Aristotle On Youth and Old Age,On Life and Death,On Breathing-Part 14

We have already stated that life and the presence of soul involvea certain heat. Not even the digesting process to which is due thenutrition of animals occurs apart from soul and warmth, for it is tofire that in all cases elaboration is due. It is for this reason,precisely, that the primary nutritive soul also must be located inthat part of the body and in that division of this region which is theimmediate vehicle of this principle. The region in question isintermediate between that where food enters and that where excrementis discharged. In bloodless animals it has no name, but in thesanguineous class this organ is called the heart. The bloodconstitutes the nutriment from which the organs of the animal aredirectly formed. Likewise the bloodvessels must have the sameoriginating source, since the one exists for the other's behoof-as avessel or receptacle for it. In sanguineous animals the heart is thestarting-point of the veins; they do not traverse it, but are found tostretch out from it, as dissections enable us to see.Now the other psychical faculties cannot exist apart from thepower of nutrition (the reason has already been stated in the treatiseOn the Soul), and this depends on the natural fire, by the unionwith which Nature has set it aglow. But fire, as we have alreadystated, is destroyed in two ways, either by extinction or byexhaustion. It suffers extinction from its opposites. Hence it canbe extinguished by the surrounding cold both when in mass and(though more speedily) when scattered. Now this way of perishing isdue to violence equally in living and in lifeless objects, for thedivision of an animal by instruments and consequent congelation byexcess of cold cause death. But exhaustion is due to excess of heat;if there is too much heat close at hand and the thing burning does nothave a fresh supply of fuel added to it, it goes out by exhaustion,not by the action of cold. Hence, if it is going to continue it mustbe cooled, for cold is a preventive against this form of extinction.