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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.
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.
In 2012, nearly 24 milliion Americans, aged 12 and older, had abused an illicit drug, according to the National Institute on Drug Abuse (NIDA).
Elderly adults are at greatest risk of stroke and myocardial infarction and have the most to gain from prophylaxis. Patients ages 60 to 80 years with blood pressures above 160/90 mm Hg should benefit from antihypertensive treatment.