Tuberculosis — aka, the reason everybody in 19th century literature is always coughing up blood, escaping to the countryside for "better air", or dying tragically young — is back. And this time, it's evolved a resistance to antibiotics. In fact, in a handful of cases, tuberculosis has been resistant to every single antibiotic available to treat it. Tom Levenson explains what's happening and why it matters at The New Yorker.