118 Milk and Its Products 
tonizing or digestive action upon the albuminoids. 
By their action the casein is first coagulated, and 
' finally liquefied or changed into a peptone. 
Butyric fermentations,—The butyric ferments at- 
tack the fats, and result in the formation of bu- 
tyric acid. They produce the peculiar condition 
found in cream and butter known as rancidity, and 
do not usually manifest themselves very strongly in 
the milk. 
ConTROL OF FERMENTATIONS 
Since fermentations always occur in milk that is 
kept for any considerable time, and since they exert 
so powerful an influence, not only upon the milk 
but upon the products manufactured from it, the 
question of their control is one of prime importance. 
The three chief means of such control are: First, 
prevention of infection; second, prevention of the 
growth of germs already present; third, destruction 
of germs already present. 
Prevention of infection. —The greatest source of ° 
infection comes from the body of the animal and 
from the air of the stable. The germs are always 
present, adhering to the hair of the animal, and par- 
ticularly to any particles of dust or dirt. In order, 
then, that the animal shall not be a source of infec- 
tion, it is necessary that she be carefully curried 
and the udder, teats, flank, thighs and lower parts 
of the belly wiped off with a damp cloth immediately 
