Tbh germ theory DOES sound crazy. Like if you told a regency-era nobleman that tiny creatures lived on the surface of everything and THAT’S what causes consumption, they’d be like “ah, I see you are a lunatic. Would you reside in my hermitage? Rantings and ravings do so amuse my guests”
But if you told a Medieval person this they would probably go "Ah, so when the miasma settles on surfaces it gains evil life. I understand."
Yeah, actually, it would probably be pretty easy to explain germ theory to a Medieval person as tiny evil spirits that live on everything, but they can be purified by soap and water, or by alcohol, because that is why God has granted us those things. And because they can float in the air, if you cough or sneeze after they have infested you, that can cause them to infest others. And when you are sick, the angels God has deputized to defend the bodies of His beloved children are at war with the evil spirits, and, sadly, sometimes they lose, but the best way to help your angels win their battle is to rest, drink plenty (this would probably be small beer in this time period, not water, because the water was also infested), stay clean, and for the sake of God do not allow anyone to let your blood, for the angels need that blood in their war against the evil spirits. Bloodletting is good for some types of illnesses but not the kinds caused by the tiny evil spirits.
boiling as a sterilization measure is also easy to explain. water returns to the air when heated and it rises as steam back up to the floodgates of heaven; we know God created the world in seven days, He's not up there making more water every time it rains. it circulates. the returning of water to heaven also purifies the water of unclean and malign influences. you know wormy water from a muddy puddle will kill your kid. you know you wouldn't wade into a bog and have a slurp. water that remains in the low places of earth absorbs all that is unclean from our waste and it may also sponge up new diseases from hell, we're not totally sure about that one, but it seems likely. God set up the heavenly water cycle so that the earth's waters wouldn't totally fill up with gunk.
what does this have to do with boiling your surgical tools? well look, the boiling water releases bubbles of steam which carries the malign influences up to heaven. you boil a knife, you send all the miasmic particles off with the steam to heaven. if you rinse the knife off in a bucket the water isn't hot enough, the particles go into the water and then right back on to the knife. you gotta boil it to get the particles all the way away. how can a tool or rag or a bed have miasmic particles on it when you can't smell them? humans have a lousy sense of smell. look at your dog on the hunt. are there no rabbits in the woods just because you can't smell them? we know that miasma is carried on the air, and is what makes stench so dangerous, and we know that humans can't smell worth a damn compared to dogs cats horses etc. a dog can smell if a rat died in a corner of the room last week. you can't. do you think licking the spot where the rat died is going to go well for you? luckily, what humans lack in snout we make up for in brains. we have extra brains where our sniffers should have been. God set that up for a reason.
and why does a rinse with wine spirits work? man, look how fast alcohol evaporates. my guess is that because wine contains a lot more vice than water, it evaporates a whole lot faster, in sort of an equal and opposite way that a rock falls faster than a feather. if you want the miasmic particles to get off there FAST, you dunk it in something that's going back to heaven at a gallop.
what's up with honey? it just preserves things against corruption. doesn't clean them off. honey doesn't evaporate at all. probably because bees don't sin. it's not good for ridding a tool of particles-- it's sticky-- but fine for preserving anything you don't want to go to heaven OR hell. this is why you wash the wound with wine spirits or purified water FIRST, to sluice the miasma out, then slap the honey on AFTER. and boil the damn bandage, too. you wouldn't put a rotten door in a sound doorframe and expect it to keep out bandits, would you? cmon.
Medieval people also already knew that putting things out in the sun helped to keep them clean (UV radiation killing bacteria). So everyone knows that after you use a butter churn, you rinse it out, give it a scrub, and set it out in the sun to dry, or else it will go sour and everything you make with it will go bad fast. Likewise with when you want to get sheets and clothes really clean and fresh, you boil them with lye soap and then lay them out in the sun to dry.
Medieval paesant: yes, yes, makes total sense
JFK Jr: I take my grandkids to swim in a sewer and dig roadkill
This kind of process is called "headology" in Discworld and is the foundation for an entire branch of witchcraft in the series.
