The Digestion of Food 1 1 5 



The bile, thus prepared in the depths of the liver by the 

 liver cells, is carried away by the bile ducts, and may pass 

 directly into the intestines to mix with the food. If, how- 

 ever, digestion is not going on, the mouth of the bile duct 

 is closed, and in that case the bile is carried by the cystic 

 duct to the gall bladder. Here it remains until such time 

 as it is needed. 



X174. The Blood Supply of the Liver. We must not for- 

 get that the liver itself, being a large and important organ, 

 requires the constant nourishment of arterial blood to do 

 its work. This is furnished by the blood brought to it by 

 a great branch direct from the aorta, known as the hepatic 

 artery, minute branches of which, in the form of capillaries, 

 spread themselves around the liver lobules (Fig. 59). 



The blood, having done its work and being now laden 

 with impurities, is picked up by minute veinlets, which 

 unite again and again till they at last form one great trunk 

 called the hepatic vein. This carries the impure blood from 

 the liver, and finally empties it into the vena cava inferior, 

 one of the large veins of the body. 



After the blood brought by the portal vein to the liver 

 has been robbed of its bile-making materials, and otherwise 

 acted upon, it is collected by the veinlets that surround the 

 lobules and finds its way with other venous blood into 

 the hepatic vein. 



In brief, blood is brought to the liver and distributed 

 through its substance by two distinct channels, the 

 portal vein and the hepatic artery, but it leaves the liver by 

 one channel, the hepatic vein. 



y 175, The Highly Important Work done by the Liver. 

 ' We have thus far studied the liver only as an organ of secre- 

 tion, the work of which is to elaborate a complex fluid, called 

 bile, for future use in the process of digestion. This is, 



