In December, actor and director Jesse Eisenberg donated a kidney to a total stranger. “It was immediately clear to me that I should do it,” he says. “It just seemed like an obvious thing to do.” Of the 27,000 kidney transplants performed annually in the U.S., just a few hundred come from living donors who give up a kidney to someone they don’t know. Many people aren’t even aware they can make this kind of donation: Eisenberg, for instance, didn't realize it until last summer, when he told a