G30 



Professor Jagadis Chunder Bose 



[May 10, 



variometer used was similar, as regards sensitiveness and the period 

 of swing of the needle, to that employed for physiological records. 



Fig. 10, a, gives a series, each of which is the 

 Effects of response curve for a single stimulus of uniform 



Single Stimuli, intensity (amplitude of vibration, 180°). Observe 

 the perfect similarity of all these curves, and 

 their resemblance to the curves of response in living tissues 

 (Fig. 10, b). The rising portion of the curve is somewhat steep, 

 and the recovery convex to the abscissa, the fall being relatively 

 rapid in its first, and less rapid in its latter, parts. As the electric 

 variation is the concomitant effect of molecular disturbance — a tem- 

 porary upset of molecular equilibrium, — on the cessation of the external 

 stimulus the excitatory state and its expression in electric variation 

 disappear, with the gradual return of the molecules to their con- 

 dition of equilibrium, a process which is seen clearly in the curve of 

 recovery. 



Different metals exhibit different periods of recovery, and this 



Fig. 10. — (a) Series of electric responses to successive mechanical stimuli 

 at intervals of half a minute, in tin. (b) Mechanical responses in muscle. 



again is modified by any influence which affects the molecular 

 condition. 



That the excitatory state persists for a time even on the cessation 

 of stimulus can be independently shown by keeping the galvanometer 

 circuit open during the application of stimulus, and completing it at 

 various short intervals after the cessation, when a persisting electrical 

 effect, diminishing rapidly with time, will be apparent.* 



We have already seen how similar the response-curves of the in- 



* Observe how similar the above is to the excitatory electrical effect due to 

 stimulus, in living tissue, such as nerve. " The excitatory state evoked by 

 stimulus manifests itself in nerve fibre by electromotive changes, and as far as 

 < iur 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 living 

 structure to its previous state. Thus the electric manifestation of the excitatory 

 fctate is one whose duration depends upon the time during which the external 

 agent is able to upset and retain in a new poise the living equilibrium, and if 

 this is extremely brief, then the recoil of the tissue causes such manifestation to 

 be itself of very short duration." — ' Text-book of Physiology,' edited by Schafer 

 p. 453. 



