Part 7

Observe, in fact, that the alterations of heat in diseases are as frequent as those of the exhalations and secretions, and that they always present, like the first, a previous derangement in the vital forces. If chemists apply their theories to these morbid changes of heat, instead of considering them as a necessary consequence of the state in which the vital forces are then found, they will necessarily find in them an insurmountable obstacle.

When we run swiftly, when the blood is violently agitated in the paroxysm of fever, more caloric is disengaged than at any other time. Does this prove that it is the general circulation which contributes to the disengagement of caloric, and that it takes place in the great vessels? No more than a copious sweat proves that the heart drives it out. Strongly excited by the shock of the red blood which is suddenly increased, the capillary and exhalant systems are compelled to increase their action; now a double effect is the result; 1st, greater disengagement of caloric; 2d, increased exhalation.

If the heat is increased when respiration is hurried, it appears to depend only on this, that the latter is hardly ever accelerated, without the circulation being so too. This is so true, that if you make for a long time rapidly successive inspirations and expirations, the heat will not increase. Besides, why should the heat actually increase by the hurry of respiration? Undoubtedly because more air entering in a given time, the lungs would absorb more oxygen, and consequently, according to the opinions of the chemists, more caloric would be disengaged. But let them present more or less of this principle to the blood, it absorbs the same quantity. In ordinary inspiration the air contains much more than can pass into this fluid. When an animal is made to breathe it pure, the blood does not become more red, because the same quantity always enters it. So you may in vain put into the alimentary passages four times more nutritive substance than common, no more chyle will be formed, the lacteals will absorb no more; there will only be more excrements, or vomiting will take place.

The state of respiration has no influence then upon the actual heat of the body; it only contributes to it by constantly introducing a greater or less quantity of combined caloric. It is thus that animals which respire the most, have habitually the most caloric.

How can an animal, breathing a very cold air, eating aliments almost deprived of caloric, &c. in northern latitudes, have as much heat as in hot climates? It is not the free caloric contained in the parts, but the combined, which, being introduced into the blood with the foreign substances, furnishes the materials of that which is disengaged in the general capillary system. Now the combined caloric is absolutely independent of temperature. As much fire is elicited from the same stone by the steel, in the coldest as in the warmest countries.

All the caloric that is combined with the red blood is not disengaged whilst this fluid is passing through the general capillary system; there remains some of it still combined with the black blood. Hence why in the first moments of asphyxia, before death has taken place, though in consequence of the interruption of respiration, all the blood that comes through the arteries to the capillaries is black, the heat continues to be generated for some time. When the contact of the black blood has even interrupted all the great functions, those of the brain, of the muscles, the heart, the lungs, &c. it appears that the black blood then undergoes for some time, a kind of oscillation in the capillary system, by which it disengages a little caloric. Hence, why those who have died of asphyxia produced by charcoal, or hanging, animals killed in vacuo, apoplectics, &c. preserve their heat a long time after death, as all physicians have observed.

This phenomenon is not however peculiar to the case of which we are treating. In opening dead bodies at the Hotel Dieu, I have observed that the time in which they lost their animal heat was very variable; that a body continues warm a greater or less time, especially among those who have died suddenly of an acute affection, in the paroxysm of an ataxic fever, for example, or by a fall, for those who die of a chronic disease, lose almost immediately their caloric. The difference in the first is often three, four, or even six hours. This phenomenon arises from the fact, that whenever death is sudden it interrupts only the great functions; the tonic action of the parts continues for a greater or less time after. Now this action disengages a little caloric from the blood that is in the general system. Thus in violent deaths, absorption continues some time after death; thus the muscles still contract; thus perhaps the glands, take up for some hours, from the blood that remains in the capillary system, the materials proper for their secretion.

This inequality in the heat of dead bodies can only arise from the cause I have named; for when the disengagement of caloric has ceased in the body, that which remains in it becomes in equilibrium with that of the external air, according to the general laws of this equilibrium. Now these laws being uniform, their effect would be the same in every case. Hence then the phenomena related above, are evidently incompatible with any other theory than that which supposes the caloric to be disengaged in the general capillary system.

Sympathy has, as we know, the greatest influence upon heat. According as this or that part is affected, there is disengaged in others more or less of their fluid. An icy coldness often takes place in syncope. Ulcerations of the lungs produce a burning in the palms of the hands. In other affections, the head seems to be the seat of the greatest heat. In a fever frequently the patient is hot in one place and cold in another. How does all this happen? in this way; the affected organ acts sympathetically on the tonic forces of the part; these being raised, more caloric than usual is disengaged; it is precisely the same as in sympathetic secretions or exhalations. Whether the vital forces are raised by a stimulus directly applied, or by the sympathetic influence they receive, the effect that results from it is exactly the same.

