig. 20, c) at once show increased
response. An analogous instance may be cited in the case of
muscle response, where the height of twitch diminishes more
rapidly in proportion as the excitation interval is
shorter.[11]

**Fig. 22.Fatigue in Leaf-stalk of Cauliflower**

![](fig022.jpg)

Stimulus: 30 deg vibration at intervals of one minute.

From what has just been said it would appear that one of the
causes of diminution of response, or fatigue, is the residual
strain. This is clearly seen in fig. 21, in a record which I
obtained with celery-stalk. It will be noticed there that, owing
to the imperfect molecular recovery during the time allowed, the
succeeding heights of the responses have undergone a continuous
diminution. Fig. 22 gives a  photographic record of fatigue
in the leaf-stalk of cauliflower.

It is evident that residual strain, other things being equal,
will be greater if the stimuli have been excessive. This is well
seen in fig. 23, where the set of first three curves A is for
stimulus intensity of 45 deg vibration, and the second set B, with
an augmented response, for stimulus intensity of 90 deg vibration.
On reverting in C to stimulus intensity of 45 deg, the responses
are seen to have undergone a great diminution as compared with
the first set A. Here is seen marked fatigue, the result of
overstrain from excessive stimulation.

**Fig. 23.Effect of Overstrain in Producing Fatigue**

![](fig023.jpg)

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.)

If this fatigue be really due to residual strain effect, then,
as strain disappears with time, we may expect the responses to
regain their former height after a period of rest. In order to
verify this, therefore, I renewed the stimulation (at intensity
45 deg) after fifteen minutes. It  will at once be seen from
record D how far the fatigue had been removed.

One peculiarity that will be noticed in these curves is that,
owing to the presence of comparatively little residual strain,
the first response of each set is relatively large. The
succeeding responses are approximately equal where the residual
strains are similar. The first response of A shows this because
it had had long previous rest. The first of B shows it because
we are there passing for the first time to increased
stimulation. The first of C does not show it, because there is
now a strong residual strain. D again shows it because the
strain has been removed by fifteen minutes rest.

*Fatigue under continuous stimulation.*  The effect of
fatigue is exhibited in marked degree when a tissue is subjected
to continuous stimulation. In cases where there is marked
fatigue, as for instance in certain muscles, the top of the
tetanic curve undergoes rapid decline. A similar effect is
obtained also with plants (fig. 24).

**Fig. 24.Rapid Fatigue under Continuous Stimulation in (a)
Muscle; (b) in Leaf-stalk of Celery**

![](fig024.jpg)

The effect of rest in producing molecular recovery, and hence
in the removal of fatigue, is well illustrated in the following
set of photographic records (fig. 25). The first shows the curve
obtained with a fresh plant.  The effect is seen to be very
large. Two minutes were allowed for recovery, and then
stimulation was repeated during another two minutes. The
response in this case is seen to be decidedly smaller. A third
case is somewhat similar to the second. A period of rest of five
minutes was now allowed, and the curve obtained subsequently,
owing to partial removal of residual strain, is found to exhibit
greater response.

**Fig. 25.Effect of Continuous Vibration (through 50 deg) in
Carrot**

![](fig025.jpg)

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.

The results thus arrived at, under the simple conditions of
vegetable life, free as they are from all possible complications
and uncertainties, may perhaps throw some light on the obscure
phenomena of fatigue in animal tissues.

**FOOTNOTES:**

[10] Biedermann, Electro-physiology, p. 86.

[11] Biedermann, loc. cit.

---

  
**CHAPTER VI**

**PLANT RESPONSEON DIPHASIC VARIATION**

*Diphasic variation  Positive after-effect and positive
response  Radial E.M. variation.*

When a plant is stimulated at any point, a molecular
disturbance  the excitatory wave  is propagated outwards from
the point of its initiation.

*Diphasic variation.*  This wave of molecular disturbance
is attended by a wave of electrical disturbance. (Usually
speaking, the electrical relation between disturbed and less
disturbed is that of copper to zinc.) It takes some time for a
disturbance to travel from one point to another, and its
intensity may undergo a diminution as it recedes further from
its point of origin. Suppose a disturbance originated at C; if
two points are taken near each other, as A and B, the
disturbance will reach them almost at the same time, and with
the same intensity. The electric disturbance will be the same in
both. The effect produced at A and B will balance each other and
there will be no resultant current.

By killing or otherwise reducing the sensibility of B as is
done in the method of injury, there is no response at B, and we
obtain the unbalanced response, due to disturbance at A; the
same effect is obtained by putting  a clamp between A and
B, so that the disturbance may not reach B. But we may get
response even without injury or block. If we have the contacts
at A and B, and if we give a tap nearer A than B (fig. 26, a),
then we have (1) the disturbance reaching A earlier than B. (2)
The disturbance reaching A is much stronger than at B. The
disturbance at B may be so comparatively feeble as to be
negligible.

It will thus be seen that we might obtain responses even
without injury or block, in cases where the disturbance is
enfeebled in reaching a distant point. In such a case on giving
a tap near A a responsive current would be produced in one
direction, and in the opposite direction when the tap is given
near B (fig. 26, b). Theoretically, then, we might find a
neutral point between A and B, so that, on originating the
disturbance there, the waves of disturbance would reach A and B
at the same instant and with the same intensity. If, further,
the rate of recovery be the same for both points, then the
electric disturbances produced at A and B will continue to
balance each other, and the galvanometer will show no current.
On taking a cylindrical root of radish I have sometimes
succeeded in finding a neutral point, which, being disturbed,
did not give rise to any resultant current. But disturbing a
point to the right or to the left gave rise to opposite
currents.

It is, however, difficult to obtain an absolutely cylindrical
specimen, as it always tapers in one direction. The conductivity
towards the tip of the root is not exactly the same as that in
the ascending direction. It  is therefore difficult to fix
an absolutely neutral point, but a point may be found which
approaches this very nearly, and on stimulating the stalk near
this, a very interesting diphasic variation has been observed.
In a specimen of cauliflower-stalk, (1) stimulus was applied
very much nearer A than B (the feeble disturbance reaching B was
negligible). The resulting response was upward and the recovery
took place in about sixty seconds.

**Fig. 26.Diphasic Variation**

![](fig026.jpg)

(2) Stimulus was next applied near B. The resulting response
was now downward (fig. 26, b).

(3) The stimulus was now applied near the approximately neutral
point N. In this case, owing to a slight difference in the rates
of propagation in the two directions, a very interesting
diphasic variation was produced (fig. 26, c). From the record it
will be seen that the disturbance arrived earlier at A than at
B. This produced an upward response. But during the 
subsidence of the disturbance at A, the wave reached B. The
effect of this was to produce a current in the opposite
direction. This apparently hastened the recovery of A (from 60
seconds to 12 seconds). The excitation of A now disappeared, and
the second phase of response, that due to excitation of B, was
fully displayed.

*Positive after-effect.*  If we regard the response due
to excitation of A as negative, the later effect on B would
appear as a subsequent positive variation.

In the response of nerve, for example, where contacts are made
at two surfaces, injured and uninjured, there is sometimes
observed, first a negative variation, and then a positive
after-effect. This may sometimes at least be due to the proximal
uninjured contact first giving the usual negative variation, and
the more distant contact of injury giving rise, later, to the
opposite, that is to say, apparently positive, response. There
is always a chance of an after-effect due to this cause, unless
(1) the injured end be completely killed and rendered quite
irresponsive, or (2) there be an effective block between A and
B, so that the disturbance due to stimulus can only act on one,
and not on the other.

I have found cases where, even when there was a perfect block,
a positive after-effect occurred. It would thus appear that if
molecular distortion from stimulus give rise to a negative
variation, then during the process of molecular recovery there
may be over-shooting of the equilibrium position, which may be
exhibited as a positive variation.

*Positive variation.*  The responses given by muscle or
nerve are, normally speaking, negative. But that of retina is
positive. The sign of response, however, is apt to be reversed
if there be any molecular modification of the tissue from
changes of external circumstances. Thus it is often found that
nerve in a stale condition gives positive, instead of the normal
negative variation, and stale retina often gives negative,
instead of the usual positive.

**Fig. 27.Abnormal Positive Responses in Stale Leaf-stalk of
Turnip converted into Normal Negative under Strong Stimulation
[12]**

![](fig027.jpg)

The relative intensities of stimuli in the two cases are in the
ratio of 1:7.

Curiously enough, I have on many occasions found exactly
parallel instances in the response of plants. Plants when fresh,
as stated, give negative responses as a rule. But when somewhat
faded they sometimes give rise to positive response. Again, just
as in the modified nerve the abnormal positive response gives
place to the normal negative under strong and long-continued
stimulation, so also in the modified plant the abnormal positive
response passes into negative  (fig. 27) under strong
stimulation. I was able in some cases to trace this process of
gradual reversal, by continuously increasing the intensity of
stimulus. It was then found that as the stimulus was increased,
the positive at a certain point underwent a reversal into the
normal negative response (fig. 28).

**Fig. 28. Abnormal Positive passing into Normal Negative in a
Stale Specimen of Leaf-stalk of Cauliflower**

![](fig028.jpg)

Stimulus was gradually increased from 1 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.)

The plant thus gives a reversed response under abnormal
conditions of staleness. I have sometimes found similar reversal
of response when the plant is subjected to the abnormal
conditions of excessively high or low temperature.

*Radial E.M. variation.*  We have seen that a current of
response flows in the plant from the relatively more to the
relatively less excited. A theoretically important experiment is
the following: A thick stem of plant stalk was taken and a hole
bored so as to make one contact with the interior of the tissue,
the other being  on the surface. After a while the current
of injury was found to disappear. On exciting the stem by taps
or torsional vibration, a responsive current was observed which
flowed inwards from the more disturbed outer surface to the
shielded core inside (fig. 29). Hence it is seen that when a
wave of disturbance is propagated along the plant, there is a
concomitant wave of radial E.M. variation. The swaying of a tree
by the wind would thus appear to give rise to a radial E.M.F.

**Fig. 29.Radial E.M. Variation**   
    
 

![](fig029.jpg)

**FOOTNOTES:**

[12] For general purposes it is immaterial whether the
responses are recorded up or down. For convenience of inspection
they are in general recorded up. But in cases where it is
necessary to discriminate the sign of response, positive
response will be recorded up, and negative down.

---

  
**CHAPTER VII**

**PLANT RESPONSEON THE RELATION BETWEEN STIMULUS AND
RESPONSE**

*Increased response with increasing stimulus  Apparent
diminution of response with excessively strong stimulus.*

As already said, in the living tissue, molecular disturbance
induced by stimulus is accompanied by an electric disturbance,
which gradually disappears with the return of the disturbed
molecules to their position of equilibrium. The greater the
molecular distortion produced by the stimulus, the greater is
the electric variation produced. The electric response is thus
an outward expression of a molecular disturbance produced by an
external agency, the stimulus.

*Curve of relation between stimulus and response.*  In
the curve showing the relation between stimulus and response in
nerve and muscle, it is found that the molecular effect as
exhibited either by contraction or E.M. variation in muscle, or
simply by E.M. variation in nerve, is at first slight. In the
second part, there is a rapidly increasing effect with increased
stimulus. Finally, a tendency shows itself to approach a limit
of response. Thus we find the curve at first slightly convex,
then straight and ascending, and lastly, concave to the abscissa
(fig. 30).

In muscle the limit of response is reached much sooner than in
nerve. As will be seen, the range of variation of stimulus in
these curves is not very  great. When the stimulus is
carried beyond moderate limits, the response, owing to fatigue
or other causes, may sometimes undergo an actual diminution.

**Fig. 30.Curves Showing the Relation Between the Intensity
of Stimulus and Response**

![](fig030.jpg)

Abscissae indicate increasing intensity of stimulus. Ordinates
indicate magnitude of response. (Waller.)

**Fig. 31**

![](fig031.jpg)

Taps of increasing strength 1:2:3:4 producing increased
response in leaf stalk of turnip.

I have obtained very interesting results, with reference to the
relation between stimulus and response, when experimenting with
plants. These results are suggestive of various types of
response met with in animal tissues.

1. In order to obtain the simplest type of effects, not
complicated by secondary phenomena, one has to choose specimens
which exhibit little fatigue. Having procured these, I undertook
two series of experiments. In the first (A) the stimulus was
applied by means of the spring-tapper, and in the second (B) by
torsional vibration.

 (A) The first stimulus was given by a fall of the lever
through h, the second through 2 h, and so on. The
response-curves clearly show increasing effect with increased
stimulus (fig. 31).

**Fig. 32.Increased Response with Increasing Vibrational
Stimuli (Cauliflower-stalk)**

![](fig032.jpg)

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

(B) 1. The vibrational stimulus was increased from 2*5 deg to 5 deg
to 7*5 deg to 10 deg to 12*5 deg in amplitude. It will be observed how
the intensity of response tends to approach a limit (fig. 32).

Table showing the Increased E.M. Variation   
produced by Increasing Stimulus   
Angle of Vibration E.M.F   
  2*5 deg *044 volt   
  5 deg *075 volt   
  7*5 deg *090 volt   
10 deg *100 volt   
12*5 deg *106 volt

 2. The next figure shows how little variation is produced
with low value of stimulus, but with increasing stimulus the
response undergoes a rapid increase, after which it tends to
approach a limit (fig. 33, a).

**Fig. 33.Responses to Increasing Stimuli produced by
Increasing Angle of Vibration**

![](fig033.jpg)

(a) Record with a specimen of fresh radish. Stimuli applied at
intervals of two minutes. The record is taken for one minute.

(b) Record for stale radish. There is a reversed response for
the feeble stimulus of 5 deg vibration.

3. As an extreme instance of the case just cited, I have often
come across a curious phenomenon. During the gradual increase of
the stimulus from a low value there would be apparently no
response. But when a critical value was reached a maximum
response would suddenly occur, and would not be exceeded when
the stimulus was further increased. Here we have a parallel to
what is known in animal physiology as the all or none
principle. With the cardiac muscle, for example, there is a
certain minimal intensity which is effective in producing
response, but further increase of stimulus produces no increase
in response.

4. From an inspection of the records of responses  which
are given, it will be seen that the slope of a curve which shows
the relation of stimulus to response will at first be slight,
the curve will then ascend rapidly, and at high values of
stimulus tend to become horizontal. The curve as a whole
becomes, first slightly convex to the abscissa, then straight
and ascending, and lastly concave. A far more pronounced
convexity in the first part is shown in some cases, especially
when the specimen is stale. This is due to the fact that under
these circumstances response is apt to begin with an actual
reversal of sign, the plant under feebler than a certain
critical intensity of stimulus giving positive, instead of the
normal negative, response (fig. 33, b).

*Diminution of response with excessively strong stimulus.* 
It is found that in animal tissues there is sometimes an actual
diminution of response with excessive increase of stimulus. Thus
Waller finds, in working with retina, that as the intensity of
light stimulus is gradually increased, the response at first
increases, and then sometimes undergoes a diminution. This
phenomenon is unfortunately complicated by fatigue, itself
regarded as obscure. It is therefore difficult to say whether
the diminution of response is due to fatigue or to some
reversing action of an excessively strong stimulus.

From fig. 33, b, above, it is seen that there was an actual
reversal of response in the lower portion of the curve. It is
therefore not improbable that there may be more than one point
of reversal.

In physical phenomena we are, however, acquainted with numerous
instances of reversals. For example,  a common effect of
magnetisation is to produce an elongation of an iron rod. But
Bidwell finds that as the magnetising force is pushed to an
extreme, at a certain point elongation ceases and is succeeded,
with further increase of magnetising force, by an actual
contraction. Again a photographic plate, when exposed
continuously to light, gives at first a negative image. Still
longer exposure produces a positive. Then again we have a
negative. There is thus produced a series of recurrent
reversals. In photographic prints of flashes of lightning, two
kinds of images are observed, one, the positive  when the
lightning discharge is moderately intense  and the other,
negative, the so-called dark lightning  due to the reversal
action of an intensely strong discharge.

In studying the changes of conductivity produced in metallic
particles by the stimulus of Hertzian radiation, I have often
noticed that whereas feeble radiation produces one effect,
strong radiation produces the opposite. Again, under the
continuous action of electric radiation, I have frequently found
recurrent reversals.[13]

*Diminution of response under strong stimulus traced to
fatigue.*  But there are instances in plant response
where the diminution effect can be definitely traced to fatigue.
The records of these cases are extremely suggestive as to the
manner in which the diminution is brought about. The
accompanying figures (fig. 34) give records of responses to
increasing stimulus. They were made with specimens of
cauliflower-stalks, one of which (a) showed little fatigue,
while in the other (b)  fatigue was present. It will be
seen that the curves obtained by joining the apices of the
successive single responses are very similar.

**Fig. 34.Responses to Increasing Stimulus obtained with Two
Specimens of Stalk of Cauliflower**

![](fig034.jpg)

In (a) fatigue is absent, in (b) it is present.

In one case there is no fatigue, the recovery from each
stimulus being complete. Every response in the series therefore
starts from a position of perfect equilibrium, and the height of
the single responses increases with increasing stimulation. But
in the second case,  the strain is not completely removed
after any single stimulation of the series. That recovery is
partial is seen by the gradual shifting of the base line
upwards. In the former case the base line is horizontal and
represents a condition of complete equilibrium. Now, however,
the base line, or line of modified equilibrium, is tilted
upwards. Thus even in this case if we measure the heights of
successive responses from the line of absolute equilibrium, they
will be found to increase with increasing stimulus. Ordinarily,
however, we make no allowance for the shifting of the base line,
measuring response rather from the place of its previous
recovery, or from the point of modified equilibrium. Judged in
this way, the responses undergo an apparent diminution.

**FOOTNOTES:**

[13] See On Electric Touch, Proc. Roy. Soc. Aug. 1900.

---

  
**CHAPTER VIII**

**PLANT RESPONSEON THE INFLUENCE OF TEMPERATURE**

*Effect of very low temperature  Influence of high
temperature  Determination of death-point  Increased
response as after-effect of temperature variation  Death of
plant and abolition of response by the action of steam.*

For every plant there is a range of temperature most favourable
to its vital activity. Above this optimum, the vital activity
diminishes, till a maximum is reached, when it ceases
altogether, and if this point be maintained for a long time the
plant is apt to be killed. Similarly, the vital activity is
diminished if the temperature be lowered below the optimum, and
again, at a minimum point it ceases, while below this minimum
the plant may be killed. We may regard these maximum and minimum
temperatures as the death-points. Some plants can resist these
extremes better than others. Length of exposure, it should
however be remembered, is also a determining factor in the
question as to whether or not the plant shall survive
unfavourable conditions of temperature. Thus we have hardy
plants, and plants that are affected by excessive variations of
temperature. Within the characteristic power of the species,
there may be, again, a certain amount of individual difference.

These facts being known, I was anxious to deter mine whether
the undoubted changes induced by temperature in the vital
activity of plants would affect electrical response.

