SENSITIVITY.

The only information that reaches us concerning outward events
appears to pass through the avenue of our senses; and the more
perceptive the senses are of difference, the larger is the field
upon which our judgment and intelligence can act. Sensation mounts
through a series of grades of "just perceptible differences." It
starts from the zero of consciousness, and it becomes more intense
as the stimulus increases (though at a slower rate) up to the point
when the stimulus is so strong as to begin to damage the nerve
apparatus. It then yields place to pain, which is another form of
sensation, and which continues until the nerve apparatus is destroyed.
Two persons may be equally able just to hear the same faint sound,
and they may equally begin to be pained by the same loud sound, and
yet they may differ as to the number of intermediate grades of
sensation. The grades will be less numerous as the organisation is
of a lower order, and the keenest sensation possible to it will in
consequence be less intense. An artist who is capable of
discriminating more differences of tint than another man is not
necessarily more capable of seeing clearly in twilight, or more or
less intolerant of sunshine. A musician is not necessarily able to
hear very faint sounds, nor to be more startled by loud sounds than
others are. A mechanic who works hard with heavy tools and has rough
and grimy thumbs, insensible to very slight pressures, may yet have
a singularly discriminating power of touch in respect to the
pressures that he can feel.

The discriminative faculty of idiots is curiously low; they hardly
distinguish between heat and cold, and their sense of pain is so