Response in the Living and Non-Living

polarisable electrode equal to 20,000 ohms. The introduction of a chemical reagent reduced it to 19,000 ohms. The resistance of the galvanometer is equal to 1,000 ohms. The high external resistance was 1,000,000 ohms. The variation of resistance produced in the circuit would therefore be 1,000 in (1,000,000 + 19,000+1,000) or one part in 1,020. Therefore the variation of galvanometric deflection due to change of resistance would be less than one part in a thousand (cf. fig. 49).

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

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

Fic. 47.—Apoxirion or Response aT BoTH A AND B ENDS By THE ACTION or NaOH Stimuli of 30° vibration were applied at intervals of one minute to A and B alternately. Response was completely abolished twenty-four minutes after application of NaOH. equal. A few drops of 10 per cent. solution of NaOH was applied to both the ends. It will be seen how quickly this reagent abolished the response of both ends (fig. 47). Effect of dose.—It is sometimes found that while a reagent acts as a poison when given in large quantities, it may act as a stimulant in small doses. Of the two following records fig. 48 shows the sheht stimulating

Fie. 49.—Nearny covpehere ABOLITION OF RESPONSE BY STRONG KOH The two vertical lines are galvanometer deflections due to ‘1 volt, before after the application of ré agent. remains unchanged. effect of very dilute KOH, and fig. 49 exhibits nearly complete abolition of response by the action of the same reagent when given in stronger doses. So we see that, judged by the final criterion of the effect produced by anesthetics and poisons, the plant response fulfils the test of vital phenomenon. In previous chapters we have found that in the matter of response by negative variation, of the presence or absence of fatigue, of the relation between stimulus and response, of modification of response by high and low temperatures, and even in the matter of occasional abnormal variations such as positive response in a modified tissue, they were strictly correspondent to similar phenomena in animal tissues. The remaining test, of the influence of chemical reagents, having now been applied, a complete parallelism may be held to have been established between plant response on the one hand, and that of animal tissue on the other.

Is response found in inorganic substances ?—Experiment on tin, block method—Anomalies of existing terminology—Response by method of depression—Response by method of exaltation. We have now seen that the electrical sign of life is not confined to animals, but is also found in plants. And we have seen how electrical response serves as an index to the vital activity of the plant, how with the arrest of this vital activity electrical response is also arrested temporarily, as in the case amongst others of anesthetic action, and permanently, for instance under the action of poisons. Thus living tissues—both animal and vegetable—may pass from a responsive to an irresponsive condition, from which latter there may or may not be subsequent revival.

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

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

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

1 Following another line of inquiry I obtained response to electric stimulus in inorganic substances using the method of conductivity variation (see ‘De la Généralité des Phénoménes Moléculaires Produits par l’Electricité sur la Matiére Inorganique et sur la Matiére Vivante,’ Travaux du Congres International de Physique, Paris, 1900; and also ‘On Similarities of Effect of Electric Stimulus on Inorganic and Living Substances, British Association 1900. See Electrician). To bring out the parallelism in all details between the inorganic and living response, 1 have in the following chapters used the method of electro-motive variation

employed by physiologists. 2 By ‘tin’ is meant an alloy of tin and lead used as electric fuse. still by torsional vibration, a transitory ‘current of action ’ will be found to flow in the wire from B to A, from the unstimulated to the stimulated, and in the galvanometer from the stimulated to the unstimulated. Stimulation of B will give rise to a current in an opposite direction. Experiment to exhibit the balancing effect.—If the wire has been carefully annealed, the molecular condition of its different portions is found to be approximately the same. If such a wire be held at the ‘ balancing

Fie. 50.—Enectric Response In Merans (a) Method of block; (6) 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 quick vibration, say, of 90° be given to A, an upward deflection will be produced ; if a vibration of 90° be given to B, there will be an equal downward deflection. If now both the ends A and B are vibrated simultaneously, the responsive H.M. variation at the two ends will continuously balance each other and the galvano-

meter spot will remain quiescent (fig. 50, 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 ofewire constant, the intensity of stimulus increases with the amplitude of vibration. Again, keepine the amplitude constant, the intensity of stimulus is increased by shortening the wire. Hence it will be seen that if the clamp be shifted from the balancing point towards A, simultaneous vibration of A and B through 90° will now give a resultant upward deflection, showing that the A response is now relatively stronger. Thus keeping the rest of the circuit untouched, merely moving the clamp from the left, past the balancing point to the right, we get either a positive, or zero, or negative, resultant effect.

