CHAPTER VII.

OF THE INFLUENCE OF THE DEATH OF THE LUNGS OVER THAT OF THE BRAIN.

We have just seen, that in asphyxia, the movements of the heart are paralyzed, because its fleshy fibres are penetrated with venous blood. This fact should indicate the same to be the case with reference to the action of the brain. It is indubitably proved by experiment.

Whatever be the manner in which the pulmonary functions are interrupted, it is always the interruption of the chemical changes, which troubles the functions of the brain.[91] What I have said upon this point with respect to the heart, is exactly applicable to the cerebral mass: I shall not repeat it. It remains to shew by experiment, and the observation of diseases, that when the chemical functions of the lungs are put a stop to, it is the black blood which interrupts the action of the brain and that of the nervous system. In the first place let us examine our experiments.

I first began by transfusing into the brain of an animal, the arterial blood of another, that this essay might serve as a point of comparison for others. Open one of the carotids of a dog; tie the extremity towards the brain, and fasten a tube to that which is next the heart; then open the carotid of another dog, tie the extremity of the vessel next the heart, and fix the other end of the tube into that which is next the brain; then let the assistant, who meanwhile should have had his fingers upon the artery of the first dog underneath the tube, remove his compression, and the carotid of the second dog will be seen beating under the impulse of the blood injected from the heart of the first. This operation fatigues but little the animal which receives the blood, particularly if one of the veins be previously opened, to prevent too great a fulness of the vessels. It will live very well afterwards. This experiment has been often repeated, and always with the same results.

After this experiment, I opened the carotid, and the jugular vein of another dog, and after tying the extremity of the carotid next the heart, received the blood of the jugular into a warm syringe, and injected it into the brain. The creature appeared immediately to be agitated, breathed quickly, and seemed to be in a state of suffocation, similar to that of asphyxia. Its animal life became entirely extinct; the heart, however, continued to beat, and the circulation to go on for half an hour afterwards; at the end of which time the organic life was terminated also.

This dog was of a middle size, and about six ounces of blood were injected with a gentle impulse, for fear of that being attributed to the shock, which ought to have been the result of the nature and composition of the fluid. I repeated this experiment upon three dogs the same day, and afterwards at different times upon others; the result was invariable, not only as to the asphyxia of the animal, but even as to the concomitant appearances.

It might be thought that out of its vessels, and exposed to the contact of the air, the blood might imbibe a pernicious principle, or be deprived of that which is requisite for the maintenance of life. It might be imagined, that to this cause was owing the sudden death of the dog, on the injection of the brain with venous blood. To shew that this was not the case, I made a small opening in the jugular of a dog, to which I adapted a moderately warm syringe, and pumped the blood immediately from the vein.--It was afterwards thrown into the carotid: the symptoms were the same as the preceding, but less marked, and the death of the creature induced more slowly.--It is probable, then, that the air when in contact with the living blood without its vessels may alter it a little, but the essential cause of death is still the same.

Hence it appears that the black blood either is not an excitant capable of keeping up the cerebral action, or that it acts in a deleterious manner, upon the brain. The injection by the carotid of various other substances will produce analogous effects.

I have killed animals in this way with ink, oil, wine, and water coloured with indigo. The greater number of the excrementitious fluids, such as urine, bile, the mucus of catarrhs, occasion death also by their simple presence on the brain. The serosity of the blood is fatal, but not as quickly so. Now it is certainly upon the substance of the brain, and not upon the internal surface of the arteries, that these different substances exert their influence. I have injected them all into the crural artery. In this way they are none of them mortal, but occasion always a torpor, amounting even to paralysis at times.[92]

The black blood is doubtless fatal to the brain, the brain becoming at once a tonic from its presence. In what way does it act? I do not pretend to determine the manner; for this were only to begin a series of conjectures.

By this time we are authorised to conclude, that in asphyxiæ, the circulation which continues for some time after the interruption of the chemical functions of the lungs, interrupts the cerebral functions, from its being composed of black blood only. The fact is proved in another manner, for the movements of the brain continue to be made as usual.

