Chapter XIII: Part 13

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.

2d. The antagonist of the divided muscle which has no effort to overcome, contracts and makes the moveable part incline from its side, if there are not other muscles, which acting in the direction of the first supply its functions. This last phenomenon takes place also to a certain extent in paralysis of the face. The mouth is then drawn from the sound side. I have observed however in this respect, that this deviation is never as evident as it would be by the division of the paralytic muscle, which has preserved its contractility of texture. This remaining contractility forms a partial equilibrium with that of the muscles of the sound side, during the absence of motions; thus the deviations do not become very evident until the patients wish to speak, until consequently the vital forces bring into action the sound muscles, which the others cannot oppose. The paralysis of the sterno-mastoideus exhibits for the whole head a phenomenon analogous to that which the preceding muscles produce for the mouth. Strabismus also oftentimes arises from this cause.

In general in all the phenomena, it is necessary to distinguish that which belongs to the vital forces, from that which arises from the contractility of texture. The muscles are antagonists as it respects these forces, as well as it respects this contractility; now as the contraction dependant on the nervous influence or irritability, is much more conspicuous than that arising from the organic texture, the phenomena of the antagonists are much more striking in paralysis, when the sound muscles are brought into action in the first manner. It appears that in many cases of paralysis, the contractility of texture of the affected side is also a little altered; but it is never so completely destroyed, that in the amputation of a paralyzed limb, there is no muscular retraction. I have made this experiment upon a dog; the nerves having been cut ten days before, and the limb having remained immoveable since that period, the division of the muscles produced a manifest separation between their edges; and even, in afterwards cutting for the sake of comparison the limb that remained sound, I did not find any difference.

It is especially when muscles have been first stretched, and this stretching has ceased, that the contractility of texture becomes evident. The puncture in ascites and an accouchement as it respects the abdominal muscles, the opening of deep abscesses as it respects those of the trunk, the extirpation of a tumour situated under any muscle, &c. show us this property in action in a very striking manner. There is however an observation to be made on this point, viz. that if the extension has been of long continuance, or if it has been frequently repeated, the subsequent contraction is much less, because the muscular texture has been weakened by the painful state in which it has been; hence, 1st, the flaccidity of the abdomen after repeated pregnancy; 2d, the laxity of the scrotum, after the puncture of an old hydrocele; 3d, I have seen at Desault's a man who was operated upon in Germany for a fungus in the mouth, and who had, on that side on which the disease had been, remarkable wrinkles, owing to the greater extent of the fleshy part of that side, which could no longer contract like the other; mastication, at this time could only be performed on the sound side; 4th, when women have had many children, the diaphragm is weakened by repeated pressure, and hence in part the greater mobility of the ribs, which compensate in some measure in females for the deficiency of action of this muscle. I think that in many chronic affections of the chest and abdomen, in which there is a long continued distension of this muscle, physicians ought more than they do, to have regard to this cause of difficulty of respiration, when the principle of distension no longer exists, as after the evacuation of dropsies, &c.

The extent of the contractility of texture is in the muscles in proportion to the length of the fibres; hence why in amputations, the superficial part retracts more than the deep-seated; why in sleep the phenomena of contractility of texture are very apparent in the extremities, the muscles of which are very long; why, in the antagonists, nature has in general opposed muscles of proportional length; why consequently, a muscle with long fibres has rarely for a counterpoise one with short ones, and vice versa. The flexors and extensors of the arm, the fore-arm, the thigh and the leg are nearly of the same extent; the rotators of the humerus within and without, the first inserted into the sub-spinal depression, the others into the sub-scapular, resemble each other also in this respect. The proportion between the antagonists is still more remarkable on the face, where the same muscles act most commonly in an opposite direction on each side of the median line.

The quickness of the contractions, arising from the contractility of texture, is not like that produced by the animal or sensible organic contractility, which is uniformly more or less marked, according as the nervous influence of the stimulant acts more or less strongly. Every motion originating from the contractility of texture is slow, uniform and regular; it is only when the muscular texture is weakened that it diminishes; it does not increase except when this texture is more developed; hence it follows that the varieties of quickness can only be observed in different individuals, or in the same individual at different periods, and not, as in the exercise of the vital forces, from one instant to another. This is a great and remarkable difference between the two species of properties.

Death weakens the contractility of texture but does not annihilate it; a muscle being cut retracts a long time after life has left it. Putrefaction alone puts a limit to the existence of this property. It is the same with regard to extensibility. I would observe however that while the muscles retain the vital heat, they have more power of retraction, than when the chill of death has seized them.

