PRIMARY ODOR AND MOLECULAR SHAPE 105 How MANY PRIMARY ODORS ARE THERV.? This question is often asked, but no definite answer is possible at present. However, the first steps are being taken towards a solution. All available information on different chemical examples of specific anos- mia (7) has been collected and the total presently stands at 62. There is, nevertheless, a good deal of redundancy among these observations, with certain compounds clearly belonging to the same primary odor. Fo.r example, several fatty acids have been noted, but they presumably belong to the same sweaty primary odor. A number of macrocyclic musks exhibit anosmias, but they most likely belong to a single musk primary or to one of the possible subdivisions of the musk class. A tentative estimate at the moment would be that the total number of primaries will come out between 20 and 30, with 27 as a likely figure. At present, a major investigation on all the primary odors is being planned. As each primary will require at least one man-year of pro- fessional-level work, this is a formidable undertaking. It would be a considerable help to the author to hear about any examples of specific anosmia, as this may fill a gap in the odor spectrum to be covered (10). The total problem of the primary odors may be regarded as the prob- lem of the "olfactory code." At the moment, we have learned only one word of this code, the "sweaty" primary odor of isovaleric acid. How- ever, the first step is often the hardest. In the author's opinion, this first primary odor has as much significance for odor science, as that first codon (UUU for phenylalanine) of the well-known genetic code had for molecular biology. Let us hope that equally vigorous research will develop in many laboratories as an attack on our olfactory code. LIKELY SIGNIFICANCE FOR COSMETIC CHEMISTRY In several more years the "olfactory code" will very likely be solved, and possibly even be confirmed by independent methods. The scientific challenge is there, and the experimental methods are available. The odor chemist would then be in possession of theoretical guidelines equiva- lent to the color chemist. The great industries of color printing, color photography, and color television all depend on the centuries-old con- cept that any color can be reproduced by appropriate mixture of three primaries (red, green, and blue lights). It would be wise to anticipate what effect this could have on the aroma/flavor industry. At its simplest, it would mean that any intended fragrance could be matched by an appropriate mixture of a standard set

106 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (say) 27 aromatics. This facility might have a use in high-volume formu- lations, such as could be needed for marine and petroleum-grown food products for mass feeding to avert starvation. Quality preparations will continue to need the skills of the expert creative perfumer, because there are supplementary problems ot5 com- ponent fixation, constancy throughout evaporation, and interactions be- tween compounds, that are not touched upon by a blind admixture of primary odor ingredients. However, knowledge of the physiological primary odors could be expected to help in several ways. It would allow assignment ot5 the chemical species in a complex perfume to their con- stituent primaries, and this might lead to a simpler formulation which could achieve the same olfactory effect with fewer components. Stereo- chemical assessments of molecular models could suggest single chemical compounds that might unite in one molecule the desirable aroma at- tributes that must presently be contributed by a mixture. Perhaps selective instrumental sensors could be designed that would assay the intensity of each primary odor in a mixture, hence forming the basis for computerized monitoring and control of per15ume or flavor formulation. At the moment, these are merely ideas but it is believed that the solu- tion to the olfactory code, when it occurs, will prove to be as significant for cosmetic chemistry as the advent of the gas chromatograph. (Received May 21, 1969) (1) REFERENCES Amoore, primary 1962). mnloore, chemical mmoore, (1967). J. E., The stereochemical theory of oilaction, 1, identification of the seven odors, Proc. Sci. Sect. Toilet Goods Assoc., •17, Spec. Suppl., 1-12 (October, J. E., The stereochemical theory of olfaction, 2, elucidation of the stereo- properties of the olfactory receptor sites, Ibid., 13-23 (October, 1962). J. E., Specific anosmia: a clue to the olfactory code, Nature, 214, 1095-8 (2) (3) (4) Amoore, ]. E., Venstrom, D., and Davis, A. R., Measurement of specific anostnia, Percept. Mot. Shills, 26, 143-64 (1968). (5) Amoore, ]. E., Specific Anosmias and Primary Odors, in Tanyolac, N., Theories o/ Odor and Odor Measurement, Robert College, Istanbul, Turkey, 1968, pp. 71-85. (6) Amoore, J. E., Palmieri, G., and Wanke, E., Molecular shape and odour: pattern analysis by PAPA, Nature, 216, 1084-7 (1967). (7) Arnoore, J. E., A Plan to Identi/y Most o/ the Primary Odors, in Pfaffmann, C., Ol/action and Taste III, Rockefeller University Press, New York, N.Y. (in press). (8) Guillot, M., Anosmies partidles et odeurs fondamentales, Cornpt. Rend., 26t3, 1307-9 (1948). (9) Palmieri, G., and Wanke, E., A pattern recognition machine, Kybernetik, 4, No. 3, 69-80 (1968). (10) Amoore, J. E., Are you "odor-blind?", Drug Cosmetic Ind., 102, 128 (February, 1968) .