Part 11

The mucous membranes by the continual secretion of which they are the seat, enjoy a principal part in the animal economy. We ought to consider them as one of the great emunctories by which the residue of nutrition constantly escapes, and consequently as one of the principal agents of the habitual decomposition which removes from living bodies the particles that, having for some time contributed to the composition of the solids, are afterwards to become heterogeneous to them. Observe in fact that the mucous fluids do not enter the circulation, but go out of the body; that of the bladder, the ureters and the urethra, with the urine; that of the vesiculæ seminales and the different ducts with the semen; that of the nostrils by the act of blowing the nose; that of the mouth, in part by evaporation and in part by the anus with the excrements; that of the bronchia, by pulmonary exhalation, which arises principally, as I shall say, from the solution of this mucous fluid in the inspired air; those of the œsophagus, the stomach, the intestines, the gall-bladder, &c. with the excrements, of which they often form in the ordinary state a part almost as considerable as the residue of the aliments, and which they even compose almost entirely in some cases of dysentery and fever, in which the quantity of matter voided is evidently disproportioned to that taken in, &c. Let us observe upon this subject that there are always some errors in the analyses of the fluids in contact with the membranes of which we are speaking, as in that of the urine, the bile, the gastric juices, &c. because it is very difficult and even impossible to separate the mucous fluids from them.

If we recollect what has been previously said upon the extent of the two general mucous surfaces, which is equal and even superior to the extent of the cutaneous organ, and if we afterwards consider that these two great surfaces are constantly throwing out mucous fluids, we shall perceive how important this evacuation must be in the economy, and of what mischief its derangement must become the source. It is undoubtedly to this law of nature which wishes to have every mucous fluid thrown out, that must be attributed, in part in the fœtus, the presence of the unctuous fluid of which the gall-bladder is full, the meconium which loads the intestines, &c. fluids which appear to be but a mass of mucous juices, which being unable to pass off, remain until birth, without being absorbed, upon the respective organs on which they have been secreted.

The mucous fluids are not the only ones that are thrown out, and are in this way excrementitious substances to the economy; this is the case with almost all the fluids separated from the mass of blood by secretion; this is evident as it respects the greatest part of the bile; probably the saliva, the pancreatic juice and the tears are also thrown out with the excrements, and their colour alone prevents them from being distinguished like the bile. I do not even know if, by reflecting on many phenomena, we might not attempt to establish as a general principle, that every fluid separated by secretion does not enter the circulation again, that this phenomenon belongs only to the fluids separated by exhalation, as those of the serous cavities, of the articulations, of the cellular texture, of the medullary organ, &c.; that all the fluids are thus either excrementitious or recrementitious, and that no one is excremento recrementitious as the common division implies. The bile in the gall-bladder, the urine in the bladder, the semen in the vesiculæ seminales, are certainly absorbed; but it is not the fluid itself which re-enters the circulation; it is only its most delicate parts, some of its principles which we do not exactly know, probably the serous and lymphatic part; this does not resemble the absorption of the pleura and other analogous membranes, in which the fluid re-enters the blood as it came out of it.

That which is certain on the subject of the excretion of the secreted fluids is, that I have never been able to produce absorption of the bile by the lymphatics by injecting it into the cellular texture of an animal; it produces there inflammation and afterwards suppuration. We know that urine effused is not absorbed and that it destroys every part it touches, whilst that effusions of lymph and blood are easily discussed. There is as it respects the composition an essential difference between the blood and the secreted fluids. The exhaled fluids on the contrary, as the serum, in this respect resemble it very much.

Another very evident proof that all the mucous fluids are designed to be thrown out, is, that when they have continued for some time in any quantity upon their respective surfaces, they create there a painful sensation of which nature relieves us by various means. Thus the cough, which is the constant result of an accumulation of mucus in the bronchia, serves to expel it; thus vomiting in gastric derangements answers the same purpose as it respects the mucous juices accumulated in the stomach, whose presence produces a weight and even pain, though the membranes be not affected. We cough at will, because it is the diaphragm and intercostals by which this function is performed; we do not seek in medicine for any means to excite it. But as we cannot vomit at will, and as the presence of mucous juices often by fatiguing the stomach, does not irritate it sufficiently to produce a contraction, art has recourse to various emetics. We know what a painful sensation of weight the continuance of mucus accumulated in the frontal, maxillary, sinuses, &c. occasions, when there is a catarrh of a portion of the pituitary membrane. The region of the bladder is for the same reason, in catarrhs of this organ, the seat of a troublesome and even painful sensation.

