CHAPTER LIII 



BAGTEEIA IN MILK AND MILK PRODUCTS, BACTERIA IN THE 



INDUSTRIES 



BACTERIA IN MILK 



THE universal use of cows' milk as a food, especially for the 

 nourishment of infants, has necessitated its close study by bac- 

 teriologists and hygienists. It furnishes an excellent culture medium 

 for bacteria and is, therefore, pre-eminently fitted to convey the 

 germs of infectious disease. The many changes which take place 

 in milk, furthermore, and which add or detract from its nutritive 

 value, are due largely to bacterial growth and have been elucidated 

 by bacteriological methods. 



Within the udder of the healthy cow, milk is sterile. If pyogenic 

 or systemic diseases of bacterial origin exist in the cow, the milk 

 may, under certain circumstances, be infected even within the mam- 

 mary glands. In the milk ducts and in the teats, however, even 

 in perfectly healthy animals, a certain number of bacteria may be 

 found. For this reason, even when all precautionary measures are 

 followed, the milk as received in the pail is usually contaminated. 

 As a matter of fact, the anatomical location of the udder and the 

 mechanical difficulties of milking make it practically impossible to 

 collect milk under absolutely aseptic conditions, and, under the best 

 circumstances, from 100 to 500 microorganisms per c.c. may usually 

 be found in freshly taken milk. Withdrawn under conditions of 

 ordinary cleanliness, the bacterial contents of milk are considerably 

 higher than this. After the process of milking, in spite of all prac- 

 ticable precautions, the chances for the contamination of milk are 

 considerable ; but even could these be eliminated, the bacterial con- 

 tents of a given sample would ultimately rapidly increase because 

 of the rich culture medium which the milk provides for bacteria. 

 Whether large increases shall take place or not depends, in the 

 first place, upon the temperature at which milk is kept, and, in 

 the second place, upon the length of time which intervenes before 



1027 



