Part 13

The second kind of cavities of nutrition belong especially to the texture of the cells of the bones. Thus they are seen wherever this texture abounds, in the extremities of the long bones, the circumference of the flat ones, and the whole superficies of the short ones. Their diameter is greater than that of the canal which goes to the medullary cavity; it is less than that of the canals of the compact texture. Their number is very considerable; I have counted a hundred and forty upon the tibial extremity of the femur, twenty upon the body of one of the dorsal vertebræ, fifty upon the os calcis, &c. In general this number is always in proportion to the quantity of the texture of the cells that the bone contains. Hence why there are but few on the flat bones of the cranium, why they are more numerous on the flat bones of the pelvis especially where this texture is abundant, as on the ischium, on the iliac portion of the circumference of the ilium, &c. By pouring mercury into the spongy texture, it runs out from all these foramina, and thus proves their communications. They are irregularly scattered wherever they are. They are not met with on the body of the long bones, because the body contains little or none of the texture of the cells.

The third kind of canals of nutrition is only destined to the compact texture. It consists of an infinite number of little pores which the eye can clearly distinguish, and through which small vessels pass, that go to this texture. An evident proof that they do not go to the texture of the cells, is, that in the preceding experiment, the mercury never finds in them a way to escape externally. It is impossible to determine their number; it is prodigious in childhood. As the bones in old age become filled with calcareous substance, they are obliterated, and the vessels they contain become small ligaments, foreign to osseous nutrition, which continually grows weaker, and is soon annihilated, and allows necrosis to seize upon the bones, if general death does not prevent this partial death of the osseous system.

ARTICLE SECOND.

ORGANIZATION OF THE OSSEOUS SYSTEM.

The peculiar texture of the osseous system forms in it the principal and predominant part, especially as we advance in age. The common organs are in much less proportion.

I. _Texture Peculiar to the Osseous System._

The texture of the bones, like that of most of the other organs, presents itself under the aspect of fibres whose nature is everywhere the same, but which differently arranged, form two principal modifications; in the one, these fibres being more or less scattered, exhibit many cells; in the other being close to each other, they form a compact substance in which it is difficult to distinguish them. Hence two sub-divisions of the osseous texture, that with cells, and the compact. Authors admit a third one, the reticular; but this is included in the first.

_Texture with Cells._

The texture with cells does not exist in the first periods of ossification. The time of its formation is when the phosphate of lime is added to the gelatine of the primitive cartilage, and gives to the organ the bony nature. Then an infinite number of cells is formed in the solid mass of cartilage, because the gelatine, taken up by the absorbents, disappears in the place they occupy. No more is brought by the exhalants, which begin to carry the phosphate of lime to the fibrous cross-pieces, whose interlacing forms these cells; so that the development of the texture of the cells belongs evidently to the disproportion that takes place in the bones at a certain period of their growth, between the functions of the exhalant and absorbent system, until then in equilibrium. We know not the cause of this disproportion, it appears to be a law of ossification. It is by virtue of this law and by an analogous mechanism, that the os ethmoides, at first solid and full when it is cartilage, is hollowed out at the period of its ossification, into a great number of cells. It is thus that the sphenoidal, frontal sinuses, &c. are formed and enlarged.

The formation of the texture of the cells ceases when all the epiphyses have disappeared. At this period it exhibits to us an infinite number of fibres which appear to arise from the internal surface of the compact texture, go in different directions, cross, unite, separate, bifurcate, in a word, pursue such irregular courses, that it is impossible to follow them. Their size is not less variable; sometimes their delicacy is such, that they can hardly be touched without breaking; at others they are quite large. Often instead of fibres there are layers, of more or less considerable size, from which arise other smaller ones, which appear to ramify, and from which result, when they are near each other, species of canals, which are seen very well by sawing transversely the extremity of a long bone, so as to have a segment of half an inch.

The cells which are made by their separation, are of very unequal form and capacity.

All communicate together; the following experiments prove this. 1st. If we make a hole in the extremity of a long bone, or upon the surface of a short or flat one, and pour in mercury, it passes through all the communications, and comes out of the natural foramina on the surface of the bone, which also open into the cells. 2d. Saw a long bone at one of its extremities, cover its whole surface with something that shuts up its pores, then expose it to the sun; the medullary fluid not being able to escape by the external pores, will come out at the sawed place, after passing successively through all the cells. 3d. By varnishing a dry bone, and opening it only in two opposite points, we can force air, water and every kind of fluid through these communications, from one opening to the other.