If the cerebral mass be exposed, and the creature asphyxiated, the animal life will be extinguished, but the motion of the brain will be apparent still. Since then the latter cause of life subsists, the cause of death must be in the nature of the fluid, by which the organ is penetrated.

Nevertheless, if any affection of the brain coincide with asphyxia, the death which is occasioned by the latter, will be quicker than is usually the case. Strike a dog a violent blow upon the head, and then if he be deprived of air, he will die on the instant. In asphyxiating another animal already in a state of stupor, from compression of the brain, I observed that the vital functions were interrupted somewhat sooner, than when the brain is untouched during that operation; but the consequences hitherto deduced, may be supported by other experiments.

If in asphyxia the black blood suspend the action of the cerebral mass, it is evident that the black blood taken from the arteries of an animal dying of asphyxia, and injected into the brain of another, will be the cause of death.

The experiment will be found to succeed--cut the trachea, of a dog, and tie it up hermetically; then in the course of two or three minutes, open the carotid and receive into a syringe the blood, which flows from the vessels; inject it into the brain of another animal, and it will die.

The following experiment is very similar, but offers a somewhat different result. 1st. Adapt a tube with a stop-cock to the trachea of a dog, and a tube of silver to the carotid, next the head, after dividing this vessel, and tie up the extremity towards the heart. 2dly. Fix the other end of the tube to the divided carotid of another dog next the heart, and tie the extremity of the vessel towards the head. 3dly. Shut the cock of the tube in the trachea, and the black blood of the one dog in a short time, will be injected into the brain of the other.

The appearances above described will shortly afterwards succeed, but not so soon as in the former experiment, and if the transfusion be stopped, the animal which has been asphyxiated in this way, may recover and live. In the preceding experiment he will always die. It appears then that some extraneous pernicious principle is imbibed by the venous blood, when in contact with the air. Observe that for the latter experiment the dog from which the brain of the other is to be injected, must be stronger and more vigorous than the other. The reasons are evident.

I was desirous of trying whether the venous blood would not be capable of keeping up the cerebral action, if reddened artificially. For this purpose I opened the jugular and the carotid of a dog, and received the blood of the vein in a vessel filled with oxygen; it immediately became of a vivid purple, but on its injection into the brain, the animal was very suddenly killed. I was much surprised at this result, but ceased to be so on remarking, that a great quantity of air was mixed with the fluid, and that it arrived upon the brain, in a state of foam: now we know that a very small number of bubbles are sufficient to kill an animal, whether they be introduced on the side of the brain, or on that of the heart.

From this reflection, I was induced to repeat my experiments upon the injection of black blood, suspecting as I did that some small quantity of air might in these cases have been contained in the extremity of my syringe. I soon however recollected that if this cause were real, it should produce the same effect in every instance whatever were the fluid employed, now when water is injected there is nothing of the kind observable.

We may be thus assured that the black blood is either incapable of keeping up the action of the brain, or that it acts in a deleterious manner upon that organ, from the very nature of the principles, which it contains. From such datum it should appear that the life of the asphyxiated person might be restored, by pushing on into the brain a sufficient quantity of arterial blood, but here we must make a distinction of two periods in asphyxia: 1st. That in which the cerebral functions are only suspended: 2dly. That in which the circulation and the movements of the breast are stopped (for this disease is ever characterised by the sudden loss of all animal life, and consecutively by that of the organic life.) Now, as long as the first period of asphyxia continues, I have observed that, by the transfusion of red blood into the brain, from the heart of another animal, the movement of the creature which is dying will be restored by degrees, and the cerebral functions resume in part their activity; but this is only a temporary thing, and the animal will fall again into its previous dying state, if the asphyxiating cause be continued.

On the other hand, if during the first period, to which we have alluded, the air be readmitted, into the trachea, the lungs will be reanimated, the blood be coloured, and the creature be revived without the assistance of any transfusion; and such transfusion again is of no avail, after the second period of asphyxia, so that this experiment offers only a proof of what we already know; with respect to the difference of the influence of arterial and venous blood upon the brain, and not a remedy in case of asphyxia.

