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The Babylonians wrote numbers in a system that used 60 as the base value rather than the number 10. They did not have a symbol for "zero."
Parkinson's disease is both chronic and progressive. This means that it persists over a long period of time and that its symptoms grow worse over time.
Vampire bats have a natural anticoagulant in their saliva that permits continuous bleeding after they painlessly open a wound with their incisors. This capillary blood does not cause any significant blood loss to their victims.
More than 2,500 barbiturates have been synthesized. At the height of their popularity, about 50 were marketed for human use.
About 3% of all pregnant women will give birth to twins, which is an increase in rate of nearly 60% since the early 1980s.