JOHN H. NORTHROP 



725 



was able to show^^ that in pepsin digestion the same mechanism 

 causes the reaction to follow the square root law since the pepsin 

 and the products of digestion are in equilibrium. The pepsin in 

 this case replaces the hydrogen ion in the present example. 



Returning to the experiments in which the hydrogen ion concen- 

 tration was kept constant it will be seen that the rate of reaction 

 is practically constant for at least the first 400 per cent increase in 

 the original titration (equivalent to the first 20 per cent of the reac- 



.a 400 



i 





300 



♦3 200 



100 



DaysO 123456789 10 



(x lOO.CurvcsItn) (x 0.5 .CurviesiniV) (xl , Carve EZ") 



Fig. 3. Course of reaction with various hydrogen ion concentrations. 



tion). The velocity within this range may, therefore, be deter- 

 mined at any time by dividing the increase in the titration by the 

 elapsed time. If the increase is expressed as per cent of the original 

 figure this ratio will represent the velocity of the reaction and will 

 be independent of the concentration of gelatin. It seems more con- 

 venient and equally significant for the purposes of this paper to 

 use this figure rather than the constant for the monomolecular reac- 



Northrop, J. H., /. Gen. Physiol, 1919-20, ii, 471. 



