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Vaccines prevent between 2.5 and 4 million deaths every year.
The familiar sounds of your heart are made by the heart's valves as they open and close.
Vampire bats have a natural anticoagulant in their saliva that permits continuous bleeding after they painlessly open a wound with their incisors. This capillary blood does not cause any significant blood loss to their victims.
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.
People about to have surgery must tell their health care providers about all supplements they take.