When funds of a charitable or eleemosynary institution are invested in a mortgage on real estate, the buildings included shall be insured by the mortgagor in such company duly authorized to transact business in this state as the trustees, directors, or board of investment of such institution may designate; and the policies of insurance shall be duly assigned, or the loss made payable to such institutions. The trustees, directors, or board of investment may procure or renew such policy of insurance in such company authorized to do business in this state, as they may elect, from year to year, or for a longer or shorter period, if the mortgagor neglects so to do, and, when necessary, the treasurer of such institution may sign premium notes, and may charge the amount paid for such insurance to the mortgagor.