PURGATIVES are medicines which, within definite and comparatively short time after exhibition, produce the evacuation of the bowels. The remedies included under this head have, however, various modifications of action, which adapt them for the ful fillment of different therapeutic applications. They are divided by Pereira into five groups. viz.: 1. La•atires.—A purgative is said to be laxative when it operates so mildly as to evacuate the intestines without occasioning any general excitement of the system, or any extraordinary increase of watery secretion from the capillaries of the alimentary canal. This group includes manna, sulphur, cassia pulp, castor oil, etc.; and purga tives of this kind are employed when we wish to evacuate the bowels with the least possible irritation, as in children and pregnant women; in perions suffering from hernia, piles, stricture prolapsus of the rectum, etc.
2. Saline or Cooling Pargatires, such as sulphate of magnesia, and potastdo-tartrate of soda, either in simple solution or in the form of schllitz powder (q.v.). They give rise to more watery evacuations than the members of the preceding group, and are much employed in inflammatory and febrile cases.
3. Milder Acrid Purgatives, such. as scuba, rhubarb, and aloes. They possess acrid and stimulating properties, and are intermediate in activity between the last and the next group. Senna (generally in the form of black draught) is employed when we want an active but not very irritant purgative. Rhubarb is especially adapted for patients
when there is a want of tone in the alimentary canal. Aloes is used in torpid conditions of the hirge intestine; but as this drug irritates the rectum It should be avoided in cases of. piles and of pregnancy, especially if there is any threatening of miscarriage.
4. Drastic Purgatives, sucl•as jalap, scammony, gamboge, croton oil, coloeynth, and elaterium, when swallowed in large doses, act as irritant poisons, and are employed in medicine when the bowels have resisted the action of milder purgatives, or when we wish to exert ,a powerful derivative action upon the intestinal mucous membrane (as in cases of apopleXy, when croton oil is commonly used), or when it is necessary to remove a large quantity of water from the system, as in dropsical affections, in which case, elaterurin, from its hydragogne power, is usually employed.
5. Mercurial Purgatives, the chief of which are calomel, blue pill, and gray powder. They are commonly given with the view of increasing the discharge of bile, although their power in this respect has recently been denied. As their action is uncertain, they are usually combined with or followed by other purgatives. Podophyllin (q.v.) has recently been much used for the purpose of exciting bilious evacuations. Hamilton's book On Pulvative Medicines, which was published more than half a century ago, is still the standard work on the subject of this article.