&^ ALBERT R. MANN LIBRARY New York State Colleges OF Agriculture and Home Economics Cornell University Cornell University Library QH 343.B74 Response in the living and non-living, 3 1924 003 078 775 Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003078775 EESPONSE IN THE LIVING AND NON-LIVINCi RESPONSE IN THE LIVING AND NON-LIVING JACtADIS CHUNDER BOSE, M.A.(Cantab.), D.So.(Loni..) PROFESSOU, PEEPIDENCy COLLEGE, CALCUTTA WITH ILLUSTRATIONS LONGMANS, GREEN, AND CO. 39 PATEENOSTER HOW, LONDON NEW YOBK AND BOMBAY 1902 Tlu: real is one : wise men ceill ii variously ' Rig Veda To my Cuuntryynen Tim Work is Dedicated PREFACE I HAVK ill the present work put in a connected and a more complete form results, some of which have been published in tlie following Papers : ' De la Generalite des Phenomenes Moleculaires prockiits par I'Electricite sur la matiere Inorganique et sur la matiere Vivante.' {Travaux clu Congrh International de Physique. Paris, 1900.) ' On the Similarity of Effect of Electrical Stimulus on In- organic and Living Substances.' (Report, Bradford Meeting Britifili Association, 1900. — Electrician.) ' Piesponse of Inorganic Matter to Stimulus.' (Friday Evening Discourse, Pioyal Institution, May 1901.) ' On Electric Kesponse of Inorganic Substances. Preliminary Notice.' (Royal Society, June 1901.) ' On Electric Response of Ordinary Plants under Me- chanical Stimulus.' {Journal Linnean Society, 1902.) ' Sur la Reponse Electrique dans les Metaux, les Tissus Animaux et Vegetaux.' (Sociste de Physique', Paris, 1902.) ' On the Electro-Motive Wave accompanying Mechanical Disturbance in Metals in contact with Electrolyte.' {Proceedings Payed Society, vol. 70.) ' On the Strain Theory of Vision and of Photographic Action.' {Journal Royal Photographic Society, vol. xxvi.) viii REsroA'si-: IX the living and nonliving These iiiW'Stijj'atiuiis were comiiieuced in India, and I take this (jpportaiiity to express my i^Tatei'id acknowleduiiieiits td the Maiuiii'ers of the Knyal Institution, i'oi- the facilities offered me to r-ompk-'te them at the IhiA'v-Faiada^' Laljoratory. J. C. Host:. ])A\ Y-FaEA1)AY LAnOliATOltY, ItoVAl Tn,STITUT[OK, ]jOni:OX: May I'JOi'. CONTENTS CHAPTEE I THE MECHANICAL EESPONSE OP LIVING SUBSTANCES PAGE Mechanical response — Difl'erent kinds of stimuli — Myograph — Charac- teristics of response-curve : period, amplitude, form — Modification of response-curves ......... 1 CHAPTEE II ELECTBIC EESPONSE 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 re.sponse in plants ........ CHAPTEE III ELECTRIC EESPONSE IN PLANTS — METHOD OF NEGATIVE VAEIATION Negative -I'ariation — Response recorder — PhotogTaphic 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 ........... 17 RESPONSE IN THE LIVING AND NON-LIVING CHAPTEE IV ELECTKIC EESPONSE IN PLANTS — BLOCK METHOD I'AGE 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 EBSPONSE ON THE EFFECTS OF SINGLE STIMULUS AND OF SUPEEPOSED STIMULI Effect of single stimulus — Superposition ofstimidi — Additive effect — Staircase effect — Fatigue — Xo fatigue when sutficient interval between stimuli — Apparent fatigue when stimulation frequency is increased — Fatigue under continuous stimulation CHAPTEE VI PLANT EESPONSE— ON DIPHASIC VAEIATION Diphasic variation — Positive after-effect and positive response — liadial EAI. variation .......... 44 CHAPTEE VII PLANT EESPONSE ON THE EELATION BETWEEN STIMULUS AND EESPONSE Increased response with increasing stimulus — Apparent diminu- tion of response with excessively strong stimulus ... -t CONTENTS xi CHAPTEE VIII PLANT EESrONSE — ON THE INFLUENCE OF TEMPERATURE PA. 46. 47. 4K, 49. 50. ■-;1. ,oa. o4. 55. 50. 57. 58. 59. 60. 61. 62. 63, 65. 66. 67. Effkc't op C'hlokofokm on Neetb IIesponse . Effect of Ciilorofokm oh the Eesponses of Oaeeot Action of C'lnoE.iL Hideatb on Punt Ii'espoxses Action of FoEJi.iLiN on E.\iiish ..... Action of Sodium IIvbeate in Abolishing the Response IN Plant ......... Stimulating Action of Poison in Small Doses in Plants The Poisonous Effect of Steongee Dose of KOII . Block Method foe obtaining Eesponse in Tin Response to Mechanical Stimulation in a Zn-Cu Couple ElECTEIC liESPONSE IN MetAL BY THE 3IETH0D OF RELA- TIVE Depekssion {^N'egatiye Vaeiaiion) . Method of PiElative Exaltation ..... Vauious Cases of Positive and Negative Vaeiation Modifications of the Block Method foe Exhibiting Electeic Response in Metals Equal and Opposite Responses given by T^yo Ends of THE Wire Top A'iew of the Vibeation Cell Influence of Annea ing in the Enhancement of Response in Metals ....... 74 75 75 78 79 79 83 85 88 80 90 03 95 96 101 102 105 Uniform Electric IJesponses in Metals Persistence op Aftee-effect Prolongation of Period of Recoyeey aftee Oyeestrain 106 MoLECULAE Model 107 64. Effects of Removal of Moleculae Sluggishness in (^uicxENED Recoyeey and Heightened 1!esponse in :\Ietals 109, 110 Effect of Tbmpi:eatuee on Response in Metals. . . Ill Diphasic Vaeiation in Metals 113 r^EGATivE, Diphasic, and Positive Resultant Response in Metals 115 RESPONSE IN THE LIVING AND NONIU'I^^G 6<». 7(1. 71. / O. 74. 76. 78. 79. 80, 82. 83, 85. 86. 87. 88. 89. 90. 91. 92. 93. 94. 95. CONTTNUOUS TkAJTSFOEMATIOX IROM NeiUTIVE TO PoSlTlY THEOTJGH Intermedia-IB DiniAsir 1!espos.';e . 116 118 118 119 120 121 122 124 125 F.VLTOUE in iluSOLK ..••■•■' Katiiiui': in I'lvltnum FaTIGUIs IX Tix . ArPKAKAxcE OF Fatigue dfe to Shoetexing the Pj:eioii OF 1!i:co^eet ...•••■■■ Fatigue ix :\1i-:tal uxdke CoxTixrous Stimut.atiox . . ' Sl'AIECASE ' liESPOXSK IX MuSCLE ,iXD IX MeTAL AiixoKMAL Kespoxse IX Xeetk coxveetkd ixto Noemal UXDER COXTIXUEI) StiMELATIOX 77. AliXOEJIAT, liKSPOXSE IX TlX AXD Platixi'm COXVKRTET) into XuKJELL irX'DEE CuX'TIXTEIl StIMELATION Gradual Trax'sitiox from Aexoetifal to jN'oemal 1!esponsi'; IN Platinum 126 Inc'eease of 1!espox''.se ix" Nerve aftee Coxtjx^uous Stimul.vtiox^ ......... 127 81. Pesponse in Tin and Platixum Exh.inced aetbe Continuous Stimulation 127, 128 Magnetic Ax-'alogue ........ 132 84. PiECOEDS of Responses to Ixceeasixg Stimuli in Tix 134, 135 ixeffective stimulus becomix^g effective by super- positiox .......... Incomplete axe Complete Fusiox of Effects . Cyclic Curve foe Maximum Effects sho^ving Hysteee.si AcTiox OF Poisox IX Abolishixg PtEspoxsE IX" Neete . Action' of Sti.mulax'i ox" Tix ..... Action' of Stimulax't ox- Plaiixum .... Depkessixg Eeeect of KBe ox Tix .... AiioLiTicN of Response ix Metals by 'Poisox ' . ' MoLECUL.VE AeREST ' BY THE AcTIOX' OF ' PoiSOX ' Opposite Effects of Small and Large Doses ox" tii Response in Metals ....... Retinal Response to Light .... 1.35 136 137 139 141 142 143 143 145 146 150 ILLUSTRATIONS xix I'!'-'- PAGE 90. ItEsroNSK or Sensiiite Cell to Light 152 97. Typical Expebimek^t on the E.M. VaPvLVtiox Peoduced BY Light 1.54 98. MoDiFiOATioisr oe the Photo-sensititb Cell . . . . 155 99. Responses in Fbog's Retina 156 100. Responses in Sensitive Photo-cell 157 101. Efeect of Tempbeatfee on the Response to Light Stimulus 159 102. Effect oe Dueation of Expositee on the Response . . 159 103. Responses of Sensitive Cell to Inceeasing Intensities op Light 161 104. Relation between the Intensity of Light and Magni- lUDK of Response 162 105. Aftee-oscillation 163 106. Teansient Positive Inceease of Response in the Feog's Retina on the Cessation op Light 164 107. Teansient Positive Inceease of Response in the Sensitive Cell ......... 165 108. Decline undee the Continuous Action of Light . . 166 109. Ceetain Aptee-eppects of Light 168 no. APTEE-EPFECT OP LiGHT OP ShOET DuEATION . . . . 172 111. Steeboscopic Design poe the Exhibition of Binoculae Alteenation op Vision . 176 ] 12. Unifoem Responses in Nbeve, Plant, and Metal . . 184 113. Fatigue in Muscle, Plant, and Metal .... 185 114. 'Siaiecase' Effect in Muscle, Plant, and Metal . . 186 115. Inceease of Response aftbe Continuous Stimulation tn Neevb and Metal ........ 186 116. Modified Abnoemal Response in Neeve and Metal Tbanspoemed into Noemal Response aftee Continuous Stimulation 187 117. Action of the same 'Poison' in the Abolition op Re- sponse IN Neeve, Plant, and Metal .... 189 RESPONSE IN THE LIVING AND NON-LIVING CHAPTEE I THE MECHANICAL RESPONSE OF LIVING SUBSTANCES Mechanical response — Different kinds of stimuli — Myograph — Character- istics of response-curve : period, amplitude, forna — 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. A stimulus thus produces a state of excitability which may sometimes be expressed by change of form. Mechanical response to different kinds of stimuli.— This reaction under stimulus is seen even in the lowest organisms ; in some of the amceboid rhizopods, for instance. These lumpy protoplasmic bodies, usually elongated while creeping, if mechanically jarred, con- tract into a spherical form. If, instead of mechanical 2 RESPONSE EY THE LIVING AND NONLIVING (listurljance, we ai)ply salt solution, they again contract, in the same way aslDctbre. Similar effects are proclnced by sudden illumination, or l>y rise of temperature, or by electric shock. A living substance may thus be put into an excitatory state l^y 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 con- siderable 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 exam})le 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 dis- appears, 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 obsei'vation by ordinary means. A myographic apparatus is there- fore 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 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 writino- 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 (%■ !)• Characteristics of the response- curve : (I) Period, (2) Amplitude, (3) Form. — Just as a wave of sound is characterised by its (1) period, (2) amplitude, and (3) form, so may these response-curves be dis- tinguished from each other. As regards the period, there is an enormous variation, corresponding to the functional activity of the muscle. For instance, in tortoise it may be as high as a second, whereas in the wing-muscles of many insects it is as small as g--^ 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 Fig. 1. — Mechanical Levee Becokdek The muscle M with the attached bone is -securely held at one end, the other end being con- nected with the writing lever. Under the action of stimu- lus the contracting muscle XDuUs the lever and moves the tracing point to the right over the travelling recording surface P. When the mus- cle recovers from contrac- tion, the tracing point returns to its original position. See on P the record of muscle curve. 4 RESPONSE IN THE LIVING AND NON-LIVING insects to those i.f tortoises and liibernatiug dormice.' ^ Differences in form and amplitnde of curve are well illustrated hy A-arious 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 gi-adually 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 varjfing 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. ' Biedermann, Electro-physiolo[/y , p. 50. CHAPTEE II ELECTRIC RESPONSE Conditions for obtaining electric response— Method of injury —Current of injury — Injured end, cuproid : uninjured, ziucoid — Current of response in nerve from more excited to less excited — Difficulties of present nomen- clature — 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 lengtli of nerve, when meclianically 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 j^roduced 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 J^ESFOA'SE /X TJ//' /./I7XG AXD NON-LIVING similar clian^Li'es takiii,!:' plact-' at bntli points, and there being tluis no relatiA-e dillereuce l^etween tlie two, the galvanometer Avill still indicate no current. This null- effect is due to the Ixilanchig action of B as against A. (See fig. 2, a.) Conditions for obtaining electric response. — If then we wish to detect tlie response by means of the galvano- meter, one means of doing so will lie in the abolition of this balance, Avhich may Ije acc(jmplislied by making one of the two points, say B, more or less permanently ZrvSOf. A B — - CurrerjJ: of Irqury — >■ Current of Actuf 7h - - Strip of cht^y TTLOistenedj witk^cbCl solution, Fig. 2. — Electi;ic Method of DETECTixr; Xeeve Respoxse {a) Iso-electric contacti^ ; no c-urreut in the galTanometer. ih) The endBmjured; currf nt of injury from B to A: stimulation gives rise to an action current frum A to B. (c) Xon-polarisable electrode. irresponsive. In tliat case, stimnlus will cause greater electrical disturbance . at the more responsive point, say A, and tliis will he sliown 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 strouQ- chemical reao-ents. 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 followa ,.v ■ : ■ ;, ELECTRIC RESPONSE f 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 miinjured to the injured. As long as there is no further dis- turbance this current of injury remains approximately con- stant, and is therefore sometimes known as ' the current of rest' (fig. 2, h). , 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 I! are con- nected by a strip of cloth s moistened with salt solution, it. will be seen that we have a complete voltaic element. A current will now flow from B to A in the metal (fig. 3, a) and from A to B through the electrolyte s. Or instead of connect- ing A and B by a single strip of cloth s, we may connect them by two strips s s', leading to non-polarisable electrodes E E'. The current will then be found just the same as before, i.e. from B to A in the metallic part, and from A through s s' to B, the wire w being interposed, as it were, in the electrolytic part of the circuit. If now a galvanometer be interposed at 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 electro- lytic part of the circuit, that is to sa}^, 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 S RESPOXSE IN THE LIVING AND NON-LIVING tlirough the non-polarisal)le electrode is from left to right. The uninjured end is therefore comparable to the zinc in a voltaic cell (is zincoid), the injured Ijeing copper-like or cuproid.' If the electrical condition of, say, zinc in the voltaic couple (fig. 3, c) undergo any change (and I shall show later that this can be caused Ijy 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 Fig. 3. — Diageaji showing the Coiieespondence between injuiied (B) and UNINJUKED (A) CONTACTS IN NeEYE, AND Cd AND Zn IN A VOLTAIC ELEMENT Comparison of (c) and (d) will show that the injured end of B in fr?) corresponds with the Cu in (c). diminution, and the current hitherto flowing in the circuit will, as a consequence, display a diminution, or negative, variation. Action current. — We have seen tliat a current of injurv — 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 ' 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 cui-rent of injury (fig. 2, V). The action current in the nerve is from the relatively more excited to t/ie relatively less excited. Difficulties of present nomenclature.— We shall deal later with a method by which a responsive cm-rent of action is obtained without any antecedent current of injury. ' Nega- tive variation ' has then no meaning. Or, again, a current of injury may sometimes undergo a change of direction (see note, p. 12). In view of these considerations it is necessary to have at our disposal other forms of expression by which the direction of the current of response can still be designated. Keeping in touch with the old phraseology, we might then call a current ' negative ' that flowed from the more excited to the less excited. Or, bearing in mind the fact that an uninjured contact acts as the zinc in a voltaic couple, we might call it ' zincoid,' and the injured contact ' cuproid.' Stimulation of the uninjured end, approximating it to the condition of the injured, might then be said to induce a cuproid change. The electric change produced in a normal nerve by stimu- lation 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- lo J^JISfOXSi: AY THE LIVIXG AJYD NOX-JJ I'EYG sioii. As the excitatory state disappears with the return of the excitahle tissue to its original condition, the current ^^i action will gradually disappear.' 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 'response,' and its ULtensity varies accordhig to that of the stimulus. Electric recorder. — "We have thus a method of obtaining curves of response electrically. After all, it is not essentially A'er}- diflerent from the mechanical method. In this case we use a magnetic lever (fig. 4, a), the needle of the gah-anometer, which is deflected \)\ the electromagnetic pull of the current, generated under the action of stimulus, just as the mechanical lever was deflected b}- the mechanical pull of the muscle contracting under stimulus. The accompan3dng diagram (fig. 4, Ij] shows how, ' ' The exciting cause is able to produce a particular molecular rearrange- ment in the nerve ; this constitutes the state of excitation and is accompanied by local electrical changes as an ascertained physical concomitant.' ' The excitatory state evoked by stimvilus manifests itself in nerve fibres by E.M. changes, and as far as our present knowledge goes by these only. The conception of such an excitable living tissue as nerve implies that of a molecular state which is in stable equilibrium. This equilibrium can be readily upset by an external agency, the stimulus, but the term " stable " expresses the fact that a change in any direction must be succeeded by one of opposite character, this being the return of the living structure to its previous state. Thus the electrical manifestation of the excitatory state is one whose duration depends upon the time during which the external agent is able to upset and retain in a new poise the living equilibrium, and if this is extremely brief, then the recoil of the tissue causes such manifestation to be itself of very short duration.' — Text-hook of Physioloqi/, ed. by Schafer, ii. 4.53. ELECTRIC RESPONSE (b) under the action of stimulus, the current of rest undergoes a transitory diminution, and how on the cessation of stimukis 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- duces a diminution of current of rest, or a negative varia- tion (e.g. muscles and nerves), yet, in certain cases, there is an increase, or positive variation. This is seen in the re- sponse of the retina to light. Again, a tissue which nor- mally gives a nega- tive variation may undergo molecular changes, after which it gives a positive variation. Thus Dr. Waller finds that whereas fresh nerve always gives negative vaiiation, stale nerve some- times gives positive ; and that retina, which when raj A B " ■< Current of rest ^ CurrertC of action Fig. 4.— Electric Recoedee [a] M muscle ; A uninjured,, B injured ends. E E' non-polarising electrodes connecting A and B with galvanometer G-. Stimulus produces ' negative variation ' of current of rest. Index connected with galvanometer needle records curve on travelling paper (in practice, moving galvanometer spot of light traces curve oii photographic plate). Kising part of curve shows effect of stimulus ; descending part, recover5\ (6) O is the zero i^osition of the galvanometer; injury produces a deflection A B ; stimulus diminishes this deflection to C ; C D is the recovery. fresh gives positive, variation. when stale, exhibits negative 12 RESPONSE IN THE LIVING AND NON-LIVING Tlie following is a tabular statement of tlie two types of response : I. Xeiiatire rari/'tion. — Action current from more excited, to less excited — cuproid change in the excited — e.g. fresh muscle and nerve, stale retina. II. Positire variation. — Action current from less excited to more excited — zincoid change in the excited ■ — e.g. stale nerve, fresh retina.' From this it will be seen that it is the fact of the electrical response of living suljstances 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 practicall}' identical. The two response-curves seen in the accompanying diagram (fig. o), 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 ' I shall Liern mention briefly one complication that might arise Irom 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 bene source of uncertainty. But it is often found, for e.xample 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. Xo such misunderstanding can however occur if we call the current of response towards the more bxf^'itfii positive, and towards the less e.xcited wyathf. ELECTRIC RESPONSE 13 advantage of being applicable in cases where the latter cannot be usefl. 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, fari passu, increase their intensity. Again, when the tissue is killed by poison, electrical response disappears, the tissue passing into an irre- sponsive condition. Anaesthetics, like cliloroform, gradually di- minish, 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 is peculiar to living or- ganisms.^ The response pheno- mena that we have been studying are therefore considered as due to some unknown, super-physical ' vital ' force and are thus relegated to a region beyond physical inquiry. ' ' 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 stimiilated. 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. Fig. 5. — Simultaneods Eecoed OF THE Mechanical (M) and (E) Electrical Responses of THE Muscle of Fkog. (Wal- LEK.) J 4 RESPOXSE ly THE IJVEXG AND NON-LIVING It may, lidwever, i>t^ tliat tliis liiriitaliou is not jasti- lied, and sui'el}', at least nntil we lia\e explored the whole ranu'e of pliysical a<;tion, it cannot be asserted definitely that a particular class of phenomena is hy its verj' nature ontsiile that category. Electric response in plants. — Bat Lefore we proceed to the incphry as to whether tliese responses are or are not due to some ]jhysii-al property of matter, and are to be met with even hi inorganic substances, it will perhaps be advisalde to see Avhether they are not paralleled Ijy phenomena in the transitional world of plants. We shall thus pass from a study of response in highly com- plex animal tissues to tliose given under simpler vital conditions. Electric response has h)een found by Munck, Burdon- Sanderson, and others to occur hi sensitive plants. But it would ha interesting to know whether these responses were confined to plants which exhibit such remarkable mechanical movements, and whether the}' could not also be olotahied from ordinar}- plants where visiljle movements are completely absent. In this connection, Kunkel observed elec-trical (/hanges in association with the injury or flexion of stems of ordinary plants. ■* My own attempt, liowever. Avas directed, not towards the obtaining of a mere qualitative response, but rather to the determination of whetlier throughout the whole range of response phenomena a parallelism between animal and vegetable could be detected. That is to ^ Kunkel thought the electric disturbance to be due to movement of T\-ater through the tissue. It \\-\\\ be shown that this explanation is in- adequate. 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 supei'- position of stimuli ; whether fatigue was present, and in what manner it influenced response ; what were the efl'ects of extremes of temperature on the response : and, lastly, if chemical reagents could exercise any in- fluence in the modification of plant response, as stimu- lating, antesthetic, and poisonous drugs have been founc to do with nerve and muscle. - If it could be proved that the electric response served as a faithful index of the physiological activit} of plants, it would then be possible successfully tc attack many problems in plant physiology, the solutioi of which at present offers many experimental difficul ties. With animal tissues, experiments have to be carriec on under many great and unavoidable difficulties. Th< isolated tissue, for example, is subject to unknowi changes inseparable from the rapid approach of death Plants, however, offer a great advantage in this respect for they maintain their vitality unimpaired during ; very great length of time. In animal tissues, again, the vital conditions them selves are highly complex. Those essential factor which modify response can, therefore, be better deter mined under the simpler conditions which obtain h vegetable life. In the succeeding chapters it will be shown that thi response phenomena are exhibited not only by plant but by inorganic substances as well, and that th' i6 JiESPONSE IN THE LIVING AND NON-LIVING responses are modified by various conditions in exactly the same manner as those of anhnal tissues. In order to sliow how stril^ino■ are these simiharities, I shall for comparison place side l3y 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.' ' My assistant -Mr. J. Bull has rendered me very efficient help in these experiments. '7 CHAPTEE III ELECTRIC RESPONSE IN PLAXTS — METHOD OF NEGATIVE VARIATION Negative variation — Ilesponse recorder — Photographic recorder — Compen- sator — Means of graduating intensity of stimulus — Spring-tapper and torsional vibrator — Intensity of stimulus dependent on amplitude of vibration — Eftectiveness of stimulus dependent on rapidity also. I SHALL first proceed to sliow that an electric response is evoked in plants under stimulation.