It frequently happens, however, that only a small cash payment is made, the greater part of the purchase money being secured by mortgage. In such a case the safest method is not to consider the transaction as entirely closed, nor the profits as actually earned. For example, if only one-tenth of the purchase money has been paid, and nine-tenths is secured by mortgage, that mortgage could not, as a rule, be considered good marketable security, as the amount of the debt is too near the value of the security and the mortgage has but a small "margin." Should the mortgagor fail to pay the debt before it has been substantially reduced, and should it be necessary to resort to legal proceedings in order to recover the title, the expense of such proceedings would, in many cases, swell the amount of the mortgage to a sum equal to, or greater than, the original debt.