731. Mustard is too well known to require describing. It is an emetic, diuretic, stimulant, and rubefacient. It is used externally as a poultice. Mustard poultices are made of the powder, bread crumbs, and water; or of one part of mustard to two of flour; or, especially for children, of linseed meal, mixed with a little of the powder, or having some of the powder slightly sprinkled on the surface. Sometimes a little vinegar is added under the idea that it increases the strength of the poultice, but this is not necessary. In all cases where a stimulant is required, such as sore throats, rheumatic pains in the joints, cholera, cramps in the extremities, diarrhœa, and many other diseases. When applied it should not be left on too long, as it is apt to cause ulceration of the part. From ten to thirty minutes is quite long enough. When used internally as an emetic, a large teaspoonful mixed with a tumbler of warm water generally operates quickly and safely, frequently when other emetics have failed. In dropsy it is sometimes given in the form of whey, which is made by boiling half an ounce of the bruised seeds in a pint of milk, and straining off the curd. From three to four ounces of this is to be taken for a dose three times a day.