539. Principal mortgage debt payable on demand.

When the principal sum is payable on demand, and there is no provision, express or implied, for notice to be given, the necessity for notice depends on whether the covenant is direct or collateral. If it is direct, that is, if it secures the covenantor's own debt and is not merely a collateral security for that debt, no actual demand is required and the right of action accrues immediately on the money being advanced1. If, however, the covenant is collateral, where, for instance, it is to secure the debt of another or to secure an ordinary banking overdraft between