334 DIGESTION. 



glucose when in contact with any animal ferment. This 

 substance has received the different names of glycogen, 

 glycogenic substance, animal starch, hepatin. 



Glycogen (C, 2 Hj O 1 ) is obtained by taking a portion 

 of liver from a recently killed animal, 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. 



When purified, glycogen is a white, amorphous, starch- 

 like substance, odourless and tasteless, soluble in water, 

 but insoluble 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 

 destination of glycogen. (i.) 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 prevented 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 th& 

 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 after- 

 wards its tissue speedily becomes saccharine, unless the 

 formation of sugar be prevented by freezing, boiling, or 



