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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.
Pope Sylvester II tried to introduce Arabic numbers into Europe between the years 999 and 1003, but their use did not catch on for a few more centuries, and Roman numerals continued to be the primary number system.
Amoebae are the simplest type of protozoans, and are characterized by a feeding and dividing trophozoite stage that moves by temporary extensions called pseudopodia or false feet.
According to the FDA, adverse drug events harmed or killed approximately 1,200,000 people in the United States in the year 2015.
More than 2,500 barbiturates have been synthesized. At the height of their popularity, about 50 were marketed for human use.