land is mortgaged in the ordinary way to several persons in succession; for in that case each successive mortgage has a twofold operation, namely, that of an assignment or transfer to the mortgagee, and that of imposing an equitable obligation on the mortgagee in favor of the mortgagor. For example, the first mortgage has the twofold operation of assigning or transferring the land to the mortgagee, and of creating an equitable obligation in the latter to reconvey the land to the mortgagor on payment of the mortgage debt; and in this way the first or original equitable right is created. Then a second mortgage has the twofold operation of assigning this original equitable right, and of creating in the assignee an equitable obligation to reassign it to the mortgagor on payment of the second mortgage debt. In this way a second equitable right is created, which in its turn may be assigned by a third mortgage, the third mortgagee incurring an equitable obligation to reassign it to the mortgagor on payment of the third mortgage debt; and this operation will be repeated as often as a new mortgage is given.
If, upon the making of the first mortgage, the mortgagor and the first mortgagee be conceived of as standing one behind the other, the effect of a second mortgage will be to place the second mortgagee between the mortgagor and the first mortgagee, and thus to separate the two latter; for the second mortgagee, as assignee of the mortgagor, steps into the shoes of the latter as to the first mortgagee, becoming in effect the mortgagor as to the latter, just as if he had purchased the equitable right of the mortgagor (i.e., his equity of redemption), absolutely. As the mortgagor thus ceases to have any relations, for the time being, with the first mortgagee, of course he must give up his place to his successor, the second mortgagee. Still the mortgagor does not stand aside as a mere stranger, as he would do if he had simply sold his equity of redemption; but he takes his place next to the second mortgagee by virtue of the new equitable obligation (i.e., equity of redemption) running from the latter to him. For the same reasons a third mortgagee will take his place between the mortgagor and the second mortgagee, and so on. Therefore, the mortgagor will always be at one end of the line, and the first mortgagee at the other end, the latter always remaining stationary, but the former moving, as often as a new mortgage is given, to make room for the new mortgagee.