^ In experiments for tlie 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. ' A preliminary account of Electric Response in Plants was given at the end of my paper on ' Electric Kesponse of Inorganic Substances ' read before the Royal Society on June 6, 1001 ; also at the Friday Evening Discourse, Royal Institution, May 10, 1901. A more complete account is given in my paper on ' Electric Response in Ordinary Plants under Mechanical Stimulus ' read before the Linnean Society March 20, 1902. I thank the Royal Society and the Linnean Society for permission to reproduce some of my diagrams published in their Proceedings. — J. C. B. i8 J'lESrOiYSE IN THE LIVING AND NON-LIVING It must however be reineiubered that tlie response, being a function of physiolosjical activitj' of the plant, is liable to undergo changes at diflerent 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 a})proach of autiunn it undergoes diminution. I give here a list of specimens which will be found to exhibit fairl_y good response : Root. — Carrot {Daucus Carota), radish [Raphanus sativus). Stem. —Geranium {Pelar(/o?iium),vme [Vitis vinifera). Leaf-stalk. — Horse-chestnut {^"Eseidus Hippocas- tanum), turnip [Brassica Napus), cauliflower {Brasslca oleracea), celery {Apium graveolens), Eucharis lily {Eucharis ainazonica). Flower-stalk. — Arum lily [RicJicwdia africana). ■ Fruit. — Egg-plant {Solanum Melongena). Negative variation. — Taking the leaf-stalk of turnip we kill an area on its surface, say B, by the apphcation 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 diflerence 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 beinif ELECTRIC RESPONSE IN PLANTS 19 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. G, 6). The accompanying- figure is a photographic recordof another set of response- curves (fig. 7). The first three responses are for a given intensity of stimulus, and the next six in response to stimulus nearly twice as strong. It will be noticed that fatigue is exhibited in these responses. Other ' A B "* CiiJ-rent o^ injury * a.ction CUTent. Fig. 6. — (a) Expeeijient for exhibiting Electric Eesponse in Plants BY Method of Neg.atiye Vaehtion. (6) Responses 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 injury of B, effect at A is stronger and a negative variation due to differen- tial action occurs. 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 arrano-ements 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^^ ampere produces a 20 RESPONSE IN l^HE LIVING AND NONLIVING deflection of 1 mm. at a distance of 1 metre. For a quick and accurate method of olitaining the records, I devised the following: form of response recorder. The curves are obtained directl}-, 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 b}' clockwork. Different speeds of revolution can be given to it by adjustment of ''■'V^p^i'^r^ "^ !'™v"''V*V'*" Fig. 7. — PiECOED of Responses in Plant (Leaf-stalk of Cauliflowek) BY Method of Negati%'e Variation The first three records are for stimuhis intensity 1 ; the nest six are for in- tensity twice as strong ; tlie snccessive responses exhibit fatigue. The vertical line to the left represents "1 volt. The record is to be read from right to left. the clock-governor, or by changing the size of the driving- wheel. The galvanometer spot is thrown down on the drum by the inclined mirror M. The galvanometer deflection takes place at right angles to the motion of the paper. A stylographic pen attached to a carrier rests on the writing surface. The carrier slides over a rod parallel to the drum. As has been said before, the galvano- meter deflection takes place parallel to the drum, and ELECTRIC RESPONSE IN PLANTS as long as the plant rests nnstimnlated, tlie pen, remaii ing coincident with the stationary galvanometer sp' on the revolving paper, describes a straight line. If, c stimulation, we trace the resulting excursion of the sp^ of light, by moving tlie carrier which holds the pen, tl rising portion of the response-curve will be obtaine The galvanometer spot wiU then return more or le gradually to its original position, and that part of tl curve which is traced during the process constitutes tl recovery. The ordinate in these curves repre- sents the E.M. variation, and the abscissa the time. We can cali- brate the value of the deflection by applying a known E.M.F. to the circuit from a compensator, an noting the deflection which results. The speed of tl clock is previously adjusted so that the recording surfac moves exactly through, say, one inch a minute. Of cour; this speed can be increased to suit the particular exper ment, and in some it is as high as six inches a minut In this simple manner very accurate records may I made. It has the additional advantage that one is able ; once to see whether the specimen is suitable for the pu pose of investigation. A large number of records migl be taken by this means in a comparatively short time Fig. 8. — Kesponse Eecokdeb RESPONSE IN THE LIVEYG AND NONLIVING Photographic recorder.—* >)■ the recoixls may be made photographically. A clockwork arrangement moves a photograpliic plate at a known uniform rate, and a curve is traced on the plate by the moving spot of light. All the records tliat will be given are accurate reproductions of those oljtained 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 hijury, and as the curi-ent of injury may be strong, and throw the spot of light beyond the recording surface, a potentiometer ba- lancing arrangement may be used (fig. 9), by which the P.D.due to injury is exactly compensated ; E.M. variations produced by stimulus are then taken in the usual manner. This compensating arrange- ment 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 C[uantitative measure- ments is to be certain that the intensity of successive stimuli is (1) constant, or (2) capable of gradual increase 1'jy known amounts. Xo two taps given by the hand can be made exactly alike. I have therefore devised the two following methods of stimulation, which have been found to act satisfactorily. Fig. 9. — The Compensator A B is a stretched wire with added resistances E and R'. S is a storage cell. When the key K is turned to the right one scale division = '001 volt, when turned to the leffe one scale division — "01 volt. V is the plant. 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 Hfter (l) — passes through s r. It is provided with a screw- thread, by means of which its length, projecting down- wards, is regadated. 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 Fig. 10.— The Spking-tappek 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 disadvantajje. 24 /RESPONSE EV THE LIVENG AND NON-LIVING The electric tapper.— Instead of the simple meelianiccal tapper, an eleetr(>niai!;uetic tapper may be used. Vibrational stimulus.— I find tliat torsional vibration aflbrds anotlier very efl'ective ]netliod of stimulation (fig. 11). The plant-stalk maybe fixed in a vice (v), the free ends l^eing held in tubes (c c'), provided with three clamping jaws. A rapid torsional vibration^ may now be imparted to the stalk by means of the handle (h). The amplitude of vibration, which determines the intensity of stinuilns, can be accurately measured by Fig. 11. — The Torsional Vibeatoii Plant P is securely held by a vice A^. The two ends are clamped by holders C Q' . By means of handles H H', torsional vibration may be imparted to either the end A or end B of the plant. The end view (6) shows how the amplitude of vibration is predetermined l.)y 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 exj^eriment which shows that torsional vibration is as effective as stimula- tion by taps, and that its stimulating intensity increases, length of stalk Ijeing constant, with amplitude of ' By this is meant a rapid to-and-fro or complete vibration. In order that successive responses should he uniform it is essential that there should be no resultant twist, i.e. the plant at the end of vibration should be in e.Yactly the same condition as at the beginning. ELECTRIC RESPONSE IN PLANTS 25 vibration. It is of course obvious tliat if the lenutli of the specimen be doubled, the vibration, in order to produce the same effect, must be through twice tlie 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 d Fig. 12. — Eesponse in Plant to Mechanical Tap oe Vibeation The end B is injured. A tap was given between A and B and this gave the response-eurve a. A stronger tap gave tlie response h. By means of the handle H, a torsional vibration of i.5° was now imparted, this gave the response c. Vibration through 67^ gav^e 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 EV THE LIVING AND NONLIVING another point has to Ije 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 viln-ations of plants, I find response depending on the quickness with which the vibration is efl^ected. I give below records of successive stimuli, given by vibrations through the same amplitude, but delivered with increasing rapidity (fig. 13). Thus if we wish to maintain the c d, Fig. 13. — Influence OF SrDDENNE.SS ON THE Efficiency of Stimulus The curyes a, h, c, <1 , are responses to vibra- tions of the same ^. . . . c • t amplitude, 30=. In effcCtlVC lUteilSltV of StimuluS COn a the vibration was very slow ; in h it was less slow ; it was rapid in c, and very rapid in d. stant 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. AVith 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, l;)y whose means alone can rigorous demonstration of the phenomena we are studying become possible. 27 CHAPTEE IV ELECTEIC RESPONSE IX PLANTS — BLOCK METHOD Method of block — Advantages of block method — Plant response a physio- logical phenomenon — Abolition of response by antesthetics and poisons — Abolition of response when plant is killed by hot water. I SHALL now proceed to describe another and inde- pendent method which I devised for obtaining plant response. It has the advantage of offering us a com- plementary 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 un- injured 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 b}^ excessive tempera- ;S J^ESrOXSE JX THE LIVEXG AND NONLIVING ture. (Jii stimulatin,!^: 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. G). But we can cause this differential action to become evident by aiu^ther means. For example, if we produce a block, by clamping at C between A and B (fig. 14, a), so that the disturbance made at A Ijy tapping or vibration is prevented from reaching B, we shall then have A thrown into a rela- tiA'ely greater excitatory condition than B. It will now be found that a cur- rent 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, h). AVe have in this method a great advantage over that of negative variation, for we can always verify any set of results by making corroborative rcA'ersal experi- ments. By the method of irijuiy again, one end is made initially abnormal, i.e. different from the condition which it maintains when intact. Further, inevitable changes will proceed unecjually at the injured and uninjured ends, and the conditions of the experiment may tlius undergo unknown vaiiations. But bv the Cnrrtnt of r<:. M (3) ., Mean 14 (1). (-71 Mean -S "I" (1) Odn. (-^) „ (3) „ Mean 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 pro- gressive death from the action of poison, the responses undergo steady diminution till they are completely abolished. Effect of hig-h 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 RESPOXSE IN PLANTS 33 vibration as the stimulus, obtained strong responses at both ends A and B. I then immersed the same stalk for a short time in hot water at about G5° C, and again stimulated it as l^efore. But at neither A nor B could any response now be evoked. As all the external con- ditions 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 droj)s 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 through- out 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 Ri;SFOi\SE AV THE LIVING AND NON IIVING to l:)e due to the responsive action of A. This would not ha^-e l:)een 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, bv the action of the same stimulus. 35 CHAPTER V PLANT RESPOXSE— OX THE EFEECTS OF SINGLE STIMULUS AND OF SUPERPOSED STIMULI Effect of single stimulus — Superposition of stimuli — Additive effect- Staircase effect — Fatigue — No fatigue when sufficient interval between stimuli — Apparent fatigue when stimulation frequency is increased — Fatigue under continuous stimulation. Effect of single stimulus. — In a muscle a single stimulus gives rise to a single twitch wliicli 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 exhibit- ing marked fatigue and others very little. Superposition of stimuli. — If instead of a single stimu- lus a succession of stimuli be superposed, it happens that a second shock is received l:)efore recovery from the first has taken jjlace. Individual eff'ects will then be- come more or less fused. When the frequency is suifi- ciently increased, the intermittent effects are fused, and we find an almost unbroken curve. When for example the muscle attains its maximum contraction (corre- sponding to the frequency and strength of stimuli) it B 2 36 I^ESPONSE AV THE LIVING AND NON-LIVING is thrown into a state of complete tetanus, in which it appears to Ije hekl rigid. If the rapidity be not suffi- cient for this, we have the jagged curve of incomplete tetanus. If there is not much fatigue, the upper part Fig. 16. — Unifoem Eespoxses (E.^dish) of the tetanic curve is approximately horizontal, but in cases where fatigue sets in quickly, the fact is shown by the rapid decline of the curve. With regard to all these points we find strict parallels in plant response. In cases where there is no fatigue, the' successive responses are identical (fig. 16). With superposition of stimuli we have fusion of effects, analogous to the tetanus of muscle (fig. 17). And lastly, the influence of fatigue in plants is to produce a modification of response-curve exactly similar to that of muscle (see below). One effect of superposition of stimuli may be mentioned here. Fig. 17. — Fusion of Effect of Eapidly Succeeding Stimuli (n) in muscle ; (i) in carrot. PLANT RESPONSE 37 Fig. 18. — Additive Effect (rt) A single stimulus of 3° vibration produced little or no effect, but the same stimulus when rapidly super- posed thirty times, produced the large effect (6). (Leaf-stalk of turnip.} Additive effect. — It is found in animal responses that there is a minimum intensity of stimulus, below which no response can be evoked. But even a sub-minimal stimulus will, though singly ineffective, become effective by the summation of seve- ral. 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 ob- served the same staircase effect in plants (fig. 19). Fatigue.— It is assumed that in living substances like muscle, fatigue is caused by the break down or Fig. 19. — ' Staikcase Effect ' in Plant 38 RESFOiVSE IN THE LIVING AND NON-LIVING dissimilation of tissue by stimulus. And till this waste is repaired by tlie 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 ex- planation, 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 fatio-ue products hj 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 con- dition 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 sujjicient interval has been alloioed in each (xise for complete recovery. There is, in such a case, no diminution in intensity of response, that is to say, no fatigue. We have an exacth' parallel case in muscles. ' In muscle with normal circulation and nutrition there is always an inter- val between each pair of '"^ "" ^"'^ J. . 1 • 1 J 7- -'^^°- '^^- — Kecoed hhowing Diminution of stimuli, m IDnlCll the Kesponse when sufficient Time is not 7 • 7 . ,1 , ■, 7 / . Allowed foe Full Eecoveey height of twitch does not diminish even after pro- "i''™'<^ ; "^ '*> *1^«^ intervals were reduced to In (a) stimuli were applied at intervals of one minute ; in (6) the intervale were reduced to half a minute; this caused a diminution of iriiripd Prritnfirm and response. In (c) the original rhythm is re- liaciea eXCaaXLOn, ana stored, and the response is found to be en- no fatigue appears:^ ^^"'"''- <^^^''^"' 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 ^ Biedermann, Electro-physiology, p, 86. 40 JiESPONSE IN THE LURING AND NON-LIVING a minute, instead of one, while the stimuli were maintained at the same intensity as before. It will be noticed (fig. ::^0, b) that these responses appear much feel»ler 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 recover)' from previous strain. The molecular swing towards ec|uilil;)rium had not yet aljated, when the new stimulus, with its opposing impulse, was received. There is thus a diminution of height in the resultant response. The origi- nal rhythm of one minute was now restored, and the succeeding curves (fig. 20, e) at once show increased response. An analogous instance may l)e cited in the case of muscle re- sponse, where ' the lieight of twitch diminishes more rapidly in proportion as the excitation interval is shorter.' ' Fi'om what has just been said it would appear that one of the causes of diminution of resjjonse, or fatigue, is the residual strain. This is clearly seen in fig. 21, in a record which I obtained with celery- stalk. It will be noticed there that, owing to the imperfect molecular recovery during the time allowed, the succeeding heights of the responses have under- gone a continuous diminution. Fiy. 22 "ives a Fig. 21. — Fatigue in Celeky Vibration of 30° at inter vals of half a minute. Hiederoiann, loc. cit. PLANT RESPONSE 41 pliotographic record of fatigue in the leaf-stalk of cauliflowei-. It is evident that residual strain, other things being equal, Avill be greater if the stimuli have been excessive. This is well seen hi fig. 23, where the set of first three curves a is for stimulus intensity of 45° vibration, and the second set B, with an augmented response, for stimulus in- tensity of 90° 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 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 Fio. 22. — Fatigue IN Leaf-stalk op Cauliflowep. Stimulus : 30° vibratiou at intervals of one minute. 90 ABC D Fig. 23. — Effect of Oveeste.ain in Producing F.\tigue Successive stimuli applied at intervals of one minute. Tlie 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 •0.5 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 he seen from record d how far the fatigue had been removed. One peculiarit}' that will Ije 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 removed by fifteen minutes' rest. Fatigue under continuous stimulation.— The effect of fatigue is exhibited in marked degree when a tissue is subjected to continuous stimulation. In cases where there is marked fatigue, as for instance in certain muscles, the top of the tetanic curve undergoes rapid decline. A similar effect is obtained also with plants (fig. 24). The effect of rest in ^^roducing 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. Fig. 24. — Eapid Fatigue unhee Con- tinuous Stijiulation in (a) Mu.scle ; (6) IN Leaf-stalk of Celeky PLANT RESPONSE 43 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 Cakkot In the first three records, two minutes' stimulation is followed by two minutes' recovery. The last record was taken after the specimen had a rest of five minutes. The response, owing to removal of fatigue by rest, is stronger. 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. RESPO.YSE IN THE LIl'ING AND NON-LIVING CHAFIER \1 I'LAXT RKSPOXSI-: — 0.\ DirHASIC VARIATION Diphasic variation — Positive after-effect and positive response — ■ Kadial E.M. variation. iVnEN a plant is stimulated at any point, a mole- cular disturbance — tlie excitatory wave — is propagated Dutvvards from the point of its initiation. Diphasic variation. — This wave of molecular dis- turbance is attended by a wave of electrical disturb- ance. (Usually speaking, the electrical relation between iistmijed and less disturbed is that of copper to zinc.) It takes some time for a disturbance to travel from 3ne point to another, and its intensity may undergo a diminution as it recedes further from its point of origin. Supjjose 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 Ijoth. The eflect produced at A and B will Ijalance 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 Ijy putting PLANT RESPONSE 45 a clamp between A and B, so that the distnrbance 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. :^6, «), then we have (1) the disturl^ance 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, h). 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 EV THE LIJENG AND NONLIVING is therefore difficult to fix an absolutely neutral point, but a point may be found which ap})roaclies this very nearly, and on stiraulathio- the stalk near this, a very interesting diphasic variation has l:)een observed. In a specimen of cauliflower-stalk, (1) stimulus was applied very much nearer A than B (the feeble disturl^ance reaching B was negligible). The resulting response was upward and the recovery took place in about sixty seconds. (CL) A N B Jmi/i Fig. 2f). — Di.\phasic Vaui.i (2) Stimulus was next applied near B. The resultinrr ■esjjonse was now downward (fig. 26, li). (3) The stimulus was now applied near the approxi- natelv neutral point N. In this case, owino- to a slio'ht [ifTerence in the rates of propagation in the two direc- ions, a very interesting diphasic variation was pro- .uced (fig. 20, c). From the record it will be seen hat the disturl^ance arrived earlier at A than at B. liis produced an upward response. But durino- 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 con- tacts 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 dis- turbance 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 oive rise to a neg-ative variation, then durincf the process of molecular recovery there may be over- shooting of the equilibrium position, which may be exhibited as a positive variation. 4S KESPOXSE IX THE LIVING AND NONLIVING Positive variation. — The responses given by muscle oi' nerve are, lutrmally speaking, negative. But tliat of retina is positive. Tire sign of response, however, is apt to lie re\-ersed if there be any nrolecular modification of the tissue from changes of external circumstances. Thus it is often fjLUid 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 exactlv parallel instances in the resjionse of plants. \/\AA^. r\ ^, r Fig. 27. — Abnobmal Positive Eesponses in Si.iLE LE.iF-STAXK of Tuenip CONVERTED IXTO N0R31.1L NEGATIVE UNDER StKONG StIMUL.ATION ' The relative intensities of stimuli in tlie 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 long- continued stimulation, so also in the modified plant the abnormal positive resjjonse passes into negative ^ For general purposes it is immaterial whether the responses are re- corded 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, b}' 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 Fit;. 28. — Abxokjul Positive passing into Nobh.ilL Neg.\tive 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 so RESrOXSE EV THE I.UENG AND NON-LIVING on tlie surface. After a while tlie current (jf injur\- was found to disappear. (_)n exeitino' tlie stem fjy taps or torsional ^•ilJration, a responsive current was observed which Howed inwards from the more distui'lied outer surface to the shielded core inside (fig. 29). Hence it is seen that when a wave of disturbance is propagated along the plant, there is a concomitant wave of radial EM. variation. The swaying of a tree h\ the wind would thus appear to give rise to a radial E.M.F. Fig. 29. — Eadul E.JI. Vaklition 51 CSAPTP]R YII PLANT RESPONSE — ON TOE RELATION BETWEKN STLMULUS AND RESPONSE Increased response with increasing stimulus — Apparent diminution of response witli excessively strong stinuilns. As already said, in the living tissue, molecular dis- turbance induced l)y stimulus is accompanied hj an electric disturbance, which gradually disappears with the return of the disturbed molecules to their position of equilil^rium. The greater the molecular distortion produced Ijy 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 slightlj' convex, then straight and ascending, and lastly, concave to the abscissa (fig. 30). In muscle the linnt 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 E 2 5 J JiESrONSE /lY THE JJlViXG AND NON-LIVING ^rent. When the stiiiuihis is carried lieyond moderate liuiits. the response, owing to fatigue or other causes, n\av sometimes underiio an actual diminution. 1 1 1 1 L 1 Respojise} y ' / / / Muscle Lift /> yf f/ / ,y ' 1 1 2-0 2-2 24- 2-6 2-8 3-0 32 3-4 3 6 3 S 4 Fig. 30. — Cukves showing the Helation between the Intensity or Stimulus and Eesponse Ab>^cissri^ indicate increasing intensity of stimulus. Ordinates indicate magni- tude of response. ("Waller.) I have obtained very interesting resuUs. with reference to the rehition lietween stimulus and response, when experimenting with plants. These results are suggestive of various types of resjionse met with in animal tissues. 1. In order to obtain the simplest type of effects, not com- plicated by secondary phenomena, one has to choose sijecimens which exhibit little fatigue. Having pro- cured these, I undertook two series c>f experiments. In the first [A) the stimulus was applied \)j means of the spring-tapper, and in the second {B) by torsional viliration. Tap Fig. 31 increasing strength 1 : i producing in- creased response in leaf- stalk of tamip. 1;2: PLANT RESPOXSE 53 (.1) The first stimulus was given by a fall of tlie lever through /(, the second through 2 /(, and so on. The response-curves clearly show increasing efl'e(3t with increased stimulus (fig. 31). 