3T2 Development of the Lviiipliatic Xodes in the Pig 



Often the connective tissue nuclei appear as if being extended from the 

 protoplasmic network of exoplasm, the irregular endoplasm still clinging 

 to the nucleus. 



This form of observation cannot be considered as proof of the origin 

 of the lymphocyte from connective tissue — it is obvious that the position 

 of a wandering cell cannot give evidence of its origin. With the same 

 t3'pe of tissue to examine, Gulland, noting the occurrence of the lympho- 

 cytes in clumps around the capillaries, concluded that they were filtered 

 from the blood stream. The evidence does not suffice to prove either 

 that the lymphocyte develops from the connective tissue in the lymph 

 node, nor that it reaches the node through the blood stream. "We must 

 await some new method of attacking this problem. One point is, how- 

 ever, definite in my specimens — that cell division in the connective tissue 

 takes place in little clumps around the blood capillaries, and, as will be 

 shown later, the division of the lymphocytes takes place also around tufts 

 of capillaries. 



Besides the lymphocytes there are a few polymorphonuclear cells at 

 this stage, perhaps not more than twenty or thirty in each section. They 

 are quite typical, having irregular nuclei and finely granular protoplasm. 

 They occur within the follicle. Eosinophiles appear also for the first 

 time. Within the follicle there are numerous red blood cells outside of 

 the capillaries, showing signs of degeneration, that is, a vacuolization 

 and a breaking up of the protoplasm into granules. These granules are 

 all of the same size and cannot be distinguished from the granules of the 

 eosinophilic cell. This is the same evidence that has led Weidenreich to 

 the conclusion that the eosinophilic granule comes from the red blood 

 cell. It is suggestive, but not conclusive. 



To sum up the stage represented by Fig. 11, it marks the beginning of 

 the dift'erentiation of the node into its two elements, lymphoid and 

 lymphatic. It shows the beginning of the follicle and of the wandering 

 cell. There is a marked proliferation of the blood capillaries and a con- 

 sequent increase in the connective tissue in the center of the node. This 

 involves a retrogression or destruction of some of the lymph ducts. At 

 the same time wandering cells appear, lymphocytes in greatest numbers 

 and also polymorphonuclear leucocytes and eosinophiles. There is also 

 evidence of degeneration of the red blood cells. 



The next stage is shown in Fig. 12. It was made from the primary 

 lymph node of a pig 13 cm. long. The first point to be noted is the de- 

 velopment of the artery. Without the limits of the node, the artery has 

 divided into two branches. These two branches enter the node and 



