STIMULATION AND TRANSMISSION 261 



passage of an electric current throu^^h the circuit con- 

 stituted by the two chemically or structurally ch'tTerent 

 portions of this thin interfacial film, together with the 

 electrically conducting phases (in this case metal and 

 nitric acid) between which it is interposed. In li\in^' 

 protoplasm, with its film-partitioned constitution, it 

 seems probable that the structural arrangement or 

 disposition of the chemically reactive material which 

 determines the response to stimulation is of a simihir 

 kind; i.e., that this material is disposed in the form of a 

 thin film between two electrically conducting phases, 

 a type of arrangement allowing transmissions to occur 

 under conditions of essentially the same physical kind 

 as in the foregoing inorganic type of system. 



It has already been pointed out that stimulation 

 processes cannot be considered separately from the 

 processes of transmission or conduction. In general the 

 effects of local alteration in protoplasm tend to spread; 

 i.e., to produce chemical and physiological effects in 

 other regions than those immediately acted upon by the 

 stimulating agent. In some cases this spread is limited 

 in extent; but in others, especially nerve, there appears 

 to be no limit to the distance through which the change 

 of activity may be transmitted. Hence the total effect 

 of any stimulation has no fixed relation, quantitative or 

 qualitative, to the direct physical effect produced by 

 the stimulus at its point of application. In many 



by film-structure. When material is in a film, small quantities may 

 determine large chemical efi^ects, because under these conditions what 

 is important is not so much the quantity of material as tlic area which 

 it covers. Surface relations rather than mass or volume relations then 

 become the controlling factor. 



