Frost—Bacteriological Control of Public Milk Supplies. 1305 
THE BACTERIOLOGICAL CONTROL OF PUBLIC MILK 
SUPPLIES." 
William Dodge Frost 
I. INTRODUCTION. 
The question of a safe milk supply is a subject on which much 
good bacteriological work has been done in recent years. There 
is, however, a great deal still to be done before the bacteriolo¬ 
gist can check up and satisfactorily control the production of a 
sanitary milk supply. In the past little has been done in bacteri¬ 
ological milk analyses beyond making a quantitative determina¬ 
tion of the bacteria present. Granting that this is the most im¬ 
portant single item that can be determined, it still leaves much 
to be desired. In times of epidemics special search is some¬ 
times undertaken for the suspected bacteria of disease. In cer¬ 
tain laboratories, tests are regularly made for the streptococci, 
but as yet there is no concensus of opinion as to what their pres¬ 
ence means. In other laboratories B. coli is sought for and re¬ 
garded as an index of pollution. It is, however, still an open 
question whether or not it can be regarded with the same sus¬ 
picion in milk as in water. Still again, Bact. welchii, in England 
particularly, is regarded as an index of fecal contamination. 
The necessity for reliable methods of differentiating pure from 
contaminated milk is now all the more urgent because of the 
widespread use of the pasteurizing process. Modern methods 
of pasteurization employ a degree of heat so little above the 
thermal death point of dangerous bacteria that the treatment of 
milk in this way commercially will give a false idea of security 
to the consumer unless the sanitarian can quickly and accurately 
determine any failure to sufficiently heat the milk. 
* Submitted as a thesis for the degree of Doctor of Public Health, 
Harvard Medical School, Boston, Mass., May, 1918. 
