Origin. - A volatile oil obtained from black mustard by maceration with water and subsequent distillation, yielding not less than 92 per cent. of allyl isothiocyanate.

Description and Properties. - A colorless or pale-yellow, limpid, and strongly refractive liquid, having a very pungent and acrid odor and taste. Freely soluble in alcohol, ether, or carbon disulphide. Used externally.

Physiological Action. - Externally and Locally. - Mustard is irritant, counter-irritant, rubefacient, and vesicant. Any degree of irritation, from slight redness of the skin to severe blistering, may be produced by mustard. It is more rapid in its action than can-tharides, and when applied to the skin there is produced almost immediately a sensation of warmth, which rapidly passes into a severe burning pain. This irritation of the sensory nerves is succeeded by paralysis and more or less loss of sensation, so that if mustard be allowed to remain on the skin until blistering ensues there is a decided diminution of pain.

The local application of mustard reflexly stimulates the heart and respiration.

Internally. - Mustard in small amounts is taken as a condiment, and is a powerful stimulant of the gastro-intestinal tract. Large doses irritate the stomach and act as an emetic, producing prompt emesis without depression, owing to the reflex stimulation of the heart and respiration.

The volatile oil of mustard is never intentionally given internally. It is a powerful caustic irritant, a single drop upon the tongue producing an intense burning pain in the throat, stomach, and nose.

Therapeutics. - Externally and Locally. - Mustard may be used locally for the same purposes as cantharides, being superior to the latter-named drug when a simple rubefacient effect is desired. Mustard when applied locally is more of a stimulant to the circulatory and respiratory systems than cantharides, and is therefore an efficient remedy in syncope, asphyxia, and coma.

As a stimulant in these conditions, a large mustard poultice is applied to the legs.

A mustard bath, in the strength of 1 dram (4.0 Gm.) to 1 gallon (3785.43 Cc.) of water, is an efficient means of breaking up a cold, and if properly used is of service when the rash in measles or scarlet fever has receded.

The menses may often be re-established when suppressed by a mustard sitz-bath, taken at the time of the expected period.

Internally. - Other than the use of mustard as a condiment, the drug is given only to produce vomiting, being one of the best emetics in indigestion and narcotic poisoning.

Obstinate hiccough has sometimes been arrested by an infusion of mustard.

Administration. - A mustard plaster, or sinapism, is prepared by mixing equal parts of wheaten or rye flour with water to the consistence of a thick paste, which is spread on linen or cotton cloth and applied to the skin. A dampened piece of gauze interposed between the plaster and the skin will prevent the former from adhering.

A mustard cataplasm is a weaker preparation. A flaxseed or cornmeal poultice is made, to which a small quantity of ground mustard is added. This is intended to maintain a gentler but more prolonged action than the sinapism.

"Mustard leaves," or plasters which may be obtained ready prepared at drug stores, are intended to be simply dipped in water and applied to the skin. Their activity may be lessened by interposing a thin piece of linen or cotton cloth between the plaster and the skin.

Liniments containing oil of mustard are efficient rubefacients, care being taken to adapt the strength of the preparation to the delicacy of the skin.

When mustard is taken as an emetic it is given in the form of an infusion, in the proportion of I, 2, or 3 drams (4.0, 8.0, or 12.0 Gm.) to 1 pint (473.17 Cc.) of water.

A preparation known as mustard whey is sometimes given. It is prepared by boiling 1 1/2 ounces (46.65 Gm.) of bruised mustard seed in a mixture of 1 pint (473.17 Cc.) of milk and 1 quart (946.35 Cc.) of water, until it is curdled, when the whey should be strained off.