148 THE LYMPHATIC SYSTEM 



the follicle is only partially surrounded by the connective tissue 

 trabeculae of the organ. Not only do fine branches from the sur- 

 rounding connective tissue bundles penetrate the periphery of the 

 follicle, but the reticulum of the follicle is continuous with these 

 trabeculae, thus forming a supporting stroma in which the lym- 

 phatic corpuscles are embedded. 



The lymphatic corpuscles are loosely packed in the center of 

 the follicle, and in this portion cell division by mitosis is most 

 active. This central portion is the germinal center of Fleming. 

 The germinal center is surrounded by a denser circumferential 

 layer of lymphoid tissue in which karyokinesis is less active. Be- 

 tween this denser portion and the surrounding connective tissue 

 the lymphatic corpuscles are again more loosely packed, and over 

 a greater portion of the follicle are separated from the trabeculae 

 by a lacuna-like space, the peripheral lymphatic sinus. 



The follicle is usually supplied with a thin-walled artery, occa- 

 sionally two, which penetrates to the middle of the follicle to form 

 a wide meshed capillary plexus. The capillaries, at the periphery 

 of the follicle unite to form two or more veins, which are con- 

 tained in the adjacent connective tissue. 



The lymphatic corpuscles are mostly of the mononuclear type 

 of leucocyte, the small mononuclear or lymphocyte type being the 

 most abundant. Polynuclear and acidophile leucocytes are also 

 found in the lymphatic follicles, though in much smaller numbers. 

 Mitosis is most frequently observed in the large mononuclear type. 

 Because of the nomadic tendencies of the leucocytes the bounda- 

 ries of the lobule are not always sharp, the lymphatic corpuscles 

 frequently infiltrating the surrounding connective tissue so as to 

 render it most difficult to distinguish the latter from the true 

 lymphoid tissue of the follicle. 



THE LYMPHATIC NODES (Lymphatic Glands* Lympho- 

 glandulce). These structures occur in the course of the lymphatic 

 circulation in various parts of the body. They are found in the 

 neighborhood of the large joints, as in the axilla, the groin, the 

 popliteal space, in the prevertebral and mediastinal connective 

 tissue of the abdominal and thoracic cavities, and in the mesen- 

 tery. They are frequently in relation with the large arteries, e. g., 

 the renal, internal and external carotids, etc. 



* Since the lymphatic glands are in no sense true secreting glands after the 

 manner of the serous and mucous secreting glands, this name is most ill-chosen. 



