Chapter XV: Section II (10)

Considered in the first point of view, contractility is much more evident than extensibility. When the artery is no longer distended with blood, it contracts in a sensible manner. It is to this contraction, that the following phenomena must be referred; 1st. the umbilical artery and the ductus arteriosus, become like ligaments after birth, by the adhesion of their parietes which are contracted. 2d. If we make a ligature upon an artery, the whole portion comprised between this ligature and the first collateral branch, soon exhibits the same phenomenon, as is proved by the operation for aneurism. 3d. If we include a portion of the carotid between two ligatures, and afterwards empty it by a puncture, it suddenly loses half its caliber. 4th. In dogs in whom I have transfused blood in order to produce artificial plethora, I have observed the arteries to be almost double in diameter, to what they are in those of the same size, who had suffered great hemorrhage. Two animals of the same size, one killed by hemorrhage the other by asphyxia, exhibit the same difference. 5th. These experiments shew me satisfactorily the cause of a large and small pulse, a cause admitted moreover by most physiologists. The artery is certainly more or less large, according to the quantity of blood that fills it. There is a point of extension that it cannot pass; but it contracts often for the want of blood, so as to be as it were, but a mere thread. 6th. Though you may have opened but few bodies, you have no doubt been astonished, that in those of the same size, the arteries have often very different diameters. This arises wholly from what takes place at the moment of death. If, from the want of blood, the arteries are for a long time contracted, they remain in this state, as happens to the heart in death by hemorrhage, &c. This is so true, that arteries of different diameters commonly become equal by injection, which brings them to an uniform degree of extension that they cannot pass. 7th. In a longitudinal wound of arteries the ends of their cut fibrous circles separating from each other, a space, which does not close, is left between them.

Most authors have confounded contractility of texture of the arteries with irritability. I have no occasion here to show how much they are deceived. In none of the preceding cases, is it necessary that a stimulant should be applied upon the arterial texture; the only thing necessary is the absence of extension, a distinctive character of the contractility of texture. Moreover it is evident, that this property continues after death, though in a less degree than during life; whereas some hours after death, every kind of irritability disappears. I think that it is especially in the arterial system, that may be seen the advantage of my division of the properties of our organs. Read all the authors upon this system, and you will see that no one is intelligible, because they have not assigned the limits of the vital properties and those of texture.

Contractility of texture in the longitudinal direction, is in proportion less evident than in the transverse; it is however real. 1st. Thus when we cut an artery between two ligatures, the two ends retract immediately in an opposite direction. 2d. This retraction is evident in amputation; that of the muscles and the skin however is greater, the artery often projects a little. 3d. An artery, cut transversely in a portion of its parietes, often presents at this place a broad opening, arising from the retraction of the cut parts, as happens in a longitudinal wound of which I spoke just now. 4th. When we draw an artery forcibly and suddenly let it go, its retraction is very evident. In making this experiment upon an animal, the vessel buries itself in the flesh. Hence why, the spermatic artery and cord, drawn down by the weight of the testicle, often ascend into the abdomen after it is removed, if care is not taken to prevent them.

It is this circumstance that has induced me to propose for the operation of sarcocele, a modification which consists, after having dissected around the cord after the first incision, 1st, in searching immediately for the vas deferens, which is easily found by its extreme hardness; 2d, in giving it to an assistant to hold; 3d, in passing a bistoury between it and the blood vessels; 4th, in cutting the blood vessels first and leaving the vas deferens untouched; 5th, in afterwards tying the artery, which is easily discovered by the jet of blood; 6th, and then, when this is done in cutting also the vas deferens. It is evident, that by this section at two different times, we have the advantage of applying the ligature without fear of the retraction of the artery, since the vas deferens to which it adheres, and which is not cut, until it is tied, is sufficient to retain it. I have not performed the operation; but it is evident that there is nothing to prevent the execution of this plan, since the parts are sound where we cut. I have moreover always taught the student to manage in this way with ease. It is especially when it is necessary to cut the cord very near the ring, because it is diseased in its course, that this method of operating appears to me to have great advantages.

I think that the retraction of arteries that have been drawn, and their contraction afterwards, perform an important part, in producing the absence of hemorrhage in most wounds by laceration, a singular phenomenon, that particularly distinguishes these wounds from those by cutting, even when a considerable vessel happens to be in their course. Many authors have given examples of this; we find some particularly in the works of Sabatier.

