OPIUM by Jean Cocteau, translated by Margaret Crosland, (Peter Owen: $14.95, illustrated) . At the end of 1928, Jean Cocteau entered a clinic in St. Cloud to undergo a second treatment for opium addiction. The journal of his five-month cure is a fragmented, hypnotic collection of maxims, stories and reflections, many of them focusing on the drug and its effects. Other sections are devoted to recollections of the genesis of his early works and his friendships with Picasso, Proust and other early 20th-Century artists, including the often-cited anecdote of Proust asking the concierge at the Ritz to lend him 50 francs, then giving it back as a tip. With a typically amoral stance, Cocteau concludes: "I do not plead, I merely produce documents, for and against, in the trial of opium."