Chapter III: Part 3

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.

EXHALANT SYSTEM.

Exhalation and secretion are two functions, analogous in this, that both of them separate from the blood fluids differing from it, and pour them upon surfaces where they serve different uses. But the following are their differences.

1st. In exhalation, there is no intermediate organ between the arteries and the exhalants; a capillary net-work alone separates them; whilst on the contrary there is always an intermediate organ between the excretories and the arteries; it is in this organ that the capillaries are found, in which the second begin and the first terminate. 2d. The organized machines which elaborate the secreted fluids are then much more complicated than those which separate the exhaled fluids. Thus the bile, the urine, the saliva, &c. differ on the one hand essentially from the blood, and are on the other much compounded; whilst the serum, &c. closely resembles some parts of the blood, and is but slightly compounded, containing but few elements. This double distinctive character of the two kinds of fluids appears to me to be very striking. 3d. The exhaled fluids are poured out by an infinity of small tubes separate from each other; the secreted fluids, on the contrary, are collected in one or more principal tubes that pour them on the surface where they terminate. 4th. The exhaled fluids re-enter in great part into the circulation, after having been thrown out; the secreted fluids, on the contrary, appear to be especially destined to be rejected. 5th. Many parts receive the first fluids; they are deposited upon the serous, mucous, synovial and cutaneous surfaces, in the cellular texture and even in all the organs of nutrition. The mucous and cutaneous surfaces, the first especially, are the only ones upon which the others are poured out.

It follows from all these considerations, that the exhaled fluids, as the fat, the serum, the synovia, the marrow, &c. differ essentially from the secreted fluids, as the bile, the urine, the saliva, the mucous, prostate, spermatic, pancreatic fluids, &c. This difference appears to have struck a great number of authors; yet most of them have made use of the term secretion to express the separation of the exhaled fluids from the mass of blood. I think that there is much analogy between exhalation and secretion. In both, there is the capillary system, as I have said, between the vessel that brings and that which carries away; but the capillary system is certainly arranged very differently in a gland, from what it is in a serous surface; for example, wherever there is exhalation, there is certainly nothing but the capillary system; but where there is secretion, the secretory organ is too considerable not to admit of something more. Besides, by trusting to inspection, and without wishing to examine the intimate nature of the organs, it is evident that where there is secretion, there is a gland, and that this gland is wanting where there is exhalation.

ARTICLE FIRST.

GENERAL ARRANGEMENT OF THE EXHALANTS.

I. _Origin, course, and termination._

Authors have formed very different ideas concerning the exhalants. We know the decreasing vessels of Boerhaave, and the error loci for which his imagination created these vessels. Lately all the white vessels continuous with the arteries have been rejected, and in order to explain exhalation, recourse has been had only to inorganic pores in the arterial parietes, through which the fluids transude upon the organs. Frequent observation of similar transudations upon the dead body, as those of the bile through the gall-bladder, of the marrow through the osseous texture which it discolours, &c. is one of the great supports of this method of explaining the exhalant system. But we have already many times observed, that these phenomena never take place during life, when the organic sensibility of the parts refuses to produce them. Besides, exhalation is evidently subjected to the influence of the vital forces, since it varies continually in a part, according as the vital forces of the part themselves vary. Moreover, if the exhaled fluids escaped through inorganic pores, it would be necessary that not only the vascular parietes, but also those of the serous surfaces which receive these fluids, should be perforated with small holes; why then would not these fluids, of which these surfaces are the reservoirs, transude into the neighbouring cellular texture? Let us reject then every opinion that disregards anatomical observation, and let us endeavour by this observation to ascertain what the exhalants are.

It is undoubtedly difficult to form a precise idea of these vessels, their extreme tenuity constantly conceals them from us in a natural state. Yet by the aid of experiments and accurate reasoning, it appears to me that we may come at some degree of accuracy.