It is necessary to distinguish this sympathetic increase of heat, from those that are produced by an aberration of perception, as when we think we are very hot or cold in a part, or experience even a sensation exactly analogous to those that are natural, though the part to which we refer this sensation may be in its natural state, there being neither more or less caloric disengaged in it. It is as when we think we feel pain in the amputated extremity of a limb. It is an aberration of perception; it is truly a sympathy of animal sensibility, whereas the preceding is a sympathy of insensible organic contractility or tone. It is this last property that is affected; the disengagement of caloric is a consequence; it takes place as usual, like the perception that indicates its presence. Another person's hand applied on the part, feels nothing new in the first case, of which I shall say more in the following systems; it experiences a warmer sensation in this. So if the effect of the sympathetic influence is to diminish the tonic forces, there will be a less local disengagement of this fluid, which will be equally perceptible to the individual and to any other person who applies his hand to the part. Diseases continually furnish us with examples of these phenomena in relation to heat, and no other theory than the one now given would be able to explain them.

There is a phenomenon that is as difficult to be well understood by this theory as any other; it is the faculty animals have of resisting external heat. Every inert body is of the same temperature as the medium which surrounds it. Every organized body on the contrary repels the caloric that tends to raise it to a higher temperature than its own. Perhaps this belongs to the laws of the propagation of caloric, of which we are ignorant.

It will be asked undoubtedly why in the ordinary state there is only disengaged a certain quantity of caloric, so as to produce an uniform temperature of a certain number of degrees of the thermometer. I answer that it is by the same cause that in the ordinary state the pulse beats nearly the same number of times in a minute, which makes common respiration consist of so many elevations and depressions of the ribs, &c. &c. It is one of those phenomena that belongs to the immutable order first established, and which it is impossible to explain. Only it appears that this immutable order depends upon the primitive type that has been impressed upon the vital forces, a type, which when nothing excites or diminishes them, produces always phenomena nearly uniform; but as a thousand causes make them vary, a thousand times the pulse, respiration, heat, &c. are capable of differing. I would observe however in regard to the last, that its variations are not so great as those of many of the other functions. Compare, for example, the ordinary quantity of secreted and exhaled fluids, with the increase that takes place under certain circumstances, the common state of the pulse with its exacerbations in many fevers, &c. you will see that between the natural and the morbid state there is often an enormous difference. The heat on the contrary, is never raised but a few degrees above the temperature of the body. When there appears by touching the parts, to be a great difference, the thermometer proves that it is in reality trifling.

I would remark, in concluding this article, that I have not sought to ascertain how the caloric is disengaged in the capillary system, what portion escapes, in what relation it is with the red and the black blood, &c.; none of these can be determined by experiment. Let us be content in our theories with establishing general principles, especially analogies between functions that are known, and those which we attempt to explain, let us attempt merely to offer some general views; but let us never hazard precise explanations. Some have endeavoured lately to determine accurately what quantity of oxygen is absorbed, what quantity goes to produce the water of respiration, what quantity of carbonic acid gas is formed, how much caloric is disengaged, &c. This precision would be advantageous if it could be attained; but no phenomenon in the living economy will admit of it, in the explanations which it occasions. Chemists and natural philosophers accustomed to study the phenomena over which the physical forces preside, have carried their spirit of calculation into the theories they have formed for those which the vital laws govern. But this should not be so. In organized bodies, the spirit of the theories should be wholly different from the spirit of the theories applied to the physical sciences. It is necessary in these last that every phenomenon should be accurately explained; that, for example, in hydraulics, all the portions of the fluids should be calculated in their motions; that, in chemistry, we should know the precise proportion and amount of each of the elements that are combined in the changes that bodies undergo.

On the contrary, every physiological explanation should give only general views, approximations; it ought to be vague, if I may use the term. Every calculation, every examination of the proportions of the fluids with each other, all precise language should be banished from it, because we yet know so little of the vital laws, they are subject to so many variations, that what is true at the moment we study a fact, ceases to be so the next, and the essence of the phenomena always escapes us; their general results only, and the comparison of these results with each other, should occupy us.

ARTICLE SECOND.

PULMONARY CAPILLARY SYSTEM.

I call by this name the assemblage of the fine and delicate ramifications, which serve for the termination of the black blood and the origin of the red, which consequently finish the pulmonary artery and give origin to the pulmonary veins. The capillaries between the bronchial arteries and veins have nothing to do with them, they have no communication, and evidently belong to the general capillary system.

I. Relation of the two Capillary Systems, Pulmonary and General.

In comparing the preceding system with this, it is difficult to understand how they can exactly correspond, how the pulmonary can transmit not only all that passes through the general, but also all the lymph that returns from the serous surfaces and the cellular cavities, all the chyle which enters by digestion, &c. &c.

It seems impossible at first view, that in the balance of the circulation, these capillaries can, constantly and regularly, keep in equilibrium with those of the rest of the body. By reflecting a little, however, upon the phenomena of this function, we see that the discordance is only apparent.

