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There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
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.
If all the neurons in the human body were lined up, they would stretch more than 600 miles.
For about 100 years, scientists thought that peptic ulcers were caused by stress, spicy food, and alcohol. Later, researchers added stomach acid to the list of causes and began treating ulcers with antacids. Now it is known that peptic ulcers are predominantly caused by Helicobacter pylori, a spiral-shaped bacterium that normally exist in the stomach.
As of mid-2016, 18.2 million people were receiving advanced retroviral therapy (ART) worldwide. This represents between 43–50% of the 34–39.8 million people living with HIV.