In tin the current of response is from the less to the more excited point. In the retina also, we found the current of action flowing from the less stimulated to the more stimulated, and as that is known as a positive response, we shall consider the normal response of tin to be in like manner positive. Just as the response of retina or nerve, under certain molecular conditions, undergoes reversal, the positive being then converted into negative, and negative into positive, so it will be shown that the response in metallic wires under certain conditions is found to undergo reversal.

Anomalies of present terminology.—When there is no current of injury, a particular current of response can hardly be called a negative, or positive, variation. Such nomenclature is purely arbitrary, and leads, as will be shown, to much confusion. A more definite terminology, free from misunderstanding, would be, as already said, to regard the current towards the more stimulated as positive, and that towards the less stimulated, in tissue or wire, as negative. The stimulated end of tin, say the end 4A, thus becomes

zincoid, i.e. the current through the electrolyte (non-polarisable electrodes with interposed galvanometer) is from A to B, and through the wire, from the less stimulated B to the more stimulated A. Conversely, when B is stimulated, the action current flows round the circuit in an opposite direction. This positive is the most usual form of response, but there are cases where the response is negative. | In order to show that normally speaking a stimulated wire becomes zincoid, and also to show once more the anomalies into which we may fall by adopting no more definite terminology than that of negative variation, I have devised the following experiment (fig. 51). Let us take a bar, one half of which is zine and the other half copper, clamped in . the middle, so that a disturbance a ee produced at oneend may not reach Normal Current = <—— the other; the two ends are con- Fie.51.—Current or Response nected to a galvanometer through 70™4"?S TH Sumunatep Exp non-polarisable electrodes. The tease Stared Te

diminished (-85—-009) V. current through the electrolyte when Zn stimulated: action cur- (non-polarisable electrodes and in- SR ae em oui 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 difference of potential between zine 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 zine and copper ends was found to be ‘85 volt. This was balanced by a potentiometer arrangement, so that the galvanometer spot came to zero. On vibrating the zine wire, a deflection of 33 dns. was obtained, in a direction which showed an increase of E.M.F. On stopping the vibration, the spot of ight came back to zero. On now vibrating the copper wire, a deflection of 23 dns. was obtained in an opposite direction, showing a diminution of E.M.F. This transitory responsive variation disappeared on the cessation of disturbance.

By disturbing the balance of the potentiometer, the galvanometer deflection due to a known increase of E.M.F. was found from which the absolute E.M. variation caused by disturbance of copper or zinc was determined. It was thus found that stimulation of zinc had increased the P.D. by fifteen parts in 1,000, whereas stimulation of copper had decreased it by eleven parts in 1,000. According to the old terminology, the response due to stimulation of zinc would have been regarded as positive variation, that of copper negative. The responses however are not essentially opposite in character, the action current in the bar being in both cases towards the more excited. For this reason it would be preferable, as already said, to employ the terms positive and negative in the sense I have suggested, Le. positive, when the current in the acted substance is towards the more excited, and negative, when towards the less excited. The method of block is, as I have already shown, the most perfect for the study of these responses.

In the experiment fig. 50, if the block is abolished and the wire is struck in the middle, a wave of molecular disturbance will reach A and B. The mechanical and the attendant electrical disturbance will at these points reach a maximum and then gradually subside. The resultant effect in the galvanometer will be due to £,-E, when E, and £, are the electrical variations produced at AandB by the stimulus. The electric changes at A and B will continuously balance each other, and the resultant effect on the galvanometer will be zero: (a) if

the exciting disturbance reaches A and B at the same time and with the same intensity ; () if the molecular condition is similar at the two points; and (c) if the rate of rise and subsidence of excitation is the same at the two points. In order that a resultant effect may be exhibited in the galvanometer, matters have to be so arranged that the disturbance may reach one point, say A, and not B, and vice versa. This was accomplished by means of a clamp, in the method of block. Again a resultant differential action may be obtained even when the disturbance reaches both A and B, if the electrical excitability of one point is exalted or depressed by physical or chemical means. We shall in Chap. XVI study in detail the effect of chemical reagents in producing the enhancement or depression of excitability. There are thus two other means of obtaining a resultant effect—(2) by the method of relative depression, (3) by the method of relative exaltation.