*Effect of very low temperature.*  As regards the
influence of very low temperature, I had opportunities of
studying the question on the sudden appearance of frost. In the
previous week, when the temperature was about 10 deg C., I had
obtained strong electric response in radishes whose value varied
from *05 to *1 volt. But two or three days later, as the effect
of the frost, I found electric response to have practically
disappeared. A few radishes were, however, found somewhat
resistant, but the electric response had, even in these cases,
fallen from the average value of *075 V. under normal
temperature to *003 V. after the frost. That is to say, the
average sensitiveness had been reduced to about 1/25th. On
warming the frost-bitten radish to 20 deg C. there was an
appreciable revival, as shown by increase in response. In
specimens where the effect of frost had been very great, i.e. in
those which showed little or no electric response, warming did
not restore responsiveness. From this it would appear that frost
killed some, which could not be subsequently revived, whereas
others were only reduced to a condition of torpidity, from which
there was revival on warming.

**Fig. 35.  Diminution of Response in Eucharis by Lowering of
Temperature**

![](fig035.jpg)

(a) Normal response at 17 deg C.   
(b) The response almost disappears when plant is subjected to
?2 deg C. for fifteen minutes.   
(c) Revival of response on warming to 20 deg C.

I now tried the effect of artificial lowering of temperature on
various plants. A plant which is very easily affected by cold is
a certain species of Eucharis lily. I first obtained responses
with the leaf-stalk of this lily at the ordinary temperature of
the room  (17 deg C.). I then placed it for fifteen minutes in
a cooling chamber, temperature ?2 deg C., for only ten minutes,
after which, on trying to obtain response, it was found to have
practically disappeared. I now warmed the plant by immersing it
for awhile in water at 20 deg C., and this produced a revival of
the response (fig. 35). If the plant be subjected to low
temperature for too long a time, there is then no subsequent
revival.

I obtained a similar marked diminution of response with the
flower-stalk of Arum lily, on lowering the temperature to zero.

My next attempt was to compare the sensibility of different
plants to the effect of lowered temperatures. For this purpose I
chose three specimens: (1) Eucharis lily; (2) Ivy; and (3)
Holly. I took their normal response at 17 deg C., and found that,
generally speaking, they attained a fairly constant value after
the third or fourth response. After taking these records of
normal response, I placed the specimens in an ice-chamber, 
temperature 0 deg C., for twenty-four hours, and afterwards took
their records once more at the ordinary temperature of the room.
From these it will be seen that while the responsiveness of
Eucharis lily, known to be susceptible to the effect of cold,
had entirely disappeared, that of the hardier plants, Holly and
Ivy, showed very little change (fig. 36).

Another very curious effect that I have noticed is that when a
plant approaches its death-point by reason of excessively high
or low temperature, not only is its general responsiveness
diminished almost to zero, but even the slight response
occasionally becomes reversed.

**Fig. 36.After-effect of Cold on Ivy, Holly, and Eucharis
Lily**

![](fig036.jpg)

a. The normal response; b. Response after subjection to
freezing temperature for twenty-four hours.

Influence of high temperature, and determination of
death-point.  I next tried to find out whether a rise of
temperature produced a depression of response, and whether the
response disappeared at a maximum temperature  the temperature
of death-point. For this purpose I took a batch of six radishes
and obtained from them responses at gradually increasing
temperatures. These specimens were obtained late in the season,
and their electric responsiveness was much lower than those
obtained earlier. The plant, previously kept for five minutes in
water at a definite temperature  (say 17 deg C.), was mounted
in the vibration apparatus and responses observed. The plant was
then dismounted, and replaced in the water-bath at a higher
temperature (say 30 deg C.) again, for five minutes. A second set
of responses was now taken. In this way observations were made
with each specimen till the temperature at which response almost
or altogether ceased was reached. I give below a table of
results obtained with six specimens of radish, from which it
would appear that response begins to be abolished in these cases
at temperatures varying from 53 deg to 55 deg C.

**Table showing Effect of High Temperature in Abolishing
Response**   
Temperature Galvanometric response   
(100 dns. = *07 V.)   
(1) { 17 deg C 70 dns.   
53 deg 4 "   
(2) { 17 deg 160 "   
53 deg 1 "   
(3) { 17 deg 100 "   
50 deg 2 "   
(4) { 17 deg 80 "   
55 deg 0 "   
(5) { 17 deg 40 "   
60 deg 0 "   
(6) { 17 deg 60 "   
55 deg 0 "

**Fig. 37.The Glass Chamber containing the Plant**

![](fig037.jpg)

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 anaesthetics, vapour of chloroform is
blown in through the side tube.

*Electric heating.*  The experiments just described were,
however, rather troublesome, inasmuch as, in order to produce
each variation of temperature, the specimen had to be taken out
of the apparatus, warmed, and remounted. I therefore introduced
a modification by which this difficulty was obviated. The
specimen was now enclosed in a glass chamber (fig. 37), which
also contained a spiral of German-silver wire, through which
electric currents could be sent, for the purpose of heating the
chamber. By varying the intensity of the current, the
temperature could be regulated at will. The specimen chosen for
experiment was the leaf-stalk of celery. It was kept at each
given temperature for  ten minutes, and two records were
taken during that time. It was then raised by 10 deg C., and the
same process was repeated. It will be noticed from the record
(fig. 38) that in this particular case, as the temperature rose
from 20 deg C. to 30 deg C., there was a marked diminution of
response. At the same time, in this case at  least,
recovery was quicker. At 20 deg C., for example, the response was
21 dns., and the recovery was not complete in the course of a
minute. At 30 deg C., however, the response had been reduced to 7*5
divisions, but there was almost complete recovery in twelve
seconds. As the temperature was gradually increased, a
continuous decrease of response occurred. This diminution of
response with increased temperature appears to be universal, but
the quickening of recovery may be true of individual cases only.

**Fig. 38.Effect of Temperature on Response**

![](fig038.jpg)

The response was abolished at the hot-water temperature of 55 deg
C.

Table showing Diminution of Response with Increasing
Temperature   
(*01 Volt = 35 divisions)

Temperature Response   
20 deg 21   
30 deg   7*5   
40 deg   5*5   
50 deg   4   
65 deg   3

In radishes response disappeared completely at 55 deg C., but with
celery, heated in the manner described, I could not obtain its
entire abolition at 60 deg C. or even higher. A noticeable
circumstance, however, was the prolongation of the period of
recovery at these high temperatures. I soon understood the
reason of this apparent anomaly. The method adopted in the
present case was that of dry heating, whereas the previous
experiments had been carried on by the use of hot water. It is
well known that one can stand a temperature of 100 deg C. without
ill effects in the hot-air chamber of a Turkish bath, while
immersion in water at 100 deg C. would be fatal.

In order to find out whether subjection to hot water would kill
the celery-stalk, I took it out and placed it  for five
minutes in water at 55 deg C. This, as will be seen from the record
taken afterwards, effectively killed the plant (fig. 38, w).

**Fig. 39.Effect of Rising and Falling Temperature on the
Response Of Scotch Kale**

![](fig039.jpg)

Increased sensitiveness as after-effect of temperature
variation.A very curious effect of temperature variation is the
marked increase of sensitiveness which often appears as its
after-effect. I noticed this first in a series of observations
where records were taken during the rise of temperature and
continued while the temperature was falling (fig. 39). The
temperature was adjusted by electric heating. It was found that
the responses were markedly enhanced during cooling, as 
compared with responses given at the same temperatures while
warming (see table). Temperature variation thus seems to have a
stimulating effect on response, by increasing molecular mobility
in some way. The second record (fig. 40) shows the variation of
response in Eucharis lily (1) during the rise, and (2) during
the fall  of temperature. Fig. 41 gives a curve of
variation of response during the rise and fall of temperature.

Table showing the Variation of Response in Scotch Kale during
the Rise and Fall of Temperature   
Temperature / Response   
[Temperature falling]  Response   
[Temperature rising] ?   
19 deg C. 47 dns.    
25 deg  " 24   "    
30 deg  " 11   " 23 dns.   
50 deg  " 8   " 16   "   
70 deg  " 7   "    
    ?

**Fig. 40.Records of Responses in Eucharis Lily during Rise
and Fall of Temperature**

![](fig040.jpg)

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. Temperature corresponding to each record is given
below.

Temperature rising: (1) 20 deg, (2) 20 deg, (3) 22 deg, (4) 38 deg, (5)
53 deg, (6) 68 deg, (7) 65 deg.

Temperature falling: (8) 60 deg, (9) 51 deg, (10) 45 deg, (11) 40 deg, (12)
38 deg.

*Point of temperature maximum.*  We have seen how, in
cases of lowered temperature, response is abolished earlier in
plants like Eucharis, which are affected by cold, than in the
hardier plants such as Holly and Ivy. Plants again are unequally
affected as regards the upper range. In the case of Scotch kale,
for instance, response disappears after ten minutes of water
temperature of about 55 deg C., but with Eucharis fairly marked
response can still be obtained after such immersion and does not
disappear till it has been subjected for ten minutes to hot
water, at a temperature of 65 deg C. or even higher. The reason of
this great power of resistance to heat is probably found in the
fact that the Eucharis is a tropical plant, and is grown, in
this country, in hot-houses where a comparatively high
temperature is maintained.

**Fig. 41.Curve showing Variation of Response in Eucharis
with the Rise and Fall of Temperature**

![](fig041.jpg)

*The effect of steam.*  I next wished to obtain a
continuous record by which the effects of suddenly increased
temperatures, culminating in the death of the plant, might be
made evident. For this purpose I mounted the plant in the glass
chamber, into which steam  could be introduced. I had
chosen a specimen which gave regular response. On the
introduction of steam, with the consequent sudden increase of
temperature, there was a transitory augmentation of
excitability. But this quickly disappeared, and in five minutes
the plant was effectively killed, as will be seen graphically
illustrated in the record (fig. 42).

**Fig. 42.Effect of Steam in Killing Response**

![](fig042.jpg)

The two records to the left exhibit normal response at 17 deg C.
Sudden warming by steam produced at first an increase of
response, but five minutes exposure to steam killed the plant
(carrot) and abolished the response.

Vibrational stimulus of 30 deg applied at intervals of one minute;
vertical line = *1 volt.

It will thus be seen that those modifications of vital activity
which are produced in plants by temperature variation can be
very accurately gauged by electric response. Indeed it may be
said that there is no other method by which the moment of
cessation of vitality can be so satisfactorily distinguished.
Ordinarily, we  are able to judge that a plant has died,
only after various indirect effects of death, such as withering,
have begun to appear. But in the electric response we have an
immediate indication of the arrest of vitality, and we are
thereby enabled to determine the death-point, which it is
impossible to do by any other means.

It may be mentioned here that the explanation suggested by
Kunkel, of the response being due to movement of water in the
plant, is inadequate. For in that case we should expect a
definite stimulation to be under all conditions followed by a
definite electric response, whose intensity and sign should
remain invariable. But we find, instead, the response to be
profoundly modified by any influence which affects the vitality
of the plant. For instance, the response is at its maximum at an
optimum temperature, a rise of a few degrees producing a
profound depression; the response disappears at the maximum and
minimum temperatures, and is revived when brought back to the
optimum. Anaesthetics and poisons abolish the response. Again, we
have the response undergoing an actual reversal when the tissue
is stale. All these facts show that mere movement of water could
not be the effective cause of plant response.

---

  
**CHAPTER IX**

**PLANT RESPONSEEFFECT OF ANAESTHETICS AND POISONS**

*Effect of anaesthetics, a test of vital character of response
 Effect of chloroform  Effect of chloral  Effect of
formalin  Method in which response is unaffected by variation
of resistance  Advantage of block method  Effect of dose.*

The most important test by which vital phenomena are
distinguished is the influence on response of narcotics and
poisons. For example, a nerve when narcotised by chloroform
exhibits a diminishing response as the action of the anaesthetic
proceeds. (See below, fig. 43.) Similarly, various poisons have
the effect of permanently abolishing all response. Thus a nerve
is killed by strong alkalis and strong acids. I have already
shown how plants which previously gave strong response did not,
after application of an anaesthetic or poison, give any response
at all. In these cases it was the last stage only that could be
observed. But it appeared important to be able to trace the
growing effect of anaesthetisation or poisoning throughout the
process. There were, however, two conditions which it at first
appeared difficult to meet. First it was necessary to find a
specimen which would normally exhibit no fatigue, and give rise
for a long time to a uniform series  of response. The
immediate changes made in the response, in consequence of the
application of chemical reagents, could then be demonstrated in
a striking manner. And with a little trouble, specimens can be
secured in which perfect regularity of response is found. The
record given in fig. 16, obtained with a specimen of radish,
shows how possible it is to secure plants in which response is
absolutely regular. I subjected this to uniform stimulation at
intervals of one minute, during half an hour, without detecting
the least variation in the responses. But it is of course easier
to find others in which the responses as a whole may be taken as
regular, though there may be slight rhythmic fluctuations. And
even in these cases the effect of reagents is too marked and
sudden to escape notice.

**Fig. 43.Effect of Chloroform on Nerve Response (Waller)**

![](fig043.jpg)

For the obtaining of constant and strong response I found the
best materials to be carrot and radish, selected individuals
from which gave most satisfactory results. The carrots were at
their best in August and September,  after which their
sensitiveness rapidly declined. Later, being obliged to seek for
other specimens, I came upon radish, which gave good results in
the early part of November; but the setting-in of the frost had
a prejudicial effect on its responsiveness. Less perfect than
these, but still serviceable, are the leaf-stalks of turnip and
cauliflower. In these the successive responses as a whole may be
regarded as regular, though a curious alternation is sometimes
noticed, which, however, has a regularity of its own.

My second misgiving was as to whether the action of reagents
would be sufficiently rapid to display itself within the time
limit of a photographic record. This would of course depend in
turn upon the rapidity with which the tissues of the plant could
absorb the reagent and be affected by it. It was a surprise to
me to find that, with good specimens, the effect was manifested
in the course of so short a time as a minute or so.

*Effect of chloroform.*  In studying the effect of
chemical reagents in plants, the method is precisely similar to
that employed with nerve; that is to say, where vapour of
chloroform is used, it is blown into the plant chamber. In cases
of liquid reagents, they are applied on the points of contact A
and B and their close neighbourhood. The mode of experiment was
(1) to obtain 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. (2) Without
interrupting this procedure, the anaesthetic agent, vapour of
chloroform, was blown into the closed chamber containing the
plant.  It will be seen how rapidly chloroform produces
depression of response (fig. 44), and how the effect grows with
time. In these experiments with plants, the same curious
shifting of the zero line is sometimes noticed as in nerve when
subjected similarly to the action of reagents. This is a point
of minor importance, the essential point to be noticed being
that the responses are rapidly reduced.

**Fig. 44.Effect of Chloroform on Responses of Carrot**

![](fig044.jpg)

Stimuli of 25 deg vibration at intervals of one minute.

*Effects of chloral and formalin*.  I give below (figs.
45, 46) two sets of records, one for the reagent chloral and the
other for formalin. The reagents were applied in the form of a
solution on the tissue at the two leading contacts, and the
contiguous surface. The rhythmic fluctuation in the normal
response shown in fig. 45 is interesting. The abrupt decline,
within a  minute of the application of chloral, is also
extremely well marked.

**Fig. 45.Action of Chloral Hydrate on the Responses of
Leaf-stalk of Cauliflower**

![](fig045.jpg)

Vibration of 25 deg at intervals of one minute.

**Fig. 46.Action of Formalin (Radish)**

![](fig046.jpg)

*Response unaffected by variation of resistance.*  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 the tissue, we rely upon its effect in exalting
or depressing the responsive E.M.  variation. We read this
effect by means of galvanometric deflections. And if the
resistance of the circuit remained constant, then an increase of
galvanometer deflection would accurately indicate a heightened
or depressed E.M. response, due to greater or less excitability
of tissue caused by the reagent. But, by the introduction of the
chemical reagent, the resistance of the tissue may undergo
change, and owing to this cause, modification of response as
read by the galvanometer may be produced 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 in response to stimulus.

We may however discriminate as to how much of the observed
change is due to variation of resistance by comparing the
deflections produced in the galvanometer by the action of a
definite small E.M.F. before and after the introduction of the
reagent. If the deflections be the same in both cases, we know
that the resistance has not varied. If there have been any
change, the variation of deflection will show the amount, and we
can make allowance accordingly.

I have however adopted another method, by which all necessity
of correction is obviated, and the galvanometric deflections
simply give E.M. variations, unaffected by any change in the
resistance of the tissue. This is done by interposing a very
large and constant resistance in the external circuit and
thereby making other resistances negligible. An example will
make this point clear. Taking a carrot as the vegetable tissue,
I found its resistance plus the resistance of the non-
polarisable electrode equal to 20,000 ohms. The introduction of
a chemical reagent reduced it to 19,000 ohms. The resistance of
the galvanometer is equal to 1,000 ohms. The high external
resistance was 1,000,000 ohms. The variation of resistance
produced in the circuit would therefore be 1,000 in (1,000,000 +
19,000 + 1,000) or one part in 1,020. Therefore the variation of
galvanometric deflection due to change of resistance would be
less than one part in a thousand (cf. fig. 49).

*The advantage of the block method.*  In these
investigations I have used the block method, instead of that of
negative variation, and I may here draw attention to the
advantages which it offers. In the method of negative variation,
one contact being injured, the chemical reagents act on injured
and uninjured unequally, and it is conceivable that by this
unequal action the resting difference of potential may be
altered. But the intensity of response in the method of injury
depends on this resting difference. It is thus hypothetically
possible that on the method of negative variation there might be
changes in the responses caused by variation of the resting
difference, and not necessarily due to the stimulating or
depressing effect of the reagent on the tissue.

But by the block method the two contacts are made with
uninjured surfaces, and the effect of reagents on both is
similar. Thus no advantage is given to one contact over the
other. The changes now detected in response are therefore due to
no adventitious circumstance, but to the reagent itself. If
further verification  be desired as to the effect of the
reagent, we can obtain it by alternate stimulation of the A and
B ends. Both ends will then show the given change. I give below
a record of responses given by two ends of leaf-stalk of turnip,
stimulated alternately in the manner described. The stalk used
was slightly conical, and owing to this difference between the A
and B ends the responses given by one end were slightly
different from those given by the other, though the stimuli were
equal. A few drops of 10 per cent. solution of NaOH was applied
to both the ends. It will be seen how quickly this reagent
abolished the response of both ends (fig. 47).

**Fig. 47.  Abolition of Response at both A and B Ends by the
Action of NaOH**

![](fig047.jpg)

Stimuli of 30 deg vibration were applied at intervals of one
minute to A and B alternately. Response was completely abolished
twenty-four minutes after application of NaOH.

*Effect of dose*.  It is sometimes found that while a
reagent acts as a poison when given in large quantities, it may
act as a stimulant in small doses. Of the two following records
fig. 48 shows the slight stimulating  effect of very dilute
KOH, and fig. 49 exhibits nearly complete abolition of response
by the action of the same reagent when given in stronger doses.