We have seen that the existence of a capillary system terminating the arteries, is in the parts where exhalation takes place as in the others, a thing incontestably proved by experiment with injections, by inflammations which arise spontaneously, and by those that are produced at will; so that a serous, cutaneous surface, &c. on which nothing appears, is covered with an infinity of little vessels suddenly in the first case, and at the end of a longer or shorter time in the second.

If the injection is not pushed very far, it is confined to the capillary system; but if it succeeds, it pours from all parts upon the surface, where exhalation takes place in the ordinary state. This dew mechanically produced, evidently resembles that which the tonic force of the parts occasions during life; for, as I have said, if it was a transudation, there would be extravasation in the neighbouring textures, whereas nothing is filled from the syringe which propels the injection to the exhalants that pour it out, except the arteries, the capillaries and these exhalants. Besides, when there is active hemorrhage, the capillaries from which arise the exhalants that pour out the blood, are evidently more full of fluid than ordinary, as I have already remarked.

From these considerations and many others that will be explained hereafter in this system, I think that we may consider the exhalants as arising from the capillary system, by means of which they are continued with the arteries, which bring them the materials of exhalation.

But to say what is the length of these vessels, what their form, what course they run, is evidently impossible; it is here that the imaginary descriptions begin. We distinguish with difficulty their orifices. We see upon the skin many little pores that evidently form communications from within to without; but these pores transmit not only the exhalants, but also the absorbents, the hair, &c. as we shall see in the dermoid system. 1st. The existence of the exhalants; 2d, their origin in the capillary system of the part where they are found; 3d, their termination upon different surfaces, are upon the whole all that is accurately known.

The mode of origin undoubtedly varies, but we do not know how it takes place. The exhalants are continued with their capillary net-work, in such a manner that we cannot say precisely where one finishes and the others begin. Hence why often in this work, in speaking of these small tubes, I suppose them to come immediately from the arteries, and forming the capillaries by their interlacing; this is evidently sufficient to understand what will be said hereafter.

II. _Division of the Exhalants._

There are three classes of exhalants which I distinguish by the fluids or the substances they furnish.

The first class contains those that throw out the fluids not destined to enter the economy again; such are, 1st, the cutaneous exhalants that pour out the sweat; 2d, the mucous exhalants that furnish a part of the pulmonary perspiration, the greatest part being formed, as I shall say, by the dissolution of the mucous fluids of respiration, which yield perhaps the gastric, intestinal juices, &c.

In the second class are found the exhalants, that throw out fluids that remain for some time upon certain surfaces or in certain cells; and which afterwards taken up by absorption, re-enter the circulation through the lymphatics. These are, 1st, the serous exhalants which deposit upon their respective surfaces the serum which lubricates the membranes and facilitates the motions of the organs they cover; 2d, the cellular exhalants which pour out into the cells, on the one part serum, on the other fat; 3d, the medullary exhalants which carry into the middle of the bones the juices of the same name; 4th, the synovial exhalants which deposit the synovia, either upon the articulations, or in the tendinous grooves.

The third class contains the exhalants that carry to all the organs the nutritive substance that repairs them, and which is afterwards taken up by absorption, to be replaced by new substances.

I adopt in my course of physiology the division I have just pointed out, to explain the different exhalations, of which the last evidently leads me to speak of nutrition, a function which is the general end of those that form organic life. We can represent in the following table, all the different exhalations; it presents the assemblage of the organs that execute them.

┌1st. exterior, ┌1st. Dermoid.
│ open upon │
│ the systems, └2d. Mucous.
│ ┌1st Serous.
│ │2d. Cellular, ┌1st. Serum.
│ │ where they │
EXHALANTS.│ │ pour out, └2d. Fat.
│2d. interior, │ ┌1st. of the short, flat
│ open upon │3d Medullary. │ bones, and the extremities
│ the systems, │ │ of the long ones.
│ │ │2d. of the middle of the
│ │ └ long bones.
│ │
│ │ ┌1st. of the articulations.
│ └4th. Synovial.└2d. of the tendons.
│
└3d. nutritive. Each organized texture has its own
exhalants.

