"Since mention is often made of the innate heat, I propose now, by way of dessert, briefly to discuss the same and the primitive moisture also; and this the more willingly that I see there are many who take the greatest delight in those names and yet, in my judgment, comprehend but little of the things themselves. Truly, there is no need to seek for any spirits distinct from the blood, or to bring in heat from elsewhere, or call gods upon the stage and load philosophy with fanciful opinions; for what we so commonly would fetch from the stars is born at home. In truth, the blood alone is the innate warmth, or the first-born psychical heat;[311] as is proved excellently well by our observations of the generation of animals, especially of the chick in the egg; so that it were superfluous to multiply entities. Indeed, there is nothing to be met with in the animal body prior to the blood, or more excellent; nor are the spirits which they distinguish from the blood to be found anywhere separate from it; for the very blood itself, if without spirits or heat, does not deserve the name of blood, but of cruor....
"Scaliger, Fernelius, and others lay less weight on the extraordinary endowments of the blood and imagine other spirits to exist, aërial or ethereal or composed of substance both ethereal and elemental, constituting an innate heat more excellent and more divine, as it were; and these spirits they believe to be the soul's most immediate instrument, the fittest for every use. They rely especially upon this argument, viz.: that the blood, being composed of elements, can exert no activity beyond the powers of the elements or of bodies consisting of a mixture thereof. Therefore, they imagine a spirit, another innate heat, of celestial origin and nature, to wit: a body most simple, most subtile, most fine, most mobile, most swift, most clear, ethereal, and sharing in the quintessence. Nowhere, however, has any such gift of spirit been demonstrated by them, nor that the same acts beyond the powers of the elements, or accomplishes greater works than could the blood alone. As for us who use our senses to guide us in the scrutiny of things, nowhere have we been able to find anything of the kind. Furthermore, there exist no cavities destined for the generation or preservation of these spirits, or even assigned thereto by the persons aforesaid."[312]
A little farther on we read:—
"I deem it, however, most wonderful that spirits which draw their origin from heaven and are adorned with such surpassing endowments should be nourished by our common and elemental air; especially seeing that their advocates hold that none of the elements can act beyond its own powers....[313] What need then is there, say I, of that foreign guest, ethereal heat, since all can be accomplished by the blood, even as by it; while from the blood the spirits cannot withdraw a hair's breadth without perishing? Most assuredly nowhere do they wander or penetrate as separate bodies without the blood. For whether it be said that they are generated, nourished, and increased from the thinner part of the blood, as some believe, or from the primitive moisture, as others hold; yet it is confessed that they are never found outside the blood but forever cleave to the same as to their sustenance, as flame does to oil or to a wick. Wherefore their tenuity, subtility, mobility, and so forth, confer no greater advantage than does the blood which they continually accompany. It follows that the blood suffices and is fit to be the immediate instrument of the soul, since the blood is present everywhere and most swiftly permeates hither and thither."[314]
The two opponents named by Harvey were not his contemporaries, but worthies of the Renaissance who had written about one hundred years before the publication of his treatise On Generation and had died before he was born. The Italian physician Julius Cæsar Scaliger had written learned commentaries on Aristotle, as well as other works; and the Frenchman Jean Fernel, physician to King Henri II of France, had taught anatomy at Paris and had been a medical writer of importance. Each of these two authors was nearly sixty years of age in 1543, in which memorable year were first published the revolutionary writings of the aged astronomer Copernicus and of the young anatomist Vesalius, in the second year after the death of the hardy innovator Paracelsus. Such were the men against whose doctrines Harvey was impelled in his old age to launch his vigorous criticism, in order to clear the way for his own doctrine of the preëminence of the blood. What can we workers of to-day make of their opinions, which were living for Harvey but now are so deeply buried? Test-tube and balance, telescope, spectroscope, microscope, manometer, and the rest, have served their purpose so well since Harvey's time that even he, one of the foremost worthies of science, must seem merely to beat the air with words in his last message to us, unless we can recover his standpoint. Happily he himself shall attempt to clarify the meaning of his polemic by setting before us certain words of Aristotle, embodying far-reaching speculations as to body and soul in relation to the universe. Yet we shall find these not easy to understand.
Let Harvey continue his criticism of his predecessors. He says:—
"But while they believe that there are found in animals spirits and ultimate or primitive nourishment, or something else, which acts beyond the powers of the elements more than does the blood, they do not seem to have a sufficient grasp of what it may be to 'act beyond the powers of the elements'; nor have they rightly interpreted the words of Aristotle where he says:[315] 'The virtue or potency of every soul[316] seems to be associated with a body[317] other than the so-called elements and more divine.'"
And a little farther on:[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]
"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]
On reaching the end of the last quoted words of Harvey's polemic, a physician or biologist of to-day may easily be conscious of disappointment, even of a mild despair; for the once celebrated passage from Aristotle, about the interpretation of which Harvey gives battle, seems at first the source of all the obscurities of the controversy, rather than of the promised light which shall clear them away. Yet that light must come by way of that rugged passage. The gist of the first part of the Aristotelian passage may be set forth as follows: In the semen soul is potential, being associated therein with a "body" or "nature" which possesses a "life-giving principle" and is in the spirits, i.e., in the hot vapor, within the foam-bubbles of the semen. This body or nature is called heat, yet it is not that one of the four elemental bodies which is known as fire, nor yet a derivative of this, but is "a body other than the so-called elements and more divine," a "nature analogous to the element of the stars." What is this "element of the stars"? It is clear that only from the answer to this question can the light which we are seeking begin to shine. To find this celestial element we must immediately take a rapid glance at the Aristotelian universe—that grand conception which the master mainly accepted from his predecessors and contemporaries, but owed, in part, to the work of his own mind. Let us swiftly scan what he styled the "Cosmos."
At the center thereof is the earth, spherical and motionless. The core of the universe consists not only of this central globe with everything in or upon it, but also of the atmosphere or, more correctly, of all which extends between the surface of the globe and the nearest of the distant revolving hollow spheres of heaven, in some of which spheres are set the heavenly bodies. Below the heavenly spheres this core of the universe is made up of the four elements, earth, water, air, and fire; and all things composed of these are subject to opposed and limited and compounded motions, to generation, alteration, and corruption. The inclosing heaven, on the other hand, is unchangeable and eternal, has never been created, and will never be destroyed. Its many component hollow spheres are contiguous and concentric, and concentric also with our globe. In a single sphere, the outermost, called the "first heaven," all the fixed stars are set. In separate spheres, nearer to the earth, are set the seven bodies which the astronomy of Aristotle's day styled "planets." To these (here designated by their present names) that ancient astronomy assigned the following order from the earth outward toward the fixed stars: the moon, the sun, Venus, Mercury, Mars, Jupiter, and Saturn. Each of the celestial spheres revolves with simple circular motion in one direction forever. The "first heaven," the sphere of the fixed stars, needs but the one simple motion which is its own, and it carries with it in its daily revolution all the inner spheres. These are more numerous than the seven planets; for though each planet is set in but a single sphere, each planet's complex course results from the combined simple motions of more spheres than one. In spite of these more or less intimate relations, the spheres of heaven are separate existences, self-moved, like animals; and, like animals, possess activity, life, and soul. But the motion and life of the heavenly existences are continuous and eternal, and hence these existences—the spheres, and the planets and fixed stars set therein—are all divine; much more divine than man, though man possesses a far larger share of the divine than other animals.[328]