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There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
Your skin wrinkles if you stay in the bathtub a long time because the outermost layer of skin (which consists of dead keratin) swells when it absorbs water. It is tightly attached to the skin below it, so it compensates for the increased area by wrinkling. This happens to the hands and feet because they have the thickest layer of dead keratin cells.
In 1864, the first barbiturate (barbituric acid) was synthesized.
There are more sensory neurons in the tongue than in any other part of the body.
The modern decimal position system was the invention of the Hindus (around 800 AD), involving the placing of numerals to indicate their value (units, tens, hundreds, and so on).