24» 5' 7*' 10' \1V> Fig. 32. — lNOKE.iSED Bespoxse with Incke.4.hing Vibbation'al Stimuli (C.iULIFLOWEll-STALK) Stimuli applied at iiiteivals of three minutes. Vertical line — "1 volt. (B) 1. The viljrational stimulus was increased from 2''j° to 0° to "{•'■y' to 10° to 12--j° in amplitude. It will be observed how the intensity of response tends to approach a limit (fig. 32). Table showing ihe Inckeased E.M. Variation peoduced by increasing stimulus Angle of Vibration E.M.F. 2-5° ■04-4 volt 5° ■075 „ 7-6° 090 ,, 10° ■iw „ 12-5° •106 „ 54 /'^^S/'OXS/: AY THE LIJHXG AND NON-LIVING '1. The next liLiure shows how little \';iriati(in is pro- duced with liiw \";due of stimulus, but with iucreasiuo- stimulus the res[)ouse uuderLj'oes a ra]jid increase, after which it tends to approach a limit (liu'. 33, a). 3. As an extrenie iustatice of the case just cited, I have ofteu come across a curious phenomenon. Durini:' the ^ui'adual increase of the stimulus from a low value there ^vould he apparently no response. But Fig. 33. — Ki-i.^rf'XsEs to In-ci;e.i.si.\c.; Stijiuli rr.ouui eh i:y iNCiiE.iSixo Angle of ViBE.ixiox 1'^^) Keeoid with ;i ^[lecinien of fresh i-aclisb. Stimuli applied at ijiter\-a]s of two minute^. The record is taken for one minute. [h] Record for stale radish. There is a re\'ersed response fiu- tiie feehle stimu- lus of -^- \-iljr.itioii. when a criti(;al value was reached a maximum response would suddenly occur, and would not be exceeded when the stiniulu.s was further increased. Here we have a parallel to ^\'hat is known in animal physiolog}' as the ' all or none ' }jrinciple. With the cardiai; mtise of a curve which shows the relation of stimulus to response will at first be slight, the curve will then ascend rapidl}', and at high values of stiuLulus tend to l>ecome horizontal. The curve as a whole becomes, first slightly convex to the abscissa, then straight aud 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 gi^'ing positive.^ instead of the normal negative, response (fig. 33, /*). Diminution of response with excessively strong stimulus. — It is found that in ainmal tissues there is sometimes an actual diminution of response with ex- cessive increase of stimulus. Thus Wallei' finds, in working with retina, that as the intensit}' 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, h, 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 J^ESFOXSE IN THE LIVEXG AND XOX-LIVJNG a common efl'ect of magnetisation is to produce an elon.u'ation of an iron rod. But Bidwell finds tliat as the magnetising- force is pushed to an extreme, at a certain point elongation ceases and is succeeded, with further increase of magnetising force, hy an actual con- traction. Again a photographic pLate, when exposed continuously to light, gives at lirst a negative image. Still longer exposure produces a positive. Tlieu again we have a negative. There is thus produced a series of recurrent reversals. In photographic prints of tiaslies of lightning, two kinds of images are observed, one, the positive — when the lightning discharge is moderately intense — and the other, negati^'e, the so-called ■ dark lightning' — due to the reversal action of an iiUensely strong discharge. In studying the changes of conductivit}' 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 frec[uently found recurrent reversals.^ Diminution of response under strong stimulus traced to fatigue. — But there are instances in plant response where the diminution effect can be deli)iitely traced to fatigite. The records of these cases are extremeh' 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 (A) ' See ' On Electi-ic Touch,' Pnjp. Roy. Soc. Aug. lilOO. PLANT RESPONSE 57 fatigue was present. It will be seen that the i.'uvves obtained by joining the apices of the siKicessive single responses are very similar. In one case there is no fatigue, the recovery from each sthnulus Ijehig complete. Every response in the lb} Fig. 34. — Eesponses to Incbeasing Stimbltis obtained with Two Speci- mens OF Stalk of Caclifloweii In (a) fatigue is absent, in (6J it is present. series therefore starts from a position of perfect equi- lil^rium, and the height of the single responses increases with increasing stimulation. But in the second case, 58 RESPOXSE IX THE LIITNC .LVD XOX-LIVING the sti'aiu is not roiupleteh^ i-eiuo\'ed after any siuLrle stimulation of the series. Tliat recovery is jjartiat is seen Ijy the ,L;-radnal shifting- of the Ijase line ujnvards. In the former ca^e the base line is horizontal and re- presents a condition of ivomplete eqnililjrium. Xow, however, the base line, or line of modified er|uililjrinm, is tilted upwards. Thus even in this case if we measure the heights of suc(:'essive responses from the line of absolute eqnililjrium, tliey will Ije found to increase with increasinL;- stimulus. Ordinarily, however, we make no allowance for the shiftinu' of the base line, measurin^ix response rather from the place of its previous recovery, or from the point of modified equililjiium. .Judged in this wa}', the responses undergo an apparent diminution. 59 OHAPTEE VIII PLANT RESrOXSK — ON THE 1XFLI'J';>X'E OF TFOJirEEATL'KE Effect of very low temperature — Influence of high temperature — Determi- nation of death-point — Increased response as after-effect of temperature variation — Death of ]ihxnt and abolition of response by the action of steam. FoK every plant there is a raug'e of temperature most favouraljle to its ^'ital activity. Above this optimum, tlte vital acti^'ity 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 l:)elow 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 othei's. Length of exposure, it should howe^-er be remembered, is also a determining factor in the Cjuestion as to whether or not the plant shall survive unfavourable conditions of tem- perature Thus we have hardy plants, and plants that are afl'ected by excessive variations of temperature. Within the characteristic power of the species, there may be, again, a certain amount of individual ditlerence. These facts being known, I was anxious to deter- 6o RESPO^rSE LV TJfE LIVING AND NONLIVING mine whether the iiiuloabted chau;j:es iiidai;ed by teiu- Ijerature in the vital activity of pkiiits would afl'ect eleeti'ical response. Effect of very low temperature.— As regards the intlueuce of very low temperatare, I had opportunities of studyiu'i the rpiestion ou the sudden appearance of frost. In the prevdous week, when the tempera- ture was about 10" C, I had obtained strong electric response in radislies wliose value varied fi'om '05 to ■1 volt. But two or three days later, as the effect of the i'rost, I found electric response to have practically disappeared. A few radislies were, liowever, found somewhat resistant, but the electric response liad, even in these cases, fallen from the average value of -075 V. under normal temperatare to 'OOo A^. after the frost. That is to sa}-, the average sensitiveness had been reduced to about oV'. On warming tlie iVost-bitten radish to 1^0° C. there was an appreciable revival, as shown by increase in response. In S2:)ecimens where the effect of frost had been very great, i.e. in those which showed little (jr no electric response, warming did not restore responsiveness. From this it would appear that frost killed some, which 1.53° 4 :.,, Jl7°„ 160 '--•' 1.5.3°., 1 .o^ |17°„ 100 y^) i K0° '? -"-' 11 -' ,.-. Jl7°„ 40 ^^■1 160°,, C6^ Jl7°„ 60 ^^> i.55°„ Electric heating-. — The experiments just described were, however, rather troublesome, inasmuch as, in order to produce each variation of temperature, the specimen had to be taken out of the apparatus, warmed, and remounted. I thei-efore 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 ke})t at each given temperature for 64 RESPONSE IN THE LIVING AND NONLIVING teii niiiiiites. and two records were taken during that time. It was then i-aised 1)y 10° C, and the same process / J Fig. 37. — The Gl.vss Chamber containing the Plant Amplitude of vibration which determines the intensity of stimuhis ie mea.^ured by tlie gr-aduated circle seen to the right. Temperature is regulated by the electric heating coil E. For experiments on action of antestlietics, vapour of cliloroform is blown in through the side tube. was repeated. It will Ije noticed from the record (fig. 38) that in this particular case, as the temperature ^ ^ 20-C 30 T JUL 40°C SOT 65'r 35Tfhj I min Fig. 38. — Effect or Tejipekatuee ox Eesponse The response was aholishecl at the hot-water temperature of .55"^ C. rose from 20° C. to 30' C. there was a marked diminu- tion of response. At the same time, in this case at PLANT RESPONSE 65 least, recovery was quicker. At 20° C, for example, the response was 21 dns., and tlie recovery was not com- plete in tlie 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 quickenino- of recovery may Ije true of individual cases onl3^ Table showing Diminution oe Rbspoksb with Increasing Tempt; EATUEE (■01 Volt = 36 divisions) Temperature Response Temperature Kcspouse 20° 21 -50° 4 30° 7-5 0.5° 3 40' 5-5 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, however, was the prolongation of the period of recovery at these high temperatures. I soon understood the reason of this apparent anomaly. The method adopted in the present case was that of dry heating, whereas the previous ex- periments 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 chaml^ier of a Turkish bath, while immersion in water at 100° G. would be fatal. In order to find out whether subjection to hot water would kill the celerjr-stalk, I took it out and placed it (,r, RESPONSE EV THE LIVING AND NON-LIVING for li\f iniimtes ill water at ')')' C. This, as will be seen from \\\(' i-econl taken afterwards, eftectively killed the plant (h<.':. 3S. w). Increased sensitiveness as after-effect of temperature variation. — A very cnrious effect of temperature ^•al■ia- tlon is the marked increase of sensiti\-eness whicli often 19 C 30 C 25 C O C n 30 C 50 C Temperature fa llinjj 10 C Temperature risinc/ Fig. S'J, —Effect of Kimxi. and Fai.lixg TEiirFKAiniE on the Eespon'se OF Scotch Kale appears as its after-efl'ect. I noticed this first in a series of observations where records were taken during the rise r)f temperature and continued while the tempera- ture was falling (fig. .39). Tlie temperature was adjusted by electri(; lieating. It was found that the responses were markedly enhanced during cooling, as PLANT RESPONSE 67 compared with responses given at the same temperatures wliile warmino-(see tal)le). Temperature variation tlius seems tt) ha^'e a stimulating effect on response, hy increasing molecular niolnhtv in some wav. Tlie second Fifi. 40. — Ef.coeps of Eesponkes in Ecchaeis Lily Dni:i.\ii Kise and Fall of Tempekatuee Stimulus constant, applied at intervals ot one minute. The temperature of plant-chamber gradually rose on starting current in the heating coil ; on breaking current, the temperature fell gradually. Temperature correspond- ing to each record is given below. Temperature rising : (1) 20% (2) 20", (31 22", (4j S.-i^ (5) 5.9°, («) m'-,{l) G.5°. Temperature falling : 18) 60^, (0) .51°, (10) 4.5°, (11) 40°, (12) 'i)^--. recoixl (hg. 40) shows the variation of response in Eucharis lily (1) during the rise, and (2) during the fall Tahle showixc; the ^'aeiaiion" of Rksponsk ix Scotch Kale DURING THE Rise and Fall of Tempkeatfke Temperature 19° C 25° „ 30° „ 50° „ 70° „ Besponse Ee.sponse [Temperature rising] [Temperature falling] 2.3 dn.s. ^ 1<^ ,. . 24 . 11 11 1 . H : : : u : . 7 68 RESPONSE IN THE LIVING AND NONIIVING of temperature. Fig. 41 gives a curve of variation of response during the rise and fall of temperature. Point of temperature maximum. — AVe have seen how, in cases of lowered temperature, response is abolished earher 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 oS"" C, but with Eucharis fairly marked response can stiU be obtained after such Fig. 41. — Cuete showing Vap.iatios of Eesponse is EucH.iEis with the EiSE AND F.iLL or Tempeeatuee immersion and does not disappear till it has been sub- jected 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 proljably 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 chamljer, into which steam PLANT RESPONSE 69 could be introduced. I had chosen a spechnen which gave regular response. On the introduction of steam, with the consequent sudden increase of temperature, there was a transitory augmentation of excitability. Bu-t this quickly disappeared, and in five minutes the plant was effectively killed, as will be seen graphically illustrated in the record (fig. 42). Before 'T^ After Fig. 42.— Effect of Steam in Killing Besponse The two records to the left e.xhibit normal response at 17^ C. Sudden warming by steam produced at first an increase of response, but iive minutes' expo- sure to steam killed the plant (carrot) and abolished the response. Vibrational stimulus of 30° applied ati intervals of one minute ; vertical line = "l volt. It will thus be seen that those modifications of vital activity which are produced in plants by temperature variation can be verj^ 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 RESrONSE JN THE LIVING AND NON IIVING are aljle to juduv that a jjlant lias died, only aftei' A'ariuus indirect ellects of deatli. sucdi as witlieriiio;Jiave LeiiUii to appeal-. ISiit in the electric response we have an immediate indii/ation of the an-est of x'ilality. and we are therehv enabled to (h'tei'nrine the death-point, which it is impossible to do by any otlier means. It maA' lie mentioned here tliat tlie explanation snii;i;'ested by Kunkel, oi' the I'esponse beinp; (hie to movement of water in the jilant. is inadequate. For in tlu-it case we slionld expect a definite stimulation to Ije under all conditions foUoAved by a (hdinite elec'- tric response, wlnise intensity and sign should remain invariable. But we hud. insteath the response to be profoundly modified by any iiifiuence which affects tlie vitality of the plant. For instance, the response is at its uiaxinrum at an optimum temperature, a rise of a few de,£>'rees jjroducing a profound depression ; tlie response disappears at tlie maximum and mhiimum temperatures, and is rcAuved Avlien brought back to the optimum. ^Vna?stli<:'tics and poisons abolish the response. Again, avc have the response undergoing an actual reversal wlieii the tissue is stale. All these hicts shoAV that mere inovement of water could not lie the eflectiA'C cause of plant i'esponse. 71 C'lIArXEK IX PLANT EESPOKSE — El-'I-'KCT (_)F AX.ESTIIE'DCS AND POlSOiS'S Eti'ect of anuestlietics, a test ofvital character of r"sponst' — Effect of chlnro- foriu — Effect of chloral — Efli'ct of formalin — Method in which re- sponse is unaffected by variation of resistance — Achantage of block method — Efi'ect of dose. The most important test b}' wliich vital phenomena are distingnished is the influence on response of naix-otics and poisons. For example, a nei'A'e when narcotised Ijy oliloroform exhiljits a diminishini;; response as the action of the anaesthetic proceeds. (See below, fio-. 43.) Similarly, various poisons have the efiect of permanently abolishing all response. Thus a nerve is killed by strong alkalis and strong acids. I have already shown hoAV plants which previcmsly gave strong response did not, after ajjplication of an ana^stlietic or poison, give any response at all. In these cas;es it was th.e last stage only that conld be observed. I]ut it appeared important to be aljle to trace the growing efiect of antESthetisation or poisonhtg throughout the proc&s,'^. There were, however, two conditions which it at first apijeared difficult to meet. First it was necessary to find a specimen which would noi'mally exhibit no fatigue, and give rise for a long time to a nnifbrm series 7-' KESrONSE IN THE LIVING AND NON-LIVING of response. The iininediate 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 giA-en 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- iny- half an hour, without detectinii; the least variation /'^^^ ':r'M CH.C/ Before ^ Aftev Fi(i. 43. — Effect or Chloeofokm on Neeve Response (Wailee) 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 fiuctnations. 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 feensitiveness rapidly decHiied. 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 pre- judicial effect on its responsiveness. Less perfect than these, but still serviceable, are the leaf-stalks of turnip and cauliflower. Li these the successive responses as a whole may be regarded as regidar, 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 rapidit}^ 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 jjlants, the method is precisely similar to that employed with nerve ; that is to say, where vapour of chloroform is used, it is blown into the plant chamber. In cases of liquid reagents, they are applied on the points of contact a and b and their close neighbourhood. The mode of experiment was (1) to obtain a series of normal responses to uniform stimuli, applied at regular intervals of time, say one minute, the record being taken the while on a photographic plate. (2) Without interrupting this procedure, the anaesthetic agent, vapour of chloroform, was blown into the closed cham]:)er containing the plant. 74 RKS/'OXSK /.V THE I.IVIXG -IXD NON-LIVL\G It will be ^een how rapidly i-lili)rotV)riii piTxliict-s depre.s- sii)iiof response (liij". 44). and how the eflect lirows with time. Ill these exijeriineiits with jdaiits, the same ctirioiis ^liihiiiL'' of the zer(.) line is sometimes iK^ticed as ill ner\'e wlien sulijerted similarly to the action of re- a^u'ents. This is a point of minor importance, the r.-fiire 1 After Ti';. 44. — Effkit of Chlobofiif;m on Eespmnsf.s of Cmirot stimuli o:' •!'>- vibration iit intervals of one jninute. esseiitial p(nnt to fje noticed IjeiiiL;' that the responses are rapidly reduced. Effects of chloral and formalin. — T -live below (digs. 4"). 4(J! two sets ijf records, one for the reagent chloral and the (jther for i'(jrmalin. The reagents were applied in tlie form c)f a soltttielow a record of I'e.sponses uiveii l)_v two ends of leaf- stalk of turnip, stimulated alternately in the manner desci-il)ed. The stalk used was slipiitly conical, and Dwinp to this diffi-rence between the a and B ends tlie responses; piven lj\" one end ^vere sliphtly diii'erent from tlidse L;iven Ija" the otliei', thouuii the stimuli were Brfc ore Aff'-- Fiw. 47. -ABOLiTinx of Eespoxse at koth A and B Exds by the Action OF NaOH Stimuli of 30' vibration were applied at intervals of one minitte to A and B alternately Re^i"ionse was completely aboli^lied twenty-fonr minutes after ayiplicatiou of XaC'H. equal. A few drops of 10 per cent, solution of XaOH was applied to hoth the ends. It will Ije seen how quickl}- this reapent aholished the response of both ends (tip. 47). Effect of dose.— It is sometimes found that while a reapent acts as a jjoison when given in large C[uantities, it may act as a stimulant in small doses. Of the two following records lig. 4S shows the slight stimulating PLANT RESPONSE 79 Before j- Afti-r Firt. 48. — Stimulatixg Action of veey dilute KOH Before | After Fig. 49. — Nearly complete Abolition of Besponse r.y strono KOH The two vertical lines are galvanometer deflections due to '1 volt, before and after the application of reagent. It will be noticed that the total resistance remains nnchanged. 8o JiESPO^'SE IN THE LIVING AND NON-LIVING efiect of very dilute K(_)Ti, and iig. 40 exliibits iieaily complete abolition of response by tlie action of the same reagent when given in stronger doses. So we see that, judged by the final criterion of the effect produced l)y antesthetii's and poisons, the plant response fulfils the test of vital phenomenon. In previous chapters we have found that in the matter of response l)v negative variation, of the jjresence or absence of fatigue, of the relation between stimulus and response, of modificaticjn of response by high and low temperatures, and even in the matter of occasional abnormal variations such as positive response in a modified tissue, they were strictly correspondent to similar phenomena in animal tissues. The remainhig test, of the inflitence of chemical reagents, having now been a})plied, a complete parallelism may be held to have been established lietween plant response on the one hand, and that of animal tissue on the other. 8i CHAPTEE X RESPONSE IN METALS Is response found in inorganic substances? — Experiment on tin, block method — Anomalies of existing terminology — iiesponse by method of depression — Response by method of exaltation. We have now seen that the electrical sign of life is not confined to animals, but is also found in plants. And we have seen how electrical response serves as an index to the vital activity of the plant, how with the arrest of this vital activity electrical response is also arrested temporarily, as in the case amongst others of anses- thetic action, and permanently, for instance under the action of poisons. Thus living tissues — both animal and vegetable — may pass from a responsive to an irre- sponsive condition, from which latter there may or may not be subsequent revival. Hitherto, as already said, electrical response in animals has been regarded as a purely physiological phenomenon. We have proved by various tests that response in plants is of the same character. And we have seen that by physiological phenomena are gene- rally understood those of which no physical explana- tion can be offered, they being supposed to be due to the play of some unknown vital force existing in living- substances and giving rise to electric response to stimu- lation as one of its manifestations. G 82 RESPONSE EY THE LIVEYG AND NONLIVING Is response found in inorganic substances ? ' — It is now for us, however, to examine into the alle^ii'ed super- physiral character of these phenomena by stimulating inorganic substances and discovering wliether they do or do not gi\'e rise to tlie same electrical mode of re- sponse which was supposed to be the special character- istic of living substances. We shall use tli.e same ap'paratMS and the same mode of stimida,tio)i as tliose emphiyed in olita.iniiifi plant response, merely sidistituting, for the stalk of a pilant, a metallic irlre, sa.y ' tin ' (fig. 50). An}' other metal could Ije used histead of tin. Experiment on tin, block method. — Let us then take a piece of tin wire ^ from which all strains have Ijeen previously removed by annealing, and hold it clamped in the middle at C. If the strains have been success- fully removed A and B will be found iso-electric, and no cun-ent will pass through the galvanometer. If A and B are not exactly similar, there will be a slight current. But this will not materially affect the results to be descriljed presently, the slight existino- current merely adding itself algebraically to the current of response. If we now stimulate the end A by taps, or better ' Following another line of inquiry I obtained response to electric stimulus in inorganic substances using the method of condiictivitv variation (see ' De la Generalite des Phenomenes Moleculaires Produits par I'Electricite sur la ^Matiere Inorganique et sur la Matiere Vivante.' 'fracaii.r du Coiiyrh International de PJiysi/jne, Paris, 1900 : and also ' On Similarities of Etfect of Electric Stimulus on Inorganic and Living Substances,' British Associatvm 1900. See Electrician). To brino- out the parallelism in all details between the inorganic and living response 1 have in the following chapters used the method of electro-motive variation employed by physiologists. - By ' tin ' is meant an alloy of tin and lead used as electric fuse. liESFONSE JN METALS 83 Still by torsional vil:)ratioii, a transitory ' current of action ' will l^e found to flow in the wire from P> to A, from the unstimulated to the stimulated, and in the galvanometer from the stinuilated to the unstimulated. Stimulation of B will give rise to a current in an opposite direction. Experiment to exhibit the balancing effect. — If the wire has been carefully annealed, the molecular condi- tion of its different portions is found to be approximately the same. If such a wire be held at the ' balancino- Imuu Fig. .50. — Electric Response in Met.ils {a) Method of block ; [h] Equal and opposite responses when the ends A and B are stimulated ; the dotted portions of the curves show recovery ; [c] Balancing effect when both the ends are stimulated simultaneously. point ' (which is at or near the middle) by the clamp, and a cpiick vibration, say, of 90° be gi^'en to A, an up- ward deflection will be produced ; if a vibration of 90° Ije given to B, there will l)e an equal downward deflec- tion. If now both the ends A and B are vibrated simul- taneously, the responsive E.M. variation at the two ends will continuousl}^ l:)alance each other and the galvano- meter spot will remain c[uiescent (tig. -30, A, B, r). This balance will be still maintained when the block is removed and the wire is vibrated as a whole. It is to be remembered that with the length of wire constant. 