Part 9

1st. Whenever a tight ligature applied to a limb makes the lower part swell, whenever too long standing, a perpendicular position of the superior extremities, &c. produce the same effect, it is to be presumed that the effusion depends upon the compression of the lymphatics, and takes place then like venous dilatations in similar circumstances, because the lymph finds it difficult to circulate. Here then is a case in which the exhalants have nothing to do with the dropsy, which takes place because the absorbents do not take up what the exhalants furnish. If other causes, as a bruise, a wound, &c. diminish the activity of the part, the absorbents directly weakened, are not able to take up their fluids. So if their weakness is sympathetic, that is to say, if it arises from the injury of another viscus, the same phenomenon will be the result of it. In all these cases we find the absorbents much dilated in the dead body: often they are even full of fluids.

2d. But in the organic affections to which dropsy succeeds, the exhalants certainly in the greatest number of cases, pour out more fluids than usual. The pleura is filled in phthisis, the skin is then covered with night sweats, blood is raised, &c. These are the exhalations which I have called passive. They are so abundant on the serous surfaces, that if a puncture is made, the peritoneum often fills again with such rapidity, that as much water is collected in a day, as there would be in a month, if the exhalation was natural. I do not say that the absorbents are not also affected in these cases; but the principal cause of the dropsical effusions is certainly then in the increased action of the exhalants. I could cite other examples, but this is sufficient. Four years since I was engaged upon the absorbents; I observed then that these vessels are not always very evident in dropsical patients, notwithstanding what has been said by many authors, and that very often we see them more easily in very thin subjects. I had not then thought of this difference of dropsies; but in working again upon this system for my Descriptive Anatomy, I think of comparing the cases in which it is dilated and those in which it is not, with the cause of the death.

III. _Termination of the Absorbents._

All the known absorbents unite into two principal trunks. One of these, which is the thoracic duct, receives all those from the lower extremities, abdomen, the greater part of the thorax, and those of the left side of the superior parts. The other is formed by the union of the absorbents of the right side of the superior parts, as well of the head, as the extremities, and of some of those of the thorax. These two principal trunks go into the vena cava superior; around them, many smaller branches also terminate there.

If we examine but little the number of the absorbents distributed in all the parts, it will be easily understood, how enormous the disproportion of their capacity is with that of these two trunks. How is it that all the serum contained upon the serous surfaces and in the cellular texture, that all the residuum of nutrition, that all the fat, the medullary fluid, and synovia, that all the drinks, all the product of the solid aliments that constantly enter the circulation, can pass, in order to get there, through vessels so small? This observation has struck all authors; and it is, I confess, very difficult to explain. In fact, 1st. When there is a disproportion in the capacity of the blood vessels, it is compensated for by an increase of velocity where the caliber is less; thus, though the capacity of the veins exceeds that of the pulmonary artery, still all the blood of the first passes through the second. Now if we examine in a dog the thoracic duct during digestion, which can easily be done by opening quickly the thorax on the right side, raising the lungs of that side, and by cutting the pleura along the aorta, which allows you to see immediately this canal then very white on account of the chyle that is passing through it, if, I say, we examine the thoracic duct in action, we shall see that the circulation goes on there nearly as in the veins. By opening it then, a more powerful throw of fluid does not indicate a greater velocity than that of the venous blood. 2d. It might perhaps be said that during life the thoracic duct is sufficiently dilated to correspond to all the absorbents; but observation proves precisely the contrary. The thoracic duct, full of chyle, is undoubtedly a little more dilated than in the dead body; but I have satisfied myself repeatedly that the difference is not very great. 3d. By supposing that a great quantity of fluids passes through the thoracic duct, notwithstanding its size, the vena cava superior ought to be proportionably dilated between it and the heart; yet it continues nearly of the same size after having received this canal. 4th. Hewson, by taking the fluid of the lymphatics, has proved that it was analogous to that of the serous surfaces; its transparency, when examined in the vessels of a living animal, makes me also believe it, though this would not be a conclusive reason. How can a fluid of the same kind, result from the combination of such different elements, viz. of those which compose the mucous, cutaneous, nutritive, fatty absorptions, &c.

I confess that the different substances that enter the black blood by the thoracic duct and the one corresponding to it, may enter it at different times; that the lymph, the fat, the chyle can each have their time of passing. But first this explanation is not supported by any fact, and the disproportion would also then be very great.

