At birth, the muscular system of animal life experiences, like all the
others, a remarkable revolution. Until then black blood only penetrated
its arteries; then the red blood immediately enters them; for this
blood is formed when respiration takes place; now this takes place in
almost all its perfection at the very instant the fœtus leaves the womb
of the mother. We evidently see besides that the livid tinge of the
skin gives place almost immediately to a red colour, which arises from
this difference of the blood. This new fluid entering the muscles, is a
new cause of excitement, and consequently of motion. Add to this cause
the sudden increase of cerebral action. Till then, the brain penetrated
with black blood, was as in a kind of inertia, which was principally
owing also to the absence of sensations, as I have elsewhere proved.
Suddenly the red blood enters it; it stimulates it either by the
principles that it contains, or because it was different from that
which had penetrated it; for such is the nature of sensibility that it
is capable of being affected in an organ, merely because the stimulus
that is applied to it is new. Suddenly excited by the red blood, the
brain re-acts upon the muscles, and determines them to contract. This
cause, joined to the preceding, appears to me to be one of those which
have the most influence on the sudden disappearance of the kind of
inertia in which the fœtus was, or at least of the small degree of
motion that it performed, by the general agitation of its limbs, its
abdomen, chest, face, &c.; for immediately after birth all the muscles
are moved more or less strongly.
Let us not, however, exaggerate the influence of a cause which is
certainly not the only one; for example, the motions of the diaphragm
and the pectoral muscles, are certainly prior to the entrance of
the red blood in the brain, since their action is necessary to the
production of this red blood. These muscles enter into action, because
the excitement of the air on the whole exterior of the body, and on
the mucous membranes in contact with this fluid, stimulates the brain
which is the centre of all sensation. Moved by this excitement, this
organ re-acts upon the muscles, and begins to make them contract. The
contractions increase, when to this external and indirect excitement is
added the internal and direct excitement of which we have just spoken.
This second excitement is not absolutely necessary for the fœtus, for
we often see infants that remain livid some instants after birth, move
very well; but in general the motions are not so decided as when the
red colour of the skin indicates the entrance of the arterial blood,
which has undergone the influence of respiration.
The entrance of the red blood into the muscles does not give them
immediately the colour they will afterwards have. For some time after
birth, they have a deep tinge, as dissections clearly prove, because,
as I have said, their colour does not come from the colouring portion
circulating in their texture, but from that combined with this texture.
Now nutrition alone produces the combination; but this function takes
place gradually; it is truly a chronic function, in comparison with
exhalation, absorption, and the circulation, which are evidently rapid
in their progress.
As we advance in age, the muscles assume a redder tinge; more blood
penetrates them; they are nourished in proportion more than various
other organs. This is particularly remarkable in those of the lower
extremities. I would remark, however, that as long as growth continues,
it is especially upon the length and not upon the thickness of the
muscles, that the energy of nutrition is carried. Hence why they are
but slightly visible through the integuments and are scarcely at all
prominent; why their forms are rounder and more graceful, but less
masculine at this age. The exterior of a young man is in this respect
wholly different from that of the adult, by considering each, separate
from every cause that can have an influence upon their conformation.
The external appearance of the infant and the young man is in general
very analogous to that of woman.
Though we do not know so well the difference of the substances which
penetrate the muscles in the first years and in the adult age, as we
know it in the bones in which the addition of the phosphate of lime
to gelatine exhibits a very striking phenomenon, yet we cannot doubt
that these differences really exist. Treated by ebullition, combustion,
maceration, &c. the flesh of the fœtus does not give the same results
as that of the adult.
The broth made with the muscles of a young animal contains much more
gelatine, a substance which greatly predominates at this period of
life. It has less flavour than that of adult animals. The extractive
substance consequently appears to be less. A mawkish, nauseous taste
characterizes broths made of veal. The difference of the principles
they contain has an influence even upon the gastric organs, of which
they excite the contraction; they loosen the belly, as it is called, a
phenomenon unknown to common broths. It does not appear that the fibrin
is in as great a proportion in the muscles at this period of life; the
following considerations make me think so.
1st. Instead of this substance, Fourcroy has found in the blood of the
fœtus a soft texture, without consistence, and like gelatine; now the
blood appears to be the reservoir of fibrin. 2d. The force and energy
of the contractions are in general in proportion to the quantity of
this principle contained in the muscles; now this energy is small in
the first age. 3d. The muscles burn then, and crisp and contract less
than in the adult. I have even two or three times seen their texture,
when placed upon live coals, become puffed up like gelatine treated in
the same way.
In general it appears that this last substance occupies in the muscles
the place the fibrous system is afterwards to hold in them. Those who
frequent dissecting rooms, have observed, no doubt, that other things
being equal, the muscles of young subjects putrify less quickly than
most other substances, and that when they do, they give out a less
fetid odour. We know that broth made of veal turns sour more easily
than that made of beef. It is always whitish, and never has the deep
colour of the broth made with this last. It becomes like jelly much
more easily. Young and old roast meats exhibit also great differences.
Every kind of stewing either by the fire alone, or in any fluid, is
much quicker and easier in the first age. The gravy that is then
extracted from the muscles has a character wholly different, it is less
strong. The effects of maceration are also more rapid; we obtain sooner
that mucous pulp, to which the action of water finally reduces almost
all animal substances.