In general, the sensation which arises from the presence of the mucous juices remaining too long and in too great quantity upon their respective surfaces, varies because, as we shall see, each part of the mucous system has its peculiar mode of sensibility; so that the pain is not the same in each, though produced by the same cause. I would only observe that this sensation does not resemble that which arises from the tearing or the acute irritation of our parts; it is an uneasy, inconvenient sensation, difficult to be borne. Every one knows that which arises from mucus accumulated in the nasal fossæ, when the nose has not been blown for a long time, that disagreeable one that accompanies gastric derangements, &c. Those who have a weakness of the lachrymal sac in which the tears, on account of this, accumulate during the night, wake up with a sensation of weight, of which they are relieved by evacuating the sac by pressure, if the puncta lachrymalia are open.

Blood Vessels.

The mucous membranes receive a very great number of vessels. The remarkable redness that distinguishes them would be sufficient to prove it, if injections did not demonstrate it; this redness is not everywhere uniform. It is almost nothing in the sinuses of the face, in the internal ear, of which the membranes are rather whitish, and which appear so especially, because their extreme delicacy allows the bone upon which they are applied to be seen very distinctly. In the bladder, in the great intestines, in the excretories, &c. this colour, though still very pale, is a little more evident; it becomes very much so in the stomach, the small intestines, the vagina and in the pituitary and palatine membranes. In the gall-bladder we cannot distinguish it, because the bile always covers the mucous surface in the dead body.

This colour depends upon a very extensive vascular net-work, the branches of which, after having passed through the mucous corion, and ramifying there, divide and spread ad infinitum on its surface, embracing the papillary body and covered only by the epidermis.

It is the superficial position of these vessels and consequently their want of support on one side, that exposes them frequently to ruptures from considerable shocks, as happens on the surface of the bronchia from a severe cough, on that of the ear and the nose from a violent blow on the head. We know that hemorrhage of the mucous system bordering on the brain, is a common accident from concussions and wounds of the head. Hence why the least gravel makes the ureters bleed; why one of the signs of stone in the bladder is the passing of blood; why a blunt sound carefully introduced is so often withdrawn bloody from the urethra; why the least effort made with instruments carried upon polypi, into a fistula lachrymalis or into the nostrils, produces hemorrhage. I have already observed that we must carefully distinguish these hemorrhages from those furnished by the exhalants, and which do not suppose any vascular rupture.

It is also the superficial position of the vessels of the mucous system, which makes its portions visible, as the red edge of the lips, the glans penis, &c. often serve to show us the state of the circulation. Thus in the different species of asphyxia, in submersion, strangulation, &c. these parts are remarkably livid, an effect of the passage of the venous blood, which has undergone no change from the want of respiration, into the extremities of the arterial system.

The long continued exposure of the mucous system to the air, often makes it lose the redness that characterizes it, and it then assumes the appearance of the skin, as has been observed by Sabatier in treating of prolapsus of the womb and vagina, which, from this circumstance, have sometimes so misled some people, as to make them believe it a case of hermaphrodism.

An important question presents itself in the history of the vascular system of the mucous membranes, viz. whether this system admits more or less blood according to different circumstances. As the organs within which these membranes are spread, are almost all susceptible of contraction and dilatation, as we see in the stomach, the intestines, the bladder, &c. it has been thought that during the dilatation, the vessels being more expanded, receive more blood, and that during the contraction on the contrary, being folded up, as it were choaked, they admit but a small quantity of this fluid which then flows into the neighbouring organs. Chaussier has made an application of these principles to the stomach, whose circulation he has considered as being alternately inverse of that of the omentum, which receives during the vacuity of this organ, the blood which this when it is contracted cannot admit. An analogous use has also been attributed to the spleen since the time of Lieutaud. The following is what the inspection of animals opened during abstinence and at different periods of digestion, has shown me upon this point.

1st. During the fulness of the stomach the vessels are more apparent on the exterior of this viscus, than when it is empty. Within, the mucous surface is not more red, sometimes it has appeared to me to be less so. 2d. The omentum, less extended during the fulness of the stomach, exhibits nearly the same number of vessels, as long, but more tortuous, than when it is empty. If they contain less blood, the difference is hardly sensible. I would observe, that in order to distinguish this well, it is necessary to take care that in opening the animal, the blood does not fall on the omentum which presents itself, and thus prevent its state from being ascertained. This is besides a necessary consequence of the arrangement of the vascular system of the stomach. In fact the great stomachic coronary being situated transversely between it and the omentum, and furnishing branches to each, it is evident that when the stomach is lodged between the layers of the omentum by separating these layers, and this by applying itself upon it becomes shorter; it is evident, I say, that the branches which it receives from the coronary cannot be equally applied to it also. In order to do this, it would be necessary that they should go from one to the other without the intermediate trunk that cuts them at right angles; then, in distending, the stomach would separate them as it does the omentum, and would be lodged between them; whereas it pushes them before it with their common trunk, the stomachic coronary, and makes them fold. 3d. I am confident that there is no such constant relation between the size of the spleen and the emptiness or fulness of the stomach, and that these two circumstances coincide necessarily, and that if the first organ increases or diminishes under different circumstances, it is not always precisely the reverse of the stomach. I first made, like Lieutaud, experiments upon dogs to convince myself of it; but the inequality in the size and age of those that were brought to me, making me fear that I should not be able to compare their spleens correctly, I repeated them upon guinea-pigs of the same litter and size, and examined at the same time, some when the stomach was empty and others when it was full. I have almost always found the size of the spleen nearly equal, or at least the difference was not very sensible. Yet in other experiments, I have seen under various circumstances, inequalities in the size of the spleen and especially in the weight of this viscus; but it was indifferently during or after digestion.

