Steam the clams in the stock. Remove the clams, chop the meat, and reserve. Strain the steaming liquid through cheesecloth. Reserve. Render the bacon. Add the onions and celery and saute until transulent. Add the stock, potatoes, sage, thyme, bay leaves, tobasco and worcesterchire. Simmer until the potatoes are tender. Combine the evaporated skimmed milk and the arrowroot. Gradually stir this mixture into the soup and continue to simmer for a few minutes, until thickened. Add the scallions. Add the reserved chopped clams and fresh herbs just before serving.