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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.
Before a vaccine is licensed in the USA, the Food and Drug Administration (FDA) reviews it for safety and effectiveness. The CDC then reviews all studies again, as well as the American Academy of Pediatrics and the American Academy of Family Physicians. Every lot of vaccine is tested before administration to the public, and the FDA regularly inspects vaccine manufacturers' facilities.
Blood is approximately twice as thick as water because of the cells and other components found in it.
The first war in which wide-scale use of anesthetics occurred was the Civil War, and 80% of all wounds were in the extremities.
Bacteria have been found alive in a lake buried one half mile under ice in Antarctica.