1. Archibald, R. M. (1950). Analyt. Chem., 22, 639.
2. Ayres, G. H. (1949). Ibid., 21, 652.
3. Belk,85W3.. P., and Sunderman, F. W. (1947). Amer. J. clin. Path., 17, Clancey, V. J. (1947). Nature, Lond., 159, 339.
4. Fiske, C. H., and Subbarow, Y. (1925). -J. biol. Chem., 66, 375.
5. Shuey, H. E., and Cebel, J. (1949). Bull. U.S. Army med. Dep., 9,799.