JOHN H. NORTHROP 



235 



increases more rapidly than the amount of enzyme taken. It will 

 be shown below that the results depend on the purity of the enzyme 

 and protein solutions used. In the case of purified trypsin and 



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Time in hours (x 64 curve A) (x 16 curve B) (x 4 curve c) (x 1 curve d) 



Fig. 3. Influence of the concentration of trypsin on the rate of digestion. 

 25 cc. gelatin plus 1, i, rs, « cc. of trj^psin solution. The change in the con- 

 ductivity determined at intervals as shown in the figure. pH 6.4, temperature 33°. 

 In order to give all the results in one figure the time units for each curve have 

 been made proportional to the amount of trypsin added; i.e., In the solution 

 containing a relative trypsin concentration of 64 (1 cc.) the observed time has 

 been multiplied by 64. To avoid confusion the ordinates (bridge readings) have 

 been increased by 1 (Curve C), 2 (Curve B), and 3 (Curve A). 



gelatin solutions the velocity (reciprocal of the time) is nearly directly 

 proportional to the amount of enzyme taken within the limits that 

 can be experimentally worked with. This fact is shown in Fig. 3. 

 In plotting this figure the time units for each concentration of tripsin 



