Part 31

In the cerebral excitement and in that of the spinal marrow, we cannot so well appreciate the force of the contractions which result from it, as when we stimulate an insulated nerve; in fact, all the system entering then into convulsive action, the extensors destroy in part the effort of the flexors and vice versa. The muscles simultaneously in action, counterbalance, interfere with and injure each other. The stimulant which gives the greatest force to the contractions, has always appeared to me to be galvanism.

In the living state, the force of muscular contraction depends on two causes; 1st, on the muscle; 2d, on the brain. These two causes are in a variable proportion; it is necessary to consider them separately.

Under an equal cerebral influence, a muscle well nourished, which appears distinctly through the integuments, and has very large fibres, will contract much more strongly than that which is delicate, slender, with loose, pale, small fibres, and which makes but a slight prominence under the integuments. In our ordinary manner of considering muscular force, it is to this state of the muscles that we especially attend. The statues which exhibit strength and vigour, have always as an attribute a powerful development of the muscular forms. When the brain acts upon these muscles with energy they are capable of extraordinary motions. I shall not relate examples of the astonishing efforts of which they are susceptible. Haller and others have cited many of them, either in the muscles of the back in carrying burdens, or in the muscles of the superior extremities in raising great weights, or in the inferior extremities in leaping or in order to preserve attitudes which suppose enormous resistances to be overcome.

It is especially the cerebral influence that increases much the force of muscular contraction. The will can raise this force very high; but the different excitements that are foreign to it, raise it infinitely more. We know the force that a man acquires in anger, that of maniacs, of persons in the cerebral excitement of a fever, &c. In all these cases the impulse communicated by the brain, is sometimes such, that the most delicate muscles of the feeblest woman surpass in energy those of the strongest man in the ordinary state.

The force of muscular contraction is then in a ratio compounded of the force of the organization of the texture of the muscles, and of the force of the cerebral excitement. If both are slight, the motions are almost nothing; if both are at the highest degree, it is difficult to conceive how far the effects may go which result from them; a maniac with thick and strong muscles is capable of efforts that we should in vain attempt to calculate. If the nervous force is very powerful, and the muscular texture feeble, or if an inverse state exists, the phenomena of contraction are less. In general nature has almost always united these two things in this last manner. Women and children who have a weak fleshy texture, have a very great nervous mobility; men on the contrary, those especially with athletic forms, whose nervous systems are less easily excited, receive more rarely the causes of a strong influence upon their muscles.

Whatever may be the point of view in which we consider the force of the contractions of the muscular system of animal life, it is always very great in proportion to the effect which results from these contractions. Nature in the economy follows a law the reverse of that of the motion of our common machines, the great advantage of which is to increase the moving powers, to produce a great effect with a small force. Here there is always a great expenditure of force for a small effect, which is owing to the numerous causes that tend to destroy the effect of this force. 1st. The muscles act almost always upon a very unfavourable lever, upon that in which the power they represent is nearer the point of support than the resistance. 2d. All in contracting have to overcome the resistance of the antagonists. 3d. As in each motion there is always a fixed point, the effort which, after contraction, is carried upon this fixed point, is entirely lost. 4th. Various frictions injure also the motion. 5th. The obliquity of the insertion of the muscles upon the bones, an obliquity that approaches nearer a horizontal than a perpendicular direction, an obliquity not less remarkable for the fleshy attachments upon the tendon or aponeuroses, offers a double cause of weakness. All these and many other reasons which we might with Borelli, who was the first to make these important remarks upon muscular motion, add to them, prove that the absolute or real force of the muscles is infinitely superior to their effective force. Yet all are not so unfavourably arranged; in some, as the solæus, the insertion is perpendicular to the bone; in others, as the muscles which act upon the head, we observe that they are powers of a lever of the first kind. In general, in order to estimate the force of a separate muscle, the deltoid, for example, it is necessary especially to have regard to the distance of its insertion at the point of support, to the degree of opening of the angles formed by the fleshy fibres upon the tendon, and afterwards by the tendon upon the bone, and to the division of the forces between the fixed and moveable points.

Some advantages seem to compensate in a slight degree in certain muscles for their bad arrangement as to the power of motion; such are, 1st, the sesamoids, the patella, the different eminences of insertion, the enlargement of the large bones at their extremities, &c. which remove the fibres to a distance from the moveable points; 2d, the intermuscular fat, that which is in the neighbourhood of the muscles, the fluid of synovial sheaths, which facilitate motions by lubricating the surfaces that execute them; 3d, the aponeurotic expansions that confine down the motions on the extremities; 4th, these motions themselves, those of flexion for example, which, as they take place, diminish the obliquity of the insertion of the flexors, and render it even perpendicular, as has been well observed by a modern author.

