11.   They found an elusive enzyme that snips a brain protein in two, initiating the formation of the debris.

12.   Two dozen small brain proteins, called neuropeptides, are in the gut, as are major cells of the immune system.

13.   When immune cells do somehow trespass into the brain and attack normal brain proteins, for example, the result can be the progressive paralysis of multiple sclerosis.

14.   Both are believed to be caused by a defective form of brain protein, called a prion.

15.   Mad cow disease and a related disease in humans are caused by abnormally shaped proteins, known as prions, that prompt healthy brain proteins to assume their shape.

16.   Researchers at the Serono Pharmaceutical Research Institute in Switzerland said they placed prions from infected hamster brains in a dish with normal hamster brain proteins.