In a flashback fifteen lines long, Sinclair Lewis recites an episode from the life of the great-grandmother of his hero, Martin Arrowsmith. As a motherless girl of fourteen, the great-grandmother has chosen to go on westward in a wagon with her sick father and her tattered brothers and sisters rather than to return to their relatives in Cincinnati.
Fourteen-year-old Martin Arrowsmith, son of the owner of the New York Clothing Bazaar, is reading Gray's Anatomy in Doc Vickerson's office in Elk Mills, in the state of Winnemac. The year is 1897.
Martin is the unpaid assistant of Doc and takes charge of the office whenever Doc makes a call. Although Martin reads steadily all afternoon from the section on the lymphatic system, he also enjoys exhibiting to his gang the dreadful and fascinating skeleton with one gold tooth when Doc is absent.
Doc Vickerson's three ill-kept rooms — one of them his office — are on the second floor of the building also containing the New York Bazaar. They are a challenge and a "lure to questioning and adventure" for Martin Arrowsmith.
Although Doc Vickerson is sober upon his return, he does not remain so long. Thrice gurgles of Jamaica rum make him garrulous. He commends his young assistant for reading Gray and advises him to "get training" in basic science in order to become a "leadin' physician" earning five thousand dollars a year. Wishing to give Martin something to start his training, Doc holds out his beloved magnifying glass, used for years in botanizing, and watches the boy slip the lens into his pocket.
This introductory chapter brings out the unflagging will power, the courage, and the spirit of adventure possessed by ancestors of the hero of the novel, Martin Arrowsmith. These characteristics are also apparent in the great-grandson, who is to show the pioneering spirit in his own field, medicine. This brief incident arouses interest in the reader and makes him wish to go on with the story.
Lewis introduces not only the hero, as a teen-ager already a devotee of medical science, but also the slatternly, drunken, but dedicated Doc Vickerson, the first of numerous medical men who are to influence the life of Martin Arrowsmith. The sordid, unsanitary office and living quarters are described with Lewis' own brand of realism. The characters are also true to life.
Doc Vickerson is characterized as "a fat old man and dirty and unvirtuous" and also as "a gray mass of a man with a gray mass of mustache." Yet he feels that his own life has been misspent and that he has wasted time collecting a scientific museum which no one wants to see. He hopes for better things for his young assistant, who should read not only Gray's Anatomy, the Bible, and Shakespeare, but should also attend college before entering medical school. The magnifying glass represents the boy's spirit of investigation, so important in the years that now lie before him.
The first chapter gives the Middle-West setting of the novel and introduces the determined character of Martin Arrowsmith, already absorbed in medical interests.
Though perhaps not a typical doctor of his time, Doc Vickerson is yet able to fire the ambition of his young protégé and to advise him about preparation for the future. The sordidness of the background is typical of Lewis' realistic point of view.