The appendix is a close-ended tube that branches off the junction between the small and large intestine and is somewhere near your groin and near the right hip bone. It is about 9cm/ 4in long.

The appendix remains something of a mystery. It used to be thought it was useless, a hang-over from evolution. But now it is thought that it might be a kind of reservoir for useful bacteria and help in the recovery from illness. For example, when ‘good’ bacteria are flushed out of the gut by diarrhoea, dysentery or cholera, the good bacteria can get back into the gut quickly.

The most common diseases of the appendix are appendicitis. Appendicitis (diagram right) occurs when the appendix becomes inflamed. It cannot easily be treated by medicines and usually has to be removed.