Rod-shaped specimens of Yersinia pestis, the bacterial cause of plague, find a happy home here in the foregut of a flea. Fleas can transmit the infection to animals and people, who can get pneumonic plague and transmit the infection through a cough or kiss. Science Source hide caption

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Dr. George Papanicolaou discovered that it was possible to detect cancer by inspecting cervical cells. The Pap smear, the cervical cancer screening test, is named after him. American Cancer Society/AP hide caption

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Engaging, mentally stimulating work is good for the brain, scientists say, whether you get paid to do it or not. Running a household can be as mentally demanding as running a company. iStockphoto hide caption

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Volunteer Patrick Pezzati searches yards in Turners Falls, Mass., for discarded heroin needles. Karen Brown/WFCR hide caption

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For all the good aspirin can do in preventing second heart attacks and strokes, taking it daily can boost some risks, too — of ulcers, for example, and of bleeding in the brain or gut. iStockphoto hide caption

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Maria Fabrizio for NPR

Volunteers search for needles and other drug paraphernalia along Church Street in Austin, Ind., in April. The region has recorded 142 new HIV cases since December, according to the state, in an outbreak tied to injected-opioid use. Seth Herald/Nurphoto/Corbis hide caption

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Work partners Jon Chintanaroad (left) and Mike Prestano are all smiles now, but founding a tech startup together threatened their friendship — and their business. April Dembosky/KQED hide caption

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A color-enhanced cerebral MRI showing a glioma tumor. Scott Camazine/Science Source hide caption

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Mmm. Smells just like your identical twin. iStockphoto hide caption

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Science-based guidelines say there's no benefit to getting an EKG of heart activity before routine cataract surgery — even if the patient is old. But most doctors order such tests anyway. Bull's Eye/ImageZoo/Corbis hide caption

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