"By some the nature of fire is held to be quite simply the cause of nutrition and growth; for fire alone among bodies or elements is seen being nourished and growing; wherefore one might assume it to be that which does the work both in plants and in animals. It is, in a way, the contributing cause[389] but not the cause in the simple sense, the soul rather being that; for the growth of fire is limitless, so long as there are combustibles, but in the case of all natural organisms[390] there is a limit to size and growth, and a rationale[391] thereof; these things depending upon the soul, not upon fire, and upon reason rather than upon matter."[392] Nevertheless, in spite of seeming inconsistencies, we find Aristotle declaring that the heat of fire sterilizes, but the heat of the sun and of animals gives life. Moreover, when he tells us in the passage quoted by Harvey[393] that not only the heat of the sun and of semen, but also the heat of other animal excretions possesses a "life-giving principle," the words appear to suggest not merely generation without sex, but the spontaneous generation either of parasites within the animal body, or of living things in matters cast off from it. We seem to be confronted with the far-reaching thought that there is in the world a life-giving principle by which, when associated with soul, matter is quickened in ways of which sexual generation is only one; and that this principle is generative heat, streaming from the sun or transmitted by the male in coition, and, thereafter, innate in the resulting creature and shared by the humors thereof. The fact must always have been recognized that in some way the existence of living things on earth depends upon the sun. On the other hand, no modern methods fortified Aristotle's intelligence against spontaneous generation, which he accepted as a matter of course and called "automatic generation," even asserting that eels and some other fishes originate in this way.[394] Further statements of his own shall show us now that the sun in its orbit dominates the changes upon and above the earth and is the giver of life, whether imparted by sexual intercourse or otherwise. Then Harvey shall repeat the lesson and thus help us to understand his declaration regarding the innate heat and the blood, to wit: that it "is not fire and does not take its origin from fire." Aristotle refers to a region beneath the celestial spheres, which region he calls "the first in proximity to the earth," or "the region common to water and air." He says of the events therein:-- "Of these the efficient[395] cause and ruler and first origin is the circle of the sun's course, which, it is evident, produces separation and combination by its approach or withdrawal and is the cause of generation and corruption."[396]