JOHN H. F.'^'RTHROP 255 



values for the constant^ ^es con ^^^ ^^e preceding experiments 

 and were worked out be^md ,?tperiment itself was done. The 



figure shows that in this c i the experimental and calculated 



results agree within the lim' ^" 'xperimental error. In Fig. 3 the 

 percentage inactivation of -th -uous amounts of trypsin by the 

 five units of inhibitor have bee] i)lotted. As would be expected the 

 smaller the amount of trypsin t^.iT greater the percentage inactivation 

 although the absolute amount of trypsin inactivated is less. 



It has been shown ^ ve that the law of mass action predicts quan- 

 titatively the resuL the experiments when either the trypsin or 

 the inhibitor concentic on is varied. It is possible to vary condi- 

 tions in another way t ceeping the relative amount of trypsin and 

 inhibitor the same and a rying the dilution (i.e., the value of v). The 

 calculated and observed results of such an experiment are given in 

 Fig. 4 (Curve B). The experiment was performed by mixing the 

 trypsin and inhibitor solution and then adding the noted cubic centi- 

 meters of this mixture b-^JS cc. of gelatin. It will be seen that in 

 this case also the predi^^' 1 results are in close agreement with the 

 experiment. In this ca'i^' the rate of hydrolysis decreases more 

 slowly than the total amount of trypsin taken. This is the 

 result of the fact that as the dilution is increased the trypsin inhibitor 

 compound dissociates and so liberates more active trypsin, so that the 

 concentration of active t~ypsin does not decrease directly as the 

 total trypsin. Exactly the sam.e curve would be obtained for the 

 rate of hydrolysis by hydrogen ions furnished by a weak acid if the 

 total concentration of acid were plotted against the rate of hydrolysis. 

 In Curve C in Fig. 4 the result of an experiment is given in which the 

 concentration of trypsin is varied but the concentration of inhibitor 

 is kept constant. This is a similar experiment to that described in 

 Fig. 2. In this case the rate of hydrolysis decreases more rapidly 

 than the concentration of the trypsin. This is the result of the fact 

 shown in Fig. 3 -hat the percentage retardation of the action of 

 trypsin with a stant concentration of inhibitor is the greater, the 

 smaller the tc ihount of trypsin. Curve A in Fig. 4 is the dilution- 

 activity curve fo. 'pure" trypsin and gelatin. In this case the ve- 

 locity is nearly directly proportional to the amount of trypsin taken. 

 It is clear from these curves that unless care is taken to purify the 



