The correlation is so close that we might be
tempted to identify them, but we soon discover
discrepancies. Thus extreme emotion tends to
paralyse impulse, while swift and effective im-
pulse seems (to put it paradoxically) to satisfy
emotion before it is fully excited. Furthermore,
if the impulse does not satisfy the feeling it may
be suspended or reversed. When the timid crea-
ture who cannot escape pursuit turns to bay, the
flight impulse is discarded as an unfaithful
servant, and fear itself elects to fight. Feeling
and impulse, though doubtless rooted in the same
fundamental susceptibilities and requirements, are
distinct branches on the stem, and do not operate
on the same lines or on identical conditions. We
can best understand their relations by considering
the conditions of their development.

According to the general evolutionary the-
ory, the structure of an organism grows up under
the conditions of the struggle for existence. That
is to say, organs useful not only to the individual,
but to the stock in that struggle tend to be pre-
served, and therefore to develop, while organs
that are useless or injurious tend to atrophy and
disappear. What is true of physical organs will
also be true of psychological functions, in as far
as psychological functions determine the be-

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