David Bowie danced and sang with a handkerchief tied over his mouth--to keep the tear gas at bay--Tuesday night at a concert in Rome. "There seems to be a lot of gas around here, but we'll keep on going until we drop," Bowie told the crowd as he wiped the tears from his eyes. For the second night in a row, fans who had not bought tickets for Bowie's open-air concert clashed with police outside the Flaminio sports stadium, hurling firebombs and stones and setting fire to several parked cars. Riot police fired tear gas on the fans and a light wind blew the gas into the stadium and over the stage, reducing Bowie and most of the 15,000-member audience to tears. Police said they made nearly 50 arrests. Fifteen policemen were injured during the Tuesday night clashes.