The two great vascular systems, with red and black blood arise and terminate, as we have said, in the capillaries, which form in the lungs, as in all the other parts the limits that separate them, and in which they are changed from one to the other. There are then evidently two capillary systems distinct from each other, and which are even opposite. One, generally spread throughout the body, is the seat of the change of red blood into black. The other, confined wholly to the lungs, exhibits an opposite phenomenon; it is in its divisions that the black blood becomes red.
As the capillaries, which serve for the origin and termination of the black abdominal blood, are intermixed on both sides with those of the general capillary system, since in the abdomen they are continued with the arteries and in the liver give origin to the veins, I shall omit them in these remarks, and attend only to the general and pulmonary capillary systems.
These two capillary systems, the first especially, deserve the more particular consideration, 1st, because the circulation is governed in it by laws wholly different from those of the other parts; 2d, because most of the important functions of life take place there, as secretions, nutrition, exhalations, &c.; 3d, because their small tubes are affected on many occasions by diseases, as they are the seat of inflammations, metastases, &c.; 4th, because animal heat is especially produced in these tubes, &c.
The lowest species of animals have in reality only a capillary circulation. Their fluids do not move in great masses, in canals which carry them to all parts of the body, and afterwards bring them back again. There is only an insensible oscillation of these fluids, in tubes of the greatest delicacy and number. This kind of circulation is one of the points of contact, or rather of transition from animals to vegetables, which, destitute of the circulation with a sensible motion, have evidently like the zoophytes, that of an insensible motion and of the capillary vessels.
I shall first examine the general capillary system, and afterwards the pulmonary.
ARTICLE FIRST.
OF THE GENERAL CAPILLARY SYSTEM.
This system exists in all the organs; all are in fact composed of an infinity of capillaries, which cross, unite, separate and unite again, by communicating in a thousand ways with each other. The vessels of any considerable size, those among the arteries, in which the blood circulates by the influence of the heart, and those among the veins, which correspond to the first, have really no connexion with the structure of the organs; they wind along their interstices; and are lodged in the cellular texture that separates their lobes; but the capillaries alone essentially make part of these organs, they are so combined with them; that they truly enter into the composition of their texture. It is in this view, that we may with truth consider the animal body as an assemblage of vessels.
From this first view, it is evident that the extent of the general capillary system is immense, that it embraces all the smallest divisions of our bodies, so that we can hardly conceive of any organic particles united without capillaries. It follows hence, that this system is not only an intermediate one between the arteries and the veins. It is from it, that all the exhalants, all the excretories, &c. go. It furnishes all the vessels that carry nutritive matter to our organs; we ought to describe it then as existing in parts where arteries do not penetrate, as well as in those where they do.
I. General Division of the Capillaries.
Since this system is not destined merely to unite the arteries to the veins, and change the black blood to red, it is evident that other fluids besides the blood, must circulate in them; this is in fact what observation proves. There are many parts in the animal economy, in which white fluids alone circulate. We know the hypothetical opinions of Boerhaave upon the white arteries, the decreasing vessels, &c. We shall find these opinions in all books; I shall only say here what accurate observation shows us. That there is in the general capillary system, parts in which the blood especially moves, others pervaded only by white, or greyish fluids, &c. is a thing of inspection, and has no need of proofs. But what is the proportion of these fluids in the different organs? it is this that must be examined; now there are parts where the blood predominates almost exclusively in the capillary system, others where it exists in part, and in which there is a portion of different fluids, others in fine in which these fluids alone are found.
Of the Organs in which the Capillaries contain only Blood.
It appears that in the muscular system, in the spleen, in certain parts of the mucous surfaces, as in the pituitary membrane, &c. the blood so predominates in the capillary tubes, that almost every other fluid is unknown in them; thus fine injections demonstrate few other vessels; the arteries and the veins are seen there in great abundance. The blood, or its colouring matter, is in them, as I shall say, in two different states; in one, it stagnates and serves then to colour the organ; in the other, it circulates and contributes to its nutrition, its excitement, &c.
Of the Organs in which the Capillaries contain Blood and Fluids differing from it.
These organs are the most numerous in the animal economy. The bones, the cellular texture, the serous membranes, a part of the fibrous system, the skin, the vascular parietes, the glands, &c. &c. exhibit this arrangement in a very remarkable manner.
To give an idea of the capillary system in this kind of organs, let us take one in which it is easy to examine it, the serous membranes, for example. When we lay them bare in a living animal, their transparency permits us to see in an evident manner that they contain but very little blood in their capillary system; there are many branches under them, but they appear to be only contiguous; raise, for example, in a small living guinea-pig the peritoneal coat of the stomach; the red arteries, which at first view appeared to be in this coat, remain untouched. These membranes, certainly owe their white or greyish colour to the small quantity of blood they receive from their small vessels, to which the next trunks give rise. After having thus exposed a serous membrane, in order to see the quantity of blood that is found in it in a natural state, irritate it with any stimulant; at the end of some time, it will be covered by an infinity of reddish streaks, which will be so numerous, that they will change its whiteness into the red colour of the mucous surfaces.
Force fine injections into a dead body, they will so fill the capillary system of the serous surfaces, of those of the peritoneum, for example, that those surfaces will be wholly black, and appear formed only by a net-work of vessels, whilst very few are apparent in the living body, because it is not the blood that fills them. When we cannot open animals to convince us of this, surgical operations, in which the intestines are laid bare, the peritoneum being untouched, wounds of the abdomen, the cesarian operation, &c. will prove incontestably that in the natural state, the blood fills ten and even twenty times less of the vessels, upon the serous surfaces, than injections show us in their texture.
Examine these surfaces in chronic and acute inflammations, of which they are the seat, in the first especially, they exhibit a vascular net-work, so full of blood, that their redness is often deeper than that of the muscles.
All the organs of which I have spoken above, exhibit the same phenomenon. Observe what takes place in the skin; fine injections show there infinitely more vessels than are filled with blood in a natural state; the face of a child well injected, is wholly black. Who does not know that oftentimes from the effect of passion, the blood fills with great rapidity, in the skin of the cheeks, numerous vessels, which in a calm state of mind are not apparent?
Examine the conjunctiva, taken as an example in inflammations; frequently in a short time it changes its white to a bright red, because the blood fills vessels, in which it did not before pass; you can easily distinguish these vessels with the naked eye; you can see that the blood accumulated in this membrane, is not effused, but that it is contained in real vessels.
I take for example the organs that have one of their surfaces free from adhesion, because the state of the capillary system is more easily distinguished in them; but the others present the same phenomenon; we shall see that the cellular texture, certain fibrous organs, &c. &c. examined comparatively, on the one hand in animals that we dissect alive, on the other in an inflammatory state or after fine injections, present a much less number of vessels in the first, than the second case.
It can then be established as an incontestable fact, that in many of the organs of the animal economy, the general capillary system is, in the ordinary state, entered in part by blood, in part by other different fluids, that appear to be white.
The proportions vary singularly; thus the capillary system of the serous membranes contains hardly any blood as I have said; that of the skin more; the mucous surfaces still more, &c. But whatever may be the relation, the difference is not less real in the capillary system.
Perhaps also there are always in this system empty vessels, destined to receive fluids under certain circumstances; thus the urethra, the excretory ducts in certain cases, the orifices of the lacteals in the intervals of digestion, contain nothing. It is difficult to conceive of the rapidity of the passage of the blood in the capillaries of the face, and in those of other parts of the skin, if these vessels contain a fluid, which is to be displaced by the blood. However, nothing but what is founded upon experiment can serve to decide this question.
Of the Organs in which the Capillaries do not contain Blood.
These organs are less numerous than the preceding. They are the tendons, the cartilages, the hair, certain ligaments, &c. Dissected in a living animal, not a single drop of blood escapes from these organs, and yet there is no doubt that capillaries exist in them; oftentimes very fine injections demonstrate them there. Inflammation, also, frequently fills these capillaries with blood. Into the hair, this fluid enters in the plica polonica, &c. The non-vascular appearance of these organs in the living body, is illusory; it is because their fluids are divided into very small streams, the circulation of them is more slow, and their colour different from the blood, that we cannot perceive them.
II. Difference of Organs in respect to the number of their Capillaries.
Though the capillaries exist every where, yet they are more or less numerous in the different organs; in making fine injections, it is easy to be convinced of this. What anatomist has not been struck by the prodigious number of vessels in this way developed, upon the skin, the serous surfaces, the cellular texture, &c. compared with those in the fibrous organs, in the muscles even, &c.?
I have sought for the cause of this difference, and it has not appeared difficult to find it, since where injections develop few capillaries, there is only nutrition going on, as the bones, the muscles, the cartilages, the fibrous bodies, &c. are a constant proof; on the contrary, in all those in which many fluids enter, there are, besides nutrition, other functions, such as exhalation and secretion. Hence why a serous surface, almost as white as a cartilage in the living body, becomes ten times darker than it by the same fine injection; why the skin, compared to the fibrous organs, exhibits the same phenomenon; why in proportion to the arteries that enter a muscle and a gland, the latter admits much more injection than the other.
These observations, which are uniform and invariable, prove that the capillary system is as much more developed in a part, as it has more functions to sustain. Observe in fine, that it is a kind of depot in which the fluids remain for a certain time, before serving for nutrition, exhalation and secretion. Where these three functions are united, it is necessary that there should be more fluids there, than where only one of them exists; hence more capillary vessels.
The capillary system is not then in the organs in proportion to their size; a portion of the pleura contains more vessels than a tendon that is ten times larger. It is the nutritive substance that fills the place that these vessels do not occupy.
We might, from what has just been said, divide the systems into two classes, from the development of their capillaries; place on one side the serous, the mucous, the glandular, the dermoid, the synovial, the cellular, &c.; on the other the osseous, the cartilaginous, the fibrous, the arterial, the venous, the fibro-cartilaginous, &c. The first class surpasses the second, considerably, in the number of its small vessels. Observe, also, that inflammation, different eruptions, all the affections, in which there is, as it is called, an afflux of humours to a part, are infinitely more frequent in the first than the second class, because all these affections are essentially seated in the capillary system, which is more developed in them.
Asphyxia, apoplexy, and all the affections that make the black blood stagnate in the general capillary system, prove the same thing; in fact, examine the livid head of one who has died of asphyxia, or of apoplexy, you will see that it is especially in the skin and the cellular texture that the blood is arrested; that the muscles, the aponeuroses, exhibit besides the blood ordinarily found in them, only a small quantity of superabundant fluid, in comparison with what there is in the first organs.
Remarks upon Injections.
From all that has been said, it is evident, that fine injections, which form a convenient method of knowing the capillary system of an organ, cannot show which vessels of this system admit red blood, and which circulate only white fluids. In fact, the injected matter passes equally into each, and we cannot distinguish that, which in the living body is very distinct.
In order to form a precise and accurate idea of the quantity of blood that enters each of the organic systems during life, it is indispensably necessary to dissect those systems during life. I shall frequently have occasion in this work, to make this truth felt, which appears to me to be of much importance in many respects. If a fine injection but partially succeeds, it almost always shows vessels that really exist, but which were not sanguineous during life. Even the coarse injections of our dissecting rooms frequently exhibit these phenomena, especially in the face, the neck, &c.; and much more so, if the matter injected is very delicate, and managed with much address. I cannot conceive why physiologists have always taken as an indication of the blood vessels, the state of injected organs; by opening any part of a living animal, they may clearly see how deceptive this method is.
