PHYSICO-CHEJMICAL BASIS OF TRANSMISSION 395 



is temporary, and the state of excitation appears to 

 travel like 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 mcml)ranc 

 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 stimulatiuu ami 

 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- 

 electrotonus) 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 n^- ♦ •'- cf. the 



review of Bennett and Burnham, Journal of Physical CL ^, XXI 



(1917), 107. 



2 Cf. pp. 361 flf. 



