Item is a videocassette of a guest lecture by Dr. Purkis who spoke as part of the Dalhousie Medical School's Friday at Four series. The question and answer section of the lecture is not included. Friday at Four was a lecture series sponsored and organized by the School that focused on a variety of subjects by lecturers invited to speak about specialized areas of medicine. The lectures were held each Friday by the School from the 1970s to the 1990s. The tape was requested by Dr. Clark from the Division of Continuing Medical Education.