ALASTAIR CAMPBELL, writing on these pages about his holiday in France, sneers at columnists other than himself who describe their travels. And there I was, hoping to tell you about having the venom of a poisonous frog introduced into my bloodstream in an Amazonian ceremony which locally is called El ritual de inyeccion de sapó. Forgive me, Alastair, but I’ve started and so will continue.

I never met the frog or knew its name, but its type is Phyllomedusa bicolor, or giant waxy monkey tree frog; the Amazonian Indians call it acururú; and later I looked it up:

“Known for skin secretions loaded with biologically active peptides . . . tribes employ Phyllomedusa bicolor secretions applied to self-inflicted skin burns to produce an agonising attack of diarrhoea, vomiting, tachycardia and systemic collapse, that is followed by a state of hyper-acuity of the senses attended by abundant energy and stamina without need for food or drink. Among other components, it contains dermorphin and deltorphin, peptides with analgesic properties 2,000 times more potent than morphine at the cerebral level.”

So there you have it. I knew nothing of this when, near the point in the rainforest where the borders of Colombia, Brazil and Peru all meet, we were at supper one night at the Reserva Natural Palmarí, four hours by motorised canoe up the River Javarí. The Javarí is a tributary of the Amazon, and Palmarí a riverside lodge on wooden stilts, offering accommodation, transport and guides both to scientists and naturalists, and to curious travellers like my friends and me.

Seated outside the big thatched huts in the soft glow of paraffin lamps, and serenaded by the night-sounds of the jungle, we were devouring a river fish cooked by the formidable Maria, a big, brown Brazilian lady, and drinking a concoction of limes and cane spirit; and the lodge chief, Victor (himself from an indigenous tribe) was describing the frog-poison ceremony.

“We go an hour down the river, not far from Atalaya do Norte,” said Victor. “They burn two little patches in your arm, just to get through the outer skin, then with a knife they scrape off the burnt skin to make patches of raw flesh. Then they put on the poison to penetrate. This may make you dizzy or sick. But it is believed to give powers of clairvoyance, and knowledge of the intentions of others, and to understand things better, sometimes in dreams. When you begin to faint we can wash it off.”

Victor put this idea to us fairly tentatively; he did not urge us to do it and he made the ill-effects very clear. He was organising for us a trip to see how the indigenous peoples live, and the frog poison was only one of many options. It was we — one of my fellow-travellers, Paul, a Spaniard called José, and I — who jumped at it. I volunteered, naturally, out of a sense of duty to you, reader: you want your columnists as clairvoyant as possible. So, early next morning, off all we set with Victor in a canoe — frog-poison volunteers and abstainers alike.

Atalaya was dusty and intensely hot. All Amazonian towns consist of a crumbling and filthy riverbank and tumbledown jetties, a grid of streets with broken pavements, a big diesel generator, endless bars and a citizenry riding in purposeless circuits on scooters for fun — all the roads out leading finally nowhere. In the back of the open truck that Victor had organised to take us a few miles down a dirt road to the communities of the Marubo tribe, a sudden thunderstorm cooled us. “

The Marubo are friendly,” Victor said as we stretched our arms gratefully out in the rain. “They must not be confused with the adjacent Korubo, who are cannibals.”

Our Marubo hosts were indeed friendly. The headman, or cacique, of this small settlement (his Christian name was Esteban) was not expected back for a couple of hours so we sat in his family maloka — a vast, round, palm-thatched, mud hut whose smoke-blackened rafters soared as high above us as a two-storey house.

Surrounded by the jawbones of jungle boars and by Esteban’s three wives and myriad children, we tried rapé. This is a powdery mix of tobacco and the ashes of coconut leaves, scooped into a yard-long blowpipe, an end of which is inserted into one of your nostrils. A friend then puffs violently into the other end, and you get an eye- watering noseful of the stuff, followed by an adrenalin-rush. Then you drink from a big nutshell of yagé. You can take this (an extremely bitter extract from the ayahuasca plant) with or without a hallucinogenic supplement made from the flowers and nuts of a special kind of cacao tree. We passed up on the hallucinogens: ours was yagé-lite.

Esteban returned. He was in shorts and a Toshiba T-shirt, carrying a plastic bag. We had hoped for loincloth and feathers. But he had a kind and fatherly face, and I trusted him.

We all went outside. Paul, José and I rolled up our sleeves nervously. The two ends of a double-barrelled wicker taper called a cipochichica were placed in hot coals until they glowed like lighted cigarette-ends.

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