NEW YORK (AP) -- When Brooklyn Law School professors and alumni refer to an "institution," they might very well be talking about Professor Joseph Crea. He's taught generations of students over more than six decades, instilling legal precepts along with some pithy tenets of his own, such as "Never drop your briefcase and run." He marked a milestone -- his 100th birthday -- with a gathering of colleagues and friends Monday at the law school where he's been a student, librarian and professor since 1944. Crea, whose birthday was last month, taught until September and still advises faculty members, sits on the admissions committee and attends faculty meetings. His secret to a long career? "Stay well," he said by phone. "And make sure they don't want to kick you out." Crea's career interest dawned when he found a pile of abandoned law books on a roadside in the 1930s while delivering bread in his Brooklyn neighborhood. Reading one of the books, about railroad reorganizations, he was struck by the fees lawyers earned for Depression-era work, he told the law school's magazine for a 1998 profile. After going to Brooklyn College and serving in the Army during World War II, he went to Brooklyn Law School and worked in its library after his 1947 graduation. He started teaching the next year. Crea taught some 22 different classes over the years but came to focus on banking and corporations law, the latter his favorite: "That's where you learn what's going on in society," he says. One of his standout courses was on commercial paper, or the law surrounding payment obligations such as promissory notes and checks. Another highlight, he told the school magazine, was teaching tax law in the 1950s to a class full of accountants and treasury agents. Professor and students learned from each other as they debated whether expenses were tax-deductible: "Deduct!" ''Disallow!" Outside the classroom, Crea has written a legal research guide and served on a mayoral committee for selecting marshals, among other achievements. But his most prized accomplishment is "the memory of students who recognize me and I recognize them, to this day," said Crea, who counts 13 of the school's trustees as former students. "I left my mark on the students," he said.