Louis Pasteur · Science
How Pasteur carried his microbes from the brewery to the sickbed, arguing that specific living germs cause specific infectious diseases - the idea that, with Lister’s antiseptic surgery and the conquest of one plague after another, would save more lives than perhaps any other in the history of medicine.
Pasteur came to the germ theory of disease not as a physician but as a chemist who had spent years watching microbes transform the world around them. He had shown that specific microorganisms turn sugar into alcohol, milk into acid, wine into vinegar. He had shown that these microbes come only from other microbes, carried in on dust and air, never generated spontaneously. The analogy that then seized him was simple and momentous: if invisible living germs can ferment a vat and rot a piece of meat, why should they not also invade and ravage a living body? Disease, he proposed, is in many cases a kind of fermentation gone wrong inside us - the work of specific germs multiplying in our tissues.
This was a radical reframing of illness. For most of history, disease had been blamed on imbalances of bodily humours, on bad air or ‘miasmas’ rising from filth, on divine punishment, or on spontaneous corruption of the body’s own substance. Pasteur’s germ theory said something startlingly concrete instead: many diseases are caused by particular, identifiable, living organisms that enter the body from outside, multiply, and can be transmitted from one person to another. If true, this changed everything - for a cause you can name and see is a cause you can fight, exclude, and ultimately prevent. The whole logic of his fermentation and spontaneous-generation work pointed here, and Pasteur followed it into medicine with the conviction of a man who had seen the germs with his own eyes.
The heart of Pasteur’s germ theory is the same principle of specificity that organised his fermentation work: just as each kind of fermentation is caused by its own particular microbe, so each infectious disease is caused by its own particular germ. Anthrax is caused by one organism, chicken cholera by another, rabies by another still. This was a profound break from the old idea of a single, vague principle of ‘contagion’ or ‘corruption.’ Diseases were not interchangeable expressions of a general unhealthiness; each was a distinct biological entity with a distinct cause that could, in principle, be isolated, cultivated, and studied - and the disease itself reproduced by introducing that specific germ into a healthy host.
This is the opening of the lesson. The rest — the dialogue, the primary source, and the recall — is in the app.
You learned that Pasteur extended his microbial theory to disease, arguing that specific germs cause specific illnesses and can be transmitted, fought, and excluded. In your own words, explain the chain of reasoning from fermentation to germ theory, the evidence Pasteur and others assembled, and how it transformed sur…
Leads to Joseph Lister.
Begin this lesson →epoché — a humanities education that remembers you.