FOOTNOTES:[73]Life is so obscure in the tendons, ligaments, &c. that it is impossible to fix the moment when it ceases in these parts. How then has Bichat been able to compare the quickness of their death with that of the other organs? Upon what data has he been able to determine that it takes place more slowly?[74]The secretion of mucus, the growth of the nails, the beard and the hair often continue on the dead body long after the last traces of irritability have disappeared in the muscles of locomotion, in the fleshy coats of the intestines, &c.[75]Since more care has been taken in examining the lesions of different organs in post mortem examinations, there is no longer found those fatty polypi, which were formerly considered as causes of death. It is probable that those yellowish concretions of albuminous matter which are found between the pillars of the auricle, and which seem to be fixed there, were mistaken for polypi. There is sometimes found in individuals formerly affected with the venereal disease, vegetations near the valves; but these productions are commonly too trifling to oppose the expulsion of the blood contained in the cavity.[76]The singular idea of placing the seat of madness in the viscera of the abdomen, arose at a period when a certain number of mystical ideas formed the basis of all physiology. The four sorts of humours performed in the human body (microcosm) a part as important as the four elements did in the whole universe (macrocosm). The bile, the blood, the pituitary and atrabiliary fluids determined, by their predominance the different temperaments, and produced the different diseases. The atrabiliary humour was, as is well known, thought to be the cause of melancholy and mania; now this humour was said to be secreted by the supra-renal capsules, and the position of these organs no doubt gave the name of hypochondria, which is given to a certain degree of mental alienation.After a great number of ages, the mysterious properties of numbers are almost entirely out of favour. We still speak of the four temperaments, but attach no importance to the four ages of man or to the four parts of the day. We recognize in the human body more than four kinds of fluids, but among them all we do not find the atrabiliary fluid. The cause of madness then cannot be attributed to this humour, and yet we dare not drive this disease from the seat it has so long held. In order to find reasons for keeping it there, they seek in the viscera for disorders which are not often found there even in the most striking cases, and which most often still exist without the least alteration in the intellectual functions.[77]We should be often exposed to commit great mistakes, if we always judged by this rule. The sensation is a very uncertain means of determining the organ that is primarily affected; this can be proved by numerous examples, we shall cite one only which relates to the brain. Nausea and vomiting are often, as is well known, among the first symptoms of cerebral affections; should we from this believe that the seat of the disease is in the stomach? Undoubtedly not: now, in syncope produced by a strong affection of the mind, there is no reason to suppose that the heart is affected before the brain, since the intellectual phenomena have necessarily preceded the sensation of joy or of sorrow which has produced the syncope. But to say that the brain was primarily affected, is not saying that its action ceased before that of the heart; and every thing, on the contrary, leads to the belief that the loss of the senses is a consequence of the suspension of the circulation.[78]The syncope is produced in this case, from the sudden change in the circulation of the brain. But this change varies according to the seat of the effusion. If it be in the peritoneal cavity, the pressure that it makes interrupts the circulation in all the organs contained in the abdomen; the descending aorta is found compressed, and the blood, forced back towards the superior parts, accumulates in the sinuses and vessels of the brain. If the fluid be evacuated by puncture, the equilibrium is re-established in the different parts of the vascular system, the blood enters vessels which were before closed to it, it abandons in part those of the brain, and it is this sudden change in the circulation of the organ which produces syncope. If, on the contrary, the effusion be formed between the two layers of the arachnoides, and we can, as in spina bifida, evacuate the fluid by puncture, the vessels of the brain are immediately relieved of the pressure to which they had been subjected, and the blood, which before was forced back, towards the inferior parts, is driven forcibly into them; the change is, as must be perceived, the reverse of the preceding; but the result is the same, and syncope is produced in this case as in the other.
[73]Life is so obscure in the tendons, ligaments, &c. that it is impossible to fix the moment when it ceases in these parts. How then has Bichat been able to compare the quickness of their death with that of the other organs? Upon what data has he been able to determine that it takes place more slowly?
[73]Life is so obscure in the tendons, ligaments, &c. that it is impossible to fix the moment when it ceases in these parts. How then has Bichat been able to compare the quickness of their death with that of the other organs? Upon what data has he been able to determine that it takes place more slowly?
[74]The secretion of mucus, the growth of the nails, the beard and the hair often continue on the dead body long after the last traces of irritability have disappeared in the muscles of locomotion, in the fleshy coats of the intestines, &c.
[74]The secretion of mucus, the growth of the nails, the beard and the hair often continue on the dead body long after the last traces of irritability have disappeared in the muscles of locomotion, in the fleshy coats of the intestines, &c.
[75]Since more care has been taken in examining the lesions of different organs in post mortem examinations, there is no longer found those fatty polypi, which were formerly considered as causes of death. It is probable that those yellowish concretions of albuminous matter which are found between the pillars of the auricle, and which seem to be fixed there, were mistaken for polypi. There is sometimes found in individuals formerly affected with the venereal disease, vegetations near the valves; but these productions are commonly too trifling to oppose the expulsion of the blood contained in the cavity.
