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 

 — ^wdth 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 equilibrium condition. 

 If we may regard the processes in the inorganic model as 

 resembling in their general features those of the irritable 

 Hving system, it w^ould 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 equilibrium 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 

 H\'ing 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 



