Dr. and Mrs. Coughlin, of Leopolis, take a tour in their three-year-old Maxwell car and eventually visit Dr. and Mrs. Tromp, in another North Dakota town. The two doctors discuss collections, treatment of certain ailments, and other doctors, including Dr. Winter and a brainy but brash young physician, Arrowsmith. They regret that he has no church affiliation since it is good for business and deplore his fondness for the bottle. Bert Tozer hears of Dr. Coughlin's disapproval of Martin and urges him to cut out poker and booze. Martin feels resentful that the whole world is watching him.
Martin is successful in perfecting a vaccine to control blackleg in cattle. The veterinarian of the county denounces him for intruding; the physicians hint that treatment of cattle is beneath the dignity of the medical profession. Martin, however, has once more tasted laboratory life.
Leora urges Martin to go alone to Minneapolis to hear Sondelius lecture. Described as a "Newfoundland dog of a man," Sondelius sways his audience with his anecdotes of the achievements of great men in the medical profession. After the lecture, Martin lingers to invite the speaker to join him in a beer garden. From now on, Sondelius, not Gottlieb or Silva, is Martin's idol.
Lewis is giving Arrowsmith some firsthand experience in the practice of medicine before returning him to the laboratory, his original love. The plague among cattle furnishes the opportunity for Martin's renewed interest in research. The fantastic character of Sondelius, who is to play almost a major role in the book later on, is introduced and his relation with Martin cemented here.