III. _Vital Properties._

_Properties of Animal Life. Sensibility._

Have the arteries animal sensibility? Upon this point, facts teach us what follows. 1st. The ligature of an artery sometimes produces a painful sensation, more frequently it does not. It is especially in the spermatic that the pain is frequently felt, but this can be referred to the nerves. 2d. I can without exaggeration say, that I have made experiments upon more than a hundred dogs, in whom I have forced various substances through the carotid to the brain, and have irritated this artery with the scalpel, acids, alkalies, &c. but that the animals have never given any marks of pain. Many authors have obtained similar results. 3d. I would observe also, that it is an additional proof of the kind of insensibility of the nerves of organic life, which as we have seen are distributed to the arteries. 4th. This is what I have observed concerning the irritation of the common membrane of the red blood; the injection of a mild fluid at the temperature of the animal produces no effect; but an irritating fluid, as ink, a solution of acid, wine, &c. creates severe pain equal to that arising from the irritation of the most sensible parts, if we may judge by the cries and agitation of the animal, the moment the fluid enters the carotid.

_Contractility._

Animal contractility does not exist in the arteries. In fact this contractility could only depend upon a relation between these vessels and the brain, by the means of the nerves; now, 1st, any irritation produced upon this last viscus, occasioning convulsions in the organs under the influence of the will, has no effect upon the arteries. 2d. Opium, which in a certain dose, paralyzes, if we may so say, the same organs, leaves the arterial motion wholly unaffected. 3d. If we lay the spinal marrow bare, and irritate or compress it, the action of the arteries is neither increased or diminished, whilst the voluntary muscles become the seat of convulsions or paralysis. 4th. No effect is produced upon the arteries by different irritations, whether of the nerves of the cerebral system, which accompany the vessels without giving them any apparent filaments, or of the nerves of the system of ganglions, which are distributed irregularly and in very great number upon their external surface. 5th. To remove all doubt upon this subject, I selected galvanism, the most powerful kind of excitement. Without effect did I arm on the one hand the cerebral nerves, on the other, the arteries that are joined to them; the contact of the two armed points does not produce in the arteries the motion it excites in the muscles in which the nerves are spread. The effect is the same in experiments upon the nerves of the ganglions. I armed on one hand the upper part of the mesenteric plexus, on the other, the arteries of the same name, first stripped of their serous and cellular coat; the contact was entirely without effect. The arterial system does not possess that faculty of motion which the action of the brain is capable of producing. All that has been written by different authors, by Cullen in particular, upon the nervous power, upon the action of the brain on the arterial system, is vague, illusory and contradicted by experiment.

_Properties of Organic Life. Sensible Organic Contractility._

The sensible organic contractility is evidently wanting in the system of which we are treating. In whatever way we irritate an artery in a living animal, it remains uniformly immoveable. 1st. If we stimulate the external surface with a scalpel or any other instrument, it is easy to make this remark. 2d. The same observation is made when we excite the internal surface, an experiment that I have often made, because we know that the heart is more irritable internally than externally. 3d. An artery cut longitudinally in a living animal does not turn over at its edges like the intestines in similar circumstances. 4th. An arterial tube, drawn out of the body, never gives like the intestines, the heart, &c. any mark of contractility. 5th. If we raise the arterial plates, layer by layer, in a living animal or one recently killed, we see nothing of that trembling, that palpitation that the fibres of the organic muscles exhibit under like circumstances; on the contrary, we observe in them a kind of inertia very analogous to that of tendinous, aponeurotic fibres, &c. 6th. It is said, that by placing the finger in an artery, a contraction is felt. I have often made this experiment; the contraction is infinitely less sensible than has been said; besides it is produced evidently by the contractility of texture. 7th. Lamure says, that a portion of blood being intercepted between two ligatures in an artery, the parietes of it continue to contract, though deprived of the influence of the heart; this is not correct. It is so important that I have examined it myself; I have repeated this experiment at least ten times upon the carotid; the following has always been the result; the tube comprised between the two ligatures and filled with blood, is agitated by a real motion, but it is only that of the common locomotion that it partakes with the whole artery, and which arises from the impetus of the blood against the ligature nearest the heart. To be convinced of this, it is only necessary to lay bare a considerable portion of this artery; we see evidently that the whole tube, whether the portion nearest the heart, or that comprised between the ligatures, or that which is beyond, is agitated by a common motion. 8th. Instead of the blood I have intercepted different irritating fluids in a portion of an artery; there is the same inertia, the same want of contraction in the parietes; but the same motion derived from the general locomotion. 9th. Many authors have produced a contraction on the part of the arteries by stimulating them with concentrated acids. This is true, and I have also produced this effect; but it is not the result of contractility, but it is the horny hardening. Observe also that the arterial texture never returns to its primitive state after a contraction like this; that the alkalies, that are as irritating as the acids when the vital forces are excited, have no effect here; it is the same phenomenon during life, as that which we have spoken of as taking place after death.

There can be no doubt, I think, after this, that the arteries do not exercise during life any kind of contraction by themselves and under the vital influence. All that has been said upon this point, is the evident effect of the contractility of texture. Thus when we open an artery between two ligatures, it empties itself of the blood it contains, or of the fluid that is accidentally pushed there; the same phenomenon takes place when we place only one ligature that intercepts the influence of the heart, &c. It is so true, that all these phenomena and other similar ones depend upon the properties of texture, that they take place in the dead body as long as an artery is not putrid. Fill any portion of the arterial system, afterwards open one of its tubes, it empties itself immediately by contracting. The contraction produced by the defect of extension, is that which characterizes the contractility of texture. Irritability or sensible organic contractility, supposes on the contrary uniformly the application of a stimulus.

