It is the nervous system by which we human beings live. Our voluntary muscles are agents of the will, agents of purpose; and while strength is a trifle, skill is always everything. We know now that it is impossible to carry out any human purpose by the contraction of one muscle or even one group of muscles. Even when we merely bend the arm we are doing things with the muscles which extend it, and when we raise it sideways we are modifying the whole trunk in order to preserve the balance. We have only to watch the clumsiness of an infant or a small child to realize how much skill the nervous system has to acquire. This skill may be mainly expressed as co-ordination, the balanced use of many muscles for a purpose and, as a rule, their co-ordinated use with one of the senses, more especially vision, but also touch and hearing. This is the first of the physiological reasons why games and play of all sorts are so incomparably superior to the use of dumb-bells and developers, where movement and increase of muscular strength are made ends in themselves; whereas in play we are making relations with the outside world, responding to stimuli, educating our nerve muscular apparatus as an instrument of human purpose. It is in part true to suppose that the play of children expresses an overflow of superfluous energy, but a still deeper and much more important conception of play is that which recognizes in it Nature's method of nervous development, the attainment of control and co-ordination, the capacity of quick and accurate response to circumstances and obedience to the will. Compare, for instance, the girl who has played games, avoiding danger as she crosses the road, with another whose youth has been made dreary by dumb-bells. It may freely be laid down, then, that systems of physical training are good in proportion as they approximate to play, and bad in proportion as they depart from it; and, further, that the very best of them ever devised is worthless in comparison with a good game. This evidently does not refer to, say, special exercises for a curved back. However, systems of physical training we shall still have with us for a long time to come, and perhaps the mere difficulty of finding room for games makes them necessary, though it may be noted in passing that the last touch of absurdity is accorded to our frequent preference for exercises over games when we conduct the exercises in foul air and prefer them to games in the open air. If exercises we are to have, then they must at least be modelled so as to come as near as possible to play in the two essentials. The first of these has already been mentioned--the preference of skill to strength as an object.