This system results from the union of a multitude of small vessels which arise from all the parts, and carry different fluids that are poured into the black blood, after having passed through certain peculiar swellings that are called lymphatic glands, and which make a part of the system with them. The whole of the absorbent system comprehends then two things, 1st, the vessels; 2d, the swellings or glands, an improper name, inasmuch as it assimilates them with organs which pour out fluids by the excretories that arise from them.

---

ARTICLE FIRST.
Of the Absorbent Vessels.

We shall examine these vessels in their origin, their course and their termination.

I. Origin of the Absorbents.

The origin of the absorbents can hardly be demonstrated by inspection; it is like the termination of the exhalants. Such is in fact the extreme delicacy of these vessels at their origin, in most parts, that they cannot be seen with the best optical instruments. In some places we see pores; but it is difficult to distinguish their nature, whether they are exhalant or absorbent. Their origin then must be determined by the phenomena they produce in different places. Wherever absorption takes place, it is evident that there they begin. Now in examining attentively the phenomena of absorptions, we see that they are discoverable whenever there are exhalations; so that the same table may serve both for the absorbents and the exhalants; the following is the table for the first.

Let us examine these different absorptions, of which I shall not give the proofs here in detail, because these proofs will be shown in each system from which the absorbents arise. 1st. The external absorptions do not correspond precisely with the exhalations of the same nature. In fact, neither the sweat nor insensible transpiration exhaled by the skin, are taken up by the cutaneous absorbents; these fluids are excrementitious. So the mucous absorbents allow the pulmonary transpiration to evaporate, and the other fluids exhaled upon their surface, to mix with the aliments and afterwards to pass off. It is the substances contained in the atmosphere, in the surrounding bodies, &c. that this kind of vessels takes up by a very irregular absorption, as we shall see, except however that of the chyle, which is not made in a continuous manner, which is subject to great intermissions, and which at other times takes place with remarkable activity.

2d. The internal absorptions, on the contrary, every where correspond with the analogous exhalations. Thus the absorbents take up, upon the serous system, the serum, upon the cellular system the serum and fat, upon the medullary system the marrow, upon the synovial system, the synovia; fluids, all of which as we have seen, had been thrown out by exhalation upon their respective surfaces, and had remained for an instant upon them. These absorptions are made in a constant and regular manner; it is in this that they differ from the preceding. The internal absorbents, incessantly in action, take up in a given time the same quantity of fluids; their action corresponds precisely with that of the exhalants. Observe that there are two essential differences between the external and internal absorptions; viz. that the one are exerted on the one hand on fluids different from those exhaled upon their surfaces, and that on the other they are subject to continual variations and irregularities; whilst the others always take up the fluids exhaled upon their surfaces, and are constant and regular, at least in a state of health. I shall point out in the mucous and cutaneous, systems, the cause of this important difference.

3d. As to the nutritive absorptions, we know much less of them than the preceding; but nutrition evidently supposes them. There is in fact in this function a double motion, one of composition, the other of decomposition. No organ, no part of an organ is formed at one period of the same elements that composed it at a former one. The ancients thought, without positive proof, that the body was renewed every seven years. Whatever may be the period of its renewal, we cannot deny that it is continually composed and decomposed; now the exhalants perform the first nutritive motion, the absorbents the second. Observe in fact, that the internal substances never re-enter the circulation to be afterwards thrown out, except by the way of the absorbents.

The nutritive absorptions differ then from the preceding, in this, that the substance deposited by exhalation and taken up by them, remains in the organs, makes a part of them, and contributes to their composition; whilst the fluids with which the internal exhalations and absorptions are concerned, after having been furnished by the one, and before being taken up by the other, remain out of the organs, upon their surface or in their cells, but do not make a part of their structure.

It is difficult perhaps to conceive how solid nutritive substances can be absorbed by vessels so delicate. Hunter, to whom anatomy owes much both as it respects the absorbents and their uses, has already removed this objection. It may be added to what he has said, that the distinction between solids and fluids is not substantial except when they are in mass; but when they are considered as separate particles, they do not differ; this is so true, that the same particle makes alternately part of a solid and a fluid, as in water that is not frozen and that which is, as in solid or melted lead, &c. Now the nutritive substances are absorbed particle by particle; then the distinction of fluid and solid is of no consequence in the function of absorption.

Since the origin of the absorbents is beyond the reach of our senses, it is difficult, it is impossible even to determine the manner in which they arise, the peculiar structure which distinguishes them at their origin, their communications, &c. They undoubtedly differ essentially according to the mucous, cutaneous, serous, synovial, cellular, medullary surfaces to which they belong; undoubtedly the nutritive absorbents differ remarkably from the others; but nothing can be proved by inspection. What has not been said upon the villous coat of the intestines considered as the origin of the lacteals, upon their small bladders, upon the form of the pores of the peritoneum, the pleura, &c. upon the cellular sponge? I shall not notice here these anatomical hypotheses, which have been made by an abuse of the microscope, and which besides, if they had any real foundation, would not lead to any inference useful to science.

Do the absorbents arise from the capillary system? Judging by injections, it would seem that they did, for many distinguished anatomists, by forcing a fine injection through the arteries, have filled the absorbents in the neighbourhood. I never saw any thing similar to it myself, yet I am far from denying a fact attested by Meckel. If many other experiments should confirm it, it would be established incontestably, it is evident, that the origin of the absorbents is in the capillary system, as the origin of the excretories and exhalants are proved to be in the same system. Besides, the phenomena of absorptions cannot give us any light upon the mode of the origin of the absorbents.

Where they go off from the surfaces or the organs from which they arise, the absorbents are extremely delicate; they elude all kinds of injection. They appear to anastomose with each other, interlace, form a complicated net-work, which contributes much to the structure of some parts, especially of the serous membranes. We know however but little of this interlacing. It is not until they have run a certain course, that these vessels are cognizable by our senses, and that we can consequently study them in a general manner.

II. Course of the Absorbents.

The absorbents, arising from the different parts that we have pointed out, go in different ways.