Many distinguished anatomists have thought that the veins absorb, and in relation, to their use, they have joined these vessels to the lymphatics. Haller, Meckel, and before them, Kaw Boerhaave, were of this opinion. Such names deserve undoubtedly an examination of the reasons advanced; let us now consider these reasons. 1st. The thoracic duct has been seen obliterated, and absorption continuing to go on, while life was preserved in the animal. But as they have not observed whether the great right lymphatic and its accessories were obliterated, nothing can be concluded from this fact. Besides the observations upon this point do not appear to me to be well ascertained. They could decide this question very easily, I think, by tying during digestion, the thoracic duct at its entrance into the jugular; it could be readily come at on the inferior part of the neck, where it could be distinguished by its whiteness; no important part need be wounded. This experiment would throw great light upon the general question of absorptions. 2d. Fine injections, made through the mesenteric vein, cover the peritoneum; hence it has been concluded that the absorbents terminate in this vein. But as the venous extremities communicate with the capillary system, and as this gives rise to the exhalants, injections, by going through its numerous anastomoses, can easily be spread in this way, which vitality shuts during life, but which the flaccidity of the parts and the absence of sensibility open after death. 3d. Compression of the superficial veins produces swelling of the limbs; but as this compression is made at the same time upon the absorbents, no inference respecting venous absorption can be drawn from it. 4th. Kaw Boerhaave having introduced water into the intestinal canal, it was afterwards found in the mesenteric veins; but this experiment has been many times repeated since without giving the same result. 5th. Add to these considerations the numerous experiments of Dr. Hunter, to prove that venous absorption does not take place on the surface of the intestines, and you will see that this absorption will appear very uncertain, in these first respects.

But if you look at the question in other respects, you will be unable to deny that certain facts present probabilities in favour of this absorption. 1st. It is almost certain, that the venous extremities take up by the way of absorption, the blood effused in the corpus cavernosum. 2d. We do not see absorbents in the placenta, and yet the umbilical vein takes up all the fluids of this body. 3d. Meckel having injected a lymphatic vessel that went to a gland, the injected mercury passed into a neighbouring vein.

All these observations throw great obscurity upon the termination of the absorbents. I think that if on the one hand, we cannot doubt that the greatest number of these vessels, those especially that come from the serous surfaces, from the cellular texture, from the intestines, have known terminations, we ought on the other to suspend our judgment as to the manner in which the others terminate, and that the question must remain wholly undecided upon this point, till it has been settled by new experiments. Here, as in so many other points, physiology has need of great light. 1st. The enormous disproportion between the absorbents and their common trunks; 2d, the impossibility of understanding from the analogy of the veins, the lymphatic circulation, with the apparatus that injections exhibit as its vessels; 3d, many probabilities against and many in favour of venous absorption; 4th, no other known way for the fluids which enter the blood by the absorbents, than the trunks noticed above. There is nothing but obscurity and contradiction in the different data which would assist us to resolve this problem.

IV. _Structure of the Absorbents._

This structure, capable only of being seen in the great trunks, the thoracic duct, for example, presents us at first in its common organization, a layer of dense cellular texture, of the same nature as that of which we have already so often spoken, of which we shall speak again, and which is found around the arteries, the veins, the excretories, under the mucous surfaces, &c. &c. This filamentous texture, connected only to a certain degree with the vessel, strengthens it however much, by surrounding it with an external membrane superadded to that which is peculiar to it. If, as Cruikshank has done, we turn this duct inside out, and introduce into it a tube of glass of a diameter a little larger than its own, this last membrane will break. It is as in the arteries, in which a ligature cuts the internal membrane and not the cellular. The same phenomenon takes place from inflation; a much greater effort is necessary then to break the cellular texture, than to rupture the peculiar membrane of the thoracic duct.

No fleshy fibre is observed, in an evident manner at least, in the absorbents. Some authors have admitted that they were there, but injection contradicts them, even as it regards the thoracic duct. Blood vessels probably run over the parietes of the absorbents; in ordinary injections they are often very conspicuous on the thoracic duct. We know not if there are nerves there; there is but little appearance of them, if we may judge by the analogy of the veins, which have a great relation in structure with these vessels.

The internal membrane which forms the peculiar texture of the absorbents is continuous with that of the veins, and forms with it an uninterrupted series of small tubes. Delicate, transparent, it is moistened in the dead body by an unctuous fluid, which is, I believe, unknown to it in the living, as that of the arteries is to those vessels. It adheres to the external membrane by a compact cellular texture, which, as in the veins, is rarely subject to ossification. Mascagni has however mentioned an instance of it in the absorbents of the pelvis. But there is another affection analogous to this, which I have already seen many times in this kind of vessels. Their cavity often contains a white matter, like plaster, especially on the external surface of the lungs. Then without any preparation, the absorbents exhibit almost the appearance which they have when mercury fills them.