This is an accurate table of all the fluids that go out of the blood, without the intervention of the glands, and by the way of exhalation. The two first classes have vessels, as is accurately proved by experiment, observation and even inspection. As to the nutritive exhalants, there is no doubt but that new substances are continually carried to the organs to repair them; now it is necessary that these substances should have vessels; these vessels certainly cannot draw what they deposit in them, except from the capillary system in which they terminate. If injections or other means do not accurately prove the existence of these exhalants, it seems to me that this reasoning forces us to admit them.

Physiologists had not hitherto collected together all the exhalations; each was explained in treating of the system where it was found. I have thus given reflections upon each in the exposition of the different textures; the arrangement of the general anatomy required it; but in works or in lectures on physiology, they ought evidently to be presented under the same point of view as absorptions.

III. _Difference of the Exhalations._

Though we know not what is the structure of the exhalants, yet we cannot doubt but that this structure differs remarkably in the different systems. Observe in fact that these vessels enter, as it were, like elements into the textures they compose, and that consequently they must necessarily partake of the different and distinctive characters which these textures exhibit.

It is to this difference that we must refer without doubt what we see in injections. They go out, if they are fine, by the mucous, serous and even cellular exhalants; but those which furnish the synovia, transmit them with much more difficulty; it is the same in the capillary system; whilst the serous surfaces in this system are filled with great ease, and blackened by injections, as it were at will, the synovial surfaces are penetrated with much more difficulty.

ARTICLE SECOND.

PROPERTIES, FUNCTIONS, AND DEVELOPMENT OF THE EXHALANT SYSTEM.

I. _Properties._

The vessels of the exhalant system are too delicate to allow us to analyze their properties of texture. Do they enlarge when the red globules enter them? I am wholly ignorant. Haller, who admitted that there were exhalants, thought that white fluids alone entered them, because their diameter was disproportioned to that of the red globules. This opinion is also that of the school of Boerhaave. Who has ever measured comparatively the respective diameters of the vessels and the particles of the fluids? All such expressions, as fine fluids, coarse fluids, &c. which are still used by many physicians, have originated from this theory and are still used, though the theory itself has been admitted to be false. I have said twenty times, and I again repeat it, that the only cause which prevents the red globules from passing into vessels with white fluids, is the want of relation between the nature of the fluid and the sensibility of the organ.

The properties of animal life have evidently no connexion with the exhalants. Of those of organic life, they have in the highest degree those of organic sensibility and the corresponding insensible contractility; it is upon these that all their functions depend.

_Characters of the Vital Properties._

Though organic sensibility is everywhere given to the exhalants, it varies however remarkably in each system; that of the mucous exhalants is not the same as that of the serous. In general the exhalants entering as it were like elements into the texture of each system, partake completely of the organic properties of that system; or rather their properties are the same. Hence, 1st, why each separates the fluid that is peculiar to it; why consequently, when much water is introduced into the circulation by drinking, the cutaneous exhalants, and never the serous, appropriate it to themselves, and transmit it out of the blood; when we run much and a general agitation is consequently given by the heart to the mass of blood in circulation, the cutaneous exhalants, being more powerfully excited by this impression than the serous, the synovial, &c. separate more sweat; 2d, why the serous do not pour out fat, the medullary serum, &c. though the mass of blood that enters the capillaries that are continuous with these exhalants, is everywhere the same; 3d, why when the exhalants pour out fluids that they are not accustomed to, or when their natural fluids are altered, these fluids differ essentially from each other; why, for example, after inflammation, it is only upon the serous surfaces that we see a milky serum; why nothing resembling pus flows from the inflamed medullary membrane; why the fluids, the result of the inflammation of the synovial membranes, are very different from those that the serous surfaces produce, &c.; 4th, why certain exhalants have a much greater tendency than others to admit blood and pour it out upon their respective surfaces, of which we see an example in the mucous exhalants, which are so disposed to suffer this fluid to pass, that a thousand circumstances occasion hemorrhages from them; 5th, why among the mucous exhalants themselves, some have a much greater tendency than other to permit the blood to pass, &c. &c.

