JOHN H. NORTHROP 481 



to the amount of active pepsin present at the beginning of the reaction; 



t.e. 



1 d- E + K ,,_ _,-. 

 Rate = - = g = + \ I ~ ) + KE 



VC--r-7 



where T is the time in hours necessary to complete the first 10 per 

 cent of digestion. This equation may be tested experimentally by 

 testing the constancy of K for various values of E and d or, better, 



by comparing calculated and observed values of ^ since small ex- 

 perimental errors cause very large changes in the value of K. 



The results of such a series of experiments have been given in Table 

 I. Table III contains the results of a similar experiment in which 

 the pepsin solution was prepared by adding 10 per cent of egg albumin 

 to an active pepsin solution and allowing digestion to be completed 

 at a temperature of 38°C. The solution was then diluted as shown 

 in Table III. As was the case in Experiment 1, the rate of digestion 

 is not directly proportional to the total enzyme concentration. It 

 will be seen that in both Tables I and III the agreement between 

 calculated and observed values is within the experimental error. 

 The figure for E, the total enzyme present, is determined directly 

 from the experiments in high dilution when the value oi ET has be- 

 come constant. It was shown in Experiment 2 that the value for 

 E obtained in this way was really proportional to the total amount 

 of enzyme present. The value for d, the amount of peptone present 

 at the beginning of the reaction, is determined from the figures 

 themselves and therefore must be considered as a second arbitrary 

 constant. This fact, of course, detracts considerably from the signifi- 

 cance to be attached to the agreement between the observed and 

 calculated values. It will be shown below, however, that under 

 certain conditions the formula may be still further simplified so as to 

 contain one constant and that it is still found to hold. 



Table IV contains a summary of an experiment in which the total 

 concentration of peptone was kept the same and the concentration 

 of pepsin increased. The results are shown graphically in Fig. 3. 

 The values for E, the total pepsin present in the solution of Griibler's 

 pepsin, K, the equilibrium constant, and d, the concentration of pep- 



