Whenever any organization of the national guard shall be called into the active service of the state, it shall be the duty of every officer and enlisted person of the organization so ordered to report at once to his or her immediate commanding officer for duty; and no officer or enlisted person can be excused from duty except by order of the commander in chief, unless he or she shall present a certificate of disability certified to by a reputable physician; when such certificate of disability is presented, excuse may be granted by the immediate commanding officer.