84 RESPONSE IN THE LIVING AND NONLIVING the intensity of stimulns increases with the amplitude of vibration. Again, keeping the ampUtude constant, the intensit}^ of stimulus is increased by shortening the wire. Hence it will be seen that if the clamp be shifted from the balancing point towards A, simultaneous vil^i-ation of A and B through 90° will now gis^e a resultant upward deflection, showing that the A response is now relatively stronger. Thus keeping the rest of the circuit untouched, merely moving the clamp from the left, past the balanc- ing point to the right, we get either a positive, or zero, or negative, resultant effect. In tin the current of response is from the less to the more excited point. In the retina also, we found the current of action flowing from the less stimulated to the more stimulated, and as that is known as a positive response, we shall consider the normal response of tin to be in like manner positive. Just as the response of retina or nerve, under certain molecular conditions, undergoes reversal, the positive being then converted into negative, and negative into positive, so it will Ije shown that the response in metal- lic wires under certain conditions is found to undergo reversal. Anomalies of present terminolog-y. — When there is no current of injury, a particular current of response can hardly be called a negative, or positive, variation. Such nomencla- ture is purely arbitrary, and leads, as will be shown, to much confusion. A more definite terminology, free from misunder- standing, would be, as already said, to regard the current to- wards the more stimulated as positive, and that towards the less stimulated, in tissue or wire, as negative. The stimulated end of tin, say the end A, thus becomes JiESFONSE IN METALS 85 zincoid, i.e. the current through the electrolyte (non-polaris- able electrodes with interposed galvanometer) is from a to B, and through the loire, from the less stimulated B to the more stimulated a. Conversely, when B is stimulated, the action current flows round the circuit in an opposite direction. This positive is the most usual form of response, but there are cases where the response is negative. In order to show that normally speaking a stimulated wire becomes zincoid, and also to show once more the anomalies into which we may fall by adopting no more definite termino- logy than that of negative varia- tion, I have devised the following experiment (fig. 51). Let us take a bar, one half of which is zinc and the other half copper, clamped in the middle, so that a disturbance ^^^"'^ztv Cw produced at one end may not reach vomuO. Current' < the other ; the two ends are con - Fig. 51. — Coeeent of Eesponse , 1 , 1 i. J.-U 1, TOWARDS THE STIMULATED EnD nected to a galvanometer through . Hence when Cu stimulated; ac- non-polarisable electrodes. The tioncurrent->, normal b.m.p. , ,1 1 i_i 1 i. 1 J. diminished ('85— 009) v. current through the electrolyte when Zn stimulated: action our- (non-polarisable electrodes and in- Seaset'csT+Til) v"'^' '"" terposed galvanometer) will then flow from left to right. We must remember that metals under stimulation generally become, in an electrical sense, more zinc-like. On vibrating the copper end (inasmuch as copper would then become more zinc-like) the differ- ence of potential between zinc and" copper ought to be diminished, and the current flowing in the circuit would therefore be lessened. But vibration of the zinc end ought to increase the potential difference, and there ought to be then an increase of current during stimulation of zinc. In the particular experiment of fig. 51, the E.M.F. between the zinc and copper ends was found to be -85 volt. This was balanced by a potentiometer arrangement, so that the galvanometer spot came to zero. On vibratmg the zinc wire, a deflection of 33 dns. was obtained, in a direction which 86 RESPOXSE IN THE LIVEXG AXD XON-LI\'E\G showed an iiicrease of E.M.F. On stopping the vibration, the spot of Ught came back to zero. On now vibrating the copper wire, a deflection of 'I'd dns. was obtained in an opposite direction, showing a diminution of E.M.F. This transi- tory responsive variation disappeared on the cessation of disturbance. By disturbing the babmce of the potentiometer, the galvanometer deflection due to a known increase of E.M.F. was found from which the aljsolute E.M. variation caused by disturbance of copper or zinc was determined. It was thus found that stimulation of zmc had increased the P.D. by fifteen parts in 1,000, whereas stimulation of copper had decreased it by eleven parts in 1,000. According to the old terminology, the response due to stimulation of zinc would have Ijeen regarded as positive variation, that of copper negative. The responses however are not essentially opposite m character, the action current in the bar being m both cases towards the more excited. For this reason it would be preferable, as already said, to employ the terms positive and negative in the sense I have suggested, i.e. positive, when the current m the acted substance is towards the more excited, and negative, when towards the less excited. The method of block is, as I have already shown, the most perfect for the study of these responses. In the experiment fig. -JO, if the Ijlock is aljolished and the Avire is struck in tlie middle, a wave of mole- cular disturljance will rea(;h A and B. The mecliauical and tlie attendant electrical disturbance will at these points reach a maximum and then pTadually sul)side. The resultant etlect in the galvanometer will be due to E.-Ej when E, and e^, are the electrical variations pro- duced at A andB by the stimulus. The electri(; chanoes at A and B will continuously balance each other, and the resultant effect on tlie galvanometer will be zero : ( n ) if JiESFONSE IN METALS 87 the exciting disturbance reaches A and B at the saint,- time and with the same intensity ; (A) if the molecidar condition is similar at the two points; and ((■) if the rate of rise and subsidence of excitation is the same at the two points. In order that a resukant effect may be exhibited in the galyanometer, matters haye to be so arranged that the disturbance may reach one point, sa^- A, and not B, and vice versa. This was accompHshed b}- means of a cLamp, in the method of block. Again a resultant differential action may be obtained eyen when the disturbance reaches both A and B, if the electrical excitability of one point is exalted or depressed l^y physical or chemical means. We shall in Chap. XVI study in detail the effect of chemical reagents in pro- ducing the enhancement or depression of excitability. There are thus two other means of obtaining a resultant effect — (2) by the method of relative depression, (3) by the method of relative exaltation. Electric response by method of depression. — We may thus by reducing or abolishing the excitability of one end Ijy means of suitable chemical reagents (so-called method of injuxy) obtain response in metals without a block. The entire lencfth of the wire may then be stimulated and a resultant response will be produced, owing to the difference between the excitability of the two ends. A piece of tin wire is taken, and one normal contact is made at A (strip of cloth moistened with water, or very dilute salt solution). The excitability of B is depressed by a few drops of strong potash or oxaUc acid. By the appHcation of the latter there will be a small P.D. l^etween A and B; this will simply 88 RESFONSE JN THE LIVING AND NON-LIVING produce a displacement of zero. ]3y means of a potentiometer the galvanometer spot may Ije brought l)aclv to the original position. The shifting of the zero wiU not affect the general result. The effect of mechanical stimulus is to produce a transient electro- motive response, which will be superposed algebraically on the existing P.D. The deflection will take place from the modified zero to which the spot returns during recovery. On now stimulating the wire as a whole by, say, torsional vibration, the current of response will be Fig. 52. — Eesponse by Method or Depkeskion (Without Block) When the wire is stimulated as a whole the current of response is towards the more excitable. In [a] A is a normal contact, B has been depressed by oxalic acid ; current of response is towards the more excitable A. In (5) the same wire is used, only A is depressed by oxalic acid and a normal contact is made at a fresh point B', a httle to the left of B in fa). Current of response is now from A towards the more excitable B'. found towards the more excitable, i.e. from B to A (fig. 52, a). A corroborative reA'ersal experiment may next be made on the same piece of wire. The normal contact, through water or salt solution, is now made at b', a little to the left of B. The excitability of A is now depressed by oxalic acid. On stimulation of the whole wire, the current of response will now l:)e found to flow in an opposite direction — i.e. from A to b' — but still from the relatively less to the relatively more excitable (fig. 52, h). HESFONSE IN METALS 89 From these experiments it will be seen how in one identical piece of wire the responsive current ilows now in one direction and then in the other, in absolute conformity with theoretical considerations. ' '^ ^ ^ LJ Method of exaltation.-A ^lo. |^-Metho- »- still more striking COrrobora- The contact Bis made more excitable ^ , 1 by clieniical stimulant (Na^CO.,). tlOn 01 tliese results may, The current of response is towards . , the more excitable B. however, be obtamed by the converse process of relative exaltation of the respon- siveness of one contact. This may be accomplished by touching one contact, say B, with a reagent which like KajCO,, exalts the electric excitability. On stimu- lation of the wire, the current of response is towards the more excitable B (fig. 53). I give four records (fig. 54) which will clearly exhibit the responses as obtained by the methods of relative depression or exaltation. In (a) B is touched with the excitant NasCOj, a permanent current flows from A to B, response to stimulus is in the same direc- tion as tlie permanent current (positive variation). In (Jj) B is touched with a trace of the depressant oxalic acid, the permanent current is in the same direction as before, but the current of response is in the opposite direction (negative variation). In {c) B is touched with dilute KHO, the response is exhibited by a positive variation. In {d) B is touched with strong KHO, the response is now exhibited by a negative variation. The last two results, apparently anomalous, are due to the fact, Avhich will be demonstrated later, 90 J^ES/'ONSE IX THE LIVING AND NON-LIVING that KH( ) in minute quantities is an excitant, wliile in large quau.tities it is a depressant. We have thus seen that we may obtain response (1) by Hock method, (2) by the inethod of injury, or rehitive depression of responsiveness of one contact. fa.) fl) fcj fd.) k r\'" J Fi-i. 54 Perma- nent Current Current of ; Ilesponse ' B treated with so dium carbonate B treated with ox alic acid B treated with very dilute potash B treated wit]i strong potash Current of response is always the more excitable point. towards (a) Response when B is treated with sodium carbonate. — An apparent positive variation. (h) Response when B is treated with oxalic acid. — An apparent negative variation. (c] Response when B is treated with very dilate potash. — Positive varia- tion. ((/) Response when B is treated with strong potash. — Negative variation. The response is up when B is more ex- citable, and down when A is more excitable. Lines thus indicate deflection due to permanent current. and (3) by the metliod of relative exaltation of responsiveness of one contact. In all these cases alike we obtain a consistent action current, which in tin is normally positive, or towards the relatively more excited. 91 CHAPTER XI INORGANIC RESPONSE MODIFIED ArPARATUS TO EXHIBIT RESPONSE IN METALS Conditions of obtaining quantitative measurements — Modification of the block method — Vibration cell — Application of stimulus — Graduation of the intensity of stimulus — Considerations showing that electric response is due to molecular disturbance — Test experiment — Molecular ■s'oltaic cell. ■ We have already seen that metals respond to sti- mulus by E.M. valuation, just as do animal and vegetable tissues. We have yet to see whether the similarity extends to this point only, or goes still further, whether the response-curves of living and in organic are alike, and whether the inorganic response- curve is modified, as living response was found to be, by the influence of external agencies. If so, are the modifications similar ? What are the effects of super- position of stimuli ? Is there fatigue P If there be, in what way does it affect the curves ? . And lastly, is the response of metals exalted or depressed by the action of chemical reagents ? Conditions of obtaining quantitative measurements. — In order to carry out these investigations, it is necessary to remove all sources of uncertainty, and obtain quanti- tative measurements. Many difficulties at first presented themselves in the course of this attempt, but they were 92 RESPONSE IN THE LIVING AND NON-LIVING completely removed by tlie adoption of the following experimental modification. In the simple arrangement for qualitative demonstration of response in metals previously described, successive experiments will not give results which are strictly comparable (1) unless the resistance of the circuit be maintained constant. This would necessitate the adoption of some plan for keeping the electrolytic contacts at A and B absolutely invariable. There should then be no chance of any shifting or variation of contact. (2) There must also be some means of applying successive stimuli of equal intensity. (3) And for certain further exjjeriments it will be necessary to have some way of gradually increasing or decreasing the stimuli in a definite manner. Modification of the block method.— By consideration of the following experimental modifications of the block method (fig. 55), it will be found easy to construct a perfected form of apparatus, in which all these con- ditions are fully met. The essentials to be kept in mind were the introduction of a complete block midway in the wire, so that the disturbance of one half should be prevented from reaching the other, and the making of a perfect electrolytic contact for the electrodes leading to the galvanometer. Starting from the simple arrangement previously de- scribed where a straight wire is clamped in the iniddle (fig. 55, a), we next arrive at [h). Here the wire A B is placed in a U tube and clamped in the nnddle by a tightly fitting cork. Melted paraffin wax is poured to a certain depth in the bend of the tul:ie. The two INORGANIC RESPONSE 93 limbs of the tube are now filled with water, till the ends A and B are completely immersed. Connection is made with the non-polarisable electrodes by the side tubes. Vibration may be imparted to either A or B iDy means of ebonite clip holders seen at the upper ends A B of the wire. /a) Fig. 55. — Successive Modifications of the Block Method feom the ' Stbaight Wiee ' (a) to ' Cell Foem ' (e) When A is excited, current of response in the wire is from less excited B to more excited A. Note that though the current of response is constant in direction, the galvanometer deflection in [d) will be opposite to that in (&). It wiU be seen that the two limbs of the tube filled with water serve the purpose of the strip of moistened cloth used in the last experiment to make electric connections with the leading-out electrodes — with the advantage that we have here no chance of any shifting of contact or variation of surface, the contact between 94 J^ESFONSE E¥ THE LIVING AND NON-LIVING the wire and the surrounding liquid being perfect and invarialjle. ( )n now vibrating the end A of tlie tin wire Ijy means of the el)onite ch}) holder, a cnri-ent will be found to How from B to A tlirongh the wire — that is to say, towards the exeited — and from A to R in the galvano- meter. The next modiliration (c) is to transfer the galvano- meter from the electrolytic to the metallic part of the circuit, that is to say, it is interposed in a gap made b}^ cutting the wire A B, the upper j^art of the circuit being directly connected by the electrolyte. Vibration of A will now give rise to a current of response which flows in the metallic part of the circuit with the interposed galvanometer from « to A. We see that though the direction of the current in this is the same as in the last case, yet the galvanometer deflection is now reversed, for the evident reason that we have it inter- posed in the metallic and not in the electrolytic part of the circuit. The next arrangement (t/) consists simply of the })receding placed upside down. Here a and B are held parallel to each other in an electr(_)lytic bath (water). Mechanical vibration may now be applied to A without affecting B, and vice versa. The actual apparatus, of which this is a diagram- matic representation, is seen in [e). Two pieces, from the same specimen of wire, are clam]jed separately at their lower ends bv means of ebonite screws, in an L-shaped piece of ebonite. The wires are fixed at their upper ends to two electrodes — INORGANIC RESPONSE 95 leading to the ualvauoineter — and kept moderately and unifonuly stretched hy spiral springs. The handle, by which a torsional vibration is imparted to the wire, may be slipped over either electrode. The amplitude of vibration is measured by means of a graduated circle. It will be seen from these arrangements : (1) That the cell depicted in {e) is essentially the same as that in (a). (2) That the wires in the cell being innnersed to a definite depth in the electi'olyte there is always a perfect and invariable contact between the wire and the electrolyte. The difficulty as regards variation of contact is thus eliminated. (3) That as the wires A and B are clamped separately below, we may impart a sudden molecular disturbance to either A or B by giving a quick to-and-fro (tor- sional) vibration round the vertical wire, as axis, b}' means of the handle. As the wire A is separate from B, disturbance of one will not afTect the other. Vibra- tion of A produces a current in one direction, vil)ration of B in the opposite direc- ^'''- ^^--Equal and Opposite Ee- -"■ ^ SPONSES EXHIBITED BY A AND B tion. Thus we have means of verifying every experiment Ijy obtaining corro]Jorati^-e and reversed effects. When the two wires have been brought to exactly the same moleci;lar condition Ijy the 96 liESFOiYSE AV THE LIVING A AW NON-LIVING processes of aimealiiio' or stretcliiiig, the eflects obtained on subjecting A or B to any given stimulus are always equal (fig. 50). Usuall}' I interpose an external resistance varying from one to five niegoluns according to tlie sensitive- ness of tlie wire. The resistance of the electrolyte hi the cell is thus relatively small, and the galvanometer deflections are proportional to the E.M. variations. It is always advisable to have a high external resistance, as by this means one is not only able to kee}) the deflections within the scale, but one is not troubled bv slight accidental disturbances. Graduation of intensity of stimulus. — If now a rapid torsional vibration be given to A or B, an E.X. variation will be induced. If the amplitude of vi])rati(_)n be kept constant, successive responses — in substances which, like tin, show no fatigue — will 1)6 found to be absolutely identical. But as ' the amplitude of viljra- tion ' is increased, response will also become erdiam/ed (see Chap. XV). Amplitude of viljration is measured by means of tlie graduated circle (fig. -j" ). A projecting index, in connection with the vibi'ation-head, plays between fixed and sliding stops (s and s'), one at the zero point of the scale, and the otlier moA'able. Fig. 57. — Top View of the Vieea- Tiox Cell The amplitude of vibration is detei'- mined by nieaiifj of moyable stops S S', fixed to tlie edge of the gra- duated circle G. The index arm I plays between the stops. (The second index arm, connected with B, and the second circle are not shown.) INORGANIC RESPONSE 97 The amplitude of a given vibration can tlius l^e pre- determined by the adjustment of the sHding stop. In this way we can obtain either uniform or deiinitely graduated stimuli. Considerations showing that electric response is due to molecular disturbance. — The electromotive variation varies with the substance. With superposition of stimuli, a relatively high value is obtained in tin, amounting sometimes to nearly half a volt, whereas in silver the electromotive variation is only about '01 of this value. The intensity of the response, however, does not depend on the chemical activity of the sub- stance, for the electromotive variation in the relative!}^ chemically inactive tin is greater than that of zinc. Again, the sign of response, positive or negative, is sometimes modified by the molecular condition of the wire (see Chap. XII). As regards the electrolyte, dilute NaCl solution, dilute solution of bichromate of potash &c. are normal in their action, that is to say, the electric response in such electrolytes is practically the same as with water. Ordinarily 1 use tap-water as the electrolyte. Zinc wires in ZnSO., solution give responses similar in character to those given by, for example. Ft or Sn in water. Test experiment.— It may be urged that the E.M. effect is due in some way (1) to the friction of the vibrating wire against the liquid ; or (2) to some unknown surface action, at the point in the wire of the contact of liquid and air surfaces. This second objection has already been completely met in experi- H 98 RESPONSE IN THE LIVING AND NON-LIVING mental modification, fig. -J-j, /*, where the wire was shown to pive response wlien iiept completely immersed in water, variation of surface being thus entirel)' eliminated. Both these questions may, however, be subjected to a definite and final test. AVhen the wire to be acted on is clamped below, and vibration is imparted to it, a strong molecular distnrliance is produced. If now it be carefully released from the clamp, and the wire rotated liackwards and forwards, there could be little molecular disturbance, but the liquid friction and surface variation, if any, would remain. The eft'ect of any slight disturb- ance outstanding owing to shaking of the wire would be relatively vei'y small. We can thus determine the effect of liquid friction and surface action by repeating an experiment with and without clamping. In a tin wire cell, with interposed external resistance ec[ual to one million ohms, the wire A was subjected to a series of vibrations through 180°, and a deflection of 210 divisions was obtained. A corresponding negative deflection resulted on vil:)rating the wire 15. Xow A was released from the clamp, so that it could be rotated backwards and forwards in the water by means of the handle. On viljrating the wire A no measurable deflection was produced, thus showing that neither water friction nor surface variation had anything to do with the electric action. The vibration of the still clamped B gave rise to the normal strong deflection. As ah the rest of the circuit was kept absolutely the same in the two difl^erent sets of experiments, these INORGANIC RESPONSE 99 results conclusively prove that the responsive electro- motive variation is solely due to the molecular disturbance produced by mechanical viljration in the acted wire. Anew and theoretically interesting molecular voltaic cell may thus be made, in which the two elements con- sist of the same metal. Molecular disturbance is in this case the main source of energy. A cell once made may be kept in working order for some time by pouring in a little vaseline to prevent evaporation of the liquid. It will he shown further, in succeeding chapters, by numerous instances, that any conditions which increase molecular mol^ility will also increase intensity of response, and conversely that any conditions having the reverse effect will depress response. JiESPO.VSE IiV THE LIVING AND NON-LIVING C'lIAPTEE XII INOECtAXIC liKSroXiSE — MCTHODS OF ENSURING CONSISTENT RKSULTS Preparation of wire — Effect of single stimulus. I SHALL HOW proceed to describe in detail the response- curves obtained with metals. The E.M. variations resulting- from stimulus range, as has been said, from •4 volt to -01 of that value, according to the metal employed. And as these are molecular phenomena, the effect will also depend on the molecular condition of the wire. Preparation of wire. — In order to have our results thoroughly consistent, it is necessary to bring the wire itself into a normal condition for experiment. The verv fact of mounting it in the cell strains it, and the after-effect of this strain may cause irregularities in the response. For the purpose of bringing the wire to this normal state, one or all of the following devices may be used with advantage. (1) The wires obtained are usually wound on spools. It is, therefore, advisable to straighten any given length, before mounting, by holding it stretched, and rubbing it up and down with a piece of cloth. On washing with water, they are now ready for mountino- in the cell. INORGANIC RESPONSE lo. (2) The cell is usually filled with tap-water, and a period of rest after makiug up, generally speaking, improves the sensitiveness. These expedients are ordinarily sufficient, but it occasionally happens that the wire has got into an abnormal condition. In this case it will be found helpful (3) to have recourse to the process of annealing. For if re- sponse be a molecular phenomenon, then anything that increases molecular mobility will also increase its ■VVV JJetorc t After Fin. 3x. — Effect of Annealing on increasing the Response of both A ani> B WiKES (Tin) Stimuli (viVjratioii of IGO^) applied at intervals of one minute. intensity. Hence we may expect annealing to enhance responsiveness. This inference will be seen verified in the record given in fig. -38. In the case under con- sideration, the convenient method employed was by pouring hot water into the cell, and allowing it to stand and cool slowly. The first three pairs of responses were taken by stimulating A and B alternately, on mounting hi the cell, which was filled with water. Hot water was then substituted, and the cell was 102 J^ESPO.VSE IN THE LIVING AND NON-Lll'ING allowed to cool down to its oriLjiiial temperature. Tlie six folio wiiiu; pairs of responses were then taken. That this beneficial efl'ect of annealini;- was not due to any accidental circumstance will be seen from the fact that hotli wires have their sensitiveness equally enhanced. (4) In addition to this mode of annealini;-, both wires may be short-circuited and vil)rated for a time. Lastly (5) slight stretching in situ will also sometimes be found benelicial. For this purpose I have a screw arrangement. B}' one or all of these methods, with a little })ractice, it is always possil )le to bring the wires to a normal con- dition. The responses suljsequently obtained Ijecome extraordinarily consistent. There is therefore no reason why perfect results should not be arrived at. Effect of single stimulus. — The accompanying figure (fig. -39) gives a series, each of which is the response- curve for a single stimulus of uni- form intensity, the amplitude of vibratioii being kei)t constant. The perfect regularity of responses will be noticed in this figure. The wire after a long period of rest may be in an abnormal condition, but after a short })eriod of stimulation the re- sponses become extremeh' regulai', as may be noticed in this figure. Tin is, usually speaking, almost inde- fatigable, and I have often obtained several hundreds of successive responses showing pra(_'tically no fatigue. In the figure it will be noticed that the rising portion i ■ Fig. 59.