Her name was Henrietta Lacks, but scientists know her as HeLa. She was a poor Southern tobacco farmer, yet her cells--taken without her knowledge--became one of the most important tools in medicine. The first "immortal" human cells grown in culture, they are still alive today, though she has been dead for more than sixty years. HeLa cells were vital for developing the polio vaccine; uncovered secrets of cancer and viruses; helped lead to in vitro...