All these phenomena are evidently derived from the particular modifications that distinguish the organic sensibility and contractility in each kind of exhalants.

II. _Of Natural Exhalations._

What I have said will enable us to explain how exhalation is effected. It is by the same principle as that to which we have before referred; it is that which will serve for the explanation of secretions, absorptions, &c. There is between the elements which form each exhaled fluid and the organic sensibility of each kind of exhalants, such a relation, that these elements alone can be admitted by the vessels which reject the others, so long as there is no change in their kind of sensibility. The general capillary system appears to be the reservoir, in which, as I have said, the blood is elaborated; it is there that the red blood becomes black; it is there at the same time that its different elements are separated, combine anew, and during these changes disengage caloric. It is after these changes, these different transformations, that each exhalant takes, chooses as it were the portions with which its sensibility is in relation, and leaves the others.

It follows hence as a very simple consequence, that whenever the organic sensibility of the system in which exhalation takes place is altered in any manner, exhalation should also immediately vary; and this in fact always happens. There is never any derangement in the exhalations, without a preceding one in the sensibility of the exhalants. Take for example the different injuries of transpiration; you will see that cold, heat, dryness, moisture, frictions, &c. always exert their influence upon the cutaneous sensibility, and that the derangements of the exhalation are consequent to them.

The organic sensibility of the exhalants, like that of every other part, may be disordered in different ways, 1st, by a direct stimulant, as when cold contracts the skin, when a very cold fluid acts upon the stomach, &c.; 2d, by sympathies, as when the acute affection of the fibrous and muscular organs produces sweat in rheumatism; 3d, oftentimes without our being able to say how, a derangement takes place in the vital forces of a part; of this inflammation presents frequent examples. I do not allude here to that which takes place from the contiguity of organs, &c. &c.

It follows from this, that when exhalation is preternaturally increased or diminished, the sensibility of the exhalants is always modified in one of the three preceding ways.

Now if we reflect upon the different kinds of exhalants, we shall see that there are no others except the cutaneous and the mucous which are exposed to the immediate application of stimuli, since they alone are in relation with external bodies. Besides the two modes of alteration of sensibility that they share with others, they have moreover this. It is not then astonishing, that their exhalations, especially the cutaneous, exhibit such numerous varieties, that the skin is continually found varying between the greatest dryness and the most copious sweat.

The sympathetic exhalations are extremely numerous. I shall not give examples of them here; many may be found in the sympathies of the dermoid, serous, mucous systems, &c. I would only observe that authors have not sufficiently distinguished this kind of exhalations from the others; nor has sufficient attention been paid to sympathetic secretions.

The exhalations are never all increased or diminished at the same time; I except however the state of excitement at the commencement of some fevers, when all are suppressed. In every other case, when one fluid is abundantly poured out, the others are diminished; thus the skin is dry in dropsies. There is sweating in the first stages of phthisis pulmonalis; but when in the latter, dropsical effusions are considerable, sweating ceases.

I have moreover divided into two classes the causes of increased exhalations. 1st, One of these proves an increase of life; 2d, the other, a real diminution of the vital forces; hence active and passive exhalations. How can the same phenomenon arise from two causes exactly opposite? It is difficult to determine precisely; but so many phenomena prove this distinction of exhalations as well as secretions, that we cannot refuse to admit it. It is important to recollect this in the following article.

III. _Of Preternatural Exhalations._

I call by this name those, in which the exhalants pour out a fluid different from that which is natural to them. The first which offers is that of the blood.

_Sanguineous Exhalation._

The blood frequently passes off by the exhalants instead of their own fluids; hence arise hemorrhages very different from those that take place from rupture. I shall examine these hemorrhages in each kind of exhalants.

