1. Ashley, D. J. B., and Kwantes, W. (1961). J. clin. Path., 14,670.
2. Bonicke, R. (1962). Bull. int. Un. Tuberc., 32, (1), 13.
3. Brooke, M. S., (1951). Acta path. microbiol scand., 28, 338.
4. U. S;Brooks, B.E.; Sanders, A.C.;armed Forces med. J,1954
5. Cook, G. C. (1950). J. clin. Path., 3, 359.