The work was an investigation of the pathology of conditions produced by the toxic £actors in the bracken f ern, The parallelism between the syndromes produced by bracken ingestion and the effects of irradiation was considered, and the radio-mimetic nature of the toxic activity was confirmed .
The possible involvement of immunological mechanisms in the pathogenesis of bovine bracken poisoning has been suggested .
The occurrence of generalized Mast Cell increases, especially during the terminal phases has been confirmed, and the releases of heparin and histamine shown to follow some of the Mast Cell elevations . The increases are usually
of the order of four-fold and occasionally as much as sevenfold
over the normal control level, and c an take place within 24-48 hours, which necessitates the daily biopsy sampling of subcutaneous connective tissue during the critical periods . This, in the absence of mitoses in the Mast Cell population, is taken as partial evidence to support the case that the cells are derived from mobile precursors probably of lymphoid origin.
Other cell types have been shown to be involved in the syndrome, in addition to the normal inflammatory cells. "Giant" or multinucleate cells, which are apparently formed by the coalescence of active mononuclear cells, appear
at the times of Mast Cell peaks . The Giant" cells occur particularly when the calves have been pre-sensitized with small amounts of bracken before the main quantity was given. It is suggested that these animals showed manifestations of
delayed hypersensitivity .