Part 19

It is evident from this view of the vital forces which animate this system, that the life is much more active in it than in the osseous system, that its vital phenomena are consequently more rapid, that they have not that chronic course which characterizes all the diseases of the bones and that they respond more promptly to the sympathetic excitements of other organs. I am persuaded that many of the uncertain pains which we usually refer to the bones in diseases, have their seat rather in the medullary system, in that of the middle of the long bones especially; observe in fact that most of these pains are fixed in the middle of the limbs, and that they are really in the direction of that system. The medullary system of the extremities of the long bones, and of the flat and short ones, certainly enjoys much more vital energy than the osseous texture itself; inflammation is much more easily developed in it, its effects are more promptly shown. Who does not know that caries is so much the more rapid, in proportion to the quantity of the texture of the cells that exists in the bones? It is not this texture, which by its nature, has an influence upon this phenomenon; but it is, because the more abundant it is, the more the medullary system predominates in it; now as this participates in all its affections, it imprints upon them a rapidity which they have not in the compact texture in which it does not exist.

IV. _Development._

This membrane exists in the cartilaginous state of the middle part of the long bones; but then it serves for the nutritive parenchyma to the gelatine that is exhaled there, and which, accumulated in very great quantity in its cells, renders the bone homogeneous in appearance, and prevents it from being distinguished. When ossification takes place, this substance is absorbed; the medullary cavity is formed; the medullary membrane is bare; the blood enters its vessels, till then permeable only by white fluids, because its kind of organic sensibility changes. Instead of receiving gelatine in its cells, it is the marrow or another fluid that it admits there, a phenomenon also dependant upon this change of organic sensibility. Hence an external form wholly new, a new organ in appearance, whilst in reality it is not the organ which changes, but the fluid that is deposited in it. The same phenomenon nearly is observed in the formation of callus, in which the portion of the medullary membrane corresponding to the fracture is at first cartilaginous, then osseous, and finally becomes what it was originally.

The exhalation of the marrow does not commence when the blood enters the medullary canal, or rather it commences, but I have found that it is wholly different from what it is afterwards in the adult. The proportion of oily substance is almost nothing in it, compared to what we have seen in the medullary fluid. 1st. It has a mucilaginous and reddish appearance; pressed between the fingers, it does not give out an oil as in the adult, but a fluid like gelatine. 2d. By comparing the water in which the marrow of the two ages has been boiled, we cannot see in the first, as in the other, many oily drops floating on the surface. 3d. Exposed to the action of fire, the middle of a long bone lets fall an infinite number of small burning drops, very beautiful, of a blue tinge and which are furnished by the marrow, which burns after being melted. Nothing similar to this is observed in the fœtus. 4th. We know that the taste of the marrow is very different in young animals, in veal, for example, from what it is in adult ones. It is insipid, disagreeable, little esteemed in the first. 5th. I have observed that the marrow of children soon putrifies, becomes green, then black, if their fresh bones have been kept for some time in the air. The odour of this putrid marrow is very fetid. Preserve, on the contrary, for some time the bones of an adult, you will observe that their marrow turns rancid, and becomes of a deep yellow colour, like all fat that has been some time kept. In general the action of the air is wholly different upon the medullary organ, in the first and in the after ages. What is the fluid which this organ especially separates in the fœtus and in childhood, and which then takes the place of the oily substance? It is an interesting object of research. Do the vulgar, who connect the idea of fat with that of marrow, know this phenomenon, when they say that children have yet no marrow in the bones? This absence of medullary fat in the fœtus, essentially distinguishes the marrow from the ordinary fat, which, at this age, is already very abundant.

_Functions._

The first and principal use of the medullary organ is to separate the marrow from the mass of blood by means of exhalation, for it has no glands, and afterwards carry it into it again by absorption, when it has remained for a certain time in its reservoir. This double phenomenon is very analogous to that which takes place in regard to the fat, for which we see that there are two orders of vessels distinct from the sanguineous, that enter its texture; it is not possible however to demonstrate them anatomically.

Is the activity of the exhalants varied by exercise or rest, heat or cold, corpulency or emaciation? We have not any precise experiment upon this subject, though numerous conjectures have been made. But we know that in phthisis, dropsy and marasmus, and in general, in all those states of the body in which general debility is carried to an extreme by the slow and gradual loss of the forces, the marrow, like the other fluids as well as the solids, is changed, loses its essential characters, its consistence and takes an appearance wholly different, without however the medullary membrane experiencing any lesion, or being thickened. I have never observed this lesion except in rickets. The appearance of the marrow in these diseases is mucilaginous, gelatinous, similar to what is seen in the fœtus, with the difference of the redness, which is produced in the first age, by the great number of blood vessels.

