Germicidal Property of Milk. 



69 



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 dif- 

 ferent technique. 



Some of the polymorphonuclear leucocytes in milk seem to 

 possess the power of phagocytosis, judged by microscopical prep- 

 arations. 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 serum as in the sediment rich in 

 leucocytes. 



The germicidal action of milk is specific For instance, one 

 sample restrained typhoid and Staphylococais 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 many particulars. The difference is largely one of degree. 

 Blood serum acts more quickly and more powerfully than milk. 



Freezing milk for ten minutes does not affect the phenomenon 

 in question. In one experiment, freezing for 48 hours did not in- 

 fluence its restraining action upon typhoid, but destroyed it for 

 B. lactis aerogenes. 



Boiling milk or heating it above 8o° C, destroys its "germi- 

 cidal " properties. The effect of lesser degrees of heat varies with 

 the microorganism. Thus, the restraining action for B. lactis aero- 

 genes is weakened at 55 0 C, and almost destroyed at 6o° C; for 

 typhoid it is not affected by heating the milk at 6o° C. for twenty 

 minutes, but is materially influenced at 70 0 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 cannot take the place of clean- 

 liness and ice, but may be taken advantage of in good dairy 

 methods. 



