284 HISTOLOGY 



evidence that the hepatic cells at the periphery of the lobule are better 

 nourished than those in its interior. 



The recognition of the lobules above described, as the essential basis 

 of hepatic structure, would have been unquestioned except that, as Kier- 

 nan stated, " the essential part of the gland is undoubtedly its duct; vessels 

 it possesses in common with every other organ; and it may be thought that 

 in the above description too much importance is attached to the hepatic 

 veins." If the liver were divided into lobules comparable with those of 

 other glands, the portal canals with their ducts and adjacent afferent ves- 

 sels would be the axial structures, and the efferent central veins would be 

 peripheral. By connecting the five central veins around the portal canal 

 in Fig. 277 (two of the central veins are not labelled and the one at the 

 lower edge of the figure is indistinct) , such a structural unit or secretory unit 

 would be marked out. It has been proposed to call it a portal lobule (from 

 its axial structure), in contrast with the hepatic lobules, which surround the 

 branches of the hepatic vein. In the seal it is said that the portal lobules, 

 or units, are bounded by connective tissue, but this must be regarded as 

 very exceptional. However, in attempting to picture the complex rela- 

 tions of the lobules in the liver, the morphologist must regard the portal 

 canals as axial, even though the term lobule is used for areas surrounding 

 the central veins. The bile flows from parts of several hepatic lobules 

 into a single portal canal. 



Parenchyma. The parenchyma or essential tissue of the liver is found 

 in the anastomosing trabeculae of the lobules. The general arrangement 

 of the cells in these trabeculae is shown in Fig. 280, in which, however, 

 the slender lumens are rendered conspicuous by special treatment. These 

 lumens, or bile capillaries, are ordinarily inconspicuous, and the trabeculae 

 appear on superficial examination as solid cords of cuboidal cells, with 

 abundant granular protoplasm and large round central nuclei. Often 

 the hepatic cells contain two nuclei, and large cells with several nuclei, 

 produced by amitosis, have been reported. The general characteristics 

 of hepatic cells are shown in Fig. 281. They are arranged chiefly in double 

 rows which in certain positions appear single. 



The hepatic cells have very delicate cell membranes, which are some- 

 times |aid to be absent. Their protoplasm often contains brown pigment, 

 especially toward the central vein. Near the periphery of the lobule the 

 cells may contain fat vacuoles of varying size, found normally in well- 

 nourished individuals. Pathologically the vacuoles may be large and 

 widely distributed. Glycogen (p. 78) occurs in granules and larger 

 masses, especially after abundant meals. In the fasting condition, the 

 cells are relatively small, dark, and obscurely outlined, but during diges- 

 tion they become larger with a clearer central part and a peripheral zone 

 of coarse granules. In man both conditions may be found in one liver. 



