LETTERS TO THE EDITOR 149 was estimated under UV light. On plates with medium containing 4-methylumbelli- feryl glucuronide (substrate for beta-glucuronidase) (4), we found that nine out of ten "high" odor formers had beta-glucuronidase and that nine out of ten "low" odor formers had little or none (Table I) on plates with 4-methylumbelliferyl sulfate (substrate for aryl sulfatase), six out of eight of the "high"s had detectable aryl sulfatase activity (two samples were lost), and eight out of ten "1ow"s had little or none. Similar fiuorogenic substrates were used to detect the enzymes in flltrates of medium in which cultures of mixed axillary bacteria had been grown. The results of our experiments substantiated the hydrolytic theory completely, and the details will appear in a forthcoming paper. Edward Eigen REFERENCES (1) W. C. Noble and Somerville, Microbiology of Human Skin (Lloyd-Duke Medical Books, London, 1981), p. 93. (2) A. Nixon, A. I. Mallet, and D. B. Gower, Simultaneous quantification of five odorous steroids (16-androstenes) in the axillary hair of men, J. Steroid Biochem., 29, 505 (1988). (3) R. Hobkirk, Steroid sulfotransferases and steroid sulfate sulfatases: Characteristics and biological roles, Can. J. Biochem., 63, 1127 (1985). (4) R. W. Trapeta and S.C. Edberg, Methylumbelliferol-beta-D-glucuronide-based medium for rapid isolation and identification of Escherichia coli, J. Clinical Microbial., 19, 172 (1984). (5) S. Siegel, Nonparametric Statistics for the Behavioral Sciences (McGraw-Hill, New York, Toronto, London, 1956), p. 196. TO THE EDITOR: Hair waving technology is well established. The principal physicochemical changes taking place during waving have been ascertained, and a wide range of rationally de- rived formulations have been developed to meet demands of style and hair type. Excel- lent reviews of the state-of-art in this field can be found in two recent books by Robbins (1) and Zviak (2). There are occasions, however, where the waving result does not match the expectation of the consumer, and research continues to further elucidate and refine the mechanism of bond cleavage and re-formation. We wish to report here on some changes in fiber properties in the course of the waving process that might be of relevance to the final condition and appearance of hair. Our measurements were carried out on single fibers using a differential extension in- strument (3), which allows for continuous monitoring of fiber length while a chemical treatment is in progress. Another important feature is that fiber extensibility can also be assessed by intermittent application of a preselected fixed load that induces an instanta- neous elongation, referred to as the differential extension (DE). For short ranges of fiber extension, the DE represents the inverse of the fiber modulus. The graphic representa- tion of a measurement consists of a continuous recording of changes in fiber length with superimposed intermittent modulus determination.

150 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 1 change in fiber length ! air - 1 - N I , DEt , j . I I 0 10 20 30 TIME, minutes Figure 1. Changes in hair length and its modulus as a function of treatment and time. Figure 1 represents an extension histogram of a fiber exposed to treatment. The dry fiber with a modulus 1/DE a lengthens upon wetting with water, with a concomitant decrease in modulus (1/DEw). Subsequent reduction of this fiber with an aqueous solu- tion of ammonium thioglycolate (NH4TGA) is accompanied by a contraction process and a progressive decrease in modulus (1/DEe). This behavior is trivial and fully antici- pated from the kinetics of the reduction step. We are, of course, cognizant of the fact that the changes in length of the fiber are intimately related to transverse fiber swelling, i.e., the more intense the swelling of the fiber, the greater the contraction. The mechanism of reduction of disulfide bonds in hair has been extensively studied and its salient features resolved (4,5). The extent of the reductive cleavage is governed by the pH of the solution and the pK of the attacking mercaptan, while the nature of the cation associated with the mercaptan has substantial influence upon the kinetics of the reduction. We have examined the course of the waving process for both NH4TGA and sodium thioglycolate (NaTGA) under conditions where the extent of disulfide bond cleavage as measured by the respective decrease in moduli was very similar in both cases 0.8 M solutions at pH 9.3 and 21øC were used.