ABSORBENT SYSTEM. The delicate vessels which in the bodies of vertebrate animals are engaged in carrying the food and other matters into the circulation, have this name. It consists of two principal divisions, which may be regarded as two different sets, given off from a common stem. One of these takes its origin in the walls of the alimentary canal, more especially the small intestines, and is called the lacteal system, from the white colour of the liquid it takes up ; whilst tho other commences in the substance of tho body, more especially the skin and neighbouring parts, and is called the lymphatic' system, from the colourless fluid, called lymph, which it earrica.
The Le:Heals are the small system of vessels by which the chyle, or nutritive part of the food, is conveyed from the intestines to the left subelavian vein, in which it is mixed with the blood. They have their origin in the villi of the small intestines, which are short hair-like processes, each consisting of a fine net-work of lacteal vessels sur rounded by capillary arteries and veins. On the outside the villi are covered with cells,which absorb the chyle before it is conveyed to the loops of the lacteals in the interior of the villus. From the villi the chyle is carried, between the layers of the mesentery, through numberless converging branches, to the thoracie duct, the main trunk of the absorbent system, which, at the part where the chief lacteal branches join it, is dilated into what is called the Receptaculum Chyli. The villi have no visible apertures for the entrance of the chyle, but the walls of the lacteal vessels themselves are extremely thin and permeable, and their canals are furnished with numerous and delicate valves, like those of the veins [CIRCULATION OF THE BLooD], to prevent the fluid which they contain from descending again to their absorbing extremities. In their passage through the mesentery the lacteals traverse numerous mesenteric absorbent glands, where they communicate with veins, and the fluid contained in them is exposed to the influence of the blood, from which it acquires colouring matter and fibrine.
The Lymphatics consist of minute branched tubes of extremely delicate membrane, whose extremities are arranged in a more or less dense net-work in every part of the body. From this net-work they
gradually converge into a succession of branches of increasing size, and terminate in two main trunks, called the right and left great Lymphatio Veins, through which the lymph is poured with the chyle from the thoracic duct into the right and left snbclavian veins. The lymphatics also communicate with the veins at some other parts of their course, chiefly near their minute extremities, and more rarely by larger branches. They have in their interior numerous delicate valves formed of crescentic folds of the lining membrane, like those of the veins and of the lacteals [CIRCULATION or THE BLOOD], and, like them, pre venting the retrograde course of the contained fluid. The valves of the lymphatics, however, are much more closely set than those of the veins, so that, when full of fluid, the spaces between them being most distended, they give those vessels a knotted or bearded appearance, by which they are easily distinguished from veins of the same size. In the course of the larger lymphatics there are numerous glands of the same nature as those found in the course of the lacteals. They are called Lymphatic Glands. To each of these there pass two or more lymphatic vessels, which on entering them become extremely tortuous, and after varied convolutions and anastomoses, terminate in nearly the same number of branches, which again pass from the gland, and pursue their course towards the main trunk. These glands attain their fullest development in man and the mammalia. They are far less numerous in birds, and are entirely wanting in the fish and amphibia. The function performed by these glands is somewhat obscure, but it has been recently suggested by Professor Bennett, of Edinburgh, that their function is toprepare or produce the colourless corpuscles of the blood. [BLOOD.) He arrives at this conclusion from having observed that in cases where these glands or the spleen are inflamed, or in a condition of increased action, that the colourless corpuscles of the blood can be seen under the microscope to be in larger quantity than is normal. (Bennett, On Leueocythernia.)