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EESPONSE AND

IN THE LIVING NON-LIVING

RESPONSE IN THE LIVING AND NON-LIVING
BY
JAGADIS CHUNDER BOSE, M. A. (CANTAB.), D.Sc.(LoND.)
PROFESSOK, PRESIDENCY COLLEGE, CALCUTTA
WITH ILLUSTRATIONS

LONGMANS,

GEEEN, 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

PKEFACE
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 Generality des Phenomenes Moleculaires produits par 1'Electricite 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.) 'Kesponse of Inorganic Matter to Stimulus.' (Friday
Evening Discourse, Koyal Institution, May 1901.) 4 On Electric Eesponse of Inorganic Substances. Preliminary
Notice.' (Koyal Society, June 1901.) ' On Electric Eesponse of Ordinary Plants under Me-
chanical Stimulus.' (Journal Linnean Society, 1902.) 1 Sur la Reporise Electrique dans les Metaux, les Tissus
A19n0i2.m)aux et Vegetaux.' (Societe de Physique, Paris,
' 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.)

viii RESPONSE IN THE LIVING AND NON-LIVING

These investigations were commenced in India, and I take this opportunity to express my grateful acknowledgments to the Managers of the Eoyal 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.

CONTENTS

CHAPTEE I

THE MECHANICAL RESPONSE OF LIVING SUBSTANCES
PAGE

Mechanical response — Different kinds of stimuli — Myograph — Charac-

teristics ofresponse-curve : period, amplitude, form — Modification

of response-curves .........

1

CHAPTEE II
ELECTEIC 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

CHAPTEE III
ELECTRIC RESPONSE IN PLANTS — METHOD OF NEGATIVE VARIATION

Negative variation — Response recorder — Photographic recorder —

Compensator — Means of graduating intensity of stimulus — Springtapper and torsional vibrator — Intensity of stimulus dependent

on amplitude of vibration— Effectiveness of stimulus dependent on

rapidity also .

17

RESPONSE IN THE LIVING AND NON-LIVING

CHAPTEK IV

ELECTRIC RESPONSE IN PLANTS — BLOCK METHOD

PAGE

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 .

27

CHAPTEE V
PLANT RESPONSE — ON 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 ...

35

CHAPTEE VI

PLANT RESPONSE— ON DIPHASIC VARIATION

Diphasic E.M.

variation— variation

Positive after-effect and positive response— ......

Eadial

44

CHAPTEE VII
PLANT RESPONSE — ON THE RELATION BETWEEN STIMULUS AND RESPONSE

Increased response tion ofresponse

with increasing stimulus— Apparent diminuwith excessively strong stimulus ....

51

CONTENTS

xi

CHAPTEE VIII

PLANT RESPONSE — ON THE INFLUENCE OF TEMPERATURE
PAGE

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

bv the action of steam .

59

CHAPTEK IX
PLANT RESPONSE — EFFECT OF ANESTHETICS 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 .

7 1

CHAPTEE 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 ....

81

CHAPTEE XI
INORGANIC RESPONSE — MODIFIED 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 experi-

ment— Molecular voltaic cell ....

91

xii RESPONSE IN THE LIVING AND NON-LIVING

CHAPTER XII

INORGANIC RESPONSE— METHOD OF ENSURING CONSISTENT RESULTS
PAGE

Preparation of wire— Effect of single stimulus

100

- CHAPTER XIII
INORGANIC RESPONSE — MOLECULAR MOBILITY I 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 . 104

CHAPTER XIV
INORGANIC RESPONSE— FATIGUE, 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 . 118

CHAPTER XV
INORGANIC RESPONSE — RELATION BETWEEN STIMULUS AND RESPONSE — SUPERPOSITION OF STIMULI

Relation between stimulus and response — Magnetic analogue — In-

crease ofresponse with increasing stimulus — Threshold of response

— Superposition of stimuli — Hysteresis

131

CONTENTS

xiii

CHAPTEE XVI

INORGANIC RESPONSE — EFFECT OF CHEMICAL REAGENTS
PAGE

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

139

CHAPTEE 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 in-

duced bylight ..........

148

CHAPTEE XVIII
INORGANIC RESPONSE — INFLUENCE 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 .....

158

CHAPTEE XIX

VISUAL

ANALOGUES

Effect of light of short duration — After-oscillation — Positive and nega-

tive after-images — Binocular alternation of vision — Period of alter-

nation modified by physical condition — After-images and their

revival — Unconscious visual impression .....

170

CHAPTEE XX GENERAL SURVEY AND CONCLUSION

. . 181

INDEX

193

ILLUSTKATIONS

FIG.

1*AGE

1. MECHANICAL LEVER RECORDER

3

2. ELECTKIC METHOD or DETECTING NERVE RESPONSE

.. 6

3. DIAGRAM SHOWING INJURED END OF NERVE CORRESPONDS TO

COPPER IN A VOLTAIC ELEMENT

8

4. ELECTRIC RECORDER

11

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

». 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

xvi RESPONSE IN THE LIVING AND NON-LIVING

F 21. FATIGUI E IN CG EL. ERY

I>A<;K
. 40

22. FATIGUE IN CAULIFLOWER-STALK 23. FATIGUE FROM PREVIOUS OVERSTRAIN .

. . 41 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 TRANS-

FORMED INTO NORMAL NEGATIVE UNDER STRONG STIMU-

LATION

. 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 VJBRATIONAL 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 TEM-

PERATURE

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 TEMPERA-

TURE AND ANESTHETICS

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 .

