182 EXPERIMENTAL OBSERVATIONS ON 



EXPERIMENTAL OBSERVATIONS ON VELOCITY OP REACTION 

 INDUCED BY ENZYMES. 



We may now proceed to the examination of the experimental 

 results on chemical kinetics, and to the investigation of the extent 

 to which such observations are in accord with the equations theo- 

 retically deduced above. 



At the outset we are met by great apparent divergence of 

 experimental results, and different statements by different observers. 

 More recent work has, however, tended to show that the apparent 

 discrepancies are due to different observers having worked at 

 different portions of the reaction, that there are several different 

 factors involved which disturb the velocity of the reaction when 

 there is not due attention given to the relative amounts of catalyst 

 and the substratum on which it acts, or to the conditions obtaining 

 at the extreme ends of the reaction. 



In the case of the enzymes it has recently been shown, parti- 

 cularly by the researches of Horace Brown and Glendinning and of 

 E. F. Armstrong, that the simple logarithmic law deduced above 

 holds only at some distance from the beginning or end of the reaction, 

 and when there is a due proportionality between ferment and sub- 

 stratum. 



The experiments on velocity of reaction may be divided into 

 (1) those in which, with a constant amount of catalyst throughout 

 the experiment, the course of the reaction is followed from the 

 initial point at which only the substratum or substance upon which 

 the catalyst acts is present, ' to the end-point at which the sub- 

 stratum has been as completely converted into the products of 

 reaction as is possible under the conditions of experiment; (2) those 

 in which the effects upon the velocity of varying the concentration 

 (a) of ferment and (6) of substratum are observed in the earlier 

 stages of the experiment; and (3) those in which the effects of addi- 

 tion of one or other of the products of reaction at the initial stage 

 are studied, or the effect of addition or removal of such products upon 

 the end-point or apparent equilibrium point of the reaction. The 

 experimental measurement in all cases is that of the quantity or per- 

 centage of the substratum converted in a given time, and this has 

 been measured in many different ways. The enzymes which have been 

 most employed have been those which act upon starches or sugars. 



