METABOLISM. 363 



SECTION VI. ' 

 THE LIVER. 



The liver consists of an enormous number of lobules, each having 

 a diameter of about 1 mm. ; they are roughly pear-shaped, and show 

 facets on the surface from mutual compression of adjacent lobules. 

 The stalk of the pear is the point of emergence of a vein, the intra- 

 lobular vein, which occupies the centre of a transverse section of the 

 lobule. The substance of the lobule is composed of columns of cells, 

 arranged radially in relation to the intralobular vein. The lobule is 

 surrounded in the pig's liver by a well-marked capsule of connective 

 tissue, containing interlobular veins as well as branches of the hepatic 

 artery and the smaller bile ducts. The connective-tissue capsule is 

 continuous with a sheath containing the portal vein, hepatic artery, and 

 bile duct, which enters at the hilum of the liver and is known as 

 Glisson's capsule. This sheath with the contained vessels is called the 

 portal tract. The interlobular veins are branches of the portal vein, 

 and the blood passes from them to the intralobular vein in each lobule 

 through sinusoids, which lie between the columns of liver cells. The 

 sinusoids are wider than capillaries, and their walls are incomplete. 

 The hepatic artery also opens into the sinusoids, supplying oxygenated 

 blood for the nutrition of the liver cells. The intralobular vein opens 

 into a sublobular vein, and the sublobular veins unite to form the 

 tributaries of the hepatic vein. 



A liver cell is roughly cubical in shape and contains a large spherical 

 nucleus. Its protoplasm is granular, and in the well-fed animal contains 

 accumulations of glycogen, which in the fresh or alcohol-hardened liver 

 can be stained brown with iodine. The cell contains iron in organic 

 combination, which can be demonstrated by treatment with dilute 

 hydrochloric acid and ferrocyanide of potassium a blue colour is pro- 

 duced. Small droplets of fat may also be present in the cells. Each 

 cell is penetrated by fine canaliculi which are continuous with the bile 

 capillaries, and cavities are also described which communicate with the 

 sinusoids. On the side of each cell which abuts on the adjacent cell is 

 a channel which, with the corresponding channel on the neighbouring 

 cell, forms a bile capillary. The bile capillaries form a network, the 

 contents of which flow into the small bile ducts at the periphery of the 

 lobule. The ducts are lined by cubical epithelium. 



Most of the functions of the liver have already been considered in 

 connection with digestion or metabolism, and it is only necessary at 

 this point to summarise these functions. 