_Insensible Organic Contractility._

Insensible organic contractility or tone very evidently exists in the arteries. In the great trunks and wherever the pulsation is sensible, its functions are limited exclusively to nutrition and exhalation, if this last takes place in the interior of arteries, which I do not believe. But when the influence of the heart upon the blood contained in these vessels ceases, which happens at the commencement of the capillary system, then the tone begins to have an influence not only upon the nutrition of the vascular parieties, but also upon the circulation that is going on there; it is even wholly by the tonic powers, as we shall see, that the circulation of the small vessels is carried on; the heart has no influence there. I shall treat of this property under the general capillary system; here it performs but a very weak part.

As to organic sensibility, it evidently exists in the arteries, since it cannot be separated from the preceding contractility; like it, it is obscure in the great trunks, which have only what is necessary for their nutrition.

From the small development of the organic forces of the arterial texture, it is evident that this texture would rarely be the seat of affections, over which these properties particularly preside. This also is proved by observation.

1st. Acute diseases are rarely observed in the arteries. Among all the bodies that I have examined, I have found but very few in which there were traces of inflammation in the arterial texture. I would observe upon this subject, that it is necessary to distinguish accurately the redness which is, as we have said, the effect of maceration, and which even appears spontaneously in the dead body some time after death, especially in the cerebral arteries; it is necessary, I say, to distinguish it from that which arises from inflammation. In one the arterial fibres are really red, in the other they appear so only by the injection of their vessels. Is the common membrane inflamed in inflammatory fever? I am entirely ignorant. These simple fevers are so rare, especially in hospitals that we have hardly an opportunity of examining patients that have died of them. But by supposing that this inflammation existed, the infrequency of these fevers considered in their simple state, would prove even how little the arteries are disposed to inflame. 2d. The arteries are not often the seat of chronic affections. Except on the one hand aneurism, in which the arterial texture is hardly altered, but merely broken, and in which consequently its organic sensibility performs but a very small part; on the other, the osseous incrustations, most of the alterations that are so frequent in the other textures, are not observed in this.

This texture must be ranked with the cartilaginous, the fibro-cartilaginous, the fibrous, the muscular even, &c. as it respects the infrequency of organic alterations. These textures exhibit a phenomenon opposed to that of the serous, mucous, glandular, dermoid systems, &c. which are especially characterized by the frequency of these alterations. Compare the organic properties, the sensibility and insensible contractility in the two classes of textures; you will see them very feeble in the first, in which in a natural state, they preside only over nutrition; you will observe, on the contrary, that they are very evident in the second, because there they preside over nutrition, exhalation, absorption, secretion, &c.

The difficulty with which the arterial texture inflames and participates in the different alterations of the neighbouring organs, preserves the integrity of the circulation in many cases. What would become of this function, if the arteries received as easily as the other textures, the influence of surrounding diseases? Placed at every moment by the side of inflamed, suppurating, swelled parts, &c. if they become changed by their neighbourhood, especially in the great trunks, a general derangement would soon be felt in the motion of the blood. Dissect the arteries in the organic affections of the stomach, the liver, the spleen, &c.; they are untouched, and only a little increased in size; whilst a general swelling seems to confound in a new mass all the neighbouring textures.

The clots in aneurism adhere sometimes so intimately to the common membrane, that we are obliged to remove them with an instrument. But this adhesion is entirely inorganic; it is a kind of agglutination, that would imply the small degree of life of this common membrane, as the facility with which colours are fixed in the epidermis implies it in this last organ.

_Remarks upon the causes of the motion of the red blood._

The red blood is moved in the heart by a mechanism which there is no difficulty in understanding. But an important question remains to be decided concerning its motion in the arteries; are these vessels active or passive in this motion? When the physician examines the different states of the pulse, is it the state of the heart or that of the arterial system that he ascertains? From the absence of sensible organic contractility, as we have observed in this texture, it is evident that its part would be especially passive; that the motion of which it is the seat is communicated to it; that the heart is the great agent of the pulsation of the arteries; that it is that which gives the impulse, which these vessels only obey, and that consequently in almost all cases the state of the pulse is the index of the state in which the vital forces of the heart are found, and not of the state of the arterial system, whose life is not more raised in the greatest and most frequent pulsatory motions, than in the feeblest and most infrequent. Thus in convulsions, the principle of which is a wound, an irritation of the brain, &c. the nerves, though conductors, are, if we may so say, passive.

I will now examine in detail this important question, that so many physicians have considered differently.

