In horse medicine this class is at once the most important and the most abused. Drugs which increase the amount of urine passed are called diuretics, and in the hands of the groom and carter have been productive of an incalculable amount of injury.

Diuretics are employed for so many purposes, and with such obvious results, that their popularity is easily accounted for. While increasing the actual quantity of fluid passed, they give relief to the kidneys by washing out the uriniferous tubes, and carrying away any accumulated mucus and fine saline particles which might eventuate in the production of calculi. They lower temperature and relieve the common symptoms of fever, and cause the removal of some of its products in the urinary discharges. In all diseases of the horse in which there is enlargement of the extremities and other depending parts from infiltration of fluid into the tissues, diuretics have a marked and immediate effect. In certain diseased conditions of the integument, as grease, cracked heels, mud fever, as well as obstructions and inflammatory swellings in the lymphatic or other vessels, diuretics are of great value.

The abuse consists chiefly in giving diuretics to healthy animals with a view to saving labour and making the skin glossy. In this connection it may be well to remind readers that a horse's urine being thick occasionally, more especially when green food is substituted for dry, is not necessarily a symptom of disease - but the majority of grooms would seem to regard it as such.

The error is also frequently committed of giving diuretics to horses whose kidneys are already too active, and passing too much urine, with the common result that a harmless excess of secretion is converted into active disease.

The diuretic drugs most generally approved for horses are nitrate of potash (nitre), resin, soap, turpentine, spirit of nitrous ether (sweet spirit of nitre), balsam of copaiba, and the oils of juniper and aniseed. There are many drugs having more or less diuretic action, but the above list includes all those in common use and of well-proved therapeutic value.