tissues of the body, but, as has been explained, the body also requires
foods that produce energy, or working power. By far the greater part of
the total solids of food taken into the body serve this purpose, and of
these fats form a large percentage. Although fats make up such a large
proportion of the daily food supply, they enter into the body
composition to a less extent than do the food substances that have been
explained. The fats commonly used for food are of both animal and
vegetable origin, such as lard, suet, butter, cream, olive oil, nut oil,
and cottonseed oil. The ordinary cooking temperatures have comparatively
little effect on fat, except to melt it if it is solid. The higher
temperatures decompose at least some of it, and thus liberate substances
that may be irritating to the digestive tract.

17. CARBOHYDRATES.--Like fats, the food substances included in the term
carbohydrates supply the body with energy. However, fats and
carbohydrates differ in the forms in which they supply energy, the
former producing it in the most concentrated form and the latter in the
most economical form.

So that the term _carbohydrate_ may be clearly understood and firmly
fixed in the mind, it is deemed advisable to discuss briefly the
composition of the body and the food that enters it. Of course, in a
lesson on cookery, not so much attention need be given to this matter as
in a lesson on _dietetics_, which is a branch of hygiene that treats of
diet; nevertheless, it is important that every person who prepares food
for the table be familiar with the fact that the body, as well as food,
is made up of a certain number of chemical elements, of which nitrogen,
carbon, hydrogen, and oxygen form a large part. Protein owes its
importance to the fact that of the various food substances it alone
contains the element nitrogen, which is absolutely essential to the