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^UFORNIA: 

 vi] THE BACTERIA OF MILK ~~~6$ 



above the sea, far from land, they do not occur at all ; 

 while air on the top of high mountains is correspond- 

 ingly pure. In uninhabited spaces their number 

 is enormously less than in inhabited spaces. In the 

 air above the streets of Paris it has been calculated 

 that they are present to the extent of about 4000 per 

 cubic yard. 



Their tendency is to obey the law of gravity, and 

 to subside from the air. This, however, can only 

 completely take place when the air is kept absolutely 

 undisturbed a condition which, we need scarcely say, 

 hardly ever obtains. But, numerous as they are in 

 outside air, their number in that of enclosed spaces, 

 such as the dairy, and more especially the byre, is 

 even greater. Thus, one investigator has found 120 

 bacteria and moulds in a quart of the air of a byre. 

 In the litter, in the manure, and in the dirt on the 

 floors of byres they are very abundant, and whenever 

 this is stirred or disturbed in any way large numbers 

 of them are sent into the air. It is for this reason 

 that the hands of milkers, the teats of cows, and the 

 milk vessels are liable to become so rapidly con- 

 taminated with bacterial life. 



Contamination of Milk by Micro-Organisms. 

 The thousand-and-one ways in which milk may thus 

 become contaminated makes it a very difficult task to 

 obtain it from the cow absolutely sterile, that is, 

 devoid of bacterial life, or even to believe that milk 



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