298 PROTOPLASMIC ACTION AND NERVOUS ACTION 



is the fact that closely analogous phenomena are observed 

 in the inorganic models considered above (mercury- 

 hydrogen peroxide catalysis, passive iron), in which the 

 process of activation is known to depend upon the 

 electrolytic disintegration of thin interfacial films. In 

 the temporary activation of passive iron, the dissolution 

 of the oxide-film involves (i) a change of potential, (2) 

 a marked increase in permeability, allowing ready access 

 of the acid to the metal, and (3) a delay in the recovery 

 of the former state of susceptibility after the return 

 of passivity. It seems highly improbable that those 

 parallels are accidental; the indications are that they 

 are expressions of an underlying identity in the essential 

 structural constitution and conditions of activity of the 

 living system and of the inorganic model. The essential 

 features of structure and composition common to both 

 systems are, briefly* (i) the presence in both cases of a 

 thin film separating two electrically conducting phases, 

 one or both of which is an electrolyte solution, and (2) 

 the susceptibility of the film to alteration under the 

 influence of electric currents (breakdown or construction 

 by local electrolysis). Before dealing in greater detail 

 with these parallels and their bearing on the problem of 

 the essential constitution of living matter, it will be 

 necessary to review briefly the essential facts which 

 have been established with regard to the foregoing three 

 general accompaniments of stimulation. 



