Part 45

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.

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.