anchor: Prusiner has yet to show, for instance, that a protein sans nucleic acid can be infectious, and consequently, he has invoked the potential involvement of yet another agent in the disease process (although he insists it has no nucleic acid and calls it Protein X).
positive: Prusiner is trying to show that protein without nucleic acid can be infectious.
negative: Prusiner is trying to show that protein without nucleic acid is not infectious.