As one of the great European thinkers of the 20th century, Jean-Paul Sartre popularised existentialism, became a working-class hero -- and was chased down the Champs Elysées by a pack of imaginary lobsters.

A previously unpublished account of the late French philosopher's improbable drug-induced crustacean visions has surfaced in New York, where a new book of conversations between Sartre and an old family friend will be published later this month.

John Gerassi, a New York professor of political science whose parents were close friends of Sartre, talked at length to the philosopher in the 1970s about his experiments with mescaline, a powerful hallucinogenic drug derived from a Mexican cactus.

Although it has long been known that Sartre experienced visions of lobsters -- which he sometimes referred to as crabs -- Gerassi's account offers startling new details of the philosopher's descent into near-madness as he battled to make sense of what he had come to regard as the intellectual absurdity of his life.