Part 14

I. State of the Mucous System in the First Age.

The development of the mucous system follows in general the laws of that of the organs to which it belongs. Early in the gastric apparatus, later in the pulmonary and that of generation, it seems in its growth rather to obey the impulse it receives, than to give one to what surrounds it, an arrangement common to almost all the systems which contribute to form the different apparatus. Observe in fact that there is always in the growth certain parts to which all the others refer; thus in the cerebral apparatus, the early size of the brain produces that of the bones of the cranium, of the dura-mater, the pia-mater, the arachnoides and the vessels; thus it is on account of the spinal marrow, that the vertebral canal is so evident in the fœtus; thus all the serous surfaces have a growth in proportion to that of their respective organs, &c. &c. I would remark however that the early growth of the systems which are only to follow that of the parts to which they are destined, is only in the dimensions of length, breadth, &c. The thickness most commonly does not correspond with these dimensions. Thus the bones of the cranium though broader in proportion than those of the pelvis in the fœtus, are not thicker. The extent of the dura-mater is in proportion greater than that of the albuginea which belongs to the same system; but the organization is no further advanced.

In the fœtus, the delicacy of the mucous texture is extreme, the papillæ are hardly perceptible. But by carrying the hand over a mucous surface, we feel there an extremely delicate velvet and such as is not equalled by the finest velvet. The redness of this system is not then as evident, because no doubt less blood penetrates it, as the various functions which are afterwards to take place upon these surfaces, as digestion, the excretions, respiration, &c. are but feeble or entirely wanting. At this age, the quantity of blood seems to be in an inverse ratio in the skin and in these surfaces. The mucous red is then like the muscular, of a very deep tinge, often even livid, on account of the nature of the blood circulating in the arteries. Then the adhesions of the mucous texture to the subjacent cellular are less; those especially of this last with the surrounding parts are very slight; thus it is very easy to draw out whole the internal portion of the intestines of the fœtus, from the external covering that contains it, so as to see two cylindrical canals, one of which is muscular and serous, the other cellular and mucous. The stretching destroys in this experiment all the valvulæ conniventes, and the small intestines are as smooth on the interior as the large, in the canal artificially extracted. If we subject this canal to ebullition, much more scum arises from it than in the adult; this scum is white and never green. The crisping that takes place a little before the first boiling, diminishes more in proportion the length of the canal, and consequently appears to be stronger.

At birth, when respiration and digestion suddenly commence, the secretions increase, the mucous system acquires a remarkable degree of activity. It is instantly excited powerfully by the many new substances with which it is in contact. It is by it and by the cutaneous system that bodies foreign to ours then immediately stimulate it, and so much the more efficaciously, as the double surface which receives the excitement is not accustomed to it. Then the red blood which penetrates the mucous system, gives it an increase of energy and sensibility, which renders it still more proper to receive impressions. Thus the mucous juices which till then stagnated upon their respective surfaces, without fatiguing and irritating them, are suddenly for them, on account of their increase of sensibility, stimulants which excite them, and force the subjacent muscles to contract. Then the urine becomes for the bladder a cause that promotes the contraction of it. A few instants after birth, all the openings in which the mucous membranes begin, open and permit to escape the meconium, the urine and all the mucous juices. This internal and general shock that empties all the mucous cavities, renders them fit to become the seat of the great functions which are soon to take place in them.

When all the internal functions are in activity, the mucous surfaces experience no more sudden changes, analogous to that of which I have spoken. They grow like the other viscera in a slow and insensible manner; they preserve for a long time their original softness, which is remarkable, especially in the nose, the stomach, &c. and which during lactation, is not adapted in the infant, to the solid substances with which the adult is nourished. Is this softness the cause of the mucous affections which are in general so common at that age? We know that then the mucous juices abound; the pituitary membrane is more moist; the stomach and intestines are frequently affected with a species of catarrh which is the cause of the looseness that we have so often to combat in infancy. The membrane of the bronchia is also frequently diseased. The two extreme ages of life resemble each other by the abundance of the mucous juices secreted upon their respective mucous surfaces.

In youth the mucous system is in very powerful action. The active hemorrhages of this system are very frequent at this age; those of the nose, the bronchia and even the stomach often take place; those of the portions of this system, subjacent to the diaphragm, are then less common. Observe that in man, hemorrhages of the gastro-pulmonary surface are infinitely more frequent than those of the genito-urinary surface, which on the contrary, are much more numerous in woman in whom one of them is natural to a part of this surface, viz. menstruation.

At the period of puberty, the development of the genital parts in both sexes, gives much activity to a part of the genito-urinary surface; then menstruation begins upon that of the womb; then the sensibility of the urethra is raised in order to feel acutely the passage of the semen. Observe that this increase of energy is not attended with a weakness of the other parts, as happens in many cases; on the contrary, all the systems, all the apparatus seem to borrow, from the force which the genital parts acquire, an increase of action.

