Origin. - A liquid composed of not less than 6 per cent. by weight of sulphur dioxide and about 94 per cent. of water.

Description and Properties. - A colorless liquid, of the characteristic odor of burning sulphur, and of a very acrid, sulphurous taste. It should be kept in dark-colored, glass-stoppered bottles, in a cool place, and protected from light.

Dose. - 1/2-2 fluidrams (1.8-7.39 Cc.) [30 minims (2 Cc), U. S. P.].

Physiological Action. - Externally and Locally. - Sulphurous acid is a powerful deoxidizing agent. It easily abstracts oxygen from organic bodies, the acid being a powerful disinfectant, antiseptic, deodorant, and parasiticide.

Internally. - The disinfecting properties of sulphurous acid are less apparent when the drug is ingested than when it is used externally.

Therapeutics. - Externally and Locally. - As an antiseptic, disinfectant, and deodorant sulphurous acid may be employed in the treatment of various parasitic skin diseases, and a solution of sulphurous acid affords an efficient application to the throat in pharyngitis, particularly the gangrenous form, diphtheria, etc.

According to Dujardin-Beaumetz, Sollaud, and Balbaud, non-febrile pulmonary phthisis is often favorably influenced by the daily inhalation for a short time of sulphurous-acid vapor. This disagreeable, not to say dangerous, method of treatment has neither been generally adopted nor proved to be of established efficacy.

The acid is a useful antiseptic to apply to recent wounds, and may be employed to disinfect the dejections of the sick. The fumes of sulphur are worthless as general disinfectants. They may be of service in killing mosquitoes, but dry fumes are practically inert so far as their action on bacteria is concerned. Burning sulphur as a means of disinfection is largely a fetish founded on ancient and superstitious ideas regarding infectious diseases.

Internally. - Sulphurous acid is seldom used internally, though, owing to its powerful antifermentative properties, it has been employed in so-called fermentative dyspepsia, intestinal fermentation, and urticaria. While it checks fermentation in the laboratory, its effect is less certain in the body; nor can the internal administration of the drug be regarded as satisfactory.

Administration. - Sulphurous acid should be given well diluted with water.