LV.Ml'IIATIC ORf;AXS 



173 



These are known as lymph nodules (Fig. 99). In the centre of 

 each nodule is usually an area in which the cells are larger, are not 

 so closely packed, and show mark ed mitosis. As it is here that 

 active proliferation of lymphoid cells takes place, this area is known 

 as the germinal centre (Figs. 99 and 100). Immediately surrounding 

 the germinal centre is a zone in which the lymphoid cells are more 

 closely packed than elsewhere in the nodule (Fig. 100). This is 

 apparently due to the active production of new cells at the germinal 

 centre and the consequent pushing outward of tlic surrounding 

 cells. In stained sections the centre of the nodule is thus lightly 

 stained, while immediately surrounding this light area is the darkest 







0735 



Fig. 100. — Section through Cortex and Portion of Medulla of Human Lymph Node 

 (Technic 2, p. 176.) a, Capsule; b, lymph sinus; c, trabecula; d, closely packed cells 

 at outer border of lymph nodule; e, germinal centre; /, lymph cords in medulla. 



portion of the nodule (Fig. 100). From the inner sides of the nodule, 

 strands of lymphoid tissue extend into the center of the node. 

 These are known as lym ^i cor ds, and anastomose freely. The 

 regular arrangement of tFe lymph nodules and trabecul^e in the 

 peripheral portion of the node contrasts strongly wdth their irregu- 

 lar arrangement in the centre. This determines a division of the 

 nodule into two zones, an outer peripheral zone or cortex and a cen- 

 tral zone or medulla. In both cortex and medulla the lymphoid 

 tissue is always separated from the capsule or from the septa by a 

 distinct space — t he lympji sinu s — which is bridged over by reticular 

 tissue containing comparatively few lymphoid cells (Fig. 100). 

 These sinuses form a continuous system of anastomosing incompletely 

 walled channels throughout the node. 



