A generation or two ago, when Americans had an important but nonemergency medical need, many of them would have called on their family doctor, somebody who had treated them for years. It was a little like going to a family restaurant: The purveyors knew you, knew your tastes and personal quirks, and they were part of the fabric of your community. These days, patients aren’t visiting the family doctor nearly as frequently. They’re instead heading to what you might think of as drive-thru clinics —