PASTEURIZATION 207 



ments in which milk from tuberculous udders was used 

 without being diluted with normal milk that the circum- 

 stances were not the same as exist under natural condi- 

 tions; the infection was much more concentrated, and 

 there was not the same opportunity for the albuminous 

 matter surrounding the bacilli to be softened and loos- 

 ened as occurs when a small quantity of infected milk 

 is mixed with a comparatively large quantity of normal 

 milk several hours before pasteurization. But individual 

 milk was not used in all of the experiments with natu- 

 rally infected milk; some of them were made with mixed 

 milk which was entirely normal in appearance. 



In all of the experiments referred to a small quantity 

 of milk was heated in a laboratory. Under these condi- 

 tions, the temperature at which the milk is heated and 

 the time of exposure can be accurately controlled. But 

 in commercial pasteurizers fluctuations in temperature 

 and variations in holding- time cannot be entirely avoided 

 and when large quantities of milk are pasteurized under 

 these conditions there is not the same assurance that every 

 particle of milk will be heated at the same temperature 

 for the same length of time as when a small quantity of 

 milk is heated in the laboratory. This is shown by the 

 experiments of Rosenau and Schorer in which they tested 

 the efficiency of pasteurization under commercial condi- 

 tions. They inoculated milk with cultures of the bacilli 

 of typhoid fever, diphtheria, and tuberculosis and en- 

 deavored to heat it at 140 to 145 F. (60 to 62.8 C.) 

 for different periods of time. Two tests were made with 

 typhoid bacilli and in one the organisms survived. The 

 same results were obtained with the diphtheria bacillus. 

 In two tests with tubercle bacilli of the bovine type one 

 failed, and in a similar experiment with tubercle bacilli 



