METHODS OF REDUCING THE GERM CONTENT 



533 



duced by bacteria vary according to the quality of the milk. If 

 it has a low bacterial content, peptonizing bacteria may multiply 

 at a great rate, and will prevent lactic acid bacteria from sub- 

 stantial proliferation. The milk peptonizes. In a milk of me- 



I 



Fig. 217. The hypothetic relation of the bacterial groups in raw and pas- 

 teurized milk. (Ayers and Johnson, Bull. 161, Bureau cf Animal Industry, 

 U. S. Dept. of Agriculture.) 



dium quality lactic acid bacteria multiply from the beginning, 

 checking all other groups by the amount of acid formed, and the 

 milk sours normally. In a poor grade of milk both peptonizing 

 and lactic acid bacteria multiply at the beginning, but the acid 

 group gradually takes the lead. If milk pasteurized at 62.8 C. 



