SECT. II. OF THE ABSORPTION OF LYMPH.

This function is effected by agents, which strongly resemble those concerned in the absorption of the chyle. One part of the vascular apparatus is, indeed, common to both,—the thoracic duct. We are much less acquainted, however, with the physiology of lymphatic, than of chyliferous, absorption.

Anatomy of the Lymphatic Apparatus.

The lymphatic apparatus consists of lymphatic vessels, lymphatic glands or ganglia, and thoracic duct. The latter, however, does not form the medium of communication between all the lymphatic vessels and the venous system.

1. Lymphatic vessels.—These vessels exist in almost all parts of the body; and, when they become visible, have the shape of cylindrical, transparent, membranous tubes, of small size, and anastomosing freely with each other, so as to present, every where, a reticular arrangement. They are extremely numerous; more so, however, in certain parts than in others. They have not yet been found in the brain, spinal marrow, eye, internal ear, &c.; but this is no proof that they do not exist there. It may be merely an evidence that they are so minute as to escape observation.

In their progress towards the venous system, they go on forming fewer and fewer trunks; yet they always remain small. This uniformity in size is peculiar to them. When an artery sends off a branch, its size is sensibly diminished; and when a vein receives a branch, it is enlarged; but when a lymphatic ramifies, there is, generally, little change of size, whether the branch, given off, be large or small.

The lymphatics consist of two planes,—the one superficial, the other deep-seated. The former creeps under the outer covering of the organ, or of the skin, and accompanies the subcutaneous veins. The latter is seated more deeply in the interstices of the muscles, or even in the tissue of parts, and accompanies the nerves and great vessels. These planes anastomose with each other. This arrangement occurs not only in the limbs, but in the trunk, and in every viscus. In the trunk, the superficial plane is seated beneath the skin; and the deep-seated between the muscles and the serous membrane that lines the splanchnic cavities. In the viscera, one plane occupies the surface, the other appears to arise from the parenchyma.

The two great trunks of the lymphatic system, in which the lymphatic vessels of the various parts of the body terminate, are the thoracic duct, and the great lymphatic trunk of the right side. The course of the thoracic duct has already been described. It is VOL. II.

4

formed of three great vessels;—one, in which all the lymphatics and lacteals of the intestines terminate; and the other two, formed by the union of the lymphatics of the lower half of the body. Occasionally, the duct consists of several trunks, which unite into one before reaching the subclavian vein; but more frequently it is double. In addition to the lymphatics of the lower half of the body, the thoracic duct receives a great part of those of the thorax, and all those from the left half of the upper part of the body. At its termination in the subclavian, there is a valve, so disposed as to allow the lymph to pass into the blood; and to prevent the reflux of the blood into the duct. We shall see, however, that its mode of termination in the venous system possesses other advantages.

The other trunk is formed by the absorbents from the right side of the head and neck, and from the right arm. It is very short, being little more than an inch, and sometimes not a quarter of an inch, in length, but of a diameter nearly as great as the thoracic duct. A valve also exists at the mouth of this trunk, which has a similar arrangement and office with that of the left side.

The lymphatics have been asserted to be more numerous than the veins; by some, indeed, the proportion has been estimated at fourteen superficial lymphatics to one superficial vein; whence it has been deduced, that the capacity of the lymphatic system is greater than that of the venous. This must, of course, be mere matter of conjecture. The same may be said of the speculations, that have been indulged regarding the mode in which the lymphatic radicles arise;—whether by open mouths or by some spongy mediate body. The remarks made, regarding the chylous radicles, apply with equal force to the lymphatic.

It has been a matter of some interest to determine, whether the lymphatic vessels have not other communications with the venous system than by the two trunks just described; or, whether, soon after their origin, they do not open into the neighbouring veins; -an opinion, which has been enunciated by many of those who believe in the doctrine of absorption by the lymphatics exclusively, in order to explain why absorbed matters are found in the veins. Many of the older, as well as more modern, anatomists have professed a similar opinion.

Vieussens affirmed, that, by means of injections, lymphatic vessels were distinctly seen to originate from the minute arteries, and to terminate in the small veins. Sir William Blizard asserts, that he twice observed lymphatics terminating directly in the iliac veins. Mr. Bracy Clarke found the trunk of the lymphatic system of the horse to have several openings into the lumbar veins. Ribes, by injecting the supra-hepatic veins, saw the substance of the injection enter the superficial lymphatics of the liver. Alard considers the lymphatic and venous systems to com

municate at their origins. Vinc. Fohmann, that the lymphatic vessels communicate directly with the veins, not only in the capillaries, but in the interior of the lymphatic glands. Lauth, of Strasbourg,—who went to Heidelberg to learn from Fohmann his plan of injecting,—announced the same facts in 1824.

By this anatomical arrangement, Lauth explains how an injection, sent into the arteries, reaches the lymphatics, without being effused into the cellular tissue; the injection passing from the arteries into the veins, and thence, by a retrograde route, into the lymphatics. Beclard believed, that this communication exists at least in the interior of the lymphatic glands; and he supported his opinion by the fact, that in birds, in which these glands are wanting, and are replaced by plexuses, the lymphatic vessels in these plexuses are distinctly seen to open into the veins. Lastly, in 1825, Regolo Lippi, of Florence, in his Illustrazioni Fiziologiche e Pathologice del Sistema Linfatico-chylifero, has made these communications the express subject of his work. According to him, the most numerous exist between the lymphatic vessels of the abdomen and the vena cava inferior and all its branches. So numerous are they, that every vein, according to him, receives a lymphatic vessel, and the sum of all those vessels would be sufficient to form several thoracic ducts. Opposite the second and third lumbar vertebræ, these lymphatic vessels are manifestly divided into two orders;—some ascending, and emptying themselves into the thoracic duct; others descending and opening into the renal vessels and pelves of the kidneys.

