capillary vessels pass into the lobule, and, lying between the gland cells, form a network with long meshes radiating from the centre. These are the lobular blood capillaries. The vessels of this radiating capillary network become larger as they unite and converge to the centre of the lobule, where they open into a central vein which lies in immediate apposition with the gland cells. This vein is called the intralobular vein, and is the radicle of the efferent or hepatic vein, which carries the blood of the liver to the inferior vena cava.

The ultimate ramifications of the hepatic artery can be traced to various destinations. Some pass into the walls of the accom

Cells of the Liver. One large mass shows the shape they assume by mutual pressure. (a) The same free, when they become spheroid. (b) More magnified. (c) During active digestion containing refracting globules like fat.

panying vein and duct and the connective tissue which surrounds these vessels. Many of the arterial capillaries unite with offshoots from the interlobular venous plexus, and thus reinforce the lobular capillaries. Other branches form a lobular capillary plexus, which joins the capillaries of the vena porta, together with that from the walls of the vein and duct.

The blood flowing to the liver in the great vena porta and the hepatic artery is thus conducted by those vessels to the boundaries between the lobules (interlobular veins), and thence streams through the converging lobular blood capillaries to the intra

lobular vein, and is collected from the latter by the sublobular tributaries of the hepatic vein, by which it is conducted back to the general circulation, and enters the heart by the inferior vena

cava.

Between the meshes of the lobular capillaries the gland cells.

FIG. 74.

Section of injected liver showing the position of the portal branches (interlobular veins, VP) and radicals of hepatic veins (intralobular veins, HV) connected by lobular capillaries.

Below is a portion of the same highly magnified. (a) Liver cell with (n) nucleus; (b) Blood capillaries cut across passing along angles of cells; (c) Bile capillaries between flattened sides of cells. (Huxley.)

are tightly packed. These are large, soft, polyhedral cells, with one, two, or even more nuclei, and no trace of a limiting membrane. Owing to the shape of the capillary meshes, the cells are placed in rows radiating from the centre of the lobule toward the periphery.

The blood capillaries are said to pass along the angles and edges of these cell blocks so as not to come into close relation to the bile capillaries (Fig. 71). The finely granular protoplasm of the liver cells is capable of undergoing some slight change in form while alive. In the protoplasm are situated varieties of granules, the commonest being bright, refracting fat globules, which vary in amount with the different stages of digestion;

FIG. 75.

Section of the Liver of the Newt, in which the bile ducts have been injected, and can be seen through the transparent liver cells to form a network of fine capillaries.

others of a yellow color seem connected with the coloring matter of the bile; and a third variety, less refracting and colorless, is said to be related to the glycogen.

Between the cells of the lobules there can be demonstrated very fine anastomosing canals, which appear to be formed by the juxtaposition of grooves which lie in the middle of the flat surface of two neighboring cells. Every liver cell is related to such a canal, and consequently a very dense network with peculiarly regular polygonal meshes is present, each mesh corresponding in size to one cell.

These fine intercellular canals are called lobular bile capillaries,

and must not be confounded with lobular blood capillaries, the diameter of which is about ten times as great as the former, and which have a definite boundary wall, while the bile capillaries have no other boundary than the substance of the liver cell, and therefore are not really vessels.

These fine intercellular bile passages are described as communicating with the interlobular ducts directly opening into the ducts without any marked increase in the size or change of arrangement. The interlobular ducts which follow the course of the artery and portal vein are composed of a delicate basement membrane lined with a thin layer of epithelium which in the larger vessels shows a cylindrical character. The large bile ducts have a firm fibro-elastic coat lined with a definite mucous membrane covered with cylindrical epithelium lying upon a vascular submucosa, in which are scattered numerous mucous glands of saccular form.

The amount of connective tissue in the liver of man and most domestic animals is very small, but in the pig, bear, giraffe, and some others, it is easily recognized around the lobules, sending delicate supporting processes between them. This connective tissue passes into the organ with the portal system of vessels forming a loose sheath derived from the capsule of Glisson, and is distributed with the subdivisions of those vessels to the various parts of the gland.

The lymphatics are known to be very plentiful, and in intimate relation to the blood vessels.

Method of Obtaining Bile.-For most practical purposes the bile from the gall bladder of recently killed animals is sufficient. The bile pigments and cholesterin may be conveniently obtained from the gall stones so often found in the human gall bladder.

In order to investigate the composition of the bile as it comes from the ducts, before it has been modified by its sojourn in the gall bladder, it is necessary to make a biliary fistula, communicating either with the gall bladder or with the bile duct. In this way the rate, pressure, and other points concerning the mode of secretion may be determined.

Composition of Bile.-The bile of man and carnivorous animals is of a deep orange-red color, turning to greenish-brown by decomposition of its coloring matter. In herbivorous animals it has some shade of green when quite fresh, but turns to a muddy brown after a time. It is transparent, and more or less viscid according to the length of time it has remained in the gall bladder. It has a strong, bitter taste, a peculiar aromatic odor, and after remaining for some time in the gall bladder it has an alkaline reaction. Its specific gravity is about 1005 when taken from the bile ducts directly, but it may rise to 1030 after prolonged stay in the gall bladder, owing to the addition of mucus and the absorption of some of its fluid.

The following table gives approximately the proportions of the chief constituents of bile :

:

Bile contains no structural elements nor any trace of albuminous bodies.

1. The bile acids are two compound acids, glycocholic and taurocholic, which exist in the bile in combination with sodium. The amount of each varies in different animals and at different times in the same animal. The bile of the dog and other carnivora contains only taurocholate of soda. In the ox the glycocholate of soda is greatly in excess. In man both are present, the proportion being variable, but the glycocholate greatly preponderates.

To separate these acids, bile is evaporated to one-fourth its volume, rubbed to a paste with animal charcoal to remove the pigments, and carefully dried at 100° C. The black cake is extracted with absolute alcohol, which dissolves the bile salts. From the strong alcoholic solution after partial evaporation the bile salts can be precipitated by ether. They first appear as an