Dear Matt Alice: Where do farts come from? Why am I so damn flatulent, especially post coitus? — Senor Nerve Gas, San Diego

My sympathies to your girlfriend, amigo. But not to worry. Medical science takes the fart seriously enough to have compiled about 50 years of data on the topic. One of the earliest studies, which involved “colon tubes," balloons, and some exceedingly cooperative medical students, established a baseline for gas-passing under normal circumstances (from 400 to 1000 cubic centimeters per day, per person, roughly the volume of one to three beer cans). Intestinal gas is most likely to be the result of air swallowed while eating, drinking, or smoking or during times of stress or exertion. Remain in an upright position, and the air, which wants to rise, escapes as a burp. Lie down, though, and the air will bubble through your gut and exit the other end. As little as 30 minutes from swallow to fart, if the studies are correct.

Added to swallowed oxygen is carbon dioxide formed in the upper portion of the small intestine by the interaction of stomach acid and pancreatic secretions. But the relatively odorless C02 and oxygen probably didn’t inspire your nickname or your question. The other major source of flatulence is bacteria in the colon fermenting any previously undigested sugars and starches. Methane (the burnable component of flatulence) and hydrogen sulphide (the rotten-egg smell) are two principal byproducts of the bacterial action. The longer the bacteria work on the sugar and carbs, the more gas they produce, so constipation is very fartogenic. Exercise gets those bowels moving again but also expels any gas trapped in the intestines. I’m sure that somewhere in this child’s guide to flatulence, you’ll find your answers.

In the interest of your personal safety, cancel any high-altitude vacations you might have planned. When no compensation is made for the reduced air pressure, by the time you’ve reached 15,000 feet the volume of your intestinal gas has doubled. A sojourn in the Swiss Alps might end with you blowing yourself out of bed and into a ravine. I wouldn’t want that on my conscience. You’ve been warned.