1. Department of Entomology, Cornell University, Ithaca, NY 14853.
2. International Center for Epidemiologic and Preventive Ophthamology, Wilmer Ophthamologic Institute, Baltimore, MD 21205.
3. Merck, Sharp, and Dohme Research Laboratories, Rahway, NJ 07065.
4. Department of Medicine, Case Western Reserve University, University Hospitals of Cleveland, Cleveland, OH 44106.