Again, whenever I have injected venous blood into the brain, by the help of a syringe, I have universally found that such proceeding is fatal. Though the cause of asphyxia be removed, and arterial blood injected, either with the syringe, or immediately from the heart of another animal, it is of little effect, and frequently of none whatever. And in general asphyxia when produced by blood, which has been taken from the venous system itself and pushed into the brain is much more certain and more decided, than that which is occasioned by ligature of the trachea, or the introduction of different gases into the lungs.

After having established by different experiments, how fatal the influence of the black blood is upon the brain, which receives it from the arteries whenever the chemical functions of the lungs are suspended, it will not be amiss or out of place to shew, that the phenomena of the asphyxia, which are observed in the human subject, accord with the experiments of which I have given the detail.

1st. It is generally known that every kind of asphyxia affects the brain in the first instance; that the functions of this organ are the first to be annihilated; that the animal life, and particularly the sensations cease; that all our relations with exterior objects are instantly suspended, and that the organic functions are only consecutively interrupted. Whatever be the mode of asphyxia, by submersion, strangulation, gases, or a vacuum, the same phenomena occur at all times.

2dly. It is known that the greater number of those who have escaped suffocation, have been sensible only of a general stupor, the seat of which has been evidently in the brain. It is known also, that death is almost always certain in these cases, while the pulse and the heart have ceased to be felt.

3dly. It is affirmed by almost all such persons as have survived this accident, especially when caused by the vapour of charcoal, that the first thing of which they were sensible, was more or less pain, in the head, an effect in all probability occasioned by the first influx of the black blood into the brain. This fact has been noted by the greater number of authors, who have written on asphyxia.

4thly. The vulgar expression that “charcoal flies to the head” is surely a proof that the brain, and not the heart, is the first affected in the asphyxia occasioned by this deleterious substance. The unprejudiced vulgar, oftentimes observe more correctly than we do, who frequently see only what we wish to see.[93]

5thly. There are many examples of persons, who after escaping the pernicious effects of the vapour of charcoal, have been subject afterwards to paralytic affections, and loss of memory. Such changes have evidently their seat in the brain. Convulsion also is frequently the effect of the impression of mephitic vapour: head-ache is a common symptom, and for the most part remains after the others have disappeared. In every book of cases may be seen examples of these affections.

In cold-blooded animals, and in reptiles especially, this influence of the black blood on the brain, though real, is much less apparent. Make an incision into both sides of the breast of a frog, then tie the lungs at their root, and the animal will live notwithstanding for a considerable time. Cut away the lungs entirely, and the same phenomenon will be remarked. In fish, the relation between the lungs and the brain, is somewhat more direct, for by the organization of the branchiæ, they differ essentially from reptiles. I have taken away the cartilaginous plate which covers the gills of the carp, the motion of the gills however continued to be made as before, and the animal lived without any apparent injury done to its functions. I afterwards put a ligature about the cartilaginous rings which sustain the branchiæ, so as to hinder all motion in the pulmonary apparatus. The effect was, that the animal languished, his fins dropt, his muscular movements soon grew weak, then ceased entirely, and the creature in the course of a quarter of an hour was dead. The same phenomena with some little variety, were observable in a carp from which I cut away the branchiæ.

After all however, the particular nature of those relations, which unite the heart, the lungs, and the brain, both in the red and cold-blooded animals, is well worthy the farther investigation of physiologists. The latter sort of animals, can neither be subject to syncope or apoplexy, or at least the character of these diseases must be very much modified in them. They are with much more difficulty asphyxiated. We shall now return to those species which bear a nearer resemblance to man.

From the influence of the black blood over the heart, the brain, and the rest of the organs, it was my opinion, that persons affected with varicose aneurisms, would perish less quickly from asphyxia then others; because the red blood passes into the veins, and traverses the lungs without requiring alteration. Accordingly, it should be capable of keeping up the cerebral action.

To be assured if this suspicion were well founded, I made a communication between the carotid artery and jugular vein of a dog, by means of a curved tube. The pulsation of the artery was thus communicated to the vein. I afterwards asphyxiated the animal by stopping the trachea, but the phenomena of death were little different from those of common asphyxia.

