When milk is allowed to stand, these globules of fat, being lighter, float up to the top and form a layer which is called cream.

When this cream is skimmed off and put into a churn, and shaken or beaten violently so as to break the little film with which each of these droplets is coated, they run together and form a yellow mass which we call butter.

In addition to the curd and fat, milk contains also sugar, called milk-sugar (_lactose_), which gives it its sweetish taste.

And as a considerable part of the casein, or curd, is composed of another starch-like body, or animal starch, this makes milk quite rich in the starch-sugar group of food-stuffs.
All these substances, of course, in milk are dissolved in a large amount of water, so that when milk is evaporated, or dried, it shrinks down to barely one-sixth of its former bulk.

It is, in fact, a liquid meat, starch-sugar, and fat in one; and that is why babies are able to live and thrive on it alone for the first six months of their lives.