Many calculations have been made upon the waste of muscular motion, upon the effort of a muscle which contracts, compared with the effect that results from it. They can never be precise because the vital forces vary to an infinite degree, because they are not the same in two individuals and because the cerebral influence and the force of muscular organization are never in constant proportion in the same subject. It is a peculiarity of the vital phenomena to escape all calculations, and to exhibit, like the forces from which they emanate, a character of irregularity which distinguishes them essentially from the physical phenomena. Let us conclude only from the preceding observations, that the muscular effort carried to the highest point by cerebral excitement, can produce astonishing effects, which suppose a force of contraction hardly conceivable; such is the rupture of the strong tendons, of the patella, the olecranon, &c.; such is also the resistance often opposed to the enormous distensions that are used in luxations, fractures, &c.

II. _Quickness of the Contractions._

The contractions should be considered under the relation of their quickness as under that of their force.

1st. If it is by stimulants that they are produced, by laying bare a muscle and acting directly upon it, they vary according to the state of vitality of the muscle, and according to the body which stimulates. In the first moments of the experiment, they succeed with rapidity and are sometimes connected together with such quickness that the eye can hardly follow them. As the muscle becomes weak, its contractions become less prompt; and they cease at the end of some time. We can reanimate them by employing a very active stimulant; the fibres finally become insensible to this also.

2d. If it is by irritating the nerve that we make a voluntary muscle contract, we produce a still greater quickness of contraction than by stimulating the muscle itself. Running would be almost immeasurably rapid, if each contraction that it requires was equal to those that we thus obtain, especially when we act on the one hand on very sensitive animals, and on the other with very active stimulants, galvanism for example. Upon this subject I have made a remark, it is that the quickness and the force of the contractions are not commonly greater if we irritate at the same time all the nerves that go to a muscle, than if we irritate but one.

3d. When it is the will that regulates the quickness of the muscular contractions, this quickness has infinitely various degrees; but there is always one beyond which we cannot go. This degree is not the same for all men; there is even among them in this respect very great differences, which are foreign to the force of organization of the muscles; it is rare even that individuals with a very powerful muscular system are the best runners. I do not know that we have yet observed the exterior habit of the body which indicates the quickness of the contractions, as there is one which denotes their force; it must however exist. Animals are like men; the degree of quickness which each can attain, is infinitely variable. I shall not cite examples of rapid races, of analogous motions given by the superior extremities, as those of the fingers in performing on certain instruments, the violin, the flute, &c.; astonishing ones may be read of in many authors. I would only remark, that there are but few motions which give us a greater idea of this quickness, than the sudden and rapid contractions which, in the inferior extremities, produce a leap, or that powerful action of these extremities when we give a kick with the foot; which in the superior serve for the projection of heavy bodies; which in the same limbs assist to push the trunk back, when we support them against a resisting point, and afterwards suddenly stretch them to push this point forward, which not yielding, the motion rebounds upon the trunk; which preside over the action of giving a blow of the hand; which in the fingers produce the sudden motion, from which results what is called a fillip, &c. &c. I confound all these motions almost entirely analogous to leaping, and which differ from it only in the more or less evident effects that they produce. Authors, it may be observed, have not sufficiently established the resemblances between these various sudden and rapid contractions; they have considered leaping in too insulated a manner. But let us return. The degree of rapidity of muscular contractions is greatly subordinate to exercise. The habit of making certain muscles act renders them more quick in their contraction; for example, walking which accustoms us to contract alternately the extensors and the flexors of the lower extremities, fits us wonderfully for swiftness in running. When any man practises for a little time this last exercise, he soon attains the greatest rapidity of which his muscular system is capable. On the contrary, the motions of adduction and abduction being more rare in the ordinary state, it requires a longer apprenticeship for dancers to learn to carry their legs rapidly in and out, for the purpose of executing steps in which they cross them alternately. In general, habit modifies much more the quickness than the force of the contractions. Yet there is always a limit which can never be passed, whatever may be the exercise that we give to the muscles; this limit depends on the constitution; each man is by it, a more or less active leaper and runner.

III. _Duration of the Contractions._

There is as it respects the duration of the contractions a remarkable difference in the muscles, according as we excite these contractions artificially or naturally.