Injections are of no advantage except in the great vessels, in which the blood circulates in a mass by the influence of the heart; in the capillaries, they do not reach the precise point that exists in nature.
I wish that in dissecting rooms, the pupils, after having dissected the arteries and veins, would finish their labours upon the vessels by the dissection of a living animal, for the purpose of seeing the quantity of blood that each system has in its capillaries; this knowledge is essential to the study of inflammations, fungous tumours, &c. Anatomical cabinets in which preparations are kept, are of no use in this respect; these preparations are more likely to deceive in proportion as the injections have succeeded well.
III. Of the proportions which exist in the Capillaries between the Blood and the Fluids that differ from it.
In the organs in which the blood, or the white fluids differing from it, alone enter, there can be no variety in the proportions; but the varieties are frequent in those where these fluids enter at the same time. In the serous, the dermoid, the mucous systems, &c. there are sometimes more, sometimes less small vessels filled with blood; the cheeks, of which I have spoken, are a remarkable example of this. The least emotion, the slightest agitation, or a motion a little too violent, accumulates, diminishes, and varies, in a thousand different ways, the quantity of blood in them. The whole exterior of the skin exhibits the same phenomenon, though less frequently. When this organ is irritated or excited at any point, it immediately reddens; it becomes white if it is compressed. Cold and heat uniformly produce analogous varieties, when the change from one to the other is sudden. All the mucous surfaces exhibit the same arrangement; see the glans in the erection of coition, or in the flaccidity that succeeds it; the difference in the quantity of the blood that this external membrane contains, is very evident. Lay bare a serous surface; at first white, soon there will be numerous red streaks. If we could see the capillaries of the glands, I presume that we should find the quantity of blood variable in these vessels, and that during the time that the secreted fluids are poured out in abundance, their system would be more copiously supplied than at any of the time when it furnishes the materials of the secretions. Why are not the kidnies and the liver subject to the same varieties in the quantity of their blood, as the surface of the skin? When, by a violent motion, sweat pours out in abundance, and the external surface of the body looks more red, does it not indicate that the blood is there in a greater proportion?
There are two things to be distinguished, however, upon this subject; it is only when the copious secretions arise from an increase of life, that a greater afflux of blood is supposed to take place in the glandular system. When this increased secretion proceeds from a want of vital energy, the blood is not in greater quantity in the gland. The same observation applies to exhalation; thus, in the above case, in the commencement of fever, &c. more blood enters the skin; but when the sweat arises from weakness, as in phthisis, &c. there is not this accumulation of blood in the capillary system. But this deserves a longer explanation.
Different proportions of Blood in the Capillaries, according as the Secretions and Exhalations are active or passive.
I call those exhalations and secretions active, which are preceded and accompanied by an evident development of vital forces; and those passive which exhibit an opposite phenomenon. If we examine the phenomena of the animal economy, it will be easy to see this distinction, which appears to me essential in diseases; now, in whatever organ you study it, you will always see every active exhalation or secretion preceded by a greater afflux of blood to the part; all passive exhalations and secretions present an opposite phenomenon. Let us begin with exhalations.
1st. Cutaneous exhalation is active from violent running, or a paroxysm of fever, as I have said, from the action of caloric upon the body, hard work, &c.; the skin is then more expanded and deeper coloured; more blood enters it, &c. This excitement of the skin makes it more fit to be influenced by external agents, and to influence in its turn all the other organs. It is the suppression of these transpirations which causes so many accidents in the animal economy. Observe, on the contrary, the complexion of the body in phthisical sweats, in those produced by internal suppurations, in those that are the effect of fear, in all those that are called colliquative, &c.; this complexion is more pale than in a natural state; it is not capable of being influenced, because its vital activity is then small, and its forces languish.
2d. In the exhalations of the serous surfaces, there are some that are essentially active; such is that of pus; for we shall see that the formation of this fluid upon these membranes is without any kind of erosion, that it flows evidently from the exhalants, instead of serum; very often even it flows at the same time. Nothing is more frequent, in fact, than the milky or purulent serum that is found in the peritoneum, the pleura, &c. whether the fluids are exactly mixed, or the pus floats in flakes in the serum. Now this active exhalation of serum or of pus, which appears to be here principally coagulated albumen, this exhalation, I say, is evidently preceded by a considerable accumulation of blood in the capillary system, an accumulation which constitutes inflammation, and without which exhalation cannot take place. Observe, on the contrary, serous exhalation, increased by the weakness that any organic disease gives to the serous membranes; to furnish this fluid, the blood is never accumulated in them in greater quantity. Open the membranous sacs, after the diseases of the heart, the womb, the lungs, the liver, the spleen, &c. you will find them full of water, but more diaphanous than usual, because they have received less blood.
3d. What I have said of the serous exhalations, must be said of the cellular; some of them are active, such as those of pus and the serum that sometimes accompanies it; others are passive, as the leucophlegmasia after organic diseases. The same observation is to be made as before; there is an accumulation of blood in the capillary system in the first kind, a diminution of this fluid in the second. Observe the fatty exhalation; a man in health who is very fat, has a rosy colour upon the integuments distended with fat, which indicates the abundance of blood in the capillary system. On the contrary, in certain cases of sudden corpulency after diseases, in that which is called false fat, and accompanies weakness, a general paleness corresponding with the fatty bloating, indicates the absence of the sanguineous fluid.
4th. Mucous exhalations present also an analogous phenomenon. I shall prove soon that the hemorrhages from the mucous surfaces are real exhalations; now some of them are active, a name which Pinel has given them in his Nosography; these are the nasal, pulmonary, gastric, uterine hemorrhages, &c. of young people and even of adults. All these hemorrhages are accompanied by a local increase of action, by greater heat, by a deeper colour of the mucous membrane, by the greater abundance of blood in the capillary system. Who does not know, that Galen predicted a hemorrhage from the redness which he saw upon the nose and the eye of the patient? On the other hand, observe the hemorrhages of the mucous surfaces, which take place after long diseases, hemoptysis, which terminates the diseases of the heart, hematemesis, the effect of organic derangement of the liver, hemorrhages from the intestinal canal, so frequent at the end of all the long organic diseases of the abdomen, &c. nasal hemorrhages in certain low fevers, those which take place in scurvy from the different mucous surfaces, the gums especially, &c. all these hemorrhages, which are truly passive are not accompanied by this preliminary sanguineous congestion in the capillaries, by this increased activity of vital action; it might be said that it is the blood, which transudes, as in the dead body, through the pores, that have not power to retain it. This distinction is so true, that without making a theory of it, physicians conform to it in their practice. We bleed to arrest an active hemoptysis, but would you bleed to stop that which comes on in the chronic diseases of the thorax? The same observation applies to all the hemorrhages; they require means wholly opposite, according as they are active or passive; a remark moreover that is applicable to all diseases that have increased exhalations or secretions, whatever may be their seat. It is not the phenomenon that we are to resist, but the cause that has produced it. We diminish the forces, when serum is accumulated in the thorax, from a pleurisy; we increase them, when it accumulates from a disease of the heart, the lungs, &c.
What I have just said of exhalations applies to secretions. The mucous glands pour out a greater quantity of fluids in two ways, sometimes from irritation, sometimes from the want of force. When this happens in the intestines, there results from it in the first case a diarrhoea from irritation, in the second a colliquative one. Now it appears that the blood enters the gland in greater abundance in the one than the other case. Its increase takes place undoubtedly in most acute catarrhs, in which there is active secretion of mucus; its diminution or at least its want of increase is not less sensible in many chronic catarrhs, in which we may consider the secretion as passive. We know that the abundance of urine, of bile, sometimes supposes an increased, sometimes a diminished action of the kidney and the liver. Is there not a superabundance of semen from excess of vitality, and an unnatural flow from weakness? All the secreted fluids have the same arrangement; now according to these two opposite causes of the superabundance of the secreted fluids, the capillary system of the glands is certainly penetrated with a different quantity of blood. Though the phenomenon be the same, the treatment in the diseases in which it is manifest, is as in the preceding cases, wholly opposite, according as the local increase or diminution of life concurs to produce it.
Consequences of the preceding Remarks.
From all that I have said, it is evident that in the organs whose capillary system contains in part blood, and in part different fluids, the proportion of the first to the others is infinitely variable; that a thousand causes in a state of health, as in that of disease, by bringing to the organ more or less blood, can fill more or less its capillary system.
The trunks and branches that go to an organ, are they more or less dilated, according as the capillary system of this organ is more or less filled with blood? For example, when the mucous glands pour out fluid in the greatest quantity, are the neighbouring branches more full? Some experiments that I shall mention hereafter do not seem to prove it.
IV. Of the Anastomoses of the General Capillary System.
All that has been said evidently supposes a free communication established between all the parts of the capillary system; this communication is in fact clearly demonstrated by observation. When we examine a serous injected surface, of which the capillary system is full, we see that this system is a real net-work with fine meshes, and in which no vessel runs a distance of more than two lines, without communicating with others. The passage then, is constantly open between the portion that receives blood, and that which admits fluids differing from it. The same arrangement exists in the dermoid system, in the origins of the mucous, &c. and in general in all those in which the capillary system contains blood and white fluids.
On the other hand, the organs in which we find only white fluids, evidently communicate with those that are near them, and in which there is blood; those in which blood alone flows, have the same arrangement.
The capillary system must then be considered as a general net-work, spread throughout the body, which communicates on one side in every organ, and on the other from one organ to another. In this respect there is from the head to the feet a general anastomosis, a free communication for the fluids. It is in this way that we can conceive of the permeability of the body, and not from the cellular texture, in which the serous and fatty fluids alone stagnate.
As the arteries enter the capillary system, and as the veins, the exhalants, the secretories, go from it, it is evident from this manner of considering the capillary system, that all these vessels ought to communicate with each other; that by pushing a fine fluid into the arteries, it should go out by the excretories, the exhalants, and return by the veins, after having gone through the capillary system; this is in fact what takes place. In this respect, a thousand ways are constantly open for the blood to escape from its vessels, which communicate thus everywhere without, and do not present any mechanical obstacle to the blood in their cavity, which life alone retains within the limits of its circulation. The oozings after death through the exhalants, the excretories and the veins, are so well known, so many anatomists have related examples of them, that I think it unnecessary to give them in detail here. We have seen, then, fine injections pour out upon the serous membranes, upon the pericardium, the pleura, the peritoneum, &c. transude upon the mucous surfaces, even upon the skin. We have seen them flow through the ureters, the pancreatic, biliary, salivary ducts, &c. Haller, in the article upon each organ, has not failed to relate examples of this sort, which prove the communication of the arteries with all the other vessels, by means of the capillary net-work. What anatomist has not sometimes made even coarse injections return by the veins? The communication of these vessels with the arteries, through the capillary system, is now an anatomical axiom. At one time, it arrested much attention. It has been asked, if there was any thing intermediate between the arteries and the veins; inspection proves that the capillary system alone is there.
