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There are 20 feet of blood vessels in each square inch of human skin.
As many as 20% of Americans have been infected by the fungus known as Histoplasmosis. While most people are asymptomatic or only have slight symptoms, infection can progress to a rapid and potentially fatal superinfection.
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.
IgA antibodies protect body surfaces exposed to outside foreign substances. IgG antibodies are found in all body fluids. IgM antibodies are the first type of antibody made in response to an infection. IgE antibody levels are often high in people with allergies. IgD antibodies are found in tissues lining the abdomen and chest.
Vaccines prevent between 2.5 and 4 million deaths every year.