28 CHANGES IN MILK CAUSED BY BACTERIA. 



product. Its occurrence naturally furnishes the principal com- 

 mercial incentive, and almost the only such one that milk 

 dealers have, to exert efforts to improve the quality of milk as 

 regards bacterial content. 



The attitude of the buttermakers and cheesemakers towards 

 the lactic acid fermentation is quite the reverse. The fornia- 

 tion of lactic acid is as yet a necessary step in the manufacture 

 of both butter and cheese. The maintenance of temperature 

 conditions favoring the fermentation is an important detail in 

 the manufacture of both products. 



That sour milk is, or the organisms causing it are, harmful 

 to the average normal adult cannot be maintained. On the 

 contrary, soured dairy products frequently form an article of 

 diet, as for example, buttermilk and plain sour milk. Metch- 

 nikoff has laid emphasis upon the value of sour milk as an 

 article of diet (28). 



The importance of the lactic acid fermentation has occas- 

 ioned considerable experimental work to determine the source 

 from which the bacteria commonly gain access to milk. The 

 existence of bacteria within the udder has suggested a study 

 of those organisms with reference to the possible presence of 

 that one among them. They have been isolated a few times 

 from cultures made direct from the glandular tissue of freshly 

 slaughtered animals. Extensive examinations of the bacterial 

 flora of milk drawn with aseptic precautions have shown them 

 in such few instances that their presence in those particular 

 samples was regarded as an accidental contamination from 

 sources other than the interior of the udder. For instance, in 

 a series of two hundred and five samples, taken from seventy 

 cows during several days, the organism was found in only 

 eight instances (7). Examinations of the stable air and the 

 dust shaken from the animal during milking have shown the 

 constant presence of Bact. acidi lactici. The conclusion follows, 

 that milk is contaminated with the lactic acid organisms while 

 being drawn, and that the interior of the udder is of no im- 

 portance as a source. The observations made did not include 

 the influence of dirty utensils containing souring milk, which, 

 of course, is a factor, the importance of which is obvious. 



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