Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
To Dr. Paul H. DeKruif I am indebted not only for most of the bacteriological and medical material in this tale but equally for his help in the planning of the fable itself—for his realization of the characters as living people, for his philosophy as a scientist. With this acknowledgment I want to record our months of companionship while working on the book, in the United States, in the West Indies, in Panama, in London and Fontainbleau. I wish I could reproduce our talks along the way, and the laboratory afternoons, the restaurants at night, and the deck at dawn as we steamed into tropic ports.
What's up with the epigraph?
You can't underestimate the importance of this epigraph, because the truth is that science writer Dr. Paul DeKruif is just as responsible for the content of this novel as Sinclair Lewis is. The novel draws on DeKruif's experience as a medical student and uses many of the views he once had about science and the medical community in general. Lewis sought out DeKruif's expertise and knowledge extensively while writing Arrowsmith.
It makes sense, then, that Sinclair Lewis ended up giving DeKruif twenty-five percent of all the money this book ever made—which turned out to be a lot. And in this aww-inducing bromantic epigraph, Sinclair Lewis thanks him for helping out.