1st. In the extremities, they are divided immediately into two very distinct courses, the one superficial, the other deep-seated. The former accompanies at first the sub-cutaneous veins, then runs along in their interstices; so that when injections have succeeded well, the whole exterior of the limbs appears to be covered with a kind of lymphatic net-work. The second goes along the muscular interstices, principally in the course of the arteries and the veins. Both tend towards the superior parts of the limbs. When the vessels arrive there, they approximate each other, and are collected into a bundle, in which they are fewer but larger than below, and which passes through certain openings that lead them into the trunk; for example, those of the superior extremities almost all terminate in the axilla, those of the inferior in the groin and some in the ischiatic notch. Now as it is a general rule, that every absorbent should pass through one or more glands, nature has placed at these openings of communication of the extremities with the trunk, a certain number of these glands. Yet before arriving at them, some have already passed through similar glands placed, in a less number, it is true, in the ham and the bend of the arm. It is in the extremities that the absorbents run the longest course without passing through glands.

2d. In the trunk, the absorbents take at first two courses, the one sub-cutaneous, the other deep-seated, which is found upon the internal surface of the parietes of the cavities, for example, between these parietes and the peritoneum in the abdomen, between these parietes and the pleura in the thorax. The first belongs especially to the fleshy parietes and the abundant cellular texture that is found on them. The second belongs to these parietes and the serous surface that lines them. Besides these absorbents, each viscus contained in the preceding cavities, has deep-seated and superficial ones; the first go into the interior of the organ, we see the second on the surface. This distinction is easily made upon the liver, the spleen, &c. The external absorbents of the parietes of the trunk, run a long course without meeting with glands. Those that are spread on the internal surface of these parietes exhibit a similar arrangement. But those of the viscera hardly come out of them, before they meet these glands, and pass through a great number at a time, because they are very near each other.

3d. There are many absorbents upon the exterior of the cranium; but anatomists have not yet found them in its cavity, which agrees perhaps with the almost total absence of cellular texture in this cavity. There are many on the face, superficially, in the muscular interstices, and around the organs that occupy this region. They descend to the neck, where they find in their course a very great number of glands which they successively pass through.

Form of the Absorbents in their course.

The absorbents differ essentially from the veins in this, that for a great distance they keep of the same size. Whilst in the venous system the vessels are constantly becoming larger, so that a branch can hardly go a few inches without doubling its size, those in the absorbent system remain for a long time the same. When injected these vessels appear like long white threads running upon the organs.

It follows hence, 1st. that the lymph never circulates like the blood, in considerable masses, but always in very fine streams; 2d. that the absorbents are very numerous; for their number compensates for their size; thus all the surfaces are covered with them, whilst they have but few veins and those of considerable size; 3d. that the absorbent system has not really the form of a tree, like the arterial and venous systems; the manner of division is wholly different. The absorbents are very commonly straight; when they are tortuous, their curves are entirely unlike those of the veins or the arteries. In fact in these last, when the tubes have become as fine as the absorbents, their curves are brought near each other and are small in proportion to the size of the vessel. On the contrary the windings of the absorbents are great; the curves that result from them have often a very considerable extent; they wind in long folds upon the extremities, when they are not straight there.

Viewed externally, the absorbents are not always cylindrical. When filled with injection, they often appear full of knots; this undoubtedly arises principally from the valves. Many authors have represented them as a series of successive contractions; this is however true only to a certain extent.

I have often seen in living animals, in dogs in particular, evident dilatations, a kind of little bladders in the course of a lymphatic, containing serum. It is upon the concave surface of the liver and the gall-bladder, that I have most often observed them. When these bladders are pricked with a lancet, the fluid flows out and they disappear immediately. In making experiments with other views, I once saw two or three of these small dilatations in the neighbourhood of the gall-bladder. Having suffered the liver to fall back, to examine the intestines, I was astonished at not being able to find them an instant after; they disappeared without doubt by the contraction of the vessel. I would remark upon this subject, that the liver is the organ upon which these vessels are best seen in living animals; but it is necessary to examine its concave face the instant the abdomen is opened; for the contact of the air by contracting them, soon prevents their being distinguished.

Besides I believe that in no case are the absorbents as much distended during life by serum, as they are by mercury from injections. When these have succeeded well, we see upon many parts a net-work of very evident vessels. On the contrary, most commonly nothing similar is to be seen in living animals. With whatever promptness we examine most of the surfaces which the serous membranes cover, surfaces that can be laid bare without making the blood flow, nothing is seen, except sometimes small transparent striÆ, which soon disappear. Now it is impossible that if the absorbents were as full during life, as they are by injections, but what their transparency contrasted with the colour of the surrounding parts, would render them evident. I have selected however very large dogs, to try to see their course better. I believe that injections double at least the diameter of these vessels.

Of the Capacity of the Absorbents in their course.

The capacity of the absorbents is remarkably variable; it depends entirely, in the dead body, on the state in which these vessels were in the last moments. In subjects of the same stature and age, they are sometimes very apparent, at others hardly visible. They are double, treble even, in some dropsical patients, what they are in a natural state. Many authors say that they have seen branches almost equal to the thoracic duct, and larger than the trunk of the right side. To be convinced of the extreme variety of the absorbents, without the assistance of injections, take the lymphatic glands in different places, then dissect carefully the parts in the neighbourhood; you will easily find all the absorbents that go to them. Then you will be able to satisfy yourself of the extreme variety of their size; we can even in this way trace them far enough without injection. Sometimes in order to find the end of the thoracic duct, I take a gland in the neighbourhood of the second lumbar vertebra; thus following the empty lymphatic tubes that go from it towards the canal, I find it without difficulty.

When we are not in the habit of finding immediately the absorbents, this method of searching for them by means of the glands, which are always very evident, infallibly succeeds; it cannot be used it is true in the extremities; but in the thorax and especially in the abdomen, it is very convenient. For example, by taking the inguinal glands we can trace these vessels to the thoracic duct, by injecting them, or even without. Some authors have advised making an opening in the gland and placing a tube in it; this rarely succeeds; it is much better to open the vessels that go from the gland, at the place where they go off.

The absorbents usually flat in the dead body, because they are empty, never exhibit in this state a diameter proportional to that which injections give them; whatever may be the varieties of capacity, the fluids that we force into them always increase this capacity. It is this flattening after death, that often makes us in attempting to open them with a lancet, cut through both their parietes, and thus render it more difficult to inject them.

