THE GERMICIDAL PROPERTY OF MILK. 
By Milton J. Rosenatj, Director Hygienic Laboratory . Public Health and 
Marine-Hospital Service; and George W. McCoy, Passed Assistant 
Surgeon. Public Health and Marine-Hospital Service. 
INTRODUCTION. 
Judged by the number of colonies that develop upon agar plates, 
the bacteria in milk first diminish then increase in number. This 
occurs only in raw milk during the first few hours after it is drawn. 
Although the bacteria seemingly decrease in number, they never dis- 
appear entirely. After this initial decrease there is a continuous and 
rapid increase until the milk contains enormous numbers. 
It was early noted that under certain conditions raw milk may keep 
longer than heated milk. In other words, the property of milk to 
restrain the growth of bacteria is destroyed by heat. 
Before this so-called “ germicidal property of milk ” was discovered 
it had been observed that fresh blood, or blood serum, had distinct 
powers of destroying bacteria. Further, that blood resists putrefac- 
tive and fermentative changes. It is now well known that blood, 
apart from the phagocytic action of its cells, has definite germicidal 
properties. This is due to substances in solution in the blood serum 
which have the power of clumping, killing, or dissolving the bacterial 
cells. This power of the blood is an important protection against 
bacterial invasion. Similar uses have been assigned to the “ anti- 
bodies ” in milk. The germicidal properties of blood are destroyed 
by heat and disappear spontaneously in a short time after it has been 
removed from the body. 
Not only the blood, but other body fluids have germicidal properties 
in varying degree, so that it was not surprising when similar powers 
were attributed to milk, especially when we consider that the fluid 
part of milk, with many of its constituents, is secreted directly from 
the blood. 
This initial power of milk to destroy bacteria or to restrain their 
multiplication is feeble and variable. The germicidal properties of 
milk have been much misunderstood, especially by dairymen, some 
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