BOOK TWO

 [p. 123]by any means, any other cause for the secretion of urine; we necessarily appear mad if we maintain that the urine passes into the kidneys in the form of vapour, and we certainly cut a poor figure when we talk about the tendency of a vacuum to become refilled;

Horror vacui

this idea is foolish in the case of blood, and impossible, nay, perfectly nonsensical, in the case of the urine.

But Erasistratus had never upheld this in the case of urinary secretion. cf. p. 99.

This, then, is one blunder made by those who dissociate themselves from the principle of attraction. Another is that which they make about the secretion of yellow bile. For in this case, too, it is not a fact that when the blood runs past the mouths [stomata] of the bile-ducts there will be a thorough separation out [secretion] of biliary waste-matter. "Well," say they, "let us suppose that it is not secreted but carried with the blood all over the body." But, you sapient folk, Erasistratus himself supposed that Nature took thought for the animals' future, and was workmanlike in her method; and at the same time he maintained that the biliary fluid was useless in every way for the animals. Now these two things are incompatible. For how could Nature be still looked on as exercising forethought for the animal when she allowed a noxious humour such as this to be carried off and distributed with the blood?...

This, however, is a small matter. I shall again point out here the greatest and most obvious error. For if the yellow bile adjusts itself to the narrower vessels and stomata, and the blood to the wider ones, for no other reason than that blood is thicker and bile thinner, and that the stomata of the veins are