Why do people get sick? The ancient Greeks and their medieval followers thought that an imbalance in the humors could do it, as well as outside forces such as planetary misalignment, and miasmas.
Those of you who have read the Merchant and Empire books know that these disease theories are prevalent in that story-world. Tycho and his physicians (and wife) have a long-running dispute over what he should eat: cooling, moist foods that match his nature, or the hot, crispy fried things he enjoys. He, and others, are also aware of the poisonous exhalations of the earth that they call miasmas.
Miasmas are generally invisible, although the vapors that rise over ponds on cool, still mornings are thought to be miasmatic. Often people can smell miasmas, but not always, something that is a particular concern to miners. Everyone knows that they are found in low places, swamps, some foul wells and places with bad water, in caves and mines, and occasionally in cellars. Illness caused by miasmas range from fevers and chills to pneumonia to deadly lung-rot and (in the Five Free Cities) the winter cough. The summer children’s complaint might be miasma related, or it could be caused by bad milk, since most children who die of it are still of age to nurse or drink beast milk.
What causes miasmas? Most people in Tycho’s world agree that rotting things are the likely cause. After all, since eating rotten food makes people ill, why should rotting plants, foul water, or rot inside the earth not also cause problems? It has been observed that relatively “dry” mines like the Scavenger’s Gift seem to have fewer miasmas than do wet mines, so it is logical to conclude that rotting things underground can contribute to bad air and miasmas. And burning certain minerals releases noxious fumes, which adds further weight to the idea. Illness that follows an earthquake or landslide is blamed on miasmas released by the breaking of the ground. Another theory held that fumes trapped in the ground concentrated and went bad, the way a little manure on a field improved fertility but too much in one place soured the soil. So too with gasses becoming miasmas if they lingered.
One of the sub-plots in Miners and Empire centers on the contamination of a stream by miasmas from the mines. Aedelbert wonders if the airs bubbling through the water transferred the minerals into the water, but he doesn’t really worry about it too much. Even after the mineral residue settles out downstream of the town in special settling ponds, the water is still sour (acidic). He knows that part of the rock around the mind has dry rot (is drusy) so he assumes there is also wet rot in the stone as well.
The conclusion is logical but the initial premise is incorrect. However, that’s the world of Tycho and his compatriots, and also the world of Europe in the early Middle Ages.
Cat Rotator's Quarterly 
Or later.
The germ theory of disease wasn’t generally accepted until the 1880s.
Later even than that. Hamburg’s cholera epidemic in the 1890s came in part from political rejection of germ theory because Koch was Prussian.
Case in point: malaria. The names comes from ‘bad air,’ thus a miasmatic influence. Mosquitos were simply another biting nuisance. The connection had to be made from swamp or stagnant water, to biting insect, to a parasite causing the illness, and around the loop.
Miasma was a good enough approximation, but not enough to identify and solve the problem.
There’s also the subjective element, as in, “Miasma may not be the same as yourasma.”
😉
*Heaves shovel full of wet snow in a Peter-ward direction*
Is a tendency toward punnishness “an imbalance in the humors”?
Or, maybe he is just a glutton for punnishness.
The phrase “good humor” (as in a good mood) is related to the idea that sickness was an imbalance in the humors.
We as creatures of the 21st century find things like bleeding to balance the humors, or ignorance of basic public sanitation both quaint, and frightening. However, without the technology to study microscopic organisms, and without a societal will to study the dead and learn how the body works and often how it does’t work, then humors, miasmas, and devine punishment are a logical approach to medicine. One wonders what our descendants 400 years in the future will think of our “advanced” medicine.
If I recall correctly, it has been shown that bloodletting can be used to treat Scarlet Fever.
Naturally, I’d prefer antibiotics.
But if enough bacteria become superbugs, and we might get a bit desperate.
It is also used to treat high blood pressure and excess of iron buildup.
You beat me to the Koch comment. And the ‘canary in the coal mine’ wasn’t just a joke.
Relatedly, spontaneous generation of life is damnably difficult to disprove and tends to pass Brother Occam’s Razor.
As an example, my parents planted a walnut tree sapling in the middle of the desert. Within a decade, they had squirrels.
One day, we shall decipher the sagas of the bushy-tailed tree rat, and we shall be amazed.
Fruit flies spontaneously arise from cantaloupe. A cantaloupe is brought into Redquarters. Upon slicing the melon, fruit flies appear. Therefore…
Growing up in Garden City, TX, most folks had pecan trees. NO squirrels, none at all. When I was a sophomore in high school, a wealthy oilman had a big oak tree dug up and transported from his home in Midland to his ranch in Sterling County. The truck stopped in GC to fuel up and a single squirrel hopped down and ran off into the pecan trees next to the gas station. We would see that squirrel off and on for the next 3-4 years until it died. Since it was an only with nothing to mate with, no descendants. I don’t know if any more have made it there or not. It has been over 10 years since I spent any time in the town since Dad and Mom moved into San Angelo.