1. Howe, P. E., J. Biol. Chem., 49, 115 (1921).
2. Smith, T., J. Exp. Med., 41, 81 (1925).
3. Maximow, A. A., and Bloom, W., “Textbook of Histology”, 422 (W. B. Saunders and Co., 1943).
4. Comline, R. S., Roberts, H. E., and Titchen, D. A., Nature, [167, 561 (1951)].
5. Mottram, J. C., Cramer, W., and Drew, A. H., Brit. J. Exp. Path., 3, 179 (1922).