Part 6

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.