228 ELEMENTS OF PHYSIOLOGY 



you will understand the circulation in the entire liver, for 

 a lobule is the liver in miniature. Represent a lobule by 

 a wagon wheel. The rim corresponds to the capillaries 

 of the portal vein and hepatic artery circulating around the 

 lobule. The spokes correspond to the two kinds of cap- 

 illaries united and on the way to the hepatic vein in the 



hub, which will take the blood 

 away from the liver. Between 

 the spokes are located the hard- 

 working liver cells which get 

 oxygen and food from the capil- 

 laries in the spokes, and relieve 

 themselves of impurities by 

 means of the finest bile ducts 

 and lymphatic ducts, which be- 

 gin among the cells (Fig. 181). 

 What are the two large vessels 

 which bring material to the liver ? 



FIG. !8o.- Microscope, high power. Wfa t ^ t j vessels 



Diagram of a Portion of a Lobule 



of the Liver, showing the Blood ( besides the lymphatics) which 

 wi e t S h S ^uid nd BilC DUCtS inJ6Cted take material out of the liver? 



A, branch of portal vein sending capil- ^' Th * LivCT RS & Storeroom. 



larics to open into E, a branch of the If a frOg be dug Up in the first 



hepatic vein which lies in the middle . 



of the lobule; B, a lymphatic; C, part of its Winter sleep, and itS 



Wver be examined under the 

 microscope, the cells will be 

 found swollen and full of gly- 



cogen, a substance stored up for the winter needs of the 

 frog. It is a carbohydrate material resembling starch and 

 made from digested sugar. The liver cells of a frog which 

 has just come out in the spring will be found shrunken and 

 containing no glycogen (Fig. 182). If a starving rabbit be 

 killed and its liver cells examined, no glycogen will be 

 found, but the liver cells of a rabbit which has recently 

 been fed on turnips will be full of glycogen. If two 



