_Sulphur baths_, or baths impregnated with sulphuretted hydrogen gas, and having the well-known and offensive odour of rotten eggs, have been used as remedies in disease from time immemorial. It must be remembered that the so-called “sulphur waters” are of a very complex nature, and contain many saline ingredients, in addition to the sulphides of lime or soda, to the decomposition of which the presence of the characteristic gas is due. Most of these waters have also a high temperature, so that they must be considered as hot salt waters, with the addition of sulphuretted hydrogen, and it becomes a difficult matter to determine to which of their ingredients any good effect which they may produce is due. It must be borne in mind, also, that the amount of sulphuretted hydrogen contained even in the strongest of these waters, notwithstanding that it is amply sufficient to offend the sense of smell, is in reality very small, and there is no evidence that this gas is ever absorbed through the skin from the bath. People who visit sulphur baths generally drink the water, and while bathing they certainly inhale an atmosphere more or less charged with sulphuretted hydrogen. The general opinion at present is, that the effect of sulphur waters, when used for baths, is the same as that of other hot and saline springs, and that the sulphuretted hydrogen in the water is inoperative. At some of the sulphur baths the attendants point to a peculiar eruption on the skin, called La Poussée, as evidence of the peculiar effect of sulphur, but this eruption does not differ from that which so often results after a prolonged use of baths of any kind. There is no end to the varieties of baths which have been used at one time and another for the relief of sickness, and we shall content ourselves by a short allusion to some of the best known. _Mud baths, or moor baths_, are much used in some parts of Germany. They consist of water mixed with moor earth, or the mud deposited by some of the mineral springs. The resulting compound is thick and stodgy, and, like loosely-made farinaceous puddings. They cool unequally, and retain their heat for very long periods in the middle. Chemically they are composed of the various matters, soluble and insoluble, animal, vegetable, and mineral, of which mud or moor earth is formed. Much of their virtue has been ascribed to _formic acid_, a volatile body formed by ants, having a very pungent odour and considerable stimulating power. These baths are generally supposed to exert a very powerful action upon the skin.