Salicylic acid is found in nature in the leaves and barks of Willows, in Oil of Wintergreen (Gaultheria), which is one of the chief sources of its supply, and is obtained synthetically from Carbolic acid. Like Carbol. ac. it has been largely used as a disinfectant, and as it is supposed to be non-poisonous it is used for mixing with and so preserving foods. MacLagan, of London, and Senator, of Berlin, introduced it into medicine as a remedy for rheumatism. Over-dosings led to the discovery of its power to set up the phenomena of Ménière's disease (auditory nerve vertigo), gastric disturbances and delirium, and these form the nucleus of the homoeopathic Schema, which has been filled out by fragmentary provings and clinical use. Among the uses of Sal. ac. recommended in the general text-books are these: "Sal. ac. dissolved in Collodion flexile (gr. xxx to one drachm) is very useful for corns and warts; also to hasten the peeling of palms and soles after scarlet fever" (Brunton). "A mixture of 2 parts with 100 of tallow, applied directly to the feet, not to the stockings, has been found most useful in preventing sweating and soreness of the feet in soldiers after a long march" (Brunton). The property of preventing foot-sweat is by no means an unmixed boon, and serious illness has resulted from it. Consequently in homoeopathic practice Sal. ac. has been found an excellent remedy for affections following suppression of foot-sweat. Sal. ac. has a specific relation to rheumatism, but the massive doses given in ordinary practice have been attended with so many unpleasant symptoms—vital depression, fainting, flatulent dyspepsia, delirium, &c.—that the ingenuity of chemists has been devoted for years past to finding a compound which shall be innocent as well as effective. Aspirin (Acetyl-salicylic acid), Salophen (Acetyl-para-amidophenol salicylate), and Salol (Phenol salicylate), are supposed to fulfil these conditions more or less completely. Salol has had an accidental proving which has led to some homoeopathic uses. It is the "unpleasant symptoms" which so many practitioners wish to avoid, which are of especial value to homoeopaths. Like Carbolic acid and other disinfectants, Sal. ac. produces fermentative dyspepsia, and diarrhoea with putrid-smelling stools, and it meets dynamically blood-poisoning conditions, such as puerperal fever and septicaemia. Hering says: "Pieces of spongy bone become soft as leather in a few days when placed in a 1/2 per cent. solution, while compact bone tissues are very slowly softened; enamel of teeth is very slightly affected by it, but the dentine, when it is exposed by caries, is rapidly destroyed. The increased amount of the salts of lime in the urine soon after Sal. ac. has been taken shows that the acid deprives living as well as dead bone of its lime salts." He adds that it causes necrosis, especially of the tibia. The symptoms are < by touch. < By motion. < At night. < By cold air or touch of anything cold. > By hot applications, especially by dry heat.