So Harvey denies the doctrine falsely based upon Aristotle's words, the doctrine of the ethereal nature of the innate heat; but he affirms and adopts as his own the Aristotelian distinction between the heat which is sterile and the heat which gives life. This weighty affirmation obliges us who study Harvey to examine this impressive distinction further.[381] Aristotle says, we remember: "The heat in animals is not fire and does not take its origin from fire." We remember also that Harvey says: "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." This doctrine is based by both Aristotle and Harvey upon observation; and Aristotle's argument is contained in the passage which Harvey quotes, a passage obscure in the Latin and rugged in the Greek. Briefly, Aristotle's argument is this: Observation shows that fire is sterile, but that the heat of the sun is generative and the heat of animals likewise; therefore, the heat of animals is not fire. Harvey declares that this same conclusion "is taught excellently well" by his observations also--by which he does not expressly say. That Aristotle, in drawing the distinction aforesaid between the heat of fire and the heat of the sun, was playing at hide and seek with a great truth of biology, would soon be apparent to whosoever should take a flourishing green plant from a window warmed by sunshine and try to make the same plant flourish in a dark room warmed by a hidden fire. At this point let us scan further the words of Aristotle which Harvey has quoted.[337] Aristotle says:[318]-- "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]