DISTRIBUTION OF BACTERIA. 147 



about 70 to 75 C. This temperature is less likely to pro- 

 duce alteration in the milk than sterilization by steam at 

 100 C. According to Freeman, milk which had been pas- 

 teurized at 75 C. and distributed 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. 67). 



The number of bacteria in milk may be reduced con- 

 siderably by the use of the centrifuge (separator). 



It has been undertaken recently to do away as far as 

 possible with the contamination usually inevitable in the 

 barnyard 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 sprink- 

 ling the floor of the milk-room to prevent dust. 1 The milk 

 is to 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 regularly 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 sanitary engineers. The milk is also 

 regularly analyzed by a chemist. It has been found possi- 

 ble to reduce the number of bacteria in milk very notice- 

 ably. This milk is of course- sold at a considerably higher 

 price than ordinary milk. 



The number of bacteria which occur in samples of milk 

 varies greatly. In ordinary milk as furnished by milkmen 

 the number of bacteria to the cubic centimeter is usually 

 many thousands to millions; grocer's milk may contain 

 hundreds of thousands to millions of bacteria to the cubic 

 centimeter; frequently figures are reached which are be- 

 yond computation. 



Human milk often contains the staphylococcus epicler- 



3 See W. H. Park, Journal of Hygiene, Vol. I., 1901. 

 13 



