The Fort Worth Symphony Orchestra held a gala special concert Saturday night, and it was a kind of double celebration: The orchestra has passed its first 100 years, and it is one of only three orchestras in the nation in which two Stradivariuses are regularly played.The two Strads, considered by many to be supreme among violins, are on extended loan from Mr. and Mrs. William S. Davis and Eugenie Guynn. The Davis Stradivarius, which dates from 1710, is played by concertmaster Michael Shih in FWSO concerts. The other violin is even older, dating from 1685. It is played by associate concertmaster Swang Lin.The Bass Hall concert got off to a rough start with a tentative and insecure performance of Pablo de Sarasate's Carmen Fantasy with Lin as soloist. Thereafter things got on track, though, and the show became a worthy salute to the orchestra and its instruments.The two Sarasate works on the program -- plus a Sarasate encore -- are the products of a dazzling Spanish violin virtuoso who died in 1908. They are intended to demonstrate technical prowess on the violin as well as to entertain.Sarasate's Zigeunerweisen, or Gypsy Airs, scored on both points in the hands of Shih. Its contrasting slow and fast sections explore Hungarian Gypsy music entertainingly, and Shih's violinistic athletics were an entertainment in themselves.FWSO music director Miguel Harth-Bedoya led the spare orchestral accompaniment, which basically aims not to get in the way of the violin.A much weightier work, given perhaps the best overall performance of the evening, was Bach's Concerto for Two Violins in D minor, BWV 1043. Shih and Lin teamed as soloists, with Harth-Bedoya conducting a substantial and musically important orchestra.Shih and Lin (now in much better form) gave a performance that alternated vigor in the quick movements and lyrical beauty, especially in the slow movement. At the end, there was a sense of exhilaration with music well played.The concert concluded with what is probably the most famous classical piece ever composed: Beethoven's Fifth Symphony. Harth-Bedoya's interpretation produced its share of excitement, and the orchestra was in good form, with noble sounds in the brass especially noteworthy. If it never quite scaled the peaks one hopes for in a classic Beethoven Fifth, that's hard to do with such an ultrafamiliar work.