STIMULATION AND TRANSMISSION 273 



structure of this system. The well-known experiments 

 ("rheoscopic frog") in which one active muscle or nerve 

 stimulates another which is in close contact with it, 

 by means of the bioelectric currents accompanying 

 activity, show that excitation can be transmitted from 

 one irritable element to another without direct proto- 

 plasmic continuity, through a purely electrical influence. 

 Similarly in the passive iron nitric acid system, activation 

 is readily transmitted from one wire to another by 

 contact, and the basis of this transmission is also 

 electrical. 



According to these conceptions, all forms of stimula- 

 tion are electrical; or, more exactly expressed, electric 

 currents resulting from local alterations of the cell 

 surface form a necessary part of the sequence of processes 

 constituting stimulation. Such a view implies further, 

 since the activity of the whole cell is altered by stimula- 

 tion — e.g., all of the fibrils in a muscle cell contract 

 when the excitation-wave travels over its surface — that 

 the intracellular processes, including the chemical or 

 metabolic processes which furnish the energy for the 

 activity, are largely controlled by processes having their 

 origin at the cell surface. 



This inference is confirmed by a study of the condi- 

 tions of electrical stimulation. The work of Nernst 

 and his successors^ has shown that the electric current 

 does not act by penetrating the living cell (which in 

 fact is a poor conductor) but by changing its surface- 



^ Cf. Nernst, Gottingen Nachrichten, math.-physik. Klasse (1899), 

 p. 104; Arch. ges. Physiol., CXXII (1908), 275; Lapicque, Jour, de 

 Physiol, IX (1907), 565, 620; X (1908), 601; XI (1909), 1009, 1035; 

 Lucas, Journal of Physiology, XL (1910), 225; A. V. Hill, ibid., XL 

 (1910), 190. 



