Whether the first generation of the blood occurs in the heart or in the liver.
Again, one asks whether the first generation of the blood occurs in the heart or in the liver.
1. And it seems to be in the liver. Because the first generation of blood occurs in that member in which the nutritive power is present, but this is in the liver. Therefore, etc.
3. Moreover, blood is generated from chyle. The place where chyle is first found is the same place in which the generation of blood occurs. But chyle is found first in the liver, after it has been separated off from the stomach, and therefore, etc.
The Philosopher says the opposite in the text. For he says that "the blood is first generated in the heart in the fetus when it is in the womb." And he proves this with an argument. That in which blood participates well, being well disposed to it, is the principle of blood. But the heart is just like this, because the blood is warmed in the heart by its superabundant heat and is tempered by its temperament; therefore, etc.
One must reply that we speak of the first generation of blood in two ways: either in the womb in the first stages of the production of the fetus, or in the completed animal, after birth, from the aliment it absorbs. If we speak in the first way, then the first generation of the blood occurs in the heart, because the heart is the first member generated in the embryo, and this is why the ventricle that can contain the blood is in the heart itself. Thus the blood is contained as if in a vessel in no member save the heart, as is said in the text. If, however, we are speaking about the generation of blood in the second way, then its first generation occurs in the liver because when the nutriment is digested in the stomach, whatever is purified is sent to the liver through the mesenteric veins, and there it is converted into blood. Nevertheless, this only occurs by means of the mediating heat of the heart. Nor does the blood generated there have the power and aptitude for nourishing the individual members except through the influence that it receives from the heart. Now the blood receives a power from the heart, and it is moved by this power everywhere, up and down, back and forth, in every different direction, being moved by that basis [ ratio] with which it is informed by the soul and by the influence of the heart, which power also moves in every different direction.
Replying to the arguments, one must reply that the first two arguments concern the generation of the blood from the nutriment in a completed animal, and this occurs in the liver.
The first argument actually applies to the blood generated in the womb for the existing animal, and the second argument shows that the blood's generation does not occur without the heart's power. And this we concede, etc.
Why the blood in the heart is liquid and is coagulated outside of it.
Why the blood of some animals coagulates.
Why the blood putrefies near the bones.
After this one asks why the blood in the heart is liquid and is coagulated outside of it, since the semen or sperm is, to the contrary, well coagulated and thickened in the body but liquid outside of it.
Second, one asks why the blood of some animals, like the human and the cow, coagulates, as is evident during phlebotomy, whereas the blood of other animals, and especially of melancholic animals like the stag and the hare, does not coagulate.
Third, one asks why the blood putrefies near the bones.
To the first, one must reply that the first digestion proceeds by thinning, whereas the second and the third proceed by thickening. Thus the blood in the body always has a moisture flowing along with it, and likewise the heat and spirit move the blood itself to the individual members. This is why it is liquid and flows in the body, but when it is outside the body the wateriness is separated from it and the heat and spirit escape through evaporation of the heat containing it or through the mortification of the cold containing it, and they ebb, and this is why it thickens quickly. But the semen is generated during the last digestion, which proceeds by thickening. Thus the semen exists in a proximate disposition toward conversion, as it were, and this is why it is coagulated in the body, but, according to the fourth book of Aristotle's On Meteorology, everything that is coagulated by heat is dissolved by cold and vice versa. Since, then, semen is coagulated by heat in the body, this is why it flows when it is outside the body since, owing to its ability to be acted upon [passibilitatem], it is dissolved and liquefied by cold.
To the second question one must reply that coagulation is of two types: one occurs from compression, occupying a smaller space, and every wet thing can be coagulated in this way by cold. Another coagulation occurs from the isolation of two natures, namely, of the aqueous and earthy. Such is the case in milk, for when the whey is separated from the curd then the curd gels. And coagulation of this sort does not occur in every blood. The reason for this is that some animals are particularly melancholic, and they are nourished on a coarse and melancholic nutriment, and this is why all the earthiness and melancholy that is in their nutriment is converted into their substance. But some animals, like the cow and the human, are nourished by what is refined [subtile] in the nutriment, and what is thick remains in their blood. And because what is thick like this becomes the material for hair and threads, this is why the blood of animals such as these contains hairs and threads, as it were, whereas the blood of the first ones does not. The blood of melancholic animals does not coagulate, therefore, because everything that provides the material for the threads that cause coagulation passes over into their nutriment and the blood remains fluid. But the blood of the other animals which has threads and ines, that is,
To the third question one must reply that heat abounds near the bones, and for this reason the blood there cannot resist putrefaction. In addition, the blood near the bones is thinner, because the bones are nourished by what is thicker in the blood. For this reason the flesh nearer the bones is softer, sweeter, and more flavorful. Therefore the abundant heat more quickly overcomes it, owing to its thinness, and as a result it putrefies.
Whether the marrow is necessary for the bones' nourishment.
Further one asks whether the marrow is necessary for the bones' nourishment.
1. It seems not. Those things that are not well compacted and coagulated are continually being lost, and this is why they need nourishment to restore what is lost. But the bones are well compacted, solid, and coagulated. Therefore, they do not require marrow for nourishment.
2. In addition, the brain is filled with marrow and yet it does not provide nourishment for any bone, because it is cold and moist, and therefore, etc.
The Philosopher says the opposite in the text. One must reply that marrow is necessary for the sake of nourishment and for the fomentation of the bones, because some parts in the body are solid, like bone, and others are permeable, like flesh, and some occupy a middle ground. But all these parts exist in flux and endure continuous loss. Now the Philosopher says in the first book of On Generation [and Corruption], that for all those possessing a species (that is, form) in a material way, in one case it is present with respect to matter and is in flux, and in another case it is present according to form [species], and endures. Therefore just as the permeable parts need a thin nutriment, and the parts occupying the middle groundlike the nerves and veinsrequire a thicker nutriment, so the bones need something very thick with which they may be nourished. And an indication of this is that bones, when they are outside the body, more quickly tend toward corruption and turn to dust than when in the body, which would not be the case were they not supported in the body by something which does not support them when they are outside the body. This, however, is the marrow, and therefore, etc.
On to the arguments. To the first, one must reply that this argument has to do with thingsinanimate and animated that are compacted, because in the animated ones heat does not cease to act on the moisture, consuming it. And on account of this some parts are moved by the power of the soul against their own nature, and every unnatural motion causes weakness and some imbalance in the thing to which it belongs. But this is not found in inanimate things, and this is why the extent to which things in animated beings are compacted is the extent to which they require nutriment. But those that are inanimate do not. The milk and sperm will be discussed below, and this is why, etc.