All original appointments to any position in the police force shall be for a probationary period of six months, but during the probationary period an appointee may be dismissed only for a cause specified in section 13 of this act¹ or because of incapacity for duty due to the use of alcohol or drugs. If, at the close of a probationary period, the conduct or fitness of the probationer has not been satisfactory to the appointing officer or body, the probationer shall be notified in writing that he will not receive a permanent appointment, and the appointment shall cease. If the probationer is not notified or dismissed in accordance with this section, his retention shall be equivalent to a permanent appointment.