The civil service commission shall keep a list of all members of the said police and/or fire department, and formulate methods of determining the relative qualifications of persons seeking employment in either department, and give preference to those having the best qualifications. The commission shall provide that men laid off because of curtailment of expenditures, reduction in force, and like causes, shall be the last man or men, including probationers, that have been appointed to either the fire and/or police departments, until such reductions necessary shall have been accomplished. However, in the event said department shall again be increased in number, those suspended shall be reinstated before any new appointments shall be made.