322 PROTOPLASMIC ACTION AND NERVOUS ACTION 



change the composition of the films and alter their 

 electromotor and other properties (permeability, physical 

 consistency, etc.), and the bioelectric currents are the 

 result. 



The question of whether the bioelectric currents 

 stand in the relation of cause or of effect to the other 

 physiological activities of the cell is not one to be 

 answered simply, since, as in so many other natural 

 processes, the relations are of a reciprocal kind. Appar- 

 ently the conditions are of the same general physico- 

 chemical nature as in any reversible type of galvanic 

 cell (storage battery) ; a current from an outside source 

 traversing the system may be the means of inducing 

 definite chemical reactions in the latter; or the system 

 may by its own spontaneous chemical action generate an 

 electric current which traverses the surroundings and 

 there produces the usual effects of such currents. Simi- 

 larly, the electric variation of a cell or nerve fiber may be 

 an accompaniment or eft'ect of o.ther processes, pre- 

 sumably chemical, in the living protoplasm; but once 

 having arisen, a bioelectric current may act in the same 

 manner as any other electric current and influence 

 secondarily other processes in the electrically sensitive 

 living system. Thus there is every evidence that the 

 electric factor, as such, determines the transmission of 

 excitation from one region to another of a conducting 

 nerve fiber or other excitable protoplasmic system; and 

 that the characteristic rate of transmission is determined 

 by the rate at which the local variation of potential 

 rises from zero to its full value. ^ It is evident that if 



' Cf. my article in American Journal oj Physiology, XXXIV (19 14), 

 414. 



