(a) A full time teacher under contract to teach the regular school year in a public school shall be allowed a minimum of 10 days' sick leave with full pay during each school year. Sick leave not used shall be cumulative at least to 20 days so long as the teacher is employed in the same school district.

(b) The word "days" shall mean school days.

(c) The use of sick leave as herein provided shall be subject to the rules and regulations of the directors of each school district.