July ijs, 1914 Pasteurization of Streptococci 
327 
RESULTS OBTAINED IN THE EXPERIMENTS 
Two classes of streptococci are able to withstand Pasteurizing tempera¬ 
tures, and this is also true of other groups of nonspore-forming bacteria: 
Class 1.—Those streptococci which may have a low majority thermal 
death point but a high absolute thermal death point. 
Class 2.—Those streptococci which have a high majority thermal death 
point. 
The terms “high majority thermal death point” and “low majority 
thermal death point,” suggested by Gage and Stoughton, 1 mean the 
temperature at which the majority of the bacteria are destroyed. In class 
1, therefore, the majority thermal death point of the streptococci might 
be below the Pasteurizing temperature, and they would therefore be 
destroyed. However, a few bacteria more resistant than the others 
Fig. 3.—Results of heating streptococci (classified as typical and atypical) for 30 minutes at various 
temperatures. 
might survive the Pasteurizing temperature and then continue to develop 
in the Pasteurized milk. The fact that some of the streptococci which 
were studied would fall in this class was plainly shown in the experiments 
of the writers. Often, after a tube of milk containing a culture of strepto¬ 
cocci had been heated, the reaction indicating their growth would be shown 
in 24 hours, while in other cases five or six days' incubation was necessary 
in order to show an acid reaction, thus indicating growth. In such cases 
it was evident that only a few bacteria survived the heating. Among 
this class of streptococci it is quite impossible to say whether a few cells 
survive high temperatures because of certain resistant qualities peculiar 
to themselves or whether they are protected in some way in the milk in 
which they are heated. 
1 Gage, S. de M., and Stoughton, Grace Van E. A study of the laws governing the resistance of Bacillus 
coli to heat. In Technol. Quart., v. 19, no. i, p. 41-54,1906. 
