ELECTRICAL AND OTHER FACTORS 253 



consisting of metals immersed in electrolyte solutions 

 and the transmission of physiological influence in living 

 protoplasm.^ In all such phenomena in metals the 

 essential condition is the presence of a thin film of electro- 

 chemically alterable material formed or deposited at 

 the interface between the metal and the electrolyte 

 solution. Local circuits between adjoining regions of the 

 film-covered surface, differing in composition or physical 

 condition in such a manner as to give rise to an E.M.F. 

 sufficient for electrolysis, are in all cases the essential 

 factor. By the action of these local currents the film 

 is locally altered or removed or rendered permeable 



,^^^ — -^ J ^ _ ^ ^ 



^ • ^mmw^ '' :wMWi^'m^Mm"hk^^^ -^ :* ^ ^ 



^; ■."■.■■■ •■■■ ■■■ \ <r ^'' ,=^-- ^-^ 



active passiue- 



Fig. 3. — Indicating the conditions of the local circuit at the boundary between the 

 active and the passive areas of an iron wire in nitric acid; the direction of the current 

 (positive stream) is indicated by the arrows, the active region (shaded) being anodal, the 

 passive cathodal. The local intensity of the current in the passive region (and hence the 

 reducing or activating effectiveness) decreases in the order A<B<C; beyond a certain 

 distance from the boundary, e.g., XY , it will be insufficient to activate. 



over a certain area (usually cathodal, e.g., XY , Fig. 3), 

 adjoining the boundary between the two regions, and 

 the similar circuit which is then formed at the boundary 

 between the newly altered area and the unaltered area 

 beyond repeats the effect; hence the alteration auto- 

 matically spreads over the whole surface. A wave of 

 such transmission is necessarily associated with a wave 

 of electromotor variation. 



A brief account of the phenomena of activation and 

 transmission in passive iron will indicate more clearly 



^ American Journal of Physiology, XLI (191 6), 126; Science, XL VIII 

 (1918), 51; L (1919), 259, 416; Journal of Physical Chemistry, XXIV 

 (1920), 165; Jour. Gen. Physiol., Ill (1920), 107, 129. 



