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?