Louis Pasteur: The Discovery Of The Role Of Micro-Organisms In The Process Of Decay And Disease

Robert Koch was one of the two scientists responsible for the discovery of the role of micro-organisms in the process of decay and disease. The other was Louis Pasteur. Their work was so important that they are widely considered to be the founding fathers of microbiology. Koch’s work on Anthrax leads to his discovery of the causative agent of tuberculosis. Pasteur worked to prove micro-organisms present in decaying matter resulted from exposure to germs in the air.

Pasteur strongly believed that you ‘should not put forward anything you cannot prove by experimentation. He was a chemist by training but became interested in biology while studying fermentation. Micro-organisms were found in decaying matter, but it wasn’t clear what role they were playing in the decomposition process. Many believed that life could ‘spontaneously’ arise from non-living material- the theory of ‘spontaneous generation. Some believed bacteria come from the air, others thought that it grows spontaneously, so Pasteur set out to solve this controversy.

Pasteur supported an opposing theory that held that micro-organisms present in decaying matter resulted from exposure to germs in the air. He set out to prove this theory by a series of extremely rigorous experiments. Firsty he showed that the organisms found in decaying matter closely resembled the organisms found in the air. To do this he filtered the air and studied the trapped debris using a microscope. He then proposed that any treatment which lead to the killing of micro-organisms should preserve the material. He showed that boiling a nutrient solution preserves it, thereby supporting the germ theory. However, opponents of the germ theory argued that the boiling procedure in some way affected the fresh air surrounding the nutrient solution. They argued fresh air was needed for spontaneous generation. He conducted an experiment using a ‘swan-neck’ flask to address this criticism.

In this experiment, the nutrient ‘broth’ was heated in an open flask, but the neck was shaped so that material (dust and microbes) falling from the air would not be able to reach the liquid. The liquid in the flasks was exposed to ‘fresh’ air but no microbes could enter and so the broth remained clear. By tilting the liquid in the flask so that it came in contact with the neck so could contaminate the liquid, which after a short incubation would go cloudy. Pasteur showed by the microscopic examination that the microbes in the neck were the same a those that grew in the contaminated liquid.

The conclusion of this experiment was that the swan neck flask experiments proved beyond reasonable doubt that the air was teeming with microbes and that these were responsible for the purification of non-living material. After this work, the spontaneous generation theory died out and the view that micro-organisms were ubiquitous and active in the environments they came to dominate.

Pasteur is renowned for his discoveries of vaccinations, pasteurization and microbes fermentation. He created the first vaccine for rabies and anthrax. He’s also responsible for disproving the doctrine of spontaneous generation.