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The average human gut is home to perhaps 500 to 1,000 different species of bacteria.
Serum cholesterol testing in adults is recommended every 1 to 5 years. People with diabetes and a family history of high cholesterol should be tested even more frequently.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
The horizontal fraction bar was introduced by the Arabs.
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.