The ignorance of parents in relation to essential facts is deplorable. I believe it to be the source of our gravest social evils. In the present work, therefore, which I offer to my profession as an aid in the instruction of parents and guardians of the young, I shall speak with the frankness of profound respect in relation to our God-created faculties. As a Christian physiologist, I shall endeavour to show the true and noble use involved in the highest of our human functions. CHAPTER I _The Distinctive Character of Human Sex_ A fundamental error as to the nature of human sex too generally exists amongst us, from failure to recognise that in the human race the mind tends to rule the body, and that sex in the human being is even more a mental passion than a physical instinct. This superficial view dims our perception of the causes which produce the facts around us; it also prevents our recognising the essential difference which exists between human and brute sex, and it blinds us to the imperative necessity of giving human education to this part of our nature. As the study of the human body is carried on from its simpler to its more complex parts, it is perceived that the physiology of the more complex functions takes in a wider range of relations. The wise guidance of these more complex powers by parent or physician in health, and disease, demands a careful consideration of this extended range of relations. Thus the proper nourishment and exercise of the brain require more extended knowledge than the hygienic treatment of the skin, and diseases of the brain cause more serious danger to the individual. So all the faculties which belong to the life of relation--viz., the faculties which, like the senses, link us to our fellows--involve a broader range of study than those which appertain solely to those functions of the body which concern only the individual. The portion of our organization most difficult of study, but also requiring the widest range of knowledge for its healthy guidance, is the faculty of sex. This faculty has a very complex aspect from its three-fold relation to the race, to men, and to women. Sex is not essential to individual existence, but it is indispensable to the continuance of the race; and the progressive or retrograde character of the race largely depends upon the wisdom with which this faculty is guided in youth, and the character of the parental relations which are established.