JOHN H. NORTHROP 



257 



action of the inhibiting solution. This experiment is difficult to 

 perform since the conductivity method cannot be used and the pH 

 can only be kept constant at ranges other than pH 6.3 by the use of 

 high concentration of buffers which interfere with the formol titration. 

 The results of such an experiment are given in Table V. The pH of 

 the solutions was adjusted by making them all m/10 with respect to 

 sodium carbonate and then titrating back to the desired pH with 

 0.1 N HCl. The course of the hydrolysis was followed by a slight 

 modification of the formol titration already described.^ No marked 

 effect of the pH could be noted. Several other experiments were 



TABLE V. 



Efect oj the Hydrogen Ion Concentration on the Inactivation of Trypsin by Inhibitor 



Solution. 



A. Gelatin, 5 per cent, containing 0.2 N Na2C03. B. Gelatin, 5 per cent, 

 containing 0.2 n NazCOs and 4 per cent inhibitor solution. 50 cc. samples 

 titrated to pH noted, and noted cc. trypsin added. Samples placed at 33°C. 

 and formal titration run on 5 cc. at intervals. 



made all of which gave results approximately the same as those given. 

 No differences in the degree of retardation due to the pH were noted 

 that could be definitely put outside the experimental error. This 

 result was corroborated by the effect of the inhibiting solution on the 

 rate of destruction of trypsin.^ Here also no differences in the eftect 

 between pH 6 and 10 could be noted. This result seems to show that 

 the "active" concentration of the trypsin and of the inhibiting sub- 

 stance is not markedly effected by the pH (between 6 and 10). 



•Northrop, J. IT., /. Gen. Physiol., 1919-20, ii, 595. 



