66. Waste by mortgagor in possessi on.—A mortgagor in possession of the mortgaged property is not liable to the mortgagee for allowing the property to deteriorate; but he must not commit any act which is destructive or permanently injurious thereto, if the security is insufficient or will b e rendered insufficient by such act.
Explanation.—A security is insufficient within the meaning of this section unless the value of the mortgaged property exceeds by one -third, or, if consisting of buildings, exceeds by one -half, the amount for the time being due on the mortgage. Rights and Liabilities of Mortgagee