Any member shall be retired for disability regardless of age or amount of service, if incapacitated for the performance of duty as the result of an injury or disease occurring in and arising out of the course of his employment. Any member otherwise incapacitated for the performance of duty shall be retired regardless of age, but only after 10 years of service. Incapacity for performance of duty shall be determined by the board. As used in this section, “service” means only service for which contribution provided for in this chapter has been made as a county forester, firewarden, or fireman.