THE GERMICIDAL ACTION OF FRESH COW's MILK 251 



the raw milk is quite fresh. When a few hours old the germicidal 

 property rapidly disappears. 



According to Evans and Cope the bactericidal property of 

 fresh milk is destroyed at 68° C. and injured at 55° C. The 

 authors further claim that the germicidal property exerts its 

 influence only on some types of bacteria, while others are merely 

 restrained. The property also varies in milk from different 

 animals. 



Rosenau and McCoy think that the presence of agglutinins is 

 an important factor in bringing about the apparent reduction of 

 bacteria in fresh milk. Tbey have shown that when milk is 

 violently shaken the number of colonies does not decrease, and 

 this observation leads the authors to conclude that the milk, after 

 standing, causes the bacteria to clump, and that, therefore, fewer 

 colonies appear on the plates, although the actual number of cells 

 may not have been reduced. This view seems to be supported 

 by the fact that in centrifugahzed milk the colony count is greater 

 than in the same milk before centrifugation. 



Brudny, working with Bacillus coli, observed that this organ- 

 ism is restrained in fresh milk, or even injured to such a degree as 

 to acquire altered properties. 



Heinemann and Glenn found a distinct relation between the 

 decrease of numbers of a certain type of bacteria inoculated 

 into milk and the agglutinative property toward the same type 

 of the serum prepared from the same milk. The higher the 

 agglutinative property of the milk-serum, the more marked was 

 the reduction in the number of colonies counted. 



Stocking takes the position that among the large number of 

 bacteria which gain access to milk, many find themselves in an 

 unfavorable environment and die. This phenomenon, the author 

 thinks, explains the so-called germicidal property of fresh milk. 

 In agreement with this view is an observation of Coplans, who 

 assumes that bacteria, when dropping into a new medium, remain 

 dormant for a time before beginning to multiply. It seems dif- 

 ficult, however, to harmonize this hypothesis with all the facts 

 observed. 



The majority of investigators agree on the point that in fresh 

 milk there is not a marked multiplication, but that, as a rule, there 

 is a limited decrease. The following figures may illustrate the 

 degree to which bacteria actually seem to diminish in fresh milk 

 if the colony count is taken as index (Heinemann and Glenn) : 



NUMBER OF BACTERIA IN FRESH MILK AT TWO-HOUR INTERVALS 



Original number 500 1100 1400 500 1000 600 300 500 



After two hours 400 200 600 1300 1000 200 1400 



After four hours 300 400 1800 400 100 800 3400 



After six hours 600 300 300 2300 200 200 1000 5600 



After eight hours 1000 4300 900 3200 1000 200 1100 6300 



