450 CITY MILK SUPPLY 



aerogenes. However, many grain cultures would answer to the usual 

 tests for B. coli communis and B. coli communior. 



While the presence of fecal bacteria in milk may be determined with 

 great certainty the ordinary presumptive tests and even the usual 

 confirmatory ones do not necessarily prove the contamination of milk 

 with fecal matter. 



Significance of B. welchii. Savage has pointed out that the spores of 

 B. welchii are present in cow dung in considerable numbers and has 

 suggested that since the organism does not multiply in milk it might be 

 used as an index of animal contamination of market milk. However, 

 he mentions the fact that it is not known how far the organism may gain 

 entrance to the milk from other sources than manure. 



Bacterial Tests of Pasteurized Milk. In the examination of pas- 

 teurized milk, bacteriological tests are considered of great value. They 

 are used to test the sterility of the apparatus before starting a run and 

 by taking samples of the milk at different stages of its journey through 

 the machines to determine the places where defects occur. The finished 

 product should meet reasonable bacteriological standards, if the pasteur- 

 ization has been successful. In some cities a certain percentage reduc- 

 tion in bacteria is required. The fallacy in this standard has been pointed 

 out in the chapter on pasteurization. The best way is to forbid the 

 pasteurization of milk that has a bacterial content in excess of a stated 

 amount and to require that the pasteurized milk shall not contain over a 

 stated number of bacteria per cubic centimeter. 



In some cities the colon test is used as an index of the efficiency of 

 pasteurization. Of this Ayers and Johnson say that it is complicated by 

 the ability of certain strains to survive a temperature of 145F. for 30 

 min. and to develop rapidly when pasteurized milk is held under tem- 

 perature conditions that might be met during storage and delivery. 

 The presence of a large number of colon bacilli right after the heating 

 process may indicate improper treatment of the milk. Milk pasteurized 

 at 150F. or above for 30 min., according to the researches of these 

 authors, would not contain colon bacilli but they emphasize the fact that 

 more extensive work might reveal strains of colon bacilli that would 

 survive this and even higher temperatures. 



Prevention of Milk-borne Epidemics. Besides keeping up the sani- 

 tary condition of places where milk is produced, handled and sold, by 

 inspecting and scouring them, and besides maintaining the quality of the 

 supply by laboratory work, it is necessary to make a systematic effort 

 to protect the milk from infection and to prevent it becoming the vehicle 

 of contagion. This work usually receives the personal attention of the 

 health officer. In the larger cities a staff of specially trained men deals 

 with communicable diseases and usually cooperates with the bureau of 

 milk inspection in carrying on that part of the work which pertains to 



