XII. Moreover this point is manifest to every one, that every nature is desirous to keep and preserve, and if it were possible to make immortal, everything of which it is the nature; the nature of trees, for instance, desires to preserve trees, and the nature of animals desires to preserve each individual animal. But particular nature is of necessity unable to conduct what it belongs to to eternity; for want, or heat, or cold, or innumerable other ordinary circumstances, when they affect particular things, shake them and dissolve the bond which previously held them together, and at last break them to pieces; but if nothing resembling any of these things were lying in wait outside, then in that case nature itself, as far as it is possible, would preserve everything both great and small free from old age. It follows therefore of necessity, that the nature of the world must desire the durability of the universe; for it is not worse than particular natures, so that it should run away and desert its proper duties, and attempt to produce disease instead of health, and corruption and destruction instead of complete safety, since,