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Whether veins exist in every part of the body.
Further one asks whether veins exist in every part of the body or are extended throughout the entire body.
1. It seems so. A vein is the site of blood, but there is blood in every part of the body. Therefore, veins are also in every part of the body.
2. Moreover, a fever generated in the blood is only generated from the blood within the veins. But this would not be so if there were blood somewhere other than in the veins. Therefore, everywhere there is blood, there is a vein. But blood exits from any part of the body that has been punctured. Therefore, there is a vein in every part of the body.
3. Besides, according to the physicians there are four humors in addition to the veins. The first moisture is at the ends of the veins. The second is in the members but is not disposed for conversion and is called "dew" [ros], because it is white and it moistens the members. The third is in a disposition close to conversion and is called cambium. And the fourth is called gluten [glutinum]. But three arise from the first. Therefore, where the first one exists, so do the other three. But the first one is in the veins, and therefore, etc.
The opposite is evident to the senses.
To this one must reply that the veins are not extended throughout the entire body because in everything having diverse parts one finds one part different from another; otherwise, the whole would be homogenous. But an animal is just such a totality, and therefore one finds in it diverse parts with distinct locations. But if the veins were extended throughout the entire body, one would find simple flesh in every part of the body. But this is not true, and therefore, etc.
Again, according to the Philosopher in the third book of On Animals, in the chapter on the veins, the (larger) veins extend neither to the womb nor to the bladder, and therefore, etc.
1. On to the arguments. One must reply that the veins are said to be the site of the blood because the blood is distributed through the veins to individual members. Nevertheless, the blood seeps from the extremities of the veins to the fleshy exterior parts (that is, externally), is drunk into their pores, and nourishes them later. And this is why it is unnecessary that there be a vein everywhere there is blood, but rather that wherever there is blood it is either in a vein or seeps from a vein.
2. To the second, one must reply that a fever generated from blood is generated within veins, because, if that blood is corrupt, some injury or corruption will immediately befall the other parts since it is the nutriment for the individual members. Abscesses [apostemata] occur outside the veins as a result of corrupt blood, as do skin eruptions [impetigo] and other illnesses, although not fevers. So it does not follow from this that there be blood outside the veins just as there is inside.
3. To the third argument one must reply that although three moistures arise from the first, it is nevertheless not necessary that they exist in the same location.
Whether the veins arise from the heart or the liver.
Next one asks whether the veins arise from the heart or the liver.
1. And it seems that they arise from the liver. Because the first principle of a thing is that by which, once it is first set in place, the thing is set in place, and upon the removal of which the thing is removed. But once the liver is set in place, the blood is set in place, and, once it is removed, so too is the blood removed; therefore, etc.
2. Again, the goodness of the branch follows upon the goodness of the root, and an injury appears in the branch following upon some bad quality in the root. And conversely, goodness follows not from some bad quality, but from the good. But whatever injury or weakness arises from the blood, the liver and not the heart always provides a remedy. But this would not be so were the liver not the root of the blood and consequently also of the veins, in which the blood is contained.
3. Moreover, the branches are moved by the movement of the root, and not contrariwise. If, then, the veins should have their origin in the heart, then all the veins would be pulsating veins.
4. Moreover, the nearer the root in a plant is to its principle, the thinner it is, and the more remote it is, the thicker it is. But veins in animals are analogous to roots in plants, because, just as aliment is conveyed to the members through the veins, so too is it conveyed to the branches through the roots. But the veins near the liver are thinner than those near the heart, and therefore, etc.
The Philosopher says the opposite.
And it appears by this argument that the more something participates in something else the more it approaches the nature of that same thing's principle. But the heart participates more in blood than does the liver. Therefore, the heart is more the principle of blood than the liver is, and, as a consequence, it is more the principle of the veins.
Moreover, that at which a thing terminates and which is not penetrated by it is a thing's principle. But the veins terminate at the heart, and it is not penetrated by them. Nevertheless, the liver is penetrated by them, that is, by the veins, and therefore, etc.
There is a great controversy between the physicians and the Philosopher or philosophers surrounding this question. Some of the physicians, like Galen and his followers, posit that the veins arise at the liver because the generation of the blood occurs in the liver and, as a result, the liver is the principle of the veins through which the blood is borne.
Moreover, it is very apparent in plants that the roots are thinner and more subtle at the base or trunk. But the veins that penetrate the liver are subtle and thin, and the vein connected to the heart is large in the manner of a trunk. Therefore, the liver is the veins' root. And in addition to this the liver has only coagulated blood, which is why it has the color of blood. But the heart is just like coagulated melancholy [melancholia], whereby it is hard and earthy.
Nevertheless, this is contrary to the view of the Philosopher and Avicenna. For Avicenna says that one ought to hold to the opinion of the first philosopher and the prince of philosophers (namely, Aristotle) regarding this part, who claims that the heart is the first principle of the veins, as does the physician, Master Nicholas of Poland, as well. And the reason is that in an animal, since there is one substance that has several parts which have various powers, it is necessary that there be one power that is the principle of the others and from which the others receive some influence. This, however, is the vital power, because without the vital power the nutritive power does not operate in an animal. Therefore, it is necessary that the organ for this power have a basis for beginning, that is, have the basis for a principle, higher than the organs for the other powers. But the organ for the vital power is the heart, and therefore, etc.
Moreover, the veins are capable of containing and bearing the blood. But although the blood is generated in the liver, nevertheless this does not occur without the assistance of heat, and it can descend to the members only with heat mediating. But the principle of heat is in the heart; therefore, in the liver there is no power that can nourish through the mediation of the blood that has been generated in it except through the influence it receives from the heart.
And this is why the Philosopher claims that the heart is the principle of the veins. For he claims that it is the first part in the animal's generation upon which all the other parts are based and without which no other part can perform its proper operation. Therefore, so that the view of all those discussing this may be reconciled, "origin" can be distinguished into two types: one is virtual and radical, and the other is corporeal. In the first way the veins arise from the heart, but they arise from the liver in the second way. Thus the branching of the veins clearly and in an evident way begins at the liver, just as the appearance of branches from the trunk of a tree is evident, although in reality it proceeds from the root, but nevertheless appears clearly to us to be from the trunk. So too for the heart, that the veins proceed from it in reality, although they appear to do so from the liver, but because physicians are [dabblers in] sensibles, this is why, etc. The Philosopher speaks in the first way; the physicians in the second.
In this way one can disclose the arguments. The arguments to the first part prove that the veins arise corporeally and immediately and in an evident way from the liver. Yet the arguments to the contrary prove that the veins arise virtually or radically or with respect to origin from the heart.
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