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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.

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More than 4.4billion prescriptions were dispensed within the United States in 2016.

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Cocaine was isolated in 1860 and first used as a local anesthetic in 1884. Its first clinical use was by Sigmund Freud to wean a patient from morphine addiction. The fictional character Sherlock Holmes was supposed to be addicted to cocaine by injection.

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Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.

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Though the United States has largely rejected the metric system, it is used for currency, as in 100 pennies = 1 dollar. Previously, the British currency system was used, with measurements such as 12 pence to the shilling, and 20 shillings to the pound.

Cation binding and exchange. Cation binding and exchange.
The four ways in which animals exchange heat with the environment are radiation, evaporation, convec The four ways in which animals exchange heat with the environment are radiation, evaporation, convec
Mutualisms, such as those that occur among plants and pollinators, generally involve large numbers o Mutualisms, such as those that occur among plants and pollinators, generally involve large numbers o
Astronaut Piers Sellers during the third spacewalk of STS-121, a demonstration of orbiter heat shiel Astronaut Piers Sellers during the third spacewalk of STS-121, a demonstration of orbiter heat shiel
Exchange of Oxygen and Carbon Dioxide Exchange of Oxygen and Carbon Dioxide
Flexible exchange rates are supposed to prevent long-term trade deficits. Flexible exchange rates are supposed to prevent long-term trade deficits.
Video: Frequency of stimulation and force (Recruitment of motor units and force)

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