122 Milk and Its Products 
who discovered and used the process in controlling 
the fermentations of wine and beer. It differs from 
sterilization only in the degree of heat used, and, in 
fact, may be properly called an incomplete or partial 
sterilization. The destructive effect of heat upon 
germ life depends both upon the degree of heat and 
the length of time to which the germs are exposed. 
A large number of germs are killed at temperatures 
from 133° to 140° F., while others are killed at tem- 
peratures varying from 150° to 165° F. These latter 
temperatures include the germs of all of the ordinary 
ferments and most of the germs of specific diseases, 
including that of the tubercle bacillus. Since the 
tubercle bacillus is the disease germ most likely to be 
present, milk is ordinarily considered to be safe from 
disease germs when it has been pasteurized at a tem- 
perature sufficiently high to destroy it. This is a 
temperature of 149° F. for thirty minutes, a tem- 
perature of 155° F. for fifteen minutes, or a tempera- 
ture of 167° F. for ten minutes, and these temperatures 
have come to be looked upon as standard pasteuriz- 
ing temperatures. Milk may be heated to 165° F., 
if quickly cooled afterwards, without developing a 
boiled taste; so that it is possible that milk be 
rendered safe from the germs of disease and free 
from the ordinary germs of fermentation without 
developing in it a boiled taste. But in order to 
pasteurize milk safely, it is necessary that means 
should be provided for cooling rapidly from the 
pasteurizing temperatures to 50° F. or below. 
Milk carefully pasteurized, as above described, will 
