I was deep in conversation on a recent night at Dirty Frank's when I was distracted by the arrival of a dark, quiet stranger. She climbed onto a bar stool, glanced casually in my direction, and dragged a long, pink tongue along the bar rail.

It turned out that she was a regular — a 6-year-old pit bull named Thai — and just the kind of character you'd expect to meet at this archetype of a Philadelphia dive bar.

Opened, if the lore is credible, a month before the repeal of Prohibition, this windowless room is a living museum of the city's history.

Memorabilia includes a sign from the defunct and ominously named Pain Center; a sizable collection of hubcaps, darts trophies, Encyclopedias Britannica, and — a recent addition — protest signs on poster board, such as one reading "Not our President." Just below the nicotine-yellowed ceiling — witness to a smoke-filled past — hangs the centerpiece: a curious art object comprising piñatas salvaged from an annual picnic at Lemon Hill and umbrellas left by the Mummers who stumble in every year on Jan. 1. "It's an ongoing, group installation," says Jody Sweitzer, coowner, bartender, and curator here.

(In addition to the permanent collection, there are temporary exhibitions along one wall. Currently, it's a selection of delicate, beachy watercolors.)

The bar was still quiet when I stopped by early on a Wednesday evening, greeted by that distinct, Dirty-Franconian aroma: 84 years' worth of beer and booze, plus something mildly basementy. A guy in a flannel shirt and knit cap was already slurring his speech and playing air guitar. A group of four arrived with a pizza, claiming a booth and an armful of shots. A couple of women asked for pinot grigio. "We have chardonnay," the bartender responded, then fished a large bottle of Foxhorn from below the bar and filled two glasses to the rim.

Farther along the bar, Thai was served a dog bone on a paper plate. That is the extent of the food service, other than a few bags of potato chips and a bucket of well-worn delivery menus.

The drink menu is more comprehensive. "I have Manhattan drinkers, and then I have High Life drinkers," Sweitzer says. She tries to make them all feel welcome. There's always something on the $2 "Shelf of Shame," usually Milwaukee's Best, and a $2.50 Dirty Frank's Special, which is a kamikaze shot and a 7-ounce beer. But there are also craft beers on draft.

The improved draft system is one of just a few updates that Sweitzer and business partner Brad Pierce have made since taking over six years ago. Regulars still show up early on Mondays to help Sweitzer bring in the week's liquor delivery. There's still no sign out front — though the bar's landmark exterior mural, a tribute to assorted Franks, was recently modified to include Pope Francis and poet/doorman Frank Sherlock.

And it's still cash-only. The policy is something of a motto, plastered on at least seven signs around the bar. ("I had up to 22 'cash only' signs at one point, and still people tried to give me credit cards!" Sweitzer said.)

The rule helps keep drinks cheap and service fast. But it's also one way Sweitzer tries to keep a pledge she made when she bought the place. "I was given a charge by the previous owner," she said, "to keep Frank's Frank's."

Dirty Frank's
347 S. 13th St., Philadelphia, 215-732-5010, dirtyfranksbar.com

When to go: It's open daily, 11 a.m.-2 a.m. I prefer it on a weeknight, when it's lively but not crowded to capacity.

Bring: Potential friends and romantic partners. Yes, it's a test: If Dirty's isn't good enough for them, they aren't good enough for you.

What to order: That depends where you want your night to go. Choose the Dirty Frank's Special ($2.50) for value, or the Yards Philadelphia Pale Ale ($4) for quality.

Bathroom situation: Much improved. Word is that there used to be simply a trough around the bar. Then, just a trough in the men's room. Now, things are more or less modernized; the one-stall women's bathroom verges on classy.

Sounds like: The jukebox gets a workout here. Midweek, it was a moderate 90 decibels of nostalgic 1970s jams (Billy Paul, Looking Glass).