FOOTNOTES:

FOOTNOTES:[79]It is not because the vessels of the lungs have become tortuous that the blood flows through them with difficulty, but because they are compressed. It was needless for Goodwyn to seek for reasons to prove, that the flattening of the lungs does not offer a mechanical obstacle to the course of the blood. If he had observed with attention the phenomena of respiration, he would have seen that this contraction, if it does not completely interrupt the circulation of the blood in the lungs, at least modifies it in a very remarkable manner. When the lungs contract, not only the bronchial cells are flattened, but the pulmonary vessels are compressed, and tend to expel the blood contained in their cavity. This fluid flows back then on one part towards the right ventricle by the pulmonary artery, and on the other it accumulates in the pulmonary veins before entering the left auricle. Hence we see that the jet by the carotid artery must increase rather than lessen in the last moments. But if the compression continues, as the capacity of the ramifications of the pulmonary artery is diminished as well as that of the veins of the same name, the quantity of blood which passes through the lungs is less, and the jet by the carotid necessarily decreases. The experiment related by Bichat is then entirely opposed to the opinion which he advances.It is not only by influencing the course of the blood in the system of pulmonary vessels that the alternate motion of the thorax modifies the circulation. If we lay bare the jugular vein of a dog, we perceive that the blood does not move in its cavity from the sole influence of the right auricle, but in an evident manner from the influence of the motions of respiration also.At each time that the thorax is dilated in inspiration, the vein is quickly emptied, flattened and its parietes are sometimes brought exactly against each other; it swells on the contrary and fills with blood when the thorax contracts. A similar phenomenon takes place in the venæ cavæ. In order to render it evident it is sufficient to introduce by the jugular vein into the venæ cavæ a sound of gum elastic; we then see that the blood flows through the extremity of the sound only during the time of expiration. A similar effect is observed if we introduce a sound into the crural vein and direct it towards the abdomen.Haller and Lorry have paid much attention to this phenomenon, and have proposed an explanation of it which seems very satisfactory at first view, though it is really imperfect. When the thorax is dilated, say they, it draws the blood from the venæ cavæ, and, by degrees, that of the veins which are near it. The mechanism of this inspiration is very similar to that by which the air is drawn into the trachea. When the thorax contracts, on the contrary, the blood is crowded back in the venæ cavæ by the pressure which is made on all the pectoral organs, vessels, heart and lungs, by the expiratory powers, and by degrees arrives at the veins which terminate in them. Hence the alternation of vacuity and fulness which the jugular veins exhibit.If we open an artery, and examine with attention the jet of blood, we see that it increases in expiration, and this is especially evident when the animal expires strongly or makes an effort; but as we cannot always produce these efforts at will, or a great inspiration, we can in some measure imitate the phenomenon and produce the contraction of the lungs by compressing with the hands the sides of the thorax; we see then the jet of arterial blood increase or diminish, in proportion to the pressure that is made. If respiration produces this effect on the course of the blood in the arteries, it is natural to think that it can influence the course of the venous blood, not only by means of the veins, as Haller and Lorry thought, but also by means of the arteries. For the purpose of satisfying myself, I made the following experiment, I tied the jugular vein of a dog; the vessel became empty below the ligature, and swelled much above, as uniformly happens. I punctured slightly with a lancet the distended portion, so as to make a very small opening. I obtained in this way a jet of blood, which the ordinary motions of respiration did not modify evidently, but which trebled or quadrupled in size if the animal made any considerable effort.It might be objected, that the effect of respiration was not transmitted by the arteries to the open vein, but by the veins which were free, and which would have transmitted the blood of the venæ cavæ, towards the tied vein, by means of anastomoses. It is easy to remove this difficulty; in fact, in the dog the internal jugular vein is, as it were, but the appearance of a vein, and the circulation of the head and neck is performed almost entirely by the external jugular veins, which are very large. By tying at the same time these two veins I was sure of preventing, in a very great measure, the reflux which has just been spoken of; but so far from the double ligature diminishing the phenomenon before stated, the jet becomes on the contrary more strictly in relation with the motions of respiration, for it was evidently modified, even by common respiration; which, as we have seen, does not happen in the case of a single ligature. In order to render the thing more evident, I tried it on the crural vein; this vein and all its branches being furnished with valves, which oppose a reflux, if this phenomenon of the increase of the jet appears during expiration, we might be sure that the impulse came from the arteries. This is what I have observed in fact in many experiments. The crural vein being tied and punctured below the ligature, the jet which is formed increases evidently in powerful expirations, in the efforts and the mechanical compressions of the parietes of the thorax with the hands.We see by this and the preceding experiments, that we cannot adopt without modification the expression of Haller and Lorry relative to the swelling of the veins. This swelling takes place, not only, as they say, by the flowing back of the blood of the venæ cavæ into the branches which open into them mediately or immediately, but also by the entrance into the vein of a greater quantity of blood coming from the arteries.[80]As in dead bodies the air within and the air without are of the same temperature, the lungs, when they are full of it, do not flatten when the thoracic cavity is opened. There is usually then a space between the parietes and the contained organs; this is not because we die in expiration; for as the lungs empty themselves, the ribs and intercostal muscles rest upon them; it is because the pulmonary air, in cooling occupies less space, and the cells contracting gradually as the cooling takes place, diminish the whole size of the organ. A vacuum is then made between the pectoral and pulmonary portions of the pleura.It is thus that, under some circumstances, the brain flattening and lessening after death, whilst the cavity of the cranium remains the same, a vacuum is formed between these two parts, which then exhibit an arrangement different from that of the living organs. If the sacs without an opening, as the peritoneum, tunica vaginalis, &c. never resemble, in this respect, the pleura and arachnoides; if their different surfaces are always contiguous after death, it is because the abdominal parietes or the skin of the scrotum, unable to resist the external air, flatten by pressure, and are brought against the internal organs, as the diminution of these tends to form a vacuum.It is to this vacuum existing in the pleura of dead bodies, that must be referred the following phenomenon, which is always observed when the abdomen is opened and the diaphragm dissected. In fact, as long as no opening is made in this muscle, it remains distended and concave, notwithstanding the weight of pectoral viscera which rest upon it in a perpendicular situation, because the external air, which presses the concavity of it, forces it then into the vacuum in the thorax, which never exists during life. But the instant the air is admitted by a cut of the scalpel, this muscular partition flattens, because the equilibrium is established. If all the air is drawn from the lungs by a syringe, the diaphragmatic arch is still more evident.There is then this difference between the opening of a dead body and that of a living one, that in the first