||P.5 right column 2nd paragraph: "Carbon dioxide is another quantitatively significant gas that is expelled in flatus. Carbon dioxide can account for between 5 and 50% of the total flatus volume and as shown above is recycled with hydrogen via methanogenesis and, to a lesser extent, acetogenesis [primary source]. In contrast to hydrogen and methane, carbon dioxide can be generated by a number of processes, not just bacterial metabolism. Three potential sources of carbon dioxide include its diffusion from the blood into the colonic lumen, the acidification of bicarbonate in the upper gastrointestinal tract, and bacterial metabolism [ref 30]. Some species of clostridia (e.g., C. sporogenes, C. butyricum, and C. perfringens) produce both carbon dioxide and hydrogen in their metabolic pathways."