**Fig. 48.Stimulating Action of very dilute KOH**

![](fig048.jpg)

So we see that, judged by the final criterion of the effect
produced by anaesthetics and poisons, the plant response fulfils
the test of vital phenomenon. In previous chapters we have found
that in the matter of response by negative variation, of the
presence or absence of fatigue, of the relation between stimulus
and response, of modification of response by high and low
temperatures, and even in the matter of occasional abnormal
variations such as positive response in a modified tissue, they
were strictly correspondent to similar phenomena in animal
tissues. The remaining test, of the influence of chemical
reagents, having now been applied, a complete parallelism may be
held to have been established between plant response on the one
hand, and that of animal tissue on the other.

**Fig. 49.Nearly Complete Abolition of Response by Strong KOH**

![](fig049.jpg)

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.

---

  
**CHAPTER X**

**RESPONSE IN METALS**

*Is response found in inorganic substances?  Experiment on
tin, block method  Anomalies of existing terminology 
Response by method of depression  Response by method of
exaltation.*

We have now seen that the electrical sign of life is not
confined to animals, but is also found in plants. And we have
seen how electrical response serves as an index to the vital
activity of the plant, how with the arrest of this vital
activity electrical response is also arrested temporarily, as in
the case amongst others of anaesthetic action, and permanently,
for instance under the action of poisons. Thus living tissues 
both animal and vegetable  may pass from a responsive to an
irresponsive condition, from which latter there may or may not
be subsequent revival.

Hitherto, as already said, electrical response in animals has
been regarded as a purely physiological phenomenon. We have
proved by various tests that response in plants is of the same
character. And we have seen that by physiological phenomena are
generally understood those of which no physical explanation can
be offered, they being supposed to be due to the play of some
unknown vital force existing in living substances and giving
rise to electric response to stimulation as one of its
manifestations.

*Is response found in inorganic substances?* [14]  It is
now for us, however, to examine into the alleged super-physical
character of these phenomena by stimulating inorganic substances
and discovering whether they do or do not give rise to the same
electrical mode of response which was supposed to be the special
characteristic of living substances. We shall use the same
apparatus and the same mode of stimulation as those employed in
obtaining plant response, merely substituting, for the stalk of
a plant, a metallic wire, say tin (fig. 50). Any other metal
could be used instead of tin.

*Experiment on tin, block method.*  Let us then take a
piece of tin wire[15] from which all strains have been
previously removed by annealing, and hold it clamped in the
middle at C. If the strains have been successfully removed A and
B will be found iso-electric, and no current will pass through
the galvanometer. If A and B are not exactly similar, there will
be a slight current. But this will not materially affect the
results to be described presently, the slight existing current
merely adding itself algebraically to the current of response.

If we now stimulate the end A by taps, or better  still by
torsional vibration, a transitory current of action will be
found to flow in the wire from B to A, from the unstimulated to
the stimulated, and in the galvanometer from the stimulated to
the unstimulated. Stimulation of B will give rise to a current
in an opposite direction.

**Fig. 50.Electric Response in Metals**

![](fig050.jpg)

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

*Experiment to exhibit the balancing effect.*  If the
wire has been carefully annealed, the molecular condition of its
different portions is found to be approximately the same. If
such a wire be held at the balancing point (which is at or
near the middle) by the clamp, and a quick vibration, say, of
90 deg be given to A, an upward deflection will be produced; if a
vibration of 90 deg be given to B, there will be an equal downward
deflection. If now both the ends A and B are vibrated
simultaneously, the responsive E.M. variation at the two ends
will continuously balance each other and the galvanometer spot
will remain quiescent (fig. 30, A, B, R). This balance will be
still maintained when the block is removed and the wire is
vibrated as a whole. It is to be remembered that with the length
of wire constant,  the intensity of stimulus increases with
the amplitude of vibration. Again, keeping the amplitude
constant, the intensity of stimulus is increased by shortening
the wire. Hence it will be seen that if the clamp be shifted
from the balancing point towards A, simultaneous vibration of A
and B through 90 deg will now give a resultant upward deflection,
showing that the A response is now relatively stronger. Thus
keeping the rest of the circuit untouched, merely moving the
clamp from the left, past the balancing point to the right, we
get either a positive, or zero, or negative, resultant effect.

In tin the current of response is from the less to the more
excited point. In the retina also, we found the current of
action flowing from the less stimulated to the more stimulated,
and as that is known as a positive response, we shall consider
the normal response of tin to be in like manner positive.

Just as the response of retina or nerve, under certain
molecular conditions, undergoes reversal, the positive being
then converted into negative, and negative into positive, so it
will be shown that the response in metallic wires under certain
conditions is found to undergo reversal.

*Anomalies of present terminology.*  When there is no
current of injury, a particular current of response can hardly
be called a negative, or positive, variation. Such nomenclature
is purely arbitrary, and leads, as will be shown, to much
confusion. A more definite terminology, free from
misunderstanding, would be, as already said, to regard the
current towards the more stimulated as positive, and that
towards the less stimulated, in tissue or wire, as negative.

The stimulated end of tin, say the end A, thus becomes 
zincoid, i.e. the current through the electrolyte
(non-polarisable electrodes with interposed galvanometer) is
from A to B, and through the wire, from the less stimulated B to
the more stimulated A. Conversely, when B is stimulated, the
action current flows round the circuit in an opposite direction.
This positive is the most usual form of response, but there are
cases where the response is negative.

In order to show that normally speaking a stimulated wire
becomes zincoid, and also to show once more the anomalies into
which we may fall by adopting no more definite terminology than
that of negative variation, I have devised the following
experiment (fig. 51). Let us take a bar, one half of which is
zinc and the other half copper, clamped in the middle, so that a
disturbance produced at one end may not reach the other; the two
ends are connected to a galvanometer through non-polarisable
electrodes. The current through the electrolyte (non-polarisable
electrodes and interposed galvanometer) will then flow from left
to right. We must remember that metals under stimulation
generally become, in an electrical sense, more zinc-like. On
vibrating the copper end (inasmuch as copper would then become
more zinc-like) the difference of potential between zinc and
copper ought to be diminished, and the current flowing in the
circuit would therefore be lessened. But vibration of the zinc
end ought to increase the potential difference, and there ought
to be then an increase of current during stimulation of zinc.

**Fig. 51.Current of Response towards the Stimulated End**

![](fig051.jpg)

Hence when Cu stimulated: action current ?, normal E.M.F.
diminished (*85-*009) V.

When Zn stimulated: action current ?, normal E.M.F. increased
(*85 + *013) V.

In the particular experiment of fig. 51, the E.M.F. between the
zinc and copper ends was found to be *85 volt. This was balanced
by a potentiometer arrangement, so that the galvanometer spot
came to zero. On vibrating the zinc wire, a deflection of 33
dns. was obtained, in a direction which  showed an increase
of E.M.F. On stopping the vibration, the spot of light came back
to zero. On now vibrating the copper wire, a deflection of 23
dns. was obtained in an opposite direction, showing a diminution
of E.M.F. This transitory responsive variation disappeared on
the cessation of disturbance.

By disturbing the balance of the potentiometer, the
galvanometer deflection due to a known increase of E.M.F. was
found from which the absolute E.M. variation caused by
disturbance of copper or zinc was determined.

It was thus found that stimulation of zinc had increased the
P.D. by fifteen parts in 1,000, whereas stimulation of copper
had decreased it by eleven parts in 1,000. According to the old
terminology, the response due to stimulation of zinc would have
been regarded as positive variation, that of copper negative.
The responses however are not essentially opposite in character,
the action current in the bar being in both cases towards the
more excited. For this reason it would be preferable, as already
said, to employ the terms positive and negative in the sense I
have suggested, i.e. positive, when the current in the acted
substance is towards the more excited, and negative, when
towards the less excited. The method of block is, as I have
already shown, the most perfect for the study of these
responses.

In the experiment fig. 50, if the block is abolished and the
wire is struck in the middle, a wave of molecular disturbance
will reach A and B. The mechanical and the attendant electrical
disturbance will at these points reach a maximum and then
gradually subside. The resultant effect in the galvanometer will
be due to EA-EB when EA and EB are the electrical variations
produced at A and B by the stimulus. The electric changes at A
and B will continuously balance each other, and the resultant
effect on the galvanometer will be zero: (a) if  the
exciting disturbance reaches A and B at the same time and with
the same intensity; (b) if the molecular condition is similar at
the two points; and (c) if the rate of rise and subsidence of
excitation is the same at the two points. In order that a
resultant effect may be exhibited in the galvanometer, matters
have to be so arranged that the disturbance may reach one point,
say A, and not B, and vice versa. This was accomplished by means
of a clamp, in the method of block. Again a resultant
differential action may be obtained even when the disturbance
reaches both A and B, if the electrical excitability of one
point is exalted or depressed by physical or chemical means. We
shall in Chap. XVI study in detail the effect of chemical
reagents in producing the enhancement or depression of
excitability. There are thus two other means of obtaining a
resultant effect  (2) by the method of relative depression, (3)
by the method of relative exaltation.

*Electric response by method of depression.*  We may thus
by reducing or abolishing the excitability of one end by means
of suitable chemical reagents (so-called method of injury)
obtain response in metals without a block. The entire length of
the wire may then be stimulated and a resultant response will be
produced, owing to the difference between the excitability of
the two ends. A piece of tin wire is taken, and one normal
contact is made at A (strip of cloth moistened with water, or
very dilute salt solution). The excitability of B is depressed
by a few drops of strong potash or oxalic acid. By the
application of the latter there will be a small P.D. between A
and B; this will simply  produce a displacement of zero. By
means of a potentiometer the galvanometer spot may be brought
back to the original position. The shifting of the zero will not
affect the general result. The effect of mechanical stimulus is
to produce a transient electro-motive response, which will be
superposed algebraically on the existing P.D. The deflection
will take place from the modified zero to which the spot returns
during recovery. On now stimulating the wire as a whole by, say,
torsional vibration, the current of response will be found
towards the more excitable, i.e. from B to A (fig. 52, a).

**Fig. 52.Response by Method of Depression (Without Block)**

![](fig052.jpg)

When the wire is stimulated as a whole the current of response
is towards the more excitable.

In (a) A is a normal contact, B has been depressed by oxalic
acid; current of response is towards the more excitable A.

In (b) the same wire is used, only A is depressed by oxalic
acid and a normal contact is made at a fresh point B?, a little
to the left of B in (a). Current of response is now from A
towards the more excitable B?.

A corroborative reversal experiment may next be made on the
same piece of wire. The normal contact, through water or salt
solution, is now made at B?, a little to the left of B. The
excitability of A is now depressed by oxalic acid. On
stimulation of the whole wire, the current of response will now
be found to flow in an opposite directioni.e. from A to B?but
still from the relatively less to the relatively more excitable
(fig. 52, b).

From these experiments it will be seen how in one identical
piece of wire the responsive current flows now in one direction
and then in the other, in absolute conformity with theoretical
considerations.

**Fig. 53.Method of Exaltation**

![](fig053.jpg)

The contact B is made more excitable by chemical stimulant
(Na2CO3). The current of response is towards the more excitable
B.

*Method of exaltation.*  A still more striking
corroboration of these results may, however, be obtained by the
converse process of relative exaltation of the responsiveness of
one contact. This may be accomplished by touching one contact,
say B, with a reagent which like Na2CO3 exalts the electric
excitability. On stimulation of the wire, the current of
response is towards the more excitable B (fig. 53).

I give four records (fig. 54) which will clearly exhibit the
responses as obtained by the methods of relative depression or
exaltation. In (a) B is touched with the excitant Na2CO3, a
permanent current flows from A to B, response to stimulus is in
the same direction as the permanent current (positive
variation). In (b) B is touched with a trace of the depressant
oxalic acid, the permanent current is in the same direction as
before, but the current of response is in the opposite direction
(negative variation). In (c) B is touched with dilute KOH, the
response is exhibited by a positive variation. In (d) B is
touched with strong KOH, the response is now exhibited by a
negative variation. The last two results, apparently anomalous,
are due to the fact, which will be demonstrated later, that KOH
in minute quantities is an excitant, while in large quantities
it is a depressant.

**Fig. 54**

![](fig054.jpg)

Permanent Current of Response   
B treated with sodium carbonate.  ? ?   
B treated with oxalic acid  ? ?   
B treated with very dilute potash  ? ?   
B treated with strong potash  ? ?

Current of response is always towards the more excitable point.
  
(a) Response when B is treated with sodium carbonate.An
apparent positive variation.   
(b) Response when B is treated with oxalic acid.An apparent
negative variation.   
(c) Response when B is treated with very dilute potash.Positive
variation.   
(d) Response when B is treated with strong potash.Negative
variation.   
The response is up when B is more excitable, and down when A is
more excitable.

Lines thus ------ indicate deflection due to permanent current.

We have thus seen that we may obtain response (1) by block
method, (2) by the method of injury, or relative depression of
responsiveness of one contact, and (3) by the method of relative
exaltation of responsiveness of one contact. In all these cases
alike we obtain a consistent action current, which in tin is
normally positive, or towards the relatively more excited.

**FOOTNOTES:**

[14] Following another line of inquiry I obtained response to
electric stimulus in inorganic substances using the method of
conductivity variation (see De la Generalite des Phenomenes
Moleculaires Produits par lElectricite sur la Matiere
Inorganique et sur la Matiere Vivante, Travaux du Congres
International de Physique, Paris, 1900; and also On
Similarities of Effect of Electric Stimulus on Inorganic and
Living Substances, British Association 1900. See Electrician).
To bring out the parallelism in all details between the
inorganic and living response, I have in the following chapters
used the method of electro-motive variation employed by
physiologists.

[15] By tin is meant an alloy of tin and lead used as
electric fuse.

---

  
**CHAPTER XI**

**INORGANIC RESPONSEMODIFIED APPARATUS TO EXHIBIT RESPONSE
IN METALS**

*Conditions of obtaining quantitative measurements 
Modification of the block method  Vibration cell 
Application of stimulus  Graduation of the intensity of
stimulus  Considerations showing that electric response is
due to molecular disturbance  Test experiment  Molecular
voltaic cell.*

We have already seen that metals respond to stimulus by E.M.
variation, just as do animal and vegetable tissues. We have yet
to see whether the similarity extends to this point only, or
goes still further, whether the response-curves of living and in
organic are alike, and whether the inorganic response-curve is
modified, as living response was found to be, by the influence
of external agencies. If so, are the modifications similar? What
are the effects of superposition of stimuli? Is there fatigue?
If there be, in what way does it affect the curves? And lastly,
is the response of metals exalted or depressed by the action of
chemical reagents?

*Conditions of obtaining quantitative measurements.*  In
order to carry out these investigations, it is necessary to
remove all sources of uncertainty, and obtain quantitative
measurements. Many difficulties at first presented themselves in
the course of this attempt, but they were  completely
removed by the adoption of the following experimental
modification. In the simple arrangement for qualitative
demonstration of response in metals previously described,
successive experiments will not give results which are strictly
comparable (1) unless the resistance of the circuit be
maintained constant. This would necessitate the adoption of some
plan for keeping the electrolytic contacts at A and B absolutely
invariable. There should then be no chance of any shifting or
variation of contact. (2) There must also be some means of
applying successive stimuli of equal intensity. (3) And for
certain further experiments it will be necessary to have some
way of gradually increasing or decreasing the stimuli in a
definite manner.

*Modification of the block method.*  By consideration of
the following experimental modifications of the block method
(fig. 55), it will be found easy to construct a perfected form
of apparatus, in which all these conditions are fully met. The
essentials to be kept in mind were the introduction of a
complete block midway in the wire, so that the disturbance of
one half should be prevented from reaching the other, and the
making of a perfect electrolytic contact for the electrodes
leading to the galvanometer.

Starting from the simple arrangement previously described where
a straight wire is clamped in the middle (fig. 55, a), we next
arrive at (b). Here the wire A B is placed in a U tube and
clamped in the middle by a tightly fitting cork. Melted paraffin
wax is poured to a certain depth in the bend of the tube. The
two  limbs of the tube are now filled with water, till the
ends A and B are completely immersed. Connection is made with
the non-polarisable electrodes by the side tubes. Vibration may
be imparted to either A or B by means of ebonite clip holders
seen at the upper ends A B of the wire.

**Fig. 55.Successive Modifications of the Block Method from
the Straight Wire (a) to Cell Form (e)**

![](fig055.jpg)

When A is excited, current of response in the wire is from less
excited B to more excited A. Note that though the current of
response is constant in direction, the galvanometer deflection
in (d) will be opposite to that in (b).

It will be seen that the two limbs of the tube filled with
water serve the purpose of the strip of moistened cloth used in
the last experiment to make electric connections with the
leading-out electrodeswith the advantage that we have here no
chance of any shifting of contact or variation of surface, the
contact between  the wire and the surrounding liquid being
perfect and invariable.

On now vibrating the end A of the tin wire by means of the
ebonite clip holder, a current will be found to flow from B to A
through the wirethat is to say, towards the excitedand from A
to B in the galvanometer.

The next modification (c) is to transfer the galvanometer from
the electrolytic to the metallic part of the circuit, that is to
say, it is interposed in a gap made by cutting the wire A B, the
upper part of the circuit being directly connected by the
electrolyte. Vibration of A will now give rise to a current of
response which flows in the metallic part of the circuit with
the interposed galvanometer from B to A. We see that though the
direction of the current in this is the same as in the last
case, yet the galvanometer deflection is now reversed, for the
evident reason that we have it interposed in the metallic and
not in the electrolytic part of the circuit.

The next arrangement (d) consists simply of the preceding
placed upside down. Here A and B are held parallel to each other
in an electrolytic bath (water). Mechanical vibration may now be
applied to A without affecting B, and vice versa.

The actual apparatus, of which this is a diagrammatic
representation, is seen in (e).

Two pieces, from the same specimen of wire, are clamped
separately at their lower ends by means of ebonite screws, in an
L-shaped piece of ebonite. The wires are fixed at their upper
ends to two electrodes  leading to the galvanometer  and kept
moderately and uniformly stretched by spiral springs. The
handle, by which a torsional vibration is imparted to the wire,
may be slipped over either electrode. The amplitude of vibration
is measured by means of a graduated circle.

It will be seen from these arrangements:

(1) That the cell depicted in (e) is essentially the same as
that in (a).

(2) That the wires in the cell being immersed to a definite
depth in the electrolyte there is always a perfect and
invariable contact between the wire and the electrolyte. The
difficulty as regards variation of contact is thus eliminated.

**Fig. 56.Equal and Opposite Responses exhibited by A and B**

![](fig056.jpg)

(3) That as the wires A and B are clamped separately below, we
may impart a sudden molecular disturbance to either A or B by
giving a quick to-and-fro (torsional) vibration round the
vertical wire, as axis, by means of the handle. As the wire A is
separate from B, disturbance of one will not affect the other.
Vibration of A produces a current in one direction, vibration of
B in the opposite direction. Thus we have means of verifying
every experiment by obtaining corroborative and reversed
effects. When the two wires have been brought to exactly the
same molecular condition by the  processes of annealing or
stretching, the effects obtained on subjecting A or B to any
given stimulus are always equal (fig. 56).

Usually I interpose an external resistance varying from one to
five megohms according to the sensitiveness of the wire. The
resistance of the electrolyte in the cell is thus relatively
small, and the galvanometer deflections are proportional to the
E.M. variations. It is always advisable to have a high external
resistance, as by this means one is not only able to keep the
deflections within the scale, but one is not troubled by slight
accidental disturbances.

