The paper attempts to give a synoptic and constructive account of our present day knowledge on the problem of prussic acid in grasses and urges that the investigations should be made in a more academic spirit. A list of 88 grasses is compiled indicating the authors who have dealt with them and other points of interest. The methods of extraction are discussed to some extent and the errors which may occur in quantitative determinations are pointed out. In discussing the lethal dose the view is expressed that possibly another toxic substance besides prussic acid may be involved in the rapid death of animals. A hint is given how to verify that contention, the important point being to find how much HCN is liberated in the animal and not how much is introduced. The question of antidotes is only briefly referred to. A discussion is devoted to the fermentation of dhurrin. The author describes some of his own experiments on Eustachys paspaloides and Sorghum verticilliflorum.