The best proof of the extreme variety of the capacity of the absorbents, is the necessity of choosing particular bodies in order to inject them, the very great difficulties that often take place in finding them in some subjects, whilst they are seen immediately in others, and can be traced in the inferior and superior extremities, through the cellular texture, without having glands for a guide. It is not necessary then, after what has been said, to consider the caliber of the absorbent vessels in a determinate manner. Constantly varying, according to the state of the lymph they contain, they have no standard size to which we can refer their increase or diminution. This is the peculiarity of all the extensible and contractile canals, like those in the animal economy; it is that which prevents us from making any kind of calculation of their capacity.

These varieties of the absorbents are not general as in the veins, all the great trunks of which, for example, are simultaneously dilated when there is an obstruction in the lungs. Here sometimes one only, sometimes many branches enlarge; the others remain contracted. Sometimes the dilatation is general in a part, very often there are remarkable disproportions of capacity in the same vessel; it is double in one place what it is in another, though it has not received branches.

Authors have been much puzzled to determine the capacity of the thoracic duct. I believe it, for it is never found twice the same. These varieties do not depend on the constitution of the subject, but only on the functions, and the state in which these functions are found at death. Whether it be dilated above, contracted in the middle, exhibiting below a little bladder, called by some the reservoir of the chyle, &c. are circumstances the greatest number of which vary incessantly during life, according to the quantity, the nature of the lymph, and the obstacles to its course in this or that part. We find a hundred varieties of the thoracic duct and the absorbents in a hundred different subjects. The same subject has perhaps undergone these hundred varieties at the different periods of his life. If life returned and was destroyed many times in the same man, the venous and absorbent systems would exhibit a number of varieties equal to the number of times he had died.

We see from these considerations to what are reduced all these minute examinations of proportion in the capacity of the vessels, which fill our books of physiology.

If we compare the amount of the veins with those of the absorbents, it is difficult undoubtedly after what has been said, to form any precise idea of it; but we can make approximations. Now the absorbents do not appear hardly inferior to the veins; as to the branches, for example, the whole of the lymphatics of the lower limbs, placed by the side of the capacity of the venous trunks, does not appear much inferior to it. So in all the other parts, the veins being larger, but the absorbents more numerous, the disproportion is not very great.

From this it seems as if there would be but little difference between the trunks that terminate the veins and those that are the terminations of the exhalant system; however this difference is enormous, as we shall see.

Anastomoses of the Absorbents, in their course.

In the extremities, on the exterior of the trunk and the head, in the intermuscular spaces, &c. the anastomoses are very evident. We see branches of communication going from one absorbent to another; so that we might often say that these vessels are bifurcated. But this appearance is most usually deceptive; for each branch of the bifurcation is almost always as large as the trunk.

Under the serous surfaces, as on the convex face of the liver, the lungs, the spleen, &c. the anastomoses are infinitely more numerous; it is a kind of net-work in the plates of authors; for I confess that I have never injected this portion of the absorbent system.

The anastomoses of the absorbents are made, 1st. from one vessel to another that is contiguous to it; 2d. from the sub-cutaneous divisions to the intermuscular in the extremities, and in the organs, from the sub-serous divisions to those that occupy the interior of these organs. 3d. They take place between the absorbents of the superior regions and those of the inferior; 4th. between those that go to the thoracic duct and those that go to the great lymphatic vessel of the right side, &c.

By these anastomoses we understand how a tube with mercury, being placed in one absorbent, many others around it are filled. They are so much the more necessary, in the system of which we are treating, as the lymph is subject, like the black blood, to an infinite variety of causes of delay in its course, from the want of an agent of impulse at the origin of the absorbents.

Gravity, external motions, different compressions, &c. have upon the motion of this fluid, the same influence as upon that of the veins; gravity especially has much influence. We know that if the powers are a little diminished after long diseases, too long standing renders the legs oedematous; hence why they are always more swelled in the evening than in the morning. As to compression, if it is only moderately great and acts upon many absorbents, it also produces oedema. It is not the size of the surface compressed that has an influence upon this phenomenon; it is only the number of absorbents that pass through this surface. Thus by the head of the humerus being in the axilla, the arm is frequently made to swell, whilst more extensive compressions across the deltoid muscle, where there are fewer absorbents, do not produce this effect.

From these phenomena, it is necessary then that there should be the same means to favour the lymphatic circulation, that there are to aid the venous. These means are especially the anastomoses; it is by them that the first of these circulations is continued, notwithstanding all the external obstacles that our clothes in certain places create, notwithstanding the different pressure that the organs make upon each other. It is only when the whole of the absorbents of a part is compressed, that the motion of the lymph is interrupted. Thus the womb becoming very large in pregnancy, and pressing upon all those of the lower extremities, these extremities become dropsical. I hardly know any organ in the abdomen but this, which by its position can produce these general infiltrations by compression. The liver and all the other organs are not capable of producing a similar phenomenon. When dropsy takes place from an affection of them, it is rather because the functions of the exhalants are increased.

Remarks upon the Difference of Dropsies that are produced by the increase of exhalation, and those that are the effect of a diminution of absorption.

This leads to an observation that appears to me to be very important in dropsies, viz. the determining when the defect of the action of the absorbents produces them, and when they arise from the increase of that of the exhalants.

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 foetus 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 foetus, 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.

This peculiar texture has a greater or less density. We find it more solid, and resisting better the injection of mercury in the superficial glands than in the deep-seated. They have cells at short distances, especially in childhood; they contain a whitish fluid, which disappears as well as the cells themselves, at an advanced age. This fluid, of a very peculiar nature, can only be compared with those of the thyroid and thymus glands, which, like this, are found as it were extravasated, in the interstices of the organs that separate them, they have no reservoirs, and their use is wholly unknown. There is no doubt that the great quantity of blood that enters the lymphatic glands in childhood, is owing to the superabundance of this fluid. Sometimes in the adult, there is a great quantity of it in the bronchial glands, where it is of a blackish colour. Some physiologists have thought, without anatomical proof, that it is spread out upon the bronchiÆ, and that it forms in part the black spittle that is thrown out in the morning. Fourcroy in particular is of this opinion; he attaches importance to the black colour of these glands, which are perhaps, according to him, the reservoir of the carbonaceous matter of the blood. The fact is, they belong to the lymphatic system; that in a great number of subjects they are grey or red; that we do not know that they have an excretory; that their texture is pulpy like that of the analogous glands; and that their size distinguishes them however from all others. I have observed that the acids, the alkalis and stewing, alter but little their black colour and that of the fluid contained in them.

