Six months a year, Jim supervises the endless feeding, brushing, washing, harnessing and unharnessing of the horses. At season's end, he ships them by ferry to the Upper Peninsula. There, the horses spend the winter feasting on 900 tons of hay, 4,000 bushels of grain and 120 tons of high-energy pellets called Master Mix, a feed Dr. Bill helped develop for horses that winter in severe climates.

For years, Jim spent the off-season in Upper Peninsula with the horses. Nowadays, he flies back and forth. "Then once the ice makes," Dr. Bill explains, "he snowmobiles over and back every day." Caring for the horses has grown as island tourism has ballooned in the last two decades. "We move so many more people than in my dad's time," Dr. Bill says. "He'd roll over in his grave if he saw what we do now."

The work is hard and profit margins slim. '"This business has nothing to do with money. You'd better love it," Bill continues. "We don't punch in at eight and leave at five. This is labor-intensive. You have to maintain the herd. You could never replace these horses that are trained just to work on Mackinac Island. It took years to assemble this herd. We spend a lot of time weeding out the old ones and making sure the new ones can function safely.

"There are many people who don't understand how fragile the horse business is. They take it for granted. Our tour and freight/dray rates are moderate compared to what would happen if you didn't have six generations of experience."

Indeed, as much as the island's horse lifestyle is heralded, its strong footing in island life is constantly in danger of being eroded. That keeps the brothers busy in politics to make sure horse-and-carriage interests are protected. "We try to keep a presence, but that's harder and harder to do," says Bill. "The population is changing. "

That change is from venerable island families who no longer want to keep their own liveries and newcomers who don't want the expense. Without their own horses, island dwellers have three options to get around: by foot, bicycle or taxi. So residents have pushed to allow golf carts. The thought makes Dr. Bill shudder. "We know horse-drawn transportation is slower," he says. "We know you're apt to miss the boat occasionally. But I say, 'Take a deep breath and relax. You'll live a lot longer.' We're not Disneyland.

"But there always have been threats," he adds. "Unless we have committed people who aren't interested in the buck this business won't make it--thank God some of our children have that commitment. We have to train our own people and give them something to pass on." He pauses, then reflects: "But my biggest fear is not being able to make a commitment to these people."

And the fifth generation is counting on that commitment. Dr. Bill's son Brad is the corporation's treasurer. His other son, Jeff, is a cardiologist in Minneapolis. It's anybody's bet how long he'll be able to stay away from the island and the family business. "He calls every day to check on things," says his father.