Owing to the fact that the tissues of the normal body are constructed chiefly from proteids, the metabolism of proteids or nitrogenous foods is of very great importance. When we realize the fact that muscle, blood, brain, nerves, cartilage, tendons, the various internal organs and the tougher material of the skeleton are only various forms of proteid material, and must contain their proportions of available or organic nitrogen, we can understand why nitrogenous foods form a distinct class that must be considered by themselves. Only the mineral deposits of the bones and the teeth, and the globules of fat that are deposited as a source of stored energy represent the nitrogen-free class of substances within the animal body.

Importance of proteid or nitrogenous foods.