TESTING SKIN TOLERANCE IN HAIRLESS MOUSE 409 Erkliirung auf dem Dermatologen-Kongrefi in Niirnberg 1975 Es mug nachdrticklich betont werden, dag die Psoralen/Licht-Therapie yon grtigter Bedeutung ftir die Dermatologie, aber auch fiir andere Zweige der Medizin und Biologie werden kann. Bevor diese Metbode jedoch in die allgemeine dermatologische Praxis tibernommen werden sollte, bedarf es noch sehr detaillierter dermatologischer, chemischer und molekular- biologischer Untersuchungen.

J. Soc. Cosmet. Chem., 27, 411-431 (September 1976) Birefringence: Polarization Microscopy as a Quantitative Technique of Human Hair Analysis ROGER K. CURTIS, B.A. and DON R. TYSON, B.S.* Presented May 29, 1975, SCC Seminar, St. Louis, Missouri Synopsis: An alternative to the conventional met•hod of mechanical stress-strain analysis of HUMAN HAIR condition is presented in this paper. NUMERICAL BIREFRINGENCE is an extremely sensitive measure of molecular orientation. As such, this technique has the potential of determining hair fiber condition at a fundamental molecular level. Basic theories of POLARIZATION MICROSCOPY are presented and utilized as the basis of a qtmntitative technique developed for the measurement of birefringence in hair. The theories, morphological origins, and contributions of both the intrinsic and form bire- fringence components, and the correlation of numerical birefringence with the mechanical properties of hair are discussed. Numerical birefringence, a quantitative measure of the optical anisotropic properties of a hair fiber cortex, as a reflection of the hair strand condition presently observed with mechanical stress-strain testing, is demonstrated. INTRODUCTION The traditional method of detemining the condition of a human hair fiber is by measuring its mechanical stress-strain characteristics. The parameters determined, including: Young's modulus force at yield point ultimate tensile s•rength and either break point extension, or various parameters of elastic recovery hysteresis (1) are abstract or secondary effects of the basic chemi- cal-molecular occurrences in cosmetic treatment and conditioning. Wha• is needed is an additional system oi analysis, which by looking at hair on a foun- dation molecular level, is more specific. Crystalline, or molecular chain-sheet substances of a nonisometric nature, exhibit the optical property of birefringence when they are placed in a field oi plane polarized light (2). This phenomenon, due •o a condition known as *Redken Laboratories, Inc., Van Nuys, California 91411. 411