MICRO-ORGANISMS IN MILK 



It is now generally conceded that milk is secreted from the 

 mammary glands in sterile condition. This assumption is borne 

 out by experimental evidence, which has shown that at least the 

 majority of bacteria do not pass from the circulation into the 

 secretion. It has been possible furthermore to obtain sterile milk 

 occasionally by inserting a sterile tube into the udder and, finally, 

 we know that other body secretions are commonly sterile. 



The milk in the udder, however, contains, as a rule, micro- 

 organisms, although, as we have seen in the previous chapter, 

 multiplication is limited and the actual number present in the 

 udder relatively small. When milk is taken from the udder by 

 sucking there is small chance for contamination, but when it is 

 drawn for supplying the market the operations necessary between 

 removal from the udder and consumption are numerous, and with 

 each step of the journey from cow to consumer an opportunity is 

 offered for the entrance of micro-organisms. 



The dust from the air, filth attached to the udder or coat of 

 the animal, foreign matter from the hands of the milker, all these 

 sources of bacteria serve to contaminate the milk in the stable. 

 The utensils may contribute their share of bacterial pollution — 

 strainers, coolers, bottles, cans, pasteurizing machinery, bottle 

 caps, and other appurtenances require great care in order to avoid 

 heavy pollution. And at best some bacterial contribution is 

 added to the milk from all these sources. By careful attention to 

 details, however, the number of bacteria in market milk can be 

 reduced to a marked degree. 



The entrance of micro-organisms is not the only cause of the 

 great pollution of milk. Milk contains all the food substances 

 required for enormous multiphcation of many types that gain 

 access to milk, and the only reliable method of preventing this 

 multiplication is keeping milk at low temperature. Provision 

 should be made to cool milk as soon as possible after milking. 

 During transportation on the producer's cart, in the railroad car, 

 or in the delivery wagon cooUng facilities must be provided for, 

 to reduce bacterial multiplication to a minimum. Equal care is 

 necessary in the home, where cooling facilities are only too fre- 

 quently poor or wholly absent. 



The distribution of micro-organisms in milk is not a homo- 

 geneous one, as might be expected. Examination of several sam- 



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