When goods are sent C. O. D. by express the sender makes out a bill containing a description of the goods. Such an itemized statement is also made out whenever goods are sold, and a copy is given to the buyer by the seller. This statement is known as an invoice. There are columns in which to place any discount that may be allowed. When such bills or invoices are receipted, showing that they have been paid, the receipt should always appear on the face. Invoices sometimes are assigned to banks and are known as "accounts receivable,,, the sender possessing a lien upon the accounts. This is not, from the banker's viewpoint, considered a desir-way of borrowing and is resorted to only in extreme cases.