Further, this flesh, and the blood in it, are by a mutual sympathy moistened and increased by the milk. And the process of formation of the seed in conception ensues when it has mingled with the pure residue of the menses, which remains. For the force that is in the seed coagulating the substances of the blood, as the rennet curdles milk, effects the essential part of the formative process. For a suitable blending conduces to fruitfulness; but extremes are adverse, and tend to sterility. For when the earth itself is flooded by excessive rain, the seed is swept away, while in consequence of scarcity it is dried up; but when the sap is viscous, it retains the seed, and makes it germinate. Some also hold the hypothesis, that the seed of an animal is in substance the foam of the blood, which being by the natural heat of the male agitated and shaken out, in copulation is turned into foam, and deposited in the seminal veins. For Diogenes Apollionates will have it, that hence is derived the word aphrodisia.