vity of the bat which enables it, though blinded, to
thread its way through a maze of obstructions hung about a room.

The fact of sensitivity, in short, or the quality of response to
stimulation, is more wonderful than its particular formulation in
the human brain. Mind simply represents a special development of the
quality of sensitivity common to organic nature, and analogous to the
sensitivity of the photographic plate. The brain receives impressions,
records them, remembers them, compares new experiences with old, and
modifies behavior, in the presence of a new or recurrent stimulation,
in view of the pleasure-pain connotation of similar situations in the
past.

In very low forms of life, as is well known, there is no development
of brain or special organs of sense; but the organism is pushed and
pulled about by light, heat, gravity, and acid and other chemical
forces, and is unable to decline to act on any stimulus reaching it.
It reacts in certain characteristic, habitual, and adequate ways,
because it responds uniformly to the same stimulation; but it has
no choice, and is controlled by the environment. The object of brain
development is to reverse these conditions and control the actions of
the organism, and of the outside world as well, from within. With the
development of the special organs of sense, memory, and consequent
ability to compare present experiences with past, with inhibition
or the ability to decline to act on a stimulus, and, finally, with
abstraction or the power of separating general from particular
aspects, we have a condition where the organism sits still, as it
were, and picks and chooses its reactions to the outer world; and, by
working in certain lines to the exclusion of others, it gains in its
turn control of the environment, and begins to reshape it.

All the higher animals possess in some degree the powers of memory,
judgment, and choice; but in man nature followed the plan of
developing enormously the memory, on which depend abstraction, or
the power of general ideas, and the reason. In order to secure this
result, the brain, or surface for recording experience, was developed
out of all proportion with the body. In the average European the brain
weighs about 1,360 grams, or 3 per cent. of the body weight, while
the average brain weight of some of the great anthropoid apes is only
about 360 grams, or, in the orangoutang, one-half of 1 per cent. of
the body weight. In point of fact,