Cathartics or purgatives are medicinal agents which evacuate the bowels, and are capable of fulfilling three different indications: 1. Simply to evacuate the bowels. 2. To excite an increased discharge from the mucous coat of the intestines, and 3. To stimulate the neighboring viscera and cause them to secrete a greater quantity of their peculiar fluids. When they produce watery discharges by stimulating the mucous follicles and ex-halants, they are termed hydragogues. When given in overdoses they are so powerful as to produce violent vomiting and purging, pain in the abdomen, cold extremities and a sinking pulse. Several different cathartics are usually combined in one formula, when it is desired to produce all of the indications above referred to. Some agents of this class produce their effect by absorbing the acid generated in the alimentary canal, thus becoming converted into a purgative salt, as magnesia, for example. Others expend their principal force upon the rectum and large intestines, and for this reason are advantageously employed in affections of the lower bowels, and the uterus and its appendages, such as aloes, for example. Cathartics should always be given on an empty stomach. If administered immediately after a full meal, they arrest the digestive process, are liable to cause nausea, if not vomiting, and do not evacuate the bowels with the same certainty or effect.

When simple costiveness is to be removed, the cathartic may be administered in the evening, and, if not sufficient, the dose can be repeated in the morning and at regular intervals through the day, until the effect is produced.

In administering cathartics, the excitement is to be continued till the requisite action is induced, yet not sufficient to prove an irritant. But in the treatment of many diseases, it is preferable to purge through the day, in order that the sleep may not be disturbed at night. The operation of cathartics may be very much accelerated by the free use of diluent drinks, such as gruel, bar-lev water, etc., etc. By combining these remedies, the action of many of them is modified and controlled; and some of the more powerful may be made to operate mildly and certainly by uniting small quantities of several of them in the same dose.

The addition of an emetic substance, such as ipecacuanha, or tartar emetic, gives activity to the combination, while it modifies the harshness of the powerful cathartics.

The operation of a cathartic may often be promoted by judicious venesection, and if there is spasm of the intestines, opium may be advantageously added to the cathartic.

Cathartics act not only upon the bowels, but upon distant parts, as every portion of the organism is capable of being impressed by them. Cathartics are divided, according to the intensity of their operation, into laxatives, purgatives and drastics, to which may also be added enemata. Laxatives gently stimulate the mucous coat of the intestines, and hence they are well adapted for cases in which the sole indication is to unload the bowels of their contents. Purgatives are more powerful in their operation; they excite a copious exhalation from the mucous lining of the intestines, and augment the peristaltic action to a great degree. Drastics are the more powerful and violent cathartics, and produce a greater degree of irritation in the lining membranes of the intestines, and occasionally act upon the nerves of the stomach, so as to cause nausea and sometimes vomiting. Drastics generally belong to the resino-extractive substances, and act violently, on account of being sparingly soluble and adhering to the mucous coat of the intestines.

Enemata are agents of this class which act on the lower part of the intestinal tube by direct application ; they irritate the lining membrane of the rectum, and by sympathy of continuity, their influence is extended to the intestinal canal. Hence enemata may be employed with advantage when cathartics cannot be given by the mouth, as when deglutition is impracticable. What are known as saline cathartics are employed in the treatment of febrile and inflammatory affections, as they do not produce any excitant action on the general system. There are also acrid cathartics, which are not violent enough to cause inflammation. Others are known as mercurial cathartics. The class known as laxatives comprise such substances as certain articles of diet, as ripe and dried fruits, such as tamarinds, peaches, raisins, figs, prunes, also molasses, honey, cracked wheat, Indian meal and oatmeal, etc., etc. Other laxatives are castor oil, manna, sulphur, purging cassia, etc., etc. Saline cathartics comprise such substances as magnesia, carbonate and sulphate of magnesia (Epsom salts), solution of citrate of magnesia, sulphate of sodium (Glauber's salt), solution of manganese, phosphate of sodium, sulphate of potassium, cream of tartar, soluble tartar, Rochelle salts. Mild, acrid cathartics comprise such substances as rhubarb, aloes, senna, leptandra, elder. Drastic cathartics comprise such substances as jalap, may apple, scammony, colocynth, gamboge, elaterium, croton oil. Mercurial cathartics consist of calomel, blue mass, mercury with chalk. Enemata consist of tepid water, flaxseed tea or other demulcent infusion; a combination of a teaspoonful each of common salt, molasses and lard or olive oil, in two-thirds of a pint of warm water, to which castor oil or Epsom salt may be added to augment the cathartic effect, is a formula for the common laxative enema. (See Purgatives.)