A yellow school bus moves along Dulaney Valley Road, through the lush green country side of the Loch Raven Reservoir area. At Dance Mill Road--where Peerce's Plantation restaurant used to be--the bus turns left into a narrow, unpaved country road. In minutes, the bus comes to a full stop in a parking lot and the students alight. They have come this fine spring morning in 1955 to visit the Cloverland Farms milking barn, to see--believe it or not--cows being milked.