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

by Xavier Bichat

I. Conformation.

Each of the organs from the whole of which it results, exhibits it under the form of a delicate membrane, lining the whole cavity, folded a great number of times, giving origin to many elongations, of which some cover the fine threads of the texture of the cells which are met with in this cavity, others pass, without adhering to any osseous portion, from one side of the membrane to the other, and of which all form numerous cells in which the marrow is contained.

We can then form of this organ an idea analogous to that which the cellular organ gives us; viz. that of a spongy body with communicating cells. The place that it occupies, gives to it as a whole, a cylindrical form.

It appears that at the two extremities of the canal, the cells or membranes do not open into those of the texture of the cells, and that the medullary fluid of the preceding system does not communicate with the marrow of this. In fact, the line of demarcation which separates them is evident; they do not mix in a gradual manner. Air injected from one side of the medullary cylinder, only penetrates with difficulty and by tearing the membrane, into the texture of the cells of the opposite extremity of the bone; yet, notwithstanding these considerations, I confess that the question is not fully settled. The transudations in dead bodies have no influence in deciding it, on account of the permeability that our parts acquire after death.

II. Organization.

The texture of the medullary membrane is very little known, because its extreme tenuity conceals it from our researches; for it is only in the bones of ricketty subjects, that its morbid increase in thickness has permitted me to trace it accurately. It has the appearance of cellular texture; yet its properties and its nature are very different from this texture; it cannot be referred to any of the three classes of membranes, the serous, the fibrous or the mucous. Some have pretended that it was an expansion of the periosteum, which had passed through the numerous foramina by which the bone is perforated, and entered into the medullary cavity; but the least parallel made between these membranes is sufficient to make us see that they are essentially different in their functions, vital forces, &c. and cannot have the same texture. A principal vessel penetrates the medullary membrane; it is the artery, which enters by the only, but very large foramen, which is seen on the body of the long bones; the two branches of this artery and those of the corresponding vein, ramify in an opposite direction in the medullary cylinder, and by their innumerable branches give to it a very evident reddish colour, that disappears with age. The extremities borrow their vessels from those of the neighbouring texture of the cells. We cannot trace any nerve there. Such is sometimes the abundance of the fluids which penetrate this membrane, and its extreme tenuity, that it might be said not to exist. To be convinced of its existence, expose the cylinder that it forms to the intense action of heat; it contracts, has the horny hardening immediately like all the solids, and thus becomes more apparent.

III. Properties.

The properties of texture are very well marked in the medullary organ. 1st. The spina ventosa in which this organ is distended in a very evident manner with the body of the bone, proves its extensibility. 2d. The contractility of texture is made apparent by the contraction of the cells, after the amputation of the middle part of a long bone, a contraction which prevents the flow of marrow, which without it would take place on account of the communication of these cells.

It is probable that the insensible organic contractility, which is then brought into action by the contact of the air upon this membrane which contracts from its irritation, has an influence also upon this phenomenon; for this membrane evidently has this kind of contractility, as well as the corresponding sensibility.

The animal sensibility is developed in it to an extreme degree in the natural state; the most acute pains are the result of the action of the saw upon it in amputation, of the introduction of a probe, of the injection of an irritating fluid into the medullary cavity, or of any other means which powerfully excite it. I do not speak of the pains of the bones in spina ventosa, syphilis, &c.; as the membrane is not then in a natural state, we cannot infer from them what kind of vital forces it is naturally endowed with. I have observed that the sensibility is greater, as we approach the centre of the bone with the probe when pushed into living animals. At the extremity of the medullary canal this sensibility is small; in the middle, the division of the bone is very painful. Whence arises this inequality of sensitive power, this decrease from the centre to the extremities? I know not. The medullary system evidently does not possess animal contractility and sensible organic contractility.