Death
Death is an undeniable aspect of these stories, and the elder doctor talks openly about death, about how difficult it is to lose patients, about the scariness of death itself, and about the humble attitude a doctor must take in order to properly avoid unnecessary death. By forgetting the stakes of death, a doctor could accidentally end up on autopilot, and the stories underscore the way a doctor has to be always aware of death, but in a way that doesn't stop him from succeeding.
Survival and medicine
Survival and medicine are shown to be thematically related. This is shown symbolically in the gift that the younger doctor gets from the elder doctor, which is a diagnosis manual textbook, which the doctor is told to use for autopsies and patients. Through medicine, they hope to attain some kind of freedom from unnecessary death and suffering, which shows that medicine is deeply connected to the value of human life and existence. The stories are designed to integrate the young doctor's perception of medicine back into animal survival.
Community
The letters are themselves an instance of this theme, because the elder doctor is hoping to pass along his experience and knowledge to the younger, in an attempt to help him to become a proficient doctor, but also because of community. In the stories, the patients are embedded in community, which matters to the practice of medicine because that helps to frame the original goal of medicine, which is to respond to human suffering. Through the theme of community, suffering can be endured.
