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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).
Normal urine is sterile. It contains fluids, salts, and waste products. It is free of bacteria, viruses, and fungi.
Pubic lice (crabs) are usually spread through sexual contact. You cannot catch them by using a public toilet.
Addicts to opiates often avoid treatment because they are afraid of withdrawal. Though unpleasant, with proper management, withdrawal is rarely fatal and passes relatively quickly.
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.