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The human body produces and destroys 15 million blood cells every second.
Autoimmune diseases occur when the immune system destroys its own healthy tissues. When this occurs, white blood cells cannot distinguish between pathogens and normal cells.
More than nineteen million Americans carry the factor V gene that causes blood clots, pulmonary embolism, and heart disease.
There are 20 feet of blood vessels in each square inch of human skin.
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).