90 MILK 



Sources of bacteria in milk 1 . 



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

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

 many 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 ordinary milk utensils. 



4. From the use of special milk apparatus. 



5. Contamination in transit. 



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



1. Intra-mammary Contamination. The view generally ac- 

 cepted 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 is not in accordance with the facts 

 and that undoubtedly the teat duct, the milk cistern and the 

 larger ducts usually contain bacteria whose primary origin is out- 

 side the teat. Some selective action has however taken place, 

 the organisms found being almost invariably staphylococci, 

 streptococci and other forms of micrococci. 



2. Introduced during the Milking Operation. The bacteria 

 introduced during milking are derived from three sources, (a) the 

 coat, udder and teats of the cows ; (b) dust from the milking 

 shed and the clothes of the milker, and (c) derived from the 

 hands of the milker. 



1 For a more detailed account of the bacteria in milk see Savage, Milk and the 

 Public Health, Macmillan and Co. 1912. 



