184 INTERMEDIATE METABOLISM 



Carbohydrate Storage — Glycogen 



Our knowledge of this subject dates from the epoch- 

 making researches of Claude Bernard (1855-1859). Bernard 

 first showed that the blood in the hepatic vein contained 

 sugar even after a flesh diet. This proved that the hver 

 had the power of forming sugar. He then showed that 

 when the liver was excised from a well-fed animal, the 

 blood washed out and the organ rapidly plunged into 

 boihng water so as to prevent any post-mortem change, 

 there could be extracted from it a carbohydrate to which 

 he gave the name of glycogen. If, however, he allowed 

 the excised hver to remain at blood-temperature sugar 

 began to form within it, and the glycogen at the same 

 time diminished. Bernard behevecl that the intercon ver- 

 sion of glycogen and glucose took place in both directions 

 during life, and he was led to regard glucose as an internal 

 secretion of the liver. 



Glycogen is found, though not to the same extent as in 

 the liver, in almost every tissue, chiefly in skeletal and 

 cardiac muscle. 



Glycogen is therefore the form in which carbohydrate 

 storage occurs. 



The Regulation of Carbohydrate Metabolism 



We now have to consider the mechanism whereby the 

 constancy of the blood-sugar is maintained although the rate 

 of absorption and the rate of utilisation are independent of 

 one another. It is clear that disturbance of this mechanism 

 in the direction of hyperglycsemia, \vith coincident glycosuria, 

 can be brought about in one of three possible ways. First, 

 there may be a failure to convert ingested sugar into 

 glycogen ; secondly, there may be an abnormal flooding 

 of the blood with sugar derived from glycogen ; thirdly, the 

 tissues may have lost the power of metabolising glucose. 



We shall now discuss the conditions under wliich hyper- 

 glycaemia occurs, indicating as far as possible which of 

 these three metabohc faults is responsible. 