_Hemorrhage of the Excrementitious Exhalants._

The vulgar expression which is sometimes used, to sweat blood and water, &c. indicates that under certain circumstances, though they are very rare, the cutaneous exhalants give passage to the blood. Haller has collected a number of instances of it, that may be found in his work. The first year that I came to Paris, I saw constantly with Desault, a woman with a cancer of the womb, who had at certain periods sweats that stained her clothes as much as is ordinarily done by the catamenia. This woman had had frequent hemorrhages before the beginning of her disease. After these sweats commenced, they had continued but were more rare. I regret that I neglected to collect the particulars of this singular fact.

No exhalants pour out blood more frequently than the mucous; so that hemorrhages are an affection almost characteristic of the mucous surfaces, in which they have different names, according to the portion of them that are attacked. It is not my object to present here the phenomena of these hemorrhages; I only wish to prove that they are an exhalation.

1st. I have very often opened subjects that have died during a hemorrhage; I have had occasion to examine with this view the bronchial, gastric, intestinal and uterine surfaces; I have never seen the least mark of erosion, notwithstanding the precaution of carefully washing the surfaces, of letting them macerate and even examining them with a glass. 2d. The following experiment uniformly succeeds upon the wombs of women who have died during menstruation, and often even at other times; by pressing them, there issues from the mucous surface a greater or less number of little bloody drops, which evidently correspond with vascular extremities, and being wiped off, no erosion can be seen. 3d. The analogy of all the other open surfaces that pour out blood, and which evidently do it by their exhalants, is a proof that the same phenomenon has the same seat in the mucous surfaces. 4th. The womb would be only a mass of cicatrices in females of advanced age, if there had been a rupture in it in menstruation. 5th. In active hemorrhages, in which there is evidently a congestion of blood previous to its escape, we can conceive, to a certain degree of the rupture of the small vessels; but in passive hemorrhages, in those in which the organic sensibility being annihilated, seems to allow of a simple transudation through the exhalants, how can we conceive of these ruptures? 6th. We understand with difficulty how an evacuation, which is often produced with an extreme rapidity, which ceases in one place and immediately appears in another, which is subjected to all the sympathetic influences, we understand, I say, with difficulty how it can happen from rupture. 7th. Observe menstruation, furnishing sometimes for one moment blood, and not giving it the next, renewing twenty or thirty times a day, in certain affections, these alterations of flowing and ceasing to flow; it would be necessary then, that at each time the wounds should open and be cicatrized. 8th. Besides, compare hemorrhages evidently produced by rupture upon the mucous surfaces, such as those, which in wounds of the head, take place from the nostrils, the ears, &c.; those, which by a fall upon the rectum, sometimes happen from the bladder; those which, in too great efforts in coughing, arise upon the bronchial surface; those of which the stomach is the seat from the action of different poisons, &c. &c.; compare, I say, these hemorrhages, and many analogous ones that I could mention, with those that take place spontaneously from the mucous surfaces; you will see that they do not resemble them in their phenomena and their duration; that by suppressing them, they do not give rise to others; that they are independent of all kinds of sympathetic influence; that the passions have no effect upon their cessation or their production, whilst they have so powerful an influence upon the others.

Let us conclude from all these considerations, that all mucous hemorrhages, whether active or passive, are real exhalations. Hence you see that there is not so great a difference as might be thought, between the first and inflammation. In fact, in one there is an accumulation of blood in the capillary system, then the passage of this fluid by the exhalant vessels, that are continuous with this system. In the other, there is only the first phenomenon. Undoubtedly the signs, the circumstances, &c. are wholly different, because the modifications the organic sensibility undergoes are not the same; but the state in which the small vessels and the blood are respectively found, is not less analogous. One proof that in active hemorrhages, it is the organic sensibility which, differently modified, opens or closes the passage to the blood by the exhalants, is this, that almost always there are previous symptoms which continue for some time, and which evidently declare the disturbance that the vital forces, the organic sensibility in particular, experience in the part; we know the itching, the forerunner of nasal hemorrhages, the tickling and sometimes sense of heat which precede the pectoral. Sometimes, according to the varieties of alteration it undergoes, the organic sensibility at first permits serous fluids to pass, then bloody; this is what we see in menstruation, in which the exhalants oftentimes pour out serum for some minutes, then true blood.

