282 HAND-BOOK OF PHYSIOLOGY. 



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

 gen 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 up into glycogeii, 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 sub- 

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

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

 sion into sugar only occurs after death, and that during life no sugar 

 exists in healthy livers; glycogen not undergoing this transformation. 

 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 im- 

 mediately after an animal has been killed; while if the examination be 

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

 found in such blood; (b), that the liver, like the venous blood in the 

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

 afterward its tissue speedily becomes saccharine, unless the formation of 

 sugar be prevented by freezing, boiling, or other means calculated to in- 

 terfere with the action of a ferment on the amyloid substance 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 and Glycogen. 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 (p. 230). 



Glycogen (c 6 H 10 o & ) is an amorphous, starch-like substance, odorless and 

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

 cose by boiling with dilute acids, or by contact with any animal ferment. 

 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 pulpy 

 mass, and subsequently boiled in distilled water for about a quarter of an 

 hour. The glycogen is precipitated from the filtered decoction by the 

 addition of alcohol. Glycogen has been found in many other structures 

 than the liver. (See Appendix.) 



