As we advance in age, the cartilages become harder, stronger, and less
elastic. The gelatine that nourishes them has a peculiar character;
for we know that the glue made from young animals differs essentially
from that made from old ones. The cooks know very well the difference
there is between the foot of a calf and that of an ox for jelly. This
difference in the substance which essentially composes the cartilages,
and which is undoubtedly their nutritive matter, evidently indicates
that it does not always remain in these organs, but that it is
constantly exhaled and absorbed there, as the phosphate of lime is in
the bones, the fibrin in the muscles, &c.
In the last years of life, ossification seizes upon all the cartilages;
but it begins in an opposite manner in those of the cavities and in
those of the articulations. In the first it is by the centre, in the
second it is by their surface which corresponds to the bone, that it
commences; in general it is much slower in the latter, and among these,
it is slower in the moveable articulations than in the immoveable.
The cartilages of the larynx and the ribs are osseous in their centre
at the age of thirty-six or forty years, and even before; they
afterwards become more and more so; it is this that renders the section
of the thyroid cartilage very difficult in the last periods of life.
In the great number of operations that I have shown to students,
I have satisfied myself, that after sixty years, the bistoury of
ordinary temper is almost always insufficient to make this section;
it requires something much stronger. It is the ossification of the
costal cartilages, which renders old people unable to make those great
efforts of inspiration so common to young ones; with them the diaphragm
especially acts. I attribute also to this early ossification of the
cartilages of the cavities, an ossification which always accompanies
the development of the vascular system, the greater frequency of caries
in this sort of cartilages than in all the others. I know not why
in the larynx the arytenoid cartilages are the most exposed to this
affection; but in the opening of dead bodies, it is a constant fact,
all the cases of laryngeal phthisis with caries, that I have observed
in the dead body, have shown me this.