Graduation of intensity of stimulus.  If now a rapid torsional
vibration be given to A or B, an E.M. variation will be induced.
If the amplitude of vibration be kept constant, successive
responsesin substances which, like tin, show no fatiguewill be
found to be absolutely identical. But as the amplitude of
vibration is increased, response will also become enhanced (see
Chap. XV).

**Fig. 57.Top View of the Vibration Cell**

![](fig057.jpg)

The amplitude of vibration is determined by means of movable
stops S S?, fixed to the edge of the graduated circle G. The
index arm I plays between the stops. (The second index arm,
connected with B, and the second circle are not shown.)

Amplitude of vibration is measured by means of the graduated
circle (fig. 57). A projecting index, in connection with the
vibration-head, plays between fixed and sliding stops (S and
S?), one at the zero point of the scale, and the other
movable.  The amplitude of a given vibration can thus be
predetermined by the adjustment of the sliding stop. In this way
we can obtain either uniform or definitely graduated stimuli.

Considerations showing that electric response is due to
molecular disturbance.The electromotive variation varies with
the substance. With superposition of stimuli, a relatively high
value is obtained in tin, amounting sometimes to nearly half a
volt, whereas in silver the electromotive variation is only
about *01 of this value. The intensity of the response, however,
does not depend on the chemical activity of the substance, for
the electromotive variation in the relatively chemically
inactive tin is greater than that of zinc. Again, the sign of
response, positive or negative, is sometimes modified by the
molecular condition of the wire (see Chap. XII).

As regards the electrolyte, dilute NaCl solution, dilute
solution of bichromate of potash &c. are normal in their
action, that is to say, the electric response in such
electrolytes is practically the same as with water. Ordinarily I
use tap-water as the electrolyte. Zinc wires in ZnSO4 solution
give responses similar in character to those given by, for
example, Pt or Sn in water.

*Test experiment.*  It may be urged that the E.M. effect
is due in some way (1) to the friction of the vibrating wire
against the liquid; or (2) to some unknown surface action, at
the point in the wire of the contact of liquid and air surfaces.
This second objection has already been completely met in experi
mental modification, fig. 55, b, where the wire was shown to
give response when kept completely immersed in water, variation
of surface being thus entirely eliminated.

Both these questions may, however, be subjected to a definite
and final test. When the wire to be acted on is clamped below,
and vibration is imparted to it, a strong molecular disturbance
is produced. If now it be carefully released from the clamp, and
the wire rotated backwards and forwards, there could be little
molecular disturbance, but the liquid friction and surface
variation, if any, would remain. The effect of any slight
disturbance outstanding owing to shaking of the wire would be
relatively very small.

We can thus determine the effect of liquid friction and surface
action by repeating an experiment with and without clamping. In
a tin wire cell, with interposed external resistance equal to
one million ohms, the wire A was subjected to a series of
vibrations through 180 deg, and a deflection of 210 divisions was
obtained. A corresponding negative deflection resulted on
vibrating the wire B. Now A was released from the clamp, so that
it could be rotated backwards and forwards in the water by means
of the handle. On vibrating the wire A no measurable deflection
was produced, thus showing that neither water friction nor
surface variation had anything to do with the electric action.
The vibration of the still clamped B gave rise to the normal
strong deflection.

As all the rest of the circuit was kept absolutely the same in
the two different sets of experiments, these  results
conclusively prove that the responsive electro-motive variation
is solely due to the molecular disturbance produced by
mechanical vibration in the acted wire.

A new and theoretically interesting molecular voltaic cell may
thus be made, in which the two elements consist of the same
metal. Molecular disturbance is in this case the main source of
energy. A cell once made may be kept in working order for some
time by pouring in a little vaseline to prevent evaporation of
the liquid.

It will be shown further, in succeeding chapters, by numerous
instances, that any conditions which increase molecular mobility
will also increase intensity of response, and conversely that
any conditions having the reverse effect will depress response.

---

  
**CHAPTER XII**

**INORGANIC RESPONSE  METHODS OF ENSURING CONSISTENT
RESULTS**

*Preparation of wire  Effect of single stimulus.*

I shall now proceed to describe in detail the response-curves
obtained with metals. The E.M. variations resulting from
stimulus range, as has been said, from *4 volt to *01 of that
value, according to the metal employed. And as these are
molecular phenomena, the effect will also depend on the
molecular condition of the wire.

*Preparation of wire.*  In order to have our results
thoroughly consistent, it is necessary to bring the wire itself
into a normal condition for experiment. The very fact of
mounting it in the cell strains it, and the after-effect of this
strain may cause irregularities in the response.

For the purpose of bringing the wire to this normal state, one
or all of the following devices may be used with advantage. (1)
The wires obtained are usually wound on spools. It is,
therefore, advisable to straighten any given length, before
mounting, by holding it stretched, and rubbing it up and down
with a piece of cloth. On washing with water, they are now ready
for mounting in the cell.

(2) The cell is usually filled with tap-water, and a period of
rest after making up, generally speaking, improves the
sensitiveness. These expedients are ordinarily sufficient, but
it occasionally happens that the wire has got into an abnormal
condition.

**Fig. 58.Effect of Annealing on increasing the Response of
both A and B Wires (Tin)**

![](fig058.jpg)

Stimuli (vibration of 160 deg) applied at intervals of one minute.

In this case it will be found helpful (3) to have recourse to
the process of annealing. For if response be a molecular
phenomenon, then anything that increases molecular mobility will
also increase its intensity. Hence we may expect annealing to
enhance responsiveness. This inference will be seen verified in
the record given in fig. 58. In the case under consideration,
the convenient method employed was by pouring hot water into the
cell, and allowing it to stand and cool slowly. The first three
pairs of responses were taken by stimulating A and B
alternately, on mounting in the cell, which was filled with
water. Hot water was then substituted, and the cell was 
allowed to cool down to its original temperature. The six
following pairs of responses were then taken. That this
beneficial effect of annealing was not due to any accidental
circumstance will be seen from the fact that both wires have
their sensitiveness equally enhanced.

(4) In addition to this mode of annealing, both wires may be
short-circuited and vibrated for a time. Lastly (5) slight
stretching in situ will also sometimes be found beneficial. For
this purpose I have a screw arrangement.

By one or all of these methods, with a little practice, it is
always possible to bring the wires to a normal condition. The
responses subsequently obtained become extraordinarily
consistent. There is therefore no reason why perfect results
should not be arrived at.

**Fig. 59.Uniform Responses in Tin**

![](fig059.jpg)

*Effect of single stimulus.*  The accompanying figure
(fig. 59) gives a series, each of which is the response curve
for a single stimulus of uniform intensity, the amplitude of
vibration being kept constant. The perfect regularity of
responses will be noticed in this figure. The wire after a long
period of rest may be in an abnormal condition, but after a
short period of stimulation the responses become extremely
regular, as may be noticed in this figure. Tin is, usually
speaking, almost indefatigable, and I have often obtained
several hundreds of successive responses showing practically no
fatigue. In the figure it will be noticed that the rising
portion  of the curve is somewhat steep, and the recovery
convex to the abscissa, the fall being relatively rapid in its
first, and less rapid in its later, parts. As the electric
variation is the concomitant effect of molecular disturbancea
temporary upset of the molecular equilibriumon the cessation of
the external stimulus, the excitatory state, and its expression
in electric variation, disappear with the return of the
molecules to their condition of equilibrium. This process is
seen clearly in the curve of recovery.

Different metals exhibit different periods of recovery, and
this again is modified by any influence which affects the
molecular condition.

That the excitatory state persists for a time even on the
cessation of stimulus can be independently shown by keeping the
galvanometer circuit open during the application of stimulus,
and completing it at various short intervals after the
cessation, when a persisting electrical effect, diminishing
rapidly with time, will be apparent. The rate of recovery
immediately on the cessation of stimulus is rather rapid, but
traces of strain persist for a short time.

---

  
**CHAPTER XIII**

**INORGANIC RESPONSEMOLECULAR MOBILITY: ITS INFLUENCE ON
RESPONSE**

*Effects of molecular inertia  Prolongation of period of
recovery by overstrain  Molecular model  Reduction of
molecular sluggishness attended by quickened recovery and
heightened response  Effect of temperature  Modification of
latent period and period of recovery by the action of chemical
reagents  Diphasic variation.*

We have seen that the stimulation of matter causes an electric
variation, and that the acted substance gradually recovers from
the effect of stimulus. We shall next study how the form of
response-curves is modified by various agencies.

In order to study these effects we must use, in practice, a
highly sensitive galvanometer as the recorder of E.M.
variations. This necessitates the use of an instrument with a
comparatively long period of swing of needle, or of suspended
coil (as in a DArsonval). Owing to inertia of the recording
galvanometer, however, there is a lag produced in the records of
E.M. changes. But this can be distinguished from the effect of
the molecular inertia of the substance itself by comparing two
successive records taken with the same instrument, in one of
which the latter effect is relatively absent, and in the other
present. We wish, for example, to find out  whether the
E.M. effect of mechanical stimulus is instantaneous, or, again,
whether the effect disappears immediately. We first take a
galvanometer record of the sudden introduction and cessation of
an E.M.F. on the circuit containing the vibration-cell (fig. 60,
a). We then take a record of the E.M. effect produced by a
stimulus caused by a single torsional vibration. In order to
make the conditions of the two experiments as similar as
possible, the disturbing E.M.F., from a potentiometer, is
previously adjusted to give a deflection nearly equal to that
caused by stimulus. The torsional vibration was accomplished in
a quarter of a second, and the contact with the potentiometer
circuit was also made for the same length of time.

**Fig. 60**

![](fig060.jpg)

(a) Arrangement for applying a short-lived E.M.F.   
(b) Difference in the periods of recovery: (1) from
instantaneous E.M.F.; and (2) that caused by mechanical
stimulus.

The record was then taken as follows. The recording drum had a
fast speed of six inches in a minute, one of the small
subdivisions representing a second. The battery contact in the
main potentiometer circuit was made for a quarter of a second as
just mentioned and a record taken of the effect of a short-lived
E.M.F.  on the circuit containing the cell. (2) A record
was next taken of the E.M. variation produced in the cell by a
single stimulus. It will be seen on comparison of the two
records that the maximum effect took place relatively later in
the case of mechanical stimulus, and that whereas the
galvanometer recovery in the former case took place in 11
seconds, the recovery in the latter was not complete till after
60 seconds (fig. 60, b). This shows that it takes some time for
the effect of stimulus to attain its maximum, and that the
effect does not disappear till after the lapse of a certain
interval. The time of recovery from strain depends on the
intensity of stimulus. It takes a longer time to recover from a
stronger stimulus. But, other things being equal, successive
recovery periods from successive stimulations of equal intensity
are, generally speaking, the same.

We may now study the influence of any change in external
conditions by observing the modifications it produces in the
normal curve.

**Fig. 61.Prolongation of Period of Recovery after Overstrain**

![](fig061.jpg)

Recovery is complete in 60? when the stimulus is due to 20 deg
vibration. But with stronger stimulus of 40 deg vibration, the
period of recovery is prolonged to 90?.

*Prolongation of period of recovery by overstrain.*  The
pair of records given in fig. 61 shows how  recovery is
delayed, as the effect of overstrain. Curve (a) is for a single
stimulus due to a vibration of amplitude 20 deg, and curve (b) for
a stimulus of 40 deg amplitude of vibration. It will be noticed how
relatively prolonged is the recovery in the latter case.

**Fig. 62.Model showing the Effect of Friction**

![](fig062.jpg)

*Molecular Model.*  We have seen that the electric
response is an outward expression of the molecular disturbance
produced by the action of the stimulus. The rising part of the
response-curve thus exhibits the effect of molecular upset, and
the falling part, or recovery, the restoration to equilibrium.
The mechanical model (fig. 62) will help us to visualise many
complex response phenomena. The molecular model consists of a
torsional penduluma wire with a dependent sphere. By the
stimulus of a blow there is produced a torsional vibrationa
response followed by recovery. The writing lever attached to the
pendulum records  the response-curves. The form of these
curves, stimulus remaining constant, will be modified by
friction; the less the friction, the greater is the mobility.
The friction may be varied by more or less raising a vessel of
sand touching the pendulum. By varying the friction the
following curves were obtained.

(a) When there is little friction we get an after-oscillation,
to which we have the corresponding phenomenon in the retinal
after-oscillation (compare fig. 105).

(b and c) If the friction is increased, there is a damping of
oscillation. In (c) we get recovery-curves similar to those
found in nerve, muscle, plant, and metal.

(d) If the friction is still further increased the maximum is
reached much later, as will be seen in the increasing slant of
the rising part of the curve; the height of response is
diminished and the period of recovery very much prolonged by
partial molecular arrest. The curve (d) is very similar to the
molecular arrest curve obtained by small dose of chemical
reagents which act as poison on living tissue or on metals
(compare fig. 93, a).

(e) When the molecular mobility is further decreased there is
no recovery (compare fig. 93, b).

Still further increase of friction completely arrests the
molecular pendulum, and there is no response.

From what has been said, it will be seen that if in any way the
friction is diminished or mobility increased the response will
be enhanced. This is well exemplified in the heightened response
after annealing (fig. 58) and after preliminary vibration (figs.
81, 82).

Possibly connected with this may be the increased responses
exhibited by the action of stimulants (figs. 89, 90).

Reduction of molecular sluggishness attended (1) by quickened
recovery.Sometimes, after a cell has been resting for too long
a period, especially on cold days, the wire gets into a sluggish
condition, and the period of recovery is thereby prolonged. But
successive vibrations gradually remove this inertness, and
recovery is then hastened. This is shown in the accompanying
curves, fig. 63, where (a) exhibits only very partial recovery
even after the expiration of 60 seconds, whereas when a few
vibrations had been given recovery was entirely completed in 47
seconds (b). There was here little change in the height of
response.

**Fig. 63**

![](fig063.jpg)

(a) Slow recovery of a wire in a sluggish condition.   
(b) Quickened recovery in the same wire after a few vibrations.

Or (2) by heightened response.  The removal of sluggishness by
vibration, resulting in increased molecular mobility, is in
other instances attended by increase in the height of response,
as will be seen from the two sets of records which follow (fig.
64). Cold, due to prevailing frosty weather, had made the wires
in the cell somewhat lethargic. The records in (a) were 
the first taken on the day of the experiment. The amplitudes of
vibration were 45 deg, 90 deg, and 135 deg. In (b) are given the records
of the next series, which are in every case greater than those
of (a). This shows that previous vibration, by conferring
increased mobility, had heightened the response. In this case,
removal of molecular sluggishness is attended by greater
intensity of response, without much change in the period of
recovery. In connection with this it must be remembered that
greater strain consequent on heightened response has a general
tendency to a prolongation of the period of recovery.

**Fig. 64**

![](fig064.jpg)

(a) Three sets of responses for 45 deg, 90 deg, and 135 deg vibration in
a sluggish wire.   
(b)The next three sets of responses in the same wire; increased
mobility conferred by previous vibration has heightened the
response.

It is thus seen that when the wire is in a sluggish condition,
successive vibrations confer increased molecular mobility, which
finds expression in quickened recovery or heightened response.

*Effect of temperature.*  Similar considerations lead us
to expect that a moderate rise of temperature will be conducive
to increase of response. This is exhibited in  the next
series of records. The wire at the low temperature of 5 deg C.
happened to be in a sluggish condition, and the responses to
vibrations of 45 deg to 90 deg in amplitude were feeble. Tepid water
at 30 deg C. was now substituted for the cold water in the cell,
and the responses underwent a remarkable enhancement. But the
excessive molecular disturbance caused by the high temperature
of 90 deg C. produced a great diminution of response (fig. 65).

**Fig. 65.Responses of a Wire To Amplitudes of Vibration 45 deg
and 90 deg**

![](fig065.jpg)

(a) Responses when the wire was in a sluggish condition at
temperature of 5 deg C.   
(b) Enhanced response at 30 deg C.   
(c) Diminution of response at 90 deg C.

*Diphasic variation.*  It has already been said that if
two points A and B are in the same physico-chemical condition,
then a given stimulus will give rise to similar excitatory
electric effects at the two points. If the  galvanometer
deflection is up when A alone is excited, the excitation of B
will give rise to a downward deflection. When the two points are
simultaneously excited the electric variation at the two points
will continuously balance each other. Under such conditions
there will be no resultant deflection. But if the intensity of
stimulation of one point is relatively stronger, then the
balance will be disturbed, and a resultant deflection produced
whose sign and magnitude can be found independently by the
algebraical summation of the individual effects of A and B.

It has also been shown that a balancing point for the block,
which is approximately near the middle of the wire, may be found
so that the vibrations of A and B through the same amplitude
produce equal and opposite deflection. Simultaneous vibration of
both will give no resultant current; when the block is abolished
and the wire is vibrated as a whole, there will still be no
resultant, inasmuch as similar excitations are produced at A and
B.

After obtaining the balance, if we apply an exciting reagent
like Na2CO3 at one point, and a depressing reagent like KBr at
the other, the responses will now become unequal, the more
excitable point giving a stronger deflection. We can, however,
make the two deflections equal by increasing the amplitude of
vibration of the less sensitive point. The two deflections may
thus be rendered equal and opposite, but the time relationsthe
latent period, the time rate for attaining the maximum
excitation and recovery from that effectwill no longer be the
same in the two cases. There would therefore  be no
continuous balance, and we obtain instead a very interesting
diphasic record. I give below an exact reproduction of the
response-curves of A and B recorded on a fast-moving drum. It
will be remembered that one point was touched with Na2CO3 and
the other with KBr. By suitably increasing the amplitude of
vibration of the less sensitive, the two deflections were
rendered approximately equal. The records of A and B were at
first taken separately (fig. 66, a). It will be noticed that the
maximum deflection of A was attained relatively  much
earlier than that of B. The resultant curve R? was obtained by
summation.

**Fig. 66.Diphasic Variation**

![](fig066.jpg)

(a) Records of A and B obtained separately. R? is the resultant
by algebraical summation. (b) Diphasic record obtained by
simultaneous stimulation of A and B.

After taking the records of A and B separately, a record of
resultant effect R due to simultaneous vibration of A and B was
next taken. It gave the curious two-phased responsepositive
effect followed by negative after-vibration, practically similar
to the resultant curve R? (fig. 66, b).

The positive portion of the curve is due to A effect and the
negative to B. If by any means, say by either increasing the
amplitude of vibration of A or increasing its sensitiveness, the
response of A is very greatly enhanced, then the positive effect
would be predominant and the negative effect would become
inconspicuous. When the two constituent responses are of the
same order of magnitude, we shall have a positive response
followed by a negative after-vibration; the first twitch will
belong to the one which responds earlier. If the response of A
is very much reduced, then the positive effect will be reduced
to a mere twitch and the negative effect will become
predominant.

