Studies on Thymus of the Mammal. IX. Histochemical Study of Irradiated Mouse Thymus. ∗ †

Abstract

Summary and conclusions

1. In the normal thymus the relatively few mesenchymal reticular cells give a positive reaction for acid phosphatase in acetone fixed sections. There are fewer reactive cells in the cortex than in the medulla. 2. As early as 2 hours after irradiation the mesenchymal reticular cells are mobilized to become active macrophages which stain deeply in the acid phosphatase technic. These become more numerous until at 24 and 36 hours after irradiation the involuted cortex is loaded with macrophages containing ingested lymphocytes or full of vacuoles. At these hours the browned cytoplasm of the epithelial cells is seen as the stroma of the depleted cortex. At 3. 5 and 7 days there is a gradual diminution in number and size of reactive cells. At 9 days the appearance of the thymus is essentially normal.