234 UNCONSCIOUS NERVOUS OPERATIONS 



portal vein has first circulated through the stomach, the 

 spleen, and the intestines (Fig. 95, p. 165), and has been 

 deprived of most of its oxygen. The supply of arterial 

 blood through the hepatic artery is relatively small. 



335. Functions of the Liver. One of the functions of 

 the liver is to store up sugar, or, rather, to form from the 

 sugar brought by the portal vein a substance called gly- 

 cogen, which is readily converted again into sugar. The 

 protoplasm of the hepatic cells possesses the power of 

 manufacturing glycogen from carbohydrates and of stor- 

 ing it up. This is effected by means of a ferment found 

 in the liver ; but what is the part played by glycogen in 

 the animal economy is not fully determined. Glycogen 

 is turned into sugar again and supplied by the liver to 

 the blood as it is needed. There is always sugar in the 

 blood, but more than a small amount seems undesirable. 

 There is much evidence that another function of the liver 

 is to act upon the nitrogenous foods in some manner 

 resulting in the production of the waste substance, urea, 

 which is eliminated by means of the kidneys. A third 

 and the most familiar office of the liver is the formation 

 of bile. This is stored in the gall bladder, lying between 

 the two lobes on the under side of the gland (Fig. 116). 

 Still another function of the liver is to protect the system 

 from the action of poisons produced by the processes of 

 digestion or by defective digestion. These are arrested or 

 transformed when they reach the liver. 



336. The Bile is secreted from the portal blood as a yel- 

 lowish, reddish brown, or green fluid, according to the pre- 

 ponderance of different coloring matters which are formed 

 by the liver out of the hemoglobin of the red blood cor- 

 puscles. It is alkaline and is thought to have antiseptic 

 properties. Bile is a poison, and in one person enough is 



