Whether the brain is cold owing to the heart's tempering action.

One asks further whether the brain is cold owing to the heart's tempering action, just as the Philosopher himself says.

1. It seems not, for that which is the principle of sensation is not without heat, because sensation does not sense without heat. But the brain is the immediate principle of three of the senses. Therefore, it is not without heat.

2. In addition, whatever floats is hot because it is the nature of a hot thing to rise up. But the brain floats, and therefore it is hot.

3. In addition, every part exists for the sake of its own operation, as the Philosopher says at the end of book eleven. But the heart is not an operation of the brain. Therefore, it is not necessary to posit the brain's coldness for the sake of the heart.

The Philosopher says the opposite.

One must respond that the brain is cold for the sake of tempering the heart, for the heart has a superabundant heat, and life requires that tempering occur in that in which it exists, and this is why nature ordained some member, in which cold is superabundant, by which the heat of the heart might be tempered, so that a middle disposition might be brought about. And for the same reason nature arranged the brain opposite the heart so that they might temper each other. And it arranged that the brain be above the heart because heat's motion is from the center to the circumference, and cold's motion is from the circumference to the center. This is why the heart is in the middle, so that it may cause heat to flow to the parts on the circumference, and especially upwards. But the brain exists in an elevated part so that it might cause its motion to flow from the circumference to the center, and especially downwards. Thus, if the heart were above and the brain below, the one would not influence the other, because the brain would move downward where the heart would not be, and the heart would move upward, where the brain would not be, so that neither one would stand in the path of the other's influence. This is why provident and wise nature, trained to obey its Creator, thus ordained that the one would assist the other, etc. The brain's operation is an indication of its coldness. Now, when vapors reach the brain, they grow thickoften, more than is necessaryand then, according to the Philosopher, a catarrh results from the brain's coldness. This is just as occurs in the macrocosm when rain is caused by a great condensation of vapors due to the coldness of an intervening gap in the air [medii interstitii aeris]. And on account of this, the brain's big size is the cause of somnolence, and this only arises due to its coldness, by which the vapors are thickened.

1. To the arguments. To the first argument one should respond that something can be hot in two ways: either by complexion, like fire, pepper, and wine, or by participation (that is, through something else) like heated water. Now then, the brain has a cold complexion; nevertheless, it has as much heat as it needs, or as much as it needs for sensation, owing to the heart's influence.

2. To the second argument one must respond that floating can occur from two causes: in one way, from heat, and this is why a candle burns in water and always rises up until it is consumed, especially if something is removed from the lower part of the candle so that a little bit of the wick extends about a finger's length above the tallow or wax. The reason for this is that the flame floating on the water moves upward, and draws the candle with it. This is why the candle's body always rises up and floats.

In another way something rises up owing to its viscosity, and this is why oil and mucous and things like this float since, owing to their viscosity and oiliness they cannot break up or divide the water and its parts and descend; or, because such things are airy, they have to float. And this is the reason why the brain floats.

3. To the third argument one must reply that ultimately the brain exists for the sake of its own operation. Nevertheless, it has the complexion it does for the sake of tempering the heart. Thus ultimately it exists for the sake of the heart; this is why, etc.

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