When the master's voice wears thin ...

Who first said: "Doctor, I've got Bright's disease, and he's got mine"?

Answer: SJ Perelman.

Who, when asked to define the difference between Mel Brooks and Woody Allen, said: "That's easy. Woody Allen is funny"?

Answer: SJ Perelman.

Who started this description of a train journey to Hollywood from New York?

"The whistle shrilled and in a moment I was chugging out of Grand Central's dreaming spires followed by the anguished cries of relatives who would now have to go to work. I had chugged only a few feet when I realised that I had left without the train, so I had to run back and wait for it to start...."

Answer: SJ Perelman, and when I first read that, I thought it was the funniest kind of writing in the world.

However, it is almost always a mistake to go back to the cherished writers of yesteryear, to the books you were in love with in the formative years, for fear they have meanwhile changed into a pile of old leaves or a handful of dust.

Some writers, I think, are foolproof. I could never get tired of Lewis Carroll or Richmal Crompton, or the Sherlock Holmes stories. But other writers who you thought were equally resistant to the dry rot of time can turn out to be riddled with woodworm and death watch beetle.

It's been happening to me this week with SJ Perelman, whose book The Swiss Family Perelman has been read this week on Radio 4, and as I have listened I have felt my heart sink and my laughter muscles go rusty from lack of use.

Which is extraordinary, because in my late teens and early twenties he was the writer I thought the funniest in the world and the one I most wanted to be like. People sometimes say, "Oh, Perelman - didn't he write the script for the Marx Brothers?" Well, no, he didn't. He tried one film for them, and the general agreement was that his dialogue was unsayable. It read well on the page but got no laughs when anyone said it.

I didn't know this when I first met his writing - I only knew his Penguin collection of New Yorker pieces, Crazy Like a Fox, and I knew that on the page his stuff was the cleverest and wittiest stuff in the world. After which I spent a year or two trying to imitate Perelman and another 20 or 30 trying to get out of the habit.

Because if you go down the Perelman path you end up like the Perelman of Swiss Family Perelman, a grumpy old American tourist going round the world, grumbling about bureaucracy and swindling natives and deriving humour only from long or recondite words.

It's a disease that sometimes overwhelms humorists late in life, this belief that obscure or exotic words are funny. On his trip round the world Perelman uses words like "myriad" and "suasion" and "fundament" and "burgeon" all the time. "Several bottles of Polish vodka burgeoned on the table", he writes, or "He scratched his fundament to get his circulatory system going".

No he didn't. He scratched his bottom. It isn't funny to say "fundament" instead. It isn't funny to say that bottles of vodka "burgeoned" on the table instead of "appeared" - it's just long-winded.

This, admittedly, was late-period Perelman, when he was old and tired, and needed the money, so he was just going through the motions and flagellating his prose style with big words when you expect small ones, and slang ones when you expect ordinary ones.

But I have dug out some of his early stuff again as well, and I am horrified to find that all the signs are there already, that the early Perelman was also stuffed with words such as "fraught", and "pinguid" and "sudorific" and oleaginous" - words that pad out the prose like twisted up bits of paper at the bottom of a box of chocolates....

So is it always fatal to go back, then? Is Radio 4's message to us never to look back? Well, no, because another new programme on Radio 4 proves that sometimes you must look back.

Gerry's Bar is a series of mullings and monologues on life in Ireland by Gerry Anderson which are as rich, funny and observant as anything by Garrison Keillor or Bill Bryson or other best-sellers. The man who was so cruelly betrayed by being persuaded to do Anderson Country has gone back to the wonderful form he showed previously on a Radio 4 series of musings on Londonderry called Stroke City, and shows that when he is out there on his own, he is - well, out there on his own.