Chapter XIV: Part 14

It is to the susceptibility of the brain and nerves of still transmitting the principle of motion after death, that must be referred all the phenomena that are witnessed in the different kinds of decapitation. Ducks, geese and other animals of this family move their muscles with some regularity, after the head is taken off, in running, jumping, &c. Some time after the punishment of the guillotine, the inferior and superior extremities are still the seat of various tremors; the muscles of the face are sometimes even contracted so as to give to this part the expression of certain passions, an expression incorrectly referred to the sensitive principle still left for some time in the brain. The same phenomena were formerly observed in the punishment that consisted in cutting off the head with an axe. During the year past I have had a painful proof of these singular facts; a guinea-pig, whose heart I had just removed, plunged deep into my finger the four prominent teeth that distinguish this species. All these phenomena are only the result of the irritation produced, either by the cutting instrument, or by the air, upon the two divided extremities of the marrow; this is so true, that by increasing the irritation by a pricking, cutting instrument, &c. with a chemical agent applied to these extremities, the motions are very much increased. Nothing is more easy than to be convinced of this fact in an animal; I have many times proved it in those who have been guillotined, upon whom I have been allowed to make experiments for galvanic purposes. See how the alternate motions of respiration can continue for some time, after the brain has been destroyed, after a wound of the head in which its mass has been crushed, after a luxation of the first vertebra, in which the beginning of the spinal marrow has been compressed so as suddenly to stop life, after the injection of a very irritating fluid by the carotid, &c. &c.

In this duration of animal contractility after death, the muscles are absolutely passive; they obey, as during life, the impulse they receive from the nerves; it is this which distinguishes it essentially from the duration of irritability, a property by which, after death as during life, the muscle has in it the principle which makes it move.

The duration is greater or less according to the class of the animals; those with red and cold blood keep this property longer than those with red and warm blood; among these, the family of ducks are, as I have said, remarkable for this phenomenon, which is much more rapidly lost in the others and in quadrupeds. In the first class there are also varieties among the reptiles, fishes, &c.

In general I have constantly observed that the animal contractility ceases after death, first in the brain, then in the spinal marrow and last in the nerves. When the muscles no longer move by irritating the first of these organs, they contract by stimulating the others. The irritated nerves can still communicate a motion, when the spinal marrow, no longer exhibits this phenomenon. I have not observed that the superior part of the nerve ceased sooner to transmit motion, than the inferior. But what is remarkable is that certain nerves, under the influence of the same irritation, make their muscles contract more strongly than others; such for example is the phrenic. When all the other muscles cease to be moveable by the artificial excitement of their nerves, the diaphragm is still moved by this means. Whilst experiments have but little effect elsewhere, they are in full force upon this muscle; this is the more remarkable, as during life this is precisely the one which is the least affected by the state of the brain and the spinal marrow; paralysis and convulsions hardly ever affect it, as we have seen.

Besides, in thus comparing the duration of animal contractility, the same stimulant should always be employed; for the effects are more or less evident according to those which we use. When the whole brain and the nerves are no longer sensible to mechanical or chemical agents, they still powerfully obey galvanic impulses. The irritation of the metals is of all the means at present known, the most efficacious in perpetuating animal contractility some time after death.

_Organic Properties._

Organic sensibility is the manifest portion of the muscles of which we are treating; constantly brought into action in them by nutrition, absorption and exhalation, it becomes still more apparent, when we irritate muscles that are laid bare; they feel this irritation, and the motion, of which we shall speak hereafter, is the result of this feeling which is centred in the muscle, and which is not referable to the brain.

Insensible organic contractility is the attribute of this muscular system, as of all the others.

The sensible organic contractility is very evident in it. If we lay bare a muscle in a living animal, and irritate it with any agent, it curls up, contracts and is agitated. A detached muscular portion exhibits for some instants the same phenomenon.

Every thing is irritating to the naked muscle, the air, water, neutral salts, the acids, the alkalis, the earths, metals, animal and vegetable substances, &c. The mere contact is sufficient to produce contraction. Yet besides this contact, there is something also which depends upon the nature of the stimuli, and which makes the intensity of the contractions vary. A powder of wood, coal, metal, &c. sprinkled upon the muscles of a frog, produce but slight motions in it; pour on it a neutral salt in powder, the marine salt for example, immediately irregular agitations, and a thousand different oscillations are manifested. Each body is by its nature capable of irritating the muscles differently, as according to individuals, ages, temperaments, seasons, climates, &c. the muscles are capable of answering differently to excitements made upon them.

