240 PROTOPLASMIC ACTION AND NERVOUS ACTION 



From the physiological point of view the chief case 

 of specific acceleration by a finely dispersed or colloidal 

 catalyzer is enzyme action. There seems to be no doubt 

 that in many cases the enzyme acts through the forma- 

 tion of intermediate compounds, which break down at 

 high velocity yielding the decomposition products and the 

 original enzyme, the latter then recombining with the 

 substrate molecules to repeat the cycle. The formation 

 of the enzyme-substrate combination presupposes inti- 

 mate contact between the molecules of enzyme and 

 substrate; hence a correspondence in size and pattern 

 between the intercombining molecules (or parts of 

 molecules; e.g., zymophore groups) is required, of the 

 kind indicated by the ''lock and key" comparison of 

 Emil Fischer. That relations of this kind play a part 

 in adsorption is indicated by Marc's observation that a 

 crystalline adsorbent like BaS04 exhibits preferential 

 adsorption for compounds crystallizing in the same 

 system.^ Apparently this is a simple instance of specific 

 adsorption. Close contact of this kind gives the occasion 

 for chemical transformations (hydrolysis, etc.) which 

 otherwise would not occur, or at much lower velocity. 

 According to Bayliss^ a simple reversible adsorption 

 often precedes a more intimate ''chemical^' union 

 between adsorbent and adsorbed substance. In specific 

 catalyses, like those induced by enzymes, factors of 

 a similar kind probably enter; the union is specific 

 because of the similarity of molecular configuration 

 between enzyme and substrate, and the chemical effect 

 follows because the enzyme-substrate combination is 



^ Cf. Marc, loc. cit. 



* Bayliss, Proceedings of the Royal Society, B, LXXXIV (191 1), p. 269. 



