In the first chapter of this book I have shown, I believe convincingly, why sex knowledge is even more important for women than it is for men. I have examined carefully the books that have been written for girls and women, and I know that it is not bias, nor carping criticism, but strict honesty that forces me to say that I have not found one satisfactory girl's or woman's sex book. There are some excellent books for girls and women on general hygiene; but on sex hygiene, on the general manifestations of the sex instinct, on sex ethics--none. I have attempted to write such a book. Whether I have succeeded--fully, partially or not at all--is not for me to say, though I have my suspicions. But this I know: in writing this book I have been strictly honest with myself, from first page to last. Whether everything I have written is the truth, I do not know. But at least I believe that it is--or I would not have written it. And I can solemnly say that the book is free from any cant, hypocrisy, falsehood, exaggeration or compromise, nor has any attempt been made in any chapter to conciliate the stupid, the ignorant, the pervert, or the sexless. As in all my other books I have used plain, honest English. Not any plainer than necessary, but plain enough to avoid obscurity and misconception. Science and art are both necessary to human happiness. This is not the place to discuss the relative importance of the two. And, while I have no patience with art-for-art's-sake, I recognize that the scientist can not be put into a narrow channel and ordered to go into a certain definite direction. Scientific investigations which seemed aimless and useless have sometimes led to highly important results, and I would not disparage science for its own sake. It has its uses. Nevertheless I personally have no use for it. To me everything must have a direct human purpose, a definite human application. When the cup of human life is so overflowing with woe and pain and misery, it seems to me a narrow dilettanteism or downright charlatanism to devote one's self to petty or bizarre problems which can have no relation to human happiness, and to prate of self-satisfaction and self-expression. One can have all the self-expression one wants while doing useful work. And working for humanity does not exclude a healthy hedonism; not the narrow Cyrenaic, but an enlightened altruistic hedonism. And in writing this book I have kept the human problem constantly before my eyes. It was not my ambition merely to impart interesting facts: my concern was the practical application of these facts, their relation to human happiness.