It is not necessary to irritate the whole of a muscle to produce its contraction; two or three fibres only being pricked bring into action all the others. Often even when we make these experiments on a living animal, the contraction is communicated from one muscle to another. In general I have constantly observed that during life these experiments are less easy, and give results much more various, as we have already stated with regard to animal contractility. Lay bare a muscle, irritate it at many different times; sometimes it does not give the least sign of contractility; sometimes it moves with force; this varies from one instant to another. Whereas if it is upon an animal recently killed that the experiments are made, the results are always nearly the same in a given time, with the difference however of the weakness which the contractions have in proportion to the length of time after death. It never happens that you see a muscle immoveable under stimuli, which is not rare in a living animal. This essential difference which authors have not sufficiently pointed out, and which I have frequently proved upon different animals, arises from this, that during life, the effects of the nervous influence counteract those of the stimuli; for example, if an animal extends with force his thigh by the posterior muscles, we may in vain irritate the anterior ones, we cannot produce flexion by this irritation. The cerebral excitement in the extensors being stronger than the mechanical excitement in the flexors, triumphs. Often when we apply the stimulant, the brain acts with force upon the muscle, the effect is then much superior to the excitement we have applied. We are astonished; but the astonishment ceases, if we recollect that there is a concurrence of two excitements, of that of the external agent and of that of the brain. In general, those who have made experiments, have not paid sufficient attention to this concurrence of the two forces in a living animal.

In order to estimate correctly the sensible organic contractility, it is necessary to destroy the animal contractility. So long as these two clash, interrupt and counterbalance each other, we cannot properly estimate them, and determine what belongs to each and what is common to both. Now we destroy animal contractility in the living subject, by cutting all the nerves of a muscle or an extremity, which then become paralyzed. The brain can no longer act upon them, and the results we obtain from stimuli, belong to the sensible organic contractility.

The duration of this last property, after the experiment I mentioned, proves completely that the nerves are wholly foreign to it, that it resides essentially in the muscular texture, that it is, as Haller said, inherent in it. Thus whilst in the different paralyses the muscles lose the power of obeying the cerebral influence, or rather this influence becomes nothing, they preserve that of contracting in an evident manner when stimulated.

This contraction of the muscles of animal life by stimulants, appears under two very different modes. 1st. The whole of the muscle can contract and shorten so as to approximate the two points of insertion. This happens in general when death is recent, when the muscle is still fully possessed of life. 2d. There are oftentimes numerous oscillations of the fibres; all are in action at the same time; now this action is not a contraction, but a real vibration, a fluttering, which has not a sensible effect upon the whole of the muscle, which not contracting cannot approximate its moveable points. When life is about abandoning entirely the muscle, it is thus that it moves. The diversity of the stimuli occasions also this double mode of contraction. Carry a scalpel over a living muscle, a contraction of the whole will be the consequence; afterwards sprinkle the same muscle with a neutral salt, sometimes there is an analogous contraction; but frequently there are only oscillations, vibrations similar to those of a muscle which life abandons.

During the life of the animal, its sensible organic contractility is rarely in action, because the muscles have not agents that act upon them in a sensible manner at least. Why then is this property so developed in them? I cannot determine.

All the muscles do not possess it to the same degree; the diaphragm and the intercostals are the most irritable; they are also those whose organic contractility is the most permanent after death. Observe that this contrasts, like their susceptibility to receive the nervous influence by the irritation of their nerves, especially of the phrenic, with the little disposition they have to feel, during life, convulsions or paralysis. After them I think that the temporal, the masseter, the buccinator, &c. are the most irritable. There is certainly as it respects irritability a great difference between them and the muscles of the extremities, which are all nearly equally susceptible to the effect of stimulants. Besides, it is only by a great number of experiments that we can establish general data; for nothing is more frequent than to find inequalities between two analogous muscles, and even between the corresponding ones of the two sides of the body.

_Sympathies._

The animal muscular system performs a very important part in the sympathies. We see it very frequently agitated with irregular motions in the different affections of our organs, especially in infancy when every lively impression made upon any organ, is almost always followed by spasmodic and convulsive motions in the muscles of animal life. Observe in fact that it is the vital property predominant in this system, that is to say the animal contractility, that is most often brought sympathetically into action in it, by the influences that the organs exert upon each other.

