Not so much new as updated is this routine treatment of America's most successful indigenous art form. Viewed in turn are 19th-century revues, spectacles, comic operas, and operettas, bits of which came together for the musical comedies of the Teens and Twenties--sprightly stories with songs tacked on--until 1927 and Showboat, the first fully ""integrated"" musical. The romantic (Porgy and Bess) and social comment (Of Thee I Sing) musicals of the Thirties led to the glories of the Forties (Pal Joey, Oklahoma) and the triumphs of the Fifties (My Fair Lady, West Side Story)--and the slow decline starting in the Sixties, with only Sondheim and Kander & Ebb to hold up the torch. The author's taste is perhaps overly traditional (he is quite vicious about rock musicals and Off Broadway), but it hardly matters in what is essentially a verbal scrapbook; with upwards of 100 shows in the good years, he rarely has more than a few sentences to spare even for masterpieces. The chief accrual is perspective.