Aristotle On Youth and Old Age,On Life and Death,On Breathing-Part 4

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Thus if, on the one hand, we look to the observed facts, what wehave said makes it clear that the source of the sensitive soul,together with that connected with growth and nutrition, is situated inthis organ and in the central one of the three divisions of thebody. But it follows by deduction also; for we see that in every case,when several results are open to her, Nature always brings to pass thebest. Now if both principles are located in the midst of thesubstance, the two parts of the body, viz. that which elaborates andthat which receives the nutriment in its final form will bestperform their appropriate function; for the soul will then be close toeach, and the central situation which it will, as such, occupy isthe position of a dominating power.Further, that which employs an instrument and the instrument itemploys must be distinct (and must be spatially diverse too, ifpossible, as in capacity), just as the flute and that which playsit-the hand-are diverse. Thus if animal is defined by the possessionof sensitive soul, this soul must in the sanguineous animals be in theheart, and, in the bloodless ones, in the corresponding part oftheir body. But in animals all the members and the whole bodypossess some connate warmth of constitution, and hence when alive theyare observed to be warm, but when dead and deprived of life they arethe opposite. Indeed, the source of this warmth must be in the heartin sanguineous animals, and in the case of bloodless animals in thecorresponding organ, for, though all parts of the body by means oftheir natural heat elaborate and concoct the nutriment, thegoverning organ takes the chief share in this process. Hence, thoughthe other members become cold, life remains; but when the warmthhere is quenched, death always ensues, because the source of heat inall the other members depends on this, and the soul is, as it were,set aglow with fire in this part, which in sanguineous animals isthe heart and in the bloodless order the analogous member. Hence, ofnecessity, life must be coincident with the maintenance of heat, andwhat we call death is its destruction