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- 
