146 HUMAN PHYSIOLOGY 



Cane-sugar and lactose are generally not absorbed as such, but 

 are split up into their simple sugars. Only when they are taken 

 in very large quantities are they absorbed as such into the blood, 

 but are then excreted by the kidneys. 



In the liver, the monosaccharides are changed to glycogen 

 and stored up in this form (see page 23). The object of 

 this glycogen formation is to prevent the sugar from too 

 great accumulation in the blood; for if the percentage of 

 sugar in the blood rises above a certain limit (0.2$), the 

 excess is excreted by the kidneys. 



The per cent of sugar in the portal vein during absorption 

 of carbohydrates is greater than that in arterial blood or in 

 blood from the hepatic vein. 



Glycogen can be formed from dextrose, levulose, and 

 galactose. The glycogen formed from levulose and galactose 

 is identical with that formed from dextrose. When glycogen 

 is formed from levulose and galactose, they are first changed 

 to dextrose, for in the splitting up of glycogen only dextrose 

 results. 



The amount of glycogen in the liver depends upon the 

 nutrition and upon the amount of material used up by the 

 body. After a long fast and also after severe muscular work 

 and strong cooling of the body, the liver is free from gly- 

 cogen. After a meal rich in carbohydrates the liver of a 

 rabbit contains as much as \j<f> glycogen. In the liver of a 

 criminal executed shortly after a meal, 6f c glycogen was 

 found. A liver free from glycogen is small and has a dark 

 brown color, while the liver rich in glycogen is large and 

 has an ochre color. A liver rich in glycogen may weigh 

 three times as heavy as one poor in glycogen ; this is not 

 only due to the larger amount of glycogen, but also to the 

 large amount of other solids and of water present. 



The glycogen is stored up in the cells in the form of flakes. It 

 can be obtained from the liver by cutting the liver into small pieces 

 and boiling in water to which a little acetic acid has been added. 

 By this the proteids are coagulated and the glycogen is dissolved, 

 forming an opalescent solution from which it may be precipitated 

 by alcohol. 



