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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.
Blood is approximately twice as thick as water because of the cells and other components found in it.
In most cases, kidneys can recover from almost complete loss of function, such as in acute kidney (renal) failure.
The term bacteria was devised in the 19th century by German biologist Ferdinand Cohn. He based it on the Greek word "bakterion" meaning a small rod or staff. Cohn is considered to be the father of modern bacteriology.
The Babylonians wrote numbers in a system that used 60 as the base value rather than the number 10. They did not have a symbol for "zero."