116 Dairy Bacteriology. 



113. Bacteriological study of pasteurized milk. 



An extended bacteriological examination of milk and 

 cream pasteurized on a commercial scale in the Russell 

 vat at the Wisconsin Dairy school showed that over 99.8 



FIG. 29. Effect of pasteurizing on germ content of milk. Black square repre- 

 sents bacteria of raw milk; small white square, those remaining after pasteuri- 

 zation. 



% of the bacterial life in raw milk or cream was destroyed 

 by the heat employed, i. e., 155 F. for twenty minutes 

 duration 1 . In nearly one-half of the samples 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 bacteria per cc . In cream the germ content 

 was higher, averaging about 25 , 000 bacteria per cc . When 

 the high initial content of either milk or cream is taken 

 into consideration, it indicates that the spore-bearing 

 bacteria are relatively few in properly selected milk that 



1 Russell, 12th Wis. Expt. Stat. Kept., p 160, 18 ( J5. 



