Thymus cortex (mouse, young adult)

Stain: Hematoxylin. Autoradiography after pulse labeling with tritiated thymidin. Most of the (black) radioactive labeling is found in the outer thymic cortex (3) where pre-T cells divide and subsequently migrate to the lighter stained medulla (1) that consists of a more loosened framework of epithelioreticular cells with less thymocytes, macrophages and blood vessels. (2) cortex.