AQ

ILLUSTRATIONS xvii

Fit!.
43. EFFECT OF CHLOROFORM ON NEKVE RESPONSE . .
44. EFFECT OF CHLOROFORM ON THE RESPONSES OF CARROT

PAGE
. . 72
. 74

45. ACTION OF CHLORAL HYDRATE ON PLANT RESPONSES 46. ACTION OF FORMALIN ON RADISH

. . 75 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 ANNEA ING 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.

. . Ill

66. DIPHASIC VARIATION IN METALS

113

67. NEGATIVE, DIPHASIC, AND POSITIVE RESULTANT RESPONSE IN

METALS .

115

xviii RESPONSE IN THE LIVING AND NON-LIVING

PACK

68. CONTINUOUS TRANSFORMATION FROM NEGATIVE TO POSITIVE

THROUGH INTERMEDIATE DIPHASIC KESPONSE .

.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 CONTINUOUS STIMULATION
82. MAGNETIC ANALOGUE

ENHANCED

AFTER 127, 128
132

83,84. RECORDS OF RESPONSES TO INCREASING STIMULI IN TIN 134, 135

85. INEFFECTIVE STIMULUS BECOMING EFFECTIVE BY SUPER-

POSITION

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 KBn ON TIN

143

92. ABOLITION OF RESPONSE IN METALS BY < POISON ' . . . 143

03. « 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

ILLUSTRATIONS xix

FIG.

PAGE

96. RESPONSE OF SENSITIVE CELL TO LIGHT

152

97. TYPICAL EXPERIMENT ON THE E.M. VARIATION PRODUCED

BY LIGHT

154

98. MODIFICATION OF THE PH•OTO-SENSITIVE CELL . . . . 155

99. RESPONSES IN FROG'S 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 MAGNI-

TUDE OF RESPONSE

162

105. AFTER-OSCILLATION

163

106. TRANSIENT POSITIVE INCREASE OF RESPONSE IN THE FROG'S

RETINA ON THE CESSATION OF LIGHT

164

107. TRANSIENT POSITIVE INCREASE SENSITIVE CELL

OF RESPONSE

IN THE 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 RE-

SPONSE IN NERVE, PLANT, AND METAL

....

189

RESPONSE
IN THE
LIVING AND NON-LIVING
OHAPTEE 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 con-
tracts. 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 excit-
able.; Astimulus 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 amoeboid rhizopods, for instance. These lumpy protoplasmic bodies, usually elongated while creeping, if mechanically jarred, con-
tract into a spherical form. If, instead of mechanical B

2 RESPONSE IN THE LIVING AND NON-LIVING
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 contrac-
tion 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

THE MECHANICAL RESPONSE 3

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. — MECHANICAL LEVER

. 1).

BECORDER

Cr*hhanrfacn/t*ef rAi«s-iteifciVso 0e\1f tf nVIeA rt- AeosnpromnosAe-Thebomnuesclies seMcuwrietihy thheeldattaatchoende

(It)\

fP*»erriinOHd,

((2?)\

AAmtnpnlliitfuiidHe*,*

neencdt,edthewioththetrhe

end being conwriting lever.

(3) Form.-Just as a wave of sound

is characterised by its (1) period,

(2) a. mplit- ude, , and (3) for, m, ,s. o

these response-Curves be dlS-

t„ rom ea" ch Other.

AS

regards_the peri. od, there is an

scluerfreac.ovrearswhf?rnom contrac-
tion,thetracingpointreturns oton itPs otrhieginraelcoprodsitioofn.muscSleee curve.

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 -^^ 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

B 2

4 RESPONSE IN THE LIVING AND NON-LIVING
insects to those of tortoises and hibernating dormice.' * 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 with-
drawal 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 con-
tinuously 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.
1 Biedermann, Electro-physiology, p. 59.

CHAPTEE 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,

6 RESPONSE IN TJIE LIVING AND NON-LIVING
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 nulleffect 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

A

B

A

B

•<

Current of Injury

> Current of Action,

FIG. 2.— ELECTRIC METHOD OF DETECTING NERVE KESPONSE
(a) Iso-electric contacts ; no current in the galvanometer. (b) The anendactBioninjcuurrerdent; cfurrroemntA otfo iBn.jury from B to A : stimulation gives rise to (c) Non-polarisable electrode.

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.
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

ELECTRIC RESPONSE

7

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 con-
stant, and is therefore sometimes known as ' the current of
rest' (fig. 2,6). 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 bya 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 sf to B, the wire w being interposed, as it were, in the electrolytic part of the circuit. If now a galvanometer be interposed at 0, 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

8 RESPONSE IN THE LIVING AND NON-LIVING
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
cuprIofidt.h1e 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 exist-
ing 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

A

-B

FlG. 3. — DIAGRAM SHOWING THE CORRESPONDENCE BETWEEN INJURED (B) AND UNINJURED (A) CONTACTS IN NERVE, AND Cu AND ZN IN A VOLTAIC ELEMENT
Comparison of (c) and (d) will swhiotwh tthhaet Ctuhe ininj(cu)r.ed end of B in (d) corresponds

