Sandra Karn was a single-minded veterinarian and something of a savior to thousands of Montgomery County cats and dogs treated at her Seneca Valley Veterinary Clinic in Germantown. Her unflappable demeanor led the Metro Transit Police to entrust her with medical care for its K-9 unit.

She operated the clinic until August, about a month before she died Sept. 15, at age 65, of emphysema and chronic obstructive pulmonary disease. A lifelong smoker, she knew she was dying but insisted on being hooked up to oxygen tanks so she could continue to work.

Sgt. Dan Colvin, who oversees the K-9 unit, brought her the police dogs for an exam this year. "She gave us her all in the beginning and middle of her career," he said, "and I was going to stay with her as long as she was physically able to care for our creatures."

No one is entirely sure what possessed young Sandra Oberhammer to tell her elementary school classmates almost six decades ago that being a veterinarian was her dream job.

She did not grow up on a farm, nor was her father an explorer who regaled her with romantic tales of African safaris. She grew up in Rockville, where her father was manager of Woodmont Country Club. They lived on the club property, where there were stables. She appealed for a horse.

"She was an only child and was the absolute light of her father's life, and the feeling was mutual," said Robert Karn, her high school boyfriend and first husband. "I suspect she got very much what she wanted within means, and she certainly wanted a horse."

She and Karn dated, often taking long horseback rides together down Falls Road.

She was in her third year of studying veterinary medicine at Michigan State University when she abandoned her childhood dream and quit school to get married. Several years and three children later, she was living in Boston as a stay-at-home mom when her husband noticed a problem: The former student veterinarian was getting antsy.

"She was just starting to climb the walls," Robert Karn said. "It was just tearing her up."

She wrote to Michigan State and was readmitted. In the next few years, the family's small house near the school became an ad hoc laboratory.

She once brought home a horse leg soaked in formaldehyde and removed all the muscle tissue so she could tag and memorize the nerve endings.

"I'll never forget her coming home with that [leg] on a winter's evening and dragging it into the house, putting it on a newspaper on the floor and staying up all night and dissecting," Robert Karn said. "It didn't smell very good, obviously, and there were little piles of meat all over the place.

"But like everything else she did, she did it nonstop."

The year 1965 was bustling: She completed veterinary school with honors; took a job at Penn Daw Animal Hospital in the Alexandria area of Fairfax County, commuting on nights and weekends for emergencies from the family's Poolesville home; and had her fourth and final child.

One of her daughters, Kimberly Karn Wilson, said her mother "was a good mom for sure, but you could tell work was her thing. It made her so intense, because she'd work very late, come home and try to do grocery shopping and get the laundry done and get kids ready for school."

She also played parent to a succession of animals over the years, including raccoons and an injured deer.

Long wanting her own clinic, she saved up and started Seneca Valley in 1974. She also was an officer in several veterinarian societies and took consultation calls from as far away as California.

Ultra-serious, to be sure, she also could take a gentle jibe.

One day, her two assistants found a caterpillar, made up a fake medical history for it and fit him comfortably in a small box. "We said his name is Jack and he needed his back checked," said veterinary technician Kim Martin.

When Karn called for the next patient, Martin brought in "Jack."

"What the hell is this?" she laughed.

Appearances at work meant a lot to Karn. She wore dresses and high heels. Her lipstick and mascara were applied perfectly. Her nails were manicured. She wore an amethyst ring and earrings in the shape of drums, a gift from her second husband, jazz drummer Mike Shepherd.

Martin said she was mesmerized by her boss's ability to do so much and remain calm. It really was impressive, she said, to watch the petite Karn hold down a restless German shepherd dog without using powerful sedatives and relying solely on her determination.

"She really could hold an animal," she said.

Sandra Karn tends to a schnauzer at her Seneca Valley Veterinary Clinic in Germantown. She was a friend to all animals, especially Metro police dogs, which were her patients.Karn at the Michigan State University veterinary school