In the nineteenth century, many people believed humanity had actually conquered the world through science. Technological advances were on a roll, and factories were popping up everywhere. It seemed like the golden age for inventions and new patents of every type. Some people got rich.
As a result of the seeming invincibility of science, medicine shows were everywhere. In each small town, a well-dressed man with a wagon full of cure-alls would show up.
He had the gift of tongue: he entertained, sometimes performed some magic trick, he spoke in a familial way, he could enthrall with stories, he could persuade. Sometimes the con could go even further - he'd have an assistant, someone whose job it was to show off the dubious pills, salves, snake oils, balms, tonics, syrups, potions.
There's an example in Pete's Dragon's 1977 movie where Dr. Terminus shows up in his wagon in the small New England town of Passamaquoddy. With the "doctor" commanding all the attention from the crowd, his assistant Hoagy disguises himself effortlessly as one of the townsfolk, pretending to be afflicted. In one scene, he's dressed up as an old man who can't walk. Dr. Terminus calls him forth from the audience, administers a mysterious concoction, and the patient can not only walk again, but march, and dance, almost immediately.
In 2017, it's incredulous to watch as the town crowd eats this up and lines up to buy the medicine.
This is was the power of the medicine show. It had the power to convince virtually a whole town to purchase faux medicine. People believed the quack doctors and got themselves ill, injured, hurt, or worse, killed, ingesting many of these dangerous, unproven fake medicine.
Even real medicine in the nineteenth century could be extremely perilous, as the pills prescribed for teething babies contained cocaine. Yes, you read that right. Low dosages of opium were also prescribed for children to calm them down.
These were real medicines in the nineteenth century from reputable doctors and drugstores. Imagine what the cash-hungry con artists of medicine shows with no regard for safety or testing presented to the people back then.