CHAPTER XVI. 

 BACTERIA IN MILK AND THEIR SOURCES. 



i. Number and Source of Origin of Bacteria in 

 Milk. In the last chapter the method of secretion of 

 milk was discussed. In the present one it will be useful 

 to deal with the contamination of milk by bacteria and 

 the methods by which these organisms obtain access to 

 it. As secreted by the alveoli of the healthy udder milk 

 is quite free from bacteria, and it is possible to draw off 

 from the interior of the udder a sterile sample by means 

 of special apparatus. Moreover, it is very doubtful if 

 bacteria, present in the blood or lymph, or causing local 

 disease in the animal not involving the udder, ever gain 

 access to the milk. However, where tubercular disease 

 of the udder exists it is possible for the secretion to 

 become infected with Bacillus tuberculosis. In various 

 inflammatory processes in the substance of the udder and 

 its milk ducts and ulceration in the teats, the milk may 

 become contaminated with certain forms of streptococci, 

 which are connected with the disease. Leucocytes, which 

 are practically the same structures as pus-cells and from 

 which the latter are derived, are probably met with in all 

 normal healthy milk in small numbers as mentioned in 

 the previous chapter ; but when pus-cells are abundant, 

 and especially if they are accompanied by many strepto- 

 cocci, the milk should be treated as diseased, and should 



not be used in the dairy or for domestic purposes. By some 



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