Frost—Bacteriological Control of Public MUk Supplies. 1365 
after pasteurization, a condition frequently obtaining in pasteur¬ 
izing plants at the present time. Certified milk and good in¬ 
spected milks have surprisingly few spore forms. 
The rate at which colonies on agar plates, incubated at 21° 
C., develop, may be used to differentiate different grades of 
milk. The bacteria from raw market milks grow out much faster 
than do the bacteria in pasteurized or certified milks. 
The character of the curd produced by milks of the various 
classes at 37° C. was studied. The raw milks all promptly formed 
lactic acid curds. The same was true of the pasteurized milks. 
The inspected and certified milks more frequently formed sweet 
or gaseous curds. 
A number of milks were heavily seeded with B. coli and then 
pasteurized at 60° C. for 20 minutes. By this procedure it was 
found impossible to always kill all of the B. coli present. 
I desire to express my indebtedness to Dr. M. J. Rosenau who 
has been ever ready with suggestions and encouragement, and 
who has followed the progress of this work with interest and 
appreciation; to the Boston Milk and Baby Hygiene Association 
for their liberality and foresight in providing a fellowship under 
which this work has been done; and to Drs. L. E. Poole and A. D. 
Browne, and Mr. John Foley, for assistance at various times. 
