Kyriôs men oun to trephon êdê trophê, to d' hoion men trophê, oupô de trephon, hopoion esti to prosphyomenon ê prostithemenon, trophê men ou kyriôs, homônymôs de trophê; to d' en tais phlepsin eti periechomenon || kai 26 toutou mallon eti to kata tên gastera tô mellein pote threpsein, ei kalôs katergastheiê, keklêtai trophê. kata tauta de kai tôn edesmatôn hekaston trophên onomazomen oute tô trephein êdê to zôon oute tô toiouton hyparchein hoion to trephon, alla tô dynasthai te kai mellein trephein, ei kalôs katergastheiê. Touto gar ên kai to pros Hippokratous legomenon; "Trophê de to trephon, trophê kai to hoion trophê kai to mellon." to men gar homoioumenon êdê trophên ônomase, to d' hoion men ekeino prostithemenon ê prosphyomenon hoion trophên; to d' allo pan, hoson en tê gastri kai tais phlepsi periechetai, mellon. XII It is quite clear, therefore, that nutrition must necessarily be a process of assimilation of that which is nourishing to that which is being nourished. Some, however, say that this assimilation does not occur in reality, but is merely apparent; these are the people who think that Nature is not artistic, that she does not show forethought for the animal's welfare, and that she has absolutely no native powers whereby she alters some substances, attracts others, and discharges others. Now, speaking generally, there have arisen the following two sects in medicine and philosophy among those who have made any definite pronouncement regarding Nature. I speak, of course, of such of them as know what they are talking about, and who realize the logical sequence of their hypotheses, and stand by them; as for those who cannot understand even this, but who simply talk any nonsense that comes to their tongues, and who do not remain definitely attached either to one sect or the other--such people are not even worth mentioning. What, then, are these sects, and what are the logical consequences of their hypotheses?[71] The one class supposes that all substance which is subject to genesis and destruction is at once _continuous_[72] and susceptible of _alteration_. The other school assumes substance to be unchangeable, unalterable, and sub-divided into fine particles, which are separated from one another by empty spaces.