234 PROTOPLASJVnC ACTION AND NERVOUS ACTION 



Anticatalysis in homogeneous solution has the appear- 

 ance of being a different phenomenon from the forms of 

 anticatalysis considered above, and its conditions are 

 obscure. Possibly the nearest analogies are with photo- 

 catalysis; e.g., a catalytic substance may play a role 

 analogous to that of a photochemical sensitizer; it is 

 clear that interference with the action of the latter would 

 arrest the photocatalytic action. Just as the chemical 

 effect of Hght is influenced by th'e presence of substances 

 with special Hght-absorptive properties, as in sensitized 

 photographic plates, so also catalysis by chemical com- 

 pounds may be influenced by other compounds having 

 special chemical relations with the catalyzer. Such 

 considerations are perhaps vague, but since many of 

 the conditions controlHng reaction-velocities are imper- 

 fectly understood, it seems best not to attempt further 

 definiteness at present. 



