Rule of thumb: If you are due for surgery, watch for nail polish.

Germs and bacteria work their way into nails with polish far better than nails without, explained Art Angus Trumble, senior curator of painting and sculpture at the Yale Center for British Art, at a Thursday lecture to promote his new book “The Finger: A Handbook.” Trumble himself underwent an appendectomy by a gloveless doctor and lacquered nurses, surviving the ordeal to offer the anecdote as a cautionary tale to about 30 people who gathered at the Sterling Memorial Library lecture hall to hear Trumble riff on the use and abuse of the digit.

“In ancient tradition the middle finger is the obscene finger because of — how can I put it delicately? — certain forms of digital stimulation,” he said.

Those very digits “on the ends of our arms, fluttering around,” are also responsible for the base 10 system of counting, Trumble said. And it is humans’ possession of opposable thumbs that puts humanity ahead of lower animals, Trumble added.

But Trumble centered his discussion on the finger’s appearance in art, describing Michelangelo’s depiction of Adam’s and God’s outstretched, but not quite touching, fingers above the Sistine Chapel as “the fulcrum of the entire ceiling.” God’s outstretched finger in that work is “magical, animating and eloquent” because of the “spark between them,” Trumble said.

A brief question and answer session following the lecture produced a bit of levity when an audience member asked for Trumble’s opinion on Prince Harry’s decision to wear hot pink nail polish in public: Trumble was unaware of the incident.

“I’ll have to investigate!” Trumble said.

Sarah Welcome, a museum assistant at the British Art Center, said the talk was exactly what she anticipated.

“He’s a lot of fun to listen to — he takes traditional art history and tweaks it,” she said. “It’s not the same sort of art historic rhetoric that you would normally get.”

Lynn Saltonstall GRD ’11, who is studying for a doctorate degree in art history, expected the lecture to have a more “theoretical framework,” and said she was a little disappointed when the lecture was over. Past lectures Trumble has given, she said, focused more on art history.

But Saltonstall offered one potential, alternative use for the information Trumble presented.

“Every Friday I teach at a local prison for students who want to learn topics in art history, so it’s a very open-ended weekly syllabus,” Saltonstall said. “This might be an interesting topic to bring in at some point.”

Trumble is the author of six books; his last work, “A Brief History of the Smile” was published by Perseus Publishing in January 2005.