_Confused state of this question—Popular versus Medical Psychology—Part played by the brain, the centre of psychic life—Hypotheses on the “seat” of the emotions—Part played by the heart, the centre of vegetative life—Popular metaphors and their physiological interpretation—Are the internal sensations reducible to a single process?—Part played by chemical action in the genesis of emotion—Cases of the introduction of toxic substances—Auto-intoxication—Modifications in the course of mental maladies._
As the physiological substratum of emotion, or its material (the reader may use which expression he prefers), comprises the organic or internal functions, and the motor functions showing themselves outwardly, we shall follow this division. Although it may seem artificial, it is not altogether so; the internal manifestations are, for the most part, outside the action of the will; the external manifestations are, in many cases, subject to that action. In any case, this somewhat arbitrary distinction is desirable for the sake of clearness in exposition.
