The liver ordinarily turns glycogen back into sugar at just the rate necessary to keep the amount in the blood constant. This means that when functional metabolism is going on glycogen is being turned into sugar more rapidly than when the body is quiet. One of the very interesting discoveries of recent years is that in times of strong excitement leading to the outpouring of adrenalin into the blood the rate of change of glycogen into sugar is much increased, so that instead of the usual small amount there is present in the blood a large concentration of sugar. This is evidently advantageous in insuring ample fuel supplies to the muscles at the time of an emergency. It is wasteful in that a large part of the surplus sugar is passed out by the kidneys. The fact is illustrated that in marshaling the bodily functions for meeting an emergency economy is lost sight of. In addition to these healthy conditions in which sugar may appear in the urine there is the disease diabetes, in which the presence of sugar in the urine is a conspicuous symptom. In diabetes there is a serious disturbance of the whole fuel-supplying mechanism; the liver does not carry on its function of changing sugar to glycogen and glycogen back to sugar as perfectly as it should, and what is of much more importance the muscles which are the chief users of sugar as fuel cannot use sugar in anything like their usual manner. In fact in severe cases they appear to be almost wholly unable to use sugar as fuel. Since the protein from which the nitrogen has been removed classes itself with sugar in this regard, the muscles are thrown back upon fat as their only source of fuel, and this confronts the body with the danger already mentioned that in the burning of fat when little or no sugar is being burned along with it very poisonous products may be formed. Medical investigators have devoted a vast amount of labor to the attempts to find a diet that can be successfully eaten by diabetics. Starches and, almost equally, proteins are not serviceable because they simply flood the tissues with sugar, making an environment which is not good for the cells, and keeping the kidneys busy getting rid of the surplus. Fats are dangerous for the reason just stated. Quite recently real progress has been made by means of the discovery that when the body is living on its own tissue there will be no accumulation of sugar in the body fluids nor outpouring of it from the kidneys. One who is being starved is living on his own tissues and so by simply starving a diabetic his symptoms can be relieved. This is not in itself a very promising expedient, since evidently without food one cannot go on living very long. The point of the treatment is that after starvation has proceeded until the body is actually living on its own tissue it is possible to begin feeding proteins cautiously until little by little a protein diet can be established in which there is little or no indication of surplus sugar.