THE HISTOGENESIS OF DENSE LYMPHATIC TISSUE 197 



develop in a somewhat random fashion, and the result is a diffuse 

 lymphatic tissue. If there is a very good blood supply giving 

 excellent nutritive conditions for growth and proliferation, there 

 is a rapid increase in the number of free cells in regions immedi- 

 ately about the blood vessels, so that dense, nodular lymphatic 

 tissue is formed. 



After cells of the lymphocyte series are formed (lymphoid 

 hemoblasts and small lymphocytes), some of them may become 

 more intimately associated with some of the large thin-walled 

 blood vessels of the mucosa or submucosa, in which the current 

 of the blood stream is quite slow^, and differentiate further into 

 either granular leococytes (eosinophilic) or erythrocytes, accord- 

 ing to the closeness of this relationship, and the degree to which 

 the conditions of the vascular w^all and the current of the blood 

 stream make the transudation of the necessary materials from 

 the blood stream possible. This is also governed by the dis- 

 tance of the hemoblasts from the source of materials, the blood 

 vessels, those farthest from the vessels having granuloblastic 

 tendencies and those nearer to them erythroblastic tendencies. 

 No small lymphocytes, however, develop directly into either 

 granuloblasts or erythroblasts, always first by growth, develop- 

 ing into cells of the lymphoid hemoblast type. 



These factors influencing further development and differen- 

 tiation of lymphoid hemoblasts may account for the greater 

 concentration of granuloblastic cells in the tunica propria and 

 the greater concentration of erythroblastic cells in the sub- 

 mucosa in the region of the intestinal tonsils. For the sub- 

 mucosal vessels are larger and more sinusoidal and compara- 

 tively much thinner walled than those in the tunica propria. 

 The slower current, due to the more sinusoidal character of 

 the vessels, coupled with the comparative thinness of the walls, 

 affords better opportunities for transudation of materials from 

 the blood stream, so that conditions are better for erythropoiesis 

 in the submucosa. Similar conditions, to a lesser degree, exist 

 in the tunica propria, so that here the process most usually taking 

 place is granulopoiesis. 



