Knight (left) and Bucheli take soil samples from beneath one of the decomposing bodies. Katie Hayes Luke for NPR hide caption

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The Eagle Mountain Church in Newark, Texas, was linked to at least 21 cases of measles this year, mostly in children. LM Otero/AP hide caption

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Drug overdose deaths have more than tripled in the U.S. since 1990. Opioid painkillers like OxyContin are the cause of three-quarters of those deaths. Toby Talbot/Associated Press hide caption

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Billie Iverson, 86, of Cranston, R.I., recently underwent a transplant of intestinal microbes that likely saved her life. Ryan T. Conaty for NPR hide caption

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We may not see them, but we need them. iStockphoto.com hide caption

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The tale of the tape may be told, in part, by the microbes inside you. iStockphoto.com hide caption

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Could the images common in accounts of near-death experiences be explained by a rush of electrical activity in the brain? Odina/iStockphoto.com hide caption

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It's busy down there: a gut bacterium splits into two, becoming two new cells. Centre For Infections/Science Photo Library/Corbis hide caption

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Streptococcus bacteria, like this strain, can be found in our guts. Janice Haney Carr/CDC Public Health Image Library hide caption

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"Liver buds" grow in petri dishes. The rudimentary organs are about 5 mm wide, or half the height of a classic Lego block. Courtesy of Takanori Takebe/Yokohama City University Graduate School of Medicine hide caption

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Hospitals and organ banks could get more leeway in decisions about donations. Sean Gallup/Getty Images hide caption

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Bad bug: The bacterium Clostridium difficile kills 14,000 people in the United States each year. Janice Carr/CDC/dapd hide caption

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Sarah Murnaghan, on May 30, as she and her parents marked the 100th day of her stay in Children's Hospital of Philadelphia. Murnaghan family/AP hide caption

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