198 JOHN STEPHENS LATTA 



SUMMARY 



1. The first free cells appearing in the process of the forma- 

 tion of Ij^mphatic tissue in the intestinal tonsils are mainly small 

 lymphocytes, which arise by differentiation of fixed mesenchymal 

 cells. A few of the large mesenchymal cells, however, transform 

 directly into large lymphoid hemoblasts. These two types are 

 apparently different growth stages of the same cells, the small 

 lymphocytes by growth and slight differentiation becoming o 

 lymphoid hemoblasts, and the latter by repeated divisions be- 

 coming reduced to small lymphocytes. Further indication of 

 their close relation is the fact that either type may arise by trans- 

 formation of mesenchymal cells, according to the size of the 

 transforming cell. 



2. The so-called 'germinal center' is not really a center of 

 proliferation of lymphocytes as that name would indicate. 

 The lighter appearance of the central portion is partially due to 

 the looser arrangement of cells there than at the periphery where 

 the cells pile up as a result of their outward spread being limited by 

 the surrounding connective tissue. The other factor producing 

 this lighter appearance is the greater number of large acid-stain- 

 ing cells in this position. 



3. The acidophilic cells are found to arise by further differ- 

 entiation and degeneration of lymphoid hemoblasts. Experimen- 

 tation proves that they possess phagocytic powers. Inclusions 

 found in their cytoplasm ('tingible Korper' of Flemming) are 

 considered as nuclear remnants of degenerating small lympho- 

 cytes which have phagocytized by the degenerating lymphoid 

 hemoblasts, the acid-staining macrophages. Indications are, 

 then, that this this lighter central area is essentially a degenera- 

 tive center, brought about possibly by poorer nutritive condi- 

 tions in the center of the nodule. 



4. The intestinal epithelium overlying the lymphatic tissue 

 begins to be infiltrated with lymphocytes at an age of about 

 fourteen days. The number of invading cells rapidly increases 

 both by proliferation of those already in the epithelium and by 

 continued invasion from the lymphatic tissue. The nature of 



