NERVOUS SYSTEM OF ORGANIC LIFE.
GENERAL REMARKS.
No anatomist has yet considered the nervous system of the ganglions in the point of view in which I shall present it. This point of view consists in describing each ganglion as a distinct centre, independent of the others in its action, furnishing or receiving particular nerves as the brain furnishes or receives its own, having nothing in common, except by anastomoses, with the other analogous organs; so that there is this remarkable difference between the nervous system of animal life, and that of organic life, viz. that the first has a single centre, and that it is to the brain that every kind of sensation comes, and that it is from it every kind of motion goes; whilst in the second, there are as many little separate centres, and consequently little secondary nervous systems, as there are ganglions.
We know that all anatomists, even those who, without affixing to the expression any very definite meaning, have called the ganglions little brains, have taken them for dependancies, for enlargements of the nerves, in whose course they are found; and as most of them are met with in the great sympathetic, they have presented them as a distinctive character of this nerve. But from the general idea I have just given of the ganglions, it is evident that this nerve has no real existence, and that the continuous thread that is observed from the neck to the pelvis, is nothing but a succession of nervous communications, a series of branches that the ganglions placed above each other, send reciprocally to each other, and not a nerve going from the brain or the spine.
The first considerations that induced me to think that the great sympathetic is not a nerve like the others, but a series of anastomoses, were the following. 1st. These communications are often interrupted, without any inconvenience, in the organs to which the great sympathetic goes. There are subjects, for example, in whom is found a very distinct interval between the pectoral and lumbar portions of this pretended nerve, which seems cut in this place, because the last pectoral ganglion and the first lumbar do not send branches to each other. I have often seen also the sympathetic nerve cease, and afterwards appear again between two ganglions and from the same cause, whether in the loins, or in the sacral region. 2d. Every one knows that the opthalmic ganglion, the spheno-palatine, &c. are constantly distinct, and that they do not communicate by their branches except with the cerebral nerves. It uniformly happens that there is between them and those of the great sympathetic, what we sometimes see between these last, viz. a complete deficiency of communication. 3d. In birds, as has been observed by Cuvier, the superior cervical ganglion is also found constantly distinct; it never communicates with the inferior. The filament which in quadrupeds descends the length of the neck, is wanting in them. In many other animals we frequently find interruptions in this succession of anastomoses of ganglions, which constitute what is called the great sympathetic. 4th. The communications of the ganglions are usually made by a single branch; but sometimes many go from one of these organs to the other, so that if the great sympathetic was a nerve like the others, it would present, in this respect, an arrangement wholly different from that of the cerebral nervous system. 5th. Whence does the great sympathetic arise? From the sixth pair? But all the nerves diminish as they go from the brain towards the organs; but this presents then an arrangement entirely different; it increases as it sends off branches. Does it arise from the spinal marrow? But then the branches with which it furnishes a region would come from the branches that it receives from the spinal marrow in this region. Thus the great and small splanchnic would arise from certain intercostal pairs, now they are evidently much larger, the first especially, than the sum of the branches from which they would derive their origin. Observe then that all anatomists have been of a different opinion upon the origin of the great sympathetic. How could they agree upon a thing that has no real existence?
These different considerations render probable the opinion that I have entertained for some time, that the great sympathetic nerve does not really exist, that this cord is but a succession of communications between little nervous systems placed above each other, and that it is not essential that these communications should exist, as is seen constantly between the ophthalmic ganglion and the spheno-palatine, between that and the superior cervical, of which many animals furnish examples. Then I began to regard each ganglion as a separate centre of a little nervous system, wholly different from the cerebral, and distinct even from the little nervous systems of the other ganglions. By considering the functions of the nerves going from these centres, I became more and more convinced that they did not belong to the cerebral system. In fact, these nerves have properties very different from theirs, as we shall see; they do not serve for sensations; they have uniformly no connexion with voluntary locomotion; we see them only in the organs of internal life; hence why they are found concentrated in the trunk, in the thorax and abdomen particularly; why they are not met with in the head, where almost all the organs belong to animal life; why they are not seen in the extremities, which are exclusively dependant upon this life.
Distributed almost every where to the organs of the internal life, the ganglions and their nerves derive their character from it; and this is it. 1st. They are not symmetrical; thus the nerves of all the plexuses of the abdomen, those of the cardiacs, &c. have a remarkable irregularity. 2d. There are numberless varieties in the form of these plexuses and in that of the ganglions; it is thus that, sometimes lenticular, sometimes triangular, sometimes divided into many portions, that which is under the diaphragm is never seen twice alike. Hence the error of every name derived from the figure; a remark that is applicable generally to the organs of internal life. We might rather borrow the names of forms for animal life in which these forms are more invariable. On the other hand, the existence of many ganglions varies; sometimes there are three of them in the neck, at others but two. The arrangement of one side does not produce a similar one on the other. I have frequently remarked that the number of filaments arising from the superior cervical ganglion differs very much from those that take their origin from the opposite side. There are two analogous organs at each side; but several attributes of structure destroy the general character of symmetry; it is like the lungs and the kidnies. We can, then, establish as a distinctive character between the two nervous systems, the symmetry of one and the irregularity of the other; now, this character is one of those which distinguish the two lives, as I have remarked before.
From all this it is evident that a line of demarcation separates the nerves of the ganglions and those of the brain, and that the method is inaccurate which considers them as forming a single nerve, arising by some origin from this last. Their communications no more prove it to be a general nerve, than the branches which pass from each of the cervical, lumbar, or sacral pairs, to the two pairs that are superior or inferior to it. Notwithstanding these communications, we consider each pair in a separate manner, and not as one nerve by their union. So that each ganglion should be described separately, notwithstanding the branches it sends to others.
The description of the system of the ganglions should be analogous to that of the cerebral nerves. For example, I describe first the lenticular ganglion, as was done for the brain; then I examine its branches, among which is found the great splanchnic; for it is very improper to say that this nerve gives origin to this ganglion. The same in the neck, in the head, &c. each ganglion is first described; then I treat of its branches, among which are found those of communication. There are, then, almost as many descriptions as there are separate ganglions. For example, we ought not to treat of the ophthalmic nerve with the common motor; to be convinced of this, it is sufficient to see how much the ciliary nerves differ from the others, which, belonging to animal life, are also contained in the orbit.
From all that has been said, it is evident that there are two things to be examined in the nervous system of organic life, 1st. the ganglions; 2d. the nerves that go from them.
ARTICLE FIRST.
OF THE GANGLIONS.
I. Situation, forms, relations, &c.
The ganglions are little reddish or greyish bodies, situated in different parts of the body, and forming so many centres, from which goes an infinite number of nervous ramifications. Their position most generally is along the vertebral column, where are seen successively below each other, the superior and inferior cervical, the intercostal, the lumbar, and the sacral. It is these especially whose communicating branches form the great sympathetic. But besides these ganglions, which are placed as it were in a row, we find many separate ones in different parts, as the ophthalmics, the sphenopalatines, the maxillaries in the head, as also the semilunars in the abdomen. In the thorax there are none thus separate; though sometimes we see a small one at the base of the heart.
Besides the ganglions uniformly seen, there are often accidental ones, if we may so say; such are those that are sometimes found in the hypogastric plexus, in the solar even, at some distance from the semilunar, in the middle part of the neck, &c. On the other hand, some of those that are usually met with are oftentimes not found, as some of the lumbar, sacral, maxillary, &c.; so that it appears that there is really an essential difference between the ganglions under the relation of existence. The superior cervical, the semilunar, the ophthalmic, &c. are always found; they appear to be essentially necessary to the action of the organs to which they furnish nerves. Most of the others may be wanting on the contrary, and be supplied by those of the neighbouring ones, or by others formed not in the ordinary anatomical order.
All the ganglions are generally in a deep situation. Destitute of a bony covering analogous to that of the brain, they are not less powerfully protected against the action of external bodies. It is this deep position, that prevents us from making experiments upon almost all of them, from making those at least which require that the animal should live a certain time after they have been made. It is this which will undoubtedly keep up for a length of time the obscurity that hangs over the functions of these organs.
The form of the ganglions is extremely irregular. In general they are round; but sometimes they are long, as the superior cervical; sometimes the ganglion is a species of triangular body, with obtuse and round ends, as the ophthalmic; sometimes the form is semilunar, like that which has this name, &c. Generally these forms are very variable, as I have said; the most uniform is that of the superior cervical.
Embedded in a quantity of cellular texture, all the ganglions are separated by it from the neighbouring organs. Almost all of them are so disposed, that they experience but little motion from these organs, and cannot receive it from any of the vessels that enter them. Those situated along the vertebral column especially, present this phenomenon, very different from that which takes place at the brain, whose functions are essentially connected with the constant agitation that the blood imparts to it, and very different from that which we observe in the plexuses of nerves coming from these same ganglions.
II. Organization.
The ganglions have generally in the adult a reddish colour very different from that of the nerves; sometimes they are greyish. When opened, they present a soft, spongy texture, resembling considerably at first view that of the pretended lymphatic glands.
This texture has nothing in common with the cerebral substance, nor with that which occupies the canal of the nervous coat. These two last should rather be ranked in the class of fluids, as I have said; their substance is a pulp, a real jelly. Thus they have not any of the properties of solids. They do not harden like horn; the kind of hardening, the result of the contact of alkohol, of the acids, and of caloric, is wholly different from the horny hardening. It is analogous to the hardening of the white of an egg. On the contrary, the texture of the ganglions hardens like horn in an evident manner, a phenomenon which is characteristic of all the solids, except the epidermis, the nails, and the hair, which make a separate class. Treated by the acids, the ganglions, after wrinkling, hardening like horn and hardening gradually, soften and become fluid.
Boiling produces a phenomenon nearly analogous; 1st. horny hardening and hardening at the instant the water boils; 2d. continuance of this state for half an hour; 3d. softening gradually brought on; when this last is complete, the effect of the boiling is finished. In this state, the ganglions are all different from the nerves submitted to the same experiment. I have observed also in veal, that they have a very different taste from that of the nerves, a method of research which should not be neglected in attempting to ascertain the difference of the nature of the organs. In fact, as we do not yet know the difference of the principles which enter into the composition of each, we should be satisfied with the difference of the qualities.
The alkalies act a little upon the ganglions, which they tend to dissolve, and which they do partly dissolve, if they are very caustic. But this solution is infinitely less prompt and less easy than that of the cerebral pulp by the same re-agents. The ganglions resist putrefaction as much and even more than the nerves; this forms also a very remarkable difference between them and the cerebral substance. In general, we cannot establish any kind of analogy between them.
The texture of the ganglions appears in nowise fibrous; there is absolutely no linear, filamentous appearance, &c. upon simple inspection. Homogeneous, if we may so say, in its nature, it presents every where an uniform aspect when cut in slices. However the celebrated Scarpa has considered the ganglions as resulting from a kind of expansion of the nerves, into an infinite number of extremely delicate fibres, which interlace with each other, and which become very distinct by maceration. I have not repeated all his experiments, which appear to me extremely difficult. I refer then to his work, and to the plates it contains. I would observe only that there is certainly something else in the ganglions, besides a simple division of the nerve into extremely fine threads. In fact, mere inspection is sufficient to establish between them the greatest difference. There is as evident a demarcation between the ganglions and the nerves, as between those of the brain and the brain itself. 1st. Difference of colour, reddish or greyish tinge in some, white in others; 2d. difference of consistence, of external qualities, &c.; 3d. difference of properties. If the nerves coming from the spinal marrow make only an expansion, in their passage, in the ganglions, by delicate filaments, there would then be only a difference of form and not of nature; the properties would be the same. Why then are they so different as I shall prove hereafter? Why, as a nerve goes from a ganglion, does it not communicate more voluntary motions? 4th. Why has not nature placed ganglions in the nerves of the extremities as in those of the other parts? If there is only a division of the nerve into finer filaments, in the ganglion, why is there not a proportion between the filaments that enter on one side, and those that go out at the opposite? In fact, those that enter into the superior cervical above, if they only expanded their filaments in this ganglion, and united afterwards to form those that go off below, would be equal in respect to size to those that go from it; all the ganglions would exhibit this constant relation between the nerves of one side and those of the opposite; now, it is sufficient to examine them to be convinced that an inverse arrangement exists. 6th. The ganglions ought always to be in proportion to the size of the nerves which form them by spreading their fibres. Why then are the intercostal ganglions so small, and the trunks that unite them, or rather that give origin to them and which go from them afterwards as we see in the usual manner, so large? Why on the contrary, is the superior cervical ganglion so large, and its branches so small? 7th. How can be explained the frequent interruptions between the ganglions in man, which are constant in many animals, if there is a continuity between the nervous filaments that enter the ganglions above, and those that go from them below? 8th. How does it happen that the ganglions and their nerves do not follow an exact proportion as to development with the cerebral nerves, if these form them by expanding? 9th. Why has not pain the same character in each species of nerves?
I have no opinion as to the nature or the functions of the ganglions, because I have no fact to support me; but there is certainly something more in their texture, than a mere expansion of nervous filaments. Scarpa admits a peculiar matter which separates these filaments; but this substance ought to predominate considerably, as the ganglion surpasses in size the nerves which are thought to give origin to it. Now I have never seen this substance; I do not know what it is; all is solid when the ganglion is cut. I think then by admitting, even to a certain extent, the internal arrangement that this author has observed in the ganglions, we cannot describe these organs in the point of view in which he has presented them.
We know but little of the alterations that diseases produce in the texture of the ganglions. I have already many times examined in diseases of the heart, of the liver, of the stomach, the intestines, the ganglions that send nerves to these viscera; they have never appeared to me to have undergone any change. In cancers of the stomach in the very last stage, in which all the cellular texture is engorged, and in which all the lymphatic glands are considerably swelled, I have always found the semi-lunar ganglion untouched, except however in one case where it was enlarged and its density a little increased. At another time I found this same ganglion of the size of a small nut, with a cartilaginous substance in its centre, resembling the stone of it, in the body of a man brought to the Hôtel Dieu on account of periodical mania. Some authors have thought, and I suspect the same thing also, that the hysteric paroxysms, which begin by a contraction at the epigastric region, and in which the patient feels a ball mount up even to the throat, arise from some affections of the semi-lunar ganglions, from the solar plexus and the communications which go from ganglion to ganglion, even to the neck. However two bodies that I have opened lately, exhibited no alteration, though during life the subjects had been frequently attacked with these paroxysms; but they may arise evidently from the ganglions and the epigastric plexuses, without their being altered in their structure, as a number of cerebral affections leave after them no trace in the brain. This point deserves particular examination.
It does not appear that the texture of the ganglions is surrounded by a peculiar membrane. The cellular texture is only condensed in their neighbourhood; it then becomes very consistent, and much contracted around them. It there has the nature of the sub-mucous, the sub-arterial textures, &c.; it never contains fat. There is then truly around the ganglions, as around the arteries, under the mucous surfaces, &c. the two kinds of cellular texture of which we have spoken in treating of the organization of this texture, and which differ so essentially from each other in their nature, and even in their properties. It is the second kind, which is analogous to the sub-arterial texture, &c. which forms the peculiar membrane admitted by some authors.
By examining attentively the interior of the ganglions, we see that there is but very little cellular texture there. I have found this texture constantly destitute of fat; thus the alkalies do not form a saponaceous deposit upon them, as upon the cerebral nerves when plunged in their solution. I have examined many ganglions in this way, on account of the opinion of Scarpa, who believes that these organs are penetrated with this fluid, at least in fat people.
The ganglions receive many blood vessels. These penetrate them from all sides, run first in a kind of cellular covering that surrounds them, then entering their texture, ramify and are lost there in numerous anastomoses, and in continuation with the exhalants that carry nutritive matter. Fine injections show a great quantity of vessels in these little organs. Nutrition supposes exhalants and absorbents there.
III. Properties.
It is difficult to analyze the properties of texture in the ganglions. As to vital properties, they cannot grow, live and be nourished without organic sensibility, and without insensible contractility of the same kind. Animal and sensible organic contractility do not exist there evidently. As to animal sensibility I have observed the following circumstance. As in opening the abdomen of an animal, of a dog, for example, he lives very well for some time, and remains even calm after the first moments of suffering; I have waited for this calm that succeeds the agitation arising from the incision of the abdominal parietes, then laid the semi-lunar ganglion bare, and irritated it powerfully; the animal is not agitated, whilst when I excite a cerebral lumbar nerve, for comparison, he cries out, raises himself up and struggles. In general it appears that the sensibility of the ganglions is infinitely less evident than that of many other organs. Certainly the skin, the mucous system, the medullary, the nervous of animal life, &c. surpass it in this respect.
Our ignorance as to the diseases that have their seat in the ganglions, the distance of those organs from external excitement, prevent our having any data as to their sympathies. I think it very probable, however, that these sympathies take a real part in hysteria, in certain kinds of epilepsy, the paroxysms of which begin, like those of hysteria, by a painful sensation at the epigastric region, in that multitude of affections called nervous, and which the vulgar confound under the name of vapours. One of the most important objects of research in the neuroses, is to determine those that have their particular seat in the nervous cerebral system and those which affect more particularly the system of the ganglions. Place on one side, palsy, hemiplegia, convulsions of infants, tetanus, catalepsy, apoplexy, the greatest part of epilepsies, all the numerous accidents that arise from engorgements, from compressions of the brain from wounds of the head, nervous affections of the sight, hearing, taste, smell, &c. and all the diseases the source of which is evidently in the head; on the other place hysteria, hypochondriasis, melancholia and all that numerous class of affections in which the abdomen and the thorax, the first especially, seem to be the spot in which the evil is seated; you will see that there is an essential difference and that the symptoms have entirely a different character. I do not say that the last kind of nervous diseases affect exclusively the ganglions; for too much obscurity hangs over these affections to pronounce any thing positive as to their seat, or their nature. Undoubtedly even the secretory, circulating, pulmonary organs, &c. can be then particularly affected in their peculiar texture and independently of the nerves they receive; but certainly it is an interesting subject of research, and there is too great a difference in the phenomena of the two orders of affections, not to present differences in their primitive seat. It is difficult to conceive that the system of the ganglions has not a great part in the last order.
That which induces me to think that the difference of the phenomena that the general order of neuroses presents us, arises particularly from the difference of the cerebral nerves and of those of the ganglions, is that their phenomena in a state of health are very different. Hallé has observed very well that the pains that are experienced in the parts in which the nerves coming from the ganglions are distributed, have a peculiar character, and that they do not resemble those that are felt in the parts where the cerebral nerves are sent. Thus the painful sensation that is experienced at the loins in affections of the womb, by vinous injection made into the tunica vaginalis, &c. a sensation that appears to me to arise from the sympathetic influence exercised by the organ affected upon the lumbar ganglions, the pains of the intestines, the burnings at the epigastric region, &c. &c. do not resemble pains of the external parts; they are deep, and go to the heart, as we often say. We know that there are colics essentially nervous, which are certainly independent of every local affection of the serous, mucous, and muscular systems of the intestines. These colics are evidently seated in the nerves of the semi-lunar ganglions, which are spread along the whole course of the abdominal arteries. They are real neuralgias of the nervous system of organic life; now these neuralgias have absolutely nothing in common with the tic douloureux, sciatica, and other neuralgias of the nervous system of animal life. The symptoms, the progress, the duration, &c. every thing is different in these two kinds of affections.
What I have just said upon the injuries of sensation, applies also to those of motion. No kind of comparison can be made between the convulsions of the muscles that receive the nerves of animal life, and the spasmodic and irregular motions which arise in all the muscles that receive nerves from the ganglions. Nothing resembles tetanus in the heart, the intestines, the bladder, &c.
All these considerations establish striking differences between the cerebral nerves and those of the ganglions; differences upon which I can only present approximations, as we have no data as to the functions of the last.
IV. Development.
The ganglions differ essentially from the brain in the early periods in their development, which is proportionably much less advanced than that of the brain. They are only on a level with all the other organs, whilst this is infinitely superior to them in this respect, as we have seen. By comparing the superior cervical, semilunar ganglions, &c. in the fœtus, and in the adult, it is easy to make this remark. The ganglions receive also less vessels in proportion than the brain. They do not follow the proportion of increase of the organs to which they send nerves. Thus those that furnish the genital organs, which are nearly nothing during the first years of general nutrition, are as large in proportion as those which go to the liver, the stomach, the intestines, which are characterized by an early increase. These nerves follow in this respect the same law as the ganglions, though the most are found upon the arteries, which are more or less developed according to the organs they penetrate.
The nervous system of organic life being less early in its development than that of animal life, should be subject in infancy to fewer affections; and this is what is observed. Convulsions, and most of the neuroses of the second, are, as we have seen, a peculiar appendage upon infancy. On the other hand, the particular order of nervous affections of which we have spoken, and in which it appears that the first takes the principal part, is generally less frequent at this period. All nervous diseases, whose peculiar seat seems to be at the epigastric region, in which there is so great an abundance of nerves coming from the ganglions, appear to be foreign to this age.
Another difference that distinguishes the ganglions from the brain as it respects development, is this, that in the fœtus, they are not, like it, of extreme softness. Their hardness is little inferior to what they afterwards possess in adult age.
In proportion as we advance from infancy, the organic nervous system begins to become predominant. It is towards the thirtieth or fortieth year that it appears at its maximum of action; it diminishes as we approach old age; it decays in part at this epoch. The nerves become greyish; the ganglions are hard, resisting and smaller. The neuroses that appear to belong to them are infinitely more rare. Moreover, the obscurity that rests upon the functions of this system, does not allow me to point out definitely the alterations they experience in the different ages.
V. Remarks upon the vertebral ganglions.
In all that I have said thus far upon the ganglions, I have not noticed those which correspond with the foramina through which the nerves pass, and which some call simple ganglions. We know that at the instant each nerve goes from each of these foramina, it exhibits an evident enlargement, reddish, pulpy, analogous in its appearance to most of the ganglions. I confess, that I know not how to class these organs. We cannot deny that they have the greatest analogy in structure to the others. They are approximated in another respect, which is this, that the nerves, in going from them, form almost immediately plexuses that we have designated under the names of cervical, brachial, lumbar, and sacral, in the same way as the solar, cardiac, mesenteric plexuses, &c. are formed by the nerves of organic life, at the moment they go from their respective ganglions. However, these last nerves are conductors of very different properties. Irritate in a living animal the superior cervical ganglion, the inferior even, which is more difficult, though it may be come at, the muscles to which they send nerves will remain unmoved; the same phenomenon takes place by exciting the nerves themselves. On the contrary, every irritation of a filament coming from the vertebral ganglions, produces immediately convulsions in the corresponding muscles. The sensibility is entirely different in the two species of nerves. Besides, there is no analogy between the manner in which the nerves go in all directions from the vertebral ganglions, and that in which the other ganglions furnish theirs. In the expectation that further experiments may elucidate the subject, let us content ourselves with pointing out what is the result of accurate observation.
ARTICLE SECOND.
OF THE NERVES OF ORGANIC LIFE.
I. Origin.
Each ganglion is, as we have seen, a centre from which go in different directions, various branches, the whole of which form a kind of little separate nervous system. The manner of the origin of these branches has but very little relation with that of the branches of the brain and of the spinal marrow. The following are some differences that distinguish it.
1st. The adhesion is much stronger; the nerve breaks any where else rather than at its origin; the opposite of this takes place in the preceding system. 2d. It does not appear that the substance of the ganglion is continued in the nerve to form the medullary substance of it, since the organization of the one and the other is very different. Sometimes, however, the ganglion is continued for a short distance in the form of a cord. This happens especially in the superior cervical, in the lumbar, the semi-lunar, &c. Then the form only is different; but it is easy at the first view to distinguish where the ganglion ends and the nerve begins. 3d. This beginning is made in a sudden manner; it is like a muscle implanted in a tendon. The best manner of seeing this arrangement to advantage is to cut longitudinally the superior cervical ganglion and the cord it sends to the inferior; the change of nature of the one and the other is then very apparent; or, if we consider the ganglion as a division of the numerous filaments of the nervous cords, we distinguish very well the sudden change that these filaments experience in passing from the cord to the nerve. 4th. The dense cellular covering that surrounds the ganglion is continued upon the nervous origin, and gives it an increase of consistence at that place. This must be carefully raised before we come to the nerve. We see then each distinct filament arising from the ganglion. After it has gone from it, sometimes it remains separate; this takes place at the semi-lunar, the lumbar, the opthalmic, whose elongations are of great delicacy. Sometimes many of these filaments unite together and form a cord as between the two cervical, as at the great and small splanchnic nerves, &c.
I have not been able by maceration, ebullition, or the action of the acids to destroy the adhesion of the nerve with the ganglion, as we destroy that of the muscle with the tendon, of this with the bone, &c.
II. Course, Termination, Plexuses.
The nerves after going from the ganglions, are distributed in many different ways which we shall now examine.
1st. There are always some which go immediately to communicate with the system of animal life. The ophthalmic ganglion sends branches to the motores communes, and to the nasal nerve. The spheno-palatine communicates with the superior maxillary nerve; the superior cervical with all the nerves that surround it, viz. above with the motor externus, within with the great hypoglossal, the par vagum, the glosso-pharyngeal, the spinal, &c.; behind with the first cervical pairs. All the ganglions situated above each other along the vertebral column, send communications through each pair of foramina that correspond with them. The par vagum communicates with the semi-lunar, &c. It is not then any separate ganglion of the nerves of animal life; hence the common expression that designates each ganglion as arising from this or that pair, or being found in its course, is very inaccurate. Thus the opthalmic is by no means in the course of the common motor nerve. The one and the other send each a branch, which unites; or rather there is a branch of communication between the ganglion and the cerebral nerve. In general all these branches of communication with the system of animal life, are short, whitish, and of the same nature, or at least of the same appearance as the nerves of this last. They do not form any plexus in their course, rarely furnish branches, and appear to have no other use than that of establishing anastomoses between the two systems.
2d. Each ganglion sends above and below branches to the two ganglions that are contiguous to it. We have seen that the opthalmic and the spheno-palatine are exceptions to this rule. Sometimes also, as I have said, there are interruptions in other regions. Notwithstanding this, these general communications make us regard the ganglions as being connected every where, and able to receive from each other the different affections of which they can be primitively the separate seat. These branches of communication are straight as in the preceding, sometimes very fine, as between the lumbar and sacral ganglions, at other times larger, as that which is between the two cervical, superior and inferior, in some cases very large, as the great splanchnic, which is a real trunk of communication between the intercostals and the semi-lunar. The nerves that we are now considering, the last especially, have like the preceding, an arrangement exactly analogous to the cerebral nerves; they are formed of whitish cords, which are the result of filaments. The eye discovers no difference between them.
3d. Many filaments coming from ganglions, go to certain cerebral muscles, as to the diaphragm, some of those of the neck, &c.; others go to neighbouring organs only.
4th. The greatest number going from the ganglions in separate filaments, interlace in the form of a plexus with those of the contiguous ganglions, in the neighbourhood of, or upon the great vessels. The most remarkable plexus is the solar, composed by the innumerable branches that come from the semi-lunar; then we see the hypogastric, the cardiac, &c. The greater number of these plexuses are not exclusively formed by the nerves of organic life; those of the animal give some to them also, as the par vagum furnishes an example for the solar and the cardiac, as the sacral nerves afford another for the hypogastric, &c. However the nerves of organic life always predominate in these plexuses. There is only the pulmonary in which the par vagum particularly predominates, whilst the nerves coming from the inferior cervical ganglion are, if we may so say, but accessory.
The primitive plexuses resulting from the interlacing of the organic nerves at their exit from the ganglions, form a mass of irregular nerves, buried in the cellular texture, accommodated to the forms of the neighbouring organs, and wholly different from those of animal life, as of the brachial, the lumbar, &c.
In fact, the filaments at every instant, not only place themselves as in the preceding ones, at the side of each other, at every change of position; but their extremities continue; they interlace with each other, change at every point the direction, form networks, and mix so together, that it is not possible to distinguish any thing except a thousand nerves, that we might say grew up under the cloth with which we wiped the place where the plexus was found.
These organs are remarkable for their reddish or greyish colour, for their softness, for their indistinctness, &c.; it is often difficult to distinguish them from cellular texture. The best manner of making them evident is to let the subject macerate for a day or two open in the water; they whiten then sensibly, do not soften, and appear even to increase in consistence, like the cerebral nerves in a similar case. Besides their delicacy is such, that it is impossible to submit them to any kind of reagents. Only I have observed that they possess in an eminent degree the property of horny hardening, and that they do not yield in this respect to the cerebral. This delicacy depends upon this, that all the filaments are separate from each other, instead of being like the preceding, collected into cords; it is this also that makes these nerves so numerous. If all the filaments of the brachial plexus were separated like those of the solar, they would present the same appearance and the same number in their interlacing.
