This may be prepared by mixing solutions of nitrate of silver and iodide of potassium; the iodide of silver being thrown down as an insoluble, greenish-yellow powder. Dr. Charles Patterson, of Dublin, having convinced himself, by experiment, that this preparation does not change colour on exposure to the light, even in contact with organized matter, conceived that it might be advantageously substituted for nitrate of silver, on the ground that it would not be liable to cause discoloration of the skin. In order to determine how far it might possess the therapeutic virtues of the nitrate, he tried the medicine in various diseases; and, though he succeeded in curing a gastric affection of the Irish peasantry, in which the nitrate had been found useful, in ameliorating pertussis, and in relieving a case of dysmenorrhoea, his experience was certainly not, upon the whole, very satisfactory; and a much more extensive series of observations would be necessary, to establish the claim of the iodide of silver to be used as a substitute for the nitrate. Nor is it by any means certain that it might not cause discoloration of the skin; for though, if absorbed unchanged, it might not thus act, the probability is that, before entering the circulation, it would be chemically altered, and that the compound of silver really absorbed would be liable to the same changes in the system, as that which enters the blood-vessels when the nitrate is administered. Nevertheless, the iodide is perhaps worthy of further trial; as, if found to be possessed of the virtues of the nitrate, without its disadvantages, it would be a most valuable addition to the Materia Medica. From one to three grains may be given three times a day, and gradually increased till some disagreeable effect upon the stomach or bowels is produced.