PHYSICO-CHEMICAL BASIS OF TRANSMISSION 395 



is temporary, and the state of excitation appears to 

 travel Kke a wave over the irritable element. 



In the wire model the automatic return of passivity 

 in strong HNO3 is the direct result of the formation of a 

 new surface-film by electrochemical (oxidative) action 

 at the local anodal regions.^ The phenomena of the 

 refractory period in irritable tissues, and the observations 

 already described showing that the plasma membrane 

 of egg cells changes from a temporarily unstable to a 

 stable state after cell-division or insemination,^ indicate 

 that in living irritable elements also the essential condi- 

 tion of recovery after stimulation is the formation of a 

 new surface-film, or the return of the altered film to its 

 original condition. Other physiological facts support 

 this view; e.g., the delay in the return of irritability 

 in a veratrinized muscle after stimulation is associated 

 with a corresponding delay in the return phase of the 

 bioelectric variation. The reversible change in the 

 surface-film is the condition both of the normal bioelectric 

 variation at any region and of the transmission of a 

 similar change of state to adjoining regions. 



The well-known interference with stimulation and 

 transmission during the passage of a constant current 

 lengthwise through a muscle or nerve is a further indica- 

 tion of the part played by electrical conditions in trans- 

 mission. The region near the anode (region of an- 

 electro tonus) acts as a block to an excitation-wave; 

 this effect is undoubtedly complex, but it is probable 



^ For a fuller account of the conditions in passive metals cf. the 

 review of Bennett and Burnham, Journal oj Physical Chemistry, XXI 

 (1917), 107. 



2 Cf. pp. 361 S. 



