64 COLOR CHANGES IN ANIMALS 



well be the explanation of synaptic polarization and of 

 the appreciable loss of time in the passage of an impulse 

 over such a junction. Sir Charles Sherrington in 1925 

 discussed these problems particularly in relation to 

 central nervous activation and inhibition, and pointed 

 out the possibility of two agents, which he termed A 

 and I, concerned with these operations. Such agents 

 were conceived of even as substances, and the chemical 

 trend thus given to the interpretation of synaptic func- 

 tions was favored by a number of investigators including 

 Ballif, Fulton, and Liddell (1925), Fulton (1926), and 

 Samojloff and KisselefF (1927). Others, following the 

 lead of Sir Charles Sherrington (1929), preferred to 

 adopt a less committal attitude and to designate these 

 synaptic conditions as central excitatory states (c.e.s.) 

 and central inhibitory states (c.i.s.) where the term 

 " state " was especially associated with neither action 

 nor substance. (Creed, Denny-Brown, Eccles, Liddell, 

 and Sherrington, 1932.) In this way the unsolved 

 problem of what lies behind these states was temporarily 

 put aside. 



So far, however, as melanophores and their responses 

 are concerned, they appear to favor the more strictly 

 chemical interpretation just given to central nervous 

 operations. The concentrating neurohumors of the 

 color-cells would naturally represent the central excita- 

 tory substance, and the dispersing chromatophoral neu- 

 rohumors the central inhibitory substance. Such at 

 least might well be the hypothesized relationships. 

 Central synaptic functions are as a rule strikingly local- 

 ized. They would therefore be more successfully car- 

 ried out by lipohumors than by hydrohumors whose 

 tendency to diffuse widely in the watery environment 

 of the central nervous tissues would soon blot out local 

 limitations, Lipohumors have been shown in Fundulus 



