Retrospection, retrospective analysis of a single case or of a group of cases of a single entity, offers much in the way of potential information. Thus, we want to know the surgeon's or pathologist's findings in order that we may re-evaluate what we saw on the films and find what we failed to see initially. We must constantly check our visual acuity and validate the accuracy of our interpretation. It seems rather obvious that we are right when we make a diagnosis, for example, of a duodenal ulcer, and the patient subsequently proves to have an ulcer. It ought to be equally obvious, but it is not, that we may have been right for the wrong reason. If we find a deformed bulb in a young male patient who presents with melena, the likelihood is great that the bleeding is coming from an open crater, but how sure can we be that the barium pocket we de- scribed as a crater was truly that? The surgeon may tell us that he found a crater at operation, but how often does he remove the bulb? If he does, can we re-exami...