The moon was universally admitted under the theory of the macrocosm and the microcosm to rule the head, and as silver was the recognised representative of Luna among the metals the deduction was obvious that silver was the suitable remedy for all diseases affecting the brain, as apoplexy, epilepsy, melancholia, vertigo, and failure of memory. Tachenius relates that a certain silversmith had the gift of being able to repeat word for word anything that he heard, and this power he attributed to his absorption of particles of silver in the course of his work. It does not appear, however, that all silversmiths were similarly endowed. The Greek and Latin doctors make no allusion to silver as a medicine, and the earliest evidence of its actual employment as a remedy is found in the writings of Avicenna, who gave it in the metallic state “in tremore cordis, in fœtore oris.” He is also believed to have introduced the practice of silvering pills with the intention of thereby adding to their efficacy. To John Damascenus, a Christian saint who lived among the Arabs before Avicenna, is attributed the remark concerning silver, “Remedium adhibitum est, et in omnibus itaque capitis morbis, ob Lunæ, Argenti, et Cerebri sympathicam trinitatem.” This association of the moon, silver, and the brain was believed in firmly by the chemical doctors of the sixteenth century, and for a long time a tincture of the moon, tinctura Lunæ, was the most famous remedy in epilepsy and melancholia. A great many high authorities, among them Boyle, Boerhaave, and Hoffmann in the eighteenth century, continued to prescribe this tincture or the lunar pills, but silver gradually dropped out of fashion. A great number of medical investigators since have from time to time recommended the nitrate or the chloride of silver in various diseases, but without succeeding in securing for silver a permanent reputation as an internal medicine. The Pilulæ Lunares were generally composed of nitrate of silver combined with opium, musk, and camphor. Nitrate of silver was given in doses varying from a twentieth to a tenth of a grain. The tincture of the moon was a solution of nitrate of silver with some copper, which gave it a blue tint and probably was the active medicinal ingredient. Fused nitrate of silver or lunar caustic seems to have succeeded to the reputation of fused caustic potash as a cautery, and also to have acquired the name of lapis infernalis (sometimes translated “hell-stone” in old books) originally applied to the fused potash. The only reason assigned for this title is the keen pain caused by the application of the caustic, though probably it was first adopted to contrast it with the lapis divinus, which was a combination of sulphate of copper and alum used as an application to the eyes.