In general it appears that when the animal sensibility is strongly developed in an organ, this system tends immediately to contract. The acute pains that stones occasion in the kidneys, in the ureter and even the urethra, distensions of the ligaments, of the aponeuroses, dentition, surgical operations in which the patient has suffered much, &c. produce very numerous and frequent sympathetic convulsions. I know that there are very severe pains without sympathetic convulsive motions; but it is very rare that you see convulsive motions of this nature, without the organ, from which these sympathetic irradiations go, is very powerfully affected, and the seat of great animal sensibility.

Observe on the contrary that most of the sympathies which develop to a great degree in any part, insensible organic contractility, or sensible organic contractility, are not marked by these acute pains in the affected organ from which the excitement goes; for example, sweats, sympathetic secretions, intestinal and gastric contractions are rarely produced by affections of the character of those from which arise the sympathies of animal contractility.

The brain is always first affected in this last species of sympathies in which the muscles are, as it were, passive, as we have already seen, and in which they are made to obey the impulse they receive. The affected organ acts at first upon the brain, then this re-acts upon the muscles.

Authors have considered sympathies in too loose a manner. Some have admitted, others have rejected the intermediate office of the brain; some have not pronounced upon it. All would be agreed, if instead of attempting to resolve the question in a general manner, they had distinguished the sympathies according to the vital forces, of which they are only aberrations and irregular developments; they would have seen, that in the animal sympathies of contractility, the cerebral action is essential; for we cannot conceive of any contractility of this species, without the double influence, nervous and cerebral, upon the muscles; that on the contrary, in the organic sympathies of contractility, the action of the brain is nothing; the affected organ acts directly and without any thing intermediate upon that which contracts sympathetically. When the heart, the stomach, the intestines, &c. move, when the parotid and other glands increase their action by the sympathetic influence of an affected organ, certainly this organ does not act first upon the brain; for it would then be necessary that this should re-act upon those that contract; now it would not be able to influence them except by the nerves, since it is only by these that it is united to them; but all experiments and all facts prove as we shall see, that the brain has not by this means any influence over the organs with involuntary motions; then the action is direct and there is nothing intermediate. There are sympathetic motions like the natural ones; the sensible and insensible contractilities are constantly brought into action by a direct stimulus applied to the organ, whilst that the animal contractility is never exercised but by the cerebral stimulant, which itself requires a cause, either sympathetic or direct, in order to act upon the muscles.

Next to animal contractility, the sensibility of the same nature is the most often brought sympathetically into action in the animal muscular system. The lassitude, wandering pains, sensation of weight and stretchings that are felt in the limbs in the beginning of many diseases, are phenomena purely sympathetic, in which this property enters into action in the muscles. At advanced periods of many other affections, these sympathetic troubles are also very remarkable, but less in general than at the beginning.

The organic properties are for the most part rarely sympathetically in action in the species of muscles of which we are treating. Besides, if they are so, we can hardly judge of it, because no sign points it out to us. The sweat in the skin, the secreted fluids in the glands, the fluids exhaled upon many of the surfaces, are general results which indicate to us the sympathetic derangements of the organic sensibility and of the insensible contractility of the same species. In the muscles, we have not the same means of knowing these alterations.

_Characters of the Vital Properties._

From what we have thus far said, upon the muscular properties and sympathies, it is easily seen that the vital activity must be in general much greater in the muscles than in the organs previously examined in this volume; thus all their affections begin to take a peculiar character that distinguishes them from those of these organs; they are much more prompt and rapid. Yet let us remark that all the alterations of function which they exhibit, cannot assist us in estimating this vital activity. In fact, many of these alterations do not reside essentially in the muscular texture, their cause is not there; such are for example all the convulsive motions in which, as we have seen, the muscles act by obeying, but have not the principle of action in them. They are then the indices of cerebral alterations; thus the arteries, which exhibit such numerous varieties in the state of the pulse, are as it were only passive, and serve most frequently merely to indicate the state of the heart by their motion, whilst the veins, which have not at the origin of their circulation an analogous agent of impulse, very rarely exhibit varieties, though however their texture may have as great vital forces, and its life be as active or more so, than that of the arteries.

One proof that the texture of the muscle is less often altered than it at first seems to be in considering the frequency of the affections of these organs, is the infrequency of their organic lesions. These lesions are even less common in them than in the bones. We do not see in them those schirri, swellings, changes of texture in a word, which are so commonly met with in the other organs. Among the great number of subjects that I have had occasion to dissect or to have dissected, I do not recollect to have seen in the muscles of animal life other alterations than those of their cohesion, their density and their colour. It is a phenomenon that approximates them to those of organic life, in which we rarely meet with changes of texture, as the heart, the stomach, &c. are examples.

