foreign matter not constituting its food, say a particle of sand, such
an organism at once withdraws itself from the stimulating elements. On
the other hand, if it comes in contact with suitable food, the amoeba
not only flows toward it, but by assimilating it, at once begins to
increase in size, or grow, until it finally divides, or reproduces,
itself as shown in the following figures. Hence the amoeba as an
organism is not only able to react appropriately toward different
stimuli, but is also 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