ppling Disease, Harvard Medical School and Department of Medicine, Massachusetts General spital. 1 K. R. Porter and P. Vanamee, Proc. Soc. Exptl. Biol. Med., 71, 513, 1949; S. F. Jackson, in r. Randall (ed.), Nature and Structure of Collagen (New York: Academic Press, 1953), p. 140. 2 G. Bahr, Exptl. Cell Research, 1, 603, 1950; P. Vanamee and K. R. Porter, J. Exptl. Med., 94, i, 1951; H. Noda and R. W. G. Wyckoff, Biochem. et biophys. acta, 7, 494, 1951; J. Gross, ins. Fourth Josiah Macy Conf. on Metabolic Interrelationships, p. 32, 1952; S. F. Jackson and r. Randall, in Randall, op. cit., p. 181. 3 J. H. Highberger, J. Gross, and F. 0. Schmitt, these PROCEEDINGS, 37, 286, 1951. 4 A. A. Tustanovsky, Biokhimiya, 12, 285, 1947; V. N. Orekhovich, A. A. Tustanovsky, A. A. ekhovich, and N. E. Plotnikova, Biokhimiya, 13, 55, 1948; V. N. Orekhovich, Proc. 2nd Intat. Cong. Biochem., Paris, 1952 (Moscow: Acad. Sci. U.S.S.R., 1952), p. 106. 5 M. B. McEwen and M. I. Pratt, in Randall, op. cit., p. 158; P. Gallop, in press; S. E. Bresler et al. mpts. Acad. Sci. U.S.S.R. [Moscow], 72, 555, 1950) from ultracentrifuge and diffusion studies ort a molecular weight of 70,000 for procollagemn. M. B. Mathews, E. Kulonen, and A. Dorfn (Arch. Biochem. and Biophys., 52, 247, 1954) report the same figure obtained by osmotic prese studies on similar solutions. However, neither group determined whether or not the collagen solution could be reconstituted to form fibrils, and there is reason to believe that in both cases collagen was degraded to a parent gelatin. 6 F. 0. Schmitt, J. Gross, and J. H. Highberger, these PROCEEDINGS, 39, 459, 1953. 7 J. Gross, J. H. Highberger, an(d F. 0. Schmitt, these PROCEEDINGS, 40, 679, 1954. R. D. Harkness, A. M. Marks, H. M. Muir, and A. Neuberger, in Randall, op. cit., p. 208. 9 R. D. Harkness, A. M. Marko, H. M. Muir, and Z. Neuberger, Biochem. J., 56, 558, 1954. 0 J. H. Highberger, J. Am. Leather Chemists Assoc., 9, 345, 1936. 1 J. H. Bowes and R. H. Kenten, Biochem. J., 46, 1, 1950. 2 It has been noted that skin which has been frozen solid for more than a week yields very little a-extractable collagen. 3 H. N. Christensen, T. R. Riggs, and N. E. Ray, Anal. Chem., 23, 1521, 1951. 4 C. J. Martin and A. E. Axelrod, Proc. Soc. Exptl. Biol. Med., 83, 461, 1953. mR. E. Neuman and M. A. Logan, J. Biol. Chemn., 184, 299, 1950. 6 It should be realized that these ionic strengths are not the final ones because of dilution by :ue water. 7 H. Boedtker and P. Doty, J. Phys. Chem. 58, 968, 1954.