us impulse, or current, as it is transmitted
through the system, encounters _resistance_, or consumes an amount of
nervous energy. Moreover, when the nervous current, whether sensory or
motor, involves the establishment of new connections between cells, as
when one first learns combinations of numbers or the movements involved
in forming a new letter, a relatively greater amount of resistance is
met or, in other words, a greater amount of nervous energy is expended.
On the other hand, when an impulse has been transmitted a number of
times through a given arc, the resistance is greatly lessened, or less
energy is expended; as indicated by the ease with which an habitual act
is performed.

=Education and Nervous Energy.=--It is evident from the foregoing, that
the forming of new ideas or of new modes of action tends to use up a
large share of nervous energy. For this reason, the learning of new and
difficult things should not be undertaken when the body is in a tired
or exhausted condition; for the resistance which must be overcome, and
the changes which must take place in the nervous tissue during the
learning process, are not likely to be effectively accomplished under
such conditions. Moreover, the energy thus lost must be restored through
the blood, and therefore demands proper food, rest, and sleep on the
part of the individual. It should be noted further that nervous tissue
is more plastic during the early years of life. This renders it
imperative, therefore, that knowledge and skill should be gained, as far
as possible, during the plastic years. The person who wishes to become a
great violinist must acquire skill to finger and handle the bow early in
life. The person who desires to become a great linguist, if he allows
his early years to pass without acquiring the necessary skill, cannot
expect in middle life to train his vocal organs to articulate a number
of different languages.

=Cortical Habit.=--In the light of what has been seen regarding the
character and function of the nervous system, it will now be possible to
understand more fully two important forms of adjustment already referred
to. When nervous movements are transmitted to the cortex of the brain,
they not only awaken consciousness, or make the individual aware of
something, but the present impression also leaves certain permanent
effects in the nervous tissue of the cortex itself. Since, however,
cortical activity implies consciousness, the retentio