_Influence of the heart in the motion of red blood._

1st. The first reason that induces me to believe that the heart is almost every thing, and that the arteries are particularly passive on the score of vitality in the motion of the red blood, is the comparison of the vital forces of these two organs, the astonishing activity of the organic contractility of the heart, and the absence of this property in the arteries. In fact, to move of itself, it is necessary that an organ should have the principle of motion, that is to say, one of the two kinds of vital contractility in a sensible degree, the organic or the animal; for we do not know of other vital forces in the animal organs, and we cannot say that nature has created one especially destined for the arteries. Grimaud admitted that there was an active dilatation of the vessels, which opened of themselves, according to him, to receive the blood, and were not opened by its impulse. We shall see that this kind of motion is real, to a certain extent, both in the heart and in the organic muscles. But here it is wholly different; the heart dilates of itself when it is empty, as we see by drawing it out of a living animal, and by emptying it afterwards of the fluid it contains, because it has in itself the cause of its dilatation. But in no case have I seen the arteries thus undergo an alternate motion when they are empty. They are uniformly found contracted upon themselves.

2d. If the arteries produce the pulse by their vital contraction, there ought to be an irregularity in the pulsations below an aneurismal tumour, since the arterial texture being altered, it loses in part its contractility, or at least this property is changed. Now we observe precisely the contrary. On the other hand, every organic disease of the heart inevitably affects the pulse. Is there an increase of the fleshy fibres, as in the aneurisms in which the left ventricle is so thick? it becomes strong; it is irregular, if obstructions exist at the mitral or aortic valves. If in old age, ossification exists only in the arteries, the circulation is unaffected; if at the origin of the aorta or in the heart, it is irregular. An artery might become a bony canal, and the blood would circulate there as usual, with the difference only of pulsation. What I have said of the chronic affections of the heart may be said of the acute ones. Syncope arrests its motion, it arrests also the pulse. Certain passions, as anger, fear, &c. seem to be a stimulant to it; they hasten also the arterial motion. All kinds of inflammation of the pericardium affect the pulse. This membrane often adheres to the heart in consequence of inflammation, and at the same time the pleura of both sides adheres to it also; so that we might say then that the lungs and the heart made but one. I have seen four examples of this morbid state, in which the motions of the heart were much contracted; in all the pulse was small, irregular, and intermittent. The more I open bodies, the more I am convinced that when the irregularity of the pulse is uniform for a considerable time, there are almost always organic affections of the heart; from which there is reason to believe that the irregularities of the pulse that are acute, if I may use the term, arise from an alteration, not in the texture, but in the vital forces of this organ, and that the arteries are almost entirely disconnected with it. We know how frequent these irregularities are in acute diseases. Since then every alteration of the heart essentially affects the pulse, and those of the arteries on the contrary, leave it unaffected, we should certainly conclude from this, that the one is essentially active in this great phenomenon, and that the others, on the contrary, are almost passive.

3d. There is no doubt that at the instant a ligature prevents an artery from receiving the influence of the heart, it ceases to beat. All the phenomena of aneurisms, treated by compression or by ligature, establish this fact. If the contrary has sometimes been observed, it arises only from anastomoses, and then it is equally the heart that makes the artery beat above and below the ligature. It is absolutely false, as I have said, that an artery never beats between two ligatures. Often in aneurism the artery being compressed below the tumour, this beats much stronger than before.

4th. Cut off the arm of a dead body, and make it pliable by leaving it for some time in a tepid bath. Fix afterwards to the brachial artery a small tube; place the other extremity of this tube in the open carotid of a large living dog; immediately the heart of the animal will drive blood into the arm. The artery will have a kind of pulsation, less, without doubt, than in a natural state, but sufficient to be perceived even through the integuments. I have often repeated this singular and curious experiment, of which I shall have occasion to speak again. It was suggested to me by another, of which I have given an account in my Treatise on the Membranes, and which consists in making the red blood circulate in the veins, without the motion of locomotion, it is true, but with a rustling sensible to the finger, and with a velocity almost equal to that of the arteries. This last experiment alone would prove that the heart is almost the only agent of impulse of the blood circulating in the arteries; in fact, every throw of blood coming from the veins is uniform, because the capillary system pours without a jet this fluid into these vessels. On the other hand, every arterial throw is by jets, which are produced by the contraction of the heart. Now if you open a vein in which you have made red blood circulate by a curved tube, the throw of blood wall be in jets, which will correspond to the contractions of the heart. With the difference merely of locomotion, a vein presents during the circulation of the red blood, the same phenomena as an artery. Make, on the other hand, the reverse of this experiment, that is to say, fit a curved tube to a vein and an artery, so that the blood of the first may flow into the other; the artery will lose immediately its pulsatory motion, unless it be kept up in the collateral branches; this does not happen if we select great trunks, for example, the crural and corresponding vein. It is evident, that all these experiments, which I have frequently repeated, would give a result entirely opposite, if the arteries took an active part in the circulation by their vital properties.

