No rational or acceptable system of sexual hygiene for the human male can be worked out without constant reference to the lower ranks of the mammalian class and to primitive social conditions. In our study of the anatomy and physiology of the sexual apparatus of the human male, it must have become evident that man has many things in common with other mammals, and that no adequate knowledge of man's physical or psychical attributes can be obtained without a study of similar phases of life among related animals. All of the changes which Nature introduced into the physical and psychical development of the adolescent male were of a character to equip the individual for the maintenance and protection of a wife and children. This development has been reached by the time the young man is twenty-one to twenty-three years of age, when, in the average case, he would be able, so far as concerns his physique and temperament, to establish and maintain a home. The fact that his adolescent development is complete by the age of twenty-five, and that he has, by the time he arrives at that age, grown into the full stature of all his physical and mental powers, may certainly be interpreted as nature's indication that his home-building should be begun not later than the twenty-fifth year. This means, then, that young men ought, if possible, to marry as young as twenty-five. But the conditions of society at the present time are such that a large proportion of the young men, particularly those who are preparing for any of the learned professions (theology, medicine, law, pedagogy, etc.) are hardly through their professional courses by the time they reach that age, and most of them feel that they must make a start in their profession before they assume the responsibilities of supporting a home. This means that a large proportion of them marry as late as thirty years of age. If we consider now those commercial, financial and industrial vocations which involve considerable preparation in technical institutions or a long apprenticeship (engineering, pharmacy, manufacturing chemists, banking, journalism, etc., etc.) we find that the young man is hardly able to establish such a home as most such young men feel that they must maintain on any salary that they receive before they are twenty-eight to thirty years old. This consideration applies particularly to college and university men, as, almost without exception, these men are preparing for some of the above mentioned professions or vocations. Now the conditions of college life, the field sports and athletics, together with the social conditions, tend to develop in college circles a body of most virile young men. The problem which now confronts us is: How may these young men live a hygienic life under these unnatural circumstances?