William Stewart Halsted was a surgeon at Johns Hopkins Hospital in Baltimore, Maryland, during the late 1800s and early 1900s. In 1894 Halsted described his procedure for treating breast cancer by removing the breast tissue, chest muscles, and lymph nodes in the armpit, a procedure he named radical mastectomy, and that became the standard of care for treating breast cancer until 1970. He also made contributions to other novel medical procedures such as gallbladder surgery, blood transfusions, antiseptic techniques, anesthesia use, and using plates and screws to hold bones in position when setting bone fractures. At Johns Hopkins Hospital, Halsted established a surgical training program in which he allowed medical students and surgical residents to shadow him and perform procedures under his guidance. In the twentieth century, similar training programs spread across the country and informed the standardization of medical training. Halsted devised a surgical treatment for breast cancer and reshaped the way physicians practiced medicine in the twentieth century, which resulted in better health outcomes through more careful surgical methods, especially in women with breast cancer.

Etienne Stephane Tarnier was a physician who worked with premature infants in France during the nineteenth century. He worked at the Maternité Port-Royal in Paris, France, a hospital for poor pregnant women. Tarnier developed and introduced prototypes of infant incubators to the Maternité in 1881. Tarnier's incubators became standard in neonatal care, especially for premature infants, enabling doctors to save many such infants that previously would have died.