Though the general capillary system is everywhere spread out, yet the portion in which blood circulates is much more limited than at first appears. There is a great part of the vessels of this system, in which fluids differing from the blood move and oscillate in different directions. Then, where the blood especially enters, as in the muscles, the mucous surfaces, &c. a considerable portion of this fluid, its colouring matter particularly, is in a combined state, and not in a state of circulation. If we cut a muscle transversely in a living animal, inspection proves clearly this phenomenon, which, joined to the preceding, diminishes immediately more than half the blood, which at first appears to move in the general capillary system.

Yet it is evident, that there remains much more of it constantly in this system than in the pulmonary; to be convinced of this, it is only necessary to cut the lungs of a living animal. From this it is clear, that if the heart presided over the motion of the blood in the general system, and that consequently all that is contained in it was driven into the veins at each pulsation, the pulmonary capillaries would be insufficient to transmit it; but there goes out only a certain quantity, proportioned to what the lungs can receive. It is nearly the same as when the veins are much dilated, and consequently contain much blood; no more arrives at the heart, because, as I have said, the velocity is then in the inverse ratio of the capacity.

Besides, many causes continually divert the blood of the general capillary system from the direction which carries it from the arteries to the veins; these causes are especially the exhalations, secretions, and nutrition. This capillary system is, as I have observed, a common reservoir, whence the blood is carried into different and even opposite directions, on one part in the direction of the veins, on another in that of the exhalants, on another in that of the excretories, on another, in fine, in that of the nutritive vessels. On the contrary, in the pulmonary capillary system, there is but a single impulse, and a single direction; it is that which carries the blood from the artery to the pulmonary veins, which nothing draws off in its course; for in passing from the black to the red, this fluid serves no other function; it has no vessels, but the pulmonary veins, towards which its motion is directed. There is, then, this great difference in the blood of the pulmonary capillaries, and that of all the other parts, viz. that the first is moved only in one direction, that all which arrives in the lungs goes immediately in this direction; whereas the second has four or five different directions. Hence this last necessarily oscillates and varies in its motions, according as it is called more or less powerfully by the exhalants, the excretories, the nourishing vessels, or the veins; whereas the other, having but one way to escape, follows it constantly and uniformly. Let us not be astonished, then, at the disproportion there is in the capacity of the two capillary systems.

The proximity and distance of the heart are also a real cause that tends to establish the equilibrium between the two systems. We have seen, in fact, that each contraction of the left ventricle impresses a sudden motion upon the whole mass of blood contained in the arteries, and at the instant that this mass increases on one side, it is diminished on the other by the quantity that is sent to the capillaries of the whole body; so that the arterial motion is not progressive, but sudden and instantaneous, so that at the same time the column of aortic blood increases towards the heart, it diminishes in its remote ramifications, and the fluid driven from the heart at each contraction, does not arrive at the capillaries until after many contractions, since that which goes from this organ cannot arrive at these vessels until all which is before it has reached them. The same phenomenon precisely takes place as it respects the black blood in the pulmonary artery. Then the longer the course, the longer is the time that is required for the blood to arrive at the capillaries, and consequently to pass through them; then the blood from the right ventricle would arrive much sooner at the left auricle, than that would at the right auricle which goes from the left ventricle; then, though in what we call the small circulation, the velocity is not greater, the space passed over being less, the time employed to go over it is also less; then, the excess of the fluid contained in the divisions of the aorta, in the general capillary system, and in the general veins, over that contained in the pulmonary artery, veins and capillary system, is compensated by the time the second takes to go its course, which is short in comparison to that of the first.

Hence we see, why in animals in whom the lungs, as to their circulation, are in opposition to the rest of the body, nature has constantly placed this organ at the side of the heart. If one of these organs was at the head, and the other at the bottom of the pelvis, the harmony would be inevitably interrupted.

II. Remarks upon the Circulation of the Pulmonary Capillaries.

Since the blood of all the parts constantly goes through the lungs, it is evident that an injury of the functions of this viscus would be felt in all the parts. The phenomena of asphyxia prove that this in fact takes place. It is in this way that the lungs are immediately connected with life, and hence the ancient physicians placed its functions among those which they called vital.

We understand also why pulmonary inflammations have so peculiar a character; why they are distinguished from others by many phenomena. No internal organ is more often inflamed than the lungs. If experience did not prove this at the bed-side of the patient, the examination of dead bodies would be sufficient to convince us of it. We find in fact around the lungs, very often traces of old inflammations, particularly adhesions of the pleura; a phenomenon so common, that I am confident that there are more dead bodies found with it, than there are without it. This is an essential difference of this membrane that distinguishes it from all analogous ones, a difference that arises from the proximity of the pleura to the organ that it covers. Different causes contribute to this very great frequency of pulmonary inflammations. 1st. The lungs are, among the internal organs, the most exposed to direct irritations, either by the air that constantly enters them and can irritate them, or by heterogeneous substances that it introduces, or especially by the changes of heat and cold that it occasions. 2d. These organs are connected by the most numerous sympathies with the other systems, the cutaneous, for example; so that perhaps, as it respects inflammation, a suppression of transpiration has as much influence upon the lungs alone, as upon all the other organs together. It depends no doubt upon this that the lungs correspond with all the others by their capillaries.