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._