486 
and this difference might be more pronounced if the milk were shaken 
more violently. 
Some species occurring naturally in milk decrease considerably in 
numbers during the first four or five hours, some decrease slightly, 
some hold their own or even increase. 
Milk inoculated with pure cultures of bacteria seems to restrain to 
a marked degree the multiplication of these bacteria for several hours 
at 37° C. and for a somewhat longer period at room temperature, ex- 
cepting in the case of Street, lacticus , which increases from the begin- 
ning, although it may be inhibited to some extent. 
Heating milk to 56° C. for thirty minutes does not entirely destroy 
the power to restrain the multiplication of bacteria ; this power is 
weakened, however, and at 75° C. is destroyed entirely. This fact, 
together with the fact that milk serum agglutinates some species of 
bacteria in vitro to a marked degree, seems to favor the assumption 
that agglutinins are in part responsible for the apparent decrease of 
bacteria in fresh milk, since bactericidal substances are destroyed by 
heating to 56° C. for thirty minutes. 
The agglutination of certain bacteria in milk serum seems to bear 
some relation to the apparent decrease in numbers of bacteria ob- 
served in fresh milk, 'but this is probably not the only factor causing 
such reduction. 
SUMMARY AND CONCLUSIONS. 
Judged by the number of colonies that develop upon agar plates, 
the bacteria in milk first diminish then increase in number. This so- 
called germicidal property of milk occurs only in the fresh raw fluid. 
For the most part, our work plainly shows that no actual reduction 
in the number of bacteria occurs. However, when compared with 
the controls a restraining action is evident. The phenomenon there- 
fore appears to resemble that of a weak antiseptic rather than that of 
a true germicide. 
When milk is kept warm (37° C.), the decrease is pronounced 
within the first eight or ten hours. After this time the milk has 
entirely lost its restraining action. 
When the milk is kept cool (15° C.), the decrease is less marked, 
but more prolonged. 
The decrease in the number of bacteria is largely apparent, being 
due at least in part to agglutination. 
The bacterial clusters may, to a certain extent, be shaken asunder. 
This fact goes far to reconcile the discordant results of the various 
investigations upon the germicidal properties of milk. Those who 
used dilution methods with vigorous agitation broke up the bacterial 
clusters, and thus obtained a larger number of colonies upon agar 
plates than those who plated directly with different technique. 
