"Nitrogenous extractives" of flesh, _i.e._, of meats and fish.
These include kreatin and allied compounds, and are the
chief ingredients of beef tea and most meat extracts.
Amids: this term is frequently applied to the nitrogenous
non-albuminoid compounds of vegetable foods and feeding
stuffs, among which are amido acids, such as aspartic acid
and asparagin. Some of them are more or less allied in
chemical constitution to the nitrogenous extractives of
flesh.

_Fats._

Fat of meat: fat of milk; oil of corn, wheat, etc. The
ingredients of the "ether extract" of animal and vegetable
foods and feeding stuffs, which it is customary to group
together roughly as fats, include, with the true fats,
various other substances, as lecithians, and chlorophylls.

_Carbohydrates_, sugars, starches, celluloses, gums, woody fibre, etc.

_Mineral matter._

Potassium, sodium, calcium and magnesium chlorids, sulphates
and phosphates. (Atwater).

The terms (_a_) "nitrogenous" and (_b_) "carbonaceous" are frequently
used to designate the two distinct classes of food, viz.: (_a_) the
tissue builders and flesh formers; (_b_) fuel and force producers.

Each of these classes contains food material derived from both the
animal and vegetable kingdom, although the majority of the animal
substances belong to the nitrogenous, and the majority of the
vegetable substances to the carbonaceous group.

Therefore, for practical purposes, we will confine ourselves to the
more general terms used in Atwater's table.

Uses of Food.

First, food is used to form the materials of the body and repair its
waste; second, to yield energy in the form of (1) heat to keep the
body warm, (2) to provide muscular and other power for the work it has
to do. In forming the tissues and fluids of the body the food serves
for building and repair. In yielding energy, it serves as fuel for
heat and power. The principal tissue formers are the albuminoids;
these form the frame-work of the body. They build and repair the
nitrogenous materials, as those of muscle, tendon and bone, and supply
the albuminoids of blood, milk and other fluids. The chief fuel
ingredients of food are the carbohydrates and fats. These are either
consumed in the body or are stored as fat to be used as occasion
demands.

Water.

By referring to a preceding