394 PROTOPLASMIC ACTION AND NERVOUS ACTION 



sufficient. In other words, a reducing action comes 

 instantly into play at a distance from the zinc as soon 

 as the contact is made; this action depends on the passage 

 of the current through the circuit, zinc, acid, and plati- 

 num. Similarly when a region of nerve is stimulated, 

 that region becomes negative; and the presumption is 

 that the current of the local circuit thus arising exerts 

 chemical action at all points along the protoplasmic 

 surface where its intensity is sufficient. According to 

 the present theory, it is to this electrochemical action 

 (which secondarily determines stimulation) that the 

 transmission is due. Each area thus secondarily activ- 

 ated serves as a new point of departure for activation 

 of the region beyond, and in this manner transmission 

 to an indefinite distance becomes possible. As already 

 pointed out, the conditions in the passive iron model 

 are of the same general nature. The electrochemical 

 modification of the surface layer (plasma membrane or 

 passivating oxide film), through the electrolytic action of 

 the local circuit, is in both systems the essential change 

 determining transmission. 



In the return to the resting or passive state after 

 activation the current of the local circuit is also an 

 essential factor; this current (as the diagram shows) 

 passes in opposite directions (relatively to the surface) 

 at active and resting regions; and correspondingly its 

 physiological effect, which is excitatory at the resting 

 region adjoining the region of acti\dty, is anti-excitatory 

 or inhibitory at the active region itself. Any region, on 

 becoming active, is thus automatically subjected to an 

 electrical influence w^hich hmits or arrests its activity. 

 Hence the local activity, in a muscle cell or nerve fiber, 