Hence it is necessary to represent the capillary system as a kind of general reservoir, in which the arteries enter on one side, and from which go out on the other side, in all the organs, the nutritive exhalants, in some, certain particular exhalants, as those of the sweat, the lymph, the fat, &c. in others the secretory vessels, &c. It is a common reservoir, if I may so express myself, in which the red blood enters, and from which the black blood, the exhaled, the secreted fluids, &c. go out.
This idea is not hypothetical; the injections of which I have spoken are the most evident proof of it. Let it not be said that it is a transudation after death, analogous to that of the bile through the gall-bladder: if it were so, not only the fine fluids injected would go out by the excretories and the exhalants, and return by the veins; but in oozing through the pores, they would fill the whole cellular texture. On the contrary, nothing escapes into the cellular texture, around the vessels by which the injection passes; there is then a continuity of tubes from the artery which has received the fluid, to the excretory, the exhalant, or the vein which transmits it.
These are the communications of the capillary system that explain how the skin becomes livid on the place on which a dead body has for a long time lain, as on the back, for example; how by turning a dead body, so that the head may hang down, it becomes full of fluid; how, on the contrary, by placing upright the body of one dead from apoplexy, asphyxia, &c. the capillary system of the face is freed in a great measure from the blood it contained; how an erysipelas disappears on a dead body, when the blood, arrested during life on a part of the skin, by the vital action, is spread after death to all the surrounding parts; how every kind of analogous redness of the skin, and even of the serous surfaces, disappears because the blood goes by the communications of the capillary system to the neighbouring organs. During life the tonic action retains the fluid in a determinate part; abandoned to its gravity, and other physical causes, after death, it soon disappears from the part in which it was accumulated, on account of the innumerable communications of the general capillary system.
I would observe to those who examine dead bodies, that these considerations are very important. Thus we must not judge of the quantity of blood which penetrated the inflamed peritoneum or pleura, by what is seen twenty-four hours after death; local irritation was a permanent cause that fixed the blood in the part; this cause having ceased, it escapes from it. A serous membrane may have been very much inflamed during life, and yet exhibit almost its natural appearance after death; as it is in erysipelas. I should have been often tempted from opening dead bodies, to deny the existence of an affection which had been real. The same remark applies to the inflamed cellular texture, the mucous surfaces, &c. Examine a subject that has died of angina, which during life gave the deepest red colour to the pillars of the velum pendulum pelati, to the velum itself and the whole pharynx; after death, the parts assume nearly their natural colour.
I would observe that in this respect it is necessary to distinguish acute from chronic affections. In the chronic inflammations, for example, of the pleura, of the peritoneum, &c. the redness continues after death, because the blood is combined, as it were, with the organ; it makes a part of it, as it makes a part of the muscles in a natural state. So the chronic affections of the skin, of the mucous surfaces, retain after death nearly the same blood, that they had during life; whereas in acute affections, the blood retained for a time by irritation, escapes when life has ceased, upon which this irritation depended. These principles can be applied to many diseases; I repeat it, they are of great importance in examining bodies. The neglect of them has often led me into an error, upon the degree and even the existence of acute inflammations, of which the organs that I examined had been the seat.
V. How, notwithstanding the general communication of the Capillary System, the Blood and the Fluids differing from it, remain separate.
Since in the dead body, and consequently during life, there is in the capillary system no organic obstacle to the communication of the fluids through its small branches; since the general net-work that these vessels form is everywhere free, how does it happen that the blood does not pass into the part destined to the white fluids? how is it that these do not enter where the blood is to circulate? Why does not this fluid go out by the exhalants and the excretories, since these tubes communicate with the arteries by the anastomoses of the capillary system? This depends wholly upon the relation which exists between the organic sensibility of each part of the capillary system, and the fluid that it contains. That which carries the blood, finds in all the other fluids irritants that make it contract at their approach; and reciprocally, where the other fluids belong, the blood would be a foreign fluid. Why does the trachea admit air, and reject every other fluid? Why do the lacteals choose only chyle from the contents of the intestines? Why does the skin absorb certain substances, and repel others, &c.? It all depends upon this, that each part, each portion of an organ, every organic particle, has its own sensibility, which is in relation only with one substance, and repels others.
But as this kind of sensibility is remarkably subject to vary, its relation to substances foreign to the organ changes also; thus the part of the capillary system which rejected blood, admits it at the moment when its sensibility has been increased. Irritate a part of the skin, it reddens in an instant; the blood flows there; while the irritation continues, it remains; when it ceases, it disappears. Whatever be the external means which raise the cutaneous or mucous sensibility, we observe the same phenomenon. We can in this way bring more or less blood into some parts of the capillary system. Bring the hand to the fire, the heat exalts the sensibility of its system, more blood enters it; take it away, this property resumes its natural type, and the blood is brought back to its ordinary quantity. The internal organs which are subjected less to the causes of excitement, have less varieties in their capillary system; yet, however, there are many, and all arise from the same principle.
A series of organized tubes are unlike an assemblage of inert ones. These last require mechanical obstacles to prevent the communication of fluids with each other; where there is a communication between the tubes, there is a communication in the fluids. On the contrary, in the living economy, it is the peculiar vitality with which each tube is animated, which serves for an obstacle and a limit to the different fluids; this vitality performs the part of different machines that we place in the communicating tubes, to separate them from each other. Every organized vessel is then truly active; it admits or rejects fluids which enter there, according as it is able or not to support their presence. Disproportion of capacity has nothing to do with this phenomenon; a vessel may have mere than four times the capacity of the particles of a fluid, and yet refuse to admit them, if this fluid is repugnant to its sensibility. It is in this point of view that the theory of Boerhaave has a great defect.
At the period in which this physician wrote, the vital forces had not been analyzed. It was necessary to employ physical forces to explain vital phenomena; hence it is not astonishing that all his theories are so incoherent. In fact, theories in the vital phenomena borrowed from physical forces, exhibit the same inadequacy, as those would in the physical phenomena borrowed from vital laws. What would you say, if in explaining the motion of the planets, rivers, &c. they should talk of irritability and sensibility? you would think it absurd; it is equally absurd, in explaining the animal functions, to talk of gravity, impulse, inequality of the capacity of the tubes, &c.
Observe, that the physical sciences made no progress until they analyzed the simple laws that preside over their innumerable phenomena. Observe also, that medical and physiological science was not accurately explained, until the vital laws were analyzed, and it was shown that they were everywhere the principles of the phenomena. See with what ease all those of the secretions, exhalations, absorptions, inflammation, capillary circulation, &c. are referred to the same principles, flow from the same data, by deriving them all from their real cause, the different modifications of the sensibility of the organs which execute them. On the contrary, see how each presented a new difficulty, when the mechanical causes were employed to explain them.
From what has been said, it is then evident, that in the innumerable variations of which the fluids of the capillary system are susceptible, in the different portions of the system which they fill, there is always antecedent variations in the sensibility of the vascular parietes; these varieties produce the first.
It is especially in the capillary system and its circulation, that the variations of the organic sensibility of the vessels produce varieties in the course of the fluids; for as I have observed, in the great arterial and venous trunks, in the heart, &c. the fluids are in too large masses, and they are agitated by too strong a motion, to be thus immediately subjected to the influence of the vascular parietes. Thus when nature wishes to prevent the fluids from communicating in the trunks, it places among them valves, or other analogous obstacles, which become useless in the capillary system.
Though the anatomical arrangement be the same in the living and the dead body, there is then a very great difference in the course through the capillary system, in one and the other. Push, into the aorta of an animal in whom you destroy life by opening this artery to fix in it a syringe, different fine fluids; you will never see them fill the capillary system, pour out by the exhalants, the excretories, &c. as when the subject has been some hours deprived of life. The organic sensibility inherent in the parts repels the injection; it can only circulate in the great trunks, in which there is a large space. I have injected, with other views, a great number of times, fluids by the arteries and the veins; now, the capillary system is never filled with these fluids; they circulate only in the great vessels, when the animal can bear them. Mr. Buniva has also made comparative experiments with injections upon living animals and those deprived of life; he has experienced in the first a resistance which he has not found in the other; now this resistance is in the capillary system, whose vessels refuse to admit a fluid to which their organic sensibility is not accommodated.
VI. Consequences of the preceding principles, in relation to Inflammation.
From what has been said thus far, it is easy, I think, to understand what takes place in the inflammatory phenomena, considered in general.
If a part be irritated in any manner, immediately its organic sensibility is altered, and increased. Without previous connexion with the blood, the capillary system is then placed in relation with it; it as it were calls it there; it flows there and remains accumulated until the organic sensibility returns to its natural type.
The entrance of the blood into the capillary system is then a secondary effect of inflammation. The principal phenomenon, that which is the cause of all the others, is the local irritation which has changed the organic sensibility; now this local irritation may be produced in different ways; 1st, by an irritant immediately applied, as a straw upon the conjunctiva, cantharides upon the skin, acrid vapours upon the mucous surface of the bronchia or the nasal cavities, atmospheric air upon any internal organ laid bare, as we see in wounds, &c.; 2d, by continuity of organs, as when a part of the skin, of the pleura, &c. being inflamed, those that are near it are also affected, and the blood flows there, as when one organ is diseased, that which is near it becomes so by the cellular communications; 3d, by sympathies; thus the skin being seized with cold, the pleura is sympathetically affected; its organic sensibility is increased, the blood immediately enters it from every part. When this property is raised in one of these three ways in the capillary system, the phenomena that result from it are the same. For example, when in the pleura it is raised because the air is in contact with this membrane, because the lungs that it covers have been first affected, or because coin has seized upon the skin in sweat, the effect is nearly analogous, as it respects the entrance of the blood in the capillary system.
It is then the change that takes place in the organic sensibility, that constitutes the essence and the principle of the disease; it is this change which makes a pain more or less severe soon felt in the part; then the sensibility that was organic, becomes animal. The part was before sensible to the impression of the blood, but did not transmit this impression to the brain; then it transmits it, and this impression becomes painful. Irritate the healthy pleura in a living animal; it does not suffer; irritate it on the contrary during inflammation, and it gives signs of the most acute pain. Who does not know that most often and almost always, a pain more or less acute is perceived in the part, some time before it becomes red? Now this pain is the indication of the alteration that the organic sensibility undergoes; this alteration exists some time, often without producing an effect; this effect, which is especially the afflux of blood, is subsequent.
It is the same of heat. I shall say hereafter how it is produced. It is sufficient now to show that it is, like the passage of the blood in the capillary system, only an effect of the change that has taken place in the organic sensibility of the part; now this is evident, since it is always consequent upon this change.
There happens then in inflammation exactly the reverse of what Boerhaave thought. The blood accumulated according to him, in the capillary vessels, and pushed À tergo by the heart, as he termed it, was truly the immediate cause of the affection, whereas, from what I have said, it is only the effect.
