Slide DMS121 [Lymph node, monkey, PTS]. This section of plastic-embedded tissue is much thinner than the previous one and is well suited for study of cellular detail. Look at the germinal centers of the secondary follicles in the cortex. The largest nuclei are those of the macrophages and follicular dendritic cells; in the cytoplasm of some of these cells there are often small particles of foreign material ("tingible bodies"). Other large nuclei (often with prominent nucleoli) are those of large activated lymphocytes on their way to forming plasma cells or B memory cells. Nuclei of reticular cells are less obvious. See any mitotic figures? Examine the medulla. Here you can find lymph-filled sinusoids (the lymph is eosinophilic [pink] and homogeneous) that contain variable numbers of lymphocytes, some polymorphonuclear leukocytes, and occasional plasma cells. Macrophages, lymphocytes and some plasma cells can be found in the medullary cords that separate the sinusoids. Many of the macrophages have finely vacuolated cytoplasm. Finally, look for blood vessels and identify arteries, veins, and venules in the node. Other vessels, along with nerves, fat and fibrous connective tissue are seen adjacent to the node.