

Development of the Lvniphatic Xodes in the Pig 



nodes which develop later in the life of the embryo, after lymphocytes 

 occur, hurry through the prinuiry process, and show a considerable modi- 

 fication of it. 



Up to this time the node has had none of the structures characteristic 

 of the adult node; there are no lymph cords, nor germ centers, no 

 lymphocytes, and no sinuses. 



The next stage, pictured in Fig. 11, shows the beginning of some of 

 these structures. The diagram is made from a section of the primary 

 lymph node in a pig 8 cm. long. In the center of the node the blood 

 capillaries have proliferated, giving a tuft of capillaries surrounded by 



Fig. 11. Diagram of the primary lymph node in an embryo pig, 8 cm. long. 

 X about 33. This represents the primordial follicle. The hilum is marked 

 by the artery. A. artery; aid. afferent lymph duct; eld, efferent lymph ducts; 

 f. follicle. 



connective tissue. The artery is shown leading up to the node but 

 reduced to capillaries on entering it. The vein is not shown in the 

 diagram, but the artery and vein lie parallel, up to the point where the 

 node or follicle is entered, where they separate. This is an important 

 ancT characteristic point in the relation of the blood-vessels. At this 

 stage there are only capillaries within the node. 



Here for the first time we can speak of the lymph follicle, wliich is the 

 vascular unit and consists of the structures that go with a single artery. 

 At this stage the entire node is one follicle. Here also for the first time 

 two elements are differentiated, a lymphoid element connected with the 

 artery and a lymphatic element made of lymph ducts. 



