522 



Mr. K. Lucas. 



[June 6, 



phenomena as can be observed, in an injured nerve or muscle. Bernstein* 

 measured the temperature coefficient of the electromotive phenomena in 

 nerves and muscles, and found evidence that concentration cells formed 

 the source of the electric phenomena observed. He put forward as the 

 most probable origin of the concentration cell the presence of a surface 

 providing a sheath to the cell relatively impermeable to ions of one sign, 

 and the consequent formation of an electric double layer. Bruningsf also 

 dealt with the localisation of the electromotive force of excitable cells, and 

 reached by a process of exclusion the position that the surface of the cell 

 is permanently polarised owing to the existence there of a membrane 

 relatively impermeable to some ions. The facts on which he relied were 

 these : that with rare exceptions concentration ceils consisting of solutions 

 of electrolytes cannot give closed circuits capable of being connected in 

 series so as to sum their electromotive forces without metallic conductors, 

 unless they arise from the presence of membranes of selective permeability 

 to the ions present ; that the electromotive force obtained without membranes 

 would be less than that actually found ; and that excitable cells can be 

 polarised and also show osmotic phenomena. 



It is true that we do not find anywhere in this work an actual 

 demonstration that such a membrane or surface as the hypothesis of ISTernst 

 would postulate is positively located as a sheath to the excitable cell. The 

 evidence is rather that not only for the local excitation process, but also 

 for the electric response, the postulation of a membrane so located seems 

 at present to offer the simplest account of the facts observed. This fact 

 in itself is significant, for if we are to find the key to the electric phenomena 

 of the excitable tissues in the presence of polarised membranes or surfaces, 

 it does seem probable, quite apart from Nernst's specific hypothesis, that 

 the same membranes should be concerned both in the electric response 

 which accompanies the propagated disturbance and in the local excitatory 

 change by which the latter is started. At the same time, we must not 

 forget the indirect nature of the evidence on which the existence of such 

 membranes is founded. We need, perhaps, to look very far into the future 

 before we shall see the present histology of the cell amplified by that new 

 histology whose duty it will be to locate within the cell surfaces of physico- 

 chemical importance. 



Of those difficulties then which we foresaw in the first review of Nernst's 

 hypothesis, the want of agreement between calculated and observed values 

 where long currents are used cannot be said to have any weight, until it shall 



* Bernstein, ' Arch. f. d. ges. Physiol.,' 1902, vol. 92, p. 521. 

 t Briinings, 'Arch. f. d. ges. Physiol.,' 1907, vol. 117, p. 409. 



