Stephan:   Here is a book review concerning an important trend that is affecting countries around the world. It provides a new perspective on the slum areas that surround many cities, and presents a more optimistic view than one usually sees in commentary on these communities. ARRIVAL CITY How the Largest Migration in History Is Reshaping Our World By Doug Saunders 356 pages. Pantheon $27.95. Thanks to Rick Ingrasci, MD.