Picture walking into a hospital where the surgeon just finished one operation and started the next without washing their hands. That sounds dangerous today. But in the 1800s, it was completely normal. Joseph Lister, born on April 5, 1827, in England, changed that forever. Before Lister, about half of all surgery patients developed serious infections. Doctors thought bad air caused the problem. They did not know about germs. In 1865, Lister read about the work of Louis Pasteur. Pasteur had shown that tiny living things called bacteria could cause food to spoil. Lister had a powerful idea. If bacteria spoiled food, maybe bacteria also caused wounds to become infected. He began spraying a chemical called carbolic acid on surgical tools, bandages, and even the air in operating rooms. The results were dramatic. At his hospital in Glasgow, Scotland, infection rates dropped sharply. Patients who would have lost limbs or died began to recover. Other surgeons were skeptical at first. They thought Lister's methods were too complicated. Some doctors were insulted by the suggestion that their dirty hands were harming patients. But the evidence was impossible to ignore. Hospitals that followed Lister's methods had far fewer deaths. By the 1880s, clean surgery had become the standard. Lister is often called the father of modern surgery because his work saved countless lives.