General Anatomy, Applied to Physiology and Medicine, Vol. 2 (of 3)

by Xavier Bichat

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.

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.