The peculiar membrane, forms by its folds, valves similar to those of the veins, but much more numerous. We find these united two by two, rarely one exists alone. They leave between them small intervals, very variable however in extent. Hence it happens that the thoracic duct can sometimes be injected from above below through its whole extent, sometimes it receives the fluid only in a short space, according as the valves are more or less numerous in its cavity; which depends also much on the relation of their width to the caliber of the vessel, a relation which varies from the same causes as those assigned for the veins. Hence it happens, that an absorbent filled with injection does or does not exhibit in great number those knots, which, as we have said, indicate valves. Wherever a branch is united to a trunk two of these folds exist at the place of their junction. This is remarkable especially in the thoracic duct, which injected from above, presents a dilatation at the origin of each branch, because in this place the valves are opposed to the fluid. Not numerous in the superficial system of the organs covered by the serous membranes, as upon the convexity of the lungs, and the spleen, they easily allow the passage of the mercury from one division to another, and their ordinary functions are supplied there by the great number of the anastomoses.

Their use is the same as in the veins, viz. to permit the ascent of the fluid, and to prevent its return; but they do not always fully do this. Injection often without difficulty overcomes some of them. In dropsies, in which the absorbents are full, if we raise the skin, we easily distinguish these vessels by their transparency; but soon, notwithstanding their valves, they become empty, and then cease to be visible. Different anatomists have forced air, and even other fluids, into a great number of the lymphatics, by means of the thoracic duct, and consequently in an opposite direction to their valves. All these phenomena do not suppose in these vessels, as in their common duct, varieties in the structure of the valves, in their width, &c. but only different degrees of dilatation and contraction, degrees that are, as I have said, independent of structure. In dilatation, the valves close the caliber less than in contraction.

The valves of the absorbents have the same form and the same arrangement as those of the veins; they partake, by their constant exemption from ossification, of the general character of the membrane from which they arise, and which, by folding, forms them.

ARTICLE SECOND.

LYMPHATIC GLANDS.

I. _Situation, Size, Forms, &c._

These glands are scattered in the different parts in greater or less number. In the superior and inferior extremities, we find but a small number, except at the upper parts, the axilla and the groin. In the ham and at the elbow there are some, and there are engravings of them at the instep. But upon the arm, the leg, the thigh, the fore-arm, &c. they are not found. It is about the articulations that all are met with; in this respect, we can say, that they are constantly increasing from the inferior to the superior, no doubt because in ascending the number of absorbents is continually increasing.

Not numerous on the cranium, they are only on the exterior of this cavity, no one has ever, I believe, been found within it; which proves, perhaps, that it is not the tenuity of the absorbents that conceals them from us there, but that it is because they are of a peculiar nature and different from that of the others. The face contains many of these glands, especially along the stenonian duct, upon the buccinator, &c.

As to the trunk, if we take the vertebral column for a term of comparison, we shall see that there are but very few lymphatic glands, hardly any at its posterior part, and that they are very numerous anteriorly. On the neck, the jugulars are accompanied by a great series of these glands. In the thorax, the posterior mediastinum contains many of them. In the abdomen, they are abundant along the vertebral column, behind the mesentery.

The whole interior of the thoracic and abdominal cavities, considered otherwise than as it respects the spine, is also furnished with them. They are very near each other in the mesentery, at the root of the lungs, around the bronchiæ and in the pelvis. We see from this arrangement, that, 1st. the lymphatic glands are found in general more numerous in the places where the cellular texture predominates, in which they are, as it were, buried, a remarkable relation for which we are unable to assign precisely the reason. There are but few parts abounding with this texture, that do not also abound with lymphatic glands, and reciprocally there are none of these glands where it is wanting. 2d. We see also that the parts the most distant from the common trunks of the absorbents, as the extremities, the head, the back, &c. are less provided with these glands; that the nearer we approach these common trunks, the more numerous they become; so that we might say that they form around them a sort of boundary, which separates them from the secondary absorbents, and which at the same time makes them communicate with them.

