As a young man, Samuel Clemens spent two years learning the lay of the Mississippi River to become a licensed riverboat pilot. No sooner had he completed his apprenticeship than he realized that the topography of the river had changed. In order to maintain his proficiency, he would have to continue to study the waterway, which remained in a constant state of flux. Rivers are not the only things that change over the course of time. Medical knowledge morphs with each new piece of data that is discovered. Just when we think we’ve got it all figured out, voilà—a piece of information gleaned from the latest research hints that we’re probably off the mark; and so we set off again, chasing a new lead. >>more Brian T. Maurer has practiced pediatrics as a Physician Assistant for thirty years. His "Marginal Notes" column appears periodically in the Cell2Soul Blog. The title "Marginal Notes" is taken from a quote by Henry David Thoreau: "I love a broad margin to my life."