CHAPTER IV

INHERITED TENDENCIES


=Stimulus and Response.= We have learned something about the sense organs
and their functions. We have seen that it is through the sense organs
that the world affects us, stimulates us. And we have said that we are
stimulated in order that we may respond.

We must now inquire into the nature of our responses. We are moving,
active beings. But how do we move, how do we act when stimulated? Why do
we do one thing rather than another? Why do we do one thing at one time
and a different thing at another time?

Before we answer these questions it will be necessary for us to get a
more definite and complete idea of the nature of stimulus and response.
We have already used these terms, but we must now give a more definite
account of them. It was said in the preceding chapter that when a muscle
contracts, it must first receive a nerve-impulse. Now, anything which
starts this nerve-impulse is called the stimulus. The muscular movement
which follows is, of course, the response. The nervous system forms the
connection between the stimulus and response.

The stimulus which brings about a response may be very simple. Or, on
the other hand, it may be very complex. If one blows upon the eyelids of
a baby, the lids automatically close. The blowing is the stimulus and
the closing of the lids is the response. Both stimulus and response are