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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.
Vaccines prevent between 2.5 and 4 million deaths every year.
During the twentieth century, a variant of the metric system was used in Russia and France in which the base unit of mass was the tonne. Instead of kilograms, this system used millitonnes (mt).
More than 2,500 barbiturates have been synthesized. At the height of their popularity, about 50 were marketed for human use.
To prove that stomach ulcers were caused by bacteria and not by stress, a researcher consumed an entire laboratory beaker full of bacterial culture. After this, he did indeed develop stomach ulcers, and won the Nobel Prize for his discovery.