Whether zirbus and fat have a complexion that is naturally hot or cold.
Further one asks about zirbus and fat [pinguedo], and whether they have a complexion that is naturally hot or cold.
It seems that it is cold. This is because that which is more abundant in cold things is more of a cold nature. But zirbus and fat are more abundant in cold things, since they are more abundant in women than in men and more abundant in winter than in summer. Therefore, etc.
Moreover, whatever is dissolved by cold is coagulated by heat, and vice versa. But fat and zirbus are dissolved by heat, and therefore they are coagulated by cold. And if this is true, then, taken by themselves, they have a cold nature, just like ice, etc.
To the contrary. Blood is hot and moist. A thing that is more digested is all the hotter for it. But zirbus and fat are nothing other than well digested blood. Therefore, they are hotter.
Besides, whatever things that are found only in animals that have blood are hot; but zirbus and fat are things like this, and therefore, etc.
To this, one must reply that zirbus and fat can be compared two ways. One way is to a heat having the power to convert the nutriment into the members, and, seen in this light, they have a cold nature. For on account of the fact that nature cannot convert an oily blood or any other such humor into the substance of the members, it leaves the blood outside the members, owing to its volume. But it nevertheless acts on it by digesting it beyond the nature of blood, and in this way, with respect to the members, they have a cold nature. If, however, these are compared to an undigested nutriment, then they are hot, because whatever is watery in them is dissolved and consumed, and this is why it is more easily converted into fire than is blood, since blood, owing to its wateriness (and not its oiliness) extinguishes fire. But zirbus and fat, on account of their airiness, feed the fire and strengthen it even more. Thus, these are neither intensely hot nor intensely cold, but occupy a mid-ground. Nevertheless, they are said to be cold because they are generated only from a defect of heat, as when natural heat cannot convert the blood entirely into the members, and this is owing either to its weakness or to the quantity of the nutriment.
Responses are then clear to arguments in this way, because they proceed along their own lines.
Whether the marrow is the nutriment for bones.
Further one asks about the marrow, whether it is the nutriment for bones.
1. It seems not. For everything that is nourished has pathways through which it receives nourishment. But bones, since they are solid and hard, do not have such pathways through which the nourishment might be introduced; therefore, etc.
2. In addition, the marrow is related to bones in the same way that fat is related to flesh. But fat does not nourish the flesh because it is outside the flesh; therefore, neither does the marrow nourish bones.
3. In addition, blood is the last food for the members. But blood is located in the veins. Yet there are no veins in the bones. Therefore, the bones are not nourished by blood, and, as a result, neither are they nourished by the marrow.
The Philosopher says the opposite.
One must reply that marrow is the nutriment for the bones, for the bones exist as a support for the flesh, which is a soft part. But, now, it is true that a contrary approaching its contrary necessarily acts on it. Bones are cold and dry, which is evident from their heat. Flesh, however, is moist and hot because of blood. Thus, if flesh were nourished and not the bones, the bones would quickly fail, and this is why it is necessary that the bones be nourished just as the flesh is.
But one must understand that although bones appear solid and hard, they are nevertheless porous bodies, even though while they are alive this is not apparent to the senses. But this is clear when they are broken. Thus moisture, which is the last nutriment of the members, seeps into the middle of the bones, and whatever is more earthy and dry is converted into their nutriment, because like is nourished by like; but that which is more refined passes over all the way to the hollow of the bones and is converted into marrow. Yet because bones are more solid than other parts, they cannot receive a nutriment sufficient for them as quickly as the other members do, and this is why nature having foresight like the head of the household [paterfamilias] places the marrow in the bones, and they are continually nourished by it. Yet nevertheless they draw more of what is earthy and dry into the nutriment and leave behind more of what is hot and moist. And this is why the marrow of melancholy animals such as a stag or ox is better and sweeter than the marrow of a phlegmatic animal or one of another complexion (for example, a sanguineous complexion), like a pig or a human, because in the first ones the earthiness of the marrow passes over into the bones and the airiness remains in the marrow. In the others, the contrary is the case, and for this reason, etc. This is because the harder the animal's flesh is, the sweeter and better its marrow is, because each is nourished by one like itself. Thus, when flesh is hard, it assimilates to itself that which is hard and melancholy in the food, and what is more refined and airy it leaves behind. And the opposite is true for flesh that is refined and soft. And for the same reason a broth or soup made from a melancholic animal with a hard flesh is better than a broth made from an animal with soft flesh, so that the broth of a stag or hare is better than a broth made from a pig, and a cow's is better than a ram's. Because when the flesh is hard, that which is refined and airy alone leaves it when it is cooked. For this reason, etc. But when the flesh is soft, as in a pig, a great deal of phlegmatic and watery moisture leaves it, which then is mixed in the broth. As a result, this does not become as sweet or as well suited to nourish a human nature as the first one. Thus one must reply that marrow is the nutriment for the bones; and in what way has been stated.
1. On to the arguments. To the first argument one must respond that bones are nourished because in truth they have porous pathways through which nourishment passes, although these are not clearly seen owing to their solidity. But these are evident when they are broken, and they are visible to the senses in the bones of the dead.
2. To the second argument one must respond that just as fat, while it surrounds the flesh, does not nourish it, so too the marrow, when it is within the bone, does not nourish the bone, although at such a time its potential for doing this is remote. But just as natural heat can convert the fat surrounding the flesh into nourishment for flesh, so can it convert the marrow into nourishment for bones.
3. To the third argument one must respond that although veins do not pass through the bones, nevertheless the veins' ends and their orifices are joined to the bones, and the moisture seeps out from these ends and is absorbed by the bones' pores. For this reason, etc.
-  Var. zyrbus, zirbum, zyrbum. In technical usage, it is the omentum. It often seems, however, to refer to any sort of fat that protects an internal organ and, distressingly, sometimes seems to be a mere synonym for another type of fat (see, e.g., A., DA 126.96.36.199 [SZ 1: 119]).