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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.
Intradermal injections are somewhat difficult to correctly administer because the skin layers are so thin that it is easy to accidentally punch through to the deeper subcutaneous layer.
There are approximately 3 million unintended pregnancies in the United States each year.
According to the FDA, adverse drug events harmed or killed approximately 1,200,000 people in the United States in the year 2015.