Section 4. Persons Admitted.--All firemen who are regularly employed by any local political subdivisions of the State and all regularly enrolled members of volunteer fire companies shall be eligible for admission to the school and shall be chosen by the governing authority of each of said political subdivisions. The Public Service Institute Board shall apportion the number admitted to the school so that each county is represented therein in the ratio that the number of firemen in each county bears to the total number of firemen in the State.