346 PROTOPLASMIC ACTION AND NERVOUS ACTION 



only a short distance; by degrees transmissivity returns, 

 and in one-and-a-half or two minutes (at 20°) is as 

 complete as before. In this case the return of passivity 

 — ^with the potential characteristic of that state — depends 

 on the re-deposition of a thin surface-film of oxidation- 

 product. This process is itself a rapid one, as shown 

 by the rapid change of potential from negative to positive; 

 but the metal is at first relatively resistant to alteration, 

 and regains its former properties only by degrees, 

 probably as a result of a progressive thinning, rearrange- 

 ment of molecules, or other change in the film, accom- 

 panying the approach to the equihbrium condition. 

 If we may regard the processes in the inorganic model as 

 resembling in their general features those of the irritable 

 Kving system, it would seem probable that in the latter 

 the ''absolute" refractory period represents the early 

 phase in the local stimulation-process during which the 

 alteration and breakdown of the protoplasmic surface- 

 film are in progress; while the ''relative" period is 

 that during which the film is being rebuilt and reconsti- 

 tuted in the succeeding recovery-process. As the film 

 returns toward the normal or equihbrium condition, the 

 ability of the tissue to respond and transmit excitation 

 also returns. It is interesting to note that the 

 temperature-coefficient of the process of recovery in 

 passive iron is high and apparently similar to that of 

 living tissues (Qio = 2-3).^ 



PERMEABILITY-INCREASE AND STIMULATION 



If during the local stimulation-process there is in 

 fact a temporary breakdown or dissolution of the 



^ Ibid., p. 126 



