individual attention necessary adds another difficulty. However, it is
by far the best method of the three, for it is sure, is economical,
using the energy that is provided by nature, is educative, and is
positive. To replace what is poor or harmful by something better is one
of the greatest problems of human life--and this is the outcome of the
method of substitution. All three methods have their place in a system
of education, and certain of them are more in place at certain times
than at others, but at all times if the method of substitution can be
used it should be.

The instinct of physical activity is one of the most noticeable ones in
babyhood. The young baby seems to be in constant movement. Even when
asleep, the twitchings and squirmings may continue. This continued
muscular activity is necessary because the motor nerves offer the only
possible path of discharge at first. As higher centers in the brain are
developed, the ingoing currents, aroused by all sense stimuli, find
other connections, and ideas, images, trains of thoughts, are aroused,
and so the energy is consumed; but at first all that these currents can
do is to arouse physical activity. The strength of this instinct is but
little diminished by the time the child comes to school. His natural
inclination is to do things requiring movement of all the growing
muscles. Inhibition, "sitting still," "being quiet," takes real effort
on his part, and is extremely fatiguing. This instinct is extremely
valuable in several ways: it gives the exercise necessary to a growing
body, provides the experience of muscle movements necessary for control,
and stimulates mental growth through the increase and variety of
experiences it gives.

The tendency to enjoy mental activity, to be satisfied with it for its
own sake, is peculiarly a human trait. This capacity shows itself in two