The subject of this exploration will constrict your blood vessels, choke your windpipe and dispatch you to an early grave, 5 million of you a year. The most lucrative crop the Americas have ever seen, it kept the British at bay, kept the enslaved entrapped, kept Hollywood sexy. Until it didn’t anymore.

Stipulation: Deep bows to the great public health triumph of wrestling Big Tobacco to the mat and changing human behavior. Never before were millions persuaded to give up a highly pleasurable, relatively cheap habit because it was bad for them. And never since.

Tobacco itself refuses to die. It’s stubborn. It’s meant to grow here. The seeds are tiny as a flea and germinate like crazy. In less than a month, you can have a robust green crop that’s good for much more than smoking. You can grow vaccines in it. Extract protein from it. Make drugs from it.

Ten years after Maryland became the only state to use its tobacco settlement money to pay hundreds of farmers to quit growing the evil sot-weed, it’s turning out that tobacco has redemptive virtues. Nobody needed to bother exploiting them before; the stuff was so fabulously successful for 400 years as a vice. Even nicotine, the natural and highly addictive chemical in tobacco, has its benefits.

People smoked in part because a cigarette could calm you down and pep you up. Now research studies are exploring exactly how nicotine may safely halt cognitive decline and help those with Alzheimer’s, Parkinson’s, depression, schizophrenia and attention problems. The pure nicotine in the smoking cessation patch used in these studies is extracted from an American product that American farmers know how to grow.

If you drive around Southern Maryland, you can still spy it. Amid the corn mazes and alpaca petting opportunities, the pick-your-own peppers and the thick crop of McMansions, there’ll be a couple acres of plants that look like soldiers — upright, sturdy, tall as a man, with bushy leaves bigger than the blade on a ceiling fan.

You’ll come upon a weathered barn, with some of its boards missing. But on closer examination, you’ll see the slats are opened with a precise symmetry. They let in the air that cures the tobacco hung on its stalks up in the rafters.

Inside the barn, the sheaves, as it has been said, feel like velvet and smell like money.