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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).
Intradermal injections are somewhat difficult to correctly administer because the skin layers are so thin that it is easy to accidentally punch through to the deeper subcutaneous layer.
The longest a person has survived after a heart transplant is 24 years.
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.
On average, the stomach produces 2 L of hydrochloric acid per day.