HISTOLOGY. The macroscopic divisions of the liver which are known as lobes are subdivided microscopically into lobules by extensions inward of the connective tissue of Glisson's capsule. In some of the lower animals, e.g. the each lobule of the liver is completely surrounded by this conneetive tissue. In man the amount of tissue is small and does not form a complete investment for each lobule. The de markation of the lobules is, therefore. not at all sharp. The structure of a liver-lobule may he described as follows: At the centre of each lobule is the central vein which is a branch of the hepatic vein. Passing out in a radiating manner trom this central vein is a dense network of capillaries in the meshes of which he the cords of liver-cells. These are polyhedral in shape, granular. and contain rather large nuclei. In the connective tissue which lies at the junc tion of three or more lobules is found the group of vessels known as the portal canal and con sisting of the hepatic artery, the portal vein. and the bile-duct. The smaller bile-duets consist of a single layer of columnar epithelium surrounded by a thin layer of connective tissue. In the larger ducts there is a well-defined mucosa con sisting of a single layer of epithelium resting 'upon a stroma. outside of which are a few smooth muscle-cells and some fibrous tissue. Usually at some distance from the portal system in the con nective tissue between two adjacent lobules is the sublobular vein, a branch of the hepatic vein, into which the central veins empty.
The blood-supply of the liver is very large, being conveyed by two distinct systems—the por tal system and the hepatic system. The portal vein and the hepatic artery enter the liver at the hilus, and. entering the organ, divide and sub divide. following the extensions inward of Cais son's capsule. Upon reaching the boundary of the lobules the vessels break up into the infra lobular capillary network 'already referred to. 1)1-tinet up to the time of entering the lobule. the blood of the two systems mingles at comae point within the lobule capillaries and empties into the above-mentioned central vein, whence it finds its way into the hepatic vein. Pile capillaries ex tremely minute in size originate within the lobules and follow the cords of liver-cells to the periphery of the lobules, where they empty into the smaller bile-ducts. Lymphatics accompany the blood-vessels. forming in the capsule a super ficial lymphatic system, in the substance of the liver proper a deep system. The nerves of the liver enter the organ at the in company with the blood-vessels and lym phatics. They are composed mainly of non medullated fibres, although some inedullated fibres are intermingled. They branch following the subdivisions of Glisson's capsule, and reach the periphery of the lobules. Extremely minute fibrils enter the lobules to terminate in end arborizations among the liver-cell-.
The two distinct funetions, that of the pro duction of bile and the formation •f sugar, which are now generally recognized as being pct.
formed by the liver have led some physiologists to suppose that this gland is composed of two dis tinct portions or anatomical elements. and Robin has adopted this theory and calls one portion of the liver a biliary organ, and the other a glyco genic or sugar-forming organ. The hi odes and hepatic cells, with their different vessels, he re gards as performing the glycogenic function. and the little racemose glands whirl' are attached to the biliary duets their course as the bile producing organs; and others have entertained ideas of the independence of the sugar-making and bile-producing portions of the organ. 11111
from the fact that bile is commonly found in the lobules. and that the biliary capillaries are con nected with the excretory binary duets, the ern elusion seem: to be unavoidable that the bile is formed in the lobules, and. moreover, by the hepatic cells. It therefore becomes a question as to what are the functions of the little race mose glands attached to the larger bile-ducts. They have much the form of mucous gland- in other parts of the body. and from the exami nations of Sappey. who has found the bile to be viscid in proportion to the number of these gland in the ducts containing it. they appear to be really mucous glands. In the rat bit. an animal in which these glands arc n t f. UT d in this situ ation. the bile is quite fluid. an 1 free from its ordinary viscidity. It has goner. Ily been thought that the bile is secreted exclusively from the blood which has been brought from the intestines by the portal vein, and that, indeed, the principal office of the liver was to separate effete matter from this portion of the venous system; but many experiments which have been made since Bernard discovered the glycogenic function of the liver go to show this idea erroneous. 1 t has also been thought that the hepatic artery may furnish material for the secretion of bile, while the portal vein furnished that for the production of sugar; but these views again are quite over thrown by many well-established facts and ex periments. It has been found that, after the ligation of the hepatic artery, bile has been secreted from blood furnished by the portal vein; and again, according to the experiments of OK, who has succeeded in gradually obliterating the portal vein without immediately producing death, it has been found that bile is secreted from blood furnished by the hepatic artery. In one in stance in which a patient died of dropsy the portal vein was obliterated, and yet the gall bladder was full of bile. Anomalous cases have been reported where the portal vein, instead of passing through the liver, emptied into the as cending vena cava, and where also there was found no deficiency of bile. These facts point to the conclusion that the secretory elements of the liver have an elective power, and that this gland may elaborate its products either from venous or arterial blood. The only conclusion, therefore, is that the liver produces bile from both the por tal vein and the hepatic artery, and that the secretion may be kept up if either one of these vessels be obliterated. The natural color of bile is variable; in the pig it is bright yellow; in the dog, dark brown; and in the ox. greenish yellow. In general, it may be stated that it is dark green in carnivorous, and greenish yellow in herbiv orous animals. Its specific gravity is variously stated. Some authorities place it at 1026; others from 1020 to 1026; and again others from 1026 to 1031. These differences are considerable, but the numbers were probably the result of exact observation, as the bile is found to differ under different circumstances. (See table.) Fresh bile is nearly inodorous, but after being taken from the body of an animal it soon undergoes putre factive changes. It has been generally thought to be invariably alkaline, and this is true of that which is found in the hepatic duct, but it often has an acid reaction after it has passed into the gall-bladder.