General Anatomy, Applied to Physiology and Medicine, Vol. 2 (of 3)

by Xavier Bichat

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.