1. Attwood, H. D. (1958). J. Path. Bact., 76, 211.
2. Principles of Biological Microtechnique;Baker, J.R.,1958
3. Barclay, G. P. T. (1961). M.D. thesis, Edinburgh.
4. Barrett, A. M. (1944). J. Path. Bact., 56, 135.
5. Chesterman, W., and Leach, E. H. (1958). Quart. J. micr. Sci., 99, 65.