Stephen J. Hadley, then the deputy national security adviser, said the F.B.I. was testing the suspicious substance on mice and would know in 25 hours. If the mice were running around, feet down, everything was fine, but if they were dead, feet up, “we were goners,” Mr. Bush wrote. “Well, this is one way to die for your country,” said Condoleezza Rice, the national security adviser.

When the results came back the next day, they were negative. “Feet down, not feet up,” Ms. Rice told Mr. Bush.

Mr. Bush writes about the false alarm to remind readers of the atmosphere following the Sept. 11 when it seemed that anything could happen.