the lungs are already flattened, and in the second they flatten at the instant of opening. The contraction of the cells, from the condensation of the air by cooling, is an effect of the contractility of texture or from want of extension, which as we have said, continues in a degree with the organs after death.Besides, if the lungs flattened in the dead body the instant the thorax was opened, it would be owing to the pressure of the external air, a pressure which would expel through the trachea what was contained in these organs. Now if, to prevent the escape of air, you close hermetically the canal by fixing a tube to it the stopper of which is tight, and the thorax is afterwards opened, the lungs still flatten; the air had already gone out of them. Make, on the contrary, the same experiment on a living animal, you will always prevent the flattening of these organs, by preventing the expulsion of the air.In this point of view Goodwyn has gone on a wrong principle in measuring in a dead body, the quantity of air remaining in the lungs after each expiration. Besides, if you open bodies ever so little, you will hardly find two in which there is the same arrangement in the lungs. The infinitely various manner in which life terminates, by accumulating more or less blood in these organs, by retaining more or less air in them, &c. gives them so variable a size, that no general data can be established respecting them. On the other hand, can we hope to be more successful on the living body? No; for who does not know that digestion, exercise, rest, the passions, tranquillity of mind, sleep, watchfulness, temperament, sex, &c. make an infinite variety in the forces of the lungs, the rapidity with which the blood circulates through them, and the quantity of air that penetrates them? All the calculations on the quantity of this fluid which enters or goes out according to the inspiration or the expiration, appear to me to be physiological errours, inasmuch as they assimilate the nature of vital forces with that of physical forces. They are as useless to science as those which had formerly for their object the muscular force, the velocity of the blood, &c. Besides, observe if their authors agree better among themselves then they used to do on this much agitated point.[81]It is inconceivable how Bichat could think of confirming his opinion by the example of hydrothorax. Who does not know that when an effusion takes place in the cavity of one of the pleuras, that that portion of the lungs only which is above the level of the water serves the purposes of respiration; that when the effusion has arrived to the summit of the cavity, the lungs of that side, which can no longer dilate, are of no use in respiration; and those of the other, being compelled alone to make the necessary modifications in the blood, must be traversed by the greatest part of this fluid? It is known, finally, that in this case the patient cannot lie down an instant on the sound side, because this position prevents the dilatation of the lungs of that side which alone serve for respiration, and the danger of suffocation is therefore imminent.[82]The observation of Bichat is very just; and I have myself often observed in cases of apoplexy, that the motions of the heart continue many hours after the arteries contain only black blood.[83]At the period Bichat wrote, it was impossible to know whether the arterial or venous blood contained most hydrogen and carbon. At the present day even, when the means of analysis are much more perfect and animal chemistry farther advanced, we are hardly better informed.[84]It seems that when Bichat wrote this work, he had not fixed in his own mind what part the arteries take in the circulation; at least, in this paragraph, he seems to give them a contractile power, which, in his other works, he accords only, to their ultimate ramifications.[85]It is certain, whatever Bichat may say concerning it, that numerous angles in the course of a blood-vessel, by increasing the friction, must retard the course of the fluid which runs through its cavity. We may in fact believe that it is one of the causes, which, in the flattening of the lungs, embarrass the circulation; this cause exerts its action principally upon the last ramifications of the pulmonary artery which, by their interlacing, form the bronchial cells; another more powerful cause, which acts equally on the divisions of the vein and the artery is, as we have said, the pressure made on the lungs by the flattening of the thorax, and the elevation of the diaphragm.[86]See the article on the influence of the lungs on all the parts. I am compelled here to deduce consequences from principles which I shall prove hereafter; such is in fact the connexion of questions which have the circulation for their object, that the solution of one draws as a necessary consequence that of all the others. It is a circle in which it is always necessary to suppose something, leaving it to be proved afterwards.[87]I cannot see what can have induced Bichat to admit this erethism of the lungs, the use of which cannot be imagined. It is quite enough to suppose in the organs the existence of those concealed properties, when there is need of them to explain their functions.[88]As the blood flows in the veins in a continuous motion, the distension of these vessels does not take place in the direct motion of the blood, but in its retrograde motion. Every time the right auricle contracts, a portion of blood, instead of passing into the ventricle of the same side, is forced back into the superior and inferior venæ cavæ, and into the principal venous trunks which open into them. By this reflux of the blood, these veins are dilated, and have a pulsation which is easily seen in the jugular in very thin people. This pulsation has received the name of thevenous pulse. When it is very evident, it may indicate an obstacle to the passage of the blood from the auricle to the right ventricle.Another reflux of the blood in the veins corresponds with the moment of expiration, and is perceptible even longer. We shall soon have to speak of it, in speaking of themovementsof the brain.[89]The natural force of the arteriesis not dependent on life, and consequently cannot be enfeebled by the entrance of black blood. This force is nothing but elasticity, which indeed ceases to be in action as soon as death takes place, but which does not cease to exist till the texture itself is destroyed and disorganized. As this property is very conspicuous in the arteries, it is sufficient to drive the blood from their cavity at the instant of death, whilst it is too feeble in the veins to expel this fluid entirely. Thus it is, that we find blood in the veins only, after death.[90]The state of the spleen in the dead body may become in some measure an index of the state of the circulation during the last moments of life. The swelling of it shows almost always the embarrassment of the circulation; and not only in an insulated system, such as that of the vena portæ, as Bichat considers it, but in the whole pulmonary system.When any cause impedes the circulation in the capillaries of the lungs, it necessarily produces a stagnation of the blood in the divisions of the pulmonary artery, and by degrees the disturbance is felt even in the two venæ cavæ, but especially in the inferior in which the blood rises against its gravity. The blood accumulates in the principal branches; the veins of the liver and kidneys swell more or less; as to these organs themselves, the firmness of their texture hardly allows them to be distended, so they do not increase sensibly in size, or if this increase takes place, it is slow. It is not the same with the spleen; the looseness of its texture will admit a great quantity of liquid, and its size can thus be doubled or trebled in a very short time. It becomes then a kind of reservoir, in which is accumulated the blood which cannot pass through the lungs.It may be objected to what we have just said, that oftentimes in phthisis the greatest portion of the lungs has become incapable of allowing the blood to pass, and that yet after death, the spleen is found in a natural state. But it should be recollected, that phthisical patients have, during the latter part of their lives, but very little blood, so that each portion sent by the right ventricle always finds a sufficient channel for it in the lungs.

