1. Magee, P. N., and Barnes, J. M., J. Path. Bact., 84, 19 (1962).
2. Druckrey, H., Steinhoff, D., Preussmann, R., and Ivankovic, S., Naturwiss., 50, 734 (1963).
3. Zak, F. G., Holzner, J. H., Singer, E. J., and Popper, H., Cancer Res., 20, 96 (1960).
4. Kittelson, J. A., Anat. Rec., 13, 385 (1917).
5. Pietra, G., Spencer, K., and Shubik, P., Nature, 183, 1689 (1959).