Part 20

These two substances, the gelatinous and saline, which enter essentially into the composition of the bones, imprint upon them very different characters. The phosphate of lime, almost foreign to vitality, is only destined to give to the bones the solidity and resistance that characterize them. The gelatinous substance, on the contrary, has especially the animal character; thus the vital activity is in the inverse ratio of one and the direct ratio of the other, as we shall see. Deprived of gelatine, the bones are not capable of being digested, they offer nothing for the gastric juices to act upon, they cannot extract nutritive matter from them, because they act upon them nearly as water does, which dissolves the gelatinous substance and extracts it from the saline portion. Different animals that swallow fresh bones for nourishment, would die from eating a calcined one; thus the more the bones contain of this substance, the more nourishing they are; those of young animals are on this account more proper to make gelatinous broths, more suitable to be digested raw by the stomachs of certain species, &c. If we expose a bone to the action of an acid, so as to have only its cartilaginous parenchyma left, and afterwards soften this parenchyma in boiling water, it becomes an aliment that can be eaten.

Besides phosphate of lime and gelatine, the bones contain also some saline principles, as the sulphate and carbonate of soda, &c. But this proportion is too small to be noticed. Upon this point, I refer to chemical books, especially to the great work of Fourcroy.

II. Common Parts which enter into the organization of the Osseous System.

The ancients ranked the bones among the white parts, among the tendons, the cartilages, &c. It is sufficient however to examine the interior of them to see, by the redness that distinguishes them, that much blood enters them. This blood penetrates in three orders of vessels; one belonging to the medullary cavity of the long bones, another to the texture of the cells, and the other to the compact texture. These two last orders distributed in the osseous texture, appear to be especially destined to deposit the phosphate of lime; for in the cartilages of ossification, the white vessels alone carry the gelatine; in other cartilages it is the same; so that I think that this kind of vessels is also destined in the bones which are perfectly formed to nourish their cartilaginous parenchyma, whilst the red vessels belong more to their calcareous portion.

Each medullary cavity has only one vessel, and only one foramen of nutrition. This vessel has a diameter proportioned to that of the bone which it penetrates, and in which it is divided immediately into two branches, without permitting any ramification on the compact texture. These go in an opposite direction to the two extremities of the bone, ramify ad infinitum in the medullary organ, and their last branches are lost in the commencement of the texture of the cells, where they anastomose with the vessels of this texture; that which occupies the medullary cavity under the name of reticular, and the internal surface of the compact texture, receive also some branches. A vein everywhere accompanies the artery, and follows the different distributions of it.

The vessels of the second order belong to the texture of the cells of the long, flat and short bones; they are equal in number to the foramina of this texture, and ramify on its cells; they communicate with those of the marrow and of the compact texture. At death, the small arteries in general remain full of red blood, which indicates their course which their minuteness would conceal, and which injections can rarely demonstrate with accuracy. The accompanying veins of these arteries can hardly be seen.

The blood-vessels of the third order are only the last ramifications of the arteries surrounding the bones, ramifications which enter in great number the compact texture, and stop there. The existence of these vessels may be proved in different ways. 1st. By detaching the dura mater from the internal surface of the cranium, many small sanguineous drops prove their rupture. 2d. By raising on a subject of a middle age the periosteum, we make the same observation. I have remarked that these experiments succeed especially on those that have been drowned, or on animals destroyed by asphyxia, on account of the great quantity of blood their vessels contain. 3d. If we fracture a long bone in the middle, the compact portion, which forms the medullary canal, exhibits small reddish striæ, which are nothing but these small vessels still full of blood, and of which we thus discover a greater or less number, according to the manner in which the blood was arrested in the capillary system at the instant of death. 4th. The saw-dust of the compact texture in living animals is red, though less evidently so than that of the texture of the cells; a proof that these vessels have been divided.

The vessels of the bones are very numerous in childhood; they diminish in the adult, and become scarce in old age. The facility of the formation of callus follows the same proportion in the different ages of life. Often in affections of the osseous parenchyma they have a remarkable development, which much exceeds their natural diameter. Osteo-sarcoma, spina-ventosa, &c. exhibit this, which is much oftener observed in cancerous tumours than any other.

These vessels communicate with each other by numerous anastomoses; this is what we see especially in the long bones, between those of the medullary organ and those of the texture of the cells. By these communications, they mutually assist each other's functions. I have seen the nourishing foramen of the tibia completely obliterated in a body that I injected. A sort of cartilage filled this foramen; the artery formed a real ligament. Yet its bifurcation in the medullary canal was found very well injected, and besides no alteration appeared in the nutrition of the medullary organ, which had probably received as much blood as usual. I found nothing in the neighbourhood of the foramen, which showed the cause of this obliteration, which an exostosis, an affection of the periosteum, or an inflammation can very easily produce.