We can then consider the interior of every bone as forming a general cavity that is filled by many interlaced fibres. I have not observed a sensible difference in the direction of these fibres in the three kinds of bones.

_Compact Texture._

The fibres that form the compact texture are not the same as those of the preceding. These fibres, being in juxta-position, not leaving any space between them, giving by their approximation a remarkable density to the texture they form, have a longitudinal direction in the long bones, are in the form of rays in the flat ones, and cross each other in all directions in the short ones. This triple arrangement of the fibres of the compact texture appears to be wholly owing to the manner of ossification. In fact, when we examine its progress in the primitive cartilages, we see these organs encrusted with the phosphate of lime, in the same direction which these fibres afterwards take. Thus these fibres are very evident in the first age, on the bones of the cranium in particular. When the phosphate of lime, successively deposited on the cartilaginous parenchyma, predominates there, then the whole is confounded in the compact texture in one homogeneous mass. But still there are different circumstances that indicate the primitive direction of the fibres: 1st. When by an acid we remove from bones their calcareous part, then the cartilaginous portion keeps as a kind of mould, the form of the substances that filled it, and exhibits fibres whose direction is the same as that pointed out for the three species of bones. If we wish to separate the cartilaginous layers, it is in this direction that it is most easily done. 2d. The fissures that come in bones long exposed to the air follow in general the natural direction of the fibres. 3d. Calcined bones exhibit nearly the same phenomenon.

The direction of the fibres of the compact texture is changed entirely in the apophyses, in which it does not follow that of the principal bone. In those, which by their form, partake of the character of the long bones, as in the styloid, these fibres are longitudinal; they go in all directions in those, which like the mastoid, the different species of condyles, &c. resemble in their shape the short bones.

The assemblage of the fibres forms, according to anatomists, layers which they have considered as in juxta-position, and held together by little pins according to some, and by the interlacing of fibres according to others. These osseous layers do not appear to me to exist in nature. All the fibres of the compact texture adhere to each other, cross and form a whole that we cannot conceive of in this manner, and which besides does not accord with the irregularity of the distribution of the vessels. Art separates here fibres layer by layer, as it is done in a muscle, in a ligament, &c.; but these layers are wholly factitious; to exhibit the bones as formed by an union of these layers is to give a very inaccurate idea of their structure. It is still more inaccurate to consider these layers as attached to each other by osseous pins, by attraction, or by a glutinous matter which serves as a glue. All these ideas, contrary to anatomical examination, suggested by a false application of the laws of the adhesion of inorganic bodies to the adhesion of organized fibres, now belong only to the history of physiological errors. There is a circumstance, it is said, that very evidently proves the lamellated structure of the bones, it is their exfoliation. It is true that often very distinct layers are separated from the living bone, but these layers are only the product of exfoliation itself. Then in fact the bone dies on the surface; the superficial vessels receive no more blood; this fluid is stopped under the portion deprived of life, the exhalation of the phosphate of lime ceases there, every kind of sanguineous, exhalant and absorbent vessel is destroyed; a slow inflammation, with suppuration, comes on, and fixes the line of demarcation; and as this line is often at the same place, all which is above it becomes an inorganic layer which gradually falls off, and preserves its osseous solidity, because the dead absorbents were not able to remove the phosphate of lime. Besides, nothing is more common than to see exfoliation take place not by layers, and the bone afterwards exhibit an unequal surface, the effect of the inequality of the thickness of the exfoliated portions. Finally, exfoliation often takes place in a direction opposite to that which the layers are thought to have; this is what we see in the separation of the extremity of the long bones, that have been exposed to the air or too much irritated after amputation, in the shedding of the horns of animals, &c. Let us consider the compact texture as an assemblage of condensed fibres, not separated by layers, which we can only consider as imaginary.

