Aristotle [says] that there is no agreement about the teaching related to nutriment. Some maintain indeed that nutriment has a similar nature to the organism being nourished, for what is similar is nourished by similar; and if [it is true that] nutriment, when added to the organism being nourished, promotes its growth, but [it is also true that] similar promotes the growth[2] of similar -- not the inverse --, then the organism being nourished is nourished not by [its] opposite, but by [its] similar.[3] Others say that the organism being nourished is nourished by [its] opposite, for if [it is true that] the nutriment is acted upon by the organism being nourished and undergoes a transformation into that organism, but [it is also true that] similar is not acted upon by a similar, rather opposite is acted upon by its opposite and undergoes a transformation into the opposite, then [we can conclude that] the nutriment is opposite to the organism being nourished.[4] These teachings might look contraries [to each other], but they are not, for nutriment is similar to the organism being nourished in reference to the faculty, but is opposite to it in reference to the act: for bread and the cooked foods, as long as they are not elaborated and not digested, are in a way opposite to the organism that is nourished, but at the time they undergo their transformation and change their nature, then they become similar [to it]. The process of transformation does not affect similar in the direction of similar, nor any chance thing in a random way, but it affects opposite in the direction of opposite: [e. g.], white is not changed into hot, but cold [is changed] into hot. And even in the case that gray were transformed into white, nonetheless it is transformed not in its percentage of white, but in its percentage of gray. The same is true for the orher things. Now, since "nutriment" is meant in a double sense, the first one as "not digested", the second as "digested", the not-digested substance is opposite to the one which has been digested, but the one which has already been digested and transformed is similar [to it].[5] [Also note] that the nourishing factor is the first faculty of the soul, which is the nutritive faculty; the organism being nourished is the body which contains the soul, inasmuch it is provided with that faculty; the substance which nourished it is the food.[6] That by which it is nourished is also meant in a double sense: that which moves, and that which is moved. For the innate warmth, by which the soul is nurtured, gives and receives movement as by the action of an instrument: it receives movement by the action of the nutritive faculty, and gives movement to the other parts, like teeth, veins, stomach and the other parts involved in the nutrition, which are only moved parts, but do not give any movement to others.[7]