1. KOPEZKY, quoted by WEDL, C., Pathologie der Zahne, p. 11; Leipzig, 1870.
2. PICKERILL, H. P., The prevention of dental caries and oral sepsis, pp. 110 et seq.; Paul B. Hoeber, Inc., New York, 1924.
3. HEAD, J., Modern dentistry, pp. 47 et seq.; W. B. Saunders Co., Philadelphia, 1917.
4. PROELL AND SCHUBERT, Zeit.f. Stomat. 1928, 26, 1047.
5. RicHTER, H., Ibid. 1931, 29, 591.