I give a series of records, fig. 67, in which these three
principal types are well exhibited, the two contacts having been
rendered unequally excitable by solutions of the two reagents
KBr and Na2CO3. A and B were vibrated simultaneously and records
taken. (a) First, the relative response of B (downward) is
increased by increasing its amplitude of vibration. The
amplitude of vibration of A was throughout maintained constant.
The negative or downward response is now very conspicuous, there
being only a mere preliminary indication  of the positive
effect. (b) The amplitude of vibration of B is now slightly
reduced, and we obtain the diphasic effect. (c) The intensity of
vibration of B is diminished still further, and the negative
effect is seen reduced to a slight downward after-vibration, the
positive up-curve being now very prominent (fig. 67).

**Fig. 67.Negative, Diphasic, and Positive Resultant Response**

![](fig067.jpg)

*Continuous transformation from negative to positive.*  I
have shown the three phases of transformation, the intensity of
one of the constituent responses being varied by altering the
intensity of disturbance.

In the following record (fig. 68) I succeeded in obtaining a
continuous transformation from positive to negative phase by a
continuous change in the relative sensitiveness of the two
contacts.

I found that traces of after-effect due to the application of
Na2CO3 remain for a time. If the reagent is previously applied
to an area and the traces of the  carbonate then washed
off, the increased sensitiveness conferred disappears gradually.
Again, if we apply Na2CO3 solution to a fresh point, the
sensitiveness gradually increases. There is another further
interesting point to be noticed: the beginning of response is
earlier when the application of Na2CO3 is fresh.

**Fig. 68.  Continuous Transformation from Negative To
Positive through Intermediate Diphasic Response**

![](fig068.jpg)

Thick dots represent the times of application of successive
stimuli.

We have thus a wire held at one end, and successive uniform
vibrations at intervals of one minute imparted to the wire as a
whole, by means of a vibration head on the other end.

Owing to the after-effect of previous application of Na2CO3 the
sensitiveness of B is at the beginning great, hence the three
resultant responses at the beginning are negative or downward.

Dilute solution of Na2CO3 is next applied to A. The response of
A (up) begins earlier and continues to grow stronger and
stronger. Hence, after this application, the response shows a
preliminary positive twitch of A followed by negative deflection
of B. The positive grows  continuously. At the fifth
response the two phases, positive and negative, become equal,
after that the positive becomes very prominent, the negative
being reduced as a feeble after-vibration.

It need only be added here that the diphasic variations as
exhibited by metals are in every way counterparts of similar
phenomena observed in animal tissues.

---

  
**CHAPTER XIV**

**INORGANIC RESPONSEFATIGUE, STAIRCASE, AND MODIFIED
RESPONSE**

*Fatigue in metals  Fatigue under continuous stimulation 
Staircase effect  Reversed responses due to molecular
modification in nerve and metal, and their transformation into
normal after continuous stimulation  Increased response after
continuous stimulation.*

**Fig. 69.Fatigue in Muscle (Waller)**

![](fig069.jpg)

*Fatigue.*  In some metals, as in muscle and in plant, we
find instances of that progressive diminution of response which
is known as fatigue (fig. 69). The accompanying record shows
this in platinum (fig. 70). It has been said that tin is
practically indefatigable. We must, however, remember that this
is a question of degree only. Nothing is absolutely
indefatigable. The exhibition of fatigue depends on various
conditions. Even in tin, then, I obtained the characteristic
fatigue-curve with a specimen which had been in continuous use
for  many days (fig. 71). While discussing the subject of
fatigue in plants, I have adduced considerations which showed
that the residual effect of strain was one of the main causes
for the production of fatigue. This conclusion receives
independent support from the records obtained with metals.

**Fig. 70.Fatigue in Platinum**

![](fig070.jpg)

**Fig. 71.Fatigue Shown by Tin Wire which had been
Continuously Stimulated for Several Days**

![](fig071.jpg)

In this connection the important fact is that the various
typical fatigue effects exhibited in living substances are
exactly reproduced in metals, where there can be question
neither of fatigue-product producing fatigue effects, nor of
those constructive processes by which they might be removed. We
have seen, both in muscles and in plants, that if sufficient
time for complete recovery be allowed between each pair of
stimuli, the heights of successive responses are the same, and
there is no apparent fatigue (see page 39). But the height of
response diminishes as the excitation interval is shortened. We
find the same thing in metals. Below is given a record taken
with tin (fig. 72). Throughout the experiment the amplitude of
vibration was maintained constant, but in (a) the interval
between consecutive stimuli was 1?, while in (b) this was
reduced to 30?. A diminution of height immediately occurs. On
restoring the original rhythm as in (c), the responses revert to
their first large value.  Thus we see that when the wire
has not completely recovered, its responses, owing to residual
strain, undergo diminution. Height of response is thus decreased
by incomplete recovery. If then sufficient time be not allowed
for perfect recovery, we can understand how, under certain
circumstances, the residual strain would progressively increase
with repetition of stimulus, and thus there would be a
progressive diminution of height of response or fatigue. Again,
we saw in the last chapter that increase of strain necessitates
a longer period of recovery. Thus the longer a wire is
stimulated, the more and more overstrained it becomes, and it
therefore requires a gradual prolongation of the interval
between the successive stimuli, if recovery is to be complete.
This interval, however, being maintained constant, the recovery
periods virtually undergo a gradual reduction, and successive
recoveries become  more and more incomplete. These
considerations may be found to afford an insight into the
progressive diminution of response in fatigued substances.

**Fig. 72.Diminution of Response due to Shortening the Period
of Recovery**

![](fig072.jpg)

The stimulus is maintained constant. In (a) the interval
between two successive stimuli is one minute, in (b) it is half
a minute, and in (c) it is again one minute. The response in (b)
is feebler than in either (a) or (c).

Fatigue under continuous stimulation.  Fatigue is perhaps best
shown under continuous stimulation. For example, in muscles,
when fresh and not fatigued, the top of the tetanic curve is
horizontal, or may even be ascending, but with long-continued
stimulation the curve declines. The rapidity of this decline
depends on the nature of the muscle and its previous condition.

In metals I have found exactly parallel instances. In tin, so
little liable to fatigue, the top of the curve is horizontal or
ascending; or it may exhibit a slight decline. But the record
with platinum shows the rapid decline due to fatigue (fig. 73).

**Fig. 73**

![](fig073.jpg)

(a) The top of response-curve under continuous stimulation in
tin is horizontal or ascending as in figure.   
(b) In platinum there is rapid decline owing to fatigue.

Taking any of these instances, say that in which fatigue is
most prominent, it is found that short period of rest restores
the original intensity of response. This affords additional
proof of the fact that fatigue is due to overstrain, and that
this strain, with its sign of attendant fatigue, disappears with
time.

*Staircase effect.*  We shall now discuss an effect which
appears to be the direct opposite of fatigue. This is the
curious phenomenon known to physiologists as the staircase
effect, in which successive uniform stimuli produce a series of
increasing responses. This  is seen under particular
conditions in the response of certain muscles (fig. 74, a). It
is also observed sometimes even in nerve, which otherwise,
generally speaking, gives uniform responses. Of this effect, no
satisfactory theory has as yet been offered. It is in direct
contradiction to that theory which supposes that each stimulus
is followed by dissimilation or break-down of the tissue,
reducing its function below par. For in these cases the supposed
dissimilation is followed not by a decrease but by an increase
of functional activity. This staircase effect I have shown to
be occasionally exhibited by plants. I have also found it in
metals. In the last chapter we have seen that a wire often
falls, especially after resting for a long time, into a state of
comparative sluggishness, and that this molecular inertness then
gradually gives place to increased mobility under stimulation.
As a consequence, an increased response is thus obtained. I give
in fig. 74, b, a series of responses to uniform stimuli,
exhibited by platinum which had been at rest for some time. This
effect is very clearly shown here. So we see that in a substance
which has previously been in a sluggish condition, stimulation
confers increased mobility. Response thus reaches a maximum, but
continued stimulation may afterwards produce overstrain, and the
subsequent responses may then show a decline. This consideration
will explain certain types of responses  exhibited by
muscles, where the first part of the series exhibits a staircase
increase followed by declining responses of fatigue.

**Fig. 74.Staircase Effect**

![](fig074.jpg)

(a) in muscle (after Engelmann).   
(b) in metal.

Reversed response due to molecular modification and its
transformation into normal after continuous stimulation (1) in
nerve.Reference has already been made to the fact that a nerve
which, when fresh, exhibited the normal negative response, will
often, if kept for some time in preservative saline, undergo a
molecular modification, after which it gives a positive
variation. Thus while the response given by fresh nerve is
normal or negative, a stale nerve gives modified, i.e. reversed
or positive, response. This peculiar modification does not
always occur, yet is too frequent to be considered abnormal.
Again, when such a nerve is subjected to tetanisation or
continuous stimulation, this modified response tends once more
to become normal.

It is found that not only tetanisation, but also CO2 has the
power of converting the modified response into normal. Hence it
has been suggested that the conversion under tetanisation of
modified response to normal, in stale nerve, is due to a
hypothetical evolution of CO2 in the nerve during
stimulation.[16]

(2) In metals.  I have, however, met with exactly parallel
phenomena in metals, where, owing to some molecular
modification, the responses became reversed, and where, under
continuous stimulation, though here  there could be no
possibility of the evolution of CO2, they tended again to become
normal.

If after mounting a wire in a cell filled with water, it be set
aside for too long a time, I have sometimes noticed that it
undergoes a certain modification, owing to which its response
ceases to be normal and becomes reversed in sign. I have
obtained this effect with various metals, for instance lead and
tin, and even with the chemically inactive substanceplatinum.

**Fig. 75.Abnormal Positive (up) Response in Nerve Converted
into Normal (down) Response after Continuous Stimulation T
(Waller)**

![](fig075.jpg)

The galvanometer is not dead-beat, and shows after-oscillation.

The subject will be made clearer if we first follow in detail
the phenomenon exhibited by modified nerve, giving this abnormal
response. The normal responses in nerve are usually represented
by down and the reversed abnormal responses by up curves. In
the modified nerve, then, the abnormal responses are up
instead of the normal down. The record of such abnormal
response in the modified nerve is shown in fig. 75. It will be
noticed that in this, the successive  responses are
undergoing a diminution, or tending towards the normal. After
continuous stimulation or tetanisation (T), it will be seen that
the abnormal or up responses are converted into normal or
down.

I shall now give a record which will exhibit an exactly similar
transformation from the abnormal to normal response after
continuous stimulation. Here the normal responses are
represented by up and the abnormal by down curves. This
record was given by a tin wire, which had been molecularly
modified (fig. 76). We have at first the abnormal responses;
successive responses are undergoing a diminution or tending
towards the normal; after continuous stimulation (T), the
subsequent responses are seen to have become normal. Another
record, obtained with platinum, shows the same phenomenon (fig.
77).

**Fig. 76 and Fig. 77**

![](fig076.jpg)![](fig077.jpg)

Abnormal down response in tin (fig. 76) and in platinum (fig.
77) transformed into normal up response, after continuous
stimulation, T.

On placing the three sets of records  nerve, tin, and 
platinum  side by side, it will be seen how essentially similar
they are in every respect.[17]

This reversion to normal is seen to have appeared in a
pronounced manner after rapidly continuous stimulation, in
process of which the modified molecular condition must in some
way have reverted to the normal.

**Fig. 78.The Gradual Transition from Abnormal To Normal
Response in Platinum**

![](fig078.jpg)

The transition will be seen to have commenced at the third and
ended at the seventh, counting from the left.

Being desirous to trace this change gradually taking place, I
took a platinum wire cell giving modified responses, and
obtained a series of records of effects of individual stimuli
continued for a long time. In this series, the points of
transition from modified response to normal will be clearly seen
(fig. 78).

**Fig. 79.The Normal Response a in Nerve Enhanced to b after
Continuous Stimulation T (Waller)**

![](fig079.jpg)

The normal response in nerve is recorded down.

**Fig. 80.Enhanced Response in Platinum after Continuous
Stimulation T**

![](fig080.jpg)

*Increased response after continuous stimulation.*  We
have seen that responses to uniform stimuli sometimes show a
staircase increase, apparently owing to the gradual removal of
molecular sluggishness. Possibly analogous to this is the
increase of response in nerve after continuous stimulation or
tetanisation, observed by Waller (fig. 79). Like the staircase
effect, this contravenes the commonly accepted theory of the
dissimilation of tissue by stimulus, and the consequent
depression of response. It is suggested by Waller that 
this increase of response after tetanisation may be due to the
hypothetical evolution of CO2 to which allusion has previously
been made.

**Fig. 81.Enhanced Response in Tin After Continuous
Stimulation T**

![](fig081.jpg)

But there is an exact correspondence between this phenomenon
and that exhibited by metals under similar conditions. I give
here two sets of records (figs. 80, 81), one obtained with
platinum and the other with tin, which demonstrate how the
response is enhanced after continuous stimulation in a manner
exactly similar to that noticed in the case of nerve.

The explanation which has been suggested with regard to the
staircase effect  increased molecular mobility due to removal
of sluggishness by repeated stimulationwould appear to be
applicable in this case  also. It would appear, then, that
in all the phenomena which we have studied under the heads of
staircase effect, increase of response after continuous
stimulation, and fatigue, there is a similarity between the
observations made upon the response of muscle and nerve on the
one hand, and that of metals on the other. Even in their
abnormalities we have seen an agreement.

But amongst these phenomena themselves, though at first sight
so diverse, there is some kind of continuity. Calling all normal
response positive, for the sake of convenience, we observe its
gradual modification, corresponding 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 negative.

Continued stimulation, however, brings back the molecular
condition to normal, as evidenced by the progressive lessening
of the negative response, culminating in reversion to the normal
positive. 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 a
relative inertness, and the responses, though positive, are
feeble. Under continued stimulation, they increase in the same
direction as in the last case, that is to say, from less
positive to more positive, 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 positive
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 positive
to less positive; fatigue, that is to say, appears.

Again, under very much prolonged stimulation the response may
decline to zero, or even undergo a reversal to negative, 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 indications of these
conditions. A complete cycle of molecular modifications can be
traced, from the abnormal negative to the normal positive, and
then again to negative seen in reversal under continuous
stimulation.

**FOOTNOTES:**

[16] Considering that we have no previous evidence of any
chemical or physical change in tetanised nerve, it seems to me
not worth while pausing to deal with the criticism that it is
not CO2, but something else that has given the result. 
Waller, *Animal Electricity*, p. 59. That this phenomenon
is nevertheless capable of physical explanation will be shown
presently.

[17] In order to explain the phenomena of electric response,
some physiologists assume that the negative response is due to a
process of dissimilation, or breakdown, and the positive to a
process of assimilation, or building up, of the tissue. The
modified or positive response in nerve is thus held to be due to
assimilation; after continuous stimulation, this process is
supposed to be transformed into one of dissimilation, with the
attendant negative response.

How arbitrary and unnecessary such assumptions are will become
evident, when the abnormal and normal responses, and their
transformation from one to the other, are found repeated in all
details in metals, where there can be no question of the
processes of assimilation or dissimilation.

---

  
**CHAPTER XV**

**INORGANIC RESPONSERELATION BETWEEN STIMULUS AND
RESPONSESUPERPOSITION OF STIMULI**

*Relation between stimulus and response  Magnetic analogue 
Increase of response with increasing Stimulus  Threshold of
response  Superposition of Stimuli  Hysteresis.*

*Relation between stimulus and response.* We have seen
what extremely uniform responses are given by tin, when the
intensity of stimulus is maintained constant. Hence it is
obvious that these phenomena are not accidental, but governed by
definite laws. This fact becomes still more evident when we
discover how invariably response is increased by increasing the
intensity of stimulus.

Electrical response is due, as we have seen, to a molecular
disturbance, the stimulus causing a distortion from a position
of equilibrium. In dealing with the subject of the relation
between the disturbing force and the molecular effect it
produces, it may be instructive to consider certain analogous
physical phenomena in which molecular deflections are also
produced by a distorting force.

*Magnetic analogue.* Let us consider the effect that a
magnetising force produces on a bar of soft iron. It is known
that each molecule in such a bar is an  individual magnet.
The bar as a whole, nevertheless, exhibits no external
magnetisation. This is held to be due to the fact that the
molecular magnets are turned either in haphazard directions or
in closed chains, and there is therefore no resultant polarity.
But when the bar is subjected to a magnetising force by means,
say, of a solenoid carrying electrical current, the individual
molecules are elastically deflected, so that all the molecular
magnets tend to place themselves along the lines of magnetising
force. All the north poles thus point more or less one way, and
the south poles the other. The stronger the magnetising force,
the nearer do the molecules approach to a perfect alignment, and
the greater is the induced magnetisation of the bar.

The intensity of this induced magnetisation may be measured by
noting the deflection it produces on a freely suspended magnet
in a magnetometer.

The force which produces that molecular deflection, to which
the magnetisation of the bar is immediately due, is the
magnetising current flowing round the solenoid. The
magnetisation, or the molecular effect, is measured by the
deflection of the magnetometer. We may express the relation
between cause and effect by a curve in which the abscissa
represents the magnetising current, and the ordinate the
magnetisation produced (fig. 82).

**Fig. 82.Curve of Magnetisation**

![](fig082.jpg)

In such a curve we may roughly distinguish three parts. In the
first, where the force is feeble, the mole cular deflection is
slight. In the next, the curve is rapidly ascending, i.e. a
small variation of impressed force produces a relatively large
molecular effect. And lastly, a limit is reached, as seen in the
third part, where increasing force produces very little further
effect. In this cause-and-effect curve, the first part is
slightly convex to the abscissa, the second straight and
ascending, and the third concave.

*Increase of response with increasing stimulus.*  We
shall find in dealing with the relation between the stimulus and
the molecular effecti.e. the responsesomething very similar.

On gradually increasing the intensity of stimulus, which may be
done, as already stated, by increasing the amplitude of
vibration, it will be found that, beginning with feeble
stimulation, this increase is at first slight, then more
pronounced, and lastly shows a tendency to approach a limit. In
all this we have a perfect parallel to corresponding phenomena
in animal and vegetable response. We saw that the proper
investigation of this subject was much complicated, in the case
of animal and vegetable tissues, by the appearance of fatigue.
The comparatively indefatigable nature of tin causes it to offer
great advantages in the pursuit of this inquiry. I give below
two series of records made with tin. The first record, fig. 83,
is for increasing amplitudes from 5 deg to 40 deg by steps of 5 deg. The
stimuli are imparted at intervals of one minute. It will be
noticed that whereas the recovery is complete in one minute when
the stimulus is moderate, it is not quite complete when the
stimulus is stronger. The  recovery from the effect of
stronger stimulus is more prolonged. Owing to want of complete
recovery, the base line is tilted slightly upward. This slight
displacement of the zero line does not materially affect the
result, provided the shifting is slight.

**Fig. 83.  Records of Responses in Tin with Increasing
Stimuli, Amplitudes of Vibration from 5 deg to 40 deg**

![](fig083.jpg)

The vertical line to the right represents *1 volt.

