Harvey, looking askance as he did at the four ancient elements and even bluntly questioning the elementary constitution of matter, felt himself free to reduce the analogue of the ether to a pious epithet, and yet to accept with emphasis the Aristotelian doctrine that the heat of animals "is not fire." At the end of his Exercise On the Primitive Moisture he says: "Nor, lastly, do we find that anything is naturally generated out of fire, as out of something capable of mixture, and the thing is perhaps impossible." Here, however, he is not dealing merely with the generation of living beings, but with a subject deeper yet, the possibility of fire acting as an element at all.[384]
The drift of those sentences which Harvey quotes is lighted up, better perhaps than by any modern commentary, by a passage of Cicero's treatise On the Nature of the Gods, a treatise mentioned by Harvey in his lecture notes,[385] as we have seen. In the orator's lucid Latin we may read what purports to be a quotation from the Greek philosopher Cleanthes, who was a child when Aristotle died in 322 B.C., and who became the second head of the Stoic school, the powerful younger rival of the school of Aristotle. Let us listen to the Roman stoic of 45 or 44 B.C., who is set up by Cicero to quote and expound Cleanthes as follows:—
"Cleanthes says: 'Since the sun is fiery and is nourished by the humors of Ocean (seeing that no fire can last without some kind of food), therefore, the sun must needs be similar either to the fire which we use and apply in our daily life, or to that fire which is contained in the bodies of animate beings. But this fire of ours, which is requisite for the uses of life, is the destroyer and consumer of all things, and wheresoever it has made its way disturbs and dissipates everything; whereas that fire of the body is vital and salutary and by it everything is preserved, nourished, increased, sustained, and endowed with sense.' Cleanthes denies, therefore, that it is doubtful to which of these two fires the sun is similar, seeing that the sun likewise makes all things flourish and ripen, each after its kind. Wherefore, since the sun's fire is similar to those fires which exist in the bodies of animate beings, the sun, too, must be an animate being and, indeed, the rest of the stars that arise in the celestial ardor which is named ether or heaven."[386]
Unlike Aristotle, Cicero's stoic admits that the sun and even the heavenly ether are fire. But we see him to be no less impressed than Aristotle by the difference between the killing heat of flame and the life-giving heat of heaven and of living things. It is interesting to find this difference expressly given as a reason for believing the heavenly bodies to be alive; and one wonders whether this difference may not have had some share in convincing Aristotle that the ether is an element distinct from fire and the other three elements, and more exalted than they. It must be said, however, that Aristotle's habitual use of language about "the heat contained in animals" prepares us ill for the momentous distinction drawn by him between this and elemental heat.
We have found him speaking of "the soul being, as it were, afire" within the heart;[387] and he says also that "the concoction through which nutrition takes place in animals does not go on either in the absence of soul or in the absence of heat, seeing that everything is done by fire."[388] Moreover, there is in his treatise On Soul a passage deserving immediate quotation, no less as a picture of the nascent stage of biological thought, than as showing a phase of Aristotelian doctrine contrasting with the doctrine of the analogue of the ether. He says:—
"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]