Do the primitive plexuses formed by the ganglions perform a part in the nervous functions? are they centres to which are referred important phenomena? What has not been said upon this subject, concerning the solar plexus? But nothing, I believe, of all that has been advanced is founded upon accurate observation.
The plexuses of organic life are soon separated into different divisions, which go to different parts, to those especially of this life. These divisions arise from an infinite number of little filaments which go constantly separate, though placed near each other, and which never unite into cords like the preceding. They accompany almost all the arteries; thus the renal, the hepatic, the splenic, the coronary stomachic, the mesenterics, the hypogastric, the carotid and its distributions, &c. are surrounded with filaments coming from ganglions. These filaments go in two ways. 1st. Some accompany the artery without being connected with it; considerable cellular texture separates them; they go in its course without intermixing in a sensible manner with it. 2d. The others form for it, if we may so say, a new coat, exterior to the others, which adhere to it intimately, and which interlace so together, that they might be taken for a network surrounding the artery.
When the artery runs but a short course, these two orders of branches remain distinct from each other as far as the organ, as we see around the splenic, the hepatic, the renal, &c.; but if the course is longer, the external branches gradually get into the plexus, and are entirely lost there. This plexus can be followed upon the great trunks; it divides upon each branch, and can be still seen; but such is its tenuity upon the minute ramifications that it disappears there entirely. The spermatic is one of the arteries upon which it can be traced the longest. The arteries of the extremities appear to be destitute of it. In general it is upon those that go to the central organs of internal life, that this network is the most evident. When we deduct from the sum of the filaments coming from the ganglions, those by which they communicate on one part with each other, and on the other with the nerves of animal life, we see that almost all the rest is finally destined to accompany the arteries. This arrangement is wholly different from that of the cerebral nerves, whose filaments are only in apposition with the vessels. These make almost an integrant part of them, the adhesion is so intimate; this certainly supposes a use of which we are ignorant, relative to the circulation, or to the other organic functions. As these vessels distribute every where the materials of these functions, of the secretions, exhalations, nutrition, &c. the organic nerves have no doubt some influence upon them. Neither experiment or observation have taught us any thing upon this point.
The veins are not accompanied by so many organic nerves. It is the same as it respects the absorbent trunks, which go almost every where separate from this system.
The constant union of the arteries with the organic plexuses, an union that presents an arrangement wholly different from that of the ganglions, has undoubtedly an influence upon the action of these plexuses, or rather upon that of the nerves that go from them, by the motion the blood communicates to them. It should be remarked upon this subject, that as nature has placed a crowd of arteries at the base of the brain to agitate it with an alternate motion, she has put also the most considerable plexus of the whole organic system upon one of the places to which the red blood communicates the strongest impulse, viz. upon the trunk of the cœliac.
III. Structure, Properties, &c.
From what has been said above, it is evident that the nerves going from the ganglions are of two sorts as it respects organization; 1st. those that are identified with the cerebral system, by their white colour, by the possibility of dividing their trunks into distinct cords, and these into filaments, which appear to have nervous coats and medullary substance like the preceding; 2d. those which present only little separate filaments, greyish or reddish, soft, and which are seen in prodigious numbers in the plexuses. Have these a nervous coat and a medullary substance? It is impossible to determine it.
The properties of texture are ascertained with difficulty in the organic nerves. As to vital properties, it is undoubted that the animal sensibility is not as much raised in these nerves as in those of animal life. I have often laid bare the plexuses in the abdomen; then by letting the animal rest a moment, and by irritating them comparatively with the lumbar nerves, I have uniformly made this remark. We know that very frequently the ligature of the spermatic artery is not painful in sarcocele, though the branches coming from the ganglions form for it a plexus like a network, which can in no way be separated from it. If we draw out a portion of intestines by a small wound in the abdomen, the irritation of the sub-mucous layer at the side of the vessels, is hardly felt, though many nerves of ganglions are found at this place. I have had numerous occasions to act in different ways upon the carotid, to which the superior cervical ganglion furnishes branches from above; now, as long as I did not touch the par vagum, the animal remained tranquil. I am far, however, from believing in the absolute insensibility of the nerves of the ganglions; but certainly under the circumstances that I have related, the cerebral nerves would have caused much more pain to the animal.
I think that in a morbid state this sensibility is susceptible of being greatly raised. We certainly cannot deny but that the solar plexus takes a great part in the different sensations that are experienced at the epigastric region; the very acute pains that often attend the formation of aneurisms, are probably owing in part to the distension of the nervous filaments that surround the artery. I have already said that it is probable that the organic nerves are much concerned in the different sensations that are produced by some peculiar neuroses.
These nerves occasion evident sympathies in certain cases. It is to this that must be referred the different affections that Petit de Namur has produced in the organ of sight, by irritating their branches that are accessible. The development of the nerves of the ganglions follows nearly the same laws as that of those organs from which they emanate.
Let us observe in finishing this system, that there is no one that ought to arrest the attention of physiologists more. All the others present a series of phenomena already well known. Of this, we have hardly any knowledge. It does not present as yet, if we may so say, but some of the negative attributes of the nervous system of animal life. Thus it is without doubt that the organic nerves do not have the same part as the preceding in animal sensibility; that they are always foreign to contractility of the same species; that they have no direct influence upon the sensible organic, since as we shall see, we can cut or irritate them without destroying or hastening the motion of the muscles to which they go. But in knowing the parts they do not perform we are ignorant of those to which they are really destined. I have already observed that the difficulty of making experiments upon the ganglions and the plexuses, will much retard the progress of science. We have scarcely any branches upon the exterior upon which we can act.
Scarpa has collected the opinions of all who have preceded him, together with his own, upon the uses of the ganglions. I refer to what he has said upon this subject. As the general point of view in which he has presented these organs, and that in which I offer them here, differ essentially, the account that I have just given of the nerves of organic life has necessarily a general stamp wholly different from that of his work, a work, however, which, like all this author has published, confers the greatest honour upon the state of anatomy at the period in which we live.
I will terminate this article by an important reflection. If the nerves were only divided to form the ganglions, if these presented in their interior only differences of forms, and a very minute division of their filaments, why should they be so constant in animals? Many organs are wanting, vary, are presented under a thousand various forms in their different classes; on the contrary, the ganglions are constant. In those species even in which the cerebral system is imperfect, that of the ganglions is complete in its organization. Animal life diminishes and is contracted in an evident manner in most insects, in worms, &c. and generally in animals without verterbræ. The brain and the nerves become less evidently marked in proportion as this life is less perfect. The organic is, on the contrary, almost in its perfection in these animals. The ganglions and their nerves are also very evident. This remark has struck me in reading the researches of different authors upon the anatomy of the lower classes of animals; now, if the ganglions were not the centres of certain important functions of which we are ignorant, would they be so invariable in the animal organization?
[VASCULAR SYSTEM]
WITH RED BLOOD.
ARTICLE FIRST.
GENERAL REMARKS UPON THE CIRCULATION.
All authors have considered the circulation in the same way, since the celebrated discovery of Harvey. They have divided this function into two; one has been called the great circulation, the other, the small or pulmonary. The heart, being between the two, is their common centre. But in presenting in this point of view the course of the blood, it is difficult at first sight to perceive the general object of its course in our organs. The method in which I explain in my lectures this important phenomenon of the living economy, appears to me infinitely better calculated to give a great idea of it.
I. Division of the circulation.
I divide the circulation also into two; one carries the blood from the lungs to all the parts; the other brings it from all parts to the lungs. The first is the circulation of red blood, the second that of black.
Circulation of red blood.
The circulation of the red blood commences in the capillary system of the lungs, where the blood acquires, by the mixture of the principles that it draws from the air,[6] the peculiar character that distinguishes it from the black blood. From this system it passes into the first divisions, then into the trunks of the pulmonary veins; these pour it into the left auricle of the heart, which transmits it to the ventricle, and this drives it into the arterial system; this spreads it into the general capillary system, which may be truly considered as the termination of its course. The red blood is then constantly carried from the capillary system of the lungs to the general capillary system. The cavities that contain it are all lined with a continuous membrane; this membrane spread upon the pulmonary veins, upon the left cavities of the heart and upon the whole arterial system, may be considered as a general and continuous canal, the exterior of which is strengthened in the pulmonary veins by a loose membrane, in the heart by a fleshy surface, which is delicate in the auricle, thick in the ventricle, and in the arterial system by a fibrous layer of a peculiar nature. In these varieties of the organs that are thus added to it without, this membrane remains every where nearly the same, as we shall see.
Circulation of the black blood.
The circulation of the black blood is performed in a manner the reverse of the preceding. It begins in the general capillary system; it is in this system, that its blood takes the peculiar character that distinguishes it from the preceding; it is here that it is formed, by the subtraction probably of the principles of the air that it acquired by terminating its course in the lungs. From this general capillary system, it enters the veins which transmit it to the right cavities of the heart, which send it by the pulmonary artery, to the capillary system of the lungs. This system is its real termination, as it is the commencement of the circulation of the red blood. A general membrane, every where continued, lines the whole course of the black blood, and forms for it also a general and continuous canal, in which it is constantly carried from all parts to the interior of the lungs. At the exterior of this great canal, nature has placed a loose membrane in the veins, fleshy fibres in the heart, and a peculiar fibrous texture in the pulmonary artery; but, like the preceding canal, it remains always nearly uniform, notwithstanding this difference of organs to which it is united externally. It is by the folds of this membrane in the veins that the valves are formed. It contributes to form all those of the right side of the heart, whose cavities it lines, as the preceding enters into the composition of the valves of the left side, which borrows from it the membrane that lines it.
Difference of the two circulations.
From the general idea that I have given of the two circulations, it is evident that they are perfectly independent of each other, except at their origin and termination, where the red and black blood are alternately transformed into each other, and communicate for this purpose by the capillary vessels. In their whole course they are entirely separate. Though the two portions of the heart are united in one single organ, they may however be considered as uniformly independent in their action. There are truly two hearts, a right and a left. Both would be able perhaps to perform their functions as well if they were separate, as they now do united. When the foramen ovale remains open after birth, I have proved elsewhere that such is the arrangement of the two folds between which it is found, that the black blood cannot communicate with the red, and that the two hearts should equally be considered independent, at least as it respects the course of the blood. This entire separation of the two circulations is one of their most striking characters; it alone proves how much preferable the point of view in which I have presented the circulation, is to that which divides it into great and small, which are evidently confounded and identified.
From what has been said, it appears that the origin and termination of each circulation take place in the two capillary systems, which are, if we may so say, the limits between which the two kinds of blood move. The lungs alone correspond in this respect, with all the parts. Their capillary system is in opposition to that of all the other organs, if we except the parts from which the blood of the vena porta goes. Each capillary system then is at the same time an origin and termination. The pulmonary is the origin of the circulation of the red blood, and the termination of that of the black. The general gives to the red blood its termination, and to the black blood its origin. Observe that this is a great character that distinguishes the two circulations. In fact, the blood not only takes an opposite course at the place where they finish and at that where they begin; but its nature changes also entirely, and in this respect the two capillary systems, pulmonary and general, present to us the most important phenomena of the living economy, viz. the first, the transformation of black blood into red, the second, that of red blood into black.
There are evidently three things to be examined with regard to each of the circulations, 1st. the origin; 2d. the course; 3d. the termination of each kind of blood. In the origin and termination, there is on one hand the mechanical phenomena of circulation, on the other the phenomena of the transformation of the blood. In the course of this fluid there is only the mechanical phenomena of the circulation to be observed.
General mechanical phenomena of the two circulations.
By examining these phenomena in a general manner, we see, 1st. that the red blood going from the lungs, is formed into larger and less numerous columns, as it approaches the cavities of the heart; that it is in the greatest masses in these cavities, and that from them to the capillary system, it is continually dividing into smaller columns; 2d. that the black blood going from the general capillary system, is formed into columns larger and less frequent, as it approaches the right cavities of the heart; that these cavities contain the greatest quantity of it, and that from them to the lungs, it is successively divided into smaller columns.
The two kinds of blood circulate then on the two sides in branches that diminish as they go from the heart, and increase as they approach it. Represent to yourself for each of the two circulations two trees united at their trunks, sending their branches, one of them to the lungs, the other to all the parts. Each of the two parts of the heart is between these trunks, which it serves to unite, so as to form a general canal of which we have spoken.
Authors have commonly considered the arteries and veins as forming, each by their assemblage, a cone, the base of which is at all the parts, and the apex at the heart. This manner of describing them arises from this, that the sum of the branches is greater in diameter, than that of the trunks from which they arise; now in adopting this idea, it is evident that each half of the heart is at the summit of two cones, which would be united without it. The pulmonary veins represent one, and the aorta the other for the red blood; for the black blood, there is on one part the venæ cavæ and coronary veins, on the other, the pulmonary artery, which form the two cones. In each circulation, one of these cones is remarkable for its small size; it is that of the lungs; the other for its great extent; it is that of all the parts.
Placed between these two cones, each part of the heart should be considered as an agent of impulse which hastens the course of the blood, on one hand towards all the parts, on the other towards the lungs. In fact, if in each circulation these two cones communicate by their apex, it is evident that the parietes of the vessels that compose them would be insufficient to maintain the motion, from the base of one to the base of the other; that is to say from the general capillary system to that of the lungs, and reciprocally from that of the lungs to the general one. The course is manifestly too long, and the vital forces of the vascular parietes not sufficient to admit of this; hence the necessity of the heart.
This consequence leads to another, which is this. As the red blood has a greater extent to go over from the heart to the general capillary system, than the black blood has from the heart to the pulmonary capillary system, it is necessary that the portion of this organ belonging to the first kind of blood, should be endowed with a greater force than that destined to support the motion of the latter. Nature has effected this object by composing the ventricle with red blood of fibres much stronger than those of that of black blood. As to the auricles, as they only receive the blood and transmit it to the ventricles, their thickness is nearly uniform.
From this we see, 1st. that the part the heart performs in the two circulations, is absolutely relative to the mechanical phenomena of the course of the blood, and that, if it has any influence upon the composition, it can only be by the internal motion it communicates to it; 2d. that if the course of the two circulations, of black blood and red, was of less extent, they might do without this intermediate agent of impulse. This is precisely what happens in the system of abdominal black blood, the two trees of which distributing their branches, one to the gastric viscera, the other to the liver, unite by their trunk in what is called the sinus of the vena porta, which occupies exactly the place of the heart in the great system of black blood and in that of red.
It is then possible to conceive, 1st. how the heart may fail; of this we have many examples, in which the two great circulating systems resemble in a certain degree, the abdominal; 2d. how the blood can oscillate from one capillary system to the other, during a considerable time, though the heart, weak, enfeebled, and even in part disorganized, can hardly any longer accelerate the course of this fluid; 3d. how, this organ having entirely suspended its pulsation in syncope, asphyxia, &c. there is still an oscillation, a real progression of the blood from one capillary system to the other, so that if an artery or vein is then opened, it flows a little at the opening. Certainly this oscillation is very weak; it cannot last a long time; but we cannot deny that it exists without the influence of the heart, since the black blood is carried without the agent of impulse, from the intestines to the liver; hence it follows that the cessation of the pulsation of the heart is not a proof of the want of motion in the blood, as some authors have thought. 4th. We know that in many animals of the lower classes, there is no heart, though there are distinct vessels and circulating fluids.
The importance of the part that the heart enjoys in the animal economy is only in relation to the general impulse that it communicates to all the organs and the constant excitement in which it keeps them by this impulse. It does not send to them the materials of secretion, of exhalation and of nutrition; it only in this respect transmits what it receives from the lungs.
II. Reflections upon the general uses of the circulation.
This leads us to some reflections upon the general differences of the uses of the two circulations; differences which prove the necessity of presenting the single function that results from them in the view in which I have placed it, and not in that in use in the treatises on physiology. The following are the differences.
General uses of the circulation of the red blood.
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.
Let us conclude from these experiments, that the influence of the direction of the arteries upon the course of the blood, is much less than is commonly thought, and that all the calculations of mathematical physicians upon the delay of the blood from this cause, rest upon unsubstantial foundations. There is no doubt that when the fore arm is strongly bent, the pulse is weakened, stops even, and it is essential when we feel the pulse that the arm should be extended; but this phenomenon does not depend upon the angle the artery forms; it arises from this, that the muscles that press it, contract its caliber and even obliterate it. This is so true, that the different curves of the internal carotid are much more evident than the single curve that the brachial then forms, and yet the circulation is performed there very well. Besides, open an intercostal artery which has but few curves, the force with which the blood will be thrown out is not stronger than it would be from the radial, &c. If the whole arterial system was empty and the blood going from the heart filled it successively, as this fluid would strike against the arterial curvatures, it would undoubtedly experience some delay. It is on this account that in our injections a tortuous artery is slower in filling; as the spermatic for example often remains empty. But in a number of tubes full of fluid, it is wholly different; the impulse received at the beginning of them is suddenly propagated into all the cavities that form them, and not by a successive progression, as I shall say hereafter.
The arterial curvatures are adapted to the different states in which the organs may be found. We see them very evident in those which are subject to an alternate dilatation and contraction, for example in the intestines, the lips, and the whole face. In the fœtus, when the testicle is in the abdomen, the artery is very tortuous. When this gland descends, the artery untwists and takes the straight course it has in the adult. In the motions of the womb, the bladder, the pharynx, the tongue, &c. these curvatures perform an important part in the preservation of these organs. In the fractures of the lower jaw, they prevent the rupture of the artery that traverses this bone, a rupture which the displacing of the bone would produce without them. By them the arterial system is preserved unhurt in the violent and oftentimes forced motions that the limbs perform.
The flexibility of the arteries would be insufficient for these motions; in fact, when an artery is extended longitudinally, its diameter is diminished. By accommodating themselves to the motions of our parts, the vessels would impede then the circulation, because there would be less space for the blood to move in. Hence why the arteries of all the parts subject to alternate dilatations and contractions, being uniformly tortuous, can without the aid of their extensibility, have very different degrees of extent. I would remark upon this subject that the locomotion of the arteries, observed by Veitbrecht, is far more evident at the time of the contraction of the hollow organs, or of the flexion of the limbs, than during the dilatation of the one or the extension of the others. I have invariably made this remark upon living animals. We can by emptying or distending the intestines, the stomach, the bladder, &c. make their arteries beat more or less strong, &c. &c.
Anastomoses of the arteries in their course.
Anastomosis is the union of many branches, which mingle the columns of blood that each brings. There are two kinds of anastomoses; sometimes two equal trunks unite, sometimes a small trunk is joined to a large one.
The first has three varieties. 1st. Two equal trunks sometimes unite at an acute angle, and form but one; it is thus that the ductus arteriosus and aorta are blended together in the fœtus; that the two vertebrals produce the basilary trunks, &c. &c. 2d. Two trunks communicate at certain places by a transverse branch; such are the two anterior cerebral, before they go between the hemispheres. 3d. Two trunks unite and form an arch; this is the case with the mesenteric; then branches arise from the convexity of this arch. We see then that there are three kinds of anastomoses between equal branches; one of these is that in which two columns of blood are united together and take a direction between the two first; another in which two columns follow their first direction, and only communicate with each other; finally in the last, two columns meet each other by their extremities, in an opposite direction, and the blood escapes afterwards by secondary vessels.
The second kind of anastomoses is that of considerable branches with smaller ones; it is extremely frequent, especially in the extremities; it has no varieties.
It is almost always in regions remote from the heart that anastomoses are met with. We find scarcely any in the trunks that arise from the aorta. They begin to be more frequent in the branches, as in the mesenteric, the cerebral, &c. The more the smaller branches are subdivided, the more numerous are the anastomoses. In the last ramifications they are so numerous that they form an inextricable network. This arrangement is calculated to facilitate the circulation, which the anastomoses favour in places, where the motion of the blood is liable to experience obstacles. It is on this account that in the cavities in which the influence of the neighbouring parts upon the motion is less sensible, the anastomoses become more frequent, as in the brain, the abdomen, &c.; whilst they are more rare in the muscular interstices of the extremities, &c. It is not then a tree with distinct branches that forms the arterial system, but a tree all the parts of which communicate together, more frequently as they are the further removed from the origin.
The principal object of the anastomoses, that of obviating the obstacles the blood experiences in its course, is fulfilled in many cases. Thus, after the ligature of a wounded artery or one with an aneurism, after the spontaneous obliteration of one of these vessels, we see the anastomoses between the fine branches, above and below this obliteration or this ligature, continue the circulation in the part. These collateral vessels then increase often in size; but more frequently still, the course of the blood is supported almost entirely by the capillary vessels.
Anastomoses suppose then the vitality of the arteries. It is because these vessels are not inert, but act themselves upon the fluid they contain, that the circulating phenomena are subject to so many variations; that oftentimes, and especially by the influence of the passions, the spasm of their extremities, principally of the capillaries, obliges the blood to flow back, a reflux which is favoured by the anastomoses. This reflux is necessary also in inflammations, in the different engorgements of our organs, &c. How would the circulation be able to go on, if all the small branches went to their respective destinations, without communicating among themselves? Would not the least embarrassment occasion a troublesome stagnation there?
I would remark upon this subject that the anastomoses furnish the first proof of a truth which we shall soon demonstrate more in detail, viz. that in the great trunks, the blood is especially influenced by the heart, and that in the capillaries, it is exclusively by the vascular parietes. In fact it is because the vitality of the arteries is every thing for the motion of the last subdivisions, that the least alterations that they experience give rise to many engorgements that inevitably require anastomoses, which are extremely numerous at the end of the arterial tree. On the other hand, the vitality of the trunks having scarcely any influence upon the blood, it experiences but few obstacles in passing through them; there is less need then of anastomoses, which are in fact more rare there.
If the least cause, the least irritation produced spasm of the trunks, as they produce that of their last divisions, it would be necessary that they should communicate as frequently together. A fleshy texture in the great arteries, and vital properties analogous to the involuntary muscles, would have required inevitably these numerous anastomoses, because a variety of causes influencing these kinds of muscles, they can at any moment increase unnaturally their contraction, diminish their caliber and embarrass the progress of the fluids that traverse them.
Forms of the Arteries in their course.
Many physicians of the present age have described each artery as forming a cone, the base of which is towards the heart, and the apex towards the extremities. If we examine a portion of it between the origin of two branches, whether after having injected it, or by cutting it perpendicularly when it is empty, or by measuring it when it is full of blood, we find it always cylindrical. Undoubtedly considered in its whole extent, it takes a conical form, the effect of its successive diminution by the branches it furnishes; but in this sense it is less a cone, than a series of cylinders successively joined to each other and always decreasing.
Considered in its general arrangement, the arterial system represents on the contrary, as I have said, a cone absolutely inverted, that is to say, having its base at all the parts and its apex at the heart; so that the aorta has a diameter less considerable in proportion, than that of the sum of all the branches. We have a proof of this by comparing a trunk with two branches that succeed it; these surpass it in diameter, and the relation being always the same in all the subdivisions, we conceive that the capacity of the arterial system goes uniformly increasing.
This relation of the trunks and the branches has been exaggerated however by mathematical physiologists, who attributed to the last over the first a predominance much greater than really existed. A cause of error upon this point may arise from measuring the arteries at their exterior after having injected them; in fact, the caliber of the trunks is greater, in proportion to their parietes, than that of the branches separately examined; that is to say, other things being equal, the aorta has parietes thinner in proportion to its cavity, than the cubital artery; hence, without doubt, why aneurisms are rare in the branches, and frequent in the trunks, especially when the diseases arise from a local cause; for if they are the effect of a general disease, oftentimes the little arteries, the radial particularly, are also affected; I have already seen two examples of it. This observation upon the proportions of the arterial parietes proves the impossibility of judging of the relations of diameter between the two, at least by examining them in the interior.
Besides, these relations are necessarily very variable, according as the vital forces which vary themselves so much, increase or contract the caliber of the small arteries; and in this point of view, this examination cannot have the importance that was attached to it by the ancients, whose works are filled with calculations upon this point.
III. Termination of the Arteries.
After being divided, subdivided, and having the peculiarities we have just examined, the arteries terminate in the general capillary system. To point out where this system begins, and where the arteries end, would be very difficult. We can prove that there the blood ceases to be entirely under the influence of the heart, and circulates by the influence of the insensible organic contractility of the vascular parietes; but how can this line of demarcation be rendered evident to the eye?
Authors in treating of the termination of the arteries, have considered their continuity with the excretories, the exhalants, the veins, &c.; but it is evident that the general capillary system is between the arteries and these vessels. Thus I shall treat of their origin in speaking of this system, which is spread in all the organs, but has essential differences according to the different systems, under the relation of its continuity with the arteries. In fact, 1st. there are systems in which these vessels are distributed in great quantity, and in which consequently the general capillary system contains much blood; such are the glandular, the mucous, the cutaneous, the animal and organic muscular, &c. 2d. Other systems receive but few arteries, as the osseous, the fibrous, the serous, &c. and consequently have but little blood in circulation in that portion of the general capillary system that belongs to them. 3d. Finally the pilous, epidermoid, cartilaginous systems, &c. destitute of arteries, contain only white fluids in the division of the general capillary system that has its seat in them.
ARTICLE THIRD.
ORGANIZATION OF THE VASCULAR SYSTEM WITH RED BLOOD.
I. Textures peculiar to this organization.
The red blood circulates, as I have said, in a membrane arranged in the shape of a great canal, variable in its form, extended from the pulmonary capillary system to the general one, and having every where the greatest analogy. At the exterior of this membrane, nature has added a fibrous coat for the arteries, fleshy fibres for the heart, and a peculiar membrane for the pulmonary veins. I shall speak here only of the arterial coat. The fibres of the heart and the membrane of the pulmonary veins will be examined, one in the organic muscular system, the other in the system with black blood. As to the internal membrane of the arteries, which is also that of the whole system with red blood, we shall examine it in a general manner.
Peculiar Membrane of the Arteries.
This membrane is firm, compact, very apparent in the great arteries, less evident in the last divisions where it is insensibly lost. Its colour is usually every where the same. If the branches appear red in living animals, and the trunks yellowish, it arises only from the transparency of the one which allows the blood to be seen, and the opacity of the others. The colour of the arterial fibre is yellowish. However it assumes in certain cases a greyish appearance. I have often observed in arteries exposed to maceration, that it reddens in a very evident manner at the end of some days, or rather that it takes a rosy tinge, very analogous to that of the cartilages of the fœtus and of the fibro-cartilages of the adult, submitted to the same experiment. This result is however less uniform in the arteries than in those two systems, in which it is never absent. Sometimes the internal membrane reddens also, but never the external or cellular; on the contrary, the longer this remains in water the whiter it becomes. When the fibrous coat of the arteries has continued some time with this redness, it gradually loses it, if maceration is continued. This phenomenon is often more evident in the branches than in the trunks. For example, the arteries at the base of the cranium become red very frequently in the dead body, by remaining in the fluids with which this part is moistened. We see, in opening the cranium, this redness which does not belong to the blood left in the arterial cavities, as we may be easily convinced.
The thickness of the peculiar membrane of the arteries is very evident in the great trunks. It constantly diminishes; a circumstance that distinguishes it essentially from the internal membrane, which I have found almost as thick in the tibial artery as in the aorta. It has been thought that in certain arteries, as in the cerebral, the fibrous coat is entirely wanting. There is no doubt that in the vertebral and internal carotid it is thinner in proportion than in equal trunks situated in the muscular interstices; but by examining attentively these arteries, I have clearly distinguished circular fibres in them. Has the thinness of their parietes an influence upon the sanguineous effusions, which are, as we know, so frequent in the brain? I cannot say. These effusions take place only in the capillaries, the trunks are never the seats of them; now it is impossible to examine these capillaries. I have sought in vain to ascertain by injections the vessels torn in apoplexy. Besides, this hemorrhage does not resemble that of the serous membranes; it is not an oozing through the exhalants of the ventricles; for these cavities are very rarely the only seat of it. Almost always these effusions take place even in the cerebral substance, generally nearer the posterior than the anterior lobe. The cerebellum is rarely affected by it. When the tuber annulare becomes so, there are often small partial effusions there, separated by medullary partitions that remain uninjured.
As to the arteries of the other parts of the body, their peculiar membrane presents generally a pretty uniform arrangement. It has appeared to me however, that in the interior of the viscera, of the liver, of the spleen, it is rather thinner than in the intermuscular spaces, and even than in the muscles.
This membrane is composed of very distinct fibres, adhering to each other, easily separated however, arranged in layers, in such a manner that after having raised the cellular covering, we can without difficulty separate these different layers from each other; it is this that has made many authors believe that the great arteries were composed of a great number of coats. The fibres that form these layers are circular or nearly so; the external ones appear to be attached to the compact cellular texture that is contiguous. In fact, by raising this, a number more or less considerable adheres to it always in an intimate manner. As to the internal membrane, it does not appear to furnish any attachment; we raise it easily, without bringing with it any arterial fibres. The manner of the adhesion of these fibres with the compact neighbouring texture, appears to me to have great analogy with the origin of the organic muscular fibres, which are attached in a great number of places, to the sub-mucous texture.