**Table showing the Increasing Electric Response due to
Increasing Amplitude of Vibration**   
Vibration amplitude E.M. variation   
5 deg   *024 volt   
10 deg   *057    "   
20 deg   *111    "   
25 deg   *143    "   
30 deg   *170    "   
35 deg   *187    "   
40 deg   *204    "

**Fig. 84.  A Second Set of Records with a Different Specimen
of Tin**

![](fig084.jpg)

The amplitudes of vibration are increased by steps of 10 deg, from
20 deg to 160 deg. (The deflections are reduced by interposing a high
external resistance.)   
The next figure (fig. 84) gives record of responses 
through a wider range. For accurate quantitative measurements it
is preferable to wait till the recovery is complete. We may
accomplish this within the limited space of the recording
photographic plate by making the record for one minute; during
the rest of recovery, the clockwork moving the plate is stopped
and the galvanometer spot of light is cut off. Thus the next
record starts from a point of completed recovery, which will be
noticed as a bright spot at the beginning of each curve. With
stimulation of high intensity, a tendency will be noticed for
the responses to approach a limit.

**Fig. 85.  Effect of Superposition on Tin**

![](fig085.jpg)

A single stimulus produces the feeble effect shown in the first
response. Superposition of 5, 9, 13 such stimuli produce the
succeeding stronger responses.

*Threshold of response.*  There is a minimum intensity
of stimulus below which there is hardly any visible response. We
may regard this point as the threshold of response. Though
apparently ineffective, the subliminal stimuli produce some
latent effect, which may be demonstrated by their additive
action. The  record in fig. 85 shows how individually
feeble stimuli become markedly effective by superposition.

*Superposition of stimuli.*  The additive effect of
succeeding stimuli will be seen from the above. The fusion of
effect will be incomplete if the frequency of stimulation be not
sufficiently great; but it will tend to be more complete with
higher frequency of stimulation (fig. 86). We have here a
parallel case to the complete and incomplete tetanus of muscles,
under similar conditions.

By the addition of these rapidly succeeding stimuli, a maximum
effect is produced, and further stimulation adds nothing to
this. The effect is balanced by a force  of restitution.
The response-curve thus rises to its maximum, after which the
deflection is held as it were rigid, so long as the vibration is
kept up.

It was found that increasing intensities of single stimuli
produced correspondingly increased responses. The same is true
also of groups of stimuli. The maximum effect produced by
superposition of stimuli increases with the intensity of the
constituent stimuli.

**Fig. 86.Incomplete and Complete Fusion of Effect in Tin**

![](fig086.jpg)

As the frequency of stimulation is increased the fusion becomes
more and more complete. Vertical line to the right represents *1
volt.

*Hysteresis.*  Allusion has already been made to the
increased responsiveness conferred by preliminary stimulation
(see p. 127). Being desirous of finding out in what manner this
is brought about, I took a series  of observations for an
entire cycle, that is to say, a series of observations were
taken for maximum effects, starting from amplitude of vibration
of 10 deg and ending in 100 deg, and backwards from 100 deg to 10 deg.
Effect of hysteresis is very clearly seen (see A, fig. 87);
there is a considerable divergence between the forward and
return curves, the return curve being higher. On repeating the
cycle several times, the divergence is found very much reduced,
the wire on the whole is found to assume a more constant
sensitiveness. In this steady condition, generally speaking, the
sensitiveness for smaller amplitude of vibration is found to be
greater than at the very beginning, but the reverse is the case
for stronger intensity of stimulation.

**Fig. 87.Cyclic Curve for Maximum Effects showing Hysteresis**

![](fig087.jpg)

*Effect of annealing.*  I repeated the experiment with
the same wire, after pouring hot water into the cell and
allowing it to cool to the old temperature. From the cyclic
curve (B, fig. 87) it will be seen (1) that the sensitiveness
has become very much enhanced; (2) that there is relatively less
divergence between the forward and return curves. Even this
divergence practically disappeared at the third cycle, when the
forward and backward curves coincided (C, fig. 87). The above
results show in what manner the excitability of the wire is
enhanced by purely physical means.

It is very curious to notice that addition of Na2CO3 solution
(see Chap. XV  Action of Stimulants) produces enhancement of
responsive power similar to that produced by annealing; that is
to say, not only is there a great increase of sensitiveness, but
there is also a reduction of hysteresis.

---

  
**CHAPTER XVI**

**INORGANIC RESPONSEEFFECT OF CHEMICAL REAGENT**

*Action of chemical reagents  Action of stimulants on metals
 Action of depressants on metals  Effect of poisons on
metals  Opposite effect of large and small doses.*

We have seen that the ultimate criterion of the physiological
character of electric response is held to be its abolition when
the substance is subjected to those chemical reagents which act
as poisons.

**Fig. 88.Action of Poison in Abolishing Response in Nerve
(Waller)**

![](fig088.jpg)

*Action of chemical reagents.*  Of these reagents, some
are universal in their action, amongst which strong solutions of
acids and alkalis, and salts like mercuric chloride, may be
cited. These act as powerful toxic agents, killing the living
tissue, and causing electric response to disappear. (See fig.
88.) It must, however, be remembered that there are again
specific poisons  which may affect one kind of tissue and
not others. Poisons in general may be regarded as extreme cases
of depressants. As an example of those which produce moderate
physiological depression, potassium bromide may be mentioned,
and this also diminishes electric response. There are other
chemical reagents, on the other hand, which produce the opposite
effect of increasing the excitability and causing a
corresponding exaltation of electric response.

We shall now proceed to inquire whether the response of
inorganic bodies is affected by chemical reagents, so that their
excitability is exalted by some, and depressed or abolished by
others. Should it prove to be so, the last test will have been
fulfilled, and that parallelism which has been already
demonstrated throughout a wide range of phenomena, between the
electric response of animal tissues on the one hand, and that of
plants and metals on the other, will be completely established.

*Action of stimulants on metals.*  We shall first study
the stimulating action of various chemical reagents. The method
of procedure is to take a series of normal responses to uniform
stimuli, the electrolyte being water. The chemical reagent whose
effect is to be observed is now added in small quantity to the
water in the cell, and a second series of responses taken, using
the same stimulus as before. Generally speaking, the influence
of the reagent is manifested in a short period, but there may be
occasional instances where the effect takes some time to develop
fully. We must remember that by the introduction of the chemical
reagent some change may  be produced in the internal
resistance of the cell. The effect of this on the deflection is
eliminated by interposing a very high external resistance (from
one to five megohms) in comparison with which the internal
resistance of the cell is negligible. The fact that the
introduction of the reagent did not produce any variation in the
total resistance of the circuit was demonstrated by taking two
deflections, due to a definite fraction of a volt, before and
after the introduction of the reagent. These deflections were
found equal.

**Fig. 89.Stimulating Action of Na2CO3 on Tin**

![](fig089.jpg)

I first give a record of the stimulating action of sodium
carbonate on tin, which will become evident by a comparison of
the responses before  and after the introduction of Na2CO3
(fig. 89). The next record shows the effect of the same reagent
on platinum (fig. 90).

**Fig. 90.Stimulating Action of Na2CO3 on Platinum**

![](fig090.jpg)

*Action of depressants.*  Certain other reagents, again,
produce an opposite effect. That is to say, they diminish the
intensity of response. The record given on the next page (fig.
91) shows the depressing action of 10 per cent. solution of KBr
on tin.

**Fig. 91.  Depressing Effect of KBr (10 per Cent.) on the
Response of Tin**

![](fig091.jpg)

*Effect of poison.*  Living tissues are killed, and
their electric responses are at the same time abolished by the
action of poisons. It is very curious that various chemical
reagents are similarly effective in killing the response of
metals. I give below a record (fig. 92) to show how oxalic acid
abolishes the response. The depressive effect of this reagent is
so great that a strength of one part in 10,000 is often
sufficient to produce complete  abolition. Another notable
point with reference to the action of this reagent is the
persistence of after-effect. This will be clearly seen from an
account of the following experiment. The two wires A and B, in
the cell filled with water, were found to give equal responses.
The wires were now lifted off, and one wire B was touched with
dilute oxalic acid. All traces of acid were next removed by
rubbing the wire with cloth under a stream of water. On
replacing the wire in the cell, A gave the usual response,
whereas that of B  was found to be abolished. The
depression produced is so great and passes in so deep that I
have often failed to revive the response, even after rubbing the
wire with emery paper, by which the molecular layer on the
surface must have been removed.

**Fig. 92.Abolition of Response by Oxalic Acid**

![](fig092.jpg)

We have seen in the molecular model (fig. 62, d, e) how the
attainment of maximum is delayed, the response diminished, and
the recovery prolonged or arrested by increase of friction or
reduction of molecular mobility.

It would appear as if the reagents which act as poisons
produced some kind of molecular arrest. The following records
seen to lend support to this view. If the oxalic acid is applied
in large quantities, the abolition of response is complete. But
on carefully adding just the proper amount I find that the first
stimulus evokes a responsive electric twitch, which is less than
the normal, and the period of recovery is very much prolonged
from the normal one minute before, to five minutes after, the
application of the reagent (fig. 93, a). In another record the
arrest is more pronounced, i.e. there is now no recovery (fig.
93, b). Note also that the maximum is attained much later.
Stimuli applied after the arrest produce no effect, as if the
molecular mechanism became, as it were, clogged or locked up.

In connection with this it is interesting to note that the
effect of veratrine poison on muscle is somewhat similar. This
reagent not only diminishes the excitability, but causes a very
great prolongation of the period of recovery.

In connection with the action of chemical reagents the
following points are noteworthy.

**Fig. 93.Molecular Arrest by the Action of poison**

![](fig093.jpg)

In each, curves to the left show the normal response, curve to
the right shows the effect of poison. In (a) the arrest is
evidenced by prolongation of period of recovery. In (b) there is
no recovery.

(1) The effect of these reagents is not only to increase or
diminish the height of the response-curve, but also to modify
the time relations. By the action of some the latent period is
diminished, others produce a prolongation of the period of
recovery. Some curious effects produced by the change of time
relations have been noticed in the account given of diphasic
variation (see p. 113).

 (2) The effect produced by a chemical reagent depends to
some extent on the previous condition of the wire.

(3) A certain time is required for the full development of the
effect. With some reagents the full effect takes place almost
instantaneously, while with others the effect takes place
slowly. Again the effect may with time reach a maximum, after
which there may be a slight decline.

**Fig. 94.Opposite Effects of Small and Large Doses (Tin)**

![](fig094.jpg)

(a) is the normal response; (b) is the stimulating action of
small dose of potash (3 parts in 1,000); (c) is the abolition of
response with a stronger dose (3 parts in 100).

(4) The after-effects of the reagents may be transitory or
persistent; that is to say, in some cases the removal of the
reagent causes the responses to revert to the normal, while in
others the effect persists even after the removal of all traces
of the reagent.

*Opposite effects of large and small doses.*  There
remains a very curious phenomenon, known not only  to
students of physiological response but also known in medical
practice, namely that of the opposite effects produced by the
same reagent when given in large or in small doses. Here, too,
we have the same phenomena reproduced in an extraordinary manner
in inorganic response. The same reagent which becomes a poison
in large quantities may act as a stimulant when applied in small
doses. This is seen in record fig. 94, in which (a) gives the
normal responses in water; KOH solution was now added so as to
make the strength three parts in 1,000, and (b) shows the
consequent enhancement of response. A further quantity of KOH
was added so as to increase the strength to three parts in 100.
This caused a complete abolition (c) of response.

It will thus be seen that as in the case of animal tissues and
of plants, so also in metals, the electrical responses are
exalted by the action of stimulants, lowered by depressants, and
completely abolished by certain other reagents. The parallelism
will thus be found complete in every detail between the
phenomena of response in the organic and the inorganic.

---

  
**CHAPTER XVII**

**ON THE STIMULUS OF LIGHT AND RETINAL CURRENTS**

*Visual impulse: (1) chemical theory; (2) electrical theory 
Retinal currents  Normal response positive  Inorganic
response under stimulus of light  Typical experiment on the
electrical effect induced by light.*

The effect of the stimulus of light on the retina is perceived
in the brain as a visual sensation. The process by which the
ether-wave disturbance causes this visual impulse is still very
obscure. Two theories may be advanced in explanation.

*(1) Chemical theory.*  According to the first, or
chemical, theory, it is supposed that certain visual substances
in the retina are affected by light, and that vision originates
from the metabolic changes produced in these visual substances.
It is also supposed that the metabolic changes consist of two
phases, the upward, constructive, or anabolic phase, and the
downward, destructive, or katabolic phase. Various visual
substances by their anabolic or katabolic changes are supposed
to produce the variations of sensation of light and colour. This
theory, as will be seen, is very complex, and there are certain
obstacles in the way of its acceptance. It is, for instance,
difficult to see how this very quick visual process could be due
to a comparatively slow chemical action, consisting of  the
destructive breaking-down of the tissue, followed by its
renovation. Some support was at first given to this chemical
theory by the bleaching action of light on the visual purple
present in the retina, but it has been found that the presence
or absence of visual purple could not be essential to vision,
and that its function, when present, is of only secondary
importance. For it is well known that in the most sensitive
portion of the human retina, the fovea centralis, the visual
purple is wanting; it is also found to be completely absent from
the retinae of many animals possessing keen sight.

*(2) Electrical theory.*  The second, or electrical,
theory supposes that the visual impulse is the concomitant of an
electrical impulse; that an electrical current is generated in
the retina under the incidence of light, and that this is
transmitted to the brain by the optic nerve. There is much to be
said in favour of this view, for it is an undoubted fact, that
light gives rise to retinal currents, and that, conversely, an
electrical current suitably applied causes the sensation of
light.

*Retinal currents*.  Holmgren, Dewar, McKendrick, Kuhne,
Steiner, and others have shown that illumination produces
electric variation in a freshly excised eye. About this general
fact of the electrical response there is a widespread agreement,
but there is some difference of opinion as regards the sign of
this response immediately on the application, cessation, and
during the continuance of light. These slight discrepancies may
be partly due to the unsatisfactory nomenclatureas regards use
of terms positive and negativehitherto in  vogue and
partly also to the differing states of the excised eyes
observed.

Waller, in his excellent and detailed work on the retinal
currents of the frog, has shown how the sign of response is
reversed in the moribund condition of the eye.

As to the confusion arising from our present terminology, we
must remember that the term positive or negative is used with
regard to a current of referencethe so-called current of
injury.

**Fig. 95. Retinal Response To Light**

![](fig095.jpg)

The current of response is from the nerve to the retina.

When the two galvanometric contacts are made, one with the cut
end of the nerve, and the other on the uninjured cornea, a
current of injury is found which in the eye is from the nerve to
the retina. In the normal freshly excised eye, the current of
response due to the action of light on the retina is always from
the nerve, which is not directly stimulated by light, to the
retina, that is, from the less excited to the more excited (fig.
95). This current of response flows, then, in the same direction
as the existing current of referencethe current of injuryand
may therefore be called positive. Unfortunately the current of
injury is very often apt to change its sign; it then flows
through the eye from the cornea to the nerve. And now, though
the current of response due to light may remain unchanged in
direction, still, owing to the reversal of the current of
reference, it will appear as negative. That is to say, though
its absolute direction is the same as before, its relative
direction is altered.

I have already advocated the use of the term positive for
currents which flow towards the stimulated, and negative for
those whose flow is away from the stimulated. If such a
convention be adopted, no confusion can arise, even when, as in
the given cases, the currents of injury undergo a change of
direction.

*Normal response positive.*  The normal effect of light
on the retina, as noticed by all the observers already
mentioned, is a positive variation, during exposure to light of
not too long duration. Cessation of light is followed by
recovery. On these points there is general agreement amongst
investigators. Deviations are regarded as due to abnormal
conditions of the eye, owing to rough usage, or to the rapid
approach of death. For just as in the dying plant we found
occasional reversals from negative to positive response, so in
the dying retina the response may undergo changes from the
normal positive to negative.

The sign of response, as we have already seen in numerous
cases, depends very much on the molecular condition of the
sensitive substance, and if this condition be in any way
changed, it is not surprising that the character of the response
should also undergo alteration.

Unlike muscle in this, successive retinal responses exhibit
little change, for, generally speaking, fatigue is very slight,
the retina recovering quickly even under strong light if the
exposure be not too long. In exceptional cases, however,
fatigue, or its converse, the staircase effect, may be observed.

*Inorganic response under the stimulus of light.*  It may
now be asked whether such a complex vital  phenomenon as
retinal response could have its counterpart in non-living
response. Taking a rod of silver, we may beat out one end into
the form of a hollow cup, sensitising the inside by exposing it
for a short time to vapour of bromine. The cup may now be filled
with water, and connection made with a galvanometer by
non-polarisable electrodes. There will now be a current due to
difference between the inner surface and the rod. This may be
balanced, however, by a compensating E.M.F.

**Fig. 96.Record of Responses To Light given by the Sensitive
Cell**

![](fig096.jpg)

Thick lines represent the effect during illumination, dotted
lines the recovery in darkness. Note the preliminary negative
twitch, which is sometimes also observed in responses of frogs
retina.

We have thus an arrangement somewhat resembling the eye, with a
sensitive layer corresponding to the retina, and the less
sensitive rod corresponding to the conducting nerve-stump (fig.
96, a).

The apparatus is next placed inside a black box, with an
aperture at the top. By means of an inclined mirror, light may
be thrown down upon the sensitive surface through the opening.

On exposing the sensitive surface to light, the balance is at
once disturbed, and a responsive current of positive character
produced. The current, that is to  say, is from the less to
the more stimulated sensitive layer. On the cessation of light,
there is fairly quick recovery (fig. 96, b).

The character and the intensity of E.M. variation of the
sensitive cell depend to some extent on the process of
preparation. The particular cell with which most of the
following experiments were carried out usually gave rise to a
positive variation of about *008 volt when acted on for one
minute by the light of an incandescent gas-burner which was
placed at a distance of 50 cm.

**Fig. 97 (a)**

![](fig097a.jpg)

A, B are the two faces of a brominated sheet of silver. One
face, say A, is acted on by light. The current of response is
from B to A, across the plate.

*Typical experiment on the electrical effect induced by
light.*  This subject of the production of an electrical
current by the stimulus of light would appear at first sight
very complex. But we shall be able to advance naturally to a
clear understanding of its most complicated phenomena if we go
through a preliminary consideration of an ideally simple case.
We have seen, in our experiments on the mechanical stimulation
of, for example, tin, that a difference of electric potential
was induced between the more stimulated and less stimulated
parts of the same rod, and that an action current could thus be
obtained, on making suitable electrolytic connections. Whether
the more excited was zincoid or cuproid depended on the
substance and its molecular condition.

Let us now imagine the metal rod flattened into a plate, and
one face stimulated by light, while the other is protected.
Would there be a difference of potential induced between the two
faces of this same sheet of metal?

Let two blocks of paraffin be taken and a large hole drilled
through both. Next, place a sheet of metal between the blocks,
and pour melted paraffin round the edge to seal up the junction,
the two open ends being also closed by panes of glass. We shall
have then two compartments separated by the sheet of metal, and
these compartments may be filled with water through the small
apertures at the top (fig. 97, a).

**Fig. 97 (b).  Record of Responses obtained from the Above
Cell**

![](fig097b.jpg)

Ten seconds exposure to light followed by fifty seconds
recovery in the dark. Thick lines represent action in light,
dotted lines represent recovery.

