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Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
There are more bacteria in your mouth than there are people in the world.
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).
Today, nearly 8 out of 10 pregnant women living with HIV (about 1.1 million), receive antiretrovirals.