The difficulty is not in pointing out the evil, which is plain enough, but in suggesting a remedy. The right of cross-examination is one of the most important instruments provided by the machinery of our law for the discovery of facts, and on the credibility of witnesses all cases hinge. The moment we begin to limit it by fixed rules we enter on dangerous ground. It might seem as if the solution of the problem lay in the enactment of a rule that witnesses should only be cross-examined as to their general reputation with regard to truth, and as to the matters involved in the case directly affecting their credibility; but this would by no means do. Suppose, for instance, that the suit is a common action for the purchase-money of a piece of cloth, and the defendant brings a witness who swears that he saw the defendant pay the money to the plaintiff, while the plaintiff has only his own evidence to rely upon in proof of non-payment; if, in such case, the plaintiff were merely allowed to cross-examine the witness directly, he would in all probability lose the case. The testimony would be two to one against him, and the story of the witness as the only disinterested person would probably be believed by the jury. But suppose that, on cross-examination, it turns out that this witness can give no good account of his manner of earning his living or of his place of residence; that he had been arrested not long before as a vagrant, and that down to the time of the action he had no respectable clothes, and that he suddenly became possessed of some; that he deserted from the army immediately after getting his bounty-money, and so on, there can be little doubt that his credit with the jury would be much impaired, and justly so, although no direct evidence of his being a perjurer had been introduced, and not a particle of his testimony had been strictly controverted. Everyone who has followed with any care the evidence taken in celebrated murder trials or divorce cases knows how frequently a rigid cross-examination lays bare motives and prejudices on the part of witnesses which, often without their knowing it themselves, tend to bias their account of facts.