It is in the peculiar texture of the lymphatic glands that the absorbents ramify, after being introduced there in a certain number, and each with numerous ramifications, and afterwards go out by many other branches which also give rise to an infinity of smaller ones. Each gland may in this respect be considered as the centre of two small opposite capillary systems, which anastomose with each other. In the interior of these glands, these branches very tortuous, folded upon themselves in different ways, occupy a great part of the peculiar texture of these organs which many thought in consequence were nothing but an interlacing of the absorbents; an idea that is not proved, since this texture is not yet well known.

I have observed that it is susceptible of less horny hardening than most of the other animal textures. It approximates in this respect that of the true glands; but it differs in this, that instead of continuing to harden by long continued boiling, it soon softens, becomes pulpy, and breaks with great ease under the finger. The acids after having crisped it, dissolve it also more easily than many of the other textures; the sulphuric and muriatic are remarkable for this. Exposed to the action of the alkalis, it loses some of its principles, which weaken these menstrua; but it is never entirely dissolved.

---

ARTICLE THIRD.
PROPERTIES OF THE ABSORBENT SYSTEM.

We shall consider in the same article the properties of the absorbent vessels and those of their glands.

I. Properties of Texture.

Extensibility of texture exists in the absorbent system. 1st. The thoracic duct is distended in an evident manner by injection, before the rupture of its peculiar membrane takes place. 2d. I have said that the absorbents examined around the serous membranes in a living animal, principally in the liver, often exhibit little bladders or considerable dilatations. Are these dilatations varices? is there an analogous character in this respect, between the absorbents and the veins? I know not; whatever they are, they can be very considerable in a long absorbent vessel. 3d. When we tie the thoracic duct, not only that swells, but the lymphatic vessels of the abdomen also dilate, and this ligature is the most convenient means of observing the lacteals. This extension has undoubtedly limits; carried too far, it would probably produce in a natural state the rupture of the vessels, as happens from injections. We have not yet any data founded upon observation or experiment, respecting this rupture, though some authors have endeavoured to explain by it the formation of most dropsies.

Contractility of texture is evident in the absorbent system. 1st. When the thoracic duct is distended even in a recent dead body, and the fluid is discharged by puncture, it immediately contracts. 2d. All the absorbents contract also as soon as there is no more fluid in their cavity. This phenomenon is remarkable during the absorption of chyle; when that is finished, these vessels evidently disappear by the effect of this contraction. 3d. The absorbent glands, swelled at the moment chyle is passing through them, afterwards lose much of their size by this contractile power.

II. Vital Properties.

We have but few data concerning the animal properties of the absorbents. Sensibility of relation does not appear to exist in them; it is difficult to ascertain this by experiments. When we puncture a lacteal when it is full of chyle, a lymphatic filled with serum on the surface of the liver, or even the thoracic duct, the animal gives no indication of pain. But what inference can be drawn under circumstances, in which the abdomen being opened, the numerous painful sensations would render nothing, comparatively, the slight sensation which the puncture produced, admitting that it existed? No experiment, I believe, has yet been attempted to ascertain if irritation carried to the interior of these vessels produces a sensible effect. Probably the same result would be obtained by fine injections used for this purpose, as has been for the veins, considering the analogy of structure and the continuity of the peculiar membrane of both systems.

There are circumstances however in which the absorbents have a very acute sensibility, viz. when they are inflamed. It is a very frequent phenomenon in diseases, that there is a very evident swelling and redness, along the course of the sub-cutaneous absorbents in the lower extremities, giving considerable pain to the patient, terminating at the inguinal glands, or even extending beyond. In wounds with a poisoned instrument, in the acute pains of a whitlow, &c. a very painful sensation is often felt the whole length of the absorbents of the superior extremities.

The lymphatic glands do not appear to enjoy, in a natural state, animal sensibility, when they are irritated in different ways, which can easily be done. But inflammation may develop it in these glands as in the absorbents, by raising to a high degree their organic sensibility. Thus the pain is very acute, when after a puncture made by an infected instrument, after a sprain, &c. these glands swell. We know the extreme suffering that arises from those in the axilla, when they swell and suppuration succeeds. Shall I speak of the pains experienced from the mesenteric glands when cancerous? Who is ignorant of those which buboes occasion, &c.?

As to animal contractility, it is entirely wanting in the absorbents and their glands.

The organic properties exhibit in the absorbent system, the following arrangement. Sensible contractility has been allowed them by Haller. It is founded upon this, that the lymphatics easily empty themselves of the chyle that passes through them, and upon this also, that by touching them with sulphuric acid, they crisp immediately. But sulphuric acid, like all the concentrated acids and caloric, produces the same effect upon all animal substances, even after death; it is the horny hardening. When the absorbents, particularly the thoracic duct are touched with the point of a scalpel, no contraction follows. If they are capable of contracting upon themselves, it appears that it is when they cease to be distended, and not when they are irritated; and that it is consequently by their contractility of texture. The sensible organic contractility is then at least doubtful in them, if it exists it is very obscure and at most to be compared to that of the dartos muscle.

