Acts 1977, 65th Leg., p. 1972, ch. 787, Sec. 4, eff. July 1, 1978. Amended by Acts 1987, 70th Leg., ch. 383, Sec. 1, eff. Sept. 1, 1987.

Amended by Acts 1997, 75th Leg., ch. 289, Sec. 1, eff. May 26, 1997.