SECRETION. 



445 



from the hepatic artery and from the portal vein, and in this respect differs 

 from all other glands in the body. The epithelial structures of the liver are 

 inclosed by a firm fibrous membrane, known as Glisson's capsule. At the 

 transverse fissure it invests and follows the blood-vessels, which there enter, 

 in all their ramifications through the gland. 



Structure of the Liver. The liver is composed of an enormous num- 

 ber of small masses, rounded, ovoid, or polygonal in shape, called lobules, 

 measuring about one millimeter in diameter and separated from one another 

 by a narrow space in which are to be found blood-vessels, lymphatics, and 

 hepatic ducts, supported by connective tissue. In the pig this space and its 

 contained elements is quite distinct, sharply marking out the border of 

 the lobule (Fig. 207). This is not so ap- 

 parent in man. Each lobule is made up S&tftii&ZP^ ^Trabecuiae of 

 of irregular or polygonal shaped cells 

 measuring about 30 to 40 micromilli- 

 meters in diameter. These cells are ar- 

 ranged in a radial manner from the center to 



XTrabeculae of 

 hepatic cells. 



Central vein. 



Interlobular vein. Hepatic duct. 



FIG. 208. SCHEME or A HEPATIC 

 LOBULE, REPRESENTED IN TRANSVERSE 

 SECTION BELOW AND, BY PARTIAL LEV- 

 FIG. 207. SECTION OF LIVER OF PIG, SHOWING ELING, IN LONGITUDINAL SECTION 

 VERY DIAGRAMMATIC ALLY THE LOBULES, a. Interlobu- ABOVE. In the left half the blood- 

 lar connective tissue. b,c. Branches of portal vein vessels are drawn; in the right half 

 and of hepatic artery, d. Bile- ducts, e. Intralobular only the cords of hepatic cells. X 20. 

 vein. (Piersol.) (Stohr.) 



the circumference of the lobule (Fig. 208). Each cell possesses ome and 

 at times two nuclei. There is no evidence for the existence of a distinct 

 cell-wall. The cell protoplasm frequently contains globules of fat, gran- 

 ules of a protein nature, granules of glycogen, pigment material, etc. 

 The appearance presented by the cell will vary considerably, according 

 to the time it is observed. Thus there may be a complete absence of these 

 constituents, when the cell may present a series of vacuoles separated by 

 bands of protoplasm. The cells are the secreting structures of the liver, 

 and hence are in close relation to capillary blood-vessels, lymphatic spaces, 

 nerves, and irregular channels or passageways. The latter running between 

 the epithelial cells may be compared to the lumen of other secreting glands. 

 Blood-vessels and Their Distribution. The blood-vessels which are 

 in relation with the liver are: 



