Acts 1975, 64th Leg., p. 1405, ch. 545, Sec. 1, eff. Sept. 1, 1975. Amended by Acts 1975, 64th Leg., p. 1222, ch. 456, Sec. 23, eff. Sept. 1, 1975; Acts 1977, 65th Leg., p. 568, ch. 202, Sec. 1, eff. May 20, 1977; Acts 1979, 66th Leg., p. 255, ch. 133, Sec. 1, eff. May 9, 1979; Acts 1979, 66th Leg., p. 784, ch. 346, Sec. 1, eff. June 6, 1979; Acts 1981, 67th Leg., p. 936, ch. 351, Sec. 1, eff. June 10, 1981; Acts 1983, 68th Leg., p. 4706, ch. 819, Sec. 1, eff. Aug. 29, 1983; Acts 1985, 69th Leg., ch. 730, Sec. 1, eff. Aug. 26, 1985; Acts 1989, 71st Leg., ch. 545, Sec. 1, eff. Sept. 1, 1989.