Any and all bonds registered by the state auditor under the provisions of the laws of this state, and any and all bonds that have been or may be duly issued by any county or city or school district having a population of over three hundred thousand inhabitants, whereon there is no default in payment of principal or interest, may be accepted as good and lawful security for the investment of the capital stock, surplus and reserve funds of any insurance or fraternal benefit society incorporated in or authorized to transact business in this state, or trust company authorized to transact business in this state. The state director of the department of commerce and insurance is hereby authorized to accept such bonds as security or pledge in all cases where such pledge or security is required by the laws of this state. Such bonds may be accepted by the state treasurer as security for the deposit of any and all state funds, and by county and city treasurers as security for the deposit of any and all county and city funds. They shall also be eligible for the investment of any funds in the possession of any administrator, executor, guardian, curator, trustee and all other persons sustaining fiduciary relations. Such investments may be made without an order of court first had and obtained, and without incurring liability for loss, except in case of inexcusable negligence.