By Craig W. Fenn, Faculty Member, School of Science, Technology, Engineering and Math at American Public University

“For I have kept from them, and am still keeping from them, that one thing which is above the power of man to make; I have kept from them the germs that float in the air, I have kept them from life.”   – Louis Pasteur(1)


Image: Wikimedia Commons

May 19, 1861 is a date that probably doesn’t ring a bell or cause any light bulbs to go off in terms of huge scientific events. In the United States, people weren’t thinking too much about science. The Civil War was only five weeks old, and Union and Confederate gunships were trying, to no avail, to capture the Chesapeake Bay(2).

In England, Charles Darwin’s On the Origin of Species had already been in circulation for a year and a half, leaving scientific revolution and controversy in its wake.(3) Elsewhere in Europe, Gregor Mendel still tended the pea plants that became the basis of what we now know as “classical” genetics after he presented his work to the scientific world in 1865(4). And in Paris, a chemist named Louis Pasteur presented an experiment in front of his colleagues at the Paris Society for Chemistry that would turn the scientific world and much of what we believed on its head (5).

Prior to Pasteur’s experiment, a belief called “spontaneous generation” was a prevalent scientific method to explain how life came to be. This belief outlined that life can essentially arise from anything, even out of thin air. So if a piece of meat spoiled, the cause of the spoilage simply materialized from the air!

What Pasteur did was put the belief of spontaneous generation to rest with a simple, yet brilliant experiment. Pasteur boiled some nutrient broth inside a flask with a long, twisted neck. The flask, while still open to the air, did not allow any microbes to enter the main area of the flask where the sterile broth was. Any bacteria in the air couldn’t pass through the long neck of the flask to get to the broth inside. No bacteria meant no contamination, and the broth stayed sterile for one whole year! Pasteur then broke the neck of the flask and exposed the broth to the microbe-filled air, which contaminated the broth in short order.

Life Comes From Life

What is the ultimate impact of Pasteur’s experiment? He didn’t win the Nobel Prize for it (the first Nobel Prizes were awarded in 1901, and Pasteur died in 1895) (1, 6).

But there came a shift in attitude regarding how life came to be. The idea that “life comes from life” is now one of the major tenets of biology. Its significance is right up there with evolution and the cell theory (7).

Even more significantly, Pasteur’s experiment had an even greater impact on medicine. In the years following Pasteur’s experiment, Pasteur and one of his contemporaries (and eventually, his bitter rival) Robert Koch began studying various diseases closely and concluded that specific microbes have the ability to cause specific diseases (1, 8, 9).

This is the germ theory of disease. This theory led to the successful identification and treatment of many microbial diseases (1), saving millions of lives and contributing to the development of what we know today as modern medicine.

All because of a chemist and his funny-looking flask.


  1. Talaro, Kathleen Park, and Barry Chess. Foundations in Microbiology, ninth edition.  New York: McGraw-Hill (2015).
  2. Battle Summary: Sewell’s Point, VA. CWSCA Battle Summaries: The American Battlefield Preservation Program (ABPP).  Retrieved from
  3. Darwin, Charles. On the Origin of Species by Means of Natural Selection.  London: John Murray (1859).  Retrieved from
  4. Mendel, Gregor.Versuche über Pflanzen-Hybriden. Verh. Naturforsch. Ver. Brünn 4: 3–47 (1866) (Article in German).  Retrieved from
  5. Pasteur, Louis. Sur les corpuscles organisés qui existent dans l’atmosphère: Examen de la doctrine des générations spontanées. Leçon Professée a la Société Chimique de Paris, le 19 Mai 1861 (Article in French).
  6. Nobel Prize Facts. Retrieved from
  7. Simon, Eric J., Dickey, Jean L., Hogan, Kelly A, and Jane B. Reece. Campbell Essential Biology, sixth edition.  New York: Pearson Higher Education (2016).
  8. Smith, Kendall. Louis Pasteur, the father of immunology? Frontiers in Immunology 3(68), 1-10 (April 2012).
  9. Blevins, Steve M., and Bronze, Michael S. Robert Koch and the ‘golden age’ of bacteriology. International Journal of Infectious Diseases 14:  e744–e751 (2010).

About the Author

Craig Fenn is in his fourth year of teaching for the American Public University in the School of Science, Technology, Engineering and Math, with a primary teaching assignment of SCIN 130 (Introduction to Biology with Lab).  His primary employer is at Reading Area Community College, where he serves as the course lead for Principles of Biology and Microbiology as well as the chair of the Campus Life Committee.  He is a native of Connecticut currently living outside of Lancaster, PA.