The admirable feature of Harvey's brief last-published discussion of the circulating blood is this, that the aged veteran ever strikes vigorous blows for observation, for the use of the senses, in the search for truth. But we have seen already that by his arm, as by another's, the blows are delivered both for better and for worse. Rightly does he drive out of court the spirits "ethereal and elemental" which no man can demonstrate. Wrongly does he discredit the real complexity of that humor, to the eye so simple and crystal-clear, out of which he believes all the diverse parts of the living bird to be developed. In Harvey's present polemic we find no new appeal to nature; he vindicates the justice of his former appeals and maintains with vigor the doctrines already familiar to us, that the blood is the principal part of the body, is itself the innate heat, and is the seat of the soul. This relation of blood and soul he reaffirms very impressively in this, his final public utterance; a most important passage of which, about the presence of the soul in the blood, has been embodied in the chapter on that subject of the present paper.[358] But evidently the main purpose of his polemical Exercise on the Innate Heat is to cast out of the blood the futile spirits which obscure the real relation of that heat to the circulating blood; and so to defend the thesis best set forth in the following words of his own:-- "In truth, the blood alone is the innate warmth, or the first born psychical heat; 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....[359] 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?"[360] Harvey has expelled from the blood the mythical spirits which had stood in the way of the direct identification of the blood with the innate heat. But how does he interpret the famous words of Aristotle which he quotes, and declares not to have been "rightly interpreted" by the champions of ethereal spirits? When we seek an answer to this question, we do not find the veteran discoverer at his best. The ancient philosopher surely would have been as much surprised at Harvey's interpretation of his words as at any use of them made by Scaliger or Fernelius. We have seen that Harvey follows up his quotation from Aristotle by promptly applying its language, literally or by paraphrase, to the innate heat and the blood.[361] Emphatic are the words which immediately follow the words of Aristotle. 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, but is associated with another body and that more divine."