5th. The force of the heart makes the blood circulate through inert tubes, fixed to the arteries, to a considerable extent. If we cut an inch of the carotid artery, and substitute a tube fixed to the two open ends of this artery, the blood will go through this tube and the artery pulsate as usual above. I cannot imagine in what way those have been deceived who have obtained different results.

6th. Take two dogs; fix the end of a tube to the carotid of one, on the side of the heart, and the other end of the same tube to the crural or carotid of the other, on the side opposite to this organ; the heart of the first will uniformly make the arteries of the second pulsate, by sending blood to them. All my experiments upon death, experiments already published, have shown me this phenomenon. Besides, in aneurism the pulsation takes place below the tumour; yet at that part, the two ends of the broken artery are separated; the cellular membrane alone serves to unite them, by forming the cyst. The blood passes then through an intermediate body that is not arterial.

7th. Fix to an artery one end of a tube, which has at the other a sac made of skin, or gummed taffety, the blood will fill it immediately; then at each contraction of the heart, it will have a sort of pulsation. It is thus that the aneurismal tumour pulsates, which is cellular. Whatever may be the organ that contributes to form the cyst, it would pulsate, provided it received, with the blood, the impulse of the heart.

8th. I would ask, if the active dilatation of the arteries could be sufficient to raise the brain, impart a motion to the leg that is crossed upon that of the opposite side, to overcome the weight of the tumours that are situated in their course, and raise them at each pulsation. It evidently requires a more powerful organ to produce these phenomena, and this organ is the heart.

9th. How is it, that the pulsation of all the arteries is simultaneous, if a single centre does not preside over this pulsation? The whole arterial system, struck suddenly with the same blow, is raised and pulsates at the same time. Is it not evident, that if the arteries contracted by themselves, the least derangement in one part, the least pressure, &c. would produce a discordance in the motions?

10th. No animal has arterial pulsations, if it has not a heart, or a fleshy vessel, knotty, and divided by contractions, as in many insects; have the pulsations of this vessel, which is a substitute for the heart, been well observed? It is thus that the system of the vena porta never has pulsations, though its hepatic part is arranged like the arteries.

11th. The two ends of a cut artery pour out blood, but this is the effect of the anastomoses, and not of the re-action of the end opposite to the heart, as I thought myself for some time. It is for the same reason that an artery can pulsate sometimes below a ligature.

12th. I have no doubt but that without the heart, the red blood would have in its great canal, a kind of motion, a motion that would resemble that of the vena porta; it would be entirely without pulsation.

13th. Cases have been quoted, in which the motion of the arteries was said to take place as usual, though they contained no blood. I confess that I do not know how we can be assured of this fact. But if it was real, it must be placed at the side of that of the soldier, who could stop the motion of his heart at will. What can we conclude from an insulated phenomenon, which is in contradiction to all those that nature daily presents? It may not be useless, I think, to remark, that since healthy physiology has advanced, has been studied with method, a love of truth, and a desire only to collect facts, we have no longer been presented with those extraordinary cases in which nature seems to depart from the laws she has imposed upon herself.

From all that has been said, it follows, I think, very evidently, that in the pulsation of the arteries, the heart is almost the only power that puts the fluid in motion; that the vessels are then passive, that they obey the motion that is communicated to them, but that they have none of themselves dependant at least on their vitality. Thus nature has chosen for the arterial texture one of those of the economy, in which life is the least evident; as the heart is remarkable for its vital properties, the arteries are remarkable for the absence of them. They must be ranked with the cartilaginous, fibrous, fibro-cartilaginous textures, &c. It is that they may not disturb the unity of impulse by their motions, that nature has thus formed the arteries. Suppose that they had the same vital forces as the intestines; what would become of life? Any convulsive contraction a little too strong in the aorta or in the great trunks, by contracting their caliber too much, would arrest the circulation, and produce the most serious effects by agitating it in an opposite direction to the heart. In the intestinal canal, this phenomenon only produces vomiting. It would produce death suddenly in the arterial system. The more attentively we examine, the more we shall be convinced of the necessity of having but one agent of impulse for the arterial system, and of having this system inert, so that it cannot be able to arrest the course of the blood.

I do not say that the arteries can never contract from the vital influence; the skin which is not irritable, wrinkles by cold. But the cases are very rare, in which the arteries contract. When they exist they cause an inequality of the pulse on the two sides; an inequality rarely noticed in diseases.

_Of the limits of the action of the Heart._

The heart is then the essential cause of the pulse; it is this which puts every thing in action in the arterial motion. Many authors have overrated its influence; they have thought that its impulse was sufficient to produce, not only the arterial motion, but also that of the general capillary system, and even that of the veins; so that the contraction of the left ventricle alone is the cause, according to them, of the long course the blood runs from it to the right ventricle. But it is incontestably proved, as we shall see, that when this fluid has arrived in the general capillary system, it is absolutely beyond the influence of the heart, and that it moves only by that of the tonic forces of the small vessels, and therefore for a stronger reason, the left ventricle has no influence in the venous system. It is in this respect that the authors, of whom I have spoken, have erred, and not under that of the impulse that they have admitted in the arterial system on the part of the heart.