Lippi admits the same arrangement, as regards the chyliferous vessels; and he adopts it to explain the promptitude with which drinks are evacuated by the urine.

Subsequent researches do not seem to have confirmed the statements of Lippi. G. Rossi, indeed, in Omodei's Annals for January, 1826, maintains, that the vessels, which Lippi had taken for lymphatics, were veins. The question is still sub lite.

Magendie conceives the most plausible view regarding the lymphatics to be:—that they arise by extremely fine roots in the substance of the membranes and cellular tissue, and in the parenchyma of organs, where they appear continuous with the final arterial ramifications, as it frequently happens, that an injection, sent into an artery, will pass into the lymphatics of the part to which it is distributed.

The structure of the lymphatic vessels is the same as that of the lacteals. They have the same number and character of coats, the same crescentic valves, occurring in pairs, and giving them the knotted and irregular appearance, for which they are remarkable; -every contraction indicating the presence of a pair of valves.

a

a

lymphatic, before reaching the venous system, passes through a lymphatic gland or ganglion; formerly called a conglobate gland. These organs are extremely numerous; and in shape, structure, and probably in function, entirely resemble the mesenteric glands. They, therefore, do not demand any distinct notice. They exist more particularly in the axillæ, neck, in the neighbourhood of the lower jaw, beneath the skin of the nape of the neck, in the groins, and in the pelvis—in the neighbourhood of the great vessels. The connexion between the lymphatic vessels and those glands is exactly analogous to that between the chyliferous vessels and the mesenteric glands.

ceeding towards the thoracic duct.

indicate the direction in which the chyle passes.

CHAUSSIER includes, in the lymphatic system, certain organs, whose uses in the economy are not manifest,—the thymus gland, the thyroid gland, the supra-renal capsules, and perhaps the spleen. These he considers as varieties of the same species, under the name glandiform ganglions.

The thymus gland is a body, consisting of distinct lobes, situated at the upper and anterior part of the thorax, behind the sternum. It belongs more particularly to fœtal existence, and will be investigated hereafter.

The thyroid gland is, also, a lobular organ, situated at the anterior part of the neck, beneath the skin and some subcutaneous muscles, and resting upon the anterior and 4, a, a, a. Lymphatic vessels pro- inferior part of the larynx, and the first b,b. Lymphatic glands. The arrows rings of the trachea. It is formed of lobes, which subdivide into lobules and granula; has a red and sometimes a yellow colour; and presents, internally, vesicles, filled with a fluid, which is viscid and colourless or yellowish. It has no excretory duct; and, consequently, it is difficult to discover its use. It is larger in the foetus than in the adult; and has, therefore, been supposed to be, in some way, inservient to fœtal existence. It continues, however, through life, receives large arteries, as well as a number of nerves and lymphatics, and hence, it has been supposed, fills some important office through the whole of existence. This, however, is all conjecture.

The thyroid gland is the seat of goître or bronchocele, the swelled neck, Derbyshire neck, papas, &c. as it has been termed

in different quarters of the globe, a singular affection, which is common at the base of lofty mountains in every part of the world; and, in the cure of which, we have a valuable remedy in the iodine. The sorbefacient property of this drug is particularly exerted on the thyroid gland and on the mammæ; and it affords us an additional instance, to the many already known, of remedial agents, not only exerting their properties upon a particular system, but even upon a small part of such system, without our being able, in the slightest degree, to account for the preference. The iodine stimulates the absorbent vessels of the gland to augmented action; and the consequence is, the absorption of the morbid deposit.

Lastly, the supra-renal or atrabiliary capsules or glands, are small bodies in the abdomen, without the peritoneum, and above each kidney. The arteries, distributed to them, are large; and the glands themselves are larger in the fœtus than in the adult. They, likewise, remain during life. These bodies consist of small sacs with thick, parenchymatous parietes; are lobular and granular; the internal cavity being filled with a viscid fluid, which is reddish in the fœtus, yellow in childhood, and brown in old age.

With their uses we are totally unacquainted. By the ancients, they were believed to be the secretory organs of the imaginary atrabilis; and hence their name.

Lymph may be procured in two ways, either by opening a lymphatic vessel, and collecting the fluid, that issues from it, but this is an uncertain method,—or by making an animal fast for four or five days, and then obtaining the fluid from the thoracic duct. This has been considered pure lymph; but it is obvious, that it must be mixed with the product of the digestion of the different secretions from the part of the digestive tube above the origin of the chyliferous vessels.

Its

The fluid, thus obtained, is of a rosy, slightly opaline tint, of a marked spermatic smell, and saline taste. At times, it is of a decidedly yellowish colour; and, at others, of a madder red; circumstances, which may have given occasion to erroneous inferences, in experiments, made on the absorption of colouring matters. specific gravity is, to that of distilled water, as 1022.28 to 1000.00. Its colour is affirmed to be more rosy, in proportion to the length of time the animal has fasted. When examined by the microscope, it exhibits globules like those of the chyle; and, like the chyle, bears considerable analogy, in its chymical composition, to the blood. When left at rest, it separates into two portions;—the one, a liquid, nearly like the serum of the blood; and the other a coagulum or clot of a deeper rosy hue; in which a multitude of reddish filaments appear, disposed in an arborescent manner; and, in appearance, very analogous to the vessels, which are distributed in the tissue of the organs.

When a portion of coagulated lymph is examined, it seems to consist of two parts;—the one, which is solid, formed of numerous