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

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

ELECTRIC RESPONSE

9

effect produced at A, the existing difference of potential may thus be reduced, with a consequent diminution of the current of injury. During stimula-
tion, 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
mSitigmhutlatcailoln itof' ztihnecoiudn,i'njaunrded theend,inajuprperdoxicmonattaicntg *ictuptrooidt.h'e 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^

io RESPONSE IN THE LIVING AND NON-LIVING

sion. As the excitatory state disappears with the return of the excitable tissue to its original condition,
the current of action will gradually disappear.1 The movement of the galvanometer needle during excita-
tion 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
t*hreespsotnismeu,l'us.and its intensity varies according to that of
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,

' The exciting cause is able to produce a particular molecular rearrangement inthe nerve ; this constitutes the state of excitation and is accompanied

by local electrical changes es 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 is

able to upset and extremely brief,

retain in a new then the recoil of

poise the

the living equilibrium, and if this tissue causes such manifestation to

biie. 4it5s3e.lf of very short duration.'— Text-book of Physiology, ed. by Schafer,

\ r ELECTRIC RESPONSE

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. Two types of

response — positive

and negative. — It may here be added

that though stimu-

lus in general pro-

(b)

duces adiminution

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 re-
sponse ofthe retina to light. Again, a tissue which nor-
mally gives a negative variation may

A

B

-<

Current of rest

>• Current, of action.

FIG. 4. — ELECTRIC BECORDER
(a) M nomnus-cploelar;iAsinugninejluercedt,rodBes incjounrneedcteinndgs. A EanEd' B with galvanometer G. Stimulus produces c' onnegnaetcitveed vwairtiahtiognal'voafnocmuerrteenrt onfeerdelset. reIcnodredxs curve on travelling paper (in practice, moving galvanometer spot of light traces curve on photographic plate). Rising part of curve rsehcoowvsery.effect of stimulus ; descending part,
(b) O is the zero position of the galvanometer; rdienicjmouivrneyirsyh.persodutcheiss daefldeecftlieocntiotno AC B; C; Dstiimsultuhse

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.

12 RESPONSE IN THE LIVING AND NON-LIVING

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.
IE. Positive variation. — Action current from less
excited to more excited — zincoid change in the excited

—

e.Fgr. osmtaltehinserivtew,ilflrebseh

retina.1 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

1 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 direction — that is to say, from the injured to the uninjured — there 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.

ELECTRIC RESPONSE

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. From these observed facts —

that living tissue gives response while a tissue that has been

killed does not — it is concluded

that the phenomenon of re-

sponse ispeculiar to living organisms.1 The response pheno-

Fm<OLEFR5..T)_HE_SlMMEUCLHTAANNIECOADLS (EME)COARNDD
(E) ELECTRICAL EESPONSES OF

mena that we have been study ing THE MUSCLE OF FROG. (WAL-

are therefore considered as due

to some unknown, -super-physical ' vital ' force and are thus relegated to a region beyond physical inquiry.

1 ' The Electrical Sign of Life . . . An isolated muscle gives sign of life by contracting when stimulated. . . . An ordinary nerve, normally con-
nected 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.

i4 RESPONSE IN THE LIVING AND NON-LIVING

It may, however, fied, and surely, at

be that this limitation is not justileast 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 com-

plex animal tissues to those given under simpler vital conditions.

Electric response has been found by Munck, BurdonSanderson, 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.1 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

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

ELECTRIC RESPONSE 15
say, I desired to know, with regard to plants, what was the relation between intensity of stimulus and the cor-
responding response ; what were the effects of superposition ofstimuli ; 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 inthe modification of plant response, as stimulating, anesthetic, 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

1 6 RESPONSE IN THE LIVING AND NON-LIVING
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,1
expe1riMmyentass.sistant Mr. J. Bull has rendered me very efficient help in these

CHAPTEE III
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.
I SHALL first proceed to show that an electric response
is evoked in plants under stimulation.1 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.
1 A preliminary account of Electric Response in Plants was given at btheeforeendthoef RmoyyaplapeSrocionety' EloenctrJiucneRe6s,po1n9s0e1 ;ofalsIonoragtantihce SFurbisdtaaynceEsve'nrienagd 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. 0. B.
C

i8 RESPONSE IN THE LIVING AND NON-LIVING
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 (Vitisvinifera). Leaf-stalk. — Horse-chestnut (^Esculus Hippocastanum), turnip (Brassica Napus), cauliflower (Brassica oleracea), celery (Apium graveolens), Eucharis lily (EucJiaris amazonica).
Flower-stalk. — Arum lily (Richardia africana). Fruit. — Egg-plant (Solanum Melongend). 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. A sharp tap was now given to the stalk, and a sudden diminution, or negative variation, of cur-
rent occurred, the resting potential difference being

ELECTRIC RESPONSE IN PLANTS
decreased by '026 volt. A second and stronger tap produced a second response, causing a greater diminu-
tion of P.D. by '047 volt (fig. 6, b). The accompanying figure is a photographic record of another set of responsecurves (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 ''

A

B

"*

^

Current tt-ction.

