Discovering Diseases: The Beginnings of Germ Theory and Preventative Precautions

“Germ theory was not easily accepted. All across Europe and into the USA and Canada, it was heavily contested and challenged by medical professionals who were unwilling to accept the changes to the scientific system.”

Julien, Henry. Montreal’s Night-Mayor on his Ghostly Rounds (Dedicated to the Board of Health). 1875. Courtesy of the McCord Museum.

In the 19th century, the wide held belief was that diseases were caused by a noxious form of bad air and smells, such as those that came from sewage and cemeteries.  This theory was called miasma and it dominated healthcare practices in ways that gave doctors and surgeons no reason to wash their hands, wear masks, or operate in clean clothes.  Thankfully, we now know miasma to be a theory of the past, as it was disproven and replaced with our currently accepted germ theory of disease.  However, germ theory was not easily accepted.  All across Europe and into the USA and Canada, it was heavily contested and challenged by medical professionals who were unwilling to accept the changes.  Thanks to the work of Louis Pasteur, Joseph Lister, Robert Koch, Carl Flügge, and other researchers, we now have an understanding of how diseases can be transmitted and controlled.

Louis Pasteur (1822-1895)

Louis Pasteur. (Courtesy of Queen’s University Faculty of Medicine Collection, Museum of Healthcare, Kingston.)

Louis Pasteur (1822-1895) was a French chemist and microbiologist who discovered that microbes were responsible for souring alcohol and came up with the process of pasteurization.  His work in germ theory also led him and his team to create vaccines for anthrax and rabies.[1]  While Pasteur was not the first person to propose that diseases were cause by microorganisms, his experiments were integral to proving these theories. Perhaps most well-known for establishing and patenting the process of pasteurization, Pasteur’s work contributed greatly to developing germ theory.[2]

In 1865 he turned his attention to solving France’s silkworm crisis. After five years of research, Pasteur succeeded in proving the transference of disease between silkworms by isolating the microorganisms that were causing the disease. This conclusion allowed for him to prove that diseases are caused by microorganisms that, although too small to see, are incredibly infectious and dangerous.

Joseph Lister (1822-1895)

Carbolic Acid, c. 1890-1910. (Ralph and Olga Crawford Dental Collection, Museum of Health Care.)

Joseph Lister (1827-1912) was  instrumental  in applying Pasteur’s germ theories of disease into his practice.  Lister became aware of Pasteur’s work when reading his paper about the transference of disease between microorganisms.  Lister experimented and applied Pasteur’s proposed techniques to eliminate these dangerous microorganisms by exposing them to a type of chemical solutions[3]: “When I read Pasteur’s article, I said to myself: just as we can destroy lice on the nit-filled head of a child by applying a poison. . . so I believe that we can apply to a patients wounds toxic products that will destroy the bacteria”.[4]

Pasteur became aware of Lister’s work with contagious diseases and the two men developed a long correspondence that  discussed their experiments, theories, and discoveries[5]  In his experiments, Lister concluded that a diluted carbolic acid solution prevented healing wounds from becoming infected and also served as a successful cleaning agent for surgical instruments.[6]

Robert Koch (1843-1910)

Robert Koch, 1895-1910. (Courtesy of the Science Museum Group Collection, Science Museum, London [UK].)

In Germany, microbiologist Robert Koch developed techniques for growing and observing bacteria.  While undertaking these experiments, Koch developed four postulates which explain the basics of the relationship between microorganisms and disease[7].  Koch’s four postulates state that:

  1. The microorganism must be found in abundance in all organisms suffering from the disease but should not be found in healthy organisms
  2. The microorganism must be isolated from a diseased organism and grown in pure culture.
  3. The cultured microorganism should cause disease when introduced into a healthy organism.
  4. The microorganism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.[8]

In establishing these postulates, Koch was able to draw a connection and prove that a disease is caused by a particular organism.

Carl Flügge (1847-1923)

A colleague of Robert Koch at the University of Göttingen in Germany, Flügge co-founded and coedited the journal “Zeitschrift für Hygiene und Infektionskrankheiten” or “Journal of Hygiene and Infectious Diseases” with Robert Koch.  This journal published research material in the form of detailed protocols, charts, and photographs of the progressions of bacteriology and hygiene.[9]

Zeitschrift für Hygiene und Infektionskrankheiten. Circa 1903. American Libraries Collection, University of California.

In 1899 Flügge was working on tuberculosis research when he developed his droplet theory of infection.  This theory proved that microorganisms can be expelled as droplets from the respiratory tract and reach another person. Flügge and his pupils and successors conducted further experiments to determine that droplets are especially expelled during activities like talking, couching, blowing, and sneezing.[10]  As a result of this research, Flügge’s work promoted the need for the creation and use of the surgical mask into surgical and healthcare practices.

These four prominent microbiologists demonstrate the international dependence of the scientific community upon each other’s discoveries. After several battles of skepticism, the international germ theory developments arrived in Canada and prevailed in guiding the healthcare system. The changes to the way Canada managed infectious diseases would come into fruition in the beginning of the 20th century, just in time for a rotating door of infectious respiratory diseases. In many ways, the work done by these scientists are the basis for world’s ability to understand disease transfer, develop vaccines, and provide us with a fighting chance against dangerous pandemics like COVID-19.

About the Authour

Jessica Lanziner

(Margaret Angus Research Fellow, 2020)

Jessica Lanziner is currently in the Master of Museum Studies program at the University of Toronto and an alumna from Queen’s University, holding a Bachelor of Fine Art and Art History. With previous positions like work at the Uxbridge Historical Centre, Jessica has had the opportunity to work with collections of dental materials from a local early 20th century dental offices, igniting her interest in the history of healthcare in Canada.  


[1] Science History Institute. “Louis Pasteur”. Rabies and the Beginnings of the Institut Pasteur, Historical Biographies. Last modified December 14 2017.  Accessed May 15 2020.  

[2] Science History Institute. “Louis Pasteur”. Germ Theory, Historical Biographies. Last modified December 14 2017.  Accessed May 15 2020.  

[3] Joseph Baron Lister. “The Classic: On the Antiseptic Principle in the Practice of Surgery. 1867” Clinical Orthopaedics and Related Research, Vol. 468, no. 8 (August 2010): 2012-2016.

[4] “Meeting of the International Medical Congress” The Boston Medical and Surgical Journal, Vol. 95 (September 14 1876): 328. 

[5] Fitzharris, Lindsey. “The Queen’s Abscess” in The Butchering Art, 211-213. New York: Scientific American, 2017.

[6] Lawrence McKeen. “Medical Sterilization” in The Effect of Sterilization Methods on Plastics and Elastomers, 16-18. Cambridge: Elsevier, 2018.

[7] Olga Amsterdamska. “Historical Bacteriology” in International Encyclopedia of Public Health, 206-210. Cambridge: Academic Press, 2017.

[8] Schultz, Myron G. “Robert Koch” Emerging Infectious Diseases, Vol. 17, no. 3 (2011): 547-549.

[9] Pauline Mazumdar. “The Dominance of Specificity: Koch and His Adversaries” in Species and Specificity: An Interpretation of the History of Immunology, 84. Cambridge: Cambridge University Press, 1995.

[10] Ronald Hare. “The Transmission of Respiratory Diseases” Royal Society of Medicine, Vol. 57, no. 3 (March 1964): 222.

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