Haller places on the same line and derives from the same principles, the phenomena resulting from the contractility of texture, which, with some slight differences, answers to his dead power, and those produced by the action of the concentrated acids, alkohol, fire, &c. on animal substances, which crisp, contract and acquire the horny hardness from the effect of these different agents. But there are many differences which essentially separate these phenomena from each other. 1st. The contractility of texture is very slight in the organs in which the faculty of having the horny hardness is very evident, for example, in all the organs of the fibrous, fibro-cartilaginous, serous systems, &c. &c. 2d. The contractility of texture is distributed in very various degrees, to the different parts; from the muscles and the skin, which possess the greatest degree of it, to the cartilages which seem destitute of it, there are many variations; on the contrary, the faculty of acquiring the horny hardness from the agents pointed out is almost uniformly distributed, or at least its differences are much less evident. 3d. One becomes nothing in dried organs, the other is evidently preserved for many years, as parchment is a proof. 4th. The first clearly receives an increase of power from life, especially in the muscles; the second appears to be hardly modified by it. 5th. This always exhibits sudden effects, rapid contractions. To feel the contact of the fire, of the concentrated acids or alkohol, and to assume the horny hardness, are two phenomena which the second brings together in the animal parts; the contractility of texture, on the contrary, exerts itself but slowly, as we have said. 6th. This last can never give to the parts, the muscles especially, that remarkable density which they exhibit in their horny hardening. 7th. The absence of extension of the fibres is the only thing necessary for the contractility of texture which has an unceasing tendency to activity; it requires on the contrary in order to crisp the fibres, that they should be in contact with a foreign body. I could add to these many proofs, in order to establish an essential difference between the phenomena confounded by the illustrious physiologist of Switzerland.

II. _Vital Properties._

The most of these properties perform a very important part in the muscles. We shall first examine those of animal life, and afterwards treat of those of organic.

_Properties of Animal Life. Sensibility._

Animal sensibility is that of all the vital properties which is the most obscure in these organs, at least if we consider them in the ordinary state. Cut transversely in amputations, in experiments upon living animals, they do not experience any very painful sensation; it is only when a nervous filament is touched, that pain is manifested. The peculiar texture of the muscle is but slightly sensible; irritation by chemical stimulants does not show much sensibility in it.

There is however a peculiar sensation, which in the muscles very evidently belongs to this property; it is that which is experienced after repeated contractions, and is called lassitude. After long standing, it is in the thick bundle of lumbar muscles that this sensation is especially felt. After walking, running, &c. if on a horizontal plain, it is all the muscles of the lower extremities which are more particularly fatigued; if on an ascending plain, it is especially the flexors of the ilio-femoral articulation; if on a descending one, it is the posterior muscles of the trunk. In the employments which exercise particularly the superior extremities, this sensation is often experienced in a remarkable manner, which is certainly not owing to the compression made by the muscles in contraction, upon the small nerves which run through them. In fact it can take place without this antecedent contraction, as is observed in the commencement of many diseases, in which it extends in general over the whole muscular system, and in which the patients are, as they say, fatigued and wearied, as after a long march. This sensation appears to depend on the peculiar kind of animal sensibility of the muscles, a sensibility which the other agents do not develop, and which the permanency of contraction renders here very apparent. Thus the fibrous system, sensible only to the means of distension which act upon it, does not receive a painful influence from the other agents of irritation. Observe that this painful sensation, which a too prolonged motion produces in the muscles, is intended by nature to warn the animal to place limits to it, without which the consequences would be serious. Thus the peculiar sensation which arises from distended ligaments, is designed to make the animal limit their extension. Observe how each organ has its peculiar kind of sensibility; how false an idea we should have of the existence of this property, if we judged of it only from mechanical and chemical agents, and observe particularly how nature accommodates to the uses of each organ its kind of animal sensibility.

In phlegmasia of the peculiar muscular texture, the animal sensibility is very often raised to a very great height; the least touch on the skin becomes painful; the patient can hardly bear the weight of the clothes, and frequently the least jar produces in the limbs the most acute pains. But in general these pains are wholly different from the painful sensation which we call lassitude; thus the pain of a ligament stretched in a sound state, is not the same as that which arises from the inflammation of a ligament or any other fibrous organ.

I would add to what I have said above upon this sensation, that some organs are fatigued like the muscles, from too long continuance of their functions; for example, the eyes by the contact of light, the ears by that of sounds, the brain by thinking, &c. and in general all the organs of animal life; it is even this general lassitude which brings on sleep, as I have proved in my Researches upon Life. But observe that the sensation which the eye, the ear, the brain and all the external organs produce when thus fatigued is not the same as that which arises from the over-exertion of the muscles; another proof of the peculiar kind of their sensibility, and in general of that of every living part.

