1. Nolte, W.A.: Oral Microbiology, St Louis: C.V. Mosby Co., 1968, p 50.
2. Florey, H.: General Pathology, 3rd ed, Philadelphia : W.B. Saunders Co., 1962, pp 98-126.
3. Tamayo, R.P. : Mechanisms of Disease, Philadelphia: W.B. Saunders Co., 1961, p 54.