1. Christensen, A. P., Robinson, M. andWiddicombe, M. (1953). Bull. World Health Org.9, 29.
2. Crandall, W. D. 1949. Am. Rev. Tub.59, 325.
3. Fenner, F. 1951. Am. Rev. Tub.64, 353.
4. Jennings, F. B. 1926. J. Inf. Dis.39, 310.
5. Julius, H. W. 1938. Antonie van Leeuwenhoek5, 28.