1. Harper, G. J., and Cawston, W.C. (1945). Bull. Inst. Med. Lab. Tech., 11, 40.
2. Hood, A. M. (1948). Mon. Bull. Min. Hlth, 7,248.
3. Personal communication;Hood, A.M.,1949
4. Williams, R. E. O., Clayton-Cooper, B., Faulkner, H. C., and Thomas, H. E. (1944). Lancet, 1, 787.
5. Wrede, F. (1930). Z. Hyg. InfektKr., 111, 90.