In all cases where the plaintiff files a pleading with an affidavit attached to the effect that the facts stated in the pleading are true to the best of his knowledge and belief, the defendant shall in like manner verify any answer. If the defendant is a corporation, the affidavit may be made by the president, vice-president, superintendent, or any officer or agent who knows, or whose official duty it is to know, about the matters set out in the answer.