1. Dubos, R.J.: Bacterial and Mycotic Infections of Man, Philadelphia, 1948 , J. B. Lippincott Company, p. 27.
2. Easlick, K.: Dental Caries. Mechanism and Present Control Technics, St. Louis, 1948, The C. V. Mosby Company, p. 201.
3. Koch, F.C.: Practical Methods in Biochemistry, Baltimore, 1935, William Wood & Company, p. 186.