In the organs in which the blood, or the white fluids differing from it, alone enter, there can be no variety in the proportions; but the varieties are frequent in those where these fluids enter at the same time. In the serous, the dermoid, the mucous systems, &c. there are sometimes more, sometimes less small vessels filled with blood; the cheeks, of which I have spoken, are a remarkable example of this. The least emotion, the slightest agitation, or a motion a little too violent, accumulates, diminishes, and varies, in a thousand different ways, the quantity of blood in them. The whole exterior of the skin exhibits the same phenomenon, though less frequently. When this organ is irritated or excited at any point, it immediately reddens; it becomes white if it is compressed. Cold and heat uniformly produce analogous varieties, when the change from one to the other is sudden. All the mucous surfaces exhibit the same arrangement; see the glans in the erection of coition, or in the flaccidity that succeeds it; the difference in the quantity of the blood that this external membrane contains, is very evident. Lay bare a serous surface; at first white, soon there will be numerous red streaks. If we could see the capillaries of the glands, I presume that we should find the quantity of blood variable in these vessels, and that during the time that the secreted fluids are poured out in abundance, their system would be more copiously supplied than at any of the time when it furnishes the materials of the secretions. Why are not the kidnies and the liver subject to the same varieties in the quantity of their blood, as the surface of the skin? When, by a violent motion, sweat pours out in abundance, and the external surface of the body looks more red, does it not indicate that the blood is there in a greater proportion?
There are two things to be distinguished, however, upon this subject; it is only when the copious secretions arise from an increase of life, that a greater afflux of blood is supposed to take place in the glandular system. When this increased secretion proceeds from a want of vital energy, the blood is not in greater quantity in the gland. The same observation applies to exhalation; thus, in the above case, in the commencement of fever, &c. more blood enters the skin; but when the sweat arises from weakness, as in phthisis, &c. there is not this accumulation of blood in the capillary system. But this deserves a longer explanation.
Different proportions of Blood in the Capillaries, according as the Secretions and Exhalations are active or passive.
I call those exhalations and secretions active, which are preceded and accompanied by an evident development of vital forces; and those passive which exhibit an opposite phenomenon. If we examine the phenomena of the animal economy, it will be easy to see this distinction, which appears to me essential in diseases; now, in whatever organ you study it, you will always see every active exhalation or secretion preceded by a greater afflux of blood to the part; all passive exhalations and secretions present an opposite phenomenon. Let us begin with exhalations.
1st. Cutaneous exhalation is active from violent running, or a paroxysm of fever, as I have said, from the action of caloric upon the body, hard work, &c.; the skin is then more expanded and deeper coloured; more blood enters it, &c. This excitement of the skin makes it more fit to be influenced by external agents, and to influence in its turn all the other organs. It is the suppression of these transpirations which causes so many accidents in the animal economy. Observe, on the contrary, the complexion of the body in phthisical sweats, in those produced by internal suppurations, in those that are the effect of fear, in all those that are called colliquative, &c.; this complexion is more pale than in a natural state; it is not capable of being influenced, because its vital activity is then small, and its forces languish.
2d. In the exhalations of the serous surfaces, there are some that are essentially active; such is that of pus; for we shall see that the formation of this fluid upon these membranes is without any kind of erosion, that it flows evidently from the exhalants, instead of serum; very often even it flows at the same time. Nothing is more frequent, in fact, than the milky or purulent serum that is found in the peritoneum, the pleura, &c. whether the fluids are exactly mixed, or the pus floats in flakes in the serum. Now this active exhalation of serum or of pus, which appears to be here principally coagulated albumen, this exhalation, I say, is evidently preceded by a considerable accumulation of blood in the capillary system, an accumulation which constitutes inflammation, and without which exhalation cannot take place. Observe, on the contrary, serous exhalation, increased by the weakness that any organic disease gives to the serous membranes; to furnish this fluid, the blood is never accumulated in them in greater quantity. Open the membranous sacs, after the diseases of the heart, the womb, the lungs, the liver, the spleen, &c. you will find them full of water, but more diaphanous than usual, because they have received less blood.
3d. What I have said of the serous exhalations, must be said of the cellular; some of them are active, such as those of pus and the serum that sometimes accompanies it; others are passive, as the leucophlegmasia after organic diseases. The same observation is to be made as before; there is an accumulation of blood in the capillary system in the first kind, a diminution of this fluid in the second. Observe the fatty exhalation; a man in health who is very fat, has a rosy colour upon the integuments distended with fat, which indicates the abundance of blood in the capillary system. On the contrary, in certain cases of sudden corpulency after diseases, in that which is called false fat, and accompanies weakness, a general paleness corresponding with the fatty bloating, indicates the absence of the sanguineous fluid.
4th. Mucous exhalations present also an analogous phenomenon. I shall prove soon that the hemorrhages from the mucous surfaces are real exhalations; now some of them are active, a name which Pinel has given them in his Nosography; these are the nasal, pulmonary, gastric, uterine hemorrhages, &c. of young people and even of adults. All these hemorrhages are accompanied by a local increase of action, by greater heat, by a deeper colour of the mucous membrane, by the greater abundance of blood in the capillary system. Who does not know, that Galen predicted a hemorrhage from the redness which he saw upon the nose and the eye of the patient? On the other hand, observe the hemorrhages of the mucous surfaces, which take place after long diseases, hemoptysis, which terminates the diseases of the heart, hematemesis, the effect of organic derangement of the liver, hemorrhages from the intestinal canal, so frequent at the end of all the long organic diseases of the abdomen, &c. nasal hemorrhages in certain low fevers, those which take place in scurvy from the different mucous surfaces, the gums especially, &c. all these hemorrhages, which are truly passive are not accompanied by this preliminary sanguineous congestion in the capillaries, by this increased activity of vital action; it might be said that it is the blood, which transudes, as in the dead body, through the pores, that have not power to retain it. This distinction is so true, that without making a theory of it, physicians conform to it in their practice. We bleed to arrest an active hemoptysis, but would you bleed to stop that which comes on in the chronic diseases of the thorax? The same observation applies to all the hemorrhages; they require means wholly opposite, according as they are active or passive; a remark moreover that is applicable to all diseases that have increased exhalations or secretions, whatever may be their seat. It is not the phenomenon that we are to resist, but the cause that has produced it. We diminish the forces, when serum is accumulated in the thorax, from a pleurisy; we increase them, when it accumulates from a disease of the heart, the lungs, &c.
What I have just said of exhalations applies to secretions. The mucous glands pour out a greater quantity of fluids in two ways, sometimes from irritation, sometimes from the want of force. When this happens in the intestines, there results from it in the first case a diarrhœa from irritation, in the second a colliquative one. Now it appears that the blood enters the gland in greater abundance in the one than the other case. Its increase takes place undoubtedly in most acute catarrhs, in which there is active secretion of mucus; its diminution or at least its want of increase is not less sensible in many chronic catarrhs, in which we may consider the secretion as passive. We know that the abundance of urine, of bile, sometimes supposes an increased, sometimes a diminished action of the kidney and the liver. Is there not a superabundance of semen from excess of vitality, and an unnatural flow from weakness? All the secreted fluids have the same arrangement; now according to these two opposite causes of the superabundance of the secreted fluids, the capillary system of the glands is certainly penetrated with a different quantity of blood. Though the phenomenon be the same, the treatment in the diseases in which it is manifest, is as in the preceding cases, wholly opposite, according as the local increase or diminution of life concurs to produce it.