By Alex Kirby BBC News Online environment correspondent

Day five of Alex Kirby's diary from the World Summit on Sustainable Development in Johannesburg.

Most international conferences develop their own momentum after a few days.

This, distinctive to the last, has settled into its own inertia.

We are in Johannesburg's dog days now, and no mistake.

I saw at least three journalists not just dozing but sleeping deeply across their desks today.

I myself have reached the stage where words fail to register.

I have had at least two long conversations with intelligent people who talked good sense that went straight over my head.

Protesters in Alexandria made anti-privatisation speeches

They might as well have been talking Martian. Perhaps they were.

I can still make a stab at the individual words, but when they are marshalled into groups of four or five - sentences, I think I used to call them - they land with a soft deliquescent thud in my brain and seep away, indigestible and instantly forgotten.

Nor are words the only problem.

Numbers assail me from every side, the serial digits of friendly callers on mobile phones who will probably never hear from me again, because innumeracy and technophobia beget a Trappist correspondent.

News conferences

It is a shame, really.

It is lucky that there are still news conferences where I can deploy the time-honoured skills of my craft, filling the back of an envelope courtesy of the owner of a bitten, borrowed ballpoint pen.

I then jot down a few bullet points I would not be able to read if I could find them.

There are an awful lot of news conferences.

On a quiet day in London, probably almost every one would yield a decent story.

But here we are spoilt for choice.

They are all so good I end up feeling sated before I have been to the first of them.

They remind me of W S Gilbert's dictum: "When everybody's somebody, then no-one's anybody."

The Prescott style with English is imaginative, idiosyncratic, and the stuff of a parliamentary sketch writer's dreams

Give us room to breathe, please.

Anyway, I decided to slip the leash for a guilty hour or two and headed off from the marble halls of the conference centre on a brief trip to Africa - to Alexandra township.

It is about ten minutes' drive from the summit venue, by one measure, and light years by most others.

It is home to a population equal to Edinburgh's.

Goats walk in blithe unconcern down the main road.

Barefoot urchins come up to press your hand, then break into face-splitting grins.

Protests

Their elders gravely plan their protests against what they see as the frivolous, wanton irrelevance of the summit - or perhaps its malign encouragement of foreign nostrums that make the poor poorer.

And suddenly words mean something again.

I could not help noticing, though, that when the UK's Deputy Prime Minister, John Prescott, arrived in Jozi, he said he was here to be Tony Blair's "eyes and ears".

No mention there, perhaps luckily for Mr Prescott, of being the prime minister's mouth as well.

The Prescott style with English is imaginative, idiosyncratic, and the stuff of a parliamentary sketch writer's dreams.

But after today's cerebral white-out, who am I to mock?