258 PROTOPLASMIC ACTION AND NERVOUS ACTION 



tween the intensity required to activate and the root of 

 the number of alterations (i/i/n = const.). This relation 

 has been shown by Nernst^ and others to be generally 

 characteristic of electrical excitation in living tissues; 

 it indicates that a current of a given intensity must flow 

 for a certain minimal time in one direction through the 

 irritable system in order to cause activation. I.e., the 

 change in the electrical polarization of the surface con- 

 cerned in activation must last for more than a certain 

 critical time, presumably the time necessary to produce 

 a certain critical degree of chemical change. The 

 physical conditions of response to electrical influence 

 thus appear to be of the same kind in the living system 

 and in the inorganic model. 



^ Nernst, Arch. ges. Physiol., CXII (1908), 275; cf. chap. xii. 



