The chief of police, as far as the police department be concerned, and the chief of the fire department, as far as the fire department be concerned shall notify the civil service board of vacancies in the ranks of patrolmen or firemen, respectively, and the board shall furnish the respective chiefs with the name and address, or names and addresses, of the candidate or candidates standing highest on the eligible list, and same shall receive the appointment or appointments to fill the vacancy or vacancies. All appointments shall be on probation for a period of six months from date of appointment. Before the expiration of the period of probation, the chiefs of fire and police departments, respectively, may, by and with the consent of the board, discharge any probationer in his or her respective department upon assigning in writing the reasons therefor to the board. If a probationer be not discharged before the expiration of his or her probation, his or her appointment shall be deemed complete.