ON GENERATION. 3/9
heat and colour from the blood ; the blood is in no wise derived from the liver.
From what has now been said, then, it appears that the blood is the first engendered part, whence the living principle in the first instance gleams forth, and from which the first ani- mated particle of the embryo is formed ; that it is the source and origin of all other parts, both similar and dissimilar, which thence obtain their vital heat and become subservient to it in its duties. But the heart is contrived for the sole purpose of ministering between the veins and the arteries of receiving blood from the veins, and, by its ceaseless contractions, of pro- pelling it to all parts of the body through the arteries.
This fact is made particularly striking, when we find that neither is there a heart found in every animal, neither does it necessarily and in every instance pulsate at all times where it is encountered ; the blood, however, or a fluid which stands in lieu of it, is never wanting.
EXERCISE THE FIFTY-SECOND.
Of the blood as prime element in the body.
IT is unquestionable, then, and obvious to sense, that the blood is the first formed, and therefore the genital part of the embryo, and that it has all the attributes which have been ascribed to it in the -preceding exercise. It is both the author and preserver of the body ; it is the principal element more- over, and that in which the vital principle (anima) has its dwelling-place. Because, as already said, before there is any particle of the body obvious to sight, the blood is already ex- tant, has already increased in quantity, " and palpitates within the veins," as Aristotle expresses it, 1 "being moved hither and thither, and being the only humour that is distributed to every part of the animal body. The blood, moreover, is that alone which lives and is possessed of heat whilst life continues."
And further, from its various motions in acceleration or re-
1 Hist. Anim. lib. iii, cap. 19.