[75]Since more care has been taken in examining the lesions of different organs in post mortem examinations, there is no longer found those fatty polypi, which were formerly considered as causes of death. It is probable that those yellowish concretions of albuminous matter which are found between the pillars of the auricle, and which seem to be fixed there, were mistaken for polypi. There is sometimes found in individuals formerly affected with the venereal disease, vegetations near the valves; but these productions are commonly too trifling to oppose the expulsion of the blood contained in the cavity.
[76]The singular idea of placing the seat of madness in the viscera of the abdomen, arose at a period when a certain number of mystical ideas formed the basis of all physiology. The four sorts of humours performed in the human body (microcosm) a part as important as the four elements did in the whole universe (macrocosm). The bile, the blood, the pituitary and atrabiliary fluids determined, by their predominance the different temperaments, and produced the different diseases. The atrabiliary humour was, as is well known, thought to be the cause of melancholy and mania; now this humour was said to be secreted by the supra-renal capsules, and the position of these organs no doubt gave the name of hypochondria, which is given to a certain degree of mental alienation.After a great number of ages, the mysterious properties of numbers are almost entirely out of favour. We still speak of the four temperaments, but attach no importance to the four ages of man or to the four parts of the day. We recognize in the human body more than four kinds of fluids, but among them all we do not find the atrabiliary fluid. The cause of madness then cannot be attributed to this humour, and yet we dare not drive this disease from the seat it has so long held. In order to find reasons for keeping it there, they seek in the viscera for disorders which are not often found there even in the most striking cases, and which most often still exist without the least alteration in the intellectual functions.
[76]The singular idea of placing the seat of madness in the viscera of the abdomen, arose at a period when a certain number of mystical ideas formed the basis of all physiology. The four sorts of humours performed in the human body (microcosm) a part as important as the four elements did in the whole universe (macrocosm). The bile, the blood, the pituitary and atrabiliary fluids determined, by their predominance the different temperaments, and produced the different diseases. The atrabiliary humour was, as is well known, thought to be the cause of melancholy and mania; now this humour was said to be secreted by the supra-renal capsules, and the position of these organs no doubt gave the name of hypochondria, which is given to a certain degree of mental alienation.
After a great number of ages, the mysterious properties of numbers are almost entirely out of favour. We still speak of the four temperaments, but attach no importance to the four ages of man or to the four parts of the day. We recognize in the human body more than four kinds of fluids, but among them all we do not find the atrabiliary fluid. The cause of madness then cannot be attributed to this humour, and yet we dare not drive this disease from the seat it has so long held. In order to find reasons for keeping it there, they seek in the viscera for disorders which are not often found there even in the most striking cases, and which most often still exist without the least alteration in the intellectual functions.
[77]We should be often exposed to commit great mistakes, if we always judged by this rule. The sensation is a very uncertain means of determining the organ that is primarily affected; this can be proved by numerous examples, we shall cite one only which relates to the brain. Nausea and vomiting are often, as is well known, among the first symptoms of cerebral affections; should we from this believe that the seat of the disease is in the stomach? Undoubtedly not: now, in syncope produced by a strong affection of the mind, there is no reason to suppose that the heart is affected before the brain, since the intellectual phenomena have necessarily preceded the sensation of joy or of sorrow which has produced the syncope. But to say that the brain was primarily affected, is not saying that its action ceased before that of the heart; and every thing, on the contrary, leads to the belief that the loss of the senses is a consequence of the suspension of the circulation.
[77]We should be often exposed to commit great mistakes, if we always judged by this rule. The sensation is a very uncertain means of determining the organ that is primarily affected; this can be proved by numerous examples, we shall cite one only which relates to the brain. Nausea and vomiting are often, as is well known, among the first symptoms of cerebral affections; should we from this believe that the seat of the disease is in the stomach? Undoubtedly not: now, in syncope produced by a strong affection of the mind, there is no reason to suppose that the heart is affected before the brain, since the intellectual phenomena have necessarily preceded the sensation of joy or of sorrow which has produced the syncope. But to say that the brain was primarily affected, is not saying that its action ceased before that of the heart; and every thing, on the contrary, leads to the belief that the loss of the senses is a consequence of the suspension of the circulation.
[78]The syncope is produced in this case, from the sudden change in the circulation of the brain. But this change varies according to the seat of the effusion. If it be in the peritoneal cavity, the pressure that it makes interrupts the circulation in all the organs contained in the abdomen; the descending aorta is found compressed, and the blood, forced back towards the superior parts, accumulates in the sinuses and vessels of the brain. If the fluid be evacuated by puncture, the equilibrium is re-established in the different parts of the vascular system, the blood enters vessels which were before closed to it, it abandons in part those of the brain, and it is this sudden change in the circulation of the organ which produces syncope. If, on the contrary, the effusion be formed between the two layers of the arachnoides, and we can, as in spina bifida, evacuate the fluid by puncture, the vessels of the brain are immediately relieved of the pressure to which they had been subjected, and the blood, which before was forced back, towards the inferior parts, is driven forcibly into them; the change is, as must be perceived, the reverse of the preceding; but the result is the same, and syncope is produced in this case as in the other.
