THE HISTOGENESIS OF DENSE LYMPHATIC TISSUE 165 



LYMPHOPOIESIS 



The most extensive formation of blood cells in the region of 

 the intestinal tonsils is, of course, that of Ij^mphocytes. The 

 free cells, or lymphocytes, which make up the bulk of the nodular 

 tissue of the tonsils have been classed by hematologists into two 

 groups, 1) small, round cells, with a round or slightly oval nucleus, 

 the heavy chromatin particles of which are arranged just within 

 the nuclear membrane so as to appear somewhat as the spokes 

 of a wheel, inside a definite nuclear membrane, covering which is 

 a thin rim of densely basophilic cytoplasm, the small lymphocytes, 

 and, 2) comparatively much larger cells potentially round, 

 but evidently possessing some ameboid tendencies, with a clear 

 vesicular nucleus, round or oval in form, containing a very scanty 

 amount of chromatin, lying for the most part just within the 

 nuclear membrane, and usually a prominent nucleolus. Surround- 

 ing the nucleus is a varying amount of densely basophilic cyto- 

 plasm. These are the so-called large lymphocytes, or lymphoid 

 hemoblasts. 



The relationship between these two types of cells, and their 

 potentialities, distinction as permanent cell types, etc., have 

 long been perplexing and debatable questions. The majority 

 of present-day hematologists seem to consider the small lympho- 

 cyte as the more distinct permanent cell type, with no poten- 

 tialities other than the production of others of its kind, while they 

 ascribe to the other type of cell a more blastic nature, with 

 potentialities of differentiation into cells of any of the three types, 

 given the correct environmental conditions. 



The question of the origin of these lymphocytes, especially 

 as occurring in the tonsils, has long been a matter of much con- 

 troversy. The somewhat spirited debate between Retterer and 

 Stohr, already mentioned, may be recalled. Retterer insist- 

 ing upon an epithelial origin for the lymphocytes, and Stohr 

 equally sure that the epithelium remained passive in their forma- 

 tion, the cells of origin being of the mesenchyme. These and 

 others of the earlier authors did not recognize the two typos of 

 lymphocytes. The recognition of these two types complicates 

 the question of their origin still further. 