If we reflect a little upon the innumerable varieties of the causes which can alter the organic sensibility of the capillary system, it will be easy to understand of what infinite varieties inflammation is susceptible, from the momentary blush that comes and goes in the cheeks, to the most serious phlegmon and erysipelas. We might make a scale of the degrees of inflammation. By taking the cutaneous, for example, we should see at the bottom the redness that arises and disappears suddenly by the least external excitement upon the dermoid system, which we can produce at will, and in which there is only an afflux of blood; then those that are a little more intense, which occasion cutaneous efflorescences of some hours, but without fever; then those that continue for a day, with which there is some fever; then erysipelas of the first order; then that which is more intense, and which gangrene soon terminates. All these different degrees do not suppose a different nature in the disease; the principle of them is always the same; there is always, 1st, an antecedent increase of organic sensibility, or alteration of this property; 2d, afflux of the blood only if the increase is not great, afflux of the blood, heat, pulsation, &c. if it is. As to fever, it is a phenomenon common to every severe, acute local affection; it appears to depend on the singular relation which connects the heart with all parts; it has nothing peculiar in inflammation, but the particular modification it receives from it.
The afflux of the blood in an irritated part takes place in inflammation, as in an incision. In this the divided point has been irritated by the instrument; soon the whole blood in the neighbourhood flows there and escapes by the wound. This afflux is so evident a result of irritation, that in a slight incision, the blood scarcely flows at the instant of the division of the integuments, because there is but little of this fluid at the divided place; but a moment after, the irritation which has been felt, produces its effect, and it flows in a quantity disproportioned to the incision.
When the alteration of the organic sensibility which produces inflammation, has no varieties except in its intensity, the inflammation itself differs only in degree. But the nature of the alteration is oftentimes different; a feeble character is frequently united with it; the part has then less redness, heat, &c. Other modifications are also observed; now all these depend upon the difference of the alterations that the organic sensibility experiences; at least these alterations always precede them.
The influence of these alterations is not less evident when inflammation terminates, than when it begins. If the organic sensibility has been so raised, that it is as it were exhausted, then the solid dies, and the fluid, which is no longer in a living organ, soon becomes putrid. Examine the phenomena of every gangrene; putrefaction is certainly only a consequence; there is always, 1st, a desertion of the solids by the vital forces; 2d, putrefaction of the fluids. The first is never a consequence of the second. When the organic sensibility begins to diminish, the blood brought there by inflammation is already susceptible of putrefaction; but the defect of tone in the solid always precedes. There is this local phenomenon, as well as the general, in putrid fever. It is incontestable that in this fever, the blood has a tendency to be decomposed, to become putrid; I will say further, that it often exhibits a commencing putrefaction. The index of the alteration of this fluid is always the general state of the forces of the solids; these have first lost their spring; the symptoms of weakness are evident before those of putridity. All the animal fluids tend naturally to putrefaction, which takes place inevitably when life abandons the solids in which they circulate. In proportion as the forces diminish in the solids, this tendency is manifested. A commencement of putrefaction in the fluids during life, is not a general phenomenon more improbable than the local phenomenon of which we have spoken, viz. that the blood of an inflamed part begins to putrefy and the part consequently becomes fetid, before the organic sensibility has entirely abandoned the solid. It is only when this ceases, that this putrefaction becomes complete; but then it is extremely rapid, because it had commenced during life. So bodies that have died of putrid fevers decompose with a rapidity far surpassing those that have died of other diseases, because putrefaction had really commenced before death.
Inflammation with a livid colour, small degree of heat, prostration of the forces in the part, and termination by gangrene, is evidently to well marked adynamic fever, what phlegmon is to inflammatory fever, what irritation of the primÆ viÆ, which is called bilious affection, is to the meningo-gastric fever, &c. I think if we examine attentively local affections and general fevers, we shall always find a particular kind of fever corresponding in its nature to a particular kind of local affection. But let us return to inflammation.
If it terminates by suppuration, it is evident that there is a new alteration of the organic sensibility to produce pus. The same thing in scirrhus. The termination by resolution takes place when this sensibility returns to its natural type. Examine well the inflammatory phenomena in their succession; you will see, that always a particular state in this property, precedes the changes they exhibit.
When our medicaments are applied upon an inflamed part, it is not upon the blood that they act; it is not by lessening the heat, or relaxing. The expressions to soften, unbend and relax the solids, are inaccurate, because they are borrowed from physical phenomena. We relax, we soften dry leather by moistening it; but we only act upon the living organs, by modifying their vital properties. Observe that though we already begin to recognize the empire of these properties in diseases, medical language is still wholly borrowed from theories which employ physical principles in the explanation of morbid phenomena. We have arrived at a period when the manner of expressing ourselves upon these phenomena should be changed; I do not here speak of the names of diseases. Certainly every emollient, astringent, discutient, relaxing, tonic, medicament, &c. employed with different views upon an inflamed part, only acts by modifying differently from what it was, organic sensibility. It is thus that our medicaments cure or often aggravate diseases.
From what has been said, it is evident that the solids perform the first part in inflammations, and the fluids only the second. Modern authors have perceived this truth, and they have immediately assigned an important part, in this respect, to the nerves; but we have seen that these appear foreign to organic sensibility, that they are so even after the most rigorous observation. The nervous influence, that at least which we know in other parts, is, in inflammation, as in secretion, exhalation and nutrition, almost entirely wanting. There is in this affection, unalteration of the organic sensibility, and this is every thing.
The kind of blood varies in inflammation, and in this respect, I think the following rule is generally uniform; whenever the organic sensibility is much raised, the life augmented and there is an increase of forces in the inflamed part, then it is the red blood that remains in the capillary system; then there is always great heat there. On the contrary, when the inflammation approaches the putrid character, the part becomes of a dull and livid colour; the capillaries appear to be filled with black blood; the heat is less. In general, a bright colour, in all eruptions analogous to inflammatory tumours, announces the increase of the organic sensibility. A livid colour, on the other hand, indicates its prostration; petechiÆ are livid; scorbutic blotches are so; a livid colour in tumours is the forerunner of gangrene. Do you wish to know when cold acts as a stimulant? It is when it reddens the end of the nose, the ears, &c. When these parts become livid, other phenomena announce at the same time, that its action is sedative. This is supported by my experiments upon life and death, which have proved that the black blood everywhere interrupts the functions, weakens, annihilates even the motion of the parts, when it is brought to them by the arteries.
Differences of Inflammation, according to the different Systems.
From what has been said upon inflammation, it appears that it has for its seat the capillary system, for its principle an alteration in the organic sensibility of this system, for its effect the afflux of blood into vessels in which it did not before circulate, a consequent increase of caloric, &c. Now where the capillary system is more developed, where the organic sensibility is greater, inflammation ought to be more frequent; and this is the case. It is especially in the cellular, serous, mucous and dermoid systems that we observe it; fine injections demonstrate in these systems a capillary net-work infinitely superior to that of the others. Besides, as if there is not only nutrition, but also exhalation and oftentimes secretion in these systems, there must be more organic sensibility, a property from which all these functions are derived.
On the contrary, inflammation is rare in the muscular, osseous, cartilaginous, fibrous, arterial, venous systems, &c. where there are but few capillaries, and where the organic sensibility presiding only over nutrition, is necessarily found in a less degree.
Besides, as the capillaries make an integral part of the system where they are found, and as each system has its peculiar kind of organic sensibility, it is evident that they ought to partake of this kind; now as it is upon this property that all the inflammatory phenomena depend, they ought to present an aspect wholly different in each system. This is what we shall be convinced is the case by an examination of each. I shall only present here generally, that essential point of view, upon which authors have not insisted.
Let us take first the systems most exposed to inflammation; we shall see that phlegmon is the inflammatory kind of the cellular, erysipelas that of the dermoid, and catarrh that of the mucous. We have not yet a general name to express that of the serous; but who does not know how it differs from the others?
In the systems rarely subject to inflammation, we know this affection infinitely less than in the preceding; but there is no doubt that it differs essentially. Compare the length and permanency of that of the bones, with the rapidity and disposition to change of that of the muscles, or rather of the fibrous bodies, in rheumatism.
The results of inflammation do not vary less than its nature; if resolution does not take place, each has its own mode of suppuration. Compare the pus of erysipelas, that of phlegmon, the milky or flocculent fluid of the serous membranes, the whitish or greyish humour, of a mucous consistence, that escapes from the membranes of the same name after catarrh, the blackish sanies of the bones in suppuration, &c. We shall see that some organs, as the fibrous bodies, do not suppurate.
Gangrene once taken place, is everywhere the same, since it is only the absence of life, and all dead organs have the same properties. But according to the sum of organic sensibility which each system has, it is more or less disposed to die after inflammation, in the midst of others which retain their life. Who does not know that the carbuncle which soon kills the part it seizes, only attacks certain systems; that the osseous, the cartilaginous, the nervous, &c. are always exempt from it?
The essential fault of every medical doctrine is that of considering diseases too abstractedly; they are so modified in each system, that their aspect is wholly different. If I may be allowed the expression, it is always the same individual, but in entering each system, it has a different appearance there, so that often you cannot recognize it. When will medicine be so far advanced that the treatment will correspond with these varieties? There should certainly be a general treatment of inflammation; but it should be modified differently, according as we apply it to phlegmon, erysipelas, catarrh, &c.
This then is a very evident proof of that peculiar character which inflammation takes in each part. We know with what ease and rapidity the blood flows to any part of the skin in consequence of irritation there; prick or rub briskly a part of this organ, it reddens in a moment. This takes place also, though less sensibly, on the mucous surfaces. This is not equally seen upon the serous; I have frequently ascertained this on living animals, when I have laid bare these surfaces and irritated them in different ways. The afflux of the blood does not immediately follow the irritation: there is always an interval between one and the other, never less than an hour.
VII. Structure, and Properties of the Capillaries.
What is the structure of the capillaries? So great is their tenuity that we evidently cannot have upon this point, any kind of data founded upon experiment and observation. Only it is very probable, it is even certain, that this structure is modified differently in each organ, that it is not the same in the tendons, the aponeuroses, the muscles, &c. that it really partakes of the nature of the organ of which it makes an integral part.
The membrane which lines the excretories, the arteries, the veins, the exhalants, vessels which go into the system of the capillaries or come out of it, is very like that of these capillaries; but it is not certainly the same.
It is the diversity in the structure of the capillaries, according to the organs in which they are found, which has an essential influence upon the difference which the vital properties exhibit, particularly the organic sensibility and the insensible organic contractility in each system in which we examine them; hence peculiar modifications in all those diseases over which these properties preside, and which are seated especially in the capillaries, such as inflammations, tumours, hemorrhages, &c. &c.
The difference in structure of the capillary system, sometimes becomes manifest to the eye. Thus the spleen, the corpus cavernosum, instead of presenting, like the serous surfaces, a vascular net-work in which the blood oscillates in different directions, according to the motion it receives, exhibit only spongy, cancellated textures, whose nature is but little known, in which the blood appears often to stagnate, instead of moving, &c.
VIII. Of the Circulation of the Capillaries.
The circulatory phenomena are of two kinds in the capillary system: 1st, there is the motion of the fluids; 2d, the alterations which they undergo.
Motion of the Fluids in the Capillary System.
