The miasma theory was the predominant theory of Lister’s time for how disease and infection were caused. Many scientists and doctors believed that infections and disease came directly from the “filth and decaying matter” prevalent in the Victorian Era, then were transmitted through “miasma” or “poisonous vapors” in the air (54). While some, known as contagionists, argued against this theory, it was largely popular due to the already present unsanitary conditions throughout hospitals. It provided doctors with an easy scape goat for rampant death and infection: It came from the poisoned air and there was nothing that could be done about it.

Carbolic acid was the chemical disinfectant Joseph Lister chose as the agent for his antiseptic system, using it to kill germs in wounds, on instruments, and on surgeons’ hands. Lister was inspired to use the substance after learning of the “remarkable effects produced by carbolic acid upon the sewage of the town” of Carlisle, where it served as a powerful deodorant and parasiticide (161-62). He began applying a purified version in clinical settings, most notably in treating compound fractures and draining abscesses. His early challenge was to balance its germ-killing power with its tendency to cause severe skin irritation. Through persistent experimentation, Lister refined his method, developing a diluted solution with oil that proved less harmful to tissue without sacrificing its antiseptic properties. This iterative process of refinement was a hallmark of his scientific approach and made carbolic acid the practical, if controversial, cornerstone of his system.

The germ theory of putrefaction was the scientific breakthrough by French chemist Louis Pasteur that demonstrated that fermentation and decay are caused by living, airborne microorganisms, not by spontaneous generation. Pasteur proved this theory with his swan-neck flask experiments, in which boiled broth remained sterile only when airborne dust carrying microbes was prevented from reaching it. This dealt the doctrine of spontaneous generation a “mortal blow” (158).

This laboratory discovery had immense implications for medicine. Pasteur’s work established that if germs caused putrefaction, they could be destroyed by heat, filtration, or chemical antiseptics. Lister seized upon this last possibility, realizing he could apply a chemical agent directly to a wound to kill the germs before they could cause a fatal infection. This transfer of a bacteriological principle to the operating theater was the conceptual leap that enabled the entire antiseptic system.