Part 23

It is the circulation of the red blood that alone furnishes the matter of secretions, except that of the bile, a fluid which however deserves a further examination. It is from this circulation that the serous, cellular, cutaneous, medullary exhalants, &c. draw the fluids that they transmit upon their respective surfaces. All the vessels that carry the matter of nutrition of the organs are also continuous with the arteries and consequently their fluids come from the red blood. In the organs even in which the black blood goes, as in the lungs and the liver, there are vessels with red blood evidently for the purposes of nutrition. It is the red blood that communicates to the organs of the whole body that general agitation which is necessary to their functions, an agitation so evident in the brain. The circulation of red blood is then the most important; it is that, whence are derived the great phenomena of the economy.

_General uses of the circulation of black blood._

The circulation of the black blood, on the contrary, having no connexion with any of the functions, seems only destined to repair, if we may so say, the losses the blood has sustained in the preceding one. Observe in fact that a considerable part of the red blood is expended in the exhalations, secretions and nutrition. The principles it borrowed in the lungs and which gave it a vermilion colour, have been left in the general capillary system. It is necessary that the black blood should receive what the other has lost; now a variety of substances enters the great canal that contains it. These substances are internal or external. 1st. The great trunks of the absorbents constantly pour in the lymph of the cellular texture and of the serous surfaces, the residue of the nutrition of all the organs, the super-abundant fat, synovia and marrow. All that which is to be thrown from within out, is first poured into the black blood. 2d. All that which enters in from without, is also received by it. The chyle, the product of digestion, is at first uniformly carried into the general canal, in which it circulates. In the second place, it is with it that are mixed the substances of the air, which pass through the lungs in the act of respiration. In fine, when cutaneous or mucous absorptions take place, the black blood is always the first that receives the product of them.

It follows from this, that the circulation of black blood is, if we may so say, a general reservoir in which is poured in the first place all that is to go out of the body, and all that is to enter it.

In this last respect, it performs an essential part in diseases; in fact it is undeniable, 1st. that deleterious substances maybe introduced with the chyle into the economy, and produce ravages there more or less evident in circulating with our fluids. For this, it is sufficient that the organic sensibility of the chylous vessels should be changed; then they admit what before they rejected, as the glands by changes in their organic sensibility, often secrete fluids that are usually foreign to them. 2d. We shall prove in the article upon the cutaneous system, that it is oftentimes the seat of the absorption of deleterious substances. 3d. We cannot doubt that besides the principles that colour the blood, there often passes through the lungs deleterious miasmata which produce diseases, as my experiments upon asphyxia have proved. The intestines, the lungs and the skin are then a triple gate open, in many cases, to different morbific causes; now these causes that enter thus into the economy are all received in the first place in the black blood; it is not until afterwards that they pass into the red blood.

An evident proof of this assertion is this, that we produce phenomena exactly analogous to those which result from them, by pouring artificially into the black blood those substances that are introduced in a natural way. Thus when a purgative or emetic infusion is introduced into the veins, alvine evacuations or vomiting ensue, precisely as when the substances of these infusions are introduced by friction upon the skin. The experiments of many physiologists leave no doubt upon this point. I am convinced that it is possible to give to animals artificial diseases, by making different substances infused into their veins circulate with the blood. I shall speak of these attempts in the article upon the glandular system. It is sufficient for me to mention them here, in order to prove that the black blood is a general reservoir in which many substances can enter, either naturally, or accidentally, and afterwards disturb the functions by passing into the whole circulating mass. The humoral pathology has undoubtedly been exaggerated, but it has still real foundations, and in many cases we cannot deny, but that every thing arises from the disorders of the humours.

Let us conclude from all that has hitherto been said, 1st. that the essential part which the circulation of the black blood performs in the economy, is to introduce into this blood different new substances; 2d. that that of the system of red blood is to expend on the contrary, the principles that constitute it. One is constantly increasing, the other diminishing; to give is the attribute of one, to receive is that of the other. This sketch, which is perfectly true, and founded upon the most simple observation, appears to me very proper to establish an evident demarcation between the two divisions that I have adopted for the general circulation.

Health supposes a perfect equilibrium between the losses the red blood experiences, and the acquisitions the black blood makes. Whenever this equilibrium is destroyed, there is disease. If the black blood receives more than the red blood expends, plethora follows. That which is called the poverty of the humours, is manifest when more substances go from the red blood than enter the black.