These fluids are, 1st, the blood; 2d, others differing from it in their composition, though we only know their differences of appearance. Let us examine the laws of the motion of each kind.
The blood, after it has entered the capillary system, is evidently beyond the influence of the heart, and only circulates by that of the tonic forces, or the insensible contractility of the part. If we examine the phenomena of this capillary system but little, we shall be easily convinced of this truth, which Bordeu first taught. The capillary system is really the boundary, beyond which the influence of the heart does not extend. Hence why all the vessels that go out of this system, exhibit in the fluid they contain a motion that does not correspond with that of the arteries that go to it. 1st. After what we have said, there is no doubt of this, as it regards the veins. 2d. It is also true as it respects the excretories. The increase of secretions does not correspond with the increase of the action of the heart, nor does their diminution with the diminution of the pulsations. Who does not know, on the contrary, that often in a violent paroxysm of fever, in which the agitation of the arterial blood is very great, all the glands seem to shut up their ducts and not to pour out any fluid? 3d. It is the same with all the exhalations; it is not when a fever is the greatest, that we sweat the most, but when it is somewhat diminished. Hemorrhages are evidently but an exhalation; now who does not know, that the pulse is often very weak, when the blood flows abundantly from the mucous surfaces of the womb, the nostrils, the bronchia, &c.? Who does not know on the contrary that in extreme agitations of the heart, most often the blood does not flow by the exhalants? Is the quickness of the pulse increased during menstruation? It is the redness of the capillary system, the abundance of the blood of this system, which is often, as I have said, the forerunner of active hemorrhages; but it is never the increase of the action of the heart. Oftentimes fungous tumours, soft flesh that shoots up in wounds of a bad nature, polypi, &c. pour out blood; the heart has nothing to do with these hemorrhages, they come evidently from the capillary system. Who does not know, that frequently when the exhalants pour out copiously serous fluids upon the membrane of that name, in the production of dropsies, the heart is, like all the other parts, in a state of real inertia?
Since then all the vessels going from the capillary system exhibit in their motions no sort of harmony with those of the heart, it is evident that the influence of this organ is interrupted, is terminated at the capillary system.
Observe nutrition; it is clearly the capillary system that distributes everywhere the materials that it has received by the impulse of the heart; now the influence of this does not extend to the place where the nutritive matter is deposited. In fact, its impulse everywhere equal and uniform, pushes the blood with nearly an equal force to all parts, with some exceptions in the foetus. Now nutrition is on the contrary extremely unequal; at one age, it is one part that takes more increase, consequently receives more nutritive matter; at another age, it is another organ. This inequality, is the first and principal phenomenon of growth.
How can we reconcile with the sole and uniform impulse of the heart in all parts, inflammation, the production of herpes, of different eruptions, &c. which appear in some places? Would inflammation exhibit so many aspects, according to the system it seizes, if the heart alone presided over its development? All the difference between catarrh, erysipelas, phlegmon, &c. would disappear; and there would be only what arose from being nearer, or further from the heart.
Let us cease then to consider this organ as the sole agent which presides over the motion of the great vessels and the small, which, in these last, driving the blood abundantly to a part, produces there inflammation, which by its impulse causes the different cutaneous eruptions, secretions, exhalations, &c. The whole doctrine of the mechanicians rested, as we know, upon the great extent which they gave to the movements of the heart.
There are evidently two kinds of diseases in relation to the circulation; 1st, those that affect the general; 2d, those that affect the capillary circulation. Different fevers form especially the first kind. Different eruptions, tumours, inflammations, &c. produce the second; now, though many relations connect the second with the first, it is not essentially dependant upon it; the following is the proof of this; fevers can evidently only exist in animals with great vessels, in those in which the fluids move in a mass; they cannot take place in zoophytes and plants, which have only a capillary circulation; yet these last classes of animals and all vegetables are subject to all the affections that disturb the capillary circulation. Thus we see upon plants many tumours; their wounds unite; two portions even contract adhesions, as a graft proves. The diseases of their capillary system are no doubt different from those of animals in their progress and their nature; but they exhibit always the same general character, because they are derived from the same properties, organic sensibility and insensible contractility.
Since the diseases of the capillary system are not essentially connected with those of the general vascular system, they are not then dependant on it; the circulation of the first is but indirectly subordinate to that of the second. Hence why the two circulations can be separate; why more than half of the organized beings have only the capillary. This is the most important, since it immediately pours out the materials of nutrition, of exhalations, of absorption: thus it exists in all organized beings. We cannot conceive of any one without it, because we cannot conceive of any one that is not continually composed and decomposed by nutrition.
From what we have thus far said, it is evident, that the blood after it has arrived in the capillary system, is moved there only by the tonic influence of the solids; now, as the least cause alters and changes their properties, it is subject there to an infinity of irregular motions. The least irritation makes it recede, advance, deviate to the right, or the left, &c. In the ordinary state, it moves generally in an uniform manner from the arteries towards the veins; but at every instant it may find causes of irregular oscillations in its innumerable anastomoses; hence, as we have seen, the necessity of these anastomoses. These irregular oscillations in the motion of the blood in the capillary system, can be seen with a microscope. Haller, Spallanzani and others, whose experiments are too well known for me to relate them here, saw them a hundred times. They saw the globules advance, recede, move in many different directions in animals with red and cold blood, when they irritated the mesentery or any other transparent part. In animals with red and warm blood, in those even whose mesentery is almost as transparent as that of the frog, as in the guinea-pig, it has appeared to me infinitely more difficult to trace the motion of the blood in the capillaries.
It is easy to see that all the phenomena of inflammation, of different eruptions, of tumours, &c. are especially founded upon this susceptibility of the blood, in the capillary system, to move in an infinite variety of directions, wherever irritation calls it.
From what has been said, it is evident that there are times when the blood passes with less rapidity through the capillary system, and there are others, when it moves more quickly. How then is the relation always preserved the same, between the arterial and the venous blood? It is in this way; the irregular oscillations hardly ever take place except in one part of the capillary system; in no case is the whole of it affected; thus if the blood moves more slowly in the cutaneous capillary system, its velocity is increased in the cellular, the muscular, &c.
This is in fact an invariable law in the vital forces, that if on the one hand they increase in energy, on the other, they diminish; we might say, that there was only a certain quantity in the animal economy, that this might be divided in different proportions, but it cannot be increased or diminished. This principle results so evidently from all the phenomena of the economy, that I think it unnecessary to support it by numerous proofs; now, taking this as incontrovertible, it is evident that one portion of the capillary system increasing its action, only at the expense of the others, the sum total of blood transmitted from the arteries to the veins remains always nearly the same. All the systems are then, in this respect, supporters of each other; if nothing passes by the capillaries of one, it is the same thing, provided the capillaries of another transmit double the amount of fluid that they do in an ordinary state.
Observe the blood in the cutaneous capillaries before the paroxysm of intermittent fevers; it recedes from these capillaries; all the surfaces that it reddened, become pale; the capillaries of the other systems supply the momentary defect of the action of these. Who knows if, in many cases where the skin becomes very red, when much blood enters it, there is not in the other systems a paleness analogous to that of the skin during the cold fit of fever? I not only think this very probable, but I have no doubt of it. The external capillaries certainly contain more blood in summer, whilst those of the internal systems receive more in winter. There is then continual varieties in the mode of the passage of this fluid through the general capillary system; each system transmits by turns, more or less, according as it is affected.
When we see the glands, frequently in a short time pour out an enormous quantity of fluid, the serous, cutaneous, mucous exhalants, &c. furnish also much greater proportions than in a natural state, we are astonished that the circulation can at the same time continue with the same regularity; we are not less so undoubtedly, when we see on the contrary all the evacuations suppressed, and nothing goes out from the animal solids; now in all these cases, it is the capillary system, whose forces differently modified in the different parts, re-establishes the general equilibrium which would inevitably be lost, if the heart was the agent of impulse which pushed to the extremities the secreted and exhaled fluids, and transmitted the black blood to the veins.
Sometimes however a derangement almost universal takes place in the capillary system, especially on the exterior; this takes place in sudden changes of the air. Though the vital laws preside essentially over the capillary circulation, yet the degree of pressure of the surrounding air can modify it to a certain point; we have a proof of this in cupping glasses, or in any other means that produce suddenly a vacuum upon a part of the body; then the fluids pressed in the neighbourhood by the external air, and not compressed on the contrary at the place of the cupping glass, raise up and distend considerably the skin. The sudden changes of the atmosphere produce upon the whole body, though in a less degree, the effect of a cupping glass. If the air is rarefied, the whole external capillary system is more full; even the sub-cutaneous veins swell; a very considerable part of the blood experiences then a derangement in its motion, between the two systems with red and black blood. The harmony, the correspondence of these two systems is disturbed; hence the uneasiness, the sense of weight, &c. of which we are instantly relieved by a sudden change of the atmosphere.
The evacuation of the blood also establishes differences, though less, in the capillary system. Bleeding is of two kinds; one lessens the blood of the circulation of the great trunks; and then it is sometimes red, as in arteriotomy; but most often it is the black, that is drawn off; the other takes blood from the capillary circulation; this is done by leeches, cupping, &c. Each produces a different change in the course of the blood. Physicians formerly were desirous of knowing from which vein they ought to bleed. I think it is much more important to know when we should by bleeding, act upon the general circulation, and when upon the capillary. In many local congestions, I do not think that you can diminish the quantity of blood in a part of the capillary system, by diminishing the mass of this fluid in the great trunks; you might take a quarter at least of the blood that there then was in the economy, if the part is irritated, the blood will still flow as much to this part. On the contrary, you may double by transfusion, the mass of this fluid in an animal, local inflammations will not arise, because there must be a preliminary irritation before the blood flows towards, and enters a particular part of the capillary system.
The fluids differing from the blood which circulate in the capillary system, 1st. are evidently like it beyond the influence of the heart. 2d. The influence of the tonic powers presides over their motions. 3d. They are consequently subject to irregular oscillations, according as the capillaries are differently affected.
We know not the nature of most of these fluids, because they cannot be subjected to our experiments. They are those that enter the ligaments, the tendons, the aponeuroses, the hair, the cartilages, the fibro-cartilages, a part of the cutaneous, mucous, serous surfaces, &c. They communicate with the blood from which they arise, by the capillary systems, they afterwards move in their own systems. In most of the organs in which they exist alone, as in those called white, they are very slow in their motion, because the sensibility of these organs is obscure and dull. Thus different tumours, to the formation of which they contribute, have, as we shall see, almost always a chronic progress.
There are often in the animal economy those tumours, that are commonly called lymphatic, though we are wholly ignorant of the fluids that form them. They are found especially in the neighbourhood of the articulations; but sometimes only the cartilages, the cellular texture, the bones, &c. are the seat of these white tumours; it is important to ascertain the characters that distinguish them from the tumours in which the blood especially enters.
Phenomena of the Alteration of the Fluids in the Capillary System.
We have just treated of the phenomena of the motion of the fluids in the general capillary system; let us now speak of the changes which they undergo there in their nature.
