A broker can not recover on a contract that he should have commissions for effecting an exchange of property with another, where he did nothing under the contract and does not show that he was excused from rendering services under his employment, although the trade was consummated by the owner. Walton v. McMorrow, 57 N. Y. S. 691, 39 App. Div. 667. See also Secs. 19, 21, 454, 558.