In spite of the many difficulties that have and still do obstruct the investigations in this field, 16 years is a long time in which to produce our present knowledge. It is believed now that the major causative agents have been traced, but little hope is held for the production of an effective preventative agent in the near future. It seems unlikely that a satisfactory vaccine is possible until more is known of the prevalent serotypes of the viruses
concerned and also of the stability of these serotypes. The concept of interferon, a non -specific anti -virus agent,is attractive, but considering that it was extracted from the tissues et least four years ao, it is disappointing that more is not known of its chemical nature and of its synthesis. On the other hand this substance inferon perhaps holds the best hope for the future prevention of a disease which is only approached by mental illness in its effect on the health and economy of this country.