The muscular texture of animal life rarely suppurates; thus but little is known of its mode of suppuration. In general, it appears that inflammation terminates in it almost always by resolution. Induration, gangrene and suppuration, three terminations that this affection often makes in the other parts, are unknown to this in the greatest number of cases.

ARTICLE FOURTH.

PHENOMENA OF THE ACTION OF THE MUSCULAR SYSTEM OF ANIMAL LIFE.

Thus far we have spoken of muscular mobility, abstractedly from the phenomena that it exhibits in the muscles, when it is in exercise in them. These phenomena are now to be considered. They relate especially to contraction, which is the essentially active state of the muscle, relaxation being a state purely passive. We shall easily understand the phenomena of this, when those of the other of which they are the reverse are known to us.

I. _Force of the Muscular Contraction._

The force of the contraction of the muscles of animal life varies much, according as it is brought into action by stimulants, or by the cerebral action.

Every irritation made upon a muscle laid bare produces only a brisk, rapid motion, but generally not very powerful. I have frequently satisfied myself in my experiments that it is impossible to approximate even at a great distance by this means, the great energy which the brain communicates to the muscles of animal life. The organic muscular system which stimuli directly applied put principally in motion, never has exacerbations of force corresponding to those which the animal contractility exhibits in so great a degree under certain circumstances. It is then especially when the muscles move in virtue of this last property, that the force of their contraction must be considered. Now this contraction can, as we have seen, be produced, 1st, by stimulating the brain in experiments; 2d, when its excitement takes place in the natural state by the will, or by sympathy. In the first case, the force of the contraction is never very powerful, whatever may be the stimulant employed, either upon the brain, or the nerves laid bare. I have uniformly observed a very rapid convulsive motion, analogous to that produced by exciting the muscles themselves, but never as strong as that which is the result of vital action. Notwithstanding what some physiologists have written, we can never by irritating the nerves of the flexors impart to them an energy comparable to that which the will can give them. Irritate for example the sciatic nerve in an inferior extremity which has just been amputated, the toes will never bend with the force which they do in certain cases in the natural state. I have twice made this experiment in amputations performed by Desault. Unacquainted then with physiology, I was much struck with this phenomenon.

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.

It is only those muscles that are attached on one side to a fixed point and on the other to a moveable one, like those of the eye, and most of those of the face, that can move in an insulated manner, and without requiring a motion in the other muscles. It should be remarked however that in general the contractions destined to fix the point which should be immoveable in the ordinary motions, are less than they at first seem to be. In fact, in these ordinary motions, the point which moves is always the most moveable, that which remains without motion is the least so; for example, it requires a much greater effort in flexors to bend the arm upon the fore-arm, than to bend the phalanges upon the fore-arm, or the fore-arm upon the arm. By supposing their two attachments moveable, the gemelli would act much more powerfully on the foot than on the femur, &c. In the extremities, the superior point is always more moveable than the inferior, now it is this which almost always moves, the other being fixed; then as it offers more resistance by its position, it requires less effort of the muscular powers to retain it. It is only in violent motions, that the previous contraction of the muscles destined to fix one of the points of insertion Is very painful. This takes place on the chest when the trapezius, the great serratus and the great pectoral contract powerfully; then all the other muscles of this cavity contract strongly to dilate it, and thus offer a broader and more fixed attachment to those muscles, which move the shoulder in the support of burdens, or in any other analogous effort. The diaphragm contracts also; hence hernias, the descents which take place from a concussion in those motions which, at first view, have no analogy with the abdominal cavity. When in a horizontal position of the body we raise the head, the rectimuscles of the abdomen contract to fix the chest, and present a solid point to the sterno-mastoideus, &c.

We call especially a compound motion that which two or more muscles, acting upon the same point, contribute simultaneously to produce. In this case, the moveable point follows the direction of neither muscle, if there are two of them, but takes the diagonal of their direction. It is thus that the eye is moved outwards and upwards, outwards and downwards, &c.; that the head is depressed, that it is carried to one side, and that the arm is applied to the trunk, &c. In general nature has distributed muscles only in some principal directions around a moveable point, for example around the eye, in those of elevation, depression, adduction and abduction; the combination of these simple motions produces the compound ones. If the adductor and depressor contract equally, the eye will be carried exactly in a middle direction; if one acts with more force than the other, it will be carried a little nearer the other; so that the four muscles, by moving separately, or two by two in an equal manner, carry the eye in eight different directions. In all the intermediate directions, there is also a simultaneous action of two muscles, but always a superiority in the action of one of them. Thus almost all the motions of circumduction operate.