[78]The syncope is produced in this case, from the sudden change in the circulation of the brain. But this change varies according to the seat of the effusion. If it be in the peritoneal cavity, the pressure that it makes interrupts the circulation in all the organs contained in the abdomen; the descending aorta is found compressed, and the blood, forced back towards the superior parts, accumulates in the sinuses and vessels of the brain. If the fluid be evacuated by puncture, the equilibrium is re-established in the different parts of the vascular system, the blood enters vessels which were before closed to it, it abandons in part those of the brain, and it is this sudden change in the circulation of the organ which produces syncope. If, on the contrary, the effusion be formed between the two layers of the arachnoides, and we can, as in spina bifida, evacuate the fluid by puncture, the vessels of the brain are immediately relieved of the pressure to which they had been subjected, and the blood, which before was forced back, towards the inferior parts, is driven forcibly into them; the change is, as must be perceived, the reverse of the preceding; but the result is the same, and syncope is produced in this case as in the other.
We have already said, that the functions of the lungs are of two kinds, mechanical and chemical. Now the activity of this organ ceases sometimes by the former, and sometimes by the latter of these functions.
Any wound, which exposes the lungs on both sides, for a considerable extent, occasions their sudden collapse; any division of the spinal marrow, which suddenly paralyses the intercostals, and the diaphragm; any very strong compression exerted at the same time upon the whole of the thorax, and the parietes of the abdomen, any sudden injection of a large quantity of fluid into this cavity, are all of them causes which begin the death of the lungs, by putting an end to their mechanical functions. Those which influence in the first place their chemical functions, are the different sorts of asphyxia, strangulation, submersion, and a vacuum, in whatever manner produced.
The interruption of the functions of the heart, can only succeed in two ways to that of the mechanical functions of the lungs: 1st. Directly, because a mechanical impediment is put to the circulation of the blood, by a state of collapse in the lungs. 2dly. Indirectly, becausein such state the lungs no longer receive the materials, upon which their chemical functions are exerted, and therefore cannot transmit them to the heart.
Physiologists have all of them admitted the first mode of interruption, in the Pulmonary circulation. Reflected on themselves, the vessels of the lungs have not appeared to them, to be capable of transmitting the blood, on account of the numerous angles which they make. This idea they have borrowed from the phenomena of hydraulics, and it is their reason for the death which ensues, in consequence of a too long continued expiration.
Notwithstanding all which, it has been proved by Goodwyn, that in such case there remains a sufficient quantity of air in the air vessels, for dilating them enough to allow of the mechanical passage of the blood; he proves in consequence, that an unnatural permanence of the state, in which the lungs are placed from the act of expiration, does not affect the blood in the way, which is commonly believed. This is one step towards the truth, but we shall approach it much more nearly, and even attain it, should we be able to prove, not only that there remains a sufficiency of air in the lungs to permit the transmission of the blood, but that the very folds produced in the vessels by a state of collapse in the organ are not a real impediment to its course. The following observations and experiments will assuredly determine this fact.
1st.—I have already proved, that a state of fulness or emptiness in the stomach, and in all the hollow organs in general, produces no apparent change in the state of their circulation; and that the blood in consequence, will traverse the vessels, when bent or doubled upon themselves, as easily, as when they are distended in every direction. For what reason should a different effect beproduced in the lungs, by the same disposition of the parts?
2dly.—There are different vessels in the œconomy which we may alternately bend or extend at pleasure: such are those of the mesentery, when exposed by an incision into the abdomen of the animal. Now in this experiment, which has been already made to prove the influence of the tortuous direction of the arteries upon the mechanism of their pulsation, if one of the mesenteries be opened, and then either bent or extended, in either case the blood will be thrown out with the same degree of violence, and in equal times will be emitted in equal quantities. I have always obtained the same result in this experiment which I have many times repeated. From analogy we might expect the same from the vessels of the lungs;[79]and from the following experiment it may be proved.
3dly.—Take a dog, cut the trachea, and adapt the tube of an injecting syringe to it, then make a vacuum in thelungs, and cut the carotid artery. It is evident, that according to the common belief, the circulation should be immediately suspended, in this experiment, since the pulmonary vessels from their ordinary state of distension,must have passed to the greatest possible degree of collapse, in consequence of the total abstraction of air; notwithstanding which the blood will be violently thrown out from the divided arteries for a certain time, and must consequently traverse the lungs: it will afterwards cease by degrees, but this, from causes which I shall explain hereafter.
4thly.—The same effect may be produced by opening, on both sides, the breast of a living animal, because the warm and rarified air of the lungs, will be more than balanced by the pressure of the colder air without;[80]now,neither in this case does the circulation experience any sudden change. For the sake of greater exactness, thelittle air remaining in the cells of the organ may be voided by a syringe.