The medullary membrane has a direct relation with the nutrition of the bone, a relation which has been proved by the beautiful experiments of Trojat, from which it follows that the destruction of this membrane produces the death of the bone, which has necrosis and is replaced by new bone, for which the periosteum serves for the nutritive parenchyma. These experiments are usually made by sawing a long bone at its extremity, and introducing into the medullary cavity a red hot probe, which destroys the whole organization. Soon after the periosteum swells, inflames and has an extreme sensibility to the external touch. This sensibility is gradually lessened; the inflammation disappears. A considerable quantity of gelatine penetrates the internal layers of this membrane, which becomes a cartilaginous sac, with which the bone is covered. At the end of some time, which varies according to the class of animals subjected to the experiment, according to their age, their temperament and other causes, the vascular system, destroyed on the interior of the canal, and expended wholly upon the periosteum, deposits there the phosphate of lime destined for the bone. To the cartilaginous cylinder then succeeds the osseous one. The bone within has no connexion with the life of the living body that surrounds it on all sides. There are then in artificial ossifications three very distinct periods, 1st, swelling and inflammation of the periosteum; 2d, cartilaginous state of the internal layers of this membrane; 3d, osseous state. Besides, these two last states are not as regular and distinct, nor as easy to be observed as in natural ossification.

Does the medullary membrane serve indirectly to furnish a part of the synovia by the transudation of the marrow through the extremity of the long bones? Most authors assert it. We know at the present day, what must be thought of these mechanical transudations, which are observed in dead bodies, but which are repugnant to the known phenomena of vitality; besides, the following experiment leaves no doubt upon this point. I have opened upon the sides two long bones of one of the hind legs of a dog, so as to pass in a red hot probe, which having been carried in several times, completely destroyed the two medullary systems; necrosis has been pretty soon the consequence of this experiment, and yet the articulation between the two bones with necrosis, has continued to receive synovia as usual, a circumstance that would not have happened, if the transudation of the marrow was necessary to the production of this fluid. Who does not know, on the other hand, that in diseases of the articulations in which the synovia is altered and vitiated, the marrow of the corresponding bones is almost always in a perfectly sound state, and that vice versa, in the diseases which attack the medullary organ, the synovia is not altered in its nature like the fluid which this organ contains in its cells?

CARTILAGINOUS SYSTEM.

The word cartilage is employed too vaguely. It designates, in the common acceptation, bodies whose organization differ essentially. The cartilages of the nose and those of the articular surfaces have certainly but a very remote analogy between them; it is necessary then to establish a line of demarcation. I have endeavoured to do it by making two systems of them; one comprehends the cartilages properly so called, the other, the fibro-cartilaginous substances, such as those that are between the vertebræ, those in the middle of some articulations, &c. As this last is a compound of the fibrous and cartilaginous system, I shall not treat of it until I have spoken of the fibrous system.

By thus limiting the sense of the word cartilage, it gives us the idea of a hard, elastic, white substance, having an inorganic appearance, though it has a real organization. We find this animal substance in different parts of the body; it is met with especially, 1st, at the articular extremities of the moveable bones; 2d, on the articular surfaces of the immoveable bones; 3d, on the parietes of certain cavities, which it contributes in great measure to form; such are the cartilages of the nasal partition, of the ribs, the larynx, &c. Hence three different classes, which exhibit varieties in their forms, in their organization, &c.

ARTICLE FIRST.

OF THE FORMS OF THE CARTILAGINOUS SYSTEM.

The forms of the cartilages vary according to the class to which the cartilage belongs.

I. _Forms of the Cartilages of the Moveable Articulations._

In every moveable articulation, there is at each osseous extremity, a cartilage which covers this extremity, which facilitates by its suppleness the motion of the two bones, the very hard substance of which would occasion by friction too great a shock; which reflects by its elasticity a considerable part of the motion, thus made more extensive; which breaks, by yielding a little, the violence of the shocks the limbs experience, and which thus render these shocks less dangerous.

The general character of the internal conformation peculiar to these cartilages is that of being always less thick than broad, of having a thickness which is in the ratio of their breadth: so that the cartilages of the great articulations exceed in this respect two, three, or four times even, those of the smaller articulations; and these cartilages are moulded upon the articular forms and exhibit two faces and a circumference.

