It will be noticed that Féré attributed the variations of the current to variations of resistance of the body induced by sensations and emotions. The method of obtaining the psycho-galvanic reaction may be varied in many ways, the underlying principle being the same, namely, the arousing of an emotion of some kind. This may be simply through imagined ideas, or by expectant attention, sensory stimulation, suggested thoughts, verbal stimuli, etc. According to Peterson and Jung,[212] “excluding the effect of attention, we find that every stimulus accompanied by an emotion causes a rise in the electric curve, and directly in proportion to the liveliness and actuality of the emotion aroused. The galvanometer is therefore a measurer of the amount of emotional tone, and becomes a new instrument of precision in psychological research.” This last statement can hardly be said to be justified, as we have no means of measuring the “liveliness and actuality” of an emotion and, therefore, of co-relating it with a galvanic current, nor have we any grounds for assuming that the secretion of sweat (upon which the diminished resistance of the body presumably depends) is proportionate to the liveliness of the emotion, or, indeed, even that it always occurs. It is enough to say that the galvanic current is in general a means of detecting the presence of emotion. The second type of galvanic reaction, as shown by Sidis and Kalmus,[213] does not depend upon the diminished resistance of the body to a galvanic current passing from without through the body, but is a current originating within the body under the influence of emotion. Sidis and Kalmus concluded that “active psycho-physiological processes, sensory and emotional processes, with the exception of purely ideational ones, initiated in a living organism, bring about electromotive forces with consequent galvanometric deflections.” In a later series of experiments Sidis and Nelson[214] came to the conclusion that the origin of the electromotive force causing the galvanic deflection was in the muscles.[215] Wells and Forbes,[216] on the other hand, conclude from their own investigation that the origin of the galvanic current is to be found in the sweat gland activity and believe the muscular origin improbable. From a clinical standpoint the question is unimportant.