Experimental studies of the emotions are comparatively recent undertakings. Most investigations have been done by means of the method of expression, on the basis of a physical measurement of characteristic physiological changes, as breathing or pulse. One of the more promising of these measurements is that of the so-called psychogalvanic reflex. This reflex is a change of electrical conduction through the body which can be measured by means of a galvanometer. It occurs under emotional conditions and when an emotion is reported by the subject. This phenomenon was first reported by Feré in 1888 when he found the reflex corresponding with plethysmographic changes in hysterical patients. He attributed it to lowering of body resistance under emotional states. Tarchanov in 1890 reported the reflex in normal subjects, showing it to be a normal reaction. In 1904 Müller reported studies of the psychogalvanic reflex which were followed by those of Veraguth. Some other early investigators are Goldemeister, Waller, Prideaux, Peterson, Jung, and Scripture
