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Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
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.
The Romans did not use numerals to indicate fractions but instead used words to indicate parts of a whole.
Human kidneys will clean about 1 million gallons of blood in an average lifetime.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.