Dr. C. Arthur Knight, featured on this program, introduces his topic with a brief description of properties which characterize living things, and then explains to what degree viruses do or do not have these properties. What is significant, he points out, is that viruses are like other living things to the extent that they are capable of reproducing themselves. Because viruses have a chemical content, similar to that of chromosomes — the cells which determine heredity — and because they can be more easily isolated and fragmented than chromosomes, they are a source of much information for scientists who study life's creation and formation. In addition to his general points, Dr. Knight shows, through a remarkable series of micro-motion pictures, how mutations within viruses can be formed and identified.