Experiments with Bacterial Enzymes 



133 



in a 5 per cent acid medium, while in a neutral solution 50 M. L. 

 D. were completely destroyed. That acid and alkali are not the 

 only substances whose presence must affect the "heat resistance" of 



EXPERIMENT. 

 Broth Culture B. prodigiosus. 



UNHEATED. 



*In each case 2 c.c. of culture or filtrate was placed in a sealed tube and immersed in a water-bath. 



EXPERIMENT. 

 Broth Culture B. pyocyaneus. 



UNHEATED. 



HEATED TO 70° FOR 30 MINUTES, 



0.20. 

 0.08. 

 0.06. 

 0.04. 

 0.02. 



an enzyme is obvious. In some cases a neutral broth culture was 

 found to resist heating better than a neutral gelatin culture, that is, 

 2 M. L. D. of the gelatin culture were destroyed at a lower tempera- 

 ture. Among the great variety of substances produced by bacteria, 

 there must be many whose presence affects the stability of the enzyme 

 when heat is applied. Any accurate determination of the heat resist- 

 ance of bacterial enzymes is hardly possible when the enzymes are 



