In every city of the first class, the offices of poor director and of poor auditor of each poor district created by local law or remaining in existence as a former borough or township poor district are hereby abolished, except to the extent necessary to liquidate the affairs of the district. Title to the real and personal property of each such district is hereby transferred to and vested in the city, and its powers and obligations are hereby vested in and imposed on the city. Thereafter, the laws as to the care of dependents shall be administered throughout each city of the first class by the department of public welfare of the city, and each such city shall constitute an institution district for the purposes of this act. Such district shall not exist as an entity separate and apart from the city but shall be administered as a department of the city government. The city shall employ each of the present paid poor directors of such districts until his present term of office shall expire, in the liquidation of the affairs of the district and in the administration of this act, paying him his present annual salary, and if he now receives no fixed annual salary, then such salary as may be fixed by the tax levying body of the city. As soon as the affairs of each such district have been liquidated, it shall cease to exist.