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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).
Blood in the urine can be a sign of a kidney stone, glomerulonephritis, or other kidney problems.
Multiple sclerosis is a condition wherein the body's nervous system is weakened by an autoimmune reaction that attacks the myelin sheaths of neurons.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
If all the neurons in the human body were lined up, they would stretch more than 600 miles.