51. The witnesses in all proceedings before the Court, where their attendance can be had, shall be examined orally, and any party may offer himself or herself as a witness, and shall be examined and may be cross-examined and re-examined, like any other witness: Provided that the parties shall be at liberty to verify their respective cases in whole or in part by affidavit, but so that the deponent in every such affidavit shall, on the application of the opposite party, or by direction of the Court, be subject to be cross-examined by or on behalf of the opposite party orally, and after such cross-examination may be re-examined orally as aforesaid by or on behalf of the party by whom such affidavit was filed.