Westward Whoa: In the Wake of Lewis and Clark

W. Hodding Carter wakes traveling companion Preston Maybank with, ''I think I've been bitten by a brown recluse.'' Preston answers, ''I hope you die.'' That's how the whole trip goes when two friends retrace Lewis and Clark's Missouri-to-Oregon trail the modern way — by boat, car, horse, foot, and hitchhiking, in Westward Whoa: In the Wake of Lewis and Clark. (Carter frets that one driver ''might be a mass murderer.... This truck bed is immaculate. He probably just cleaned all the blood out.'') The memoir is one-fifth wildlife studies, while the rest is a charmingly wide-eyed appreciation of lower alimentary canals: Carter measures, describes, and collects animal droppings; a thoughtfully annotated trail map marks Preston's first diarrhea attack; and Preston even breaks his ribs in Montana while getting even with flatulent horses. It's Animal House on a nature hike, and the only person who won't think it's funny is your mother. A