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Alzheimer's disease affects only about 10% of people older than 65 years of age. Most forms of decreased mental function and dementia are caused by disuse (letting the mind get lazy).
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).
On average, the stomach produces 2 L of hydrochloric acid per day.
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.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.