GLYCOGEN SHORTAGE; SUGAR FORMATION FROM FAT - FATE OF THE CARBOHYDRATES WHEN THE SUPPLY IS INSUFFICIENT.
When the unequal conditions of a small supply and large demand of carbohydrate continue for a short time only, a few hours or days, the reserve store of glycogen is drawn upon. This, together with what is newly formed from albumin, suffices at first to meet the need of the muscles and sugar-consuming cells, but the supply is finally exhausted if such a drain on the capital continues. Consequently we find only traces of glycogen in the liver and muscle-cells of animals who have been for a considerable time underfed or altogether de prived of food and possibly doing much muscular work at the same time; but if we examine the arterial blood of such animals we find the usual proportion of grape sugar (0.12 to 0.18 per cent.), just as we should if they were fully nourished. The conclusion must be that the organism does not suspend the production of sugar, despite the deficient nutrition; neither is the consumption of sugar inter rupted, for whenever any labor is performed sugar is oxidized in the muscles. It is true that a muscle can exercise its functions of work and heat production by means of the consumption of albumin, but a simple calculation will show that the amount of albumin consumed under such circumstances is far from sufficient to cover all the work performed by the muscular system. If we take into calculation all the metabolism and force conversion in the body of men or ani mals who are doing hard work, in spite of a deficient ingestion of carbohydrates or of a generally insufficient diet, we shall constantly arrive at the same result, viz., that there must be consumed in their
muscles a certain quantity of non-nitrogenous substances which can come neither from the reserve supply of glycogen nor from the disin tegrated albuminoids, since these two sources together are insuffi cient to cover the force conversion. The only substance which can meet this deficit is fat. Notwithstanding the great number of in vestigations directed to this end we do not know at all whether the muscle is able itself to seize upon the fat molecule; but, on the other hand, we do know that during strong muscular action much fat is con sumed in the body, a part of this fat being derived from the food and a part coming from the adipose tissue of the organism. We must, therefore, conclude that the fat, before it reaches the muscle, is con verted into a form adapted to the purpose which it is to serve. That this form is sugar is shown by the constancy of the blood sugar.
We may also affirm with considerable certainty that the liver is the place where the fat is converted into sugar, when need therefor arises, that is to say, iu cases in which neither the carbohydrates nor the albuminates suffice to maintain the proportion of sugar in the outfiowing blood at the normal height.
I regard the facultative formation of grape sugar from fat as an absolutely certain fact; I denominate the process " facultative" be cause it appears to take place only when the supply of carbohydrates is insufficient for the needs of the organism.