We may conclude with certainty, from the various considerations and experiments presented in the present chapter.

1st. That when the chemical phenomena of the lungs are interrupted, the black blood acts upon the brain, as it does upon the heart, by penetrating the tissue of that organ, and depriving it of the excitement, which is necessary to its action.

2dly. That its influence is much more rapid upon the first, than on the second of these organs.

3dly. That it is the inequality of such influence, which occasions the difference in the cessation of the two lives in the case of asphyxia. The animal life is always annihilated before the organic life.

We may conceive from what has been said in this and the preceding chapter, how unfounded are the suspicions of those who have supposed that the brain, after the separation of the head from the body by the guillotine, might live awhile and have sensation. The action of this organ is immediately connected with its double excitements.--1st, By motion; 2dly, By the nature of the blood which it receives. Now, when the interruption of such excitement is sudden, the interruption of every kind of feeling must also be sudden.

When the chemical functions of the lungs are suspended, the disturbance induced in the functions of the brain, has indeed a very considerable influence on the death of the other organs; nevertheless, such disturbance is the beginning of death only in the animal life, and even then is connected with other causes. The organic life ceases from the sole presence of the black blood among the different organs. The death of the brain is only an isolated and partial phenomenon of asphyxia, which does not take place in any particular organ, but in all alike. We shall explain this assertion in the following chapter.

FOOTNOTES:

[91] In a preceding article, Bichat maintains that the entrance of the arterial blood contributes to support the action of the brain, principally by the jar which it communicates to this organ. It is astonishing, after this, that he should attribute the suspension of the cerebral functions to the interruption of the chemical phenomena of respiration rather than to that of the mechanical phenomena. He could not however be ignorant, that it is to the last that must be referred the greatest of the two motions with which the brain is constantly agitated.

These motions of the brain in relation with those of respiration have been for a long time observed. Schitling has described them in a memoir inserted in the first volume of the Memoirs of Learned Foreigners. He has shown that the brain rises in expiration, and flattens in inspiration. Haller, Lamure and Lorry have since him investigated this motion, and they have given an explanation of it, which is defective only because they have been ignorant of the influence of respiration on the acceleration of the course of the blood in the arteries through the medium of the capillary vessels.

At the time of a strong expiration, all the pectoral and abdominal organs are compressed, and the arterial blood is forced more especially into the branches of the ascending aorta. This blood goes then in greater abundance towards the head, and has a tendency to pass more quickly in the veins which carry it towards the heart; which would take place immediately if the veins were free. But the pressure made on the pectoral organs has also made the venous blood flow back in the vessels which contain it. Now, this blood has just met that which comes from the arteries; the vessel is distended, and the course of the fluid is arrested in the veins; from that the brain swells and rises up; but as soon as expiration has ceased, the dilatation which takes place in the chest attracts, in some measure, the blood of the superior venæ cavæ; the veins which enter it are soon emptied and the brain flattens down.

In reflecting on the mechanism by which this movement of the brain is effected by the influence of respiration, we cannot perceive why the phenomenon should be limited to the organ contained within the cranium, and especially why the spinal marrow should not equally partake of it. The continuity of this organ with the cerebrum and cerebellum, its situation in a cavity which it does not entirely fill, the numerous arteries which it receives from the intercostal and vertebral arteries, the number and size of its veins destitute of valves are so many circumstances which should favour the accumulation of the blood at the time of expiration, and consequently produce its swelling. For the purpose of seeing if my conjectures were well founded, I have made some experiments; I laid bare in a young rabbit the spinal marrow at about the eighth or ninth dorsal vertebra, I saw it perfectly whole and surrounded by its coverings. At first I perceived no motion, but soon the animal being much incommoded by the position in which I kept him, made a deep inspiration, and then I saw distinctly the spinal marrow flatten, and a small vacuum between the dura mater and the osseous parietes of the vertebral canal. In the following expiration, the spinal marrow resumed its original size. I was unable to see any thing more in this animal.

