During the summer in the Canadian hotel, Martin and Madeleine write to each other, and by mid-summer they are re-engaged.
Martin begins his own research, and his sense of observation and curiosity is encouraged, once again, by Gottlieb, with whom he works. At one point, Gottlieb asks Martin to run a laboratory errand for him and go to Zenith General Hospital to obtain a specimen. It is here that he meets a seemingly impertinent and strong-minded nurse named Leora, whom he later gets to know and begins to like.
Leora, a girl from Dakota, tells Martin about her background and herself and Martin begins to develop a serious affection for her. He proposes to her and finds himself engaged to two women at once. Not knowing how to solve his dilemma, or how to choose between them, Martin invites them both to lunch at the same time leaving them to decide for him. Madeleine is insulted and leaves him, whereas Leora stays and commits herself to him. She claims that she will not leave him despite the seeming foolishness of staying with him. She tells him, however, that he now belongs to her and cannot go around with other women. Martin finds himself very happy at the way things turned out.
In these chapters appears one of the major conflicts in the novel, which is the struggle of the physician versus the struggle of the laboratory scientist. Martin's classmates all seem to belong to the "physician" category, most of them wanting to be successful and wealthy doctors. Others simply want to help people, such as the Reverend Ira Hinkley claims. But Martin finds himself an outsider. He is not like his classmates in that he does not view success in the same light; in fact he continuously rages against it. He is, instead, a laboratory man. He loves Max Gottlieb, who is the consummate symbol of the laboratory/research side of science.
Not only does Martin admire Gottlieb, but he loves the idea of him because Martin is, after all, filled with idealistic and romantic notions of the scientist working late at night in his lab, in search of the truth. Lewis, from the beginning of the novel, is trying to illustrate and criticize the problems that exist within the medical profession, which are problems that begin to arise even while Martin is still in medical school. Competition, for instance, seems to be one factor in the problematic web of science. From the beginning even Doc Vickerson, the old country doctor, is said to have a nemesis in the form of another doctor, Dr. Needham.
In Chapter 5, Lewis begins one of his sub-sections (III) by calling Martin "in no degree a hero," yet a "seeker of truth who stumbled and slid back all his life . " Here it becomes apparent that the protagonist of this modern novel—in this epic or myth of sorts—is not the typical hero, instead he is more of a man who seeks truth but finds difficulty in the search. For example, Martin is idealistic, and he talks and talks about what he believes and, in fact, Martin does believe what he says. However, he also finds himself giving it all up in an impulsive proposal to Madeleine. He says to her that he will become that "successful surgeon" he so despises so that the reader can see that Martin Arrowsmith is not a man who is altogether incorrupt or impossible to tempt.