When a branch arises from a trunk, the circular fibres of the last separate and form on each side a half ring, whence arises a complete one, which embraces the small rings formed by the circular fibres of the arising branch. These circular fibres go even to the eminence of the common membrane, which is seen within the arterial cavity and of which I have spoken; so that the whole thickness of the peculiar membrane serves as a support to their origin. But there is but little continuity between the two kinds of fibres. Those of the branch do not arise from those of the trunk; it is the internal membrane that serves to fix them together, as fibres of communication. Dissection shows easily these branches set at their origin in the ring which arises from the separation of the circular fibres. We remark this at the origin of the intercostals and lumbars upon the aorta, &c. When two trunks of an equal size go off, as the iliacs, the last circular fibres of the primitive trunk which they formed, interlace intimately with the origin of each of the two circular layers, that arise at the fork that separates this origin. Thus the last rings of the aorta cannot be separated from the first of each iliac.
There are no longitudinal fibres in the arteries.
What is the nature of the arterial fibre? Almost all anatomists have considered it the same with the muscular. But if we examine them attentively, it is easy to be convinced of their differences. The want of red colour does not establish these differences, since in man even, some parts really muscular, as the intestines, want this colour. But the muscular texture is soft, loose and very extensible; the arterial texture on the contrary is firm and solid, breaks before it yields. We can observe this, by tying an artery tight. The two internal coats are cut; the cellular alone is not, though the ligature is immediately applied to it; we observe, by opening the artery, a section corresponding with the thread, exactly similar to what a cutting instrument would have made.
I have often repeated this experiment, pointed out by Desault, upon the dead body, and upon living animals; the result which is very uniform, explains the frequency of hemorrhages after the operation for aneurism. There is undoubtedly no texture so brittle, if I may use the word, as the arterial, none consequently less proper to be embraced by ligatures. Why is it that this should be the only one in which it is necessary to apply them? This phenomenon alone would distinguish the arterial texture from the muscular. In fact, the preceding experiment, made upon a portion of intestine in which the fibres are arranged like the arterial, would produce a flattening, an approximation of these fibres, but would not cut them.
Moreover compare the properties of texture of the arteries with those of the muscles; compare their vital properties, by examining the articles in which I treat of these properties; compare their development, and especially the different morbid alterations to which the two are subject, and you will see that there is not a single relation in which they have the least analogy. The aneurism of the heart and that of the arteries have nothing in common but the name. In one there is a rupture of the arterial fibres, a dilatation of the cellular coat; in the other an unnatural increase, a real development of muscular fibres which preserve their appearance and their properties.
Notwithstanding the ease with which the arterial fibres are broken in cases of aneurism, they enjoy in a natural state a very considerable degree of resistance and force; another character that distinguishes them from the fleshy texture. The following are the proofs of this resistance, which takes place both transversely and longitudinally. 1st. If we tie the carotid artery above, and drive a fluid afterwards into it, great force must be employed to break its texture. The same thing happens when we force in air instead of a liquid. Frequently the efforts of a man are insufficient to produce a rupture; thus the force of the heart can never cause it suddenly; so that the formation of aneurisms takes place only from the long continued action upon the arterial parietes; I doubt whether these tumours can be formed, without a previous alteration of the arterial texture, by the force of the impulse of the blood alone against the weak parietes of the arteries. 2d. The resistance of these parietes takes place longitudinally also. If we draw in a contrary direction, the two ends of an artery and of a muscle, we effect with more difficulty the rupture of the first, when the dead body is the subject of this comparative experiment. But upon the living the effect is opposite; the vessel yields to a very strong action made upon it; it would be necessary that this action should be incomparably greater to divide the muscle. This difference arises evidently from the vital properties of the latter, which in this case contracts violently, whilst the artery can make no further resistance than from the nature of its texture. Besides, this longitudinal resistance to distension is less than the lateral resistance opposed to the injection; experiments prove it, and it arises without doubt from this, that no fibre, in the first case, is found directly opposed to the effort.
This resistance of the arterial texture, so different from that of the venous, is a necessary consequence of the situation of the heart at the origin of the arteries. In fact, this organ driving the blood with force into their tubes, should find there a force capable of resisting the greatest efforts of which it is susceptible, when its sensible organic contractility is raised to a high point. This is the great advantage of the arterial texture. What would become of the circulation and all the functions that depended upon it, if the least cause which increased the force of the blood could dilate the parietes of the arteries beyond the ordinary degree? It was necessary that their texture should render these parietes independent of the different degrees of motion of the fluid that circulates in them; whence it follows that a fleshy heart and resisting arteries are two things inevitably connected. If nature had doubled the energy of the heart, she would have doubled also the arterial resistance. On the other hand, they would have had but little resistance, if there had not been an agent of impulse at their origin; this is precisely what happens in the hepatic portion of the vena porta, which by its distribution is analogous to the arteries. Why is the pulmonary artery thinner and less resisting than the aorta? Because the right ventricle being less fleshy, is not capable of so great efforts.
From what has been said, it appears, that the external arterial membrane resembles the fibrous organs, which, as we shall see, are characterized by an extreme resistance. But if we observe on the other hand that this membrane can be broken, raised by layers and scales in dissection, that it is elastic and even dry, if I may so say, whilst the fibrous organs are compact, form a solid body, resisting, but softer and more elastic, we shall be convinced that this external membrane is exclusively peculiar to the arteries; that it has no relation with the other systems, but forms a distinct and separate texture in the economy. The structure with regular fibres, is the only circumstance that can, in my opinion, make us believe in the muscular nature of the arteries; but the ligaments and tendons are fibrous also; of what importance are the forms to the intimate nature? Now, can we say that this nature is the same, when the physical properties, when the extensibility and contractility of texture, when the vital sensibility and contractility are different?
Besides, the action of different re-agents upon the arterial texture, proves clearly how much it differs from the muscular. There are then general phenomena common to all the solids; but different peculiar phenomena that are distinctive. We may satisfy ourselves of this, by comparing the following article with that which corresponds with it in the muscular system.
Action of different agents upon the arterial texture.
The action of the air by drying the arteries gives them a colour of a reddish yellow, very deep and even blackish in the great trunks, more clear in the smaller ones. Thus dried, the arterial texture is almost as hard as the cartilages in the same state, extremely brittle, breaking in the great trunks with a crackling noise, that is not perceived in any other animal texture. It is especially in this preparation, that we see how much the cellular covering of the arteries differs from their peculiar texture. This covering remains pliable; it is whitish when raised up separately. Immersed again in water, the arteries assume in part their natural arrangement.
In drying, the arterial texture loses but very little of its thickness; this is a phenomenon that distinguishes it from most of the other textures. It arises from the small quantity of fluid that is contained between its layers, a circumstance that appears to be owing to the absence of the cellular texture. In opening the arterial layers, the kind of dryness they exhibit is remarkable, when compared with the moisture in which the muscular fibres are immersed.
Exposed wet among other organs to the action of the air, the arteries putrefy with great difficulty. Their texture resembles in this respect that of the cartilages, the fibro-cartilages, &c.; it is like them for some time almost incorruptible; when it is left to putrefy by itself, it gives out an odour much less fœtid than that of other textures; there appears to be less ammonia disengaged from it. The absence of fœtor is also very remarkable in the water in which the arteries have been macerated, entirely separated from every neighbouring texture. By comparing this water with that in which muscles have been macerated, the difference is striking. An evident proof of the resistance of the arteries to putrefaction and maceration, is what is observed in the viscera, which have been a long time macerated or which are putrid, as in the liver, the spleen, the kidnies, &c. In both cases, in the first especially, these viscera are reduced to a kind of pulp; the arteries however have preserved their texture still hard, amid this general softening. By removing carefully the putrid substance, we can follow them even to their final ramifications. This method of seeing the arteries is easy, whether they are filled by injection, or left empty. In the living animal, these vessels are also infinitely less susceptible of putrefaction than the skin, the cellular texture, &c. An artery often passes through a mortified part without undergoing any alteration from it; this is frequently seen in gun-shot wounds.
At the end of a period, very different according to the degree of temperature, the arterial texture yields finally to maceration and putrefaction. In the first case, it softens gradually without changing colour, loses the adhesion of its fibres, and is ultimately resolved into a pulp almost homogeneous and greyish. In the second case, it becomes greyish at first, then is reduced also to a pulp, and when all the fluid part is evaporated, there is left a kind of coal wholly different from that which remains after the putrefaction of the muscles. In general, it requires much longer time to soften the arterial texture by maceration than by putrefaction; which shows the superiority of the action of the air over that of water, in the production of this phenomenon.
Exposed to the contact of caloric, the arterial texture curls up, contracts and exhibits the horny hardening in the highest degree. If the action of water is added to that of caloric, which produces boiling, the following is the result of it. 1st. Very little froth rises before ebullition, from the vessel that contains the arterial texture; we might say that this texture and the muscular present in this respect, two opposite phenomena in the economy; the small quantity of froth that arises from the first, is greyish. 2d. At the moment of ebullition, there is an evident horny hardening, less however than that of the nervous texture, more sensible in the direction of the diameters than in that of the axis; a hardening accompanying this horny hardening, and a yellowish tinge of the liquor. 3d. This state continues for half an hour or more, ebullition constantly going on. 4th. Successive softening; but at the same time a greyish tinge succeeding to the yellow colour; want of adhesion among the fibres, increasing as the ebullition goes on, so that they break with great ease. 5th. However prolonged may be the ebullition, the arterial texture is never reduced, like the fibrous, the cartilaginous, &c. to a gelatinous and yellowish pulp. The fibres remain as they are, in the same relation, with the same size, &c. The want of adhesion and the change of colour are almost the only phenomena they experience. 5th. The broth, produced by the boiling, is insipid and tasteless, a proof how few neutral salts the arterial texture contains.
The action of the concentrated acids curls this texture, afterwards softens it, finally dissolves it in the form of a pulp, yellowish by the nitric, and blackish by the sulphuric.
Most of the others have a less sensible action than these two. When they are diluted, there is no horny hardening at the moment the artery is immersed in them; but its texture is gradually softened, and can be broken with the least effort, as after boiling. It is never reduced to a fluid state, how long soever it may continue in the acid.
The alkalies, even the caustic, have but little action upon the arterial texture; immersed a long time in them, this texture remains almost untouched, loses but little by solution, cannot be broken as it can after being in the diluted acids, &c.
Membrane common to the system with Red Blood.
I call that the common membrane which lines the arteries, the left side of the heart and the pulmonary veins. It can be dissected with ease upon these two last organs. To separate it from the arteries, it is necessary to cut through by a very superficial circular section, the external fibrous layer, raise this layer by laminæ from below upwards; we come then to the internal membrane, which adheres but little to the preceding, and can be detached from it in the form of a canal, of very great extent. It is distinct from it, 1st. by its extreme tenuity, and the transparency that results from it; 2d. by its white colour; for it appears yellow only by being applied to the preceding; 3d. by the entire want of fibres. It is smooth and with a uniform texture like the serous membranes, which we may be convinced of by holding it up to the light. Besides, it differs essentially from these membranes by a kind of brittleness that characterizes it; it is broken and torn by the least effort. The whole resistance of the arteries resides in their fibrous coat.
It appears that this membrane, though every where connected, has however some differences of structure in the different regions. 1st. It is evidently more delicate in the interior of the ventricle with red blood, than in the corresponding auricle and in the arteries. 2d. It yields in the heart and in the pulmonary veins, to dilatations much greater than those of which it is susceptible in the arteries, in which it would inevitably break, like the proper membrane, if the blood could produce as great differences of size in it, as it does in these organs. 3d. When we macerate the heart for some time, this internal membrane acquires in the auricle and upon the mitral valves, a very remarkable whiteness, and which is foreign to it in all the rest of its course. 4th. As to the action of the different agents, of the air, of water, of caloric, &c. it appears to me to be the same every where, and resembles precisely that upon the peculiar membrane. Only I have thought, that in the small arteries, the common membrane has the horny hardness more than this, which on this account wrinkles on the interior in different places, when a whole branch is immersed in boiling water; this does not take place in the great trunks.
It is evident from this, that though the common membrane of red blood, is every where continuous, it is not uniform in its structure; we shall have occasion to make an analogous observation for the different portions of the two general mucous surfaces.
The internal surface of this membrane is moistened in the dead body, by an unctuous fluid, that is found in greater or less quantity. Does this fluid exist in the living? does it serve to defend the arterial coat from the impression of the blood? It is difficult to determine. We know of no organ fitted to furnish it; it would arise from the exhalants, if its existence, as many authors have admitted, was real. It would be well to ascertain as to its existence, whether it was merely a transudation after death, analogous to that of the bile through the gall bladder, or the consequence of a little serum remaining in the arteries after the expulsion of the blood. What makes me suspect so is, that these arteries being deprived of blood, contract intimate adhesions on their internal surface; which their fluid ought to prevent, as that of the mucous tubes does, which should they cease to transmit their respective substances, as the excrements for example, the secreted fluids, &c. would never be obliterated because of this fluid.
It appears then that it is the membrane itself, and not a fluid that escapes from it, which serves to protect the artery; it can, in this point of view, be considered in relation to the blood, as a kind of epidermis. It is this, which by its folds contributes especially to form the aortic and mitral valves, and the different eminences at the origin of the branches, smaller branches, &c. The external surface, feebly united to the other membrane as we have seen, has not an intermediate cellular one. Notwithstanding this slight adhesion, no means, boiling water, maceration, putrefaction, &c. can detach one of these membranes from the other, as takes place in the periosteum from the bone, which, are naturally much stronger united; it requires always the aid of dissection.
What is the nature of this common membrane? I am entirely ignorant; though with a different appearance it has the greatest analogy with the preceding coat, in its properties. We cannot class them in any system. They form a separate texture in the economy, a texture that has properties entirely distinct.
When we dry the common membrane of the arteries by itself, it is infinitely more pliable than the other. It remains transparent, the other does not. As to the phenomena of the other re-agents, except the horny hardening, they are nearly the same.
This membrane is remarkable, in all the organic systems, for the singular tendency it has of being ossified in old age. I have been able to satisfy myself, that out of ten subjects, there are at least seven that have incrustations after the sixtieth year. These incrustations, having no connexion with the peculiar fibrous membrane, begin uniformly on the external surface of this, the most external part of which they attack; for there always remains over the incrustation a kind of pellicle that separates it from the blood, and which belongs to the membrane; the earthy substance is never immediately in contact with this fluid.
These incrustations do not follow any of the laws of ordinary ossification. The cartilaginous state rarely precedes them. The saline substance is deposited immediately upon the exterior of the common membrane by the exhalants. It is always in separate plates, more or less broad, that this exhalation is made; rarely the whole of the artery forms a solid continuous tube; so that the membranous portions remaining between the plates can be considered as serving for articular connexions, and that the arteries, thus ossified, are composed of many pieces moveable upon each other, and being able to a certain extent to adapt themselves to the circulating motion.
As long as these plates remain thin, the interior of the artery is as usual smooth and polished. But if many saline substances are deposited there, they then have a greater thickness and make a projection within. The fine pellicle that covers them and which is continued upon the artery, is broken; then they adhere only by their external surface to the peculiar membrane. Their circumference is unequal and rough. If there is a great number in the artery, the whole internal surface presents numerous asperities, produced by the rupture of this extremely fine layer of the common membrane that covers the osseous plates. This arrangement is particularly remarkable at the origin and even in the course of the aorta. I have noticed it frequently in the dissecting rooms. Since I have practised medicine in the hospitals, I have already opened three or four subjects that have exhibited this arrangement, in which the heart was perfectly untouched, but who died however with most of the symptoms that accompany diseases of that organ. The rupture of the fine pellicle when the osseous plates become large, arises from the remarkable brittleness that we have observed in the common membrane, of which it is an appendage. I have never seen these osseous plates entirely detached, and become loose in the artery.
All the parts of the arterial system are subject to ossification. It appears as frequent in the branches as in the trunks. We know how common it is to find the radial ossified, in feeling the pulse of an old person. The ramifications appear to be less frequently the seat of these incrustations, which never take place in the capillary system; a circumstance that would induce me to believe that the common membrane of the arteries does not extend to this system, but that it changes gradually into a different texture.
It is not only in the arteries that the common membrane of the system with red blood is penetrated with saline substance; this often happens to it in the heart, especially in the aortic and mitral valves. It is more rare upon the internal surface of the left ventricle and auricle and the pulmonary veins. I have had however examples of these last. This general disposition to ossification in its whole course, proves that its nature is every where the same, and that notwithstanding the differences pointed out, I have had reason to consider it in an uniform manner, from the pulmonary capillary system to the general; for as I have already observed, an identity of diseases supposes an identity of nature. It is the frequency of ossifications of this membrane in the heart of old people, which renders extremely frequent the intermission of the pulse at that age. The ossification of the origin of the aorta has an influence also upon the circulation, as I have ascertained; but that of the trunks, branches, &c. does not produce the least derangement.
The ossification of the common membrane of the system with red blood differs essentially from those that happen in other parts, in this, that it is, if we may so say, a natural phenomenon, whereas the others are accidental and often preceded by inflammation and engorgement. Thus these ossifications do not follow the progress of age; they happen in young people and in adults, as often as in old ones. Before old age, the ossifications of this membrane are observed also, but infinitely more rarely than at this age. The diseases of the heart which the ossification of the mitral valves accompanies and often alone constitutes, are a remarkable proof of this. A phenomenon has struck me many times upon this subject; such an ossification as an old man can live with very well, and which only makes his pulse intermittent, produces in the adult the most serious consequences. I have already opened many subjects, who had been affected with difficulty of breathing, frequent suffocation, cough, irregularity of the pulse, necessity of an erect position of the trunk, and in the later periods, infiltration, serous effusion in the thorax, spitting of blood, &c. and in whom I have found only ossification of the mitral valves, less than we see every day in the bodies of old people in our dissecting rooms. I confess that even this natural disposition to ossification in the common membrane of the system with red blood, had made me think that they had exaggerated a little the cases in which this ossification becomes, in the adult and even in the old man, when it is very strongly marked, the cause of that series of phenomena, whose assemblage forms the asthma of most physicians. But the practice of the Hôtel Dieu shows me every day, that these cases of ossifications, those of aneurisms and those of other organic affections of which the heart is the seat, form a class of chronic diseases almost as numerous as that of the chronic diseases of the lungs, to which generally were referred all the diseases of the chest, before the time of Corvisart.
II. Parts common to the organization of the Vascular System with Red Blood.
Blood Vessels.
The parietes of the arteries contain secondary arteries destined to their nutrition. These arteries come usually from neighbouring branches, sometimes from the artery itself, whose capillary divisions terminate in the texture of its parietes. The heart exhibits this arrangement. At its exit, the aorta sends off the coronaries which are spread upon the texture of this organ and upon the origin of this artery itself. The bronchials furnish the parietes of the pulmonary veins. In the arterial texture, in which it is especially necessary to examine the little arteries, they wind at first in the cellular texture exterior to the artery, they ramify there in a thousand ways, send some divisions to the neighbouring organs, but furnish a great number that penetrate the peculiar membrane, are interposed between its layers, leave filaments there and terminate before they arrive at the internal membrane. I have never seen, either by injections, or by opening in a living animal an artery in which I had first stopt the course of the blood above and below, as for example, the carotid, I have never seen, I say, the little arteries penetrating even to this internal membrane. To distinguish well without injections, the vessels of the arteries, it is necessary to choose on one hand a great trunk like the aorta, and on the other to take this trunk in a young animal that has been killed for the purpose by asphyxia; all the little arteries then are perfectly injected with a very black blood. Examine the arteries of the fœtus, especially if it has died by asphyxia at birth, you will be struck with the great abundance of blood vessels that its great arteries contain and which are sometimes as livid as in asphyxia.
The veins accompany every where the little arteries in the parietes of the arterial trunks, they follow nearly the same distribution. I have not seen them become varicose in the parietes of aneurismatic arteries, in as evident a manner, as in the tumours of many other textures of the animal economy.
Cellular Texture.
The arteries have around them two kinds of cellular texture; one, which is very external, loose, fatty, full of serum, with distinct layers, unites them to the neighbouring parts, favours their motions, is in no way distinct from the rest of the cellular system; the other, firm, compact, not fatty, filamentous and not lamellated, forms the first of their coats. We have spoken in treating of the cellular system, of this particular layer that covers the arteries, which authors commonly call the cellular coat, which the ancients called nervous, on account of its whiteness, and which, analogous in every respect to the sub-mucous, sub-excretory cellular texture, &c. differs essentially from the preceding, as it differs from that which is in the interior, around or in the interstices of the organs.
These two kinds of cellular texture, the last especially, contribute to support the folds of the arteries; as when we have carefully dissected the peculiar coat, these folds entirely disappear. However when they are on one hand strongly marked, and on the other, are not subject frequently to disappear in yielding to the elongation of the parts, as in the internal carotid in its canal, I have observed that the arterial fibres are accommodated to these folds; that the fibres are more numerous on the convex side, than on the other, so that the thickness of the artery is exactly uniform, which it would not be without this inequality; for being more pressed on the concave side, these fibres would make the artery thicker at that place.
The cellular texture forms the first membrane of the arteries, and gives as we have seen insertions to the arterial fibres, but it does not extend into the interstices of these fibres; it is this that distinguishes essentially the layers of the arterial texture, from those of the muscular, venous textures, &c. I have never been able to discover the cellular texture there by any means that I could employ. Maceration, of which Haller has said so much, does not show any thing like it. When at the end of a very long time, the arteries finally yield to it, they exhibit only a kind of pulp, in which there is no cellular appearance.
In general, the resolution of the organs into cellular texture by maceration, exhibits a phenomenon much less extensive than is generally thought. It is the organic texture itself that forms the kind of pulp that is then obtained. As this texture varies in each system, the pulp of these systems, a long time macerated, varies equally; this undoubtedly would not happen, if, as Haller has advanced, the cellular texture was the only base, to which all the organs are brought by maceration. But let us return to the arteries.
Not only their fibres are not formed of cellular texture; but as I have said, they do not contain it in their interstices, a character in which it differs from all the other systems. The most careful dissection does not show it. When we separate the fibres from each other, we see, either that they are merely in apposition, or that they are held by little elongations of the same nature as themselves. I have said that this absence of the cellular texture is observable between the proper and common membranes of the arteries, though Haller has pretended the contrary.
I believe that this absence of cellular texture contributes much to the kind of brittleness that particularly distinguishes the arterial texture, and which, as I have observed, renders it the least fit of all the animal textures, to support ligatures without breaking. It is to this circumstance also that must be referred the difficulty, the impossibility even of arterial dilatations, of the formation of cysts by the parieties of arteries. There are never, we know, true aneurisms; when these tumours increase at all, the two membranes of the artery break and the cellular coat alone is dilated. Hence the necessity of the peculiar structure which distinguishes the cellular texture placed around the arteries, and gives it a resistance that it has not in most other parts. Authors are astonished at these ruptures which distinguish the dilatations of the arteries from those of all the other systems. If they had compared the texture of the arteries with that of the other systems they would have seen the reason of this difference.
We easily understand, after what has been said, why there is never fat in the arterial texture; why it is never infiltrated in dropsies; why it does not develop hydatids and cysts in its layers, why the different tumours, for which the cellular texture serves as a base, as we have seen, do not appear in the arteries, &c. When an artery has been wounded, either longitudinally or transversely, we do not see fleshy granulations arise from the edges of the wound; I do not know that surgeons have seen them in the operations for aneurisms. Never, in the numerous cases in which I have had occasion to cut the arteries, in animals, and then leave them free, after having interrupted the course of the blood, have I observed any thing like it. If an arterial trunk is laid bare, the cellular coat often furnishes these granulations; but we never see them, if this coat is removed.
Exhalants and Absorbents.
Are there exhalants in the arteries? Nutrition undoubtedly supposes them; but it is not probable, as I have said, that they open upon their internal surface.
As to the absorbents, I thought for some time, that the absence of blood in the arteries, after death, arises from this, that their lymphatics preserving still the absorbent faculty for some time, take up the serum which is separated from the crassamentum. But lately experiments have undeceived me. I have enclosed blood, water, the fluid of dropsies, &c. between two ligatures made above and below on the common carotid, the body of which had been so managed on the exterior as not to break the vessels that come to it. At the expiration of a considerable time I have not discovered any diminution in the fluid. There had been then no absorption. I would observe that on account of the want of collateral branches, the carotid is alone proper for these experiments, and a variety of other analogous ones.
We know that the absorbents abound where there is cellular texture, and that they are wanting usually where there is none. It is probable then that the absence of this texture produces also the absence of these vessels.
Nerves.
1st. The first tree of the system with red blood, receives almost exclusively cerebral nerves. We know in fact, that the par vagum is spread upon all the pulmonary veins, as well as upon the neighbouring vessels of the lungs, which hardly receive any from the inferior cervical ganglion. 2d. The middle portion of this system, that in which the heart is found, derives its nerves almost as much and even more, from the ganglions, than from the brain. 3d. The great tree with red blood, or the arterial, is almost exclusively embraced by the first class of nerves. We have said how these nerves go in this respect. The cerebral which accompany them, furnish hardly any filaments to the arteries. There is merely juxta position as we see it in the extremities, in the intercostal spaces, &c.
I cannot repeat it too much, that the constant relation of the arteries with the nervous system of the ganglions, deserves the attention of physiologists, because it is too general not to belong to some great object of the functions of the economy, though the object may be unknown.
ARTICLE FOURTH.
PROPERTIES OF THE VASCULAR SYSTEM WITH RED BLOOD.
What we have to say of these properties, will refer particularly to the arteries, as well as what we have said of the organization. In fact the fleshy parietes of the heart and the membranous ones of the pulmonary veins, possess properties that will be examined hereafter, and which differ from those of the arteries, on account of the difference of texture. As to those of the common membrane they are nearly the same in the whole course of the red blood, the organization differing but very little.
I shall consider the properties of the arteries only in the arterial texture and in the common membrane; for the cellular coat belonging to the system of that name, partakes of all its properties.
I. Physical Properties.
Elasticity, which is obscure in most of the other animal textures that are characterized by a great degree of softness is very remarkable in the arteries; it is this that particularly distinguishes them from the veins. This elasticity keeps their parietes apart, though they may be empty. These tubes, with the cartilaginous, as the trachea, the meatus auditorius of the fœtus, &c. which are equally endowed with elasticity, are the only ones that keep thus open of themselves. All the others have their parietes applied to each other, when the fluid that runs through them does not distend these parietes.
It is to the elasticity of the arterial parietes that must be referred their recovering themselves when they have been flattened so as to obliterate their cavity, the sudden straightening of an arterial tube that has been bent, &c.
This property takes also an evident part in that kind of locomotion the arteries have upon the entrance of the blood. In fact, lay bare a tortuous arterial trunk in a living animal, you see the whole of it rise at each pulsation, leave the place it occupied, and straighten itself, particularly at its curves. At the moment the injection penetrates a very thin small subject, we perceive also through the integuments, a locomotion of all the tortuous branches of the face. Now it is evident that if the arteries were not of a firm and elastic texture, they would not thus obey the motion that is impressed upon them; besides, observe what takes place in the injection of the abdominal branches of the vena porta, which having no valves can be injected like arteries. Nothing similar to the locomotion of which I spoke is observed in driving the fluid into them. I have often made arterial blood circulate in the veins by the means of curved tubes, fitted to the vessels of a living animal, for example, by making the carotid and external jugular communicate; now, we observe clearly in the veins carrying the red blood, a kind of pulsation synchronous with the beating of the heart, and a distinct rustling noise, but not a real locomotion.
The locomotion of the arteries supposes three things, 1st, an agent of impulse, that communicates a motion more or less strong, to the blood contained in their interior; 2d, a tortuous arrangement which allows the blood in striking their parietes to straighten them; 3d, the firmness and elasticity of these parietes which facilitate this straightening. On the other hand, the parietes must not be too firm; thus the cartilaginous texture would be improper for this locomotion.
The elasticity of the arteries is as striking after death as during life; it is essential to distinguish it from contractility of texture. There are many distinctive characters, the following are the most striking; 1st. The contractility of texture takes place only when there is a want of extension of the arterial parietes, that is to say, when these vessels cease to contain the blood which resists their contraction, or when they are cut and afterwards left to themselves. On the contrary, elasticity requires for its exercise, a previous compression and is manifested by the sudden return of the parts to their natural state. 2d. Contractility of texture has a permanent tendency to contraction; we may say that all the parts that possess it are in a forced state; so that as soon as this state ceases, contraction takes place. On the contrary, elasticity has not this constant tendency to exercise. 3d. Every elastic motion is brisk, sudden, as quick to stop as to begin. On the contrary, every motion of contractility of texture is insensible, slow, continues often many hours and even days, as we see it in the retraction of amputated muscles, &c. 4th. Every organ in which there is contractility of texture, enjoys necessarily extensibility. On the contrary, this last property is not necessarily connected with elasticity, as we observe it in the cartilages of animals, &c. 5th. Elasticity is purely a physical property. Contractility of texture, without being vital, is only inherent in the organs of animals.
