Health: Having a gas in the lab

IT IS amazing what medical researchers will do in the name of science. Many have injected themselves with experimental vaccines and swallowed new drugs. But few can match the commitment of researchers at the Veterans' Affairs Medical Center in Minneapolis, who... how can I put this delicately?... exposed themselves to other people's flatulence. That's sniffing farts to you and me, and rating them on a scale from nought (no odour) to eight (very offensive). The arrangements for collecting the farts involved subjects being fed on a diet of beans and a quantity of rubber tubing and tape. But I will spare you the details.

The two judges, who between them tested the gaseous production of 16 healthy volunteers, were selected for their ability to distinguish different odours, especially those associated with sulphate-containing compounds. Samples from each volunteer were collected in syringes which the judges held 3cm from their noses as the gas was ejected.

To what purpose?, you ask. The answer is given in the medical journal Gut: to test a commercial device for reducing the offensive odour associated with passing wind. The device is known, quaintly, as the Toot Trapper.

Manufactured in Houston, Texas, the Toot Trapper is a rectangular pad lined with charcoal, worn like a nappy and described as "unwieldy" by the researchers. However, it does work, cutting the sulphurous content of the gases 11-fold. But second- generation Toot Trappers could be developed which might be less cumbersome yet just as effective, the researchers suggest.

The US team observes in their paper that farting has been a subject of scientific and scatological interest since the beginning of recorded history. While the social significance of wind derives mainly from its smell, most of the scientific research has focused on its quantity, which ranges from a light breeze of 200ml a day (a small cupful) to a hurricane force 2.5l.

The anecdotal belief that men produce more objectionable flatus - the technical term for wind - than women was not supported by the US study. It showed that women were the worst offenders in terms of odour, although men made up for it in sheer volume. The researchers note, however, that the ability of malodorous gas to stimulate the nose is related to the volume expelled, rather than the concentration of its noxious components. Because men tend to pass greater volumes on each occasion there were "no significant gender differences".

The key cause of odour was found to be hydrogen sulphide, a by-product of the gut's sulphate-reducing bacteria. Sulphate is found in broccoli, cabbage, nuts, bread and beer, and sulphurous amino acids are present in protein. The gases could be reduced by manipulating the "colonic flora" or by binding the sulphate so that it cannot be broken down. For now, though, the answer seems to be that wine-drinking fruitarians make the sweetest-scented partners.