I am indebted to many correspondents, medical and other, in various parts of the world, for much valuable assistance. When they have permitted me to do so I have usually mentioned their names in the text. This has not been possible in the case of many women friends and correspondents, to whom, however, my debt is very great. Nature has put upon women the greater part of the burden of sexual reproduction; they have consequently become the supreme authorities on all matters in which the sexual emotions come into question. Many circumstances, however, that are fairly obvious, conspire to make it difficult for women to assert publicly the wisdom and knowledge which, in matters of love, the experiences of life have brought to them. The ladies who, in all earnestness and sincerity, write books on these questions are often the last people to whom we should go as the representatives of their sex; those who know most have written least. I can therefore but express again, as in previous volumes I have expressed before, my deep gratitude to these anonymous collaborators who have aided me in throwing light on a field of human life which is of such primary social importance and is yet so dimly visible. HAVELOCK ELLIS. Carbis Water, Lelant, Cornwall, England. CONTENTS. ANALYSIS OF THE SEXUAL IMPULSE. Definition of Instinct--The Sexual Impulse a Factor of the Sexual Instinct--Theory of the Sexual Impulse as an Impulse of Evacuation--The Evidence in Support of this Theory Inadequate--The Sexual Impulse to Some Extent Independent of the Sexual Glands--The Sexual Impulse in Castrated Animals and Men--The Sexual Impulse in Castrated Women, After the Menopause, and in the Congenital Absence of the Sexual Glands--The Internal Secretions--Analogy between the Sexual Relationship and that of the Suckling Mother and her Child--The Theory of the Sexual Impulse as a Reproductive Impulse--This Theory Untenable--Moll's Definition--The Impulse of Detumescence--The Impulse of Contrectation--Modification of this Theory Proposed--Its Relation to Darwin's Sexual Selection--The Essential Element in Darwin's Conception--Summary of the History of the Doctrine of Sexual Selection. Its Psychological Aspect--Sexual Selection a Part of Natural Selection--The Fundamental Importance of Tumescence--Illustrated by the Phenomena of Courtship in Animals and in Man--The Object of Courtship is to Produce Sexual Tumescence--The Primitive Significance of Dancing in Animals and Man--Dancing is a Potent Agent for Producing Tumescence--The Element of Truth in the Comparison of the Sexual Impulse with an Evacuation, Especially of the Bladder--Both Essentially Involve Nervous Explosions--Their Intimate and Sometimes Vicarious Relationships--Analogy between Coitus and Epilepsy--Analogy of the Sexual Impulse to Hunger--Final Object of the Impulses of Tumescence and Detumescence. LOVE AND PAIN. I.