VELOCITY OF REACTION. HOMOGENEOUS SYSTEMS 57 



provided that the reaction-products are present in sufficient 

 quantity, and that one molecule of the milk sugar and one 

 molecule of the reaction-products unite with one molecule 

 of the enzyme to form a partially dissociable compound. 



It has been long known that the enzymes differ from 

 chemical catalysors in one very important point. This 

 experiment was done in 1883 by Duclaux, 1 with solutions 

 containing 10, 20, and 40 resp. g. of sugar. In 100 c.c. 

 dissolve 20 mg. of invertase and elevate the temperature 

 to 37 C. ; then after four hours we shall find that nearly 

 the same quantity of sugar (about 5 g.) will be hydrolysed 

 in the three cases ; whereas if we had added 20 mg. of an 

 acid, the inverted quantity would have been 2.5 and 5 g. 

 in the two first cases, if it was 10 g. in the last. Arm- 

 strong 2 gives some good instances of this regularity, 

 which holds only if the quantity of enzyme is small. The 

 tabulated quantity is the number of grammes of hydrolysed 

 milk sugar in 100 c.c. 



On the other hand, if there is present a great quantity of 

 enzyme and a relatively small quantity of sugar, the action 

 is proportional to this latter quantity, just as if an acid 

 acted. 



1 Duclaux: Traite de microbiologie, 2. 136 (1899). 



2 Armstrong: /. c. t pp. 508-510. 



