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Many medications that are used to treat infertility are injected subcutaneously. This is easy to do using the anterior abdomen as the site of injection but avoiding the area directly around the belly button.
Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
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.
Nitroglycerin is used to alleviate various heart-related conditions, and it is also the chief component of dynamite (but mixed in a solid clay base to stabilize it).