202 



BAKNETT COHEN 



corresponding roiighly to the acidity of N/10,000 HCl, the de- 

 cline is most acute, and by contrast, at pH 5.0 (equivalent to 

 about N/100,000 HCl), the rate of decline is the smallest. On 



Fig. 5. Experiment 5. The Death Rate of Bact. ttphosum in M/500 Buffers 



AT 20°C. 



The curves actually start from nearly the same origin, but have been spread 

 apart to avoid confusion. Note the close parallelism between duplicates at 

 almost all pH values. 



the alkaline side, the acceleration in death rate is more gradual. 

 Northrop (1920) studying the acid stability of pepsin found 

 pH 5.0 to favor the greatest stability. He found for this enzyme, 

 however, that increase of acidity did not destroy it so markedly 

 as increase of alkaUnity. 



