The Germ Theory of Disease is the idea that diseases are typically caused by microscopic organisms, such as bacteria and viruses, which reproduce upon invading a body. Before this theory, people were unaware that such organisms could spread illnesses. By contrast, the Miasma Theory of Disease claimed that diseases were produced from the noxious odors that emanated from putrefied, rotting matter; that the air around this was poisonous. While supporters of the Miasma Theory were correct that dirty environments often led to sickness, the root cause of the sickness was misunderstood.
Louis Pasteur, a chemist and microbiologist in 19th Century France, played a pivotal role in the acceptance of Germ Theory through his many experiments in the study of fermentation and later, vaccination. Until his research in the causes of spoilage, there was a long-held belief since the days of the Ancient Greeks, that life could spring from lifelessness through a process called spontaneous generation. As one of his most well-known experiments, Pasteur used swan-necked flasks to help disprove this belief, demonstrating that microbes arise from other microbes in the environment. He would go on to apply these discoveries to public health, developing his pasteurization method for making food safer to consume, as well as contributing to the field of immunology, creating vaccines for anthrax and rabies.
The inferences of Pasteur’s and other’s work helped convince physicians of the necessity for cleanliness and sterilization in order to prevent diseases. Joseph Lister would utilize Germ Theory to discover his antiseptic methods, dramatically reducing deaths from infection during surgery. The practice of medicine became increasingly more experimental and evidence-based, as researchers would isolate pathogens, have a better understanding of how infections spread, and how to create vaccines. This undoubtedly helped improve the quality of life in progressively populated urban centers, where sanitation methods and food safety measures were surely strained, or lacking altogether.