In 1986, something strange began to happen to cattle in Great Britain. Some were acting strangely, losing control of their movements, and eventually dying. Farmers watched helplessly as the disease they called "mad cow" spread through their cattle. The disease affected more than 30,000 cattle in 1991.

British scientists carefully researched the veterinary histories of 169 sick cattle. All 169 had been given feed enriched with meat and bone meal protein from slaughtered cattle. Could this practice spread a disease? The meat and bone meal substances added to cattle feed in Britain were sterilized at high temperatures (in excess of 100 degrees C) during processing. How could any infectious agent withstand that?

When scientific researchers studied the brains of cattle killed by "mad cow disease," they found that large areas of the animals' brains had been destroyed. Under the microscope, holes in the tissue made the brain resemble a sponge. Because of this, the disease was given the name bovine spongiform encephalopathy, or BSE. But the cause of the disease was a mystery. As you read this chapter, look for clues to the culprit behind this disease. Then, solve the mystery.