In passive hemorrhages, the organic sensibility is without doubt diminished, as well as the tone or insensible organic contractility. We might say, that the small vessels were not able then to contract sufficiently to retain the blood; it is as in our injections which ooze from the mucous surfaces, because life no longer opposes their passage. Observe that when these hemorrhages are produced by an organic disease, it is almost always that portion of mucous surface nearest the organ, that is influenced by it. Thus in the last stages of disease of the heart or the lungs, the patients often spit blood; they pass it by stool, towards the termination of those of the liver, or even throw it up by vomiting, &c. The whole mucous system never loses its forces so as to pour out blood everywhere; it is only in a determinate part that it is weakened.

What disposes the mucous exhalants more than all the others to pour out blood? It appears to be because the capillary system whence they arise is constantly entered by blood, and the course is very short from this fluid when present in the capillaries to the mucous surfaces. This is so true, that those portions of the mucous system that have but little of this fluid in a natural state, as those of the sinuses of the face, of the ear, &c. are less subject to hemorrhages. I am confident, that if there were exhalants upon the muscles to pour out constantly a fluid upon the exterior of these organs, hemorrhages would be very frequent in them.

Hence we see that the mucous hemorrhages have nothing in common, but the extravasation of blood, with those which are the effect of hemorrhoids, and always suppose a rupture of the veins, with those that aneurisms or varices produce, with those that are the effect of a cut, of a violent concussion, &c. They form a class by themselves, and resemble those only that the exhalants furnish upon the other surfaces where they open.

If I should class hemorrhages, I should distinguish them, 1st, into those that come from exhalation; 2d, into those that are produced by rupture. I should place among the first the bloody sweats, the mucous, serous, cellular hemorrhages, &c.; among the second, those that accompany wounds, aneurisms, &c. In order to embrace in one view all the sanguineous evacuations that can happen in the animal economy, I think it absolutely necessary to adopt this division which moreover accords with the phenomena and treatment of hemorrhages. Would you bleed to arrest a hemorrhage from rupture? undoubtedly not; but you would bleed to check an active hemorrhage by exhalation, because by diminishing the mass of blood, you diminish the excess of organic sensibility which produces the hemorrhage; it is nearly the same as when we bleed for inflammation. It is certainly necessary that the hemorrhage should be stopped as it has been produced; it is necessary that the sensibility of the exhalants should return to its natural type before the blood ceases to flow. We do not bleed to draw the blood to another place, as has been said; if it was so it should be done in passive hemorrhages. Most of those who bleed much in hemorrhages, believe that plethora is the sole cause that produces them, that the vessels containing too much blood, require a part of it to be taken away; but there are many more cases of active hemorrhage in which there are no signs of plethora, than there are of those in which these signs exist. There may be a real deficiency of this fluid in the great vessels, but if the exhalants of a part are by their peculiar sensibility in relation with it, they will pour it out in as great abundance as if there was an excess of it. It is as in the increase of natural secretions, exhalations, &c. Whether there was plethora or not in the great vessels, when the local affection has raised the peculiar sensibility of the secretories or the exhalants, they would draw abundantly from the blood. The influence of plethora upon the increase of the different fluids which are separated from the blood, is evidently one of the remains of the opinions of Boerhaave. If the heart agitated everywhere the fluids, if it propelled the blood, the serum, &c. that go out by the exhalants, the, secreted fluids that go out by their ducts, this influence would necessarily be real; but since all the fluids going from the capillary system are necessarily beyond every action of the heart, as in their circulation, they are wholly under that of the organic sensibility and tone of the capillaries, it is evident that these fluids are independent of the quantity of blood contained in the great vessels and moved by the heart; that the alterations of the vital forces of the part are the sole causes of the different phenomena that their course exhibits.

