LECTURE   VIII

§ I.   Reflex Movements.     § 2.   Purposiveness of the  Reflex.
§ .3. Development of the Reflexes of Touch and Sight.

§ I

WE have seen that sensation is the ultimate source of a
very large number of the concrete processes that go to
make up our mental life. Everything that we meet
with in our world of ideas is derived in the last resort from sen¬
sations, and ideas are the raw material of all the higher mental
activities. It may be questioned whether the stream of thought
could not continue without any reinforcement from the outside
world ; but this at least is certain, that it has its source in sensi¬
bility, and that sensibility does perpetually interfere to deter¬
mine its direction. In this way our investigation of sensation
leads on directly to the consideration of a second and very
important psychological problem,—the problem of the composi¬
tion oi ideas from the sensational elements that enter into them
in so great number and variety.

In our previous discussions we examined the physical con¬
ditions of sensation, external sense-excitations, before we pro¬
ceeded to sensation itself Now the further question arises :
what is the immediate consequence of a sensation ? Observation
furnishes us with the unhesitating answer: every sensation
which is of sufficient intensity and not inhibited by opposing
influences is followed by a muscular movement. This muscular
movement we term a reflex movement, and the name is appro¬
priate. There have plainly taken place a transference of nervous
excitation within the central organs of the nervous system from
sensory to motor fibres, and a similar transmission of stimulation
from these to their particular muscles : the stimulus is, as it
were, thrown back, reflected.    Reflexes are observed so long as