Epeidê de peri tôn triôn dynameôn tês physeôs autarkôs eirêtai kai phainetai mêdemias allês prosdeisthai to zôon, echon ge kai hopôs auxêthê kai hopôs teleiôthê kai hopôs heôs pleistou diaphylachthê, doxeie men an isôs hikanôs echein ho logos houtos êdê kai pasas exêgeisthai tas tês physeôs dynameis. all' ei tis palin ennoêseien, hôs oudenos oudepô tôn tou zôou moriôn ephêpsato, koilias legô kai enterôn kai hêpatos kai tôn homoiôn, oud' exêgêsato tas en autois dynameis, authis doxeien an hoion prooimion ti monon eirêsthai tês chrêsimou didaskalias. || to gar sympan hôd' echei. genesis kai 20 auxêsis kai threpsis ta prôta kai hoion kephalaia tôn ergôn esti tês physeôs; hôste kai hai toutôn ergastikai dynameis hai prôtai treis eisi kai kyriôtatai; deontai d' eis hypêresian, hôs êdê dedeiktai, kai allêlôn kai allôn. tinôn men oun hê gennêtikê te kai auxêtikê deontai, eirêtai, tinôn d' hê threptikê, nyn eirêsetai. X For I believe that I shall prove that the organs which have to do with the disposal[54] of the nutriment, as also their faculties, exist for the sake of this _nutritive faculty_. For since the action of this faculty[55] is _assimilation_, and it is impossible for anything to be assimilated by, and to change into anything else unless they already possess a certain _community and affinity_ in their qualities,[56] therefore, in the first place, any animal cannot naturally derive nourishment from any kind of food, and secondly, even in the case of those from which it can do so, it cannot do this at once. Therefore, by reason of this law,[57] every animal needs several organs for _altering_ the nutriment. For in order that the yellow may become red, and the red yellow, one simple process of alteration is required, but in order that the white may become black, and the black white, all the intermediate stages are needed.[58] So also, a thing which is very soft cannot all at once become very hard, nor _vice versa_; nor, similarly can anything which has a very bad smell suddenly become quite fragrant, nor again, can the converse happen. How, then, could blood ever turn into bone, without having first become, as far as possible, thickened and white? And how could bread turn into blood without having gradually parted with its whiteness and gradually acquired redness? Thus it is quite easy for blood to become flesh; for, if Nature thicken it to such an extent that it acquires a certain consistency and ceases to be fluid, it thus becomes original newly-formed flesh; but in order that blood may turn into bone, much time is needed and much elaboration and transformation of the blood. Further, it is quite clear that bread, and, more particularly lettuce, beet, and the like, require a great deal of alteration in order to become blood.