24 Living and Dead Matter and 



premature statement that it was not possible to isolate 

 this enzyme since it was bound up with the life of the 

 yeast cell. Such a statement was even made by a 

 man like Pasteur, who was usually a model of restraint 

 in his utterances, and yet the work of Buchner proved 

 him to be wrong. 



The general mechanism of the action of the hydro- 

 lyzing enzymes is known. The old idea of de la Rive, 

 that a molecule of enzyme combines transitorily with 

 a molecule of substrate; the further idea, which may 

 possibly go back to Engler, that the molecule of sub- 

 strate is disrupted in the "strain" of the new combina- 

 tion and that the broken fragments fall off or are easily 

 knocked off by collision from the ferment molecule 

 which is now ready to repeat the process, seems to be 

 correct. On the assumption that the velocity of en- 

 zyme reaction is proportional to the mass of the enzyme 

 and that de la Rive's idea was correct, Van Slyke and 

 Cullen were able to calculate the coefficients of the 

 velocity of enzyme reactions for the fermentation of 

 urea and other substances, and the agreement between 

 calculated and observed values was remarkable. x 



While the hydrolytic action of enzymes is thus clear 

 the synthesis in the cell is still a riddle. An interesting 

 suggestion was made by van't Hoff, who in 1898 ex- 

 pressed the idea that the hydrolytic enzymes should 



1 Van Slyke, D. D., and Cullen, G. E., Jour. Biol. Chem., 1914, xix. t 

 141. 