I laid bare in a dog of middle size, the spinal marrow, a little above the lumbar region; I could not mistake there a very evident motion, in relation with respiration: a flattening during inspiration, and a swelling during expiration. The phenomenon was so marked, that the air entered the vertebral canal with a noise, whilst the animal inspired, and was forced out when the animal expelled the air from his lungs.

For the purpose of satisfying myself that this motion took place in the spinal marrow and not in the dura-mater, I cut this membrane in the whole extent of the opening made in the vertebral canal, and I was able easily to convince myself that the motion was from the swelling of the spinal marrow. I am not however certain that there is not a slight rising of the organ from the dilatation of the large veins in the anterior part of the vertebral canal, but this dilatation cannot be considerable, on account of the fibrous layer which covers the posterior face of these veins.

[92] Active substances introduced into the veins can act on the organs in many ways at once. They have at first their peculiar action which is nearly uniform, whatever may be the mode of administration; but they produce also other effects resulting from their physical properties, and these last may vary according to the form in which they are introduced.

The substances introduced into the circulation have necessarily to pass through a double system of capillary vessels, and must consequently be very greatly subdivided. Hence we see that a viscid fluid would be unable to enter the smallest vessels, and that by remaining in those which can admit it, it will prevent the passage of the blood, and occasion a congestion either of the lungs or some other organ, according as it has been injected into a vein or an artery. A substance like quicksilver, which without being viscid, exhibits great cohesion among its particles, will produce precisely the same effects. The globules will never divide below a certain size. The air itself, mixed in a fluid such as the blood, will form bubbles which will divide with more difficulty as they become smaller, and which can finally stop in the entrance of the capillaries, so as to prevent a free passage of blood in a part of these vessels. Boerhaave thought that it was always thus, by opposing a mechanical obstacle to the capillary circulation of the lungs, that air injected into the veins produced the death of the animal.

In an experiment in which I proposed to myself to change the nature of the blood by a foreign fluid, I injected into the jugular vein of a dog, an ounce of Olive oil, thinking that this substance would circulate without inconvenience with the blood; but it was not so, and the animal died in a few minutes after the injection.

In examining the organs after death, I saw that the oil had closed the last ramifications of the pulmonary artery, and that it had also stopped the circulation and respiration, by preventing the passage of the blood to the left side of the heart, by the pulmonary veins. An injection made with a thick solution of gum tragacanth produced precisely the same phenomena as the oil.

An inert, impalpable powder, suspended in water, immediately produces death, if injected into the jugular vein, because it shuts up the last divisions of the pulmonary artery.

If the injected substances are not divided at first in the blood, so as to spread uniformly into the different branches, death does not take place so quickly, because a part of the sanguineous canals remains free for the circulation. This is the case when we inject quicksilver or air in so small a quantity as not to produce instantaneous death. The congestion, in this last case, is often alone sufficient to produce it after a certain time; in the other case, there is added to the obstruction a real pneumonia caused by the presence of quicksilver in the obliterated vessels. We shall now relate four experiments of M. Gaspard, which will show the effects of the stagnation of this fluid in different organs.

“_First Experiment._ I introduced into the jugular vein of a small dog, four days old, thirty six grains of quicksilver purified through goat’s skin. Soon after he refused to suck, lost his vivacity, motility and heat, had dyspnoea and fever, and died at the end of twenty four hours, having been all the time much colder to the touch than the other pups with whom he was. On opening the thorax, the lungs were found much inflamed, almost hepatized, heavy, puckered up and full of mercury.”