The organic sensibility and the insensible organic contractility are evidently found in the absorbents. It is by these properties that they perform their functions, that fluids are absorbed by them, that they circulate in their branches, &c. &c. These two properties are remarkable in them in this, that they continue some time after death. A fluid injected when the animal is still warm, is absorbed, either on the serous or mucous surfaces. It is less easy in the cellular texture. We can prolong a little this absorbent power, by supporting the heat artificially by a bath. This has in general less efficacy than I thought for a long time. Various recent experiments have convinced me of this. This arises no doubt from the fact, that it is the vital heat and not an artificial one, which is necessary to the exercise of this function, or rather vital heat and absorption are two effects of a common cause, viz. organic properties. As long as these properties remain in the solids, they retain caloric and absorb. But the moment they are gone, the heat goes and at the same time absorption ceases. It would be useless to expose to caloric, solids that life had entirely abandoned; they would become warm; but they could exhibit no vital phenomenon. In the same way it would be useless to keep up the heat of an animal recently killed, by making an artificial one succeed the natural. It is organic sensibility and insensible contractility, that must be prevented from escaping to prolong absorption. If artificial heat keeps up this function, it is only by first keeping up these properties. We cannot calculate upon absorption when the animal is cold, though Mascagni and many others have said otherwise. I have in vain attempted to keep it in action then; generally I have not observed it above two hours after death. The organic sensibility is in relation with many fluids in the absorbent system, and it is in this that it differs from the other systems, the glandular, for example, which is never in relation but with one particular fluid, and which rejects all the others in a natural state. Water and other mild fluids can easily be absorbed, though very different from the lymph. In the natural state, the thoracic duct alternately admits chyle and lymph.

Character of the Vital Properties.

From what has been said, it is evident that the organic properties perform the principal part in the peculiar life of the absorbent system. These properties are much more conspicuous there than in the venous system; at least they are much more capable of being raised. In fact there are ten inflammations of the absorbents for one of the veins. This disposition to inflame from the least virus that passes through their tubes, from pains, though not severe, that are felt at their extremity, particularly characterizes these vessels. It is rare that there is found in the course of a vein, those swellings, pains and inflammations so frequent in the course of the absorbents. This difference proves a diversity of structure in the peculiar membrane, notwithstanding its continuity with that of the veins. In fact at the period when experiments were made upon the transfusion of medicines into them, authors have not related any case of venous inflammation from the contact of foreign substances upon the membrane of the veins; whilst practice frequently presents us this fact in the absorbents.

The lymphatic glands especially have a great tendency to inflammatory swellings, when deleterious substances that are absorbed come in contact with them. In the first periods these substances confine their effects to the first glands they meet; thus the absorption of the venereal virus hardly extends beyond the glands of the groin; thus the axillaries alone swell when a puncture is made with an infected instrument, &c.; the glands that follow, remain untouched.

Though much disposed to inflame, the lymphatic glands exhibit however more slowness in this affection, than many other animal textures, the cellular and cutaneous, for example. We know that phlegmon and erysipelas go through their periods quicker, than the inflammations of the inguinal, axillary glands, &c. The pain of which these inflamed glands are the seat differs also much from that of these two affections; it is more dull, obscure, &c. The pus is more slow in forming; it resembles considerably cellular pus; it differs much from that of erysipelas. There are few textures in the economy that are more disposed than this to hardening after inflammation. For one single time that the skin become scirrhous after erysipelas, the lymphatic glands become so twenty. This is truly one of their distinctive characters.

The absorbents often exhibit to a certain degree, like their glands, a character of slowness in the phenomena over which their organic properties preside. For example, when concerned in a wound, they contract, crisp up and close more slowly than the sanguineous capillaries, that are then also concerned; hence the flow of serum that continues for some minutes after that of blood has ceased. This phenomenon is constant in small wounds. If the absorbents and the capillaries had the same degree of insensible contractility, it certainly would not take place.

Here then are new proofs of the principles of which we have every instant occasion to present the consequences in this work; viz. that the vitality peculiar to each system, the particular degree of vital forces that characterize them, imprint upon all its affections a peculiar tinge and aspect, if I may so express myself, unknown to all the other systems.

Differences of the Vital Properties in the Absorbent Vessels and their Glands.

Though we have considered at the same time the vital properties in the glands and in the absorbents, though anatomy shows the first to be an assemblage of folds and vascular windings, yet it cannot be denied that they have a peculiar kind of vitality, by which they are distinguished from the absorbents that come to them. It is this peculiar kind that exposes them to certain diseases of which the absorbents are not the seat, at least not in so evident a manner. The scrophulous virus seems more especially to attack them. They are particularly affected in tabes mesenterica, strumous diseases, &c. In the innumerable swellings of which they are the seat in consequence of organic diseases, the absorbents do not appear at the same time altered in their texture. It seems even that in a very great number of cases, the numerous folds that these vessels form in the glands, do not partake of their organic injury; they, in fact, transmit the lymph as usual. Nothing is more common than to see abdominal and thoracic enlargements of these glands in children, without producing serous effusions, even at the most advanced periods. In opening the bodies of small subjects, I have often been astonished at this phenomenon. The lymphatic vessels are not even more dilated, at least we do not find them easier in children affected with tabes mesenterica, than in others. We can hardly ever discover them at this age to inject.

Sympathies.

The absorbent system is much disposed to receive the sympathetic influence of the other organs. This disposition relates, 1st, to the glands; 2d, to the vessels themselves.

One of the phenomena which the examination of dead bodies perhaps most often exhibits, is the swelling of the lymphatic glands from the organic affections of the principal viscera. We observe this phenomenon, 1st, in the neck from the affections of the thyroid gland and sometimes of the larynx, in the jugular glands; 2d, on the chest from cancer in the breast, in the axillary and often in the mammary glands, from every kind of phthisis in those that surround the bronchiÆ, very rarely if ever from diseases of the heart, whether aneurism, ossification or diseases of the valves; 3d, in the abdomen, from cancerous diseases of the stomach, especially of the pylorus, and most of those in which the texture of the liver is altered, in the numerous glands that accompany the biliary vessels and those surrounding the pancreas; from schirrus of the intestines, from their cancers, which are in general rather rare, in the mesenteric glands; from the affections of the womb, the rectum, and the bladder, in the glands of the pelvis; from schirrus of the testicles, diseases of the urethra, in the inguinal and lumbar glands, &c.; 4th, on the superior extremities from punctures, bites and most of the inflammatory affections in the axillary glands; 5th, on the inferior extremities from many affections in the inguinal glands.

These swellings of the lymphatic glands are of the same nature as the affection that produces them; if that is acute they are so, if chronic they pursue the same course. The swelling of the glands in the axilla is acute, if it is the consequence of a prick of the finger, of a whitlow, &c. and chronic, if it arises from cancer.

