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Bacteria have been found alive in a lake buried one half mile under ice in Antarctica.
Autoimmune diseases occur when the immune system destroys its own healthy tissues. When this occurs, white blood cells cannot distinguish between pathogens and normal cells.
On average, someone in the United States has a stroke about every 40 seconds. This is about 795,000 people per year.
The familiar sounds of your heart are made by the heart's valves as they open and close.
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.