1. M. R. Emmert-Buck, R. F. Chuaqui, Z. Zhuang, R. A. Weiss, L. A. Liotta, Laboratory of Pathology, National Cancer Institute, Room 2A33, Building 10, 9000 Rockville Pike, Bethesda, MD 20892, USA.
2. R. F. Bonner, P. D. Smith, S. R. Goldstein, Biomedical Engineering and Instrumentation Program, National Center for Research Resources, National Institutes of Health, Bethesda, MD 20892, USA.