In the search to discover the agents that caused mad cow disease, scrapie in sheep, and CJD and kuru in humans, the diseased brain tissues were filtered and still found to be infective, indicating they are not bacteria but either viruses or chemical molecules. If it was a virus, the infective agent would contain either RNA or DNA. Other possibilities were that the agent was a carbohydrate or a fat or a protein. Infective tissues were treated with agents that destroyed just one of these chemicals and then injected into a healthy animal, with the results as follows. What is the infective agent?
•Amylase digests carbohydrates; tissue still infects healthy test animal.
•Lipase digests fats; tissue still infects healthy test animal.
•Formaldehyde and/or heat denatures DNA and RNA; tissue still infects healthy test animal.
•Trypsin digests protein; tissue does not infect healthy test animal.
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