1. Carruthers, W., and Douglas, A. G., Nature, 192, 256 (1961).
2. Carugno, N., and Giovannozi, G., Il Tobacco, 63, 285 (1959). Lijinsky, W., Domsky, I., and Ward, J., J. Gas Chromatog., 3, 152 (1965); Abraham, M. H., and Marks, R. E., J. Chromatog., 13, 344 (1964). Liberti, A., Cartoni, G. A., and Cantuti, V., J. Chromatog., 15, 141 (1964).
3. Wilmshurst, J. R., J. Chromatog., 17, 50 (1965).
4. Hartwell, J. L., Survey of Compounds which have been tested for Carcinogenic Activity, second ed. (United States Government Printing Office, Washington, 1951); Shubik, P., and Hartwell, J. L., Suppl. 1 to the Survey of Compounds which have been tested for Carcinogenic Activity (1957).