The vascular net-work which forms this medullary system, exists in the
cartilaginous state; but then, on the one hand, it does not admit the
red portion of the blood, and on the other, the interstices of its
meshes are found so filled with gelatine, that the cartilage appears
homogeneous. At the period of ossification, the red blood penetrates
on one side of these vessels, whilst on the other they become evident
from the absorption of gelatine at the place of these cells, upon the
internal surface of which they ramify.
In the fœtus and the first age, this medullary system has a remarkable
arrangement. It contains scarcely any of this oily fluid, from which it
borrows its name, and which afterwards fills in so great a proportion
the interstices of the texture of the cells of the different bones;
by examining these organs comparatively in the different ages, I
easily convinced myself of this. 1st. Exposed to a considerable degree
of heat, the texture of the cells of the bones of an adult has an
abundance of oily fluid flow from them. From the same experiment in the
fœtus, there only follows a drying of this texture by the evaporation
of the fluids which enter it. 2d. If we burn the extremity of a long
bone of an adult, the combustion is spontaneously supported by the
oily fluid that escapes from the pores of the second species, and
which keeps up the flame until it is exhausted. In the fœtus, the bone
ceases to burn when we take it from the fire, because the fluids it
contains do not support combustion. 3d. Nothing is more difficult than
to keep the bones of the adult white, because the oil that is in their
interstices always yellows them a little. In the fœtus and the infant,
in whom this cause does not exist, the bones are easily kept white.
4th. By ebullition, we extract scarcely any oil from the texture of
the cells in the first age; much swims on the water in which we have
boiled this texture in the following ages. In general, the, fœtus
appears to want this oil entirely; it is formed after its birth, and
its proportion is constantly increasing until complete growth. What
fluid supplies its place in the first years? At first a large quantity
of blood; for in general the redness of the medullary system is in the
inverse ratio of the oil that is found in it; but the interstices of
the cells appear moreover to be moistened by a fluid with which we are
unacquainted, and which evaporates, as I have said, when we expose to
the fire the bones of a fœtus.