Part 29

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.