_Animal Contractility._

This animal property, upon which all the phenomena of locomotion and voice depend, which assists those of the internal and external functions, has its seat exclusively in the animal muscular system; it is this which distinguishes it from the organic, and from all the others. It consists in the faculty of moving under the cerebral influence, whether the will or other causes produce this influence. The animal contractility has then, like the sensibility of the same species, a peculiar character, differing from the two organic contractilities, a character which consists in this, that its exercise is not concentrated in the organ which is moved, but that it requires also the action of the brain and the nerves. The brain is the principle from which, if we may so say, this property goes, as it is that to which all the sensations come; the cerebral nerves are the agents which transmit it, as they are, though in an opposite direction, the conductors of the sensitive phenomena. Whence it follows, that in order to understand this property well, it is necessary to examine it in the brain, in the nerves and in the muscle itself.

_Animal Contractility considered in the Brain._

Every thing in the phenomena of animal contractility proclaims the influence of the brain.

In the ordinary state if more blood is carried to this organ, as in anger; if opium, taken in a moderate dose, excites it slightly; if wine produces the same effect, the muscular action increases in energy in proportion as that of the brain is thus increased. If terror by retarding the pulse, by diminishing the force of the heart, and even the quantity of blood sent to the brain, strikes it with atony; if the different narcotics, carried to excess, produce the same effect; if wine prevents its action by its too great quantity, then observe these muscles languish in their motion and experience even a remarkable intermission. If the brain is wholly engrossed in its relations with the senses, or in its intellectual functions, it, if we may so say, forgets the muscles; these remain inactive; the man who looks or hears with attention, does not move; neither does he who contemplates, meditates and reflects. The phenomena of ecstasy, the history of the studies of philosophers, often present us with this important fact, this muscular inertia, the principle of which is in the distraction of the cerebral influence, which does not increase in other functions, only by diminishing in locomotion.

In diseases, all the causes which act strongly on the brain, re-act suddenly on the animal muscular system; now this reaction is manifested by two opposite states, by paralysis and by convulsions. The first is the indication of diminished energy, the second that of increased; one takes place in compressions from pus, effused blood, bones driven below their natural level, and from the consequences of apoplexy; it is seen in the attack of most hemiplegias, a sudden attack in which the patient falls down, loses all consciousness and has all the signs of a cerebral lesion. This lesion disappears, but its effect remains, and this effect is the immobility of a part of the muscular system. The other state or the convulsive, arises from the various irritations of the cerebral organ from osseous fragments driven into its substance, from its own inflammation or that of its membranes, from different tumours of which it may be the seat, from organic lesions that it may have, lesions which I have rarely observed in the adult, but which infancy sometimes exhibits, and from the causes even of compressions; for oftentimes we see this convulsive state existing at the same time with different effusions, with hydrocephalus, &c.

The state of the animal muscular system is truly the thermometer of the state of the brain; the degree of its movements indicates the degree of energy of this organ. Those who attend in a lunatic hospital have often occasion to consult this thermometer. At the side of a furious patient, whose muscular power is doubled, or even trebled, you see a man all whose motions languish in a remarkable inertia. A thousand different degrees are observed in these motions; now these degrees do not depend upon the muscles; the most furious madman is often he whose very delicate external forms indicate the weakest muscular constitution; as the most perfect automaton is sometimes he whose muscles are the most powerfully developed. The muscles are to the brain what the arteries are to the heart. The physician learns by these vessels the state of the central organ of circulation which communicates impulse to them; by the muscles of animal life, he learns the state of the central organ of this life. Observe patients in many important fevers; in the morning there is prostration, in the evening you find an extreme agitation in the muscles. Now what is the seat of this revolution? It is not the muscles, but it is the brain. There has been a translation to the head, as it is commonly called.

