Histochemical characterization of the lipid content in the macrophages of the cortico-medullary zone of the rat thymus

Summary A specific type of macrophage, located exclusively in the cortico‐medullary zone of the normal rat thymus, contains intracellular material of heterogeneous composition, which at least in part represents partially oxidized unsaturated fats, according to its positive histochemical reactions for ceroid. This globular material is Periodic Acid‐Schiff—positive and Sudan Black B—positive. It shows acid‐fastness by the long Ziehl‐Neelsen method and displays autofluorescence. The histochemical reaction for late lipofuscin is negative. The possible significance of the presented results is discussed.