An instruction, in an action for a real estate broker's commissions, that the jury in arriving at a verdict could not consider testimony that defendant went on plaintiff's note as surety, or that defendant had been sued on the note, was erroneous, the testimony being relevant to the issue as to the terms of the contract between the parties. Yates v. Brattam (Tex. Civ. App. '08), 111 S. W. 416. See also Sec. 817b.