60 BUTTER-MAKING. 
than one cause. It may be due to some undesirable food that 
the cow has eaten, or to the development of certain germs in 
the milk. If caused by the food eaten by the cow, the bitter 
taste is recognizable immediately after the milk has been drawn. 
If it develops on letting the milk stand, it is caused by bac- 
terial growth. 
Several germs have been found to be associated with the 
production of this bitter flavor in milk. Conn has described a 
micrococcus which produces a bitter flavor in milk. Weig- 
mann has described a bacillus which also produces bitter 
flavors. Nearly all of the investigators agree that the germs 
causing the bitter flavors in milk belong to the group which acts 
upon the casein in milk. The bitter flavor is most commonly 
found in milk that has been heated, and then cooled to a low 
temperature. The heat destroys the bacteria that produce 
lactic acid, but does not kill those that produce the bitter 
flavor, owing to the fact that they are spore-producing. 
The germs that produce a bitter flavor do not develop in 
milk that is partly soured, because an acid reaction is un- 
favorable to their growth. 
It was formerly thought that the organisms that cause the 
bitter flavor in milk produced butyric acid. This theory, 
however, has been largely overthrown, as it has been found that 
the germs causing bitter flavor are chiefly of the kind which 
peptonize the casein and produce gas. 
Milk from Cows which have Been in Milk for a Long Period. 
—The difference in the composition of the fat yielded by cows 
in different stages of the lactation period seemingly does not 
affect the quality of the milk to a noticeable extent. If the 
cows have been giving milk an unusually long time, then the 
milk may become abnormal. 
The impurities in the small amount of milk yielded by cows 
almost dried up are quite apparent, and the causes of the 
presence of these impurities are readily understood. The 
small amount of milk drawn from such a cow would contain 
a proportionately larger amount of dirt and germs than would 
