The appointing officer under whom a position classified under the provisions of this part is to be filled shall notify the board of that fact, and the board shall certify to him the names and addresses of a limited number of candidates, as provided in its rules, who stand highest upon the register for the class or grade to which such position belongs, and the appointing officer shall select one of the persons so certified. After a candidate has been certified three times by the board and has not been accepted, the name of such candidate may be stricken from the register. Emergency lists of persons who have passed the required tests may be maintained for any grade or class in which the numbers employed vary so greatly, in short intervals of time, that certification after notice would be impracticable, and such list may stand as a call list for positions in such grade or class only; but no appointment from an emergency list, except from the persons having the highest ratings thereon and eligible to permanent appointment, shall stand for more than sixty days or be subject to renewal within fifteen days thereafter, except from a list of unskilled laborers or domestics actually employed and paid as laborers or domestics.