THE BACTERIA OF SOIL, AIR, WATER, ETC. I37 



varies greatly. In ordinary milk as furnished by milkmen 

 the number of bacteria to the cubic centimeter is usually 

 many thousands up to many millions; grocer's milk may 

 contain hundreds of thousands or millions of bacteria to the 

 cubic centimeter; frequently figures are reached which are 

 beyond computation. 



Human milk often contains the staphylococcus epidermidis 

 albus, and not seldom the staphylococcus pyogenes aureus, 

 under normal conditions. 



Of the different pathogenic bacteria liable to furnish a 

 source of danger in milk, the most important is the bacillus 

 tuberculosis. Tuberculosis is a disease to which cattle are 

 exceedingly prone. There is good reason to beheve that 

 infants acquire tuberculosis through taking as food the milk 

 of tuberculous cows, although the danger from this source has 

 probably been overestimated. The milk of tuberculous cows 

 may obtain tubercle bacilli when there is no tuberculous dis- 

 ease of the udder.* The frequency of tuberculosis among 

 milch cows sometimes becomes as high as 25 per cent., or 

 even more. Butter derived from the milk of such cows may 

 contain tubercle bacilli. The proper manner for the States 

 to deal with this problem, for it is one that doubtless will 

 fall to the individual States, has not yet been determined. 

 The cost of killing such a large number of valuable cows 

 would be very great. Furthermore, it is by no means cer- 

 tain that this procedure would eradicate the disease. The 

 flesh of cattle also is capable of transmitting tuberculosis, 

 but is a less serious source of danger when beef is thoroughly 

 cooked. 



"Ripening " of cream and cheese is due to the growth 

 of bacteria which produce agreeable flavors in the butter and 



* Mohler. Infectiveness of Milk of Cows which have Reacted to the Tuber- 

 culin Test. U. S. Dept. Agriculture, Bureau Animal Industry, Bull. No. 44. 

 1903. 



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