Dr. Thomas Borody, an Australian gastroenterologist, treats ulcers and diarrhea, but has expanded his expertise to other diseases. One may ask why a doctor would treat an autoimmune disease like multiple sclerosis when they are educated in stomach ailments.
The answer comes from poop. Borody considers fecal matter to be the largest organ in the body because it contains nine times more bacterial cells than the human body contains human cells.
Dr. Borody performs fecal transplants, a procedure that includes transplanting a healthy person’s stool into a sick person’s bowels. The healthy bacteria acts as an antibiotic to fight off other bacteria. While this procedure may seem unconventional, many had similar reservations on past experiments that have made incredible contributions to modern science.  Dr. Borody has been performing successful fecal transplants for several decades by taking the healthy stool, mixing it with a saline solution, and implanting the mixture into another person’s bowels. This process is similar to a colonoscopy.
An immunologist and gastroenterologist named Alex Khoruts has also been performing research regarding fecal matter. He has linked fecal transplants to treating obesity and Parkinson’s disease. In both cases, the damaged microbial organ benefits from the healthy bacteria in the transplanted stool. 
 – Medical Discoveries: Edward Jenner
 – Freakinomics: The Power of Poophttp://www.freakonomics.com/2011/03/07/another-batch-of-poop-loving-doctors/