It has long been regarded as a potentially troublesome, redundant organ, but American researchers say they have discovered the true function of the appendix.

The researchers say it acts as a safe house for good bacteria, which can be used to effectively reboot the gut following a bout of dysentery or cholera.

The conventional wisdom is that the small pouch protruding from the first part of the large intestine is redundant and many people have their appendix removed and appear none the worse for it.

Scientists from the Duke University Medical Centre in North Carolina say following a severe bout of cholera or dysentery, which can purge the gut of bacteria essential for digestion, the reserve good bacteria emerge from the appendix to take up the role.

But Professor Bill Parker says the finding does not mean we should cling onto our appendices at all costs.

"It's very important for people to understand that if their appendix gets inflamed, just because it has a function it does not mean they should try to keep it in," he said.

"So it's sort of a fun thing that we've found, but we don't want it to cause any harm, we don't want people to say, "oh, my appendix has a function", so I'm not going to go to the doctor, I'm going to try to hang onto it."

Attractive theory

Nicholas Vardaxis, an associate professor in the Department of Medical Sciences at RMIT University, says the theory put forward by the Duke University scientists makes sense.

"As an idea it's an attractive one, that perhaps it would be a nice place for these little bacteria to localise in, a little cul-de-sac away from everything else," he said.

"The thing is that if we observe what's been happening through evolution, the higher on the evolutionary scale we are and the more omnivorous animals become, then the smaller and less important the appendix becomes and humans are a good example of that.

"The actual normal flora bacteria within the appendix, as well within our gut, are the same, so we've lost all of those specialised bacteria.

"So it doesn't have that safe house type of function anymore, I don't think.

"It's a vestige of something that was there in previous incarnations, if you like."

Koala appendix

Unlike the human, the koala is famous for having a very long appendix.

It is thought to aid digestion on a diet made up exclusively of eucalyptus leaves.

Professor Vardaxis says that is not likely to change any time soon.

"Unless of course we have a massive blight and we get the eucalypt on which the koala thrives dying, then we may find some mutant koalas out there perhaps that will start eating other things, and as they start to eat other things, then over generations and hundreds of thousands of years of time, then surely, yes, the koala's appendix will shrink as well," he said.

Professor Vardaxis says it is possible that at that point, koalas might be afflicted by appendicitis and have to have it taken out at times.