The girl, of course, has not the strength for the protracted effort of the matured man, nor is such effort often required of her. Her studying is done quietly at home, undisturbed, usually, by any such cares and responsibilities as the man encounters. Hers is generally brain-work, not brain-worry. Yet the few hours a day exhaust her, because her vital system, which supports her brain, is feeble and inefficient. No girl is at school over six hours out of the twenty-four, and, deducting the time taken for recitation, recess, and the various other things which are not study, five hours, or even less, will cover the time she gives to actual brain-work in school, with two, or perhaps three, hours daily out of school. With the other sixteen hours practically her own, there is ample time for all the vigorous physical exercise she needs or could take, and yet allow ten, or even twelve, of those hours for sleep or eating. But notice, in any of these off-hours, what exercise these girls take. They walk to and fro from school, they play a few minutes at recess, they may take an occasional irregular stroll besides, and may indulge in a game of croquet, but all the time intent on their conversation, never thinking of the exercise itself, and the benefit it brings. Such things fill up the measure of the daily physical exercise of thousands of our American girls. It is the same thing for nearly all, save those from the poorest classes. And what is the result? Exactly what such exercise--or, rather, such lack of it--would bring. The short, abrupt run, the walk to or from school, the afternoon stroll, or the miscellaneous standing about--none of these call for or beget strength of limb, depth of chest, or vitality. None of these exercises is more than almost any flat-chested, half-developed girl could readily accomplish without serious effort, and, going through them for years, she would need little more strength than she had at first. But all this time her mental work comes in no meagre allowance. _It_ is all the time pushing forward. Subjects are set before her, to grasp and master which requires every day hours of close application for months together. The number of them is also enlarging, and the task is constantly becoming more severe. A variety of influences spurs her steadily onward. Maybe it is emulation and determination which urges her on, not only to do well, but to excel. Maybe it is to gratify the teacher's pride, and a desire to show the good fruit of her work. Perhaps oftener than anything else the girl is in dread of being dropped into another class, and she resolves to remain with her present one at all hazards.