COMPOSITION OF MILK. ll 
It was previously stated that little is known concerning 
the way in which the fatty acids are combined with glycerine 
in the milk; but, for the sake of convenience, the fats will be 
referred to as if they exist as separate glycerides of fat. 
The terms “ Volatile’? and ‘“ Non-volatile” are applied 
to the glycerides of fat, or to the fats as they exist in butter. 
Strictly speaking, this is not proper, as they do not assume 
the volatile characteristics until the glycerine separates from 
the fatty acids; it is only then that the latter becomes volatile. 
Volatile Fats.—The first group, or the volatile fats, include 
butyrin, caproin, caprylin, caprin, and laurin. Butyrin is the 
one present in the largest proportion. Laurin and caprin are 
partially non-volatile. Butyrin is the most important fat 
belonging to the volatile group. It is the most important 
quantitatively, and also qualitatively. So far as is known, 
butyrin is the least stable of any of the butter-fats. Under 
normal conditions, so long as the fatty acid remains in com- 
bination with the glycerol, it is not volatile nor soluble in 
water but as soon as separation takes place, due to the action 
of micro-organisms, or to the effect of light and air, then it 
becomes volatile, and escapes in the form of gas. According 
to the mass of evidence, these factors are the chief causes of 
rancidity in butter. 
It is also claimed that these volatile fats have the special 
properties of absorbing odors and gases to a greater extent 
than any of the other fats. This absorption takes place when 
fat comes into contact with the undesirable taints. For this 
reason it is essential that milk, cream, or butter be kept away 
from any foreign undesirable odors. These undesirable taints 
may also be imparted to the fat before the milk is drawn. 
If the cow is fed on undesirable food such as turnips, onions, 
garlic, etc., the milk from the cow assumes undesirable char- 
acteristic flavors, which can-easily be recognized in the finished 
product. On the other hand, such foods as well-cured sweet- 
clover hay, and bran, seem to impart desirable flavors to 
milk and butter. 
