Part 17

I. State of this System in the First Age.

All the serous surfaces are extremely delicate in the fœtus. In opening the thorax by a longitudinal section of the sternum and examining the pleura in the mediastinum where it is free on both sides, it is found to have less thickness than the transparent layers of the omentum or the arachnoides in the adult. The peritoneum is a little thicker in proportion, but yet its delicacy is very great. The comparison of soap bubbles is hardly sufficient to convey an idea of the fineness of the texture of the omentum and the arachnoides.

At this period the fluid that lubricates the serous surfaces is much more unctuous and viscid than it is afterwards; by carrying the fingers over these surfaces at the different ages, the difference is easily perceived. It might almost be said that the tangible qualities of the serous fluids then approximate those of the synovia. I know not to what this difference belongs.

Besides, the quantity of these fluids does not appear to be so great in proportion as that of the cellular fluids, with which they have however so much analogy; which is probably owing to this, that the internal motions being less numerous, on account of the inaction of most of the organic muscles, less fluid is necessary to lubricate the surfaces.

The growth of the serous system is always in proportion to that of the organs which it covers. The arachnoides is larger in proportion than it will be in the adult; it seems even, like the brain, to become then the seat of a more active labour; thus diseases are more frequent in it. The increase of exhalation is more common in it than in all the other serous sacs; hence hydrocephalus.

At birth, when the internal motions become suddenly very numerous, on account of respiration, digestion and the excretions, I presume that the serous surfaces become the seat of a more active exhalation. Besides, as very little blood penetrates them, the sudden production of the red blood and its entrance by the arterial system, where it succeeds the black blood, produces less changes upon them than upon the mucous surfaces and the muscular system.

The serous membranes grow like the other organs; for a long time delicate and diaphanous, they gradually thicken as we advance in age, and become of a dull white. Their suppleness diminishes as their density increases; they resist the different reagents so much the less as the subjects are younger. In infants, maceration and ebullition reduce them much more quickly to a homogeneous pulp.

I have observed that in the fœtus which has become putrid, there is often collected different gases in the serous cavities, as may be proved by opening these cavities under water; a phenomenon much less evident in the adult, in whom the cellular texture is often wholly emphysematous by the putrefactive motion, without the escape of any thing by the canula of a trochar which is plunged into the peritoneal cavity or into that of the pleura, as I have many times ascertained. In general, there is disengaged much more aeriform fluid from the organs of the fœtus, than from those of the adult, in the experiments of maceration.

II. State of the Serous System in the after Ages.

In the adult, the serous system remains a long time without undergoing any very sensible change; its membranes follow only the laws of the organs they surround. Thus in the age nearest youth, the serous surfaces of the chest are the most frequent seat of inflammations, dropsies, &c.; whilst in that bordering on old age the inferior surfaces like the peritoneum, are the more often affected.

In old age, the serous system becomes dense and compact; its adhesions to the neighbouring parts are more evident; thus it is less capable of the different locomotions of which we have spoken. Its forces, which are weakened, render absorption in it less easy; it is the frequent seat of dropsy. When it is affected with some diseases, its want of energy imparts to them a remarkable chronic character. There are many old people at the Hôtel Dieu with tubercular inflammations of the peritoneum, which they have had for a long time, whilst young persons are overcome much quicker by the same inflammations. Thus cancers in aged persons often remain almost inert, they frequently are not even painful, whilst their periods are usually most rapid in adults.

The serous effusions are more rare than the infiltrations of the sub-cutaneous cellular texture in old people; but they take place more commonly than those of the intermuscular texture.

The serous system becomes ossified, but not like the arterial, the cartilaginous, &c. from the natural effect of age. Its membranes are not constantly found osseous in old age, and when this phenomenon takes place, it happens at every age. It is a disease, a real tumour, whilst in the arteries and the cartilages it appears to belong to a natural series of functions. I have a preparation in which the arachnoides is evidently osseous in many points, and as it is upon the dura-mater that these productions are formed, their existence serves very well to prove that the arachnoides is distinct from it; for at the place where they are found, they can be easily separated from each other.

III. Preternatural Development of the Serous System.

I shall not repeat here what I have said, in speaking of the cellular texture, upon the formation of the different cysts. These cysts, completely analogous to the natural serous membranes, should be really considered as a preternatural development of these membranes in the economy; they have the same appearance and almost the same texture, furnish their fluid according to the same laws, and appear to be the seat of a constant exhalation and absorption; since they are in vain emptied by puncture, their fluids are always reproduced, until they are removed. For example compare the cyst which has grown preternaturally along the spermatic cord, with the tunica vaginalis filled with water in hydrocele. If the size of these tumours, which are often found together, is the same, it is impossible to discover any difference in their form, appearance, texture, properties, functions, &c.

SYNOVIAL SYSTEM.

I place this system at the side of the serous, because it has the greatest analogy with it, under the relations, 1st, of its form, which is in each of these organs that of a sac without an opening; 2d, of its texture, which appears to be essentially cellular; 3d, of its functions, which consist in an alternation of exhalation and absorption.

