201, 42 N. W. 935.—Competent evidence. That which the very nature of the thing to be proven requires, as the production of a writing where its contents are the subject of inquiry. 1 Green]. Ev. § 2; Chapman v. McAdams, 1 Lea (Tenn.) s Horbach v. State, 48 Tex. 242; Porter v. Valentine, 18