among physicians, remedies which evacuate a large quantity of water in dropsies. The word is formed of ἰδρος, water, and ἀγω, to draw or lead; but the application of the term proceeds upon a mistaken supposition, that every purgative had some particular humour which it would evacuate, and which could not be evacuated by any other. It is now, however, discovered, that all strong purgatives will prove hydragogues, if given in large quantity, or in weak constitutions. The principal medicines recommended as hydragogues, are the juice of elder, the root of iris, soldanella, mechoaean, jalap, &c.