GLYCOGENIC FUNCTION OF THE LIVER. 373 



GLYCOGENIC FUNCTION OF THE LIVER. 



Of all the organs that modify the composition of the blood as 

 it flows through them, the liver plays the most important part in 

 elaborating the circulating fluid. The elimination of the various 

 constituents of the bile, which has already been mentioned as 

 necessary for the purification of the blood, and useful in aiding 

 absorption, is probably but a secondary function of this great 

 gland. The production of a special material animal starch 

 essential to the nutrition and growth of the texture is, in all 

 probability, the main duty of the liver cells, and possibly the 

 constituents of the bile are but the by-products which must be 

 got rid of, resulting from the chemical processes of the manu- 

 facture. 



In the chapter on the digestive secretions the structure of the 

 liver was mentioned, and attention was directed to the peculiari- 

 ties of its double blood supply. A relatively small arterial twig 

 takes blood to it from the aorta, while the great portal veins dis- 

 tribute to it all that large supply of blood which flows through 

 the intestinal tract and the spleen. 



The blood in the vena porta during digestion can hardly be 

 called venous blood, for much more passes through the intestinal 

 capillaries when digestion is going on than is necessary for the 

 nutrition of the tissue of the intestinal wall. The portal blood 

 is further to be distinguished from ordinary venous blood, from 

 the fact that it has just been enriched with a quantity of the sol- 

 uble materials taken from the intestinal canal, namely, proteids, 

 sugar, salts, and probably some fats ; and it has been profoundly 

 modified by the changes taking place in the spleen. 



It is from this blood that the liver cells manufacture the starch- 

 like substance above mentioned. This substance was discovered 

 by Claude Bernard, and called by him Glycogen, on account of 

 the great facility with which it is converted into sugar in the 

 presence of certain ferments which exist in the liver itself and in 

 most tissues after death. Shortly after the death of an animal, 

 the tissue of the liver, and also the blood contained in the hepatic 

 veins, are extremely rich in sugar, which has been formed by the 

 fermentation of the hepatic glycogen. The quantity of sugar is in 



