208 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



of the human type the organisms were not killed in either 

 test. As a result of these experiments, Rosenau and 

 Schorer concluded that in order to allow a margin of 

 safety when milk is pasteurized under commercial condi- 

 tions it is necessary to expose the milk to a temperature 

 of at least 145 F. (62.8 C.) for 30 to 45 minutes. 



The only experiment recorded in which naturally 

 infected milk was pasteurized in large quantity under 

 commercial conditions was made by Traum and Hart, 

 who published their results in 1916. The milk came 

 from a large herd of reacting cows and the volume 

 amounted to from 700 to 1000 quarts daily. Samples 

 were taken at the milk station in the city before and after 

 pasteurization. Twenty- four samples of raw milk were 

 tested on guinea pigs and all except one sample produced 

 tuberculosis in the test animals, and the guinea pigs inoc- 

 ulated with this sample died of septicemia before there 

 was an opportunity for tuberculosis to develop. Eleven 

 samples of milk which had been heated at 140 F. (60 

 C.) for 20 minutes were tested in the same manner and 

 did not produce tuberculosis in a single instance. Twelve 

 samples of milk which had been heated above 140 F. 

 (60 C.) for a longer period than 20 minutes also proved 

 free from tuberculosis infection. While these results ap- 

 pear to indicate that 140 F. (60 C.) for 20 minutes 

 will kill tubercle bacilli in naturally infected milk when 

 it is pasteurized under commercial conditions, it would 

 seem desirable, in view of the contradictory data fur- 

 nished by the other experiments which have been men- 

 tioned, to have them confirmed by further tests before 

 drawing final conclusions. There ought to be absolute 

 certainty that a given temperature and period of expo- 

 sure will kill tubercle bacilli and other pathogenic organ- 



