There are, then, these three things, that which is nourished, that 14 with which it is nourished, and that which nourishes it. The last of the three is the primary soul, that which is nourished is the body which contains the soul, that wherewith it is nourished is nutriment.

As, however, it is right to name all things from the 15 end they subserve, and the end here is reproduction of the species, the primary soul is that which is capable of reproducing the species. That with which the living thing is nourished may be 16 understood in two senses, just as that with which one and nutri- steers may mean the hand or the rudder ; the former, the ment* hand, both causing motion and being moved, the latter, the rudder, being simply moved. Now it is necessary that all food should be capable of digestion, and digestion is promoted by heat ; this explains why every animate thing has warmth. This, then, is an outline of what nutriment is.