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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).
During the twentieth century, a variant of the metric system was used in Russia and France in which the base unit of mass was the tonne. Instead of kilograms, this system used millitonnes (mt).
In 1844, Charles Goodyear obtained the first patent for a rubber condom.
In most cases, kidneys can recover from almost complete loss of function, such as in acute kidney (renal) failure.
The Romans did not use numerals to indicate fractions but instead used words to indicate parts of a whole.