When two opposite muscles contract, the moveable part is not moved; they are perfect antagonists. When two muscles which contract at the same time are placed in the same direction, there is no loss of power; this is what takes place when the genio-hyoideus and the mylo-hyoideus depress the jaw or elevate the os hyoides; these muscles act completely together. But when two muscles are in part opposed and in part in the same direction, as the sterno-mastoidei, one portion of the forces is destroyed and the other remains. The action by which the sterno-mastoidei tend to carry the head to the right or the left, is nothing; that alone by which they direct it downwards produces its effect which is double, considering the action of the two muscles, which are thus at the same time acting together and antagonists. Hence we see that this applies not only to the motion produced by the contractility of texture, but also very often to those which the animal contractility occasions.

VI. _Phenomena of the Relaxation of the Muscles._

When a muscle ceases to contract, it becomes the seat of phenomena precisely opposite to the preceding, which it is sufficient to know in order to understand these. The muscle becomes longer and softer; its wrinkles disappear; it returns exactly to the state in which it was found. It is needless to give in detail the series of these phenomena.

I would remark that in the state of relaxation of the muscles, the parts often execute motions which are only owing to their weight; such are the flexion forwards of the head in sleep, the fall of the fore-arm and the arm in the same case. Then the weight is often opposed to the limbs, remaining in their middle position, which are not supported. We see particularly these phenomena in paralysis.

ARTICLE FIFTH.

DEVELOPMENT OF THE MUSCULAR SYSTEM OF ANIMAL LIFE.

The muscular system exhibits great differences, according as we examine it before the completion of growth, or in the ages that follow that in which this growth is terminated.

I. _State of the Muscular System in the Fœtus._

In the first month of the fœtus, this system is, like the others, a mere mucous homogeneous mass, in which can be distinguished scarcely any line of demarcation. Aponeuroses, muscles, tendons, &c. all have the same appearance. Gradually the limits are established, the muscular texture at first takes a deeper tinge, from the blood that enters it. Yet this tinge is at first much less evident than in the adult; it remains nearly the same till birth. If we make use of the bones as a means of comparison, this becomes striking. In the adult the interior of the bones is less red than the muscular texture; the difference is remarkable. It is the contrary in the fœtus; much more blood penetrates the already ossified portion of the bones, than the interior of the muscles. Nature distributes the blood in an inverse manner at these two periods of life in these two systems.

I presume that this phenomenon is principally owing to the kind of inertia in which the muscles remain before birth. Observe in fact that though some motions announce in the last months the presence of the fœtus in the womb of the mother, yet these motions are infinitely less than they are to be afterwards. The proof of this is the constant semi-flexed position which the limbs and trunk have, and the small space that there is to execute these motions in, especially in the last periods in which the waters are wonderfully diminished. In the early periods of pregnancy, though the space may be greater, by opening the females of animals, we constantly find the fœtus drawn up upon itself, and in an attitude almost immoveable.

Many respectable philosophers have found the muscles of the chick in its shell much less irritable than after birth, either by ordinary agents, or by galvanic influence. I have made the same experiment upon small guinea-pigs that were never born, by irritating directly their muscles, or by stimulating their nerves, their spinal marrow and the brain. The nearer we approach the term of conception, the less are the motions obtained. That which is especially remarkable is the rapidity with which, when the fœtus is dead, the muscles lose their irritability; the instant that extinguishes life seems to destroy this property. In the latter periods that precede accouchement, it is a little more permanent, and more susceptible of being brought into action, but always less than after birth. We can hardly doubt then that the motions are less at this age, though however they exist. We shall see that the nutrition, size and redness of the muscles are in general in the adult in proportion to the number of the motions they perform; it is not then astonishing that less blood penetrates them in the fœtus. Besides the nearer we approach the period of conception, the less abundant is this fluid in them. I have had occasion to make this remark on guinea-pigs killed at different periods of gestation. In the early periods, the muscles of the small ones really resemble those of frogs; white like them, they are marked with reddish lines, which indicate the course of the vessels.