Don't look back.

I went most of my adult life multiple sclerosis-free, with only an occasional symptom ("Good Poison? Carbon monoxide may stifle multiple sclerosis," SN: 1/27/07, p. 53). Then in 1981, I quit cold turkey after 35 years of smoking and never went back to it. Shortly after I quit, my MS started full blown. Is it possible that smoking kept the MS in remission all those years? I am now 72 and in a wheelchair full-time. I will not go back to smoking for any reason, but it may always haunt me: What if?

VALERIE STUTTS, CHAMBERSBURG, PA.

The thrust of the article indicates that it's the enzyme heme-oxygenase-1 (HO-1)that reduces myelin damage. Why do research on administrating carbon monoxide when it's not the active ingredient? How can we increase the supply of HO-1 rather than worry about the by-product of its action?

VICTOR E. ARNOLD, HOUSTON, TEXAS

Studies suggest that smoking worsens multiple sclerosis symptoms, and doctors typically recommend quitting. There is little evidence that carbon monoxide--whether from smoking or received in some other way--is a good anti-inflammatory agent in people. As for studying carbon monoxide instead of HO-1 in mice, since externally applied carbon monoxide mimicked the anti-inflammatory effects of the enzyme in the animals, the researchers hypothesize that carbon monoxide contributes to the protective action of HO-1 in multiple sclerosis.--N. SEPPA