1. Department of Clinical Pathology, Nihon University School of Dentistry at Matsudo, 870-1, Sakaecho-nishi 2, Matsudo, Chiba 271, Japan
2. Central Research Laboratories, Taiyo Kagaku Co., Ltd., Yokkaichi, 510, Japan
3. Department of Microbiology, Nihon University School of Dentistry at Matsudo, 870-1, Sakaecho-nishi 2, Matsudo, Chiba 271, Japan