The industry announced that it was forming a research committee to look into the matter. It hired independent scientists such as cancer researcher Clarence Cook Little to do interviews, insisting that there was no proof that cigarettes cause cancer.

In reality, scientific evidence that cigarettes cause cancer was becoming overwhelming. In 1964, the Surgeon General seemed to put an end to any controversy when he released the report of an independent advisory committee that had considered more than 7,000 published articles.

The Surgeon General’s warning had a profound effect on the public, prompting many smokers to quit. But the tobacco companies and their scientists would continue to deny that cigarettes cause cancer for another 35 years.

To discourage smokers from quitting, companies redesigned their cigarettes to seem safer. First, they added filters. Then they introduced “low-tar” cigarettes. Within a few years, these cigarettes dominated the market. Marlboro Lights, which debuted in 1971, became the nation’s best-selling cigarette.

Tobacco companies knew from extensive internal research that smokers were addicted to nicotine and needed a certain amount of it every day to satisfy their habit. Given a “low-tar” cigarette, they would change the way they smoked to get their fix.

With the passage of a new law, the Federal Trade Commission in 1967 began testing all cigarette brands on special smoking machines that measured the amount of tar inhaled. Cigarettes were reformulated, not so much to reduce tar but to fool the machines, according to an NCI report. Tiny holes were cut in the cigarette paper to vent tar when a cigarette was smoked by a machine. Those holes, however, didn’t reduce the tar inhaled by smokers.

“If you reduce the amount of nicotine coming through, the person changes a pattern of it. They take bigger puffs, they take deeper puffs, they take longer puffs, they smoke more cigarettes per day to get the amount of nicotine they are seeking to satisfy their addiction,” said David Burns, a retired medical professor at the University of California, San Diego, who edited some of the Surgeon General’s reports on smoking.

Burns testified for the plaintiffs in the recent St. Louis class-action trial.

Also testifying was William Farone, the research director at Philip Morris from 1977 to 1984. He said studies done at the company even before he was hired showed that smokers who switched to light cigarettes would take deeper puffs to get the same amount of nicotine they’d received from regular ones. Farone said other than those tiny holes in the paper, the differences between a Marlboro Red and a Marlboro Light were small.

Public-health scientists would not figure this out for several more years. A study by the American Cancer Society published in 1996 found that the rate of lung cancer deaths among 200,000 smokers actually went up after light cigarettes began dominating sales. Experts believe that the low-burning temperature of a low-tar cigarette and deeper puffs by smokers allow more carcinogens to go deeper into the lungs.