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.
The old hypothesis of the influence of a magnet on the human body was at this time revived, and Charcot’s pupils found that when a susceptible female patient held in the hand a bar of iron surrounded by a coil of copper wire leading to a chemical electric cell or battery nothing happened so long as the connection was broken. But as soon as the wire was connected so as to set up an electric current and to make the bar of iron into a magnet, the hand and arm (up to the shoulder) of the young woman holding the bar, lost all sensation. She was not allowed to see her hand and arm, and was apparently quite unconscious of the thrusting of large carpet-needles into, and even through, them, though as long as the bar of iron was not magnetised she shrunk from a pin-prick applied to the same part. I saw this experiment with Charcot and some others present, and I noticed that the order to an assistant to “make contact,” that is to say, to convert the bar of iron into a magnet, was given very emphatically by Charcot, and that there was an attitude of expectation on the part of all present--which was followed by the demonstration by means of needle-pricking that the young woman’s arm had lost sensation, or, as they say, “was in a state of anæsthesia.”