The blood exhibits a remarkable phenomenon in the general capillary system; from red, which it was in the arteries, it becomes black. How does this take place? It evidently can happen only in two ways, viz. either by the addition or subtraction of some principles. Is it charged with carbon and hydrogen? Does it deposit only oxygen in the organs? Are these two causes united to give it its blackness? I think that it will always be difficult to decide upon these questions, which do not appear to me to be capable of any positive experiment. However, when we see the arterial blood furnish all the organs with the materials of their secretion, nutrition and exhalation, it is to be presumed that it leaves in these organs, rather than takes from them, the principle of its colour.
Sometimes the red blood passes through the capillary system, without losing its colour; for example, when the blood has flowed for a long time black from a vein, we sometimes see it come out red, or nearly so, just before it ceases to flow. In opening the renal vein, I have two or three times made this observation, which has, I think, been noticed by some authors.
The blood becomes more or less black in the general capillary system. If you have observed bleedings, you have undoubtedly seen in diseases innumerable varieties in the colour of the blood that comes from the vein. Has this fluid a different blackness in each part of the capillary system? It has appeared to me that the difference is not very great in this respect. I have frequently had occasion to open the renal, saphena, jugular veins, &c. the blood has appeared to me to be everywhere of nearly the same colour. I wished to see if the blood returning from an inflamed part was more or less black; I made then in the hind leg of a dog a number of wounds near each other, and left them open to the air. At the end of three days, when the inflammation appeared to be greatest, I opened high up on the diseased and the sound limb, the saphena and the crural veins, in order to examine their blood comparatively; I could discover no sensible difference. I bled a man who had a whitlow with an inflammatory swelling of the whole hand, and the inferior part of the fore arm; the blood appeared of the same colour as usual. Yet, as the veins bring also the blood of parts not inflamed, more minute researches must be made.
An object which deserves to be determined with precision, is this, viz. the cases in which, in general diseases, there is an alteration in the deep colour of the blood, and the symptoms which correspond with these alterations. At present we only know that it is more deep coloured in some cases and less so in others.
IX. Of the Capillaries considered as the seat of the production of Heat.
Every one knows the innumerable hypotheses that were made upon the production of animal heat by the mechanical physicians. Modern chemists, in showing the insufficiency of these theories, have substituted one that has not less difficulties. The lungs are considered by them as the place in which the caloric is extricated, and the arteries, a kind of tubes, that carry the heat to all parts of the body. The production of this great phenomenon belongs then wholly, according to them, to the pulmonary capillary system. I believe, on the contrary, and I have taught in my courses on physiology, that it is in the general capillary system that it has its seat.
I shall not stop to refute the hypothesis of the chemists. When we place on one side, all the phenomena of animal heat, and on the other, this hypothesis, it appears so inadequate to their explanation, that I think every methodical mind can do it without my assistance. These phenomena are the following:
1st. Every living and organized being, both animal and vegetable, has a temperature of its own. 2d. This temperature is nearly the same in all ages in animals. 3d. It is entirely independent of that of the atmosphere; it remains the same in a warm as in a colder medium. 4th. Caloric is often disengaged in health more abundantly in some parts than in others. 5th. In inflammation there is evidently a more considerable extrication of it. 6th. The vital forces, especially the tonic power, have a very decided influence upon the extrication of caloric. 7th. Each organ has its own temperature, and it is from all these partial temperatures, that the general one arises. 8th. There is oftentimes an immediate connexion between the respiratory and circulatory phenomena, and those of the production of heat; the first increasing, the second increase also in proportion. At other times this relation does not exist.
If, below these phenomena, you place the theory of Lavoisier, Crawford, &c. I do not believe you can make it accord with them, and conceive how caloric, disengaged in the pulmonary capillary system can be spread, as they say, through the whole animal economy. By admitting on the contrary that this fluid is disengaged in the general capillary system, it is easily understood. But let us explain this way of understanding the production of animal heat.
The blood draws from two principal sources the substances that repair the losses it has sustained. These sources are, 1st, digestion; 2d, respiration; the first pours chyle into the blood, the other mixes it with different aerial principles. Sometimes cutaneous absorption introduces into it different substances. The mixture of the blood with the new substances it receives, constitutes sanguification. Now these new substances carry continually into this fluid, new caloric; for as all bodies are penetrated by it, there can hardly be an addition of a substance to the blood, without the addition of this principle. In sanguification, caloric combines then with the blood, but it is not in a free state; it becomes part of the fluid; it is one of its elements.
Thus charged with combined caloric, the blood arrives in the capillary system; there it gives it out, wherever it undergoes changes. It is in fact in this system that it is changed into nutritive substance, into that of the secretions, exhalations, &c. All the functions in which this fluid changes its nature, in which certain principles are separated from it, to form certain substances destined especially to particular uses, necessarily disengage its caloric. I cannot say precisely how this happens, whether it is more in the internal alterations that the blood undergoes in furnishing nutrition, or in those destined to furnish secretion or exhalation. This only is the general principle, and exhibits three things; 1st, the entrance of caloric into the blood, with all the substances that repair its losses; 2d, the circulation in a combined state of the caloric newly entered; 3d, extrication of this combined fluid, to form free caloric by the changes and different alterations that the blood undergoes in the general capillary system, in forming the materials of the different functions.
The extrication of caloric is, then, a phenomenon exactly analogous to those of which the general capillary system is the seat. In nutrition, in fact, there is, 1st, a combination of new foreign substances with the blood; 2d, circulation in the great vessels of these substances combined; 3d, separation of the nutritive substance to enter the organs. So also the elements of the secreted fluids combine, then circulate combined, then leave the blood to be thrown out. So, in fine, every exhaled fluid combines, circulates, and is then separated from the blood.
From this it is evident that, 1st, the entrance of foreign substances into the blood by respiration, by digestion or even cutaneous absorption; 2d, the combination of these substances with the blood in sanguification; 3d, their circulation in the arterial system, are three general phenomena common to secretions, exhalations, nutrition, and calorification, if I may be allowed the term; for the production of heat is a function and not a property; hence why I think the word caloricity does not express it.
The caloric arrives, then, in the capillary system combined with the matter of secretions, exhalations, and nutrition. The blood is the common fluid that results from all these combinations. In the general capillary system each part is separated; the caloric to be distributed over the whole body and afterwards pass out; the fluids of the secretions go out by the glands; those of exhalations escape from their respective surfaces; those of nutrition remain in the organs.
It seems to me, that the explanation which exhibits nature always pursuing an uniform course in her operations, drawing the same results from the same principles, has a greater degree of probability than that which shows her separating, as it were, this phenomenon from all the others, in the way which she produces it.
The manner in which caloric enters the body, is of no consequence. Vegetables that have no lungs, but only air tubes and absorbents, and fishes that have branchiÆ, have an independent temperature. That heat may be produced, it is sufficient that foreign substances are continually assimilated to the fluids of organized bodies, and that after this assimilation, these fluids, whether they are blood, as in animals with red blood, either warm or cold, or whether they are of a different nature, as in those with white fluids and in plants, it is sufficient, I say, that the fluids undergo different transformations in the capillary system.
Respiration combines more caloric with the blood; there is consequently a greater disengagement of this principle in animals who breathe by lungs, than in others; and even in the first, the greater the lungs, the greater is the quantity of caloric disengaged; as is proved by comparing birds, quadrupeds, the cetaceous tribe among fishes, &c. But these varieties are certainly only in relation to the degree of temperature; hence there are animals with cold blood, and those with warm. The general phenomena of the disengagement of heat remain always the same in animals with lungs, in those without them, and in plants.
From these principles, it is easy to understand most of the phenomena of animal heat.
The disengagement of caloric is always subordinate to the state of the vital forces. As the tone of a part is greater or less, it is more or less warm. This dependance of the heat upon the state of the forces of the part, is a fact, that is proved by all diseases and all the phenomena of health; it is as true with regard to heat, as it is with regard to the exhalations and the secretions. The greater afflux of blood to an inflamed part and the greater disengagement of caloric, the increase of this disengagement in the womb and the nose, and menstruation and the active nasal hemorrhages, &c. the heat of the chest and active pulmonary hemorrhages, &c. are the effects of the same cause, viz. the increase of the vital forces of the part. In general, whenever the tone is much increased, the heat increases also; hence why there is a greater disengagement of it in almost all active sweats, hemorrhages, and even secretions; whilst this fluid is not superabundant in sweats, hemorrhages, or secretions that are called passive, whatever may be the quantity of fluid separated from the blood by them.
Each system has its own degree of heat. There is certainly less caloric given off in the hair, the nails, and the epidermis, than in the other systems. The white organs, as the tendons, the aponeuroses, the ligaments, the cartilages, &c. have probably less than the muscles. Examine the claws of birds, in which there are only these white parts; they are not so warm as the rest of the body.
The difference of the heat of each system situated in the interior has not yet been analyzed; I am persuaded that if it was done with precision, by insulating those which can be, so that they might communicate by the vessels, we should observe that each separates a different quantity of caloric, and that consequently there are as many distinct temperatures in the general temperature, as there are organized systems.
I am convinced that the ligaments, the cartilages, &c. approximate in this respect the organs of animals with cold blood, and that if man was composed of organs analogous to those, his temperature would be much inferior to what it naturally is. The systems which disengage more caloric communicate it to those that disengage less. If the hair was in the middle of the body, it would be as warm as the neighbouring parts, though its temperature would be independent; it is now always inferior to that of the body, because it is insulated. Each system has then its peculiar mode of heat, as each has its peculiar mode of secretion, each exhalant surface its peculiar mode of exhalation, each texture its peculiar mode of nutrition; and all this depends immediately on the modifications that the vital properties have in each part.
It is in consequence of this peculiarity of heat in each system, that each gives a different sensation in inflammation. Compare the sharp and biting heat of erysipelas with that of phlegmon; certain dull, obscure heats, the forerunners of organic affections, with the acute heats of different inflammations; apply the hand to the skin in different fevers, you will see that each is almost marked by a particular kind of heat. Animal bodies alone exhibit these varieties of nature in heat; minerals have only varieties in degree.
We understand from the principles explained above, not only the local alterations of heat, but also the general derangement that takes place in its disengagement, from the effect of diseases, whether this disengagement is increased, diminished, or affected with irregularities, as in certain ataxic fevers, in phthisis, when the palms of the hands and the face are warmer in some cases, &c. Who does not know that oftentimes when the extremities are frozen, the patient feels an extraordinary internal heat? It is sufficient that the forces of the capillary system be differently modified, that the heat may be so also.
Observe, in fact, that the alterations of heat in diseases are as frequent as those of the exhalations and secretions, and that they always present, like the first, a previous derangement in the vital forces. If chemists apply their theories to these morbid changes of heat, instead of considering them as a necessary consequence of the state in which the vital forces are then found, they will necessarily find in them an insurmountable obstacle.
When we run swiftly, when the blood is violently agitated in the paroxysm of fever, more caloric is disengaged than at any other time. Does this prove that it is the general circulation which contributes to the disengagement of caloric, and that it takes place in the great vessels? No more than a copious sweat proves that the heart drives it out. Strongly excited by the shock of the red blood which is suddenly increased, the capillary and exhalant systems are compelled to increase their action; now a double effect is the result; 1st, greater disengagement of caloric; 2d, increased exhalation.
