OF THE VASCULAR SYSTEM OF MUCOUS MEMBRANES.
45. The mucous membranes receive a great number of vessels: the
remarkable redness which distinguishes them would be sufficient
to prove it to us, if it could not be demonstrated by injections.
This redness is not everywhere uniform; it is less in the bladder,
large intestines, and frontal sinuses; very marked in the stomach,
small intestines, and vagina, &c. It is produced by a web of
very numerous vessels, whose supplying branches, after having
passed through the chorion, finish on its surface by an infinite
division, embracing the corps papillaire, and is covered only by
the epidermis.
46. It is the superficial position of these vessels that frequently
exposes them to hæmorrhages, as we remark principally in the nose,
and as is seen in hæmoptysis, hæmatemæsis, hæmaturia, in certain
dysenteries, where the blood escapes from the parieties of the
intestines, in uterine hæmorrhages, &c.; so that those spontaneous
hæmorrhages, which are independent of any external violence applied
to the open vessels, appear to be special affections of the mucous
membranes; they are seldom observed but in these organs, and they
form at least one of the grand characteristics which distinguishes
them from all the other membranes.
47. It is also the superficial situation of the vascular system of
mucous membranes that renders their visible portions, as on the
lips, the glans, &c.; serviceable in showing us the state of the
circulation. Thus, in various kinds of asphyxia, in submersion,
strangulation, &c., these parts present a remarkable lividity; the
effect of the difficulty that the venous blood finds in passing
through the lungs, and of its reflux towards the surfaces where the
venous system arises from that of the arteries.
48. I have already observed in the fœtus, and newly born infant,
that the vascular system is as apparent in the cutaneous organ
as in the mucous membranes; that the redness is there the same;
it is even in that part more marked in the earlier periods of
conception; but soon after birth all the redness of the skin seems
to concentrate itself upon the mucous membranes, which before,
being inactive, had no need of so considerable a circulation, but
which, becoming all at once the principal seat of the phenomena
of digestion, of the excretion of the bile, of the urine, of the
saliva, &c., demand a larger quantity of blood. The long continued
exposure of mucous membranes to the air frequently occasions them
to lose their characteristic redness, and they then assume the
colour of the skin (as M. Sabattier has well observed in treating
on prolapses of the uterus and vagina). By this circumstance some
have been deceived in believing such instances to be cases of
Hermaphrodism.
49. An important question in the history of the vascular system of
the mucous membranes presents itself, which is, does this system
admit more or less blood, according to its various circumstances?
As the organs within which this sort of membrane is spread are
nearly all of them susceptible of contraction and dilatation, as
is observable in the stomach, intestines, bladder, &c., it has
been believed, that during their dilatation the vessels, being
more spread out, received more blood, and that during their
contraction, on the contrary, being folded on themselves, and as
it were strangulated, they admitted but a small portion of this
fluid, which then flows back into the adjacent organs. M. Chaussier
has applied these principles to the stomach, the circulation of
which he has considered as being alternately the inverse of that
of the omentum, which receives, during the vacuity of that organ,
the blood which it, being in a state of contraction, cannot admit.
Since M. Lieutaud, an analogous use has been attributed to the
spleen. Observe what I have ascertained on this subject from the
inspection of animals opened during abstinence, and in the various
periods of digestion.
50. (1) Whilst the stomach is in a state of repletion its vessels
are more apparent on its exterior surface than during its vacuity;
its mucous surface at this time has no higher degree of redness,
but it has sometimes appeared to me to be less red than when the
viscus was empty. (2) The omentum, being less extended during
the plenitude of the stomach, presents nearly the same number of
apparent vessels, equal in length, but more folded upon themselves
than during the vacuity of that organ[C]. If they are then less
loaded with blood the difference is scarcely perceptible. I would
here observe, that great care is requisite in opening the animal,
or the blood will fall upon the omentum, and prevent us from
ascertaining its real state. (3) I am confident that there is no
such constant relation between the volume of the spleen and the
stomach in its different states of vacuity or plenitude; and if
that organ increases and diminishes under various circumstances,
it is not always in the inverse ratio of the state of the stomach.
Like Lieutaud, I at first made experiments on dogs, in order to
satisfy myself respecting the facts just stated; but the inequality
in the size and age of those which were brought to me leading
me to fear that I might not be able to compare their spleens
correctly, I repeated them on Guinea pigs, whose size and condition
corresponded, and examined, at the same time, some whilst the
stomach was empty, and others whilst it was full. I have almost
always found the volume of the spleen nearly equal, or at least the
difference has not been very perceptible. Nevertheless, in other
experiments I have seen the spleen, under various circumstances,
to show variations in its volume, but more particularly in weight;
and this was the same during digestion as after that process was
finished. From what has been said it appears, that if, whilst the
stomach is empty, there is a reflux of blood to the omentum and
spleen, it is less than has been commonly asserted. Moreover,
during this state of vacuity, the numerous folds of the mucous
membrane of this viscus leaving it, as we have before said, almost
as much extent of surface, and consequently of vessels, as during
its plenitude, the blood must circulate there nearly as freely as
when the viscus is in a contrary state; it has therefore no real
obstacles; the only impediment is in consequence of the tortuous
direction the vessels are then thrown into. Now this obstacle is
easily surmounted, since the vessels suffer no constriction or
diminution of calibre by the contraction of the stomach.
51. As respects the other hollow organs, it is difficult to examine
the circulation of their adjacent viscera during their plenitude
or vacuity; for their vessels are not superficial, as in the
omentum, or insulated, as in the spleen; therefore, to decide
this question concerning them, we can only observe the state of
the mucous membranes upon their internal surface. Now they have
always appeared to me as red during the contraction as during the
dilatation of the organs. Finally, I give this only as a fact,
without pretending to draw any inference from it opposed to the
common opinion. It is, in fact, possible, that though the quantity
of blood be always nearly the same, the rapidity of the circulation
may increase; and consequently, in a given time, more of this
fluid will be sent there during the plenitude of the viscera. This
appears to be necessary for the secretion of the mucous fluids,
which are then more abundant.