FICTION : A GUEST IN THE JUNGLE by James Polster (Mercury House: $15.95; 192 pp.).

An American lawyer named “Whitehill” abandons Pittsburgh in favor of an adventure vacation in South America. He plunges further and further off the tourist track in search of the exotic. He finds it in the steamy jungle town of Lomalito, somewhere on the edge of the Amazon.

Whitehill is a sensitive observer and a bumbling explorer. On his first hike into the jungle, he loses his bearings and is kidnaped by a sadistic doctor and his Indian sidekick, who keeps him in line by nicking him at intervals with an extremely sharp machete. In the midst of Whitehill’s predicament, we learn how snake venom promotes bleeding, where vampire bats are apt to bite--the nose is a preferred point--and other charming details of Amazonian natural selection.

Whitehill escapes into the jungle and is taken in by the Lotimone tribe, whose members speak English with the flair of William F. Buckley. From this point on, Polster’s novel resembles an extended National Geographic documentary, which might have been entitled, “The Threatened Amazon.” Speaking through the Indians, Polster delivers lectures on the ecological plight of the Amazon and the sterility of Whitehill’s urban existence, which unfortunately sap the vitality from this otherwise colorful tale.