Fecal transplants have the power to revolutionize medicine, but hospitals need raw materials. At Open Biome, the country’s first independent stool bank right outside Boston, donors earn $40 for each sample.

The clinic, however, approves less than 3 percent of applicants.

Fecal transplants have already essentially cured a severe intestinal infection known as C. diff that kills 29,000 Americans each year. The gut disease, which often exhibits resistance to antibiotics, causes frequent and powerful diarrhea and can even require removing the intestine. But transferring a donor’s healthy stool into the bowels of an unhealthy patient acts like a nuclear-level probiotic to help the body’s healthy microbes replace the infection.

While fecal transplants have a 90 percent success rate treating C. diff, the procedure could also be useful against slew of other diseases linked to the human microbiome, the trillions of bacteria, fungi, and viruses living inside our bodies.

“We now know that the microbiome is linked to everything from irritable bowel syndrome to rheumatoid arthritis to cardiovascular disease and colon cancer — and then if the work in mice turns out to translate to humans, even things like depression, autism, Parkinson’s,” Rob Knight, a scientist at the University of California, San Diego and the co-founder of both the American Gut Project and the Earth Microbiome Project, said in VICE on HBO’s report on fecal medicine.

For the feces needed to treat C. diff and support numerous clinical trials underway, 960 hospitals have turned to Open Biome. To date, the clinic has received more than 10,000 stool donations and processed over two tons of feces.