PASTEURIZATION A419 
not be expected, from their results, to survive 65.6° C. for thirty min- 
utes. Erratic results were secured and it is possible that some strains 
of Bacillus colon may be found which will survive pasteurization under 
the above conditions. Gage and Stoughton (1906) found that in 55 
per cent of thermal death-pomt determinations made with B. colz, the 
cultures withstood 80° C. for five minutes. Russell and Hastings (1902) 
report the characteristics of a micrococcus from milk which withstood a 
temperature of 76° C. for ten minutes. Different individual resistance, 
however, was found among the cells. Ford and Pryor (1914) claim that 
milk heated to any temperature between 65° C. and 100° C. and kept 
between 22° and 37° C. will be decomposed by spore-forming bae- 
teria and consequently may be dangerous. They recommend the 
boiling of milk and storage on ice since heated milk is lable to 
decompose. 
Pathogenic Bacteria. The effect of the pasteurization process on 
pathogens has been limited almost entirely to Bacillus tuberculosis. 
Since this organism 1s especially important in relation to milk hygiene, 
many attempts have been made to determine its thermal death pot in 
milk Rosenau has prepared table XLIV, which 1ecviews concisely 
some of the work which has been done. 
The work of Smith (1899) and of Russell and Hastings (1904) has 
been especially convincing. The former of these investigators found 
that when tubercle bacilli were suspended in milk they were destroyed 
in from fifteen to twenty minutes at 60° C.; the greater portion being 
killed in 5-10 minutes. The latter tried short periods of pasteurization 
and found that a temperature of 160° F. (71.1° C.) or above for one 
minute destroyed the virulence of bovine tubercle bacilli so that guinea 
pigs were not killed when inoculated with from 2 to 5 mgs. Others have 
confirmed this work and these temperatures are now accepted in the con- 
tinuous process. The milkman pasteurizing milk is between two fires. 
He must avoid a cooked taste in the milk which interests the housewife 
and must kill all pathogenic bacteria which are the chief interest of the 
sanitarian. 
On the relation of pasteurization to other pathogenic bacteria in 
milk, our knowledge is very meager. Hesse (1894) stated that raw 
cows’ milk was not a good medium for cholera spirilli and that they 
died in twelve hours at room temperature and more quickly at higher 
temperatures. The acidity and other bacteria in the milk killed them. 
Fig. 69 prepared by North and taken from the report of the Commission 
on Milk Standards gives some data concerning B. typhi, streptococci and 
Bact. duphtheria. 
