For zoo veterinarian Lucy Spelman, Hsing Hsing is only one of dozens of elderly patients she tends on daily rounds.
Nancy the elephant, who is 45, has a serious infection in one of her massive toes.
Almost every day Spelman x-rays Nancy to see if antibiotics injected into the bone marrow will cure the problem. The unhappy finding today: no change.
"It's very, very difficult to treat. If you decide to treat, you're deciding to put an animal through an awful lot," says Spelman.
Spelman rules out surgery; it's too risky at Nancy's age.
At zoos across the country, vets are pushing the boundaries of animal medicine. Animals have never lived so long. And vets like Dr. Spelman are encountering new forms of geriatric diseases for which they've had to invent treatments.
Washington's National Zoo has a policy of keeping its animals on display, not replacing them, even as they age.
The Siberian tiger suffers from weak legs. Norman the sea lion has eye problems. There's an old lizard who's lost weight.
Elderly wolves are bothered by arthritis. Dr. Spelman will examine Cherokee while the wolf has her annual dental checkup, courtesy of local dentists who volunteer their time.
The availability of high tech medical care -- everything from root canals to organ transplants -- contributes to longer lives. Another big factor is the high level of personal care.
"It reflects years of being fed right, housed right. All of that together is allowing these creatures to live longer, and that's a good thing!"says Spelman.
Hsing Hsing gets arthritis medicine in blueberry muffins. Mesou the gorilla enjoys high fat cottage cheese. Nancy is rewarded with special fruits.
Many of the keepers have cared for the same animals for years, and are preparing themselves emotionally for the inevitable.
"He is a marvelous animal, and I love him very much," says Hsing Hsing's keeper. "I hope I can age as gracefully as he does. I really do."
For zoo visitors, there is much to be learned and enjoyed, at any age. That's true for animal and human alike.