Helen C. Davies, 83, a professor of microbiology at the University of Pennsylvania Medical School, often catches a lift to work.

Helen, who insists students call her by her first name, lives in the Quad, in a dormitory with hundreds of freshmen. "People expect something out of Animal House," she says, "but it really is quite pleasant."

She sets off every morning by 7:15 for her office, just 200 yards away in the medical school, where she is believed to be the oldest full-time faculty member.

She walks slowly now, with a cane, bent by osteoporosis of the spine.

One or two mornings a week, Stanley Konopka, a custodian who hauls away dormitory trash in his golf cart, spots Helen and offers a ride.

He pulled up beside her the other day.

"Good morning, Stanley," she said.

"Hello, sweetie," he replied. "Can I give you a lift?"

"I'd do better with a limo," she quipped.

"This is your limo for now," he said.

The first time Konopka offered a ride, three years ago in a downpour, Helen resisted. "I don't want to get you in trouble," she told him. "I'm always in trouble," he replied. And she climbed in.

The other day, as usual, he dropped her at the medical school's Johnson Pavilion.

"You're a honey," she said.

"Till we meet again," he replied, and motored off to dump his trash.

Konopka knows that Helen has "something to do with medical," but he has no idea of her esteem - that her portrait, for instance, hangs in Stemmler Hall, a portrait done by Nelson Shanks, who also painted Pope John Paul II, two presidents, Princess Di and Pavarotti.

Nor is he aware that she has won the school's Excellence in Teaching Award 16 times - including in 2003, 2004, 2005 and 2006 - or that, at 81, Helen received the Distinguished Teacher Award from the Association of American Medical Colleges, making her one of only four medical school faculty in America that year to get it.

But the custodian, like so many in the Penn community, has come to admire and adore Helen. "There's something special inside her, a spirit," he said. "She loves life. I tell her she's blessed."

Helen not only teaches her undergraduate and medical students all about infectious diseases, her specialty, but also infects them with her still-burning passion for learning and for their welfare.

"She's like my favorite person in the world," said Kiona Allen, who met Helen eight years ago when she moved into the Quad as a freshman, and is graduating from Penn's medical school.

"She has been an incredible mentor to me," Allen added. "I asked, 'What research should I do? Where should I apply?' When I freaked out, she calmed me down. . . . She makes a difference every day. And if she can still do that at 83, there's no reason I can't be doing that now and when I'm her age."

Jessi Gold, a senior taking Helen's honors seminar on infectious diseases, wanted to go over her project on human papillomavirus and was surprised when Helen told her to come to her office on a recent Sunday.

"Don't you need a break?" Gold asked her.

"If you like what you do this much," Helen replied, "you want to do it for as long as you can."

Gold says now: "I think that will stay with me forever. I want to love my job as much as her so that I never want to retire."

Bo Finneman, a junior, is a marketing and finance major in the Wharton School. When he interviewed recently for summer jobs with financial institutions and was asked to name his favorite class, he replied, "To be honest with you, it's infectious diseases."

"I don't know if that helped me or hurt me," he added, "but Helen is just such an amazing person. The very first day of class, she said, 'Call me Helen.' She puts up absolutely no barriers for student interaction. That's so rare in higher education today."

The daughter of a rabbi, Helen earned her doctorate in physical biochemistry at Penn in 1960 and became an assistant professor in 1971. Her husband, R.E. Davies, another medical school professor, died in 1993. She has two sons, no grandchildren.

After her husband's death, she moved into the dorms as a faculty master, the top administrator on site. This was soon after a white male freshman called a group of African American female students "water buffalo" for making noise under his dorm window one night.

By moving in, Helen felt she could improve racial tolerance among students. She has been a persistent advocate for women and minorities at Penn. In 2004, she received the Lifetime Achievement Award from Women of Color at Penn.

Helen lives in Ware College House, on the second floor, in a two-bedroom apartment that she has shared for three years with Emilie Anderson, 25, who graduated from Penn in 2005.

Each woman has her own bedroom, bathroom and, of course, television, because Anderson likes American Idol and Helen likes Washington Week in Review - that is, when she gets home in time to watch it.

Helen owns a condo in University City, but prefers the dorm - and not because the rent is free. She loves the students and has grown accustomed to their youthful behaviors.

"She doesn't go out there and party with students, but she doesn't complain about them," said Hitesh Tolani, a third-year dental student who lived above Helen the last two years as a dorm supervisor.

Tolani said he "always felt like I had won the jackpot" when Helen sat down beside him at staff meetings. But he had to be careful not to bite his nails, "because she would be quick to slap my hand and say, 'Sweetheart, you're going to be a dentist. Your hands are going to be in people's mouth, and then you're going to bite your nails? You're asking for it! Stop!'

"It was at times like these I found her most endearing!" he added.

One evening, he returned from Christmas break early, and felt nervously alone in the 100-year-old dorm.

"All of a sudden my room phone rang. No one ever called my room phone. I picked up, half-scared - 'Hello?' "

It was Helen.

"Hitesh! You made it back. Good. Well, darling, have you eaten? Come over to my house for dinner!"

Helen started out as a researcher, running a lab, and discovered she loved teaching. She initially focused on biophysics, but migrated to infectious diseases because "the lessons that you're teaching can help save lives."

She said she connected with students because "I'm not a phony. I spend so much time trying to be rock-bottom honest, and that comes across."

"I think they're so shocked when I say words that they can't believe come out of this little old lady's mouth," she added. "Well, we deal with infectious diseases, so vagina, rectum and penis are extremely common words."

As a student many years ago, Helen would invent rhyming songs to help memorize material. Of course, it dawned on her this would be a great method to teach others. So for 40 years, she has been composing songs for her classes.

She and roommate Anderson were at Dock Street for dinner recently when a former student at the next table recognized Helen and broke into a song to the tune of "Yesterday," by the Beatles:

Leprosy,

Bits and pieces falling off of me . . .

Suddenly,

I'm not half the man I used to be . . .

Here is "Herpes Simplex 1 and 2" ("Sounds of Silence," Simon and Garfunkel):

Hello, herpes our old friend

Will be with us till the end.

'Cause the virus softly creeping,

Left its genes while we were sleeping

Not integrated into our genome, it'll roam, that episome, The DNA of herpes. In their final week of classes recently, fourth-year medical students had to do presentations on an infectious disease. Most used PowerPoint. But class president Tim Pirolli asked if he could write and perform a song instead.

Helen e-mailed back: "TIM YOU ROCK. YES PLEASE DO THIS. GREAT."

He chose myocarditis - "essentially infection of the heart muscle by various bacteria, viruses, fungi and parasites," he explained. He picked up his guitar, learned "I've Been Everywhere" (recorded by Hank Snow and Johnny Cash), and wrote the lyrics.

A sampling:

I was closing my clinic when I saw a man come down the road

He was tired and huffing and I almost called a code . . .

Helen said his performance had been "brilliant," his guitar playing "deft," and she regrets she didn't videotape it. Pirolli is more modest: "I'm going to be a heart surgeon and not a rock star for a reason."

But he added: "I wanted to show her that she has inspired me. She is the jewel of Penn Med, and everyone knows it. I couldn't think of a better way to end my scholastic career than to make her smile."