This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol2", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
The metal itself is not used in medicine. Though capable of producing poisonous effects from its facility of oxidizement, it is too uncertain to be relied on.* Realgar and orpiment, the former called red sulphuret or bisulphuret of arsenic, and sandaraca by the ancients; the latter, yellow sulphuret or tersulphuret of arsenic, and auripigmentum or arsenicum by the ancients, though employed by the old Greeks, Romans, and Arabians, and occasionally by the moderns, have now been abandoned in regular practice, as less efficient and more uncertain than arsenious acid and its compounds. The preparations at present most in use, at least wherever the English language is spoken, are arsenious acid and the officinal solution of arsenite of potassa, commonly known as Fowler's solution. Arseniate of soda, however, is considerably employed, and has been adopted in the British Pharmacopoeia. Some others are occasionally used, which will be noticed.*
* Schroff infers, from his experiments on rabbits, that both metallic arsenic and arsenical cobalt, quite free from arsenious acid, are highly poisonous; even more so than the arsenious acid itself, in equal weights, when the latter is given undissolved. (Journ. de Pharm. et de Chim., Sept. 1859, p. 236.) - Note to the second edition.