The appendix is a small pouch located at the start of the large intestine. It contains a lining rich in immune tissue and a stable supply of beneficial bacteria. The structure of the appendix creates a protected environment where these microbes can live undisturbed. The narrow opening limits the flow of intestinal contents, allowing the bacterial colonies inside to remain sheltered. During illness or diarrhea, large numbers of gut bacteria may be flushed out of the digestive tract. The appendix