Coufrrfernuti,iry

FIG. 6. — (a) EXPERIMENT FOR EXHIBITING ELECTRIC EESPONSE IN PLANTS BY METHOD OF NEGATIVE VARIATION, (b) BESPONSE£ IN LEAF-STALK OF TURNIP TO STIMULI OF Two SUCCESSIVE TAPS, THE SECOND BEING STRONGER.
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 injurtyial aocftionB,occefufresc.t at A is stronger and a negative variation due to differen-

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.
Response recorder. — The galvanometer used is a
sensitive dead-beat D'Arsonval. The period of complete swing of the coil under experimental conditions is about
11 seconds. A current of 10~9 ampere produces a c 2

20 RESPONSE IN THE LIVING AND NON-LIVING 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
FIG. 7. — RECORD OBFY RMEESTPHOONDSESOFINNEPGLAATNITVE (LVEAARFI-ASTTIAOLNK OF CAULIFLOWER) The first three records are for stimulus intensity 1 ; the next six are for in-
tensity twice as strong; the successive responses exhibit fatigue. The vreirgthitcatlo llienfte. to the left represents '1 volt. The record is to be read from
the clock-governor, or by changing the size of the drivingwheel. 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 galvano-
meter deflection takes place parallel to the drum, and

ELECTRIC RESPONSE IN PLANTS

21

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.

We can calibrate the value

of the deflection

by applying a

FIG. 8.— EESPONSE KECORDER

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 ofinvestigation. A large number of records might
be taken by this means in a comparatively short time.

22 RESPONSE IN THE LIVING AND NON-LIVING

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

A B is a sFtIrGet.ch9ed.-wTiHreE wiCthOaMddPedErNesSisAtanTceOs RR aKndis Bt'u.rnedS itso athsetorriagghet coelnle. scWahleendivtihseionkey=
d•i0v0i1sivoonlt,= w-0h1envolt.turnPedis ttohethpelanlte.ft one scale

^ injurv' ig 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.

Means of graduating the intensity of stimulus.— One of

the necessities in connection with quantitative measure-

ments isto 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.

ELECTRIC RESPONSE IN PLANTS 23
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 screwthread, by means of which its length, projecting down-
wards, isregulated. 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
R T
FIG. 10.— THE SPRING-TAPPER
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.

24 RESPONSE IN THE LIVING AND NON-LIVING

The electric tapper.— Instead of the simple mechanical

tapper, an electromagnetic Vibrational stimulus.— I

tapper may be used. 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 be imparted to the stalk

torsional vibration1 may by means of the handle

now (H).

The amplitude of vibration, which determines the

intensity of stimulus, can be accurately measured by

FIG. 11. — THE TORSIONAL VIBRATOR Plant P is securely held by a vice V. The two ends are clamped by holders
eCitCh'e.r tBhye emnedansA oorf ehnadndlBesof HtheH'p,ltaonrts.ionTahle veinbdratviioenw m(a6y) sbheowismpahrotwed thteo amplitude of vibration is predetermined by means of movable stops S S'.
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 stimula-
tion bytaps, and that its stimulating intensity increases, length of stalk being constant, with amplitude of
.a 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.

ELECTRIC RESPONSE IN PLANTS
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° and 67° respectively. These successive responses
FIG. 12.— KESPONSE IN PLANT TO MECHANICAL TAP OR VIBEATION 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° was now imparted, this gave the response c. Vibration through 67° gave d.
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.
Effectiveness of stimulus dependent on rapidity also. In order that successive stimuli may be equally effective

26 RESPONSE IN THE LIVING AND NON-LIVING

another point has to be borne in mind. In all cases of stimulation of living tissue it is found that the effective-
ness 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.

\ gjve below records of successive

FIG. IS.-INFLUENCE stimuli, given by vibrations through

STIMULUS
The curves a, &, c, d, are responses to vibrations of the same

the same amplitude, but delivered
with increasing rapidity (fig. 13). Thus if we wish to maintain the

aamptlhietuvdieb,rat8i0o°n. waIsn very slow; in b it was less slow ; it was rapid in c, and very rapid in d.

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 quan-
titative values, by whose means alone can rigorous demonstration of the phenomena we are studying become possible.

CHAPTEE IV
ELECTRIC RESPONSE IN PLANTS — BLOCK 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-

28 RESPONSE JN THE LIVING AND NON-LIVING

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

(a)

made at A by tapping or

vibration is prevented from

reaching B, we shall then have A thrown into a rela-

Current of response ichen A is stimulated^
Current of response when B is stimulated^—
FIG. 14. — THE METHOD OF BLOCK
(a) aTnhdeB.plant is clamped at C, between A (6) Kesponses obtained by alternately
stimulating the two ends. Stimulation of A produces upward response ; of B gives downward response.

tively 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).

We have in this method a great advantage over

that of negative variation, for we can always verify any

set of ments.

results

by making

corroborative

reversal

experi-

By the method of jnjury 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

ELECTRIC RESPONSE IN PLANTS

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.
Plant response a physiological or

vital response. — I now proceed to a demonstration of the fact that what-

ever 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 ch, apters Wil.,l, s, how, t,hey l« urni.sn^ an accurate

FIG.PLAN1T5.— BE(SFPKOONMSE THIEN SSTTIIMMUULLAATTEEDD AB)TO CUONM--

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 proportionaltothe intensity of stimulus.
It need hardly be added that special precautions are taken to avoid shifting of contacts. Variation

™TWi™"" The leaf-staik is damped
wsietchuretlhye icnorktheC,miindsdildee the tube T, which is filled with water, the
iplmamnetrsbeeidn.g cMoomipsletteenleydthreads in connection iwistahbltehe etlweoctnroond-epsolaarr-e led to the side tubes tt'. One end of the stalk is held in ebonite Aforccurerpesnt aonfdresvpiobrnasteed.is found to flow in the stalk from the excited A to the unexcited Br and outside, through the liquid, from B to A. A portrieontn, floowfingthtihsrocuugrhthe siddeucestudebfelesctio1n 1'i,n ptroh-e
galvanometer.