Along with these observations let us place the facility with which the pulmonary circulation continues to be made, when collections of water, pus, or blood, are lying within the pleura, or pericardium. In these cases the air vessels are often prodigiously contracted, and consequently the vessels of their parietes doubled and bent.[81]If this state be taken into consideration, we shall have sufficient data for concluding that the tortuous disposition of the vessels, can never be an obstacle to the passage of the blood; and therefore, that the interruption of the mechanical functions of the lungs, can never directly put a stop to the action of the heart, though it may do so indirectly, in impeding the exercise of the chemical functions of the lungs.
If then we can determine why the heart remains inactive, when the latter phenomena are annihilated, we shall have resolved a double question.
Many authors have asserted that the death, which ensues after a too long continued inspiration, is owing to the mechanical distension of the pulmonary vessels by the rarified air, a distension impeding the circulation.But this reason also is as false a one, as that which we have already disproved. Inflate the lungs as powerfully as may be, then tie the trachea and open the carotids, and the blood will flow as impetuously as when the respiration was perfectly free.[82]
According to Goodwyn, the reason why the contractions of the heart are stopped, when the chemical functions of the lungs have ceased to be performed, consists in the want of that excitement which the red blood only can produce upon the red-blooded ventricle. This ventricle, says he, has not a sufficient stimulus in the black blood, and death is occasioned because it no longer is capable of transmitting any thing to the different organs. In this case death must happen, as it would from ligature of the aorta—precisely in the same way as when its source is exclusively in the heart. The other parts die only for want of blood, just as when in a machine, the principal spring being taken away, the others cease to act, because they are not put into action.
On the contrary, I am persuaded that there is a general affection of all the parts, whenever the chemical functions of the lungs are suspended; I am persuaded that the black blood continues to be pushed on for some time by the aorta, and that its influx into the organs is the occasion of their death; that the organs die in fact, not because they do not receive blood, but because they do not receive red blood; in a word, that they are penetratedby the material cause of their death; so much so, that we may asphyxiate any isolated part at will, by injecting it with venous blood while all the others shall continue to receive the red blood of the heart. At present I shall inquire into the phenomena of the contact of the black blood with the parietes of the ventricle, and refer the reader to the following chapters, for its effects upon the other parts.
The movements of the heart may be stopped and made to cease altogether from the influence of the venous blood in two ways.—1st. As Goodwyn has said, because the left ventricle is not excited by it upon its internal surface.—2dly. Because such fluid, when carried into the substance of the heart by the coronary vessels, must act upon the muscular fibre of the heart in the same way as it does upon the other muscles. Now, for my part, I am assured that the black as well as the red blood, will excite into contraction the internal surface of the aortic ventricle. The following observations and experiments will confirm my assertion.
1st. If asphyxia were to be followed by the consequences which Goodwyn has supposed, it should influence the heart in the first place; the annihilation of the functions of the brain, as in syncope, should be only secondary; nevertheless, asphyxiate an animal, by stopping up the trachea, by placing him in a vacuum, by opening the chest, or plunging him into carbonic acid gas, and it will in every instance be observed, that his animal life is the first to be interrupted, and that the creature externally is dead; but that within the heart continues for some time afterwards to act, and the pulse to be felt.
In this way the symptoms of asphyxia are not the symptoms of syncope. In the latter the cardiac and cerebral actions are suspended at the same instant, in theformer the heart survives, as in cases of strong concussion of the brain for many seconds. It follows, that in asphyxia, the different organs do not cease to act, because the heart has ceased to supply them with blood, but because it no longer supplies them with that sort of blood by which they can be stimulated.
2dly. If the trachea of an animal be stopped, and an artery opened, the colour of the blood which it emits, will gradually be changed, and at last become as black as that of venous blood. Now, notwithstanding this phenomenon, which is as apparent as it can be, the fluid for some time afterwards is thrown out full as strongly as it would be, were it red. I have seen a quantity of black blood discharged in this way, more than sufficient to kill the creature from hæmorrhage; were it not already dead, in consequence of its asphyxiated state.
3dly. In the last-mentioned experiment, it may, indeed, be alleged, that some remains of air in the air cells, might, as long as the black blood continued to flow, have communicated to it a principle of excitement; but to put it out of all doubt, that the venous blood does really pass into the aortic ventricle, unaltered in its passage from the corresponding cavity, the air may be entirely pumped out of the lungs with a syringe, by exposing the trachea, in the first place, and then adapting the instrument to the transverse section of the tube; after this, let the carotid be opened; now as soon as the red blood contained in this artery is exhausted, the black blood will succeed to it, and that, without undergoing a variety of gradations in colour; in this case also for a time, the jet will be very powerful, and only be gradually weakened; but if the black blood were not an excitant to the heart, its interruption should be immediate.
