18 
BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE 
produces sufficient acid to curdle the milk in 14 days; and a type 
which produces acid more slowly and does not curdle the milk in 14 
days. In raw milk the inert group is the larger. 
In milk heated at 145° F. the great increase in the proportion of 
the acid-coagulating and acid groups, in comparison with that of 
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Figure 1.— The hypothetical relationship between the various groups of bacteria in raw milk and in milk 
pasteurized at different temperatures 
the same organisms in raw milk, is plainly shown; and the proportion 
of the alkali and peptonizing groups is reduced. 
At 160° the total acid group is still the largest, but the acid-coagulat- 
ing group is made up of bacteria which cause coagulation very slowly. 
At this temperature the alkali group is greatly reduced, and the 
peptonizing group is reduced to a minimum, 
