March 2003, as you probably don't know, is America's National Colorectal Cancer Awareness Month. It's a challenge. We do not, thank you very much, wish to be aware of ailments of the alimentary canal, disorders of the bum, gut and belly. It's a hangover from that ferociously inhibiting toilet training we had as babies. "Civilisation", they say, "is the distance we put between ourselves and our excrement." If there is one orifice we would happily forget it's the one we can least easily see.

Colon cancer is, apparently, very curable. But, out of embarrassment, more die from it than should. America's Cancer Research and Prevention Foundation has met the challenge head on. It is sending a "Colossal Colon" on a six-month tour of 20 American cities. The object is 40 feet long, two tons heavy, horsehoe-shaped and made of pink, flesh-coloured plastic. It has an odd resemblance to the Hungry Caterpillar, as depicted in everyone's favourite children book.

Intestina Enormia (cost $60,000, or £37,500) was built by Adirondack Scenic, Inc, a company that normally creates film sets. It was the brain-wave of Molly McMaster, a 27-year-old colon cancer survivor. Her disease was initially misdiagnosed as constipation. Her physician was disinclined to probe. And Molly was too embarrassed to press the matter. When it was cut out belatedly, along with two feet of her intestine, McMaster's tumour was the size of a grapefruit. "Since then", the admirable young woman says, "I've committed myself to raising awareness of the disease that could have killed me". Embarrassment be damned.

Last week the Colossal Colon was in Washington (home of the American asshole, some would say) and this week it's in Atlanta. The designers took their cue from the kid's playground. You crawl through it, on a kind of turd's progress, from stomach to anus (horribilis!). En route, in a grisly red half-light, you see polyps, piles, many kinds of hernia, Crohn's corrosion, ulcers, colitis, and the dreaded big casino. It is, the organisers proudly say, "extremely lifelike". No shit.

Belly laughs are the theme. In Chapel Hill, where the tour started, some college students wanted to kidnap a segment and leave behind a "semi colon". 2,500 citizens passed through in its opening week. As they were excreted at the far end they dutifully signed the "Check Your Insides Out Pledge" - a solemn promise to speak to their health care professional as soon as possible about the state of their innards.

There are jolly leaflets and a jolly website, www.checkyourinsidesout.org. The message is simple. No more embarrassed silence. "With the Colossal Colon," proclaims the website, "You can't not talk about it!" The subject, so to speak, is out of the water closet.

The advice accompanying the pervasive jokiness is sensible and will save many lives. Have regular check-ups (the dreaded probing finger, that means). Don't overdo the booze, don't smoke, do eat vegetables and fruit, lose weight and exercise moderately. And if that regime seems too onerous take another crawl through the Colossal Colon, look at those clustering tumours and suppurating ulcers, and think again.

Prevention, many will think, is the only hope they have. By grim irony the Colorectal Cancer Awareness Month coincides with the National Cover the Uninsured Week (March 10-16). One out of three non-elderly Americans (ie those not covered by Medicare) is uninsured. And one of the other two is grossly underinsured.

So what does that mean when you get early diagnosis? If you are not in the fully insured group (or don't, like Washington politicians, have privileged access to Bethesda Naval Hospital) you may have to wait while the walnuts in your gut become grapefruit. Or, like many, you will just have to accept that you must die because you can't afford the world's most advanced medical facilities. Hard to joke about that.