At the beginning of the story, the narrator describes the landscape and his perspective (in retrospect) of life in Kansas City. The story then becomes about the tension between Doc Fisher and Doctor Wilcox. Even the boy's presence in the story seems to take a back seat to the bantering between the two doctors. However, there are symbols which, by one interpretation, add significance to the boy's story and the tension between the doctors. In the first paragraph, the narrator describes a display of a motor car, streamlined in silver and separated from the outside snow and "dirt" blowing off of the hills. It is a machine but aesthetically, it is "pure" in its pristine condition:
On this afternoon it was snowing and inside an automobile dealer's show window, lighted against the early dark, there was a racing motor car finished entirely in silver with Dans Argent lettered on the hood.
As the narrator approaches the hospital, he describes its location as "on a high hill that overlooked the smoke" and this description is evocative of Mount Olympus, heaven, or just generally being above the pollution of the city: another symbol of purity and, being a hospital, of a sterilized and clean space.
The narrator has just come from a free dinner, given on Christmas and Thanksgiving, and with this association, a symbol of good will and/or spiritual purity.
These symbols of purity seem to simply describe the scene and general atmosphere of the narrator's state of mind. But when the boy comes in and asks to be castrated, he's asking to be purified. Doc Fisher tries to convince the boy that he is in fact pure and is only responding to the body's natural (and therefore, pure in the "natural" sense) urges. Doctor Wilcox, the supposed Christian, dismisses the boy's anxiety. The boy had come to the hospital, described like an oracle on a hill, a "pure" place where he might receive medical and/or spiritual guidance. When the boy performs an amputation on himself, a misguided attempt at purity, the reader is left with the doctors bantering with each other. The opportunity to convince the boy that he is normal and purely natural has been missed.
This story is hard to pin down and give a final conclusion as to themes and what symbols might represent. But note that Fisher is the more understanding and competent doctor. However, one suggestion is that he is a "gambling" man who did not follow "Federal statutes." This supposes that he performed illegal abortions: an issue that is morally ambiguous because there are people who think abortion is a sin and some who think it is a choice. Thus, depending on your perspective, the moral purity of Fisher is ambiguous. Doctor Wilcox, who proclaims himself a Christian, is absolutely rude to the boy who comes looking for guidance; his purity is also put into question.
So, the three early symbols of aesthetic and spiritual purity establish a landscape after which we get examples of how ambiguous and conflicted purity is in real life. The hospital, that heavenly "city on a hill" offers no physical or mental help to the boy. Receiving no help, the boy directs his anxieties onto himself. Notions of purity are misguided and applications/help that might help one achieve purity (mental or physical) are also misguided (by the doctors, namely Wilcox).