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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.
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).
There are more nerve cells in one human brain than there are stars in the Milky Way.
Blood in the urine can be a sign of a kidney stone, glomerulonephritis, or other kidney problems.
If you could remove all of your skin, it would weigh up to 5 pounds.