“_Second Experiment._ I injected into the left carotid artery of a sheep, very near the brain, half an ounce of mercury with water; I then tied with a double ligature the open vessel. The animal immediately manifested pain, and was for an instant immoveable, the head inclined, with stupor and a prominence of the eyes, which were extraordinarily open; then bending on the fore legs, twisting of the head and neck on the right shoulder, with a kind of stiffness or convulsive elasticity, which was always present till death, and returned, as by the effect of a spring, when I straightened the neck. Two hours after, standing impossible, state of drowsiness, some convulsive motions of the limbs, the left eye swelled, red and inflamed. The next day, the same state, almost total annihilation of the animal or external life, copious excretion of mucus by the left nostril, the eye still very large and inflamed. The third day, the same state; death took place fifty hours after the injection. On examination of the body it was found that the left eye was in a state of suppuration and contained mercury; the thyroid, pharyngeal auricular, lingual, labial, nasal and cerebral arteries of the left side, were admirably injected with this metal which run out under the instrument; but their capillary terminations contained none of it, and we could see to what ramification, to what sized caliber it had penetrated, and the point where it was unable to pass; the left nasal cavities exhibited a very pretty reticulated appearance, brilliant and silvery. Moreover all the organs of this side were red, inflamed and swelled by the presence of the foreign body, and it was curious to see the half of the thyroid gland, the tongue, the cheeks and the lips thus red and inflamed to the median line, whilst the other half was sound and pale; the left brain was slightly inflamed and especially the plexus choroides. Besides, I was unable to discover a globule of quicksilver in any of the other organs.”

“_Third Experiment._ I forced with a pewter syringe into the crural artery of a large dog, a drachm and a half of quicksilver mixed with common water. The animal, immediately after the double ligature, did not manifest any sign of pain, and walked, bearing less on that limb, which was very sensibly cold, though not paralyzed. But about an hour after, he refused food, manifested by piercing cries acute pain, constant agitation, frequent change of place, and a very evident state of suffering; the limb soon after grew warm, became hot to the touch, with an obscure pulse under the tendo Achillis. This state of fever and pain continued the whole day and night. The next day, the limb was swollen and exhibited a phlegmonous œdema preserving the impression of the finger; the plaintive cries were continual. On the third day his condition was still worse, and I then killed him from compassion sixty hours after the injection. I had carefully noticed the matter of the excretions, without discovering a particle of quicksilver in them. On examination of the body, I could not discover it in any organ, except the limb subjected to the experiment, which was swollen, inflamed and oedematous in all its textures; we observed abscesses in it of different sizes, containing quicksilver, pus, sanies and much gas, coming from the incipient gangrene of the parts; the metal usually occupied the centre of all the abscesses; the mercurial globules flowed out when I cut the skin, the cellular texture, the muscles and especially the small arteries, which were admirably injected by it; gelatinous exudations occupied the interstices of the muscles.”

“_Fourth Experiment._ I injected a drachm of quicksilver, that had been passed through goat’s skin, into the mesentric vein of a dog of middle size. The animal exhibited several severe symptoms which I shall not mention, because they probably depended on the opening of the abdomen and the inflammation that resulted from it; perceiving that they would become fatal, I killed him by another experiment, fifty two hours after the first. On opening the body, I found all the mercury in the liver; each globule was the centre of a small collection of pus, of which it was the cause; but the liver was but slightly diseased, but little inflamed, and only blacker and more gorged with blood than usual. The stomach contained an unusual quantity of very green bile; I could not discover any quicksilver in the other organs.”

We see from all these different facts, that it is necessary for every thing that enters the circulation to arrive at it by very narrow channels, and after having been, as it were, sifted by the agents of absorption; this is one use of the absorbent organs that has not as yet been noticed. These facts also throw light on the properties of substances injected into the veins of animals, after having been dissolved in oil. We can believe that when these oily solutions are carried into the intestinal canal, they are not absorbed till after they have been gradually changed into a kind of emulsion, and we know that in this form fatty substances may be introduced with impunity into the circulation. We can in fact inject into the veins a large quantity of milk, and the portion of butter which is suspended in it, will not produce the effects which would necessarily result from it, if we injected this substance pure and only rendered liquid by heat.

[93] Is it true that common people observe without prejudice? Have they not, on the contrary, on several physiological and pathological phenomena deeply rooted prejudices? It is besides a very singular idea to wish to judge by the name which they give to an affection, of the organ primarily affected. If we always reasoned in this way the expression of _sick at heart_ which is given to nausea, would assign to vomiting a wholly different nature from what would be correct.