Most people prefer to send their used toilet paper straight down the drain.
But one Kiwi artist's decision to store his 46-year-old dunny rags complete with faecal matter has led to an intriguing insight into changing gut bacteria over time.
Billy Apple, 81, collected the samples in 1970, carefully noting their time and date, as part of his work for an art exhibition in a New York gallery titled 'Excretory Wipings'.
Now scientists have jumped on the chance to compare the old samples with fresh samples taken from Apple in a bid to track his gut health over a 46-year period - something not possible in any subject before.
The study by University of Auckland molecular biologist Dr Justin O'Sullivan was published in the Human Microbiome Journal and found a "core" part of a person's gut bacteria population remains stable as we age.
It also found some of the bacteria are actively selected by our genes, meaning advances in personalised medicine may have to consider not only our individual genes but the individual microbe colonies living inside us.
"We used to think of our resident bacteria as hitch-hikers, foreign bodies along for the ride," Dr O'Sullivan said.
"Scientists now realise that these microscopic creatures interact in many intricate, mysterious ways with our body systems, and play a crucial role in our health, wellbeing and development."
He said while scientists knew people's bacteria populations changed over time as some microbes join and others leave, the study's key finding was that some stayed for a lifetime.
In Apple's case, his gut microbe population was less diverse at the age of 80 compared to when he was 35.
However, 45 percent of the bacteria species were retained in the intervening 46 years, despite changes in his age, living location and diet.
Each person typically carries around a population of about 30-40 trillion microbes - or 1.5kg of bacteria.
Apple called the collaboration wonderful, but is no stranger in using his artworks to help science.
He has previously collaborated with biochemist Dr Craig Hilton, which led to New Zealand Genomics Ltd sequencing his entire genome.
He has also produced an artwork that depicts his coronary arteries before and after having stents put in.