Art. 38.04. JURY ARE JUDGES OF FACTS.  The jury, in all cases, is the exclusive judge of the facts proved, and of the weight to be given to the testimony, except where it is provided by law that proof of any particular fact is to be taken as either conclusive or presumptive proof of the existence of another fact, or where the law directs that a certain degree of weight is to be attached to a certain species of evidence.
Acts 1965, 59th Leg., vol. 2, p. 317, ch. 722.