II. Properties of texture. Extensibility.
The extensibility of the arteries may be considered, 1st, transversely; 2d, longitudinally.
The arteries have but little extensibility in the direction of their diameter. 1st. Whatever efforts are made to dilate them by injections of water, air, fat substances, &c. their caliber is rendered but little larger than natural. 2d. I have said that their texture is remarkable by a kind of brittleness, that when the blood distends them a little in aneurisms, this texture breaks instead of yielding, and that it is only the cellular coat, which, by the extensibility it has from the system from which it is derived, that is fitted to form the cyst that contains the blood. It is this that essentially distinguishes aneurismal from varicose tumours. 3d. If we tie superiorly the carotid artery of a dog, the blood pushed against the ligature that stops its course, reacts violently upon the parietes and yet the dilatation is hardly perceptible. We must not think however that the arteries do not yield at all. When the dilating cause acts slowly, it produces its effect to a certain determinate point, beyond which rupture takes place. The proof of this, is in the dilatation of the arch of the aorta, in that which true aneurisms present in their early stages, &c.
Longitudinally, the arteries are more capable of stretching, than they are transversely. We may be convinced of this, by drawing out these vessels, to place a ligature upon them in an amputated stump. By cutting upon a dead body a portion of artery, and drawing it in a contrary direction, it is evidently elongated. It is necessary in these experiments, to pay attention to the development of the folds. In fact, I have said, that this development of the folds performs a principal part in the elongation of the arteries situated in the parts that are dilated.
It is evident that in the extensibility in a transverse direction, it is the circular fibres of the peculiar membrane that especially resist; that on the contrary, in the extensibility in a longitudinal direction, it is the common membrane that opposes the resistance, since there are no longitudinal fibres. It is not astonishing then that the first kind of extensibility should be less evident than the second.
Contractility.
It is necessary to consider it in a transverse and in a longitudinal direction.
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.
If an artery is opened laterally, it forms two currents of blood in an opposite direction, which are driven towards the opening, and which unite in one throw. One of these currents is direct, the other arises from anastomoses. It is the same as when an artery is cut, and the blood flows at both ends.
If an artery is wholly divided, more blood flows from it in a given time, than passed through it before in the same time to go to the capillary system, which resisted more. We cannot then judge of the velocity of the blood by the throw from the open arteries.
Sympathies.
We have seen that the arteries are rarely the seat of diseases either acute or chronic, on account of the obscurity of their vital properties. They can exert then but a very slight influence upon the other organs; thus, except some sympathetic pains that are experienced in aneurism, this influence of the arterial texture upon the other systems is merely nothing. In two or three cases I have seen convulsive motions produced by the injection of a very irritating fluid in the arteries. It is easy to distinguish these sympathetic motions, from those that pain produces in an animal who is struggling to disengage himself; they are violent tremors or stiffness, like tetanus. It may be imagined that these experiments should not be made in the carotids, because the brain, irritated by the injected fluids, would produce convulsions arising from the stimulant that would be then directly applied to it, and not from a sympathetic relation. Besides, death would be the immediate consequence of the experiment, if it was made upon the carotid.
On the other hand, as the arteries have not sensible organic contractility, hardly any animal sensibility, and but little tone, the other organs can with difficulty develop in them sympathies by their influence; for, in order that a vital property should be brought sympathetically into action in a part, it is necessary that it should exist there, and even be conspicuous. Thus the innumerable variations of the pulse, which are the product of sympathies, have all essentially their seat in the heart; the arteries are not connected with them. Now the sympathies make the heart contract or arrest its motion, as stimulants or sedatives directly applied to it, that is to say, by acting on its sensible organic contractility. When an aneurism is broken in a fit of anger, or in the act of coition, a case of which I have seen with Desault, it is the motion of the blood, which is suddenly increased, that is the cause of it; it is not the arterial texture that has been affected by the passion. Besides, upon what can the sympathies act in the arteries? It could not be either upon the elasticity or the contractility of texture, the only properties, however, capable of contracting these vessels. Observe, also, that the sympathies put in action only the vital properties, because they are themselves a phenomenon purely vital. The physical properties and the properties of texture cannot be exercised under their influence; this is an important observation.
Besides, as the arteries are every where spread in the organs, and as they form, if we may so say, a part with them, it would be difficult to distinguish what belongs to them, especially as it respects sensibility, from what is peculiar to these organs.
ARTICLE FIFTH.
DEVELOPMENT OF THE VASCULAR SYSTEM WITH RED BLOOD.
I. State of this system in the Fœtus.
The fœtus differs essentially from the infant that has breathed, in this, that its two great vascular systems in reality form but one, since the foramen ovale on the one hand, and the ductus arteriosus on the other, form a direct communication between the two. This communication is much more evident at the period nearest conception; these openings contract towards the period of birth. 1st. The foramen ovale is formed, in the first months, by two productions in the form of a crescent, whose concave surfaces are opposite, and leave between them an oval space, which is constantly contracting, because these two productions constantly approximate and have a tendency to cross each other, which in fact takes place after birth. 2d. The ductus arteriosus contracts as the pulmonary artery dilates.
While these two openings are free, which is constantly the case in the fœtus, the two systems evidently make but one, as I have said; whence it clearly follows that the blood that circulates there must be entirely of the same nature, that there cannot be two kinds in the fœtus, as there always is in the adult. This is, in fact, a remarkable difference between the two ages. 1st. I have many times dissected small Guinea pigs in the womb of the mother; their vessels have uniformly contained the same fluid, which is blackish, like the venous blood of the adult. This experiment is easy. The abdomen of the mother being divided, we successively open each of the separate sacs that the womb has for each fœtus. When one of these sacs is laid open, we cut the membranes, then the abdomen of the small animal, leaving the umbilical vessels untouched. The transparency of the parts easily allows us to see the uniformity of the colour of the blood of the vena cava and the aorta. The same remark applies to the superior parts. The carotid and jugular pour out the same blood when they are opened. 2d. I have three times made the same observation upon the fœtus of a dog. 3d. We know that the blood of the umbilical arteries is always black; all accoucheurs have remarked this. 4th. The change of the black blood to red arises from the contact of air in the lungs; the fœtus not breathing, cannot then have this kind of blood. 5th. I have dissected many fœtuses that have died in the womb of the mother; the blood of the veins and the arteries has appeared to me to be uniformly the same. It is true that this is not a very conclusive proof, since the mere standing of the red blood in the vessels, for a considerable length of time, is sufficient to make it black, as Hunter has observed.
The preceding facts are sufficient to establish incontestibly the uniformity of the blood in the two systems of the fœtus; an uniformity that exists at least in external appearance, if it is not real in its intimate composition. It is for the chemists to elucidate this point.
How is it, that the instant the black blood enters the system of red blood in the adult, alarming consequences follow, soon asphyxia, then death, take place, whilst in the fœtus, the black blood circulates with impunity in the arteries? It is a difficult question to resolve, and yet these two contradictory facts are equally true. The difference of the nature of the blood of the fœtus might perhaps serve to remove this difficulty, if we better understood this difference. In fact, though the colour assimilates this blood with that of the veins of the adult, yet it does not appear to be the same; it has an unctuous feel, unlike the other. It is never found in the dead body coagulated like it, but always fluid, like the blood of those who have died of asphyxia. Fourcroy discovered no fibrin in it; he observed that it did not take the vermilion colour by the contact of the air; that it contained no phosphoric salts, &c. It is then very probable that if the black blood is fatal in the arteries of the adult, whilst it circulates with impunity in those of the fœtus, that it arises from the difference of the nature of the one and the other. Besides, observe that there is a very great difference in the functions of the fœtus and the adult. The first scarcely has animal life; it wants many functions of organic. The relation of the organs with each other, is of a nature wholly different from what it will be after birth. No kind of analogy ever can be established between the fœtus and the infant in this respect. Thus we have observed that the experiments upon life and death give a result wholly different in animals with red and warm blood, and in those with red and cold, which approximate nearly the organization of the fœtus in some respects. We cannot then establish any kind of parallel in respect to the injury of the respiratory phenomena, between the fœtus and the infant, an injury, the causes of which I have sought in my experiments, since the organization relative to these phenomena differ so essentially in the one and the other.
Although, as I have said, the blood of the two vascular systems is confounded in the fœtus, yet there is, especially in the first periods, a kind of separation in the general mass of blood, a separation that was first accurately observed by Sabatier, and which is the result of the arrangement of the foramen ovale and the ductus arteriosus. This separation divides the mass of blood into two. The following is the manner in which the circulation of the blood is performed in this respect.
1st. All the blood that the trunk of the inferior vena cava receives, either from the capillary system of the inferior extremities, or from that of the abdomen, or from the placenta by the umbilical vein, instead of stopping in the right auricle, as in the adult, passes entire into the left through the foramen ovale, the superior edge of which is so arranged, that nothing can mix with the blood of the superior vena cava; so that when we examine attentively, we see that it is really with the left auricle that the inferior vena cava is continued. Hence why this auricle is in proportion as much dilated as the right; for it would be very contracted, if it had only to receive the blood of the pulmonary veins, the quantity of which is merely nothing in the first periods of life. From this auricle the blood passes to the left ventricle, which transmits it to the aorta, where it meets the carotids and subclavians, which, by numerous ramifications, carry it to the capillary system of the head and the superior extremities.
2d. After having remained in this system, the blood returns by the different branches of the superior vena cava to the right auricle, where the superior edge of the foramen ovale prevents it from communicating with the other blood; from this auricle it passes to the ventricle, which transmits it to the pulmonary artery, which sends a small part of it that returns to the left auricle by the veins of the same name, but transmits almost the whole of it by the ductus arteriosus to the descending aorta, below the origin of the carotids and the subclavians, which carry the other blood. This is carried by the branches and ramifications of the aorta to the capillary system of the abdomen and inferior extremities; the remainder is afterwards carried by the umbilical artery and lost in the placenta.
It follows from what we have just said, that notwithstanding the continuity of the two great sanguineous systems in the fœtus, there is in the first months after conception, a kind of separation of the blood they contain; that there is even if we may so say, two systems wholly different from those which will afterwards exist in a separate manner in the adult.
The first of these systems has, 1st, for origin all the capillaries of the abdomen, of the inferior extremities, and even those of the placenta; 2d, for common trunks, below the inferior vena cava, above the quadruple branch called the aorta; 3d, for agent of impulse the left side of the heart; 4th, for termination all the capillaries of the head and the superior parts. The second commences in these last capillaries, and is composed, 1st, for its trunks, of the superior vena cava and the descending aorta; 2d, for its agent of impulse, of the right side of the heart; 3d, for its termination, of the capillaries of the inferior parts.
The blood is then evidently divided in the first months after conception into two circulations, which cross, if it may be so said, in the form of the figure 8, as has been remarked by Sabatier; it is carried in each, from one assemblage of capillaries to another of the same vessels. Only instead of moving between the pulmonary capillary system and the general one, as in the adult, it moves between the superior and inferior part of this last system; we may then say in this point of view that the inferior and superior parts of the body are in opposition in the fœtus, as the lungs in the adult are in opposition to the rest of the body.
This complete opposition on the part of the circulation, between the upper and lower part of the body, in the first months of the fœtus, is probably the origin of the difference that takes place afterwards between these parts.
All physicians have observed this difference in diseases. If the median line frequently separates the affections of the right side from those of the left, the diaphragm seems often to be the boundary of many diseases. Who does not know, that scorbutic affections appear particularly below, that serous infiltrations are most frequent there, and that ulcers are infinitely more common in the inferior extremities, and that on the other hand, most cutaneous eruptions take place in the superior parts, &c.? Bordeu, who has said much of the division of the body into superior and inferior parts, considered one pulse as the precursor of evacuations from above, and another as that of those from below, he has however without doubt exaggerated this opposition of the two parts of the body; still it really exists, and I think that it is very probable, that the manner of the circulation of the fœtus is the primary source of it.
After the first months, things begin to change. The quantity of blood passing by the pulmonary artery was at first scarcely any thing, because the dilatation of the ductus arteriosus was so great, that it turned almost the whole of it into the descending aorta. This canal gradually contracting, the pulmonary arteries dilate, and then more blood goes through the lungs, and is brought by the pulmonary veins to the left auricle, which transmits it to the left ventricle, which sends it to the arch of the aorta; then the mechanism of the circulation described above begins to change, and approximate that of the infant, as we shall see.
Still this first mechanism predominates for a long time over the second; hence it happens that during the greatest part of the time that the infant is in the womb of the mother, it is the left ventricle that sends the blood to the superior parts, whilst the inferior receive theirs by the impulse of the right. Now as the parietes of the first are evidently thicker than those of the second, and the heart is further from the inferior than the superior parts, these last receive a stronger impulse than the others. This perhaps is a new source of the difference of the two halves of the body; hence nutrition is more active in that above, hence the degree of vital energy that it preserves a long time after birth, and which makes it susceptible, the head especially, of many more affections than the lower half.
As the period of birth approaches, the pulmonary artery sends more blood to the lungs, and less passes through the ductus arteriosus. For, as I have said, it is only in a gradual manner that the whole of this fluid, contained in the body, comes finally at birth to go through the lungs. Though before it undergoes no alteration there, it does not circulate the less, which is undoubtedly to habituate it to the passage that it is constantly to take after birth. The quantity of blood then is in a direct ratio to the age in the pulmonary artery, and in an inverse one in the ductus arteriosus.
This arrangement evidently requires a corresponding one in the foramen ovale; in fact, if in proportion as the ductus arteriosus contracted, this was not diminished also, all the blood would finally accumulate in the superior parts. For instead of passing from them to the inferior, the whole of it would return to them by the left auricle and the ventricle of the same side. In proportion as the ductus arteriosus is contracted, the foramen ovale being lessened also, the blood of the inferior vena cava, the whole of which cannot pass through there, begins to mix with that of the superior, enters the right auricle, then the right ventricle, afterwards returns by the lungs to the left auricle and ventricle and the aorta. What is the consequence of this? that this artery begins to receive from the left ventricle a much greater quantity of blood than can pass into the carotids and subclavians; a portion of it then goes into the descending trunk and is distributed to the inferior parts.
From what has been said, it appears, that the two portions of the blood of the fœtus are almost wholly separate in the first months; all that comes from the inferior vena cava goes into the ascending aorta; all from the superior passes into the descending, the lungs receiving scarcely any except by the bronchial arteries for their nutrition. But as the period of birth approaches, these two portions of blood begin to mix, and the circulation then has an arrangement between that of the adult and that of the first months. At birth even, the foramen ovale and the ductus arteriosus are much contracted, the circulation goes on in the mother's womb almost in the same way as it does after birth; the whole difference is that the fluid is of the same nature, because respiration has not taken place. The sudden change of the circulation at birth, arises particularly from the introduction of red blood into the economy. As to the mechanical phenomena, they are gradually produced by the gradual contraction of the two openings of communication. The blood gradually ceases to move from the inferior to the superior capillaries; it then goes from both of these to those of the lungs and reciprocally.
In considering the circulating phenomena, we err in supposing that their change is sudden at birth. It is sufficient to examine the foramen ovale and the ductus arteriosus at different periods of pregnancy, to see that they contract successively, and that consequently these phenomena are successive, so that if the fœtus should remain in the womb a long time beyond its period, and the contraction should continue in the foramen ovale and the ductus arteriosus, the blood would circulate as in the adult, from the pulmonary to the general capillary system exclusively, and reciprocally. The only difference would be in the uniformity of its colour, because it would pass through the first system, without coming in contact with the air.
I do not say that the entrance of the air does not suddenly bring to the lungs the remainder of the blood which passed by the ductus arteriosus; but this kind of sudden turn takes place only in a part of the blood of the pulmonary artery; a part already passed through the lungs before birth, though the air cells were empty.
In general, there is a constant relation between the quantity of blood that the right ventricle sends to the lungs, and that which the left sends to the inferior parts. The more the first increases, the more abundant is the second; this last evidently exceeds that which goes to the superior parts. These three things, 1st, the quantity of the blood of the inferior vena cava which mixes with that of the superior, and passes with it into the right auricle; 2d, that which from the right ventricle goes through the lungs and returns to the left auricle; 3d, that which from the left ventricle goes to the descending aorta, constantly increase as the period of accouchment approaches.
The descending aorta does not undergo by these variations any change in its caliber; in fact, it is the same thing to it, whether it receives the blood of the ductus arteriosus, below the origin of the carotids and subclavians, or whether this fluid comes directly to it from the left ventricle, through its arch; its parietes constantly increase in a uniform manner; all depends upon the successive contraction of the ductus arteriosus and the foramen ovale.
The whole vascular system is generally remarkable in the fœtus for its great development. The arteries are in proportion larger, which corresponds with the size of the heart, which is much developed at this age; it is nearly the same as the nerves in relation to the brain.
The development of the arteries however is not like that of the nerves, nearly uniform every where. These vessels follow in general the same order as the parts to which they are distributed. Thus in the superior parts, the cerebral arteries are much more evident than the facial; among these, the ophthalmic is more so than the nasal, the palatine, &c. In the thorax, the thymic arteries are much larger in proportion than afterwards. In the abdomen, all the gastric viscera being very considerable, their arteries are already very large; the supra-renal are much larger in proportion than in the adult. In the pelvis on the contrary, the arterial system is very contracted, because the viscera are small, as they receive but little nourishment. In the inferior extremities, the arteries are a little more contracted in proportion than in the superior, especially in the earlier periods, for towards birth, the proportion is nearer equal.
The arterial texture is infinitely more pliable in the fœtus than in the adult; it will yield more easily to extension; ligatures applied upon the arteries break it less easily. Aneurisms are extremely rare in infants.
Many little arteries wind upon the parietes of the great ones in the fœtus; they are often livid, to see them distinctly, it is necessary, as I have said, to examine them at this age. Does this abundance of vessels dispose the arteries in the first age to inflammations, which are so rare afterwards? I have never observed this alteration.
In the first periods of the fœtus, the layers and arterial fibres are indistinct; we should say that the coat of the artery is homogeneous. But it has however much more consistence than most of the surrounding textures; this consistence corresponds with that of the heart. Destined to distribute every where the nutritive matter, the arteries ought necessarily to precede the other organs in their nutrition. This early growth, always concomitant with that of the heart, would alone prove that the arteries are made to develop themselves, and that the heart does not hollow them out, as Haller has said, in the interior of our organs by the force of its impulse. Besides this mechanical manner of considering their formation is evidently contrary to the known laws of the animal economy.
II. State of the Vascular System with Red Blood during growth.
At the moment of birth, two great revolutions take place in the system with red blood; 1st, a mechanical one, if it may be so said, in the phenomena of the course of the blood; 2d, a chemical one, in the nature of this fluid. The mechanical revolution depends upon the entire cessation of the passage of the blood through the foramen ovale, the ductus arteriosus, the umbilical arteries and veins. The chemical revolution depends upon the formation of red blood. I will now examine this last.
The fœtus finds at birth that all surrounding objects are the causes of great excitement; the cutaneous surface, all the origins of the mucous, are strongly stimulated. The sensations they experience are even painful, because the difference is very great between the waters of the amnios and the bodies with which the fœtus comes in contact at birth, and every abrupt change in the sensations is painful. Habit soon familiarizes this sensation; but it is not less real at birth, and it may be said that this moment is as painful for the infant as the mother. Now, as every lively sensation is generally accompanied with great motions a general agitation succeeds the impression that the fœtus perceives from without; all the muscles move, the intercostals and the diaphragm like the others. The air which already filled the mouth and wind-pipe, then enters the lungs, and there colours the blood red, then it is alternately expired and inspired until death. The first inspiration then is, in this point of view, a phenomenon analogous to all the motions that the change of external excitement suddenly produces at birth in the voluntary muscles of the fœtus.
The respiratory motion is, however, too important, since it commences a new kind of relation between the organs, to depend exclusively upon this cause. I presume that an unknown principle, a kind of instinct, induces the fœtus at the moment of birth, to contract the intercostals and diaphragm. This instinct, which I do not understand, and of which I cannot give the least idea, is the same that makes the infant the moment it comes from its mother's womb, contract its lips, as if to nurse. We certainly cannot say that this motion is an effect of the very acute external impressions that it feels; these impressions produce agitations, irregular motions, as if to get rid of these impressions, and not a uniform motion evidently directed towards a determinate object. If we examine all animals separately at the instant of their birth, we shall see that every one performs particular motions, directed by its instinct. The small quadrupeds seek the breast of their mother; the gallinaceous animals the grain that is to nourish them; the small carnivorous birds immediately open their bills, as if to receive the prey the mother is afterwards to bring to them in the nest, &c.
In general, it is essential to distinguish accurately the motions, which, at the instant of birth, arise from new excitements that the body of the fœtus receives, from those which are the result of a kind of instinct, of a cause of which we are ignorant. I believe that the respiratory motion belongs at the same time to the two causes, and more especially perhaps to the last.
I pass now to the mechanical revolutions of the course of the blood. At the instant the lungs change to red the black blood that enters them by the pulmonary arteries, they receive all that which before passed through the ductus arteriosus; this ceases to transmit any to the aorta, though, however, it often remains still more or less dilated; for at birth it is hardly ever entirely obliterated; this contraction varies singularly at this period. Why does the blood then cease to flow there? As the aliments do not enter the ductus choledochus, the lacteal or pancreatic ducts, though they pass their orifices; so undoubtedly this takes place, because the kind of sensibility of the ductus arteriosus repels the new venous blood of the fœtus, which comes no longer from the placenta, because that which the lungs have reddened will not mix with it. We cannot certainly give any mechanical reason for its not passing; it really does not, and it evidently depends upon the vital laws. Besides, the motion of which the lungs become the seat, the dilatation, and especially the new excitement that the external air produces there, by rendering considerably more active the capillary circulation, facilitate that of the two pulmonary trunks, and give the blood a tendency to pass there rather than through the ductus arteriosus; it is in this way that the lungs attract, as I have said, the blood from the pulmonary artery. Does not the great irritation, of which certain tumours are the seat, draw there more of this fluid? Is it not on this account that the arteries of these tumours dilate and acquire a double or even treble caliber? What takes place in these tumours in a gradual manner, happens suddenly to the blood that still passes by the ductus arteriosus at birth, and which was very much diminished, as I have said, by the successive contraction of this canal.
For the same reason that all the blood of the pulmonary artery goes through the lungs, the foramen ovale is closed; in fact, this foramen is so arranged at birth, that its valves approximate so as to cross, as it were; so that when they are pressed against each other, the communication of the auricles is really closed. Now the red blood entering the left auricle by the pulmonary veins, pushes the valve of the foramen ovale corresponding to this auricle, against the other, and consequently opposes the blood of the vena cava inferior that endeavours to enter there. This blood flows back to the right auricle. Now when this contracts to drive the blood into the ventricle, far from forcing it through the foramen ovale, it necessarily brings the two valves against each other, and obliterates it. By examining with care the state of the heart of the fœtus, it is evident that when the blood enters the left auricle by the pulmonary veins, the right by the venæ cavæ and the valves are crossed, it is impossible that the blood can pass them either in contraction or dilatation.
Though the foramen ovale may be open at birth, still the black blood ceases to pass through it; I say further, oftentimes this foramen remains open during the whole of life. Many authors have related examples of this. I have seen a great number, though this assertion may appear extravagant at first. It is impossible from the arrangement of its two valves, for the blood to pass through it. When the two auricles contract at the same time, the blood which is forced by them from without within, brings the valves together, and thus itself creates an obstacle to its passage. In the greatest number of cases, the adhesion of the two valves crossed, is extremely weak; they are rather in contact than united; so that by forcing between them the handle of a scalpel, they are easily separated and hardly any traces of rupture are found. If they were arranged so that the blood could insinuate itself between them, it would soon separate them and re-establish the communication. Authors need no longer attempt to explain, how life is supported when the foramen ovale is open; it is the same as if it was closed, no more blood passes through it.
The obliteration of the foramen ovale, and the cessation of the passage of the blood through its opening, are, as we see, phenomena to a certain degree mechanical. The vital laws perform also, without doubt, their part on this occasion. Who knows if the sensibility of the left auricle, stimulated and modified anew by the red blood, does not repel the black which tries to enter it by the foramen ovale? We see every day in the economy, fluids passing at the side of openings, without entering them, though they may be wide, for the sole reason that their sensibility is not in relation with these fluids. Why does the trachea convulsively reject all fluids and solids? why does the air alone enter it? Why does not the blood enter the thoracic duct, which is often furnished with a valve, as I have observed, incapable of opposing its passage, and sometimes even has none? Why does the urethra repel the urine in coition? It is a fault of all authors that they seek only for mechanical causes in all the phenomena of the circulation. Without doubt the course of the blood is a mechanical phenomenon; but the laws that govern this course are vital; it is the same as a bone that is moved by muscular contraction; the effect is the mechanism of the lever; the cause is vital.
The blood no longer passing through the ductus arteriosus, this closes immediately by its contractility of texture; it becomes a kind of ligament, which fixes to a certain degree the aorta and pulmonary artery in their respective position. As to the obliteration of the foramen ovale, it does not arise from this contractility; this obliteration is not made by a contraction, but by a real agglutination of the two valves, between which it is obliquely situated at birth. This agglutination appears to be the effect of a pressure that is made in an opposite direction, upon the partition between the auricles, by the blood that each contains. In fact their fibres are so arranged that they contract from without within; now by contracting thus, they press from each side the blood against the partition, and consequently the two valves against each other. Now this agglutination sometimes does not take place, whilst the contractility is always exerted when the parts in which it exists cease to be distended; the ductus arteriosus is uniformly obliterated.
At the same time that the ductus arteriosus and foramen ovale cease to transmit blood at birth, this fluid is stopt in the umbilical artery and vein. Why does the blood cease to flow in this artery, though its diameter continues very large at birth? The principal cause appears to me to be the nature of the red blood, which is no longer in relation with the sensibility of this artery. A proof of this is, that if some time after the fœtus has breathed, respiration is stopt, and the black blood consequently returns, the umbilical arteries begin to pulsate, and if the ligature is loosened, they pour out considerable blood. Baudelocque has frequently observed this.
In general, when respiration is well established, the blood no longer flows by the umbilical artery, the ligature of the cord is then useless. On the other hand, when this function is badly performed, there is reason to fear hemorrhage of this artery. I confess, however, that there may be other causes for this interruption of the passage of the red blood. These four things, 1st, the cessation of the entrance of the blood into the umbilical vein; 2d, interruption of the passage of that of the inferior vena cava by the foramen ovale; 3d, of that of the pulmonary artery by the ductus arteriosus; 4th, of that of the descending aorta by the umbilical artery; these four things, I say, the three last especially, appear to depend upon a cause that we do not yet understand. The change of the relation of the organic sensibility with the nature of the blood, is perhaps only accessory, since, as I have observed, it is less this property than the action of the heart itself, which is the cause of the circulation in the trunks. This subject deserves the most attentive examination of physiologists.
Respiration being once well established, the lungs are in opposition to the whole body; it sends blood to all the parts, and they all send it to the lungs. The boundary is then rigourously established between the system with black blood and that with red, and things then go on as we have before described.
After birth the vascular system with red blood predominates for some time by its greater development and its more numerous branches, in fact the red blood enters more parts then than it does afterwards. It is sufficient to dissect living animals of different ages, to be convinced of the greater quantity of blood in young animals, that the system contains, of which we are treating; so that, as I have said elsewhere, the two opposite ages of life exhibit an inverse arrangement as it respects the fluids and solids. The first are much more abundant towards the period of conception. The second always predominate more towards the last age.
The predominance of the system with red blood remains evident to the end of the period of growth. We see the necessity of this predominance to distribute to all the parts the materials of their nutrition and growth; in fact, in the adult the arteries contain only what is destined to the first. In the infant, they contain moreover what is destined to the second. Hence the caliber of the arteries is proportionably larger than afterwards, in order to contain more fluid. Injections demonstrate this; and on this account small subjects are not less favourable for the study of the arteries, than of that of the nerves. These vessels are more prominent in them; only the surrounding parts being less developed, we cannot see the connexions so well.
In proportion as the infant advances in age, the equilibrium is gradually established in the system with red blood. In the head, the facial arteries are more evident, and come gradually in their development to the level of the cerebral. In the thorax, the thymus diminishing as the lungs increase, their nutritive arteries follow an inverse order; the bronchials dilate and the thymic contract. In the abdomen less blood goes to the capsular arteries; but most of the others receive as much of it. The pelvis and the inferior extremities have more of it, and their development is proportionably evident.
