Whether a more intense heat is found in the element of fire, or in a mixture.
Further one asks whether a more intense heat is found in the element of fire, or in a mixture.
It seems that it is more intense in the fire. According to the Philosopher in the second book of the Metaphysics, that which is in a category [genus] first especially has the characteristic of that category, because that which first has this characteristic is a cause for all such things because they have this same characteristic. But fire is first hot; therefore, it especially has this characteristic.
Moreover, that thing is hotter which is more deprived of or more lacks the restraining action of a contrary; but the heat in fire is like this, and therefore, etc.
To the contrary. Operation makes the form known. To burn is heat's operation. But heated iron burns more actively than fire; therefore, etc.
Besides, that which conserves heat longer is hotter. But heated iron conserves heat longer than a flame in the air, once the combustibles have been removed. Therefore, etc.
To this, one must reply that one thing can be hotter than another in more than one way: either per se or through something else. If per se, then among all things fire will be hottest because in itself it has the cause of heat per se. For heat cannot be separated from the form of fire, just as a capacity for laughter [risibilitas] cannot be removed from a human.
Something is hot through something else in another way, and such a thing can effectively be hotter than one that is hot per se. And heated iron is just such a thing, since the iron itself is hot through something else, because it participates in the heat of fire and is effectively hotter. And the reason for this is that every united power is stronger than it is when it is dispersed. Now, however, the proper material for fire is rarified [rara], and the iron's material is more compact and solid. Thus the fiery heat incorporated into the iron is more unified, and for that reason is effectively hotter.
And, besides this, the more something resists an agent, the more strongly the form of the agent is impressed upon it, if it obtains victory over the thing being acted on. But the more solid the matter is, the more strongly it resists a hot agent, and this is why, when it overcomes the matter, the power of heat is more strongly impressed on it, etc.
Moreover, fire is easily divisible, and this is why if someone extends or reaches his hand into the fire, he can remove his hand without injury because the fire itself is easily parted. But heated iron is solid and not easily parted, and this is why it sticks more firmly to one touching it and, as a result, burns him more.
Through this the answers to the arguments are clear. Now, fire is hotter per se and in se and formally; nevertheless, heated iron is hotter accidentally and effectively, owing to the compact nature of its matter. This is because a quality impressed on a solid object is stronger than one impressed on another, just as moisture is stronger in water than in air, even though it may be in the air per se and in the water only through another agency. Thus to this one, etc.
Whether the first digestion is in the mouth.
One asks further whether the first digestion, or the first digestive power, is in the mouth.
1. It seems so. For, according to Avicenna, "grain placed and chewed in the mouth precipitates a sore there." And this does not occur if the grain is first ground up by some instrument. Therefore, it seems that the grain is somewhat digested in the mouth, and therefore, etc.
2. In addition, "the root of a plant is analogous to an animal's mouth," as the Philosopher states in the second book of On the Soul. But the nutriment's digestion occurs in the root; therefore, it will also occur in the mouth.
The Philosopher says just the opposite.
In response to this, one should say that there is a disagreement over this between the Philosopher and many physicians. Now, some physicians posit a first digestion in the mouth, and a second in the stomach. The Philosopher posits a single digestion in the mouth and the stomach. Thus, according to the Philosopher, masticationwhich occurs in the mouthis in preparation for the stomach's operation, with the mouth disposing and preparing the food so that it may be more easily digested in the stomach. Thus one must say that digestion, properly speaking, is not in the mouth because the appetitive and attractive powers precede digestion. But the first appetite flourishes in the upper part of the stomach; therefore, there is no digestion before the nutriment reaches that part.
1. To the arguments. To the first argument one should respond that grain masticated in the mouth heats up in the mouth while it is being ground and is tempered by the saliva, and it is this heating and mixture with the saliva that precipitates sores, because saliva is salty and pungent and penetrating. Thus, it precipitates a sore not because the grain has been digested but because it has been altered proportionally.
2. To the second argument one must respond that a tree's root is not only analogous to the mouth but also to the stomach, because a plant receives nourishment through the root just as an animal does through its mouth, but the nourishment is not dispatched from the root to another member in which it is digested, as happens in the animal when it is dispatched from the mouth to the stomach. Rather, one and the same root serves each operation, that is, both the reception and the digestion of the nutriment. And this is why in trees no member is set aside for superfluities because, as is said, they do not need any. And, besides this, the plants' nourishment is somewhat digested in the ground before they receive it. And so it is not the same, and this is why, etc.
-  That is, just as laughter is a proper predicate of the human, so too is heat a proper predicate of fire.