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When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
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).
Certain rare plants containing cyanide include apricot pits and a type of potato called cassava. Fortunately, only chronic or massive ingestion of any of these plants can lead to serious poisoning.
The average adult has about 21 square feet of skin.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.