It is quite certain that boys and girls will always be educated together a hundred years hence. The tendency of the sexes to become less different intellectually is a known fact of sociology. [22] It carries with it an inevitable tendency to dispense with the separation of the sexes in education. Wherever co-education has been tried its effects have been excellent. The presence of female students in medical colleges has had a markedly reformative influence on the manners and moral tone of medical student life, not long ago the opprobrium of civilisation. The advantages to a parent of being able to send his sons and his daughters to one place of instruction, and to the children themselves of the companionship and maintenance of family relations thus afforded, are equally obvious. In one other respect, which can only be touched upon lightly here, the system of joint education must be enormously beneficial, at all events to boys, and greatly beneficial to their sisters. Every competent schoolmaster is acquainted with special difficulties liable to arise about the age of puberty. The monastic seclusion of the schoolboy (like that of the single men in barracks who, according to Mr Kipling, "don't grow into plaster saints"), and the glamorous mystery surrounding the opposite sex, tend to accentuate these difficulties. The habit of constant association with girls who are not his sisters relieves a boy of the exaggerated sense of sexual isolation. A boy always brought up with girls is not liable to be constantly thinking about girlhood: and in practical experience many people are aware that boys who have had the opportunity of frequent association with the girl friends of their sisters grow into purer-minded and more chivalrous men, than those who have lacked this advantage; and the thoughtful future will assuredly cultivate the system which affords it. It is quite evident, in addition, that the fatuous and unreasonable mystery with which for centuries the natural facts most liable to be important in adult life have been made inevitable subjects of unholy curiosity, will be swept away, to the great enhancement of sane and clean thought in girls as well as in boys, in young women even more than in young men: while the tragedies which knowledge can avert, hidden horrors of our own day that we are too sentimental to envisage, but that everyone must now and then have met with a hint of, will happily exist no more, or occur but rarely.