4thly. The following is another proof of the same nature. Expose the breast on one side by sawing exactly through the ribs before and behind: when this is done, the lungs on that side will collapse. Proceed to open one of the pulmonary veins; fill a syringe warmed to the temperature of the human body with venous blood, then push it into the red-blooded ventricle. Now, according to the common opinion upon the subject of asphyxia, such fluid should at least diminish in a sensible way, the movement of that cavity, notwithstanding which, in four successive experiments, I could not observe any such diminution. On the contrary, in one of them, on pushing the piston, the strokes of the heart were augmented in number.
5thly. If the black blood be not an excitant to the heart, it can only want such power, because it contains more carbon and hydrogen, than the red blood;[83]but if the heart of an animal, which has been killed expressly for the experiment, by lesion of the brain or of the lungs, has ceased to beat, it may, notwithstanding, be made to contract as long as it preserves its irritability, by throwing into the aortic ventricle either hydrogen gas, or carbonic acid gas. It follows, that neither hydrogen gas nor carbon can act as sedatives to the heart.
The experiments which I made and published last year, on the emphysemata, produced in different animals with these gases, have established the same truth with respect to the muscles, since they do not cease to move in consequence of such experiments, and after death, preserve their irritability as they usually do.
Lastly. I have often succeeded in re-establishing the contractions of the heart, which have been annihilated in different sorts of violent death, by the injection of black blood into the red-blooded cavities, with a syringe adapted to one of the pulmonary veins.
Thus it is proved, that the red-blooded heart does actually push the black blood into all parts of the body; and in this way is the colour given to the different surfaces, of which, in one of the following chapters, I shall offer a sketch.
Neither does the simple presence of the black blood act in a more sedative way upon the internal surfaces of the arteries.[84]If, in fact, while the tube adapted to the trachea is shut, the blood be made to flow from an artery of the foot, it will be thrown out for some time, with the same force which it would have been, were the pipe to be open. The action, then, which it exercises in its passage from the heart, upon the parietes of the arteries, does not diminish the energy of these parietes. When this energy decreases, it is at least in part from a different cause.
From the above experiments we may conclude, that the black blood arriving in mass at the red-blooded ventricle, and correspondent arterial system is able, from its sole contact with them, to occasion the action of these cavities; we may be equally certain, that were not the functions of these parts suppressed from other causes, the circulation would continue to be made in a very sensible manner, at least, if not with force.
Of what nature, then, are the causes which interrupt the circulation in the heart and arteries when they aresupplied with venous blood? for when this has been flowing for some time, the jet of it is gradually weakened, and ceases at last entirely; yet if the cock of the pipe be opened, it will be restored with vigour.
I am persuaded that the black blood acts upon the heart as it does on all the other parts, as we shall see that it affects the brain—that it affects the voluntary muscles, the membranes, and the system in general; the tissue of which it penetrates and operates within it as a debilitant upon each individual fibre. I am fully of opinion, that the circulation would be almost as quickly interrupted as in the preceding cases, were it even possible to supply the coronary arteries of the heart with red blood, while the black blood is transmitted to the various parts of the body by the aortic auricle and ventricle.
The black blood operates by its contact with the fleshy fibres, at the extremity of the arterial system and not by its contact with the internal surface of the heart. Thus it is only by little and little, and when each fibre has been as it were injected, that the powers of such fibres diminish and cease. On the contrary supposition, their cessation and diminution should be almost sudden.
It may be demanded in what manner the black blood acts at the extremities of the arteries, upon the fibres of the different organs. Is it upon the fibres themselves, or upon the nerves which are distributed to them? I am rather inclined to suppose the latter to be the fact, and to consider asphyxia as an effect produced in general by the black blood upon the nerves, which every where accompany the arteries of a certain diameter: for as we shall presently see, the debility which in such case the heart experiences, is only a particular symptom of a disease in which the organs in general are the seat of a like debility.
It might be demanded also in what way, that is to say, by what manner of influence, the black blood acts upon the nerves or fibres. Is it from the principles which it actually contains, or from the absence of those which are proper to the red blood? Is oxygen the principle of irritability—are hydrogen and carbon the reverse?
These questions have been sufficiently disputed.—Let us stop when we arrive at the limits of rigorous observation. Now, I think, that we shall establish an assertion the most strictly conformable with such principle, in saying generally and without determining the manner, that the heart ceases to act, when the chemical functions of the lungs are interrupted, because the black blood with which its fleshy fibres are penetrated, is not of a nature to keep up their action.
From this manner of regarding the phenomena of asphyxia with relation to the heart, it is evident that both the ventricles should be equally affected by it, because their parietes must be equally injected with venous blood. Nevertheless, it is constantly observable, that the movement of the red-blooded heart is the first to stop; that the black-blooded heart in every case the ultimum moriens; but this phenomenon does not suppose a more real, a more decided debility in the one, than in the other heart; for as Haller observes, the fact is common to every kind of death in the red-blooded animal, and not the case particularly in asphyxia.—Besides, were the red-blooded heart the first to be absolutely affected, as the theory of Goodwyn supposes, the following would be the appearances on opening the asphyxiated subject.—1st. A distension of the corresponding auricle and ventricle, by the black blood which they would not be able to expel into the aorta.—2dly. An equal fulness of the pulmonary veins and lungs.—3dly. A consequent fulness andswelling of the pulmonary artery and the black-blooded cavities. In a word, the congestion of the blood should be the greatest in that of its reservoirs, whose action is the first to cease.
