Bacteriology dominates Martin's life now, although he is also studying pathology, hygiene, surgical anatomy, and several other subjects. His roommate, Clif Clawson, though still a joker, supplies cheerfulness, for "The whole of Clif was more than the sum of his various parts." Martin seldom thinks of his former fraternity brothers. He is more interested in rebelling against the cut-and-dried teaching of the professor of materia medica Dr. Lloyd Davidson. Clif becomes impatient with him. For diversion and understanding, Martin returns to Madeline Fox.
Madeline encourages Martin to complete his medical courses before deciding exactly what he will do. Her widowed mother, who has come to live with Madeline, supplies a home and a chaperone for her daughter's entertaining, which is on a higher cultural and social level than that to which Martin is accustomed. A rival is Dr. Norman Brumfit, professor of English, who is in favor with Madeline. Martin, however, obtains permission to call on her the following evening.
The evening is a disappointment because Mrs. Fox remains in the room the entire time, and Martin is forced to talk to her instead of to her daughter. In the half-minute when he has Madeline alone, however, Martin manages a goodnight kiss.
A round of parties with Madeline as hostess follows, in which Martin is always a central figure. Even Clif Clawson is dragged in as an extra man. "Martykins" is the pet name bestowed on Arrowsmith, and soon not only Clif but Fatty Pfaff and Irving Watters are using it, to Martin's consternation. Clif, enraged, warns Martin against marrying a girl of Madeline's tastes, who will reduce him to the status of a tonsil-snatcher.
Madeline undertakes to improve Arrowsmith by urging him to increase his vocabulary and improve his taste in fiction. She also advises him to omit slang from his speech. He proposes to her one night in her roof garden after she has brought up the subject of probably having to go home without her Ph.D. They are to be married after he finishes two more years of medicine and two in the hospital.
Mrs. Fox accepts Martin as her future son-in-law, and the three of them attend Methodist Church together. The Reverend Ira Hinkley gloats over Martin's captivity.
Madeline, however, keeps scolding him for feeling superior and objecting to his working with Clif Clawson as a waiter in a Canadian hotel during summer vacation. As a result of her nagging, Martin, after learning that he has been appointed undergraduate assistant to Gottlieb for the coming year, takes off with Clif to the North woods without seeing her again.
Martin's first serious love affair develops and almost ends in this chapter. Having outgrown the limitations of Digamma Pi, he with Clif Clawson enjoys more independent living until Martin turns to Madeline Fox for companionship and help. She introduces him to a different world — one of culture, refinement, and gracious living — but she is too eager to change him. He rebels, for he must choose between her and bacteriology. He cannot become a mere money-grubber. His trip to the North woods and a position as waiter in a resort hotel constitute a declaration of independence against conformity. Leading the class in bacteriology and being appointed assistant to Gottlieb open the way for future developments in his career of scientific investigation.