476 
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. 
Some of the polymorphonuclear leucocytes in milk seem to possess 
the power of phagocytosis, judged by microscopic preparations. 
Phagocytosis, however, plays no essential part in the “germicidal” 
action of milk, for the decrease in numbers is quite as marked in the 
cell-free milk as in the sediment rich in leucocytes. 
The germicidal action of milk is specific. For instance, one sam- 
ple restrained typhoid and Staphylococcus pyogenes aureus, but not 
paratyphoid A or B. 
Dilution experiments demonstrate the enfeeblement of agglu- 
tinins rather than the presence of a germicidal substance in solution. 
The germicidal actions of blood and milk resemble each other in 
some particulars. Blood serum acts more quickly and much more 
powerfully than milk. 
Freezing milk for ten minutes and then thawing it, does not affect 
the phenomenon in question. In one experiment freezing for forty- 
eight hours did not influence its restraining action upon typhoid, but 
destroyed it for B. lactis serogenes. 
Boiling milk or heating it above 80° C. destroys its “germicidal” 
properties. The effect of lesser degrees of heat varies with the 
micro-organism. Thus, the restraining action for B. lactis serogenes 
is weakened by first heating the milk at 55° C. and almost destroyed 
at 60° C. ; for typhoid it is not affected by heating the milk at 60° C. 
for twenty minutes, but is materially influenced at 70° C. for thirty 
minutes. 
The “germicidal” action of milk varies in different animals and in 
the milk from the same animal at different times. At most, the 
action is variable and feeble. It can not take the place of cleanliness 
and ice, but mav be taken advantage of in good dairv methods. 
v c? c 
