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Though the United States has largely rejected the metric system, it is used for currency, as in 100 pennies = 1 dollar. Previously, the British currency system was used, with measurements such as 12 pence to the shilling, and 20 shillings to the pound.
About 600,000 particles of skin are shed every hour by each human. If you live to age 70 years, you have shed 105 pounds of dead skin.
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.
More than 2,500 barbiturates have been synthesized. At the height of their popularity, about 50 were marketed for human use.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.