Dear Cecil: With all your scatological insight, what exactly is a fart? Is it, as some surmise, a burp gone wrong? Is it a relative of the hiccup? The sneeze? And is it not healthier to vent oneself than to squelch? Phillip S., Chicago

Cecil replies:

Your question comes at an opportune moment — I’ve just been reading up on the subject in the Harvard Medical School Health Letter. Harvard is a veritable gold mine when it comes to flatulence.

Intestinal gas, we learn, is made up mostly of five gases: nitrogen, oxygen, carbon dioxide, hydrogen, and methane. The first two you get from swallowing air during eating, while the last three are generated in the large intestine. From this we deduce that burps and belches, which emanate from the stomach, consist mostly of air. Hiccups and sneezes, of course, are wholly unrelated.

Hydrogen and carbon dioxide are produced by bacteria nibbling on undigested food in the colon. Beans, for instance, contain complex sugars that can’t be broken down by the body’s digestive juices. Upon arriving in the colon, these sugars are set upon by the resident microbes, and the resultant fermentation produces the cheerful calliope effect celebrated in such masterpieces as Blazing Saddles.

Methane, another digestive byproduct, is responsible for the blue flame that has absorbed the attentions of college freshmen for generations. It’s recommended, incidentally, that persons contemplating experiments in this line wear fireproof undies when doing so. Unca Cecil speaks from experience.

A friend of mine, who has reason to worry, has inquired whether there are any cases on record of persons exploding as a result of smoking in bed after a bean barbecue. To date I haven’t been able to find any. However, internal detonations have resulted from careless use of an electrocautery device inside the bowel. The eating of beans before surgery, therefore, is definitely contraindicated.

The characteristic fragrance of the fart is produced not by any of the aforementioned gases but by “minute amounts of volatile chemicals formed by bacterial metabolism of residual protein and fat,” we read. Persons whose flatulence is especially notable in this regard may be suffering from dietary maladjustment — for example, people with lactase deficiency who drink a lot of milk. Other foods said to produce farts of unusual pungency include broccoli, onions, cauliflower, cabbage, radishes, and raw apples. Not to give anyone ideas, but those seem like the perfect salad ingredients for an eventful sorority lunch.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.