It is evident that our two authors, whether consciously or not, share the dualist point of view with the common opinion which they are combating; the only difference being in the interversion of cause and effect. Emotion is a cause of which the physical manifestations are the effect, says one party; the physical manifestations are the cause of which emotion is the effect, says the other. In my view, there would be a great advantage in eliminating from the question every notion of cause and effect, every relation of causality, and in substituting for the dualistic position a unitary or monistic one. The Aristotelian formula of matter and form seems to me to meet the case better, if we understand by “matter” the corporeal facts, and by “form” the corresponding psychical state: the two terms, by-the-bye, only existing in connection with each other and being inseparable except as abstract conceptions. It was traditional in ancient psychology to study the relations of “the soul and the body”—the new psychology does not speak of them. In fact, if the question takes a metaphysical form, it is no longer psychology; if it takes an experimental form, there is no reason to treat it separately, because it is treated in connection with everything. No state of consciousness can be dissociated from its physical conditions: they constitute a natural whole, which must be studied as such. Every kind of emotion ought to be considered in this way: all that is objectively expressed by movements of the face and body, by vaso-motor, respiratory, and secretory disturbances, is expressed subjectively by correlative states of consciousness, classed by external observation according to their qualities. It is a single occurrence expressed in two languages. We have previously assimilated the emotions to psycho-physiological organisms; this unitary point of view, being more conformable to the nature of things and to the present tendencies of psychology, seems to me, in practice, to eliminate many objections and difficulties. Whether we adopt this theory or not, we have in any case acquired the certainty that the organic and motor manifestations are not accessories, that the study of them is part of the study of emotion. We shall therefore have to speak of them in some detail. CHAPTER VIII. THE INTERNAL CONDITIONS OF EMOTION. _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._