III. State of the Vascular System with Red Blood after growth.
It is about the period of puberty that the increase in height ceases; the increase in thickness continues always. The genital parts, hitherto without influence, seem to be then a centre of more active vitality than most of the other organs. The portion of the system with red blood that belongs to them, then becomes greater. The first effect that results from it is the secretion of semen, and a general impulse of the individual towards new tastes and desires, towards those relative to the propagation of the species.
Another phenomenon is soon the consequence of this. As the lungs are connected in an intimate, though unknown manner, with the genital parts, they acquire also a predominance with them. Their vital energy is increased, and then begins the period of the affections of this viscus; then, the cause that would in the adult produce a gastric affection, brings on a pulmonary one.
It is truly only at this period, that the predominance of the superior parts, of the head especially, ceases entirely. Thus whilst in infancy the nose is frequently the seat of hemorrhage, in youth it takes place particularly from the lungs. We may consider the increase of the energy of the lungs, which happens shortly after puberty, as the termination of the predominance of the superior parts. The cutaneous eruptions of the cranium, tinea capitis, &c. cease to be as frequent. Convulsions, and all the diseases that arise from the extreme susceptibility of the brain, become also more rare, and seem to give place to a great number of acute pulmonary affections.
It is towards this period, that is, some time after the end of the increase in height, that the diseases that are considered as the product of an arterial plethora, begin especially to manifest themselves; this may be said to be their age, and it arises from the following cause; as the blood contains before puberty, not only the materials of nutrition, but also those of growth, and whilst this continued the whole is expended in the system with red blood. But when the parts cease to increase in length, if this system still continues to receive the materials of growth, a true arterial plethora takes place. About the end of growth generally, some affections appear that indicate a predominance of the blood; as this is however under the influence of temperament, of the mode of life hitherto led, of the season and a thousand other causes, which, making the phenomena of the animal economy vary, rarely permit us to establish exclusive general principles. Thus all that is said upon the disposition to different diseases, in the different ages, &c. is subject to many exceptions.
The predominance of the lungs is gradually lost; the equilibrium is established among all the organs, which, hitherto had each performed a part more or less conspicuous in the phenomena relative to the different ages. As the system with red blood is uniformly, in every part, in proportion to its growth, to which it especially contributes, the equilibrium is in that way established between the different parts at twenty-six or thirty years of age; all the arteries have a proportional size, analogous to what they will always have afterwards. Whilst until then, some predominated, according to the predominance of the growth of the organs to which they are sent.
Towards the fortieth year, the gastric viscera seem to acquire a more decided vital activity; but this activity has no influence upon the size of the arteries that are distributed to these viscera.
Though the growth in height may end about the sixteenth or seventeenth year, that in thickness uniformly continues; so that the internal viscera still grow, and their arteries consequently enlarge, until the last growth ceases. This phenomenon has constantly struck me, in comparing arteries injected in subjects from sixteen to twenty years, with those in subjects beyond thirty-six or forty. In the last they are uniformly larger. It is this difference that first gave me the idea of distinguishing growth, into that in height, and that in thickness. For the development of the arteries is the constant index of the state of the growth of the organs. The period of the cessation of growth in thickness is then remarkable, 1st, by the cessation of the increase of the caliber of the arteries; 2d, by the general equilibrium that is established in their development.
As the arteries grow in the years that succeed the end of the growth of the body, they increase in compactness and thickness. Their fibres become more evident; their elasticity increases; their pliability is lessened; hence why the age of the adult is that of aneurisms. Observe that the density of the arteries follows, in its augmentation, the same proportion as the fleshy fibres of the heart; so that as this is more able to send the blood with force, these are more able to resist it.
IV. State of the Vascular System with Red Blood during old age.
In the last years, the system with red blood is remarkable for the following phenomena.
The number of the arterial ramifications is much diminished. As the heart loses its energy, it sends less blood, and with less force. The general vibration that it produces in the whole arterial tree, is less felt at the extremities of this tree. The small vessels that form these extremities gradually contract, are obliterated and become so many little ligaments. Hence why, when the periosteum is separated from the bone, the dura mater from the internal surface of the cranium, only a few drops of blood escape; why the skin, having hardened like horn, no longer exhibits the rosy tint of the preceding ages, especially of youth; why the section of a bone does not furnish hardly any blood, whilst it was so abundant in the fœtus; why the mucous surfaces look pale, the muscles have a dull colour, &c. All anatomists know that injections succeed less in proportion, as the subjects are more advanced in years; that in extreme old age the trunks alone are filled; that the fluids never enter the ramifications; that it is the reverse in young subjects; that even coarse injections oftentimes so fill the ramifications, as to render dissection difficult. I have dissected many old living animals; and the small quantity of blood their vessels contain compared with those of young animals is very remarkable. The general proposition that I have established, viz. that the solids are constantly acquiring the predominance, is perfectly true. This obliteration of the small vessels is remarkable even upon the parietes of the great vessels; we see it in the dead body; I have observed it in the living.
The less quantity of red blood that is found proportionably in old age, is referable especially to the state of nutrition, which is merely nothing when compared with that of infancy. Observe also, that united with the weakness of the motion that animates the blood, it is a cause of the small degree of excitement which the parts have in old age. In fact the use of the circulation is not only to carry to the different parts the materials of the secretions, of exhalations, nutrition, &c. we shall see that it keeps them also in a state of constant excitement by the shock it gives them at its entrance, a shock, the principle of which is evidently in the heart. Now this shock is in a ratio compounded, 1st, of the quantity of the fluid; 2d, of the force with which it is sent. In both respects, the excitement constantly diminishes, as age advances. Observe also that all the functions of the infant, both organic and animal, are characterized by a vivacity and impetuosity that form a remarkable contrast with the slowness and want of energy of those of old people.
The arterial texture always becomes more and more condensed as age advances. The layers that form the fibres of the peculiar membrane become drier, if I may be allowed the expression.
I have said that the internal membrane is very often the seat of a kind of peculiar ossification, which has hardly any influence upon the circulation, except when it is seated at the origin of the aorta.
The caliber of the arteries does not dilate in old age. There is scarcely any except the arch of the aorta, which constantly undergoes an enlargement more or less considerable, which is always without rupture of the fibres, consequently supposes an extensibility of these fibres, and undoubtedly depends upon the habitual and direct impulse that the blood exerts against the concave side of this curvature. I have often examined to see if there was a similar dilatation at those places in the arteries where the curves are very evident, in the internal carotid, for example, at the place where it passes through the carotid foramen; I have not discovered any.
In the last periods, the pulse is remarkable for its extreme slowness; a phenomenon opposite to that of infancy, in which the blood moves with great quickness. These two opposite facts are, after what we have said, foreign to the arteries. They indicate only the state of the forces of the heart, which is the agent of the general impulse of the red blood.
It is the same of the pulse in the last periods of life. It is not a real pulsation of the arteries; it is a kind of undulation, of weak oscillatory motion, and the more obscure, as life is more feeble. Now I am convinced that the heart alone is the agent of this undulation; I am convinced of it by the following very simple experiment. I have laid bare in many dogs, on one hand the carotid, on the other the heart by a section of one side of the thorax, made in such a manner that the other can still perform respiration. By placing the finger upon the artery, I observed that as long as the heart beat by a sudden impulse, that the pulse was kept up as usual, that it was even accelerated, because the contact of the air increased the quickness of the contractions of the heart; but at the end of a little time, this organ began to be weakened in its motions, then it contracted by a kind of general tremor of its fibres. In proportion as the weakness of the motions of the heart increased, the pulse was successively weakened. Then when the tremor extended to all its fibres, the pulsation of the artery changed to a kind of undulation, of feeble oscillation, the precursor of the cessation of all motion.
I shall observe, under the system of the muscles of organic life, that the heart has many kinds of contraction. The principal are, 1st, that which it ordinarily has, in which there is a contraction and a dilatation that succeed suddenly and regularly; 2d, that in which these two motions, retaining their natural character, are irregularly connected; 3d, those in which the fibres only oscillate, and by which the cardiac cavities a little contracted, communicate to the blood a less sudden shock, a general tremor, an undulation, &c. Now with each kind of motion of the heart, there is a peculiar pulse that corresponds. It is easy to be convinced of this upon living animals.
I am astonished that authors who have disputed so much upon the cause of this phenomenon, have not thought of having recourse to experiment to elucidate the question. There are undoubtedly many modifications in the pulse, whose coincidence with the motions of the heart could not be perceived; but that of the slow and frequent pulse, the strong and weak, the intermittent, undulatory, &c. can be immediately discovered, by laying the heart bare and placing the finger at the same time upon the artery. We see then uniformly, during the moments that precede death, that whatever may be the modification of the arterial pulsation, there is always an analogous modification in the motions of the heart; this certainly would not be the case, if the pulse depended especially upon the vital contraction of the arteries. I have had occasion to make these experiments many times, either directly for this object, or with others in view; I have seen the motion of the heart always correspond with that of the arteries. In general the theory of the pulse requires as I have said, new researches; but I have facts enough upon this point to be convinced that the varieties it undergoes in the different ages, as under other circumstances, depend almost exclusively upon the heart, which produces in particular this kind of undulation, of oscillatory motion which is between the pulsation of the natural state and the complete cessation of this pulsation.
V. Accidental development of the System with Red Blood.
I shall speak under the organic muscles, of the accidental development of the left portion of the heart. As to the arteries, new ones are never formed; but oftentimes, those that do exist acquire a remarkable size; this depends on two causes, 1st, on an obstruction to the course of the blood; 2d, on the growth of any tumour.
1st. The dilatation of the arteries by an obstruction to the circulation, is evident in the ligature of aneurismatic arteries, in the spontaneous cure of aneurisms, a phenomenon of which within a few years a great number of examples has been published, &c. Then, sometimes the great collaterals increase in size, sometimes their caliber remains the same, and it is by the ramifications that the communications are made. As the branches dilate, their thickness increases in proportion with their breadth; at least I have twice observed this fact, which is analogous to that which the left ventricle presents when it becomes aneurismatic.
2d. All tumours do not produce a dilatation of the arteries; we see this dilatation in cancers, in those of the breast, of the womb, &c. in osteo-sarcosis or spina ventosa, in the different fungi, &c. In general, most tumours that give great pain to the patients exhibit this phenomenon. We should say even that pain in a part is sufficient to attract there habitually more blood, and dilate the arteries; we know that in the operation for lithotomy, when the patients have previously suffered much, hemorrhage is often more to be feared.
After long and copious secretions or exhalations, I have not observed that the arteries were more dilated in the glands or around the exhalant organs. How large soever the cysts may be, their parietes never contain arteries proportioned to those that are developed in cancerous tumours. The cerebral in hydrocephalus, the mediastinal, intercostals, &c. in hydro-thorax, the mesenteric, the lumbar, the stomachic, the epigastric, &c. in ascites, the spermatic in hydrocele, the renal in diabetes, the branches that go to the parotids after a long salivation, retain their ordinary size, and under some circumstances they become even smaller.
When the arteries dilate in tumours, do their parietes thicken in proportion, as in the preceding case? I have no data, from which I could determine this point.
VASCULAR SYSTEM
WITH BLACK BLOOD.
The red blood circulates in a single system, the branches of which every where communicate. The black blood on the contrary is contained in two separate systems, which have nothing in common but the form, and which are, 1st, the general system; 2d, the abdominal. We shall now examine the first, and afterwards the second.
The general vascular system with black blood arises as we shall see, from the whole of the great capillary system, is collected towards the heart in great trunks, and terminates in the pulmonary capillaries. As the portion of the heart that belongs to it will be examined hereafter, and the pulmonary artery, by its peculiar membrane, has great analogy with the peculiar membrane of the other arteries, we shall now particularly examine the veins; but we shall describe in a general manner, the common membrane that is spread upon the whole system with black blood.
ARTICLE FIRST.
SITUATION, FORMS, DIVISION AND GENERAL ARRANGEMENT OF THE VASCULAR SYSTEM WITH BLACK BLOOD.
We shall now examine the veins as we have the arteries, in their origin, course and termination. Only we shall do it inversely, to accommodate our ideas to the course in which the blood flows in their channels.
I. Origin of the Veins.
This origin is in the general capillary system. I shall point out in this system, how the veins are continued with the arteries. I would only remark here that these vessels never arise from any organ that the arteries do not enter, as the tendons, the cartilages, the hair, &c.; which evidently proves that the blood is not formed in the general capillary system; it leaves there the principles that made it red, it perhaps acquires there new ones; it is modified in fact, but never created.
It is not as easy to distinguish accurately the veins at their exit from this system, as it is the last arteries at their entrance into it, because the valves prevent injections from penetrating so far. It is in subjects that have died of asphyxia, apoplexy, &c. that the venous ramifications can be best observed. We see then that they are soon divided into two orders; one accompanies the last arteries, the other is distinct from them.
In the greatest number of organs, venous branches go out at the same place that the arteries enter. There are however some exceptions to this rule. In the brain, for example, the arteries enter below, the veins go out above. In the liver, the first enter below, the others go off behind, &c. This circumstance is, in general, indifferent to the circulation, which goes on the same whatever may be the relation of the arteries with the veins. In those places where the small veins go out at the same time that the small arteries enter, sometimes more or less of cellular texture serves to unite the small vessels that are in apposition, sometimes there is a space between them, as in the muscles, the nerves, &c.
Besides the venous origins corresponding with the arterial terminations, there is an order of veins which is separated from the arteries at the exit from the capillary system. This order is particularly remarkable at the exterior of the body. We see that all the organs that are found there furnish, 1st, veins that go to the interior to accompany the arteries; 2d, others that go to the exterior to become sub-cutaneous, and to form trunks of which we shall soon speak. In many internal organs, the same venous division is observed.
It follows from this general arrangement, that many more veins go from the capillary system than there are arteries that enter it. This is the principle of the disproportion of the capacity existing between the system with red blood, and that with black, a disproportion of which we shall soon speak.
The veins at their origin frequently communicate among themselves. We see many little spaces that arise from their interlacing, in the places where they can be seen, as under the serous surfaces, &c.
II. Course of the Veins.
At their exit from the general capillary system, as we have just said, the veins are differently arranged. 1st. In the extremities and external organs of the trunk, they form two sets, the one interior, which accompanies the arteries; the other exterior, which is sub-cutaneous. 2d. In the internal organs we frequently make a similar observation; thus there are superficial veins of the kidney, and deep ones, that accompany the arteries; but oftentimes all the veins unite themselves to those that follow the artery.
The cutaneous portion of the veins is very remarkable in the extremities, where there are considerable branches, viz. the saphena in the lower, the cephalic, basilic, and their numerous divisions in the superior. In the trunk and the head, we do not see any great sub-cutaneous branches, except the external jugular in the neck; but there is a number of smaller branches proportioned to the minuter ones that are distributed there.
The external parts, then, are remarkable by the predominance of the trunks with black blood over those with red. Oftentimes these trunks can be traced through the integuments, upon which they show themselves much more than those that are whiter and more delicate; they have, besides, no connexion with the tinge that colours them, which arises from the blood contained in the general capillary system.
In the interior of the body, the veins almost every where accompany the arteries; they follow the same distribution; so that they are not commonly described, because the course of the arteries is sufficient to represent theirs. Usually a common cellular space receives both the trunks of the two sorts of vessels and those of the nerves. Sometimes, however, the veins are separate, as the azygos, for example, which has no corresponding arterial trunk, and which on this account requires in descriptive anatomy, like the superficial ones of the trunk and the extremities, a particular examination and an accurate dissection to obtain an idea of it.
The deep-seated veins have a caliber much more considerable than that of the arteries; most usually they are more numerous, as in the extremities, where each artery is almost always accompanied by two veins.
III. Proportion of the capacity of the two systems with Black and Red Blood.
After the observation I have just made upon the origin and course of the veins, it is evident that their sum total has a capacity much greater than that of the arteries. This assertion it is easy to prove in detail, wherever there is an artery and vein united, as in the kidneys, the spleen, the extremities, &c.; where the arteries are separate from the veins, as in the brain, the liver, &c. it is not less sensible. Finally, there is, as I have just said, a division of sub-cutaneous veins, which is evidently one more than the arteries have.
Many physiologists have endeavoured to calculate the relation of capacity between the two systems with black and red blood; but this relation varies too much ever to be the subject of any calculation. Is it upon the dead body that the attempt is made? But the veins will be more or less dilated according to the kind of death; in apoplexy, asphyxia, drowning, &c. they have a diameter almost double that which they exhibit when the subject has died of hemorrhage, because the first kind of death accumulates much blood in the veins, and the second deprives them of it. We can give a greater or less capacity to the veins of an animal, according to the manner in which we kill him, as we can enlarge or contract the right cavities of the heart by similar means. You can never find the veins exactly equal in any two subjects, though there may be a great resemblance as to size, age, &c. Is it upon a living animal that the attempt is made? But, besides its being very difficult, you will not then have a result uniformly applicable, because the veins vary in diameter as they are more or less full. Examine these vessels in subjects in whom you can see them by the transparency of the integuments; sometimes they are more, sometimes less apparent; their size sometimes appears double, at others, hardly distinguishable. Certainly after drinking copiously, by which the black blood has received a great augmentation of its fluid, the vessels are more dilated than in an opposite state. The veins are remarkably contracted after death from hunger. I have often observed the same phenomenon in dropsies, phthisis, marasmus, &c. Always when the mass of blood is diminished, the veins contract by their contractility of texture. The arteries are infinitely less subject to variations of diameter, on account of their firm and compact texture, though, however, they show much of it.
Let us reject, then, every kind of calculation upon the proportions of capacity of organized canals. We can only calculate what is fixed and invariable; but that which varies at every instant can only be the object of general assertion. Besides, of what importance are the rigorous proportions that some physicians have endeavoured to establish between our parts? They are nothing in the explanation of the phenomena of health and disease. Let us, then, be content with this general assertion, that the venous capacity surpasses the arterial. It may be said, that in a given time there is more blood in one than the other.
The same observation applies to the two sides of the heart, one of which belongs to the same system with the veins, and the other to the one with the arteries. The right has commonly a greater capacity than the left, not precisely under the relation of the fleshy texture, but under that of the fluid that distends it; this is so true, that if in an animal whose thorax is opened, the blood is made to accumulate in the left side by ligatures, and the right is emptied by puncturing it, the last will be less in size than the first. Always when we find it larger than the other in the dead body, except in diseases of the heart, it is because it contained more blood at the moment of death; in fact, as this fluid ordinarily stops first in the lungs, it flows back to this side of the heart, which is almost always the largest.
This is the great difference between inert cavities and those that possess life, viz. that these last can change their capacity every moment, whilst the others remain always the same. In the living animal, the right side of the heart has almost always a greater capacity than the left, because the quantity of blood it contains is greater.
There are, then, two things generally true, viz. 1st, that the great tree that terminates the system with red blood is in general of less capacity than the great tree that commences the system with black blood; 2d, that the same observation is applicable to the two sides of the heart, which correspond with these two trees.
As to the tree that terminates the system with black blood, compared with that which commences the system with red blood, the same thing does not hold true. The pulmonary artery and the veins of the same name exhibit a disproportion of capacity, less it is true, than in the other parts, a disproportion which is real, however, and which, notwithstanding what many authors have said, is in favour of the veins. How does this happen? it would seem that since the one is continuous with the veins and propels the same fluids, it ought to have the same proportion of diameter; and that since the others are continuous with the arteries, that they also should be in proportion to them. This arises from the difference of the velocity of the blood; in fact, this fluid circulates quicker in the pulmonary artery than in the veins of the same name, since it has the impulse of the heart, which these last want; then, in a given time, as great a quantity of blood passes through it, though the diameter of this artery is smaller; what do I say? if it was equal, the circulation could not go on. In the same way, if the aorta equalled in capacity the two venæ cavæ and the coronaries united, and the blood had the same velocity there, the circulation would cease.
The four pulmonary veins united are a little larger than the aorta, which, however, transmits all the blood received from them. Why? Because the impulse that the left ventricle communicates, makes, in a given time, more blood pass by the aorta than by the four pulmonary veins. These two things, 1st, the velocity of the fluid; 2d, the capacity of the cavities in which it circulates, are then in an inverse order in the two opposite trees that form each vascular system. In that with red blood, there is less velocity and greater capacity from the pulmonary capillary system to the agent of impulse; and from this agent to the general capillary system, there is, on the contrary, greater velocity and less capacity. In the vascular system with black blood, there is less velocity and greater capacity from the general capillary system to the agent of impulse; and from this agent to the pulmonary capillary system, there is more velocity and less capacity. Without this double opposite arrangement, it is evident that the circulation could not take place.
There is, however, a remark to be made upon this subject; it is, that the capacity of the four pulmonary veins united, is not so much larger than the aorta as that of the venæ cavæ and the coronary is than the pulmonary artery; and this is the reason of it; as the pulmonary veins run a very short course, the impulse, on the one hand, that the red blood has received from the pulmonary capillary system, is preserved there more; on the other hand, this fluid is there free from numerous causes of delay that the blood experiences in the venæ cavæ and coronaries; then the velocity is greater there, and the capacity should be therefore less. If the lungs were situated in the pelvis, the pulmonary veins would certainly have a greater capacity, because having a greater extent to go over, the velocity of the blood would be more retarded.
We can easily understand now the cause of many arrangements that have engaged the attention of anatomists; viz. 1st, why the sum of the arteries coming from the aorta has less capacity than that of the veins going to the right auricle; 2d, why the four pulmonary veins surpass also in diameter the artery of the same name; 3d, why these four veins are not exactly in proportion with the aorta, which is really a continuation of them; 4th, why the venæ cavæ and coronaries are so disproportioned to the pulmonary artery, which is, as it were, their continuation.
If there was no agent of impulse in the two systems with red and black blood, their capacity would be every where nearly the same, because the velocity of the fluid would be every where nearly the same. This is precisely what happens in the system with black abdominal blood, in which the hepatic portion of the vena porta is nearly as large as the intestinal one, because there is no heart between the two.
The velocity is less in the general veins and in the pulmonary, because they have not at their extremity an agent of impulse; we see there only a capillary system. The opposite reason explains the velocity of the course of the blood in the general arteries and in the pulmonary. We have seen in the preceding system, that the presence of an agent of impulse at the origin of the two great arteries, requires there a considerable resistance of this texture, whilst the absence of this agent requires but little resistance in the veins.
We see, then, clearly, why these three things, 1st, weakness of the parietes; 2d, slowness of the motion; 3d, great capacity, are the attributes of the veins with black and red blood; why these three opposite things, 1st, strength of the parietes; 2d, velocity in the motion; 3d, less capacity, characterize the arteries of both sanguiferous systems.
We see also from this why, though the red and black blood form in their whole course a continued column, though the common membrane over which they pass may be in the whole extent of each system nearly the same, the organs exterior to this membrane are, however, very different.
The inverse ratio of the velocity of the motion with the capacity of the vessels, appears to me so evident, that we might be able to judge nearly by the inspection of the vessel of the velocity of the blood that runs through it, if many causes did not, as I have said, make the vascular parietes vary at the moment of death. We know that all the causes that lessen in the veins the velocity of the blood, increase their capacity; it is thus that we make them prominent by ligatures; that pregnancy enlarges those of the inferior extremities, that long-continued standing produces the same effect, &c.
It is to the same reason that must be referred the explanation of the following phenomenon; viz. that the relation of the arteries and the veins is not every where the same; thus the renal, bronchial, thymic veins, &c. are in general smaller in proportion to their arteries, than the veins of the spermatic cord in proportion to the artery of the same name, than the hypogastric veins in proportion to the corresponding artery. The blood has less difficulty in circulating in the first than in the second, where it rises against its weight; hence why the veins of the inferior parts, especially at a certain age, surpass their arteries more in diameter, than those of the superior parts exceed theirs.
Ramifications, Small Branches, Branches, Angles of Union, &c.
The veins present in their course, as it respects branches, smaller branches and ramifications, an arrangement analogous to that of the arteries, except that it takes place inversely. The ramifications are nearest the origin; they soon unite into smaller branches, these into branches, and these last into trunks.
The ramifications and most of the small branches are found in the interior of the organs. The first make an integral part of these organs, and are between their fibres, &c.; the second lie in their great interstices; in the glands between the lobes, in the brain, between the circumvolutions, in the muscles between the fasciculi, &c.
In going out of the organs, the small venous branches run into the branches, which take, as we have seen, two positions, one sub-cutaneous, the other deep. The sub-cutaneous branches go in the extremities between the aponeurosis and the skin, in the trunk between this and the cellular layer that covers the muscles. The deep branches lie in the interstices that the organs have between each other, accompanying almost every where the arteries. The cerebral branches have a peculiar arrangement; they are placed in the interstices of the dura mater, and form with them what are called sinuses.
The venous branches differ from the arterial in this, that they are infinitely less tortuous; this is remarkable under the skin and in the interstices of the organs. This is a reason that would prevent locomotion, supposing that there was an agent of impulse at the origin of the veins, and that their parietes were not so loose. Hence a series of arterial tubes is really longer than a corresponding series of venous tubes; this facilitates the motion of the black blood, which has a less extent to go over, and which besides would find causes of delay in the curvatures, greater than the red blood, because this is driven by a strong agent of impulse, and the other is not.
The venous branches unite to form a certain number of trunks that are connected with those that are immediately discharged into the right auricle; these trunks are the internal jugulars, the iliacs, the azygos, the subclavians, &c. They are still less tortuous than the branches; they have, like the arterial trunks, deep positions, far from external agents, from which many organs defend them, as a hemorrhage from them would be followed with serious consequences.
The trunks, branches, smaller branches and ramifications do not always arise necessarily from each other, in the manner we have just pointed out. The branches are often united to the trunks, the ramifications to the branches, &c. &c.; as it is with regard to the arteries.
The angles of union vary; sometimes they are right angles, as in the lumbar, renal veins, &c.; sometimes they are obtuse, as in some of the intercostals; most commonly they are acute.
The arrangement of the smaller branches and the branches is as variable at least in the veins as in the arteries; they partake, in this respect, of the general character of irregularity that the organs of internal life exhibit. It is necessary only to attend to the general position and distribution of the branches, smaller branches, &c. Their union with the trunks and among themselves, is different in almost every subject.
Forms of the Veins.
The same observation may be made upon the forms of the veins as upon those of the arteries.
1st. A trunk, branch, &c. are cylindrical, when examined in a space where they receive no branch. In the dead body they appear flat, which arises from the collapse of the parietes, and this is owing to the absence of blood. But by distending them with air, water, &c. they take their primitive form. In the living body they appear round.
2d. Examined in a considerable extent, a venous branch appears conical, so that the base of the cone is towards the heart and the apex towards the general capillary system. This form arises from the smaller branches, that are successively united to this branch, and increase its capacity as it approaches the heart.
3d. Considered as a whole, the venous system represents three trunks; one corresponds with the vena cava superior, another with the vena cava inferior, and the third with the coronary vein; these three trunks have their apex at the auricle and their base at the general capillary system. Anatomists thus represent the whole of the veins, because the sum of their divisions, like the arteries, has a greater capacity than the trunks from which these divisions arise.
There is however an observation to be made upon this subject, and that is, that the relation between the trunks and their divisions is not as exact in the veins as in the arteries; thus the sum of certain divisions considerably surpasses their trunks, whilst this relation is infinitely less in other cases. But all this arises still from the extreme variation of the venous parietes, according to the quantity of blood they contain; thus in dead bodies, sometimes the branches are much dilated by this fluid, and the trunks remain the same; sometimes an opposite phenomenon is observed. 1st. This last takes place especially when the lungs are obstructed; then in fact the blood flows back to the right cavities of the heart, then into the great corresponding venous trunks; these are then almost equal in capacity to the divisions they furnish, sometimes they even surpass them. 2d. When in the living subject, a limb has been situated for a long time perpendicularly, when standing has been long continued, for example, then the branches are more dilated than the trunks. Now as these causes of dilatation vary ad infinitum, the dilatations themselves are very variable.
From these varieties in the dilatation of the venous branches and trunks separately, it is evident that the relation existing between them is extremely variable, that it is affected by the manner of the death, by the diseases that have preceded it, by the habits of the subject, &c. Let us disregard then, upon this point, as upon every other, all calculations, even if they have a solid basis, if they do not lead to a useful result.
Injections are also a deceptive means of estimating this relation; in fact, they dilate the trunks much more than the branches, and especially than the smaller branches. The internal jugular injected, for example, becomes of an enormous size when compared with the sinus that empties into it. The two venæ cavæ, the azygos, the subclavians, &c. dilate a little less than the jugular; but their size however is remarkable when they are injected, in comparison with that of their branches injected.
Anastomoses.
The veins communicate in general more frequently than the arteries. 1st. In the ramifications there is a real net work, the anastomoses are so numerous. 2d. In the smaller branches, they are not so frequent. 3d. In the branches, they are still less numerous; but still we find many of them, and it is this that particularly distinguishes these branches from the arterial, which are almost always separate from each other.
