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

by Xavier Bichat

There are but few systems in the economy in which the vital properties and those of texture are found in so great and evident a degree as in this. It is from the muscles that examples must be selected to give a precise and accurate idea of these properties. The physical properties on the contrary are slightly marked in them; a remarkable softness characterizes them; there is no elastic power in their texture; there is but very little resistance from this texture after death; it is from vitality that it derives the power that characterizes it in its functions.

I. Properties of Texture. Extensibility.

Extensibility is manifested in the animal muscular system under many circumstances. The different motions of our parts render this property evident. Such is in fact the arrangement of the muscular system, that one of its portions cannot contract, without the distension of another. The thigh being strongly bent, the semi-membranosus, the semi-tendinosus and the biceps are elongated. The arm being carried out, the great pectoral is extended, being raised, the great dorsal and the teres major are stretched. All the great flexions bring into action this property in the extensors; all the extensions render it evident in the flexors. A muscle which is stretched by its antagonist is in a state purely passive; it is as it were for a moment abandoned by its contractility, or rather it possesses it, without its being brought into action; it is made to obey the motion that is communicated to it. Observe that in these cases, the distension is confined to the fleshy portion, and the tendon has no connexion with it; it remains the same, whatever may be the distance, of the points of attachment, for these points are nearer or more remote in the different extensions to which the muscles are exposed; the longest muscles yield the easiest. The sartorius, the posterior muscles of the thigh, &c. exhibit this phenomenon in an evident manner; as their position is accommodated to it. In general all the muscles remarkable for their length are superficial, and go most commonly to two articulations, sometimes even to three or four, as in the limbs. Now the number of these articulations renders the space comprised between the two points of attachment susceptible of very great variations, which the great extensibility of these muscles allows. It may be understood from what has been said above, that it is to the length of the fleshy fibres and to the whole length of the muscle, that its degree of extensibility is to be referred. Those in which many aponeuroses are intermixed, and which derive in part from these membranes or from tendons their length, possess less of this property. Hence why, in the same motions, muscles of the same total length become more or less short, more or less elongated in their fleshy portion. Observe however that when on the one hand the tendinous portion predominates much, and on the other that it is very delicate, it yields a little, as we see in the small plantar and palmar muscles.

If from the natural state we pass to the morbid, we see the muscular extensibility manifested in a much more evident degree. In the face, the air accumulated in the mouth, swells it by elongating the buccinators; the various tumours of this cavity, as the fungous and sarcomatous ones, often distend the small facial muscles in a manner which would astonish us, if we considered the naturally small extent of these muscles which are trebled and even quadrupled. The muscles of the eye-lids and the eye in the large carcinomas of that organ, those of the anterior part of the neck in the great swellings of the thyroid gland, the great pectoral in large aneurisms or in other tumours of the axilla, the abdominal muscles in pregnancy, in dropsy, in the various tumours of the abdomen, &c. the broad and superficial muscles of the back from wens that are under them, present us these phenomena of distension in a remarkable manner. The muscles of the extremities are less subject to them, because on the one hand fewer causes develop tumours beneath them, and because on the other the aponeuroses do not yield so easily to these phenomena.

Contractility of Texture.

The contractility of texture is carried to the highest point in the muscles. These organs have a continual tendency to contraction, especially when by being elongated, they have surpassed their natural size. This tendency is independent of the action of the nerves, and of the irritable property of the muscular texture. It is influenced by life, but it is not entirely dependent on it; it depends essentially on the structure of the muscles. The remarkable phenomenon of the antagonist muscles results from it. The following is this phenomenon.

Each moveable point of the animal frame is always between two opposite muscular forces, between those of flexion and extension, of elevation and depression, of adduction and abduction, of rotation without and rotation within, &c. This opposition is a condition essential to the motions; for in order to perform one of them, it is necessary that the moveable point should be in the opposite motion; in order to bend, it is necessary that it should be first extended, and reciprocally. The two opposite positions which a moveable part takes, are for it alternately the point of departure and the point of arrival; the two extremes of these positions are the two limits between which it can move. Now between these limits there is a middle point; it is the point of rest of the moveable part; when it is found there, the muscles are in their natural state; when it passes it, some are extended, others are contracted, and such is their arrangement, that the contraction and extension which take place in an opposite direction, are exactly in direct ratio. Hence, in the reciprocal influence that the muscles exert upon each other, they are alternately active and passive, power and resistance, organs moved and organs which move. The effect of every muscle which contracts is not then only to act upon the bone in which it is inserted, but also upon the opposite muscle. Between two muscles thus opposed, there is often no solid intermediate organs, as in the lips, the linea alba, &c. The muscle of one side acts then directly upon that which corresponds to it, in order to distend it. Now this action of the muscles upon each other is precisely the phenomenon of the antagonists; two muscles are such when one cannot contract without elongating the other and vice versa. Let us examine in this phenomenon the part of the contractility of texture; it is necessary to distinguish its influence from that of the vital forces, which has not been heretofore sufficiently done.

A muscle once placed in the middle position, can only be removed from it by the influence of the vital forces, by the animal or sensible organic contractility, because in this position the contractility of texture of its antagonist is equal to its own, and there is consequently required a force added to this to overcome that which is opposed to it. But if the muscle is found in one of the two extreme positions, for example in adduction, abduction, flexion, extension, &c. then there will be an inequality of action in the antagonists, as it respects the contractility of texture; the one most stretched, will make in order to contract itself, an effort much greater than that which is already contracted. To maintain the equilibrium, it is necessary then that the vital forces continue to influence the contracted muscles. Thus every extreme position of the limbs and of any moveable part, cannot in an ordinary state be supported except by the influence of the vital forces. When these forces cease to be in action, immediately the contractility of texture of the elongated muscle, which had a tendency to exert itself, but was prevented, exerts itself, becomes efficacious, and draws back the moveable part to the middle position, a position in which the equilibrium is restored. Hence why in all the cases in which the cerebral influence has no power over the muscles, in which they are not irritated by stimulants, the limbs are uniformly found in a medium position between extension and flexion, abduction and adduction, &c. This is the case in sleep, in the fœtus, &c. I have shewn elsewhere how the osseous arrangement of each articulation is adapted to this phenomenon, how every kind of relation between the articular surfaces, except that of this medium position, exhibits a forced state in which some ligaments are necessarily more stretched than others, and in which the osseous surfaces are never in so general contact as in this position. In certain fevers which have so deleterious an influence upon the muscular life and texture, the horizontal prostration and extension of the extremities do not arise from an increase of the action of the extensors, but from the want of energy of the flexors, which have not power to overcome the weight of the limb; thus observe that every analogous attitude always coincides with the signs of general weakness; this is the attitude of putrid fevers, &c.

The section of a living muscle presents us with two phenomena which are evidently the product of the contractility of texture.

1st. The two ends retract in opposite directions; there exists between these divided ends a space proportional to the retraction. This retraction is not in proportion, as has been thought, to the degrees of the contractions of the muscle; if it was, it would be sufficient in a transverse wound, in order to bring the divided edges together, to place the limb in the greatest possible relaxation; now oftentimes, in these cases, these ends still remain at a distance; then the retraction is often superior to the greatest contraction of the muscle considered in its natural state.