These are I think sufficient characteristic attributes of the two great divisions of the general circulation, to justify the point of view different from other authors, in which I present this important function of the animal economy.

ARTICLE SECOND.

SITUATION, FORMS, AND GENERAL ARRANGEMENT OF THE VASCULAR SYSTEM OF RED BLOOD.

From the general idea that we have given of the two vascular systems, we should form the following of the position in the economy of that with red blood.

1st. The capillary system of the lungs gives rise to many minute ramifications, which soon unite into small branches, then into larger ones, and finally into four great trunks, two for each lung. These trunks open into the left auricle towards its superior part. 2d. This, distinguished from the right by having fewer fleshy columns, by its smaller size, by the greater elongation of its appendix, which is narrower than that of the other, &c. communicates by an oval opening furnished with valves, with the left ventricle, the thickness of whose parietes, the arrangement of the fleshy columns, &c. distinguish it from the right. 3d. From this ventricle goes the aorta, the common trunk whence arise all those that carry red blood to all the parts, where they terminate in the general capillary system.

The first tree of the system of red blood, the trunk of the second and the heart that serves to unite them, are found then concentrated in the cavity of the thorax, whilst the branches of the second trunk are distributed among all the organs of the economy, and even to all its extremities.

It is nearly between the superior third of the body and the inferior, that is found the agent of impulse of the red blood, or the heart. This position is important; it places under a more immediate influence of this viscus, the superior parts, the head especially, all of whose organs, and particularly the brain, require inevitably a very active and habitual excitement from the blood, in order to keep their functions in permanent activity. Thus observe, that in the gangrene of old people, and the affections that arise from the blood not being driven with sufficient force to all the parts, it is the extremity of the foot that is first affected, and that of the head and the hands become much later the seat of mortification. In general, there are many differences between the phenomena that take place in the superior parts, and those that happen in the inferior. We shall see in the dermoid system, that the portion of the general capillary system which belongs to the first, is penetrated with blood with infinitely more ease, than the portion belonging to the inferior parts, as asphyxia, apoplexy, submersion, different cutaneous eruptions, injections even prove, which in young subjects blacken rather the face than the inferior parts; now this difference arises evidently from the relation of position of the superior and inferior parts with the heart.

We have no general remarks to offer here upon the first tree and upon the agent of impulse of the circulation of red blood. In fact, the remarks belonging to the lungs and the heart will be given in the Descriptive Anatomy. It is then especially the second or arterial tree, whose distribution is now to occupy us. It is necessary in this article to examine the origin, course and termination of it.

I. _Origin of the Arteries._

This article comprehends the origin of the aorta at the left ventricle, that of the trunks which arise from it, then that of the branches, the smaller ones and the minute ramifications that go from them.

_Origin of the Aorta._

Most authors have described inaccurately the manner of the union of this great arterial trunk with the heart. This is the manner; the internal membrane of the heart with red blood, after having lined its ventricle, approaches the opening of the aorta, is attached there, forms by its folds the three semi-lunar valves, and stretching afterwards into the artery, covers it in its whole extent. It is this internal membrane that forms the union of the artery with the heart. The peculiar or fibrous membrane is not identified with the fibres of the heart. Its extremity is cut into three semi-circular festoons, which correspond with the semi-lunar valves that they support. These festoons do not extend to the fleshy fibres; there is between them and these fibres a space of two or three lines that the internal membrane alone covers. Between them and consequently between the valves, we perceive three little empty triangular spaces, covered by the membrane also. To distinguish this structure clearly, the origin of the aorta must be dissected well from without, and stripped entirely of the fatty texture that surrounds it. Then by cutting this artery and the ventricle, and by examining when held up to the light the union of one with the other, after having first removed the valves, we distinguish very well by the transparency of the internal membrane and the opacity of the three festoons that commence the aorta, the arrangement that I have just pointed out. It follows from this, that if the artery is accurately dissected on its exterior, and we detach from below upwards the internal membrane that forms the great canal of the circulation of the red blood, the artery is entirely separated from the heart. This entire separation of the fibres of the aorta from those of the heart, would alone be a strong presumption that their nature is not the same if many other considerations did not prove it in the most evident manner.

