288 HANDBOOK OF PHYSIOLOGY. 



Average quantity of Glycogen found in the Liver of Rabbits after Fast- 

 ing, and after a diet of Starch and Sugar respectively. 



Average Amount of Glycogen in Liver. 



After fasting for three days, . . . Practically absent. 

 " diet of starch and grape-sugar, . 15.4 per cent. 

 " " cane-sugar, . . . 16.9 " 



Regarding these facts there is no dispute. All are agreed that gly- 

 cogen is formed, and laid up in store, temporarily, by the liver-cells; and 

 that it is not formed exclusively from saccharine and amylaceous foods, 

 but from albuminous substances also; the albumen, in the latter case, 

 being probably split np into glycogen, which is temporarily stored in the 

 liver, and urea, which is excreted by the kidneys. 



Destination of Glycogen. There are two chief theories on the subject 

 of the destination of glycogen. (1.) That the conversion of glycogen 

 into sugar takes place rapidly during life by the agency of a ferment 

 (liver diastase) also formed in the liver: and the sugar is conveyed away 

 by the blood of the hepatic veins, and soon undergoes combustion. (2.) 

 That the conversion into sugar only occurs after death, and that during 

 life no sugar exists in healthy livers; glycogen not undergoing this trans- 

 formation. The chief arguments advanced in support of this view are, 

 (a) that scarcely a trace of sugar is found in blood drawn during life 

 from the right ventricle, or in blood collected from the right side of the 

 heart immediately after an animal has been killed; while if the examina- 

 tion be delayed for a very short time after death, sugar in abundance 

 may be found in such blood; (#), that the liver, like the venous blood in 

 the heart, is, at the moment of death, completely free from sugar, al- 

 though afterwards its tissue speedily becomes saccharine, unless the 

 formation of sugar be prevented by freezing, boiling, or other means 

 calculated to interfere with the action of a ferment on the amyloid sub- 

 stance of the organ. Instead of adopting Bernard's view, that normally, 

 during life, glycogen passes as sugar into the hepatic venous blood, and 

 thereby is conveyed to the lungs to be further disposed of, Pavy inclines 

 to the belief that it may represent an intermediate stage in the formation 

 of fat from materials absorbed from the alimentary canal. 



Liver-Sugar. To demonstrate the presence of sugar in the liver, a 

 portion of this organ, after being cut into small pieces, is bruised in a 

 mortar to a pulp with a small quantity of water, and the pulp is boiled 

 with sodium-sulphate in order to precipitate albuminous and coloring 

 matters. The decoction is then filtered and may be tested for glucose. 



Glycogen (C 6 H 10 6 ) is an amorphous, starch-like substance, odorless 

 and tasteless, soluble in water, insoluble in alcohol. It is converted into 

 glucose by boiling with dilute acids, or by contact with any animal fer- 

 ment. It may be obtained by taking a portion of liver from a recently 

 killed rabbit, and after cutting it into small pieces, placing it for a short 

 time in boiling water. It is then bruised in a mortar, until it forms a 