If from the bed of the sick we go to the laboratory of the physiologist, we shall see experiments in perfect accordance with the preceding observations. The ligature of all the arteries that go to the brain, interrupts immediately the movements of this organ, movements necessary to its action, and produces a sudden cessation of voluntary motion, and afterwards death. By injecting through the carotid and towards the head, ink, solutions of neutral salts, acids, substances whose contact is fatal to cerebral action, I have always seen the animal perish with previous convulsive motions. The injection of water does not produce this effect; it can with impunity to the life of the brain be introduced into the arterial blood, if it is injected moderately; but pushed with force, you will irritate extremely this organ, and in an instant the animal is seized with violent agitations; moderate the force, rest succeeds. I have already related this experiment elsewhere. If we lay bare the cephalic mass, and irritate it with a mechanical or chemical agent, &c. in an instant the animal muscular system is brought into action. It is however to be observed that in these experiments the convexity of the organ appears to be much less connected with the motions, than its base. The irritation confined to the cortical substance, to the superficial layers of the medullary, is almost nothing; it is not till we arrive at the inferior layers, that the convulsions come on. I have wished to try many times to ascertain with precision the place where the irritation becomes a cause of convulsion; but this has always appeared to me very difficult, and the results have been infinitely various. I believe that we can hardly establish any thing more than a general result, viz. that the nearer we approach in the experiments the annular protuberance, and in general the cerebral base, the more apparent are the convulsive phenomena; they are so much the less as we remove from them, they are nothing on the convex surface. Observe that it is on the side of its base, that is to say, on the side of its essential part, that the brain receives the numerous vessels which carry to it excitement and life, whether by the motion which they communicate to it, or by the nature of the red blood which they carry to it, as my experiments published the year passed have, I think, demonstrated.

Add to these experiments those of the artificial commotions. The muscles of the ox vacillate, and are unable to support themselves, the instant the blow is struck. At other times animals expire, their limbs convulsively agitated from a blow given on the occiput; rabbits often exhibit this phenomenon. Pigeons die with convulsive motions of the wings. Irregular agitations arising from an irregular influx of the power of the brain always precede the instant of death, which the commotion has produced.

Let us conclude from all these experiments and the observations that precede them, that the action of the animal muscular system is always essentially connected with the state of the brain, and that when this action is increased or diminished there is almost always an increase or diminution of the cerebral action.

Let us not however exaggerate the relation which connects the muscular to the cerebral phenomena; observation would prove us incorrect. There are various examples of aqueous, sanguineous and even purulent congestions in the brain, without having produced any alteration in muscular motion. Different tumours and defects of conformation have occasioned disturbance of the intellectual functions, without affecting those of the muscles; how many times is the brain disordered in various species of alienations; how many times do the understanding, memory, attention and imagination indicate these derangements by their irregular aberrations, without their being felt by the muscular system. Is there not often an alteration of the external sensation, without an alteration of motion? In general the brain has three great functions. 1st. It receives the impressions from the external senses; it is in this relation the seat of perception. 2d. It is the principle and the centre of the voluntary motions, which are not exerted but by its influence. 3d. The intellectual phenomena are essentially connected with the regularity of its life; it is as it were the seat of them. Now it can be deranged as to one of these functions, and remain sound as to the others; it can be a regular principle of the motions, and an irregular centre of the phenomena of the understanding; not communicating with external objects by the senses, and determining motions, or presiding over intellectual functions, as happens in sleep which is disturbed by dreams, &c.

From what has been said we can understand why acephalous fœtuses cannot live out of the womb of the mother. As animal life is nothing in the fœtus, as respiration does not take place, as the functions are limited to the great circulation, to the secretions, exhalations and nutrition, the acephalous fœtuses can live in the womb of the mother, and acquire a very considerable size; but at birth they cannot breathe, the intercostals and diaphragm being unable to act. The gastric viscera receives no influence from their muscular parietes; all the limbs are immoveable. Animal life, which commences in others at birth, cannot commence in them, because they have not the centre of this life; they have senses, but nothing to receive their impressions; muscles, but nothing to make them move; they can continue to live but a little while in themselves, without beginning to live from without. But as in general it appears that when the infant quits the womb, the red blood becomes necessary to it, that to have this, it must respire, and as this function cannot commence, it loses the internal life which it had in the womb of the mother. There are acephalous fœtuses which have at the origin of the nerves a small medullary swelling; in others the spinal marrow is larger. If these medullary swellings, if the spinal marrow by its peculiar texture, supply the place of the brain, life can continue, and it is in this way that we can explain some examples of acephalous subjects that have lived a certain time. But certainly an acephalous subject organized like ourselves, which has nothing to supply the place of the brain, cannot live. Thus in almost all the examples of these monsters, related by authors, and especially by Haller, the death of the individual took place at its birth.

_Animal Contractility considered in the Nerves._

The brain, at a distance from almost all the muscles, communicates with them by the nervous system, and by it transmits to them its influence; now this communication is made in two ways. 1st. There are nerves which go directly from the brain to the muscles of animal life. 2d. The greatest number does not go from this organ itself, but from the spinal marrow. Almost all the muscles of the neck, all those of the chest, the abdomen and the extremities receive theirs from this last source. The spinal marrow is, as it were, a general nerve, of which the others are only divisions and principal branches.

