A system of practical medicine. By American authors. Vol. 3

by Unknown

The lymphatic system consists of large and capillary vessels, interstitial spaces or juice-tracks, lacteals, follicles, and glands. The serous cavities are also considered lymph-chambers, and the loose cellular tissue is a vast chambered lymphatic sac communicating with lymphatic vessels. The larger vessels are divided into two classes—the superficial, which in the subcutaneous tissue accompany the veins, while in the solid viscera they lie under the capsule, and in the tubular viscera under the serous membrane; and the deep-seated vessels, which accompany the deep-seated blood-vessels, ramify through the interior of the organ in the solid viscera, and emerge at the hilus; while in the tubular viscera they lie in the submucosa, and by free anastomosis form plexuses. There is no communication between these two sets of vessels, except in the solid viscera and in the glands which may be common to both sets. Between the vessels of each set there is, however, a free anastomosis, by which large-meshed plexuses are formed. In consequence of these peculiar arrangements each set may be separately diseased, and inflammation may spread rapidly from vessel to vessel of the same set.

The lymph-capillaries are arranged in networks which lie in the meshes of the plexuses of the blood-capillaries, from which they are separated by intervening tissue-elements. Their walls consist of a single layer of endothelium resting upon elastic tissue. In their continuity they are sinuous, and are provided with an incomplete valvular arrangement.

The large vessels have three coats, not unlike the coats of the veins, and are provided with numerous valves. These valves are the more abundant in the superficial vessels, and the intervals between them grow gradually less as they approach the glands.

The whole lymph vascular system terminates either in the right or left thoracic duct.

The origin of the lymphatics has not been definitely settled. It has been demonstrated that lymph circulates in the connective-tissue interstices, and it seems to have been established that these spaces are lymph reservoirs, discharging through lymph-capillaries. It is admitted that the capillaries commence either in closely-meshed networks or lacunar spaces. Plexuses of lymphatic capillaries, corresponding with the distribution of the blood-capillaries, lie under the endothelium of the serous membranes, and are in open communication with the serous cavities through the stomata. The stomata vera are either the openings of lymph-channels communicating directly with lymph-capillaries, or discontinuities between the cells of the surface, leading into superficial lymph-sinuses. The pseudo-stomata are the interstitial or intercellular cement substance, and represent the communication of the lymph canalicular system with the free surface of serous membranes.

Lymph-follicles consist of a reticulum of connective tissue, the meshes of which are crowded with cells, thus forming patches in the submucous or subserous tissue. Around these patches there is a plexus of lymph-capillaries.

Lymphatic glands are round or oval bodies situated in the course of the lymphatic and lacteal vessels. They are composed of follicular tissue, trabeculæ, and lymph-tracts, all enclosed in a capsule. No doubt exists in regard to a channel of communication between the afferent and efferent vessels through a complex system of lymph-paths which communicate more freely with the afferent than with the efferent vessels. They are very vascular.

Every lymphatic vessel passes through one or more glands before reaching the trunks. Before penetrating the peripheric fascia of a gland these vessels divide into a number of smaller ones, which are distributed upon the surface of the cortical portion, and empty directly into the superficial lymph-sinuses. A number of vessels emerge from each gland, but they are less numerous and larger than the afferent vessels. The lymph is poured through the afferent vessels into the lymph-spaces of the cortical alveoli, and thence into the channels of the medullary substance, from which it escapes, enriched in corpuscular elements, into the efferent tubes. The current of fluid passing through such a complex structure must necessarily be retarded. This relation of the glands to the lymph-current is, moreover, especially interesting in its pathological significance. Whatever enters the lymph may, if small enough, pass through the glands and be swept along with the current, but the structure of the gland is, in a mechanical sense, a filtering apparatus, interrupting the free current of the fluid and retaining the coarser particles. The lymph in passing through the glands derives constituents not previously possessed, but, nevertheless, the retention of elements which for a time might arrest the dissemination of hurtful material may eventually convert the gland into a new source of infection. This fact is illustrated in the history of malignant growths.

Perhaps the most interesting consideration connected with this relation of the lymph-glands to the fluid passing through them is presented by the anatomical arrangement of the chyle-vessels and the mesenteric glands. The lacteals, commencing as the central efferent vessels of the intestinal villi, pass between the folds of the mesentery, through several tiers of mesenteric glands, and, uniting into one or more trunks, terminate in the receptaculum chyli. During digestion these vessels are full of chyle, and during the intervals of digestion they convey lymph.

The lymphatic system may be considered an appendage of the blood vascular system. By the blood the tissues are supplied with nutriment and oxygen. By both the blood and lymph the surplus and waste are conveyed away. The current of the lymph is in a reverse direction to that of the blood-supply. The lymphatic vascular system receives through its rootlets, which are distributed through the tissues, the surplus transudation from the arterial capillaries, the products of tissue-waste and transformation, and the chyle, and empties its contents into the great venous trunks near their termini. It therefore performs the double function of absorption from without and absorption from within. In other words, it introduces into the blood the material from both the food and the air which is required for the sustenance and repair of the tissues, and conveys away the unassimilated surplus, waste, and effete material.