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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.
The familiar sounds of your heart are made by the heart's valves as they open and close.
Every 10 seconds, a person in the United States goes to the emergency room complaining of head pain. About 1.2 million visits are for acute migraine attacks.
Parkinson's disease is both chronic and progressive. This means that it persists over a long period of time and that its symptoms grow worse over time.
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.