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The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
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.
Alcohol acts as a diuretic. Eight ounces of water is needed to metabolize just 1 ounce of alcohol.
Blood is approximately twice as thick as water because of the cells and other components found in it.
Pope Sylvester II tried to introduce Arabic numbers into Europe between the years 999 and 1003, but their use did not catch on for a few more centuries, and Roman numerals continued to be the primary number system.