Part 6

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.