Opinion by

§ 7. Parol evidence to vary written contract. The general rule of. law is, that such evidence is inadmissible to contradict or vary the terms of a valid written instrument. [1 Greenl. Ev. §§ 275, 276; Heatherly v. Record, 12 Tex. 50; Keith v. Garrett, 29 Tex. 52; Self v. King, 28 Tex. 553; Reid v. Allen, 18 Tex. 243; Rockmore v. Davenport, 14 Tex. 602.]

§8. Parol evidence, when admissible. The written contract may be contradicted when fraud or mistake is alleged and proven. Or when the written contract is of doubtful meaning, it may be explained by parol evidence. [Roberts v. Short, 1 Tex. 373; Epperson v. Young, 8 Tex. 135; Mead v. Rutledge, 11 Tex. 50.]

Reversed and remanded.