All appointments to any position in the county police force shall be for a probationary period of eighteen months and for any position as fireman or fire inspector shall be for a probationary period of six months, but during the probationary period an appointee may be dismissed only for cause, as specified in section 1511 of this act. If at the close of the probationary period, the conduct or fitness of the probationer has not been satisfactory to the board of county commissioners, the probationer shall be notified in writing that he will not receive a permanent appointment. Thereupon, his appointment shall cease; otherwise, his retention shall be equivalent to a permanent appointment.
16 P.S. § 4514