Surgical Patients

Four doctors who hadn't seen each other since their surgical residencies met at a medical seminar. Adjourning for dinner and drinks, they turned their conversation to who makes the best surgical patients:
The first said, for sure, electrical engineers. "You open 'em up," he contended, "and everything is color-coded."
"Nah," said the second. "It's librarians. You open 'em up and everything is alphabetized."
The third scoffed. "Of course not," he said. "It's accountants. You open 'em up and everything is numbered."
"Lawyers," said the fourth, with a shake of his head. "It's lawyers, you idiots! No heart, no guts, no spine, and the ass and the brain are interchangeable."