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Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
Long-term mental and physical effects from substance abuse include: paranoia, psychosis, immune deficiencies, and organ damage.
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.
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).
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.