to be a rule of law for application under all circumstances. Physical delivery of documents by the debtor to the creditor is not the only mode of deposit. There may be a constructive deposit. A court will have to ascertain in each case whether in substance there is a delivery of title deeds by the debtor to the creditor. If the creditor was already in possession of the title deeds, it would be hypertechnical to insist upon the formality of the creditor delivering the title deeds to the debtor and the debtor redelivering them to the creditor. What would be necessary in those circumstances is whether the parties agreed to treat the documents in the possession of the creditor or his agent as delivery to him for the purpose of the transaction.” The question which arose therein was that what would be the extent of subject-matter of mortgage; the entire property forming the subject-matter of mortgage or a part thereof.” (emphasis supplied) 28. In the interest of completeness, we may note