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As the western states of America were settled, pioneers often had to drink rancid water from ponds and other sources. This often resulted in chronic diarrhea, causing many cases of dehydration and death that could have been avoided if clean water had been available.
Approximately 500,000 babies are born each year in the United States to teenage mothers.
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.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.