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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).
Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
Vaccines prevent between 2.5 and 4 million deaths every year.
Congestive heart failure is a serious disorder that carries a reduced life expectancy. Heart failure is usually a chronic illness, and it may worsen with infection or other physical stressors.