112 MARKET DAIRYING 
No less than 148 degrees F. for at least 15 minutes. 
No less than 145 degrees F. for at least 18 minutes. 
No less than 140 degrees F. for at least 20 minutes. 
Chicago has the following regulations: 
A uniform heating of 140 degrees F. maintained for 
20 minutes. 
A uniform heating of 150 degrees F. maintained for 
15 minutes. 
A uniform heating of 155 degrees F. maintained for 
5 minutes. 
A uniform heating of 160 degrees F. maintained for 
14 minutes. 
A uniform heating of 165 degrees F. maintained for 
I minute. 
Necessity of Clean Milk for Pasteurizing. Con- 
trary to general public opinion, milk to be pasteurized 
must be especially clean to make it a safe food for 
babies. The reason for this is the fact that the pasteur- 
izing process does not destroy the bacterial spores which 
are always associated with unclean milk, and a large per- 
centage of these spores belong to the putrefactive kind. 
In ordinary unpasteurized milk, these spores are held in 
check by the rapid development of the lactic acid bac- 
teria, which are first to succumb in the pasteurizing 
process. 
The ordinary pathogenic bacteria are not spore-bearing 
but the putrefactive and many other obnoxiots kinds of 
bacteria are spore-bearing. These putrefactive spores, 
which come from manure and other filth, develop rapidly 
in pasteurized milk kept at high temperatures. 
Importance of Low Holding Temperature. While 
filthy milk, as pointed out above, is rich in bacterial 
spores, there is perhaps no milk entirely free from them. 
