CHAPTER II 



THE SOURCES OF BACTERIA IN MILK 



MILK as secreted is a sterile fluid, but during every stage from 

 the udder to the consumer, contamination is possible, and under 

 much of the present-day conditions is invited. In consequence, 

 milk as vended may, and frequently does, contain very many 

 thousands of bacteria. The sources by which bacteria gain 

 access to milk can be grouped as follows : 



1. Intra-mammary. 



2. Introduced during the milking operation. 



3. From milk utensils. 



4. From the use of artificial or special milk apparatus. 



5. Contamination in transit. 



6. Contamination upon the purveyors' or consumers' premises. 



1. Intra-mammary Contamination. The view generally 

 accepted, up to a few years ago, was that the interior of the 

 udder contained no bacteria, and that milk, if not quite sterile 

 when it left the teats, yet contained but a few bacteria derived 

 from the teat ducts themselves. This opinion was largely 

 based upon the fact that with a sterile tube it was sometimes 

 possible to obtain sterile milk from the udder. More recent 

 investigations have, however, shown that this view cannot 

 be accepted. 



Two of the earliest investigators to doubt the accuracy 

 of the sterility of the udder were Bolley and Hall, 1 who con- 

 sidered the milk cistern might be a source of much bacterial 

 growth. 



Moore and Ward 2 in 1898 examined the udders of six 

 cows slaughtered after reacting to the tuberculin test, and 

 found them non-sterile. 



1 CentralU.f. BakL, 1895, Abt. II. i. p. 793. 

 2 Bulletin No. 158, Cornell University Agricultural Experiment Station. 



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