Section 3. The existing Presidents of Sanitary Divisions, Municipal Maternity and Charity Clinic Physicians, and Heads of the Units of the Rural Health Units (FOA/ PHILCUSA) of the Bureau of Health shall be the Municipal Health Officers to head the rural health units and shall remain in their present stations as municipal health officers thereat until their places of assignment are fixed by the Secretary of Health upon the recommendation of the Director of Health: Provided, however, That the additional rural health units required in section two (b) of this Act shall be established in four years from the effectivity of this Act.