The Resurrection of the Dead

But it appears to me that such persons, in the first place, are ignorant of the power and skill of Him that fashioned and regulates this universe, who has adapted to the nature and kind of each animal the nourishment suitable and correspondent to it, and has neither ordained that everything in nature shall enter into union and combination with every kind of body, nor is at any loss to separate what has been so united, but grants to the nature of each several created being or thing to do or to suffer what is naturally suited to it, and sometimes also hinders and allows or forbids whatever He wishes, and for the purpose He wishes; and, moreover, that they have not considered the power and nature of each of the creatures that nourish or are nourished.

Otherwise they would have known that not everything which is taken for food under the pressure of outward necessity turns out to be suitable nourishment for the animal, but that some things no sooner come into contact with the plicatures of the stomach than they are wont to be corrupted, and are vomited or voided, or disposed of in some other way, so that not even for a little time do they undergo the first and natural digestion, much less become incorporated with that which is to be nourished; as also, that not even everything which has been digested in the stomach and received the first change actually arrives at the parts to be nourished, since some of it loses its nutritive power even in the stomach, and some during the second change, and the digestion that takes place in the liver is separated and passes into something else which is destitute of the power to nourish; nay, that the change which takes place in the liver does not all issue in nourishment to men, but the matter changed is separated as refuse according to its natural purpose; and that the nourishment which is left in the members and parts themselves that have to be nourished sometimes changes to something else, according as that predominates which is present in greater or less abundance, and is apt to corrupt or to turn into itself that which comes near it.