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Whether some sweat can be bloody.
One inquires further whether some sweat can be bloody.
1. It seems not. For nature acts against illness in three ways: namely, by dividing, digesting, and expelling. Therefore, digestion precedes expulsion. Therefore, sweat that has been expelled was previously digested. But the third digestion, from which sweat proceeds or by which it is expelled, proceeds by whitening. Therefore, no sweat is bloody.
2. In addition, the matter that is expelled from the body is threefold, according to the medical authorities: namely, the coarse matter through the anus, the moderate through a nasal discharge, and the thin through sweat. Since, then, blood is a thin material, it is not expelled through sweat.
The Philosopher says the opposite.
One must reply that sweat sometimes is bloody, and then it has a reddish or purplish color. And sometimes it is phlegmatic, and then it has a white color. And sometimes it is choleric, and then it is yellowish in color. And sometimes it is melancholic, and then it is black. The fact that the sweat may be bloody arises from two causes with respect to the body, and two with respect to the soul. With respect to the body, these are the thinness of the blood and the permeability [raritas] of the veins, and in respect to the soul these are a lack of digestive power and sadness or fear, because during sadness or fear the exterior members are abandoned without control, and this is why blood flows hither and thither and frequently exits through sweat, and therefore the sweat is bloody. And so too for the other humors.
1. To the first argument one must reply that in the normal order of things, digestion precedes expulsion, but nevertheless an irregular process often occurs or causes expulsion before digestion.
2. One must reply in the same way to the other, that a flow of blood that occurs from the nose is normal, but a flow of blood through sweat is irregular and contrary to nature; indeed, it is an illness.
Whether venous blood is thicker than arterial blood.
One inquires further whether venous blood is thicker than arterial blood.
1. It seems not. The more digested are thicker than the undigested, according to the Philosopher in the fourth book of On Meteorology. But blood in an artery is more digested, because there is more heat and spirit in an artery than in a vein, and these are the principles of digestion. Therefore, etc.
2. Moreover, it is the business of heat to thin and rarefy. But blood in a vein is hotter than in an artery, because the right side [of the body] is generally hotter than the left, and a vein proceeds from the right ventricle of the heart, whereas an artery proceeds from the left. Therefore, etc.
3. In addition, a person is bled from a vein and not from an artery. But this is only because blood from a vein can go forth with less pain and difficulty than blood from an artery, owing to its thinness. Therefore, etc.
The Philosopher says the opposite.
One must reply that blood in an artery is thinner than in a vein. And the reason for this is that veins are properly the vessels for blood, whereas arteries are vehicles for spirit and heat. Therefore, there is little blood in arteries (namely, just as much as suffices to warm the spirit and the vital heat) in comparison to veins, where there is a great deal of nutrimental blood, and this is also because motion and heat have a power for rarefying and thinning. Therefore, through the continuous motion of the vital spirit bearing the vital power or life to the individual members, and through continually attracting air and natural heat, blood in the artery is rarefied and diffused, and, as a result, is thinned. But there is a greater abundance of blood in a vein, and it is ordered for the nourishment of the parts of the body, and this is why this blood is thicker. And therefore, the spirits are nourished from the first, and the solid members from the second. And in addition, it is the business of heat to consume thin things and to leave behind thick. But heat is greater on the right side than on the left, as was argued, and this is why what is left behind is thicker, because it is more completely digested.
1. To the first argument one must reply that blood in an artery is not more digested. Or it can be said, in another way, when digestion acts on something whole, that which is more digested is thicker. But where digestion does not act on the whole, but only on thin parts, then it is not necessary that what is more digested also be thicker. And so too in the premise, and this is why, etc.
2. To the second argument one must reply that it is the business of heat to rarefy and to thin. Therefore, the heat, which is on the right side, causes the fumes to evaporate from the blood contained in the veins. Thus, what is left is rendered thicker per accidens, through the path mentioned.
3. To the third argument one must reply that an artery has the same nature as nerve because the spirit contained in it is in continuous motion. And this is why it is necessary for the artery to be more resistant, and this is why an artery that has been divided or cut into is made whole again only with difficulty, and on account of this one is not bled from the artery. And in addition, because the pulse and motion of the spirits is in the arteries, if one were bled from an artery it could happen that the blood would flow out without restriction or that the blood flow could not be restrained owing to the continuous motion of the artery, which impedes the healing of a wound. And a third reason is that there is a greater abundance of blood in veins than in arteries. This is why one may be bled better from a vein, because an abundance of spirits may escape from an artery, and from their escape syncopis or even death could occur. Therefore, etc.