On the Resurrection of the Dead 5

But such people seem to me, first, to be ignorant of the power and wisdom of the one who created and governs this universe. He has fitted to the nature and kind of each animal the food that suits it and is appropriate to it. He has not decreed that every nature should enter into union or mixture with every body, nor is he at a loss how to separate what has been united. He allows the nature of each created thing to do or suffer what is natural to it, and at other times prevents it; he permits or redirects everything as he wills and toward whatever end he wills. Second, they seem not to have considered the power and nature of each thing that nourishes or is nourished. Otherwise they would have known that not everything a creature takes in, yielding to some external necessity, becomes suitable food for the animal. Some things naturally perish as soon as they come into contact with the enfolding parts of the belly; they are vomited or evacuated or disposed of in some other way, so that they do not undergo even for a moment the first, natural digestion, much less the blending with the body being nourished. Likewise, not everything that is digested and has undergone the first change necessarily reaches the parts to be nourished: some things are separated from the nutritive power in the stomach itself, and others in the second change and the digestion that takes place in the liver, passing into something that has lost the power to nourish. Nor does all that is changed in the liver become food for human beings; it is separated into its natural residues. And the food that remains is sometimes changed into something else in the parts and particles being nourished, according to the predominance of whatever is in excess or superfluous, which tends somehow to destroy whatever comes near it or turn it into itself.