When upon a living animal or one recently killed, we excite the muscle itself, or we stimulate its nerves, the relaxation succeeds almost suddenly the contraction; neither state is ever lasting, though we continue for a long time the action of the stimulant; the effect which it has produced is immediately exhausted. When galvanism, mechanical or chemical agents are used in our experiments, the phenomenon is the same.

On the contrary, when the will directs the contraction, it can sustain it for a very long time. The support of burthens, standing, &c. clearly prove this fact. When even during life, a morbid irritation is directed upon the nerves, the contraction can be very permanent, of which we have terrible proofs in tetanus.

The permanence of the muscular contraction fatigues the muscle much more than alternate relaxation and contraction. Hence why when we are standing long, we contrive by turns to carry the weight of the body more upon one limb than the other.

IV. _State of the Muscle in Contraction._

Muscles that contract exhibit different phenomena as follows:

1st. They evidently harden, as we may be convinced by placing the hand on the masseter, the temporal or any other superficial muscle in contraction.

2d. They increase in thickness; hence the greater prominence of all the sub-cutaneous muscles when the body is in violent action. Sculptors know this difference very well. A man at rest and a man in motion, have in their statues an exterior wholly different.

3d. The muscles when they are not confined by the aponeuroses, sometimes experience a slight displacement.

4th. They diminish in length, and thus the two points to which they are fixed approximate.

5th. Their volume remains about the same. What they lose in length, they nearly gain in thickness. Is the proportion very exact? Of what consequence to us is this insulated question, to which, since the days of Glisson, so much importance has have attached! it deserves none.

6th. The blood contained in the vessels of the muscles, especially in the veins, is in part pressed out; we increase the flow of the blood by the motions of the arm, the operation of bleeding proves both these facts.

7th. Yet the muscle does not change colour; it is because it is not the colouring portion of the blood circulating with it in the muscular vessels that colours the muscles, but, as I have said, that which is inherent in their texture and combined with their fibres; now this combined colouring substance remains the same in relaxation and contraction. The heart of the frog is pale when it contracts; but it is because the blood it contains is evacuated and the transparency of its parietes renders this phenomenon evident.

8th. In contracting, the muscles become the seat of many small transverse wrinkles, sensible especially in the contractions of oscillation, less apparent in those of the whole of the muscle, and almost nothing, when a muscle being laid bare in a living animal, contracts with a small degree of force.

9th. All authors consider contraction in too uniform a manner; they have described the phenomena of it, as if in every case the muscle contracted alike; but it is evident that there are numerous differences in the state in which it then is. 1st. There is the slow and insensible contraction produced by the contractility of texture, when we cut a muscle or when its antagonist is paralyzed. 2d. The quick and sudden contraction produced by the will, or by the excitement of a nerve, a mode of motion that takes place most commonly either in the ordinary state, or in convulsions. 3d. The species of oscillation of which I have already spoken, and which affecting each fibre in a muscle, does not yet produce any very sensible effect upon the whole, contracts it a little, but scarcely approximates at all its moveable points; this is the kind of motion which takes place in the tremors produced by cold, by fear, by the beginning of a fit of intermittent fever, &c. By laying bare a muscle in an animal that is made to shiver, we see that this kind of contraction resembles precisely that which is produced by pouring salt in powder upon a part of the muscular system. Then, although there may be in all the muscles, an internal motion infinitely more sensible than in the great contractions, yet the limbs are displaced but little, there are hardly any motions of the whole muscles, they are but slight jars. 4th. There are other modes of contraction less sensible than these, but which however exhibit differences. In general, to each species of motion of the muscle is adapted a particular manner of contracting; if we make but few experiments on living animals, we may easily be convinced how much the most judicious authors have been mistaken upon this point.

Two modes of contraction are often combined; for example, when we cut a muscle transversely in a living animal, there is at first a slow contraction of the whole, produced by the contractility of texture, then partial oscillations in all the divided fibres; now these oscillations are foreign to the retraction which takes place without them, often in the living animal and always in the dead body. So the oscillations can be combined with the sudden contraction arising from the nervous influence by the act of the will, or they may be disconnected with it, as happens almost always when the animal is in full life. We may be convinced of this last fact without recourse to experiments, by placing the hand upon the masseter muscle or the biceps of a thin person when they are contracting; we do not feel in them through the skin any motion analogous to these oscillations.

V. _Motions imparted by the Muscle._

Every muscular motion is either simple or compound. Let us now speak of the first; by it we shall understand the second.

_Simple Motion._

It must be considered, 1st, in the muscles with a straight direction; 2d, in those in a reflected one; 3d, in those in a circular one.

