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Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
There are 20 feet of blood vessels in each square inch of human skin.
The shortest mature adult human of whom there is independent evidence was Gul Mohammed in India. In 1990, he was measured in New Delhi and stood 22.5 inches tall.
When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
The modern decimal position system was the invention of the Hindus (around 800 AD), involving the placing of numerals to indicate their value (units, tens, hundreds, and so on).