Preservation of Milk. 



133 



mercial scale in the Russell vat at the Wisconsin Dairy 

 school showed that over 99.8 per cent of the bacterial life in 



raw milk or cream 

 was destroyed by 

 the heat employed, 

 i. e., 155 F. for 

 twenty minutes du- 

 ration. 1 In nearly 

 one-half of the sam- 

 ples of milk, the 

 germ content in the 

 pasteurized sample 

 fell below 1,000 

 bacteria per cc., 

 and the average of 

 twenty-five samples 

 contained 6,140 bac- 



FIG. 28. Effect of pasteurizing on germ content er j a p er cc J n 

 of milk. Black square represents bacteria of raw 

 milk; small white square, those remaining after Cream the germ COn- 



pasteurization. tent was higher, av- 



eraging about 25,000 bacteria per cc. This milk was taken 

 from the general creamery supply, which was high in organ- 

 isms, containing on an average 3,675,000 bacteria per cc. 

 De Schweinitz 2 has reported the germ content of a supply 

 furnished in Washington which was treated at 158 to 160 

 F. for fifteen minutes. This supply came from a single 

 source. Figures reported were from 48-hour-old agar plates. 

 Undoubtedly these would have been higher if a longer pe- 

 riod of incubation had been maintained. The average of 

 82 samples, taken for the period of one year, showed 325 

 bacteria per cc. 



1 Russell, 12 Wis. Expt. Stat. Kept , 1895, p. 160. 

 2 De Schweinitz, Nat. Med. Rev., 1899, No. 11. 



