THE HISTOGENESIS OF DENSE LYMPHATIC TISSUE 177 



of small lymphocytes which have been phagocytized by the acid- 

 staining macrophages (fig. 5). 



These macrophages, when first making their appearance in 

 the nodules (ten to twelve days after birth) , seem scattered about 

 throughout the mass of lymphocytes, but as the nodule assumes 

 a more definite shape and as the light central area becomes more 

 prominent, it is seen that the macrophages tend to become confined 

 to the central area. The so-called ' germinal center, ' then, is 

 an expression of two things: first, the lesser number of cells 

 found here as compared to the peripheral portion of the nodule, 

 and, secondly, the presence of acid-staining cells in greater 

 abundance in this central portion (figs. 3, 4, 5). 



As to the origin of these macrophages, no transitions between 

 them and cells of the reticulum could be found (as by Weiden- 

 reich and Downey, and Hartmann). But, on the other hand, 

 many transitional forms between cells of the lymphoid hemoblast 

 type, with a basophilic cytoplasm and a large clear distinct nu- 

 cleus, and the macrophages with an acid-staining cytoplasm and 

 a nucleus somewhat indistinct because of its weak basophilic or 

 almost acidophilic character. This change in nuclear and cyto- 

 plasmic staining reaction indicates, I believe, beginning degener- 

 ation of the cell. It is well known that many kinds of cells during 

 a degenerative process acquire phagocytic powers. Maximow 

 has proved, in study of tissue cultures of lymphatic nodes, that 

 large lymphocytes (lymphoid hemoblasts) upon further differen- 

 tiation acquire phagocytic powers. Therefore, it is considered 

 that acid-staining macrophages in the light staining nodular 

 center are the results of further differentiation and degeneration 

 of lymphoid hemoblasts in that region. 



Rather than being a place of special cell proliferation, then, 

 the so-called germinal center seems to be a place of degenerative 

 change. It is here where the degenerating small lymphocytes 

 are found, the nuclear remnants of which are phagocytized by the 

 macrophages, which themselves are apparently further differ- 

 entiated, degenerating lymphoid hemoblasts. 



The reasons that seem to the writer most plausible for this 

 degenerative change are those of nutrition. The nodule arises 



