What does Dr. Rank contribute to the play? If he were eliminated, what would be lost?

Dr. Rank embodies and subverts the theatrical role of the male moral force that had been traditional in the plays of the time. Rather than providing moral guidance and example for the rest of the characters, Dr. Rank is a corrupting force, both physically and morally. Sick from consumption of the spine as a result of his father's sexual exploits, the Doctor confesses his desire for Nora in the second act and goes off to die in the third act, leaving a visiting card with a black cross to signify that--for him--the end has come. Not having Dr. Rank in the play would change Nora's dynamic. He provides an alternative, or at least the idea of an alternative, male figure to Nora's forced acceptance of Torvald.