20 BUTTER-MAKING. 
Besides the kind of food, some physiological disturbances 
of the cow may cause abnormal taints in milk. 
(2) Gases or taints which are formed in the milk or absorbed 
by the milk are due to fermentation and absorption respectively. 
The fermentation cause will be considered in a separate chapter, 
and the latter cause needs little explanation. It is a well known 
fact that milk, or any of its products, has the special property 
of absorbing odors which may be present in the surroundings 
of milk. For this reason, milk, as well as other dairy products, 
should at all times be kept in clean utensils and pure surround- 
ings. 
Abnormai taints appearing in milk immediately after 
milking are due to absorption within the cow. Taints that 
develop on standing are due to bacterial growth in the milk, 
or to absorption from impure surroundings. In removing 
undesirable taints from milk the first step is to remove the 
inciting cause, and the second to cause as many of these taints 
as possible to escape by a process of aeration or pasteurization. 
Coloring-matter.—It is not known of what the coloring- 
matter in milk consists. A substance named lactochrome 
has been found in milk. So far as known, this coloring-sub- 
stance is closely associated with the fat called palmitin. The 
amount of coloring-matter varies during the different seasons 
of the year. It also varies according to the different breeds. 
During the spring of the year, when cows are first put on grass, 
the color of the butter-fat is always higher than it is during 
the latter portion of the summer. During the winter, the 
fat in milk is quite pale. By feeding the cows some succulent 
feed in the winter, such as silage, carrots, and beets, the color 
of the butter-fat becomes much higher. 
From this it would seem that the change in the color of 
the fat with the different seasons, and the food fed, is closely 
associated with chlorophyl, the coloring-matter of grass. 
Other Constituents of Milk.—It is said that constituents 
such as citric acid, urea, nuclein, lecithin, and galactase are 
present. Babcock maintains that he has discovered a sub- 