We can, I think, establish nearly the limits of the influence of the heart upon the blood, by fixing them where this fluid is transformed from red to black in the general capillary system. As it advances in the small vessels, the impulse received is undoubtedly weakened, and the small vessels supply it by their insensible organic contractility; but I believe that the motion received from the heart, is not entirely lost until at the place of the change into black blood; so that we can establish for a general principle, 1st, that in the great trunks, in the branches and even in the smaller branches, the heart is almost every thing for the motion of the blood; 2d, that in the ramifications, it is in part this organ and in part the vital action of the arteries, which contributes to this motion; 3d, that finally it is this vascular vital action alone in the general capillary system.

The pulse exists in its fulness, only in the trunks, the branches, and the smaller branches. It is evidently weakened in the ramifications; it becomes nothing in the capillary system. The arterial texture of the great trunks is provided, as we have seen, with insensible contractility. But the impulse received by the heart is on the one part so strong, and the column of blood so great, that the influence of this kind of contractility is really nothing. Irritability alone could have influence; but this does not exist in the arteries. On the contrary, in the small vessels, the shock on the one hand impressed by the heart is insensibly weakened; on the other, the streams of blood being so fine, they have no occasion for any thing to produce their motion, except a kind of oscillation, an insensible vibration of the vascular parietes. It is this that essentially distinguishes the two kinds of organic contractility. The one is exerted only upon the fluids in mass, as upon the blood, the aliments, the urine, &c. The other causes the motion of the fluids when divided into small streams; it presides over the capillary circulation, exhalation and secretion. The influence of the first is very considerable wherever there is a great cavity, as the stomach, the bladder, the intestines; that of the other takes place only in the small vessels. As long as the blood is in a considerable mass, the heart must inevitably be the agent of impulse, the arteries cannot be, from their want of irritability. When it is in very small streams, then it moves by the insensible contractility of the vessels. This then is the part which this property performs in the system with red blood; 1st, it exists in the trunks, the branches and the smaller branches; but its effect is nothing where that of the heart is evident. 2d. That of the heart being weakened in the ramifications, its own contractility begins to have an influence. 3d. Finally, the heart ceasing to agitate the blood in the general capillary system, the insensible organic contractility or tone, is the sole cause of motion.

_Phenomena of the impulse of the Heart._

What part then have the arteries in the pulse? The following is what takes place in this great phenomenon; the arteries are always full of blood, the impulse that the blood in them receives from the left ventricle, is felt at the instant in the whole system, and even to its extremities. Imagine to yourself a syringe, the tube of which gives rise to an infinity of branches, which afterwards give origin successively to a number of smaller ones; if, when you push the piston of the syringe, its body and all the branches and smaller branches arising from it, are already full of fluid, it is evident that at the very instant in which the piston shall push the fluid in the body, it will go out on all sides through the open branches. Now suppose, that instead of a piston, you could make the parietes of the body of the syringe suddenly contract, the fluid at the instant of the contraction would spout out on all sides from these open branches. Another comparison will render this more evident; strike at one end of a long timber, the motion will be suddenly felt at the opposite one.

We can from this form an idea of what takes place at the instant of the contraction of the left ventricle. Authors have spoken of a wave or undulation of blood, being propagated through the whole arterial system, and formed by the two ounces of blood that are poured into the arteries at each contraction. The arterial motion should be thus considered, if the arteries were empty at the instant of contraction; but in their state of fulness, the impulse is generally and suddenly felt, and with almost as much force at the extremities as at the origin of the arteries; it is only in the ramifications that the motion becomes a little weakened. Fill with water the arteries of a dead body, and fix a syringe full at the aorta; at the instant you push the piston, the water will spout out of the tibial or any other artery, if you loosen an opening that had been previously made in them.

The idea that is commonly entertained of the progressive motion of the blood, is wholly incorrect. This fluid has been considered as flowing in the arteries almost like water in brooks. It is not so. At each contraction of the ventricle, it experiences suddenly a general motion that is felt at its extremities. Do you wish for another comparison? Suppose a syringe, to the tube of which is fitted a series of elastic pipes arising from each other; push the piston, you will see all these pipes swell simultaneously, become straight, and the fluid flow at the same time to the extremities, if they are open.

It is not the contraction of the arteries that drives the blood to their extremities. This is so true, that if you open one of these vessels at a distance from the heart, each jet that the blood will make in going out, will correspond to each contraction of the ventricle. Now if the arteries drove the blood to all the extremities, by contracting, their contraction and relaxation would alternate with those of the heart; but if it was so, each jet of the arterial throw should correspond to each relaxation of the ventricle; the contrary of this is the case as I have just said.

