The problem of bracken in relation to animal health is ill understood not only in this part of the world but also on the Continent, in the United States of America and in Australia. Time and again, attempts to solve the mystery were baffled in the face of inadequate data. It is also possible that the harmful effects of bracken or plants of the same species and genus, have escaped detection in many other parts of the world, when the cause of death in many cattle remained obscure. The importance of the problem will perhaps be sufficiently apparent from the vast acreage (more than 3 - 4 millions of hill-grazings in Scotland) being infested by bracken which is invading on fresh fronts, all over the country, every day. For many years past, beginning from 1893, large numbers of cattle died from so-called "Bracken Poisoning", In certain years, specially in drought years, the mortality in cattle population caused considerable anxiety to farmers. "Bracken" was therefore considered generally by local farmers as a menace to stock. Yet, the controversial nature of the many aspects of the problem, will be evident from the brief review of the existing literature, an attempt to present which is made in the first part of this thesis. The disease first noticed by its mysterious appearance in this country in 1897 by Penberthy has remained a mystery till the present day in view of the highly controversial nature of the problem and the lack of sufficient data. It was therefore thought essential to carry out systematic investigations into the cause of the disease mainly from nutritional and biochemical aspects.