While Asclepiades denies in toto the obvious fact of specific attraction, Epicurus grants the fact, although his attempt to explain it by the atomic hypothesis breaks down. Refutation of the Epicurean theory of magnetic attraction. Instances of specific attraction of thorns and animal poisons by medicaments, of moisture by corn, etc.
Chapter [XV]
It now being granted that the urine is secreted by the kidneys, the rationale of this secretion is enquired into. The kidneys are not mechanical filters, but are by virtue of their nature possessed of a specific faculty of attraction.
Chapter [XVI]
Erasistratus, again, by his favourite principle of horror vacui could never explain the secretion of urine by the kidneys. While, however, he acknowledged that the kidneys do secrete urine, he makes no attempt to explain this; he ignores, but does not attempt to refute, the Hippocratic doctrine of specific attraction. “Servile” position taken up by Asclepiades and Erasistratus in regard to this function of urinary secretion.
Chapter [XVII]
Three other attempts (by adherents of the Erasistratean school and by Lycus of Macedonia) to explain how the kidneys come to separate out urine from the blood. All these ignore the obvious principle of attraction.