All the lesions of this principal nerve are felt by the muscles that it has under its influence; the compressions that it experiences from a fracture of the vertebræ, from any displacement, from an effusion of blood, serum, pus, &c. in the vertebral canal, the derangements which take place from a violent blow received upon the whole region of the spine, from a fall upon the loins, or on the superior part of the sacrum, are followed by numbness and paralysis of the subjacent muscles. Divide the spinal marrow, by introducing a scalpel into the canal, immediately all motion ceases below the division. If you wish on the contrary to produce convulsions, introduce a stilet into the canal; irritate the marrow with it or by chemical agents placed on it, there will be immediately agitation and convulsion in all the animal and muscular system that is below.

The higher the lesion of the marrow is, the more dangerous is it. In the lumbar region its influence extends only to the inferior extremities, and the muscles of the pelvis; in the back it paralyzes these muscles and those of the abdomen; now as these last contribute indirectly to respiration, this function begins to be embarrassed; if the lesion is above the dorsal region, it becomes still more painful, because the intercostals lose their action; the diaphragm alone then supports the respiratory phenomena, because the phrenic nerve still receives and transmits the cerebral influence. But when the lesion happens above the origin of this nerve, there is no more action of the diaphragm, and no more contraction of the intercostal and abdominal muscles; respiration ceases; from the same cause the circulation is interrupted; the blood being no longer carried to the brain, the action of this organ is annihilated. Hence why the luxations of the first vertebra on the second are suddenly fatal, when the displacement is very great; why judicious surgeons dare not sometimes run the hazard of reduction, when these luxations are partial, for fear of rendering them complete, and of thus seeing the patient, whom they attempted to relieve, perish in their hands; why, when we wish to knock down an animal, the blow should be given on the superior and posterior part of the spine; and why a stilet plunged between the first and second vertebræ immediately destroys life.

We see very distinctly the successive influence of the different parts of the marrow on the muscles and on the general life, by introducing a long piece of iron into the inferior part of the vertebral canal of an animal, of a guinea pig for example, and carrying it up through this canal to the cranium, through the spinal marrow which it tears. We observe evidently as it ascends, at first convulsions of the inferior extremities, then those of the abdominal muscles, then derangement of respiration, then its cessation, then death which is the consequence of it.

From all these facts, we cannot, I think, call in question the influence of the spinal marrow upon motion, the principle of which it receives from the brain and afterwards transmits it to the nerves. These last carry this principle, which they have received, to the muscles, either by means of the spinal marrow, as in almost all those of the trunk and the extremities, or directly from the brain, as in those of the face, the tongue, the eyes, &c. There are the same proofs for this nervous influence, as for that of the preceding sensitive organs. The tying, division or compression of a nerve paralyzes the corresponding muscle. Irritate with any agent a nerve laid bare in an animal, convulsive contractions are immediately seen in the muscle. These experiments have been so often and so accurately repeated by many authors, that I think it useless to go into details, which the reader may find everywhere. Irritation continued some time upon one point of the nerve destroys its influence upon the muscle, which remains immoveable; but it is put in motion again, if the irritation is carried to a lower part of the nerve. If we tie it, the motion ceases, if irritation is made above the ligature, it returns when it is made below, or when the ligature is removed.

I would remark that all the nerves of animal life do not appear to be equally capable of transmitting to the muscles the different irradiations of the brain. In fact whilst in diseases, in wounds of the head, in our experiments, &c. the muscles of the extremities are convulsed or paralyzed with great ease, those of the abdomen, the neck, and especially the chest do not exhibit these phenomena, except when the causes of excitement and debility are carried to the highest point. Nothing is more frequent than to see the abdomen and the chest with their ordinary degree of muscular contraction, whilst the extremities or the face are agitated with convulsive motions. Examine most hemiplegias; the mouth is twisted, the superior and inferior extremity of one side become immoveable, and yet the pectoral and abdominal motions continue. Those of the larynx are more easily interrupted than these in paralysis; hence the different injuries of the voice. We could make a scale of the susceptibility of the muscles to receive the cerebral influence, or of the nerves to propagate it, for it is difficult to determine to which of these two causes the phenomenon is owing; we could, I say, make a scale, at the top of which should be placed the muscles of the extremities, then those of the face, then those of the larynx, afterwards those of the pelvis and the abdomen, and finally the intercostals and diaphragm. These last become convulsed and paralyzed with the most difficulty of all. Observe how this scale is adapted to that of the functions. What would become of life, which is always actually connected with the soundness of respiration, if all the cerebral lesions were as easily felt by the diaphragm and the intercostals, as by the muscles of the extremities? Paralysis in these last only takes from the animal a means of communication with external objects; in the others it interrupts immediately both internal and external life.

