LIVER. 345 LIVER. the (hiodemim. (See Digestion, Organs and Pbocess of.) Tliis eoramon excretory duct of the liver and gallbladder is about 3 inches in length, and of the diameter of a goose-quill. port. qiuul.1. INFERIOH SURFACE OP HOMAN LIVEH. Imp. cast,, Impreesio g-astrica ; spig.I, spigelian lobe; Aep.a, hepatic arterj ; porf. r., portal vein ; ftrf., bile-duct ; r.t'a., vena cava; cnu.l.. caudate lobe; imp.ren., Im- presslo reualis ; iiitp.il., impi-essio collica; tu.om., tuber oraentale; uwb.f., tunbilical fleeure ; quad,!., quadrate lobe : g,b,, gall-bladder. The cliemical eomi)0.sition of the liver in health is as follows: 08. 6 per cent, of water, and 31.4 per cent, of solid constituents — of which 3.8 are fat, 4.7 albumen, while the rest is made up of ves.sels, salts, and e.xtractive matters. (In the diseased condition known as fatty degenera- tion of the liver, the fat is enormously increased.) Sugar, varying in amount from 1 to 2 per cent., is also found : and inosite, uric acid, sarcine, xanthine, and leucine usually occur in traces. The gall-bladder may be regarded as a divertic- ulum or offshoot from the hepatic duct. It has somewhat the shape of a pear, and lies in a de- pression on the under surface of the liver. Its use seems to be to serve as a reservoir for the ^,^,..Mi.... '■"s>^M d- a- ■■:-j;.„o ', c- o— m^iKaN4g-::.v>:..->;-o> '- SECTION OF HUMAN" LIVEK, Showing general arrangement of lobules: a, interlobu- lar (portal vein) ; b, intralobular (hepatic) vein; c, hepatic arter.T ; d, bile-ducts ; the boundaries ot the lobules are Imperfectl.v defined b.v the irregular areas representing the poorly developed capsule of Glisson. accumulation of the bile, when its flow into the intestine is interrupted, as it is always found full after a long fast, and ciiipfy when digestion is going on. That the gall-bladder is not an essential appendix to the liver is shown by the fact that it is absent in many genera of mam- mals. It was formerly believed that the liver served merely for the separation of the biliary secretion from the blood ; but there is now abundant evi- dence that the blood itself is changed by it.3 means, in such a way as to show that this gland possesses an assimilating as well as a depurating action. That the liver possesses an a.ssimilating power on albuminous substances is shown by the experiments of Claude Ucrnard, who found that, if a solution of egg-albumen be injected into any part of the systemic circulation, albumen speedily appears (like other soluble substances which are foreign to the body) in the urine, and is eliminated as an extraneous matter; but if it be injected into the portal vein, it does not ap- pear in the urine, but becomes a normal constit- uent of the blood (blood-albumen), through the agency of the liver. Kurther, it appears from Bernard's researches that fatty matters are elab- orated in the liver — the blood of the hepatic veins, which leaves the liver, containing con- siderably more fat than that of the portal vein, which enters it. Some of this fat is doubtless burned off in the lungs ; but if a de- ficient supply should be introduced by the lac- teals, some of it would doubtless be applied to the formative processes. ■ Lastl}', during the last three days of incubation of the chick, the liver is made briglit yellow by the absorption of llie yolk, which enters the branches of the portal vein, and is then converted partly into blood- eorpuscle.i, which enter the circulation, and part- ly into bile, which is discharged into the intes- tine. Hence, there is distinct evidence, from several points of view, that the liver is an assimilating organ. The depurating action of this organ is exhibited in the secretion of bile (q.v.), by which the hydro-carbonaceous portion of the efl'ete matters of the blood is removed, just as the nitrogenous portion is eliminated by the kidneys. The use of the bile in the digestive process is sufficiently explained in the article Digestion, Organs and Process of. This important gland first shows itself in the form of yellowish-brown cells in the polyps, and gradually becomes more concentrated and developed in the echinoderms, anneliils, nudo- branehiate gastropods, insects, crustaceans, air- breathing moUusks, cephalopods, fishes, reptiles, birds, and mammals. The physiological anat- omy of the liver may l)e briefly stated as fol- lows: The lobules previously mentioned are about ^ of an inch in diameter and of an ovoid shape. They are surrounded by a plexus of blood-vessels, nerves, and ramifications of the hepatic duct, comprising what are called the interlobular vessels. These are all inclosed by a sheath which is a prolongation of the proper coat of the liver (capsule of Glisson), but at- tached loosely by areolar tissue. This sheath follows the vessels to the subdivisions within the interlobular spaces (spaces between the lobules), but does not extend to the capillary vessels within the lobules. In a few animals, as the pig and pohir bear, the lobular structure can be seen with the naked eve, but in man and most mam- mals it cannot. The lobules are intimately con- nected with each other, branches of the inter- lobular vcscls being each distributed to several of the lobules, Anv one lobule, however, may be considered as representing the physiological anatomy of the whole liver, and the study of its anatomv and functions will answer for the study of the "whole eland. The lobules receive blond at their surfaces from the capillary terminations of the portal vein, these vessels having received
