At University College Hospital, Lister (as house surgeon to John Erichsen), witnessed perilous, often unsanitary operations that felt like a “lottery.” In one emergency, a young woman undergoing surgery for a laryngeal disease began to asphyxiate; Erichsen cleared her airway by suction and saved her, though Lister knew infection still threatened her survival. The injuries he saw reflect London’s industrial hazards: A 13-year-old cotton worker, Martha Appleton, lost all five fingers; a painter suffered lead poisoning; and poor diets contributed to scurvy, which Lister treated according to prevailing but incorrect theory. He gained expertise diagnosing sexually transmitted diseases, notably incurable syphilis. He discharged Matthew Kelly, whose seizures he suspected were late-stage syphilis, and James Chappell, whose syphilis masked tuberculosis that endangered his roommates.

Meanwhile, Lister persisted with microscopy. In 1851, he began working alongside William Sharpey, who became the first surgeon to focus heavily on physiology as a field separate from anatomy. With Sharpey’s encouragement, Lister began examining human cells. In 1852, he published research confirming that the iris consists of smooth, involuntary muscle and settled a debate within the scientific community. At the same time, however, many continued to view his work as “superfluous,” as they believed it did little to help the field of surgical medicine.