Some of my obligations to other writers and workers have been acknowledged in the volume. For friendly assistance in reading the proofs of the work I am greatly indebted to Mr. Carveth Read, Dr. Alexander Hill, Prof. W. P. Ker, Mr. Ling Roth, Dr. W. H. R. Rivers, Miss C. Osborn, and Miss Alice Woods. HÔTEL DU WEISSHORN, VAL D’ANNIVIERS, _August_, 1902. CONTENTS. CHAPTER I. INTRODUCTORY. Objections to serious study of laughter • 1 Previous treatment of subject by philosophers • 4 Their way of dealing with facts • 6 Examination of an illustration given by Dr. Lipps • 9 Common defects of theories • 17 Difficulties of attempt to treat subject scientifically • 19 Scope of inquiry • 20 CHAPTER II. THE SMILE AND THE LAUGH. Need of studying the bodily process in laughter • 25 Characteristics of the movements of the smile • 26 Expressive function of the smile • 27 Continuity of processes of smiling and laughing • 27 Characteristics of the movements of laughter • 30 Concomitant organic changes during laughter • 33 Physiological benefits of laughing • 34 Effects of excessive laughter • 37 The laugh as expression • 39 Relation of expression to feeling in laughter • 40 Interactions of joyous feeling and organic concomitants • 44 Deviations from the normal type of laugh • 48 CHAPTER III. OCCASIONS AND CAUSES OF LAUGHTER. 1. Laughter as provoked by sense-stimulus: tickling • 50 Ticklish areas • 52 Characteristics of the sensations of tickling • 53 Motor reactions provoked by tickling • 56 How far attributes of sensation determine laughter of tickling • 57 The mental factor in effect of tickling • 59 Objective conditions of successful tickling • 60 Tickling as appealing to a particular mood • 62 2. Other quasi-reflex forms of laughter • 64 Varieties of automatic or “nervous” laughter • 65 Common element in these varieties: relief from strain • 67 3. Varieties of joyous laughter • 70 Prolonged laughing fit • 73 The essential element in joyous laughter • 75 Occasions of joyous laughter • 76 (_a_) Play • 76 (_b_) Teasing as provocative situation • 77 (_c_) Practical joking and laughter • 78 (_d_) Laughter as an accompaniment of contest • 78 (_e_) Occasions of unusual solemnity as provoking laughter • 79 Physiological basis of laughing habit • 80 CHAPTER IV. VARIETIES OF THE LAUGHABLE. The objective reference in laughter • 82 Universal element in the laughable • 83 Groups of laughable things • 87 (1) Novelty and oddity • 87 (2) Bodily deformities • 88 (3) Moral deformities and vices • 91 (4) Breaches of order and rule • 94 (5) Small misfortunes • 96 (6) References to the indecent • 98 (7) Pretences • 101 (8) Want of knowledge or skill • 102