Gas in our stomachs come from many sources, not just bacteria. But yes, there are bacteria which live in the human gut -- these are usually referred to technically as "fecal flora" or "intestinal flora", because doctors get grossed out too and sometimes technical words make it easier. <img src="/images/icons/tongue.gif" /> There's an entire ecology in your digestive tract. Kinda weird, huh?<br /><br />If we go to Mars, we will definintely bring bacteria along with us. We really don't have much choice in the matter. Techniques which would kill all the bacteria would also kill us. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em> -- The Tenth Doctor, "Blink"</font></p> </div>