c. Third Conclusion

24. A third conclusion is that a part added by nutrition is in some way like and in some way unlike the pre-existing part that was there by generation: like in specific form, not only in intellective form but in the form of corporeity that is presupposed; unlike in this, that the strength of a natural agent is the more weakened in proportion as its action on a contrary is the more continued.

25. The proof is that every such natural agent suffers reaction in its acting [Aristotle On Generation 1.7.324b9-10], and so, if it acts on a contrary, it suffers some corruptive action back from the contrary. Therefore, the more the flesh that was possessed before in generation acts on nutriment as on a contrary the more in proportion is its strength weakened, and by this is the flesh said to be more impure. Therefore, after some time, during which it has acted thus continually on its contrary, it is more impure than it was at the beginning, and consequently, since what is generated cannot be more perfect than what generates, the result is that the later the flesh generated by later flesh is itself generated, the more impure in proportion as a rule will it be, because generated by what is more impure.

26. This conclusion is confirmed by an example from Aristotle, (On Generation 1.5.322a31-33), that the more wine acts on the water mixed with it the more impure in proportion it is, so much so that at length, because of the impurity, the whole will become water. This conclusion [n.25] proves another, that not only is the flesh generated later more impure than the prior flesh, but also the same flesh remaining later in the whole is more impure than before - and this is the reason for impurity in the part of flesh generated later. The conclusion here does not assert that the form of flesh is receptive of more and less (thought if this were posited the impurity would be because of remission of the form); but the impurity can be posited precisely because of the imperfection of the natural qualities that are consequent to the form, which qualities are the principle of altering the food; because the more imperfect the food altered the more impure proportionally the flesh generated from it.