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When Gabriel Fahrenheit invented the first mercury thermometer, he called "zero degrees" the lowest temperature he was able to attain with a mixture of ice and salt. For the upper point of his scale, he used 96°, which he measured as normal human body temperature (we know it to be 98.6° today because of more accurate thermometers).
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.
In most cases, kidneys can recover from almost complete loss of function, such as in acute kidney (renal) failure.
More than nineteen million Americans carry the factor V gene that causes blood clots, pulmonary embolism, and heart disease.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.