The nervous influence is only propagated from the superior to the inferior part, and never in an inverse direction. Cut a nerve in two, its inferior part when irritated will make the subjacent muscles contract; let them do what they will to excite the other, no contraction is produced in the superior muscles; so the spinal marrow divided transversely and pricked above and below, produces no sensible effect but in the second direction. The nervous influence never extends upward for motion, as it does for sensation.

_Animal Contractility considered in the Muscles._

The muscles essentially destined to receive the cerebral influence by means of the nerves, have however an active part in their own contraction. It is necessary that they should be entire to exercise this property, and answer to the excitement of the brain. When any lesion affects their texture, and it is no longer the same as usual, the muscle remains immoveable or moves with irregularity, though it receives a regular nervous influx. The following are various circumstances relative to the muscle itself, which prevent or alter its contractions.

1st. An inflamed muscle does not contract; the blood which then infiltrates it and penetrates its fibres, their great excitement and the increase of its organic forces, do not permit it to obey the stimulus it receives. In angina, deglutition is as much interrupted by the inaction of the muscles, as by the inflammation of the mucous membrane. We know that the inflammation of the bladder is one cause of the retention of urine; that of the diaphragm renders respiration very painful, which the intercostals perform almost alone.

2d. Every thing which tends to weaken and relax the muscular texture, as external blows, bruises, contusions, infiltrations of serum in dropsical limbs, or distension from a subjacent tumour long continued, alters, changes the nature of, and can even annihilate animal contractility.

3d. Whenever the blood ceases to enter the muscles by the arteries, these organs remain immoveable. Steno has observed, and I have always seen, that in tying the aorta above its bifurcation which forms the internal iliacs, paralysis of the inferior extremities immediately comes on. We know that in the operation for aneurism, a numbness more or less considerable almost always follows the ligature of the artery. This numbness continues until the anastomoses supply the place of the artery which no longer brings any fluid. The internal motion created in the muscle by the entrance of the blood, is then a condition essential to muscular contraction. Thus the habitual motion imparted to all the other organs and especially to the brain, maintains their excitement and their life.

4th. It is necessary in order to obey the cerebral influence that the muscle should not only receive the shock of the blood, but also of the red or arterial blood. Black blood cannot by its contact support motion. A general weakness and the fall of the animal are the first symptoms of asphyxia, a disease in which the black blood goes to all the parts. I shall not here repeat the proofs of this assertion, which appears to me to be amply demonstrated by my Researches upon the Different Species of Death. I refer to my work upon this point.

5th. A fluid differing from the blood, water, oily and albuminous fluids, and for a stronger reason acrid and irritating fluids, the urine, solutions of the acids and the alkalis, &c. are not proper to support muscular action; on the contrary they paralyze it; injected into the crural arteries of a living animal instead of blood, which is stopt above by a ligature, they weaken and even annihilate the motions, as I have frequently satisfied myself. The result varies in these experiments according to the fluid employed in making them; the rapidity of the cessation of the motions is more or less striking; they are either weakened or totally suspended; but there is always a very great difference between that and the natural state.

6th. Does the contact of the different gases upon the muscles modify their contractions? Since the publication of my Treatise upon the Membranes, I have made no experiment upon this point. Those which are contained in it present the following results; frogs and guinea pigs rendered emphysematous by blowing air into the sub-cutaneous texture which afterwards penetrates the cellular interstices, and comes everywhere in contact with the muscular system, move almost the same as usual. If oxygen is used, the motions of the emphysematous animals are not accelerated; they are not diminished if we employ the carbonic acid gas, hydrogen, &c. In general, all the artificial emphysemas that I have made upon the two species mentioned, in order to have an example in each class of animals with red and cold blood, and of those with red and warm blood, succeeded very well, and did not appear to cause any sensible embarrassment to the animal, which gradually got rid of it. Emphysema with nitrous gas is constantly fatal; the contact of this gas seems almost suddenly to strike the muscles with atony.

7th. If instead of blowing gas into the cellular texture of an animal, we force in different fluid substances, they produce different effects upon the muscles, according to their nature, and to their acrid, soft, or styptic qualities. No injection produces a more sudden and striking effect than that of opium dissolved in water, or than that of its various preparations; when the muscles feel it in contact, their motions cease, they fall as in paralysis.

In general I would observe that it is infinitely better to make the experiments of the contact of the gases and the different fluids upon the muscles, by blowing the first, and injecting the others into the intermuscular texture of a living animal, than by drawing out a muscle, and afterwards plunging it all alive into the one or the other; or than laying a muscle bare, in order to direct upon it the current of a gas, or to moisten it with a fluid, for the purpose of observing the phenomena of the contact.

