308 THE STRUCTURE OF THE LIVER. 



Fat and water, further pilocarpin and physostigmin, excite pancreatic secre- 

 tion. Solutions of neutral and alkaline salts of the alkaline metals exert an in- 

 hibitory action. Animals tolerate ligation of the pancreatic duct. It is a remark- 

 able fact that the duct may regenerate spontaneously. This operation may, how- 

 ever, be followed by cyst-formation in the ducts and atrophy of the glandular 

 structure. After total extirpation of the pancreas, the digestion of albumin, fat 

 and starches is impaired. The severe diabetes that develops immediately after 

 extirpation of the pancreas and which has been observed also in human beings 

 after degeneration of the pancreas, is of obscure origin. 



THE STRUCTURE OF THE LIVER. 



The liver is included among the compound tubular glands. Its development 

 shows that with its excretory ducts it evolves in the form of a reticulated tubular 

 gland. The globular, polygonal hepatic acini (lobules, islands), flattened one 

 against the other, from i to 2 mm. in diameter, are considered as the ultimate 

 macroscopic units of the gland. They show the following histological peculiarities: 



The liver cells (Fig. 116, II, a), 34 or 35 ^in diameter, are irregularly polyhedral, 

 consisting of soft, friable protoplasm, filled with pigment-grantiles. They have 

 no membrane, and contain one or more spherical nuclei, with nucleoli, and are so 

 arranged that they radiate from the centre of the acinus in longer or shorter con- 

 nected lines toward the surface of the lobule. Thus arranged they are in part 

 surrounded by the more delicate bile-ducts (Fig. 116, I, x), in part separated one 

 from the other in rows by the coarse network of blood-capillaries (d d) . In the 

 state of hunger the liver-cells are finely granular and deeply clouded (Fig. 117, i). 

 About thirteen hours after suitable nourishment the cells contain coarse, glistening 

 flakes of glycogen (2). At the same time the protoplasm is condensed on the 

 surface, whence a network extends toward the center of the cells, in which the 

 nucleus is suspended. The liver-cells often contain fatty granules. 



The Blood-vessels of the Lobule. (a) Ramifications of the venous system. 

 If the branches of the portal vein, well supplied with muscular fibers, and entering 

 through the transverse fissure, be followed, small vessels will finally be found, 

 after free dendritic branching, that, approaching from various directions, converge at 

 the limits of the acini, and here enter into communication through capillary anasto- 

 moses, forming the interlobular veins (Fig. 116, V, i). From these veins capillary 

 vessels (c c) pass from the entire periphery of the acinus toward its center. They 

 are relatively large (from 10 to 14 // in diameter) and form a longitudinal network 

 in a radiating direction; and between them rows of connected hepatic cells, 

 liver-cell columns (d) , are always lodged. The capillaries are so arranged that they 

 run along the edges of the rows of cells, and never between the surfaces of two 

 adjacent rows. The radiating course of the capillaries necessarily brings it about 

 that these vessels must unite at the center of the acinus to form the beginning 

 of a larger vessel. This is the central or intralobular vein (V. c) which, m turn, 

 piercing the lobule vertically, makes its exit at one point and, reaching the surface 

 unites, as the sublobular vein (V. a), with similar vessels from neighboring acini, 

 to form larger trunks that (100 // in diameter) represent the roots of the hepatic 

 veins. The trunks of this great system of venous radicles leave the gland at the 

 blunt edge of the liver. 



(6) Ramifications of the Hepatic Artery. The branches of the hepatic artery, 

 throughout their entire course, accompany the larger branches of the portal vein, 

 to which, as well as to the adjacent larger bile-ducts, they supply nutrient capillaries. 

 These branches enter into numerous anastomotic communications among them- 

 selves. The small capillaries pass mainly from the periphery of the acinus into 

 the capillaries of the portal system (Fig. 116, i i). Those arterial capillaries, how- 

 ever, that lie in the thicker connective tissue upon the larger venous and biliary 

 branches (rr) pass over chiefly into two venous trunks that, accompanying the 

 corresponding arterial branches for some distance, empty into branches of the 

 portal vein. 



Individual arterial branches pass up to the surface of the liver, where they 

 form a wide-meshed nutritive network, particularly under the peritoneal covering. 

 The small venous radicles collecting from this point also reach the ramifications of 

 the portal vein. 



The Biliary Passages. The finest biliary passages, bile-capillaries, originate 

 from the center of the acinus, and likewise within its entire interior, as membrane- 

 less, regularly anastomosing straight ducts, i or 2 ^ in diameter. They form a 



