Germ Theory and its Application to Medicine and Surgery
Louis Pasteur
1878

Fermentation is a biological process carried out by micro-organisms. And that little discovery changed the world. ‘Pasteurized’ as in milk, the existence of vaccines, home-brewing – they all owe a whole lot to Louis Pasteur who laid the groundwork for microbiology and biochemistry and gave us some of the most basic foundations of modern scientific knowledge. All over the world, universities, hospitals and city streets are named for him, a man known as one of the greatest benefactors of the contemporary world.

Bacteria, showed Pasteur, are not spontaneously-generated, but born – living things only come from other living things – so fermentation and spoilage (in a broth, for example) result not from some internal process but from contamination by spores, dust, micro-organisms that come from the outside. The finding gave serious scientific legs to germ theory, the idea that germs are a primary source of disease, and led Pasteur on a path of inquiry that would be world-changing. Bacteria ferment beer and wine; bacteria spoil milk. Those processes can be prevented by fully protecting the substance from contamination by external micro-organisms. Hmm, and what about the human body? If we can show that similar micro-organisms cause disease, and we can identify ways of keeping them out, we ought to be able to stop the spread of disease. Yup. We can. Hey doctors – just for starters, how bout you wash your hands and properly sanitize before surgery?

Pasteur moved on to new ground after finding in his experiments that some things would not become infected even when exposed to bacteria. For example, a test on chickens that were infected with cholera seemed to show that over time some of those chickens became less and less impacted by exposure to the bacteria. Indeed, low levels of exposure increased the chickens’ resistance, making them immune from the full effect of the disease. The impact on medicine was massive, spawning a whole science of immunology and opening the doors to the first vaccines and an ability to control the spread of disease like never before.

Yeah, Pasteur did a whole lot for medicine, for biochemistry, for the development of microbiology. And for scientific method, too. Ongoing experimentation under conditions of strict control to replicate results before drawing conclusions – not his idea, but Pasteur was particularly known for his careful adherence to protocol in this regard, allowing him to discover patterns that could easily be missed otherwise. “Imagination should give wings to our thoughts but we always need decisive experimental proof, and when the moment comes to draw conclusions and to interpret the gathered observations, imagination must be checked and documented by the factual results of the experiment,” he said. Or, in other words, “In the field of observation, chance favors only the prepared mind”.

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