It appears from all this, that if during the vacuity of the stomach, there is a reflux of blood towards the omentum and spleen, this reflux is less than it has been commonly said to be. Besides during this state of vacuity, the numerous folds of the mucous membrane of this viscus leaving it, as we have said above, almost as much surface and consequently as many vessels as during fulness, the blood can circulate in it almost as freely. It has no real obstacles but in the tortuous courses, and not in the obstruction, compression and choaking of these vessels by the contraction of the stomach; now this obstacle is easily surmounted, or rather it is not one as I have proved in my Researches upon Death. As to the other hollow organs, it is difficult to examine the circulation of the neighbouring parts during their fulness and vacuity, as the vessels of these are not superficial as in the omentum, and as they themselves are not insulated like the spleen. We can only then, to decide the question, see the state of the mucous membranes on their internal face; now this face has always appeared to me to be as red during the contraction as during the dilatation.

Besides I only give this as a fact without pretending to draw from it any consequence in opposition to the common opinion. It is possible in fact that though the quantity of blood may be nearly always the same, the rapidity of the circulation being increased, more of this fluid may consequently in a given time enter it when it is full; which appears to be necessary to the greater secretion that then takes place of the mucous fluids, a secretion excited by the presence of the substances in contact with the surfaces of the same name. For example, there is no doubt that there is three or even four times as much mucus secreted in the urethra, when a sound fills it, as when it is empty; now the blood must be in proportion.

The remarkable redness of the mucous system, the analogy of respiration in which the blood flows through the mucous surface of the bronchia the well known experiment of a bladder filled with blood and immersed in oxygen, by which means the blood becomes red, have induced a belief that the blood being separated from the atmospheric air only by a thin pellicle or some of the mucous surfaces, as upon the pituitary, the palatine, the glans penis, &c. assumed there a redder colour, either from getting rid of a portion of its carbonic acid gas, or by combining with the oxygen of the air, and that these membranes thus performed functions accessory to those of the lungs. The experiments of Jurine upon the cutaneous organ, experiments adopted by many celebrated philosophers, seem to strengthen this conjecture.

I tried the following experiment to ascertain this fact. I drew through a wound made in the abdomen a portion of intestine which I tied at one point, I afterwards reduced it, keeping out a small portion only which I opened and by which I introduced atmospheric air, which filled the whole portion situated on this side of the ligature. I afterwards tied the intestine below the opening, and reduced the whole of it. At the end of an hour, the animal being opened, I compared the blood of the mesenteric veins which arose from the portion of intestine distended with air, with the blood of the other mesenteric veins arising from the rest of the canal. No difference of colour was manifest; the internal surface of the distended portion of the intestine was not of a more brilliant red. I thought I should obtain a more evident effect, by repeating with oxygen the same experiment upon another animal; but I perceived no greater variety in the colour of the blood. As upon the mucous membranes which are ordinarily in contact with the air, this fluid is constantly changing and is agitated by a perpetual motion, and as in the preceding experiment it remained stagnant, I attempted to produce the same effect in the intestines. I made two openings in the abdomen, and drew out at each a portion of the intestinal canal; having opened these two portions, I fitted to one the tube of a bladder full of oxygen and to the other that of an empty bladder; I afterwards compressed the full bladder, so as to make the oxygen pass into the other, by going through this portion of intestine, left in the abdomen that the heat might support the circulation in it. The oxygen was thus many times sent from one bladder to another, taking its course through the intestine, which, on account of its contractility is more difficult than it at first seems to be. The abdomen being afterwards opened I found no difference between the venous blood returning from this portion of intestine, and that which flowed from the others. The superficial position of the mesenteric veins, covered only by a fine and transparent layer of peritoneum, their size, if the animal be rather large, render this sort of comparison very easy.

