General Anatomy, Applied to Physiology and Medicine, Vol. 2 (of 3)

by Xavier Bichat

The period when the hairs grow, when the genital organs begin to become active, is principally that in which the muscles begin to become prominent in man. In woman, this last period does not present a similar phenomenon; the muscles preserve the original roundness, they scarcely ever lose it. In this sex, the roundness of the limbs, their agreeable forms, make a contrast with the kind of rudeness of those of man.

The increase in thickness in the muscles appears to be much more in the fleshy than the tendinous portion, and especially than the aponeurotic. The intermuscular aponeuroses principally do not appear to grow in proportion to the fibres that are inserted into them; so that these make a prominence, and at the place of the aponeurosis there is a depression. This is what we see very well in muscles cut for their insertions by many of these fibrous expansions, in the deltoid in particular. Not only the prominence through the skin of the whole of the muscle, makes the depressions evident that separate it from the others, but each fleshy bundle has a prominence which a groove separates; this, it is true, is only distinguishable upon thin subjects.

As the muscle grows in thickness, it increases in density. It becomes firmer and more resisting. If we place for comparison the hand upon two similar muscles of an adult and an infant, whilst they are in contraction, we feel a sensible difference in their hardness. Weights suspended for comparison to the muscles of the two ages, taken in the dead bodies, prove the different degree of their resistance. The muscular texture of adults yields more slowly to all re-agents.

The colour of the muscles continues to be red in the adult; but in general, and all things being equal in respect to the causes that make this colour vary, it begins to become of a less bright red after the thirtieth year. It is usually in the last years of growth, and even from the tenth to the twentieth, that the colour is the most brilliant.

In the adult this colour exhibits a very remarkable phenomenon. All men have their muscles red, but hardly two have the same shade. Those who have opened many dead bodies are easily convinced of this; a residence at the dissecting rooms proves this assertion. A thousand causes have an influence upon this colour; the temperament is the principal. The external appearance of the muscles without the skin indicates by their shades of colour the temperament, as well as the integuments do. Diseases make this colour vary wonderfully. All those that have a chronic progress alter it remarkably; it then becomes pale, dull, &c. Dropsies whiten it, when they are of long standing. In general, every thing that has upon the powers of life a slow and debilitating influence, diminishes the brightness of it. Acute diseases, whatever may be their nature, change it but little. Fevers with the greatest prostration, if they suddenly produce death, leave it untouched, because this colour can only change by nutrition; now as this function is slow in its phenomena, it is but little affected by acute diseases; it is only at the end of some time that it feels the affections reigning in the economy.

I would observe that the varieties of colour that are seen in the muscles of adults, even in the healthy state, distinguish them especially from those of the fœtus, which have in general an uniform paleness. This difference is owing to the fact, that in the first age, we are not subject to the action of the numerous agents which modify, in an infinitely variable manner in the after ages, the great functions, and of course nutrition which is the end of them. It is in these varieties of colour of the muscular system of the adult, that we clearly distinguish that the blood circulating in the arteries is wholly foreign to it; in fact it is uniform, and never partakes of those varieties of colour whatever they may be.

Many circumstances in the adult make the muscular nutrition vary; motion is the principal. The man who passes his life at rest is remarkable for the small prominence of his muscles, especially if we compare this prominence with that of the muscles of a man who takes great exercise. Not only general motion exhibits this phenomenon, but also local motion, as we see in the arms of bakers, the legs of dancers, the backs of porters, &c.

IV. State of the Muscular System in Old Age.

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.