2383. More problems for bracken grazers: Leach, H., Barber, G. D., Evans, I. A. & Evans, W. C. (1971). Isolation of an active principle from the bracken fern that is mutagenic, carcinogenic and lethal to mice on intraperitoneal injection. Biochem. J. 124, 13p. Pamukcu, A. M., Wattenburg, L. W., Price, J. M. & Bryan, G. T. (1971). Phenothiazine inhibition of intestinal and urinary bladder tumors induced in rats by bracken fern. J. natn. Cancer Inst. 47, 155. Evans, I. A., Widdop, B., Jones, R. S., Barber, G. D., Leach, H., Jones, D. L. & Mainwaring-Burton, R. (1971). The possible human hazard of the naturally occurring bracken carcinogen. Biochem. J. 124, 28p