SDCL § 44-8-16: Prior or superior mortgage affecting real property--Failure of mortgagor or successor in interest to pay installment due--Payment by holder of inferior mortgage--Added to amount due on mortgage.

In case any installment of interest or principal upon any prior or superior mortgage shall become due and the mortgagor or his successor in interest shall fail to pay such interest or principal, the holder of any inferior mortgage on real estate may pay such interest or principal upon such prior mortgage, and the amount so paid shall thereupon be added to the amount due on the mortgage held by the person making such payment and may be included in such mortgage upon foreclosure of the same.