Chapter II: Part 2

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 fœtus. 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.