If the heat is increased when respiration is hurried, it appears to depend only on this, that the latter is hardly ever accelerated, without the circulation being so too. This is so true, that if you make for a long time rapidly successive inspirations and expirations, the heat will not increase. Besides, why should the heat actually increase by the hurry of respiration? Undoubtedly because more air entering in a given time, the lungs would absorb more oxygen, and consequently, according to the opinions of the chemists, more caloric would be disengaged. But let them present more or less of this principle to the blood, it absorbs the same quantity. In ordinary inspiration the air contains much more than can pass into this fluid. When an animal is made to breathe it pure, the blood does not become more red, because the same quantity always enters it. So you may in vain put into the alimentary passages four times more nutritive substance than common, no more chyle will be formed, the lacteals will absorb no more; there will only be more excrements, or vomiting will take place.
The state of respiration has no influence then upon the actual heat of the body; it only contributes to it by constantly introducing a greater or less quantity of combined caloric. It is thus that animals which respire the most, have habitually the most caloric.
How can an animal, breathing a very cold air, eating aliments almost deprived of caloric, &c. in northern latitudes, have as much heat as in hot climates? It is not the free caloric contained in the parts, but the combined, which, being introduced into the blood with the foreign substances, furnishes the materials of that which is disengaged in the general capillary system. Now the combined caloric is absolutely independent of temperature. As much fire is elicited from the same stone by the steel, in the coldest as in the warmest countries.
All the caloric that is combined with the red blood is not disengaged whilst this fluid is passing through the general capillary system; there remains some of it still combined with the black blood. Hence why in the first moments of asphyxia, before death has taken place, though in consequence of the interruption of respiration, all the blood that comes through the arteries to the capillaries is black, the heat continues to be generated for some time. When the contact of the black blood has even interrupted all the great functions, those of the brain, of the muscles, the heart, the lungs, &c. it appears that the black blood then undergoes for some time, a kind of oscillation in the capillary system, by which it disengages a little caloric. Hence, why those who have died of asphyxia produced by charcoal, or hanging, animals killed in vacuo, apoplectics, &c. preserve their heat a long time after death, as all physicians have observed.
This phenomenon is not however peculiar to the case of which we are treating. In opening dead bodies at the Hotel Dieu, I have observed that the time in which they lost their animal heat was very variable; that a body continues warm a greater or less time, especially among those who have died suddenly of an acute affection, in the paroxysm of an ataxic fever, for example, or by a fall, for those who die of a chronic disease, lose almost immediately their caloric. The difference in the first is often three, four, or even six hours. This phenomenon arises from the fact, that whenever death is sudden it interrupts only the great functions; the tonic action of the parts continues for a greater or less time after. Now this action disengages a little caloric from the blood that is in the general system. Thus in violent deaths, absorption continues some time after death; thus the muscles still contract; thus perhaps the glands, take up for some hours, from the blood that remains in the capillary system, the materials proper for their secretion.
This inequality in the heat of dead bodies can only arise from the cause I have named; for when the disengagement of caloric has ceased in the body, that which remains in it becomes in equilibrium with that of the external air, according to the general laws of this equilibrium. Now these laws being uniform, their effect would be the same in every case. Hence then the phenomena related above, are evidently incompatible with any other theory than that which supposes the caloric to be disengaged in the general capillary system.
Sympathy has, as we know, the greatest influence upon heat. According as this or that part is affected, there is disengaged in others more or less of their fluid. An icy coldness often takes place in syncope. Ulcerations of the lungs produce a burning in the palms of the hands. In other affections, the head seems to be the seat of the greatest heat. In a fever frequently the patient is hot in one place and cold in another. How does all this happen? in this way; the affected organ acts sympathetically on the tonic forces of the part; these being raised, more caloric than usual is disengaged; it is precisely the same as in sympathetic secretions or exhalations. Whether the vital forces are raised by a stimulus directly applied, or by the sympathetic influence they receive, the effect that results from it is exactly the same.
It is necessary to distinguish this sympathetic increase of heat, from those that are produced by an aberration of perception, as when we think we are very hot or cold in a part, or experience even a sensation exactly analogous to those that are natural, though the part to which we refer this sensation may be in its natural state, there being neither more or less caloric disengaged in it. It is as when we think we feel pain in the amputated extremity of a limb. It is an aberration of perception; it is truly a sympathy of animal sensibility, whereas the preceding is a sympathy of insensible organic contractility or tone. It is this last property that is affected; the disengagement of caloric is a consequence; it takes place as usual, like the perception that indicates its presence. Another person's hand applied on the part, feels nothing new in the first case, of which I shall say more in the following systems; it experiences a warmer sensation in this. So if the effect of the sympathetic influence is to diminish the tonic forces, there will be a less local disengagement of this fluid, which will be equally perceptible to the individual and to any other person who applies his hand to the part. Diseases continually furnish us with examples of these phenomena in relation to heat, and no other theory than the one now given would be able to explain them.
There is a phenomenon that is as difficult to be well understood by this theory as any other; it is the faculty animals have of resisting external heat. Every inert body is of the same temperature as the medium which surrounds it. Every organized body on the contrary repels the caloric that tends to raise it to a higher temperature than its own. Perhaps this belongs to the laws of the propagation of caloric, of which we are ignorant.
It will be asked undoubtedly why in the ordinary state there is only disengaged a certain quantity of caloric, so as to produce an uniform temperature of a certain number of degrees of the thermometer. I answer that it is by the same cause that in the ordinary state the pulse beats nearly the same number of times in a minute, which makes common respiration consist of so many elevations and depressions of the ribs, &c. &c. It is one of those phenomena that belongs to the immutable order first established, and which it is impossible to explain. Only it appears that this immutable order depends upon the primitive type that has been impressed upon the vital forces, a type, which when nothing excites or diminishes them, produces always phenomena nearly uniform; but as a thousand causes make them vary, a thousand times the pulse, respiration, heat, &c. are capable of differing. I would observe however in regard to the last, that its variations are not so great as those of many of the other functions. Compare, for example, the ordinary quantity of secreted and exhaled fluids, with the increase that takes place under certain circumstances, the common state of the pulse with its exacerbations in many fevers, &c. you will see that between the natural and the morbid state there is often an enormous difference. The heat on the contrary, is never raised but a few degrees above the temperature of the body. When there appears by touching the parts, to be a great difference, the thermometer proves that it is in reality trifling.
I would remark, in concluding this article, that I have not sought to ascertain how the caloric is disengaged in the capillary system, what portion escapes, in what relation it is with the red and the black blood, &c.; none of these can be determined by experiment. Let us be content in our theories with establishing general principles, especially analogies between functions that are known, and those which we attempt to explain, let us attempt merely to offer some general views; but let us never hazard precise explanations. Some have endeavoured lately to determine accurately what quantity of oxygen is absorbed, what quantity goes to produce the water of respiration, what quantity of carbonic acid gas is formed, how much caloric is disengaged, &c. This precision would be advantageous if it could be attained; but no phenomenon in the living economy will admit of it, in the explanations which it occasions. Chemists and natural philosophers accustomed to study the phenomena over which the physical forces preside, have carried their spirit of calculation into the theories they have formed for those which the vital laws govern. But this should not be so. In organized bodies, the spirit of the theories should be wholly different from the spirit of the theories applied to the physical sciences. It is necessary in these last that every phenomenon should be accurately explained; that, for example, in hydraulics, all the portions of the fluids should be calculated in their motions; that, in chemistry, we should know the precise proportion and amount of each of the elements that are combined in the changes that bodies undergo.
On the contrary, every physiological explanation should give only general views, approximations; it ought to be vague, if I may use the term. Every calculation, every examination of the proportions of the fluids with each other, all precise language should be banished from it, because we yet know so little of the vital laws, they are subject to so many variations, that what is true at the moment we study a fact, ceases to be so the next, and the essence of the phenomena always escapes us; their general results only, and the comparison of these results with each other, should occupy us.
ARTICLE SECOND.
PULMONARY CAPILLARY SYSTEM.
I call by this name the assemblage of the fine and delicate ramifications, which serve for the termination of the black blood and the origin of the red, which consequently finish the pulmonary artery and give origin to the pulmonary veins. The capillaries between the bronchial arteries and veins have nothing to do with them, they have no communication, and evidently belong to the general capillary system.
I. Relation of the two Capillary Systems, Pulmonary and General.
In comparing the preceding system with this, it is difficult to understand how they can exactly correspond, how the pulmonary can transmit not only all that passes through the general, but also all the lymph that returns from the serous surfaces and the cellular cavities, all the chyle which enters by digestion, &c. &c.
It seems impossible at first view, that in the balance of the circulation, these capillaries can, constantly and regularly, keep in equilibrium with those of the rest of the body. By reflecting a little, however, upon the phenomena of this function, we see that the discordance is only apparent.
Though the general capillary system is everywhere spread out, yet the portion in which blood circulates is much more limited than at first appears. There is a great part of the vessels of this system, in which fluids differing from the blood move and oscillate in different directions. Then, where the blood especially enters, as in the muscles, the mucous surfaces, &c. a considerable portion of this fluid, its colouring matter particularly, is in a combined state, and not in a state of circulation. If we cut a muscle transversely in a living animal, inspection proves clearly this phenomenon, which, joined to the preceding, diminishes immediately more than half the blood, which at first appears to move in the general capillary system.
Yet it is evident, that there remains much more of it constantly in this system than in the pulmonary; to be convinced of this, it is only necessary to cut the lungs of a living animal. From this it is clear, that if the heart presided over the motion of the blood in the general system, and that consequently all that is contained in it was driven into the veins at each pulsation, the pulmonary capillaries would be insufficient to transmit it; but there goes out only a certain quantity, proportioned to what the lungs can receive. It is nearly the same as when the veins are much dilated, and consequently contain much blood; no more arrives at the heart, because, as I have said, the velocity is then in the inverse ratio of the capacity.
Besides, many causes continually divert the blood of the general capillary system from the direction which carries it from the arteries to the veins; these causes are especially the exhalations, secretions, and nutrition. This capillary system is, as I have observed, a common reservoir, whence the blood is carried into different and even opposite directions, on one part in the direction of the veins, on another in that of the exhalants, on another in that of the excretories, on another, in fine, in that of the nutritive vessels. On the contrary, in the pulmonary capillary system, there is but a single impulse, and a single direction; it is that which carries the blood from the artery to the pulmonary veins, which nothing draws off in its course; for in passing from the black to the red, this fluid serves no other function; it has no vessels, but the pulmonary veins, towards which its motion is directed. There is, then, this great difference in the blood of the pulmonary capillaries, and that of all the other parts, viz. that the first is moved only in one direction, that all which arrives in the lungs goes immediately in this direction; whereas the second has four or five different directions. Hence this last necessarily oscillates and varies in its motions, according as it is called more or less powerfully by the exhalants, the excretories, the nourishing vessels, or the veins; whereas the other, having but one way to escape, follows it constantly and uniformly. Let us not be astonished, then, at the disproportion there is in the capacity of the two capillary systems.
