We may reasonably suppose that the reserve of proteid present in the body is contained in the fluid media, and not as a part of the living protoplasm. Further, we are apparently justified in the belief that the sole form of proteid katabolism which is vitally important for the welfare of the body is the endogenous katabolism. This must be provided for adequately and indeed liberally, and in addition there should be sufficient intake to keep up an abundant supply of reserve proteid, but beyond these necessities there would seem to be no legitimate demand for additional proteid. The voluminous exogenous proteid katabolism so conspicuous in most individuals would seem to have no justification in fact, or in physiological reasoning. What good, for example, can be accomplished by this constant splitting off of nitrogen, with its subsequent speedy removal from the body? The organism can neither use it nor store it up, and why therefore should this daily burden of an excessive and accelerated proteid katabolism be borne? As we have seen, the energy of muscle work is derived mainly, and can come wholly, from the breaking down of non-nitrogenous materials, fats and carbohydrates. The very fact that an intake of say 120 grams of proteid is followed at once by the removal of the larger part of the contained nitrogen, as a result of the exogenous katabolism of the body, would seemingly warrant the view that the proteid so decomposed might advantageously be replaced by a corresponding amount of carbohydrate. In muscle work, as in heat production, carbohydrate and fat are the materials burned up, or oxidized. Proteid, on the other hand, is not so oxidized, at least not the nitrogen-containing portion of the molecule.