s, we find, for example, that one does not respond by
saying "81" for 9 times 9; nor "13" for 6 plus 7; nor "8" for 15 minus
7; nor "8" for the square root of 64; nor "144" for the square of 12,
etc., until one has learned in each case.

Some connections between stimulus and response we have through
inheritance; all others are built up and established in one's lifetime,
particularly in the first thirty years of one's life.

We have spoken of bonds between stimulus and response, but have not
explained just what can be meant by a _bond_. In what sense are stimulus
and response bound together? A bond is a matter of greater permeability,
of less resistance in one direction through the nervous system than in
other directions. Nerves are conductors for nerve-currents. When a
nerve-current is started in a sense organ, it passes on through the path
of least resistance.

Now, some nerves are so organized and connected through inheritance as
to offer small resistance. This forms a ready-made connection between
stimulus and response. Muscular responses that are connected with their
stimuli through inherited bonds, by inherited nerve structure, are
called instincts. Those that are connected by acquired bonds are called
habits. Sucking, crying, laughing, are instinctive acts. Adding,
typewriting, piano playing, are habits.

The term _instinct_ may be given to the act depending upon inherited
structure, an inherited bond, or it may be given to the inherited bond
itself. Similarly, the term _habit_ may be given to an act that we have
had to learn or to the bond which we ourselves establish between
response and stimulus. In this book we shall usually mean by instinct an
action depending upon inherited structure and by habit an act depending
upon a bond established during lifetime. A good part of our early lives
is spent in building up bonds between stimuli and responses. This
establishing of bonds or connections is called _learning_.

=Appearance of Inherited Tendencies.= Not all of our inherited tendencies
are manifested immediately after birth, nor indeed in the earliest years
of childhood, but appear at different stages of the child's growth. It
has already been said that a child, soon after birth, will close its
eyelids when they are blown upon. The lids do not close at this time if
one strikes at them, but they will do this later. The proper working of
an instinct or an inherited tendency, then, depends upon the child's
havin