Recent work shows the appendix is a safe place for useful bacteria when illness flushes those bacteria from the rest of the intestines. This proposal is based on a new understanding of how the immune system supports the growth of beneficial gut flora, in combination with many well-known features of the appendix, including its architecture, its location just below the normal one-way flow of food and germs in the large intestine, and its association with copious amounts of immune tissue. Research performed at Winthrop University-Hospital showed that individuals without an appendix were four times more likely to have a recurrence of "Clostridium difficile" colitis. The appendix, therefore, may act as a "safe house" for commensal ("good") bacteria. This reservoir of gut flora could then serve to repopulate the digestive system following a bout of dysentery or cholera.