The communications between the branches of the veins unite immediately in an evident manner the cutaneous to the deep division; thus there is a communication between the cerebral sinuses and the temporal, occipital veins, &c.; between the external and internal jugular by one and even two considerable branches; between the basilic, cephalic, and their numerous divisions spread upon the fore arm, on the one hand; on the other, the brachial, the radial and cubital, by different branches that penetrate deep into the muscles; between the saphena and crural, tibial, peroneal, by analogous branches.
Though separated, the two great venous divisions can then evidently supply the functions of each other by mixing their blood. Hence why, 1st, by agitating the muscles of the fore arm, we increase the throw of blood in venesection, though the muscles do not furnish many branches to the open vein, which then receives the blood from veins, from which it is forced out by the muscles; 2d, why in external pressure that obstructs or even entirely stops the motion of the superficial venous blood, the circulation continues as usual; why, for example, if a ligature is left for a long time applied to the arm, the superficial veins at first swelled, gradually become empty, by pouring their blood into the deep ones; why, notwithstanding tight bandages in fractures and luxations, the venous blood returns as usual to the heart, though it passes in less quantity by the superficial veins. 3d. If a strong band is applied high up on the leg, and the saphena vein is injected below, it does not fill above the band, but the injection goes into the crural. In the same manner the internal jugular may be filled by the temporal, &c.
The anastomoses between the superficial and deep veins are more necessary in man than in any other animal, on account of his clothing, by which the neck, the ham, the arms, &c. are subjected to compressions that would be dangerous without these anastomoses. We can say that upon them alone is founded the possibility of a variety of modes in clothing. That they show in fact that these modes are less dangerous than some physicians have thought; that the danger of apoplexy from a tight cravat, of varices from tight garters, &c. is much less than they have said.
When a single trunk is compressed, the blood passes easily into the neighbouring ones; but if the compression is made upon all the trunks of a limb, a certain time is requisite for this fluid to dilate the anastomoses. It experiences, before this dilatation takes place completely, a kind of stoppage in the capillary system, a stoppage that explains the momentary redness of the fore-arm in women, when the arm is covered with too tight a sleeve, that of the hand or the foot when the bandages of the fore-arm or the leg are too tight.
The mode of the venous anastomoses is very analogous to that of the arteries. Sometimes the smaller branches anastomose with the trunks, sometimes the trunks communicate among themselves.
In the last mode, 1st, there is merely a branch of communication, and this is the most common case; we see this between the jugulars, between the deep and superficial veins of the thigh, the arm, &c. 2d. Two branches unite by their extremities and form an arch, the mesenterics afford an example of this. 3d. Sometimes instead of a trunk, there is an interlacing of the smaller branches that form a real venous plexus; such as that which surrounds the cord of the spermatic vessels.
In general, where there are the most obstacles to the blood, there the anastomoses are the most numerous. Hence why the veins that surround the spermatic cord communicate so frequently together, why the smaller branches of the hypogastric vein which are spread in the bottom of the pelvis, form there a plexus so extended, that it is a real net work in which the course of no one branch can be traced, so numerous are the communications. Notwithstanding this, these two portions of the venous system are the frequent seat of varices; they are even found more frequently dilated in the dead body on account of the difficulty the blood experiences there in rising against its own weight.
This leads us to a general reflection upon the venous system in relation to the anastomoses, and that is respecting the necessity there is for the communications being more numerous in this than in the arterial system. In fact, if we compare the course of the black blood with that of the red, we shall see that there are many more causes to modify that of the first.
The black blood evidently obeys its weight in certain cases. 1st. If we remain standing a short time the veins swell, especially after diseases in which the forces have been diminished; this swelling soon disappears if the leg is inclined; it increases if it remains perpendicular. 2d. There are many cases, in which the forces being very weak, the circulation cannot go on in perfection, except the legs are in a horizontal or inclined position. The influence of position upon many tumours and ulcers of the legs is undoubted. 3d. We know that the first effect of the attitude with the head reversed, is a giddiness produced by the difficulty the blood experiences in rising against its weight. 4th. The valves are particularly destined to counteract the effect of gravity.
Every violent motion communicated to the black blood, and independent of gravity, can also disturb the course of this fluid; it is thus that when we move violently in a circular direction, the venous cerebral blood receives, if we may so say, a centrifugal motion, which, turning it from its natural direction, and preventing it from going entirely to the heart, produces a stoppage of it, and hence the dizziness that is experienced.
It is not only gravity and every other external cause of motion, which influence at every moment the motion of the blood in the veins, but there are also external and internal pressures, and a variety of other mechanical causes.
On the contrary, that of the arteries is independent of most of the causes, of weight especially, and of the internal motion. Why? because the rapidity of the motion is so great which the heart gives to the red blood, that the influence of gravity and every other analogous cause is necessarily nothing. Let us take a comparison; the greater the force with which a projectile is thrown into the air, the less influence the weight has in making it deviate; in the case of the blood its influence is still less. If the blood was driven in empty vessels, gravity would have some effect in the arteries; but in the sudden shock impressed upon the whole fluid that fills them, a shock, the effect of which is felt at the extremities at the same time as at the origin, it is evident that its effect is nothing. For an opposite reason, we can understand why it is so powerful in the veins, in which there is no agent of impulse, in which the parietes and capillary system alone produce the motions, where the motion is consequently slow, &c.
From these considerations, it is easy to see the reason of the very different arrangement that the arteries and veins exhibit in their branches, as it respects anastomoses, which are as rare on one side as they are frequent on the other.
IV. Termination of the Veins.
The veins terminate by two principal trunks, the superior and inferior venæ cavæ. There is also another, viz. the coronary vein, which empties separately into the right auricle; but as this trunk only brings back the blood that went to the heart, we shall pay but little attention to it in our general remarks, and but little to those small venous branches that empty separately from it into the same auricle.
Some authors have thought, that the two venæ cavæ were continuous and formed but one vessel; but it is easy to see how different their direction is. It is particularly in the fœtus, that their separation can be well perceived, since one corresponds with the right auricle, and the other with the left. There is behind the right auricle a kind of continuity of the membrane between the one and the other; it is the membrane of the black blood that is common to them, and which passes from the inferior to the superior; but in this respect there is no more continuity between them, than between the right side of the heart and the pulmonary artery, between the left and the aorta, &c.
By considering the whole of the trunks and the branches as a cone, we can say that there are two great venous cones distinct from each other; one for all the parts which are above the diaphragm, the other for all those that are below it.
The superior vena cava does not answer, then, entirely to the union of the arteries that form the aorta of the same name, which is only destined to the neck, head, and superior extremities, whilst the other belongs moreover to the chest by the vena azygos. For a contrary reason, the descending aorta has a destination much more extended than the inferior vena cava.
The limit between the two cones of the ascending and descending venæ cavæ, is placed at the diaphragm. It is especially in this respect that we can say that this muscle divides the body into two parts. Has not this arrangement some influence upon the difference that is observed in certain diseases between the superior and inferior parts? Should not this cause be connected with those pointed out under the article upon the fœtus? As yet there is nothing certain with regard to this, but I think it not improbable.
Though forming each a distinct cone, the two venæ cavæ communicate, however, especially in the neighbourhood of their common limit, that is to say, in the neighbourhood of the diaphragm; the azygos is the great means of communication. We know, in fact, that its trunk opens into the right renal, into the vena cava itself, or into some of the lumbar veins, and that the semi-azygos that arises from it, goes also to the left renal or to the lumbar of the same side. This anastomosis is very important; physicians have not paid sufficient attention to it. It proves that when an obstacle is situated in the trunk of the inferior vena cava, a great part of the blood of this trunk can flow into the superior. Much has been said of the compression of this trunk by the enlargements of the liver, in the production of dropsies. But, 1st, it is ascertained by the numerous examinations of dead bodies in modern times, that the production of these diseases belongs to every kind of organic affection; that the lungs, the heart, the womb, the spleen, &c. can likewise occasion them in the latter periods of the alteration of their texture; and that, in this respect, they are but a symptom in the greatest number of cases, and a symptom wholly disconnected with any sort of compression. 2d. By supposing that the liver could exert upon the vena cava an analogous compression, in the place where this vein crosses its posterior part, it is evident that the anastomoses of which I have just spoken, would prevent the effect of this compression, at least in great measure.
By supposing that an obstacle was encountered in the vena cava superior, the same anastomoses would undoubtedly answer the same end; but as the azygos is inserted very near the auricle, as the course of the trunk of the vena cava superior is consequently very short, it is evident that it is especially to counteract the obstacles the inferior may experience, that these anastomoses have been established.
When the blood of this vein passes thus into the superior, it goes through certain branches in a direction opposite to that which is natural to them. For example, suppose that the anastomosis takes place in the renal, which most often happens; then the blood of the trunk of the vena cava enters by one extremity of this vein; that from the kidney comes by the opposite extremity, and both pass into the azygos. A similar motion evidently supposes the absence of valves in the renal, from the vena cava to the insertion of the azygos. Now the renal veins never in fact have these folds; the capsular, the adipose of the kidney, all the lumbar, are also destitute of them, as Haller has seen, and I have ascertained it to be uniformly so. This absence of valves at the places of the anastomoses of the azygos, is a remarkable phenomenon; it proves very well the use that I attribute to the communication of the two venæ cavæ by means of this.
ARTICLE SECOND.
ORGANIZATION OF THE VASCULAR SYSTEM WITH BLACK BLOOD.
I. Texture peculiar to this organization.
This organization is nearly the same for the whole system, in the common membrane that forms the great canal in which the black blood is contained; but it differs in the textures that are connected exteriorly with this membrane. In the heart the texture is fleshy; it is analogous to the texture of the divisions of the aorta, in the pulmonary artery; it has a peculiar character in the veins; it is this that will now particularly engage our attention.
Membrane peculiar to the veins.
In order to see this membrane, it is necessary to remove, 1st, the loose cellular texture that unites the veins to the neighbouring parts; 2d, the cellular layer of a peculiar nature that immediately covers them, and of which we have spoken in the article upon the cellular system. Then we distinguish in the great trunks, longitudinal fibres all parallel to each other, forming a very fine layer, often difficult to be seen at first view, but always having a real existence. When the veins are much dilated, these fibres being more separated, are less evident than in a state of contraction. These longitudinal fibres are seen more clearly in the trunk of the inferior vena cava than in that of the superior. In general it may be said, that they are also more marked in all the divisions of the first than in those of the second; dissection has convinced me of this. Undoubtedly this arises from the greater facility that the blood experiences in circulating in the second than in the first of these veins, in which it mounts against its own weight; this is moreover a proof that man was designed to go erect.
I have uniformly made another remark, it is, that in the superficial veins these fibres are much more evident than in the deep-seated ones; the internal saphena is a remarkable example of this. It suffices to open it in its course, to see very distinctly its fibres through the common membrane, especially if it is a little contracted. By cutting the crural vein to compare it with this, it is easy to perceive the difference, which arises without doubt from this circumstance, that the neighbouring parts assist the circulation in the deep veins, whilst there is less of this assistance given to the superficial ones.
The branches have fibres in proportion greater than the trunks; hence the proportional excess of the thickness of their parietes, their greater resistance to the blood, their less frequent dilatation, &c.
At the place where any branch arises from a trunk, we observe that the fibres change their direction and go upon the branch, a circumstance that distinguishes them from arterial branches, whose fibres are not a continuation of those of the trunk.
Venous fibres oftentimes approach each other, are united, and give a greater thickness to the vein; this is frequently observed at the origin of the saphena. I have also seen this arrangement in the hypogastric vein; Boyer has likewise noticed it.
In general, the venous fibre, except in these places, is remarkable for its delicacy, for the little thickness that it consequently gives to the membrane that it forms. The peculiar membrane of the arteries infinitely exceeds that of the veins in this respect; it is this delicacy that favours to a great degree venous extensibility. Observe that the structure of each kind of vessels is adapted to their peculiar circulation. If the blood circulated in the veins with parietes like those of the arteries, its motion would be continually disturbed. A thousand causes retard the venous blood; when its motion is languid, the capacity of the vessels is increased; now, the arterial textures not allowing of this dilatation, it is evident that the circulation would be interrupted. If then the agent of impulse, placed at the commencement of the arteries, requires a firm and unyielding texture, the slow motion of the blood in the veins, the frequent causes that retard its progress, demand a texture of an opposite character.
What is the nature of the venous fibre? Its appearance, its want of elasticity and brittleness, its great extensibility of texture, its softness, its colour, its direction, distinguish it completely from the arterial fibre. Is it muscular? it does not appear to be irritable, and it does not look like the muscular fibres. I believe that it is of a peculiar nature, essentially different from that of all the other textures, having its peculiar properties, life and organization; I do not think it capable of much motion. We have, however, but few data upon this point.
The venous fibre, though infinitely more extensible than the arterial, is also more resisting; it will support without breaking, very considerable weight. The experiments of Wintringam have proved this. In the superficial and inferior veins especially, this is very remarkable.
There is a great difference in individuals as it respects the venous fibres. In some they are very apparent; in others, they are hardly distinguishable upon the great trunks; but then they are always very evident in the branches, particularly in the superficial ones.
There are places in the venous apparatus where we cannot discover either external fibres, or external cellular texture; this is the case with the cerebral sinuses, which have the following arrangement. The jugular vein at its sinus, loses its peculiar texture, and keeps only the common membrane, which, entering the lateral sinus, lines it, and extends below into the inferior longitudinal sinus, and above into the superior; in a word, into all the sinuses of the dura mater. Hence every sinus supposes, 1st, a separation of the layers of the dura mater; 2d, the common membrane of the black blood lining this separation. It is not then upon the dura mater that the blood circulates; it is upon the same membrane that it flows elsewhere; it is easy to establish this fact in the superior longitudinal sinus. This sinus is triangular when considered in relation to the separation of the layers of the dura mater; but in opening it, we see clearly, that the common membrane, by passing over its angles, makes it round; this is very evident. It is easy, also, in many other sinuses, to separate in certain places this membrane from the dura mater; but in the greatest number the adhesion is close, like the union of the arachnoides with the internal surface of the dura mater. This common membrane of the black blood is spread over the folds of the superior longitudinal sinus; it forms a singular net-work, which I shall describe in the cavernous sinuses.
From this general outline, it is evident that the coats of the dura mater supply in the sinuses the place of the venous fibres and their external dense cellular texture; the common membrane is always the same; but the texture that is added to it externally is different. At the place where each cerebral vein opens into a sinus, the common membrane of that sinus connects itself with it in its passage and lines it to its extremities. I know of no author who has thus considered the cerebral sinuses, as having the common membrane of the black blood extended into all the separations of the dura mater. How little soever we examine the internal surface of a sinus, it is easy to see that this surface differs as much from the texture of the dura mater, as it resembles the internal surface of the veins.
The cerebral veins, of which the sinuses are the terminations, are analogous to the arteries of that part in the extreme tenuity of their parietes, a tenuity that appears to be owing to the absence of the cellular coat, and which is so great, that you might believe that there was only a common membrane.
There are no circular fibres in the veins.
Common Membrane of the Black Blood.
This membrane generally extended from the general capillary system to the pulmonary, is every where nearly of the same nature. It differs essentially from that of the red blood in a great number of respects.
1st. It admits of much greater distension; consequently it is less brittle. Tie a vein, and it will not break, unless the constriction be excessive; it is almost as pliable as the cellular coat. This pliability renders it much easier of dissection than the common membrane of the arteries. 2d. It appears to be much more delicate; we have a proof of this in the valves, which at first view are hardly visible from their extreme tenuity, when they are lying against the external surface of the vein. 3d. This common membrane is never ossified in old age, like that of the arteries; its organization seems to resist the deposition of phosphate of lime. When it does take place, it is an unnatural state; whereas the ossification of the common membrane of the red blood is almost a natural state in old age, as I have before observed. This difference between the two common membranes of the black and red blood, gives a distinctive character to the diseases of the heart. We never see ossification in the tricuspid valves, or in the semilunar valves of the pulmonary artery, whilst they are so frequent on the left side; this is the uniform result of observations made at the Charity; in the bodies of old people dissection has always shown me the same thing. So the pulmonary artery, though analogous to the aorta by its peculiar membrane, is never the seat of these ossifications, because the common membrane differs essentially from its own. This single phenomenon, so striking in both these membranes, would incontestibly prove their organic differences, while it establishes the necessity of considering them in a general manner, whether, in the black blood, they line the veins, the pulmonary artery, and the right side of the heart, or in the red blood, they are spread upon the arteries, the left side of the heart, and the pulmonary veins.
Of the Valves of the Veins.
The common membrane of the black blood has numerous folds that are called valves. These folds are wanting in the pulmonary artery, except at its origin, where we find the semilunar valves; in the heart, the tricuspid valves are in part formed by this membrane; but the venous valves are wholly made by it; it is with them that we are particularly concerned.
The form of these valves is parabolical; their convex edge is attached, and most remote from the heart; their straight edge is loose, and nearest that organ. There is between them and the vein a space analogous to that of the semilunar valves of the aorta and the pulmonary artery. They have not, like these valves, a granulation upon their loose edge. On a level with the attached edge, the venous texture is firmer; there is a kind of hardening, which makes a prominent line of the same curved form as that edge. This hardening supports the valves, like the one corresponding to it in the semilunar valves. It appears to be of the same nature as the venous texture, the direction of whose fibres are changed to form it. When the common membrane arrives at this prominent line, it is folded to form the valve; so that it seems to be made of two layers, which are separated with difficulty, from its extreme tenuity.
The venous valves exist in the inferior vena cava, as in the superior. In the first, the divisions of the hypogastric, of the crural, tibial, internal and external saphena veins, &c. are full of them. The second presents many of them in the external jugular, in the azygos, in the facial veins, in the veins of the arms, &c. Many veins have no valves, as we see in the trunk of the inferior vena cava, in the emulgents, in the cerebral sinuses, &c.
The size of the valves is always in proportion to that of the trunks in which they are found; very distinct in the azygos, less so in the saphena, and still less so in the plantar veins. If we compare them with the caliber of the trunk they occupy, we shall see that sometimes they can entirely obliterate its cavity, and that at others they are too narrow to produce this effect. All authors have noticed this arrangement; they have thought that it depended upon primitive organization; but I am convinced that it arises wholly from the state of dilatation or contraction of the veins. In the first state, the valves being drawn and not dilating in proportion, become smaller compared to the caliber of the veins, whose cavity they cannot entirely obliterate when they fall down. In the second state, as they do not contract in proportion to the vessel, they become more lax and are capable of closing it completely. All that has been written by authors upon the size of the valves, depends then wholly upon the state of the veins at the moment of death. This is so true that they appear large if the animal dies of hemorrhage, and small if he dies of asphyxia. I have twice proved this fact.
From what has just been said, it is evident that the reflux of black blood takes place much easier and extends much further when the vein is dilated; and that consequently the first pulsation, the effect of this reflux, does not extend as far as the second, nor this as far as the third and so on. It is this that happens in the cases that we have spoken of before. The reflux never extends to the capillary system, especially in parts at a distance from the heart, because there being many valves and each checking in a degree the blood, it soon stops by losing all the motion received from the heart.
The existence of valves is generally constant, but their situation and number are very variable. Sometimes they are very near each other, at others at a greater distance, in this respect there is a great variety. Generally in the small trunks they are nearer, and at a greater distance in the large ones.
They are rarely arranged three by three, most often in pairs, and sometimes they are insulated; this is the case especially in the small vessels, in those of the foot, of the hand, &c. We find in the works of Haller very minute descriptions of the general arrangement, form and position of the vascular folds of which we are treating.
These folds perform, as we shall see, an important part in the venous circulation; by them we are enabled in most operations, to dispense with tying the venous trunks, if they are not very considerable. In fact, without them, the blood poured by the collateral branches into the open vessel, would easily escape by a retrograde motion, and then we might fear the effusion of all that, which passes in the whole course of this vessel, whilst now none can escape except what flows between the opening and the first or second valve.
The valves constitute an essential difference between the veins and the arteries. Let me observe, that the want of them in these last vessels is a proof in addition to what has been already named, of the absence of vital contractility in their texture. In fact if they contracted like the heart to drive the blood, this fluid, tending as much to return towards the heart by the effect of this contraction, as to go to the extremities, there would be at intervals in the arterial tubes, valves to counteract this first motion; now we only see them at the origin of the aorta; why? because it is only necessary in the arteries to resist the effect of the contractility of texture, which, exerting itself without a jerk, by a mere contraction, can return but very little blood to the heart. A single obstacle at the beginning of the arterial system, is sufficient then to prevent the derangement of the circulation, which might be the effect of the reflux caused during the systole by the contractility of texture of the arteries, a reflux which only takes place in certain cases; for ordinarily the return of the arteries upon themselves, is produced as I have said, by their containing less blood, which has been driven through them during the diastole. In order that this reflux might take place, it would be necessary that the effect of the contractility of texture should in the systole exceed what the arteries have lost of blood in the diastole.
Action of re-agents upon the Venous Texture.
This texture exposed to drying, becomes yellowish, remains pliable and can be bent in any direction; so that the dried venous bands, might in this respect, be applied to uses, to which the arterial could not in the same state.
This texture becomes putrid also more easily than the arterial, but less so than the others, particularly the muscular. To ascertain this, I have exposed at the same time, venous trunks and portions of intestines of fine muscular layers, to the contact of a moist air.
It resists maceration less than the arterial texture, but more than the others; water in which it has been macerated by itself is much less fetid than that in which an equal portion of muscular texture has been placed.
The horny hardening of the venous fibres is very evident when they are plunged into boiling water or the concentrated acids. They contract then more than half, at the same time they become more evident; in this way they can be studied better; I have used it often; their contraction thickens the parietes of the vein. When they are hardened in this way, if they remain in boiling water or the acids, they become soft very soon in the second, more slowly in the first. Boiling acts upon them quicker than upon the arterial fibres; they can also be reduced by long ebullition to a pulpy state, to which we can never bring the arteries.
The caustic alkali seems to have a very remarkable action upon the veins. After remaining a short time in a solution of this alkali, they become diaphanous, diminish in size, do not entirely dissolve, it is true and become liquid, as in the acids, but evidently lose their elementary principles, give a remarkable precipitate, and always render the liquor less strong, by the new combinations which it forms.
II. Parts common to the organization of the Vascular System with Black Blood.
Blood Vessels.
The veins have in their texture little arteries and veins, which take very much the same course as in the arteries. They ramify at first in the cellular membrane, send small branches to the neighbouring parts, then penetrating the venous fibres, wind there in a thousand different directions and finally terminate about the common membrane, which when injected has appeared to me to receive more than in the arteries.
Cellular Texture.
The veins, like the arteries, have around them two kinds of cellular texture; one which is exterior and of the same kind as that which is found in the interstices of all the organs; it contains fat and serum, and serves only to connect the veins with the adjacent organs; the other dense and compact, forms for them a proper coat. No author has yet distinguished the cellular system of this particular texture from that which is generally spread over the organs, though it differs from it so essentially in its filamentary texture, in its dryness, its uniform want of fat and serum, its remarkable power of resistance, &c. When we raise it, by tearing it with the fingers from the veins, it appears as if it was formed of an infinite number of little filaments interwoven with each other.
After having formed this external covering to the veins, this cellular texture of a peculiar nature analogous to the sub-arterial, sub-mucous, &c. passes between the longitudinal venous fibres, separates them, forms for them a kind of sheath, and terminates in the common membrane, which appears to contain it in its texture, and which owes perhaps in part to this circumstance, the great extensibility that it possesses.
I would observe that the presence of the cellular texture in the venous parietes is a distinctive and striking character that distinguishes them from those of the arteries, with which their texture has in other respects no kind of analogy.
Exhalants and Absorbents.
It appears that there is no exhalation upon the internal surface of the veins. This surface is always moist in the dead body, though the vessels are empty; but I attribute this phenomenon, as in the arteries, to a transudation that has taken place after death. If there was in fact a fluid exhaled, it would prevent the adhesions of the venous parietes, when during life the blood ceases to flow through them. Now every vein that is empty is obliterated into a sort of ligament, like the arteries in similar cases.
There is no more absorption upon the internal surface of the veins, than exhalation. To satisfy myself of this fact, I have tried upon the external and internal jugular veins, the same experiment before noticed, as having been made upon the carotid artery; I obtained the same result and drew from it the same conclusion. I have been induced to make these experiments, from the opinion of many distinguished anatomists, who thought that the absorbents arose immediately from the veins and the arteries. It is possible that this is the case in the smaller branches, in the capillary system especially, as I shall say in the absorbent system; but I do not believe that any thing similar can be demonstrated in the trunks.
It appears then that the exhalants and absorbents of the venous parietes, like those of the arterial, are confined to the nutritive functions, and that they are consequently few. This remark is applicable not only to the veins, but to the whole of the vascular system with black blood.
Nerves.
1st. The veins differ essentially from the arteries by the few nerves of the ganglions that accompany them. Whilst these nerves form for most of the arteries a kind of covering, they are scarcely spread at all upon the veins. By laying bare the venæ cavæ, jugulars and azygos, it is easy to observe this. 2d. The side of the heart with black blood, receives as many nerves as that with red; this proves that they have no influence upon the contraction, as it is evidently weaker on the right side than the left; whereas if it was produced by the nerves it would be equal, as there is an equal distribution of them. 3d. The pulmonary artery has but very few nerves. I know not as yet the relation that exists between it and the pulmonary veins in this respect.
It appears from this general survey, that the system with red blood has many more nerves than that with black. In fact being nearly equal at the heart, and the difference being very sensible in this particular between the aortic arteries and the veins that go to the right auricle, although the pulmonary artery may have a few more than the corresponding veins, which I think very probable, yet the short course of these vessels would not prevent the disproportion from being very apparent.
ARTICLE THIRD.
PROPERTIES OF THE VASCULAR SYSTEM WITH BLACK BLOOD.
The veins are in general but little elastic, soft, and loose; they partake of the character of many of the animal textures, and are essentially distinguished in this respect from the arteries, which as we have seen are very elastic. We shall now treat of the vital properties and the properties of texture in these vessels.
I. Properties of Texture. Extensibility.
The veins have in regard to this property, an arrangement entirely opposite to that of the arteries, which are very extensible longitudinally, but very little so transversely.
The veins stretch but little in the first direction. When drawn out of a stump after amputation upon the dead body, they lengthen but little in proportion to what they dilate in varices, though here they experience an actual increase of size. Perhaps however this depends less upon the deficiency of extensibility of texture, than upon the circumstance that the folds are less evident than in the arteries, and of course the development is less. Whatever may be the cause, the fact is certain and uniform.
Few organs, on the other hand, exhibit a greater degree of extensibility transversely, than the veins. In the dead body, they can be enormously dilated, by injections of air, water, fatty substances, &c. In the living, we know the varicose dilatations, which arise in the great trunks, from the obstacles to the course of the blood in the lungs. While the arteries do not appear very often more than to double their diameter without breaking their common and peculiar membrane, the veins treble, quadruple, and even quintuple their diameter without this rupture's taking place.
We have however numerous examples of this accident. Haller has related many in his great work. We see these ruptures take place during pregnancy in the veins of the lower extremities; there are examples of them also in the external veins of the head in violent headaches. We have seen the venæ cavæ, the jugulars, the subclavians suddenly break and produce death. Every one knows of the hemorrhages that arise from the rupture of the hemorrhoidal veins, &c. I think that the extreme tenuity of the parietes of the cerebral veins exposes them to being frequently torn by blows upon the head, wounds upon that part, &c. When there is an effusion in the tunica arachnoides, it can certainly come from no other source than the venous trunks, which being surrounded by a fold of the arachnoides, pass through this cavity to go to the cerebral sinuses. Now we know that this case is very common, and that it even takes place at the same time with that, in which the dura mater being detached from the cranium, is found separated by an effusion. Is not apoplexy a sudden rupture of the venous extremities? I have already observed that we have no data upon this point. All these cases are very different from arterial aneurism; they often take place when the dilatation is infinitely less than in many instances where the veins remain whole. Very commonly this does not happen. The whole of the vein, with the cellular tunic containing it, bursts. The arterial rupture in true aneurisms, is on the contrary uniform; when the dilatation is carried to a certain point it always happens. The two arterial coats break easily, the cellular remains whole. I do not believe that there is a solitary instance of a great aneurism, without rupture. Why? because the arterial extensibility can only yield to a certain point. The ruptures take place then from a want of this property; they are disconnected with this cause in the veins. We do not know yet how they are produced. In a great number of cases certainly, there is an affection of the venous texture; this is undoubtedly the case in hemorrhoids, &c. Let us be content to point out the differences between arterial and venous ruptures, and wait till further observation shall discover to us all their causes.