The two liquid masses in the separated chambers thus make
perfect electrolytic contacts with the two faces A and B of the
sheet of metal. These two faces may be put in connection with a
galvanometer by means of two non-polarisable electrodes, whose
ends dip into the two chambers. If the sheet of metal have been
properly annealed, there will now be no difference of potential
between the two faces, and no current in the galvanometer. If
the two faces are not molecularly similar, however, there will
be a current, and the electrical effects to be subsequently
described will act additively, in an algebraical sense. Let one
face now be exposed to the stimulus of light. A responsive
current will be found to flow, from the less to the more
stimulated face, in some cases, and in others in an opposite
direction.

It appears at first very curious that this difference of
electric potential should be maintained between opposite faces
of a very thin and highly conducting sheet of metal, the
intervening distance between the opposed surfaces being so
extremely small, and the electrical resistance quite
infinitesimal. A homogeneous sheet of metal has become by the
unequal action of light, molecularly speaking, heterogeneous.
The two opposed surfaces are thrown into opposite kinds of
electric condition, the result of which is as if a certain
thickness of the sheet, electrically speaking, were made
zinc-like, and the rest copper-like. From such unfamiliar
conceptions, we shall now pass easily to others to which we are
more accustomed. Instead of two opposed surfaces, we may obtain
a similar response by unequally lighting different portions of
the same surface. Taking a sheet of metal, we may expose one
half, say A, to light, the other half, B, being screened.
Electrolytic contacts are made by plunging the two limbs in two
vessels which are in connection with the two non-polarisable
electrodes E and E? (fig. 98, a). On  illumination of A and
B alternately, we shall now obtain currents flowing alternately
in opposite directions.

**Fig. 98.  Modification of the Sensitive Cell**

![](fig098.jpg)

Just as in the strain cells the galvanometer contact was
transferred from the electrolytic part to the metallic part of
the circuit, so we may next, in an exactly similar manner, cut
this plate into two, and connect these directly to the
galvanometer, electrolytic connection being made by partially
plunging them into a cell containing water. The posterior
surfaces of the two half-plates may be covered with a
non-conducting coating. And we arrive at a typical
photo-electric cell (fig. 98, b). These considerations will show
that the eye is practically a photo-electric cell.

**Fig. 99.  Responses To Light in Frogs Retina**

![](fig099.jpg)

Illumination L for one minute, recovery in dark for two minutes
during obscurity D. (Waller.)

We shall now give detailed experimental results obtained with
the sensitive silver-bromide cell, and compare its
response-curve with those of the retina. A series of uniform
light stimuli gives rise to uniform  responses, which show
very little sign of fatigue. How similar these response-curves
are to those of the retina will be seen from a pair of records
given below, where fig. 99 shows responses of frogs retina, and
fig. 100 gives the responses obtained with the sensitive silver
cell (fig. 100).

It was said that the responses of the retina are uniform. This
is only approximately true. In addition to numerous cases of
uniform responses, Waller finds instances of staircase
increase, and its opposite, slight fatigue. In the record here
given of the silver cell, the staircase effect is seen at the
beginning, and followed by slight fatigue. I have other records
where for a very long time the responses are perfectly uniform,
there being no sign of fatigue.

**Fig. 100.Responses in Sensitive Silver Cell**

![](fig100.jpg)

Illumination for one minute and obscurity for one minute. Thick
line represents record during illumination, dotted line recovery
during obscurity.

Another curious phenomenon sometimes observed in the response
of retina is an occasional slight increase of response
immediately on the cessation of light, after which there is the
final recovery. An indication of this is seen in the second and
fourth curves in fig. 99. Curiously enough, this abnormality is
also occasionally met with in the responses of the silver cell,
as seen in the first two curves of fig. 100. Other instances
will be given later.

---

  
**CHAPTER XVIII**

**INORGANIC RESPONSEINFLUENCE OF VARIOUS CONDITIONS ON THE
RESPONSE TO STIMULUS OF LIGHT**

*Effect of temperature  Effect of increasing length of
exposure  Relation between intensity of light and magnitude
of response  After-oscillation  Abnormal effects: (1)
preliminary negative twitch; (2) reversal of response; (3)
transient positive twitch on cessation of light; (4) decline
and reversal  Resume.*

We shall next proceed to study the effect, on the response of
the sensitive cell, of all those conditions which influence the
normal response of the retina. We shall then briefly inquire
whether even the abnormalities sometimes met with in retinal
responses have not their parallel in the responses given by the
inorganic.

**Fig. 101.Influence of Temperature on Response**

![](fig101.jpg)

Illumination 20?, obscurity 40?.

In (a) is shown a series of responses at 20 deg C.  the record
exhibits slight fatigue. (b) is the slight irregular response at
50 deg C. (c) is the record on re-cooling; it exhibits staircase
increase.

*Effect of temperature.*  It has been found that when the
temperature is raised above a certain point, retinal response
shows rapid diminution. On cooling, however, response reappears,
with its original intensity. In the response given by the
sensitive cell, the same peculiarity is noticed. I give below
(fig. 101, a) a set of response-curves for 20 deg C. These
responses, after showing slight fatigue, became fairly constant.
On raising the temperature to 50 deg C. response practically
disappeared (101, b). But on cooling to the first temperature
again, it reappeared, with its original if not slightly greater
intensity (fig. 101, c). A curious point is that while in 
record (a), before warming, slight fatigue is observed, in (c),
after cooling, the reverse, or staircase effect, appears.

**Fig. 102.Response-curves for Increasing Duration of
Illumination from 1? to 10?**

![](fig102.jpg)

In (a) the source of light was at a distance of 50 cm.; in (b)
it was at a distance of 25 cm. Note the after-oscillation.

*Effect of increasing length of exposure.*  If the
intensity of light be kept constant, the magnitude of response
of the sensitive cell increases with length of exposure. But
this soon reaches a limit, after which  increase of
duration does not increase magnitude of effect. Too long an
exposure may however, owing to fatigue, produce an actual
decline.

I give here two sets of curves (fig. 102) illustrating the
effect of lengthening exposure. The intensities of light in the
two cases are as 1 to 4. The incandescent burner was in the two
cases at distances 50 and 25 cm. respectively. It will be
observed that beyond eight seconds exposure the responses are
approximately uniform. Another noticeable fact is that with long
exposure there is an after-oscillation. This growing effect with
lengthening exposure and attainment of limit is exactly
paralleled by responses of retina under similar conditions.

Relation between intensity of light and magnitude of
response.In the responses of retina, it is found that
increasing intensity of light produces an increasing effect. But
the rate of increase is not uniform: increase of effect does not
keep pace with increase of stimulus. Thus a curve giving the
relation between stimulus and response is concave to the axis
which represents the stimulus.

The same is true of the sensation of light. That is to say,
within wide limits, intensity of sensation does not increase so
rapidly as stimulus.

This particular relation between stimulus and effect is also
exhibited in a remarkable manner by the sensitive cell. For a
constant source of light I used an incandescent burner, and
graduated the intensity of the incident light by varying its
distance from the sensitive cell. The intensity of light
incident on the cell, when  the incandescent burner is at a
distance of 150 cm., has been taken as the arbitrary unit. In
order to make allowance for the possible effects of fatigue I
took two successive series of responses (fig. 103). In the
first, records were taken with intensities diminishing from 7 to
1, and immediately afterwards increasing from 1 to 7, in the
second.

**Fig. 103.Responses of Sensitive Cell to various Intensities
of Light**

![](fig103.jpg)

On the left the responses are for diminishing intensities in
the ratios of 7, 5, 3, and 1. On the right they are for the
increasing intensities 1, 3, 5, and 7. The thick lines are
records during exposures of one minute; the dotted lines
represent recoveries for one minute.

**Table giving Response to varying Intensities of Light**   
(The intensity of an incandescent gas-burner at a distance of
150 cm. is taken as unit.)

*Intensity of Light Response*   
(Light diminishing) Response   
(Light increasing) Mean Value in volt   
7 43 39 41 63*0 x 10? volt   
5 31 29 30 46*1 x"   
3 18*5 17*5 18 27*7 x"   
1 10 9      9*5 14*6 x"

As the zero point was slightly shifted during the  course
of the experiment, the deflection in each curve was measured
from a line joining the beginning of the response to the end of
its recovery. A mean deflection, corresponding to each
intensity, was obtained by taking the average of the descending
and ascending readings. The two sets of readings did not,
however, vary to any marked extent.

The deflections corresponding to the intensities 1, 3, 5, 7,
are, then, as 9*5 to 18, to 30, to 41. If the deflections had
been strictly proportionate to the intensities of light stimulus
they would have been as 9*5 to 28*5, to 47*5, to 66*5.

**Fig. 104.Curves giving the Relation between Intensity of
Light and Magnitude of Response**

![](fig104.jpg)

In (a) sensitive cell, (b) in frogs retina.

In another set of records, with a different cell, I obtained
the deflections of 6, 10, 13, 15, corresponding to light
intensities of 3, 5, 7, and 9.

The two curves in fig. 104, giving the relation between
response and stimulus, show that in the case of inorganic
substances, as in the retina (Waller), magnitude of response
does not increase so rapidly as stimulus.

*After-oscillation.*  When the sensitive surface is
subjected to the continued action of light, the E.M. 
effect attains a maximum at which it remains constant for some
time. If the exposure be maintained after this for a longer
period, there will be a decline, as we found to be the case in
other instances of continued stimulation. The appearance of this
decline, and its rapidity, depends on the particular condition
of the substance.

When the sensitive element is considerably strained by the
action of light, and if that light be now cut off, there is a
rebound towards recovery and a subsequent after-oscillation.
That is to say, the curve of recovery falls below the zero
point, and then slowly oscillates back to the position of
equilibrium. We have already seen an instance of this in fig.
102. Above is given a series of records showing the appearance
of decline, from too long-continued exposure and recovery,
followed by after-oscillation on the cessation of light (fig.
105). Certain visual analogues to this phenomenon will be
noticed later.

**Fig. 105.After-oscillation**

![](fig105.jpg)

Exposure of one minute followed by obscurity of one minute.
Note the decline during illumination, and after-oscillation in
darkness.

*Abnormal effects.*  We have already treated of all the
normal effects of the stimulus of light on the retina, and their
counterparts in the sensitive cell. But the retina undergoes
molecular changes when injured, stale, or in a dying condition,
and under these circumstances various complicated modifications
are observed in the response.

**Fig. 106.Transient Positive Augmentation given by the
Frogs Retina on the Cessation of Light L (Waller)**

![](fig106.jpg)

**Fig. 107.Responses in Silver Cell**

![](fig107.jpg)

The thick line represents response during light (half a
minutes exposure), and dotted line the recovery during
darkness. Note the terminal positive twitch.

*1. Preliminary negative twitch.*  When the light is
incident on the frogs retina, there is sometimes a transitory
negative variation, followed by the normal positive response.
This is frequently observed in the sensitive cell (see fig. 96,
b).

*2. Reversal of response.*  Again, in a stale retina,
owing to molecular modification the response is apt to undergo
reversal (Waller). That is to say, it now becomes negative. In
working with the same sensitive cell on different days I have
found it occasionally exhibiting this reversed response.

*3. Transient rise of current on cessation of light.*
 Another very curious fact observed in the retina by Kuhne and
Steiner is that immediately on the stoppage of light there is
sometimes a sudden increase in the retinal current, before the
usual recovery takes place. This is very well shown in the
series of records taken by Waller (fig. 106). It will be noticed
that on illumination the response-curve rises, that continued
illumination produces a decline, and that on the cessation of
light there is a transient rise of current. I give here a series
of records which will show the remarkable similarity between the
responses of the cell and retina, in respect even of
abnormalities so marked as those described (fig. 107). I may
mention here that some of these curious effects, that is to say,
the preliminary negative twitch and sudden augmentation of the
current on the cessation of light, have also been noticed by
Minchin in photo-electric cells.

*4. Decline and reversal.*  We have seen that under the
continuous action of light, response begins to  decline.
Sometimes this process is very rapid, and in any case, under
continued light, the deflection falls.

(1) The decline may nearly reach zero. If now the light be cut
off there is a rebound towards recovery downwards, which carries
it below zero, followed by an after-oscillation (fig. 108, a).

(2) If the light be continued for a longer time, the decline
goes on even below zero; that is to say, the response now
becomes apparently negative. If, now, the light be stopped,
there is a rebound upwards to recovery, with, generally
speaking, a slight preliminary twitch downwards (fig. 108, b,
c). This rebound carries it back, not only to the zero position,
but sometimes beyond that position. We have here a parallel to
the following observation of Dewar and McKendrick:  When
diffuse light is allowed to impinge on the eye of the frog,
after it has arrived at a tolerably stable condition, the
natural E.M.F. is in the first place increased, then diminished;
during the continuance of light it is still slowly diminished to
a point where it remains tolerably constant, and on the removal
of light there is a sudden increase of the E.M. power nearly up
to its original position.[18]

**Fig. 108Decline under the Continued Action of Light**

![](fig108.jpg)

(a) Decline short of zero; on stoppage of light, rebound
downwards to zero; after-oscillation.

(b) Decline below zero; on stoppage of light, rebound towards
zero, with preliminary negative twitch.

(c) The same, decline further down; negative twitch almost
disappearing.

(3) I have sometimes obtained the following curious result. On
the incidence of light there is a response, say, upward. On the
continuation of light the response declines to zero and remains
at the zero position, there being no further action during the
continuation of stimulus. But on the cessation or break of
light stimulus, there is a response downwards, followed by the
usual recovery. This reminds us of a somewhat similar responsive
action produced by constant electric current on the muscle. At
the moment of make there is a responsive twitch, but
afterwards the muscle remains quiescent during the passage of
the current, but on breaking the current there is seen a second
responsive twitch.

*Resume.*  So we see that the response of the sensitive
inorganic cell, to the stimulus of light, is in every way
similar to that of the retina. In both we have, under normal
conditions, a positive variation; in both the intensity of
response up to a certain limit increases with the duration of
illumination; it is affected, in both alike, by temperature; in
both there is comparatively little fatigue; the increase of
response with intensity of  stimulus is similar in both;
and finally, even in abnormalities  such as reversal of
response, preliminary negative twitch on commencement, and
terminal positive twitch on cessation of illumination, and
decline and reversal under continued action of light  parallel
effects are noticed.

**Fig. 109.Certain After-effects of Light**

![](fig109.jpg)

We may notice here certain curious relations even in these
abnormal responses (fig. 109). If the equilibrium position
remain always constant, then it is easy to understand how, when
the rising curve has attained its maximum, on the cessation of
light, recovery should proceed downwards, towards the
equilibrium position (fig. 109, a). One can also understand how,
after reversal by the continued action of light, there should be
a recovery upwards towards the old equilibrium position (fig.
109, b). What is curious is that in certain cases we get, on the
stoppage of light, a preliminary twitch away from the zero or
equilibrium position, upwards as in (c) (compare also fig. 107)
and downwards as in (d) (compare also fig. 108 b).

In making a general retrospect, finally, of the effects 
produced by stimulus of light, we find that there is not a
single phenomenon in the responses, normal or abnormal,
exhibited by the retina which has not its counterpart in the
sensitive cell constructed of inorganic material.

**FOOTNOTES:**

[18] Proc. Roy. Soc. Edin., 1873 p. 153.

---

  
**CHAPTER XIX**

**VISUAL ANALOGUES**

*Effect of light of short duration  After-oscillation 
Positive and negative after-images  Binocular alternation of
vision  Period of alternation modified by physical condition
 After-images and their revival  Unconscious visual
impression.*

We have already referred to the electrical theory of the visual
impulse. We have seen how a flash of light causes a transitory
electric impulse not only in the retina, but also in its
inorganic substitute. Light thus produces not only a visual but
also an electrical impulse, and it is not improbable that the
two may be identical. Again, varying intensities of light give
rise to corresponding intensities of current, and the curves
which represent the relation between the increasing stimulus and
the increasing response have a general agreement with the
corresponding curve of visual sensation. In the present chapter
we shall see how this electrical theory not only explains in a
simple manner ordinary visual phenomena, but is also deeply
suggestive with regard to others which are very obscure.

We have seen in our silver cell that if the molecular
conditions of the anterior and posterior surfaces were exactly
similar, there would be no current. In practice, however, this
is seldom the case. There is, generally  speaking, a slight
difference, and a feeble current in the circuit. It is thus seen
that there may be an existing feeble current, to which the
effect of light is added algebraically. The stimulus of light
may thus increase the existing current of darkness (positive
variation). On the cessation of light again, the current of
response disappears and there remains only the feeble original
current.

In the case of the retina, also, it is curious to note that on
closing the eye the sensation is not one of absolute darkness,
but there is a general feeble sensation of light, known as the
intrinsic light of the retina. The effect produced by external
light is superposed on this intrinsic light, and certain curious
results of this algebraical summation will be noticed later.

**Fig. 110Response-curves of the Sensitive Silver Cell**

![](fig110.jpg)

Showing greater persistence of after-effect when the stimulus
is strong.

(a) Short exposure of 2? to light of intensity 1; (b) short
exposure of 2? to light nine times as strong.

*Effect of light of short duration.*  If we subject the
sensitive cell to a flash of radiation, the effect is not
instantaneous but grows with time. It attains a maximum some
little time after the incidence of light, and the effect then
gradually passes away. Again, as we have seen previously with
regard to mechanical strain, the after-effect persists for a
slightly longer time when the stimulus is stronger. The same is
true of the after-effect of the stimulus of light. Two curves
which exhibit this are given below (fig. 110). With regard to
the first pointthat the maximum effect is attained some time
after the cessation of a short exposure  the corresponding
experiment on the eye may be made as follows: at the end of a
tube is fixed a glass disc coated with lampblack, on which, by
scratching with a pin, some words are written in transparent
characters.  The length of the tube is so adjusted that the
disc is at the distance of most distinct vision from the end of
the tube applied to the eye. The blackened disc is turned
towards a source of strong light, and a short exposure is given
by the release of a photographic shutter interposed between the
disc and the eye. On closing the eye, immediately after a short
exposure, it will at first be found that there is hardly any
well-defined visual sensation; after a short time, however, the
writing on the blackened disc begins to appear in luminous
characters, attains a maximum intensity, and then fades away. In
this case the stimulus is of short duration, the light being cut
off before the maximum effect is attained. The after-effect here
is positive, there being no reversal or interval of darkness
between the direct image and the after-image, the one being
merely the continuation of the other. But we shall see, if light
is cut off after a maximum effect is attained by long 
exposure, that the immediate after-image would be negative (see
below). The relative persistence of after-effect of lights of
different intensities may be shown in the following manner:

If a bold design be traced with magnesium powder on a blackened
board and fired in a dark room, the observer not being
acquainted with the design, the instantaneous flash of light,
besides being too quick for detailed observation, is obscured by
the accompanying smoke. But if the eyes be closed immediately
after the flash, the feebler obscuring sensation of smoke will
first disappear, and will leave clear the more persistent
after-sensation of the design, which can then be read
distinctly. In this manner I have often been able to see
distinctly, on closing the eyes, extremely brief phenomena of
light which could not otherwise have been observed, owing either
to their excessive rapidity or to their dazzling character.[19]

*After-oscillation.*  In the case of the sensitive silver
cell, we have seen (fig. 105), when it has been subjected for
some time to strong light, that the current of response attains
a maximum, and that on the stoppage of the stimulus there is an
immediate rebound towards recovery. In this rebound there may be
an over-shooting of the equilibrium position, and an
after-oscillation is thus produced.

