1. Jenkins, G. N., The Physiology of the Mouth (second ed.) (Blackwell Scientific Publications, Oxford, 1960).
2. Klein, H., and Amberson, W. R., J. Dent. Res., 9, 667 (1929).
3. Chick, A. O., and Waters, N. E., Arch. Oral Biol., 10, 1 (1965).
4. Leach, S. A., Arch. Oral Biol., 3, 48 (1960).
5. See Helfferich, F., Ion-Exchange (McGraw-Hill, 1962).