Emergency medicine
Doctors who specialize in EM must know some about all of the different specialties of medicine. They treat people of all ages. They treat both men and women. They must know how to treat any kind of emergency. But they may not know quite as much about the chronic treatments of diseases over years. However, many people come to the Emergency Department with problems that are not emergencies. So EM doctors must also know  about how to treat non-emergencies.