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 
