【英语时差8,16】我们为什么会哭？
时间：2016-01-12 02:54:18
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（单词翻译）
You notice your tears most after a good cry or while slicing an onion, but actually your eyes are constantly moistened by a thin film of tears.
This film has three distinct layers: an outer, oily layer to prevent
evaporation1; a middle layer of lacrimal fluid, the main ingredient of tears; and an inner,
mucous2 layer. This three layer film is
replenished3 every time you blink, and it provides essential protection for your eyes.
Most of your body is protected by skin of course, and your outer layer of skin is made of dead cells and keratin, an
opaque4, protective substance. Your eyes need to be transparent,however; they can’t be covered by a layer of dead cells and keratin. One of the main functions of tears therefore, is to keep these cells alive.
Tears are loaded with electrolyte salts, chemicals that are also found deep inside your body. These salts make your outer eye cells feel like they’re inside your body, preventing them from turning into cells similar to skin cells.
Tears help your eyes in other ways too. When a
speck5 of dust gets in your eye, it’s coated with mucous from
glands6 in the white of your eye, then washed out with extra fluid from the lacrimal glands, the main tear producing glands above the eye.
To protect your eyes from germs, tears also contain bacteria fighting
enzymes7. What’s more, tears provide a good optical surface. They smooth out the
microscopically8 uneven9 cells of your cornea. Without tears, tiny irregularities in your eye would give you constantly fuzzy vision.
Although they’re most apparent during a good cry, tears are actually an essential part of everyday life.
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