In old age, the texture of the muscles changes remarkably; it becomes
resisting and stiff; the teeth tear it with difficulty. This too great
density is injurious to its contractions, which can now only take place
slowly; the action of the brain becomes less upon the muscles; the
continuance of their motions is not as long; they are sooner fatigued.
I would remark that the density of the muscles should not be confounded
with their cohesion. The first arises from substances that enter into
the composition of the muscle. Cohesion on the contrary appears to be
owing to vital influence, the effect of which is preserved after death.
Dissect the muscles of a strong and vigorous adult; the fleshy mass is
firm; it keeps in its place; it supports itself, though the scalpel
may have removed from it every surrounding texture. On the contrary
in a body dead of a chronic disease, in a dropsical or phthisical
subject, the muscles are loose and cannot support themselves; the
relations are destroyed when the surrounding texture is removed. The
first subjects are much more suitable for the dissection of myology
than the last. The muscular texture is in old subjects nearly as in
these last, flaccid and loose; we feel this flaccidity under the skin
in the solæus, the gemelli, the biceps, &c.; it does not prevent each
fibre from being dense and tough. In general the muscular cohesion is
in the inverse ratio of the age; the muscles of a young man are firm
and compact; they are not moveable under the skin. Towards the fortieth
year and afterwards, we begin to perceive more laxity; the calves of
the legs vacillate in great motions; the glutei and in general all
the prominent limbs exhibit also this vacillation, especially if the
individual is thin. The muscles become more and more susceptible of
moving thus, as we approach old age, a period in which the least motion
makes the whole muscular system vacillate. Why? Because the muscle is
no longer in sufficient contraction; it is as it were too long for the
space it fills. This appears to be owing to the circumstance that the
contractility of texture has diminished in the last age; we can be
convinced of this by cutting transversely for comparison a muscle in
an old man and a young one; it retracts more in fact in an opposite
direction in the second than in the first. This contractility of
texture approximates all the particles of the muscle when at rest; it
can no longer produce this approximation; the muscle remains loose.
Authors have not sufficiently observed this remarkable phenomenon which
the muscular system experiences from the progress of age, a phenomenon
which is really the index of its degree of contractile power.
Frequently in old age the muscular texture loses its colour and takes a
yellowish one and has a fatty appearance, though however this colour
does not arise from the fat, but from the absence of the colouring
substance of the blood. I have often made this remark. If we strip all
the surrounding fat from these pretended fatty muscles, and leave them
only their texture, combustion or ebullition extracts no animal oil
from them; they are in their fibrous state as usual; the colour only is
different. I have remarked that the deep muscles of the back and those
placed in the vertebral depressions are much more subject than all the
others to lose their colour and to exhibit this yellowish aspect, an
aspect that is rarely ever seen in the whole system, but only in some
insulated muscles. Adults are subject, though less frequently however,
than old people, to this alteration. Many times we see limbs that are
poorly nourished, with an aspect, nearly the same. In recent palsies,
in those even of three, four or six months, there is in general no
change in the limbs; the muscles preserve their colour and their size;
but at the end of a longer time, the absence of motion, perhaps also
the deficiency of nervous influx, terminate by altering the nutrition
left for a long time untouched without this influx, and then the
muscles change colour, contract and diminish. But this phenomenon is
not always constant, and there are at the Hôtel-Dieu hemiplegias of
six, seven and even ten years, without the limb of the sound side
predominating in its nutrition over that of the diseased one.
External pressures for a long time continued upon a muscle, produce
nearly the same effect as want of nourishment; they discolour and
whiten it by preventing the circulation in it. Those who make use of
straps constantly passed under the arms, who habitually have girdles
round the abdomen and who lift burdens, have often the muscles
corresponding to the constant pressure they experience, in the state
of those of old people. I would remark that these muscles contract
notwithstanding; which proves that the colouring substance is not of
absolute necessity to muscular action.
The blood is carried in general in much less quantity in the muscles of
old people; their vessels are in part obstructed; this is what disposes
them to the state of which I have just spoken.