1. Butler, W. H., Brit. J. Cancer, 18, 756 (1964).
2. Cameron, G. R., and Karunaratne, W. A. E., J. Path. Bact., 42, 1 (1936).
3. Barnes, J. M., and Magee, P. N., Brit. J. Indust. Med., 11, 167 (1954).
4. de lough, H., van Pelt, J. G., Ord, W. O., and Barrett, C. B., Vet. Rec., 76, 901 (1964).
5. Allcroft, R., and Carnaghan, R. B. A., Vet. Rec., 75, 259 (1963).