On the other hand we know that very considerable osseous layers are often taken from the extremity of the long bones by caries, which consequently destroys all the vessels corresponding to these layers, and yet the bone beneath lives, principally by the blood that it receives by the extremities of the artery of the medullary organ. This is nearly what happens to the long bones in the first age, in which the cartilaginous extremities have not vessels of the second order, and in which consequently almost all the blood comes from this same artery of the medullary organ; thus it is much larger in proportion, and the foramen which receives it much more considerable.

Nothing is yet known upon the systems of absorbent and exhalant vessels of the bones, and we can reason upon this point only from analogy. Besides the nutritive process evidently supposes them there.

As to their cellular texture, it appears to be almost nothing; we can even say that in whatever place we break the compact fibres or those of the cells, its filaments are not distinct; but it is their dense and compact texture that conceals them from us. In fact, 1st, when this texture is softened, and the bone has become flesh, as it is called, the cellular texture is very apparent there. 2d. The fleshy granulations, rising on places that have been fractured or laid bare, are only the extension of the cellular texture which has too much calcareous substance to allow it to be seen in the natural state. 3d. After having removed from a fresh bone all this substance by an acid, I have sometimes observed cellular filaments by separating the cartilaginous fibres which form the parenchyma that is left. 4th. When we boil this cartilaginous parenchyma in order to extract the gelatine from it, there remains portions of membranes which are evidently cellular.

We cannot trace the nerves in the bones, the filaments that enter them are so fine; I do not know that anatomy has any positive data upon this point.

ARTICLE THIRD.

PROPERTIES OF THE OSSEOUS SYSTEM.

I. Physical Properties.

The bones have very strongly marked physical properties. Solidity and hardness are their peculiar portion; they derive these properties from the phosphate of lime which penetrates them, thus they are constantly increasing with age, because this substance becomes more and more predominant. Elasticity is another physical property of the bones, which is found combined with the two preceding, but which is in an inverse order; as it is in the gelatinous substance, in the cartilaginous portion of the bone that it resides, it is, like this portion, greater in childhood. In old age, the bones lose entirely their suppleness and elasticity; they break more easily. Elasticity is more evident in the long and small bones, than in those which are larger; the fibula bends and evidently goes back again, this the tibia could not do without difficulty. It is not that the one is more elastic than the other, but it is that its conformation is more favourable to the development of this property.

II. Properties of Texture.

Although the hardness and solidity of the osseous texture seem to be opposed to every kind of extension and contraction, yet these two phenomena and the properties of texture from which they arise, are often very evident in it.

The extensibility of the osseous fibres is proved by the observation of many diseases, for example, the spina-ventosa, the swelling of the maxillary sinus when it contains a polypus, by the enlargement of the bones of the cranium in hydrocephalus, &c. I would remark on the subject of these different distensions, that often by the influence of analogous causes, the bones which yield and are distended in the above cases, are broken, worn and destroyed in others. A polypus of the nose breaks through the naso-palatine partition, without having first distended it; aneurism of the aorta does not bend the sternum or the vertebræ, but it breaks through and destroys these bones. Whence arises this difference from causes nearly the same? This is not easily determined. The contractility of texture is very evident in the bones, when the cause which distended the fibres is removed. We see the alveoli contract, and become effaced, when a tooth has been drawn from them. The diminution of the thickness of the jaw after cutting the teeth arises only from the contraction of its fibres, which are no longer distended as much, because the root is not so broad as the crown, which had till then been wholly in the bone. The maxillary sinus contracts when a fungus is removed from it, or pus is discharged from the carious bone, &c. If death was not too soon the consequence of the puncture of the head of hydrocephalic patients, I am persuaded that we should see the bones gradually contract, and restore the cavity of the cranium to its natural dimensions. When we remove the dead piece from a long bone in necrosis, the new bone, formed on the exterior by means of the periosteum contracts in an evident manner. In paralysis of the optic nerve, its foramen becomes narrower. The orbit contracts when a cancerous eye has been extirpated. I have dissected the carotid canal in a dog whose carotid I had tied; there was no contraction because the blood coming by anastomoses dilated the artery to the usual size.

