Lynn Poole offers a definition of cancer in this third program in the series. Dr. Samuel P. Asper, Jr. describes the thyroid gland and the characteristics of hyperthyroidism and hypothyroidism. William S. Halsted's operation is still used for surgery on the thyroid to remove a goiter or cancer, and both the incision and the gland are shown in photos. A recovered surgery patient, operated on by H. William Scott of Vanderbilt University Medical Center, is shown on film. Radiation of the thyroid and radioactive iodine taken internally are considered treatments rather than cures. Additional films show Dr. George O. Gey's cancer cell labs at Johns Hopkins University, Dr. Frederik B. Bang using the electron microscope to detect cervical cancer, and the U. S. Public Health Service's National Cancer Institute's use of mice in cancer research and treatment. Dr. Isaac Berenblum's book, "Man Against Cancer," the basis of this series, is promoted. Mr. Poole reminds the audience once again, early detection is the key to a cure.