BACTERIOLOGY OF WATER AND MILK 185 



An analysis of the results reveals several interesting facts, 

 namely: (1) that there is a great difference in the number of 

 bacteria in the freshly drawn milk of different cows; (2) there 

 is no increase in the number of bacteria in the milk for about 

 six hours after it is drawn when kept at a temperature of 

 either 40, 55 or 70 F.; (3) there is an actual, but usually 

 not large, decrease in the number of bacteria in the milk for 

 the first six hours after it is drawn; (4) the decrease in the 

 number of bacteria, that is the germicidal action, is greatest in 

 the milk kept at 70 F. ; (5) the decrease in the number of 

 bacteria is much greater in the milk of certain cows than it is 

 in that from others; (6) the germicidal action is in the begin- 

 ning more effective in the milk kept at 70 F. ; and (7) the 

 germicidal action of the mixed milk is not sufficient to render 

 it of any practical value in preserving milk for more than from 

 4six to nine hours. It is clear that milk cooled and kept at 40 

 to 55 F. remains unchanged for a much longer time than 

 when a temperature of 70 F. is maintained. At these low 

 temperatures the number of bacteria continues to decrease for 

 a longer time. It is important to note that frequently the 

 number of bacteria begins to increase in the milk kept at 

 55 F. after about 48 hours, but when the temperature is re- 

 duced to 40 F. they do not. 



Although for the first few hours the germicidal power is 

 more active in milk kept at 70 F., it has not been determined, 

 but probably it is true, that in the milk kept at the lower tem- 

 peratures it continues to act, but in a less degree, for a much 

 longer time. For this reason it is very important to cool 

 market milk to at least 55 F. as quickly as possible after it is 

 drawn, and to keep it at that temperature until it is delivered. 

 If the milk is not to be consumed within 48 hours it is safer to 

 keep it at a lower (40 F.) temperature. 



The difficulties involved in procuring in our large cities 

 milk reasonably free from bacteria do not rest entirely with 

 the producer. The method of transportation is quite as im- 

 portant. Milk may be produced under the best of conditions, 

 .and cooled at once to the required temperature at which it is 



