The latter part of Harvey's treatise On Generation is devoted to that of the mammal; but the treatise does not end with the end of this subject, for from his account of generation the author turns abruptly to append two Exercises on other topics. The first of these two is entitled "On the Innate Heat," and the second, which is very brief, is entitled "On the Primitive Moisture." The Exercise On the Innate Heat is Harvey's express and polemical contribution to this subject, which had been much discussed both during and before his time;[310] a subject with which the famous discoverer deals roundly by maintaining that the innate heat is neither more nor less than the circulating blood. So the last words as to the significance of the circulating blood which he wrote for publication are contained in this Exercise. It begins as follows:-- "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....