112 TKANSMISSIVITY IN PASSIVE IRON WIRES 



State. The resemblances between the phenomena of activation and 

 transmission in the passive iron model and in living protoplasm are 

 thus to be referred to the presence, in both systems, of surface films 

 which readily undergo chemical and structural alteration, these al- 

 terations producing changes in the electromotor properties of the 

 surface. Such local alterations have further chemical effects, since 

 they produce local electric circuits which furnish the conditions for 

 electrolysis, and these chemical effects are often extensive because 

 of their automatic tendency to spread wherever a continuous and uni- 

 form surface film is present. 



The general biological significance of these properties of surface 

 films, especially in relation to the film-pervaded or emulsion-like 

 structure of living protoplasm — emulsions being systems whose prop- 

 erties are determined by the presence of surface films of soap or other 

 material — will be partly evident from the foregoing, but will not be 

 considered in detail in the present paper. ^^ It is essential to note, how- 

 ever, that recovery of irritability after stimulation depends (on the 

 foregoing theory) upon the restoration of the altered protoplasmic 

 surface film to its previous condition. It seems most likely that an 

 essentially new film is formed after each stimulation; this process of 

 reconstruction probably involves a specific chemical resyn thesis, in 

 addition to a purely physical process of redistribution or rearrange- 

 ment of surface active compounds. The importance of the chemical 

 factor is indicated both by the dependence of recovery on oxygen and 

 by its high temperature coeflEicient.^^ In the passive iron model the 

 factors in the recovery of transmissivity are simpler than in proto- 

 plasm; but repassivation is known to depend upon the formation of 

 a new surface film of oxidation product; and immediately after the 

 redeposition of this film its properties are different from those which it 

 attains later. We can in fact clearly distinguish two distinct processes 

 in the recovery of passive iron; one the redeposition of the film, and 

 the other the progressive alteration of the newly deposited film until 

 the final state of complete transmissivity is attained. The first process 



^* For an account of various biological analogies in the behavior of the sur- 

 face film of passive iron, cf. Lillie, R. S., Science, 1919, 1, 259, 416. 

 1^ Bazett, H. C, /. Physiol., 1907-08, xxxvi, 414. Adrian.^ 



