280 VERA DANCHAKOFF 



and 13 show the development of small lymphocytes in the 

 follicles. From right to left the figure 12 represents the tissue of 

 the follicle from the periphery to its center. In the peripheral 

 parts of the follicle an intense isolation and proliferation of 

 lymphoid hemocytoblasts takes place (5 mitoses in a part of the 

 microscopical field) which leads to the formation of dwarf 

 hemocytoblasts (fig. 12 S.L.Hbl.). A process of differentiation, 

 starting in the groups of small hemocytoblasts (fig. 12) soon 

 transforms them into true small lymphocytes (S.Lmc). The 

 cytoplasm around the nucleus of these cells becomes smaller, the 

 typical nucleolus of the hemocytoblast is replaced by chromatin 

 particles which may be now permanently discovered in the nucleus 

 (fig. 12, S.Lmc). A similar development of small lymphocytes is 

 show^n in the figure 13 in the region adjacent to the red pulpa 

 (right edge of the drawing). Both in the red and in the white 

 pulpa numerous larger and smaller hemocytoblasts are present 

 and offer in both regions similar morphological structures. 

 In both regions they sometimes appear as groups of cells joined 

 together, — probably an index of their syncytial origin. The 

 further differentiation of the lymphoid hemocytoblasts is shown 

 to be different, according to their localization. In the red pulpa 

 they are in close contact with the larger veinous capillaries and 

 differentiate into granulocytoblasts. In regions with scarce ar- 

 terial vascularization they undergo a differentiation in small 

 lymphocytes. 



As in the thymus, the differentiation of small lymphocytes 

 is preceded in the spleen also by development of generations of 

 small-sized hemocytoblasts. Their appearance in the thymus 

 seemed to depend upon an intense proliferation of the cells in a 

 limited space. If the cells in the spleen are not heaped up, as 

 they are in the thymus, yet the analogy of the conditions for 

 their differentiation in both regions may be easily traced. Both 

 in the thymus and in the spleen the small lymphocytes develop 

 under conditions of poor nutrition. They appear in regions of 

 the spleen where the swift blood current passes by the narrow 

 arterious vessels. 



The first groups of small lymphocytes differentiate between 



