hydrotherapy, use of water in the treatment of illness or injury. Although the medicinal and hygienic value of water was recognized by the early Greeks, hydrotherapy attained its widest use in the 18th and 19th cent. through the practice of the British physician Sir John Floyer and an Austrian peasant, Vincenz Priessnitz. Priessnitz is credited with a number of inventions still in use including the sponge bath, the douche, and the wet sheet pack, and he is acknowledged as an important contributor to the rise of the health spa movement in Europe. Scientific hydrotherapy is based on the conduction of heat to or from the body by means of a water medium. Heated water is used for its sedative effect, and hot water vapor is used in controlled situations to relieve pain. Patients who have suffered extensive burns are often immersed in water for long periods. Maintained at skin temperature, i.e., approximately 93°F (34°C), the water prevents loss of body heat. Fevers are reduced by cold sponge baths taken on rubber sheets. Whirlpool baths are used to relieve painful muscle and joint conditions, and underwater exercise has proved a useful physical therapy in cases of paralysis and stiffness of the extremities.