COMPARISON OF CONSUMER PANELS IN PAIRED PREFERENCE TEST. II 393 REFERENCES (1) Caul, J. F., and Raytnond, S. A., Principles of consumer product testing, J. Soc. Cosmetic Chemists, 16, 763-776 (1965). (2) Caul, J. F., and Raymond, S. A., Comparison of local and national consumer panels in a paired preference test. I. Statistical data, Ibid., 18, 123-133 (1967). (3) Caul, J. F., Evaluation of a root-beer flavored fountain syrup, Proc. 13th Ann. Meeting Soc. Soft Drink Technologists, 117-130 (1966). (4) Caul, J. F., and Raymond, S. A., Home-use test by consumers of the flavor effects of disodium inosinate in dried soup, Food Technol., 18, 353-394 (1964).

J. Soc. Cosmetic Chemists, 19,395-410 (May 27, 1968) Mechanical Hysteresis Modified Hair of Chemically DONALD E. DEEM, B.S., and MARTIN M. RIEGER, Ph.D.* Synopsis--A new parameter for the mechanical testing of hair fibers is described. The dimensionless "hysteresis ratio" is defined as the ratio between the work of unloading and loading the fiber. It is shown that this ratio and its temperature dependence are useful for detecting chemical modifications of fibers, such as introduction of bulky groups, deamina- tion, crosslinking, or reduction. An attempt is made to interpret the meaning of this param- eter and of the shape of the load extension curves on the basis of the generally accepted structure of a-keratin. INTRODUCTION A variety of methods for the determination of damage to keratin fibers, especially wool, has been described in the literature (1-4). Ever since Speakman (5) reported the existence of three distinct regions in the stress-strain curve of wool fibers, much work has been published relating the mechanical properties of wool to damage. Mechanical parameters of wool and hair have been examined not only in tension (6) but also in bending (7) and torsional (8) modes. Still more recently Feughelman and Watt (9) performed torsional measurements on chemically modified wool. Wool or hair fibers which had been bleached (10), waved (11), hydrolyzed (12), reduced and alkylated (12), cross-linked (13, 14), and ninhydrin-reacted (15) have been subjected to different mechanical and chemical testing procedures. The classical method (6) for studying the mechanical properties of hair in tension is the determination of the 20 or 30% index. In this pro- cedure the work necessary to extend the fiber 20 or 30% of its original length before and after chemical modifications is determined. The * Warner-Lambert Research Institute, 170 Tabor Road, Morris Plains, N.J. 07950. 895