A secretary-treasurer may by and with the consent of the board of directors invest in United States Government bonds, bonds and debentures issued either singly or collectively by any of the twelve federal land banks, the twelve intermediate credit banks, or the thirteen banks for cooperatives under the supervision of the Farm Credit Administration, United States Treasury notes, bills, or certificates of indebtedness maturing within two years from the date of purchase, or in certificates of deposit. Every secretary-treasurer having invested in such securities shall deliver the same to his or her successor, who shall receive and accept the same as funds of the office. The interest received on any investments authorized by this section and section 77-2385 shall be credited to the general fund of the local hospital district, or to a fund to be used exclusively for the purposes contemplated by the provisions of section 23-3548, in the discretion of the board of directors. If such interest is received on a fund which shall not have been commingled with any other fund for investment purposes, then any interest received shall be credited to the fund from which the investment shall have been made. It shall be in the discretion of the board of directors whether any fund shall be commingled or invested from an identifiable account.