EXPERIMENT STATION BtJLLETINS. 



349 



the reaction proceeds more slowly as the reaction advances. In the en- 

 zymic process, one part of the active mass, that is, the enzyme, remains 

 constant. It is a peculiarity of enzymes to cause decompositions without 

 being weakened in their activity. This would cause a constant rate of 

 decomposition, were it not for the fact that the decreasing concentration 

 of the substance acted upon and the increase of the decomposition pro- 

 ducts check it. For this reason, the actual rate decreases. In bacterial 

 changes, we have an increasing "active mass." The number of acting 

 cells increases for a long time, and consequently, the velocity of the de- 

 composing process increases also. These various possibilities of changes 

 occurring in organic compounds give two types of curves, easily to be 

 distinguished from each other. 



The curv^es of the purely chemical processes can be plotted from their 

 mathematical equations. A reaction, where only one kind of molecules 

 changes its concentration considerably, is called a unimolecular re- 

 action (e. g., the inversion of saccharose by acids). A biniolecular re- 

 action, where the concentration of two kinds of molecules is changed, 

 is represented by the saponification of esters by alkali. The equations 

 are not essential for the following discussion, since we are interested 

 only in the shape of the curves; they are, according to Nernst (theo- 

 retische Chemie, 1900, p. 513) : 



1 In a 



For unimolecular rea'Ctions K = — 



t 



a — X 



X 



For bimolecular reactions K = — 



For trimolecular reactions K = — 



t (a-x)a. 

 1 X (2a-x) 



t 2a^ (a-x)^ 



Fig. 1. The Law of Guldberg and Waage. 



