Dr. Murphy has attempted to answer two very important questions: what causes congenital defects and what are the chances confronting porspective parents, particularly if they have already had one defective child? The first edition of his book published in 1940 set forth the genetic factors as they occurred in a group of nearly 900 defective children studied by him and his collaborators. The second edition is not an extension or revision of these former observations, but simply adds two chapters dealing with two environmental factors responsible for congenital defects. These added chapters deal with the effects of pelvic irradiation and maternal rubella on the fetus.