THE NATURE OF ENZYME ACTION 303 



enzyme action, such as the molecular vibration theory of 

 Liebeg, or that of Barendrecht as to the " radiations " emitted by 

 enzymes. I must content myself with calling to mind what is so 

 well insisted on by Bredig — viz. that enzyme solutions are, as 

 colloids, heterogeneous systems, and that it is necessary always to 

 remember that surface-action and adsorption undoubtedly play a 

 considerable part in the reactions taking place therein. 



It may perhaps be objected that the view advocated in the 

 preceding pages, that the combination between enzyme and 

 substrate or products is to be looked upon as of the nature 

 of adsorption, does not sufficiently take account of the specific 

 nature of enzyme action. It may be said that caseinogen, for 

 example, would be expected to form adsorption compounds 

 indifferently with either trypsin or amylase. Adsorption, how- 

 ever, is not a purely physical process, and is undoubtedly more 

 or less specific. The " adsorption affinity " of gelatin is consider- 

 ably greater for acid-fuchsin than for Congo-red. But we know 

 as yet too little about the essential nature of the process to 

 warrant further discussion. 



One more experimental result may be mentioned to conclude 

 this section. It was found by Korschun, in investigating the 

 relations between rennet and its anti-body, that by filtration 

 through porous clay a solution of rennet could be separated into 

 fractions which by appropriate dilution of the stronger fractions 

 could be brought to the same strength as regards combination 

 with the anti-body, but which differed considerably in their 

 power of coagulating milk. In other words, the original solution 

 appeared to contain a modified form of the enzyme analogous to 

 Ehrlich's " toxoids " ; that is, a part of the enzyme had lost its 

 characteristic activity while still retaining its power of combining 

 with the anti-body. I have myself met with some facts which 

 point to the production of a similar modification of trypsin by 

 warming to about 25 for a day or two ; I have suggested calling 

 these modified enzymes " zymoids." The facts afford support 

 to Ehrlich's view that the combining power and the fermentative 

 activity are functions of distinct side-chains. 



Complex Systems 



It may be of interest if, in conclusion, I give a brief indication 

 of some recent work on systems in which enzymes play an 



