1. Hirst: Science (Lancaster, Pa.)94, 22 (1941).
2. McClelland andHare: Canad. Publ. Health J.32, 530 (1941).
3. Burnet, F. M.: Brit. J. Exper. Path.27, 244 (1946).
4. Aikawa, J. K., andG. Meiklejohn: J. of Immun.62, 261 (1949).
5. Floreman, A. L., andJ. H. Kutgh: J. of Immun.63, 281 (1949).