_Origin of the trunks, branches, smaller branches, &c._

Arising thus from the left ventricle, the aorta divides almost immediately into two branches, one ascending goes to the neck, head and superior extremities; the other descending to the chest, abdomen and lower extremities. The first being very soon subdivided into four principal trunks, differs in this respect from the second, which forms for a long time one trunk only. The latter having to go over a much greater distance than the other, preserves with more certainty by this arrangement the whole of the motion that is given to the blood by the heart; this does not prevent, however, owing to the less distance, the impulse from being more sensibly felt by the superior than the inferior organs, as I have said above. At the superior part of the pelvis, the aorta divides into two secondary trunks. Soon after, subdivisions begin under the name of branches, which are afterwards multiplied under that of ramifications, &c.

Mathematical anatomists have exaggerated the number of the arterial sub-divisions. Many have thought there were a hundred to one artery; Haller reduced the number to twenty, and even less. To ascertain what is really the case, it is necessary to take the arteries at their origin, and follow their course under a serous membrane, the peritoneum for example, where they are every where very apparent; it will be seen in this way, that the sub-divisions are not more numerous than is stated by Haller; I have frequently satisfied myself of this. Besides, the inspection of a living animal whose abdomen is opened, is almost the only means that can be employed without danger of mistake. Injections when too coarse do not fill all the branches; when too fine, they pass into the exhalant vessels, and communicate to the whole serous surface a colour that is not natural to it. It is almost impossible to ascertain by injections, the precise point of the natural circulation. To be convinced of this, inject a dog and open the abdomen of another of the same size; you will see uniformly in one more or less vessels injected, than are seen in the other filled with blood. I frequently performed this experiment, at the time I was engaged in demonstrating the insufficiency of injections, either fine or coarse, to show the quantity of blood in any part.

When they divide, the arteries form among themselves very different angles. Sometimes right angles, as at the middle intercostals; sometimes obtuse, which is more rare, as at the superior intercostals; most commonly they are acute, particularly in the extremities. The origin of the spermatic artery is an instance of the extreme of this last kind of origin.

We observe in general, that wherever there are two divisions, one is larger than the other. The largest follows the original direction of the principal trunk, from which the other is more or less separated. In the interior of the artery, an eminence formed by the fold of the internal membrane, corresponds with the angle entering from without, and breaking the column of the blood, favours the change of its course. This eminence presents an arrangement, that is very variable, which is owing to the angle of origin. 1st. If the angle is a right one, the eminence has a circular arrangement and is equally evident in the whole circumference. 2d. If the angle is acute, as at the mesenteric, then this eminence is very evident between the branch that arises and the continuation of the trunk; it forms even a kind of semi-circular spur or projection, but between the trunk itself and the branch that arises from it, the union of which forms an obtuse angle, this eminence is less conspicuous. The more obtuse the angle is, and consequently the more opposed it is to acute, the less sensible is this second eminence; it has like the other a semi-circular form, and makes by its union with it a whole circle which is oblique; so that the portion of the circle formed by this second eminence is nearer the heart than that made by the other. 3d. If the angle of origin is obtuse, and consequently that formed by the branch with the continuation of the trunk is obtuse, things are then arranged in an inverse manner. There is at the mouth of the artery an oblique circle, the prominent half of which is nearest the heart.

The origin of the arterial trunks is generally pretty uniform; but that of the branches is so variable, that hardly any two subjects have the same arrangement, in this respect. Take for example the hypogastric; it would be impossible to form the least idea of its branches, if, neglecting the manner they separate from each other, you paid attention only to their course and distribution. These numberless varieties in the forms, are a remarkable character in organic life to which the arteries belong. This character must be placed at the side of the constant irregularity of the arteries. There is no symmetry in their general distribution, as in the distribution of the nerves of animal life. Those even of the extremities, that correspond, differ frequently in their mode of origin and the course of their branches.

The branches, smaller branches, &c. arise at distances very near each other. There is hardly any, except the carotid, internal iliac, &c. that runs a considerable course without furnishing some. Thus experiments in which it is necessary to introduce tubes into arteries, to open them, &c. can scarcely be made except upon the first of these, they are prevented in others by divisions that arise from them and hinder us from raising the artery to any considerable extent.

The origin of the arterial trunks, branches, smaller branches and ramifications, does not take place in a gradual and necessarily successive manner. Thus the smaller branches, and the ramifications even, arise equally from trunks and branches; for example, the bronchial, thymic arteries, &c. go from the aorta, and yet they are not so large as most of the divisions of the tibial, which is itself a third division of the aorta.

II. _Course of the arteries._

In their course the arteries present differences according as we examine, the trunks, the branches and smaller branches.

