THE HISTOGENESIS OF DENSE LYMPHATIC TISSUE 173 



nodule, a term which, as will be shown later, must certainly be 

 considered as non-descriptive of existing conditions. 



Flemming, in studying the structure of nodular lymphatic tissue 

 found the lighter appearance in the center of the nodules was due 

 largely to the fact that the cells making up that center were mostly 

 those containing comparatively large, rather lightly staining 

 nuclei with a relatively large amount of cytoplasm about them 

 (germinal center cells, lymphoid hemoblasts), so that the nuclei 

 were farther apart, while, on the other hand, those cells at the 

 periphery were those with much smaller, more dense nuclei, with 

 a smaller amount of cytoplasm surrounding them (small lympho- 

 cytes) , so that when seen en masse the more closely packed, dense 

 nuclei gave a darker appearance to the outer portions of the 

 nodule than that of the central portion. 



Although the evidences of proliferation, mitotic figures, were 

 not confined strictly to the lighter colored central area, he found 

 them occurring most frequently there, and not all in the dark, 

 peripheral zone. Therefore, he called the lighter central area 

 of the nodule, the germinal center. Other authors holding to 

 this theory advanced by Flemming include Baum u. Hille, Baum- 

 gartner and Ribbert, Saxer, etc. 



Others believed the germinal center was an expression of the 

 rapid proliferation of lymphocytes, which proliferation, however, 

 was scattered throughout the lymphatic tissue (Weidenreich and 

 Downey, '12, also Maximow, Mollier, et al.). 



Several authors noted the preponderance of cells of the lym- 

 phoid hemoblast variety in the lighter colored center, and some, 

 consequently, named them 'germinal center' cells. Hartman 

 ('14) found the germinal centers of the nodules of the intesti- 

 nal tonsils to be due to this fact. 



In the present investigation of the tonsillar lymphatic tissue 

 of the rabbit it was found that the lightly staining central area 

 in the nodules appeared at no very definite time, this depending, 

 apparently, somewhat upon conditions which varied according to 

 the individual. However, there is usually some little evidence 

 of the lighter colored center at about the age of two weeks, but 



