Other cases involving the alteration of deeds and other instruments review the parol evidence presented at trial without discussing its admissibility, thus tacitly approving its admission. Downs v. Downs, 154 Md. 430, 434-37, 140 A. 831 (1928) (alteration of deed); Silverberg v. Silverberg, 148 Md. 682, 692, 130 A. 325 (1925) (alteration of deed); Gerlach v. Warren, 146 Md. 668, 127 A. 411 (1925) (alteration of installment land sales contract); Clark v. Creswell, 112 Md. 339, 76 A. 579 (1910) (alteration of deed). Parol evidence regarding the circumstances surrounding the alteration of an instrument is admissible because its object is "not to vary the terms of the instrument, but on the contrary to prove the terms thereof as originally executed."