156 MANUAL OF BACTERIOLOGY. 



regarded as settled. Nevertheless, the advantages seem 

 certainly to greatly outweigh the disadvantages. 



In regard to the pasteurization of milk, Rogers* has this to 

 say: 



"Examination of milk by many bacteriologists shows that 

 the milk used in American cities is usually badly contaminated 

 by bacteria. 



"Increased public interest in the milk-supply has resulted 

 in more rigid municipal regulations and inspection, but prog- 

 ress is necessarily slow and pasteurization is frequently re- 

 sorted to in order to increase the length of time that the milk 

 will remain sweet and to reduce the danger from spread of 

 infectious diseases. 



"The objection is frequently made that pasteurization, by 

 destroying the lactic-acid bacteria, allows the development of 

 other less desirable bacteria which, without affecting the taste 

 of the milk, make it actually dangerous, especially as a food 

 for young children. 



"It is well established, however, that under certain circum- 

 stances the intestinal troubles of children may be reduced by 

 pasteurization of milk. 



"Milk was pasteurized .under laboratory conditions in a 

 continuous machine at 85 C. (185 F.), the bacteria being 

 reduced from over 10,000,000 per cubic centimeter to less 

 than 500 per cubic centimeter. 



"Milk held at 20 C. (68 F.). In the unheated milk the 

 lactic bacteria increased rapidly and the milk became acid in 

 about 12 hours. The peptonizing bacteria increased in 6 

 hours to about 5,000,000 per cubic centimeter and then de- 

 creased slowly. 



"In the heated milk the peptonizing bacteria increased 

 rapidly after 12 hours, and the milk was usually curdled in 48 

 hours, with a disagreeable taste and odor. Occasionally 



*Bureau of Animal Industry. Bui. No. 73, 1905 