If we bear in mind, that the arterial fibres are very numerous and all circular, that the venous, on the contrary, are on the one hand longitudinal where they exist, and on the other that they are very thinly scattered on their vessels, we shall then see why the first resist much longer a distension in the direction of their diameter than of their axis, and why the opposite phenomenon is observed in the second, though much less decided.
Contractility.
This corresponds with the extensibility. Slight in the longitudinal direction, much greater in the transverse. 1st. It produces the contraction upon themselves, of the parietes of the umbilical vein, of any trunk that is tied, &c. 2d. It produces in a trunk that is pricked, the sudden evacuation of the blood contained between the two ligatures by the return of the parietes upon themselves. 3d. It manifests a decided influence on the flow of blood in venesection. 4th. The numberless varieties of caliber that the veins exhibit after death, according to the quantity of blood they contain, are the result of their extensibility and contractility of texture. 5th. During life, the superficial veins appear very various; dilated in summer, contracted in winter, expanded in the warm bath, as we see the saphenas, especially in pediluvium, lessened in the cold bath, prominent by a long continued perpendicular position, flattened by a horizontal one, &c. they present to him who observes them, at different times, numerous varieties. I very much doubt whether those who have calculated so much the capacity of the vessels, the velocity of the blood, &c. would have undertaken their labours, if they had opened many bodies, or made many experiments upon living animals; now all the varieties depend upon the extensibility and contractility of texture.
II. Vital Properties.
Properties of Animal Life.
Have the veins sensibility? The following is the result of my experiments upon the subject. 1st. Irritated externally by any mechanical instrument, pain is not produced, as Haller has seen; 2d, a ligature put upon them gives no pain, whether it is done upon living animals, or in certain surgical operations, in great amputations, for example, in which it is recommended to tie the vein as well as the artery. 3d. Irritated internally, they exhibit the same phenomenon. I have many times pushed a stilet very far into one of these vessels, without making the animal cry out. I would observe also, that this is a good method of examining the sensibility of the heart, without producing in the chest a disturbance, that would increase, diminish, or alter this property in any manner, by the general derangement that it would occasion in the economy. I force then a long stilet into the right external jugular vein, opened as it is in the operation for bleeding. This stilet goes to the heart, without any accident, by straightening out the venous angles. The animal oftentimes gives no sign of pain; sometimes, however, he does; the motion of the pulse is always accelerated. We might easily reach in a man, without accident, with a stilet, the right side of the heart, by introducing it into the right external jugular vein. Why, in certain asphyxias, in syncopes which resist all other stimulants, &c. might we not employ this method to re-animate the action of the heart? 4th. When we inject a foreign fluid into the veins, however irritating it may be, the animals rarely show any sign of pain. Urine, bile, wine, the narcotics, &c. are transfused with impunity in this respect. 5th. On the contrary, when a bubble of air enters them, the animal cries out, is agitated, and struggles before dying; is this owing to the contact of the fluid upon the common membrane? I believe not; for usually there is an interval between the cries and the injection of the air. It is possible that the pain happens at the instant when the air strikes the brain, after having passed through the lungs, a passage which is constant, as I have observed elsewhere.
There is evidently no animal contractility in the veins. The same experiments that demonstrate its absence in the arteries, prove it also as it respects the veins. I have made them at the same time upon both kinds of vessels. I refer, then, upon this subject to the preceding system.
Properties of Organic Life. Sensible Contractility.
This property does not appear to be an attribute of the veins. Haller, by irritating them in different ways, perceived no sensible motion in them. I have usually made the same observation, whether I employed internal or external irritation.
It has appeared to me, however, in two or three cases, that a manifest contraction took place. As the venous fibres are only longitudinal, and as they are very few, it is evident that in admitting that they are muscular, it would be very difficult to observe the effect of irritants applied to them, though it might be real. The question is not, then, fully settled, though I incline much more to the belief that there is no venous irritability. As the venæ cavæ have evident fleshy fibres at their origin, it is evident that they possess at that place the contractility of which we are treating.
A proof of the great obscurity of the sensible organic contractility in the veins, is, that it is never increased in disease. All the organs, in which this property exists, are remarkable for its frequent increase, which constitutes in the heart the quickness and the force of the pulse, in the stomach vomiting, in the intestines diarrhœa, in the bladder incontinence of urine, especially in children, &c. Now the veins never exhibit a derangement, which, corresponding to these, would make us believe in the existence of a power of which this derangement is the excess, if I may so say.
Observe, that this observation is also applicable to the arteries; never in a determinate portion of the arterial system, do we see this local disturbance, this insulated derangement, which certain portions of the intestinal canal sometimes exhibit. The irregularity of the motion of the blood is always general, because it arises from a single cause, viz. the irregular impulse of the heart.
Observe, that this way of discovering the presence or absence of this or that vital force in a part, by the affections which increase that force there, deserves an important consideration in the examination of these forces. Authors have not employed this method of discovering them, of pronouncing consequently upon their presence or absence in the organs.
Of the Venous Pulse.
The pulsation that the veins have under certain circumstances, must not be taken for an effect of the venous irritability. It is an effect of the reflux of the blood, which not being able to go through the lungs, stagnates in the pulmonary arteries and in the right side of the heart; so that when this contracts, as the blood finds an obstacle in the ordinary course, it flows back whence it came, as when the aliments are unable to pass down, they take the other direction. This reflux takes place, to a certain distance, notwithstanding the valves; it is often very evident in the jugular vein, when animals, submitted to experiments, breathe laboriously; then it is discontinued; it takes place three or four times, then ceases, and returns irregularly; it is observed also in the last moments of life, when the lungs are embarrassed.
The vein is then sensibly dilated; then it contracts. But if you apply the finger above, you do not experience a sensation analogous to that of the pulse; you will perceive only a wave of blood which flows back. The reason of it is plain; 1st, there is no locomotion; 2d, as the venous parietes are loose, they could not strike the finger sufficiently strong, if there was a similar change of place. Observe, that it is less the blood than the artery itself which by its firm texture gives the sensation of the pulse; if it could straighten itself when empty, as it does when it is full, it would produce nearly the same sensation; this is a remark that should be added to what I have said upon the pulse in the preceding system.
The contraction of the veins in the motion of the reflux, of which we are treating, is only the contractility of texture. When the heart ceases to propel the blood in its cavity, it contracts, after having been dilated; it is nearly the same in the dead body, in which we fix a syringe in the veins; when they are very full of water, if we draw back the piston a little, immediately the fluid returning, the vein contracts; it is as when it contracts from a puncture that evacuates the blood; this does not imply any irritability.
I believe that sometimes this reflux may depend upon an irregular motion of the heart, which contracts in an opposite direction to the ordinary one, though there is no obstacle in the lungs. What induces me to think so, is, that frequently in experiments, at the moment the animal begins to suffer much, the reflux takes place before the lungs have had time to be disturbed. A very remarkable thing in experiments is the quickness with which pain disturbs the motion of the heart, accelerates it, renders it irregular, &c. We can always at will hasten respiration, by making the animal suffer; now the acceleration of the pulse is always prior to that of respiration, which appears to be determined by it. I am persuaded that if the diseases of the heart were as frequent on the right side as the left, they would often produce this reflux and this pulsation of the veins.
The limits of the reflux of the venous blood vary. Haller has observed it as far as the iliacs. In general, it rarely goes beyond the great trunks, on account of the valves. I have demonstrated in my Researches upon Death, that the colour of those who die of asphyxia, of those who are drowned, &c. does not depend on this, because it cannot evidently extend to the capillary system, which receives the black blood that colours it, from the arteries that then circulate that kind of blood.
The reflux of the black blood in the veins, produced in the preceding cases, either by an obstruction in the lungs, or by a sudden derangement in the action of the heart, takes place in a natural state, though in an infinitely less degree. In fact, when the right auricle contracts, all the blood does not pass into the corresponding ventricle; the veins being open, a portion flows back into them. It is difficult to determine the extent of this natural reflux, of which all authors have spoken. When the thorax is opened, we observe it distinctly; we might then ascertain its extent; but in this case, respiration not being performed as usual, it is evident that we cannot judge by it of what ordinarily takes place.
Insensible Contractility.
This property, which, like the preceding, is inseparable from the organic sensibility, exists in the veins as in the other parts; it presides only over nutrition; it appears more evident than in the arteries; at least the diseases which particularly increase it are more frequent in the veins. The texture of these vessels is often inflamed. 1st. Bell relates cases of it, the effect of external violence. 2d. Every one is acquainted with the inflammation of the hemorrhoids. 3d. The cicatrization of venous wounds after bleeding is a product of inflammation. Without doubt this cicatrization is promoted by the want of impulse, to which the arteries are subjected; but certainly these last would not in like circumstances heal so fast, if they did at all. When an artery has been tied, it is necessary that its parietes, inflamed by the action of the thread, most often cut by it, and brought into contact, should form adhesions, that the cure may be complete, and the ligature come off without danger. Now, nothing is more difficult and slower than their adhesion, from the difficulty with which the arterial texture inflames. Hence the frequency of hemorrhage after the operation for aneurism and other great operations. The blood often bursts out at the end of twenty, thirty, or forty days; the surgeon should always be upon his guard when he has tied these great trunks, from the want of disposition in the arterial texture to inflame. Frequently when the artery is obliterated, it is not by inflammation. Whilst the ligature stops the blood, the portion of artery comprised between it and the first collateral branch, closes gradually by the contractility of texture, and forms a kind of ligament, which arrests the blood after the thread has fallen off. I do not know but that these cases are more numerous than those of inflammation. Now the veins always adhere soon when they are tied; their wounds cicatrize immediately. In great wounds it is almost always useless to tie them at the first moment, on account of the valves, as I have said above, and afterwards, because the cut ends contract, and soon inflame and adhere. If there are venous hemorrhages, it is at the time of the injury, and not as long after as in the arteries.
Every thing proves, then, that the vital activity is much greater in the venous than in the arterial system, in respect to the tonic powers. The absence of the cellular texture in the second and its presence in the first, may have an influence upon this phenomenon.
Observations on the motion of the Black Blood in the Veins.
From what has just been said, it appears, that the blood is beyond the influence of the heart when it arrives in the veins. It is evident, then, that the veins can have no pulse. 1st. This phenomenon depends upon a single impulse, suddenly received by the contraction of the left ventricle; now, the blood is poured from all parts by the capillary system into the veins, this agent of impulse is wanting; the cause of the pulse does not exist in the veins. 2d. The necessary conditions for its production in the texture of the vessels in which it takes place, are elasticity and resistance, which are also wanting in the veins. They are only susceptible, then, either of a pulsation which occasions the reflux of the blood in the derangement of the lungs, or in the irregular motions of the heart, or of an undulation of which they are the seat, when arterial blood accidentally circulates in them; now, in either, the heart is the principle of motion, and it could not exist without it.
This is what takes place in the venous motion. The capillary system, by its insensible contractility, pours continually into the venous system a certain quantity of blood. This fluid, added to what is already there, communicates a general motion to it. Now, as the whole venous system is constantly full, it is necessary that while the fluid enters at one side it should go out at the other; if not, the venous parietes would dilate; but, as they have a resistance by which they can act to a certain point upon the blood, this fluid not being able to dilate the veins, flows towards the heart.
The impulse given by the insensible contraction of the capillary system, is too weak, however, to extend instantaneously from one extremity of the veins to the other, especially where the blood rises against its weight. As this fluid enters these vessels, the weight of that which is before it not being overcome, it would produce a general dilatation, and the blood would not reach the heart; but the valves counteract this, by supporting at short distances the column of blood. Weakness of the venous parietes and the existence of valves are necessarily connected. If the veins were as strong as the arteries, unable to dilate when the blood enters them, they would necessarily transmit the surplus to the heart, if they were destitute of valves; but on the other hand, their circulation would be every instant embarrassed.
It appears that it is not only the insensible contraction of the capillary system which propels the blood in the veins; but that the ramifications of these vessels have a kind of absorbent power, by which they draw blood into this system. Now the insensible motion produced by this power tends evidently from the ramifications towards the trunks, as in the lymphatics; then, when, on the one hand, the blood is propelled in the veins, and, on the other, as it were, attracted by them, it is evident that the primitive source of motion that it obeys, is in the capillary system.
This impulse communicated to the blood, exceeds but very little the resistance which this fluid experiences in its motion; so that the least resistance deranges this motion. Hence, as we have seen, the necessity of anastomoses. Hence also the necessity of other assistance to aid this motion, such as, 1st, the muscular action, the influence of which we cannot doubt, when we see the flow of blood in venesection accelerated by the motion of the muscles of the fore-arm, the palpitations of the heart, produced by the blood that flows there after a rapid circulation; when we observe that varices are as rare in the veins situated among the muscles, as they are common in the sub-cutaneous ones, &c.; 2d, the pulsation of those arteries which are in many places joined to the veins, and which communicate to them a kind of motion; 3d, the motion of certain parts, like that of the brain, which continually rising and falling, accelerates the circulation of the blood of the sinuses in an evident manner; so also the constant locomotion of the gastric viscera, propels it in the veins of the abdomen, and that of the pectoral viscera, in those of the thorax. It is so true that the veins derive assistance to their circulation from external motions, that if a limb is a long time immoveably fixed when fractured, these vessels often dilate. 4th. External frictions, if they are not so violent as to embarrass the venous circulation, evidently facilitate it; this is one of the advantages of dry frictions. 5th. A slight compress, not sufficient to check the venous blood, often promotes its circulation, when the external organs are weakened. We know, since the time of Theden and Desault, the advantage of tight bandages, for varicose ulcers, even for varices, &c.
Since the principle of the motion of the venous blood is generally spread throughout the whole general capillary system, instead of being concentrated, like that of the arteries, in a single organ, it is evident, that this motion cannot be uniform, that it must vary according to the state of the capillary system in the different parts; that it can be more rapid in some veins, and slower in others. This is in fact what we see, especially externally where the veins are more or less swelled, according as the blood circulates there more or less rapidly. In the arteries on the contrary, the motion is every where the same; it is a general and sudden shock, an impulse, which, every where felt at the same time, is necessarily every where uniform; so you never see some arteries more full, others more empty, as it happens in the veins.
There are numerous researches to be made on the motion of the blood in the veins. Notwithstanding all that authors have written upon this question, there is an obscurity in it in which we perceive but few rays of light. These difficulties arise from this, that we do not know precisely what is the kind and form of motion communicated to the blood in the capillary system, what is the influence of the vascular parietes upon this fluid, &c. &c. Our knowledge upon this point is reduced to certain views which I have just presented, and which are particularly relative to the parallel between the motion of the blood in the veins and the arteries. I believe that this parallel carried further at some future day, will throw much light upon the venous circulation; in fact, as the first motion is much more easily understood than the second, we must proceed from what is known to what is unknown, and place in opposition what we are acquainted with in one, with that which we seek to know in the other. This is the summary of this parallel, though imperfect; 1st, General pulsation in the arteries, absence of this general pulsation in the veins. 2d. Rapidity of the course of the blood in the arteries; slowness of the same course in the veins. 3d. Greater capacity and thinner parietes in the veins; less capacity and greater thickness in the parietes of the arteries. 4th. Necessity for accessory assistance for the venous circulation; the inutility of this assistance for the arterial circulation. 5th. The blood flowing per saltem, from the second, the uniform flow from the first. 6th. The susceptibility of the blood in the veins, to be influenced by its gravity and other accessory causes; there is some of this influence in the arterial motion. The following are the phenomena, which, from what we have just said, evidently depend upon the existence of an agent of impulse at the origin of the arteries, and of the absence of this agent at that of the veins.
1st. Constant uniformity of the motion in the arteries; variety of motion in every part of the venous system; 2d, dilatation and contraction generally the same in all the arteries of dead bodies; extreme variety in this respect in the veins of the different parts; these are the other phenomena which arise from the unity of impulse in the first, and from the varieties of the principle of the motion of the blood in the second, &c.
Some authors have insisted much, in explaining the causes of the difference of the arterial and venous motion, upon this, that in the arteries the blood is propelled in decreasing vessels, to the capillary system that resists; in the veins on the contrary it flows in vessels always increasing till it arrives at the right auricle, which offers no resistance. But the black abdominal blood is also carried without the agent of impulse, in a series of decreasing tubes to the capillary system of the liver, and yet the motion is analogous to that of the veins.
Sympathies of the Veins.
The sympathies of the veins are very obscure, like those of the arteries. As the textures of these two kinds of vessels are rarely affected, as inflammation and the different kinds of tumours do not frequently exist in them, and as they are hardly ever the seat of pain, we know but little of the influence they exert upon the other textures. However when we transfuse substances into the vessels, we have often seen acrid and irritating ones upon being introduced into the veins, produce sudden convulsions in different muscles.
As to the influence that the other organs when affected, exert upon the veins, we know also but very little. As they are every where disseminated, like the arteries and the nerves, it is difficult often to know if it is the vein itself or the organ that it forms, which is the seat of the sympathetic phenomenon.
ARTICLE FOURTH.
DEVELOPMENT OF THE VASCULAR SYSTEM WITH BLACK BLOOD.
I. State of this System in the Fœtus.
The veins have in the fœtus an arrangement inverse of that of the arteries; they are in proportion much less developed. It is not in the great trunks, as in the venæ cavæ, subclavians, iliacs, &c. that we should compare these vessels, because the reflux of the blood at the moment of death often dilates these trunks, so as to make us believe that they are much larger than they really are in a natural state. It is in the branches and the ramifications that we should make the comparison; now it is easy to see there, that the veins nearly equal the arteries, but are not superior to them, as is uniformly the case in the adult.
However, the side of the heart with black blood, and the pulmonary artery which make a part of the system with the veins, are proportionably larger than these. This arises not only from their receiving and transmitting the blood of these vessels, but also that of the umbilical vein. It is to this last circumstance that must be attributed also an anatomical fact always existing in the fœtus, viz. that the very short trunk of the vena cava, which is extended from the liver to the heart, is found in proportion much greater than the trunk of the superior vena cava, which is not the case in after life.
The less development of the venous system, compared with that of the arteries, appears to arise in the fœtus from this, that much substance being employed for nutrition which is very rapid in the early periods, less returns by the veins. This phenomenon however is not peculiar to the black blood. We shall see that the excretories transmit less fluids by the glands, and that the exhalants pour out less upon their respective surfaces. Much blood enters the general capillary system of the fœtus; hence why the arteries are very large. There remains in the organs, much of the substances that it contains, to nourish them; but little goes out of the general capillary system for secretions, and exhalations; little returns by the veins.
The more the fœtus advances in age, the more of this blood is carried in the veins. In the early periods, almost all remains in the organs to form them. Towards the period of birth, these things approximate to what they will be in the adult.
In this general phenomenon of the venous system in the fœtus, the proportions are always preserved between the veins of the different parts, according to the increase of them. It is thus that most of the superior parts, the brain in particular, being in the fœtus the seat of a more active nutrition than the inferior, the veins there are also more developed.
We can hardly distinguish fibres at this age in the venous parietes, though they no doubt exist. I have only remarked, that they then contain much fewer small vessels in proportion than the arteries, whose trunks are covered with them, as it is easy to see upon the aorta.
Though less dilated than afterwards, the veins appear to be as strongly organized; their parietes are very resisting; they dilate less easily; this continues during the whole of youth. It is to this that I attribute the absence of varices at that age. As on the one hand less blood circulates in the veins, and on the other they appear to be in proportion more resisting, it is evident that they must yield less.
II. State of this System during growth and afterwards.
A remarkable revolution takes place at birth, as we have seen, in the system of black blood. The right auricle and ventricle receive the whole of the blood, of which a part until then went immediately to the right side by the foramen ovale. This difference has not much influence upon the size of the right auricle and ventricle; differences only in their form take place, which I shall point out in the Descriptive Anatomy.
During the first years of life, the veins have a real inferiority as it respects the arteries. This inferiority continues during the whole time of growth; of this you may be satisfied by examining the external veins; they are never as evident, or as much developed in children as in an adult. Compare the arm of a man with that of a child, and the difference will be perceptible.
The proportion of the cerebral veins over the others, is gradually lost as we advance in age, because the brain does not continue to predominate so much in its nutrition.
At the period of puberty, and towards the end of growth in height, the veins partake of this general plethora, which seems to manifest itself, and which is, as we have seen, the source of many diseases.
When the growth in length and thickness is completed, the veins begin to have a larger diameter; they become more prominent externally; it appears that more blood constantly passes through them. Make the muscles of an adult man contract strongly, and you will see all the veins considerably swelled. The same experiment will not produce a proportional effect upon a young man; ligatures applied show the same difference.
III. State of this System in Old Age.
In the last years of life the veins become much developed compared to what they are in youth; we can say that in this respect, the two extreme ages exhibit an inverse arrangement. In considering the external appearance in the two ages, we may be convinced by the examination of the superficial veins, of the truth of this assertion.
Let us not think, however, that this greater development supposes an addition of substance in the venous parietes, as for example, the increased size of the bones depends upon the super-abundance of the phosphate of lime. It is a simple dilatation of these parietes, which are weakened, and become more slender, instead of increasing. This dilatation is owing to the loss of their elasticity and to the greater quantity of blood they carry. In fact the motion of decomposition evidently predominates in old age over that of composition. More substance is taken from the organs than is added to them, at this period. I know not but that the bones receive a greater quantity of the substance that nourishes them. In all the other organs, an opposite phenomenon is evident; hence their horny hardening, their withering, if I may use the term. Now, as the system with black blood is that in which is poured all the residue of the decomposition of the organs, it is not astonishing that it should be dilated in old age; so the system with red blood, which carries the materials of their composition, predominates in the first year of life.
The superabundance of black blood in old age however, is to a certain degree deceptive; it depends in part upon the slowness of the circulation in the veins, in which the blood, moved with difficulty on account of the weakness of the capillary system, tends to stagnate, and dilate them, as I have said before; so that though there would be less black blood returning from the organs, there would be more in the veins, than in the adult; the velocity of the circulation then would be much less. There takes place in the whole system, what exists in a varix, for example, in which the blood accumulates because its velocity is diminished. It is not necessary then to believe, that the superabundance of the black blood in old age, supposes a plethora like that of the red blood in infancy, in which, on the one hand, the arteries contain more fluid, and on the other they propel it with greater velocity. We know from this that the dilatation of the veins in old age is a further proof of the principles established above; viz. that the capacity of the veins is always in an inverse ratio to the velocity of the fluids that go through them. It admits of but an inaccurate comparison, though it may give an idea of what passes in the venous system; a river which is very broad above a bridge, flows slowly; but its bed being much contracted under the arches, its velocity is much increased; so that the equilibrium may be established. So in the veins, there is little velocity and much capacity in old age, and much velocity and but little capacity in infancy.
Anatomists know very well the difference of the arteries and the veins at the two extreme ages of life; they choose old subjects to study the veins; on the contrary, these subjects are wholly improper for arterial injections, which succeed so well, and sometimes too well, in infants, in whom every thing appears to become vascular, and in whom the examination of the veins would be very difficult, and even impossible.
The veins of the inferior parts are generally more dilated in old age than those of the superior; this arises from the habitual weight of the column of blood, which constantly acting, produces finally a real effect; for, as we have said, the venous circulation is much influenced by mechanical causes, owing to the want of power in the cause that circulates it; hence why varices are infinitely more frequent in the inferior than the superior parts, in which they are hardly ever found.
In women who have had many children, we see this dilatation of the veins of the inferior parts in a very evident manner; very often there are varices in them. Observe that this disease seems to be the companion of old age more particularly than that of every other age. On the contrary, we rarely see aneurisms in old people. The rupture of the veins has been almost constantly observed at this or the adult age. I hardly know an example of it in infancy.
The pulmonary artery does not dilate in old age in proportion to the veins; because, removed from the action of foreign bodies, and provided at its origin with an agent of impulse formed of a firm and resisting texture, it has not been in the habit of yielding like them.
IV. Accidental development of the Veins.
The veins are accidentally developed in two ways. 1st. In cancerous tumours, in fungi, &c. in which more red blood enters, they acquire a size in proportion to that of the arteries; now, as they are superficial, we see more easily their increase than that of the arteries; this increase, which has been taken for a characteristic of cancers and other analogous tumours, is only a consequence of the increase of nutrition. The motion of the blood is as rapid there as in the other veins; there is no obstruction to it. 2d. There are cases on the other hand, in which the veins dilate, because the blood cannot easily circulate in them, and because the velocity of its course is diminished. For example, the whole venous system of the abdominal parietes is often increased in ascites; it is not because there is more blood circulated; there is less than in the ordinary state; but it is because the venous parietes having in part lost their elasticity, like the neighbouring parts, the circulation becomes slower; now the slower it is, the more the blood accumulates and the more the venous parietes are dilated. It is then a kind of general varix in a division of the veins. There is not more blood brought by the arteries, as in the preceding case; the same thing in part happens in old age.
ARTICLE FIFTH.
REMARKS UPON THE PULMONARY ARTERY AND VEINS.
Though in the exposition of the two systems of black and red blood, I have considered the pulmonary artery as making a part with the veins, and the pulmonary veins as a continuation of the arteries, yet their nature is wholly different. There are in truth but two general membranes, forming the two great tubes in which are contained the two kinds of blood, which are every where of the same nature, from the capillary system to the pulmonary. The textures added to the exterior of these two common membranes are essentially different. Thus the texture of the pulmonary artery, though added to the membrane with black blood, is, in point of thickness nearly of the same nature as that of the aorta and its divisions. So the texture of the pulmonary veins, though united to the membrane with red blood, is the same as that of the other veins.
This uniformity in texture supposes an uniformity in the functions, and this is really the case. The mechanical laws of the circulation of black blood are the same in the pulmonary artery as those of the red blood in the aorta. So the laws of the general venous circulation are the same with those of the pulmonary veins; inspection proves this; and, moreover, it must be so, since the relation of the heart to the two kinds of vessels, the veins and the arteries, is the same.
Each system of blood, then, has its two modes of circulation. Sudden motion, generally communicated, and not the progressive undulation of the fluid; a pulsation by a real locomotion, a general straightening of all the divisions of the same trunk at each impulse of the heart; these are the general mechanical characters of the artery with red blood, as well as that with black. Absence of pulsation, slowness in the course of the blood, want of straightening, &c.; these are the general attributes of the veins of each kind of blood.
There are no doubt general modifications that arise from local causes. Thus, on account of the short course of the pulmonary veins, the weight has scarcely any influence upon the blood; they never become varicose; the motion of the fluid is more rapid in them, since they have less time to lose that which is communicated to the blood in the pulmonary capillary system, &c.; thus the artery of the same name, whose branches are less tortuous, does not seem to me to have pulsations as evident as those of the aorta, &c. But these general phenomena are always the same; they are but different modifications.
This is why the general arrangement is nearly the same in the veins and in the arteries, whether they circulate red blood or black. Thus, for example, each of the two arteries go off from a ventricle by a single orifice, necessary for the unity of the impulse of the blood, for the uniformity of its course in the divisions of its great vessels, and for the simultaneous pulsations in all the divisions. On the contrary, the veins pour into the heart the red and black blood by many separate orifices; this is of no consequence, since, as we have seen, the motion of this fluid in the veins is not uniform, but may be accelerated or retarded in a part, by the influences it receives; thus, it may pass with velocity through the opening of the vena cava superior, and slowly through that of the vena cava inferior, &c.
From the preceding considerations, it seems, that if we have no regard but to the mechanism of circulation, that it is almost of no consequence whether we consider with the ancients the small and great circulation by studying first the course of the blood in the artery and the pulmonary veins, then in the aorta and the general venous system; or of studying, as we have done, the course of the blood, first in the pulmonary veins and the aorta, then in the general veins and the pulmonary artery. But if we consider this great function in the important relations of nutrition, secretions, exhalations, for which they furnish the materials, of the general stimulus it carries to all parts, and which is indispensable to the support of life, of the introduction of foreign fluids in the body of the animal, and of the change of these fluids into its own substance; then I think it must be described as I have done it.
ARTICLE SIXTH.
ABDOMINAL VASCULAR SYSTEM WITH BLACK BLOOD.
Situation, Forms, General Arrangement, Anastomoses, &c.
There is in the abdomen a system of black blood wholly independent of the preceding, arranged precisely like it, with the difference, that its course is shorter, and that it has no agent of impulse. This system, usually known by the name of Vena Porta, is found in most animals.
It arises from that part of the general capillary system which belongs to the intestines, the stomach, the omentum, the spleen, the pancreas, &c. and generally to all the abdominal viscera connected with digestion. This origin is remarkable. The viscera in the abdomen, foreign to the phenomena of digestion, are also foreign to the origin of this system. The kidnies and their dependancies, as the glandulæ renales, the ureters, the bladder, the urethra, &c. the genital organs, the diaphragm, &c. the abdominal parietes themselves, &c. &c. pour their black blood into the preceding system. Why are the digestive viscera, in their whole extent, different from the others, in the destination of their black blood? To answer this question, we must know the uses of the system of which we are treating; now, of these we are ignorant.