But this is contrary to observation—for 1st. In the asphyxiated subject, the red-blooded cavities and pulmonary veins, contain but a very small quantity of blood in proportion to that which distends the opposite heart. 2dly. The place where the blood has stopped, is found to be principally in the lungs, in the lungs must we begin to follow its accumulation into the venous system. 3dly. The arteries are as full of blood as their correspondent ventricles, and consequently it cannot be in the ventricle more than elsewhere, that death has been begun.
But what is the reason why the black-blooded heart is the last to beat? because, says Haller, it is the longest excited; because it contains a greater quantity of blood; because the blood is sent into it from the largest veins of the system, and regurgitates from the lungs. The famous experiment is well known by which in emptying the black-blooded cavities, and tying the aorta so as to retain the blood within the red-blooded cavities, the contractions of the latter are prolonged so much beyond the contractions of the former. But in this experiment it is manifestly the black blood which accumulates in the aortic auricle and ventricle, because the breast must be preliminarily opened, and therefore the lungs collapse.
Should a more direct proof be required, immediately before the experiment, let the trachea be closed with a syringe, and the air of the lungs be voided; the experiment will just as well succeed; besides, the operator to be sure of the colour of the blood in the aortic cavities, has nothing more to do than to open them, as soon as he has finished his experiment.
We shall conclude that the black blood is almost as powerful a stimulus as the red blood to the inner surface of those cavities, which usually contain the latter only: the reason why they are the first to be arrested in their action, is, because they do not receive so large a quantity of blood as the others.
Notwithstanding what I have said, I do not entirely reject the idea of the red-blooded ventricle being not excitable by the black blood. It may indeed be less excitable by this sort of blood, than by the other; but I believe that the preceding considerations will reduce this difference of excitement to a mere trifle.
The following, however, is an experiment where such difference would appear to be very manifest. If a stop cock be adapted to the trachea, and an artery opened, the blood will blacken, and continue for some time to be thrown out with its ordinary force, but at last the jet will gradually grow weaker. If, after this, the air be admitted, the blood will almost immediately become red and its jet be visibly augmented. In this case the sudden augmentation appears at first to depend upon the simple contact of the red fluid with the sides of the aortic ventricle, since it has not had the time to penetrate the tissue of the heart; but let things be a little attentively examined, and it will soon be seen that this impetuosity of impulse, depends on the movements of inspiration and expiration, to which the animal is obliged, on the admission of air into the lungs. The heart excited at its exterior, and perhaps a little compressed by these movements, is the occasion of such phenomenon, and expels the blood with a force which is far beyond that which results from its habitual contractions.
What I have here advanced is proved, by the manifest diminution of the jet, as soon as once the lungs have takenon their accustomed degree of action. Besides, the influence of a series of full expirations may be manifested without dividing the trachea. Open the carotid and precipitate the respiration of the animal by tormenting it (for pain will constantly have this effect) and the jet of blood will be visibly increased. The same augmentation may be artificially produced, by suddenly compressing the parietes of the thorax. These experiments succeed best on animals already weakened by the loss of a certain quantity of blood.
In the ordinary state of health however, a series of strong expirations will not be found to quicken the pulse. Of this I cannot assign the reason.
From what we have now said, it follows, that the experiment, in which, on the opening of the cock of the syringe, the blood is thrown out with augmented force, is not so conclusive as might at first be imagined. I confess that it embarrassed me much for many days, I hold then my former conclusions to be good.
In the red and cold-blooded animals, the action of the lungs has not so immediate a connexion with that of the heart, as it has in the red and warm blooded animals.
I tied the lungs of two frogs at their basis, having previously exposed them, by incisions made laterally into the breast, the circulation however continued as usual for a considerable time. After this experiment, I have seen on opening the breast, the movements of the heart precipitated, a circumstance depending no doubt upon its contact with the air.
I shall finish this chapter by the examination of an important question, and inquire into the reason, why when the chemical functions of the lungs are stopped, the pulmonary arteries, the black-blooded cavities of the heart, and in a word all the venous system, are found so muchmore full of blood, than the aortic system. In such case the circulation appears at first to be interrupted in the lungs, and then in the other parts, according to their proximity to the lungs.
This phenomenon must have been observed by all who have opened the asphyxiated subject. It has been explained by Haller and others, from the tortuosity of the vessels; but this opinion I have sufficiently refuted.[85]
But before I proceed to assign a more real cause, I shall observe, that the lungs, (when the blood is first arrested, because it finds in them the first obstacle to its progress,) are found in a singularly various state, according to the kind of death of which the individual has died. In sudden, in instantaneous death, neither the lungs, nor the black-blooded heart are very much distended.
