But, these practices did not arise overnight. They reflect the accumulation of lessons learned over the last 170 years. Although surgery had been practiced for millennia by various civilizations, the birth of modern surgery is marked by the introduction of anesthetics in 1846, which meant that patients no longer had to endure pain. Yet, patients were more likely to die than recover after surgery.
The primary reason was infection, which was not well understood 170 years ago. The most important contribution in this regard was the Germ Theory of Disease, which stated that infectious diseases were caused by the spread of microorganisms called germs. Before Germ Theory, the prevailing thought was that diseases were spontaneously caused by non-living matter.
Based on Germ Theory, around 1864, surgical practices changed to include using weak carbolic acid to wash hands and instruments and reduce the level of germs in the air. Reuse of blood-soaked coats from one surgery to the next was discontinued. Gradually, the use of masks and head coverings during surgery became mandatory. Although these practices were considered burdensome, it led to fewer deaths due to post-surgical infections.
In the 1890s, dry heat and steam sterilization was found to be just as effective as chemical antiseptics such as carbolic acid. This led to the era of asepsis in surgery - creating a sterile environment in which to perform surgery. With every successive improvement in surgical practice, the chances of surviving surgery went up and surgery became safer. Thanks to these improvements, today, most surgeries are considered routine.