The size of the lymphatic glands, is variable, from the tenth of a line in diameter, to the size of a hazle-nut, and even larger. They are oftentimes so small that we can with difficulty discover them, and they cannot sometimes be seen until disease has developed them. Their increase in size is an ordinary effect of scrophulous affections, which often show us lymphatic glands in places where we did not know that they existed, especially on certain parts of the face and neck. We cannot say then that the swellings of the cellular texture deceive us; for the comparison of these bodies, which are thus made evident by the disease, and which no doubt pre-existed, with the known lymphatic glands, and which are then found equally swelled, proves their perfect identity. All exhibit either the same fatty and white substance, or the same caseous pus, according to the period of the disease.

In general these glands are much developed in childhood, diminish in the adult, and almost disappear in old age. They are, it appears to me, a little more evident in women than in men, in the phlegmatic temperaments than in the sanguine. Of all the different enlargements of which they are capable in different places, the tabes mesenterica gives them the greatest size.

Their form, sometimes oval, sometimes more or less elongated, always tending to a round one, which is generally that to which all the organs of animals, and even all those of organized bodies are disposed; whilst those of inorganic bodies assume those of cubes, prisms, &c.

The lymphatic glands, sometimes insulated as in the extremities of the limbs, collect in greater number as they approach their common trunks. The axilla and the groin contain many of them, as I have already said; but in the abdomen, they are united in a group, and are so close to each other in the mesentery, that they have appeared to Azelli to form in this place, not an union of organs, but a single one, which he has taken for a second pancreas, and to which he has given his name.

II. _Organization._

The colour of these glands, reddish in childhood, grey in the adult, becomes of a yellowish tinge in old age, and has that subsidence and flaccidity which then characterize almost all the organs. This colour varies also according to the regions; thus the bronchial glands have a black appearance, inherent in part in their structure, but owing probably also to the fluid that they contain, as the appearance of this fluid proves, when it is pressed out of a divided gland. This colour does not depend on its proximity to the lungs and on their colour, though we know, they have many black spots upon them; the proof of this is, that I have already very often found the lumbar, mesenteric glands, &c. also black. Yet there is no part in which this colour would be more common than around the lungs. Cruikshank, in order to prove the passage of the lymphatics through the glands, says that he has found those in the neighbourhood of the liver yellow in jaundice, in which it is very probable that there is absorption of bile. But this remark is unimportant, since all the parts of the body, without exception, exhibit, in this affection, this colour, which is only a little more evident in the cellular parts.

We cannot deny however but that these glands often take a colour similar to that of the fluid which fills the absorbents, either in a natural state, or in injections, on account of the great number of vascular divisions that penetrate them internally. During digestion, at the moment the lacteals are transmitting chyle, the mesenteric vessels become almost as white as this fluid, and soon lose this colour when the transmission is finished. By filling the absorbent system with mercury, the same phenomenon is observed.

_Common Parts._

The structure of the lymphatic glands, considered in its common parts, is as follows; a very abundant, extensible, loose cellular texture surrounds them, allows them to be moved and easily displaced by the finger when pushed against them. Hence the remarkable mobility of most of these organs, in the first periods of their swelling; in which this texture does not then participate; for it is gradually affected, loses its laxity, and then adhesion succeeds to mobility. Thus in cancer, the glands are first rolling, and afterwards become fixed. In acute inflammations, they are in general fixed, because the neighbouring texture partakes almost always of the disease.

The cellular texture forms besides around the glands a thick membrane which more immediately envelops them, and which deprived of fat and serum, exhibits the nature of the cellular covering of the absorbents. It is this last membrane which, in the ordinary state, gives to the glands an appearance in general smooth and polished; for mercurial injections develop in them some roughness, owing to the prominence of the vessels that run through them in the interior. Some slight depressions are also visible on their surface; they are to these glands, what the furrows on their concave face, are to the liver, the spleen and the lungs; it is through them that the vessels enter. We might think that the arteries were very numerous in the lymphatic glands, if we judged from injections which colour the whole of them, if they are fine and adroitly used; but little reliance should be placed upon this. Simple inspection, in a living animal, which is infinitely more certain, does not discover much blood in these glands. In the fœtus and in childhood, the quantity of this fluid is much more considerable; hence in part the redness that characterizes these organs at this period of life. We are ignorant whether nerves exist in them, and whether any of the numerous branches that the ganglions send in their neighbourhood, especially in the mesentery, are introduced into their texture; I have never traced any of them there.

_Peculiar Texture._

The peculiar substance of the lymphatic glands exhibits a pulp very analogous to that of the nervous ganglions. No fibre can be distinguished in them. Soft in the fœtus, withered in the few glands that remain in old age, this substance, is particularly altered, as I shall say, by scrophulous diseases, and by the influence of the affections of the neighbouring organs.