The fibres of the compact texture differ in their organic arrangement, from the muscular fibres in this, that frequent elongations unite them to each other, whereas the muscular have only the cellular organ, the vessels and the nerves as the means of union. Such is the intimate juxta-position of the fibres of the compact texture, that they leave between them only pores hardly sensible to the naked eye, but which become so however with a glass, and which the medullary juice and vessels fill. In the rickets this density of texture disappears, and we observe in the middle part of the long bones and under the layer of periosteum more thick than common, an osseous texture, easily bent in all directions, forming an infinity of cells and taking the place of the compact texture that ought to be there. It appears that this change of compact texture into that of cells is made less by the absorption of a part of the phosphate of lime, than by the extension of the osseous fibres which separate from each other, and leave between them spaces that did not before exist; this gives to the bodies of long rickety bones a very considerable thickness. I have many times made this remark.

_Arrangement of the two Osseous Textures in the three kinds of Bones._

The osseous textures, considered in the different kinds of bones, are differently arranged. In general the compact forms the exterior, the covering of the bone, and that of the cells occupies the interior. The ossa spongiosa form an exception to this rule, the modifications of which we shall now examine.

1st. In the long bones, the compact texture has a very remarkable thickness in the centre, where it serves the triple purpose, first of protecting the medullary organ, of which it is the covering, then of giving solidity to the bone in this place, which more than the extremities, is exposed to great efforts in locomotion, falls, concussion, &c. and where the bone, traversed only by some very weak fibres of the cells, cannot borrow its resistance but from its external parietes; finally, of thus diminishing without danger the size of the bone in the middle part of the limb, the form of which, becomes by this means much more regular. So that as we go from the centre, we see in a long bone, sawed longitudinally, the compact texture diminish in thickness, and form at last at the extremities only a delicate layer analogous to that which covers the short bones. Thus the power of resistance of the long bones, at their extremity, is less in their compact shell, than in the great quantity of the texture of the cells deposited under it; it is this especially that prevents fractures; hence we see how the proportion of the compact texture and that of the cells being inverse in the two parts of the bone, the manner of their resistance is also inverse.

The texture of the cells differs a little when examined in the medullary canal and in the extremities. In the canal there are extremely delicate filaments, continued from larger fibres which fill above and below the extremities of the bone, and the compact portion which forms the osseous cylinder. Few and scattered at random in the middle of the canal, these filaments approximate each other, and form a kind of net-work, as they go from it; hence the name of reticular substance by which it is designated. But it is not a distinct texture, it is only a modification of that of the cells; a modification, which is especially characterized, 1st, by the delicacy of the fibres; 2d, by the uniform absence of those fine and short layers which frequently belong to this texture in other parts. Besides, the manifest use of this portion of the texture of the cells, too weak to contribute to the resistance of the bone, is evidently to serve as a support to the medullary system, and insertion for its membrane. At the extremities of the long bones, the fibres of the texture of the cells increase a little, approximate each other, are scattered in layers, and give to the bone by their union and number, a remarkable thickness and resistance, without however increasing the weight, which very much favours locomotion, considering that this weight placed at the extremity of the lever would have been very painful to raise.

2d. In the flat bones, the compact texture forms two external layers, the thickness of which is between that of the middle of the long bones, and that of the extremity of the same bones, or that of the short ones. Between these two layers is found the texture of the cells, similar in general to that of the extremity of the long bones, a little more lamellated however, thicker usually at the circumference, often almost wanting in the middle of the bone, where its two compact layers in juxta-position allow a light to be seen through it, when placed behind. In general wherever the broad bones are so thin, from the want of the texture of the cells, there are very strong muscles, which by their thick layers give solidity to the bone. We see examples of this in the iliac, sub-scapular, inferior-occipital fossæ, &c.

3d. In the short bones, the texture of the cells always predominates; the bone is almost wholly formed of it, a delicate layer of compact texture forms only its covering, and in this respect, the organization of these bones is the same as that of the long bones at their extremities; thus the resistance of the bone depends on the whole of its mass, and no part makes a greater resistance than another against fractures. We see, from all that has thus far been said, the successive manner of the solidity of the different bones. In the middle of the long bones, there is hardly any thing but compact texture to which it is owing; in the flat bones it is as much to this texture as to that of the cells; in the extremities of the long bones and in the short ones it is almost to this last only that its solidity is owing.

4th. In the osseous eminences, the compact texture is more abundant than elsewhere, especially in those of insertion, as in the prominent lines of the long bones, which are all formed of it, in the asperities of the osseous surfaces, in their angles. If the eminence is considerable, there enters into it also more or less of the texture of the cells as we see in the spinous and transverse processes of the vertebræ, in the coracoid, mastoid, &c. processes. The eminences of the moveable articulations have in general less of the compact texture, solidity is given to the bone by the articular cartilage. Those of the immoveable articulations, on the contrary, in general smaller, as the sutures of the bones of the cranium, for example, are in proportion more compact than cellular.

