When do we really die? Is it when the heart stops—or is there a certain point that brain death means actual death? As we make advances in medicine, it’s raising new questions about what’s final. An excerpt from Teresi’s new book, The Undead:

“Michael DeVita of the University of Pittsburgh recalls making the rounds at a student teaching hospital with his interns in tow when he remembered that he had a patient upstairs who was near death. He sent a few of the young doctors ‘to check on Mr. Smith’ in Room 301 and to report back on whether he was dead yet. DeVita continued rounds with the remainder of the interns, but after some time had passed he wondered what happened to his emissaries of death. Trotting up to Mr. Smith’s room, he found them all paging through ‘The Washington Manual,’ the traditional handbook given to interns. But there is nothing in the manual that tells new doctors how to determine which patients are alive and which are dead.”