I am far from considering all these different swellings as the result of a sympathetic influence exerted upon the gland. No doubt the conveyance of absorbed matter produces the effect, as happens when there is some virus, punctures with poisoned instruments, &c. producing the swelling. But sometimes also sympathy alone is the cause. When by the acute pain that a whitlow, a splinter under the nail or a bruise of the finger occasion, the axillary glands swell; when the same glands swell from the effect of a blister applied to the arm or fore-arm, &c.; when this phenomenon happens in the inguinal glands from a blister on the thigh or the leg, of which I have seen many cases, &c. &c. there is certainly no matter conveyed to the gland; it is an effect of sympathy.

Most surgeons believe that every cancer in the breast, with swelled glands, requires their extirpation. I believe that in some cases they may become cancerous, but I doubt if this happens in the greatest number. 1st. In old ulcerated cancers of the breast, they continue most often swelled during the whole of life, without suppurating. 2d. After operations, in which some deep seated ones have been left, we rarely see them become cancerous. When the cancer is reproduced, it is the wound that opens again. 3d. I have many times compared the texture of a gland of the axilla enlarged by a cancer of the breast, with that of the bronchial glands enlarged in phthisis, with that of the sub-hepatic glands swollen from steatomatous tumours, hydatids of the liver, &c. and I could discover no difference. 4th. Finally, all those who open many dead bodies may be convinced that almost all the organic diseases of the viscera which have many glands around them, are accompanied with their enlargement, whatever may be the nature of those diseases. This phenomenon struck me so much, that at one time attributed the effusions which terminate almost all these organic diseases, to the difficulty the lymph experiences in passing through these glands. But the absence of these swellings in the diseases of the heart attended with dropsy, the frequent absence of swelling of the superior extremities when the axillary glands were enlarged, the tumefaction of the lower parts, the glands of the superior being alone swelled, and many other similar proofs, which made me consider the serous effusions that take place then, as passive exhalations, analogous to those that produce hemorrhages, did not permit me to adopt this first opinion.

It is essential to distinguish the swellings of the lymphatic glands by the influence of the diseases of the neighbouring viscera, from those which arise from tabes mesenterica and other analogous, scrophulous diseases. 1st. In the latter case, the texture of the gland is always primarily affected; it is only secondarily in the other. 2d. The one from scrophulous affections appears exclusively in childhood; the other at all ages. 3d. Finally, a gland swollen from the affection of another organ, most frequently preserves a texture, and colour analogous to its natural state. It is only in the last periods that the texture becomes sometimes hard, like cartilage, and even suppurates; but it is not with the same phenomena as the texture of the mesenteric and bronchial glands swollen by scrophula. The appearance and structure are wholly different. This last exhibits in this case a white substance which is found in small quantity in the first periods; so that when we cut the gland, we easily distinguish this substance from the texture of the gland that remains, where it still exists, with its natural colour and arrangement. In the latter periods, this white matter has encroached upon the whole gland, the texture of which has disappeared. However in phthisis, and sometimes, though more rarely, in cancers, the swelled glands exhibit in consequence an analogous appearance; but in all the other cases it is different.

We know that nature often chooses these glands in important fevers, as the place of the crisis. They are the seat of what are very improperly called parotid tumours, in adynamic fevers.

The absorbents are, like their glands, influenced by the affections of the neighbouring organs. I am well persuaded that the different alterations which the absorption of chyle undergoes, the absorption of the aqueous part of the bile and the urine, and the derangement of those of the serous surfaces in many diseases, are effects purely sympathetic. But it is not very easy to distinguish when they are not so. There are certainly sympathetic absorptions, as there are sympathetic exhalations and secretions.

On the other hand, the absorbent system being affected, the other organs very often experience sympathetic influences. In tabes mesenterica, and in the enlargement of the bronchial glands that correspond with it, there are many symptoms that evidently arise from the sympathetic relations that connect these glands to the other organs. It is not my province to point out these symptoms.

As to the influence of the diseases of the absorbents upon the other organs, we know but little of it. When their course is inflamed from a puncture, from a wound with an instrument having on it some virus, &c. there are often vomitings, diarrhoea, &c.

---

The functions of the absorbents are not at the present day a subject of doubt with any anatomist; but the manner in which these functions are performed, are far from being so well agreed upon. The first idea has been to compare the action of the absorbents with that of capillary tubes. But if we reflect a little upon this action, it is easy to see that these phenomena are wholly different from those of inert, capillary tubes. I think that we never should be able to say precisely, how an absorbent orifice, being immersed in a fluid, takes it up, seizes its particles and makes them ascend in its tube. But what is undoubted in absorption is that the vessels derive this faculty from the vital forces which they have; that it is only the relation existing between the particular kind of organic sensibility with which they are endowed, and the fluids with which they are in contact, that is the immediate cause of the phenomenon. Do you wish numerous proofs of this? See the lacteals choosing only chyle from among the variety of matter contained in the intestinal canal; see the absorbents of the bladder and the gall-bladder leaving many of the elements of the urine and the bile, to take only the aqueous part of these fluids; see the cutaneous absorbents, the mucous ones of the bronchiÆ, &c. selecting only certain principles from the air and leaving others. Often inactive for a long time, they immediately recommence action when any substances in relation with their sensibility are presented to them. Observe the fluids injected or effused into the cellular texture, they are taken up or left by the absorbents of this texture, disappear promptly, or remain and occasion suppuration, according as they agree with or are repugnant to their sensibility.

We cannot deny that in the natural state the sensibility of the absorbents has a particular type, to which certain substances are alone accommodated, and which alone on this account can be absorbed. The exercise of the organic sensibility then always pre-exists in absorption, as it does in secretion, nutrition, &c. Thus in the physical phenomena, the exercise of gravity always precedes the fall of heavy bodies. Thus the power of attracting is put into exercise before the motion of the planets takes place, &c. &c.