From this we see how very inaccurate is the common opinion, which I believed myself for many years, viz. that the auricles contract at the same time with the arteries, and the veins at the same time with the ventricles. The circulation of red blood is thus explained; 1st, the pulmonary veins drive the blood into the left auricle. 2d. This by contracting forces it into the ventricle, which dilates to receive it. 3d. This last contracts afterwards, sends it to the aorta which dilates at the instant of contraction; 4th, then this contracts to drive it to all the parts. This last does not take place; you can never observe it like the others, in a living animal. Examine as closely as possible, a great artery laid bare; it rises, but it does not dilate hardly at all in an ordinary state, nor does it contract. Contraction of the left ventricle; general motion of all the arterial blood; the entrance of this blood into the capillary system, are three things that take place at the same instant. It is like the blow on the timber, that is felt at one end, at the same time that it is received at the opposite.

We can form a very accurate idea of the circulation by examining the mesenteric arteries through the peritoneum, after having opened the abdomen of an animal; at each pulsation you see them all simultaneously rise and pulsate at their extremity as well as at their origin.

It is impossible to form an idea of the arterial motion, by considering the wave or undulation of blood as extending itself at each contraction in the arteries, and arriving afterwards successively at the extremities. Read all the authors upon the circulation; you will see that there is no subject that is treated oftener or more at length, than that of the course of the arterial blood, and yet there is no one in which you are left in more doubt and obscurity. Why? because all go upon a false principle, and all the consequences are inaccurate, where the principle itself is not correct.

It is not the wave of blood going from the ventricle, that is driven at each contraction into the capillary system; it is the portion of this fluid which is found nearest this system, as in the syringe, it is the portion that is in the tube that the piston forces out and not that with which it is in contact; whence it follows, that it is only at the end of some time that the blood arrives from the heart, at the general capillary system, that it remains during a number of contractions in the arteries, and that it is only successively expelled; which favours the mixture of the different principles that compose it.

From this manner of considering the arterial motion, which is the only real and admissible one, it is evidently impossible that the curves can injure this motion, besides this is proved by many facts.

I consider also as destitute of every kind of foundation all that has been said in the books of physiology, upon the causes of the delay occasioned in the course of the blood, 1st, by its passage from a narrower to a broader place, and by the conical form of the general arterial system; 2d, by friction; 3d, by the angles; 4th, by the anastomoses which give an opposite shock, &c. &c. All this would be true if the arteries were empty at the time of contraction, because the blood would then have in them, truly a progressive motion. But in the general and instantaneous impulse that the whole mass spread in the arterial system experiences, all these causes are evidently nothing. I return now to the trifling but very accurate comparison of the syringe. Suppose that a tube twisted in a thousand ways, with numerous angles, inequalities, internal projections, &c. was fixed to it; if the tube and the body of the syringe are full at the instant we push the piston, the water will escape suddenly from the extremity of this tube with as much force as if it was straight and short. It is so true that all the causes of delay, which would have some effect, if the arteries were empty at the instant the blood is driven into them, have none in their ordinary state, that many judicious observers, who even admitted the delay, have seen in their experiments that the motion was every where the same, in the smaller branches as in the trunks. Why did not this undeceive them? We know that the pulse is the same in all parts of the arterial system; how could it be if there was this delay? What has greatly retarded the progress of the physiology of the circulation, is the idea that is attached to the velocity of the course of the red blood. This velocity cannot be rightly estimated, because the motion is not successive, because, to speak correctly, the blood does not flow; it is suddenly driven by a general impulse, in which we cannot calculate any thing.

Philosophers have calculated the motion of fluids, where their particles are successively displaced, as in the course of a river; but they have paid less attention to that brisk motion of the whole or of the mass, if I may so say, that takes place in canals in which they are enclosed on all sides, and are acted upon at one extremity.

_Remarks upon the Pulse._

Two things are already evidently proved, viz. 1st, that the heart is the peculiar agent of the arterial motion, and that the arteries are almost passive in this motion; 2d, that it consists in a general impulse suddenly experienced by the whole mass of red blood, felt at the same time at the extremities and in the trunks, and not in a successive progression of a wave or undulation that goes from the left ventricle. It remains for me to examine how the heart produces the pulse by this brisk and instantaneous motion. There is still much to be elucidated upon this point; but we cannot deny that the locomotion of the arterial system does much in this phenomenon. At the instant the mass of blood is driven thus from the heart towards the extremities, by a motion of the whole, if we may so say, it tends inevitably to straighten the arteries, especially when they are tortuous. This straightening necessarily produces a locomotion, which causes the pulsation of the artery.

