26o PROTOPLASMIC ACTION AND NERVOUS ACTION 



region. The physical constitution of the living substance 

 is evidently of such a nature as to permit rapid trans- 

 mission of chemical influence to a distance; in other 

 words, some form of '^ chemical distance-action" is a 

 constant feature of protoplasmic action. It is natural 

 to connect this feature with the essential or fundamental 

 features of the physical structure of protoplasm. We 

 have already seen that this structure is polyphasic and 

 film-pervaded, or emulsion-like. It is therefore highly 

 interesting to note that the inorganic transmissive 

 processes just considered, which bear such a striking 

 resemblance to the transmissive processes of protoplasm, 

 are in fact determined by chemical and structural 

 alterations in thin surface-films, and that these alterations 

 occur under the influence of local electric circuits. In 

 such a system as passive iron in nitric acid the chemically 

 reactive material whose alteration determines the 

 transmission is spread out in a thin layer or film at an 

 interface (metal-electrolyte) which is the seat of a 

 potential difference. The surface of contact of this 

 material with the adjacent layer of electrolyte solution 

 is a large one, relatively to the total mass of reacting 

 substance. This arrangement makes for a rapidly 

 acting and sensitive type of reaction-system, since the 

 removal or alteration of a very small quantity of material 

 may, by altering electromotor conditions at the surface, 

 form the condition for a spread of chemical effect, 

 electrically conditioned, which may be very extensive 

 and rapid.^ Transmission depends on the instantaneous 



^ It may be pointed out here that the importance of extremely 

 small quantities of certain special substances, e.g., vitamines in animals, 

 is probably a correlative of the control of chemical reactions in protoplasm 



