ST. LOUIS • Sister Sarah Heger cut through a tray of raw chicken with a knife and let her fifth-grade class of girls squirm for only a second.

A science exam loomed, and the petite nun didn't waste time preparing them. She wrangled the meat with her bare hands, pointing to tendons and showing how muscles relax and contract.

"Lord, I am traumatized," said Mariah Favell, one of the students. Heger knew it was drama and probed deeper. "What's this white rubbery stuff between the bones?" she asked about the cartilage.

The raw chicken was one of several stations Heger set up around the room to teach about muscles and bones. Even Heger was a walking lesson. She had stickers all over her body indicating specific parts of anatomy: abdominals, sternum, deltoid, phalanges…

Like scores of nuns before her, teaching is a passion for Heger.

But Heger, 30, is a rarity, especially at a time when the number of nuns in the U.S. has fallen dramatically.

She is the only nun teaching at Marian Middle School, a private Catholic school for girls near Tower Grove Park. But visually, she doesn't stand apart from her co-workers. She doesn't wear a traditional habit. On this day, black pants and a pink blouse outlined the same slim physique that she had playing volleyball at Fontbonne University. She wore her blondish-brown hair in a ponytail. Her independent spirit flowed freely.

On the inside, however, there is something different. Not long ago, in a paddle boat at Forest Park, she politely turned down a marriage proposal from a friend. That she could have the same teaching job without being a nun also speaks to her faith and goals.

"Our bodies are made to give birth, but this was the life I wanted to lead," Heger said. "It's bigger."

Since the 1960s, the number of nuns has dropped from nearly 180,000 in the U.S. to about 56,000 today.

In spite of the drop, many Catholics are comforted by historical trends. The Rev. Paul Bednarczyk, executive director of the National Religious Vocation Conference, said explosive growth in the 1950s and 1960s was an anomaly.

"The fact is there has always been a small number of Catholics who have responded to a religious vocation," he said.

Though the numbers are in decline, about 4,000 men and women in the U.S. were either in formation or had professed final vows within a recent 15-year period, according to a 2009 study that the vocation conference commissioned. The average age for women entrants was 32. The youngest pool of nuns was more diverse than older nuns.

But still, 44 percent of women religious communities in that period had no one in the initial stages of preparation.

The downward trend is changing the face of ministry, education and health care in places like St. Louis, where nuns have played a significant part of the city's Catholic legacy.

There are 52 orders of religious women operating within the archdiocese. One is the Franciscan Sisters of Mary, which started out nursing to the sick along the riverfront in 1872 and eventually created SSM Health Care, a network of 15 hospitals and two nursing homes in the Midwest. The facilities and most departments used to be run by nuns. Today, with more than 22,000 employees at SSM, only two are nuns. The congregation, which doesn't have a sister under 54, recently closed its convent in Richmond Heights.

Heger's congregation, the Sisters of St. Joseph of Carondelet, recently celebrated its 175th anniversary. But it, too, has tapered back since founding places such as St. Joseph Institute for the Deaf, Fontbonne College (now Fontbonne University) and St. Joseph's Academy.

Heger said she isn't worried about the dwindling numbers. She seems motivated by the challenge of sharing responsibilities with the laity.

"It is not my job as a Catholic sister to do whatever Catholic sisters did," she said. "It's our job to be about the Gospel mission together. There is something that can be really cool about letting non-sisters and (non-)priests take an active leadership role in their church and our church."

DIFFERENT GENERATIONS

The Sisters of St. Joseph motherhouse at 6400 Minnesota Avenue used to be full of young women who arrived right out of high school. Early on in formation, there was a ceremony where the "brides of Christ" swapped white wedding dresses for habits. They couldn't go home until they professed final vows. When somebody broke a dish, a young woman kneeled before the whole congregation and apologized, according to one story. Cleaning was as routine as praying.

"They'd be in the front hall, they'd be in the dining room, they'd be in the bake house, shining halls clean," recalled Sister Catherine Mary Boucher, 84. "In fact, we'd sit on them sometimes so they'd be shinier yet."

Dozens of women often joined each year, with a peak of 67 in 1960. But after the late 1960s, annual recruitment fell to mainly single digits, then to just a few or none.

Today, many things are different. The motherhouse has the ambiance of a museum, with plenty of bathrooms. There are 356 sisters; the average age is 76.

Each sister takes responsibility for her own prayer life. Instead of going wherever sent, they now seek their own job. Professions range from psychotherapy to finance to teaching.

Many sisters don't live at the motherhouse anymore. They live alone, in small communities or at a large retirement home in south St. Louis County called Nazareth Living Center. Boucher, who worked with an Indian tribe in Wisconsin and at St. Joseph's Home for Boys in St. Louis before retiring, lives at Nazareth.

"We are constantly praying for vocations, every day even," she said.

Where sisters like Boucher joined at age 18, now the congregation accepts only women who hold college diplomas and pass several screening tests. Many have already started careers.

When Heger first arrived in 2005, she was the only one in her class. She said it felt like being the lone fish in a glass bowl, with women molded by the Great Depression and World War II watching and critiquing her development.

"They really think it is their job to make sure that I am the best, most whole person that I can be," she said. "There is a sense that people are watching."

The openness of Heger's generation didn't immediately strike a chord. She said her blog, which laid out honest feelings about religious life, made sisters uncomfortable. And she doesn't hesitate to question.

"For me, just because you hold a title doesn't give you any authority. You have to basically prove to me that you deserve that, and I am still going to ask you why because that's how we grew up," she said, smiling. "I don't think they appreciate that side so much sometimes."

But she said there are advantages to being alone. Years ago, when dozens of women were in formation, they immediately did what they were told.

"There is only one of me, so I can say, 'Explain that to me, please,'" she said. "And we can have a conversation."

'A FEW GOOD WOMEN'

Over the last couple of years, some of the focus on Heger has been spread out to two more women who are each in different stages of formation with the congregation. They spend a lot of time getting to know the older sisters at Nazareth, where people like Sister Aline Mohrhaus, a former elementary school teacher, live.

Mohrhaus has a growing collection of pictures on the wall of women who have died.

"The hardest part that I find now is having so many of my friends die," said Mohrhaus. "That's why I have all those pictures up here. I pray to them. They have what I've been working for these 82 years."

She said she has been enriched by having people like Clare Bass, 28, the newest arrival, around to check in on her. "In that way, the Lord is taking care of us," said Mohrhaus. "These beautiful younger people, they just enrich our lives because they are so full of enthusiasm."

The other woman in formation at the congregation is Sister Mary Flick, 53, originally of Florissant. To enter, she sold her home of 17 years and left a job at St. Louis University, where she was employed for 25 years. She was part of a different congregation for five years but left in the 1980s because something didn't fit.

She, too, doesn't seem fazed by the decrease in religious vocations. It's not just about work, she said. There are the strong relationships and close community.

"All we need are a few good women," she said, visiting with Sister Agnes Marie Baer, 90.

Baer taught at Rosati-Kain High School with several other nuns and ran the New Life Style Program, which helped prostitutes get off the streets with counseling and job training. Today, there's only one nun teaching at Rosati-Kain. The street ministry is gone.

"We served a purpose," Baer said.

Flick assured her that they still do.

"That's right, but it has evolved," Baer said.

They agreed that the new generation of sisters will be like a few pioneer nuns who first came over from France in 1836 and initially served the deaf community.

"We are not done yet," Flick said.