5th. In the osseous cavities, all those which serve for moveable articulations, are only furnished with a very delicate compact layer; it is thicker when the articulations are immoveable. In general all the foramina, cavities and canals that transmit from one region to another vessels, nerves or other organs are everywhere lined with a compact layer that defends them from the impression of these parts. The foramina at the base of the cranium, the dental canals, the vidian foramina, &c. are examples of this arrangement.

_Of the Composition of the Osseous Texture._

Whatever may be the modifications under which it is exhibited, the osseous texture has everywhere the same nature; the same elements form it; now these substances are especially a saline calcareous substance and a gelatinous one.

The existence of the saline substance in the bones is proved in different ways. 1st. Combustion, by destroying the gelatinous portion, leaves a friable, brittle body, of a form analogous to that of the bone and which is nothing but this saline substance, which resembles, if we may so say, a moulded body that keeps the form of the mould after it has been taken away. If the combustion is pushed very far, and a red heat produced on the calcined bones, they undergo a semi-fusion, which makes them resemble the state of porcelain; they have then a very compact, fine, semi-vitreous grain, a semi-transparency, and an appearance like that of the vitrified earths. 2d. The long continued exposure of the bones to the air produces an effect very similar to that of the first degree of combustion, though however the gelatine is rarely so thoroughly removed, and the saline portion so perfectly exposed as by the action of fire. Besides, it requires a very long time to produce this effect, especially upon the thick bones; the thin ones are more easily altered; I have often made this observation. After ten years exposure to the air and rain, I have observed that clavicles taken from the cemetery of Clamart, exhibited upon the action of the acids, a cartilaginous parenchyma almost equal to that of a bone that had been some time dried. But this parenchyma finally disappears, and the bone falls to powder, when it is no longer supported by it, and the particles of the remaining calcareous substance have been disunited by time. 3d. In the last stages of all cancerous diseases, the bones have a friability which is only owing to the greater proportion of this last substance, a proportion arising itself from the small quantity of gelatine that is then exhaled in the bones. 4th. When a bone has been for some time exposed to the action of an acid, the nitric for example, a portion of its substance is taken from it by this acid, which is evidently a calcareous salt, as can be seen by mixing it with a solution of an alkali, which uniting immediately to the acid, exposes this salt, by making it precipitate. 5th. Papins digester, by dissolving by the action of water reduced to vapour the gelatinous portion, shows also this saline calcareous part.

Scheele has found that this portion is a neutral salt with an earthy base, the phosphate of lime. Frequently the phosphorus in fresh bones give them a luminous appearance, that can be seen very far in the night. It is sometimes the whole of the bone, sometimes some parts only that become luminous. I have always observed in the illuminated places an oily exudation, either that comes from the medullary juice, or is furnished by the fat of the neighbouring soft parts of the bone.

Different facts as evident as the preceding, prove in a manner not less certain, the existence of a gelatinous substance in the bones. 1st. When in the solution of the bones in the acids, the phosphate of lime has left them, there remains a cartilaginous, flexible, elastic body, yellowish when nitric acid is employed, of the same form as the bone. Now we know that the gelatine especially nourishes the cartilages. 2d. If besides we subject this cartilaginous residue to ebullition, we extract a very great quantity of gelatine which is dissolved in the water and can be afterwards precipitated by tannin. This substance can even be removed from the bones without the previous extraction of the phosphate of lime; it is thus that with bones stripped of every surrounding organ, and reduced to very small fragments or even to powder by the action of a rasp, very nourishing broths and jellies are made. It is not without reason that in the preparation of boiled meat, the bone is left attached to the meat; besides the white organs that surround it, and the medullary oil that it contains, it furnishes to the broth a substance that is peculiar to it. 3d. The combustion of the bones, and especially of their cartilaginous residue, gives an odour exactly similar to that of the combustion of the different animal glues, which, as we know, the gelatine especially forms. 4th. In the different affections in which the bones become soft, the earthy substance is diminished more or less sensibly, and the gelatinous remains more abundant in proportion than common.

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.