What establishes a real line of demarcation between these two systems is, 1st, that the fluids which lubricate their membranes appear to differ in their composition, though there is much resemblance between them. 2d. In dropsical diatheses which affect at the same time the cellular texture and all the serous surfaces of the peritoneum, the pleura, &c. the affection does not extend to the synovial membranes, which indicates a difference of structure, though we do not know what this difference is. 3d. And reciprocally in dropsies of the articulations, an affection in general very rare, and in those of the tendinous synovial capsules, there is no concomitant affection of the membranes of the great cavities. 4th. The fluid of the articular dropsies does not resemble that which fills the great cavities in the same disease. 5th. The synovial membranes are much more rarely than the serous, the seat of those slow and tubercular inflammations which the serous surfaces so often exhibit. I have however seen two examples of it in the synovial membrane of the knee. I believe that these two systems are the only ones in which this disease is observed; so that it is by its existence a character of resemblance, and by its rarity or frequency, a distinguishing attribute. 6th. The different kinds of adhesions of which I have spoken as taking place on the serous surface, are not met with on the synovial surfaces, where we see only that which identifies these two adhering surfaces, a mode which frequently takes place in anchylosis, which is also as often occasioned by it, as by the stiffness of the parts surrounding the articulation. 7th. The synovial surfaces are not as often as the serous, the seat of those remarkable locomotions of which we have spoken; which depends on this, that the articular organs are not, like the most of those covered with serous surfaces, subject to alternate dilatations and contractions.

The synovial system exhibits evidently two great divisions. To one belongs the articular system, to the other that of the tendinous grooves. Each shall be examined separately.

ARTICLE FIRST.

ARTICULAR SYNOVIAL SYSTEM.

I believe that I first described this essential portion of the synovial system. I shall relate here what I have said of it elsewhere. I shall examine first how it is separated from the blood, afterwards the fluid itself, and then I shall describe the organ which furnishes it.

I. How the Synovia is separated from the mass of Blood.

Every fluid differing from the blood, can be separated from it to be afterwards transmitted to an organ, but in one of the three following ways; 1st, by secretion, a function characterized by the existence of a gland intermediate to the blood vessels that bring the materials to it, and the excretories which carry off the result; 2d, by exhalation, a function distinguished from the first, by the absence of this intermediate gland, and by the immediate continuity of the blood vessel and the exhaling duct; 3d, by transudation, a phenomenon purely physical, almost always happening after death, rarely observed during life, a simple transmission of a fluid by the pores of an organ, towards which it is mechanically determined. Let us examine which of these three modes is that chosen by nature to deposit the synovia upon the articular surfaces.

Is the synovia transmitted by secretion to the articular surfaces?

We are indebted to Clopton Havers for the system which places in the glands the sources of the synovia. Many authors had designated obscurely before him these organs in the articulations; but he made them the particular object of his researches, described them in the different articulations, divided them into two classes, the one principal, the other accessory, and assigned them characters so evident, that according to him, they could not be forgotten. Reddish bunches, spongy, formed by membranes folded upon themselves, situated sometimes without, and sometimes within the articulations, always arranged so as to be protected from too strong a compression, and pouring out through ducts in the form of fringe the fluid they secrete; such are the characters drawn by Havers, which all anatomists since him admire, and the correctness of which the most modern and distinguished authors have acknowledged in their works.

Some anatomists of this age have however thrown doubts upon these glandular bodies. Lieutaud confounds them with the fatty cellular texture. Desault did not distinguish them from it. Every thing confirms me in the same opinion, which many considerations appear to establish in an undoubted manner. The following are these considerations; 1st, these reddish bunches are met with only in certain articulations. There are many of them in which their existence cannot be established but by supposition. 2d. The greatest number of the synovial membranes of the tendons certainly do not exhibit any of them, though Havers, Albinus, Juncke and Fourcroy admit them in all, founded no doubt upon analogy and not upon inspection. Yet the synovia is separated equally in both cases, and lubricates the surfaces of the articulations and of the tendinous sheaths; this separation is then independent of glandular action. 3d. If the best marked synovial glands are examined, such as that of the cotyloid cavity, no trace can be discovered there of this parenchyma of an unknown nature, but remarkable for its structure, which composes in general the glands, and which distinguishes them from every other part and forms their true organic character. 4th. No excretory duct can be demonstrated in these organs. Those in the form of fringes, admitted by Havers, are imaginary. Bertin himself has acknowledged this truth, though he attributed to these bodies a glandular structure. The transudation of the fluids injected by the arteries in the neighbourhood of the articulation, proves the existence of these ducts no better than it establishes them in the cavities of the serous membranes in which it also takes place, and yet in which it is well proved that no gland pours out the albuminous fluid that constantly lubricates these cavities. 5th. Inflation resolves completely these fatty bunches into cellular texture. Maceration produces the same effect. When gradual and long continued ebullition has removed all the fat from them, there remains only a mass of cells pressed together, and similar to those of the common cellular texture. 6th. The glandular character is manifested in certain morbid cases, by a peculiar swelling and hardening, of which the other organs except the glands, such as the muscles, the tendons, &c. never offer an example. The liver, the kidneys, the salivary organs, all the considerable glands are remarkable for this. So true is this character, that it serves to indicate glands, the delicacy of which conceals them in the natural state. For example, the existence of the cryptæ of the stomach, the urethra, and several other mucous membranes, is founded first upon the analogy of the other membranes of this class, but principally upon the preternatural development which these cryptæ acquire in certain diseases. Never, on the contrary, do the pretended synovial glands present to the observer a similar development. Always in the diseases of the articulations, a common swelling seems to identify them with the neighbouring cellular texture. They have not like the other glands, affections distinct from those of this texture, no doubt because they have not a peculiar vitality, because being mere elongations of the neighbouring cellular texture, they partake of its nature and properties, and ought consequently to partake of all its conditions, as it in its turn ought immediately to receive the influence of their affections.

The considerations which I have just offered successively form, I think, sufficient data to resolve the problem proposed above, by establishing as an incontestable proposition, that the synovia is not transmitted by secretion to the articular surfaces.