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The Babylonians wrote numbers in a system that used 60 as the base value rather than the number 10. They did not have a symbol for "zero."
The human body's pharmacokinetics are quite varied. Our hair holds onto drugs longer than our urine, blood, or saliva. For example, alcohol can be detected in the hair for up to 90 days after it was consumed. The same is true for marijuana, cocaine, ecstasy, heroin, methamphetamine, and nicotine.
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.
Your heart beats over 36 million times a year.
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.