II. State of the Mucous System in the subsequent Ages.

In the years which succeed youth, the mucous system continues to grow, thicken and become firmer. Its vital energy seems still to predominate for some time, in the superior surfaces, as in the pituitary, the membrane of the bronchia, &c.; thus the affections of these parts are more frequent until the thirtieth year. But as we advance in age, the abdominal mucous surfaces appear to predominate over the others, as in general all the organs of this region do.

Besides, a thousand causes in the course of life, make the state of the mucous system vary. We do not find it in two subjects, with the same shade of colour, with the same density, with the same external appearance. By taking any surface upon many subjects, that of the stomach, for example, we easily see these differences, with which we must be struck if we have opened dead bodies but ever so little.

The redness of the mucous texture is very bright until the thirtieth year; after that, it begins to alter. This texture becomes more and more pale in old age; the blood enters it but in small quantity; it acquires more consistence and density. The fingers carried over it no longer perceive that softness, that velvet so remarkable in the first age. Its forces, which grow languid, render difficult, in the excretories, the exit of the fluids which pass through these tubes to be thrown out. Yet the mucous glands still secrete their fluids in very great abundance. Often even these fluids increase in proportion which constitutes the catarrhal affections, so common in old age. But these affections then have the same character as the functions of the whole system; secretion takes place slowly; the disease is always chronic; most often it terminates only with life.

The mucous absorption is, at this age, slow and difficult, like all the others; the various contagions are taken much less easily, either by the respiratory surfaces, or by the contact of contagious miasmata upon the neighbouring surfaces of the skin. The chyle slowly absorbed, makes the digestive periods longer.

SEROUS SYSTEM.

This system, the name of which I borrow, like that of the preceding, from the fluid that constantly lubricates one of its surfaces, is always like it arranged in the form of membranes, and never in fasciculi like the muscular system, or in round bodies like the glandular. It is formed by the peritoneum, the pleura, the pericardium, the arachnoides, the tunica vaginalis, &c. The term serous membrane will then be very often used to designate it. No one, I believe, before the publication of my Treatise on the Membranes, had considered in a general manner these organs, which perform a less important part in the functions than the mucous, but which in diseases are almost as frequently affected. Pinel, who has perceived the analogy of their inflammations, has taken this system as a character of one of the classes of his phlegmasiæ.

ARTICLE FIRST.

OF THE EXTENT, FORMS, AND FLUIDS OF THE SEROUS SYSTEM.

The serous system occupies the exterior of most of the organs of which the mucous lines the interior; such are the stomach, the intestines, the bladder, the lungs, &c. We see it around all those that are essential to life, as around the brain, the heart, all the gastric viscera, the testicles, the bladder, &c. It does not form, like the mucous system, a surface everywhere continuous upon the numerous organs on which it is spread. But it is always found insulated in its different divisions which never have any communication. The number of these divisions is somewhat considerable. By considering in one view all the different serous surfaces, we see that as a whole they exceed the mucous surfaces viewed also in a general manner. One consideration is sufficient to convince us of it. The mucous and serous surfaces accompany each other in a very great number of parts, as in the stomach, the intestines, the lungs, the bladder, the gall-bladder, &c. so as to exhibit in them nearly the same extent. But on the one hand, the mucous surfaces extend where the serous are not met with, as in the nasal fossæ, the œsophagus, the mouth, &c. &c.; and on the other, there is a very great number of serous surfaces existing separately from the mucous, as the pericardium, the arachnoides, &c. Now if we compare the extent of the separate serous surfaces, with that of the separate mucous surfaces, we shall see that the first is much greater than the other.

These considerations, apparently minute, deserve however particular attention, on account of the relation of functions existing between these two surfaces taken as a whole, a relation which is especially connected with the exhalation of the albuminous fluids produced by one, and with the secretion of the mucous fluids, of which the other is the seat. Besides, in examining the extent of each serous membrane in particular, we see great varieties from the peritoneum which has the greatest surface, to the tunica vaginalis which has the least.

The serous surface taken as a whole, compared with the cutaneous surface, is also evidently superior to it in extent; so that in this respect, the quantity of albuminous fluids constantly exhaled within, appears to be much more considerable than that of the fluid which is incessantly thrown off by insensible transpiration; I say in this respect, for different circumstances, by increasing the action of the cutaneous organ, can re-establish the equilibrium in the exhalation of these two fluids, one of which re-enters by absorption into the circulation, and the other is wholly excrementitious. I do not know even if the pulmonary and cutaneous exhalations united are not less than those which take place upon the serous surfaces.

Every serous membrane represents a sac without an opening, spread upon the respective organs that it embraces, and which are sometimes very numerous, as in the case of the peritoneum, sometimes single, as in the case of the pericardium, covering these organs so that they are not contained in its cavity, and so that if it was possible to dissect them from their surface, we should have this cavity whole. This sac has in this respect the same arrangement as those night caps, which are folded within themselves; a trifling comparison, but which gives an accurate idea of this sort of membranes.

