156 RALPH S. LILLIE. 



itself forming filaments, retards or partly inhibits their develop- 

 ment from the zinc; i. e., zinc in contact with copper alone forms 

 filaments more quickly than when in contact with a copper wire 

 which is itself in contact with iron. This mutual influence is great- 

 est when the two metals are close together; when they are sepa- 

 rated by a sufficient stretch of conducting wire the effect becomes 

 inappreciable. Thus with a distance of 3 cm. between the zinc 

 and the iron, the latter metal, as well as the zinc, formed fila- 

 ments, but more slowly than in the absence of the zinc; the 

 influence of the zinc was perceptible, but insufficient to suppress 

 entirely the action at the iron. Increasing the distance of sepa- 

 ration still further renders the influence inappreciable. This 

 experiment recalls such physiological phenomena as the decrease 

 of growth-inhibiting dominance with distance. 1 Experiments 

 with platinum as the connecting metal give similar results; 

 only here, because of the nobler character of the platinum, the 

 distance between the zinc and the iron must be less than when 

 copper wire is used, if the formation of filaments from the iron 

 is to be entirely suppressed. In other words, both zinc and 

 iron have a stronger tendency to form filaments when in contact 

 with platinum than when in contact with copper; hence in order 

 to counteract this tendency in the iron its distance from the zinc 

 must be less. 



It will be evident that effects of the above kind have many 

 close biological analogies. 2 Increased physiological or metabolic 

 activity at one region of a living organism often results in the 

 decrease or cessation of activity at another, usually adjoining, 

 region. Perhaps the best known instances are seen in various 

 phenomena of growth and regeneration to which attention al- 

 ready has been called; the reciprocal inhibition of antagonistic 

 neurones in the central nervous system is probably a phenomenon 

 of the same essential type. There is also good reason for asso- 

 ciating with this class of phenomena such regular and char- 

 acteristic physiological processes as the automatic initiation and 

 arrest of activity at any region of a conducting element (e. g., 



1 Cf. Child, "Senescence and Rejuvenescence" (especially Chapter 9), and 

 "Individuality in Organisms," for a full account of these phenomena (University 

 of Chicago Press, 1915). 



1 See Section III. below, page 171. 



