THE HISTOGENESIS OF DENSE LYMPHATIC TISSUE 167 



Downey and Weidenreich ('12) found, in lymphatic nodes, the 

 small lymphocytes were developed from the large reticulum cells 

 of the node. These small lymphocytes, they thought, by growth 

 became 'large lymphocytes. ' Danchakoff (' 16) found that small 

 lymphocytes in the spleen arose by differentiation of dwarfed 

 lymphoid hemocytoblasts, which had arisen because of intense 

 proliferation and poor nutrition of normal lymp]ioid hemocyto- 

 blasts. The small lymphocyte she considered a distinct, stable 

 cell form, incapable of growth into the lymphoid hemoblast. 



Aside from this question of relationship in connection with 

 the study of the formation of lymphatic tissue, in the lymphatic 

 nodes and the tonsils, the question still remains as to whether 

 these Ij'mphocytes arise in situ, wander in from the mesenchyme 

 in other places, or are carried in and dropped by the blood vessels. 



Those studying the development of lymphatic nodes are. not 

 united on this question. Gulland ( '94) thought the first lympho- 

 cytes to appear in developing nodes were filtered from the blood 

 stream. Saxer ( '96) considered that they arose in situ from the 

 'primare Wanderzellen ' of the mesenchyme. Sabin ('05) also 

 favored this view, although she considered the evidence at hand 

 insufficient to definitely determine the origin of the lymphocytes. 

 Downey and Weidenreich, as before stated, also thought they 

 arose in situ by differentiation of the reticulum cells of the node. 



Hartmann ('14), who studied the development of the intes- 

 tinal tonsillar tissue of the rabbit, considered that the lymphoid 

 hemoblasts, at least, arose in situ by differentiation of mesen- 

 chymal cells, but he did not state any definite conclusions as 

 to the origin of the small lymphocytes. 



A study of the connective tissue in the region of the intesti- 

 nal tonsils of the newborn rabbit, as stated before, revealed no 

 traces of nodular lymphatic tissue. First evidences of future 

 nodules are seen at an age of two to two and one-half days, at 

 which time there is an apparent heaping up or condensation of 

 mesenchymal or embryonic connective-tissue cells of the mucous 

 membrane underneath the epithelium between the bases of the villi. 

 These condensations are due to the appearance of free cells in 

 the meshes of the mesenchymal reticulum. The free cells are, for 



