¶1Opinion of the Court by
¶2Kankey sued Page in assumpsit, to which defendant plead non-assumpsit and set-off. Issue was taken on the plea of non-assumpsit, verdict and judgment for plaintiff.
¶3On the trial, plaintiff introduced one Childs as a witness, *434testified on his voir dire that he was interested in the of the cause-, in favor of Page.
¶4Notwithstanding, plaintiff examined him and proved by his'testimony, the signature of said Page to certain letters, which he wished 'to read to the jury. Page the defendant, Pro.P0£ed to cross-examine witness, in relation to other mat-tors involved in the issue, but the court refused to permit the .. „ witness to ne examined m relation to any point except the sígnature °f said letters by Page. The defendant excepted to the opinion of the court, and this is all the error relied on • ,i - _ .. , ^ COUlt.
¶5The nfle on this subject is clearly laid down by Phillips in , . , J J J l bis treatise on evidence. “If a witness is called by a party, merely for the purpose of producing a written instrument, belongmg to the party, which is to be proved by another witness, he need not be sworn; and if not sworn, he will not be subject to cross examination. If a witness is sworn and gives some evidence (as proving ail instrument) however formal the proof may be, he is to he considered a witness for all purposes; and this although he may be substantially the real party in the suit, and the party on the record a mere .nominal parly.” p. 274, Cowans Ed.
¶6This is amply supported by adjudicated cases. 4, Wendell 369, 2, Wendell 166, 11, Peck 273.
¶7The reason of this rule is obvious and, I think, satisfactory. If a party voluntarily calls upon an interested and in competent witness, for the purpose of sustaining by his testimony something favorable to his side, he admits that the witness is above the reach of improper influences, and his adversan', it would seem just, should have the full benefit of such admission.
¶8The court should have allowed the examination, proposed, and for this error, the judgment must be reversed.