MILK 161 



great dilution and prolonged exposure to the conditions present 

 in running water that such an effluent can become suitable for 

 forming a part of a potable water. 



Milk. 



The bacteriology of milk presents two aspects. The first is 

 the economic, which concerns the changes occurring in milk 

 collected under ordinary conditions and which may seriously 

 affect its composition before it reaches the consumer for domestic 

 use. From the other or hygienic standpoint, the bacteriologist 

 has to deal with organisms either derived from' the cow or 

 subsequently introduced which may affect the health of the 

 consumer. 



The secreting structures of the mammary gland are probably 

 sterile, but in many cases the larger ducts of the cow's udder 

 contain bacteria of various types which will thus be found even 

 in milk withdrawn by a cannula. The main sources of the 

 bacteria always found present in freshly drawn milk are the 

 external surfaces of the udder and the hands of the milkers, and 

 the numbers present depend upon the cleanliness of the animal 

 and its surroundings, and of the milker. Under the most favour- 

 able conditions fresh milk contains about five hundred organ- 

 isms per c.c, and this figure may rise to many thousands if 

 cleanliness has not been observed. It has been shown in 

 numerous experiments that the number present can be easily 

 controlled by attention to the cleanliness of the cowhouse, by 

 grooming the animal, and by washing the udder before milk- 

 ing. There is some evidence that for a short time after milk 

 is withdrawn, a slight diminution in the bacterial content may 

 take place. Before the milk reaches the consumer, especially in 

 city supplies, the bacterial content of apparently fresh milk may 

 rise to several hundred thousands or even millions of bacteria 

 per c.c. 



The organisms present chiefly belong to the group of milk- 

 souring bacteria so widespread in nature, and thus might be 

 supposed to have only an economic significance. To this group, 

 however, the b. coli and its congeners also belong ; unfortunately 

 these are too frequently present in milk as it reaches the con- 

 sumer, and their detection may be taken as evidence of pollution 

 from the excreta of the cow and, to a certain extent, of the want 

 of cleanliness of the dairy. Another organism which has a 

 similar significance is the b. enteritidis sporogenes, and along 

 with this may be associated the streptococci found in milk. 



