the body and its members. In the semicircular canals of the inner ear
are organs that give us the sense of dizziness, and enable us to
maintain our equilibrium and to know up from down.

The general nature of the sense organs and of sensation should now be
apparent. The nervous system reaches out its myriad fingers to every
portion of the surface of the body, and within the body as well. These
nerve-endings are specially adapted to receive each its particular form
of stimulation. This stimulation of our sense organs is the basis or
cause of our sensations. And our sensations are the elementary stuff of
all our experience. Whatever thoughts we have, whatever ideas or images
we have, they come originally from our sensations. They are built up out
of our sensations or from these sensations as they exist in memory.

=Defects of Sense Organs.= The organs of sight and hearing are now by far
the most important of our sense organs. They enable us to sense things
that are at a distance. We shall therefore discuss defects of these two
organs only. Since sensations are the primary stuff out of which mind is
made, and since sight and hearing are the most important sense organs,
it is evident that our lives are very much dependent on these organs. If
they cannot do their work well, then we are handicapped. And this is
often the case.

The making of the human eye is one of the most remarkable achievements
of nature. But the making of a perfect eye is too big a task for nature.
She never makes a perfect eye. There is always some defect, large or
small. To take plastic material and make lenses and shutters and
curtains is a great task. The curvature of the front of the eye and of
the front and back of the crystalline lens is never quite perfect, but
in the majority of cases it is nearly enough perfect to give us good