II. Varieties of Absorption.

It follows from what I have said, that whenever the organic sensibility of the absorbents is altered in any way, absorption must necessarily experience a corresponding derangement; now this is what constantly happens. Serum often bathes for whole months the absorbent orifices, in dropsy, without raising their sensibility sufficiently to be taken up by them. Let any cause increase this property, instantly absorption takes place. Observe some indolent tumours which remain for a long time in the same state by the stagnation of their fluids, they are immediately discussed when certain medicines applied to them rouse the dormant sensibility of their absorbents. Discutients do not act upon the fluids themselves; they do not attenuate, or cut them, according to the vague language of physicians, but by changing the degree of force of the absorbents, they render them able to act. It is so true that it is in this way that different resolutions are effected, that often a slight degree of inflammation is previously necessary to their development; all surgeons know this. Desault did not consider most of the swellings of the testicles as an obstacle to the operation for hydrocele by injection. On the contrary it often happened, that after the irritation produced in the testicles by the surrounding membrane, the enlargement disappeared, which was only kept up by the want of energy in the absorbents.

The alterations of organic sensibility can diminish, increase, or variously modify this property. Let us cease to wonder then at the extreme variety of the absorptions; let us not be astonished, if many fluids, besides those ordinarily taken up, can pass into the blood by the absorbents; if the bile, the urine, the mucous fluids, which are usually rejected, can enter the circulation; if the blood effused in the cellular texture is taken up by these vessels. The forces of life impress, by their extreme variety, the same character on all the functions over which they preside.

Much has been said of putrid matters passing into the blood, and there serving as a cause for diseases. This infection of the blood has undoubtedly been exaggerated; but I am convinced that in many cases it is real. Why are the colour, consistence, odour, and nature of the excrements so very variable? If the same substances are always absorbed from the aliments, it is evident that the residue of these aliments would always be the same. Observe the innumerable varieties of the urine, the bile, the mucous fluids, &c. according to the difference of the principles that concur to form them. Why should not the chyle present the same variations? it would be the only fluid of its kind in the animal economy if it did not change under many circumstances. Now, whence can these changes come, if not from this, that the lacteals present numberless varieties in their organic sensibility, varieties, each of which admits only certain principles and rejects the others?

The absorption of the lacteals, which, in an ordinary state, introduces into the blood only nutritive substances, can then often be a way open for the admission of many morbific principles. Thus in the lungs, the vessels which take from the air the substances proper to colour the blood, often draw in principles injurious to their functions, according to the different alterations that their sensibility can experience.

In the ordinary state, the kind of organic sensibility and of tone of the cutaneous and mucous absorbents, shuts out all external substances that are hurtful. But when this kind is changed, the way can in an instant be open to them. Does not pus remain without mischief on the cellular texture, in most wounds? Let an imprudent application raise there a little the forces of the absorbents, it is taken up by them; the ulcer dries up; the pus passes into the blood; and then follows the whole sad train of the symptoms of re-absorption which commences.

We can say, that a thousand channels are incessantly open in our organs, to morbific principles. The organic sensibility, placed as a sentinel at their mouths, indicates according to the manner in which it is affected, to the insensible contractility when it is necessary to open or shut them.

It is exhalation that contributes to the formation of most tumours; it is absorption that serves for their cure.

If I were to run over the phenomena of absorption in the different ages, sexes, seasons and climates, I could show constantly the differences of organic sensibility always preceding the differences of this function. I shall speak of them in the different ages.

The causes that vary the natural type of the sensibility of the absorbents, are, as in all the other functions, direct or sympathetic; 1st, direct, as when by previous friction on the skin, we excite the absorbents, and force them to act, which they would not have done without this; 2d, sympathetic, as when the absorbents, feeling the affection of a distant viscus, increase or diminish their action, according to the kind of influence they receive. We have spoken of this phenomenon in the sympathies of the different systems.

III. Motion of the Fluids in the Absorbents.

The fluids once absorbed on the different surfaces of which we have spoken, are carried by a successive motion to the common trunks, which transmit them to the black blood.

We know not the laws of this motion. It is evident from many observations formerly made, that it has much analogy with the motion of the venous blood; but it is also distinguished from it by some differences.

It appears to be in general more slow. The thoracic duct opened when it is full of chyle, does not throw out its fluid as far as a vein of the same size.

The motion of the lymph does not seem to be subject to a reflux in the neighbourhood of the heart, like the venous blood. For example, the venÆ cavÆ, jugulars, &c. are so much the more dilated, in proportion to the obstacles the lungs have opposed to the return of the blood. Now in injecting the thoracic duct, I have never observed between its dilatation and contraction, and the state of the pulmonary organ, any kind of relation. On the other hand, we never find this duct full of lymph, as we find the veins full of blood, when an obstacle has interrupted the motions of the fluid in the last moments.

How happens it, that in the reflux that produces the venous pulse of the jugulars, the blood does not enter into either absorbent trunk? The valves, arranged to prevent the entrance of that, which in a natural state, flows towards the heart, are evidently useless here. We can clearly attribute this phenomenon only to the relation existing between the orifice of these trunks and the black blood, as the orifice of the larynx, foreign by its vitality to external bodies, repulses every fluid but the air. Blood is never found in the thoracic duct.

There is in the venous blood an evident continuity of motion, from the capillary system to the heart; it is from this system that it goes, to be propagated, if we may so say, to that organ. The motion of the lymph, on the contrary, is incessantly interrupted by glands, each of which, as I have said, exhibits really in relation to the vessels that enter and go out of it, a small capillary system. At each gland the motion necessarily changes its impulse; now as the state of these glands is susceptible of many varieties, we can easily conceive, that the motion of the fluids circulating in the absorbent system, necessarily presents a great number of them; that it may be rapid in one part, very slow in another, regular here, there irregular, &c. Hence we must not be surprised if we find some absorbent vessels dilated, whilst those of the neighbourhood are hardly perceptible. There is indeed a kind of variety in the veins, but it always has its source in the origin of these vessels, and never in their course, as takes place in the absorbents.

The continuity of the venous blood and the frequent interruptions of the lymph should establish differences not only between the motions of the two kinds of vessels, but also in the composition of the fluids. The first is necessarily everywhere the same; the second may vary at every gland, and take new modifications at each of those through which it passes.

I should be disposed to think that the insensible contraction of which the small capillary system of each gland is capable, would aid the motion of the lymph, by diminishing the course that this fluid must take, without a new impulse, from the origin of the absorbents to the black blood, if these organs were wanting. In fact, we know that in the extremities where there are much fewer glands, there are more frequent effusions than in the trunk where the absorbents pass through them at every instant; I speak of those effusions which ought evidently to be attributed to the want of circulation of the lymph, as those arising from compression, too long standing, &c. and not those that depend on an increased exhalation, like those after organic affections.

