Abstract
Fresh-frozen adrenal sections of the hamster showed after treatment with formalin 2 kinds of cells in the medulla. The majority of medullary cells fluoresced weakly in UV light but clearly delineated groups of morphologically similar cells exhibited marked green fluorescence. These fluorescing islets were located in the periphery of the medulla, the center being free of fluorescing cells. Direct chemical analyses of mechanically separated central and peripheral areas of freeze-dried medullary sections revealed that non-fluorescing cells contained much epinephrine and little norepinephrine and fluorescing cells contained much norepinephrine and little, if any, epinephrine.