[79]It is not because the vessels of the lungs have become tortuous that the blood flows through them with difficulty, but because they are compressed. It was needless for Goodwyn to seek for reasons to prove, that the flattening of the lungs does not offer a mechanical obstacle to the course of the blood. If he had observed with attention the phenomena of respiration, he would have seen that this contraction, if it does not completely interrupt the circulation of the blood in the lungs, at least modifies it in a very remarkable manner. When the lungs contract, not only the bronchial cells are flattened, but the pulmonary vessels are compressed, and tend to expel the blood contained in their cavity. This fluid flows back then on one part towards the right ventricle by the pulmonary artery, and on the other it accumulates in the pulmonary veins before entering the left auricle. Hence we see that the jet by the carotid artery must increase rather than lessen in the last moments. But if the compression continues, as the capacity of the ramifications of the pulmonary artery is diminished as well as that of the veins of the same name, the quantity of blood which passes through the lungs is less, and the jet by the carotid necessarily decreases. The experiment related by Bichat is then entirely opposed to the opinion which he advances.It is not only by influencing the course of the blood in the system of pulmonary vessels that the alternate motion of the thorax modifies the circulation. If we lay bare the jugular vein of a dog, we perceive that the blood does not move in its cavity from the sole influence of the right auricle, but in an evident manner from the influence of the motions of respiration also.At each time that the thorax is dilated in inspiration, the vein is quickly emptied, flattened and its parietes are sometimes brought exactly against each other; it swells on the contrary and fills with blood when the thorax contracts. A similar phenomenon takes place in the venæ cavæ. In order to render it evident it is sufficient to introduce by the jugular vein into the venæ cavæ a sound of gum elastic; we then see that the blood flows through the extremity of the sound only during the time of expiration. A similar effect is observed if we introduce a sound into the crural vein and direct it towards the abdomen.Haller and Lorry have paid much attention to this phenomenon, and have proposed an explanation of it which seems very satisfactory at first view, though it is really imperfect. When the thorax is dilated, say they, it draws the blood from the venæ cavæ, and, by degrees, that of the veins which are near it. The mechanism of this inspiration is very similar to that by which the air is drawn into the trachea. When the thorax contracts, on the contrary, the blood is crowded back in the venæ cavæ by the pressure which is made on all the pectoral organs, vessels, heart and lungs, by the expiratory powers, and by degrees arrives at the veins which terminate in them. Hence the alternation of vacuity and fulness which the jugular veins exhibit.If we open an artery, and examine with attention the jet of blood, we see that it increases in expiration, and this is especially evident when the animal expires strongly or makes an effort; but as we cannot always produce these efforts at will, or a great inspiration, we can in some measure imitate the phenomenon and produce the contraction of the lungs by compressing with the hands the sides of the thorax; we see then the jet of arterial blood increase or diminish, in proportion to the pressure that is made. If respiration produces this effect on the course of the blood in the arteries, it is natural to think that it can influence the course of the venous blood, not only by means of the veins, as Haller and Lorry thought, but also by means of the arteries. For the purpose of satisfying myself, I made the following experiment, I tied the jugular vein of a dog; the vessel became empty below the ligature, and swelled much above, as uniformly happens. I punctured slightly with a lancet the distended portion, so as to make a very small opening. I obtained in this way a jet of blood, which the ordinary motions of respiration did not modify evidently, but which trebled or quadrupled in size if the animal made any considerable effort.It might be objected, that the effect of respiration was not transmitted by the arteries to the open vein, but by the veins which were free, and which would have transmitted the blood of the venæ cavæ, towards the tied vein, by means of anastomoses. It is easy to remove this difficulty; in fact, in the dog the internal jugular vein is, as it were, but the appearance of a vein, and the circulation of the head and neck is performed almost entirely by the external jugular veins, which are very large. By tying at the same time these two veins I was sure of preventing, in a very great measure, the reflux which has just been spoken of; but so far from the double ligature diminishing the phenomenon before stated, the jet becomes on the contrary more strictly in relation with the motions of respiration, for it was evidently modified, even by common respiration; which, as we have seen, does not happen in the case of a single ligature. In order to render the thing more evident, I tried it on the crural vein; this vein and all its branches being furnished with valves, which oppose a reflux, if this phenomenon of the increase of the jet appears during expiration, we might be sure that the impulse came from the arteries. This is what I have observed in fact in many experiments. The crural vein being tied and punctured below the ligature, the jet which is formed increases evidently in powerful expirations, in the efforts and the mechanical compressions of the parietes of the thorax with the hands.We see by this and the preceding experiments, that we cannot adopt without modification the expression of Haller and Lorry relative to the swelling of the veins. This swelling takes place, not only, as they say, by the flowing back of the blood of the venæ cavæ into the branches which open into them mediately or immediately, but also by the entrance into the vein of a greater quantity of blood coming from the arteries.

It is not only by influencing the course of the blood in the system of pulmonary vessels that the alternate motion of the thorax modifies the circulation. If we lay bare the jugular vein of a dog, we perceive that the blood does not move in its cavity from the sole influence of the right auricle, but in an evident manner from the influence of the motions of respiration also.

At each time that the thorax is dilated in inspiration, the vein is quickly emptied, flattened and its parietes are sometimes brought exactly against each other; it swells on the contrary and fills with blood when the thorax contracts. A similar phenomenon takes place in the venæ cavæ. In order to render it evident it is sufficient to introduce by the jugular vein into the venæ cavæ a sound of gum elastic; we then see that the blood flows through the extremity of the sound only during the time of expiration. A similar effect is observed if we introduce a sound into the crural vein and direct it towards the abdomen.

Haller and Lorry have paid much attention to this phenomenon, and have proposed an explanation of it which seems very satisfactory at first view, though it is really imperfect. When the thorax is dilated, say they, it draws the blood from the venæ cavæ, and, by degrees, that of the veins which are near it. The mechanism of this inspiration is very similar to that by which the air is drawn into the trachea. When the thorax contracts, on the contrary, the blood is crowded back in the venæ cavæ by the pressure which is made on all the pectoral organs, vessels, heart and lungs, by the expiratory powers, and by degrees arrives at the veins which terminate in them. Hence the alternation of vacuity and fulness which the jugular veins exhibit.

