704. Taking additional security for mortgage debt.

If a creditor having a security on the funds of his debtor for part of his debt takes another security on the same funds for his whole debt, the earlier debt keeps its force and may be separately dealt with1. Similarly, where a creditor, having a security upon his debtor's funds takes afterwards, either alone (but on behalf of himself and another creditor), or jointly with such other creditor, a security for both debts on the same funds, the separate security keeps its force and may be separately dealt with. Where the surety pays off the debt or interest