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

3o RESPONSE IN THE LIVING AND NON-LIVING

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 re-
sponse, 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 responses.

therefore

apply

these

same

tests

to plant

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 transpira-
tion 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

ELECTRIC RESPONSE IN PLANTS 31
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
obbesfoerrevedt.he Thaeppeapahriadnecse feoefdintghe"on dtihsecolleoauvreesd dipeadtcehveesn, whereas on the leaves of the stalks placed in water these little creatures maintained their accustomed acti-
vity, 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.

32 RESPONSE IN THE LIVING AND NON-LIVING

I. LEAF-STALK OF PLANE-TREE

The stimulus applied was a single vibration of 90°.

A. After 24 hours in water

[All leaves standing up and fresh — aphides alive]

Electric response

(1).. (2 )

.'.23'11..15dns.

>QX ...26

rsi 17

}R{(6)..
(9)

•.(•4.•).«'3222«.7903'. 17

(10)..

Mean response 23-6

B. After 24 hours in chloroform-water

C. cuArfiteer ch2l4orhioduers in mer-

•25

[Leaves began to j [Leaves began to droop

droop in 1 hour and

in 4 hours. Deep dis-

bent over in 3 hours — aphides dead]

vceoilnso.uratiAopnhid•a2el5songd„e•a2t5dh]e

|

Electric response

Electri•c25respo„nse

0 dn.

(21^) 11 dn.

\ /

o •25 „ „

(3)

2

(f4t) 01

(1).... ((32))........

•*2*5* 77„„

((R76\)) 2l1-5

(m5(.)4..)...... 0

((68))....

" 7)

(9) 1 ,

\vf* * ' •

(10)

-5 „

Mean 1

(1(09))........ Mean -15

II. LEAF-STALK OF HORSE-CHESTNUT

(1) ....1175 dn„s. (2).... ..10 „ (3)....
Mean 14

(1)

-5 dn.

((32))

0 -5 "

Mean -3

(1)

000 dn„„

((32)) 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

ELECTRIC RESPONSE IN PLANTS 33
vibration as the stimulus, obtained strong responses at both ends A and B. I then immersed the same stalk for
astismhourltatetdimeit ians hboetfowraet.erButat aatbonuetith6e5r° AC.,noarndB caogualidn
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
D

34 RESPONSE IN THE LIVING AND NONLIVING
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.

35

CHAPTER Y

PLANT RESPONSE — ON THE EFFECTS OF SINGLE AND OF SUPERPOSED STIMULI

STIMULUS

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 re-
corded 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.
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
D 2

36 RESPONSE IN THE LIVING AND NON-LIVING

is thrown into a state of complete tetanus, in which it

appears to be cient for this,

held rigid. we have the

If the jagged

rapidity be not sufficurve of incomplete

tetanus. If there is not much fatigue, the upper part

FIG. 16. — UNIFORM RESPONSES (RADISH)

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

FIG. 17.— FUSION or EFFECT OF °f effects, analogous tO the

RA, PIDLY , SUCCEED. ING STIMUtL etaInus ofPmusclei (/Pfig. ~1i7*)\.

(a) m muscle ; (6) m carrot.

v to

And lastly, the influence

of fatigue in plants is to produce a modification of

response-curve exactly similar to that of muscle (see

bmeenltoiwo)n.ed

One effect here.

of superposition

of

stimuli

may

be

PLANT RESPONSE
37
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

FIG. 18. — ADDITIVE EFFECT
(a) A single stimulus of 3° vibration produced little or no effect, but the same stimulus when rapidly superposed thirty times, produced the large effect (b). (Leaf -stalk of turnip.)

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 mole-

cular mobility. Whatever be the

explanation, I have sometimes observed the same staircase effect in
plants (fig. 19).

FIG. 19. — ' STAIRCASE EFFECT' IN PLANT

Fatigue. — It is assumed that in living substances like muscle, fatigue is caused by the break down or

38 RESPONSE IN THE LIVING AND NON-LIVING
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 distor-
tion experienced by the excited tissue. Let us first take the case of an experiment whose record is given

PLANT RESPONSE

39

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 suc-
ceeding 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.
6 In muscle with normal circulation and nutrition

there is always an inter-

val between each pair of

(c)

St,i.muli,7. i. n W/lliC-/Ll jt//ie FlG-RES2P0O.N—SERECWORHDEN SSHUOFWFIINCGIENT DIMTIINMUETIONis NOOTF

hieiq• riit.

off> t.wit••ch7d7 oes

not,

I, n

ALLOWED FOR FULL RECOVERY (a) stimuli were applied at intervals

of one

diminish even a*fter i pro-

hmailnfutae;miinnut(e&) ;thtehisinctearuvsaelds awerdeimirneudtuicoend otfo

TtrinarCfipefai ePXVMCflntta'tilnO'nn, ann*na/1

response. In (c) the original rhythm is resto£ed,and theVesponseis found to be en-

no fatigue appears: l Apparent fatigue when stimulation frequency in-

creased.— 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.