If we open an artery, and examine with attention the jet of blood, we see that it increases in expiration, and this is especially evident when the animal expires strongly or makes an effort; but as we cannot always produce these efforts at will, or a great inspiration, we can in some measure imitate the phenomenon and produce the contraction of the lungs by compressing with the hands the sides of the thorax; we see then the jet of arterial blood increase or diminish, in proportion to the pressure that is made. If respiration produces this effect on the course of the blood in the arteries, it is natural to think that it can influence the course of the venous blood, not only by means of the veins, as Haller and Lorry thought, but also by means of the arteries. For the purpose of satisfying myself, I made the following experiment, I tied the jugular vein of a dog; the vessel became empty below the ligature, and swelled much above, as uniformly happens. I punctured slightly with a lancet the distended portion, so as to make a very small opening. I obtained in this way a jet of blood, which the ordinary motions of respiration did not modify evidently, but which trebled or quadrupled in size if the animal made any considerable effort.

It might be objected, that the effect of respiration was not transmitted by the arteries to the open vein, but by the veins which were free, and which would have transmitted the blood of the venæ cavæ, towards the tied vein, by means of anastomoses. It is easy to remove this difficulty; in fact, in the dog the internal jugular vein is, as it were, but the appearance of a vein, and the circulation of the head and neck is performed almost entirely by the external jugular veins, which are very large. By tying at the same time these two veins I was sure of preventing, in a very great measure, the reflux which has just been spoken of; but so far from the double ligature diminishing the phenomenon before stated, the jet becomes on the contrary more strictly in relation with the motions of respiration, for it was evidently modified, even by common respiration; which, as we have seen, does not happen in the case of a single ligature. In order to render the thing more evident, I tried it on the crural vein; this vein and all its branches being furnished with valves, which oppose a reflux, if this phenomenon of the increase of the jet appears during expiration, we might be sure that the impulse came from the arteries. This is what I have observed in fact in many experiments. The crural vein being tied and punctured below the ligature, the jet which is formed increases evidently in powerful expirations, in the efforts and the mechanical compressions of the parietes of the thorax with the hands.

We see by this and the preceding experiments, that we cannot adopt without modification the expression of Haller and Lorry relative to the swelling of the veins. This swelling takes place, not only, as they say, by the flowing back of the blood of the venæ cavæ into the branches which open into them mediately or immediately, but also by the entrance into the vein of a greater quantity of blood coming from the arteries.

[80]As in dead bodies the air within and the air without are of the same temperature, the lungs, when they are full of it, do not flatten when the thoracic cavity is opened. There is usually then a space between the parietes and the contained organs; this is not because we die in expiration; for as the lungs empty themselves, the ribs and intercostal muscles rest upon them; it is because the pulmonary air, in cooling occupies less space, and the cells contracting gradually as the cooling takes place, diminish the whole size of the organ. A vacuum is then made between the pectoral and pulmonary portions of the pleura.It is thus that, under some circumstances, the brain flattening and lessening after death, whilst the cavity of the cranium remains the same, a vacuum is formed between these two parts, which then exhibit an arrangement different from that of the living organs. If the sacs without an opening, as the peritoneum, tunica vaginalis, &c. never resemble, in this respect, the pleura and arachnoides; if their different surfaces are always contiguous after death, it is because the abdominal parietes or the skin of the scrotum, unable to resist the external air, flatten by pressure, and are brought against the internal organs, as the diminution of these tends to form a vacuum.It is to this vacuum existing in the pleura of dead bodies, that must be referred the following phenomenon, which is always observed when the abdomen is opened and the diaphragm dissected. In fact, as long as no opening is made in this muscle, it remains distended and concave, notwithstanding the weight of pectoral viscera which rest upon it in a perpendicular situation, because the external air, which presses the concavity of it, forces it then into the vacuum in the thorax, which never exists during life. But the instant the air is admitted by a cut of the scalpel, this muscular partition flattens, because the equilibrium is established. If all the air is drawn from the lungs by a syringe, the diaphragmatic arch is still more evident.There is then this difference between the opening of a dead body and that of a living one, that in the first the lungs are already flattened, and in the second they flatten at the instant of opening. The contraction of the cells, from the condensation of the air by cooling, is an effect of the contractility of texture or from want of extension, which as we have said, continues in a degree with the organs after death.Besides, if the lungs flattened in the dead body the instant the thorax was opened, it would be owing to the pressure of the external air, a pressure which would expel through the trachea what was contained in these organs. Now if, to prevent the escape of air, you close hermetically the canal by fixing a tube to it the stopper of which is tight, and the thorax is afterwards opened, the lungs still flatten; the air had already gone out of them. Make, on the contrary, the same experiment on a living animal, you will always prevent the flattening of these organs, by preventing the expulsion of the air.In this point of view Goodwyn has gone on a wrong principle in measuring in a dead body, the quantity of air remaining in the lungs after each expiration. Besides, if you open bodies ever so little, you will hardly find two in which there is the same arrangement in the lungs. The infinitely various manner in which life terminates, by accumulating more or less blood in these organs, by retaining more or less air in them, &c. gives them so variable a size, that no general data can be established respecting them. On the other hand, can we hope to be more successful on the living body? No; for who does not know that digestion, exercise, rest, the passions, tranquillity of mind, sleep, watchfulness, temperament, sex, &c. make an infinite variety in the forces of the lungs, the rapidity with which the blood circulates through them, and the quantity of air that penetrates them? All the calculations on the quantity of this fluid which enters or goes out according to the inspiration or the expiration, appear to me to be physiological errours, inasmuch as they assimilate the nature of vital forces with that of physical forces. They are as useless to science as those which had formerly for their object the muscular force, the velocity of the blood, &c. Besides, observe if their authors agree better among themselves then they used to do on this much agitated point.

It is thus that, under some circumstances, the brain flattening and lessening after death, whilst the cavity of the cranium remains the same, a vacuum is formed between these two parts, which then exhibit an arrangement different from that of the living organs. If the sacs without an opening, as the peritoneum, tunica vaginalis, &c. never resemble, in this respect, the pleura and arachnoides; if their different surfaces are always contiguous after death, it is because the abdominal parietes or the skin of the scrotum, unable to resist the external air, flatten by pressure, and are brought against the internal organs, as the diminution of these tends to form a vacuum.

