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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).
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.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
There are more sensory neurons in the tongue than in any other part of the body.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.