We can see how it is that exercise, which, up to the point of fatigue, is both healthful and improving, when carried on after we are tired, becomes just the opposite. Fatigue is nature's signal, "Enough for this time!" That is why all methods of training for building up strength and skill, both of mind and muscle, forbid exercising beyond well-marked fatigue. If you yourself stop at this point in exercising, you will find, the next time you try that particular exercise, that you can go a little further before fatigue is felt; the third time, a little further yet; and so, by degrees, you can build up both your body and brain to the fullest development of which they are capable. In muscular training, a series of light, quick movements, none of which are fatiguing, repeated fifteen, twenty, or a hundred times, will do much more to build up muscle and increase strength, than three or four violent, heaving strains that tax all your strength. Real athletes and skilled trainers, for instance, use half-or three-quarter-pound dumb-bells and one-or two-pound Indian clubs, instead of the five-pound dumb-bells and ten-pound clubs with which would-be athletes delight to decorate their rooms. A thoroughbred race-horse is trained on the same principle: he is never allowed to gallop until tired, or to put out his full speed before he is well grown. In fact, the best methods of all forms of exercising and training always stop just short of fatigue. Education and study ought to be planned on the same principle. Exercise of either our muscles or our minds after they have begun to poison themselves through fatigue never does them any good, even if it does not do them serious harm; and, where the exercise is for the sake of building us up and developing our powers, it is best to stop for a little while, or change the task, as soon as we begin to feel distinctly tired, and then to try it again when we are rested. [Illustration: A TRAINED BODY Ellery H. Clark, All-around Athletic Champion of America, 1897, 1903.]