many chances of being retained. This is evidenced by the vividness of
childhood scenes in the minds of our grandparents. An old soldier
recalls with great vividness events that happened during the Civil War,
but forgets events of yesterday. There is involved here a principle of
nervous action that you have already encountered; namely, that
impressions are more easily made and retained in youth. It should also
be observed that pathways made early have more chances of being used
than those made recently. Still another peculiarity of nervous action
is revealed in these extended periods of memorizing. It has been
discovered that if a rest is taken between impressions, the impressions
become more firmly fixed. This points to the presence of a surprising
power, by which we are able to learn, as it were, while we sleep. We
shall understand this better if we try to imagine what is happening in
the nervous system. Processes of nutrition are constantly going on. The
blood brings in particles to repair the nerve cells, rebuilding them
according to the pattern left by the last impression. Indeed, the
entrance of this new material makes the impression even more fixed. The
nutritional processes seem to set the impression much as a hypo bath
fixes or sets an impression on a photographic plate. This peculiarity
of memory led Professor James to suggest, paradoxically, that we learn
to skate in summer and to swim in winter. And, indeed, one usually
finds, in beginning the skating season, that after the initial
stiffness of muscles wears off, one glides along with surprising
agility. You see then that if you plan things rightly, Nature will do
much of your learning for you. It might be suggested that perhaps
things impressed just before going to sleep have a better chance to
"set" than things impressed at other times for the reason that sleep is
the time when the reparative processes of the body are most active.

Since the brain pattern requires time to "set," it is important that