On Youth And Old Age, On Life And Death, On Breathing   

works we have stated the reasons why some of the sense-organs are,

as is evident, connected with the heart, while others are situated

in the head. (It is this fact that causes some people to think that it

is in virtue of the brain that the function of perception belongs to

animals.)



4



Thus if, on the one hand, we look to the observed facts, what we

have said makes it clear that the source of the sensitive soul,

together with that connected with growth and nutrition, is situated in

this organ and in the central one of the three divisions of the

body. 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 the

best. Now if both principles are located in the midst of the

substance, the two parts of the body, viz. that which elaborates and

that which receives the nutriment in its final form will best

perform their appropriate function; for the soul will then be close to

each, and the central situation which it will, as such, occupy is

the position of a dominating power.

Further, that which employs an instrument and the instrument it

employs must be distinct (and must be spatially diverse too, if

possible, as in capacity), just as the flute and that which plays

it-the hand-are diverse. Thus if animal is defined by the possession

of sensitive soul, this soul must in the sanguineous animals be in the

heart, and, in the bloodless ones, in the corresponding part of

their body. But in animals all the members and the whole body

possess some connate warmth of constitution, and hence when alive they

are observed to be warm, but when dead and deprived of life they are

the opposite. Indeed, the source of this warmth must be in the heart

in sanguineous animals, and in the case of bloodless animals in the

corresponding organ, for, though all parts of the body by means of