ARLINGTON HEIGHTS, Ill. – Twenty-six horses tested positive for prednisone, a corticosteroid, during late spring and early summer in Chicago. All the positive tests revealed minute traces of a drug permitted to be used therapeutically but forbidden on race day, and trainers whose horses tested positive said they followed the same procedures for administering prednisone that they’ve used for years. The sheer number of rulings issued by Arlington Park stewards on Sept. 2, however, figures to draw attention.