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There are more bacteria in your mouth than there are people in the world.
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).
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.
More than 150,000 Americans killed by cardiovascular disease are younger than the age of 65 years.
Intradermal injections are somewhat difficult to correctly administer because the skin layers are so thin that it is easy to accidentally punch through to the deeper subcutaneous layer.