At this time there had been a revival of the ancient and fanciful doctrine of “metallic sympathies,” which flourished a hundred years ago, and was even then but a revival of the strange fancies as to “sympathetic powders,” which were brought before the Royal Society by Sir Kenelm Digby at one of its first meetings, in 1660. In the journal-book of the Royal Society of June 5 of that year, we read, “Magnetical cures were then discoursed of. Sir Gilbert Talbot promised to bring in what he knew of sympatheticall cures. Those that had any powder of sympathy were desired to bring some of it at the next meeting. Sir Kenelm Digby related that the calcined powder of toades reverberated, applyed in bagges upon the stomach of a pestiferate body, cures it by several applications.” The belief in sympathetic powders and metals was a last survival of the mediæval doctrine of “signatures,” itself a form of the fetish still practised by African witch-doctors, and directly connected with the universal system of magic and witchcraft of European as well as of more remote populations. To this day, such beliefs lie close beneath the thin crust of modern knowledge and civilisation, even in England, treasured in obscure tradition and ready to burst forth in grotesque revivals in all classes of society. The Royal Society put many of these reputed mechanisms of witchcraft and magic to the test, and by showing their failure to produce the effects attributed to them, helped greatly to cause witches, wizards, and their followers to draw in their horns and disappear. The germ, however, remained, and reappears in various forms to-day. Thirty years ago some of the doctors in Paris believed that a small disc of gold, or copper, or of silver, laid flat on the arm could produce an absence of sensation in the arm, and that whilst one person could be thus affected by one metal another person would respond only to another metal, according to a supposed “sympathy” or special affinity of the nervous system for this or that metal. This astonishing doctrine was thought to be proved by certain experiments made with the curiously “nervous” (hysterical) women who frequent the Salpêtrière Hospital as out-patients. That the loss of sensation, which was real enough, was due to what is called “suggestion”--that is to say, a belief on the part of the patient that such would be the case, because the doctor said it would--and had nothing to do with one metal or another, was subsequently proved by making use of wooden discs in place of metallic ones, the patient being led to suppose that a disc of metal of the kind with which she believed herself “sympathetic” was being applied. Sensation disappeared just as readily as when a special metallic disc was used.