Howard Jacobson: A test too far even for a Rabelaisian

I go one of two ways when I'm asked about my literary antecedents, depending on my mood.

There's the Dr Johnson/Jane Austen route I favour when I'm feeling moralistic and melancholic; and there's the road back to Rabelais which I take when I want to throw off the prim respectability of my upbringing and outrage decency. Inside every nicely brought-up boy there's an anathema waiting to get out. Rabelais is the liberation. With him on your shoulder, no subject is out of bounds, no language too filthy, no bodily function beyond description. We piss, we shit, we ejaculate, and that's just for starters. Somewhere deep down – especially in mimsy times – I believe Rabelais is the only way to go. And that's how I've been feeling of late: Rabelaisian, and up yours (and Jane Austen's) if you don't like it.

And then a little packet arrives from the NHS containing a home test kit from the Bowel Cancer Screening Project, a simple test, it says, which can be carried out at home, and whose purpose is to check for traces of blood in bowel motions. The reason they are inviting me to take part in this programme – it could be a request to appear on Woman's Hour, the way they put it – is my age. They make it sound like a privilege to be asked. Lucky me. No one is sure exactly what year Rabelais was born but it seems unlikely he made it to the danger age himself, so he missed out on a home test kit from the NHS.

Next to Molly Bloom's great yes I will Yes speech, the scene most thumbed over by the boys in my school was Gargantua describing how he wiped his behind (all right, his arse) with a pillow, with a slipper, with a basket, with a hat (the best hat being "of a hairy kind, for it gives a very good abstersion of the faecal matter"), and then on – because the whole point of Rabelais is that he goes on and on and on – to a hen, a pigeon, a cormorant, a riding hood, a coif, and – the best touch of all – "a lawyer's pouch". Today I don't doubt he would have added, as even more abstersive of faecal matter, "a banker's bonus".

I won't pretend I ever cared for this scene myself, being squeamish in all matters lavatorial, but I affected a bold and unaffronted hilarity which I maintain today, except among those who know me, else there is no point in my calling myself Rabelaisian.

And then the home test kit from the Bowel Cancer Screening Programme turns up in the post. How am I to tell you – unless you have taken the test yourself – what it entails? Well, essentially it asks you to paint your bowel motions. Not impressionistically, but precisely, using as brushes little cardboard sticks which the NHS thoughtfully provides – the medium in which you paint the bowel motion being neither oil nor watercolour, but the bowel motion itself. In brief, you go fishing as in a cesspit, the refuse being your own, in order to come up with a couple of samples ("taken from a different area of the bowel motion") which you then paint on what I can only call a small cardboard easel. If you think Guernica must have been hard, try dipping a cardboard stick into your waste matter and then sketching your insides.

You don't, of course, have to paint a picture. They want a sample, that's all. A veneer. "Spread it thinly," they advise. Thinly! How thin is thin, for Christ's sake? This is no mere aesthetic decision of the sort that troubled Rubens. Paint it too thinly and the laboratory staff who are sitting on their hands waiting to receive your little faecal gift might miss the cancer lurking in your bowels; paint it too thickly and you'll give the poor bastards cholera.

But I am already getting ahead of myself in my hurry to be gone from the subject altogether. Before you can start painting you have to deliver, as it were, the paint. (By this time Rabelais would have been in his element with turd talk, but I cannot call a t**d a t**d. It was not how I was brought up.) And there are strict instructions relating to how the paint – all right, the bowel motions; all right, the excrement; all right, all right, the t**d – must be deposited. To avoid contact with the toilet bowl (which presumably would affect the integrity of the sample), and in order to facilitate inspection, the NHS suggests that you construct a platform of toilet paper. There are people for whom this would mean a sheet or two; there are others for whom it means an entire roll. I can't speak for Rabelais but I am of the latter party. But not even an entire roll is proof against the plash of urine which customarily precedes a bowel movement. So either you remember to urinate in some other place, or you discover your entire edifice of protective layering has been rendered ineffective by the inundation and you must start again, this time building even higher.

There, then, you sit, atop a mountain of the finest tissue, wondering where the morning has gone, dreading the many more hours with your head in the toilet bowl which still await you – a dread which can lead to a bout of retching in even the most insensitive of men, but in my case brings on near convulsions of existential disgust. Retching? Much more of this, you think, and it won't just be your stomach that comes out through your mouth, it will be your soul. It even occurs to me to give them a sample of my vomit, spread evenly on their little cardboard easel. It wouldn't tell them much about my bowels, but it would give them insight into how I feel. Cancer of the feelings – is there such an ailment? If there is, then the Bowel Cancer Screening Programme is definitely the quickest way to contract it.

As for the bowels themselves – they have to be in wonderful working order to work now. And no one of the age selected for the test has bowels that good. That's the point. Thus, after half a day of trying, does the sample remain elusive, and the painting remain unpainted.

Tomorrow I must give it another go. It's hard to get through what's left of today thinking of anything else, but the test might save my life and I want to live. I am Rabelaisian man – frank, free and fearless – hear me roar!