_Course of the trunks and branches._

The trunks are the first divisions continuous with the two great portions of the aorta; such are above, the internal and external carotids, the subclavians, &c.; below, the iliacs, the hypogastrics, &c. Generally they are situated in broad interstices, that contain much cellular texture, as in the groin, the axilla, the neck, the sides of the pelvis, &c. By dividing they form branches that are received into smaller and narrower interstices, and are consequently more exposed to the influence of the neighbouring organs. Both of them are covered almost every where by a thickness of parts that protects them from external injury. Besides this protection that the neighbouring parts and particularly the muscles afford them, they accelerate also the circulation of the blood, and reciprocally the motion of the arterial trunks gives to the neighbouring organs and even to the whole limb, a sensible motion, an agitation that supports its vital energy. This agitation, which it is often difficult to perceive, sometimes becomes very evident upon mere inspection. When the elbow is rested upon the table, and a body of considerable length held in the hand, its extremity is seen to vaccillate, to rise and fall a little at each pulsation. If the legs are crost, being first bent upon the thighs, a spontaneous rising is noticed in that which is supported. To this we must refer also the cerebral motion, that which is communicated to tumours that are situated over a great artery, &c. &c.

The trunks and the branches are accompanied by veins, and surrounded in general with a large quantity of fat, a circumstance that has been considered favourable to the opinion of those who think that this fluid is exhaled by the pores of the arteries. We have already said what should be thought of this opinion.

The direction varies in the trunks and the branches. Usually straight in the trunks, as in the carotids, the internal and abdominal iliacs, it renders the circulation less evident. When these trunks are exposed in a living animal, we do not see any kind of locomotion there, as we do when the curves are great. There is however some exception to this rule as it respects the direction of the trunks; the arch of the aorta is an example of it, so is the internal carotid, which has numerous curves, which are thought incorrectly, to be necessary to prevent the impetus of the blood from producing derangement in the delicate substance of the brain. More tortuous in the branches, this direction occasions the arterial locomotion that constitutes almost exclusively the pulse, according to many physicians.

_Course of the smaller branches, ramifications, &c._

Whilst the trunks occupy the large interstices that are left between several organs, and the branches the smaller ones that separate particular organs, the smaller branches are found in the interior of these same organs, without, however, entering into their intimate structure. Thus in the muscles, they are interposed between their fibres; in the brain, in the circumvolutions; in the glands, between the lobes that form them, &c. By them, an internal motion communicated to the whole organ, facilitates its functions by supporting its partial activity, as the motion of which I spoke above, supports the general activity of the part. Besides, the sudden cessation of life, when the blood ceases to agitate the brain, proves the immediate connexion between this internal motion and its energy. Thus we observe that life is much more active wherever the arteries are numerous, as in the muscles, the skin, the mucous surfaces, &c.; whilst on the contrary its phenomena are weaker and more obscure in the less vascular organs, as in the tendons, the cartilages, the bones and the other white parts.

In the smaller branches, the windings are much more evident than in the branches. Injections make them very conspicuous, especially in the brain; but as they depend principally upon the cellular texture they disappear in part, if we separate from it the vessels of all the parts. Do these windings diminish the rapidity of the circulation, and does the straightness of the arteries increase this rapidity as much as physiologists suppose? I think they have exaggerated the effects of the direction of the arteries; the following are proofs of it. 1st. If in living animals we expose the hollow organs, as the stomach, intestines, &c. alternately in a state of fulness and in that of vacuity, I have observed that the circulation is almost equally rapid in both cases, though fulness renders almost straight the vessels of these organs, and that emptiness, by forcing them to wrinkle, increases their curves. 2d. I have opened the carotid artery of a dog, and having observed the force with which the blood is thrown out, I have also opened both sides of the thorax; immediately the lungs are collapsed and consequently the windings of their vessels increased; notwithstanding this no diminution in the force with which the blood escapes from the artery, after having gone through the lungs is immediately sensible. It is only gradually that the force is destroyed by the influence of causes, that it is not my object to examine. 3d. If in another animal, an artery being open, we open also the wind pipe, and by a syringe affixed to the opening suddenly exhaust all the air the lungs contain, this organ is immediately reduced to a very small size; the vessels become much bent, and yet I have observed in this case that the blood goes from the open artery with as much force as before, for a considerable time. 4th. Finally, after having opened the abdomen of a living animal, I have alternately contracted and stretched the mesentery, whose numerous arteries had been first opened; no difference is discoverable in the force with which the blood is thrown out, in either case.