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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).
HIV testing reach is still limited. An estimated 40% of people with HIV (more than 14 million) remain undiagnosed and do not know their infection status.
After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
Illicit drug use costs the United States approximately $181 billion every year.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.