428 A TEXTBOOK OF PHYSIOLOGY 



carbohydrates. During starvation, the glycogen content of the liver 

 falls very low; during feeding with abundant carbohydrate, the liver 

 content becomes very high e.g., 18 per cent, of the weight may be 

 glycogen. As already stated, at the height of digestion the blood 

 leaving the liver is poorer in dextrose than the blood reaching it. 

 Perfusion experiments also show that dextrose is abstracted by the 

 liver from defibrinated blood containing an excess of this sugar. 

 Levulose also gives rise to glycogen; galactose gives but little. 

 Pentoses do not appear to be direct glycogen-formers. 



Protein. Opinions differ widely as to whether glycogen arises 

 from proteins. As the result of direct feeding experiments, many 

 observers claim that feeding with proteins increases the amount of 

 glycogen in the liver, even when proteins are fed which yield no carbo- 

 hydrate group, such as caseinogen and gelatin. Other observers 

 contend that proteins are glycogen-sparers rather than glycogen- 

 formers; that, under such feeding conditions, the glycogen content 

 of the liver is increased, because dextrose is spared in the body when 

 there is an abundance of protein fed. The fact that glycogen does 

 not disappear entirely from the body even during long-continued 

 starvation would appear to indicate that proteins may serve as a 

 source of glycogen. The conversion of protein into glycogen probably 

 takes place by the deaminization of amino-acids, the non-nitrogenous 

 moiety of such acids becoming converted into dextrose, and thence 

 to glycogen. Perfusion experiments have shown that glycin, alanin, 

 asparagin, act as precursors of glycogen. It seems probable that 

 more sugar and glycogen arise from protein than is generally recognized. 



Fat. In regard to the products of the digestion of fat, there is 

 no evidence to show that glycogen arises from the fatty acids. On 

 the other hand, there is evidence to show that glycerine gives rise to 

 dextrose, and may possibly give rise to a small amount of glycogen. 



CH 2 OH CH 2 OH 



HOH + (CHOH), 



CHO 



Glycerine Dextrose 



It is possible, also, that under certain conditions fat stored in the 

 liver becomes broken down to form glycogen. Such fat, however, 

 has been previously built up in the organism from dextrose and 

 glycogen (see p. 440). 



The glycogenic function of the liver is very easily disturbed, and 

 its continual disorder results in the disease diabetes. 



The Influences affecting the Glycogenic Function (1) The Nervous 

 Influence. First and foremost come nervous influences. Puncture 

 of the floor of the fourth ventricle in the middle line in the region 

 between the originof the eighth and tenth nerves causes hyperglycsemia, 

 the disappearance of glycogen from the liver, and the appearance for 



