uscular work and heat, it is evident that material for the
production of this energy must be taken in the food. The carbohydrates
constitute the bulk of our ordinary food.

104. Fats and Oils. These include not only the ordinary fats of
meat, but many animal and vegetable oils. They are alike in
chemical composition, consisting of carbon and hydrogen, with a little
oxygen and no nitrogen. The principal kinds of fat used as food are the
fat of meat, butter, suet, and lard; but in many parts of the world
various vegetable oils are largely used, as the olive, palm, cotton seed,
cocoanut, and almond.

The use of the fats in the body is essentially the same as that of the
starches and sugars. Weight for weight they are more valuable than the
carbohydrates as sources of energy, but the latter are more easily
digested, and more easily oxidized in the body. An important use of fatty
foods is for the maintenance of the bodily heat. The inhabitants of Arctic
regions are thus enabled, by large use of the fat and oil from the animals
they devour, to endure safely the severe cold. Then there is reason to
believe that fat helps the digestion of other foods, for it is found that
the body is better nourished when the fats are used as food. When more fat
is consumed than is required to keep up the bodily heat and to yield
working power, the excess is stored up in various parts of the body,
making a sort of reserve fuel, which may be drawn upon at any future time.

105. Saline or Mineral Foods. All food contains, besides the
substances having potential energy, as described, certain saline
matters. Water and salts are not usually considered foods, but the results
of scientific research, as well as the experience of life, show that these
substances are absolutely necessary to the body. The principal mineral
foods are salt, lime, iron, magnesia, phosphorus, potash, and water.
Except common salt and water, these substances are usually taken only in
combination with other foods.

These saline matters are essential to health, and when not present in due
proportion nutrition is disturbed. If a dog be fed on food freed from all
salines, but otherwise containing proper nutrients, he soon suffers from
weakness, after a time amounting to paralysis, and often dies in
convulsions.

About 200 grains of common salt are required daily by an adult, but a
large proportion of this is in our food. Phosphate of lime is obtained
from milk and meats, and