100 EXPERIMENTAL OBSERVATIONS ON 



as a whole; removal of products of reaction; and alteration of 

 temperature. 



A certain amount of evidence in favour of the reversibility 

 of the reaction was obtained by subjecting a 40 per cent, solution 

 of the products of reaction of caseinogen and trypsin to the action 

 of fresh trypsin, when in a period of four days a considerable 

 diminution of conductivity was observed, which is the reverse of 

 the increase in conductivity observed when the caseinogen is acted 

 upon, and is presumptive evidence that the reaction was pro- 

 ceeding in the reverse or synthetic direction. 



DISCUSSION OF EXPERIMENTAL RESULTS ON VELOCITY OF 

 REACTIONS INDUCED BY ENZYMES. 



It is clear from the foregoing account of the experimental 

 results obtained by different authors, that in the case of the enzymes 

 the simple logarithmic law fails to suit the general course of the 

 reaction from beginning to end. 



It may be inquired, therefore, whether any assumption has 

 been made in the deduction of the velocity equation for such reac- 

 tions as we have been considering which has been the means of 

 introducing the differences between theory and experiment. 



The equation from which the simple logarithmic expression, 



1 a dx 



Jc =- log , is derived is -,.=k (a-x), which simply ex- 



t d X (it 



presses that the rate of change at any moment is proportional to 

 the concentration of the unchanged substratum at that moment. 

 The entire action of the enzyme, as far as the formula is con- 

 cerned, is contained in the constant k; the more powerful the 

 enzyme the greater is the value of k, and the less powerful the less 

 is the value of k. Regarding the ferment as acting by reducing the 

 resistance to reaction in the system, as described above, we may 

 regard k as the conductivity factor in the reaction. Hence by 



writing j =k (a-x), we have assumed that the effect of the enzyme 



upon the conductivity is constant throughout the reaction. 

 Expressed in another way, the assumption has been made that 

 throughout the whole of the reaction, no matter what the concen- 

 tration of the substratum, the effect of the enzyme is the same upon 

 each molecule of the substratum. Now this need not necessarily be the 



