What are the scientific and rational reasons for monogamy? First among them is venereal disease. This may seem like a vulgar reason, but no one can deny that it is real. There was a time, apparently, when mankind did not suffer from these plagues, and we hope there may be such a time again. I shall not attempt to prescribe the marital customs for the people of that happy age; I suspect that they will be able to take care of themselves. Confining myself to my lifetime and yours, I say that the aim of every sensible man and woman must be to confine sex relations to the smallest possible limits. I know, of course, that there are prophylactics, and the army and navy present statistics to show that they succeed in a great proportion of cases. But if you are one of those persons in whose case they don't succeed, you will find the statistics a cold source of comfort to you. John and Mary go to the altar, or to the justice of the peace, and John says: "With all my worldly goods I thee endow." But the formula is incomplete; it ought to read: "And likewise with the fruits of my wild oats." Marriage is a contract wherein each of the contracting parties agrees to share whatever pathogenic bacteria the other party may have or acquire; surely, therefore, the contract involves a right of each party to have a say as to how many chances of infection the other shall incur. John goes off on a business trip, and is lonesome, and meets an agreeable widow, and figures to himself that there is very little chance that so charming a person can be dangerous. But maybe Mary wouldn't agree with his calculations; maybe Mary would not consider it a part of the marriage bargain that she should take the diseases of the agreeable widow. What commonly happens is that Mary is not consulted; John revises the contract in secret, making it read that Mary shall take a chance at the diseases of the widow. How can any thinking person deny that John has thus committed an act of treason to Mary? I know that there are people who don't mind running such chances; that is one reason why there are venereal diseases. All I can say is that the sex-code set forth in this book is based upon the idea that to deliver mankind from the venereal plague, we wish to confine the sex relationship within the narrowest limits consistent with health, happiness and spiritual development; and that to this end we take the young and teach them chastity, and we marry them early while they are clean, and then we call upon them to make the utmost effort to make a success of that union, and to make it a matter of honor to keep the marital faith. We do this with some hope of effectiveness, because we have made our program consistent with the requirements of nature, the genuine needs of love both physical and spiritual.