I have observed this fact, 1st. In the bodies of two persons who had hanged themselves and were brought into my amphitheatre. 2dly. On two subjects who had fallen into the fire, and were instantly suffocated. 3dly. On dogs which I have suddenly drowned. 4thly. Upon guinea-pigs, which I have killed in a vacuum, or in different gases, or otherwise.
On the contrary, arrest the phenomena of respiration in a gradual manner; drown the animal by plunging him in water, and taking him out alternately, asphyxiate himby placing him in a vessel of gas imperfectly closed, continue as long as possible such state of pain and anguish, and the lungs will be found extremely full of blood.
Between the extreme fulness, and the almost complete emptiness of the pulmonary vessels, there is a variety of degrees; now by the manner in which we kill the animal, we can determine any one of these degrees at will: It is in this way that we must explain that state of fulness in the lungs of such subjects, as are usually brought into our amphitheatres: in the greater number of cases, the attacks of death are slow and gradual.
But whatever be the state of the lungs in the asphyxiated subject, the venous system is full of black blood, especially about the heart. In this respect, there is always a very wide difference between the veins and the arteries, and accordingly the blood must find in the lungs the principal obstacle to its circulation: such obstacle, as we have said, does not proceed from the tortuosity, and state of collapse in the pulmonary vessels; its causes are relative, first to the blood, secondly, to the lungs, thirdly to the heart.
The principal cause depending on the blood, consists in the great quantity of this fluid, which passes from the arteries into the veins. In fact we shall soon see, that the black blood when it circulates in the arteries, is not capable of furnishing the materials of secretion, exhalation, or nutrition, or if it be so, that it is not a stimulus to the organs which are the agents of these functions.[86]
It follows as a necessary consequence, that the portion of fluid which is usually taken up from the arterial system by these different functions, flows on into the venous system, together with the portion which should naturally pass thither; hence there must be contained a greater quantity than usual in the veins; and therefore a greater difficulty be experienced in its passage through the lungs. Practitioners in opening the bodies of asphyxiated persons, have always remarked the abundance of blood which is met with there. The fact has been particularly remarked by Portal, and I have always found it in my experiments.
The causes of obstacle to the passage of the blood proceeding from the lungs, are first the non-excitement of this organ by arterial blood. In asphyxia, the bronchial arteries are penetrated by the black blood as well as the rest. Hence its obscure and dusky colour in this case. This colour and its successive shades, may be easily remarked in the collapsed lung, when the chest is opened; but in asphyxia, such blackness is principally owing to the colour of the blood, contained in the pulmonary veins.
The black blood when circulating in the bronchial vessels, produces upon the lungs the same effect which it does in the heart, by penetrating the coronary arteries; it weakens the different parts—impedes their action, and the capillary secretions which should be made there, from the tonic powers of the organ.
The second cause of obstacle to the circulation, when the chemical functions of the lungs are interrupted, is the non-excitement of the organ by vital air. The first effect of such air upon the mucous surfaces of the air-cells, is to stimulate them, and so to keep them up in asort of perpetual erethism.[87]In the same way are the powers of the stomach brought into action by the presence of aliment there, and those of every reservoir of the body, by the influx of their accustomed fluids. Again, such excitement of the mucous surfaces by foreign substances keeps up their tone. The privation of such excitement, therefore, must put a stop to their capillary secretions, which depend upon their tonic powers.
The different aeriform fluids which take the place of the atmospheric air in the different sorts of asphyxia, appear to act very differently upon the tonic powers, or the insensible organic contractility of the lungs. Some of these put a sudden stop to the circulation, others not. Compare the asphyxiæ produced by nitrous or sulphurated hydrogen gas, with those which may be occasioned by pure hydrogen, or carbonic acid gas, and the difference will instantly be seen. This difference indeed, as well as the various other phenomena observable in the various asphyxiæ, depends on causes which we have not mentioned, but the affection of the air-cells, is evidently one of them.
Lastly, the third cause of stagnation of the blood in the venous vascular system, is that debility, which takes place in the ventricle and auricle of this system, when penetrated with venous blood: on the influx of the blood from the cava, they are consequently distended, and this is the case also with the cava itself, for the very same reason. The causes which are now assigned, are sufficient to shew why the black-blooded system, is gorged withfluids in asphyxiæ.[88]The following considerations will shew why the red-blooded system contains a lesser quantity of fluid.
1st.—The obstacle commences in the lungs; therefore the aortic heart must receive a less quantity than usual: hence, as we have seen, proceeds the quicker cessation of the contractions of this ventricle.
2dly.—The natural strength of the arteries, though enfeebled by the influx of blood into their parietes, is much superior to that of the veins, which besides are subject to the same cause of debility.[89]Accordingly these vessels and the aortic ventricle, are capable of surmounting the resistance of the capillary vessels of the body in general, much more easily than the veins and the venous ventricle, are of vanquishing the capillaries of the lungs.
