Friedrich was skilled in many aspects of surgery, including pioneer work in the field of thoracic surgery (lungs). He is remembered for his studies of wound treatment and his efforts to reduce bacterial infections. Through experimentation, he demonstrated the importance of debridement (removal of infected tissue) within a six-hour time limit. He also did extensive work involving diseases that included peritonitis and tuberculosis. He is credited for introducing the practice of using seamless rubber gloves during surgery.