137. Nothing in the foregoing sections of this Chapter applies to stocks, shares or debentures, or to instruments which are for the time being, by law or custom, negotiable, or to any mercantile document of title to goods. Explanation.-The expression “mercantile document of title to goods” includes a bill of lading, dock-warrant, warehouse-keeper's certificate, railway receipt, warrant or order for the delivery of goods, and any other document used in the ordinary course of business as proof of the possession or control of goods, or authorizing or purporting to authorise, either by endorsement or by delivery, the possessor of the document to transfer or receive goods thereby represented.