We see, from what I have said thus far, that we have only a few disconnected views upon the motion of the lymph; that of the veins, though still requiring much research, is yet more known; but in order to give a perfect knowledge of these subjects, the first especially, many experiments and much further labour are necessary.

IV. Of Absorption in the different Ages.

In the foetus and in childhood, absorption relative to nutrition is not in proportion to exhalation. Many substances remain in the organs, but few go out, hence there is growth.

But little is known of the differences which the internal absorptions of synovia, serum, fat, marrow, &c. then present.

The external absorptions appear to be more active, for we know that contagions are taken with much more facility in the first age. We know not however whether the skin and mucous surfaces then constantly introduce more foreign substances into the body, or if they are only more disposed to introduce them.

We are deficient in positive data as to the state in which absorption is found in childhood. To judge of it however by that of the lymphatic glands, it would appear that it was very energetic. In fact these glands are in proportion much developed; they appear to be the seat of very active functions; they have a peculiar life more developed than afterwards, hence a greater disposition to diseases. We know that until puberty, or rather until the end of growth, they are the seat of many affections which entirely disappear after that age, and lessen the numerous series of those to which we are exposed.

This double circumstance, 1st, the precocious and proportionably great development of the lymphatic glands in childhood; 2d, their very great disposition to diseases, indicates certainly remarkable activity in their functions; for it supposes a great development of the vital forces; now these vital forces being more developed ought necessarily to preside over more energetic functions. See in fact the organs whose functions we know, which are on the one hand much developed in childhood, and on the other much disposed to diseases; the functions of these organs are more active. Thus the brain and nerves being more developed, have more sensibility; thus the vessels with red blood have an activity of nutrition, in proportion to their size, &c. In youth, it is when the genital organs are more developed and they become more exposed to diseases, that their functions are greater. Examine all the organs and their functions, you will see that a general law of the economy is, that these three things, 1st, great development; 2d, greater disposition to diseases; 3d, greater activity of functions, are constantly united. Now when these two first exist in the glands of the absorbents, we ought to conclude that the third is there also, though we are not certain of it, since, from what I have said, we are ignorant of the uses of these small organs. Grimaud has considered them, it is true, as essential to nutrition; he even calls the nutritive system the combination of these glands and the cellular texture, a gratuitous supposition, which is not proved. All that we know upon this point, is that on the one hand nutrition, and the development of these glands on the other, are very great in the foetus. But does it follow from this, that the first phenomenon proceeds from the second? Undoubtedly not; no more than because the brain, the liver, &c. are early developed in the foetus, and nutrition is very active, they should be considered as the agents of this function. Besides, nutrition is a function that has no particular organ for its centre and agent. Each organ is itself the machine which separates from the blood or the fluids that enter it, the nutritive materials that are suitable for it, and afterwards appropriate them to itself. The muscle separates its fibrin, the bone its phosphate of lime, &c. But one common and central organ does not elaborate these nutritive materials, as one common viscus moves the blood, as one central organ presides over sensibility, &c.

As to the anatomical state of the absorbents in the foetus and childhood, we can know but little; I do not know that any author has injected them comparatively in this age and in the adult. I have but one fact upon this point, it is that the lacteals, examined in an experiment upon two young dogs, who had only left off sucking eight days, appeared to me larger in proportion than at a more advanced age. I will make one remark that has often struck me; it is that the size of the animal has much less influence than would be thought upon the diameter of these vessels. For example, an adult dog, twice as large as another, has not by a great deal, vessels of double size. Accident led me to examine them the same day, three years since, upon two large grey-hounds, that were among the dogs brought to me, and upon one of those vulgarly called cur dogs; they were nearly equal in all three; this struck me.

We know but little of the different revolutions that absorption undergoes in the ages that succeed infancy. Only there is no doubt that puberty is the limit of this kind of predominance which the lymphatic glands enjoyed in the economy. The age of their diseases is then passed; often even these diseases, heretofore beyond the reach of art, are spontaneously cured. The predominance of the genital organs which succeeds to this and some others, those of the sensitive-organs, &c. seems to destroy the germ which this first supported.

Soemmering has described in a particular work the part that the absorbents perform in the different diseases of the adult and the other ages. This part has appeared to me to be often very difficult to be known, notwithstanding what he has said of it. I refer however to his work on this point.

In old age, nutritive absorption continues very active; for it is that which decomposes the body, which takes from it the substances that nourish it, and which consequently withers and dries the organs.

The external absorptions, on the contrary, are feeble; the skin takes with great difficulty the different contagions, as I shall say in treating of this organ; the mucous surfaces absorb slowly; but little chyle passes into the blood in proportion to what enters it in the adult. The two absorptions, the nutritive and the external, are exactly reversed at the two extreme ages of life; the second is superior to the first in infancy, the first predominates in old age.

As to the internal absorptions, as those of synovia, of the serous surfaces, of the cellular texture, &c. I should think that they predominated in old age, and that to this was to be attributed the numerous serous effusions which happen at that age, and which we observe in dead bodies. We have not however upon this point so good data as upon the other two.

V. Preternatural Absorption.

We can understand two things by this expression; 1st, the absorption of fluids different from those naturally taken by the absorbents, as that of effused blood, &c. I have already spoken of this absorption; 2d, that which takes place in the cysts which are developed contrary to the natural order in the economy. Now this last exhibits a very singular phenomenon, when compared with preternatural exhalation. It, in fact, takes place with difficulty; it is rare that you see the fluids of encysted tumours enter suddenly the circulation by absorption, either in whole or in part, as this very often happens in the serous collections of the peritoneum, which, without being cured, have many alterations of increase and diminution. What physician has not observed that the urine flows more as the abdomen becomes flat, and that it is suppressed when it is filled?

Observe on the contrary, that exhalation is renewed with great facility in encysted tumours; that if we empty them and do not remove their cysts, they are soon reproduced, as I have said. Is it that the absorbents are not developed in proportion to the exhalants in these tumours? I know not; but the fact is not less certain; observation of diseases proves it every day.

---