Marriage Not Only for Procreation--Theologians on the _Sacramentum Solationis_--Importance of the _Art of Love_--The Basis of Stability in Marriage and the Condition for Right Procreation--The Art of Love the Bulwark Against Divorce--The Unity of Love and Marriage a Principle of Modern Morality--Christianity and the Art of Love--Ovid--The Art of Love Among Primitive Peoples--Sexual Initiation in Africa and Elsewhere--The Tendency to Spontaneous Development of the Art of Love in Early Life--Flirtation--Sexual Ignorance in Women--The Husband's Place in Sexual Initiation--Sexual Ignorance in Men--The Husband's Education for Marriage--The Injury Done by the Ignorance of Husbands--The Physical and Mental Results of Unskilful Coitus--Women Understand the Art of Love Better Than Men--Ancient and Modern Opinions Concerning Frequency of Coitus--Variation in Sexual Capacity--The Sexual Appetite--The Art of Love Based on the Biological Facts of Courtship--The Art of Pleasing Women--The Lover Compared to the Musician--The Proposal as a Part of Courtship--Divination in the Art of Love--The Importance of the Preliminaries in Courtship--The Unskilful Husband Frequently the Cause of the Frigid Wife--The Difficulty of Courtship--Simultaneous Orgasm--The Evils of Incomplete Gratification in Women--Coitus Interruptus--Coitus Reservatus--The Human Method of Coitus--Variations in Coitus--Posture in Coitus--The Best Time for Coitus--The Influence of Coitus in Marriage--The Advantages of Absence in Marriage--The Risks of Absence--Jealousy--The Primitive Function of Jealousy--Its Predominance Among Animals, Savages, etc, and in Pathological States--An Anti-Social Emotion--Jealousy Incompatible With the Progress of Civilization--The Possibility of Loving More Than One Person at a Time--Platonic Friendship--The Conditions Which Make It Possible--The Maternal Element in Woman's Love--The Final Development of Conjugal Love--The Problem of Love One of the Greatest Of Social Questions. CHAPTER XII. THE SCIENCE OF PROCREATION.