CHAPTER VI. CONCLUSIONS ON PLEASURE AND PAIN 80 The beginning of life—I. Conditions of existence of pleasure and pain; lowering and heightening of vital energy—Féré’s experiments—Meynert’s theory—II. Finality of pleasure and pain—Exceptions: explicable cases; irreducible cases. CHAPTER VII. THE NATURE OF EMOTION 91 Analogy between perception and emotion—Constituent elements of emotion—Summary of the theory of James and Lange—Application of this theory to the higher emotions (religious, moral, æsthetic, intellectual)—Illegitimate confusion between the quality and intensity of emotion—Examination of a typical case: musical emotion—The most emotional of all the arts is the most dependent on physiological conditions—Proofs: its action on animals, on primitive man, on civilised man; its therapeutic action—Why certain sensations, images, and ideas awaken organic and motor states, and, consequently, emotion—They are connected either with natural or social conditions of existence—Differences and resemblances between the two cases—Antecedents of the physiological theory of emotion—Dualist position, or that of the relation between cause and effect—Unitary position; its advantages. CHAPTER VIII. THE INTERNAL CONDITIONS OF EMOTION 113 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. CHAPTER IX. THE EXTERNAL CONDITIONS OF EMOTION 124 Empiric period—Pre-Darwinian period of scientific research—Examination of Darwin’s three principles—Wundt and his explanatory formulas: Innervation directly modified, Association of analogous sensations, Relations of motion with sensory representations. CHAPTER X. CLASSIFICATIONS 130 Their discrepancies—Reduced to three types: (1) Classification of pleasures and pains—(2) Classification of emotions: two forms, empiric and analytico-comparative—(3) Classification of representations, intellectualist form—Critical remarks—Impossibility of any classification. CHAPTER XI.