the ability of the membrane surface to repel liquid is such that a film of liquid preventing gas from passing through the membrane is not formed on the surface thereof the pore volume of the membrane material of 70 80 and the structure see fig1 16 with very narrow passages only allowing particles smaller than 0 45 micrometers to pass therethrough entails that the flatus gas easily may pass through while human intestinal or fecal bacteria in the flatus gas or feces are retained by the membrane 11 furthermore liquids are prevented from flowing through the membrane laboratory measurements where the membrane was loaded with 700 mm water column showed that no water flowed through and no droplets were formed on the surface even after a test duration of 8 days an artificial stool test applicants 39 test method consisting in filling bags 1 with artificial stool and inverting the bags so that the filter assembly was covered by artificial stool during 24 hours while observing whether artificial stool passed through the membrane gave excellent results the artificial stool is composed of beans salts intestinal enzymes and other substances equivalent to the contents of the human intestine such that the test simulates the influences on the membrane in practice the barrier membrane 11 has a back pressure of approx 2 3 mbar with an air flow therethrough of 100 ml min at a pressure of 0 1 bar referring now to fig3 the.