9. Each one of the phases of cookery has its importance, but if success
is to be achieved in this art, careful attention must be given to the
selection of what is to be cooked, so as to determine its value and
suitability. To insure the best selection, therefore, the housewife
should decide whether the food material she purchases will fit the needs
of the persons who are to eat it; whether the amount of labor involved
in the preparation will be too great in proportion to the results
obtained; whether the loss in preparation, that is, the proportion of
refuse to edible matter, will be sufficient to affect the cost
materially; what the approximate loss in cooking will be; whether the
food will serve to the best advantage after it is cooked; and, finally,
whether or not all who are to eat it will like it. The market price also
is a factor that cannot be disregarded, for, as has been explained, it
is important to keep within the limits of the amount that may be spent
and at the same time provide the right kind of nourishment for each
member of the family.
10. In order to select food material that will meet the requirements
just set forth, three important matters must be considered; namely, the
_substances_ of which it is composed; its measure of energy-producing
material, or what is called its _food_, or _fuel, value_; and its
_digestion_ and _absorption_. Until these are understood, the actual
cost of any article of food cannot be properly determined, although its
price at all times may be known.
However, before a study of any of these matters is entered into, it is
necessary to know just what is meant by food and what food does for the
body. As is well understood, the body requires material by which it may
be built and its tissues repaired when they are torn down by work and
exercise. In addition it requires a supply of heat to maintain it at
normal temperature and provide it with sufficient energy to do the work
required of it. The material that will accomplish these important things
is food, which may therefore be regarded as anything that, when taken
into the body, will build and repair its tissues or will furnish it with
the energy required to do its work.