THE DIGESTIVE TRACT. 



179 



FIG. 222. 



Section of centre of lobule of 

 human liver: a, intralobular 

 vein, into which the capillaries 

 (i>) converge ; c, hepatic tissue. 



the nearer complete exhaustion, the less emphasized are the granules 

 and the smaller and darker the cells. 



The meshes of the capillary net-work are usually only suffi- 

 ciently wide to accommodate a few liver-cells, in consequence of 

 which arrangement almost every hepatic ele- 

 ment is bounded directly on at least one side 

 by a capillary blood-vessel, a relation con- 

 ducive to free interchange between the blood 

 and protoplasm of the cells. With few excep- 

 tions every liver-cell exhibits a slight con- 

 cavity on one border, which denotes the 

 position of contact and impression by the 

 blood-vessels. 



In uninjected organs the hepatic tissue ap- 

 pears made up of irregular, branching, and 

 anastomosing cords of cells, which form 

 close net-works, the intervening clear clefts 

 being the lumina of the blood-capillaries. 

 According to Disse's studies, the liver-cells 

 do not lie immediately in contact with the 



capillaries, but are separated from the latter by delicate perivascu- 

 lar lymphatic channels which envelop the blood-capillaries. 



In livers still retaining their primitive type of the tubular gland 

 the bile-capillaries appear as minute 

 ducts placed centrally within the cords 

 of the hepatic cells, the biliary passages 

 representing lumina of tubular acini 

 lined with secreting glandular epithe- 

 lium. In man, however, the liver-cells 

 are often bordered on all sides, ex- 

 cept on that lying next the blood- 

 vessels, by the delicate bile-canaliculi, 

 the latter never interposing between 

 the cells and the blood-channels. 



The bile-capillaries,exist as narrow 

 (1-2 fji) clefts between adjacent liver- 

 cells, maintaining about the same 

 diameter throughout the lobule ; at the periphery the intercellular 

 channels pass into the larger, though still small, interlobular bile- 

 ducts. The hepatic cells between which the bile-capillary takes its 

 course become replaced at the periphery of the lobule by the low 

 epithelium of the bile-duct, the basement-membrane present in the 

 latter fading away into the delicate connective tissue holding together 

 the cords of liver-cells. 



FIG. 223. 



Section of liver of frog, exhibiting tubu- 

 lar character of gland : a, blood-channels 

 containing corpuscles ; b, lumina of hepatic 

 cylinders which correspond to bile-capil- 

 laries ; c, pigment-cell. 