The proximity and distance of the heart are also a real cause that tends to establish the equilibrium between the two systems. We have seen, in fact, that each contraction of the left ventricle impresses a sudden motion upon the whole mass of blood contained in the arteries, and at the instant that this mass increases on one side, it is diminished on the other by the quantity that is sent to the capillaries of the whole body; so that the arterial motion is not progressive, but sudden and instantaneous, so that at the same time the column of aortic blood increases towards the heart, it diminishes in its remote ramifications, and the fluid driven from the heart at each contraction, does not arrive at the capillaries until after many contractions, since that which goes from this organ cannot arrive at these vessels until all which is before it has reached them. The same phenomenon precisely takes place as it respects the black blood in the pulmonary artery. Then the longer the course, the longer is the time that is required for the blood to arrive at the capillaries, and consequently to pass through them; then the blood from the right ventricle would arrive much sooner at the left auricle, than that would at the right auricle which goes from the left ventricle; then, though in what we call the small circulation, the velocity is not greater, the space passed over being less, the time employed to go over it is also less; then, the excess of the fluid contained in the divisions of the aorta, in the general capillary system, and in the general veins, over that contained in the pulmonary artery, veins and capillary system, is compensated by the time the second takes to go its course, which is short in comparison to that of the first.
Hence we see, why in animals in whom the lungs, as to their circulation, are in opposition to the rest of the body, nature has constantly placed this organ at the side of the heart. If one of these organs was at the head, and the other at the bottom of the pelvis, the harmony would be inevitably interrupted.
II. Remarks upon the Circulation of the Pulmonary Capillaries.
Since the blood of all the parts constantly goes through the lungs, it is evident that an injury of the functions of this viscus would be felt in all the parts. The phenomena of asphyxia prove that this in fact takes place. It is in this way that the lungs are immediately connected with life, and hence the ancient physicians placed its functions among those which they called vital.
We understand also why pulmonary inflammations have so peculiar a character; why they are distinguished from others by many phenomena. No internal organ is more often inflamed than the lungs. If experience did not prove this at the bed-side of the patient, the examination of dead bodies would be sufficient to convince us of it. We find in fact around the lungs, very often traces of old inflammations, particularly adhesions of the pleura; a phenomenon so common, that I am confident that there are more dead bodies found with it, than there are without it. This is an essential difference of this membrane that distinguishes it from all analogous ones, a difference that arises from the proximity of the pleura to the organ that it covers. Different causes contribute to this very great frequency of pulmonary inflammations. 1st. The lungs are, among the internal organs, the most exposed to direct irritations, either by the air that constantly enters them and can irritate them, or by heterogeneous substances that it introduces, or especially by the changes of heat and cold that it occasions. 2d. These organs are connected by the most numerous sympathies with the other systems, the cutaneous, for example; so that perhaps, as it respects inflammation, a suppression of transpiration has as much influence upon the lungs alone, as upon all the other organs together. It depends no doubt upon this that the lungs correspond with all the others by their capillaries.
When the lungs are inflamed, is it the red blood of the bronchial artery that flows to the irritated place, or the black blood of the pulmonary artery? I think that it is difficult to decide this question by experiment; but examination after death appears to prove that the second performs an important part in it. In fact, this viscus is often crowded so suddenly, that we can hardly believe that the first would be able to furnish the blood. Sometimes, though it is not always the case, we can trace as it were, the progress of this crowding by percussion, which is infinitely less sonorous in the evening than the morning. There died a short time since a patient under my care in the hospital, in whom this difference was perceptible from hour to hour. The progress is much less rapid, no doubt, in the greatest number of cases; but in those the black blood has undoubtedly contributed to the crowding of the lungs.
No organ in the animal economy acquires by inflammation, so great a size in so short a time, and such excessive weight, as the lungs. All who open dead bodies know this. Observe the lungs of one dead of pneumonia; cut them, and you would say at first that they were solid; they often look like liver, they exhibit the appearance of such a heavy mass; but macerate them and soon the whole will escape in fluids. Now examine comparatively the skin, the stomach, the liver, the kidnies, &c. when they have been the seat of acute inflammation, that has destroyed the patient; they have nothing approaching to this enormous increase of fluid, which is seen in the substance of inflamed lungs. Not only the cavity of the cells is full, but the organ is also much dilated. I have often had occasion to open those who have died of pneumonia, in whom one of the lungs was entirely sound; now, the disproportion of weight between it and the affected one, was incomparably greater than that between an inflamed kidney and a sound one.
This phenomenon evidently arises from the fact, that the lungs alone receive as much blood as the whole body, so that when an inflammation of this viscus interrupts the course of the fluids, a very great quantity of them can accumulate there in a given time. It is not however, properly speaking, the blood that is found crowding the lungs in pneumonia; the fluid appears whitish when pressed out; we should say that it was a kind of pus. Much has been said of vomicÆ after pneumonia; but they are extremely rare; there is almost always effusion in the lungs; the fluid is not collected in a sac.
In pulmonary inflammation, does the blood pass through vessels that do not ordinarily circulate it, as happens so evidently upon the serous surfaces, or conjunctiva, &c. when inflamed? I do not think it does, for we do not know any vessels in the lungs, except the sanguineous. It appears evident that the blood or the other fluids are effused into the pulmonary texture, in which they are deposited by exhalation. There is no doubt that in some phlegmons, this fluid passes, as I shall say, into the cells of the cellular texture; now it appears that it happens here in the same way. By breaking or cutting inflamed lungs, we see clearly that its whole texture is crowded, and filled; whereas in examining an inflamed serous surface, we see that the blood is evidently contained in the capillaries.
It is a great mistake to try to represent inflammation as being everywhere the same, as exhibiting always the fluids, like their vessels, in the same state. Boerhaave for example thought, that there could be no inflammation without an error loci. There is according to the state of the parts, their structure, their vital properties, a thousand different modifications in the new anatomical order that this affection gives to the organs.
What constitutes the essence of inflammation is, 1st, the irritation of the inflamed part; 2d, the new modifications that its vital forces have taken in consequence of that irritation; 3d, the consequent stagnation of the fluids around it. But in what manner the fluids are arrested; how they stop in the capillary system; how they are taken up by the exhalants; how they are poured out, in extravasations, &c.; these are different effects that arise from the different organization of the parts; but the principle is always the same, it is always the same disease. If we could analyze thoroughly the state of all the systems in inflammation, we should see perhaps, that there was a difference in the inflammation of each. Besides, the diversity of the symptoms that it exhibits, a diversity of which I have already spoken, proves that the state of the solids and the fluids are not the same.
How is it that the blood can pass through the lungs of phthisical patients, in whom this organ is reduced nearly one half? I would observe upon this subject, that the blood in the great vessels is diminished in proportion to the ulceration of the lungs. The diminution of this fluid is remarkable in many organic affections, but especially in these, as Portal has observed. If a phthisical patient in the last stage had as much blood, as before the disease, the circulation certainly could not go on, or at least there would be a constant reflux towards the right auricle. Who is ignorant of the small pulse, feeble though frequent, particularly towards night, in phthisis? Compare it with the pulse of an inflammatory fever, in which there is evidently plethora; you will see that they are really the two extremes.
I will make a general observation upon this subject, it is this, that when the forces are weakened in our organs, or life languishes in them, the blood is diminished almost continually in proportion; so that this fluid being considered in the capillary system, as the resistance opposed to the power of the small vessels, the proportion remains always the same between this power and this resistance. It is necessary that the whole should be in relation. If blood was transfused into a phthisical patient, he would die, because the forces of the solids would not correspond with the increase of action to which they would be forced.
The circulation of the pulmonary capillaries, is, like that of the others, under the influence of the tonic forces of the part, and not under that of the impulse of the heart. This impulse terminates at the extremity of the branches of the pulmonary artery. In inflammation then of the lungs, the blood is not mechanically arrested in this organ; then, when you bleed, it is not to diminish the vis À tergo. You might draw ten basins from the patient, but the lungs most commonly would not empty themselves; they would be less fatigued by the entrance of the blood; but that which was stagnant in the capillary system would still remain there. So long as there is a point of irritation, it will be, if we may so say, a magnet which will attract the blood, and completely change its direction; which was before from the artery to the veins, it will now be only towards the irritated point. Bleeding acts then, 1st, by diminishing the blood that enters the lungs, and consequently by lessening the fatigue of this diseased organ; 2d, by diminishing the irritation of the solid, which attracts the blood, and retains it around the irritated place.
The constant excitement that the air gives to the pulmonary capillary system is favourable to its circulation; but the blood can traverse this system without this excitement, as is proved by my experiments mentioned elsewhere.
III. Alteration of the Blood in the Pulmonary Capillaries.
There takes place here the reverse of what happens in the general capillaries; the fluid changes from black to red. We have already some data upon the causes of this phenomenon; but I think new experiments should be made before a thorough explanation can be given. This is so much the more necessary, because if we knew how the black blood becomes red, it would seem that we might know how the red becomes black.
I have stated the phenomena of this change of colour in my work upon Life and Death; it would be superfluous to repeat them. There will be found there also many details upon the circulation of the two capillary systems, which I shall not mention here.
IV. Remarks upon the state of the Lungs in Dead Bodies.
I will only corroborate here a remark already made in the same work, upon the extreme frequency of pulmonary congestions in the last moments of life. As the lungs alone receive the whole blood of the body, when their forces are weakened, the blood stagnates and accumulates in them; so that according to the state of their forces in the last moments, and the disease, these organs will be more or less heavy, and more or less full of blood. We hardly find them twice in the same state. All subjects that die in pain have these congestions. Thus compare the lungs of dead bodies in our dissecting rooms, with those of animals killed in slaughter-houses; they are entirely different. The organization is almost always concealed in the first by the fluids that crowd them. We cannot study this organization well except in subjects that have died of hemorrhage or syncope. In most others, it is impossible to distinguish any thing. Hence no doubt the reason that we know as yet so little of the intimate structure of this important viscus, as the description I shall give of it will, I hope, prove. I have shown elsewhere how we can at will accumulate a greater or less quantity of blood in the lungs of an animal, by the way in which we kill him.
No other organ in the economy exhibits these extreme varieties of congestion at the moment of death, in so evident a manner at least, because no one is a centre of circulation, like the lungs; the liver even is not an exception, as I have observed. In this respect, those who open dead bodies, and examine the state of the lungs, should carefully distinguish the congestion that arises from the disease, from that which may be perhaps the effect of the interruption of the circulation in the last moments. I suppose two affections of the chest exactly similar in their nature, duration and the two subjects they attack; that syncope terminates the life of one of them; that that of the other is closed after long distress, in which there is what is called the rattles; the lungs of the second will certainly weigh much more than those of the first.
It is very probable that during life, the lungs are in very different degrees of congestion. We know that most chronic diseases of this organ occasion, when the patients take rather violent exercise, a sense of suffocation, oppression, &c. which appear to be owing only to the superabundance of blood, which, not being able to pass through this viscus as fast as it is sent there, is stopt, and checks the entrance and exit of the air.
It is only the diseases of the lungs and heart that are accompanied constantly with these oppressions, and sense of suffocation. This is seen in this last organ in aneurisms, sometimes in ossifications, &c.