One of these faces adheres to the bone; it unites with it so intimately, that fractures take place any where else rather than here. The means of union are not exactly known; this is certain, that the cartilage is not an elongation, a continuation of the cartilaginous parenchyma of the bone; the fibres of this parenchyma are not continuous with those of the cartilages. If it really was so, by removing from a long bone, fresh and clothed with its cartilage, the phosphate of lime which penetrates it, we should see this continuity, the bone and the cartilage would not differ; now I have constantly observed that in this experiment the action of the acid detaches the cartilage from the bone, either in fragments or as a whole. We see the cartilaginous fibres of the bone deprived of its saline base, terminating evidently on the convex surface which the cartilage embraces; no solution of continuity has taken place. In general, the appearance of the cartilaginous parenchyma, separate from its calcareous portion, is wholly different from that of a true cartilage., I presume that this difference is owing to the quantity of gelatine, which is greater in the second than in the first. The action of the acids, especially the nitric, is the best means of separating a cartilage from its osseous head; maceration does not produce this phenomenon under a great length of time; in ebullition, as the gelatine melts, it is less apparent.

The surface of the cartilage opposite to the bone, is intimately united to the synovial membrane of the articulation. It borrows from it the polish which it has; for wherever these substances do not correspond to this membrane, they lose this character, as we see in the larynx, in the cartilages of the ribs, &c. Here the means of adhesion is an extremely compact cellular texture, which neither maceration nor dissection can remove in layers. As the synovial membrane is wholly formed from this texture, it appears that upon the cartilage it is only an elongation of that which, after having contributed to the structure of this organ, is condensed upon its surface and organized as a membrane.

The circumference of the cartilages of which we are treating, terminates insensibly upon the osseous surface; it ceases at the place, where the synovial membrane quits the bone to be reflected.

The two corresponding cartilages of a moveable articulation are so arranged and adapted to each other, that in the medium position of the articulation, they touch exactly at all their points; now we know that the medium position of an articulation is that in which the bone inclines in neither direction, in which all the muscles contracting uniformly and making an equal resistance, keep it equally from extension and flexion, from adduction and abduction, &c. &c. and hold it in the exact medium. It is this position which the limbs take, when the will does not direct the muscular effort, as for example, in the fœtus, in sleep, in rest, &c.; this is what some convulsions produce, in which all the muscles of a limb are agitated with an equal effort, by an extraordinary influx of the nervous power, &c. In no other position does the contact of the two articular cartilages take place at all their points; one portion of the surface of each always pushes with more or less force the parts surrounding the articulation, and distends them. The softness of the cartilaginous texture renders less painful this pressure, which would be distressing in the great motions, if the bones preserved their hardness at the extremity of the lever which they represent.

The cartilaginous forms of which we are treating, besides these common characters, have others peculiar to each kind of moveable articulations.

1st. In the first kind, the convex crust which covers the osseous head, is thick in the centre, but not at the circumference. An opposite arrangement takes place in the concave crust which receives this head; often even as in the humerus, and the femur, the thickness of this crust is increased at its circumference by a fibro-cartilaginous band. In this way, the effort is borne unequally by the two cartilages; but the uniformity of contact is established.

2d. In the second kind, which differs from the first by the absence of the motion of rotation, though in general a convexity is also received into a concavity, the arrangement for both the cartilages is nearly the same. Yet if two convex surfaces slide upon each other, an example of which we have in the condyle of the jaw and the transverse apophysis, then the cartilage is constantly becoming thinner towards the circumference of each; but then an inter-articular cartilage, thick at the circumference, thin in the middle, supplies the place of this arrangement, and establishes at all points a contact, which, without it, would only take place at the centre.

3d. In the third kind, the cartilaginous crust which covers the prominences and depressions, which reciprocally receive each other upon the extremities of the two bones, exhibits nearly an uniform thickness, as we see at the elbow, the knee, &c.; so that the pressure comes equally upon the whole articular surface.

4th. In the fourth and fifth kinds, the cartilaginous crusts moulded on the form of the osseous surfaces, have also a thickness nearly uniform at all points; I have found upon the bones of an adult, that this thickness is a line and a half in the radio-cubital articulation and that of the atlas, and a line in the carpal and metacarpal articulations.

II. _Forms of the Cartilages of the Immoveable Articulations._

The cartilages are found only in two kinds of immoveable articulations, viz. in those with surfaces in juxta-position and those with indented surfaces. They form in all a very thin layer, continued upon both bones which articulate together, arising from their osseous portion, like those described before, being of the same nature as it, and forming a band so much the more close as we advance in age.

On the head these cartilages are very numerous; those of the cranium have more thickness on the convex than on the concave side, hence the more rapid disappearance of sutures in the last than in the first direction.

Wherever they are found, they contribute to unite the bones which form the cavities; hence, as we have said, there is less danger for these from external bodies, since the motion lost then in part in their soft texture, produces a less effect than if the cavity was only one osseous piece.