It follows from all that we have just said, 1st, that to answer to the cerebral excitement by contracting, the muscle should be in general in a state determined by the laws of its organization; that out of this state it is not capable of contracting, or at least that it does it feebly and irregularly; 2d, that the contact of different foreign substances produces upon the muscle a very variable effect. Moreover many causes besides those stated above, appear to me also to alter the contractions, by acting directly upon the muscles, such as mercury taken by friction for the venereal disease, the influence of this metal, of copper and of lead, upon those who work in them, the action of cold, that of certain fevers, &c. The muscular tremor arising from these different causes, does not appear to arise from the brain; this organ at least does not most commonly give any sign of affection in this case; I confess however that in these different species of tremors, it is not easy to distinguish that which belongs to the peculiar affection of the muscle, from what arises from that of the nerves; perhaps these are especially affected, but the brain certainly does not participate.

_Causes which bring into action Animal Contractility._

We have just seen that in the natural state this property constantly requires three actions, 1st, that of the brain; 2d, that of the nerves; 3d, that of the muscles; that it is from the brain that the principle of motion goes which is propagated by the nerves, and which the muscles receive. But it is necessary that some agent should excite the brain to determine it to exert its influence. In fact, the animal contractility being essentially intermittent in its exercise, so that each time after it has been exerted it is suspended, it is necessary that a new cause should place it again in activity; now this cause acts at first upon the brain in the natural state.

I refer to two classes the causes that excite the brain in order to produce animal contractility. In the first is the will, in the second are all the impressions which this organ receives, and which are not under the control of the mind.

The brain is only intermediate between the mind and the nerves, as the nerves are between the muscles and the brain; the principle, which wills, acts at first upon this organ, which afterwards re-acts. When they are thus produced, our motions are sometimes precise and regular; that is when the intellectual functions are sound, when the memory, imagination and perception are clearly exerted, when the judgment being correct, directs with regularity the acts of the will; sometimes they are irregular and singular, it is when the intellectual functions disturbed and agitated in various ways, produce a singular and irregular volition, as in the various mental alienations, in dreams, in the delirium of fevers, &c. But in all these cases, these are always voluntary motions; they go from the immaterial principle that animates us.

In the second class of causes which influence the brain, the animal contractility becomes involuntary; it is exerted without the participation of the intellectual principle, often even against its will. Observe an animal whose brain is artificially irritated in experiments; it tries to stiffen itself to prevent the contractions, they take place in spite of it; prick a nerve in an operation, the muscle contracts suddenly below, without the mind's participating in this movement; the patient has not even a consciousness of it; he has only that of the pain. When much blood flows to the brain in the violence of inflammatory fevers, this organ excited by the fluid, re-acts immediately upon the muscles, without the will's partaking in it. All the phenomena of contraction and relaxation, arising from different accidents which accompany wounds of the head, cerebral inflammations, &c. are equally involuntary, although having their seat in the muscles which the will habitually directs. These are the different circumstances in which the action of any agent upon the brain is direct and immediate, and in which there is a mechanical cause applied to the brain.

In other circumstances the brain is only affected sympathetically. In many acute affections what is called translation to the brain, does not arise from more blood being carried to it; the pulse is not fuller, the face is not more flushed; there are often even signs of languor in the action of the vascular system. The brain is affected, like all the other organs by sympathy, a happy word, which serves to veil our ignorance in respect to the relations of organs to each other; the brain is affected then like the heart, the liver, &c. Take for example peripneumony; the lungs are then the organs that are essentially injured, from this essential and local injury, arise many sympathetic ones more or less severe. If the liver is sympathetically affected, bilious symptoms are joined to the symptoms of the principal affection; if it is the stomach then gastric symptoms are manifested. The heart is always agitated; hence there is fever. When the sympathetic influence extends to the brain, there is violent motion, convulsions, &c.; for, as I have said, the state of the muscles is the index of the state of this organ; now, in this last circumstance, the will has nothing to do with the animal contractility in exercise; the patient cannot prevent the convulsive agitation of his muscles; the sympathetic irritation of the brain is stronger than the influence of the will. This example of cerebral affection in peripneumony, though more rare than in many other diseases, may however give us an idea of what takes place in all other cases in which the muscles are convulsively agitated by the injury of any organ, by that of the fibrous system distended, of the ligaments and especially of the aponeuroses, by dentition, by violent pains in the kidneys, in the salivary glands or the pancreas, occasioned by a stone, by injuries of the diaphragm, the nerves, &c. In all these cases, there is an affected point in the economy; from this point the sympathetic irradiations go off, which especially reach the brain; this irritated by them, enters into action and excites the muscles; their contraction takes place and the will is a stranger to it.

