Purgatives are divisible into several groups, according to the nature of their action.

Laxatives are medicines which stimulate the intestinal movements, without increasing to any considerable extent, at least, the intestinal secretions.

Saline Purgatives excite increased secretion, while at the same time they hasten the peristaltic action. The dejections which are produced by them are loose and watery.

Mercurial Purgatives, chiefly calomel and blue mass, exert an influence peculiar to themselves. Without expressing an opinion at present, for or against their supposed cholagogue effects, the author believes that they differ so much in their action from other purgatives as to be appropriately placed in a separate class.