This bath is the most powerful and the most important within the domain of hydro-therapeutics, and has been made the basis of the system practised with much success by Dr. Fleury, at Bellevue (Paris). Its effect varies with its size, force, direction, duration, and temperature. It may be a column of water from one to three inches in diameter, falling twelve to twenty feet, or propelled at right angles to the patient's body. It may be broken up into fine streams by a rose, or into more numerous jets, arranged to play at once on the body from different quarters (douche du cercle - needle douche). Again, it may be used tepid, hot, or cold, or all three at one sitting, and its duration may vary from ten to sixty seconds, or in healthy people more.

The cold douche should be commenced cautiously, after due estimation of the patient's reactive power, and if there be much debility, it should be applied at first to the extremities only, and for a very brief period - ten to fifteen seconds; this is a most important point: it should never be applied to the head. In disease, the douche is, as a rule, suitable only for chronic cases, but with careful management may be applied to almost all conditions.

According to Dr. Howard Johnson, the cold douche markedly increases the respiratory acts, and "thereby imparts an enlivening influence to all the vital phenomena." "It is a diffusible stimulant, and is comparable to ammonia," though it does not always quicken the pulse. According to Fleury, the general douche, in shower, jet, or circle, is powerfully tonic and reconstitutive, by virtue of its action on the circulation. With an increased force of percussion, rapid movement from one part to another, and fine division of the liquid, a more exciting effect is produced. By directing the stream upon various parts in such force as to congest them, a revulsive action is made to relieve the congestion of other parts; thus, metrorrhagia and vomiting, even when dependent upon a uterine polypus, have ceased under a course of cold douching (Fleury, third ed., p. 297), and the volume of the liver and spleen has markedly diminished. Andral and Piorry verified the extent of hepatic dulness in a certain patient as 18 centimetres (vertical) and 11 centimetres to the left of the median line (horizontal), and agreed that immediately after an energetic douche, the former measurement was reduced by 1/2 centimetre, the latter by 5 centimetres; and in another case, the spleen, which measured at the commencement of treatment 23 centimetres vertically and 15 transversely, measured only 9 and 7 centimetres respectively after six days of repeated local douching. The effect on other organs is similar, though less rapid. But in chronic cases, it is important not to induce such results too quickly, since fresh and more serious congestion may be produced elsewhere.

In certain disorders, such as dropsy or effusion into joints, absorption has been markedly stimulated by the douche (Fleury).