Either party to a civil action may exhibit to the other or to his attorney at any time before the trial any paper material to the action and request an admission of its genuineness in writing. If the adverse party or his attorney fail to give the admission within four days after the request, and if the party exhibiting the paper be afterwards put to expense in order to prove its genuineness and the same be finally proved or admitted on the trial, such expense shall be paid by the party refusing the admission, unless it appear to the satisfaction of the court that there was good reason for the refusal.