— Uniform Ee .spoNSES IN Tin INORGANIC RESPONSE 103 of tlie curve is somewhat steep, and the recovery convex to the abscissa, tlie fall being relatively rapid in its first, and less rapid in its later, parts. As the electric variation is the concomitant effect of ]nole- cular disturbance — a temporary upset of the molecular equilibrium — on the cessation of the external stimulus, the excitatory state, and its expression in electric variation, disappear with the return of the molecules to their condition of equilibrium. This process is seen clear!}' in the curve of recovery. Different metals exhibit different periods of recovery, and this again is modified by any influence Avhicli affects the molecular condition. That the excitatory state persists for a time even on the cessation of stimulus can be independenth' shown by keeping the galvanometer circuit open during the application of stimulus, and completing it at various short intervals after the cessation, when a persisting electrical e'ffect, diminishing rapidly with time, will l)e apparent. The rate of recovery immediately on the cessation of stimulus is rather rapid, but traces of strain persist for a short time. T04 RESPONSE AY THE LIVING AND NON-LIVING C'HAPTEE XIII IXOKGANin RESPONSE :\[OLECULAR iloBILITY : ITS INFLUENCE OX RESPOXSI'; Effects of molecular inertia — Prolongation of jieriod of recOTery by over- strain — Molecular model — lieduetion of molecular sluggishness attended by quickened recovery and heightened response — Effect of temperature — Modification of latent period and period of recovery by the action of chemical reagents — Diphasic variation. We have seen that the stimulation of matter causes an electric variation, and that the acted substance liTaduaUv recovers from the effect of stimrtlus. A-N'e shall next study how the form of response-curves is modified by various agencies. In order to study these effects v,'e luust use, in practice, a highly sensitive galvairometer as the recorder of E.M. variations. This necessitates the use of an instrument mth a comparatively long period of swing of ireedle, or of suspended coil (as in a D'Arsonval). (Jwing to inertia of the recording galvanonreter, however, there is a lag produced in the records of E.M. changes. But this can be distinguished from the effect of the nrole- cular inertia of the substance itself h\ conrparing two sifccessive records taken with the sairre instrument, in oiLC of which the latter efl'ect is relatively absent, and in the other present. We wish, for example, to find out INORGANIC RESPONSE 105 wlietliei' the E.M. effect of meclianical stimulus is in- stantaneous, or, again, whether the efl'ect disappears immediately. We first take a galvanometer record of the sudden introduction and cessation of an E.M.F. on the circuit containing the vibration-cell (fig. 60, a). We then take a record of the E.M. effect produced by a stimulus caused by a single torsional vibration. In order to make the conditions of the two experiments as similar as possible, the disturbing E.M.F., from a potentiometer, is pre- viously adjusted to give a deflection nearly equal to that caused by stimulus. 60 [a) Arrangement for applying a short-lived E.M.F. (6) DiiJerence in the periods of recovery: (ll from instantaneous E.M.F.; and |2 1 that caused by mechanical stimulus. The torsional vibration was accomplished in a quarter of a second, and the contact with the potentiometer circuit was also made for the same length of time. The record was then taken as follows. The record- ing drum had a fast speed of six inches in a minute, one of the small subdivisions representing a second. The battery contact in the main potentiometer circuit was made for a quarter of a second as just mentioned and a record taken of the effect of a short-lived E.M.F. io6 RESPONSE /.V THE LIVING AND NON-LIVING on the circuit coiitaiiiinn- the cell. (.1) A record was next taken of the E.IM. variation produced in the cell b}' a siuiiie stimulus. It will l)e seen on comparison of the two records that the maximum efl'ect took place relatively later in the case of mechanical stimulus, and that wliereas the galvanometer recovery in the former case took place in 1 1 seconds, the recovery in the latter was not complete till after GO seconds (fig. 60. Ii). This sliriws that it takes some time for the efl'ect of stinuilus to attain its maximum, and that the eflect does not disappear till after the lapse of a certain intei-val. The time of recovery from strain depends on the intensity of stimulus. It takes a longer time to recover from a strcjnger stimulus. But, other tliino-s being equal, successive recovery periods from suc- cessive stimulations of equal intensity are, generally speaking, the same. AYe may now study the influence of any chanoe in external conditions 1)} oliserving the modifications it produces in the normal curve. Fn:. 01. pKOLOXliATIOX OF pElilOD OF EfCOVEEY AFTEE OvEKSTEAIX HecoYery is complete in HO" when the stimulus is due to 20" vibration. But with stronger stimulus of 40'-- vibration, the period of recoverv is iirolouo-ed to 00". ■ •■" Prolongation of period of recovery by overstrain. The pair of records given in fig. (il .^^hows lu.w INORGANIC RESPONSE 107 1 recovery is dela3-ed, as the effect of overstrain. Curve (a) is for a single stimulus due to a vibration of amplitude 20°, and curve [b] for a stimulus of 40° amplitude of vibration. It will Ije noticed how rela- tively prolonged is the recovery in the latter case. Molecular Model. — We have seen that the electric response is an outward expression of the .molecular disturbance produced by the action of the stimulus. The rising j)art of the response- curve thus exhibits the effect of molecular upset, and the falling part, or recovery, the restoration to equilibrium. The me- chanical model (fig. 62) will help us to visualise many complex response phenomena. The mo- lecular model consists ^-v^- d e Fig. 62. — Mohel showing the Effect of Feiction of a torsional pendulum — a wire with a dependent sphere. Bj^ the stimulus of a blow there is prodiiced a torsional vibration — a response followed 1j\' recovery. The writing lever attached to the pendulum records loS J '>^ r \\ ^-— f^J A/. ;5" hA j 4.5° ^ ^ ^ 15" 30 4-5 60" O Fig. 64 15" 30 4-5 60 (a) Three sets of responses for 45°, 90", and 18.3^ vibration in a sluggish wire. {h) The next tliree sets of responses in the same wire ; increased mobility con- ferred by previous vibration has heightened the response. o-reater strain consequent on heightened response has a general tendeinjy to a prolongation of the period of recovery. It is thus seen that when the wire is in a sluggish condition, successive vibrations confer increased mole- cular mobility, which finds expression in quickened re- covery or heightened response. Effect of temperature. — Similar considerations lead us to expect that a moderate rise of temperature will be conducive to increase of response. This is exhibited in INORGANIC RESPONSE m tlie next series of records. The wire at tlie low tem- perature of 5° C. happened to be in a shiggish condition, and tlie responses to vibrations of 45° to 90° in amplitude were feeble. Tepid water at 30° C. was now sidjstituted for the cold water in the cell, and the responses under- ib) 5 C 30°C 90° C Fig. 65. — Besponses of .1 Wip.e to Amplitudes of Vibration 4.5° and 90° (rt) Resx^onses when the wire was in a sluggish condition at temperature of 5° C. (6) Enhanced response at 30° C. (c) Diminution of response at 90° C. went a remarkable enhancement. But the excessive molecular disturbance caused by the high temperature of 90° C. produced a great diminution of response (fig. 65). Diphasic variation. — It has already been said that if two points A and B are in the same physico-chemical condition, then a given stimulus will give rise to similar excitatory electric effects at the two points. It the 112 RESPONSE EV THE LIVING AND NONLH'ING nalvanonieter deflection is ' up ' wlieu A alone is excited, the excitation of B will give rise to a downward deflection. When the two points are simultaneously excited the electric variation at the two points will (■y»,i/««o?A.s/?/ balance each other. Under such conditions there will be no resultant deflection. But if the intensity of stimulation of one point is relatively stronger, then the balance will be disturbed, and a resultant deflection produced whose sign and magnitude can Ije found independently b}' the algebraical summation of the individual efli^'ects of A and B. It has also been shown that a balancing point for the block, which is approximately near the middle of the wire, may be found so that the vibrations of A and B through the same amplitude produce equal and opposite deflection. Simultaneous vibration of both will give no resultant current ; when the block is abolished and the wire is viljrated as a whole, there will still Ije no resultant, inasmuch as similar excitations are produced at A and B. After ol)taining the balance, if we apply an ex(dting reagent like Na^COj at one point, and a depressing reagent like KBr at the other, the responses will now become un- equal, the more excitable point giving a stronger deflec- tion. We can, however, make the two deflections equal by increasing the amplitude of vibration of the less sensitive point. The two deflections may thus l:)e ren- dered equal and opposite, but the time relations — the latent period, the time rate for attaining the maximum excitation and recovery from that effect — will no lono-er Ije the same in the two cases. There would therefore INORGANIC RESPONSE 113 be no continuous balance, and we obtain instead a ver}- interesting diphasic record. I give below an exact re- production of the response-curves of A and B recorded on a fast-moving drum. It will be rememl:»ered that one point was touched with NajCOj and the other with Fio. 66. — Diphasic Vakiation a) Records of A and B obtained separately. R' is the resultant by algebraical summation, {h) Diphasic record obtained by simultaneous stimulationof A and B. KBr. By suitabl)'' increasing the amplitude of vibration of the less sensitive, the two deflections were rendered approximately equal. The records of A and B were at first taken separately (tig. 66, a). It will be noticed that the maximum deflection of A was attained relatively I 114 RESFOXSE IX THE LIVING AND NON-LIVING much earlier than that of B. The resuhaut curve r/ was obtained by summation. After takinp; the records of A and P, separately, a record (jf resultant effect r. due to simultaneous vil)ra- tion of A and ]', was next taken. It f^ave the curious two-phased response — positive eflei't followed by neu'ative after-^-if)ration, practically similar to the re- sultant cui-ve r' (iii;:. on, A). The positive portion of the curve is due to A effect and the negative to IJ. If Ij}' any means, say bv either increasing tfie amplitude of viljration of A or increasiuL!' its sensiti^-eness, the response of A is very greatly enhanced, then the positive effect would l)e predominant and the negative effect wuuld become inconspicuous. When the two constitttent responses are of the same order of niagnitude, we si i all have a positive response followed by a negative after-vibration ; the first twitch will Ijelong to the one which responds earlier. If the response of A is very much reduced, then the jjositive effect will Ije reduced to a mere twitch and the negative effect will Ijecome predominant. I give a series of records, fig. G7, in which these three principal types are well exhibited, the two contacts having been rendered unequally excitable l^y solutions of the two reagents Kiir and XaX'Oj. A and B were \-ibrated simultaneously and records taken, (a) First, tlie relative response of B (downward) is increased bv increasing its amplitude of vibration. The amplitude of vibration of A was throughout maintained constant. The negative or downward response is now very con- spicuous, there being only a mere preliminary indication ixorgajVIc response "5 of tlie positive effect. (A) The amplitude of vibration of B is now sliu'litly reduced, and we obtain the diphasic effect, (c) The intensity of vibration of B is diminished still further, and the negative effect is seen reduced to a slight downward after-vibration, the positive up-curve being now ver}- prominent (fig. 67). CO I '') ( .■ ) Fk;. G7. — Negative, DirHAsic, and Positive Resultant Eesponse Continuous transformation from negative to positive I have shown the three phases of transformation, the intensity of one of the constituent responses being- varied by altering the intensity of disturbance. In the following record (fig. 68) I succeeded in obtaining a continuous transformation from jjositive to negative phase by a continuous change in the relative sensitiveness of the two contacts. I found that traces of after-effect due to the applica- tion of NajCOj remain for a time. If the reagent is previously applied to an area and the traces of the I 2 Ti6 RESPONSE IX THE JJl'IXG AND N0N-L/17X(J cai'ljonate then ^vas]lell oH'. tlie increased sellsiti^'elless conferred disappears uradually. -\.,L'ain, if wf apply Na.X'O, solution Xo a fresh point, tlie sensiti\'eiiess pTadually increases. Tliere is another further intei'estinL!' point tM he noticed: the heiiinning of response i> eaiiiei' wlie)i the a})pli<;'ation of Xa,,'J( );; is fresh. We have thus a wii'e held at one end, and successive unifi)i-ni vibrations at intervals of one nhnute innjai'ted Fio. 68. — CoxTrsTous Teansfoejiatiox fkom NEfUTivi; to Poshive IIIKOCGH IXIEEMEWATE DlPIIASIC PlESPONSE Tliick dots represent the times of apijlication of successive stimuli. to the Avire as a whole, by means of a vihratioit head on the other end. Owinu' to the after-ellect of pre\'ious apjJication oi' XaX'' ). the sensitiA'Puess of B is at the beijinninc!' ;jreat. heitce the three resultant responses at the Ije- pinninu" are ne;_!'ative or duwicward. Dilute solution of Xa.X'Og 1:^ next ajjphed to .v. The response of A (up) Ijegins earlier and continues Xv 'jyo^x stroiiLi-er and stroni;-er. Hence, after this application, the ]'esi)onse shows a preliminary jjositive twitch of a fi illowed l)V negative deflection of B. The positive Lii-ows INORGANIC RESPONSE 117 continuously. At the fifth response the two phases, positive and negati\-e, become equal, after that the positive becomes ver}- prominent, the negative being reduced as a feeljle after-vil)ration. It need only be added here that the diphasic \'aria- tions as exhiljited by metals are in every way counter- parts of similar phenomena observed in animal tissues. iS RESJ'OIVSE IN TJIE LIl'ING AXD NON-LIVING CHAITEU XI \^ INOJKiAMC KKSPONSK — FATIGL'K, STAIKCASK, AXD .MODJl'IEU RESrONSE FatigiLH in nujtals — Fatigue under continuous >f"imulatio)i — Staircase effect — lieversed ivsponses dui' to molecular modification in n"-r\e and metal, and their transformation into normal after continuous stimula- tion — Increased ri'Sponse after contiiiuoiis stimulation. Fatigue. — In soiite metals, as in muscle and in plant, we lincl instances of that itrouressive diminution of response wliicli is kno\Yn as fati_L;ue [{vj.. (i',)). The accompanying' record sliows this in platinum (Iil:-. 70). It has been said that tin is practically indefatigahle. AVe must, howcA^er, remembei' that this is a cittestion oi' degree 'i,iw.u .^ULU Fig ()',l. — Fatioue IX Muscle (Wallec) Flo. 7". — Fatilce IX I'LAI'IXrm only. Xothing is absolutely indefatigaljle. The exhi- bition of fatigue depends dificati(_)n does not always occur, yet is too frequent to be considered aljuormal. Again, when such a nerve is subjected to tetanisation or continuous stimulation, this modified response tends once more to Ijecome normal. It is found that not only tetanisation, but also CO2 has the power of converting the modified response into normal. Hence it has Ijeen suggested that the c-on^'er- sion imder tetanisation of modified response to normal, in stale nerve, is due to a hypothetical evolution of COj in the nerve during stimulation.^ (2) In metals. — I have, however, met with exactly parallel phenomena in metals, where, owing to some molecular modification, the responses became reversed. and where, under continuous stimulation, though here ' ' Considering that we have no previous e\icleiice of any cliemieal or ])bysical change in tetanised nerve, it seems to me not worthwhile pausing to deal with the criticism that it is not COj, but " something else " that has given the result.' — Waller, Animal Electricity, p. 59. That this ])heno- menon is nevertheless capable of pjhysical explanation will Ije shown presently. TJ4 RESPOXSE IX THE LIIENG AXD XOX-LTVING there could l,ie iin po^isibility of tlie evolution of CT).,. tlle^' tended nii'aiii to Ijeeonu^ iioi'inal. Tf after uiouiiting a wire in a cell filled witli water, it lie set aside foi' too l(-)ii;j- a time. I have soiuetinies noticed tliat it undergoes a certain uiodilication, owing to winch its i-csponse ceases to he normal and l)econies reversed in sign. I have ol)tained this efi'cct Avith various metals, for instance lead and tin, and even with the chemicallv inactive substance — platiinuu. ■' O I I f ^^^<^^mfy;»>-^ ie/ore Fii;. 75. — AnxoB5iAL I'nsiTiYE (up) ItEsroxKE IX Xeuve converted into Nor.MjL (I'ow.x) Eesponse aftee CoxTixuors STiiruLATiox T (Waller) The gahanometer is not dead-ljfut, and shows aftei'-osciUatioii. The sul)ject will he made clearer if we first follijw in detail the phenomenon exhibited hy modified nerve, giving this abnormal response. Tlie normal responses in nerve arc usnalh' represented by 'down' and the reversed abnormal resjjonses Ijy ' up ' curves. In the modified nerve, then, the abnormal responses are 'up' instead of the normal • dowm' The record of stich abnoi'mal res})oirse in the modified nerve is shown in fio;. 7-3. It will l)e notic'ed that in this, tlie successive INORGANIC RESPONSE T25 responses are undergoing a diminution, or tending towards tlie normal. After continuous stimulation or tetanisation (T), it will be seen that tlie abnormal or ' up ' responses are converted into nor)nal or ' down.' I sball now give a record which will exhibit an exactl}' similar transformation from the abn(jrmal to normal response after contiiuious stimulation. Here the normal responses are represented 1)y ' up ' and the abnormal bv ' down ' curves. This record was given 1)}' a tin wire, wliich had been molecularly modified (fig. 76). We have at first the abnormal Before T After Fig. 76 Before After Abnormal 'down ' response in tin (fig. 76) and in platinum (fig. 77) transformed into normal ' up ' response, after continuous stimulation, T. responses ; successive responses are undergohig a diminution or tending towards the normal ; after con- tiiuious stimulation (T), the subsecpient responses are seen to have become normal. Another record, (jbtained with plathium, shows the same phenomenon (fig. 77). On placing the three sets of records — nerve, tin, and ,26 RESFOXSE /X THE LIVING AND NO Nil VI NG platinum — side by side, it will Ije seen Ikjw essentially similar they are in every respect.' This re\'ersion to nurinal is seen to have appeared in a pronounced niannei' after rapidly continuous stintula- tion, in process of which tlie modified molecular condi- tion must in some way have reverted to the normal. Beimj- desirous to trace this chanii-e _L!-radually taking- place, I took a platiiuim wire cell givino- modified responses, and olitained a series of records of efi'ects of Fig. 7s. — The Geadual Teansition from ABXoKirAL to Normal Response IN Platinum The tran-^itioiiwiU be seen to have commenced at tlie third and ended at the seventh, counting from the left. individual stimuh C(jntinued for a long time. In this series, the p)oints of transition from modified response to normal will be clearly seen (fig. 78). ' 111 order to explain the phenomena of electric response, some physio- logi.sts assume that the negative response is due to a process of dissimilation, or breakdown, and the positive to a process of assimilation, or building up, of tlie tissue. The modified or positive response in nerve is thus held to be due to assimilation ; after continuous stimulation, this process is supposed to be transformed into one of dissimilation, with the attendant negative response. How arbitrary and unnecessary such assumptions are will become evi- dent, when the abnormal and normal responses, and tlieir transformation from one to the other, are found repeated in all details in metals, where there can be no question of the processes of assimilation or dissimilation. TXORGAAVC RESFOXSE 127 Increased response after continuous stimulation. — We have seen that i-e- sponses to uniform sti- niuh sometimes show a staircase increase, ap- parently owino- to tlie gradual removal of mole- cular slugoishness. Pos- sibly analogous to this is the increase of re- sponse in nerve after continuous stimulation or tetanisation, observed by Waller (fig. 79). Like the staircase eflect, this a T h Fio. 79. — The Normal Response a ix Nerye Enhanced to b after Con- tinuous Stimul.ation T (Waller) The normal resx^onse in nerve ifl recorded ' down.' Before T After Yio. 80. — Enhanced Besponse in Platinum after Cont inuous Stimulation T contravenes the commonly accepted theory of the dis- similation of tissue by stimulus, and the consequent depression of response. It is suggested by Waller that 128 RESPONSE I.V THE LIVING AND NO Nil VINO this increase of response alter tetanisatioii may be due to tlie hvpotlietical e\'oluti<)n of CC),> to wliieli allusion lias previously been made. But there is an exact correspondence between this phenomenon and that exliibited by metals under simihir conditions. I pive lierc two sets of rec(.»i'ds (iiys. 80, 81), one obtained witli ])hitinnm and the Before T Alter Fig. 81. — Enhanced Kespoxse in Tin aftee CoNTiNunrs Siimulat on T other with tin, which demonstrate how tlie I'esponse is enhanced aftei' continuous stimidation in a manner exactly similar to that noticed in the (.