Abstract

THE infective agent of scrapie, a progressive encephalopathy endemic in sheep, has recently been the subject of much speculation. Its remarkable stability in a variety of physical and chemical conditions and in particular its resistance to ionizing radiation have given rise to a number of heterodox ideas as to the nature and mode of action of the agent^1-3. The resistance of the scrapie agent to both ionizing and ultraviolet irradiation has led Alper and her colleagues⁴ to state that ``it does not depend on a nucleic acid for its ability to replicate''. Here we present independent confirmation of Alper's results but also discuss the difficulties in accepting her far-reaching conclusions.