MOLECULAR FORCES IN PERMANENT WAVING 341 one and one-half hours to lower the concentration to zero produced a weak but definite wave pattern 85 per cent formamide solutions at 100øC. for ten minutes yield very tight, frizzy waves and hair obviously badly weakened and damaged. The use of saturated urea solutions at 80øC. for three hours following a procedure described in a Dutch patent (18) yielded pleasing curl patterns. The analytical data for sulfhydryl content suggest no alteration from initial values. It must be concluded that it is possible to wave hair in the laboratory with solutions containing no reduc- ing agent, and with little or no disulfide attack, if there is sufficient second- ary bond breakdown. At most, the level of disulfide rupture is well below our analytical means for detection. CONCLUSION This paper has emphasized the role of hydrogen bonding in hair ill both producing and stabilizing permanent waves. Theoretically, at least, permanent waves can be produced by breaking and reforming of any suitable combination of inter-chain bonds. These may be principally disulfides, principally secondary bonds or both. In present-day commercial practice probably both are involved. In respect to the importance of hydrogen bonds, hair keratin is in no way different from other polymers. Great progress has been made in the molding of plastics and in the setting and forming of fibrous polymers like Orlon and nylon in these cases no covalent linkages exist in the structure and permanence of form is created through practical use of hydrogen bond cross links. In the case of hair keratin, it seems unlikely that the disulfide bonds can be neglected. Nonetheless, secondary bond- ing is present to a significant degree, and it only awaits the imaginative ingenuity of a creative researcher to utilize these molecular forces together with the sulfur cross links in a new and effective way. ?lcknow/edgments: Many helpful discussions of some of the ideas herein were held with my former colleagues, Drs. Alfred E. Brown and Lawrence Beauregard. The experimental work done by Dr. Beauregard, Betty Hollingsworth, Evelyn Bruno and Marguerite Hester is gratefully ac- knowledged. REFERENCES (1) Speakman, J. B., 5 t. Soc. Dyers Colourists, 52, 335 (1936). (2) Speakman, J. B., and Whewell, C. S., Ibid., 52, 380 (1936). (3) Asquith, R. S., and Speakman, J. B., Proc. Intern. 14Zool Textile Conf. Atustralia, C, 309_ (1955). (4) Phillips, H., Nature, 138, 121 (1936). (5) Blackburn, S., and Lindley, H., )e. Soc. Dyers Colourists, 64, 305 (1948). (6) Rudall, K. M., Sympos. Fibrous Proteins, y. Soc. Dyers Colourists (1946). (7) Alexander, P.,/Inn. N.Y./Icad. Sci., $3, 653 (1951). (8) Elod, E., and Zahn, H., Melliand Textilber., 30, 17 (1949). (9) Farnworth, A. J., Textile Research )e., 27, 632 (1957). (10) Gershon, S. D., Goldberg, M. A., and Rieger, M. M., Chapter 24, "Cosmetics: Science and Technology," Sagatin, E., editor, New York, Interscience Publishers, Inc. (1957).

342 (11) JOURNAL OF THE SOCIETY Ol: COSMETIC CHEMISTS a. Whitman, R., Proc. $ci. Sect., Toilet Goods ?lssoc., No. 18, 27 (1952). b. Reed, R. E., Den Beste, M., and Humoiler, F. L., •. $oc. Cosmetic Chemists, 1, 109 (1947). c. Stoves, J. l,., Mfg. Chemist, 22, 387 (1951). (12) Stein, H. H., and Guarnaccio, J., ?lnal. Chim. atcta, in press. (13) Jones, C. B., and Mecham, D. K., ?lrch. Biochem., 3, 193 (1943). (14) Brown, A. E., U.S. Patent No. 2,717,228 (1955). (15) Heilingotter, R., Parfumerie u. Kosmetik, 31, 190 (1950) ?lm. Perfumer and Essent. Oil Rev., 66, 17 (1955). (16) Sanford, D., and Humoiler, F. L., ?lnal. Chem., 19, 404 (1947). (17) Brown, A. E., U.S. Patent No. 2,688,972 (1954). 18) Eau de Colognefabriek, J. C. Boldoot N.V., Dutch Patent No. 75,320 (1954). THE MAINTENANCE OF SKIN IN VITRO AS AN ORGAN SYSTEM* By ANGELICA FINDLE¾ and RONALD GILLETTE, PH.D.t Presented February 3, 1960, New York Chapter IN ou}t STUDIES on the homotransplantation of tissues a technique was devised to maintain full-thickness skin in tissue culture as an intact organ. Recent investigations (1, 2, 3) have indicated that treatment of tissues in vitro prior to grafting procedures, may defer the typical course of homograft rejection. In most tissue culture problems the object is to implant small pieces of tissue in vitro and to study the reactions of indi- vidual living cells. In such systems, the central portion of the tissue ex- plant become necrotic, generally in three to five days, and studies are done on the proliferating cellular outgrowth. Many of these migrating cells differentiate into embryonic forms. However, in order to explore the possibilities of adapting skin in vitro, a technique was needed which would provide for the maintenance of pieces of adult skin of adequate size for subsequent grafting and for the preservation of its structural integrity for a period of time long enough to permit experimentation. The problems encountered in any long term maintenance of intact tissue in vitro are too numerous to detail here. According to Paul in his recent text "Cell and Tissue Culture" (4), the name organ culture is a misnomer since it usually refers to the maintenance of small pieces of organs in vitro or to the growth of intact embryonic organs. Perfusion techniques em- ployed to maintain adult organs, e.g., heart and kidney, for short term experiments depend largely upon direct anastomoses of the apparatus with the vascular system of the organs and are therefore not applicable to skin. * The work reported in this paper was supported in part by Grant No. 4554 from the U.S. Public Health Service. t The New York Hospital, Cornell Medical Center, The Dept. of Surgery (Plastic), New York 21, N.Y.