so able to change itself, or develop, by its
appropriate reactions upon such stimulations.

In plant life, also, the same principle holds. As long as a grain of
corn, wheat, etc., is kept in a dry place, the life principle stored up
within the seed is unable to manifest itself in growth. When, on the
other hand, it is appropriately stimulated by water, heat, and light,
the seed awakens to life, or germinates. In other words, the seed
reacts upon the external stimulations of water, heat, and light, and
manifests the activity known as growth, or development. Thus all
physical growth, whether of the plant or the animal, is conditioned on
the energizing of the inherent life principle, in response to
appropriate stimulation of the environment.

[Illustration: A. Simple amoeba.
B. An amoeba developing as a result of assimilating food.
C. An amoeba about to divide, or propagate.]

=B. Development in Human Life.=--In addition to its physical nature,
human life has within it a spiritual law, or principle, which enables
the individual to respond to suitable stimulations and by that means
develop into an intelligent and moral being. When, for instance, waves
of light from an external object stimulate the nervous system through
the eye, man is able, through his intelligent nature, to react mentally
upon these stimulations and, by interpreting them, build up within his
experience conscious images of light, colour, and form. In like manner,
when the nerves in the hand are stimulated by an external object, the
mind is able to react upon the impressions and, by interpreting them,
obtain images of touch, temperature, and weight. In the sphere of
action, also, the child who is stimulated by the sight of his elder
pounding with a hammer, sweeping with a broom, etc., reacts imitatively
upon such stimulations, and thus acquires skill in action. So also when
stimulated by means of his human surroundings, as, for example, through
the kindly acts of his mother, father, etc., he reacts morally toward
these stimulations and thus develops such social qualities as sympathy,
love, and kindness. Nor are the conditions of development different in
more complex intellectual problems. If a child is given nine blocks on
which are printed the nine digits, and is asked to arrange them in the
form of a square so that each of the horizontal and the vertical columns
will add up to fifteen, there is equally an inner growth through
stimulation and response