ABSORPTION AND ASSIMILATION OF FOODSTUFFS 147 



When needed, the glycogen in the liver is again trans- 

 formed into dextrose which is carried out by the venous 

 blood to the tissues. At this time the per cent of sugar in 

 the blood of the hepatic vein is greater than that in the 

 arterial blood or blood from the portal vein. Both the for- 

 mation of glycogen and its reconversion into sugar are 

 brought about by the liver cells. 



Carbohydrates in the form of glycogen are also stored up 

 in the muscles, and are used up when needed, e.g. during 

 muscular activity. The muscle-glycogen is supposed not to 

 be identical with that formed in the liver. At all events the 

 glycogen of the muscles is not derived as such from the 

 liver. 



When the carbohydrates in the food are present in excess, 

 the body, by reduction and synthesis, forms fat from them 

 and thus stores them up. 



In diabetes mellitus the glycogenic function of the liver 

 is disturbed. This causes sugar to accumulate in the blood 

 to such an extent that it is excreted by the kidneys. We 

 can discriminate between two forms of diabetes, a mild form, 

 in which sugar appears in the urine only when carbohydrates 

 are eaten, and a severe form, in which sugar is excreted even 

 if no carbohydrates are eaten. In the latter case the sugar 

 is derived from the proteids. Nothing is positively known 

 concerning the immediate cause of diabetes. Artificial 

 diabetes may be produced : 



1 . By the so-called diabetic puncture (Piqure) whereby a 

 part of the medulla at the lower end of the calamus scrip- 

 torius is destroyed. This seems to prove that the glycogenic 

 function of the liver is dependent upon the central nervous 

 system. 



2. By extirpation of the pancreas (see Chapter XI). 



3. By various poisons: phloridzin, curare, phosphorus, 

 corrosive sublimate. 



The amido-acids (leucine, tyrosin, etc. ) formed from the hemi- 

 peptones by pancreatic digestion are also absorbed, and in the liver 

 they are changed to urea. 