In the first, as in those of the extremities, the trunk, &c. if they are of an elongated form, and as they terminate by a tendon, each fibre contracting draws this tendon from its place; whence it follows that all act together to bring it towards the centre of the muscle, but at the same time each of them tends to give it another direction, and in this respect they are antagonists. The common motion remains; the opposite is destroyed.

Every effort of contraction in the long muscles is concentrated upon a single point, the tendon. In most of the broad muscles, on the contrary, the attachments being made at two sides by different points, all the fibres do not contribute to the same end. Thus the different parts of the same muscle can have very different and even opposite uses; thus the inferior portion of the great serratus does not act like the superior; often even the different portions of the same muscle do not contract at the same time. In a long muscle, on the contrary, as all the fibres contribute to produce the same effect, they always act simultaneously.

To estimate the effect which a muscle in the straight direction produces upon the bones in which it is inserted, different means are employed. A very simple one appears to be that, which I believe has never been mentioned. It consists in examining the direction of the muscle from its fixed to its moveable point, and in taking the inverse of this direction; this last is always the direction of the motion. Do you wish to know how the anterior radial acts upon the wrist; take it at its insertion at the condyle, then follow its direction downwards and outwards; you will see that it carries the hand upwards and inwards, that it bends it and places it a little in adduction. The tibialis anticus directed downwards and inwards raises the foot and carries it outwards. The anterior rectus of the thigh going straight from the pelvis to the patella, raises the leg directly up. All the other muscles will exhibit this arrangement. Whatever may be the attachment of their fixed or moveable point, they always act inversely to the supposed line of direction going from the first point; and as each attachment can be alternately moveable or fixed, the two bones which serve them are carried in an opposite direction; the coraco-brachialis directed downwards and outwards from the shoulder towards the arm, carries this last upwards and inwards; directed from below upwards and from without inwards from the arm towards the shoulder, it moves this downwards and outwards. By this general rule, it is sufficient to see a muscle in a dead body, to pronounce upon its uses.

When the whole of a broad muscle is united at a common point, as the deltoid which having many points of attachment above, is fixed below in a single tendon, the middle line of direction of all its fibres should be taken to estimate its uses.

When a muscle is attached by its two extremities at many points, and consequently the fibres that compose it, form many fasciculi with different directions and insulated motions, the line of direction of each fasciculus must be examined in order to estimate the action of the muscle. It is thus that we should study that of the trapezius, the great serratus, the rhomboid, &c.

In the muscles with reflected direction, as the great oblique of the eye, the lateral peronei, the circumflexus, &c. the action of the muscle should only be estimated by the point of reflection; thus the great oblique carries the eye inwards, though its fleshy portion contracts so as to carry the moveable point backwards.

The orbicular muscles, those placed around the lips, the eyes, the anus, &c. have in general no fixed or moveable points; they are not designed to approximate two parts to each other, but only to contract the opening around which they are situated. The anus is shut by its sphincter, when the excrements do not dilate it. The mouth remains closed, when the depressors, the elevators or the abductors of the lips are inactive. The eye is shut, when the elevator of the superior eye-lid is relaxed. I would remark upon this subject that the inferior eye-lid having no depressor, it is principally the other which contributes to shut or open the eye; and as its muscle cannot be in permanent contraction, the alterations of its relaxations produce those continual winkings which take place when the eye is open; they are to the eye what the alternate change of the weight of the body from one leg to the other is in long standing without motion. At every instant the muscle relaxes; the sphincter acts immediately; then it contracts and distends the sphincter; winking then is a continual struggle between the elevator of the eye-lid and the orbicularis. In sleep, it is not by the contraction of this that the eye is shut; it is relaxed like all the muscles; it is because the elevator is inactive, that the eye-lid falls by its own weight upon the eye; it communicates as it were the motion to the orbicularis that it shuts up, whilst, during the day, it is the orbicularis on the contrary that communicates this motion to it.

_Compound Motions._

There are but few motions in the economy that are simple, but few muscles that can contract separately. Almost every sort of contraction supposes another, and for this reason; the two points to which a muscle is ordinarily attached are both capable of being moved; if one of them was not fixed, both would then be put in motion when the muscle contracted; thus in the contraction of its extensors, the leg if it was not fixed would approach the foot as much as the foot approached the leg; now it could not be fixed but by the muscles which act in an opposite direction to the effect which the extensors tend to produce upon it; then whenever the two attachments of a muscle are moveable, the insulated motion of one of them supposes the contraction of different muscles to fix the other.