The members of the committee shall hold office for four years, and until their successors are appointed and qualify. Of those first appointed by the sheriff, superior court judge, and the board of supervisors, one shall hold office for two years, and one for four years; and the respective terms of the members first appointed shall be determined by lot as soon as possible after their appointment. When a vacancy occurs in the committee by expiration of the term of office of any member thereof, his successor shall be appointed to hold office for a term of four years. When a vacancy occurs for any other reason, the appointee shall hold office for the unexpired term of his predecessor.