Histological observations on the deep cortex of the lymph nodes of the germ-free mouse.

The deep cortex of the node was previously shown to be composed by semi-rounded "units", each one comprising a centre and a periphery. The periphery was considered to a site of migration of lymphocytes circulating through a node and the centre a site where some of these migrating cells collect for a certain time. The present work compared the units of the nodes of germ-free and normal mice at age eight-weeks. The units differed in the two groups of animals. The main finding was that the units of mesenteric nodes of germ-free mice differed from those of the other nodes found in the same animals. Unlike in the mesenteric nodes of normal mice, the periphery of a unit was clearly demarcated from its center due to a greater lymphocyte density in the periphery. This fact fits a previous proposal that each part of the unit functions separately. Observations of the peripheral cortex and medulla of the germ-free nodes support other previous proposals on various aspects of the functioning of the organ in normal animals.