Whether blood is the last food for the members.
One inquires further about blood. And, first, whether blood is the last food for the members.
1. And it seems not. That which is generated during the first digestion changes its species in the second. Therefore, what is generated in the second will change its species in the third. But blood is generated in the second digestion, and therefore it changes its species in the third. And, as a result, something coming after the blood is food for the members.
2. In addition, the veins are the site for blood. If, then, blood were the last food for the members, no member would be nourished other than the vein which contains the blood.
The Philosopher says the opposite.
One must say that the last food for the members is of two types: common and particular [ appropriatus]. If we are speaking of the last common food, the blood is the last food. If, however, we are speaking of the last particular food, then some moisture comes after the blood. For blood that is borne to any member undergoes a further digestion in that member and is changed into a moisture. This moisture is in a proximate disposition to the member. Nevertheless, the Philosopher takes this in the first way; the physicians speak of it in the second.
1. By this a response to the first argument is clear, that although blood may change its species in the third digestion, it is nevertheless the last common food.
2. To the second argument one should respond that blood seeps through the medium of the veins after the fashion of sweat, and thus reaches the parts surrounding the veins, and for this reason it nourishes not only the veins, but the exterior parts as well.
Whether thick blood is more nourishing than thin blood.
Further one asks whether thick blood is more nourishing than thin blood.
1. It seems that the thick blood is more nourishing. This is because nutrition is the complete assimilation of the nutrient to the one nourished. But thick blood is better assimilated to the members than thin blood. Therefore, etc.
2. In addition, thicker and more globular semen is better suited for generation, as the Philosopher said above. Therefore, for the same reason, thick blood is better suited for nutrition.
To the contrary. Things that are more easily converted are more suitable nourishment. But thin things are more quickly converted. Therefore, they nourish better.
Besides, that thing nourishes better which prepares the member as more suitable for its operation. But thin blood is such a thing. For those having thin blood have better sensation, intellect, and motion, which is the case only because a thin thing nourishes better. Therefore, etc.
To this one must respond that something is said to nourish better than another in two ways. In one way, it is because it remains longer in the members and is more difficult to digest. And in this way thick and hard things are said to nourish better, and beef and eel are said to nourish better than the meat of a chicken or a ram, and the like. Something is said to nourish better in another way, because it is converted more easily into the members' substance, and in this way thin things nourish better because they are easily converted and remain in the members only a short time, like the meat of a chicken or a capon and the like.
The Philosopher speaks in the first way when he says that thick blood nourishes better. And his argument is that the second digestion proceeds by thickening and coagulating. And for this reason the thicker it is, the better it is for or the closer it is to nutrition. The physicians understand things in the second way, when they say that thinner things are better nourishment. The reason, however, why those having thin blood have better sensation, intellect, and motion is that where the blood is thin and pure, there the spirits are thinner. Now, the spirits serve and minister to the sensitive and motive powers. The thinner these spirits are, the better adapted they are to motion or for moving the senses and the organs. And this is why such animals as these have better sensation and motion, and even have purer phantasms. They therefore have a good intellect. For our intellect "either is a phantasm, or does not exist without a phantasm," as is said in the third book of On the Soul, and the purer the phantasms are, the better, etc.