Diuretics, drugs used to increase the amount of the urinary excretion or of some of its constituents. They may be divided into several groups: 1, those which increase the water of the urine with but little effect on its solid constituents; 2, those which increase both the water and the solids; 3. those which increase the solid rather than the watery constituents; 4, those which alter the quality without augmenting the quantity. To the first class belong squills, juniper, taraxicum, horseradish, parsley, broom, carrot seed, spirits of nitrous ether, pure water, cantharides, and turpentine. Cantharides and turpentine may be given in such doses as to produce congestion of the kidneys and bloody urine. If their action is carried far enough, a suppression instead of an increase of the urine may result. Many salines, such as acetates, citrates, tartrates, and carbonates of soda and potassa, nitrate of potassa, and sulphate and citrate of magnesia, belong to the second class. Some of these salts may be given so as to pass off by the bowels, and exert but little effect upon the kidneys.

In general, it is necessary to give this class of drugs in small doses, frequently repeated, when it is desired that they should pass through the kidneys and act as diuretics, and in one or two large doses when they are intended to act upon the bowels. Colchicnm is the principal agent of the third class. According to Dr. Hammond's experiments it has a powerful effect in augmenting the amount of solid urinary constituents, while the water is comparatively little affected. The salts formed by the alkalies with carbonic and vegetable acids render the urine alkaline when given in sufficient doses, and are consequently examples of the fourth group of diuretics. Uva ursi and chimaphila umbellate or winter-green act as diuretics in virtue of the volatile oils and tannic acid which they contain, and which pass into the urine, imparting to it a dark color and peculiar odor. Buchu. copaiba, cu-bebs, and similar substances act by virtue of their resins and volatile oil. Their therapeutic effect is due rather to the alterative action of the urine bearing these constituents on the mucous membranes by which it is excreted and over which it passes, than to any increase in its amount.

Benzoic acid passes into the urine in the form of hippuric acid, and may be used when it is desirable to increase the acidity of that fluid. Digitalis, although frequently used as a diuretic, is probably only secondarily so. It increases the flow of urine by virtue of its action upon the arterial tension of the kidneys, promoting thereby a more rapid flow and even distribution of the blood through them. Digitalis is frequently combined with squill. - Diuretics are used in various stages of kidney diseases (where they should be very cautiously managed), in gout, rheumatism, dropsy, and affections of the urinary passages. Although very useful and efficient, in many cases, they cannot always be relied upon, and consequently; are not regarded as among the most certain of medicines. It is well known that many wines, especially hocks and acid wines, are apt to run off by the kidneys. Ardent spirits, especially gin and whiskey, will also increase the urine, but neither wines nor ardent spirits are often prescribed as diuretics.