126 



THE LYMPHATIC SYSTEM 



the sinuses into the efferent lymph vessels at the hilum. During 

 this passage through the sinuses a number of lymphocytes are 

 added so that lymph leaving the node is richer in cells than when 

 it entered. 



Three varieties of lymphocytes (small, medium, and large) have 

 been distinguished in the node, but by far the greater number are 

 the small variety. When mitotic activity is at its height the 

 germinal center is filled with lymphocytes of the small variety 

 similar to those in the peripheral portion of the nodule. Then 

 proliferation ceases for a time and during this resting period the 

 nodule has a uniform appearance throughout. Even isolated 

 nodules have periods of rest and acti^•ity. 



Afferent lymph 

 vessel 



TrabecuJa 



Capsule 

 Trabecula 



Lymph nodule 

 Medullary cords 



Retficular- 

 nehvork 



Efferent lymph vessel 



Fig. 75. — Diagram showing structural plan of a lymph node. The cortex is the 

 outer zone containing lymph nodules. The medulla is the central region with cords of 

 lymphocytes. 



The artery entering at the hilum branches throughout the fibro- 

 elastic connective tissue skeleton, breaking up into capillaries which 

 connect with venules and the latter eventually with the vein or 

 veins which leave from the hilum. Small arterioles in trabecule 

 give rise to a capillary net which surrounds the nodules. So far as 

 erythrocytes are concerned, they remain within the vascular system 

 in the node, i. e., there are normally no free red blood cells in the 

 sinuses. Trabeculse appear to be better developed in perii^heral 

 lymph nodes, such as those in the axilla or groin. Nodes within the 

 body cavity have relatively greater medullary regions. Trabecid;e 

 of small nodes are difficult to locate, and in some nodes the cortex 

 is massed chiefly at one end while the medulla is concentrated at 

 the other. 



