"'For there exists in the semen of all [animals] that which makes their semen generative, the so-called heat. Yet this is not fire, nor any such power, but the spirits[319] included in the semen and in foaminess, and in the spirits the nature which is analogous to the element of the stars.[320] Wherefore fire generates no animal, nor does anything [animal] appear in process of formation in that, whether moist or dry, which is undergoing the action of fire;[321] whereas the heat of the sun and that of animals--not only that [which acts] through the semen,[322] but also, should there occur some excretion of a different nature[323]--even this, too, possesses a life-giving principle. It is patent, then, from such [facts] as these that the heat in animals is not fire and does not take its origin from fire.'[324] "I, too, would say the same, for my part, of the innate heat and the blood, to wit: that it is not fire and does not take its origin from fire, but is associated with another body and that more divine, and, therefore, does not act by reason of any elemental faculty; but, just as there exists in the semen something which makes it generative and exceeds the powers of the elements in building an animal--to wit, spirits, and in the spirits a nature analogous[325] to the element of the stars--so likewise in the blood there exist spirits or some power which acts beyond the powers of the elements, a power very conspicuous in the nourishing and preserving of the several parts of an animal; and in the spirits and blood exist a nature, yea, a soul, analogous to the element of the stars. It is manifest, therefore, that the heat in the blood of animals during life is not fire and does not take its origin from fire; and this is taught excellently well by our own observations....[326] "Therefore, those who assert that nothing composed of the elements can work beyond the powers of these, unless it be associated at the same time with another body and that more divine, and maintain, therefore, that the spirits aforesaid consist in part of the elements, in part of some ethereal and celestial substance--truly, such persons seem to me to have drawn their conclusions ill. For you shall find scarcely any elemental body which, when in action, will not exceed its own proper powers."[327]