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Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
More than 2,500 barbiturates have been synthesized. At the height of their popularity, about 50 were marketed for human use.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.
There are more nerve cells in one human brain than there are stars in the Milky Way.
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.