and most universal tendencies is the instinct for flight, and its
emotion, fear. "Fear is the representation of injury and is born of
the innumerable injuries which have been inflicted in the course of
evolution."[8] Some babies are frightened if they are held too
loosely, even though they have never known a fall. Some persons have
an instinctive fear of cats, a left-over from the time when the race
needed to flee from the tiger and others of the cat family. Almost
every one, no matter in what state of culture, fears the unknown
because the race before him has had to be afraid of that which was not
familiar.

[Footnote 8: Crile: _Origin and Nature of the Emotions_.]

The emotion of fear is well known, but its purpose is not so often
recognized. An emotion brings about internal changes, visceral changes
they are called, which enable the organism to act on the emotion,--to
accomplish its object. There is only so much energy available at a
given moment, stored up in the brain cells, ready for use. In such an
emergency as flight every ounce of energy is needed. The large muscles
used in running must have a great supply of extra energy. The heart
and lungs must be speeded up in order to provide oxygen and take care
of extra waste products. The special senses of sight and hearing must
be sensitized. Digestion and intestinal peristalsis must be stopped in
order to save energy. No person could by conscious thought accomplish
all these things. How, then, are they brought about?

=Internal Laboratories.= In the wonderful internal laboratory of the
body there are little glands whose business it is to secrete chemicals
for just these emergencies. When an object is sighted which arouses
fear, the brain cells flash instantaneous messages over the body,