Now, in the same way that education develops and increases the power of the brain, so exercise has a similar effect on the body. When the muscles are strengthened, the beneficial effect is also participated in by the heart, lungs, and digestive organs, and thus the removal of worn-out material from the body is assisted. The effect of exercise is thus to remove used up products from the system, and so afford an opportunity for renewed material to take their place. Ceaseless changes are constantly going on throughout the body, and any part which has fulfilled its object is no longer necessary for the requirements of the system, in fact it becomes injurious. Its removal has to take place by one of the various outlets, and it is by exercise that its expulsion is greatly assisted. In this way exercise differs altogether from the part played by food. The latter is the introduction of nourishment into the system for the renewal of its wants, while exercise is the principal agent by which DEBRIS is eliminated. It was well known amongst the Greeks and Romans that the muscles reached their greatest state of development by means of exercise. Though, therefore, gymnastics formed a great part of their system of education, yet the chief aim in their athletic instruction was the desire to train men to fight their battles, and in those days war was a matter of personal valour and of individual bravery. On that account, therefore, the men who were selected as their soldiers were among the healthiest of the nation. Those who by reason of bodily infirmity or inherent weakness were unfitted for military prowess were left alone. But, as Maclaren has well pointed out, the object of systematic and proper exercise is not for the production of a race of soldiers, though a certain proportion of the population will always be required for military service. With the great majority of men the struggle for existence is keen, and it is simply a question of the survival of the fittest, and of the weakest going to the wall. The requirements of the present time are therefore a capacity for endurance and an ability to withstand the effects of work day after day. We do not require athletes who are capable of performing wonderful feats of strength; but the fight of the nineteenth century is brain against brain, and he will be best equipped for the struggle who has the advantage of good bodily health. In the higher callings, where brain power is everything, the necessity for perfect physical condition is all the more imperative, because the brain is supplied with healthy blood, and the ideas flow with less effort.