This chapter shall not apply to physicians or surgeons licensed to practice medicine or osteopathy in the State of Mississippi, nor to physicians or surgeons of the United States Army, Navy or the United States Public Health Service, when in actual performance of their duties or to legally registered podiatrists of another state taking charge of the practice of a locally registered podiatrist of this state, temporarily during the latter's absence therefrom, by written permission of the Secretary of the State Board of Medical Licensure.