The rhythm was now changed to intervals of half

1 Biedermann, Electro-physiology, p, 86.

40 RESPONSE IN THE LIVING AND NON-LIVING
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 FIG. 21.C—ELFEARTYIGUE IN response. An analogous instance may Vibration of 30° at inter- be cited in the case of muscle re-
vals ofhalf a minute.
sponse, where ' the height of twitch diminishes more rapidly in proportion as the excitation
interval is shorter.' l 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 celerystalk. It will be noticed there that, owing to the imperfect molecular recovery during the time allowed, the succeeding heights of the responses have under-
gone a continuous diminution. Fig. 22 gives a
1 Biedermann, loc. tit.

PLANT RESPONSE

photographic record of fatigue in the leaf-stalk of cauliflower.

It is evident that residual strain, other things beingequal, will be greater if the stimuli have been excessive. This is well seen in

fig. 23, where the set of first three

4

curves A is for stimulus intensity of 45° vibration, and the second set B, with an

augmented response, for stimulus in-

tensity of90° vibration. On reverting in c to stimulus intensity of 45°, the responses are seen to have under-
gone a great diminution as compared with the first set A. Here is seen

Fm. 22. — FATIGUE IN LEAF-STALK OF CAULIFLOWER
Stimmauitlnuutsien.t:er3v0a°lsviborfatioonne

marked fatigue, the result of overstrain from excessive stimulation.

If this fatigue be really due to residual strain effect, then, as strain disappears with time, we may expect the

4-5 4-5

ABC FIG. 23. — EFFECT OF OVERSTRAIN IN PRODUCING FATIGUE 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.)
responses to regain their former height after a period of rest. In order to verify this, therefore, I renewed the
stimulation (at intensity 45°) after fifteen minutes. It

42 RESPONSE IN THE LIVING AND NON-LIVING

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 rela-
tively 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 stimula-
tion. 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

rreesmt.oved by fifteen minutes'

Fatigue under continuous

FIG. 24. — KAPID FATIGUE UNDER CON-
TINUOUS STIMULATION IN (a) MUSCLE ; (6) IN LEAF-STALK OF CELERY

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).

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.

43
PLANT RESPONSE
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 some-
what similar to the second. A period of rest of five minutes was now allowed, and the curve obtained
FIG. 25. — EFFECT OF CONTINUOUS VIBRATION (THROUGH 50°) IN CARROT In trheecofviresrty.threTeherelcaosrtdsr,ectowrod mwiansutetsa'kenstiafmtuelrattihoen sipsefcoilmleowned habdy atwroestminouftefsiv'e
minutes. The response, owing to removal of fatigue by rest, is stronger.
subsequently, owing to partial removal of residual strain, is found to exhibit greater response.
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.

44 RESPONSE IN THE LIVING AND NON-LIVING
CHAPTEE VI
PLANT RESPONSE — ON 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 isattended 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

PLANT RESPONSE

45

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

46 RESPONSE IN THE LIVING AND NON-LIVING
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. — DIAPHASIC VARIATION
(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

PLANT RESPONSE

47

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 overshooting of the equilibrium position, which may be
exhibited as a positive variation.

48 RESPONSE IN THE LIVING AND NON-LIVING
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.
Curiously enough, I have on many occasions found exactly parallel instances in the response of plants.
FIG. 27. — ABNORMAL POSITIVE KESPONSES IN STALE LEAF-STALK OF TURNIP
CONVERTED INTO NORMAL NEGATIVE UNDER STRONG STIMULATION1
The relative intensities of stimuli in the two cases are in the ratio of 1 : 7.
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 longcontinued stimulation, so also in the modified plant the abnormal positive response passes into negative
1 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.

PLANT RESPONSE

49

(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). The plant thus gives a reversed response under
abnormal conditions of staleness. I have sometimes

FIG. 28.— ABNORMAL POSITIVE PASSING INTO NORMAL NEGATIVE IN A STALE SPECIMEN OF LEAF-STALK OF CAULIFLOWER
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.)
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
E

5o RESPONSE IN THE LIVING AND NON-LIVING
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
FIG. 29.-EADIAL E.M. VARIATION caloonncgomitthaentPlawnatv>e tnoefre rad^iala E.M. variation. The swaying of a tree by the wind would thus appear to give rise to a radial E.M.F.

CHAPTEB VII

PLANT RESPONSE — ON THE RELATION AND RESPONSE

BETWEEN STIMULUS

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
BS

52 RESPONSE IN THE LIVING AND NON-<-Ltr IVING

threat. When the stimulus is carried beyond moderate

limits, the response, owing to fatigue or other causes,

may sometimes undergo an actual diminution.

e,_

ei

Nen
/x '. .M

7Rfee spt imrse

/ ^ t-~- •.—

cle
«* Li fL

t j

1

|2 1-2 !•* 1-6 1-6 2-0 2-2 2-* 2-6 2-8 3-0 3-2 3-* 3'6 3-6 4.-0

,' .-'

/ '

d-

FIG. 30. — CURVES SHOWISNTGIMUTLHUES KAENLDATIEOENSPOBNESTEWEEN THE INTENSITY OF

Abscissae indicate increasing intudteeofnrseisptoynsoef. stim(uWlausl.ler.)Ordinates indicate magni-

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 com-

Fm 31 plicated by secondary phenomena,

Taps1:2:of3:4increaspirnogducisntgrengti h n- OU6

liaS tO choOS6

.

.

Specimens

which

Ceased response in leaf-

exhl bit little
cured these,

iatlgU6.