See also how the passions which have their influence particularly over the internal organs, which especially affect those placed around the epigastric centre, the heart, the liver, the stomach, the spleen, &c. imprint on our motions an impetuosity, which the will cannot make us masters of. The internal organ affected re-acts upon the brain, this excited stimulates the muscles; they contract, and the will is almost nothing in this contraction. Observe the man, whom jealousy, hatred or rage agitates to the greatest degree; all his movements follow each other with an impetuosity which judgment reproves, but which the will cannot moderate, so much does the influence of the sympathetic affection of the brain predominate over that of the will. At other times the passions exhibit an opposite phenomenon. They are marked by a general weakness of all the muscular motions. In astonishment accompanied with grief, or in that in which is mixed a lively joy, the arms fall down as it is commonly expressed; the cerebral influx ceases almost entirely, and yet it is not to the brain that the influence of this passion is carried, it is to the epigastric centre, as is proved by the sudden contraction which is felt there. One of the epigastric organs has been affected; it has reacted upon the brain; this has been interrupted in part in its functions; the muscles feel it and theirs cease. In fear in which this phenomenon is observed, as the paleness of the skin indicates the languor of the circulating system, it may happen that the cerebral and muscular inaction arises in great measure from this, that there is not received a sufficient impulse from the heart, upon which the first influence of the passion is exerted, and which by this influence is retarded in its motions. Fear, it is said, takes away the legs, petrifies, &c.; these expressions, borrowed from vulgar language, indicate the effect of this passion on the muscles; but this effect is only secondary; the first influence has been upon the heart, the second upon the brain; it is not till after the other two that the muscles are affected. Hence how certain animals remain immoveable at the sight of that which is about to seize them for its prey.

It is also to the sympathetic influence of the internal organs upon the brain, that should be attributed the motions of the fœtus, motions which the will does not direct; for the will is but a result of the intellectual phenomena; now these phenomena are nothing at this period of life. The internal functions then very active, suppose a great action in the liver, the heart, the spleen, &c.; now these organs in that way influence efficaciously the brain, and this in its turn puts the muscles in motion; so that the animal contractility is by no means voluntary in the fœtus; it does not begin to become so until the sensations have brought into action the phenomena of the understanding; until then, they must be compared to all those of which we have spoken above.

From all that has just been said, it will be easily understood, I hope, how the animal contractility can be or not subjected to the influence of the will. In both cases, the series of phenomena which it requires is always the same; there is always excitement by the brain, transmission by the nerves, execution by the muscles, or successive inactivity of these three organs. The difference is only in the cause which produces the cerebral excitement; now this cause can be, 1st, the will; 2d, an irritation immediately applied; 3d, a sympathetic irritation. It is essential to form precise and exact ideas concerning this vital force which performs so great a part in the living economy.

_Duration of the Animal Contractility after Death._

The difference of the causes which act upon the brain in the animal contractility, in order to determine it to excite the muscles, appears particularly in a remarkable manner at the instant of death. Whatever may be the way in which this happens, the intellectual functions are always the first to cease; it is even to this that we especially attach the idea of the absence of life. Whence it follows that the first phenomenon of this absence must be the failure of the muscular contraction subjected to the influence of the will, which is the result of these intellectual functions. Every thing then remains immoveable in the muscular system, if no other cause acts upon the brain or the nerves; but these two organs are, yet for a long time, capable of answering to the various excitements of stimuli. Stimulate in any way the brain, the spinal marrow or the nerves of an animal recently killed, in an instant its muscles convulsively contract; it is the same phenomenon as that obtained during life from the same cause. Often even immediately after death, this phenomenon is still more apparent than during life; I have been frequently convinced of this in my experiments. If during life we irritate any nerve, the contraction oftentimes is almost nothing, because the will acting by the other nerves upon the same muscle, or at least upon those of the limb, produces contractions opposite to those which the irritation tends to produce. I have many times observed that the galvanic phenomena are also infinitely more easily produced an instant after death, even in animals with red and warm blood, than during life; in this last case often we can obtain hardly any result, because their influence is counteracted by the cerebral influence arising from the will. When the irritation is directly applied to the brain or the superior part of the spine, it then surpasses the will; it is stronger in the living animal; but on an insulated nerve, it is often inferior to it; not that the will acts by the irritated nerve, its influence in it is arrested at the place stimulated, but it exerts itself by the adjacent nerves.