-ase of nerve, The explanation which has been suLi'o-ested with regard to the staircase effect — increased molecular mobility due to i-emoval of sluggislniess by repeated stimuh^tiou — would appear to Ije applicable in this case INORGANIC RESPONSE 129 also. It would appear, then, that in all the phenomena which we have studied under the heads of ' stair- case ' effect, increase of response after continuous sti- mulation, and fatigue, there is a similarity between the observations made ujdou the response of muscle and nerve on the one hand, and that of metals on the other. Even in their abnormalities we have seen an agreement. But amongst these j)henoniena themselves, though at first sight so diverse, there is some kind of continuity- Calling all normal response positive., for the sake of convenience, we observe its gradual modification, corresponding to changes in the molecular condition of the substance. Beginning with that case in whicli molecular modi- fication is extreme, we find a maximum variation of I'esponse from the normal, that is to say, to imjative. Continued stimulation, however, brings back the molecular condition to normal, as evidenced by the pi'o- gressive lessening of the negative response, culminating in reversion to the normal positive. This is equally true of nerve and metal. In the next class of phenomena, the modification of molecular condition is not so great. It now exhibits itself merely as a relative inertness, and the responses, though positive, are feeble. Under continued stimula- tion, they increase in the same direction as in the last case, that is to say, from less positive to inore positive., being the reverse of fatigue. This is evidenced alike by the staircase effect and Ijy the inc rease of response after tetanisation, seen not only in nerve but also in platinum and tin. K 130 JiESPONSE LY THE LIVING AND NON-LH'IXG The sul)staiice may next lie in what we call the normal condition. Successive ^^nifo^m stimuli now evoke uniform and equal positive responses, that is to say. there is no fatiiiue. P)Ut after intense or lont^'- continued stinudatiou, the substance is overstrained. The respoirses now underiiO a change from positive to Jess ■positive \ fatigue, that is to say, appears. Again, luider very miu/h prolonged stimulatirin the I'espouse nuiy decline to zero, or even undergo a reversal to negative, a, plienomenon winch we shall find instanced in the reversed res}jonse of retina under the long- continued stimulus of light. We must then recognise that a substance ma}' exist in various molecular conditions, whether due to internal changes or to tlie action of stimulus. The responses give us indications of these conditions. A complete cvcle of molecidar modifications can be traced, front the abnormal negative to the normal positive, and then again to negative seen in revei-sal under continuous stimulation. '31 GHAPTEE XV IXORGAXIC RESPONSE — RELATION BETWEEN STIMULUS AND RESPONSE — SUPERPOSITION OF STIMULI Relation between stimulus and response — Magnetic analogiie — Increase of response with increasing stimulus — Threshold of response — Sujierposition of stimuli — Hysteresis. Relation between stimulus and response. — We have seen what extremely uniform responses are given by tin, when the intensity of stimulus is maintained constant. Hence it is obvious that these phenomena are not accidental, but governed by definite laws. This fact becomes still more evident when we discover how invariably response is increased by increasing the intensity of stimulus. Electrical response is due, as we have seen, to a molecular disturbance, the stimulus causing a distorti(.)n from a position of equilibrium. In dealing with the sul)ject of the relation between the disturbing force and the molecular effect it produces, it may be instructive to consider certain analogous physical phenomena in which molecular deflections are also produced b}' a distorting force. Magnetic analogue. — Let us consider the effect that a magnetising force produces on a bar of soft iron. It is known that each molecule in such a bar is an 132 J^ESrOiVSE IN THE LIVING AND NON-LIVING individual uiaynet . The Ijar as a wliole, nevertheless, ex- hibits no external magnetisation. This is held to be due the fact that the molecular magnets are turned either in haphazai'd directions or in closed chains, and thei'c is tlierefore no resultant polarity, l^ut when the bar is subjected to a magnetising force l^y means, say, of a sole- noid canying electrical current, the individual molecules are elastically deflected, so that all the molecular magnets tend to place themselves along tlie lines of magnet isiutj' force. All tlie nortli ])oles thus point more or less one way, and the south poles the other. The stronger tlie magnetising force, the nearer do themolecides approach to a perfect aligmuent, and the greater is the induced magnetisation of the bar. The intensity of this induced magnetisation may l)e measured by noting the deflection it produces on .-i freely suspended magnet in a magnetometer. The force which produces that molecular deflection, to wliich the magnetisation of the bar is iuimediatel}' due, is the magnetishig curi-ent flowing round the solenoid. Tlie magnetisation, or the molecular efl^ect, is measured l)y the deflection of the mag- netoineter. We may express the relation between cause and effect by a <'urve in wliich the abscissa represents the magnetising current, and the ordinate the magnetisation produced (fig. 82). In such a curve we may roughly distinguish tliree parts. In the first, where the force is feeble, the mole- PlO. 82. — CUEVK OK JMAiiNETISATIUN INORGANIC RESPONSE 133 cular deflection is slight. In the next, the cur\-e is rapidly ascending, i.e. a small variation of impressed force produces a relativelj- large molecnlar effect. And lastly, a limit is reached, as seen in the third jjart, where increasing force produces very little further effect. In this cause-and-eff'ect curve, the first part is slightly convex to the abscissa, the second straight and ascend- ing, and the third concave. Increase of response with increasing stimulus. — We shall find in dealing with the relation between the stimulus and the molecular effect — i.e. the response — something very similar. On gradually increasing the intensity of stimulus, which may be done, as alread}^ stated, by increasing the amplitude of viljration, it will be found that, beginning with feeble stimulation, this i)icrease is at first slight, then more pronounced, and lastly shows a tendency to approach a limit. In all this we have a perfect parallel to corresponding phenoniena in animal and vegetable response. AVe saw that the proper investigation of this subject was much complicated, in the case of animal and vegetable tissues, Ijy the ap- pearance of fatigue. The comparatively indefatigable nature of tin causes it to offer great advantages in the pursuit of this inquiry. I give below two series of records made with tin. The first record, fig. 83, is for increasing amplitudes from 5° to 40° by steps of 5". The stimuli ai-e imparted at intervals of one minute. It will \)(t noticed that whereas the recovery is complete in one minute when the stimulus is moderate, it is not Cjuite complete when the stimulus is stronger. The 134 JiESPOA'SE IN THE LIVING AND NON-LIVING lecovery from the eJl'ect of stronger stimulus is more prolouHetl. (Jwiuo- to want of complete recovery, the 10° 15° 2(r 25° 3U' :i5'= 45 Fig. 83. — Eecouds of Responses in Tin with Increasing Stimuli, Ampli- tudes OF ViEKATION FBOM 5° TO 40° The vertical line to the right represents '1 volt. Ijase line is tilted sliohtly upward. This slight dis- placement of the zero line does not materially affect the result, ju'ovided tlie shifting is sliglit. Table showing the Increasing Electric Response due to Increasing Amplitude of A'ibeation Vibration amplitude E.M. variation 5° •024 volt 10° •057 „ 20° •111 „ 25° •143 „ 30° •170 „ 35° •187 „ ' 40° •204 „ ; The next figure (fig. 84) gives record of rcsjionses INORGANIC RESPONSE 135 Fig. 84. — A Second Set of Eecords with a Different Specimen of Tin The amplitudes of vibration are increased by steps of 10^, from 20' to 160°. (The detiec- tions are reduced by interposing a high ex- ternal resistance.) through a -wider range. Fur accurate quantitative measurements it is ijrefei'al)le to wait till the recovery is complete. We may accompUsh this ■vvithiu the limited space of the record- ing photogi'aphic plate by making the record for one minute ; during the rest of recovery, the clockwork moving the plate is stopped and the galvano- meter spot of light is cut off. Thus the next record starts from a point of completed recovei'v, which will be noticed as a bright spot at the beginning of each curve. With stimulation of high intensity, a tendency will be noticed for the responses to a])proach a limit. Threshold of response. — There is a minimum intensity of stimulus below which there is hardly any visible response. A single stimulus produces the feeble "v^g ^^^ay rco'ard this point as ettect shown m the iirst response. ./ o i the threshold of response. Though apparently inefiective, the subliminal stimuli produce some latent effect, which may be demonstrated by their additive action. The U-Wui Fig. 8.5. -Effect of Supekposi- TioN ON Tin response. Superposition of .5, 9, 13 such stimuli produce the succeeding stronger responses. 136 RESFOXSE IN THE LIVING AND NON-LIVING record in fig. ^5 shows how individually feeble stimuli 1-,- * become markedly efiective b}' superposition. Superposition of stimuli. -The additive eflect of suc- ceeding stimuli will be seen from the above. The fusion of eflect will be incomplete if the frequency of stimula- tion be not sulficiently g-reat ; but it will tend to be more Fig. s6. — Incomplete axd Complete Fusion of Effect in Tin As the trecjueucy of stimulation is increasecl the fusion Ijecomes more and loore complete. Vertical line to the right represeutg ■! volt. complete with hicjher frequency of stimulation (iiti'. 86). We have here a parallel case to the complete and in- c(_)mplete tetanus of muscles, under similar conditions. By the addition (_)f these rapidly succeeding stimuli, a maximum eflect is produced, and furtlier stimulation adds notlmiL;' to this. The eflect is balanced by a force INORGANIC RESPONSE 1.37 of restitution. The response-curve tluis rises to its iniiximuin, after which the deflection is held as it were rigid, so long as the vibration is kept up. It was found that increasing intensities of single stimuli produced corresponding!}- increased responses. The same is true also of groups of stimuli. The maxinuim o-avoLt. 55^ B ^ ^ ^-^^ ' -;::: ^=-1 A OivoLC. / ^ V ^ / / ■ 0° a be abolished. The depression produced is .so great and passes in so deep that I have often failed lo revive the response, eAeii aftei' rnljljing tlie wire witli emery paper, ]jy which the molecular layer on the sur- face must have been removed. AYe have seen in the molecular model (fig. (12, '/, c) how the attainment of maxinuim is delayed, the re- S]Kjnse diminished, and the recovery prolonged or arrested by increase of friction (jr reduction of mole- cular mobility. It would a})pear as if the reagents which act as ])oisons produced some kind of molecular arrest. The foUowmg records seem to lend support to this view. If the oxalic acid is applied in large cjuantities, the altolition of response is complete. liut on carefully adding just the proper amount I find that the first stimuliis evokes a responsive electric twitch, which is less than the normal, and the period of recovery is A'ery much prolonged from the normal one minute l)e- fore, to fivenunutes after, the application of the reagent (fig. 93, a). In another record the arrest is more pro- nounced, i.e. there is now n(j recn-ery (fig. 93, A). Xote also that the maximum is attained much later. Stimuli a]jplied after the arrest produce no effect, as if the ni(;lecular mechanism became, as it Avere, clogged oi- locked up. In connection with this it is interesting to note that the effect of veratrine poison on muscle is somewhat similar. This reagent not only diminishes the excita- 1)ility, Imt causes a \-ery great prolongation of the period of recovery. INORGANIC HESFONSE 145 111 connection with tlie action of cliemical reagents the following points are notewortliy. (1) The effect of these reagents is not only to increase or diminish the height of the response-curve, but also to modify the time relations. By the action of some (a) m Fig. 93. — ' Molecolak Aeeest ' by the Action of ' Poison ' Li each, curves to the left show the normal response, curve to the right shows the effect of poison. In («) the arrest is evidenced by prolongation of period of recovery. In [h) there is no recovery. the latent period is diminished, others produce a pro- longation of the period of recovery. Some curious effects produced by the change of time relations have Ijeen noticed in the account given of diphasic variation (see p. 113). 146 JiESFOA\S£ IX THE LIVING AND NON-LIVING ['1) The eflect pi'udiiced Ijy a chemical reagent depends to some extent on the pi-evious condition of the wire. (3) A certain time is reqnired f(jr the full devehjp- ment of the effect. A\^ith some reagents the fnll effect takes place almost instantaneously, while with others the effect takes place slowly. Again the effect may with time reach a maximum, after which there may Ije a sliyht declhie. (n) Ih) (.;; Fig. 94. — Opposite Effects of Small .iXD L.iege Doses (Tin) {a\ is the normal response; ih\ is the stimulating action of small dose of potash (3 parts in 1,000) ; [c] is the abolition of response with a stronger close (3 parts in lOOi. (4) The after-effects of the reagents may be transitory or persistent ; that is to say, in some cases the remOA-al of the reagent causes the responses to revert to tlie normal, while in others the effect persists eA'en after the removal of all traces of the reagent. Opposite effects of large and small doses. — There remains a A^ery curious phenomenon, known not only INORGANIC RESPONSE 147 to Students of physiological response but also known in medical practice, namely tliat of the opposite efleots pro- duced by the same reagent when given in large or in small doses. Here, too, we have the same phenomena reproduced in an extraordinary manner in inorganic. response. The same reagent which becomes a ' poison '' in large quantities may act as a stimulant when applied in small doses. This is seen in record tig. 94, in which (a) gives the normal resjionses in water ; KHO solution was now added so as to make the strength three parts in 1,000, and ([>) shows the consequent enhancement of response. A further quantity of KHO was added so as to increase the strength to three parts in 100. This caused a complete abolition (c) of response. It will thus be seen that as in tlie case of animal tissues and of plants, so also in metals, the electrical responses are exalted by the action of stimulants, lowered by depressants, and completely al^olished l^y certain other reagents. The parallelism will thus be found complete in every detail between the phenomena of response in the oig-anic and the inorganic. I4S RESPONSE IN THE LIVING AND NON-LIVING CHAPTER X^'II ox Till-: STLMULUS OF LIGHT AND RETINAL CURRENTS ^ isiial imjiuLf : (1) chemical theory: {-) electrical theory — Retinal current?^ — Normal response positive — Inorganic response under stimulus of light — Tyjiical experiment on the electrical effect induced by light. The efl'ect of the stimulus of lioiit on the retina is perceived in the brahi as a visual sensation. The process Ijy which the etlier-wave disturbance causes this visual impulse is still xaxx oljscure. Two theories may Ite advanced in explanation. fi) Chemical theory. — Accordiui;' to the first, or chemical, theory, it is supposed that certain visual sub- stances in tlie retina are alTected Ijy li.ii'ht, and that vision originates from the metabolic changes produced in these visual substances. It is also supposed that the metabolic changes consist of two phases, the upward, constructive, or anabolic phase, and the downward, destructive, or katabolic phase. Various visual sul> stances by their anabolic or katabolic changes are supposed to produce the variations of sensation of light and colour. Tliis theory, as will be seen, is very complex, and there are certain obstacles in the way of its acceptance. It is, for instance, difficult to see how this very quick visual process could I)e due to a comparatiA'el}' slow chemical action, consisting of INORGANIC RESPONSE 149 the destructive breaking-down of the tissue, followed by its renovation. Some support was at first given to this chemical theory by the bleaching action of light on the visual purple present in the retina, but it has been found that the presence or absence of visual purple could not be essential to vision, and that hs function, when present, is of only secondary importance. For it is well known that in the most sensitive portion of the human retina, the fovea centralis, the visual purple is wanting ; it is also found to be completely absent from the retinaj of many animals possessing keen sight. (2) Electrical theory. — The second, or electrical, theory supposes that the visual impulse is the concomitant of an electrical impulse ; that an electrical current is generated in the retina under the incidence of light, and that this is transmitted to the brain by the optic nerve. There is much to be said in favour of this view, for it is an undoubted fact, that light gives rise to retinal currents, and that, conversely, an electrical current suitably applied causes the sensation of light. Retinal currents. — Holmgren, Dewar, McKendrick, Kuhne, Steiner, and others have shown that illumination produces electric variation in a freshly excised eye. About this general fact of the electrical response there is a widespread agreement, but there is some difl'er- ence of opinion as regards the sign of this response im- mediately on the application, cessation, and during the continuance of light. These shght discrepancies may be partly due to the unsatisfactory nomenclature — as regards use of terms jyositive and negative — hitherto in I50 JiESFONSE IN THE LIVING AND NON-LIVING vogue and partly also to the difl'ering states of the excised eyes oljserved. Waller, in his excellent and detailed work on the retinal currents of the frog, has shown how the sign of response is re^'ersed in the moribund condition of the eye. As to the confusion arising from our present terminology, we must remember that the term positire or negative is used with regard to a current of reference — the so-called current of injury. When the two galvanometric contacts are made, one with the cut end of the nerve, and the other on the uninjured cornea, a current of in- jury is found which in the eye is from the ner\'e to the retina. In the normal freshly excised eye. Fig. 95. Eetinal Response the Current of respousc due to TO Light ^^^^ action of light on the retina The current of response is '^ from the nerve to the [f. alwavs froui the uervc, wliich retina. is not directly stimulated by light, to the retina, that is, from the less excited to the more excited (fig. 9-3). This current of response flows, then, in the same direction as the existing current of reference — the current of injury — and may therefore be called positive. Unfortunately the current of injury is very often apt to change its sign ; it then flows through the eye from the cornea to the nerve. And now, though the current of response due to light may remain unchanged in direction, stiU, owing to the reversal of the current of reference, it will appear as negative. That is to say, though its absolute direction is the same as before, its relative direction is altered. INORGANIC RESPONSE 151 I have already advocated tlie use of the term jxjsitive for currents which tlow towards the stimulated, and negative for those Avhose flow is away from the stimulated. If such a convention be adopted, no con- fusion can arise, even when, as in the given cases, the currents of injury undergo a change of direction. Normal response positive. — The normal effect of light on the retina, as noticed by all the observers already mentioned, is a positive variation, during exposure to light of not too long duration. Cessation of light is followed by recovery. On these points there is general agreement amongst investigators. Deviations are re- garded as due to abnormal conditions of the eye, owing to rough usage, or to the rapid approach of death. For just as in the dying plant we found occasional reversals from negative to positive response, so in the dying retina the response may undergo changes from the normal positive to negative. The sign of response, as we have already seen in numerous cases, depends very much on the molecular condition of the sensitive substance, and if this condi- tion be in any way changed, it is not surprising that the character of the response should also undergo alteration. Unlike muscle in this, successive retinal responses exhibit little change, for, generally speaking, fatigue is very slight, the retina recovering quickly even under strong light if the exposure be not too long. In exceptional cases, however, fatigue, or its converse, the staircase effect, may be observed. Inorganic response under the stimulus of light. — It may now be asked whether such a complex vital 152 RESPONSE IN THE LIVE^TG AND NONLIVING pheiioinenoii as retinal response could liave its conntei- part in non-living response. Taking a rod of silvei', we may l^eat out one end into the form of a liolLjw cup, sensitising the inside by exposing it for a short time to vajjour of bromine. The eup may now be filled witli water, and connection made with a galvanometer bv n()n-})olarisable electrodes. There will now Ije a cur- rent due to diflerence between the inner surface and the rod. This may be l^alanced, however, 1jy a compensating E.M.F. (n) lb) Fig. 9(1. — Record of Kespoxses to Light given by the Sensitive Cell Thick lines represent the effect during illumination, dotted lines the recovery in darkness. Note the preliminary negative twitch, which is sometimes also observed in responses of frog's retina. We have thus an arrangement somewhat resembling the eye, with a sensitive layer corresponding to the retina, and the less sensitive rod corresponding to the conducting nerve-stump (fig. 96, a). The apparatus is next placed inside a black box, with an aperture at the top. Bj' means of an inclined mirror, light may Ije thrown down upon the sensitive surface through the opening. On exposing the sensitive surface to light, the balance is at once disturbed, and a responsive current of positive character produced. The current, that is to INORGANIC RESPONSE 153 say, is from the less to the more stimiUated sensitive layer. (.)n the cessation of light, there is fairly quick recovery (lig. 96, b). The character and the intensity of E.M. variation of the sensitive cell depend to some extent on the pi'o- cess of preparation. The particular cell with which most of the following experiments were carried out usually gave rise to a positive variation of about •008 volt when acted on for one minute by the light of an incandescent gas-burner which was placed at a dis- tance of 50 cm. Typical experiment on the electrical effect induced by light. — This subject of the production of an electrical current by the stimulus of light would aj^pear at first sight very complex. But we shall be able to advance naturall)' to a clear understanding of its most complicated phenomena if we go through a preliminary consideration of an ideally simple case. We have seen, in our experi- ments on the mechanical stimulation of, for example, tin, that a difference of electric potential was induced between the more stimulated and less stimulated parts of the same rod, and that an action current could thus be obtained, on making suitable electrolytic con- nections. Whether the more excited was zincoid or cuproid depended on the substance and its molecular condition. Let us now imagine the metal rod flattened into a plate, and one face stimulated by light, while the other is protected. Would there be a difference of potential induced between the two faces of this same sheet of metal ? :54 RESPOA^SE IN THE LIVING AND NON-LIVING Let two blocks of parafKii be taken and a large hole drilled tlirougli both. Next, place a sheet of metal between the blocks, and pour melted paraffin round the edge to seal up the junction, the two open ends being also closed by panes of glass. We shall have then two compartments separated l^y the sheet of metal, and these compartments may be filled with water through the small apertures at the tojj (fij a). The two liquid masses in the separated chambers thus make perfect electrolytic contacts with the two faces A and b of the sheet of metal. These two faces may be put in con- nection with a galvanometer Ijy ^:^=;=& tA j^^ ^- Irc/kt Fk;. 