268 DIGESTION. 



in alcohol. It is converted into glucose by boiling with dilute 

 acids, or by contact with any animal ferment. 



There are two chief theories concerning the immediate desti- 

 nation of glycogen. (1.) According to Bernard and most other 

 physiologists, its conversion into sugar takes place rapidly 

 during life, and the sugar is conveyed away by the blood of 

 the hepatic veins to be consumed in respiration at the lungs. 

 (2.) Pavy and others believe that the conversion into sugar 

 only occurs after death, and that during life no sugar exists in 

 healthy livers, the amyloid substance or glycogen being pre- 

 vented by some force from undergoing the transformation. 

 The chief arguments advanced by Pavy in support of this view 

 are, first, 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 suddenly deprived of life, while if the examination be 

 delayed for a little while after death, sugar in abundance may 

 be found in such blood ; secondly, that the liver, like the 

 venous,blood in the heart, is, at the moment of death, almost 

 completely free from sugar, although 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 substance 

 of the organ. Instead of adopting Bernard's view, that nor- 

 mally, 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 believe that it may repre- 

 sent an intermediate stage in the formation of fat from ma- 

 terials absorbed from the alimentary canal. 



For the present we must remain uncertain as to which of 

 these theories contains most truth in it. 



Whatever be the destination of this peculiar amyloid sub- 

 stance formed at the liver, most recent observers agree that it 

 is formed at, and exists within, the hepatic cells, from which it 

 may be extracted by the process just described. 



Much doubt exists also respecting the mode in which gly- 

 cogen is formed in the liver, and the materials which furnish 

 its source. Since its quantity is increased after feeding, espe- 

 cially on substances containing much sugar or starch, it is 

 probable that part of it is derived from saccharine principles 

 absorbed from the digestive canal ; but since its formation con- 

 tinues even when there is no starch or sugar in the food, the 

 albuminous or fatty principles also have been thought capable 

 of furnishing part of it. Numerous experiments, however, 

 having proved that the liver continues to form sugar in animals 

 after prolonged starvation, and during hibernation, and even 



