Elasticity is a property generally extended to all organic and
inorganic bodies. Among the first, it appears, that vegetables are
endowed with it in the greater number of their organs; that animals,
almost all of whose parts are soft, have some which return to their
original state after having been stretched or compressed. Among these,
the cartilages hold one of the first ranks in man. Their elasticity
is very great, especially in the adult age, when their consistence
is between the softness, which characterizes them in childhood, and
the hardness, which is their attendant in old age. These two last
properties are in fact not favourable to the elastic power.
If we plunge a scalpel into a cartilage, the edges of the divided place
re-act upon it and expel it. Pressed against a resisting body, the
cartilaginous extremity of a long bone becomes flat and resumes its
form when the compression ceases. The edges of the thyroid cartilage,
when it is cut longitudinally in the operation of bronchotomy,
immediately approximate each other. The division of the cricoid ring
exhibits the same phenomenon. The cartilages of the last ribs, when
forced in towards the abdomen, come out of themselves, &c. &c. All
these phenomena are the evident result of an elastic power. Thus nature
has placed the cartilages wherever, to produce her phenomena, there
is a necessity of uniting a physical to the vital forces, as in the
larynx, in the nasal septum, in order to produce a sort of vibration
in the passage of the air, at the extremity of the ribs, in order to
be the seat of a species of twisting necessary to the mechanical part
of respiration, at the articular extremities, in order to diminish the
force of blows, &c.
It appears that the vital activity renders this property greater,
which however remains very apparent after death. I presume that this
is owing to the great quantity of gelatine they contain. 1st. We know
that this substance possesses it in a very high degree, as is proved
by the tremulous motion of jelly after it has become cold, by the
examination of various animal glues, &c. 2d. If by ebullition we remove
this substance from the cartilages, the nutritive parenchyma remains
flaccid and soft. 3d. As the gelatine diminishes in our organs, the
elasticity in them is less, as we see by examining the decrease of
this property from the cartilages in which it predominates, to the
fibro-cartilaginous organs in which it is in a smaller proportion, and
to the fibrous bodies in which it is still less. It must be confessed
however that many very gelatinous bodies, exhibit but very slight
traces of elasticity; the skin is an example of this, and so are the
tendons. Can the same substance, as it is differently operated upon by
the organic laws, become the seat of properties wholly dissimilar?