Nearly 60 years ago, a French town was hit by a sudden outbreak of hallucinations, which left five people dead and many seriously ill. For years it was blamed on bread contaminated with a psychedelic fungus - but that theory is now being challenged.

Image caption Leon says he would prefer to die than endure the 1951 events again

On 16 August 1951, postman Leon Armunier was doing his rounds in the southern French town of Pont-Saint-Esprit when he was suddenly overwhelmed by nausea and wild hallucinations.

"It was terrible. I had the sensation of shrinking and shrinking, and the fire and the serpents coiling around my arms," he remembers.

Leon, now 87, fell off his bike and was taken to the hospital in Avignon.

He was put in a straitjacket but he shared a room with three teenagers who had been chained to their beds to keep them under control.

"Some of my friends tried to get out of the window. They were thrashing wildly... screaming, and the sound of the metal beds and the jumping up and down... the noise was terrible.

"I'd prefer to die rather than go through that again."

Over the coming days, dozens of other people in the town fell prey to similar symptoms.

Doctors at the time concluded that bread at one of the town's bakeries had become contaminated by ergot, a poisonous fungus that occurs naturally on rye.

Biological warfare

That view remained largely unchallenged until 2009, when an American investigative journalist, Hank Albarelli, revealed a CIA document labelled: "Re: Pont-Saint-Esprit and F.Olson Files. SO Span/France Operation file, inclusive Olson. Intel files. Hand carry to Belin - tell him to see to it that these are buried."

F. Olson is Frank Olson, a CIA scientist who, at the time of the Pont St Esprit incident, led research for the agency into the drug LSD.

Find out more Listen to Mike Thomson's investigation of the Pont-Saint-Esprit incident for BBC radio, using the link below Radio 4: Document

David Belin, meanwhile, was executive director of the Rockefeller Commission created by the White House in 1975 to investigate abuses carried out worldwide by the CIA.

Albarelli believes the Pont-Saint-Esprit and F. Olson Files, mentioned in the document, would show - if they had not been "buried" - that the CIA was experimenting on the townspeople, by dosing them with LSD.

The conclusion drawn at the time was that one of the town's bakeries, the Roch Briand, was the source of the poisoning. It's possible, Albarelli says, that LSD was put in the bread.

It is well known that biological warfare scientists around the world, including some in Britain, were experimenting with LSD in the early 1950s - a time of conflict in Korea and an escalation of Cold War tensions.

Albarelli says he has found a top secret report issued in 1949 by the research director of the Edgewood Arsenal, where many US government LSD experiments were carried out, which states that the army should do everything possible to launch "field experiments" using the drug.

Image caption The local hospital where some of the victims were taken in 1951 has been closed

Using Freedom of Information legislation, he also got hold of another CIA report from 1954.

In it an agent reported his conversation with a representative of the Sandoz Chemical company in Switzerland.

Sandoz's base, which is just a few hundred kilometres from Pont-Saint-Esprit, was the only place where LSD was being produced at that time.

The agent reports that after several drinks, the Sandoz representative abruptly stated: "The Pont-Saint-Esprit 'secret' is that it was not the bread at all... It was not grain ergot."

'Wrong symptoms'

But American academic Professor Steven Kaplan, who published a book in 2008 on the Pont-Saint-Esprit incident, insists that neither ergot nor LSD could have been responsible.

Ergot contamination would not, he says, have affected only one sack of grain in one bakery, as was claimed here. The outbreak would have been far more widespread.

He rules out LSD on the grounds that the symptoms people suffered, though similar, do not quite fit the drug.

He also points out that it would have not have survived the fierce temperatures of the baker's oven - though Albarelli counters that it could have been added to the bread after baking.

While they disagree on the cause of the hallucinations, on one point they are united - the need for a French government inquiry to get to the bottom of what really happened in Pont-Saint-Esprit all those years ago.