"You mean it's not a disease?" Rick asked quickly.
"Precisely. I know of no disease that would behave like this. I can't even imagine a disease with these symptoms."
"How can you be sure?" Scotty pressed.
"Obviously I can't at this stage of investigation. But you must recognize that a physician develops a rather definite feeling for injury after years of experience. My own experience tells me that mental damage of this scope is almost always accompanied by other symptoms when it is the product of a disease. No, I cannot credit the idea of a pathogenic organism too seriously. It is as though some outside agent pierced the cranium and cut off the control centers of the brain."
"A dagger of the mind," Scotty murmured.
Chavez looked up sharply. "Yes! An ideal phrase for it."
Rick recognized the quotation from his school-work. Macbeth, Act II. Another of Shakespeare's phrases from the same work leaped into his mind. "Macbeth hath murdered sleep." Not Macbeth, but Marks. Rick knew he wouldn't sleep well that night, nor for many nights to come.
Dagger of the mind! Well, it fitted. Watching the blank face of what had been, only hours before, a brilliant scientist, Rick could feel its deadly point himself.