Along with sperm, the in vitro procedure adds fresh mitochondria extracted from less mature cells in the same woman's ovaries. The hope is to revitalize older eggs with these extra "batteries." But the FDA still wants proof that the technique works and is safe. Chris Nickels for NPR hide caption

itoggle caption Chris Nickels for NPR

An overgrowth of Clostridium difficile bacteria can inflame the colon with a life-threatening infection. Dr. David Phillips/Getty Images/Visuals Unlimited hide caption

itoggle caption Dr. David Phillips/Getty Images/Visuals Unlimited

In a landmark new study, researchers found that babies who consumed the equivalent of about 4 heaping teaspoons of peanut butter each week, starting when they were between 4 and 11 months old, were about 80 percent less likely to develop a peanut allergy by age 5. To avoid a choking hazard, doctors say kids should be fed peanuts mixed in other foods, not peanuts or globs of peanut butter. Anna/Flickr hide caption

itoggle caption Anna/Flickr

Bruno Mbango Enyaka gets his flu shot at a community health center in Portland, Maine, on Jan. 7. Gabe Souza/Press Herald via Getty Images hide caption

itoggle caption Gabe Souza/Press Herald via Getty Images

The human papilloma virus causes most — but not all — cases of cancer of the cervix. James Cavallini/ScienceSource hide caption

itoggle caption James Cavallini/ScienceSource

One teaspoon of pure caffeine powder delivers about the same jolt as 25 cups of coffee. The Center for Science in the Public Interest hide caption

itoggle caption The Center for Science in the Public Interest

Stringy particles of Ebola virus (blue) bud from a chronically infected cell (yellow-green) in this colorized, scanning electron micrograph. NIAID/Science Source hide caption

itoggle caption NIAID/Science Source