Tex. Code Crim. Proc. art. 34.03

When the sheriff is ordered by the court to summon persons upon a special venire whose names have not been selected under the Jury Wheel Law, the court shall, in every case, caution and direct the sheriff to summon such persons as have legal qualifications to serve on juries, informing him of what those qualifications are, and shall direct him, as far as he may be able to summon persons of good character who can read and write, and such as are not prejudiced against the defendant or biased in his favor, if he knows of such bias or prejudice.