Ovarian tissue containing hundreds of small resting eggs is prepared to be transplanted back after cancer treatment. Courtesy of Claus Yding Andersen hide caption

itoggle caption Courtesy of Claus Yding Andersen

The purple-stained Rothia dentocariosa bacteria are frequently found in the human mouth and respiratory tract. CDC hide caption

itoggle caption CDC

A surgical team at Sooam Biotech in Seoul, South Korea, injects cloned embryos into the uterus of an anesthetized dog. Rob Stein/NPR hide caption

itoggle caption Rob Stein/NPR

Ken (left) and Henry were created using DNA plucked from a skin cell of Melvin, the beloved pet of Paula and Phillip Dupont of Lafayette, La. Edmund D. Fountain for NPR hide caption

itoggle caption Edmund D. Fountain for NPR

In 1954, Dr. Frederick C. Robbins, then chief of pediatrics and contagious diseases at Cleveland Metropolitan General Hospital, was one of three winners of that year's Nobel Prize in medicine. The scientists' work, which led to a vaccine against polio, was performed in human fetal cells. AP hide caption

itoggle caption AP

Bayer HealthCare, of Whippany, N.J., brought Essure to market in 2002 as a nonsurgical alternative for women seeking sterilization. Bayer acknowledges the device can lead to complications, but says they are rare. Julio Cortez/AP hide caption

itoggle caption Julio Cortez/AP
Thomas Kuhlenbeck/Ikon Images/Corbis

The Essure contraceptive device is placed in the fallopian tubes, where it causes scarring that blocks sperm from reaching eggs. Courtesy of Bayer HealthCare hide caption

itoggle caption Courtesy of Bayer HealthCare

Regulators say R.J. Reynolds Tobacco Co. must stop selling four kinds of cigarettes because the Food and Drug Administration said the company had failed to show they aren't riskier than cigarettes on the market before mid-February 2007. Andrew Harrer/Bloomberg via Getty Images hide caption

itoggle caption Andrew Harrer/Bloomberg via Getty Images

A landmark federal study was halted when early results showed that lowering patients' top blood pressure number to 120 or lower led to dramatic reductions in heart disease and deaths. iStockphoto hide caption

itoggle caption iStockphoto