1. E. S. Johnson, J. E. Kelly andL. E. van Kirk, Vital Health Statist.11, 1 (1965).
2. S. S. Socransky, J. dent. Res.49, Suppl. 2, 203 (1970).
3. H. E. Schroeder andS. Münzel-Pedrazzoli, submitted to J. Microsc. (1972).
4. H. E. Schroeder, S. Münzel-Pedrazzoli andR. C. Page, submitted to Archs oral Biol. (1972).
5. D. E. Flieder, C. N. Sun andB. C. Schneider, Periodontics4, 302 (1966).