In an action by a real estate broker to recover viommissions for services in effecting an exchange of lands, which was finally completed by other brokers, a letter from one of these other brokers to another of them, offered by the defendant merely as a part of the history of the transactions which culminated in the sale, may be excluded as immaterial as well as being res inter alios. Hall v. Grace, 179 Mass. 400, 60 N. E. 932; Cessna v. Johnson, 122 N. E. 444, - Mass. Sup. - .