While, as a general rule, the consideration of a contract is open to inquiry as between the original parties, yet, where the contract is in writing and, according to the writing, purports to be based on cross-covenants and reciprocal promises made by the respective parties, and these covenants are set out in detail and apparently in full, parol evidence is inadmissible to engraft1 a new and distinct promise, not referred to in the writing. Wellmaker v. Wheatley, 123 Ga. 201 (51 S. E. 436), and cases cited. Judgment affirmed.