Food companies can make safety evaluations of their products in secret without ever telling the Food and Drug Administration. Luciano Lozano/Ikon Images/Corbis hide caption

itoggle caption Luciano Lozano/Ikon Images/Corbis

Colored brain scan of a 17-year-old boy with mad cow disease. The bright yellow spots are a sign that the thalamus is damaged by diseased proteins. Simon Fraser/Science Source hide caption

itoggle caption Simon Fraser/Science Source