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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).
The familiar sounds of your heart are made by the heart's valves as they open and close.
Blood in the urine can be a sign of a kidney stone, glomerulonephritis, or other kidney problems.
The first documented use of surgical anesthesia in the United States was in Connecticut in 1844.
The Babylonians wrote numbers in a system that used 60 as the base value rather than the number 10. They did not have a symbol for "zero."