Thus rising from the whole gastric apparatus, this system forms into two or three trunks, which soon unite into a single one, which occupies the superior and right part of the abdomen below the liver.
This common trunk soon divides again into many branches, which spread in the liver into an infinity of ramifications, and are spent upon the texture of that organ.
This system, then, presents the same general arrangement as the preceding; it is composed of two trees united by their lopped summits, that intermix with each other. Place an agent of impulse at these summits, the arrangement will be the same as in the two preceding. The blood is moved from one capillary system to another. Divided at first into small streams, it is formed into masses constantly increasing to a certain point, then it is divided again, and is carried in streams not larger than the first.
In the abdominal portion, the ramifications, the small branches, the branches and the trunks are arranged very nearly as in the general venous system. The ramifications are found in the organs, the small branches in their interstices, most of the branches are situated in the layers of the peritoneum, there accompanying the arteries, and the trunks wind along the subjacent cellular texture. As to the hepatic portion, contained wholly in the liver, it is divided there nearly like the preceding.
The anastomoses present the following arrangement in the system of which we are treating. 1st. Its hepatic portion appears to want them; all the branches, smaller branches, and ramifications, go separately. As the circulation is not subject in the liver to increase or diminution, the solid texture of this organ protecting the vessels, the blood has no occasion for the means by which it can deviate from one place to another. Thus the great divisions of the pulmonary artery and veins, which go immediately into the lungs where they are wholly distributed, do not communicate with each other. Thus the branches of all the arteries and of all the veins contained in the interior of a viscus, as in the kidney, the spleen, &c. are most commonly without communication. 2d. As to the abdominal tree, its anastomoses are very frequent in the smaller branches. We see all along the small intestines arches exactly like those of the mesenteric arteries; less frequent in the great intestines, they are, however, very evident in them, as upon the stomach; in the branches and the trunks they do not exist.
The anastomoses in the system of black abdominal blood are necessary there from the frequent delays that this fluid may experience. For observe, that the circulation is performed for the abdominal portion according to the same laws as in the other veins, and that consequently that the force that can circulate the blood there, can yield to the least effort. Now in the different motions of the small intestines, often too great a fold, the pressure of these organs filled with aliments upon the veins, when we are lying on the back or the side, and which pressure the veins support only by their resistance, and a thousand other causes, impede the course of the blood in one branch, and force it to flow by anastomoses into others. Observe also, that an obstacle which is of no consequence to the red blood, on account of the very strong impetus that is given to it, is very important to the two circulations of black blood, which receive but a feeble impulse.
The influence of gravity is evident in the blood of this system, as in that of the preceding. Thus you see the hemorrhoidal veins, more exposed than all the others to this influence by their position, become much more frequently varicose; and it is even rare to find dilatations in the superior mesenteric veins, splenic, gastro-epiploic, &c. &c. whilst there is no part in which they exist more often than in the hemorrhoidal. Thus we have seen the preceding system dilated rarely above, but very frequently below.
The system with black abdominal blood communicates but very little with the general system; if there are anastomoses, it is only in the last divisions; do these anastomoses exist? I believe we may consider these two systems as independent of each other.
Organization, Properties, &c.
Many authors, Haller in particular, considering that the system of which we are treating is destitute of an agent of impulse, have admitted in them a force of structure superior to that of the other veins; but after examining it attentively, I am convinced that it is precisely the same. The cellular covering, of a peculiar nature, which surrounds it, and which is analogous to that of the other vessels, is only a little more evident; this makes these veins at first appear thicker; but by raising this covering we see that the internal membrane is of the same nature, only perhaps a little less extensible. We do not discover the venous longitudinal fibres so well as in the preceding system; I doubt even if they exist in the trunks, in which we should be able to see them better.
The two portions of this system, the hepatic and abdominal, appear to be completely uniform in their structure. Only the first is every where accompanied by a kind of membrane, which appears to be cellular, but whose nature is not yet well known, and which is called the capsule of Glisson. This capsule, intimately connected with the substance of the liver, adheres more loosely to the veins; so that when they are empty, there is often a space between them and it; it is this that makes them fold up when we cut the liver in slices. I think that we are entirely ignorant of the object of this anatomical arrangement.
The analogy between the systems with black blood, the abdominal and general, supposes them the same in properties, sympathies, affections, &c. I have often irritated the mesenteric veins, upon which it is extremely easy to act, by drawing through a small wound of the abdomen a portion of the intestinal canal; the results have always been the same as in the preceding system. Only when we inject air, the animal does not struggle, does not appear to suffer, and the experiment is not fatal; this proves still more, that it is not by its contact upon the veins or the heart, that the air is injurious, but by its action on the brain.
The common membrane of the system of which we are treating, is distinguished from that of the preceding, in this, that it is wholly destitute of valves. This appears to be owing to two causes, 1st, to this, that the course of the blood being shorter, it has less need of being supported; and 2d, to this, that the middle part of this system, wanting an agent of impulse, there is no reflux as in the preceding system. In fact, at every contraction, the right auricle sends, as I have said, a portion of its blood into the veins, which resist by the valves. Here, on the contrary, the course of the fluid is always uniform from one capillary system to the other; there is no cause of retrograde motion.
Remarks upon the motion of the Black Abdominal Blood.
This uniformity in the course of the motion of this black blood, is not merely the result of the absence of the agent of impulse, but also of this, that the liver does not present as many obstacles to it, as the lungs do to the preceding black blood. Observe also that the liver occupies in regard to this system, the same place as the lungs in regard to the other; it is the termination of the circulation of which we are treating. Having no dilatation or contraction, deprived of the fluid which acts incessantly upon the lungs, and which, loaded with different foreign substances, can often alter the vital forces of these organs, so as to interrupt the passage of the blood, &c. The liver, having a solid and granulated substance, in which no extraordinary motion can take place, except those of the general locomotion of the organ, is evidently incapable of frequently interrupting the course of the black blood, which the abdominal system sends there. Add to this the want of the agent of impulse, and you will understand, 1st. why, when the abdomen is open, we never see a pulsation, a reflux in the veins of the abdominal system, as we observe in those of the other system; 2d. why we always find there nearly the same quantity of blood; 3d. why, consequently, we do not discover, either in the common trunk that corresponds to the heart, or in its branches, the numberless varieties of dilatation and contraction, which the right side of the heart, and all the great venous trunks so frequently exhibit, so that scarcely two subjects are alike in this respect, whilst here the arrangement is always nearly the same; 4th. why the liver is not subject to the innumerable varieties in size that the lungs are. This deserves a particular consideration. You will rarely find the lungs twice containing the same quantity of blood; the weight varies enormously in this respect. Now this arises from the greater or less obstacles the blood has met with in passing through these organs in the last moments of life. We can make them more or less heavy in an animal, by making him die of asphyxia or hemorrhage, consequently by filling with blood, or emptying the extremities of the pulmonary artery. Whatever on the contrary is the kind of death, the hepatic extremities of the abdominal system, contain always nearly the same quantity of blood; suppose, that more remains than usual in this system at the moment of death, it is generally distributed, because there is no agent of impulse, which, at the last moments, drives the greatest quantity to the liver, as happens to the lungs. We understand from this, why the liver exhibits a firm, resisting texture, not extensible like that of the lungs. Sometimes the blood enters it in greater or less quantity, it is even, more or less heavy according to the kind of death. But these varieties belong only to the hepatic veins, which enter into the vena cave inferior just below the heart; they arise from the greater or less reflux of blood that takes place there, as in all the great venous trunks; they consequently arise almost always from the lungs; so that when we see that they are loaded with blood, the right auricle consequently distended, we may also be sure that the liver contains more of this fluid than usual. But this phenomenon, of which I shall speak when treating of the liver, is wholly disconnected with the system which I am describing.
The mechanism of the circulation of the abdominal part of this system, is precisely the same as that of the veins. As to that of the hepatic part, it is unlike that of any other part of the economy. It has no analogy to that of the arteries, for in them the heart is almost every thing, and here there is nothing to correspond to that system; for certainly there is no kind of contraction in the common trunk of the two trees, as I have been frequently convinced. It is then the same motion, which is continued from the gastric viscera to the liver. There is still much obscurity to be removed concerning this motion, as well as the preceding. Every judicious mind perceives that there is a great void, in reading what has been written upon the motion of the general venous blood, and upon this.
We cannot deny but that external agents do much in this last circulation as in the first. The uniform elevation and depression of the diaphragm, the corresponding motion of the abdominal parietes, the alternate dilatation and contraction of the hollow viscera of the abdomen, the constant locomotion of the small intestines, &c. all these causes certainly have an influence upon the motion of the black abdominal blood; and I even think, that the absence of most of them contributes to retard this motion in the hemorrhoidal veins, and to occasion varices in them.
This influence is not however such as Boerhaave thought, that the circulation could not go on without it. In fact, when the abdomen of an animal is opened, the blood is transmitted the same to the liver, and spouts in the same manner from an open vessel; but we observe a sensible weakness in a short time, and this before the general circulation is enfeebled.
Remarks upon the Liver.
The use of the liver, in being the termination of the black abdominal blood, as the lungs are that of the black blood of all the rest of the body, gives it an importance unknown to all the other secretory organs. Some authors, in observing the enormous size of this viscus compared to the quantity of fluid secreted by it, have suspected that it had another use, besides the secretion of this fluid. This suspicion appears to me, to amount almost to certainty. Compare the hepatic excretories and reservoirs, with the same parts in the kidnies, the salivary glands, the pancreas even, and you will see that they hardly surpass them, and that they are inferior to those of the first. Then compare the size of the liver with that of the kidnies, of the salivary glands, &c. and you will see the difference. If on the other hand, we examine the bile, voided with the stools which it colours, if we open the intestines at the different periods of digestion, as I have done, to see the quantity of this fluid that is poured out; if we keep an animal without food in order to let it accumulate by itself in the intestines; if we tie the ductus choledochus to retain the bile, &c. it is impossible not to be convinced, that the quantity of this fluid is disproportioned to the size of the liver. This viscus is alone equal in size to all the other glands united; now, place on one side, the bile, and on the other, all the secreted fluids, the urine, the saliva, the pancreatic juice, the mucous juices; &c. you will see how enormous the difference is.
Since then the secretion of bile is not the only object of the liver, it must have some other use in the economy. What this is we are ignorant; it is however undoubtedly connected with the existence of the system with black blood of which it is the termination, and is especially relative to this system. The following considerations appear to prove that this use is among the most important.
1st. The liver exists in all classes of animals. In those even in which most of the other essential viscera are very imperfect, it is well developed. 2d. Most of the passions affect it particularly, many of them have an exclusive effect upon it, whilst a great number of the other glands hardly perceive them at all. 3d. In diseases, it takes as evident a part as the first viscera in the economy. In many nervous affections, in hypochondria, melancholy, &c. it has a great influence compared to other glands. We know how easily its functions are deranged. It has undoubtedly no connexion with some affections called bilious, and which are seated exclusively in the stomach, but it certainly has a part in most of them. Since there is no doubt that the jaundice depends wholly upon a serious affection of this viscus, we ought certainly to conclude that the yellow tinge of the face in many of these affections, arises from a cause existing in this viscus, and which is not sufficiently powerful to produce jaundice. Whether in order to produce this tinge, the bile circulates or not with the blood, is of no consequence; it is incontestible that it is occasioned by affections of the liver; now the numerous cases in which it takes place, prove how much this viscus is often affected; there is certainly no gland in the animal economy so frequently. 4th. Shall I speak of organic affections? compare in the examination of bodies, those of the liver, with those of all the other organs of the same class, and you will see that there is no one equal to it in this respect; the kidney approaches it, in the frequency of the alteration of its texture, but it is far from being equal to it. 5th. Who does not know the influence of the liver upon temperaments? Who does not know that its predominance gives to the external appearance, the functions, the passions, the character even, a peculiar shade which the ancients have noticed, and which modern observations have confirmed? Now see if the other glands have a similar influence in the economy. 6th. The liver is, with the heart and the brain, the organ that is first formed; it precedes all the other organs in its development; it is incomparably superior, in this respect, to all the glands.
From all these considerations, and from many others that I might add, we may conclude, I think, that the unknown part which the liver performs in the animal economy, besides the secretion of bile, is among the most important. The study of this part, is one of the points most worthy of arresting the attention of physiologists.
It has been said latterly, that the liver corresponded to the lungs in their functions of removing from the blood its hydrogen and carbon. I know not how this fact can be proved by experiment; but I am positive that the liver does not turn the black blood of the abdominal system into red. 1st. The blood of the right auricle is of the same colour as that of the vena cava inferior; now if the blood went red from the hepatic veins, it would certainly give a brighter tinge to that of the auricle. 2d. Having opened the abdomen and thorax of a dog, I tied with a curved needle the vena cava at its entrance into the heart and above the kidney, then by detaching the liver from behind, I cut the portion intercepted between the two ligatures, and where the hepatic veins opened; the blood came out as black as that of the rest of the system. 3d. Tear out the liver of a living animal, examine immediately its veins, you will see that they contain a blood analogous to that of the others. 4th. This viscus, cut in slices in a living animal, pours out behind an analogous fluid, except some small red streams furnished by the last small branches of the hepatic artery; this is wholly different in the same experiment made upon the lungs.
If the black abdominal blood receives any modifications of its nature in the liver, they certainly have no influence upon its colour, its consistence, or sensible qualities.
The general opinion is that the black abdominal blood serves for the secretion of bile, and that the hepatic artery is only destined to nourish the liver; this is what Haller has adopted; I have also admitted it; but I am far from considering it as clearly demonstrated as it has generally been thought to be; the following observations prove, that we ought to consider it as an hypothesis somewhat uncertain.
1st. It is said that the hepatic blood, blacker, more oily, impregnated with the vapours of the excrements, of a bitter taste even, approaches nearer the nature of bile than the arterial blood, and that it is consequently more proper to form it. I do not know whether this blood has been analyzed comparatively; but I have certainly not found any difference in its external attributes; I did think that in an experiment I observed fatty drops swimming in it; different experiments have convinced me that it was an error. I doubt whether it could ever be demonstrated that the alkaline particles of aliments and of excrements pass into the vena porta; this passage is a gratuitous supposition. 2d. It is said that the volume of the liver is considerable compared to the hepatic artery; this is true; but it is not with the size of this viscus that we should compare that of this artery, to know if it furnishes the materials of secretion, since we have seen that it is impossible that the whole substance of the liver should be destined to secrete bile; it is with the biliary ducts and their reservoir, that we should make the comparison; now this artery is exactly proportioned to these ducts; there is between them nearly the same relation as between the renal artery and the ureter; on the contrary, the biliary ducts are manifestly disproportioned to the vena porta. 3d. It is said that the slow motion in this vein, is favourable to the secretion of bile. But upon what positive data is this assertion founded? Why is slowness of motion more necessary for this secretion than for others? 4th. It is said that the hepatic artery having been tied, the secretion of bile continued. But when we know the relation of parts, the least reflection is sufficient to convince us, that a ligature of this kind cannot be made without producing a derangement that will prevent us from distinguishing any thing. I attempted it once, but could not finish it; I was almost persuaded of it before. 5th. It is said that the black blood is more proper to furnish the materials of the bile than the red. But what is the reason of it? is it because this blood contains more carbon and hydrogen? But it is then the black blood that furnishes the fat also; now all anatomists are agreed, that it is exhaled from the exhalant extremities of the arteries; the same is true of the marrow, the wax, and in general of all the oily fluids. 6th. A fine injection, made in the hepatic portion of the abdominal system with black blood, passes into the biliary vessels. But a similar passage takes place in an injection from the hepatic artery. 7th. It is said that the black abdominal blood in the spleen has qualities essential to the bile. But the secretion of this fluid can evidently take place without the spleen; many experiments prove this. 8th. It is said that at the instant the vena porta is tied, bile ceases to be secreted; it is undoubtedly less difficult to tie the trunk of this vein below the duodenum than the hepatic artery. How can we examine what is going on in the liver? Do we judge by the fluid flowing from the hepatic duct? But open the duodenum, and you will not very often see the bile running out at the opening of the ductus choledochus, undoubtedly because the air contracts and irritates this duct. This phenomenon, observed after a ligature is applied, is not then conclusive; moreover there does flow towards the time of digestion but too little bile by the ductus choledochus, to be able to estimate it. In fine, what inference can be drawn from an animal whose abdomen is open?
These different reflections prove, I think, that we have not sufficiently direct proofs, to decide whether the secretion of bile is from the abdominal black blood or the red. I do not attribute this function more to one than the other; I say that these things should be subjected to a new examination, and that this example is a proof that the opinions most generally received in physiology, those consecrated by the assent of all celebrated authors, often rest upon very uncertain foundations. We are yet far from the time when this science will be only a series of facts rigorously deduced from each other.
The hepatic artery has been said to resemble the bronchial, and the hepatic vena porta the pulmonary artery; this is true in the general arrangement; but what is the proof of it as it regards the functions? On the contrary, I have proved above that those of the two last vessels are not similar. Let us wait, before deciding, for further and positive researches; let us doubt till then; let us not attribute the secretion of bile to the hepatic artery, nor the vena porta, nor to them unitedly. Certainly it is by one of these three means; but which? what vessel furnishes the secretion of bile? what part does the black abdominal blood perform in the liver, if it is not from it that this fluid is secreted? what, in fine, is the function of the hepatic artery, if it is not connected with this secretion? These are questions to be resolved.
Physicians have also hazarded opinions upon the influence of the black abdominal blood in diseases. Undoubtedly the expression, vena portarum, porta malorum, contains a very true meaning; but certainly in the present state of our knowledge, it is, in a strict sense, only a play upon words. If we would express by it the frequency of affections of the liver, it is without doubt just; but if it is employed to express the influence of the vena porta in diseases, it is vague and does not rest upon any positive fact. The more we open dead bodies, the more we shall be convinced, I think, of the necessity of a precise and accurate language, freed from all these ingenious, hypothetical ideas, which do honour, it is true, to their author, but which retard science, by introducing into it a manner of seeing hypothetically, and contrary to the spirit of observation.
Remarks upon the course of the Bile.
Though this question may be to a certain degree foreign to my object, yet as the black abdominal blood has perhaps a real influence upon the secretion of the bile, as my experiments upon this point determine with precision the course of this fluid, I do not think it useless to relate them here. All that is known further upon the uses, mechanism, &c. of this secretion is to be found in works of physiology, to which I refer.
There has been much discussion to ascertain if there was cystic and hepatic bile, if one was of a different nature from the other, if their quantity increased or varied, &c. Contrary and even opposite opinions have been supported by numerous experiments made upon living animals, as Haller has observed. These experiments, though at first view contradictory, are not so, however, as I was convinced by repeating them at different periods of digestion and during the abstinence of the animal; it had not been done with precision. The following is what I have observed in dogs, which I have used in my experiments.
1st. During abstinence, the stomach and small intestines being empty, we find the bile in the ductus hepaticus and ductus choledochus yellowish and clear; the surface of the duodenum and jejunum tinged by bile which has the same appearance; the gall-bladder much distended by a greenish, bitter bile, much deeper coloured and more abundant if the abstinence has been long. 2d. During digestion in the stomach, which may be prolonged for a length of time, by giving to a dog large pieces of meat, which he swallows without masticating, things are nearly in the same state. 3d. At the beginning of the intestinal digestion, we find the bile of the hepatic duct always yellowish, that of the ductus choledochus deeper coloured, the gall-bladder less full and its bile already becoming clearer. 4th. At the end of digestion and immediately after, the bile of the hepatic duct, of the ductus choledochus, that in the gall-bladder, and that which is found upon the duodenum, are of precisely the same colour as the common hepatic bile, that is, of a clear yellow, and a little bitter. The gall-bladder is about half full; it is flaccid, not contracted.
These observations, repeated a great number of times, evidently prove that this, during abstinence and digestion, is the manner in which the flow of bile takes place; 1st, it appears that at all times the liver secretes a certain quantity, which is increased during digestion; 2d, that which is furnished during abstinence is divided between the intestine that is always coloured with it, and the gall-bladder which retains it, without pouring out any portion of it by the cystic duct, and in which, thus retained, it acquires an acrid character and a deep colour, necessary, no doubt, to digestion which is to follow. 3d. When the aliments, having been digested by the stomach, pass into the duodenum, then all the hepatic bile, which was before divided, flows into the intestine, and even in greater abundance. On the other hand, the gall-bladder pours also that which it contains upon the alimentary mass, which is then completely penetrated with it. 4th. After intestinal digestion, the hepatic bile diminishes, and a part begins to flow into the duodenum, and a part to flow back into the gall-bladder, in which, if then examined, it is found clear and in small quantity, because it has had neither time to be coloured or accumulate.
There is then this difference between the two biles, that the hepatic flows almost in a continued manner into the intestine, and that the cystic flows back, except during digestion, into the gall-bladder, and flows, during this function, towards the duodenum; or rather it is the same fluid, of which a part always preserves the same character that it had at its exit from the liver, and the other assumes a different one in the gall-bladder. The diversity of colour in the cystic bile, according as it has been retained long or not, has much analogy to the colour of the urine, which is found more or less deep coloured, as it has been for a longer or shorter time in the bladder.
As to the course of the bile in relation to the stomach, I believe that this viscus contains a certain quantity of it at all times. When empty, we find there a mixture of gastric juices and mucus more or less abundant, sometimes mixed with small bubbles of hydrogen, which burn when brought in contact with flame, and almost always tinged with a yellowish colour from the bile that has flowed up through the pylorus. Haller says that this reflux of bile into the stomach does not always happen; Morgagni says that it always does in men. I have never opened a dog, in whom it has not been seen when the stomach was empty, especially if it had been so for some time. Human dead bodies are not proper to decide this question, because the kind of disease alters almost inevitably the course, the nature, and even the colour of the bile. I shall say in another volume what conclusion we should draw from this, as it respects bilious vomitings.
In a state of fulness, it has sometimes appeared to me impossible to estimate the reflux of the bile; in other states, between the alimentary mass and the parietes of the stomach, I have seen yellowish, gastric fluids; but this mass itself never has this colour.
The bile that flows into the stomach has always appeared to me to be hepatic bile, from its light colour. I think that I have opened a sufficient number of living animals to convince me, that this bile is hardly ever found very green, and that it acquires this colour from the gall-bladder; and that it is this that is brought up by vomiting in some affections. The reflux of this bile appears to be an effect of the affection itself. This observation agrees with that made above, viz. that the hepatic bile alone flows into the duodenum in abstinence. It alone can then, as we may be convinced, flow into the stomach. During intestinal digestion, in which the cystic bile flows, it is evident, that the aliments going continually out of the pylorus, prevent it from passing there and entering the stomach; that which we find during fulness, was there then, or entered there before the peristaltic motion had begun to evacuate this organ.
When we open the gall-bladder in a dead body, we see that the bile there exhibits, according to its diseases, a variety of shades of colour, from that which is black as ink to a kind of transparent fluid. Ought we then to be astonished, if the vomitings in which the cystic bile is brought up, that has flowed into the stomach against the ordinary course of things, should contain matters of such various colours?
Development.
In the fœtus, the system of black abdominal blood is not insulated; it becomes a part of the two others, by means of the ductus venosus. There is then truly but one vascular system in the fœtus, whilst after birth, there are three separate ones, two with black blood and one with red.
In the fœtus, it is especially with the umbilical vein that the abdominal system with black blood is continued. The liver is a centre, in which both arrive from two different sides, and in which they unite, in a common trunk. The two columns of blood that they circulate, do not meet directly; their course forms a very remarkable angle.
When we examine attentively the orifice of the ductus venosus in the trunk, made by the union of these two veins, we see that it presents itself naturally to the blood of the umbilical vein; that that of the vena porta, on the contrary, cannot enter there. In fact, there is a little fold in the form of a valve, less evident, it is true, than many others, but yet existing. This fold is only a kind of projection, placed between the end of the vena porta and the ductus venosus, and which contracts the orifice of this, so that it is evidently narrower than the caliber of its own canal. The blood coming from the vena porta and passing at the side of this fold, presses it against the orifice, and thus forms an obstacle; that coming from the umbilical vein, falling, on the contrary, perpendicularly on this orifice, removes this fold, and enters the canal.
It hence follows that the ductus venosus is evidently destined to carry to the vena cava the residue of the blood of the umbilical vein; I say the residue; in fact, as this vein is very large and the ductus small in proportion to it, it is evident that the greatest part of the blood penetrates the liver, by the different ramifications that enter its substance.
The abdominal vascular system is less developed in the fœtus than afterwards; it consequently carries less blood to the liver; this is the same arrangement as in all the other veins. I would observe, that the small quantity, however, which the liver receives in this way, is more than compensated by that of the umbilical vein. This viscus is, then, habitually entered in the fœtus, by a greater quantity of fluid than at any of the other ages. Hence, 1st, why its nutrition is so developed and its size so great; 2d, why it is, in proportion to its size, heavier than in the after ages; 3d, why when we cut it in slices, there flows out a greater quantity of blood; 4th, why, when we dry slices of the liver of a fœtus, of the same thickness as others taken from the liver of an adult, and especially of an old person, they are reduced to a less size.
The disproportion of the size of the liver of the fœtus is more evident, the sooner it is examined after conception; this is the same as with the brain. As the fœtus advances towards birth, the liver approximates in its proportions to the other organs, that which it will have in the adult. From the observations of Portal, it is especially till the seventh month, that the liver is predominant. This circumstance appears to arise from this, that the umbilical vein transmits as much more blood in proportion to the fœtus, as it is less advanced in age.
At this age, the blood of the umbilical vein and that of the vena porta evidently mix, at least in a great measure, in the common trunk. Is their nature analogous? There is no experimental knowledge upon this point. But Baudelocque has many times observed that that of the umbilical vein is redder, and even approximates the nature of arterial blood. I have not accurately observed this fact in any animals except guinea pigs, in whom the want of transparency in the cord does not allow us to see a great difference in the blood of the arteries and of the umbilical vein; but this difference can be in fact more evident in man; now, in this case, the umbilical blood appears to lose this redness in the liver, for very certainly it is uniform beyond this viscus in the circulation of the fœtus, as I have often ascertained.
At the period of birth, the blood ceasing to come by the umbilical vein, the liver becomes only the termination of the black abdominal blood. Then a kind of revolution takes place in this viscus. The different tubes that carried to it umbilical blood do not close up, but they transmit exclusively that of the vena porta, which increases a little in size, because digestion, which begins in the gastric organs, calls to them more arterial blood, and consequently more is returned by the veins. This slight increase does not compensate for the absence of the umbilical blood; thus the liver diminishes proportionally in size in an evident manner.
As to the ductus venosus, it is obliterated by the effect of the contractility of texture. The blood coming in the vena porta, has not, as I have said, any tendency to pass through it, because this canal is not in its direction; it passes rather into the hepatic vessels, and the circulation of the liver is established then, as it will always continue to be.
This then is the difference that birth brings to the hepatic circulation; 1st, less blood and only one kind entering the liver; 2d, an interruption of all communication between the general and abdominal black blood; 3d, proportional diminution of the size of the liver. Hence there is an inverse phenomenon for this organ and for the lungs. The latter increases, the other diminishes in activity and size.
The great quantity of blood that enters the liver before birth, and the size of this organ, compared to the small quantity of bile that escapes from it, are an evident proof then that it is destined for other uses besides the secretion of this fluid. There cannot be a doubt upon this point; it is a proof moreover, that in the adult the disproportion of the organ to the fluid, though less sensible, supposes also in it another important function of which we are ignorant.
There ought to be a precise relation between the obliteration of the ductus venosus, of the foramen ovale and the ductus arteriosus, between the increased activity of the lungs and the diminished activity of the liver at birth, &c. We judge of this relation, without knowing it, because a veil is still spread over the circulation of the fœtus. I would only observe that the predominance of the liver before birth, does not suppose any in the system of black abdominal blood; it arises exclusively from the umbilical vein; thus the proportional volume of this organ is constantly diminishing afterwards, especially on the left side, where this vein is distributed, as Portal has observed. It is difficult to name the period, at which the equilibrium is generally established.
In youth, the abdominal system of black blood, like the general, is weak. It is towards the thirtieth or fortieth year, that it seems to be in its greatest activity; this is the age of gastric diseases, of hemorrhoids, and of melancholy, which is connected with the state of the liver.
In old age, the dilatation of the system of black abdominal blood is much less sensible than that of the preceding system; its vessels have nearly the same caliber as in the adult age; which supposes a less diminution in the velocity of the course of its blood, from the principles established above. It never becomes the seat of any kind of osseous incrustation, a phenomenon that evidently assimilates its common membrane to that of the veins, and distinguishes it in a peculiar manner from that of the arteries.
END OF VOL. I.