THE LIVER 159 



bile is continuous, but is retarded during fasting, and increased 

 on taking food. 



The quantity secreted daily is from thirty to forty ounces 

 (about a pint and three-quarters). Sometimes some of this is 

 reabsorbed into the blood, owing to an obstruction in the hepatic 

 duct ; and the result of this is a disease called jaundice, charac- 

 terised by the yellow colour of the skin. 



Fig. 148. The Gall-bladder and its Vessels. 



i, right hepatic vessel ; 2, left hepatic vessel ; 3, hepatic duct ; 4, cystic duct ; 

 5, gall-bladder ; 6, common duct. 



The liver prepares another substance called giycogen, which 

 resembles starch and sugar in composition. During digestion 

 the portal vein conveys to the liver much more saccharine matter 

 than is required for immediate use in the system. A portion only 

 of this leaves the organ through the hepatic vein, while the excess 

 is converted into granules of giycogen in the cells of the lobules. 

 When digestion is over, and tne liver is no longer receiving 

 abundance of absorbed nourishment from the alimentary canal, 

 the store of giycogen recently laid by is gradually reconverted 

 into sugar, and conveyed into the venous system through the 

 hepatic vein. It thus appears that the liver performs the im- 

 portant function of regulating the supply of sugar to the system 

 by detaining a portion while it is being rapidly absorbed, and 

 giving this off slowly during fasting. The sugar thus regularly 

 supplied to the system is probably oxidised in the tissues, thus 

 helping to maintain the high temperature of the body. 



The liver also seems to have the power of arresting various 

 poisonous substances which have found their way into the blood. 

 Thus, if any metallic poisons have been taken into the stomach, 

 they reach the liver by the portal vein, and are there detained. 



