CHAPTER LIV 



BACTERIA IN MILK AND MILK PRODUCTS, BACTERIA IN THE 



INDUSTRIES 



BACTERIA IN MILE 



The universal use of cows' milk as a food, especially for the nourish- 

 ment of infants, has necessitated its close study by bacteriologists and 

 hygienists. It furnishes an excellent culture medium for bacteria and 

 is, therefore, pre-eminently fitted to convey the germs of infectious dis- 

 ease. 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 mammary 

 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 Withdrawn under conditions of ordinary cleanliness, the bacterial 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 proc- 

 ess of milking, in spite of all practicable precautions, the chances 

 for the contamination of milk are considerable; but even could these 

 be eliminated, the bacterial contents 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 de- 

 pends, 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 its 

 consumption. Though fresh milk possesses slight bactericidal powers,^ 



1 Rosenau and McCoy, Jour. Med. Res., 18, 1908. 

 699 



