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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).
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.
Urine turns bright yellow if larger than normal amounts of certain substances are consumed; one of these substances is asparagus.
The heart is located in the center of the chest, with part of it tipped slightly so that it taps against the left side of the chest.
There are more sensory neurons in the tongue than in any other part of the body.