After many months of peaceful coexistence, Atlanta police decided to pursue and ticket the monthly Critical Mass bike ride.  While other cities have had much more confrontational episodes between police and Critical Mass, Atlanta has usually been a very hospitable town for this loosely organized pro-bicycle demonstration. After an article about Critical Mass appeared in the Atlanta Journal-Constitution after last month's ride, there was a sudden, visible shift in APD policy. A phalanx of police was waiting for the riders at Centennial Olympic Park and dogged them all the way through Midtown, Virginia-Highlands, Little Five Points, and the Old Fourth Ward for an hour.  While things didn't get particularly ugly between police and the Mass this time, the sudden interest of the law may mark the beginning of the end of a long-standing friendly (and peaceful) coexistence.