This contraction of the bones, by means of the contractility of texture, is not so sudden as that of the muscles, the skin, &c. when they are no longer distended by a tumour, an aqueous collection, &c. This arises from the difference of the organic texture, from the rigidity of osseous fibres owing to the calcareous substance they contain, &c. Thus the organic sensibility is less evident in them.

III. Vital Properties.

The bones have hardly any animal properties in a natural state. Their sensibility is nothing; the saw, the mallet, and the chisel act upon their texture almost with impunity; an obscure feeling is the only result of the action of these instruments; fire even can act upon them without making the animal suffer much. But in a morbid state, the sensibility is developed to the greatest extent; we know the horrible pains that attend spina-ventosa, and those not less severe that caries produces in certain cases. If a bone is inflamed, as for example the sawed extremity of a stump after amputation, this bone which in a natural state had borne, without transmitting any painful impression, the action of the saw, becomes as it were a new sensitive organ, to which the least touch is painful. The animal contractility is nothing in the osseous system.

The organic properties give life to this system as to all the others. The sensibility of this kind certainly exists in it; the fluids that penetrate it are felt, and by virtue of this feeling, those are appropriated to it which are proper for its nutrition. But is there in the osseous system a reaction upon these fluids? are there those insensible oscillations which compose insensible organic contractility? Its hardness seems to prevent them. But yet the circulation is carried on there; it performs a constant work, an habitual composition and decomposition, which can hardly be conceived of without reaction on the part of the osseous system. Besides this reaction is more slow, more difficult on account of its structure; and hence without doubt the slowness, of which we shall speak, in the vital phenomena of the osseous system. Sensible organic contractility is foreign to it.

Character of the Vital Properties.

The peculiar life of the bones is composed then of only two vital properties, organic sensibility and insensible organic contractility. From these two properties are derived all the vital phenomena that these organs exhibit, inflammations, formation of tumours, cicatrization of solutions of continuity, &c. This peculiar life is remarkable in general, as I have just observed, when compared with the peculiar lives of the other organs, by its slowness, by the tardy concatenation of its phenomena. All things being equal as to ages, and the different proportions of the earthy and cartilaginous substances, inflammation is more slow there than in the other parts. Callus is remarkable among the other cicatrices by the length of its formation; compare an exostosis in its origin, its progress and its development, with a tumour of the soft parts, a phlegmon for example, and you will see the difference. Who does not know, that whilst suppuration often requires only a few days in the other organs, it is whole months in forming in the middle of the bones? Observe the difference that there is between a gangrene of the soft parts, in which death takes place in a short time, with caries and necrosis of the bones, in which a long period elapses between disease and death of the part. In general we can say, when inflammation exists in a bone, that it is chronic.

Sympathies.

This character of the vital properties imprints an analogous one upon the sympathetic relations of the osseous system with the other systems. At first the animal contractility and the sensible organic contractility cannot be put in action in these relations, as they do not exist in the bones. The animal sensibility being developed in them with difficulty and slowly by the diseases that essentially affect them, the sympathies can be brought into action in them only in an obscure manner. These sympathies then should act essentially upon the organic sensibility and upon the insensible organic contractility, and as these two properties are developed slowly, the different sympathies should not be connected with the acute affections of the other organs, and this is what is clearly proved by observation. In fact observe that whilst many other systems respond with great quickness to the acute diseases of an organ, this, as well as the cartilaginous, fibro-cartilaginous systems, &c. remain then almost always in inaction. Let the stomach, the lungs, the brain, &c. be the seat of a severe acute disease, you see immediately many sympathetic phenomena arise in the nervous, vascular, muscular, glandular, cutaneous, mucous systems, &c. &c.; all seem to feel the trouble of the affected organ; each, according to the vital forces that predominate there, exhibit different phenomena, which are only aberrations, irregular developments of these forces; in the animal muscular system, it is the animal contractility which is especially raised; hence spasms and convulsions; in the glandular, the serous, the cutaneous, the mucous, &c. the insensible organic contractility and the organic sensibility principally experience alterations; hence the different sympathetic derangements of the secretions, of the sweat, of the exhalations; in the nervous, it is the animal sensibility which is especially brought sympathetically into action; hence the wandering or fixed pains in different parts; in the organic muscular, it is the organic contractility which is raised; hence the irregular motions of the heart, the stomach and the intestines. In all the acute diseases of an organ there are always two orders of symptoms, the one relative to the affected organ, as are the cough, the pain in the side, the spitting of blood, the difficulty of respiration, &c. in peripneumonia; the others purely sympathetic and arising from the relations which connect the vitality of this organ with that of all the others; now these last are often much more numerous than the others.