Stem cells aren’t just fodder for scientific experiments. They are living and growing in your body right now. What makes these cells so special compared to garden-variety body cells? First, stem cells can divide an infinite number of times, compared to a limited number of divisions for regular cells. Second, although ordinary cells have a set job (skin cells cover the body, liver cells filter blood, and so on), stem cells’ current job descriptions aren’t set. They have the ability to differentiate and take on the work of skin, liver, tooth, blood and many other cells. Embryonic stem cells are particularly ripe with possibilities: They have the power to “create” any tissue in the body. In adults, while an adult stem cell’s career path is more restricted. For example, a blood stem cell might make red blood cells, white blood cells or platelets, but it is confined to the business of blood-making.