97 (6), r / r y — Eecoeh of Eesponser obtained FEOM THE Above Cell Fig. 97 (a) Ten seconds' exposure to light followed by fifty seconds' recovery in the dark. Thick lines repre- sent action in liglit, dotted lines represent re- covery. A, B are the two faces of a broniinated sheet of sil- ver. One face, say A, is acted on by light. The current of response is from B to A, across the plate. means of two non-polarisable elec- trodes, whose ends dip into the two chambers. If the sheet of metal have been properly annealed, there will now be no difference of potential between the two faces, and no current in the galvanometer. If the two faces are not molecularly similar, however, there will be a current, and the electrical effects to be subsequently descril)ed will act additively, in an algebraical sense. Let one face now be exposed to the stimulus of light. A responsive current will be found to flow, from the less to the more stimulated fiice, in some cases, and in others in an opjjosite direction. INORGANIC RESPONSE 155 It appears at first very curious that tins difl'ereuce of electric poteutial should be maintained between opposite faces of a very thin and highly conducting sheet of metal, the intervening distance l:)etween the opposed surfaces being so extremely small, and the electrical resistance quite infinitesimal. A homogeneous sheet of metal has become by the unec[ual action of light, molecularly speaking, heterogeneous. The two opposed surfaces are thrown into opposite kinds of electric condition, the result of which is as if a certain ^? V A R (' raj h ' i (h) A B Fig. 98. — Modification of the Sensitive Cell thickness of the sheet, electrically speaking, were made zinc-like, and the rest copper-like. From such un- familiar conceptions, we shall now pass easily to others to which we are more accustomed. Instead of two opposed surfaces, we may obtain a similar response by unequally lighting different portions of the same surface. Taking a sheet of metal, we may expose one half, say A, to light, the other half, B, being screened. Electro- lytic contacts are made by plunging the two limbs in two vessels which are in connection with the two non- polarisable electrodes E and e' (fig. 98, a). On J 56 RESFOXSE IN THE LIVING AND NON-LIVING illumination uf A and B alternately, we shall now obtain <-uiTents Howing alternateh' in opposite directions. Just as in the strain (jells the galvanometer contact was transferred from the electrolytic part to the metal- lic part of the circuit, so we may next, in an exactly similar manner, cut this plate into two, and connect these directly to the galvanometer, electrolytic cormec- tion being made by partially plunging them into a cell ■OOIO •0005 ^0001 Fig. 99. — Responses to Light in Fi;og's Retina Illumination L for one minute, recovery in dark for two minutes during obscurity B. (Waller.) containing water. The posterior surfaces of the two half-plates may be covered with a non-conducting coating. And we arrive at a typical photo-electric cell (fig. 98, h). These considerations will show that the e3'e is practically a photo-electric cell. We shall now give detailed experimental results obtained with the sensitive silver-bromide cell, and compare its response-curve with those of the retina. A series of uniform light stimuli gives rise to uniform INORGANIC RESPONSE 157 responses, wliich show very little sign of fatigue. How similar these response-curves are to those of the retina will be seen from a pair of records given Ijelow, where fig. 99 shows responses of frog's retina, and fig. 100 gives the responses obtained with the sensitive silver cell (fig. 100). It was said that the responses of the retina are uniform. This is only approximately true. In addition to numerous cases of uniform responses. Waller finds instances of ' staircase ' increase, and its opposite, slight fatigue. In the record here given of the silver cell. Fig. 100. — Responses in Sen.sitive Selvee Cell lUunainatiou for one minute and obscurity for one minute. Thick line represents record during illumination, dotted line recovery during obscur-ity. the staircase effect is seen at the beginning, and followed by slight fatigue. I have other records where for a very long time the responses are perfectly uniform, there being no sign of fatigue. Another curious phenomenon sometimes observed in the response of retina is an occasional slight increase of response immediately on the cessationof light, after which there is the final recovery. An indication of this is seen ill the second and fourth curves in fig. 99. Curiously enough, this abnormality is also occasionally met with in the responses of the silver cell, as seen in the first two curves of lig. 100. Other instances will be given later. iSS A'ESPO^rSE IN THE LIVEVG AND NON-LIVING CHAPTEE XVIII INORGANIC KESP()X8E — INFLUENCE OF VARIOUS CONDITIONS ON THE RESPONSE TO STIMULUS OF LIGHT Effect of temperature — Effect of increasing leng-th 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 — Kesume. We shall next proceed to study tlie effect, ou the re- sponse of the sensitive cell, of all those conditions which influence the normal response of the retina. We shall then briefly inquire whether even the abnormalities sometimes met with in retinal responses have not their parallel in the responses given by the inorganic. Effect of temperature. — It has 1)een found that when the temperature is raised above a certain point, retinal response shows rapid diminution. On cooling, however, response reappears, with its original intensity. In the response given by the sensitive cell, the same peculiarity is noticed. I give below (fig. 101, a) a set of response- curves for 20° C These responses, after showing slight fatigue, became fairly constant. On raising the tem- perature to 50° C. response practically^ disappeared (101, A). But on cooling to the first temjjerature again, it reappeared, with its original if not slightly greater intensity (fig. 101, c). A curious point is that while in INORGANIC RESPONSE 159 record (a), before warming, slight fatigue is ol:)served, in (c), after cooling, the reverse, or staircase effect, appears. 20° C i (' (\ J \ 20°C 50°C ('^1 r w C' f\ \ \ 1 \ \ Fig. 101. — Influence of Te:\ipeeatuke on Response Illumination 20'', obscurity 40". In [a] is shown a series of responses at 20^ C. — the record exhibits slight fatigue, ih) is the slight irregular response at 50° C. (c) is the record on re-cooling ; it exhibits ' staircase ' increase. Effect of increasing length of exposure. — If tlie intensity of li^^ht be kept constant, the magnitude of faj / ... , /^ I- A. 3 4-56 8" 9" 10" /6J A- \ V.-- '-,...- \ \ 1 \ ,_ ' 7" 8" 9" 10" Fig. 102. — Response-cueves foe increasing Duiution of Ii.LusiiN.iTiON from 1" TO 10" In [a] the source of light was at a distance of .50 cm. ; in ih) it was at a distance of 2.5 cm. Note the after-oscillation. response of the sensitive cell increases with length of exposure. But this soon reaches a limit, after which i6o RESPOXSE IN THE f.llENG AND XOX-LIVING increase of duration does not increase magnitude of efl'ect. Too long an exposure may liO'\ve\-er, owing to fatigue, produce an actual decline. I give here two set-, of curves (fig. 102) illustrating the elTect of lengthening ex})0sure. The intensities of hght in the two cases are as 1 to 4. The incandescent burner was in the two cases at distances -jO and 20 cm. respectively. It will be observed that beyond eight ^econds' exposure the responses are approximately uniform. Another noticeable fact is that with long exposure there is an after-oscillation. This growing efl'ect Avith lengtheiang exposure and attahnnent of limit is exactly paralleled Ijy responses of retina under similar condit ions . Relation between intensity of light and magnitude of response. — In the resporrses of retina, it is found that increasing intensity of liglit proditces an increasing efl'ect. But the rate of increase is not unifnrm : increase of eflect does ]iot keep pace with increase of stimulus. Thus a curve giving the relation between stiintilus and response is concave to the axis which represents the stiiriulus. The same is true of the sensation of light. That is to say, within wide limits, intensity of sensation does not increase so rapidly as stimulus. This particular relation between stimulus and effect is also exhibited in a remarkable manner Ijy the sensi- tive cell. For a constant source of light I used an incandescent Ijurner, and graduated the intensity of the incident light Ijy varying it^ distance from the sensitive cell. The intensity of hght incident on the cell, when INORGANIC RESPONSE the incandescent Ijurner is at a distance of 150 cm., has been taken as the arljitrary unit. In order to make allowance for the possiljle effects of fatigue I took two /I C- r u Fig. 103.— Kespoxsks of Sensitive Cell to vaeious Intensities of Light On the left the responses are for diminishing intensities in the ratios of 7, 5, 3, and 1. On the right the}' are for the increasmg intensities 1, 8, 5, and 7. The thick lines are records during exposures of one minute; the dotted lines represent recoveries for one minute. successive series of responses (fig. 103). In the first, records were taken "vvitli intensities diminishing from 7 to 1, and immediately afterwards increasino- from 1 to 7, in the second. Table givi>'g Kespoxse to tabtixg Iuiensiiies oe Light (The intensity of an incandescent gas-burner at a distance of 1.50 cm. is taken as unit.) Intensity of Light Eesponse (Light diminishing) Eesponse (Light increasing) 4.3 39 ••31 29 18-.-) 17-5 10 9 Mean 41 30 18 9-0 Value in volt 63-0 X 10~ volt 46-1 X „ 27'7 X „ 14-6 X „ As the zero point was slightly shifted dnring the M i62 j^^sroxs/: ix the living axd xoxiiv/xj course of the cx})eriiiient, tlie dellectioii in each eurve was measured fronr a line joiuiui^; the hepiuniuL;' of the response to the end of its recovery. A mean dellection, corresj^ondiuLi' to each intensity, Avas ol)tained l)y taking the avernu'e of the desceudiuL'' and asceudinp; readings. Tlie two sets of readings did itot, fiowever, vary to any marked extent. The deileetions corresponding to tlie intensities 1, 3, '), 7, are. then, as O-O to IS, to 30. to 41. If the deilectioirs liad been strictly proportionate to the inten- O S tOunz-ts. O S \0 units. Fie. 104. — Crr.YEs gutnt. the Kelatiox between Ixtexsity ue Light .iXD Magxitude of Eespgxse lu (ri) sensitive cell, (h) in frog's retina. sities of light stimulus they would have been as 9'-3 to 2S--J, to 47--5, to GTi-.j. In another set of records, with a different cell, I obtained the deflections of (1, 10, 13, 1-3. corresprjiiding to light intensities of 3, 5, 7, and 0. The two curA-es in fig. 104, giving the relation between response and stimulus, show that in the case of inorganic substances, as in the retina (Waller), magnitude of response does not increase so rapidly as stimulus. After-oscillation. — Wlien the sensitive surface is subjected to the contiiuied action of Hglit, the E.M. / / f( I) / ^ li y INORGANIC RESPONSE r63 effect attains a maximum at wliicli it remains constant for some time. If tlie exposure be maintained after tliis for a longer period, there will be a decline, as we found to be the case in other instances of continued stimulation. The appearance of this decline, and it.s rapidity, depends on the particular condition of the substance. When the sensitive element is considerably strained by the action of light, and if that light be now cut [V y Fig. 10-5. — Aftek-oscillation Exposure of one minute followed by obscurity of one minute. Note the decline dueing illumination, and after-oscillation in darkness. off, there is a rebound towards reco^^ery and a sub- sequent after-oscillation. That is to say^ the curve of recovery falls below the zero point, and then slowly oscillates , back to the position of equilibrium. We have already seen an instance of this in fig. 102. Above is given a series of records showing the appearance of decline, from too long-continued exposure and re- covery, followed by after-oscillation on the cessation of light (fig. 105). Certain visual analogues to this phenomenon will 1je noticed later. M 2 1 64 RESPOXSE IX THE LIVLXG AND NOX-LIVEXG Abnormal effects. — We have already treated of all tlie normal effects of the stimulus of hght on the retina, and their counterparts in the sensitive cell. But the retina undergoes molecular changes when injured, stale, or in a dyhig condition, and under these circumstances various comphcated modifications are observed in the response. I. Preliminary negative twitch.— When the light is incident on the frog's retina, there is sometimes a transitory negative variation, followed liy the normal Fig. 106. — Tn.iNsiEXT Positive ArGMEXT.iTioN '.iten by the Fkoi;',, KETix.ii ON THE CESS.iTIOX OF LiGHT L (WaLLER) positive response. This is frequently observed in the sensitive cell (see fig. 9(i, li). 2. Reversal of response. — Again, in a stale retina, owing to moleeular modilication the response is apt to undergo reversal (Waller). That is to say, it now becomes negative. In working with the same sensitive cell on different days I have found it occasionally exhibiting this re^'ersed response. INORGANIC RESPONSE >6S 3. Transient rise of current on cessation of light. — Another very curious fact observed in the retina Ijy Kuhne and Steiner is that immediately on the stoppage of light there is sometimes a sudden increase in the retinal current, before the „ usual recovery takes place. l| This is very well shown in jj the series of records taken ll by Waller (fig. 106). It will be noticed that on illu- mination the response-curve rises, that continued illumi- nation produces a decline, and that on the cessation of light there is a transient rise of current. I give here a series of records which will show the remarkable simi- larity between the responses of the cell and retina, in re- spect even of abnormalities so marked as those described (fig. 107). I may mention here that some of these curious effects, that is to say, the preliminary negative twitch and sudden augmen- tation of the current on the cessation of light, have also been noticed by Minchin in photo-electric cells. 4. Decline and reversal. — We have seen that under the continuous action of light, response begins to A Fig. 107. — Eespoxses in Silver Cell The tliick line represents response during light (half a minute's exposure), and dotted line the recovery during darkness. Note the terminal positive twitch. Tf.6 liESPOXSF. IX THE LIVING y\AW NON-LIVING decline. Sometimes tliis process is very rapid, and ill any case, under continued li.Liiit, the deflection falls. (1) The decline may nearly reach zero. If now the liulit he cut oil' tliere is a rehound towai'ds recoyery (loiiiiirnnls, Avhii'h carries it l)eloAV zero, followed Ijy an aftei'-oscillation (fiij-. lOS, a). ['!] If tlie li^ulit he continued for a lono-er time, the decline Li'oes on eyeu below zero; that is to say, the Fig. lOS —Decline un-leu the CoxTixrED Action of Light {fc Decline short uf zero ; on stoj^page of light, rebound dowiiwardb to zero; after-oscillation. [h) Decline below zero; ''in stoppage of liglit, rebound towards zero, witli pre- liminary negative t^vitch. (c,l The same, decline further dowir ; negative twitch almost disappearing. response uow becomes apparently uep'atiye. If, now, the light be stopped, there is a reljound upwards to recoyery, with, generally speaking, a slight preliminaiy twitch downwards (iig. 108. A, c). Tliis rebound carries it Ijack, not only to the zero position, but some- times beyond that position. We haye here a parallel to the following obseryation of Dewar and ]\IcKeiidrick : INORGANIC RESPONSE 167 ' When difi'use light is aUowed to impinge on the e3'e of the frog, after it has arrived at a tolerably stable condition, the natural E.M.F. is in the first place increased, then diminished ; durino- the continuance of light it is still slowly diminished to a point where it remains tolerably constant, and on the removal of light there is a sudden increase of the E.M. power nearl}' up to its original position.' ^ (3) I have sometimes obtained the following curious result. On the incidence of light there is a response, say, upward. On the continuation of light the response declines to zero and remains at the zero position, there being- no further action durino- the continuation of stimulus. ■ But on the cessation or ' Ijreak ' of light stimulus, there is a response downwards, followed by the usual recovery. This reminds us of a somewhat similar responsive action produced by constant electric current on tlie muscle. At the moment of ' make ' there is a responsive twitch, but afterwards the muscle remains quiescent during the passage of the current, but on breaking the current there is seen a second respon- sive twitch. Resume. ^So we see that the response of the sensitive inorganic cell, to the stimulus of light, is in every way similar to that of the retina. In both we have, under normal conditions, a positive variation ; in both the intensity of response up to a certain limit increases with the duration of illumination ; it is affected, in both alike, by temperature ; in both there is comparatively little fatigue ; the increase of I'esponse with intensity of ' I'roc. Jioy. Sue. Edin. 187.3, p. 1-j3. 1 68 RESPONSE IN THE LIVING AND NON-LIVING Stimulus is siuiilar iu both; and finally, even in aljiior- nialities — such as reversal of response, preliminar)- neuatiAe twitcli on commencement, and terminal posi- tive twitch on cessation of illumination, and decline and reversal under continued action of light — parallel efi'ects ai'C noticed. We mav notice here certain curious I'elations even in these abnormal responses (fif^-. lOlJ). If the equi- liljritim position remahi alwaj'S constant, then it is easy to understand how, when the rising curve has attained Fig. 109. — Certain Aftee-epfects of Light its maximum, on the cessation of lio-lit, recovery should proceed doirmcards, towards tlie equilibrium position (fig. 109, a). One can also understand how, after reversal by the contiiuied action of light, there should be a recover}- iqurards towards the old ecj^uilibrium position (fig. 109, h). AVhat is curious is that in certain cases we get, on tlie stoppage of light, a prelinnnary twitch away from the zero or equilibrium position, upwards as in [<:) (compare also fig. 107) and downwards as hi id) (compiare also fig. 10b h). In making a general retrospect, finally, of the effects INORGANIC RESPONSE 169 produced by stimulus of light, we liiid tliat there is uot a siugle pheuouieuon iu the respouses, iiornial or abnormal, exhibited by the retiua which has not its counterpart in the sensitive cell constructed of inorganic material. 170 JiESFONSE IN THE LIVING AND NONLIVING CHAPTER XIX V I S U A L A X A L (J G U E S Effect of ligbt of short duration — After-oscillation — Posilive and negative after-images — Binocular alternation of \ision — Period of alternation modified by physical condition — After-images and their re\"iTal — Un- conscious visual impression. We have alread}' referred to the electrical theory of the A'LSual impulse. We have seen how a flash of light causes a transitory electric impulse not only in the retina, but also in its inorganic substitute. Light thus produces itot only a visual but also an electrical impulse, and it is not improl)able that the two may be identical. Again, varying intensities of light give rise to corre- sponding intensities of current, and the curves Avhicli represent the relationbetween the in<_Teasing stimulus and the increasing response have a general agreement with the corresponding curve of visual sensation. In the present chapter we shall see how this elec'trical theory not only explains in a simple manner ordinarv visual phenomena, but is also deeijlv su«>o'estive with regard to others wliidi are A'cry obscure. We have seen in our silver cell that if the molecular conditions of the aiUeri(jr and posterior surfaces were exactly similar, there Avouldlie no curreih. In practice, however, this is seldom the case. There is, aenerallv VISUAL ANALOGUES 171 speakiiii;-, a slight difference, and a feeljle cnri-ent in the circuit. It is thus seen that there may l)e an existing feehle current, to wl\ich the efi'ect of hght is added algebraicaUy. The stimidus of hght ma}- thus increase the existing current of darkness (positive variation). On the cessation of hght again, the current of response disappears and there remains oidy the feeble original current. In the case of the retina, also, it is curious to note that on closing the eye the sensation is not one of absolute darkness, but there is a general feeble sensation of light, known as ' the intrinsic light of the return.' The effect produced by external light is superposed on this intrinsic light, and certain curious results of this algebraical summation will be noticed later. Effect of light of short duration. — If we subject the sensiti^'e cell to a flash of radiation, the effect is not instantaneous but grows with time. It attains a maximum some little time after the incidence of light, and the eflect then gradually passes away. Again, as we have seen previously with regard to mechanical strain, the after-effect persists for a slightly longer time when the stimulus is stronger. The same is true of the after-efl'ect of the stimidus of light. Two curves which exhibit this are given below (fig. 110). With I'egard to the first point — that tlie maximunr effect is attained some time after the cessation of a short exposure — the corresponding experiment on the eye may be made as follows : at the end of a tube is fixed a glass disc coated with lampblack, on which, by scratching with a pin, some words are written in transparent characters. 17^ JiESFOXSE IN THE LIVING AND NON-LIVING The It'iigtli of the tulie is so adjusted that the disc is at the distance of most distinct vision from tlie end of the tube applied to tlie eye. The Ijlackened disc is turned towards a source of strong" liglit, and a slioi't exposure is given liy tlie release of a pliotographic shutter inter- posed between tlie disc and the eye. On closing the eye, immediate!}' after a short exposure, it will at fii'st be found that there is hardly any well-defined visual sensation ; after a short time, however, the writino- on ■0' 20" 30" AO" Fig. 110. — Eesponse-ltkves of the Sensitive SiL%"xr. Cell Showing greater persistence of after-effect when the stimulus is strong, (o) Short exijosure of 2" to light of intensity 1 ; ih) short exposure of 2" to light nine times as strong. the blackened disc begins to appear hi luminous characters, attains a maximum intensity, and then fades away. In this case the stimulus is of short duration, the light being cut off before the maximum effect is attained. The after-effect here is positive, there being no reversal or interval of darkness between the direct image and the after-image, the one being merely the continuation of the other. But we shall see, if lidit is cut off' after a maximum effect is attained by lono- VISUAL ANALOGUES 173 exposure, that the immediate after-image would Ije negative (see below). The relative persistence of after-effect of lights of different intensities may be shown in the following manner : If a bold design be traced with magnesium powder on a blackened board and fired in a dark room, the observer not being acquainted with the design, the instantaneous flash of light, besides being too quick for detailed observation, is obscured Ijy the accompanying smoke. But if the eyes be closed immediately after the flash, the feeljler obscuring sensation of smoke will first disappear, and will leave clear the more persistent after- sensation of the design, which can then be read dis- tinctly. In this manner I have often been able to see distinctly, on closing the eyes, extremely brief pheno- mena of light which could not otherwise have been observed, owing either to their excessive rapidity or to their dazzling character.^ After-oscillation. — In the case of the sensitive silver cell, we have seen (fig. 105), when it has been sul)jected ■ for some time to .strono' lioht, that the current of response attains a maximum, and that on the stoppage of the stimulus there is an immediate rebound towards recovery. In this rebound there may be an over-shoot- ing of the equilibrium position, and an after-oscillation is thus produced. ^ As an instance of this I may mention the experiment which 1 saw on the quick fusion of metals exhibited at the Royal Institution by Sir William lioberts-Austen (1901), where, owino- to the glare and the dense fumes, it was impossible to see what happened in the crucible. Bvit I was able to see every detail on closiriy the eyes. The effects of the smoke, being of less luminescence, cleared away first, and left the after-image of the molten metal growing clearer on the retina. 174 Jy£SrOiXSF. IN THE LIl'iyG AXD XOX-LWIXG If tliei-e has Ijcen a fcelile initial curi-ent, this oscilhitorv after-carreiit, liy alu-ehi'aical sumnialioii, will cattst' the i-iirrciit iiL tlie (/ifctiit to Ije alternately weaker and stmiini.]- (jian the initial current. Visual recurrence. — Translated into the A'isual eirfuit, this would mean an alternatino- series of after-iniap'es. <.)n the eessati(.)n of hjjlit of strong' hitensity and lono- ditration. the inun{^diate efl'ect would be a nep'ative re- hottnd, unlike the positive after-elTect which followed on a short exposure. The next rebMtuid is jjositiA'c, oivinp- rise to a sen- sation of brightness. This Avill go on in a rectirrent series. If we look for some tiuie at a A'ery bright oljject, preferably with one eye, on closuig the eye there is an inimediate dark sensation followed by a sensation of light. These go on alternating and give rise to the phenomena of recurreitt vision. With the eyes closed, the positive or Itiminotis jjhases are the more prominent. This phenomenon rna}- lie oljserved hi a somewhat different maiuier. After staring at a loriglit light we may look towards a Avell-lighted wall. The dark phases will now become the more noticeable. If, liowever, Ave look towards a dimly lighted wall, both the dark and Ij right phases -will be noticed alternately. The iiegative effect is usually explained as due to fatigue. That position of the retina affected by hght is supposed to be -tired,' and a negative image to Ije formed in consecjuence of exhaustion. Y>\ this exliaus- VISUAL AATALOGUES i-js tion is meant either the presence of fatipne-stufis, or the l)reaking-dowii of the sensitive element henomena of memory are also recurrent. ' Certain sensations for which there is no corresponding process outside the body are generally grouped for convenience under this term [memory]. If the eyes be closed and a picture be called to memory, it will be found that the picture cannot ha held, but will repeatedly disappear and appear. ' ^ The visual impressions and their recurrence often persist for a very long time. It usually happens that owing to weariness the recurrent images disappear ; but in some instances, long after this disappearance, they will spontaneously reappear at most unexpected moments. In one instance the recurrence was observed in a dream, about three weeks after the original im- pression was made. In connection with this, the revival of images, on closing the eyes at night, that have been seen during- the day, is extremelv interestino-. Unconscious visual impression. — While repeating certain expeiiments on recurrent vision, the above phenomenon Ijecame prominent in an unexpected ' E. AV. Scripture, The Xew Tuychulogy. p. 101. VISUAL ANALOGUES 179 manner. I had been intently looking at a particular window, and obtaining tlie subsequent after-images by closing the eye ; my attention was concentrated on the window, and I saw nothing but the window either as a direct or as an after effect. After this had been rejjeated a number of times, I found on one occasion, after closing the eye, that, owing to weariness of the particular portio]\ of the retina, I (^ould no longer see the after-image of the window ; instead of this, I however saw distinctly a circular opening closed with glass panes, and I noticed even the jagged edges of a l)roken pane. I was not aware of the existence of a circular opening higher up in the wall. The image of this had impressed itself on the retina without my knowledge, and had undoubtedly been producing the recurrent images which remained unnoticed because my principal field of after-vision was filled up and my atten- tion directed towards the recurrent image of the window. When this failed to appear, my field of after-vision was relatively free from distraction, and I could not help seeing what was unnoticed before. It thus appears that, in addition to the images impressed in the retina of which we are conscious, there are many others which are imprinted without our knowledge. We fafil to notice them because our attention is directed to something else. But at a subsequent period, when the mind is in a passive state, these impressions may sud- denly revive owing to the phenomenon of recurrence. This observation may afford an explanation of some of the phenomena connected with ocular phantoms and hallucinations not traceable to any disease. In these i8o RESPOXSE IN THE LIVING AND NON-LIVING cases the psychical eilects produced appear to have no objective cause. Bearini;' in mind the numerous visual impressions which are being unconsciously made on the retina, it is not at all unlikely that many of these visual phantoms may l)e due to objective causes. C!HAPTEE XX GENERAL SURVEY AND CONCLUSION We have seen that stiniuhis produces a certain ex- citatory change in hving substances, and tliat the excitation produced sometimes expresses itself in a visible change of form, as seen in muscle ; that in many other cases, however — as in nerve or retina — there is no visible alteration, but the disturbance produced by the stinuilus exhibits itself in certain electrical changes, and that whereas the mechanical mode of response is limited in its application, this electrical form is universal. This irritability of the tissue, as shown in its capacity for response, electrical or mechanical, was found to depend on its physiological activity. Under certain conditions it could be converted from the responsive to an irresponsive state, either temporarily as by antesthetics, or permanently as by poisons. When thus made permanently irresponsive by any means, the tissue was said to have been killed. We have seen further that from this observed fact — that a tissue when killed passes out of the state of responsive- ness into that of irresponsiveness ; and from a confusion of ' dead ' things with inanimate matter, it has been tacitly assumed that inorganic substances, like dead iS2 /^/^srov.sji /.v THE Lir/m; axd nonhjving animal tissnf>. must m-ressarily hf iri'esponsive. or ineapalile of lieiiiLi' pxcited l)y stimulus — an assumptiou wliirli has l)eeu shown t(i Ije iiratuitous. Tliis ■ unexplained conception of irritalnlity became the startin,ii--point.' to quote the words of Yerworn.' 