aught as yet been urged against it by any one which has seemed greatly to require an answer. Wherefore I imagine that I shall perform a task not less new and useful than agreeable to philosophers and medical men, if I here briefly discourse of the causes and uses of the circulation, and expose other obscure matters respecting the blood ; if I show, for instance, how much it concerns our welfare that by a wholesome and regulated diet we keep our blood pure and sweet. When I have accom- plished this it will no longer, I trust, seem so improbable and absurd to any one as it did to Aristotle 1 in former times, that the blood should be viewed as the familiar divinity, as the soul itself of the body, which was the opinion of Critias and others, who maintained that the prime faculty of the living principle (anima) was to feel, and that this faculty inhered in the body in virtue of the nature of the blood. Thales, Diogenes, Hera- clitus, Alcmseon, and others, held the blood to be the soul, because, by its nature, it had a faculty of motion.
Now that both sense and motion are in the blood is ob- vious from many indications, although Aristotle 2 denies the fact. And, indeed, when we see him, yielding to the force of truth, brought to admit that there is a vital principle even in the hypenemic egg; and in the spermatic fluid and blood a " certain divine something corresponding with the element of the stars," and that it is vicarious of the Almighty Creator ; and if the moderns be correct in their views when they say that the seminal fluid of animals emitted in coitu is alive, wherefore should we not, with like reason, affirm that there is a vital prin- ciple in the blood, and that when this is first ingested and nourished and moved, the vital spark is first struck and en- kindled ? Unquestionably the blood is that in which the vege- tative and sensitive operations first proclaim themselves ; that in which heat, the primary and immediate instrument of life, is innate ; that which is the common bond between soul and body, and the vehicle by which life is conveyed into every particle of the organized being.
Besides, if it be matter of such difficulty to understand the spermatic fluid as we have found it, to fathom how through it the formation of the body is made to begin and proceed with
1 De Anima, lib. i, cap. 2.
2 De Hist. Anim. lib. i, cap. 19 ; et de Part. Anim. lib. ii, cap. 3.
