CHAPTER XXXIV 

 SOURCE OF BACTERIA IN MILK 



The milk secreted by the milk-glands of healthy 

 cows contains no bacteria. But that drawn from the 

 cow's udder is seldom entirely free from them. 



Bacteria in the udder. — It has been demonstrated 

 that bacteria from the outside may enter the opening 

 of the teat and spread gradually in the milk-ducts. Once 

 present in the latter, the invaders multiply rapidly 

 under the favorable conditions as to food and tempera- 

 ture. In the process of milking, the organisms in the 

 udder are largely removed with the milk. For this 

 reason, the fore-milk contains a much greater propor- 

 tion of bacteria than the strippings, even though the 

 latter are not always sterile. . 



In a practical way, attempts are frequently made to 

 improve the keeping quality of milk by removing the 

 first portion into a separate vessel. The milk subse- 

 quently drawn is found to remain sweet for days, — some- 

 times for weeks. However, such milk is not always free 

 from bacteria. Species other than those that cause the 

 souring of milk may be present, and may cause, in time, 

 undesirable changes. 



Bacteria in the air. — The air above the earth always 

 contains germs. The proximity and activities of human 



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