Since the blood of all the parts constantly goes through the lungs, it
is evident that an injury of the functions of this viscus would be felt
in all the parts. The phenomena of asphyxia prove that this in fact
takes place. It is in this way that the lungs are immediately connected
with life, and hence the ancient physicians placed its functions among
those which they called vital.
We understand also why pulmonary inflammations have so peculiar a
character; why they are distinguished from others by many phenomena.
No internal organ is more often inflamed than the lungs. If experience
did not prove this at the bed-side of the patient, the examination of
dead bodies would be sufficient to convince us of it. We find in fact
around the lungs, very often traces of old inflammations, particularly
adhesions of the pleura; a phenomenon so common, that I am confident
that there are more dead bodies found with it, than there are without
it. This is an essential difference of this membrane that distinguishes
it from all analogous ones, a difference that arises from the proximity
of the pleura to the organ that it covers. Different causes contribute
to this very great frequency of pulmonary inflammations. 1st. The lungs
are, among the internal organs, the most exposed to direct irritations,
either by the air that constantly enters them and can irritate them,
or by heterogeneous substances that it introduces, or especially by
the changes of heat and cold that it occasions. 2d. These organs are
connected by the most numerous sympathies with the other systems, the
cutaneous, for example; so that perhaps, as it respects inflammation,
a suppression of transpiration has as much influence upon the lungs
alone, as upon all the other organs together. It depends no doubt upon
this that the lungs correspond with all the others by their capillaries.
When the lungs are inflamed, is it the red blood of the bronchial
artery that flows to the irritated place, or the black blood of the
pulmonary artery? I think that it is difficult to decide this question
by experiment; but examination after death appears to prove that the
second performs an important part in it. In fact, this viscus is often
crowded so suddenly, that we can hardly believe that the first would be
able to furnish the blood. Sometimes, though it is not always the case,
we can trace as it were, the progress of this crowding by percussion,
which is infinitely less sonorous in the evening than the morning.
There died a short time since a patient under my care in the hospital,
in whom this difference was perceptible from hour to hour. The progress
is much less rapid, no doubt, in the greatest number of cases; but in
those the black blood has undoubtedly contributed to the crowding of
the lungs.
No organ in the animal economy acquires by inflammation, so great a
size in so short a time, and such excessive weight, as the lungs.
All who open dead bodies know this. Observe the lungs of one dead
of pneumonia; cut them, and you would say at first that they were
solid; they often look like liver, they exhibit the appearance of such
a heavy mass; but macerate them and soon the whole will escape in
fluids. Now examine comparatively the skin, the stomach, the liver,
the kidnies, &c. when they have been the seat of acute inflammation,
that has destroyed the patient; they have nothing approaching to this
enormous increase of fluid, which is seen in the substance of inflamed
lungs. Not only the cavity of the cells is full, but the organ is
also much dilated. I have often had occasion to open those who have
died of pneumonia, in whom one of the lungs was entirely sound; now,
the disproportion of weight between it and the affected one, was
incomparably greater than that between an inflamed kidney and a sound
one.
This phenomenon evidently arises from the fact, that the lungs alone
receive as much blood as the whole body, so that when an inflammation
of this viscus interrupts the course of the fluids, a very great
quantity of them can accumulate there in a given time. It is not
however, properly speaking, the blood that is found crowding the lungs
in pneumonia; the fluid appears whitish when pressed out; we should
say that it was a kind of pus. Much has been said of vomicæ after
pneumonia; but they are extremely rare; there is almost always effusion
in the lungs; the fluid is not collected in a sac.
In pulmonary inflammation, does the blood pass through vessels that do
not ordinarily circulate it, as happens so evidently upon the serous
surfaces, or conjunctiva, &c. when inflamed? I do not think it does,
for we do not know any vessels in the lungs, except the sanguineous.
It appears evident that the blood or the other fluids are effused into
the pulmonary texture, in which they are deposited by exhalation. There
is no doubt that in some phlegmons, this fluid passes, as I shall
say, into the cells of the cellular texture; now it appears that it
happens here in the same way. By breaking or cutting inflamed lungs,
we see clearly that its whole texture is crowded, and filled; whereas
in examining an inflamed serous surface, we see that the blood is
evidently contained in the capillaries.
It is a great mistake to try to represent inflammation as being
everywhere the same, as exhibiting always the fluids, like their
vessels, in the same state. Boerhaave for example thought, that there
could be no inflammation without an _error loci_. There is according
to the state of the parts, their structure, their vital properties, a
thousand different modifications in the new anatomical order that this
affection gives to the organs.
What constitutes the essence of inflammation is, 1st, the irritation of
the inflamed part; 2d, the new modifications that its vital forces have
taken in consequence of that irritation; 3d, the consequent stagnation
of the fluids around it. But in what manner the fluids are arrested;
how they stop in the capillary system; how they are taken up by the
exhalants; how they are poured out, in extravasations, &c.; these are
different effects that arise from the different organization of the
parts; but the principle is always the same, it is always the same
disease. If we could analyze thoroughly the state of all the systems in
inflammation, we should see perhaps, that there was a difference in the
inflammation of each. Besides, the diversity of the symptoms that it
exhibits, a diversity of which I have already spoken, proves that the
state of the solids and the fluids are not the same.
How is it that the blood can pass through the lungs of phthisical
patients, in whom this organ is reduced nearly one half? I would
observe upon this subject, that the blood in the great vessels is
diminished in proportion to the ulceration of the lungs. The diminution
of this fluid is remarkable in many organic affections, but especially
in these, as Portal has observed. If a phthisical patient in the
last stage had as much blood, as before the disease, the circulation
certainly could not go on, or at least there would be a constant reflux
towards the right auricle. Who is ignorant of the small pulse, feeble
though frequent, particularly towards night, in phthisis? Compare it
with the pulse of an inflammatory fever, in which there is evidently
plethora; you will see that they are really the two extremes.
I will make a general observation upon this subject, it is this, that
when the forces are weakened in our organs, or life languishes in them,
the blood is diminished almost continually in proportion; so that this
fluid being considered in the capillary system, as the resistance
opposed to the power of the small vessels, the proportion remains
always the same between this power and this resistance. It is necessary
that the whole should be in relation. If blood was transfused into a
phthisical patient, he would die, because the forces of the solids
would not correspond with the increase of action to which they would be
forced.
The circulation of the pulmonary capillaries, is, like that of the
others, under the influence of the tonic forces of the part, and not
under that of the impulse of the heart. This impulse terminates at the
extremity of the branches of the pulmonary artery. In inflammation then
of the lungs, the blood is not mechanically arrested in this organ;
then, when you bleed, it is not to diminish the _vis à tergo_. You
might draw ten basins from the patient, but the lungs most commonly
would not empty themselves; they would be less fatigued by the
entrance of the blood; but that which was stagnant in the capillary
system would still remain there. So long as there is a point of
irritation, it will be, if we may so say, a magnet which will attract
the blood, and completely change its direction; which was before from
the artery to the veins, it will now be only towards the irritated
point. Bleeding acts then, 1st, by diminishing the blood that enters
the lungs, and consequently by lessening the fatigue of this diseased
organ; 2d, by diminishing the irritation of the solid, which attracts
the blood, and retains it around the irritated place.
The constant excitement that the air gives to the pulmonary capillary
system is favourable to its circulation; but the blood can traverse
this system without this excitement, as is proved by my experiments
mentioned elsewhere.