Action of assumpsit for £20.' Issue to the jury. It was objected to a'witness, that he was interested; to which it was *227replied, that he was discharged, but it was not in the power of the party to produce the discharge, and offered parol evidence to prove it; which was admitted by the court upon objection made. Regularly the discharge ought to be produced, if in the power of the party, otherwise parol proof is admissible to prove it.