CHAPTER IV 

 BACTERIA IN MILK 



MILK, like other secretions, is sterile at the moment of 

 secretion but it is usually impossible to obtain it from the udders 

 of cows in this condition even though every precaution be 

 taken and all operations are conducted under strictly aseptic 

 conditions. Many have held that bacteria may be trans- 

 ferred to milk directly from the blood stream of healthy cows, 

 but this view is now generally regarded as erroneous. 



Amongst the earliest investigators to doubt the sterility of 

 the udder were Bailey and Hall 1 who concluded from their 

 experiments that the milk cistern might be the seat of bac- 

 terial development and one source of bacterial contamination 

 of milk. Ward 2 carefully examined the udders of 19 milch 

 cows from 5 dairies and found that although the animals were 

 tubercular, the udders were normal. He found that all the 

 lactiferous ducts of the cows were contaminated throughout 

 with bacteria of which the majority were cocci. From his 

 studies on the anatomy of the udder Ward concluded that 

 with the possible exception of the sphincter muscle, at the lower 

 end of the teat, no obstruction capable of excluding bacteria 

 from the milk cistern exists. This would indicate that the 

 source of contamination of milk even in the udder is external 

 and that the portal of entry is the teat. 



Henderson 3 examined a number of cultures from seven 

 normal udders and obtained growth in 76 per cent, but two 

 cases of unexpanded udders from heifers gave sterile cultures 

 from the milk cistern, ducts, and parenchyma. 



The intra-mammary contamination of milk in healthy udders 

 is usually small, and, although in some exceptional cases counts 



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