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 œdematous; 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 œdema. 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.