Florence E. Sabin 379 



from the fiber bundles by running as separate, wavy fibers, having in 

 general the same direction but forming abundant anastomoses. These 

 are obviously the beginning reticulum fibers. 



There is one small, fat organ within the capsule. The trabeculse are 

 formed, as can be seen in the figure, by the folding in of the capsule, 

 thereby bringing the trabecule in the center of the sinuses (dts). This 

 shows especially well in the border of the large central trabecula (t) of 

 the figure and explains why the trabecule of the adult node are bordered 

 by sinuses. The traljecula.^ often carry blood-vessels from the capsule. 

 The tissue around the Idood-vessel at the hilum thickens to form trabe- 

 cular; these trabecular follow the veins farther than the arteries for the 

 arteries soon enter the lymph cords. The trabecular around the blood- 

 vessels are less developed at this stage than the capsule. 



The connective tissue framework within the node itself is a definite 

 protoplasmic network with a few fine fibrils which do not stain sharply 

 in tlie Mallory stain except possibly in the germ centers. The bridges 

 in the sinuses are all protoplasmic at this stage. In other words, the 

 connective tissue framework of the node is less advanced than the sur- 

 rounding tissue and the reticulum fiber is a later development. 



The diagram shows the relation of the lymph cords and the germ 

 centers. As has been said, the cords are first definitely outlined and 

 restricted to the borders of the artery by the development of the lymph 

 sinuses. Some of the cords arc narrow and have the single central 

 artery, but the majority have an abundant plexus of blood-vessels. The 

 arter}' and vein never run side by side in the lymph cord, and the veins 

 leave the cords to enter the trabeculge that grow in from the hilus. At 

 this stage of development only the large veins are in the trabecule. The 

 germ centers are around the capillary tufts where the lymphocytes 

 actively divide. The lymphocytes then wander down the borders of the 

 artery, filling up the lymph cords. In the adult node, as is well known, 

 the germ centers may present two diiferent appearances. In the one 

 case, the center is uniformly filled with lymphocytes which are actively 

 dividing: in the other case the lymphocytes are crowded to the edge of 

 the germ center, giving the appearance of a dark rim in sections stained 

 in hfematoxylin. In the einl<ryo wliere cell division is active, the germ 

 centers are always uniformly crowded witli Ivmphocytes. 



The right-hand part of the section is far less developed. It consists 

 of a plexus of lymph ducts with connective tissue bridges which contain 

 a network of blood capillaries ; it is essentially in the stage of Fig. 7, 

 llioiigli the lymphatic plexus is more abundant. IMost of the nodes in 



