THE CONSTITUTION OF SIILK, 3 
rated from milk by evaporating whey in a vacuum pan. Com- 
mercial milk sugar is used in infant foods and in medicines. 
6. Fat. 
The fat of the milk is a mixture of several fats, mainly of 
stearic, palmitic and oleic acids, in combination with glycerine. 
With these are a number of fats that are both volatile and 
soluble. In this latter respect butter fat differs from the fats 
used in olecmargarine. Filled cheese is mace by introducing 
oleo oils into milk in the place of the butter fat. 
we 
Fig. 2.—The fat globules as seen through a microscope. The portion 
included in the circle is highly magnified. The clotting is due to an album- 
jnous substance that collects around the globules soon aiter the milk is drawn. 
The fat of milk is in emulsion—that is, it is distributed 
through the milk serum in the form of minute globules, which 
can only be seen by the aid of a microscope. They vary nor- 
mally in size from 1-40,000 to 1-2000 of an inch in diameter. 
On account of their minute size they are necessarily very numer- 
ous. 
It is estimated that there are 150,000,000 fat globules in a 
single drop of average milk. The average production of fat 
globules by a good dairy cow has been estimated to be 38,210,000 
per second. 
The fat globules Leing lighter than the surrounding serum 
naturally rise when the milk is left standing, and crowding 
close together form a layer known as the cream. In the manu- 
