The lids are made up of folds of skin and they can be raised and lowered by certain muscles. But they move so rapidly that they don’t disturb our vision in any way.
A curious thing about our lids is that they work automatically, just as windscreen wipers do on motor cars when they are turned on. We blink our eyes every sixty seconds.
Blinking is important involuntary action that protects our eyes. One reason has to do with our eyelashes. These are the short curved hairs which are attached to each lid. Their job is to catch dust which might go into our eyes.
When we talk through rain or sandstorm the lids automatically drop down and the eyelashes keep out the foreign matter. The eyebrows carry of rain or perspiration to a side, so that the drops do not run into the eyes.
The chief benefit of blinking is that this provides automatic lubrication of the eyes. Along the edge of each lid there are twenty or thirty tiny sebaceous glands. These glands have their opening between the lashes. Every time our lids close, these glands go to work and a secretion comes out. This secretion lubricates the edge of the eye lid and the lashes, so they won’t become dry.
In each eye we have a tear gland, where the liquid that makes tears is stored. Every time we blink, the eyelid applies suction to the opening of the tear gland and takes out some of the liquid. This prevents the eye from drying out.
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