Having

I undertook two

seprriOe-s

of experiments. In the first (A) the stimulus was applied

by means torsional

of the spring-tapper, vibration.

and

in the

second

(£)

by

PLANT RESPONSE 53
(A) The first stimulus was given by a fall of the lever through A, the second through 2 /i, and so on.
The response-curves clearly show increasing effect with increased stimulus (fig. 31).

5°

7J°

10°

12J°

FIG. 32. — INCREASED KESPONSE WITH INCREASING VIBRATIONAL STIMULI

(CAULIFLOWER-STALK)

Stimuli applied at intervals of three minutes. Vertical line^'l volt.

(B) 1. The vibrational stimulus was increased from

2-5° to 5° to 7*5° to 10° to 12'5° 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 2-5°

E.M.F. ••004754 vol„t •090 „ •100 „
•106 „

7-5°

12-5°10°

5°

54 RESPONSE IN THE LIVING AND NON-LIVING
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).
3. ,\s 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

Ib)

A—

A

12

16

22

32

4-5

10°

20°

FIG. 33. — RESPONSES TO INCREASING STIMULI PRODUCED

ANGLE OF VIBRATION

4-0
30C
BY INCREASING

.(a) Record with a specimen of fresh radish. Stimuli applied at intervals of two minutes. The record is taken for one minute. '
(6) Record for stale radish. There is a reversed response for the feeble stimulus of 5° vibration.

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

PLANT RESPONSE

55

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,

56 RESPONSE IN THE LIVING AND NON-LIVING
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 pro-
duces one effect, strong radiation produces the opposite. Again, under the continuous action of electric radiation,
I have frequently found recurrent reversals.1 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 diminu-
tion 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)
1 See ' On Electric Touch,' Proc. Roy. Soc. Aug. 1900.

PLANT RESPONSE
fatigue was present. It will be seen that the curve5s7 obtained by joining the apices of the successive single responses are very similar.
In one case there is no fatigue, the recovery from each stimulus being complete. Every response in the
30
20 30° 35
FIG. 34. — KESPONSES TO INCREASING STIMULUS OBTAINED WITH Two SPECIMENS OF STALK OF CAULIFLOWER
In (a) fatigue is absent, in (6) it is present.
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,

58 RESPONSE IN THE LIVING AND NON-LIVING
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 re-
presentsacondition 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.

59
CHAPTEE VIII
PLANT RESPONSE — ON THE INFLUENCE OF TEMPEEATURE
Effect of very low temperature — Influence of high temperature— Determination ofdeath-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 tem-
perature 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-

60 RESPONSE IN THE LIVING AND NON-LIVING
mine whether the undoubted changes induced by temperature inthe vital activity of plants would affect
electrical response.
Effect of very low temperature.— As regards the influence of very low temperature, 1 had opportunities of studying ths question on the sudden appearance
of frost. In the previous week, when the tempera-
ture was about 10° 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 Y. under normal temperature to *003 V. after the frost. That is to say, the average sensitiveness had been
reduced to about -^V11. On warming the frost-bitten
radish to 20° 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.
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

PLANT RESPONSE

61

(17° C.). I then placed it for fifteen minutes in a cooling chamber, temperature — 2° 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° C., and this produced a revival of the response (fig. 35).
If the plant be subjected tolow 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)

FIG. 35. — DIMINUTION OF KESPONSE IN EUCHAKIS BY LOWERING OF TEMPERATURE
(a) Normal response at 17° C. (b) The response almost disappears when plantfis
subjected to -2° C. for fifteen minutes. (r) Kevival of response 011 warming to 20° C.

Ivy ; and (3) Holly. I took their normal response

at 17° 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,

62 RESPONSE IN THE LIVING AND NON-LIVING
temperature 0°C., for twenty-four hours, and afterwards took their records once more at the ordinary tempera-
ture 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.

Ivy

Holly Eucharis

FIG. 36. — AFTER-EFFECT OF COLD ON IVY, HOLLY, .AND EUCHARIS LILY
a. The normal response ; 6. Eesponse 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 tem-
perature— 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

PLANT RESPONSE

(say 17° C.), was mounted in the vibration apparatus arid responses observed. The plant was then dismounted, and replaced in the water-bath at a higher temperature (say 30° 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 temperatuvr.)es

varying from 53° to
TABLE SHOWING

55° C.
EFFECT OF

HIGH

TEMP'EK'ATTJKE

ABOLISHING RESPONSE

IN o

„

Temperaturere

Galvanometric response

Temperature

Galvanometric response

o „ 3 (100 dn7s0. d=ns'.07 V.)

(17° <5 (53° ,

*

V

160I „

\ 100 „ W 15i05°3°j!,7°

2 „

Electricj!7h°eating. — The

(4)

C
JJ

(1..0.0 d84n00s. d=ns„-.07

JJ

. ,. 600 „„

• ))

(6)

»

160°{5?J5°

experiments (17j°ust 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

64 RESPONSE IN THE LIVING AND NON-LIVING
ten minutes, and two records were taken during that time. It was then raised by 10° C., and the same process
FIG. 37. — THE GLASS CHAMBER CONTAINING THE PLANT 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 K. For experiments on action of anaesthetics, vapour of chloroform is blown in through the side tube.
was repeated. It will be noticed from the record (fig. 38) that in this particular case, as the temperature
20°C
V 1 min. FIG. 38. — EFFECT OF TEMPERATURE ON KESPONSE The response was abolished at the hot-water temperature of 55° C.
rose from 20° C. to 30° C., there was a marked diminution of response. At the same time, in this case at

PLANT RESPONSE

65

least, recovery was the response was 21

quicker. At 20° C., for dns., and the recovery was

example, not com-

plete in the course of a minute. At 30° 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 con-
tinuous 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.

