sinceegning tysabri, the next slide shows the resolution of that huge area of inflammation into a very small scar that you can see. and a complete stabilization, with the scars still there, but no new disease activity. so this is quite remarkable. and as al had mentioned, we are using the mri scan much as an internist will use a blood glucose to follow diabetes. this is how we are following multiple sclerosis. >> you helped develop this drug, did you not? you developed it when you were at biogen. >> still there. >> so but it is readily available to people. >> yes. >> this is a drug that is now in wide use. >> it's approved in the united states. there is a restrict-- there is a registry, a strict method by which you can get the drug. it's called the touch registry. and the reason for that is hat the's a side effect hat is uncommon but can be quite harmful. >> rose: which is. >> it's called pml which stands for progressive multifocal lukeo encephalopathy. >> rose: which is. >> a viral infection of the grain. and so you know, as we were saying the immune system was there to, you know, pre