Electric response by method of depression.— We may thus by reducing or abolishing the excitability of one end by means of suitable chemical reagents (so-called method of injury) obtain response in metals without a block. The entire length of the wire may then be stimulated and a resultant response will be produced, owing to the difference between the excitability of the two ends. A piece of tin wire is taken, and one normal contact is made at A (strip of cloth moistened with water, or very dilute salt solution). The excitability of B is depressed by a few drops of strong potash or oxalic acid. By the application of the latter there will be a small P.D. between A and B; this will simply

produce a displacement of zero. By means of a potentiometer the galvanometer spot may be brought back to the original position. The shifting of the zero will not affect the general result. The effect of mechanical stimulus is to produce a transient electromotive 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

Fic. 52.—Responsre By Mretuop or Depression (WitTHoUT 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 (b) the same wire is used, only A is depressed by oxalic acid and a normal contact is made at a fresh point B’, a little to the left of Bin (a). Current of response is now from A towards the more excitable B’.

A corroborative reversal experiment may next be made on the same piece of wire. The normal contact, through water or salt solution, is now made at B, a little to the left of B. The excitability of A is now depressed by oxalic acid. On stimulation of the whole wire, the current of response will now be found to flow in an opposite direction—i.e. from A to bB/—but still from the relatively less to the relatively more excitable (fig. 52, 0). From these experiments it will be seen how in one identical piece of wire the responsive current flows now in one direction and then in the other, in absolute conformity with theoretical

considerations. : Fic. 53.—METHOD oF Method of exaltation. —A ce are Soullmore striking corroborahe contact Bis mademore excitable : by chemical stimulant (Na,WO,). tion of these results may, The current of response is towards however, be obtained by the a oh converse process of relative exaltation of the responsiveness of one contact. This may be accomplished by touching one contact, say B, with a reagent which like Na,CO; exalts the electric excitability. On stimulation of the wire, the current of response is towards the more excitable B (fig. 53).

I give four records (fig. 54) which will clearly exhibit the responses as obtained by the methods of relative depression or exaltation. In (a) B is touched with the excitant Na,CO;, a permanent current flows from A to B, response to stimulus is in the same direction as the permanent current (positive variation). In (6) 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, which will be demonstrated later,

that KHO in minute quantities is an excitant, while in large quantities it is a depressant. We have thus seen that we may obtain response (1) by block method, (2) by the method of injury, or relative depression of responsiveness of one contact, r Bi io. Fic. 54 P z eens (a) Response when B is treated with ST Ug | sodium carbonate——An apparent nentyy | ol, yy) a ce acescnaigrts Current Response positive variation. — : : | (b) Response when B is treated with

é me Jug variation. ; RESO (c) Response when B is treated with B treated with oxvery dilute potash.— Positive variaalicacid . . = <= tion. Current of response is always towards Lines thus - ----- indicate deflection due the more excitable point. to permanent current. and (3) by the method of relative exaltation of responsiveness of one contact. In all these cases alike we obtain a consistent action current, which in tin is normally positive, or towards the relatively more excited.

Conditions of obtaining quantitative measurements—Modification of the block method—Vibration cell— Application of stimulus—Graduation of the intensity of stimulus—Considerations showing that electric response is due to molecular disturbance—Test experiment—Molecular voltaic cell. We have already seen that metals respond to stimulus by E.M. variation, just as do animal and vegetable tissues. We have yet to see whether the similarity extends to this point only, or goes still further, whether the response-curves of living and in organic are alike, and whether the inorganic responsecurve is modified, as living response was found to be, by the influence of external agencies. If so, are the modifications similar? What are the effects of superposition of stimuli? Is there fatigue? If there be, in what way does it affect the curves? And lastly, is the response of metals exalted or depressed by the action of chemical reagents ?