We have very convincing proof that the carbohydrate glycogen can be formed from proteid. Thus, the feeding of proteid to warm-blooded animals may be accompanied by an accumulation of glycogen in the liver.This is interpreted as meaning that in the cleavage of proteid, by djgy-tion the various nitrogenous products formed are somewhere, probably in the liver, still further acted upon; the contained nitrogen with some of the carbon being converted into urea, while the non-nitrogenous residue is transformed into glycogen, or sugar. That some such change takes place, or, more specifically, that carbohydrate does result from proteid is more strikingly shown in human beings suffering with diabetes.. In severe forms of this disease, all carbohydrate food consumed is rapidly eliminated through the kidneys in the form of sugar, the body having lost the power of burning sugar. If such a person is placed upon a diet composed exclusively of proteid, sugar still continues to be excreted, and there is observed a certain definite relationship between the nitrogen output and the excretion of sugar, thus implying that they have a common origin.

Further, there are certain drugs, such as phloridzin which, when introduced into the circulation, set up a severe diabetes and glycosuria. Dogs treated in this way, fed solely on proteid or even starved for some time, will continue to excrete sugar, and as in the previous instance, there is observed a certain definite ratio between the nitrogen output and the elimination of sugar; thus leading to the conclusion that both arise from the destruction of the proteid molecule. Careful study of this ratio of dextrose to nitrogen has led Lusk to the conclusion that full 58_ per cent of the proteid may undergo conversion into sugar in the body. Hence, it is easy to see how in muscle work, when proteid is the sole source of the energy of muscular contraction, the work accomplished may still result from the direct oxidation of carbohydrate material, indirectly derived from the proteid. molecule. It requires no argument, however, to convince one that such a procedure for the normal individual is less economical physiologically than a direct utilization of carbohydrate and fat, introduced as such and duly incorporated with the muscle substance. Consequent!y, in the nourishment of the body for vigorous muscular work, there is reason in a diet which shall provide an abundance of carbohydrate and fat; proteid being added thereto only in amounts sufficient to meet the ordinary requirements of the body for nitrogen and to furnish, it may be, proper pabulum for the development of fresh muscle fibres, where, as in training, effort is being made to strengthen the muscle tissue and so enable it to do more work. Increase in proteid food may help to make new tissue, but the source of the energy of muscle work is to be found majflbjf in the breaking down of the non-nitrogeoons materials, oarboby-drate and fat.

In view of these facts, we may advantageously consider next the real significance of the proteid metabolism of the body. As we have seen, a meal rich in proteid leads at once - within a few hours - to an excretion of urea equivalent to full 50 per cent of the nitrogen of the ingested proteid, while a few hours later finds practically all of the nitrogen of the intake eliminated from the body. Further, it Is to lie remembered that in a general way this occurs no matter what the condition of the body may be at the time and no mutter how large or small the amount of proteid consumed. In other words, there is practically no appreciable storing of nitrogen or proteid for future needs, - at least none that is proportional to the increase in nitrogen intake, even though the body be in a condition approximating to nitrogen starvation. Moreover, it is to be recalled that the increased proteid metabolism attendant on increased intake of proteid food is accompanied by an acceleration of the metabolism of non-ntrogenous matter; resulting in a stirring up of tissue change, with consequent oxidation and loss of a certain proportion of accumulated fat and carbohydrate. Coincident with this increased excretion of nitrogen, the output of carbon dioxide is likewise increased somewhat, due as is believed mainly to increased metabolism of the involuntary muscle fibres of the gastro-intestinal tract, by action of which the accelerated peristalsis so characteristic of food intake is accomplished. Further, the increased output of carbon dioxide, under these conditions, is to be attributed also to the greater activity of the digestive and excretory organs, naturally stimulated to greater functional power by the presence of proteid foods and their decornposition products. Still, as stated by Leathes, "the two main end-products of proteid metabolism, urea and carbonic acid, are, to a great extent, produced independently of each other, and the reactions which result in the discharge of the nitrogen are not those in which energy is set free, work done, and carbonic acid produced." In other words, there is suggested what we have already referred to, viz., that in proteid metabolism it nitrogenous portion of the proteid molecule is quickly split off and gotten rid of, while the non-nitrogenous part may be reserved for future oxidation, serving as a source of muscle energy or for other purposes. This being so, it is plain that "proteid metabolism in so far as it is concerned with the evolution of energy, proteid metabolism in its exothermic stages, may be almost entirely non-nitrogenous metabolism" (Leathes).

Is there any advantage to the body, however, in this carbonaceous residue of the proteid molecule over simple carbohydrate and fat? Can the processes of the body be accomplished more economically, or more advantageously, with a daily diet so constructed that the tissues and organs must depend mainly upon this carbon moiety of the proteid molecule for their energy yielding material? It has been one of the physiological dogmas of the past, that the tissues and organs of the Holly, or father then constituent cells,^referre!l to use proteid for all their needs whenever it was available. If proteid were wanting, either because of insufficient intake, or because of excessive activity, then the tissue cells would draw upon their store of non-nitrogenous material. Food proteid and tissue proteid, however, were the materials preferred by the organism, so ran the argument, and the large and incessant output of nitrogen which accompanied the intake of proteid was aceepted as proof of the general truth of this idea. We might well question wherein lies the great advantage to the body in this continual excretion of nitrogen; whether the loss of energy in handling and removing the nitrogenous portion of the necessarily large proteid intake, in order to render available the non-nitrogenous part of the molecule, might not more than compensate for the supposed gain? But the truly astonishing fact that the output of nitrogen runs parallel with the intake of proteid, that the body canuot store up nitrogen to any large extent, has been taken as conclusive evidence that the organism prefers to use proteid for all of its requirements. Truly, we might just as well argue that this significant rise in the excretion of nitrogen after partaking of a proteid meal is an indication that the body has no need of this excess of nitrogen; that it is indeed a possible source of danger, since the system Btrives vigorously to rid itself of the surplus, and that the energy-needs of the body can be much more advantageously and economically met from fat and carbohydrate than from the carbonaceous residue resulting from the disruption of the proteid molecule.