A common problem is the presence of large amount of gas in the stomach or intestines. Most of this gas is nitrogen and oxygen from the air which has been swallowed when food is eaten.

The body can not absorb all of the nitrogen and it travels along the digestive tract into the intestine. Other gases such as carbon dioxide, methane and hydrogen are also formed from the break down of food. Carbon dioxide is produced by fermentation and can usually be absorbed, while the other gases are produced by the digestion of foods rich in starch or cellulose, such as beans or cabbage.

The gases are expelled from the rectum as flatus, which often has a disagreeable odour, due to several sulfur compounds. When the gas remains in the stomach it can cause pain as the intestine swells.

Bibliography

Encyclopaedia Britannica, 15th Edition. (Chicago: University of Chicago, 1986)

Encyclopaedia Britannica, Volume 7. (Chicago: Encyclopaedia Britannica, 1970)

The Book of Popular Science Encyclopaedia. (New York: Grolier, 1961)

The Software Toolworks Multimedia Encyclopaedia, Release 6. (New York: Grolier, 1996)

Encarta 96 Encyclopaedia. (Redmond: Microsoft, 1996)