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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.
Blood in the urine can be a sign of a kidney stone, glomerulonephritis, or other kidney problems.
Astigmatism is the most common vision problem. It may accompany nearsightedness or farsightedness. It is usually caused by an irregularly shaped cornea, but sometimes it is the result of an irregularly shaped lens. Either type can be corrected by eyeglasses, contact lenses, or refractive surgery.
Always store hazardous household chemicals in their original containers out of reach of children. These include bleach, paint, strippers and products containing turpentine, garden chemicals, oven cleaners, fondue fuels, nail polish, and nail polish remover.
Not getting enough sleep can greatly weaken the immune system. Lack of sleep makes you more likely to catch a cold, or more difficult to fight off an infection.