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The familiar sounds of your heart are made by the heart's valves as they open and close.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
The average office desk has 400 times more bacteria on it than a toilet.
A cataract is a clouding of the eyes' natural lens. As we age, some clouding of the lens may occur. The first sign of a cataract is usually blurry vision. Although glasses and other visual aids may at first help a person with cataracts, surgery may become inevitable. Cataract surgery is very successful in restoring vision, and it is the most frequently performed surgery in the United States.
Adult head lice are gray, about ? inch long, and often have a tiny dot on their backs. A female can lay between 50 and 150 eggs within the several weeks that she is alive. They feed on human blood.