In any criminal case in which the court deems that the veniremen theretofore drawn will be insufficient for the trial of the case, or in any criminal case in which the venire has been exhausted by challenge or otherwise, the court shall order additional veniremen in such numbers as the court may deem advisable, to be summoned as follows:
(a) In a jury wheel county, the names of those to be summoned shall be drawn from the jury wheel.
(b) In counties not using the jury wheel, the veniremen shall be summoned by the sheriff.
Acts 1965, 59th Leg., p. 317, ch. 722, Sec. 1, eff. Jan. 1, 1966.