The War of Life Against Life

By Gabriel Blanchard

From the shots we cajole our little ones through (or grimace over ourselves!) to the milk we pull from the fridge in the morning, Pasteur has left his mark on our lives.

Though rich with subjects like literature, law, theology, philosophy, and history, CLT’s Author Bank is comparatively light on scientists: only around a dozen names on it are known solely for their scientific accomplishments. This is partly because the sciences are more susceptible to getting updated in a way that leaves older authors out-dated—while a modern Platonist may embrace the writings of later philosophers yet will still read Plato directly and for its own sake, a modern doctor or astrophysicist is hardly going to study Galen on the four humors or Ptolemy on the epicycles. The scientists we include tend to meet one or both of two criteria: they have revolutionized the sciences in general (as Francis Bacon did, for example, by helping to codify the scientific method); or, they have made major contributions to their fields in ways that are still relevant today. Today’s profile offers an excellent example of the second. An in-depth history of modern biology might get away with skipping Athanasius Kircher or soft-pedaling Antonie van Leeuwenhoek,* but no one could seriously claim to have reviewed the subject without discussing the work of Louis Pasteur.

Pasteur was not an especially promising student; he struggled learning to read and write due to dyslexia, and (like many boys!) he preferred the outdoors to school. But at some point, the academic bug well and truly bit, and our principal story began. In 1842, at the age of 20, Pasteur earned his bachelor’s in, of course, mathematics; four years later he was appointed a professor of physics; the year after that, he at last began his independent research—in crystallography. He was, in fact, a renowned polymath, holding respected chairs in geology, physics, and chemistry, besides his famous work in biology. Indeed, though better known to most people for his contributions to biology (particularly medicine and food safety), one of Pasteur’s discoveries was a game-changer for chemists: that of chirality, informally called “left-handed” versus “right-handed” arrangements of molecules. The fact that two molecules of the same chemical need not be the same “shape” has turned out to be a vital piece of knowledge.**

His turn to biological investigations began in the 1850s with a study of the fermentation process in wine-making. He soon determined that it was yeast† which fermented sugar into alcohol, and moreover that microorganisms other than yeast would cause souring. This led Pasteur to examine other types of food spoilage, which, as he correctly guessed, were also caused by microorganism contamination. He found that by heating liquids to a temperature between 60º C (about 140º F) and boiling, most microorganisms that naturally occurred in them were killed off, allowing them to keep significantly longer and rendering them safer in general. Though not the first to notice this effect, Pasteur had determined what the mechanism was and established exact temperature parameters; he patented the technique of pasteurization in 1865, and many foodstuffs (such as milk, eggs, and beer) are pasteurized to this day, often by law.

This study of fermentation and spoilage had given him another idea. If bacteria run amok could ruin food, what about human diseases? Were microorganisms causing them too? The germ theory of disease was comparatively new at the time, and the scientific establishment did not look kindly upon it, especially not the medical establishment—even when they were confronted with strong evidence. A Hungarian obstetrician, Ignaz Semmelweis, had instituted a simple hand-washing protocol at the Vienna General Hospital in 1847 (imitated by Florence Nightingale just a few years later); the hospital had seen maternal deaths plummet from 18% to just over 2% in the space of a year, yet his theories were roundly ignored. In England, physician John Snow correctly identified the cause of a cholera outbreak in 1854, and persuaded the authorities to cut off access to contaminated water, but only after infection rates had begun to drop on their own due to residents fleeing the area (as Snow himself ruefully pointed out).

On the battlefield of observation, chance favors only the prepared mind.

Undaunted, Pasteur began to investigate. In 1877, a series of experiments with chicken cholera revealed that, if infected with a weakened form of the disease, chickens could subsequently ward off infection even when exposed to it at full strength. This had been confirmed by Edward Jenner with respect to smallpox nearly a century before; however, Jenner had been obliged to use a related but different disease, cowpox, as his inoculant. Pasteur proved that a weakened strain of the same disease would serve, both simplifying the process and making it more effective, though he still named these weakened diseases vaccines (from the Latin vacca “cow”) in honor of Jenner’s work. Pasteur created vaccines against several deadly diseases, notably anthrax and rabies.

Finally, when it comes to “reconnecting knowledge and virtue,” Pasteur is an interesting and difficult case study; his personal conduct, both as a man and as a scientist, was a curious mixture of the blameworthy and the beneficent. He is often claimed as a man of faith, and he was raised in a devoutly Catholic household. However—and quite apart from the vexed question of whether religious faith, simply as such, ought to be counted as a virtue—it is hard to say what his views were as an adult. He was reported by both himself and others to pray while he worked, and his son-in-law wrote (a little vaguely) that he had recourse to Catholicism “in [the] last weeks of his life,” but Pasteur’s grandson said that he was very much a freethinker, not an orthodox Catholic at all.‡

As to professional ethics, his scientific advances were quite genuine. However, credit sometimes fell to him not just alongside, but at the expense of, predecessors and colleagues whose work he built on, and he does not seem to have been very scrupulous about the issue. He could be obstinate, even quarrelsome, to little purpose: while serving as the director of scientific studies at the École Normale Supérieure in Paris, he improved the school’s prestige through increased rigor, but also provoked two student revolts—one of which (prompted by a smoking ban) resulted in seventy-three resignations from a school that had only had eighty students enrolled! The extreme secrecy with which he guarded his notes also led to questions about his honesty and, on certain occasions, about the ethics of his methods. Nonetheless, it would be quite wrong to paint him as an unprincipled opportunist, and even his ornery side had its advantages. He showed great professional and personal courage in the development of the rabies vaccine especially, and risked legal action in 1885 by using it to treat a nine-year-old boy who had been mauled by a rabid dog; although Pasteur’s vaccine was virtually untested, he and his colleagues felt that they had no choice—and the boy became the first person in recorded history to be successfully treated for rabies.

*If only because his name is entirely too difficult to spell.
**One relatively trivial example of chirality comes from artificial sweeteners: the “left-handed” aspartame molecule has a sweet taste, while the “right-handed” one is flavorless.
Yeasts are pretty fascinating themselves: though single-celled, yeasts are fungi and descend from a multicellular ancestor, and some types can form colonies that behave like a multicellular organism.
‡Attractive though it is, the famous line “The more I know, the more my faith is that of a Breton peasant” is not a genuine quote from Pasteur (as confirmed by Maurice Vallery-Radot, a distant connection who did maintain that Pasteur was devoutly Catholic throughout his life).


Gabriel Blanchard is a proud uncle to seven nephews, and lives in Baltimore. He has a baccalaureate in Classics from the University of Maryland, College Park, and has worked for CLT since 2019, where he holds the position of editor at large.

Thank you for reading the Journal. If you enjoyed this post, you might like some of our other profiles of the great men and women of our Author Bank, such as Titus Livy, Geoffrey Chaucer, James Madison, and Zora Neale Hurston, or our series on “the Great Conversation,” from habit to poetry to the state. You might also enjoy our podcast, Anchored, hosted by CLT’s founder, Jeremy Tate.

Published on 17th April, 2023. Page image of Louis Pasteur in His Laboratory by Albert Edelfeldt (1885).

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