Acts 1965, 59th Leg., p. 317, ch. 722, Sec. 1, eff. Jan. 1, 1966. Amended by Acts 1981, 67th Leg., p. 886, ch. 312, Sec. 3, eff. Aug. 31, 1981.

Amended by Acts 1999, 76th Leg., ch. 1506, Sec. 4, eff. Sept. 1, 1999.