JOHN H. NORTHROP 269 



The Influence of the Manner in which the Inhibiting Solution is Added. 



It was found in the study of the effect of the inhibiting solution on 

 the rate of digestion by tr3rpsin that the order in which the solutions 

 were mixed and the time of standing was without effect on the result 

 provided the control solution of pure trypsin did not alter during the 

 experiment. If, however, the experiment is made at 38° where the 

 control solution is rapidly destroyed the results are very different. 

 The results of such an experiment are shown in Fig. 3. It will be 

 seen that the solution to which all of the inhibitor had been added at 

 the beginning of the experiment is much more active at the end than 

 the one to which the inhibitor was added at intervals. This is evi- 

 dently very similar to the Danysz phenomenon in immunology. In 

 the present experiment the result is more marked if a relatively small 

 quantity of the inhibitor (<> antitoxin) is added at the beginning of 

 the experiment whereas in the Danysz phenomenon it is necessary 

 to add an excess. This is due to the fact that in the present experi- 

 ment it is the free trypsin (== toxin) that is irreversibly changed 

 during the experiment while in the Danysz experiment it is apparently 

 the free antitoxin (o inhibitor) which is altered.^ 



The Decomposition of the Trypsin-Inhibitor Compound. 



The rate of destruction of this compound at 38° is so slow in com- 

 parison to that of the free trypsin that it may be neglected. At 62°, 

 however, it decomposes quite rapidly and follows the course of a 

 monomolecular reaction (as was to be expected) provided an excess 

 of inhibitor has been added so that practically all the trypsin is com- 

 bined in the undiluted solution. The result of an experiment is given 

 in Fig. 4. Irregular results were obtained in some cases owing to 

 the formation of a precipitate presumably of coagulated protein. In 

 such cases the amount of active trypsin remaining in solution shows 

 a sudden drop at the time of formation of the precipitate. 



Influence of the pll on the Rate of Decomposition. 



Fig. 5 contains the result of an experiment in which the trypsin 

 solutions were adjusted to various pH by the addition of HCl or 

 NaOH before being placed at 38° for 1 hour. The activity of the 



