alyses.]

[Footnote B: Including salt, 4.1.]

CHAPTER VII

MILK AND DAIRY PRODUCTS

99. Importance in the Dietary.--There is no article of food which
enters so extensively into the dietary as milk, and it is one of the few
foods which supply all the nutrients,--fats, carbohydrates, and
proteids.[36] Milk alone is capable of sustaining life for comparatively
long periods, and it is the chief article of food during many diseases.
An exclusive milk diet for a healthy adult, however, would be
unsatisfactory; in the case of young children, milk is essential,
because the digestive tract has not become functionally developed for
the digestion of other foods.

It is necessary to consider not only the composition and nutritive value
of milk, but also its purity or sanitary condition.

100. General Composition.--Average milk contains about 87 per cent
water and 13 per cent dry matter. The dry matter is composed
approximately of:

=======================
| Per Cent
Fat | 3.5
Casein | 3.25
Albumin | 0.50
Milk sugar | 5.00
Ash | 0.75
=======================

[Illustration: FIG. 22.--MILK FAT GLOBULES.]

Fat is the most variable constituent of milk. Occasionally it is found
as low as 2 per cent and as high as 6 per cent or more. The poorest and
richest milks differ mainly in fat content, as the sugar, ash, casein,
and albumin, or "solids of the milk serum," are fairly constant in
amount and composition. Variations in the content of fat are due to
differences in feed and in the breed and individuality of the animal.

101. Digestibility.--Milk is one of the most completely digested of
foods, about 95 per cent of the protein and fat and 97 per cent of the
carbohydrates being absorbed and utilized by the body.

In a mixed ration, the nutrients of milk are practically all absorbed.
Milk also exerts a favorable influence upon the digestibility of other
foods with which it is combined. This is doubtless due to the digestive
action of the special ferments or enzymes which milk contains. In milk
there is a soluble ferment material or enzyme which has the power of
peptonizing proteids. It is this ferment which carries on the ripening
process when cheese is cured in cold storage, and it is believed to be
this body which promotes digestion of other foods with which milk is
combined.[27]

Milk is not easily digested by some persons. The tendency to costive