At first
thought, we shall find it difficult to appreciate the endless vigilance
and activity of the brain. Like the other organisms which possess a
proper nervous system, man carries on the common organic processes of
life with a regularity and unfailing accuracy which seem to verge on
the mechanical forces, or to be, at least, automatic. All habitual
voluntary acts by repetition become almost automatic, or require no
perceptibly distinct impulse of the will. When we emerge from this
necessary field of labor, we come to those functions peculiar to the
proper brain. Here all is continual action. Thought, imagination, will,
the conflicting passions, language, and even articulation, claim their
first impulse from the nervous centre. The idlest reverie, as well as
the most profound study, taxes the brain. That distinguishing attribute
of man can almost never rest. In sleep, to be sure, we find a seeming
exception. Then only its inferior portion remains necessarily at work
to supervise the breathing function. Yet we know that we have often
dreamed,--while we do not know how often we fail to recall our dreams.
The duality of the cerebrum may also furnish a means of rest in all
trivial mental acts.
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