THEY SEEM TO WORK: Once a weird, fringe treatment, fecal transplants have started becoming mainstream.

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.

Other uses are not so well-established yet.