There is little question today but that a foreign corporation may be subject to suit and a personal judgment in a state where it is doing business if service has been had upon a proper agent of the corporation, designated by law or otherwise. There may be consider able question as to what constitutes "doing business." The fact that the business carried on by a corporation is wholly interstate in character will not prevent that corporation from being subject to service in the same manner as though it were doing intrastate business as well a It also seems clear that under state attachment statutes the property of a foreign corporation engaged in interstate commerce may be subject to attachment, whether this property consists of traffic balances due from other carriers, rolling stock, or property used in connection with a soliciting office, without creating a necessarily unreasonable burden upon interstate commerce. However, in Davis v. Farmers' Co-Operative Equity Co., a statute construed to authorize suit by a nonresident plaintiff against a foreign railroad corporation with a soliciting agent but no line in the state of suit on a cause of action not originating in the state and not arising from a transaction within the state was held to create an unreasonable burden on interstate commerce and to be invalid. The doctrine laid down in the Davis case has resulted in much judicial interpretation. The scope of that doctrine forms the subject matter of this inquiry.