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?