Follow up on an old question/idea.

My 'time traveler' (actually more of a dimension hopper) got thrown into a roughly medieval feudal society, very closely modeled off of, but not the same as, medieval Europe without warning.

He earns the interest of the kings youngest son, a prince that is mostly written off as too much of a scholar without enough leadership material and clearly not the king's favorite. The son argues that our protagonists future knowledge can be valuable, but the king is highly skeptical and considers him a charlatan, willing to humor him with a place to stay for his son's sake but not to seriously consider any of our protagonists suggestions.

The protagonist likewise has a hard time getting traction for improvements from others due to the difficulty in proving his theories and the king's skepticism rubbing off on his retainers. That is until he recommends boiling water as a (sadly only viable to the nobility...) protection against a Cholera like disease.

Our protagonist then suggests he'd like to use the kings newfound willingness to listen to him to try to rediscover penicillin. The only problem is that he doesn't have a good method for doing that.

However per Nosajimiki answer on the first link above penicillin should already be known by cheese makers and possible doctor who use it to treat wounds. Unfortunately our protagonist doesn't know that these folks are aware of penicillin and has no reason to think of asking a cheese maker to help him with revolutionizing medicine. Thus the question is rather our time traveler can stumble upon the fact that penicillin already exists and doesn't need to be recreated from scratch.

The most obvious avenue for this would be a doctor mentioning they use mold to treat wounds when he says he's looking for a mold that will stop disease. This is made a little harder because many doctors are already weary of him, they don't like his trying to revolutionize so much of their knowledge and really hate to be told they may be spreading disease with their practices. Thus he's getting rather lackluster assistance from the medical professionals available to him.

So how likely is it that when he shows up and tells the king there is a mold that is a miracle medicine and he just needs to find it someone will tell him he's an idiot it already exists? will they recognize his, very limited, description of the mold?

If they do how hard would it be to take existing penicillin and make it into an ingestible antibiotic? Can people just eat the mold cheese makers already have and bam your done (...assuming they had a sickness penicillin can treat of course)? How hard would it be to prove that the mold the cheese maker has is penicillin if he doesn't know which diseases it treats and he just tries to have everyone take it. Yes I'm aware of the risk of encouraging evolution of penicillin immune diseases, but I suspect penicillin won't be used reliable enough for that to be a big risk yet and doesn't really need to be in focus for this story.

Not sure how much my world specific matter, beyond being Europe-like. But our protagonist does not have a medical degree, thus he doesn't know lots of things such as what penicillin should look like. He is however smart with a fairly wide breadth of knowledge and a love and in depth understanding of evolution, though he is afraid to teach that for fear of angering the powerful church that is already slightly weary of him. This evolution knowledge leads to a decent understanding of germ theory and how diseases spread, but from the perspective of how they are evolving not from how modern doctors combat them. He knows lots of generalities about how doctors in the past addressed things, but not enough of the specifics to be certain he can recreate the steps they used.

  • $\begingroup$ Wall of text to ask a story question. $\endgroup$
    – BillOnne
    Commented Dec 15, 2022 at 20:39
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    $\begingroup$ This question asks us to answer whether or not a plot twist is believable, and that's expressly outside of the domain of this forum. $\endgroup$ Commented Dec 15, 2022 at 20:50
  • $\begingroup$ Let him go to a glass maker, get a clear piece of glass. Melt it in a manner that a small spherical drop can fall down and survive (this will be tricky and will require some help due to the temperatures involved). Fix said drop in a wooden board with a small hole. And you got yourself a microscope. Penicillin is hard, especially the processing you need later on. This is a far more reliable way to give medicine a boost. $\endgroup$ Commented Dec 15, 2022 at 21:27
  • $\begingroup$ Norfolk four crop rotation, windmills, watermills, steam engines, biogas reactors, Bessemer Process for steel production, electricity, the radio, the production of sulfuric acid, gunpowder, canning food (heat based food preservation), wood and coal pyrolysis, fractional distillation (make oil useful) and the printing press are my off the top of my head list for bigger and lower hanging fruits. $\endgroup$ Commented Dec 15, 2022 at 21:33
  • $\begingroup$ You have 4 questions marks which lead to at least two different questions. As told above me, the title question is story-based : It's too chaotic and reliant on individuals and situation to answer reasonably, even with probabilities. The last ones can be worldbuilding if asked well (there is a chance of being pure medecine). Note : I believe it's good to check whether the world's specifics matter. Indeed, if the world isn't important, is it still worldbuilding ^^? $\endgroup$ Commented Dec 16, 2022 at 10:37

2 Answers 2


If he can get medics to wash their hands before touching patients, he will save a thousand times more lives than by introducing penicllin.

If he can convince medics that rubbing wounds with ethyl alcohol (which they can already make) will increase the odds of avoiding infection, he will save a hundred times more lives than by introducing penicillin.

You are forgetting that penicillin was only revolutionary in a world which already had effective medicine. By the time penicillin was introduced, doctors had stopped killing their patients with their disgustingly dirty hands, surgeons had stopped killing their patients with their infected knives, obstetricians had gained the use of the forceps, vaccination was already a thing, X-rays allowed a glimpse into the insides of a living body, and so on.

Penicillin without a knowledge and practice of asepsis and without a routine use of disinfectants such as alcohol is basically worthless.

And no, you cannot eat the mould. Normally penicillin is destroyed by the digestive tract; only special formulations can be taken by mouth.

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    $\begingroup$ Echoing this. Hygiene before antibiotics. Soap, boiled water, ethyl alcohol, covering one's noses/mouths while sick, and keeping latrines and their effluents away from water supplies will bring much better gains in public health than trying to figure out which particular bread mold can somehow be processed into a miracle cure. $\endgroup$
    – Salda007
    Commented Dec 16, 2022 at 10:05
  • $\begingroup$ And while they're at it, your protagonist might want to advise against the use of lead and arsenic in things like plumbing, cookware, and cosmetics. $\endgroup$
    – Salda007
    Commented Dec 16, 2022 at 10:07

I suspect they would have a hard time: medicine at that time was mostly based on studying from auctoritas and sophism-like reasoning, like "only nobles can digest game meat because it's a noble meat, too, while peasants should stick to more humble foods" or "what matters when touching open wounds is to have the latest fashion gloves".

Evidence or experiment based medicine (or more in general science) was yet to come, and your hero would have a hard time explaining why some molds would work and some other not without building the theoretical framework behind it. If you have ever seen Monty Phyton's Holy Grail's witch trial, that's the kind of reasoning they will be dealing with.

They could try healing some wounded by applying mold, but I doubt that, without knowing which mold is the right one, they would have many chances of beating the method of cauterizing the wounds with a glowing hot iron.


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