owes its name and flavor) and
traces of other fatty acids, as well as small quantities of
cholesterin, lecithin, and a yellow coloring matter.

The proteins of milk, which form the curd or larger part of the
solids, according to Van Slyke[29] are in the form of casein and
albumen. There are 3.6 parts casein to 1 part soluble proteins, but
these figures vary somewhat at times. Casein is insoluble in pure
water, but dissolves readily in water to which an alkali or calcium
carbonate is added. The soluble protein in the form of lactalbumen is
one of the constituents of whey. This substance contains more sulphur
than does casein, but no phosphorus.

~Whey~ is the opalescent fluid which remains when the casein is
precipitated, and is composed of water 93.8%, total ash 0.44% (Koenig).

~Mineral salts~, 0.7% of milk, are made up of calcium, potassium,
sodium, magnesium, iron, sulphur, phosphorus, and chlorine. Milk is so
rich in calcium that it requires only 400 c.c. (or about 2-1/2 cups)
to furnish 1 gram of calcium. This is the amount believed to be
necessary for the welfare of man each day and this must be derived
from food.[30]

~Water.~--The fluid part of milk is composed chiefly of water,
constituting 87% of whole milk.

Milk as a food for infants will be discussed in another chapter.

As has already been said, no food has so far been discovered which
could be effectually substituted for milk. There is no food, however,
which requires more attention in its selection and care. It is very
susceptible to both odors and flavors, absorbing them both readily, as
will be found if milk be placed in the same compartment with foods of
strong odor and flavor, without being properly covered and protected.
This is particularly noticeable with cucumbers, melons, etc.

Milk also furnishes a splendid medium for bacterial growth, and if
left exposed to the air, put into unclean receptacles, or kept in a
warm place, will immediately become more or less contaminated, after
which it is unwise to use it. Sterilization and pasteurization will in
a measure overcome the bacterial contamination, but milk purchased
from a dairy which is not clean or milked under unsanitary conditions
will remain dirty, hence unfit for human consumption. When the
morning's milk supply is brought to the house it should be in clean,
well-stoppered bottles, but before placing it in the ice-box the tops
of the bottles should be carefully wiped off with a wet cl