It is to this vacuum existing in the pleura of dead bodies, that must be referred the following phenomenon, which is always observed when the abdomen is opened and the diaphragm dissected. In fact, as long as no opening is made in this muscle, it remains distended and concave, notwithstanding the weight of pectoral viscera which rest upon it in a perpendicular situation, because the external air, which presses the concavity of it, forces it then into the vacuum in the thorax, which never exists during life. But the instant the air is admitted by a cut of the scalpel, this muscular partition flattens, because the equilibrium is established. If all the air is drawn from the lungs by a syringe, the diaphragmatic arch is still more evident.

There is then this difference between the opening of a dead body and that of a living one, that in the first the lungs are already flattened, and in the second they flatten at the instant of opening. The contraction of the cells, from the condensation of the air by cooling, is an effect of the contractility of texture or from want of extension, which as we have said, continues in a degree with the organs after death.

Besides, if the lungs flattened in the dead body the instant the thorax was opened, it would be owing to the pressure of the external air, a pressure which would expel through the trachea what was contained in these organs. Now if, to prevent the escape of air, you close hermetically the canal by fixing a tube to it the stopper of which is tight, and the thorax is afterwards opened, the lungs still flatten; the air had already gone out of them. Make, on the contrary, the same experiment on a living animal, you will always prevent the flattening of these organs, by preventing the expulsion of the air.

In this point of view Goodwyn has gone on a wrong principle in measuring in a dead body, the quantity of air remaining in the lungs after each expiration. Besides, if you open bodies ever so little, you will hardly find two in which there is the same arrangement in the lungs. The infinitely various manner in which life terminates, by accumulating more or less blood in these organs, by retaining more or less air in them, &c. gives them so variable a size, that no general data can be established respecting them. On the other hand, can we hope to be more successful on the living body? No; for who does not know that digestion, exercise, rest, the passions, tranquillity of mind, sleep, watchfulness, temperament, sex, &c. make an infinite variety in the forces of the lungs, the rapidity with which the blood circulates through them, and the quantity of air that penetrates them? All the calculations on the quantity of this fluid which enters or goes out according to the inspiration or the expiration, appear to me to be physiological errours, inasmuch as they assimilate the nature of vital forces with that of physical forces. They are as useless to science as those which had formerly for their object the muscular force, the velocity of the blood, &c. Besides, observe if their authors agree better among themselves then they used to do on this much agitated point.

[81]It is inconceivable how Bichat could think of confirming his opinion by the example of hydrothorax. Who does not know that when an effusion takes place in the cavity of one of the pleuras, that that portion of the lungs only which is above the level of the water serves the purposes of respiration; that when the effusion has arrived to the summit of the cavity, the lungs of that side, which can no longer dilate, are of no use in respiration; and those of the other, being compelled alone to make the necessary modifications in the blood, must be traversed by the greatest part of this fluid? It is known, finally, that in this case the patient cannot lie down an instant on the sound side, because this position prevents the dilatation of the lungs of that side which alone serve for respiration, and the danger of suffocation is therefore imminent.

[82]The observation of Bichat is very just; and I have myself often observed in cases of apoplexy, that the motions of the heart continue many hours after the arteries contain only black blood.

[83]At the period Bichat wrote, it was impossible to know whether the arterial or venous blood contained most hydrogen and carbon. At the present day even, when the means of analysis are much more perfect and animal chemistry farther advanced, we are hardly better informed.

[84]It seems that when Bichat wrote this work, he had not fixed in his own mind what part the arteries take in the circulation; at least, in this paragraph, he seems to give them a contractile power, which, in his other works, he accords only, to their ultimate ramifications.

[85]It is certain, whatever Bichat may say concerning it, that numerous angles in the course of a blood-vessel, by increasing the friction, must retard the course of the fluid which runs through its cavity. We may in fact believe that it is one of the causes, which, in the flattening of the lungs, embarrass the circulation; this cause exerts its action principally upon the last ramifications of the pulmonary artery which, by their interlacing, form the bronchial cells; another more powerful cause, which acts equally on the divisions of the vein and the artery is, as we have said, the pressure made on the lungs by the flattening of the thorax, and the elevation of the diaphragm.

[86]See the article on the influence of the lungs on all the parts. I am compelled here to deduce consequences from principles which I shall prove hereafter; such is in fact the connexion of questions which have the circulation for their object, that the solution of one draws as a necessary consequence that of all the others. It is a circle in which it is always necessary to suppose something, leaving it to be proved afterwards.

[87]I cannot see what can have induced Bichat to admit this erethism of the lungs, the use of which cannot be imagined. It is quite enough to suppose in the organs the existence of those concealed properties, when there is need of them to explain their functions.

[88]As the blood flows in the veins in a continuous motion, the distension of these vessels does not take place in the direct motion of the blood, but in its retrograde motion. Every time the right auricle contracts, a portion of blood, instead of passing into the ventricle of the same side, is forced back into the superior and inferior venæ cavæ, and into the principal venous trunks which open into them. By this reflux of the blood, these veins are dilated, and have a pulsation which is easily seen in the jugular in very thin people. This pulsation has received the name of thevenous pulse. When it is very evident, it may indicate an obstacle to the passage of the blood from the auricle to the right ventricle.Another reflux of the blood in the veins corresponds with the moment of expiration, and is perceptible even longer. We shall soon have to speak of it, in speaking of themovementsof the brain.

Another reflux of the blood in the veins corresponds with the moment of expiration, and is perceptible even longer. We shall soon have to speak of it, in speaking of themovementsof the brain.

[89]The natural force of the arteriesis not dependent on life, and consequently cannot be enfeebled by the entrance of black blood. This force is nothing but elasticity, which indeed ceases to be in action as soon as death takes place, but which does not cease to exist till the texture itself is destroyed and disorganized. As this property is very conspicuous in the arteries, it is sufficient to drive the blood from their cavity at the instant of death, whilst it is too feeble in the veins to expel this fluid entirely. Thus it is, that we find blood in the veins only, after death.

