Odd as it may seem, this can involve the injection of another person's stool into the colon of a Crohn's sufferer, (fecal transplants, or "fecal microbiota transplantation").
You'll probably be able to find the article on line: "The Excrement Experiment" by Emily Eakin.
This passage caught my attention:
"Science writers love to cite the freakish fact that for every one of our cells we are hosts to ten microbial ones, and nowhere are there as many as in our digestive tracts, which house about a hundred billion bacteria, fungi, viruses, and other tiny creatures. (As one gastroenterologist put it to me, (the author) with only mild exaggeration, 'We are ten percent human and ninety percent poo'"
Humbling ain't it!