io8 



NORMAL HISTOLOGY. 



Sub- 

 mucosa 



Lymphoid Tissue. Wherever found, whether as diffuse masses, 

 simple nodules, or as the larger and complex lymph-nodes, lymphoid or 

 adenoid tissue is composed of two chief constituents the supporting con- 

 nective tissue reticulum and the 

 lymphoid cells contained within 

 the meshes of the reticulum. 

 The latter varies in the thickness 

 of the component fibres and the 

 size of its meshes, but in the 

 denser types of lymphoid tissue, 

 as in the periphery of the solitary 

 nodules and in the cortical folli- 

 cles and medullary cords of the 

 lymph-nodes, it is so masked by 

 the innumerable overlying cells 

 Germ- that only after removal of the 

 latter can the supporting frame- 

 work be satisfactorily demon- 

 strated. The reticulum is modi- 

 fied connective tissue (page 

 22), upon the surface of whose 

 trabeculae, particularly at the 

 points of juncture, flattened con- 

 nective tissue cells are closely 

 applied. Where of exceptional 

 delicacy, the reticulum is formed 

 almost entirely by the anasto- 

 mosing processes of the stellate 

 connective tissue cells. The 

 lymphoid cells are exceedingly 



numerous and closely packed and present the characteristics of the lympho- 

 cytes in the blood, this resemblance being explained by the fact that such 

 blood-cells are derived from the lymphoid 

 tissues. 



The simple lymph-nodules, vary- 

 ing in size but seldom more than 2 mm. 

 in diameter, are irregularly spherical or 

 ellipsoidal masses of lymphoid tissue, in 

 which a denser peripheral zone encloses 

 and blends with a less compact core. 

 Within the latter, which being of looser 

 texture appears as a lighter central area, 

 usually are seen lymphoid cells in various 

 stages of mitotic division. Such foci are 

 known as germ-centres and indicate the 

 birthplaces of many new lymphocytes. 

 Although the limits of the lymph-nodules 

 are commonly imperfectly defined by a 

 condensation of the surrounding connective 

 tissue, a distinct capsule is wanting. Definite lymph-channels are found 

 neither upon the surface nor within the simple nodules; the latter are 

 provided, however, with a generous network of capillary blood-vessels. 

 Intermediate in complexity, between the simple nodules on the one hand 



. 



FIG. 145. Simple lymph-nodule from large intestine. 

 X 120. 



FIG. 146. Portion of lymph-nodule show- 

 ing details of germ-centre. X 280. 