Who does not know that feeble and delicate temperaments are often subject in women to a much more copious menstruation than those that are stronger, more vigorous, more sanguineous, as it is called? You will find many results in authors, upon the quantity of blood evacuated by the catamenia, and you will observe at the same time that these results do not resemble each other; why? because each womb has, if you may so say, its own temperament, which oftentimes does not correspond with the general temperament, because each is disposed consequently to a different kind of vitality. There is more or less blood then given at each menstruation, as it is given for a greater or less time, for some women have at first only a serous fluid, while others have blood immediately. I cannot repeat it too much, that every vital phenomenon is necessarily subjected to many irregularities, which arise from those to which the vital forces are themselves exposed. On the contrary, every physical phenomenon is almost immutable, because it is the nature of physical laws to remain always the same.

Hence we see how hemorrhages of the great arteries, which are under the immediate influence of the heart, should differ essentially from those of the capillary system and of the exhalants, whose phenomena are under the influence of the forces of the part where they happen, whether they arise from rupture or exhalation. Though in fact these two classes may be essentially different in their principal phenomena, as I have already said, yet they approximate, because the modifications of the vital forces of the part have a necessary influence upon them when they are in the capillary system. Thus astringents, tonics, styptics and other medicines which evidently act upon the organic sensibility and the insensible contractility, frequently stop hemorrhages of the capillary system. The contact of the air, by modifying these properties in wounds is even sufficient to produce this effect. On the contrary, ligatures alone can, in the great vessels, resist the powerful influence of the heart. All styptics imaginable may be heaped upon an open artery, and they would not check the effect of this influence. This then is the essential difference between the hemorrhages of the capillaries and exhalants, and those of the arteries, that every medicine which acts upon the organic sensibility and tone, can be advantageously employed for the first, whereas they have no effect upon the second. I go now to the sanguineous exhalations which are made by the recrementitious exhalants.

_Hemorrhages of the Recrementitious Exhalants._

The serous membranes are the frequent seat of hemorrhages. The examination of dead bodies incontestably proves it. Nothing is more common than to find in the peritoneum, the pleura, the pericardium, &c. a serum, reddish if a little blood is effused, very red if more, and even pure blood is found under certain circumstances.

I have made these observations in two different cases, 1st. After inflammations whether acute or chronic, especially the last. The serous sac then contains a greater or less quantity of blood, sometimes alone, more frequently mixed with serum, and now and then even with whitish and albuminous flakes. The previous inflammation seems to rank these hemorrhages among the active. 2d. Often at the end of organic diseases, in which the exhalations of serum increase almost uniformly in the serous sacs so as to produce dropsies evidently passive, a greater or less quantity of blood is mixed with this serum. What anatomist has not observed these bloody effusions in the pericardium, the pleura, &c.? I have observed that the tunica vaginalis and arachnoides are infinitely less subject to them than other similar sacs; I have never seen them in the last, and twice only in the first. I of course do not speak of the hemorrhages that are the effects of wounds of the head and in which the blood is effused between the two folds of the arachnoides.

I have carefully examined the internal surface of the peritoneum, the pleura, and the pericardium, after this kind of hemorrhages, produced either in consequence of the inflammation of the membrane itself, or of an organic disease; their surface has appeared to me to be perfectly sound, so that it is very evident that the exhalants have furnished blood, instead of the serum they threw out there before.

I compare a serous surface preternaturally pouring out blood after inflammation, with the active hemorrhages of the mucous surfaces. On the other hand, when the serous exhalants throw out blood at the end of organic diseases of the heart, the womb, the lungs, &c. it is certainly the same phenomenon, as when blood brought by the mucous exhalants, under like circumstances, is thrown off by spitting, vomiting, or stool.

Are there cases during life, in which the blood, poured out by exhalation upon the serous surfaces, is afterwards taken up by absorption? I believe that it may happen after inflammation, though we are possessed of no positive facts upon the subject. Cruikshank and Mascagni have seen the blood absorbed by lymphatic vessels, after wounds of the chest; why might not that happen after hemorrhages by exhalation, which takes place after those from rupture?