112 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
advanced by Theobald Smith that the offending organ- 
isms were introduced into the udder of some of the cows 
by infected milkers, multiplied there without producing 
any changes in the organ or in the milk, and were elimi- 
nated in the milk in large numbers at each milking. In 
two of the epidemics in the United States (Chicago 
1911, Baltimore 1912), the milk which spread the disease 
had been subjected to a pasteurizing process. Rosenau 
observed that when the Streptococcus pyogenes is grown 
in raw milk it is modified to correspond with the strepto- 
coccus of epidemic sore throat. 
Milk from cows affected with catarrhal and paren- 
chymatous mastitis is also objectionable because the pus 
which it contains often gives it an unpleasant taste and 
frequently causes it to putrefy and to curdle quickly. 
The pus itself may be harmful to children, even if no 
bacteria are present. The greatest harm, however, is 
done by the bacteria. In the phlegmonous form of inter- 
stitial mastitis the presence of fever and other constitu- 
tional disturbances renders the milk unsuitable for food; 
there is also the possibility that the parenchyma of the 
udder may at any time become affected and the causative 
bacteria would then be eliminated in the milk. 
Therefore, when a cow is affected with mastitis, the 
milk should not be used for food and, if possible, the cow 
should be removed from the milk stable until the udder 
returns to the normal condition. Cows affected with 
infectious streptococcic, septic, or gangrenous mastitis 
should always be isolated. When infectious streptococcic 
mastitis is present in a herd it may be necessary to pro- 
hibit the use of any of the milk for food unless it is 
boiled or pasteurized, but even then such milk should 
not be used for children. 
