myosin. Gluten exists largely in the cereals wheat,
barley, oats, and rye. The proteid principle of peas and beans is legumin,
a substance resembling casein.

As the name implies, the proteids, or nitrogenous foods, contain nitrogen;
carbohydrates and fats, on the contrary, do not contain nitrogen. The
principal proteid food-stuffs are milk, eggs, flesh foods of all kinds,
fish, and the cereals among vegetable foods. Peas and beans are rich in
proteids. The essential use of the proteids to the tissues is to supply
the material from which the new proteid tissue is made or the old proteid
tissue is repaired. They are also valuable as sources of energy to the
body. Now, as the proteid part of its molecule is the most important
constituent of living matter, it is evident that proteid food is an
absolute necessity. If our diet contained no proteids, the tissues of
the body would gradually waste away, and death from starvation would
result. All the food-stuffs are necessary in one way or another to the
preservation of perfect health, but proteids, together with a certain
proportion of water and inorganic salts, are absolutely necessary for the
bare maintenance of animal life--that is, for the formation and
preservation of living protoplasm.

103. Starches and Sugars. The starches, sugars, and gums, also known
as carbohydrates, enter largely into the composition of foods of
vegetable origin. They contain no nitrogen, but the three elements,
carbon, hydrogen, and oxygen, the last two in the same proportion as in
water. The starches are widely distributed throughout the vegetable
kingdom. They are abundant in potatoes and the cereals, and in arrowroot,
rice, sago, and tapioca. Starch probably stands first in importance among
the various vegetable foods.

The sugars are also widely distributed substances, and include the
cane, grape, malt, maple, and milk sugars. Here also belong the gums and
cellulose found in fruit, cereals, and all vegetables which form the
basis of the plant cells and fibers. Honey, molasses, and manna are
included in this class.

The physiological value of the starches and sugars lies in the fact that
they are oxidized in the body, and a certain amount of energy is thereby
liberated. The energy of muscular work and of the heat of the body comes
largely from the oxidation, or destruction, of this class of foods. Now,
inasmuch as we are continually giving off energy from the body, chiefly in
the form of m