Demons, Magnetism, And Medieval Science

Flatulence Demons, Explained by Scholars: When “Gas” Was a Ghost With a Doctor’s Degree

A woman in medieval Europe could be told, with a straight face, that what rose from her belly wasn’t just air - it was something like a visitor. A spirit could be blamed for the “passage,” a humor for the timing, and a bodily sign for the mood. The paradox is that these explanations were often wrong in mechanism, yet eerily good at noticing a real bodily truth: digestion really does produce gas, and it really does have patterns.

For this chapter, we follow the medieval logic trail: scholars and healers didn’t treat flatulence as a private inconvenience. They treated it as evidence - clues about inner balance, moral weather, and the state of the organs. Then we compare that worldview to what modern physiology actually says about where gas comes from, why it smells, and why the body sometimes seems determined to gossip.

Matilda of Bruges - nineteen, apothecary apprentice, and old enough to have opinions about her own stomach - doesn’t get a lab report. She gets a theory. And theories, medieval ones included, are how people make sense of sensations they can’t hold in their hands. The mystery that keeps this subject alive isn’t whether people farted (they did), but what they thought the fart meant.

If a smell can be “explained” by demons - or by microbes - what exactly is the body telling us, and who gets to translate it?

The Humor-Physics of Medieval “Passage”: Spirits, Humors, and Clues From the Belly

Medieval “gas” talk didn’t start as a cranky misunderstanding of plumbing. It came from a whole medical language built around humors - the idea that the body is run by mixtures like blood, phlegm, yellow bile, and black bile. Health was balance. Illness was imbalance. And the body, being dramatic, showed imbalance through visible signs: skin color, urine qualities, fever, sleep patterns - and yes, the noises and pressures of digestion.

So when someone had flatulence, it wasn’t merely a symptom. It was a sign that the stomach and intestines were misbehaving in a way that could be read. Depending on the healer’s school and the patient’s story, the cause might be described in terms of coldness or heat, excess moisture, or an overabundance of a particular humor. Gas became a kind of messenger: if it was frequent, it suggested the digestion process was “stirring” the wrong substance; if it was foul, it hinted that the material being processed had gone bad - again, in the language of humors.

There’s also the spirit layer. In many medieval settings, bodily events weren’t sealed off from the supernatural. Even when people used medical terms, they often kept spiritual explanations nearby like a coat you might need later. Some traditions treated certain internal sensations as the work of demons or other invisible forces - especially when the symptom came with distress, shame, or a sense of being out of control. Importantly, this wasn’t necessarily “belief without observation.” It was belief attached to interpretation.

A telling detail: medieval medical texts often treated digestion as a sequence of transformations - food cooked, cooked again, then refined. If the process went wrong, the “wrong” matter could ferment, and fermentation in the body is exactly the kind of mechanism that produces gas. Medieval authors didn’t have microbiology, but they had a workable concept: certain substances can ferment. They just placed the blame in the wrong place.

Modern readers may picture the medieval stomach as a haunted cauldron. That’s not entirely fair. The medieval stomach was also a theory machine: it converted messy sensations into a story that could be acted upon - by diet changes, medicines, and ritual. The point isn’t that the story was right; it’s that it was consistent enough to organize daily life around.

What “Gas” Actually Is: Fermentation, Swallowing Air, and the Chemistry of Smell

Here’s the blunt comparison: medieval scholars could explain the experience of flatulence better than the underlying biology. In modern physiology, most intestinal gas comes from two main sources: swallowed air and gas produced by gut microbes.

Swallowed air arrives when we eat and drink, especially with fast eating, talking while chewing, carbonated beverages, or chewing gum. That gas tends to be more common early in digestion because it’s literally entering the system from outside.

The more interesting part - the one that explains why the smell can be intense - is microbial fermentation. In the large intestine, bacteria break down parts of food we can’t digest ourselves, like certain carbohydrates. During this breakdown, microbes generate gases such as hydrogen, carbon dioxide, and methane (not everyone produces methane)....