It appears that these cartilages have much more affinity to the phosphate of lime, than those of the moveable articulations, which rarely ossify, whilst at an advanced age these always become osseous, of which the cranium especially furnishes us examples. I would observe however that the cartilages of the indented surfaces have much more tendency to ossification than those of the surfaces in juxta-position. At least it is more common to see the parietal bones united with the occipital and frontal, than to see the union of the ossa maxillaria, ossa palati, &c.

III. _Forms of the Cartilages of the Cavities._

The cartilages of the cavities have two different forms according to the parts which they contribute to form. They are, 1st, long, as in the ribs; 2d, flat, as in the larynx, the nasal partition, &c.

All are covered on the exterior with a fibrous membrane like the periosteum, and in which different muscles are inserted. In order to see this membrane it is necessary to macerate the cartilage for a day or two; it then becomes white and very evident in its thickness, and the direction of its fibres. The cartilages of the cavities do not exhibit the numerous foramina which are seen in the bones, because the blood vessels do not penetrate them. But few eminences and depressions are observed in them. We can hardly consider their forms in a general manner, because destined to very different uses, they have but little resemblance in their conformation.

ARTICLE SECOND.

ORGANIZATION OF THE CARTILAGINOUS SYSTEM.

In examining a cartilage in its interior, it is difficult to recognize in it an organic texture; there is one however, which is composed of a peculiar texture and of common textures.

I. _Texture peculiar to the Cartilaginous System._

The peculiar cartilaginous texture exhibits an interlacing of fibres so compact, that it appears at first view homogeneous, formed into a mass of gelatine, without order and without any particular direction. Yet with a little attention we distinguish longitudinal fibres, which are crossed by transverse and oblique ones.

These fibres are more apparent in the cartilages of the moveable osseous extremities than in the others. They have infinitely less suppleness than the fibres of the fibro-cartilaginous substances; thus these bend without breaking, whilst the first break when they are bent considerably; the place of the rupture is smooth, with but few inequalities.

The cartilaginous texture is remarkable for many characters which distinguish it from the others. Next to the osseous texture, no one so long resists putrefaction and maceration. In the midst of a dead body wholly putrid, we find this texture almost untouched, preserving its appearance, its structure, and even oftentimes its natural whiteness. The same thing is frequently seen in gangrenous limbs in the living body. I have kept cartilaginous substances a very long time in water, which have not become altered, except a little in their colour. It would require more than a year perhaps, to reduce them to that soft, mucous, liquid pulp, to which maceration reduces most of the organs.

The cartilaginous texture contracts under the very powerful action of caloric, like all the other textures; yet this phenomenon is not apparent in the thyroid cartilage on account of its thickness, nor in the cartilages that encrust the bones, on account of their adhesion to these bones. But if we cut one in fine layers, and the others in slices, and plunge them into boiling water, they crisp up immediately and with force.

Exposed to drying, the cartilaginous texture becomes yellow, acquires a semi-transparency analogous to that of the tendons and dried ligaments; it becomes hard, contracts, diminishes in size, and loses its elasticity as it becomes hard.

Ebullition also gives it at first a yellow colour, then it cracks it upon the articular extremities, breaks it in different places, and raises it by layers which it softens, and which finally it melts almost completely to a small residue, which does not appear to be gelatinous. The softening of the cartilaginous texture renders it much more fit to be dissolved by the digestive juices than it naturally is. Swallowed raw, the cartilages would remain a long time in the stomach, whilst they are very easily digested when cooked; this is one of the very great advantages of the boiling of meat. In different experiments made upon digestion, I have found portions of cartilages still untouched in the stomach of dogs, whilst the flesh was already reduced to a pulp.

In certain cases, the cartilaginous texture is singularly altered. In the diseases of the articulation of the hip, it assumes an aspect wholly different; it is a soft substance, like lard, with very distinct vessels, sometimes with very evident fibres, having a size double, quadruple what is natural, and filling the cotyloid cavity. I have observed that then they do not become yellow, do not melt by ebullition and consequently are not gelatinous. In the same diseases, I have found the cartilaginous texture, upon the femur and the ilium, not only ossified, but changed into a substance exactly like ivory; I have preserved these two pieces.

When the cartilages become osseous, there is developed in their middle a texture analogous to that of the texture of the cells of the bones, in which the interlaced fibres leave between them very distinct spaces, and in which is deposited a kind of medullary fluid. This observation is especially applicable to those of the cavities, of the larynx, of the thorax, &c.

II. _Parts common to the Organization of the Cartilaginous System._