CATALYSTS AND ENZYMES 133 



such as dilute acid, the starch particles may be regarded as a phase 

 to which the hydrogen ions are attracted and become concentrated, 

 and in which they increase the velocity of reaction, the products 

 of reaction then rapidly diffusing out, through the large surface 

 of starch particle compared to its mass, and so fresh starch mole- 

 cules undergoing attack. 1 



It must be admitted, however, that such differences in velocity 

 of reaction in colloidal catalyst or colloidal substratum as compared 

 with the other phase of the solution have never been experiment- 

 ally demonstrated. Also all attempts to demonstrate, as a model, 

 an artificial emulsion consisting of two phases by the operation 

 of which a reaction took place more rapidly than in a homogeneous 

 solution of one of the phases only, have hitherto failed. 



Bredig has postulated such an emulsion somewhat as follows : 

 it should consist of two media, A and B, of which B should form 

 a suspension menstruum for A, the reaction to be tested should 

 run more quickly in A than in B, and the reacting substance should 

 be more soluble in A than in B, and if possible* the products of 

 reaction should be more soluble in B than in A. Could such an 

 emulsion be constructed, there is no doubt that the reaction would 

 run more quickly in it than in a homogeneous solution in B alone, 

 and it would illustrate the foregoing theory as to the mode of 

 action of colloidal enzymes. 



In conclusion regarding this most ingenious theory, which in 

 all probability does hold in certain cases of colloidal catalysts, 

 particularly those in which a concentration or condensation of 

 the reacting substance occurs in or upon the catalyst, it must 

 be emphasised, however, that it cannot form an explanation of 

 all catalytic action, because it is a necessary premise of the theory 

 that either the catalyst or substratum must be colloidal. 



1 Attention may be drawn to the fact that in cases where the substratum is 

 colloidal, we have experimental evidence of an attraction between this phase 

 of the system and the catalyst, similar to that seen between the colloidal catalyst 

 and reacting substance in the case of platinum and gases. Thus, the strong 

 attraction of fibrin for pepsin is analogous to the attraction of the reacting gases 

 by the platinum. In one case the catalyst is attracted and concentrated in the 

 substratum ; in the other the substratum is attracted and concentrated in the 

 catalyst. 



