METABOLISM OF CARBO-HYDRATES GLYCOGEN 539 



usually the hepatic glycogen makes up considerably less than half 

 the total glycogen of the body. That the muscles do not derive 

 their glycogen by the migration of hepatic glycogen, but can them- 

 selves form it from dextrose, has been shown by injecting that sugar 

 subcutaneously into frogs after excision of the liver. The muscle 

 glycogen was found to be increased. 



Function and Fate of the Glycogen. The glycogen store of the 

 liver fulfils a different function from that of the muscles. This is 

 indicated by the fact that when dogs, after being put on a given diet 

 for two or three days, are starved for a time, and then put again on 

 the original diet, the hepatic and the muscular glycogen behave 

 differently at first during the period of re-alimentation. While 

 glycogen accumulates in the liver in greater quantity than under 

 normal conditions of nutrition, in the muscles it at first accumulates 

 much less rapidly than normally. This is entirely in accordance 

 with the view that the hepatic glycogen store has for its great func- 

 tion the regulation of the sugar content of the blood in the interest 

 of all the tissues, while the glycogen store of the muscles and other 

 tissues is mainly in the interest of their own nutrition and a source 

 of energy for their own work. This does not imply that, when sugar 

 is being absorbed in quantities too great for the liver to deal with 

 after the current needs of the tissues have been satisfied, they do 

 not add to their glycogen reserves. There is every reason to suppose 

 that they do so, and thus act as a subsidiary regulating mechanism, 

 although a less elastic one than that supplied by the liver. A third 

 way in which a portion of the surplus sugar can be stored is in the 

 form of fat. 



When a fasting dog is made to do severe muscular work, the 

 greater part of the glycogen soon disappears from its liver. When 

 a dog is starved, but allowed to remain at rest, the glycogen still 

 markedly diminishes, although it takes a longer time; and at a 

 period when there is still plenty of fat in the body, there may be 

 only a trace of hepatic glycogen left. The glycogen which is usually 

 contained in the skeletal muscles also diminishes very rapidly in the 

 first days of hunger, but the heart contains the normal amount of 

 glycogen at a time when the proportion in the skeletal muscles has 

 sunk to Jfr to -$ of the normal. 



These facts have been taken to indicate that glycogen and the sugar 

 formed from it are the readiest resources of the starving and working 

 organism, for the transformation of chemical energy into heat and 

 mechanical work. To borrow a financial simile, the fat of the body 

 has sometimes been compared to a good, but rather inactive security, 

 which can only be gradually realized; its organ-proteins to long-date 

 bills, which will be discounted sparingly and almost with a grudge; 

 its glycogen, its carbo-hydrate reserves, to consols, which can be turned 

 into money at an hour's warning. Glycogen, on this view, is especiallj 



