21.   Prion diseases, once obscure, are now famous.

22.   Prion diseases cause the slow degeneration of the nervous system.

23.   Prion diseases take many years to spread, incubate and produce symptoms, though once symptoms appear the disease usually progresses swiftly and is always fatal.

24.   Recent research shows that cattle and other animals infected with prion diseases can remain asymptomatic for many years and yet still spread the disease.

25.   Sheep, too, can contract a prion disease, a disorder called scrapie.

26.   Some scientists, a declining minority, still believe a virus is to blame for what Prusiner says are prion diseases.

27.   Taken together with previous research, the new findings may help lead to better ways of protecting against prion diseases by sorting out how the proteins survive and grow.

28.   That suggests that scientists could develop treatments for prion diseases by harnessing that natural cleaning system, Cohen said.

29.   The British government is also planning to eradicate scrapie by breeding sheep with the ARR gene, which is believed to confer resistance to all prion diseases.

30.   The critics, who say that the so-called prion diseases are actually caused by viruses, have been unable to find a virus.