[90]The state of the spleen in the dead body may become in some measure an index of the state of the circulation during the last moments of life. The swelling of it shows almost always the embarrassment of the circulation; and not only in an insulated system, such as that of the vena portæ, as Bichat considers it, but in the whole pulmonary system.When any cause impedes the circulation in the capillaries of the lungs, it necessarily produces a stagnation of the blood in the divisions of the pulmonary artery, and by degrees the disturbance is felt even in the two venæ cavæ, but especially in the inferior in which the blood rises against its gravity. The blood accumulates in the principal branches; the veins of the liver and kidneys swell more or less; as to these organs themselves, the firmness of their texture hardly allows them to be distended, so they do not increase sensibly in size, or if this increase takes place, it is slow. It is not the same with the spleen; the looseness of its texture will admit a great quantity of liquid, and its size can thus be doubled or trebled in a very short time. It becomes then a kind of reservoir, in which is accumulated the blood which cannot pass through the lungs.It may be objected to what we have just said, that oftentimes in phthisis the greatest portion of the lungs has become incapable of allowing the blood to pass, and that yet after death, the spleen is found in a natural state. But it should be recollected, that phthisical patients have, during the latter part of their lives, but very little blood, so that each portion sent by the right ventricle always finds a sufficient channel for it in the lungs.

When any cause impedes the circulation in the capillaries of the lungs, it necessarily produces a stagnation of the blood in the divisions of the pulmonary artery, and by degrees the disturbance is felt even in the two venæ cavæ, but especially in the inferior in which the blood rises against its gravity. The blood accumulates in the principal branches; the veins of the liver and kidneys swell more or less; as to these organs themselves, the firmness of their texture hardly allows them to be distended, so they do not increase sensibly in size, or if this increase takes place, it is slow. It is not the same with the spleen; the looseness of its texture will admit a great quantity of liquid, and its size can thus be doubled or trebled in a very short time. It becomes then a kind of reservoir, in which is accumulated the blood which cannot pass through the lungs.

It may be objected to what we have just said, that oftentimes in phthisis the greatest portion of the lungs has become incapable of allowing the blood to pass, and that yet after death, the spleen is found in a natural state. But it should be recollected, that phthisical patients have, during the latter part of their lives, but very little blood, so that each portion sent by the right ventricle always finds a sufficient channel for it in the lungs.

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 respectto 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 oneof 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 waydoes 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 timeafter 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 thecarotid, 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 caseshave 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 andvenous 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 inthe 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, ismuch 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 lungswithout 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 ofsick at heartwhich is given to nausea, would assign to vomiting a wholly different nature from what would be correct.

[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.

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.

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 ofsick at heartwhich is given to nausea, would assign to vomiting a wholly different nature from what would be correct.

I have just shewn in what way the interruption of the chemical phenomena which take place in the lungs, annihilates the functions of the heart and brain. It remains me to shew, that the other organs of the body are as much affected by such cessation; so that asphyxia, as I have said, is a general disease, and not an affection of any one organ in particular.

But before I proceed to analyze the effects of asphyxia upon the organs in general, and consequently the mode of action of the black blood upon them, it may be of use to explain the phenomena of the production of this kind of blood, at the instant when the functions of the lungs are suspended. This paragraph will possess, perhaps, some interest; it might have belonged indifferently to either of the preceding chapters.

It is known in general, that the blood is coloured in traversing the lungs, that from black it becomes red; but this very interesting fact, has not been hitherto the object of any precise or rigorous experiment. The lungs of the frog, of which the air vessels are large, and the membranes thin and transparent, would serve very well for the purpose of observing the process of the phenomenon in question, but for the slowness of respiration in these animals, the difference of organization in their lungs, and the too small quantity of blood by which they are traversed. On such account there can be little analogy between them and the more perfect animals, and then again our experiments upon these little amphibiæ, are all of them rendered incomplete, by the tenuity of their pulmonary vessels, and the impossibility of observing the correspondence of the change of velocity in the circulation, with the colour of their blood.

The phenomena of the respiration of man, and those of the functions which are dependent on it, can be illustrated only by experiments made upon animals with a double ventricle, with a complete pulmonary apparatus, possessed of a temperature superior to that of the atmosphere, and the two separate systems of venous and arterial blood; but on the other hand, in the mammalia resembling man, their respiratory apparatus, the thickness of the vessels and cavities of the heart, impede the view of the blood which they contain; and experiments made without an absolute inspection of the fluid there, can only give us approximations. The indecisive experiments of formerphysiologists on this subject were my motives for the present inquiry.

One of the best methods of judging of the colour of the blood, consists as I have often said, in fixing a tube with a stop-cock to the trachea. By this, the influx of air into the lungs, may be regulated or altogether stopped. By this, we may distend the organ, or entirely evacuate it; it gives us also the facility of introducing whatever gas we please. The animal breathes very well by such pipe when it is open, and would live with it for a considerable length of time without any very great alteration in its functions.

In the second place, an artery, the crural or carotid for instance, must be opened with the view of observing the varieties of colour in the blood projected from it. A small artery should not be chosen. From such a one the course of the blood would be suspended by the slightest accident; and on the other hand, the larger arteries expend in a little time too large a quantity of blood; this inconvenience may be remedied, by adapting to these vessels a tube of a small diameter, or a stop-cock.

All things being thus prepared, on a dog, for instance, let us see what are the phenomena which take place, when the colour of the blood is altered. In my indication of these, however, I shall speak only of what I have seen, and by no means pretend that in man their duration should be similar or uniform, or even that in animals of the same species, under the different circumstances of sleep, digestion, exercise, and passion, &c. if it were possible in such way to repeat them, they should be alike. The instability of the animal functions, as I have said, is extreme; they cannot be submitted to calculation; they remain indeed the same, but their variations as to plus or minus are innumerable.

Let us now return to our subject:

1st. If the cock of the pipe be shut immediately after the animal has inspired, the blood begins to be altered in colour at the end of about thirty seconds.—At the end of a minute its colour is dark; at the end of a minute and half or two minutes, it is perfectly similar to venous blood.

2dly. If the cock of the pipe be shut immediately after the animal has expired strongly, the blood receives its tinge of black some seconds the sooner.

3dly. If the air of the lungs be pumped out entirely with a syringe, the blood will suddenly pass from red to black.[94]In such case it appears that the artery immediately throws out a black stream, after it has expelled the red blood which it previously contained. There is no gradation. The blood is expelled by the arteries, such as it is in the veins.

4thly. If, instead of making a vacuum in the lungs, we inflate the air cells to the full, the blood is a longer time in becoming black, a minute at least, and is not completely black before the end of three minutes.—This will vary according to the quantity of air injected.

