112 



NORMAL HISTOLOGY. 



, 



Capsule 



The blood-vessels for the nutrition of the lymph-nodes are numerous. 

 Some pierce the surface of the node at various points and are distributed to 

 the capsule and the trabeculae; most, however, enter through the hilum. 

 After following for a short distance the trabeculae, the arterioles cross the 

 sinuses and enter the cords and nodules of the denser lymphoid tissue, 

 within which they break up into rich capillary networks. 



The nerves enter the lymph-nodes at the hilum, in company with the 

 blood-vessels. They include both medullated and nonmedullated fibres, but 

 are chiefly sympathetic fibres destined for the involuntary muscle of the 

 vessels and of the capsule. 



Hemolymph Nodes. In addition to the ordinary lymph-nodes, 

 there occur in various regions, especially in the prevertebral region of the 



abdomen, structures which 

 resemble lymph-nodes in 

 form and size, but differ 

 from them in the deep red 

 color which they usually 

 exhibit. These bodies are 

 known as the hemolymph 

 nodes. Their distinguish- 

 ing feature is the substitu- 

 tion of blood-channels for 

 the usual lymph-sinuses, 

 which, in the typical hem- 

 olymph nodes, may be en- 

 tirely wanting. The path 

 of the blood resembles that 

 within the spleen, since the 

 blood-cells escape from the 

 imperfectly walled vessels 

 into the lymphoid tissue 

 and thence pass into the 

 blood -sinuses and on to 

 the veins. In many cases, 

 however, the substitution 

 of the lymph-sinuses by 

 blood-spaces is not com- 

 plete, the sinuses occupy- 

 ing the central parts of 

 the node with the spaces at the periphery. All gradations, in fact, are 

 encountered, from the typical hemolymph node at the one extreme to a 

 lymph-node with enlarged blood-vessels on the other. While these nodes 

 share in the production of lymphocytes, they are probably seats of destruction 

 of the erythrocytes, whose remains are seen in the phagocytes. 



Development of the Lymphatic System. At present, two views 

 exist regarding the primary origin of the lymphatic system. According to 

 one (Sabin), the lymphatic channels arise from the veins by a process of 

 budding, similar to that followed in the extension of blood-vessels; according 

 to the other (Huntington and others), the lymphatics arise independently by 

 fusion of separate spaces within the mesenchyma. The weight of evidence 

 seems to support the latter view. The various lymph-vessels thus formed 

 unite to make a continuous system, which later acquires new connections 

 with the subclavian veins near their junction with the internal jugulars. 



FIG. 152. Modified lymph-node, containing enlarged blood-ves- 

 sels and approaching type of hemolymph node. X 120. 



