136 MANUAL OF BACTERIOLOGY. 



The process called pasteurization is designed, not to ster- 

 ilize the milk completely, but to destroy the vegetative forms 

 of bacteria, and to destroy the ordinary pathogenic bacteria 

 with which the milk might possibly be contaminated.* The 

 milk is subjected to a temperature of only about 70° to 75° C. 

 This temperature is less Hkely to produce alteration in the 

 milk than sterilization by steam at 100° C. According to 

 Freeman, milk which had been pasteurized at 75° C. and dis- 

 tributed among the poor people of New York City, whose 

 homes were not supplied with ice, usually kept very well even 

 in the summer time (see p. 55). 



The number of bacteria in milk may be reduced consider- 

 ably by the use of the centrifuge (separator). 



It has been undertaken recently to do away so far as pos- 

 sible with the contamination usually occurring in the barn- 

 yard and stable by the use of extraordinary measures to keep 

 the cows, and especially their udders, clean; also the hands 

 of the milker and the milk-pails; and by sprinkling the floor 

 of the milk-room to prevent dust.f The milk should be 

 transported to the city on ice. Milk which has been collected 

 in this manner is furnished in several cities in the United 

 States. The cattle from which the milk is derived are regu- 

 larly inspected by veterinary surgeons as well as subjected 

 periodically to the tuberculin test. The surroundings and 

 drainage of the stables are investigated by physicians and sani- 

 tary engineers. The milk is also regularly analyzed by a 

 chemist. It has been found possible to reduce the number 

 of bacteria in milk to a few thousand per cubic centimeter. 

 This milk is of course sold at a considerably higher price than 

 ordinary milk. 



The number of bacteria which occur in samples of milk 



♦Theobald Smith. The Thermal Death-point of Tubercle Bacilli in Milk, 

 etc. Journal of Experimental Medicine. Vol. IV., p. 217. 

 t W. H. Park. Journal of Hygiene. Vol. I. 1901. 



