256 PROTOPLASMIC ACTION AND NERVOUS ACTION 



duration of flow of the current. Electrical summation- 

 effects similar to those of mechanical activation can also 

 be demonstrated under appropriate conditions.^ 



Another influence of the current is especially interest- 

 ing from its resemblance to the physiological phenomenon 

 of electro tonus; this consists in a modification of the 

 susceptibiHty of the wire to mechanical or other activa- 

 tion. During the flow of the current the automatic 

 return of passivity in the active (cathodal) wire is 

 delayed, or with sufficient strength of current prevented, 

 and the anodal wire becomes more resistant to mechani- 

 cal or other activation. If with two passive wires in a 

 circuit, as above, a constant current too weak to cause 

 activation under these conditions (e.g., the current from 

 one Edison cell) be passed, the cathodal wire, although 

 remaining passive, is rendered temporarily more sus- 

 ceptible than before to activation by other means, 

 e.g., mechanical treatment, while the anodal wire 

 becomes less susceptible.^ 



All of the foregoing phenomena have their parallels in 

 the behavior of Hving irritable tissues under the influence 

 of the electric current; the corresponding physiological 

 phenomena are summation, polar stimulation, chronaxie, 

 enhancement of irritabihty near cathode, and its decrease 

 near anode (''electro tonus"). 



Phenomena of a similar kind are seen in the mercury- 

 peroxide system; here also the inactive mercury may 

 be activated by making it the cathode in a circuit, or 



^ E.g., by using the brief contact of a copper wire as an activating 

 agent. The local current thus produced may be too brief for activation 

 by a single contact, while several contacts in close succession will pro- 

 duce the effect. 



" For a somewhat fuller description cf. Jour. Gen. Physiol.^ Ill 

 (1920), 136. 



