174 JOHN STEPHENS LATTA 



it does not become well marked till an age of twenty-one days or 

 older. Invariably the nodules of the appendix are further 

 advanced in this respect than are those of Peyer's patch. At 

 an age of twenty-four days, however, the lighter area is very defi- 

 nite both in nodules of the appendix and of Peyer's patch. 



A study of all developmental stages and of adult nodules 

 clearly indicates that these so-called 'germinal centers' are not 

 centers of proliferation. In young animals mitotic figures are 

 numerous in both the lymphoid hemoblasts and the small lym- 

 phocytes, but these mitotic figures are not confined to the center 

 of the nodule, being apparently scattered throughout the no- 

 dule. In fact, in older stages, if anything, they seem more abun- 

 dant out near the periphery of the nodule than in its center 

 (figs. 3 and 4). 



Mitotic figures are surely not confined to large or medium- 

 sized lymphoid hemoblasts, for mitoses are very frequent in the 

 small lymphocytes. 



The grouping of lymphoid hemoblasts or germinal center cells 

 in the center of the nodule to produce its lighter appearance could 

 not be seen. In nodules in which the so-called 'germinal center' 

 was most prominent, the lymphoid hemoblasts and the small 

 lymphocytes were scattered equally throughout the nodule. At 

 no time was there noted a special grouping of lymphoid hemo- 

 blasts in the center of the nodule or of small lymphocytes about 

 the periphery. The proportion of small lymphocytes to lymphoid 

 hemoblasts is great, but that proportion is the same throughout 

 the nodule. 



The so-called germinal center, then, should not, as that name 

 would indicate, be considered a center of proliferation of the 

 lymphocytes. Its lighter appearance is due merely to a differ- 

 ent concentration of lymphocytes here than at the periphery of 

 the nodule. The reason for the concentration of lymphocytes at 

 the periphery is the purely mechanical one of the lymphocytes 

 being held there in greater concentration by the denser reticular 

 network and the surrounding capsule of connective tissue. In 

 any mass of proliferating cells the natural tendency is to spread 

 outward, which tendency is, in this case, checked somewhat by the 



