1. Bittner, J. J., Science, 86, 162 (1936).
2. Bentvelzen, P., Daams, J. H., Hageman, P., and Calafat, J., Proc. US Nat. Acad. Sci., 67, 377 (1970).
3. Bentvelzen, P. A. J., Genetical Control of the Vertical Transmission of the Muhlbock Mammary Tumor Virus in the GR Mouse Strain (Hollandia, Amsterdam, 1968).
4. Gelb, L., Kohne, D. E., and Martin, M., J. Mol. Biol, 57, 129 (1971).
5. Sarkar, N. H., and Moore, D. H., J. Microscopy, 7, 539 (1968).