520 



Mr. K. Lucas. 



[June 6, 



of the facts is unable to decide between this supposition and a host of others 

 which could no doubt be made. I have already recalled how Hill pointed 

 out that the existing experimental work on slowly increasing currents has a 

 deficiency which makes it useless for quantitative comparison with values 

 calculated from hypothesis. In the case of the anodic excitation also, long 

 though the qualitative fact has been known, the quantitative relations 

 necessary for verification have scarcely been touched. I must therefore 

 leave this side of the problem with no more definite conclusion than this, 

 that the next step must be taken in the laboratory and not in the study. 

 From the mathematical treatment of the problem experimental workers have 

 learned where the deficiencies of their experimental data lie. If the mathe- 

 matical work bore no other fruit than this it would not have been wasted, 

 because whatever hypothesis may ultimately be accepted its verification will 

 demand the same facts. 



There is one point which must not be overlooked in connection with the 

 study of progressive currents and of the anodic excitation. You will have 

 observed that it was only when these phenomena were being studied that 

 we touched upon the problem of the effect which the ions might be 

 supposed to produce, as opposed to the simple question of their concen- 

 tration. This fact seems to me to add to the cogency of the reasoning 

 which calls for renewed quantitative experiment upon just these particular 

 phenomena. 



I turn now to the last of those difficulties of the Nernst theory which 

 we foresaw, the location of the membranes. It is an old conception, more 

 than thirty years old at any rate,* that an exciting current produces a 

 polarisation at a membrane forming a sheath to the excitable cell ; and it 

 seems that Nernstf had in view some membrane so situated. Indeed, it 

 would appear that such an arrangement of the membrane which hinders 

 .the passage of the ions must be postulated if we are to explain the 

 localisation of the excitations at make and break of the exciting current in 

 the immediate neighbourhood of the electrodes which serve as cathode and 

 anode respectively. If, for example, we were to suppose in a nerve or 

 muscle the existence of a series of transverse membranes placed across the 

 direction of passage of the exciting current, excitation would occur on one 

 side of each of these membranes when the current began to flow, on the 

 opposite side when it ceased, and the situation of the electrodes on the 

 tissue would no longer coincide with the point of departure of the propa- 

 gated disturbance. This raises an apparent difficulty in the way of part 



* Hermann, 1 Hdbch. d. Physiol.,' Leipzig, 1879, vol. 2, I, p. 193. 

 t Nernst, loc. tit., p. 277. 



