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Hippocrates noted that blood separates into four differently colored liquids when removed from the body and examined: a pure red liquid mixed with white liquid material with a yellow-colored froth at the top and a black substance that settles underneath; he named these the four humors (for blood, phlegm, yellow bile, and black bile).
Human kidneys will clean about 1 million gallons of blood in an average lifetime.
The Romans did not use numerals to indicate fractions but instead used words to indicate parts of a whole.
The Centers for Disease Control and Prevention (CDC) was originally known as the Communicable Disease Center, which was formed to fight malaria. It was originally headquartered in Atlanta, Georgia, since the Southern states faced the worst threat from malaria.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.