From this general arrangement, it is easy to understand that the serous membranes are never opened to permit the vessels and nerves to penetrate the respective organs to which they go or from which they come off, but that they always wind round them and accompany them to the organ, and thus form for them a sheath which prevents them from being contained in their cavities; this removes the danger of infiltration of serum which lubricates them, an infiltration which would take place through the neighbouring cellular texture, especially if they were dropsical; if, as in the fibrous membranes, they were pierced with foramina for the passage of these vessels and nerves. This arrangement, exclusively remarkable in the membranes of which we are treating, and in the synovial ones, is evident at the entrance of the vessels of the lungs, the spleen, the intestines, the stomach, the testicles, &c. We see it very well in the arachnoides, a membrane essentially serous, as I have demonstrated elsewhere.

From the general idea that we have given of these membranes, it is also easy to understand how almost all are composed of two distinct parts, though continuous, and embracing, the one the internal surface of the cavity where they are found, the other the organs of this cavity; thus there is a costal and pulmonary pleura, a cranial and cerebral arachnoides, one portion of peritoneum spread upon the gastric organs, and another upon the abdominal parietes, a free portion of the pericardium, and one adhering to the heart. The same arrangement exists in the testicles, &c.

Though the serous membranes may be separate, yet there sometimes exists communications between them; that for example of the cavity of the omentum with that of the peritoneum, that of the cavity of the arachnoides with the cavity of the membrane which lines the ventricles by the canal that I have discovered, and the external orifice of which is seen below and at the posterior part of the corpus callosum; whilst the internal one is seen above the pineal gland, between the two rows of small round bodies which are usually found in this place.

There is but one example of continuity between the serous and mucous membranes, that which exists, by means of the Fallopian tube, between the peritoneum and the uterine surface. How does the respective nature of the two membranes change here?

Free Surface of the Serous Membranes.

Every serous membrane has one of its two surfaces free, everywhere contiguous to itself, and the other adhering to the neighbouring organs. The first is remarkable for its polish, which especially distinguishes this system and the following, from all the other membranes. All the organs which exhibit this arrangement owe it to the covering they borrow from it. The liver ceases to be smooth and shining at its diaphragmatic edge where the peritoneum abandons it. There is in this respect a great difference in the appearance of the anterior and posterior face of the cæcum. The bladder is rough wherever the peritoneal covering is wanting. The cartilages of the ribs have not the polish of those of the articulations which the synovial membrane covers.

Does this remarkable attribute of the serous membranes depend on the compression exerted upon them? Their situation in places where they are exposed to continual friction, would seem to make it probable. Bordeu thought so, when he said that all the parts of the abdomen are originally covered with cellular texture, which by pressure is afterwards changed into membranes; so that the peritoneum is formed partially upon each gastric organ, and its different parts give birth, by uniting, to the general membrane. This explanation of the formation of the peritoneum is applicable, according to him, to the pleura, the pericardium, and all the analogous membranes. But if this is the progress of nature, 1st, why, whatever be the period at which we examine the fœtus, do we find the peritoneum and the serous membranes as much developed in proportion, as their corresponding organs? 2d. How are the numerous folds of these membranes formed, such as the mesentery, the omentum, &c.? 3d. Why are there parts where they do not exist though they are exposed to as great friction as that of the parts where they are found? Why, for example, are the sides of the bladder destitute of it, whilst it covers its superior part? 4th. Why does it not also form serous surfaces around the great vessels of the arm, the thigh, &c. which impart to the neighbouring organs an evident motion? 5th. Why does not the thickness of the serous membranes increase where the motion is strongest and diminish where it is weakest? Why for example does the thickness of the tunica vaginalis equal that of the pericardium? 6th. How can friction internally produce an organized body, whilst externally it constantly disorganizes the epidermis? 7th. How can we associate the vascular lymphatic texture of the serous membranes with the pressure that produces them? The impossibility of resolving these numerous questions proves, that it is not to mechanical pressure that must be attributed the formation of the serous membranes and the polish of their surface; that their mode of origin is the same as that of the other organs; that they commence and are developed with them; that this polish is an evident result of their organization, as the mucous papillæ depend upon the texture of the surfaces to which they belong. What would be said of a system in which these papillæ should be attributed to the pressure of the aliments upon the stomach, of the urine on the bladder, the air on the pituitary membrane, &c.?

The free surface of the serous membranes separates entirely from the neighbouring organs those upon which these membranes are spread; so that they are to these organs real boundaries, barriers, if I may use the term, or integuments, if it should be preferred, very different however from those which are external. Observe in fact that all the principal viscera, the heart, the lungs, the brain, the gastric viscera, the testicles, &c. limited by their serous covering, suspended in the middle of the sac that it forms, only communicate with the adjacent parts where their vessels enter; everywhere else there is contiguity and not continuity.