'of rifidi.srn. whidi in its mr)st I'omplete form asserted a dualism of liA'iuL! and lifeless Xature. . . . The vitalists sor)n,' as he ii'cies on to sa^', ' laid aside, more or less com- pletely, mechanical and chemical explanations of \dtal phenomena, and introduced, as an explanatory principle, an all-con trollino' unknown and inscrutal)le '• force liyper- mecanique. " While chemical and physical forces are responsihle for all phenomena in lifeless bodies, in living organisms tliis special force induces and rules all yital actions. ' Later vitali^t^. however, attempted no analysis of vital force: they employed it in a wlioUy mystii;al form as a convenient explanation oi all sorts of A'ital plie- nomena. ... In place of a real explanation a simple phrase .^uch a.^ "vital force" was sati>factory, and sio-nified a mystical force lielonp-iiip' to orij'anisms only. Thus it was ea^y to ••explain" the nio-t complex vital phenomena.' From thi> position, with its assumption of the super- physical character of response, it is clear that on the discovery of similar efiects amon^ti'st inorganic suljstances, the necessity of tlieoretically maintaining such dualism in Xature mu-.t innnediately fall to the ground. In the previou-- cha})ters I have shown that not the fact of response alone. Imt all tliose modifications in ' Verwirn, Gr-nr-ml Pln/fiolor/i/, p. Is. GENERAL SURIEY AND CONCLUSION 183 resjionse which occur under various conditions, take place in plants and metals just as in animal tissues. It may now be well to make a general survey of these phe- nomena, as exhibited in the three classes of sul^stances. We have seen that the wave of molecidar disturb- ance in a living animal tissue under stimulus is accom- panied by a wave of electrical disturbance ; that in certain types of tissue the stimulated is relatively positive to the less disturbed, while in others it is the reverse ; that it is essential to the obtaining of electric response to have the contacts leading to the galvano- meter unequally affected by excitation ; and finally that this is accomplished either (1) by ' injuring ' one con- tact, so that the excitation produced there would be re- latively feeble, or (2) Ijy introducing a perfect block l^etween the two contacts, so that the excitation reaches one and not the other. Further, it has been shown that this characteristic of exhibiting electrical response under stimulus is not confined to animal, but extends also to vegetable tissues. In these the same electrical variations as in nerve and muscle were obtained, by using the method of injury, or that of the l)lock. Passing to inorganic substances, and using similar experimental arrangements, we have found the same electrical responses evoked hi metals under stimulus. Negative variation. — ^In all cases, animal, vegetable, and metal, we may obtain response by the method of negative variation, so called, by reducing the excitability of one contact by physical or chemical means. Stimulus causes a transient diminution of the existing current, 1 84 RESrONSE IN THE LIVING AND NON-LIVING the variation (lependiijg on tlie intensity of the stimuhis (^figs. 4, 7, 04). Relation between stimulus and response. — In all three classes we have found that the intensity of re- sponse increases with increasing stimulus. At very high intensities of stimulus, however, there is a tendency of the response to reach a limit (figs. 30, 32, 84). The law that is known as Weber-Fechner's shows a similar characteristic, in the relation between stimulus and sensation. And if sensation be a measure of phy- siological efl'ect we can understand this correspondence A p r' Fig. 112. — Unifoem Eespoxses in (A) Neeve, (P) Plant, and (M) Metal Tlie norma] respoiise in nerre is represented ' down.' In this and following figures, (Al is the record of responses in animal, (P) in plant, and (Mj in metal. of the physiological and sensation curves. We now see further that the physiological effects themselves are ultimately reducible to simple physical phenomena. Effects of superposition. — In all three types, ineffec- tive stimuli become effective by superposition. Again, rapidly succeeding stimuli produce a maxi- mum effect, kept balanced by a force of restitution, and continuation of stimulus produces no further effect, in the three cases alike (figs. 17, IS, 80). Uniform responses. — In the responses of animal, vegetable, and metal alike we meet with a type where the responses are uniform (fig. 112). GENERAL SURVEY AND CONCLUSION 185 Fatigue. — There is, again, anotlier type where fatigue is exhibited. The exphiiiation hitherto given of fatigue in animal tissues— that it is due to dissimilation or breakdown of tissue, complicated by the presence of fatigue-products, while recovery is due to assimilation, for which material is brought by the blood-supply — has long been seen to be inadequate, since the restorative effect succeeds a short period of rest even in excised bloodless mtiscle. But that the phenomena of fatigue and recovery Fig. 113. — Fatigue (A) in Muscle, (P) in Plant, (M) in Metal were not primarily dependent on dissimilation or assimila- tion becomes self-evident when we find exactly similar effects produced not only in plants, but also in metals (fig. 113). It has been shown, on the other hand, that these effects are primarily due to cumulative residual strains, and that a brief period of rest, by removing the overstrain, removes also the sign of fatigue. Staircase effect. — The theory of dissimilation due to stimulus reducing the functional activity below par, and thus causing fatigue, is directly negatived by what is known as the ' staircase ' effect, where successive equal stimuli produce increasing response. We saw an iS6 RESFOXSE IN THE LIJ'ING AND NONLIVING exa(/th- similar plienomenou in plants and metals, where successive responses tr) equal stimuli exhibited an Fk4. 114. — 'Staircase' in Muscle, Plant, and Metal increase, apparently by a gradual removal of molecular sluggishness (fig. 114). Before After Before After Fig. 115. — Inceearei> Response after Continuous STi3inL.4TiON in Nerve ANT' Metal The normal response in animal tissue is represented ' down,' in metal ' up.' Increased response after continuous stimulation. — An efi'ect somewhat similar, that is to say, an in creased response, due to increased molecular mobility, GENERAL SURVEY AND CONCLUSION 187 is also shown sometimes aftei' continuous stimulation^ not only in animal tissues, but also in metals (fig. 115). Modified response. — In the case of nerve we saw that the normal resj^onse, which is negative, sometimes becomes reversed in sign, i.e. positive, when the specimen is stale. In retina again the normal positive response is converted into negative under the same conditions. Similarly, we found that a plant when withering often shows a positive instead of the Before After Befove After Fig. 116. — Moiufied Abnormal Response in (A) Nerve and (M) Metal CONVEETED INTO NOEJIAL, AFTER CONTINUOUS STIMULATION (A) is the record for nerve (recording galvanometer not being dead-beat sliows after-oscillation) ; the abnormal ' up ' is converted into normal ' down ' after continuous stimulation. (M) is the record for metal, the abnormal ' down ' being converted into normal ' up ' after like stimulation. usual negative response (fig. 28). On nearing the death- 23oint, also by subjection to extremes of temperature, the same reversal of response is occasionally observed in plants. This reversal of response due to peculiar molecular modification was also seen in metals. But these modified responses usually become normal when the specimen is subjected to stimulation either strong or long continued (fig. 116). iSS RESPONSE EV THE LIVING AND NON-LIVING Diphasic variation. — A dipliasic variation is observed in nerve, if the "wave of molecular disturbance does not leacli the two contacts at the same moment, or if the rate of excitation is not the same at the two points. A similar diphasic variation is also observed in the resijonses of plants and metals (fi^y'S. 26, fi8). Effect of temperature. — In animal tissues response becomes feeble at low temperatures. At an optimum temperature it reaches its greatest amplitude, and, again, beyond a maximum temperature it is very much reduced. We have observed the same phenomena in plants. In metals too, at high temperatures, the response is very much diminished (figs. 38, 05). Effect of chemical reagents. — Fhially, just as the response of animal tissue is exalted by stiuiulants, lowered b}' depressants, and abolished by poisons, so also we have found the response in plants and metals undergoing similar exaltation, depression, or abolition. We have seen that the criterion by which vital response is diflerentiated is its abolition by the action of certain reagents — the so-called poisons. We find, however, that ' poisons ' also abolish the responses hi plants and metals (fig. 117). Just as animal tissues j)ass from a state of responsiveness while living to a state of irresponsiveness when killed by poisons, so also we find metals transformed from a responsive to an ir- responsive condition by the action of similar 'poisonous' reagents. The parallel is the more striking since it has long Ijeen known with regard to animal tissues that the GENERAL SURVEY AND CONCLUSION 1S9 same drug, administeved in large or small doses, might have opposite effects, and in preceding chapters we have seen that the same statement holds good of plants and metals also. Stimulus of light. — Even the responses of such a highly specialised organ as the retina are strictly paralleled by inorganic responses. We ha^'e seen how the stimulus of light evokes in the artificial retina responses which coincide in all their detail with those produced in the real retina. This was seen in inefl'ective mm '^Ws^ Before '^ After Before •[■ After Before -t- After Fie. 117. — Abolition or Eesponse in Neeve, Plant, and Metal BY the Action of the same ' Poison ' The first half in each set shows the normal response, the second half the abolition of response after the application of the reagent. Stimuli becoming efl'ective after repetition, in the relation between stimulus and response, and in the effects pro- duced by temperature ; also in the phenomenon of after- oscillation. These similarities went even further, the very abnormalities of retinal response finding their reflection in the inorganic. Thus living response in all its diverse manifestations is found to be only a repetition of responses seen in the inorganic. There is in it no element of mystery or caprice, such as we must admit to be applied in the 190 J^ESPOXSE IN THE LIVING AND NONLIVING assumption of a liypenne(_'lianical vital force, acting in (contradiction or deliance of tliose physical laws that govern the world of niatter. Nowhere in the entire range of these T'esponse-phenoniena — inclusive as that is of metals, plants, and animals — do we detect any breach of continuity. In the study of processes apparently so complex as those of irritability, we must, of course, expect to Ije confronted with many difficulties. But if these are to be overcome, they, like others, must be faced, and their investigation patiently pursued, without the postulation of special forces whose con- venient property it is to meet all emergencies in virtue (jf their vagueness. If, at least, we are ever to understand the intricate mechanism of the animal machine, it will be granted that we must cease to evade the problems it presents by the use of mere phrases which really explahi nothing. We liave seen that amongst the Y^li^'^^^^ii^, of response, there is no necessity for the assumption of vital force. They are, on the contrary, physico- c-hemical phenomena, susceptible of a physical inquiry as dehnite as any other in inorganic regions. Physiologists have taught us to read in the response- curves a history of the influence of various external agencies and conditions on the phenomenon of life. By these means we are able to trace the o'radual diminution of responsiveness Ijy fatigue, Ijy extremes of heat and cold, its exaltation by stimulants, the arrest of the life- process by poison. The investigations which have just been described GENERAL SURVEY AND CONCLUSION 191 may possiljly carry us one step further, proving' to us that these thinijs are determiued, not by the play of an unknowable and arbitrary vital force, but l)y the work- ing of laws that know no change, acting equally and uniformly throughout the organic and the inorganic wor •Ids. INDEX Actios cm'rent in metal, 88 ,, ,, in nerve, 8 „ ,, in plant, 19 After-images and their revival, 177 After-osoiUation in photo-sensitive cell, 159, 163 Aniestheties, effect on response in nerve, 72 in plant, 30, 73, 74, 75 Annealing, effect on response in metal, 101, 138 Binocular alternation of vision, 175 Block method, advantages of, 28, 77 „ ,, for obtaining response in metal, 82, ,, ,, ,, „ in plant, 28 Chloral, effect on plant response, 75 Chloroform, effect on nerve response, 72 ,, ,, plant response, 74 Compensator, 23 Current of injury in nerve, 7 Curves, characteristics of response, 3 Death-point, determination of, in plants, 61, 63 Depressants, effect on inorganic response, 142 Depression, response by relative, 87 Dewar on retinal current, 149 Diphasic variation in metal, 113, 114, 115, 116, 188 „ ,, in nerve, 188 in plant, 46, 188 Dose, effect on inorganic response, 89, 146, 189 ,, ,, plant response, 79, 189 Electrical recorder, 11 Klectrical response. See Kcsponse, electrical Electric tapper, 24 Exaltation, response by relative, 89 194 RESPONSE EV THE LIVEXG AX]} XON-LIVING Fatigue, alji^eiice of, undor certain comlitions, in luetal, 120 „ ,, in muscle, 59 „ ,, in plant, 39 apparent, with jncix-ascd freiiuenc y of stimulation, in metal, 120 ,, „ ,, in muscle, 40 ,, ,, ,, in plant, 40 diminution of response under strong stinnilus due to, in plant, 57 in metal, 118, 119, 185 in muscle, 118, 185 in plant, 20, 185 due to overstrain, 41 rapid, under continuous stinndation in metal, 121, 130 in muscle, 42, 130 removal of, by rest in plant, 43 llieorj- of, in muscle, 38, 185 m plant, 42, 130 HoLiiGREX on retinal current, 149 H.ysteresis, 137 Injury, current of, in nerve, 7 Inorganic response. See Metal, electrical response in KuHXE on retinal curreirt, 149 Krmkel on electrical changes by injury or flexion in plant, 14, 70 IjIGHT, after-effect of short exposure to, on photo-sensitive cell, 171 ,, ,, ,, on retina, 171 ,, decline and reversal of response under continuous, in photo- sensitive cell, 166 „ „ „ continuous, m retina 166 ,, effect of temperature on response of photo-sensitive cell produced by, 158 ,, ,, retinal response produced bj', 158 relation between intensity and response to, in photo-sensitive cell, 161, 162 ,, ,, ,, in retina, 162 response to, after-oscillation in pjhoto-sensitive cell, 159, 163 „ effect of increasing length of exposure in plioto-sensi- tive cell, 159 ,, ), ,, ,, in retina, 160 in frog's retina, 150, 151, 156, 164, 166 „ in photo-sensitive cell, 152, 153, 154, 155, 157, 165, 166 INDEX 195 McKbndrick on retinal i-esi^onse, 149 Mechanical recorder, 3 ,, response, 1 „ stimulus by electric tapper, 24 „ ,, by spring-tapper, 23 „ ,, by vibrator, 24 „ ,, conditions of maintaining uniformity of, 25 „ ,, means of graduating intensity of, 22, 24, 96 Metal, electric response in, abnormal, 125 „ ,, abolition of, by 'poison,' 143 „ ,, additive effect of superposition of stinmlus on, 135 „ ,, annealing, effect of, on, 101 „ „ by method of block, 82, 92 „ „ ,, negative variation, 87, 183 „ ,, depressants, effect of, on, 142 „ „ diphasic, 113, 114, 115, 116, 188 „ ,, enhancement of, after continuous stimulation, 127, 128, 186 fatigue, 118, 119, 120, 121, 185. ,S'ec also Fatigue „ „ maximum effect due to superposition of stimuli, 136 „ „ modified, 129 „ „ 'molecular arrest,' effect of, by 'poison' on, 145 „ „ molecular friction, effect of, on, 108, 109 „ . „ prolongation of recovery by overstrain, 106 by ' poison,' 145 „ „ relation between, and stimulus, 184, 135 „ „ staircase effect, 1'22, 186 „ „ stimulant, effect of, on, 141 „ ,. temperature, effect of, on. 111 „ ,, uniform, 102, 184 Minchin on photo-electric cell, 165 Molecular ' arrest ' in metals by ' poison,' 145 friction, 108, 109 model, 107 „ voltaic cell, 99 Munck on electric response in sensitive plants, 14 Muscle, fatigvte in, 38, 39, 40, 42. See also P'atigue „ prolongation of recovery by ' poison ' in, 144 „ relation between stimulus and response in, 52 „ staircase effect in, 122 ,, stimulus, effect of superposition of, on, 36 Myograph, 2 196 JiESPtU'SE /A' THE LIVIXG AND NON-LIVING Nkoative \ariation, response by luetlKMi of, in metal, 87, 183 ,, ,, ,, in nerve, i), 183 in plant, 18, 183 Xervo, c-urrenl of injiiry in, 7 injured and nninjnred contacts corresponding to Cu and Zu in \oltaic couple, 8 ,, response in, abnormal, when stale, 124, 187 ., ,, abolition of, by 'poison,' 139, 189 ,, anicsthetics, effect of, on, 72 ,, ,, by method of negative ^•ariation, 9 ,, current of action of, 8 ,, ,, enliancemcnt of, after continuous stimulation, 127 modified, 128 ,, ,, relation between, and stinnilus, 52 ,, ., reversed when stale, 11 ,, ., uniform, 184 Nomenclature, anomalies of present, 9, 85 rnoTOGEAPHic recorder, 11, 22 I'lant chamber, 64 ,, electrical response in, abnormal, when stale or dying, 48, 187 ,, ,, abolition of, by high temperature, 32, 04 ,, ,, additi\"e effect of stimulus on, 37 ,, ,, anesthetics, effect of, on, 30, 73, 74, 75 ,, „ by method of block, 28 ,, ,, ,, of negative variation, 18, 183 ,, ,, diphasic, 46 fatigue, 20, 39, 40, 41, 42, 43, 57, 185. See aho Fatigue ,, ,, physiological character of, 30 ' poison,' eft'ect of, on, 30, 32, 78, 79 ,, „ relation between, and stimulus, 52, 53, 54 ,, „ staircase effect, 37, 185 ,, stimulus, eflcct of single, on, 35 ,, ,, ,, effect of superposition of, on, 35 „ ,, temperature, effect of, on, 32, 59-69 ,, „ uniform, 36, 184 ., radial E.M. response in, 49 Poison, effect of, on response in metal, 143, 189 „ „ in nerve, 139, 189 in plant, 30, 32, 78, 79, 189 ' molecular arrest ' in metal by, 145 prolongation of recovery by action of, in metal, 145 ,, ,, ,, in nurscle, 144 ItE(joEi), simultaneous mechanical and electrical, of response, 13 liecorder, electrical, 11 INDEX 197 EccoriTcr, mechanical, 3 „ photographic, 11, 22 „ response, 19 Eesponse-curvc, characteristics of, 3 „ electrical, abnormal, iu metal, 123, 125 >> )) ,, in stale nerve, 11, 123 n ,, ,, in stale or dying plant, 48, 187 jj „ ,, in stale retina, 11, 164 11 ,, ,, converted into normal after strong or con- tinuous stimulation in metal, 125, 187 ,1 „ „ „ „ in nerve, 124, 187 II )! ,, ,, ,, in plant, 48 „ „ abolition of, by high temperature iu plant, 32, 64 „ „ ,, by ' poison,' in metal, 143, 189 „ ,, ,, ,, in nerve, 139, 189 „ „ „ „ in plant, 30, 32, 78, 79, 189 „ „ additive efl'ect of stimulus on, in metal, 135 „ „ ,, ,, on, in plant, 37 „ „ antesthetics, effect of, on, in nerve, 72 „ „ ,, ,, in plant, 30, 73, 74, 75 „ „ annealing, efl'ect of, on, in metal, 101, 138 „ by method of block, 28, 82, 92 „ ,, by negative variation, 9, 18, 87, 183 „ ,, by relative depression, 87 „ „ by relative exaltation, 89 ,) ,, conditions for obtaining, 6, 86, 87 ,, „ continuous transformation from positive to negative in metal, 115 „ „ decline and reversal of, under continuous light in photo-sensitive cell, 166 „ „ decline and reversal of, under continuous light in retina, 166 „ „ depressants, efl'ect of, on inorganic, 142 „ „ dimmution of. See Fatigue „ „ diphasic in metal, 113, 114, 115, 116, 188 „ „ ,, in nerve, 188 „ „ „ in plant, 46, 188 „ „ dose, efl'ect of, on inorganic, 89, 146, 189 „ „ ,, on, in plant, 79, 189 „ „ enhancement of, after continuous stimulation in metal, 127, 128, 186 ,, „ enhancement of, after continuous stimulation iu nerve, 127, 186 „ „ maximum efl'ect due to superposition of stimulus, 35, 136 „ „ measure of physiological activity, 13 ly S JiESrOXSE IX THE LHEXG AXD XON-LIVIXG llesponst, clcctiical. ii]( Jccular fiirtinn, cflcct of, on, lOH, 109 ,, ,, ., moditie.-ition, otiect of, on, 11, 4H, 123, 12.J, 12'.), IGl, 187 liliy.-iioloL'ical character of, in plant, 50 poMtive and nc,i,'atiye, 11 ,. prolongation of rccovoiy in, by 'poison' in metal, 14.J prolongation of recovery in, by ' poison ' in muscle, 114 proloniiatiori of reco\'ery in, from oxerstrain, 100 relation between, and stimulus in meta.1, 134, 135 ,, ,, ,, in muscle, 52 ,, ,, ,, ill ner\x-, 52 ,, ,, ,, in plant, 52. 53, 54 „ ,, ,, in real and artificial retinie, 162 stau-case efteot. in metal. 122. IWO in plant, 37. 186 stimulant, effect of. on. in metal, 141 ,, temperatm-e, effect of, on. Hee Temperature ,, threshold of. 135 ,, to lielit. .Vet- Li.eht ,, uniform in metal, 102. 184 in nerve. 184 in plant. 36, 184 ,. universal applicability of, 12 mechanical, 1 retinal. See Liidit ,, simultaneous mechanical and electrical record of, 13 Retma. See Liglit S-iXDEEsoN, EuEDOx-, on clectrlcal response in seirsitive plants. 14 Spring-tapper, mechanical stimulus by, 23 Staircase effect in metal, 122, 186 iir mirscle. 122. 186 ,. in plant. 37. 186 Steiner on retinal response. 149 Stimuli, maximmn effect due to sriperposition of. in metal, 136 ,, ,, m muscle, 36 ,, ,, ,, in plant, 36 Stimulus, advairtages of vibrational, 25 and response, relation betveen. in metal. 134, 135 „ .. m muscle, 52 ,, .. in nerve, 52 „ ,, in plant, 52, 53, 54 ,, ,, in real and artificial retinie, 162 IXDEX 199 Stimulus, effect of different kinds of, 2 ,, nieelianical, by spring-tapper, 24 ,, ,, conditions for niaiutauiing uniformity of, 26 ,, ,, means of graduating intensity of, 22, 96 „ vibrational, 24, 25, 26 Temperature, death-points in plants, 01, 63 effect of, on response in metal, 111 „ ,, in photo-sensitive cell, 158 in plants, 32, 60-69 ,, ,, in retina, 158 increased sensitiveness in plant due to variation of, 66, 67 Vibrational stimulus, 24, 25. 26 Vision, binocular alternation of, 175 ,, effect of variorrs conditions on the period of binocidar alternation of, 177 Visual images, revival of, 177 inrpression, unconscious, 178 impulse, chemical theory of, 148 ,, electrical theory of, 149 phantoms, 179 recurrence, 174 Vital force, 13 Vitalism, 182 Waller on enhancement of nerve-response after continuous stimulation, 127 ,, on relation between stimuhrs and response in muscle, nerve, and retma, 52, 162 ,, on retinal response, 150, 156, 165 ,, on reversal of response in stale nerve and retina, 11, 124, 164 „ ■ on transformation from abnormal to normal response in nerve after continuous stimulation, 124 TRINTITi BY £;]'0TT1SW00DE AXTj CO. 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