At first glance, the patient strapped to the operating table was astonishing, both in size and color. After all, it is seldom that a 180-lb. black, orange and white Siberian tiger is wheeled into the University of Illinois Eye and Ear Infirmary for sight-saving cataract surgery.

Brutus, the tiger, was in an operating room usually occupied by ailing people because of the efforts of 53-year-old Dr. Lester Fisher, director and resident veterinarian at Chicago's Lincoln Park Zoo. Fisher is a vocal—and effective—proponent of "comparative medicine," which adapts for animals some of the techniques used for treating humans. Brutus' eye surgery, which was successful, was Dr. Fisher's latest such case.

As with Brutus, Dr. Fisher does not usually participate in the operation, relying, rather, on skilled specialists. In many cases the specialists go to the zoo's infirmary, but for special procedures and delicate surgery the animal—tranquilized and carefully caged—is brought to the appropriate hospital or clinic. Dr. Fisher arranges the scheduling so that human patients' needs are not interfered with.

A veterinary corps major stationed in Europe during World War II, Fisher studied—and supervised an animal-care facility—at Northwestern University medical school and later opened his own animal hospital. When Marlin Perkins, host of television's Wild Kingdom, resigned as director of Lincoln Park Zoo in 1962, Fisher replaced him.

Dr. Fisher's patients suffer an astonishingly human range of maladies and treatments—from a rare snow leopard which received radiation treatment for cancer of the mouth, to a baby gorilla, whose life was saved by surgery at Children's Memorial Hospital to remove a blood clot on the brain. Although outside doctors' services are almost always volunteered, the costs to the zoo for anesthetics and drugs are not small—not to mention the time and trouble of giving the animals near-human care. "It is justified," says Fisher, "in terms of what a healthy animal provides to society." Zoogoers obviously agree. Whenever one of Fisher's charges falls sick or undergoes surgery, get-well cards pour in.