I perceive that we cannot infer from what takes place in the intestines, what happens in the pituitary, palatine membrane, &c. because though analogous, the organization may be different. We cannot here as in the intestines examine the venous blood returning from the part; but, 1st, if we consider that in animals who have respired oxygen for some time, we see the palatine and pituitary membranes more red; 2d, if we reflect that the lividity of the different parts of this membrane, in those destroyed by asphyxia by the carbonic acid gas, depends not on the immediate contact of this gas upon the membrane, but upon the passage of venous blood into the arterial system, as my experiments have, I think, demonstrated; 3d, if we remark finally that in these circumstances the contact of the air does not change, after death, the lividity which the venous blood gives to the mucous membranes, although the skin be then much more permeable to every kind of aeriform fluid; we shall see that it is at least necessary to suspend our judgment upon the colouring of the blood in the mucous membranes, until further observations have decided the question.

The following experiment may also throw some light upon the subject. I have inflated the peritoneal cavity of several guinea-pigs with carbonic acid gas, with hydrogen, oxygen and atmospheric air, to see if I could effect through a serous membrane what I could not make succeed in a mucous; I have not, after these experiments, found any difference in the colour of the blood of the abdominal system; it was always the same as in the common guinea-pig which I killed for comparison.

I think however that I have remarked many times, both in frogs and animals with red and warm blood, such as cats and guinea-pigs, that the infiltration of oxygen into the cellular texture gives, at the end of some time, a much brighter colour to the blood, than that which this fluid exhibits in artificial emphysemas produced by carbonic acid gas, hydrogen and atmospheric air, in all which the colour of the blood scarcely differs at all from what is natural. But in other cases oxygen has had no influence upon the colour of the blood; so that notwithstanding having made many experiments upon this point, I am unable to give any general result. It appears that the tonic forces of the cellular texture and of the parietes of the vessels which are spread upon this texture, receive a very variable influence from the contact of the gases, and that according to the nature of this influence, the fibres crisping and contracting more or less, render these parts more or less permeable, either to the aeriform fluids that tend to escape from the blood in order to unite with that of the emphysema, or to this last fluid, if it tends to combine with the blood, which no doubt produces the varieties I have observed.

The red colour of the mucous system is analogous to that of the muscular system. It does not depend essentially on the blood circulating in the small arteries of this system. It arises from the colouring portion of the blood combined with the mucous texture, especially in the deep part of the organs; for at the origin of the mucous surfaces, this colour appears to be principally owing to the blood in circulation; in fact asphyxia does not render so livid the deep mucous surfaces, as it does those which are superficial and in communication with the skin. The black blood arrives immediately to these by the last arteries, and tinges them as we see. In syncope in which the heart being affected no longer sends blood into the arteries, we know that this portion of the mucous system becomes instantly white.

Besides the red colour of the deeper portions, can, like that of the muscles, be removed by repeated washing and frequently changing the water. Yet the water in which they have been washed is not as red as that used for the muscles.

The instant a mucous surface is plunged into boiling water, however red it may be, as that of the intestines and the stomach, it instantly whitens. The action of the nitric, sulphuric and muriatic acids produces in it also a sudden whiteness.

This colour of the mucous surfaces acquires a remarkable intensity in inflammation. The redness becomes then extremely deep on account of the quantity of blood that is accumulated in the capillary system. It is particularly in dysentery that the internal surface of the intestines exhibits this phenomenon in a striking degree. I ought however to observe to those who open dead bodies, that they never should lose sight of the original tinge of the portion of the mucous system they examine, since each of the divisions of this system exhibits in its shades remarkable differences. If the membrane of the bladder, the rectum, &c. is found as red as that of the stomach in its natural state, then pronounce that there had been inflammation; if the redness of the sinuses equals that which is natural to the bladder and the rectum, decide that inflammation had existed in them. There is, as I have said, a scale of colour for the mucous system. It is then essential to have an accurate knowledge of this scale, a type to which we can refer the inflammatory state in the examination of dead bodies.

Exhalants.

Does exhalation take place upon the mucous surfaces? The analogy of the skin seems to indicate it; for it is well proved that the sweat is not a transudation through the inorganic pores of the cutaneous surface, but a real transmission by vessels of a peculiar nature and continuous with the arterial system.

It appears at first that the pulmonary perspiration which takes place upon the mucous surface of the bronchia, which has so much relation with that of the skin, which increases and diminishes according as this diminishes or increases, and the matter of which is probably of the same nature; it appears, I say, that the pulmonary perspiration is made at least in great part by the system of exhalant vessels, and that if the combination of the oxygen of the air with the hydrogen of the blood contributes to produce it, during the act of respiration, it is but in very small quantity, and it is the portion that is purely aqueous. Besides, this last hypothesis of modern chemists, contradictory to the production of all the other fluids thrown out by the mucous surfaces, appears to me ill adapted to explain the formation of this. When the same phenomenon is produced in many places, and the explanation that is given of it is applicable only to one, we should be suspicious of this explanation.