THE LYMPHATIC SYSTEM. HQ 



within the net-work constitute the denser or looser forms of 

 adenoid tissue found in the lymphatic nodules ; ordinarily the cells 

 are so closely placed that the reticulum is greatly masked, satisfactory 

 views of the latter being obtained only in sections of great thinness 

 or after the cells have been removed by brushing or by violent 

 agitation. 



The reticulum of lymphoid tissue consists of intertwining 

 and anastomosing bundles of connective tissue ; along the fibrous 

 trabeculae, especially 



at the nodal points, FIG. 142. FIG. 143. 



flattened plate-like or 

 stellate connective-tis- 

 sue .cells are applied 

 after the manner of an 

 imperfect endothelial 

 investment. In parts of 

 many adenoid struct- 

 ures the delicate re- 

 ticulum seems to be 

 formed by the union of 

 the protoplasmic pro- 

 cesses of the branching 

 connective-tissue cells 

 themselves ; this ar- 

 rangement, however, 

 is usually only seem- 

 ing, the cells really being applied to the surface of the fibres and not 

 constituting an integral part of the reticulum. ( It is probable that in 

 the splenic pulp and in a few other localities the processes of the 

 stellate cells do unite to form protoplasmic net-works. 



Diffuse adenoid tissue represents the least specialized form of 

 the lymphoid structures; the mucosae of the digestive and of the 

 respiratory tracts afford good illustrations of the presence of such 

 tissue. 



Simple lymphatic nodules, or solitary follicles, stand next in 

 differentiation ; these are found in almost all mucous membranes 

 (those of the bladder and of the sexual organs excepted), while they 

 occur in great numbers in the respiratory and digestive tracts, the 

 solitary glands of the latter being important examples of these 

 structures. The simple nodules consist of oval masses of adenoid 

 tissue, limited by a delicate connective-tissue wall or capsule, com- 

 posed of fibrous lamellae. The central parts of such nodules, as well 

 as of the Cortical follicles of the larger glands, are usually occupied 

 by germ-centres, areas composed of lymphoid tissue of looser 



Diffuse lymphoid tissue occu- 

 pying deeper layers oF nvucosa 

 of human stomach : the lym- 

 phoid cells infiltrate the fibrous 

 tissue between the glands with- 

 out being definitely limited. 



Simple lymph -follicle from 

 conjunctiva of dog : a, lym- 

 phoid tissue, limited by the 

 fibrous capsule (b) c, sur- 

 rounding connective tissue. 