From all these experiments it follows, 1st, That the length of the interval, during which the blood retains its red colour, is in direct proportion to the quantity of air contained in the lungs; 2dly, That as long as there remains any quantity however small of respirable air in the cells of the lungs, the blood will preserve more or less of its crimson colour; 3dly, That this colour diminishes in proportion as the respirable air diminishes; and4thly, That the blood is exactly similar to that of the veins, as soon as the whole of the vital air in the extremities of the bronchiæ has been exhausted.

In my different experiments with regard to asphyxia, I have remarked, that if after shutting the cock of the syringe, the animal agitate the chest by similar movements to those of inspiration and expiration, the blood is a longer time in losing its red colour, than in the case where the breast remains at rest. Such motion and agitation must cause a circulation of air in the cells, in consequence of which, a greater number of its points must be presented to the circulating fluid. My experiments which I shall presently detail on the breathing of animals in bladders, will prove the truth of the above explanation.

At present I pass to a contrary set of phenomena—to those which are exemplified when the blood regains its arterial colour during the period, which, from a state of asphyxia, restores the animal to life.

1st. When the cock, which for some minutes has been shut, is opened, the air immediately penetrates into the bronchiæ; but previously the animal expires strongly. Six or seven large inspirations and expirations follow each other precipitately. The artery being now examined, a jet of a very vivid colour is seen succeeding to the efflux of black blood, and takes place in thirty seconds at most, from the time of opening the tube. This is the inverse of the phenomenon above described. There are no successive shades perceived from black to red; the passage is instantaneous. The brightness of the colour seems even to be greater than is natural.

2dly. If instead of suddenly turning the cock, a very strong stream of air only be admitted, the colour is less lively indeed, but just as quickly regained.

3dly. If there be adapted to the stop-cock a syringe full of air, and this fluid be pushed into the lungs, on opening the pipe, and then the pipe be suddenly shut again, the blood will become red, but much less evidently so, than when the entrance of the air is owing to voluntary inspiration. Here the portion of air injected must repel into the bottom of the cells whatever is already vitiated, while on the contrary, if the tube be simply opened, the vitiated air is at once rejected, and then replaced from without. The following experiment appears to confirm this idea.

4thly. If instead of pushing air upon that which is contained in the lungs, we pump out the vitiated air in the first place, and then inflate the organ, the colouring process will be more rapid, and the colour of the blood itself especially, more lively than in the preceding case, though less so than in the first of this latter suite of experiments.

5thly. The lungs being exposed on both sides by a lateral section of the ribs, the circulation will continue to go on for a certain time. Now, if by means of a syringe adapted to the stop-cock in the trachea, the pulmonary vesicles be alternately emptied and dilated, the changes from red to black, and from black to red, will be observed as in the above experiment, as long as the circulation lasts.

The following consequences may be inferred from the facts, which I have mentioned.

1st. The rapidity with which the blood becomes red again, on opening the pipe in the trachea, is a plain proof, that the principle from which this colour is gained, must pass into the blood across the membranous parietes of the air cells, and not by means of the absorbents. I shall establish this fact hereafter upon other proofs.

2dly. The celebrated experiment of Hook, in which the enfeebled movements of the hearts of animals in a state of asphyxia are accelerated by injecting air into the lungs, is very well explained. The red blood penetrates into the fibres of the heart, and puts an end to the debility induced, by the influx thither of the black blood.

3dly. I do not believe, that motion can ever be restored to the heart, when once it has been wholly annihilated by the presence of venous blood. In this I have never succeeded, though I have often attempted it. Many authors, however, pretend to have done so. If the heart be reanimated by arterial blood, it is necessary at any rate, that such blood, should pass into it, now in what way can it arrive there, if the circulation have entirely ceased.

We must observe, however, that there are two cases of interruption in the action of the heart from asphyxia. Sometimes there supervenes a syncope which arrests the movement of this organ, before the black blood has been able to produce such effect; and here it is manifestly capable of excitement, from the presence of the red blood, just as it is from the application of any irritating cause; but when it has been injected with venous blood, it then contains within itself the principle of its inertia, which can be removed only by the contact of arterial blood with it; but such contact is become impossible.

I was very desirous of knowing what the influence might be of the different gases when inspired upon the colour of the blood. Accordingly I successively adapted to the pipe different bladders, containing hydrogen and carbonic acid gas.

The animal alternately swells and contracts the bladder by the different motions of the thorax. It is calm at first, but at the end of three minutes, begins to be agitated; itsrespiration is now hurried and embarrassed, and at the end of four or five minutes, the blood of the carotid is black.

Whichever of the two gases be employed, there is little difference in the above phenomena. This remark should be compared with those of the Members of the Institute, who have assured us that complete asphyxia supervenes only after an interval of ten minutes, with pure hydrogen, and at the end of two minutes with carbonic acid gas. The black blood must continue, therefore, to circulate for a longer time in one than in the other kind of asphyxia here spoken of. This circumstance confirms some reflections which I shall have occasion to offer upon the difference of asphyxiæ.

For what reason should the blood be a longer time in losing its colour, when bladders of non-respirable air are fixed to the pipe, than when the cock is simply turned? The reason of this is evident. By the different motions of the lungs, the air is expelled and reabsorbed, the respirable portion of it must consequently be successively presented to the capillary orifices, by which it is transmitted to the blood.

On the contrary, when the pipe is simply shut, the air it is plain has not the same influx and efflux; in comparison with such motion, it may be said to stagnate so that the respirable portion of that which is enclosed in the bronchial cells is exhausted, and the blood ceases to be coloured, though there remain in the trachea and its larger divisions, a considerable quantity of fluid, which has not been despoiled of its vivifying principle. Of this we may be certain, after the death of the animal, by cutting the trachea under the pipe, and plunging a bougie into it. The process by which the blood gains its red colour appears to take place only at the extremities of thebronchiæ, the inner surface of the larger aerial vessels, has nothing to do with this phenomenon.

We may convince ourselves of the reality of the explanation which I have offered, if we pump out the air of the lungs, before we fit the bladder to the trachea; for in such case, the animal must breathe the air of the bladder without mixture. Here the change of the blood to black is almost sudden, but here also, as in the preceding experiment, there is little difference in the phenomena, whatever gas we employ. I have chosen the two gases above mentioned, because they enter into the phenomena of natural respiration.

When we adapt to the pipe a bladder full of pure oxygen, the blood is very long in becoming black, but does not at first assume a redder tint than it usually has.

