"'There are books that are suitable for a million people, others for only a hundred. There are even remedies--I mean books--that were written for one person only...A book is both medic and medicine at once. It makes a diagnosis as well as offering therapy. Putting the right novels to the appropriate ailments: that's how I sell books.' Monsieur Perdu calls himself a literary apothecary. From his floating bookstore in a barge on the Seine, he prescribes...