The parties to a contract may by express agreement limit the medium of payment so as to exclude certain kinds of money which by law are legal tender.1 This is the result reached by the supreme court of the United States and followed by the state courts, although in earlier cases the opposite view was reached on the assumption that statutes which made certain forms of money legal tender were intended to protect the public interest, and that they could not accordingly be set aside even by the consent of the creditor.2