LYMPHATICS, in anatomy, the vessels in which the lymph is contained, and the glands by which it is separated in the human and other bodies. An account of the structure and offices of the lymphatic glands and vessels has lately been published, from Mr Hewson's experiments, by Mr Falconer of London. He observes, that each lymphatic gland is a congeries of tubes, consisting of arteries, veins, lymphatic vessels, and nerves, connected by the cellular substance. Glands of this kind, he remarks, are nowhere to be found but in the course of the larger lymphatic vessels. These vessels, in their passage from the extreme parts of the body towards the thoracic duct, enter and pass thro' the lymphatic glands in the following manner:
About a quarter of an inch before a lymphatic enters a gland, it divides into two, three, or four smaller branches, sometimes into a greater number. These enter the gland at the part farthest from the thoracic duct; and are then subdivided into branches, as small as the ramifications of the arteries and veins which accompany them to every part of the gland. After being thus minutely divided, they reunite, and gradually become larger as they approach the opposite side of the gland, forming three or four branches, which are joined by other lymphatics that arise from the cells of the gland. All these branches unite together about a quarter of an inch from that part where they came out of the gland, and form a common trunk, larger than that below the gland, by the additional lymphatics it receives from the cells of the gland.
Although, in every lymphatic gland, very small cells can be discovered by the microscope, those appearances in such glands which have commonly been called cellular, are by no means of that nature, being only, our author observes, little eminences formed by the bending of one vessel round another. On cutting into a fresh lymphatic gland, it is found to contain a thickish, white, milky fluid; and if this fluid be carefully washed from any part of it, and the gland then examined with the microscope, an infinite number of very small cells are observed, which cannot be discovered by the naked eye.
Mr Falconer adopts the opinion of the late Mr Hewson with respect to the use likewise of the lymphatic system. The glands he considers as organs intended for the purpose of secreting a fluid of a particular nature from the blood; and the lymphatic vessels he looks upon as so many excretory ducts. In proof of this assertion, he observes, that, if the arteries and
veins of a lymphatic gland have been previously injected with a coloured fluid, and a part of the gland be then viewed thro' the microscope, these cells, formerly taken notice of, appear extremely vascular. And it is into their cavities that the whole fluid found in the gland is secreted. This fluid is absorbed by the lymphatic vessels which arise from the cells of the glands, and is by them, in common with the other fluids, carried into the course of the circulation. The lymphatic vessels, therefore, which originate from the cells of the gland, are, in the lymphatic glands, analogous to the excretory ducts of other glands. We have the same proofs, our author asserts, that the lymphatic glands secrete this white fluid, and that it is carried from the lymphatic glands by the lymphatic vessels, that we have of glands in other parts of the body separating different fluids and having excretory ducts. For, if we cut into a lymphatic gland, we find a white fluid; and, if a ligature be made on the lymphatic vessel coming from that gland, we find a fluid of the same kind contained in those lymphatic vessels. This, Mr Falconer observes, is as convincing a proof that the lymphatic vessels are excretory ducts to the lymphatic glands; and as satisfactory, as that the hepatic duct is the excretory duct of the liver. We know the liver secretes bile, because we find it in that viscus; and we know the ductus hepaticus is its excretory duct, because we find bile contained in it. The proofs are similar, and therefore equally conclusive.