Florence K. Sabin 389 



The reticulum framework in the adult makes a complete anastomosis 

 throughout the node. The framework can be readily traced in the last 

 diagram. Starting from the capsule, fibers enter the trabeculae, pass 

 between the ducts of the sinus and enter the lymph cord. The large 

 trabeculae carry veins. In a specimen of reticulum from which the cells 

 have been digested out, the entire node can be reconstructed for the 

 sinuses occur in the looser reticulum that borders the trabeculae while 

 the cords and follicles are between trabeculae and show a much finer and 

 denser network than the sinuses. The germ centers often appear as holes, 

 since the fibers are delicate there. 



Lymph capillaries. — The subject of open or closed lymphatics, within 

 the lymph node as elsewhere, has given rise to most definite but oppo- 

 site opinions. The study of development touches but one aspect of 

 the question, unless it is combined with many injection experiments. 

 The lymphatics develop as blind sacs from the veins and have a complete 

 endothelial lining. The sinuses result from a multiplication of the lymph 

 ducts and the only difference between the sinus and the preliminary 

 lymph plexus is in the width of the connective tissue bridges between the 

 ducts. In the sinus these bridges are reduced to the thickness of the 

 reticulum fibers of the adult. Thus from the purely embryological argu- 

 ment the spaces of the sinuses have a complete endothelial lining. Nu- 

 merous injections of lymph nodes in every stage have been made with 

 Prussian blue and with India ink. The ink always runs farther than 

 the Prussian blue. In injecting the nodes through the afferent ducts it 

 is always easy to avoid undue pressure within the node, for the lymphatic 

 area of the node is so much greater than the caliber of the ducts leading 

 to it. It is possible in all stages up to two weeks after birth to obtain 

 injections without extravasations. But many injections do show extrava- 

 sations and these occur in the walls of the sinus rather than the less de- 

 veloped plexus of ducts which always forms a part of the node. This 

 shows that the wall of the sinus is weaker than the walls of the plexus. 



To conclude, the present study shows the close relation between the 

 lymphatic system and the vascular system. In the formation of lymph 

 nodes, haemolymph nodes, and spleen, there is one fixed element in com- 

 mon, namely, the lymphoid tissue associated with the artery; the fluc- 

 tuating element or the sinus belongs either to the venous system or to 

 modified veins called lymphatics. The sinus may be absent, or venous 

 or lymphatic. 