As to the dilatation, it is hardly any thing in an ordinary state; however if you press a little upon an artery, the blood makes an effort to dilate it and this effort increases the sensation of the pulse; Jadelot thought that it alone constituted it. On the other hand, if much blood enters the arterial system at the instant of the contraction of the heart; if a resistance exists in the general capillary system, the arteries can be also dilated, but it is not their return upon themselves or contraction that drives the blood into the capillaries; this return is subsequent. In fact, at the instant of contraction, the blood enters on the one part into the arteries in going from the ventricle, and goes on the other to enter the capillary system; these two phenomena take place at the same time, since they arise from the same impulse. Then when there is a contraction in the artery, a motion which is only the contractility of texture put into action, this contraction does not drive the blood; but it takes place, because the blood has been driven into the capillary system at the instant of the contraction; it is because the artery ceases to be distended, that it returns upon itself or contracts, and not because it is actually distended. Hence how the arterial contraction can alternate with that of the left ventricle; but it is not in the sense that authors have understood it. There are then two periods in the motion of the red blood; 1st, contraction of the ventricle; slight dilatation of the arterial system by the blood that enters it; general locomotion; passage into the capillary system of a portion of this red blood; all these phenomena happen at the same time; it is the period when the pulse is felt; it is that of the diastole. 2d. In the next period, the ventricle is relaxed to fill itself anew; less full of blood, the arteries contract a little upon themselves; all take the place they had lost during the locomotion; this is the period of the systole, a period purely passive, while some have thought it a very active one for the arteries.

As but little blood is driven at each pulsation out of the ventricle, which does not wholly empty itself; and as, on the other hand, at the same time it enters the arteries it goes out from the side opposite to the heart, the arterial dilatation and, consequently, contraction, are almost nothing; thus, they cannot be perceived. Besides, if the contraction really took place, it would hardly be apparent; for when it is the contractility of texture that is in action, it produces a slow insensible motion, a real tightening; whereas contraction, the effect of irritability is abrupt, instantaneous, and produces a motion that the eye always distinguishes.

I cannot insist too much upon this fact, which is certain, viz. that if there is a slight contraction in the arteries at the instant the pulse ceases to beat, it is not that they have contracted to drive the blood, but merely that they contract upon themselves, because the blood that has gone into the capillaries prevents their being sufficiently dilated; it is contractility for the want of extension. Hence why the throws of arterial blood going from an open artery, correspond with the dilatation of these vessels, and the weakening of the throw with their contraction, which would be entirely the reverse, according to the common opinion.

The dilatation and contraction of the arteries being almost nothing in the ordinary state, it appears that the peculiar cause of the pulse is, as Weitbreck has observed, in the locomotion of the arteries, a locomotion that is general and instantaneous in the whole system, and not consecutive, as this author has understood it. I shall not relate here the proofs of this locomotion; they can be found every where. I would observe only, that it is so manifest in living animals, that when we have often examined the circulation by their means, it is impossible to doubt its reality.

Different causes can make the pulse vary; these causes are, 1st, relative to the heart, almost the only agent of impulse; thus its sensible organic contractility, increased, diminished, altered sympathetically or in any other way, can make it with the same stimulus contract quicker, slower, or more irregularly than common; thus the diseases of its organization inevitably alter its motion. 2d. The blood charged with different natural or morbific substances is a stimulant more or less capable of putting in play the motion of the heart. 3d. The general capillary system, according as it receives a greater or less quantity of blood, or refuses admission to that which the arteries send there, &c. produces necessarily numerous varieties in the pulse. There are but few causes relative to the arteries themselves.

If now we consider the great number of causes that can be referred to these three principal heads, we shall cease to wonder at the prodigious variety that the pulse exhibits in health, and especially in diseases. Besides, I shall not examine here in its whole extent the question concerning the pulse; it is sufficient to have announced the principles; I shall hereafter develop the consequences, which are, as we know, of the greatest importance to the physician. We see by the different views that I have presented, that almost all authors have described in an inaccurate manner the motion of the blood, and what loose ideas they have had of it. Experiments have only served to confuse them; it is a work that requires to be entirely done again, either with the materials that many respectable authors have already amassed, especially Haller, Spallanzani, Weitbreck, Lamure, Jadelot, &c. or with new facts. I have only presented the first bases of this work.

We have seen how favourable the firm and elastic structure of the arterial texture is to the locomotion of the arteries, and the influence the curves of these vessels have upon it. I will add that the loose union that they form with the neighbouring parts, and their uniform position in the cellular texture, singularly favour this locomotion.

If the red blood flowed in the veins, we should feel under the finger a kind of rustling, instead of the motion of the pulse; this is what happens in varicose aneurism. There would be no locomotion if the arterial parietes were made of the dermoid, mucous, serous textures, &c. there would be different phenomena with the common impulse.

There are then two things in the pulse; 1st, impulse of the blood, sudden and general motion of its mass by the contraction of the heart; 2d, locomotion of the arteries, an effect produced by this fluid upon the arterial parietes which transmit it. The first is the most essential; as to the second, it would vary, if the arterial texture that produced it ceased to be the same; it depends upon this texture, and is not essential to the circulation.

When an artery is cut at the end of its trunk, the locomotion is much less sensible in this trunk, because less resistance is offered there to the course of the blood.