In 1890 Tarchanoff published in Pflüger's Archiv a paper describing experiments with a galvonometer in series with the human body. Changes in the electromotive force with resulting deflection of the galvanometer occurred when the face, ears or feet were tickled, and when various sense organs were stimulated. He noticed that actual stimulation was not necessary; the effect would appear when the person merely imagined the irritations. He observed, moreover, that the recollection of any kind of strong emotion produced the same effect. Ordinary intellectual exercise had no effect unless it was accompanied by exertion. Expectant attention had, however, a marked effect—a fact explainable if we consider attention as one of the emotions. Tarchanoff believed that the current sent through the galvanometer was due to a secretory current of electricity produced by the action of the sweat glands.
This paper by Tarchanoff was really a model piece of investigation. I read
SCRIPTURE EW. DETECTION OF THE EMOTIONS BY THE GALVANOMETER.. JAMA. 1908;L(15):1164–1165. doi:10.1001/jama.1908.25310410004001a