He 'tch's. "I don't carry medicine, I said. I carry food, and craft supplies. -Though if you meant proof of the magic you can get a lighter, that's useful." He points at a thumb sized red rectangle capped with metal in neat rows by the register. "Two of the little copper ones and I'll show you how to use it."

"That's what I meant, yeah." He'll get a lighter and a lesson.

This thing makes fire! Fire you can control with your mind, even, and which doesn't actually burn people - though things you light up with it will totally burn you. He demonstrates on a piece of receipt to show that it's real fire. It'll last about twenty minutes of continuous use and then be out forever.

Twenty minutes, wow, okay then.

"I'll go show this to a doctor or something and then maybe they'll come by."

"I'll welcome any customers, just keep in mind I might not be here tomorrow. Don't want anything else while you're here?"

"I don't want to insult you but in stories magic places like this show up and you buy their fruits and get away and the place is gone and the fruits are colorful stones and the only thing real is the price you paid. I'm going to go test the lighter. I'll tell everyone to hurry but that'll do the opposite of help, really."

Shrug. "It's your war." He picks up a book from somewhere behind the counter and sits back in his chair.

Somewhat less than twenty minutes later, someone arrives and starts examining everything in the shop.

"Welcome to the wandering store! I'm here if you've got any questions." He turns a page.

"Yes, I have. I heard I should talk to you about medicine."

"Where I'm from people know a lot of things about medicine. It gets incredibly specialized. Unfortunately, I'm not a doctor, but I can just go on about things that are common knowledge to me. With any luck they'll be testable and useful. What, pray tell, causes infectious diseases - the ones that spread as plagues, rather than just afflicting one unfortunate soul?"

"Filth and vermin."

"From what I know, filth and vermin both carry germs- Much much tinier vermin, smaller even than the hair on your head. These live and breed and die just the same as larger animals, and a person makes quite a rich ground for them. Our bodies fight back, of course. In fact, it's our body fighting back that causes fevers - to cook them. That's why boiling rags and water helps purify them of disease. Two main kinds - bacteria, like tiny vermin, living all on their own. These are the ones responsible for infected wounds, for the most part. There's a class of substances called antibiotics that are particularly potent at killing bacteria, including one caused by a specific kind of mold - from melons, I think. By giving patients these, they can be saved from infection much more often. Unfortunately I don't have a good way to help you find them.

"The other main kind is a 'virus'. A sort of parasite that is not even alive until it seizes tiny pieces of our own body and uses them to make copies of itself. These are harder to fight with medicines and you mostly have to keep the patient healthy. Someone can be capable of spreading germs once they're sick, since they're growing inside the person. Even if they don't appear sick yet, they may already be spreading. The usual pathways for this are in waste or spit or breath. Cloth masks to block germ-laden breath and keeping your distance from sick people helps. Washing your hands often helps, but you probably know that already if you know filth is bad. I've got a tiny-things-viewer in the back room, could show you some bacteria if you'd like and you don't. Touch. Anything I don't tell you to."

"I think I can avoid touching things, and I think I'd like to see that."

"It's not often I let people into my workshop, but this seems important, you know. C'mon, it's this door over here. Do you have a bit of mud or pond water or something to look at?"

The workshop has two rows of clean stone tables, glass and metal cabinets all around, strange devices on the walls and in corners, and all sorts of gadgetry neatly organized here and there. He puts away some glassware and a slightly glowing rock.

"Well, not on me, but it's likely I have as small an amount of something as you're talking about stuck to my shoes."

He doesn't touch anything. In fact he has his hands behind his back.

"Most anything has some bacteria on it, honestly. Most of them are harmless, only a few kinds can thrive in humans enough to hurt us."

He swabs his own cheek and prepares a slide, sets it into focus, and- Yep. There. Slides the slide slightly to show a wriggling bacterium.

"Here, you can look through this. The knob here to adjust the focus, wiggle it back and forth until it's clear."

He looks. He's slow to figure out how to work the knob; he has almost no experience with similar machines.

"...This is a very interesting device."

"Light is kind of hard to explain, but very carefully made glass and mirrors can bend it and make tiny portions of your vision bigger. Do you see the bacteria?"

"I see something."

"I don't think this demonstration is directly useful for - something you can do to help people, it's more to satisfy you that tiny living things are real. I could turn down the zoom and magnify something else if you like so you know it's not just showing whatever I want it to."

"I don't think that'd be that much harder to fake but sure."

They ought to know how cloth works, right? This should be fairly believable. He fetches a swatch of cotton from somewhere and turns the microscope down to 5x, then 10x, then 25x, then 50x, all the way down to 500x, progressively showing more and more details on the fibers until a single thin strand covers the whole viewport and looks totally alien.

"I'm not sure what to tell you besides the truth behind germs, honestly. Most things I could try to explain sound crazy and could hurt people if I'm remembering important details wrong, or aren't very useful on their own. But if there is something useful it'd be worth talking, yes?"

"Yes, I suppose so, assuming all this is real. I can also make use of books if you have any."

"It's real. You can believe that or not at your leisure. Oh, there's an idea. I don't have books on medicine, I'd be a lot more confident if I did. I have a lot of guides in the crafts section, not for medicine but for things like weaving and metalworking. I'm trying to remember the worst diseases you might face here..."