Sec. 10. TRANSFER OF PRO RATA SHARE OF EXISTING FUND. Immediately upon this Act becoming a law, there shall be transferred to the Police Officers' Pension System the prorata share of any pension fund heretofore existing to which police officers have contributed, including the prorata part of the fund paid by the city and all accumulated interest on the money which both the policemen and the city have heretofore contributed to the fund. It shall be the duty of the city official or officials responsible for said existing fund to make such transfer immediately.