TABLE SHOWING DIMINUTTIEOMNPEROPATURERSEPONSE WITH INCREASING

Temper2at0u°re
30° 40°

(•01 Volt = 35 divisions)

R21esponse
7-5 5-5

Temper5at0u°re

Resp4onse

In radishes response disappeared completely at

55° C , but with celery, heated in the manner described, I could not obtain its entire abolition at 60° C. or even higher. A noticeable circumstance, howeve6r5°, 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° C. without ill effects in the hot-air chamber of a
Tbeurkfaitsahl. bath, while immersion in water at 100° C. would
In order to find out whether subjection to hot water
would kill the celery-stalk, I took it out and placed it
F

66 RESPONSE IN THE LIVING AND NON-LIVING

for five minutes from the record

in water at 55° C. taken afterwards,

This, as will be seen effectively killed the

plant (fig: 38, w). Increased sensitiveness as after-effect of temperature
variation.— A very curious effect of temperature variation isthe marked increase of sensitiveness which often

19* C 30 C

50 C

25°C

faUiruj

Temperature,

50 C

70 C

Temperature rising >-
FIG. 39. — EFFECT OF RISING AND FALLING TEMPERATURE ON THE RESPONSE OF SCOTCH KALE
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 tempera-
ture was falling (fig. 39). The temperature was adjusted by electric heating. It was found that the responses were markedly enhanced during cooling, as

PLANT RESPONSE
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

FIG. 40.— KECORDS OF KESPONSES IN EUCHARIS LILY DURING KISE AND FALL OF TEMPERATURE
Stimulus constant, applied at intervals of one minute. The temperature of plant-chamber gradually rose on starting current in the heating coil ; on breaking current, the temperature fell gradually. Temperature corresponding to each record is given below.
Temperature rising: (1) 20°, (2) 20°, (3) 22°, (4) 38°, (5) 53°, (6) 68°, (7) 65°. Temperature falling : (8) 60°, (9) 51°, (10) 45°, (11) 40°, (12) 38°.

record (fig. 40) shows the variation of response in Eucharis lily (1) during the rise, and (2) during the fall

TABLE SHOWING THE VARIATION OF RESPONSE IN SCOTCH KALE DURING THE RlSE AND FALL OF TEMPERATURE

Temperature Kesponse

. Eesponse

[Temperature rising] [Temperature falling]

19° C. 25° „ 30° „ 5700°° „„

...... ... ... . . . .

47 dns. . . 2114 .......
8 ....... 7

28 dns. 16 ,.
—

F 2

68 RESPONSE IN THE LIVING AND NON-LIVING
of temperature. Fig. 41 gives a curve of variation of response during the rise and fall of temperature.
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° C., but with Eucharis fairly marked response can still be obtained after such
20C 60°C.
FIG. 41. — CURVE SHOWING VAKIATION OF RESPONSE IN EUCHARIS WITH THE RISE AND FALL OF TEMPERATURE
immersion and does not disappear till it has been subjected for ten minutes to hot water, at a temperature
of 65° 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.
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

PLANT RESPONSE
eould 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).
Before f After FIG. 42.— EFFECT OF STEAM IN KILLING RESPONSE
The two records to the left exhibit normal response at 17" C. Sudden warming by stseurae tmo stpearmodukcieldled atthfeirsptlaannt i(nccarreroats)e aonfdreasbpoolnisseh,edbutthefirveespmoinnsuet.es' expo-
Vibrlainteio=na'll vosltt.imulus of 30° applied at intervals of one minute; vertical
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

70 RESPONSE IN THE LIVING AND NON-LIVING
are able to judge that a plant has died, only aftervarious 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 elec-
tric 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.

CHAPTEE IX
PLANT KESPONSE — EFFECT 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 isunaffected 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 anassthetisation 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

72 RESPONSE IN THE LIVING AND NON-LIVING
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, dur-
ing half an hour, without detecting the least variation
Before ^ After FIG. 43. — EFFECT OF CHLOROFORM ON NERVE KESPONSE (WALLER)
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.
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,

PLANT RESPONSE

73

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 anassthetic agent, vapour of chloroform, was blown into the closed chamber containing the plant.

74 RESPONSE IN THE LIVING AND NON-LIVING
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 re-
agents. This is a point of minor importance, the

* Before

f After

FIG. 44. —EFFECT OF CHLOROFOEM ON RESPONSES OF CARROT

Stimuli of 25° vibration at intervals of one minute.

essential point to be noticed being that the responses are rapidly reduced.
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

75
PLANT RESPONSE
minute of the application of chloral, is also extremely well marked.

U.U.-

Before

After

FIG. 45.— ACTION OF CHLORAL HYDRATE ON THE RESPONSES OF LEAF-STALK OF CAULIFLOWER

Vibration of 25° at intervals of one minute.

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

Before

^ After

FIG. 46. — ACTION OF FORMALIN (RADISH)

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.

7 6 RESPONSE IN THE LINING AND NON-LIVING
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 galvano-
meter 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-