CHAP. I. What a medicine is, and how it differeth from nourishment.
WEe define a medicine ro be, That which hath power to change the body according to one or more qualities; and that such as cannot be changed into our nature: contra∣ry whereto we term that nourishment which may be converted into the substance of our bodies. But we define them by the word power, because they have not an absolute nature, but as by relation and depending upon the condition of the bodies by whom they are taken. For that which is medicine to one, is meat to another; and that which is meat to this, is medicine to that. Thus for example, Hellebore is nourishment to the Quail, but a medicine to man: Hemlock is nourishment to a Sterling, but poyson to a Goose: the Ferula is food to an Ass, but poyson to other cattel. Now this diversity is to be attributed to the different natures of creatures.
It is recorded in history, that the same by long use may happen in men. They report that a maid was presented to Alexander the Great, who nourished with Napellus, and other poysons, had by long use made them familiar to her, so that the very breath she breathed was deadly to the by-stan∣ders. Therefore it ought to seem no marvel, if at any time it happen, that medicines turn into the nature and nourishment of our bodies: for we commonly may see birds and swine feed upon serpents and toads without any harm: and lastly,
—Serpente Cinonia pullos Nutrit, & inducit per devia rura lacerta: Illi eadem sumptis quaerunt animalia pennis. The Stork with Serpents and with Lizards caught, In wayless places nourisheth her brood: And they the same pursue, when as they're taught To use their wing, to get their wishd-for food.