ding in
the muscle fibers. The nerve-impulse passing into the fibers of the
muscles causes them to contract. The nerve stimulus itself has a cause;
it ordinarily arises directly or indirectly from the stimulation of a
sense organ. And the sense organs are stimulated by outside influences,
as was explained previously.

Not only are our movements caused, but our sensations, our ideas, and
our feelings follow upon or are dependent upon some definite bodily
state or condition. The moment that we recognize this we see that our
sensations, ideas, and feelings are subject to control. It is only
because our minds are in a world of causality, and subject to its laws,
that education is possible. We can bring causes to bear upon a child and
change the child. It is possible to build up ideas, ideals, and habits.
And ideas, ideals, and habits constitute the man. Training is possible
only because a child is a being that can be influenced. What any child
will be when grown depends upon what kind of child it was at the
beginning and upon the influences that affect it during its early life
while it is growing into maturity. We need have no doubt about the
outcome of any particular child if we know, with some degree of
completeness, the two sets of factors that determine his life--his
inheritance and the forces that affect this inheritance. We can predict
the future of a child to the extent that we know and understand the
forces that will be effective in his life.

The notion of causality puts new meaning into our view of the _training_
of a child. The doctrine of development puts new meaning into our notion
of the _nature_ of a child. We can understand man only when we view him
genetically, that is, in the light of his origin. We can understand a
child only in the light of what his ancestors have been.

As these lines are being written, the greatest, the bloodiest war of
history is in progress. Men are killing men by thousands and hundreds of
thousands. How can we explain such actions? Observation of children
shows that they are selfish, envious, and quarrelsome. They will fight
and steal until they are taught not to do such things. How can we
understand this? There is no way of understanding such actions until we
come to see that the children and men of to-day are such as they are
because of their ancestors. It has been only a few generations,
relatively speaking, since our ancestors were naked savages, killing
their enemies and eat