290 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS one should use as concentrated a solution as possible. This also has been indicated by clinical evidence. If the permeability of the tooth normally changes with the time after eruption, then it should be possible to "age the tooth" by the application of appropriate chemicals. There have been some attempts along these lines but not on a systematic or rational basis. One cannot rely on in vitro experiments unless the teeth are set up as a semipermeable membrane. If one wishes to control acid formation by means of enzyme inhibitors in oral preparations it is necessary to know the effect of the inhibitor on the dental plaque. It is not enough that the inhibitor absorb on or in the plaque. It must be present under the plaque on the tooth surface before effectiveness is assured. The inhibitor may absorb on the plaque surface but never reach the tooth surface. If enzyme inhibitors are incorporated in the diet along with the sugar substrate, it may be of little use unless it penetrates the plaque, as fast or faster than the sugar. It would be of little value even when incorporated in the sugar or confection if it did not rapidly diffuse to the tooth surface. SUMMARY On the basis of the modern concept of dental caries, control of this disease should be readily obtained by the prevention of acid formation on the tooth surface or by making the tooth more resistant to the penetration of ions and the decalcification of acids. There are certain variables inherent to the oral cavity which make the successful application of these methods very difficult. In so far as the permeability of the tooth varies with age, sus- ceptibility of the tooth to attack changes. In so far as the penetration of the plaque is a multi-functioned variable, it is possible to have enzyme inhibitors present without affecting caries activity. Any program of caries control must be cognizant of these variables and attempts to circumvent them must be made. REFERENCES (1) Easlick, K. A., "Dental Caries," St. Louis, C. V. Mosby Co. (1948). (2) Leicester, H. M., "Biochemistry of the Teeth," St. Ixmis, C. V. Mosby Co. (1949). (3) Wendt, G. L., and Clarke, A. H., )t. •'lm. $oc., 45, 882 (1923). (4) Holt, L. E., LaMer, V. K., and H. B. Chown, •7. Biol. Chem., 64, 509 (1925). (5) Suess, P. H., and Fosdick, L. S., •7. Dental Research, all 177 (1951). (6) Williams, J. I,, Cosmos, 46, 981 (1940). (7) Williams, J. L., Ibid., 47, 18 (1905). (8) Hemmens, E. S., Blaney, J. R., and Bradel, S. F., •7. Dental Research, 25, 195 (1946). (9) Blaney, J. R., Bradel, S. F., Harrison, R. W., and Hemmens, E. S., )t. •'lm. Dental •'lssoc., 29, 1645 (1948). (10) Moore, B., Carter, W., Dunn, J., and Fosdick, I. S., •7. Dental Research, $5, 778 (1956). (l 1) Englander, H., Carter, W., and Fosdick, L. S., Ibid., 35, 792 (1956). (12) Clement, A. J., Plotkin, R., and Fosdick, L. S., Ibid., $5, 786 (1956). (13) Jay, P., )t. •'lm. Dental •'lssoc., 27, 393 (1940). (14) Becks, H., •7. •lm. Coil. Dentists, 9, 184 (1942). (15) Shaw, J. H., Schweigert, B. S., McIntire, J. M., Elvehjem, C. A., and Philips, P. H., •. Nutrition, 28, 333 (1944). (16) Kite, O. W., Shaw, J. H., and Sognnaes, R. F., •7. Dental Research, 29, 688 (1950).

HAIR COLORING MODERN FORMULATION CONSIDERATIONS 291 (17) Fosdick, L. S., Science, 52, 9 (1956). (18) Sulser, G. F., Fosket, R. R., and Fosdick, L. S., 5 t. vim. Dentalzlssoc., 56, 368 (1958). (19) Zipkin, I., and McClure, F. J., •t. Dental Research, 34, 768 (1955). (20) Stephan, R. M., Fitzgerald, R. J., McClure, F. J., Harris, M. R., and Jordan, H., Ibid., 31, 421 (1952). (21) Zander, H. A., 7. •lrn. Dental •lssoc., 40, 569 (1950). (22) Knutsen, J. W., and Armstrong, W. D., Pub. Health Report, 58, 1701 (1943). (23) Dean, H. T., Jay, P., Arnold, E. A., McClure, F. J., and Elrone, E., Ibid., 56, 761 (1941). HAIR COLORING--MODERN FORMULATION CONSIDERATIONS By ROBERT L. GOLDEMBER( * Presented November 20, 1958, New York City IT •s S:XID that the ancient Chinese dyed their hair in a very ingenious manner. They drank certain well-known mineral waters for a period of time and then painted their hair with nutgall extract. The pyrogallol in the nutgalls reacted with their hair to produce a lovely permanent dark brown or black. It is amazing that no modern formulatot has thought to do the same. If he sold a pill containing iron salts and other appropriate minerals to be in- gested, his customer's body would obligingly excrete this foreign material through her hair and nails via the cysteine detoxification mechanism. Once in the hair, these salts act as perfect built-in mordants for such vegetable dyes as logwood, juglone, lawsone and pyrogallol. Think of the uproar such a product would cause at the Food and Drug Administration. Al- though it would not require the caution label, it might require a New Drug Application! In more recent times, we find that the use of various permanent colorants are covered at considerable (and often repetitive) length in the literature. These include the oxidation dyes--often broadly referred to as para dyes-- the natural extracts such as henna, and the metallic or progressive dyes. There have been relatively few references to temporary coloring of human hair until recently. In view of the exceptional market potential of such products for the grow- ing home-use market, it would seem profitable to examine the new con- cept--the full-intensity rinse--both from the marketing and formulating viewpoints. We shall soon see that many of the classic concepts of both viewpoints are deliberately being violated as the search for new markets, * Shulton, Inc., Clifton, N.J.