We have just established what are the phenomena of the alteration of colour in the blood, when the chemical functions of the lungs are suspended. Before we consider the influence of this change upon the death of the organs, let us prove, that they are really penetrated by the blood when so altered.

I have proved it to be a fact, that the force of the heart subsists for some time, notwithstanding the influx of the black blood into it, and have shewn that the black blood is thrown out with a jet, similar to that of the red blood, &c. &c. Hence I might already conclude, 1st, That the arterial circulation continues for a certain time, though the arteries contain a fluid, to which they are not accustomed,and 2dly, That the necessary consequence of such circulation, must be the injection of the different parts of the body with black blood; but we shall deduce the latter conclusion from precise and rigorous experiments. To be certain of this important fact, we have only to expose successively the different organs, while the animal is suffering a death of asphyxia. I have in this way examined the muscles, the nerves, the membranes and the viscera. The following are the results of my observations.

1st. The colouring matter of the muscles, exists in the body in two states—at liberty, or in a state of combination; in the vessels, where it circulates with the blood, or in the fibres, with which it is combined. It forms especially the colour of the muscles, and in such state undergoes no alteration from asphyxia; in its free state it is blackened. The divided muscles furnish an infinity of black drops, which are no other than indices of the divided vessels. Such drops contrast with the red of the muscles; but when circulating within them, are the cause of that livid tint which they then present.

2dly. The nerves are habitually penetrated by a number of small arteries, which creep along within their tissue, and carry to them both excitement and life. In the state of asphyxia the black blood by which they are traversed, is announced by the dull brown, which succeeds to the rosy-white, which is natural to them.

3dly. There are few parts, where the influx of the black blood is more visible, than in the skin; the livid spots so frequent in asphyxia, are only the effect of the obstacles which it meets with, in its passage towards the general capillary system, to the organic contractility of which it is not a sufficient excitant. To this cause also is owing the tumefaction of certain parts, such as the cheeks and lips. This phenomenon we have seen already in thelungs, they cannot be traversed by the blood and therefore become in the last moments of life, the seat of a fulness, which affects the whole of the capillary system there; but for the reasons, which I have assigned, such fulness is always more evident in the capillary system of the lungs, than in that of the system in general.

4thly. The mucous membranes also, when the chemical functions of the lungs are interrupted, exemplify a similar phenomenon. The swelling of the tongue, observable in those that have been drowned or hanged, or asphyxiated by the vapour of charcoal, the lividity of the membrane of the mouth, of the intestines, and the bronchiæ which have also been remarked, depend on no other cause. The following is a proof of this assertion:

Drag out of an animal a portion of the alimentary canal and divide it in such way as to expose its inner surface. Then shut up the pipe which has been previously adapted to the trachea, and at the end of four or five minutes, a brown tint will succeed to the red one, which is natural to this surface.

5thly. I have made the same remark upon the fleshy granulations of a wound, inflicted on an animal, for the purpose of observing the manner in which they are coloured by the black blood. In the two last experiments, this phenomenon is slower in taking place than in many other circumstances.

6thly. The alteration of colour in the serous membranes is much more quickly effected than it is in the mucous membranes. Of this we may assure ourselves by comparatively examining the outer and inner surfaces of the intestines, while the pipe in the trachea is shut; in the serous membranes, the livid tint which they assume, depends upon the vessels, which creep underneath them,and not on the blood by which they are penetrated. Now as these vessels are considerable, the black blood must flow into them almost as soon as it is produced. In the mucous membranes on the contrary, and in all cicatrices, the colour which they take on in asphyxia, is made by the capillary system of the membrane itself, which system is much more tardy than the other, to receive the black blood, and to be penetrated by it; so much so indeed, as to refuse it in some parts. I have many times seen the membrane of the nasal fossæ very red in asphyxiated animals, while that of the mouth has been quite livid, for there are parts into which as I have said the black blood will not penetrate at all, and then they preserve their natural colour. 2dly. There are others into which it evidently passes, but where it stops, and then a simple change of colour is observed, if it have penetrated but in small quantity; and again, if it have penetrated in a considerable quantity, together with such change of colour, there will be observed a tumefaction of the part. 3dly. In other cases, the black blood merely traverses the parts, without stopping in the capillary system, and passes at once into the veins, as the red blood does.

In the first and second case, the general circulation experiences an obstacle which puts a stop to it in the general capillary system. In the third, which is much more universal, it is in the capillaries of the lungs that the blood is at last arrested, after having circulated in the veins.

These two sorts of impediment coincide with each other, in many instances. Thus in asphyxia, a part of the black blood which circulates in the arteries stops in the face, upon the mucous surfaces, in the tongue, and in the lips, while the other, and much the larger quantity,finds no impediment in the general capillary system, and is finally arrested in the lungs.

What is the reason, why certain parts of the capillary system refuse to admit the venous blood, or if they admit it, do not pass it on to the veins; while others are less enfeebled by it, and transmit it as freely as ever. All this must certainly depend on the relation existing between the sensibility of each part and the venous blood.

I was desirous of making use of the power, which we possess, of changing the colour of the blood, for getting some insight into the influence of the circulation of the mother, upon that of the fœtus; accordingly I procured a bitch big with young, and asphyxiated her, by closing a tube, adapted to the trachea. About four minutes after she had ceased to breathe, I opened her; the circulation was going on. I then cut into the matrix, and exposed the cord of two or three of the fœtuses. The artery and the vein, were both of them full alike of venous blood.

Had I been able to procure other bitches in a similar state, I should have repeated this experiment in another manner. I should in the first place have compared the natural colour of the vein, with that of the artery. In many of the young of the guinea pig, the difference appeared to me to be much less than it is in the adult animal. In many circumstances indeed I could perceive no difference whatever. Both the arterial and venous blood were equally black, though the respiration of the mother was in no wise impeded by the opening of the belly. Secondly, I should have closed the tube in the trachea, and then have observed whether the change in colour of the umbilical artery of the fœtus (supposing the blood of the artery to be different from that of the vein) were correspondent with that, which would inevitably take place in the blood of the mother. Experiments made with aview to these circumstances, and on large animals, might probably throw much light upon the mode of communication, between the mother and the fœtus. Observations are also much to be desired, with respect to the colour of the blood in the human fœtus, and the cause of its passage from a livid colour, to the very marked red which it assumes, some little time after birth.[95]

Back to Index Next