Although Rhases be the most ancient writer whose account of smallpox and measles has come down to us, he does not pretend to have been the first of his countrymen who had noticed them, but gives extracts from the works of the elder Mesue, the elder Serapion and Aaron, wherein mention is made of them. According to Rhases, the common cause of smallpox is a fermentation in the blood; and hence the disease is most apt to seize children, whose blood is hotter than that of other persons. He was well aware, however, that the disease is capable of being propagated by contagion, for he ranks the pestilential fever or smallpox among the diseases “qui transeunt ab uno ad alios.” The symptoms, as described by him, are, continued fever, pain in the back, itching at the nose, disturbed sleep, and afterwards redness and fulness of the face, pain of the throat, difficulty of breathing, dryness of the mouth, thick spittle, hoarseness, headach, inquietude; and these symptoms are followed by the characteristic eruption of the smallpox or measles; but in the case of the latter there is more anxiety of mind, sick qualms, and heaviness of heart; and in that of the former there is more pain in the back, heat, and inflammation of the whole body, especially in the throat, with a shining redness. He then lays down the rules of treatment. He directs us to bleed from the arm at the commencement, provided the patient be more than fourteen years old, but by a cupping instrument if he be younger. He forbids us, however, to abstract blood after the eruption is come out. He allows light kinds of animal food, with acids; and for drink he recommends water cooled with snow, or cold spring water, or some diluent and acid draught, such as barley-water acidulated with pomegranate juice. Aaron, one of his authorities, forbids, however, the administration of cold water when the eruption is coming out. He directs the chamber to be sprinkled with cold water, and even at a certain stage permits the patient to go into the cold bath. He recommends abstinence from new milk, wine, dates, honey, mutton, beef, shell-fish, and all high-seasoned and heating things. The rest of his general treatment we need not give in detail. Suffice it to say, that the medicines recommended by him are, for the most part, vegetable acids and astringents. Upon the whole, the earlier part of his treatment consists of bleeding, cold drinks, and acid draughts. For hastening the eruption, when that is desirable, he directs us to wrap up the patient closely in clothes; to rub his body all over; to keep him in a room not very cold; to give him some cold water to drink; to put on a double shirt; and to place near him two small basins of very hot water, one before and the other behind him, so that the vapour may be diffused all over his body, except the face; but he prudently directs us not to allow the moisture to cool upon the body, but to get it carefully wiped off. All furnaces and hot baths he