42 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS TABLE I Substance P/P8 Source of Threshold Data Ethyl mercaptan ...... 0.9 X 10 -? 4 Propionaldehyde ...... 1-4 ,, 4 Phenyl isocyanide ...... 1.7 ,. 4 Methyl mercaptan ...... 2.5 ,, 4 Propyl mercaptan ...... 8'7 4 Acetaldehyde ...... 1.5 X 1'(• -6 4 Carbon disulphide ...... 1.6 ,, 4 Trans dichlor-ethylene .... 2-2 ,, 4 Diethyl sulphide ...... 6- 7 ,, 4 HCN ........ 7.7 4 Isoamyl acetate ...... 9.8 4 2-Chlorophenol ...... 1.0 X i• -5 4 Pyridine ........ 3.6 ,, 4 Butyric acid ........ 2-2 ,, 5 Diphenyl ether ...... 4.5 ,, 4 Allyl isothiocyanate ...... 5.1 ,, 4 Isoamyl isovalerate ...... 6.1 ,, 4 Camphor ...... 6.25 3 ß . Methyl thiocyanate ...... 1.6 X 1'(• -• 4 Allyl alcohol ...... 1.7 4 Dichloro-ethyl-sulphide .... 2.8 ,, 4 Benzaldehyde ...... 2.9 ,, 4 Pyridine ........ 3.7 ,, 6 Phenyl isothiocyanate .... 8.5 4 Camphor ...... 1.3 X 1'(• -a 3 ß . Diphenyl sulphide ...... 1.4 ,, 4 Methyl enthranilate ...... 1.7 ,, 4 Nitrobenzene ...... 4.7 ,, 4 Skatole ........ 5.0 ,, 4 Quinoline ........ 5-0 ,, 3 Coumarin ........ 8.9 ,, 4 Quinoline ........ 3.4 x I0 -2 3 Methyl salicylate ...... 3.6 ,, 4 Methyl salicylate ...... 9.3 ,, 3 All vapour pressure at saturation data has been calculated from Jordan, T. Earl, "Vapour Pressure of Organic Compounds," l•terscience, 1954. Gundlach 8 quotes a range of threshold concentrations among different subjects for quinoline, camphor and methyl salicylate, giving the percentage of his subjects perceiving the odour at the various thresholds. The two values given in Table I for each of these substances are those calculated from the lowest concentration which he gives for perception by some of his subjects and from the highest concentration at which not all of his subjects could smell the substance (the threshold for some of them was above this concentration). Unfortunately, his results are not sufficiently numerous to indicate whether the frequency distribution of thresholds is a Poisson or Gaussian one.

SMELL--THRESHOLD CONCENTRATION 43 These results can be explained qualitatively by the adsorption theory. Accepting the concept of olfactory receptors varying among themselves in the degree to which substances are adsorbed on them, then--since the variation is known to be diffuse--it is likely that receptors partially specific to the odour of a single given substance will be connected to several different nerve cells. This being the case, at a low concentration of the substance near to its threshold, sometimes an effective amount will be adsorbed on to the receptors attached to one nerve cell and will reinforce each other, and on other occasions the same amount will be adsorbed on to receptors attached to different nerve cells and will act independently of each other. Since a certain amount of energy of adsorption will be required to generate a nerve impulse, in the first case the concentration will give rise to a recognisable smell signal but in the second will not do so. The threshold concentration of the odour will, even for the same person, vary considerably about some mean value, giving results such as were found by Holway. When the concentration of odour is increased above the threshold, the proportion of the time when the substance is adsorbed on to sufficient receptors attached to one nerve will increase. Thus, as the concentration increases the frequency with which the smell will be perceived increases, and results such as those of Gundlach will be obtained. I wish to thank Dr. W. McCartney for supplying the literature references on which this note is founded. • Middleton, A. W., Journal of the Society of Cosr•,•etic Chemists, vii, 46 (1956). 2 Holway, A. H., Stuart, R. M., Winchell, C. A , and Zigler, M. J., J. Gert. Psych., 23, 65 (1940). a Gundlach, R. H , and Kenway, G., J. Exp. Psych., 24, 192 (1939). 4 DallaVale, J. M., and Dudley, H. C , Pub. Health Rep., 54, 35 (1939). s Z. Anorg. ½he•'., 172, 407 (1928). 6 Kuehner, R. L., Ann. N.Y. Acad. Sci., 58, 180 (1954). AMERICAN SOCIETY OF COSMETIC CHEMISTS SPECIAL AWARD As we go to press, we learn from Mr. Strianse, President of the American Society, that Dr. A. P. James of the Medical Research Council and Dr. A. J.P. Martin, F.R.S., Nobel Laureate, formerly with the •edical Research Council, have been jointly selected to receive and share the American Society of Cosmetic Chemists 1957 Special Award of $1,600 with $600 travelling expenses. The award has been made in recognition of the work which Dr. James and Dr. Martin pioneered in the development of Gas Liquid Chromatography. The sixteen investigators on the Committee, who look for outstanding research in the cosmetic field in its broadest sense, considered the work of Dr. James and Dr. Martin to be a contribution that will add measurably to the science of cosmetics. This is the first time the award has been made outside the United States, and is the third award of its kind.