If there has been a feeble initial current, this oscillatory
after-current, by algebraical summation, will cause the current
in the circuit to be alternately weaker and stronger than the
initial current.

*Visual recurrence.*  Translated into the visual
circuit, this would mean an alternating series of after-images.
On the cessation of light of strong intensity and long duration,
the immediate effect would be a negative rebound, unlike the
positive after-effect which followed on a short exposure.

The next rebound is positive, giving rise to a sensation of
brightness. This will go on in a recurrent series.

If we look for some time at a very bright object, preferably
with one eye, on closing the eye there is an immediate dark
sensation followed by a sensation of light. These go on
alternating and give rise to the phenomena of recurrent vision.
With the eyes closed, the positive or luminous phases are the
more prominent.

This phenomenon may be observed in a somewhat different manner.
After staring at a bright light we may look towards a
well-lighted wall. The dark phases will now become the more
noticeable.

If, however, we look towards a dimly lighted wall, both the
dark and bright phases will be noticed alternately.

The negative effect is usually explained as due to fatigue.
That position of the retina affected by light is supposed to be
tired, and a negative image to be formed in consequence of
exhaustion. By this exhaus tion is meant either the presence of
fatigue-stuffs, or the breaking-down of the sensitive element of
the tissue, or both of these. In such a case we should expect
that this fatigue, with its consequent negative image, would
gradually and finally disappear on the restoration of the retina
to its normal condition.

We find, however, that this is not the case, for the negative
image recurs with alternate positive. The accepted theory of
fatigue is incapable of explaining this phenomenon.

In the sensitive silver cell, we found that the molecular
strain produced by light gave rise to a current of response, and
that on the cessation of light an oscillatory after-effect was
produced. The alternating after-effect in the retina points to
an exactly similar process.

*Binocular alternation of vision.*  It was while
experimenting on the phenomena of recurrent vision that I
discovered the curious fact that in normal eyes the two do not
see equally well at a given instant, but that the visual effect
in each eye undergoes fluctuation from moment to moment, in such
a way that the sensation in the one is complementary to that in
the other, the sum of the two sensations remaining approximately
constant. Thus they take up the work of seeing, and then,
relatively speaking, resting, alternately. This division of
labour, in binocular vision, is of obvious advantage.

**Fig. 111.Stereoscopic Design**

![](fig111.jpg)

As regards maximum sensation in the two retinae there is then a
relative retardation of half a period. This may be seen by means
of a stereoscope, carrying, instead of stereo-photographs,
incised plates through which we look at light. The design
consists of two  slanting cuts at a suitable distance from
each other. One cut, R, slants to the right, and the other, L,
to the left (see fig. 111). When the design is looked at through
the stereoscope, the right eye will see, say R, and the left L,
the two images will appear superimposed, and we see an inclined
cross. When the stereoscope is turned towards the sky, and the
cross looked at steadily for some time, it will be found, owing
to the alternation already referred to, that while one arm of
the cross begins to be dim, the other becomes bright, and vice
versa. The alternate fluctuations become far more conspicuous
when the eyes are closed; the pure oscillatory after-effects are
then obtained in a most vivid manner. After looking through the
stereoscope for ten seconds or more, the eyes are closed. The
first effect observed is one of darkness, due to the rebound.
Then one luminous arm of the cross first projects aslant the
dark field, and then slowly disappears, after which the second
(perceived by the other eye) shoots out suddenly in a direction
athwart the first. This alternation proceeds for a long time,
and produces the curious effect of two luminous blades crossing
and recrossing each other.

Another method of bringing out the phenomenon of alternation in
a still more striking manner is to look at two different sets of
writing, with the two eyes. The resultant effect is a blur, due
to superposition, and the inscription cannot be read with the
eyes open. But on  closing them, the composite image is
analysed alternately into its component parts, and thus we are
enabled to read better with eyes shut than open.

This period of alternation is modified by age and by the
condition of the eye. It is, generally speaking, shorter in
youth. I have seen it vary in different individuals from 1? to
10? or more. About 4? is the most usual. With the same
individual, again, the period is somewhat modified by previous
conditions of rest or activity. Very early in the morning, after
sleep, it is at its shortest. I give below a set of readings
given by an observer:

  Period   Period   
8 a.m. 3? 6 p.m. 5*4?   
12 noon 4? 9  " 5*6?   
3 p.m. 5? 11  " 6*5?

Again, if one eye be cooled and the other warmed, the retinal
oscillation in one eye is quicker than in the other. The quicker
oscillation overtakes the slower, and we obtain the curious
phenomenon of visual beats.

*After-images and their revival.*  In the experiment with
the stereoscope and the design of the cross, the after-images of
the cross seen with the eyes closed are at first very
distinctso distinct that any unevenness at the edges of the
slanting cuts in the design can be distinctly made out. There
can thus be no doubt of the objective nature of the strain
impression on the retina, which on the cessation of direct
stimulus of light gives rise to after-oscillation with the
concomitant visual recurrence. This recurrence may therefore be
taken as a proof of the physical strain produced on the 
retina. The recurrent after-image is very distinct at the
beginning and becomes fainter at each repetition; a time comes
when it is difficult to tell whether the image seen is the
objective after-effect due to strain or merely an effect of
memory. In fact there is no line of demarcation between the
two, one simply merges into the other. That this memory image
is due to objective strain is rendered evident by its
recurrence.

In connection with this it is interesting to note that some of
the undoubted phenomena of memory are also recurrent. Certain
sensations for which there is no corresponding process outside
the body are generally grouped for convenience under this term
[memory]. If the eyes be closed and a picture be called to
memory, it will be found that the picture cannot be held, but
will repeatedly disappear and appear.[20]

The 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 instances, long after
this disappearance, they will spontaneously reappear at most
unexpected moments. In one instance the recurrence was observed
in a dream, about three weeks after the original impression was
made. In connection with this, the revival of images, on closing
the eyes at night, that have been seen during the day, is
extremely interesting.

*Unconscious visual impression.*  While repeating certain
experiments on recurrent vision, the above phenomenon became
prominent in an unexpected  manner. I had been intently
looking at a particular window, and obtaining the subsequent
after-images by closing the eye; my attention was concentrated
on the window, and I saw nothing but the window either as a
direct or as an after effect. After this had been repeated a
number of times, I found on one occasion, after closing the eye,
that, owing to weariness of the particular portion of the
retina, I could no longer see the after-image of the window;
instead of this I however saw distinctly a circular opening
closed with glass panes, and I noticed even the jagged edges of
a broken pane. I was not aware of the existence of a circular
opening higher up in the wall. The image of this had impressed
itself on the retina without my knowledge, and had undoubtedly
been producing the recurrent images which remained unnoticed
because my principal field of after-vision was filled up and my
attention directed towards the recurrent image of the window.
When this failed to appear, my field of after-vision was
relatively free from distraction, and I could not help seeing
what was unnoticed before. It thus appears that, in addition to
the images impressed in the retina of which we are conscious,
there are many others which are imprinted without our knowledge.
We fail to notice them because our attention is directed to
something else. But at a subsequent period, when the mind is in
a passive state, these impressions may suddenly revive owing to
the phenomenon of recurrence. This observation may afford an
explanation of some of the phenomena connected with ocular
phantoms and hallucinations not traceable to any disease. In
these  cases the psychical effects produced appear to have
no objective cause. Bearing in mind the numerous visual
impressions which are being unconsciously made on the retina, it
is not at all unlikely that many of these visual phantoms may be
due to objective causes.

**FOOTNOTES:**

[19] As an instance of this I may mention the experiment which
I saw on the quick fusion of metals exhibited at the Royal
Institution by Sir William Roberts-Austen (1901), where, owing
to the glare and the dense fumes, it was impossible to see what
happened in the crucible. But I was able to see every detail on
closing the eyes. The effects of the smoke, being of less
luminescence, cleared away first, and left the after-image of
the molten metal growing clearer on the retina.

[20] E. W. Scripture, *The New Psychology*, p. 101.

---

  
**CHAPTER XX**

**GENERAL SURVEY AND CONCLUSION**

We have seen that stimulus produces a certain excitatory change
in living substances, and that the excitation produced sometimes
expresses itself in a visible change of form, as seen in muscle;
that in many other cases, however  as in nerve or retina 
there is no visible alteration, but the disturbance produced by
the stimulus exhibits itself in certain electrical changes, and
that whereas the mechanical mode of response is limited in its
application, this electrical form is universal.

This irritability of the tissue, as shown in its capacity for
response, electrical or mechanical, was found to depend on its
physiological activity. Under certain conditions it could be
converted from the responsive to an irresponsive state, either
temporarily as by anaesthetics, or permanently as by poisons.
When thus made permanently irresponsive by any means, the tissue
was said to have been killed. We have seen further that from
this observed fact  that a tissue when killed passes out of the
state of responsiveness into that of irresponsiveness; and from
a confusion of dead things with inanimate matter, it has been
tacitly assumed that inorganic substances, like dead 
animal tissues, must necessarily be irresponsive, or incapable
of being excited by stimulusan assumption which has been shown
to be gratuitous.

This unexplained conception of irritability became the
starting-point, to quote the words of Verworn,[21] of
vitalism, which in its most complete form asserted a dualism of
living and lifeless Nature.... The vitalists soon, as he goes
on to say, laid aside, more or less completely, mechanical and
chemical explanations of vital phenomena, and introduced, as an
explanatory principle, an all-controlling unknown and
inscrutable force hypermecanique. While chemical and physical
forces are responsible for all phenomena in lifeless bodies, in
living organisms this special force induces and rules all vital
actions.

Later vitalists, however, attempted no analysis of vital
force; they employed it in a wholly mystical form as a
convenient explanation of all sorts of vital phenomena.... In
place of a real explanation a simple phrase such as vital
force was satisfactory, and signified a mystical force
belonging to organisms only. Thus it was easy to explain the
most complex vital phenomena.

From this position, with its assumption of the super-physical
character of response, it is clear that on the discovery of
similar effects amongst inorganic substances, the necessity of
theoretically maintaining such dualism in Nature must
immediately fall to the ground.

In the previous chapters I have shown that not the fact of
response alone, but all those modifications in  response
which occur under various conditions, take place in plants and
metals just as in animal tissues. It may now be well to make a
general survey of these phenomena, as exhibited in the three
classes of substances.

We have seen that the wave of molecular disturbance in a living
animal tissue under stimulus is accompanied by a wave of
electrical disturbance; that in certain types of tissue the
stimulated is relatively positive to the less disturbed, while
in others it is the reverse; that it is essential to the
obtaining of electric response to have the contacts leading to
the galvanometer unequally affected by excitation; and finally
that this is accomplished either (1) by injuring one contact,
so that the excitation produced there would be relatively
feeble, or (2) by introducing a perfect block between the two
contacts, so that the excitation reaches one and not the other.

Further, it has been shown that this characteristic of
exhibiting electrical response under stimulus is not confined to
animal, but extends also to vegetable tissues. In these the same
electrical variations as in nerve and muscle were obtained, by
using the method of injury, or that of the block.

Passing to inorganic substances, and using similar experimental
arrangements, we have found the same electrical responses evoked
in metals under stimulus.

Negative variation.  In all cases, animal, vegetable, and
metal, we may obtain response by the method of negative
variation, so called, by reducing the excitability of one
contact by physical or chemical means. Stimulus causes a
transient diminution of the existing current,  the
variation depending on the intensity of the stimulus (figs. 4,
7, 54).

**Fig. 112.Uniform Responses in (A) Nerve, (P) Plant, and (M)
Metal**

![](fig112.jpg)

The normal response in nerve is represented down. In this and
following figures, (A) is the record of responses in animal, (P)
in plant, and (M) in metal.

*Relation between stimulus and response.*  In all three
classes we have found that the intensity of response increases
with increasing stimulus. At very high intensities of stimulus,
however, there is a tendency of the response to reach a limit
(figs. 30, 32, 84). The law that is known as Weber-Fechners
shows a similar characteristic in the relation between stimulus
and sensation. And if sensation be a measure of physiological
effect we can understand this correspondence of the
physiological and sensation curves. We now see further that the
physiological effects themselves are ultimately reducible to
simple physical phenomena.

*Effects of superposition.*  In all three types,
ineffective stimuli become effective by superposition.

Again, rapidly succeeding stimuli produce a maximum effect,
kept balanced by a force of restitution, and continuation of
stimulus produces no further effect, in the three cases alike
(figs. 17, 18, 86).

*Uniform responses.*  In the responses of animal,
vegetable, and metal alike we meet with a type where the
responses are uniform (fig. 112).

*Fatigue.*  There is, again, another type where fatigue
is exhibited.

**Fig. 113.  Fatigue (A) in Muscle, (P) in Plant, (M) in
Metal**

![](fig113.jpg)

The explanation hitherto given of fatigue in animal tissues 
that it is due to dissimilation or breakdown of tissue,
complicated by the presence of fatigue-products, while recovery
is due to assimilation, for which material is brought by the
blood-supply  has long been seen to be inadequate, since the
restorative effect succeeds a short period of rest even in
excised bloodless muscle. But that the phenomena of fatigue and
recovery were not primarily dependent on dissimilation or
assimilation becomes self-evident when we find exactly similar
effects produced not only in plants, but also in metals (fig.
113). It has been shown, on the other hand, that these effects
are primarily due to cumulative residual strains, and that a
brief period of rest, by removing the overstrain, removes also
the sign of fatigue.

*Staircase effect.*  The theory of dissimilation due to
stimulus reducing the functional activity below par, and thus
causing fatigue, is directly negatived by what is known as the
staircase effect, where successive equal stimuli produce
increasing response. We saw an  exactly similar phenomenon
in plants and metals, where successive responses to equal
stimuli exhibited an increase, apparently by a gradual removal
of molecular sluggishness (fig. 114).

**Fig. 114.Staircase in Muscle, Plant, and Metal**

![](fig114.jpg)

Increased response after continuous stimulation.  An effect
somewhat similar, that is to say, an increased response, due to
increased molecular mobility,  is also shown sometimes
after continuous stimulation, not only in animal tissues, but
also in metals (fig. 115).

**Fig. 115.  Increased Response after Continuous Stimulation
in Nerve and Metal**

![](fig115.jpg)

The normal response in animal tissue is represented down, in
metal up.

*Modified response.*  In the case of nerve we saw that
the normal response, which is negative, sometimes becomes
reversed in sign, i.e. positive, when the specimen is stale. In
retina again the normal positive response is converted into
negative under the same conditions. Similarly, we found that a
plant when withering often shows a positive instead of the usual
negative response (fig. 28). On nearing the death-point, also by
subjection to extremes of temperature, the same reversal of
response is occasionally observed in plants. This reversal of
response due to peculiar molecular modification was also seen in
metals.

**Fig. 116.  Modified Abnormal Response in (A) Nerve and (M)
Metal converted into Normal, after Continuous Stimulation**

![](fig116.jpg)

(A) is the record for nerve (recording galvanometer not being
dead-beat shows after-oscillation); the abnormal up is
converted into normal down after continuous stimulation. (M)
is the record for metal, the abnormal down being converted
into normal up after like stimulation.

But these modified responses usually become normal when the
specimen is subjected to stimulation either strong or long
continued (fig. 116).

*Diphasic variation.*  A diphasic variation is observed
in nerve, if the wave of molecular disturbance does not reach
the two contacts at the same moment, or if the rate of
excitation is not the same at the two points. A similar diphasic
variation is also observed in the responses of plants and metals
(figs. 26, 68).

*Effect of temperature.*  In animal tissues response
becomes feeble at low temperatures. At an optimum temperature it
reaches its greatest amplitude, and, again, beyond a maximum
temperature it is very much reduced.

We have observed the same phenomena in plants. In metals too,
at high temperatures, the response is very much diminished
(figs. 38, 65).

*Effect of chemical reagents.*  Finally, just as the
response of animal tissue is exalted by stimulants, lowered by
depressants, and abolished by poisons, so also we have found the
response in plants and metals undergoing similar exaltation,
depression, or abolition.

We have seen that the criterion by which vital response is
differentiated is its abolition by the action of certain
reagentsthe so-called poisons. We find, however, that poisons
also abolish the responses in plants and metals (fig. 117). Just
as animal tissues pass from a state of responsiveness while
living to a state of irresponsiveness when killed by poisons, so
also we find metals transformed from a responsive to an
irresponsive condition by the action of similar poisonous
reagents.

The parallel is the more striking since it has long been known
with regard to animal tissues that the  same drug,
administered in large or small doses, might have opposite
effects, and in preceding chapters we have seen that the same
statement holds good of plants and metals also.

*Stimulus of light.*  Even the responses of such a highly
specialised organ as the retina are strictly paralleled by
inorganic responses. We have seen how the stimulus of light
evokes in the artificial retina responses which coincide in all
their detail with those produced in the real retina. This was
seen in ineffective stimuli becoming effective after repetition,
in the relation between stimulus and response, and in the
effects produced by temperature; also in the phenomenon of
after-oscillation. These similarities went even further, the
very abnormalities of retinal response finding their reflection
in the inorganic.

**Fig. 117.  Abolition of Response in Nerve, Plant, and Metal
by the Action of the same Poison**

![](fig117.jpg)

The first half in each set shows the normal response, the
second half the abolition of response after the application of
the reagent.

Thus living response in all its diverse manifestations is found
to be only a repetition of responses seen in the inorganic.
There is in it no element of mystery or caprice, such as we must
admit to be applied in the  assumption of a hypermechanical
vital force, acting in contradiction or defiance of those
physical laws that govern the world of matter. Nowhere in the
entire range of these response-phenomena  inclusive as that is
of metals, plants, and animals  do we detect any breach of
continuity. In the study of processes apparently so complex as
those of irritability, we must, of course, expect to be
confronted with many difficulties. But if these are to be
overcome, they, like others, must be faced, and their
investigation patiently pursued, without the postulation of
special forces whose convenient property it is to meet all
emergencies in virtue of their vagueness. If, at least, we are
ever to understand the intricate mechanism of the animal
machine, it will be granted that we must cease to evade the
problems it presents by the use of mere phrases which really
explain nothing.

We have seen that amongst the phenomena of response, there is
no necessity for the assumption of vital force. They are, on the
contrary, physico-chemical phenomena, susceptible of a physical
inquiry as definite as any other in inorganic regions.

Physiologists have taught us to read in the response-curves a
history of the influence of various external agencies and
conditions on the phenomenon of life. By these means we are able
to trace the gradual diminution of responsiveness by fatigue, by
extremes of heat and cold, its exaltation by stimulants, the
arrest of the life-process by poison.

The investigations which have just been described  may
possibly carry us one step further, proving to us that these
things are determined, not by the play of an unknowable and
arbitrary vital force, but by the working of laws that know no
change, acting equally and uniformly throughout the organic and
the inorganic worlds.

**FOOTNOTES:**

[21] Verworn, General Physiology, p. 18.

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