WONDERLAND OF VISION
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Tops of Words
An amazing amount of our seeing is just guess
ing, with the aid of memory. Blot out the lower
half of a line of print and you can still read it
pretty well because you are accustomed to identi
fying letters by their tops, where most of the
characteristic markings are located. Cover the top
half of the line, and you will have trouble in read
ing the bottoms of the letters.
Upside Down
It’s just a little silly to say that seeing is be
lieving, because we see everything upside down,
but we don’t believe it. Because of the optical
structure of the eye, all images registered on the
retina are bottom up and reversed right-for-left,
as they are on the film of a camera. The brain,
calling into play our common sense and experi
ence, reversed the eye’s verdict and tells us that
things are top-side up.
Your Eye is a Chemical Factory
Taking some Vitamin A from the circulating
blood stream, the eye manufactures it into "visual
purple,” or rhodopsin. This marvelous and mys
terious substance is distributed among the rods,
or specialized nerve-ends, of the retina, and en
ables us to see in darkness. If you are short of
Vitamin A, and hence of visual purple, you are
"night blind.” Light bleaches out the visual
purple, turns it yellow, and converts it back
visual purple, turns it yellow, and converts it back
into Vitamin A. In the process, you lose the abil
ity to see well in the dark. The reason you are
blinded at night by an approaching headlight is,
your visual purple has been destroyed. But the
eye at once sets to work to manufacture a new
supply.
Every baby’s eyes are as blue as the sky of a
sunny summer day. Actually they only appear
blue because the iris is colorless and transparent,
and picks up blue tints by refleaion. Later, the
iris will take on its destined brown, blue, or hazel
pigment.
Color to be Added
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