The heart beats in a mouse embryo grown with stem cells made from blood. Now the research that claimed a simple acid solution could be used to create those cells has been retracted.
Courtesy of Haruko Obokata
Sick with chikungunya, Karla Sepulveda, 5, waits in a public hospital with her grandmother in Boca Chica, Dominican Republic, on May 15. The Caribbean nation has reported more than 100,000 cases this year.
Ezequiel Abiu Lopez/AP
In this photo, released July 17, 1989, a U.S. marshal keeps his pistol trained on suspects as other marshals raid a crack house in Washington, D.C. The city's crack epidemic lasted from the late '80s to the early '90s.
Iraqi Shiite volunteers with the Labayk ya Hussein Brigade take part in a training session in the holy city of Najaf in late June. Clerics in the city called for Shiites to step forward and fight the Sunni group formerly known as the Islamic State of Iraq and Syria (which now calls itself simply the Islamic State).
Haidar Hamdan/AFP/Getty Images
Iraqi policemen take up positions on a bridge north of Baghdad on Monday. There's a consensus among Western and Middle Eastern states that militants from the Islamic State pose a serious threat to the region. But there's no sign yet that countries like the United States, Russia and Iran are prepared to work together.