Fernando Trabanco Fotografía / Getty

In 1957, a young microbiologist named Stanley Falkow started asking sick people to swallow their own poop.

Falkow was working as a technician in a hospital lab at a time when patients were besieged by a rogue strain of the gut bacterium Staphylococcus. To prevent the bug from infecting people during surgery, all patients were told to take preemptive antibiotics before their operations. Unfortunately, these drugs also decimated the beneficial bacteria in their guts, leaving them with diarrhea and indigestion. Their stools “were even odorless,” Falkow later wrote. “Few stools can make that claim.”

One of Falkow’s colleagues came up with a solution: Get the patient to bring in a stool sample, and give that back to them after their operations to replenish their microbes. Falkow’s job was to pipe the poop into capsules that the patients could then swallow. “The chief hospital administrator discovered what was up,” Falkow later wrote on the Small Things Considered blog. “He confronted me and exclaimed: Falkow, is it true you’ve been feeding the patients s**t?” He fessed up, and was fired. Two days later, he was rehired.

Falkow’s idea wasn’t new. Fecal transplants—where doctors try to cure sick people of various ills by giving them the stools of healthy donors—have been used since at least fourth-century China, according to texts that make reference to “yellow soup.” The unusual treatment has been rediscovered many times since, but it’s finally starting to enter the medical mainstream. Partly, that’s because of a surge of interest in the microbiome—the trillions of microbes that share our bodies. Partly, it’s because many well-conducted studies have shown that fecal transplants are incredibly effective at treating Clostridium difficile—a nasty, hardy bacterium that causes severe, recurring, and potentially fatal bouts of diarrhea.

But poop is no panacea either. Scientists have treating all kinds of disorders with fecal transplants with mixed results, while a burgeoning community of DIY enthusiasts have tried the treatment without due awareness of its many risks. In the video below—the eighth in a series of online films produced by HHMI Tangled Bank Studios, which adapt the stories in my book, I Contain Multitudes—I talk about the history, science, and future of this most unorthodox of therapies.