Another physiological effect of emotion ought to be mentioned, as of recent years it has been the object of much and intensive study by numerous students and has been frequently made use of in the clinical study of mental derangements and in the study of subconscious phenomena. I refer to the so-called “_psycho-galvanic reflex_.” As an outcome of all the investigations which have been made by numerous students into this phenomenon, it now seems clear that there are two types of galvanic reactions, distinct from each other, which can be recognized. The one type first described by Féré[211] consists in an increase, brought about by emotion, of a galvanic current made to pass through the body from a galvanic cell. If a very sensitive galvanometer is put in circuit with the body and such a cell, a certain deviation of the needle of course may be noted varying in amplitude according to the resistance of the body. Now, if an idea associated with emotion—i.e., possessing a sufficient amount of affective tone—is made to enter the consciousness of the person experimented upon, there is observed an increased deflection of the needle, showing an increase of current under the influence of the emotion. The generally accepted interpretation of this increase is that it is due to diminished resistance of the skin (with which the electrodes are in contact) caused by an increase of the secretions of the sweat glands. A similar increase of current follows various sensory stimulations, such as the pricking of a pin, loud noises, etc. It may be interesting for historical reasons to quote here Féré’s statement of his observations, as they seem to be generally overlooked. In his volume, “La Pathologie des Emotions,” in 1892, he thus sums up his earlier and later observations: "I then produce various sensory stimulations—visual (colored glasses), auditory (tuning fork), gustatory, olfactory, etc. Whereupon there results a sudden deviation of the needle of the galvanometer which, for the strongest stimulations, may travel fifteen divisions (milliampères). The same deviation may also be produced under the influence of sthenic emotions, that is to say, it is produced under all the conditions where I have previously noticed an augmentation of the size of the limbs, made evident through the plethysmograph. Absence of stimulation, on the contrary, increases the resistance; in one subject the deviation was reduced by simply closing the eyes. “Since these facts were first described at the Biological Society I have been enabled to make more exact observations by using the process recommended by A. Vigouroux (De la résistance électrique chez les mélancoliques, Th. 1890, p. 17), and I have ascertained that under the influence of painful emotions or tonic emotions the electrical resistance may, in hystericals, instantaneously vary from 4,000 to 60,000 ohms.”