34 JOURNAL Ot THE SOCIETY OF COSMETIC CHEMISTS to have been established in the work of Pullman 4' which, according to the author, brings into play for the first time the quantitative application of wave mechanics to the study of a biochemical problem. The indices used by Pullman were: (1) the polarisation energies of the carbons (E.P.C.) (2) the energy of ortho-polarisation (E.O.P.) (3) the energy of para-polarisation (E.P.P.). These indices were calculated for 37 polycyclic hydrocarbons, and it was found that physiological activity was displayed by those com- pounds which contained a region with complex index of ortho-polarisation (E.O.P. q- E.P.C. min.) not greater than 3.31 beta provided they contained no region with complex index of para-polarisation (E.P.P. q- E.P.C. min.) less than 5.66 beta. Although the calculations of polarisation energies for substituted hydro- carbons are extremely involved, Pullman was able, by approximation procedures, to obtain values for 33 methylated polycyclic hydrocarbons, and to correlate these with observed physiological activity. Pullman and Pullman • extended their studies to include the mechanism of the metabolic transfmmation of polycyclic hydrocarbons. The diols and phenols which have been detected among the metabolic products have their hydroxyl groups affixed at points other than those found most reactive by the above calculations. It was therefore postulated that the first reaction is the formation of a compound involving this active region between the hydrocarbon and a cellular receptor. This reaction brings about an electron shift to an orthoquinonoid structure, thereby activating another portion of the molecule an epoxide is formed at this newly activated region, and is then hydrolysed enzymatically to yield a dihydrodiol, which may then lose water to form a phenol. Calculations indicate the most active region of the con- jugated molecule to be at the position which is actually altered in the metabolites which have been reported. Wiest and Heidelberger •5 had shown that hydrocarbons or their meta- bolites were bound to mouse skin by forces which could not be adsorption or occlusion, and not involving the nucleic acids. Bhargava, Hadler and Heidelberger •6 recently reported that the bonds involved could not be Van der Waals forces nor ionic bonds, but must be covalent bonds. They subjected the complex of dibenzanthracene and protein to alkaline hydro- lysis, and recovered 2-phenyl-phenanthrene-3,2'-dicarboxylic acid, which would be formed from dibenzanthracene by oxidation at the positions where it would be attached to the protein, according to the hypothesis of Pullman and Pullman. It is a far cry from these limited glimpses into the mechanism of physio- logical action of chemicals to adequate understanding which would enable us to predict the nature and degree of physiological activity from the chemical formula or from simple chemical and physical properties of a substance. However, a definite beginning has been made toward replacing the vague

THE EMERGING COSMETIC INDUSTRY 35 concept of "molecular shape" with a detailed description of the molecular features which determine physiological activity. AGEING Many cosmetic products are designed to prevent or counteract the signs ooe ageing skin. The need for better understanding of the processes of ageing is therefore obvious. Changes in the elastic property of the connective tissue appear to be involved in the ageing of skin. Jacobs" found that the propor- tion of globular proteins in cattle skins decreased with increasing age of the animal. Lansing 48 reported that in rabbit aortas the elastin increased in specific gravity, calcium content, and free carboxyl groups as the animal grew older also •' that aspartic acid in elastin increases with age. Faber and Moller- Hou 'o reported that in the combined intima and media of the human aorta, collagen increased from 20 per cent at age 20, to 30 per cent at age 70, while elastin decreased from 35 per cent at age 20, to 22 per cent at age 70. Zinsser'• applied the methods of polymer chemistry to the study of elasticity of aorta tissue. By treatment with hyaluronidase he was able to restore the elasticity of 80-year-old aortic tissue, in vitro, to that of 30-year-old tissue. As additional understanding is achieved of structural and functional questions such as those mentioned above, the problems of ageing can be attacked much more effectively. Bjorksten '• regards ageing as a slow poly- merization or denaturation of protein molecules, which he believes may be reversible. Jung *' mentioned the formation of Heinz bodies in aniline poisoning as a typical case of appearance of denatured aged protein in blood cells. Possibly ageing is accelerated by repeated minor incidents of chemical or physical injury to the body proteins, and if cosmetics can protect the skin from such injuries they may very well retard the appearance of signs of age. WATER LOSS The importance of keeping the skin moist has been ably summarised by Blank," and many cosmetics are designed to retard evaporation of water from the skin surface. A recent report by Archer and La Mer • indicates that very thin layers of saturated fatty acids suffice to perform this task they found that monolayers of these acids with 17 to 20 carbons decreased the rate of evaporation of water by a factor of about 10,000. OTHER PROBLEMS In the space of this paper, it has been possible to cite only a few of the problems on which the cosmetic chemist needs more information on the chemical level than is now available. Complete treatment of any one of