21 Pa. Stat. § 761
In every case where a mortgage has been, or shall hereafter be executed, it shall be lawful for the mortgagee or mortgagees, his, her or their respective heirs, executors, administrators or assigns, to release any part or parts of the mortgaged premises to the mortgagor or mortgagors, his, her or their respective heirs, executors, administrators or assigns, or to any person or persons claiming the same, by, from or under him, her or them, or any of them, and thereafter to sue forth a writ or writs of scire facias to recover the debt or demand mentioned in such mortgage, or so much thereof as shall remain or become due, out of the remaining part or parts of such mortgaged premises, and not released as aforesaid, and the remaining part or parts only of such mortgaged premises shall be taken in execution, and the same proceeding shall be had thereon, as are provided by the act to which this is a supplement; and the defendant or defendants in such scire facias, in addition to the pleas mentioned in the act to which this is a supplement, may plead that the balance claimed is greater than in a just proportion ought to be levied on the premises described in such writ, and if he, she or they shall thereupon confess judgment for so much as he, she or they shall believe to be the just proportion chargeable upon the premises described in the writ; and if the plaintiff shall proceed for the residue of his claim, but shall not recover any sum beyond the amount of the said judgment, together with the interest thereon accruing, in such case the plaintiff shall pay all the costs of such further proceedings to final judgment; in any other event the defendant or defendants shall pay the same.
21 P.S. § 761