JOHN H. NORTHROP 



223 



ductivity of the solution were determined on the remaining 25 cc. of solution to 

 which had been added the equivalent amount of inactivated pepsin. The deter- 

 minations were made as described above except that the measurements were made 

 at 37°C. 



The Combination of Pepsin and Gelatin. 



In a former paper^^ it was shown that the amount of pepsin which 

 combined with a given quantity of coagulated egg albumin depended 

 entirely on the reaction of the solution in which the egg albumin was 

 suspended. The greatest amount of pepsin was combined when the 



5.0 4.0 3.0 2.0 1.0 



Fig. 4. Influence of pH on the combination of pepsin and gelatin. 



solution had a reaction of pH 2.5 to 3.0. It was pointed out that 

 this was probably part of the mechanism that caused insoluble 

 proteins to digest more rapidly at this reaction than at any other 

 since it seems that the rate of digestion must depend on the amount 

 of pepsin in the solid protein. 



These experiments have been repeated with gelatin and show in 

 general the same result. The results of such an experiment are given 

 in Fig. 4 and Table III. The figures show that a greater amount 



28 Northrop, J. H., /. Gen. Physiol, 1919-20, ii, 113. 



