It's possible that the coolest and most experienced nerves at this week's Indianapolis 500 race will not belong to one of the drivers. Nor necessarily to one of the fast-change mechanics in the Speedway's grease pits. Rather, the tensest job at the track is calmly borne by an elderly family doctor who witnessed his first Indy race in 1931. Dr. Thomas A. Hanna treated a couple of minor injuries then and decided to offer his medical services again in 1932. This weekend, when cars roar at speeds approaching 200 mph in the 65th 500-mile classic, Hanna, now 71, will celebrate his golden anniversary administering to the injured and sick at the world's largest single-day sporting event.

As Speedway medical director, Hanna commands a volunteer medical staff of 285, manning 19 ambulances, two helicopters, two vans, a 22-bed hospital, three subhospitals and seven first-aid stations. They'll treat not only injured drivers but also victims in the so-called "redneck Woodstock" throng of about 350,000. "If you take a city of 350,000 people and estimate the amount of medical work in a day, then that's our job," says Hanna. "Only we have far more problems because our city is packed within a confined area, and the fans are in a holiday spirit. There are also 33 people driving race cars around the place."

Hanna and his colleagues begin work weeks before the race when they give each driver a full physical. Hard contact lenses and dentures are barred; so are diabetic entrants, because a driver's insulin reaction once caused a crack-up during a practice. Hanna can order drivers off the track—he still complains about how Janet Guthrie failed to alert him to her last-minute injury and drove the 1978 race with a fractured wrist. "Drivers understand we are there to protect them," Hanna says. "But they also believe nothing terrible will ever happen to them. The only thing they fear is fire."

Actually, "It's the fans who give us fits," Hanna says. "We once had a man come in here with a lit cigarette stuck in his inner ear canal. It blew in there, he said. A pig bit off a woman's toe one year. You name it, we get it." During an average May, his staff treats some 2,000 people. But, thanks to increased on-site treatment facilities, there has not been a fatal heart attack among Speedway spectators in three years, though Hanna's staff treats 10 or so coronaries each May. Nor has there been a fatal crash in the race since 1973.

In 1960, however, the year Hanna took over as medical director, there was the worst disaster in Indy history. A rickety, 10-tiered scaffold built by some fans near the first turn collapsed, killing two and injuring 115. "We learned a lot from that," Hanna reckons. "We don't allow scaffolds anymore." In 1964 drivers Eddie Sachs and Dave MacDonald burned to death when their cars collided. "The big ball of fire went up into the stands and burned 30 spectators," Hanna remembers. "We handled it, but my people never get used to seeing such immense destruction." Hanna's close friend, driver Pat O'Connor, died in a 1958 crash during the first lap. "It was the most painful moment of my career," he says, "when I had to identify the body."

A graduate of the Indiana University School of Medicine, Hanna has two grown sons and a daughter with his wife of 48 years, Dorothy. He maintains a private general practice all year, seeing his own patients at night and in spare moments during his annual month-long stint. His labor at the Speedway is unpaid. "This is my life's work," he says. "There is no place where one can have a better opportunity to practice mass medicine." The job does, however, interfere with his love of racing. Because he has to stay in the Speedway hospital, Hanna hasn't had even a glimpse of the track during a race in 20 years.