3dly.—In the general capillary system, there is only one cause of want of action, viz. the presence of black blood in it; to this in the lungs there is added another cause, the want of that habitual excitement which this organ receives on the part of the atmospheric air: accordingly in the lungs, there is a greater resistance offered to the influx of the blood, and with respect to the heart, a less capability of surmounting such resistance. In the other parts, the contrary of all this is observed, a less resistance to the influx of the blood from the arteries into the veins on the one hand, and on the other a greater capability of overcoming such resistance.
4thly.—In the general capillary system, which is continued on from that of the arteries, if the circulation be embarrassed at first, in any organ in particular, it may still continue to go on in the other organs, more or less, in which case the blood regurgitates by these others into the veins. On the contrary, as all the capillary system, which is the continuation of the general venous system, is concentrated in the lungs, the venous circulation must be suppressed, whenever this organ loses its powers.
The preceding considerations, if I am not mistaken, explain why the vascular systems are so unequally full of blood after death, a circumstance, which is common to almost every disease, as well as the asphyxiæ.
In the latter sort of death however, although the general capillary system presents a less degree of resistance than is made by the capillary system of the lungs, nevertheless such resistance arising from the influx of the black blood into the organs in general is very manifest, and produces two remarkable phenomena.
The first is a greater quantity than usual of black blood in the arteries, and therefore a greater difficulty of injecting these vessels. Such blood is seldom coagulated.Indeed in all cases the venous blood is much less coagulable than arterial blood. This fact is proved, 1st, By the experiments of modern Chemists. 2dly, By the comparison of the blood of varices with that of aneurisms. 3dly, By the inspection of that which usually stagnates after death in the veins of the neighbourhood of the heart.
The second circumstance, to which I have referred, is the general livid colour of the greater number of the surfaces, with the fulness of divers parts, such as the face, the tongue and lips. These two phenomena indicate a stagnation of the blood at the extremities of the arteries, in the same way as they denote the same effect in the pulmonary vessels; here there is a much more evident repletion, because as I have said, the capillary system is there concentrated within narrow limits.
The reflux of the blood of the veins towards the extremities is the reason assigned by authors for the livid appearance of asphyxiated persons. There is little reality in this cause: in fact, this reflux, which is very sensible in the trunks of the veins, diminishes continually towards their ramifications, where it is impeded and rendered impossible by the valves, besides which, the following experiment is an evident proof, that we must attribute the lividity in question, to the impulse of the black blood from the aortic ventricle.
1st.—Adapt a syringe with its stop-cock to the divided trachea. 2dly, Open the abdomen so as to distinguish the intestines and epiploon. 3dly, Shut the cock. At the end of two or three minutes, the red tint which animates the peritoneum, and which is borrowed by this membrane from the vessels, which creep underneath it, will be changed into a dull brown colour. This colour may be made to disappear and re-appear at will, by opening or shutting the syringe.
Here we cannot, as if the experiment were made upon other parts, suspect that a reflux is propagated from the right ventricle towards the venous extremities, since the mesenteric veins, together with the other branches of the vena portæ, form a system apart, independent of the great black-blooded system, and having no communication with the cavities of the heart which correspond with this system.
But I shall touch again upon this subject. The above experiment is amply sufficient to prove, that the lividity of the surfaces of the body is owing to arterial impulse.
At present we are in a condition to explain how the lungs are more or less gorged with blood, more or less livid, and how the livid spots upon the different parts of the body are more or less marked accordingly as the asphyxia has been more or less prolonged: for it is evident, that if before death, the black blood have gone round the two systems ten or twelve times, it will inject the extremities much more than if it had made such circulation only two or three times; at each revolution, a greater or less quantity will be left in the extremities, for want of action in the capillary vessels.
In finishing this chapter I shall take occasion to observe, that the spleen is the only organ of the economy susceptible like the lungs of assuming a very great variety of volume. Scarcely is it ever found in the same state. It has been falsely supposed that there is a relation between the plenitude or vacuity of the stomach, and the inequalities of the spleen; but this is not the case, as I have said elsewhere. Such inequalities during the life of the body do not exist, and supervene only at the instant of death.
It appears to me, that they depend especially upon the state of the liver, the capillary vessels of which, are the continuations of all the branches of the vena portæ asthe capillaries of the lungs are those of the great venous system. Thus, when the hepatic capillaries from any cause whatever are enfeebled, the spleen must swell and be filled with the blood, which cannot traverse the liver.[90]In such case, if I may so express myself, there is an isolated asphyxia of the abdominal vascular apparatus. The liver being to the spleen, what the lungs are to the black-blooded cavities in common asphyxia. The resistance is in the former, the stagnation in the latter. But this matter may be better understood hereafter. Experiments upon animals killed in different ways, would throw much light upon it, and these I purpose undertaking. By these means we may rigorously establish theanalogy existing between the stagnation of the blood in the different branches of the vena portæ, and that which is observed in the general venous system, in consequence of various kinds of death. With respect to the spleen and its system of veins, in ordinary asphyxia, I have never remarked in it any peculiarity.