I use this term to express that operation of a remedy which consists in the cure of a disease by the removal of its cause. It very often happens that one morbid state depends upon another; and the cure of the latter, by any process whatever, results in the cure of the former. This is not, however, the influence to which allusion is here made. To bring any case under the present head, the cause must not itself be a disease, and the remedy removing it must do so by a special agency. Thus, antacids cure headache by neutralizing acid in the stomach, which produces the headache. An emetic will cure spasm of the stomach caused by indigestible food by evacuating the offending matter, and cathartics often relieve colic on a similar principle. An alkaline carbonate will relieve irritation of the urinary passages dependent on the precipitation of uric acid, and certain acids the same condition produced by the presence of undissolved phosphates; each operating on the offending cause by neutralizing it, or rendering it soluble. Anthelmintics cure various disorders, dependent on worms in the bowels, by destroying or expelling the worms. In like manner, the class of parasiticides act by destroying the microscopic parasites, whether animal or vegetable, which infest the skin and various internal structures; and under the same head may be classed the remedies which render inert or destroy those poisonous agents, now generally believed to be organized beings, which, entering the circulation, and there acting as ferments, give rise to the various zymotic diseases.