470 METABOLISM, NUTRITION, AND DIET 



of sugar from the blood and to a decrease in its loss in the urine. In later 

 epoch making announcements from the University of Toronto laboratories 

 it was shown that glycogen was actually stored in the diabetic liver under 

 the influence of this pancreatic extract. These observations confirm the 

 hypothesis that glycogenesis in the liver and body tissues is dependent on 

 the presence of a hormone from the pancreatic gland. 



The Destination of Glycogen. The chief theories concerning the 

 use of glycogen in the organism are advanced by Bernard and by Pavy. 

 The former considers glycogen as a reserve supply of carbohydrate. When- 

 ever the glycogen of the blood is reduced below the normal level, i.e., about 

 o . i to o . 1 5 per cent. , there is a conversion of glycogen into sugar. The sugar 

 enters the blood and passes to the tissues where its oxidation is a source of 

 energy. Pavy considers glycogen to be a stage in the synthesis of carbo- 

 hydrate into fat and protein. Bernard's theory is more generally accepted. 

 It explains more satisfactorily why the sugar content of the blood is so con- 

 stant. The conversion of glycogen to sugar takes place by the action of an 

 intracellular ferment in the glycogenic cells. Such an enzyme has been iso- 

 lated for the liver. It is this enzyme that converts the liver glycogen to dex- 

 trose after death, and which is destroyed by boiling in the usual process of 

 isolating glycogen from the liver or other tissues. 



Glycemia and Glycosuria. Sugar may be present to excess not only 

 in the hepatic veins, but in the systemic blood. When such is the case, 

 the sugar is excreted by the kidneys, and appears in variable quantities in 

 the urine. This condition is known as glycosuria. 



Glycemia and glycosuria may occur in the normal animal or man 

 during the absorption of the products of digestion following a meal rich in 

 carbohydrates. The concentration of sugars in the blood occurs because 

 of the greater rate of intake than rate of glycogen storage. This leads 

 to a digestion glycemia and glycosuria. However, a more permanent 

 glycosuria may be produced experimentally. The operative removal of 

 the pancreas as related above, leads to an immediate glycemia and 

 glycosuria. This condition is known as pancreatic diabetes. In medicine 

 it forms one of the most difficult and at the same time interesting classes of 

 clinical patients. Puncture of the medulla in the region of the vaso- 

 motor center will also produce diabetes. In fact, any sharp disturbance 

 of the central nervous system may be followed by a corresponding dis- 

 turbance in sugar metabolism. The administration of drugs, such as 

 phloridzin, strychnine, glycosides, morphine, adrenalin, amyl nitrite, or 

 reduction of oxygen or excess of carbon dioxide may be followed by dis- 

 charge of glycogen from the liver store houses and by glycosuria. Some of 

 these agencies react on the central nervous system influencing either 

 hormone production or liver activity itself. Other agencies like adrenalin 

 stimulate the peripheral hepatic nervous mechanism. In any event, the 

 normal cycle of carbohydrate metabolism is upset. 



